Itchy NEW knee? Find out why.
Jan 14, 2019
Approximately 10% to 20% of yearly total joint replacement surgeries have to be done
because the previous implant failed. Several of the usual reasons cited for failure are
typically instability, infection, and dislocation. Recently, however, experts are looking at
metal hypersensitivity as a possible cause. Metal hypersensitivity occurs when the
body develops an immune response to the metal in the implant.
Superficial skin allergies as measured by patch testing, to metal such as nickel, cobalt,
and chromium are generally in the range of 10-15%. Since these same metals are
used in joint replacement products, professionals have begun to wonder if these same
patients are developing post-operative allergies to their implants. These may manifest
as joint pain, effusions, rash and even systemic symptoms. Some estimate the
percentage of SKIN hypersensitivity reactions in joint replacement patients with
malfunction could be as high as 60%. However, the association between these metals
and joint malfunction is currently not clear.
Metal hypersensitivity is typically seen more in women, and is usually reported
between 2-24 months post op. Patients typically present with synovitis and swelling
around the new joint, and sometimes a red, scaly, eczematous type rash.
Typically metal hypersensitivity has been seen as a diagnosis of exclusion, and only
considered after more familiar causes have been ruled out. The options for metal
hypersensitivity testing include skin patch testing, lymphocyte transformation testing,
modified lymphocyte stimulation testing, and leukocyte migration inhibition testing.
Skin patch testing MAY predict that a patient is more likely to have a reaction to their
implant, and some recommendations currently include pre-op testing for patients who
have a history of metal allergy. If a patient has a positive reaction to the metal in the
planned implant, they should be switched to a component made of some
hypoallergenic material such as ceramic, titanium or zirconium. HOWEVER, skin
patch testing is imperfect, and doesn’t always predict even cutaneous reactions, in
addition to systemic ones. The data are currently anecdotal and insufficient, and these
reactions often don’t conform to well understood norms.
If you find post-op joint problems, including superficial rash, it seems prudent to keep
metal hypersensitivity on your list of potential etiologies.
Celia Brown, MD 2019