Finite element analysis for comparison of spinous process osteotomies technique with conventional laminectomy as lumbar decompression procedure

Biomechanical effects of iatrogenic muscle-ligaments complex damage on adjacent segments following posterior lumbar interbody fusion: A finite element analysis

OBJECTIVE

To analyze the biomechanical effects of proximal iatrogenic muscle-ligaments complex (MLC) damage on adjacent segments following posterior lumbar interbody fusion (PLIF) by finite element (FE) analysis.

METHODS

The multifidus muscle force was loaded in the validated intact lumbosacral finite element model. Based on whether undergoing PLIF or the proximal MLC damage, three models were established. Range of motion (ROM) and the maximum von Mises (VM) stress of adjacent segments were analyzed, as well as the average muscle force and work capacity in four loading directions.

RESULTS

PLIF results in significant changes in ROM and stress. ROM changed significantly in the upper adjacent segment, the PLIF model changed the most in extension, and the largest change in the lower adjacent segment occurred after MLC damage. The VM stress of the upper adjacent segment occurred in extension of the PLIF model, and that of the lower adjacent segment occurred in rotation after MLC damage. In flexion, ROM, and stress of the damaged MLC fusion model were significantly increased compared with the normal and PLIF models, there was a stepwise amplification. The average muscle force comparison of three models was 5.8530, 12.3185, and 13.4670 N, respectively. The total work capacity comparison was close to that of muscle force.

CONCLUSION

PLIF results in increased ROM and the VM stress of adjacent segments, the proximal MLC damage will aggravate this change. This may increase the risk of ASD and chronic low back pain. Preserving the proximal MLC reduces the biomechanical effects on adjacent segments.

Biomechanical effects of individualized artificial titanium alloy lamina implantation after laminectomy: A finite element analysis

Background and objectives: Laminectomy is a common surgical procedure in spine surgery. However, disruption of the posterior ligamentous complex of the spine may lead to a range of postoperative complications. Artificial lamina as a kind of bionic implant can well restore the posterior spinal structure. In this study, an individualized artificial titanium alloy lamina was designed to reconstruct the posterior spinal structure after laminectomy and explored its biomechanical effects, which could provide a theoretical basis for the clinical application of the artificial lamina.

Methods: Three finite element models were constructed, namely the nonlinear and non-homogeneous intact model of the whole lumbar spine, the lumbar decompression alone surgical model, and the artificial lamina implantation surgical model. The range of motion, intradiscal pressure, and annulus fibrosus peak stress were compared between the three models at the surgical and adjacent segments. The stresses of the artificial lamina and fixation screws were also analyzed for the four movement states.

Results: Compared with the intact model, the lumbar decompression alone surgical model showed an increase in range of motion, intradiscal pressure, and annulus fibrosus peak stresses at the surgical segment and adjacent segments under all conditions. The artificial lamina implantation surgical model showed an increase in these measurements only in flexion, increasing by 7.5%–22.5%, 7.6%–17.9%, and 6.4%–19.3%, respectively, over the intact model, while there was little difference under other conditions. The peak stresses in both the screw and the artificial lamina were highest in axial rotation, i. e. 46.53 MPa and 53.84 MPa, respectively. Screw stresses were concentrated on the connection between the screw and the artificial lamina, and artificial lamina stresses were concentrated on the spinous root, around the screw hole, and the contact with the vertebral body.

Conclusion: An individualized artificial titanium alloy lamina can effectively reduce the range of motion, intradiscal pressure, and annulus fibrosus stress at the surgical segment and adjacent segments. The application of artificial lamina could better preserve the biomechanical properties of the intact lumbar spine and reduce the risk of adjacent segmental disease.

Biomechanical effects of reconstruction of the posterior structures after laminectomy with an individualized poly-ether-ether-ketone (PEEK) artificial lamina

BACKGROUND

Laminectomy is a traditional method for treating lumbar diseases; however, the destruction of the posterior structures may cause postoperative symptoms. An individualized poly-ether-ether-ketone (PEEK) artificial lamina was designed to reconstruct the posterior structures after laminectomy. This study aimed to explore the biomechanical effects of reconstruction of the posterior structures with an individualized PEEK artificial lamina using validated finite element models.

OBJECTIVE

To examine the biomechanical effects of individualized PEEK artificial lamina on postlaminectomy lumbar.

METHODS

A finite element (FE) model of L3-5 was developed based on computed tomography images. Four surgical models (laminectomy, artificial lamina alone, ligament reconstruction, and osseointegration) were constructed, representing different stages of L4 artificial lamina implantation. The range of motion (ROM), intradiscal pressure (IDP), stresses in the annulus fibrosus at the surgical level and cephalad adjacent level, and stresses in the artificial lamina and screws were measured.

RESULTS

The ROM, IDP, and stresses in the annulus fibrosus of the different artificial lamina models decreased compared to those of the laminectomy model at both surgical and adjacent levels for all motion patterns, most notably in the osseointegration model. In addition, the results of the stresses in the implants showed that the artificial lamina could enhance the lumbar isthmus and disperse the abnormally concentrated stresses after laminectomy.

CONCLUSION

The application of a PEEK artificial lamina has the potential to stabilize the postlaminectomy lumbar spine and prevent adjacent segment disease (ASD) and iatrogenic lumbar deformities, resulting in a reduction in the incidence of post-lumbar surgery syndrome.

Lumbar stability following graded unilateral and bilateral facetectomy: A finite element model study

BACKGROUND

Excision of excessive amount of facet joint during lumbar discectomy or decompression can cause segmental instability of the lumbar spine. This study was performed to assess the segmental instability, facet joint loading and intradiscal pressure following graded lumbar facetectomy. This biomechanical study was performed using a verified and validated L3-S1 finite element model.

METHODS

Nine scenarios were analysed. Intact model as control, 30%, 45%, 60% and complete facet joint excision in unilateral and bilateral setting. The effect of progressive graded facetectomy of L4-L5 on the segmental mobility, facet loading and intradiscal pressure was assessed.

FINDINGS

In comparison with control 30% excision of the facet joint mainly caused increase in mediolateral mobility. With 45% excision of the facet joint there was increase in both anteroposterior and mediolateral mobility, this was worse in bilateral and unilateral models respectively. This worsened with larger facet excision scenarios. Facet load increased significantly on extension with excision of 45% & 60% unilaterally and 100% bilaterally. Flexion produced rise in intradiscal pressure in all scenarios.

INTERPRETATION

The increased spinal mobility, facet loading and intradiscal pressure with more than 30% facetectomy highlights the importance of preserving the facets during decompression thereby safeguarding accelerated degeneration of these segments and iatrogenic segmental instability. The findings from this study could also potentially explain the correlation between spinal instability, disc degeneration and facet joint arthrosis as noted in clinical studies.

Comparative study of two spinous process (SP) osteotomy techniques for posterior decompression surgery in lumbar spinal stenosis: SP base versus splitting osteotomy

PURPOSE

To compare the postoperative clinical and radiological outcomes of the SP base osteotomy versus SP splitting techniques for PD for treating LSS.

METHODS

Of 139 patients who underwent PD surgery for LSS, 97 who met the study criteria were enrolled in the study. Group A comprised 53 patients who underwent SP base osteotomy, and group B included 44 patients who underwent SP splitting osteotomy. The primary study endpoint was intensity of lower back pain (LBP) and pain radiation to the lower extremities measured with the visual analogue scale (VAS). Secondary endpoints included (1) clinical outcomes assessed using Oswestry disability index and 12-short health form questionnaire; (2) surgical outcomes; and (3) procedure-related complications.

RESULTS

LBP was more or less greater in SP base osteotomy group than in SP splitting osteotomy group at postoperative 1 week and 1 year (P = 0.04 and 0.03), but radiating pain was no significant difference between the groups throughout the 1-year follow-up period. One year after the surgery, the fusion rate at the osteotomized site was significantly greater in SP splitting osteotomy group (77%) than in SP base osteotomy group (55%) (P = 0.03). Clinical outcomes, surgical outcomes, and complications did not differ significantly between groups during follow-up times.

CONCLUSIONS

The two SP osteotomy techniques offer excellent clinical and radiological outcomes at least for the first year after the surgery. In fusion rate at the osteotomized SP site, the SP splitting technique was superior to the SP base osteotomy technique. These slides can be retrieved under Electronic Supplementary Material.

Outcomes of multisegmental transforaminal enlarged decompression plus posterior pedicle screw fixation for multilevel lumbar spinal canal stenosis associated with lumbar instability

PURPOSE

The aim of this study was to evaluate the clinical and radiologic results of multisegmental transforaminal enlarged decompression (TED) plus posterior pedicle screw fixation in the treatment of multilevel lumbar spinal canal stenosis (LSCS) with lumbar instability (MLSCSI).

METHODS

113 patients with MLSCSI underwent surgery were recruited in this study. All patients were suffering from symptoms typical of degenerative LSCS and treated with either TED plus fusion (TEDF group) or conventional laminectomy plus fusion (CLF group). Clinical and radiologic parameters were evaluated. The clinical data, including Visual Analog Scale (VAS) for back and leg pain, Oswestry Disability Index (ODI), operative time, intraoperative blood loss, postoperative drainage, hospital stay, and the rate of postoperative complications, were assessed. With respect to radiologic parameters, mean disc height (MDH) and lumbar lordotic angle (LLA) were measured using plain radiographs. Patient satisfaction was evaluated according to the North American Spine Society (NASS) Outcome Questionnaire.

RESULTS

No serious complications occurred during the follow-up. The operative time was significantly shorter for TEDF group than for CLF group, and similar results were found with regard to the blood loss and postoperative drainage (p < .05). The improvements in ODI, leg and back VAS scores were observed in both groups after surgery and follow-up (P < .05). In the last follow-up, ODI and back VAS scores in TEDF group were significantly higher than those in CLF group (P < .05). Regarding radiologic variants, MDH and LLA were improved after operation for 3 months (P > .05) and were all well maintained in the final follow-up in both groups. Patients in TEDF group were more satisfied than patients in the CLF group (85.2% vs 76.9%, p = .092).

CONCLUSIONS

Satisfactory clinical and radiological outcomes can be achieved with the use of multisegmental TED plus lumbar fusion for the treatment of MLSCSI. This technique can reduce surgically induced instability and obviously improve the symptoms and signs of the patients, suggesting a safe and effective therapeutic procedure for MLSCSI.

Biomechanical analysis of lumbar decompression surgery in relation to degenerative changes in the lumbar spine - Validated finite element analysis

BACKGROUND

There are no studies about the biomechanical analysis of lumbar decompression surgery in relation to degenerative changes of the lumbar spine. Therefore, the purpose of this study was to compare, by using finite element (FE) analysis, the biomechanical changes of the lumbar spine in terms of annulus stress and nucleus pressure after two different kinds of lumbar decompression surgery in relation to disc degenerative changes.

METHODS

The validated intact and degenerated FE models (L2-5) were used in this study. In these two models, two different decompression surgical scenarios at L3-4, including conventional laminectomy (ConLa) and the spinous process osteotomy (SpinO), were simulated. Therefore, a total of six models were simulated. Under preloading, 7.5 Nm moments of flexion, extension, lateral bending, and torsion were imposed. In each model, the maximal von Mises stress on the annulus fibrosus and nucleus pressure at the index segment (L3-4) and adjacent segments (L2-3 and L4-5) were analyzed.

RESULTS

The ConLa model and disc degeneration model demonstrated a larger annulus stress at the decompression level (L3-4) under all four moments than were seen in the SpinO model and healthy disc model, respectively. Therefore, the ConLa model with moderate disc degeneration showed the highest annulus stress at the decompression level (L3-4). However, the percent change of annulus stress at L3-4 from the intact model to the matched decompression model was less in the moderate disc degeneration model than in the healthy disc model.

CONCLUSIONS

Although the ConLa model with moderate disc degeneration showed the highest annulus stress, the degenerative models would be less influenced by the decompression technique.

Improving the Process of Adjusting the Parameters of Finite Element Models of Healthy Human Intervertebral Discs by the Multi-Response Surface Method

The kinematic behavior of models that are based on the finite element method (FEM) for modeling the human body depends greatly on an accurate estimate of the parameters that define such models. This task is complex, and any small difference between the actual biomaterial model and the simulation model based on FEM can be amplified enormously in the presence of nonlinearities. The current paper attempts to demonstrate how a combination of the FEM and the MRS methods with desirability functions can be used to obtain the material parameters that are most appropriate for use in defining the behavior of Finite Element (FE) models of the healthy human lumbar intervertebral disc (IVD). The FE model parameters were adjusted on the basis of experimental data from selected standard tests (compression, flexion, extension, shear, lateral bending, and torsion) and were developed as follows: First, three-dimensional parameterized FE models were generated on the basis of the mentioned standard tests. Then, 11 parameters were selected to define the proposed parameterized FE models. For each of the standard tests, regression models were generated using MRS to model the six stiffness and nine bulges of the healthy IVD models that were created by changing the parameters of the FE models. The optimal combination of the 11 parameters was based on three different adjustment criteria. The latter, in turn, were based on the combination of stiffness and bulges that were obtained from the standard test FE simulations. The first adjustment criteria considered stiffness and bulges to be equally important in the adjustment of FE model parameters. The second adjustment criteria considered stiffness as most important, whereas the third considered the bulges to be most important. The proposed adjustment methods were applied to a medium-sized human IVD that corresponded to the L3–L4 lumbar level with standard dimensions of width = 50 mm, depth = 35 mm, and height = 10 mm. Agreement between the kinematic behavior that was obtained with the optimized parameters and that obtained from the literature demonstrated that the proposed method is a powerful tool with which to adjust healthy IVD FE models when there are many parameters, stiffnesses, and bulges to which the models must adjust.