LUXATION OF THE SCAPULO-HUMERAL JOINT. 63 



secondly, because it is often impossible to maintain the reduction and to 

 preserve complete immobilisation of the injured joint. 



Treatment should not be undertaken except in young animals which 

 have not yet attained full development. 



In attempting to reduce outward or inward luxation of the tibia the 

 animal should be cast on the side opposite to the lesion. Counter- 

 extension is practised by passing a length of webbing around the limb in 

 the region of the groin ; extension in the direction of the length of the 

 femur by means of a loop of webbing fixed to the cannon bone : the 

 operator uses both hands in endeavouring to replace the head of 

 the tibia. 



In forward luxation of the tibia counter-extension is effected by 

 means of a loop of webbing passed above the hock and drawn forward. 

 Extension is made backwards in an oblique direction, the operator again 

 being left free to effect reduction with both hands. 



Eeduction of backward luxation of the tibia is still more difficult, in 

 consequence of the contraction of the mass of muscle at the back of 

 the thigh. 



Plaster bandages are the most convenient means of immobilising the 

 parts after reduction. 



LUXATION OF THE SCAPULO-HUMERAL JOINT. 



This luxation, like that of the femoro-tibial articulation, is exceptional. 

 It may assume one of two forms, depending on whether the head of the 

 humerus is displaced inwardly, or tow^ards the back of the glenoid cavity ; 

 but as a rule luxation occurs inwardly. Forward luxation of the head 

 of the humerus is almost impossible, in consequence of the resistance 

 offered by the tendons of the flexor brachii and antea spinatus muscles. 

 Similarly, luxation outwards is very difficult, the tendon of the postea 

 spinatus being very powerful and offering enormous resistance. 



Inwardly, on the other hand, the insertion of the subscapularis is 

 much less powerful, and there is no real opposition to movement of the 

 head of the humerus. 



Causation. Violent mechanical shocks transverse to the upper third 

 of the arm may, by sheer force, displace the head of the humerus in an 

 inward direction, causing rupture of the internal wall of the capsular 

 ligament and of the subscapularis muscle. Jumping from high to low 

 ground and falling on the front limbs tend to disj)lace the glenoid cavity 

 in front of the head of the humerus, and often result in luxation of the 

 bone in a backward direction, a luxation, however, which almost always 

 assumes a postero-internal direction. The commonest causes of these 

 luxations are the sideward falls of animals which have attempted to 



