Influence of developmental hip dislocation on femoral head sphericity: experimental study in dogs.

The aim of this study was to assess the growth and the changes in the shape of a femoral head in dog puppies with dislocated and unstable hip joints. Ten 5-week-old, mountain shepherd puppies were divided into two subgroups. In five animals, the femoral head was dislocated, and in the other five dogs, femoral head was reduced after the dislocation procedure, making the joint congruent but unstable. After 4 weeks the animals were euthanised. The optical method of contour measurement of the femoral head sphericity was used. The shape of the dislocated femoral head differed from the normal one. The medial part was extended into beard-like form. The overgrowth of the femoral heads was significant and from 38% to 61% larger compared with the normal contralateral head. The unstable head of the second group did not differ in the shape nor in its size from the contralateral normal one. The large adaptive and deforming changes of shape in the dislocated femoral heads in our study show the pronounced malformation of the joint. The shape of beard-like deformity may be explained by the enlargement of contact surface between the medial part of the head and illiac bone. The restricting modelling role of the acetabulum, the minor vascular impairment during the surgery and the short time of follow-up were possible factors contributing to the minimal changes of the affected femoral head in the unstable but congruent hip joint.