Evaluation of muscle volume and degeneration after total hip arthroplasty: a comparison of the posterolateral approach and the anterolateral supine approach

BACKGROUND: Muscle strength around the hip after total hip arthroplasty (THA) is crucial for preventing dislocation and limping. This study aimed to assess and compare muscle volume and degeneration after THA using the posterolateral (PL) and anterolateral (AL) approaches. METHODS: Sixty-four hips in 64 patients who underwent primary THA were retrospectively analyzed. Patients were segregated into the PL group (35 hips) and AL group (29 hips) for evaluating pre- and postoperative muscle volumes and degeneration around the hip. Computed tomography (CT) examinations were performed preoperatively and 6 months post THA. The muscle volume and Hounsfield units (HU) of the gluteus maximus (G-max), gluteus medius (G-med), tensor fasciae latae, internal obturator muscle, and external obturator muscle were measured. RESULTS: In the PL group, the postoperative muscle volume of the G-max significantly increased than the preoperative muscle volume. In contrast, the postoperative muscle volume of the internal obturator muscle was significantly lower than the preoperative muscle volume. The postoperative HU of the internal and external obturator muscles were significantly lower than the preoperative HU. In the AL group, the postoperative muscle volumes of the G-max, G-med, and tensor fasciae latae significantly increased than their preoperative muscle volumes. The postoperative HU of the G-med and tensor fasciae latae were significantly higher than the preoperative HU values. CONCLUSION: The PL approach can lead to degeneration of the internal and external obturator. The AL approach is more beneficial for recovering the G-med, tensor fasciae latae, and internal obturator muscle than the PL approach.