RELEASE OF LUBRICATING SYNOVIAL SURFACTANT BY INTRAARTICULAR STEROID

This study was undertaken to determine whether glucocorticosteroids pr omote the secretion of lubricating surfactant, i.e. surface-active pho spholipid (SAPL), into the joint. A standard clinical dose (100 mg) of methylprednisolone acetate (MPA) in 2.5 ml of saline was injected int o the load-bearing right radiocarpal joint of five horses and 2.5 ml o f saline injected into each of the contralateral joints used as contro ls. Synovial fluid (SF) was aspirated from all 10 joints before inject ion and at intervals of 16 and 32 h after injection, and then analysed by standard methods. All test joints showed an elevated level of SAPL , the increases averaging 112% after 16h and 76% after 32 h, which wer e highly significant relative to the control joints. A large increase at 16h was also found in proteolipid as a possible further marker of s urfactant release. Significant quantities of proteolipid were also fou nd in human SF. Since intra-articular steroids can dramatically improv e joint mobility in both humans and horses, it is proposed that part o f the benefit may be derived from improved lubrication arising from th e remarkable ability of SAPL to lubricate under high load. Other possi ble benefits of elevating surfactant levels in the joints include cont rol of cartilage hydration, promotion of macrophage activity and the a bility to scavenge oxygen free radicals.