LAMENESS IN THE HIND LEG 237 



mitting movement only in a direction parallel with the long axis 

 of the body. 



Because of the quality of their temperaments, nervous animals 

 possessing no particular congenital structural defects of the 

 hock and having no history of spavined progenitors, are subject 

 to spavin when kept at work likely to produce tarsal sprain. 

 Spavin usually develops early in such subjects and examples of 

 this kind may be frequently observed in agricultural sections 

 of the country. Where spavin develops in unshod colts at three 

 and four years of age, shoeing is not an influencing agency when 

 animals are not worked on pavements. 



Exciting causes of spavin are sprain and concussion. Various 

 hypotheses are recorded as to how sprains are influenced and 

 among others may be mentioned that of McDonough^, which is 

 that the foot is robbed of its normal manner of support by the 

 ordinary three-calked shoe. With such a shoe, little support is 

 given the sides of the foot; hence, undue strain is put upon the 

 collateral ligaments of the tarsus. ^Moreover, the shoe with its 

 calks increases the length of the leg and adds to the leverage 

 on the hock, by virtue of such added length. This makes for 

 greater strain upon the mesial or lateral tarsal ligaments when- 

 ever the foot bears upon a sloping ground surface, so that one 

 side (inner or outer) is higher or lower than the other. But 

 according to McDonougli's theory (a good one concerning horses 

 that work on pavements), the chief error in shoeing lies in that 

 the foot is deprived of its normal base or support on the sides 

 — the three-calked shoe being an unstable support — and that 

 this manner of shoeing city horses working on pavements is an 

 "inhumane" practice, a "diabolical method." 



Wliether spavin has its point of origin within the articulation 

 as a rarefying ostitis of the cancellated structure of the lower 

 tarsal bones as suggested by Eberlein ; or, as Diekerhoff asserts, 

 that the cunean bursa may be the initial point of affection, is 

 unsettled ; but it is reasonable to consider occult spavin as having 

 its origin within the articulation, and that cases readily yielding 



i"Hock-Joint Lameness," by Dr. James McDonough, Proceedings of the 

 A. V. M. A., 1913, page 545. 



