EP9.13 Sequential Releases for Femoral Mobilization During Direct Anterior Total Hip Arthroplasty: A Cadaveric Biomechanical Model

Abstract Background Femoral exposure is among the most challenging aspects of total hip arthroplasty (THA) through a direct anterior approach (DAA). Soft tissue releases are performed to improve exposure, although the contribution of each structure to femoral mobility is not well quantified to date. The purpose of this study was to quantify release-related femoral displacement during DAA THA. Methods Eight hips from cadaveric specimens underwent a DAA. A mechanical testing device applied 110N of anterior distraction force through a hook inserted into the proximal femur. Displacement was recorded in triplicate at baseline and after each sequential release: inferomedial capsule (A), superior capsule (B), obturator internus for left hips (C1) or piriformis for right hips (C2), piriformis for left hips (D1) or obturator internus for right hips (D2), obturator externus (E), quadratus femoris (F), tensor facia lata (G), sartorius (H), and direct head of the rectus femoris (I). Results Baseline anterior femoral mobility measured 31.7±10.1mm and changed minimally after inferomedial (30.2±9.7mm) and superior capsular release (32.8±11.1mm). Larger increases occurred with the isolated addition of obturator internus (+18.8mm, p=0.065) or piriformis (+9.5mm, p=0.024) release. Greater additional anterior femoral mobility resulted from subsequent piriformis (+41.0mm, p=0.001) or obturator internus release (+27.2mm p=0.010). Additional releases demonstrated progressively increasing anterior displacement. Conclusion Femoral exposure can be challenging and may require varying degrees of soft tissue release. This biomechanical model quantifies the displacement achieved with each sequential release through extensive mobilization and provides objective reference values to guide surgeons in obtaining safe and adequate femoral exposure.