Pelvic Insufficiency Fracture Imaging
- Author: Wilfred CG Peh, MD, MHSc, MBBS, FRCP(Glasg), FRCP(Edin), FRCR; Chief Editor: Felix S Chew, MD, MBA, MEd more...
Insufficiency fracture is a subgroup of stress fracture. Unlike the other subtype (ie, fatigue fracture), insufficiency fracture is caused by normal or physiologic stress upon weakened bone. Loss of bone trabeculae decreases the bone's elastic resistance.[1, 2, 3, 4, 5, 6, 7] (See the images below.)
Awareness is increasing concerning the occurrence of these fractures among older persons. Sites frequently affected by insufficiency fractures are the thoracic vertebra, the tibia, the fibula, and the calcaneus.[8, 9, 10, 1, 11]
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.[12, 13] Bone scintigraphy and magnetic resonance imaging (MRI) are the imaging modalities of choice.[14, 15, 16, 17, 18, 19, 20, 21] MRI is sensitive for the detection of fractures, soft tissue edema, and marrow changes and may be better at demonstrating alternative diagnoses than bone scintigraphy or computed tomography (CT) scanning is.[22, 23, 24]
Cabarrus et al compared the sensitivities of CT scanning and MRI in detecting pelvic insufficiency fractures and found MRI to be substantially better in detecting such fractures. In patients undergoing both imaging modalities, 128 of 129 (99%) of fractures were detected by MRI, whereas only 89 of 129 fractures (69%) were detected by CT.
CT provides further definition of the fracture, especially if MRI is unavailable or bone scintigraphy is inconclusive.
Limitations of techniques
Bone scintigraphy is highly sensitive, but it relies on accurate interpretation of the uptake pattern, and atypical uptake patterns may be difficult to interpret. Abnormal uptake may persist for several months.
Failure to recognize insufficiency fractures of the pelvis may result in an incorrect diagnosis of malignancy. This may occur when areas of increased uptake are seen on bone scan or when marrow signal changes of the pelvis are observed on MRI, especially in patients who have undergone pelvic irradiation for gynecologic malignancies. Care should be taken to recognize the bone scan uptake pattern, particularly atypical patterns; on MRI, altered bone marrow signal in the sacrum is cause for suspicion.
CT scanning may not accurately detect fractures oriented transversely.
Radiographic findings depend on the site of the fracture. Parasymphyseal and pubic ramus fractures may have an aggressive appearance, depending on the stage of fracture maturity.
Findings include sclerosis, lytic fracture line, bone expansion, exuberant callus, and osteolysis, although a lytic fracture line or cortical break rarely is observed. The most common finding is a sclerotic band or line. (See the image below.)
The degree of confidence is low. Sacral fractures are difficult to detect because of osteoporosis, overlying bowel gas, and calcified vessels. Parasymphyseal and pubic ramus fractures often are mistaken for malignant lesions. Sacral, iliac, and supra-acetabular fractures often are difficult to detect.
On CT scans, sacral fractures typically are oriented vertically and are located parallel to the sacroiliac joints. (See the image below.)
A linear fracture line with surrounding sclerosis is observed, and pubic fractures are seen as a lytic fracture line often surrounded by callus. (See the images below.)
Typically, a soft tissue mass is absent, bone destruction is lacking, and adjacent fascial planes are preserved. CT also is useful for detecting large bony sacral defects, such as Tarlov cysts (see the image below) and for the diagnosis of coexisting malignant lesions.
CT findings may be definitive for the diagnosis of insufficiency fractures of the pelvis. CT is specific and is useful as an alternative to MRI or bone scintigraphy when radiographs are inconclusive.
Magnetic Resonance Imaging
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; such bands are parallel to the sacroiliac joints. (See the image below.)
On T2-weighted images, the fracture line may be seen if it is surrounded by adjacent marrow edema. (See the images below.)
MRI is highly sensitive and highly specific. However, it cannot be used in patients with pacemakers, which is a significant limitation in the elderly population.
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; the transverse limb of the H extends across the sacral body. (See the image below.)
Other sacral variant uptake patterns occur frequently and include the unilateral ala, incomplete H, and horizontal linear dot patterns. (See the images below.)
Iliac fractures are seen as linear areas of uptake, while 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. (See the image below.)
The degree of confidence may 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. For variant or incomplete patterns of uptake, the findings may be mistaken as signifying malignancy or other diseases. CT or MRI is useful in such cases.
Peh WCG, Davies AM. Stress fractures. Davies AM, Johnson K, Whitehouse RW. Imaging of the hip and bony pelvis. Berlin: Springer; 2006. 247-66.
Uezono H, Tsujino K, Moriki K, Nagano F, Ota Y, Sasaki R, et al. Pelvic insufficiency fracture after definitive radiotherapy for uterine cervical cancer: retrospective analysis of risk factors. J Radiat Res. 2013 May 17. [Medline].
Igdem S, Alço G, Ercan T, Barlan M, Ganiyusufoglu K, Unalan B, et al. Insufficiency fractures after pelvic radiotherapy in patients with prostate cancer. Int J Radiat Oncol Biol Phys. 2010 Jul 1. 77(3):818-23. [Medline].
Kim HJ, Boland PJ, Meredith DS, Lis E, Zhang Z, Shi W, et al. Fractures of the sacrum after chemoradiation for rectal carcinoma: incidence, risk factors, and radiographic evaluation. Int J Radiat Oncol Biol Phys. 2012 Nov 1. 84(3):694-9. [Medline].
Shih KK, Folkert MR, Kollmeier MA, Abu-Rustum NR, Sonoda Y, Leitao MM Jr, et al. Pelvic insufficiency fractures in patients with cervical and endometrial cancer treated with postoperative pelvic radiation. Gynecol Oncol. 2013 Mar. 128(3):540-3. [Medline].
O'Connor TJ, Cole PA. Pelvic Insufficiency Fractures. Geriatr Orthop Surg Rehabil. 2014 Dec. 5 (4):178-90. [Medline].
Davies AM, Bradley SA. Iliac insufficiency fractures. Br J Radiol. 1991 Apr. 64(760):305-9. [Medline].
Finiels H, Finiels PJ, Jacquot JM, Strubel D. [Fractures of the sacrum caused by bone insufficiency. Meta-analysis of 508 cases]. Presse Med. 1997 Nov 1. 26(33):1568-73. [Medline].
Gotis-Graham I, McGuigan L, Diamond T, et al. Sacral insufficiency fractures in the elderly. J Bone Joint Surg Br. 1994 Nov. 76(6):882-6. [Medline].
Weber M, Hasler P, Gerber H. Insufficiency fractures of the sacrum. Twenty cases and review of the literature. Spine. 1993 Dec. 18(16):2507-12. [Medline].
Peh WC, Khong PL, Yin Y, et al. Imaging of pelvic insufficiency fractures. Radiographics. 1996 Mar. 16(2):335-48. [Medline].
Campbell SE, Fajardo RS. Imaging of stress injuries of the pelvis. Semin Musculoskelet Radiol. 2008 Mar. 12(1):62-71. [Medline].
Blomlie V, Lien HH, Iversen T, et al. Radiation-induced insufficiency fractures of the sacrum: evaluation with MR imaging. Radiology. 1993 Jul. 188(1):241-4. [Medline].
Blomlie V, Rofstad EK, Talle K, et al. Incidence of radiation-induced insufficiency fractures of the female pelvis: evaluation with MR imaging. AJR Am J Roentgenol. 1996 Nov. 167(5):1205-10. [Medline].
Gibbon WW, Hession PR. Diseases of the pubis and pubic symphysis: MR imaging appearances. AJR Am J Roentgenol. 1997 Sep. 169(3):849-53. [Medline].
Grangier C, Garcia J, Howarth NR, et al. Role of MRI in the diagnosis of insufficiency fractures of the sacrum and acetabular roof. Skeletal Radiol. 1997 Sep. 26(9):517-24. [Medline].
Hosono M, Kobayashi H, Fujimoto R, et al. MR appearance of parasymphseal insufficiency fractures of the os pubis. Skeletal Radiol. 1997 Sep. 26(9):525-8. [Medline].
Mammone JF, Schweitzer ME. MRI of occult sacral insufficiency fractures following radiotherapy. Skeletal Radiol. 1995 Feb. 24(2):101-4. [Medline].
Cabarrus MC, Ambekar A, Lu Y, Link TM. MRI and CT of insufficiency fractures of the pelvis and the proximal femur. AJR Am J Roentgenol. 2008 Oct. 191(4):995-1001. [Medline].
Kwon JW, Huh SJ, Yoon YC, Choi SH, Jung JY, Oh D, et al. Pelvic bone complications after radiation therapy of uterine cervical cancer: evaluation with MRI. AJR Am J Roentgenol. 2008 Oct. 191(4):987-94. [Medline].
Al-faham Z, Rydberg JN, Oliver Wong CY. Use of SPECT/CT with 99mTc-MDP bone scintigraphy to diagnose sacral insufficiency fracture. J Nucl Med Technol. 2014 Sep. 42 (3):240-1. [Medline].
Ugurluer G, Akbas T, Arpaci T, Ozcan N, Serin M. Bone complications after pelvic radiation therapy: evaluation with MRI. J Med Imaging Radiat Oncol. 2014. 58 (3):334-40. [Medline].
Park SH, Kim JC, Lee JE, Park IK. Pelvic insufficiency fracture after radiotherapy in patients with cervical cancer in the era of PET/CT. Radiat Oncol J. 2011 Dec. 29 (4):269-76. [Medline].
Salavati A, Shah V, Wang ZJ, Yeh BM, Costouros NG, Coakley FV. F-18 FDG PET/CT findings in postradiation pelvic insufficiency fracture. Clin Imaging. 2011 Mar-Apr. 35(2):139-42. [Medline].