Spine, SI Joints, Scoliosis and Myelography

Cervical AP Views

C1, the atlas, is a ring with no body, and C2, the axis, carries the dens. For the AP axial projection the central ray is angled 15 to 20 degrees cephalad to C4, at the thyroid cartilage, to open the disk spaces from C3 to T2. For the AP open-mouth projection, a line from the lower edge of the upper incisors to the mastoid tips is perpendicular, and the central ray is perpendicular through the open mouth. The incisors and skull base should superimpose: incisors over the dens mean raise the chin, and skull base over the dens means lower it. When the upper dens stays hidden in a non-trauma patient, the Fuchs method raises the chin until the mentomeatal line is nearly vertical and directs the central ray parallel to it.