5i. Articulations of the Pelvis

The ligaments connecting the bones of the pelvis with each other may be divided into four groups: 1. Those connecting the sacrum and ilium. 2. Those passing between the sacrum and ischium. 3. Those uniting the sacrum and coccyx. 4. Those between the two public bones. 1
1. Sacroiliac Articulation (articulatio sacroiliaca).—The sacroiliac articulation is an amphiarthrodial joint, formed between the auricular surfaces of the sacrum and the ilium. The articular surface of each bone is covered with a thin plate of cartilage, thicker on the sacrum than on the ilium. These cartilaginous plates are in close contact with each other, and to a certain extent are united together by irregular patches of softer fibrocartilage, and at their upper and posterior part by fine interosseous fibers. In a considerable part of their extent, especially in advanced life, they are separated by a space containing a synovia-like fluid, and hence the joint presents the characteristics of a diarthrosis. The ligaments of the joint are: 2
The Anterior Sacroiliac.
The Posterior Sacroiliac.
The Interosseous.

The Anterior Sacroiliac Ligament (ligamentum sacroiliacum anterius) (Fig. 319).—The anterior sacroiliac ligament consists of numerous thin bands, which connect the anterior surface of the lateral part of the sacrum to the margin of the auricular surface of the ilium and to the preauricular sulcus. 3

FIG. 319– Articulations of pelvis. Anterior view. (Quain.) (See enlarged image)

The Posterior Sacroiliac Ligament (ligamentum sacroiliacum posterius) (Fig. 320).—The posterior sacroiliac ligament is situated in a deep depression between the sacrum and ilium behind; it is strong and forms the chief bond of union between the bones. It consists of numerous fasciculi, which pass between the bones in various directions. The upper part (short posterior sacroiliac ligament) is nearly horizontal in direction, and passs from the first and second transverse tubercles on the back of the sacrum to the tuberosity of the ilium. The lower part (long posterior sacroiliac ligament) is obique in direction; it is attached by one extremity to the third transverse tubercle of he back of the sacrum, and by the other to the posterior superior spine of the ilium. 4

FIG. 320– Articulatios of pelvis. Posterior view. (Quain.) (See enlarged image)

The Interosseous Sacroiliac Ligament (ligamentum sacroiliacum interosseum).—This ligament lies deep to the poserior ligament, and consists of a series of short, strong fibers connecting the tubeosities of the sacrum and ilium. 5
2. Ligaments Connecting the Sacrum and Ischium (Fig. 320). 6
The Sacrotuberous. The Sacrospinous.

The Sacrotuberous Ligament (ligamentum sacrotuberosum; great or posterior sacrosciatic ligament).—The sacrotuberous ligament is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends; attached by its broad base to the posterior inferior spine of the ilium, to the fourth and fifth transverse tubercles of the sacrum, and to the lower part of the lateral margin of that bone and the coccyx. Passing obliquely downward, forward, and lateralward, it becomes narrow and thick, but at its insertion into the inner margin of the tuberosity of the ischium, it increases in breadth, and is prolonged forward along the inner margin of the ramus, as the falciform process, the free concave edge of which gives attachment to the obturator fascia; one of its surfaces is turned toward the perineum, the other toward the Obturator internus. The lower border of the ligament is directly continuous with the tendon of origin of the long head of the Biceps femoris, and by many is believed to be the proximal end of this tendon, cut off by the projection of the tuberosity of the ischium. 7

Relations.—The posterior surface of this ligament gives origin, by its whole extent, to the Glutæus maximus. Its anterior surface is in part united to the sacrospinous ligament. Its upper border forms, above, the posterior boundary of the greater sciatic foramen, and, below, the posterior boundary of the lesser sciatic foramen. Its lower border forms part of the boundary of the perineum. It is pierced by the coccygeal nerve and the coccygeal branch of the inferior gluteal artery. 8

The Sacrospinous Ligament (ligamentum sacrospinosum; small or anterior sacrosciatic ligament).—The sacrospinous ligament is thin, and triangular in form; it is attached by its apex to the spine of the ischium, and medially, by its broad base, to the lateral margins of the sacrum and coccyx, in front of the sacrotuberous ligament with which its fibers are intermingled. 9

Relations.—It is in relation, anteriorly, with the Coccygeus muscle, to which it is closely connected; posteriorly, it is covered by the sacrotuberous ligament, and crossed by the internal pudendal vessels and nerve. Its upper border forms the lower boundary of the greater sciatic foramen; its lower border, part of the margin of the lesser sciatic foramen. 10
These two ligaments convert the sciatic notches into foramina. The greater sciatic foramen is bounded, in front and above, by the posterior border of the hip bone; behind, by the sacrotuberous ligament; and below, by the sacrospinous ligament. It is partially filled up, in the recent state, by the Piriformis which leaves the pelvis through it. Above this muscle, the superior gluteal vessels and nerve emerge from the pelvis; and below it, the inferior gluteal vessels and nerve, the internal pudendal vessels and nerve, the sciatic and posterior femoral cutaneous nerves, and the nerves to the Obturator internus and Quadratus femoris make their exit from the pelvis. The lesser sciatic foramen is bounded, in front, by the tuberosity of the ischium; above, by the spine of the ischium and sacrospinous ligament; behind, by the sacrotuberous ligament. It transmits the tendon of the Obturator internus, its nerve, and the internal pudendal vessels and nerve. 11
3. Sacrococcygeal Symphysis (symphysis sacrococcygea; articulation of the sacrum and coccyx).—This articulation is an amphiarthrodial joint, formed between the oval surface at the apex of the sacrum, and the base of the coccyx. It is homologous with the joints between the bodies of the vertebræ, and is connected by similar ligaments. They are: 12
The Anterior Sacrococcygeal.
The Posterior Sacrococcygeal.
The Lateral Sacrococcygeal.
The Interposed Fibrocartilage.
The Interarticular

The Anterior Sacrococcygeal Ligament (ligamentum sacrococcygeum anterius).—This consists of a few irregular fibers, which descend from the anterior surface of the sacrum to the front of the coccyx, blending with the periosteum. 13

The Posterior Sacrococcygeal Ligament (ligamentum sacrococcygeum posterius).—This is a flat band, which arises from the margin of the lower orifice of the sacral canal, and descends to be inserted into the posterior surface of the coccyx. This ligament completes the lower and back part of the sacral canal, and is divisible into a short deep portion and a longer superficial part. It is in relation, behind, with the Glutæus maximus. 14

The Lateral Sacrococcygeal Ligament (ligamentum sacrococcygeum laterale; intertransverse ligament).—The lateral sacrococcygeal ligament exists on either side and connects the transverse process of the coccyx to the lower lateral angle of the sacrum; it completes the foramen for the fifth sacral nerve. 15
A disk of fibrocartilage is interposed between the contiguous surfaces of the sacrum and coccyx; it differs from those between the bodies of the vertebræ in that it is thinner, and its central part is firmer in texture. It is somewhat thicker in front and behind than at the sides. Occasionally the coccyx is freely movable on the sacrum, most notably during pregnancy; in such cases a synovial membrane is present. 16
The Interarticular Ligaments are thin bands, which unite the cornua of the two bones. 17
The different segments of the coccyx are connected together by the extension downward of the anterior and posterior sacrococcygeal ligaments, thin annular disks of fibrocartilage being interposed between the segments. In the adult male, all the pieces become ossified together at a comparatively early period; but in the female, this does not commonly occur until a later period of life. At more advanced age the joint between the sacrum and coccyx is obliterated. 18

Movements.—The movements which take place between the sacrum and coccyx, and between the different pieces of the latter bone, are forward and backward; they are very limited. Their extent increases during pregnancy. 19
4. The Pubic Symphysis (symphysis ossium pubis; articulation of the pubic bones) (Fig. 321).—The articulation between the pubic bones is an amphiarthrodial joint, formed between the two oval articular surfaces of the bones. The ligaments of this articulation are: 20
The Anterior Pubic.
The Posterior Pubic.
The Superior Pubic.
The Arcuate Pubic.
The Interpubic Fibrocartilaginous Lamina.

The Anterior Pubic Ligament (Fig. 319).—The anterior pubic ligament consists of several superimposed layers, which pass across the front of the articulation. The superficial fibers pass obliquely from one bone to the other, decussating and forming an interlacement with the fibers of the aponeuroses of the Obliqui externi and the medial tendons of origin of the Recti abdominis. The deep fibers pass transversely across the symphysis, and are blended with the fibrocartilaginous lamina. 21

The Posterior Pubic Ligament.—The posterior pubic ligament consists of a few thin, scattered fibers, which unite the two pubic bones posteriorly. 22

The Superior Pubic Ligament (ligamentum pubicum superius).—The superior pubic ligament connects together the two pubic bones superiorly, extending laterally as far as the pubic tubercles. 23

The Arcuate Pubic Ligament (ligamentum arcuatum pubis; inferior pubic or subpubic ligament).—The arcuate pubic ligament is a thick, triangular arch of ligamentous fibers, connecting together the two pubic bones below, and forming the upper boundary of the pubic arch. Above, it is blended with the interpubic fibrocartilaginous lamina; laterally, it is attached to the inferior rami of the pubic bones; below, it is free, and is separated from the fascia of the urogenital diaphragm by an opening through which the deep dorsal vein of the penis passes into the pelvis. 24

The Interpubic Fibrocartilaginous Lamina (lamina fibrocartilaginea interpubica; interpubic disk).—The interpubic fibrocartilaginous lamina connects the opposed surfaces of the pubic bones. Each of these surfaces is covered by a thin layer of hyaline cartilage firmly joined to the bone by a series of nipple-like processes which accurately fit into corresponding depressions on the osseous surfaces. These opposed cartilaginous surfaces are connected together by an intermediate lamina of fibrocartilage which varies in thickness in different subjects. It often contains a cavity in its interior, probably formed by the softening and absorption of the fibrocartilage, since it rarely appears before the tenth year of life and is not lined by synovial membrane. This cavity is larger in the female than in the male, but it is very doubtful whether it enlarges, as was formerly supposed, during pregnancy. It is most frequently limited to the upper and back part of the joint; it occasionally reaches to the front, and may extend the entire length of the cartilage. It may be easily demonstrated when present by making a coronal section of the symphysis pubis near its posterior surface (Fig. 321). 25

FIG. 321– Symphysis pubis exposed by a coronal section. (See enlarged image)

Mechanism of the Pelvis.—The pelvic girdle supports and protects the contained viscera and affords surfaces for the attachments of the trunk and lower limb muscles. Its most important mechanical function, however, is to transmit the weight of the trunk and upper limbs to the lower extremities. 26
It may be divided into two arches by a vertical plane passing through the acetabular cavities; the posterior of these arches is the one chiefly concerned in the function of transmitting the weight. Its essential parts are the upper three sacral vertebræ and two strong pillars of bone running from the sacroiliac articulations to the acetabular cavities. For the reception and diffusion of the weight each acetabular cavity is strengthened by two additional bars running toward the pubis and ischium. In order to lessen concussion in rapid changes of distribution of the weight, joints (sacroiliac articulations) are interposed between the sacrum and the iliac bones; an accessory joint (pubic symphysis) exists in the middle of the anterior arch. The sacrum forms the summit of the posterior arch; the weight transmitted falls on it at the lumbosacral articulation and, theoretically, has a component in each of two directions. One component of the force is expended in driving the sacrum downward and backward between the iliac bones, while the other thrusts the upper end of the sacrum downward and forward toward the pelvic cavity. 27
The movements of the sacrum are regulated by its form. Viewed as a whole, it presents the shape of a wedge with its base upward and forward. The first component of the force is therefore acting against the resistance of the wedge, and its tendency to separate the iliac bones is resisted by the sacroiliac and iliolumbar ligaments and by the ligaments of the pubic symphysis. 28

FIG. 322– Coronal section of anterior sacral segment. (See enlarged image)

FIG. 323– Coronal section of middle sacra segment. (See enlarged image)

If a series of coronal sections of the sacroiliac joints be made, it will be found possible to divide the articular portion of the sacrum into three segments: anterior, middle, and posterior. In the anterior segment (Fig. 322), which involves the first sacral vertebra, the articular surfaces show slight sinuosities and are almost parallel to one another; the distance between their dorsal margins is, however, slightly greater than that between their ventral margins. This segment therefore presents a slight wedge shape with the truncated apex downward. The middle segment (Fig. 323) is a narrow band across the centers of the articulations. Its dorsal width is distinctly greater than its ventral, so that the segment is more definitely wedge-shaped, the truncated apex being again directed downward. Each articular surface presents in the center a marked concavity from above downward, and into this a corresponding convexity of the iliac articular surface fits, forming an interlocking mechanism. In the posterior segment (Fig. 324) the ventral width is greater than the dorsal, so that the wedge form is the reverse of those of the other segments—i. e., the truncated apex is directed upward. The articular surfaces are only slightly concave. 29

FIG. 324– Coronal section of posterior sacral segment. (See enlarged image)

Dislocation downward and forward of the sacrum by the second component of the force applied to it is prevented therefore by the middle segment, which interposes the resistance of its wedge shape and that of the interlocking mechanism on its surfaces; a rotatory movement, however, is produced by which the anterior segment is tilted downward and the posterior upward; the axis of this rotation passes through the dorsal part of the middle segment. The movement of the anterior segment is slightly limited by its wedge form, but chiefly by the posterior and interosseous sacroiliac ligaments; that of the posterior segment is checked to a slight extent by its wedge form, but the chief limiting factors are the sacrotuberous and sacrospinous ligaments. In all these movements the effect of the sacroiliac and iliolumbar ligaments and the ligaments of the symphysis pubis in resisting the separation of the iliac bones must be recognized. 30
During pregnancy the pelvic joints and ligaments are relaxed, and capable therefore of more extensive movements. When the fetus is being expelled the force is applied to the front of the sacrum. Upward dislocation is again prevented by the interlocking mechanism of the middle segment. As the fetal head passes the anterior segment the latter is carried upward, enlarging the antero-posterior diameter of the pelvic inlet; when the head reaches the posterior segment this also is pressed upward against the resistance of its wedge, the movement only being possible by the laxity of the joints and the stretching of the sacrotuberous and sacrospinous ligaments. 31

6. Articulations of the Upper Extremity. a. Sternoclavicular Articulation

The articulations of the Upper Extremity may be arranged as follows: 1
I. Sternoclavicular.
VI. Wrist.
II. Acromioclavicular.
VII. Intercarpal.
III. Shoulder.
VIII. Carpometacarpal.
IV. Elbow.
IX. Intermetacarpal.
V. Radioulnar.
X. Metacarpophalangeal.
XI. Articulations of the Digits.

Sternoclavicular Articulation (Articulatio Sternoclavicularis) (Fig. 325)

The sternoclavicular articulation is a double arthrodial joint. The parts entering into its formation are the sternal end of the clavicle, the upper and lateral part of the manubrium sterni, and the cartilage of the first rib. The articular surface of the clavicle is much larger than that of the sternum, and is invested with a layer of cartilage, 68 which is considerably thicker than that on the latter bone. The ligaments of this joint are: 2
The Articular Capsule.
The Interclavicular.
The Anterior Sternoclavicular.
The Costoclavicular.
The Posterior Sternoclavicular.
The Articular Disk.

The Articular Capsule (capsula articularis; capsular ligament).—The articular capsule surrounds the articulation and varies in thickness and strength. In front and behind it is of considerable thickness, and forms the anterior and posterior sternoclavicular ligaments; but above, and especially below, it is thin and partakes more of the character of areolar than of true fibrous tissue. 3

The Anterior Sternoclavicular Ligament (ligamentum sternoclaviculare anterior).—The anterior sternoclavicular ligament is a broad band of fibers, covering the anterior surface of the articulation; it is attached above to the upper and front part of the sternal end of the clavicle, and, passing obliquely downward and medialward, is attached below to the front of the upper part of the manubrium sterni. This ligament is covered by the sternal portion of the Sternocleidomastoideus and the integument; behind, it is in relation with the capsule, the articular disk, and the two synovial membranes. 4

The Posterior Sternoclavicular Ligament (ligamentum sternoclaviculare posterius).—The posterior sternoclavicular ligament is a similar band of fibers, covering the posterior surface of the articulation; it is attached above to the upper and back part of the sternal end of the clavicle, and, passing obliquely downward and medialward, is fixed below to the back of the upper part of the manubrium sterni. It is in relation, in front, with the articular disk and synovial membranes; behind, with the Sternohyoideus and Sternothyreoideus. 5

The Interclavicular Ligament (ligamentum interclaviculare).—This ligament is a flattened band, which varies considerably in form and size in different individuals, it passes in a curved direction from the upper part of the sternal end of one clavicle to that of the other, and is also attached to the upper margin of the sternum. It is in relation, in front, with the integument and Sternocleidomastoidei; behind, with the Sternothyreoidei. 6

The Costoclavicular Ligament (ligamentum costoclaviculare; rhomboid ligament).—This ligament is short, flat, strong, and rhomboid in form. Attached below to the upper and medial part of the cartilage of the first rib, it ascends obliquely backward and lateralward, and is fixed above to the costal tuberosity on the under surface of the clavicle. It is in relation, in front, with the tendon of origin of the Subclavius; behind, with the subclavian vein. 7

FIG. 325– Sternoclavicular articulation. Anterior view. (See enlarged image)

The Articular Disk (discus articularis).—The articular disk is flat and nearly circular, interposed between the articulating surfaces of the sternum and clavicle. It is attached, above, to the upper and posterior border of the articular surface of the clavicle; below, to the cartilage of the first rib, near its junction with the sternum; and by its circumference to the interclavicular and anterior and posterior sternoclavicular ligaments. It is thicker at the circumference, especially its upper and back part, than at its center. It divides the joint into two cavities, each of which is furnished with a synovial membrane. 8

Synovial Membranes.—Of the two synovial membranes found in this articulation, the lateral is reflected from the sternal end of the clavicle, over the adjacent surface of the articular disk, and around the margin of the facet on the cartilage of the first rib; the medial is attached to the margin of the articular surface of the sternum and clothes the adjacent surface of the articular disk; the latter is the larger of the two. 9

Movements.—This articulation admits of a limited amount of motion in nearly every direction—upward, downward, backward, forward, as well as circumduction. When these movements take place in the joint, the clavicle in its motion carries the scapula with it, this bone gliding on the outer surface of the chest. This joint therefore forms the center from which all movements of the supporting arch of the shoulder originate, and is the only point of articulation of the shoulder girdle with the trunk. The movements attendant on elevation and depression of the shoulder take place between the clavicle and the articular disk, the bone rotating upon the ligament on an axis drawn from before backward through its own articular facet; when the shoulder is moved forward and backward, the clavicle, with the articular disk rolls to and fro on the articular surface of the sternum, revolving, with a sliding movement, around an axis drawn nearly vertically through the sternum; in the circumduction of the shoulder, which is compounded of these two movements, the clavicle revolves upon the articular disk and the latter, with the clavicle, rolls upon the sternum. 69 Elevation of the shoulder is limited principally by the costoclavicular ligament; depression, by the interclavicular ligament and articular disk. The muscles which raise the shoulder are the upper fibers of the Trapezius, the Levator scapulæ, and the clavicular head of the Sternocleidomastoideus, assisted to a certain extent by the Rhomboidei, which pull the vertebral border of the scapula backward and upward and so raise the shoulder. The depression of the shoulder is principally effected by gravity assisted by the Subclavius, Pectoralis minor and lower fibers of the Trapezius. The shoulder is drawn backward by the Rhomboidei and the middle and lower fibers of the Trapezius, and forward by the Serratus anterior and Pectoralis minor. 10
Note 68. According to Bruch, the sternal end of the clavicle is covered by a tissue which is fibrous rather than cartilaginous in structure. [back]
Note 69. Humphry, On the Human Skeleton, page 402. [back]

6b. Acromioclavicular Articulation

(Articulatio Acromioclavicularis; Scapuloclavicular Articulation) (Fig. 326)

The acromioclavicular articulation is an arthrodial joint between the acromial end of the clavicle and the medial margin of the acromion of the scapula. Its ligaments are:
The Articular Capsule. The Articular Disk.
The Superior Acromioclavicular. The Coracoclavicular {Trapezoid and Conoid.
The Inferior Acromioclavicular.

The Articular Capsule (capsula articularis; capsular ligament).—The articular capsule completely surrounds the articular margins, and is strengthened above and below by the superior and inferior acromioclavicular ligaments.

The Superior Acromioclavicular Ligament (ligamentum acromioclaviculare).—This ligament is a quadrilateral band, covering the superior part of the articulation, and extending between the upper part of the acromial end of the clavicle and the adjoining part of the upper surface of the acromion. It is composed of parallel fibers, which interlace with the aponeuroses of the Trapezius and Deltoideus; below, it is in contact with the articular disk when this is present.

The Inferior Acromioclavicular Ligament.—This ligament is somewhat thinner than the preceding; it covers the under part of the articulation, and is attached to the adjoining surfaces of the two bones. It is in relation, above, in rare cases with the articular disk; below, with the tendon of the Supraspinatus. 4

The Articular Disk (discus articularis).—The articular disk is frequently absent in this articulation. When present, it generally only partially separates the articular surfaces, and occupies the upper part of the articulation. More rarely, it completely divides the joint into two cavities. 5

The Synovial Membrane.—There is usually only one synovial membrane in this articulation, but when a complete articular disk is present, there are two. 6

The Coracoclavicular Ligament (ligamentum coracoclaviculare) (Fig. 326).—This ligament serves to connect the clavicle with the coracoid process of the scapula. It does not properly belong to this articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion. It consists of two fasciculi, called the trapezoid and conoid ligaments. 7
The Trapezoid Ligament (ligamentum trapezoideum), the anterior and lateral fasciculus, is broad, thin, and quadrilateral: it is placed obliquely between the coracoid process and the clavicle. It is attached, below, to the upper surface of the coracoid process; above, to the oblique ridge on the under surface of the clavicle. Its anterior border is free; its posterior border is joined with the conoid ligament, the two forming, by their junction, an angle projecting backward. 8
The Conoid Ligament (ligamentum conoideum), the posterior and medial fasciculus, is a dense band of fibers, conical in form, with its base directed upward. It is attached by its apex to a rough impression at the base of the coracoid process, medial to the trapezoid ligament; above, by its expanded base, to the coracoid tuberosity on the under surface of the clavicle, and to a line proceeding medialward from it for 1.25 cm. These ligaments are in relation, in front, with the Subclavius and Deltoideus; behind, with the Trapezius. 9

FIG. 326– The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula. (See enlarged image)

Movements.—The movements of this articulation are of two kinds: (1) a gliding motion of the articular end of the clavicle on the acromion; (2) rotation of the scapula forward and backward upon the clavicle. The extent of this rotation is limited by the two portions of the coracoclavicular ligament, the trapezoid limiting rotation forward, and the conoid backward. 10
The acromioclavicular joint has important functions in the movements of the upper extremity. It has been well pointed out by Humphry, that if there had been no joint between the clavicle and scapula, the circular movement of the scapula on the ribs (as in throwing the shoulders backward or forward) would have been attended with a greater alteration in the direction of the shoulder than is consistent with the free use of the arm in such positions, and it would have been impossible to give a blow straight forward with the full force of the arm; that is to say, with the combined force of the scapula, arm, and forearm. “This joint,” as he happily says, “is so adjusted as to enable either bone to turn in a hinge-like manner upon a vertical axis drawn through the other, and it permits the surfaces of the scapula, like the baskets in a roundabout swing, to look the same way in every position, or nearly so.” Again, when the whole arch formed by the clavicle and scapula rises and falls (in elevation or depression of the shoulder), the joint between these two bones enables the scapula still to maintain its lower part in contact with the ribs. 11

The Ligaments of the Scapula—The ligaments of the scapula (Fig. 326) are: 12
Coracoacromial, Superior and Inferior Transverse.
The Coracoacromial Ligament (ligamentum coracoaromiale).—This ligament is a strong triangular band, extending between the coracoid process and the acromion. It is attached, by its apex, to the summit of the acromion just in front of the articular surface for the clavicle; and by its broad base to the whole length of the lateral border of the coracoid process. This ligament, together with the coracoid process and the acromion, forms a vault for the protection of the head of the humerus. It is in relation, above, with the clavicle and under surface of the Deltoideus; below, with the tendon of the Supraspinatus, a bursa being interposed. Its lateral border is continuous with a dense lamina that passes beneath the Deltoideus upon the tendons of the Supraspinatus and Infraspinatus. The ligament is sometimes described as consisting of two marginal bands and a thinner intervening portion, the two bands being attached respectively to the apex and the base of the coracoid process, and joining together at the acromion. When the Pectoralis minor is inserted, as occasionally is the case, into the capsule of the shoulder-joint instead of into the coracoid process, it passes between these two bands, and the intervening portion of the ligament is then deficient. 13

The Superior Transverse Ligament (ligamentum transversum scapulæ superius; transverse or suprascapular ligament).—This ligament converts the scapular notch into a foramen. It is a thin and flat fasciculus, narrower at the middle than at the extremities, attached by one end to the base of the coracoid process, and by the other to the medial end of the scapular notch. The suprascapular nerve runs through the foramen; the transverse scapular vessels cross over the ligament. The ligament is sometimes ossified. 14

The Inferior Transverse Ligament (ligamentum transversum scapulæ inferius; spinoglenoid ligament).—This ligament is a weak membranous band, situated behind the neck of the scapula and stretching from the lateral border of the spine to the margin of the glenoid cavity. It forms an arch under which the transverse scapular vessels and suprascapular nerve enter the infraspinatous fossa. 15

6c. Humeral Articulation or Shoulder-joint

(Articulatio Humeri) (Fig. 326)

The shoulder-joint is an enarthrodial or ball-and-socket joint. The bones entering into its formation are the hemispherical head of the humerus and the shallow glenoid cavity of the scapula, an arrangement which permits of very considerable movement, while the joint itself is protected against displacement by the tendons which surround it. The ligaments do not maintain the joint surfaces in apposition, because when they alone remain the humerus can be separated to a considerable extent from the glenoid cavity; their use, therefore, is to limit the amount of movement. The joint is protected above by an arch, formed by the coracoid process, the acromion, and the coracoacromial ligament. The articular cartilage on the head of the humerus is thicker at the center than at the circumference, the reverse being the case with the articular cartilage of the glenoid cavity. The ligaments of the shoulder are: 1
The Articular Capsule.
The Glenohumeral.
The Coracohumeral.
The Transverse Humeral.
The Glenoidal Labrum. 70

The Articular Capsule (capsula articularis; capsular ligament) (Fig. 327).—The articular capsule completely encircles the joint, being attached, above, to the circumference of the glenoid cavity beyond the glenoidal labrum; below, to the anatomical neck of the humerus, approaching nearer to the articular cartilage above than in the rest of its extent. It is thicker above and below than elsewhere, and is so remarkably loose and lax, that it has no action in keeping the bones in contact, but allows them to be separated from each other more than 2.5 cm., an evident provision for that extreme freedom of movement which is peculiar to this articulation. It is strengthened, above, by the Supraspinatus; below, by the long head of the Triceps brachii; behind, by the tendons of the Infraspinatus and Teres minor; and in front, by the tendon of the Subscapularis. There are usually three openings in the capsule. One anteriorly, below the coracoid process, establishes a communication between the joint and a bursa beneath the tendon of the Subscapularis. The second, which is not constant, is at the posterior part, where an opening sometimes exists between the joint and a bursal sac under the tendon of the Infraspinatus. The third is between the tubercles of the humerus, for the passage of the long tendon of the Biceps brachii. 2

The Coracohumeral Ligament (ligamentum coracohumerale).—This ligament is a broad band which strengthens the upper part of the capsule. It arises from the lateral border of the coracoid process, and passes obliquely downward and lateralward to the front of the greater tubercle of the humerus, blending with the tendon of the Supraspinatus. This ligament is intimately united to the capsule by its hinder and lower border; but its anterior and upper border presents a free edge, which overlaps the capsule. 3

FIG. 327– Capsule of shoulder-joint (distended). Anterior aspect. (See enlarged image)

Glenohumeral Ligaments.—In addition to the coracohumeral ligament, three supplemental bands, which are named the glenohumeral ligaments, strengthen the capsule. These may be best seen by opening the capsule at the back of the joint and removing the head of the humerus. One on the medial side of the joint passes from the medial edge of the glenoid cavity to the lower part of the lesser tubercle of the humerus. A second at the lower part of the joint extends from the under edge of the glenoid cavity to the under part of the anatomical neck of the humerus. A third at the upper part of the joint is fixed above to the apex of the glenoid cavity close to the root of the coracoid process, and passing downward along the medial edge of the tendon of the Biceps brachii, is attached below to a small depression above the lesser tubercle of the humerus. In addition to these, the capsule is strengthened in front by two bands derived from the tendons of the Pectoralis major and Teres major respectively. 4
The Transverse Humeral Ligament (Fig. 327) is a broad band passing from the lesser to the greater tubercle of the humerus, and always limited to that portion of the bone which lies above the epiphysial line. It converts the intertubercular groove into a canal, and is the homologue of the strong process of bone which connects the summits of the two tubercles in the musk ox. 5
The Glenoidal Labrum (labrium glenoidale; glenoid ligament) is a fibrocartilaginous rim attached around the margin of the glenoid cavity. It is triangular on section, the base being fixed to the circumference of the cavity, while the free edge is thin and sharp. It is continuous above with the tendon of the long head of the Biceps brachii, which gives off two fasciculi to blend with the fibrous tissue of the labrum. It deepens the articular cavity, and protects the edges of the bone. 6

Synovial Membrane.—The synovial membrane is reflected from the margin of the glenoid cavity over the labrum; it is then reflected over the inner surface of the capsule, and covers the lower part and sides of the anatomical neck of the humerus as far as the articular cartilage on the head of the bone. The tendon of the long head of the Biceps brachii passes through the capsule and is enclosed in a tubular sheath of synovial membrane, which is reflected upon it from the summit of the glenoid cavity and is continued around the tendon into the intertubercular groove as far as the surgical neck of the humerus (Fig. 327). The tendon thus traverses the articulation, but it is not contained within the synovial cavity. 7

FIG. 328– Glenoid fossa of right side. (See enlarged image)

Bursæ.—The bursæ in the neighborhood of the shoulder-joint are the following: (1) A constant bursa is situated between the tendon of the Subscapularis muscle and the capsule; it communicates with the synovial cavity through an opening in the front of the capsule; (2) a bursa which occasionally communicates with the joint is sometimes found between the tendon of the Infraspinatus and the capsule; (3) a large bursa exists between the under surface of the Deltoideus and the capsule, but does not communicate with the joint; this bursa is prolonged under the acromion and coraco-acromial ligament, and intervenes between these structures and the capsule; (4) a large bursa is situated on the summit of the acromion; (5) a bursa is frequently found between the coracoid process and the capsule; (6) a bursa exists beneath the Coracobrachialis; (7) one lies between the Teres major and the long head of the Triceps brachii; (8) one is placed in front of, and another behind, the tendon of the Latissimus dorsi. 8
The muscles in relation with the joint are, above, the Supraspinatus; below, the long head of the Triceps brachii; in front, the Subscapularis; behind, the Infraspinatus and Teres minor; within, the tendon of the long head of the Biceps brachii. The Deltoideus covers the articulation in front, behind, and laterally. 9
The arteries supplying the joint are articular branches of the anterior and posterior humeral circumflex, and transverse scapular. 10
The nerves are derived from the axillary and suprascapular. 11

Movements.—The shoulder-joint is capable of every variety of movement, flexion, extension, abduction, adduction, circumduction, and rotation. The humerus is flexed (drawn forward) by the Pectoralis major, anterior fibers of the Deltoideus, Coracobrachialis, and when the forearm is flexed, by the Biceps brachii; extended (drawn backward) by the Latissimus dorsi, Teres major, posterior fibers of the Deltoideus, and, when the forearm is extended, by the Triceps brachii; it is abducted by the Deltoideus and Supraspinatus; it is adducted by the Subscapularis, Pectoralis major, Latissimus dorsi, and Teres major, and by the weight of the limb; it is rotated outward by the Infraspinatus and Teres minor; and it is rotated inward by the Subscapularis, Latissimus dorsi, Teres major, Pectoralis major, and the anterior fibers of the Deltoideus. 12
The most striking peculiarities in this joint are: (1) The large size of the head of the humerus in comparison with the depth of the glenoid cavity, even when this latter is supplemented by the glenoidal labrum. (2) The looseness of the capsule of the joint. (3) The intimate connection of the capsule with the muscles attached to the head of the humerus. (4) The peculiar relation of the tendon of the long head of the Biceps brachii to the joint. 13
It is in consequence of the relative sizes of the two articular surfaces, and the looseness of the articular capsule, that the joint enjoys such free movement in all directions. When these movements of the arm are arrested in the shoulder-joint by the contact of the bony surfaces, and by the tension of the fibers of the capsule, together with that of the muscles acting as accessory ligaments, the arm can be carried considerably farther by the movements of the scapula, involving, of course, motion at the acromio- and sternoclavicular joints. These joints are therefore to be regarded as accessory structures to the shoulder-joint (see pages 314 and 316). The extent of the scapular movements is very considerable, especially in extreme elevation of the arm, a movement best accomplished when the arm is thrown somewhat forward and outward, because the margin of the head of the humerus is by no means a true circle; its greatest diameter is from the intertubercular groove, downward, medialward, and backward, and the greatest elevation of the arm can be obtained by rolling its articular surface in the direction of this measurement. The great width of the central portion of the humeral head also allows of very free horizontal movement when the arm is raised to a right angle, in which movement the arch formed by the acromion, the coracoid process and the coracoacromial ligament, constitutes a sort of supplemental articular cavity for the head of the bone. 14
The looseness of the capsule is so great that the arm will fall about 2.5 cm. from the scapula when the muscles are dissected from the capsule, and an opening made in it to counteract the atmospheric pressure. The movements of the joint, therefore, are not regulated by the capsule so much as by the surrounding muscles and by the pressure of the atmosphere, an arrangement which “renders the movements of the joint much more easy than they would otherwise have been, and permits a swinging, pendulum-like vibration of the limb when the muscles are at rest” (Humphry). The fact, also, that in all ordinary positions of the joint the capsule is not put on the stretch, enables the arm to move freely in all directions. Extreme movements are checked by the tension of appropriate portions of the capsule, as well as by the interlooking of the bones. Thus it is said that “abduction is checked by the contact of the great tuberosity with the upper edge of the glenoid cavity; adduction by the tension of the coracohumeral ligament” (Beaunis et Bouchard). Cleland 71 maintains that the limitations of movement at the shoulder-joint are due to the structure of the joint itself, the glenoidal labrum fitting, in different positions of the elevated arm, into the anatomical neck of the humerus. 15
The scapula is capable of being moved upward and downward, forward and backward, or, by a combination of these movements, circumducted on the wall of the chest. The muscles which raise the scapula are the upper fibers of the Trapezius, the Levator scapulæ, and the Rhomboidei; those which depress it are the lower fibers of the Trapezius, the Pectoralis minor, and, through the elavicle, the Subclavius. The scapula is drawn backward by the Rhomboidei and the middle and lower fibers of the Trapezius, and forward by the Serratus anterior and Pectoralis minor, assisted, when the arm is fixed, by the Pectoralis major. The mobility of the scapula is very considerable, and greatly assists the movements of the arm at the shoulder-joint. Thus, in raising the arm from the side, the Deltoideus and Supraspinatus can only lift it to a right angle with the trunk, the further elevation of the limb being effected by the Trapezius and Serratus anterior moving the scapula on the wall of the chest. This mobility is of special importance in ankylosis of the shoulder-joint, the movements of this bone compensating to a very great extent for the immobility of the joint. 16
Cathcart 72 has pointed out that in abducting the arm and raising it above the head, the scapula rotates throughout the whole movement with the exception of a short space at the beginning and at the end; that the humerus moves on the scapula not only while passing from the hanging to the horizontal position, but also in travelling upward as it approaches the vertical above; that the clavicle moves not only during the second half of the movement but in the first as well, though to a less extent—i. e., the scapula and clavicle are concerned in the first stage as well as in the second; and that the humerus is partly involved in the second as well as chiefly in the first. 17
The intimate union of the tendons of the Supraspinatus, Infraspinatus, Teres minor and Subscapularis with the capsule, converts these muscles into elastic and spontaneously acting ligaments of the joint. 18
The peculiar relations of the tendon of the long head of the Biceps branchii to the shoulder-joint appear to subserve various purposes. In the first place, by its connection with both the shoulder and elbow the muscle harmonizes the action of the two joints, and acts as an elastic ligament in all positions, in the manner previously discussed (see page 287). It strengthens the upper part of the articular cavity, and prevents the head of the humerus from being pressed up against the acromion, when the Deltoideus contracts; it thus fixes the head of the humerus as the center of motion in the glenoid cavity. By its passage along the intertubercular groove it assists in steadying the head of the humerus in the various movements of the arm. When the arm is raised from the side it assists the Supraspinatus and Infraspinatus in rotating the head of the humerus in the glenoid cavity. It also holds the head of the bone firmly in contact with the glenoid cavity, and prevents its slipping over its lower edge, or being displaced by the action of the Latissimus dorsi and Pectoralis major, as in climbing and many other movements. 19
Note 70. The long tendon of origin of the biceps brachii also acts as one of the ligaments of this joint. See the observations on page 287, on the function of the muscles passing over more than one joint. [back]
Note 71. Journal of Anatomy and Physiology, 1867, i. 85. [back]
Note 72. Ibid., 1884, vol. xviii. [back]

6d. Elbow-joint

(Articulatio Cubiti) (Figs. 329, 330)

The elbow-joint is a ginglymus or hinge-joint. The trochlea of the humerus is received into the semilunar notch of the ulna, and the capitulum of the humerus articulates with the fovea on the head of the radius. The articular surfaces are connected together by a capsule, which is thickened medially and laterally, and, to a less extent, in front and behind. These thickened portions are usually described as distinct ligaments under the following names:
The Anterior.
The Posterior.
The Ulnar Collateral.
The Radial Collateral.

FIG. 329– Left elbow-joint, showing anterior and ulnar collateral ligaments. (See enlarged image)

FIG. 330– Left elbow-joint, showing posterior and radial collateral ligaments. (See enlarged image)

The Anterior Ligament (Fig. 329).—The anterior ligament is a broad and thin fibrous layer covering the anterior surface of the joint. It is attached to the front of the medial epicondyle and to the front of the humerus immediately above the coronoid and radial fossæ below, to the anterior surface of the coronoid process of the ulna and to the annular ligament (page 324), being continuous on either side with the collateral ligaments. Its superficial fibers pass obliquely from the medial epicondyle of the humerus to the annular ligament. The middle fibers, vertical in direction, pass from the upper part of the coronoid depression and become partly blended with the preceding, but are inserted mainly into the anterior surface of the coronoid process. The deep or transverse set intersects these at right angles. This ligament is in relation, in front, with the Brachialis, except at its most lateral part.

The Posterior Ligament (Fig. 330).—This posterior ligament is thin and membranous, and consists of transverse and oblique fibers. Above, it is attached to the humerus immediately behind the capitulum and close to the medial margin of the trochlea, to the margins of the olecranon fossa, and to the back of the lateral epicondyle some little distance from the trochlea.

Below, it is fixed to the upper and lateral margins of the olecranon, to the posterior part of the annular ligament, and to the ulna behind the radial notch. The transverse fibers form a strong band which bridges across the olecranon fossa; under cover of this band a pouch of synovial membrane and a pad of fat project into the upper part of the fossa when the joint is extended.

In the fat are a few scattered fibrous bundles, which pass from the deep surface of the transverse band to the upper part of the fossa. This ligament is in relation, behind, with the tendon of the Triceps brachii and the Anconæus.

The Ulnar Collateral Ligament (ligamentum collaterale ulnare; internal lateral ligament) (Fig. 329).—This ligament is a thick triangular band consisting of two portions, an anterior and posterior united by a thinner intermediate portion. The anterior portion, directed obliquely forward, is attached, above, by its apex, to the front part of the medial epicondyle of the humerus; and, below, by its broad base to the medial margin of the coronoid process. The posterior portion, also of triangular form, is attached, above, by its apex, to the lower and back part of the medial epicondyle; below, to the medial margin of the olecranon. Between these two bands a few intermediate fibers descend from the medial epicondyle to blend with a transverse band which bridges across the notch between the olecranon and the coronoid process. This ligament is in relation with the Triceps brachii and Flexor carpi ulnaris and the ulnar nerve, and gives origin to part of the Flexor digitorum sublimis. 4

The Radial Collateral Ligament (ligamentum collaterale radiale; external lateral ligament) (Fig. 330).—This ligament is a short and narrow fibrous band, less distinct than the ulnar collateral, attached, above, to a depression below the lateral epicondyle of the humerus; below, to the annular ligament, some of its most posterior fibers passing over that ligament, to be inserted into the lateral margin of the ulna. It is intimately blended with the tendon of origin of the Supinator. 5

Synovial Membrane (Figs. 331, 332).—The synovial membrane is very extensive. It extends from the margin of the articular surface of the humerus, and lines the coronoid, radial and olecranon fossæ on that bone; it is reflected over the deep surface of the capsule and forms a pouch between the radial notch, the deep surface of the annular ligament, and the circumference of the head of the radius. Projecting between the radius and ulna into the cavity is a crescentic fold of synovial membrane, suggesting the division of the joint into two; one the humeroradial, the other the humeroulnar. 6
Between the capsule and the synovial membrane are three masses of fat: the largest, over the olecranon fossa, is pressed into the fossa by the Triceps brachii during the flexion; the second, over the coronoid fossa, and the third, over the radial fossa, are pressed by the Brachialis into their respective fossæ during extension. 7
The muscles in relation with the joint are, in front, the Brachialis; behind, the Triceps brachii and Anconæus; laterally, the Supinator, and the common tendon of origin of the Extensor muscles; medially, the common tendon of origin of the Flexor muscles, and the Flexor carpi ulnaris. 8
The arteries supplying the joint are derived from the anastomosis between the profunda and the superior and inferior ulnar collateral branches of the brachial, with the anterior, posterior, and interosseous recurrent branches of the ulnar, and the recurrent branch of the radial. These vessels form a complete anastomotic network around the joint. 9
The nerves of the joint are a twig from the ulnar, as it passes between the medial condyle and the olecranon; a filament from the musculocutaneous, and two from the median. 10

Movements.—The elbow-joint comprises three different portions—viz., the joint between the ulna and humerus, that between the head of the radius and the humerus, and the proximal radioulnar articulation, described below. All these articular surfaces are enveloped by a common synovial membrane, and the movements of the whole joint should be studied together. The combination of the movements of flexion and extension of the forearm with those of pronation and supination of the hand, which is ensured by the two being performed at the same joint, is essential to the accuracy of the various minute movements of the hand. 11
The portion of the joint between the ulna and humerus is a simple hinge-joint, and allows of movements of flexion and extension only. Owing to the obliquity of the trochlea of the humerus, this movement does not take place in the antero-posterior plane of the body of the humerus. When the forearm is extended and supinated, the axes of the arm and forearm are not in the same line; the arm forms an obtuse angle with the forearm, the hand and forearm being directed lateral-ward. During flexion, however, the forearm and the hand tend to approach the middle line of the body, and thus enable the hand to be easily carried to the face. The accurate adaptation of the trochlea of the humerus, with its prominences and depressions, to the semilunar notch of the ulna, prevents any lateral movement. Flexion is produced by the action of the Biceps brachii and Brachialis, assisted by the Brachioradialis and the muscles arising from the medial condyle of the humerus; extension, by the Triceps brachii and Anconæus, assisted by the Extensors of the wrist, the Extensor digitorum communis, and the Extensor digiti quinti proprius. 12

FIG. 331– Capsule of elbow-joint (distended). Anterior aspect. (See enlarged image)

FIG. 332– Capsule of elbow-joint (distended). Posterior aspect. (See enlarged image)

The joint between the head of the radius and the capitulum of the humerus is an arthrodial joint. The bony surfaces would of themselves constitute an enarthrosis and allow of movement in all directions, were it not for the annular ligament, by which the head of the radius is bound to the radial notch of the ulna, and which prevents any separation of the two bones laterally. It is to the same ligament that the head of the radius owes its security from dislocation, which would otherwise tend to occur, from the shallowness of the cup-like surface on the head of the radius. In fact, but for this ligament, the tendon of the Biceps brachii would be liable to pull the head of the radius out of the joint. The head of the radius is not in complete contact with the capitulum of the humerus in all positions of the joint. The capitulum occupies only the anterior and inferior surfaces of the lower end of the humerus, so that in complete extension a part of the radial head can be plainly felt projecting at the back of the articulation. In full flexion the movement of the radial head is hampered by the compression of the surrounding soft parts, so that the freest rotatory movement of the radius on the humerus (pronation and supination) takes place in semiflexion, in which position the two articular surfaces are in most intimate contact. Flexion and extension of the elbow-joint are limited by the tension of the structures on the front and back of the joint; the limitation of flexion is also aided by the soft structures of the arm and forearm coming into contact. 13
In any position of flexion or extension, the radius, carrying the hand with it, can be rotated in the proximal radioulnar joint. The hand is directly articulated to the lower surface of the radius only, and the ulnar notch on the lower end of the radius travels around the lower end of the ulna. The latter bone is excluded from the wrist-joint by the articular disk. Thus, rotation of the head of the radius around an axis passing through the center of the radial head of the humerus imparts circular movement to the hand through a very considerable arc. 14

6e. Radioulnar Articulation

(Articulatio Radioulnaris)

The articulation of the radius with the ulna is effected by ligaments which connect together the extremities as well as the bodies of these bones. The ligaments may, consequently, be subdivided into three sets: 1, those of the proximal radioulnar articulation; 2, the middle radioulnar ligaments; 3, those of the distal radioulnar articulation. 1

Proximal Radioulnar Articulation (articulatio radioulnaris proximalis; superior radioulnar joint).—This articulation is a trochoid or pivot-joint between the circumference of the head of the radius and the ring formed by the radial notch of the ulna and the annular ligament. 2

FIG. 333– Annular ligament of radius, from above. The head of the radius has been sawn off and the bone dislodged from the ligament. (See enlarged image)

The Annular Ligament (ligamentum annulare radii; orbicular ligament) (Fig. 333).—This ligament is a strong band of fibers, which encircles the head of the radius, and retains it in contact with the radial notch of the ulna. It forms about four-fifths of the osseo-fibrous ring, and is attached to the anterior and posterior margins of the radial notch; a few of its lower fibers are continued around below the cavity and form at this level a complete fibrous ring. Its upper border blends with the anterior and posterior ligaments of the elbow, while from its lower border a thin loose membrane passes to be attached to the neck of the radius; a thickened band which extends from the inferior border of the annular ligament below the radial notch to the neck of the radius is known as the quadrate ligament. The superficial surface of the annular ligament is strengthened by the radial collateral ligament of the elbow, and affords origin to part of the Supinator. Its deep surface is smooth, and lined by synovial membrane, which is continuous with that of the elbow-joint. 3

Movements.—The movements allowed in this articulation are limited to rotatory movements of the head of the radius within the ring formed by the annular ligament and the radial notch of the ulna; rotation forward being called pronation; rotation backward, supination. Supination is performed by the Biceps brachii and Supinator, assisted to a slight extent by the Extensor muscles of the thumb. Pronation is performed by the Pronator teres and Pronator quadratus. 4

Middle Radioulnar Union.—The shafts of the radius and ulna are connected by the Oblique Cord and the Interosseous Membrane. 5

The Oblique Cord (chorda obliqua; oblique ligament) (Fig. 329).—The oblique cord is a small, flattened band, extending downward and lateralward, from the lateral side of the tubercle of the ulna at the base of the coronoid process to the radius a little below the radial tuberosity. Its fibers run in the opposite direction to those of the interosseous membrane. It is sometimes wanting. 6

The Interosseous Membrane (membrana interossea antebrachii).—The interosseous membrane is a broad and thin plane of fibrous tissue descending obliquely downward and medialward, from the interosseous crest of the radius to that of the ulna; the lower part of the membrane is attached to the posterior of the two lines into which the interosseous crest of the radius divides. It is deficient above, commencing about 2.5 cm. beneath the tuberosity of the radius; is broader in the middle than at either end; and presents an oval aperture a little above its lower margin for the passage of the volar interosseous vessels to the back of the forearm. This membrane serves to connect the bones, and to increase the extent of surface for the attachment of the deep muscles. Between its upper border and the oblique cord is a gap, through which the dorsal interosseous vessels pass. Two or three fibrous bands are occasionally found on the dorsal surface of this membrane; they descend obliquely from the ulna toward the radius, and have consequently a direction contrary to that of the other fibers. The membrane is in relation, in front, by its upper three-fourths, with the Flexor pollicis longus on the radial side, and with the Flexor digitorum profundus on the ulnar, lying in the interval between which are the volar interosseous vessels and nerve; by its lower fourth with the Pronator quadratus; behind, with the Supinator, Abductor pollicis longus, Extensor pollicis brevis, Extensor pollicis longus, Extensor indicis proprius; and, near the wrist, with the volar interosseous artery and dorsal interosseous nerve. 7

Distal Radioulnar Articulation (articulatio radioulnaris distalis; inferior radioulnar joint).—This is a pivot-joint formed between the head of the ulna and the ulnar notch on the lower end of the radius. The articular surfaces are connected together by the following ligaments: 8
The Volar Radioulnar.
The Dorsal Radioulnar.
The Articular Disk.

The Volar Radioulnar Ligament (anterior radioulnar ligament) (Fig. 334).—This ligament is a narrow band of fibers extending from the anterior margin of the ulnar notch of the radius to the front of the head of the ulna. 9

The Dorsal Radioulnar Ligament (posterior radioulnar ligament) (Fig. 335).—This ligament extends between corresponding surfaces on the dorsal aspect of the articulation. 10

The Articular Disk (discus articularis; triangular fibrocartilage) (Fig. 336).—The articular disk is triangular in shape, and is placed transversely beneath the head of the ulna, binding the lower ends of the ulna and radius firmly together. Its periphery is thicker than its center, which is occasionally perforated. It is attached by its apex to a depression between the styloid process and the head of the ulna; and by its base, which is thin, to the prominent edge of the radius, which separates the ulnar notch from the carpal articular surface. Its margins are united to the ligaments of the wrist-joint. Its upper surface, smooth and concave, articulates with the head of the ulna, forming an arthrodial joint; its under surface, also concave and smooth, forms part of the wrist-joint and articulates with the triangular bone and medial part of the lunate. Both surfaces are clothed by synovial membrane; the upper, by that of the distal radioulnar articulation, the under, by that of the wrist. 11

FIG. 334– Ligaments of wrist. Anterior view (See enlarged image)

Synovial Membrane (Fig. 336).—The synovial membrane of this articulation is extremely loose, and extends upward as a recess (recessus sacciformis) between the radius and the ulna. 12

FIG. 335– Ligaments of wrist. Posterior view. (See enlarged image)

Movements.—The movements in the distal radioulnar articulation consist of rotation of the lower end of the radius around an axis which passes through the center of the head of the ulna. When the radius rotates forward, pronation of the forearm and hand is the result; and when backward, supination. It will thus be seen that in pronation and supination the radius describes the segment of a cone, the axis of which extends from the center of the head of the radius to the middle of the head of the ulna. In this movement the head of the ulna is not stationary, but describes a curve in a direction opposite to that taken by the head of the radius. This, however, is not to be regarded as a rotation of the ulna—the curve which the head of this bone describes is due to a combined antero-posterior and rotatory movement, the former taking place almost entirely at the elbow-joint, the latter at the shoulder-joint. 13

FIG. 336– Vertical section through the articulations at the wrist, showing the synovial cavities. (See enlarged image)

1F. Radiocarpal Articulation or Wrist-joint

(Articulatio Radiocarpea) (Figs. 334, 335)

The wrist-joint is a condyloid articulation. The parts forming it are the lower end of the radius and under surface of the articular disk above; and the navicular, lunate, and triangular bones below. The articular surface of the radius and the under surface of the articular disk form together a transversely elliptical concave surface, the receiving cavity. The superior articular surfaces of the navicular, lunate, and triangular form a smooth convex surface, the condyle, which is received into the concavity. The joint is surrounded by a capsule, strengthened by the following ligaments:
The Volar Radiocarpal.
The Ulnar Collateral.
The Dorsal Radiocarpal.
The Radial Collateral.

The Volar Radiocarpal Ligament (ligamentum radiocarpeum volare; anterior ligament) (Fig. 334).—This ligament is a broad membranous band, attached above to the anterior margin of the lower end of the radius, to its styloid process, and to the front of the lower end of the ulna; its fibers pass downward and medialward to be inserted into the volar surfaces of the navicular, lunate, and triangular bones, some being continued to the capitate. In addition to this broad membrane, there is a rounded fasciculus, superficial to the rest, which reaches from the base of the styloid process of the ulna to the lunate and triangular bones. The ligament is perforated by apertures for the passage of vessels, and is in relation, in front, with the tendons of the Flexor digitorum profundus and Flexor pollicis longus; behind, it is closely adherent to the anterior border of the articular disk of the distal radioulnar articulation. 2

The Dorsal Radiocarpal Ligament (ligamentum radiocarpeum dorsale; posterior ligament) (Fig. 335).—The dorsal radiocarpal ligament less thick and strong than the volar, is attached, above, to the posterior border of the lower end of the radius; its fibers are directed obliquely downward and medialward, and are fixed, below, to the dorsal surfaces of the navicular, lunate, and triangular, being continuous with those of the dorsal intercarpal ligaments. It is in relation, behind, with the Extensor tendons of the fingers; in front, it is blended with the articular disk. 3

The Ulnar Collateral Ligament (ligamentum collaterale carpi ulnare; internal lateral ligament) (Fig. 334).—The ulnar collateral ligament is a rounded cord, attached above to the end of the styloid process of the ulna, and dividing below into two fasciculi, one of which is attached to the medial side of the triangular bone, the other to the pisiform and transverse carpal ligament. 4

The Radial Collateral Ligament (ligamentum collaterale carpi radiale; external lateral ligament) (Fig. 335).—The radial collateral ligament extends from the tip of the styloid process of the radius to the radial side of the navicular, some of its fibers being prolonged to the greater multangular bone and the transverse carpal ligament. It is in relation with the radial artery, which separates the ligament from the tendons of the Abductor pollicis longus and Extensor pollicis brevis. 5

Synovial Membrane (Fig. 336).—The synovial membrane lines the deep surfaces of the ligaments above described, extending from the margin of the lower end of the radius and articular disk above to the margins of the articular surfaces of the carpal bones below. It is loose and lax, and presents numerous folds, especially behind. 6
The wrist-joint is covered in front by the Flexor, and behind by the Extensor tendons. 7
The arteries supplying the joint are the volar and dorsal carpal branches of the radial and ulnar, the volar and dorsal metacarpals, and some ascending branches from the deep volar arch. 8
The nerves are derived from the ulnar and dorsal interosseous. 9

Movements.—The movements permitted in this joint are flexion, extension, abduction, adduction, and circumduction. They will be studied with those of the carpus, with which they are combined.

6g. Intercarpal Articulations

(Articulationes Intercarpeæ; Articulations of the Carpus)

These articulations may be subdivided into three sets: 1
1. The Articulations of the Proximal Row of Carpal Bones.
2. The Articulations of the Distal Row of Carpal Bones.
3. The Articulations of the Two Rows with each Other.

Articulations of the Proximal Row of Carpal Bones.—These are arthrodial joints. The navicular, lunate, and triangular are connected by dorsal, volar, and interosseous ligaments. 2

The Dorsal Ligaments (ligamenta intercarpea dorsalia).—The dorsal ligaments, two in number, are placed transversely behind the bones of the first row; they connect the navicular and lunate, and the lunate and triangular. 3

The Volar ligaments (ligamenta intercarpea volaria; palmar ligaments).—The volar ligaments, also two, connect the navicular and lunate, and the lunate and triangular; they are less strong than the dorsal, and placed very deeply behind the Flexor tendons and the volar radiocarpal ligament. 4

The Interosseous Ligaments (ligamenta intercarpea interossea) (Fig. 336).—The interosseous ligaments are two narrow bundles, one connecting the lunate with the navicular, the other joining it to the triangular. They are on a level with the superior surfaces of these bones, and their upper surfaces are smooth, and form part of the convex articular surface of the wrist-joint. 5
The ligaments connecting the pisiform bone are the articular capsule and the two volar ligaments. 6
The articular capsule is a thin membrane which connects the pisiform to the triangular; it is lined by synovial membrane. 7
The two volar ligaments are strong fibrous bands; one, the pisohamate ligament, connects the pisiform to the hamate, the other, the pisometacarpal ligament, joins the pisiform to the base of the fifth metacarpal bone (Fig. 334). These ligaments are, in reality, prolongations of the tendon of the Flexor carpi ulnaris. 8

Articulations of the Distal Row of Carpal Bones.—These also are arthrodial joints; the bones are connected by dorsal, volar, and interosseous ligaments. 9

The Dorsal Ligaments (ligamenta intercarpea dorsalia).—The dorsal ligaments, three in number, extend transversely from one bone to another on the dorsal surface, connecting the greater with the lesser multangular, the lesser multangular with the capitate, and the capitate with the hamate. 10

The Volar Ligaments (ligamenta intercarpea volaria; palmar ligaments).—The volar ligaments, also three, have a similar arrangement on the volar surface. 11

The Interosseous Ligaments (ligamenta intercarpea interossea).—The three interosseous ligaments are much thicker than those of the first row; one is placed between the capitate and the hamate, a second between the capitate and the lesser multangular, and a third between the greater and lesser multangulars. The first is much the strongest, and the third is sometimes wanting. 12

Articulations of the Two Rows of Carpal Bones with Each Other.—The joint between the navicular, lunate, and triangular on the one hand, and the second row of carpal bones on the other, is named the midcarpal joint, and is made up of three distinct portions: in the center the head of the capitate and the superior surface of the hamate articulate with the deep cup-shaped cavity formed by the navicular and lunate, and constitute a sort of ball-and-socket joint. On the radial side the greater and lesser multangulars articulate with the navicular, and on the ulnar side the hamate articulates with the triangular, forming gliding joints. 13
The ligaments are: volar, dorsal, ulnar and radial collateral. 14

The Volar Ligaments (ligamenta intercarpea volaria; anterior or palmar ligaments).—The volar ligaments consist of short fibers, which pass, for the most part, from the volar surfaces of the bones of the first row to the front of the capitate. 15

The Dorsal Ligaments (ligamenta intercarpea dorsalia; posterior ligaments).—The dorsal ligaments consist of short, irregular bundles passing between the dorsal surfaces of the bones of the first and second rows. 16

The Collateral Ligaments (lateral ligaments).—The collateral ligaments are very short; one is placed on the radial, the other on the ulnar side of the carpus; the former, the stronger and more distinct, connects the navicular and greater multangular, the latter the triangular and hamate; they are continuous with the collateral ligaments of the wrist-joint. In addition to these ligaments, a slender interosseous band sometimes connects the capitate and the navicular. 17

Synovial Membrane.—The synovial membrane of the carpus is very extensive (Fig. 336), and bounds a synovial cavity of very irregular shape. The upper portion of the cavity intervenes between the under surfaces of the navicular, lunate, and triangular bones and the upper surfaces of the bones of the second row. It sends two prolongations upward—between the navicular and lunate, and the lunate and triangular—and three prolongations downward between the four bones of the second row. The prolongation between the greater and lesser multangulars, or that between the lesser multangular and capitate, is, owing to the absence of the interosseous ligament, often continuous with the cavity of the carpometacarpal joints, sometimes of the second, third, fourth, and fifth metacarpal bones, sometimes of the second and third only. In the latter condition the joint between the hamate and the fourth and fifth metacarpal bones has a separate synovial membrane. The synovial cavities of these joints are prolonged for a short distance between the bases of the metacarpal bones. There is a separate synovial membrane between the pisiform and triangular. 18

Movements.—The articulation of the hand and wrist considered as a whole involves four articular surfaces: (a) the inferior surfaces of the radius and articular disk; (b) the superior surfaces of the navicular, lunate, and triangular, the pisiform having no essential part in the movement of the hand; (c) the S-shaped surface formed by the inferior surfaces of the navicular, lunate, and triangular; (d) the reciprocal surface formed by the upper surfaces of the bones of the second row. These four surfaces form two joints: (1) a proximal, the wrist-joint proper; and (2) a distal, the mid-carpal joint. 19
1. The wrist-joint proper is a true condyloid articulation, and therefore all movements but rotation are permitted. Flexion and extension are the most free, and of these a greater amount of extension than of flexion is permitted, since the articulating surfaces extend farther on the dorsal than on the volar surfaces of the carpal bones. In this movement the carpal bones rotate on a transverse axis drawn between the tips of the styloid processes of the radius and ulna. A certain amount of adduction (or ulnar flexion) and abduction (or radial flexion) is also permitted. The former is considerably greater in extent than the latter on account of the shortness of the styloid process of the ulna, abduction being soon limited by the contact of the styloid process of the radius with the greater multangular. In this movement the carpus revolves upon an antero-posterior axis drawn through the center of the wrist. 73 Finally, circumduction is permitted by the combined and consecutive movements of adduction, extension, abduction, and flexion. No rotation is possible, but the effect of rotation is obtained by the pronation and supination of the radius on the ulna. The movement of flexion is performed by the Flexor carpi radialis, the Flexor carpi ulnaris, and the Palmaris longus; extension by the Extensores carpi radiales longus and brevis and the Extensor carpi ulnaris; adduction (ulnar flexion) by the Flexor carpi ulnaris and the Extensor carpi ulnaris; and abduction (radial flexion) by the Abductor pollicis longus, the Extensors of the thumb, and the Extensores carpi radiales longus and brevis and the Flexor carpi radialis. When the fingers are extended, flexion of the wrist is performed by the Flexor carpi radialis and ulnaris and extension is aided by the Extensor digitorum communis. When the fingers are flexed, flexion of the wrist is aided by the Flexores digitorum sublimis and profundus, and extension is performed by the Extensores carpi radiales and ulnaris. 20
2. The chief movements permitted in the mid-carpal joint are flexion and extension and a slight amount of rotation. In flexion and extension, which are the movements most freely enjoyed, the greater and lesser multangulars on the radial side and the hamate on the ulnar side glide forward and backward on the navicular and triangular respectively, while the head of the capitate and the superior surface of the hamate rotate in the cup-shaped cavity of the navicular and lunate. Flexion at this joint is freer than extension. A very trifling amount of rotation is also permitted, the head of the capitate rotating around a vertical axis drawn through its own center, while at the same time a slight gliding movement takes place in the lateral and medial portions of the joint. 21
Note 73. H. M. Johnston (Journal of Anatomy and Physiology, vol. xli) maintains that n ulnar and radial flexion only slight lateral movement occurs at the radiocarpal joint, and that in complete flexion and extension of the hand there is a small degree of ulnar flexion at the radiocarpal joint. [back]

6h. Carpometacarpal Articulations

(Articulationes Carpometacarpeæ)

Carpometacarpal Articulation of the Thumb (articulatio carpometacarpea pollicis).—This is a joint of reciprocal reception between the first metacarpal and the greater multangular; it enjoys great freedom of movement on account of the configuration of its articular surfaces, which are saddle-shaped. The joint is surrounded by a capsule, which is thick but loose, and passes from the circumference of the base of the metacarpal bone to the rough edge bounding the articular surface of the greater multangular; it is thickest laterally and dorsally, and is lined by synovial membrane.

Movements.—In this articulation the movements permitted are flexion and extension in the plane of the palm of the hand, abduction and adduction in a plane at right angles to the palm, circumduction, and opposition. It is by the movement of opposition that the tip of the thumb is brought into contact with the volar surfaces of the slightly flexed fingers. This movement is effected through the medium of a small sloping facet on the anterior lip of the saddle-shaped articular surface of the greater multangular. The Flexor muscles pull the corresponding part of the articular surface of the metacarpal bone on to this facet, and the movement of opposition is then carried out by the Adductors. 2
Flexion of this joint is produced by the Flexores pollicis longus and brevis, assisted by the Opponens pollicis and the Adductor pollicis. Extension is effected mainly by the abductor pollicis longus, assisted by the Extensores pollicis longus and brevis. Adduction is carried out by the Adductor; abduction mainly by the Abductores pollicis longus and brevis, assisted by the Extensors. 3

Articulations of the Other Four Metacarpal Bones with the Carpus (articulationes carpometacarpeæ).—The joints between the carpus and the second, third, fourth, and fifth metacarpal bones are arthrodial. The bones are united by dorsal, volar, and interosseous ligaments. 4

The Dorsal Ligaments (ligamenta carpometacarpea dorsalia).—The dorsalligaments, the strongest and most distinct, connect the carpal and metacarpal bones on their dorsal surfaces. The second metacarpal bone receives two fasciculi, one from the greater, the other from the lesser multangular; the third metacarpal receives two, one each from the lesser multangular and capitate; the fourth two, one each from the capitate and hamate; the fifth receives a single fasciculus from the hamate, and this is continuous with a similar ligament on the volar surface, forming an incomplete capsule. 5

The Volar Ligaments (ligamenta carpometacarpea volaria; palmar ligaments).—The volar ligaments have a somewhat similar arrangement, with the exception of those of the third metacarpal, which are three in number: a lateral one from the greater multangular, situated superficial to the sheath of the tendon of the Flexor carpi radialis; and intermediate one from the capitate; and a medial one from the hamate. 6

The Interosseous Ligaments.—The interosseous ligaments consist of short, thick fibers, and are limited to one part of the carpometacarpal articulation; they connect the contiguous inferior angles of the capitate and hamate with the adjacent surfaces of the third and fourth metacarpal bones. 7

Synovial Membrane.—The synovial membrane is a continuation of that of the intercarpal joints. Occasionally, the joint between the hamate and the fourth and fifth metacarpal bones has a separate synovial membrane. 8
The synovial membranes of the wrist and carpus (Fig. 336) are thus seen to be five in number. The first passes from the lower end of the ulnar to the ulnar notch of the radius, and lines the upper surface of the articular disk. The second passes from the articular disk and the lower end of the radius above, to the bones of the first row below. The third, the most extensive, passes between the contiguous margins of the two rows of carpal bones, and sometimes, in the event of one of the interosseous ligaments being absent, between the bones of the second row to the carpal extremities of the second, third, fourth, and fifth metacarpal bones. The fourth extends from the margin of the greater multangular to the metacarpal bone of the thumb. The fifth runs between the adjacent margins of the triangular and pisiform bones. Occasionally the fourth and fifth carpometacarpal joints have a separate synovial membrane. 9

Movements.—The movements permitted in the carpometacarpal articulations of the fingers are limited to slight gliding of the articular surfaces upon each other, the extent of which varies in the different joints. The metacarpal bone of the little finger is most movable, then that of the ring finger; the metacarpal bones of the index and middle fingers are almost immovable. 10

6i. Intermetacarpal Articulations

(Articulationes Intermetacarpeæ; Articulations of the Metacarpal Bones with Each Other)

The bases of the second, third, fourth and fifth metacarpal bones articulate with one another by small surfaces covered with cartilage, and are connected together by dorsal, volar, and interosseous ligaments. 1
The dorsal (ligamenta basium oss. metacarp. dorsalia) and volar ligaments (ligamenta basium oss. metacarp. volaria; palmar ligaments) pass transversely from one bone to another on the dorsal and volar surfaces. The interosseous ligaments (ligamenta basium oss. metacarp. interossea) connect their contiguous surfaces, just distal to their collateral articular facets. 2
The synovial membrane for these joints is continuous with that of the carpometacarpal articulations. 3

The Transverse Metacarpal Ligament (ligamentum capitulorum [oss. metacarpalium] transversum) (Fig. 337).—This ligament is a narrow fibrous band, which runs across the volar surfaces of the heads of the second, third, fourth and fifth metacarpal bones, connecting them together. It is blended with the volar (glenoid) ligaments of the metacarpophalangeal articulations. Its volar surface is concave where the Flexor tendons pass over it; behind it the tendons of the Interossei pass to their insertions.

6j. Metacarpophalangeal Articulations

(Articulationes Metacarpophalangeæ; Metacarpophalangeal Joints) (Figs. 337, 338)

These articulations are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the first phalanges, with the exception of that of the thumb, which presents more of the characters of a ginglymoid joint. Each joint has a volar and two collateral ligaments. 1

FIG. 337– Metacarpophalangeal articulation and articulations of digit. Volar aspect. (See enlarged image)

FIG. 338– Metacarpophalangeal articulation and articulations of digit. Ulnar aspect. (See enlarged image)

The Volar Ligaments (glenoid ligaments of Cruveilhier; palmar or vaginal ligaments).—The volar ligaments are thick, dense, fibrocartilaginous structures, placed upon the volar surfaces of the joints in the intervals between the collateral ligaments, to which they are connected; they are loosely united to the metacarpal bones, but are very firmly attached to the bases of the first phalanges. Their volar surfaces are intimately blended with the transverse metacarpal ligament, and present grooves for the passage of the Flexor tendons, the sheaths surrounding which are connected to the sides of the grooves. Their deep surfaces form parts of the articular facets for the heads of the metacarpal bones, and are lined by synovial membranes. 2

The Collateral Ligaments (ligamenta collateralia; lateral ligaments).—The collateral ligaments are strong, rounded cords, placed on the sides of the joints; each is attached by one extremity to the posterior tubercle and adjacent depression on the side of the head of the metacarpal bone, and by the other to the contiguous extremity of the phalanx. 3
The dorsal surfaces of these joints are covered by the expansions of the Extensor tendons, together with some loose areolar tissue which connects the deep surfaces of the tendons to the bones. 4

Movements.—The movements which occur in these joints are flexion, extension, adduction, abduction, and circumduction; the movements of abduction and adduction are very limited, and cannot be performed when the fingers are flexed. 5

6k. Articulations of the Digits

(Articulationes Digitorum Manus; Interphalangeal Joints) (Figs. 337, 338)

The interphalangeal articulations are hinge-joints; each has a volar and two collateral ligaments. The arrangement of these ligaments is similar to those in the metacarpophalangeal articulations. The Extensor tendons supply the place of posterior ligaments. 1

Movements.—The only movements permitted in the interphalangeal joints are flexion and extension; these movements are more extensive between the first and second phalanges than between the second and third. The amount of flexion is very considerable, but extension is limited by the volar and collateral ligaments. 2

Muscles Acting on the Joints of the Digits.—Flexion of the metacarpophalangeal joints of the fingers is effected by the Flexores digitorum sublimis and profundus, Lumbricales, and Interossei, assisted in the case of the little finger by the Flexor digiti quinti brevis. Extension is produced by the Extensor digitorum communis, Extensor indicis proprius, and Extensor digiti quinti proprius. 3
Flexion of the interphalangeal joints of the fingers is accomplished by the Flexor digitorum profundus acting on the proximal and distal joints and by the Flexor digitorum sublimis acting on the proximal joints. Extension is effected mainly by the Lumbricales and Interossei, the long Extensors having little or no action upon these joints. 4
Flexion of the metacarpophalangeal joint of the thumb is effected by the Flexores pollicis longus and brevis; extension by the Extensores pollicis longus and brevis. Flexion of the interphalangeal joint is accomplished by the Flexor pollicis longus, and extension by the Extensor pollicis longus. 5

7. Articulations of the Lower Extremity. a. Coxal Articulation or Hip-joint

The articulations of the Lower Extremity comprise the following:
I. Hip.
V. Intertarsal.
II. Knee.
VI. Tarsometatarsal.
III. Tibiofibular.
VII. Intermetatarsal.
IV. Ankle.
VIII. Metatarsophalangeal.
IX. Articulations of the Digits.

1

Coxal Articulation or Hip-joint (Articulatio Coxæ)

This articulation is an enarthrodial or ball-and-socket joint, formed by the reception of the head of the femur into the cup-shaped cavity of the acetabulum. The articular cartilage on the head of the femur, thicker at the center than at the circumference, covers the entire surface with the exception of the fovea capitis femoris, to which the ligamentum teres is attached; that on the acetabulum forms an incomplete marginal ring, the lunate surface. Within the lunate surface there is a circular depression devoid of cartilage, occupied in the fresh state by a mass of fat, covered by synovial membrane. The ligaments of the joint are: 2
The Articular Capsule.
The Pubocapsular.
The Iliofemoral.
The Ligamentum Teres Femoris.
The Ischiocapsular.
The Glenoidal Labrum.
The Transverse Acetabular

The Articular Capsule (capsula articularis; capsular ligament) (Figs. 339, 340).—The articular capsule is strong and dense. Above, it is attached to the margin of the acetabulum 5 to 6 mm. beyond the glenoidal labrum behind; but in front, it is attached to the outer margin of the labrum, and, opposite to the notch where the margin of the cavity is deficient, it is connected to the transverse ligament, and by a few fibers to the edge of the obturator foramen. It surrounds the neck of the femur, and is attached, in front, to the intertrochanteric line; above, to the base of the neck; behind, to the neck, about 1.25 cm. above the intertrochanteric crest; below, to the lower part of the neck, close to the lesser trochanter. From its femoral attachment some of the fibers are reflected upward along the neck as longitudinal bands, termed retinacula. The capsule is much thicker at the upper and forepart of the joint, where the greatest amount of resistance is required; behind and below, it is thin and loose. It consists of two sets of fibers, circular and longitudinal. The circular fibers, zona orbicularis, are most abundant at the lower and back part of the capsule (Fig. 342), and form a sling or collar around the neck of the femur. Anteriorly they blend with the deep surface of the iliofemoral ligament, and gain an attachment to the anterior inferior iliac spine. The longitudinal fibers are greatest in amount at the upper and front part of the capsule, where they are reinforced by distinct bands, or accessory ligaments, of which the most important is the iliofemoral ligament. The other accessory bands are known as the pubocapsular and the ischiocapsular ligaments. The external surface of the capsule is rough, covered by numerous muscles, and separated in front from the Psoas major and Iliacus by a bursa, which not infrequently communicates by a circular aperture with the cavity of the joint. 3

FIG. 339– Right hip-joint from the front. (Spalteholz.) (See enlarged image)

The Iliofemoral Ligament (ligamentum iliofemorale; Y-ligament; ligament of Bigelow) (Fig. 339).—The iliofemoral ligament is a band of great strength which lies in front of the joint; it is intimately connected with the capsule, and serves to strengthen it in this situation. It is attached, above, to the lower part of the anterior inferior iliac spine; below, it divides into two bands, one of which passes downward and is fixed to the lower part of the intertrochanteric line; the other is directed downward and lateralward and is attached to the upper part of the same line. Between the two bands is a thinner part of the capsule. In some cases there is no division, and the ligament spreads out into a flat triangular band which is attached to the whole length of the intertrochanteric line. This ligament is frequently called the Y-shaped ligament of Bigelow; and its upper band is sometimes named the iliotrochanteric ligament. 4

FIG. 340– The hip-joint from behind. (Quain.) (See enlarged image)

The Pubocapsular Ligament (ligamentum pubocapsulare; pubofemoral ligament).—This ligament is attached, above, to the obturator crest and the superior ramus of the pubis; below, it blends with the capsule and with the deep surface of the vertical band of the oliofemoral ligament. 5

The Ischiocapsular Ligament (ligamentum ischiocapsulare; ischiocapsular band; ligament of Bertin).—The ischiocapsular ligament consists of a triangular band of strong fibers, which spring from the ischium below and behind the acetabulum, and blend with the circular fibers of the capsule (Fig. 340). 6

The Ligamentum Teres Femoris (Fig. 341).—The ligamentum teres femoris is a triangular, somewhat flattened band implanted by its apex into the antero-superior part of the fovea capitis femoris; its base is attached by two bands, one into either side of the acetabular notch, and between these bony attachments it blends with the transverse ligament. It is ensheathed by the synovial membrane, and varies greatly in strength in different subjects; occasionally only the synovial fold exists, and in rare cases even this is absent. The ligament is made tense when the thigh is semiflexed and the limb then adducted or rotated outward; it is, on the other hand, relaxed when the limb is abducted. It has, however, but little influence as a ligament. 7

FIG. 341– Left hip-joint, opened by removing the floor of the acetabulum from within the pelvis. (See enlarged image)

The Glenoidal Labrum (labrum glenoidale; cotyloid ligament).—The glenoidal labrum is a fibrocartilaginous rim attached to the margin of the acetabulum, the cavity of which it deepens; at the same time it protects the edge of the bone, and fills up the inequalities of its surface. It bridges over the notch as the transverse ligament, and thus forms a complete circle, which closely surrounds the head of the femur and assists in holding it in its place. It is triangular on section, its base being attached to the margin of the acetabulum, while its opposite edge is free and sharp. Its two surfaces are invested by synovial membrane, the external one being in contact with the capsule, the internal one being inclined inward so as to narrow the acetabulum, and embrace the cartilaginous surface of the head of the femur. It is much thicker above and behind than below and in front, and consists of compact fibers. 8

FIG. 342– Hip-joint, front view. The capsular ligament has been largely removed. (See enlarged image)

FIG. 343– Capsule of hip-joint (distended). Posterior aspect. (See enlarged image)

The Transverse Acetabular Ligament (ligamentum transversum acetabuli; transverse ligament).—This ligament is in reality a portion of the glenoidal labrum, though differing from it in having no cartilage cells among its fibers. It consists of strong, flattened fibers, which cross the acetabular notch, and convert it into a foramen through which the nutrient vessels enter the joint. 9

Synovial Membrane (Fig. 343).—The synovial membrane is very extensive. Commencing at the margin of the cartilaginous surface of the head of the femur, it covers the portion of the neck which is contained within the joint; from the neck it is reflected on the internal surface of the capsule, covers both surfaces of the glenoidal labrum and the mass of fat contained in the depression at the bottom of the acetabulum, and ensheathes the ligamentum teres as far as the head of the femur. The joint cavity sometimes communicates through a hole in the capsule between the vertical band of the iliofemoral ligament and the pubocapsular ligament with a bursa situated on the deep surfaces of the Psoas major and Iliacus. 10
The muscles in relation with the joint are, in front, the Psoas major and Iliacus, separated from the capsule by a bursa; above, the reflected head of the Rectus femoris and Glutæus minimus, the latter being closely adherent to the capsule; medially, the Obturator externus and Pectineus; behind, the Piriformis, Gemellus superior, Obturator internus, Gemellus inferior, Obturator externus, and Quadratus femoris (Fig. 344). 11

FIG. 344– Structures surrounding right hip-joint. (See enlarged image)

The arteries supplying the joint are derived from the obturator, medial femoral circumflex, and superior and inferior gluteals. 12
The nerves are articular branches from the sacral plexus, sciatic, obturator, accessory obturator, and a filament from the branch of the femoral supplying the Rectus femoris. 13

Movements.—The movements of the hip are very extensive, and consist of flexion, extension, adduction, abduction, circumduction, and rotation. 14
The length of the neck of the femur and its inclinations to the body of the bone have the effect of converting the angular movements of flexion, extension, adduction, and abduction partially into rotatory movements in the joint. Thus when the thigh is flexed or extended, the head of the femur, on account of the medial inclination of the neck, rotates within the acetabulum with only a slight amount of gliding to and fro. The forward slope of the neck similarly affects the movements of adduction and abduction. Conversely rotation of the thigh which is permitted by the upward inclination of the neck, is not a simple rotation of the head of the femur in the acetabulum, but is accompanied by a certain amount of gliding. 15
The hip-joint presents a very striking contrast to the shoulder-joint in the much more complete mechanical arrangements for its security and for the limitation of its movements. In the shoulder, as has been seen, the head of the humerus is not adapted at all in size to the glenoid cavity, and is hardly restrained in any of its ordinary movements by the capsule. In the hip-joint, on the contrary, the head of the femur is closely fitted to the acetabulum for an area extending over nearly half a sphere, and at the margin of the bony cup it is still more closely embraced by the glenoidal labrum, so that the head of the femur is held in its place by that ligament even when the fibers of the capsule have been quite divided. The iliofemoral ligament is the strongest of all the ligaments in the body, and is put on the stretch by any attempt to extend the femur beyond a straight line with the trunk. That is to say, this ligament is the chief agent in maintaining the erect position without muscular fatigue; for a vertical line passing through the center of gravity of the trunk falls behind the centers of rotation in the hip-joints, and therefore the pelvis tends to fall backward, but is prevented by the tension of the iliofemoral ligaments. The security of the joint may be provided for also by the two bones being directly united through the ligamentum teres; but it is doubtful whether this ligament has much influence upon the mechanism of the joint. When the knee is flexed, flexion of the hip-joint is arrested by the soft parts of the thigh and abdomen being brought into contact, and when the knee is extended, by the action of the hamstring muscles; extension is checked by the tension of the iliofemoral ligament; adduction by the thighs coming into contact; adduction with flexion by the lateral band of the iliofemoral ligament and the lateral part of the capsule; abduction by the medial band of the iliofemoral ligament and the pubocapsular ligament; rotation outward by the lateral band of the iliofemoral ligament; and rotation inward by the ischiocapsular ligament and the hinder part of the capsule. The muscles which flex the femur on the pelvis are the Psoas major, Iliacus, Rectus femoris, Sartorius, Pectineus, Adductores longus and brevis, and the anterior fibers of the Glutæi medius and minimus. Extension is mainly performed by the Glutæus maximus, assisted by the hamstring muscles and the ischial head of the Adductor magnus. The thigh is adducted by the Adductores magnus, longus, and brevis, the Pectineus, the Gracilis, and lower part of the Glutæus maximus, and abducted by the Glutæi medius and minimus, and the upper part of the Glutæus maximus. The muscles which rotate the thigh inward are the Glutæus minimus and the anterior fibers of the Glutæus medius, the Tensor fasciæ latæ and the Iliacus and Psoas major; while those which rotate it outward are the posterior fibers of the Glutæus medius, the Piriformis, Obturatores externus and internus, Gemelli superior and inferior, Quadratus femoris, Glutæus maximus, the Adductores longus, brevis, and magnus, the Pectineus, and the Sartorius. 16

7b. The Knee-joint

(Articulatio Genu)

The knee-joint was formerly described as a ginglymus or hinge-joint, but is really of a much more complicated character. It must be regarded as consisting of three articulations in one: two condyloid joints, one between each condyle of the femur and the corresponding meniscus and condyle of the tibia; and a third between the patella and the femur, partly arthrodial, but not completely so, since the articular surfaces are not mutually adapted to each other, so that the movement is not a simple gliding one. This view of the construction of the knee-joint receives confirmation from the study of the articulation in some of the lower mammals, where, corresponding to these three subdivisions, three synovial cavities are sometimes found, either entirely distinct or only connected together by small communications. This view is further rendered probable by the existence in the middle of the joint of the two cruciate ligaments, which must be regarded as the collateral ligaments of the medial and lateral joints. The existence of the patellar fold of synovial membrane would further indicate a tendency to separation of the synovial cavity into two minor sacs, one corresponding to the lateral and the other to the medial joint. 1
The bones are connected together by the following ligaments: 2
The Articular Capsule.
The Anterior Cruciate.
The Ligamentum Patellæ.
The Posterior Cruciate.
The Oblique Popliteal.
The Medial and Lateral Menisci.
The Tibial Collateral.
The Transverse.
The Fibular Collateral.
The Coronary.

The Articular Capsule (capsula articularis; capsular ligament) (Fig. 345).—The articular capsule consists of a thin, but strong, fibrous membrane which is strengthened in almost its entire extent by bands inseparably connected with it. Above and in front, beneath the tendon of the Quadriceps femoris, it is represented only by the synovial membrane. Its chief strengthening bands are derived from the fascia lata and from the tendons surrounding the joint. In front, expansions from the Vasti and from the fascia lata and its iliotibial band fill in the intervals between the anterior and collateral ligaments, constituting the medial and lateral patellar retinacula. Behind the capsule consists of vertical fibers which arise from the condyles and from the sides of the intercondyloid fossa of the femur; the posterior part of the capsule is therefore situated on the sides of and in front of the cruciate ligaments, which are thus excluded from the joint cavity. Behind the cruciate ligaments is the oblique popliteal ligament which is augmented by fibers derived from the tendon of the Semimembranosus. Laterally, a prolongation from the iliotibial band fills in the interval between the oblique popliteal and the fibular collateral ligaments, and partly covers the latter. Medially, expansions from the Sartorius and Semimembranosus pass upward to the tibial collateral ligament and strengthen the capsule. 3

The Ligamentum Patellæ (anterior ligament) (Fig. 345).—The ligamentum patellæ is the central portion of the common tendon of the Quadriceps femoris, which is continued from the patella to the tuberosity of the tibia. It is a strong, flat, ligamentous band, about 8 cm. in length, attached, above, to the apex and adjoining margins of the patella and the rough depression on its posterior surface; below, to the tuberosity of the tibia; its superficial fibers are continuous over the front of the patella with those of the tendon of the Quadriceps femoris. The medial and lateral portions of the tendon of the Quadriceps pass down on either side of the patella, to be inserted into the upper extremity of the tibia on either side of the tuberosity; these portions merge into the capsule, as stated above, forming the medial and lateral patellar retinacula. The posterior surface of the ligamentum patellæ is separated from the synovial membrane of the joint by a large infrapatellar pad of fat, and from the tibia by a bursa. 4

FIG. 345– Right knee-joint. Anterior view. (See enlarged image)

The Oblique Popliteal Ligament (ligamentum popliteum obliquum; posterior ligament) (Fig. 346).—This ligament is a broad, flat, fibrous band, formed of fasciculi separated from one another by apertures for the passage of vessels and nerves. It is attached above to the upper margin of the intercondyloid fossa and posterior surface of the femur close to the articular margins of the condyles, and below to the posterior margin of the head of the tibia. Superficial to the main part of the ligament is a strong fasciculus, derived from the tendon of the Semimembranosus and passing from the back part of the medial condyle of the tibia obliquely upward and lateralward to the back part of the lateral condyle of the femur. The oblique popliteal ligament forms part of the floor of the popliteal fossa, and the popliteal artery rests upon it. 5

The Tibial Collateral Ligament (ligamentum collaterale tibiale; internal lateral ligament) (Fig. 345).—The tibial collateral is a broad, flat, membranous band, situated nearer to the back than to the front of the joint. It is attached, above, to the medial condyle of the femur immediately below the adductor tubercle; below, to the medial condyle and medial surface of the body of the tibia. The fibers of the posterior part of the ligament are short and incline backward as they descend; they are inserted into the tibia above the groove for the Semimembranosus. The anterior part of the ligament is a flattened band, about 10 cm. long, which inclines forward as it descends. It is inserted into the medial surface of the body of the tibia about 2.5 cm. below the level of the condyle. It is crossed, at its lower part, by the tendons of the Sartorius, Gracilis, and Semitendinosus, a bursa being interposed. Its deep surface covers the inferior medial genicular vessels and nerve and the anterior portion of the tendon of the Semimembranosus, with which it is connected by a few fibers; it is intimately adherent to the medial meniscus. 6

FIG. 346– Right knee-joint. Posterior view. (See enlarged image)

FIG. 347– Right knee-joint, from the front, showing interior ligaments. (See enlarged image)

The Fibular Collateral Ligament (ligamentum collaterale fibulare; external lateral or long external lateral ligament) (Fig. 348).—The fibular collateral is a strong, rounded, fibrous cord, attached, above, to the back part of the lateral condyle of the femur, immediately above the groove for the tendon of the Popliteus; below, to the lateral side of the head of the fibula, in front of the styloid process. The greater part of its lateral surface is covered by the tendon of the Biceps femoris; the tendon, however, divides at its insertion into two parts, which are separated by the ligament. Deep to the ligament are the tendon of the Popliteus, and the inferior lateral genicular vessels and nerve. The ligament has no attachment to the lateral meniscus. 7
An inconstant bundle of fibers, the short fibular collateral ligament, is placed behind and parallel with the preceding, attached, above, to the lower and back part of the lateral condyle of the femur; below, to the summit of the styloid process of the fibula. Passing deep to it are the tendon of the Popliteus, and the inferior lateral genicular vessels and nerve. 8

The Cruciate Ligaments (ligamenta cruciata genu; crucial ligaments).—The cruciate ligaments are of considerable strength, situated in the middle of the joint, nearer to its posterior than to its anterior surface. They are called cruciate because they cross each other somewhat like the lines of the letter X; and have received the names anterior and posterior, from the position of their attachments to the tibia. 9
The Anterior Cruciate Ligament (ligamentum cruciatum anterius; external crucial ligament) (Fig. 347) is attached to the depression in front of the intercondyloid eminence of the tibia, being blended with the anterior extremity of the lateral meniscus; it passes upward, backward, and lateralward, and is fixed into the medial and back part of the lateral condyle of the femur. 10

FIG. 348– Left knee-joint from behind, showing interior ligaments. (See enlarged image)

The Posterior Cruciate Ligament (ligamentum cruciatum posterius; internal crucial ligament) (Fig. 348) is stronger, but shorter and less oblique in its direction, than the anterior. It is attached to the posterior intercondyloid fossa of the tibia, and to the posterior extremity of the lateral meniscus; and passes upward, forward, and medialward, to be fixed into the lateral and front part of the medial condyle of the femur. 11

The Menisci (semilunar fibrocartilages) (Fig. 349).—The menisci are two crescentic lamellæ, which serve to deepen the surfaces of the head of the tibia for articulation with the condyles of the femur. The peripheral border of each meniscus is thick, convex, and attached to the inside of the capsule of the joint; the opposite border is thin, concave, and free. The upper surfaces of the menisci are concave, and in contact with the condyles of the femur; their lower surfaces are flat, and rest upon the head of the tibia; both surfaces are smooth, and invested by synovial membrane. Each meniscus covers approximately the peripheral two-thirds of the corresponding articular surface of the tibia. 12
The medial meniscus (meniscus medialis; internal semilunar fibrocartilage) is nearly semicircular in form, a little elongated from before backward, and broader behind than in front; its anterior end, thin and pointed, is attached to the anterior intercondyloid fossa of the tibia, in front of the anterior cruciate ligament; its posterior end is fixed to the posterior intercondyloid fossa of the tibia, between the attachments of the lateral meniscus and the posterior cruciate ligament. 13

FIG. 349– Head of right tibia seen from above, showing menisci and attachments of ligaments. (See enlarged image)

The lateral meniscus (meniscus lateralis; external semilunar fibrocartilage) is nearly circular and covers a larger portion of the articular surface than the medial one. It is grooved laterally for the tendon of the Popliteus, which separates it from the fibular collateral ligament. Its anterior end is attached in front of the intercondyloid eminence of the tibia, lateral to, and behind, the anterior cruciate ligament, with which it blends; the posterior end is attached behind the intercondyloid eminence of the tibia and in front of the posterior end of the medial meniscus. The anterior attachment of the lateral meniscus is twisted on itself so that its free margin looks backward and upward, its anterior end resting on a sloping shelf of bone on the front of the lateral process of the intercondyloid eminence. Close to its posterior attachment it sends off a strong fasciculus, the ligament of Wrisberg (Figs. 348, 349), which passes upward and medialward, to be inserted into the medial condyle of the femur, immediately behind the attachment of the posterior cruciate ligament. Occasionally a small fasciculus passes forward to be inserted into the lateral part of the anterior cruciate ligament. The lateral meniscus gives off from its anterior convex margin a fasciculus which forms the transverse ligament. 14

The Transverse Ligament (ligamentum transversum genu).—The transverse ligament connects the anterior convex margin of the lateral meniscus to the anterior end of the medial meniscus; its thickness varies considerably in different subjects, and it is sometimes absent. 15
The coronary ligaments are merely portions of the capsule, which connect the periphery of each meniscus with the margin of the head of the tibia. 16

Synovial Membrane.—The synovial membrane of the knee-joint is the largest and most extensive in the body. Commencing at the upper border of the patella, it forms a large cul-de-sac beneath the Quadriceps femoris (Figs. 350, 351) on the lower part of the front of the femur, and frequently communicates with a bursa interposed between the tendon and the front of the femur. The pouch of synovial membrane between the Quadriceps and front of the femur is supported, during the movements of the knee, by a small muscle, the Articularis genu, which is inserted into it. On either side of the patella, the synovial membrane extends beneath the aponeuroses of the Vasti, and more especially beneath that of the Vastus medialis. Below the patella it is separated from the ligamentum patellæ by a considerable quantity of fat, known as the infrapatellar pad. From the medial and lateral borders of the articular surface of the patella, reduplications of the synovial membrane project into the interior of the joint. These form two fringe-like folds termed the alar folds; below, these folds converge and are continued as a single band, the patellar fold (ligamentum mucosum), to the front of the intercondyloid fossa of the femur. On either side of the joint, the synovial membrane passes downward from the femur, lining the capsule to its point of attachment to the menisci; it may then be traced over the upper surfaces of these to their free borders, and thence along their under surfaces to the tibia (Figs. 351, 352). At the back part of the lateral meniscus it forms a cul-de-sac between the groove on its surface and the tendon of the Popliteus; it is reflected across the front of the cruciate ligaments, which are therefore situated outside the synovial cavity. 17

FIG. 350– Sagittal section of right knee-joint. (See enlarged image)

Bursæ.—The bursæ near the knee-joint are the following: In front there are four bursæ: a large one is interposed between the patella and the skin, a small one between the upper part of the tibia and the ligamentum patellæ, a third between the lower part of the tuberosity of the tibia and the skin, and a fourth between the anterior surface of the lower part of the femur and the deep surface of the Quadriceps femoris, usually communicating with the knee-joint. Laterally there are four bursæ: (1) one (which sometimes communicates with the joint) between the lateral head of the Gastrocnemius and the capsule; (2) one between the fibular collateral ligament and the tendon of the Biceps; (3) one between the fibular collateral ligament and the tendon of the Popliteus (this is sometimes only an expansion from the next bursa); (4) one between the tendon of the Popliteus and the lateral condyle of the femur, usually an extension from the synovial membrane of the joint. Medially, there are five bursæ: (1) one between the medial head of the Gastrocnemius and the capsule; this sends a prolongation between the tendon of the medial head of the Gastrocnemius and the tendon of the Semimembranosus and often communicates with the joint; (2) one superficial to the tibial collateral ligament, between it and the tendons of the Sartorius, Gracilis, and Semitendinosus; (3) one deep to the tibial collateral ligament, between it and the tendon of the Semimembranosus (this is sometimes only an expansion from the next bursa); (4) one between the tendon of the Semimembranosus and the head of the tibia; (5) occasionally there is a bursa between the tendons of the Semimembranosus and Semitendinosus. 18

FIG. 351– Capsule of right knee-joint (distended). Lateral aspect. (See enlarged image)

Structures Around the Joint.—In front, and at the sides, is the Quadriceps femoris; laterally the tendons of the Biceps femoris and Popliteus and the common peroneal nerve; medially, the Sartorius, Gracilis, Semitendinosus, and Semimembranosus; behind, the popliteal vessels and the tibial nerve, Popliteus, Plantaris, and medial and lateral heads of the Gastrocnemius, some lymph glands, and fat. 19
The arteries supplying the joint are the highest genicular (anastomotica magna), a branch of the femoral, the genicular branches of the popliteal, the recurrent branches of the anterior tibial, and the descending branch from the lateral femoral circumflex of the profunda femoris. 20
The nerves are derived from the obturator, femoral, tibial, and common peroneal. 21

Movements.—The movements which take place at the knee-joint are flexion and extension, and, in certain positions of the joint, internal and external rotation. The movements of flexion and extension at this joint differ from those in a typical hinge-joint, such as the elbow, in that (a) the axis around which motion takes place is not a fixed one, but shifts forward during extension and backward during flexion; (b) the commencement of flexion and the end of extension are accompanied by rotatory movements associated with the fixation of the limb in a position of great stability. The movement from full flexion to full extension may therefore be described in three phases: 22
1. In the fully flexed condition the posterior parts of the femoral condyles rest on the corresponding portions of the meniscotibial surfaces, and in this position a slight amount of simple rolling movement is allowed. 23

FIG. 352– Capsule of right knee-joint (distended). Posterior aspect. (See enlarged image)

2. During the passage of the limb from the flexed to the extended position a gliding movement is superposed on the rolling, so that the axis, which at the commencement is represented by a line through the inner and outer condyles of the femur, gradually shifts forward. In this part of the movement, the posterior two-thirds of the tibial articular surfaces of the two femoral condyles are involved, and as these have similar curvatures and are parallel to one another, they move forward equally. 24
3. The lateral condyle of the femur is brought almost to rest by the tightening of the anterior cruciate ligament; it moves, however, slightly forward and medialward, pushing before it the anterior part of the lateral meniscus. The tibial surface on the medial condyle is prolonged farther forward than that on the lateral, and this prolongation is directed lateralward. When, therefore, the movement forward of the condyles is checked by the anterior cruciate ligament, continued muscular action causes the medial condyle, dragging with it the meniscus, to travel backward and medialward, thus producing an internal rotation of the thigh on the leg. When the position of full extension is reached the lateral part of the groove on the lateral condyle is pressed against the anterior part of the corresponding meniscus, while the medial part of the groove rests on the articular margin in front of the lateral process of the tibial intercondyloid eminence. Into the groove on the medial condyle is fitted the anterior part of the medial meniscus, while the anterior cruciate ligament and the articular margin in front of the medial process of the tibial intercondyloid eminence are received into the forepart of the intercondyloid fossa of the femur. This third phase by which all these parts are brought into accurate apposition is known as the “screwing home,” or locking movement of the joint. 25
The complete movement of flexion is the converse of that described above, and is therefore preceded by an external rotation of the femur which unlocks the extended joint. 26
The axes around which the movements of flexion and extension take place are not precisely at right angles to either bone; in flexion, the femur and tibia are in the same plane, but in extension the one bone forms an angle, opening lateralward with the other. 27
In addition to the rotatory movements associated with the completion of extension and the initiation of flexion, rotation inward or outward can be effected when the joint is partially flexed; these movements take place mainly between the tibia and the menisci, and are freest when the leg is bent at right angles with the thigh. 28
Movements of Patella.—The articular surface of the patella is indistinctly divided into seven facets—upper, middle, and lower horizontal pairs, and a medial perpendicular facet (Fig. 353). When the knee is forcibly flexed, the medial perpendicular facet is in contact with the semilunar surface on the lateral part of the medial condyle; this semilunar surface is a prolongation backward of the medial part of the patellar surface. As the leg is carried from the flexed to the extended position, first the highest pair, then the middle pair, and lastly the lowest pair of horizontal facets is successively brought into contact with the patellar surface of the femur. In the extended position, when the Quadriceps femoris is relaxed, the patella lies loosely on the front of the lower end of the femur. 29
During flexion, the ligamentum patellæ is put upon the stretch, and in extreme flexion the posterior cruciate ligament, the oblique popliteal, and collateral ligaments, and, to a slight extent, the anterior cruciate ligament, are relaxed. Flexion is checked during life by the contact of the leg with the thigh. When the knee-joint is fully extended the oblique popliteal and collateral ligaments, the anterior cruciate ligament, and the posterior cruciate ligament, are rendered tense; in the act of extending the knee, the ligamentum patellæ is tightened by the Quadriceps femoris, but in full extension with the heel supported it is relaxed. Rotation inward is checked by the anterior cruciate ligament; rotation outward tends to uncross and relax the cruciate ligaments, but is checked by the tibial collateral ligament. The main function of the cruciate ligament is to act as a direct bond between the tibia and femur and to prevent the former bone from being carried too far backward or forward. They also assist the collateral ligaments in resisting any bending of the joint to either side. The menisci are intended, as it seems, to adapt the surfaces of the tibia to the shape of the femoral condyles to a certain extent, so as to fill up the intervals which would otherwise be left in the varying positions of the joint, and to obviate the jars which would be so frequently transmitted up the limb in jumping or by falls on the feet; also to permit of the two varieties of motion, flexion and extension, and rotation, as explained above. The patella is a great defence to the front of the knee-joint, and distributes upon a large and tolerably even surface, during kneeling, the pressure which would otherwise fall upon the prominent ridges of the condyles; it also affords leverage to the Quadriceps femoris. 30

FIG. 353– Posterior surface of the right patella, showing diagrammatically the areas of contact with the femur in different positions of the knee. (See enlarged image)

When standing erect in the attitude of “attention,” the weight of the body falls in front of a line carried across the centers of the knee-joints, and therefore tends to produce overextension of the articulations; this, however, is prevented by the tension of the anterior cruciate, oblique popliteal, and collateral ligaments. 31
Extension of the leg on the thigh is performed by the Quadriceps femoris; flexion by the Biceps femoris, Semitendinosus, and Semimembranosus, assisted by the Gracilis, Sartorius, Gastrocnemius, Popliteus, and Plantaris. Rotation outward is effected by the Biceps femoris, and rotation inward by the Popliteus, Semitendinosus, and, to a slight extent, the Semimembranosus, the Sartorius, and the Gracilis. The Popliteus comes into action especially at the commencement of the movement of flexion of the knee; by its contraction the leg is rotated inward, or, if the tibia be fixed, the thigh is rotated outward, and the knee-joint is unlocked. 32

7c. Articulations between the Tibia and Fibula

The articulations between the tibia and fibula are effected by ligaments which connect the extremities and bodies of the bones. The ligaments may consequently be subdivided into three sets: (1) those of the Tibiofibular articulation; (2) the interosseous membrane; (3) those of the Tibiofibular syndesmosis.

Tibiofibular Articulation (articulatio tibiofibularis; superior tibiofibular articulation).—This articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula. The contiguous surfaces of the bones present flat, oval facets covered with cartilage and connected together by an articular capsule and by anterior and posterior ligaments.

The Articular Capsule (capsula articularis; capsular ligament).—The articular capsule surrounds the articulation, being attached around the margins of the articular facets on the tibia and fibula; it is much thicker in front than behind.

The Anterior Ligament (anterior superior ligament).—The anterior ligament of the head of the fibula (Fig. 347) consists of two or three broad and flat bands, which pass obliquely upward from the front of the head of the fibula to the front of the lateral condyle of the tibia.

The Posterior Ligament (posterior superior ligament).—The posterior ligament of the head of the fibula (Fig. 348) is a single thick and broad band, which passes obliquely upward from the back of the head of the fibula to the back of the lateral condyle of the tibia. It is covered by the tendon of the Popliteus.

Synovial Membrane.—A synovial membrane lines the capsule; it is continuous with that of the knee-joint in occasional cases when the two joints communicate. 6

Interosseous Membrane (membrana interossea cruris; middle tibiofibular ligament).—An interosseous membrane extends between the interosseous crests of the tibia and fibula, and separates the muscles on the front from those on the back of the leg. It consists of a thin, aponeurotic lamina composed of oblique fibers, which for the most part run downward and lateralward; some few fibers, however, pass in the opposite direction. It is broader above than below. Its upper margin does not quite reach the tibiofibular joint, but presents a free concave border, above which is a large, oval aperture for the passage of the anterior tibial vessels to the front of the leg. In its lower part is an opening for the passage of the anterior peroneal vessels. It is continuous below with the interosseous ligament of the tibiofibular syndesmosis, and presents numerous perforations for the passage of small vessels. It is in relation, in front, with the Tibialis anterior, Extensor digitorum longus, Extensor hallucis proprius, Peronæus tertius, and the anterior tibial vessels and deep peroneal nerve; behind, with the Tibialis posterior and Flexor hallucis longus. 7

Tibiofibular Syndesmosis (syndesmosis tibiofibularis; inferior tibiofibular articulation).—This syndesmosis is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough concave surface on the lateral side of the tibia. Below, to the extent of about 4 mm. these surfaces are smooth, and covered with cartilage, which is continuous with that of the ankle-joint. The ligaments are: anterior, posterior, inferior transverse, and interosseous. 8

The Anterior Ligament (ligamentum malleoli lateralis anterius; anterior inferior ligament).—The anterior ligament of the lateral malleolus (Fig. 355) is a flat, triangular band of fibers, broader below than above, which extends obliquely downward and lateralward between the adjacent margins of the tibia and fibula, on the front aspect of the syndesmosis. It is in relation, in front, with the Peronæus tertius, the aponeurosis of the leg, and the integument; behind, with the interosseous ligament; and lies in contact with the cartilage covering the talus. 9

The Posterior Ligament (ligamentum malleoli lateralis posterius; posterior inferior ligament).—The posterior ligament of the lateral malleolus (Fig. 355), smaller than the preceding, is disposed in a similar manner on the posterior surface of the syndesmosis. 10

The Inferior Transverse Ligament.—The inferior transverse ligament lies in front of the posterior ligament, and is a strong, thick band, of yellowish fibers which passes transversely across the back of the joint, from the lateral malleolus to the posterior border of the articular surface of the tibia, almost as far as its malleolar process. This ligament projects below the margin of the bones, and forms part of the articulating surface for the talus. 11

The Interosseous Ligament.—The interosseous ligament consists of numerous short, strong, fibrous bands, which pass between the contiguous rough surfaces of the tibia and fibula, and constitute the chief bond of union between the bones. It is continuous, above, with the interosseous membrane (Fig. 356). 12

Synovial Membrane.—The synovial membrane associated with the small arthrodial part of this joint is continuous with that of the ankle-joint.