The FCU is the ulnar wrist flexor and the most powerful wrist deviator toward the ulnar side, inserting primarily on the pisiform and through the pisiform's ligamentous connections to the hamate and fifth metacarpal. It is the site of ulnar nerve compression at the elbow (cubital tunnel), where the nerve passes between the two FCU heads beneath the arcuate ligament.
| Origin | Medial epicondyle via the common flexor origin; Medial olecranon and posterior ulna upper two-thirds via an aponeurosis |
|---|---|
| Insertion | Pisiform (and via pisohamate and pisometacarpal ligaments to the hamate hook and fifth metacarpal base) |
| Nerve Supply | Ulnar nerve (C7, C8) |
| Blood Supply | Ulnar artery |
| Actions | Wrist flexion; Ulnar deviation of the wrist |
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The FCU is the primary muscle active during the power grip position of wrist flexion and ulnar deviation used in hammering, throwing, and racket sports. Its two-headed origin creates the roof of the cubital tunnel through which the ulnar nerve passes.
FCU calcific tendinitis at the pisiform produces acute ulnar wrist pain with visible calcification on radiograph. The cubital tunnel where the ulnar nerve passes between the FCU heads is the second most common upper limb nerve entrapment site after carpal tunnel. Flexing the elbow tightens the arcuate ligament spanning the two FCU heads and exacerbates cubital tunnel compression.
The FCU tendon is palpable as the medial wrist tendon between the ulnar artery and the medial forearm border during resisted wrist flexion and ulnar deviation.
Calcium pyrophosphate deposition at the pisiform producing acute ulnar wrist pain managed with anti-inflammatories and aspiration when accessible.
