Abstract
Introduction
Metal on metal (MoM) bearings have been dealt a severe blow in the past few years. The release of metal ions may have arisen from corrosion, wear, or a combination of the two. Edge loading due to implant malposition is thought to cause a failure of lubrication and to contribute to excessive wear and increased metal ion release [1]. Literature reports aseptic lymphocytic vasculitis-associated lesions (ALVAL) are associated with a variety of failures which occur to some degree in all implanted metal femoral components [2, 3]. Moreover, Willert et al [4] has described ALVAL in non-MoM bearing designs too. This paper has investigated the metal ion release due to total hip replacement (THR), Hip Resurfacing (HR) and total knee replacement (TKR).
Methods
Following human ethics approval 200 patients were enrolled in this single surgeon randomised controlled study. The treatment groups were total knee replacement (TKR) (n=100), HR (n=50) and THR (n=50). Serum cobalt (Co) and chromium (Cr) ion levels were taken preoperatively for baseline measurement then at 6 month, 1 year and 2 years postoperatively.
Results
A preliminary observation of the data was performed to investigate the release trend of the Metal Ions (Figs 1 & 2). Initially there is a significant difference (p<0.05) between TKR and THR for the 6 month ion levels. At the 1 year time-point there is no difference between the TKR and THR for Cr levels. However, there is a significant difference (p<0.05) between TKR and HR for Cr levels at the 1 year time-point and a highly significant difference (p<0.001) between TKR, THR and HR for Co levels at 1 year. At the 2 year time-point there is no difference (p>0.05) between the TKR and THR for Cr levels. However, there is still a highly significant difference (p<0.001) between TKR, THR and HR for Co levels at 2 years. There was no significant difference detected between THR and HR (p>0.05) for both Co and Cr levels at all time-points.
Discussion and Conclusion
All patient metal ion levels were in the safe range. Whilst there are other reported studies comparing the effect of head diameter of MoM bearings on systemic release of metal ions, this is the first paper to compare MoM hip bearings with TKR bearings. There was no difference between the release of Cr levels for the TKR and THR at the 2 year time-point. The trend of metal ion release is similar for all implants. However, THA deviates from HR at the 12 month time-point for Co levels. This paper demonstrates that surgical technique plays an important role in metal ion release and the long term integrity of a MoM bearing.
