An experimental study of deep brain stimulation lead fracture: possible fatigue mechanisms and prevention approach

Lead fracture is a common and troublesome hardware-related complication in deep brain stimulation therapy. Frequent cervical movements are suspected as the main cause, but the underlying mechanisms are still unclear. We propose the integrity of the helical structure of the lead wires is important and conduct systematic experiments to demonstrate this. We aim to provide a new view on how lead fracture takes place.

Flexural fatigue tests were conducted on intact and stretched lead wires with a custom-made testing machine. Number of cycles until failure was recorded as the fatigue life, and the fracture morphology was observed under optical and scanning electron microscopes.

The fatigue life of the lead wires showed dramatic decline with the severity of deformation, from 434,112 ± 10,277 cycles for an intact specimen down to 19,435 ± 2,622 cycles for a specimen elongated by approximately 20%. The morphology of the fractures revealed characteristic beach marks and striations indicating a fatigue failure.

We demonstrate that integrity of the helical structure of the wires is crucial to the fatigue performance of the lead. Although the results cannot be directly extrapolated to human subjects, they suggest a possible lead fracture mechanism. The implanted lead may undergo deformation due to large-amplitude motions (e.g., falls) and develop fracture due to the deterioration in fatigue resistance, especially when it is placed at or migrates to the neck. It may be possible to effectively protect the lead by using certain surgical techniques during implantation, such as placing the connector on the calvaria or in a drilled trough at the retroauricular region with reliable fixation.