BIOMECHANICAL CONSEQUENCES OF FRACTURE AND REPAIR OF THE POSTERIOR WALL OF THE ACETABULUM

We measured the distribution of contact area and pressure between the acetabulum and the femoral head of cadaveric pelves in three different conditions: intact, with an operatively created fracture of the poste rior wall, and after anatomical reduction and fixation of the fracture with a buttress plate and interfragmentary screws. The study involved eight cadaveric hip joints from five pelves loaded to 2000 newtons in simulated single-limb stance. Measurements were made with pressure-se nsitive film. The acetabulum was divided into three areas - the anteri or wall, the superior aspect, and the posterior wall - for the analysi s of the data. Creation of a fracture of the posterior wall was follow ed by an increase in contact area, maximum pressure, and contact force in the superior aspect of the acetabulum. A concomitant decrease in t hese parameters was observed in the anterior and posterior walls. Anat omical reduction and fixation of the fracture with a plate and screws did not restore the pattern of loading to pre-injury levels. CLINICAL RELEVANCE: This study demonstrates the marked alteration in the mechan ics of load transmission across the hip after a fracture of the poster ior mall of the acetabulum. These findings are consistent ,vith the cl inical observations of Rowe and Lowell that large fractures of the pos terior wall of the acetabulum that have been treated non-operatively p redispose the hip joint to osteoarthrosis. The failure of acute anatom ical reduction and internal fixation to restore normal joint-loading p arameters supports the current clinical practice of restricting weight -bearing after operative repair of these fractures.