SPONTANEOUS LUXATION OF THE PATELLA. 
143 
with a state of debility. Having since that period seen many cases 
of this description, when neither mechanical injury nor any exter- 
nal cause was known to account for its occurrence, and not being 
aware that such an opinion had been entertained and publicly de- 
scribed by any one, I am disposed to think that these symptoms — 
as I am inclined to believe in M. Conte’s case — are sometimes 
mistaken as arising from other causes, and that, when luxation of 
this bone is known to exist, some external cause only is looked 
for, and attributed to have occasioned it. Of this I have known 
an instance that was almost as annoying to the person who was 
attending it — a very intelligent farrier of the old school — as if he 
had pronounced it dislocation of the hock. He, with the tact 
usually practised by these worthies, as soon as he discovered the 
nature of the case, which his experienced eye was not long in de- 
tecting, attempted equally quickly to ascertain what, as he ob- 
served, had knocked it — the patella — off. 
In a few minutes, a brick, projecting about half its length from 
the wall on the side of the stall corresponding to that on which 
the animal was injured being observed, it was pounced upon as 
the offending body ; but, mark his astonishment, when, after re- 
ducing this dislocation, and attempting to back the animal in her 
stall, he discovered that the contrary side was in the same predi- 
cament. This, of course, softened his assurance, and he came to 
me to inquire if 1 ever knew of such a circumstance, and what 
could have possibly removed both these bones at one time. 
This is not a solitary case, in which I have known both to be 
displaced at one time, but, more commonly, one slipping off when 
reduction has been efFected of the other ; and which still more con- 
firms me in the opinion I have formed of its cause, viz. the peculiar 
formation of the animal, as a want of the usual and necessary de- 
gree of convexity in that part of the condyles of the femur (more 
particularly the external one) with which the patella articulates, 
when the thigh is not flexed, or when the foot is on the ground. 
This being naturally the less protuberant part of the condyles, 
admits of its dislocation more easily at the moment the foot is about 
to leave the ground than when the thigh, is bent, as it then ap- 
proximates with the more convex surface of these prominences, 
and is further retained in its situation by the muscles inserted into 
it being put upon the stretch, having to cover a greater space in 
the direction of their fibres. 
The relaxed state of these muscles from any debilitating cause, 
as disease, want of exercise, or low condition, I look upon as the 
immediate cause of its occurrence, more particularly in young 
horses, in whom these processes are not fully developed. That 
the former exists as the predisposing cause 1 have proved to my- 
