Movement of the Thumb: Origin, Insertion, and Action

Extensor pollicis brevis

O: Distal posterior radius, and interosseus membrane I: Base of proximal phalanx of thumb (dorsal side) A: Extension of the thumb (at the MP and CM joints)

Abductor pollicis brevis

O: Flexor retinaculum, trapezium and scaphoid I: Base of proximal phalanx of thumb (radial side) A: Abduction of the thumb

Extensor pollicis longus

O: Middle posterior ulna, and interosseus membrane I: Base of distal phalanx of thumb (dorsal side) A: Extension of the thumb ( at the IP, MP & CM joints)

Abductor Digiti Minimi

O: Pisiform and tendon of the flexor carpi ulnaris I: Proximal phalanx of little finger (base of phalanx of the ulnar side) A: Abduction of the little finger

Abductor pollicis longus

O: Posterior ulna and radius, and interosseus membrane I: Base of meta carpal #1 (radial side) A: Abduction and extension of the thumb (at the CM joint), and radial deviation (abduction) at the wrist