Deficiency of lubricating surfactant lining the articular surfaces of replaced hips and knees

While preceding papers have demonstrated that the active load-bearing agentin the boundary mode of joint lubrication is surface-active phospholipid(SAPL)--probably adsorbed as the outermost layer of articularcartilage--this study is designed to determine whether that layer isdeficient in osteoarthritis (OA). This layer has been studied on 12 hipsand 31 knees obtained from surgically replaced joints afflicted with OA.Measurement of the contact angle (theta) subtended by a droplet of salineclearly demonstrated a highly significant decrease in hydrophobicity, thetafalling from 100 degrees for 13 bovine controls (78 degrees for five humancontrols) to 56 degrees for arthritic hips and 63 degrees and 68 degreesfor the 'worn' and 'unworn' areas of arthritic knees, respectively. Thesechanges were reflected in the quantities of SAPL (and proteolipid)recovered from the same articular surfaces by solvent rinsing, yields ofSAPL being 36% lower in hips and 25% lower in 'worn' areas of knees, butnot significantly different in 'unworn' areas. These results indicate thatthe outermost lubricating layer of SAPL deposited onto articular cartilagefrom SF is deficient in OA.