Metal Ion Level testing is a valuable way to screen for excessive wear of metal bearing implants. We recommend routinely measuring cobalt chromium and titanium levels 2 years after surgery on every patient in order to discover adverse wear failures early. In certain patients we recommend repeat monitoring thereafter. Most patients with metal bearing hip replacements as well as metal-plastic bearing knee replacements have some elevation of cobalt and chromium in their blood. There is no known problem caused by this.

Speculations of increased cancer risk have been disproven by numerous long-term studies. There is no evidence that kidney damage can occur due to circulating ions, but abnormal kidney function can lead to ion level elevation in the blood. There is no agreed upon acceptable level for joint implant patients. The normal levels in patients without implants is about 2 ug/L. We have done extensive studies on metal ion levels. The lowest level we have seen associated with an adverse wear failure (AWF) is 15ug/L. Sometimes a level higher than this is seen without evidence for AWF.

Implant loosening may be another failure mode that can be associated with elevated levels. There have been a handful of case reports of generalized systemic side effects possibly caused by very high metal ion levels. We have seen more than 10 AWF cases with levels between 50-200ug/L and none exhibited any systemic symptoms. It appears that systemic effects do not occur at levels that are typically seen in well functioning cases, and are even rare with very high levels seen in AWF cases. We obtain levels at 2 years because it is known that implants go through a run-in wear period of 1-2 years. Less is known about what is an acceptable level during this time. The earliest time that we have ever seen an AWF is after 2 years; it takes time to develop these problems.

We currently recommend metal ion testing:

• Routinely on all patients at 2 years postop
• When evaluating a painful hip implant
• Prior to performing a second hip surgery on the opposite hip
• Repeat levels periodically if levels are above 10ug/L, there is a steep acetabular inclination angle, the patient has a recalled DePuy ASR implant

We recommend obtaining a metal suppression CT or MARS MRI whenever we encounter a ion level above 10ug/L. Significant soft tissue inflammatory mass (not cancer) or large fluid collections indicate a probable AWF. All case of AWF so far have occurred in cases where the acetabular inclination angle is above 50. But only 5% of patients with AIA>50 develop AWF.