A 3‐year‐old mixed‐breed dog was presented with acute onset of non‐weight bearing right thoracic limb lameness. Radiographs revealed dislocation of the ulnar styloid and a small slab fracture of the medial cortex of the distal ulna. Moderate medial and mild lateral instability without hyperextension were detected, and carpal bone fractures were excluded on stress radiographs and computed tomography. The surgical repositioning of the ulnar bone revealed multiple torn ligaments. To reinforce primary repair, the collateral ligaments were augmented medially and laterally using screws, washers and synthetic suture material. Postoperatively, external coaptation, followed by a soft neoprene brace, was used for further rehabilitation. Seven months postoperatively, the dog exhibited pre‐traumatic function. There is no proper classification for multi‐ligamentous injuries, and little is known regarding the long‐term outcomes and limitations of primary carpal ligament repair. In this case, medial and lateral ligament prostheses provided a feasible treatment option with excellent outcomes.