What is the best imaging modality to diagnose a patient with severe pain when lifting the leg, suspected of having either a small non-displaced fracture or a groin strain?

Best Imaging for Suspected Small Non-Displaced Fracture or Groin Strain

For a patient with severe pain when lifting the leg who may have a small non-displaced fracture or groin strain, radiography (X-ray) should be the initial imaging modality, followed by MRI if radiographs are negative but clinical suspicion remains high. 1

Initial Imaging Approach

Step 1: Plain Radiography (X-ray)

• Standard radiographs should be the first-line imaging for suspected fracture
• For hip/groin area: Anteroposterior (AP) pelvis and lateral hip views
• For knee: AP and lateral views
• For ankle/foot: Three-view series (AP, lateral, and oblique)

Plain radiographs are cost-effective and readily available, making them the appropriate initial test for suspected fractures. However, they have limitations in detecting small non-displaced fractures and soft tissue injuries.

Step 2: Advanced Imaging (if radiographs are negative)

MRI (Preferred next step)

MRI is the optimal next imaging study when:

• Radiographs are negative but clinical suspicion for fracture remains
• Symptoms persist beyond 1-2 weeks
• Soft tissue injury (groin strain) is suspected

MRI offers several advantages:

• Superior for detecting occult fractures with associated bone marrow edema patterns 1
• Excellent for evaluating soft tissue injuries including muscle strains, tendon tears, and ligamentous injuries 1
• Can detect stress fractures before they are visible on radiographs
• No radiation exposure

CT Considerations

While CT is excellent for fracture detection and characterization, it has limitations:

• Less sensitive than MRI for bone marrow abnormalities and soft tissue injuries 1
• May miss stress reactions and early stress fractures
• Involves radiation exposure
• CT is most appropriate when:
  • Complex fracture patterns need detailed evaluation
  • MRI is contraindicated
  • Surgical planning is required

Specific Considerations by Location

Hip/Groin Region

• For suspected femoral neck fractures: MRI is the study of choice if radiographs are negative 2
• MRI can differentiate between:
  • Stress fractures of the femoral neck or pubic ramus
  • Muscle strains (adductor, iliopsoas, rectus abdominis)
  • Osteitis pubis
  • Sports hernia
  • Avulsion injuries 3, 4

Knee Region

• For suspected occult knee fractures: MRI has many advantages over CT 1
• MRI can detect bone marrow contusions, meniscal tears, and ligamentous injuries that may be associated with the patient's symptoms 1

Ankle/Foot Region

• For persistent ankle/foot pain after negative radiographs: MRI is preferred over CT 1, 5
• MRI is particularly valuable for midfoot injuries due to complex anatomy and predominance of soft tissue structures 5

Common Pitfalls to Avoid

1. Relying solely on radiographs when clinical suspicion for fracture is high - small non-displaced fractures may not be visible initially
2. Delaying advanced imaging when symptoms persist - early diagnosis improves outcomes
3. Choosing CT over MRI for soft tissue evaluation - CT is inferior for muscle, tendon, and ligament assessment
4. Failing to consider stress fractures in patients with activity-related pain - these may require MRI for diagnosis
5. Not obtaining weight-bearing views when Lisfranc injury is suspected 1

Algorithm for Imaging Decision

1. Obtain appropriate radiographs based on location of pain
2. If radiographs are positive → Treat according to fracture type
3. If radiographs are negative but clinical suspicion remains high → Proceed to MRI
4. If MRI is contraindicated → Consider CT as an alternative
5. For persistent symptoms with negative imaging → Consider specialist referral and follow-up imaging

By following this approach, you can efficiently diagnose both bony and soft tissue injuries in patients with severe pain when lifting the leg.