Risk factors for scaphoid nonunion in acute fractures treated with cast immobilization.

Aims: There is a lack of published evidence relating to the risk factors for nonunion seen in acute scaphoid fractures. We aimed to describe the risk factors for nonunion in adult patients (aged ≥ 16 years) treated with cast immobilization for acute scaphoid fractures. Methods: We conducted a single centre cohort study of patients with an acute scaphoid fracture and who were followed up with a CT scan to assess union. Data were gathered retrospectively. Outcomes were classified as union or nonunion based on CT scan follow-up. Descriptive and regression analyses were performed. Results: Of 502 patients, there were 50 nonunions (10%), of which 39 (78%) were male. The risk of nonunion tripled when fracture displacement was ≥ 1 mm compared with < 1 mm displacement (odds ratio (OR) 3.10; 95% CI 1.42 to 6.71. There was strong evidence that age was a risk factor for nonunion and the relationship between age and nonunion was non-linear. The reference age was 26 years and the highest risk of nonunion was in the 26- to 36-year age group. The risk of nonunion steadily reduced as age increased above aged 36 years; for example, patients aged 40 years older (66 years old) had a 91% lower risk of nonunion respectively relative to the reference age group. Conclusion: The two risk factors for scaphoid nonunion in those treated with cast immobilization were fracture displacement and age. Further assessment and research could help inform clinical decision making and may help guide future research to improve clinical pathways of care.