1. Static and dynamic loading tests were made on fifty femora from dissecting-room, adult cadavera of known sex, age, and race. The cause of death was also known, and no grossly pathological bones were used. All bones were not loaded to failure.
2. Most of the bones were "stresscoated" so that the tensile deformation pattern produced during the tests was obtained.
3. In each test the magnitude, point of application, direction, and type of force, as well as the orientation of the bone, were the controlled variables. These factors, however, were not uniform in all tests.
4. Vertical transverse fractures of the femoral neck were produced by static vertical loading of the fensoral head. No torsional force was involved.
5. Static vertical loading of the femur clearly demonstrated its behavior as an elastic body.
6. Subcapital, intertrochanteric, abduction, horizontal, and oblique fractures of the neck were obtained by static and dynamic loading of the greater trochanter, with the bone in slightly different positions. No torsion was involved in the fracture mechanism.
7. Spiral fractures of the shaft were produced by static torsion loading.
8. Transverse fractures of the shaft were produced by cross-bending loads.
9. The "stresscoat" deformation patterns obtained in the fractured bones clearly demonstrated that, with the possible exception of the abduction type, each of the various kinds of fractures arose from the failure of the bone as the result of the tensile strain.
10. Contrary to a rather general belief, transverse fractures of the femoral neck are not produced by torsional forces. There is no mechanism in the living body that can produce torsional strain in the femoral neck.
11. Shearing force is also not involved in the fracture mechanism although, depending upon the obliquity of the fracture line, it can be a serious factor in the treatment of such fractures.
12. Spiral fractures of the shaft are merely other examples of the failure of the bone as the result of the tensile strain. They do not arise from shearing stress.