Preliminary Diagnosis: Anterior Cruciate Ligament Tear (knee)

I. What imaging technique is first-line for this diagnosis?

MRI, with no need for contrast

II. Describe the advantages and disadvantages of this technique for diagnosis of ACL tears.

Advantages

  • Diagnostic for anterior cruciate ligament (ACL) tears

  • Useful for categorization of the ACL tears according to severity (mild sprain, partial tears, complete tears, and detachments), location (proximal/middle/distal, anteromedial bundle/posterolateral bundle), as well as for depicting other abnormalities related to the mechanism of injury, such as chondral/osteochondral injuries, fractures, bone bruises, meniscal tears, medial collateral ligament (MCL) tears, and hemarthrosis

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  • It does not include exposure to ionizing radiation

  • Increasingly available imaging method that is covered by most insurance companies

Disadvantages

  • Expensive and time-consuming imaging modality

  • Requires patient cooperation and the images are susceptible to motion artifact; uncooperative patients may need sedation

  • Closed bore magnets may be uncomfortable for claustrophobic and obese patients

III. What are the contraindications for the first-line imaging technique?

  • Patients with non-MRI compatible implanted electronic devices, such as pacemakers, defibrillators, and nerve stimulators, which may be damaged by the magnetic field

  • Patients with non-MRI compatible clips/implants/foreign bodies, especially older aneurysm clips and cochlear implants, which may move when placed in the magnetic field

  • Relatively contraindicated in pregnant women during the first trimester due to the lack of studies regarding the effect of the magnetic field on the embryo

IV. What alternative imaging techniques are available?

  • Plain radiographs.

  • Computed tomography with intraarticular injection of contrast (CT arthrography).

  • Knee arthrograms (serial radiographs after intraarticular injection of contrast, with or without air).

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of ACL tears.

Plain radiographs
Advantages

  • Readily available, fast, low-cost imaging technique

  • May identify several fractures that are specific for, or imply the likelihood of, an ACL tear.

Disadvantages

  • Exposure to ionizing radiation

  • Plain film imaging is limited for soft tissue evaluation, offering poor anatomic detail

  • Plain film findings are often indirect signs and not specific

CT arthrography and plain knee arthrography
Advantages

  • Both methods do not involve magnetic fields, representing a suitable method for patients with formal contraindications to MRI.

  • Both techniques might be diagnostic or require additional evaluation.

Disadvantages

  • Exposure to ionizing radiation

  • Both are considered more invasive procedures, including intraarticular injection of contrast media, with possible complications, including chemical synovitis, infection, hemorrhage, and pain.

  • There is conflicting literature regarding the accuracy and multiple technique descriptions for CT arthrography in diagnosing ACL tears.

  • As this technique is rarely used, its performance highly depends on the experience of the arthrographer.

VI. What are the contraindications for the alternative imaging techniques?

Plain films

Relatively contraindicated in pregnant women, especially during the first and second trimesters.

CT arthrography

  • Contraindicated in pregnant women, especially within first and second trimesters.

  • In patients with prior allergic reactions (e.g., itching, rash, angioedema of the throat, anaphylaxis) to iodinated intravenous contrast, one should consider the risks and benefits of CT arthrography and arthrography. These patients should be pretreated with steroids and antihistamines for a minimum of 13 hours prior to imaging.

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