In recent years, biomechanical studies have supported complete capsular closure following hip arthroscopy to restore native joint kinematics. Most studies, however, base these conclusions on joint behaviors at the extremes of range of motion; the relevance of this to joint behavior during simple activities of daily living (ADL) is not clear. The purpose of this in vitro cadaver biomechanics study was to evaluate the effects of capsulotomies and repair on joint behavior during gait, stand-to-sit and sit-to-stand using a joint motion simulator.
Seven hips were positioned on the AMTI VIVO after removing extracapsular soft tissues. The effect of capsulotomies and repair were then evaluated during simulated ADL. Joint forces associated with gait, stand-to-sit and sit-to-stand, previously measured using instrumented implants, were applied to the femur using a 6-degree of freedom (DOF) joint motion simulator. Testing occurred after portals, interportal capsulotomy (IPC), IPC repair, T-capsulotomy, partial T-capsulotomy repair and full T-capsulotomy repair. During force application, anterior-posterior (AP), medial-lateral (ML), and axial compression DOF were operated in force control; joint rotations (flexion-extension [FE], adduction-abduction [AA] and internal-external [IE] rotation) were manipulated in displacement control. Joint reaction torques resulting and femoral head translations were recorded and evaluated. Subsequently, the root mean squared (RMS) differences of each mean-centered motion relative to the intact motion were calculated.
For joint torques, repeated measures ANOVA identified that capsular condition significantly impacted mean AA torques during simulated gait and stand-to-sit, however pairwise comparisons only identified a significant decrease in mean torque required to achieve end ROM in the full T-capsulotomy repair condition compared with T-capsulotomy.
For femoral head translations, ANOVAs identified a significant effect on the RMS differences in the ML direction during gait (p = 0.016) and stand-to-sit motions (0.034). Pairwise comparisons only identified a significant difference between the interportal capsulotomy and interportal repair (increase of 0.07 ± 0.08% of the femoral head radius after interportal repair, p = 0.021). There were no other statistically significant differences in the ML direction, and no significant effects of capsule condition in the AP direction.
In this cadaveric biomechanical study, capsulotomy and repair minimally affected torque and resultant femoral head translation during simulated ADLs. Capsular repair may not be as critical for joint stability in the tested position, however it remains important to optimize end-range kinematics and patient reported outcomes.