[The place of apatite in rheumatic diseases. Study of 25 cases by x-ray microanalysis and scanning electron...

The importance of "apatite deposition disease" among the arthropathies has been recognized for some years: it is well known that X-ray microanalysis (XRMA) is an efficient method of determining the elemental constitution of microcrystalline deposits obtained from synovial fluids or from tendon washing solutions during examination in scanning electron microscopy. In all 25 patients studied (11 intraarticular and 14 extraarticular samples), alizarine red S staining was positive and XRMA confirmed the diagnosis of apatite deposition by determination of the phosphorus/calcium (P/Ca) ratio in the deposits. In the 25 patients the mean values obtained for the P/Ca ratios were situated between 0.362 and 0.450, with a general mean value of 0.411, i.e. a ratio clearly lower than the P/Ca ratio of pure hydroxyapatite specimens (0.438) measured in identical conditions. This apparent discrepancy seems to be related to the probable presence of carbonated apatites. The study confirmed the presence of apatite microcrystals in intra- and extraarticular location; in the first condition, these were generally found in patients with severe destructive arthrosis, whereas in the second condition the calcifications derived from supraspinatus tendons.