Genu valgus deformity occur when :

In genu valgum or knock-knee deformity, as the mechanical axis shifts laterally, pathological stress is placed on the lateral femur and tibia, inhibiting growth and possibly leading to a vicious cycle. Not only is physeal growth inhibited, but also the Hueter-Volkmann effect upon the entire epiphysis prevents its normal expansion. According to the Hueter-Volkmann principle, continuous or excessive compressive forces upon the epiphysis have an inhibitory effect upon growth. Consequently, growth in the lateral condyle of the femur is suppressed globally, resulting in a shallow femoral sulcus and a propensity for the patella to tilt and subluxate laterally.