Chi Xu, Timothy L. Tan, Feng-Chih Kuo, Karan Goswami, Qiaojie Wang, Javad Parvizi. J Arthroplasty 2019, doi: 10.1016/j.arth.2019.06.048.

Summary by Dr. Marjan Wouthuyzen-Bakker

In this paper of the week, Xu et al. evaluated the sensitivity of serum CRP (> 100 mg/L), synovial leucocyte count (> 10,000 cells/μL) and its percentage of PMN (>90%) in the diagnosis of an acute PJI. Intraoperative cultures were used as a gold standard. 218 patients were evaluated. The reported sensitivity was 55%, 60% and 51%, respectively. Combining all 3 tests resulted in a sensitivity of 84%. Sensitivity greatly depended on the microorganism causing the infection, with the lowest sensitivity observed in infections caused by Coagulase Negative Staphylococci.

Sensitive markers to diagnose an acute PJI are needed in our field in order to decide whether a DAIR procedure should be performed or if a conservative, “wait and see” approach is an acceptable option. The study performed by Xu et al. clearly demonstrates that serum CRP and synovial leucocyte counts are insufficient and should not be used in this decision making process. Techniques with a higher diagnostic accuracy to detect a bacterial infection are needed, especially with a high negative predictive value. Until then, a DAIR should be performed as soon as a clinical suspicion of an infection arises, and should not be postponed [1.

Although the specificity of the studied biomarkers were not evaluated in the study of Xu et al., it is important to realize that according to the current diagnostic criteria, a proportion of the acute PJIs will probably be misqualified as “culture negative PJIs” based on serological testing [3-4]. As a result, these patients will be subjected to unnecessary long-term antibiotic treatment. In contrast to chronic infections, planktonic, free-floating bacteria are abundantly present in acute infections, and these types of bacteria are easy to culture. Thus, a PJI can be ruled out in patients with negative cultures, provided that a sufficient number of cultures were obtained and the patient was not on antibiotic treatment. To conclude about the specificity of the current markers, a control arm of patients with a clinical suspicion of an acute PJI, but with negative cultures during DAIR should be performed.

References

1. Triantafyllopoulos GK, Poultsides LA, Sakellariou VI et al. Irrigation and debridement for periprosthetic infections of the hip and factors determining outcome. Int Orthop. 2015; 39(6):1203-9.
2. Triantafyllopoulos GK, Poultsides LA, Zhang W et al. Periprosthetic knee infections treated with irrigation and debridement: outcomes and preoperative predictive factors. J Arthroplasty. 2015; 30(4):649-57.
3. Bedair H, Ting N, Jacovides C et al. The Mark Coventry Award: diagnosis of early post-operative TKA infection using synovial fluid analysis. Clin Orthop Relat Res 2011; 469: 34-4-.
4. Kim SG, Kim JG, Jang KM et al. Diagnostic value of synovial white blood cell count and serum C-reactive protein for acute periprosthetic joint infection after knee arthroplasty. J Arthoplasty 2017; 32: 3724-8.