Magnetic Resonance Imaging Assessment of Muscle Damage After Postero-lateral Versus Supercapsular...

The supercapsular percutaneously-assisted total hip approach for total hip arthroplasty (THA) may reduce soft-tissue injury, but objective evidence comparing muscle damage with a conventional postero-lateral approach (PLA) is limited. This randomized controlled trial compared postoperative periacetabular muscle damage using magnetic resonance imaging (MRI).

Patients undergoing primary unilateral THA were randomized to SuperPATH or PLA. The primary outcome was the between-group difference in quadratus femoris muscle fatty infiltration at 12 months on MRI. The secondary outcomes included atrophy and tendon integrity of multiple periacetabular muscles, perioperative variables, Visual Analog Scale (VAS), and Harris Hip Score (HHS). There were 82 patients who completed follow-up.

At 12 months, MRI showed no significant differences in fatty infiltration or atrophy of the piriformis, obturator internus, or gluteus minimus muscles between groups. However, the minimally invasive approach better preserved the quadratus femoris muscle, with major less fatty infiltration (7.3 and 85.4%, P < 0.001), less atrophy (P = 0.008), and superior tendon continuity (100 and 56.1%, P < 0.001). The minimally invasive approach had a longer operative time and greater blood loss, but a smaller incision and superior early clinical outcomes (VAS and HHS at one month, P < 0.05); these differences were not significant at 12 months. There were two early dislocations that occurred in the PLA group.

The minimally invasive approach provides better structural preservation of the quadratus femoris muscle than the PLA, although 1-year clinical outcomes were similar. These structural findings may partly explain the superior early functional outcomes observed in the minimally invasive approach; however, their long-term clinical significance remains to be determined.