Tendon Transfers for Radial Nerve Palsy

Indication. Symptomatic, irreparable radial nerve or posterior interosseous nerve (PIN) palsy with absent wrist, finger and/or thumb extension that has no realistic prospect of recovery — established clinically and electrophysiologically — in a hand with supple joints, strong expendable donors and intact median and ulnar function, in a patient motivated to complete a 6 to 12 month re-education programme. Absolute indications - Irreparable high radial nerve injury (complete transection with a gap greater than 4 cm, or a failed primary repair with no recovery at 12 to 18 months)

• Established PIN palsy with no clinical or EMG recovery after 9 to 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 a very proximal injury with a 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 all be met before any transfer - Full passive range of motion at the wrist (greater than 40 degrees extension), the MCP joints (full extension) and the thumb CMC and IP joints
• Donor muscle strength MRC grade 4 or greater against resistance
• An expendable donor (PT, FCR and PL preferred; FCU only when FCR is unavailable)
• Intact median and ulnar nerve function (the flexors and intrinsics must power the transfers)
• A motivated patient willing to commit to a prolonged re-education programme (6 to 12 months)
• No active infection or uncontrolled medical comorbidity Contraindications - Absolute: a fixed joint contracture greater than 20 degrees that cannot be corrected pre-operatively; donor muscle strength less than MRC 4; a non-functional hand (absent median or ulnar motor function); a patient unable or unwilling to comply with therapy and re-education.
• Relative: age greater than 70 years with low functional demand (consider tenodesis or arthrodesis instead); a heavy manual worker who cannot tolerate loss of donor strength; active smoking or uncontrolled diabetes (higher infection and adhesion risk). Consent specifically for incomplete correction, over- or under-tensioning, donor morbidity (especially if FCU is harvested), infection (less than 2 percent), adhesions requiring tenolysis (5 to 10 percent) and the need for 6 to 12 months of therapy and re-education. Set-up. Supine, arm abducted 90 degrees on a hand table, forearm in neutral or slight pronation for the volar exposure. An upper-arm tourniquet (250 mmHg) is inflated after exsanguination, and loupe magnification (2.5 to 3.5x) is mandatory — tendon, nerve and vessel identification is the whole game. Regional (axillary or supraclavicular) block or general anaesthesia; WALANT is not suitable because multiple incisions and prolonged dissection are required.

The goal is to restore wrist, finger and thumb extension using the classic three-transfer set: pronator teres (PT) to ECRB for wrist extension, FCR to EDC for finger extension, and PL to a rerouted EPL for thumb extension. The donors are exposed through the volar (Henry) approach; the recipients through a longitudinal dorsal approach. The exposure of donors and recipients is laid out in full as the first operative steps below — it is the foundation on which every transfer depends.

View larger

Rehabilitation | Phase | Timing | Immobilisation | Therapy | |-------|--------|----------------|---------| | 1 | 0 to 4 weeks | Static splint: wrist 30 to 40 degrees extension, MCP full extension, thumb extended and abducted, IP slight flexion | Elevation and oedema control; passive ROM within splint limits; education on donor-activation concepts | | 2 | 4 to 8 weeks | Removable splint for therapy sessions only; continue night splint in extension | Active donor activation begins — pronation drives wrist extension, wrist flexion drives finger and thumb extension — with verbal and tactile cues | | 3 | 2 to 6 months | Night splint only if any tendency to contracture | Progressive resistance, functional task training and cortical re-mapping drills (mirror therapy, mental imagery, repetitive donor activation) | | 4 | 6 to 12 months | None | Fine tuning; unrestricted use by 3 to 6 months in most patients; return to heavy manual work after 6 months if grip is adequate | Most patients achieve MRC 4 wrist extension and useful finger and thumb extension. PT to ECRB restores wrist extension to MRC 4 in greater than 85 percent; FCR to EDC restores finger MCP extension to MRC 3 to 4 in 80 to 90 percent; PL to a rerouted EPL restores thumb extension and abduction in 75 to 85 percent. Implants and fixation. No implants are required for the transfers themselves. Pulvertaft weaves use 3-0 or 4-0 braided permanent suture (Ethibond or equivalent); skin closure uses 4-0 or 5-0 absorbable suture. Bone-tendon fixation with small anchors or interference screws is only needed when a tendon weave is not possible. Complications

Palsy patterns drive the plan. The transfer set is chosen according to which muscles the lesion has taken.

Donor muscles — anatomy and expendability - Pronator teres (PT): origin from the medial epicondyle and coronoid process; inserts on the radial shaft. Expendable because pronator quadratus also pronates. Strong (MRC 5) and synergistic with wrist extension via tenodesis.

• Flexor carpi radialis (FCR): origin from the medial epicondyle; inserts on the base of the second metacarpal. Expendable because FCU and PL provide wrist flexion. A strong donor with easy re-education (synergistic with finger extension via tenodesis).
• Flexor carpi ulnaris (FCU): origin from the medial epicondyle and ulna; inserts on the pisiform and fifth metacarpal base. Powerful but not expendable without consequence — its loss removes the only ulnar deviator and weakens grip.
• Palmaris longus (PL): present in about 85 percent of people; origin from the medial epicondyle; inserts on the palmar fascia. Completely expendable; weak but adequate for thumb extension after rerouting. Recipient tendons — anatomy and insertion - ECRB: the preferred wrist recipient because it inserts centrally on the third metacarpal base and produces pure extension without radial deviation.
• EDC: four tendons to the index through little fingers, inserting into the extensor hood at MCP level; all four must be tensioned equally to avoid differential extension.
• EPL: inserts on the distal phalanx of the thumb; it must be released from the third compartment and rerouted to avoid acute angulation after transfer. Critical landmarks. The PT insertion is on the radial border of the radius at the junction of the middle and distal thirds. The FCR is palpated radial to the FCU at the wrist flexion crease, with the median nerve lying deep and ulnar to it. The EPL is released from the third extensor compartment at the wrist and rerouted subcutaneously or through an enlarged third compartment. The dorsal sensory branch of the radial nerve crosses the radial styloid subcutaneously and must be protected during the dorsal incisions. Donor choice for finger extension — the evidence summary

Timing of nerve exploration versus early transfer. Exploration and repair or grafting within 3 to 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 a failed prior repair) and there is no recovery by 12 months, tendon transfer is the reconstructive option of choice. EMG evidence of reinnervation without clinical recovery by 12 to 15 months may justify observation up to 18 months, but most surgeons proceed to transfer once the window for useful nerve recovery has closed. Classic transfer 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 to 4 in 80 to 90 percent; FCU to EDC produces slightly stronger extension but sacrifices ulnar deviation. PL to a rerouted EPL restores thumb extension and abduction in 75 to 85 percent, whether the reroute runs through the third compartment or a subcutaneous tunnel, provided tension is correct. Special case — PIN palsy (wrist extension preserved). When ECRL is intact, wrist extension is present but radially deviated. PT to ECRB may still be performed to centralise extension and increase power; the 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 by multiple transfers.