Evaluation of biomechanical properties of anterior atlantoaxial transarticular locking plate system using three-dimensional finite element analysis.

PURPOSE: To evaluate a new anterior atlantoaxial transarticular locking plate system using finite element analysis. METHODS: Thin-section spiral computed tomography was performed from occiput to C2 region. A finite element model of an unstable atlantoaxial joint, treated with an anterior atlantoaxial transarticular locking plate system, was compared with the simple anterior atlantoaxial transarticular screw system. Flexion, extension, lateral bending, and axial rotation were imposed on the model. Displacement of the atlantoaxial transarticular screw and stress at the screw-bone interface were observed for the two internal fixation systems. RESULTS: Screw displacement was less using the anterior atlantoaxial transarticular locking plate system compared to simple anterior atlantoaxial transarticular screw fixation under various conditions, and stability increased especially during flexion and extension. CONCLUSIONS: The anterior atlantoaxial transarticular locking plate system not only provided stronger fixation, but also decreased screw-bearing stress and screw-bone interface stress compared to simple anterior atlantoaxial transarticular screw fixation.

Treatment planning of implants when 3 mandibular posterior teeth are missing: a 3-dimensional finite element analysis.

PURPOSE: To analyze the biomechanics of 3 designs of implant treatment for 3 teeth missing in posterior low arch quadrants. MATERIAL AND METHODS: A posterior portion of the human mandible missing 44, 45, 46 and three 4.1 × 10 mm threaded ITI implants with crowns were used to construct the finite element model. According to 3 implants being single, splinted or 2 implants support fixed partial denture (FPD) fixed in bone segments. Three implant support conditions were prepared with ANSYS 10.0. A load of 100 N was applied at the central fossa of the occlusal surfaces of the crowns at 45 degrees buccolingually along the triangular ridge of the buccal cusp. The von Mises stress and strain distributions in periimplant bone were observed. RESULTS: The results demonstrated that the von Mises stress in the supporting bone of the 2-implant supported FPD significantly increased compared with that in the 3-implant replacement. Meanwhile, when 3 implants were splinted, only the median implant had a decreased and more homogenous stress distribution, and the other implants did not exhibit significant differences when splinted. CONCLUSION: This study suggests that when space and cost permit, a 2-implant supported FPD should not be used, and 1 implant for each missing tooth being single is recommended.

[A finite element investigation of bilateral atlantoaxial trans-articular screws and atlas laminar hooks instrumentation].

OBJECTIVES: To investigate the mechanical properties of bilateral atlantoaxial trans-articular screws and atlas laminar hooks instrumentation with finite element method. METHODS: There was a volunteer with age of 28 years old, body height 172 cm, body weight of 60 kg and without cervical deformity by X rays. The ligamentous, nonlinear, three-dimensional finite element models of normal upper cervical spine (C0-3) was developed and validated. The destabilized model with bilateral atlantoaxial trans-articular screws and atlas laminar hooks was evaluated for quasistatic loading. RESULTS: The finite element model of upper cervical spine consists of 229,047 nodes and 152,475 elements, and correlated well with experimental data for all load cases and could be used for experiment. The finite model with bilateral atlantoaxial trans-articular screws and atlas-laminar hooks predicted that the maximum Von Mises Stress was in the region in which screws penetrated the atlantoaxial articular facet. The novel instrumentation resulted in sufficient stability. CONCLUSION: The bilateral atlantoaxial trans-articular screws and atlas laminar hooks instrumentation is useful and effective for atlantoaxial arthrodesis.

Biomechanical effect of vertebroplasty on the adjacent intervertebral levels using a three-dimensional finite element analysis.

OBJECTIVE: To investigate the biomechanical effect of different volume, distribution and leakage to adjacent disc of bone cement on the adjacent vertebral body by three-dimensional osteoporosis finite element model of lumbar. METHODS: L(4)-L(5) motion segment data of the cadaver of an old man who had no abnormal findings on roentgenograms were obtained from computed tomography (CT) scans. Three-dimensional model of L(4)-L(5) was established with Mimics software, and finite element model of L(4)-L(5) functional spinal unit (FSU) was established by Ansys 7.0 software. The effect of different loading conditions and distribution of bone cement after vertebroplasty on the adjacent vertebral body was investigated. RESULTS: This study presented a validated finite element model of L(4)-L(5) FSU with a simulated vertebroplasty augmentation to predict stresses and strains of adjacent untreated vertebral bodies. The findings from this FSU study suggested the endplate and disc stress of the adjacent vertebral body was not influenced by filling volume of bone cement but unipedicle injection and leakage to the disc of bone cement could concentrate the stress of adjacent endplate. CONCLUSIONS: Asymmetric distributions and leakage of cement into intervertebral disc can improve the stress of endplate in adjacent vertebral body. These results suggest that optimal biomechanical configuration should have symmetric placement and avoid leakage of cement in operation.

Metformin is associated with survival benefit in pancreatic cancer patients with diabetes: a systematic review and meta-analysis.

BACKGROUND: Pancreatic cancer is a highly lethal disease with a poor prognosis while metformin has been associated with a decreased risk of pancreatic cancer. Although the benefit of metformin was observed for pancreatic cancer prevention, it is not clear whether it can also affect the survival of pancreatic cancer patients with type 2 diabetes mellitus. A systematic review and meta-analysis was conducted to assess the effect of metformin on the survival of pancreatic cancer patients with type 2 diabetes mellitus. METHODS: Two independent authors searched PubMed and Web of science up to 08/07/2016. We assessed studies for eligibility, extracted data, and examined their quality, with the primary outcome as overall survival. We used published hazard ratio (HR) available or estimated based on other survival data. We pooled the data and used a random-effect model to combine direct comparisons from included articles. We also investigated treatment effects by different countries, quality and the time of metformin initiation. RESULTS: We found that there was a relative survival benefit associated with metformin treatment compared with non-metformin treatment in both overall survival (OS) ([HR] 0.84; 95% confidence interval [CI]: 0.73 - 0.96). These associations were also observed in subgroups of Asian countries and high quality articles. CONCLUSIONS: Our results support the notion that metformin maybe the best anti-diabetic medicine of choice in patients with pancreatic cancer and concurrent type 2 diabetes mellitus. The perspectives of enhancing survival of pancreatic cancer patients with diabetes mellitus by the use of metformin deserve more attention in future research and clinical practice.

[Stress distribution on the femoral neck at different abduction angles of the hip joint: a finite element analysis].

OBJECTIVE: To analyze the stress distribution and its changes of the femoral neck at different abduction angles of the hip joint to provide biomechanical evidence for the treatment of hip joint disease. METHODS: A three-dimensional finite element model of the femoral head region was reconstructed on the basis of data available in the dataset of No.1 Virtual Male Chinese. Different abduction angles of the hip joint were simulated under the load of body weight, and the stress distribution on the femoral neck was calculated and compared. RESULTS: With different abduction angles of the hip joint, the stresses on the medial and lateral sides of the femoral neck were obviously greater than those on the anterior and posterior regions. As the abduction angle of the hip joint increased, the stress on the posterior aspect of the femoral neck decreased while that in other regions increased (except for the anterior aspect of the femoral neck which remained unchanged). CONCLUSION: The lateral aspect of the femoral neck withstands the most intense stress of the body weight, which increases with the abduction angle of the hip joint.

[Femoral tunnel positioning in posterior cruciate ligament double-bundle reconstruction by computer aided design].

OBJECTIVE: To study mechanical affect of knee joint of reasonable positioning of femoral tunnel during knee posterior cruciate ligament (PCL) double-bundle reconstruction and graft fixation after reconstruction by virtual reality interactive technology and evaluate the biomechanical response of knee after reconstruction by finite element analysis. METHODS: Knee specimens from five fresh frozen cadavers were used. Computer simulations and biomechanical experiments were used in this study. Experiments on flexion and extension movements of the knee joint were performed on specimens of fresh human knee joint. Laser three dimensional scanning was used to record and calculate the indexes of movements. Three-dimensional models of knee joint bone structure were then reconstructed on computer with the experimental data. Simulations of flexion and extension movements were carried out on the models to show the spatial positions of femur and tibia and label the attachment sites of PCL. Ten test points in the anterior,posterior, proximal, distal at the femoral attachment area of anterior and lateral bundle (ALB) and postoperior medial bundle (PMB) were selected and the central points of tibial en attachment areat anchored. The distance btween each two points of two article surface was calculated and contacted by software of Geomagic. Model was import software Ansys, adopting the tetrahedron unit a finite element model of complex tibial and femoral was set up to simulat human walking in one leg,on this condition the the joint surface force of model under weight impact load were analyzed. RESULTS: The three-dimensional models could demonstrate the spatial positions of the bone structure of the knee in different flexions and extensions. The models could be used to measure the spatial distance between 2 points on the femoral and tibial planes by software Geomagic. There was significantly difference among the length changes of anterolateral bundle and posteromedial bundle at every fixed point with different flexion angles (P<0.05), so the fixed angle with different points. The length changes of anterior lateral bundle's A2, A1 and posterior medial bundle's B3, B1 points were (1.35±0.19) mm, (5.41±1.22) mm, (1.95±0.04) mm and (5.23±2.21) mm, respectively. The A2 and B3 points' length changes were the less, and that of the Al and B1 points were the more. It had no significant difference between the length changes of anterior lanteral bundle's A2 and A3 point (P=0.913>0.05). All of the maximal length changes of anterior lateral bundle's A2, A3 and postterior medial bundle's B3 points were less than 2 mm. CONCLUSION: The models of knee joint were builded through computer technology and it can be measure the lenth of cruciate ligament with software Geomagic exactly. The femoral tunnel for the PCL double-bundle reconstruction should be located as follows: ALB at the middle point of upper edge of femoral attachment site (proximal point),while PMB at the middle point of femoral attachment site (proximal point). This model provides a satisfactory method for the evaluation of the biomechanical response of knee after cruciate ligament reconstruction.

[Finite element analysis of shape memory alloy intrasegmental fixator for lumbar spondylolysis].

OBJECTIVE: To study the tensile strength of shape memory alloy intrasegmental fixator and tensile stress distribution in the device during force loading with finite element method (FEM). METHODS: The designed parameters, scanning image, and mechanical properties of shape memory alloy intrasegmental fixator were input into computer for the construction of the FEM model of the device in inherent coordinate of ANSYS. The model was extended with restriction in different parts, and the tensile strength and the distribution of tensile stress in the model was calculated. RESULTS: When the device was loaded with pulling force to induce a relative displacement of 2 mm between the 2 hooks along the two midpoints, the pull was about 281 N, and the tensile stress concentrated more on the middle of device than on the two sides. CONCLUSION: The shape memory alloy intrasegmental fixator is strong enough against tensile stress, which concentrates in the middle portion of the device where fatigue breakage is liable to occur when excessive force is loaded.

[Finite element analysis of lumbar facet joint contact model].

OBJECTIVE: To establish a finite element model of the fourth and fifth lumber segments in order to analyze the biomechanical characteristics of facet joints under different pressure loads. METHODS: CT sectional images of L(4-5) segments were obtained to construct a finite element model, adopting contact model to simulate the condition the superior and inferior facets were in. RESULTS: The facet joint exhibited different performances under different conditions, and more loads was forced on it when the model was twirled. CONCLUSION: The facet joints should be simulated as in condition of contact to help correct understanding of the biomechanical characteristics of the spinal segment.

[Reconstruction of the mandibular model using a three-dimensional laser scanner].

OBJECTIVE: To construct a three-dimensional (3D) mandibular model using a 3D laser scanner, and explore a new method for reconstructing the finite element geometry model. METHODS: A mandible specimen was scanned with the 3D laser scanner to form the point clouds of the mandibular surface, which were subsequently aligned for reconstruction of the mandibular model. RESULT: A 3D model of the mandible surface was reconstructed, which could be used for finite element simulation. CONCLUSION: The 3D laser scanning system can be used to reconstruct the 3D model with irregular geometry for finite element simulation.

[Biomechanical response of the femur-tibia model under impact loading of the body weight].

OBJECTIVE: To study the biomechanical response and the role of articular surface on the femur-tibia model under impact loading of the body weight. METHODS: A three-dimensional finite element (FE) model of the femur-tibia composite was reconstructed using the image data of the knee joint of Virtual Chinese Human No.1 Male, and FE calculation was performed to simulate the impact of the body weight on the knee joint while walking. RESULTS: The femur-tibia composite was compressed during the impact with obvious protrusive movement. Diffusion and attenuation of the stress occurred during its conduction to the articular surface. CONCLUSION: The femur-tibia composite is unstable under the vertical impact loading of the body weight, with obvious protraction movement, and the articular surface may serve as the buffer of the impact.

[Three-dimensional reconstruction of the knee joint of digitized Virtual Chinese Male No.1 by finite element simulation].

To provide a three-dimensional (3D) model of the knee joint of digitized Virtual Chinese Male No.1 for finite element simulation, the digitized image data of the serial sections of the virtual human knee joint were imported to a computer for 3D reconstruction using Mimics software after image segmentation and registration. Surface smoothing of the reconstructed model was performed with FreeForm system and transformation to IGES format executed. Following these procedures, the 3D model of IGES format of knee point was reconstructed, which can be used for finite element simulation.

Role of the biomechanical property of the endplate in anterior cervical fusion.

OBJECTIVE: To study the distribution of the biomechanical properties in the cervical vertebrae with or without the endplate, so as to evaluate the importance of the endplate in cervical anterior fusion. METHODS: Indentation tests were performed at 20 standardized testing points chosen on each surface of the endplate with the impact adjusted perpendicular to the endplate surface using a hemispherical indenter 2 mm in diameter. The failure load and rigidity at each test site were determined from the load-displacement curves. Independent sample t test and factorial analyses were used to analyze the results. RESULTS: On either superior or inferior endplate surface, both the failure load and rigidity differed significantly between the endplate-intact and endplate-removed groups (P < 0.001). The posterior region of the superior endplate and the lateral regions of the inferior endplate were stronger and more rigid than any other region across the endplate surface in the endplate-intact group, while for enplate-removed group, the posterior region of the superior endplate and the posterolateral regions of the inferior endplate were the stronger and more rigid. CONCLUSION: The endplate plays an important role in deciding the success of anterior cervical fusion, and due attention should be paid to the endplate in the intervertebral implant device designing and the surgical approach modification.

A new internal fixation system using vertebral pedicle screw for unstable lumbar spine: an in vitro biomechanical stability evaluation.

OBJECTIVE: To evaluate the effect of a new internal fixation system utilizing vertebral pedicle screw in fixing unstable lumbar spine in vitro. METHODS: Twelve lumbar spine specimens (L(2 to 5)) obtained from fresh human cadavers were randomly divided into 2 equal groups, namely groups A and B. All intact specimens were subjected to nondestructive testing in 6 loading modalities on a universal testing machine, before complete L(2 to 5) instability was produced by means of a wedge fracture induced by resection of the posterior ligamentous structures. Specimens in group A were fixed with the new internal fixation system, and group B with SOCON pedicle screw. The same nondestructive testing was repeated to determine the structural stability of the spine after fixation in both groups. RESULTS: The injured spines fixed with implants in both groups were significantly more stable than the intact specimens in all modes of tests (P < 0.05), especially in flexion and extension tests, in which a stability increase by 62.8% for flexion and 63.9% for extension was recorded in group A, and 54.9% for flexion and 51.0% for extension in group B. The two fixation systems exhibited similar effect in stabilizing the injured lumbar in all the 6 loading modalities (P < 0.05). CONCLUSION: This internal fixation system with vertebral pedicle screw is capable of providing biomechanical stability for unstable lumbar spine.

Effects of prednisone on bone mineral density and biomechanical characteristics of the femora and lumbar vertebras in rats.

OBJECTIVE: To explore effects of prednisone on the bone mineral density (BMD) and biomechanics of the femora and lumbar vertebras in rats. METHODS: Twenty one 3-month-old male Sprague-Dawley rats weighing 226+/-12 g were randomly divided into basal control, age-matched and hormone groups. The rats in basal control group were killed at the beginning of the experiment without any treatment, and those in age-matched group were given oral normal saline (5 ml x kg(-1) x d(-1)) while the rats in hormone group received oral prednisone acetate (4.5 ml x kg(-1) x d(-1) twice a week) to establish osteoporotic models. The treatment for the latter 2 groups of rats lasted for 90 days, after which the BMD and mechanical measurements of the femurs and L5 vertebra were carried out by way of torsion, three-point bending and compression tests. The measurements were also conducted in the basal control group at the time indicated above. RESULTS: In hormone group, the total BMD of the femora and L5 vertebra was decreased by 14.64%(P<0.01), and the BMD in the right and left distal femoral segments and the vertebra decreased by 21.42% (P<0.01), 19.62% (P<0.05) and 23.48%(P<0.01), respectively, in comparison with the control group. In the meantime, the loads of three-point bending test in hormone group was decreased by 17.1%(P<0.05), whereas the rest parameters tended to decrease as compared with the control group. CONCLUSIONS: Chronic use of corticosteroid is more liable to cause bone mass loss in rat cancellous bone than in the cortical bone, and mechanical properties of the cortical and cancellous bone, especially those of the latter, will also decline, to give rise to easy bone fracture at the trabecular bone in osteoporotic conditions.

[Establishment of Internet-based database of the Virtual Chinese Human dataset].

To establish an Internet-based database for the dataset of Virtual Chinese Human that is accessible to the interested researchers, modifications and compression of the original VCH-format dataset of Virtual Chinese Human were performed before it was uploaded to the server, and RAID0+1 storage technology was adopted with specific download accesses designed for different users. After dataset modification and compression, the data size was considerably reduced to allow convenient data storage and transfer. The RAID0+1 storage technology guarantees the security and high-speed download of data through different means established. Internet-based database provides important accesses for sharing the achievement in virtual human study between world-wide researchers, which has been imperative in the present situation of science development.

Construction of dataset for Virtual Chinese Male No.1.

OBJECTIVE: To establish digitized Virtual Chinese Human Male No.1 (VCH-M1) image dataset with a 0.2-mm equal interval. METHODS: The body of a 24-year-old male was used for this study. Perfusion with phenol and vermilion of the arteries was performed, followed by body shape adjustment by cold saline and pre-embedding with broken ices in an upside-down position, which was completed in a stepwise procedure to minimize body shape deformation. Section milling was conducted subsequently with the section thickness of 2 mm and the section images were captured by digital camera, which were immediately transferred to a computer for storage and processing. RESULTS: A total of 9 232 sections were obtained for the whole body, and the resolution of each of the image in TIF format was 3 024x2 016 pixels, resulting in the size of approximately 18 M for each image and about 161 G for the whole dataset. CONCLUSIONS: Compared with VCH-F1, the image quality in VCH-M1 dataset is significantly improved, demonstrated by much clearer tissue boundary in the images and minimized body shape deformation during the embedding process.

[Research report of experimental database establishment of digitized virtual Chinese No.1 female].

OBJECTIVE: To establish digitized virtual Chinese No.1 female (VCH-F1) image database. METHODS: A 19 years old female cadaver was scanned by CT, MRI, and perfused with red filling material through formal artery before freezing and em- bedding. The whole body was cut by JZ1500A vertical milling machine with a 0.2 mm inter-spacing. All the images was produced by Fuji FinePix S2 Pro camera. RESULTS: The body index of VCH-F1 was 94%. We cut 8 556 sections of the whole body, and each image was 17.5 MB in size and the whole database reached 149.7 GB. We have totally 6 versions of the database for different applications. CONCLUSIONS: Compared with other databases, VCH-F1 has good representation of the Chinese body shape, colorful filling material in blood vessels providing enough information for future registration and segmentation. Vertical embedding and cutting helped to retain normal human physiological posture, and the image quality and operation efficiency were improved by using various techniques such as one-time freezing and fixation, double-temperature icehouse, large-diameter milling disc and whole body cutting.

[Comparative study of vertebral body stress distribution following insertion of artificial lumbar intervertebral disc].

OBJECTIVE: To study vertebral body stress distribution of normal disc, post-Diskectomy and artificial disk respectively by 3-D finite element methods, and to explore artificial intervertebral disk insertion impact on stress distribution of vertebral body. METHODS: Models of normal disk, post-Diskectomy, artificial disk and L(4 - 5) motion segment were established by using finite element software MSC. MARK, then vertebral body stress was analyzed through model of L(4 - 5) motion segment respectively. RESULTS: The vertebral body's stress was the smallest after insertion of artificial intervertebral disk (AID), and its stress distributed equally. But the stress under post-discectomy was bigger than the normal disc's in all the motion state. On the other hand, the stress distribution state of the post-discectomy changed while the spine were in different motion state, during the spine flexion, the stress in the anterior of vertebral body was the biggest; While extension, in the posterior and in right flexion state, the biggest stress was in the right. While vertical compression and rotation, the stress distributed equally. CONCLUSION: The results illustrate that the vertebral body's stress is the smallest after insertion of AID in 3 groups of all motion state, and its stress distributes equally. But the level of vertebral body stress increases after discectomy comparing with the normal group. In generally, it is much more reasonable that the disc is reconstructed with AID because of the biomechanical effect on vertebral body made by AID insertion.

[The effect of disc degeneration on the structural property distributions in the cervical vertebral endplates].

OBJECTIVE: To study the effect of disc degeneration on the structural property distributions in the cervical vertebral endplates. METHODS: A 2 mm-diameter hemispherical indenter was used to perform indentation tests at 0.03 mm/s to the depth of 2 mm at 20 normalized locations in 50 bony endplates of intact human cervical vertebrae (C2 approximately C7). The resulting load-displacement curves were used to extract the failure load and stiffness of each test site. Grade of disc degeneration was determined using Nachemson's grading scale. One-way ANOVA, factorial analyses, SNK tests and correlate analyses were used to analyze the result data. RESULTS: Both the failure load and stiffness decreased with disc degeneration in the cervical endplates (P <0.001, both), and correlated significantly with the disc degeneration (rs=-0.429 and rs=-0.244, respectively). Only the distribution of superior cervical endplate changed with disc degeneration, but that of inferior cervical endplate changed little. CONCLUSIONS: The structural property distributions in the cervical vertebral endplates change significantly in the degenerated discs. It suggests that disc degeneration is an important factor to evaluate the intervertebral implant subsidence in anterior cervical fusion.