Muscles of the wrist and hand

1. Carpal muscles act at the wrist and, in some cases, the elbow.

   • EXTENSOR CARPI RADIALIS LONGUS
   • EXTENSOR CARPI RADIALIS BREVIS
   • EXTENSOR CARPI ULNARIS

   • FLEXOR CARPI RADIALIS
   • FLEXOR CARPI ULNARIS
   • PALMARIS LONGUS

   Extrinsic hand muscles act on the wrist and the digits

   Extrinsic hand mm that act on the second through fourth digits:
   • EXTENSOR DIGITORUM
   • EXTENSOR INDICIS (PROPRIUS)
   • EXTENSOR DIGITI MINIMI (PROPRIUS)

   • FLEXOR DIGITORUM SUPERFICIALIS
   • FLEXOR DIGITORUM PROFUNDUS

   Extrinsic thumb muscles that act on the first digit:

   • FLEXOR POLLICIS LONGUS

   • EXTENSOR POLLICIS LONGUS
   • EXTENSOR POLLICIS BREVIS
   • ABDUCTOR POLLICIS LONGUS

   Intrinsic hand muscles act only the digits

   • THENAR MUSCLES and ADDUCTOR POLLICIS
   • HYPOTHENAR MUSCLES
   • LUMBRICALES
   • DORSAL INTEROSSEI
   • PALMAR INTEROSSEI

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Muscles that act only at the wrist (and elbow):

The muscles' names reflect their actions on the carpus (wrist).	EXTENSOR CARPI RADIALIS LONGUS EXTENSOR CARPI RADIALIS BREVIS EXTENSOR CARPI ULNARIS FLEXOR CARPI RADIALIS FLEXOR CARPI ULNARIS PALMARIS LONGUS

The only muscle in this group whose name does not suggest its action is palmaris longus. Although palmaris longus flexes the wrist, its line of application passes directly over the wrist's A-P axis, so that it possesses no moment arm to produce motion, either radial or ulnar deviation, in the frontal plane.

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Extrinsic hand muscles

The muscles' names reflect their actions on the digits. However, each one crosses the wrist and produces movement in the sagittal plane around the wrist's lateral axis, and in the frontal plane around its A-P axis.

EXTENSOR DIGITORUM (ED) EXTENSOR INDICIS (EI) EXTENSOR DIGITI MINIMI (EDM) FLEXOR DIGITORUM SUPERFICIALIS (FDS) FLEXOR DIGITORUM PROFUNDUS (FDP)	FLEXOR POLLICIS LONGUS (FPL) EXTENSOR POLLICIS LONGUS (EPL) EXTENSOR POLLICIS BREVIS (EPB) ABDUCTOR POLLICIS LONGUS (APB)

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Effect of the extrinsic hand muscles on wrist flexion/extension

Extrinsics to 2nd - 5th digits:		Extrinsics to thumb
Wrist extensors	Wrist flexors	Wrist extensors	Wrist flexors*
EDC EI EDM	FDS FDP	EPL	FPL EPB APL

*These muscles produce wrist flexion moments through very small moment arms. Kendall doesn't even list EPB as a wrist flexor/extensor.

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Effect of the extrinsic hand muscles on wrist radial/ulnar deviation

Whether an extrinsic hand muscle produces wrist radial or ulnar deviation depends on its line of application's (LOA) position with regard to the wrist joint's A-P axis.

Some muscles have LOA that pass directly over the wrist joint's AP axis, and so produce no frontal plane motion:

• EDC
• EI
• FDS
• FDP

Others produce wrist movement in the frontal plane:

• EDM ulnarly deviates
• various extrinsic thumb muscles (EPL EPB APL FPL) radially deviate

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Last updated 7-18-00 ©Dave Thompson PT
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