OBJECTIVE: To assess the impact of a postoperative fracture gap on implant failure following radius and ulna fracture repair in toy breed dogs. STUDY DESIGN: Retrospective multicenter cohort study. ANIMALS: A total of 80 client-owned toy breed dogs. METHODS: Medical records and radiographs were reviewed for dogs <
3.5 kg that had surgical repair of simple transverse radius and ulna fractures at four institutions from 2005 to 2019. Data collected included signalment, fracture location, implant types and thickness, plate working length, evidence of a postoperative fracture gap in the caudal cortex, postoperative care, occurrence of implant failure, and other complications. The association between potential risk factors and complications was examined using multivariable logistic regression. RESULTS: A postoperative fracture gap in the caudal cortex was noted in 37 cases, and 10 cases experienced implant failure. Of the 43 cases without a gap, one case experienced implant failure. After adjusting for other variables, the fracture gap was significantly associated with implant failure (odds ratio = 23.0 [95% confidence interval: 2.7
197.9], p = .004). Prolonged external coaptation was associated with minor and major complications other than implant failure (p = .04), while the absence of coaptation confounded the effects of the fracture gap on implant failure. CONCLUSION AND CLINICAL SIGNIFICANCE: Reduction of the caudal cortex of the radius is imperative to promote bone healing and prevent implant failure in transverse radius and ulna fractures of toy breed dogs.