For a post-surgical right knee, do you recommend a CT (Computed Tomography) scan with or without contrast to check on screws?

CT Without Contrast is Recommended for Post-Surgical Knee Evaluation of Screws

For a post-surgical right knee evaluation to check on screws, CT without contrast is the most appropriate imaging modality. 1

Rationale for CT Without Contrast

• CT without contrast provides superior visualization of orthopedic hardware compared to other imaging modalities 2
• According to the ACR Appropriateness Criteria, CT without contrast is rated highly (8/9) for suspected periprosthetic fractures and hardware evaluation 1
• CT without contrast is specifically rated as "usually appropriate" (9/9) for measuring component rotation in knee arthroplasty 1

Advantages of CT Without Contrast for Hardware Evaluation

• Better visualization of bony structures and metal hardware without interference from contrast
• Superior ability to detect:
  • Screw position and potential misplacement 3
  • Periprosthetic fractures
  • Hardware loosening
  • Component alignment issues

Why Not Use Other Modalities?

• X-rays: While useful as initial screening (rated 9/9 for asymptomatic TKA follow-up), they have limited sensitivity for detecting screw misplacement (only 52% sensitivity) 3
• CT with contrast: Rated as "usually not appropriate" (1/9) for hardware evaluation 1, as contrast adds no benefit and may obscure hardware details
• MRI: Limited by metal artifacts and less accurate than CT for bone detail and hardware assessment 4

Clinical Algorithm for Post-Surgical Hardware Evaluation

1. Initial assessment: Standard radiographs (AP and lateral views)
2. When hardware details are needed: Proceed to CT without contrast
3. If infection is suspected: Different protocol applies (joint aspiration would be indicated)

Important Considerations

• Modern CT protocols have significantly reduced radiation exposure compared to older techniques 5
• 3D CT reconstructions provide particularly valuable information for evaluating hardware integrity and healing progress 2
• CT scans have been shown to be 99% accurate in evaluating prosthetic components 5

Common Pitfalls to Avoid

• Relying solely on radiographs to evaluate screw placement (misses up to 80% of medial misplacements) 3
• Using contrast when evaluating hardware (unnecessary and potentially interferes with visualization)
• Attempting to use MRI as primary hardware evaluation tool (inferior to CT for this specific purpose) 4

By following this evidence-based approach with CT without contrast, you'll obtain the most accurate assessment of screw placement and hardware status in the post-surgical knee.