A Comparison of Clinical Outcomes After Total Knee Arthroplasty in Patients With Preoperative Nickel Allergy Receiving Cobalt Chromium or Nickel-Free Implant
Siljander BR. HSS New York
J Arthroplasty 2023 Jul; 38(7 Suppl 2): S194-S198
doi: 10.1016/j.arth.2023.04.048. Epub 2023 Apr 25
[Link]
Further evidence has now emerged regarding the whole issue of whether or not there is really such a thing as metal allergy, with respect to total knee replacement implants. Skin sensitivity to nickel is common, and most knee replacement implants are made of cobalt-chrome alloys that may have trace amounts of nickel in them. Implants made of titanium tend to be more ‘pure’, with lower amounts of other elements within them; however, even though titanium is very hard, it also has a tendency to be brittle and more prone to scratching, and hence it tends not to be the preferred metal of choice for most implant companies.
The published science shows a few important facts about this whole subject, namely that:
- The immune mechanism that causes skin reactions is different from the immune system inside the actual body,
- Patch-testing for skin allergies is very inaccurate, with high false positive rates, and
- There is no proper evidence that metal surgical implants can actually cause an allergic reaction within the body.
Probably, the most direct and useful article on this subject in the last 10 years or so was published in The Bone and Joint Journal back in 2016 by the team at The Exeter Knee Unit [link]. In this paper, the authors explored the literature about potential metal hypersensitivity/allergy and knee replacement surgery, particularly with respect to the use of so-called ‘hypoallergenic implants’. The conclusion of the paper was that there was no evidence to support the use of hypoallergenic implants. Also, there is no evidence to support the use of pre-operative allergy skin patch testing for nickel.
In an annotation in the Bone & Joint360 journal from October 2016 [link], it was stated that the rise in patients concerned about the possibility of metal allergy affecting outcomes after total knee replacement could actually be coming from an increase in “the increasingly connected neurotic few”!
Interesting data from the Danish joint registry and the Danish patch registry has shown no association between metal allergy and hip replacement outcomes (although there was not enough data to extrapolate this to knee replacements).
In the most recent study on this subject, from the team at The Hospital for Special Surgery in New York, a retrospective review of nearly 18,000 patients was undertaken, with over 20,000 knee replacements having been performed in this group. Of these patients, 282 had been tested for nickel allergy pre-operatively. Of these patients, the authors compared outcomes between those receiving nickel-free implants versus cobalt-chromium standard implants. Importantly, the authors showed no difference in clinical outcomes and no difference in revision rates between those patients having the cobalt-chrome implants versus those who had nickel-free implants.
There will, inevitably, always be a percentage of patients who have their own firm fixed ideas about things regardless of the published evidence and regardless of whatever expert advice might be offered to them from a specialist knee surgeon. Importantly, these patients have an absolute right to determine their own healthcare interventions. At the same time, however, surgeons also have a right not to perform procedures the any patient that they are uncomfortable about or that they feel he is not actually in the patient’s best interests.
Personally, I believe that the best clinical outcomes after knee replacement surgery are seen specifically with the use of custom-made prostheses, and there are excellent long-term outcomes data available from the use of Conformis custom-made knees now. These prostheses are made of cobalt-chrome. Therefore, if any patient did come to me asking for a guaranteed nickel-free implant, then that would preclude them from being able to have a Conformis custom-made prosthesis, and I would therefore politely encourage them to seek a separate opinion elsewhere from another surgeon, rather than knowingly proceed with non-evidence-based surgery with a suboptimal prosthesis.