Reduction Quality Determines Failure Behavior in Stable Intertrochanteric Fractures: A Mesh-Free Simulation Comparing DHS and TFNA.

INTRODUCTION

Stable 2-part intertrochanteric hip fractures (Arbeitsgemeinschaft für Osteosynthesefragen/Orthoapedic Trauma Association [AO/OTA] 31A1.2) are commonly treated with dynamic hip screw (DHS) or trochanteric fixation nail advanced (TFNA). Although nails are increasingly favored, superiority in stable patterns remains unproven with DHS remains widely used. This study applied mesh-free simulation to investigate construct mechanics and failure behavior in stable fracture models, with implant migration and construct stability as surrogate measures for cutout risk.

METHODS

Particle models of AO/OTA 31A1.2 fractures were obtained from cadaveric computed tomography scans with bone mineral density mapping. Using volumetric particle modelling (100-400 μm resolution), either DHS (316L stainless steel lag screw/barrel) or TFNA (Ti6Al4V extra low interstitial nail/blade) was inserted at a tip-apex distance of <25 mm. A standardized axial compression test approximating single-leg stance was simulated at 2 m/s along the Z-axis. Two implant conditions were tested: sliding (allowing screw/blade migration) and non-sliding (rigid). Two fracture reductions were modelled: anatomical (0 mm gap) and proximal gap (5 mm). Outcomes were maximum load, displacement at failure, load-displacement curves, and von Mises stress distribution.

RESULTS

With anatomical reduction, DHS and TFNA showed nearly identical curves up to 3-4 mm displacement; DHS resisted higher loads beyond. In non-sliding, DHS reached a maximum load of 4,066 N vs. 3,945 N for TFNA; in sliding, DHS reached 4,156 N vs. 3,790 N for TFNA. With gap, early performance was similar, but DHS reached higher loads (2,161-2,504 N) vs. TFNA (1,643-1,877 N). Displacement at failure was comparable (approximately 5 mm). DHS exhibited a more gradual postpeak decline, whereas TFNA showed a steeper loss of resistance.

CONCLUSION

DHS and TFNA provide comparable initial stability but diverge with increasing displacement and reduction imperfection. Rather than establishing implant superiority, these findings highlight differences in construct mechanics and tolerance to suboptimal reduction.

CLINICAL RELEVANCE: DHS may better tolerate reduction imperfections in stable intertrochanteric fractures, potentially guiding implant selection when anatomical reduction is challenging. Results should be interpreted as mechanistic insights requiring clinical validation.

LEVEL OF EVIDENCE: No level of evidence. See Instructions for Authors for a complete description of levels of evidence.