Biomechanical properties of mixtures of blood and synovial fluid

Synovial fluid (SF) is a viscous ultrafiltrate of plasma that lubricates articulating joint motion. During acute trauma and certain cartilage repair procedures, blood is introduced into the joint and mixes with variable amounts of SF. The hypothesis of this study was that the dilution of blood with SF alters the rheological properties of the blood and the mechanical properties of the clot formed. The objectives were to determine the composition (solid fraction, protein content), coagulation (fibrin polymerization time, torsional strength), and mechanical (stiffness, permeability) properties of mixtures of blood with 10% or 50%SF. While the initial stages of coagulation of blood were not markedly affected by the presence of the SF, dilution with SF altered the coagulation torque profile over time, decreased the final clot structure mechanical stiffness (42–90% decrease), and increased the fluid permeability of the clots (41‐ to 468‐fold). Compared to diluting blood with PBS, SF had a smaller effect on the mechanical properties of the clot, possibly due to the presence of high molecular weight hyaluronan. These properties of blood/SF mixtures may facilitate an understanding of the repair environment in the joint and of mechanisms of cartilage repair. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:240–246, 2011