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The synovial membranes of 5 young rabbits about 6 weeks old and 5 older rabbits about 3-4 years old were studied with the light and electron microscopes, with a view to discovering any age-associated changes that might occur. Several age-associated changes were noted. These included: (1) a reduction in the overall population of synovial intimal cells; (2) a statistically significant reduction in type B cells and a relative increase in type A cells; (3) the emergence of atrophic cells poorly endowed with organelles; (4) decreased vascularity; and (5) fibrosis. more...

A light and transmission electron microscopical study of 6 to 8 months old rabbit semilunar cartilages has shown that the cells in this tissue resemble chondrocytes more than fibroblasts. The prominent organelles in these cells were rough endoplasmic reticulum and the Golgi complex. An unusual finding was the occurrence of filamentous material in Golgi sacs and vesicles, and collagen fibrils within smooth membrane-bound tubular structures, apparently within the cells. Collagen fibrils forming fibres, fibre bundles and lamellae constituted the major component of the menisci. Protein-polysaccharide particles and associated fine filaments were found in the interfibrillary matrix and in the sparse territorial matrix adjacent to the chondrocytes. Numerous immature elastic fibrils, and rare mature elastic fibres with an electorn-lucent amorphous core, were also found in the general matrix amongst the collagen fibrils. more...

Scanning electron microscopic studies revealed numerous humps on the surface or articular cartilage from a 7 years old boy and from 1 month old rabbits. This shows that the surface topography of articular cartilage in young individuals is different from that of older individuals (human and rabbit) where the surface is beset by numerous pits. In 2 months old rabbits an intermediate situation was witnessed, for both shallow pits and occasional humps were present. Ridges and undulations were not seen on the articular surface of the 7 years old boy, except near the cut edge of the specimen. They were, however, found on air-dried specimens of 1 month old rabbit cartilage, but were absent from specimens dried by the critical-point method. The collective evidence supports the idea that ridges and undulations are not a constant feature of the normal articular surface, but that such features are artefactual, a typical or pathological. more...

A morphometric study was carried out to assess the thickness of the fibrous lamina in the nuclei of cells adjacent to tears in semilunar cartilages and in cells from relatively normal uninjured parts of semilunar cartilages. Comparisons of mean thickness of the lamina showed a statistically significant thickening of the lamina at the site of injury. This observation supports the growing body of evidence indicating that the fibrous lamina is not a static structure of fixed dimensions for a given cell type but a dynamic structure whose thickness varies as a result of altered physiological or pathological states. more...

The articular surface of the femoral condyle of kittens (2 days to 2 months old) and cats (6 months to 20 months old) was studied by examining air dried and critical point dried specimens in the scanning electron microscope. The surface of kitten cartilage was found to be populated by innumerable humps which were more prominent in air dried than in critical point dried specimens. Undulations and ridges were seen on air dried kitten cartilage, which was markedly shrunken and distorted, but undulations and ridges were absent from critical point dried specimens where shrinkage was more modest or even undetectable. The surface of the articular cartilage of 12 months and 20 months old cats was populated by innumerable pits. A rare hump in a pit was seen in specimens from the 12 months old cat, but not from the 20 months old animal. In 6--8 months old cats an intermediate situation prevails, for in some specimens pits were present on the posterior part of the condyle but humps and humps in pits were present on the anterior aspect. This study shows that the surface of young articular cartilage is populated by humps, but as the cartilage matures these formations are either transformed into pits or replaced by pits. more...

The surface of rabbit, cat, monkey and human semilunar cartilages was examined with the scanning electron microscope. A common feature was the occurrence of numerous ridges, undulations and furrows on the surface, but this was thought to be due to marked shrinkage and distortion of cartilage not firmly attached to bone. Humps were seen on the semilunar cartilages of young animals, but pits occurred in adults. This is thought to reflect a maturation change. Humps were seen in a young human semilunar cartilage, but pits were not seen in adult specimens. It is not clear whether pits are truly absent or just masked by the severe ridging produced during the preparation of large human specimens. more...

The surface of dog articular cartilage attached to subchondral bone shows many humps on its surface when examined with the scanning electron microscope. The situation here contrasts with that in man and rabbit where large numbers of pits are seen of the surface. Such species variations cast doubts on the idea that pits and humps play a vital role in joint mechanics and lubrication. Ridges and undulations were not found in normal dog cartilage attached to bone, but complex systems of ridges did develop when the cartilage was cut or detached from bone. more...

Intramatrical lipid debris and calcified bodies were found in the matrix of injured and uninjured portions of semilunar cartilages obtained from patients ranging in age from 16 to 60 years. Most of the calcified bodies were homogeneously electron-dense and they were roughly spherical or cuboidal in shape. Much rarer was the occurrence of calcified bodies containing long, slender crystals. Electron-probe X-ray analysis showed that the homogeneously electron-dense bodies contain phosphorus, calcium and magnesium. more...

The surface of normal rabbit articular cartilage attached to subchondral bone has a pitted appearance when examined with the scanning electron microsope. It is thought that these pits are similar to those seen in human cartilage and that they reflect the presence of underlying chondrocytes and lacunae, shrunken by preparative procedures. Ridges or undulations were not seen on the normal articular surface with the scanning electron microscope but complex systems of coarse and fine ridges were produced when cartilage was damaged by cutting, by making a hole in it or by detaching it from subchondral bone. Humps or mound-like elevations also developed in some instances when cartilage was damaged by cutting or by making a hole in its substance. more...

Normal human menisci obtained at autopsy (seven cases) and the injured and uninjured portions of torn menisci obtained at surgery (nine cases) were studied with the electron microscope. The surface of menisci is composed of collagen fibrils surmounted by an electron-dense surface coat. Most of the cells in menisci are chondrocytes but a few fibroblasts and cells of an intermediate form difficult to classify as either fibroblasts or chondrocytes also occur. Mast cells are found at the vascularised periphery of the meniscus. Myofibroblasts were found in the injured portions of menisci in three out of the nine cases studied. A territorial matrix containing fibrils and proteoglycan particles with associated filaments is seen around or adjacent to chondrocytes, but sometimes this matrix is sparse or absent. The interterritorial or general matrix comprises collagen fibrils of widely varying diameters (25-180 nm) set in a sparse interfibrillary matrix containing proteoglycan particles. A few mature elastic fibres and several small or immature elastic fibres and collections of electron-dense filaments are seen in the general matrix. Also seen in this region are calcified bodies and matrical lipidic debris derived by the shedding of cell processes and in situ necrosis of cells. Other features seen in the matrix of the injured portion of the meniscus include: (1) membrane-bound cystic structures; (2) parting and fraying of collagen fibrils; and (3) pools of proteoglycan particles. more...

The purpose of this study was to ascertain whether the surface asperities detected with the transmission electron microscope in shavings of young adult articular cartilage detached from bone reflect an in vivo condition or are artefacts. With this in view shavings of rabbit articular cartilage processed in the conventional manner were compared with pieces of cartilage attached to bone processed by a new method which we have evolved. An undulating surface and asperities up to about 0.3 micrometer deep were found in cartilage shavings processed in the conventional manner, but such asperities were not seen on cartilage processed attached to bone. We have therefore concluded that such asperities are artefactual and that they are engendered by cartilage curling. Cartilage processed attached to bone has an amazingly smooth surface; any so-called 'asperities' are less than 0.03 micrometer in depth and are confined to the surface coat which seems to be of a transient nature. On rare occasions, however, focal areas of roughening were found, where the asperities reached a depth of about 0.15 micrometer. Several past studies (reviewed in this paper) have shown that virtually all the asperities seen with the scanning electron microscope on the articular surface are artefacts of tissue processing. We have now shown that even most of the much smaller asperities seen with the transmission electron microscope are also artefacts. Therefore one has to conclude that the articular surface of young adults is remarkably smooth and that the surface asperities must be attributed to artefacts, ageing or pathological changes. more...