Total Knee Arthroplasty Periprosthetic Joint Infection With Concomitant Extensor Mechanism Disruption and Soft-Tissue Defect: The Knee Arthroplasty Terrible Triad

Background 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 a cohort of patients who have the Terrible Triad. Methods From 2000 to 2022, 127 patients underwent operative management for PJI alone, 25 for PJI with soft-tissue defects (defined as defects requiring flap reconstruction or being a factor contributing to the decision of performing above-knee amputation (AKA) or arthrodesis), 14 for PJI with EMD, and 22 for the Terrible Triad. A composite outcome of infection status, range of motion, extensor lag, and ambulatory status at final follow-up was used to compare the proportion of patients in each group with a favorable overall knee outcome. Differences between groups were determined using one-way analyses of variance with post hoc Tukey's tests and Pearson's Chi-square tests or Fisher's exact tests with post hoc Bonferroni adjustments, where applicable. Odds ratios (OR) were calculated for comparison of the overall knee outcome between groups. A Kaplan-Meier survival analysis for patient mortality was performed. Results The mean follow-up was 8.4 years and similar between groups (P = 0.064). Patients who had the Terrible Triad had a 45.5% incidence of AKA, or arthrodesis, and an 86.4% incidence of an unfavorable outcome. Compared to patients in the PJI group, patients in the PJI who had a soft-tissue defect (OR=5.8, 95%CI [confidence interval] 2.2 to 15.7), PJI with EMD (OR=3.7, 95%CI 1.0 to 12.9), and Terrible Triad groups (OR=11.6, 95%CI 3.3 to 41.5) showed higher odds of an unfavorable knee outcome. Conclusions This study demonstrates that the TKA Terrible Triad is a dreaded diagnosis with poor outcomes. Clinicians and patients might consider early treatment with amputation or arthrodesis.