What is the recommended imaging study to diagnose an Achilles tendon tear?

MRI for Achilles Tendon Tear Diagnosis

MRI is the recommended imaging modality for diagnosing Achilles tendon tears due to its high sensitivity (95%) and specificity (95%) in detecting both complete and partial ruptures. 1

Diagnostic Approach for Suspected Achilles Tendon Tear

Initial Clinical Assessment

• Thompson/Simonds squeeze test (squeezing calf muscle to observe plantar flexion)
• Assessment for decreased ankle plantar flexion strength
• Palpation for a gap in the tendon
• Evaluation of increased passive ankle dorsiflexion
  • Note: Clinical examination alone has sensitivity values of 73-84% and specificity of 77-78% when using a combination of these tests 1

Imaging Selection Algorithm

1. MRI (First-line imaging)

   • Provides excellent visualization of tendon integrity
   • Accurately differentiates between complete and partial tears
   • Sensitivity of 95% and specificity of 95% 1
   • Detects associated pathologies that may mimic or coexist with tendon tears
   • Particularly valuable for:
     • Partial tears (superior to ultrasound)
     • Chronic tendinopathy with possible partial tearing
     • Preoperative planning
     • Postoperative assessment 2

2. Ultrasound (Alternative option)

   • Good for initial screening or when MRI is contraindicated
   • High sensitivity (92%) for differentiating full versus partial tears 1
   • Less sensitive for tendinopathy (58%) compared to MRI 1
   • Advantages: lower cost, dynamic assessment capability
   • Limitations: operator-dependent, less accurate for partial tears

MRI Protocol Considerations

• Sagittal and coronal sections are essential for assessing distance between tendon stumps in complete ruptures 2
• Fat suppression sequences help detect focal lesions 2
• T2-weighted images are valuable for identifying tears (appear hyperintense)
• Contrast-enhanced sequences indicated for:
  • Postoperative assessment
  • Suspected infection
  • Suspected tumor or inflammatory arthritis 2

Important Clinical Considerations

Advantages of MRI over Other Modalities

• Superior to ultrasound for detecting partial tears 2
• Provides comprehensive assessment of surrounding structures
• Not operator-dependent like ultrasound
• Allows for detailed preoperative planning

Potential Pitfalls

• MRI can lead to treatment delays (average 5.1 days to obtain MRI after injury) 3
• Normal twisted subtendons with thin high signal septae can mimic tears on MRI 2
• Post-surgical healing tissue can appear similar to re-rupture on T2W images 4
• In acute, clinically obvious complete ruptures, MRI may be unnecessary and delay treatment 3

When to Consider Alternative Imaging

• When immediate diagnosis is needed (clinical examination may be sufficient)
• When MRI is contraindicated
• For dynamic assessment of tendon function (ultrasound)
• For cost considerations (ultrasound is less expensive)

Summary

MRI remains the gold standard for diagnosing Achilles tendon tears with excellent sensitivity and specificity. While clinical examination is highly sensitive for complete ruptures, MRI provides definitive assessment, particularly valuable for partial tears, chronic cases, and preoperative planning. Ultrasound serves as a reasonable alternative when MRI is unavailable or contraindicated, but has limitations in detecting partial tears and is highly operator-dependent.