How to evaluate sacroiliac (SI) joint fusion via fluoroscopic images?

Fluoroscopic Imaging for Sacroiliac Joint Fusion: Best Practices for Evaluation

For optimal evaluation of sacroiliac (SI) joint fusion via fluoroscopic images, biplanar fluoroscopy with simultaneous anteroposterior (AP) and lateral projections is the most effective imaging approach. 1

Imaging Modalities for SI Joint Assessment

Initial Imaging Selection

• X-ray of the sacroiliac joints is recommended as the first-line imaging method for initial evaluation of SI joint pathology 2
• For post-procedural evaluation of SI fusion implant placement, fluoroscopy and CT are the primary modalities

Fluoroscopic Technique for SI Joint Fusion

1. Biplanar fluoroscopy setup:

   • Position patient prone with legs spread apart in "Da Vinci position"
   • Place one x-ray arch at right angle to patient for lateral projection
   • Position second x-ray machine with arch between patient's legs for AP projection
   • This configuration allows simultaneous AP and lateral views without repositioning equipment 1

2. Required fluoroscopic views:

   • Anteroposterior (AP) view
   • Lateral view
   • Outlet view (particularly critical after guide-pin placement to evaluate pin depth) 3
   • Multiple views from different angles to confirm proper implant positioning 4

Accuracy of Imaging Modalities

Comparative Effectiveness

• CT imaging provides superior accuracy (kappa 0.906) compared to fluoroscopy (kappa 0.641) for detecting malpositioned implants 4
• However, thorough evaluation with multiple fluoroscopic views can still effectively assess implant position, identity, and breach direction 4

Critical Assessment Points

• Verify implant position relative to neural structures (L5, S1, S2 nerve roots)
• Confirm implants are properly positioned within bone and not breaching cortices
• Assess depth of implant placement to avoid foraminal encroachment
• Evaluate for proper transfixation across the SI joint 3

Procedural Considerations

Navigation Options

• Traditional fluoroscopy requires frequent repositioning for different views
• 3D navigation systems (cone-beam CT) can be used for more precise guidance
• When using navigation, place a reference pin in the contralateral posterior superior iliac spine 3
• Even with navigation, periodic radiographic confirmation is essential 3

Implant Placement Verification

• For triangular titanium implants (lateral approach): verify 2 implants in S1 and 1 in S2 3
• For posterior approach: confirm placement at S1/S2 level or mid-segment SIJ fixation 5
• Ensure implants cross the SI joint and enter the center of the sacrum lateral to neural foramina 3

Safety Considerations

Avoiding Complications

• Improper placement can lead to:

  • Superior gluteal artery injury if too ventral
  • Iliac artery injury if not staying within bone
  • L5 nerve injury if implant is too ventral
  • S1 or S2 nerve injury if implant is too deep into the foramen 3

• Multiplanar post-placement imaging of the pelvis is essential before completing the procedure 3

Pitfalls to Avoid

• Relying on single-view fluoroscopy can miss malpositioned implants
• Failure to confirm final position with multiple views increases risk of complications
• Inadequate visualization of sacral dysmorphism or anatomical variants 3

Intraoperative CT imaging provides the most accurate assessment of implant position and should be used when available to minimize the risk of unplanned returns to the operating room 4.