In osteoarthritis the articular cartilage becomes roughened, fibrillar, softened, thinned, and finally eroded, with secondary changes occurring in the underlying bone. Histologically, early cartilage lesions in osteoarthritis are characterized by loss of metachromasia in the matrix, and it has been postulated that the initial disturbance involves the intercellular substance (1, 2). The decrease in metachromatic material in the matrix apparently is not due to degenerative changes in the cartilage cells; on the contrary, areas of osteoarthritis usually show proliferation of chondrocytes and increased radiosulfate uptake (2). The loss of metachromasia has been attributed to a diminution in chondroitin sulfate content. Hirsch has shown a decreased sulfate concentration in chondromalacia of the patella, associated with loss of metachromatic staining and loss of elasticity of the cartilage (3). Matthews (4) reported a fall in hexosamine-hydroxyproline ratio in fibrillar osteoarthritic cartilage, and Kuhn and Leppelmann (5) showed a fall in galactosamine and glucosamine concentration of femoral articular cartilage in individuals with "arthrosis deformans." Such observations suggest that metabolic changes occur in the cartilage lesions of osteoarthritis.In the studies to be reported, chondroitin sulfate concentration was determined as glucuronic acid, a more specific assay for this polysaccharide than hexosamine, since the latter is also present in the keratosulfate in cartilage; for example, the hexosamine concentration of adult rib cartilage is four times greater than can be accounted for as chondroitin sulfate (6). A decrease in chondroitin sulfate concentration was found in osteoarthritic cartilage, most marked in the more advanced lesions. In addition, qualitative changes in the polysaccharide-protein complex of osteoarthritic cartilage * Supported by U. S. Public Health Service research grant AM-03421 and training grant 2A-5233. were found, suggesting that polysaccharide breakdown was responsible for the decreased concentration of chondroitin sulfate.
METHODSArticular cartilage was obtained from the knee and shoulder of 20 subjects 6 to 18 hours post-mortem. Knee cartilage was excised from the condylar surfaces of the femur or the posterior surface of the patella; in a few instances, samples were taken from the tibial plateau. Shoulder cartilage was taken from the anterior portion of the humeral head. Each sample was graded and processed separately. The degree of cartilage erosion in each area was quantitated on the basis of the smoothness of the surface, thickness, and consistency by the following criteria. Normal: Cartilage was smooth, white, glistening, and firm; pale yellow discoloration was occasionally present. Grade 1 osteoarthritis: Earliest lesions; minimal pitting and fraying of the surface, sometimes visible only in strong light; normal consistency and thickness. Grade 2 osteoarthritis: Obvious irregularity of cartilage surface with pitting and fraying; some softening, but normal thickness. Grade 3 o...