An eight-year-old, neutered female Rottweiler was presented with lameness of seven days duration. Radiographs were consistent with a distal radial bone tumour. Limb-sparing surgery was performed using a commercially available endoprosthesis with a locking bone plate. Histopathological examination of the resected bone revealed an intraosseous fibrosarcoma, and postoperative adjuvant chemotherapy was initiated three weeks after surgery. Despite initial satisfactory limb function, lameness worsened four months after surgery. Radiographs revealed large areas of bone lysis around the proximal and distal screws, leading to significant resorption of the radius and radial carpal bone with subsequent construct failure. Further treatment was declined by the owner and the dog was subsequently euthanased. This case illustrates that implant failure is not necessarily averted by the use of locking (compared with non-locking) implants combined with an endoprosthesis to treat distal radial tumours in dogs.