MRI assessment of muscle damage after posterolateral versus SuperPATH approach for total hip arthroplasty

The minimally invasive SuperPATH approach for total hip arthroplasty (THA) is theorized to reduce soft tissue damage, but objective evidence comparing muscle injury to the conventional posterolateral approach (PLA) is lacking. This study aimed to objectively compare postoperative periacetabular muscle damage between the two approaches using magnetic resonance imaging (MRI). Hypothesis: The SuperPATH approach demonstrates superior efficacy in protecting posterior hip muscles compared to the PLA. In this retrospective comparative cohort study, patients undergoing primary unilateral THA for osteonecrosis or osteoarthritis by a single surgeon were enrolled. Patients with hip dysplasia, BMI > 35 kg/m², history of cerebrovascular disease or cognitive dysfunction or prior ipsilateral hip surgery were excluded. The patients were divided into two groups based on the surgical approach: the SuperPAHT group and the PLA group.The primary outcome was muscle damage assessed on MRI at 12 months postoperatively, including fatty infiltration (using the modified Goutallier classification) and muscle atrophy (via cross-sectional area or maximal transverse diameter measurements). Secondary outcomes included perioperative variables, Visual Analog Scale (VAS) pain scores, and Harris Hip Scores (HHS). At 12 months, MRI revealed no significant intergroup differences in the degree of fatty infiltration or atrophy for the piriformis, obturator internus, or gluteus minimus muscles. However, the SuperPATH approach provided superior protection for the quadratus femoris, demonstrating significantly less fatty infiltration (7.3% vs. 85.4%, p < .05), preserved muscle bulk, and maintained tendon continuity in all cases (100% vs. 56.1%, p < .05) compared to PLA. Tendon discontinuity was significantly more frequent in the PLA group for the piriformis (61.0% vs. 36.7%, p = .027), obturator internus (39.0% vs. 9.8%, p = .002), and quadratus femoris (43.9% vs. 0%, p < .05) than that in the SuperPATH group.Perioperatively, the SuperPATH group had a longer operative time and greater intraoperative blood loss but a smaller incision length (p < .05). The SuperPATH group exhibited statistically better early VAS and HHS scores with lower VAS pain and higher HHS at 1 month (p < .05), but these differences were not significant at the 12-month follow-up. Two early dislocations occurred in the PLA group, with none in the SuperPATH group. The SuperPATH effectively preserves the integrity of the quadratus femoris, the obturator internus, and the gluteus minimus muscles, with minimal damage to the quadratus femoris. However, the injuries to the piriformis muscle, the obturator muscle, and the gluteus minimus are comparable to those caused by PLA.Clinical Trial Registeration: This study was registered in the Chinese Clinical Trial Register (ChiCTR2600118828).