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

Research output: Contribution to journalArticlepeer-review

33 Citations (Scopus)


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.

CONCLUSION: 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.

Original languageEnglish
Pages (from-to)2011-2023
Number of pages13
JournalEuropean Radiology
Issue number5
Early online date30 Aug 2016
Publication statusPublished - 1 May 2017


  • Femoroacetabular impingement
  • Hip
  • Multidetector computed tomography
  • Reference value
  • Variant


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