OBJECTIVES: To quantitatively determine the minimal screw number needed for stable side plate fixation to the femoral shaft in treating unstable intertrochanteric hip fractures. DESIGN: Laboratory/biomedics study. SETTING: Orthopaedic biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS: The convenience sample was made up of one saw bone, one steel pipe, and ten human cadaveric femur specimens. Human specimens were selected by ruling out pathology and excess osteopenia. Ten specimens were tested to completion. INTERVENTION: Telescoping hip screw and hip screw side plate secured with various numbered combinations of side plate screws. MAIN OUTCOME MEASURES: Decreases in tension experienced by all previously inserted screws when an additional screw was applied were recorded and labeled as "protection." RESULTS: Protection offered by a third screw on all previous screws was 787.3 newtons in the steel pipemodel, 71.2 newtons in the sawbone model, and 158.3 newtons in the human model (p < 0.005). A fourth bone screw did not decrease tension in previous screws by more than 11 newtons. The protective effect of the fourth screw on screw #3 increased with decreasing screw application torque by a maximum of 21.8 newtons (p < 0.005). CONCLUSION: This study suggests that three bone screws provide an optimal distribution of tensile forces. The insertional torque used to place screws, once screw-plate contact has been established, does not play a significant role in screw protection. Additional studies are needed to assess the role of cortical bone density, and cyclical loading and bending forces experienced by the side plate screws, before definite clinical recommendations can be made.
OBJECTIVES: To quantitatively determine the minimal screw number needed for stable side plate fixation to the femoral shaft in treating unstable intertrochanteric hip fractures. DESIGN: Laboratory/biomedics study. SETTING: Orthopaedic biomechanics laboratory. PATIENTS OR OTHER PARTICIPANTS: The convenience sample was made up of one saw bone, one steel pipe, and ten human cadaveric femur specimens. Human specimens were selected by ruling out pathology and excess osteopenia. Ten specimens were tested to completion. INTERVENTION: Telescoping hip screw and hip screw side plate secured with various numbered combinations of side plate screws. MAIN OUTCOME MEASURES: Decreases in tension experienced by all previously inserted screws when an additional screw was applied were recorded and labeled as "protection." RESULTS: Protection offered by a third screw on all previous screws was 787.3 newtons in the steel pipemodel, 71.2 newtons in the sawbone model, and 158.3 newtons in the human model (p < 0.005). A fourth bone screw did not decrease tension in previous screws by more than 11 newtons. The protective effect of the fourth screw on screw #3 increased with decreasing screw application torque by a maximum of 21.8 newtons (p < 0.005). CONCLUSION: This study suggests that three bone screws provide an optimal distribution of tensile forces. The insertional torque used to place screws, once screw-plate contact has been established, does not play a significant role in screw protection. Additional studies are needed to assess the role of cortical bone density, and cyclical loading and bending forces experienced by the side plate screws, before definite clinical recommendations can be made.