A New Knee System: The Right Way to Replace Broken Joints

Ultra high molecular weight polyethylene is not only fun to say, but it is also an incredibly versatile material commonly used as a bearing surface in joint replacements. Polyethylene has low friction, good fracture toughness, and fatigue resistance. Despite its remarkable material properties, there was a pandemic of loosening with early generation polyethylene implants. Scientists discovered microscopic wear particles from the polyethylene generate an immune response which destroys surrounding bone, subsequently causing joint replacements to lose their fixation.

To combat this issue highly cross-linked polyethylene was developed. Exposing the plastic to radiation creates crosslinks which drastically decreases the amount of wear particles. Unfortunately, these implants suffered early catastrophic failure. It was discovered that letting the irradiated plastic interact with oxygen created free radicals, weakening the implant. Now these implants are stored in a vacuum or inert gas, which prevents the destructive oxidation.

And this brings us to present day. While oxidation of polyethylene implants is not as dire a problem as in the past, it is still a concern. Both when stored on the shelf and in the body, these implants suffer some amount of oxidative degeneration. A recent development is the concept of infusing an antioxidant in the polyethylene (such as vitamin E) to neutralize free radicals.

A new product in this relatively new field of antioxidant infused implants is DePuy's AOX antioxidant polyethylene for use in the Sigma rotating platform total knee replacement and LCS complete mobile bearing knee systems. DePuy has just announced that these devices have received FDA Premarket Approval (PMA). DePuy says their new antioxidant stabilizes free radicals while having no effect on the mechanical properties of the polyethylene. While these promising implants have been shown to resist oxidation in the laboratory, whether or not they improve joint replacement longevity remains to be seen.


This post also appears on medGadget, an Atlantic partner site.

Presented by

medGadget is written by a group of MDs and biomedical engineers.

Never Tell People How Old They Look

Age discrimination affects us all. Who cares about youth? James Hamblin turns to his colleague Jeffrey Goldberg for advice.

Join the Discussion

After you comment, click Post. If you’re not already logged in you will be asked to log in or register.

blog comments powered by Disqus

Video

Never Tell People How Old They Look

Age discrimination affects us all. James Hamblin turns to a colleague for advice.

Video

Would You Live in a Treehouse?

A treehouse can be an ideal office space, vacation rental, and way of reconnecting with your youth.

Video

Pittsburgh: 'Better Than You Thought'

How Steel City became a bikeable, walkable paradise

Video

A Four-Dimensional Tour of Boston

In this groundbreaking video, time moves at multiple speeds within a single frame.

Video

Who Made Pop Music So Repetitive? You Did.

If pop music is too homogenous, that's because listeners want it that way.

More in Health

Just In