What are the recommended imaging modalities for diagnosing an Achilles tendon rupture?

Imaging for Achilles Tendon Rupture

Clinical examination is the gold standard for diagnosing Achilles tendon rupture, and ultrasound should be the first-line imaging modality when imaging is needed, with MRI reserved only for equivocal cases or complex surgical planning. 1

Clinical Diagnosis Takes Priority

• Physical examination alone has 100% sensitivity for diagnosing acute Achilles tendon ruptures when using standardized criteria 2
• The diagnosis requires two or more of the following clinical findings: positive Thompson test (Simmonds squeeze test), decreased ankle plantar flexion strength, palpable gap in the tendon, and increased passive ankle dorsiflexion 1
• When all three classic findings are present (abnormal Thompson test, decreased resting tension, and palpable defect), imaging adds no diagnostic value 2

When to Use Imaging

Imaging should be reserved for:

• Equivocal clinical findings where diagnosis is uncertain 1, 3
• Patients who do not respond to recommended conservative care 4
• Preoperative planning for complex surgical interventions 1
• Differentiating partial from complete tears when clinical examination is limited by swelling or pain 1

First-Line Imaging: Ultrasound

Ultrasound is the recommended first-line imaging modality with the following performance characteristics:

• Sensitivity of 94.8% and specificity of 98.7% for complete ruptures 1
• Can differentiate full-thickness from partial-thickness tears with 92% accuracy 1
• Sensitivity ranges from 79.6% to 100% across studies, with some showing perfect specificity 3
• Offers dynamic assessment capability and bilateral comparison 5, 6

Practical advantages of ultrasound:

• Cost-effective compared to MRI 4
• Immediate availability and ease of use 4
• Can guide treatment decisions for both operative and conservative management 6

Second-Line Imaging: MRI

MRI should be reserved for specific situations:

• When ultrasound findings are inconclusive or equivocal 1
• Planning complex surgical interventions where identification of associated injuries is needed 1
• Evaluating chronic degenerative changes or incomplete ruptures where MRI is superior to ultrasound 7
• Sensitivity exceeds 90% for diagnosing tendon tears 1, 5

Important caveats about MRI:

• Causes significant treatment delays (mean 12.4 days to surgery vs 5.6 days without MRI) 2
• Can lead to unnecessary additional procedures 2
• More expensive and time-consuming than ultrasound 2
• Should not be used routinely for straightforward acute ruptures 2

Role of Plain Radiographs

• X-rays cannot directly visualize the tendon or evaluate rupture extent 1
• Should be obtained first to rule out fractures using Ottawa Ankle Rules if clinically indicated 1
• Not recommended as a primary diagnostic tool for suspected Achilles tendon abnormality 1

Critical Pitfalls to Avoid

Do not order MRI for acute Achilles ruptures with classic clinical findings - this delays treatment without improving diagnostic accuracy 2

Ultrasound quality is operator-dependent - results are more dependent on operator skill and expertise compared to MRI 1

Excessive swelling can limit examination - consider re-examination after 3-5 days if initial assessment is unclear due to acute swelling 8

Imaging abnormalities don't always correlate with symptoms - always correlate imaging findings with clinical examination 5