Spinal ankylosis and sex-specific predisposing factors in type II odontoid fractures: a comparison with sub-axial fractures.

Abstract

Study design: Retrospective cohort study.

Purpose: We assessed the predisposition to type II odontoid fractures (T2OFs) in elderly people by comparing patients who had T2OFs with those who had sub-axial fractures.

Overview of literature: T2OFs are common among elderly people; osteoporosis and degenerative changes in the upper cervical spine are major risk factors. However, the role of spinal ankylosis remains unclear.

Methods: We analyzed data from 45 patients with T2OFs and 79 with sub-axial fractures, all aged ≥75 years. Hounsfield unit (HU) values at C2-C4, the prevalence of ankylosis, and degenerative changes were assessed via computed tomography. We performed sex-specific analysis and logistic regression to identify factors associated with T2OF. In addition, we used the Swedish Fracture Registry (SFR) to analyze the prevalence of spinal ankylosis among Swedish patients with T2OFs and sub-axial fractures.

Results: Among patients with T2OFs, in comparison with those with sub-axial fractures, spinal ankylosis was less prevalent (2.2% vs. 31.6%, p<0.001), HU values were lower (p<0.05), atlanto-occipital degeneration was less prevalent (p=0.009), and facet joint degeneration was more prevalent (p=0.03). Logistic regression revealed that atlanto-occipital degeneration (odds ratio, 0.33; p=0.02) and spinal ankylosis (odds ratio, 0.06; p=0.01) were negative predictors of T2OF. Sex-specific analysis revealed that HU values were lower for women with T2OFs (p<0.05) and ankylosis was less prevalent among men with T2OFs (p<0.001) than among sex-matched patients with subaxial fractures. The SFR confirmed that ankylosis was less prevalent among patients with T2OFs (3.3%) than among those with sub-axial fractures (28.3%, p<0.0001).

Conclusions: Spinal ankylosis and atlanto-occipital degeneration are significant risk factors for T2OF. According to sex-specific analysis, spinal ankylosis was less prevalent among men with T2OFs than among those with sub-axial fractures, whereas C2-C4 HU values were significantly lower in among women with T2OFs.