Is osteomyelitis (infection of the bone) present in the left foot, as indicated by X-ray (radiograph)?

From the Guidelines

X-ray of the left foot is a reasonable initial imaging study to evaluate for osteomyelitis, given its wide availability and relatively low cost, as suggested by the International Working Group on the Diabetic Foot (IWGDF) guidance 1.

Key Considerations

• The X-ray should include multiple views (anteroposterior, lateral, and oblique) to provide comprehensive visualization of the foot's bony structures.
• While X-rays can show bone destruction, periosteal reaction, and soft tissue changes that might suggest osteomyelitis, these findings typically appear only after 10-14 days of infection when 30-50% of bone mineral density has been lost.
• Early osteomyelitis may not be visible on X-ray, resulting in false negatives.
• If clinical suspicion remains high despite negative X-ray findings, more sensitive imaging such as MRI (with a sensitivity of 90-95%) should be considered, as recommended by the IWGDF/IDSA guidelines 1.

Advanced Imaging

• MRI is particularly valuable as it can detect early bone marrow edema and soft tissue involvement.
• Other advanced imaging techniques like FDG-PET/CT may offer high specificity (0.92) for diagnosing osteomyelitis, but their availability and cost may vary in different geographic locations 1.

Laboratory Tests

• Laboratory tests including white blood cell count, erythrocyte sedimentation rate, and C-reactive protein can support the diagnosis, though they are not specific to osteomyelitis.

Clinical Judgment

• Clinical judgment and suspicion of osteomyelitis should guide the decision to proceed with further imaging or diagnostic tests, even if initial X-ray findings are negative.
• The IWGDF/IDSA guidelines suggest that advanced imaging is not needed in many patients, but when needed, MRI is the most commonly ordered technique 1.

From the Research

Diagnostic Approach for Osteomyelitis

• The initial imaging procedure for diagnosing osteomyelitis is radiography, but its sensitivity is low in the early stages of the disease 2, 3.
• Magnetic resonance imaging (MRI) has a higher sensitivity for detecting areas of bone necrosis in advanced stages 2, 3.
• MRI findings, such as bone marrow edema, T2-weighted image hyperintensity, T1-weighted image confluent signal, and cortical erosion, are indicative of osteomyelitis 4.
• The sensitivity and specificity of MRI for diagnosing osteomyelitis are 90% and 80%, respectively 4.

Imaging Tests for Osteomyelitis

• MRI, positron emission tomography (PET), and single-photon emission computed tomography (SPECT) have high diagnostic accuracy for osteomyelitis 5.
• The diagnostic accuracy of MRI, PET, and SPECT does not appear to vary with the potential cause of osteomyelitis or with the body part scanned 5.
• Radiography, computed tomography, and scintigraphy have generally inferior diagnostic accuracy compared to MRI, PET, and SPECT 5.

Laboratory Tests for Osteomyelitis

• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are routinely ordered inflammatory biomarkers for evaluating foot infection 6.
• Optimal cutoff values for ESR and CRP to diagnose osteomyelitis in patients with diabetes-related foot infections are 60 mm/h and 7.9 mg/dL, respectively 6.
• An ESR threshold of 60 mm/h demonstrates a sensitivity of 74% and specificity of 56% for osteomyelitis, while a CRP threshold of 7.9 mg/dL has a sensitivity of 49% and specificity of 80% 6.