Diffuse reflectance spectroscopy-enhanced bone drill for directional feedback during spinal fusion surgery

Abstract

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.