Anterior head-neck offset (Nötzli) angle. Point A, anterior point where distance from center of the head (hc) exceeds radius (r) of subchondral surface of femoral head. α is then measured as angle between A-hc and hc-nc, with nc being center of neck at narrowest point. A, Hip in normal individual. B, Typical deformation. The greater anterior head-neck offset angle, the smaller arc of motion required to cause cam-type impingement on acetabular rim.