E ff e c t o f E x e rc i s e o n A r t i c u l a r Ca r t i l a g e Harpal K. Gahunia, MSc, PhDa,*, Kenneth P.H. Pritzker, MD, FRCPCb,c,d KEYWORDS ! Articular cartilage ! Exercise ! Biomechanics ! Aging
and little information was available on human cartilage. Recent improvements in magnetic resonance imaging (MRI) technology has allowed visualization of human articular cartilage in vivo enabling researchers to investigate the variations in the morphologic and biochemical components of human knee articular cartilage during loading and compressive forces while exercising as well as in diseased states.12–14 Physical exercise, performed frequently over time, has been shown to increase bone and muscle mass (eg, body building), whereas states of inactivity or microgravity have been associated with tissue atrophy.15,16 The biosynthetic activity of chondrocytes has also been experimentally shown to be regulated by mechanical stimuli.17,18 Based on these in vitro findings, mathematical models have been developed that explain the variable thickness of cartilage between joints based on differences in mechanical loading magnitude.19–22 Current findings suggest that the human cartilage deforms very little in vivo during physiologic activities and recovers from deformation within 90 minutes after loading.12,13 Several studies have shown that with immobilization cartilage undergoes atrophy when subjected to reduced loading conditions and that cartilage thickness is only partially restored with exercise.23–29 Both clinical and animal research have shown that continuous passive motion of the joint, after joint procedures, is an important stimulus for articular cartilage regeneration.30–32
The authors have no conflicts of interest to disclose. a Orthopedic Science Consulting Services, Oakville, Ontario, Canada b Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada c Department of Surgery, University of Toronto, Toronto, Ontario, Canada d Pathology and Laboratory Medicine, Mount Sinai Hospital, 600 University Avenue, Toronto, Ontario, Canada, M5G 1X5 * Corresponding author. E-mail address: harpal.gahunia@utoronto.ca Orthop Clin N Am 43 (2012) 187–199 doi:10.1016/j.ocl.2012.03.001 0030-5898/12/$ – see front matter ! 2012 Elsevier Inc. All rights reserved.
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Joints are composed of specialized connective tissues which, from a functional point of view, act synergistically to effectively and efficiently deal with the mechanical loads encountered over a lifetime.1,2 When performing various tasks such as standing, walking or running, the knee frequently encounters forces up to several magnitudes higher than body weight.3–5 Articular cartilage plays a crucial role in maintaining mechanical competence by providing an almost frictionless gliding surface of synovial joints. Under physiologic conditions, knee cartilage has the unique capability to withstand hydrostatic pressure and the ability to uniformly transmit and dissipate enormous forces across the joint from one subchondral bone to the other during motion. These cartilage features are due to its molecular composition and 3-dimensional architecture, coupled with its highly hydrated state and biomechanical properties.1,2,6-11 As such, articular cartilage has the ability to withstand high compressive forces associated with not only activities of daily living but also activities with markedly increased locomotive stresses such as sports. However, the ability of the cartilage to perform its biomechanical functions can be compromised by changes in tissue properties that occur with normal aging, injury, or diseases such as chondromalacia patella, osteochondritis dissecans, osteoarthritis (OA), and rheumatoid arthritis. Traditionally, the effects of exercise on articular cartilage have been examined in animal models,