Best Imaging for Suspected Metatarsal Stress Fracture
Start with plain radiographs of the foot in at least two views, and if negative but clinical suspicion remains high, proceed directly to MRI without contrast for definitive diagnosis. 1, 2
Initial Imaging: Plain Radiographs
Conventional radiographs should always be obtained first despite their low sensitivity of 15-35% for stress fractures, as all authorities agree this is the appropriate initial modality. 1
Early radiographic findings are often nonspecific (subtle periosteal reaction, "gray cortex" sign) or completely absent on initial imaging. 1
Late radiographic findings that suggest stress fracture include linear sclerosis perpendicular to major trabecular lines, periosteal reaction, patchy endosteal sclerosis, and soft-tissue swelling. 1
If radiographs show conclusive findings of fracture, no further imaging is needed. 1
Second-Line Imaging: MRI Without Contrast
When radiographs are negative but clinical suspicion persists, MRI without IV contrast is the preferred next study. 1, 2
MRI demonstrates stress abnormalities as early as bone scintigraphy but with significantly greater specificity (considerably more specific than bone scan). 1
Fluid-sensitive sequences (STIR or T2-weighted) are the favored initial MRI sequences, showing bone marrow edema patterns with a fracture line on small field-of-view imaging. 1
MRI provides both diagnostic and prognostic information, allowing prediction of time to return to activity based on the pattern and extent of periosteal and marrow edema. 1, 2
Intravenous contrast provides no additional diagnostic information and should not be used. 1
Critical Consideration: High-Risk Metatarsal Locations
The proximal second metatarsal and fifth metatarsal base are considered high-risk stress fracture locations where delayed diagnosis can lead to significant complications including nonunion and displacement. 1, 2
For suspected fractures in these high-risk locations, proceed directly to MRI rather than waiting for follow-up radiographs to avoid fracture progression. 2
Alternative Imaging Options (Less Preferred)
Follow-Up Radiographs
- Short-term follow-up radiographs at 10-14 days show increased sensitivity (30-70%) compared to initial films due to overt bone reaction. 1
- However, this approach delays diagnosis and risks fracture progression, particularly in high-risk locations. 2
Bone Scintigraphy
- Three-phase bone scan has high sensitivity (92.9%) but lower specificity (73.8%) compared to MRI. 1
- Bone scan cannot distinguish between stress reaction and actual stress fracture as reliably as MRI. 1
CT
- CT is not typically used as first- or second-line imaging but may serve an adjunctive role when MRI is equivocal. 1
- CT has specificity ranging from 88-98% but is less sensitive than MRI and involves ionizing radiation. 1
Ultrasound
- Limited evidence supports ultrasound for metatarsal stress fractures, with one study showing 83% sensitivity and 76% specificity. 3
- Ultrasound findings include periosteal thickening, cortical irregularity, and local hyperemia, but cannot evaluate subcortical bone. 1
- Ultrasound is operator-dependent and similar findings can occur with osteomyelitis or neoplasm. 1
Common Pitfalls to Avoid
Do not rely solely on negative initial radiographs to rule out stress fracture when clinical suspicion is high, as they miss 65-85% of early stress fractures. 1, 2
Do not wait 2-3 weeks for repeat radiographs if urgent diagnosis is needed—proceed directly to MRI instead. 2
Do not delay appropriate imaging when symptoms persist, as this can lead to fracture progression from stress reaction to complete fracture. 2
Recognize that the proximal second metatarsal and fifth metatarsal base require particularly vigilant evaluation due to their high-risk status. 1