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Articular cartilage and osteoarthrosis. The role of molecular markers to monitor breakdown, repair and disease.

Osteoarthrosis (osteoarthritis, arthrosis, OA) represents a considerable burden both to the individual patient and society: in 1988 in the USA the total cost of arthritis was estimated at $54.6 billion, most of which was due to OA (Kramer et al. 1983). More than 500000 arthroplasty procedures are performed in the USA annually. Arthritis is the leading chronic condition reported by the elderly; it is reported by almost 50 % of persons aged 65 y and older (Praemer et al. 1992) and more than one third are limited in 5 or more physical activities (Yelin, 1992). Since reports on OA epidemiology consistently show an almost exponential increase of prevalence with increasing age (Danielsson et al. 1984; Felson et al. 1987, 1988; Lawrence et al. 1989; Badley & Tennant, 1992; Steven, 1992; Yelin, 1992), the rapidly changing demographic structure in many countries will in the future only emphasise the magnitude of this problem. OA is not a single disease entity but a common endstage of cartilage and joint failure (Fig. 1). Inherent in this definition is a multifactorial pathogenesis with many recognised risk factors. Of the endogenous risk factors, age, sex, race and inherited susceptibility have all been shown to play a role, but with different weights at different joint sites. The rare single base mutation of 519 arg -* cys in the human type II procollagen gene, which has been shown to cause mild chondrodysplasia and early-onset OA, represents one example of a defined inherited susceptibility (AlaKokko et al. 1990; Katzenstein et al. 1990). Exogenous factors such as obesity, use and abuse of joints and abnormal joint shape are also proven risks, again with different weighting factors for different sites, sex and age (Felson 1988, 1993; Felson et al. 1988, 1992). Risk factors are probably additive; for example, patients with a presumed systemic risk factor shown by the development of distal interphalangeal OA had an increased risk of developing OA in the knee after meniscectomy (Doherty & Dieppe, 1983). There is good evidence for the association of occupational risk factors with OA. For example, farmers and soccer players have an increased relative risk of hip OA, and excessive knee loading is