Radiographic Changes in the Cervical Spine Following Anterior Arthrodesis

Background: Adjacent segment degeneration frequently develops following anterior cervical discectomy and fusion. The objectives of the present study were to characterize the long-term evolution of degenerative radiographic changes at segments adjacent to anterior cervical fusion and to identify factors associated with the development of these changes, including the preoperative condition of the cervical spine and parameters related to arthrodeses. Methods: One hundred and sixty six patients who underwent anterior cervical discectomy and fusion for symptomatic cervical spondylosis or disc herniation were followed radiographically for a mean time of 12.7 years (range, 5 to 30 years). Radiographic changes representing degeneration at adjacent levels, including disc height loss, osteophyte formation, end plate sclerosis, and facet arthrosis, along with changes in sagittal alignment of the fusion segment and cervical spine, were recorded preoperatively and at the time of the latest follow up. Regression models were used to identify the parameters that affect these degenerative changes. Results: More than 90% of patients had worsened anterior and posterior osteophytes at segments immediately adjacent to the fusion. Degenerative changes were significantly affected by the proximity of the level to the fusion and were inversely affected by the preoperative degenerative changes present at the segment (p < 0.0001). The time elapsed since the surgical procedure was a significant predictor of degenerative changes (p < 0.0001). However, the patient age, the number of levels fused, and the sagittal alignment of the fusion segment had no influence on the degenerative changes at adjacent segments. Conclusions: Multiple factors likely contribute to adjacent segment degeneration following cervical arthrodesis. Although mechanical parameters associated with arthrodesis, such as length and alignment of the fusion, did not appear to play a role, the preoperative degenerative condition of the spine and inclusion of C5-C6 in the arthrodesis influenced the incidence of adjacent segment degeneration.