Impact of Frailty on Total Knee Arthroplasty Outcomes: A Propensity-Matched Study of 133,264 Patients Using the Modified Frailty Index

BACKGROUND: Frailty is a known critical determinant of surgical outcomes. However, it lacks routine integration into total knee arthroplasty (TKA) risk assessment. This study evaluated the association between preoperative frailty, measured by the five-factor modified frailty index (mFI-5), and adverse medical and surgical outcomes following TKA. METHODS: This retrospective cohort analysis utilized a large national database (2003 to 2020), including patients ≥ 50 years undergoing primary TKA. Patients were stratified by mFI-5 score: nonfrail (0 to 1), moderately frail (2), and severely frail (≥ 3). Propensity score matching (1:1) balanced cohorts for age, sex, race, and body mass index. Outcomes included 90-day medical and surgical complications, 2- and 5-year surgical outcomes (revision, periprosthetic fracture, mechanical complications, and infection), mortality, and health care utilization (readmissions and emergency department visits). Relative risks with 95% confidence intervals were calculated, applying Bonferroni corrections (significance P < 0.0167). RESULTS: Frailty severity demonstrated a clear graded increase in complications. Severely frail patients had significantly higher 90-day risks of mortality, myocardial infarction, acute kidney failure, pneumonia, sepsis, anemia, falls, readmissions, and emergency department visits compared with nonfrail patients (all P < 0.0167). Surgical risks similarly increased over time, with severely frail patients showing higher 5-year rates of revision, periprosthetic joint infection, mechanical complications, and periprosthetic fracture. Moderately frail patients demonstrated complication patterns that fell between those of nonfrail and severely frail groups. Frailty was also associated with increased 2- and 5-year mortality. CONCLUSIONS: The mFI-5 effectively stratifies TKA patients by frailty severity and reveals a dose-dependent relationship with adverse outcomes. Prediction of moderate and severe frailty independently increased 90-day, 2-year, and 5-year morbidity, mortality, and health care use. Integrating mFI-5 into preoperative assessment may benefit orthopaedic surgeons in targeted optimization and counseling to mitigate risks in high-risk TKA patients.