Stats
Hip and knee arthroplasties are effective treatments for degenerative joint disease, but may subsequently require surgical revision after joint replacement. For example, the National Institutes of Health Consensus Development Conference on total knee replacement stated that primary total knee replacements are highly successful even though the prosthesis failure rate is about 1 percent per year requiring revision. These revisions represent a burden to patients, surgeons and the health care system; therefore, estimates of the future prevalence of hip and knee replacement revision surgeries should be evaluated.
Historically, increases in revision total hip arthroplasty (THA) and total knee arthroplasty (TKA) procedures have been fueled by the increase in patients receiving primary procedures (Fig. 1). These revisions have a significant impact on the health care system. In economic terms, revision THA is estimated to have consumed 20 percent of Medicare hip replacement expenditures between 1997–2001, whereas TKA revisions consumed 9 percent of total annual knee replacement expenditures during this time period.
Projected procedures
Reliable projections of revision arthroplasties would be particularly useful, as they consume greater economic resources than primary procedures. Thus far, little information is available to quantify the expected number of hip and knee revision arthroplasty surgeries in the future. As such, we undertook a study to provide statistical projections of the number of primary and revision arthroplasty in the United States between 2005 and 2030 based on available historic data from 1990 to 2003.
Specifically, inpatient discharge records for THA and TKA were obtained from the National Inpatient Sample (NIS) program. The NIS is an annual federal-state cooperative program initiated in 1988 to compile a representative sample of U.S. hospital discharge records. It has about 8 million inpatient records from approximately 1,000 hospitals in 37 states (based on 2003 data), which represent less than 20 percent of all U.S. community hospitals. These records contain useful information about patient demographics (e.g., age, gender, race/ethnicity), disease diagnoses and surgical procedures. Historic (1990-2003) discharge records for primary hip and knee arthroplasty, identified by International Classification of Diseases (ICD-9-CM) codes 81.51 and 81.54, respectively, were extracted. Similarly, corresponding revision procedures were derived from 81.53 and 81.55 codes.
National THA and TKA projections were calculated by adding the projections for each age, gender, race/ethnicity and census region population subgroup for which both the population and the prevalence of surgery were modeled to vary over time. Projected population statistics through 2025 were obtained from the U.S. Census Bureau. The future size of each population subgroup was estimated from census data, while the future prevalence of surgery was estimated from historic NIS data (1990–2003). The annual incidence of THA and TKA surgery was modeled using a Poisson regression to account for differences in incidence among age, gender, race/ethnicity, and census region population subgroups, as well as for changes over time. Surgery incidence was calculated by dividing the number of surgeries estimated from the NIS for each population subgroup by the corresponding population from the Census Bureau.
This study also quantified the potential growth in number of orthopaedic surgeons from 1992–1993 and 2004–2005 American Academy of Orthopaedic Surgeons membership surveys of board-certified orthopaedic surgeons in active practice. The caseload per surgeon was determined by averaging the projected number of THA and TKA procedures by the projected number of practicing surgeons.
What lies ahead
Substantial increases in the number of hip and knee replacement surgeries were predicted (Fig. 2 and 3). Primary THA is estimated to grow by 174 percent, from 208,600 in 2005 to 572,100 by 2030
(Fig. 2), while primary TKA is projected to grow from 450,400 to 3.48 million procedures during the same period (more than 673 percent).
Overall, the total number of revision arthroplasty procedures performed in 2005 is expected to double by the year 2026 for revision THA and by 2015 for revision TKA (Fig. 2). THA revisions are projected to grow from 40,800 in 2005 to 96,700 in 2030 (more than 137 percent). TKA revisions are projected to grow from 38,300 in 2005 to 268,200 in 2030 (more than 601 percent). The number of board certified orthopaedic surgeons in active practice grew by 29 percent from 13,523 to 17,486 between 1992–1993 to 2004–2005, and is projected to grow to 26,455 in 2030 (Fig. 2). The projected caseload per surgeon is estimated to grow from 51.9 procedures in 2010 to 167 procedures in 2030. Our projections demonstrate a massive expected increase in demand for primary and revision total joint surgeries over the next two decades, a demand that will need to be addressed with a combination of increased economic resources, operative efficiency, technical capacity (i.e., additional surgeons) and implant longevity. The trends established by historic data may not persist in the future, however, due to significant changes in implant technology or unforeseen changes in economics (e.g., insurance coverage, Medicare reimbursement) associated with these surgeries.
The recent changes in coding and reimbursement by CMS with the formation of separate DRGs for primary and revision procedures (DRGs 544 and 545, respectively), reflect heightened awareness and acceptance by CMS of the greater burden that revisions place on patients, surgeons and hospitals.
The revision projections in the study provide the necessary foundation for future cost-benefit analyses at a national level, which will allow for quantification of the increasing societal impact—whether related to the education of orthopaedic surgeons or deployment of economic resources for joint arthroplasty—of revisions in the United States.
Steven Kurtz, principal engineer; Edmund Lau, senior managing scientist; Michael Halpern, principal scientist; and Kevin Ong, managing engineer, work for Exponent Inc., a scientific research consulting firm based in Philadelphia.
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