For recovery of intrinsic muscle function in a patient with a high ulnar nerve injury (near or above the elbow) to shorten the distance between the donor nerve and the recipient muscles

The ulnar nerve enters the anterior (flexor) compartment of the forearm between the two heads of flexor carpi ulnaris (FCU) and innervates one and a half muscles (FCU and medial half of FDP to the ring and small fingers). It runs along the ulna with the ulnar artery, and the two travel distally under the FCU. Proximal to the wrist, the fascicles of the motor branch lie ulnar to the sensory fascicles. The ulnar nerve and artery pass superficial to the flexor retinaculum into the Guyon canal. In the Guyon canal, the ulnar artery is radial to the ulnar nerve. At the radial side of the pisiform bone, the ulnar nerve is divided into the superficial and deep branches. The deep branch of the ulnar nerve curves laterally to supply the hypothenar muscles and runs across the palm with the deep palmar arch; it terminates by supplying the first dorsal interosseous and the deep head of the flexor pollicis brevis (Fig. 14-1).

The AIN is a branch of the median nerve that supplies the deep muscles on the front of the forearm. It accompanies the anterior interosseous artery and runs on the anterior surface of the interosseous membrane in the interval between the FPL and FDP, supplying the whole of the former and the radial half of the latter. The AIN terminates in the volar capsule of the wrist joint after it innervates the PQ (see Fig. 14-1).

The procedure is performed under general anesthesia under tourniquet control. Regional anesthesia is not used so that nerve stimulation can be performed. The patient is positioned supine with the affected extremity on a hand table.

A 10-cm curvilinear incision begins at the pisiform and curves gently radially and proximally. This incision will expose the ulnar nerve in Guyon canal and the AIN in the distal forearm (Fig. 14-2). The skin and subcutaneous fat are dissected in the distal half of the incision to expose the ulnar nerve in Guyon canal. In the proximal half of the incision, the antebrachial fascia is divided ulnar to the palmaris longus. The median nerve is identified below the palmaris longus to expose the flexor tendons. The palmaris longus, median nerve, and flexor tendons to the radial two fingers are retracted radially, and the flexor tendons to the ulnar fingers are retracted ulnarly to expose the PQ.

A splint is used to maintain the wrist in neutral position for 3 weeks. The patient is instructed in range-of-motion exercise of the fingers, elbow, and shoulder to maintain movement and nerve gliding proximal and distal to the repair site.

Postoperative rehabilitation includes motor rehabilitation. The patient is initially instructed in resisted forearm pronation exercises. With evidence of reinnervation of the intrinsic muscles, the patient is then instructed in pinching exercises in resisted forearm pronated positions.

Although the distal anterior interosseous nerve is not a powerful donor, one can at least expect to prevent clawing, improve pinch strength, and avoid tendon transfers.