• Manaster BJ, Grossman JW, Dalinka MK, Daffner RH, DeSmet AA, El-Khoury GY, Kneeland JB, Morrison WB, Pavlov H, Rubin DA, Schneider R, Steinbach LS, Weissman BN, Haralson RH III, Expert Panel on Musculoskeletal Imaging. Stress/insufficiency fracture, including sacrum, excluding other vertebrae. [online publication]. Reston (VA): American College of Radiology (ACR); 2005. 7 p. [38 references]

This is the current release of the guideline.

This guideline updates a previous version: Manaster BJ, Dalinka MK, Alazraki N, Berquist TH, Daffner RH, DeSmet AA, el-Khoury GY, Goergen TG, Keats TE, Newberg A, Pavlov H, Haralson RH, McCabe JB, Sartoris D. Stress/insufficiency fractures (excluding vertebral). American College of Radiology. ACR Appropriateness Criteria. Radiology 2000 Jun;215(Suppl):265-72.

The appropriateness criteria are reviewed annually and updated by the panels as needed, depending on introduction of new and highly significant scientific evidence.

ACR Appropriateness Criteria®

Clinical Condition: Stress/Insufficiency Fracture, Including Sacrum, Excluding Other Vertebrae

Variant 1: Suspect stress/insufficiency fracture. First imaging modality.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 2: Suspect stress fracture in patient with need to know diagnosis, not hip or sacrum. Radiographs normal.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 3: Suspect stress fracture, not hip or sacrum. Radiographs normal. Bone scan positive and nonspecific.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 4: Suspect stress fracture in otherwise normal patient. Radiographs and bone scan or MRI normal.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 5: Clinical differential fracture versus metastasis in long bone. Radiographs normal, bone scan hot but nonspecific.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 6: Clinical differential insufficiency fracture versus metastasis in sacrum. Radiographs normal, bone scan hot but nonspecific.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 7: Suspect insufficiency fracture in sacrum/pelvis; elderly patient. Radiographs normal. Bone scan hot in linear pattern typical for fracture.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 8: Suspect insufficiency fracture in osteoporotic patient or patient on long-term steroid therapy, not hip. Radiographs normal.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 9: Suspect insufficiency fracture in osteoporotic patient or patient on long-term steroid therapy; not hip. Radiographs and bone scan (3-phase) normal at 48 hours.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Variant 10: Suspect subacute insufficiency fracture of hip in osteoporotic patient or patient on steroid therapy. Radiographs normal.

Note: Abbreviations used in the tables are listed at the end of the "Major Recommendations" field.

Although many stress/insufficiency fractures are self-limited because they heal with or without diagnosis, there is usually value to making the diagnosis. With continued activity, some stress fractures will progress to completion and require more invasive treatment or prolonged delay in return to activity. Also the differential diagnosis of stress/insufficiency fractures includes entities that would be treated significantly differently than stress fractures (osteoid osteoma or osteomyelitis in the younger patient, metastases in the older patient).

The clinical setting is often highly suggestive of the diagnosis of stress or insufficiency fractures. Such clinical settings include repetitive or new athletic activity for stress fractures, osteoporosis, radiated bone, or resumption of activity post-arthroplasty for insufficiency fractures. Specific athletic activities often result in specific sites of stress fracture. Insufficiency fractures also occur at fairly predictable sites. Thus, radiographic diagnosis using such pattern and site recognition is usually quite specific. Late radiographic findings may be quite typical in appearance as well: linear sclerosis, often perpendicular to the major trabecular lines. However, early radiographic findings are less specific (subtle periosteal reaction; "gray cortex sign") or even nonexistent. Radiographs in stress/insufficiency fractures may be negative initially in 60 to 82% and remain negative in 46 to 60%, depending on different specifications of bone scan gold standards. Additionally, radiographs are more likely to be negative initially in older or osteoporotic patients, insufficiency fractures, and the sooner that the patient is imaged after the symptoms begin. Additionally, radiographs may remain negative depending on the timing of re-imaging, the patient's metabolic bone status, and the type and location of the fracture. Thus, radiographs are specific but significantly insensitive. All references agree that radiographs should be the initial imaging modality; if the findings are conclusive, no further imaging need be performed.

Bone scans have long been accepted as extremely sensitive for detecting stress/insufficiency fractures, especially if single photon emission computed tomography (SPECT) is used. The objection to the studies quoting high accuracy for bone scan is that, in each, a positive bone scan is taken as the gold standard for detecting stress fractures and therefore sensitivity is 100%. However, depending on the staging criteria for bone scan pattern, the abnormalities may in fact be stress reactions rather than actual stress fractures. Nonetheless, it is clear that bone scans show stress fractures days to weeks earlier than radiographs in many instances, and differentiate between osseous and soft tissue injury as well. In some cases, the pattern of fracture is such that the diagnosis is secure, and no further imaging is required (for example, the H sign of sacral insufficiency fractures). However, in most cases bone scans lack specificity (with synovitis, arthritis, degenerative joint disease, stress reactions, and tumor appearing similar) and supplemental imaging may be necessary for conclusive diagnosis or to avoid false positives.

Because of the sensitivity of bone scan, 80% of all fractures show bone scan abnormality 24 hours post injury and 95% at 72 hours. A normal bone scan generally excludes the diagnosis of stress/insufficiency fracture, and the patient may return to normal activity. However, there are exceptions. Elderly or osteoporotic patients may have a delay in bone scan activity that may last several days. Patients using steroids may also have less sensitive bone scan results.

Because of the (often) nonspecificity of bone scan, the length of time necessary for the examination, and the frequency with which supplemental imaging is required, there is a growing body of literature suggesting that cross sectional imaging should supersede bone scan as the imaging of choice for stress fracture when the radiograph is negative. There are specific sites for which CT is particularly well-suited.

However, axial CT alone may have false negatives due to the constraint of the axial plane (in one study, half of stress fractures were adequately demonstrated on CT. Therefore, if CT is used to confirm stress fracture in a long bone, reformatting is necessary.

MRI is extremely sensitive and appears to demonstrate stress abnormalities as early as bone scan and with as much sensitivity. Short tau inversion recovery (STIR) sequences are emerging as the favored initial sequence for MRI screening. With a small field of view (FOV), STIR and/or T1 imaging will usually demonstrate a fracture line, surrounded by edema. In the absence of an actual stress fracture, stress reaction or muscle/tendon injuries are identified in the STIR sequence. Thus, a careful MRI may be as sensitive as a bone scan, but also considerably more specific. One study suggests that MRI exam of an osseous stress injury may contain prognostic as well as diagnostic information, with demonstration of an actual fracture line or cortical signal portending a longer healing time required.

The critical time for MRI becoming positive has not yet been established, although it seems that the edema pattern would be present within hours of the injury.

The choice of cross sectional imaging modality is not always clear cut. Some studies demonstrate that the MRI pattern is nonspecific and even confusing when only edema and not the fracture line is shown. This problem seems particularly severe in differentiating sacral or pelvic insufficiency fractures from metastases. Over reliance on nonspecific low-signal T1 and high-signal T2 MRI patterns leads to misdiagnosis of stress fractures as more aggressive lesions. In these cases, CT may be necessary to add specificity to the diagnosis.

MRI may, however, also demonstrate other reasons for occult pelvic pain, such as soft tissue abnormality or the supra-acetabular stress fractures recently described in some osteoporotic patients. Conversely, it is recommended that MRI for hip fractures also include the sacrum since stress fractures of the sacrum appear to be associated with stress-related hip pain in young adult patients.

MRI of long bones often shows the fracture line itself; in this case, MRI becomes not only sensitive but quite specific (fracture line seen in 11/14 stress fractures, 7/9 hip fractures, and 13/13 true positive hip fractures. The site where this phenomenon has been evaluated most completely is the hip, which may yield false negatives early on both radiographs and bone scan of the osteoporotic patient. A single T1 coronal MRI sequence yielded 100% accuracy in studies of 23 and 20 hips (8 and 13, respectively). Some experts recommend that a single T1 MRI sequence in the plane of interest be performed and initially evaluated when stress fracture is suspected. If a fracture line is clearly seen, the examination may be terminated. If the question persists after the single sequence, other MRI sequences may be used for more complete examination (e.g., STIR or FST2 sequences for even more sensitive evaluation of marrow edema, or nearby soft tissue injury). Intravenous contrast should not be required. In a younger patient population (e.g., military recruits), STIR imaging was found to have a higher accuracy than T1 imaging and may be chosen as the initial MRI sequence.

Another circumstance that deserves specific attention is the longitudinal stress fracture. Longitudinal stress fractures of the tibia have been emphasized in the literature recently. Up to 25% may appear normal on radiographs, but CT or MRI findings are characteristic. MRI is very sensitive to the bone marrow edema accompanying these longitudinal fractures, and may give a misleadingly aggressive appearance. Ultrasound has not been shown to be useful in diagnosing longitudinal stress fractures.

Abbreviations

• CT, computed tomography
• MRI, magnetic resonance imaging
• NUC, nuclear medicine

Algorithms were not developed from criteria guidelines.

The recommendations are based on analysis of the current literature and expert panel consensus.

• Manaster BJ, Grossman JW, Dalinka MK, Daffner RH, DeSmet AA, El-Khoury GY, Kneeland JB, Morrison WB, Pavlov H, Rubin DA, Schneider R, Steinbach LS, Weissman BN, Haralson RH III, Expert Panel on Musculoskeletal Imaging. Stress/insufficiency fracture, including sacrum, excluding other vertebrae. [online publication]. Reston (VA): American College of Radiology (ACR); 2005. 7 p. [38 references]

Not applicable: The guideline was not adapted from another source.

1995 (revised 2005)

American College of Radiology - Medical Specialty Society

The American College of Radiology (ACR) provided the funding and the resources for these ACR Appropriateness Criteria®.

Committee on Appropriateness Criteria, Expert Panel on Musculoskeletal Imaging

Panel Members: B.J. Manaster, MD, PhD; Jeffery W. Grossman, MD; Murray K. Dalinka, MD; Richard H. Daffner, MD; Arthur A. De Smet, MD; George Y. El-Khoury, MD; John B. Kneeland, MD; William B. Morrison, MD; Helene Pavlov, MD; David A. Rubin, MD; Robert Schneider, MD; Lynne S. Steinbach, MD; Barbara N. Weissman, MD; Robert H. Haralson III, MD

Not stated

This is the current release of the guideline.

This guideline updates a previous version: Manaster BJ, Dalinka MK, Alazraki N, Berquist TH, Daffner RH, DeSmet AA, el-Khoury GY, Goergen TG, Keats TE, Newberg A, Pavlov H, Haralson RH, McCabe JB, Sartoris D. Stress/insufficiency fractures (excluding vertebral). American College of Radiology. ACR Appropriateness Criteria. Radiology 2000 Jun;215(Suppl):265-72.

The appropriateness criteria are reviewed annually and updated by the panels as needed, depending on introduction of new and highly significant scientific evidence.

None available

This summary was completed by ECRI on May 6, 2001. The information was verified by the guideline developer as of June 29, 2001. This summary was updated by ECRI on March 28, 2006.