[Cartilage: from biomechanics to physical therapy]

To review the current knowledge about the relationship between physical activities, cartilage biology, osteoarthritis and rehabilitation.

PubMed, Ovid, Cochrane Data base were interrogated for the period 1966-2000. Key words were: chondrocyte, cartilage, osteoarthritis, mechanical stimulation, exercises, physical therapy, rehabilitation. Were reviewed: the mechanical biology of the chondrocytes and the cartilage, the mechanisms of transduction, the metabolic response of the chondrocytes to mechanical stresses; the effects of physical activity and immobilization on the cartilage in animal models, the main studies on the epidemiology of limbs osteoarthritis and clinical trials on rehabilitation.

In vitro studies have demonstrated that some molecules are involved in the transduction of mechanical stress into intracellular biological event. Chondrocytes and cartilage are sensitive to mechanical stress and cartilage extracellular matrix synthesis and degradation can be modulated by mechanical events. Applications of cyclic loads usually lead to an enhanced matrix synthesis while static loads usually decrease matrix production. In animal models, intensive physical activity or immobilization lead to cartilage alteration mimicking osteoarthritis. In human, intensive and prolonged physical activities are probably associated with hip and knee osteoarthritis. However, there is evidence that exercise therapy and continuous passive motion have beneficial effects on patients with knee or hip osteoarthritis. Fundamental and clinical studies are still needed to determine if exercise programs could have an effect on chondromodulation. Continuous passive motion could help, in the future, to better understand the relationship between mechanical stimulation and cartilage homeostasis.

Rehabilitation could be beneficial in the therapeutic management of limbs osteoarthritis. The protocols of rehabilitation should however be more evaluated in controlled trials.