title: An index for diagnosing infant hip dysplasia using 3-D ultrasound: the acetabular contact angle.
abstract: BACKGROUND
  Developmental dysplasia of the hip (DDH) is a common condition that is highly treatable in infancy but can lead to the lifelong morbidity of premature osteoarthritis if left untreated. Current diagnostic methods lack reliability, which may be improved by using 3-D ultrasound.
  
  
  OBJECTIVE
  Conventional 2-D US assessment of DDH has limitations, including high inter-scan variability. We quantified DDH on 3-D US using the acetabular contact angle (ACA), a property of the 3-D acetabular shape. We assessed ACA reliability and diagnostic utility.
  
  
  METHODS
  We prospectively collected data from January 2013 to December 2014, including 114 hips in 85 children divided into three clinical diagnostic groups: (1) normal, (2) initially borderline but ultimately normal without treatment and (3) dysplastic requiring treatment. Using custom software, two observers each traced acetabula twice on two 3-D US scans of each hip, enabling automated generation of 3-D surface models and ACA calculation. We computed inter-observer and inter-scan variability of repeatability coefficients and generated receiver operating characteristic (ROC) curves.
  
  
  RESULTS
  The 3-D US acetabular contact angle was reproduced 95% of the time within 6° in the same scan and within 9° in different scans of the same hip, vs. 9° and 14° for the 2-D US alpha angle (P < 0.001). Areas under ROC curves for diagnosis of developmental dysplasia of the hip were 0.954 for ACA and 0.927 for alpha angle.
  
  
  CONCLUSIONS
  The 3-D US ACA was significantly more reliable than 2-D US alpha angle, and the 3-D US measurement predicted the presence of DDH with slightly higher accuracy. The ACA therefore shows promising initial diagnostic utility. Our findings call for further study of 3-D US in the diagnosis and longer-term follow-up of infant hip dysplasia.
authors: Department of Radiology and Diagnostic Imaging, University of Alberta, 2A2.42 Walter Mackenzie Health Sciences Centre, Edmonton, Alberta, T6G 2B7, Canada. mmabee@ualberta.ca.
authors: Myles G
authors: MG
authors: Mabee
authors: Department of Radiology and Diagnostic Imaging, University of Alberta, 2A2.42 Walter Mackenzie Health Sciences Centre, Edmonton, Alberta, T6G 2B7, Canada.
authors: Abhilash Rakkunedeth
authors: AR
authors: Hareendranathan
authors: Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada.
authors: Richard B
authors: RB
authors: Thompson
authors: Department of Surgery, University of Alberta, Edmonton, Alberta, Canada.
authors: Sukhdeep
authors: S
authors: Dulai
authors: Department of Radiology and Diagnostic Imaging, University of Alberta, 2A2.42 Walter Mackenzie Health Sciences Centre, Edmonton, Alberta, T6G 2B7, Canada.|Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta, Canada.
authors: Jacob L
authors: JL
authors: Jaremko
mesh_terms: D005260:Female; D006618:Hip Dislocation, Congenital / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011446:Prospective Studies; D015203:Reproducibility of Results; D014463:Ultrasonography / Q000379:methods*
keywords: Developmental dysplasia of the hip; Hip; Infants; Quantitative indices; Three-dimensional ultrasound; Ultrasound