A comparison of blood metal ions in total hip arthroplasty using metal and ceramic heads
- Peter B. White, BA, Morteza Meftah, MD, Amar S. Ranawat, MD, Chitranjan S. Ranawat, MD
- J. Arthroplasty, Volume 31, Issue 6, June 2016
- Level of Evidence:
- None given
White et al. evaluated serum cobalt, chromium, and nickel content in 60 patients implanted with the same THA type and brand (titanium alloy stem) and 32 resp. 36mm metal-on-polyethylene (MoP) or ceramic-on-polyethylene (CoP) bearing (30 hips each) at their 5-year follow up. Patients receiving a ceramic (BIOLOX®delta) head were significantly more than 10 years younger (mean 60.6 years) compared to those receiving a metal (CoCrMo alloy) head (mean 74.2 years). All patients also had clinical evaluations at 6 weeks, 1-, 2-, and 5-year follow up.
56.7% of patients with a MoP bearing had detectable cobalt levels, with a mean of 2 μg/L, 20% greater 4 μg/L and 3.3% greater 7 μg/L. 17% of patients with MoP bearings had detectable chromium levels (mean 0.3 μg/L). None of the 30 patients with CoP bearings had any detectable metal ion level and no patient in either group had detectable nickel ions.
In regard to head size, patients with 36mm metal heads had significantly higher cobalt levels compared with patients with 32mm metal heads. However, there was no difference of chromium levels in correlation to metal head size.
No significant differences were found for most clinical evaluations between the two groups. The authors only found a slight statistical difference in the WOMAC function sub-score and total score, with patients in the CoP group scoring slightly better. No outcome scores correlated significantly with ion release. Most patients, except one in the CoP group and 3 in the MoP group, were asymptomatic. Seven patients with MoP bearings underwent further imaging for possible adverse local tissue reaction (ALTR) due to cobalt ion levels greater than 4 μg/L (6 patients) or clinical symptoms (1 patient). In 4 of those patients ALTR was identified and two of them were subsequently revised.
The authors conclude that 36mm metal heads result in a higher cobalt level compared to 32mm metal heads and that the use of ceramic (BIOLOX®delta) heads reduces the incidence and magnitude of cobalt and chromium ion release significantly.
- Detection limit for cobalt and chromium ions in serum was high.
- Results are not generalizable to other hip systems.
- Titanium ion levels were not measured.
- Age difference between the groups was > 10 years.
- Patient number was low.
- No information regarding specific patient inclusion/exclusion criteria
- No patient with CoP bearings had detectable cobalt or chromium level.
- No patient with CoP bearings had any adverse reaction.
- 56.7% of patients with a metal head had detectable cobalt levels in serum.
- 13% of patients with MoP bearings had ALTR, 2 of them have been revised.
- Larger metal heads release larger amounts of cobalt.