ABSTRACT
BACKGROUND: Cervical spondylotic radiculopathy could be effectively treated by cervical rotatory manipulation, but the symptoms may be exacerbated when rotated to the wrong direction. OBJECTIVE: To simulate the cervical rotatory manipulation in left/right rotation by three-dimensional finite element, and then investigate the effect of this manipulation on the displacement of cervical disc and the volume of intervertebral foramen so as to provide a basis for effectiveness and safety of cervical rotatory manipulation in treating cervical spondylotic radiculopathy. METHODS: With Mimics10.01, Geomagic Studio and Solidworks 14.0 software, a three-dimensional geometric CAD model of C5-6was developed from the CT scan images of a 25-year-old normal adult female. The model was imported into Ansys Workbench 14.5, and a three-dimensional finite element model was verified and simulated the cervical rotatory manipulation. The cervical rotatory manipulation was decomposed by principium of manipulation in left lateral flexion and rotated to the left/right side. The parameter of mechanics was analyzed with the finite element system. The change of displacement in cervical disc and volume in intervertebral foramen simultaneously were displayed during simulating the manipulation. RESULTS AND CONCLUSION: In left lateral flexion and rotated to the left side, the posterior part of the left side of annulus fibers was expanded 0.46 mm into posterior, and the posterior part of the right side of annulus fibers was retracted 0.77 mm. The volume of left intervertebral foramen became small and the right side became large. However, in left lateral flexion and rotated to the right side, the posterior part of the left side of annulus fibers was retracted 0.71 mm, and the posterior part of the right side of annulus fibers was expanded 0.43 mm into posterior. The volume of left intervertebral foramen became large and the right side became small. Therefore, the posterior part of the rotated side of cervical disc was expanded into posterior, while the posterior part of the contralateral side of cervical disc was retracted. The volume of intervertebral foramen in rotated side became small, while the volume of intervertebral foramen in contralateral side became large. We should rotate to the contralateral side when cervical spondylotic radiculopathy was treated with cervical rotatory manipulation.
ABSTRACT
Objective To compare biomechanical properties of pedicle screw with different axial angles and interbody cage with different positions for unilateral transforaminal lumbar interbody fusion (TLIF) surgery. Methods The normal L3-5 finite element (FE) model was established and validated. Then one bilateral TILF reconstruction FE model and four unilateral TILF reconstruction FE models with different pedicle screw-cage combination types at L4-5 level were constructed, respectively. Namely, Model A (a small axial angle-implanted screw and an ipsilaterally-placed cage), Model B (a small axial angle-implanted screw and a contralaterally-placed cage), Model C (a large axial angle-implanted screw and an ipsilaterally-placed cage), Model D (a large axial angle-implanted screw and a contralaterally-placed cage). The range of motion (ROM) of 4 reconstruction models under various physiological stresses as well as the maximum Von Mises stresses on pedicle screw, cage-L4 inferior endplate were compared. Results The ROMs at fusion segment (L4-5) in 4 unilateral TLIF reconstruction models were significantly decreased compared with the normal model, but they were still larger than bilateral TLIF reconstruction model. For 4 unilateral TLIF reconstruction models, Model C showed the largest decrease in stability, and the ROM of Model C was 50.7%, 89.9%, 90.3% of the normal model in flexion-extension, lateral bending, axial rotation, respectively. When comparing the maximum Von Mises stress of posterior pedicle screw and cage-L4 inferior endplate in 4 unilateral TLIF reconstruction models, Model C could bear relatively smaller stress under most loading modes, except in ipsilateral lateral bending and axial rotation. Conclusions The unilateral TLIF reconstruction model with a large axial angle-implanted screw and an ipsilaterally placed-cage can achieve the optimal stability. By narrowing the difference in stability with the bilateral TILF model, the unilateral TLIF reconstruction model can reduce the risk of screw failure and cage subsidence, which is worth of clinical application.
ABSTRACT
Objective To compare biomechanical properties of pedicle screw with different axial angles and interbody cage with different positions for unilateral transforaminal lumbar interbody fusion (TLIF) surgery.Methods The normal L3-5 finite element (FE) model was established and validated.Then one bilateral TILF reconstruction FE model and four unilateral TILF reconstruction FE models with different pedicle screw-cage combination types at L4-5 level were constructed,respectively.Namely,Model A (a small axial angle-implanted screw and an ipsilaterally-placed cage),Model B (a small axial angle-implanted screw and a contralaterally-placed cage),Model C (a large axial angle-implanted screw and an ipsilaterally-placed cage),Model D (a large axial angle-implanted screw and a contralaterally-placed cage).The range of motion (ROM) of 4 reconstruction models under various physiological stresses as well as the maximum Von Mises stresses on pedicle screw,cage-L4 inferior endplate were compared.Results The ROMs at fusion segment (L4-5) in 4 unilateral TLIF reconstruction models were significantly decreased compared with the normal model,but they were still larger than bilateral TLIF reconstruc-tion model.For 4 unilateral TLIF reconstruction models,Model C showed the largest decrease in stability,and the ROM of Model C was 50.7％,89.9％,90.3％ of the normal model in flexion-extension,lateral bending,axial rotation,respectively.When comparing the maximum Von Mises stress of posterior pedicle screw and cage-L4 inferior endplate in 4 unilateral TLIF reconstruction models,Model C could bear relatively smaller stress under most loading modes,except in ipsilateral lateral bending and axial rotation.Conclusions The unilateral TLIF reconstruction model with a large axial angle-implanted screw and an ipsilaterally placed-cage can achieve the optimal stability.By narrowing the difference in stability with the bilateral TILF model,the unilateral TLIF reconstruction model can reduce the risk of screw failure and cage subsidence,which is worth of clinical application.
ABSTRACT
Objective To compare the biomechanical differences in 3 posterior fixation methods with or without crosslink for treatment of thoracolumbar fractures, so as to find the optimal posterior fixation methods. Methods On the basis of the validated finite element model of T12-L2 segments to simulate L1 vertebra burst fracture, the superior 1/2 cortical bone of T12 segment was removed and the superior 1/2 cancellous bone was assigned with the material damage property of cancellous bone. Then 6 thoracolumbar fracture models by intermediate unilateral pedicle screw fixation without or with crosslink (Model A1, A2), traditional short-segment pedicle screw fixation without or with crosslink (Model B1, B2), intermediate bilateral pedicle screw fixation without or with crosslink (Model C1,C2) were established, respectively. The range of motion (ROM) as well as the maximum Von Mises stress of the pedicle screw and rod for 6 models under various physiological loading conditions were compared. Results The ROM under flexion-extension and lateral bending in Model A and Model C was obviously smaller than that of Model B. Under flexion-extension, no significant difference was found in ROM between Model A and Model C; under lateral bending, the ROM of Model C was smaller than that of Model A. The stress was concentrated in the root of upper screw and the rob located between upper screw and intermediate screw; the maximum stress of upper screw in Model C was smaller than that in Model A and Model B. The crosslink could increase the stability of all fixation groups under axial rotation stress condition, and decrease the maximum stress on upper screw and rod under axial rotation stress condition, but no significant difference was found under flexion-extension and lateral bending. Conclusions Additional pedicle screws at the level of fracture vertebra can achieve the better biochemical stability. The additional crosslink not only increases the torsional rigidity, but also decreases the maximum torsional stress of the screw and rod, which is a better choice as the treatment of thoracolumbar fractures.
ABSTRACT
Adjacent vertebral fractures are common in patients with osteoporotic vertebral compression fractures (OVCFs) after kyphoplasty. This finite element study was to examine whether short segment pedicle screw fixation (PSF) with kyphoplasty may decrease the fracture risk of the treated and adjacent non-treated vertebrae after kyphoplasty for OVCFs. By simulating cement augmentation with or without short segment pedicle screw fixation (PSF), two tridimensional, anatomically detailed finite element models of the T10-L2 functional spinal junction were developed. The insertion of pedicle screws into the intact vertebra apparently decreased the stress distribution of the treated vertebra in vertical compression and other load situations. The stress distribution in the bone structures of the intact vertebra adjacent to the intact-screwed vertebra was much less than that in the one adjacent to the treated vertebra. The insertion of pedicle screws into the intact vertebra greatly decreased the maximum displacement of the cortical bones and cancellous bones of the vertebrae. Our results indicated that short segment PSF with kyphoplasty may decrease the fracture risk of the treated and adjacent non-treated vertebrae in the management of OVCFs.