The superficial head is the median-innervated component inserting on the radial sesamoid. It is the primary MCP flexor and works with APB in opposition.
| Origin | Flexor retinaculum — radial portion and trapezium |
|---|---|
| Insertion | Radial sesamoid at the MCP joint |
| Nerve Supply | Recurrent (thenar) branch of median nerve (C8, T1) |
| Blood Supply | Superficial palmar branch of radial artery |
| Actions | Flexes the thumb MCP joint — primary flexor; Contributes to thumb opposition via sesamoid rotation |
|---|
Combined APB and superficial FPB weakness with preserved deep FPB (ulnar) is the hallmark of median nerve palsy at the wrist. Tenosynovitis of FPB at MCP level produces trigger thumb.
Palpable as the deep radial thenar muscle during resisted thumb MCP flexion with IP extended.
Loss of superficial FPB producing thenar flattening and weak MCP flexion, requiring tendon transfer for thumb abduction restoration.
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