Fresh specimen of human femutn was measured with electrical technique to observeand analyze the stress - strain relationship under different loadings.In patients with transverse fracture of the femur treated with bone lengthening and internal fixation of medullary pins, the effects of loading compression and deformity endurance of the internal fixation were determined.It was found that when a loading of 980N was given, the compression of the medial side of the femoral shaft was- 8.04?106?1.96?106pa,higherthan posterior side.At the same time, the lateral side of the corresponding transverse section sustained-8.82?106?1.27?106pa,higher than ante-nolateral side.It was also shown that the stability of the fracture fragments is dependent upon a reliable internal fixation. When the closely contacted fractured ends were under loading, both bone and the medullary pins sustained the compression loading stress of which 62% was sustained by the medullary pins and 38% by the bone tissue.When the femur was lengthened,the filling of the defect in the compression stress area with a large Piece of bone tissue from the ileum could effectively increase the anti-bending loading and anri-compression strength o: the femur.Before the healing of fracture, the loading of the medullary Pm should not exceed 196N. Over loading is bound to result in the weakening and plastic deformty the pin metal,which is known as 'Baushinger effect'. Consequently, the medullary pin will be bonded and even broken to delay the healing of fracture. 原