P129. Impact of muscle health on patient reported outcomes after lumbar microdiscectomy

Abstract

<h3>BACKGROUND CONTEXT</h3> Poor muscle health has been implicated as a source of back pain among patients with lumbar spine pathology. However, the impact of muscle health on postoperative outcomes following spine surgery remains to be investigated. <h3>PURPOSE</h3> To determine whether muscle health measured by preoperative psoas and paralumbar muscle cross-sectional areas impact achievement of MCID for PROMs following lumbar microdiscectomy. <h3>STUDY DESIGN/SETTING</h3> Retrospective cohort study. <h3>PATIENT SAMPLE</h3> Consecutive patients who underwent 1-level lumbar microdiscectomy in a single institution between 2017-2021. <h3>OUTCOME MEASURES</h3> Rate of MCID achievement, time to MCID achievement, PROMs including Oswestry Disability Index (ODI), visual analog scale for back pain (VAS back), VAS leg, Short Form 12 Physical Component Summary (SF-12 PCS), SF-12 Mental Component Summary (SF-12 MCS) and Patient Reported Outcomes Measurement Information System Physical Function (PROMIS PF). <h3>METHODS</h3> Two previously validated methods for muscle health grading were applied. Axial T2 MRI were analyzed for muscle measurements. The psoas-based method utilized the normalized total psoas area (NTPA), which is the psoas cross-sectional area divided by the square of patient height (mm2/m2). Patients were divided into low and high NTPA groups based on sex-specific lowest quartile NTPA thresholds. The paralumbar-based method incorporated the paralumbar cross-sectional area normalized by body mass index (PL-CSA/BMI) and Goutallier classification. Score of 1 was added for either PL-CSA/BMI >130 or Goutallier class of 2. "Good" muscle health was defined as score of 2, and "poor" muscle health was defined as score of 0-1. Prospectively collected PROMs were analyzed at 2-week, 6-week, 3-month, 6-month, 1-year and 2-year postoperative timepoints. The rate of and time to MCID achievement were compared among the cohorts. Bivariate analyses were performed to assess for correlations between psoas/paralumbar cross-sectional areas and change in PROM scores from baseline. <h3>RESULTS</h3> The total cohort included 163 patients with minimum followup of 6 months and mean followup of 16.5 months. Forty patients (24.5%) were categorized into the low NTPA group, and 55 patients (33.7%) were categorized into the poor paralumbar muscle group. Low NTPA was associated with older age, lower BMI and greater frequencies of Charlson Comorbidity Index (CCI) 1. Poor paralumbar muscle health was associated with older age, female sex, higher BMI and CCI 1. There were no differences in rates of MCID achievement for any PROMs between low vs high NTPA groups or between poor vs good paralumbar groups. Low NTPA was associated with longer time to MCID achievement for ODI, VAS back, VAS leg and SF-12 MCS. Poor paralumbar muscle health was associated with longer time to MCID achievement for VAS back, and SF-12 PCS. NTPA negatively correlated with change in VAS back (6-week, 12-week) and VAS leg (6-month). <h3>CONCLUSIONS</h3> Among patients undergoing lumbar microdiscectomy, patients with worse muscle health grades achieved MCID at similar rates but required longer time to achieve MCID. Lower NTPA was weakly correlated with larger improvements in pain scores. Our findings suggest that with regards to functional outcomes, patients with worse muscle health may take longer to recuperate postoperatively compared to those with better muscle health. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.