When should an MRI (Magnetic Resonance Imaging) of the knee be ordered?

When to Order MRI of the Knee

MRI of the knee without IV contrast is usually appropriate as the next imaging study after radiographs do not show fracture in patients with suspected occult knee fractures or internal derangement after a fall or acute twisting trauma to the knee. 1

Indications for Knee MRI

Primary Indications

• Persistent knee pain after normal radiographs
• Suspected internal derangement (meniscal, ligamentous injuries)
• Clinical instability of the knee joint
• Joint effusion with persistent pain
• Suspected occult fractures not visible on radiographs

Clinical Scenarios Warranting MRI

1. Acute Trauma with Normal Radiographs

   • For adults or skeletally mature children with persistent symptoms after radiographs show no fracture 1
   • For skeletally immature children with suspected occult fractures or internal derangement 1

2. Tibial Plateau Fractures

   • MRI without IV contrast is appropriate to evaluate for additional bone or soft-tissue injury after radiographic diagnosis of tibial plateau fracture 1

3. Persistent Mechanical Symptoms

   • Locking, catching, or giving way that persists despite 6-12 weeks of conservative management 2
   • Suspected meniscal tears with symptoms that haven't responded to conservative treatment 2

Imaging Pathway Algorithm

1. Initial Assessment

   • Standard knee radiographs (X-rays) should be the first imaging study for evaluating knee pain 2
   • CT may be superior for fracture detection but is not routinely used as initial imaging 1

2. When to Order MRI

   • When radiographs are normal but pain persists
   • When joint effusion is present
   • When clinical suspicion of internal derangement exists
   • When clinical instability is present 2

3. Special Considerations

   • For knee dislocation with suspected vascular injuries, CTA lower extremity with IV contrast is appropriate 1
   • For patients with significant trauma (e.g., motor vehicle accidents), radiographs and CTA may be ordered simultaneously 1

Clinical Pearls and Pitfalls

Common Pitfalls

• Ordering MRI without first obtaining radiographs - 62.2% of patients over 50 with knee pain had MRIs without recent radiographs 3
• Ordering MRI for patients with substantial osteoarthritis who subsequently undergo total knee arthroplasty (occurs more frequently with primary care physicians than orthopedic surgeons) 4
• Failing to recognize that MRI only changed management in 23% of patients with documented pre-MRI plans in those over 50 with knee pain 3

Best Practices

• Always obtain radiographs before ordering MRI 2, 3
• Consider patient age and clinical presentation when ordering MRI
• MRI is most beneficial for younger patients, those with acute symptoms, and those with a history of trauma 4
• MRI is particularly useful when arthroscopy is being contemplated to evaluate cartilage, menisci, and ligaments 5

Special Populations

Patients Over 50 Years

• MRI should be ordered selectively in patients over 50 with knee pain
• MRI should be considered only if symptoms are not explained by osteoarthritis alone or if the appropriate treatment option requires MRI 3
• MRI assists with management in only 9.5% of patients over 50 with knee pain 3

Patients with Suspected Knee Dislocation

• MRI without contrast is accurate for evaluation of soft-tissue, osseous, and neural injuries after knee dislocation 1
• MRA may be performed simultaneously with MRI for evaluation of internal derangement and vascular injuries 1

By following these evidence-based guidelines for ordering knee MRI, clinicians can ensure appropriate use of this valuable diagnostic tool while avoiding unnecessary imaging.