Lateral Mass Screws Versus Pedicle Screws at C7: Reoperation Rates for Operative Adjacent Segment Disease and Nonunion in Posterior Cervical Fusion

Study Design.A retrospective cohort study. Objective.To determine if there is a difference in reoperation rates for symptomatic adjacent segment disease (operative ASD) and symptomatic nonunions (operative nonunions) in posterior cervical fusions (PCFs) stopping at C7 using either lateral mass screws (LMS) or cervical pedicle screws (CPS) at C7. Summary of Background Data.Stopping PCFs at C7 has been controversial because of the risks of adjacent segment disease or nonunions. The two commonly used fixation techniques at the C7 level are LMS and CPS. Materials and Methods.A retrospective analysis from the Kaiser Permanente Spine Registry identified a cohort of patients with cervical degenerative disk disease who underwent primary PCFs stopping at C7 with either LMS or CPS at C7. Demographic and operative data were extracted from the registry, and operative ASD and operative nonunions were adjudicated through chart review. Patients were followed until validated operative ASD or nonunion, membership termination, death, or end of study (March 31, 2022). Descriptive statistics and multivariable Cox proportional hazards models were calculated for operative ASDs and operative nonunions. Results.We found 481 patients with PCFs stopping at C7 with either LMS (n=347) or CPS (n=134) at C7 with an average follow-up time of 5.6 (+/- 3.8) years, time to operative ASD of 3.0 (+/- 2.8) years, and to operative nonunion of 1.2 (+/- 0.7) years. There were 11 operative ASDs (LMS=8, CPS=3) and eight operative nonunions (LMS=4, CPS=4). There was no statistical difference between patients stopping at C7 with LMS versus CPS for operative ASDs (HR: 0.68, 95% CI=0.17-2.77, P=0.60) or operative nonunions (HR: 2.09, 95% CI=0.45-8.58, P=0.37). Conclusion.A large cohort of patients with PCFs stopping at C7 with an average follow-up of > 5 years found no statistical difference in reoperation rates for symptomatic ASD (operative ASD) or operative nonunion using either LMS or CPS at C7.