Anterior Lumbar Interbody Fusion Model Research Articles

Does Lumbar Interbody Fusion Modality Affect the Occurrence of Complications in an Osteoporotic Spine Under Whole-Body Vibration? A Finite Element Study

To evaluate the effects of 3 lumbar interbody fusion techniques on the occurrence of complications in an osteoporotic spine under whole-body vibration. A previously developed and validated nonlinear finite element model of L1-S1was modified to develop anterior lumbar interbody fusion (ALIF), posterior lumbar interbody fusion (PLIF), and transforaminal lumbar interbody fusion (TLIF) models with osteoporosis. In each model, the lower surface of the sacrum was absolutely fixed, a follower load of 400N was applied through the axis of the lumbar spine, and an axial sinusoidal vertical load of ±40N (5 Hz) was imposed on the superior surface of L1, to perform a transient dynamic analysis. The maximal values of intradiscal pressure, shear stress on annulus substance, disc bulge, facet joint stress, and screw and rod stress, along with their dynamic response curves, were collected. Among these 3 models, the TLIF model generated the greatest screw and rod stress, and the PLIF model generated the greatest cage-bone interface stress. At the L3-L4 level, compared with the other 2 models, the maximal values and dynamic response curves of intradiscal pressure, shear stress of annulus ground substance, and disc bulge were all lower in the ALIF model. However, the facet contact stress at the adjacent segment in the ALIF model was higher than that in the other 2 models. In an osteoporotic spine under whole-body vibration, TLIF has the highest risk of screw and rod breakage, PLIF has the highest risk of cage subsidence, and ALIF has the lowest risk of upper adjacent disc degeneration, but the highest risk of adjacent facet joint degeneration.

Does Osteoporosis Affect the Adjacent Segments Following Anterior Lumbar Interbody Fusion? A Finite Element Study

Adjacent segment degeneration is a common complication following anterior lumbar interbody fusion (ALIF). Osteoporosis is becoming increasingly prevalent in the elderly population and thus patients undergoing ALIF may experience osteoporosis with age. However, the influence of osteoporosis on adjacent segment degeneration after ALIF remains unclear. Three finite element models of the L3-S1 segment, including a healthy model, an ALIF model, and an ALIF with osteoporosis model, were used for analysis. ALIF was simulated at the L4-L5 segment. Based on a hybrid test method, the models were imposed with a preload of 400 N and an adjusted moment in flexion, extension, lateral bending, and axial torsion. Intradiscal pressure, shear stress on anulus fibrosus, and range of motion at L3-L4 and L5-S1 were calculated and compared. In each direction, the maximal values of intradiscal pressure and shear stress on anulus fibrosus at L3-L4 and L5-S1 were found in the ALIF model, and the minimal values were found in the healthy model. At L3-L4 and L5-S1, the maximal values of range of motion in most directions were found in the ALIF model followed by the ALIF with osteoporosis model, and the minimal values were found in the healthy model. However, the maximal value of range of motion at L5-S1 in axial torsion was found in the ALIF with osteoporosis model. Osteoporosis may mitigate the adverse influence of ALIF on adjacent segments.

Autologous blood coagulum containing rhBMP6 induces new bone formation to promote anterior lumbar interbody fusion (ALIF) and posterolateral lumbar fusion (PLF) of spine in sheep.

In the present study, we evaluated an autologous bone graft substitute (ABGS) composed of recombinant human BMP6 (rhBMP6) dispersed within autologous blood coagulum (ABC) used as a physiological carrier for new bone formation in spine fusion sheep models. The application of ABGS included cervical cage for use in the anterior lumbar interbody fusion (ALIF), while for the posterolateral lumbar fusion (PLF) sheep model allograft devitalized bone particles (ALLO) were applied with and without use of instrumentation. In the ALIF model, ABGS (rhBMP6/ABC/cage) implants fused significantly when placed in between the L4-L5 vertebrae as compared to control (ABC/cage) which appears to have a fibrocartilaginous gap, as examined by histology and micro CT analysis at 16weeks following surgery. In the PLF model, ABGS implants with or without ALLO showed a complete fusion when placed ectopically in the gutter bilaterally between two decorticated L4-L5 transverse processes at a success rate of 88% without instrumentation and at 80% with instrumentation; however the bone volume was 50% lower in the instrumentation group than without, as examined by histology, radiographs, micro CT analyses and biomechanical testing at 27weeks following surgery. The newly formed bone was uniform within ABGS implants resulting in a biomechanically competent and histologically qualified fusion with an optimum dose in the range of 100μg rhBMP6 per mL ABC, while in the implants that contained ALLO, the mineralized bone particles were substituted by the newly formed remodeling bone via creeping substitution. These findings demonstrate for the first time that ABGS (rhBMP6/ABC) without and with ALLO particles induced a robust bone formation with a successful fusion in sheep models of ALIF and PLF, and that autologous blood coagulum (ABC) can serve as a preferred physiological native carrier to induce new bone at low doses of rhBMP6 and to achieve a successful spinal fusion.

Dnmt3a-Mediated DNA Methylation Changes Regulate Osteogenic Differentiation of hMSCs Cultivated in the 3D Scaffolds under Oxidative Stress.

Oxidative stress (OS) caused by multiple factors occurs after the implantation of bone repair materials. DNA methylation plays an important role in the regulation of osteogenic differentiation. Moreover, recent studies suggest that DNA methyltransferases (Dnmts) are involved in bone formation and resorption. However, the effect and mechanism of DNA methylation changes induced by OS on bone formation after implantation still remain unknown. Three-dimensional (3D) cell culture systems are much closer to the real situation than traditional monolayer cell culture systems in mimicking the in vivo microenvironment. We have developed porous 3D scaffolds composed of mineralized collagen type I, which mimics the composition of the extracellular matrix of human bone. Here, we first established a 3D culture model of human mesenchymal stem cells (hMSCs) seeded in the biomimetic scaffolds using 160 μM H2O2 to simulate the microenvironment of osteogenesis after implantation. Our results showed that decreased methylation levels of ALP and RUNX2 were induced by H2O2 treatment in hMSCs cultivated in the 3D scaffolds. Furthermore, we found that Dnmt3a was significantly downregulated in a porcine anterior lumbar interbody fusion model and was confirmed to be reduced by H2O2 treatment using the 3D in vitro model. The hypomethylation of ALP and RUNX2 induced by H2O2 treatment was abolished by Dnmt3a overexpression. Moreover, our findings demonstrated that the Dnmt inhibitor 5-AZA can enhance osteogenic differentiation of hMSCs under OS, evidenced by the increased expression of ALP and RUNX2 accompanied by the decreased DNA methylation of ALP and RUNX2. Taken together, these results suggest that Dnmt3a-mediated DNA methylation changes regulate osteogenic differentiation and 5-AZA can enhance osteogenic differentiation via the hypomethylation of ALP and RUNX2 under OS. The biomimetic 3D scaffolds combined with 5-AZA and antioxidants may serve as a promising novel strategy to improve osteogenesis after implantation.

FOXO1-suppressed miR-424 regulates the proliferation and osteogenic differentiation of MSCs by targeting FGF2 under oxidative stress

Recently, microRNAs (miRNAs) have been identified as key regulators of the proliferation and differentiation of mesenchymal stem cells (MSCs). Our previous in vivo study and other in vitro studies using miRNA microarrays suggest that miR-424 is involved in the regulation of bone formation. However, the role and mechanism of miR-424 in bone formation still remain unknown. Here, we identified that the downregulation of miR-424 mediates bone formation under oxidative stress, and we explored its underlying mechanism. Our results showed that miR-424 was significantly downregulated in an anterior lumbar interbody fusion model of pigs and in a cell model of oxidative stress induced by H2O2. The overexpression of miR-424 inhibited proliferation and osteogenic differentiation shown by a decrease in alkaline phosphatase (ALP) activity, mineralization and osteogenic markers, including RUNX2 and ALP, whereas the knockdown of miR-424 led to the opposite results. Moreover, miR-424 exerts its effects by targeting FGF2. Furthermore, we found that FOXO1 suppressed miR-424 expression and bound to its promoter region. FOXO1 enhanced proliferation and osteogenic differentiation in part through the miR-424/FGF2 pathway. These results indicated that FOXO1-suppressed miR-424 regulates both the proliferation and osteogenic differentiation of MSCs via targeting FGF2, suggesting that miR-424 might be a potential novel therapeutic strategy for promoting bone formation.

Effects of Lumbar Arthrodesis on Adjacent Segments

A finite element analysis. To evaluate the differences between surgical techniques in terms of the effects of arthrodesis on adjacent segments. Augmentation with posterior rigid fixation combined with transpedicular screw insertion, which is one of the most popular techniques for lumbar arthrodesis, shows benefits in immediate stabilization and a higher fusion rate but is reportedly correlated with greater stress on adjacent segments. However, the increased stress on adjacent segments needs further evaluation because the differences of the effects on adjacent segments between surgical techniques, including anterior lumbar interbody fusion, posterior lumbar interbody fusion, and semirigid fixation, have not yet been determined. A finite element model of the human lumbar spine was developed. Three spinal segments (L2-L5) were used to investigate. The intact spinal model was validated by comparing it with previously reported models. Then, 4 arthrodesis models were analyzed and compared: (1) anterior lumbar interbody fusion model; (2) posterior lumbar interbody fusion model; (3) semirigid fixation model combined with posterior lumbar interbody fusion; and (4) rigid fixation model combined with posterior lumbar interbody fusion. Among these 4 models, the rigid fixation model showed the greatest amount of stress, with increased intervertebral disc pressure and contact force of the facet joints of both upper and lower adjacent segments. The second highest stress levels were seen in the semirigid fixation model and the lowest stress levels were seen in the anterior lumbar interbody fusion model. Although bony fusion had been completed, the effects of lumbar arthrodesis on adjacent segments could vary according to the surgical technique used for arthrodesis. Semirigid fixation combined with arthrodesis deserves careful consideration and further detailed study because it may cause less stress on adjacent segments than rigid fixation while maintaining the benefits of the latter procedure.

The influence of different magnitudes and methods of applying preload on fusion and disc replacement constructs in the lumbar spine: a finite element analysis

In a finite element (FE) analysis of the lumbar spine, different preload application methods that are used in biomechanical studies may yield diverging results. To investigate how the biomechanical behaviour of a spinal implant is affected by the method of applying the preload, hybrid-controlled FE analysis was used to evaluate the biomechanical behaviour of the lumbar spine under different preload application methods. The FE models of anterior lumbar interbody fusion (ALIF) and artificial disc replacement (ADR) were tested under three different loading conditions: a 150 N pressure preload (PP) and 150 and 400 N follower loads (FLs). This study analysed the resulting range of motion (ROM), facet contact force (FCF), inlay contact pressure (ICP) and stress distribution of adjacent discs. The FE results indicated that the ROM of both surgical constructs was related to the preload application method and magnitude; differences in the ROM were within 7% for the ALIF model and 32% for the ADR model. Following the application of the FL and after increasing the FL magnitude, the FCF of the ADR model gradually increased, reaching 45% at the implanted level in torsion. The maximum ICP gradually decreased by 34.1% in torsion and 28.4% in lateral bending. This study concluded that the preload magnitude and application method affect the biomechanical behaviour of the lumbar spine. For the ADR, remarkable alteration was observed while increasing the FL magnitude, particularly in the ROM, FCF and ICP. However, for the ALIF, PP and FL methods had no remarkable alteration in terms of ROM and adjacent disc stress.

Fusion Performance of Low-Dose Recombinant Human Bone Morphogenetic Protein 2 and Bone Marrow-Derived Multipotent Stromal Cells in Biodegradable Scaffolds

A large animal study comparing interbody fusion of a bioresorbable scaffold loaded with either low-dose recombinant human bone morphogenetic protein 2 (rhBMP-2) or bone marrow-derived multipotent stromal cells (BMSCs). To compare the quality of fusion resulting from implantation of medical grade poly (ε-caprolactone)-20% tricalcium phosphate (mPCL/TCP) scaffolds and two different bone growth stimulating agents. Nondegradable cages have been used for interbody fusion with good results. However, the overall advantage of lifelong implantation of a nondegradable device remains a subject of ongoing debate. The use of bioresorbable scaffolds might offer superior alternatives. In this study, we evaluated the quality of fusion obtained with two potential bone graft substitutes. Eleven Yorkshire pigs underwent a bisegmental (L2/L3; L4/L5) anterior lumbar interbody fusion (ALIF) in four groups, namely: (1) mPCL/TCP + 0.6 mg rhBMP-2; (2) mPCL/TCP + BMSCs; (3) mPCL/TCP (negative control); and (4) autologous bone grafts (positive control). RESULTS. The mean radiographic scores at 9 months were 3.0, 1.7, 1.0, and 1.8 for groups 1 to 4, respectively. The bone volume fraction of group 1 was two-folds higher than group 2. Histology, micro-computed tomographic scanning and biomechanical evaluation demonstrated solid and comparable fusion between groups 1 and 4. However, group 2 showed inferior quality of fusion when compared with groups 1 and 4 while group 3 showed no fusion even at 9 months. In addition, there was no evidence of implant rejection, chronic inflammation or any other complications. mPCL/TCP scaffolds loaded with low-dose rhBMP-2 is comparable to autograft bone as a bone graft substitute in this large animal ALIF model. Although BMSCs lagged behind autograft bone and rhBMP-2, evidence of bone ingrowth in this group warrants further investigation. Our results suggest that mPCL/TCP scaffolds loaded with rhBMP-2 or BMSCs may be a viable alternative to conventional cages and autograft bone.

Does anterior lumbar interbody fusion promote adjacent degeneration in degenerative disc disease? A finite element study

BackgroundThe increase in the number of anterior lumbar interbody fusions being performed carries with it the potential for the long-term complication of adjacent segmental degeneration. While its exact mechanism remains uncertain, adjacent segment degeneration has become much more widespread. Using a nonlinear, three-dimensional finite element model to analyze and compare the biomechanical influence of anterior lumbar interbody fusion and lumbar disc degeneration on the superior adjacent intervertebral disc, we attempt to determine if anterior lumbar interbody fusion aggravates adjacent segment degeneration. MethodsA normal three-dimensional non-linear finite element model of L3–5 has been developed. Three different grades of disc degeneration models (mild, moderate, severe) and one anterior lumbar interbody fusion model were developed by changing either the geometry or associated material properties of the L4–5 segment. The 800 N pre-compressive loading plus 10 Nm moments simulating flexion, extension, lateral bending and axial rotation in five steps was imposed on the L3 superior endplate of all models. The intradiscal pressure, intersegmental rotation range and Tresca stress of the annulus fibrosus in the L3–4 segment were investigated. ResultsThe intradiscal pressure, intersegmental rotation range and Tresca stress of the L3–4 segment in the fusion model are higher than in the normal model and different degeneration models under all motion directions. The intradiscal pressures in the three degenerative models are higher than in the normal model in flexion, extension and lateral bending, whereas in axial rotation, the value of the mild degeneration model is lower. The intersegmental rotation ranges in the three degenerative models are higher than in the normal model in flexion and extension. The values for the mild degeneration model in lateral bending and all the degeneration models in axial rotation are lower than in the normal model. The Tresca stresses are higher in the three degenerative models than in the normal model. ConclusionAnterior lumbar interbody fusion has more adverse biomechanical influence than disc degeneration on the adjacent upper disc and may aggravate the adjacent upper segmental degeneration.

Does tlif aggravate adjacent segmental degeneration more adversely than alif? a finite element study

To determine whether transforaminal lumbar interbody fusion aggravate adjacent segmental degeneration more adversely than anterior lumbar interbody fusion. A normal finite element model, an anterior lumbar interbody fusion model and a transforaminal lumbar interbody fusion model of L3-5 were developed. 800 N compressive loading plus 10 Nm moments simulating flexion, extension, lateral bending and axial rotation were imposed on L3 superior endplate. The intradiscal pressure, intersegmental rotation and tresca stress in L3-4 were investigated. Under all loading directions, the values of three parameters in transforaminal lumbar interbody fusion model were the highest and those in normal model were the lowest, and the values in the ALIF model were higher than the normal model while lower than the TLIF model. In the ALIF and normal models, the values of the three parameters on left lateral bending and axial rotation were equal to those on right lateral bending and axial rotation. However, in the TILF model, the values on right lateral bending and axial rotation were larger than those on left lateral bending and axial rotation. Transforaminal lumbar interbody fusion aggravates adjacent segmental degeneration more adversely than anterior lumbar interbody fusion.

Does disc space height of fused segment affect adjacent degeneration in alif? a finite element analysis

The restoration of disc space height of fused segment is essential in anterior lumbar interbody fusion, while the disc space height in many cases decreased postoperatively, which may adversely aggravate the adjacent segmental degeneration. However, no literature available focused on the issue. A normal healthy finite element model of L3-5 and four anterior lumbar interbody fusion models with different disc space height of fused segment were developed. 800 N compressive loading plus 10 Nm moments simulating flexion, extension, lateral bending and axial rotation were imposed on L3 superior endplate. The intradiscal pressure, the intersegmental rotation, the tresca stress and contact force of facet joints in L3-4 were investigated. Anterior lumbar interbody fusion with severely decreased disc space height presented with the highest values of the four parameters, and the normal healthy model presented with the lowest values except, under extension, the contact force of facet joints in normal healthy model is higher than that in normal anterior lumbar interbody fusion model. With disc space height decrease, the values of parameters in each anterior lumbar interbody fusion model increase gradually. Anterior lumbar interbody fusion with decreased disc space height aggravate the adjacent segmental degeneration more adversely.

Load- and displacement-controlled finite element analyses on fusion and non-fusion spinal implants

This study used finite element (FE) analysis with the load-controlled method (LCM) and the displacement-controlled method (DCM) to examine motion differences at the implant level and adjacent levels between fusion and non-fusion implants. A validated three-dimensional intact (INT) L1-L5 FE model was used. At the L3-L4 level, the INT model was modified to surgery models, including the artificial disc replacement (ADR) of ProDisc II, and the anterior lumbar interbody fusion (ALIF) cage with pedicle screw fixation. The LCM imposed 10 Nm moments of four physiological motions and a 150 N preload at the top of L1. The DCM process was in accordance with the hybrid testing protocol. The average percentage changes in the range of motion (ROM) for whole non-operated levels were used to predict adjacent level effects (ALE%). At the implant level, the ALIF model showed similar stability with both control methods. The ADR model using the LCM had a higher ROM than the model using the DCM, especially in extension and torsion. At the adjacent levels, the ALIF model increased ALE% (at least 17 per cent) using the DCM compared with the LCM. The ADR model had an ALE% close to that of the INT model, using the LCM (average within 6 per cent), while the ALE% decreased when using the DCM. The study suggests that both control methods can be adopted to predict the fusion model at the implant level, and similar stabilization characteristics can be found. The LCM will emphasize the effects of the non-fusion implants. The DCM was more clinically relevant in evaluating the fusion model at the adjacent levels. In conclusion, both the LCM and the DCM should be considered in numerical simulations to obtain more realistic data in spinal implant biomechanics.

Bone ingrowth characteristics of porous tantalum and carbon fiber interbody devices: an experimental study in pigs

Background context In preclinical and clinical joint replacement applications, porous tantalum has been shown to be osteoconductive and effective for biological fixation. Relatively little research has been undertaken to investigate the porous tantalum implants for potential application in intervertebral spinal fusion. Purpose The current study was designed to assess the radiographic and histological performance of porous tantalum and carbon fiber devices in the porcine anterior lumbar interbody fusion (ALIF) model. Study design A total of 10 Danish Landrace pigs underwent a three-level anterior intervertebral lumbar arthrodeses at L2–L3, L4–L5 and L6–L7. Each level was randomly allocated to one of three implants: a solid piece of porous tantalum, a porous tantalum ring packed with autograft or a carbon fiber cage, likewise packed with autograft. Two staples for fixation were supplemented in front of implant. Methods Pigs were sacrificed 3 months after operation. Specimens were evaluated by plain radiography, conventional tomography and histology. Results Bone graft filled into the central hole of the porous tantalum ring was less than that of the carbon fiber cage (p<.001). Radiolucencies around the porous tantalum solid were significantly higher than the carbon fiber cage (p = .02) and were not different between the porous tantalum ring and the carbon fiber cage. The bone volume in the hole of implants, within the pores of the porous tantalum and in the implant interface did not differ between implants. Bone volume in the hole of the porous tantalum ring did not differ from that of the adjacent vertebral bone; however, it was significantly different in the carbon fiber cage and the adjacent vertebral bone (p = .005). Conclusions In this porcine ALIF model, the radiographic and histological appearances of the porous tantalum ring were equivalent to those of the carbon fiber cage. The high presence of radiolucencies and fibrous tissue layer at the vertebrae–implant interface suggests that an initial stabilizing biomechanical environment is important in order to achieve bone ingrowth in the interbody fusion devices in this ALIF model.