Median Nerve Lesions

Median nerve lesions are characterized predominantly by:

• Weak pronation of the forearm
• Weak flexion and radial deviation of wrist
• Inability to oppose the thumb
• Inability to flex the thumb

Variable anaesthesia is experienced over:

• Lateral palm
• Lateral 3½ fingers on palmar surface, and distal ½ of the lateral 3½ fingers on the dorsal surface

Lesions at the carpal tunnel will spare palmar sensation.

The most common causes include:

• Trauma (especially at the wrist)
• Compartment syndromes at the carpal tunnel

Investigation and management depend on:

• The cause and location of the lesion
• Acuteness of onset
• Severity of symptoms

Anatomy

Course of the Median Nerve

• Roots: C5–T1
• Arises from lateral and medial cords of the brachial plexus
• Descends lateral then medial to the brachial artery
• Passes through cubital fossa under bicipital aponeurosis
• Passes between heads of pronator teres and gives off anterior interosseous nerve
• Travels between FDS and FDP
• Emerges at wrist lateral to FDS tendons and behind palmaris longus
• Enters palm behind flexor retinaculum and divides into lateral and medial branches
• Palmar cutaneous branch arises proximal to flexor retinaculum and remains superficial

Innervations

Forearm:

• Pronator teres
• Flexor carpi radialis
• Palmaris longus
• Flexor digitorum superficialis

Anterior interosseous nerve:

• Lateral half of FDP (digits I & II)
• Flexor pollicis longus
• Pronator quadratus

Hand:

• Thenar muscles (abductor pollicis brevis, flexor pollicis brevis, opponens pollicis)
• 1st and 2nd lumbricals
• Cutaneous innervation to lateral palm and 3½ lateral fingers (palmar and distal dorsal)

Muscle Actions

Muscle	Action
Pronator teres	Pronates & flexes forearm
Flexor carpi radialis	Flexes & abducts wrist
Palmaris longus	Flexes hand
FDS	Flexes middle phalanx, assists proximal phalanx & wrist flexion
FDP (lateral)	Flexes distal phalanx I & II, assists proximal joints
Flexor pollicis longus	Flexes distal phalanx of thumb
Pronator quadratus	Pronates forearm
Thenar muscles	Thumb opposition, abduction, flexion
1st & 2nd lumbricals	MCP flexion & IP extension of index & middle fingers

Clinical Assessment

Pathology

Causes

1. Trauma:
   • Penetrating/blunt injuries
   • Fractures/dislocations at wrist (e.g. lunate dislocation)
2. Neuropraxia:
   • Direct trauma
   • Anterior compartment syndrome
   • Carpal tunnel syndrome
3. Mass lesions:
   • Tumours, abscesses
4. Neuropathies:
   • Mononeuritis (e.g. DM, vasculitis, infections, malignancy)

Median Nerve Deficits

At the Elbow:

• Motor: Loss of forearm pronators and wrist/finger flexors (except FCU, medial FDP)
• Sensory: Loss over lateral palm and 3½ fingers (palmar + distal dorsal)

At the Wrist:

• Motor: Thenar muscle paralysis, simian hand deformity, 1st/2nd lumbrical weakness
• Sensory: Same as above
• Main disability: Loss of thumb opposition and lateral finger sensation

Investigations

• Nerve conduction studies:
  • Confirm diagnosis, assess extent
• Bloods (as indicated):
  • FBC, U&Es, glucose, CRP, ESR, heavy metals
• Imaging:
  • CT/MRI for mass lesions or visualisation of nerve/spine (C5–6)
• Biopsy:
  • Rare; e.g. for suspected mononeuritis, leprosy

Management

• Treat underlying cause
• Fasciotomy if compartment syndrome
• Occupational therapy: Splints, aids
• Physiotherapy: Rehab or prevent complications

Disposition

Dependent on:

• Cause of the lesion
• Severity of symptoms
• Acuteness of onset

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Appendix 1

Median Nerve Anatomy

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Appendix 2

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Appendix 3

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References

Publications

• Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 8e 2021
• Fuller G. Neurological Examination Made Easy. 6e 2019
• O’Brien M. Aids to the Examination of the Peripheral Nervous System. 6e 2023

FOAMed

• Coni R. Neuro 101: Peripheral Nervous System. LITFL
• Nickson C. Myotomes and Differentiating Nerve Lesions. LITFL