Cartilage softening is an early manifestation of osteoarthritis. The unique structure and composition of cartilage provides its ability to withstand the enormous amounts of load present in in vivo situations. Early cartilage degeneration is associated with loss of proteoglycans. Sodium spectroscopy and imaging is capable of tracking the amount of sodium ions present in cartilage. Characterization of sodium ion migration from cartilage under compression would provide information about the conditions that lead to the deterioration of its load bearing ability. We have studied sodium spectroscopy and imaging of bovine articular cartilage under compression. We found that 40% of sodium signal reduction occurs in the first 5% minutes of application of pressure (100 psi) and reaches steady state at about an hour. During application of pressure T1 and slow T2 components are increased and the fast T2 component is almost unchanged. We have performed similar studies on proteoglycan degraded cartilage. We are currently in the process of applying this method in vivo to determine the cartilage softening in normals as well as subjects with arthritis.
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