Biomechanical comparison of different prosthetic reconstructions in total en bloc spondylectomy: a finite element study

Finite element analysis of additive manufactured porous peek artificial vertebral bodies in lumbar total en bloc spondylectomy

BACKGROUND

Lumbar total en bloc spondylectomy and internal fixation allows the removal of spinal tumors and the reconstruction of spinal stability. However, postoperative internal fixation failure due to unmatched spinal biomechanics remains obscure.

PURPOSE

This study aimed to assess the biomechanical characteristics of additive manufactured (AM) porous polyetheretherketone (PEEK) artificial vertebral body for total en bloc spondylectomy and internal fixation.

STUDY DESIGN/SETTING

Comparative finite element (FE) study.

METHODS

We created porous artificial vertebral bodies using medical-grade PEEK filaments and fused deposition modeling (FDM) technology, and evaluated the mechanical properties of the solid and porous implants. A finite element model of intact L1-L5 was created to analyze biomechanical characteristics of 5 operative constructs for reconstructing the lumbar anterior column. The lumbar anterior column was reconstructed using a titanium alloy mesh and bone graft (Ti+B) and AM PEEK artificial vertebral bodies with solid or porous structures. The maximum von Mises stresses of implants and adjacent structures were analyzed and compared under physiological conditions.

RESULTS

AM PEEK artificial vertebral bodies reduced von Mises stress on the artificial vertebral body, adjacent vertebral bodies, and intervertebral discs. The AM porous PEEK artificial vertebral body (PEEK-500) exhibited the lowest von Mises stress of the artificial vertebral body, adjacent vertebral bodies, and intervertebral discs.

CONCLUSIONS

Ti+B increased the maximum stress on adjacent vertebral bodies, suggesting that it has the potential for mesh subsidence. Moreover, PEEK-500 had minimal impact on the internal implants and adjacent structures. This indicated that the lumbar anterior column reconstructed with AM porous PEEK artificial vertebral bodies may decrease the risk of postoperative internal fixation failure and adjacent segment degeneration.

CLINICAL SIGNIFICANCE

Manufactured porous PEEK artificial vertebral bodies demonstrated a minimal impact on both the internal implants and adjacent structures. This suggests that reconstructing the lumbar anterior column with AM porous PEEK artificial vertebral bodies can decrease the risk of postoperative internal fixation failure and adjacent segments degeneration.

Biomechanical Effects of Different Spacing Distributions Between the Cemented Superior Boundary and Surgical Vertebral Superior Endplates After Percutaneous Vertebroplasty for Osteoporotic Vertebral Compression Fractures: A Three-Dimensional Finite Element Analysis

OBJECTIVE

Patients with osteoporotic vertebral compression fractures (OVCF) treated with vertebroplasty (PVP) are experiencing an increasing number of problems such as pain recurrence, mainly due to recompression fractures of the operated vertebral body within a certain period of time after the operation, which is closely related to the distribution of intraoperative bone cement. The aim of this study is to investigate the effect of different spacing distributions between the upper boundary of the cement and the upper endplate of the operated vertebra on the biomechanics of the operated vertebra after percutaneous vertebroplasty for OVCF using finite element analysis (FEA).

METHODS

One patient with L1 vertebral body OVCF was selected, and computed tomography (CT) of the thoracolumbar segment was performed. The CT data were extracted to establish an FEA model of the T12-L2 vertebral bodies. Bone cement was injected into the L1 vertebral body. Based on the spacing between the upper boundary of the bone cement and the vertebral body's upper endplates, the model vertebrae were divided into 0, 2, 4, and 6 mm spacing groups, and the human body's upright, flexion-extension, lateral flexion, and rotational positions were simulated. The biomechanical effects of different spacing distributions on the postoperative L1 vertebral body and the injected bone cement were evaluated.

RESULTS

In this paper, we found that the Von Mises stress of the L1 vertebrae was the smallest when the spacing between the upper boundary of the bone cement and the vertebral body's upper endplates was 0 mm. The larger the spacing in a certain range between the upper boundary of the bone cement and the vertebral body's upper endplates, the greater the Von Mises stress of the L1 vertebrae. However, in the stress comparison of the injected bone cement, the Von Mises stress of the bone cement was greatest when the spacing between the upper boundary of the bone cement and the upper endplate of the vertebral body was 0 mm; the larger the spacing, the smaller the Von Mises stress.

CONCLUSION

When the contact spacing between the upper boundary of the bone cement and the upper endplate of the vertebral body is 0 mm, it can effectively eliminate and transfer the pressure caused by the load, thus reducing the stress on the cancellous bone and further reducing the risk of vertebral refracture after surgery.

Comparison of Single or Double Titanium Mesh Cage for Anterior Reconstruction After Total En Bloc Spondylectomy for Thoracic and Lumbar Spinal Tumors

OBJECTIVE

To compare the clinical efficacy of anterior column reconstruction using single or double titanium mesh cage (TMC) after total en bloc spondylectomy (TES) of thoracic and lumbar spinal tumors.

METHODS

A retrospective cohort study was performed involving 39 patients with thoracic or lumbar spinal tumors. All patients underwent TES, followed by anterior reconstruction and screw-rod instrumentation via a posterior-only procedure. Twenty-two patients in group A were treated with a single TMC to reconstruct the anterior column, whereas 17 patients in group B were reconstructed with double TMCs.

RESULTS

The overall follow-up is 20.5 ± 4.6 months. There is no significant difference between the 2 groups regarding age, sex, body mass index, tumor location, operative time, and intraoperative blood loss. The time for TMC placement was significantly shortened in the double TMCs group (5.2 ± 1.3 minutes vs. 15.6 ± 3.3 minutes, p = 0.004). Additionally, postoperative neural complications were significantly reduced with double TMCs (5/22 vs. 0/17, p = 0.046). The kyphotic Cobb angle and mean intervertebral height were significantly corrected in both groups (p ≤ 0.001), without obvious loss of correction at the last follow-up in either group. The bone fusion rates for single TMC and double TMCs were 77.3% and 76.5%, respectively.

CONCLUSION

Using 2 smaller TMCs instead of a single large one eases the placement of TMC by shortening the time and avoiding nerve impingement. Anterior column reconstruction with double TMC is a clinically feasible, and safe alternative following TES for thoracic and lumbar tumors.

Surgical outcomes and risk factors for surgical complications after en bloc resection following reconstruction with 3D-printed artificial vertebral body for thoracolumbar tumors

BACKGROUND

The outcomes of patients with tumors of the thoracolumbar spine treated with en bloc resection (EBR) using three-dimensional (3D)-printed endoprostheses are underreported.

METHODS

We retrospectively evaluated patients with thoracolumbar tumors who underwent surgery at our institution. Logistic regression analysis was performed to identify the potential risk factors for surgical complications. Nomograms to predict complications were constructed and validated.

RESULTS

A total of 53 patients with spinal tumors underwent EBR at our hospital; of these, 2 were lost to follow-up, 45 underwent total en bloc spondylectomy, and 6 were treated with sagittal en bloc spondylectomy. The anterior reconstruction materials included a customized 3D-printed artificial vertebral body (AVB) in 10 cases and an off-the-shelf 3D-printed AVB in 41 cases, and prosthesis mismatch occurred in 2 patients reconstructed with the off-the-shelf 3D-printed AVB. The median follow-up period was 21 months (range, 7-57 months). Three patients experienced local recurrence, and 5 patients died at the final follow-up. A total of 50 perioperative complications were encountered in 29 patients, including 25 major and 25 minor complications. Instrumentation failure occurred in 1 patient, and no prosthesis subsidence was observed. Using a combined surgical approach was a dependent predictor of overall complications, while Karnofsky performance status score, lumbar spine lesion, and intraoperative blood loss ≥ 2000 mL were predictors of major complications. Nomograms for the overall and major complications were constructed using these factors, with C-indices of 0.850 and 0.891, respectively.

CONCLUSIONS

EBR is essential for the management of thoracolumbar tumors; however, EBR has a steep learning curve and a high complication rate. A 3D-printed AVB is an effective and feasible reconstruction option for patients treated with EBR.

Biomechanical behaviour of a novel bone cement screw in the minimally invasive treatment of Kummell's disease: a finite element study

OBJECTIVE

To investigate and evaluate the biomechanical behaviour of a novel bone cement screw in the minimally invasive treatment of Kummell's disease (KD) by finite element (FE) analysis.

METHODS

A validated finite element model of healthy adult thoracolumbar vertebrae T12-L2 was given the osteoporotic material properties and the part of the middle bone tissue of the L1 vertebral body was removed to make it wedge-shaped. Based on these, FE model of KD was established. The FE model of KD was repaired and treated with three options: pure percutaneous vertebroplasty (Model A), novel unilateral cement screw placement (Model B), novel bilateral cement screw placement (Model C). Range of motion (ROM), maximum Von-Mises stress of T12 inferior endplate and bone cement, relative displacement of bone cement, and stress distribution of bone cement screws of three postoperative models and intact model in flexion and extension, as well as lateral bending and rotation were analyzed and compared.

RESULTS

The relative displacements of bone cement of Model B and C were similar in all actions studied, and both were smaller than that of Model A. The minimum value of relative displacement of bone cement is 0.0733 mm in the right axial rotation of Model B. The maximum Von-Mises stress in T12 lower endplate and bone cement was in Model C. The maximum Von-Mises stress of bone cement screws in Model C was less than that in Model B, and it was the most substantial in right axial rotation, which is 34%. There was no substantial difference in ROM of the three models.

CONCLUSION

The novel bone cement screw can effectively reduce the relative displacement of bone cement by improving the stability of local cement. Among them, novel unilateral cement screw placement can obtain better fixation effect, and the impact on the biomechanical environment of vertebral body is less than that of novel bilateral cement screw placement, which provides a reference for minimally invasive treatment of KD in clinical practice.

A novel artificial vertebral implant with Gyroid porous structures for reducing the subsidence and mechanical failure rate after vertebral body replacement

BACKGROUND

Prosthesis subsidence and mechanical failure were considered significant threats after vertebral body replacement during the long-term follow-up. Therefore, improving and optimizing the structure of vertebral substitutes for exceptional performance has become a pivotal challenge in spinal reconstruction.

METHODS

The study aimed to develop a novel artificial vertebral implant (AVI) with triply periodic minimal surface Gyroid porous structures to enhance the safety and stability of prostheses. The biomechanical performance of AVIs under different loading conditions was analyzed using the finite element method. These implants were fabricated using selective laser melting technology and evaluated through static compression and subsidence experiments.

RESULTS

The results demonstrated that the peak stress in the Gyroid porous AVI was consistently lower than that in the traditional porous AVI under all loading conditions, with a maximum reduction of 73.4%. Additionally, it effectively reduced peak stress at the bone-implant interface of the vertebrae. Static compression experiments demonstrated that the Gyroid porous AVI was about 1.63 times to traditional porous AVI in terms of the maximum compression load, indicating that Gyroid porous AVI could meet the safety requirement. Furthermore, static subsidence experiments revealed that the subsidence tendency of Gyroid porous AVI in polyurethane foam (simulated cancellous bone) was approximately 15.7% lower than that of traditional porous AVI.

CONCLUSIONS

The Gyroid porous AVI exhibited higher compressive strength and lower subsidence tendency than the strut-based traditional porous AVI, indicating it may be a promising substitute for spinal reconstruction.

Comparison of anterior column reconstruction techniques after en bloc spondylectomy: a finite element study

Total en bloc spondylectomy (TES) effectively treats spinal tumors. The surgery requires a vertebral body replacement (VBR), for which several solutions were developed, whereas the biomechanical differences between these devices still need to be completely understood. This study aimed to compare a femur graft, a polyetheretherketone implant (PEEK-IMP-C), a titan mesh cage (MESH-C), and a polymethylmethacrylate replacement (PMMA-C) using a finite element model of the lumbar spine after a TES of L3. Several biomechanical parameters (rotational stiffness, segmental range of motion (ROM), and von Mises stress) were assessed to compare the VBRs. All models provided adequate initial stability by increasing the rotational stiffness and decreasing the ROM between L2 and L4. The PMMA-C had the highest stiffness for flexion-extension, lateral bending, and axial rotation (215%, 216%, and 170% of intact model), and it had the lowest segmental ROM in the instrumented segment (0.2°, 0.5°, and 0.7°, respectively). Maximum endplate stress was similar for PMMA-C and PEEK-IMP-C but lower for both compared to MESH-C across all loading directions. These results suggest that PMMA-C had similar or better primary spinal stability than other VBRs, which may be related to the larger contact surface and the potential to adapt to the patient's anatomy.

Biomechanical analysis of sandwich vertebrae in osteoporotic patients: finite element analysis

Objective

The aim of this study was to investigate the biomechanical stress of sandwich vertebrae (SVs) and common adjacent vertebrae in different degrees of spinal mobility in daily life.

Materials and methods

A finite element model of the spinal segment of T10-L2 was developed and validated. Simultaneously, T11 and L1 fractures were simulated, and a 6-ml bone cement was constructed in their center. Under the condition of applying a 500-N axial load to the upper surface of T10 and immobilizing the lower surface of L2, moments were applied to the upper surface of T10, T11, T12, L1, and L2 and divided into five groups: M-T10, M-T11, M-T12, M-L1, and M-L2. The maximum von Mises stress of T10, T12, and L2 in different groups was calculated and analyzed.

Results

The maximum von Mises stress of T10 in the M-T10 group was 30.68 MPa, 36.13 MPa, 34.27 MPa, 33.43 MPa, 26.86 MPa, and 27.70 MPa greater than the maximum stress value of T10 in the other groups in six directions of load flexion, extension, left and right lateral bending, and left and right rotation, respectively. The T12 stress value in the M-T12 group was 29.62 MPa, 32.63 MPa, 30.03 MPa, 31.25 MPa, 26.38 MPa, and 26.25 MPa greater than the T12 stress value in the other groups in six directions. The maximum stress of L2 in M-T12 in the M-L2 group was 25.48 MPa, 36.38 MPa, 31.99 MPa, 31.07 MPa, 30.36 MPa, and 32.07 MPa, which was greater than the stress value of L2 in the other groups. When the load is on which vertebral body, it is subjected to the greatest stress.

Conclusion

We found that SVs did not always experience the highest stress. The most stressed vertebrae vary with the degree of curvature of the spine. Patients should be encouraged to avoid the same spinal curvature posture for a long time in life and work or to wear a spinal brace for protection after surgery, which can avoid long-term overload on a specific spine and disrupt its blood supply, resulting in more severe loss of spinal quality and increasing the possibility of fractures.

Biomechanical effects of transverse connectors on total en bloc spondylectomy of the lumbar spine: a finite element analysis

BACKGROUND

The influence of total en bloc spondylectomy (TES) on spinal stability is substantial, necessitating strong fixation to restore spinal stability. The transverse connector (TC) serves as a posterior spinal instrumentation that connects the left and right sides of the pedicle screw-rod system. Several studies have highlighted the potential of a TC in enhancing the stability of the fixed segments. However, contradictory results have suggested that a TC not only fails to improve the stability of the fixed segments but also might promote stress associated with internal fixation. To date, there is a lack of previous research investigating the biomechanical effects of a TC on TES. This study aimed to investigate the biomechanical effects of a TC on internal fixation during TES of the lumbar (L) spine.

METHODS

A single-segment (L3 segment) TES was simulated using a comprehensive L spine finite element model. Five models were constructed based on the various positions of the TC, namely the intact model (L1-sacrum), the TES model without a TC, the TES model with a TC at L1-2, the TES model with a TC at L2-4, and the TES model with a TC at L4-5. Mechanical analysis of these distinct models was conducted using the Abaqus software to assess the variations in the biomechanics of the pedicle screw-rod system, titanium cage, and adjacent endplates.

RESULTS

The stability of the surgical segments was found to be satisfactory across all models. Compared with the complete model, the internal fixation device exhibited the greatest constraint on overextension (95.2-95.6%), while showing the least limitation on left/right rotation (53.62-55.64%). The application of the TC had minimal effect on the stability of the fixed segments, resulting in a maximum reduction in segment mobility of 0.11° and a variation range of 3.29%. Regardless of the use of a TC, no significant changes in stress were observed for the titanium cage. In the model without the TC, the maximum von Mises stress (VMS) for the pedicle screw-rod system reached 136.9 MPa during anterior flexion. Upon the addition of a TC, the maximum VMS of the pedicle screw-rod system increased to varying degrees. The highest recorded VMS was 459.3 MPa, indicating a stress increase of 335.5%. Following the TC implantation, the stress on the adjacent endplate exhibited a partial reduction, with the maximum stress reduced by 27.6%.

CONCLUSION

The use of a TC in TES does not improve the stability of the fixed segments and instead might result in increased stress concentration within the internal fixation devices. Based on these findings, the routine utilisation of TC in TES is deemed unnecessary.

Combining Virtual Surgical Planning and Patient-Specific 3D-Printing as a Solution to Complex Spinal Revision Surgery

With the advent of three-dimensional printing, rapid growth in the field and application in spinal and orthopedic surgery has been seen. This technology is now being applied in creating patient-specific implants, as it offers benefits over the generic alternative, with growing literature supporting this. This report details a unique application of virtual surgical planning and manufacture of a personalized implant in a case of cervical disc replacement failure with severe osteolysis and resultant hypermobility. Where this degree of degenerative bone loss would often necessitate a vertebrectomy to be performed, this case highlights the considerable customizability of 3D-printed patient-specific implants to contour to the bony defects, allowing for a smaller and safer operation, with the achievement of stability as early as 3 months after the procedure, by the presence of osseointegration. With increasing developments in virtual planning technology and 3D printing ability, the future of complex spinal revision surgery may adopt these technologies as it affords the patient a faster, safer, and less invasive and destructive procedure.