Several decades after they are inserted, artificial orthopaedic implants - hips, knees, elbows - corrode and release metals into the body that could, over a long period of time, build up to toxic levels.
To measure the levels of these released metals, an ultra-sensitive measurement technique is being developed by scientists at the Institute of Technology, Sligo.
Some implants are left in for 40 or 50 years. All possible short-term tests have been done to confirm that the implants are not toxic, and this research project, still in its initial stages, will try to confirm their long-term safety, according to a doctor specialising in orthopaedics who is associated with the project. He stressed, however, that implants, according to current research, are very safe and there is more danger for a patient from a tooth filling.
In a project directed by Dr Ted McGowan of IT Sligo, the aim is to develop methods to measure the level of metals in tissue or saliva. Tissue is a difficult sample to study because, as well as the trace metals in the sample, there is fat and protein and other materials. So it is hard to measure individually the trace metals, Dr McGowan said.
"If an implant is placed in the body, minute amounts of material may leech into the surrounding tissue. We are developing and characterising new measurement technologies to quantify the levels of these trace elements," he said. His new analytical method is called inductively coupled plasma mass spectrometry (ICP-MS), a technique that separates out the different elements after exposure to temperatures of between 5,000 and 10,000C, allowing the trace elements to be measured on their own.
Because of the volume of implants used today, it would not be possible to remove and replace every one of them if, for example, there was a doubt about the long-term effect of some of them. The technique, however, may enable doctors to test patients with implants - without operating on them - to see if the metals are reaching a toxic level and need to be removed. Orthopaedic specialists can then decide if the implant should be replaced, as well as seeing if some categories of metal corrode more than others. Designers of implants may also use the technique to examine new materials that could be used for implants, Dr McGowan said.
The main difficulty in this type of research is that the levels of leaked metal would be minute: the trace elements could be one millionth or less of the sample's total weight.
Current analytical methods are not sensitive enough to detect these tiny amounts of trace metals in these samples. The technology developed by Dr McGowan can. It is the only machine of its type used at present in Irish third-level research institutions, he said.
The three main types of metals currently implanted are: stainless steel, titanium and a chrome/ cobalt alloy, all of which corrode to some extent in the body, releasing metal ions, including nickel, chromium, vanadium and molybdenum. "These metals are usually benign, but little is known about their effects over a long period of time, and at certain levels some of these elements are essential. Above these levels they may become toxic," said Dr McGowan. It is important to find the extent of this release to better understand the effects on the body, including possible tissue damage in the area around the implant, he said.
As yet, there have been no general body contaminations from these implants. The amount of metals released would be insignificant in this context. The part of the metal that leeches does so into the tissue surrounding the implant, where it stays. It does not spread all around the body.
The accepted normal limits for these trace metals are being refined all the time as a precaution. The whole implant does not corrode. Its outermost layer corrodes slightly because of the body's salt environment and the metal's natural corrosion. No metal is completely inert or neutral - they all corrode to some extent over time.
The work is supported by Forbairt and the Cappagh Trust and it is part of an on-going research collaboration between the Institute of Technology, Sligo, and Sligo General Hospital, where most of future research work will be carried out.