286 JOHN C. KOCH 



weight. The paths and amounts of the maximum internal 

 stresses are computed in this normal fenmr and demonstrated to 

 agree exactly witli the position of the trabeculae in the upper 

 femur. 



The load on the femur-head in the normal, standing position 

 is 0.3 of the body weight (on each femur) : in walking, the weight 

 carried alternately by the loaded femur-head is approximately 

 0.8 of the body weight: in running, the dynamic effect of the 

 sudden application of the load produces stresses twice as great 

 as in walking, or the effect is the same as double the static load 

 of walking, or 1.6 times the body w^eight. In the particular 

 case analyzed, the body weight being 200 pounds, the stresses in 

 the loaded femur due to standing, walking and running are those 

 due to a load on the femur-head of 60, 160 and 320 pounds, 

 respectively. 



Hence, to determine the stresses produced in standing, walk- 

 ing or running, the stresses produced in the femur at any section 

 by the assumed load of 100 pounds are multiplied by 0.6, 1.6 

 and by 3.2, respectively. 



The femur is shown to have the external form and internal 

 structure to resist economically the stresses produced by the 

 preponderant load, which is that on the femur-head due to the 

 body weight in running. The spongy structure of the head of 

 the femur resists in the most economical manner the vertical 

 and horizontal shearing stresses which are greatest in the head 

 and neck. In the shaft, where the shearing stresses are a mini- 

 mum and the stresses due to bending moment relatively large, 

 the compact bone of the hollow shaft resists these stresses most 

 efficiently because the greater the distance of the bone from the 

 neutral plane the greater the resisting strength of the bone. Fi- 

 nally, the large expansion of the lower end of the femur, to render 

 the hinge-action of the knee joint strong against lateral bending, 

 is produced by the transition of the compact bone to spongy 

 bone requiring but a slightly greater amount of bony material 

 for greatly increased stiffness. Thus the compact and spongy 

 bone act in unison to produce the maximum of strength with the 

 minimum of material. 



