Transfer of the distal terminal motor branch of the extensor carpi radialis brevis to the nerve of the flexor pollicis longus: an anatomic study and clinical application in a tetraplegic patient.

BACKGROUND In tetraplegics, thumb and finger motion traditionally has been reconstructed via orthopedic procedures. Although rarely used, nerve transfers are a viable method for reconstruction in tetraplegia. OBJECTIVE To investigate the anatomic feasibility of transferring the distal branch of the extensor carpi radialis brevis (ECRB) to the flexor pollicis longus (FPL) nerve and to report our first clinical case. METHODS We studied the motor branch of the ECRB and FPL in 14 cadaveric upper limbs. Subsequently, a 24-year-old tetraplegic man with preserved motion in his shoulder, elbow, wrist, and finger extension, but paralysis of thumb and finger flexion underwent surgery. Seven months after trauma, we transferred the brachialis muscle with a tendon graft to the flexor digitorum profundus. The distal nerve of the ECRB was transferred to the FPL nerve. RESULTS The branch to the ECRB entered the muscle in its anterior and proximal third. After sending out a first collateral, the nerve runs for 2.4 cm alongside the muscle and bifurcates intramuscularly. A main branch from the anterior interosseous nerve, which entered the muscle 3 cm from its origin on the radius, innervated the FPL. The ECRB and FPL nerves had similar diameters (∼1 mm) and numbers of myelinated fibers (∼180). In our patient, 14 months after surgery, pinching and grasping were restored and measured 2 and 8 kg strength, respectively. CONCLUSION Transfer of the ECRB distal branch to the FPL is a viable option to reconstruct thumb flexion.