Background Inter- and intra patient morphological differences and absence of visual feedback make the placement of pedicle screws technically very demanding. As the spine is surrounded by neurovascular tissue, complications can have severe consequences, including paralysis. Guidance techniques are often very expensive and can overexpose surgeons to radiation, while there is a high variability in reported accuracy rates. Diffuse reflectance spectroscopy (DRS) is a technique that allows for real-time tissue discrimination using an optical fiber which can e.g. be placed in a K-wire. It can detect difference in fat fraction between cortical and cancellous bone. Purpose This master thesis aims at investigating the capability of the DRS equipped K-wire to anticipate cortical breach by measuring a decrease in fat fraction, while being oscillated with a power hammering tool. Mechanical experiments investigate the amount of control over penetration depth during powered hammering insertion of a K-wire. Methods This thesis contains three experiments. Two focus on mechanical properties and one on optical properties. In the mechanical experiments, a 1.6 X 60 mm trocar tip K-wire without integrated optical fibers is used. In the first experiment, the K-wire and its oscillator are attached to a carriage on a horizontal guide rail. A mechanical bone phantom is placed at the end of the rail and is penetrated at varying oscillation frequencies (0 – 50 Hz). To move the carriage towards the bone phantom, masses are attached in discrete steps of 250 grams. Penetration depth is measured as insertion mass increases at constant oscillation frequency. In the second mechanical experiment, the same K-wire and K-wire oscillator are attached to a vertical linear stage. The K-wire penetrates the mechanical bone phantom at an oscillation frequency of 0 Hz or 35 Hz. Feed rates are varied (0.5 – 2.5 mm/s) and force on the bone phantom is continuously measured. For the optical experiment, a 1.6 X 300 mm fiber-optic K-wire is used with fiber distance equalling 1.22 mm. The K-wire with the oscillator are attached to a linear stage, and lowered at constant feed rate (0.5 mm/s) into an optical bone phantom. NIR spectra are acquired with a sampling frequency of 1.6 Hz. The effect of varying oscillation frequency (0 – 50 Hz) on measured fat fractions is quantified. Results The first mechanical experiment showed that for every oscillation frequency, penetration started at the first weight increment (0.1 kg). Without oscillations, phantom penetration initiated at a mass of 1.85 Kg. Regression analysis proved the penetration depth depends on the square root of applied axial force. In the mass range of 0 – 1.6 kg, 45 Hz led to the largest penetration depth (25 mm), with a relatively narrow 95% confidence interval (17 – 33 mm). The second mechanical experiment showed that measured mean force is lower when oscillating the K-wire (1.4 – 5.8 N vs. 9.5 – 12.3 N, p<0.0001). Effect of feed rate on measured mean force is found not significant (p=0.15 for oscillating and p=0.61 for not oscillating). In the optical test, it was found that look ahead distance (LAD) increases with increasing oscillation frequency and amplitude. 50 Hz was the only frequency where the LAD was larger than its oscillation amplitude (1.22 mm and 0.5 mm, respectively). Conclusion Powered hammering of a K-wire requires a lower axial force for penetration and therefore allows for more control over penetration depth. From the tested range, this effect is most significant for oscillations with high frequencies, adequate forces and low amplitudes. It is possible to measure a decrease in fat fraction with a fiber-optic k-wire during penetration. High oscillation frequencies with low amplitudes allow for earliest anticipation. An adequate sized sampling frequency is required to allow for breach anticipation.

Introduction. In spinal surgery, the misplacement of spinal screws is a problem that causes (severe) pain, bleedings or even paralysis [2]. Screw misplacements are common as navigating in the spine is difficult due to the small vertebral dimensions and a lack of anatomical landmarks [3] [4]. In order to improve the navigational support of spine surgeons, this research focuses on the development of an optical sensing diffuse reflectance spectroscopy (DRS) surgical drill that identifies bone tissue boundaries. The developed drill concept introduces a stagnant optical fiber-equipped probe into a cannulated orthopaedic drill. To verify the clinical applicability of the developed system, the accuracy of the optical tissue boundary detection has been analysed under different tissue penetration speeds, as well as the axial drilling force increases due to the introduction of a stagnant probe into a drill.
Results. When increasing the drilling feed rate in the optical phantom, the drill overshoot (the difference between the DRS-derived tissue boundary location identification and the actual location of the phantom boundary) shows a larger spread. The maximum feed rate at which no overshoot takes place is 0,5mm/s. Increasing the sampling frequency –especially decreasing the inactive period between the measurements– can improve this.
None of the K-wire equipped drills can penetrate the used Sawbones® cortical bone phantom. The axial peak feed forces occurring in the Sawbones® cancellous bone phantom while using a regular 2,7mmØ orthopaedic drill is 38,2N. When using the 2,7mmØ orthopaedic drill with a 1,6mmØ K-wire, a peak of 57,6N is observed. Because the data from drilling in the Sawbones® cancellous bone is not normally distributed, a benchmark experiment on cheese is analysed. On average, the introduction of a K-wire increases the required drilling forces by a 296% (roughly a factor 3). Among the different feed rates and drill types, the force increase of introducing a stagnant K-wire varies between 16% and 575%.
Conclusion. To prevent orthopaedic screws from breaching the bone surface (an overshoot of 0mm) in spinal surgery, the established feed rate speed limit of 0,5mm/s is too low. To meet the observed feed rates applied by surgeons of up to 5mm/s, it is of interest to reduce the DRS sampling time – the inactive period between two measurements in particular. The feed force increase of approximately a factor 3 can be regarded as a challenge for surgeons, who indicated that they preferred feed forces to be kept low. Further testing on real (cadaveric) vertebrae can more give information about the DRS drill’s optical performance in pedicles, and whether the identified feed force increase proves to be problematic for clinical applications.

In spinal surgery, the misplacement of spinal screws is a common problem that causes (severe) pain, bleedings or even paralysis [1] [2] [3]. In order to improve the navigational support of spine surgeons, this research focuses on the development of an optical sensing diffuse reflectance spectroscopy (DRS) orthopaedic drill that identifies bone tissue boundaries, based on fat fraction. The developed drill concept introduces a stagnant optical fiber-equipped probe into a cannulated orthopaedic drill. To verify the clinical applicability of the developed system, the accuracy of the optical tissue boundary detection has been analysed under different tissue penetration speeds, as well as the axial drilling force increases due to the introduction of a stagnant probe into a cannulated drill. The maximum feed rate at which the drill consistently detects the tissue boundary before breaching it, is 0,5mm/s. The force increase due to the introduction of a stagnant probe is a factor 2,96 on average and varies widely between different feed rates and probe diameters (a factor 1,15–5,75). The established feed rate speed limit of 0,5mm/s is lower than drilling feed rates of up to 5mm/s, observed in the operation room. Increasing the sampling frequency –especially decreasing the inactive period between the measurements– is required. The feed force increase of approximately a factor 3 can be regarded as a challenge for surgeons, who indicated that they preferred feed forces to be kept low.