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During the past three decades there has been a dramatic, 130-fold increase in knee replacement surgeries, particularly among individuals in their 50s, a Finnish study found.

The incidence of total knee arthroplasty rose from 0.5 per 100,000 in 1980 to 65 per 100,000 in 2006, for an incidence rate ratio (IRR) of 1.19 (95% CI 1.19 to 1.20, P<0.001), according to Jarkko Leskinen, MD, of Helsinki University Central Hospital, and colleagues.

And among those ages 50 to 59, the incidence increased from 1.5 to 160 per 100,000, with an IRR of 16.8 (95% CI 12.2 to 23.2, P<0.001), the researchers reported online in Arthritis & Rheumatism.

Knee arthroplasty is a common and effective treatment for patients with severe osteoarthritis who are not responsive to medical therapy. In the U.S., demand for the procedure is expected to increase by almost 675% by the year 2030.

Most long-term data are for patients who were 60 and older at the time of the surgery, but younger patients increasingly have been undergoing total or partial knee replacements.

To explore trends in incidence over time among younger patients, Leskinen and colleagues analyzed data from the national Finnish arthroplasty register, which now includes 98% of patients with these implants.

Among the 95,577 primary knee arthroplasties done in the country between 1980 and 2006, 8,961 were for osteoarthritis in individuals younger than 60.

A total of 65% of these were in women, and mean age at implantation was 55.

The most rapid increase overall for total knee replacement was between 2001 and 2006, when the rate rose from 18 to 65 per 100,000.

The incidence of partial, or unicondylar, arthroplasty also rose, though less than for the total knee procedure, increasing from 0.2 to 10 per 100,000 (IRR 1.19, 95% CI 1.19 to 1.20, P<0.001).

Throughout the study period, women were the recipients more often than men, reaching a 1.6 to 2.4-fold higher incidence during the last ten years.

When the researchers looked at the data according to age groups, they found only minor increases for both total and partial arthroplasties in patients ages 30 to 39 and those 40 to 49.

As with total knee arthroplasty, the incidence of partial replacement rose most rapidly among patients ages 50 to 59, with an IRR of 147.2 (95% CI 66 to 328.5, P<0.001) when that group was compared with those ages 30 to 39, according to Leskinen and colleagues.

The researchers also looked at trends in incidence according to the volume of procedures by hospital, and found that low- and intermediate-volume centers had the greatest increases.

The IRR between intermediate- and high-volume centers was 1.23 (95% CI 1.16 to 1.31, P<0.001) and 1.23 (95% CI 1.13 to 1.34, P<0.001) for low- versus high-volume centers.

Despite the significant increases in these procedures since 1980, the researchers noted that the incidence of osteoarthritis has actually fallen in Finland in that time.

"Possible explanations for this phenomenon include the high functional and quality of life demands of younger patients," they observed.

Greater awareness of treatment options among Baby Boomers and ongoing refinements of surgical technique also are likely to have contributed.

Leskinen and colleagues cautioned that long-term data are needed on the use of knee arthroplasty among younger patients, because their outcomes and risks may be different than older patients.

That concern was echoed in an editorial by Elena Losina, PhD, and Jeffrey N. Katz, MD, of Harvard University in Boston.

"Since younger patients are likely to have more strenuous physical demands and to make treatment choices that support an active lifestyle, the longevity or 'survival' of knee implants in this group may be lower than in older patients," Losina and Katz wrote.

"In fact, as data on this issue emerge, it appears that rates of failure leading to revision in younger patients are two-fold higher than in older patients," they observed.

The editorialists called for further "intensive study" before even wider adoption of knee arthroplasty for younger patients.

"We would be wise to heed the time-honored investment advice that past performance may not guarantee future success," they warned.

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