Diagnosing Diabetic Foot Osteomyelitis: What Current Evidence Says About Probe-to-Bone, Imaging, and Bone Biopsy
Diabetic foot osteomyelitis (DFO) is one of the most consequential complications a person with diabetes can develop. It is present in roughly 10–15% of moderate diabetic foot infections and in up to 50% of severe infections, and overall, between 20% and 68% of patients with a diabetic foot infection eventually develop bone involvement (Senneville et al., 2024). The stakes of getting the diagnosis right are high: published cohorts report amputation rates as high as 66% and one-year mortality of 6–14% in patients with DFO. Yet because the foot tolerates infection silently in the setting of neuropathy and ischemia, the diagnosis is often missed or delayed. The 2023 IWGDF/IDSA infection guidelines and several recent systematic reviews now provide a clearer evidence-based pathway.
Why bone infection is easy to miss
Most cases of DFO arise by contiguous spread from an overlying ulcer, particularly in the forefoot, where roughly 90% of bone infections are located, compared with about 5% each in the midfoot and hindfoot (Winkler et al., 2022). Because peripheral neuropathy blunts pain perception, classical signs of infection—throbbing pain, fever, leukocytosis—are frequently absent. Persistent non-healing of an ulcer, a wound that probes to bone, an enlarging “sausage toe,” or unexplained elevation of inflammatory markers should all raise suspicion for underlying bone involvement.
Initial work-up: probe-to-bone, plain films, inflammatory markers
The 2023 IWGDF/IDSA guideline recommends combining the probe-to-bone (PTB) test, plain radiographs, and an inflammatory marker (ESR, CRP, or procalcitonin) as the initial diagnostic battery (Senneville et al., 2024). The PTB test is performed by gently advancing a sterile blunt metal probe through the wound; contact with hard, gritty bone is considered a positive result. In patients with clinical suspicion of DFO, a positive PTB has good positive predictive value, while a negative PTB in a low-risk patient meaningfully lowers the probability of bone infection.
Plain radiographs of the affected foot are the appropriate first imaging study. Cortical erosion, periosteal reaction, and focal osteolysis are suggestive, but radiographic changes typically lag behind disease by 10–14 days, and early DFO is often invisible on X-ray. Inflammatory markers add complementary information—an ESR > 70 mm/h has been particularly associated with underlying osteomyelitis—but the guideline emphasizes that no single test, including PTB, plain films, ESR, CRP, or procalcitonin, can reliably rule DFO in or out on its own.
When advanced imaging is needed
When clinical findings, plain films, and laboratory data leave the diagnosis uncertain, advanced imaging is indicated. Magnetic resonance imaging (MRI) is the preferred next step. A meta-analysis pooling 22 studies reported an MRI sensitivity of approximately 96% and specificity of approximately 84% for DFO, and MRI provides the additional benefit of mapping abscess, sinus tracts, and soft-tissue extent for surgical planning (Llewellyn et al., 2020).
When MRI is contraindicated or when prior surgery, hardware, or coexisting Charcot neuro-osteoarthropathy obscures interpretation, nuclear medicine techniques are useful alternatives. The 2024 EANM evidence-based guidance and a meta-analysis by Lauri and colleagues support white blood cell scintigraphy with SPECT/CT and 18F-FDG PET/CT, with FDG-PET demonstrating sensitivity of approximately 89% and specificity of approximately 92% (Lauri et al., 2017; Glaudemans et al., 2024).
The role of bone biopsy
Bone biopsy with histopathology and culture remains the diagnostic gold standard, with reported sensitivity around 87% and specificity around 93% (Senneville et al., 2024). The IWGDF/IDSA 2023 guideline recommends obtaining bone (rather than soft-tissue) samples for culture, percutaneously through uninvolved skin or intraoperatively, whenever DFO is suspected and antibiotic therapy is being planned. Soft-tissue swabs are unreliable: superficial flora correlate poorly with the deep pathogens actually colonizing bone, and treatment guided by swabs alone is often misdirected. A targeted bone biopsy enables narrower antibiotic selection, shorter therapy, and better stewardship.
Key takeaways
Diabetic foot osteomyelitis is common, frequently silent, and associated with high amputation and mortality risk. No single bedside test is sufficient to rule DFO in or out. The current evidence supports a tiered approach: begin with probe-to-bone, plain films, and inflammatory markers; escalate to MRI or nuclear imaging when uncertainty remains; and rely on bone biopsy as the gold standard to guide antibiotic therapy.
References
- Senneville É, Albalawi Z, van Asten SA, et al. IWGDF/IDSA guidelines on the diagnosis and treatment of diabetes-related foot infections (IWGDF/IDSA 2023). Diabetes/Metabolism Research and Reviews. 2024;40(3):e3687.
- Lavery LA, Ryan EC, Ahn J, et al. Does complete resection of infected bone improve clinical outcomes in patients with diabetic foot osteomyelitis? International Wound Journal. 2024;21:e70072.
- Winkler E, Schöni M, Krähenbühl N, Uçkay I, Waibel FWA. Foot osteomyelitis location and rates of primary or secondary major amputations in patients with diabetes. Foot & Ankle International. 2022;43(7):957–967.
- Llewellyn A, Kraft J, Holton C, Harden M, Simmonds M. Imaging for detection of osteomyelitis in people with diabetic foot ulcers: a systematic review and meta-analysis. European Journal of Radiology. 2020;131:109215.
- Lauri C, Tamminga M, Glaudemans AWJM, et al. Detection of osteomyelitis in the diabetic foot by imaging techniques: a systematic review and meta-analysis comparing MRI, white blood cell scintigraphy, and FDG-PET. Diabetes Care. 2017;40(8):1111–1120.
- Glaudemans AWJM, Jutte PC, Cataldo MA, et al. Diagnostic imaging of the diabetic foot: an EANM evidence-based guidance. European Journal of Nuclear Medicine and Molecular Imaging. 2024;51(9):2603–2622.
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