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Tendon Transfer: A Complete Guide

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1. DEFINITION

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2. INDICATIONS

1. Peripheral nerve injuries - when nerve repair is not possible or has failed (radial nerve palsy, ulnar nerve palsy, median nerve palsy, brachial plexus injuries)
2. Irreparable tendon ruptures - e.g., rotator cuff tears that cannot be directly repaired, rheumatoid arthritis-related tendon rupture (Vaughan-Jackson syndrome)
3. Poliomyelitis - to restore function after motor paralysis
4. Cerebral palsy - to correct dynamic muscle imbalance
5. Spinal cord injuries - partial cord lesions with selective muscle preservation
6. Congenital anomalies - muscle absence (e.g., Poland syndrome)
7. Spastic conditions - stroke, traumatic brain injury causing muscle imbalance
8. Leprosy - with resultant intrinsic muscle paralysis
9. Spina bifida / myelomeningocele - to balance foot/ankle
10. Scapular winging - failure of serratus anterior or trapezius

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3. PREREQUISITES (REQUISITES)

Campbell's Key Principles (the "Seven Pillars"):

Amplitude of Excursion Reference Table (Curtis, 1974):

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4. TIMING OF TENDON TRANSFER

• Soft-tissue conditions: Transfer should not occur until scar tissue has matured and been replaced, or until a healthy soft-tissue bed (with fat) is available. Transferred tendons must be surrounded by fat to prevent adhesion to raw bone or subcutaneous scar.
• Passive joint motion: Must be restored before surgery - stiff joints cannot be corrected by transfer alone, and will cause the transferred tendon to adhere permanently.
• Bony alignment: Osteotomy and bone grafting must precede transfer.
• Sensory restoration: If sensory loss is present, procedures to restore sensibility should precede tendon transfer.
• Poliomyelitis: Wait at least 18 months post-acute phase before transfer, as recovery can continue for this duration. Any recovery after this is unlikely to exceed one grade.
• Nerve injury: Early "prophylactic" or "internal splint" transfers may be performed in some high-radial nerve injuries to maintain joint position while awaiting nerve recovery - these can be converted to permanent transfers if recovery fails.

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5. PLANNING THE TENDON TRANSFER

1. Function lost - which muscles are paralyzed?
2. Function retained - which muscles are working?
3. Function possible - what reconstruction can achieve?

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6. TECHNICAL CONSIDERATIONS

Intraoperative Assessment

• At surgery, the color of the donor muscle confirms suitability: a healthy donor is dark pink or red (indicating normal nutrition and muscle fibers). A pale pink, small muscle with reduced excursion at surgery is unsuitable.
• Muscles that do not contract with pinch or electrocautery stimulus are likely nonfunctional and should not be used.

Line of Pull

• The muscle-tendon unit must have as straight a line of action as possible between origin and new insertion. An acute angle reduces efficiency.
• If an angle is unavoidable, a pulley must be created (e.g., FCU loop in Bunnell opponensplasty), but friction at the pulley reduces efficiency.

Routing

• With few exceptions, transferred tendons should be routed subcutaneously. A tendon crossing raw bone, passing through tight fascia, or buried within scarred tissue will not glide and will form adhesions.
• When the tendon must cross fascia, the opening must be generously sized.

Tension at Suture

• If a muscle has been detached from its insertion for some time, it will develop a contracture; therefore anchor it under more tension than usual because it will stretch and regain some excursion postoperatively.
• A muscle that has been detached should be set with the wrist in neutral and the fingers/thumb in the desired functional position.

Fixation Technique

• Attachment is most commonly end-to-side (into the side of the recipient tendon) - important when there is a possibility of later nerve recovery restoring the original function.
• Weave or side-by-side suture techniques are preferred as they allow early mobilization.
• The attachment must be strong enough to withstand early rehabilitation forces.

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7. TYPES AND SPECIFIC TRANSFERS

A. Upper Extremity

Radial Nerve / PIN Palsy

• PT to ECRB is the gold standard for wrist extension restoration in radial nerve palsy.
• FCU to EDC is preferred by many surgeons as FCU is synergistic with finger extension.

Low Median Nerve Palsy (Opponensplasty)

High Median Nerve Palsy (adds FPL, FDP index/long)

• Brachioradialis (BR) to FPL for thumb IP flexion
• FDP index and middle fingers tethered side-to-side to the intact FDP of ring/little fingers (ulnar innervated)

Low Ulnar Nerve Palsy (claw deformity)

Shoulder: Irreparable Rotator Cuff Tears

• Latissimus dorsi transfer (Gerber technique): for irreparable posterosuperior cuff tears (supraspinatus + infraspinatus). Restores external rotation and abduction. Neurovascular pedicle must be preserved.
• Lower trapezius transfer: for external rotation deficit; rules - excursion and tension must match; one function per transfer.
• Pectoralis major transfer: for subscapularis replacement (anteroinferior cuff).

Scapular Winging

• Medial winging (serratus anterior palsy): split pectoralis major sternal head transfer to the inferior angle of the scapula.
• Lateral winging (trapezius palsy): modified Eden-Lange triple transfer (levator scapulae, rhomboid minor, rhomboid major moved laterally).

B. Lower Extremity

Foot Drop / Talipes Equinovarus (Poliomyelitis, CP)

• Anterior transfer of posterior tibial tendon (Barr procedure): through the interosseous membrane to the middle cuneiform. Removes varus deforming force and provides active dorsiflexion.
• Split posterior tibial tendon transfer (SPOTT): half to peroneus brevis insertion (cuboid) to balance varus without over-correcting to valgus. 78% poor results reported with full tendon transfer due to over-correction and calcaneus deformity. The split transfer acts as a dynamic sling balancing forces evenly across the foot.

Cerebral Palsy (Foot)

• Split transfers preferred over full transfers (lower complication rate).
• In CP foot-drop: split anterior tibial tendon transfer (SPLATT) to the peroneus brevis.

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8. POSTOPERATIVE REHABILITATION

1. Immobilization: Typically 3-4 weeks in a position that relaxes the transfer (protects the repair).
2. Controlled mobilization: Begins after healing; the patient must learn to re-educate the transferred muscle to perform its new function.
3. Synergistic transfers are easier to re-educate because the brain already fires the donor muscle in a pattern compatible with the new function.
4. Non-synergistic transfers may require biofeedback, electrical stimulation, and intensive occupational therapy.
5. Full functional recovery typically takes 3-12 months.

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9. DISADVANTAGES AND LIMITATIONS

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10. OUTCOMES

General

• Results depend heavily on strict adherence to the prerequisites above.
• Patients can reliably expect approximately one MRC grade less than the donor's preoperative strength.
• When all prerequisites are met, tendon transfer provides durable, long-term functional improvement.

Upper Extremity

• Radial nerve palsy transfers (PT to ECRB; FCU to EDC): Generally excellent results - most patients regain functional wrist and finger extension. Grade 4 function commonly achieved.
• Opponensplasty for median nerve palsy: Good outcomes with FDS ring (Bunnell) or EIP transfer; patients regain opposition for pinch and precision grip.
• Ulnar claw correction: Dynamic transfers (FDS to lateral bands) provide better intrinsic function than static procedures (capsulodesis, tenodesis) but require more rehabilitation.
• Latissimus dorsi transfer for posterosuperior rotator cuff (Gerber): Satisfactory outcomes in pain relief and forward elevation in selected patients; external rotation gain is variable. EMG studies show the transferred latissimus functions synergistically in abduction/external rotation post-transfer.

Lower Extremity

• Split posterior tibial tendon transfer (CP): In one study of 37 transfers in 30 children (8-year follow-up): 30 excellent, 4 good, 3 poor results. Results did not deteriorate with time; most patients ambulatory without braces.
• Full posterior tibial tendon transfers: 78% poor results in one study - now largely abandoned.

Factors Predicting Success

1. Strict donor selection (expendable, grade 4-5)
2. Supple soft-tissue bed
3. Full passive joint motion pre-operatively
4. Synergistic transfer pair
5. Motivated patient with good cognitive function (for re-education)
6. Experienced rehabilitation team

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11. SUMMARY TABLE

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Wallerian Degeneration: A Complete Guide

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1. DEFINITION

• Fragmentation and dissolution of the axon distal to the injury site
• Breakdown of the myelin sheath into ovoids and debris
• Phagocytic clearance of debris by Schwann cells and macrophages
• A transition from degeneration to a regenerative environment

"The degeneration of axons that occurs when they are cut is now called Wallerian degeneration. Because it can be detected with certain staining methods, Wallerian degeneration was an early strategy used to trace axonal connections in the brain." - Neuroscience: Exploring the Brain, 5th Ed

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2. FUNDAMENTAL BASIS: AXONAL TRANSPORT

• Anterograde transport (soma → terminal): Carried by kinesin along microtubules at up to 1,000 mm/day (fast) or 1-10 mm/day (slow). Delivers organelles, vesicles, proteins, and membrane components.
• Retrograde transport (terminal → soma): Carried by dynein, providing feedback signals about metabolic needs of the terminal.

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3. ETIOLOGY - CAUSES

• Trauma: laceration, crush, stretch/traction, avulsion, gunshot wound
• Compression: entrapment neuropathy (severe/chronic - e.g., carpal tunnel syndrome)
• Ischemia: nerve infarction (vasculitic neuropathy)
• Toxic/metabolic: severe axonal neuropathies (diabetic, alcoholic, chemotherapy-induced)
• Infections: leprosy, Lyme disease, HIV neuropathy
• Radiation injury
• Cold injury / electrical injury

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4. THE STAGES AND PROCESS OF WALLERIAN DEGENERATION

Stage 1: Acute Axonal Changes (Minutes to Hours)

• Separation of the proximal and distal ends
• Rapid influx of extracellular calcium and sodium through the disrupted axonal plasma membrane
• This calcium influx activates calcium-dependent proteases (calpains) - a cascade that shares features with programmed cell death (apoptosis)
• Axonal injury triggers recruitment of leukocytes and initiates a cytokine-mediated signaling cascade (TNF-α, IL-1α, IL-1β, IL-10)
• Synthesis of neurotrophins, chemokines, extracellular matrix molecules, and proteolytic enzymes begins
• The transected membranes are initially sealed

Stage 2: Axon Fragmentation - Distal Segment (Days 1-7)

• By day 3: Schwann cells retract from the node of Ranvier
• The distal axon begins to swell, then fragment into irregular segments
• The axon breaks down into ovoids (digestion chambers of Cajal) - irregular membrane-bound packets of axoplasm and organelles
• The myelin sheath breaks into blocks and ovoids around these axonal fragments
• Myelin lamellae decompact and fragment into lipid droplets (neutral fats) and cholesterol esters
• The entire axonal degeneration process takes approximately 1 week

Stage 3: Myelin Degeneration

• The Schwann cell (the myelinating cell in the PNS) - unlike the axon - survives the process
• Schwann cells undergo a profound phenotypic switch from myelin-manufacturing cells to repair cells, driven by upregulation of c-Jun protein
• They begin to actively phagocytose their own myelin (myelinophagy) - taking up and degrading myelin debris
• The myelin breakdown products (neutral fats, cholesterol esters) are packaged for export
• In the CNS, oligodendrocytes and their myelin carry growth-inhibitory molecules (myelin-associated glycoprotein), which is one reason CNS regeneration is far less effective than PNS regeneration

Stage 4: Phagocytic Clearance (Days 3-14 and beyond)

• Activated Schwann cells and recruited macrophages (both tissue-resident endoneurial macrophages and circulating hematogenous macrophages entering via the leaky blood-nerve barrier) collaborate to phagocytose myelin ovoids and axonal debris
• Schwann cells handle early myelin clearance (the first 1-2 weeks); macrophages take over progressively from day 7 onwards
• Macrophages are guided by chemokines (MCP-1) secreted by Schwann cells
• This clearance is critical: axonal regeneration cannot begin until the endoneurial tubes are cleared of debris
• The cleared debris is carried via the bloodstream
• This process is much more rapid and efficient in the PNS than in the CNS (where microglia are slower), explaining the superior regeneration in the PNS

Stage 5: Chromatolysis - Cell Body Changes (Retrograde Reaction)

• Chromatolysis: The rough endoplasmic reticulum (Nissl substance) breaks up, disperses, and migrates from the center to the periphery of the cell body
• The nucleus swells and moves to an eccentric (peripheral) position
• The cell body itself swells
• Increased expression of transcription factors switches gene expression from "axon maintenance" to "protein synthesis for regeneration" (growth-associated protein GAP-43, cytoskeletal proteins)
• This reflects the soma ramping up its metabolic machinery for axonal regrowth
• Chromatolysis begins within 1-2 days after injury and peaks at about 2 weeks
• Importantly: chromatolysis is reversible if the neuron survives and re-establishes its distal process

• After distal nerve transection, approximately 30% of primary sensory neurons die
• After proximal injury (e.g., avulsion), neuronal death is greater - some motor neurons and DRG neurons also die
• Very proximal injury (e.g., after proximal arm amputation) may lead to apoptosis of the cell body itself

Stage 6: Bands of Büngner Formation (Day 3 onwards)

• Schwann cells, having cleared myelin, now proliferate rapidly
• They elongate and align themselves within the intact endoneurial tube (basal lamina scaffolding)
• These aligned columns of Schwann cells form the bands of Büngner - cellular highways bounded by the original basal lamina
• The bands express adhesion molecules (cadherins, immunoglobulin superfamily, laminin) and neurotrophins (NGF, BDNF, NT-3, NT-4, GDNF, CNTF, IL-6)
• These molecular cues attract and guide regenerating axon sprouts from the proximal stump
• If reinnervation is delayed, Schwann cells atrophy, lose their pro-regenerative phenotype, and die - this begins by 2 months and becomes well-established thereafter

Stage 7: Transneuronal Degeneration (Variable)

• Retrograde transneuronal degeneration: Neurons that synaptically project onto the injured neuron (upstream neurons) may degenerate because they lose their postsynaptic target
• Anterograde transneuronal degeneration: Neurons that receive synapses from the injured neuron (downstream neurons) may degenerate because they are deprived of their presynaptic input
• The magnitude is variable and depends on the degree of dependence of connected neurons on trophic signals from the injured cell

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5. DETAILED TIMELINE

"The distal axon takes some days to weeks to degenerate fully and may remain partially electrically active during this time. As a result, neurophysiology studies are not considered diagnostically reliable for some 3 to 6 weeks after proximal nerve injury." - Rockwood & Green's, 10th Ed

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6. HISTOPATHOLOGY

1. Digestion chambers (of Cajal): Ovoid membrane-bound structures containing fragmented axon and myelin debris
2. Myelin ovoids: Spherical/oval lipid debris within endoneurial tubes, visible with osmium tetroxide staining
3. Endoneurial tube collapse: Empty endoneurial tubes after debris clearance; at 250 days without regeneration, tubes are largely empty with residual Schwann cells
4. Bands of Büngner: Parallel columns of Schwann cells within intact basal laminae visible on longitudinal section
5. Regenerated fibers: Smaller diameter, shorter internodal segments, thinner myelin than original (visible on toluidine blue stained resin sections)

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7. ELECTRODIAGNOSTIC CORRELATES

• In the first 3-7 days after nerve injury: The distal nerve segment remains electrically excitable because WD is not yet complete. NCS may appear near-normal even in complete transection - this is a false-negative window
• After 7-21 days: WD is complete; the distal segment no longer conducts. NCS shows:
  • Loss of CMAP (compound muscle action potential) amplitude
  • Loss of SNAP (sensory nerve action potential) amplitude in sensory fibers
• After 21 days: EMG shows fibrillation potentials and positive sharp waves - spontaneous muscle fiber activity due to denervation supersensitivity to acetylcholine
• Fibrillation potentials are absent in neurapraxia (no WD, axon intact) - this distinguishes it from axonotmesis/neurotmesis

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8. WD IN THE CNS VS. PNS

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9. NERVE REGENERATION AFTER WD

1. Proximal stump activity: After a 2-3 week latency, neurites (sprouts) begin emerging from the proximal axon face. Multiple sprouts (up to 100 per axon) grow distally.
2. Growth cone: The motile tip of each sprout bears lamellipodia (sheet-like projections) and filopodia (finger-like projections) rich in actin. These sense guidance molecules in the microenvironment.
3. Neurotropism: Growth cone direction is guided by:
   • Attractive signals: Neurotrophins (NGF, BDNF, NT-3, NT-4, GDNF), laminin, fibronectin in the bands of Büngner
   • Repulsive signals: Semaphorins, ephrins, netrins, slits
   • Plasminogen activators: Secreted by the growth cone to dissolve debris plugging endoneurial tubes
4. Rate of regeneration: Approximately 1-2 mm/day (or ~1 inch/month). Proximal lesions regenerate faster (2-3 mm/day), distal lesions slower (~1 mm/day).
5. Types of recovery:
   • Collateral sprouting: Intact motor axons sprout to reinnervate denervated muscle fibers; begins within 4 days; clinically evident at 3-6 months
   • Axon regeneration: Main mechanism from 6-24 months; requires crossing the repair site, traversing the distal stump, and reaching the target organ

• ~50% of regenerating fibers fail to cross the repair site, forming a neuroma-in-continuity
• Mismatch of fiber type specificity (motor axon entering sensory endoneurial tube)
• Topographic misdirection (sensory axon to wrong cutaneous territory)
• Progressive Schwann cell atrophy with chronic denervation
• Endoneurial tube fibrosis and shrinkage with prolonged denervation
• Irreversible muscle fiber atrophy after ~24 months of denervation

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10. OUTCOMES

• Proximal vs. distal injury: Proximal injuries have poorer outcomes - longer regeneration distance, greater likelihood of muscle atrophy before reinnervation
• Age: Younger patients regenerate more effectively
• Time to repair: Early repair (within 10-14 days) yields best results
• Tension-free repair: Critical - repair must be in a clean, well-vascularized bed without tension
• Muscle viability: Irreversible after 24 months of denervation

"Recovery is much slower with Wallerian or axonal degeneration, often requiring months to a year or more because the axon must first regenerate and then reinnervate the muscle, sensory organ, or blood vessel before function returns." - Adams & Victor's Principles of Neurology, 12th Ed

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11. SUMMARY DIAGRAM OVERVIEW