Kuopio Regional Institute of Occupational Health, PL BOX 93, FIN-70701 Kuopio, Finland
I read with interest the results of the study by Galois et al. [1]. Physical loading of a joint from work or from free-time physical activity is a risk factor for osteoarthritis (OA) if the exposure level is high or if the joint is injured. There is already a lot of evidence that moderate physical exercise does not increase the risk of developing OA if the joint is not injured [24]. During recent years it has been speculated that physical loading or exercise can prevent OA. Recently two good reviews have been published [5, 6]. In the review by Helminen et al. [6] it is suggested that regular load-bearing directs the development and fate of the collagen fibril network of articular cartilage in the synovial joint, especially in young persons. These effects probably contribute to the establishment and strengthening of the network and prevent OA in middle and old age.
In this field of research, there are many methodological problems with regard to epidemiology, and animal studies are probably also needed. The diagnosis of OA is not easy. Symptoms and radiographic changes should be considered. Microscopic findings after prolonged joint loading are not known to be due to degeneration or adaptation [6]. Because OA develops gradually over a long period, assessment should be made of physical exercise throughout the patient's life. Future studies should also focus on measuring levels of exposure to activity. According to the review by Helminen et al. [6], age probably also influences the effect of joint loading in the prevention of OA. In the study of Galois et al. [1], a favourable effect of physical exercise in the prevention of secondary OA was observed. However, finding the optimal level of joint loading in the prevention of secondary OA after injury may be even more complicated than preventing primary OA. I agree with the excellent old aphorism by Sokoloff [7]: Cartilage can survive in a large range of solicitation, but below and beyond it will suffer. A lot of work remains to be done before the optimal range of joint loading is found.
Notes
Correspondence to: P. Manninen. E-mail: pirjo.manninen{at}ttl.fi
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