8o THE SUPERIOR EXTREMITY 



adopted in elevating the dorsal ligaments of the wrist and 

 carpus. Through the space obtained by first excising the 

 triquetrate (cuneiform) bone, the surgeon is able to divide the 

 hook of the hamate. This process and the pisiform are left 

 behind whenever possible, as they provide attachments for 

 the muscles of the hypothenar eminence and for the transverse 

 carpal (anterior annular) ligament. The remainder of the 

 carpus may then be removed piecemeal, but, if practicable, the 

 greater multangular bone (trapezium), which gives attachment 

 to the transverse carpal ligament, is left behind. Further, the 

 separate carpo-metacarpal joint of the thumb, which is not neces- 

 sarily affected by the disease, is opened into when the greater 

 multangular bone is removed, and the subsequent movements 

 of the thumb (p. 84) are seriously restricted. After removal 

 of the carpus, the extremities of the radius, ulna, and metacarpals 

 may be dislocated into the wound and resected, if necessary. 

 The wrist is subsequently dorsi-flexed, lest the powerful flexors 

 should overstretch the weaker extensor muscles. 



In Dislocation of the Capitate Bone (Os Magnum) the head of the 

 bone projects dorsally, opposite the base of the third metacarpal, and the 

 deformity is increased on flexion of the hand. 



The Lunate (Semilunar) Bone may be dislocated forwards by 

 forcible extension of the hand. In this case the ulnar nerve may be injured. 



The Navicular Bone may be fractured at its narrowest part when it 

 is driven against the distal end of the radius by the rounded head of the os 

 capitatum (os magnum). Forward displacement of the greater and lesser 

 multangular bones (trapezium and trapezoid) sometimes accompanies this 

 injury. 



THE HAND. 



Bony Landmarks. The base of the First Metacarpal is 

 readily felt in the angle between the tendons of the extensor 

 pollicis brevis and longus, and the dorsal surface of its shaft 

 can also be felt, though it is somewhat obscured by the extensor 

 tendons. 



In Bennetfs Fracture, which passes obliquely through the 

 base of the first metacarpal, the large, distal fragment is drawn 

 proximally and slightly backwards by the combined action of 

 the flexors and extensors of the thumb. The small, proximal 

 fragment, which generally includes a part of the ulnar side of 

 the shaft, suffers little displacement. Abnormal movement 



