Modular necks in total hip replacement (THR) can be a source of metal ion release.
Methods
We measured the level of cobalt (Co) and chromium (Cr) ions in the serum of 23 healthy volunteers with a well-functioning ceramic-on-ceramic THR of a particular design, containing a cobalt-chrome (Co-Cr) stem and a Co-Cr modular neck.
Results
Average Co in serum was 1,71 μg/l; median Co was 1.50 μg/l. No patient had Co levels higher than 3.70 μg/l. Average Cr level was 0.49 μg/l; in all but one patient Cr was below the detection limit (≤0.50 μg/l). Co was higher for varus necks compared to all other subtypes: 2.14 μg/l vs 1.58 μg/l (p≤0.05). The same system with Titanium modular necks shows lower Co serum levels: 1.26 μg/l (p≤0.01). In conclusion, the hybrid THR Profemur Xm® – Procotyle L® with a Co-Cr modular neck on a Co-Cr stem design shows very low Cr ion serum levels in a randomly selected group of well-functioning hip patients.
Conclusions
Co ion serum levels are low, but significantly higher for 8° varus necks, and Co levels are significantly higher than values of this system with a Titanium modular neck.
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