A study finds that women aged 60 or more are at higher risk of complications after total hip or knee replacement surgery because they are hypersensitive to metals used in joint implants.

The results suggested that immune sensitisation to implant metals was 49 percent in women, compared to 38 percent of men. Prior to blood testing, 29 percent of women were in pain after joint replacement and said they had allergic skin reactions to metals, compared to four percent of men.

"These findings may explain, at least in part, the sex disparity in the outcomes of certain TJA [total joint arthroplasty] implant designs," said lead researcher Nadim J. Hallab and colleagues from Rush University Medical Center, Chicago. The team analysed 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.

The patients were of the average age of 62; 60 percent of the patients were women. The research appeared in the journal of Bone & Joint Surgery. The average time since the joint replacement was about three years, and in most cases less than two years.

All the patients underwent a blood test--the Lymphocyte Transformation Test, or LTT--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. The results show a "remarkable and significant" increase in immune cell sensitivity to metals in women compared to men with unexplained pain after total hip or knee replacement.

"This supports both our hypothesis and previous reports that females may have a higher risk of adverse responses to implant metals," authors concluded.