The FCU is the only wrist flexor innervated by the ulnar nerve. The ulnar nerve passes between its humeral and ulnar heads (Osborne's ligament between the heads) — the most common site of ulnar nerve compression at the elbow.
| Origin | Humeral head: medial epicondyle; Ulnar head: posterior border of ulna — upper two-thirds via an aponeurosis |
|---|---|
| Insertion | Pisiform bone and via pisometacarpal ligament to the fifth metacarpal base |
| Nerve Supply | Ulnar nerve (C7, C8) — the nerve runs in the ulnar groove between the two heads |
| Blood Supply | Ulnar artery |
| Actions | Flexes the wrist — strongest wrist flexor; Adducts the wrist (ulnar deviation); Fixes the pisiform as a sesamoid for the abductor digiti minimi |
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Cubital tunnel syndrome (ulnar nerve entrapment at the elbow) involves the nerve between the FCU heads. FCU is the landmark for surgical decompression. The FCU is an important donor for tendon transfer to restore digital extension in radial nerve palsy and in cerebral palsy surgery.
Palpated at the medial volar forearm and at the pisiform during resisted wrist flexion with ulnar deviation.
Ulnar nerve entrapment between the two FCU heads at the cubital tunnel, released by division of the fascial arcade between the humeral and ulnar heads.
