Imaging Workup for Achilles Tendon Injury
For suspected Achilles tendon rupture, clinical examination alone is sufficient for diagnosis, and routine imaging is not necessary—however, when imaging is required, ultrasound is the preferred initial modality over MRI or CT. 1
Clinical Diagnosis First
The diagnosis of acute Achilles tendon rupture should be established clinically using:
- Thompson test (calf squeeze test) - most reliable
- Decreased ankle plantar flexion strength
- Palpable gap in the tendon
- Increased passive ankle dorsiflexion
The 2010 AAOS guidelines explicitly state they are unable to recommend for or against routine use of MRI, ultrasonography, or radiography to confirm the diagnosis of acute Achilles tendon rupture 1. This is a critical point: imaging is not routinely needed when clinical examination is clear.
When Imaging Is Indicated
Primary Imaging: Ultrasound
When imaging is necessary (unclear clinical picture, monitoring treatment, or surgical planning), ultrasound is the recommended first-line modality 2:
- Sensitivity: 79.6-100% for detecting rupture
- Specificity: up to 100% in quality studies
- Use 7.5 MHz or higher frequency probes (recent studies trend toward higher frequencies)
- Scan bilaterally in prone position
- Provides dynamic assessment capability
- Cost-effective and radiation-free 3, 2
Common Pitfall: Clinical exam and ultrasound may not accurately assess tendon approximation after splinting—one study found 50% of patients had residual gapping on MRI despite ultrasound showing complete approximation 4. This matters for nonoperative treatment decisions.
Secondary Imaging: MRI
MRI is reserved for specific scenarios 5, 2:
- Complex or atypical tears (partial tears, intratendinous pathology)
- Diagnostic uncertainty after ultrasound
- Preoperative planning for complex cases
- Assessment of associated injuries (bone marrow edema, other soft tissue injuries)
MRI showed the highest overall diagnostic accuracy in comparative studies (95% for insertional tendinopathy, 87% for midportion) 5, but this advantage doesn't justify routine use given ultrasound's excellent performance and practical advantages.
CT Imaging: Limited Role
CT has essentially no role in isolated Achilles tendon injury workup 6:
- CT is not indicated for soft tissue tendon evaluation
- Only useful for associated bony injuries (avulsion fractures, calcaneal fractures)
- The ACR Appropriateness Criteria do not recommend CT for Achilles tendon assessment
Exception: Recent 2026 research suggests dual-energy CT with Rho/Z mapping may have emerging utility (94.9% accuracy) 7, but this is not yet standard practice and lacks guideline support.
Practical Algorithm
- Start with clinical examination - Thompson test, palpation, strength testing
- If diagnosis is clear clinically → No imaging needed, proceed to treatment
- If diagnosis is uncertain → Ultrasound (7.5+ MHz, bilateral, prone position)
- If ultrasound is inconclusive or shows complex pathology → MRI without contrast
- If bony injury suspected → Plain radiographs first, then CT if needed for fracture characterization
Monitoring Treatment
For monitoring healing during nonoperative treatment, ultrasound remains preferred over MRI 2, though the clinical relevance of imaging findings during healing is not well-established. Shear wave elastography showed the only significant change at 6-month follow-up in one study, but monitoring accuracy was only 60-71% 5.
Key Caveat: Don't rely solely on ultrasound to confirm tendon approximation when deciding on nonoperative management—clinical assessment of gap and function should drive treatment decisions 4.