This study examines the trends in volume, utilization, and outcomes of primary and revision total knee arthroplasty (TKA) among Medicare beneficiaries in the United States from 1991 to 2010. The analysis is based on Medicare Part A data files, identifying 3,271,851 patients who underwent primary TKA and 318,563 who underwent revision TKA. Key findings include: 1. **Volume and Utilization**: - Primary TKA volume increased by 161.5% from 93,230 to 226,177 procedures. - Per-capita utilization of primary TKA increased by 99.2%. - Revision TKA volume increased by 105.9% from 9,650 to 19,871 procedures. - Per-capita utilization of revision TKA increased by 56.8%. 2. **Outcomes**: - Hospital length of stay (LOS) for primary TKA decreased from 7.9 days in 1991-1994 to 3.5 days in 2007-2010. - All-cause 30-day readmission rates for primary TKA increased from 4.2% to 5.0%. - For revision TKA, hospital LOS decreased from 8.9 days to 5.0 days, but 30-day readmission rates increased from 6.1% to 8.9%. 3. **Discharge Disposition**: - The percentage of patients discharged to inpatient rehabilitation increased, while the percentage discharged to skilled care/ outpatient rehabilitation also increased. 4. **Complications**: - Rates of surgical complications such as wound infection, hemorrhage, sepsis, and myocardial infarction increased significantly, particularly after revision TKA. The study highlights the increasing demand for TKA, driven by both an increase in the number of Medicare enrollees and per-capita utilization. It also underscores the need for further research to evaluate the appropriateness of TKA procedures and to address the rising costs and complications associated with shorter hospital stays.This study examines the trends in volume, utilization, and outcomes of primary and revision total knee arthroplasty (TKA) among Medicare beneficiaries in the United States from 1991 to 2010. The analysis is based on Medicare Part A data files, identifying 3,271,851 patients who underwent primary TKA and 318,563 who underwent revision TKA. Key findings include: 1. **Volume and Utilization**: - Primary TKA volume increased by 161.5% from 93,230 to 226,177 procedures. - Per-capita utilization of primary TKA increased by 99.2%. - Revision TKA volume increased by 105.9% from 9,650 to 19,871 procedures. - Per-capita utilization of revision TKA increased by 56.8%. 2. **Outcomes**: - Hospital length of stay (LOS) for primary TKA decreased from 7.9 days in 1991-1994 to 3.5 days in 2007-2010. - All-cause 30-day readmission rates for primary TKA increased from 4.2% to 5.0%. - For revision TKA, hospital LOS decreased from 8.9 days to 5.0 days, but 30-day readmission rates increased from 6.1% to 8.9%. 3. **Discharge Disposition**: - The percentage of patients discharged to inpatient rehabilitation increased, while the percentage discharged to skilled care/ outpatient rehabilitation also increased. 4. **Complications**: - Rates of surgical complications such as wound infection, hemorrhage, sepsis, and myocardial infarction increased significantly, particularly after revision TKA. The study highlights the increasing demand for TKA, driven by both an increase in the number of Medicare enrollees and per-capita utilization. It also underscores the need for further research to evaluate the appropriateness of TKA procedures and to address the rising costs and complications associated with shorter hospital stays.