With the baby boomer population remaining active while still exerting significant stress on their bodies, the number of joint replacement surgeries is increasing dramatically and expected to continue. As such, implant makers need materials that can help patients avoid "revision" surgeries. Ceramics may be the material solution they seek.
(Ceramic Knee Components.)
By John MastrogiacomoJohn Mastrogiacomo is the product development manager for Kyocera Industrial Ceramics Corporation. He focuses on large scale programs in the medical and impact protection markets. Mastrogiacomo can be reached at 732-563-4340 or firstname.lastname@example.org.
A paper presented during the March 2008 meeting of the American Academy of Orthopedic Surgeons (AAOS) reveals a dramatic trend affecting medical device manufacturers. The number of knee-joint replacements performed annually in the U.S. is expected to rise about 525% by 2030. Hip joint replacements will also more than double, to a projected 573,000 per year. America’s changing demographics make these increases virtually inevitable.
Longer life expectancies, active lifestyles, and the tendency to be overweight are all taking a toll on our joints. As the baby boomer generation nears retirement, increasing numbers of patients, at an earlier age, are undergoing joint replacement. These patients have many more productive years remaining and are likely to remain physically active after surgery.
Engineers now face rising performance expectations for joint replacement systems, and the reason is simple. The sedentary patient of 75 may experience favorable results with a joint replacement lasting 15 years; the hiking, cycling, swimming patient of 60 needs a much more durable solution.
Healthy hip joints can bear loads up to five times our body weight. In other words, an active individual weighing 200 pounds creates hip loads of about 1,000 pounds, placing tremendous recurring stress on a hip prosthesis.
While hip replacement has become an effective way to reduce pain and restore mobility, patient selection and implant materials are the keys to success. Over years, normal movement produces wear in the load-bearing components of the prosthesis. This results in particulate debris that may inflame surrounding tissues and eventually necessitate further surgery, including “revision”—the complete replacement of the prosthesis. Surgeons strive to avoid this since the patient’s age is usually advanced and recuperative capacity diminished by the time revision becomes necessary.
According to AAOS data, the probability of a hip replacement lasting 20 years is approximately 80%. Active patients and those weighing more than 165 pounds experience lower rates of success.
Because wear debris has been a common problem, many prosthesis manufacturers are incorporating components of engineered ceramic. Ceramic’s extreme hardness makes it highly resistant to wear. The ceramic is polished to an ultra-smooth finish to form a low-friction bearing interface with another biocompatible material, such as ultra-high-molecular-weight polyethylene (UHMWPE). Since this combination offers great promise in reducing wear debris, engineers are now turning their attention toward ensuring that ceramic components can function for the duration of a younger patient’s life—a goal that may be attainable through step-by-step advances.
Even incremental advances can be significant. A recent example is the mechanical interface in hip replacement components from Japan Medical Materials Corp. A patented design adds a titanium sleeve to the tip of the titanium femoral stem, where the ceramic ball attaches. Unique sleeve geometry ensures even distribution of load forces throughout the ceramic-titanium interface, which greatly reduces a potential cause of failure in the ceramic.
In 1900, just 6.9% of the world population was age 60 or older. Today it’s 10%, rising to a projected 22.1% by 2050, and an astounding 28.1% by 2100. No wonder joint replacement is a growth industry.
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