Intended for healthcare professionals

Rapid response to:

Practice ABC of wound healing

Infections

BMJ 2006; 332 doi: https://doi.org/10.1136/bmj.332.7545.838 (Published 06 April 2006) Cite this as: BMJ 2006;332:838

Rapid Response:

The use of the "probe to bone" test for the prediction of osteomyelitis in diabetic wounds is unjustified.

While the article by Drs Healy and Freedman provided a concise and
authoritative summary of the management of infection in wound care, we
were disappointed to note in the section on osteomyelitis that the authors
recommend the use of the “probe to bone” test in diagnosis. We believe
that this test has acquired an unjustified position in clinical diagnosis
- based more on the simplicity of the concept than on its scientific
validity.

The evidence is based on a single study1 in which the sensitivity,
specificity, positive and negative predictive values (PPV and NPV) were
reported to be 66%, 85%, 89% and 56%, respectively, for the diagnosis of
osteomyelitis. However, this work has been criticised because of the high
prevalence of osteomyelitis (66%) in the small cohort (of hospital in-
patients with overt infection) tested 2. Calculations of sensitivity,
specificity, PPV and NPV are dependent on the prevalence of active disease
in the sample studied and the prevalence in this cohort was extremely
high. The “probe to bone” test was never evaluated in an independent
sample.

We have recently published our own findings3 in a population with a
lower pre-test probability of disease. We studied 81 consecutive patients
(with a total 104 foot ulcers) attending a specialist out-patient diabetic
foot clinic. A total of 21 ulcers (20.2% of 104) were associated with
osteomyelitis. The ‘probe to bone’ test was positive in 8 of these 21
ulcers, but was also positive in 7 of the 83 without associated bone
infection (sensitivity 38%, specificity 91%). While the NPV was 85%, the
PPV (the probability that a patient with a positive test would have
osteomyelitis) was only 53%. In a population with an even lower pre test
probability of osteomyelitis, such as in primary care or a podiatry based
clinic, the performance of the test is likely to be worse.

There is a danger that clinicians who place uncritical reliance on
the use of the “probe to bone” may diagnose osteomyelitis when it does not
exist, and this can lead to inappropriate antibiotic use, with the
associated problems of costs and the evolution of multi-resistant
organisms. Rather than state (as they did) that the “diagnosis of
osteomyelitis should be considered in any … wound (especially in diabetes)
that can be probed to bone”, it would be more precise to say that the
diagnosis is unlikely in any wound that cannot be probed to bone.

1.Grayson ML, Gibbons GW, Balogh K, Levin E, Karchmer AW. Probing to
bone in infected pedal ulcers. A clinical sign of underlying osteomyelitis
in diabetic patients. JAMA 1995; 273: 721-3.

2.Wrobel JS, Connolly JE. Making the diagnosis of osteomyelitis. J
Amer Pod Med Assoc 1998; 88: 337-43.

3.Shone A, Burnside J, Chipchase S, Game F, Jeffcoate W. Probing the
validity of the probe-to-bone test in the diagnosis of osteomyelitis of
the foot in diabetes. Diab Care 2006; 29: 945.

Competing interests:
None declared

Competing interests: No competing interests

22 April 2006
Frances Game
Consultant Physician
Alison Shone, Jaclyn Burnside and William Jeffcoate
Foot Ulcer Trials Unit, Nottingham University Hospitals NHS Trust. NG5 1PB