407 Screw Angle Variability in Posterior Cervical Fusions

INTRODUCTION: Variability in pedicle and lateral mass screw angle may influence biomechanical stability, fusion rates, and risk of implant-related complications following posterior cervical fusion (PCF). METHODS: Elective PCF patients from a single institution from 2010-22 were identified. Screw angles were collected using the screw midline and superior endplate. Independent variables were: a) standard deviation (SD) of angles among all screws, and b) mean difference between screw angles of adjacent screws. Outcomes included reoperations, radiographic evidence of implant failure, and PROs, including neck disability index (NDI%), neck and arm pain visual analogue score, and quality of life at 3, 12 and 24 months. Multivariable regression models were conducted controlling for age, BMI and smoking status. RESULTS: Among 367 patients undergoing PCF for degenerative cervical pathology, mean age was 62.2±10.2; 218 (59.4%) were male. The mean screw angle was 29.4±9.0º and follow-up, 4.1±3.4 years. Screw angle SD (p=0.763) and difference between adjacent screw angles (p=0.808) between patients were not associated with reoperation. Patients with radiographic evidence of implant failure (n=51, 13.9%) had greater screw angle SD (16.1±6.3 vs. 13.4±7.2º, p=.016) and difference between adjacent screw angles (10.6±4.3 vs. 8.5±5.0º, p=.003) than patients without implant failure. On cox-proportional hazard regression, screw angle SD (HR=1.04, 95% CI=1.00-1.08, p=.036) and difference between adjacent screw angles (HR=1.07, 95% CI=1.02-1.13, p=.008) increased the risk for implant failure. Screw angle SD (ρ=0.16, p=.004; β=0.39, 95% CI=0.13-0.66, p=.004) and difference in adjacent screw angles (ρ=0.13, p=.019; β=0.47, 95% CI=0.09-0.85, p=.016) were associated with increased 3-month NDI, with no association to other PROs. CONCLUSIONS: In our cohort of PCF patients, greater screw angle SD and difference between adjacent screw angles were associated with increased risk for implant failure and worse 3-month neck disability.