Imaging for Suspected Stress Fracture
Conventional radiographs (X-rays) in at least two planes should always be obtained as the initial imaging study for any patient with suspected stress fracture, despite their poor sensitivity of only 15-35%. 1
Initial Imaging Approach
- Plain radiographs are mandatory first-line imaging for all suspected stress fractures, as recommended by the American College of Radiology, even though they frequently miss early fractures 1, 2
- If radiographs are conclusive for fracture, no further imaging is needed 1, 2
- Early radiographic findings are often nonspecific (subtle periosteal reaction, "gray cortex" sign) or completely absent 1, 3
- Late radiographic findings that suggest stress fracture include linear sclerosis perpendicular to trabeculae, periosteal reaction, patchy endosteal sclerosis, and soft-tissue swelling 1
When Initial X-rays Are Negative
For Immediate "Need-to-Know" Diagnosis
MRI without IV contrast is the preferred second-line imaging study when clinical suspicion remains high despite negative radiographs. 1, 4, 2
- MRI demonstrates stress abnormalities as early as bone scintigraphy but with considerably greater specificity 1, 4
- MRI has near 100% sensitivity for occult fractures and provides superior soft-tissue evaluation compared to all other modalities 2
- Fluid-sensitive sequences (STIR or T2-weighted) are the favored initial MRI sequences for screening 1
- MRI shows linear T1 and T2 hypointense fracture lines surrounded by T1 hypointense and T2 hyperintense bone marrow edema 4
- MRI is particularly critical for high-risk fracture locations (femoral neck, femoral head, tarsal navicular, proximal second metatarsal) where delayed diagnosis can lead to displacement, nonunion, avascular necrosis, or significant complications 1, 4, 5
For Non-Urgent Situations
- Follow-up radiographs in 10-14 days increase sensitivity to 30-70% due to overt bone reaction and callus formation 1, 4
- However, follow-up radiographs are still less sensitive than MRI and should not be used when immediate diagnosis is needed for high-risk locations 4, 2
Alternative Imaging Modalities
CT Without Contrast
- CT is not typically used as first- or second-line imaging but may offer an adjunctive role when MRI is equivocal 1
- CT has specificity ranging from 88-98% but is less sensitive than MRI or bone scintigraphy 1
- CT is useful for characterizing fracture displacement or comminution for surgical planning 5
- CT should be considered when MRI is contraindicated or unavailable, accepting lower sensitivity (69% vs 99% for MRI) 2
Bone Scintigraphy
- Bone scintigraphy may be reasonable in claustrophobic patients but is superseded by MRI due to lower specificity 2
- Planar scintigraphy combined with SPECT is more accurate than planar imaging alone 1
Ultrasound
- Ultrasound is not appropriate for comprehensive stress fracture evaluation despite its ability to detect periosteal thickening and cortical irregularity 1, 2
- Ultrasound cannot evaluate subcortical or trabecular bone, so trabecular stress fractures may be missed 1, 5
- Ultrasound is operator-dependent and has poor sensitivity for deep bone assessment 2
Critical Pitfalls to Avoid
- Never rely solely on negative initial radiographs to rule out stress fracture when clinical suspicion is high, especially in athletes with persistent symptoms 4, 5
- Do not delay MRI for high-risk fracture locations (femoral neck, navicular) by waiting for follow-up radiographs, as this can lead to fracture progression and serious complications 4, 5
- Do not add IV contrast for fracture detection on either MRI or CT, as it provides no additional diagnostic value 2
- Do not assume negative CT excludes fracture, as CT misses 13-31% of fractures detected by MRI, particularly nondisplaced and trabecular fractures 2