Role of femoral anterior Bow in cephalomedullary nailing: finite element analysis and New index estimation

BACKGROUND: Cephalomedullary Nail (CMN) is seen as the mainstay of internal fixation in femoral fractures. The purpose of the study was to present an accurate calculation method by simulating diverse anterior bow femoral models with finite element software. We hypothesized that anterior cortical penetration in distal femur would occur in patients whose femoral anterior bow was identified as too large for nailing by preoperative measurement of contralateral X-ray. METHODS: A 31-year healthy male was selected for building 3D bone model through computed tomography (CT) scan of right femoral femur. In Creo Parametric 2.0, the middle section of the femur was twisted gradually to simulate the different femoral anterior bow. Ratio of chord height and half chord length, belonging to the middle section arc, was defined as the tangent value of the femoral anterior bow. The value corresponding to the penetration of the CMN at the distal femur was regarded as critical value, showing the extreme curvature for CMN. RESULT: Three types of right femoral CMNs (ø10, 11, 12 mm × 350 mm; Smith-Nephew Co.) were involved in our study. The CMN passed through distal femur anterior cortex when the tangent value of the femoral anterior bow are 0.140185, 0.133073, 0.092415 respectively, and the corresponding central angle are 21.72°, 20.92°, 16.32°. CONCLUSIONS: The tangent value of the femoral anterior bow would be a precise calculated method, that eliminate the deviation by description of ratio rather than length of radius. An application of this preoperative evaluation can aid surgeons during surgical planning. TRIAL REGISTRATION: Retrospectively registered.