Poster 214: Cross Sectional Area of Hip Muscles Before and After Surgery for Femoroacetabular Impingement

Abstract

Objectives: Femoroacetabular impingement (FAI) syndrome is a common cause of hip pain and surgery is a treatment option for patients who do not respond to conservative treatment. Previous studies have identified increases in postoperative hip muscle volume and cross-sectional area (CSA) as associated with increases in patient reported outcomes following hip surgery. There has been a lack of literature analyzing the change of hip muscle cross sectional CSA on MRI following arthroscopic hip surgery for FAI and the effect of changes in hip muscle CSA on patient reported outcomes following surgery. The purpose of this study is to analyze the change in hip muscle cross sectional area (CSA) after arthroscopic surgery for FAI syndrome. Methods: This is a single center, single surgeon, retrospective analysis performed between August 2007 and May 2023. All patients who had a pre-operative MRI within 1 year of their date of surgery and at least one postoperative MRI were included in the study. Cross sectional areas were measured by one blinded researcher and results were checked for reliability by a musculoskeletal radiologist. Statistical analysis was completed using SPSS, Version 24 and normally distributed continuous variables between cohorts were compared using the two-sample Student t test. Results: Initially 1390 patients were included in the study but only 95 were found to have a preoperative hip MRI within 1 year of their date of surgery as well as a postoperative MRI. The average age of the cohort was 35.8 ± 15.7, the cohort was 33.7% male and 66.3% female, and had an average BMI of 23.3 ± 8.1. The mean time between surgery and postoperative MRI was 14.8 ± 8.3 months. There was a significant difference between preoperative and postoperative hip muscle CSA for gluteus maximus (4298.6±883.6 mm2 vs. 4384.6±967.6 mm2, p<0.01), gluteus minimus (1037.0±199.2 mm2 vs. 1074.9±202.3 mm2, p<0.001), and pectineus (415.7±121.9 mm2 vs. 426.7±106.3 mm2, p=0.04). There were no other significant differences between preoperative and postoperative hip muscle CSA values between the other muscles analyzed. A linear regression found that an increase in the change in CSA of the gluteus maximus significantly predicted an increase in mHHS at 1 year (β=3.103, p=0.046) when controlling for age, sex, BMI and time from surgery to postoperative MRI. A linear regression found that an increase in the change in cross sectional area of the pectineus significantly predicted an increase in NAHS at 1 year when controlling for age, sex, BMI and time from surgery to post-op MRI (β=0.186, p=0.037). Conclusions: Patients who undergo surgery for FAI have significantly increased gluteus maximus, gluteus minimus and pectineus muscle CSA on post-operative MRIs. Furthermore, increases in both gluteus maximus and pectineus muscle CSA was found to be significantly associated with increases in mHHS and NAHS at 1 year follow up respectively.