This hyperflexion injury to the knee damages the chondroepiphysis, the mostly cartilaginous secondary ossification center of the proximal tibia. The patient will typically have knee pain, with significant effusion, and will refuse to move the knee. It is important to be alert for damage to other knee structures. Tenderness, especially at the joint line, suggests mid- to posterior meniscal injury. This specialized view outlines the femoral notch and tibial eminence.
Management depends on the amount of displacement and comminution of the fragment.
Aspirating the joint may make the patient more comfortable and able to extend the knee farther. If he or she can't extend the knee fully, there may be a mechanical block, perhaps from a malrotated fracture fragment or a trapped meniscus. Fixation is required for the displaced fragments once they are reduced. There is often mild anterior translation on follow-up examination, but this does not result in functional instability. In this injury, the chondral part of the osseous patella is pulled off by the patellar tendon, usually by a hyperflexion injury.