Ankle X-ray for Assessing Septic Arthritis vs Osteomyelitis vs Gout/Pseudogout

Initial Imaging Approach

Standard radiographs of the ankle are the appropriate first-line imaging modality for all suspected musculoskeletal infections and crystalline arthropathies, providing an excellent anatomic overview and helping to exclude other causes of pain and swelling such as fractures and tumors, according to the American College of Radiology 1, 2
The initial radiographic series should include anteroposterior (AP) view, lateral view, and mortise view, as recommended by the American College of Radiology 1, 2, 3

Joint effusion is a key finding in septic arthritis, with soft tissue swelling around the joint and effacement of fat planes, according to the American College of Radiology 1, 2
Early stages of septic arthritis may show minimal findings, while later stages may show joint space narrowing and erosions, as noted by the American College of Radiology 1, 2

Early acute osteomyelitis may show only mild soft tissue swelling or appear normal on radiographs, while acute osteomyelitis is characterized by erosions and periosteal reaction, and chronic osteomyelitis by bone sclerosis, according to the American College of Radiology 1, 2
Sequestrum, a dead bone fragment, may be present in chronic osteomyelitis cases, as reported by the American College of Radiology 4

The American College of Radiology recommends starting with standard radiographs of the ankle, including AP, lateral, and mortise views, for suspected septic arthritis, osteomyelitis, or crystalline arthropathies 1, 2
If radiographs are normal or show only joint effusion/soft tissue swelling, and septic arthritis is suspected, the American College of Radiology suggests proceeding to joint aspiration for definitive diagnosis, while for suspected osteomyelitis, MRI without and with contrast is recommended 4, 5, 6

For suspected septic arthritis or soft tissue infection, MRI without and with IV contrast is rated 9/9 for appropriateness by the American College of Radiology, and ultrasound-guided aspiration may be used for definitive diagnosis 5, 6
For suspected osteomyelitis, MRI without and with IV contrast is also rated 9/9 for appropriateness, and CT with IV contrast may be used if MRI is contraindicated, with a rating of 7/9 by the American College of Radiology 4, 6

The American College of Radiology warns against relying solely on radiographs to rule out infection, as early septic arthritis and osteomyelitis may have normal radiographs, and delaying joint aspiration when septic arthritis is suspected can lead to adverse outcomes 2, 5
Overlooking the need for additional imaging, such as MRI, when radiographs are normal but clinical suspicion for infection remains high, can also lead to delayed diagnosis and treatment, according to the American College of Radiology 4, 6