MRI and CT of Insufficiency Fractures of the Pelvis and the Proximal Femur

AJR 2008;191:995-1001R4

Stress fractureFatigue fractureNormal bone is subjected to repetitive stressesCommon site : Metatarsal, calcaneus, tibial shaft, femoral neck, pubic ramus Insufficiency fractureNormal stress applied to Abnormal boneRisk factors : Osteoporosis (most often afflicting elderly women), chronic steroid use, radiation therapy to the pelvis, RA

PurposeTo compare the sensitivity of CT and MRI in detecting insufficiency fractures; to analyze the typical location, morphology, and combinations thereof in these fractures.

SubjectsJanuary 1997~ June 2007MRI and CT studies with a reported diagnosis of pelvic, sacral, or proximal femur insufficiency fracturesPts who had clinical history, imaging findings, cross-sectional f/u studies consistent with the diagnosis of an insufficiency fracture. - absence of metastatic disease to pelvic bones, other bone marrow disease, metabolic disease

307 fractures in 145 consecutive patients ( 41 men, 104 women; average age, 65.9 17.7 years) Materials and Methods

MRI1.5 T (Signa, GE Healthcare)All 145 subjectsPelvis MRI in 125 pts coronal T1-wieghted fast spin-echo (TR/TE : 600msec/minimum) coronal T1-wieghted STIR (3000/68; inversion time, 150msec) axial T1-weighted (600msec/minimum) fat-saturated T2-weighted fast spin-echo (3000/68) section thickness : 4mm, matrix size : 192x192 mm, FOV : 32-36cmLumbar spine including sacrum in 20 pts sagittal and axial T1-wieghted (TR/TE : 500-600msec/minimum) fat-saturated T2-weighted fast spin-echo (TR/TE : 3500-4000msec/60-90) coronal T1-weighted fast spin-echo (500msec/minimum) section thickness : 4mm, matrix size : 256x192 mm, FOV : 16-24cm

Materials and Methods

CT MDCT 8-, 16-, 64-MDCT (Lightspeed series, GE Healthcare)64/145 subjectsEntire pelvis slice thickness : 1.25-7mm, 125 kVp, 150-300mAMaterials and Methods

Image AnalysisTwo radiologists, by consensusAnalyze MRI and CT separately in random order

Standard of referenceclinical history, imaging datas, imaging follow up

Materials and Methods

Image AnalysisCT and MRI - presence, number and location of fracture - fracture lines - presence of soft tissue lesions

MRI : presence of BM edema pattern CT: focal sclerotic areas, adjacent radiolucency

Materials and Methods

ResultsFracture Locations andNumbers in All 145 Subjects

CT Versus MRIDetection of pelvic insufficiency fracturesAmong 64 pts, 129 fracturesMRI : 128 fractures in 63 pts (sensitivity, 98%, 128/129) CT: 89 fractures in 34 pts (sensitivity, 53%, 89/129)

MRI > CT (p < 0.01)Results

CT Versus MRIFracture detection rates and locations Results

M/53, history of esophageal cancer, chemotherapy, osteoporotic BMD on DXAResults

CT Versus MRIDepiction of fracture morphology 32/88 (36.4%, MRI>CT), 26/88 (29.5%, CT>MRI)Detection of fracture lines122/128 on MRI (95.3%), 78/89 on CT (89.7%)Detection of soft tissue abnormalities103 lesions in 57 of 64 pts102/103 on MRI (99%), 13/103 on CT (12.6%)

Results

Overall characteristicsMore than one fracture in 102 of 145 pts (70.3%)Results

M/18 with ulcerative colitis and primary sclerosing cholangitisResultsFST2

Overall characteristics on MRIPresence of BM edema pattern and fracture lines 267/307 (87%), BM edmea with fracture line 21/307 cases (6.8%),only fracture lines 19/307 (6.2%) cases, only BM edema

Soft tissue abnormalities Common in femoral, acetabular, pubic fracturesLess in sacral fractures

ResultsAssociated clinical findingAssociated with Prior malignancy: 63/145 (34.4%) Rheumatologic disease : 6/145(4.1%) Corticosteroid tx : 18/145(12.4%)

ConclusionMust be familiar with these findings, their location, morphology, and associated clinical features(malignancy)

MRI is superior technique compared with CT and should be imaging technique of choice

Multiple pelvic insufficiency fractures are frequently found (pubic or acetabular) fracture Careful search for concomitant fractures

Was based on the following scoresFinal decisions regarding the score were reached by consensusADC maps of lung nodules were not available because of their susceptibility artifacts.The definition of a standard of reference for astudy in which no surgical procedures or pathologicexaminations are performed is challenging. In ourstudy, we used all available imaging data andimaging follow-up, together with the clinical history,as a standard of reference. The diagnosis of aninsufficiency fracture was supported by CT followupstudies that showed fracture lines more clearlyand areas of increased sclerosis or periosteal boneformation; and by MRI follow-up studies that showedpersistent or decreasing areas of bone marrow edemaor better visualization of fracture lines.Only one patient (2%)had a fracture that was detected on CT but noton MRI, 33 patients (52%) had fractures thatwere detected on both CT and MRI, and 30patients (47%) had fractures detected on MRIbut not on CTCT MR 64 129 fracture CT MR Only one patient (2%)had a fracture that was detected on CT but noton MRI, 33 patients (52%) had fractures thatwere detected on both CT and MRI, and 30patients (47%) had fractures detected on MRIbut not on CT*Fig. 170-year-old man with lower back pain and history of esophageal cancer, chemotherapy, andosteoporotic bone mineral density on dual x-ray absorptiometry.AC, Axial T1-weighted (A), axial fat-saturated T2-weighted (B), and sagittal fat-saturated T2-weighted (C) MRimages show bilateral sacral fractures (arrows), with mild displacement at S2 visualized on sagittal image (C).D, CT image obtained within 2 weeks after MRI using standard pelvis protocol (contrast-enhanced; slicethickness, 5 mm) does not show these fractures.*88 fracture CT MR .

Fig. 418-year-old man with ulcerative colitis and primary sclerosing cholangitis who is scheduled to undergoliver transplantation.A and B, Coronal STIR (A) and T1-weighted fast spin-echo (B) sequences show bilateral femoral neck fractures(small arrows) and focal signal abnormalities in right femoral head (large arrow, A), which are nonspecific andcould indicate either insufficiency reaction or ischemic changes.C and D, Axial fat-saturated T2-weighted fast spin-echo sequences show additional fractures at bilateralischium (arrows). In D, signal changes at bilateral femoral neck are also shown, reflecting neck fractures.Note relatively low signal of bone marrow on T1-weighted fast spin-echo image (B), which is likely reflectingactivated hematopiesis due to anemia.*Therefore, ifit is available, MRI should be the primarydiagnostic technique when insufficiency oroccult pelvic fractures are suspected. Otherimportant findings were that patients frequentlyhad multiple pelvic insufficiencyfractures and that pubic fractures in particularwere typically associated with concomitantfractures. Also, insufficiency fractureswere frequently associated with a history ofmalignant disease.multiple pelvicinsufficiency fractures are frequently found,particularly in the presence of a pubic or anacetabular fracture. Consequently, the entirepelvis must be imaged in these patients, anda careful search for concomitant fractures isalways warranted.*