Low Lumbar Multifidus Muscle Status and Bone Mineral Density are Important Risk Factors for Adjacent Segment Disease After Lumbar Fusion—A Case–Control Study

Background: The quantity and quality of the paraspinal muscles are important factors that lead to spinal diseases. However, the role of paraspinal muscles in the pathogenesis of adjacent segment disease (ASD) after lumbar fusion surgery is rarely studied. The purpose of the research is to investigate the relationship between paraspinal muscles and ASD. Methods 33 patients with ASD were included, and 33 controls without ASD were matched according to the basic demographic information. Cross-sectional images of the paraspinal muscles at each intervertebral disc level (L1-S1) before the first operation were analyzed, and the cross-sectional area (CSA) and degree of fat infiltration (FI) of the multifidus (MF) muscle and the erector spinae (ES) muscle were compared. Results There was no significant difference in demographic characteristics (P > 0.05) except for the bone mineral density (BMD) (P < 0.05) between the two groups. There were significant differences in the CSA and FI of the lower lumbar multifidus (P < 0.05). The CSA of the MF muscle at L3-L4, FI of the MF muscle at L4-L5 and L5-S1, and BMD were independent risk factors for ASD. Among patients who received two-segment fusion for the first time, significant difference was observed in the degree of FI of the MF muscle in the lower lumbar segment (P < 0.05). Conclusions The CSA, FI and BMD of the lower lumbar MF muscle are closely related to the occurrence of ASD. The CSA of the MF muscle at L3-L4, the degree of FI of the MF muscle at L4-L5 and L5-S1, and BMD were independent risk factors for ASD. The number of fusion segments in the first operation has a certain impact on the abovementioned conclusions.