Optimizing initial biomechanical strength (“Time Zero”) of posterior repair in total hip arthroplasty: a biomechanical comparison of suture materials and knot configurations

INTRODUCTION: Posterior capsule repair (PCR) is commonly performed during total hip arthroplasty (THA) via the posterolateral approach to improve postoperative stability. Because biological healing of the repaired posterior structures requires time, the repair construct must provide sufficient immediate mechanical support after surgery. This study aimed to identify the suture material and knot configuration with favorable initial mechanical performance in a standardized in vitro model. MATERIALS AND METHODS: This in vitro biomechanical study was conducted in two sequential phases. Phase 1 evaluated the baseline tensile properties of three commonly used suture materials: #2 Ethibond, #0 Vicryl, and 3 - 0 PGLA. Phase 2 used a standardized porcine dermal surrogate model to compare eight suture configurations, including single- and double-strand techniques. The primary biomechanical outcomes included maximum failure load, load at 2 mm gap formation, and construct stiffness during uniaxial quasi-static load-to-failure testing. RESULTS: In Phase 1, non-absorbable #2 Ethibond showed significantly greater ultimate tensile strength (92.44 ± 8.72 N) and higher stiffness than the absorbable alternatives (P < 0.001). In Phase 2, double-strand configurations outperformed all single-strand techniques. Among them, the double-strand Nice knot achieved the highest maximum failure load (104.04 ± 8.68 N) and the greatest construct stiffness (12.59 ± 1.21 N/mm), with better resistance to gap formation than conventional single-strand techniques. CONCLUSIONS: In this in vitro model, absorbable sutures and traditional static knots showed lower initial fixation strength than double-strand constructs. Under controlled laboratory conditions, the combination of #2 Ethibond and a double-strand Nice knot was associated with higher initial biomechanical strength and stiffness than the other tested methods. These findings may help inform construct selection for posterior capsule repair, although direct clinical extrapolation should be made with caution.