How to Order an X-ray for the Achilles Tendon Area
Order a lateral ankle radiograph (lateral view of the ankle) to evaluate the Achilles tendon region. This is the standard radiographic approach, as the Achilles tendon itself is a soft tissue structure that requires specific positioning to assess indirect signs of pathology.
Ordering Specifications
When ordering imaging for suspected Achilles tendon pathology, specify:
- "Lateral ankle radiograph" or "Ankle X-ray, lateral view"
- Include the clinical indication (e.g., "suspected Achilles tendon rupture," "Achilles tendon pain," or "posterior ankle trauma")
The lateral view is critical because it allows visualization of:
- Kager's fat pad (obliteration suggests Achilles tendon rupture with 86.4% sensitivity and 91.6% specificity) 1
- Tibio-first metatarsal angle (≤100° suggests rupture, as the ankle adopts a more neutral/dorsiflexed position when the tendon is torn) 1, 2
- Calcaneal insertion (to identify bony avulsion injuries) 3
Important Clinical Context
When X-rays Are Appropriate
Plain radiography has a limited but important role in Achilles tendon evaluation 4, 5:
- Primary purpose: Rule out bony pathology (calcaneal avulsion fractures, insertional calcifications, bone spurs)
- Secondary purpose: Identify indirect signs of tendon rupture through soft tissue changes and ankle positioning
- Not for direct tendon visualization: The Achilles tendon is soft tissue and not directly visible on X-ray
Common Pitfall to Avoid
Do not order "foot radiographs" when evaluating the Achilles tendon. The ACR Appropriateness Criteria explicitly state that foot radiographs have low yield in ankle injuries and should not be performed routinely 6. The Achilles tendon inserts on the posterior calcaneus, which is best visualized on ankle radiographs, not foot series.
When Advanced Imaging Is Needed
If clinical examination strongly suggests Achilles tendon rupture (positive Thompson test, palpable gap, decreased plantar flexion strength) but you need definitive soft tissue evaluation 7:
- Ultrasound: First-line advanced imaging—real-time, dynamic assessment, cost-effective 8, 9
- MRI: Alternative to ultrasound for soft tissue detail, though not routinely needed for diagnosis 7, 4
The 2010 AAOS guideline notes that routine use of MRI or ultrasound to confirm Achilles tendon rupture receives an "Inconclusive" recommendation when clinical examination is already diagnostic 7. However, these modalities are valuable when diagnosis is uncertain or for surgical planning.
Standard Three-View Ankle Series
If ordering a complete ankle trauma series (per Ottawa Ankle Rules for broader ankle trauma), the standard protocol includes 6:
- Anteroposterior (AP) view
- Lateral view
- Mortise view
However, for isolated Achilles tendon evaluation, the lateral view is the most informative single radiograph 1, 2.