MRI for 16-Year-Old Knee Injury: Without Contrast
For a 16-year-old with a knee injury, if MRI is indicated, it should be performed WITHOUT intravenous contrast. 1, 2
Initial Imaging Approach
Start with plain radiographs, not MRI. 1 The American College of Radiology clearly states that MRI is not routinely used as the initial imaging study for acute knee trauma. 1
When to Order Initial X-rays
For a 16-year-old, obtain knee radiographs if ANY of the following are present: 1
- Focal tenderness (at patella or fibular head)
- Joint effusion
- Inability to bear weight for 4 steps
- Inability to flex knee to 90 degrees
- Gross deformity, palpable mass, or penetrating injury
Important caveat: A 16-year-old falls outside both the Ottawa Knee Rule (≥18 years) and Pittsburgh Decision Rule age criteria, but clinical judgment should guide radiograph ordering based on the presence of focal tenderness, effusion, or inability to bear weight. 1
When MRI Becomes Appropriate
MRI without contrast is the appropriate next study after negative radiographs when: 1, 2
- Suspected occult fracture
- Suspected internal derangement (meniscal or ligamentous injury)
- Significant joint effusion persists
- Inability to fully bear weight after 5-7 days
- Mechanical symptoms suggesting meniscal injury
- Joint instability suggesting ligamentous injury
Why MRI Without Contrast
The ACR Appropriateness Criteria specifically recommend MRI knee without IV contrast for skeletally mature or immature children when evaluating suspected occult fractures or internal derangement after negative radiographs. 1 MRI without contrast provides excellent visualization of: 1, 3, 4
- Meniscal tears (85-95% accuracy)
- Cruciate ligament injuries (90-95% accuracy)
- Collateral ligament injuries
- Bone marrow contusions
- Osteochondral lesions
Contrast Is Not Needed
MR arthrography (with contrast) is not routinely used for acute knee trauma evaluation. 1 Standard MRI without contrast is superior for detecting the majority of traumatic knee injuries, including soft tissue injuries that account for 93.5% of acute knee presentations. 1
Common Pitfalls to Avoid
- Don't skip radiographs: Even if you suspect soft tissue injury, radiographs must be obtained first to rule out fractures requiring immediate intervention. 1, 2
- Don't order MRI with contrast: Intravenous contrast adds no diagnostic value for traumatic knee injuries and increases cost and potential adverse effects. 1
- Don't ignore clinical examination: MRI should augment, not replace, thorough physical examination for ligament stability and focal tenderness. 5, 6