Aims. Reconstruction after osteoarticular resection of the proximal ulna for tumours is technically difficult and little has been written about the options that are available. We report a series of four patients who underwent radial neck to humeral trochlea transposition arthroplasty following proximal ulnar osteoarticular resection. Methods. Between July 2020 and July 2022, four patients with primary bone tumours of the ulna underwent radial neck to humeral trochlea transposition arthroplasty. Their mean age was 28 years (12 to 41). The functional outcome was assessed using the range of motion (ROM) of the elbow, rotation of the forearm and stability of the elbow, the Musculoskeletal Tumor Society score (MSTS), and the nine-item abbreviated version of the Disabilities of the Arm, Shoulder and Hand questionnaire (QuickDASH-9) score. Results. All patients were available for follow-up at a mean of 33 months (25 to 43) and were disease-free. The mean flexion arc was 0° to 105°. Three patients had complications. One had neuropraxia of the ulnar nerve. The symptoms resolved after three months. In one patient, the screw used for fixation of the triceps tendon became exposed and was removed, six months postoperatively. One patient with wound dehiscence required a local flap for soft-tissue cover, four months postoperatively. At a mean follow-up of 33 months (25 to 43), the mean flexion arc was 0° to 105°. All patients had full supination (85°) but none had any pronation. The mean
