MRI is More Sensitive than CT for Detecting Fractures
MRI is superior to CT for fracture detection, with sensitivity approaching 99-100% compared to CT's 69-87%, making MRI the imaging modality of choice when radiographs are negative or equivocal. 1, 2
Comparative Sensitivity Data
MRI Performance
- MRI demonstrates sensitivity of 99-100% for fracture detection across multiple anatomic sites 1, 2
- In a study of 129 patients with proximal femoral and pelvic fractures, MRI achieved 99% sensitivity compared to CT's 69% sensitivity 1
- MRI detected 128 of 129 fractures (99%) in patients with pelvic insufficiency fractures, while CT detected only 89 of 129 fractures (69%) 2
- MRI is particularly superior for detecting stress fractures, demonstrating abnormalities as early as bone scintigraphy but with considerably greater specificity 1
CT Performance
- CT sensitivity ranges from 69-87% for fracture detection, with CT missing 6 of 15 fractures in one study 1
- CT's primary strength lies in specificity (88-98%) rather than sensitivity, making it useful for confirming suspected fractures but inadequate as a screening tool 1
- CT is less sensitive than both MRI and nuclear scintigraphy for stress fractures 1
Clinical Context Where Differences Matter Most
Radiographically Occult Fractures
- For hip fractures with negative radiographs, MRI should be the preferred next imaging study 1
- MRI is substantially better at detecting undisplaced fractures, particularly in patients with osteoporosis 3, 2
- Fractures at the femoral head and acetabulum are significantly better detected with MRI than CT 2
Stress Fractures
- MRI is the procedure of choice for early diagnosis of both fatigue and insufficiency stress fractures, outperforming all other modalities including CT 1
- Fluid-sensitive sequences (STIR or T2-weighted) demonstrate fracture lines surrounded by edema with high sensitivity 1, 4
- CT is not supported as first- or second-line imaging for stress fractures but may offer an adjunct role when MRI is equivocal 1
Spine Fractures in Ankylosis
- CT and MRI have similar sensitivities for spine fractures in ankylosing spondylitis, with some fractures better detected on each modality, suggesting complementary utility 1
- CT is typically preferred in acute trauma settings due to speed and ability to image unstable patients 1
- MRI provides the added benefit of detecting soft tissue injuries including ligamentous disruption and spinal cord injury 1
Important Clinical Pitfalls
When CT May Miss Fractures
- CT missed fractures in 17% of patients with posterior pelvic ring injuries who had anterior ring fractures on radiographs 3
- Multiple studies demonstrate potential for missed fractures with CT, leading to changes in diagnosis and management when MRI is subsequently obtained 1
- In elderly patients with osteoporosis, the sensitivity gap between MRI and CT widens significantly 3, 2
Appropriate Use of CT
- CT should be reserved for situations where MRI is contraindicated, unavailable, or when rapid imaging is essential in trauma 1
- CT excels at confirming suspected fractures due to high specificity but should not be relied upon to exclude fractures 1
- In spine trauma with ankylosis, CT is typically preferred initially due to practical considerations, but MRI may be needed if neurologic deficits are present 1
Practical Algorithm for Fracture Detection
Initial Approach
- Begin with radiographs in at least two planes (sensitivity 15-35% for stress fractures, higher for acute trauma) 1, 4
When Radiographs are Negative or Equivocal
- Proceed directly to MRI without contrast for suspected stress fractures or in elderly patients with suspected insufficiency fractures 1, 4
- For suspected hip fractures in elderly patients, MRI is the preferred next study 1
- Consider CT only when MRI is contraindicated, unavailable, or in acute polytrauma requiring rapid assessment 1