Oligolamellar lubrication of joints by surface active phospholipid.

Six studies have been undertaken to test the hypothesis that oligolamellar phospholipid adsorbed to the articular surface contributes to joint lubrication. Synovial fluid (SF) proved highly surface active, rapidly depositing phosphatidylcholine (DPPC) on glass surfaces, rendering them hydrophobic--a property of well rinsed articular surface removable by the same fat solvents known to increase joint friction by 150%. Electron microscope studies demonstrated lamellar bodies (surface active DPPC) on the articular surface and in SF and lamellated phospholipid in light scrapings of joint surfaces. These were consistent with the quantity of phospholipid recovered by solvent rinsing. Friction measurements in vitro demonstrated excellent boundary lubrication imparted by multimolecular layers of DPPC under high load with coefficients of kinetic friction reaching physiological ranges (0.002-0.005).