Radial Nerve Exploration

Primary Exploration Indications (Operate Without Waiting)

Holstein-Lewis Fracture (nuanced — NOT an automatic exploration)

• Spiral fracture of the distal third humeral shaft — the radial nerve crosses the lateral intermuscular septum at this level and is at high risk of palsy
• Originally described by Holstein and Lewis (JBJS Am 1963) as a pattern prone to radial nerve injury
• Important correction to the older teaching: there is NO robust evidence that every Holstein-Lewis fracture entraps the nerve, and the historical claim of "100% entrapment requiring routine primary exploration" is not supported by good-quality data. Most closed Holstein-Lewis fractures with radial palsy still recover spontaneously, in line with the general humeral shaft literature (Shao 2005)
• Indication for primary exploration is therefore selective: open fracture, associated vascular injury requiring repair, an irreducible fracture being plated anyway, or a new palsy appearing after a closed reduction. A closed Holstein-Lewis fracture with palsy that is being managed non-operatively can be observed like any other closed shaft fracture
• If operative fixation is being performed for the fracture itself, the nerve is inspected and protected in the same field

Open Fracture or Penetrating Injury

• Any penetrating mechanism (GSW, industrial, laceration) over radial nerve territory with palsy
• Primary exploration, debridement, and nerve assessment mandatory
• Primary repair if clean division with gap under 2 cm; graft if larger gap

Vascular Injury Requiring Operative Repair

• Vascular repair of brachial artery requires anterior approach — radial nerve can be examined in the same field

Iatrogenic Palsy (Intraoperative Recognition)

• Radial nerve palsy developing during humeral ORIF — tourniquet deflation palsy vs. instrument/retractor injury
• Explore immediately if nerve function absent and there is no prior documentation of palsy

No Pre-existing Palsy, Now New Palsy After Reduction

• Closed manipulation of humeral fracture causes new-onset wrist drop — suggests nerve entrapped in fracture site
• Explore within 48–72 hours

Secondary Exploration Indications (After Failed Conservative Management)

Closed Humeral Shaft Fracture With Radial Palsy — No Recovery

• The large majority of closed injuries recover spontaneously. Shao et al. (systematic review, 1045 patients, JBJS Br 2005): overall recovery 88%, spontaneous recovery with conservative treatment approximately 71%, with no significant difference in final outcome between early exploration and expectant management
• Ring, Chin & Jupiter (JHS Am 2004, 24 high-energy palsies): every intact nerve and every closed-fracture palsy recovered; transection was confined to open fractures within complex limb injuries — supports observation of closed injuries even after high-energy trauma
• Explore at 3–4 months if: no clinical improvement AND no EMG reinnervation potentials
• Do not wait beyond 6 months from injury date

EMG-Guided Decision Algorithm

• 6 weeks: Baseline EMG (confirms diagnosis, excludes pre-existing neuropathy)
• 10–12 weeks: Early voluntary motor units = continue observation
• 16 weeks (4 months): No motor units, no change = proceed to exploration
• 6 months: Absolute deadline — operate regardless of partial improvement if significant functional deficit remains

PIN / Radial Tunnel Syndrome Indications

Radial Tunnel Syndrome (Compressive PIN Neuropathy)

• Deep aching lateral forearm pain (often misdiagnosed as lateral epicondylitis)
• Tenderness over radial tunnel (4–5 cm distal to lateral epicondyle, anterior to radial head)
• Resisted middle finger extension test positive (ECRB origin stress)
• No wrist drop in early stages — finger extension weakness is the primary finding
• Conservative management (rest, splinting, physiotherapy) for 3–6 months before surgery

Five Sites of PIN Compression — FREAS Mnemonic

1. Fibrous bands anterior to radial head (radiocapitellar joint)
2. Radial recurrent vessels (leash of Henry — fan of vessels crossing nerve)
3. Edge of ECRB (medial sharp edge of extensor carpi radialis brevis)
4. Arcade of Frohse (proximal fibrous edge of supinator) — most common
5. Supinator distal edge (distal fibrous edge of supinator tunnel)

Key Evidence

Radial Nerve Course — Proximal to Distal

Origin

• Posterior cord of brachial plexus (C5, C6, C7, C8, T1)
• Leaves axilla posterior to axillary artery, through triangular interval (bounded by long head triceps, teres major, teres minor)

Spiral Groove

• Winds around posterior humerus in a shallow bony groove (spiral/radial groove)
• Travels with the profunda brachii artery
• Located at the junction of middle and distal thirds of humerus — approximately 14–20 cm from the humeral head
• Covered by the lateral and medial heads of triceps

Lateral Intermuscular Septum Piercing

• Exits the posterior compartment by piercing the lateral intermuscular septum
• Precise location: approximately 10 cm proximal to the lateral epicondyle (distal third of shaft)
• This is the Holstein-Lewis entrapment site — spiral fractures entrap the nerve here as it pierces the septum

Anterior Compartment — Radial Tunnel

• Enters anterior compartment between brachialis (medially) and brachioradialis/ECRL (laterally)
• Gives motor branches to brachioradialis and ECRL before the elbow (important — these are preserved even with PIN palsy)
• Passes anterior to the lateral epicondyle and radiocapitellar joint
• Divides into superficial radial nerve (pure sensory) and PIN approximately at the level of the radial head

PIN Anatomy and Arcade of Frohse

PIN Entry to Radial Tunnel

• PIN enters supinator approximately 3–4 cm distal to the radial head
• Arcade of Frohse: Proximal fibrous arch of supinator — present as a defined fibrous structure in approximately 30–55% of specimens (may be tendinous or membranous)
• PIN passes beneath the arcade into the supinator tunnel
• Traverses the full length of supinator (approximately 3–4 cm)
• Exits through the distal edge of supinator to innervate all remaining finger and thumb extensors

Five FREAS Compression Sites in the Radial Tunnel

Superficial Radial Nerve

• Purely sensory branch of the radial nerve
• Courses along the radial border of the forearm beneath brachioradialis
• Exits between BR and ECRL tendons approximately 8–10 cm proximal to the wrist to become subcutaneous (Wartenberg's point)
• Sensory distribution: dorsal radial hand, dorsal thumb, index and middle finger to the level of the PIP joints

Fascicular Organisation (Clinically Relevant)

• At the spiral groove, ECRL and ECRB motor fascicles are positioned dorsoradially
• PIN fascicles are dorsal
• Superficial radial nerve fascicles are ventral
• Understanding this allows targeted neurolysis and intraoperative nerve stimulation mapping

(A) Posterior Approach to Radial Nerve — Humeral Shaft

Indications: Radial nerve exploration at the spiral groove level; Holstein-Lewis fractures; combined fracture fixation and nerve exploration

Position: Lateral decubitus or prone; arm supported; tourniquet optional (use if combined ORIF planned)

Incision: Longitudinal posterior arm incision centred over the middle-distal third junction, 10–15 cm in length; can be extended proximally or distally

8-Step Technique

1. Skin incision and superficial dissection: Incise skin and subcutaneous fat longitudinally over posterior humerus. Identify the long head of triceps medially and the lateral head laterally.

2. Identify the intermuscular interval: Split the triceps in its mid-substance or develop the plane between the long and lateral heads. Use blunt dissection to enter the posterior compartment.

3. Identify the radial nerve proximally: Find the radial nerve and profunda brachii artery in the spiral groove proximally (mid-humerus level), where the nerve is reliably identified running between the long and medial/lateral heads of triceps. Place a vessel loop around the nerve.

4. Follow nerve to the lateral intermuscular septum: Trace the nerve distally. The nerve pierces the lateral intermuscular septum at the distal third of the humerus. The septum creates a fascial window through which the nerve passes into the anterior compartment.

5. Decompress at the septum: Incise the lateral intermuscular septum proximally and distally to the nerve entry point. In Holstein-Lewis fractures, the nerve is commonly trapped in this area — carefully free the nerve from callus or bone fragments under direct vision using fine dissection.

6. Assess nerve continuity: Inspect the nerve for neuroma-in-continuity, contusion, or complete division. If intraoperative nerve action potential (NAP) testing is available, perform at this stage. Pink, soft nerve with visible fascicular pattern = favourable. Pale, indurated nerve = significant injury.

7. External neurolysis if indicated: Free the nerve from surrounding scar or callus using microscissors. Do not perform internal neurolysis (opening epineurium) unless there is an established neuroma-in-continuity with negative NAP.

8. Wound closure: Meticulous haemostasis. Re-approximate triceps muscle with 0 Vicryl. Subcutaneous 2-0 Vicryl. Skin closure. Posterior slab in neutral wrist position for 2–3 weeks if combined ORIF performed.

(B) Anterior Henry Approach — Distal Radial Nerve / Radial Tunnel Entry

Indications: Exploration of radial nerve as it transitions from posterior to anterior compartment in the distal arm; combined with ORIF of distal humerus; access to radial tunnel from the proximal

Position: Supine, arm on arm board, tourniquet to upper arm

Incision: Longitudinal anterior arm incision, lateral to biceps tendon, extending from mid-arm to the elbow crease and distally into the forearm as needed (Thompson interval)

Nerve identification: Radial nerve lies in the interval between brachioradialis (laterally) and brachialis (medially); identify nerve as it gives off branches to BR and ECRL then continues as PIN and superficial radial nerve

(C) PIN Decompression — Radial Tunnel (Thompson Interval)

Indications: Radial tunnel syndrome, PIN palsy without fracture (compressive etiology), failed conservative management

Position: Supine, arm on arm board, tourniquet, forearm supinated

Incision: Curved or straight 6–8 cm incision over the lateral forearm centred 3–4 cm distal to the lateral epicondyle, in the interval between the mobile wad (BR, ECRL, ECRB) and the extensor digitorum communis

6-Step PIN Decompression

1. Incise fascia and develop Thompson interval: Incise the deep fascia. Identify the interval between ECRB (anteriorly) and EDC (posteriorly). Retract ECRB anteriorly and EDC posteriorly.

2. Identify radial recurrent vessels (Leash of Henry): A fan of arterial branches (from the radial recurrent artery) crosses the PIN in the proximal wound. Ligate and divide these vessels — this is step one of decompression and improves exposure significantly.

3. Release the medial edge of ECRB: The sharp medial tendinous border of ECRB can compress PIN proximally. Divide this medial edge with scissors.

4. Incise the Arcade of Frohse: The proximal fibrous arch of supinator is the most critical decompression step. Divide the arch under direct vision with scissors, taking care not to injure PIN immediately beneath. Pronate the forearm slightly to move PIN anteriorly and away from the arcade.

5. Decompress full supinator tunnel: Follow PIN through the full length of supinator by incising the supinator muscle belly longitudinally along the nerve. Confirm PIN exits freely at the distal supinator edge. Neurolysis of PIN if scarred or pale.

6. Verify complete decompression and close: Confirm PIN is freely mobile through the entire radial tunnel from the radial head to the distal supinator. All five FREAS sites should be addressed. Irrigate wound. Loose fascial closure or leave open. Do not close tightly over the nerve.

Neurolysis Decision Framework

Immediate Post-operative Management (Days 0–14)

• Humeral shaft exploration: Posterior slab or functional brace depending on whether fracture fixation was performed; wrist cock-up splint (wrist extension 30–40 degrees) for wrist drop
• PIN decompression: Soft dressing only; gentle active range of motion commenced at 3–5 days
• Elevation to minimise oedema; ice therapy
• Analgesics; avoid NSAIDs for first 48 hours if haemostasis concern

Early Rehabilitation (Weeks 2–6)

• Remove splint at 2–3 weeks unless combined ORIF
• Active-assisted wrist extension and finger extension exercises
• Extensor tendon gliding exercises; passive wrist flexion to maintain joint mobility
• Dynamic wrist extension splint during the day if active extension absent
• Resting wrist splint at night throughout recovery period

Serial EMG/NCS Monitoring

Tendon Transfer Options for Irreversible Radial Nerve Palsy

In a complete radial nerve palsy, wrist extension, finger MCP extension and thumb extension are ALL lost (ECRL/ECRB, EDC and EPL denervated). A balanced reconstruction therefore needs three transfers — one for each function. The classic standard set is:

Standard Triple Transfer (complete palsy)

• PT to ECRB (restore wrist extension): pronator teres is the standard, almost mandatory donor for wrist extension — it is part of the standard set, not an optional extra
• FCU to EDC OR FCR to EDC (restore finger MCP extension): FCU is powerful but sacrifices the main ulnar-deviating wrist flexor; FCR-to-EDC (Brand) is preferred by many because it preserves FCU and gives a more synergistic action
• PL to rerouted EPL (restore thumb extension/retropulsion): palmaris longus is expendable; reroute EPL out of its third compartment to add abduction. (If PL is absent, FDS of the ring finger can be substituted)

Common variants

• Standard (FCU) set — PT-ECRB, FCU-EDC, PL-EPL
• FCR (Brand) set — PT-ECRB, FCR-EDC, PL-EPL — preferred when wrist flexion balance is to be preserved
• Boyes superficialis set — PT-ECRB, FDS(middle)-EDC, FDS(ring)-EIP+EPL — independent finger and thumb extension at the cost of two superficialis donors

Timing: No earlier than 12–18 months post-injury when nerve recovery is being awaited; EMG must show no reinnervation activity and irreversibility must be confirmed. Where the nerve injury is known to be unreconstructable from the outset, an early PT-to-ECRB transfer can act as an internal splint while awaiting recovery of the other functions.

Wrist Drop Splinting During Recovery

The wrist cock-up splint is a critical adjunct during nerve recovery — it positions the wrist in 30–40 degrees of extension, preventing contracture of wrist flexors, maintaining functional hand position for grip, and protecting extensor tendons from overstretching. Without splinting, a chronic wrist drop develops flexion contracture of the wrist and MCP joints within weeks, complicating any future tendon transfer.

Splinting protocol:

• Dynamic wrist extension splint during the day to allow partial function
• Static resting splint at night to prevent contracture
• Continue until active wrist extension is MRC grade 3 or better (active extension against gravity)
• Passive ROM exercises daily to maintain wrist and MCP joint mobility
• Occupational therapy review every 4–6 weeks to adjust splint fit as oedema resolves

Recovery Timeline Expectations

Note on axonal regeneration rate: Peripheral nerve regenerates at approximately 1 mm per day (1 inch per month) — use this to estimate reinnervation timeline from the injury or repair site to the target muscle. For a radial nerve injury at the spiral groove, distance to ECRL is approximately 12–15 cm (recovery 4–5 months), to EDC is approximately 25–30 cm (recovery 8–10 months post-repair). Planning realistic timelines with patients relies on this principle. Add 4–6 weeks latency for axonal sprouting to commence at the repair site before counting down.