Estimating the optimal entry point of the antegrade femoral nailing: Previous and novel morphometric measurements

Objective: This anatomical study aimed to investigate the possible relationships between the proximal femur parameters and verify the optimal entry point in line with the medullary canal. Methods: Both in single image series and 3D-MPR views, 63 femur bones were evaluated. One-millimeter multidetector computed tomography scans were collected and assessed by OsiriX-Lite version 8 and Horos v3.3.5. Entry point locations, projected and true femoral neck-shaft, anteversion, and newly defined nail entrance angles were measured. Results: The entry points of 16 femurs were placed at the tip of the greater trochanter, and the remaining 47 femurs were in the trochanteric fossa (i.e., piriformis fossa). Thirty-three of the entry points found in the trochanteric fossa were overlapped by the greater trochanter. When the parameters of the right and left sides were compared, it was found that; projected neck angle, nail entrance angle, and the differences between true neck angle and nail entrance angle were found significantly different. The relationship between nail entrance angle and entry point localization was assessed, and the probability of the entry point being at the tip of the greater trochanter is 63 times greater when the NEA is below 90. Conclusion: This study has demonstrated that the ideal entry point for straight nails, which is based on the anatomic axis of the femur, is found mainly at the trochanteric fossa, and the greater trochanter overlapped 70.21% of them. Level of Evidence: Level IV, Diagnostic Study