Ulnar Nerve
The ulnar nerve (C8, T1) supplies most of the intrinsic muscles of the hand — the most delicate and precise of the upper limb muscles. Injury produces a devastating functional loss, despite affecting only a small anatomical territory.
✦ The Mnemonic
"Flexors First, Hypothenar, Interossei, Lumbricals, Adductor — All Ulnar"
Muscles supplied in forearm then hand — lateral to medial
Clinical Breakdown
The ulnar nerve is the terminal branch of the medial cord. It passes posterior to the medial epicondyle in the cubital tunnel, where it is vulnerable to compression (cubital tunnel syndrome). It enters the hand via Guyon's canal (between the pisiform and hook of hamate), dividing into a superficial (sensory) and deep (motor) branch.
Ulnar claw hand: ring and little fingers adopt a position of MCP extension and PIP/DIP flexion. This is most pronounced in a distal lesion (at the wrist) because FDP to these fingers is spared — paradoxically, wrist lesions produce a worse claw than elbow lesions (ulnar paradox). All 7 interossei and medial 2 lumbricals are lost.
Froment's sign: the patient is asked to hold a piece of paper between the thumb and index finger. Loss of adductor pollicis (ulnar nerve) forces the patient to use FPL (anterior interosseous nerve/median) to hold the paper — the interphalangeal joint of the thumb flexes. A positive Froment's sign confirms adductor pollicis weakness.
⭐ Clinical Pearl
The ulnar paradox: an ulnar nerve lesion at the wrist produces a MORE obvious claw than a lesion at the elbow. This is because a wrist lesion preserves FDP (flexes the IP joints of ring and little finger), making the claw more pronounced. An elbow lesion loses BOTH the intrinsics AND FDP — so there is less active IP flexion and a less dramatic claw.
⚠ Exam Trap
Sensation: the ulnar nerve supplies the medial 1½ fingers (little finger and the medial half of the ring finger) on both dorsal and palmar surfaces. The palmar cutaneous branch of the ulnar nerve supplies the hypothenar skin — it branches proximal to Guyon's canal. Do not confuse the ulnar sensory territory with the median (lateral 3½ fingers palmar surface).