Movement Combats Knee Osteoarthritis

A research team from the Mechanical Engineering Department at the University of Delaware has proposed a mechanism that may explain how motion can cause cartilage to reabsorb fluid that leaks out over time. About 80% of cartilage tissue is composed of synovial fluid that is essential for weight bearing and lubrication of joint surfaces. This fluid is easily squeezed out of porous cartilage, decreasing its thickness and leading to joint degradation and osteoarthritis pain. Yet despite the constant fluid leakage, or deflation, the symptoms of osteoarthritis typically take decades to manifest. The team’s study is the latest to investigate the question of why.

The team tested their theory that the reabsorption process was driven by hydrodynamic pressurization, which occurs when the relative motion of 2 surfaces causes fluid between them to accelerate in the shape of a triangular wedge. The phenomenon is familiar to motorists as hydroplaning, as reduced friction causes loss of control. But if the affected tire were porous, external pressure could force the water back into the tire. By modeling joint movement using cartilage samples, the team demonstrated that with increased motion—ie, typical walking speed—the fluid lost to deflation was counteracted by fluid regained through pressurization. The conclusion, according to lead researcher David Burris, PhD, is that “It is activity itself that combats the natural deflation process associated with interstitial lubrication.” The team’s presentation, “Tribological Rehydration of Cartilage: A New Insight into an Old Problem,” is scheduled for tomorrow at the AVS 62nd International Symposium and Exhibition in San Jose, California.

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