Itchy NEW knee? Find out why.

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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