Abstract
BACKGROUND: Previous studies of knee arthroplasty infections caused by high-virulence organisms suggest poor outcomes. Polymicrobial and Gram-negative infections are less studied. QUESTIONS/PURPOSES: This study compared the results of treatment of knee arthroplasty infections by single versus polymicrobial isolates, Gram-positive versus Gram-negative, and methicillin-resistant versus -sensitive Staphylococci. METHODS: We prospectively followed 47 patients with late knee arthroplasty infections. The mean age was 72 years (range, 20-87 years). The treatment protocol included two-stage exchange and a combination of two oral antibiotics given for 6 months. Minimum followup was 1 year (average, 4.8 +/- 3 years; range, 1-12 years). Control of the infection was judged by absence of clinical, serologic, and radiologic signs of infection. The functional outcome was evaluated by Knee Society score at the last followup. RESULTS: Infection was controlled in all 15 patients with polymicrobial and in 28 of 32 (88%) with monomicrobial infections, in eight of nine patients with Gram-negative and in 35 of 38 (92%) with Gram-positive isolates. Control was also achieved in 22 of 25 patients (88%) infected by methicillin-resistant Staphylococci and in 14 of 14 by methicillin-sensitive Staphylococci. The Knee Society scores averaged 81-63 in patients with polymicrobial infections and were higher than in monomicrobial infections (75-52). The mean KSS was 85-59 in Gram-negative infections compared to 75-55 in Gram-positive infections. The mean KSS was similar in methicillin-resistant (78-54) and methicillin-sensitive Staphylococci (73-56) infections. CONCLUSIONS: Polymicrobial and Gram-negative infections can be controlled in late knee arthroplasty infections. On the other hand, infections by methicillin-resistant Staphylococci are less likely to be controlled by the regimens we used. LEVEL OF EVIDENCE: Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.