The strength of human compact bone as revealed by engineering technics

Abstract

1. 1. The average ultimate tensile strength (Ib./in. 2) and percentage elongation under tension were determined for 242 specimens of compact bone from the femurs of seven white, adult male cadavers whose age and cause of death were known. 2. 2. All specimens were of a standardized size and were tested by approved engineering technics which are described. Half of the specimens were air dried at room temperature and tested dry while the other half were placed in a physiologic saline solution and tested wet. 3. 3. Drying the specimens increased their average tensile strength (Ib./in. 2) but reduced their percentage elongation under tension. The percentage elongation under tension is a good index of the energy (in. Ib./in. 3) absorbed by the specimen up to the time of fracture. 4. 4. The samples tested wet had a greater percentage elongation under tension, and hence greater energy-absorbing capacity, than did the dry samples. This is also evident from the shape of the stress-strain curve which is a straight line to fracture for the dry samples but a curve for the wet specimens. 5. 5. The specimens from the middle third of the femoral shaft had the greatest average tensile strength and energy-absorbing capacity, as indicated by their percentage elongation under tension. 6. 6. The age of the individual seemed to have little influence on the tensile strength and energy-absorbing capacity of the femur. 7. 7. Similar comparative studies on all the long bones of the inferior extremity of three adult male cadavers revealed that the tibia had the greatest average tensile strength (Ib./in. 2) and the fibula the greatest percentage elongation under tension. The femur was the weakest in these respects. 8. 8. As in the femur the middle third of the tibia and fibula had the greatest average tensile strength (Ib./in. 2). The middle third of the tibia also had the greatest percentage elongation but in the fibula, and also the femurs of these individuals, the proximal third of the bone had the greatest elongation. These comparative results should be considered as tentative but also indicative of a trend. 9. 9. The values for the physical properties of the wet-tested specimens probably more nearly approximate similar properties in living bone than do those of dry-tested specimens. 10. 10. The significance and implications of the tests are discussed.