Is Reoperation Higher Than Expected after Below-the-knee Amputation? A Single-center Evaluation of Factors Associated with Reoperation at 1 Year

Background Below-the-knee amputation (BKA) is relatively common among patients with vascular disease, infection, trauma, or neoplastic disease. Many BKAs are performed in patients with incompletely treated medical comorbidities, and some are performed in patients with acute high-energy trauma or crush injuries, malignant neoplasm undergoing time-sensitive limb removal, and diabetes with active infection or sepsis. Consequently, revision is common. Prior studies of outcomes after BKA, including several based on the American College of Surgeons-National Surgical Quality Improvement Program (ACS-NSQIP) database, have follow-up periods that do not cover the entire at-risk period. Questions/purposes (1) What is the survivorship free from unplanned reoperation within 1 year of BKA? (2) What patient characteristics are associated with reoperation within 1 year of BKA? Methods We retrospectively studied all BKAs performed by the orthopaedic surgery service at a Level 1 trauma center from 2008 to 2018, as identified by Current Procedural Terminology (CPT) codes. Twenty-eight percent (38 of 138) underwent amputation as treatment for traumatic injury, 57% (79 of 138) for infection, and 15% (21 of 138) for malignancy. A total of 17% (23 of 138) had a final follow-up encounter before the 1-year study minimum, without differential loss to follow-up by surgical indication (p = 0.43) or hemoglobin A1c (p = 0.71). Median (range) follow-up was 570 days (6 to 3375). The primary outcome was survivorship from unplanned reoperation within 1 year of BKA index surgery or last planned reoperation, as determined by Kaplan-Meier estimation. Secondarily, we identified patient characteristics independently associated with reoperation within 1 year of BKA. Collected data included age, indication, BMI, diabetes, hemoglobin A1c level, closure method, and substance use. Unplanned reoperation was defined as irrigation and debridement, stump revision, or revision to a higher-level amputation; this did not include planned reoperations for BKAs closed in a staged manner. Factors associated with reoperation were determined using multivariate logistic regression analyses. All endpoints and variables related to patients and their surgical procedures were extracted from electronic medical records by someone other than the operating surgeon. Results Using Kaplan-Meier estimation, 38% of patients (95% confidence interval 29 to 46) who underwent BKA had an unplanned reoperation within 1 year of their index surgery. Twelve percent of patients (95% CI 7 to 17) who underwent BKA did not reach 30 days with the limb survivorship free from unplanned reoperation. The median (range) time between the initial surgery and reoperation was 54 days (6 to 315). After controlling for potential confounding variables like age, gender, platelet count, albumin, and the reason for undergoing amputation, a hemoglobin A1c level greater than 8.1% (relative to A1c <= 8.1%) was the only variable independently associated with increased odds of reoperation (odds ratio 4.6 [95% CI 1.3 to 18.1]; p = 0.02). Conclusion BKA carries a higher risk for reoperation than currently reported in studies that use 30-day postoperative follow-up periods. Clinicians should critically assess whether BKA is necessary, especially in patients with uncontrolled diabetes assessed by hyperglycemia. Before planned BKA, patients should have documented glycemic control to minimize the odds of reoperation. Because many of this study's limitations were due to its retrospective single center design, we recommend that future work cover a clinically appropriate surveillance period using a larger cohort such as a national database and/or employ a prospective design.