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Graphite Is Connected to the Hip Bone

Scientists have discovered that graphitic carbon, not proteins, lubricates metal-on-metal hip implants.

If you think graphite is found only in your pencil, think again. A team of scientists has discovered that in metal-on-metal hip implants, the lubricating layer that forms on both the implanted ball and socket consists of graphitic carbon.

This layer reduces friction, and prevents the implant from wearing out and corroding. Scientists used to think proteins formed this lubricating layer as they do in the body’s natural joints.

Why is this important? Understanding the composition of this lubricating layer may allow the development of hip implant devices that last longer.

Every year, more than three-quarters of a million people have a hip or knee replaced. The most common causes are arthritis and other diseases, as well as injuries, according to the National Institute of Arthritis and Musculoskeletal and Skin Disorders (NIAMS). By the time people reach the point of considering hip or other joint replacement, they are frequently hobbled by pain and have severely limited mobility.

Joint replacement is major surgery, and the decision to have it can’t be made lightly. After a two- to three-day hospital stay, patients require extensive physical therapy. And full recovery may take as long as three to six months following hip replacement, NIAMS says.       

People in their 50s, 60s, or younger who are considering hip replacement must also take into account the fact that hip implants, which may be made of metals, polymers or ceramics, don't last forever. More than 96 percent of hip replacements last 10 years, notes Douglas Garland, M.D., medical director of MemorialCare Joint Replacement Center at Long Beach Memorial.

Beyond the 10-year mark, the failure rate of hip implants goes up, especially among those who are active. There is no data on how many hip replacements last 20 years, Dr. Garland says.

The joint surface may wear away, causing inflammation and pain. For this reason, younger people frequently delay having the surgery, not wanting to face revision surgery during their lifetime. Revision surgery is more difficult than the initial hip replacement, and the outcomes are not as good, according to NIAMS.

A group of engineers and physicians from Northwestern University, Rush Presbyterian Hospital in Chicago, and the University of Duisburg-Essen in Germany used electron and optical microscopes to analyze hip implants that had been removed from patients. They examined how the atoms in the lubricating layer bonded, which led to their discovery that graphitic carbon forms the layer on the implant. Graphitic carbon is a solid lubricant like that used to keep an engine running smoothly.

With further understanding of how this graphitic carbon is produced in the body after hip implant surgery, scientists may be able to create the surfaces of hip implant metal so that more of the lubricating layer forms. This would cut friction and wear and tear and extend the life of the implant, reducing the number that have to be redone. Potentially, metal-on-metal hip implants could come with a lifetime guarantee.

If you want to know more about joint replacement surgery, contact the MemorialCare Joint Replacement Center at Long Beach Memorial at 562-933-9027.

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