Posterior approach to sacroiliac joint. A, Skin incision. B, Right triangle on outer table of posterior ilium. PIIS, Posterior inferior iliac spine; PSIS, posterior superior iliac spine.(Redrawn from Ebraheim NA, Lu J, Biyani A, et al: Anatomic considerations for posterior approach to the sacroiliac joint, Spine 21:2709, 1996.) SEE TECHNIQUE 37.28