Natural joints: Boundary lubrication and antiphospholipid syndrome (APS).

Graphical abstract Highlights • Lipid profiles of injured and healthy knees' synovial fluids show significant differences. • Osteoporosis changes the SF content and the lipid profile substantially. • An increase in phospholipids over the fractured ones and in the lysophosphatidylcholine levels was observed. • The frictional behavior of the solid bilayer lubricant is dominated by lamellar slippage of bilayers. • The high concentration of PL during inflammation (APS) is of secondary importance in the frictional behavior. Abstract The paper shows that osteoporosis (OA) changes the SF content and the lipid profile substantially. To estimate the implication of the lipid environment in case the articular cartilage (AC) changes, we measured friction coefficient normal samples, with early and late stages of (OA). During joint inflammation and osteoarthritis, enzymatically activated β 2 -Glycoprotein I is transformed into antibody conformation. Our hypothesis about cartilage degradation of PL bilayers by antibodies (β 2 -Glycoprotein I) is considering antiphospholipid syndrome (APS), which was not discussed in the literature before. Deactivated PL molecule has no ability to form bilayers, lamellar phases, and liposomes. The phospholipid content in synovial fluid (SF) during joint inflammation, osteoarthritis, and rheumatoid arthritis is significantly higher (2–3 times) above the normal concentration of PL, and has a poor boundary-lubricating ability is deactivated. [ABSTRACT FROM AUTHOR]