Can I have a Magnetic Resonance Imaging (MRI) scan of my knee after a knee replacement?

MRI After Knee Replacement: Appropriateness and Limitations

MRI of the knee after a knee replacement is generally rated as "may be appropriate" (rating 3-6 out of 9) and can be performed in specific clinical scenarios, but is not the first-line imaging modality for routine post-arthroplasty evaluation.

Initial Imaging Approach After Knee Replacement

• Standard radiographs (X-rays) are the first-line imaging modality for evaluating knee replacements, rated as "usually appropriate" (9/9) 1
• These should include standing AP, lateral, and tangential axial views of the patellofemoral joint

When MRI May Be Appropriate After Knee Replacement

MRI without contrast may be appropriate (rating 3-6/9) in several specific scenarios:

1. Suspected periprosthetic soft-tissue abnormalities (rating 6/9) 1

   • Quadriceps or patellar tendinopathy
   • Arthrofibrosis
   • Patellar clunk syndrome
   • Soft tissue impingement

2. Component rotation assessment (rating 6/9) 1

3. Suspected periprosthetic fracture (rating 5/9) 1

   • Note that CT without contrast is preferred (rating 8/9) for this indication

4. Clinical concern for instability (rating 5/9) 1

5. Suspected granulomas/osteolysis (rating 6/9) 1

Technical Considerations for MRI After Knee Replacement

• MRI must use robust metal artifact reduction techniques 1
• Modern MRI sequences can significantly reduce metal artifacts, allowing evaluation of preserved structures 2
• Despite advances, image quality may still be compromised compared to non-prosthetic knees

Important Limitations and Caveats

1. Metal artifacts: Despite reduction techniques, prosthetic components will cause some degree of artifact

2. CT is superior for certain indications:

   • Component loosening assessment
   • Periprosthetic fractures (CT rated 8/9 vs MRI rated 5/9) 1
   • Component rotation measurement (CT rated 9/9 vs MRI rated 6/9) 1

3. Contrast administration: MRI with contrast is rated as "usually not appropriate" (1/9) for most post-arthroplasty evaluations 1

4. Diagnostic accuracy: CT provides more dimensionally accurate bone models than MRI when precise measurements are needed 3

Clinical Decision Algorithm

1. First obtain standard radiographs (standing AP, lateral, and patellofemoral views)

2. If radiographs are normal but symptoms persist:

   • For suspected infection → proceed to joint aspiration (rated 9/9) 1
   • For suspected component loosening → CT without contrast (rated 7/9) 1
   • For soft tissue pathology → MRI without contrast (rated 6/9) 1

3. Consider MRI only when:

   • Soft tissue pathology is the primary concern
   • CT is contraindicated
   • Specialized metal artifact reduction protocols are available

Conclusion

MRI can be performed after knee replacement with appropriate metal artifact reduction techniques, but it is not the first-line imaging modality for routine evaluation. Radiographs remain the initial imaging study, with CT often preferred for bone and component assessment, while MRI may be more valuable for evaluating soft tissue structures around the prosthesis.