Experimental determination of the emissivity of bone

Comparison of k-wire insertion using oscillatory and unidirectional drilling modes under constant thrust force

Heat generation during the Kirschner wire (K-wire) insertion process, under either unidirectional or oscillatory drilling mode, places bone at risk of thermal osteonecrosis which can lead to infection. There is a lack of quantitative understanding of the heat generation difference between the two drilling modes and knowledge of optimal thrust force level under each mode is missing. The goal of this study is to investigate the effects of drilling modes and thrust force levels on the bone drilling outcomes. Controlled machine-based constant thrust force K-wire insertion experiments were conducted with key process parameters monitored and compared quantitatively. Statistical analysis showed that the oscillatory mode consumed 2.6 times more electricity than the unidirectional mode but generated 53% less thermal energy and 23% lower peak temperature. However, the oscillation also led to 18% higher peak torque in the transient drilling stage and 23% shallower drilling depth. The optimal choice of the drilling mode depends on specific surgical needs to minimize bone damage (control of peak temperature vs. exposure time and torque control). Heat generation was dominated by the torque and corresponding rotational power under both modes. To minimize the bone temperature while keeping high drilling speed efficiency, a moderate thrust force is preferred under the unidirectional mode to balance between feed force and compressed debris resistance. For oscillatory mode, a small thrust force to keep the K-wire engaged with the bone is optimal.

Comparison of Long-Wave and Mid-Wave Infrared Imaging Modalities for Photothermal Coherence Tomography of Human Teeth

The ability to detect dental caries at early stages lies at the heart of minimal intervention dentistry, enabling the curing or arresting of carious lesions before they advance to the cavity stage. Enhanced truncated-correlation photothermal coherence tomography (eTC-PCT) using mid-wave infrared (MWIR) cameras has recently been shown to offer tomographic visualization of early caries. The tomographic slicing ability of such systems, however, is believed to be limited by direct radiative thermal emission through the translucent dental enamel in the 3-5 m MWIR spectral range. Such radiative emissions can dominate the delayed conductive thermal contributions needed for tomographic reconstruction of internal dental defects. It has been hypothesized that long-wave infrared (LWIR) eTC-PCT systems may offer better tomographic performance by taking advantage of the intrinsic attenuation of direct radiative emission by dental enamel in the LWIR spectral range, enabling more effective delayed conductive thermal contributions from subsurface caries. More than an order of magnitude lower cost of the system is another key attribute of LWIR eTC-PCT which can open the door for downstream translation of the technology to clinics. In this report, we offer a systematic comparison of the performance/effectiveness of caries detection with LWIR and MWIR eTC-PCT systems for detecting natural caries, bacterial caries, and artificially demineralized enamel surfaces. Our results suggest that the low-cost LWIR based eTC-PCT system provides 3D visualization and 2D slice-by-slice images of early caries and internal micro-cracks similar to those obtained from the more expensive MWIR-based eTC-PCT system, albeit with ~1.3dB lower signal-to-noise ratio.

Finite element simulation and integration of CEM43 °C and Arrhenius Models for ultrasonic-assisted skull bone grinding: A thermal dose model

The aim of the study was to develop a novel automated setup for bone grinding to limit the temperature to below 43 °C. The feasibility of using ultrasonic actuation during bone osteotomy was explored with different machining variables, such as rotational speed, feed rate and ultrasonic frequency, in terms of the criterion variable (i.e., temperature). A thermal dose model based on the CEM43 °C and the Arrhenius model was developed for the prediction of tissue damage during bone grinding. CEM43 °C is a normalizing method to convert the time-temperature relationship into an equivalent number of minutes at 43 °C. For every degree rise in temperature above 43 °C, the cell viability significantly increased. The temperature generated during bone grinding was measured with an infrared thermography technique. The increase in temperature above threshold levels of 43 °C and 47 °C may harm the bone tissues and cause thermogenesis and osteonecrosis, respectively. A finite-element simulation was conducted to visualise the spatial and temporal distribution of temperature on the bone surface after bone grinding. Furthermore, simulation results were used to measure the depth of thermogenesis and osteonecrosis at the grinding site. Evaluation of the optimised set of bone grinding process parameters was supported with analysis of variance at the 95% confidence level.

Analysis of machining process and thermal conditions during vibration-assisted cortical bone drilling based on generated bone chip morphologies

When the temperature during bone drilling exceeds the safety threshold, the bone tissue surrounding the drilling site can be irreversibly damaged. To investigate the influence of vibration-assisted drilling (VAD) methods on the temperature increase during bone drilling and the causes for temperature increase, drilling experiments were performed on fresh bovine femur samples. The morphology and granularity distribution of the generated bone chips were innovatively used to directly compare the machining processes and thermal conditions of conventional drilling (CD), low-frequency vibration-assisted drilling (LFVAD), and ultrasonic vibration-assisted drilling (UVAD). The experimental results indicated that LFVAD produced the lowest temperature increase of 31.4°C, whereas UVAD produced the highest temperature increase of 44.1°C with the same drilling parameters. Additionally, the morphologies and granularity distributions of the bone chips significantly differed among these methods. We concluded that the smaller temperature increase in LFVAD was mainly attributed to the improved thermal conditions resulting from the periodic cutting/separation motion and the reliable geometric chip-breaking mechanism. In contrast, the unfavourable thermal conditions of UVAD were caused by the higher applied frequency, which created a significantly larger amount of friction heat. This was the main cause for the highest observed temperature increase, resulting in bone crushing processes that generated additional heat.

Experimental investigation of the temperature elevation in bone drilling using conventional and vibration-assisted methods

Bone drilling is widely used in orthopaedics for inserting screws and fixing prostheses. Thermal necrosis is one of the major problems that may seriously affect post-operative recovery. Accordingly, this paper mainly focuses on comparing the influences of conventional drilling (CD), ultrasonic vibration-assisted drilling (UVAD) and low-frequency vibration-assisted drilling (LFVAD) methods, and drilling parameters on the temperature elevation in bone drilling process. A full factorial experiment was performed, and the temperatures were measured using an infrared camera. The lowest temperature elevation was obtained by LFVAD compared with CD and UVAD at the same drilling conditions. Setting CD as a reference, the maximum difference between LFVAD and CD was approximately -4 °C, whereas that between UVAD and CD was approximately 16 °C. The temperature elevation increases linearly with the spindle speed and follows an inverted U-shaped curve, with the feed rate having a peak at 40 min/mm in each drilling method. The results were discussed with regard to the features of LFVAD and UVAD. It was expected that the LFVAD could achieve minimal thermal damage and attain better results in the medical bone drilling process.

Comparison of wear and temperature of zirconia and tungsten carbide tools in drilling bone: in vitro and finite element analysis

Drilling is extensively used in operations on bones and dental implants, and yet poses a considerable challenge because it can damage cells as well as cause mechanical and thermal stresses to the bone. The goal of this study was to assess the temperature changes and instrument wear using both zirconium dioxide (ZrO₂) ceramics and tungsten carbide (WC) tools using a 3-dimensional finite element analysis (FEA) of bone drilling. The wear of conical burrs made from ZrO₂ and tungsten carbide was measured using scanning electron microscopy (SEM) and image processing software. Temperature was measured by an infrared thermometer. As well as 3-dimensional FEA, the temperature and wear of the burrs was predicted with the aid of the Johnson-Cook model for bone material properties. Comparison between the ZrO₂ and WC burrs using SEM showed that the ZrO₂ burr was less worn than the WC burr (p = 0.044) and there was significant difference in temperature between the two (p = 0.020). We conclude that ZrO₂ tools are a suitable alternative to WC, particularly in superficial drilling with coolant, as they wear less than the WC tools. The results of the FEA successfully predicted the variation in temperature and the wear on the tools.

Infrared thermography of high-speed grinding of bone in skull base neurosurgery

For skull base tumor removal neurosurgery, skull bone grinding is required. During this process, temperature rise occurs, which may result in an irrecoverable thermal damage. In the present research, temperature variations during bone grinding have been studied. Experimental tests have been conducted in 27 states in terms of the parameters of rotational speed (three states), feed rate (three states), and cutting depth (three states) on bovine femur bone samples. Attempts have been made to determine optimal processing conditions for minimizing thermal damage during the surgery through infrared thermography and measuring thermal variations of the bone. The results indicated that the temperature rise of the bone has a direct relationship with the parameters of rotational speed, feed rate, and cutting depth. In other words, with elevation of each of these parameters, temperature rise was also intensified. Out of the cutting parameters, rotational speed had the maximum impact on temperature rise, followed by cutting depth and feed rate. Therefore, to reduce the extent of thermal damage incurred to the neural tissue, the minimum values for the cutting parameters are proposed as follows: rotational speed = 45000 r min−1, feed rate = 20–30 mm min−1 with depth of cut = 0.25 mm, and feed rate = 20 mm min−1 with cutting depth = 0.50 mm.

Drilling of bone: Effect of drill bit geometries on thermal osteonecrosis risk regions

Bone-drilling operation necessitates an accurate and efficient surgical drill bit to minimize thermal damage to the bone. This article provides a methodology for predicting the bone temperature elevation during surgical bone drilling and to gain a better understanding on the influences of the point angle, helix angle and web thickness of the drill bit. The proposed approach utilized the normalized Cockroft-Latham damage criterion to predict material cracking in the drilling process. Drilling simulation software DEFORM-3D is used to approximate the bone temperature elevation corresponding to different drill bit geometries. To validate the simulation results, bone temperature elevations were evaluated by comparison with ex vivo bone-drilling process using bovine femurs. The computational results fit well with the ex vivo experiments with respect to different drill geometries. All the investigated drill bit geometries significantly affect bone temperature rise. It is discovered that the thermal osteonecrosis risk regions could be reduced with a point angle of 110° to 140°, a helix angle of 5° to 30° and a web thickness of 5% to 40%. The drilling simulation could accurately estimate the maximum bone temperature elevation for various surgical drill bit point angles, web thickness and helix angles. Looking into the future, this work will lead to the research and redesign of the optimum surgical drill bit to minimize thermal insult during bone-drilling surgeries.

Optimization of drilling parameters for thermal bone necrosis prevention

BACKGROUND

Bone drilling is a mandatory process in orthopedic surgery to fix the fractured bones. Excessive heat is generated due to the shear deformation of bone and friction energy during the drilling process.

OBJECTIVE

This paper is carried out to optimize the bone drilling parameters to prevent thermal bone necrosis. The main contribution of this work is instead of only consider the influence of rotational speed and feed rate, the effect of tool diameter and drilling hole depth are also incorporated for optimization study.

METHODS

Response surface methodology (RSM) was used to develop a temperature prediction model. Drilling experiments were performed using finite element software DEFORM-3D. Analysis of variance (ANOVA) was conducted to investigate the drilling parameters' effect. Desirability function in RSM was used to determine the optimum combination of drilling parameters.

RESULTS

Results indicated that one applicable combination of drilling parameters could increase the bone temperature by less than 0.03%. To avoid thermal bone necrosis, eight reasonable combinations of drilling parameters were proposed. 3.3∘C residuals between in-vitro experiments and predicted values were demonstrated.

CONCLUSIONS

It is envisaged that finite element simulation with RSM can simplify tedious experimental works and useful in the clinical application to avoid bone necrosis.

Pre-operative Screening and Manual Drilling Strategies to Reduce the Risk of Thermal Injury During Minimally Invasive Cochlear Implantation Surgery

This article presents the development and experimental validation of a methodology to reduce the risk of thermal injury to the facial nerve during minimally invasive cochlear implantation surgery. The first step in this methodology is a pre-operative screening process, in which medical imaging is used to identify those patients that present a significant risk of developing high temperatures at the facial nerve during the drilling phase of the procedure. Such a risk is calculated based on the density of the bone along the drilling path and the thermal conductance between the drilling path and the nerve, and provides a criterion to exclude high-risk patients from receiving the minimally invasive procedure. The second component of the methodology is a drilling strategy for manually-guided drilling near the facial nerve. The strategy utilizes interval drilling and mechanical constraints to enable better control over the procedure and the resulting generation of heat. The approach is tested in fresh cadaver temporal bones using a thermal camera to monitor temperature near the facial nerve. Results indicate that pre-operative screening may successfully exclude high-risk patients and that the proposed drilling strategy enables safe drilling for low-to-moderate risk patients.

Real-Time Prediction of Temperature Elevation During Robotic Bone Drilling Using the Torque Signal

Bone drilling is a surgical procedure commonly required in many surgical fields, particularly orthopedics, dentistry and head and neck surgeries. While the long-term effects of thermal bone necrosis are unknown, the thermal damage to nerves in spinal or otolaryngological surgeries might lead to partial paralysis. Previous models to predict the temperature elevation have been suggested, but were not validated or have the disadvantages of computation time and complexity which does not allow real time predictions. Within this study, an analytical temperature prediction model is proposed which uses the torque signal of the drilling process to model the heat production of the drill bit. A simple Green's disk source function is used to solve the three dimensional heat equation along the drilling axis. Additionally, an extensive experimental study was carried out to validate the model. A custom CNC-setup with a load cell and a thermal camera was used to measure the axial drilling torque and force as well as temperature elevations. Bones with different sets of bone volume fraction were drilled with two drill bits ([Formula: see text]1.8 mm and [Formula: see text]2.5 mm) and repeated eight times. The model was calibrated with 5 of 40 measurements and successfully validated with the rest of the data ([Formula: see text]C). It was also found that the temperature elevation can be predicted using only the torque signal of the drilling process. In the future, the model could be used to monitor and control the drilling process of surgeries close to vulnerable structures.

Reducing temperature elevation of robotic bone drilling

This research work aims at reducing temperature elevation of bone drilling. An extensive experimental study was conducted which focused on the investigation of three main measures to reduce the temperature elevation as used in industry: irrigation, interval drilling and drill bit designs. Different external irrigation rates (0 ml/min, 15 ml/min, 30 ml/min), continuously drilled interval lengths (2 mm, 1 mm, 0.5 mm) as well as two drill bit designs were tested. A custom single flute drill bit was designed with a higher rake angle and smaller chisel edge to generate less heat compared to a standard surgical drill bit. A new experimental setup was developed to measure drilling forces and torques as well as the 2D temperature field at any depth using a high resolution thermal camera. The results show that external irrigation is a main factor to reduce temperature elevation due not primarily to its effect on cooling but rather due to the prevention of drill bit clogging. During drilling, the build up of bone material in the drill bit flutes result in excessive temperatures due to an increase in thrust forces and torques. Drilling in intervals allows the removal of bone chips and cleaning of flutes when the drill bit is extracted as well as cooling of the bone in-between intervals which limits the accumulation of heat. However, reducing the length of the drilled interval was found only to be beneficial for temperature reduction using the newly designed drill bit due to the improved cutting geometry. To evaluate possible tissue damage caused by the generated heat increase, cumulative equivalent minutes (CEM43) were calculated and it was found that the combination of small interval length (0.5 mm), high irrigation rate (30 ml/min) and the newly designed drill bit was the only parameter combination which allowed drilling below the time-thermal threshold for tissue damage. In conclusion, an optimized drilling method has been found which might also enable drilling in more delicate procedures such as that performed during minimally invasive robotic cochlear implantation.