PNS: Radial Nerve Anatomy

• The radial nerve is the terminal branch of the posterior cord of the brachial plexus.
• It arises from nerve roots C5-C8 and T1.

Palpation

• The radial nerve emerges from the triangular interval, also known as the triceps hiatus
• The borders of the triangular interval are:
  • teres major above
  • long head of triceps
  • humerus.
• Find the inferolateral edge of the teres major through palpation and muscle activation to locate the triangular interval.
• The radial nerve travels under the lateral head of the triceps brachii towards the elbow.
• At the distal posterior humerus, approximately three finger widths above the lateral epicondyle, it moves from the posterior to the lateral humerus.
• The nerve wraps anteriorly around the lateral epicondyle and enters the space between the brachialis and brachioradialis muscles.
• At the elbow, the radial nerve divides into a deep motor branch and a superficial sensory branch.
• The deep motor branch, known as the posterior interosseous nerve, passes through the supinator muscle (arcade/canal of Frohse) before running deep down the lateral posterior forearm and innervating the extensor muscles.
• The superficial sensory branch continues under the brachioradialis and emerges superficially where the brachioradialis belly becomes a tendon.
• It remains superficial along the lateral radial border down to the wrist.
• The superficial sensory branch travels over the anatomical snuffbox.
• Distal to the extensor retinaculum, it divides into many small sensory branches that innervate the dorsum of digits 1-3, excluding the fingertips.

Palpation of Affected Tissue

• Assess tone and tissue health through extensors of the upper extremity.
• Sensory assessment occurs on the dorsum of the hand on the radial side.
• A radial nerve lesion may cause anesthesia in the webspace between the pollux and digit 2.

Function of the Radial Nerve

• Motor function includes the following muscles:
  • Triceps
  • Anconeus
  • Supinator
  • Brachioradialis
  • ECRL (Extensor Carpi Radialis Longus)
  • ECRB (Extensor Carpi Radialis Brevis)
  • ED (Extensor Digitorum)
  • EDM (Extensor Digiti Minimi)
  • ECU (Extensor Carpi Ulnaris)
  • APL (Abductor Pollicis Longus)
  • EPB (Extensor Pollicis Brevis)
  • EPL (Extensor Pollicis Longus)
  • EI (Extensor Indicis)
• Sensory function includes the dorsum of digits 1-3, not including the fingertips.
• The radial nerve gives off cutaneous branches in the upper arm, focusing on the motor branch and the superficial sensory branch of the forearm.

Pathophysiology - Radial Nerve Injuries

• The radial nerve is subject to any type of nerve injury:
  • Neuropraxia
  • Axonotmesis
  • Neurotmesis
• The context dictates the type of treatment.

MOI (Mechanism of Injury)

• Fractures of the humerus, especially at the spiral groove, or the upper 1/3 of the radius, can cause "radial nerve palsy."
• Elbow dislocation
• Prolonged pressure on the lateral arm during surgery
• Compression at the axilla from the use of crutches (crutch palsy)
• Compression at the axilla or spiral groove of the radius from the arm over the back of a chair, or sleeping prone with an arm over the head in full abduction (Saturday night palsy)
• Compression of the nerve by tight forearm muscles/fibrosis, involving the supinator muscle, known as supinator syndrome.

Signs & Symptoms of Degeneration

• Complete lesion results in wrist drop.
• If the injury is proximal to the elbow, both sensory and motor branches are affected; if the injury is distal to the elbow, usually only one branch is affected.
• Muscle wasting is possible, depending on the location of the lesion.
• Possible swelling on the dorsum of the hand (etiology unknown).
• Altered sensation in the radial nerve distribution with anesthesia at the web of the thumb.
• Classic deformities include wrist drop.

Radial Nerve (C5-T1)

• Wrist Drop (Rattray) aka Drop Wrist (Magee)
• Resting: Loss of extensors leads to a flexed wrist and finger posture with inability to extend the wrist or fingers.

Palsy/Lesion Descriptions

• Radial Nerve Palsy:
  • Lesion usually due to fracture
  • Depending on location, both motor, and sensory functions are affected.
  • Occurs at the spiral groove of the humerus.
• Saturday Night Palsy:
  • Compression lesion, usually temporary
  • Prolonged compression may lead to axonotmesis.
  • Occurs at the axilla
• PIN (Posterior Interosseous Nerve) Syndrome:
  • Posterior Interosseous Nerve syndrome aka Supinator or Radial tunnel Syndrome
  • Entrapment in the arcade/canal of Frohse (supinator) or in the radial tunnel (supinator, brachioradialis, ECRL, ECRB)
  • Results in pain and weakness, (motor function only).
  • No sensory deficit.
  • Occurs at the supinator.
• SRN (Superficial Radial Nerve) Syndrome:
  • Superficial Radial Nerve Syndrome aka Wartenberg's syndrome
  • Causes Paresthesia over the dorsal radial hand and pain over the distal radial forearm of the hand
  • Occurs at the brachioradialis.

Radial Nerve Assessment

• Superficial Radial Nerve Provocation:
  • Aggravated by ulnar deviation & flexion of the wrist
  • Percussion over the lateral radial border
• Supinator or Radial Tunnel Syndrome Provocation:
  • Weakness with supinator MMT or possibly ECRB MMT
  • Muscle atrophy
• Upper Limb Tension Test 3
  • See document "PNS Tx Notes - 4. Neurodynamic Assessment & Treatment" for principles of assessment & treatment.

Radial Nerve Treatment

• Context: regenerating lesion post fracture
• Precautions:
  • Do not traction the regenerating nerve.
  • Do not stretch denervated tissue.
  • Place arm in a neutral position with pillows to reduce elbow, wrist & finger flexion.
  • Perform segmental treatment proximal to the lesion using techniques applied perpendicular to the nerve.
  • Block or stabilize the tissue just proximal to the lesion to prevent drag.
  • Treat flaccid tissue with light stroking and compression.
  • Treat unaffected tissue distal to the lesion site with strain toward (but not onto) flaccid tissue.
  • PROM to joints in the direction that shortens affected tissue & nerve.
• Goals & Approach:
  • Promote relaxation.
  • Decrease edema.
  • Decrease tone and TrP in muscles proximal to the lesion.
  • Promote tissue health in denervated tissue with light stroking that shortens the nerve/bunches up tissue or is cross-fibre and gentle compression.
  • Prevent contracture of unopposed antagonist muscles.
  • Perform segmental work distal to the lesion on unaffected muscles/antagonists only
  • Promote joint health with PROM, if possible being careful not to traction the nerve when handling.
  • Encourage returning motor function using facilitatory ROODS techniques or similar or AAROM on the returned function while incorporating visualization once some function has been regained
  • Promote tissue health in reinnervated tissue using gentle Swedish techniques or sensory stimulation with different textures.
• Hydrotherapy: If autonomic dysfunction is present, hydrotherapy is contraindicated anywhere on the affected limb, even proximal to the lesion site.
• If autonomics are not affected;
  • Cool compress over acute injury
  • Modified temperature used over affected tissue
  • Mild contrast washes
• Home Care:
  • If wearing a splint, be vigilant for pressure sores.
  • PROM of joints that shortens affected tissue.
  • Visualize performing actions with the affected limb.
  • Elevate limb if edema is present.