Evaluation of the speciation status of aluminium(III) ions in isolated osteoarthritic knee-joint synovial fluid.

High field 1H NMR spectroscopy demonstrated that the equilibration of added Al(III) ions in osteoarthritic (OA) knee-joint synovial fluid (SF) resulted in its complexation by citrate and, to a much lesser extent, tyrosine and histidine. The ability of these ligands, together with inorganic phosphate, to compete for the available Al(III) in terms of (1) thermodynamic equilibrium constants for the formation of their complexes and (2) their SF concentrations was probed through the use of computer speciation calculations, which considered low-molecular-mass binary and ternary Al(III) species, the predominant Al(III) plasma transport protein transferrin, and also relevant hydrolysis and precipitation processes. It was found that, at relatively low added Al(III) concentrations, citrate species were more favoured, whilst phosphate species became dominant at higher levels. The significance of these findings with regard to the in vivo corrosion of aluminium-containing metal alloy joint prostheses (e.g., TiAlV alloys) is discussed.