Metformin Use Is Associated with Fewer Complications in Patients with Type-2 Diabetes Undergoing Total Knee Arthroplasty

BACKGROUND: Diabetes is a well-established risk factor for complications following total knee arthroplasty (TKA), and the incidence of type-2 diabetes is increasing. Metformin is considered first-line therapy for type-2 diabetes and has been shown to reduce all-cause mortality and to possess anti-inflammatory properties. The impact of metformin use as it relates to outcomes following TKA is unknown. The purpose of this study was to investigate this relationship. METHODS: This is a retrospective cohort study using the Truven MarketScan database. Adult patients undergoing unilateral, primary TKA were identified. We included only patients with a preoperative diagnosis of type-2 diabetes and established 2 cohorts based on metformin status. Propensity score matching was performed to match patients who used metformin to those who did not (1-to-1). Patients were matched on factors including age, sex, insulin status, other diabetic medications, comorbidities, complexity of diabetes, and smoking status. Regression analysis was then performed on matched cohorts to examine 90-day outcomes. A subgroup analysis was performed on 1-year revision rates. RESULTS: After matching, there were 32,186 patients in both the metformin group and the no-metformin group, resulting in a total of 64,372 included patients. Baseline characteristics were similar between groups. Regression analysis, performed on matched cohorts, demonstrated that the no-metformin group had increased odds of readmission (odds ratio OR, 1.09 95% confidence interval (CI), 1.04 to 1.15; p < 0.001), emergency department presentation (OR, 1.09 95% CI, 1.04 to 1.14; p < 0.001), extended length of stay (OR, 1.12 95% CI, 1.06 to 1.15; p < 0.001), periprosthetic joint infection (OR, 1.30 95% CI, 1.13 to 1.50; p < 0.001), deep vein thrombosis (OR, 1.17 95% CI, 1.09 to 1.26; p < 0.001), acute kidney injury (OR, 1.21 95% CI, 1.09 to 1.33; p < 0.001), hypoglycemic events (OR, 1.25 95% CI, 1.01 to 1.54; p = 0.039), and 1-year revision (OR, 1.16 95% CI, 1.01 to 1.33; p = 0.033). CONCLUSIONS: Metformin use in patients with type-2 diabetes undergoing TKA appears to be associated with lower odds of multiple complications and resource utilization parameters, including periprosthetic joint infection and 1-year revision rates. Given the frequency with which TKA is performed in patients with type-2 diabetes, this knowledge has the potential to improve optimization protocols and outcomes in this group of patients. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.