Hip implants exhibit greater durability than previously thought

Hip implants exhibit greater durability than previously thought, orthopedic surgeons find

Hip replacement parts that were previously thought to have to be exchanged every 10 years can actually last twice as long, U.S. researchers suggest.

In the majority of cases (96 per cent), the cementless metal parts of hip implants were securely in place 20 years after surgery, say researchers who examined 124 of the devices for a study published in the May issue of the Journal of Bone and Joint Surgery.

Dr. Craig Della Valle, an orthopedic surgeon at Rush University Medical Center and his colleagues have been studying the results for 204 hip replacements that were done in the mid-1980s in a group of 184 patients age 20 to 84.

Few of the metal implants that fit into the cup-shaped hip socket, or acetabulum, became loose. But in 20 per cent of the patients still living 20 years after surgery, the plastic lining of the metal shell was worn enough that more surgery was required or recommended.

Younger age was strongly linked with a higher risk of wear-related problems, the researchers found.

With time, the number of repeat surgeries because of wear and bone resorption also increased, Della Valle said.

Resorption occurs as a result of the body's reaction to debris created by wear and corrosion of the metal implants.

"The average age of the patients in this study was 52 years, much younger than most patients who underwent hip replacement at the time," said study co-author and orthopedic surgeon Dr. Jorge Galante.

"So the high rate of wear-related complications was not completely unexpected," he added in a news release.

Hip replacements on rise

Since the previous progress report at 15 years, two metal cup implants, in addition to the three noted earlier, were found to be loose, or four per cent of the 124 implants.

Of the original 204 hip replacements, five cases, or 2.5 per cent of the total, had failed. Two of these five implants were changed, and three were left intact because the patients did not suffer significant symptoms, the team said.

Last year, the Canadian Institute for Health Information reported that hip replacements among Canadians age 45 to 54 increased by 68 per cent for men and 52 per cent for women in the past 10 years.

In Canada, 68,746 residents were hospitalized for hip and knee replacements in 2005-2006 for both first-time and corrective surgeries, a one-year increase of 17 per cent from 58,714 procedures in 2004-2005.

The study's authors reported receiving funding or grants in excess of $10,000 US from Zimmer, a manufacturer of hip implants.