Decreased volume of rectus femoris and iliocapsularis in patients with femoroacetabular impingement syndrome after primary hip arthroscopy.

Purpose: (1) to investigate the consecutive changes in hip muscle volume in patients with femoroacetabular impingement syndrome (FAIS) during the initial postoperative period, and (2) to determine the potential effect of the early changes in hip muscle volume on clinical outcomes.

Methods: Data between March 2021 and March 2022 was reviewed. Patients diagnosed with FAIS based on clinical symptoms and radiographic findings, and undergoing hip arthroscopic treatment were included. Exclusion criteria were incomplete MRI data, prior history of hip surgery, and concomitant hip conditions including hip osteoarthritis with a Tönnis grade > 1, avascular necrosis, Legg-Calvé-Perthes disease, osteoid osteoma, synovial chondromatosis, pigmented villonodular synovitis, and developmental dysplasia of the hip (DDH). MRI was performed preoperatively and 3, 6, 12-month postoperatively. Cross-sectional area (CSA) of hip muscles including rectus femoris (RF), iliocapsularis (IC), iliopsoas (IP), gluteus medius/minimus complex (G-med/min), and gluteus maximus (G-max) were collected on MRI. The CSA was corrected by body surface area (BSA). Preoperative and a minimum of 2-year postoperative patient-reported outcome (PRO) scores including Visual Analog pain Scale (VAS), modified Harris Hip Score (mHHS), and international Hip Outcome Tool, 12-component form (iHOT-12) were collected. A multivariate linear regression model was built to determine the influence of the potential factors on postoperative PROs.

Results: A total of 76 patients were included in the study. Compared to the preoperative level, decreased volume of RF and G-max, and increased IC/RF ratio were observed at postoperative 3 months (all with P < .05). Both G-med/min and G-max presented decreased volume at postoperative 6 months (all with P < .05). G-med/min presented decreased volume (P = .001) at postoperative 12 months. Changes in RF at postoperative 3 months and 12 months were positively related to improvement of iHOT-12 (Beta = 0.371, P = .012 and Beta = 0.330, P = .026, respectively). Changes in IC at postoperative 6-month was positively related to improvement of mHHS (Beta = 0.367, P = .027) and iHOT-12 (Beta = 0.315, P = .044).

Conclusion: During the initial first year following arthroscopic treatment for FAIS, decreased volume of the RF and gluteal muscles was observed. Early changes in volume of RF and IC were positively correlated to the improvement of minimum 2-year PROs.

Level of evidence: Level IV; case series.