Experimental immobilization of joints has been carried out by numerous investigators, and since the work of Menzel (1871) was reported, the morphological changes accompanying immobilization have been rather well established.
Among observations on the histochemistry of synovial membrane an those of Davies(1943) on the staining reaction of normal synovial membrane, with special reference to the origin of synovial mucin in the various animals and the human; Lever and Ford(1958) on the use of histochemical methods, particularly the periodic acid-Schiff reaction, in combination with histological and electron microscopic investigations of rabbit, cat and human synovial membranes; and Castor(1960) on the structure of normal human synovial tissues.
Roy et al. (1966) demonstrated that in traumatic effusion RNA·positive synovial cells were more frequent and that their numbers and the intensity of their staining reaction showed a significant increase with the increase in the volume of synovial
fluid. Ghadially and Roy(1967) made a study of the histochemistry of synovium in experimental haemarthrosis in the rabbit, and detailed the ultrastructure and histochemistry of synovial membrane in rheumatoid arthritis by another investigation, but no histochemical studies of synovial membrane in immobilized joints in man or experimental animals have as yet been reported.
The present investigation was undertaken to observe the morphological changes and to determine the influence upon synovial membrane, using the histochemical technique, in immobilized knee joints of albino rats.
One hundred and thirty-two healthy mature Sprague-Dawley rats weighing about 200 gm were used. Immobilization in flexed position of about 90 degrees was maintained by an internal stainless steel splint (sized 0.6 cmx3 cmxo.5 mm) secured on the
lateral aspects of the femur and tibia with steel wire. The left knees of these animals were immobilized for periods of one, two, three, four, six and eight weeks, the right knees served as controls. In one only of such controls from each group of animals, steel wires were passed through holes and tied to the tibia and femur separately. After fixation arid decalcification with Jenkins's fluid, the extremities were trimmed so that only five or six millimeters of the femoral and tibial ends remained with the joint. Before embedding of the tissue in paraffin, the joint was sectioned in the sagittal place. Serial sections were prepaid and stained with hematoxylin-eosin.
For histochemistry, the fresh synovial tissues were obtained from infrapatellar regions of the knees. To demonstrate the activity of adenosine triphosphatase, the method presented by Wachstein and Meisel(1957) was used. The sections were stained
by the periodic acid-Schiff method of Hotechkiss(1948) for glycogen, and methyl green pyronin staining with Rosa's method(1950) for ribonucleic acid. Beside these, for contrast of glycogen and ribonucleic acid, the malt diastasedigestion method
was used. For metachromasia the sections were stained with toluidine blue.
In hematoxylin-eosin stained preparation, connective tissue proliferation was present in the knees immobilized for tyro weeks and it was well established at four weeks. After four weeks, no further significant changes were observed in the extent of the connective tissue. Definite adhesions to the unapposed articular cartilage were present at four weeks and became slightly more dense and more extensive at six weeks. After eight weeks the quality and extent of the adhesions did not appear to change.
In the articular cartilages, on from three to four weeks of immobilization, some staining changes, loss of matrix homogeneity and thinning of the cartilage layer were observed. After four weeks of immobilization, vascular invasion from connective tissue adhesions wart found in some peripheral areas. After eight weeks,
intrachondral and subchondral cysts were observed in the non-weight bearing regions
The activity of adenosine triphosphatase was diminished in he synovial cells in the experimental group after four weeks of immobilization. After six weeks of immobilization the synovial cellos showed a marked decrease in the periodic acid-Schiff reaction. With methyl green pyronin staining for RNA, the synovial cells showed a definite increase in number in pyroninophilic granules and in intensity of staining reaction at three and four weeks of immobilization. After six weeks of immobilization there was a demonstrable decrease in the RNA content of synovial cells and this persisted to the end of the experiment. The surface layers of the synovial membrane, in general, were stained mon intensely than 7he deeper layers in both RNA staining and PAS staining preparations. Toluidine blue gave only faint metachromasia to the very rarely seen mast cells in the deeper layers of synovium.
It is suggested that such changes as are demonstrated in the ATP-ase activity, and in the content of glycogen and RNA of synovial membrane, are correlated with various metabolic changes of the synovial membrane following immobilization of rat knee joints.