Alpha angle (femoroacetabular impingement)

Dr Henry Knipe and Dr Yuranga Weerakkody et al.

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 2.

Radiographic features

Plain radiograph

Measured on obliquely oriented radiographs.


Measured on oblique axial images as the angle between the orientation of the femoral neck and the margin of the femoral head.

See also

Share article

Article information

rID: 68548
Tag: cases
Synonyms or Alternate Spellings:
  • Alpha angle (FAI)

Support Radiopaedia and see fewer ads

Cases and figures

  • Case 1: with measurement on plain film
    Drag here to reorder.
  • Updating… Please wait.

     Unable to process the form. Check for errors and try again.

     Thank you for updating your details.