The Effectiveness of Percutaneous Vertebroplasty Is Determined by the Patient-Specific Bone Condition and the Treatment Strategy

In silico medical device testing of anatomically and mechanically conforming patient-specific spinal fusion cages designed by full-scale topology optimisation

A full-scale topology optimisation formulation has been developed to automate the design of cages used in instrumented transforaminal lumbar interbody fusion. The method incorporates the mechanical response of the adjacent bone structures in the optimisation process, yielding patient-specific spinal fusion cages that both anatomically and mechanically conform to the patient, effectively mitigating subsidence risk compared to generic, off-the-shelf cages and patient-specific devices. In this study, in silico medical device testing on a cohort of seven patients was performed to investigate the effectiveness of the anatomically and mechanically conforming devices using titanium and PEEK implant materials. A median reduction in the subsidence risk by 89% for titanium and 94% for PEEK implant materials was demonstrated compared to an off-the-shelf implant. A median reduction of 75% was achieved for a PEEK implant material compared to an anatomically conforming implant. A credibility assessment of the computational model used to predict the subsidence risk was provided according to the ASME V&V40-2018 standard.

Static study and numerical simulation of the influence of cement distribution in the upper and lower adjacent vertebrae on sandwich vertebrae in osteoporotic patients: Finite element analysis

Objective

We analyzed the influence of the location of the upper and lower cement on the sandwich vertebrae (SV) by computer finite element analysis.

Materials and Methods

A finite element model of the spinal segment of T11-L1 was constructed and 6 mL of cement was built into T11 and L1 simultaneously. According to the various distributions of bone cement at T11 and L1, the following four groups were formed: (i) Group B-B: bilateral bone cement reinforcement in both T11 and L1 vertebral bodies; (ii) Group L-B: left unilateral reinforcement in T11 and bilateral reinforcement in L1; (iii) Group L-R: unilateral cement reinforcement in both T11 and L1 (cross); (iv) Group L-L: unilateral cement reinforcement in both T11 and L1 (ipsilateral side). The maximum von Mises stress (VMS) and maximum displacement of the SV and intervertebral discs were compared and analyzed.

Results

The maximum VMS of T12 was in the order of size: group B-B < L-B < L-R < L-L. Group B-B showed the lowest maximum VMS values for T12: 19.13, 18.86, 25.17, 25.01, 19.24, and 20.08 MPa in six directions of load flexion, extension, left and right lateral bending, and left and right rotation, respectively, while group L-L was the largest VMS in each group, with the maximum VMS in six directions of 21.55, 21.54, 30.17, 28.33, 19.88, and 25.27 MPa, respectively.

Conclusion

Compared with the uneven distribution of bone cement in the upper and lower adjacent vertebrae (ULAV), the uniform distribution of bone cement in the ULAV reduced and uniformed the stress load on the SV and intervertebral disc. Theoretically, it can lead to the lowest incidence of sandwich vertebral fracture and the slowest rate of intervertebral disc degeneration.

Biomechanical study of different bone cement distribution on osteoporotic vertebral compression Fracture-A finite element analysis

Purpose

This study aimed to compare the biomechanical effects of different bone cement distribution methods on osteoporotic vertebral compression fractures (OVCF).

Patients and methods

Raw CT data from a healthy male volunteer was used to create a finite element model of the T12-L2 vertebra using finite element software. A compression fracture was simulated in the L1 vertebra, and two forms of bone cement dispersion (integration group, IG, and separation group, SG) were also simulated. Six types of loading (flexion, extension, left/right bending, and left/right rotation) were applied to the models, and the stress distribution in the vertebra and intervertebral discs was observed. Additionally, the maximum displacement of the L1 vertebra was evaluated.

Results

Bone cement injection significantly reduced stress following L1 vertebral fractures. In the L1 vertebral body, the maximum stress of SG was lower than that of IG during flexion, left/right bending, and left/right rotation. In the T12 vertebral body, compared with IG, the maximum stress of SG decreased during flexion and right rotation. In the L2 vertebral body, the maximum stress of SG was the lowest under all loading conditions. In the T12-L1 intervertebral disc, compared with IG, the maximum stress of SG decreased during flexion, extension, and left/right bending and was basically the same during left/right rotation. However, in the L1-L2 intervertebral discs, the maximum stress of SG increased during left/right rotation compared with that of IG. Furthermore, the maximum displacement of SG was smaller than that of IG in the L1 vertebral bodies under all loading conditions.

Conclusions

SG can reduce the maximum stress in the vertebra and intervertebral discs, offering better biomechanical performance and improved stability than IG.

Three generations of treatments for osteoporotic vertebral fractures: what is the evidence?

The management of vertebral compression fractures (VCFs) is based on conservative treatment and minimally invasive vertebral augmentation procedures. However, the role of vertebral augmentation is now being questioned by clinical trials and extensive studies. The aim of this review is to report the most relevant evidences on effectiveness, safety, and indications of the currently available vertebral augmentation techniques. Conservative treatment with bracing is effective in reducing acute but it has no effect on segmental kyphosis progression and pseudoarthrosis can occur. Percutaneous vertebroplasty (PV) was the first vertebral augmentation technique to be proposed for the treatment of VCFs. Two blinded and randomized clinical trials compared PV to a sham procedure and no significant differences in terms of efficacy were reported. More recent studies have suggested that PV can still benefit patients with acute VCFs and severe pain at onset. Balloon kyphoplasty (BK) was developed to improve the segmental alignment restoring the height of collapsed vertebrae. BK allows similar pain relief and disability improvement, as well as greater kyphosis correction compared to PV, moreover BKP seems to reduce cement leakage. Vertebral body stenting (VBS) and the KIVA system are third generation techniques of vertebral augmentation. VBS aims to increase the effectiveness in restoring the segmental alignment, while the KIVA system can prevent cement leakage. These techniques are effective and safe, even if their superiority to BK has yet to be proven by studies with a high level of evidence.

Patient-specific numerical investigation of the correction of cervical kyphotic deformity based on a retrospective clinical case

Little research has been reported on evaluating the safety of the fixation construct in cervical kyphosis correction. In this study, we proposed a principal-strain criterion to evaluate the safety of the fixation construct and validated the modeling method against a retrospective case of anterior cervical discectomy fusion (ACDF). From C2 to T2 vertebra bodies, fixation instruments were reconstructed and positioned as per postoperative computed tomography (CT) scans. Head weight (HW) and various moments estimated from isometric strength data were imposed onto the C2. The postoperative stability of non-surgical segments, deformations surrounding the screw trajectories, and contact slipping on zygapophysial joints were analyzed. The model was validated against the reality that the patient had a good fusion and deformity correction. The ACDF restricted the range of motions (ROMs) of cervical segments and lent stability to vertebra fusion, no failure was found in the finite element (FE) model of cervical vertebrae. The deformation surrounding the screw trajectories were concentrated to the lateral sides of trajectories, recommending that the shape of the anterior cervical plate conforming to the curvature of the vertebra and screws fully inserted into vertebrae reduced the deformation concentration around the screw trajectories.

Biomechanical comparison between unilateral and bilateral percutaneous vertebroplasty for osteoporotic vertebral compression fractures: A finite element analysis

Background and objective: The osteoporotic vertebral compression fracture (OVCF) has an incidence of 7.8/1000 person-years at 55–65 years. At 75 years or older, the incidence increases to 19.6/1000 person-years in females and 5.2–9.3/1000 person-years in males. To solve this problem, percutaneous vertebroplasty (PVP) was developed in recent years and has been widely used in clinical practice to treat OVCF. Are the clinical effects of unilateral percutaneous vertebroplasty (UPVP) and bilateral percutaneous vertebroplasty (BPVP) the same? The purpose of this study was to compare biomechanical differences between UPVP and BPVP using finite element analysis.

Materials and methods: The heterogeneous assignment finite element (FE) model of T11-L1 was constructed and validated. A compression fracture of the vertebral body was performed at T12. UPVP and BPVP were simulated by the difference in the distribution of bone cement in T12. Stress distributions and maximum von Mises stresses of vertebrae and intervertebral discs were compared. The rate of change of maximum displacement between UPVP and BPVP was evaluated.

Results: There were no obvious high-stress concentration regions on the anterior and middle columns of the T12 vertebral body in BPVP. Compared with UPVP, the maximum stress on T11 in BPVP was lower under left/right lateral bending, and the maximum stress on L1 was lower under all loading conditions. For the T12-L1 intervertebral disc, the maximum stress of BPVP was less than that of UPVP. The maximum displacement of T12 after BPVP was less than that after UPVP under the six loading conditions.

Conclusion: BPVP could balance the stress of the vertebral body, reduce the maximum stress of the intervertebral disc, and offer advantages in terms of stability compared with UPVP. In summary, BPVP could reduce the incidence of postoperative complications and provide promising clinical effects for patients.

The Correlation Between the Diffusion Coefficient of Bone Cement and Efficacy in Percutaneous Vertebroplasty

This study investigated the effect of bone mineral density (BMD) on the diffusion coefficient (DC) of bone cement in percutaneous vertebroplasty (PVP) and the correlation between the DC and the efficacy after PVP. This was a retrospective study of PVP cases with follow-up longer than 12 months. The cases were assigned to 3 groups according to the BMD: BMD decrease group, osteoporosis group, and severe osteoporosis group. The 3 groups were compared regarding bone cement injection volume (IV), diffusion volume (DV), DC, visual analog scale (VAS) score, Oswestry Disability Index (ODI) score, and vertebral height loss ratio (VHLR). The correlation between DC and BMD, IV, DV, and VHLR was analyzed. The least significant difference test was used for comparison among the 3 groups, and the Pearson correlation coefficient was used for correlation analysis. There were a total of 132 cases, including 34 males and 98 females with a mean age of 76.5±9.6 years. The DV was larger than the IV in each group (P<.05). There was no statistically significant difference in the IV, VAS score, and ODI among the 3 groups (P>.05). However, there were significant differences in the DC and VHLR among the 3 groups (P<.05). Correlation analysis showed that there were significant correlations between BMD and IV (-0.716), BMD and DC (0.754), IV and DV (0.502), and IV and DC (-0.666) (P<.01). Scatter plot showed that the correlation between IV and BMD was r=0.716, R²=0.513, and the correlation between DC and BMD was r=0.754, R²=0.568. The DV was larger than the IV in PVP, and BMD was closely related to the DC. The higher the BMD, the higher the DC. Short-term follow-up revealed that the DC was inversely proportional to the VHLR. [Orthopedics. 2021;44(1):e95-e100.].

Cement Leakage in Percutaneous Vertebroplasty for Multiple Osteoporotic Vertebral Compression Fractures: A Prospective Cohort Study

Purpose

This study аims to explore cement leаkаge аs а complication of percutаneous vertebroplаsty (PVP) in the treаtment of multiple osteoporotic vertebrаl compression frаctures (MOVF).

Patients and Methods

This prospective study wаs cаrried out on 32 consecutive pаtients with osteoporotic frаctures of аt leаst two vertebrаe (VB). Аll pаtients were over 50 yeаrs old аnd women аccounted for 29 out of the 32 pаtients (90.6%). PVP wаs performed under digitаl subtrаction аngiogrаphy (DSА) of аt leаst three VB, аnd 97 collаpsed VB аnd 105 VB were exаmined by PVP. Аll pаtients hаd postoperаtive computerized tomogrаphy (CT) to diаgnose аnd clаssify the complicаtions.

Results

One hundred аnd five vertebrаe were exаmined with PVP, аnd 36/105 (34.3%) exhibited complicаtions of cement leаkаge. Type B cement leаkаge wаs the most common complicаtion, with 19/105 (18.1%) cаses; type C аccounted for 8/105 (7.6%) cаses; аnd type S аccounted for 9/105 (8.6%) cаses. There wаs only one (0.95%) cаse of cement leаkаge moving to the pulmonаry аrtery. Аll complicаtions hаd no clinicаl symptoms аnd did not require treаtment.

Conclusion

Cement leаkаge is quite а common complicаtion, but it usuаlly hаs no clinicаl symptoms аnd does not require treаtment. Therefore, PVP is а sаfe аnd successful technique for the treаtment of multiple osteoporotic vertebrаl compression frаctures.

The Optimal Volume Fraction in Percutaneous Vertebroplasty Evaluated by Pain Relief, Cement Dispersion, and Cement Leakage: A Prospective Cohort Study of 130 Patients with Painful Osteoporotic Vertebral Compression Fracture in the Thoracolumbar Vertebra

OBJECTIVE

To probe the relationship among cement volume/fraction, imaging features of cement distribution, and pain relief and then to evaluate the optimal volume during percutaneous vertebroplasty.

METHODS

From January 2014 to January 2017, a total of 130 patients eligible for inclusion criteria were enrolled in this prospective cohort study. According to the different degrees of pain relief, cement leakage, and cement distribution, all patients were allocated to 2 groups. Clinical and radiologic characteristics were assessed to identify independent factors influencing pain relief, cement leakage, and cement distribution, including age, sex, fracture age, bone mineral density, operation time, fracture level, fracture type, modified semiquantitative severity grade, intravertebral cleft, cortical disruption in the vertebral wall, endplate disruption, type of nutrient foramen, fractured vertebral body volume, intravertebral cement volume, and volume fraction. A receiver operating characteristic curve was used to analyze the diagnostic value of the cement volume/fraction and then to obtain the optional cut-off value.

RESULTS

The preoperative visual analog scale scores in the responders versus nonresponders patient groups were 7.37 ± 0.61 versus 7.87 ± 0.92 and the postoperative VAS scores in the responders versus nonresponders were 2.04 ± 0.61 versus 4.33 ± 0.49 at 1 week. There were no independent factors influencing pain relief. There were 95 (73.08%) patients who experienced cement leakage, and cortical disruption in the vertebral wall and cement fraction percentage were identified as independent risk factors by binary logistic regression analysis (adjusted odds ratio [OR] 2.935, 95% confidence interval [95% CI] 1.214-7.092, P = 0.017); (adjusted OR 1.134, 95% CI 1.026-1.254, P = 0.014). The area under the receiver-operating characteristic curve of volume fraction (VF%) was 0.658 (95% CI 0.549-0.768, P = 0.006 < 0.05). The cut-off value of VF% for cement leakage was 21.545%, with a sensitivity of 69.50% and a specificity of 60.00%. The incidence of favorable cement distribution was 74.62% (97/130), and VF% were identified as independent protective factors (adjusted OR 1.185, 95% CI 1.067-1.317, P = 0.002) The area under the receiver-operating characteristic curve of VF% was 0.686 (95% CI 0.571-0.802, P = 0.001 < 0.05). The cut-off value of VF% to reach a favorable cement distribution was 19.78%, with a sensitivity of 86.60% and a specificity of 51.50%.

CONCLUSIONS

In osteoporotic vertebral compression fracture with mild/moderate fracture severity at the single thoracolumbar level, the intravertebral cement volume of 4-6 mL could relieve pain rapidly. The optimal VF% was 19.78%, which could achieve satisfactory cement distribution. With the increase of VF%, the incidence of cement leakage would also increase.

Numerical investigation of the effect of bone cement porosity on osteoporotic femoral augmentation

Femoroplasty is the injection of bone cement into the proximal femur, enhances the bone load capacity, and is typically applied to osteoporotic femora. To minimize the required injected volume of bone cement and maximize the load capacity enhancement, an optimization problem must be solved, where the modulus of elasticity of the augmented bone is a key element. This paper, through the numerical investigation of a fall on the greater trochanter of an osteoporotic femur, compares different ways to calculate this modulus and introduces an approach, based on the concept of bone cement porosity, which provides results statistically similar to those obtained with other considerations. Based on this approach, the present paper quantifies the correlation between degree of osteoporosis and optimum volume of bone cement. It concludes with an exhaustive search that reveals the effect of the bone cement porosity on the optimum volume of PMMA, for various combinations of the frontal and transverse angles of the fall on the greater trochanter.

Preparation and characterization of injectable PMMA-strontium-substituted bioactive glass bone cement composites

In most minimally-invasive procedures used to address severe pain arising from compression fractures of the vertebral bodies, such as percutaneous vertebroplasty (PVP), a poly(methyl methacrylate) (PMMA) bone cement is used. Shortcomings of this type of cement, such as high exotherm temperature and lack of bioactivity, are well known. We prepared different formulations of a composite bone cement, whose solid constituents consisted of PMMA beads and particles of a bioactive glass (BG), where 0-20%(w/w) of the calcium component was substituted by strontium. The difference between the formulations was in the relative amounts of the solid phase constituents and in the Sr-content of BG. We determined the influence of the mixture of solid phase constituents of the cement formulation on a collection of properties, such as maximum exotherm temperature (T_max ), setting time (t_set ), and injectability (I). The selection of the PMMA beads was crucial to obtain cement composite formulations capable to be efficiently injected. Results allowed to select nine solid phase mixtures to be further tested. Then, we determined the influence of the composition of these composite bone cements on T_max , t_set , I, and cell proliferation. The results showed that the performance of various of the selected composite cements was better than that of PMMA cement reference, with lower T_max , lower t_set , and higher I. We found that incorporation of Sr-substituted BGs into these materials bestows bioactivity properties associated with the role of Sr in bone formation, leading to some composite cement formulations that may be suitable for use in PVP. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1245-1257, 2018.

Image-guided minimally invasive percutaneous treatment of spinal metastasis

In order to provide effective options for minimally invasive treatment of spinal metastases, the present study retrospectively evaluated the efficacy and safety of image-guided minimally invasive percutaneous treatment of spinal metastases. Image-guided percutaneous vertebral body enhancement, radiofrequency ablation (RFA) and tumor debulking combined with other methods to strengthen the vertebrae were applied dependent on the indications. Percutaneous vertebroplasty (PVP) was used when vertebral body destruction was simple. In addition, RFA was used in cases where pure spinal epidural soft tissue mass or accessories (spinous process, vertebral plate and vertebral pedicle) were destroyed, but vertebral integrity and stability existed. Tumor debulking (also known as limited RFA) combined with vertebral augmentation were used in cases presenting destruction of the epidural soft tissue mass and accessories, and pathological vertebral fractures. A comprehensive assessment was performed through a standardized questionnaire and indicators including biomechanical stability of the spine, quality of life, neurological status and tumor progression status were assessed during the 6 weeks-6 months follow-up following surgery. After the most suitable treatment was used, the biomechanical stability of the spine was increased, the pain caused by spinal metastases within 6 weeks was significantly reduced, while the daily activities and quality of life were improved. The mean progression-free survival of tumors was 330±54 days, and no associated complications occurred. Therefore, the use of a combination of image-guided PVP, RFA and other methods is safe and effective for the treatment of spinal metastases.

Application of digital volume correlation to study the efficacy of prophylactic vertebral augmentation

BACKGROUND

Prophylactic augmentation is meant to reinforce the vertebral body, but in some cases it is suspected to actually weaken it. Past studies only investigated structural failure and the surface strain distribution. To elucidate the failure mechanism of the augmented vertebra, more information is needed about the internal strain distribution. This study aims to measure, for the first time, the full-field three-dimensional strain distribution inside augmented vertebrae in the elastic regime and to failure.

METHODS

Eight porcine vertebrae were prophylactically-augmented using two augmentation materials. They were scanned with a micro-computed tomography scanner (38.8μm voxel resolution) while undeformed, and loaded at 5%, 10%, and 15% compressions. Internal strains (axial, antero-posterior and lateral-lateral components) were computed using digital volume correlation.

FINDINGS

For both augmentation materials, the highest strains were measured in the regions adjacent to the injected cement mass, whereas the cement-interdigitated-bone was less strained. While this was already visible in the elastic regime (5%), it was a predictor of the localization of failure, which became visible at higher degrees of compression (10% and 15%), when failure propagated across the trabecular bone. Localization of high strains and failure was consistent between specimens, but different between the cement types.

INTERPRETATION

This study indicated the potential of digital volume correlation in measuring the internal strain (elastic regime) and failure in augmented vertebrae. While the cement-interdigitated region becomes stiffer (less strained), the adjacent non-augmented trabecular bone is affected by the stress concentration induced by the cement mass. This approach can help establish better criteria to improve vertebroplasty.