Alpha angle (femoroacetabular impingement)

Correlation

between the prevalence of herniation pits and the alpha angle of the hip: computed tomography evaluation in healthy Chinese adults. Reconstructed CT image of proximal femora and measurement of the alpha angle. (A) View of the oblique axial plane parallel to the axis of the femoral neck. (B) Measurement of the alpha angle; see the text for definitions of the various points.

bmcmusculoskeletdisord.biomedcentral.com • CC-by-2.0

Automated

measurement of alpha angle on 3D-magnetic resonance imaging in femoroacetabular impingement hips: a pilot study. Manual alpha angle measurement. ‘hc’ = center of the femoral head. ‘nc’ = center of the femoral neck located at the neck"s most narrowed point. ‘A’ = point where the distance from the bone to the center of the femoral head exceeds the radius of the best-fit circle around the femoral head

josr-online.biomedcentral.com • CC-by-4.0

Automated

measurement of alpha angle on 3D-magnetic resonance imaging in femoroacetabular impingement hips: a pilot study. Automated alpha angle measurement using automated computer-based prototype software (MR Chondral Health 2.1, Siemens Healthcare GmbH, Erlangen, Germany)

josr-online.biomedcentral.com • CC-by-4.0

Magnetic

resonance arthrography of the hip: technique and spectrum of findings in younger patients. Cam-type of FAI: anterior bulge of the head-neck junction (white arrow) and increased alpha angle (69 degrees vs 55 degrees maximum). Anterior labrum is torn off and calcified

insightsimaging.springeropen.com • CC-by-2.0

MRI for the

preoperative evaluation of femoroacetabular impingement. Obtaining Swiss axial images and calculating the alpha angle. a The Swiss axial (axial oblique) images are obtained along the long axis of the femoral neck. b To calculate the alpha angle, the axial oblique image through the midportion of the femoral neck (red line) is chosen. A circle is drawn over the femoral head cortex (blue circle). A line is drawn through the long axis of the femoral neck at its narrowest point (purple line), through the center of the femoral head. Another line is drawn from the center of the femoral neck to the point where the femoral head–neck junction meets the circle (green line). The alpha angle is the angle between the two lines. An alpha angle of >55° is considered a risk factor for FAI

insightsimaging.springeropen.com • Open Access

Radiopaedia • CC-by-nc-sa 3.0 • de

The alpha angle is a radiological measurement proposed for the diagnosis and evaluation of surgical treatment in cam-type femoroacetabular impingement (FAI).

When initially described in 2002, Notzli et al. suggested that the pathological value was >50°.

According to one study, a value measured in an oblique CT reconstruction of the femoral neck has been thought to have a high discriminating capacity for the diagnosis of symptomatic cam-type femoroacetabular impingement where if a patient complains of hip pain and an alpha angle ≥57° is found on CT, strongly suggest that cam-type FAI may be the cause .

The term alpha angle is also used in a separate and unrelated context in the evaluation of developmental dysplasia of the hip (DDH) in children.