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Trauma

BIOMECHANICAL EVALUATION OF INTERLOCKING LAG SCREW DESIGN IN INTRAMEDULLARY NAILING OF UNSTABLE PERTROCHANTERIC FRACTURES

International Society for Fracture Repair (ISFR)



Abstract

Hypothesis

The proximal geometry and design of trochanteric nails affects initial construct stiffness, fatigue survival, and preservation of biomechanical stability over time.

Materials & Methods

Eight pairs of human cadaveric femora were implanted with two different short intramedullary nails with (Intertan, (S&N)) and without (Gamma 3, (Stryker)) interlocking lag screws. Femoral osteotomies were performed to generate a pertrochanteric multifragmentary unstable fracture (OTA 31-A 2.2). The bones were tested in a cyclic testing protocol with increasing loads of 100 N every 20.000 cycles (start point 50/500 N) simulating one leg stance. The position of the femur was 10° adduction and 10° extension. Stiffness, failure load, and cycles to failure were measured.

Results

Initially, stiffness of the interlocking lag screw nail was 40 % higher (p < 0,05) than for the non-interlocking nail. During the test, the difference in stiffness gradually decreased. Load to failure (9 %, p < 0,05) and cycles to failure (13 %, p < 0,05) were also higher for the interlocking nail construct.

Discussion & Conclusion

The interlocking screw design of intramedullary nail constructs improves the mechanical performance in unstable trochanteric fractures. This may result in improved clinical performance.