In a patient with severe osteoarthritis requiring reassessment of joint status, is magnetic resonance imaging (MRI) or computed tomography (CT) the preferred imaging modality?

Imaging for Severe Osteoarthritis Reassessment

For reassessing severe osteoarthritis, MRI is superior to CT when evaluating soft tissue structures (cartilage, menisci, ligaments, synovium), while CT is preferred specifically for detailed cortical bone assessment and when MRI is contraindicated. 1, 2

Initial Imaging Approach

Plain radiography should always be performed first before considering advanced imaging modalities. 1 The EULAR guidelines explicitly state that conventional radiography must precede other modalities, with weightbearing views recommended for knee OA to optimize detection of joint space narrowing. 1

When Advanced Imaging Is Indicated

Routine imaging for OA follow-up is not recommended unless there is:

• Unexpected rapid progression of symptoms
• Change in clinical characteristics requiring determination of whether this relates to OA severity or an additional diagnosis 1

MRI vs CT: Specific Indications

Choose MRI when evaluating:

• Soft tissue structures: cartilage, menisci, ligaments, and synovium 1
• Bone marrow lesions which correlate with pain and compartment-specific structural deterioration 3
• Synovitis and joint effusions associated with OA pain 3
• Meniscal damage which is strongly associated with progressive cartilage loss 3
• Comprehensive whole-joint assessment including all intraarticular structures and pathologies 4, 5
• Cartilage loss and thickness with greater sensitivity than radiographs for detecting joint space narrowing 6

MRI demonstrates superior soft tissue contrast and can detect bone marrow abnormalities that CT cannot visualize. 2 Studies show MRI identifies osteophytes, bone marrow lesions, subchondral cysts, effusion-synovitis, joint space narrowing, and cartilage loss as characteristic features of OA. 7

Choose CT when evaluating:

• Cortical bone destruction - CT is superior to MRI in detecting cortical bone destruction (13.6% better detection rate) 2
• Subtle matrix mineralization patterns 2
• Complex bony anatomy requiring detailed assessment 1
• When MRI is contraindicated (non-MRI-compatible implants, severe claustrophobia, pacemakers) 1, 2

CT better defines destruction of cortical bone and demonstrates subtle erosions and reparative changes that may be equivocal on radiographs. 1

Clinical Algorithm

1. Start with plain radiographs (weightbearing views for knee) 1

2. If reassessment needed due to symptom progression:

   • Primary concern is soft tissue pathology (cartilage, meniscus, ligaments, synovitis) → MRI 1, 2
   • Primary concern is cortical bone detail or mineralization → CT 2
   • MRI contraindicated → CT 2

3. Consider ultrasound as complementary for superficial soft tissues if MRI unavailable, though limited for deep joint structures 1, 4

Important Caveats

• Imaging findings do not always correlate with symptoms - only a minority of studies show correlation between imaging changes and clinical outcomes 1
• MRI detects more abnormalities than are clinically relevant - asymptomatic individuals often have MRI abnormalities 5
• CT involves ionizing radiation - this must be weighed against diagnostic benefit, particularly for serial imaging 1
• Neither modality should be used for routine follow-up without clinical indication 1

The choice ultimately depends on the specific clinical question: MRI for comprehensive joint assessment including all soft tissues, CT for detailed cortical bone evaluation or when MRI is not feasible. 1, 2