Roger J, et al. - Experts tested the presumption that suggested the presence of morphological differences in the posterior part of the femoral epiphysis in trochlear dysplasia (TD) compared to a control group. They also postulated that the posterior bicondylar angle (PCA), in the axial plane, was increased in TD. In patellar instability (PI) with TD, not only an anterior but also a posterior anomaly was seen. The severity of the anterior deformation was correlated to the PCA: in other words, in flexure the knee is placed in valgus which promoted the external dislocation of the patella.