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

• Published in: European radiology Vol. 27; no. 5; pp. 2011 - 2023
• Main Authors: Mascarenhas, Vasco V., Rego, Paulo, Dantas, Pedro, Gaspar, Augusto, Soldado, Francisco, Consciência, José G
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.05.2017; Springer Nature B.V
• Subjects: Adult; Asymptomatic; Asymptomatic Diseases; Diagnostic Radiology; Female; Femoracetabular Impingement - diagnostic imaging; Femur - diagnostic imaging; Femur Head - diagnostic imaging; Femur Neck - diagnostic imaging; Gender; Hip Joint - diagnostic imaging; Humans; Imaging; Imaging, Three-Dimensional; Internal Medicine; Interventional Radiology; Magnetic resonance imaging; Male; Medicine; Medicine & Public Health; Morphology; Multidetector Computed Tomography; Musculoskeletal; Neuroradiology; Prevalence; Prospective Studies; Questionnaires; Radiology; Reference Values; Sex Factors; Three dimensional imaging; Tomography; Tomography, X-Ray Computed - methods; Ultrasound; Lisbon Portugal; Portugal; Variant; Reference value; Hip; Femoroacetabular impingement; Multidetector computed tomography
• ISSN: 0938-7994; 1432-1084; 1432-1084
• DOI: 10.1007/s00330-016-4530-0

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 .