AUTOMATED BONE DRILLING IN THE ORTHOPEDIC SURGERY: EXPERIMENTAL ANALYSIS OF THE TEMPERATURE EFFECTS.

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1 11 th National Congress on Theoretical and Applied Mechanics, 2-5 Sept. 2009, Borovets, Bulgaria AUTOMATED BONE DRILLING IN THE ORTHOPEDIC SURGERY: EXPERIMENTAL ANALYSIS OF THE TEMPERATURE EFFECTS. T. BOIADJIEV Central Lab of Mechatronics&Instrumentation - Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 1, 1113 Sofia tonyboev@clmi.bas.bg K. DELCHEV Institute of Mechanics Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia kamen@imbm.bas.bg V. VITKOV Institute of Mechanics Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia R. KASTELOV University Hospital St. Anna, Orthopaedic and Trauma Clinic, D. Mollov St.,1, 1709, Sofia, Bulgaria rkastelov@yahoo.com G. BOIADJIEV Institute of Mechanics Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bl. 4, 1113 Sofia george@imbm.bas.bg ABSTRACT. In the work the automatic drilling module is presented as well as the experimental setup design for establishment the drilling process technical parameters and especially the temperature deviation measurement. The obtained results are shown and analyzed as well as the corresponding conclusions are done. KEYWORDS bone drilling, robot, experimental results 1. Introduction During the recent years scientific researches arise which are devoted to robot application in surgery (Robot Surgery Assistant) and also in orthopedic.

2 T. Boiadjiev, K. Delchev, V. Vitkov, R. Kastelov, G. Boiadjiev surgery, in part. The International Society for Computer Assisted Orthopedic Surgery was founded and The Symposium on Automated and Computer Aided Orthopedic Surgery is organized every year. The main topic there is research in the field of computer and automatic realization of various parts or elements of orthopedic manipulations. Such activity proves the actuality of these specific problems as well as it gives guarantee for the future development in that area. The orthopedic surgery often requires the usage of instruments to which the drives are applied for instance drilling machines, saws etc. which the surgeon holds in his hands during the time of manipulation. By reports the drilling devices are used approximately in 95% of post-trauma interventions. That shows and proves a constant interest to the researches connected with that manipulation and lots of scientific reports are devoted to such an orthopedic surgery element. Since orthopedic screws are often implanted in the bones it is needed to realize the bone drilling process before. But hand-drilling leads to some problems as getting the big outlets, breaking the tendons or blood vessels, overheating and so on. An excessive arise in temperature around a drill hole causes thermal necrosis of bone which is associated with irreversible changes in its structure and physical properties [1]. The hold of the screw is desorbed; reducing the stability and strength of the fixation and the presence of necrotic tissue may delay healing and predispose to infection. The automatic execution of drilling could remove the subjective factor presence and could avoid the problems mentioned above. 2. The experimental setup design. In previous works of the authors a mechanical structure was considered in having two degrees of freedom which choice is aimed for possible application in surgery. Its mathematical model was obtained and control low was synthesized. Fig.1. The robotized system DORO.

3 Automated Bone Drilling in the Orthopedic Surgery Some drilling process parameters can be identified by experiments only, so that the experimental setup has been designed. Until now two experimental setups are developed by the authors team in connection with the working task [2,3, 4]. On that base a first version of experimental example is realized [5]. The next one (fig.1) is characterized with smaller size and mass. On fig. 1 the machine with the control unit is shown. Both actuators are mounted inside. All the outer details and the machine surface are made by stainless steel for sterility. During the drilling process continuous contact between the machine and the bone is maintained by the accessories and supports which can be regulated (fig.1). The contact may be realized by the surgeon or passive mechanical or robot arm. Some technical data are: weight 2 kg; working zone 0 90 mm; precision 0.5 mm; working regime: hand and automatic; rotation rpm; translation 0 9 mm/s. On the control/power block (control unit) can be seen (fig.1): - the emergency button - the digital display showing the depth of the drilling - four-lamp visual system - temperature sensor SP i-tec 2005D. These systems give information for the drilling process execution, for the end of the task, for emergency situation etc. The following components are mounted in the robot Actuators Linear actuator (Haydon Switch & Instrument Inc). Stepper motor with embedded screw. Such motors assure high precision during low speeds regime. They are small enough by size and realize the needed force during the drilling process as well. The module assures translation of 1 mm for 4032 micro steps (mode 64 micro steps, 1.8 о /step, mm/step)[6]. Brushless DC motor B (Danaher). Compared to brushed DC motors, BLDC motors have many advantages: better speed versus torque characteristics, high dynamic response, high efficiency, long operating life, noiseless operation, higher speed ranges, rugged construction and so on. Also, torque delivered to the motor size is higher, making it useful in applications where space and weight are critical factors. The module gives torques Nm at rpn; with reduction (reduction ratio 35) the torque can reach the values 1.5 Nm. [7] Controllers Controllers comprise two main components controlling device and a power drive. In our case they are: Controller / Driver TMCM (fig.1) for control of one-axis stepper motor driven by linear actuator [8]. Controller / Driver TMCM-170 (fig.20) for BLDC motor [8]. The controller/driver has built-in PID-regulators for positioning and for speed. In part, only PID-regulator for speed is used for speed stabilization in

4 T. Boiadjiev, K. Delchev, V. Vitkov, R. Kastelov, G. Boiadjiev experiments. The control algorithms are executed in the specialized program language TMCL-IDE specific for the controllers [8] Sensors Temperature sensor SP i-tec 2005D (fig.2). It is an infrared non-contact temperature measuring instrument [9]. For comparison the results concerning the temperature has been measured also by means of a digital Fluke 62 Mini thermometer. Force sensor MLP-25 for the bone resistant force during the experiments. Fig.2. Temperature sensor SP i-tec 2005D 3. Experimental results The drilling mode includes the following monitored parameters: Time [s]; Linear velocity [mm/s]; Angular velocity [rpm] Resistant force [N]; Depth of penetration [mm] Temperature [deg., o C] The experiments concern two modes: drilling a preliminary desired depth and through the whole bone. The changes of the temperature in real time during drilling process are shown on fig.3-8. Lots of experiments has been executed under various conditions in the sense of different speeds, type of bones, drill-bits, hole depths etc. The results showed the upper border of the reached temperature was not greater than 45 degrees (C o ). The experiments have been done in three ways of moving back the drill-bit on its moving back from the bone with continuous rotation (in both directions) and without rotation. The measured data show the temperature keeps constant at the end of the process with no rotation. The continuous rotation causes the temperature peak at the end. It can be concluded the final step of the drilling when the task is finished is good to be done with no rotation which is an interesting effect.

5 Automated Bone Drilling in the Orthopedic Surgery Fig.3.Temperature data during full bone drilling.(2mm/s; drill bit Ø3 mm; without stop rotation) Fig.4.Temperature data during full bone drilling. (2mm/s; drill bit Ø3 mm; stop rotation) Fig.5.Temperature data - soft bone drilling (2 mm/s; depth 20 mm; drill bit Ø4 mm) Fig.6.Temperature data during full bone drilling. (2mm/s; drill bit Ø4 mm) Fig.7. Temperature data during cortex bone drilling (2 mm/s; depth 20 mm; drill bit Ø3 mm, stop rotation) Fig.8. Temperature data during cortex bone drilling (2 mm/s; depth 20 mm; drill bit Ø3 mm, without stop rotation)

6 T. Boiadjiev, K. Delchev, V. Vitkov, R. Kastelov, G. Boiadjiev 4. Discussion The temperature near and along the hole arises in real time during the bone drilling process. It is in relation with the kind of the drill bit, translation and rotation speed, bone characteristics and the number of executed holes done previously. The experimental data show the temperature behavior in the process execution under various conditions. They are very helpful for controlling the process in the sense of the temperature requirements according the orthopedic surgical practice. In the presented work temperature sensor was used only for temperature measurement in bone drilling process. The temperature sensor SP i-tec 2005D is equipped with analog output (0-5 V). This output will be used in a future works like information feedback for control algorithm optimization and real-time temperature estimation and evaluation keeping it in the safe borders. R E F E R E N C E S [1] NATALI C., INGLE P., DOWELL J. Orthopedic Bone Drills Can They Be Improved? Temperature Changing Near the Drilling Face. J. British Editorial Society of Bone and Joint Surgery, Vol. 78-B(3), 1996, pp [2] BOIADJIEV, G.., KASTELOV R., BOIADJIEV T., VASSILEVA D. (2002) Robot Application in Medicine for Orthopeadic Drilling Manipulation. The 8 th Mechatronics Forum, Int. Conf. Mechatronics 2002, 24 th 26 th June, Twente, Netherlands. (CD)., [3] BOIADJIEV T., BOIADJIEV G., VITKOV V, Surgery Assisting Robot Module for OrthopedicManipulation Bone Drilling, 11 th Int. Power Electronics and Motion Control Conference EPE-PEMC 2004, 2-4 Sept., Riga, Latvia, CD, ISBN [4] BOIADJIEV T., V. VITKOV, K. DELCHEV, K. ZAGURSKI, I. CHAVDAROV, R. KASTELOV, G. BOIADJIEV, Robotized Module for Bone Drilling in Surgery: Experimental Setup and Results, Edition of Scientific Machine Union, Vol. 6, Drjanovo, 2007, pp. 7-12, ISSN [5] BOIADJIEV T., V. VITKOV, K. DELCHEV, R. KASTELOV, G. BOIADJIEV, D. KARASTOYANOV, Automation of the Drilling in the Orthopedic Surgery, Int. Conf. on Bionics and Prosthetics, Biomechanics and Mechanics, Mechatronics and Robotics ICBBM 2008, Varna, 2008, p , ISBN [6] Linear Actuators. [7] BLDC-Motors. [8] Smart solution fo embedded motion control [9]