Metal on Metal Hip Replacement.  History and Design Rationale

Around 2005-2006, a new idea was brought to Orthopedics.  Instead of having a metal on plastic construct for hip replacements, lets make a metal articulate with metal.  The thought process was that two metals would not wear as much as metal on plastic.  As plastic wear creates small debris that then gets removed by our immune system and can lead to bone resorption (weakening), the orthopedic industry tried to make a product that would have less wear and therefore less particulate debris.  It all sounded great, a huge metal head that was very similar to the size of our current hip itself, the ultimate stability and no ability to cause plastic debris.  In theory, everything was lining up for metal on metal hip replacements to be the wave of the future.

Metal on metal hip replacement. Metal head articulates with metal liner.

2009-2012

As we started to gather data about these metal on metal hip replacements, we began to see early failures and metal ion levels increasing in the blood.  We didn't know the consequence and we didn't know what was happening.  Many surgeons began to stop using metal on metal hip replacements and in 2012 the FDA increasingly became concerned, took some products off the market and put a serious dent in the metal on metal hip replacement use.

Comparison of two hips with the right showing bone loss on the medial (inner) part of the upper stem due to ALVAL

Where did it go wrong?

While traditional hip replacement with metal on plastic had osteolysis (bone breakdown) due to the larger phagocytes (cells that eat large, foreign debris from the body), we now found that white blood cells (lymphocytes) were creating a new problem: ALVAL- aseptic, lymphocyte-dominated vasculitis-associated lesion.  ALVAL was causing pseudotumors- not cancerous but these tumors ate away at tisuse and turned it black, ruined muscle integrity and dissolved bony structure.  

A gigantic pseudtumor visible on X-Ray

I had a metal on metal hip replacement.  What do I do?

Our practice recomends immediate attention and monitoring.  We follow the guidelines made by the American Academy of Orthopedic Surgeons, which essentially involves monitoring patient blood levels of metal while also seeing patients routinely for screening for pseudotumors.  We sometimes recommend MARS MRI, which helps reduce metal aritfact while identyfing pseudotumors.

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Risk stratification after a hip replacement with a metal on metal hip. These guidelines are the best standard to ensure metal on metal hip failures are identified early and therefore unable to cause damage.