Hip and knee replacement in Germany and the USA: analysis of individual inpatient data from German and US hospitals for the years 2005 to 2011

Abstract

Background: The number of hip and knee replacement operations is rising in many industrialized countries. To evaluate the current situation in Germany, we analyzed the frequency of procedures in Germany compared to the USA, with the aid of similar case definitions and taking demographic differences into account.

Methods: We used individual inpatient data from Germany (DRG statistics) and the USA (Nationwide Inpatient Sample) to study differences in the age- and sex-adjusted rates of hip and knee replacement surgery and the determinants of trends in case numbers over the years 2005 to 2011.

Results: In 2011, hip replacement surgery was performed 1.4 times as frequently in Germany as in the USA (284 vs. 204 cases per 100 000 population per year; the American figures have been adjusted to the age and sex structure of the German population). On the other hand, knee replacement surgery was performed 1.5 times as frequently in the USA as in Germany (304 [standardized] vs. 206 cases per 100,000 population per year). Over the period of observation, the rates of both procedures increased in both countries. The number of elective primary hip replacement operations in Germany grew by 11%, from 140,000 to 155 300 (from 170 to 190 per 100,000 persons); after correction for demographic changes, a 3% increase remained. At the same time, the rate of elective primary hip replacement surgery in the USA rose by 28%, from 79 to 96 per 100 000 population, with a 13% increase remaining after correction for demographic changes.

Conclusion: There are major differences between Germany and the USA in the frequency of these operations. The observed upward trend in elective primary hip replacement operations was mostly due to demographic changes in Germany; non-demographic factors exerted a stronger influence in the USA than in Germany. With respect to primary knee replacement surgery, non-demographic factors exerted a comparably strong influence in both countries.

Figure 1

Germany: crude rates for hip and knee replacements; USA: rates standardized to match German demographics^*. ^*US rates were standardized by sex and five-year age groups to match Germany’s demographic structure for each year of the observation period (10) (direct standardization). Standardized rates show how many cases would have occurred in the USA per 100 000 population if the demographic structure were the same as in Germany. They can therefore be compared to German rates. The corresponding figures are shown in eTables 1 and 2

Figure 2

Age-specific primary hip and knee replacement rates in Germany and the USA. Only rates for age groups above 40 years are shown due to the low numbers of cases in younger age groups