56 CLINICAL APPLIED ANATOMY. 



middle and lower thirds of its shaft, and it is here that the 

 tension of the calf muscles and the weight of the body conspire 

 to produce the maximum deformity. Similarly the natural 

 forward and outward curve of the femur may become exaggerated 

 and softening of the upper part of the shaft, near the trochan- 

 ters, or of the neck may cause the latter to sink under the 

 weight of the body, and produce the condition known as coxa 

 vara. 



The mechanism of production of knock knee is disputed, and 

 possibly not always the same. It may, as already mentioned, be 

 caused by faulty posture which allows the end of the femur to 

 bend inwards, or it may be due to laxity of the internal lateral 

 ligament of the knee joint, which allows the bone to become 

 separated on the inner side. The deformity is perpetuated by 

 the unrestrained growth of the adjacent inner parts of the femur 

 or tibia or of both. This growth is usually supposed to occur 

 at the epiphysis, but some believe that the diaphysis is at fault. 

 As a result, instead of the weight of the body being transmitted 

 through the knee joint and shaft of the tibia to the centre of the 

 ankle, it falls outside the knee joint, aggravating the deformity 

 and also inducing flat foot. 



The pelvis, when deformed by rickets, usually undergoes antero- 

 posterior compression ; the weight of the trunk transmitted from 

 above causes projection of the sacral promontory and flattening 

 of the cavity. A reniform outline is thus produced. Sometimes, 

 however, especially if the rickety softening occur after the acquire- 

 ment of walking, a trefoil pelvis similar to that of osteomalachia 

 results. This is due to the additional pressure caused by the 

 indriving of the heads of the femora against the acetabula. 



The epiphyses of the upper limb are enlarged first because the 

 child crawls before learning to walk. The bones of the forearms 

 may become bent with convexity outwards if the child is in the 

 habit of supporting the weight of the body with the hands, or of 

 crawling on hands and knees. The humerus also becomes curved 

 outwards, the curve corresponding to the point of attachment of 

 the deltoid muscle. 



