A 52-year-old male carpenter from Delhi presents with a 3-month history of progressive weakness and wasting of the intrinsic muscles of his right hand. On examination, he has a positive Froment's sign and Wartenberg's sign. He reports that the symptoms began after he sustained a fall on his outstretched right hand 4 months ago, with initial severe swelling at the medial aspect of the elbow. Sensation is intact over the dorsal aspect of the hand. Which nerve is most likely compressed, and at what anatomical site?

Explanation

## Clinical Presentation Analysis **Key Point:** Froment's sign (flexion of IP joint of thumb when attempting to adduct it) and Wartenberg's sign (abduction of the little finger) are pathognomonic for ulnar nerve lesion affecting the intrinsic hand muscles. **High-Yield:** The intrinsic hand muscles are innervated by the ulnar nerve (medial 1.5 fingers) and radial recurrent branch of median nerve (lateral 3.5 fingers). Wasting of intrinsic muscles with intact sensation over dorsal hand indicates a motor-only or predominantly motor ulnar nerve lesion. ## Anatomical Localization | Feature | Cubital Tunnel (Elbow) | Guyon's Canal (Wrist) | |---------|------------------------|----------------------| | **Intrinsic hand muscles affected** | Yes (all) | Yes (only hypothenar + lumbricals 3–4) | | **Dorsal cutaneous branch** | Affected | Spared | | **Sensory loss pattern** | Medial 1.5 fingers (dorsal + palmar) | Palmar medial 1.5 fingers only | | **Common cause** | Trauma, cubital tunnel syndrome, prolonged pressure | Guyon's canal compression, hook of hamate fracture | **Clinical Pearl:** The dorsal cutaneous branch of the ulnar nerve arises 5–6 cm proximal to the wrist and supplies sensation to the dorsal medial 1.5 fingers. Preserved dorsal sensation rules out wrist-level lesions. ## Course of Ulnar Nerve ```mermaid flowchart TD A["Ulnar nerve exits medial cord<br/>at axilla"]:::outcome --> B["Descends medial to axillary artery<br/>in arm"]:::action B --> C["Passes posterior to medial epicondyle<br/>CUBITAL TUNNEL"]:::decision C --> D["Branches: Dorsal cutaneous<br/>5-6 cm proximal to wrist"]:::action D --> E["Enters hand at Guyon's canal<br/>medial to pisiform"]:::decision E --> F["Superficial branch: sensation<br/>Deep branch: intrinsic muscles"]:::outcome ``` **Key Point:** In this case, the history of trauma at the medial elbow with subsequent swelling, combined with preserved dorsal sensation but wasting of all intrinsic hand muscles, points to a **cubital tunnel compression** at the elbow level—the most common site of ulnar nerve entrapment in the upper limb. ## Why Cubital Tunnel? 1. **Anatomical vulnerability:** The ulnar nerve is superficial at the cubital tunnel, making it susceptible to external compression and trauma. 2. **Post-traumatic presentation:** Swelling at the medial elbow following a fall can compress the nerve in the cubital tunnel. 3. **Complete intrinsic involvement:** All intrinsic hand muscles are affected because the deep motor branch (supplying intrinsics) arises after the cubital tunnel. 4. **Preserved dorsal sensation:** The dorsal cutaneous branch arises distal to the cubital tunnel, explaining intact dorsal sensation. **Mnemonic:** **LOAF** — Lumbricals (medial 2), Opponens pollicis, Adductor pollicis, Flexor pollicis brevis = **median nerve**. Everything else intrinsic = **ulnar nerve**.