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Differentiation Between Septic Arthritis and Transient Synovitis of the Hip in Children with Clinical Prediction Algorithms
Scott J. Luhmann, MD1; Angela Jones, BS1; Mario Schootman, PhD2; J. Eric Gordon, MD1; Perry L. Schoenecker, MD1; Jan D. Luhmann, MD1
1 St. Louis Children's Hospital, One Children's Place, Suite 4S20 (S.J.L., A.J., J.E.G., and P.L.S.) and Suite 4S50 (J.D.L.), St. Louis, MO 63110. E-mail address for S.J. Luhmann: luhmanns@msnotes.wustl.edu
2 Division of Health Behavioral Research, Department of Pediatrics and Internal Medicine, Washington University School of Medicine, 4444 Forest Park, Suite 6700, St. Louis, MO 63110
View Disclosures and Other Information
The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive 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, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at St. Louis Children's Hospital, Washington University Medical Center, St. Louis, Missouri

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2004 May 01;86(5):956-962
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Abstract

Background: Differentiation between septic arthritis and transient synovitis of the hip in children can be difficult. Kocher et al. recently developed a clinical prediction algorithm for septic arthritis based on four clinical variables: history of fever, non-weight-bearing, an erythrocyte sedimentation rate of =40 mm/hr, and a serum white blood-cell count of >12,000/mm3 (>12.0 × 109/L). The purpose of this study was to apply this clinical algorithm retrospectively to determine its predictive value in our patient population.

Methods: A retrospective review was performed to identify all children who had undergone a hip arthrocentesis for the evaluation of an irritable hip at our institution between 1992 and 2000. One hundred and sixty-three patients with 165 involved hips satisfied the criteria for inclusion in the study and were classified as having true septic arthritis (twenty hips), presumed septic arthritis (twenty-seven hips), or transient synovitis (118 hips).

Results: Patients with septic arthritis (true and presumed; forty-seven hips) differed significantly (p < 0.05) from patients with transient synovitis (118 hips) with regard to the erythrocyte sedimentation rate, differential of serum white blood-cell count, total white blood-cell count and differential in the synovial fluid, gender, previous health-care visits, and history of fever. If the four independent multivariate predictors of septic arthritis proposed by Kocher et al. were present, the predicted probability of the patient having septic arthritis was 59% in our study, in contrast to the 99.6% predicted probability in the patient population described by Kocher et al. Statistical analyses demonstrated that the best model to describe our patient population was based on three variables: a history of fever, a serum total white blood-cell count of >12,000/mm3 (>12.0 × 109/L), and a previous health-care visit. When all three variables were present, the predicted probability of the patient having septic arthritis was 71%.

Conclusions: Although the use of a clinical prediction algorithm to differentiate between septic arthritis and transient synovitis may have improved the utility of existing technology and medical care to facilitate the diagnosis at the institution at which the algorithm originated, application of the algorithm proposed by Kocher et al. or of our three-variable model does not appear to be valid at other institutions.

Level of Evidence: Diagnostic study, Level I-1 (testing of previously developed diagnostic criteria in series of consecutive patients [with universally applied reference "gold" standard]). See Instructions to Authors for a complete description of levels of evidence.

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    Scott J. Luhmann
    Posted on July 21, 2004
    Dr. Luhmann responds:
    Washington University

    To the Editor:

    We appreciate the comments of Dr. Yagupsky. One of the main reasons we performed out our study was to assess the validity of the clinical prediction algorithm previously published by Kocher et al. In their study model, peripheral white blood cell count greater than 12,000 cells per cubic millimeter, non-weightbearing status, history or fever (greater than 38.5 degrees Celsius), and erythrocyte sedimentation rate of at least 40 millimeters per hour were demonstrated to be statistically significant predictors between the two diagnoses. We were impressed with the adjusted odds ratios between 14.4 and 38.6 for the 4 predictors and their ability to identify septic arthritis in 99.8% of cases if all 4 were present. If we could validate these 4 variables in our patient population we could improve our ability to accurately identify septic arthritis with the minimal amount of painful interventions. To maximize the ability to compare our results to that of Kocher et al, we used their study definitions, specifically the definitions of “true” septic arthritis, “presumed” septic arthritis, and transient synovitis.

    The definition of septic arthritis is imprecise and challenging, and can only be made definitively with positive culture results from the joint fluid. We agree with Dr. Yagupsky that the inclusion of several pathogens is controversial, specifically the coagulase-negative staphylococci and alpha-hemolytic streptococci. The reason for their inclusion into the septic arthritis category was based not only on the culture results, but also the associated findings of a white-blood cell count in the joint fluid of at least 50,000 cells per cubic millimeter. As defined by Kocher et al, based on cell count only, these patients would be classified as “true” or “presumed” septic arthritis.

    If we dismissed the culture results as a contaminant, these patients would be re-classified from the “true” to the “presumed” septic arthritis groups, a change which would not have altered the statistical analysis or the ultimate findings of our study. Thus, based on our findings, institution- specific algorithms for septic arthritis of the hip do not appear to be generalized to other medical centers.

    Of interest there were two cases, one each of coagulase-negative staphylococci and alpha-hemolytic streptococci, that had positive cultures obtained by percutaneous arthrocentesis in the radiology suite and in the operating room suite. Cultures obtained in the operating room suite were done after formal open anterior approach to the hip with joint fluid obtained by syringe immediately prior to arthrotomy (1 case) or after arthrotomy (1 case).

    References:

    Kocher MS, Zurakowski D, Kasser JR. Differentiating Between Septic Arthritis and Transient Synovitis of the Hip in Children: An Evidence- Based Clinical Prediction Algorithm. J Bone Joint Surg Am. 1999:81:1662- 70.

    Pablo Yagupsky
    Posted on July 01, 2004
    Contamination of Cultures Obtained from Children with Suspected Septic Arthritis
    Clinical Microbiology Laboratories, Soroka University Medical Center, Beer-Sheva, Israel

    To the Editor:

    I read with interest the article by Luhmann et al. in which the distribution of a variety of demographic, clinical and laboratory parameters in children with septic arthritis or transient synovitis of the hip was compared (1). The authors found that the two populations differed in terms of history of fever, erythrocyte sedimentation rate values, white blood cell (WBC) count in the synovial fluid and cellular composition of the peripheral blood and joint fluid leukocytes. Of 47 children included in the composite septic arthritis group, 20 had either a positive synovial fluid culture or a positive blood culture and a synovial fluid WBC count > = 50 x 109/L (”true septic arthritis”), and 27 had negative blood and synovial fluid cultures and >=50 x 109 WBC/L of synovial fluid (presumed septic arthritis). Although no explicit criteria for defining a positive bacteriological culture were stated in the Materials and Methods section of the article, examination of the list of organisms isolated from patients in the true septic arthritis population group raises some concerns.

    Overall, bacteria of dubious clinical significance, which are normal components of the skin and mucosal flora, were detected in 11 of 20 patients [coagulase-negative staphylococci in seven children and alpha-hemolytic streptococci (“Streptococcus viridans”) in four]. Isolation of these organisms from blood or synovial fluid cultures of immunocompetent individuals without intravenous devices or prosthetic joints is usually indicative of contamination of the specimen and related to the technical difficulties in obtaining blood and synovial fluid aspirates from young and uncooperative patients (2). Obviously, inclusion of children with contaminated (false-positive) cultures in the septic arthritis group, could have only attenuated real differences between patients with truly infected joints and those with transient synovitis. I believe that a allocation of patients in whom coagulase-negative staphylococci or alpha-hemolytic streptococci were isolated in the septic arthritis population should be reconsidered.

    References

    1. Luhmann SJ, Jones A, Schootman M, Gordon JE, Schoenekker PL, Luhmann JD. Differentiation between septic arthritis and transient synovitis of the hip in children with clinical prediction algorithms. J Bone Joint Surg Am 2004;86A:956-962.

    2. Trujillo M, Nelson JD. Suppurative and reactive arthritis in children. Sem Pediatr Infect Dis 1997;8:242- 249.

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