Diagnosing periprosthetic joint infection (PJI) remains a vexing task with the tools that we have for making a definitive diagnosis. Periprosthetic knee infection has been the model on which other PJI evaluations are based. The hip is no different, except that PJI of the hip may be more difficult to evaluate, as access to synovial fluid is more challenging and samples are precious.
Controversy over the diagnosis of PJI has been the progeny of the modalities utilized1-4. The historical method—and the current mainstay for a large number of institutions—is an analysis of synovial fluid white-blood cell (WBC) count with differential cell assay. Perhaps it is why PJI diagnosis using synovial fluid WBC count is often revisited: such analysis is relatively easy to perform, imparts lower morbidity and is less costly than an operative evaluation, and gives hope to the result of a true negative. After all, is not the diagnosis of hip PJI via synovial fluid analysis with the elimination of false-positive and false-negative results, and with the establishment of the optimum breakpoint, our goal?
In the current study, Higuera et al. provide insight into the utility of synovial fluid analysis of PJI of the hip. More importantly, they describe a diagnostic “gray area” regarding synovial cell counts and neutrophil percentage of the WBC count, the zone for which we must evaluate synovial fluid values with a critical eye. This gray area is the region of the receiver operating characteristic (ROC) curve that may be used as fertile ground for the use of other modalities (such as an alpha-defensin assay) to diagnose PJI as well as the development of new technologies to accurately diagnose PJI5. Orthopaedic surgeons who perform total hip arthroplasty will, by default, need to manage PJI and should welcome the information provided in this study and use the data as an impetus to think critically about the synovial fluid cell count in the setting of a potential PJI. The findings in this article contribute to solving our diagnostic dilemma. Hopefully in the near future, the diagnosis of PJI will be a singular test.
1. Matsen Ko L, Parvizi J. Diagnosis of periprosthetic infection: novel developments. Orthop Clin North Am. 2016 Jan;47(1):1-9.
2. Shahi A, Parvizi J, Kazarian GS, Higuera C, Frangiamore S, Bingham J, Beauchamp C, Valle CD, Deirmengian C. The alpha-defensin test for periprosthetic joint infections is not affected by prior antibiotic administration. Clin Orthop Relat Res. 2016 Jul;474(7):1610-5.
3. Frangiamore SJ, Siqueira MB, Saleh A, Daly T, Higuera CA, Barsoum WK. Synovial cytokines and the MSIS criteria are not useful for determining infection resolution after periprosthetic joint infection explantation. Clin Orthop Relat Res. 2016 Jul;474(7):1630-9.
4. Newman JM, George J, Klika AK, Hatem SF, Barsoum WK, Trevor North W, Higuera CA. What is the diagnostic accuracy of aspirations performed on hips with antibiotic cement spacers? Clin Orthop Relat Res. 2017 Jan;475(1):204-11. Epub 2016 Sep 26.
5. Chalmers PN, Walton D, Sporer SM, Levine BR. Evaluation of the role for synovial aspiration in the diagnosis of aseptic loosening after total knee arthroplasty. J Bone Joint Surg Am. 2015 Oct 7;97(19):1597-603.