Outcomes After Arthroscopic Management of Subspinous Impingement in Borderline Hip Dysplasia

OBJECTIVES: Arthroscopic management of femoroacetabular impingement in the setting of borderline hip dysplasia is controversial. There is concern for iatrogenic hip instability with rim-resection in an already structurally compromised acetabulum. Recently, there has been increased awareness of a prominent anterior inferior iliac spine (AIIS) resulting in subspinous impingement. The purpose of this study was to report on the outcomes of arthroscopic subspinous decompression in patients with symptomatic hip impingement and borderline hip dysplasia. METHODS: An IRB approved retrospective study of patients with symptomatic hip impingement, borderline dysplasia (LCEA 18-24°) and prominent AIIS who failed conservative management and subsequently underwent arthroscopic subspinous decompression was conducted. Eighteen patients, 19 hips (4 male and 14 female, average age 28) were identified from 2012 to 2015. 3D-CT imaging was used to categorize AIIS morphology into Type 1, 2 or 3 (Hetsroni classification). Alpha angle and femoral version were determined as well. Patient-reported outcome scores (PROs) consisting of the modified Harris Hip Score (mHHS), Hip Outcome Score-Activities of Daily Living (HOS-ADL) and Sport-Specific Subscale (HOS-SSS) were obtained preoperatively and at an average of 44 months postoperative (range, 23-61 months). RESULTS: There were no postoperative complications or symptoms of instability. Fourteen hips were of Type 2 AIIS morphology and 6 were categorized as type 1. Femoral osteoplasty was performed in 17 hips (average alpha angle 66°). Repeated measures ANOVA revealed a significant improvement in all PROs from preop to latest follow-up; (mHHS 64.7, 93.4, p< .001; HOS-ADL 62.1, 94.6, p< .001; HOS-SSS 26.5, 93.4 p< .001). An ANCOVA revealed patients with type 2 AIIS had a significantly higher post-op mHHS than those with a type 1 morphology; (88.3, 95.6, p< .01). CONCLUSION: Arthroscopic AIIS decompression in patients with co-existing borderline dysplasia and subspinous impingement leads to favorable outcomes without compromising hip stability.