Comparative Finite Element Analysis of Posterior Short Segment Fixation Constructs with or without Intermediate Screws in the Fractured Vertebrae for the Treatment of Type A Thoracolumbar Fracture

doi:10.21203/rs.3.rs-2104845/v1

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Comparative Finite Element Analysis of Posterior Short Segment Fixation Constructs with or without Intermediate Screws in the Fractured Vertebrae for the Treatment of Type A Thoracolumbar Fracture

https://doi.org/10.21203/rs.3.rs-2104845/v1

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Conventional short-segment stabiliztion for thoracolumbar fractures initially involved inserting pedicle screws in the vertebra one-above and one-below the level of injury, creating a four-screw construct connected by rods spanning. However, the reported early implant failure rate and loss of correction rate are quite high. Therefore, six-screw short-segment posterior fixation, which involves additional augmentation at the fractured vertebrae has been proposed to reduce the rates of kyphosis recurrence and implant failure. Yet, little is known about biomechanical changes to the spine, strongest advantage and the appropriate indications. The objective of this study was to investigate the biomechanical properties that are associated with augmentation of intermediate screws at the fracture vertebrae in relation to the severity of type A thoracolumbar fracture using finite element analysis. Short-segment stabilization models with or without augmentation screws at fractured vertebrae were established based on finite element model of moderate compressive fractures (AO Spine A1 and LSC grade-2 ), severe compressive fractures (AO Spine A1 LSC grade-3), and burst fracture(AO Spine A3 and LSC grade-2 ). The spinal stiffness, stresses at the implanted hardware, and axial displacement/micro-motion of the bony defect were measured and compared under mechanical loading conditions. Our results suggested that more severe fractures might benefit more from rigid fixation with six-screw constructs. Augmentation of intermediate screws at the fracture vertebrae is recommended for patients with higher wedge-shaped or burst fractures to reduce the risk of hardware failure and postoperative re-collapse of injured vertebrae.

Thoracolumbar fracture

Finite element analysis

Pedicle screw instrumentation

Biomechanics

Thoracolumbar fractures with kyphotic deformity and/or neurologic deficits usually represent indications for operative management. However, there remains a lack of consensus on an optimal method for treating traumatic thoracolumbar/lumbar fractures. Although conventional four-screw short-segment (one-level above and below the fracture level) stabilization is typically considered to provide enough stability for most type A thoracolumbar/lumbar fractures, the reported early implant failure rate and loss of correction rate are quite high(Jindal et al. 2012). In the past decades, the surgical treatment of patients with type A thoracolumbar fractures has shifted from conventional open procedures to minimally invasive surgery. Percutaneous pedicle screw-rod fixation has been developed to restore stability, alignment while promoting early mobilization of the patients with thoracolumbar/lumbar fractures(Neeley et al. 2022; Pannu et al. 2019). As a consequence, more correction loss could be observed in thoracolumbar/lumbar fractures treated by percutaneous four-screw fixation technique as compared with conventional open short segment fixation with posterolateral fusion(Hirota et al. 2022; Lorente et al. 2019). Therefore, six-screw short-segment posterior fixation, which involves additional augmentation at the fractured vertebrae has been proposed to reduce the rates of kyphosis recurrence and implant failure(Kapoen et al. 2020). Yet, little is known about the biomechanical changes to the spine that are associated with the placement of two additional pedicle screws; for example, in relation to the severity of vertebrae fracture. Intermediate screw at the fracture level is associated with greater mechanical stiffness but at the expense of longer operation times, higher risk of screw malposition and more medical costs. Thus, efforts are needed to investigate the biological efficacy and best indication of six-screw short-segment posterior fixation for thoracolumbar fractures.

In the present study, we evaluate and compare the immediate post-operative biomechanical performance of the traditional four-screw fixation and six-screw stabilization with additional augmentation at the fractured vertebrae in terms of spinal stiffness, fracture site motion, and stress at the implanted hardware. This was achieved by developing finite element (FE) models of the thoracolumbar spine that describe the above-mentioned two procedures for three different patterns of vertebral fractures, and testing them through simulations of ex-vivo biomechanical experiments.

2.1 Subject for biomechanics simulation

DICOM format files of 3 vertebrae and 2 discs between T11 and L1 of the spine were obtained by continuously scanning with 256-slice spiral computed tomography (CT) from a 29-year-old healthy male (61 kg and 175 cm) without a history of spinal injury, osteoporosis, and radiographic evidence of degeneration. The slice thickness was 0.75 mm. The procedure was approved by the Ethics Committee of PLA General Hospital and the patients provided written informed consent to participate in this study.

2.2 Establishment of FE model of an intact normal thoracolumbar spine

The CT images were imported into Mimics 21.0 (Materialise Inc., Leuven, Belgium) to create 3-dimensional (3D) vertebral models of the T11 to L1 region. The intervertebral discs and facets were created according to the contour of the adjacent vertebral body in 3-Matics 19.0 (Materialise Inc., Leuven, Belgium). Subsequently, the model was imported into the reverse engineering software Geomagic Studio 14.0 (Geomagic, Inc., Research Triangle Park, NC, USA) in STL format to be fitted to an accurate NURBS surface at the exact surface stage. Finally, the NURBS surface was imported into the Hypermesh 2019 (Altair Engineering, Inc., Executive Park, CA, USA) in Iges format for meshing, and the corresponding structures were established including the paraspinal ligament and annulus fibrosus collagen fibers.

The vertebral body was composed of the cortical bone, cancellous bone, and endplate, and the thickness of the cortical bone and endplate was set to 1 mm(Zhou et al. 2020). The intervertebral discs consisted of nucleus pulposus (NP) and annulus fibrosus which was composed of annulus matrix and collagen fibers. The annulus matrix was reinforced by collagen fibers distributed in concentric lamellae with crosswise pattern at ± 35°Orientations and the stiffness of the fiber was gradually increased from inside to outside(Schmidt et al. 2012). The nucleus area was 40% − 50% of the cross-section of the total disc(Erbulut et al. 2014). Annulus fibers and seven major ligaments including anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), flava ligament (FL), facet capsular ligament (CL), intertransverse ligament (ITL), interspinous ligament (ISL) and supraspinous ligament (SSL), were modeled as tension-only truss element(Ouyang et al. 2019). A frictionless surface to surface contact with minimum gap distance of 0.2 mm was used to simulate the facet joint (FJ) articulation (Naserkhaki et al. 2018). These model materials and properties were selected according to the previous studies (Li et al. 2015; Polikeit et al. 2003; Schmidt et al. 2007; Schmidt et al. 2012; Shen et al. 2019). The final intact T11-L1 model includes 536,959 elements and 135,938 nodes (Fig. 1).

2.3 Establishment of FE models of T12 fracture

The fractured vertebra model was created using SolidWorks 2019 (SolidWorks Corporation, Concord, MA, USA). The methods reported by Zhou et al. (Zhou et al. 2020) were used as a reference to simulate the T12 fracture. The oblique edge of resection is paralleled to the kyphotic correction angle and the size of the bony defect varies with the fracture severity according to AO Spine thoracolumbar classification system and load sharing classification (LSC). For moderate wedge fractures (AO Spine A1 and LSC grade-2), the ratio of the anterior bony defect was set to 15% of the original height after fracture reduction (Figure. 2A). For severe wedge fractures (AO Spine A1 LSC grade-3), the ratio of the anterior bony defect accounted for 50% after reduction (Figure. 2B). (Alizadeh et al. 2013; Liu et al. 2018). The burst fracture model simulating A3 type was created by extending the defect to the 30% of middle columns of the T12 vertebral body (Figure. 2C).

2.4 Implants and fixation models

Pedicle screws and rods were drawn using SolidWorks software. The diameter of conventional pedicle screw and connecting rod in this study was set to 6.0 mm and 5.0 mm, and the total length of the screw was 45 mm. The diameter of intermediate screws was 5.5 mm and the length was 30 mm. Six fixation models were established in this study using 4-screw or 6-screw constructs respectively on the basis of T12 moderate/severe wedge fractures and burst fractures FE model (Fig. 3): 1. M4: four-pedicle screw fixation for moderate wedge fracture. 2. M6: six-pedicle screw stabilization with intermediate pedicle screws at the fractured vertebrae for moderate wedge fracture. 3. S4: four-pedicle screw fixation for severe wedge fracture. 4. S6: six-pedicle screw stabilization with intermediate pedicle screws at the fractured vertebrae for severe wedge fracture. 5. B4: four-pedicle screw fixation for burst fracture. 6. B6: six-pedicle screw stabilization with intermediate pedicle screws at the fractured vertebrae for burst fracture.

2.5 Finite element analysis

All degrees of freedom at the bottom of the L1 surface were constrained. This study simulated bone fusion following surgery, therefore, the interfaces between the screw and vertebrae were set to be bonded. Abaqus CAE 2019 (Dassault Systems Simulia Corp., USA) was used for FEM analyses.

(1) the loading of the intact model and the fracture models

In order to Validation of the Intact and the fractured FE models ,pure moment of 7.5 Nm was applied on the surface of T11 to test the intact model and the fracture models under six loading conditions(flexion/extension, right/left lateral bending and right/left axial rotation).

(2) the loading of the internal fixation model

Pure moment of 7.5 Nm combined with a pre-compressive load of 350 N(Zhou et al. 2020) was applied on the surface of T11 to test six fixation FE models under six loading conditions.

Our FE analysis focused on three measurements: (1) The range of motion (ROM) of T11-L1 to estimate the spinal stiffness; (2) von Mises stress generated in implants and stress nephogram to estimate the load borne by the fixation devices; (3) axial displacement/micro-motion of the bony defect to estimate the risk of correction loss.

3.1 Validation of the intact and the fracture thoracolumbar spine model

To validate the rationalities of the models, segmental range of motion (ROM) was measured during each motion type, and the predicted results were compared with previously published literature obtained in biomechanical experiments. When the pure moment of 7.5 Nm was applied, little difference existed in the ROM of T11-T12 and T12-L1 under six loading conditions between the intact model and those of Panjabi et al (Oxland et al. 1992). As was displayed in Fig. 4, all values in different conditions were within the vitro ranges. Therefore, the T11-L1 model in the present study was valid for further analyses. Next, pure moment of 7.5 Nm was applied against the fracture models, the total ROM of T11-L1 segment were measured during flexion/extension, lateral bending, and rotation. The results were also validated against the in vitro cadaveric experiments conducted by Panjabi et al(Kifune et al. 1995). As was displayed in Fig. 5,the ROM of the fracture models were within the vitro ranges and the ROM of the serve fracture model was greater than the moderate fracture models.

3.2 ROM of the internal fixation models

The global ROM values for the 6 fixation models under the flexion, axial rotation, and lateral bending loading were shown in Fig. 6 for all the constructs investigated, the largest coupled motions were found during anterior flexion. Burst fracture models presented significantly larger ROM than compressive fracture models in all states of motion, revealing that fracture pattern plays a crucial role in the rigidity of the posterior spinal constructs. Compared to the conventional four-screw fixation models, all six-screw stabilization showed noticeably greater stiffness particularly in anterior flexion. The ROM during anterior flexion was decreased by 8.1, 13.6 and 15.6% in M6, S6 and B6 versus M4, S4 and B4 respectively, further revealed that instable thoracolumbar fracture benefited more from augmentation of intermediate screws at the fracture vertebrae. However, there was no significant decreasing percentage of ROM in M6 versus M4, and S6 versus S4 during lateral bending, and axial rotation.

3.3 Von Mises stress on the screw and rod construct.

The maximum values for von Mises stress of the pedicle screws and rods in all fixation models was shown in Fig. 7. The injury severities are also found to significantly influence stress on the constructs. The greatest von Mises stress value of rods and screws was observed in burst fracture model, followed by sever and moderate compressive fracture models at 6 different loading positions. Flexion exerted the largest mechanical stress on both the screws and rods in all implanted models ranging from 164.2 to 777.3 MPa and 101 to 544.8 MPa. Comparison between the four-screw and six-screw constructs showed that the stress of the rod in six-screw models increased while decreased that of pedicle screws. The intermediate screws at fractured vertebrae changed stress on the constructs for burst fracture models more significantly than for compressive fracture models. The increase in stress of rod in six-screw construct was noticeably greater (18%) for burst fracture than for compressive fracture (10% and 7%) during flexing and bending loading. On the contrary, the maximal von Mises stress on screws of the six-screw constructs mildly decreased in all fracture models, especially during anterior flexion. M6, S6 and B6 generated 24.2%, 26% and 11% less von Mises stress on rods under flexion compared to the M4, S4 and B4 respectively.

Stress nephogram of pedicle screws were shown in Fig. 8. The results of the pedicle screw stress distribution and demonstrated that the maximum stress areas were concentrated at the screw neck. The stress nephogram of the rods on conventional four-screw and six-screw fixation constructs for three types of fracture models under flexion load was respectively shown in Fig. 9. The distribution analysis showed that high stresses were mainly concentrated on the rods between the upper and the intermediate screws in six-screw fixation constructs, whereas stress was well distributed along connecting rods between the upper and lower screws in conventional four-screw constructs.

3.4 Postoperative axial displacement/micro-motion of the bony defect in T12

Increased bony defect motion was observed in all fixation constructs (Fig. 10). The increase was dynamic and varied under different spinal motions. Flexion resulted in maximum vertebral height reduction with an average 35.2% decrease of T12 vertebral heights while minimal height reduction was observed in extension with an average 13% decrease. The maximum axial displacement/micro-motion (absolute value) of the bony defect in the fractured vertebrae during all motions was the largest in the burst fracture model in each group, followed by severe and mild compressive facture models. The comparison between four-screw and six-screw constructs showed that the intermediate screws at fractured vertebra significantly decreased axial displacement/micro-motion of the T12 vertebra in all fixation constructs during all motions. Regarding the mean axial displacement of bony defect during all motions, M6, S6 and B6 allowed lower displacement with 0.3mm, 0.58mm, and 0.8mm, compared with M4,S4 and B4 respectively.

Conventional short-segment instrumentation for thoracolumbar/lumbar fractures initially involved inserting pedicle screws in the vertebra one-above and one-below the level of injury, creating a four-screw construct connected by rods spanning. The objective was to restore vertebral body height, correct kyphotic deformity, maintain spinal stability and indirectly decompress the spinal canal. Controversy however remains as to whether conventional four-screw short-segment instrumentation is strong enough to maintain stable reduction (Jindal et al. 2020).Traumatic thoracolumbar/lumbar fractures disrupt the structural integrity of anterior and middle columns, which directly decreases their ability to withstand longitudinal compressive loads, whereas the short-segment posterior internal fixation system lacks effective support for the anterior column, resulting in loss of reduction and undesirable rates of implant failure. Alanay and Wang(Alanay et al. 2001; Wang et al. 2008) argues that four-screw short-segment transpedicular instrumentation for type A thoracolumbar fractures is associated with a high rate of correction loss because of the absence of anterior support. The analysis of kyphotic correction made by Aly T et al (Aly 2017) indicated poorer corrections for short-segment stabilization immediately after surgery and a greater loss of this correction in the long-term follow-up. In recent years, minimally invasive spinal surgery has emerged as a promising novel method for thoracolumbar fracture patients. As an alternative procedure to treat the thoracolumbar/lumbar fractures, percutaneous pedicle screw-rod fixation aims to restore alignment similar to open surgeries, enabling early mobilization after surgery. Percutaneous insertion of cannulated pedicle screws is associated with less muscle damage and blood loss compared with open surgery, but is less stable biomechanically, and thus may result in early implant failure rate (Hirota et al. 2022). On the other hand, patients are allowed full weight-bearing ambulation and rehabilitation immediately after the surgery, though, increases the risk of loss of correction in comparison to conventional open surgery with posterolateral fusion. Hence, augmentation of pedicle screw-rod system in patients with severe type A factures may be necessary to enhance the rigidity of the construct.

The common clinical methods to improve the fixation of four-screw construct include lengthening of posterior instrumentation, which inevitably sacrifice motion and function of adjacent segments, or placement of intermediate screws at fractured vertebrae, provided the pedicles are intact and the screws can be safely inserted. Augmentation of screws at the fracture level theoretically provides additional stiffness to the construct, thereby reducing the incidence of instrumentation failure, screw pullout, and postoperative loss of correction, allowing surgeons to save motion of adjacent segments and achieving maintenance of sagittal alignment similar to long-segment stabilization(Baaj et al. 2011; Kapoen et al. 2020; Norton et al. 2014). However, more screws insertion into fractured vertebrae exposes patients to longer operating time and more blood loss along with a higher risk of screw malposition. It is also important to consider costs (resource utilization) and potential risks before making a recommendation. Therefore, its strongest advantage, the appropriate indications for six-screw short-segment fixation remain to be elucidated, and question concerning biomechanical changes to the thoracolumbar spine of augmentation screws at the fractured vertebrae need to be answered. For instance, it is important to determine to which extent six-screw construct may change the spinal stiffness compared with traditional four-screw system in relation to the pattern and severity of vertebral fracture, and what would be the implications of such changes on the biomechanical environment at fractured vertebrae and adjacent intervertebral discs.

FE analysis is a powerful and noninvasive technique to simulate and predict how materials will react when subjected to a variety of loads(Gunasekaran et al. 2022). It has widespread application as a tool of comparison between different fixation methods or models for spinal trauma(Jain et al. 2020). A high-quality 3D FE model plays a crucial role in performing an accurate analysis. The finite element model of intact thoracolumbar spine could be routinely constructed based on data collected from CT scan, but it varies widely(Jain et al. 2020) for fracture models because of the lack of standardization. Currently, the most popular finite element model of thoracolumbar fracture was established by corpectomy(Wu et al. 2019) or resecting the lower half of the vertebrae(Li et al. 2014). In most fracture models, up to 50% of the injured vertebrae was completely removed to simulate the loss of bone integrity due to fracture, which is also not reflective of the clinical situation. The results may be prone to error and inaccuracy because researchers were endeavoring to find statistical significance with models of an exaggerated integrity loss.

In this paper, we attempted to formulate new FE models of thoracolumbar fracture simulating different fracture patterns and severity. Mimicking clinical and radiological features, the ratio of the anterior bony defect was set to 15% and 50% of the original height with intact middle column in moderate and sever compressive fracture models respectively, whereas the burst fracture model was characterized by middle column disruption. These models prevented this exaggeration differences among groups, leading to more accurate perception. The FE models in this study were validated against previously published in vitro data including the ROM of the intact and the fractured models. The majority of our results remained compatible and within one SD compared to the literature.

In terms of global ROM, our simulation showed that the ROM of burst fracture models was significantly larger than compressive fracture models in all states of motion. The application of intermediate screws decreased ROM in extension, lateral bending, and axial rotation. The greatest reduction of global ROM (15.6%) was observed in six-screw stabilization for burst fracture models in comparison to compression fractures, showing that intermediate screws in unstable fractures bear more load than in compressive fractures. Therefore, especially burst fractures that are less stable due to lack of middle vertebral column support might benefit more from rigid fixation with six-screw constructs.

More than 50% of compressive load was shifted posteriorly to the pedicle screws and rods, as a result, the axial load would mostly be exerted on the construct. We investigated the maximum von Mises stress and strain energy in the implants, which was related to the risks of early implant failure if the von Mises stress surpasses the tensile yield stress. In the current study, Flexion exerted the largest mechanical stress on both the screws and rods in all implanted models and the greatest von Mises stress value of rods and screws was observed in burst fracture model as well. The results of this study showed the value of the largest maximal von Mises stress of screws decreased during nearly all states of motion in the six-screw stabilization model. The intermediate screws at fractured vertebrae carry some transmitted load, thus scattering the von-Mises stress of the internal fixation especially during flexion. Anterior flexion is the most common and important way of spinal daily activity, which has the greatest impact on the pressure of the spine. Augmentation screws at fractured vertebrae decreased the von-Mises stress of the pedicle screws, thereby reducing the rates of screw breakage and loosening risks. As shown in the stress distribution results, a maximum level of pedicle screw stress focused on the root of the screws under all loading conditions. These findings were also consistent with clinical features that most screw breaks occur at screw neck. Stress nephogram indicated high stresses were mainly concentrated on the rods between the upper and the intermediate screws in six-screw fixation constructs. Surgeons should pay close attention to these sites when there is a clinical suspicion of hardware breakage.

Continuous axial displacement/micro-motion of bone defect area influences new bone formation and causes bone resorption in intravertebral cavity, thus, results in the loss of correction/reduction and further collapse of fractured vertebrae. As a consequence of this, pseudo-arthrosis could exist at the fracture site, causing mechanical back pain or even neurological complications. Consistent with increasing stress of the pedicle screw, anterior flexion also has a significant effect on the bony defect displacement/micro-motion of the injured vertebra, which may contribute to postoperative re-collapse. The comparison between different constructs showed significantly decreased axial displacement/micro-motion in six-screw constructs during all motions. Compare with conventional four-screw constructs, the axial displacement of six-screw constructs during all motions is on average 0.3mm, 0.58mm, and 0.8mm lower in moderate compressive fracture model, severe compressive fracture model and burst fracture model, respectively. For moderate compressive fracture, the risk of correction loss for compressive fractures is lower because the middle column of the injured vertebra remains partial load bearing and stress conduction, therefore short-segment instrumentation with conventional pedicle screw is preferred. The results demonstrated that re-collapse of injured vertebrae could be avoided if unstable fractures were treated with six-screw fixation constructs. Thus, for burst fractures, we strongly advised that bilateral intermediate screws should be used to reduce early post-traumatic kyphosis and failure of reduction instead of using conventional four-screw fixation constructs.

The limitations of this study should be noted. First, simplification of fracture morphologies and the material properties in the FE model might not reflect the realistic situation, which were likely to alter the biomechanical response of tissues and the surgical constructs. Second, pedicle screws were set to rigidly attached to the surrounding bone in proposed models. But slipping between screws and bone may occur, influencing the ROM and stress distribution in the construct. Third, the computational models developed in this study did not include spinal muscles, which contribute to the stability and the stiffness of the spine during motion. However, the main conclusions of this study were based on comparisons between the surgical construct models. The above-mentioned limitations were equally applied to all models and likely had a minimal effect on the comparative differences.

In conclusion, we utilized a FE model to compare the biomechanical performances of conventional four-screw posterior fixation and augmentation of pedicle screw-rod system for different pattern and severity of type A thoracolumbar fractures. Our results suggested that severe fractures might benefit more from rigid fixation with six-screw constructs. We believe that intermediate screw insertion should be added to the treatment of thoracolumbar fractures with higher wedge-shaped or burst fractures (AO Spine A3 and A4) to maintain stable reduction except in cases with extreme destruction of the pedicle in which screw insertion may be risky. Yet, in terms of quality assessment of the studies, FE studies are not usually categorized as having a high level of evidence in rating systems, which might reduce the strength of a recommendation (Guyatt et al. 2008; Harris et al. 2001). Thus, more well-designed clinical trials are needed to clarify the proper posterior fixation strategies where the evidence is favorable.

No conflicts to declare in any way.

Author contributions

All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Cheng Xu, Xuedong Bai, Chao Zhang. The first draft of the manuscript was written by Cheng Xu, Chao Zhang, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Alanay, A., Acaroglu, E., and Yazici, M., et al. (2001). Short-segment pedicle instrumentation of thoracolumbar burst fractures: Does transpedicular intracorporeal grafting prevent early failure? Spine (Phila Pa 1976) 26, 213-217.https://doi. 10.1097/00007632-200101150-00017
Alizadeh, M., Kadir, M.R., and Fadhli, M.M., et al. (2013). The use of X-shaped cross-link in posterior spinal constructs improves stability in thoracolumbar burst fracture: A finite element analysis. J Orthop Res 31, 1447-1454.https://doi. 10.1002/jor.22376
Aly, T.A. (2017). Short segment versus long segment pedicle screws fixation in management of thoracolumbar burst fractures: Meta-Analysis. Asian Spine J 11, 150-160.https://doi. 10.4184/asj.2017.11.1.150
Baaj, A.A., Reyes, P.M., and Yaqoobi, A.S., et al. (2011). Biomechanical advantage of the index-level pedicle screw in unstable thoracolumbar junction fractures. J Neurosurg Spine 14, 192-197.https://doi. 10.3171/2010.10.SPINE10222
Erbulut, D.U., Zafarparandeh, I., Lazoglu, I., and Ozer, A.F. (2014). Application of an asymmetric finite element model of the C2-T1 cervical spine for evaluating the role of soft tissues in stability. Med Eng Phys 36, 915-921.https://doi. 10.1016/j.medengphy.2014.02.020
Gunasekaran, K., Basaruddin, K.S., Muhayudin, N.A., and Sulaiman, A.R. (2022). Corrective mechanism aftermath surgical treatment of spine deformity due to scoliosis: A systematic review of finite element studies. Biomed Res Int 2022, 5147221.https://doi. 10.1155/2022/5147221
Guyatt, G.H., Oxman, A.D., and Vist, G.E., et al. (2008). GRADE: An emerging consensus on rating quality of evidence and strength of recommendations. Bmj 336, 924-926.https://doi. 10.1136/bmj.39489.470347.AD
Harris, R.P., Helfand, M., and Woolf, S.H., et al. (2001). Current methods of the US Preventive Services Task Force: A review of the process. Am J Prev Med 20, 21-35.https://doi. 10.1016/s0749-3797(01)00261-6
Hirota, R., Teramoto, A., and Irifune, H., et al. (2022). Risk factors for postoperative loss of correction in thoracolumbar injuries caused by High-Energy trauma treated via percutaneous posterior stabilization without bone fusion. Medicina (Kaunas) 58.https://doi. 10.3390/medicina58050583
Jain, P., Rana, M., Biswas, J.K., and Khan, M.R. (2020). Biomechanics of spinal implants-a review. Biomed Phys Eng Express 6, 42002.https://doi. 10.1088/2057-1976/ab9dd2
Jindal, N., Sankhala, S.S., and Bachhal, V. (2012). The role of fusion in the management of burst fractures of the thoracolumbar spine treated by short segment pedicle screw fixation: A prospective randomised trial. J Bone Joint Surg Br 94, 1101-1106.https://doi. 10.1302/0301-620X.94B8.28311
Jindal, R., Jasani, V., Sandal, D., and Garg, S.K. (2020). Current status of short segment fixation in thoracolumbar spine injuries. J Clin Orthop Trauma 11, 770-777.https://doi. 10.1016/j.jcot.2020.06.008
Kapoen, C., Liu, Y., Bloemers, F.W., and Deunk, J. (2020). Pedicle screw fixation of thoracolumbar fractures: Conventional short segment versus short segment with intermediate screws at the fracture level-a systematic review and meta-analysis. Eur Spine J 29, 2491-2504.https://doi. 10.1007/s00586-020-06479-4
Kifune, M., Panjabi, M.M., Arand, M., and Liu, W. (1995). Fracture pattern and instability of thoracolumbar injuries. Eur Spine J 4, 98-103.https://doi. 10.1007/BF00278920
Li, C., Zhou, Y., and Wang, H., et al. (2014). Treatment of unstable thoracolumbar fractures through short segment pedicle screw fixation techniques using pedicle fixation at the level of the fracture: A finite element analysis. PLoS One 9, e99156.https://doi. 10.1371/journal.pone.0099156
Li, J., Shang, J., and Zhou, Y., et al. (2015). Finite element analysis of a new pedicle Screw-Plate system for minimally invasive transforaminal lumbar interbody fusion. PLoS One 10, e144637.https://doi. 10.1371/journal.pone.0144637
Liu, J., Yang, S., and Lu, J., et al. (2018). Biomechanical effects of USS fixation with different screw insertion depths on the vertebrae stiffness and screw stress for the treatment of the L1 fracture. J Back Musculoskelet Rehabil 31, 285-297.https://doi. 10.3233/BMR-169692
Lorente, R., Lorente, A., and Palacios, P., et al. (2019). Radiological evaluation does not reflect the clinical outcome after surgery in unstable thoracolumbar and lumbar type a fractures without neurological symptoms: A comparative study of 2 cohorts treated by open or percutaneous surgery. Clin Spine Surg 32, E117-E125.https://doi. 10.1097/BSD.0000000000000737
Naserkhaki, S., Arjmand, N., and Shirazi-Adl, A., et al. (2018). Effects of eight different ligament property datasets on biomechanics of a lumbar L4-L5 finite element model. J Biomech 70, 33-42.https://doi. 10.1016/j.jbiomech.2017.05.003
Neeley, O.J., Kafka, B., and Tecle, N.E., et al. (2022). Percutaneous screw fixation versus open fusion for the treatment of traumatic thoracolumbar fractures: A retrospective case series of 185 Patients with a single-level spinal column injury. J Clin Neurosci 101, 47-51.https://doi. 10.1016/j.jocn.2022.04.045
Norton, R.P., Milne, E.L., and Kaimrajh, D.N., et al. (2014). Biomechanical analysis of four- versus six-screw constructs for short-segment pedicle screw and rod instrumentation of unstable thoracolumbar fractures. Spine J 14, 1734-1739.https://doi. 10.1016/j.spinee.2014.01.035
Ouyang, P., Lu, T., and He, X., et al. (2019). Biomechanical comparison of integrated fixation cage versus anterior cervical plate and cage in anterior cervical corpectomy and fusion (ACCF): A finite element analysis. Med Sci Monit 25, 1489-1498.https://doi. 10.12659/MSM.913630
Oxland, T.R., Lin, R.M., and Panjabi, M.M. (1992). Three-dimensional mechanical properties of the thoracolumbar junction. J Orthop Res 10, 573-580.https://doi. 10.1002/jor.1100100412
Pannu, C.D., Farooque, K., Sharma, V., and Singal, D. (2019). Minimally invasive spine surgeries for treatment of thoracolumbar fractures of spine: A systematic review. J Clin Orthop Trauma 10, S147-S155.https://doi. 10.1016/j.jcot.2019.04.012
Polikeit, A., Nolte, L.P., and Ferguson, S.J. (2003). The effect of cement augmentation on the load transfer in an osteoporotic functional spinal unit: Finite-element analysis. Spine (Phila Pa 1976) 28, 991-996.https://doi. 10.1097/01.BRS.0000061987.71624.17
Schmidt, H., Galbusera, F., and Rohlmann, A., et al. (2012). Effect of multilevel lumbar disc arthroplasty on spine kinematics and facet joint loads in flexion and extension: A finite element analysis. Eur Spine J 21 Suppl 5, S663-S674.https://doi. 10.1007/s00586-010-1382-1
Schmidt, H., Heuer, F., and Drumm, J., et al. (2007). Application of a calibration method provides more realistic results for a finite element model of a lumbar spinal segment. Clin Biomech (Bristol, Avon) 22, 377-384.https://doi. 10.1016/j.clinbiomech.2006.11.008
Shen, H., Fogel, G.R., and Zhu, J., et al. (2019). Biomechanical analysis of different lumbar interspinous process devices: A finite element study. World Neurosurg 127, e1112-e1119.https://doi. 10.1016/j.wneu.2019.04.051
Wang, X.Y., Dai, L.Y., Xu, H.Z., and Chi, Y.L. (2008). Biomechanical effect of the extent of vertebral body fracture on the thoracolumbar spine with pedicle screw fixation: An in vitro study. J Clin Neurosci 15, 286-290.https://doi. 10.1016/j.jocn.2006.12.007
Wu, Y., Chen, C.H., and Tsuang, F.Y., et al. (2019). The stability of long-segment and short-segment fixation for treating severe burst fractures at the thoracolumbar junction in osteoporotic bone: A finite element analysis. PLoS One 14, e211676.https://doi. 10.1371/journal.pone.0211676
Zhou, F., Yang, S., and Liu, J., et al. (2020). Finite element analysis comparing short-segment instrumentation with conventional pedicle screws and the Schanz pedicle screw in lumbar 1 fractures. Neurosurg Rev 43, 301-312.https://doi. 10.1007/s10143-019-01146-9

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Comparative Finite Element Analysis of Posterior Short Segment Fixation Constructs with or without Intermediate Screws in the Fractured Vertebrae for the Treatment of Type A Thoracolumbar Fracture

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Abstract

Figures

1. Introduction

2 Materials And Methods

2.1 Subject for biomechanics simulation

2.2 Establishment of FE model of an intact normal thoracolumbar spine

2.3 Establishment of FE models of T12 fracture

2.4 Implants and fixation models

2.5 Finite element analysis

3 Results

3.1 Validation of the intact and the fracture thoracolumbar spine model

3.2 ROM of the internal fixation models

3.3 Von Mises stress on the screw and rod construct.

3.4 Postoperative axial displacement/micro-motion of the bony defect in T12

4 Discussion

5 Study Limitations

6 Conclusion

Declarations

Author contributions

References

Additional Declarations

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