A comparison of mechanical strength of the femoral neck following locked intramedullary nailing using oblique versus transverse proximal screws

OBJECTIVE: The objective of the present study was to determine whether the 130-degree oblique or transverse proximal locking technique significantly enhances or diminishes the strength of the intramedullary nail-to-bone construct in a "stancelike" loading configuration. DESIGN: Six paired fresh frozen femora were randomized to locked intramedullary nailing with either the 130-degree proximal locking technique or the transverse locking technique and tested in axial compressive loading. Torsion, shear, and impact loading were not tested. PATIENTS/PARTICIPANTS: Six paired adult fresh frozen cadavers. INTERVENTION: An unreamed eleven-millimeter by thirty-eight-centimeter intramedullary nail was placed under direct visualization in each femur. Proximal locking was randomly performed on each pair with either two transverse screws or a single oblique screw. Each femur was loaded to failure at a rate of 50.8 millimeters per minute (two inches per minute) by using an Instron tensiometer. Radiographs after nail insertion and after failure were obtained. MAIN OUTCOME MEASURES: Load to fracture and fracture pattern. RESULTS: A significant difference between load to fracture was observed across femora of different donors (p < 0.001). No significant difference was observed in paired femora from the same donor when using either 130-degree or transverse proximal locking (p > 0.05). This result was based on nonanatomical axial loading that approximated loading during stance, without hip abductor loads to help stabilize the femur. CONCLUSION: Neither technique preferentially predisposed the construct to failure for the loading pattern tested. The mode of failure was the same in all cases, with failure beginning at the nail insertion site.