The Impact of Frailty Is Age Dependent in Patients Undergoing Primary Total Knee Arthroplasty: The Age-Adjusted Modified Frailty Index

Frailty is a well-established risk factor in patients undergoing total knee arthroplasty (TKA). How age modifies the impact of frailty on outcomes in these patients, however, remains unknown. In this study, we aimed to describe and evaluate the applicability of a novel risk stratification tool-the age-adjusted modified Frailty Index (aamFI)-in patients undergoing TKA.A national database was queried for all patients undergoing primary TKA from 2015 to 2019. There were 271,271 patients who met inclusion criteria for this study. First, outcomes were compared between chronologically young and old frail patients. In accordance with previous studies, the 75th percentile of age of all included patients (73 years) was used as a binary cutoff. Then, frailty was classified using the novel aamFI, which constitutes the 5-item mFI with the addition of 1 point for patients ≥73 years. Multivariable logistic regressions were then used to investigate the relationship between aamFI and postoperative outcomes.Frail patients ≥73 years had a higher incidence of complications compared to frail patients <73 years. There was a strong association between aamFI and complications. An aamFI of ≥3 (reference aamFI of 0) was associated with an increased odds of 30-day mortality (odds ratio [OR] 8.6, 95% CI 5.0-14.8), any complication (OR 3.1, 95% CI 2.9-3.3), deep vein thrombosis (OR 1.5, 95% CI 1.2-1.8), and nonhome discharge (OR 6.1, 95% CI 5.8-6.4; all P < .001).Although frailty negatively influences outcomes following TKA in patients of all ages, chronologically old, frail patients are particularly vulnerable. The aamFI accounts for this and represents a simple, but powerful tool for stratifying risk in patients undergoing primary TKA.