IMPACT OF THE SYNOVIAL FLUID ON TEMPERATURE INCREASE DUE TO CARTILAGE VISCOELASTIC

PROPERTIES�

  The temperature increase in cartilage is in part due to the viscous behavior of this tissue, which partially dissipates the input mechanical energy into heat (1).

  While the motion of the synovial fluid inside the porous cartilage is supposed to play an important role in the regulation of the cartilage temperature, no specific study has evaluated this aspect.

Background�

M. Nassajian Moghadam, P. Abdel-Sayed, V. Malfroy Camine and D. P. Pioletti1 1Laboratory of Biomechanical Orthopedics, Ecole Polytechnique Fédérale de Lausanne, Switzerland

Developing a poroelastic model of the knee cartilage to evaluate the temperature increase in cartilage due to dissipation and the impact of synovial fluid in the cartilage heat transfer.

  A poroelastic numerical model was developed using Comsol Multiphysics 4.4 software (COMSOL Inc., Burlington, MA, USA).

  The model consisted of femoral and tibial poroelastic cartilage layers. Both cartilage layers were attached to their corresponding femoral and tibial bones. The synovial cavity was modeled as a reservoir for synovial fluid exchange during cartilage compression.

  For model parameters, DSC and Hot Disk TCA were used to measure the cartilage heat capacity and conductivity (2). Cartilage dissipation was measured form the hysteresis curve of bovine cartilage subjected to cyclic mechanical loading.

  The simulation consisted of two coupled multiphysics. (i) Poroelasticity: calculating the synovial fluid flow in and out of porous cartilage when the cartilage was deformed sinusoidally at 1.5 Hz and 15% deformation. (ii) Heat transfer interfaces: calculating cartilage temperature increase due to dissipation under cyclic loading.

Materials and Methods�

Objective�

  Figure 1 shows the cartilage deformation between two layers of tibial and femoral bone during one complete cycle of loading. The black arrows show the fluid velocity in the porous cartilages during exudation and imbibition.

Results�

References�1.  P. Abdel-Sayed, et al, J Mech Behav Biomed Mater 2014, 30, 123. 2.  M. N. Moghadam et al, J biomechaincs 2015, 48, 370.

  We showed in the present study that cartilage viscous dissipation is an important source of internal heat that can locally increase the cartilage temperature.

  The synovial fluid cannot significantly prevent the temperature increase in cartilage due to viscous dissipation. We propose that, this may be related to the cartilage low permeability value (1014m2), which does not let the synovial fluid to travel fast enough through the deep zone of cartilage to allow an effective heat exchange.

  On the other hand, the fast exchange of synovial fluid at the thin layer of the cartilage surface, observed in our study, confirms the role of the synovial fluid for joint lubrication and removing heat produced by cartilage surface friction.

Conclusion�

Figure 1: Deformation field (color code legend in mm) and synovial fluid flow (arrows) during one complete sinusoidal compression.

Figure 2.A) Maximum velocity field in cartilage, B) velocity magnitude in 3 areas (green: along L1, blue: along L2 and red: along L3).

Figure 3. Temperature increase due to dissipation with/without fluid flow.

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  Figure 2 provides a closer look at the maximum fluid velocity in cartilage during cyclic compression. The fluid velocity at the area near the cartilage surface (Zone Z2, Figure 2A) is more that 10 times higher than the velocity in deep zones (Zones Z1, Figure 2A).

  Figure 3 shows that the flow of synovial fluid has not a significant effect on temperature increase in the cartilage at the contact area. Dissipation could increase the temperature of cartilage up to 1.2°C after 10 minutes loading. This temperature increase without fluid flow was about 1.8°C.

Acknowledgement �This work was supported by the Swiss National Science Foundation

(#406240_126070, PNR 62 program).