| Objective: By measuring the front surface of Atlantoaxial complex to designtransoral anterior atlantoaxial locking anatomical plate, and have biomechanical testfor the plate.Method: By measuring some anatomical indexes of the front surface of Atlantoaxialcomplex of specimens, We design and produce two kinds of transoral anterioratlantoaxial locking plate and a kind of conical screw with diameter3.5mm singlecortical. We have some testing about plates on MTS machine:(1) Axial compressiontest.(2) Torsion test.(3) Torsion fatigue test. The experimental results werestatistically analyzed.Results: By measuring some anatomical indexes of the front surface of Atlantoaxialcomplex of specimens, we show those by their mean±standard deviation (min~max). A part of anatomical measurements have been accomplished. Such as the widthof Atlas can be revealed is45.06±1.00(43.61~47.42) mm, the distance of Lateralborder of the lateral mass of atlas to the anterior tubercle is26.28±1.27(23.79~29.20) mm, the transverse distance of the middle of the lateral mass of atlas is13.94±1.60(10.08~16.38) mm, the middle height of Lateral mass of atlas surface is17.13±1.03(15.53~19.38) mm，Atlas lateral mass screw entry point is A that the centre ofanterior surface of atlas, the distance between the middle line to the lateral border ofaxis is10.83±1.23(9.57~13.63) mm, the default line of screw installed is based onthe characteristic of anatomy and regional distribution of high bone density,Atlantoaxial lateral mass of the entrance point B. which about9mm distance from themiddle line and4.81±0.33(4.16~5.16) mm distance from the upper edge of thelateral mass, the distance of between the midline of the vertebral axis to the medial ofvertebral artery is12.28±1.17(11.10~14.58) mm, point C which the default line cross with the endplate is the entry point of axis, the linear distance between Aand B is15.63±0.56(14.44~16.30) mm, the linear distance between B and C is6.86±0.56(6.05~7.89) mm. In order to design anatomic plate,we should measurethe curvature of safety zone of Atlantoaxial front surface for screw installed. Alip-like structure at the bottom of axis surface (called anterior lip), The left and rightcurving strings of Atlantoaxial complex were31.29±0.55mm,31.35±0.55mm,respectively. The left and right arcs of Atlantoaxial complex were:32.83±0.61mm,32.88±0.62mm, respectively. No statistically significant difference between left andright p﹥0.05. Radius of curvature and the central angle of left and right of theatlantoaxial complex sagittal plane were:30.75±0.63mm,(61.18±1.34)°;30.87±0.86mm,(60.88±1.90)°, respectively. No statistically significant differencebetween left and right p﹥0.05. The curving strings and arcs and radius of curvatureand the central angle of axis anterior surface were:15.30±0.54mm；21.59±0.87mm；7.78±0.26mm；(159.13±1.88)°, respectively. The height of axis anterior lip atMidline and left and right sides were:6.01±0.29mm,5.11±0.09mm,5.10±0.092mm, respectively. No statistically significant difference between left and right p﹥0.05. According to the anatomy, We design2kinds of plates (five-hole "V" plateand six-hole "V" plate) and a diameter of3.5mm conical screws. The result ofmechanical testing:(1) Axial compression yield load of the structure mean±standarddeviation: five-hole plate is8819±576N,six-hole plate is8662±344N, No statisticallysignificant difference between five-hole plate and six-hole plate P>0.05;the structurecompressive limitation of Axial compression mean±standard deviation: five-holeplate is14188±354N, six-hole plate is,12343±416N, there is statistically significantdifference between five-hole plate and six-hole plate P <0.05. Torsion test: to reversethe structural yield load of the mean±standard deviation: five-hole plate was28166±1249N, six-hole plate is,27617±841N, No statistically significant differencebetween five-hole plate and six-hole plate P>0.05; The limitation of torsion structuremean±standard deviation:five-hole plate is55192±1748N,six-hole plate is51280±282N, there is statistically significant difference between five-hole plate andsix-hole plate P <0.05; torsional stiffness mean±standard deviation: five-hole plate is 20796±693N, six-hole plate is19698±406N, There is statistically significantdifference between five-hole plate and six-hole plate, P<0.05. Torsional fatigueexperiment: to reverse the cycle of fatigue after the torsion angle increment of onehundred thousand weeks mean±standard deviation: five-hole plate is0.09562±0.00631°, six-hole plate is0.09413±0.00772°, No statistically significantdifference between five-hole plate and six-hole plate, P>0.05.Conclusions:1:There are physiological curvatures of the safe zone of install screw onthe front surface of atlantoaxial complex. by measuring the physiological curvature ofthe front surface of the atlantoaxial complex can provide scientific basis to designanterior atlantoaxial locking anatomical plate. Anatomic plate can help reduce thedislocation of atlantoaxial.2: The measurement of bottom of axis anterior surface toguide surgery entry screw and determine angel of the screw.3: By testing two kindsof plates with compression and fatigue tests, two kinds of plates have goodmechanical strength, in a number of indicators showing: five-hole plate has a moreadvantages than six-hole plate. |
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