Abstract
Introduction
Robotic assisted placement of pedicle screws has become increasingly popular in minimally invasive lumbar surgery (MIS). Stimulated EMG measurements during robotic pedicle cannulation have previously not been possible. Although often performed as a second step during subsequent tapping, this tapping may result in the destruction of the pedicle and a breach if too medial. We developed an insulated cannulation tube for electrical measurements to increase patient safety.
Methods
We developed a custom insulated cannulation tube for robotic assisted pedicle screw placement. This was coated with a micron thick non-conductive coating with 3cm of exposure at the distal tip corresponding to the length of the pedicle. This was then used in surgery and stimulated EMG thresholds were take prior to and after tapping (with a 4.5mm tap) during robot assisted surgery. Measurements were taken using in house neural monitoring as well as using the Nuvasive NVM5 system.
Results
34 levels were cannulated using the Mazor Renaissance Robotic system in a percutenous MIS approach. No breaches were identified by stimulation criteria. (i.e all stimulation EMG thresholds were greater then 10 in all groups). The difference (absolute value) between the cannula and tap was 5.3 +/− 0.3 mA. The tap had equal or lower thresholds 75% of the time (relative to the insulated cannula) and higher values in 25% of the stimulations. When comparing between the two monitoring techniques, the variability was consistent, 3.8 +/− 0.3mA
Conclusions
An insulated cannula during percutenous robotic assisted pedicle cannulation provides accurate and reliable measures of stimulated EMG thresholds. These measurements were consistent with subsequent tapping with only small variation. Measurements between in house monitoring and Nuvasive monitoring were consistent with only slight variation.