Biomechanical responses of normal and delipidized articular cartilage subjected to varying rates of loading

Abstract

In alignment with the proposition that a lipid layer overlays the superficial zone of the articular cartilage, this study presents the consequence of the removal of lipids on the load-bearing characteristics of the tissue. Both normal unmodified and delipidized cartilage matrices were loaded at four different strain-rates of 1.3×10 -4 /s, 1.3×10 -3 /s, 1.3×10 -2 /s, and 1.3×10 -1 /s to strains of no more than 40%, to compare their stress-strain and stiffness-strain-rate characteristics. Our results demonstrate that at the lowest strain-rate of 1.3×10 -4 /s, the stiffness of the delipidized matrix was lower in comparison to that of the normal unmodified tissue. This response was reversed at higher strain-rates of 1.3×10 -2 /s and above. We conclude, therefore, that in general, at physiological rates of loading, the depletion of lipids from the articular cartilage reduces its compliance by at least 25%. We infer from the present study that this degenerative stiffening is an important contributing factor in impairing the tissue's load processing function in osteoarthritic joints.