Biomechanical Evaluation and Analysis of a Reused Telescopic Intramedullary Femoral Nail in a Child with Achondroplasia.

Introduction: Telescopic intramedullary nails (CIMT) have represented a significant advancement in limb lengthening procedures. However, their elongation capacity is limited to 5 cm in the bones of patients with achondroplasia. Consequently, techniques involving CIMT reutilization have been developed. This reuse presents mechanical and safety challenges due to material fatigue and repetitive loading, which may compromise the structural integrity of the implant. This study evaluates the biomechanical performance and potential damage of a reused CIMT.

Methods: An experimental analysis was conducted on a TIMN removed after two 5 cm lengthening procedures in a patient with achondroplasia. The nail was measured and assessed following non-destructive deconstruction, material analysis, 3D modeling through reverse engineering, and finite element analysis (FEM) to assess its behavior under different loading conditions.

Results: Mechanical and chemical damage was identified, compromising the nail's integrity. The aged Ti6Al4V alloy was validated for its resistance to complex loads. The 3D modeling showed that the gear mechanism effectively converted rotational movement into translational motion. The FEM analysis revealed that the safety factor reached its critical limit at angles of 2.44° and 2.25°, suggesting that the nail was nearing its resistance limit. The stem and guide were identified as critical components.

Conclusions: CIMT reutilization must be performed with caution due to potential material fatigue. This study provides a foundation for redesigning these implants to improve their capacity to withstand prolonged loading cycles. LEVEL OF EVIDENCE Level IV, Pre-clinical experimental study.