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

## 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.