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Letter to the Editor: False-positive Cultures After Native Knee Aspiration: True or False

Matsen, Frederick A. III MD1,a

Clinical Orthopaedics and Related Research®: November 2017 - Volume 475 - Issue 11 - p 2826–2826
doi: 10.1007/s11999-017-5488-1
Letter to the Editor

1Department of Orthopaedics, University of Washington, 1959 NE Pacific Street, 98195-6500, Seattle, WA, USA


Received July 31, 2017/Accepted August 28, 2017; previously published online September 5, 2017

(RE: Jennings JM, Dennis DA, Kim RH, Miner TM, Yang CC, McNabb DC. False-positive cultures after native knee aspiration: True or false. Clin Orthop Relat Res. 2017;475:1840-1843).

The author certifies that neither he, nor any members of his immediate family, have any commercial associations (such as consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article.

All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.

The opinions expressed are those of the writers, and do not reflect the opinion or policy of CORR® or The Association of Bone and Joint Surgeons®.

To the Editor,

The study by Jennings and colleagues [1] is important because it shows that with good harvest and culturing techniques, specimens obtained from healthy knees are likely to be culture-negative.

Two points may be worthy of consideration: First, the term “false-positive” seems problematic. If a culture is positive, it is positive, unless the laboratory technician recorded the result incorrectly. Frequently, however, the term “false-positive” is used to refer to a positive culture when the observer does not believe the cultured bacteria originated from the specimen submitted. Unfortunately, unless perfect harvesting, handling, and culturing methods are used, one cannot be absolutely sure whether cultured bacteria originated from the joint, the air, the surgical gloves, the specimen container, or the laboratory. For this reason, it is important to know the results of control culture specimens to verify the sterility of the environment and specimen management. As an example, Mook and colleagues [2] found a 13% positive Propionibacterium culture rate for a 1/2 × 1/2 cm square of sterile sponge that was placed in a sterile specimen container and set aside during shoulder surgery. These cultures were positive (not falsely positive), although the source of the cultured organisms was not clear.

Second, Propionibacterium are anaerobic organisms now recognized as being pathogenetic in arthroplasty and spine surgery. In that these organisms are sensitive to kanamycin and vancomycin, one wonders if the use of kanamycin and vancomycin in the anaerobic media used in this study may have interfered with the ability of these cultures to detect Propionibacterium.

Thanks to the authors for their well-done study.

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1. Jennings JM, Dennis DA, Kim RH, Miner TM, Yang CC, McNabb DC. False-positive cultures after native knee aspiration: True or false. Clin Orthop Relat Res. 2017;475:1840-1843 10.1007/s11999-016-5194-4.
2. Mook WR, Klement MR, Green CL, Hazen KC, Garrigues GE. The Incidence of Propionibacterium acnes in open shoulder surgery: A controlled diagnostic study. J Bone Joint Surg Am. 2015;97:957-963 10.2106/JBJS.N.00784.
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