Extraction force, energy and nail deformation for 1.5 m versus 1.0 m intramedullary femoral nail bow design: A biomechanical investigation

Abstract

Background: The impact of the nail radius of curvature, as one of the most important design features in modern femoral nails on the ease of nail removal, remains unknown. Therefore, the aim of this study was to investigate force, energy, and nail deformation of different nail designs.

Methods: Nail insertion and extraction was performed on six pairs of fresh-frozen human cadaveric femora on a material testing machine with two different nail systems - Trochanter femoral nail ADVANCED™ Nailing System with a radius of curvature of 1.0 m and Proximal Femoral Nail Antirotation System with a radius of curvature of 1.5 m. Deformation was measured after insertion (plastic and elastic deformations) and extraction (plastic deformations).

Findings: The peak force during nail removal was significantly lower in the first group (274.5 ± 130.4 N) compared to the second group (695.2 ± 158.8 N, p = 0.001). Plastic deformation was observed in all implants, being significantly larger in the Proximal Femoral Nail Antirotation System (p = 0.027). There was a strong positive correlation between the first peak force during nail removal and nail insertion (r = 0.802, p = 0.002) as well as between extracting energy and insertion energy (r = 0.943, p < 0.001).

Interpretation: The results from this study showed that a radius of curvature of 1.0 m is easier to remove from the set of cadaver femora. Furthermore, our findings support the idea of further reducing the nail radius of curvature below 1.0 m in order to more closely match the anatomy of populations with strong-bowed femora.

Keywords: Biomechanical test; Extraction force; Intramedullary nail; Nail deformation; Nail extraction; Radius of Curvature (RoC).