REGION OF THE WRIST. 



333 



The Capsular Ligament. The capsular ligament serves to retain the syno- 

 vial fluid in the joint. It is thin and filmy and possesses no strength, and therefore 

 is useless in limiting movements. 



Anterior and Posterior Radio-ulnar Ligaments. These ligaments are 

 simply a few bands which pass across from the radius to the ulna. They are not 

 strong enough to be efficient in limiting movements of the bones. 



Movements. As has already been pointed out (page 304) 

 the movements of pronation and supination have as their axis a 

 line drawn through the middle of the head of the radius, the styloid 

 process of the ulna, and the ring finger. They embrace in ordinary 

 use a range of about 140 degrees which can be increased by forced 

 effort to 1 60 degrees (Fig. 342). 



These movements are limited by various factors, the most 

 prominent being in pronation the contact of the soft parts and 

 bones, as the radius obliquely overlies the ulna, and in supination 

 by the biceps (the most powerful of the supinators) having reached 

 the dead centre. 



There is no communication between the radio-ulnar joint 

 above and the radiocarpal joint below, except when, as occasion- 

 ally happens, the triangular cartilage has a perforation. 



During pronation and supination the lower end of the radius 

 moves with the hand, but the lower end of the ulna remains at rest: 

 hence it is that the styloid process of the radius always retains the 

 same position in relation to the hand. When it is desired to iden- 

 tify the styloid process of the radius, one needs only to follow the 

 metacarpal bone of the thumb up to the snuff-box at the upper 

 edge of which the styloid process can always be felt. Also, to 

 identify the styloid process of the ulna, one must not use the hand 

 as a guide because the hand changes its position in relation to the 

 ulna; but, as the ulna remains quiet, its styloid process can be 

 found by following the posterior surface down to its extremity. 



As the interarticular triangular cartilage is fastened by its 

 base to the ulnar edge of the radius and by its apex to the base 

 of the styloid process of the ulna, it travels with the hand in the movements of 

 pronation and supination. 



FIG. 342. Axis of rota- 

 tion. 



THE RADIOCARPAL OR WRIST-JOINT. 



The wrist-joint is formed by the radius and triangular cartilage above and the 

 navicular (scaphoid), lunate (semilunar), and cuneiform bones below. These are 

 joined by the anterior, posterior, internal and external lateral, and capsular liga- 

 ments. The two lateral ligaments are strong, well-defined bands, the anterior and 

 posterior ligaments are weaker and are fused with the capsular ligament. 



The internal lateral ligament is attached above to the tip of the styloid 

 process of the ulna and the tip of the triangular cartilage ; below it is attached to the 

 border of the cuneiform bone and is continued on to the pisiform bone. 



The external lateral ligament is attached above to the tip of the styloid 

 process of the radius and below to the base of the tubercle of the navicular bone. 



The capsular ligament of the wrist-joint is composed of an anterior and a 

 posterior portion strengthened by the two lateral ligaments .just described. The 

 anterior ligament has the bulk of its fibres running downward and inward from the 

 edge of the radius to the palmar surface of the navicular, lunate, and cuneiform 

 bones. It is stronger than the posterior. The posterior ligament likewise has 

 its fibres running downward and inward to be attached to the first row of carpal 

 bones. 



Movements. The wrist is classed as a biaxial diarthrosis or condyloid joint. 

 This means that it is a double hinge-joint having movements around two axes, 

 one anteroposterior and the other transverse. A combination of these movements 

 results in circumduction, but it has at least no voluntary movement of rotation. 



