Effect of Acetabular Labral Tear Orientation on Hip Joint Kinematics: A Comparison of Radial Tears, Chondrolabral Junction Tears and Complex Tears in Cadaveric Hips.

Background: Acetabular labral tear morphology or orientation may influence hip stability.

Hypothesis: A radial tear of the acetabular labrum would result in greater rotational and translational motion compared with a chondrolabral separation.

Study design: Controlled laboratory study.

Methods: Included were 12 unpaired nonarthritic hip specimens, none of which had capsular laxity (8 male; mean age, 34.5 years). The specimens were stripped of all soft tissue except the hip capsule and labrum and, then potted using a custom jig. In 6 specimens, a 1-cm anterosuperior separation of the labrum from the acetabular rim (chondrolabral junction tear; CLJT) was created. In the other 6 specimens, a radial tear was created at the anterosuperior acetabulum. Subsequently, a complex labral tear was created in all specimens by adding a radial tear to the CLJT specimens and vice versa. The specimens were mounted on a load frame, and the femoral head displacement in the neutral and hyperextended positions was recorded at 5 N·m of internal/external rotation (IR/ER) torque and at 50 N of superior-inferior (S-I), anterior-posterior (A-P), and medial-lateral (M-L) force. Testing occurred at 0° extension and at maximal extension both before and after initial labral tear creation and again after creation of the complex labral tear. Before testing (intact state), the joint was vented to remove the effect of intra-articular pressure difference between the intact capsule and after capsulotomy for labral tear creation. The t test was used to calculate group differences by each range of motion measure (IR/ER and S-I, A-P, and M-L translations) for neutral and hyperextension.

Results: Neither the radial labral injury nor the CLJT produced differences from the vented state in any combination of hip position or plane of motion. The complex labral tear showed increased IR/ER rotation at maximal hip extension. There was no difference between CLJT and radial labral tear in any combination of hip position or plane of motion.

Conclusion: A simple labral tear did not affect hip joint stability when the capsule was intact, and no capsular laxity was present. A complex labral tear caused increased rotational laxity at maximal extension. Capsular laxity or a complex labral tear may be a prerequisite for labral injury to cause increased hip joint motion and/or translation.

Clinical relevance: Study findings suggest that labral tears in the absence of capsular laxity may not play a role in producing microinstability by increasing motion or translation.