Protruding Fiber Configurations using DRS in Bone Awls

Abstract

In recent decades, spinal fixation surgery has become a routine surgery. The procedure stiffens the spine using a combination of pedicle screws and rods and eliminate any relative motion between adjacent vertebrae. The accurate placement of the pedicle screws is crucial as inaccuracies can compromise the integrity of the fixation, as well as result in damage to the surrounding tissues including the spinal column which runs through the vertebrae. State of the art guidance techniques, such as 3D printed, patient-specific guide plates help surgeons avoid misalignments. However these techniques are expensive, resource intensive and therefore inaccessible to a large percentage of the global population, highlighting the need for a more accessible alternative guidance technology. Diffuse Reflectance Spectroscopy (DRS) is a simple form of optical spectroscopy and could act a low-cost alternative to provide guidance to surgeons during the placement of the pilot holes for pedicle screws. This study proposes integrating two optical fibers into a bone awl and to use DRS as a guidance aid by warning surgeons if the tip of the awl is about to breach into an adjacent tissue.
To understand if DRS can be used for this application, the effect of the needle-shaped tip of the bone awl on the ability of the optical probe to provide the necessary guidance is explored. The light-emitting fiber is placed along the awl’s edge, while the light-collecting fiber is placed in the center of the needle’s tip for light-collection. This means the light-collecting fiber is protruding ahead of the light-emitting fiber and the sharper the needle, the greater this protrusion. Using Monte Carlo simulations in MATLAB and phantom experiments as the angle between the two fibers increases from 0◦ (blunt tip, no protrusion) to 60◦ in increments of 10◦. The performance of the probe is assessed at each angle by determining the maximum detection depth, as well as the strength of the signal received at the light collecting fiber.
The Monte Carlo simulations yielded satisfactory detection depths (> 1mm) at all fiber configurations tested, but a significant drop in the signal strength if the needle sharpness exceeds 30◦. To validate this, phantom experiments were performed using a custom designed and manufactured optical probe. The experiments suggest that the simulations were underestimating the signal strength and the sharpest angle at which the probe can provide guidance to surgeons is at 40◦. At this angle, the detection depth is greater than 1mm and the signal strength was still satisfactory. These findings warrant further exploring how DRS can be integrated into a bone awl. This study primarily acts as a proof of concept and further research is required to improve the tissue identification of DRS.