Chronic infection of unicompartmental knee arthroplasty: one-stage conversion to total knee arthroplasty.

BACKGROUND: The main reasons for revision of unicompartmental knee arthroplasty (UKA) are loosening, wear, extension of osteoarthritis to another compartment, and infection. There have been no studies of the management of infected UKA, whose incidence varies from 0.2% to 1%. Our objective was to describe infection-related and mechanical outcomes of chronic UKA infection managed by one-stage conversion to total knee arthroplasty (TKA). PATIENTS AND METHODS: Consecutive patients with chronic UKA infection managed by one-stage conversion to TKA between January 2003 and December 2010 were included in a retrospective single-center study. All patients also received appropriate dual antibiotic therapy intravenously for 6 weeks then orally for 6 additional weeks. RESULTS: During the study period, among 233 cases of infected knee arthroplasty managed at our center, 9 met the study inclusion criteria. The UKA was medial in 6 patients, lateral in 2, and patellofemoral in 1. Median age was 67 years (range, 36-83 years) and median infection duration was 9months. In 5 patients, previous treatment with synovectomy, joint lavage, and antibiotics had failed. The following bacteria were identified: oxacillin-susceptible Staphylococci, n=6 (S. epidermidis, n=4; S. capitis, n=1; and S. lugdunensis, n=1); nutritionally deficient Streptococcus, n=1; Enterococcus durans, n=1; and Escherichia coli, n=1. Median follow-up was 60 months (range, 36-96 months). No patient experienced recurrent infection or required revision surgery for infection. No medical complications limiting the use of appropriate antibiotic therapy were recorded. The mean preoperative knee and function scores were 60 and 50, respectively; corresponding mean postoperative values were 75 and 65, respectively. DISCUSSION: UKA infection involves both the prosthesis and the native cartilage, neither of which can be treated conservatively in chronic forms. After identification of the causative organism, synovectomy and joint excision followed by same-stage TKA and combined with appropriate antibiotic therapy for 3 months is effective. LEVEL OF EVIDENCE: IV, retrospective cohort study.