Performance assessment and external validation of specific thresholds of total psoas muscle cross-sectional area as predictors of mortality in oncologic spine surgery for spinal metastases

Purpose: The purpose of this study was to assess the utility of low muscle mass (LMM) in predicting 90-day and 12-month mortality after spinal tumor surgery. Methods: We identified 115 patients operated on for spinal metastases between April 2012 and August 2022 who had available perioperative abdominal or lumbar spine CT scans and minimum 90-day follow-up. LMM was defined as a total psoas muscle cross-sectional area (TPA) at the L4 pedicle level less than 10.5 cm² for men and less than 7.2 cm² for women based on previously reported thresholds. A secondary analysis was performed by analyzing TPA as a continuous variable. The primary endpoint was 90-day mortality, and the secondary endpoint was 12-month mortality. Multivariate logistic regression analyses were performed. Results: The 90-day mortality was 19% for patients without and 42% for patients with LMM (p = 0.010). After multivariate analysis, LMM was not independently associated with increased odds of 90-day mortality (odds ratio 2.16 [95% confidence interval 0.62 to 7.50]; p = 0.223). The 12-month mortality was 45% for patients without and 71% for patients with LMM (p = 0.024). After multivariate analysis, LMM was not independently associated with increased odds of 12-month mortality (OR 1.64 [95% CI 0.46 to 5.86]; p = 0.442). The secondary analysis showed no independent association between TPA and 90-day or 12-month mortality. Conclusion: Patients with LMM had higher rates of 90-day and 12-month mortality in our study, but this was not independent of other parameters such as performance status, hypoalbuminemia, or primary cancer type.