960 OTWARD LUXATION OF THE PATELLA. 



The degree of lameness varies greatly. Sometimes it is necessary 

 to look carefully in order to recognise it at all, but in other cases 

 the patella is seen to remain fast for a moment and then suddenly 

 descend. 



The symptoms are different when the patella remains continuously 

 fixed above the internal lip of the trochlea, i.e., in stationary upward 

 luxation. Loose-jointed, weak foals with straight stifles are oftener 

 affected than well-developed horses. In consequence of violent 

 contraction of the vasti and rectus muscles occurring when rising 

 or falling, kicking outwards, or extending the limb, the patella passes 

 too far upwards, and becomes fixed. Fixation of the patella on the 

 upper portion of the internal lip of the trochlea is at once followed 

 by extension of all the joints of the limb and inability to flex them, 

 even with external assistance. The limb is therefore directed back- 

 wards, and cannot be advanced. If the animal is made to advance, 

 the fetlock alone is slightly flexed, and the toe, directed backwards, 

 is trailed on the ground. If both limbs are affected at the same 

 time, the animal stands as though rooted to the spot and cannot 

 advance ; when only one limb is affected, it can still hop forwards on 

 the other leg. Locally, very little deformity can be seen at the 

 stifle which is fully extended. By palpation, the straight patellar 

 ligaments are found very tense, and the internal trochlear lip and 

 patella are in close contact and immovable. If, whilst the patella 

 occupies this position, the rectus and vasti muscles be relaxed, the 

 patella may slip from the lip of the trochlea of the femur and stand 

 upright on its lower border, a condition which in man is known as 

 vertical luxation of the patella. The symptoms are so characteristic 

 that stationary luxation can be diagnosed from a distance, and is 

 only likely to be mistaken for dislocation of the biceps femoris 

 muscle in oxen, in which, however, the extended position is not so 

 well marked, and the limb can always be flexed, if only to a slight 

 extent, while the trochanter may be felt under the skin, and the 

 patella at least moved sideways. In luxation, on the other hand, 

 it is absolutely immovable, and lies too high. 



In some instances probably the straight ligaments of the patella 

 have become elongated, as happens in pregnant animals by con- 

 tinual confinement to the stable, or in others while passing 

 through severe attacks of debilitating diseases like influenza, 

 strangles, and pneumonia. Not infrequently such elongation is 

 congenital. 



The prognosis is generally favourable. In weakly foals, and in 

 animals attacked during convalescence, both momentary and per- 



