title: Bilateral atypical femoral fractures: how much symmetry is there on imaging?
abstract: OBJECTIVE
  To evaluate bilateral atypical femoral fractures (AFFs) and to compare imaging features of paired fractures.
  
  
  METHODS
  Bilateral femoral imaging studies of 124 patients on bisphosphonate therapy with at least one AFF were retrospectively reviewed. Time between AFF diagnoses was determined. The following imaging features were evaluated for each AFF: fracture location, femoral angle, length of cortical thickening, medial spike location, fracture orientation, and comminution. Associations between imaging findings on pairs of bilateral AFFs were assessed with Spearman's correlation (rs) and the Kappa statistic (κ).
  
  
  RESULTS
  Bilateral AFFs were present in 78/124 (62.9%) cases (3 men, 75 women; mean age 67.3 years). Average time between contralateral AFF diagnoses was 10.3 months. Contralateral AFFs were diagnosed within 12 months of the index fracture in 60/78 (76.9%) cases and within 3 years in 69/78 (88.5%) cases. There was a strong correlation between bilateral AFF locations (rs = 0.65), with 58/76 (76.3%) occurring within a distance of <5 cm and 41/76 (53.9%) within a distance of ≤2.5 cm. Bilateral AFF pairs had moderately correlated femoral angles (rs = 0.42), and weakly correlated lengths of cortical thickening (rs = 0.28). There was substantial agreement for medial spike location (κ = 0.68) and fracture orientation (κ = 0.64), and moderate agreement for lack of comminution (κ = 0.42). All findings were independent of time between AFF diagnoses.
  
  
  CONCLUSIONS
  Patients with unilateral atypical femoral fractures are likely to be diagnosed with a contralateral AFF within the first year of presentation. Bilateral AFFs commonly have similar imaging features, including location along the femur.
authors.affiliation: Department of Medical Imaging, University of Toronto, 263 McCaul Street, 4th Floor, Toronto, ON, M5T 1W7, Canada. linda.probyn@sunnybrook.ca.|Department of Medical Imaging, Sunnybrook Health Sciences Centre, Toronto, ON, Canada. linda.probyn@sunnybrook.ca.
authors.forename: Linda
authors.initials: L
authors.lastname: Probyn
authors.affiliation: Toronto General Research Institute, Toronto General Hospital, University Health Network, Toronto, ON, Canada.|Department of Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Angela M
authors.initials: AM
authors.lastname: Cheung
authors.affiliation: Department of Medical Imaging, University of Toronto, 263 McCaul Street, 4th Floor, Toronto, ON, M5T 1W7, Canada.
authors.forename: Catherine
authors.initials: C
authors.lastname: Lang
authors.affiliation: Department of Radiology, Wake Forest University School of Medicine, Winston-Salem, NC, USA.
authors.forename: Leon
authors.initials: L
authors.lastname: Lenchik
authors.affiliation: Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Adachi
authors.affiliation: Department of Medicine, Michael G. DeGroote School of Medicine, McMaster University, Hamilton, ON, Canada.
authors.forename: Aliya
authors.initials: A
authors.lastname: Khan
authors.affiliation: Department of Medicine, University of Toronto, Toronto, ON, Canada.
authors.forename: Robert G
authors.initials: RG
authors.lastname: Josse
authors.affiliation: Toronto General Research Institute, Toronto General Hospital, University Health Network, Toronto, ON, Canada.|Dalla Lana School of Public Health, University of Toronto, Toronto, ON, Canada.
authors.forename: George
authors.initials: G
authors.lastname: Tomlinson
authors.affiliation: Department of Medical Imaging, University of Toronto, 263 McCaul Street, 4th Floor, Toronto, ON, M5T 1W7, Canada.|Joint Department of Medical Imaging, Toronto, ON, Canada.
authors.forename: Robert
authors.initials: R
authors.lastname: Bleakney
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005264:Femoral Fractures / Q000000981:diagnostic imaging*; D005269:Femur / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D011859:Radiography; D015203:Reproducibility of Results; D012189:Retrospective Studies
keywords: Antiresorptive therapy; Atypical femoral fracture; Bilateral; Osteoporosis