Page 199 - Clinical Anatomy

ECA3 7/18/06 6:45 PM Page 184

184 The upper limb

Because of the greater distal projection of the radial styloid, the range of
abduction at the wrist is considerably less than that of adduction.

Muscles acting on the wrist
Flexors—all the long muscles crossing the anterior aspect of the wrist joint.
Extensors—all the long muscles crossing the posterior aspect of the joint.
Adductors — flexor carpi ulnaris acting in concord with extensor carpi
ulnaris.
Abductors — flexor carpi radialis and extensores carpi radialis longus and
brevis together with the long abductor and short extensor of the thumb.

The joints of the hand (Fig. 135)
The joints between the individual carpal bones allow gliding movements to
occur which increase the range of extension and, more particularly, flexion
permitted at the wrist joint.
The carpometacarpal joint of the thumb is saddle-shaped and permits
flexion and extension (in a plane parallel to the palm of the hand), abduc-
tion and adduction (in a plane at a right angle to the palm) and opposition,
in which the thumb is brought across in contact with the 5th finger. This
joint’s range contrasts with the limited movements of the other car-
pometacarpal joints which allow a few degrees of gliding movement of the
2nd and 3rd metacarpals and a small range of flexion and extension of the
4th and 5th metacarpals.
The opposite state of affairs holds at the metacarpophalangeal (m/p) joints;
only a 60° range of flexion and extension is possible at the m/p joint of the
thumb, whereas a 90° range of flexion and extension, together with abduc-
tion, adduction and circumduction, are possible at the four other m/p
joint’s, which are condyloid in shape.
Note that when the m/p joints of the fingers are flexed, abduction and
adduction become impossible. This is because each metacarpal head,
although rounded at its distal extremity, is flattened anteriorly; when the
base of the proximal phalanx moves on to this flattened surface, side move-
ments become impossible. Moreover, the collateral ligaments on either side
of the m/p joints become taut in flexion and thus prevent abduction and
adduction.
The m/p joints of the fingers, but not the thumb, are linked by the tough
deep transverse ligaments, which prevent any spreading of the palm when a
firm grip is taken.
All the interphalangeal (i/p) joints have pulley-shaped opposing surfaces
and are therefore hinge-joints allowing flexion and extension only. At all the
m/p and i/p joints the ligamentous arrangements are the same.
1◊◊Posteriorly—the joint capsule is replaced by the expansion of the exten-
sor tendon of the digit concerned.
2◊◊Anteriorly — the capsule is formed by a dense plate of fibrocartilage.
This palmar ligament is the response to the friction of the adjacent flexor
tendons.