Alpha angle (cam morphology)

Last revised by Joshua Yap on 7 May 2024

The alpha angle is a radiological measurement proposed for the detection of cam morphology, which is sometimes associated with femoroacetabular impingement (FAI)

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.

Measured on obliquely oriented radiographs. The Dunn projection of the hip is used.

Measured on oblique axial images as the angle between 4:

  • a line from the center of the femoral head to the center of the femoral neck at its narrowest point

  • a line from the center of the femoral head to a point where the distance from the bone to the center of the head is greater than the radius of the cartilage-covered femoral head

There is no one value that can define cam morphology 5. Initially in 2002, an alpha angle of ≥50° was proposed as pathological 4. Subsequently, a value of ≥57° was proposed in symptomatic patients 2, and in 2021, a value of ≥60° was proposed as definitional of cam morphology 5

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