178 THE SURGICAL ANATOMY OF THE HORSE 



POSTERIOR TIBIAL NEURECTOMY 



We have stated above how the posterior tibial nerve divides into the 

 internal and external plantar nerves just above the level of the summit of 

 the tuber calcis, and that the two plantar nerves pass through the tarsal 

 sheath in company with the perforans tendon. Whilst passing over the 

 back of the hock joint the external plantar nerve detaches a branch of con- 

 siderable size, and from this branch are given off a number of collateral 

 twigs, some of which are distributed over the surface of the joint, whilst 

 others penetrate the joint and supply its internal structures. 



Consequently in persistent cases of spavin, neurectomy of the posterior 

 tibial nerve has been practised. 



In performing this operation the animal is cast on the side of the 

 affected limb and placed under a general anaesthetic. Cross hobbles are 

 then placed on the upper fore and hind limbs, and the latter is drawn as 

 far forwards as possible before tying the rope connecting them. In 

 short-backed animals the hind foot may be drawn so far forwards as to 

 rest on the upper fore foot. If this can be done so much the better, as 

 the area of operation on the inner aspect of the affected limb becomes 

 thus more accessible to the operator. The inner aspect of the limb 

 above the hock should be shaved and cleansed thoroughly. 



Regarding the seat of our cutaneous incision, it will be gathered 

 from our description of the nerve that it becomes placed superficially on 

 the inner aspect of the limb where it emerges from beneath the inner 

 head of the gastrocnemius muscle, some nine inches or so (varying, of 

 course, with the size of the animal) above tl;c hock, and then takes a 

 course downwards in front of the tendo-Achilles. It does not run 

 exactly parallel to the tendon ; the distance betvv^een the nerve and tendon 

 gradually increases as we approach the joint. Most writers on the 

 subject of neurectomy of this nerve advocate a point between three and 

 four inches above the hock as the seat of operation, and the fixing of the 



