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 e nhances or diminishes the strength of the intramedullary nail-to-bone const ruct in a "stancelike" loading configuration. Design: Six paired fresh frozen femora were randomized to locked intramedul lary nailing with either the 130-degree proximal locking technique or the t ransverse locking technique and tested in axial compressive loading. Torsio n, shear, and impact loading were not tested. Patients/Participants: Six paired adult fresh frozen cadavers. Intervention: An unreamed eleven-millimeter by thirty-eight-centimeter intr amedullary nail was placed under direct visualization in each femur. Proxim al locking was randomly performed on each pair with either two transverse s crews 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 obtai ned. Main Outcome Measures: Load to fracture and fracture pattern. Results: A significant difference between load to fracture was observed acr oss femora of different donors (p < 0.001). No significant difference was o bserved in paired femora from the same donor when using either 130-degree o r transverse proximal locking (p > 0.05). This result was based on nonanato mical axial loading that approximated loading during stance, without hip ab ductor loads to help stabilize the femur. Conclusion: Neither technique preferentially predisposed the construct to f ailure for the loading pattern tested. The mode of failure was the same in all cases, with failure beginning at the nail insertion site.