Total knee arthroplasty (TKA) is one of the most commonly performed orthopaedic procedures worldwide, with numbers projected to increase substantially alongside ageing populations and rising rates of osteoarthritis [1,2]. While TKA reliably relieves pain and restores function, perioperative complications remain a significant concern, particularly among elderly patients with multiple comorbidities [3,4].

Frailty—defined as a state of increased vulnerability to physiological stressors—is an independent predictor of adverse postoperative outcomes across surgical specialties [5,6]. Several frailty assessment tools have been proposed; among these, the 5-factor modified frailty index (mFI-5) has gained considerable traction due to its simplicity, reliance on routine preoperative data, and validation across diverse surgical populations [7,8]. The mFI-5 incorporates five binary variables: diabetes mellitus, hypertension, congestive heart failure, chronic obstructive pulmonary disease, and functional dependence, each scored as 0 or 1, yielding a composite score of 0–5 [7].

Prior studies in Western populations have demonstrated that higher mFI-5 scores correlate with increased rates of Clavien-Dindo grade IV complications, surgical site infections (SSI), unplanned readmissions, and 30-day mortality following total joint arthroplasty [9–12]. However, published data from the Indian subcontinent are limited, and the prevalence and distribution of frailty-defining comorbidities differ substantially from Western cohorts, particularly with respect to the high regional burden of diabetes and hypertension [13].

This study was therefore designed to evaluate the predictive utility of the mFI-5 for postoperative morbidity after primary TKA at a tertiary care centre in Bengaluru, and to determine whether increasing frailty scores correlate with clinically meaningful differences in complication rates, ICU requirements, hospital stay, readmission, and functional recovery.

Study Design and Setting This was a retrospective observational study conducted at Sapthagiri Institute of Medical Sciences and Research Centre, Bengaluru, Karnataka, a tertiary care teaching hospital. Institutional Ethics Committee approval was obtained prior to data collection (SIMSRC/ EC-35/PG-08/ 2025-26). The study was conducted in compliance with the Declaration of Helsinki. Inclusion and Exclusion Criteria Consecutive patients aged 18 years and above who underwent primary unilateral or bilateral TKA between January 2023 and January 2026 were included. Patients undergoing revision arthroplasty, those with incomplete preoperative data, and those with prior ipsilateral knee surgery were excluded. mFI-5 Calculation The mFI-5 was calculated for each patient using five preoperatively documented variables: (1) diabetes mellitus (any type requiring medical management), (2) hypertension (on antihypertensive therapy), (3) congestive heart failure (documented on echocardiography or clinical records), (4) chronic obstructive pulmonary disease (spirometry-confirmed or treated), and (5) functional dependence (requirement of assistance for activities of daily living). Each variable was scored 0 (absent) or 1 (present), and the composite mFI-5 score ranged from 0 to 5. Patients were categorised as non-frail (mFI 0–1), moderately frail (mFI 2), or severely frail (mFI ≥3), consistent with published classification thresholds [7,8]. Outcome Measures Primary outcomes were: (1) any postoperative complication, (2) ICU admission, (3) 30-day readmission, and (4) 30-day mortality. Specific complications recorded included surgical site infection (SSI), deep vein thrombosis (DVT), pulmonary embolism (PE), and urinary tract infection (UTI). Secondary outcomes included length of hospital stay (LOS in days) and functional recovery as measured by the Knee Society Score (KSS) at baseline and at 3-month follow-up. Statistical Analysis Continuous variables are expressed as mean ± standard deviation (SD) and were compared across frailty groups using the Kruskal-Wallis test, with Mann-Whitney U test for binary group comparisons. Categorical variables are expressed as frequency and percentage and were compared using the chi-squared test or Fisher's exact test as appropriate. Odds ratios (OR) with 95% confidence intervals (CI) were calculated for binary outcomes comparing frail (mFI ≥2) versus non-frail (mFI 0–1) patients. Spearman's rank correlation was used to assess associations between mFI score and continuous outcomes. A p-value of <0.05 was considered statistically significant. All analyses were performed using Python (SciPy v1.11, pandas v2.0).

Patient Demographics and Frailty Distribution

Ninety-nine patients met the inclusion criteria. The mean age was 64.7 ± 7.6 years (range 48–86 years), and 58 patients (58.6%) were female. The distribution of mFI-5 scores was as follows: 17 patients (17.2%) scored 0, 39 (39.4%) scored 1, 35 (35.4%) scored 2, 5 (5.1%) scored 3, and 3 (3.0%) scored 4. Overall, 56 patients (56.6%) were classified as non-frail (mFI 0–1), 35 (35.4%) as moderately frail (mFI 2), and 8 (8.1%) as severely frail (mFI ≥3).

The most prevalent frailty-defining comorbidities were hypertension (60.6%, n=60) and diabetes mellitus (54.5%, n=54), followed by COPD (9.1%, n=9), functional dependence (9.1%, n=9), and congestive heart failure (4.0%, n=4). Baseline demographic data are summarised in Table 1.

Table 1: Baseline Demographics and Comorbidities by Frailty Group

Primary Outcomes

Postoperative complications occurred in 9 patients (9.1%) overall. No complications were recorded in the non-frail group, compared to 4 (11.4%) in the moderately frail and 5 (62.5%) in the severely frail group (p<0.001). Complication types included DVT in 4 patients (4.0%), SSI in 3 (3.0%), UTI in 2 (2.0%), and PE in 1 (1.0%).

ICU admission was required in 15 patients (15.2%). Rates were 7.1% (non-frail), 22.9% (moderate), and 37.5% (severe), with a statistically significant difference across groups (χ²=7.518, p=0.023). Thirty-day readmission was recorded in 9 patients (9.1%), exclusively in the frail cohort: 11.4% in the moderate group and 62.5% in the severe group versus 0% in the non-frail group (p<0.001). There were no 30-day deaths in the cohort.

Binary comparison of frail (mFI ≥2, n=43) versus non-frail (mFI 0–1, n=56) patients demonstrated that frailty was associated with a 4.47-fold increase in odds of ICU admission (OR 4.47, 95% CI 1.29–15.49; p=0.021). Both complication and readmission rates were significantly higher in the frail group, with no events in the non-frail group (Fisher's exact p=0.0003 for both).

Table 2: Postoperative Outcomes by Frailty Group

Table 3: Frail vs Non-frail — Binary Comparison of Key Outcomes

Length of Hospital Stay

Mean LOS increased significantly with frailty score: 5.5 ± 1.2 days (non-frail), 6.1 ± 1.8 days (moderate), and 8.6 ± 1.4 days (severe) (Kruskal-Wallis H=17.799, p=0.0001). Spearman's correlation confirmed a significant positive association between mFI score and LOS (r=0.212, p=0.035).

Functional Outcomes

Preoperative KSS was similar across frailty groups (104.9, 108.0, and 107.9 for non-frail, moderate, and severe respectively; p=0.12). At 3-month follow-up, mean KSS was 188.2 ± 28.6 (non-frail), 184.3 ± 24.0 (moderate), and 176.8 ± 22.1 (severe). No statistically significant difference in 3-month KSS was observed (Kruskal-Wallis H=3.991, p=0.136), and mFI score did not correlate with KSS improvement (Spearman r=−0.029, p=0.779).

Table 4: mFI-5 Score Distribution and Outcome Rates