Clinical and Radiographic Presentation of Capsular Iatrogenic Hip Instability After Previous Hip Arthroscopy
Authors: O’Neill Dillon C. , Mortensen Alexander J. , Cannamela Peter C. , Aoki Stephen K. 
Published: September 2020

Background: The clinical and radiographic features of iatrogenic hip instability following hip arthroscopy have been described. However, the prevalence of presenting symptoms and associated imaging findings in patients with hip instability has not been reported. Purpose: To detail the prevalence of clinical and magnetic resonance arthrogram (MRA) findings in a cohort of patients with isolated hip instability and to determine midterm patient-reported outcomes in this patient population. Study Design: Case series; Level of evidence, 4. Methods: We retrospectively reviewed patients from 2014 to 2016 who underwent an isolated capsular repair in the revision hip arthroscopy setting. Patients were excluded if they underwent any concomitant procedures, such as labral repair, reconstruction, femoral osteoplasty, or any other related procedure. Several clinical data points were reviewed, including painful activities, mechanical symptoms, subjective instability, Beighton scores, axial distraction testing (pain, toggle, and apprehension), and distractibility under anesthesia. Patient-reported outcomes—including modified Harris Hip Score, Hip Outcome Score–Sports Subscale, Patient-Reported Outcome Measurement Information System (PROMIS) Physical Function Computer Adaptive Test, and a return patient hip questionnaire—were collected pre- and postoperatively. Pre-revision radiographs were obtained, and lateral center-edge angle and alpha angle were measured on anteroposterior and frog-leg lateral views, respectively. Pre-revision MRAs were reviewed and evaluated for capsular changes. Capsular changes were defined as follows: 0, normal; 1, capsular redundancy; 2, focal capsular rent; and 3, gross extravasation of fluid from the capsule. Results: A total of 31 patients met inclusion criteria (5 male, 26 female; 14 right and 17 left hips). The mean age of patients was 36 years (range, 20-58 years). Overall, 27 (87%) reported hip pain with activities of daily living, and 31 (100%) experienced pain with sports or exercise. In addition, 24 (77%) had at least 1 positive finding on axial distraction testing. All patients had evidence of capsular changes on review of pre-revision MRAs. Out of 31 patients, 23 (74%) were available for follow-up at a minimum of 3.3 years and a mean ± SD of 4.6 ± 0.8 years. On average, modified Harris Hip Score improved by 20.3, Hip Outcome Score–Sports Subscale by 25.1, and PROMIS Physical Function Computer Adaptive Test by 6.4. Additionally, 20 (87%) patients reported improved or much improved physical ability, and 18 (78%) reported improved or much improved pain. Conclusion: The current study suggests that patients with hip instability demonstrate high rates of pain with activities of daily living and exercise, positive findings on axial distraction testing, and evidence of capsular changes on magnetic resonance imaging. Furthermore, these patients improve with revision surgery for capsular repair at midterm follow-up.