Brachioradialis Anatomy

Origin

• Proximal two-thirds of the lateral supracondylar ridge of the humerus — the highest origin of any forearm muscle, beginning about 10 cm proximal to the elbow joint.
• Also from the anterior surface of the lateral intermuscular septum.
• Because the origin extends so far proximally, the muscle belly lies substantially in the arm, not just the forearm — which is why it is available for elbow cover as a proximally based flap.

Muscle Belly and Tendon

• Fleshy belly for the proximal half of the forearm, then a long, flat tendon for the distal half.
• Tendon length is substantial (typically 8 to 12 cm), which is a liability in tendon transfer: a long tendon with a short muscle belly limits usable excursion, and the muscle-tendon unit must be extensively mobilised proximally to gain excursion (see the Surgical Relevance tab).

Insertion

• Lateral surface of the distal radius, at the base of and just proximal to the radial styloid process.
• Frequently blends with the fascia over the first dorsal compartment.
• The insertion is far distal, which is precisely why the flexion moment arm is so long.

Bony Landmarks to Quote

• Origin: lateral supracondylar ridge, from roughly 10 cm to 3 cm proximal to the lateral epicondyle.
• Insertion: lateral radius, 1 to 2 cm proximal to the tip of the radial styloid.

Radial Nerve (C5, C6)

• The branch to brachioradialis arises from the radial nerve proper, in the interval between brachialis and brachioradialis, proximal to the elbow joint — typically 2 to 5 cm proximal to the lateral epicondyle.
• It is the first radial nerve branch distal to the triceps and anconeus branches, followed by branches to extensor carpi radialis longus and then the division into the superficial radial nerve and the posterior interosseous nerve.
• Motor entry point: the branch enters the deep (posteromedial) surface of the muscle in the proximal third, close to the vascular pedicle. In a transfer the surgeon works distal to this point.

Root Values and Level Localisation

• The exam point: an intact brachioradialis with a finger drop localises the lesion to the posterior interosseous nerve, distal to the branches to brachioradialis and extensor carpi radialis longus. Radial deviation on attempted wrist extension is the corroborating sign, because extensor carpi radialis longus is working and extensor carpi ulnaris is not.
• C5-C6 root values also make brachioradialis the muscle behind the brachioradialis reflex (supinator jerk), tested at the distal radius and mediated by C5 and C6. An inverted supinator jerk — absent brachioradialis contraction with finger flexion instead — localises a cord lesion at C5-C6 with a reflex arc preserved at C8.

Named Vessels and Pedicle Position

• Dominant pedicle: the radial recurrent artery, a branch of the radial artery arising just distal to the radial artery origin, entering the deep surface of the muscle in its proximal third, close to the motor branch.
• Rohrich and Ingram, dissecting 53 upper extremities, found a consistent major pedicle near the elbow, arising in descending order of frequency from the radial recurrent artery, then the radial artery, then the brachial artery.
• Minor pedicles in variable number arise segmentally from the radial artery down the length of the muscle. This is a Mathes-Nahai type II pattern: one dominant proximal pedicle plus minor distal ones.

Flap Implications

• Proximally pedicled (on the radial recurrent artery) the distal muscle reached the elbow anteriorly and posteriorly in 100 per cent of Rohrich and Ingram's specimens.
• Distally pedicled (on distal radial artery perforators) the proximal muscle covered the anterior elbow in 100 per cent and the posterior elbow in 91 per cent.
• Arc of rotation: the distal half of the arm and the proximal two-thirds of the forearm; defects up to about 3 cm in the elbow region are reliably covered.
• No major vessel is sacrificed and there is no functional cost — the reason it is the go-to local muscle flap for elbow cover.

The Cubital Fossa

Brachioradialis forms the lateral boundary of the cubital fossa (pronator teres is the medial boundary, an imaginary line between the epicondyles the base, and brachialis with supinator the floor).

Deep to Brachioradialis (Proximally)

• Radial nerve and its division into the superficial radial nerve and posterior interosseous nerve — this bifurcation typically occurs at or just distal to the level of the radiocapitellar joint, deep to the mobile wad.
• Supinator and the arcade of Frohse.
• Radial recurrent artery and the leash of Henry (the radial recurrent vessels crossing the posterior interosseous nerve) — one of the classical compression sites in radial tunnel syndrome.

Deep to Brachioradialis (Distally)

• Superficial radial nerve runs on the deep surface of the brachioradialis tendon for the middle third of the forearm, then emerges between the brachioradialis and extensor carpi radialis longus tendons about 8 to 9 cm proximal to the radial styloid to become subcutaneous.
• Radial artery lies immediately medial to the brachioradialis tendon in the distal forearm — the pulse point at the wrist, and the medial structure retracted in the Henry approach.

Medial

• Flexor carpi radialis and pronator teres; the brachioradialis-flexor carpi radialis interval is the Henry approach.

Lateral and Posterior

• Extensor carpi radialis longus and brevis — the rest of the mobile wad.

Localising the Lesion by Brachioradialis

Brachioradialis is the single most useful muscle for localising a radial nerve lesion, because its branch arises above the elbow and above the division into the posterior interosseous and superficial radial nerves.

• Brachioradialis weak plus wrist drop plus finger drop plus dorsal first web numbness — lesion at or proximal to the spiral groove or lateral intermuscular septum. Classic with a humeral shaft fracture (the Holstein-Lewis distal-third spiral pattern tethers the nerve at the septum).
• Brachioradialis normal plus finger drop plus wrist extension in radial deviation plus NORMAL sensation — posterior interosseous nerve palsy, most commonly at the arcade of Frohse.
• Everything normal except dorsoradial hand pain and numbness — superficial radial nerve (Wartenberg syndrome).

Prognosis and Management Principle

• Radial nerve palsy after a closed humeral shaft fracture recovers spontaneously in the large majority of cases; observation with splinting and serial examination is standard. Brachioradialis, being the most proximal muscle supplied below the injury, is usually the first to recover and its return is the earliest clinical evidence of reinnervation.
• A Tinel sign advancing distally and the return of the brachioradialis cord on resisted mid-prone flexion are the two bedside markers to document at each review.

Compartment Anatomy of the Forearm

The forearm has three compartments, and the mobile wad is one of them:

1. Volar (flexor) — superficial and deep flexors, further divided by some authors into superficial and deep.
2. Dorsal (extensor) — the extensor group and supinator.
3. Mobile wad (lateral) — brachioradialis, extensor carpi radialis longus and extensor carpi radialis brevis.

Why It Matters

• In forearm compartment syndrome, a volar (Henry-type or curvilinear) release decompresses the volar compartment, but the mobile wad must be released separately through the same incision by opening its fascia laterally, or through a separate dorsal incision.
• Missing the mobile wad is a documented cause of persistent compartment pressure and ongoing ischaemia after apparently adequate fasciotomy.
• Clinical sign: a tense, tender lateral proximal forearm mass with pain on passive wrist and finger flexion (stretching the wad).

Volkmann Contracture

• The classical Volkmann ischaemic contracture principally affects the deep volar compartment (flexor digitorum profundus and flexor pollicis longus), because the deep muscles lie furthest from collateral flow.
• Brachioradialis, being superficial and separately compartmentalised, is frequently spared — which is exactly why it survives to be used as a donor in reconstruction of the ischaemic forearm.

Brachioradialis and the Radial Tunnel

The radial tunnel runs from the radiocapitellar joint to the distal edge of the supinator, roughly 5 cm in length. Brachioradialis and the rest of the mobile wad form its anterolateral roof.

Brachioradialis Tendinopathy and Strain

• Uncommon in isolation. Presents as pain over the lateral distal arm and proximal forearm on resisted mid-prone flexion.
• Occurs in rowers, climbers and racquet players with repetitive rapid loaded flexion.
• Must be distinguished from lateral epicondylitis (pain on resisted wrist extension and passive wrist flexion, tenderness at the extensor carpi radialis brevis origin) and from radial tunnel syndrome (tenderness 4 to 5 cm distal to the lateral epicondyle over the supinator, pain on resisted supination with the elbow extended and on resisted long-finger extension).
• The overlap trap: radial tunnel syndrome and lateral epicondylitis coexist in a meaningful minority of patients, and a lateral epicondylitis that fails to respond should prompt reassessment for a proximal nerve component.

Volar (Henry) Approach to the Radius

• Interval: brachioradialis (lateral, radial nerve) and flexor carpi radialis (medial, median nerve) — a true internervous plane.
• Skin incision: a line from just lateral to the biceps tendon at the elbow crease to the radial styloid, following the medial border of the brachioradialis.
• Superficial dissection: develop the interval; the radial artery lies deep and immediately medial to brachioradialis, and is retracted medially with the flexor carpi radialis. The superficial radial nerve lies on the deep surface of the brachioradialis and is retracted laterally with the muscle. Getting these two on the correct sides is the whole trick of the approach.
• Proximal third: after the interval is opened, the forearm is fully supinated, which brings the supinator insertion anteriorly and moves the posterior interosseous nerve laterally and posteriorly away from the field. The supinator is then elevated subperiosteally off the radius from its insertion, protecting the nerve within its substance.
• Middle third: the pronator teres insertion on the lateral radius is released and reflected, with the forearm pronated to bring it anteriorly.
• Distal third: the pronator quadratus is elevated from its radial origin, with the flexor pollicis longus retracted ulnarly.
• Ligation: the radial recurrent vessels (leash of Henry) cross the field proximally and are ligated to allow mobilisation; this sacrifices the dominant brachioradialis pedicle, so a brachioradialis flap should be planned before, not after, a Henry approach.

Structures at Risk with Distances

Brachioradialis to Flexor Pollicis Longus

The single most important transfer involving this muscle, used in two very different settings.

1. C6 Tetraplegia (Key Pinch Reconstruction)

• Indication: a patient with an International Classification for Surgery of the Hand in Tetraplegia group 1 or 2 hand, with a strong brachioradialis (grade 4 or better) and preserved elbow flexion from biceps and brachialis.
• Purpose: restore active thumb interphalangeal flexion and therefore key (lateral) pinch, the single most functionally valuable grip for a tetraplegic patient.
• Fridén and colleagues incorporate brachioradialis to flexor pollicis longus as one of seven components of their single-stage grip reconstruction, alongside extensor carpi radialis longus to flexor digitorum profundus, split flexor pollicis longus to extensor pollicis longus interphalangeal tenodesis, thumb carpometacarpal arthrodesis and passive intrinsic reconstruction.
• A split flexor pollicis longus to extensor pollicis longus tenodesis at the interphalangeal joint is usually added to prevent uncontrolled interphalangeal hyperflexion, which would otherwise convert pinch into a useless flexed posture.

2. High Median Nerve Palsy

• The deficit: loss of flexor pollicis longus, flexor digitorum profundus to the index and middle fingers, flexor digitorum superficialis, flexor carpi radialis, pronator teres and the thenar intrinsics.
• The standard reconstruction set:
  • Brachioradialis to flexor pollicis longus — restores thumb interphalangeal flexion.
  • Extensor carpi radialis longus to flexor digitorum profundus of the index and middle fingers, or side-to-side tenodesis of the index and middle profundus tendons to the intact ring and little finger profundus (ulnar-innervated).
  • Opponensplasty (extensor indicis proprius, or the Camitz palmaris longus transfer) for thumb opposition.
• Why brachioradialis for flexor pollicis longus: matched long excursion, adequate power for a single-digit flexor, expendable, and radial-innervated so it is unaffected by the median lesion.

Technical Requirements

• Mobilise extensively. The native brachioradialis muscle-tendon unit has a long tendon and a short excursion at rest. The muscle must be dissected free from the surrounding fascia and intermuscular septa for most of its length, up to the level of the motor branch entry in the proximal third, to convert its passive excursion into usable amplitude. A brachioradialis that has not been fully released will not deliver its 6 cm of travel.
• Preserve the motor branch and the radial recurrent pedicle entering the deep proximal third. Dissection stops short of them.
• Tension is set with the wrist in neutral and the thumb interphalangeal joint in slight flexion, using the tenodesis effect to confirm.
• Route the tendon subcutaneously and superficial to the radial artery and superficial radial nerve, avoiding a sharp angle of pull.

Brachioradialis as a General Donor

Selection Rules

• Expendability: the donor must be genuinely dispensable. Brachioradialis passes because biceps and brachialis power elbow flexion. But in a C5 tetraplegic with no biceps, brachioradialis may be the only elbow flexor and is then NOT expendable.
• Excursion match: flexor pollicis longus requires roughly 5 cm of excursion; brachioradialis provides about 6 cm after full mobilisation. Wrist extensors require only about 3 cm. Finger flexors require about 7 cm — which is why brachioradialis to multi-digit flexor digitorum profundus is marginal.
• Power: a transferred muscle loses approximately one MRC grade. A grade 4 brachioradialis becomes a grade 3 flexor pollicis longus, which is adequate for pinch but not for heavy grip.
• Straight line of pull and a synergistic donor where possible.

Every Interval That Uses Brachioradialis

Brachioradialis Release in Distal Radius Fracture Surgery

• The brachioradialis inserts on the radial styloid and metaphysis, and in a dorsally displaced, shortened distal radius fracture it is the principal deforming force — it pulls the styloid fragment proximally and into radial deviation, resisting length restoration.
• Release of the brachioradialis insertion is a well-described adjunct in comminuted or delayed-presentation fractures: it makes reduction dramatically easier and reduces the risk of loss of radial length. The functional cost is negligible.