What are the indications for ordering an MRI of the knee with and without intravenous (IV) contrast in a pediatric patient presenting with knee swelling in the emergency department?

From the Guidelines

MRI of the knee with and without IV contrast is primarily indicated in pediatric patients with knee swelling when there is suspicion of inflammatory, infectious, or neoplastic processes, such as suspected osteomyelitis or septic arthritis, as stated in the most recent guidelines 1. The decision to order an MRI with and without IV contrast should be based on the clinical presentation and initial evaluation, including history, physical examination, and basic imaging such as plain radiographs.

• Specific indications for MRI with and without IV contrast include:
  • Suspected osteomyelitis
  • Septic arthritis
  • Juvenile idiopathic arthritis
  • Synovitis
  • Bone or soft tissue tumors
  • Vascular abnormalities
• Contrast enhancement is useful for differentiating between viable and necrotic tissue, identifying areas of inflammation, and characterizing soft tissue masses, as noted in 1.
• Non-contrast MRI is typically sufficient for evaluating most traumatic injuries, such as meniscal tears, ligament injuries, or osteochondral lesions.
• When ordering contrast-enhanced MRI, it is essential to check renal function first, as gadolinium-based contrast agents are contraindicated in patients with severe renal impairment, and consider the risks associated with IV contrast administration in children, including allergic reactions and the rare possibility of nephrogenic systemic fibrosis, as discussed in 1.
• The radiologist should be consulted regarding the specific protocol, and the benefits of contrast must outweigh the small risks associated with IV contrast administration in children.
• The most recent guidelines from the American College of Radiology 1 and the American Academy of Pediatrics 1 provide recommendations for optimizing advanced imaging of ill and injured children in the emergency department.

From the Research

Indications for MRI of the Knee with and without IV Contrast in Pediatric Patients

The following are indications for ordering an MRI of the knee with and without intravenous (IV) contrast in a pediatric patient presenting with knee swelling in the emergency department:

• To evaluate the extent of injury in patients with pain, swelling, and effusion, where clinical assessment and conventional radiography may be limited 2
• To assess bone, cartilage, menisci, ligaments, and adjacent soft tissues in pediatric knee disorders, given its lack of ionizing radiation, multiplanar capabilities, and high resolution 2
• To identify normal variants and abnormalities of the pediatric knee, including distal femoral metaphysial irregularity, isolated popliteus tendon avulsion, juvenile idiopathic arthritis, and discoid meniscus 3
• To distinguish between Lyme arthritis and septic arthritis in children, based on MRI features such as myositis, adenopathy, and lack of subcutaneous edema 4
• To evaluate chronic monarthritis of uncertain cause in childhood, where MRI can help confirm the presence of inflammatory arthritis or investigate other causes of chronic pain and swelling 5
• To assess the knee for tumor, inflammatory disease, and developmental abnormalities, which may present with knee swelling in pediatric patients 6

Key Considerations

When ordering an MRI of the knee with and without IV contrast in a pediatric patient, it is essential to consider the following:

• The age and skeletal maturity of the patient, as injury patterns and signs of other pathologic processes may differ from those seen in adults 3
• The clinical presentation and history of the patient, including symptoms, signs, and radiographic findings 2, 5
• The potential for MRI to provide accurate assessment of bone, cartilage, menisci, ligaments, and adjacent soft tissues, which can guide diagnosis and treatment 2