Treatment of thoracolumbar fracture with pedicle screws at injury level: a biomechanical study based on three-dimensional finite element analysis

Biomechanical study of different bone cement distribution on osteoporotic vertebral compression Fracture-A finite element analysis

Purpose

This study aimed to compare the biomechanical effects of different bone cement distribution methods on osteoporotic vertebral compression fractures (OVCF).

Patients and methods

Raw CT data from a healthy male volunteer was used to create a finite element model of the T12-L2 vertebra using finite element software. A compression fracture was simulated in the L1 vertebra, and two forms of bone cement dispersion (integration group, IG, and separation group, SG) were also simulated. Six types of loading (flexion, extension, left/right bending, and left/right rotation) were applied to the models, and the stress distribution in the vertebra and intervertebral discs was observed. Additionally, the maximum displacement of the L1 vertebra was evaluated.

Results

Bone cement injection significantly reduced stress following L1 vertebral fractures. In the L1 vertebral body, the maximum stress of SG was lower than that of IG during flexion, left/right bending, and left/right rotation. In the T12 vertebral body, compared with IG, the maximum stress of SG decreased during flexion and right rotation. In the L2 vertebral body, the maximum stress of SG was the lowest under all loading conditions. In the T12-L1 intervertebral disc, compared with IG, the maximum stress of SG decreased during flexion, extension, and left/right bending and was basically the same during left/right rotation. However, in the L1-L2 intervertebral discs, the maximum stress of SG increased during left/right rotation compared with that of IG. Furthermore, the maximum displacement of SG was smaller than that of IG in the L1 vertebral bodies under all loading conditions.

Conclusions

SG can reduce the maximum stress in the vertebra and intervertebral discs, offering better biomechanical performance and improved stability than IG.

Biomechanical Comparison of Different Treatment Strategies for Thoracolumbar Burst Fracture: A Finite Element Study

OBJECTIVE

The aim of this study was to compare the biomechanical performance of 6 pedicle screw internal fixation strategies for the treatment of burst fractures of the thoracolumbar spine using finite element (FE) analysis.

METHODS

A finite element model of the T11-L3 thoracolumbar segment was established to simulate L1 vertebral burst fractures, and 6 models were conducted under multidirectional loading conditions: P2-D2, P1-D1, P2-D1,P1-D, P1-BF-D1, and P1-UF-D1. The range of motion (ROM) in the T12-L2 region and the von Mises stresses of pedicle screws and rods under the 6 internal fixation models were mainly analyzed.

RESULTS

The maximum ROM and von Mises stress were obtained under flexion motion in all models. The P1-BF-D1 model had the least ROM and screw stress. However, when the injured vertebra was not nailed bilaterally, the P1-UF-D1 model had the smallest ROM; the maximum von Mises stress on the screw and rod was remarkably higher than that recorded in the other models. Moreover, the P2-D1 model had a ROM similar to that of the P1-D2 model, but with lower screw stress. The 2 models outperformed the P1-D1 model in all 6 conditions. The P2-D2 model had a similar ROM with the P2-D1 model; nevertheless, the maximum von Mises stress was not substantially reduced.

CONCLUSIONS

The P1-BF-D1 model exhibited better stability and less von Mises stress on the pedicle screws and rods, thereby reducing the risk of screw loosening and fracture. The P2-D1 internal fixation approach is recommended when the fractured vertebrae are not nailed bilaterally.

Biomechanical evaluation of a novel anterior transpedicular screw-plate system for anterior cervical corpectomy and fusion (ACCF): a finite element analysis

Background and objective: Cervical fusion with vertebral body screw (VBS)-plate systems frequently results in limited biomechanical stability. To address this issue, anterior transpedicular screw (ATPS) fixation has been developed and applied preliminarily to multilevel spinal fusion, osteoporosis, and three-column injury of the cervical spine. This study aimed to compare the biomechanical differences between unilateral ATPS (UATPS), bilateral ATPS (BATPS), and VBS fixation using finite element analysis. Materials and methods: A C6 corpectomy model was performed and a titanium mesh cage (TMC) and bone were implanted, followed by implantation of a novel ATPS-plate system into C5 and C7 to simulate internal fixation with UATPS, BATPS, and VBS. Internal fixation with UATPS comprises ipsilateral transpedicular screw-contralateral vertebral body screw (ITPS-CVBS) and cross transpedicular screw-vertebral body screw (CTPS-VBS) fixations. Mobility, the maximal von Mises stress on TMC, the stress distribution and maximal von Mises stress on the screws, and the maximum displacement of the screw were compared between the four groups. Results: Compared with the original model, each group had a reduced range of motion (ROM) under six loads. After ACCF, the stress was predominantly concentrated at two-thirds of the length from the tail of the screw, and it was higher on ATPS than on VBS. The stress of the ATPS from the cranial part was higher than that of the caudal part. The similar effect happened on VBS. The screw stress cloud maps did not show any red areas reflective of a concentration of the stress on VBS. Compared with VBS, ATPS can bear a greater stress from cervical spine movements, thus reducing the stress on TMC. The maximal von Mises stress was the lowest with bilateral transpedicular TMC and increased with cross ATPS and with ipsilateral ATPS. ITPS-CVBS, CTPS-VBS, and BATPS exhibited a reduction of 2.3%-22.1%, 11.9%-2.7%, and 37.9%-64.1% in the maximum displacement of screws, respectively, compared with that of VBS. Conclusion: In FEA, the comprehensive stability ranked highest for BATPS, followed by CTPS-VBS and ITPS-CVBS, with VBS demonstrating the lowest stability. Notably, utilizing ATPS for fixation has the potential to reduce the occurrence of internal fixation device loosening after ACCF when compared to VBS.

Unilateral biportal endoscopic technique combined with percutaneous transpedicular screw fixation for thoracolumbar burst fractures with neurological symptoms: technical note and preliminary report

BACKGROUND

Previous studies on thoracolumbar fractures with neurological symptoms have focused on how to achieve satisfactory fracture reduction, adequate nerve decompression, and stable spinal alignment. With the development of the minimally invasive spine surgery technique, achieving satisfactory treatment results and reducing iatrogenic trauma at the same time has become a new goal of spinal surgery. This research used percutaneous transpedicular screw distraction to partially reduce the fractured vertebrae, followed by completing nerve decompression and reducing residual displacement bone fragments with the assistance of the unilateral biportal endoscopic (UBE) technique to achieve full protection of bone-ligament tissue and obtain good clinical efficacy.

METHODS

Guide wires were safely inserted into the fractured vertebra and adjacent upper and lower vertebra under the surveillance of anteroposterior and lateral X-ray fluoroscopy. Transpedicular screws were implanted via guide wires on the side with mild neurological deficits or bone fragment compression (the opposite side of the endoscopic operation). A titanium rod was installed and moderately distracted to reduce the fractured vertebra. Then, under the guidance of the endoscopic view, the laminectomy and ligamentum flavum resection were completed according to the position of the protruding bone fragment into the spinal canal, and the compressed dural sac or nerve root was fully exposed and decompressed. An L-shaped replacer was used to reduce residual bone fragments. The ipsilateral transpedicular screws and rod were installed and adjusted to match the contralateral side. The drainage tube was indwelled, and the incision was closed. The preoperative and postoperative images of the patients were evaluated, and the recovery of neurological symptoms was observed.

RESULTS

Surgery was successfully completed on all six patients, and no intraoperative conversion to open surgery was performed. Postoperative images showed good reduction of the protruding bone fragment and good placement of all screws. At the last follow-up, the neurological symptoms of all patients returned to normal.

CONCLUSION

The UBE technique combined with percutaneous transpedicular screw fixation in the treatment of thoracolumbar fractures with neurological symptoms can effectively achieve the reduction of displaced bone fragments, improve damaged nerve function, stabilize spinal alignment, and protect the integrity of bone-ligament tissue.

Biomechanical evaluation of two-level oblique lumbar interbody fusion combined with posterior four-screw fixation：A finite element analysis

OBJECTIVE

By constructing the three-dimensional finite element model of two-level OLIF lumbar spine, the aim of this study was to demonstrate the feasibility and effectiveness of posterior four-screw fixation for treatment of two-level lumbar degenerative diseases from the perspective of biomechanics.

METHODS

An intact L3-S1 segment nonlinear lumbar finite element model (M0) was constructed from the CT scanning data of a healthy adult. After verification, two-level OLIF procedure were simulated, and three patterns of finite element analysis models were constructed: two-level stand-alone OLIF group (M1), two-level OLIF + four-screw fixation group (M2) and two-level OLIF + six-screw fixation group (M3). Range of motion, stress of the cage, and stress of fixation were evaluated in the different models.

RESULTS

Under various motion modes，the ROM of M2 and M3 were significantly lower than those of M1. The ROM reduction of M2 relative to M1 was much greater than that of M3 relative to M2. Moreover, the peak von Mises stresses of endplates in M2 were almost the same as those in M3. In terms of the maximum stresses of cages, M2 and M3 were essentially identical. Besides, the maximum stresses of posterior instrumentation in M2 and M3 were similar, which were mainly concentrated at the root of pedicle screws.

CONCLUSION

There were no significant differences between M2 and M3 from the biomechanical analysis. In two-level OLIF, posterior four-screw fixation can replace six-screw fixation, which reduces surgical trauma and decreases economic burden of patients, and will be a cost-effective alternative.

Biomechanical comparison between unilateral and bilateral percutaneous vertebroplasty for osteoporotic vertebral compression fractures: A finite element analysis

Background and objective: The osteoporotic vertebral compression fracture (OVCF) has an incidence of 7.8/1000 person-years at 55–65 years. At 75 years or older, the incidence increases to 19.6/1000 person-years in females and 5.2–9.3/1000 person-years in males. To solve this problem, percutaneous vertebroplasty (PVP) was developed in recent years and has been widely used in clinical practice to treat OVCF. Are the clinical effects of unilateral percutaneous vertebroplasty (UPVP) and bilateral percutaneous vertebroplasty (BPVP) the same? The purpose of this study was to compare biomechanical differences between UPVP and BPVP using finite element analysis.

Materials and methods: The heterogeneous assignment finite element (FE) model of T11-L1 was constructed and validated. A compression fracture of the vertebral body was performed at T12. UPVP and BPVP were simulated by the difference in the distribution of bone cement in T12. Stress distributions and maximum von Mises stresses of vertebrae and intervertebral discs were compared. The rate of change of maximum displacement between UPVP and BPVP was evaluated.

Results: There were no obvious high-stress concentration regions on the anterior and middle columns of the T12 vertebral body in BPVP. Compared with UPVP, the maximum stress on T11 in BPVP was lower under left/right lateral bending, and the maximum stress on L1 was lower under all loading conditions. For the T12-L1 intervertebral disc, the maximum stress of BPVP was less than that of UPVP. The maximum displacement of T12 after BPVP was less than that after UPVP under the six loading conditions.

Conclusion: BPVP could balance the stress of the vertebral body, reduce the maximum stress of the intervertebral disc, and offer advantages in terms of stability compared with UPVP. In summary, BPVP could reduce the incidence of postoperative complications and provide promising clinical effects for patients.

Mechanical Analysis of Posterior Pedicle Screw System Placement and Internal Fixation in the Treatment of Lumbar Fractures

Objective

Image segmentation technology is applied to separate a single vertebra from the three-dimensional model of the spine, so as to separate a single vertebra image with smaller error, higher degree of automation, and better results. The objectives are to study the biomechanical characteristics of posterior short-segment pedicle screw fixation by three-dimensional finite element method, analyze the mechanical characteristics of posterior pedicle screw rod fixation system under different factors, and demonstrate the feasibility of its application in the treatment of lumbar fracture.

Methods

The authors searched the database for articles about the treatment of lumbar spine fracture, screw rod internal fixation system, and its mechanical parameters. The threshold segmentation method based on region segmentation method was used to segment the image, and the three-dimensional finite element model was used to analyze the biomechanical characteristics of different posterior internal fixation for lumbar spine fracture.

Results

The posterior pedicle internal fixation system for the treatment of multilevel spinal fractures is a mature surgical technique and has fewer postoperative complications. Transpedicle fixation is effective and reliable. It can effectively restore the coronal and sagittal curvature of the vertebral body and restore the stability of the spine better. But the choice of internal fixation method should be individualized based on fracture type, identification of critical and secondary injury sites, and stability assessment. Only after mastering the biomechanical characteristics of the posterior screw rod system for the treatment of lumbar fracture, selecting the appropriate method, and fixing the appropriate movement unit can the best fixation be achieved.

Conclusion

Threshold method is the most direct and simple image segmentation method. The core technology of thresholding is the selection of threshold, which will affect the final segmentation effect. The most common segmentation method is to calculate the segmentation threshold by histogram. The threshold method has less computation and good segmentation effect for the image with large contrast between background and target. Posterior pedicle screw rod system internal fixation has the advantages of less trauma, good reduction, reliable fixation, and less complications. The design, placement angle and depth of various internal fixation systems, and the number of fixed segments all show different mechanical characteristics. As long as we master the above characteristics, choose the appropriate method and fix the appropriate motor unit, and we can get the best fixation; it can be used as an effective treatment for lumbar fracture.

A Hybrid Uniplanar Pedicle Screw System with a New Intermediate Screw for Minimally Invasive Spinal Fixation: A Finite Element Analysis

Purpose

A hybrid pedicle screw system for minimally invasive spinal fixation was developed based on the uniplanar pedicle screw construct and a new intermediate screw. Its biomechanical performance was evaluated using finite element (FE) analysis.

Methods

A T12-L2 FE model was established to simulate the L1 vertebral compression fracture with Magerl classification A1.2. Six fixation models were developed to simulate the posterior pedicle screw fracture fixation, which were divided into two subgroups with different construct configurations: (1) six-monoaxial/uniplanar/polyaxial pedicle screw constructs and (2) four-monoaxial/uniplanar/polyaxial pedicle screw constructs with the new intermediate screw. After model validation, flexion, extension, lateral bending, and axial rotation with 7.5 Nm moments and preloading of 500 N vertical compression were applied to the FE models to compare the biomechanical performances of the six fixation models with maximum von Mises stress, range of motion, and maximum displacement of the vertebra.

Results

Under four loading scenarios, the maximum von Mises stresses were found to be at the roots of the upper or lower pedicle screws. In the cases of flexion, lateral bending, and axial rotation, the maximum von Mises stress of the uniplanar screw construct lay in between the monoaxial and polyaxial screw constructs in each subgroup. Considering lateral bending, the uniplanar screw construct enabled to lower the maximum von Mises stress than monoaxial and polyaxial pedicle screw constructs in each subgroup. Two subgroups showed comparable results of the maximum von Mises stress on the endplates, range of motion of T12-L1, and maximum displacement of T12 between the corresponding constructs with the new intermediate screw or not.

Conclusions

The observations shown in this study verified that the hybrid uniplanar pedicle screw system exhibited comparable biomechanical performance as compared with other posterior short-segment constructs. The potential advantage of this new fixation system may provide researchers and clinical practitioners an alternative for minimally invasive spinal fixation with vertebral augmentation.

Biomechanical effects of posterior pedicle fixation techniques on the adjacent segment for the treatment of thoracolumbar burst fractures: a biomechanical analysis

Posterior pedicle fixation technique is a common method for treating thoracolumbar burst fractures, but the effect of different fixation techniques on the postoperative spinal mechanical properties has not been clearly defined, especially on adjacent segments. A finite element model of T10-L2 with moderate T12 vertebra burst fracture was constructed to investigate biomechanical behavior of three posterior pedicle screw fixation techniques. Compared with traditional short-segment 4 pedicle screw fixation (TS-4) and intermediate long-segment 6 pedicle screw fixation (IL-6), mono-segment 4 pedicle screw fixation (MS-4) provides a safer surgical selection to prevent the secondary degeneration of adjacent segments in the long-term.

NUMERICAL ANALYSIS OF SHORT AND LONG INSTRUMENTATION IN THE TREATMENT OF THORACOLUMBAR FRACTURES CONSIDERING THE LIGAMENTOUS PORTION

ABSTRACT Objective: This study aims to numerically evaluate the surgical treatment of thoracolumbar fractures, comparing the strengths between the long and short fixations using the pedicle of the fractured vertebra, taking into account the supraspinous, intertransverse, and anterior longitudinal ligaments. Methods: A numerical analysis of the techniques of long and short fixation of a thoracolumbar spine fracture was performed using computed tomography images that were converted into three-dimensional models and analyzed through the ANSYS program. The two types of treatments were analyzed considering the tensions generated in the immediate postoperative period, when the fracture has not yet been consolidated. The anterior, posterior, supraspinal and intertransverse longitudinal ligaments were added, in addition to considering different vertebral geometries. Results: Taking into account that the maximum tensile stress of the material used in the metal implant, in the case of titanium, was 960 MPa, the highest tension found in the analysis of the short instrumentation was 346.83 MPa, reaching only 36.13% of the load the material supports, being, therefore, within a safety limit. The analysis performed in the spine with long instrumentation showed the highest tension value of 229.22 MPa. Conclusions: Considering the values found and the resistance of the synthesis material used, the short and long fixation can be considered in the treatment of thoracolumbar fractures with similarity and a good safety coefficient. Level of Evidence III; Case-Control.

Is Short Same-Segment Fixation Really Better than Short-Segment Posterior Fixation in the Treatment of Thoracolumbar Fractures?

STUDY DESIGN

A retrospective study.

OBJECTIVE

This retrospective study assessed whether short same-segment fixation (SSSF) is better than short-segment posterior fixation (SSPF) for reducing thoracolumbar fractures, improving the kyphosis angle, maintaining vertebral height, or reducing the incidence of broken screws.

SUMMARY OF BACKGROUND DATA

In clinical practice, single-segment thoracolumbar fractures were then more likely to be treated with SSPF that included pedicle fixation at the level of the fracture (short same-segment fixation, or SSSF). Whether SSSF could really achieve vertebral height recovery, improve the kyphosis, reduce postoperative kyphosis loss, and reduce the incidence of internal fixation failure better than SSPF.

METHODS

Patients treated with SSPF or SSSF at our institution during 2006 to 2014 were reviewed. Effects of thoracolumbar fracture reduction, improved kyphosis angle, and maintaining vertebral height were compared between groups. Logistic regression analysis was used to identify factors related to instrumentation breakage and correlation analysis to assess possible relations between loss of correction of the kyphosis angle (LAWAC) and other factors.

RESULTS

Altogether, 130 patients were enrolled (53 SSPF, 77 SSSF). SSPF (22F, 31M) group's mean (range) age was 37.7 (16-60) years, and the follow-up was 26.2 (9-120) months. SSSF (27F, 50M) group's mean (range) age was 39.3 (17-61) years, and the follow-up was 23.2 (9-60) months. All patients underwent either internal fixation or screw repair. Immediately postoperatively, restoration after middle vertebral fractures was better in SSSF patients than in SSPF patients (P = 0.003), with no differences in other fracture-related factors (P > 0.05). Only LAWAC was significantly associated with instrumentation breakage (P < 0.05). Also, immediately postoperatively, the anterior/posterior vertebral heights ratio was negatively related to LAWAC.

CONCLUSION

Pedicle fixation of the fracture did not obtain better recovery of anterior or posterior vertebral heights nor did it improve AWA restoration. There was no significant difference in LAWAC between groups or in the incidence of broken screws. LAWAC may increase the incidence of broken screws.

LEVEL OF EVIDENCE

4.

Transvertebral Bone Graft and Augmentation Versus Posterior Spinal Instrumentation in the Treatment of Simple Thoracolumbar Compression Fractures

OBJECTIVE

This retrospective cohort study was performed to investigate clinical efficacy of TBGA compared with pedicle screw fixation (PSF).

METHODS

A total of 86 eligible patients with single-level simple thoracolumbar compression fracture (TLCF) received TBGA (n = 41) or PSF (n = 45) from January 2013 to July 2015. The patients were evaluated using plain radiography, computed tomography, and magnetic resonance imaging preoperatively. The radiologic examinations were performed at each time point postoperatively. Clinical status was assessed using the Oswestry Disability Index (ODI) and visual analog scale (VAS) scores. In addition, anterior vertebral body height (AVBH), kyphosis angle (KA), radiologic adjacent segment pathology (RASP), and complication rates were also compared between the 2 groups. The average follow-up period of patients was 26.1 months.

RESULTS

Significant clinical improvements in ODI, VAS, AVBH, and KA were achieved in both TBGA and PSF groups after surgery, respectively (P < 0.05). There was no statistical difference in improvements of ODI and VAS between the TBGA and PSF groups (P > 0.05). Similarly, improvements of AVBH and KA showed no statistical difference between the 2 groups (P > 0.05). In addition, the rates of RASP and complications in PSF group were significantly higher than the TBGA group during the follow-up period (P < 0.05).

CONCLUSIONS

TBGA can achieve satisfactory clinical effects in treatment of simple TLCF. TBGA involves shorter operative time, less blood loss, lower RASP, and lower complication rates and could be more suitable for the surgical treatment of simple TLCF.

Transpedicular bone grafting and pedicle screw fixation in injured vertebrae using a paraspinal approach for thoracolumbar fractures: a retrospective study

Background

Complications in posterior pedicle screw fixation using a conventional posterior approach for thoracolumbar fractures include vertebral height loss, kyphosis relapse and breakage, or loosening of instrumentation. The purpose of this study was to evaluate the clinical effects of transpedicular bone grafting and pedicle screw fixation in injured vertebrae using a paraspinal approach for thoracolumbar fractures.

Methods

We retrospectively analyzed 50 patients with thoracolumbar fractures treated with transpedicular bone grafting and pedicle screw fixation in injured vertebrae using a paraspinal approach. Operative time, blood loss, visual analog scale (VAS) scores for back pain, and the relative height and Cobb angle of the fractured vertebrae were measured.

Results

The average operative time was 71.8 min, and the blood loss was 155 ml. Postoperative VAS scores were significantly lower than preoperative scores (P = 0.08), but there was no difference between 1 week and 1 year postoperatively (P = 0.18). The postoperative relative heights of the fractured vertebrae were higher than the preoperative heights (P = 0.001, 0.005, 0.001), but there were no differences between 1 week and 1 or 2 years postoperatively (P = 0.24/0.16). The postoperative Cobb angles were larger than the preoperative angles (P = 0.002, 0.007, 0.001), but there were no differences between 1 week and 1 or 2 years postoperatively (P = 0.19/0.23).

Conclusions

Transpedicular bone grafting and pedicle screw fixation in injured vertebrae using a paraspinal approach for thoracolumbar fractures achieved satisfactory results and can restore vertebral height, increase the stability of the anterior and middle columns of injured vertebrae, and decrease the risk of back pain.

Management of burst fractures in the thoracolumbar spine

The most common fractures in the spine take place in the thoracolumbar region. Currently there is no consensus regarding optimum treatment.

OBJECTIVE

Analyze the current medical literature available regarding treatment of compression fractures of the thoracolumbar spine.

METHODS

Research of current literature in medical databases.

RESULTS

Regarding current available literature, we found no consensus in the treatment of compression fractures in the thoracolumbar spine.

CONCLUSIONS

Burst fractures of the thoracolumbar junction is a very common condition, treatment of each patient must be individualized. Conservative treatment is recommended for stable fractures without neurological compromise and less than 35° of kyphosis.

Numerical analysis of multi-level versus short instrumentation for the treatment of thoracolumbar fractures

PURPOSE

The research analyses the strength of metallic implants in posterior spinal instrumentation for the treatment of thoracolumbar fractures, considering extended and short fixation techniques on the immediate post-surgical load. Considering that short fixation may bring the advantage of a less invasive surgical procedure to the patient and may also result in lower costs, this evaluation becomes necessary.

METHODS

Three-dimensional modelling of the thoracolumbar spine was initially performed. CT images were captured and converted for analysis with the ANSYS program. Both treatment techniques were analysed for stresses, and strains generated in the immediate postoperative period, when the fracture is still not healed.

RESULTS

The maximum stress obtained for long fixation by the theory of Von Mises was 230 MPa, and it was located in the rod area next to the L2 vertebra. The maximum stress obtained for short fixation was 274.24 MPa, and it was located in the pedicle screw on the T12 vertebra.

CONCLUSIONS

There were no significant differences between the two techniques, since the observed stresses are well below the flow stress of the material, ensuring good safety factor (ranging from 3.5 to 4.1).

Biomechanical effects of cement distribution in the fractured area on osteoporotic vertebral compression fractures: a three-dimensional finite element analysis

BACKGROUND

According to some clinical studies, insufficient cement distribution (ID) in the fractured area and asymmetrical cement distribution around the fractured area were thought to be the reasons for unrelieved pain and recollapse after percutaneous vertebral augmentation (PVA) in the treatment of symptomatic osteoporotic vertebral compression fractures.

METHODS

Finite element methods were used to investigate the biomechanical variance among three patterns of cement distribution (ID and sufficient cement distribution in the fractured area and asymmetrical cement distribution around the fractured area including upward [BU] and downward [BD] cement distribution).

RESULTS

Compared with fractured vertebra before PVA, distribution of von Mises stress in the cancellous bone was transferred to be concentrated at the cancellous bone surrounding cement after PVA, whereas it was not changed in the cortical bone. Compared with sufficient cement distribution group, maximum von Mises stress in the cancellous bone and cortical bone and maximum displacement of augmented vertebra increased significantly in the ID group, whereas asymmetrical cement distribution around the fractured area in BU and BD groups mainly increased maximum von Mises stress in the cancellous bone significantly. Similar results could be seen in all loading conditions.

CONCLUSIONS

ID in the fractured area may lead to unrelieved pain after PVA in the treatment of symptomatic osteoporotic vertebral compression fractures as maximum displacement of augmented vertebral body increased significantly. Both ID in the fractured area and asymmetrical cement distribution around the fractured area are more likely to induce recollapse of augmented vertebra because they increased maximum von Mises stress in the cancellous bone and cortical bone of augmented vertebra significantly.

Application of real-time B-mode ultrasound in posterior decompression and reduction for thoracolumbar burst fracture

This study aimed to investigate the role of real-time B-mode ultrasound in posterior decompression and reduction and to observe the signal changes in spinal cord blood flow in a thoracolumbar burst fracture (TBF). Between February 2004 and December 2008, 138 patients with TBF were divided into group A (108 cases) and group B (30 cases). In group A, under the assistance of real-time B-mode ultrasound, posterior decompression and fracture piece reduction were performed, and we observed the signal changes in spinal cord blood flow. In group B, posterior fenestration was combined with pushing the fracture piece into the fractured vertebral body using an L-shaped operative tool. Presurgical and postsurgical recovery of neurological function was evaluated according to American Spinal Injury Association (ASIA) standards, and the range of spinal decompression was determined by measuring the proportion of encroached fracture piece in the spinal canal (spinal stenosis rate) on the computed tomography (CT) image. In group A, 12 patients had a grade A spinal injury according to the Frankel grading system, and there were six cases without neurological recovery. In the other patients, neurological function increased by 1–3 grades. There were no aggravated spinal cord injuries or other serious complications. In group B, three patients were categorized as grade A and there were two cases without neurological recovery. In the other patients, neurological function increased by 1–3 grades. In groups A and B, the postsurgical spinal stenosis rate was significantly lower than the presurgical stenosis rate (P<0.05). The postsurgical spinal stenosis rate in group B was significantly higher compared with group A (P<0.05). There was no significant difference in neurological function recovery between the groups (P>0.05). Real-time B-mode ultrasound is an effective method for posterior decompression and reduction and to observe signal changes in spinal cord blood flow in TBF.