gms | German Medical Science

Objective: Recently, a novel technique for a navigation-guided frameless stereotactic approach for the placement of depth electrodes in epilepsy patients has been published by our group. It combines the high versatility of frameless methods with the accuracy and simplicity of frame-based techniques by allowing drilling, percutaneous bolt placement and insertion of the depth electrode via a bone fixated guide for depth electrode placement (GIDE) that is mounted on a Medtronic Vertek^® articulate biopsy arm (Dorfer et al., Neurosurgery 2014). To improve accuracy of the trajectory, we implemented the iSys1^® miniature robotic device into this routine. It is fixed to the Mayfield system on an articulate arm that may be realigned during surgery. Placed near the entry point, the device automatically aligns to the planned trajectory. The GIDE is inserted and the depth electrode is implanted as described.

Method: Nine patients (5m, 4f) with an overall of 43 electrodes (21 left, 22 right, 1 bilateral) were included in the study. The mean length of the planned trajectories was 51.8 ± 27.0 mm. All procedures were performed with the neuronavigation system Medtronic S7^® with Synergy Cranial version 2.2 software and the iSys1^® robot.

Results: The target alignment error before and after insertion of the percutaneous bolt as measured intraoperatively by neuronavigation was 0.06 ± 0.06 mm and 0.33 ± 0.25 mm, respectively, resulting in a mean setup stability of 0.28 ± 0.25 mm. Digital reconstruction of the postoperative CCT scans showed a real error at the entry point of 1.72 ± 0.82 mm and at the target point of 2.13 ± 1.19 mm. There was no correlation between the length of the trajectory and the real error at the target point (r=.168; p=.341). The mean duration for the implantation of one depth electrode was 15.7 min (8.5 min – 26.6 min). Compared to our data obtained from surgeries with the Medtronic Vertek^® biopsy arm with GIDE alone, the mean real error at the entry point was reduced by 50% from 3.5 ± 1.4 mm to 1.7 ± 0.8 mm. Furthermore, the mean real error at the target point was reduced by almost 30% from 3.0 ± 1.9 mm to 2.1 ± 1.2 mm. Mean duration for the implantation of one electrode declined by almost 18% from 19.1 min (13 - 35 min) to 15.7 min (8.5 - 26.6 min).

Conclusions: The iSys1 miniature robotic device is a versatile and easy-to-use tool for the frameless stereotactic navigation-guided placement of depth electrodes. It helps to improve accuracy of electrode placement and reduces duration of surgery.