Threefold Displacement of Tibia 



477 



is specially apt to occur in a knock-kneed subject, as the rectus femoris 



then inclines a good deal inwards in its descent to its insertion. And 



when it contracts with vigour it drags the patella a 



little outwards. An unusual amount of this outward 



movement lodges the bone on the front of the external 



condyle. Sudden flexion of the limb generally suffices 



to reduce the displacement ; but, if not, the leg should 



be straightened to the utmost, the thigh being flexed 



so as to slacken the rectus, when the bone can usually 



be slipped into its place. 



A characteristic threefold displacement of bead 

 of tibia occurs in cases of advanced and neglected 

 knee-joint disease. The limb rests on the outer side 

 with the knee bent, this being the most comfortable 

 position ; and, as the ligaments become softened, the 

 weight of the leg causes it to sink outwards, so the 

 inner femoral condyle projects more and more, and 

 the outer tibial tuberosity slides outwards from beneath 

 its condyle. The flexion of the joint continuing, and 

 the biceps, gastrocnemius, and the other posterior 

 muscles contracting at times with a spasmodic start, 

 the head of the tibia is steadily pulled into the pop- 

 liteal space. Lastly, the weight of leg and foot in this 

 flexed and everted position of the limb causes external 

 rotation of the tibia. Thus the threefold displacement 

 of the tibial head is outwards and backwards, with 

 some external rotation. If the disease subside, the 

 knee, even thus deformed, may be extremely service- 

 able. At any rate, forcible straightening will not 

 improve the shape ; to attempt it is to make the tibia 

 slide still further back, or to detach the femoral or 

 tibial epiphysis. If the deformity be extreme, ex- 

 cision may be needed before the limb can be made 

 straight and useful. 



A foreign body in the joint may be a piece chipped from a femoral 

 condyle or a semilunar cartilage ; a pendulous bud detached from 

 the synovial membrane, or an organised blood-clot. The substance is 

 apt to become suddenly caught between the femur and tibia, and* to 

 lock the joint. The sensory nerves are stretched and pained, and the 

 injury is likely to set up an attack of synovitis. The joint must be 

 opened at the side and the material extracted ; but if the trouble be 

 due to a loose fibro-cartilage (the inner most likely), the periphery of 

 the crescentic disc must be firmly sutured to the capsule, so as to 

 prevent further slipping. 



Supply. Arteries for the knee-joint come from the external 

 circumflex, the anastomotica magna, the popliteal (five in number, 



Fracture of patella ; 

 stretching of liga- 

 mentous union. 

 (HOLTHOUSE.) 



