Periprosthetic fracture of the ulna-a case report.

After resection of the radial head, the load transmission through the forearm is changed dramatically. Most of the axial load is transmitted to the ulna. This can happen through the interosseous membrane, if intact, thus preventing proximal migration of theradius. However, radial head resection entails some slacking of the interosseous membrane, thereby reducing its ability to transmit load. In traumatic lesions of the interosseous membrane there is no limit to the proximal migration of the radius until the ulnar head abuts on the carpus. In both cases the load transmitted by the ulna increases dramatically and can promote fractures thereof. A 52-year-old, right-handed male patient presented with a periprosthetic fracture of the right ulna 6 weeks after implantation of an ulna head prosthesis. He had previously undergone radial head excision for malunion of the radial head and secondary humeroradial osteoarthritis. This operation had reduced pain and improved the range of motion at the elbow but entailed degenerative arthritis and related symptoms at the distal radioulnar joint (DRUJ). From the spectrum of possible treatment options, ulnar head resurfacing/hemiprosthesis was elected and performed without intraoperative or postoperative irregularities. However, 6 weeks postoperatively, as he was lifting a heavy object, a periprosthetic fracture of the ulna occurred, which ultimately was treated successfully by open reduction and plate fixation. Plate fixation of periprosthetic fractures is an established treatment concept after excluding implant loosening. Periprosthetic fracture of the ulna seems to be a rare complication but can be treated similarly.