Association between the number of fused levels and surgical outcomes following posterior cervical fusion for degenerative cervical myelopathy.

STUDY DESIGN: Prospective multicenter cohort study. OBJECTIVES: To evaluate the association between the number of fused levels and clinical outcomes following posterior cervical fusion for degenerative cervical myelopathy (DCM). SETTING: Multicenter registry study in Japan. METHODS: Data from a prospective multicenter cervical spine surgery registry were analyzed. Seventy-seven patients with DCM who underwent posterior cervical fusion and completed 2-year follow-up were included. Patients were stratified by the number of fused levels: 1 level (n = 27), 2-3 levels (n = 34), and ≥4 levels (n = 16). Clinical outcomes included cervical JOA score, VAS, SF-36, NPSI, and JOACMEQ. Cervical alignment and range of motion were radiographically evaluated. RESULTS: Cervical alignment was similar among groups, whereas postoperative cervical ROM was significantly reduced in the ≥4-level group (p = 0.011). No significant differences were observed in JOA, SF-36, NPSI, or VAS outcomes. However, a lower JOACMEQ cervical function effectiveness rate was observed in groups with more fusion levels (p = 0.004). Perioperative complication rates were comparable across groups. CONCLUSION: Although a greater number of fused levels was associated with reduced patient-perceived cervical function, no significant between-group differences were observed in neurological recovery, pain relief, or overall quality of life. These findings support preoperative counselling regarding postoperative cervical function when multilevel fusion is clinically indicated. However, because fusion length was determined according to clinical indications in this observational study, residual confounding by indication cannot be excluded, and the findings should be interpreted cautiously.