The Testing Of Drilling Mechanics Parameters In Vitro Femoral Shaft For Virtual Surgery System

Background:Surgical operation is commonly used in hospital by a surgeon in or other professionals, which change the organizational structure of patient’s body by medical devices to exclude lesions for treatment. Since surgical operation is done directly in the patient’s body tissues and organs, the accuracy of it has a direct relationship with prognosis of the disease and the patient’s physical health. Therefore, it is necessary to have a related surgical procedure training exercise before surgical operation for the surgeon. The traditional surgical teaching and training is mainly completed in two ways:First, it is in accordance with the " apprenticeship " approach through the patient’s surgery, the operating room is a classroom, but also the special laboratory, the Young doctors’operative learning are from experienced doctors by the way of "do one, look at one, learn one "; Second, live animals, human or animal body, modeled on the human body and other inorganic materials synthesis model as experimental subjects are used for training and learning operate surgical techniques. The former approach has a question that the teaching content depends on patients randomly appearing, which is great unpredictability, therefore,it is difficult to form system of teaching, while this training method is bound to extend the operation time, increase the cost of surgery, and even affect the quality of operation with high frequency complication, so it is often been resisted by patients and their families; The latter approach have a lot of questions that the differences in the anatomy with the human body, the limited of number and expensive, involving ethical issues. Over traditional surgical training methods exist the defect that cannot repeat the exercise, which makes it difficult to master the young surgeon complex surgical skills in a short time. With the rapid development of computer technology in recent years, there is a new integrated information technology---Virtual Reality Technology (VRT), which had began to rise in the last century. It is a simulating natural scientific method and technique in order to better adapt and use natural. In medicine, virtual reality technology is mainly used for preoperative planning of complex surgery, teaching and training of surgical technical operations, predicting surgical outcomes and so on. Virtual surgery system has been used in a variety of surgical teaching training and achieved the desired results, which is a good remedy for the shortcomings and inadequacies exist in traditional surgical teaching training. Virtual surgery system as an emerging area of research in recent years, is the integration of virtual reality technology and computer graphics techniques, which can provide the real-time simulation for specific surgical operation and three-dimensional reconstruction of surgery lesion area involved in clinical surgery, in order to provide a virtual surgical environment for the surgeon. The most important applications of virtual reality technology in medical simulation training, which can provide arf ideal platform for teaching and training, trainees observe high-resolution three-dimensional body image, and through the force feedback haptic simulation workbench, allowing trainees to feel when cutting tissue to the reaction of apparatus, so that the surgeon’s feeling of surgery operation just like in a real human body surgery. The virtual surgery not only can let patient will neither cause life-threatening, but also can reproduce the surgical cases with high-risk and low probability. Virtual surgery system is available for surgeon repeatedly surgical training exercises. The essence of virtual reality surgical system is that allows surgeons immersed in a virtual environment which simulates various surgical procedures, and it mainly includes immersive of visual and tactile two aspects. With the development of high-resolution medical imaging equipment (CT, MRI, PET, etc.) applications and3D visualization technology, the research of visual sense immersion aspects has been more mature and able to meet the requirements for clinical use; However, due to the lack of real and reliable mechanics and tactile feedback, the research and application of tactile sense immersion needs further study to improve. Touch is the earliest form of human limbs feeling, it is considered excellent grasp the fundamental skills of clinical surgery. Therefore, it is very important that there is authentic tactile feedback in virtual surgery system, and the tactile feedback is a key component of the virtual surgery system. While most virtual surgery systems have a problem that lack of authentic tactile feedback or force feedback in recent. Although there are many research institutions at home and abroad have assembled direct or indirect sensors at the end of surgical instrument to provide corresponding force feedback, but the sensitivity and delay of the sensor will cause it to provide force feedback accuracy is not high. It has been reported that providing human tissues and mechanical parameters corresponding surgical procedure for the virtual surgery system is the most effective method to solve the problem of lack force feedback. The most direct and effective way to obtain Operative mechanical parameters is that the mechanical parameters involved in the clinical surgical procedures need to be tested. There are domestic and foreign scholars that have completed the tests of cutting force, suture strength, drilling force of biotechnology or corpse tissue.In the field of orthopedic surgery, in order to serve the purpose of fixing the bone, orthopedic surgeons often need to use an electric drill to drill through the pores. Young physicians often need to train exercises of bone drilling operation by a virtual orthopedic surgery system, in order to better training of young doctors, it is essential to provide real and reliable drilling mechanics parameters for virtual orthopedic surgery systems. Currently, in domestic and foreign, there is no bone drilling data sets that been used for the virtual drilling force feedback signal output in orthopedic virtual surgery system. To compensate for this gap, this study has tested and researched femoral drilling mechanics parameters (feed force and torque) in vitro, and grasped the relationship between bone mechanical parameters of drilling and bone density, drill diameter, drill speed, feed rate. The results will provide the basis for orthopedic virtual surgery system drilling force feedback signal output, enhance the authenticity and reliability of force feedback in virtual orthopedic surgery system, and promote the development of virtual orthopedic surgery training system.Objective:1. To establish the data acquisition system of biological tissue mechanical properties;2. To collect the drilling feed force and torque in vitro femoral different layers and bone segments, and analysis their relationships with bone density, drill diameter, drill speed, feed rate. It would provide evidence for virtual orthopedic surgery system the feedback signal output of drilling force and torque.Methods:1. The construction of data acquisition system of biological tissue mechanical propertiesThe data acquisition system of biological tissue mechanical properties consists of universal testing machines, torque meter, medical drill and with matching tooling and data acquisition, analysis, storage system configuration. 2. The acquisition of drilling feed force and torque2.1Use the data acquisition system of biological tissue mechanical properties, use commonly femoral surgery drill d=φ5.0mm with v=30mm/min,50mm/min,70mm/min three kinds of feed rate and n=500r/min,800r/min,1200r/min three kinds of drill speed, collect the feed force F and torque M of six fresh pig femoral shaft162drilling calibration locations;2.2Use the data acquisition system of biological tissue mechanical properties, use commonly femoral surgery drill d=φ4.5mm, φp5.0mm, φ5.5mm with v=10mm/min,20mm/min,30mm/min three kinds of feed rate and n=500r/min,800r/min,1200r/min three kinds of speed, collect the feed force F and torque M of nine bodies of fresh corpses and corrosion femoral shaft, respectively,910drilling calibration locations.Results:1. The drilling feed force of fresh pig femoral bilateral cortical bone was maximum (Fmax=103.63～142.59N), the drilling feed force of the canal was minimum, which was close to zero; The drilling feed force was different at different bone segments, the drilling feed force on the middle part of femoral shaft (F4、5、6=124.69N) was bigger than two ends (F1、2、3、7、8、9=121.84N); When v=30mm/min、 n=1200r/min, the drilling feed force was least Fmin=106.04N; v=70mm/min、n=500r/min, the drilling feed force was largest Fmax=139.84N.2. The drilling torque of fresh pig femoral bilateral cortical bone was maximum (Mmax=0.1154～1.2605Nxm), the drilling torque of the canal was minimum, which was close to zero; The drilling torque was different at different bone segments, the drilling torque on the middle part of femoral shaft (M4、5、6=0.7881Nxm) was bigger than two ends (M1、2、3、7、8、9=0.6657Nxm); When v=30mm/min、n=1200r/min, the drilling torque was least Mmin=0.1757N×m; v=70mm/min、n=500r/min, the drilling torque was largest Mmax=1.1246N×m.3. The fluctuation range of drilling feed force F of fresh corpses femoral was26.47～68.29N; when d=4.5mm, v=10mm/min, n=1200r/min, the drilling feed force Fmin=31.8N was minimum; when d=5.5mm, v=30mm/min, n=500r/min, the drilling feed force Fmax=65.95N was maximum; The drilling feed force of fresh cadaver femoral bilateral cortical bone was maximum (F4.5max=26.47～55.11N, F5.0max=32.58～61.21N, F5.5max=39.65～68.29N), the drilling feed force of the canal was minimum, which was close to zero.4. The fluctuation range of drilling torque M of fresh corpses femoral was0.11～1.81N×m; When d=4.5mm, v=10mm/min, n=500r/min, the drilling torque (Mmin=0.14N×m) was minimum; when d=5.5mm, v=30mm/min, n=1200r/min, the drilling torque (Mmax=1.74N×m) was maximum;The drilling torque of fresh cadavers femoral bilateral cortical bone was maximum (M4.5max=0.11～1.32N×m, M5.0max=0.31～1.51N×m, M5.5max=0.61～1.81N×m), the drilling torque of the canal was minimum, which was close to zero.5. In different drilling parameters, the mean fluctuation range of relative error of drilling feed force between predicted value and the actual measurement was2.71%-19.74%; the mean fluctuation range of relative error of drilling torque between predicted value and the actual measurement was1.57%～17.37%.Conclusion:1. A data acquisition system of biological tissue mechanical properties was built by modified universal testing machine, digital torque tester, handheld drills and other medical organizations, and through the acquisition of fresh pig femoral drilling feed force and torque data to verify the measurement of its biological tissue mechanics argument is true and reliable and has good stability, so can be used to collect biological tissue mechanical parameters test;2. In the process of drilling the femoral shaft in vitro, the drilling feed force and torque have a close relationship with the bone structure, the different hardness at the same cross-section of femoral has leaded to different drilling feed force and torque, the drilling feed force and torque of bilateral cortical bone was maximum, the drilling feed force and torque of the canal was minimum that was close to zero;3. The drilling feed force and torque have a closely relationship with drill speed, feed rate, drill diameter and bone’s density, the feed rate, drill diameter,inside the bone’s density is bigger and drill speed is smaller, the drilling feed force is larger, vice versa, the drill speed, feed rate, drill diameter,inside the bone’s density is bigger, the drilling torque is larger, vice versa.4. The empirical formula of bone drilling feed force and torque was established by using the linear regression equation analytical method from the data of fresh corpse femoral drilling feed force and torque: F=77.42×BMD0.317×d1.294×n-0.472×v0.424(N) M=0.056×BMD2.371×d0.539×n0.106×v0.024(Nxm)These empirical formulas have been verified by experiment;5. The data of drilling feed force and torque collected in this experiment were true and reliable, their results and variations could provide a basis for the drilling force feedback output of virtual orthopedic surgery system;6. The empirical formula of bone drilling feed force and torque established by this experiment can be more accurately predict the values of bone drilling feed force and torque, so as to provide a basis for the drilling force feedback output of virtual orthopedic surgery system.