The Effect of Pelvic Incidence on Outcomes Following Hip Arthroscopy for Femoroacetabular Impingement and Acetabular Labral Tears
Authors: Eberlin Christopher , Cherian Nathan , Dean Michael , Dowley Kieran , LaPorte Zachary , Kucharik Michael , Gillinov Stephen , Siddiq Bilal , Martin Scott , Torabian Kaveh 
Published: February 2024

Objectives: Left untreated, femoroacetabular impingement (FAI) poses an elevated risk for the early progression of degenerative joint disease. As a result, the utilization of hip arthroscopy has increased to counteract the maladaptive effects of FAI, as femoroacetabular osteoplasties have been shown to reconcile deleterious loading patterns caused by CAM and pincer lesions. However, variations in the sagittal alignment of the lumbosacral spine also pose an elevated risk for the early progression of degenerative joint disease. While femoroacetabular osteoplasties improve degenerative loading patterns caused by CAM and pincer lesions, variations in the sagittal alignment of the lumbosacral spine may continue to generate deleterious effects on the labrum, chondrolabral junction, and articular cartilage following hip arthroscopy for acetabular labral tears and FAI. Thus, the purpose of this study was to evaluate the impact of pelvic incidence (PI) on patient-reported outcomes measures (PROMs) and rates of achieving clinically meaningful outcomes following primary hip arthroscopy for acetabular labral tears and FAI. Methods: A retrospective review of a prospectively collected, single-surgeon database was performed to identify patients ≥18 years of age who underwent primary hip arthroscopy for the treatment of labral tears secondary to FAI with a minimum of 12 months of follow-up. Patients with a history of ipsilateral hip or spine surgery, absence of preoperative lumbar spine imaging, radiographic evidence of hip dysplasia or advanced hip osteoarthritis, and contraindicated spinal pathologies were excluded. PI, pelvic tilt (PT), sacral slope (SS), and acetabular version were measured on 2-D supine lumbar images, and patients were stratified into low PI (PI < 45°), moderate PI (45° ≤ PI ≤ 60°), and high PI (PI > 60°) cohorts. PROMs, VAS Pain, and frequencies of achieving clinically meaningful outcomes were compared between groups. PROMs and frequencies of achieving clinically meaningful outcomes were compared between cohorts using one-way analysis of variance tests and Fisher’s exact tests, respectively. Additionally, a sensitivity analysis using a linear mixed-effects model with time as a continuous variable was carried out to evaluate the weighted differences in PROM averages between cohorts. Results: A total of 74 patients undergoing primary hip arthroscopy for FAI and acetabular labral tears met eligibility criteria and were subsequently stratified into low ( n=28), moderate ( n=31), and high ( n=15) PI cohorts. The mean ± SD length of follow-up was 25.16 ± 2.91 months, and no significant differences were observed between cohorts in patient demographics. However, as expected, patients in the high PI cohort displayed significantly larger mean values for PT ( P=0.001), SS ( P<0.001), acetabular version ( P<.001), and acetabular inclination ( P=0.049). Moreover, despite no differences in preoperative outcome scores between cohorts, the high PI cohort displayed significantly inferior scores for all PROMs and VAS pain across 6-, 12, and 24-month follow-ups. This finding also extended to our sensitivity analysis, with the high PI cohort displaying significantly lower weighted averages in scores across all PROMs relative to the moderate PI cohort ( P≤.001 for all). Additionally, the high PI cohort demonstrated significantly lower rates of clinically meaningful outcome achievement and overall patient satisfaction at 12- and 24-month follow-ups compared to the moderate and/or low PI cohorts. No significant differences were found between cohorts in terms of revision hip arthroscopy, subsequent spine surgery, or conversion to THA. Conclusions: Following hip arthroscopy to address acetabular labral tears, patients with a high PI exhibit significantly inferior PROMs relative to those with moderate and low PI. Thus, despite addressing FAI deformities, variations in lumbosacral alignment may continue to impact patient outcomes. Although the current study design limits our ability to infer causality, the significantly greater acetabular version and inclination values observed in the high PI cohort lead us to speculate that the sagittal imbalance in the setting of a high PI places increased mechanical stress on the anterior-superior acetabulum, which portends poor outcomes following hip arthroscopy. Overall, our findings highlight the critical importance of analyzing pelvic alignment in order to prognosticate outcomes following hip arthroscopy for acetabular labral tears in the setting of FAI.