Nerve Transfers

Nerve transfer has revolutionised the management of brachial plexus injuries (BPI) and high peripheral nerve injuries.

This page covers the transfer (neurotization) option specifically. The broader reconstructive menu it sits within - direct epineurial/fascicular repair, grafts and conduits, and when to choose each - is on the Nerve Repairs page, the regeneration biology and the motor-end-plate time window that governs the timing on the Nerve Injury and Regeneration page, and the structure and conduction basic science on Nerve Anatomy and Physiology; the four are companion reads.

Why a transfer works. Axons regenerate at about 1mm/day. If the injury is 30cm from the muscle, they take around 300 days to reach it; transferring a donor distally cuts that distance to under 5cm, about 50 days. A high-level injury with a long regeneration time is converted into a low-level injury with a short one.

Transfer versus graft. A graft bridges the injury with sensory nerve, the sural being the standard for long gaps with the medial antebrachial cutaneous and saphenous as alternatives, and it needs two coaptations, proximal and distal, with the entire length still to regenerate. A transfer takes an expendable motor branch, makes one coaptation close to the target and leaves a short distance. The trade is numbness at the graft donor site against minor weakness in the transfer donor's distribution.

The ideal donor. The donor is chosen for what it can give and what it can afford to lose:

• Powerful: a high axon count (MCA greater than 1000)
• Expendable: its loss is acceptable
• Reach: long enough to reach the target
• Synergistic function, which makes retraining easier
• Independent excursion
• Calibre: a size match with the recipient
• Timing: available early

When to transfer. The indications are the situations in which repair or graft cannot deliver axons to a living muscle in time:

• An impossible repair, typically a root avulsion, where there is no proximal stump to graft from
• A very proximal injury with a viable distal target, where the transfer protects the motor end plates from the long wait
• Enhancing function by "baby-sitting" a muscle while the native axons regenerate down the main trunk

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Transfers are classified by where the donor comes from.

Intra-plexus transfers use roots or trunks adjacent to the injury: with a C5 rupture and a C6 avulsion, the C5 stump (if available) or the medial pectoral nerve. The donor integrates within the same limb, but the supraclavicular plexus has to be explored to reach it, and that is a danger zone.

Extra-plexus transfers bring axons in from outside the plexus altogether:

• Intercostal nerves (3rd-6th) for elbow flexion or the shoulder
• Spinal accessory (XI) for the shoulder, into the suprascapular nerve
• Phrenic nerve, sometimes used, at the risk of hemidiaphragm paralysis
• Contralateral C7 in total plexus avulsion, crossed over the neck; it requires a vascularised nerve graft (usually ulnar) to reach

Distal transfers target nerve branches close to the muscle, the Oberlin transfer being the example.

Checking the donor. The donor muscle must be at least MRC grade 4, preferably 5. Make sure that taking it will not leave an unacceptable deficit, for example where other muscles are already weak, and check that the patient can activate it easily.

Mapping the targets. The examination is organised around the three functions a transfer can restore:

• Shoulder: deltoid and rotator cuff, for the axillary and suprascapular targets. The suprascapular nerve drives supraspinatus and infraspinatus, abduction and external rotation, and spinal accessory to suprascapular is the workhorse of shoulder reanimation
• Elbow: biceps and brachialis, for the musculocutaneous target. An ulnar FCU fascicle to the biceps branch is the Oberlin transfer, a median FCR fascicle to the brachialis branch is Mackinnon's addition, and the double fascicular transfer yields the best results
• Hand: the intrinsics, supplied by the ulnar motor branch. The anterior interosseous nerve (pronator quadratus branch) transfer prevents clawing and restores power pinch, and is a standard for high ulnar nerve injuries

EMG and NCS. Electrodiagnostics confirm both halves of the operation. Motor unit potentials in the donor muscle confirm healthy axons; fibrillations and positive sharp waves in the recipient muscle confirm denervation and the need for a target. It is crucial to verify that the "expendable" donor is actually working properly before it is cut.

MRI of the plexus defines the anatomy of the injury, avulsion versus rupture. A pseudomeningocele indicates that the root has been pulled from the cord, so an extra-plexus transfer is required. CT myelography is the gold standard, but MRI is less invasive.

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When the clinical picture is set, the viva test is choosing between competing reconstructive strategies. Distinguish them by indication, not just by name.

Algorithm

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Diagnosis (day 0 to 3 weeks). Confirm the level of the injury and rule out penetrating trauma, which is explored early. For a closed injury the question is whether to wait and watch. Mechanism is key: high-velocity traction usually means avulsion.

Decision (3-6 months). If there are no signs of recovery, clinical or on EMG, by 3-6 months, the patient needs surgery.

Execution. The pattern of injury sets the plan. In Erb's palsy (C5/6) the shoulder is reanimated (XI to suprascapular) and the elbow (Oberlin). In a total palsy (C5-T1) elbow flexion (intercostal to musculocutaneous) and shoulder stability are prioritised. The function priority hierarchy:

1. Elbow flexion
2. Shoulder stability
3. Hand sensation
4. Hand intrinsics

What every transfer has in common. The cords and their motor branches are identified against the axillary vessels. The donor fascicle is stimulated to confirm it is expendable, then coapted tension-free, end-to-end (or supercharged end-to-side), as close to the recipient's motor entry point as possible to minimise the reinnervation distance.

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ShoulderElbowIntercostalHandContralateral C7

Spinal accessory to suprascapular. Through a dorsal approach, locate XI distal to its trapezius innervation and the suprascapular nerve in the suprascapular notch, release the ligament and repair directly. Taking XI distal to its important trapezius branches preserves proximal trapezius innervation and limits donor shoulder-girdle weakness.

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Radial (triceps) to axillary. Through a posterior or axillary approach, the radial nerve's branch to the long head of triceps is transferred to the anterior division of the axillary nerve, for deltoid, which restores abduction. The anterior axillary division is exposed and confirmed, an expendable triceps branch is selected with stimulation, divided distally and coapted to the recipient proximally. Paired with spinal accessory to suprascapular, it reinnervates both deltoid and rotator cuff.

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Oberlin (ulnar to biceps). Through a medial arm approach, identify the musculocutaneous nerve's branch to biceps with the ulnar nerve alongside it. The donor fascicle is selected physiologically rather than by appearance alone: stimulation finds a fascicle in the ulnar nerve with predominant FCU output while confirming that the neighbouring ulnar functions are preserved, and the chosen fascicle is tested with nerve-action-potential recording before it is divided. Cut the FCU fascicle distally and the biceps branch proximally and coapt them tension-free. FCU function is preserved by redundancy with FCR, and the patient initially flexes the elbow by thinking "flex wrist" until cortical remapping occurs.

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Double fascicular (Oberlin plus Mackinnon). The same medial-arm exposure separates the biceps and brachialis branches of the musculocutaneous nerve, and the adjacent median and ulnar nerves provide selectively stimulated donor fascicles: the ulnar FCU fascicle to biceps and a median (FCR/FDS) fascicle to brachialis. Coapt each close to the motor entry point, without tension or torsion.

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Intercostal to musculocutaneous (Somsak). This is the elbow-flexion transfer when no intraplexal donor is available. Through the chest wall and axilla, intercostal nerves 3, 4 and 5 are harvested; the motor branch is the lower one in the rib space, so the harvest runs along the inferior rib margin, and the pleura is protected throughout. The nerves are mobilised towards the axilla and coapted directly to the musculocutaneous nerve, or to the radial nerve for triceps, if they have been dissected far enough anteriorly to reach; otherwise a nerve graft is usually required. The patient learns to flex the elbow by thinking "breathe in" or "cough", because the intercostal nerve now drives the biceps.

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AIN to ulnar motor. Regeneration from the axilla to the hand is greater than 60cm, which is why a distal transfer is offered for the intrinsics in a high ulnar injury. Through a distal forearm approach, the terminal anterior interosseous nerve (the pronator quadratus branch) is coapted end-to-end to the deep motor branch of the ulnar nerve. The ulnar nerve and artery, the dorsal sensory branch and the terminal AIN to pronator quadratus are all identified before the AIN is mobilised; fascicular mapping and meticulous protection of the sensory component and the ulnar artery are mandatory. Clawing is prevented and pinch improved.

Two variants are easily confused. In the hemi-end-to-end transfer the ulnar motor and volar sensory components are separated intrafascicularly and the AIN is redirected into the motor component, with the dorsal cutaneous branch preserved. In the supercharged (reverse) end-to-side transfer, native ulnar continuity is left intact and the AIN is put into the side of the motor branch to baby-sit the muscle.

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Contralateral C7. Used in total plexus avulsion. The entire C7 root from the healthy side is cut, routed across the neck (retropharyngeal or subcutaneous), bridged with a vascularised ulnar nerve graft and connected to the median nerve for wrist and finger flexion.

Donor morbidity. Weakness in the donor distribution, trapezius weakness for example, is usually transient or well compensated. Each transfer has its own version:

• Oberlin: FCU weakness is rarely clinically significant because of redundancy with FCR; ulnar nerve injury during fascicle identification is rare but catastrophic
• Spinal accessory to suprascapular: trapezius weakness may impair overhead activities; shoulder shrug weakness is usually well tolerated
• Intercostal: chest wall pain (usually temporary); rare pneumothorax during harvest; breathing-elbow synchrony takes months to overcome
• AIN to ulnar motor: mild pronation weakness is usually not clinically apparent; the intrinsics may fail to recover despite a successful coaptation

Failure and co-contraction. The transfer may produce no reinnervation despite surgery, or the patient may have difficulty isolating the movement. Where sensory transfers are used there is sensory loss, and sensory re-education is vital to overcome cortical confusion.

The patient's part. Patients must learn that activating the donor now produces the recipient action, and that is a long-term commitment rather than a quick fix, so motivation is a key selection criterion. Pain management is essential: some patients develop chronic neuropathic pain requiring specialist input.

Reading the first signs. Triggered nascent motor-unit potentials on needle EMG can appear before visible movement. Their presence should prompt focused donor-recipient activation and biofeedback rather than prolonged protection; serial examination still determines whether the new units mature into useful MRC power.

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Early motor retraining. After a double fascicular transfer, suspension slings remove gravity while the patient deliberately couples the donor command with elbow flexion, and EMG biofeedback makes weak recipient activation visible. Assistance is progressively reduced as strength emerges, followed by donor de-activation and task-specific endurance work.

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Upper trunk (Erb's). Good prognosis; the shoulder and elbow are usually recoverable. Abduction recovery is generally 80-90% of normal range, and elbow flexion by Oberlin transfer is very reliable, with greater than 90% success.

Total plexus. Poor prognosis. The goal is a "helper hand" or just elbow flexion, and hand function is unlikely to be significantly restored. Pain relief is a major goal, with DREZ lesions for avulsion pain.

Time. Earlier is better: results degrade significantly after 6-9 months, and the "Goldilocks" period is 3-6 months. After 12 months a free functioning muscle transfer (gracilis) is the only option for motor recovery, with tendon transfers as an alternative if local muscles are available. Always have a Plan B for salvage if the transfer fails. Pre-operative counselling is crucial to manage expectations.

This table is the high-yield "menu" examiners expect you to recall: for each lost function, name the standard donor and recipient.

Global Epidemiology:

• Traumatic adult brachial plexus injury is overwhelmingly a disease of young men: most series report a male-to-female ratio of roughly 4-9 to 1 with peak incidence in the late teens to mid-30s.
• High-energy motorcycle and road-traffic trauma is the dominant mechanism worldwide, accounting for the majority of supraclavicular avulsion injuries in most published cohorts.
• The burden is disproportionately high in regions with large motorcycle populations (parts of South and Southeast Asia, Latin America), which is also where several of the landmark distal-transfer techniques were developed and refined.

Side-by-Side Society / Group Practice (no formal RCT-based guideline exists):