Femoracetabular impingement (FAI) has been postulated to be a cause of acetabular labral and articular cartilage damage to the hip. The sequelae of the condition and the damage that it causes are thought to contribute to early onset of osteoarthritis (OA). The femoral head-neck alpha angle is used to quantify the degree of femoral head asphericity in patients suspected of cam-type femoroacetabular impingement.
Ultrasound (US) has many well-established advantages over CT and MRI, is better suited to preliminary screening and can be performed quickly as a general investigation of groin symptoms that might include as a differential diagnosis FAI. US demonstrates, according to Robinson et al. (2017) good sensitivity and good NPV in calculation of the femoral head-neck alpha angle compared with CT. US calculation of the alpha angle does, however, suffer poor specificity. US measurement of the alpha angle in young patients with no prior hip surgery or trauma can, however, provide objective evidence of cam-type FAI in symptomatic young patients and direct patients to more established imaging techniques where clinically appropriate.