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Radiology > MUSCULOSKELETAL
Pelvis, Insufficiency Fractures
Article Last Updated: May 5, 2005
AUTHOR AND EDITOR INFORMATION
Section 1 of 10  
Author: Wilfred CG Peh, MD, MBBS, FRCP(Glasg), FRCP(Edin), FRCR, MHSM, Clinical Professor, Faculty of Medicine, National University of Singapore; Senior Consultant Radiologist, Programme Office, Singapore Health Services
Wilfred CG Peh is a member of the following medical societies: American Roentgen Ray Society, British Institute of Radiology, International Skeletal Society, Radiological Society of North America, Royal College of Physicians, and Royal College of Radiologists
Editors: Leon Lenchik, MD, Director, Densitometry Minifellowship, Assistant Professor, Department of Radiology, Wake Forest University Medical Center; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; William R Reinus, MD, MBA, FACR, Professor of Radiology, Temple University; Chief of Musculoskeletal and Trauma Radiology, Vice Chair, Department of Radiology, Temple University Hospital; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington
Author and Editor Disclosure
Synonyms and related keywords:
Background
Insufficiency fracture is a subgroup of stress fracture. Unlike the other subtype (ie, fatigue fracture), insufficiency fracture is caused by the effect of normal or physiologic stress upon weakened bone. Loss of bone trabeculae decreases the bone's elastic resistance. Awareness is increasing concerning the occurrence of these fractures among older persons. Sites frequently affected by insufficiency fractures are the thoracic vertebra, tibia, fibula, and calcaneus.
Pathophysiology
A fracture represents the end result of the spectrum of a bone's response to an increasing level of stress. According to Wolff's law, stress that occurs beyond the bone's elastic range causes persistent plastic deformity as a result of microfractures. In this situation, osteoclastic resorption exceeds osteoblastic activity. A strong association exists between fractures of the sacrum and those of the pubic bone (parasymphysis, pubic rami). Pubic fractures may develop as a result of increased anterior arch strain secondary to initial failure of the posterior arch (sacrum).
Frequency
United States
Insufficiency fractures are estimated to occur in 1% of women older than 55 years.
International
Insufficiency fractures are estimated to occur in 1-5% of persons, depending on the referral population.
Mortality/Morbidity
In most patients, insufficiency fractures resolve or improve significantly with conservative management.
Race
No racial predilection is reported. Fractures have been described in Americans, Europeans, Australians, Japanese, and Chinese, among others.
Sex
Women predominantly are affected.
Age
Most patients with insufficiency fractures are older than 60 years. In various studies, the mean age ranges from 62-74 years.
Clinical Details
- History: Typically, patients present with groin, low back, or buttock pain. One quarter of patients have multiple sites of pain. In most patients, pain is severe enough to render the patient nonambulatory. Usually, patients present with either no history of trauma or a history of low impact trauma.
- Physical examination: Usually, signs of insufficiency fracture are nonspecific or nonexistent. The most common physical signs are low back or groin tenderness and restricted hip movement. Neurologic deficit is rare. In patients who have undergone pelvic irradiation, local soft-tissue complications, especially affecting the rectum, frequently are encountered. Typically, a discordance exists between the severe symptoms and the mild or absent physical signs.
- Causes: The most common cause of insufficiency fracture is postmenopausal osteoporosis. Other important causes are senile osteoporosis, pelvic irradiation, corticosteroid therapy, and rheumatoid arthritis. Also reported are total hip replacement, Tarlov cyst, Paget disease, fibrous dysplasia, scurvy, osteopetrosis, primary biliary cirrhosis, lung transplantation, tabes dorsalis, vitamin D deficiency, and fluoride therapy.
- Treatment: Management is conservative and consists initially of bed rest, reduced weight bearing, and simple analgesics for pain relief. Graded exercises are started once symptomatic improvement is observed. Prognosis is good; healing is expected within 4 months. Imaging-guided sacroplasty has also been described (see Intervention).
Preferred Examination
Clinical assessment does not provide a definitive diagnosis of insufficiency fracture. Imaging has an important role in the detection and diagnosis of insufficiency fractures of the pelvis.
Bone scintigraphy and MR imaging are the imaging modalities of choice.
CT scan provides further definition of the fracture, especially if MRI is unavailable or bone scintigraphy is inconclusive.
Limitations of Techniques
- Bone scintigraphy: Bone scintigraphy relies on accurate interpretation of the uptake pattern. Bone scintigraphy is highly sensitive; however, atypical uptake patterns may be difficult to interpret. Abnormal uptake may persist for several months.
- CT scan: CT scan may not accurately detect fractures oriented transversely.
- MRI: MRI is sensitive for detection of fractures, soft-tissue edema, and marrow changes. MRI may be better at demonstrating alternative diagnoses than bone scintigraphy or CT scan.
Bone Metastases
Findings
Radiographic findings depend on the site of the fracture.
- Parasymphyseal and pubic ramus fractures may have an aggressive appearance that depends on the stage of fracture maturity.
- Findings include sclerosis, lytic fracture line, bone expansion, exuberant callus, and osteolysis (Image 1).
- The most common finding is a sclerotic band or line.
- A lytic fracture line or cortical break rarely is observed.
Degree of Confidence
The degree of confidence is low. Sacral fractures are difficult to detect because of osteoporosis, overlying bowel gas, and calcified vessels.
False Positives/Negatives
Parasymphyseal and pubic ramus fractures often are mistaken for malignant lesions.
Sacral, iliac, and supra-acetabular fractures often are difficult to detect.
Findings
- On CT scan, sacral fractures typically are oriented vertically and located parallel to the sacroiliac joints (Image 2).
- A linear fracture line with surrounding sclerosis is observed (Image 3).
- Pubic fractures are seen as a lytic fracture line often surrounded by callus (Image 4).
- Typically, a soft-tissue mass is absent, bone destruction is lacking, and adjacent fascial planes are preserved.
- CT scan also is useful for detecting large bony sacral defects such as Tarlov cysts (Image 5) and for the diagnosis of coexisting malignant lesions.
Degree of Confidence
CT scan can be definitive for the diagnosis of insufficiency fractures of the pelvis. CT scan is specific and useful as an alternative to MRI or bone scintigraphy when radiographs are inconclusive.
Findings
- MRI shows decreased signal on T1-weighted images and increased signal on T2-weighted images.
- In the sacrum, signal changes are seen as linear bands within the sacral ala and body and are parallel to the sacroiliac joints (Image 6).
- On T2-weighted images, the fracture line may be seen if it is surrounded by adjacent marrow edema (Images 7-8).
Degree of Confidence
MRI is highly sensitive and highly specific. MRI cannot be used in patients with pacemakers, a significant limitation in the elderly population.
Findings
- In nuclear studies, the typical H-shaped or butterfly pattern of uptake in the sacrum is diagnostic of insufficiency fracture. The vertical limbs of the H lie within the sacral ala, parallel to the sacroiliac joints, while the transverse limb of the H extends across the sacral body (Image 9).
- Other sacral variant uptake patterns occur frequently and include the unilateral ala, incomplete H (Image 10), and horizontal linear dot (Image 11) patterns.
- Iliac fractures are seen as linear areas of uptake.
- Pubic and supra-acetabular fractures produce areas of linear or focal uptake.
- Concomitant findings of 2 or more areas of uptake in the sacrum and at another pelvic site are considered diagnostic of insufficiency fractures of the pelvis (Image 12).
Degree of Confidence
The degree of confidence can be high. Nuclear studies are highly sensitive and highly specific when a typical pattern of sacral uptake or concomitant sacral and pubic uptake is observed. If a typical pattern of abnormality is not present, the bone scan is much less specific.
False Positives/Negatives
For variant or incomplete patterns of uptake, the findings may be mistaken for malignancy and other diseases. CT scan or MR imaging is useful in such occurrences.
Sacroplasty has been described for treatment of sacral insufficiency fractures. Sacroplasty is a procedure in which polymethylacrylate, a quick-setting bone cement, is injected into the fracture. This technique appears to be useful in providing symptomatic relief to affected patients.
Medical/Legal Pitfalls
- Failure to recognize insufficiency fractures of the pelvis may result in an incorrect diagnosis of malignancy. This may occur when increased areas of increased uptake on bone scan or marrow signal changes on MRI of the pelvis are observed, especially in patients who have undergone pelvic irradiation for gynecologic malignancies. Take care to recognize the bone scan uptake pattern, particularly atypical patterns, and be suspicious of altered bone marrow signal in the sacrum on MRI.
| Media file 1:
Anteroposterior radiograph of the pelvis demonstrates areas of sclerosis in both sacral alae. Parasymphyseal fractures oriented vertically are seen as linear areas of osteolysis and adjacent sclerosis (arrows). Insufficiency fractures subsequently were confirmed on bone scans and CT. |
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Media type: X-RAY
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| Media file 2:
Axial CT of the sacrum reveals fractures (arrows) in both sacral alae. Note the sclerosis of the adjacent bone. |
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Media type: CT
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| Media file 3:
Coronal CT of the sacrum demonstrates fractures (arrows) in both sacral alae. These fractures are oriented parallel to the sacroiliac joints. Note the prominent adjacent sclerosis. |
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Media type: CT
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| Media file 4:
Axial CT of the pubis reveals insufficiency fractures (arrows) in both parasymphyseal regions. Total hip replacement is an additional predisposing causative factor. |
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Media type: CT
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| Media file 5:
Axial CT of the sacrum reveals 2 large Tarlov cysts (arrowheads) in the sacrum. The sacral insufficiency fractures produce anterior cortical breaks (arrows). |
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Media type: CT
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| Media file 6:
Axial T1-weighted MRI of the sacrum demonstrates decreased signal in the body and both alae of the sacrum. Bilateral sacral insufficiency fractures were confirmed by CT. |
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Media type: MRI
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| Media file 7:
Axial T2-weighted MRI of the sacrum (same patient as Image 6) demonstrates linear bands of decreased signal in both sacral alae, parallel to the sacroiliac joints. Traces of fluid are observed within the fractures (small arrows). Adjacent edema is seen as areas of increased signal. Bilateral sacral insufficiency fractures were confirmed subsequently by CT. |
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Media type: MRI
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| Media file 8:
Axial CT of the sacrum (same patient as Image 6) reveals insufficiency fractures in both sacral alae and the sacral body (arrows). |
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Media type: CT
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| Media file 9:
Bone scan of the pelvis reveals a butterfly-shaped area of uptake in the sacrum (arrows). Focal uptake in the pubis (arrowhead) corresponds to an associated parasymphyseal insufficiency fracture. |
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Media type: X-RAY
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| Media file 10:
Bone scan of the pelvis reveals an incomplete (or partial) H- shaped area of uptake in the sacrum (arrows). Bilateral parasymphyseal insufficiency fractures (arrowheads) are present. |
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Media type: X-RAY
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| Media file 11:
Bone scan of the pelvis demonstrates a horizontal linear dot pattern of uptake in the sacrum. |
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Media type: X-RAY
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| Media file 12:
Bone scan of the pelvis demonstrates a linear area of uptake in the pubis (arrowheads). A concomitant H-shaped insufficiency fracture of the sacrum is observed. |
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Media type: X-RAY
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Pelvis, Insufficiency Fractures excerpt Article Last Updated: May 5, 2005
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