Summary

This study aims to better define the impact of interportal, short-T and long-T capsulotomies and their subsequent repairs on the resistive torque biomechanical properties of adult, non-arthritic hips.

Abstract

Purpose

To determine the biomechanical effects of different types of hip capsulotomies and repair on resistive capsular torque.

Introduction

The hip capsule is a complex structure composed of the iliofemoral, ischiofemoral and pubofemoral ligaments. The structure is an integral static stabilizer of the hip joint. During hip arthroscopy, various methods of hip capsulotomy can be performed to gain necessary access to the central and peripheral compartments of the hip. The effect of these patterns of capsulotomy and subsequent repair on the biomechanical properties of the hip capsule remains unclear. This study aims to better define the impact of interportal, short-T and long-T capsulotomies and their subsequent repairs on the resistive torque biomechanical properties of adult, non-arthritic hips.

Methods

Ten fresh-frozen non-arthritic cadaveric hip specimens (mean age 55 (35-65); 6 male and 4 female) were thawed and dissected, leaving the hip capsule, labrum and ligamentum teres intact. The specimens were evaluated with computed tomography (CT) to determine the bony morphology of the hip to ensure no significant osteoarthritis or differences in acetabular and femoral radiographic factors (coronal and anterior center edge angles, acetabular version, alpha angles). The femur and hemipelvis were potted and an MTS biomechanic testing apparatus was utilized to apply 100N of axial compression in neutral abduction/adduction to the specimen to simulate weight bearing. The hips were then fixed to a randomized flexion angle of 90°, 40° or -20° (extension). The femur was then internally or externally rotated in angular control at a rate of 15°/s. The intact capsule condition was tested to determine the physiologic limit of range of motion which would approach 5-Nm of resistive torque. This value was selected based on previous studies so as to engage the rotational limits of the capsule without engaging the bony limitations of motion. Once baseline range of motion was obtained, each specimen underwent randomized variations of capsulotomy (interportal (IP), short-T (ST) (defined as remaining proximal to the zona orbicularis), and long-T (LT) (defined as extending distal to zona orbicularis)) and variations of repair (interportal repair (IPR), short-T repair with 1 (STR1) or 3 (STR3) sutures, and long-T repair (LTR)). The resistive torque for each capsule condition and each flexion angle was measured in internal and external rotation.

Results

In all hip flexion angles, there was a significant difference in resistive torque between the intact capsule and all hip capsulotomy variations (IP, ST and LT) in external rotation. Between all hip capsulotomy variations (IP, ST and LT), there was no significant difference in external rotation at all hip positions.
In all hip flexion angles, there was a significant difference in resistive torque between the intact capsule and all hip capsulotomy variations in internal rotation, except for intact capsule vs. IP capsulotomy in 90° of flexion (p=0.985). Between all capsulotomy variations (IP, ST and LT), there was no significant difference in internal rotation at all hip positions.
There was no significant difference between all capsulotomy repair variations and intact capsule in -20° flexion. In 40° of flexion, there was a significant difference between intact capsule and STR1, STR3 and LTR conditions, but not in IPR (p=0.084). In 90° of flexion, there was a statistical difference between STR1 and intact capsule, but no difference in IPR, STR3 and LTR vs. intact capsule for external rotation.