Treatment methods for spinal disorders involving spinal fusion surgery often entail lengthy and expensive procedures, with a risk of damage to surrounding tissues. Breach detection tools aid in precise pedicle screw placement, thereby reducing the risk of complications or misalignment, and minimizing the need for follow-up surgeries. Accurate placement of pedicles in the vertebrae is crucial in spinal fusion surgery, as improper positioning can result in breaches that potentially harm neural tissues. This study proposes a handheld bone sensing device capable of measuring real-time reflected light from tissue using carefully selected optical elements. The selection of these optical elements was guided by analyzing porcine absorption spectra and conducting Monte Carlo light reflectance simulations. The device is designed to provide consistent real-time feedback by incorporating an electronic circuit optimized to minimize environmental signal interference. A prototype, named the optics-based bone quality sensing device, was developed using electrical discharge machining parts, 3D printed parts, an Arduino Uno, a custom-made printed circuit board (PCB), and off-the-shelf optical components such as laser and photodiodes coupled into optical fibers. Experimental validation with ex vivo porcine vertebrae revealed that the device could not detect sufficient reflected light to differentiate between cortical and cancellous bone. Despite this, the study marks significant progress in creating a handheld bone sensing device that utilizes real-time reflected light sensing minimizing interference. This device represents an important step towards developing tools to assist in precise pedicle screw placement for the treatment of spinal disorders.

Accurate placement of screws in spinal surgery is vital to mitigate risks like instability, nerve damage, or spinal cord injury, which can lead to various complications such as pain, sensory loss, muscle weakness, or paralysis below the injury site [33]. However, success rates in screw placement vary widely, ranging from 27.6% to 100% [56].

Advanced techniques, like pedicle screw placement (PSP) with enhanced guidance systems, aim to provide surgeons with better spatial awareness to prevent cortical breaches. Various guidance methods,
such as fluoroscopy, computer-assisted techniques, neurophysiological monitoring, and Electrical Impedance Spectroscopy (EIS) enabled by the PediGuard, have been developed and utilized in spinal fusion surgeries [18]. Despite their efficacy in reducing complications, these systems have limitations such as increased radiation exposure, prolonged surgery time, or lack of real-time feedback.

This study compares two sensing techniques, Electrical Impedance Spectroscopy (EIS)) and Diffuse Reflection Spectroscopy (DRS), for spinal fusion surgery. Both methods are employed to detect cortical
breaches during PSP by distinguishing between cancellous and cortical bone. Before experimentation, certain gaps in understanding must be addressed, including exploring the working principle of EIS for
vertebrae tissue and developing classifiers for both single and multiple frequencies. Additionally, efforts are made to create a vertebrae phantom with realistic electric and optical properties. EIS demonstrates an increase in impedance for cortical bone compared to cancellous bone due to the latter’s weblike structure with highly vascularized yellow bone marrow. Single-frequency analysis outperforms multiple-frequency analysis in distinguishing between vertebrae tissues. However, the development of a better model or the use of multiple single-frequency classifiers may enhance predictive
accuracy. Despite attempts to create an accurate vertebrae phantom, limitations in adjusting dielectric properties result in the utilization of the best-fit recipe.

Comparison between EIS and DRS reveals both are effective in detecting cortical breaches and tissues, with DRS exhibiting a longer look-ahead distance. EIS operates more like a step function, making it susceptible to distortions, suggesting DRS outperforms EIS in spinal fusion surgeries.

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.

Spinal fusion is a surgical treatment involving stiffening parts of the spinal column to eliminate any relative motion and improve spine stability. A critical part of spinal fusion surgery is the placement of pedicle screws because it is highly complex and can damage the vascular structures and nerves near the vertebrae. To prevent complications, a new anchoring method is developed that strengthens screw contact by following the curved trajectory of the dense cortical shell while avoiding a cortical breach. Diffuse reflectance spectroscopy (DRS) is a technique that could be used in a bone drill to obtain real-time information about the location of the drill within the vertebra. In order to drill the correct trajectory, an optical probe using DRS should determine the parallel closeness of cortical bone to the drill tip. To show the potential of this novel technology for improving spinal fusion surgery, this master thesis introduces and validates a flexible sideways-looking probe using DRS to identify the proximity of cortical bone when measuring along the cortical shell of a vertebra.

In this study, the ideal optical design to detect the proximity of cortical bone is investigated by looking into the effect of fiber angulation on the photon propagation using Monte Carlo simulations and phantom experiments. A conceptual design was created based on the ideal optical design combined with the mechanical requirements to make the probe insertable into a vertebra. As a proof of concept, a prototype was developed and tested on a bone-mimicking phantom and porcine vertebrae.

The conceptual design comprises a flexible needle with two optical fibers attached to a rigid tip with a diameter of 2.9 mm. Two mirrors are positioned in the rigid tip, emitting light 45\degree off-axis and collecting light 90\degree off-axis with a source-detector separation of 2.1 mm. These light directions were chosen because they optimize the reflectance spectrum difference between cancellous and cortical bone due to a longer path length, making detecting cortical bone closeness easier. A prototype was made that demonstrates that the probe can detect the parallel proximity of cortical bone at a depth up to 1.5 mm in an ideal phantom setting. The prototype can distinguish between pure cancellous and cortical bone in porcine vertebrae. Additionally, the prototype can also be inserted into the pedicles and bent along the cortical wall of a vertebra. These positive findings show that the flexible sideways-looking probe created in this study can potentially improve spinal fusion surgery by enabling an increase in cortical bone contact without perforating it. Although proof of concept has been provided, it is essential to improve the design for safety and usability and improve tissue type identification accuracy before continuing to clinical trials.

The spine is an intricate and crucial part of the human body. Unfortunately, spinal conditions such as scoliosis and trauma can cause instability and deformity to the spine. Patients can experience discomfort and pain. Spinal fusion surgery is used to repair and correct severe cases. During this procedure the vertebrae are fused to prevent them from moving relative to each other, thus increasing stability. Pedicle screws and rods are used to lock the vertebrae together and bone grafts are inserted to grow the vertebrae together. The insertion of the pedicle screws is a complicated procedure where breaches of the cortical wall can occur leading to tissue damage and possible complications for the patient. To prevent breaches, guidance methods have been introduced. However, these methods have considerable disadvantages in terms of patient safety and costs. Introducing an alternative guidance method, this master thesis investigates the development of a drill that uses diffuse reflectance spectroscopy (DRS). DRS is a spectroscopy method that uses diffuse reflection to determine the structural and chemical properties of a biological sample. By differentiating cortical and cancellous bone based on their fat content, directional feedback is provided to guide the user during the drilling of the pedicle. In this work, a drilling prototype was developed that uses DRS to provide directional feedback. The prototype uses integrated optical fibres to sense in two different directions: along the drilling direction and at a 90°angle to the drilling direction. This allows the device to sense the surrounding volume and provide feedback on the type of bone the drill encounters. A 3D Monte Carlo RTE solver, MCMatlab, was used to simulate photon transport inside biological tissue. Core-to-core distances larger than 1 mm were investigated to find if the corresponding look-ahead would increase distances as well as different fibre configurations for a prototype. Multiple design concepts were proposed and assessed. A prototype was made and tested on a 2-layered bone phantom. The results indicated a frontal look-ahead distance of 3.6 mm for a 4 mm core-to-core distance as well as a 1.5 mm sideways look-ahead distance for a 1.5 mm core-to-core distance. The prototype provides a proof of concept that DRS can be integrated into a drill in such a way it can provide directional feedback. Although results are promising, improvements can still be made in the collection of data to provide consistent results for directional feedback.

Introduction: Although being the most advanced spinal stabilization method, pedicle screw fixation has an increased number of complications compared to other surgical procedures, due to the complex spinal anatomy, large inter-patient anatomical variability, and the highly vulnerable surrounding tissue of the spine. Screw fixation strength can be increased by anchoring a flexible screw in a hole following the curved trajectory of the more dense cortical shell of the vertebral body, instead of the porous core. The curved trajectory can be determined by local diffuse reflectance spectroscopy (DRS) guiding. Currently, there is no commercial phantom or phantom recipe known that provides the correct optical and structural material characteristics for testing DRS guiding and curved trajectory drilling on, comparing it to similar devices, and perform surgical training sessions on. The research goal is to design and validate an integrated phantom that closes this gap. Preliminary test results: Preliminary optical and structural tests were performed separately on hybrid optical filler samples and structural matrix samples, respectively. The hybrid optical filler samples made out of water, fat (30%, 40% and 50% fat fraction) and silicone (95%, 80%, and 50%) were inspected visually, and spectra were obtained by means of a DRS device in week 0 as well as in week 10. The most promising optical filler sample consisted of 50% of silicone and 50% of water+fat, with a fat fraction of 40%. The measured DRS signals showed a clear correlation between the fitted and actual water+fat content, which, can thus be used as a tissue differentiation parameter. The stability and preservability of phantoms that were enhanced with silicone and resulted in homogeneous mixtures, was increased compared to samples without any silicone. For the structural matrix, different 3D printers, materials, and infill densities were evaluated on drill characteristics and compression characteristics. The best bone mimicking structural phantom consisted of an FDM printed part made out of ABS with a gyroid infill structure with an infill density of 50%. Integrated phantom validation: The combination of the optical filler and the structural matrix was validated by infusing the optical filler in the structural matrix with a vacuum chamber and measuring the drill characteristics and DRS spectra at various depths inside the phantom. A gradual increase in axial drilling force and a gradual change in spectral shape was noticed as a function of depth from the cancellous zone, to the pre-cortical zone and cortical zone. Discussion: The ABS material and the actual optical filler constituents (such as peanut oil and specific silicone types) should be implemented inviii the fitting algorithm. Nevertheless, the results of this research show not only great potential phantom design for a wide variety of bone types because of the structure and shape design flexibility of 3D printing, but also for soft tissues by using only the optical filler with a much better stability and preservability than traditional soft tissue phantoms.