Introduction: Medial migration of the femoral neck element (FNE) superomedially against gravity with respect to the intramedullary component of the cephalomedullary nail is a complication increasingly recognized to cause femoral head cut-out in intramedullary nailing of pertrochanteric hip fractures. Although cut-outs are common to both intra- and extramedullary fixation, especially in unstable pertrochanteric hip fractures, FNE medial migration in sliding hip screws continues to remain sparse despite increased awareness of the phenomenon. This study aims to investigate whether intramedullary nailing is biomechanically predisposed to FNE medial migration compared to extramedullary fixation with sliding hip screws to account for the discrepancy in reported FNE medial migration rates.
Materials and methods: Twelve fourth-generation synthetic femurs (Sawbones) with unstable intertrochanteric fractures were divided into 2 groups (n=6 per group). Fracture fixation was performed using the Proximal Femoral Nail Antirotation (PFNA, Synthes) (n=6) in the first group, and the Dynamic Hip Screw (DHS, Synthes) (n=6) in the second group. Both groups were subjected to bidirectional cyclic loading (600N compression loading, 120N tensile loading) at 2 Hz for 5000 cycles. The medial migration distance (MMD) was recorded at the end of the testing cycles.
Results: The mean MMD in the PFNA group was 4.56mm (SD 0.69mm) with consistent reproduction of medial migration across all constructs tested. This was significantly more compared to the MMD of 1.17mm (SD 0.69mm) in the DHS group (p<0.001).
Conclusion: Intramedullary nailing of unstable intertrochanteric hip fractures is inherently predisposed to FNE medial migration making it more susceptible to consequent cut-out compared to fixation with the DHS.
Keywords: Cephalomedullary nail; Cut-out; DHS; Extramedullary; Intramedullary; Medial migration; PFNA; Sliding hip screw; Toggling.
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