Association Between Cannabis Use and Tobacco Use With Nonunion of Nonoperative Management of Scaphoid Fractures.

BACKGROUND: Scaphoid fracture nonunion remains a clinically significant complication after nonoperative management. While tobacco use is a known risk factor, the association between cannabis use and nonunion risk is less well defined. This study evaluated whether cannabis use, alone or combined with tobacco use, is independently associated with increased rates of scaphoid fracture nonunion and subsequent surgical intervention. METHODS: A retrospective cohort study was conducted using a national health care database from 2010 to 2021. Adult patients with acute scaphoid fractures initially managed nonoperatively were identified. After inclusion and exclusion criteria were applied, 260 806 patients were analyzed and stratified into 4 groups: non-users (n = 165 699), tobacco-only users (n = 75 504), cannabis-only users (n = 4225), and combined cannabis and tobacco users (n = 15 378). Cohorts were matched for age, sex, and comorbidities. Primary outcomes included scaphoid nonunion at 6, 12, and 24 months and rates of surgical intervention. Multivariable logistic regression was used to evaluate independent associations between substance use and nonunion (P < .05). RESULTS: Cannabis use was associated with higher nonunion rates. At 12 months, nonunion occurred in 1.9% of non-users, 3.2% of tobacco-only users, 3.9% of cannabis-only users, and 6.2% of combined users (P < .001). At 24 months, rates increased to 2.0%, 3.6%, 4.3%, and 6.9%, respectively (P < .001). Multivariable analysis demonstrated increased odds of nonunion among cannabis-only users (odds ratio [OR] = 1.05, P = .043), tobacco-only users (OR 1.27, P < .001), and combined users (OR = 1.43, P < .001). CONCLUSIONS: Cannabis use is independently associated with increased scaphoid fracture nonunion following nonoperative management, with a synergistic association observed among combined cannabis and tobacco users.