The Biomechanics Research On The Brachial Plexus Roots Of The Rats

Peripheral nerve is a kind of soft tissue which has special biomechanics property, at present, the biomechanics reseach on the peripheral nerve is still superficial because of lacking of quantificational foundation and acknowleged researched critieria. Normal peripheral nerve has some extent of tensile property and flexibility, the stress strain relationship have nonlinear stress strain feature when it is in the finite deformation.The sensibility of the peripheral nerve to the force lead to structural injury when it bear a minor tensile force.The tensile force of the anastomotic stoma affect the functional recovery of the nerve directly in the course of the nerve reparation. Researchments indicate that sut the nerve directly is better than the nerve tansplantation, but the nerve will be injuried excessively at the basic of the inhere injury if the tensile force of the anastomotic stoma is excessive,so to identify the elongation rate of the brachial plexus and which operation method shoud be chosen (sut the nerve directly or the nerve tansplantation) is a important thing.So the penman design to drag the brachial plexus roots of the rats in vivo from different angle and get the elongation rate and other biomechanics index of each nerve root.The experiment not only study the property of the brachial plexus roots but also use the research result in clinical. The topic aim to identify the mechanical property of the brachial plexus roots and observe the biomechanics state of the brachial plexus root when they are dragged, then to direct the diagnosis and therapies of the brachial plexus injury in the clinical.Thirty three Wistar rats were divided into three groups, 1%Ketamine Hydrochloride Injection was injected into the abdominal cavity of the rats in order to anesthesia, we use100g/L sodium sulfide to depilate the rats,then wash it. We cut open the skin in the infraclavicula and dissect the pectoralis major as well as the pectoralis minor in the deeper layer bluntly,then we cut off the sternal end of the clavicle ,pull the muscle to upper and lower by the ecarteur,the bundle of the brachial plexus are exposed, dissect to the proximal end till the nerve roots are exposed, expose C5~T1 nerve roots,, dissect each nerve roots with the microinstruments,,cut off other tissue except the nerve roots.In order to avoid the influence of the close nerve roots we choose the C5,C7,T1 nerve roots on the right and the C6,C8 nerve roots on the left to do mechanics test,the left C5,C7,T1 nerve roots and the right C6,C8 nerve roots are used to measure the iniatial length and area of cross section of the nerve roots.We expose the nerve roots and hold the end of the measuring nerve roots with the self-made clamper, the ironwire is tied to the clamper of the experimental machine around a crown block,in the same way, clamp the vertebral column which the brachial plexus roots come out,make the angle of the axial direction of the nerve root and the vertebral column be 15°.After exposing and clamping the nerve root ,we begin to drag the root in a speed of 1.5mm/s through the controlling of the computer, keep the datas of the displacement,time and tensile force from the time of dragging to rupturing. To change the position of the crown block and make the angle that the axial direction of the nerve root and the vertebral column to be 30°,45°,60°,75°,90°,105°,120°,135°,150°,175°, we use the same method to drag the nerve root and keep those datas.We infiltrate the nerve roots continually with Sodium Chloride in the whole experimentation.The experiment is carrying out in the temperature of 20℃. Converse the loading-extending to corresponding stress(T)-strain(ε), in the course of the Conversion,we use these formulas: T=F/S(Pa),S=L0S0/L,ε=(λ2-1)/2,λ=L/L0(F is the loading, S0,L0 are the the iniatial length and area of cross section of the nerve roots, S,L are the transient length and area of cross section of the nerve roots when they are dragged. ) and then do dragging test to them(To drag single nerve root in the same inatial tensile force but in different direction ).To record a series of loading-extending and calculate a series of stressing-straining results and then we draw the stressing-straining curve of each nerve root and analyze the relationship between the peakload and the maximum strain.At last we calculate the result of the stressing and straining on the proportional limit. We get the following results through the experiment:①Different nerve roots can endure different loading, C7 can bear the maximum loading, and the peakload range from 1.55N to 2.55N in each nerve root.②The rupture parts are different when we draw the nerve roots in different direction.In the peakload,the rupture parts of each nerve root is mainly distal neural ganglion when the dragging angle is 90°, when the angles change from (45°~90°) and(90°~135°)the rupture parts is mainly proximal neural ganglion . When the angle change from (0°~45°) and (135°~180°), the rupture parts of C5,C6,C7 nerve roots are not in regulary but the rupture parts of C8,T1 nerve roots are mainly proximal neural ganglion.③The experiment shows that the peakloads are different when we drag the nerve roots in different direction, Vertical Spinal (the angle is 90°) direction we can get the maximum loading.The peakload gradually decrease with the increasing or decreasing of the angle When the angle decrease to 45°or increase to 135°, the peakload well not decrease any more,Continue to increase or decrease the angle the alteration has no regularity,it shows that the iniatial angle and the peakload have direct correlation (r=0.702, 0.681, 0.593, 0.662, 0.587; P<0.01) in the angle of (45°~90°) and inverse correlation in the angle of (90°~35°) when we analyze the correlation of the iniatial angle and the peakload, the rest angles have no correlation.④When we analyze the correlation of the iniatial area of section and the peakload the result shows that the iniatial area of section of the C5,C6,C7 nerve roots and the peakload have direct correlation (r=0.595, 0.703, 0.691; P<0.01), the iniatial area of section of the C8,T1 nerve roots and the peakload have no correlation (r=0.406, 0.392; P>0.05).The results indicate that there are differences in biological mechanics performance between each nerve root, C7 can bear the maximum loading and the maximum extension rate (70.29±1.50﹪,2.28±0.27N), the common ground is that different iniatial area of section the nerve roots can bear different load, the peakload and the rupture parts change with the different dragging angle (the rupture parts of each nerve root is mainly distal neural ganglion when the dragging angle is 90°, when the angles change from (45°~90°) and (90°~135°) the rupture parts is mainly proximal neural ganglion, the rupture parts of C5,C6,C7 nerve roots are not in regulary but the rupture parts of C8,T1 nerve roots are mainly proximal neural ganglion). It is be related with the anatomic site of each nerve root come out of myelold and the disequilibrium strees when they are dragged.