21. EFFECTS OF SYNOVIAL FLUID ON BLOOD CLOT PROPERTIES: IMPLICATIONS FOR CARTILAGE DEFECT REPAIR

Department: Bioengineering
Faculty Advisor(s): Robert Sah

Primary Student
Name: William J McCarty
Email: wmccarty@ucsd.edu
Phone: 858-534-5682
Grad Year: 2012
Resume: View Resume

Abstract
INTRODUCTION: Articular cartilage usually provides a load-bearing surface on the ends of bones, in part by facilitating fluid pressurization during load bearing. When cartilage defects are treated by microfracture, as well as when joints are subjected to trauma, blood is introduced into the joint and mixes with variable amounts of synovial fluid (SF). Comparisons of the rheological properties of clotted blood and blood mixed with synovial fluid in the context of cartilage defect repair have not been described. Objective: to determine the composition, coagulation, and mechanical properties of mixtures of blood and synovial fluid.

METHODS: Bovine SF and blood were obtained and mixtures of blood/SF of 100/0, 90/10, and 50/50 by volume were prepared. (1) Composition. Blood/SF mixtures were made to clot by addition of CaCl2 to 0.1M in a custom mold. Cylindrical discs, 1.6mm thick x 10mm diameter, were then punched free. (2) Coagulation Properties. An aPTT-like test was performed to determine the initiation time to clot formation. A TEG-like test was performed to determine the reaction time (r) and maximum amplitude (MA) parameters. (3) Compressive Properties. Clots were tested in confined compression to determine modulus and permeability. Statistics. One-way ANOVAs (effect of blood/SF ratio) with Tukey post-hoc tests. Data as mean±SEM.

RESULTS: (1) Composition. Dry weight varied with %SF (p<0.001) with significant differences between the 0 and 50% and between the 10% and 50% groups (p<0.001) (2) Coagulation Properties. The time for initiation of coagulation was <5 min and not affected by %SF. Certain TEG coagulation indices were affected by %SF. r averaged 8-13 min and did not vary significantly (p=0.24). MA diminished by 67% as %SF increased from 0 to 50% (p<0.005). (3) Compressive Properties. Clot compressive properties varied markedly with %SF. HA decreased by 75% (p<0.05) and kp increased by 200-fold (p<0.05) as %SF increased from 0 to 50%.

DISCUSSION: These results demonstrate the marked effects of SF on blood clot formation in the joint and have implications for the joint environment post-trauma as well as cartilage repair procedures. The effects of SF on the established clot (decreasing mechanical stiffness indicated by MA and HA and increasing fluid conductance indicated by kp) suggest that thorough removal of SF may benefit initial clot stability. The properties of blood clots may be important not only in microfracture-based cartilage repair procedures, but also other procedures in which blood becomes clotted in repair constructs, including tendon, ligament, and meniscus repair.

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