Irving Redler

The ultrastructure and biomechanical significance of the tidemark of articular cartilage.

Thirty specimens of human articular cartilage obtained at surgery were examined by scanning electron microscopy to determine the ultrastructure of the tidemark, the junction of the non-calcified and calcified portions of mature articular cartilage. Three distinct variations of the collagen framework of the tidemark were observed: (1) A band of randomly oriented compacted fibrils that appeared to be continuous with those of the non-calcified and calcified zones. (2) A band of flattened fibrils paralleling the undulating surface of the calcified cartilage. (3) A band of perpendicularly oriented fibrils having a distinct continuous transition between the non-calcified and calcified zones, the amount of calcified material applied about the fibrils rapidly increasing as the fibrils entered the calcified zone. The tidemark may serve to provide a tethering mechanism for the relatively flexible and perpendicularly oriented collagen fibrils of the deepest portion of the non-calcified articular cartilage and may prevent them from being sheared at their point of anchorage to the calcified zone. The undulating pattern of the tidemark affords a strong geometric pattern in providing resistance to the shearing action of articulation. Small gaps present in the tidemark may provide pathways for the passage of nutrients into the deep non-calcified zone of articular cartilage from the subchondral bone.

Some surface characteristics of articular cartilage—I. A scanning electron microscopy study and a theoretical model for the dynamic interaction of synovial fluid and articular cartilage☆

Abstract Scanning electron microscopic studies of articular cartilage show that some portion of the surface of some articular cartilage exhibits a wavy pattern. These are not due to ultrastructural organization immediately subjacent to the surface. They are regular and exist far away from the fractured edge of the specimen. A mechanism is postulated for the generation of these observed surface undulations. A theoretical model for the mechanical behavior of articular cartilage is proposed. This model incorporates some of the observed ultrastructural features of articular cartilage. Quantitative results based upon this model have been obtained and presented in Part II.

Scanning Electron Microscopy of Normal and Abnormal Articular Cartilage and Synovium

The scanning electron microscope, because of its great depth of focus, high [See figure in the PDF file] degree of resolution, and ease of specimen preparation, is most adaptable to surface study of articular tissue. Our preliminary studies of normal and pathological articular cartilage and synovium, while limited, have revealed striking morphologic differences in these tissues and justifies further study by this method.

Some surface characteristics of articular cartilage—II. On the stability of articular surface and a possible biomechanical factor in etiology of chondrodegeneration

Abstract A biomechanical model is proposed for the study of the dynamic interaction of synovial fluid and articular cartilage. This model incorporates some of the salient SEM observed ultrastructural features of articular cartilage. The tissue is considered as a two-layer system with the superficial tangential zone considered as a mechanical plate and the middle and deep zone considered as an isotropic elastic medium. This model is a generalization of previously proposed ‘protective membrane’ models of other investigators. A normal mode stability analysis shows that a streaming fluid over such a two-layer system may create an instability at the fluid-solid interface. Quantitative results show that the critical speed is governed by the elastic modulus of the middle and deep zones. The band of unstable wavelengths is governed by the stiffness of the plate. Clearly, the present model for the dynamic interaction of synovial fluid and articular cartilage is a simple model. Even so the solution demonstrates a complex mechanical interaction phenomenon between the superficial tangential zone and the middle and deep zones. The limiting membrane solution of a surface tension effect (where the thickness of the superficial tangential zone becomes vanishingly small) has also been obtained. Based upon these solutions a possible mechanism is suggested as a factor in the etiology of chondrodegeneration.

An Ultrastructural Study of Patellar Chondromalacia in Humans

Chondromalacia of the patella in humans is characterized by dedifferentiation of many superficial and middle-zone cells to fibroblast-like cells. The deep cells show structural evidence of increased protein synthesis and secretion. This is manifested by a fibrous territorial matrix and an extraterritorial rimming of matrix granules which reportedly represent acid mucopolysaccharide.

Morphological variations within a given area of articular surface of cartilage

SummarySamples of articular cartilage from four different human joints were obtained at surgery. Serial scanning electron micrographs taken at a magnification of 1000× were used to reconstruct an 0.25 mm2 area of articular surface. Within these given areas both normal and degenerated portions were seen. This study supports the concept that the surface morphology of articular cartilage varies from joint to joint and from area to area within a joint. This information should be useful for the interpretation of light and electron micrographs, as well as histochemical and biochemical data.

Ultrastructure of solitary enchondromas.

Solitary enchondromas obtained from the small bones of the hand were studied with transmission electron microscopy. Three cell types were seen as follows: (1) young looking, active cells with extensive dilated rough endoplasmic reticulum and well defined Golgi and mitochondria; (2) older looking, degenerating cells with dilated rough endoplasmic reticulum, well defined Golgi, glycogen masses, vacuoles containing tropocollagen, lipid and myelin figures; and (3) dying cells showing loss of cell membrane and lysosomal-like bodies. A young chondroblastic cell may try to mature, become a normal chondrocyte that produces normal matrix but it does not succeed and dies. Enchondromal cells are not capable of forming tropocollagen or synthesizing proteoglycans for the matrix.