LAMENESS IN THE HIND LEG 213 



Luxation of the Patella. 



Etiology and Occurrence. — This, the iwost common luxation 

 met with in tlie eijuine sul)ject, has been described by writers 

 as existing in many forms. Patellar disarticulation may be more 

 practically considered as momentary and fixed, regardless of the 

 position taken by the patella. Described under the title of false 

 luxation are recorded cases wherein the quadriceps (crural) 

 muscles become contracted in such manner that a condition sinui- 

 lating- true disarticulation of the patella obtains. Also, some 

 practictioners report cases of patellar luxation and refer to 

 pseudo-luxations, without clearly defining the conditions which 

 constitute pseudo-luxation. This has contributed to the extant 

 cause of misconception as to actual differences between luxation 

 and conditions simulating dislocation. 



Luxation of the patella is a condition wherein the articular 

 portions of the femur and patella assume abnormal relations 

 whether such displacement of the patella be momentary and 

 capable of spontaneous reduction, or fixed and requiring cor- 

 rective manipulation. Spasmodic contraction of the crural mus- 

 cles which sometimes retains the patella in such position that 

 the leg is rigidly extended, does not in itself constitute luxation 

 of the patella; and unless this bone becomes lodged on the upper 

 portion of a femoral condyle or laterally displaced out of its 

 femoral groove, luxation cannot be said to exist in the horse. 

 These are sub-luxations. 



Occasionally one may observe in suckling colts outward luxa- 

 tion of the patella wherein there is history of navel infection 

 and no marked evidence of rachitis is present. Some of these 

 cases recover. In a unilateral involvement of this kind in a 

 three-month-old mule colt, the author observed a case wherein 

 an unfavorable prognosis was given and destruction of the sub- 

 ject advised, because of the extreme dislocation of the patella. 

 This colt, however, was not destroyed and in three weeks had 

 apparently recovered. No treatment was given in this instance ; 

 the colt was allowed the run of a small pasture with its dam and 

 in time it matured, becoming a sound and servicea])le animal. 



Classification. — Two forms of true patellar luxation in the 



