Larger Zona Orbicularis Size on Magnetic Resonance Imaging Is Not Associated With Increased Resistance to Axial Distraction of the Hip Joint

Purpose

To evaluate the relation between zona orbicularis (ZO) thickness on magnetic resonance imaging and distractibility of the hip in patients undergoing hip arthroscopy.

Methods

We conducted a retrospective review of primary hip arthroscopy patients treated for femoroacetabular impingement syndrome from December 2021 to September 2022. Prior to arthroscopy, hips were subjected to 100 lb of force (lbf) with fluoroscopic images taken to calculate joint space and overall distraction distance. The ZO was measured on coronal sequences of preoperative magnetic resonance imaging or magnetic resonance arthrography. Multivariable linear regression was performed and controlled for age, sex, body mass index, and lateral center-edge angle.

Results

Sixty-eight patients were included in the final analysis. The mean age was 34.5 ± 12.4 years. The mean joint space at 100-lbf axial traction was 11.0 ± 3.8 mm, and the mean distraction distance was 6.6 ± 3.7 mm. The mean ZO size was 3.2 ± 1.0 mm. Linear regression showed no relation between ZO size and joint space at 100 lbf (β = –0.109, R = 0.107, P = .842). The results of our linear regression analysis also showed no significant association between ZO size and overall distraction distance (β = –0.15, R = 0.108, P = .977).

Conclusions

The results of this study show no significant association between ZO size and resistance to axial traction at the hip joint.

Clinical Relevance

Our results suggest that the resistance to axial traction on the hip from the ZO is conferred by its overall integrity and presence—and is not dependent on its size—and that, likely, deviations in other soft-tissue restraints contribute to the spectrum of hip stability experienced by patients.