CT Ankle is NOT Appropriate for Initial Evaluation of Ankle Pain
CT is not routinely used as a first-line imaging tool for ankle pain—plain radiographs are the appropriate initial test, and CT should be reserved only for specific scenarios after radiographs have been obtained. 1
Initial Imaging Algorithm for Ankle Pain
Step 1: Apply Ottawa Ankle Rules to Determine Need for ANY Imaging
Plain radiographs (anteroposterior, lateral, and mortise views) are indicated ONLY if: 1
- Patient cannot bear weight immediately after injury AND cannot take four steps in the emergency department, OR
- Point tenderness is present over:
- Posterior aspect of the lateral or medial malleolus
- Tip of the malleolus
- Navicular bone
- Base of the fifth metatarsal
If Ottawa Ankle Rules are negative, NO imaging is needed. The rules demonstrate 92-99% sensitivity and correctly exclude fracture in 299 of 300 patients. 2, 3
Step 2: When Radiographs ARE Indicated
Radiography should be considered the initial imaging study for ankle pain when Ottawa criteria are met. 1 Plain films can identify:
- Fractures and stress fractures
- Osteoarthritis and degenerative changes
- Osteochondral abnormalities
- Calcified or ossified intra-articular bodies
- Ankle effusions (53-74% accuracy)
- Evidence of prior trauma
- Ossific fragments indicating ligamentous injury 1
Step 3: Role of CT in Ankle Pain (NOT First-Line)
CT is explicitly NOT routinely used as the first study for evaluation of chronic ankle pain. 1
CT may be considered as a second-line study only in these specific scenarios:
- After radiographs show degenerative joint disease: CT without contrast may help visualize subchondral cysts 1
- High-energy or polytrauma injuries with neurologic impairment: CT is first-line to evaluate complex fractures (posterior malleolar fractures, posterior pilon-variant fractures) 2
- Impingement syndromes: CT is more sensitive than bone scintigraphy for evaluating impingement and soft-tissue pathology, but this is still not a first-line indication 1
Step 4: When Advanced Imaging IS Needed After Radiographs
MRI (not CT) is the preferred advanced imaging modality for ankle pain when radiographs are normal or non-diagnostic: 1
- MRI globally evaluates all anatomic structures including ligaments, tendons, cartilage, and bone 1
- MRI is highly accurate for ligament, tendon, and osteochondral abnormalities 1
- MRI is superior to CT for soft-tissue evaluation due to better soft-tissue contrast resolution, multiplanar capabilities, and lack of ionizing radiation 4, 5
MRI without contrast is indicated for: 2
- Persistent pain beyond 1-3 weeks despite appropriate treatment
- Suspected syndesmotic injury (positive crossed-leg test)
- Suspected osteochondral injury
- Professional/high-level athletes requiring detailed assessment
Common Pitfalls to Avoid
Ordering CT as initial imaging bypasses the evidence-based diagnostic algorithm and exposes patients to unnecessary radiation without providing superior diagnostic information compared to plain radiographs. 1
Skipping Ottawa Ankle Rules leads to over-imaging: 50% of ankle radiographs can be eliminated by proper physical examination, and CT would compound this problem exponentially. 3, 6
Using CT instead of MRI for soft-tissue evaluation: When advanced imaging is needed after normal radiographs, MRI is superior to CT for evaluating ligaments, tendons, and cartilage—the most common sources of ankle pain without fracture. 4, 5
Ordering any imaging before delayed physical examination: Clinical assessment of ligament damage is optimized if delayed 4-5 days post-injury when swelling has decreased, potentially avoiding the need for advanced imaging altogether. 2, 7