169 Quantifying the Effect of Fracture Morphology on Nonunion for Traumatic, Isolated Odontoid Fractures Managed Nonoperatively: A Propensity Score Matched Analysis

Abstract

INTRODUCTION: Odontoid fractures disproportionately affect older patients who have high surgical risk, but also high rates of fracture nonunion. METHODS: We examined all patients with isolated odontoid fractures treated nonoperatively at our institution between 2010 and 2020. Multivariable regression and propensity score matching were used to quantify the effect of fracture type, angulation, comminution, and displacement on bony healing by 26 weeks from injury. RESULTS: 303 consecutive traumatic odontoid fracture patients were identified, of whom 163 (53.8%) had isolated fractures that were managed nonoperatively. Selection for nonoperative management was more likely with older age (OR = 1.45 [1.14, 1.84], p = 0.003), and less likely with angulated fractures (OR = 0.31 [0.14, 0.65], p = 0.002), or higher presenting Nurick scores (OR = 0.78 [0.63, 0.97], p = 0.023). Factors associated with nonunion at 26 weeks were angulated morphology (OR = 16.14 [2.93, 89.00], p = 0.001) and Anderson-D’Alonzo Type II morphology (OR = 6.54 [2.16, 19.77], p = 0.001). Cox proportional hazards regression demonstrated slower healing time for angulated (HR 0.144 [0.044, 0.377], p = 0.0003) and type II fractures (HR = 0.380 [0.214, 0.673], p = 0.0009). Propensity score matching to assess the effect of type II fracture, fracture angulation, displacement, and comminution all yielded balanced models (Rubin's B < 25.0, 0.5 < Rubin's R < 2.0). By 26 weeks, controlling for confounders, 77.3% of type I or III fractures healed, compared to 38.3% of type II fractures (p = 0.001), and 56.3% of non-angulated fractures healed compared to 12.5% of angulated fractures (p = 0.015). Fracture displacement and comminution had no significant effect. CONCLUSIONS: Type II fracture morphology and fracture angulation significantly increase nonunion among nonoperatively managed isolated traumatic odontoid fractures, but fracture comminution and displacement do not.