Mature articular cartilage is an aneural, avascular, and alymphatic specialized form of connective tissue 1, t~>Destructive changes in synovial joints, resulting from prolonged -immobilization. have been described is humans and experimental animals ´~,.u-~´.,w. However. the fine changes ocxuriag in the early stags ofimmobilization can be appreciated ~ only by ultramicroscopical examination, which also helps to determine changes in the cell organelles is the later stages. The effects of immobilization in the areas that .remain free from contact with the opposing cartilage are also better appreciated ~ electron microscopy"` ~ ~ .
Thiry young male rabbits each weighing about 2.0 kg were used for the experimental study. Immobilization of the knee joint in flexed position of about 70 degrees was maintained by plaster of Paris, and the animals were sacrificed at time intervals of 3.7.14.21.28. and 56 daps respectively after the immobilization.
After sacrifice. distal portions of the femora were resected and on the test side right) small pieces were taken from areas free from contact with the opposing cartilage.
The tissues were decalcified sad prepared by standard pataffm ,embedding procedure and stained with hematoxglin and eosin for histologic observation: _
For electron microscopy, the specimens fixed in four percent glntaraldehyde for four. hours and postfixed for two hours at 4´C with one percent osmium tetraoxide in 0.1 M phosphate Buffer with pH 7.4"´ . All tissues were dehydrated in graded alcohol and embedded in Epon 812 according to standard procedures". Thep were cut into sections:of 500 A with a glass knife. The sections wen mounted on copper grids. stained with nranyl acetate and lead hydroxide ind obsarred i~-itlm~tlie ~´´: Hitachi HU 11-E Electron Microscope.
The results of the light and electron microscopic findings are as follows;
1. Degenerative changes in non;xontact .areas of articular cartilage. resulting from the early stages of immobilization, could be detected by the electron microscopic examination.
2. Degenerative changes in a few chondrocytes of the middle zone appeared after ?days of immobilization. and these were observed in increasing degrees of severity in the later samples. The changes were manifested by dilatation of the cisfecnae of rough endoplasmic reticulum, swelling of mitochondria, accumulation of excessive amount of fine filaments, lipid droplets and lysosomal bodies. -
3. By the light microscopic findings, mild degenerative changes in the non-contact area9 of articular cartilage appeared after 14 days of immobilization and became increasingly severe in later samples. The changes were manifested by fibrillation, cleft and hypocellularity.
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