How to Order a Foot X-ray to Rule Out Osteomyelitis
Order a three-view plain radiograph series of the foot including dorsoplantar (AP), lateral, and medial oblique views, with a radio-opaque marker placed at the site of any ulcer or wound to accurately assess structures adjacent to the lesion. 1
Initial Imaging Protocol
Standard X-ray Views Required
- Request all three standard views: dorsoplantar, lateral, and medial oblique projections of the foot 1
- Place a radio-opaque marker directly on any skin ulcer, wound, or area of concern to allow precise correlation between the lesion and underlying bone structures 1
- This marker placement is critical for determining if bone abnormalities are anatomically related to the overlying soft tissue infection 1
What the X-ray Can and Cannot Do
- Plain radiographs serve as the mandatory first imaging step, helping to exclude alternative diagnoses such as fractures, tumors, and foreign bodies 1, 2, 3
- Critical limitation: Normal x-rays do NOT rule out osteomyelitis, as early acute osteomyelitis may show only mild soft tissue swelling or appear completely normal 2, 4, 3
- Radiographic changes typically require 10-14 days to become visible, so sensitivity is very low in early disease 5, 3, 6
- If initial x-rays are normal but clinical suspicion remains high, repeat radiographs in 2-3 weeks may demonstrate changes that were not initially apparent 1
What Happens After the X-ray
If X-rays Are Normal or Inconclusive But Suspicion Remains High
Proceed directly to MRI of the foot without and with IV contrast, which is rated 9/9 ("usually appropriate") by the American College of Radiology and represents the gold standard for osteomyelitis diagnosis 1, 2, 4
MRI Specifications
- Preferred protocol: MRI without and with IV contrast provides superior soft tissue evaluation and helps distinguish infection from other inflammatory processes 1, 2
- Alternative if contrast contraindicated: MRI without IV contrast alone is acceptable (rated 7/9) but contrast is strongly preferred 1, 2
- MRI has sensitivity of 82-100% and specificity of 75-96% for detecting acute osteomyelitis 7, 8
If MRI Is Contraindicated or Unavailable
- CT with IV contrast is the next best alternative (rated 7/9 by ACR) for detecting cortical bone destruction, sequestra, and sinus tracts 1, 2, 7
- CT is less sensitive than MRI for early osteomyelitis but provides excellent bone detail for chronic changes 7
- Nuclear medicine studies (three-phase bone scan or labeled leukocyte scan with sulfur colloid marrow scan) may be appropriate in specific circumstances, particularly with orthopedic hardware present 1, 2
Common Pitfalls to Avoid
Do Not Rely on X-rays Alone
- Never use negative x-rays to rule out osteomyelitis when clinical suspicion is moderate to high, as early infection is frequently radiographically occult 2, 4, 3
- Delaying advanced imaging (MRI) when x-rays are normal but clinical concern persists leads to delayed diagnosis and worse outcomes 2, 4
Do Not Skip the Marker
- Failing to place a radio-opaque marker on wounds/ulcers prevents accurate anatomical correlation and may lead to misinterpretation of incidental bone findings unrelated to the infection 1