Abstract
Introduction
Higher concentrations of metal ion levels after Metal-on-metal (MoM) THA are a cause for concern. Elevated cobalt (Co) and chromium (Cr) ion levels in the blood indicate metal wear, and may predict secondary soft-tissue damage (adverse reaction to metal debris; ARMD). Although, it is well known that concentrations of metal ion levels are elevated in the short term after MoM, the long-term consequences in ion concentration and risk factors for increased ion levels are not clarified. We sequentially investigated the postoperative Co and Cr ion levels after MoM THA and the relationship between the metal ion levels and several risk factors.
Materials and Methods
We reviewed the data on one hundred and eighty six patients of two hundred ninety one MoM THA cases. The one hundred eighty six patients were measured at least three times after a MoM THA surgery over a five year (2005–2010) period in our institution. Serum cobalt and chromium levels were measured by inductor coupled plasma – mass spectrometry at several times in follow-up period, (measured at the preoperative period, the third month, the sixth month, the first year, the second year, and the fourth year after MoM THA). Furthermore, we investigated the correlation between the metal ion levels and various factors which might influence the release of metal ions, such as Body mass index (BMI), renal function, femoral head size, unilateral or bilateral THA, the cup position, and postoperative activity. The renal function was evaluated by measuring estimated glomerular filtration ratio (GFR) at preoperative examination. A postoperative activity was assessed with a pedometer measurement counting number of steps a day. A cup position was evaluated by lateral inclination measured by X-ray or computed tomography.
Results
Average serum Co and Cr concentrations in preoperative period were 0.69 and 0.05 mg/ ml, respectively. Postoperative serum Co and Cr ion levels were significantly increased compared with preoperative value throughout the postoperative period. There was no significant correlation with regards to BMI, renal function, femoral head size tothe metal ion level measurement. In bilateral THA cases, Co and Cr ion concentrations were significantly increased compared with unilateral THA cases. In addition, in cases that its cup inclination was more than 50 degrees, Co and Cr ion concentration were significantly increased compared with cases less than 50 degrees in the first year after surgery. There was a trend for higher metal ion levels in the group of patients who walked more than 7000 steps a day, but this did not reach statistical significance.
Conclusion
Metal ion concentrations of almost patients were increased after MoM THA surgery. Side effects related to elevation of serum Co or Cr concentration were currently not identified and overall clinical results were good. However, Longer follow-up would be necessary if the patients have overlapping risk factors, because those patients may experience elevation of the level in postoperative late stage.
