Design Of Anterior Lumbar Locked Screw-plate And Correlative Study

BackgroundLumbar spinal fusion surgery includes posterior lumbar interbody fusion(PLIF) andanterior lumbar interbody fusion(ALIF). PLIF and posterior pedicle screw fixationtechnology in the clinical use is very wide, but there are some problems difficult toovercome, such as nerve stretch injury, requiring extensive cutting and strippingparavertebral muscles, heavy trauma, excessive bleeding, slow rehabilitation, and somecomplications in some patients such as chronic low back pain, low back stiffness, implantloosening, adjacent segment degeneration, and so on.ALIF which is operated through midline or paramedian extraperitoneal approach hassuch merits as without chopping various abdominal muscles, a minimally invasive nature,reduced bleeding, simple operation, and fast postsurgical recovery. Furthermore, ALIF canobtain a greater contact surface of the vertebral bone graft, restore the intervertebral heightand lumbar lordosis, expand the foramen intervertebrale to decompress nerve root, reduceepidural scar and reduce the endorhachis and nerve root injury risk.Over the past decade, due to the minimally invasive surgical concept is widerecognition and surgical instruments and surgical technology continues to progress, ALIFsurgery gradually be loved by more spine surgeons. ALIF postoperatively often needs to becomplemented lumbar pedicle screw or facet joints screw, which increases the trauma,surgery time, anesthesia time, blood loss, so, numerous scholars hope that ALIF combinesanterior fixation, that is through the same incision completion spinal canal decompression,interbody fusion and internal fixation.At present, the lumbar front fixation devices is mainly applied in the L5/S1segment,such as Triangular PYRAMID plate、PACH and lumbosacral anterior fusing plate. Abroad,the single segment lumbar front fixation devices such as ATB plate, Unity LX Plateis still inthe experimental stage, and is no listing. To this end, on the basis of the lumbar anatomicalcharacteristics, we designed an anterior lumbar locked screw-plate which applied in L3～ S1single segment fixation and test its biomechanics. In addition, we studied anteriorlumbar surgery operation vascular safety of animal experiments.Purposes1.Measuring anatomic parameters from3rd lumbar vertebrae to sacrum through CTand designing the anterior lumbar locked screw-plate(ALLSP)which is fixed in right frontof lumbar vertebrae. In order to provide highly secure and firmly stable internal fixationdevices for lumbar fusion.2.Evaluate the biomechanical stability of an anterior lumbar locked screw-plate(ALLSP) newly developed for supplemental fixation during ALIF.3.Literatures reported lumbar anterior surgery might injury blood vessel and riskintravascular thrombosis, so we firstly carry out a large animal experiments to research thesafety of the blood vessel through imitating ALIF. The most important thing is providingexperimental basis for the installation of this screw-plate.Methods1.CT detection were performed on63adults(30males and33females).From3rdlumbar vertebrae to sacrum, survey the anatomic parameters by Computer Software:anterior lumbosacral anterior height, anterior height of intervertebral space；the longesttrajectory of the screw, forward radian of the anterior lumbosacral body, angle of Cobb ofthe adjacent lumbosacral body. On the base of L3～S1anatomical characteristics a novelanterior lumbar locked screw-plate was designed.2.Twelve fresh human cadaveric lumbar specimens (L4-L5) were apportioned among acontrol group (intact specimens) and three groups of different surgical constructs, each ofwhich included the implantation of a rectangular titanium cage. In one group ALIF wasperformed; another consisted of the ALIF combined with ALLSP fixation (ALIF+ALLSP).In the last the TLIF was combined with pedicle screw fixation (TLIF+PSF). ALIF+ALLSPand TLIF+PSF were the fixed groups. Recordings were made of spinal axial compression,flexion, extension, lateral bending, and rotation induced by applied forces over a range ofloads with a material testing machine. The biomechanical properties of the specimens weretested in a Zwick/Roell BZ2.5/TS1S material testing machine. Three measurements were performed for each specimen and the mean value obtained. Spinal range of motion in thedirections of axial compression, flexion, extension, lateral bending, and rotation wasrecorded under different loads.3. Five adult goats were used to measure the right side stretch limit of the bloodvessels by counting the number of0.5-cm-thick slabs of wood that were inserted betweenthe right edge of the lumbar and the stretch hook. Twenty-one adult goats were divided into3groups to investigate histological injury and thrombosis under different stretch intensities.GroupⅠunderwent blood vessel stretch to0.5cm for2h; group Ⅱ underwent stretch to1.5cm for2h; and group Ⅲ was used as an unstretched control (isolated abdominal aorta andinferior vena cava were not stretched). Group Ⅲ and at each time point of group Ⅰ, Ⅱwas assigned three animals. Ring-shaped blood vessel samples were collected from goats ingroups I and Ⅱon postsurgical days1,3, and7. Blood vessel samples were investigated bygeneral observation, light microscopy (haematoxylin and eosin and elastic fiber staining),and transmission electron microscopy (TEM). Thrombogenesis was examined in the iliacand femoral AtVs.Results1. The length of the plate adapted to L3～L5is34mm,36mm,38mm,40mm,42mm,44mm respectively, width is28mm, and thickness is5mm. Its sagittal convex curvature is3°,10°and20°respectively, transverse curvature is70°and the space of screw hole is8.5mm. The diameter of full thread tapping screw is6.5mm, which length is24mm～30mmrange. The orientation of the screw is10°upward or downward,5°inward. The length ofthe plate adapted to L5～S1is40mm,42mm,44mm respectively, the width of upper end is24mm, the width of lower end is28mm, and the space of screw hole in upper end is6.5mm.Its sagittal convex curvature is50°, transverse curvature of the upper end and lower end is55°and70°, respectively. The diameter of full thread tapping screw in5th vertebrae is10°,upward and7°outward. Screw cap sinking into the plate is called1stlocking, installationin the plate preventing the screw slack called2ndlocking.2. There were significant differences with regard to the range of movement for the fourgroups. Compared with the TLIF+PSF group, the ALIF+ALLSP had significantly greateraxial stiffness under applied axial compression, and significantly decreased angular displacement under flexion and rotation forces. However, compared with the ALIF+ALLSPgroup, in the TLIF+PSF group the angular displacement was less under lateral bending andextension, although this difference was not significant (P>0.05).3. The right side stretch limit of the large blood vessels in front of the lumbar spinewas1.5cm from the right edge of the lumbar. All goats survived surgery withoutdeveloping complications as peripheral arterial or pulmonary embolism. Generalobservation revealed no injury or thrombosis in the large blood vessels in front of thelumbar spine and no thrombosis in the iliac or femoral AtV. Under light microscopy, groupⅠspecimens showed only slight swelling of the endothelial cells in the abdominal aorta andthe inferior vena cava had no histological injury, whereas group Ⅱshowed obvious injuriesin the abdominal aorta. In light microscopy, the differences about A, B and C point’sdamage in Group Ⅰwith Ⅱ, Group Ⅱ with Ⅲ were statistically significant, P≤0.003;the differences about A’, B’ and C’ point’s damage among groups was not statisticallysignificant, P>0.05. At postoperative days1,3and7, the abdominal aorta of group Ⅱshowed endothelium damage, unclear organelles and incomplete cell connections by TEM.Conclusions1. Based on the parameters which were measured in front of the63cases of normaladults L3to S1vertebral anatomy, we designed the anterior lumbar locked screw-platefixation system. The fixation is in line with the lumbosacral local anatomical features, andits double locked device and streamlined appearance are its characteristic.2. The ALLSP conforms to the anatomical characteristics of the anterior lumbar spinehas good biomechanical stability, can meet the the fixed requirements within the clinicalALIF surgery lumbar, and can be used as a reliable choice to enhance the stability of ALIFsurgery.ALIF+ALLSP has biomechanical advantage than TLIF+PSF in axial compression,flexion, rotation.3. In goat blood vessels stretch models, AA and IVC stretch to the right more than thethe lumbar right side edge0.5cm is relatively safe, AA and IVC had no significanthistological damage; stretch to the right more than the the lumbar right side edge1.5cm, AAblood flow is blocked risk and abdominal aortic intimal layer showed obvious histologicaldamage, IVC had no obvious histological damage. Anterior lumbar surgery within a certain range pulling AA and IVC is safe, but stretch beyond a certain limit can lead to vascularinjury and even the risk of thrombosis.