In patients with prior lumbar surgeries, particularly those with prior open approaches, the anatomy may be distorted or complicated by scar tissue. The use of a minimally invasive approach allows for the avoidance of previously operated regions, and provides a more straightforward soft tissue dissection plane. Prior decompressions alter the bony anatomy, and may complicate docking of the Kirschner wire (K-wire) and retractor system. Patient anatomy may also be altered by iatrogenic scoliosis, proximal junctional kyphosis, prior trauma, or bony changes from prior infection or tumors. Computed tomography scans and magnetic resonance imaging allow surgeons to identify anatomic changes from prior operations, and are essential for preoperative planning in these cases. In selecting patients for MIS procedures, body habitus is often a limiting factor, and the availability of longer instruments and retractors should be considered as part of the preoperative planning.

The procedure is performed under total intravenous anesthesia such that continuous electromyographic recordings (EMGs) may be monitored intraoperatively where irritation of a nerve
root will yield a measurable motor response distally where intramuscular needle electrodes are placed and secured for intraoperative monitoring. Stimulus-evoked EMG is another modality of neurophysiologic monitoring where a voltage is applied to each lumbar pedicle screw and the amplitude of the distal current is measured. As expected, medial wall pedicle breaches should decrease the resistance to this applied voltage, resulting in a relatively higher distal current. This will therefore lower the threshold voltage at which a motor response can be obtained from an electrical stimulus to the screw.

The patient is positioned prone on a Jackson frame with chest and iliac crest support pads in position. Sterile preparation is completed in the usual fashion, and the patient is draped widely to ensure access to the intended operative levels and the posterior iliac spine if needed for anchoring of the DRA. Typically, image guidance provides relative accuracy at up to a distance of five spinal segments from the DRA, and long constructs greater than five levels may need repositioning of the DRA for further intraoperative imaging.

For placement of additional instrumentation, using the tracking tool, the level of interest is identified, and a trajectory overlying the pedicle is selected. A 2 to 3 cm skin incision is made and a navigated Jamshidi needle is introduced and docked at the junction of the transverse process and facet. It is advanced through the pedicle along the navigated trajectory. A K-wire is introduced and advanced beyond the tip of the Jamshidi needle, which is then removed. The K-wire is secured by an operative assistant to ensure it does not migrate or back out, while serial dilators are passed to obtain the operative corridor. When the surrounding soft tissue is adequately retracted, hemostasis is obtained, and a retractor of the final desired size has been placed, navigation is used to confirm the trajectory of the proposed pedicle screw. The pedicle is then tapped over the K-wire using a cannulated instrument. After cannulation, the wire is removed and the pedicle screw is placed. As described above, the screw is stimulated to ensure no pedicle breach occurred.