Optimal position of intramedullary nails in the femoral head following spiral blade resection for revision of intertrochanteric fractures: a biomechanical analysis.

purposeNo biomechanical studies have yet investigated the optimal position of extramedullary hip screws or intramedullary nails within the femoral head after revision surgery for helical blade cut-out in intertrochanteric fractures. The purpose of this study was twofold: 1) to compare the stability of different fixation methods in the revision of femoral intertrochanteric fractures, and 2) to determine the optimal placement of the lag screw in a novel proximal femoral bionic intramedullary nail (PFBN) within the femoral head during such revision procedures.

methodsUsing finite element analysis, we constructed a three-dimensional model simulating helical blade cut-out in an intertrochanteric fracture. Four experimental groups were established: PFBN type 1 (PFBN1), PFBN type 2 (PFBN2), proximal femoral nail antirotation (PFNA), and dynamic hip screw (DHS). Within each group, the position of the helical blade or lag screw in the femoral head was further divided into three subgroups-anterior, central, and posterior-based on sagittal plane placement. On the anteroposterior view, all implants were positioned centrally. Under a simulated axial load of 2100 N, von Mises stress and displacement of both the femur and internal fixation devices were evaluated for each fracture configuration.

resultsFemoral displacement values for the anterior subgroup were 6.863 mm (PFBN1), 6.790 mm (PFBN2), 8.126 mm (PFNA), and 7.769 mm (DHS). For the central subgroup, femoral displacement measured 6.802 mm (PFBN1), 6.716 mm (PFBN2), 8.080 mm (PFNA), and 8.679 mm (DHS). In the posterior subgroup, femoral displacement was 6.701 mm (PFBN1), 6.741 mm (PFBN2), 9.154 mm (PFNA), and 7.666 mm (DHS). Internal fixation displacement in the anterior subgroup was 6.298 mm (PFBN1), 6.232 mm (PFBN2), 7.460 mm (PFNA), and 7.202 mm (DHS). In the central subgroup, it was 6.201 mm (PFBN1), 6.138 mm (PFBN2), 7.396 mm (PFNA), and 8.075 mm (DHS). In the posterior subgroup, internal fixation displacement was 6.143 mm (PFBN1), 6.140 mm (PFBN2), 8.385 mm (PFNA), and 7.046 mm (DHS). The maximum stress at the femoral head-implant interface in the anterior subgroup was 5.28 MPa (PFBN1), 5.30 MPa (PFBN2), 26.41 MPa (PFNA), and 20.67 MPa (DHS). In the central subgroup, maximum stress values were 14.60 MPa (PFBN1), 9.06 MPa (PFBN2), 43.48 MPa (PFNA), and 27.20 MPa (DHS). In the posterior subgroup, maximum stress measured 6.33 MPa (PFBN1), 7.12 MPa (PFBN2), 16.91 MPa (PFNA), and 37.10 MPa (DHS).

conclusionOur biomechanical analysis demonstrates that intramedullary fixation confers greater stability than extramedullary fixation when salvaging failed internal fixations in intertrochanteric fractures. Our simulation results indicate that under revision scenarios, there may be optimal position trends specific to internal fixations. For PFBN revision of intertrochanteric fractures, posterior placement of the lag screw within the femoral head appears biomechanically favorable. For PFNA, central helical blade placement yielded minimal femoral and internal fixation displacement; however, implant-bone interface stress was higher. During revision surgery, screw trajectory should be altered whenever possible to ensure implantation into healthy bone while avoiding previous screw tracks. If utilization of original screw tracks is unavoidable, restoration of screw-bone contact through bone grafting should be considered. These findings warrant further validation through more sophisticated biomechanical models and clinical studies.