What imaging modality is recommended for a patient with knee swelling and a history of arthritis?

Imaging for Knee Swelling with History of Arthritis

Radiography is the recommended initial imaging modality for patients with knee swelling and a history of arthritis, followed by MRI if radiographs are normal or show only joint effusion but pain persists. 1

Initial Imaging Approach

• Radiographs should be the first-line imaging study for evaluating knee swelling in patients with a history of arthritis 1
• Standard knee radiographs should include at least:
  • One frontal projection (anteroposterior, Rosenberg, or tunnel view)
  • Lateral view of the affected knee
  • Tangential patellar view 1

Radiographic Findings in Arthritis

• Radiographs can effectively demonstrate:
  • Joint space narrowing and osteophyte formation in osteoarthritis 1
  • Erosions and periosteal reaction in inflammatory arthritis 1
  • Joint effusion, which appears as soft tissue swelling 1
  • Chondrocalcinosis, suggesting calcium pyrophosphate deposition disease 1

When Initial Radiographs Are Normal or Show Only Effusion

• MRI without IV contrast is the recommended next imaging study when:
  • Initial radiographs are normal or show only joint effusion
  • Pain or swelling persists despite normal radiographs 1
• MRI provides superior evaluation of:
  • Extent of effusion and presence of synovitis 1
  • Articular cartilage damage 1, 2
  • Meniscal abnormalities 1
  • Bone marrow lesions, which correlate with pain in arthritis 1
  • Subchondral cysts and other bone abnormalities 1

Special Considerations for Suspected Septic Arthritis

• If septic arthritis is suspected in a patient with arthritis and acute knee swelling:
  • Radiographs should still be the initial imaging study 1
  • Image-guided aspiration may be necessary for definitive diagnosis 1
  • MRI can help evaluate for osteomyelitis if there is concern for bone involvement 1

Ultrasound as an Alternative

• Ultrasound can be considered for:
  • Evaluation of joint effusion and synovitis 3, 4
  • Guiding joint aspiration 1
  • Assessment of inflammatory changes in superficial structures 4
  • Patients who cannot undergo MRI due to contraindications 3

Pitfalls and Caveats

• Radiographs may appear normal in early arthritis despite significant symptoms 1, 2
• MRI findings must be correlated with clinical presentation, as meniscal tears are common incidental findings in older patients with arthritis 1
• CT is generally not indicated as a first or second-line imaging study for knee arthritis unless there are specific concerns about patellofemoral anatomy or alignment 1
• Avoid unnecessary MRI in patients with clear radiographic evidence of advanced osteoarthritis, as it rarely adds clinically relevant information 5

Algorithm for Imaging Selection

1. Start with standard radiographs (AP, lateral, and patellar views) 1
2. If radiographs show definitive arthritis explaining symptoms → no further imaging needed 1
3. If radiographs are normal or show only effusion and symptoms persist → proceed to MRI without contrast 1
4. If infection is suspected → consider image-guided aspiration 1
5. If MRI is contraindicated → consider ultrasound for soft tissue/effusion assessment 3, 4