Are shoulder replacement implants compatible with Magnetic Resonance Imaging (MRI) machines?

MRI Compatibility of Shoulder Replacement Implants

MRI can be performed in patients with shoulder replacements, but it is not typically ordered as the initial evaluation method due to potential artifacts from the implants. 1

Imaging Options After Shoulder Arthroplasty

Initial Evaluation

• Radiography is the first and main imaging modality for evaluating both symptomatic and asymptomatic shoulder arthroplasty 1
• Standard radiographs should include:
  • Anteroposterior views in internal and external rotation
  • Axillary or scapula-Y view

Role of MRI in Shoulder Arthroplasty Patients

MRI can be performed on patients with shoulder replacements, with several important considerations:

1. Clinical Applications:

   • MRI can play a contributory role when fractures are occult on radiographs or CT examinations 1
   • Particularly useful for identifying:
     • Marrow edema associated with fractures
     • Fracture lines not visible on other imaging
     • Soft-tissue abnormalities in the setting of infection
     • Rotator cuff injury evaluation 1

2. Technical Considerations:

   • Modern shoulder implants (since the Neer II system) are generally compatible with MRI machines 2
   • Metal artifact reduction protocols should be used to minimize distortion
   • Image quality may be affected by the type of implant material

Alternative Imaging Modalities

When MRI is not optimal due to metal artifacts:

1. CT with Metal Reduction Protocol:

   • Useful for detecting loosening
   • Better for delineating periprosthetic fractures seen on radiographs
   • Can assess displacement, extent, and comminution of fractures 1
   • Particularly helpful when a fracture is suspected clinically but radiographs are negative

2. Ultrasound:

   • Can assess rotator cuff integrity
   • Capable of detecting cortical discontinuity and step-off in fracture settings 1
   • Limited by inability to visualize deeper structures

3. Nuclear Medicine Studies:

   • 3-phase bone scans can detect periprosthetic fractures but have low specificity
   • Specificity increases in older prostheses once postoperative remodeling has decreased 1

Practical Approach to Imaging After Shoulder Replacement

1. Start with radiographs as the initial evaluation tool
2. Consider CT with metal reduction protocol if there's concern for fracture, loosening, or mechanical issues
3. Use MRI with metal artifact reduction techniques when soft tissue evaluation is needed (rotator cuff, infection)
4. Consider ultrasound for rotator cuff assessment when MRI is contraindicated or unavailable

Cautions and Considerations

• MRI quality will be affected by the implant material and design
• Modern modular shoulder replacement systems generally allow for MRI evaluation 3
• Preoperative planning for revision surgeries can utilize both CT and MRI, with some evidence suggesting MRI may be superior for certain measurements 4
• Custom glenoid implants used in severe bone deficiency cases may create more significant artifacts 5

Remember that while MRI is possible with shoulder implants, the clinical question should determine whether it's the most appropriate imaging modality, as radiographs remain the first-line approach for evaluating shoulder arthroplasty patients.