MRI Type Recommendations for Knee Injury
Conventional MRI without contrast is the recommended imaging modality for evaluating knee injuries, with 1.5T or 3T MRI providing similar diagnostic accuracy for most knee pathologies. 1
Initial Imaging Approach
- Radiographs should be the first imaging study in acute knee trauma to rule out fractures before proceeding to advanced imaging 1
- For patients with positive Ottawa rule criteria (focal patellar tenderness, joint effusion), a minimum of two radiographic views (anteroposterior and lateral) should be obtained initially 1
- When radiographs are negative but clinical suspicion for internal derangement remains high, MRI is the next appropriate imaging study 1
MRI Protocol Recommendations
Field Strength Considerations
- Both 1.5T and 3T MRI systems provide similar high sensitivities and specificities for evaluating meniscal and ACL tears 1
- Studies show no significant improvement in diagnostic accuracy when using 3T versus 1.5T protocols for evaluating knee menisci and ACL 1, 2
- Even newer low-field MRI at 0.55T with deep learning reconstruction can yield diagnostic image quality comparable to standard 1.5T MRI for knee evaluation 2
Sequence Recommendations
The basic protocol should include: 3
- T1-weighted sequences for anatomical detail
- T2-weighted fluid-sensitive sequences for pathology detection
- Proton density (PD) weighted sequences, preferably with fat suppression
Fat-saturated PD/T2-weighted images significantly improve visualization of collateral ligament injuries compared to non-fat-saturated sequences 4
For optimal visualization of the anterolateral ligament (ALL), which is frequently injured alongside ACL tears, coronal plane imaging provides the best visualization 5
Clinical Applications and Benefits
MRI has proven highly accurate in evaluating: 1
- Bone marrow contusions and occult fractures (sensitivity >90%)
- Meniscal tears (sensitivity 85-96%, specificity 89-97%)
- Ligamentous injuries (sensitivity 91-93%, specificity 88-96%)
MRI can change management from surgical to conservative in up to 48% of patients presenting with a locked knee 1
MRI findings shorten diagnostic workup time, reduce additional diagnostic procedures, and improve quality of life in the first 6 weeks after injury 1
Special Considerations
- In patients under 40 years old with acute knee injury, knee effusion >10mm on lateral radiograph should prompt consideration for MRI examination 1
- MRI is superior to other modalities (CT, bone scan, ultrasound) for evaluating soft tissue injuries of the knee 1
- For detection of bone marrow lesions after trauma, apparent diffusion coefficient maps may be more sensitive than standard PD-weighted fat-saturated sequences 1
Pitfalls and Limitations
- MR arthrography and MRA are not routinely recommended for initial evaluation of acute knee trauma 1
- Ultrasound has limited utility in knee injury evaluation beyond detecting joint effusions and superficial tendon injuries 1
- Timing of MRI after injury can affect visualization of certain structures - anterolateral ligament injuries are better visualized within 6 weeks of acute trauma compared to later imaging 1