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Elevated ESR
2%
39/1837
Synovial WBC of 2800 cells/uL
5%
94/1837
Synovial PMN of 55%
1%
26/1837
Positive synovial leukocyte esterase
4%
69/1837
Positive synovial alpha defensin
87%
1602/1837
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This patient has a chronic periprosthetic joint infection which is most accurately predicted by a positive alpha defensin test. Immunosuppressed patients and those with inflammatory arthropathy or lifestyle risk factors (smoking, morbid obesity, etc.) are at higher risk of PJI. While ESR and CRP can be elevated in the setting of chronic PJI, they are nonspecific markers of inflammation. Diagnosis of a chronic PJI is made when either one major MSIS criteria is present, or when the composite score of the minor criteria totals >=6 points. If a patient has 2-5 points on the minor scale pre-operatively, intraoperative diagnosis of PJI may be made with >=6 points from the following criteria: intra-operative findings of purulence (3 points), positive culture (2 points), or >5 neutrophils per high powered field (HPF) in 5 fields of 400x magnification (3 points). Lee et al. performed a meta-analysis of 13 tests used in the diagnosis of PJI. The authors found that synovial fluid leukocyte count, PMN%, CRP, alpha defensin, LE, IL-6 and IL-8 all demonstrated high sensitivity for diagnosing PJI. The study concluded that while synovial LE had similar sensitivity to alpha defensin in the diagnosis of PJI, alpha defensin was more specific and had the highest diagnostic odds ratio of all the tests. Higuera et al. assessed the profile of the synovial fluid in patients with chronic THA PJI. They report that the rates of PJI for patients with synovial WBC of 3,000-5,000 was 14% and 29% for patients with PMN % of 75-85%. Their study concluded that there is a substantial "gray area" around synovial WBC and PMN% thresholds for PJI, and that the most up to date threshold for the diagnosis of chronic PJI in THA is 3966 cells/uL WBC and 80% PMN. Illustration A shows the diagnostic criteria for PJI. Incorrect Answers: Answer 1: Elevated ESR is a nonspecific marker of inflammation and is neither highly sensitive or specific for chronic PJI. Answer 2: The synovial WBC threshold for diagnosis of chronic THA PJI is 3966 cells/uL. Answer 3: The synovial PMN% which predicts chronic THA PJI is 80%. Answe 4: Positive synovial leukocyte esterase as sensitive but not as specific as synovial alpha defensin in the diagnosis of chronic THA PJI.
2.7
(3)
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