Incidence of Partial Knee Arthroplasty

CHAPTER 5 Incidence of Partial Knee Arthroplasty


A Growing Phenomenon?



William A. Jiranek, Daniel L. Riddle



Key Points



image Between 1998 and 2005, the incidence of partial knee replacement in the United States grew by over three times.

image As of 2005, partial knee replacement comprised approximately 9% of all knee arthroplasties in the United States.

image Most recent estimates for other countries providing public data indicate a utilization rate ranging from 8% of all arthroplasties in Great Britain and Canada to a high of 19% in Australia.

image Partial knee replacement appears to be a viable and potentially underutilized procedure worldwide.


Introduction


Because osteoarthritis of the knee is one of the most common disease processes in humans, data concerning the incidence of knee arthroplasty are important to estimate the societal cost of treatment for this condition. While utilization in countries that sponsor joint registries is well delineated, few data are available in the United States due to the lack of a national implant registry. While the Medicare databases give some idea of utilization of knee arthroplasty, partial versus total cannot be differentiated, and only patients covered by Medicare (generally greater than 65 years of age) are captured. Utilization of partial knee replacement can be considered in several ways, including as a percentage of total knee arthroplasties as well as the percentage of patients who have isolated unicompartmental arthritis. There have been previous spikes in the utilization of partial knee replacement that usually corresponded to an increase in the number of surgeons performing partial knee replacement, usually followed by a pullback related to an increase in the failure rate.


While the number of patients with symptomatic osteoarthritis has continued to grow significantly, it appears that the percentage of patients in which the osteoarthritis is confined to predominantly one compartment (and thus amenable to partial knee replacement) has remained relatively constant, and has been estimated at 30%. This chapter reports the incidence of partial knee arthroplasty (PKA) in all countries that have an existing registry. For the United States, which does not have a registry, we have estimated the incidence of unicondylar arthroplasty by indirect methods, using implant sales data from the major manufacturers.1 We have estimated market share by utilizing commercial databases that track market share.2



Growth of PKA in the United States


To estimate the number of PKAs performed each year, we utilized a retrospective cross-sectional design. We solicited sales data from the four major PKA orthopaedic manufacturers in the U.S. market, which included Biomet (Warsaw, IN), Zimmer (Warsaw, IN), Depuy Orthopaedics (Warsaw, IN), and Stryker Corporation (Mahwah, NJ). Stryker Corporation elected not to contribute sales figures. We multiplied each company’s market share based on determinations of a market analyst firm (DataMonitor, New York, NY) by the number of unicompartmental arthroplasty implants sold, and this allowed us to determine total units sold. Sales data and market share were used to estimate total unicondylar implants implanted for 2003 (83% market share), 2004 (74% market share), and 2005 (87% market share). We used regression analysis to estimate the sales numbers for the years 1998–2002. We then used the National Hospital Discharge Survey (NHDS) to provide data for the total amount of knee arthroplasties performed in the United States during the study years, and subtracted our estimates of unicondylar knee arthroplasties (UKAs) from those to arrive at an estimate of the number of total knee replacements (TKRs) performed each year. The estimated number of unicondylar arthroplasties increased from 6570 in 1998 to 44,990 in 2005, whereas the number of total knee arthroplasties increased from 259,000 in 1998 to 441,000 in 2004 (no NHDS data available for 2005). As a percentage of all knee arthroplasties, the number of unis increased from 2.5% in 1998 to 9.8% in 2005. Between 1998 and 2005, the incidence of PKA increased by an average of 30% a year.

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Jun 22, 2016 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Incidence of Partial Knee Arthroplasty

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