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Interfascicular Nerve Repair

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Techniques of Direct Nerve Suture

• In large nerves where fascicle groups are easily identifiable
• At distal sites where fascicles are diverging into terminal branches, enabling group repair with minimal dissection
• Some studies report more intraneural scarring with this technique, so most peripheral nerve surgeons still prefer epineurial repair

"Group fascicular repair involves separating fascicles in a nerve and suturing matching structures separately. There is potential for more surgical trauma from this type of repair. A recent literature review found no evidence that one suturing technique is superior to another." — Rockwood and Green's Fractures in Adults, 10th ed.

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Fascicular Alignment and Topography

• Epineurial vessel orientation — surface vessels serve as rotational markers
• Fascicular pattern matching — cross-sectional topography at the cut ends
• Intraoperative stimulation — identifies motor vs. sensory fascicles within the first few days after injury (while distal axons still conduct)
• Nerve action potential recording — useful at 2–3 months to detect regeneration across a lesion in continuity
• Histochemical stains — cholinesterase (motor) vs. carbonic anhydrase (sensory) differentiation

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Technical Principles of Suture Repair

• Suture material: Non-absorbable monofilament nylon
• Suture gauge: 6/0 for large nerves (sciatic), 8/0 for median/ulnar, 9/0–10/0 for digital nerves
• No tension: Tension causes ischemia and fibrosis at the repair site; it is the single most important predictor of poor outcome
• No fascicle overlap: Fascicles must be gently coapted, not overlapping
• Fibrin glue may augment the repair
• Approximate mesoneurial attachments to take tension off the nerve suture line

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Managing Nerve Gaps

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Surgical Timing — the "3+1 Rule"

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Key Principle

Peripheral Nerve Repair — Complete Notes A to Z

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1. ANATOMY OF A PERIPHERAL NERVE

• Distal repairs → less fascicular mismatch → better outcomes
• Proximal facial nerve repair → high synkinesis risk due to poor topographic segregation

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2. CLASSIFICATION OF NERVE INJURIES

Seddon Classification (3 grades)

Sunderland Classification (5 grades, extended to 6 by Mackinnon & Dellon)

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3. PATHOPHYSIOLOGY

Wallerian Degeneration (distal to injury)

• Begins within hours; axon and myelin fragment and degenerate
• Schwann cells phagocytose myelin debris
• Schwann cells then proliferate and change to a pro-regenerative phenotype — upregulating neurotrophins, forming bands of Büngner (longitudinally aligned cellular scaffolds for axon regrowth)
• Distal axon remains electrically excitable for 2–4 days after injury → neurophysiology unreliable until 3–6 weeks post-injury

Proximal (Retrograde) Changes

• Chromatolysis: cell body swells, Nissl substance disperses, nucleus peripheralizes
• Structural protein synthesis increases (pro-regenerative)
• ~30% of primary sensory neurons die after unrepaired distal transection
• After proximal injuries (e.g., brachial plexus postganglionic): greater motor neuron and sensory neuron death
• After preganglionic injury: up to 80% sensory + 50% motor neuron death

CNS Changes

• Sensory/motor homuncular maps reorganize within hours
• Denervation pain from spontaneous discharge of injured nociceptive afferents
• Root avulsion → crushing, unrelenting pain (worst prognosis)

Regeneration

• Proximal axon sprouts multiple regenerating sprouts
• Sprouts grow at ~1 mm/day (approximately 1 inch/month)
• Schwann cells guide axons along bands of Büngner
• Neurotrophic factor (BDNF, NGF) expression by denervated Schwann cells declines over time → window for repair
• Regenerated axons have smaller diameter than original; remyelination occurs but myelin sheath is thinner

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4. TIMING OF REPAIR — THE "3+1 RULE"

• Thorough wound debridement
• Fracture stabilization
• Vascular repair first
• Tendon repair
• Adequate soft tissue coverage (vascularized skin; flap if needed)

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5. PREOPERATIVE ASSESSMENT

Clinical

• Document motor and sensory deficits at presentation
• Assess zone of injury (sharp → small zone; crush/blast → wide zone)
• Mechanism: open (laceration) vs. closed (stretch, compression, avulsion)
• Gunshot wounds behave as closed injuries (blast effect, not transection, usually)

Electrodiagnostic Studies

• NCS/EMG: Not reliable until 3–6 weeks post-injury (distal axons still conduct early)
• At 3–6 weeks: fibrillation potentials → confirm denervation
• Nerve Action Potential (NAP) recording at surgery:
  • Positive NAP in a nerve in continuity → axons have regenerated across lesion → neurolysis only
  • Negative NAP → resect neuroma + repair/graft

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6. INTRAOPERATIVE NEUROPHYSIOLOGY

• Avoid neuromuscular blocking agents in anesthesia
• Bipolar stimulating electrode placed proximal to lesion; recording electrode distal
• Early exploration (within 2–4 days): stimulate distal stump to define functional fascicular topography (motor vs. sensory)
• Delayed exploration (2–3 months): NAP recording most useful for nerve in continuity
• Brachial plexus: somatosensory evoked potentials (SEPs) confirm root–cord continuity, excluding preganglionic injury
• Tourniquet limits nerve conductivity after ~30 min — deflate before neurophysiology if critical

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7. SURGICAL EXPOSURE

• Nerves are longitudinal structures → extensive exposure required above and below injury zone
• If delayed >2 weeks: identify nerve in unscarred tissue proximally and distally first, then dissect into zone of injury
• Tourniquet used if injury is sufficiently distal (bloodless field)

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8. NERVE REPAIR TECHNIQUES

A. Neurolysis

• Nerve in continuity with severe intraneural scarring
• Double-bulb swelling (Sunderland IV) to inspect fascicle integrity
• If fascicles are intact across lesion → injury ≤ Grade III → recovery possible without grafting

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B. Direct Nerve Suture (Primary/Secondary Repair)

1. Epineurial Repair (MOST COMMON)

• Sutures placed in the outer epineurium only
• External epineurial blood vessels used as rotational alignment landmarks
• 2–3 interrupted sutures typically sufficient
• Needle must pass only through epineurium — NOT catching fascicles (causes intraneural neuroma)
• Fascicles gently coapted, not overlapping
• Fibrin glue may augment repair

2. Group Fascicular (Interfascicular) Repair

• Fascicle groups are identified and internal epineurium is sutured between groups
• Matching structures sutured separately with fine interrupted nylon
• Then standard epineurial repair added
• Useful in large nerves where fascicle groups are easily identifiable; also at distal sites where fascicles are diverging into terminal branches
• Risk: more intraneural scarring than epineurial repair
• Most peripheral nerve surgeons still prefer epineurial repair

3. Individual Fascicular Repair

• Each fascicle sutured separately with perineurial sutures
• Rarely used — highest potential for surgical trauma and intraneural scarring
• Considered only when individual fascicles are distinctly separable (very distal repairs)

Suture Material and Gauge

Fascicular Alignment Strategies

• Epineurial vessel orientation (primary landmark)
• Cross-sectional fascicular pattern matching
• Intraoperative electrical stimulation (motor vs. sensory fascicle identification)
• Histochemical stains: cholinesterase (motor), carbonic anhydrase (sensory)
• NAP recording

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C. Managing Nerve Gaps (for tension-free repair)

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D. Nerve Grafting

• Trim nerve stumps serially until healthy fascicles are visible
• Grafts placed 10% longer than the gap (slack to prevent tension)
• Where possible, connect equivalent fascicular bundles with individual graft strands
• Fascicular bundles transected at different levels to stagger suture lines
• 1–2 sutures (8/0 or 9/0) per strand through epineurium of graft + epineurium of nerve (or perineurium of fascicular bundle)
• Side-to-side sutures away from coaptation for added strength
• Fibrin glue over ends only (not across repair)

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E. Nerve Allografts

• Cellular material removed; extracellular matrix scaffold preserved
• No living Schwann cells → effective length limited to ~3 cm
• No immunosuppression required
• Results: sensory recovery ~77% (useful S3 sensation); motor recovery poorer
• Increasingly used; more RCT data awaited

• Theoretical advantage: living Schwann cells present
• Highly immunogenic; require immunosuppression → not routinely used clinically

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F. Nerve Conduits (Tubes)

• Hollow tubes that bridge a nerve gap, channeling regenerating axons
• Materials: polyglycolic acid (PGA), collagen-based, poly-lactic-co-glycolic acid (PLGA)
• Indication: Short gaps (<3 cm), small-diameter nerves, usually sensory (e.g., digital nerves, gaps 8–20 mm)
• Limitations: Cannot support regeneration across >2–3 cm without Schwann cells
• Research ongoing: conduits seeded with cultured Schwann cells; not yet in clinical practice
• Freeze-thawed skeletal muscle autografts (basement membrane scaffold): useful for 1-cm defects but ineffective >5 cm

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G. Nerve Transfers (Neurotization)

• Shorter reinnervation distance → faster recovery
• Avoids long graft with multiple suture lines
• Can be performed even when proximal nerve root is avulsed (no proximal stump available)

• Donor nerve normal function will be permanently lost → select carefully
• Donor must be synergistic with recipient function (facilitates re-education)
• Direct suture preferred (no interpositional graft)
• One transfer = one function; multiple transfers needed for multiple movements
• Cannot achieve function independent of the donor nerve (co-contraction / coordination issues)

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H. Secondary (Delayed) Repair

• Performed after closed blunt injuries or failed primary repair
• Substantial exposure required (identify nerve in normal tissue before entering scar zone)
• Neuroma on proximal stump + swelling on distal stump → trim both to healthy fascicles
• Gap usually larger than anticipated after trimming
• Double-bulb swelling = Sunderland Grade IV (fascicles ruptured, only scarred epineurium in continuity) → resect and repair

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I. Tendon and Muscle Transfers (Late Reconstruction)

• Donor must be expendable and of similar excursion/power
• One transfer → one function
• Synergistic transfers are easier to rehabilitate
• Straight line of pull optimal
• Expect one grade of motor strength loss after transfer

• High radial nerve palsy: Pronator teres → ECRB (wrist extension); FCU → EDC (finger extension); PL → EPL (thumb extension)
• Low median nerve palsy (opponensplasty): FDS ring finger / EIP / ADM / PL → APB
• Free functioning muscle transfer (e.g., gracilis): for late elbow flexion or finger flexion when no local donor available

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9. OUTCOMES OF NERVE REPAIR

Factors Affecting Outcome

Hierarchy of Expected Recovery (best to worst)

1. Spontaneous recovery (no surgery needed)
2. Neurolysis alone (positive intraoperative NAP)
3. Primary direct end-to-end repair
4. Nerve graft
5. Nerve transfer (distal transfers better than proximal transfers with graft)
6. Tendon/muscle transfers

Motor Strength Grading (MRC Scale — used for outcome reporting)

Sensory Grading (modified Mackinnon-Dellon / BMRC)

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10. SPECIAL SCENARIOS

Neuroma-in-Continuity

• Blunt/traction injury; nerve appears in continuity but may have internal disruption
• Intraoperative NAP:
  • Positive NAP → axons regenerating → neurolysis only
  • Negative NAP → resect neuroma + repair/graft

Brachial Plexus Injury

• Observe 3 months for spontaneous recovery before intervention
• Preganglionic signs: Horner syndrome (ptosis, miosis, anhidrosis — sympathetic chain), scapular winging (long thoracic nerve), elevated hemidiaphragm on CXR (phrenic nerve), preserved sensory NCS with absent motor (DRG intact)
• EMG: loss of innervation in paraspinal muscles = preganglionic
• Preganglionic → no proximal stump → nerve transfer mandatory
• Priority of reconstruction: elbow flexion > shoulder > hand

Nerve Repair Priorities (Upper Extremity)

• Minimum functional goals: stable shoulder, elbow flexion, median nerve sensibility, prehensile grip

Nerve Repair Priorities (Lower Extremity)

• Minimum: stable hip + knee, tibial nerve plantar sensation (allows ambulation)

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11. KEY NUMBERS TO REMEMBER

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Anatomy of a Peripheral Nerve

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Wallerian Degeneration & Axonal Regeneration