Introduction: This study examined the identification of a cutoff value for preoperative trunk muscle mass that predicts postoperative low back pain in patients after spinal corrective fusion surgery.

Methods: Eighty-two patients who underwent spinal corrective fusion for adult spinal deformity were included (mean age 73.6 years). Preoperative trunk muscle mass was calculated from bioimpedance analysis. Postoperative back pain was defined as back pain of 30 mm or more on a visual analog scale. In the statistical analysis, cutoff values for preoperative trunk muscle mass were calculated using receiver-operating characteristic (ROC) curves, with the presence or absence of postoperative back pain as the anchor. Next, univariate and multivariate adjusted models were analyzed to examine whether the calculated cutoff values could predict the presence or absence of postoperative back pain (significance level 5%).

Results: The ROC curve showed that the cutoff value for preoperative trunk muscle mass was 6.5 kg/m² (area under the ROC curve 0.68, sensitivity 0.67, specificity 0.64). Univariate and multivariate adjusted models showed that the cutoff value of trunk muscle mass was a predictor of the presence or absence of postoperative back pain in all models.

Conclusions: The calculated cutoff value of preoperative trunk muscle mass is moderately accurate and can be used to predict the presence or absence of low back pain in patients undergoing spinal corrective surgery.