Unusual complication of an opposition tendon transfer at the wrist: ulnar nerve compression syndrome.

Restoration of thumb opposition by tendon transfer may be necessary in cases of severe thenar atrophy caused by long-standing carpal tunnel syndrome. Routing the extensor indicis proprius transfer subcutaneously around the ulna to reanimate thumb opposition is an accepted procedure and is considered safe. Ulnar nerve compression leading to palsy is possible, however, as shown in the patient presented. Neurolysis failed to improve the palsy. Rerouting of the transfer deep to the ulnar nerve was necessary to treat the iatrogenic condition. Possible nerve compression should be kept in mind when planning a tendon transfer around the ulnar side of the forearm or carpus and when following up with the patient. Early intervention is necessary to prevent permanent sequelae.