Flexor superficialis abductor transfer with carpal tunnel release for thenar palsy

In patients with advanced chronic carpal tunnel syndrome (CTS) the ability of the thumb to abduct and perform functional opposition is impaired greatly, primarily because of denervation and paralysis of the abductor pollicis brevis muscle. The purpose of this study was to evaluate the results of transfer of the flexor digitorum superficialis to the abductor pollicis brevis for restoration of thumb abduction in thenar paralysis caused by advanced chronic CTS.

Fifty patients (51 hands) with advanced CTS and loss of thumb abduction had a flexor digitorum superficialis transfer (37 small, 10 ring, 4 middle finger donors) to the abductor pollicis brevis with simultaneous carpal tunnel release (49 of 51 endoscopic). Thirty patients (60%) were women with an average age of 70 years (range, 35-90 y). Forty-three patients (84%) were in their sixth through eighth decades. We analyzed retrospectively preoperative and postoperative abduction, abduction strength, thenar muscle recovery and function, and patient satisfaction and complications.

All patients reported improved thumb and hand function. Thumb abduction increased almost 20 degrees and 3 British Medical Research Council strength grades. Abduction was improved by the transfer in all patients, with some thenar recovery found in 35 of 40 cases followed-up longer than 12 months. Harvest of the flexor digitorum superficialis from the ring and middle fingers was associated with donor finger proximal interphalangeal joint contracture, although harvest from the small finger was not.

Carpal tunnel release with simultaneous flexor digitorum superficialis-to-abductor pollicis brevis transfer provides satisfactory results for patients with profound CTS and thenar paralysis. The use of the small finger superficialis as the donor motor has minor morbidity compared with other methods and has predictable improvement and patient satisfaction. This transfer method is combined easily with endoscopic carpal tunnel release (as in 49 of our 51 cases), 2-portal, or open method releases.