Proteoglycan depletion and magnetic resonance parameters of articular cartilage

Calcium ions and various amounts of proteoglycans were removed from porcine articular cartilage explants using ethylenediaminetetraacetic acid or guanidinium chloride solutions. The water proton magnetic parameters such as T(1) and T(2) relaxation times, diffusion (D), and magnetization transfer (M(S)/M(0)) were then measured by 1D MR microscopy on native specimens, after incubation in the extracting solutions and after final reconditioning in a physiological saline. While the replacement of the interstitial fluid by the treating solutions strongly affected the various MR parameters, calcium depletion did not show any influence on the MRI appearance of the chondral tissue. Interestingly, only the longitudinal relaxation time T(1) and the diffusion coefficient D were seen to be sensitive to an extensive proteoglycan depletion of the tissue. Our results indicate that a modest proteoglycan depletion, as it occurs in the early stage of a pathological cartilage degradation, has little relevance to the above MR parameters. Further MRI studies on the macromolecular components of cartilage are, therefore, necessary for a better understanding of the interaction mechanisms between water and extracellular matrix that might lead to the early diagnosis of the cartilage damage.