Outcomes of Hip Arthroscopy for Patients with Symptomatic Borderline Dysplasia

Objectives: The outcomes of hip arthroscopy in the treatment of dysplasia are variable. Arthroscopy in severe dysplasia (LCEA<18°) results in poor outcomes and iatrogenic instability. However, in milder forms of dysplasia, favorable outcomes have been demonstrated at short-term follow-up. The purpose of this study was to compare outcomes of hip arthroscopy in borderline dysplastic patients to a control group of non-dysplastic patients undergoing hip arthroscopy for femorocetabular impingement (FAI). Methods: Between March 2009 and May 2012, 1381 patients (1593 hips) undergoing hip arthroscopy for intra-articular hip disorders were prospectively enrolled into a registry. From this cohort, a borderline dysplasia (BD) group comprising 44 patients (46 hips) with a LCEA ≥ 18° and ≤ 25° and a minimum of 2 years follow-up, was identified. A control group of 100 patients (123 hips) was also identified that had a LCEA ≥ 26° and ≤ 40°, and a minimum of 2 years follow-up. Patient-reported outcome scores, including the Modified Harris Hip Score (mHHS), the Hip Outcome Score-Activity of Daily Living (HOS-ADL), the Sport-specific Subscale (HOS-SSS), and the International Hip Outcome Tool (iHOT-33), were obtained preoperatively and at 6 months, 1, 2, and 3 years postoperatively. Continuous and categorical variables were compared with independent-samples t-tests and chi-square or Fisher's exact tests (as appropriate) respectively. Changes in outcomes scores within groups were assessed via paired t-tests. Results: The mean age (±SD) of the BD and control groups was 29.3 ± 9.2 years and 29.1 ± 10.1 years respectively. There were 24 females (55%) in the BD group and 53 females (53%) in the control group (p=0.86). The mean LCEA was 21.8° (range, 18°-25°) in the BD group and 31.7° (range, 26°-40°) in the control group (p<0.001). The mean Tönnis angle was 6.2° (range, 1°-12°) in the BD group and 2.6° (range, -10°-12°) in the control group (p<0.001). The mean preoperative alpha angle was 63.7 ± 10.3° in the BD group and 58.6 ± 13.9° in the control group (p=0.02). A subgroup analysis of alpha angle by sex showed that females had significantly lower alpha angles than males (59.2° vs 69.1°; p=0.001). Labral re-fixation and a complete capsular closure was performed in over 70% and 90% of patients in both groups respectively. At a mean follow-up of 33.2 months (range, 24-58), there was significant improvement (p<0.001) in all patient reported outcome scores in both groups. However, BD patients had smaller mean improvements in all outcomes scores, and for HOS-SSS this difference was large (difference:-6.8; p=0.112). After adjustment for age, sex, alpha angle, and pre-operative score via multiple regression there was no significant difference between the BD and control groups. Importantly, female sex did not appear to be a predictor for inferior outcomes. One patient in the BD group was revised at 13 months and is awaiting a PAO. One patient in the control group required a revision arthroscopy at 30 months. Conclusion: While we recommend caution in treating symptomatic dysplasia with hip arthroscopy, our results indicate that in borderline dysplasia, favorable outcomes can be expected when a careful approach of labral re-fixation and capsular closure is employed. These outcomes are similar to non-dysplastic patients undergoing hip arthroscopy at a mean of 33 months follow-up. Further follow-up in larger cohorts is necessary to prove the durability and safety of hip arthroscopy in this challenging group.