Molecular weight independence of the effect of additive hyaluronic acid on the lubricating characteristics in synovial joints with experimental deterioration

Objective. To assess the molecular weight dependence of the lubricating characteristics of additive hyaluronic acid in animal joints with experimental deterioration. Design. An experimental study in rabbits stifles in vitro. Background. Hyaluronic acid is used as a drug for osteoarthritis. However, the molecular weight dependence of the effect of hyaluronic acid has been unclear. Methods. Using a robotic arm under force-control, frictional coefficients were measured in fourteen rabbit stifles. The experimental conditions examined were: (1) intact joint surfaces; (2) after the joint surfaces were washed with physiological saline; (3) after the addition of 1% hyaluronic acid solution with a molecular weight of one million daltons and two million daltons, respectively. Results. The increased frictional coefficient produced by washing with saline was decreased significantly by the addition of hyaluronic acid to the joint surfaces. This effect was observed regardless of the molecular weight of the hyaluronic acid. Conclusion. The lubricating characteristics of hyaluronic acid in synovial joints do not change with molecular weight.