Dramatic increase in total knee replacement utilization rates cannot be fully explained by a disproportionate increase among younger patients.

The incidence of total knee replacement in the United States more than doubled between 1999 and 2008, increasing from approximately 263,000 to 616,000 cases. The purpose of this study is to evaluate the claim that there has been a disproportionate increase in knee replacements among younger patients owing to expanding indications for the procedure in this group. Data on the US population for individuals 18 to 44 years old, 45 to 64 years old, and 65 years and older were obtained from census data; the number of total knee replacements performed annually in each age group was acquired from the Agency for Healthcare Research and Quality and per-capita incidence rates were calculated. Applying the 1999 rates to the 2008 population, the number of knee replacements anticipated on the basis of population growth for each cohort was determined and compared with the number observed, yielding the unexplained growth. The data revealed that in 2008, approximately 305,000 knee replacements were performed beyond the number predicted by population growth alone. The largest segment of growth (151,000 cases) was among patients 65 years and older; the per-capita growth rate was highest in this cohort as well, increasing from 5.2 to 9.1 procedures per 1,000 individuals. The data show conclusively that a disproportionate increase in knee replacements among younger patients is not a full explanation for the growth in utilization. In fact, it is not even the best among alternative explanations. The main locus of growth was among traditional patients 65 years and older.