" LUXATION " OV THE PATELLA. 



441 



glided into the depression separating the two trochlear ridges ; finally, 

 the internal ligament no longer opposing any resistance, the corre- 

 sponding side of the patella rises and easily leaves the flattened surface 

 before described. 



As soon as this happens the flexors of the limb act, the superficial 

 gluteus relaxes, the patella falls into its groove, and straightway com- 

 mences its descent." 



Should, however, the animal attempt to move, and the patella 

 refuse to leave its seat, the symptoms of luxation at once appear. 



In replying to the question of why luxation occurs, M. Violet 

 regards the primary cause as probably imperfect muscular action — 

 either cramp or paralysis. In other words, luxation is due either to 

 (i) spasmodic contraction or cramp of the inferior fibres of the vastus 

 internus, which ma\' be sufficient to counteract the efforts of the super- 

 ficial gluteus ; or (2) paralysis, feebleness, or injury to the superficial 

 gluteus, which interfere with, render feeble, or disorder its contraction. 



To reduce the displacement, 

 M. Violet directs pressure to be 

 exercised backwards and in- 

 wards, whilst the horse is thrust 

 back by an assistant. 



In Germany two forms of 

 luxation of the patella have 

 been distinguished — (i) momen- 

 tary luxation, and (2) perma- 

 nent luxation. The former is 

 attributed to abnormal flatness 

 of the upper surface of the 

 trochlea before alluded to, or to (^,: 

 excessive tension of the lateral 

 ligaments of the patella ; the 

 latter to detention of the patella 

 on the upper margin of the in- 

 ternal trochlear ridge. The symptoms are similar to those already 

 alluded to. 



Moller describes a form of luxation whose symptoms are identical 

 with those in my own case. He says, " I have lately seen a peculiar 

 luxation of the patella upwards and outwards. The leg was extended 

 and directed forwards, flexion was impossible, but weight could be 

 placed on the limb. When moving the limb was carried stiffly, without 

 movement of the hip, stifle, or hock-joint, and placed far forwards ; 

 the progress of the body then brought the limb perpendicularly below 

 the hip-joint, but the leg could not be placed behind this point either 

 actively or passively. Slight pressure on the outer border of the 

 patella sufficed to return it to its position, upon which the horse could 

 advance several steps in the ordinary way ; suddenly, however, the 

 patella again became displaced, and all the symptoms returned. 



" A post-mortem examination showed the inner lateral and the 

 inner and central straight ligaments to be diseased and elongated, 

 allowing the lower edge of the patella to ride up over the inner lip of 



Fig. 56. 



