Osteoarthrosis. Changes of bone, cartilage and synovial membrane in relation to bone scintigraphy

The present study was undertaken to investigate the sites at which the 99mTc phosphorous compounds bind to skeletal tissue in general, and their localization at different stages of osteoarthritis in particular, in order thereby to arrive at a better morphological basis for interpreting the scintigrams. It was endeavoured also to relate the uptake of bone-seeking agents to abnormal changes in cartilage, synovium, and subchondral bone to obtain better insight into the pathogenesis of osteoarthritis. The bone remodelling activities in subchondral bone in osteoarthritic human femoral heads were elucidated by the alkaline phosphatase activity of osteoblasts and the acid phosphatase activity of osteoclasts. The enzyme activity was measured semiquantitatively by the initial time for the histochemical reaction. The distribution of the activity of the two enzymes in different areas proved parallel, and considerable variation in enzyme activity was seen between different areas within the same femoral head. Increased osteoarthritic cartilaginous changes were associated with increased subchondral enzyme activity, highest in denuded weightbearing areas and in the osteophytes and lowest in non-weightbearing subchondral bone and centrally in the femoral head. Studies on different histochemical staining of glycosaminoglycans in the matrix of human osteoarthritic cartilage and of normal cartilage revealed a heterogeneous distribution of the different glycosaminoglycans through the cartilage. Except for superficial loss of glycosaminoglycans, no difference was found in the distribution of keratan sulphate between osteoarthritic cartilage and control cartilage. In osteoarthritis, however, a relative increase in stainability for chondroitin sulphate was found in the territorial area, especially around the cell clusters, and only chondroitin sulphate was present in the cartilage of osteophytes. These findings were interpreted as an increased GAG metabolism, its mode of production being like that of very young cartilage. In the experimental rabbit model used in studying the uptake of bone-seeking agents this GAG regeneration was able to refill demasked collagen network with glycosaminoglycans in certain areas of the joint. The height of the depleted superficial area was estimated on patellar cartilage stained for sulphated GAG with toluidine blue-0 at pH 3, visually and by optical densitometry using the wavelength corresponding to the gamma-band of toluidine blue. The time relation of the surface depletion was elucidated. A marked depletion of GAG, seen one week postoperatively, reached a maximum at 4 weeks.(ABSTRACT TRUNCATED AT 400 WORDS)