Is a computed tomography (CT) scan or magnetic resonance imaging (MRI) better for preoperative evaluation of a hip for replacement surgery?

MRI vs CT for Preoperative Hip Replacement Evaluation

MRI is superior to CT for preoperative evaluation of a hip for replacement surgery due to its better soft tissue contrast, ability to detect early osteolysis, and avoidance of radiation exposure. 1

Imaging Modality Comparison

MRI Advantages

• Superior soft tissue contrast compared to CT 2, 1
• Direct multiplanar acquisition capabilities 3
• No ionizing radiation exposure 1, 3
• Better visualization of:
  • Soft tissue structures (muscles, tendons, ligaments)
  • Bone marrow abnormalities
  • Early osteonecrosis
  • Labral tears
  • Synovial deposits that precede bone resorption 3

CT Advantages

• Better for evaluating:
  • Suspected ceramic acetabular liner fracture
  • Medial, posterior, or superior acetabular wall deficiencies requiring bone grafting 1
  • Fractures of the hip joint 4

Clinical Decision Algorithm

1. Start with standard radiographs (X-rays) as the initial imaging modality for all patients

   • Should include AP pelvis view, lateral hip view, and frog-leg lateral view if tolerated 1

2. Progress to MRI without contrast when additional information is needed beyond radiographs

   • Preferred for most musculoskeletal conditions affecting the hip 1
   • Provides superior assessment of:
     • Labral tears
     • Tendinopathy
     • Bursitis
     • Bone marrow edema
     • Stress fractures
     • Osteonecrosis 1

3. Consider CT only for specific scenarios where bone detail is critical:

   • When radiographs suggest acetabular wall deficiencies
   • For suspected ceramic liner fracture 1

Special Considerations

• Metal artifact reduction sequences (MARS) should be used for MRI if evaluating a previously implanted prosthetic hip 1
• 3T MRI provides statistically better performance compared to 1.5T for preoperative planning 5
• 3D DP TSE sequences perform better than 3D T1 GRE sequences at both 1.5T and 3T field strengths 5

Common Pitfalls to Avoid

• Ordering CT without a specific indication when radiographs are normal 1
• Assuming CT always provides better visualization of hardware (metal artifact can limit assessment) 1
• Ordering contrast-enhanced MRI unnecessarily (increases cost and risks without significantly improving diagnostic yield) 1
• Failing to obtain appropriate clinical history to guide protocol selection 1

Impact on Surgical Outcomes

MRI is particularly valuable for preoperative planning as advanced chondral wear is the major relative contraindication for hip preservation surgery 6. By accurately assessing cartilage status, MRI helps select patients most likely to benefit from surgery, potentially improving mortality, morbidity, and quality of life outcomes.