What is the best imaging approach for evaluating the right hip and sacroiliac (sacroiliac joint) region?

Optimal Imaging Approach for Right Hip and Sacroiliac Region Evaluation

Radiographs of the pelvis should be obtained as the first-line imaging modality for evaluating the right hip and sacroiliac joint region, with MRI being the next appropriate study if radiographs are negative or equivocal and clinical suspicion remains high. 1

Initial Imaging Approach

Radiography (X-ray)

• Start with anteroposterior (AP) view of the pelvis

  • Provides visualization of both sacroiliac joints and hips simultaneously 1
  • No additional benefit from adding oblique sacroiliac joint views 1, 2
  • AP pelvis films show close agreement (86-90%) with dedicated SI joint views 2
  • Lower radiation exposure and cost compared to dedicated SI joint radiographs 2

• When to include additional spine radiographs:

  • If symptoms are referable to the spine, include cervical and lumbar spine radiographs 1
  • Thoracic spine radiographs have limited utility due to overlying structures but may be obtained for specific symptoms 1

Radiographic Findings to Look For:

• Hip joint: joint space narrowing, osteophytes, subchondral sclerosis, cysts, deformity 3
• Sacroiliac joints: erosions, sclerotic changes, ankylosis 1

Secondary Imaging (if radiographs are negative/equivocal)

MRI

• Best examination for assessment of acute inflammatory changes 1
• Protocol should include:
  • T1-weighted sequences
  • Fat-suppressed fluid-sensitive sequences (T2-weighted fat-saturated or STIR) 1, 4
  • Consider gadolinium contrast-enhanced T1-weighted fat-saturated sequences for better evaluation of inflammation 1
• Benefits:
  • Can detect inflammatory changes 3-7 years before radiographic findings appear 1
  • Superior for evaluating soft tissues, bone marrow edema, and early sacroiliitis 1
  • Allows assessment of labral abnormalities and cartilage lesions 3

CT

• Consider when:
  • Radiographs show equivocal abnormalities 1
  • MRI is contraindicated
  • Need for detailed bone anatomy evaluation 4
• Benefits:
  • Better assessment of complex SI joint anatomy 1
  • Improved sensitivity for subtle erosions and reparative changes 1
  • Superior visualization of bone structures 4

Imaging Algorithm

1. Start with AP pelvis radiograph

   • If clearly abnormal → Diagnosis established
   • If normal or equivocal → Proceed to step 2

2. MRI of sacroiliac joints and/or hip

   • If patient has short duration of symptoms, consider MRI as initial imaging 1
   • If radiographs are negative but clinical suspicion remains high 1

3. CT without contrast

   • Consider when MRI is contraindicated
   • When equivocal radiographic abnormalities exist 1
   • For better assessment of bone structures and subtle erosions 1

Important Considerations and Pitfalls

• Radiographic limitations:

  • Low sensitivity (19-72%) for early disease 1
  • Variable specificity (47-84.5%) 1
  • May miss more than half of patients with structural changes 1
  • Fair to moderate interobserver agreement 1

• MRI considerations:

  • Metal artifacts may limit evaluation if hardware is present 4
  • Requires proper technique with fat suppression for optimal evaluation 1, 4

• Ultrasound limitations:

  • Not routinely recommended for initial evaluation of sacroiliac joints 1
  • May be useful for evaluating superficial soft tissues around the hip but not for comprehensive assessment 5

By following this imaging approach, clinicians can effectively evaluate the right hip and sacroiliac region while minimizing unnecessary radiation exposure and optimizing diagnostic accuracy.