Which of the following clinical findings is characteristic of a HIGH ulnar nerve lesion (at or above the elbow)?

Question

Accepted Answer

A. Claw hand deformity affecting all four fingers with loss of wrist flexion and weakness of flexor carpi ulnaris. ## High vs Low Ulnar Nerve Lesions

### High Ulnar Nerve Lesion (at or above the elbow)

**Key Point:** A high ulnar nerve lesion affects BOTH motor and sensory branches proximal to the wrist, resulting in:

| Feature | High Lesion | Low Lesion |
|---------|-------------|------------|
| **Flexor carpi ulnaris (FCU)** | Paralyzed (wrist flexion weak) | Intact (wrist flexion preserved) |
| **Flexor digitorum profundus (FDP) to digits 4–5** | Paralyzed (DIP flexion lost) | Intact (DIP flexion preserved) |
| **Intrinsic hand muscles** | Paralyzed (claw hand) | Paralyzed (claw hand) |
| **Claw hand pattern** | Affects all 4 fingers (2–5) | Affects only digits 4–5 |
| **Wrist flexion** | Weak or absent | Normal |
| **Sensory loss** | Medial 1.5 digits + dorsal aspect | Medial 1.5 digits (palmar only) |

### Mechanism of Claw Hand in High Lesion
1. **Loss of FDP to digits 4–5** → DIP joints cannot flex
2. **Loss of intrinsic muscles** → MCP joints hyperextend (unopposed extensor digitorum)
3. **Result:** Digits 4–5 assume claw posture; digits 2–3 also claw due to loss of lumbricals
4. **Wrist weakness** → Loss of FCU causes weak wrist flexion (unlike low lesion)

**High-Yield:** The **key differentiator** between high and low ulnar nerve lesions is **wrist flexion strength** and the **number of fingers affected by claw deformity**.

### Clinical Pearl
**Froment's sign** (thumb IP flexion when pinching paper) is positive in BOTH high and low lesions — it tests the adductor pollicis (ulnar-innervated), not a discriminator between levels.

**Wartenberg's sign** (abducted little finger) occurs in low lesions due to unopposed abductor digiti minimi; in high lesions, the entire hand is clawed, so the little finger is not simply abducted.

![Ulnar Nerve — Course and Lesions diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/4051.webp)

Answer

B. Wartenberg's sign (abducted little finger) without any weakness of finger flexion

Answer

C. Claw hand deformity affecting only the 4th and 5th digits, with preserved flexion at the wrist

Answer

D. Froment's sign positive with normal intrinsic hand muscle strength

Which of the following clinical findings is characteristic of a HIGH ulnar nerve lesion (at or above the elbow)?

Explanation

High vs Low Ulnar Nerve Lesions

High Ulnar Nerve Lesion (at or above the elbow)

Mechanism of Claw Hand in High Lesion

Clinical Pearl

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Feature	High Lesion	Low Lesion
Flexor carpi ulnaris (FCU)	Paralyzed (wrist flexion weak)	Intact (wrist flexion preserved)
Flexor digitorum profundus (FDP) to digits 4–5	Paralyzed (DIP flexion lost)	Intact (DIP flexion preserved)
Intrinsic hand muscles	Paralyzed (claw hand)	Paralyzed (claw hand)
Claw hand pattern	Affects all 4 fingers (2–5)	Affects only digits 4–5
Wrist flexion	Weak or absent	Normal
Sensory loss	Medial 1.5 digits + dorsal aspect	Medial 1.5 digits (palmar only)