FRACTURE OF THE TIBIA 63 



and roughened for the attachment of the external lateral ligament of the 

 hock. This surface is crossed by a groove, which is disposed almost 

 vertically, and through which the tendon of the peroneus muscle plays. 

 The internal malleolus is similarly smooth and articular where it bounds 

 the inner groove, the other surface being convex and roughened for the 

 attachment of the internal lateral ligament of the hock. 



The tibia develops from three main centres of ossification, one for each 

 epiphysis and one for the diaphysis. In addition there are two other 

 centres, from one of which the external malleolus is developed, whilst 

 the other is for the anterior tuberosity at the proximal epiphysis of the 

 bone. 



FRACTURE OF THE TIBIA 



It will be gathered from the foregoing description that the most 

 exposed parts of the tibia are the inner surface, which is subcu- 

 taneous, and the inferior extremity, where the malleoli stand out 

 prominently. 



Cases of fractured tibia are very common. Next to the innominate 

 bone, this bone is the most frequently fractured. It is estimated that 

 of all fractures of the bones of the horse five per cent, are fractures of 

 this bone. 



Its outer surface is well protected, being clothed by the extensor 

 pedis and flexor metatarsi muscles. 



The bone is commonly fractured in its inferior third, about two 

 inches above the malleoli. The author has frequently seen cases of 

 fracture in this situation. Some have occurred in steeplechasers, whilst 

 others have resulted from the animals being cast in the stall by catching 

 the shoe of the hind foot in the chain where the block has been of 

 insufficient weight to keep the chain taut. 



The bone is also frequently fractured as a result of a kick received on 

 the inner surface of the bone whilst the animal is lying down. 



