958 UPWARD LUXATION OF THE PATELLA. 



animals luxation of the joint is of rare occurrence. Isolated cases 

 have, however, been seen in cattle and dogs. 



Thus Stolze describes complete luxation of the tibia forwards. The cow 



was unable to advance the limb, which was rigid and somewhat shortened. 

 It was still possible, however, to place weight on the leg, and the displace- 

 ment of the bone could be detected by palpation of the stifle. Reposition, 

 though difficult, was finally effected, but luxation soon recurred, in spite 

 of the animal being slung. After replacing the parts five times — an operation 

 which appeared easier on each occasion— a blister was applied ; the parts 

 remained in position, and in three months the animal could move fairly 

 well, and was able to return to grass. 



Sprain of the stifle-joint may possibly occur from violent move- 

 ments but is certainly not common in large animals. Possibly the 

 chronic inflammation of the femoro-tibial joint (gonitis chronica) 

 seen in dogs is due to such injuries. In cows, Sand noticed spontaneous 

 dislocation of the tibia following partial destruction of the inter- 

 articular cartilages, in consequence of chronic gonitis. 



II.— DISPLACEMENT OF THE PATELLA. LUXATIO PATELLA. 



The patella is retained in position by a capsular ligament 

 strengthened by two lateral ligaments, and by its straight ligaments, 

 of which the horse and ox possess three ; most other animals, however, 

 only one. Finally, the pull of the triceps extensor cruris and tensor 

 vaginae femoris muscles sustains the patella above. Horses, oxen, 

 and dogs, are the commonest sufferers, and the luxation is either — - 



(a) Upwards, over the internal lip of the trochlea of the femur ; or 



(b) To the side, and always to the outer side, except in the dog, 



in which luxation is usually inwards. 

 The two conditions, however, differ not only in their symptoms, but 

 also in their prognosis and treatment, and therefore will receive 

 separate consideration. 



(a) Luxation of the patella upwards, which occurs in oxen and 

 horses, and has been seen by Olivers in a mule, is, strictly speaking, 

 only an arrest of the patella within its articular capsule, the bone 

 passing upwards over the internal lip of the trochlea and failing to 

 return. It is fixed in this position by its lower border lying against 

 the upper margin of the inner lip of the trochlea. This luxation can, 

 therefore, only occur after excessive extension of the stifle-joint. 

 Violet advanced the theory that the patella is retained on the trochlea 

 of the femur by its internal ligament. The surface of the internal 

 lip of the trochlea describes the segment of a circle around the point 

 of insertion of the internal lateral ligament into the femur. It can, 

 therefore, easily be imagined that under certain circumstances the 



