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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.