Congenital dislocation of the hip: a biomechanical study in autopsy specimens

The role of mechanical factors in neonatal hip instability was studied in four experimental series of autopsy specimens. The induced hip deformation and dislocation were examined by serial cryosectioning and cryodissection. Loading of the hips at 45 degrees of flexion with moderate forces for 3 h resulted in deformation and dislocation similar to those found at autopsy in congenital dislocation of the hip. There was no macroscopic damage to the joints. Loading at 135 degrees of flexion--to simulate a breech position--also resulted in dislocation, but the cartilage deformation was less pronounced than after loading at 45 degrees of flexion. When the same hip was loaded first at 135 degrees of flexion for 3 h and then at 45 degrees of flexion for another 3 h, the findings were similar to those following loading at 45 degrees of flexion alone. Thus a redeformation of the hip had taken place during the second step of the experiment. After unloading of the deformed and dislocated hips, marked joint laxity was observed, and examination 3 h after unloading showed incomplete recovery of the deformation.