Imaging in osteomyelitis

Technique	Advantages	Disadvantages	Sn	Sp	Main Findings
X-ray	Inexpensive, reproducible, and accessible	Late diagnosis, confusing, and radiation	43 to 75%	75 to 83%	Lytic lesions, osteopenia, periosteal thickening, loss of trabecular architecture, new bone apposition
CT	Excellent spatial resolution	Cost, availability, radiation exposure	67%	50%	Blurring of fat planes, increased density of fatty marrow, periosteal reaction, cortical erosion or destruction, and sequestra, involucra, and intraosseous gas
US	Accessibility, inexpensive, real-time evaluation, guided aspiration/biopsy	Operator dependent, cannot image across cortical bone	To be determined		Elevated periosteum, soft tissue abscesses and fluid collections
MRI	Excellent spatial resolution, early detection, assesses extent of tissues affected	Cost, availability, time requested	82 to 100%	75 to 96%	Acute: T1 shows low-signal-intensity medullary space; T2 shows high intensity surronuding inflammatory processes and edema; Gad enhances areas of necrosis Subacute: evidence of Brodie's abscess, single or multiple radiolucent abscesses; T1 shows central abscess cavity with low intensity; T2 shows high intensity of granulation tissue surrounded by low-intensity band of bone sclerosis (double-line) Chronic: T1 and T2 show low-intensity areas of devascularized fibrotic scarring in the marrow
Bone scan	Sensitive, available, relatively cheap, early detection	Nonspecific, further imaging required	~85%	~25%	Focal hyperperfusion or hyperemia or bone uptake
Bone+WBC scan	Reliable when clearly positive or negative	Need for two isotopes with multiple imaging sessions over several days, higher radiation exposure, often equivocal results, long examination time (days)	~60%	~80%	Localized area of increased uptake

Specific Indications

• Post-fixation with hardware: WBC scan likely best, since none of the others can reliably distinguish between post-op changes and infection.
• Pressure ulcers: imaging (including MRI and WBC scan) cannot distinguish infection from bone remodeling due to pressure alone, with specificities decreasing to 15-60% range for all modalities

Further Reading

• Pineda C, Espinosa R, Pena A. Radiographic Imaging in Osteomyelitis: The Role of Plain Radiography, Computed Tomography, Ultrasonography, Magnetic Resonance Imaging, and Scintigraphy. Semin Plast Surg. 2009;23(2):080-089.
• Nuclear medicine imaging of bone infections. Nuc Med Comm. 2006;27:633–644.