When TJR was first developed, it was primarily intended for treating the elderly patient population. However, with the increasing utilization of TJR [6
], the age-related differences in the future incidence of TJR remain unexplored. This is of particular concern because more costly premium hard-on-hard bearings are intended for the younger patient population [1
], which could have substantial impact on future healthcare resources. We therefore evaluated the historical changes in demand for primary and revision TJR in the younger and older patient populations. We also tested the hypothesis that patients younger than 65 years will represent the majority (> 50%) of the anticipated demand for primary and revision TJR in the United States between 2010 and 2030. We also asked whether current trends are advancing according to earlier expectations [6
Our study has several limitations. Our projections are based on the historical growth trajectory of joint replacement surgeries, and do not take into account potential limitations in the availability of surgeons or limited economic resources by private and public payers and hospitals in the future. For example, a shortage in the number of surgeons will have a substantial influence on the actual number of procedures that are performed. We also have not incorporated the potential for future alternative technologies, such as cartilage regeneration or tissue engineering, or drug therapies that limit the progression of joint diseases, which may preempt the need for TJR. We were also unable to account for the potential impact of changes in economy, which may place additional economic burden on patients to pay substantial out-of pocket expenses for these procedures, depending on their insurance coverage. Our study also did not consider potential changes in healthcare policies, such as adoption of volume standards or regionalization of TJR to high volume centers [5
], which could limit the access to care and decrease the future demand. The above economic, policy, and scientific factors cannot be readily incorporated in the statistical model. Our study was also focused on the procedural trends in the U.S.; followup research may include an analysis of trends in other countries, though the availability of historical TJR trends in other countries may be limited. Nonetheless, these limitations in no way diminish the importance of conducting and regularly updating surgical projections to help guide future research, surgeon training, and public health policy decisions. Our study also incorporated a more conservative projection, which relied only on the future changes in population growth, while maintaining current rates of adoption of TJR. Despite these limitations, our current findings are expected to have implications in the private coverage and reimbursement of joint replacement procedures in the future, as patients less than 65 years of age are not typically covered by Medicare, which today funds the majority of total joint replacement procedures in the United States.
We found the relative size of the young patient population for TJR has grown between 1993 and 2006. While 25% to 32% of primary or revision TJRs were performed in patients less than 65 years old in 1993, these proportions have increased to 40% to 46% in the most recent NIS data. The increasing trend in younger patients undergoing TJR has also been reported for different, but partly overlapping, historical periods. For example, Jain et al. reported that the proportion of primary TKA patients aged less than 60 years increased from 12.5% to 19.5% (+56%) between 1990–1993 and 1998–2000 [4
]. In addition, for patients aged under 70 years, the proportion increased by 9% from 45.6% to 49.6%. Due to the difference in the stratification by age categories, we were unable to make a direct comparison with the data by Jain et al. [4
]. However, our findings that the historical volume of TJR procedures in the younger patient population have been increasing is consistent with these previously reported trends.
While we previously forecasted an increase in demand for primary hip and knee replacement in 2030 by 174% and 673% [6
], respectively, the current study underscores the contribution that young patients are expected to play in the future utilization of primary TJR surgery, if historical trends in prevalence continue into the future. The statistical modeling approach we have employed in the current and previous study fits a multivariate but linear Poisson regression model to the historical prevalence of TJR procedures. However, because the size of the population subgroups is free to change nonlinearly in the future based on the Census Bureau’s projection, the actual projected incidence of surgical demand is therefore not constrained to be a linear function over time. The demand for primary hip and knee arthroplasty between 2004 and 2006 generally exceeded our previous projections, which employed an identical methodology. However, we are unable to judge, based on the limited window of new data for validation, whether a more complex modeling approach would provide a more reliable forecast of demand for surgical procedures.
Our previous methodology provided a reasonable short-term forecast of the demand for revision hip and knee surgeries between 2004 and 2006. In particular, for 2006, we observed a slight decrease in the estimated number of primary THA and TKA procedures compared to 2005 (Fig. ), but this decrease fell within the uncertainty of the estimates. Additional years of data will continue to be necessary to determine whether the historical trends will continue to apply in the future. Furthermore, if the future demand for TJR procedures is based only on the population growth with no change in the surgical prevalence (constant rate approach), then the projected increase in demand is not expected be as dramatic as previously predicted for the overall patient population and young patient population (Tables , ). Furthermore, these findings have implications for the economic burden associated with TJR procedures, as younger patients often receive higher demand, more costly “premium” implants (such as hard-on-hard bearings and hip resurfacing implants), which are intended to perform better and improve implant longevity in more active patients.
Projected future demand of primary and revision TJR procedures in patients less than 65 years old by 2010
The NIS data from 2004–2006 provide a basis to judge the validity of our previous projections [6
], which were derived from 1990–2003 data. During the most recent 3-year period, the incidences of primary total hip and total knee replacements were higher than the 95% confidence limits of the previous projections. The results of our current study for primary hip and knee replacement are, therefore, higher than those reported previously. On the other hand, the 2004–2006 NIS data for revision hip and knee replacement generally fell within the 95% confidence limits of the previous projections, and little difference was observed between current and previous long-term projections. The latest findings for primary TJRs continue to underscore the importance of routinely monitoring and regularly updating projections based on the latest available national data on procedure volumes.
Based on 1993–2006 NIS data, our current projections update and supercede previous modeling efforts that employed 1990–2003 NIS data [6
]. In light of the current and anticipated demand for total joint replacement procedures by patients less than 65 years in age, emphasis on improving the reliability and survivorship of joint replacements continues to be a critical element in meeting future demands for joint replacement. It remains clear from the projected increases in the demand for revision surgery that efforts to minimize the national revision burden will be beneficial, especially in light of the increased resources that we project will be needed to meet the future demand for primary hip and knee arthroplasty procedures. A national TJR registry, which has been credited with decreasing the revision burden in Sweden [8
], does not exist in the United States and would provide a mechanism for tracking the longitudinal performance of specific implants of all age groups in this country. Current administrative databases, such as NIS or Medicare, lack this capability. The projected demand for both primary and revision joint replacements provides a basis for cost-effectiveness studies for a United States TJR registry.