The in-vitro static load-displacement properties of the intact and the injured human lumber intervertebral joint have been investigated in a loading apparatus which allows entirely unconstrained relative displacement between the joint members. The spatial relative displacement produced by a given load, alone or in combination with another load (preload), were measured using 14 specimens and emphasizing strict control of the secondary variables which are known to affect the results. An attempt has been made to interpret the results in terms of the relative load-bearing roles of the disk, the facets and the posterior ligaments as a function of the type of load. The results indicate that the disk is the major load-bearing element in lateral and anterior (with respect to a fixed superior vertebra) shears, axial compression and flexion, while the facets play a major role in posterior shear and axial torque.

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