Reconstructive Nerve Transfer Options for Restoration of Pronation

10.1055/b-0034-78105

Reconstructive Nerve Transfer Options for Restoration of Pronation

Kirsty Usher Boyd and Susan E. Mackinnon

Following proximal median nerve injury, loss of pronation results in significant impairment. Restoration of active pronation with tendon transfers is reserved for obstetrical brachial plexus injuries.1 With the recent addition of nerve transfers as a reconstructive option, the ability to restore active pronation has had a significant effect on patient recovery and ability to perform activities of daily living. Nerve transfers avoid operating within the zone of injury and provide a source of expendable donor nerves in close proximity to the motor endplate, resulting in faster and superior recovery. The most common donor nerve to restore active pronation is the nerve to the extensor carpi radialis brevis (ECRB); however, other options exist, including a nerve to the flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), or flexor carpi radialis (FCR). With the appropriate knowledge of nerve topography and anatomy, these transfers are straightforward and provide prompt, excellent results.

Indications

Nerve transfers to restore active pronation are indicated following iatrogenic injury, traumatic injury, or neoplastic resection to the proximal median nerve.
The authors have encountered situations in which partial loss of median nerve function has resulted in isolated loss of pronation. The pronator teres muscle has less redundancy in the fascicles at the root level, leaving it more susceptible to denervation and loss of function even with proximal pathology.
Loss of pronation is found frequently in C6–C7 nerve root injuries, lower brachial plexus injuries, and high median nerve injuries.
Nerve transfers to restore active pronation can be performed in conjunction with other reconstructive procedures, such as nerve transfers to restore anterior interosseous nerve (AIN) function, flexor digitorum profundus tenodesis, and opponens plasty.

Contraindications

Nerve transfers to restore pronation are contraindicated in patients with pan-plexus injuries, where motor donors need to be prioritized to restore elbow, shoulder, or wrist function.
Nerve transfers are relatively contraindicated in donor nerves with the British Medical Research Council (BMRC) grade 3 or lower strength (i.e., resistance against gravity or less), and are preferred in patients with BMRC grade 5 (normal strength with resistance), because some downgrading of the donor strength may occur.
Motor nerve transfers are contraindicated in injuries where viable axons cannot reach the target motor endplate by twelve months from the time of injury. At ~ 12 months, denervated muscle undergoes permanent fibrosis and atrophy, making reinnervation impossible.
A relative contraindication to motor nerve transfer is patient noncompliance. Motor nerve transfers require extensive rehabilitation with a hand therapist for motor reeducation and training. However, motor reeducation rehabilitation therapy to recover pronation is not difficult.

Examination/Imaging

No imaging is required for nerve transfers.
A clinical examination to document the lack of pronation and to document the potential donor nerves is essential.
In the situation of a partial nerve injury, where recovery may be a possibility, serial clinical examination and electrodiagnostic studies may assist in the surgical decision making.

Relevant Anatomy

Median Nerve Anatomy (Fig. 18.1)

The median nerve arises from the C5–T1 nerve roots and passes into the forearm through the antebrachial fossa.
It then lies between the FDS and the flexor digitorum profundus (FDP) in the proximal forearm before becoming more superficial distally, coming to be located just deep to the palmaris longus (PL) at the level of the wrist crease.
Branches from proximal to distal include: pronator teres (PT), FCR/PL, AIN, and FDS.
The AIN is the only branch to exit from the radial/lateral side of the median nerve, while all the other branches depart from the ulnar/medial side.

Ulnar Nerve Anatomy (Fig. 18.1)

The ulnar nerve arises from the C8 and T1 nerve roots and enters the forearm by traveling posterior to the medial epicondyle and then between the two heads of the FCU muscle.
It lies deep to the FCU throughout the remainder of the forearm before branching at the level of the Guyon canal.
Branches to the FCU are located at approximately the level of the elbow and are often multiple in number.

Radial Nerve Anatomy (Fig. 18.1)

The radial nerve arises from the C5–T1 nerve roots. After emanating from the spiral groove, ~ 10 cm proximal to the lateral epicondyle, the nerve passes along the anterior surface of the joint capsule and crosses into the forearm.
In the proximal arm, the radial nerve gives off branches to the triceps, anconeus epitrochlearis, brachioradialis, and extensor carpi radialis longus (ECRL).
Anterior to the radial head, the nerve branches into the posterior interosseous nerve (PIN) and the radial sensory branch.
The supinator and ECRB branches can depart from the main nerve, from the proximal PIN, or at the same level as the radial sensory branch.
The radial sensory branch lies just superficial to the antebrachial fascia.
Once identified, the radial sensory branch is the most radial/volar, followed by the ECRB (which is narrower) and then by the PIN, which is the largest and most dorsal and travels underneath the superficial portion of the supinator.