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 posterior 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-sensitive film. The acetabulum was divided into three areas - the anterior wall, the superior aspect, and the posterior wall - for the analysis of the data. Creation of a fracture of the posterior wall was followed by an increase in contact area, maximum pressure, and contact force in the superior aspect of the acetabulum. A concomitant decrease in these parameters was observed in the anterior and posterior walls. Anatomical reduction and fixation of the fracture with a plate and screws did nut restore the pattern of loading to pre-injury levels. CLINICAL RELEVANCE: This study demonstrates the marked alteration in the mechanics of load transmission across the hip after a fracture of the posterior wall of the acetabulum. These findings are consistent with the clinical observations of Rowe and Lowell that large fractures of the posterior wall of the acetabulum that have been treated non-operatively predispose the hip joint to osteoarthrosis. The failure of acute anatomical reduction and internal fixation to restore normal joint-loading parameters supports the current clinical practice of restricting weight-bearing after operative repair of these fractures.