What is the likely investigation for thigh pain following an injury?

Diagnostic Approach to Thigh Pain Following Injury

Radiographs should be the initial imaging modality for thigh pain following injury, with MRI reserved for cases where radiographs are negative or equivocal but clinical suspicion for fracture or soft tissue injury remains high. 1

Initial Evaluation

Radiographic Assessment

• First-line imaging: AP and lateral radiographs of the affected thigh/femur 1
• Include AP pelvis view to allow comparison with the contralateral side and evaluate for pelvic fractures that may refer pain to the thigh 1
• Radiographs can detect:
  • Fractures (including nondisplaced fractures)
  • Osteoarthritis
  • Bone tumors
  • Osteonecrosis
  • Stress fractures (though sensitivity is limited)

Clinical Considerations

• Radiographs have limited sensitivity for nondisplaced fractures, with up to 10% of fractures only visible on follow-up imaging 1
• Negative radiographs alone cannot exclude fracture when clinical suspicion is high 1
• Pain in the thigh may be referred from hip pathology, as hip pain can manifest in the thigh, knee, or buttock 1

Secondary Imaging for Negative/Equivocal Radiographs

MRI (Without IV Contrast)

• Preferred second-line imaging when radiographs are negative but clinical suspicion remains 1
• Highly sensitive for:
  • Soft tissue injuries (muscle tears, tendinopathy)
  • Occult fractures and stress reactions
  • Bone marrow edema
  • Labral tears when hip pathology is suspected 2
  • Cartilage injuries

Ultrasound

• Useful for evaluating specific soft tissue abnormalities:
  • Muscle tears and hematomas
  • Tendinopathy
  • Joint effusions
• Limited field of view restricts utility when symptoms cannot be well localized 1
• Operator-dependent with variable sensitivity (73%) and specificity (92%) for fractures 1

Bone Scan (Tc-99m 3-Phase)

• Consider when MRI is contraindicated or unavailable
• Sensitive for detecting bone pathology when examination is nonfocal and initial imaging is negative 1
• Useful for localizing pathology in limping patients with persistent symptoms 1
• Less anatomic detail than MRI 1

Special Considerations

Compartment Syndrome

• Rare but serious complication following thigh injury (0.3% of trauma patients) 3
• Clinical signs: tense swelling, disproportionate pain, neuromuscular deficits 4, 3
• Risk factors: vascular injury, high-energy trauma, prolonged compression 4, 3
• Requires immediate surgical consultation if suspected 3

Muscle Strains and Contusions

• Common in anterior thigh injuries, especially in athletes 5
• Ultrasound and MRI helpful to determine extent of injury 5
• Complete tendon injuries or avulsions may require operative treatment 5

Hip-Related Thigh Pain

• Hip pathology (including labral tears) can present as thigh pain 1, 2
• Consider MR arthrography for suspected labral tears if initial MRI is equivocal 2
• Diagnostic hip injection may help differentiate hip from thigh pathology 1

Pitfalls to Avoid

1. Delayed diagnosis: Failing to obtain follow-up imaging when initial radiographs are negative but symptoms persist 1
2. Missing referred pain: Not considering that thigh pain may originate from hip or pelvic pathology 1
3. Overlooking compartment syndrome: This rare but serious complication requires prompt recognition and treatment 4, 3
4. Inadequate imaging: Using only limited views rather than orthogonal projections 1
5. Premature return to activity: Allowing return before complete evaluation, potentially leading to chronic disability 5

Remember that the clinical presentation should guide the imaging approach, and persistent symptoms despite negative initial imaging warrant further investigation with advanced modalities.