For a patient presenting with knee pain and numbness over the tuberosity area after a fall on the knees, should the initial magnetic resonance imaging (MRI) be performed with or without contrast?

MRI Without Contrast for Post-Fall Knee Pain

For a patient with knee pain and numbness over the tuberosity area after a fall, order MRI of the knee WITHOUT intravenous contrast after obtaining initial radiographs. 1, 2

Imaging Algorithm

Step 1: Initial Radiographs First

• Always obtain knee radiographs as the first imaging study in acute knee trauma, regardless of clinical presentation 1
• Radiographs are essential to exclude fractures before proceeding to advanced imaging 2
• This is the standard of care per the American College of Radiology guidelines 1

Step 2: MRI Without Contrast as Next Study

• After radiographs show no fracture, MRI knee WITHOUT IV contrast is the appropriate next imaging study 1, 2
• The American College of Radiology explicitly recommends MRI without contrast for evaluation of suspected occult fractures or internal derangement after falls 1
• This applies to both adults and children (skeletally mature and immature) 1

Why MRI Without Contrast is Sufficient

What Non-Contrast MRI Detects

• Bone marrow contusions and occult fractures that are invisible on radiographs but cause significant morbidity 1, 2, 3
• Meniscal tears and ligamentous injuries (ACL, PCL, collateral ligaments) 1, 3
• Patellar tendinopathy and quadriceps tendon injury, particularly relevant given pain over the tuberosity area 2, 3
• Osteochondritis dissecans in adolescents 2
• Articular cartilage abnormalities and joint effusion extent 2

When Contrast IS Needed (Not Your Case)

• MRA (MR arthrography) is reserved for suspected vascular injuries in the setting of knee dislocation or significant trauma with suspected popliteal artery injury 1, 4
• Vascular injury occurs in approximately 30% of posterior knee dislocations and requires prompt surgical intervention 1
• Your patient's presentation (fall with tuberosity pain/numbness) does not suggest vascular injury or dislocation 1

Critical Pitfalls to Avoid

Do Not Skip MRI If Symptoms Persist

• Never assume normal radiographs exclude significant injury 2, 3
• Meniscal tears, ligament injuries, and bone marrow contusions are invisible on radiographs but cause substantial morbidity 2, 3
• The American College of Radiology explicitly warns against skipping MRI when symptoms persist after negative radiographs 2, 3

Consider Specific Pathology at Tuberosity

• Numbness over the tuberosity area suggests nerve involvement (infrapatellar branch of saphenous nerve) or bone marrow edema 2
• Patellar tendon pathology or tibial tubercle injury should be high on the differential given the anatomic location 2, 3
• In adolescents, consider Osgood-Schlatter disease (traction apophysitis), though this typically presents with chronic rather than acute post-fall pain 5

Do Not Order Contrast Unnecessarily

• Standard MRI without contrast has superb soft tissue resolution for all internal derangement evaluation 1
• Contrast adds cost, time, and potential adverse reactions without improving diagnostic accuracy for your clinical scenario 1
• Reserve MRA for cases with suspected or confirmed knee dislocation requiring vascular assessment 1, 4