When to Order Imaging for Stress (Fatigue/Insufficiency) Fracture, Including Sacrum, Excluding Other Vertebrae: ACR Appropriateness Decoded

A collegiate runner presents with insidious-onset, localized pain in her shin, worsened by activity. Your clinical suspicion for a stress fracture is high, but initial radiographs are negative. Do you order an MRI now, repeat the x-ray in two weeks, or consider a bone scan? For a patient with known osteoporosis and new hip pain, the stakes are even higher. Choosing the right imaging pathway is critical for accurate diagnosis, preventing fracture completion, and guiding management. This article decodes the American College of Radiology (ACR) Appropriateness Criteria for suspected stress, fatigue, or insufficiency fractures, providing a clear, evidence-based framework for your next imaging order.

What Does ACR Stress (Fatigue/Insufficiency) Fracture, Including Sacrum, Excluding Other Vertebrae Cover?

This ACR guideline focuses on the diagnostic imaging of suspected stress injuries to bone in adults and children. It specifically addresses both fatigue fractures, which result from abnormal stress on normal bone (e.g., in athletes), and insufficiency fractures, which occur when normal stress is applied to abnormal, weakened bone (e.g., in patients with osteoporosis or metabolic bone disease). The scope includes all non-vertebral locations, with a particular emphasis on common sites like the tibia, metatarsals, femur, pelvis, and sacrum.

This document does not cover acute traumatic fractures, pathologic fractures due to tumors, or stress fractures of the vertebral column (except for the sacrum). It is designed for clinicians evaluating patients with a subacute presentation of focal bone pain related to repetitive stress or underlying bone fragility, helping to navigate the imaging workup from initial suspicion through post-procedural assessment.

What Imaging Should I Order for Stress (Fatigue/Insufficiency) Fracture, Including Sacrum, Excluding Other Vertebrae? Recommendations by Clinical Scenario

The optimal imaging strategy for a suspected stress fracture depends on the initial findings and specific clinical context. The ACR provides clear, scenario-based recommendations to guide decision-making.

For an adult with a suspected stress fracture (excluding vertebrae) on initial imaging, the ACR finds that Radiography of the area of interest is Usually Appropriate. Radiographs are inexpensive, widely available, and can often provide a definitive diagnosis, although they have low sensitivity in the early stages (first 2-3 weeks) before periosteal reaction or a fracture line becomes visible.

When initial radiographs are negative or indeterminate in an adult, the next step is crucial. The ACR states that MRI of the area of interest without IV contrast is Usually Appropriate. MRI is highly sensitive and specific for detecting the bone marrow edema that precedes visible radiographic changes. Other options are considered less appropriate but may have a role. A repeat Radiography in 10-14 days, a Bone scan with SPECT or SPECT/CT, or a CT of the area of interest without IV contrast are all rated as May be appropriate. CT can be particularly useful for delineating cortical breaks. For more details on CT protocols, see our guide on CT Brain Without Contrast.

In special populations, the recommendations are more specific. For a pregnant patient with suspected pelvis, hip, or sacrum stress fracture and negative radiographs, radiation-free imaging is paramount. MRI of the area of interest without IV contrast is Usually Appropriate, while modalities involving ionizing radiation, like repeat radiographs, CT, or bone scans, are Usually Not Appropriate.

For patients at high risk for fracture completion (e.g., osteoporosis on bisphosphonate therapy) or when there is an immediate “need-to-know” after negative radiographs, a rapid and sensitive diagnosis is required. Again, MRI of the area of interest without IV contrast is Usually Appropriate. A CT without IV contrast May be appropriate to assess the cortex, but a repeat radiograph is deemed Usually Not Appropriate due to the delay in diagnosis.

Similarly, for a suspected subchondral stress fracture at an extremity joint with negative radiographs, MRI without IV contrast is Usually Appropriate to assess for marrow edema, subchondral collapse, and potential osteonecrosis.

Finally, if a stress fracture is already positive on radiographs but further detail is needed for surgical planning or to assess for complications like delayed healing, both MRI without IV contrast and CT without IV contrast are considered Usually Appropriate. MRI excels at evaluating soft tissues and marrow viability, while CT provides superior bony detail of the fracture pattern.

ACR Imaging Recommendations Table

Adult vs. Pediatric Stress (Fatigue/Insufficiency) Fracture, Including Sacrum, Excluding Other Vertebrae Imaging: Radiation Dose Tradeoffs

While the imaging algorithms for suspected stress fractures are similar between adults and children, radiation safety is a heightened concern in the pediatric population. Children’s tissues are more radiosensitive, and their longer life expectancy provides more time for potential long-term effects of radiation exposure to manifest. This is reflected in the ACR’s Relative Radiation Level (RRL) designations, which often include a specific pediatric notation `[ped]`.

For modalities involving ionizing radiation, such as bone scans, the pediatric RRL is often in a higher category than the adult equivalent. For example, a whole-body bone scan with SPECT/CT carries an RRL of ☢ ☢ ☢ (1-10 mSv) for adults but ☢ ☢ ☢ ☢ (3-10 mSv [ped]) for children, reflecting the greater effective dose relative to body size. This underscores the importance of the As Low As Reasonably Achievable (ALARA) principle. Consequently, non-ionizing modalities like MRI and ultrasound (where clinically appropriate) are strongly preferred in children, especially for follow-up imaging, to minimize cumulative radiation dose.

Imaging Protocol Details for Stress (Fatigue/Insufficiency) Fracture, Including Sacrum, Excluding Other Vertebrae

Once you’ve decided on the right study, the protocol matters. A well-designed protocol ensures diagnostic quality while optimizing for safety and efficiency. Our protocol guides cover technique, contrast, and reading principles for the studies recommended above. For example, understanding the specific sequences for a non-contrast MRI of the tibia or the slice thickness for a CT of the foot can make a significant difference in diagnostic confidence.

• CT Brain Without Contrast

Tools to Help You Order the Right Study

Navigating imaging guidelines and protocols can be complex. GigHz offers a suite of tools designed to support evidence-based clinical decision-making at the point of care.

For clinical scenarios beyond stress fractures, the Imaging Appropriateness Selector provides a comprehensive, searchable interface to the full library of ACR guidelines, helping you find the right test for any indication.

To ensure the selected study is performed correctly, the Imaging Protocol Library offers detailed, modality-specific protocols used at leading academic centers. This resource helps standardize care and improve diagnostic yield.

When ordering studies that involve ionizing radiation, communicating the risks and benefits to patients is essential. The Radiation Dose Calculator helps estimate cumulative radiation exposure and provides clear, patient-friendly explanations of dose levels.

Why is MRI without contrast the best test after negative X-rays for a suspected stress fracture?

MRI is highly sensitive for detecting stress-related changes in bone far earlier than other imaging modalities. It can visualize bone marrow edema, the physiological precursor to a stress fracture, within 24-48 hours of symptom onset. This allows for a definitive diagnosis weeks before a fracture line or periosteal reaction would become visible on radiographs. Intravenous contrast is generally not needed because the high fluid signal of marrow edema is readily apparent on non-contrast sequences like STIR (Short-TI Inversion Recovery) or fat-suppressed T2-weighted images.

What is the difference between a fatigue fracture and an insufficiency fracture?

Both are types of stress fractures, but they differ in the underlying bone health and the nature of the stress applied. A fatigue fracture occurs when abnormal, repetitive, and excessive stress is placed on normal, healthy bone. This is common in athletes, military recruits, or individuals starting a new, strenuous exercise regimen. An insufficiency fracture occurs when normal, physiological stress is applied to bone that has been weakened by an underlying condition, such as osteoporosis, osteomalacia, radiation therapy, or metabolic bone disease.

When is a bone scan (scintigraphy) still a good option for suspected stress fractures?

While MRI is generally preferred for its high sensitivity and lack of ionizing radiation, a technetium-99m MDP bone scan can still be useful in specific situations. It is an excellent tool for screening the entire skeleton when a patient has vague or multiple sites of pain and the clinical localization is uncertain. It may also be used when a patient has a contraindication to MRI, such as an incompatible implanted device. The addition of SPECT or SPECT/CT can improve the anatomic localization of abnormal radiotracer uptake.

Why are repeat radiographs only “May be appropriate” 10-14 days later?

Repeating radiographs after a 10-14 day interval can sometimes reveal evidence of healing, such as a visible fracture line, sclerosis, or periosteal reaction, that was not present on the initial images. However, this approach is rated as only “May be appropriate” because it introduces a diagnostic delay. In many clinical scenarios, particularly for high-performance athletes or patients at risk of fracture completion, waiting two weeks for a diagnosis is not ideal. MRI provides a much faster and more sensitive answer, allowing for immediate and appropriate management.

Are there special considerations for sacral stress fractures?

Yes. Sacral stress fractures, particularly insufficiency fractures in elderly patients with osteoporosis, are notoriously difficult to diagnose on radiographs due to the complex anatomy and overlying bowel gas. Clinical suspicion should be high in at-risk patients presenting with low back, buttock, or groin pain. Because of the low sensitivity of initial radiographs, cross-sectional imaging with MRI or CT is almost always required for diagnosis. MRI is the preferred modality to confirm the diagnosis and assess the extent of the fracture and any associated soft tissue injury.

Frequently Asked Questions

Why is MRI without contrast the best test after negative X-rays for a suspected stress fracture?

MRI is highly sensitive for detecting stress-related changes in bone far earlier than other imaging modalities. It can visualize bone marrow edema, the physiological precursor to a stress fracture, within 24-48 hours of symptom onset. This allows for a definitive diagnosis weeks before a fracture line or periosteal reaction would become visible on radiographs. Intravenous contrast is generally not needed because the high fluid signal of marrow edema is readily apparent on non-contrast sequences like STIR (Short-TI Inversion Recovery) or fat-suppressed T2-weighted images.

What is the difference between a fatigue fracture and an insufficiency fracture?

Both are types of stress fractures, but they differ in the underlying bone health and the nature of the stress applied. A fatigue fracture occurs when abnormal, repetitive, and excessive stress is placed on normal, healthy bone. This is common in athletes, military recruits, or individuals starting a new, strenuous exercise regimen. An insufficiency fracture occurs when normal, physiological stress is applied to bone that has been weakened by an underlying condition, such as osteoporosis, osteomalacia, radiation therapy, or metabolic bone disease.

When is a bone scan (scintigraphy) still a good option for suspected stress fractures?

While MRI is generally preferred for its high sensitivity and lack of ionizing radiation, a technetium-99m MDP bone scan can still be useful in specific situations. It is an excellent tool for screening the entire skeleton when a patient has vague or multiple sites of pain and the clinical localization is uncertain. It may also be used when a patient has a contraindication to MRI, such as an incompatible implanted device. The addition of SPECT or SPECT/CT can improve the anatomic localization of abnormal radiotracer uptake.

Why are repeat radiographs only “May be appropriate” 10-14 days later?

Repeating radiographs after a 10-14 day interval can sometimes reveal evidence of healing, such as a visible fracture line, sclerosis, or periosteal reaction, that was not present on the initial images. However, this approach is rated as only “May be appropriate” because it introduces a diagnostic delay. In many clinical scenarios, particularly for high-performance athletes or patients at risk of fracture completion, waiting two weeks for a diagnosis is not ideal. MRI provides a much faster and more sensitive answer, allowing for immediate and appropriate management.

Are there special considerations for sacral stress fractures?

Yes. Sacral stress fractures, particularly insufficiency fractures in elderly patients with osteoporosis, are notoriously difficult to diagnose on radiographs due to the complex anatomy and overlying bowel gas. Clinical suspicion should be high in at-risk patients presenting with low back, buttock, or groin pain. Because of the low sensitivity of initial radiographs, cross-sectional imaging with MRI or CT is almost always required for diagnosis. MRI is the preferred modality to confirm the diagnosis and assess the extent of the fracture and any associated soft tissue injury.

Reviewed by Pouyan Golshani, MD, Interventional Radiologist — May 26, 2026