Introduction: STN-DBS is now a life-altering treatment for advanced Parkinson’s disease. The ideal target point within the STN is known. However, no emphasis on the impact of trajectory exists. The ellipsoid shape of the STN and the off-centre traditional target point means that variation in the electrode inclination should affect STN engagement. Understanding of this relationship could inform trajectory selection by improving STN engagements and margins of error.
Methods: We simulated electrode placement at the clinical target through a set of trial trajectories. Twelve 3D-reconstructed STNs were created from MRI data of 6 patients. Each STN was approached through 56 simulated trajectories arranged in a grid covering a quadrant of skull around and in front of the coronal suture. A subset of 20 viable trajectories was reassessed for depth of engagement in each STN.
Results: Group averages for each trajectory are presented as traffic light maps and as an overlaid skull mask illustrating recommended electrode entry sites. Trajectories under 30 degrees anterior to the bregma and between 10 to 30 degrees off the midline accommodated over 2.4 degrees of wobble. A mean engagement of 6 mm was possible in half of the subset. The longest engagements are on trajectories which saddle the coronal suture, extending to 40 degrees lateral. Microelectrode tracts of 14 additional STNs were collated using above protocol and engagement exceeded 5 mm in all central trajectories without capsular side effects, suggesting placement away from STN borders.
Conclusions: Trajectory selection influences engagement and flexibility to accommodate electrode wobble or brain shift. We recommend having the first trial 20 degrees anterior to the bregma, moving postero-laterally in successive trials to balance both error and engagement. When wider margins of error are beneficial (e.g. second side during bilateral procedures), trajectories nearer the coronal suture and around 25 degrees off the midline are advised.
Patient Care: Could empower surgeons to achieve greater STN engagements and higher margins of error through informed trajectory selection. This may have a positive effect on patient outcomes pending confirmation through further research.
Learning Objectives: To consider the impact of electrode inclination on target engagement and margin of error. To appreciate how a relationship between electrode trajectory and these outcome parameters could influence surgical planning. To understand how proprietary planning software can be used to investigate the impact of different trajectories through simulated implantation and 3D modelling.