Cadaveric Biomechanical Evaluation of Capsular Constraint and Microinstability After Hip Capsulotomy and Repair.

BACKGROUND

It remains unclear if capsular management contributes to iatrogenic instability (microinstability) after hip arthroscopy.

PURPOSE

To evaluate changes in torque, stiffness, and femoral head displacement after capsulotomy and repair in a cadaveric model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A biomechanical analysis was performed using 10 cadaveric hip specimens. Each specimen was tested under the following conditions: (1) intact, (2) portals, (3) interportal capsulotomy (IPC), (4) IPC repair, (5) T-capsulotomy (T-cap), (6) partial T-cap repair, and (7) T-cap repair. Each capsular state was tested in neutral (0°) and then 30°, 60°, and 90° of flexion, with forces applied to achieve the displacement-controlled baseline limit of external rotation (ER), internal rotation (IR), abduction, and adduction. The resultant end-range torques and displacement were recorded.

RESULTS

For ER, capsulotomies significantly reduced torque and stiffness at 0°, 30°, and 60° and reduced stiffness at 90°; capsular repairs failed to restore torque and stiffness at 0°; and IPC repair failed to restore stiffness at 30° ( < .05 for all). For IR, capsulotomies significantly reduced torque and stiffness at 0°, 30°, and 60° and reduced stiffness at 90°; and capsular repairs failed to restore torque or stiffness at 0°, 30°, and 60° and failed to restore stiffness at 90° ( < .05 for all). For abduction, IPC significantly decreased torque at 60° and 90° and decreased stiffness at all positions; T-cap reduced torque and stiffness at all positions; IPC repair failed to restore stiffness at 0° and 90°; and T-cap repair failed at 0°, 60°, and 90° ( < .05 for all). For adduction, IPC significantly reduced torque at 0° and reduced stiffness at 0° and 30°; T-cap reduced torque at 0° and 90° and reduced stiffness at all positions; IPC repair failed to restore stiffness at 0° and 90°; and T-cap repair failed at 0°, 60°, and 90° ( < .05 for all). There were no statistically significant femoral head translations observed in any testing configurations.

CONCLUSION

Complete capsular repair did not always restore intact kinematics, most notably at 0° and 30°. Despite this, there were no significant joint translations to corroborate concerns of microinstability.

CLINICAL RELEVANCE

Caution should be employed when applying rotational torques in lower levels of flexion (0° and 30°).