PATELLAR DESMOTOMY 225 



the cure of stringhalt after having successfully applied it for 

 this defect of locomotion, but up to the present time little 

 is known of its real worth in this connection on account of 

 the dearth of data. 



INDICATIONS.— Patellar desmotomy has, therefore, 

 two indications, namely; Habitual luxation of the patella of 

 young animals, and stringhalt of the mature horses. For 

 the former it is a radical cure as well as a scientific operation, 

 while for the latter its application is empirical because the 

 method by which it effects the cure is not known. 



Habitual luxation of the patella is a congenital weakness, 

 a relaxation, of the mechanism holding the patella to the 

 femoral trochlea. The ligaments laterally and inferiorly, 

 and the muscles superiorly are too lax to prevent the bone 

 from slipping from its groove, and as the external wall of the 

 groove (the external lip of the trochlea) is relatively small, 

 the luxation is outward. In exaggerated cases the relaxa- 

 tion will let the bone slip freely across the whole trochlea. 

 When the condition prevails until the patient grows to ma- 

 turity the trochlea may be worn into a perfectly flat sur- 

 face; as a trochlea it becomes obliterated. The desease is 

 seen in foals, calves, and pups, especially in. weak rickety 

 rubjects. Its tendency- is toward improvement as an im- 

 proved diet, and medical treatment of the young and its 

 mother, promotes the general strength. If the relaxation is 

 pronounced the patella slips in and out at every step with- 

 out preventing locomotion, but if a less degree of relaxation 

 exists the patella slips over the external lip of the trochlea 

 and locks the motion of the stifle so effectually as to prevent 

 extension of the leg. If bilateral, locomotion is impossible 

 except when the patella is accidentally or manually restored 

 to its proper position. Generally the luxation will promptly 

 recur and- thus perpetuate a pitiful state of decrepitude. 

 The operation is indicated only when the patella locks itself 

 over the trochlea. If the relaxation is so pronounced as to 

 permit the bone to slip freely to any position without lock- 

 ing, the operation can do no good, because its only service 

 is that of preventing the patella from remaining in the state 

 of luxation. The cure of the relaxation will depend upon 

 gain in general strength as well as local strength of the 

 relaxed structures. 



Certain treatments, local and general, should precede the 

 operation in hope of curing the defect by easier means. It 

 is only when the condition persists that the operation should 

 be performed, but it should never be delayed until the slip- 



