Session I - Pelvic Trauma

Thursday, October 8, 1998 Session I, 1:24 p.m.

The Biomechanical Consequences of Impaction Injuries to the Femoral Head

Gregory A. Konrath, MD; Andrew J. Hamel, BSEE; Justin Guerin, MD; Steven A. Olson, MD; Brian Bay, PhD; Neil A. Sharkey, PhD, University of California Davis Medical Center, Sacramento, CA

Objectives: The purpose of this study was to measure the effect of an impaction fracture of the femoral head on load transmission in the hip joint.

Design: The authors measured the contact areas and pressure between the acetabulum and femoral head of cadaveric pelves in four different conditions: intact, with an operatively created 1 cm2 defect in the superior femoral head, with a 2 cm2 defect, and with a 4 cm2 defect. All defects were uniformly three millimeters deep.

Setting: Hips were loaded in simulated single-limb stance. Pressure and area measurements were made with Fuji pressure-sensitive film.

Specimens: Thirteen hip joints in eight whole pelves were tested.

Main Outcome Measurements: Contact area, load, and mean and maximum pressures were measured.

Results: Peripheral loading was seen in the intact acetabulum. This was not disrupted after impaction fractures of any size. A significant increase in mean maximum pressures in the superior acetabulum was seen only with 4 cm2 defects.

Conclusions: Clinical series indicate that impaction injuries to the femoral head are associated with a poor prognosis. Our investigation reveals that disruption of the peripheral distribution of load does not occur, in contrast to previous biomechanical studies of acetabular fractures. Previous biomechanical data of acetabular fractures associated with a poor prognosis have shown increases in mean and peak pressures in the superior acetabulum. This was seen only in very large impaction injuries. Other factors, such as wear of the articular cartilage during joint motion or associated microscopic damage to the remainder of the joint surface at the time of injury, may also contribute to the rapid joint deterioration seen in these injuries. Further study is indicated.