Visualizing Bone Healing in Canine Radial–Ulnar Fractures: A Novel 3D Cast Technique

Radial–ulnar fractures in toy-breed dogs are difficult to manage because of their slender bone diameter and limited soft tissue coverage. Surgical fixation provides rigid stability but risks delayed or nonunion due to stress shielding and medullary occlusion, whereas conventional casting, though non-invasive, often fails to stabilize complete fractures and requires prolonged immobilization, reducing case quality of life. This study developed a case-specific, two-phase three-dimensional (3D) cast therapy tailored to each individual case. A rigid cast was applied during the inflammatory stage to ensure alignment and protection, followed by a slit-modified 3D cast during the early repair stage to allow controlled weight-bearing and functional rehabilitation. Sequential radiographs enabled radiographic visualization of the entire bone healing process, revealing distinct phenomena: rapid callus proliferation in young dogs (“Super-Healing”) and gradual, load-guided realignment of displaced fragments (“Slide-Healing”). These findings demonstrate that controlled mechanical loading under stable, flexible fixation can actively promote bone regeneration. This conservative, visualization-based approach achieved reliable bone union without surgery, minimized activity restriction, and markedly improved case welfare. Owing to its simplicity, safety, and reproducibility, 3D cast therapy has the potential to serve as a new standard of care for managing radial–ulnar fractures in toy and small-breed dogs, while also providing a translational model that bridges clinical orthopedics and regenerative medicine.