What imaging modality can be used to assess for occult hip fracture if Magnetic Resonance Imaging (MRI) is contraindicated, such as in a patient with a nerve stimulator implant?

Alternative Imaging for Occult Hip Fracture When MRI is Contraindicated

For patients with suspected occult hip fracture and contraindication to MRI (such as a nerve stimulator implant), bone scan with SPECT/CT is the preferred alternative imaging modality due to its high sensitivity for detecting occult fractures. 1

Diagnostic Algorithm for Occult Hip Fracture When MRI is Contraindicated

1. Initial Imaging:

   • Standard pelvis and hip radiographs (first-line)
   • If negative but clinical suspicion remains high, proceed to alternative imaging

2. Alternative Imaging Options (when MRI is contraindicated):

   • First Choice: Bone Scan with SPECT/CT

     • High sensitivity for occult fractures
     • CT component increases specificity by co-registering scintigraphic activity with anatomic detail
     • A negative SPECT/CT has a high negative predictive value for occult fractures 1
     • Typically positive for occult fractures by the time of clinical presentation (1-2 weeks before radiographic changes)

   • Second Choice: CT without IV contrast

     • More readily available than bone scan in many facilities
     • Can detect radiographically occult fractures by visualizing cortex and trabeculae
     • Shorter acquisition times compared to MRI
     • Lower sensitivity (79-94%) compared to MRI for detecting occult fractures 2
     • May miss some significant fractures that would be detected by MRI 3

Strengths and Limitations of Each Modality

Bone Scan with SPECT/CT

• Strengths:

  • High sensitivity similar to MRI and CT 1
  • SPECT/CT combination improves specificity over traditional bone scan 1
  • Can reliably exclude occult fractures when negative 1

• Limitations:

  • Lower specificity than MRI or CT alone 1
  • May show increased uptake in bone contusions, osteoarthritis, and other osteoblastic processes 1
  • Delay of 24-72 hours after injury for optimal sensitivity

CT without IV contrast

• Strengths:

  • Widely available and faster than MRI
  • Good for visualizing cortical disruptions
  • Useful for surgical planning if fracture is detected

• Limitations:

  • Less sensitive than MRI for detecting occult fractures
  • In one study, CT missed 4 significant fractures (2% of total hip fractures) that were detected by MRI 3
  • Limited ability to detect bone marrow edema and soft tissue injuries 1

Ultrasound

• Strengths:

  • Can identify some extra-articular soft tissue abnormalities 2
  • No radiation exposure

• Limitations:

  • Limited literature on systematic analysis for hip fracture detection 1
  • Not recommended as primary imaging for suspected occult hip fractures 1
  • Quality varies significantly with sonographer experience 2

Clinical Considerations and Pitfalls

• Timing is critical: Delays in diagnosis of hip fractures can increase complications, hospital stays, and mortality rates 2

• Cost-effectiveness: While MRI has the highest sensitivity and specificity, a protocol using CT initially followed by MRI only when CT is negative can be cost-effective in appropriate patients 4

• Common pitfall: Relying solely on a negative CT scan to exclude hip fracture. Evidence shows that 64-slice CT can miss approximately 2% of occult hip fractures that are detectable by MRI 3

• Patient factors: Consider patient mobility, pain level, and ability to tolerate the selected imaging procedure

• Warning signs requiring urgent evaluation: Fever, severe pain preventing weight-bearing, redness or warmth around the hip area 2

By following this algorithm and understanding the strengths and limitations of each imaging modality, clinicians can make informed decisions when evaluating patients with suspected occult hip fractures who cannot undergo MRI.