Extensor tendon rupture caused by instability of the ulnar head with an osteoarthritic distal radioulnar joint: a case report

INTRODUCTION Although spontaneous extensor tendon rupture often occurs in association with rheumatoid arthritis, extensor tendon rupture associated with osteoarthritis of the distal radioulnar joint has been rarely reported. CASE PRESENTATION We present the case of a 74-year-old Asian woman with a fourth and fifth extensor tendon rupture caused by instability of the ulnar head associated with an osteoarthritic distal radioulnar joint. Intraoperative findings showed that the cause of the dorsal capsular perforation and extensor tendon rupture was mechanical friction with the unstable ulnar head, which had no osteophytes or roughness. After tendon transfer and resection of the ulnar head, our patient can extend her ring and little fingers without difficulty for her daily activities. CONCLUSIONS When a patient with osteoarthritic distal radioulnar joint has instability of the ulnar head and the 'scallop sign' on radiography, physicians should consider the possibility of extensor tendon rupture as a complication.