Recovery of Muscle Atrophy and Fatty Infiltration in Patients With Acetabular Dysplasia After Total Hip Arthroplasty

Introduction: Hip osteoarthritis (OA) with acetabular dysplasia negatively affects pelvic alignment and muscle function. We aimed to investigate the changes in muscle atrophy and fatty infiltration of the hip and trunk muscles 1 year after total hip arthroplasty (THA) in patients with hip OA with acetabular dysplasia. Methods: This study included 51 female patients who underwent THA for unilateral hip OA with acetabular dysplasia. The cross-sectional area (CSA) and muscle density of the gluteus maximus, gluteus medius, gluteus minimus, piriformis, iliopsoas, rectus abdominis, and abdominal oblique muscles using computer tomography and pelvic inclination angle using radiographs were assessed before and 1 year after THA. Results: At the 1-year follow-up, the CSA and muscle density of the gluteus medius (2,078 to 2,522 mm 2 and 30.3 to 39.4 hounsfield units [HU]), iliopsoas (715 to 901 mm 2 and 40.3 to 50.8 HU), and rectus abdominis (336 to 363 mm 2 and 28.6 to 30.6 HU) of the affected limb had increased significantly ( P < 0.05). The CSA and muscle density of the gluteus maximus (2,429 versus 2,884 mm 2 and 23.7 versus 32.6 HU), gluteus minimus (636 versus 785 mm 2 and 14.3 versus 37.1 HU), piriformis (505 versus 607 mm 2 and 23.4 versus 31.6 HU), and iliopsoas (901 versus 997 mm 2 and 50.8 versus 54.5 HU) in the affected limb were lower than those in the unaffected limb ( P < 0.01). Postoperatively, the CSA and muscle density of the rectus abdominis were not significantly different between the limbs, and the pelvic inclination angle (35.2° to 32.1°, P < 0.01) was significantly decreased. Discussion: Compared with the nonoperated limb, substantial atrophy and fatty infiltration of most hip muscles persisted in the operated limb 1 year after THA in patients with acetabular dysplasia; asymmetry in the rectus abdominis muscle fully resolved. In patients with acetabular dysplasia, the surgical technique and postoperative rehabilitation should be further considered to optimize hip muscle recovery.