Osteoarthritis

Pathophysiology of osteoarthritis

1) osteoarthritis is marked by progressive destruction of articular cartilage
2) most common in weight-bearing joints and fingers or joints subjected to trauma
3) classified as primary (or idiopathic) and secondary
4) development depends on four contributing factors – genetic predisposition, decreased resilence of articular cartilage, increased mechanical load on chrondrocytes (e.g., congenital hip dysplasia), increased stiffness of epiphyseal bone (e.g., Paget’s disease of bone)

Signs and Symptoms

1) pain in involved joint (typically worse with activity and improved with rest)
2) enlarged joints
3) morning stiffness in joints
4) presence of Bouchard’s nodes and Heberden’s nodes

Characteristic Test Findings

Radiology

1) narrowed joint spaces owing to bony overgrowth
2) increased thickness of subchondral bone
3) subchondral bone cysts
4) osteophytes
5) “lipping” pattern in vertebrae from overlapping osteophytes

Histology/Gross Pathology

1) joint narrowing
2) subchondral bone thickening
3) mild inflammation in synovium

Associated Conditions

Secondary causes

1) inflammatory diseases
2) infection (e.g., Lyme disease)
3) metabolic disease with crystal deposits
4) immune diseases with deposition of immune complexes

Biochemistry

1) initial damage occurs in setting of repair; eventually these attempts cannot keep pace with resulting destruction of joint surfaces
2) decreased proteoglycan content and aggregation
3) increased chondroitin sulfate
4) decreased keratan sulfate
5) decreased water content

Inheritance/Epidemiology

1) osteoarthritis before age 45 years is more common in men; > 45 years more common in women
2) genetic predisposition exists

Treatment

1) acupuncture
2) analgesics
3) weight loss
4) exercise
5) joint replacement in severe cases
6) some data have published concerning effectiveness of glucoasamine

Tips for USMLE

1) chondromalacia is a subtype of osteoarthritis that affects the patellar surface of the femoral condyles in young people with pain and stiffness in the knees
2) pain at base of thumb is very characteristic
3) Bouchard’s nodes are osteophytes at proximal interphalangeal joints
4) Heberden’s nodes are osteophytes at distal interphalangeal joints