Body Mass Index Moderates the Relation Between Hip Osteoarthritis Severity and Hip-Specific Recovery Following Arthroscopic Surgery for Femoroacetabular Impingement Syndrome

Introduction Femoroacetabular impingement syndrome (FAIS) is a common cause of hip pain, yet factors influencing postoperative recovery remain incompletely understood. Objective The purpose of this study was to investigate whether BMI moderates the relation between hip osteoarthritis severity and changes in hip-related QoL after arthroscopic surgery for FAIS. Methods This retrospective study included 215 adults (56% female) who underwent hip arthroscopy for FAIS. Osteoarthritis was graded using the Kellgren-Lawrence Grade (KLG), and BMI was categorized as normal (<25.0kg/m²), overweight (25.0-29.9kg/m²), or obese (≥30.0kg/m²). The 33-item International Hip Outcome Tool (iHOT-33) was assessed preoperatively and at 2, 6, 12, 26, 52, and 104 weeks postoperatively. Linear mixed-effects evaluated associations between time, BMI, KLG, and iHOT-33 recovery trajectories. Moderation was tested via a BMI × KLG × time interaction, adjusting for age and sex. Results 56% of participants had no radiographic osteoarthritis, 30% had mild, and 14% had moderate. Time was the strongest determinant of iHOT-33 improvement (β=5.26;95%CI[4.00:6.51]). Lower osteoarthritis severity was associated with greater iHOT-33 improvement (β=4.72; 95%CI[1.76:7.67]). BMI moderated the relation between osteoarthritis severity and iHOT-33 recovery (β=-0.34; 95%CI[-0.60:-0.07]). Higher BMI was associated with poorer recovery among individuals without osteoarthritis and those with moderate osteoarthritis. Participants with both moderate osteoarthritis and obesity experienced the smallest improvement over two-years. Conclusion In patients undergoing hip arthroscopy for FAIS, postoperative recovery is largely driven by time and by baseline joint structural status, but BMI modifies this relation: higher BMI is associated with attenuated recovery, particularly among those without or with moderate radiographic osteoarthritis.