A biomechanical study of 150/spl deg/ vs. 135/spl deg/ hip screws in femoral neck fractures

Femoral neck fractures have been difficult to treat with nonunion and avascular necrosis reported in 10% to 40% of cases. The hypothesis tested here was to determine whether a femoral neck fracture fixed with a 150/spl deg/ screw is more stable than that fixed with a 135/spl deg/ screw. The objectives were to measure axial stiffness, torsional stiffness, and failure strength of femoral neck fractures (Pauwels III). Also, CT derived bone mineral density (BMD in units of K/sub 2/KPO/sub 4/ mg/cc equivalent) was measured. The following results were obtained: 1) The 150/spl deg/ hip screw demonstrated greater axial stiffness, as well as a preferred mode of failure (impaction at the fracture site). This is less likely to lead to nonunion or avascular necrosis than is the shearing action at the fracture site with the 135/spl deg/ hip screw. 2) The 135/spl deg/ hip screw demonstrated greater resistance to rotation. 3) CT derived BMD did not correlate with either axial or torsional stiffness of intact or fixed bones.