Can an MRI (Magnetic Resonance Imaging) scan of the knee determine osteoarthritis?

Can MRI Determine Knee Osteoarthritis?

Yes, MRI can definitively determine osteoarthritis of the knee and is more sensitive than radiography for detecting the full extent and severity of disease, though radiographs remain the appropriate first-line imaging modality. 1

When MRI is Indicated for Osteoarthritis Assessment

MRI without IV contrast is NOT usually indicated in patients for whom radiographs are already diagnostic of osteoarthritis, unless symptoms are not explained by the radiographic findings (such as stress fractures or other complications). 1

However, MRI becomes appropriate in specific clinical scenarios:

• When radiographs are normal or show only joint effusion but pain persists - MRI without IV contrast is the next indicated examination 1
• When more accurate or serial cartilage measurements are desired - MRI has increased sensitivity for detecting osteoarthritis compared to radiography 1
• To identify pain generators in established osteoarthritis - MRI can detect bone marrow lesions (BMLs) and synovitis/effusion, which systematic reviews identify as potential sources of knee pain in osteoarthritis patients 1

What MRI Detects in Osteoarthritis

MRI provides comprehensive visualization of all joint structures simultaneously:

• Cartilage damage - MRI directly visualizes articular cartilage loss across all compartments (medial, lateral, patellofemoral) 2, 3
• Osteophytes - MRI detects osteophytes with 100% sensitivity in some compartments, including posterior locations missed by radiographs 3
• Bone marrow lesions (BMLs) - Appear as edema-like signal in subchondral bone; new or increasing BMLs correlate with increased knee pain, especially in males or patients with family history of osteoarthritis 1
• Synovitis and effusion - Both features may indicate the origin of knee pain in osteoarthritis 1
• Meniscal tears - Detected in all osteoarthritic knees, though often incidental in older patients 1
• Subchondral cysts and bone attrition 1, 2

MRI's Superior Sensitivity Compared to Radiography

MRI frequently shows tricompartmental cartilage loss when radiography shows only bicompartmental involvement. 3

Key advantages:

• Lateral compartment detection - MRI showed 60% prevalence of cartilage loss versus 35% for radiography and 25% for CT 3
• Early disease detection - MRI can identify osteoarthritic changes before they appear on radiographs 3
• Quantitative assessment - Patients aged 45-55 years with knee pain but normal radiographs exhibited elevated T2 mapping values on 3T MRI, indicating early cartilage abnormalities 1

MRI-Based Definition of Osteoarthritis

The most validated MRI definition requires cartilage damage score ≥2 AND osteophyte score ≥2, with or without BMLs or synovitis score ≥1. 4

This definition demonstrated:

• 95.2% sensitivity for radiographic osteoarthritis 4
• 94.5% sensitivity for symptomatic osteoarthritis 4
• Area under the curve of 0.67-0.69 4

Critical Limitations and Pitfalls

The ability to discriminate painful from nonpainful knees is limited, especially in patients >70 years of age, since bilateral structural abnormalities can be present with primarily unilateral symptoms. 1

Additional caveats:

• Meniscal tears are often incidental - The majority of people over 70 years have asymptomatic meniscal tears, and the likelihood of a tear is not significantly different between painful and asymptomatic knees in patients 45-55 years 1
• MRI findings don't always correlate with symptoms - Even using synovitis/effusion presence or Kellgren-Lawrence score of 2, discrimination between painful and asymptomatic knees remains limited 1
• Contrast is rarely needed - MRI without and with IV contrast is not usually indicated when initial radiograph is negative or demonstrates joint effusion 1

Algorithmic Approach

1. Start with weight-bearing radiographs (posteroanterior, lateral, sunrise patellar views) 1

2. If radiographs are diagnostic of osteoarthritis AND symptoms match the radiographic findings → MRI is NOT indicated 1

3. If radiographs are normal or show only effusion but pain persists → Proceed to MRI without IV contrast 1

4. If radiographs show osteoarthritis but symptoms are unexplained (e.g., suspicion for stress fractures, subchondral insufficiency fractures, or other complications) → MRI without IV contrast is indicated 1

5. For research purposes or when serial cartilage measurements are needed → MRI provides quantitative assessment with annual changes of -4% to -6% cartilage volume in osteoarthritis 5