PRACTICAL CONSIDERATIONS : T'HE KNEE-JOINT. 



411 



one or other condyle becomes prominent, as does, on the opposite aspect of the 

 limb, the head of the fibula or the inner tuberosity of the tibia. The patella, owing 

 to the shortness and strength of its ligament, is carried with the tibia. The lateral 

 diameter of the joint is increased. The foot is apt to be rotated in the direction of 

 the luxation owing to the tension of the biceps in the outward and of the popliteus 

 and inner hamstrings in the inward variety. 



Dislocations by rotation have also occurred. 



Internal semilunar 



cartilage 



Crucial ligaments 



External semilunar 

 cartilage 



Cavity of knee-joint 



Superior tibio-fibular 

 articulation 



Tibia Fibula 



Frontal section through knee-joint, showing articulating surfaces and epiphyseal lines. 



In the various forms of luxation the crucial, the lateral, and the posterior liga- 

 ments and the biceps and gastrocnemius muscles suffer most severely ; the popliteus 

 and semimembranosus less so. They are often compound, and may for that reason 

 necessitate amputation. The injury to the ligaments leaves the joint weak and 

 insecure for a long time. 



Subhixatioti of the semihniar cartilages occurs usually when the leg is fixed, 

 th^ knee slightly flexed, and the femur rotated upon the tibia, because the move- 

 ments of flexion and extension take place between the femur and these cartilages, 

 which, therefore, follow the motion of the tibia ; whereas in rotation — the move- 



