272 JOHN C. KOCH 



sity of the inaxiinuni unit-stresses as the distal end is approached. 

 The considerable increase in the gross area of the transverse 

 sections of this portion of the femur is secured with practically 

 no increase in the amount of bony material in these sections until 

 section 72 is reached. While the direct compressive strength of 

 the lower femur is somewhat decreased by the change to spongy 

 bone, the stiffness or resistance to bending in any direction is 

 increased greatlj^ The stiffness of the femur at section 75 is 

 more than five times as great as that of section 52, although the 

 area of the cross section in terms of compact bone is only slightly 

 more than double that of the latter. In the distal portion of 

 the femur in which the expansion takes place, there is no increase 

 in the amount of bony material used until the lowermost 1.25 

 inches is reached. 



A well-recognized principle in mechanics is illustrated by the 

 expanded lower end of the femur, by means of which the load 

 transmitted from the femur to the tibia is evenly distributed 

 over an area much greater than that of the shaft through which 

 the load has passed, thereby reducing the danger of rupture at 

 the joint. This is analogous to the foundation of large area 

 upon which all columns rest, in order to distribute the concen- 

 trated load over an area having a comparatively low supporting 

 power. By means of this expanded bearing there is greater 

 stability at the joint, and greater resistance against lateral 

 bending. 



2. Conclusions. 1. The inner architecture of the distal por- 

 tion of the femur is well adapted for the diminishing intensity 

 of the direct stresses, to which it bears a somewhat parallel 

 relation. 



2. The loads transmitted through the femur are distributed in 

 a manner that conforms to the requirements of mechanics in 

 securing strength and stability with economy of material. 



3. The inner structure of this portion of the femur is economi- 

 cally adapted to the mechanical requirements of this portion of 

 the femur. 



