Abstract
Summary
We report the first use of synchrotron xray spectroscopy to characterize and compare the chemical form and distribution of metals found in tissues surrounding patients with metal-on-metal hip replacements that failed with (Ultima hips) or without (current generation, large diameter hips) corrosion.
Introduction
The commonest clinical category of failure of metal-on-metal (MOM) hip replacements is “unexplained” and commonly involved a soft tissue inflammatory response. The mechanism of failure of the Ultima MOM total hip replacement includes severe corrosion of the metal stem and was severe enough to be removed from clinical use. Corrosion is not a feature that we have found in the currently used MOM bearings. To better understand the biological response to MOM wear debris we hypothesized that tissue from failed hips with implant corrosion contained a different type of metal species when compared to those without corrosion.
Method
Tissue from patients with two types of MOM hip arthroplasty were analysed: Ultima that failed with severely corroded femoral stems (n=12); and large diameter, current generation MOM hips that failed without visible corrosion (n=7). Comparison was also made to samples of cobalt, chromium and molybedanum standards.
We used a high energy synchrotron xray beam to map and characterise the type of metal within the tissues. This enabled us to analyse the type of chemical in a situation that is as realistic as possible: without staining; without the use of a vacuum; and the use of fresh frozen tissue sections with metals at relatively low concentrations. This could not have been achieved without a synchrotron.
Results
Comparison with standards revealed the chemical form of the chromium in the tissues surrounding metal-on-metal hip replacements was chromium (III). This was similar for both corroded (Ultima MOM) and non-corroded (large diameter, current generation MOM) hips. This was chromium (III) phosphate in the non-corroded hips but because the concentration of chromium was lower in the corroded hips it was difficult to differentiate chromium phosphate from oxide. There was some evidence of localistaion of cobalt and chromium, both in metallic form. One sample from corroded hips contained chromium (VI).
Conclusion
Chromium (III) phosphate was the predominant metallic species in the tissues surrounding metal-on-metal hip replacements. This may have arisen from corrosion, wear or a combination of both.
