OTA 1997 Posters - Hip Fractures

*Intra - vs. Extramedullary Fixation Of Subtrochanteric Fractures

Frederick J.Kummer PhD, Kenneth J. Koval MD, Jordan A. Simon MD, Charles J. Pearlman MD, Ola Olsson MD, Leif Ceder MD

Hospital for Joint Diseases, New York, NY; Helsingborg Hospital,Helsingborg, Sweden

Purpose:An intramedullary hip screw was compared to an extramedullary, dual sliding screw-plate system using a cadaver model to determine fracture stability and load bearing/sharing in stable and unstable subtrochanteric fractures.

Methods:Six matched pairs of osteopenic femurs were physiologically loaded to 1000 N with concurrent abductor forces of 0, 50 and 86% of head forces. Cortical strain was determined by strain gauges on the inferior femoral neck and calcar region; displacements were determined by linear transducers. Femurs were first tested intact as controls. Then a transverse osteotomy was made immediately below the lesser trochanter and either a Richards IMHS or a six-hole Medoff sliding plate (MSP) was inserted (lag screws unlocked and both devices axially fixed). Displacements of the femoral head, lag screw sliding, and medial strains were determined before and during 100,000 cycles of 750-N loading. The osteotomy was then destabilized by removal of a 1.0-cm lateral wedge and retested. Finally both devices were axially dynamized and the constructs retested for stability. Data was analyzed by paired t-tests.

Results:For the stable subtrochanteric fracture, both devices exhibited similar inferior head displacements (average 2.0 mm) and medial strains (~70% of intact). Increasing abductor forces decreased medial compressive strains but did not significantly affect head displacements. For the unstable fracture model, the MSP demonstrated significantly less inferior displacements of the proximal fragment (1.1 mm vs. 2.1 mm). After cycling, head displacements increased approximately 50% for both devices and medial strains increased; after biaxial dynamization, the MSP group demonstrated lateral displacement of the proximal fragment.

Discussion and Conclusion:For stable subtrochanteric fractures, there were no significant differences between the devices with respect to fixation stability; the MSP exhibited less medial strains (load sharing). In the unstable model, the MSP exhibited less inferior displacement of the proximal fragment, however when biaxially dynamized, significant lateral displacement occurred. These two devices provide sufficient stability for fixation of most types of proximal subtrochanteric fractures.