234 JOHN C, KOCH 



Effects of external load 



1. Shearing and axial loads. Referring to figure 14, the load 

 transmitted to the lioad of the femur is distributed over the 

 upper surface of the head between points G and H, as shown in 

 longitudinal section, and practically all of the head of the femur 

 above the point E is in bearing with the acetabulum, receiving 

 a load that is practically uniformly distributed. 



As the joint surface is smooth, the forces applied to the head 

 of the femur are everywhere perpendicular to the surface of 

 the femur-head. All the forces at the joint may, for simplicity, 

 be considered as acting in the line AB, in the center of pressure 

 of the femur-head, and acting as a concentrated load W, which is 

 the sum of all the vertical components of the forces acting at the 

 joint. The longitudinal axis of the femur, EDCB, is nowhere 



TABLE 5 

 Mechanical properties of the normal femur 

 Column 1 indicates the section, the position of which is indicated by the corre- 

 sponding number in figures 14, 17, 18, 19, 19a, 20 and 27 

 Column 2 gives the area of the entire section in square inches 

 Column 3 gives the area of the section occupied by compact bone 

 Column 4 gives the area of the section occupied by spongy bone 

 Column 5 gives the density of the spongy bone of the section as compared with coin- 

 pact bone 

 Column 6 gives the area of the spongy bone of the section in terms of compact bone 

 Column 7 gives the total area of the section in terms of compact bone 

 Columns 8 and 9 give the distance from the axis A- A to the extreme tension and 



compression fibers, respectively 

 Columns 10 to IS give the moments of inertia (in biquadratic inches) for the com- 

 pact bone, the spongy bone, the equivalent of the spongy bone and the combined 

 or total moment of inertia of the section, respectively . all except column 11 being 

 expressed in terms of compact bone 

 Column 14 gives the value of the section modulus, which is the strength ratio of the 

 section with respect to axis A-A. This is obtained by dividing the moment of 

 inertia about axis A-A by the distance from this axis to the extreme fiber of the 

 section 

 Columns 15 to 18 give the moments of inertia about axis B-B as indicated, all ex- 

 cept column 16 being expressed in terms of compact bone 

 Columns 19 and 20 give the distance from the axis B-B to the extreme anterior and 



posterior fibers, respectively 

 Column 21 gives the value of the section modulus {strength ratio) with respect to 

 axis B-B. This is obtained by dividing the moment of inertia of the section 

 about this axis by the distance from this axis to the extreme fiber 



