An initial stab incision is made over the ASIS, followed by impaction of an iliac pin into the bone. The StealthStation reference arc is then fixated to the iliac pin (Fig. 11.2). Additional sterile drapes are placed to cover the field, leaving the reference arc exposed. The O-arm fluoroscopy unit is then positioned to acquire a 3D image of the targeted spinal levels, which is auto-registered to the StealthStation CaSN system (Fig. 11.3). After registration, the O-arm unit is removed from the surgical field.

The initial dilator serves multiple purposes. It is used as a nerve stimulator via a clip electrode as well as for navigation when a tracking arc is attached (Fig. 11.4). This navigated dilator is used to determine the incision site on the flank. Typically, for a one-level procedure, a one-to-one and a half-inch incision is made. After dissection through the subcutaneous tissues, the fascia over the abdominal muscles is opened. The abdominal wall muscles (external oblique, internal oblique, and transversus abdominis) are split, and blunt dissection is used to enter the retroperitoneal space (Fig. 11.5). The psoas muscle can be palpated. A clip electrode for nerve stimulation is attached to the navigated dilator, which is guided into the retroperitoneal space by CaSN (Fig. 11.6). The dilator is navigated through the psoas muscle while being stimulated to prevent nerve injury and advanced into the disc space. The clip electrode and tracking frame are then removed, at which point sequential dilation is performed and an appropriate length expandable retractor is placed (Figs. 11.7 and 11.8). Note that fluoroscopy has not been used.