Probe-to-Bone Test for Diagnosing Diabetic Foot Osteomyelitis

Reliable or relic?

  1. Lawrence A. Lavery1,
  2. David G. Armstrong2,
  3. Edgar J.G. Peters3 and
  4. Benjamin A. Lipsky4
  1. 1Department of Surgery, Scott and White Hospital, Texas A&M University Health Science Center College of Medicine, Temple, Texas
  2. 2Scholl’s Center for Lower Extremity Ambulatory Research (CLEAR) at Rosalind Franklin University of Medicine and Science, North Chicago, Illinois
  3. 3Department of Infectious Diseases, Leiden University Medical Center, Leiden, the Netherlands
  4. 4VA Puget Sound Heath Care System and the Department of Medicine, University of Washington, Seattle, Washington
  1. Address correspondence and reprint requests to Lawrence A. Lavery, Department of Surgery, Scott and White Hospital, 703 Highland Spring Lane, Georgetown, TX 78628. E-mail: llavery{at}swmail.sw.org

Abstract

OBJECTIVE—We sought to assess the accuracy of the probe-to-bone (PTB) test in diagnosing foot osteomyelitis in a cohort of diabetic patients with bone culture proven disease.

RESEARCH DESIGN AND METHODS—In this 2-year longitudinal cohort study, we enrolled 1,666 consecutive diabetic individuals who underwent an initial standardized detailed foot assessment, followed by examinations at regular intervals. Patients were instructed to immediately come to the foot clinic if they developed a lower-extremity complication. For all patients with a lower-extremity wound, we compared the results of the PTB test with those of a culture of the affected bone. We called PTB positive if the bone or joint was palpable and defined osteomyelitis as a positive bone culture.

RESULTS—Over a mean of 27.2 months of follow-up, 247 patients developed a foot wound and 151 developed 199 foot infections. Osteomyelitis was found in 30 patients: 12% of those with a foot wound and 20% in those with a foot infection. When all wounds were considered, the PTB test was highly sensitive (0.87) and specific (0.91); the positive predictive value was only 0.57, but the negative predictive value was 0.98.

CONCLUSIONS—The PTB test, when used in a population of diabetic patients with a foot wound among whom the prevalence of osteomyelitis was 12%, had a relatively low positive predictive value, but a negative test may exclude the diagnosis.

Footnotes

  • A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.

    The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C Section 1734 solely to indicate this fact.

    • Accepted October 19, 2006.
    • Received July 26, 2006.
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