Do trunk muscles affect the lumbar interbody fusion rate? Correlation of trunk muscle cross sectional area and fusion rates after posterior lumbar interbody fusion using stand-alone cage

Objective: Although trunk muscles in the lumbar spine preserve spinal stability and motility, little is known about the relationship between trunk muscles and spinal fusion rate. The aim of the present study is to evaluate the correlation between trunk muscles cross sectional area (MCSA) and fusion rate after posterior lumbar interbody fusion (PLIF) using stand-alone cages. Methods: A total of 89 adult patients with degenerative lumbar disease who were performed PLIF using stand-alone cages at L4–5 were included in this study. The cross-sectional area of the psoas major (PS), erector spinae (ES), and multifidus (MF) muscles were quantitatively evaluated by preoperative lumbar magnetic resonance imaging at the L3–4, L4–5, and L5–S1 segments, and bone union was evaluated by dynamic lumbar X-rays. Results: Of the 89 patients, 68 had bone union and 21 did not. The MCSAs at all segments in both groups were significantly different (p<0.05) for the PS muscle, those at L3–4 and L4–5 segments between groups were significantly different (p=0.048, 0.021) for the ES and MF muscles. In the multivariate analysis, differences in the PS MCSA at the L4–5 and L5–S1 segments remained significant (p=0.048, 0.043 and odds ratio=1.098, 1.169). In comparison analysis between male and female patients, most MCSAs of male patients were larger than female’s. Fusion rates of male patients (80.7%) were higher than female’s (68.8%), too. Conclusion: For PLIF surgery, PS muscle function appears to be an important factor for bone union and preventing back muscle injury is essential for better fusion rate.