62 DISEASES OF THE SYNOVIAL MEMBRANES AND ARTICULATIONS. 



Causation. AVitli the sole exception of luxations or subluxations 

 due to tuberculosis (lateral luxations, either inwardly or outwardly, 

 occurring during tubercular arthritis, Avith more or less marked destruction 

 of the condyles), these luxations are always accidental or the result of 

 mechanical violence. 



They result from leaping into hollows, falling into deep ditches or 

 ravines, or galloping through broken or steep places. Any violent shock 

 affecting the femur, either in front or from the outside, is capable of 

 causing luxation l)ackwards or inwards. 



Symptoms. The most frequent condition is backward luxation of the 

 upper extremity of the tibia. Movement becomes difficult, the limb 

 is held rigidly, and all the lower part of the 

 leg is extended. None of the joints can be 

 flexed. The leg is dragged forward, without 

 the animal being able to place the foot flat on 

 the ground, and the claws are trailed over the 

 litter or the toe grazes the soil. 



On local examination the stifle is seen to be 

 deformed. The lower extremity of the femur 

 and the patella appear prominent. The upper 

 part of the tibia is thrust backwards, and seems 

 to have disappeared, leaving a depression below 

 the femoro-patellar region. The muscles form- 

 ing the back of the thigh at this level are 

 thrust out of position, and appear to project 

 abnormally. 



Yiewed from behind, the inner line of the 

 thigh appears more or less convex when the 

 upper extremity of the tibia is luxated inwardly. 

 On local examination the displacement of the 

 bones can be readily detected. In luxation 

 forwards the prominence of the stifle is caused by the summit of the 

 tibial crest and by the patella, whilst the lower extremity of the femur 

 cannot be felt. In outward luxation the upper extremity of the tibia 

 forms an abnormal prominence, above which a horizontal digital 

 depression appears. 



Diagnosis. Provided that the examination is made soon after the 

 occurrence of the accident, little difficulty will be found in coming to a 

 conclusion, but the diagnosis necessitates more care when examination is 

 deferred for two or three days, because extensive efi'usion then exists. 

 Luxations or subluxations of tuberculous origin are generally consecutive 

 to old-standing destructive tuberculous arthritis. 



The prognosis is grave — firstly, because reduction is difficult; and. 



Fig. 24.— Luxation back- 

 wards and inwards of the 

 femoro-tibial joint. (From 

 a photograph by Professor 

 Besnoit.) 



