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

Abstract

INTRODUCTION: Frailty is a well-established risk factor in patients undergoing total knee arthroplasty (TKA). How age influences the impact of frailty on outcomes in these patients, however, remains unknown. In this study, we aim to describe and evaluate the applicability of a novel risk stratification tool—the age-adjusted modified frailty index (aamFI)—in patients undergoing TKA. METHODS: The American College of Surgeons NSQIP database was queried for all patients undergoing primary TKA from 2015 to 2019. First, outcomes were assessed between chronologically young and old frail patients (< or ≥ 73-years-old, respectively). Then, frailty was classified using the novel aamFI, which constitutes the previously validated 5-item modified frailty index (mFI-5) with the addition of one point for patients ≥ 73 years. Multivariable regression was then used to investigate the relationship between aamFI and postoperative outcomes. RESULTS: A total of 271,271 patients undergoing TKA were identified. Older frail patients had a higher incidence of complications than younger frail patients. There was a strong association between aamFI and complications. An aamFI of ≥ 3 (compared to aamFI of 0) was associated with an increased odds of 30-day mortality (odds ratio [OR] 8.64, 95% confidence interval [CI] 5.04-14.84), any complication (OR: 3.08, CI: 2.86-3.32), deep vein thrombosis (OR: 1.48, CI: 1.22-1.80), and adverse discharge (OR: 6.12, CI: 5.84-6.41; all p < 0.001). CONCLUSION: While frailty negatively influences outcomes following TKA in patients of all ages, patients who are frail and old are particularly vulnerable. The aamFI accounts for this, thus improving on the previously described mFI-5. The aamFI represents a simple, but effective tool for stratifying risk in patients undergoing TKA.