The total functional stability is dependent on optimal synergic collaboration of the skeletal, ligamentous and muscular stabilizers, all working together. The skeletal geometry by its own creates a passive stability during knee motion. The geometry of the trochlear groove is of high importance during 0°-30° of flexion (30°-0° of extension) where most of the dislocations occur. The skeletal stability can be affected by patellofemoral dysplasia, where the geometric configuration of the trochlea is primarily not developed. The patella shape usually plays a secondary role even if it is found dysplastic