3D finite element analysis on pelvis under compressing manipulation by flexing hip and knee / 医用生物力学

Objective To investigate the influence from compressing manipulation by flexing hip and knee in supine position on stress distributions in the pelvis and strain distributions in the sacroiliac joints by 3D finite element method, and discuss the possibility of moving the whole sacroiliac joints under such manipulation. Methods A 3D finite element model of the normal pelvis was constructed based on CT images. According to the manipulation principle, the compressing force in flexing hip and knee was decomposed in two directions, and loaded on the 3D finite element model to calculate stress of the pelvis and strain of the sacroiliac joints. Results Under the loading of simulative manipulation, stress of the pelvis was mainly located at 1/3 part of the anterior inferior of the sacroiliac joints, the greater sciatic notch, and the middle 1/3 part of the inferior and anterior of gluteal lines. The maximum strain of the sacroiliac joints was mainly located in the posterior superior, posterior inferior and central 1/2 part of the sacroiliac joints. Conclusions The compressing manipulation by flexing hip and knee can only move 1/3 part of the interior of the sacroiliac joints, rather than the whole of the sacroiliac joints.

Femoral tunnel positioning in posterior cruciate ligament double-bundle reconstruction by computer aided design / 中国骨伤

<p><b>OBJECTIVE</b>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.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSION</b>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.</p>

Biomechanical comparison of unstable distal radius fractures fixed by locking screws with different length / 医用生物力学

Objective To compare the postoperative stability of unstable distal radius fractures fixed by locking screws with different length and analyze the stress distributions of distal screws and callus at different healing periods, so as to provide biomechanical references for choosing appropriate length of screws for treating distal radius fractures. Methods The three-dimensional finite element models of unstable distal radius fractures with fracture section and callus were established, respectively, and fixed by volar locking plates and locking screws with different length. Then different periods of fracture healing were simulated by assigning callus with different material properties. Stress distributions on callus and distal screws at different postoperative periods were analyzed, and compression stiffness of the whole fixation system was calculated according to the maximum axial displacement at fracture section. Results Under the same axial loads, the compression stiffness was basically the same by using unicortical screw with over 75% length or bi-cortical screw. With the screw length increasing, the maximum stress of callus was decreased gradually during the period of early healing; while the maximum stress of distal screws was increasing gradually with the increase of screw length at middle and last period of fracture healing, and the stress of distal bi-cortical screw was the largest. Conclusions Using the unicortical distal locking screws with at least 75% length can not only produce early stability， but also avoid extensor tendon injuries due to dorsal screw prominence.

Three-dimensional finite element analysis on mechanical behavior of the bone remodeling and bone integration between the bone-implant interface after hip replacement / 中国骨伤

<p><b>OBJECTIVE</b>To discuss the primary stability of the fixed interface between the cementless prosthesis and femur, and its influence on bone ingrowth and secondary stability under the roughened surface and press fit of different prostheses by finite element analysis.</p><p><b>METHODS</b>:A three-dimensional finite element module of total hip arthroplasty (THA) was developed with Mimics software. There was a collection of data when simulating hip arthroplasty. The frictional coefficient between the fixed interface was 0,0.15,0.40 and 1.00 representing the roughness of prosthesis surface. The press fit was 0, 0.01,0.05 and 0.10 mm according to the operation. The Vion Mises stress distribution and the contact pressure,friction stress and relative sliding displacement between the interface were analysed and compared when simulating the maneuver of climbing stairs.</p><p><b>RESULTS</b>At a fixed press fit of 0.05 mm,the contact pressure between the interface was 230 , 231, 222 and 275 MN under four different frictional coefficient (0,0. 15,0.40 and 1.00) with little change; the relative sliding displacement was 0.529, 0.129, 0.107 and 0.087 mm with a consistent and obvious decline. As the fixed frictional coefficient was 0.40,the contact pressure between the interface were 56.0,67.7 ,60.4 and 49.6 MN under four different press fit (0, 0.01, 0.05 and 0.10 mm) with a reduction; the relative sliding displacement was 0.064,0.062,0.043 and 0.042 mm with an obvious decline, and there was a maximal friction stress when press fit of 0.01 mm.</p><p><b>CONCLUSION</b>There is a dynamic process of the bone remodeling and bone integration between the interface after hip replacement, determining the long-term outcome. The interface clearance and the frictional coefficient are the key factors of the bone integration.</p>

Influence from different assigned gradients of material attributes on mechanical properties of the vertebral finite element mode / 医用生物力学

Objective To study the influence from different assigned gradients of material attributes on mechanical properties of the vertebral finite element model. Methods An adult human spine (T12-L5) was CT scanned, and the 3D models of each vertebra were reconstructed in MIMICS, which were then modified in Geomagic and imported into ANSYS for meshing. The element models were imported back to MIMICS and assigned with material properties by separating into 8 kinds of gradients (2, 4, 8, 10, 50, 100, 200, 400 divisions). These models were then imported to ANSYS again for finite element analysis under the same loading condition. Results Significant differences were found in stresses from models with 2, 4, 400 gradients, but the deviations between 8, 10, 50, 100, 200 gradients were not obvious. Conclusions The material attributes of finite element model should be appropriate, and the assigned gradient of 10 divisions could be better guarantee the accuracy of calculation and enhance the calculation speed as well, which is suitable for personalized rapid finite element modeling in clinic.

Plantar pressure distributions during support phase under different Achilles tensile loads / 医用生物力学

Objective To investigate changes in plantar pressure distributions on forefoot and hindfoot region during the support phase under different Achilles tensile loads. Methods Six fresh frozen human below-knee specimens were used and placed on the material testing machine. The ankles were kept in neutral position and the axial load of 350 N was applied on the specimens. Achilles tensile loads varied from 0 kg to 80 kg (0, 100, 200, 300, 400, 500, 600, 700, 800 N）were applied by weights. Two scales were placed under the forefoot and hindfoot region of the specimen, respectively, to record the pressure under the Achilles tensile loads. Results With the Increasing Achilles tensile force, the pressure on forefoot region was increasing, while the pressure on the hindfoot was decreasing. The percentage of average plantar pressure in forefoot and hindfoot region over the total plantar pressures presented a linear relationship with the Achilles tensile force (P<0.01, R2=0.996). Conclusions The support phase of foot in vitro was simulated and the plantar pressure distributions on forefoot and hindfoot region was investigated in this paper. The result can provide theoretical evidences for some diseases (such as diabetic foot ulcers, metatarsalgia) caused by plantar pressure changes due to Achilles tensile contracture in clinic.

Balloon inflating and cement filling for treatment of avascular necrosis of the femoral head: a three-dimensional infinite-element study / 南方医科大学学报

<p><b>OBJECTIVE</b>To evaluate the biomechanical changes of balloon inflating and cement filling in avascular necrosis of the femoral head using finite-element analysis.</p><p><b>METHODS</b>The procedure of percutaneous balloon inflating and cement filling was simulated in fresh specimen of human femoral head. CT scan and three-dimensional reconstruction were used to establish the three-dimensional model of the femoral head. The physiological load was analyzed using three-dimensional finite element model to simulate the load and calculate stress on the hip during walking. Finite element analysis was performed on the avascular necrosis model and balloon inflating and bone cement filling model to measure the Von-Mises force at the top, neck and weight-bearing area of the femoral head. Another 8 fresh specimens of femoral head necrosis of human were obtained to stimulate balloon inflating and bone cement filling procedures, and the displacement of the femoral head under different loads was recorded before and after the procedures.</p><p><b>RESULTS</b>After bone cement filling in the necrosis area, the load reduced significantly in the weight-bearing area of the femoral head, and the load distribution became more uniform at the femoral neck and the top of the head. The anti-deformation ability of the necrosis femoral head increased after bone cement filling. The infinite-element analysis and specimen biomedical test showed similar results.</p><p><b>CONCLUSION</b>Percutaneous balloon inflating and bone cement filling in the necrosis area can change the biomechanics mechanism of the femoral head and neck, improve the supporting capacity under load, and prevent the progression of head collapse.</p>

Influence of bone quality on the stress distribution for three-posterior immediately loaded implants: a three-dimensional finite element analysis / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To assess and compare the peri-implant stress distribution of three posterior implants under immediate loading with 4 different bone qualities using three dimensional (3D) finite element (FE) analysis.</p><p><b>METHODS</b>A 3D finite element model representing three implants in a portion of mandible at the 654 region was developed, and three implants received a crown each. Four types of bone qualities (B1, B2, B3 and B4) were designed for the model. Load of 100 N was applied on the occlusal surfaces of the crowns at a 45° angle to the vertical axis of the implants.</p><p><b>RESULTS</b>Von Mises stresses in the peri-implant bone of 4 in bone quality from B1 to B4 were (13.17 ± 9.32), (12.95 ± 9.14), (15.00 ± 9.44), and (16.81 ± 10.74) MPa, and those of 5 were (15.51 ± 10.32), (14.73 ± 8.96), (16.79 ± 8.40), and (18.34 ± 8.45) MPa. Stress in bone quality B4 showed the highest value, followed by B3 bone, the lowest stress were found in B1 and B2 bone. It was significantly different (P < 0.05). However, von Mises stresses in different quality of bone around 6 [(42.45 ± 25.71), (41.66 ± 25.29), (42.70 ± 23.24), (42.06 ± 23.66) MPa] were close to each other, and were as twice or three times as those of 4 and 5, irrespective of different bone qualities.</p><p><b>CONCLUSIONS</b>The stress distribution around implant under immediate loading was not only affected by different bone qualities, but also by the direction of loading, and the latter may have a greater impact when a severe load delivered.</p>

2D/3D registration system based on single X ray image and CT data / 医用生物力学

Objective To build a 2D/3D registration system based on the compute unified device architecture(CUDA) frame with single X-ray image and CT data of knee joints and apply it in the research of knee motion and stability of implanted prosthesis. Method The digital radiography(DR) equipment used in the study was calibrated by the Zhang zhengyou Calibration Method, and then digitally rendered radiographs(DRR) images were generated in the CUDA frame with light tracing algorithm, and the best 2D/3D registration parameters were calculated with a similarity operator of cross correlation; finally, the results were evaluated by using the method of 3D/3D registration with data obtained from a 3D laser scanner. Results With knee specimen X-ray images and CT data, in 6 degrees of freedom, the average errors of transform were below 1 mm, and those of rotation were below 1°. Conclusions The 2D/3D registration system can meet the precision requirement of motion detection and be used to study the knee motion and prosthesis location.

Advances in two-implant-supported single crown in molar restoration / 医用生物力学

Recently, two implant supported single crown has been applied more and more in molar restoration with the advantages of anti rotation, anti bend, distributing stress, reducing bone resorption and increasing the success rate of molar restoration. The biomechanical study of two-implant can solve the problems of clinical application such as the stress concentration and the degree of bone resorption around implants, and it could contribute to the development of two implant restoration standard of a natural two furcation simulation and regulate the two implant restoration technique, which is important for its extensive clinical application. Therefore, in this paper, the clinical application, biomechanical and biological characteristics and advantages of two implant will be reviewed.

Three-dimensional finite element analysis of biomechanical characteristics of cancellous screw in different bone densities / 南方医科大学学报

<p><b>OBJECTIVE</b>To predict the cancellous screw stress distributions and pull-out strength in cancellous bone with different densities using 3-D finite element analysis and provide biomechanical evidence for screw implant in clinical practices.</p><p><b>METHODS</b>Three-dimensional models of bones with low, medium and high bone density and a fixation screw were generated in Solidworks. Finite element analysis was performed after importing these models to Abaqus to simulate the pull- out process.</p><p><b>RESULTS</b>Stress concentrated both at the surfaces where major diameter of the screw connected the bone and at the proximal half angle of the 3 proximal screw threads. Maximum Von Mises stress of the threads decreased along the long axis of the screw. The pull-out strengths of the cancellous screw were 208.9 N, 431.45 N, and 648.80 N in low, medium and high bone density, respectively.</p><p><b>CONCLUSION</b>During the pull-out process of cancellous screw, stress concentrates at the proximal end of the screw and the pull-out strengths are proportional to the cancellous bone density.</p>

A three dimensional finite element study on stress distribution in maxillary central incisor restored with fiber post / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To study the stress changes of maxillary central incisor restored with or without fiber post using three dimensional finite element method, and analysis the role of fiber post in determining the stress distribution in dentin.</p><p><b>METHODS</b>Three dimensional finite element models of maxillary central incisor with various remaining tooth structure were established by spiral CT, Mimics software and ANSYS software. Test samples were restored with all-ceramic crown and fiber post all-ceramic crown, respectively. The von Mises stress and maximal tensile stress of dentin were recorded.</p><p><b>RESULTS</b>The stress level in dentin of maxillary central incisor restored with fiber post all-ceramic crown was smaller than that restored with all-ceramic crown, the stress distribution of both were similar.</p><p><b>CONCLUSION</b>The apply of fiber post can reduce the stress level in dentin of maxillary central incisor and decrease the risk of tooth breakage, but not change the stress pattern.</p>

A finite element investigation of bilateral atlantoaxial trans-articular screws and atlas laminar hooks instrumentation / 中华外科杂志

<p><b>OBJECTIVES</b>To investigate the mechanical properties of bilateral atlantoaxial trans-articular screws and atlas laminar hooks instrumentation with finite element method.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSION</b>The bilateral atlantoaxial trans-articular screws and atlas laminar hooks instrumentation is useful and effective for atlantoaxial arthrodesis.</p>

Biomechanical effect of vertebroplasty on the adjacent intervertebral levels using a three-dimensional finite element analysis / 中华创伤杂志(英文版)

<p><b>OBJECTIVE</b>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.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSIONS</b>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.</p>

Biomechanical evaluation of nickel-titanium shape-memory alloy enclosed interlocking intramedular nail / 南方医科大学学报

<p><b>OBJECTIVE</b>To study the biomechanical characteristics of Ni-Ti shape-memory alloy-enclosed interlocking intramedular nail Ni-Ti En for clinical application.</p><p><b>METHODS</b>Six transverse fractures were induced in 6 fresh humeral shafts and fixed with Ni-Ti En, plate, interlocking intramedullary nail, and Ender nail, respectively. The specimens then underwent stress analysis for comparison of the bending strength, twisting force, and flexibility.</p><p><b>RESULTS</b>The bending strength of Ni-Ti En was not significantly different from that of the plate and better than ender's nail; the twisting force of the interlocking intramedullary nail was comparable with the plate, but better than Ender nail.</p><p><b>CONCLUSION</b>Ni-Ti Enpossess good biomechanical property to meet the demand of osteosynthesis, and its less stress protection, freedom of distant nail locking, flexibility and stable fixation may accelerate fracture healing.</p>

Establishment of a testing system of three-dimensional spinal kinematics in vivo based on two- and three-dimensional image registration / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the feasibility of using two- and three-dimensional (2D/3D) image registration for establishing a testing system of 3D kinematics of the spine in vivo.</p><p><b>METHODS</b>CT data of the adult human lumbar spine were collected and the two orthogonal images of the same specimen were captured using an X-ray fluoroscope at two different positions. The 3D computer models of L3 and L4 vertebrae were reconstructed. A virtual fluoroscope was then created with solid modeling software to reproduce the relative positions of the orthogonal images. Two virtual cameras in the software were used to represent the X-ray sources. The 3D computer models of the L3 and L4 vertebrae were then introduced into the virtual fluoroscope respectively and projected onto the orthogonal images by the two virtual cameras. By matching the projections of the 3D model to the orthogonal images of L3 and L4 vertebrae, the 3D positions of L3 and L4 were obtained. After calculation, the relative displacement and angle of L3 were determined.</p><p><b>RESULTS</b>After 2D/3D image registration, the relative displacement and angle were calculated. Compared with position I, the positional changes of L3 were represented with an extension of 5.86 degrees, left bending of 1.85 degrees and right rotation of 2.96 degrees.</p><p><b>CONCLUSION</b>2D/3D image registration allows the simulation of 3D kinematics of the spine in vivo, but the efficiency and accuracy of this technique need further evaluation.</p>

3D image analysis of nasal orbit fossa through a laser scanner: a new method and application of 3D image / 中华整形外科杂志

<p><b>OBJECTIVE</b>This study was to introduce the method for obtaining accurate 3D data of soft tissues using a 3D scanner under non-contact condition and the standard 3D measurement of the nasal orbit fossa for plastic surgery.</p><p><b>METHODS</b>A 3D laser scanner and the Geomagic software were used to obtain the standard facial contour of 30 Chinese people. The nasal orbit fossa, as the feature of beauty, was measured and the data were analyzed.</p><p><b>RESULTS</b>3D measurement exhibited the three-dimensional facial shape at every meaningful angle, with the advantages of high precision of 0.01 mm. We determined the lowest point and described the 3D feature of the nasal orbit fossa.</p><p><b>CONCLUSIONS</b>This method can illustrate the relation of the nasal orbit fossa and the surrounding structure. It is a new approach to facilitate preoperative plans, operation simulation and postoperative evaluation.</p>

The effect of disc degeneration on the structural property distributions in the cervical vertebral endplates / 中华外科杂志

<p><b>OBJECTIVE</b>To study the effect of disc degeneration on the structural property distributions in the cervical vertebral endplates.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSIONS</b>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.</p>

Comparative study of vertebral body stress distribution following insertion of artificial lumbar intervertebral disc / 中华外科杂志

<p><b>OBJECTIVE</b>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.</p><p><b>METHODS</b>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.</p><p><b>RESULTS</b>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.</p><p><b>CONCLUSION</b>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.</p>

Biomechanical effects of osteoporosis vertebral augmentation on the adjacent intervertebral levels using a three-dimensional finite element analysis / 中华创伤骨科杂志

Objective To investigate effects of volume,distribution and leakage of bone cement in ver- tebroplasty on the adjacent intervertebral bodies using an experimentally calibrated and anatomically accurate fi- nite-element model of elderly L4-L5 vertebral bodies.Methods Computed tomography(CT)scanning was done,at 1 mm intervals,on L4-L5 vertebral bodies of the lumbar spine of an old man cadaver that had no abnormal findings on rnentgenograms.The L4-L5 motion segment data were obtained from the CT scans to establish in computer a three-dimensional finite element model of L4-L5 functional spinal unit(FSU)with the software Ansys 7.0.Compressive load after virtual vertebroplasty on the damaged model,unipedicular and bipedieolar injections and leakage of cement into the intervertebral space,and the resulting endplate and disc stresses of the adjacent vertebral bodies were analyzed in various spatial distributions of the filling material and different loading conditions. An anatomically accurate finite-element model of elderly L4-L5 vertebral bodies was developed.Results The FSU study suggested that changes in stress and strain at adjacent levels were minimal.Furthermore,endplale and disc stresses of the adjacent vertebral bodies were not influenced by bone cement filling volumes or distributions except under bending,whereas asymmetric distribution and leakage of bone cement to the disk increased the stress of adjacent endplates.Conclusion Since asymmetric distribution and significant leakage of cement into the intervertebral space can increase the stresses of endplates of adjacent vertebral bodies and may lead to a fracture, symmetric placement of cement in operation should be achieved and leakage of cement avoided.