Association between Size of Hip Capsule Defect on Magnetic Resonance Arthrogram and Overall Joint Distraction in Revision Hip Arthroscopy: An In Vivo Study.

Background: Hip instability and postoperative laxity negatively affect patient outcomes after hip arthroscopy. With the hip capsule playing a substantial role in stability, unrepaired capsulotomies and decreased capsular thickness have both been demonstrated to contribute to increased hip distractibility on axial traction studies. While capsular violation increases distractibility, the role of capsular defect size is less understood. Hypothesis/Purpose: It was hypothesized that there would be a statistically significant association between hip capsule defect size on magnetic resonance arthrogram (MRA) and hip distraction. This study evaluates the relationship between capsular defect size on MRA and hip distractibility in revision hip arthroscopy. Study Design: Case series; Level of evidence, 4. Methods: A retrospective review of a single-surgeon database of revision hip arthroscopy patients with capsular defect on preoperative MRA and available traction data was queried. Patients <18 years or a history of a previous ipsilateral hip surgery were excluded. Capsular defect was also measured on preoperative MRA (mm2), utilizing coronal and axial sequences. Axial traction was applied on a post-free traction table at intervals of 0 to 100 pounds of force, with distraction distance defined as the hip joint space. Results: Of 94 charts reviewed, 67 patients met the inclusion criteria. The mean age was 33.2 ± 9.6 years, 83.6% were women, the mean body mass index was 27 ± 6.2 kg/m2, and 39 (78%) patients had Beighton scores of <4. The mean distraction distance at 100 pounds of axial force was 8.3 ± 3.6 mm, the mean capsule defect size was 87.1 ± 77.5 mm2, with a mean length of 7.8 ± 4.6 mm, and a mean width of 10.3 ± 4.7 mm. Linear regression demonstrated no statistically significant relationship between overall distraction distance and the size (β = -0.002; R = 0.396; P = .773), length (β = -0.046; R = 0.398; P = .681), and width of the hip capsule defect (β = -0.040; R = 0.397; P = .695). Conclusion: No significant correlation was found between capsule defect size on MRA and hip distraction distance. Given that hip distractibility increases with capsular violation, we suspect that capsular disruption itself is a critical determinant of stability as opposed to the size of the defect.