SURGICAL AND CLINICAL OUTCOMES FOLLOWING MANAGEMENT OF TOTAL KNEE ARTHROPLASTY PERIPROSTHETIC JOINT INFECTION WITH EXTENSOR MECHANISM DISRUPTION AND SOFT-TISSUE DEFECT: THE KNEE ARTHROPLASTY TERRIBLE TRIAD

Periprosthetic infection (PJI) with concomitant extensor mechanism disruption (EMD) and soft tissue defect – hereinafter termed the “Terrible Triad” – is a devastating complication following total knee arthroplasty (TKA). The purpose of this study was to define the surgical and clinical outcomes following management of patients with the Terrible Triad. From 2000 to 2022, 127 patients underwent operative management for PJI, 25 for PJI with major soft tissue defect (defined as defects requiring flap reconstruction or being a main factor contributing to the decision of performing above-knee-amputation (AKA) or arthrodesis), 14 for PJI with EMD (with or without attempted repair or reconstruction), and 22 for the Terrible Triad. A composite outcome considering infection status (defined according to the 2018 ICM consensus statement for PJI management), range of motion (ROM), extensor lag, and ambulatory status at final follow-up was used to determine the proportion of patients in each group with a favorable overall knee outcome and compared across groups (Table 1) [1]. Two-year mortality from initiation of PJI treatment was compared across groups. Differences in continuous data were assessed using one-way ANOVA and Tukey's post hoc test. Differences in categorical data were assessed using Pearson's Chi-squared test or Fisher's exact test. Multivariable logistic regression was used to calculate odds ratios (OR) and 95% confidence intervals (CI). The Kaplan-Meier survival analysis and log-rank test were used to assess mortality. Statistical significance was set at α=0.05. Mean duration of follow-up was 7.71 years and equivalent between groups (p=0.053). Patients in both the Terrible Triad group and PJI with soft tissue defect group demonstrated lower incidence of infection control with no continued antibiotic therapy and higher incidence of AKA or arthrodesis (Tier 3E) compared to patients in both the PJI group and PJI with EMD group (p<0.001), and higher incidence of limited ambulation compared to those in the PJI group (p<0.001). Patients in the Terrible Triad group demonstrated higher incidence of ROM arc <90° than those in the PJI group (p=0.031), and higher incidence of extensor lag >15° than those in the PJI group and PJI and soft tissue defect group (p<0.001) (Table 2). Patients in the PJI with soft tissue defect, PJI with EMD, and Terrible Triad groups showed higher odds of unfavorable overall knee outcome than those in the PJI group (OR=5.81, OR=5.50, OR=11.61, respectively). Mean two-year mortality was 7.8%, 8.0%, 42.9%, and 9.1% in the PJI, PJI with soft tissue defect, PJI with EMD, and Terrible Triad groups, respectively (p=0.472). Symbols (§, †, ‡, ¶) within a row indicate statistically significant differences between two groups as determined by Tukey's post hoc test following one-way ANOVA for continuous data and chi squared test or fisher's exact test for categorical data. This study demonstrates that the Terrible Triad of TKA is a dreaded diagnosis with poor outcomes, leaving 86.4% of patients with an unfavorable overall knee outcome. Patients should be warned of high risk for failure with multiple revisions during their management. Early treatment with definitive fusion or AKA should be considered by patients and surgeons. For any figures or tables, please contact the authors directly.