In a patient with interbody fusion devices who recently fell, what is the appropriate initial imaging study?

Initial Imaging for Post-Fusion Fall Patient

In a patient with interbody fusion devices who recently fell, obtain plain radiographs (AP and lateral views) as the initial imaging study, followed by CT without contrast if hardware complications or fracture are suspected. 1

Algorithmic Approach to Imaging Selection

Step 1: Start with Plain Radiographs

• Obtain upright AP and lateral radiographs first 1
• These provide functional information about axial loading and are excellent for evaluating:
  • Hardware integrity (loosening, fracture, malalignment)
  • Overall spinal alignment
  • Gross hardware displacement
• Add flexion-extension views if concerned about abnormal motion or increased dynamic mobility at the fusion site 1

Step 2: Proceed to CT Without IV Contrast

CT lumbar spine without IV contrast is the next appropriate study if radiographs show concerning findings or if clinical suspicion remains high 1

CT excels at detecting:

• Hardware failure including prosthetic loosening, malalignment, or metallic fracture 1
• Osseous fusion status - can identify pseudarthrosis that plain films miss 2, 3
• New fractures through or adjacent to fusion construct
• Cage subsidence or migration 2

The 2021 ACR guidelines explicitly state that CT without contrast is equal to MRI for predicting significant spinal stenosis and excluding cauda equina impingement, while being superior for hardware evaluation 1.

Step 3: Consider MRI Only for Specific Indications

MRI lumbar spine without and with IV contrast is reserved for:

• Neurologic deficits suggesting nerve root compression or cord injury
• Suspected epidural hematoma or abscess (use contrast) 1
• Evaluation of soft tissue complications when CT is nondiagnostic

Important caveat: Metallic hardware creates significant artifact on MRI, limiting its utility in the immediate post-hardware setting 1. CT is more reliable for hardware-related complications.

Why This Sequence Matters

Radiographs are complementary to advanced imaging and provide unique functional information that CT cannot 1. The upright positioning reveals hardware stability under physiologic loading - critical information after trauma.

CT demonstrates superior accuracy compared to plain radiographs for fusion assessment. Research shows plain radiographs identify bridging trabeculation in only 4-8% of cases where CT identifies it in 90-95% 2. CT also detects cage loosening that radiographs miss entirely 2.

Common Pitfalls to Avoid

1. Don't skip radiographs and go straight to CT - you lose functional/dynamic information about hardware stability under load 1

2. Don't order CT with IV contrast - it adds no value for evaluating bony fusion or hardware integrity 1. Reserve contrast only if infection is suspected.

3. Don't order MRI as first-line imaging - metallic artifact will limit interpretation, and CT is superior for hardware complications 1

4. Don't use SPECT/CT initially - this is an adjunct study for painful pseudarthrosis evaluation, not acute trauma assessment 1

5. Avoid CT myelography as initial study - it requires lumbar puncture and is reserved for cases where MRI is contraindicated or when CT/MRI are nondiagnostic for nerve root compression 1

Clinical Decision Points

If radiographs are normal and patient is neurologically intact: Consider observation with close follow-up rather than immediate advanced imaging.

If radiographs show hardware displacement, lucency, or alignment change: Proceed directly to CT without contrast 1.

If patient has new neurologic deficits: Add MRI (preferably on 1.5T scanner with metal artifact reduction protocols) after obtaining CT to evaluate hardware 1.

If infection is suspected (fever, elevated inflammatory markers): Use CT with IV contrast or MRI with contrast to evaluate for epidural abscess 1.