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Seven of the eight carpal bones are arranged into two rows.
The proximal row is made up of three bones:
PROXIMAL ROW
¾ triquetrum
¾ lunate
¾ scaphoid
The distal row is made up of four bones:
DISTAL ROW
¾ hamate
¾ capitate
¾ trapezoid
¾ trapezium
The eighth carpal bone, the pisiform, is positioned anteriorly to the triquetrum.
The pisiform bone is the only one of the carpal bones that is easily palpated. It projects
anteriorly on the little finger side of the hand as a small rounded elevation. It is the
insertion point of the flexor carpi ulnaris muscle which flexes and adducts the wrist.
The tendon of the flexor carpi ulnaris can also be easily palpated when the wrist is
flexed. The arrangement of the pisiform and the flexor carpi ulnaris is comparable to the
arrangement of the patella and the knee extensor muscles in that the pisiform increases
the lever arm of the flexor carpi ulnaris.
pisiform
tendon of the
flexor carpi ulnaris
FIGURE 21. THE PISIFORM INCREASES THE LEVER ARM OF THE FLEXOR CARPI ULNARIS MUSCLE.
Despite its wide range of motion the wrist is a comparatively stable joint. Its stability is
derived from the intricate ligamentous structures and the precise opposition of the
multifaceted articular surfaces rather than from any inherent bony stability, such as that
found in the hip joint.
SAQ 9
(a) List the bones that form the proximal and distal rows of the wrist.
(b) How is the lever arm of the flexor carpi ulnaris muscle increased?
3.1 Articulations
The motion of the wrist joint is dependent on the numerous articulations formed
between the carpal bones and between the carpal bones and adjacent bones of the hand
Unit 3 - Biomechanics of the Upper Limb & Spine 15
PISIFORM