Residency · Residency · Plastic Surgery

Peripheral Nerve Injury and Repair

Overview

Peripheral nerve injury is common in upper extremity trauma and has profound functional consequences. Understanding nerve anatomy, classification systems, regeneration biology, and repair techniques is essential for optimizing recovery. Timing of surgery, gap management, and postoperative rehabilitation are critical determinants of outcome. ---

Peripheral Nerve Anatomy

Structure (Outer to Inner)

Epineurium: outermost connective tissue layer; external and internal components; provides structural support and contains the vasa nervorum. Perineurium: surrounds each fascicle; provides the blood-nerve barrier; strongest layer of the nerve. Endoneurium: surrounds individual nerve fibers within a fascicle; contains capillaries and Schwann cells.

Nerve Fiber Types

Myelinated fibers: motor neurons (A-alpha, A-beta) and sensory neurons (A-delta); faster conduction. Unmyelinated fibers: C fibers (pain, temperature, autonomic); slower conduction. Myelination by Schwann cells; nodes of Ranvier allow saltatory conduction.

Fascicular Organization

Proximal nerve segments have fewer, larger fascicles with more interfascicular connective tissue. Distal nerve segments have more, smaller fascicles with less connective tissue. Fascicular topography changes along the nerve length -- internal organization is not constant. Group fascicular pattern: motor and sensory fibers are grouped but intermingle.

Blood Supply

Segmental extrinsic blood supply from regional arteries. Intrinsic longitudinal vascular plexus within the epineurium and perineurium. Nerve mobilization must preserve segmental blood supply -- excessive stripping devascularizes the nerve. ---

Classification of Nerve Injury

Seddon and Sunderland Classifications

Clinical Significance

Degrees I-II: observe and expect recovery. Degree III: uncertain; observe with serial examinations and electrodiagnostics. Degrees IV-V: surgical intervention required. Neuroma-in-continuity (Degree IV): intraoperative nerve action potential (NAP) testing guides resection vs. neurolysis.

<image>Cross-sectional anatomical illustration of a peripheral nerve showing the three connective tissue layers: epineurium (outermost, containing the vasa nervorum), perineurium (surrounding each fascicle, labeled as the strongest layer and blood-nerve barrier), and endoneurium (surrounding individual axons within a fascicle with Schwann cell myelination). Adjacent to the cross-section, a five-panel diagram illustrates the Sunderland classification from Degree I through Degree V, showing progressive disruption of each layer.</image>

Wallerian Degeneration and Regeneration

Wallerian Degeneration (Distal Stump)

Begins within 24-48 hours of injury. Axon and myelin fragment and are phagocytosed by Schwann cells and macrophages. Schwann cells proliferate and align into columns (bands of Bungner) -- serve as guides for regenerating axons. Denervated muscle fibers atrophy; motor end plates remain viable for approximately 12-18 months. After 18-24 months: irreversible muscle fibrosis (motor end plate degeneration).

Proximal Stump Changes

Retrograde degeneration to the nearest node of Ranvier. Chromatolysis in the cell body (nucleus moves peripherally, Nissl substance disperses). Cell body shifts from transmission mode to synthetic/regenerative mode. Upregulation of growth-associated protein (GAP-43) and tubulin.

Axonal Regeneration

Growth cone extends from the proximal stump. Rate: approximately 1 mm/day (1 inch/month) after an initial 4-week delay. Neurotrophic factors guide the growth cone: NGF, BDNF, NT-3, GDNF. Contact guidance along Schwann cell basal lamina tubes (bands of Bungner). Advancing Tinel sign: percussion over the regenerating nerve front elicits paresthesias distally. ---

Timing of Surgery

Acute Repair

Sharp lacerations with clean wound: primary repair within 72 hours (ideally). Nerve ends are well defined, fascicular patterns can be matched.

Delayed Primary Repair

2-3 weeks post-injury. Allows demarcation of the zone of injury. Fascicular budding from the proximal stump aids identification of healthy nerve.

Timing Guidelines

Clean sharp injury: immediate repair (or delayed primary at 2-3 weeks). Crush/avulsion injuries: wait 3-6 weeks for zone of injury to declare. Closed injuries with possible neurapraxia/axonotmesis: observe for 3 months with clinical and electrodiagnostic monitoring. No clinical or EMG evidence of recovery by 3-6 months: surgical exploration.

The Clock Is Ticking

Motor end plates degenerate by 12-18 months. Muscle fibrosis is irreversible after 18-24 months. Sensory recovery remains possible for longer periods (Schwann cell tubes persist longer for sensory fibers). Calculate expected recovery time: distance from injury to target (in mm) / 1 mm/day + 4 weeks (initial delay). ---

Surgical Repair Techniques

Epineurial Repair

Most common technique for primary nerve repair. Align fascicular groups under magnification using external landmarks (epineurial blood vessels, fascicular pattern). 8-0 or 9-0 nylon sutures through the epineurium. 3-4 sutures are usually sufficient (avoid excessive sutures that increase scarring). Tension-free repair is paramount.

Group Fascicular (Perineurial) Repair

Individual fascicle groups are matched and sutured with 10-0 nylon through the perineurium. Theoretically more precise alignment. More technically demanding, more intraneural scarring. No proven superiority over epineurial repair in most clinical studies. May be beneficial for mixed motor-sensory nerves with identifiable fascicular groups (e.g., distal median nerve).

Fibrin Glue

Adjunct or alternative to sutures. Faster, less foreign body reaction, potentially less scarring. Inferior tensile strength compared to sutures alone. Often used to supplement a few epineurial stay sutures.

Nerve Conduits

Hollow tubes that bridge small nerve gaps (< 3 cm). Materials: collagen (NeuraGen), polyglycolic acid (Neurotube), porcine small intestinal submucosa. Best results for gaps < 2 cm in sensory nerves. Inferior to nerve grafting for motor nerves or gaps > 3 cm.

Nerve Wraps (Coaptation Aids)

Applied around the repair site to contain the repair and reduce scarring. Collagen wraps, amniotic membrane. May reduce perineural adhesion formation. ---

Nerve Grafting

Indications

Gaps > 2-3 cm that cannot be repaired tension-free. Even small amounts of tension are detrimental (impairs intraneural blood flow).

Autograft Donor Nerves

Sural nerve: most common donor; provides up to 30-40 cm of graft; leaves numbness on the lateral foot (acceptable). Medial antebrachial cutaneous nerve (MABC): forearm donor; useful for upper extremity nerve grafts. Lateral antebrachial cutaneous nerve: forearm donor. Posterior interosseous nerve (PIN) terminal branch: small-caliber donor for digital nerves.

Technique

Reverse the graft to prevent axonal escape through side branches. Cable grafting: multiple strands to match the diameter of the injured nerve. Tension-free coaptation at both proximal and distal junctions. Results are limited by the double regeneration interface (two coaptation sites).

Nerve Allograft

Processed (decellularized) nerve allograft (Avance): provides Schwann cell tubes without immunogenicity. Bridges gaps of 5-50 mm in sensory and mixed nerves. No need for immunosuppression (decellularized). Results comparable to autograft for gaps < 3 cm in non-critical sensory nerves.

Vascularized Nerve Grafts

For large gaps in scarred or poorly vascularized beds. Sural nerve on the sural artery pedicle. Ulnar nerve pedicled on the superior ulnar collateral artery. ---

Nerve Transfers

Concept

A functioning but expendable motor nerve (donor) is transferred directly to a denervated motor nerve (recipient) close to the target muscle. Eliminates the need for long regeneration distances. Provides a single coaptation site (vs. two in nerve grafts). Must sacrifice some donor function (choose redundant donors).

Advantages Over Nerve Grafting

Faster reinnervation (short regeneration distance). Single coaptation site. Avoids scarred zone of injury. Pure motor-to-motor or sensory-to-sensory transfers are ideal.

Common Upper Extremity Nerve Transfers

Oberlin transfer: fascicle of ulnar nerve (FCU fascicle) to biceps motor branch (musculocutaneous nerve) for elbow flexion. Double fascicular transfer (Mackinnon): ulnar nerve fascicle to biceps + median nerve fascicle (FCR) to brachialis for elbow flexion. Spinal accessory to suprascapular nerve: for shoulder abduction/external rotation. Radial nerve triceps branch to axillary nerve: for deltoid reinnervation.

AIN to ulnar motor branch (Reverse end-to-side or supercharge end-to-side/SETS): for intrinsic hand function in high ulnar nerve palsy.

Rehabilitation

Motor re-education is critical after nerve transfer. Patient must learn to activate the transferred nerve in a new context (e.g., thinking about wrist flexion to activate elbow flexion after Oberlin transfer). Cortical plasticity enables motor reprogramming over months.

<image>Surgical illustration of the Oberlin nerve transfer for restoration of elbow flexion after upper trunk brachial plexus injury. The illustration shows the medial arm approach with the ulnar nerve identified, a single fascicle (FCU fascicle) being divided and transferred to the biceps motor branch of the musculocutaneous nerve. The proximal coaptation site is highlighted with micro-sutures, and the short regeneration distance to the biceps muscle is indicated. An inset shows the cross-sectional fascicular anatomy of the ulnar nerve in the arm with the FCU fascicle identified.</image>

Electrodiagnostic Studies

Nerve Conduction Studies (NCS)

Measure amplitude (axon number) and velocity (myelination). Motor NCS: compound muscle action potential (CMAP). Sensory NCS: sensory nerve action potential (SNAP). Wallerian degeneration takes 7-10 days; studies performed before this may not show abnormalities.

Electromyography (EMG)

Evaluates muscle electrical activity. Fibrillation potentials and positive sharp waves: denervation (appear 2-3 weeks post-injury). Motor unit action potentials (MUAPs): voluntary activation; presence indicates reinnervation. Nascent MUAPs (small polyphasic potentials) are the first sign of reinnervation. Serial EMG is used to monitor recovery progression.

Timing of Studies

Baseline at 3-4 weeks post-injury (after Wallerian degeneration is complete). Repeat at 3-month intervals to monitor for recovery. Decision for surgery if no EMG evidence of reinnervation by 3-6 months. ---

Motor Re-Education Principles

Sensory Re-Education

Guided sensory exercises to retrain cortical mapping. Begin when protective sensation returns (moving two-point discrimination). Use textures, objects, stereognosis training. Dellon protocol: early and late phase sensory re-education.

Motor Re-Education After Nerve Transfer

Start early with visualization and mirror therapy. Activate the donor nerve pattern (e.g., wrist flexion for Oberlin transfer) to trigger target muscle activation. Biofeedback with surface EMG aids retraining. ---

Clinical Pearls

The rate of nerve regeneration is approximately 1 mm/day after a 4-week initial delay -- use this to calculate expected recovery time and counsel patients. Motor end plates degenerate by 12-18 months after denervation -- early repair or nerve transfer within this window is critical for motor recovery. Tension-free repair is the most important technical principle -- if a gap exists, nerve grafting or transfer is preferable to a repair under tension. The advancing Tinel sign is the most useful clinical tool for monitoring nerve regeneration -- percuss along the nerve from distal to proximal to find the point of maximum tingling.

Nerve transfers have revolutionized the management of proximal nerve injuries (brachial plexus, high ulnar/median) by bringing the repair close to the target muscle and avoiding long regeneration distances. The sural nerve is the workhorse autograft donor; sensory loss on the lateral foot is well tolerated. Degree III injuries (Sunderland) have the most uncertain prognosis -- serial clinical and EMG assessment guides the decision between observation and surgical intervention. In a neuroma-in-continuity, intraoperative nerve action potential (NAP) testing determines whether to perform neurolysis (NAP present) or resection and grafting (NAP absent). ---.

References

• Sunderland S. Nerves and Nerve Injuries. 2nd ed. Churchill Livingstone; 1978.
• Mackinnon SE, Dellon AL. Surgery of the Peripheral Nerve. Thieme; 1988.
• Oberlin C, Beal D, Leechavengvongs S, et al. Nerve transfer to biceps muscle using a part of ulnar nerve for C5-C6 avulsion of the brachial plexus. J Hand Surg Am. 1994;19(2):232-237.
• Brushart TM. Nerve Repair. Oxford University Press; 2011.
• Seddon HJ. Three types of nerve injury. Brain. 1943;66(4):237-288.
• Mackinnon SE. New directions in peripheral nerve surgery. Ann Plast Surg. 1989;22(3):257-273.
• Weber RA, Breidenbach WC, Brown RE, et al. A randomized prospective study of polyglycolic acid conduits for digital nerve reconstruction in humans. Plast Reconstr Surg. 2000;106(5):1036-1045.

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