| BackgroundIt has more than 50 years of history that Pedicle screw has been used in the application of spinal surgery, and was a milestone inventaion in the spine surgery department. In 1959,Bouchert reported that pedicle screw was applied to the lumbosacral vertebral fusion fixation from pedicle of vertebral arch to centrum and got a good effect. Then, all sorts of fixed system using pedicle screws are used for treating spine frature, tumor, deformity and various degenerative deformation.In this device, pedicle screws weren't used to maintain the stability of the joint until the joint appear to fusion. In 1993,North American Spine Society (NASS) approved that pedicle screws could be used in clinical.The pedicle is located between the vertebral body and the vertebral plate, the single channel for pedicle fixation. It has more biomechanic power, better orthopedic result and less demand of fusion segments than other methods of internal fixation. To build a proper pedicle screw path is a very difficult process, that the pedicle structure can not be seen in surgery by blind operation, since it must be very precise, and has to face the individual difference, malformation etc. The ratio of fault pedicle screw implant is between 10-33.8%. To elevate the accurace of pedicle screw implant is very important work in the field of spine surgery.Traditional studies about pedicle are mainly based on morphology (such as anatomy and imageology), observing the outside parameter about height, width, angle, and the length of the pedicle structure. Some commonly used methods are measurement and cross-check analysis on the anatomic specimen, X-ray, Computer tomography and so on. There are many location methods according to a large number of applied anatomy reseach results, too, such as Roy-Camille way, Weinstein way,Mager way,Louis way, Krag way,Muller way,AO way,and Tang TianSi way. All of these traditional methods are based on a permanent screw reference point on the back anatomic structure. However,recent researches have disclosed that axis line of the pedicle is mobiled in a realm of posterior part in the spine.Radiology researches reveal that variation reaches 4.9% and individual difference is significant,especially concerned weight and height,so can't be neglected.Many kinds of modern technologies have been used to cut down the risk of the operation and to elevate the accurance and safty of it. All of these technologies, including X-ray monitoring, computer assisted surgery and somatosensory-evokeing potentials, compound muscle action potentials, electromyography recordings,have cut down the misimplant ratio and generalized the pedicle screw technology. Nevertheless,these methods can not completely solve the misimplant problem. Moreover,some side effects have appeared, such as radioactive contamination and high medical cost.The need to develop a precise,safe,cheap,and non-contaminant method become very urgent.People has been committed to introduce the biological impedance measurement technology to the human health fields from the 18th century.In 1780 Italy neurobiologist Galvani established the bioelectricity theory by studying the phenomenon of frog nerve muscle contraction.The earlyest researcher,study biological tissues impedance is German scientist Hermannin. he successfully measured resistance of skeletal muscle in 1871.Sapegno measured capacitance of biological tissue by using AC biridge firstly in 1930.Cole K.S proposed the impedance of biological tissue can be expressed by a period of arc in the complex plane in 1944.Later, Cole R.H further developed it to be a Cole-Cole theory and set up a equivalent model of biological tissue including three components.Schwan,in 1960,successfully put forward frequency dispersion theory show that the electrical characteristic of biological tissues have a significant change in different frequency bands.So far, the electrical characteristics theory of biological tissues had been formed basically.Nyboer firstly used the biological impedance measurement way to learn biological functions.He researched arterial pulse wave and arterial blood by electrical impedance volume meter,also was used in human body measurement and obtained good results.However Thomasset,a pioneer of biological impedance measurement used it in the body composition analysis,did some bisic research for biological impedance as a whole water measurement indicator.Later, Hoffer et al. established relationship between the overall impedance and body water.On this basis,Henry et al. started evaluating body composition by using biological impedance measurement way and preliminary results indicate it feasible and valid in analysing body composition.Biological impedance measurement is considered as a very promising technology by medical researchers and workers now,widely used in blood flow diagram of heart brain and pulmonary,Breathing,lung ventilation function measurement,human body composition analysis, impedance imaging,etc. Objectives,Materials and MethodsWe innovatively combine medical electric impedance technology with screw implant surgery based on the results of many scientific studies.this technology can provide several different PS parameters to bone surgeons in an operation and improve the success rate.Main jobs:(1) To find the appropriate electrical parameters for using impedance technology into the bone surgery,we conducted a series of basic experiments on human cancellous tissue and cortical bone,cancellous bone and muscle tissue from home pigs.(2) To design and make a bipolar measurement probe, and to make it to be in consistent with the electric requisition for impedance measurement and biomechanic requisition for puncture in bone structure.(3) To design and development the hardware, software, for the measurement of a complex pedicle structure.(4) To establish a standardized measuring method based on the system..(5) To verify the result of the prophase study through imitating pedicle operation on the basis of the aforementioned measurement system, method, and result. To evaluate the correctness and availability of the guidance for pedicle screw implantment.ResultsWe have studied the impedance characteristics of bone and muscle tissue of home pigs in the frequency range from 5Hz to13MHz.We have the following results:(1) For measuring impedance difference of biological tissues,the better frequency band may be in the range of 5KHz - 200KHz.During the frequency band,impedance difference in biological tissues change little and Results of bioelectricity impedance measurement can be repeated.(2) Individual age and health are evaluated via measuring bone phase in the a frequency band andβfrequency band may not be fit for detecting three different tissues because impedance values change smaller at the same frequency point and are influenced by frequecy.(3) Freezing will change the bone microstructure, such as bone plate, constituent proteins of bone matrix degeneration and some osteocytes rupture that result in measuring impedance incorrectly. So freezed tissues cann't be represented the live tissues,and is unsuitable to the test.We also make a choice and reseach for electrode settings,electrode materials and size.We successful design and manufact bipolar measure probe,includes two types:the outlay and inlay models,their electric efficiency and biomechanics efficiency are both very satisfied.Cement filled into the cutting-edge of bipolar measure probe all have some loss ,but still maintain its mechanical stability and electrical scalability after puncturing many times in the home pig bone.To avoid low accuracy and complex measure procedure of recommended design, we optimize the test circuit. A new solution using two AD5933 microchip systems was proposed. this solution allows to measure impedance in a wide range (100Ω≤｜Zx|≤10GΩ) at measurement frequencies in the range from O.OlHz to 100KHz. |
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