Mechanical comparison of plates used in the treatment of unstable subtrochanteric femur fractures

OBJECTIVES: To determine the stiffness and strength characteristics of certain plate-composite femur models designed to simulate unstable subtrochanteric femur fractures (OTA 31-A2.3). DESIGN: Fifteen identical composite femora were osteotomized to produce like models of an unstable subtrochanteric femur fracture. The femora were fixed with either the Synthes 95 degree angled condylar blade plate, a 95 degree dynamic condylar screw plate (DCS), or a 135 degree dynamic compression hip screw (DHS). MAIN OUTCOME MEASUREMENTS: A materials testing machine was used to apply compression to the femoral head through an adapter plate. Stiffness values were calculated from the load-deformation curves obtained. RESULTS: The DHS-femur model was the stiffest (586 newtons/ millimeter), followed by the 95 degree DCS (404 newtons/millimeter) and the 95 degree condylar blade plate (260 newtons/ millimeter). The DHS also had the highest ultimate load-to-failure (4,877 newtons), followed by the 95 degree DCS (3,107 newtons) and the 95 degree condylar blade plate (2,272 newtons). All of these differences were statistically significant (p < 0.00001 ). CONCLUSIONS: Our findings suggest that the Synthes 95 degree DCS has greater stiffness and strength than the Synthes 95 degree condylar blade plate when tested in this model of an unstable subtrochanteric femur fracture. This model may not be completely appropriate for testing the 135 degree DHS because the hard plastic "cortex" of the model prevented cut-out of the screw.