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The goal of this study was to evaluate, histologically and biochemically, repair of the articular cartilage in a rabbit joint after the use of the holmium:yttrium-aluminum-garnet laser in a cartilage chondroplasty model. In 30 New Zealand White rabbits, chondroplasty was performed with the laser at an intensity of 0.8 J at a rate of 10 Hz. The animals were sacrificed 12 weeks after surgery. Histologically, the safranin O staining index of proteoglycan correlated well with the biochemical results, illustrating a decrease of proteoglycan in the repaired articular cartilage after laser articular cartilage chondroplasty. The damaged articular cartilage surface after the laser application was extensive. The damaged area observed was gradually distributed along the radius from the central point of the laser beam application. Biochemically, the amount of glycosaminoglycan in the repaired tissue (8 +/- 2 mg of hexosamine per gram of dry cartilage) was statistically less when compared with that in the sham-treated tissue (40 +/- 5 mg). The amount of sulfate incorporated into proteoglycans was 8 to 10 times less in the chondroplasty model compared with the control, suggesting that cell viability was greatly reduced in the treated tissues or expression of proteoglycans was greatly reduced. In the subchondral area, histologic evaluation showed the lack of osteocytes in lacunae of the bone tissue after use of laser energy. The architecture of the subchondral bone in the chondroplasty area was damaged, with damage also seen in the membranes of the blood vessels.

To determine the fate of transplanted cryopreserved articular cartilage, an animal model employing the proximal humerus in the rabbit has been developed. Previous studies have been hindered by problems of postoperative joint instability, secondary injury due to immobilization, and paucity of cartilage for analysis. This experiment demonstrates the survival and function of transplanted cartilage by quantitative assessment of metabolic and biochemical parameters. Forty-five New Zealand white rabbits underwent transplantation of the right proximal humerus. In 29 animals, the proximal half of the humerus was resected and replaced by a cryopreserved osteoarticular allograft. Autograft procedures were carried out in the remaining animals. Following sacrifice at 3, 6, 9, and 12 months postoperatively, articular cartilage was analyzed for gross appearance, collagen synthesis, proteoglycan synthesis, and water, hydroxyproline, hexosamine, and hexuronic acid contents. The results indicate that the cryopreserved osteoarticular allografts retained their metabolic and biochemical integrity and behaved as viable and biologically functional units 1 year postoperatively.

This study investigated the resurfacing of full-thickness articular defects in the adult rabbit medial femoral condyle using a rib perichondrial graft. The graft was secured to a 4-mm-diameter bone core removed from the femoral condyle. Two postoperative treatment protocols were studied: one group had ad libitum cage activity (CAGE; n = 95) and the other group received two weeks of passive motion (PM; n = 73; eight hours per day, five days per week) followed by cage activity. Animals in both groups were killed at six, 12, 26, and 52 weeks. Repair tissue resembling hyaline cartilage formed in a majority of animals at all time periods and in both postoperative treatment groups. The overall success rates in which repair tissue formed were 58% in the CAGE group and 56% in the PM group. However, over time, a maturation of the neocartilage into nearly normal hyaline articular cartilage was noted with the percentage of Type II collagen increasing from 55% at six weeks to 82% at one year. The complex shear modulus of the repair tissue for both groups became similar to normal cartilage with increased healing time. There was no statistical difference in shear moduli between the two treatment modalities. These results show that cartilage repair tissue derived from rib perichondrium could mature into hyaline articular cartilage over time and would not degrade by one year after repair.

Biochemical changes in the distal femoral articular cartilage (knee joint) after cemented prosthetic replacement of the femoral head were determined. Femurs from dogs (n = 10) that had undergone cobalt-chromium prosthetic hip hemiarthroplasty (6-8 months postoperatively) were analyzed for articular cartilage lipids in the distal femur. The quantity of phosphatidylserine increased from 0.59 +/- 0.14 mg (uninvolved) to 1.52 +/- 0.23 mg (hemiarthroplasty) lipid phosphorus/100 g tissue, and the quantity of arachidonic acid in the articular cartilage increased from 0.23 +/- 0.07 mg (uninvolved) to 2.07 +/- 0.29 mg/100 g tissue (hemiarthroplasty). Likewise, hydroxyproline content was higher in the recipient femurs (77.4 +/- 1.58 micrograms/mg cartilage) versus uninvolved femurs (71.8 +/- 1.03 micrograms/mg cartilage); the activity of acid phosphatase was greater in the recipient distal femoral cartilage as compared with the uninvolved femur, 0.07 +/- 0.01 and 0.06 +/- 0.02 mol hydrolyzed per kilogram per hour, respectively, and the hexosamine content was lower in the recipient femur knee cartilage versus knee cartilage from uninvolved femurs, 54.5 +/- 1.51 and 63.1 +/- 1.37 micrograms/mg cartilage, respectively. These biochemical changes may suggest degeneration of the knee joint articular cartilage after cemented hip hemiarthroplasty.

Hexosamine concentration, DNA concentration, and [35S]sulfate incorporation for articular cartilage obtained from various sites in the metacarpophalangeal and carpal joints of horses were measured. The same measurements were made on the repair tissue filling full-thickness articular defects in the intermediate carpal bone and on cartilage surrounding partial-thickness defects 6 weeks after the defects were created arthroscopically. Cellularity (measured as DNA concentration), proteoglycan content (measured as hexosamine concentration), and proteoglycan synthesis (measured as [35S]sulfate incorporation) varied according to the site sampled. Cartilage from the transverse ridge of the head of the third metacarpal bone and the radial facet of the third carpal bone had the lowest hexosamine concentration, whereas rate of proteoglycan synthesis was lowest in cartilage from the transverse ridge of the head of the third metacarpal bone and the distal articular surface of the radial carpal bone. Repair tissue filling a full-thickness cartilage defect at 6 weeks was highly cellular. It was low in proteoglycan content, but was actively synthesizing these macromolecules. In contrast, the cartilage surrounding a partial-thickness defect was unchanged 6 weeks after the original defect was made.

Using arthroscopic technique, identical diameter defects were created in the proximal articular surface of both intermediate carpal bones of 6 horses. One of each pair of defects was deepened to penetrate the subchondral plate. Removed cartilage was assayed for [35S] sulfate incorporation, total hexosamine content, and DNA content. Six weeks later, cartilage was harvested and similarly analyzed from the distolateral portion of the radius directly opposite the created lesions and the distomedial portion of the radius distant from the lesion. The repair tissue filling the full-thickness defect and the cartilage at the periphery of the partial-thickness lesion also were analyzed. There was a marked increase in synthetic activity (35S sulfate incorporation) opposite the full-thickness defect, compared with the cartilage opposite the partial-thickness defect. A marked decrease in glycosaminoglycan content in the cartilage opposite the full-thickness defect was found as compared with that opposite the partial-thickness defect. The repair tissue filling the full-thickness defect was highly cellular, high in synthetic activity, but low in glycosaminoglycan content. Insignificant changes occurred in the cartilage adjacent to the partial-thickness defect. On the basis of these results, we suggest that full-thickness defects at 6 weeks result in more detrimental change to the cartilage opposite it than do partial-thickness lesions of the same diameter.

Water binding in normal and osteoarthritic cartilage slices from human femoral heads was studied using tritiated water to measure the water binding after short exposure, total water content, and avidity with which water is held. In osteoarthritic cartilage, compared with normal cartilage, there was no increase in water binding but water content increased by 9 per cent and the avidity with which the newly bound water was held also increased. These findings were almost exactly duplicated by partial extraction of the proteoglycan from normal tissues with 4 molar guanidinium hydrochloride.

Proteoglycans were extracted from bovine articular cartilage with guanidine-HCl and fractionated in cesium chloride density gradients by equilibrium ultracentrifugation. The acidic glycosaminoglycan (AGAG) components were then determined enzymatically with chondroitinase-ABC and streptomyces hyaluronidase. Under associative and dissociative conditions, the distribution of the AGAG components was as follows: the ratio of 4-sulfated disaccharide units to total AGAG increased with decreasing density gradients whereas that of 6-sulfated disaccharide units to total AGAG increased with increasing density gradients. The ratio of disulfated disaccharide units to total AGAG increased somewhat with decreasing density gradients whereas that of non-sulfated disaccharide units tended to decrease. Although the cartilage proteoglycan macromolecules were heterogeneous, a certain regularity was observed with respect to the distribution of sulfate and the degree of sulfation in the chondroitin sulfate chains of the proteoglycans.

The recovery of adult rabbit articular cartilage after nine weekly intra-articular injections of hydrocortisone acetate was investigated using biochemical, autoradiographic, and tracer methods. After the cessation of steroid injections, the rates of synthesis of proteoglycans and collagen increased by up to 900 per cent. The increase occurred because of accelerated metabolism of existing cells and an increase (caused by mitosis) in the number of functioning chondrocytes. The proteoglycan concentration only returned to normal values after six months.

Knee joint menisci from osteoarthritic and rheumatoid knees were analyzed for nitrogen, collagen, non-collagenous proteins (NCP) and hexamine content. Degenerate areas were analyzed separately. The degenerative areas were significantly lower (P less than 0.005) in collagen but NCP and hexosamines were elevated relative to control tissue. The rheumatoid menisci revealed a reduced level of collagen and hexosamine in areas of localized degeneration. However, the collagen and hexosamine content of the remaining tissue was also diminished (P less than 0.025) relative to normal tissue of the same. age.

Proteoglycans were extracted from bovine (15-18 months old) femoral-head cartilage. The heterogeneity of the A1D1 proteoglycan fraction was examined by gel chromatography, sedimentation velocity, sucrose rate-zonal centrifugation and CS2SO4 isopycnic centrifugation. In all cases polydisperse but unimodal distributions were obtained. Chemical analysis of the preparation yielded a galactosamine/glucosamine molar ratio of 7:1, and 13C n.m.r. spectroscopy showed that the chondroitin sulphate comprised equal proportions of the 4- and 6-sulphate isomers. Gel chromatography of a papain and Pronase digest of the proteoglycan indicated that the chondroitin sulphate chains had a Mn of approx. 10500. The mean buoyant density of the proteoglycan in pure CS2SO4 was 1.46 g/ml. Physical characterization of the proteoglycan preparation in 4M-guanidine hydrochloride, pH 7.4, by using conventional light-scattering gave a radius of gyration of 42 nm and a Mw of 0.96 X 10(6). Quasi-elastic light-scattering in the same solvent yielded a translational diffusion coefficient, D020, of 5.41 X 10(-8) cm2 X S-1, and ultracentrifugation gave a sedimentation coefficient, S020, of 12.0S. Thus from sedimentation-diffusion studies a Mw of 1.36 X 10(6) was calculated. The possible origins for the differences in the two molecular-weight estimates are discussed. It is concluded that the high-buoyant-density proteoglycans from bovine articular cartilage are significantly smaller than those from bovine nasal septum, and that this is largely due to the smaller size of their chondroitin sulphate chains.

Articular cartilage was obtained from type II collagen-induced arthritic rat joints. Transmission electron microscopy showed a gradual degeneration of chondrocytes, disorganization of the collagenous extracellular matrix, and formation of microscars. Biochemical analyses indicated that type II collagen was the only collagen present and that it was normal in regard to hydroxylation of lysine and glycosylation of hydroxylysine. Analyses of the proteoglycan in the extracellular matrix revealed a 50% loss of chondroitin sulfate and keratan sulfate.

Seeking a reliable chemical index of the wear of articular cartilage during in vitro experiments, the contents of hydroxyproline, hexosamine, and the amino acid composition of adult bovine articular cartilage were determined as functions of depth from the surface. The hydroxyproline content, expressed as per cent of dry weight of tissue, was constant throughout the thickness of the tissue except in a surface region approximately twenty-five micrometers thick; the hexosamine content in this region was less than in the interior of the tissue; the collagen content was higher and the amino acid composition was less like that of pure collagen here than in the interior, indicating that the content of noncollagenous protein in the superficial layer of cartilage was greater than that in the interior. It was also evident that adult bovine articular cartilage contains significant amounts of collagen with a low hydroxylysine content, presumably Type I as well as Type II. Since the content of hydroxyproline is constant throughout the cartilage and the collagen and proteoglycan constituents of the intact tissue are relatively insoluble, the hydroxyproline content of the lubricant and the wear debris can be used to measure the extent of wear of articular cartilage during in vitro experiments. However, approximately 10 per cent of the hydroxyproline and 50 to 60 per cent of the glycosaminoglycans of the wear debris are dissolved in the lubricating fluid. Therefore, both the lubricant (solvent) and the solid wear debris must be analyzed to determine the amount of cartilage wear.

Proteoglycan subunits extracted in the presence of proteinase inhibitors from autologous knee and shoulder cartilage were examined in different donors of various ages, in order to determine the effect of weight bearing on the age-related changes in proteoglycan structure. At each age, high density proteoglycans from the two joints of the same individual were virtually identical with respect to chemical composition, hydrodynamic size, ability to aggregate with hyaluronic acid, and chondroitin sulfate chain length. The proteoglycan content of the cartilage decreased with age, as did the size of the proteoglycan subunits. In contrast, the proportions of keratan sulfate to chondroitin sulfate, protein to glycosaminoglycan, and chondroitin 6 sulfate to chondroitin 4-sulfate all increased with age. These changes occurred to the same extent in both knee and shoulder cartilage. There was no change in the ability of the proteoglycan to aggregate with hyaluronic acid. The sialic acid profile on Bio-Gel P-10 chromatography, following alkaline borohydride degradation, showed the presence of both keratan sulfate and oligosaccharide chains. The oligosaccharide content of the core protein of the proteoglycan appeared to decrease during the aging process, but it could not be ascertained whether this was related to the increased abundance of keratan sulfate.

Proteoglycans (A1 fractions) were extracted with 4M guanidine hydrochloride (GuHCl) from human articular cartilage samples of a wide age range. Distinctions were made between hip and knee, and upper and lower layers. The residues of these extractions were digested with purified collagenase, and a second extraction with 4M GuHCl was performed, which yielded appreciable amounts of proteoglycans. When proteoglycans from second extractions were compared with those from first extractions, the following changes were observed: an increase in chondroitin sulfate; a relative decrease in keratan sulfate; a decrease in protein content; and a decrease in the ratio of chondroitin 6-sulfate to chondroitin 4-sulfate. The same changes were found when nonaggregating proteoglycans were compared with proteoglycan aggregates, when proteoglycans from young cartilage were compared with those from mature cartilage, when proteoglycans from knee cartilage were compared with those from hip cartilage, and when proteoglycans from upper layers of cartilage were compared with those from deeper layers. It is suggested that the differences found between first and second extractions of cartilage, between upper and lower layers of cartilage, and between knee and hip cartilage are caused by variations in the relative amount of nonaggregating proteoglycans and/or variations in proteoglycan size.

Morphometric evaluation of 20 rhesus articular cartilage samples were correlated with hexosamine and an 18-hour incorporation of 35SO4- as a measure of proteoglycan production on samples from the same joint. Reduced chondrocyte cellularity was the basis of the reduced maintenance of the matrix by the chondrocyte. In the more cellular cartilage, the matrix/lacunae area ratio was less than 25, and the less cellular group had a ratio of greater than 40. An inverse correlation existed between morphometric cartilage matrix/lacunar area ratio and hexosamine content. A significant difference of 35SO4 incorporation was not seen between the three morphometric grades. Morphometric assessment reduces the subjectivity of articular cartilage evaluation.

Biochemical changes and in vitro rates of glycosaminoglycan synthesis were studied in thirty-seven samples of human articular cartilage from nineteen osteoarthritic and four normal control patients who were fifty to seventy-five years old. The samples were compared on the basis of histological grade of the arthritis, and subgroups based on the duration of disease, synovial pathological changes, joint studied, and sex were also compared. The osteoarthritic samples showed a progressive loss of glycosaminoglycans in the cartilage as the histological grade increased. In the early stages of the disease there was an increase in the chondroitin sulphate content as well as in the rate of glycosaminoglycan synthesis in several cases when the values for the osteoarthritic articular-cartilage samples were compared with those for the age-matched controls. In the late stages there was a progressive decrease in the rate of glycosaminoglycan synthesis and a relative decrease in chrondroitin sulphate synthesis compared with keratan sulphate synthesis, and these decreases were highly correlated with the histological grade.

The relative contents of chondroitin 4- and 6-sulfates in cartilages of different human bones are reported. Articular and vertebral body cartilages contain almost exclusively chondroitin 6-sulfate, whereas growth and subarticular cartilages contain nearly equal amounts of chondroitin 4-sulfate and chondroitin 6-sulfate. Adult cartilages, where the calcification process is complete, contain only chondroitin 6-sulfate. These results that chondroitin 4-sulfate may be an important component for the calcification process, whereas chondroitin 6-sulfate seems to be related to the integrity of the articular surfaces. A chemical defect of chondroitin 6-sulfate in a new mucopolysaccharidosis, characterized by platyspondyly and irregularities of articular surfaces, is in agreement with these results.

The flow-independent (intrinsic) tensile modulus of the extracellular matrix of human knee joint cartilage has been measured for normal, fibrillated, and osteoarthritic (removed from total knee joint replacements) cartilage. The modulus was determined in our isometric tensile apparatus and measured at equilibrium. We found a linear equilibrium stress-strain behavior up to approximately 15% strain. The modulus was measured for tissues from the high and low weight-bearing areas of the joint surfaces, the medial femoral condyle and lateral patello femoral groove, and from different zones (surface, subsurface, middle, and middle-deep) within the tissue. For all specimens, the intrinsic tensile modulus was always less than 30 MPa. Tissues from low weight-bearing areas (LWA) are stiffer than those from high weight-bearing areas (HWA). The tensile modulus of the ECM correlates strongly with the collagen/proteoglycan ratio; it is higher for LWA than for HWA. Osteoarthritic cartilage from total knee replacement procedures has a tensile stiffness less than 2 MPa.

Unlabelled: Wounds penetrating articular cartilage to bone heal with cartilage described variably as either fibrous or hyaline. In the present study, such repair cartilage was induced in the rabbit for biochemical comparison with normal articular cartilage. The main collagen in the repair tissue after three weeks was type I. By six to eight weeks, type II had become predominant and continued to be enriched up to one year; but type I still persisted as a significant constituent of the repair tissue even after a year, so the repair cartilage never fully resembled normal articular cartilage. From radiochemical analysis, type II was determined to be the major collagen synthesized by the repair tissue after three to four weeks. After six months, the repair cartilage contained more collagen and less hexosamine than control cartilage, suggesting that the fibrous texture that often developed was due to a loss of proteoglycans rather than to a change in the type of collagen., Clinical Relevance: Procedures capable of inducing the differentiation of authentic articular cartilage to resurface degenerated human joints would be invaluable. Surgical methods, such as drilling through to subchondral bone, are often attempted. It is not known, however, whether the cartilage that forms is true articular cartilage or, for example, fibrocartilage. The present experimental study in rabbits compared the properties of such repair cartilage with those of normal articular cartilage.

Rabbit knee articular cartilage was studied after the joint was submitted to immobilization, running or increased weight bearing for 24-27 days. Immobilization with a plastic splint reduced the fraction of proteoglycans not extractable with 4 M guanidinium chloride (GdnHCl). In the immobilized joints the chondroitin sulfate content was elevated as calculated from the galactosamine/glucosamine ratio. The ability of these proteoglycans to reform aggregates with endogenous hyaluronic acid in Sepharose CL-2B chromatography was reduced. Increased exercise was associated with an elevation of proteoglycans extractable with 4 M GdnHCl. The increased weight bearing occurring in the contralateral knee elevated the content of proteoglycans not extractable with 4 M GdnHCl. Other effects of weight bearing included increased glucosamine concentration, suggesting accumulation of keratan sulfate-rich proteoglycans, and an elevated hydroxyproline concentration.

The hexasamine content and swelling ratio of adult bovine articular cartilage were determined as functions of depth. Progressing from the surface downward, the hexosamine content increased rapidly to a depth equivalent to approximately 30 to 35 per cent of the total thickness of the uncalcified portion of the tissue, and thereafter decreased at a less rapid rate. The swelling ratio was relatively constant throughtout the first quarter of the tissue but diminished thereafter. At depths below 35 per cent, the curve for the decrease in swelling ratio with depth was similar in form to that for the decrease in hexosamine content. Considering the factors that determine the swelling ratio of polyelectrolyte gels, it is proposed that progressing down from the surface, the interaction between the macromolecular components of the tissue is increased to a depth equivalent to about one-third of the total thickness of the cartilage.

The effects of mechanical stress on the metabolism of dog femoral head cartilage have been investigated. The model involves exercising the dog on a treadmill for an 8-month period and isolating the cartilage proteoglycans from three different anatomical regions of the femoral head. These regions are 1) the articulating area, which shows degenerative changes, 2) the area surrounding the articulating area, and 3) the non-articulating area. The hexosamine analysis of cartilage from the exercised animals, indicates 43% and 21% decreases in regions 1 and 2, respectively, while in region 3 no significant change was observed. The size of the proteoglycan aggregates and monomers also decreased with exercise in regions 1 and 2, and the cartilage from these two regions also incorporated more radioactive sulfate, suggesting a possible attempt to repair the degenerative alterations. The proteoglycan monomer (D1) from the articulating region of exercised dogs failed to interact with hyaluronic acid, while the monomers from other regions in the same animal did interact. Glycosaminoglycan chains from region 1 were smaller than in the control tissue, and there was an increase in chondroitin-4-sulfate synthesis. The results of the present study indicate that the cartilage from the articulating area and the surrounding area resist mechanical deformation by increasing synthetic activity. These observations suggest that the exercised animal can be a valuable model and provide increased understanding of the mechanism of cartilage degeneration.

The distribution of water and glycosaminoglycan in different functional regions of bovine immature articular cartilage were studied. There was always more water in each articulating than in the corresponding growing zone, but there was less water in both zones in the areas of maximum contact. There was more hyaluronate and much more keratan sulphate in the articulating areas of maximum contact than in the minimum contact areas. In the growing zone the distribution of these two glycosaminoglycans did not vary as significantly but there was slightly more keratan sulphate in the area of maximum contact. Regional variations in chondroitin sulphate content were also present although not as striking as those of keratan sulphate. The results suggest that some keratan sulphate may be synthesized as a reaction to load.

This experimental study is complementary to the clinical series of cartilaginous autografts in the knee for medial condylar necrosis. The aim was to determine the viability of the articular cartilage in a series of grafts with variable thickness of the underlying spongy bone. The study was done on 36 adult rabbits and the cartilage was studied by biochemical, histochemical and ultrastructural methods. The results are conclusive. The earliest abnormal signs in the first few weeks affect the thinnest grafts of 4 mm whereas the 12 mm thickness grafts hardly show any lesions. It is therefore possible to use large autogenic grafts for osteocartilaginous defects provided the proportion between the area of the articular surface and the underlying spongy bone of the graft is at least 1/4. Under these circumstances, cartilaginous deterioration will be avoided and reduce long term degeneration.

The content and composition of the matrix of human articular cartilage from two sites - the condylar summits and the upper, posterior surfaces of both lateral and medial sides - of the lower femoral epiphysis of 12 autopsy cases (age 18-46 years) were analyzed. A significantly higher content of both chondroitin sulphate and especially of keratan sulphate was found in cartilage of the condylar summits. The solubility profile of keratan sulphate showed changes indicating a difference between the metabolism of cartilage of the two sites. No significant change with side (medial or lateral) was found. A small decrease in the chondroitin sulphate to keratan sulphate ratio without change in the total amount of hexosamines with age was found on the caudal condylar summits in these adult individuals below the age of 50.

Proteoglycan aggregates and proteoglycan subunits were extracted from bovine articular cartilage with guanidine-HC1 folowed by fractionation by equilibrium centrifugation in cesium chloride density gradients. The distribution of chondroitin sulfates (CS) in the cartilage proteoglycans was studied at the disaccharide level by digestion with chondroitinases. In the proteoglycan aggregate fraction, it was observed that the proportion of 4-sulfated disaccharide units to total CS increased from the bottom to the top fractions, whereas that of 6-sulfated disaccharide units was in the reverse order. Thus, the ratio of 4-sulfated disaccharide units to 6-sulfated disaccharide units increased significantly with decreasing density. The proportion of non-sulfated disaccharide units to total CS tended to increase with increasing density. These data indicate a polydisperse distribution of CS chains, under the conditions used here, in proteoglycan aggregates from bovine articular cartilage.

Living adult human articular cartilage has been maintained in tissue culture for eight days. Cartilage explants were cultured in one of three concentrations of hydrocortisone acetate or as control explants without this drug. The concentrations of hydrocortisone used were 0.01 microng/ml, 0.1 microng/ml and 1.0 mg/ml. The amount of proteoglycan shed into the medium was measured and no significant difference was found between the explants exposed to hydrocortisone and those that were not. These results suggest that hydrocortisone does not have a catabolic effect on the proteoglycan of articular cartilage. The widely held view that intra-articular corticosteroid injection causes cartilage damage, must remain in doubt.

Pig articular cartilage, from which protein-polysaccharides soluble in iso-osmotic sodium acetate had been removed, was extracted in three further stages with 8m-urea in 2m-sodium acetate and with tris-HCl buffer after bacterial collagenase digestion, followed by the same urea-sodium acetate solution, thus leaving only 2% of the original uronic acid in the tissue. The histological appearance of the cartilage was unaltered until after collagenase digestion. The collagenase used did not affect the viscosity or molecular size of a protein-polysaccharide preparation obtained previously. The protein-polysaccharides in each extract differed in size, amino acid composition and protein content, but protein and keratan sulphate contents were not related to hydrodynamic size, in contrast with protein-polysaccharides extracted previously before collagenase digestion. Hydroxyproline could not be removed from those obtained by the first urea-sodium acetate extraction until degraded by heat. The galactosamine/pentose molar ratio agreed closely with the galactosamine/serine molar ratio that was destroyed on treatment with 0.5m-sodium hydroxide, showing that chondroitin sulphate was attached only to serine residues. From these molar ratios the chondroitin sulphate chains were calculated to be of the same average length in protein-polysaccharides in all three extracts although somewhat shorter than in protein-polysaccharides extracted previously. Some threonine residues were also destroyed on alkali treatment suggesting that keratan sulphate may be attached to threonine. These findings together with previous results show that differences in size, composition and physical state extend to all the protein-polysaccharides in cartilage.

The cartilages from the hip joints of 13 normal and 15 osteoarthritic humans were analyzed for glycosaminoglycan content and distribution. The GAGs were separated by elution with CPC on a short cellulose column by the technique of Svejcar and Robertson after digestion of the tissue with pronase and papain. The eluates were identified by a variety of methods including determination of molar ratios, N-acetyl-hexosamine determinations after hyaluronidase treatment and thin-layer chromatography of unhydrolyzed and hydrolyzed GAGs. From the data obtained, it was demonstrated that cartilage from arthritic patients showed a significant increase in the concentration of chondroitin 4-sulfate and a significant decrease in keratan sulfate, with only slight changes in the total amount of GAG present. Calculations of the molar ratios showed variation in the sulfation with chondroitin 4-sulfate appearing in the "supersulfated" state in the arthritic cartilage. The data lead to speculation regarding the process of osteoarthritis, and it is concluded that the changes seen are more likely to represent an altered pattern of synthesis rather than selective degradation. Since the changes suggest a younger cartilage, a theory is advanced that the chondrocyte responds to the chronic stress of osteoarthritis by modulation to a chondroblastic phase.

Intensive rearing, and restricted activity, induce rapid growth in pigs, but they often become lame. Groups of normal and lame pigs reared intensively were killed when 10 or 25 weeks old. Although there were no differences in the overall composition of the knee-joint cartilage of lame and sound animals, the proteoglycans in the cartilage of the lame pigs were extracted more easily by a standardized sequential procedure and contained a higher proportion of molecules of smaller size as assessed by gel chromatography on 6% agarose and Sepharose 4B. These increased at the expense of both the larger and mediumsized molecules. Differences were most evident at 10 weeks of age, when there was twice as much of the smaller proteoglycans in the cartilage of lame pigs. Despite these size-differences, the compositions of the proteoglycans in corresponding sequential extracts of cartilage of lame and normal groups were the same, as were the changes in chemical composition that accompany development. Proteoglycans from lame animals may have undergone limited proteolysis, thus decreasing their size without changing their composition detectably. As the differences between normal and lame groups were greater at 10 weeks than at 25 weeks of age, the first weeks after birth (when the greatest changes occur in the proteoglycans and in the cartilage) may be a critical period in the maturation of articular cartilage in this species. At this time, rapid gain in weight produced by intensive rearing may be too great for the immature cartilage to bear.

Previous reports on the ultrastructure of cartilage matrix have described fibers, amorphous ground substance and, in some instances, dense matrix granules. The fibers are presumably collagen, but the nature of the granules is unknown. The primary purpose of this study has been to investigate the ultrastructure of cartilage matrix ih chick embryos with particular emphasis on the distribution and composition of these granules. In matrix of the zone of articular cartilage, mature collagen fibers can be seen but granules are not present. In matrix of all other zones of cartilage, fibers are smaller and granules are present. When the matrix of epiphyseal cartilage is compared to that of the zone of hypertrophic cells, fibers are similar but the granules in the latter zone are larger and more numerous. The granules in both zones were digested by hyaluronidase and positive to colloidal iron staining. Chemical analyses of cartilage from these zones indicate the hexosamine and radiosulfate content of the zone of hypertrophic cells to be higher than that of the zone of epiphyseal cartilage. The increased hexosamine was shown by column chromatography to be principally sulfated mucopolysaccharide, thereby indicating a direct correlation between size and number of granules and sulfated mucopolysaccharide content in the two zones. These data and the results of the electron microscopic histochemical studies are consistent with the concept that the granules in cartilage matrix contain acidic mucopolysaccharide.