Morphometric studies on synovium in advanced osteoarthritis: is there an association between apatite-like material and collagen deposits?

OBJECTIVE

To look for the frequency and the influence of apatite-like deposits in the synovial membrane of advanced osteoarthritic joints.

METHODS

Synovium of 16 joints undergoing total arthroplasty for advanced primary osteoarthritis was embedded in paraffin. Adjacent sections were stained with alizarin red S, Mowat's pentachrome, Hematoxylin-eosin and Gomori to show apatite-like deposits, collagen, cartilage fragments, vessels, cells and iron respectively. Histomorphometry was carried out for the apatite-like and collagen deposits by the point counting method; the density of vessels and cells was also quantified.

RESULTS

14 out of the 16 specimens contained apatite-like material, mostly on the synovial surface or just beneath. There was no correlation between the apatite-like deposits and any other measured histological parameter (fibrosis, villus length, synovial lining cell width, density of synovial vessels or cells). Interestingly, the p value for a correlation between the amounts of apatite and collagen deposits was close to significance (r = 0.53; p = 0.055) when the relative volume of the apatite-like material was less than 1.2% (n = 13).

CONCLUSIONS

Apatite-like deposits are frequently observed in the synovium of late stage osteoarthritis. Although not statistically significant, these results suggest a possible association between apatite-like and collagen deposits when the amount of apatite deposits is low. Further quantitative studies are recommended to investigate this observation.