Trapezium Bone

The axes of rotation of the CMC joint have been described as being fixed [Hollister et al., 1992], but others beUeve that a polycentric center of rotation exists [Imaeda et al., 1994]. Holhster et al. [1992] found that axes of the CMC joint are fixed and are not perpendicular to each other, or to the bones, and do not intersect. The flexion/extension axis is located in the trapezium, and the abduc-tion/adduction axis is on the first metacarpal. In contrast, Imaeda et al. [1994] found that there was no single center of rotation, but rather the instantaneous motion occurred reciprocally between centers of rotations within the trapezium and the metacarpal base of the normal thumb. In flexion/extension. 

The sellar Joint is composed of two bones whose articirlar surfaces are saddle-shaped, with one surface convex and one concave. This allows for greater motion in all planes. An example of this is the trapezium-metacarpal (thumb) artic-rrlation. 

Thumb has a different structure as compared to other fingers. Bones of thumb is known as trapezium, metacarpal, proximal and distal. Usually thumb is considered as 5 DOF consisting of interphalangeal (IP) joint, metacarpophalangeal (MCP) and trapeziometacarpal (TM) and it does not have proximal interphalangeal (PIP). 

Fig. 10.1. Schematic drawing of a coronal view through the wrist outlines the relation among carpal bones and wrist joint spaces. Distal to the radius (R) and ulna fLl),the proximal row of carpal bones includes the scaphoid (S), lunate (L), triquetrum (T) and pisiform (P), whereas the distal row is formed by the trapezium fTzj, trapezoid (Tdj, capitate (C) and hamate (H). The distal radio-ulnar joint (1) is separated from the radiocarpal joint (2) by the triangular fibrocartilage (curved arrow). The scapholunate (straight arrow) and lunotriquetral (arrowhead) ligaments separate the radiocarpal from the mid-carpal fSj joint. The carpometacarpal joint spaces (4) lie ahead of the distal carpal row...

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