Total knee arthroplasty (TKA) is a treatment method commonly used in patients with severe osteoarthritis (OA) that is refractory to conservative treatment. Good long-term results with cemented condylar prostheses have been described (1–3). The majority of patients in these studies, however, have been older than 60 years. Meanwhile, the so-called baby-boom generation (the generation born after World War II) is growing older, placing increasing demands on the health care system (4).
The estimated demand for primary TKA has been predicted to grow by 673% to 3.48 million procedures in the US by the year 2030. Similar projections have also been proposed in other Western countries (5–9). Wells et al (8) reported an increase in the incidence of TKA in younger patients (45–64 years of age) with primary OA in Australia between 1988 and 1998. Those investigators also showed a geographic variation in the incidence of TKA between the Australian states and territories. Jain et al (5) reported that the incidence of TKA had increased 54% in the group ages 50–59 years and 95% in the group ages 40–49 years in the US between the 1990–1993 cohort and the 1998–2000 cohort. They also noted that the increase in incidence was more rapid in high-volume centers (≥400 total knee replacements per year) than in low-volume centers. Similar data on the incidence of unicondylar knee arthroplasty (UKA) in young patients have not been published.
In the present study, we analyzed changes in the age group– and sex-standardized incidence of UKA and TKA in Finland between the years 1980 and 2006. In addition, we sought to identify the factors that might have effects on the incidence during the study period.
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We found that the incidence of TKAs and UKAs in Finland increased very rapidly in patients with primary knee OA who were under the age of 60 years during the study period 1980–2006. In addition, the incidence of TKA grew faster than that of UKA. Regardless of the arthroplasty method, the incidence was consistently higher in women than in men throughout the entire study period. Most of the increase in incidence occurred in patients ages 50–59 years. The incidence of TKAs increased more in the intermediate-volume and low-volume centers than in the high-volume centers during the 2000–2006 study period.
Registry-based studies have certain limitations. It has been shown that the Finnish Arthroplasty Register covers 90% of hip implants for the year 1995, and after that, the coverage increased to 98% (13). This might explain a minor part of the increase shown in our study. Because of the accurate civil register of Statistics Finland and the low level of illegal immigration in Finland, the population data can be assumed to closely correspond to the actual population. However, divergence between international health care systems might confound direct comparisons between reports from different countries. The boundaries between low-, intermediate-, and high-volume centers were arbitrary, but they adapt the previous joint registry–based studies done in Finland and in the US (5, 14), and they formed well-distinguished groups of hospitals performing arthroplasties during the twenty-first century.
There have been several reports on the general incidence of TKA in the restricted population, but most of them focus on elderly patients with primary OA of the knee (5–8). In some of those studies, the incidence of knee arthroplasty has been shown to have increased by up to 10% per year for the last 25 years (15).
In our study, a rapid increase in the incidence of TKAs was determined among younger patients in Finland, especially over the last 10 years. Jain et al (5) demonstrated the same phenomenon, although their study period ended in 2000. In an analysis from a community joint registry in St. Paul, Minnesota, Gioe et al (16) reported that over time, the total percentage of young patients (under 55 years of age) in the overall registry TKA population increased from 4.6% in 1991 to 17.1% in 2005. Their study design was similar to ours. In our study, growth was especially fast between 2000 and 2006. It must also be noted that data collected from nationwide registers describes the true incidence of UKA and TKA in different age groups more accurately than do data from narrower regional studies.
In a recent population-based study, the incidence of OA especially among women was found to have decreased in Finland during the period 1980–2000 (17). Despite the decreasing incidence of knee OA in Finland, a reciprocal rapid increase in TKAs was found in the present study. Possible explanations for this phenomenon include the high functional and quality-of-life demands of younger patients under the age of 60 years. Another reason could be that the baby boomers may opt to undergo elective operations at an earlier stage, when they have milder symptoms, than previous generations. The baby-boom generation is well-educated and aware of the contemporary treatment options, which include TKA and UKA. Nowadays, information about the different treatment options is readily available via the internet and other media. Good long-term results in terms of implant survival in TKAs among older age groups, the continuous development of anesthetic and surgical techniques, in addition to the constant updating and retraining of orthopedic surgeons may all have led to the observed increase in the incidence of knee arthroplasty.
Simultaneous with the rapid increase in the incidence of knee arthroplasties, we witnessed a clear decrease in the incidence of high tibial osteotomy in Finland (18). This may partly explain the growth in incidence in both arthroplasty groups.
In our study, there was a higher age group–standardized incidence of knee arthroplasties in women than in men. Similar findings have recently been published regarding TKAs (5–7). We found that the actual growth in the incidence of knee arthroplasties among younger patients took place in the subgroup of patients ages 50–59 years. There was, however, a minor increase in the incidence of UKAs among patients ages 40–49 years. Nonetheless, the incidence of total knee arthroplasty in the same group remained at the same low level throughout the study period. This is consistent with the results reported recently by Jain et al (5). Our study population consisted of only patients with primary knee OA as the recorded indication for arthroplasty. If we had included data for patients with secondary (posttraumatic) OA, rheumatoid arthritis, and osteonecrosis, the incidence of knee arthroplasties would have been higher in the youngest age groups.
In our study, the most rapid growth in the incidence of knee arthroplasties occurred in the low-volume and intermediate-volume hospitals. In contrast to our findings, Jain et al (5) reported that the increase in incidence was fastest in the high-volume hospitals in the US. One could reason that smaller hospitals with the combination of fewer peer review indications for knee arthroplasty on the one hand and less limited local resources on the other would be expected to vary more than larger-volume hospitals.
In conclusion, the age group– and sex-standardized incidence of TKAs and UKAs has grown rapidly in patients in Finland with primary OA who are younger than 60 years, and most of the increase took place in the 50–59-year age group. This phenomenon has been especially strong during the twenty-first century. There is no single explanatory factor for this growth. Some of the increased incidence can be explained by hospital volume. Long-term results in young patients may differ from those reported in older patients, and the risk for revision surgery may be higher. More long-term data are warranted before the widespread use of TKA in younger patients can be justified.
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- PATIENTS AND METHODS
- AUTHOR CONTRIBUTIONS
All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Leskinen had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study conception and design. Leskinen, Eskelinen, Huhtala, Paavolainen, Remes.
Acquisition of data. Leskinen, Eskelinen, Huhtala, Paavolainen, Remes.
Analysis and interpretation of data. Leskinen, Eskelinen, Huhtala, Paavolainen, Remes.