TUBEECULOSIS OF JOINTS. 133 



external violence slight amounts of traumatism are constantly 

 occurring, leading to inflammation and a favourable soil for the 

 growth of the bacilli. 



It is well to remember that the synovial membrane itself only 

 lines the inner surface of the ligaments up to the margin of the 

 articular cartilage. It is only in cases of disease that the 

 membrane tends to creep over and to veil the articular cartilage 

 a condition so common in tuberculous arthritis. 



Tuberculosis leads to the destruction of ligaments and to sub- 

 sequent pathological dislocations. The direction in which the 

 bones are displaced depends greatly upon the comparative 

 strength of the muscles acting upon them. Thus, for instance, 

 in the case of the knee-joint the tibia is drawn backwards and 

 flexed by the ham- strings which are stronger than the extensors, 

 and is rotated outwards by the biceps, the action of which is more 

 powerful than that of the internal rotators of the leg, namely the 

 sartorius and popliteus. 



