THE STRUCTURE AND FUNCTION OF ARTICULAR SYNOVIAL MEMBRANES

¹ Department of Anatomy, Stanford University

1. The inner surface of articular capsules is not formed by a distinct membrane, but by connective tissue modified as the synovial surface is reached. The cells here are more closely packed and the nuclei exhibit peculiar staining characteristics, but that does not seem to justify the use of the term membrane.

2. The superficial synovial cells are not uniform in size or shape, some being quite small and round while others are large with branching processes. This type of cell is not confined to the surface.

3. Synovial villi vary greatly in size and shape and are composed of connective tissue resembling the part of the capsule from which they arise.

4. An excellent demonstration of variation in cell outlines on the synovial surfaces of articular capsules can be obtained by the use of silver-impregnation methods. The intercellular substance is found to be abundant, in contrast to that of the pleura and peritoneum; and the apparent cell outlines are much more irregular and do not resemble those of an endothelial or mesothelial layer.

5. The presence of "stomata" in articular capsules is not confirmed.

6. Carbon particles, when injected into the knee joints of guinea-pigs, evoke an inflammatory exudate in the joint cavity, most marked on the third day after injection. Some of these carbon particles are taken up by the lymphatic vessels and are deposited in the inguinal and lumbar nodes, while others are removed from the joint cavity by the action of phagocytic cells, some of which gain the lymphatic vessels while others remain in the subsynovial connective tissue for an indefinite period.

7. Iron, in the form of ferric ammonium sulphate, disappears from joint cavities within thirty minutes after injection by way of the lymphatics.

8. Iodin in the form of lipiodol diffuses slowly through the joint capsule, a period of at least four days being required for its complete removal, as judged by skiagrams.

9. Immobilization of the tibiotarsal joints in rabbits over fifty-three days produced no marked structural changes in the joint capsule, but the amount of synovial fluid was considerably less.

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