Originally the main idea was to obtain a stable patella, i.e., to stabilize the "slipping patella". In the past many conditions like patella alta, ligamentous laxity, PF bone hypoplasia, weakness of the quadriceps muscle, genu valgum or genu recurvatum were thought to predispose to patellar instability. For a long period muscle exercises were instituted to strengthen the weak m.vastus medialis and to make vastus lateralis stronger. This pulls the patella laterally, especially during running or jumping, when lateral luxation of the patella occurs. Muscle imbalance as well as anatomical abnormalities are the basis both for patellar instabilities and reasonable surgical procedures were: proximal extensor mechanism realignment, proximal capsular reefing, patellar tendon splitting and its medial transfer. On the other hand bone procedures on the hypoplastic lateral femoral condyle were also performed by Albee, as well as tibial tubercle transfer and trochleoplasty by deepening of the trochlea (Dejour). An understanding of the pathoanatomic basis is the corner stone for