[Diagnosis and therapy of chronic patellofemoral instability].

The chronic patellofemoral instability is a multifactorial disease, which is mostly congenital. Luxation of the patella is mainly atraumatic. Sole conservative treatment is often unsuccessful. Surgical treatment is needed in most cases and requires consideration of all pathologic changes of the patella-stabilizing anatomic structures. Rupture of the medial patellofemoral ligament is almost pathognomonic. In addition, the frontal mechanical axis, rotation of femur and tibia, the trochlear shape, the distance from the tibial tuberosity to the trochlear sulcus and the patellar height play an important role. Often, in addition to soft tissue reconstruction, the bony alignment needs to be corrected. Consideration of risk factors in both adult and adolescent patients is needed to avoid recurrent instability.