Session VII Pelvis and Acetabulum

Consequences of Transverse Acetabular Fracture Malreduction on LoadTransmission across the Hip Joint

David J. Hak, MD, Steven A. Olson, MD, Andrew J. Hamel, BSEE, Brian K. Bay, PhD, Neil A. Sharkey, PhD

University of California at Davis, Sacramento, CA

Purpose: To evaluate the biomechanical loading behavior of the hip joint following anatomic reduction, gap malreduction, and step malreduction of juxtatectal and transtectal transverse acetabular fractures.

Conclusions: Both transtectal and juxtatectal transverse fractures result in a loss of normal peripheral loading of the hip. Step displacement of transtectal fractures results in significantly increased maximum contact pressures in the superior acetabular region.

Materials and Methods: Hip joint loading was studied following four transtectal and four juxtatectal transverse acetabular fractures using a cadaveric model. The pelvis and articulated femurs were mounted in a custom jig and body weight load was applied to the hip through a simulated abductor mechanism. Pressure sensitive film was applied to the femoral head in strips between layers of a commercially available latex barrier. Fractures were fixed in standard fashion using a Synthes 3.5 reconstruction plate and interfragmentary screw fixation. The intact condition, anatomic reduction, gap malreduction of 2 to 4 mm, and step malreduction of 2 to 4 mm were tested. For analysis, the acetabulum was divided into three regions: anterior wall, superior acetabulum, and posterior wall. The pressure sensitive film was digitized and the contact area; maximum pressure, mean pressure, and total load were measured for each region.

Results: In the intact acetabulum there is a peripheral distribution of load which is not restored following anatomic reduction of either transtectal and juxtatectal fractures. Mean contact area in the posterior wall was significantly reduced in transtectal fractures following gap malreduction (p 0.0015) and step malreduction (p 0.0082). Mean contact area in the anterior wall was significantly reduced in juxtatectal fractures following gap malreduction (p 0.0053) and step malreduction (p 0.0227). Step displacement in transtectal fractures caused a significant increase in the maximum contract pressure (p 0.0069) in the superior acetabulum.

Acknowledgments: This study was supported by a grant from the National Orthopaedic Surgery Fellows Foundation.