Should I order a computed tomography (CT) scan of the hip to assess hardware if the X-ray (XR) is normal?

CT Scan for Hip Hardware Assessment When XR is Normal

When X-rays of the hip are normal, a CT scan is not indicated for routine hardware assessment and should not be ordered.1

Imaging Approach for Hip Hardware Assessment

Initial Imaging

• Radiographs (X-rays) are the first-line imaging modality for assessment of hip prostheses 1
• Standard radiographic views should include:
  • AP pelvis view
  • Lateral hip view
  • Comparison with prior radiographs when available

When X-rays are Normal

• If radiographs are normal and the patient is asymptomatic, no further imaging is needed
• If radiographs are normal but the patient remains symptomatic:
  • MRI with metal artifact reduction sequence (MARS) is the preferred next imaging study, not CT 1, 2
  • MRI without contrast is highly sensitive for detecting most hip pathologies including hardware complications 2

Evidence-Based Recommendations

The American College of Radiology (ACR) Appropriateness Criteria for imaging after total hip arthroplasty clearly states:

• "There is insufficient evidence to support the use of CT of the hip as the initial imaging procedure in the evaluation of the symptomatic hip arthroplasty." 1
• A possible exception is for suspected ceramic acetabular liner fracture, where CT may be more sensitive than radiographs 1

Specific Indications for CT After Normal X-rays

CT may be appropriate in specific clinical scenarios despite normal radiographs:

1. Suspected ceramic liner fracture - This is the only scenario where CT is specifically mentioned as potentially more sensitive than radiographs 1
2. Computer navigation planning - CT may be used for surgical planning and navigation, but this is not a diagnostic indication 1
3. Assessment of acetabular wall defects - In cases where acetabular wall defects are suspected but not visible on radiographs 3, 4

Benefits of MRI over CT When X-rays are Normal

• MRI with metal artifact reduction techniques provides superior soft tissue contrast
• MRI can detect:
  • Adverse local tissue reactions
  • Pseudotumors
  • Tendon abnormalities
  • Bursitis
  • Synovitis
  • Early osteolysis
• MRI avoids radiation exposure associated with CT

Common Pitfalls to Avoid

• Ordering CT when radiographs are normal without a specific indication
• Assuming CT always provides better visualization of hardware (metal artifact can limit assessment)
• Failing to consider MRI with metal artifact reduction as the preferred advanced imaging modality
• Unnecessary radiation exposure from CT when not indicated

In conclusion, routine CT scanning for hip hardware assessment is not supported by evidence when radiographs are normal. MRI with metal artifact reduction techniques is the preferred next imaging study for symptomatic patients with normal radiographs.