Examination of Radial Nerve Palsy or Injury

Synonyms: Nervus radialis, Musculospiral nerve, Posterior or Dorsal interosseous nerve

Short Anatomy:

Origin: Posterior cord of brachial plexus

Root value: C5, C6, C7, C8, T1

Course:

  1. Exits the Axilla via Triangular interval
  2. Enters Posterior compartment of arm, along with profunda brachii artery
  3. Both descends from medial to lateral, in Radial or Spiral groove
  4. Pierces Lateral intermuscular septum (10 cm proximal to lateral epicondyle) to enter Flexor/Anterior compartment of arm
  5. Passes anterior to Lateral epicondyle, deep to brachioradialis muscle
  6. Divides into terminal branches at Radio-capitellar or Radiohumeral joint (4 cm above to 4 cm below lateral epicondyle)
    • Superficial (Sensory) branch courses under brachioradialis, lateral to radial artery to run over Anatomical snuff box
    • Posterior Interosseous Nerve or PIN (Motor branch) passes through Arcade of Frohse (Between 2 heads of Supinator), winds around radial neck to reach Posterior compartment of forearm and course to Dorsal wrist capsule

radial nerve course branches

Branches:

Axilla:

  1. Long head of triceps
  2. Medial head of triceps
  3. Posterior cutaneous nerve of arm

Radial groove:

  1. Lateral head of triceps
  2. Anconeus
  3. Inferior lateral cutaneous nerve of arm

Anterior compartment of arm:

  1. Brachialis (variable)
  2. Brachioradialis
  3. Extensor carpi radialis longus (ECRL)

Below elbow:

  1. Extensor carpi radialis brevis (ECRB): Before piercing supinator muscle
  2. Posterior Interosseous Nerve (PIN):
    • Supinator
    • Superficial group: Extensor digitorum communis (EDC), Extensor digiti minimii (EDM), Extensor carpi ulnaris (ECU)
    • Deep group: Abductor pollicis longus (APL), Extensor pollicis brevis (EPB), Extensor pollicis longus (EPL), Extensor indicis (EI)
    • Sensory fibers to dorsal wrist capsule
  3. Superficial branch of radial nerve: Dorsal surface of lateral 3 and 1/2 digits and associated palm area

Lesions of radial nerve:

All branches below the injured region will be interrupted.

1. Axilla (Very high):

Causes: Glenohumeral dislocation, Fracture proximal humerus, Crutch palsy

Deficit: Total palsy

  • Triceps weakness: Tested by resisted active extension of elbow and feeling for muscle contraction
  • Brachioradialis: Tested by resisted active flexion of elbow with forearm in midprone position and feeling for muscle contraction
  • Wrsit drop: Due to paralysis of wrist extensors
    Ask to grasp something, the wrist becomes flexed if extensors are weak
  • Finger drop: Due to paralysis of long finger extensors causing inability to extend fingers at MCPJ
  • Thumb drop: Due to paralysis of extensor pollicis longus and abductor pollicis longus
    Extensor pollicis longus is examined by stabilizing the MCPJ of thumb and resisted active extension of IP joint of thumb
  • Sensory loss: Over autonomous zone (1st dorsal webspace)

Radial nerve tests

2. Radial groove (High):

Cause: Fracture shaft of humerus, Saturday night palsy, Injection, Callus, Torniquet

Deficit: Brachioradialis weakness, Wrist drop, Finger drop, Thumb drop, Sensory loss

Radial nerve clinical tests

3. Below Elbow (Low):

Causes: Fracture of radial head, Posterior dislocation of radius at elbow joint

Deficit: Posterior Interosseous Nerve

  • No wrist drop (Sparing of Extensor carpi radialis longus which enables extension of wrist)
  • Finger drop, Thumb drop
  • No Sensory loss

Radial Tunnel Syndrome:

A compression neuropathy of the Posterior Interosseous Nerve (PIN) with pain only (no motor or sensory dysfunction)

Posterior Interosseous syndrome:

Pain at elbow and weakness with radial drift

Waternberg syndrome (Cheiralgia paresthetica):

Compression of the sensory branch of the radial nerve as it exits the Brachioradialis; compression between Extensor carpi radialis longus and Brachioradialis at pronation

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