Ulnar Nerve and Ulnar Nerve Neuropathy - hypothenar and claw hand

Question 1

Summary of ulnar nerve functions

Answer 1

Motor function:
1. Wrist flexion - FCU
2. Ring and little finger flexion
- DIP flexion - FDP
- MCPJ flexion, IPJ extension - medial 2 lumbricals
3. Little finger abduction, opposition, MPCJ flexion - hypothenar muscles
4. Thumb adduction - adductor policis
6. All fingers abduction/adduction: interossei

Sensory function: mainly to the hands, no arm and forearm sensation
1. Dorsolateral cutaneous branch to hand
2. Palmar hypothenar eminence cutaneous branch
3. Superficial branch to medial half of ring finger and little finger

Question 2

Schematic diagram of ulnar nerve and its anatomical pathway

Answer 2

Origin (roots): C8 and T1
Brachial plexus medial cord
No sensorimotor contribution to arm and forearm

After medial epicondyle and cubital tunnel:
1. Flexor carpi ulnaris (FCU)
2. Medial half flexor digitorum profundus (FDP)
No sensory innervation to forearm

Before the wrist: 2 sensory branches
1. Dorsal cutaneous branch - dorsal medial hand sensation
2. Palmar cutaneous branch - hypothenar eminence

Superficial to flexor retinaculum through Guyon’s canal:
1. Deep branch (pure motor)
- Hypothenar muscles (ADM, ODM, FDMB)
- All interossei (palmar and dorsal)
- Adductor pollicis (AP)
- Medial 2 lumbricals

2. Superficial branch (mixed)
   - Motor: palmaris brevis
   - Sensory: palmar little finger and medial half of ring finger

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. Dorsomedial cutaneous branch to hand
2. Palmar hypothenar eminence cutaneous branch
3. Superficial branch to medial half of ring finger and little finger

No contribution to arm and forearm sensation

Question 5

What are the possible sites of ulnar neuropathy?

Answer 5

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

Question 6

Examination of ulnar nerve

Answer 6

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 - dorsomedial hand
- Superficial branch + C8 - little finger tip
- Palmar cutaneous branch - hypothenar eminence

Question 7

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

Answer 7

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 (medial half FDP)
3. All fingers 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 8

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 8

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. All fingers abduction weakness (DI and ADM)
2. Little finger opposition, abduction weakness (hypothenar)
3. All 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

Question 9

Ulnar claw hand

Answer 9

1. Paralysis of medial 2 lumbricals - loss of MCPJ flexion of 4th and 5th fingers.
   - Unopposed extensor digitorum at MCPJ (by radial nerve)
   –> Hyperextension of the MCPJ of the 4th and 5th fingers.
2. Paralysis of interossei IPJ extension
   - Unopposed IPJ flexion of FDS (by median nerve) and FDP (median and ulnar nerve)
   –> Flexion of the PIP and DIP joints of the 4th and 5th fingers.

Ulnar Paradox:
Distal lesion has functionally intact FDP of 4th and 5th fingers (innervated more proximally in the forearm) contributes more significantly to the IPJ flexion, leading to a more pronounced claw deformity.

While proximal lesions affecting more muscles have less severe claw hands due to paralysis of FDP of 4th and 5th fingers.