Relation of Deep Paraspinal Muscles' Cross-Sectional Area of the Cervical Spine and Bone Union in Anterior Cervical Decompression and Fusion: A Retrospective Study

OBJECTIVE: In the cervical spine, deep paraspinal muscles (DPMs) function to preserve spinal stability and mobility. However, the relationship between DPMs and bone union after cervical fusion surgery has not yet been investigated. The objective of this study is to evaluate the relationship between the cross-sectional area (CSA) of DPMs and bone union after cage alone anterior cervical decompression and fusion (ACDF). METHODS: A total of 243 patients who underwent cage alone ACDF at the C5-6 or C6-7 segments were enrolled. The CSAs of the longus colli (LCo), longus capitis (LCa), semispinalis cervicis (SSC), and multifidus (MF) were measured using preoperative magnetic resonance imaging at 3 segments. Bone union was evaluated using dynamic radiographs. The patients were divided into 2 groups according to the presence of bone union and the fusion time. RESULTS: For the extensor (SSC and MF) CSAs, 4 and 3 segments were significantly different between the union and nonunion groups, and between the 1- and 2-union groups (all P values <0.05), respectively. The CSAs of the extensors at C5-6 were an independent factor for decreasing the possibility of nonunion in men and women (odds ratio, 0.788 and 0.699, respectively; all P values <0.05). In addition, for the standardized extensor CSAs, the C5-6 segment was significantly different between the union and nonunion groups (P values <0.05). Pearson analysis revealed that the extensor CSAs exhibited a significant negative correlation with the fusion time at 5 out of the 6 segments (all P values <0.05). CONCLUSIONS: The extensor CSAs were related to fusion rate and timing. In particular, as the extensor CSAs increased, fusion timing decreased.