44° CLINICAL VETERINARY MEDICINE AND SURGERY. 



Next day there was considerable local swelling; the patella was once 

 more out of position, and could not be replaced. Manipulation gave 

 great pain, and at last caused the animal, which had crouched down 

 on its hocks, to make a sudden movement and fall over. Just at this 

 moment the patella suddenly slipped from under the pressure of the 

 operator's thumbs, a loud sound was heard, and the horse scrambled 

 up, once more able to freely use the limb. It was immediately taken 

 back to its stall, placed on a deep bed of straw, and left to itself, the 

 only precaution taken being to wedge it up on either side with trusses 

 of straw so as to prevent its lying down or moving about much. Five 

 days later a blister was applied round the stifle to limit the movement 

 of the parts, and in a month the animal was returned to work. It 

 afterwards worked hard in a hansom cab, and appeared to have 

 suffered no ill effects from its accident. 



Note by Mr. Dollar. — The peculiar features of this case appear to 

 have been, firstly and principally, the position taken up when at rest ; 

 secondly, the rather advanced age at which the accident occurred ; and 

 lastly, the rapidity and completeness of recovery. 



To sum up the results of our inve-tigation in so far as they tend to 

 answer the three questions propounded at the commencement of this 

 article, I think we may safely conclude— (i) that the patella in by far 

 the greater number of instances is not truly displaced, but only abnor- 

 mally retained at a certain point of its ordinary travel. Where dis- 

 placement does occur, however, it is always outwards, and must be 

 accompanied by injury to the internal lateral ligament. 



(2) Such retention may be due either to failure of the nervous 

 centres to properly co-ordinate the muscular movements necessary to 

 release the patella when at its extreme upper point of travel, or to 

 spasm or paralysis of certain of the muscles involved, or merely to 

 mechanical causes interfering with their movement ; or, again, it may 

 result from excessive tension of the inner straight ligament, which 

 slips behind the groove on the inner side of the extremityof the femur, 

 and cannot be released. 



(3) That the symptoms are not always the same, and that they often 

 differ widely from those of the " classical " cases, as is shown by that 

 described by Mr. Cameron, and lastly by my own. 



English observers seem to concur in believing that in luxation of 

 the patella the leg is directed backwards, that great force is required 

 to extend it, and that all the joints, save, perhaps, the fetlock, are 

 fixed ; and most writers on the subject favour the theory of relaxation 

 or rupture of the internal lateral ligament. 



By experiments on the dead subject M. Violet (Lyons Veterinary 

 School) has shown that the patella at its highest point of travel 

 " rides on the larger lip of the trochlea." The stifle-joint cannot then 

 be flexed until it quits this position, a movement which is accomplished 

 as follows : — -" The vastus internus relaxes a little, whilst at the same 

 moment the superficial gluteus extends the femur slightly and draws 

 back the outer side of the patella, causing it to pivot from within 

 outwards ; the external straight ligament then becomes tense whilst 

 the inner relaxes, for the central prominence of the patella has now 



