What is the best approach to evaluate and manage suspected stress fractures in the feet and legs?

Evaluation of Suspected Stress Fractures in Feet and Legs

Start with plain radiographs in all cases, and if negative but clinical suspicion remains high, proceed immediately to MRI without contrast—this is the definitive diagnostic pathway recommended by the American College of Radiology. 1, 2, 3

Initial Imaging: Plain Radiographs

• Always obtain plain radiographs first as the initial imaging study for any suspected stress fracture, despite their low sensitivity of only 15-35% in early stages. 1
• Radiographs are highly specific—if findings are conclusive (showing linear sclerosis perpendicular to trabeculae, periosteal reaction, or patchy endosteal sclerosis), no further imaging is needed. 1, 3
• Early radiographic findings are often subtle or absent, including nonspecific periosteal reaction or the "gray cortex sign." 1
• Radiographs are particularly insensitive in areas with overlapping soft tissue and in elderly patients with osteoporosis. 1

Second-Line Imaging: MRI Without Contrast

When radiographs are negative but clinical suspicion persists, MRI without IV contrast is the preferred next study—it outperforms all other modalities in both sensitivity and specificity. 1, 2, 3

Why MRI is Superior:

• MRI demonstrates stress abnormalities as early as bone scintigraphy but with considerably greater specificity (versus bone scan's nonspecific uptake patterns). 1, 2
• Fluid-sensitive sequences (STIR and T1-weighted imaging) show the fracture line surrounded by edema with high diagnostic accuracy. 1
• MRI provides both diagnostic AND prognostic information, helping predict return-to-activity timelines. 1, 4
• No ionizing radiation exposure, making it ideal for repeated imaging if needed. 2, 3
• Can identify alternative diagnoses including soft tissue injuries, tendinopathy, or other causes of pain. 2, 3
• IV contrast is not needed and provides no additional diagnostic value. 1, 3

Alternative to MRI: Follow-Up Radiographs

• If MRI is unavailable or contraindicated, repeat radiographs in 10-14 days achieve improved sensitivity of 30-70% due to visible bone reaction and callus formation. 1
• This approach is less sensitive than MRI but represents a reasonable alternative when advanced imaging is not accessible. 1, 5

High-Risk Locations Requiring Urgent MRI

Certain anatomic locations are considered high-risk and warrant immediate MRI to prevent complications like displacement, nonunion, or avascular necrosis: 1, 3, 6

• Femoral neck (especially lateral "tension-type") and femoral head—prone to displacement and avascular necrosis if not recognized promptly. 1
• Anterior tibial cortex—watershed blood supply predisposes to poor healing. 6, 7
• Navicular bone—watershed blood supply area. 6, 7
• Medial malleolus. 3, 6
• Base of fifth metatarsal and proximal second metatarsal. 3, 6
• Talus and hallux sesamoids. 3, 6, 7
• Patella. 3

For these high-risk locations, do not wait for follow-up radiographs—proceed directly to MRI after initial negative X-rays. 2, 3

Imaging Modalities to Avoid or Use Sparingly

CT Scanning:

• CT is NOT a first- or second-line tool for stress fracture evaluation. 1
• CT has high specificity (88-98%) but lower sensitivity than MRI or bone scintigraphy. 1
• Reserve CT only for when MRI results are equivocal, particularly in the pelvis or sacrum. 1
• CT with IV contrast provides no additional benefit over non-contrast CT. 1, 3

Bone Scintigraphy:

• While bone scan was historically the reference standard, MRI has superseded it as the preferred advanced imaging modality. 1, 5
• Bone scintigraphy is nonspecific and frequently requires supplemental imaging. 1
• Consider only if MRI is contraindicated or unavailable. 1, 5

Ultrasound:

• Ultrasound has limited utility as it cannot evaluate subcortical bone and trabecular stress fractures may be missed. 1
• Findings (periosteal thickening, cortical irregularity, hyperemia) are nonspecific and can mimic osteomyelitis or neoplasm. 1
• Emerging evidence suggests some utility in extremity stress fractures, but it remains operator-dependent. 1

Common Pitfalls to Avoid

• Never rely solely on negative initial radiographs when clinical suspicion is high—this leads to delayed diagnosis and fracture progression. 2, 3
• Do not delay MRI for high-risk anatomic locations—waiting for follow-up radiographs can result in displacement, nonunion, or need for surgical intervention. 2, 3
• Avoid ordering MRI or CT with IV contrast for stress fracture evaluation—it adds no diagnostic value. 1, 3
• Be aware that detection is limited in areas with overlapping soft tissue or bowel gas, making advanced imaging particularly important in these regions. 1

Clinical Context Recognition

• Fatigue fractures occur in athletes with normal bone from repetitive loading—common sites include proximal femur and tibia in runners, tarsal navicular in basketball players. 1
• Insufficiency fractures occur in elderly patients with osteoporosis from normal loading on abnormal bone—typically around the pelvis. 8
• Medial tibial stress syndrome (shin splints) can be distinguished by diffuse tenderness along the posteromedial tibial shaft without focal edema. 5