Study On The Modified Placement Technique Of The Fifth Lumbar Pedicle Screw

Part 1 A novel entry point for L5 pedicle screwLumbar posterior pedicle screw fixation is commonly used in degenerative diseases, deformity, trauma, tumor and other pathological changes caused by the unstable spine. It is currently the main method of lumbosacral spinal fixation. Related researches showed that there are several methods for the lumbar spine pedicle screw placement, such as Roy-Camille’s, Magerl’s, Du’s, and Louis’, Weinstein’s, Krag’s method, etc. Now, Magerl’s and Du’s are the most commonly used. Magerl’s entry point locates at the nape of the neck of the superior articular process. Du’s starting point locates at the pars interarticularis converges at the accessory process, described as a "Λ"-shaped crest. In China, most of the surgeons chose the Du’s starting point. It has been widely used in the lumbar spine pedicle screw placements of L1-L4. But for L5, these two methods are not ideal.The distance from the pedicle to the center line gradually increases from L1 to L5 on both sides. Clinically, inserting L5 spine pedicle screw is relatively the most difficult. Wiltse first described paraspinalmuscle gap approach in 1968. However, lack of special operative instruments makes it difficult to expose strong multifidus muscle in lower lumbar spine. The conventional open approach is still the most commonly used at present. In the conventional open approach, Magerl’s method needs to be exposed to the root of the transverse process. Du’s method simply expose the "A"-shaped crest, but the "A"-shaped crest in L5 has 19% of the variation. It becomes shallow and hard to be located. Surgeons have to expand the operating field, through the transverse process, the structure of the joints and other structures. For patients with lumbar spondylolisthesis, vertebral pedicle, transverse process and the forward displacement of articular process. If we use Magerl’s or Du’s method, the operating field then seems not deep enough, and our vision will be limited, then it’s difficult to locate the entry point. Moreover, on account of the deeper position, the lift surgery operation is not easy. Holding force of the screw is insufficient, and then bone cement is often needed. Fractures occur in some elderly women who suffer osteoporosis and spondylolysis.To solve these problems, we put forward a novel entry point for L5 pedicle screw placement. The point is located on the the junction of the mid-inferior one-third of the corresponding superior articular process. The purpose of this study is to validate the accuracy and safety of new points and to compare this new method with the traditional methods during biomechanical research to evaluate the fixed strength of it. The study would be elaborated in three parts:1.Anatomical study based on the three-dimensional CT reconstruction imaging.2. Clinical research about the application of the entry point for L5 pedicle screw.3. Biomechanical study between the new entry point for L5 pedicle screw and the traditional method.1. Anatomical study based on the three-dimensional CT reconstruction imagingPurpose:This study aims to introduce and evaluate a novel unarmed security technology based on the new entry point for L5 pedicle screw placement.Methods:A total of 30 three-dimensional models were reconstructed based on computer-aided tomography (CT) images of lumbar vertebral bodies from Chinese adult volunteers. On the 3 d reconstruction images, L5 pedicle screw insertion via the novel entry point was simulated and the distance between the entry point and the pedicle axis was measured, to assess the safety of the new technique.The angle between the up-endplate and the connection of L5-S1 spinous-process trailing edge was also measured. In horizontal plane, general simulation respectively tangential pedicle screw internal and external wall of cortex, was measured with CT horizontal plane safety point of view. In the process of operation, we chose to lumbar vertebral articular process on L5 under the longitudinal center line of, a third point as the new starting point.Results:The average distance from the entry point to the pedicle axis is 4.67 mm (4.67 ± 0.31 mm,3.81 mm to 5.27 mm). With pedicle medial cross-section of tangent angle of an average of 20.84 ° (20.84 ± 7.22° and 6.26°to 35.90°). With pedicle wall cross section of tangent angle of an average of 10.22 °(10.22±7.02°and 0.00° to 22.45°). The mean transverse safe angle is 10.62° (10.62± 2.54 ° and 1.99° to 23.71°), which was Similar to previous research results (Du’s 10.48 ° and Magerl’s 14.13°).Conclusion:New above L5 into nail joints for anatomical reference, can be in nailing with L5 spinous process and spine ligament depended on nail Angle; After nailing point at which a simple and safe. According to the measured horizonal safety Angle range, we will be horizontal screw Angle (transverse screw angle, TSA) for 15°. Considering safety, regarding nailing the sagittal plane, we chose the same as the traditional method of nailing Angle:the sagittal Angle of screw (sagital screw angle, SSA)to0°.2. Clinical research about the application of the entry point for L5 spine pedicle screwPurpose:To compare the accuracy of L5 pedicle placement between the new technique and Magerl’s method based on the postoperative CT images, and to provide theoretical basis for clinical application.Methods:A total of 103 hospitalized patients from May 2014 to September 2015 (55 male,48 female, age range 37-74y, mean age 56.8 y) were included in our research. Alternating 103 people can be divided into two groups, of which 52 recieved new technique, the other 51 Magerl’s method. A total of 206 screws for L5 were inserted in our study. Regarding the screw Angle of two group were as follows:the TSA 15 °, SSA 0 °. The sagittal plane screw and L5 supraspinal ligament maintain 80 °. Postoperative CT images on L5 pedicle screws were used to grade all the screws according to Louis-Philippe Amiot classification standard.x2 test was used to compare the accuracy between the two groups.Results:A total of 103 patients,206 pedicle screws were placed. Neither nerve or vascular injury nor revision occured. Postoperative CT scans showed that a total of 23 screws penetrated pedicle cortex (new nail point group 7 cases, Magerl group 16 cases). No complications of nerve, blood vessel damage occured. According to Amiot classification method, screws in Grade 1 screw were considered to be accurate. New pin point group of accuracy was 93.3%. The accuracy in Magerl group was 84.3%. The accuracy between the two groups have significant difference (x2= 4.164, P= 0.041).Conclusion:Via the new entry point for L5 spine pedicle screw, we can achieve better accuracy than traditional methods.3. Biomechanical study between the new entry point for L5 spine pedicle screw and the traditional methodPurpose:To compare the biomechanics of the new entry point with the traditional method, and provide basis for clinical application.Methods:Six spinal L5 specimen of the human body from 6 men, (age range 56-73y, mean age 65.8 y) were used to perform this study. Before the experiment, BMD of L5 was measured and x-ray was used to rule out congenital malformations. We inserted the screws via the new entry point on the left side and Magerl’s point on the right. The max screwing torque and the maximum pullout strength (MPH) were measured during placement. Then, the screw angles of the two groups are the same:TSA 15 °, SSA 0 °. Wilcoxon rank was used to analyze the difference of screwing torque and maximum axial pull output between the two groups and Pearson correlation analysis of bone density and biomechanical testing index was performed with the inspection level of a=0.05.Results:The mean maximum screwing torque of the new L5 entry point is higher than that of Magerl’s method (163.3± 19.8 N · cm vs.98.2 ± 10.2 N · cm), the difference was statistically significant (Z=-2.201, P=0.028< 0.05). The mean maximum pullout strength of the new L5 entry point is higher than that of Magerl’s method (551.09±74.33N vs.514.68±57.41N), the difference was statistically significant (Z=-1.992, P=0.046<0.05). There are significant positive correlation between the mean maximum screwing torque of the new L5 entry point, the mean maximum pullout strength of the new L5 entry point and BMD (r=0.934, P<0.01, r =0.909, P< 0.05, r=0.979, P<0.01). There are significant positive correlation between the mean maximum screwing torque of Magerl’s method, the mean maximum pullout strength of Magerl’s method and BMD (r=0.894, P< 0.05 and r= 0.863, P<0.05 and r=0.929, P<0.01).Conclusion:We can achieve better fixation strength via the novel L5 entry point than the traditional method.Part 2 Biomechanical comparison of the entry point for L5 spine pedicle screw and L5 cortical bone trajectory technologyAt present, the pedicle screw internal fixation has been widely used for spinal diseases. Traditional pedicle screws inserted into the main path by the vertebral arch outside to the inside of the nail and transverse process and joint surface wall border into points. Traditional pedicle screw fixation often leads to some complications, such as cortex damaged, spinal cord and nerve root injury, deep infection, major vascular injury, dural tear and cerebrospinal fluid leakage, etc. There are many improvements of the entry points and the direction of the screw during decades of developments and studies. Santoni etc. first reported Cortical Bone Trajectory (CBT) technology in 2009, in which the screw is outward, and direct to the head in the placement. Santoni reported that compared with the traditional pedicle screw fixation, CBT can maximize the contact with cortical bone.Although the clinical application of CBT techniques is still in its infancy, some morphology and biomechanical studies have shown that compared with the traditional pedicle screws, CBT has better effect of internal fixation. And in clinical practice, we also explore a new kind of entry point for L5 pedicle screw. The entry point is located on the the junction of the mid-inferior one-third of the corresponding superior articular process. The angle of the screw is TSA 15 °, SSA 0 °. In previous studies, we have confirmed that the new entry point is easy to locate, safe, accurate, and strong. Now, in this biomechanical testing, we compare this new entry point with the CBT techniques, its stability evaluation is then proved.Purpose:To compare the biomechanical test results between the novel L5 pedicle screw placement technique and CBT approach, and to evaluate the stability of this novel technique.Methods:Using aqueous formaldehyde six spinal L5 specimen of the human body,6 men,4 women (age range 52-76y, mean age 64 y). Before the experiment, we measure L5 BMD, and the x-ray is used to rule out congenital malformations. The new entry point is located on the the junction of the mid-inferior one-third of the corresponding superior articular process. The direction for the screw:TSA 15 °, SSA 0 °. CBT group is based on isthmus-guided CBT pedicle screw fixation by Iwatsuki. The screw is inserted in the vicinity of the inferior articular process from the dorsal side at a point 3 mm medial to the lateral margin of the isthmus. In side views, the superior margin of the intervertebral foramen serves as the reference point.The direction for the screw:TSA-10 °, SSA 25 °. The max screwing torque is measured during placement. Then the maximum pullout strength (MPH) is measured. Using Wilcoxon rank and inspection comparison between the two groups of screwing torque and maximum axial pull output, using Pearson correlation analysis on bone density and biomechanical testing index correlation analysis:the inspection level of a= 0.05.Results:The mean maximum screwing torque of the new L5 entry point is higher than that of CBT group (167.5± 20.1 N · cm vs.161.5 ± 15.9 N · cm), the difference was statistically significant (Z=-1.988, P=0.047<0.05). The mean maximum pullout strength of the new L5 entry point is higher than that of CBT group (567.84± 72.43 N vs.530.52±54.44 N), the difference was statistically significant (Z=-2.395, P=0.017<0.05). There are significant positive correlation between the mean maximum screwing torque of the new L5 entry point, the mean maximum pullout strength of the new L5 entry point and BMD (r=0.922, P<0.01, r=0.863, P<0.01, r=0.936, P<0.01). There are significant positive correlation between the mean maximum screwing torque of CBT group, the mean maximum pullout strength of CBT group and BMD (r=0.946, P<0.01, r=0.839, P<0.01, r=0.816, P<0.01).Conclusion:The new entry point for L5 spine pedicle screw can achieve better fixed strength than CBT.