Hip simulator measures wear on implants

Paul Giles twists, lifts and bends in ways most of us think would be difficult, but just a few months ago this was impossible for Paul.

"No running. No bike riding. I'm a young father and I can't participate," said Giles, a hip resurfacing patient.

Paul is one of the growing number of 40 year olds who needs hip resurfacing, or a hip replacement. The trouble is hip implants are made to last only 15 years.

"Probably two or three times a week I'm re-doing something that's worn out," said orthopedic surgeon, Dr. Donald Knapke.

Dr. Knapke performs 600 hip replacements a year at Beaumont Hospital in Troy, Michigan. It's one of the only health care facilities in the country using a 12-station hip simulator to measure wear and tear on the implants.

"When we take this apart we can see if there's any wear marks in them," says research engineer, Jacob Shorez.

The results are recorded daily on a computer, showing the effects of five years of walking. That's five million steps, and it does it all in just three months.

"What we are going to get out of this data is how long the hip is going to last, how long it's going to wear, and what the potential effects are to the patient by having this in the body," said Shorez.

Because of research like this, implants have moved from plastic to longer-lasting ceramic and metal.

"If we have new ideas, we'd rather try them on a hip simulator rather than just put them into a patient and find out later that it wasn't a good idea," said Dr. Knapke.

Paul Giles hip surgery was a success.

"It's my goal to be a better athlete at 50 than I was 20 years ago," said Giles.

Hopefully his hip will keep up with him.

Besides durable implants, orthopedic surgeons say correct placement of the implant in the body is also the key to a successful result.

Rush University Medical Center researchers say complications from hip implants were more frequent in women of all ages and in men over 65.

Web Extra Information: Testing New Hips


Osteoarthritis of the hip is a painful condition that afflicts 10 million Americans, according to the American Academy of Orthopaedic Surgeons. It takes place when cartilage, the covering on the ends of bones of the hip joint, wears away. This causes the ball and socket that form your hip joint to rub directly against each other -- bone-on-bone -- causing pain during movement. Often, the best treatment for severe hip osteoarthritis is hip replacement surgery.

During the surgery, the head of the thighbone, or the femur, is removed and replaced with an artificial head. A cup is also placed into the hip socket to replace the worn out cartilage. Hip replacement surgery is becoming increasingly common. Mayo Clinic says 193,000 total hip replacement surgeries are performed nationwide every year, and research shows the procedure has an overall success rate of more than 90 percent.

As the population ages, hip replacements are being performed on patients that are increasingly older, but a recent study at Duke University Medical Center shows the procedure is just as successful for those in their 80s and 90s as for those in their 60s.


More recently, people have started needing the procedure at a younger age. Researchers don't completely understand why this is. "Everybody thinks you're 80 when you need a hip replacement, but really, the average age is low 60s," Donald Knapke, M.D., an orthopaedic surgeon at Beaumont Hospital in Troy, Mich., told Ivanhoe. Dr. Knapke says he also performs hip replacements on patients in their 40s every week.

The joint surfaces of artificial hips start to wear away after 15 to 20 years, so as patients get younger, second surgeries to replace artificial hips are becoming more common. These surgeries, called revision surgeries, are much more difficult than first-time hip replacements, according to the National Institutes of Health.

In addition, outcomes are not as favorable. A newer procedure called hip resurfacing addresses this problem by delaying a person's need for a total hip replacement. It offers relief from osteoarthritis without a complete replacement of the head of the femur. Instead, the femoral head's surface is reshaped and fitted with a rounded cap. A metal cup is also placed inside the hip socket. Hip resurfacing is usually recommended for younger, more active patients who might wear out a traditional artificial hip within their lifetime.

A recent study shows hip resurfacing may not be as effective in women or older men. After reviewing over 500 hip resurfacing procedures performed in the United States, researchers at Rush University Medical Center in Chicago found most serious complications after the surgery occurred in women of all ages and men over 55. The most serious complication that occurred was fracturing the area of the femur just below its head.


To lengthen the life of hip implants, researchers at Beaumont Hospital in Troy, Mich., are studying hip implants in their hip simulator lab. The lab has 12 stations that test hip implants by putting them through conditions similar to those the human body would experience.

Researchers can determine how well a replacement will work over a lifetime after observing it for just a few months. The lab plans to contract with replacement companies to evaluate their joint replacement products. Researchers in the Beaumont lab are also looking into why certain joint replacement parts have failed so improvements can be made to them in the future.



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