The preparation of human articular cartilage for scanning electron microscopy

Light and electron microscopic morphology of the temporomandibular joint in growing and mature crab-eating monkeys (Macaca fascicularis): the condylar articular layer

In an attempt to establish maturational alterations in the morphology of the articular tissue layer, mandibular condyles of four immature and four mature male monkeys (Macaca fascicularis) were studied using light microscopy as well as scanning and transmission electron microscopy. Specimens were fixed in situ by perfusion in the presence of ruthenium red to stabilize proteoglycans. Preparations intended for observation in the scanning electron microscope were first dehydrated and sputtered for the examination of articular surfaces, and afterwards treated with trypsin to expose the spatial arrangement of collagen fibrils. Gross anatomical relations between joint components indicated that the anterior and central, but not the posterior region of the condylar articular surface can be subject to compressional load. Load-bearing and non-load-bearing regions differed with respect to the morphology of the articular layer. Load-bearing surfaces were covered by a prominent articular surface lamina similar to that observed on articular cartilage. This lamina seemed to constitute an integral part of the articular layer, distinct from the lining of synovial fluid, and to be composed largely of proteoglycans. It was unaffected by maturation. The subjacent, load-bearing articular layer differed markedly in structure, both from articular cartilage, and between immature and mature animals. Articular cells of immature animals were classified as fibroblastlike, but unlike typical fibroblasts, were surrounded by a thin, often incomplete halo of fibril-free pericellular matrix, presumably consisting of proteoglycans. In mature animals, articular cells closely resembled chondrocytes, but exhibited prominent nuclear fibrous laminae, which usually are found only in fibroblasts. Thus, the load-bearing part of the articular layer seems to undergo a maturation-dependent metaplastic conversion, from a dense connective tissue with some features of fibrocartilage, to a fibrocartilage-like tissue containing chondrocyte-like cells with some features of fibroblasts. This conversion might reflect an adaptation to a maturation-associated increase in articular stress.

Low temperature and conventional scanning electron microscopic observations of dog femoral condylar cartilage surface after anterior cruciate ligament division

The left stifle joints of 16 beagle dogs were subjected to surgical division of the anterior cruciate ligament (ACL). The femoral condyles showed surface alterations and damage after 14 days when examined by low temperature (LTSEM) and conventional scanning electron microscopy (SEM). The first change was an increase in the fibrous texture of the articular cartilage surface. Folds and surface roughening were later recognised. After 112 days deformation and disruption gave way to cracking or fracture of the surface layers. Superficial damage was focal in distribution and accompanied by a decrease in the frequency of tertiary elevations. The affected areas of cartilage increased in frequency and size with time and surgery. The observations obtained from LTSEM, in which the tissue remains fully hydrated during examination, may be caused by alterations in water content and a loss of proteoglycan at the surface, together with changes in cell shape and size. Surface cracks may be the en face appearance of histological fibrillation.

Prolonged ethanol replacement by CO2 increases splits on articular cartilage surface after critical point drying

Ethanol replacement by CO2 of glutaraldehyde-fixed and ethanol-dehydrated rabbit articular cartilage specimens was monitored with both gas chromatograph and alcometer prior to critical point drying (CPD). The surface structure of the patellar specimens was also systematically registered with a semiquantitative scanning electron microscopic method. After a 2 h interval, when about 28 microliters of ethanol/15 min CO2 extract was removed, the articular surface was smooth, although small areas of striated surface and superficial splits were present. A long-term CO2 treatment (16 h) removed ethanol completely, but increased superficial splitting of the articular surface after CPD. Air-drying of the specimens gave rise to inferior preservation of the cartilage: large areas with pitted and leafy surface qualities, but no superficial splits, were present on the surface. It was evident that prolonged ethanol replacement by CO2, prior to CPD, degraded surface structure of the articular cartilage which should be taken into consideration in the planning and design of experiments. Ethanol removal by CO2 could conveniently be monitored by an alcometer.

Hyaline articular cartilage dissected by papain: light and scanning electron microscopy and micromechanical studies

Papain was used to digest the hyaline femoral condylar cartilages of 30 adult Wistar rats. Matrix proteoglycan degradation was assessed by the light microscopy of paraffin sections stained with toluidine blue. The extent of surface structural change was estimated by scanning electron microscopy, and the structural integrity of the hyaline cartilage tested by the controlled impact of a sharp pin. The results demonstrated an early loss of cartilage metachromasia, increasing with time of papain digestion, and an alteration in the shape of the cartilage splits produced mechanically. Accompanying the loss of matrix material was a conspicuous sequence of morphological changes in cartilage surface structure. The results confirm a close relationship between matrix integrity, mechanical properties, and fine structure.

Demonstration by X-ray microprobe analysis of relationship between chondrocytes and tertiary surface structure of hyaline articular cartilage

Blocks of hyaline cartilage from the femoral condyles of five young adult beagles dogs were quench-frozen in nitrogen slush at 63 K. The free cartilage surfaces of blocks from three animals were examined in the secondary electron mode; the remaining specimens were cut by cryoultramicrotone (approximately 188 K) tangential to the surface to expose midzone cartilage which was examined in the backscattered electron mode. A random array of gently convex prominences was apparent at the free cartilage surfaces. When X-ray emissions were recorded from tissue immediately below these elevations, the spectra proved to be similar to those derived from midzone chondrocytes. These spectra revealed high count rates for the X-rays characteristic of P and K. By contrast, in areas of free surface remote from these prominences, and in midzone intercellular matrix, larger count rates for the X-rays characteristic of Na, S. Cl and Ca were detected. The evidence supports the hypothesis that the elevations seen on the non-loaded articular cartilage of disarticulated mammalian synovial joints are the surface representations of superficial chondrocytes.

Ultrastructure of human tendon sheath and synovium: implications for tumor histogenesis

Normal human tendon sheath and synovium were studied by scanning an transmission electron microscopy. The lining cells of the two tissues appear to be identical ultrastructurally. The most superficial cells (B-cells) possess long cytoplasmic extensions that clothe the membrane surface. Intermingled with deeper B-cells are the so-called A-cells, which have similar cytoplasmic features but lack long processes and instead have many filopodia. the frequent occurrence of intermediate forms indicates that the two cells form part of a morphologic spectrum. Comparison with cells of tumors that have been ascribed to synovium or tendon sheath (synovial sarcoma, epithelioid sarcoma, clear cell sarcoma) do not reveal any close similarities that might support a histogenetic relationship.

Fine structure of artificial splits in femoral condylar cartilage of the rat: a scanning electron microscopic study

Artificial splits made in rat femoral condylar articular cartilage have been studied by SEM. Three types of split have been described; non-layered, unidirectional layered and multidirectional layered. The frequency of each type of split varies in the different regions of the condyle. Deformation and crack propagation are features of layered splits and the latter are often accompanied by exposure of fibres. The fibre pattern over the articulating surface of the rat femoral condyle, revealed by trypsin or NaOH treatment, has been determined and a correlation found between this pattern and the orientation of splits previously observed by ILM. The influence of fibre arrangement on split production is discussed and consideration given to other factors, such as mechanical stress, chondrocyte distribution or PG concentration gradients, which may determine both characteristic patterns. Further evidence is presented of the value of the pin prick method as a technique for exploring the nature of normal and abnormal articular cartilage.

Surface changes in the articular cartilage of rabbit knee during immobilization. A scanning electron microscopic study of experimental osteoarthritis

Osteoarthritis was produced by the immobilization of rabbit knees in extension for 1--8 weeks (with a subsequent mobilization period of 0 or 8 weeks). The development of articular surface changes in the tibia, the femur and the patella was examined with scanning electron microscopy (SEM). During the development of osteoarthritis the normal undulations and fine regular fibre network disappeared, the number of fibres and the variation in the thickness of the fibre bundles increased, and scaly irregularities appeared. Some degenerative changes in the contralateral, non-immobilized hind limb also appeared. The normal features of the articular surface of the patella differed from that of the tibial and femoral condyles. The changes seen with SEM correlated well with histological and biochemical results of earlier studies, but at 1 week of immobilization, the SEM changes were more readilly apparent than the histological changes. The SEM method seems to be useful for the study of articular surfaces; however, the area studied must be defined.

Influence of aqueous fixation on articular surface morphology. A reflected light interference microscope study

Fresh, unfixed temporomandibular fibrous articular surfaces from baboons were examined by reflected light interference microscopy. The appearances, recorded photographically, were compared with those of joints subjected to aqueous fixation in buffered glutaraldehyde and formalin. Fixation caused readily detectable, measureable changes in articular surface morphology. Reflected light interference microscopy is a valuable technique for the demonstration of the effects of fixation on articular surface morphology.

Production of split patterns on the articular cartilage surfaces of rats

A device has been designed to permit reproducible loads to be applied perpendicularly to the acutely curved cartilage surfaces of the diarthrodial joints of small animals. With this apparatus, a sharp, round pin has been used to cause splits in the hyaline articular cartilage of the lower end of the femurs of 37 Wistar rats. In the patellar groove, the splits form a longitudinal pattern. On the condylar surface, the pattern is fantail, radial or non-uniform. It is suggested that cartilage thickness, joint congruence and load per unit area, are variables related to the directional pattern of the splits. These variables, in turn, reflect the gross, microscopic and molecular anatomy of the cartilage. The effects pin-pricks are comples: they disrupt surface collagen bundles and other cartilage components. Experiments made to test the effects of drying, isotonic saline, hyaluronic acid and sodium hydroxide support the view that the state of hydration and fluid flow are important determinants of the shape of cartilage splits. However, sodium hydroxide-induced cartilage disruption, involving glycosaminoglycan loss, did not influence split configuration. Some preliminary evidence suggests that the process of crack propagation, by which splits form, may be related to the position and shape of chondrocyte lacunae. It is concluded that pin-prick testing offers a means by which the structural properties of the cartilage of small diarthrodial joints may be conveniently tested in vitro.

Scanning electron microscope studies of some normal and diseased conditions of mammalian skin as revealed in leather manufacture

Sheep, goat and bovine skins, as leather, were examined. The surface contours of dermal response to sunburn, facial eczema, rape scald, and demodicosis are illustrated. In sunburn, demodicosis and rape scald, finger-like and ridge pattern projections had developed. In the photo-sensitive condition of rape scald and facial eczema distension was apparent, and in addition in rape scald reactions of contrasting nature involving hair follicles indicated a considerable disorientation of the skin. The transition from str. basale to str. corneum in bovine epidermis has been examined in leather from which the epidermis had unintentionally been incompletely removed in the course of manufacture, during attack on the keratinous tissue by hydrosulphide ions at high hydroxyl ion concentration. A "pore" presumably related to the position of the nucleus was observed in the outer surface of each of the cells in each layer exposed by the attack. The walls of the basal and adjacent cells appeared remarkably sturdy. As judged from the basal cells the intercellular cement (cell coating) disappeared before the cell wall degraded, but intercellular bridges remained clearly visible in the prickle cell layer, while towards the exterior, adjacent cell walls appeared more closely knit and the str. corneum (residues of which were observed around the follicles) appeared to lie in sheets. Discrete and fibrous cell components were exposed. At the latest degree of degradation observed in the basal cells the wall had reduced to a fibrous network.