Every year, hundreds of thousands of patients in the U.S. elect to replace hip and knee joints with an artificial implant. According to a recent report, these patients had a mean age of 66.5 years and were 40.8 percent male and 59.2 percent female. This disparity between genders suggests that women are more likely than their male counterparts to see the benefits of a joint replacement. Unfortunately, a small percentage of these female patients could experience gender-specific complications.
A study published in the Journal of Bone and Joint Surgery examined why women were more likely than men to have a higher risk of complications, and it pointed to a hypersensitivity to the metals contained in joint implants as being a contributing factor.
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Could Earrings be the Culprit?
Dr. Kwame Ennin is a total-joint surgeon whose practice is in North Texas. He is a member of the referral line of Texas Health Spine & Orthopedic Center and has performed hundreds of hip and knee replacement procedures. He shared his insights about gender differences in these procedures.
“The primary materials used for artificial joints are titanium, cobalt and chromium alloys,” Dr. Ennin said. “The cobalt and chromium alloys contain nickel, and this is thought to be the sensitizing agent in some cases.
“Only a small percentage of women have medical issues with the metal joints and this is believed to be due to their exposure to these metals through earrings and other jewelry. Plus, women have a higher tendency to have inflammatory issues than men.”
A Very Small Number of Women are Affected
The authors of this research reviewed data on 2,613 patients who were evaluated for unexplained joint pain after total hip and/or knee replacement. All had metal-containing joint replacement components and none had signs of infection, inflammation, or other findings that would explain their pain.
“This research is in line with previous studies,” Dr. Ennin said. “Women are more likely than men to experience post-operative complications. However, the number is not significant. I would caution overreaction to this research. Women are not prone to complications at a rate significantly higher than men.
“Besides the sensitivity to metals, there are other issues women have after joint-replacement surgery. These include fractures and improper sizing of the artificial joints.
“Early in the history of joint-replacement surgery, when product lines were being developed for the procedure, the manufacturers used male-sized bones to calculate the sizing algorithm for the joints. Therefore, early female patients for this procedure were getting oversized joints for their smaller anatomy. In the past ten years, more research into how women’s bodies are shaped has been completed and the joints for women are sized more appropriately.”
What about Testing?
All patients in this study underwent a blood test called the lymphocyte transformation test (LTT) in order to evaluate immune cell sensitization to metals. The LTT can assess whether the patient has developed hypersensitivity to one or more of the metals contained in the implant components, such as cobalt, chromium, or nickel. Is this test used on most or all patients before this total joint replacement surgery?
“Actually, this test is very rarely used,” Dr. Ennin said. “The frequency of metal sensitivity after total-joint arthroplasty is less than a fraction of 1 percent. There are hundreds of thousands of hip and knee replacement being done each year and only a few will have a true metal sensitivity. These are more likely to be women but it is such an exceedingly rare issue, it is not something that we test for on a regular basis.”
What is it about gender that might make this allergy more common among women than men? Is it genetics or environmental effects?
“This is an area that we do not truly understand,” Dr. Ennin noted. “We have some suspicions about this, but there is still a great deal of research that needs to be done.”
Are there any “work-arounds” for this metal hypersensitivity in women that a surgeon can use to perform successful hip and knee replacements?
“If we suspect that a patient might have hypersensitivity to these metal alloys based on their history, we do additional testing,” he said. “There are implants that are treated in a particular manner to limit the body’s access to the metal. Some manufacturers have processed the surface to make it a ceramic material. This means the blood and tissues are never in contact with the metal, thereby preventing the allergy.
“There are also some implants that don’t contain the alloys that can lead to allergy. Several manufacturers have developed a complete line of artificial joints that are a fee of these alloys.”
If constant knee or hip pain is causing you to miss out on the things you love to do, contact us for an appointment to discuss a joint replacement.