Impact of sarcopenia and multifidus atrophy on outcomes from minimally invasive decompression surgery for lumbar spinal stenosis.

Background: In order to improve outcomes for patients with lumbar spinal stenosis, identification of better prognostic factors is necessary to guide patient selection for surgery. The purpose of this study was to investigate the prognostic value of multifidus atrophy and sarcopenia on postoperative pain and disability following minimally invasive decompression for lumbar spinal stenosis. Methods: We retrospectively reviewed medical records and imaging studies for patients with lumbar spinal stenosis who underwent minimally invasive tubular decompression. Multifidus total cross sectional area (tCSA), multifidus functional cross sectional area (fnCSA), multifidus fatty infiltration (FI), psoas tCSA, and psoas relative cross sectional area (rCSA) were evaluated by univariable and multivariable regression to identify predictors of postoperative improvement in visual analogue scores for back pain (VASB) and leg pain (VASL) and Oswestry disability index (ODI) scores for disability. Results: Minimally invasive decompression was performed at 75 spinal levels in 64 patients with an average age of 70.1±10.0 years. In multivariable analysis, lower multifidus FI was significantly associated with 5 point improvement in ODI (p=.002), 10 point improvement in ODI (p=.017), and 17 point improvement in ODI (p=.044). Only male gender (p=.030), lower preoperative VASB (p=.001), and lower preoperative VASL (p=.015) were independently predictive of postoperative deterioration in ODI, VASB, and VASL, respectively. Conclusions: Multifidus FI predicts postoperative improvement in disability following minimally invasive decompression for lumbar spinal stenosis with high accuracy. Minimally invasive decompression surgery is effective for elderly patients and sarcopenic patients, who are not at risk for poorer postoperative outcomes. Male gender and lower preoperative pain or disability are risk factors for postoperative deterioration in patient-reported outcomes.