title: Potential for change in US diagnosis of hip dysplasia solely caused by changes in probe orientation: patterns of alpha-angle variation revealed by using three-dimensional US.
abstract: OBJECTIVE
  To use three-dimensional ( 3D three-dimensional ) ultrasonography (US) to quantify the alpha-angle variability due to changing probe orientation during two-dimensional ( 2D two-dimensional ) US of the infant hip and its effect on the diagnostic classification of developmental dysplasia of the hip ( DDH developmental dysplasia of the hip ).
  
  
  METHODS
  In this institutional research ethics board-approved prospective study, with parental written informed consent, 13-MHz 3D three-dimensional US was added to initial 2D two-dimensional US for 56 hips in 35 infants (mean age, 41.7 days; range, 4-112 days), 26 of whom were female (mean age, 38.7 days; range, 6-112 days) and nine of whom were male (mean age, 50.2 days; range, 4-111 days). Findings in 20 hips were normal at the initial visit and were initially inconclusive but normalized spontaneously at follow-up in 23 hips; 13 hips were treated for dysplasia. With the computer algorithm, 3D three-dimensional US data were resectioned in planes tilted in 5° increments away from a central plane, as if slowly rotating a 2D two-dimensional US probe, until resulting images no longer met Graf quality criteria. On each acceptable 2D two-dimensional image, two observers measured alpha angles, and descriptive statistics, including mean, standard deviation, and limits of agreement, were computed.
  
  
  RESULTS
  Acceptable 2D two-dimensional images were produced over a range of probe orientations averaging 24° (maximum, 45°) from the central plane. Over this range, alpha-angle variation was 19° (upper limit of agreement), leading to alteration of the diagnostic category of hip dysplasia in 54% of hips scanned.
  
  
  CONCLUSIONS
  Use of 3D three-dimensional US showed that alpha angles measured at routine 2D two-dimensional US of the hip can vary substantially between 2D two-dimensional scans solely because of changes in probe positioning. Not only could normal hips appear dysplastic, but dysplastic hips also could have normal alpha angles. Three-dimensional US can display the full acetabular shape, which might improve DDH developmental dysplasia of the hip assessment accuracy.
authors: From the Departments of Radiology and Diagnostic Imaging (J.L.J., V.G.S., L.J.) and Biomedical Engineering (M.M., K.C., R.B.T.), 2A2.41 WC Mackenzie Health Sciences Centre, University of Alberta, 8440-112 St, Edmonton, AB, Canada T6G 2B7.
authors: Jacob L
authors: JL
authors: Jaremko
authors: Myles
authors: M
authors: Mabee
authors: Vimarsha G
authors: VG
authors: Swami
authors: Lucy
authors: L
authors: Jamieson
authors: Kelvin
authors: K
authors: Chow
authors: Richard B
authors: RB
authors: Thompson
mesh_terms: D005260:Female; D006618:Hip Dislocation, Congenital / Q000000981:diagnostic imaging*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D021621:Imaging, Three-Dimensional; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011446:Prospective Studies; D015203:Reproducibility of Results; D014463:Ultrasonography