The significance of ageing as a possible factor contributing to the pathogenesis of osteoarthrosis is debatable (Byers, Contepomi, and Farkas, 1970); moreover, the matter may require separate consideration for the hip, knee, and other joints. Necropsy studies of the incidence, natural history, and severity of age-related cartilage lesions in various joints are relevant to this question. Age changes in the hip, knee, and other joints have been studied by Heine (1926), in the knee joint by 0wre (1936) and Bennett, Waine, and Bauer (1942), in the elbow by Goodfellow and Bullough (1967), and in the hip by Byers and others (1970). These previous studies have been based mainly on a qualitative assessment of the state of the articular surfaces, the results being expressed, for example, in terms of a grading system such as that devised by Collins (1949). The present study, in contrast, is based on a quantitative method in which the results are expressed as a percentage of the articular surface area affected by destructive cartilage changes. The patello-femoral component of the knee joint was selected for study by this method, since the slight curvature of the patellar surface makes this articulation suitable for quantitation by a point-counting technique. Previous studies, with the exception of that by Goodfellow and Bullough (1967), mostly seem to have relied mainly on naked-eye inspection of unstained surfaces. The present study, in contrast, was made on surfaces which had been painted with indian ink, since such preparations make cartilage lesions more readily apparent (Bullough and Goodfellow, 1968;Meachim, 1972a) and facilitate point-counting of the various types of surface change. Naked-eye examination was supplemented by stereomicroscopy of the surface and, where indicated, by transmitted light microscopy of tangential surface slices (Meachim, 1972a). Material and methodsThe study was made on the patello-femoral articulation of one or both knee joints from a random series of necropsies within the city of Liverpool on 98 white subjects (53 male; 45 female) whose ages ranged from 4 weeks to 94 years. Persons dying from accidents and persons dying outside hospital suddenly or unexpectedly from natural causes were included as far as possible. Joints showing evidence ofprevious inflammatory disease, disuse atrophy, surgery such as meniscectomy, old injury, or injury from a recent accident were excluded. Quantitative data were obtained from indian ink preparations of the left patellar articular surface in all of the 98 subjects, from the opposing left femoral articular surface in 83 of them (43 male; 40 female), and also from the contralateral right patellar surface in thirty of the adults (14 men and 16 women). SURFACE QUANTITATIONIndian ink preparations were made by the method previously described (Meachim, 1972a). The painted articular surfaces were then examined by the unaided naked eye, by study of photographic prints at a magnification of x2, by stereomicroscopy enface at a magnification of x 10, and, where indic...