Intrinsic viscoelasticity increases temperature in knee cartilage under physiological loading

Abstract

Temperature Magnetic resonance imagingDifferential scanning calorimetry a b s t r a c t Metabolism of proteoglycans and hyaluronic acid has been shown to be temperaturedependent in cartilage explants, with optimal anabolic effects between 36 1C and 38 1C. At rest, the temperature of human knee has a value of around 33 1C. We aim to show in this study that viscoelastic properties of healthy human cartilage allow its temperature to reach those optimal temperatures during physiological mechanical loadings. We developed a model allowing to determine the temperature increase in cartilage due to viscous dissipation. The model had three parameters, which were determined experimentally. The first parameter was the energy dissipated by cartilage samples submitted to cyclic stimulation. It was obtained with standard in vitro mechanical testing. The second parameter was the cartilage heat capacity and was measured in vitro with differential scanning calorimetry. Finally, the third parameter was the time constant of cartilage heat transfer and was obtained with in vivo magnetic resonance thermometry performed on four volunteers. With these experimentally determined parameters, the model predicted that cartilage dissipation is sufficient to raise the temperature in healthy knee cartilage from 33 1C to 36.7 1C after a 1 h walking. These results showed that intrinsic viscoelastic properties of the cartilage could induce a temperature increase optimal for the production of proteoglycans and hyaluronic acid. Interestingly, degenerated cartilage did not present high enough viscoelastic properties to significantly induce a temperature increase. Taken together, these data suggest an association between cartilage dissipation and its homeostasis.

Impact of synovial fluid flow on temperature regulation in knee cartilage

“…The dissipation power was calculated from the load-displacement graphs as the integral of the area enclosed by the hysteresis curve. The detailed procedure is explained in a previous study (Abdel-Sayed et al, 2014a, 2014b.…”

“…Heat transfer coefficient of cartilage: the heat transfer coefficient (λ) was obtained from a Proton Resonance Frequency Shift (PRFS)-based MR thermometry used to monitor the temperature drop of the cartilage when the knee of 4 volunteers was immobilized after a 20 min joint activity (Abdel-Sayed et al, 2014a, 2014b. We calculated the heat transfer coefficient (λ) from the following equation:…”

“…a is the time constant derived form the curve fitting to the temperature drop curve of the cartilage following the 20 min joint activity and was detected by MR thermometry method (Abdel-Sayed et al, 2014a, 2014b, S is the surface of each cartilage element in MRI data, m is the mass of each element and c is the heat capacity of the cartilage. Since the heat transfer coefficient (λ) was calculated when the knee was at rest, meaning that no dynamic load was applied on cartilage to cause fluid flow, it includes all heat transfer mechanisms at the knee cartilage except the effect of synovial fluid flow.…”

“…However, given that cartilage is avascular and has viscous properties (Hayes and Mockros, 1971;Huang et al, 2003), a local temperature increase in this tissue could result from dissipation following a cyclic mechanical loading (Abdel-Sayed et al, 2014a, 2014bBali and Sharma, 2011). While this temperature increase could be moderate, its effect can be important on biochemical reactions.…”

“…An indirect link exists then between the dynamic loading of knee and the cartilage homeostasis through dissipative phenomenon suggesting a possible new mechanobiological pathway in cartilage (Abdel-Sayed et al, 2014a, 2014b.…”