Measurement of thermal conductivity of bovine cortical bone

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.

Thermal Conductivity of Human Bone in Cryoprobe Freezing as Related to Density

Cryoprobes create localized cell destruction through freezing. Bone is resistant to temperature flow but is susceptible to freezing necrosis at warmer temperatures than tumor cells. Few studies have determined the thermal conductivity of human bone. No studies have examined conductivity as related to density. The study goal was to examine thermal conductivity in human bone while comparing differences between cancellous and cortical bone. An additional goal was to establish a relationship between bone density and thermal conductivity. Six knee joints from 5 cadavers were obtained. The epiphyseal region was sliced in half coronally prior to inserting an argon-circulating cryoprobe directed away from the joint line. Thermistor thermometers were placed perpendicularly at measured increments, and the freezing cycle was recorded until steady-state conditions were achieved. For 2 cortical samples, the probe was placed intramedullary in metaphyseal samples and measurements were performed radially from the central axis of each sample. Conductivity was calculated using Fournier's Law and then plotted against measured density of each sample. Across samples, density of cancellous bone ranged from 0.86 to 1.38 g/mL and average thermal conductivity ranged between 0.404 and 0.55 W/mK. Comparatively, cortical bone had a density of 1.70 to 1.86 g/mL and thermal conductivity of 0.0742 to 0.109 W/mK. A strong 2-degree polynomial correlation was seen (R²=0.8226, P<.001). Bone is highly resistant to temperature flow. This resistance varies and inversely correlates strongly with density. This information is clinically relevant to maximize tumor ablation while minimizing morbidity through unnecessary bone loss and damage to surrounding structures. [Orthopedics. 2017; 40(2):90-94.].

Rotary ultrasonic drilling on bone: A novel technique to put an end to thermal injury to bone

Bone drilling is common in orthopedic procedures and the heat produced during conventional experimental drilling often exceeds critical temperature of 47 °C and induces thermal osteonecrosis. The osteonecrosis may be the reason for impaired healing, early loosening and implant failure. This study was undertaken to control the temperature rise by interrupted cutting and reduced friction effects at the interface of drill tool and the bone surface. In this work, rotary ultrasonic drilling technique with diamond abrasive particles coated on the hollow drill tool without any internal or external cooling assistance was used. Experiments were performed at room temperature on the mid-diaphysis sections of fresh pig bones, which were harvested immediately after sacrifice of the animal. Both rotary ultrasonic drilling on bone and conventional surgical drilling on bone were performed in a five set of experiments on each process using identical constant process parameters. The maximum temperature of each trial was recorded by K-type thermocouple device. Ethylenediaminetetraacetic acid decalcification was done for microscopic examination of bone. In this comparative procedure, rotary ultrasonic drilling on bone produced much lower temperature, that is, 40.2 °C ± 0.4 °C and 40.3 °C ± 0.2 °C as compared to that of conventional surgical drilling on bone, that is, 74.9 °C ± 0.8 °C and 74.9 °C ± 0.6 °C with respect to thermocouples fixed at first and second position, respectively. The conventional surgical drilling on bone specimens revealed gross tissue burn, microscopic evidence of thermal osteonecrosis and tissue injury in the form of cracks due to the generated force during drilling. But our novel technique showed no such features. Rotary ultrasonic drilling on bone technique is robust and superior to other methods for drilling as it induces no thermal osteonecrosis and does not damage the bone by generating undue forces during drilling.

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.

Exploring thermal anisotropy of cortical bone using temperature measurements in drilling

BACKGROUND

Bone drilling is widely used in orthopaedics for fracture treatment, reconstructive surgery and bone biopsy. Heat generation in bone drilling can cause rise in bone temperature resulting in prolonged healing time or loosening of fixation.

OBJECTIVE

The purpose of this study was to investigate thermal anisotropy of bone by measuring the level of temperature in bone drilling with and without cooling conditions in two anatomical directions.

METHODS

Drilling tests were performed on bovine cortical bone. A total of fifteen specimens were used to obtain data for statistical analysis. Temperature near the cutting zone was measured in two anatomical directions. i.e. along the longitudinal and circumferential direction. Temperature distribution was also found in the two prescribed directions. Analysis of variance (ANOVA) was used to identify significant drilling parameter affecting bone temperature.

RESULTS

Drilling speed, feed rate and drill size were found influential parameters affecting bone temperature. Higher drilling speed, feed rate, and large drill size were found to cause elevated temperature in bone. Much lower temperature was measured in bone when cooling fluid was supplied to the drilling region. Experimental results revealed lower temperatures in the circumferential direction compared to the longitudinal direction.

CONCLUSIONS

Thermal anisotropy for heat transport was found in the bone. This study recommends lower drilling speed and feed rate and cooling for controlling rise in bone temperature.

Numerical and Experimental Analyses on the Temperature Distribution in the Dental Implant Preparation Area when Using a Surgical Guide

PURPOSE

During dental implantation, if the temperature within the bone tissue exceeds a critical value, the thermal necrosis of bone cells may take place, inhibiting osseointegration. In contrast to conventional dental implant surgery, a surgery guided by a surgical template is a safer and more efficient technique; however, the temperature within the implant field is more difficult to control, because the surgical guide blocks irrigation water. The purpose of this study was to investigate the temperature distribution in the drilling site when preparing for dental implant placement with a surgical guide, and to derive suggestions for clinical operation.

MATERIALS AND METHODS

Initially, the sources of heat during drilling were investigated, and theoretical equations were listed. Subsequently, a measurement system using thermocouples was constructed, with which the temperature increments at specific points in the simulated bone samples were recorded during guided drilling with different cooling methods. Based on the equations and data assessed, a thermal simulation model with a finite element method (FEM) was created, and the temperature change of the whole surgical field was calculated on the basis of the numerical simulation results. Consequently, the point experiencing the highest temperature within the bone was determined.

RESULTS

From the experimental measurements, the highest temperature increment was located at a depth of 6 mm without irrigation and at 8 mm with cooling, rather than at the deepest point of the prepared hole. Because the surgical guide blocks the cooling water from entering the drilling site, the biggest increment of temperature using conventional irrigation with the surgical guide was 1.95 times that recorded when using a surgical guide consisting of cooling channels, and 3.6 times that recorded using a drill with an internal cooling hole. And from numerical analysis, during drilling for implant placement site with conventional irrigation, the highest temperature (45.6°C) was close to the critical point at which bone necrosis occurs.

CONCLUSIONS

Based on theoretical analysis, experimentation, and FEM simulation, the temperature distribution of the drilling area in the placement of dental implants under surgical guide was determined. For clinical operation, improved cooling methods, such as using a drill with an internal cooling channel, should be used, and the drill should be regularly withdrawn during drilling.

Temperature Values Variability in Piezoelectric Implant Site Preparation: Differences between Cortical and Corticocancellous Bovine Bone

Purpose. Various parameters can influence temperature rise and detection during implant site preparation. The aim of this study is to investigate local temperature values in cortical and corticocancellous bovine bone during early stages of piezoelectric implant site preparation. Materials and Methods. 20 osteotomies were performed using a diamond tip (IM1s, Mectron Medical Technology, Carasco, Italy) on two different types of bovine bone samples, cortical and corticocancellous, respectively. A standardized protocol was designed to provide constant working conditions. Temperatures were measured in real time at a fixed position by a fiber optic thermometer. Results. Significantly higher drilling time (154.90 sec versus 99.00 sec; p < 0.0001) and temperatures (39.26°C versus 34.73°C; p = 0.043) were observed in the cortical group compared to the corticocancellous group. A remarkable variability of results characterized the corticocancellous blocks as compared to the blocks of pure cortical bone. Conclusion. Bone samples can influence heat generation during in vitro implant site preparation. When compared to cortical bone, corticocancellous samples present more variability in temperature values. Even controlling most experimental factors, the impact of bone samples still remains one of the main causes of temperature variability.

Heat accumulation during sequential cortical bone drilling

Significant research exists regarding heat production during single-hole bone drilling. No published data exist regarding repetitive sequential drilling. This study elucidates the phenomenon of heat accumulation for sequential drilling with both Kirschner wires (K wires) and standard two-flute twist drills. It was hypothesized that cumulative heat would result in a higher temperature with each subsequent drill pass. Nine holes in a 3 × 3 array were drilled sequentially on moistened cadaveric tibia bone kept at body temperature (about 37 °C). Four thermocouples were placed at the center of four adjacent holes and 2 mm below the surface. A battery-driven hand drill guided by a servo-controlled motion system was used. Six samples were drilled with each tool (2.0 mm K wire and 2.0 and 2.5 mm standard drills). K wire drilling increased temperature from 5 °C at the first hole to 20 °C at holes 6 through 9. A similar trend was found in standard drills with less significant increments. The maximum temperatures of both tools increased from <0.5 °C to nearly 13 °C. The difference between drill sizes was found to be insignificant (P > 0.05). In conclusion, heat accumulated during sequential drilling, with size difference being insignificant. K wire produced more heat than its twist-drill counterparts. This study has demonstrated the heat accumulation phenomenon and its significant effect on temperature. Maximizing the drilling field and reducing the number of drill passes may decrease bone injury.

Influence of bone density and implant drill diameter on the resulting axial force and temperature development in implant burs and artificial bone: an in vitro study

PURPOSE

The aim of this study was to determine how the bone density affects the temperature development in artificial bone and drill.

METHODS

Ten single drills with diameters of 2.2, 2.8, 3.5, and 4.2 mm were used on four artificial bone blocks (density I-IV), with constant speed and external irrigation. Temperature measurement in blocks and drills was done by infrared camera. The resultant axial force was measured, and light microscopic examinations of the drills were performed before and after preparation.

RESULTS

The block density has a greater influence on resulting axial force than the drill diameter (D1 = 2.2 mm, 4.11 ± 0.64 N; 4.2 mm, 9.69 ± 0.78 N vs. D4 = 2.2 mm, 0.5 ± 0.18 N; 4.2 mm, 1.23 ± 0.08 N). For the narrowest drill, a decrease in bone density caused a significant temperature increase in the bone and drill. However, for the thickest drill, no thermal differences were found in the bone but were seen in the drill itself (D1 = 2.8 mm vs. D4 = 2.8 mm; bone p < 0.0001, drill p < 0.0001; D1 = 4.2 mm vs. D4 = 4.2 mm; bone p = 0.5366, drill p = 0.0411). An increase in the drill diameter in the highest bone density led to a significant thermal increase in the bone and drill. However, for the lowest bone density, thermal changes were observed only in the bone (D1 = 2.8 mm vs. D1 = 4.2 mm; bone p < 0.0001, drill p < 0.0001; D4 = 2.8 mm vs. D4 = 4.2 mm; bone p < 0.0102, drill p = 0.1784).

CONCLUSIONS

Thermal development depends on bone density with increasing density causing a temperature rise. However, this effect is reduced with increasing drill diameter. This may be important with regard to bone reactions and also in terms of tool wear.

Heat generation and drill wear during dental implant site preparation: systematic review

To identify factors that minimise damage during the drilling of sites for dental implants, we reviewed published papers on the amount of heat that is generated. We systematically searched English language studies published between January 2000 and February 2014 on MEDLINE/PubMed and found 41 articles, of which 27 related to an increase in temperature during preparation of the site. We found only basic research with a low level of evidence. Most of the studies were in vitro, and osteotomies were usually made in non-vital bone from cows or pigs. To measure heat in real time, thermocouples were used in 18 studies and infrared thermographs in 7. Three studies reported the use of immunohistochemical analysis to investigate immediate viability of cells. The highest temperature measured was 64.4°C and the lowest 28.4°C. Drill wear was reported after preparation of 50 sites, and there was a significant increase in temperature and a small change in the physiological balance of the proteins in the bone cells. Differences in the study designs meant that meta-analysis was not appropriate. For future work, we recommend the use of standard variables: an axial load of 2kg, drilling speed of 1500rpm, irrigation, standard artificial bone blocks, and the use of infrared thermography.

An in vitro study of thermal necrosis in ultrasonic-assisted drilling of bone

In case of human bone fracture, the best way to better and faster knitting is when a traumatologist fixes the fractured bone ends by drilling and setting the immobilization plates by screws. Heat generation during bone drilling may result in thermal injury due to exposure to elevated temperatures, with potentially devastating effect on the outcome of orthopedic surgery. A recent and promising method for reducing temperature in bone drilling is the use of ultrasonic assistance, where high-frequency and low-amplitude vibrations are added in feed direction during cutting process. In this research, experimental tests are carried out in five cutting speeds and three feed rates. The results demonstrate that ultrasonic-assisted drilling offered lower thrust forces and lower process temperatures as compared to conventional drilling at 1000 r/min. In addition, it is obvious that at 2000 r/min, since the values of temperature rise and thermal injury are independent from the feed rate, this method can be applied in the orthopedic surgery.

How bone tissue and cells experience elevated temperatures during orthopaedic cutting: an experimental and computational investigation

During orthopaedic surgery elevated temperatures due to cutting can result in bone injury, contributing to implant failure or delayed healing. However, how resulting temperatures are experienced throughout bone tissue and cells is unknown. This study uses a combination of experiments (forward-looking infrared (FLIR)) and multiscale computational models to predict thermal elevations in bone tissue and cells. Using multiple regression analysis, analytical expressions are derived allowing a priori prediction of temperature distribution throughout bone with respect to blade geometry, feed-rate, distance from surface, and cooling time. This study offers an insight into bone thermal behavior, informing innovative cutting techniques that reduce cellular thermal damage.

Multistepped Drill Design for Single-Stage Implant Site Preparation: Experimental Study in Type 2 Bone

PURPOSE

To evaluate an experimental multistepped drill for single-stage implant site preparation by means of real-time analysis of thermal variations during and postdrilling, and by implant stability evaluation.

MATERIALS AND METHODS

Temperature and time were recorded in real time by paired microprobe thermocouples during simulated osteotomy in type 2 bone similes at the cortical and cancellous zones. Three different drilling groups with a new multistepped drill design were compared: Control (2-mm diameter pilot drill + 3.3-mm three-stepped drill + 4.1-mm three-stepped drill); Test A (3.3-mm three-stepped drill); and Test B (4.1-mm three-stepped drill). Implants were inserted, and implant stability was evaluated with the Perio Test Value (PTV). Two-way anova was used to test the independent effects of osteotomy and implant diameter on temperature and stability.

RESULTS

All the drills induced thermal changes without significant differences between groups (p > .05). Drilling in cortical bone produced significant increase of the temperatures in a range of 1.8 ± 0.9°C compared with drilling in cancellous bone (p < .05). ΔT temperatures were significantly higher for test groups in cortical and cancellous bone (p < .05); ΔT10 for all groups showed a reduction of the temperature in a range of 1.7 ± 0.3°C without significant differences between groups (p > .05); the mean time to accomplish drilling was significantly longer in the control group (p < .05); test groups took 10 ± 0.3 seconds less to reach the required drilling depth. PTV values were higher in test groups compared with controls (p < .05).

CONCLUSIONS

The multistepped drills used for single-stage implant site preparation Increase temperature as in comparison with a conventional incremental protocol; Induce the temperature increment in cortical bone compared with the cancellous bone; Reduce drilling time when a multistepped drill is used alone; and Increase implant stability twofold compared with a conventional incremental protocol.

Raman Thermometry Based Thermal Conductivity Measurement of Bovine Cortical Bone as a Function of Compressive Stress

Biological materials such as bone have microstructure that incorporates a presence of a significant number of interfaces in a hierarchical manner that lead to a unique combination of properties such as toughness and hardness. However, studies regarding the influence of structural hierarchy in such materials on their physical properties such as thermal conductivity and its correlation with mechanical stress are limited. Such studies can point out important insights regarding the role of biological structural hierarchy in influencing multiphysical properties of materials. This work presents an analytic-experimental approach to establish stress–thermal conductivity correlation in bovine cortical bone as a function of nanomechanical compressive stress changes using Raman thermometry. Analyzes establish empirical relations between Raman shift and temperature as well as a relation between Raman shift and nanomechanical compressive stress. Analyzes verify earlier reported thermal conductivity results at 0% strain and at room temperature in the case of bovine cortical bone. In addition, measured trends and established thermal conductivity–stress relation indicates that the thermal conductivity values increase up to a threshold compressive stress value. On increasing stress beyond the threshold value, the thermal conductivity decreases as a function of increase in compressive strain. Interface reorganization versus interface related phonon wave blocking are the two competing mechanisms highlighted to affect such trend.

The application of cryoprobe therapy in orthopedic oncology

The cryoprobe is a relatively new surgical tool offering a more selective destruction of unwanted cells. Using expanded versions of basic thermodynamic formulas of conduction and convection, mathematical models are becoming more effective at mapping out the zone of destruction that can be expected when using cryoprobes. The development of this technology will allow for better surgical planning and postoperative care to decrease patient morbidity and mortality. It is thought that this invaluable tool will become increasingly prevalent in orthopedics.

Experimental and analytical investigation of the thermal necrosis in high-speed drilling of bone

Bone loss due to thermo necrosis may weaken the purchase of surgically placed screws and pins, causing them to loosen postoperatively. The heat generated during the bone drilling is proportional to cutting speed and force and may be partially dissipated by the blood and tissue fluids, and somehow carried away by the chips formed. Increasing cutting speed will reduce cutting force and machining time. Therefore, it is of interest to study the effects of the increasing cutting speed on bone drilling characteristics. In this article, the effects of the increasing cutting speed ranging from 500 up to 18,000 r/min on the thrust force and the temperature rise are studied for bovine femur bone. The results of this study reveal that the high-speed drilling of 6000–7000 r/min may effectively reduce the two parameters of maximum cortical temperature and duration of exposure at temperatures above the allowable levels, which in turn reduce the probability of thermal necrosis in the drill site. This is due to the reduction of the cutting force and the increase in the chip disposal speed. However, more increases in the drill bit rotational speed result in an increase in the amount of temperature elevation, not because of sensible change in drilling force but a considerable increase in friction among the chips, drill bit and the hole walls.

Novel hybrid drilling protocol: evaluation for the implant healing--thermal changes, crestal bone loss, and bone-to-implant contact

OBJECTIVES

To evaluate a new hybrid drilling protocol, by the analysis of thermal changes in vitro, and their effects in the crestal bone loss and bone-to-implant contact in vivo.

MATERIALS AND METHODS

Temperature changes during simulated osteotomies with a hybrid drilling technique (biologic plus simplified) (test) versus an incremental drilling technique (control) were investigated. One hundred and twenty random osteotomies were performed (60 by group) in pig ribs up to 3.75-mm-diameter drill to a depth of 10 mm. Thermal changes and time were recorded by paired thermocouples. In a parallel experiment, bilateral mandibular premolars P2, P3, P4, and first molar M1 were extracted from six dogs. After 2-month healing, implant sites were randomly prepared using either of the drilling techniques. Forty eight implants of 3.75 mm diameter and 10 mm length were inserted. The dogs were euthanized at 30 and 90 days, and crestal bone loss (CBL) and bone-to-implant contact (BIC) were evaluated.

RESULTS

The control group showed maximum temperatures of 35.3 °C ± 1.8 °C, ΔT of 10.4 °C, and a mean time of 100 s/procedure; meanwhile, the test group showed maximum temperatures of 36.7 °C ± 1.2 °C, ΔT of 8.1 °C, and a mean time of 240 s/procedure. After 30 days, CBL values for both groups (test: 1.168 ± 0.194 mm; control: 1.181 ± 0.113 mm) and BIC values (test: 43 ± 2.8%; control: 45 ± 1.3%) were similar, without significant differences (P > 0.05). After 90 days, CBL (test: 1.173 ± 0.187 mm; control: 1.205 ± 0.122 mm) and BIC (test: 64 ± 3.3%; control: 64 ± 2.4%) values were similar, without significant differences (P > 0.05). The BIC values were increased at 90 days in both groups compared with the 30-day period (P < 0.05).

CONCLUSIONS

Within the limitations of this study, the new hybrid protocol for the preparation of the implant bed without irrigation, increase the temperature similarly to the incremental conventional protocol, and requires twice the time for the completion of the drilling procedure in vitro. Crestal bone loss and bone-to-implant contact in the hybrid drilling protocol are comparable with the conventional drilling protocol and do not affect the osseointegration process in vivo.

Drilling- and withdrawing-related thermal changes during implant site osteotomies

BACKGROUND

Intrabony temperature increase is not only dependent on shearing energy and mechanical friction between bone and surgical drill but is also related to heat capacity and thermal conductivity of the surrounding bone and the applied surgical instrument. Thus time of occurrence of the highest temperature rise can be expected after the shearing process of the osteotomy, potentially affecting the process of osseointegration.

PURPOSE

The aim of this study was to evaluate temperature changes during the shearing and withdrawing processes during osteotomies.

MATERIALS AND METHODS

An overall 160 automated intermittent osteotomies (10/16 mm drilling depth) with 2 mm diameter twist drills and 3.5 mm diameter conical drills and different irrigation methods (without/external/internal/combined) were performed on standardized bone specimens. The drilling cycles were operated by a computer-controlled surgical system, while a linear motion potentiometer and multichannel temperature sensors in various intrabony levels ensured the real-time documentation of temperature changes during the shearing and withdrawing processes.

RESULTS

The highest temperature changes were invariably recorded during the process of withdrawal. Significantly lower temperature changes (p < .02) could be recorded at maximum drilling depths during the shearing process regardless of drilling depth, diameter or irrigation method. During coolant supply, 2 mm diameter twist drills showed higher temperatures (10 mm, p < .01/16 mm, p < .03) compared with 3.5 mm diameter conical implant drills. Internal (10 mm, p < .01) or combined irrigation (16 mm, p < .01) was associated with significantly lower temperatures compared with external irrigation by the use of conical implant drills.

CONCLUSIONS

Considering that heat generation during osteotomies is a multifactorial scenario, this study could demonstrate that the highest temperature rise during implant osteotomies occurs during the withdrawing process and that the time of occurrence is influenced by predominant factors such as osteotomy depth and mode of irrigation.

Thermal model to investigate the temperature in bone grinding for skull base neurosurgery

This study develops a thermal model utilizing the inverse heat transfer method (IHTM) to investigate the bone grinding temperature created by a spherical diamond tool used for skull base neurosurgery. Bone grinding is a critical procedure in the expanded endonasal approach to remove the cranial bone and access to the skull base tumor via nasal corridor. The heat is generated during grinding and could damage the nerve or coagulate the blood in the carotid artery adjacent to the bone. The finite element analysis is adopted to investigate the grinding-induced bone temperature rise. The heat source distribution is defined by the thermal model, and the temperature distribution is solved using the IHTM with experimental inputs. Grinding experiments were conducted on a bovine cortical bone with embedded thermocouples. Results show significant temperature rise in bone grinding. Using 50°C as the threshold, the thermal injury can propagate about 3mm in the traverse direction, and 3mm below the ground surface under the dry grinding condition. The presented methodology demonstrated the capability of being a thermal analysis tool for bone grinding study.

Drilling of bone: A comprehensive review

BACKGROUND

Bone fracture treatment usually involves restoring of the fractured parts to their initial position and immobilizing them until the healing takes place. Drilling of bone is common to produce hole for screw insertion to fix the fractured parts for immobilization. Orthopaedic drilling during surgical process causes increase in the bone temperature and forces which can cause osteonecrosis reducing the stability and strength of the fixation.

METHODS

A comprehensive review of all the relevant investigations carried on bone drilling is conducted. The experimental method used, results obtained and the conclusions made by the various researchers are described and compared.

RESULT

Review suggests that the further improvement in the area of bone drilling is possible. The systematic review identified several consequential factors (drilling parameters and drill specifications) affecting bone drilling on which there no general agreement among investigators or are not adequately evaluated. These factors are highlighted and use of more advanced methods of drilling is accentuated. The use of more precise experimental set up which resembles the actual situation and the development of automated bone drilling system to minimize human error is addressed.

CONCLUSION

In this review, an attempt has been made to systematically organize the research investigations conducted on bone drilling. Methods of treatment of bone fracture, studies on the determination of the threshold for thermal osteonecrosis, studies on the parameters influencing bone drilling and methods of the temperature measurement used are reviewed and the future work for the further improvement of bone drilling process is highlighted.

A novel standardized bone model for thermal evaluation of bone osteotomies with various irrigation methods

OBJECTIVES

Based on a novel standardized bovine specimen, the aim of this study was to investigate thermal effects of different irrigation methods during intermittent and graduated drilling.

MATERIAL AND METHODS

Temperature changes during implant osteotomies (n = 320) of 10 and 16 mm drilling depths with various irrigation methods were investigated on manufactured uniform bone samples providing homogenous cortical and cancellous areas and analogous thermal conductivity comparable to human bone. Automated sequences were performed with surgical twist drills of 2 mm ∅ and conical drills of 3.5, 4.3 and 5 mm ∅. Real-time recording of temperature increase was done using two custom-built multichannel thermoprobes with 14 temperature sensors at a predefined distance of 1 and 2 mm to the final osteotomy. The effects of drilling depth, drilling diameter and irrigation methods on temperature changes were investigated by a linear mixed model.

RESULTS

Using this uniform bone specimen, the greatest temperature rise was observed without any coolant supply with 29.87°C, followed by external with 28.47°C and then internal with 25.86°C and combined irrigation with 25.68°C. Significant differences (P ≤ 0.0156) between drill depths of 10 vs. 16 mm could be observed with all irrigation methods evaluated. With each of the irrigation methods, significantly higher temperature changes (P < 0.0001) during osteotomies could be observed between twist drills of 2 mm ∅ and conical drills of 3.5, 4.3 and 5 mm ∅. During 10 and 16 mm drilling osteotomies, external irrigation showed significantly higher temperatures (P < 0.05) for all conical drills compared with internal or combined irrigation, respectively. Significantly lower temperatures (P < 0.05) could be detected with internal or combined irrigation for the use of conical drills with various diameters and drilling depths.

CONCLUSIONS

This fully standardized bone model provides optimized comparability for the evaluation of bone osteotomies and resulting temperature changes. As regards the efficiency of the various irrigation methods, it could be demonstrated that internal and combined irrigation appears to be more beneficial than external irrigation.

Thermal effects of a combined irrigation method during implant site drilling. A standardized in vitro study using a bovine rib model

OBJECTIVES

The purpose of this study was to evaluate the temperature changes during implant osteotomies with a combined irrigation system as compared to the commonly used external and internal irrigation under standardized conditions.

MATERIAL AND METHODS

Drilling procedures were performed on VII bovine ribs using a computer-aided surgical system that ensured automated intermittent drilling cycles to simulate clinical conditions. A total of 320 drilling osteotomies were performed with twist (2 mm) and conical implant drills (3.5/4.3/5 mm) at various drilling depths (10/16 mm) and with different saline irrigation (50 ml/min) methods (without/external/internal/combined). Temperature changes were recorded in real time by two custom-built thermoprobes with 14 temperature sensors (7 sensors/thermoprobe) at defined measuring depths.

RESULTS

The highest temperature increase during osteotomies was observed without any coolant irrigation (median, 8.01°C), followed by commonly used external saline irrigation (median, 2.60°C), combined irrigation (median, 1.51°C) and ultimately with internal saline irrigation (median, 1.48°C). Temperature increase with different drill diameters showed significant differences (P < 0.05) regarding drill depth, confirming drill depth and time of drilling as influencing factors of heat generation. Internal saline irrigation showed a significantly smaller temperature increase (P < 0.05) compared with combined and external irrigation. A combined irrigation procedure appears to be preferable (P < 0.05) to an external irrigation method primarily with higher osteotomy depths.

CONCLUSIONS

Combined irrigation provides sufficient reduction in temperature changes during drilling, and it may be more beneficial in deeper site osteotomies. Further studies to optimize the effects of a combined irrigation are needed.

Theoretical study of bone cancer therapy by plasmonic nanoparticles

BACKGROUND

Progress made by the scientific community in the understanding of cell receptors and metabolic pathways has led to discovery of chemical and protein agents which act as delivery vectors to specific tissues. Conjugating these agents to noble-metal nanoparticles allows for subsequent accumulation on or within targeted cells. Utilizing the unique light absorption properties of these nanoparticles then allows for photothermal heating of the particles and surrounding tissue.

DISCUSSION

The heat equations are solved for the case of gold nanoparticles in biological hard tissues, such as bone, for applications to two future cancer therapies: nanophotothermolysis and nanophotohyperthermia.

CONCLUSIONS

A survey of recent research in bone-targeting bioconjugates and simulations of nanoparticle thermal fields shows promise for these therapies in the near future.

Cortical bone drilling and thermal osteonecrosis

BACKGROUND

Bone drilling is a common step in operative fracture treatment and reconstructive surgery. During drilling elevated bone temperature is generated. Temperatures above 47°C cause thermal osteonecrosis which contributes to screw loosening and subsequently implant failures and refractures.

METHODS

The current literature on bone drilling and thermal osteonecrosis is reviewed. The methodologies involved in the experimental and clinical studies are described and compared.

FINDINGS

Areas which require further investigation are highlighted and the potential use of more precise experimental setup and future technologies are addressed.

INTERPRETATION

Important drill and drilling parameters that could cause increase in bone temperature and hence thermal osteonecrosis are reviewed and discussed: drilling speed, drill feed rate, cooling, drill diameter, drill point angle, drill material and wearing, drilling depth, pre-drilling, drill geometry and bone cortical thickness. Experimental methods of temperature measurement during bone drilling are defined and thermal osteonecrosis is discussed with its pathophysiology, significance in bone surgery and methods for its minimization.

Attenuation, scattering, and absorption of ultrasound in the skull bone

PURPOSE

Measured values of ultrasound attenuation in bone represent a combination of different loss mechanisms. As a wave is transmitted from a fluid into bone, reflections occur at the interface. In the bone, mode conversion occurs between longitudinal and shear modes and the mechanical wave is scattered by its complex internal microstructure. Finally, part of the wave energy is absorbed by the bone and converted into heat. Due to the complexity of the wave propagation and the difficulty in performing measurements that are capable of separating the various loss mechanisms, there are currently no estimates of the absorption in bone. The aim of this paper is, thus, to quantify the attenuation, scattering, and thermal absorption in bone.

METHODS

An attenuating model of wave propagation in bone is established and used to develop a three-dimensional finite difference time domain numerical algorithm. Hydrophone and optical heterodyne interferometer measurements of the acoustic field as well as a x-ray microtomography of the bone sample are used to drive the simulations and to measure the attenuation. The acoustic measurements are performed concurrently with an infrared camera that can measure the temperature elevation during insonication. A link between the temperature and the absorption via a three-dimensional thermal simulation is then used to quantify the absorption coefficients for longitudinal and shear waves in cortical bone.

RESULTS

We demonstrate that only a small part of the attenuation is due to absorption in bone and that the majority of the attenuation is due to reflection, scattering, and mode conversion. In the nine samples of a human used for the study, the absorption time constant for cortical bone was determined to be 1.04 μs ± 28%. This corresponds to a longitudinal absorption of 2.7 dB/cm and a shear absorption of 5.4 dB/cm. The experimentally measured attenuation across the approximately 8 mm thick samples was 13.3 ± 0.97 dB/cm.

CONCLUSIONS

This first measurement of ultrasound absorption in bone can be used to estimate the amount of heat deposition based on knowledge of the acoustic field.

Analysis of Forces and Temperatures in Conventional and Ultrasonically-Assisted Cutting of Bone

Bone cutting is a frequently used procedure in orthopaedic and neuro surgeries. Current research on bone cutting is concerned with the efforts to decrease the forces generated during cutting the bone as well as temperature to avoid mechanical and thermal damage (bone necrosis) induced by surgical tools. The paper presents results of finite-element simulations of conventional cutting (CC) and ultrasonically-assisted cutting (UAC) of bone in order to understand thermomechanics of the process. The study was aimed at investigating the levels of tool-penetration force and temperatures induced in the bone when a hard cutting tool penetrates into it in both types of cutting. The models allow the quantitative analysis of forces and temperatures produced during the cutting process. The use of UAC reduces the tool penetration force and temperature in the cutting region

Heat production during different ultrasonic and conventional osteotomy preparations for dental implants

OBJECTIVES

The purpose of this study was to evaluate the intraosseous temperature changes during ultrasonic and conventional implant site preparation in vitro with respect to the effect of load and irrigation volume.

MATERIAL AND METHODS

Implant sites were prepared using two different ultrasonic devices (Piezosurgery, Mectron Medical Technology and VarioSurg, NSK) and one conventional device (Straumann) at loads of 5, 8, 15 and 20 N and with irrigation volumes of 20, 50 and 80 ml/min. During implant site preparation, temperatures were measured in fresh, equally tempered bovine ribs using two thermocouples placed at a distance of 1.5 mm around the drilling site in cortical and cancellous bone. The preparation time was recorded.

RESULTS

The heat production and time required for implant site preparation using both ultrasonic devices were significantly higher than those for conventional drilling (P<0.01). Increased loading had no effect on heat production. A higher irrigation volume was associated with a diminished temperature increase in the cortical bone for ultrasonic but not for conventional drilling, which resulted in significantly lower temperatures in cortical as compared with cancellous bone during ultrasonic implant site preparation.

CONCLUSIONS

Ultrasonic implant site preparation is more time consuming and generates higher bone temperatures than conventional drilling. However, with the levels of irrigation, ultrasonic implant site preparation can be an equally safe method.

An efficient method of modeling material properties using a thermal diffusion analogy: an example based on craniofacial bone

The ability to incorporate detailed geometry into finite element models has allowed researchers to investigate the influence of morphology on performance aspects of skeletal components. This advance has also allowed researchers to explore the effect of different material models, ranging from simple (e.g., isotropic) to complex (e.g., orthotropic), on the response of bone. However, bone's complicated geometry makes it difficult to incorporate complex material models into finite element models of bone. This difficulty is due to variation in the spatial orientation of material properties throughout bone. Our analysis addresses this problem by taking full advantage of a finite element program's ability to solve thermal-structural problems. Using a linear relationship between temperature and modulus, we seeded specific nodes of the finite element model with temperatures. We then used thermal diffusion to propagate the modulus throughout the finite element model. Finally, we solved for the mechanical response of the finite element model to the applied loads and constraints. We found that using the thermal diffusion analogy to control the modulus of bone throughout its structure provides a simple and effective method of spatially varying modulus. Results compare favorably against both experimental data and results from an FE model that incorporated a complex (orthotropic) material model. This method presented will allow researchers the ability to easily incorporate more material property data into their finite element models in an effort to improve the model's accuracy.

In vitro studies and safety assessment of Doppler ultrasound as a diagnostic tool in rhinosinusitis

We have previously proposed the use of Doppler ultrasound to noninvasively stage a sinus infection. In this study, we first investigated the acoustic properties of nonpurulent and mucopurulent sinus secretions. The density, viscosity, speed of sound and attenuation of 18 samples of sinus fluid were examined. We then assessed the safety of the method by determining the temperature increase when ultrasound is transmitted through a bone sample of the same thickness as the anterior wall of the maxillary sinus. As a measure of the probability to generate acoustic streaming, we determined the ratio of sound attenuation over the viscosity of the sinus fluid and compared this with the value obtained from acoustic streaming measurements on a model system. The results indicated that detectable levels of acoustic streaming can be generated in serous sinus fluid, which has a low viscosity, but is very unlikely in mucopurulent secretions. The attenuation of the mucopurulent sinus fluid was 10 times higher than that of the serous cyst fluid, but the viscosity of the mucopurulent secretion was a thousand times higher than that of serous fluid. The safety experiments gave a temperature increase of the bone of <1.5°C at I(spta) of 640 mW/cm(2), below the temperature increase considered to be harmful by the World Federation for Ultrasound in Medicine and Biology.

Thermal effects generated by high-intensity focused ultrasound beams at normal incidence to a bone surface

Experiments and computations were performed to study factors affecting thermal safety when high-intensity focused ultrasound (HIFU) beams are normally incident (i.e., beam axis normal to the interface) upon a bone/soft-tissue interface. In particular, the temperature rise and thermal dose were determined as a function of separation between the beam focus and the interface. Under conditions representative of clinical HIFU procedures, it was found that the thermal dose at the bone surface can exceed the threshold for necrosis even when the beam focus is more than 4 cm from the bone. Experiments showed that reflection of the HIFU beam from the bone back into the transducer introduced temperature fluctuations of as much as +/-15% and may be an important consideration for safety analyses at sufficiently high acoustic power. The applicability of linear propagation models in predicting thermal dose near the interface was also addressed. Linear models, while underpredicting thermal dose at the focus, provided a conservative (slight overprediction) estimate of thermal dose at the bone surface. Finally, temperature rise due to absorption of shear waves generated by the HIFU beam in the bone was computed. Modeling shear-wave propagation in the thermal analysis showed that the predicted temperature rise off axis was as much as 30% higher when absorption of shear waves is included, indicating that enhanced heating due to shear-wave absorption is potentially important, even for normally incident HIFU beams.