Biomechanical Assessment of Hip Capsular Repair and Reconstruction Procedures Using a 6 Degrees of Freedom Robotic System

Background: Although acetabular labral repair has been biomechanically validated to improve stability, capsular management of the hip remains a topic of growing interest and controversy. Purpose: To biomechanically evaluate the effects of several arthroscopically relevant conditions of the capsule through a robotic, sequential sectioning study. Study Design: Controlled laboratory study. Methods: Ten human cadaveric unilateral hip specimens (mean age, 51.3 years [range, 38-65 years]) from full pelvises were used to test range of motion (ROM) for the intact capsule and for multiple capsular conditions including portal incisions, interportal capsulotomy, interportal capsulotomy repair, T-capsulotomy, T-capsulotomy repair, a large capsular defect, and capsular reconstruction. Hips were biomechanically tested using a 6 degrees of freedom robotic system to assess ROM with applied 5-Nm internal, external, abduction, and adduction rotation torques throughout hip flexion and extension. Results: All capsulotomy procedures (portals, interportal capsulotomy, and T-capsulotomy) created increases in external, internal, adduction, and abduction rotations compared with the intact state throughout the full tested ROM (-10 degrees to 90 degrees of flexion). Reconstruction significantly reduced rotation compared with the large capsular defect state for external rotation at 15 degrees (difference, 1.4 degrees) and 90 degrees (difference, 1.3 degrees) of flexion; internal rotation at -10 degrees (difference, 0.4 degrees), 60 degrees (difference, 0.9 degrees), and 90 degrees (difference, 1.4 degrees) of flexion; abduction rotation at -10 degrees (difference, 0.5 degrees), 15 degrees (difference, 1.1 degrees), 30 degrees (difference, 1.2 degrees), 60 degrees (difference, 0.9 degrees), and 90 degrees (difference, 1.0 degrees) of flexion; and adduction rotation at 0 degrees (difference, 0.7 degrees), 15 degrees (difference, 0.8 degrees), 30 degrees (difference, 0.3 degrees), and 90 degrees (difference, 0.6 degrees) of flexion. Repair of T-capsulotomy resulted in significant reductions in rotation compared with the T-capsulotomy condition for abduction rotation at -10 degrees (difference, 0.3 degrees), 15 degrees (difference, 0.9 degrees), 30 degrees (difference, 1.3 degrees), 60 degrees (difference, 1.7 degrees), and 90 degrees (difference, 1.5 degrees) of flexion and for internal rotation at -10 degrees (difference, 0.9 degrees), 60 degrees (difference, 1.5 degrees), and 90 degrees (difference, 2.6 degrees) of flexion. Similarly, repair of interportal capsulotomy resulted in significant reductions in abduction (difference, 0.9 degrees) and internal (difference, 1.4 degrees) rotations compared with interportal capsulotomy at 90 degrees of flexion. In most cases, however, after the repair procedures, ROM was still increased in comparison with the intact state. Conclusion: The results of this study suggest that common hip arthroscopic capsulotomy procedures can result in increases in external, internal, abduction, and adduction rotations throughout a full range (-10 degrees to 90 degrees) of hip flexion. However, capsular repair and reconstruction succeeded in partially reducing the increased rotational ROM caused by common capsulotomy procedures. Thus, consideration should be allotted toward capsular repair or reconstruction in cases with an increased risk of residual instability. Clinical Relevance: Although complete restoration of joint stability may not be fully achieved at time zero, capsular repair and reconstruction may lead to improved patient outcomes by bringing hip rotational movements nearer to normal values in the immediate postoperative period, especially in cases in which extensive capsulotomy is performed.