Nerve Transfers for Median and Ulnar Nerve Injuries
Ryan D. Katz
Ebrahim Paryavi
INDICATIONS
Proximal motor nerve injuries can sometimes benefit from surgical intervention to restore function in the upper extremity. It is generally accepted that the rate at which peripheral nerve growth occurs from the level of neurorrhaphy is 1 mm per day.
Motor end-plate viability on the target musculature is limited to about 12 to 18 months without innervation (1). Given the rate of peripheral nerve growth described above, motor end-plate viability is not assured in any high median or ulnar nerve (UN) injury that may require more that 12 to 18 months for regenerating axons to reach their target.
Thus, any surgical modality that decreases the time to motor end-plate reinnervation may be of potential benefit to patients with high nerve injuries. Transfer of healthy peripheral nerve axons from an uninjured nerve to an injured nerve, downstream from the site of injury, remains one such modality.
Distal nerve transfers to regain or preserve motor function may also be preferred in cases where there is significant trauma resulting in extensive proximal scarring or significant nerve substance loss. Nerve transfers in these settings ensure a healthy nerve-to-nerve coaptation and may preclude the need for a free donor nerve graft (in which a normal sensory nerve is often sacrificed). In these situations, as compared to traditional nerve grafting, transferring a motor nerve from outside of the zone of injury is technically easier and has improved outcomes compared to nerve grafting and regeneration over long distances (2,3).
High Ulnar Nerve Injury
In the absence of an anatomic variation, high UN injuries result in significant hand dysfunction. These injuries affect the ulnar extrinsic profundus flexors as well as the interossei and ulnar lumbricals. The motor deficit from this injury often leads to clawing of the ring and small fingers, impaired dexterity, and decreased hand strength. Disability from this injury can be limited by minimizing the time to motor end-plate reinnervation and/or by preserving motor end plates during upstream nerve recovery. The distal anterior interosseous nerve (AIN) to motor branch of the UN transfer offers this potential benefit (4).
High Median Nerve Injury
The motor deficit from a high median nerve (MN) injury is the result of loss of function of muscles innervated by the AIN and recurrent motor branch of the MN. This causes impaired action of all the superficial flexors, the radial-sided profundus flexors, impaired thumb interphalangeal joint
flexion, and impaired thumb palmar abduction, pronation, and, as a result, opposition. The goal of surgical treatment is to restore finger flexion and prehension (5). In cases where the musculocutaneous nerve (MCN) is preserved, transfer of the brachialis branch to motor branches of the MN in the arm has proven to be anatomically feasible and clinically effective (1,5,6).
flexion, and impaired thumb palmar abduction, pronation, and, as a result, opposition. The goal of surgical treatment is to restore finger flexion and prehension (5). In cases where the musculocutaneous nerve (MCN) is preserved, transfer of the brachialis branch to motor branches of the MN in the arm has proven to be anatomically feasible and clinically effective (1,5,6).
CONTRAINDICATIONS
Nerve transfer is contraindicated in chronic nerve injuries in which the likelihood of target reinnervation is low. As motor end-plate viability decreases with time, so too does the probability of operative success. Therefore, attempts to regain native motor function 12 to 18 months after an injury should be discouraged.
Nerve transfer is also contraindicated in patients who cannot comply with a postoperative rehabilitation program or in which the potential donor nerve may be injured or diseased. Ideally, the donor motor nerve strength should be M4 or greater to maximize benefit (6).
GENERAL TECHNIQUES
Preoperative EMG to ensure viability of motor units in the target musculature is obtained.
The patient is placed supine on a well-padded table with the operative arm prepped and draped on a well-padded hand table.
A tourniquet may be used to minimize bleeding and improve visualization. A sterile tourniquet can facilitate a more proximal dissection if needed.
Intraoperative use of a nerve stimulator can be useful to aid in identification of recipient nerve targets (e.g., motor portion of UN) or prove the adequacy and specificity of proposed donor nerves (e.g., to identify the anterior interosseous portion of the MN or to differentiate between the brachialis motor branch [BMB] of the MCN from the lateral antebrachial cutaneous [LABC] branch of the MCN) (5,7).
A surgical microscope should be available in the operating room.
Fibrin glue is often used to expedite and augment the nerve coaptation.
All neurorrhaphies should be performed in a tension-free manner.
Distal Anterior Interosseous Nerve Transfer to Ulnar Nerve Motor Branch
An incision is made in the palm just ulnar to a traditional carpal tunnel approach.
This incision is carried proximally with a zigzag across the wrist flexion crease and extending approximately 8 to 10 cm from the crease in the ulnar third of the forearm (Fig. 21-1).
Dissection is carried out distally through the hypothenar fat to the hamate hook and volar carpal ligament.
The volar carpal ligament is incised, revealing the ulnar neurovascular bundle in Guyon’s canal.
The motor branch of the UN is released around the hook of the hamate and traced proximally.
Dissection proceeds proximally along the UN up to the takeoff of the dorsal ulnar sensory branch (Fig. 21-2).
The motor fascicular group of the UN can be reliably located immediately radial to the takeoff of the dorsal ulnar sensory branch, lying between it and the sensory portion of the UN (Fig. 21-3).
The motor fascicular group is dissected free from the surrounding sensory portions of the nerve.
A vessel loop is placed around this group to facilitate later identification.
The finger flexor tendons are then retracted radially to reveal the pronator quadratus (PQ).
The distal anterior interosseous nerve is visualized entering the PQ at the proximal edge of the muscle (Fig. 21-4A,B).
The overlying fascia of PQ is incised, the muscle fibers taken down with a bipolar cautery, and the nerve is traced as distally as possible through the muscle fibers (Fig. 21-5).
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