54 THE SURGICAL ANATOMY OF THE HORSE 



outwardly to the tendons and other important structures which pass 

 down the back of the knee. 



Its prominent position renders the pisiform by far the most liable to 

 fracture of all the carpal bones, and cases where it is fractured are 

 commonly met with. 



One of the most common causes is sudden and extreme contraction 

 of its flexor muscles. The bone is firmly attached to the cuneiform, 

 unciform, and head of the outer small metacarpal bone by the inter- 

 carpal ligaments, which are very powerful. The tendons inserted into 

 the upper border of the bone are likewise powerful, so that the bone is 

 very liable to snap when great tension is thrown upon the tendons. 

 The presence of the groove for the outer tendon of the flexor metacarpi 

 externus, weakens the bone in the position of the groove, and pre- 

 disposes to fracture along the line of its direction. 



When the bone is fractured the animal is unable to bear weight 

 upon the limb, as this throws strain upon the flexor tendons and 

 causes painful displacement of the injured parts. The limb is then 

 held with the joints flexed. The position of the bone favours the 

 formation of positive diagnosis by palpation. The fractured piece 

 may be easily detected, and when pressure is exerted there is 

 crepitation. 



In treating fracture of the pisiform bone a similar difficulty is 

 encountered as in treating fracture of the olecranon process, since in the 

 case under consideration the tension of the tendons of the flexors of the 

 metacarpus which are attached to the upper edge of the bone pulls the 

 fractured piece upwards, and although it is not difficult to work the 

 displaced piece of bone back into position, as soon as the animal moves 

 the limb the flexors contract and the bone is again displaced. It 

 frequently happens, therefore, that union by fibrous tissue takes place, in 

 which case the fracture is hable to recur as soon as any marked strain is 

 thrown upon the flexors. If there should be no recurrence the hmb 

 often remains permanently deformed, the joint being curved with the 



