NSQIP 30-day outcome measures for below-knee amputations by ICD-10 diagnoses

The indications for Below-Knee Amputation (BKA) are expansive and etiologic subgroups are not well defined. This analysis uses primary ICD-10 diagnosis codes to stratify patients undergoing BKA, and examines differences in subgroup characteristics and 30-day outcomes.

We performed a retrospective analysis of patients in the NSQIP database who underwent BKA between 2015 and 2020. Approximately 80% of the 12,157 NSQIP BKA entries with primary ICD-10 diagnosis codes were stratified to diabetic (n = 3,363), vascular (n = 3,632), or infectious (n = 2,743) etiological subgroups.

Patients with vascular etiologies were older, more likely to be female, underweight, ASA classification of four, and active tobacco users than patients in the other groups. Across all groups, there were incidences of 37.5% for 30-day inpatient complications, 7.0% for Clavien-Dindo Grade IV 30-day complications, 10.2% for 30-day readmission, and 4.2% for 30-day mortality. On bivariate analysis, infectious patients had the highest incidences of inpatient complications (38.6%, p = 0.030) and Clavien-Dindo Grade IV complications (7.8%, p = 0.055). Patients in the vascular group had the highest rates of readmission (12.7%, p<0.001) and mortality (4.9%, p = 0.006). In multivariate analysis, infectious etiology was an independent risk factor for 30-day mortality with an odds ratio of 1.48 (1.11-19.6, p = 0.007).

Despite significant clinical overlap of diabetic, vascular, and infectious etiologies of BKA, this study demonstrates that these patients can be grouped by primary ICD-10 code with statistically significant differences in patient characteristics and 30-day outcomes. Further delineation by etiology could focus clinical and research efforts.