OTA 1997 Posters - Pelvic & Acetabular Fractures

Biomechanical Consequences of Anterior Acetabular Fractures

Gregory A. Konrath, MD, Andrew J. Hamel, MS, Brian Bay, PhD, Neil A. Sharkey, PhD, Steve A. Olson, MD

University of California, Davis Medical Center, Sacramento, California, USA

Purpose: The purpose of this work was to evaluate the biomechanical effects of a surgically created segmental defect of the anterior wall, and a simulated high anterior wall fracture.

Methods: The authors measured the contact areas and contact pressures between the acetabulum and femoral head of cadaveric pelves in simulated single leg stance. All pelves were loaded with a simulated abductor mechanism. Seven hips in seven pelves were tested in three conditions: 1) intact; 2) following removal of an operatively created fracture of the anterior wall, and 3) after anatomic reduction and internal fixation. Six hips in six pelves were tested in four conditions: 1) intact; 2) anatomic reduction of a surgically created high anterior column fracture; 3) gap malreduction of anterior column fracture, and 4) step malreduction of anterior column fracture. Measurements were made with low and medium range Fuji film. The acetabulum was divided into anterior, superior, and posterior areas for data analysis.

Results: Anterior wall defects entered the acetabulum at a mean 9.7mm below the vertex on the CT subchondral arc. The anterior and posterior acetabulum had a significant decrease in contact area, mean and peak contact pressure, and contact force (p<.01 all values) with the anterior wall defect. There was no significant increase in mean or peak contact pressure (p=.6, .2) or contact force (p=.06) in the superior acetabulum with anterior wall defect. The power analysis for mean and peak pressures on the superior acetabulum had power = 0.75. Anterior column fractures entered the acetabulum 0.5mm below the vertex. There was a significant increase in load (p<.01), and peak pressures (p<.001) in the superior acetabulum after gap malreduction. There was a significant increase in peak contact pressures after step malreduction (p<.001) in the superior acetabulum as well.

Discussion: These findings suggest a low anterior wall defect (similar to a low anterior column fracture) does not result in an increase in loading in the superior acetabulum. However, both gap and step malreduction of the high anterior column fracture resulted in increased peak contact pressures in the superior acetabulum. Thus, malreduction of an anterior column fracture in the superior acetabulum may predispose to the development of osteoarthritis.