Injury - 2026-08-10 - Journal Article
Investigation of the biomechanically optimal length of intramedullary nails in unstable intertrochanteric femur fractures 31A2.2: A finite element analysis study.
Den S, Ueda K
Topics
Key Takeaway
In AO/OTA 31A2.2 intertrochanteric fractures, interfragmentary motion plateaus at nail lengths ≥260 mm, with no significant association between nail length and implant stress under simulated stair-climbing loads.
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Summary
This finite element analysis evaluated the effect of intramedullary nail length (170–280 mm) on fixation stability in AO/OTA 31A2.2 intertrochanteric fractures using CT-derived models of an average-sized Japanese female femur, with and without a fracture gap, under simulated stair-climbing loads. Interfragmentary motion decreased with increasing nail length and plateaued at ≥260 mm in both gap and no-gap conditions. Nail and lag screw stresses showed no significant association with nail length and remained below referenced yield strength thresholds in all constructs.
Key Limitation
The entire analysis is based on a single femoral CT model from one average-sized Japanese female, making it impossible to determine whether the 260 mm threshold applies across different bone geometries, Dorr types, or patient sizes.
Original Abstract
INTRODUCTION
Achieving sufficient stability in unstable intertrochanteric femur fractures (AO/OTA 31A2.2) is important for bone healing. Although implant-related factors such as nail diameter, proximal fixation configuration, and nail length contribute to mechanical stability at the fracture site, the appropriate nail length for specific fracture patterns remains unclear. This study evaluated the effect of nail length on fixation stability using finite element analysis.
METHODS
Finite element models of AO/OTA 31A2.2 fractures, with and without a gap, were developed using CT data from the femur of an average-sized Japanese woman. ASULOCK® intramedullary nails ranging in length from 170 to 280 mm were virtually implanted, and stair climbing was simulated to assess interfragmentary motion and implant stress.
RESULTS
Interfragmentary motion significantly decreased with increasing nail length under both gap conditions and reached a plateau at nail lengths of 260 mm or greater. Nail stress tended to be higher in the gap model, but neither nail stress nor lag screw stress showed a significant association with nail length.
CONCLUSION
In an AO/OTA 31A2.2 fracture model based on an average-sized Japanese female femur, this study demonstrated that interfragmentary motion reached a plateau at nail lengths of ≥ 260 mm, suggesting that sufficient control of interfragmentary motion may be achieved in this model. Furthermore, under simulated loading conditions, the stresses applied to both the nail and lag screw remained below the referenced yield strength under the present static loading conditions.