Introduction: The increasing rates of cervical fusion have prompted research on their potential complications, including accelerated adjacent segment degeneration (ASD). Whether ending cervical fusion at C6 or C7 changes ASD incidence remains unknown. Here, we compare the association of ending fusion at C6 or C7 with 1-year post-operative radiographic ASD incidence below the fusion.

Methods: In this retrospective cohort study, we reviewed medical records of all adult patients undergoing index cervical fusion ending at C6 or C7 performed by a single surgeon at Duke University Medical Center (February 2008 - January 2013). All patients had at least 3-month follow-up cervical spine image available. Baseline demographic, medical, and surgical characteristics were assessed. Log-binomial regression model estimated 12-month ASD risk, adjusting for degenerative disc disease (DDD) and fusion length. Kaplan-Meier analysis assessed radiographic ASD development in both cohorts, and the results were compared with log-rank test. 12-month Visual Analog Scale (VAS) scores for neck pain for patients with and without radiographic ASD were reported.

Results: 166 patients underwent index cervical fusion, 79 ending at C6 and 87 at C7. Average age was 55 years, and majority of patients had DDD, were non-smokers and non-diabetics. About half the patients had less than 3 levels fused; average baseline VAS was 5.9. On average, the 12-month risk of radiographic ASD below the fusion in the C6 group was 2.29 times as high as risk in the C7 group (95% CI: 1.29, 4.07). In the log-rank test, the null hypothesis that the two time-to-ASD functions were equivalent was rejected (chi-square: 22.4, p-value: <0.01). 12-month VAS scores were similar for patients with or without radiographic ASD.

Conclusions: Our study suggests that ending cervical fusion at C7 is associated with a lower 12-month risk of radiographic ASD below the fusion. The findings are important to surgeons’ decision-making regarding extent of cervical fusions.

Patient Care: Knowing which cervical levels are more prone to ASD development will help planning for cervical fusion procedures that minimize ASD risk (and potentially long-term patient morbidity and need for additional fusion surgeries).

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of minimizing risk of adjacent segment degeneration (ASD) development post cervical fusion, 2) Discuss, in small groups, whether certain vertebral levels are more prone to ASD development, and 3) Brainstorm potential studies to further assess clinical implication of radiographic ASD development

References: See attached manuscript.