Extrinsic muscles of the thumb
Flexor pollicus longus
- attaches to thumb's distal phalanx; only muscle that crosses IP joint on flexor side
- innervated by median nerve
Three "snuffbox muscles" that are innervated by deep interosseous branch of radial nerve:
- Extensor pollicis longus
- attaches proximally to radius, and crosses wrist, CMC, MP, and IP joints.
- only muscle that extends IP joint directly; other muscles attach to thumb's extensor mechanism.
- can assist with adduction of first MP joint, because its tendon can lie on that joint's ulnar side.
- Extensor pollicis brevis
- attaches proximally to radius, its tendon passing through common sheath with that of APL, then attaches to base of proximal phalanx.
- crosses wrist, CMC, and MP joints.
- Abductor pollicis longus
- attaches proximally to radius and ulna. Its distal attachment to base of first metacarpal is palpable at the gap on the proximal end of the first metacarpal shaft.
- extends first CMC joint in plane of palm. Its name reflects the fact that it produces frontal plane motion in anatomical position.
Last updated 7-18-00 ©Dave Thompson PT
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