Tendon Transfers for Radial Nerve Palsy

Surgical Indications

Absolute Indications

• Irreparable high radial nerve injury (complete transection with gap greater than 4 cm or failed primary repair with no recovery at 12-18 months)
• Established posterior interosseous nerve (PIN) palsy with no clinical or EMG recovery after 9-12 months and confirmed irreparable damage on exploration
• High radial nerve palsy with absent wrist, finger and thumb extension and supple joints
• Failed nerve grafting or nerve transfer with persistent complete palsy at greater than 18 months

Relative Indications

• Patient preference for earlier reconstruction when nerve recovery is unlikely (for example, very proximal injury with long gap)
• Combined nerve injuries where median or ulnar function is intact but radial function is permanently lost
• Established drop wrist with secondary contracture risk despite therapy

Prerequisites (Must Be Met Before Any Transfer)

• Full passive range of motion at wrist (greater than 40 degrees extension), MCP joints (full extension), and thumb CMC/IP joints
• Donor muscle strength MRC grade 4 or greater against resistance
• Expendable donor (PT, FCR, PL preferred; FCU only when FCR unavailable)
• Intact median and ulnar nerve function (flexors and intrinsics must power the transfers)
• Motivated patient willing to participate in prolonged re-education programme (6-12 months)
• No active infection or uncontrolled medical comorbidity

Contraindications

Absolute:

• Fixed joint contracture greater than 20 degrees that cannot be corrected pre-operatively
• Donor muscle strength less than MRC 4
• Non-functional hand (absent median/ulnar motor function)
• Patient unable or unwilling to comply with post-operative therapy and re-education

Relative:

• Age greater than 70 years with low functional demand (consider tenodesis or arthrodesis instead)
• Heavy manual worker who cannot tolerate loss of donor strength
• Active smoking or uncontrolled diabetes (higher infection and adhesion risk)

Evidence Base

Timing of Nerve Exploration versus Early Transfer

• Exploration and repair or grafting within 3-6 months of injury remains standard when the nerve is in continuity or a clean transection is present
• When the nerve is irreparable (large gap, crushed, or failed prior repair) and no recovery by 12 months, tendon transfer is the reconstructive option of choice
• EMG evidence of reinnervation without clinical recovery by 12-15 months may justify further observation up to 18 months, but most surgeons proceed to transfer once the window for useful nerve recovery has closed

Classic Transfer Sets — Outcomes

• PT to ECRB reliably restores wrist extension to MRC 4 in greater than 85 percent of patients
• FCR to EDC restores finger MCP extension to MRC 3-4 in 80-90 percent; FCU to EDC produces slightly stronger extension but sacrifices ulnar deviation
• PL to rerouted EPL restores thumb extension and abduction in 75-85 percent; rerouting through the third compartment or subcutaneous tunnel both work when tension is correct

Key Evidence

Relevant Anatomy for Transfer Planning

Radial Nerve Motor Branches and Palsy Patterns

• High radial nerve palsy (above spiral groove): loss of all radial-innervated muscles including triceps, brachioradialis, ECRL, ECRB, supinator, and all finger/thumb extensors
• PIN palsy (after branch to ECRB): spares wrist extension (ECRL intact) but loses finger and thumb extension and wrist extension power (ECRB lost); patients retain some wrist extension but with radial deviation
• The classic transfers address the high palsy pattern; PIN palsy may require only finger and thumb transfers if wrist extension is adequate

Donor Muscles — Anatomy and Expendability

• Pronator teres (PT): origin from medial epicondyle and coronoid process; inserts on radial shaft; expendable because pronation is also performed by pronator quadratus; strong (MRC 5) and synergistic with wrist extension via tenodesis
• Flexor carpi radialis (FCR): origin medial epicondyle; inserts on base of second metacarpal; expendable because FCU and PL provide wrist flexion; strong donor with easy re-education (synergistic with finger extension via tenodesis)
• Flexor carpi ulnaris (FCU): origin medial epicondyle and ulna; inserts on pisiform and fifth metacarpal base; powerful but NOT expendable without consequence — loss removes the only ulnar deviator and weakens grip
• Palmaris longus (PL): present in 85 percent of individuals; origin medial epicondyle; inserts on palmar fascia; completely expendable; weak but adequate for thumb extension after rerouting

Recipient Tendons — Anatomy and Insertion

• Extensor carpi radialis brevis (ECRB): preferred recipient for wrist extension because it inserts centrally on third metacarpal base and produces pure extension without radial deviation
• Extensor digitorum communis (EDC): four tendons to index through little finger; insert into extensor hood at MCP level; must be tensioned equally to avoid differential extension
• Extensor pollicis longus (EPL): inserts on distal phalanx of thumb; must be released from third compartment and rerouted to avoid acute angulation after transfer

Critical Landmarks and Safe Intervals

• PT insertion is on the radial border of the radius at the junction of middle and distal thirds — easily exposed through a volar Henry approach
• FCR tendon is palpated radial to the flexor carpi ulnaris at the wrist flexion crease; the median nerve lies deep and ulnar to it
• EPL is released from the third extensor compartment at the wrist; the tendon is rerouted subcutaneously or through an enlarged third compartment
• The dorsal sensory branch of the radial nerve crosses the radial styloid subcutaneously — protect during dorsal incisions

Positioning and Preparation

Patient position: Supine, arm abducted 90 degrees on hand table, forearm in neutral or slight pronation for volar exposure. A tourniquet is applied to the upper arm (250 mmHg) and inflated after exsanguination. Loupe magnification (2.5-3.5x) is mandatory.

Anaesthesia: Regional (axillary or supraclavicular block) or general anaesthesia. WALANT is not suitable because multiple incisions and prolonged dissection are required.

Consent: Discuss risk of incomplete correction, over- or under-tensioning, donor morbidity (especially if FCU harvested), infection (less than 2 percent), adhesions requiring tenolysis (5-10 percent), and the need for 6-12 months of therapy and re-education.

Step-by-Step Operative Technique — Classic Three-Transfer Set (PT to ECRB, FCR to EDC, PL to EPL)

Step 1: Incision Planning and Exposure of Donors (Volar Henry Approach)

Mark the Henry approach incision along the radial border of the forearm from the radial head to the wrist flexion crease. A second transverse or oblique incision at the wrist flexion crease exposes the FCR and PL tendons. A third dorsal incision over the third extensor compartment or a subcutaneous tunnel route is planned for EPL rerouting.

Incise skin sharply. Develop the interval between brachioradialis (radial nerve) and flexor carpi radialis (median nerve). Identify and protect the superficial radial nerve and the radial artery. Expose the PT insertion on the radial shaft.

Step 2: Exposure of Recipient Tendons (Dorsal Approach)

A longitudinal dorsal incision over the distal forearm and wrist exposes the ECRB, EDC, and EPL tendons. The Thompson approach (between ECRB and EDC) or a direct dorsal midline incision can be used. Identify the ECRB tendon (deep and central), the four EDC tendons, and the EPL tendon in the third compartment.

Release the EPL from the third compartment and reroute it subcutaneously radial to the radial styloid or through an enlarged third compartment. Create a smooth tunnel free of constricting retinacular edges.

Step 3: PT to ECRB Transfer for Wrist Extension

Release the PT tendon from its radial insertion with a periosteal strip. Weave the PT tendon into the ECRB tendon using a Pulvertaft weave (three passes) with the wrist held in 30-40 degrees extension. Secure with 3-0 braided permanent suture. Tension is set so that passive wrist flexion produces active wrist extension via tenodesis.

Step 4: FCR to EDC Transfer for Finger Extension (FCU-Sparing)

Release the FCR tendon at the wrist crease. Pass it subcutaneously or through a tunnel to the EDC tendons at the distal forearm level. Weave the FCR into the EDC tendons (all four EDC tendons) using Pulvertaft technique with the wrist in 30 degrees extension and the MCP joints in full extension. Tension is confirmed by passive wrist flexion producing full MCP extension.

If FCR is weak or previously injured, harvest FCU instead: release FCU from pisiform insertion, pass subcutaneously to EDC, and weave with identical tensioning.

Step 5: PL to EPL Transfer for Thumb Extension

Release the PL tendon at the wrist. Reroute the EPL tendon subcutaneously or through the third compartment to lie in a straight line from the PL donor. Weave PL into EPL with the thumb in full extension and abduction and the wrist in 30 degrees extension. Tension is verified by passive wrist flexion producing thumb extension via tenodesis.

Step 6: Wound Closure and Splinting

Close all wounds in layers with absorbable suture for fascia and non-absorbable for skin. Apply a bulky dressing and a plaster splint holding the wrist in 30-40 degrees extension, MCP joints in full extension, thumb in extension and abduction, and IP joints in slight flexion. The splint is maintained for 4 weeks.

Implants and Fixation

• No implants are required for the tendon transfers themselves
• 3-0 or 4-0 braided permanent suture (Ethibond or equivalent) for Pulvertaft weaves
• 4-0 or 5-0 absorbable suture for skin closure
• Optional: small bone anchors or interference screws if bone-tendon fixation is chosen instead of tendon weave (rarely required)

Post-Operative Splinting Protocol

• Weeks 0-4: static splint with wrist 30-40 degrees extension, MCP joints full extension, thumb extension/abduction, IP joints slight flexion
• Weeks 4-6: removable splint for therapy only; active donor activation begins under therapist supervision
• Weeks 6-12: progressive strengthening and re-education; night splint in extension if any tendency to contracture
• Months 3-6: unrestricted use with continued therapy for cortical re-mapping

Complications and Management

Early Complications (Less Than 6 Weeks)

• Wound infection (less than 2 percent): treat with oral antibiotics and wound care; deep infection requires surgical washout
• Haematoma: prevent with meticulous haemostasis; evacuate if causing skin tension or compartment pressure
• Splint-related pressure sores: check skin at 48 hours and weekly; pad all bony prominences

Intermediate Complications (6 Weeks to 6 Months)

• Adhesions at weave site (5-10 percent): tenolysis if no improvement after 3 months of therapy
• Over-tensioning with intrinsic-plus posture: early recognition allows splint adjustment; established deformity may require release or revision transfer
• Under-tensioning with persistent drop: revision tensioning or additional transfer after 6 months

Late Complications (Greater Than 6 Months)

• Attrition rupture of EPL at tunnel edge (2-5 percent): revision with new donor or tendon graft
• Donor morbidity after FCU harvest: permanent loss of ulnar deviation and grip strength; prevented by using FCR when possible
• Failure of cortical re-mapping: most common in elderly or non-compliant patients; may require prolonged therapy or acceptance of limited function

Post-Operative Rehabilitation and Re-Education

Phase 1 (Weeks 0-4) — Protection

• Static splint as described
• Elevation and oedema control
• Passive range of motion of all joints within splint limits
• Patient education on donor activation concepts

Phase 2 (Weeks 4-8) — Activation

• Remove splint for therapy sessions only
• Begin active donor activation: pronation (PT) produces wrist extension; wrist flexion (FCR) produces finger extension; thumb opposition or wrist flexion (PL) produces thumb extension
• Therapist guides the new movement with verbal and tactile cues
• Continue night splint in extension

Phase 3 (Months 2-6) — Strengthening and Re-Mapping

• Progressive resistance exercises
• Functional task training (grasp, release, pinch)
• Cortical re-mapping drills: mirror therapy, mental imagery, and repetitive donor activation
• Full unrestricted use by 3-6 months in most patients

Phase 4 (Months 6-12) — Fine Tuning

• Address any residual lag or over-correction with therapy or minor revision
• Return to heavy manual work after 6 months if grip strength is adequate

Special Case: PIN Palsy (Wrist Extension Preserved)

• When ECRL is intact, wrist extension is present but radially deviated
• PT to ECRB transfer may still be performed to centralise extension and increase power
• Finger and thumb transfers proceed identically
• Some surgeons omit the wrist transfer if the patient has functional wrist extension and good grip

Special Case: Combined Nerve Injuries

• Radial plus median or ulnar palsy requires staged reconstruction or alternative donors (for example, brachioradialis or ECRL if available)
• Functional goals must be realistic; a hand with multiple nerve deficits may be better served by arthrodesis or tenodesis than multiple transfers