Laird Harrison

March 14, 2014

NEW ORLEANS — Patient discomfort with some joint replacements could be related to allergies to common implant materials, a new study shows.

"If you have had a skin reaction, you should be patch-tested before having an implant," said lead investigator Karin Pacheco, MD, assistant professor of medicine at the University of Colorado Denver.

She presented the study findings here at the American Academy of Orthopaedic Surgeons (AAOS) 2014 Annual Meeting.

Although many patients test positive for allergies to implant materials, orthopedic surgeons usually don't take those allergies into account when recommending implants to their patients.

To better understand the role of allergies in implant failures, Dr. Pacheco and her team examined patients referred for possible allergy by their orthopedic surgeon.

Of the cohort, 23 candidates for joint replacement with a history of metal reactions were seen preoperatively. The other 83 had already undergone joint replacement and were complaining of stiffness or pain; however, no signs of infection or mechanical failure could be found in their implants.

Seventy-six percent of the patients had a knee replacement, 18% had a hip replacement, and 6% had some other joint replaced.

The investigators performed skin patch tests on all patients to check their sensitivity to materials commonly used in joint replacements.

About half of those with unexplained implant failure were allergic to one of the materials in the implants, as were about three quarters of the candidates for joint replacement with a history of allergic reactions.

The most common allergic reaction was to nickel, which affected 65% of the preoperative patients and 20% of the postoperative patients. That was followed by cobalt, nickel and cobalt combined, chromium, any bone cement extract, bone cement, and benzoyl peroxide.

Table: Sensitivity to Implant Materials on Skin Patch Test

Patients Positive (%) Negative (%)
Preoperative evaluation (n = 23) 74 26
Postimplant evaluation (n = 83) 53 47
All (n = 106) 58 42

 

The investigators were able to contact 63% of the patients for follow-up after the patch tests.

Of the allergic patients who underwent revision surgery to change their implants and remove the allergen, 78% reported that they were "moderately" or "a lot" better.

Of the allergic patients who did not undergo revision surgery or who underwent revision without consideration of the patch test results, only 19% reported that they were "moderately" or "a lot" better.

The difference between these 2 groups was statistically significant (P = .0002).

 
If you have had a skin reaction, you should be patch-tested before having an implant.
 

Of the preoperative patients with a positive patch test considering joint replacement, 73% based their decision on the test results. All of them reported doing "moderately" or "a lot better."

"The patch test appeared to be clinically relevant," said Dr. Pacheco.

Surgeons should take allergies into consideration more often; however, many of them believe that skin allergies are not related to deep-tissue allergies, she said. "I don't know who perpetuated that. It doesn't make sense immunologically," she added.

Surgeons have rarely considered allergies when discussing joint replacements, said session moderator William Maloney, MD, chair of orthopedic surgery at Stanford University in California.

"I can't remember seeing a patient who I thought had an allergy," said Dr. Maloney. "But we do have patients who have pain and stiffness that we can't explain, so there might be something to this."

Because nickel allergies are so common — affecting about 15% of the population — he wondered why implants don't cause even more problems.

"If you don't look for it, you won't find it," said Dr. Pacheco. She added that some patients can develop a tolerance to the allergens in their implants.

Dr. Pacheco and Dr. Maloney have disclosed no relevant financial relationships.

American Academy of Orthopaedic Surgeons (AAOS) 2014 Annual Meeting: Abstract 120. Presented March 11, 2014.

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