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Study indentifies metal ion levels predictive for failure in metal-on-metal THA
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NEW ORLEANS — Metal ion levels measuring less than 7 parts per billion are predictive of a well-functioning metal-on-metal total hip arthroplasty, according to the results of a study presented here at the 2010 Annual Meeting of Orthopaedic Surgeons.
During his presentation, Alister Hart, FRCS, said that patients who have undergone metal-on-metal total hip arthroplasty (THA) should be screened for blood metal ion levels and that high cobalt levels can predict failure in metal-on-metal hips.
High metal ions
In a prospective study of 163 metal-on-metal hips, Hart and his colleagues measured the blood metal ion levels in patients with failed implants and those of patients with well-functioning implants using mass spectrometry. They also performed a specificity and sensitivity analyses.
“This study aimed to quantify sensitivity and specificity of high blood metal ions in predicting failure,” Hart said.
The investigators identified cases with cobalt or chromium levels greater than 7 parts per billion (ppb) as outliers in the group of well-functioning hips. They, therefore, defined patients with high serum metal ion levels as those with cobalt or chromium levels greater than 7 ppb.
Sensitivity and specificity
Hart reported that 34 of the 75 patients with failed metal-on-metal hips had metal ion levels greater than 7 ppb, and eight of 88 patients with well-functioning metal-on-metal hips had metal ion levels greater than 7 ppb.
“Almost all the well-functioning hips had levels less than 7 [ppb],” he said. “Some had greater, but they are a very small proportion. Hence, the sensitivity is low, but the specificity is very high.”
In the study abstract, Hart and his colleagues recommended monitoring patients with metal ion levels greater than 7 ppb.
“High cobalt or chromium, greater than 7 parts per billion, is highly specific for failure,” Hart said during his presentation. “You have to combine it with common sense and good doctoring.”
- Reference:
Hart A, Bandi A, Sabah S, et al. High blood cobalt levels can be used to predict failure of metal on metal (MOM) hips. Paper #7. Presented at the 2010 Annual Meeting of the American Academy of Orthopaedic Surgeons. March 9-13. New Orleans.
Hart has received research or institutional support from Biomet, Corin U.S.A., DePuy, A Johnson & Johnson Company, Finsbury, Mathys Ltd, Smith & Nephew, and Stryker; he also has stock or stock options with Corin.
