Arthritis & Rheumatism, Volume 63,
November 2011 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Chicago, Illinois November 4-9, 2011.


To What Degree Is the Rise in US Total Knee Replacement Rates Attributable to Aging of the Population?

Murphy1,  Louise, Hawker2,  Gillian A., Odom1,  Erica, Helmick1,  Charles G.

Centers for Disease Control and Prevention, Atlanta, GA
Women's College Hospital, Toronto, ON

Background/Purpose:

In the past decade, total knee replacement (TKR) rates have increased resulting from multiple factors including the aging of the US population, rising prevalence of obesity and increased access to and demand for TKRs. To quantify the degree to which aging accounts for the observed increase in TKRs, we examined TKR rates, annual percent change (APC) and standardized incidence ratio (SIR) over 13 years among US adults aged >=18 years.

Methods:

Using 1997–2009 US Nationwide Inpatient Sample data – hospital discharge data for 44 states comprising 95% of all US hospital discharges -- we estimated overall and age-specific (18–44, 45–64, 65–84, and >=85 years) annual hospital discharge rates, and APC for TKRs (ICD-9-CM procedure=81.54 [excludes revisions]). Also, we calculated overall and age-specific SIRs with 1997 and 2009 data to examine whether the rise in TKR rates from 1997 to 2009 was attributable solely to changes in the age distribution of the US population. Expected 2009 values, based on estimated 1997 TKR rates (# of TKR in 2007/# of people in 2000 US Census Population) were applied to population estimates from the 2010 US Census. SIRs were the ratio of observed to expected number of TKRs in 2009.

Results:

Among all US adults aged >= 18 years, approximately 1 and 3 per 1000 people had a TKR discharge in 1997 and 2009 respectively. TKR rates (per 1000 people) in 2009 were higher than 1997 for all age groups: 18–44=0.04 and 0.1; 45–64=1.1 and 3.1; 65–84=5.9 and 9.7; and >=85 years=2.2 and 3.1. The APC was 10% among all US adults (from 264,331[1997] to 620,192 [2009]); across age groups the largest APC was among those 45–64 years (21%) (18–44=11%; 65–84=7%; >=85=6%). The overall SIR was 2.1; age-specific SIRs were 2.4, 2.9, 1.6 and 1.4 for adults aged 18–44, 45–64, 65–84, and >=85 years respectively.

Conclusion:

From 1997 to 2009, overall TKR rates tripled representing an APC of 10%. Although TKR rates rose most rapidly among people aged 45–64 years (APC=21%), observed rates in both 1997 and 2009 were highest among those aged 65–84 years (5.9 and 9.7). SIRs indicated that rates were between approximately 1.5 to 3 times higher than would be expected if the rise was attributable to aging alone. In this analysis, we were unable to quantify the effect of increased prevalence of obesity, a major risk factor for knee osteoarthritis and subsequent TKRs, and increased access to and demand for TKRs on this increase but it is likely substantial.

To cite this abstract, please use the following information:
Murphy, Louise, Hawker, Gillian A., Odom, Erica, Helmick, Charles G.; To What Degree Is the Rise in US Total Knee Replacement Rates Attributable to Aging of the Population? [abstract]. Arthritis Rheum 2011;63 Suppl 10 :882
DOI:

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