Copyright © 2008 by The Journal of Bone and Joint Surgery, Inc.
Commentary & Perspective
Commentary & Perspective by
Paul E. Di Cesare, MD*,
University of California at Davis Medical Center, Sacramento, California
Posted August 2008
While preventive measures have greatly reduced the prevalence
of periprosthetic joint infection in the United States from 10% four decades
ago to less than 1% in some centers, approximately 12,000 periprosthetic joint
infections still occur annually, necessitating revision arthroplasty at a cost
of $600 million1 and representing a substantial impact on the
patient who must undergo subsequent procedures, a prolonged hospitalization,
and a lengthy course of intravenous antibiotics. Accurate diagnosis of
periprosthetic infection after total joint arthroplasty is crucial; however,
current test modalities typically lack both high sensitivity and specificity
and may be expensive, invasive, and unavailable in some centers.
Even when the surgeon has acquired a complete patient history,
performed a thorough physical examination, and obtained appropriate preoperative
laboratory tests (measurement of the erythrocyte sedimentation rate and
C-reactive protein level and analysis of joint fluid as well as a complete
blood-cell count) and intraoperative frozen-section analysis, it is still
difficult at times to differentiate septic from aseptic failure. Specific
criteria as to what constitutes a positive or negative test for infection in
the setting of a total knee arthroplasty are lacking. Nuclear medicine studies
comprise a second line of investigation to evaluate patients with a painful total knee
arthroplasty in whom revision surgery is not otherwise indicated.
Intraoperative gross appearance of the tissue, in combination with
intraoperative gram stain, is unreliable for the detection of periprosthetic
sepsis, and neither is adequate by itself for ruling out infection at the time
of revision total knee arthroplasty. It is imperative that the surgeon who
undertakes revision total knee arthroplasty have a thorough understanding of
the relative utility of preoperative and intraoperative tests that are used in
the diagnosis of periprosthetic sepsis. Infection should always be considered
as a possible cause of pain, even in the presence of a clear mechanical cause
of the patient's symptoms. Whenever revision surgery is performed at our institution, an
intraoperative assessment is routinely performed to rule out the presence of
infection.
Fluid obtained from the joint, in addition to being sent for
cultures, can be useful in determining if a deep infection is present. Spangehl
et al.2 used a cell count of >50,000 or a specimen with >80%
neutrophils as their criteria for infection. A total cell count of >50,000
was found to have a sensitivity of only 36%, and an elevated neutrophil count (>80%)
had a poor positive predictive value of 52%. Another study, however, used
different criteria and found that a cell count of >10,000 was highly
correlated with the presence of infection, while a cell count of <3000
reliably excluded infection; overall a synovial fluid white blood-cell count of
>3000 was the most precise test with a sensitivity of 100%, specificity of
98%, and accuracy of 99%3. As a result of these varied experiences, it
appears that a cell count can be a useful adjunct in determining if an
infection is present. For most laboratory tests to be useful, a dichotomous
outcome is desired, that is, a positive or negative result. The current study
uses sound statistical analysis to define those parameters for synovial fluid
analysis: neutrophil counts of >64% combined with a fluid cell count of
>1100 cells/µL.
In summary, while several modalities are currently used to
screen for infection in patients who undergo total joint arthroplasty, many are
expensive and invasive, not universally available, and, when used as isolated
modalities, may not be sufficiently sensitive and specific to suggest the
correct diagnosis. This need is underscored in the scenario of a well-fixed
painful implant in which the potential diagnosis of infection compared with
other etiologies (e.g., reflex sympathetic dystrophy) needs to be determined
for a patient that might otherwise not require additional surgery.
Determination of synovial fluid cell count and differential appears to have the
high accuracy, on the basis of the parameters established in this study.
*The author did not receive any outside funding or grants in support of his research for or preparation of this work. Neither he nor a member of his immediate family received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the author, or a member of his immediate family, is affiliated or associated.
References
1. Lentino JR. Infections associated with prosthetic knee and prosthetic hip. Curr Infect Dis Rep. 2004;6:388-92.
2. Spangehl MJ, Masri BA, O'Connell JX, Duncan CP. Prospective analysis of preoperative and intraoperative investigations for the diagnosis of infection at the sites of two hundred and two revision total hip arthroplasties. J Bone Joint Surg Am. 1999;81:672-83.
3. Della Valle CJ, Sporer SM, Jacobs JJ, Berger RA, Rosenberg AG, Paprosky WG. Preoperative testing for sepsis before revision total knee arthroplasty. J Arthroplasty. 2007;22(6 Suppl 2):90-3. Epub 2007 Jul 26.
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