Radial Nerve and Radial Nerve Neuropathy - wrist and finger drop

Question 1

Summary of radial nerve functions

Answer 1

Motor function:
1. Elbow extension
2. Brachioradialis elbow flexion in mid-pronation
3. Wrist extension
4. Thumb extension and abduction
5. Fingers extension

Sensory function:
1. Posterior cutaneous nerve to arm
2. Lower lateral cutaneous nerve to arm
3. Posterior cutaneous nerve to forearm
4. Dorsolateral hand

Question 2

Schematic diagram of radial nerve and its anatomical pathway

Answer 2

Origin: C5, C6, C7, C8, T1
Brachial plexus posterior cord (together with axillary nerve)

Before spiral groove:
1. Motor branch to long and lateral heads of triceps brachii
2. Posterior cutaneous nerve to arm

At spiral groove:
1. Motor branch to medial head of triceps brachii
2. Lower lateral cutaneous nerve of arm
3. Posterior cutaneous nerve of forearm

Exiting spiral groove:
1. Motor branch to brachialis (with musculocutaneous nerve), brachioradialis, ECRL

After lateral epicondyle, at the cubital fossa - divides into deep (PIN) branch and superficial branch
1. Deep (PIN) branch - motor
- ECRB (before piercing supinator)
- Supinator
- Extensor digitorum communis (EDC)
- Extensor carpi ulnaris (ECU)
- Extensor digiti minimi (EDM)
- Extensor indicis proprius (EIP)
- Snuffbox muscles - abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL)

2. Superficial branch - pure sensory
   - Dorsolateral hand (snuffbox)
   - Dorsum of thumb, index, middle finger and lateral half of ring finger
   (think reverse of median nerve: radial nerve over the dorsum)

Question 3

Motor function of radial nerve

Answer 3

Elbow: extension, mid-pronation flexion (brachioradialis muscle pop out), supination
A. Elbow extension - triceps brachii
B. Elbow flexion mid-pronation - brachioradialis
C. Forearm supination - supinator

Wrist: extension
C. Wrist extension
- Radial nerve proper: ECRL, ECRB
- PIN: ECU

Thumb: extension and abduction
D. Thumb extension - EPB, EPL
E. Thumb abduction - APL

Fingers: extension
F. Fingers extension
- EDC (index, middle, ring, little MCPJ extension)
- EIP (index finger extension)
- EDM (little finger extension)
(Also assisted by lumbricals, interossei at PIPJ and DIPJ)

Question 4

Sensory function of radial nerve

Answer 4

1. Posterior cutaneous nerve to arm
2. Lower lateral cutaneous nerve to arm
3. Posterior cutaneous nerve to forearm
4. Dorsolateral hand

Question 5

Possible sites of radial nerve neuropathy

Answer 5

A. Axilla - with concomitant deltoid weakness
1. Trauma, fracture, dislocation to shoulder
2. Crutch palsy
3. Axillary tumours (lipoma, schwannoma, lymphadenopathy, mets)
4. Posterior cord of brachial plexus lesion - trauma and tumours

B. Spiral groove and humeral shaft
1. Trauma and fracture to humeral shaft or lateral epicondyle
2. External compression against humerus (Saturday night palsy or Honeymoon palsy)
3. Muscular compression (athletes)
4. Tumours, ganglion, bursitis

C. PIN syndrome - no wrist drop, no sensory loss (wrist extension by radial nerve proper)
1. Supinator entrapment syndrome
2. Trauma, fracture to radial head/proximal ulnar
3. Elbow joint synovitis

D. Wartenberg’s syndrome (cheiralgia paraesthetica)
1. Tight watches, bracelets, casts
2. Brachioradialis entrapment
3. Trauma

Question 6

Examination of radial nerve

Answer 6

Muscle weakness
1. Manoeuver - wrist and finger drop
2. Elbow extension weakness - axilla
3. Brachioradialis elbow flexion weakness in mid-pronation position - spiral groove
4. Common feature: Wrist and finger extension weakness - all levels of radial palsy except PIN
5. Thumb abduction and extension weakness - PIN

Sensory loss
1. Lower lateral cutaneous of arm - spiral groove
2. Posterior cutaneous of arm and forearm - spiral groove
3. Dorsolateral hand and anatomical snuffbox - superficial branch

Differentiating cortical wrist drop vs radial wrist drop
1. Make a fist
- Cortical drop: slight elevation of fist (synkinetic contraction)
- Radial palsy: worsened wrist drop: unopposed wrist flexors

Question 7

Axillary lesion radial nerve palsy

Answer 7

Key differentiators:
1. Shoulder abduction weakness - involvement of axillary nerve (deltoid)
2. Sensation loss throughout radial nerve distribution

Motor weakness:
1. Shoulder abduction weakness - deltoid from axillary neuropathy
2. Elbow extension weakness - triceps brachii
3. Half pronation elbow flexion weakness - brachioradialis
4. Wrist drop - wrist extensors (ECU, ECRL, ECRB)
5. Finger drop - finger extensors (EDC, EIP, EDM)
6. Thumb extension and abduction weakness - thumb extensors (EPB, EPL), APL

Sensation loss:
1. Lower lateral arm
2. Posterior arm
3. Posterior forearm
4. Dorsolateral hand

Question 8

Spiral groove and humeral shaft lesion radial nerve palsy

Answer 8

Also known as “Saturday night palsy” and “Honeymoon palsy”

Key differentiators:
1. No shoulder abduction weakness
2. Sensory spared over lateral arm and posterior arm
3. Dorsolateral numbness still present

Motor weakness:
1. Milder elbow extension weakness compared to wrist/finger
- lateral and long heads unaffected
2. Wrist drop
3. Finger drop

Sensory loss:
1. Posterior forearm
2. Dorsolateral hand
(Lateral cutaneous and posterior of arm might be spared if lesion is below spiral groove)

Question 9

PIN syndrome

Answer 9

Key differentiators:
1. Pure motor weakness of finger drop (finger extension weakness)
2. NO wrist drop
3. NO sensory loss

Pure motor weakness:
1. Finger extension weakness
2. Thumb extension weakness
3. Milder thumb abduction weakness - spared APB
4. May have wrist deviation on wrist extension

Question 10

Wartenberg’s syndrome

Answer 10

Pure sensory loss over the dorsolateral aspect of hand