Computed tomography–based assessment of gluteal muscle asymmetry one year after total hip arthroplasty and its relationship with postoperative function

Abstract

This study aimed to compare gluteal muscle quantity and quality between the operated and contralateral sides one year after unilateral total hip arthroplasty (THA). Muscle thickness, cross-sectional area (CSA), and muscle density of the gluteus maximus (Gmax), gluteus medius (Gmed), and gluteus minimus (Gmin) muscles were measured using a standard computed tomography (CT) protocol. Muscle quality was assessed using Hounsfield unit (HU)-based segmentation. Functional outcomes were evaluated using the Harris Hip Score (HHS). The parameters of the operated hip were compared with those of the contralateral hip. HHS of patients increased from 60 to 93 in the first year postoperatively ( p = 0.009). Despite clinical improvement, all gluteal muscles on the operated side were found to be significantly thinner ( p < 0.001). The CSA values of Gmax and Gmed–Gmin were also lower on the operated side than on the contralateral side. Lean muscle mass (LMM) and total muscle mass (TMM) levels of Gmax and Gmed-Gmin were found to be significantly lower on the operated side than on the contralateral side. A moderate correlation was found between Gmax CSA and HHS. At one year after unilateral THA, the operated side showed lower gluteal muscle thickness, cross-sectional area, total muscle mass, and lean muscle mass than the contralateral side, despite substantial postoperative improvement in HHS. These findings indicate that favorable postoperative hip function can coexist with side-to-side differences in gluteal muscle quantity and quality.