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Journal of Bone and Joint Infection An open-access journal of the European Bone and Joint Infection Society and the MusculoSkeletal Infection Society
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Volume 5, issue 3
J. Bone Joint Infect., 5, 118–124, 2020
https://doi.org/10.7150/jbji.44815
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
J. Bone Joint Infect., 5, 118–124, 2020
https://doi.org/10.7150/jbji.44815
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Original full-length article 22 Apr 2020

Original full-length article | 22 Apr 2020

Synovial Cell Count Poorly Predicts Septic Arthritis in the Presence of Crystalline Arthropathy

T. David Luo1, D. Landry Jarvis2, Hunter B. Yancey1, Andrey Zuskov1, Shane C. Tipton1, and Maxwell K. Langfitt1 T. David Luo et al.
  • 1Department of Orthopaedic Surgery, Wake Forest Baptist Medical Center, Winston-Salem, NC 27157, USA
  • 2Divison of Sports Medicine, Department of Orthopaedic Surgery, Duke University Medical Center, Durham, NC 27710, USA

Keywords: septic arthritis, crystalline arthropathy, gout, pseudogout, cell count, joint infection

Abstract. Introduction: A synovial cell count greater than 50,000/mm3 is the threshold most commonly used to diagnose septic arthritis. This lab value may be nonspecific in the setting of crystalline arthropathy. The purpose of this study was to evaluate the accuracy of diagnosing septic arthritis using a synovial cell count cut-off of 50,000/mm3 in the setting of crystalline arthropathy.

Methods: This was a retrospective review of joint aspirations performed between July 1st, 2013 and June 30th, 2016. Synovial fluid samples were evaluated for cell count, crystals, Gram stain, and culture. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the synovial markers were calculated.

Results: During the study period, 738 joint aspirations were sent for testing, of which 358 aspirations in 348 patients met inclusion criteria. There were 49 (13.7%) cases of culture-positive septic arthritis, and 47 patients underwent surgical irrigation and debridement. Gout and pseudogout crystals were present in 163 aspirates (45.5%). Three joints (0.8% overall rate) had concomitant crystalline arthropathy and septic arthritis, each of which had a synovial WBC ≥85,000/mm3. Increasing the WBC count cutoff to 85,000/mm3 demonstrated a specificity of 100%, but a PPV of 12.0%.

Conclusions: A cut-off of 85,000/mm3 may be more appropriate to diagnose concomitant septic arthritis and crystalline arthropathy. We recommend medical management and observation in patients with crystal-positive joint aspirations unless the synovial cell count is elevated above 85,000/mm3. Prospective studies using this treatment guideline are needed to evaluate its validity and accuracy.

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