Aspects related to the physiological environment

Titanium has a tendency to accumulate in tissues. The concentrations can be very high, as indicated in Table 9.5. Titanium was not excreted in the urine of hamsters injected with metal salts (Merritt et al, 1992). Small concentrations were found in the serum, red blood cells and organs. Only 5.5% of the injected titanium was found in the kidneys, liver, lung and spleen tissues. The authors suggest that titanium accumulates at the injection site due to the high stability of the titanium dioxide that is formed at physiological conditions. In the same study nearly all the injected vanadium was recovered in the urine. This behaviour is similar to that of nickel and cobalt, and is related to the formation of highly soluble compounds. 

High concentrations of metals were found in capsule and fibrous membranes of loose titanium and Co-Cr stems of total hip prostheses (Dorr et ai, 1990). The same work reports elevated metal ion concentrations in synovial fluid and blood whenever cemented and uncemented stems are loose, but no increase when they are fixed. The average values are given in Table 9.6. The standard deviations (not shown) were often very large, of the order of magnitude of the averages. 

Polyethylene wear debris may artefactually contribute to high ion readings in periprosthetic tissues, as indicated in Tables 9.7 and 9.8 (Meldrum et al, 1993). The high concentrations found in UHMWPE are due to the manufacturing processes. These tables show that there are statistically significant increases in Co, A1 and Ti in the nonarticulated inserts with 

All concentrations are in parts per billion (nanograms/gram This is the minimum detection limit of the spectrometer. 

Metal cation Uptake efficiency ((fmol/cell)/v,M)/h)  

Two years after implantation of femoral components made of Ti-6A1-4V, the titanium and aluminium concentrations measured in the synovial fluid were higher for cemented components than for the uncemented (200 pm HA, or porous Ti coatings) components (Karrholm et al, 1994). Table 9.10 gives the data for the synovial fluid and the aluminium concentrations in serum and urine. No significant concentrations of vanadium were found in any of the samples, which was also the case for titanium in serum emd urine. Fast clearance of vanadium from the synovial fluid, due to high solubility of vanadium complexes, and formation of stable titanium compounds, e.g. titanium phosphates (Ribeiro et al, 1995), might be reasonable explanations for these findings. 

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