COMPRESSIVE PROPERTIES OF THE CARTILAGINOUS END-PLATE OF THE BABOON LUMBAR SPINE

The viscoelastic behavior of the cartilaginous end-plate of the baboon (Papio anubis) was studied in an experiment on compressive creep. Dat a were analyzed with the biphasic poroviscoelastic constitutive theory to assess the relative contributions of flow-dependent and flow-indep endent viscoelastic mechanisms to the observed creep behavior. Materia l coefficients describing the equilibrium compressive behavior (H(A)) and both flow-independent (c, tau1, and tau2) and flow-dependent (k) v iscoelastic effects were determined for the end-plate by the curve-fit ting of the theoretical solution to the experimental creep data. Bioch emical analyses were performed to test for potential relationships bet ween material properties and composition which may give rise to the vi scoelastic behavior of the end-plate. The results indicate that the ca rtilaginous end-plate has a hydraulic permeability of 14.3 X 10(-14) m 4/N-s, which is associated with rapid transport and pressurization of the interstitial fluid in response to loading and an increased emphasi s on flow-independent viscoelastic effects. Biochemical analyses for w ater, sulfated glycosaminoglycan content, and hydroxyproline indicate that the end-plate of the baboon is compositionally similar to the car tilaginous end-plate in humans. Interpretation of the mechanical and c ompositional data suggests that fluid pressurization in the cartilagin ous end-plate may be important in the maintenance of a uniform stress distribution across the boundary between vertebral body and interverte bral disc.