Spiral fracture of proximal fibula, usually seen with tear of anterior tibiofibular ligament and resulting unstable ankle joint. Injury can be difficult to detect if there is no accompanying ankle fracture. Cause is severe external rotation of foot. Fracture should be suspected if there is medial or posterior malleolar fracture in absence of lateral malleolar fracture or widened joint space between talus and medial malleolus in absence of distal fibular fracture. Break is also associated with rupture of deltoid ligament.