Biomechanical comparison of a 2 and 3 proximal screw-configured antegrade piriformis intramedullary nail with a trochanteric reconstruction nail in an unstable subtrochanteric fracture model.

OBJECTIVE

The objective of this study was to test the stiffness and ultimate load to failure of new intramedullary (IM) nail proximal screw configurations as compared to a trochanteric reconstruction nail.

METHODS

Twenty-one synthetic composite femurs were mounted on a Material Testing System and tested in axial compression 5 times. The femurs had an 1 of 2 IM nail types inserted with 1 of 3 proximal screw configurations: a 3-screw configuration with 2 transverse screws and a screw angled into the femoral neck; a 2-screw design with a single transverse screw and a single screw angled into the femoral neck; 2 parallel screws angled into the femoral neck. There were 7 specimens in each group. An unstable fracture (OTA/AO 32-C3.2) was created. and the stiffness of these constructs was tested in compression 5 times. Each construct was then loaded to failure in compression.

RESULTS

The 3-screw construct provided more axial stiffness (214 N/mm +/- 75) than either the 2-screw construct (123 N/mm +/- 32) or the trochanteric reconstruction nail (127 N/mm +/- 21) (P = 0.017 and 0.035 for 3-screw vs. 2-screw and recon respectively, P = 0.45 for 2-screw vs. recon). Load-to-failure testing demonstrated similarity among the different screw configurations (3-screw = 2230 N +/- 265, 2-screw = 2283 N +/- 260, Reconstruction nail = 2121 N +/- 156) (P = 1.0 all groups).

CONCLUSIONS

The proximal 3-screw configuration provided more stiffness than either the 2-screw configuration or trochanteric reconstruction nail. The 2-screw configuration performed equally to a standard trochanteric reconstruction nail in stiffness testing. The ultimate loads to failure for the 3 tested constructs were not significantly different.