Editorial Commentary: The Measurement of the Alpha Angle in Femoroacetabular Impingement Syndrome With a 45° Dunn-View Radiograph Predicts the Cartilage Damage on the Acetabular Side of the Hip Joint-Is It as Simple as That?

Abstract

In recent years, femoroacetabular impingement syndrome (FAIS) has developed itself into a well-known pathology throughout the orthopaedic community worldwide. The more we learned, the more sophisticated it became: In the beginning, we measured the femoral head-neck offset; then, the alpha angle was found to be a useful measurement in detecting FAIS. We learned to perform these measurements with, for example, the 45° Dunn view. The alpha angle, but not the femoral head-neck offset, measured as described, predicts not only the acetabular cartilage damage resulting from FAIS but also the correlation between the degree of the alpha angle and the severity of the cartilage damage within the acetabular labrum articular disruption and Outerbridge classifications. The femoral head-neck offset cannot provide us with this information, but it is the first sign we all look at before taking any measurements on radiographs or magnetic resonance imaging scans if a cam morphology could be present. It is paramount to understand the underlying problems of the individual hip and distinguish instability (dysplasia) from FAIS and also to evaluate femoral torsional abnormalities to perform the appropriate treatment using magnetic resonance imaging and computed tomography scans if necessary. The alpha angle quantifies the severity of the pathology and predicts the possible cartilage damage in FAIS patients, but in our opinion, we cannot neglect the femoral head-neck offset, because it is often the first radiologic sign of FAIS that most of us realize on a radiograph. Therefore, both signs have their place in detecting and treating FAIS.