European Radiology

, Volume 27, Issue 5, pp 2011–2023 | Cite as

Cam deformity and the omega angle, a novel quantitative measurement of femoral head-neck morphology: a 3D CT gender analysis in asymptomatic subjects

  • Vasco V. Mascarenhas
  • Paulo Rego
  • Pedro Dantas
  • Augusto Gaspar
  • Francisco Soldado
  • José G Consciência



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.


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°).


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.


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.

Key Points

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.


Hip Femoroacetabular impingement Multidetector computed tomography Reference value Variant 



Femoroacetabular impingement


Femoral head/neck




Computed tomography


Magnetic resonance imaging


conventional X-ray


Omega angle


Alpha angle



The authors would like to thank José Roquette, João Sá, Isabel Vaz, and Pedro Patrício for their continuing and enthusiastic support toward clinical research at Hospital da Luz, and Rúben Teixeira, Ana Filipa Graça, Rogério Lopes, Diogo Corrente, João Novo, and Tiago Castela for their efforts toward optimizing technical issues and providing patient care

The scientific guarantor of this publication is Prof. Dr. José Roquette, MD PhD. The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article. The authors state that this work has not received any funding. One of the authors has significant statistical expertise; however no complex statistical methods were necessary for this paper. Institutional Review Board (Hospital da Luz Ethics Committee) approval was obtained and written informed consent was obtained from all participants in this study.


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Copyright information

© European Society of Radiology 2016

Authors and Affiliations

  • Vasco V. Mascarenhas
    • 1
  • Paulo Rego
    • 2
  • Pedro Dantas
    • 3
  • Augusto Gaspar
    • 1
  • Francisco Soldado
    • 4
  • José G Consciência
    • 5
  1. 1.MSK imaging Unit (UIME), Imaging CenterHospital da LuzLisbonPortugal
  2. 2.Department of Orthopaedic SurgeryHospital da LuzLisbonPortugal
  3. 3.Hospital CUF DescobertasLisbonPortugal
  4. 4.Hospital Sant Joan De DeuUniversitat De BarcelonaBarcelonaSpain
  5. 5.NOVA Medical SchoolLisbonPortugal

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