Is a CT (Computed Tomography) scan or an MRI (Magnetic Resonance Imaging) better for diagnosing a tendon injury to the ankle?

MRI is Superior to CT for Diagnosing Ankle Tendon Injuries

MRI should be used for evaluating suspected ankle tendon injuries, as CT is not routinely used for this purpose. 1

Why MRI is the Preferred Imaging Modality

Diagnostic Performance for Tendon Injuries

• MRI achieves sensitivities exceeding 90% for diagnosing ankle tendon tears, making it the gold standard for soft tissue evaluation 1

• For specific tendons, MRI demonstrates excellent diagnostic accuracy:

  • Achilles tendon: MRI detected 26 of 27 cases (96%) of tendinosis and partial rupture 1
  • Peroneal tendons: Sensitivity of 83.9% for tendinopathy and 54.5% for tendon tears 1
  • Tibialis posterior tendon: MRI is more sensitive than ultrasound, though this difference may not significantly affect clinical management 1

• MRI provides superior soft tissue contrast resolution and multiplanar imaging capabilities that are essential for visualizing tendon pathology 2

Why CT is Not Appropriate

• The ACR Appropriateness Criteria explicitly state that CT is not routinely used for evaluation of suspected tendon abnormality 1

• CT is primarily reserved for evaluating bony abnormalities and fractures, not soft tissue structures like tendons 2

• While CT can serve as a substitute when MRI is unavailable, it is inferior for soft tissue evaluation due to poor contrast resolution 2

Additional Imaging Considerations

Ultrasound as an Alternative

• Ultrasound can be effective for tendon evaluation when performed by an expert, with reported sensitivity of 100% and accuracy of 93% compared to surgical findings 1

• Ultrasound offers the advantage of dynamic assessment for tendon subluxation and dislocation, with 100% positive predictive value 1

• However, ultrasound results are highly operator-dependent, limiting its reliability compared to MRI 1

Important Clinical Caveats

• MRI findings must be correlated with clinical examination, as up to 34% of asymptomatic patients may have peroneal tendon tears on imaging 1

• MRI evidence of peroneal tendon pathology has only a 48% positive predictive value for clinical findings, highlighting that imaging abnormalities don't always correlate with symptoms 1

Clinical Algorithm

For suspected ankle tendon injury:

1. Obtain plain radiographs first to exclude fracture
2. If radiographs are negative or nonspecific and tendon injury is suspected, proceed directly to MRI 1
3. Do not order CT for tendon evaluation unless MRI is contraindicated or unavailable 1
4. Consider ultrasound only if performed by an experienced operator and MRI is not accessible 1