Can we easily and accurately predict the occurrence of bone nonunion after posterior lumbar interbody fusion based on the lumbar indentation value and the new muscle health grade?

Abstract Background: The degeneration of lumbar paraspinal muscles has been confirmed to affect bone nonunion after posterior lumbar interbody fusion combined with pedicle screw fixation (PLIF-PSF). However, there is still no convenient and accurate muscle evaluation method to predict bone nonunion after PLIF-PSF. This study aims to provide a rapid and feasible muscle evaluation method for clinical front-line surgeons to predict bone nonunion after PLIF-PSF. Methods: A total of 236 patients who received PLIF-PSF at L3–L4, L4–L5, and L5-S1 segments and the follow-up for 1 year were analyzed retrospectively. Based on the analysis of the preoperative lumbar magnetic resonance imaging (MRI), the lumbar indentation value (LIV), the cross-sectional area of paralumbar muscles/body mass index (PL–CSA/BMI), and the Goutallier classification were measured at the intervertebral disc of the L4-L5 segment, and the new muscle health grade was performed. According to the bone nonunion of these patients evaluated by lumbar X-ray, they were divided into the bone union group and the bone nonunion group. Results: In terms of LIV and PL–CSA/BMI, the bone union group was higher than the bone nonunion group at L4-L5 segments (p=0.02, 0.03). In terms of the Goutallier classification, the proportion of patients at grade 3 or 4 in the bone nonunion group was significantly higher than that in the bone union group (P < 0.01, =0.04, and =0.02). In addition, the proportion of patients at a poor muscle health grade in the bone nonunion group was significantly higher than that in the bone union group (P < 0.01, < 0.01, and < 0.01). Through the binary logistic regression, it can be revealed that the new muscle health grade was an independent predictor of bone nonunion after PLIF-PSF (p=0.01, 0.01, and 0.03). Conclusions: Compared with LIV, PL–CSA/BMI, and Goutallier classification, the new muscle health classification is more effective in predicting bone nonunion, and it is expected to be applied in clinical practice. Moreover, it can be further confirmed that the degeneration of lumbar paraspinal muscles is an important factor affecting bone nonunion.