Impact of tip–apex distance and femoral head lag screw position on treatment outcomes of unstable intertrochanteric fractures using cephalomedullary nails

BACKGROUND: Cephalomedullary nails are frequently used in unstable intertrochanteric fractures. The implant position is an important factor for surgical success. Thus, in the present study, finite element analysis methods were used to investigate the biomechanical behavior of five different cephalomedullary nail positions in unstable intertrochanteric fractures. METHODS: Five different cephalomedullary nail implant positions were investigated. The observed indicators were the maximum displacement of the lag screw, the stress on the intertrochanteric fracture with involvement of the posteromedial cortex, and the tip–apex distance. RESULTS: The smallest lag screw displacement was achieved when the implant was closer to the inferior femoral head. Lower stress was placed on the posteromedial cortex when the implant was positioned closer to the inferior femoral head. However, the tip–apex distance increased when the lag screw was positioned more inferiorly. CONCLUSIONS: The results of this study suggest that positioning the lag screw closer to the inferior aspect of the femoral head can reduce stress on the posteromedial cortex and deformation of the implant in unstable intertrochanteric fractures. These findings provide a biomechanical basis for selection of the cephalomedullary nail implantation site. LEVEL OF EVIDENCE: III.