The Wrist Joint - Computational Biomechanics of the Wrist Joint - page 3

Fig. 1.2 The radiocarpal joint from distal [ 2 ]. Illustrated are the two fossae for the scaphoid and
lunate bone
fibrocartilage ridge separating these two facets, known as the interfacet promi-
nence. Concavity with declination 10-15 o palmarly and 15-25 o ulnarly is also
observed at the distal articular surface of the radius [ 6 ]. TFCC, which functions as
a buffer between the triquetrum and the distal tip of the ulna during ulnar devia-
tion, consists of many components. Fibrocartilaginous disc, dorsal radioulnar and
palmar ligaments, ulnocarpal ligaments, and the tendon sheath of the extensor
carpi ulnaris form the TFCC [ 7 ]. Figure 1.2 illustrates the radiocarpal joint.
There are five main muscles associated with the motion of the wrist joint [ 8 ].
Radial deviation motion is performed by the extensor carpi radialis brevis, which
is inserted onto the proximal end at the dorsal surface of the third metacarpal bone.
Another tendon with the same function namely extensor carpi radialis longus is
also inserted onto the proximal end at the dorsal surface of the second metacarpal
bone. The last of the three muscles acting on the radial side, namely the flexor
carpi radialis contributes to radial deviation and flexion of the wrist joint. The
insertion is found at the palmar side of the base of the second metacarpal. The
flexor and extensor carpi ulnaris muscles which are found at the ulnar side, flex
and extend the wrist joint respectively. Both of them are acting together to perform
ulnar deviation motion. There are three insertion points for the tendon of the flexor
carpi ulnaris, where one of them is found at the pisiform. The remaining two are
connected via ligaments onto the hamate and fifth metacarpal bone.
1.2 Bone Structure
Bones at the wrist joint have unique structure, and therefore names were given
according to their shape or structure (Fig. 1.3 ). For instance, the name of the
second largest carpal bone, the scaphoid is derived from the Greek ''scaphe''
which has the same meaning as ''rowing boat'' since it shaped like a boat [ 8 ].