Diagnosis of knee prosthetic joint infection; aspiration and biopsy

The value of microbiological culture to diagnose late periprosthetic infection is limited, especially because standard methods may fail to detect biofilm-forming sessile or other fastidious bacteria. There is no agreement on the appropriate cultivation period, although this period is a crucial factor. This study was designed to assess the duration of culture that is necessary for reliable detection. Ten periprosthetic tissue specimens each were obtained during revision from 284 patients with suspected late hip or knee arthroplasty infection. Five samples were examined by microbiological culture over a 14-day period, and 5 were subjected to histologic analysis. To define infection, a pre-established algorithm was used; this included detection of indistinguishable organisms in >/=2 tissue samples or growth in 1 tissue sample and a positive result of histologic analysis (>5 neutrophils in at least 10 high-power fields). The time to detection of organisms was monitored. Infection was diagnosed in 110 patients. After 7 days (the longest incubation period most frequently reported), the detection rate via culture was merely 73.6%. Organisms indicating infection were found for up to 13 days. "Early"-detected species (mostly staphylococci) emerged predominantly during the first week, whereas "late"-detected agents (mostly Propionibacterium species) were detected mainly during the second week. In both populations, an unequivocal correlation between the number of culture-positive tissue samples and positive results of histologic analysis was noted, which corroborated the evidence that true infections were detected over the entire cultivation period. Prolonged microbiological culture for 2 weeks is promising because it yields signs of periprosthetic infection in a significant proportion of patients that would otherwise remain unidentified.

No preferred test for diagnosis of periprosthetic joint infection exists, and the algorithm for the workup of patients suspected of infection remains unclear. The work group evaluated the available literature to determine the role of each diagnostic modality and devise a practical algorithm that allows physicians to reach diagnosis of periprosthetic joint infection. Ten of the 15 recommendations have strong or moderate evidence in support. These include matters involving erythrocyte sedimentation rate and C-reactive protein level testing, knee and hip aspiration, and stopping the use of antibiotics prior to obtaining intra-articular cultures. The group recommends against the use of intraoperative Gram stain but does recommend the use of frozen sections of peri-implant tissues in reoperation patients in whom infection has not been established, as well as multiple cultures in reoperation patients being assessed for infection. The group recommends against initiating antibiotic treatment in patients with suspected infection until after joint cultures have been obtained, but recommends that prophylactic preoperative antibiotics not be withheld in patients at lower probability for infection.

The white blood-cell count and neutrophil differential of the synovial fluid have been reported to have high sensitivity and specificity in the diagnosis of periprosthetic infection following total knee arthroplasty. We hypothesized that neutrophils recruited into an infected joint secrete enzymes that may be used as markers for infection. In this prospective study, we determined the sensitivity and specificity of one of these enzymes, leukocyte esterase, in diagnosing periprosthetic joint infection. Between May 2007 and April 2010, synovial fluid was obtained preoperatively from the knees of patients with a possible joint infection and intraoperatively from the knees of patients undergoing revision knee arthroplasty. The aspirate was tested for the presence of leukocyte esterase with use of a simple colorimetric strip test. The color change (graded as negative, trace, +, or ++), which corresponded to the level of the enzyme, was noted after one or two minutes. On the basis of clinical, serological, and operative criteria, thirty of the 108 knees undergoing revision arthroplasty were infected and seventy-eight were uninfected. When only a ++ reading was considered positive, the leukocyte esterase test was 80.6% sensitive (95% confidence interval [CI], 61.9% to 91.9%) and 100% specific (95% CI, 94.5% to 100.0%), with a positive predictive value of 100% (95% CI, 83.4% to 100.0%) and a negative predictive value of 93.3% (95% CI, 85.4% to 97.2%). The leukocyte esterase level correlated strongly with the percentage of polymorphonuclear leukocytes (r = 0.7769) and total white blood-cell count (r = 0.5024) in the aspirate as well as with the erythrocyte sedimentation rate (r = 0.6188) and C-reactive protein level (r = 0.4719) in the serum. The simple colorimetric strip test that detects the presence of leukocyte esterase in synovial fluid appears to be an extremely valuable addition to the physician's armamentarium for the diagnosis of periprosthetic joint infection. The leukocyte esterase reagent strip has the advantages of providing real-time results, being simple and inexpensive, and having the ability to both rule out and confirm periprosthetic joint infection. However, additional multicenter studies are required to substantiate the results of our preliminary investigation before the reagent strip can be used confidently in the clinic or intraoperative setting.