266 JOHN C. KOCH 



iiiuily carried by tlic teiiiur. Tlio discussion of the factors of 

 safety of the femur will be taken up in later paragraphs. 



The detailed description of the inner architecture has been 

 given. The conipai'ison of the mathematical analysis of the 

 femui' witli the inner architecture of the bone will be discussed, 

 the upper femur, shaft and distal portion being considered 

 separately. 



Significance of the inner architecture of the upper femur 



1. Frontal sections. Figure 21 shows a longitudinal frontal 

 section through the upper left femur, which is the mate of the 

 right femur on w^hich the mathematical analysis was made. 

 In this mid-section the system of tensile trabeculae, w^hich rises 

 from the lateral (outer) part of the shaft and crosses over the 

 central area to end in the medial portion of the shaft, neck and 

 head, is clearly shown. This figure also shows the compres- 

 sive system of trabeculae wdiich rises on the medial portion of the 

 shaft and crosses the central area to end in the head, neck and 

 greater trochanter. By comparing the position of these tw^o 

 systems of trabeculae shown in figure 21 with the lines of maxi- 

 mum and minimum stresses shown in figure 19, it is seen that the 

 tensile system of trabeculae corresponds exactly with the posi- 

 tion of the lines of maximum and minimum tensile stresses which 

 were determined by mathematical analysis. In a similar man- 

 ner, the compressive system of trabeculae in figure 21 corre- 

 sponds exactly with the position of the lines of maximum and 

 minimum compressive stresses computed by mathematical 

 analysis. It may be explained, that the maximum compressive 

 stresses are medial to the longitudinal axis; the minimum com- 

 pressive stresses are lateral to the longitudinal axis. Also, the 

 maximum tensile stresses are lateral to the longitudinal axis, 

 and the minimum tensile stresses are medial to this axis. These 

 relations are shown graphically in figure 19 a, in which the 

 approximate intensity of the tensile and compressive stresses at 

 various points is shown together with the direction in which 

 these stresses act at the given points. 



