From the Guidelines
The best imaging modality for diagnosing osteomyelitis is MRI, which offers the highest sensitivity (82-100%) and specificity (75-96%) for detecting bone infection. MRI can identify bone marrow edema, soft tissue involvement, and abscess formation in the early stages of infection, often before changes are visible on other imaging modalities 1. For initial evaluation, plain radiographs should be obtained first as they are readily available and inexpensive, though they have limited sensitivity in early osteomyelitis and typically don't show changes until 10-14 days after infection onset.
Some key points to consider when using MRI for osteomyelitis diagnosis include:
- Fluid-sensitive sequences alone may be sufficient for diagnosis, with one study noting 100% identification of cases of septic arthritis and osteomyelitis in children 2 years of age with review of only these sequences 1.
- Children with sickle cell disease pose a diagnostic dilemma because marrow infarction and osteomyelitis may present similarly, and fat-suppressed T1-weighted imaging has been theorized as a useful differentiator but this has not been substantiated 1.
- Subperiosteal fluid has been described as a distinguishing feature of osteomyelitis, and several distinguishing MRI features have been identified to differentiate osteomyelitis from Ewing sarcoma 1.
Other imaging modalities, such as CT scans and nuclear medicine studies like three-phase bone scans, may be useful in certain clinical scenarios, but MRI is generally preferred when available and not contraindicated 1. In cases where MRI cannot be performed, a combination of CT and nuclear medicine studies may be necessary for accurate diagnosis.
It's also worth noting that the choice of imaging should be tailored to the clinical scenario, and that other factors such as the presence of orthopedic hardware or the need to evaluate soft-tissue infections may influence the selection of imaging modalities 1.
From the Research
Imaging Modalities for Diagnosing Osteomyelitis
The diagnosis of osteomyelitis involves a combination of clinical signs, symptoms, laboratory tests, imaging modalities, and cultures from blood, joint, or body fluid. Imaging plays a critical role in the diagnosis and management of osteomyelitis. The following are some of the imaging modalities used to diagnose osteomyelitis:
- Magnetic Resonance Imaging (MRI): considered the best available imaging modality due to its sensitivity in detecting early signs of osteomyelitis and high soft tissue resolution 2, 3, 4
- Computed Tomography (CT) scan: useful in detecting early osseous erosion and documenting the presence of sequestrum, foreign body, or gas formation, but less sensitive than other modalities for detecting bone infection 3, 5, 6
- Nuclear Medicine: useful in identifying multifocal osseous involvement and detecting osteomyelitis, particularly in children 3, 5, 6
- Ultrasound: useful in diagnosing fluid collections, periosteal involvement, and surrounding soft tissue abnormalities, and may provide guidance for diagnostic or therapeutic aspiration, drainage, or tissue biopsy 3
- Conventional Radiography: should always be the first imaging modality, providing an overview of the anatomy and pathologic conditions of the bone and soft tissues of the region of interest 3, 6
Characteristics of Each Modality
Each imaging modality has its own characteristics and advantages:
- MRI: high sensitivity and specificity, excellent anatomical detail, and superior soft tissue resolution 2, 3, 4
- CT scan: useful in detecting sequestra and cortical erosions in chronic osteomyelitis, but less sensitive than MRI for detecting bone infection 5
- Nuclear Medicine: useful in identifying multifocal osseous involvement, particularly in children 3, 6
- Ultrasound: useful in diagnosing fluid collections and guiding diagnostic or therapeutic procedures 3
- Conventional Radiography: provides an overview of the anatomy and pathologic conditions, but may not detect early signs of osteomyelitis 3, 6