Optimizing Initial Biomechanical Strength ("Time Zero") of Posterior Repair in Total Hip Arthroplasty: A Biomechanical Comparison of Suture Materials and Knot Configurations

Introduction: Posterior soft tissue repair (PCR) is recognized as a critical procedural step for mitigating early dislocation following total hip arthroplasty (THA) performed via the posterolateral approach. However, biological healing of the capsulotendinous structures typically requires 6 to 12 weeks, creating a prolonged window of mechanical vulnerability. Concurrently, the increasing implementation of Enhanced Recovery After Surgery (ERAS) protocols demands immediate postoperative mobilization. Consequently, the initial biomechanical strength—often referred to as "Time Zero" strength—of the repair construct serves as the primary defense against construct failure. This study aims to identify the optimal suture material and knot configuration to maximize initial repair stability and safely facilitate aggressive early rehabilitation. Materials and methods This in vitro biomechanical study was conducted in two sequential phases. Phase 1 evaluated the baseline tensile properties of three prevalent suture materials: #2 Ethibond, #0 Vicryl, and 3 − 0 PGLA. Phase 2 utilized a standardized porcine dermal surrogate to accurately model the human posterior capsule, effectively controlling for the biological heterogeneity of human cadaveric tissue. Eight distinct suture configurations, encompassing both single- and double-strand methods, were rigorously compared. Key biomechanical metrics extracted from uniaxial quasi-static load-to-failure testing included maximum failure load, load at 2mm gap formation, and construct stiffness. Results Phase 1 demonstrated that the non-absorbable #2 Ethibond possessed significantly superior ultimate tensile strength (92.44 ± 8.72 N) and structural stiffness compared to the absorbable alternatives (P < 0.001). In Phase 2, double-strand configurations significantly outperformed all single-strand techniques. Specifically, the double-strand Nice knot achieved a maximum failure load of 104.04 ± 8.68 N, nearly double that of the conventional simple interrupted suture (54.19 ± 8.24 N). Furthermore, the Nice knot exhibited the highest construct stiffness (12.59 ± 1.21 N/mm), providing superior resistance to deleterious tissue gap formation, while requiring significantly less operative time (183 ± 9.89 s) compared to complex arthroscopic sliding knots (P < 0.05). Conclusions Current absorbable sutures and traditional static knots provide insufficient fixation strength to withstand the physiological loads generated by early mobilization. A reconstructive strategy combining #2 Ethibond with a double-strand Nice knot offers optimal "Time Zero" biomechanical strength and high stiffness. This construct effectively restricts tissue gap formation to under the 2mm safety threshold, creating a secure mechanical microenvironment for biological healing and robustly supporting the implementation of immediate postoperative ERAS protocols.