The incidence of total knee arthroplasties increased from 0.5 operations per 100,000 inhabitants to 65 operations per 100,000 inhabitants aged 30-59 years during 1980-2006 in patients with primary knee osteoarthritis, according to a Finnish study.
Patients born shortly after World War II showed the most dramatic increases.
Incidences of unicondylar or partial knee arthroplasties (UKAs) were also found to grow from 0.2 operations per 100,000 inhabitants to 10 operations per 100,000 inhabitants over the same period in the same Finnish patient age group.
"This phenomenon has been especially strong during the 21st century. There is no single explanatory factor for this growth. Some of the increase in incidence can be explained by hospital volume," wrote Dr. Jarkko Leskinen, Consultant Orthopedic Surgeon, Peijas Hospital, Helsinki University Central Hospital, who was lead author of the study published in the January issue of Arthritis & Rheumatism (Arthritis Rheum. 2012;64:423-8).
"The demand for primary TKA [total knee arthroplasty] has been estimated to grow by 673 percent to 3.48 million procedures in the United States by the year 2030," reported Dr. Leskinen. Previous studies reported increases in the incidence of TKA in younger patients in Australia and the United States in the 1980s and 1990s. This study aimed to analyze the changes in age group as well as the sex-standardized incidence of UKAs and TKAs in Finland between the years 1980 and 2006.
Patient data were drawn from the Finnish Arthroplasty Registry, and population data were obtained from Statistics Finland. A total of 8,961 knee arthroplasties were performed for primary osteoarthritis in patients under age 60 during 1980-2006. In addition to evaluating the effects of age and gender on the incidences of knee arthroplasties, Dr. Leskinen and his colleagues evaluated the effects of hospital volume.
Overall, the incidence rate ratio (IRR) for the annual increase in general incidence of UKAs was lower than that of TKAs, with an IRR of 1.26 for UKAs (95% confidence interval, 1.24-1.28; P less than .001) and 6.92 for TKAs (95% CI, 6.50-7.36; P less than .001).
In particular, the study found that the TKA incidence rose sharply from 18 per 100,000 in 2001 to 65 per 100,000 in 2006. TKAs were performed more often in women than men, with a 1.6- to 2.4-fold higher incidence in women than men during the past 10 years. Since 2000, a greater number of UKAs also were performed in women than men. Most of the increased incidence in TKAs and UKAs was in women aged 50-59 years.
Regarding the incidence of TKAs by age group, patients aged 50-59 years showed the largest increase, from 1.5 TKAs per 100,000 in 1980 to 160 per 100,000 in 2006. Incidences of UKAs by age group showed a similar pattern to TKAs, with the most marked growth in patients aged 50-59 years, increasing from 0.5 to 24 operations per 100,000. Growth was most rapid after the year 2000.
"Possible explanations for this phenomenon include the high functional and quality of life demands of younger patients aged less than 60 years," the authors wrote. "Another reason could be that the baby boomers may opt for elective operations at an earlier stage with milder symptoms, than the situation that was faced by earlier generations."
Hospitals were divided into low-, intermediate-, and high-volume centers, according to the number of TKAs performed in all the hospitals in Finland in 2006. The incidence of TKAs grew more rapidly in low- and intermediate-volume hospitals, while the incidence of UKAs grew in low-volume hospitals. The IRR for TKAs was 1.23 in both comparisons of low- to high-volume centers (95% CI, 1.13-1.34; P less than .001), and intermediate- to high-volume centers (95%CI, 1.16-1.31; P less than .001).
The authors warned against the widespread use of TKAs in younger patients. "Long-term results in young patients may differ from those reported in older patients, and risk for revision may be higher," they concluded.
Dr. Leskinen and his colleagues reported having no financial disclosures.