A maturation change in the surface of cat articular cartilage detected by the scanning electron microscope.

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.

Long-term results of deep defects in articular cartilage. A scanning electron microscope study.

Core defects produced in the medial femoral condyle of the rabbit were studied by scanning electron microscopy and light microscopy over a period of 2 years. In some cases the defect was filled by hyaline articular cartilage with a fairly smooth surface, but in others the tissue was markedly fibrillated and resembled fibrous tissue and fibrocartilage. Appearances suggesting disintegration of the newly formed cartilage were seen in some cases. It would appear that a continuation of this process can lead to the exposure of subchondral bone. In one instance no repair tissue or new cartilage could be identified but the surrounding old cartilage had formed a shelf over the defect. The cartilage surrounding the defect was either normal or showed superficial fibrillation, and/or flow formation, and/or fissures.

The surface of dog articular cartilage: a scanning electron microscope study.

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.

Innervation of the lumbar spine.

Back pain, in spinal stenosis, can arise from many sources. Apart from nerve root involvement any of the structures considered above can be implicated. In degenerative conditions, where discogenic and posterior facet pain are present, excess activity tends to increase these symptoms. In addition there is evidence that impulses reaching the spinal nerve root through the sinu-vertebral nerve and possibly the posterior ramus may potentiate the irritability of that root. Whether such a mechanism contributes to the claudication of degenerative spinal stenosis is not known.

Experimental production of ridges on rabbit articular cartilage: a scanning electron microscope study.

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.

Evidence of cartilage flow in deep defects in articular cartilage.

Full thickness defects (core defects) violating subchondral bone were created in the weight-bearing area of articular cartilage lining the rabbit medial femoral condyle. The repair reaction that follows has two components: (1) a sliding and flowing of cartilage over the edge of the defect and (2) a filling of the defect by repair tissue arising from the marrow spaces. Past studies have paid little or no attention to cartilage flow but this first scanning electron microscopic study of deep defects shows that it is an important phenomenon which materially affects the changes that occur and also the outcome of such injuries. Briefly, we have found that in most cases the cartilage flows downwards into the core defect. The repair tissue then grows along and over the "toed-in" catilage. In other cases the flowing cartilage rides over the repair tissue from the marrow spaces and as a result of load bearing and joint movement, becomes frayed and drawn out into long ribbons and rope-like structures.