Surfactants identified in synovial fluid and their ability to act as boundary lubricants

Thin-layer chromatography has been used to identify phospholipids extracted from canine synovial fluid, the major component (45%) being phosphatidyl choline (PC). The extracts and their components have been shown to be surface active in reducing the surface tension of water and to be readily adsorbed to hydrophilic solids, whose surfaces then become hydrophobic. These adsorbed monolayers of synovial surfactant were then found to be excellent boundary lubricants in vitro, reducing the coefficient of kinetic friction (mu) in the dry state and under physiological loading by up to 97% for extracts and 99% for PC alone, reaching mu = 0.01. Surface-active phospholipid is put forward as the possible active ingredient in joint lubrication and shown to be consistent with previous biochemical studies to elucidate its identity. The model essentially follows the classical Hardy model for boundary lubrication imparted by surfactants. It is discussed in relation to a new approach in providing artificial lubrication and facilitating tissue release in patients with arthritis.