The Effect of Postoperative Step Count on Iliopsoas Tendonitis After Hip Arthroscopy: A Prospective Cohort Study

Purpose: To investigate the relationship between postoperative activity levels, measured via a smartphone application, and the incidence of iliopsoas tendinitis (IPT) following hip arthroscopy for femoroacetabular impingement syndrome (FAIS). We hypothesized that lower postoperative activity levels across the monitored 12-week period would be associated with increased IPT risk. Methods: This prospective cohort study enrolled patients undergoing hip arthroscopy for femoroacetabular impingement syndrome (FAIS) from June 2022 to February 2023. Average weekly step counts across the 12-week postoperative monitoring period were tracked via a smartphone application. Patients were stratified into IPT and non-IPT groups, and preoperative and postoperative outcomes, including the modified Harris Hip Score (mHHS), Nonarthritic Hip Score (NAHS), and Visual Analog Scale (VAS), were compared. Activity levels were categorized into low, moderate, and high groups based on percentile distributions. Results: A total of 54 patients (mean age 37.8 ± 11.6 years, 59.3% female) were included, with 16 (29.6%) developing IPT at an average of 2.5 ± 1.2 months postoperatively. IPT patients had lower preoperative mHHS (62.2 vs. 74.9, p = 0.026) and NAHS (53.9 vs. 66.9, p = 0.023), and greater pain (VAS 6.3 vs. 5.0, p = 0.054). Mean weekly step counts were lower in the IPT group in every postoperative week, reaching statistical significance at Weeks 3 and 12 (p = 0.042 and p = 0.012). In penalized regression adjusted for preoperative mHHS and age, each additional 1000 steps per day during Weeks 1–3 was associated with lower odds of IPT (OR 0.63, 95% CI 0.32 to 0.98, p = 0.037); associations for later periods were in the same direction but did not reach statistical significance (Weeks 10–12: OR 0.89, 95% CI 0.66 to 1.10, p = 0.29). Functional improvements at 3 months did not differ between groups. Conclusions: Lower postoperative step counts were associated with a higher risk of IPT development, with the most robust association observed in the immediate postoperative period (Weeks 1–3), highlighting the potential importance of monitored, progressive rehabilitation following hip arthroscopy. These findings are exploratory and hypothesis-generating and require prospective interventional validation.