Assessment, patient selection, and rehabilitation of nerve transfers

Abstract

Peripheral nerve injuries are common and can have a devastating effect on physical, psychological, and socioeconomic wellbeing. Peripheral nerve transfers have become the standard of care for many types of peripheral nerve injury due to their superior outcomes relative to conventional techniques. As the indications for, and use of, nerve transfers expand, the importance of pre-operative assessment and post-operative optimization increases. There are two principal advantages of nerve transfers: (1) their ability to shorten the time to reinnervation of muscles undergoing denervation because of peripheral nerve injury; and (2) their specificity in ensuring proximal motor and sensory axons are directed towards appropriate motor and sensory targets. Compared to conventional nerve grafting, nerve transfers offer opportunities to reinnervate muscles affected by cervical spinal cord injury and to augment natural reinnervation potential for very proximal injuries. This article provides a narrative review of the current scientific knowledge and clinical understanding of nerve transfers including peripheral nerve injury assessment and pre- and post-operative electrodiagnostic testing, adjuvant therapies, and post-operative rehabilitation for optimizing nerve transfer outcomes.

Keywords: electromyography; nerve transfer; nerve transfer rehabilitation; peripheral nerve injury; rehabilitation.

Figure 1

Triggered nascent motor unit action potential seen during needle EMG in the extensor digitorum communis muscle 10 weeks after nerve transfer (median nerve fascicle to flexor digitorum superficialis to the posterior interosseous nerve). Note that the nascent unit is appreciable with finger flexion as the patient activates the donor nerve. Nascent motor unit action potentials are characterized by their small amplitude, long duration, polyphasia, and instability.

Figure 2

Dynamic-assist orthosis to augment elbow flexion after double fascicular nerve transfer to restore elbow flexion. On the left, the patient is maximally contracting the elbow flexors but cannot move the arm against gravity. On the right, the assistance of rubber bands on the dynamic-assist orthosis allows the paitent to flex the elbow against gravity.

Figure 3

Gravity-eliminated exercises combining donor and recipient muscle function to flex the elbow with the assistance of suspension slings to eliminate gravity and EMG-biofeedback to improve nerve activation after double fascicular transfer (ulnar nerve fascicle to flexor carpi ulnaris to musculocutaneous nerve branch to brachialis and median nerve fascicle to flexor digitorum superficialis to musculocutaneous nerve branch to biceps). On the left is the patient's starting position. On the right, the patient is flexing the elbow while concurrently flexing the wrist and fingers to activate the donor nerves.

Figure 4

Selective activation or “donor de-activation” exercises. EMG-biofeedback of recipient muscle(s) occurs while simultaneously eliciting the recipient muscle(s) and the antagonist muscle(s) to the donor nerve. In this example, the patient has undergone double-fascicular transfer. On the left is the starting position with fingers relaxed bilaterally and the EMG-biofeedback of biceps below threshold. On the right is the final position, with bilateral finger and wrist extension while activating elbow flexors with the EMG-biofeedback of biceps above threshold.

Figure 5

Selective activation or “donor de-activation” exercises. EMG-biofeedback of the antagonist muscle(s) to the recipient muscle(s) while simultaneously eliciting the function of the donor nerve and the antagonist muscle(s) to recipient muscle(s). In this example, the patient has undergone double-fascicular transfer. On the left is the starting position, fingers flexed holding an object and elbow flexed with EMG biofeedback on the triceps below threshold. On the right is the final position, with the patient demonstrating finger flexion (holding an object) while extending the elbow.

Figure 6

Selective activation or “donor de-activation” functional exercises in the late stages of the rehabilitation (endurance phase). In these photos, a person with SCI, who underwent supinator branch to posterior interosseous nerve transfer concurrent with musculocutaneous nerve branch to brachialis to anterior interosseous nerve fascicle, completes donor de-activation exercises. In the left two images, the patient is tasked with holding the object with fingers flexed while bringing the object to the mouth with elbow flexion and forearm supination. In the right two images, the patient is tasked with bringing the object back to the table and drop it by extending the fingers with the forearm in pronation. The patient is wearing a wrist orthosis to minimize wrist tenodesis while performing exercises.