Abstract
Machined cancellous bone specimens from human cadaver knees were tested under repetitive nondestructive axial compression. Loads were applied up to 50 per cent of the ultimate strength of the specimens predicted from their mineral content measured by photon absorption technique. The stiffness increased greatly between the first two compressions, and thereafter asymptotically approached a constant level. There was a 44 per cent median increase in the modulus of elasticity from compression No. 1 to compression No. 10. Steady state was apparently reached after the fifth compression with intervals between compression cycles of not more than 2 minutes. The results were reproducible, and the precision of the modulus of elasticity determined by double measurement at compression No. 10 was Ē ± 9.8 per cent (95 per cent confidence limits). The modulus of elasticity at steady state determined as the mean of compressions 6–10 was found to be Ē ± 5.6 per cent (95 per cent confidence limits). With both methods there was a strong linear correlation between the ultimate strength and the modulus of elasticity. The correlation coefficient was r = 0.95 (p < 0.005) and r = 0.99 (p < 0.001), respectively.
Due to the calculation error the figures for ultimate stress (US) in Table 2 and Fig. 4, and ultimate stress derived from the regression equations in Table 3 are reduced by a factor of two.
The present technique allows studies of viscous properties without engaging in otherwise time-demanding creep studies; yet in order to approach the issue quantitatively, the technical arrangement must be more meticulously prepared. Studies of viscous properties may, however, be of importance to evaluate the damping effect of cancellous bone and its role in the musculo-skeletal damping system.
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