Magnesium whitlockite deposition in articular cartilage: a study of 80 specimens from 70 patients.

OBJECTIVE To examine articular cartilage from a number of joint sites, using a large sample group, for the presence of magnesium whitlockite crystal deposition. METHODS Articular cartilage specimens were taken from a total of 70 patients. The majority of specimens were taken from femoral heads, with smaller numbers from femoral condyle, tibial plateau, radius, ulna, and several small peripheral joints. Normal and osteoarthritic articular cartilage specimens were obtained from patients undergoing prosthesis replacement or amputation. Specimens were resin embedded and examined using transmission electron microscopy and x ray microanalysis. RESULTS Magnesium whitlockite crystals were identified, on the basis of morphology, size and elemental composition, in articular cartilage from all sites sampled. The distribution of crystals was similar in all samples (restricted to the superficial zone), although the density of deposition was extremely variable, with the greatest density observed in femoral head specimens. No magnesium whitlockite crystals were observed in osteophytic or epiphysial cartilage. CONCLUSIONS This study demonstrated the widespread extent of magnesium whitlockite deposition in human articular cartilage, albeit at much lower density than previously reported in femoral head articular cartilage. In consideration of possible roles for these crystals in articular cartilage, it is concluded that an opportunistic mode of formation, possibly influenced by mechanical stresses, would be most plausible.