title: Cam deformity and the omega angle, a novel quantitative measurement of femoral head-neck morphology: a 3D CT gender analysis in asymptomatic subjects.
abstract: OBJECTIVE
  Our objectives were to use 3D computed tomography (CT) to define head-neck morphologic gender-specific and normative parameters in asymptomatic individuals and use the omega angle (Ω°) to provide quantification data on the location and radial extension of a cam deformity.
  
  
  METHODS
  We prospectively included 350 individuals and evaluated 188 asymptomatic hips that underwent semiautomated CT analysis. Different thresholds of alpha angle (α°) were considered in order to analyze cam morphology and determine Ω°. We calculated overall and gender-specific parameters for imaging signs of cam morphology (Ω° and circumferential α°).
  
  
  RESULTS
  The 95 % reference interval limits were beyond abnormal thresholds found in the literature for cam morphology. Specifically, α° at 3/1 o´clock were 46.9°/60.8° overall, 51.8°/65.4° for men and 45.7°/55.3° for women. Cam prevalence, magnitude, location, and epicenter were significantly gender different. Increasing α° correlated with higher Ω°, meaning that higher angles correspond to larger cam deformities.
  
  
  CONCLUSIONS
  Hip morphometry measurements in this cohort of asymptomatic individuals extended beyond current thresholds used for the clinical diagnosis of cam deformity, and α° was found to vary both by gender and measurement location. These results suggest that α° measurement is insufficient for the diagnosis of cam deformity. Enhanced morphometric evaluation, including 3D imaging and Ω°, may enable a more accurate diagnosis.
  
  
  CONCLUSIONS
  • 95% reference interval limits of cam morphotype were beyond currently defined thresholds. • Current morphometric definitions for cam-type morphotype should be applied with care. • Cam prevalence, magnitude, location, and epicenter are significantly gender different. • Cam and alpha angle thresholds should be defined according to sex/location. • Quantitative 3D morphometric assessment allows thorough and reproducible FAI diagnosis and monitoring.
authors: MSK imaging Unit (UIME), Imaging Center, Hospital da Luz, Lisbon, Portugal. mascarenhas.vasco@gmail.com.
authors: Vasco V
authors: VV
authors: Mascarenhas
authors: Department of Orthopaedic Surgery, Hospital da Luz, Lisbon, Portugal.
authors: Paulo
authors: P
authors: Rego
authors: Hospital CUF Descobertas, Lisbon, Portugal.
authors: Pedro
authors: P
authors: Dantas
authors: MSK imaging Unit (UIME), Imaging Center, Hospital da Luz, Lisbon, Portugal.
authors: Augusto
authors: A
authors: Gaspar
authors: Hospital Sant Joan De Deu, Universitat De Barcelona, Barcelona, Spain.
authors: Francisco
authors: F
authors: Soldado
authors: NOVA Medical School, Campo Mártires Pátria, Lisbon, Portugal.
authors: José G
authors: JG
authors: Consciência
mesh_terms: D000328:Adult; D058070:Asymptomatic Diseases; D005260:Female; D057925:Femoracetabular Impingement / Q000000981:diagnostic imaging*; D005269:Femur / Q000000981:diagnostic imaging; D005270:Femur Head / Q000000981:diagnostic imaging*; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006621:Hip Joint / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D061330:Multidetector Computed Tomography; D015995:Prevalence; D011446:Prospective Studies; D012016:Reference Values; D012737:Sex Factors; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: Femoroacetabular impingement; Hip; Multidetector computed tomography; Reference value; Variant