The new modified four-factor functional frailty index (mFF-4) in colorectal surgery: A retrospective cohort study

Since its introduction, the Modified Five-Factor Frailty Index (mFI-5) has been widely applied across subspecialties using the National Surgical Quality Improvement Program (NSQIP) database. Although the mFI-5 index is predictive, it predominantly focuses on comorbidities and does not represent functional frailty aspects. We sought to apply the new Modified Four-Factor Functional Frailty Index (mFF-4) to a colorectal population.

This retrospective study using NSQIP 2021-2022 includes patients >75 years of age who underwent colon and rectal surgery. The mFF-4 frailty index is scored by adding one point for each present variable including history of falls, dementia, poor nutritional status (body mass index <18.5), and nonindependent functional status. Patients were stratified into frailty groups: mFF-4=0, 1, 2+. Univariate and multivariate regressions were performed to assess 30-day postoperative outcomes. Area under the curve (AUC) and Akaike information criterion (AIC) values assessed predictability of the mFF-4 model, in reference to mFI-5.

Our sample of n=27,875 included 21,573 in the mFF-4=0 (77.4%), 4,601 in mFF-4=1 (16.5%), and 1,701 in mFF-4=2+ (6.1%). The mFF-4 multivariate regressions had less error (lower AICs by >2) and higher AUCs (most >0.7) than the mFI-5 for predicting mortality, pneumonia, ventilator use >48 hours, delirium, length of stay >30 days, and nonhome discharge destination. For these complications, patients with high frailty (mFF-4=2+) had statistically significant odds ratios >2.0.

This new frailty index, focused on functional capabilities, is more encompassing of phenotypical frailty and is more predictive than the mFI-5. This new scale will help risk-stratify our aging colorectal population.