SAN JOSE—A research team from 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 joints. Synovial fluid is easily squeezed out of porous cartilage, decreasing its thickness and leading to joint degradation and osteoarthritis. Yet despite the constant fluid leakage, or deflation, the symptoms of osteoarthritis typically take decades to manifest. The investigator’s study is the latest to determine why this occurs.
Lead researcher David Burris, PhD, Associate Professor of Mechanical Engineering, and his research 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.
David Burris, PhD
By modeling joint movement using cartilage samples, the team demonstrated that with increased motion (e.g. typical walking speed) the fluid lost as a result of deflation was counteracted by fluid regained through pressurization.
The conclusion, said Dr. Burris, is that, “It is activity itself that combats the natural deflation process associated with interstitial lubrication.” The team presented their findings at the AVS 62nd International Symposium and Exhibition.
The investigators also used in-situ measurements to demonstrate the same fluid recovery process previously observed in-vivo. The researchers presented evidence that fluid drawn into the contact by sliding is pressurized elastohydrodynamically and subsequently forced into the porous articular surfaces to restore hydration.
The new mechanism, which study authors call tribological rehydration, suggests that motion is the engine by which the joint maintains long-term function and health.
“We observed a dynamic competition between input and output [of synovial fluid],” Dr. Burris said. “We know that cartilage thickness is maintained over decades in the joint and this is the first direct insight into why. It is activity itself that combats the natural deflation process associated with interstitial lubrication.”