Mechanical Comparison of a Distal Femoral Side Plate and a Retrograde Intramedullary Nail

OBJECTIVE:To compare quantitatively the axial and torsional stiffness of a retrograde intramedullary nail and a fixed angle screw side plate in treating a supracondylar femur fracture in osteopenic femora. To determine the modes of failure of an intramedullary nail and a side plate under axial loading. DESIGN:Matched pair cadaveric study. SETTING:Orthopaedic biomechanics laboratory. PATIENTS AND OTHER PARTICIPANTS:Eleven matched pairs of preserved human femora were selected. The cadaveric specimens were harvested from relatively elderly donors with an average age of 75.6 years, which represents the principal population at risk for poor fracture fixation. INTERVENTION:The eleven matched pairs were osteotomized to simulate segmental structural defects in the supracondylar region. One femur of each matched pair was fixed with an intramedullary nail, and the contralateral femur was fixed with a side plate. MAIN OUTCOME MEASURES:Axial and torsional stiffness values. Axial modes of failure. RESULTS:The intramedullary nail axial stiffness was 14 percent (p = 0.04) less and torsional stiffness was 17 percent (p = 0.05) less than that provided by the side plate. The axial failure of the intramedullary nail occurred distally, allowing the hardware to protrude into the articular space. The side plate also failed distally by displacing the condylar screw into a varus angulation. CONCLUSION:The mechanical advantages favor the use of the side plate if fixation stiffness is essential. The axial mode of failure occurs distally for both fixation devices.