This 2002 case-control study introduced the alpha angle as a quantitative MRI measure of anterior femoral head-neck concavity. The study compared 39 patients with clinical cam impingement to 35 asymptomatic controls to determine whether the new measurement could objectively distinguish pathological from normal hip morphology.
Young active patients with groin pain and restricted internal rotation often had normal AP radiographs before this paper, leaving clinicians without an objective way to confirm or quantify the underlying deformity.
The alpha angle changes that. When you see a patient with the classic triad — groin pain, internal rotation under 10° at 90° flexion, positive impingement test. Get an oblique axial MRI parallel to the femoral neck axis and measure the alpha angle.
An alpha angle above 55° (the lower bound of the symptomatic range in this study) places the hip well outside the normal range of 33–48° and supports cam morphology as the diagnosis. Remember that 85% of these patients already have anterolateral cartilage damage at the time of imaging. This is not a benign finding, and preserved joint space does not mean preserved cartilage.
This paper directly enabled the 2003 Ganz femoroacetabular impingement framework and established alpha angle >55° as the entry criterion used in virtually every subsequent cam FAI surgical outcome study.
This 2002 case-control study introduced the alpha angle as a quantitative MRI measure of anterior femoral head-neck concavity. The study compared 39 patients with clinical cam impingement to 35 asymptomatic controls to determine whether the new measurement could objectively distinguish pathological from normal hip morphology.
Young active patients with groin pain and restricted internal rotation often had normal AP radiographs before this paper, leaving clinicians without an objective way to confirm or quantify the underlying deformity.
The alpha angle changes that. When you see a patient with the classic triad — groin pain, internal rotation under 10° at 90° flexion, positive impingement test. Get an oblique axial MRI parallel to the femoral neck axis and measure the alpha angle.
An alpha angle above 55° (the lower bound of the symptomatic range in this study) places the hip well outside the normal range of 33–48° and supports cam morphology as the diagnosis. Remember that 85% of these patients already have anterolateral cartilage damage at the time of imaging. This is not a benign finding, and preserved joint space does not mean preserved cartilage.
This paper directly enabled the 2003 Ganz femoroacetabular impingement framework and established alpha angle >55° as the entry criterion used in virtually every subsequent cam FAI surgical outcome study.