Abstract
The experimental technique reported here was developed to provide data for mathematical models simulating the mechanical properties of the human lumbar spine. Dynamic compression tests on intervertebral joints from the lumbar region of sheep (body mass 50–70 kg) were used to assess the technique as human cadaveric material was not readily available. The loading pattern on the human spine during walking was simulated by exposing each joint to dynamic compression loads of 750 ± 250 N at a frequency of 1 Hz. The joints were tested at body temperature in Tyrode's solution. In order to detect the dominant viscoelastic properties of each joint the energy dissipation, spring stiffness, and creep response were monitored for twenty-eight hours.
The results of these long term axial compression tests on lumbar intervertebral joints from sheep show that the joint rapidly loses its capacity to dissipate strain energy. After quarter of an hour the energy dissipation (hysteresis) of the joint has dropped from 37 per cent to less than 10 per cent. The spring stiffness of the joint under these compressive loads starts at 6 MN m–1 increasing to 12 MN m–1 by the end of the test. The characteristic time for the creep response (retardation time) occurs after two and a quarter hours.
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