Hypothesis 3 
Congenital malformation of trochlear ridge
A congenital malformation of the trochlear ridge can be caused by failure to express normal antiversion of the femur, dysplasia of the quadriceps muscle, or trauma disrupting lateral femoropatella restraints.  Increased force on the medial aspect of the femur slows growth of the medial condyle and accelerates growth of the lateral condyle.  This results in medial displacement of the tibial turbercle and displacement of the patella medially.  The displacement of the patella increases overtime due to soft tissue stretching and increased skeletal deformity. This can be a unilateral or bilateral malformation and can result in varying degrees of luxation and lameness. The trochlear groove is the normal location of the patella if either trochlear ridge is smaller than normal or abnormal forces are placed on the patella it may luxate.