Axes and motions




Close-packed position

  • radio-carpal
  • mid-carpal


flexion / extension



ulnar and radial deviation

Even though flexion and extension occur at both of the wrist's articulations,
ap view of wrist complex

most wrist extension occurs around the midcarpal joint's lateral axis.

most wrist flexion occurs around the radiocarpal joint's lateral axis.

ap axis of wrist complex

Ulnar and radial deviation occur around an axis that passes through the capitate.

Two wrist creases on the hand's palmar (or volar) surface are landmarks for the locations of the radiocarpal and midcarpal joints.
ap view of wrist complex volar surface of wrist

Review: Bones of the wrist

from Charles Eaton MD, hand surgery pages.

Wrist arthrokinematics

In open chain movement, the convex surfaces of the scaphoid and lunate move on the concave surfaces of the radius and ulna.

during flexion: scaphoid/lunate roll anteriorly (toward palm) and glide posteriorly(toward dorsum)

during extension:

scaphoid/lunate roll posteriorly(toward dorsum) and glide anteriorly(toward palm).

During ulnar deviation: scaphoid/lunate roll toward ulna and glide toward radius.

During radial deviation:

scaphoid/lunate roll toward radius and glide toward ulna.

Muscles that move the wrist

To predict a muscle's action, you must know:

list of wrist and hand muscles

Examples of muscle synergies in wrist function

  1. palpate the ECRL as you make a fist or firmly grasp an object:

    • role of the FDP: the only muscle that flexes the DIP joints. Also flexes the PIP, MP, and wrist.

    • role of the FDS: flexes the MP and PIP joints; used for more forceful grasp

    • role of wrist extensors (ECRB, ECRL, ECU): maintain appropriate length and tension (force) in finger flexors so they can produce strong grip.

  2. Open your fingers forcefully and observe that the wrist flexes automatically.

    • role of the extensor digitorum: the only muscle that can open the fingers; also extends the wrist.

    • role of the wrist flexors: maintain appropriate length and tension in finger extensors they can forcefully open the hand

  3. Palpate the ECU as you quickly move the thumb away from the second digit. Why is the ECU active during this maneuver?

    • apl/epb move thumb but also radially deviate wrist;
    • ecu acts as true synergist.

  4. Carpal muscles act in helping synergies to produce:
    • wrist flexion:
    • wrist extension:
    • ulnar deviation:
    • radial deviation:

Carpal tunnel:

The "strut" that maintains the tunnel's shape is the flexor retinaculum, also called the transverse carpal ligament or the volar carpal ligament.

This ligament connects the scaphoid and trapezium on the hand's radial side with the hamate on the ulnar side.

3D view of bones of carpal tunnel
The 3-D image is modified from Charles Eaton MD

The carpal tunnel contains (from radial to ulnar side):

Repetitive motion can produce a tenosynovitis in the tendon sheaths of the long flexor muscles. This, in turn, can increase hydrostatic pressure in the tunnel, causing compression damage to median nerve. "Carpal tunnel syndrome's" impairments include pain and paresthesia in the distribution of the median nerve. They also include weakness of muscles innervated by the median nerve, the thenar muscles, and the first and second lumbricales.

The tunnel's contents are also prone to compression injury due to trauma, congenital stenosis, acromegaly, or hormonal changes.

Last updated 12-6-02 ©Dave Thompson PT