Title: Probe-to-Bone Test for Diagnosing Diabetic Foot Osteomyelitis: Reliable or relic?
Authors: Lawrence A Lavery, David G Armstrong, Edgar J G Peters, Benjamin A Lipsky
Source: Diabetes Care. 2007; 30(2):270-274
PODIATRIC RELEVANCE:
Diabetic pedal wounds constitute a high percentage of diabetic admissions to the hospital, with more and more people developing diabetes the number of these admissions will likely grow. Accordingly, the cost of managing these infections continues to increase. An inexpensive, reliable prognostic tool that can accurately determine the presence/absence of bone infection is invaluable. The probe-to-bone (PTB) test has been widely used when evaluating diabetic pedal wounds. This study assessed the accuracy of the PTB test in diagnosing foot osteomyelitis in diabetic patients.
METHODS:
This longitudinal cohort study enrolled 1,666 consecutive diabetic individuals. Individuals underwent initial standardized foot assessments followed by routine follow-up. Patients that developed a lower extremity wound underwent probe-to-bone test followed by a bone biopsy that was microbiologically analyzed.
RESULTS:
Patients were followed for an average of 27.2 months. In this time 14.8% of the 1,666 patients developed a foot wound and 9.1% developed an infection. The PTB test was performed in all of the patients presenting with a wound; the test was positive (bone or joint was palpable) in 46/247 patients with a wound, 56.5% of which had osteomyelitis. The test was positive in 86.7 % of individuals with culture- proven bone infection; however, the test was also positive in 9.2% of individuals without osteomyelitis. 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.
COMMENTS:
Grayson et al. calculated the positive predictive value of the PTB test to be 89%. In this study the positive predictive value was found to be considerably lower at 57% (nearing the odds of tossing a coin). More useful is the negative predictive power of the test, 98%, arguing against the diagnosis of osteomyelitis when wounds failed to PTB.
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Disclaimer:
Scientific Abstract Monthly postings are submitted by podiatric surgical residents. The ideas presented are not the opinions of the American College of Foot and Ankle Surgeons (ACFAS), nor are they presented as facts. ACFAS presents this information without any warranty of any kind, expressed or implied, and is not liable for its accuracy nor for any loss or damage caused by the user's reliance on information obtained in these areas.