Fixation of proximal humeral Salter-Harris type 1 fractures in a 3-dimensionally printed skeletally immature canine bone model: a biomechanical assessment of fully threaded headless cannulated screws.

OBJECTIVE: To compare the biomechanical stability of 4 fixation techniques for proximal humeral physeal fractures in skeletally immature canines using 3-D-printed models. METHODS: This experimental in vitro study was conducted from September 25, 2025, through April 22, 2026. To strictly control biological variability, identical 3-D-printed models of juvenile canine proximal humeral Salter-Harris type 1 fractures (CT-derived from a 6-month-old 26-kg Labrador Retriever) were evaluated across 4 groups: pin and tension band wire (group A), partially threaded cannulated screw (group B), fully threaded headless cannulated screw (FTHCS) alone (group C), and FTHCS with a 1.6-mm Kirschner (K)-wire (group D). Tensile loading was applied at 10 mm/min at 105° to simulate supraspinatus traction. Outcomes included loads at 1- and 2-mm displacements, maximum failure load, and failure modes. RESULTS: Twenty-four models were tested (n = 6/group). Group D exhibited significantly higher resistance at 1-mm (663.95 N) and 2-mm (1,080.33 N) displacements than other groups. At 1-mm displacement, group D outperformed groups C, A, and B (mean differences [MD]: 206.2 N, 380.6 N, and 405.7 N, respectively; P < .0083). Maximum failure load did not differ significantly. Group B failed via localized proximal crushing and subsidence, whereas FTHCS groups (C, D) preserved proximal integrity, failing distally. CONCLUSIONS: In this 3-D-printed model, FTHCS combined with a K-wire provided superior resistance to tensile displacement compared with other tested constructs. CLINICAL RELEVANCE: FTHCS augmented with a K-wire may offer a biomechanically robust alternative mitigating subhead bone collapse, providing sufficient standalone stability for early rehabilitation in immature canines.