From the Guidelines
MRI is the best imaging modality for evaluating a sacral ulcer suspected of having osteomyelitis, as it offers superior soft tissue contrast and can detect bone marrow edema with high sensitivity and specificity. According to the American College of Radiology Appropriateness Criteria 1, MRI with contrast is the modality of choice in the evaluation of osteomyelitis. The recommended protocol should include T1-weighted, T2-weighted, and STIR sequences, along with gadolinium contrast enhancement if not contraindicated.
Key Points to Consider
- CT scanning is an alternative when MRI is contraindicated, though it has lower sensitivity for early osteomyelitis 1.
- Plain radiographs have limited utility as they only show bone changes after 30-50% of bone mineral is lost, which takes 10-14 days after infection onset.
- Nuclear medicine studies like bone scans or white blood cell scans may be considered in specific situations, such as when MRI is contraindicated or when orthopedic hardware is present, but are generally less preferred than MRI 1.
- Ultrasound (US) plays a complementary role in the evaluation of osteomyelitis, primarily for detection and characterization of soft-tissue infections, and can be used for joint aspiration or abscess drainage 1.
Clinical Considerations
When ordering the MRI, it's essential to specifically mention the concern for osteomyelitis to ensure appropriate protocols are used. Clinical correlation with physical examination findings, laboratory markers (ESR, CRP), and potentially bone biopsy remains essential for definitive diagnosis, as imaging alone cannot always distinguish between osteomyelitis and other conditions like Charcot arthropathy or post-surgical changes. As stated in the ACR Appropriateness Criteria 1, joint aspiration is recommended for evaluation of septic arthritis, and labeled leukocyte scan and sulfur colloid marrow scan are a useful nuclear scintigraphic combination to evaluate active infection if orthopedic hardware is present.
From the Research
Imaging Modalities for Osteomyelitis
- The best imaging modality for a sacral ulcer suspected of having osteomyelitis is Magnetic Resonance Imaging (MRI) 2, 3, 4.
- MRI has high sensitivity and specificity for identifying areas of bone necrosis and can detect early changes in bone marrow and soft tissues 3, 4.
- MRI can also help differentiate between bone and soft-tissue infection, and separate arthritis, cellulitis, and soft-tissue abscess from osteomyelitis 4.
Alternative Imaging Modalities
- Plain film radiography can be used as an initial imaging modality, but its sensitivity is low in the early stages of disease 2, 3, 5.
- Computed Tomography (CT) scan can be used to evaluate the extent of disease, but it is not as sensitive as MRI for detecting early changes in bone marrow and soft tissues 5.
- Radionuclide imaging, such as three-phase bone scan, can be used if MRI is contraindicated 3.