Hypothesis 3 Congenital abnormalities-- A shallow trochlear groove, lateral bowing of the femur, internal rotation of the tibia, or hypoplasia of the medial femoral condyle are all congenital bone abnormalities that would cause the patellar ligament to shift out of place. This would cause the medial patellar luxation. An ectopic development of the patella medial or lateral to the trochlear groove of the femur could also lead to patellar luxation.