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.

CT/MRI

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.