POROELASTIC CREEP RESPONSE ANALYSIS OF A LUMBAR MOTION SEGMENT IN COMPRESSION

The nonlinear three-dimensional poroelastic creep response of a lumbar motion segment under a constant axial compression (400, 1200, or 2000 N) is investigated for a period of 2 h. The role of facet joints, str ain-dependent variable permeability, boundary pore pressure, and coupl ed sagittal rotation on response is studied. Biomechanics of annulus e xcision, nucleotomy, and facetectomy are also investigated. Both mater ial and geometric nonlinearities are considered. The annulus bulk is m odelled as a nonhomogeneous composite of collagenous fibers and annulu s bulk. As time progresses, axial displacement increases, pore pressur e decreases, annulus bulk undergoes larger compressive stresses, fiber layers become slack, and facets carry larger loads. Surgical alterati ons markedly soften the temporal response and increase facet forces. I n contrast, the strain-dependent variable permeability and boundary po re pressure stiffen the response and decrease forces on the facets. Ch anges in the nucleus fluid content, facet joints, boundary pore pressu re, and disc permeability markedly influence the lumbar biomechanics. Copyright (C) 1996 Elsevier Science Ltd.