Modular Revision of a Failed Patient-Specific 3D-Printed Scapulo-Humeral Endoprosthesis in a Dog with Proximal Humeral Osteosarcoma: First Clinical Communication.

Canine appendicular osteosarcoma (OSA) is typically managed by limb amputation. However, this approach may be suboptimal in dogs with concurrent osteoarthrosis (OA). Limb-sparing surgery using three-dimensional (3D)-printed patient-specific implants (PSIs) may be an alternative, although evidence on implant durability and revision strategies remains limited, in particular for proximal humeral reconstructions. This report describes a 9-year-old, overweight dog referred for a 4-week history of persistent left forelimb lameness. Computed tomography (CT) confirmed a lesion affecting the proximal humerus and severe bilateral hip OA. Fine-needle aspiration cytology supported a presumptive diagnosis of OSA. Limb-sparing surgery with 3D-printed PSIs was chosen instead of amputation due to overweight status and OA. Patient-specific guides (PSGs) and endoprosthesis (PSE) were designed based on preoperative CT. Histopathology of the resected tumour confirmed OSA with complete surgical margins. Postoperative functional recovery was favorable, with progressive return to weight-bearing and mild residual lameness up to 8 months. At 9 months, implant failure occurred due to fracture at the distal humeral fixation region. Revision surgery was performed using a novel 3D-printed modular PSE integrating the retained proximal component, allowing restoration of limb function for an additional 6 months. The dog was euthanized at 15 months due to pulmonary metastases. Post-mortem macroscopic and histological visual semi-quantitative assessment of peri-implant tissue suggested advanced osseointegration, with no local recurrence or infection. This report suggests that PSI-based limb-sparing reconstruction may be feasible in proximal humeral OSA and highlights mechanical fatigue as a key limitation. The modular revision approach suggests the potential of additive manufacturing for salvage strategies after implant failure.