Is psoas muscle index an effective predictor of outcomes following robotic total hip arthroplasty?

INTRODUCTION: Sarcopenia, the loss of muscle mass and function, is closely linked to poor health and has been associated with inferior outcomes in total hip arthroplasty (THA). Psoas Muscle Index (PMI) is a radiographic metric inversely correlated with sarcopenia. It was hypothesized that low PMI patients would have worse outcomes following THA. METHODS: A retrospective review of 515 patients who underwent robotic primary THA between 2014 and 2022 at a single, urban, academic health system with 2-year follow-up data was performed. Psoas Muscle Index was calculated from preoperative computed tomography imaging of the pelvis. Patient baseline demographics, laboratory values, perioperative data, and outcomes were collected from chart review. RESULTS: Low PMI occurred in 56 (10.8%) of 515 patients. There were no differences in readmissions or reoperations (P = 0.51; P = 0.58). Low PMI was associated with higher HOOS, JR score at 2 weeks and greater improvement from baseline (P = 0.034; P = 0.037), as well as lower Patient-Reported Outcomes Measurement Information System Pain Intensity at 3 months and greater reductions from baseline (P = 0.038; P = 0.013). CONCLUSION: Psoas Muscle Index did not reliably predict surgical outcomes following THA, and low PMI was associated with better patient-reported outcome measures after surgery. Further investigation into other means of diagnosing sarcopenia may be warranted.