Clamp-based mechanism for in vivo wired electromagnetic sensor fixation enabling multi-day measurements

Abstract

Accurate position and orientation measurements are essential for studying viscoelastic effects of dynamic implants such as in the spine during in vivo experiments. Wired electromagnetic sensors provide accurate, continuous real-time tracking and are sufficiently small compared to wireless sensors. However, their disadvantages are infection risks due to transdermal wiring and high costs. Thereto, we developed a fixation mechanism that ensures stable sensor positioning to a spinal implant for multi-day measurements while allowing controllable extraction afterwards. The mechanism incorporates a leaf spring for sensor fixation and a snap-fit interface for implant attachment. Mechanical calculations and experimental tests were performed to reinforce the sensor wire with different layers of shrink tubes and to tune the clamping force under varying extraction angles. Pull-out forces between 16-29 N were measured at different extraction angles for sensor wires with double heat-shrink tubing. In vivo experiments demonstrated that the sensors could be successfully removed after a 11-days measurement period. The proposed clamp-based fixation mechanism provides sufficient stable attachment of wired sensors to pedicle screws, while allowing controlled extraction after measurements. This approach enables real-time in vivo tracking for multi-day measurements and subsequent removal of the sensors without breaking.