Ulnar Nerve and Ulnar Nerve Neuropathy

Question 1

What are the possible sites of ulnar neuropathy?

Answer 1

1. Proximal (elbow) - cubital tunnel syndrome
2. Distal (wrist) - ulnar paradox

Question 2

Ulnar nerve and branches

Answer 2

1. Roots: C8 and T1
   No sensorimotor contribution to arm
2. Descends down posterior to bony medial epicondyle (retro-epicondylar groove), then to the cubital tunnel
   - Flexor carpi ulnaris (FCU)
   - Flexor digitorum profundus medial half (FDP)
   No sensory innervation to forearm
3. Branches near the wrist
   - Dorsal cutaneous branch - dorsal medial hand sensation
   - Palmar cutaneous branch - hypothenar eminence
4. Travels superficial to flexor retinaculum and enters hand through Guyon’s canal
   - Superficial branch - ventral surface and fingertips of little finger and medial half of ring finger
   - Deep branch - hypothenar muscles (ADM, ODM, FDMB), palmar and dorsal interossei (PI and DI), adductor pollicis (AP), medial 2 lumbricals

Question 3

Motor function of ulnar nerve

Answer 3

Forearm
1. FCU - medial wrist flexion
2. FDP medial half - ring and little finger flexion
(Ulnar paradox - proximal lesion having weakened FDP, thus lesser flexion, resulting in “less severe” clawing)

Hand
1. Hypothenar muscle
- ADM - little finger abduction
- ODM - little finger opposition
- FDMB - little finger MCPJ flexion
2. Dorsal interossei - index and ring fingers abduction
3. Palmar interossei - index, ring, little fingers adduction
4. Adductor pollicis - thumb adduction
5. Medial 2 lumbricals - ring and little finger MCPJ flexion, and IPJ extension

Question 4

Sensory function of ulnar nerve

Answer 4

Sensation over the hands - despite branching off at forearm
1. Dorsal cutaneous branch - dorsolateral hand
2. Palmar cutaneous branch - hypothenar eminence
3. Superficial branch - ventral and fingertip of little finger and medial half of ring finger

No contribution to arm and forearm sensation

Question 5

Examination of ulnar nerve

Answer 5

A. Inspection
1. Hypothenar wasting
2A. Ulnar claw - claw appearance when attempting to extend fingers due to weak ring and little finger extensors, and hyperextended MCPJs
2B. Ulnar paradox - distal lesion appears worse than proximal, due to proximal lesion causing weak ring and little finger flexion -> less clawed
3. Wartenberg’s sign - little finger abduction due to unopposed finger extension (weak palmar interossei)

B. Motor Function
1. FCU - flex wrist against resistance, supporting forearm
2. Median half FDP - flex ring or little finger DIPJ against resistance, supporting middle phalanx
3. Dorsal interossei and ADM - finger abduction against resistance, using both of your index fingers
> Patient index finger abduction for dorsal interrosei
> Patient little finger abduction for ADM
4. Palmar interrosei - finger adduction, hold paper in between 2 fingers and pull
5. Adductor pollicis - thumb adduction
- Hold paper with 2 thumbs and pull
- Alternative, thumb adduction against force
- Froment’s sign - thumb flexes at IPJ (FPL by median nerve) to substitute weak AP

C. Sensation
- Dorsal cutaneous branch - dorsolateral hand
- Superficial branch + C8 - little finger tip
- Palmar cutaneous branch - hypothenar eminence

Question 6

Proximal ulnar neuropathy (cubital tunnel syndrome)
- Causes: supracondylar or medial epicondylar fracture, compression (elbow)
- Sign: Ulnar claw

Answer 6

1. Ulnar claw hand - clawing of little and ring fingers
   - MCPJ hyperextended (lumbricals weakness), PIPJ and DIPJ flexed (interossei weakness)
2. Wartenberg’s sign - abduction of little finger (palmar interossei weakness, unopposed finger extensors)

Motor weakness
1. Wrist flexion weakness, with abduction of wrist (FCU weak + FCR strong)
2. Ring and little finger DIPJ weakness (median half FDP)
3. Ring and little finger abduction weakness (DI and ADM)
4. Little finger opposition, abduction weakness (hypothenar)
5. Fingers adduction weakness (PI)
- Froment’s sign - thumb flexes at IPJ (FPL by median nerve) to substitute weak AP

Sensory deficit
- Ventromedial and dorsomedial hand numbness
- Medial half ring finger, little finger numbness

Question 7

Distal ulnar neuropathy (wrist)
- Causes: Guyon’s canal, ulnar tunnel syndrome
- Signs: ulnar paradox worse claw hand
- Remember the pertinent negatives of distal lesion

Answer 7

1. Ulnar paradox - worse claw hand
   - FDP medial half is not affected, stronger flexion of ring and little fingers -> more clawed
2. Wartenberg’s sign - abduction of little finger (palmar interossei weakness, unopposed finger extensors)

Pertinent negatives
1. Strong wrist flexion - spared FCU
2. Little and ring finger DIPJ strong - spared FDP

Motor weakness - hand intrinsic muscle
1. Ring and little finger abduction weakness (DI and ADM)
2. Little finger opposition, abduction weakness (hypothenar)
3. Fingers adduction weakness (PI)
- Froment’s sign - thumb flexes at IPJ (FPL by median nerve) to substitute weak AP

Sensory deficit
- Ventromedial hand numbness
- Medial half ring finger, little finger numbness