UC San Diego

Articular cartilage is a connective tissue covering the ends of long bones in synovial joints that facilitates low -friction joint articulation. In the case of high loads and low sliding velocities, lubrication of synovial joints occurs in a boundary, surface-to-surface contact mode, which is governed by interactions of biomolecules, such as hyaluronan (HA) and proteoglycan-4 (PRG4), with cartilage. Injuries increase the risk of osteoarthritis (OA) at a later age, but the mechanism by which this occurs is unclear. While the lubricating ability of synovial fluid in the boundary mode becomes abnormal following injury, the time-dependent changes in SF lubricating and biochemical properties following arthroscopic treatment of acute injury is unknown. Thus, the aim of this study is to investigate the changes in SF lubricating ability and biochemical composition, as joints transition from normal to injury and repair states, and whether restoration of deficient lubricant molecules can restore normal lubricating ability. Initially normal lubricating ability, indicated by a low steady-state friction coefficient, of SF became deficient shortly following injury, but returned to normal by a longer time post-surgery. These changes were correlated with a decrease in the concentration of HA and a shift in HA towards lower molecular weight (MW) forms. Furthermore, these changes were observed independent of the type of articular cartilage repair treatment applied. Supplementation of deficiently lubricating SF samples with high MW HA restored the boundary lubricating ability, indicating the importance of HA as a lubricant molecule and also suggesting its potential therapeutic ability