U01.11.001 Upper extremity nerves

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Learning Objectives

  • Map the brachial plexus roots to their respective terminal nerves.
  • Correlate specific humerus fractures with nerve deficits (ARM mnemonic).
  • Distinguish between proximal and distal lesions of the Median and Ulnar nerves.
  • Identify classic clinical presentations like Wrist Drop, Ape Hand, and Clawing.

1. The “ARM” Mnemonic for Humerus Fractures

When the humerus breaks, the nerve injured depends on the location of the fracture, from proximal to distal.

  • Axillary: Surgical neck fracture or anterior dislocation.
  • Radial: Midshaft fracture (radial groove).
  • Median: Supracondylar fracture.

2. Nerve Injury Profiles

Nerve (Roots) Classic Injury Cause Motor & Sensory Presentation
Axillary (C5-C6) Surgical neck fracture; Anterior dislocation. Flattened deltoid; Loss of abduction > 15°; Loss of sensation over deltoid/lateral arm.
Musculocutaneous (C5-C7) Upper trunk compression. Loss of forearm flexion/supination; Loss of sensation over the lateral forearm.
Radial (C5-T1) Crutches (“Saturday night palsy”); Midshaft fracture. Wrist drop; Decreased grip strength; Loss of sensation over the posterior arm/hand.
Median (C5-T1) Supracondylar fracture; Carpal tunnel. Ape hand; Hand of Benediction (proximal); Loss of LOAF muscle function.
Ulnar (C8-T1) Medial epicondyle fracture; Hook of hamate. Ulnar claw; Radial deviation on wrist flexion (proximal lesion).

3. The Recurrent Branch and Thenar Muscles

The “million-dollar nerve” is a superficial branch of the median nerve.

  • Injury: Superficial laceration of the palm.
  • Motor Loss: Ape hand due to loss of the thenar group (Opposition, Abduction, Flexion of thumb).
  • Crucial Distinction: No loss of sensation (the sensory branch originates before the carpal tunnel).

Activity:

 

Clinical Notes & Corrections:

  • Grip Strength: Grip strength is decreased in Radial nerve injuries because wrist extension is necessary to put the flexors at an optimal length-tension relationship.
  • Saturday Night Palsy: Compression in the axilla spares the triceps if the pressure is low enough, but usually leads to loss of elbow extension if the lesion is very high.
  • Guyon Canal Syndrome: Compression of the ulnar nerve at the hook of the hamate, common in long-distance cyclists.

Activity: Nerve Deficit Identification

Memory Hooks:

LOAF: Lumbricals (1,2), Opponens pollicis, Abductor pollicis brevis, Flexor pollicis brevis.

Radial: Radial nerve extends the Radius (extensors).

Median: Median = Midline (Ape hand thumb movement).

Activity: