The ulnar nerve (C8-T1) is the terminal branch of the medial cord, descending through the medial arm and passing posterior to the medial epicondyle through the cubital tunnel, then continuing through Guyon's canal at the wrist to supply the intrinsic hand muscles (except thenar) and the medial one and a half fingers. It is the nerve of power grip and fine lateral finger coordination.
| Origin | Medial cord of the brachial plexus (C8, T1, often with a C7 contribution) |
|---|---|
| Course | Descends medial to the brachial artery, pierces the medial intermuscular septum, passes behind the medial epicondyle in the cubital tunnel, enters the forearm between the two heads of flexor carpi ulnaris, and descends on flexor digitorum profundus to enter the hand superficial to the flexor retinaculum through Guyon's canal |
| Motor |
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| Sensory |
|
Cubital tunnel syndrome (ulnar nerve compression at the medial elbow) is the second most common peripheral entrapment neuropathy. It produces little and ring finger paraesthesia, intrinsic weakness, and positive Froment sign. Conservative measures (elbow padding, night splint in extension) are first-line. Cubital tunnel release, ulnar nerve transposition (subcutaneous or submuscular), or medial epicondylectomy are surgical options. At the wrist, Guyon's canal compression produces variable patterns depending on compression zone. Proximal compression affects both motor and sensory, distal compression spares sensation.
Medial elbow aching and ring/little finger paraesthesia from sustained flexion compression, managed with activity modification, splinting, or surgical decompression.
Handlebar pressure compressing the nerve between pisiform and hamate, producing hypothenar weakness or plantar sensory loss in the ring and little fingers.
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