124 CLINICAL APPLIED ANATOMY. 



In dislocation backwards of the tibia, the posterior ligament 

 of the knee joint is as a rule torn, and many of the other ligaments, 

 particularly the crucial, must partially or completely give way. 

 The vessels and nerves of the popliteal space are severely 

 pressed upon by the posterior margin of the head of the tibia, in 

 backward dislocation of this bone, or are tightly stretched in the 

 popliteal notch in forward displacement of the tibia. In both 

 cases, the pulse in the tibial arteries may be obliterated. 



Dislocations of the Semilunar Cartilages. Displacement of 

 the internal semilunar cartilage is undoubtedly more common 

 than that of the external. As a rule, the nbro-cartilage is torn 

 away from its anterior attachment to the front of the spine of the 

 tibia, and from the anterior third of its marginal attachment. 

 The anatomical explanation of the frequency of the displacement 

 of the internal cartilage may be the following : First, that this 

 cartilage is perhaps more insecurely attached than the external, 

 particularly so far as its marginal attachment to the head of the 

 tibia is concerned ; secondly, because in the position and move- 

 ment of the joint in and during which a dislocation of the car- 

 tilage occurs, namely, flexion at the knee with rotation outwards 

 of the leg, the lower end of the femur is driven as it were against 

 the circle of the cartilage and tears it from its attachment, forcing 

 it away from the interior of the joint. Sometimes the prominence 

 formed by it after dislocation on the inner side can be distinctly 

 palpated and the joint is locked, so that extension cannot be 

 brought about until the cartilage has been forced into position. 



If dislocation of the cartilage constantly recurs, its removal 

 operation as a rule brings about a very satisfactory result, the 

 loss of the cartilage in no way affecting the function of the 

 joint even when a small portion near the posterior attachment is 

 left behind. 



Dislocations at the Ankle- Joint. Owing to the conformation of 

 this joint, dislocation of the whole foot including the astragalus 

 can only occur backwards or forwards, apart from an accompanying 

 fracture, lateral dislocations of necessity requiring a solution of 

 continuity of one of the bones. 



