 In this condition, the patella repetitively subluxates and places strain on the medial restraints and excessive stress/tension on the patellofemoral joint.Patellar subluxation can be caused by osseous abnormalities, such as incorrect articulation of the femoral groove with the patella, trochlear dysplasia, or patella alta, which is a distance of greater than 20 mm between the tibial tubercle and the trochlear groove.It can also result from soft-tissue abnormalities, such as a torn medial patellofemoral ligament, or a weakened vastus medialis obliquus.