²³Na and ²H magnetic resonance studies of osteoarthritic and osteoporotic articular cartilage

In this study, the short component of the ²³Na T₂ (T_2f) and the ²³Na and ²H quadrupolar interactions (υ_Q) were measured in bone-cartilage samples of osteoarthritic (OA) and osteoporotic (OP) patients. ²³Na υ_Q was found to increase in osteoarthritic articular cartilage relative to controls. Similar results were found in bovine cartilage following proteoglycan (PG) depletion, a condition that prevails in osteoarthritis. ²³Na υ_Q and 1/T_2f for articular cartilage obtained from osteoporotic patients were significantly larger than for control and osteoarthritic cartilage. Decalcification of both human and bovine articular cartilage resulted in an increase of ²³Na υ_Q and 1/T_2f, showing the same trend as the osteoporotic samples. Differences in the ratio of the intensity of the large ²H splitting to that of the small one in the calcified zone were also observed. In osteoporosis, this ratio was twice as large as that obtained for both control and osteoarthritic samples. The ²H and ²³Na results can be interpreted as due to sodium ions and water molecules filling the void created by the calcium depletion and to calcium ions being located in close association with the collagen fibers. To the best of our knowledge, this is the first study reporting differences of NMR parameters in cartilage of osteoporotic patients.