Cross-Sectional Area of the Lumbar Spine Trunk Muscle and Posterior Lumbar Interbody Fusion Rate: A Retrospective Study

Study Design: A retrospective study. Objective: To investigate the relationship between trunk muscle cross-sectional area (MCSA) and fusion rate after posterior lumbar interbody fusion using pedicle screw fixation (PLIF-PSF). Summary of Background Data: Although trunk muscles of the lumbar spine contribute to spinal stability and alignment, effect of trunk muscles on spinal fusion rate and time to fusion is unclear. Methods: A total of 192 adult patients with degenerative lumbar disease who underwent PLIF-PSF at L3-L4 or L4-L5 were included. The MCSA of the flexor (psoas major, PS), extensor (erector spinae, ES; multifidus, MF) were measured using preoperative lumbar magnetic resonance imaging at 3 segments. Bone union was evaluated using lumbar dynamic plain radiography. Patients were divided into 2 groups according to the presence of bone fusion. Results: Most PS MCSAs in the fusion group were significantly larger than in the nonfusion group, except for MCSA at the L2-L3 segment (all P<0.05). In cases of ES and MF MCSAs, 4 of 6 segments were significantly large. Multivariate analysis revealed that the PS MCSA at L4-L5 was an independent factor for decreased possibility of nonfusion status in both segments (OR=0.812, P=0.028). Pearson analysis demonstrated that the most trunk MCSAs were negatively correlated with time to fusion for both segments and PS MCSAs exhibited a significant correlation with time to fusion except for MCSA at the L2-L3 segment. Conclusions: Trunk MCSAs were significantly larger for a fusion group than a nonfusion group. As trunk MCSAs increased, fusion timing decreased.