962 LATERAL LUXATION OF THE PATELLA. 



tissue separates the synovial membrane from the ligament, there is 

 little danger of opening the articulation. The operation is followed 

 by immediate relief, the patella resuming its normal position on the 

 trochlea. Bassi. Cadiot, and others have operated successfully on 

 horses, but Morey failed, luxation at once recurred, though it was 

 more easily reduced than before operation. Cavallari performed 

 the operation with immediate and lasting benefit on both stifles 

 of a cow, and Savio was equally successful with four cases in cattle. 

 Probably failure of the operation in horses is sometimes due to 

 persistent abnormal contraction or shortening of the triceps, which 

 by carrying the patella upwards, tends constantly to reproduce 

 luxation, even when both the internal and middle straight ligaments 

 have been divided and reduction has been temporarily effected 

 (Cadeac). To counteract this muscular contraction, repeated daily 

 massage of the extensor muscles, after reduction of the luxation, 

 has been recommended. 



B. Lateral luxation of the patella. 



In horses and cattle, the patella may be displaced laterally, and 

 almost always towards the outer side. In dogs, inward luxation 

 is the rule, and the condition may be congenital and bilateral, and 

 due to abnormal conformation of the internal lip of the femoral 

 trochlea. 



Acquired outward luxations are dependent on rupture or excessive 

 strain of the inner lateral patellar ligament. As the inner lip of 

 the femoral trochlea is much larger than the outer lip, inward luxation 

 is extremely rare in horses and cattle, though Stockfleth saw one 

 case in a cow. In outward luxation the patella may rest to some 

 extent over the external lip (incomplete luxation), though it is 

 generally thrust on to its outer surface (complete luxation). Meyer 

 saw luxation of this kind in two cows. 



Causes. The predisposing causes of lateral luxation are upright- 

 ness of the limb, obliquity of the quarters, and youth of the animal. 

 The condition may appear in both limbs. Another factor may 

 consist in relaxation and weakness of the ligaments. In dogs the 

 outer lateral ligament is much slighter than the inner. 



Everything favouring rupture or strain of the internal lateral 

 ligaments may produce the condition. Meyer believed it was caused 

 by rheumatic contraction in or excessive action of the abductors, 

 but failed to effect a cure by dividing them. 



The prognosis is less favourable than in upward luxation, 

 particularly in dogs. Pugs often suffer congenitally, and little can 

 be done for them. As in other cases, the older the luxation the greater 



