Tear of the joint capsule. Initial dislocation of the patella Rupture of quadriceps tendon. Torn menisci do not usually result in hemarthroses. The inner two thirds of the menisci are cartilaginous and avascular. The outer one third is fibrous and vascular.
Most tears occur in the inner avascular portions.
To be thorough, check active motion first, and if it is abnormal, passive motion and in selected cases, resisted motion. Pay particular attention to the end point of extension. When checking passive extension, apply a reasonable amount of force while watching the patient's facial expression for evidence of induced pain. A slight limitation of extension, or pain at the extreme of extension may be caused by an underlying abnormality such as an effusion or a meniscal tear. Compare the normal side to the affected side.