Should an MRI of the knee for an Anterior Cruciate Ligament (ACL) tear be performed with or without contrast?

MRI of Knee for ACL Tear: Without Contrast

For suspected ACL tears, MRI of the knee should be performed WITHOUT intravenous contrast. 1, 2

Standard Imaging Protocol

Non-contrast MRI is the definitive imaging study for ACL tears and provides all necessary diagnostic information. 1, 2 The American College of Radiology explicitly recommends MRI without IV contrast as the standard approach for ligament injuries, including ACL tears. 1, 2

Why Contrast is Unnecessary

• Ligamentous structures are adequately visualized on standard non-contrast sequences due to their inherent signal characteristics and the excellent contrast provided by surrounding joint fluid and soft tissues. 1
• MRI without contrast accurately depicts all relevant pathology including the ACL tear itself, associated bone marrow contusions, meniscal tears, collateral ligament injuries, and cartilage damage. 2
• Adding IV contrast provides no additional diagnostic value for routine meniscal or ligamentous injuries and should be avoided. 2

Appropriate Imaging Sequence

Initial Evaluation

• Begin with plain radiographs to rule out fractures before proceeding to MRI, as recommended by the American College of Radiology. 2
• If radiographs are negative and internal derangement is suspected, proceed directly to MRI without contrast. 2

MRI Technical Considerations

• Standard 1.5-Tesla or 3-Tesla MRI sequences are sufficient for diagnosing ACL tears with high accuracy (sensitivity 95.45%, specificity 91.67%, accuracy 94.87%). 3
• MRI demonstrates both primary signs (ACL fiber discontinuity, thickening, edema, abnormal orientation) and secondary signs (bone marrow contusions, meniscal tears, posterior cruciate ligament buckling). 4, 3

When Contrast IS Indicated (Rare Exceptions)

Intravenous contrast should only be considered in specific non-ACL scenarios:

• Suspected neoplastic masses or inflammatory pseudotumors require contrast for tissue characterization. 1
• Pigmented villonodular synovitis (PVNS) benefits from contrast to assess extent and vascularity. 1
• Quantifying synovitis severity in chronic knee pain when precise grading impacts treatment decisions (though this correlates only moderately with histology). 1

MR Arthrography Distinction

• Intra-articular gadolinium (MR arthrography) is NOT routinely used for acute ACL tears or initial evaluation of suspected ligamentous injuries. 5, 2
• MR arthrography is reserved for patients with prior meniscal surgery, complex chondral lesions, or when standard MRI is equivocal. 1

Clinical Pearls and Pitfalls

Diagnostic Accuracy

• MRI accuracy for complete ACL tears is 92.86% and for partial tears is 94.74%, making it highly reliable for surgical planning. 3
• Clinical examination tests (Lachman, anterior drawer) can be equally or more accurate than MRI when performed by skilled examiners, but MRI provides comprehensive assessment of associated injuries. 6, 7

Common Mistakes to Avoid

• Do not order MRI with contrast for routine ACL evaluation - this adds cost, time, and potential contrast-related risks without diagnostic benefit. 2
• Do not skip initial radiographs - fractures must be excluded first, and radiographs guide subsequent imaging decisions. 2
• Be aware that standard 1.5-Tesla MRI may not reliably identify anterolateral ligament tears associated with ACL injuries, though this rarely changes acute management. 8

Associated Injuries

• MRI without contrast effectively identifies concomitant injuries including meniscal tears (present in majority of ACL injuries), bone marrow contusions, cartilage damage, and collateral ligament injuries. 5, 2, 3
• In cases of suspected knee dislocation, vascular assessment may be necessary due to risk of popliteal artery injury. 2