126 THE SURGICAL ANATOMY OF THE HORSE 



LUXATION OF THE HOCK JOINT 



This is extremely rare, particularly as applied to the tibio-tarsal 

 articulation, a point which will be readily conceded when we consider 

 the conformation of the articular surfaces, and the firm manner in 

 which the bones are held together by the intricate arrangement of the 

 ligamentous apparatus. Recorded cases have usually been the result 

 of some very serious injury associated with fracture of the malleoli 

 of the tibia. Luxation occurs more readily in the dog and cat, 

 owing to the fact that the ridges are not so prominent, and the 

 grooves, consequently, not so deep in these animals. The small bones 

 are united to one another in a particularly firm manner, and owing 

 to the slight degree of movement naturally occurring between them, 

 it is questionable whether luxation of the small articulations ever 

 occurs. 



Regarding luxation of the tibio-tarsal joint, Moller states that " the 

 strong ligamentous apparatus, together with the prominences on the 

 articular surfaces of the tibia and of the astragalus, produce so firm and 

 so secure a union of the two bones that luxation of the astragalo-tibial 

 joint is exceedingly rare." Jowett reported the following case of 

 luxation of the astragalo-tibial joint : 



" The subject, an ' unbroken ' Argentine mare, aged six years — 

 whilst being exercised in a circle ' lunged ' and travelling to the left, 

 slipped and fell to the ground. During the process it appears the left 

 hind foot caught in the turf in some way, whilst the off hind leg slipped 

 outwards. The mare immediately regained her feet without assistance 

 — lameness was very marked and she was just able to hobble very slowly 

 on three legs to the stable (a distance of about 500 yards), practically no 

 weight being placed on the injured limb. 



" On examination it was found that the portion of the leg from the 

 astragalus downwards could be moved to a very considerable extent 



