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SI joints
AP axial 30 to 35° cephalad for both joints; posterior obliques 25 to 30° show the joint on the side that is up.
Patient and part
SI joint views are ordered for back or buttock pain, sacroiliitis, ankylosing spondylitis and trauma. The routine is an AP axial of both joints and a posterior oblique of each joint. For the AP axial, the patient is supine with the knees slightly flexed, the pelvis level and the MSP centered. For the posterior obliques, turn the patient 25 to 30 degrees into an LPO and then an RPO, supporting the raised side. The joints angle backward about 25 degrees, so this small rotation lines the beam up with the joint on the raised side.