726 
DISEASES OF THE HOCK. 
to the rotary movement in the limb and the tendency to displacement of 
the bones in the affected section of the joint. 
Ihe ‘ spavin test” is sometimes nsetul in diagnosing spavin lameness: 
it consists in lifting the limb and keeping the hock-joint flexed for one 
minute and then trotting the horse. Lameness is very marked. 
This test, however, requires to be used with considerable care, 
especially in old horses, which may show similar difficulty in movement 
after the limb has been kept bent,, even without having spavin. 
"Various hypotheses have from time to time been advanced as to the 
immediate cause of lameness. Whilst the older practitioners considered 
the pain to be due to pressure of the exostosis on the periosteum, and 
supported their view by reference to the uneven surface of the macerated 
bones, we have known since Havemann’s time that the changes within 
the joint were not only the essence of the disease, but also the cause of 
the lameness. Though Hering opposed this, stating that spavin lame¬ 
ness is sometimes seen without disease of the joint, either his observa¬ 
tions were due to errors in diagnosis, or the process was only in a 
developmental stage, the articular surface not yet having suffered. As a 
rule, the onset and course of the lameness entirely agree with the 
observations made in men suffering from arthritis chronica, who at 
first only show lameness for a few steps. The lameness is probablv 
due to changes partly in the articular surfaces, partly in the ligaments. 
Dieckerhoff adds disease of the bursa of the flexor metatarsi muscle. It 
seems doubtful whether chronic inflammation of this bursa ever produces 
lameness. Under certain circumstances, exostoses may mechanically 
limit free movement of the joint. 
(2) The exostosis may even precede the lameness in cases where the 
disease develops slowly : as a rule, the two appear simultaneously, but 
sometimes the bony swelling does not occur until two or three weeks 
afterwards. Its detection requires an accurate knowledge of the normal 
configuiation of the hock-joint, and may be effected by viewing the joint 
either from the front or back. For this purpose the operator takes up a 
position eithei some steps in front of or behind the horse, and compares 
the inner surfaces of the hocks. In this way experts can detect the 
slightest diffei ences, though it is by no means possible to determine by 
this examination alone whether or not spavin exists, especially in 
English thoioughbreds, whose hocks are seldom absolutely symmetrical. 
But even in other breeds a want of symmetry in the hocks cannot of 
itself be regarded as a certain sign of spavin. The terms “ coarse,” &c., 
used m speaking of formation, are tacit acknowledgments of this fact, 
and are often only circumlocutions for spavin. 
(3) Ihe above signs of spavin are often accompanied by atrophy of 
the muscles of the quarter, as usually happens in chronic painful 
