Stent-Screw Assisted Internal Fixation of Osteoporotic Vertebrae: A Comparative Finite Element Analysis on SAIF Technique

Space between bone cement and bony endplate can trigger higher incidence of augmented vertebral collapse: An in-silico study

BACKGROUND

The pathogenesis of postoperative complications in patients with osteoporotic vertebral compressive fractures (OVCFs) undergoing percutaneous vertebroplasty (PVP) is multifaceted, with local biomechanical deterioration playing a pivotal role. Specifically, the disparity in stiffness between the bone cement and osteoporotic cancellous bone can precipitate interfacial stress concentrations, potentially leading to cement-augmented vertebral body collapse and clinical symptom recurrence. This study focuses on the biomechanical implications of the space between the bone cement and bony endplate (BEP), hypothesizing that this interface may be a critical locus for stress concentration and subsequent vertebral failure.

METHODS

Leveraging a validated numerical model from our previous study, we examined the biomechanical impact of the cement-BEP interface in the L2 vertebral body post-PVP, simulated OVCF and PVP and constructed three distinct models: one with direct bone cement contact with both cranial and caudal BEPs, one with contact only with the caudal BEPs and one without contact with either BEP. Moreover, we assessed stress distribution across cranial and caudal BEPs under various loading conditions to describe the biomechanical outcomes associated with each model.

RESULTS

A consistent trend was observed across all models: the interfaces between the bone cement and cancellous bone exhibited higher stress values under the majority of loading conditions compared to models with direct cement-BEP contact. The most significant difference was observed in the flexion loading condition compared to the mode with direct contact between BEP and cement. The maximum stress in models without direct contact increased by at least 30%.

CONCLUSIONS

Our study reveals the biomechanical significance of interfacial stiffness differences at the cement-BEP junction, which can exacerbate local stress concentrations and predispose to augmented vertebral collapse. We recommend the strategic distribution of bone cement to encompass a broader contact area with the BEP for preventing biomechanical failure and subsequent vertebral collapse.

Combined vertebroplasty and pedicle screw insertion for vertebral consolidation: feasibility and technical considerations

PURPOSE

To assess the feasibility and technical accuracy of performing pedicular screw placement combined with vertebroplasty in the radiological setting.

METHODS

Patients who underwent combined vertebroplasty and pedicle screw insertion under combined computed tomography and fluoroscopic guidance in 4 interventional radiology centers from 2018 to 2023 were retrospectively assessed. Patient demographics, vertebral lesion type, and procedural data were analyzed. Strict intra-pedicular screw positioning was considered as technical success. Pain score was assessed according to the Visual Analogue Scale before the procedure and in the 1-month follow-up consultation.

RESULTS

Fifty-seven patients (38 men and 19 women) with a mean age of 72.8 (SD = 11.4) years underwent a vertebroplasty associated with pedicular screw insertion for the treatment of traumatic fractures (29 patients) and neoplastic disease (28 patients). Screw placement accuracy assessed by post-procedure CT scan was 95.7% (89/93 inserted screws). A total of 93 pedicle screw placements (36 bi-pedicular and 21 unipedicular) in 32 lumbar, 22 thoracic, and 3 cervical levels were analyzed. Mean reported procedure time was 48.8 (SD = 14.7) min and average injected cement volume was 4.4 (SD = 0.9) mL. A mean VAS score decrease of 5 points was observed at 1-month follow-up (7.7, SD = 1.3 versus 2.7, SD = 1.7), p < .001.

CONCLUSION

Combining a vertebroplasty and pedicle screw insertion is technically viable in the radiological setting, with a high screw positioning accuracy of 95.7%.

'Armed kyphoplasty' with posterior stabilization avoids corpectomy in complex thoracolumbar spine fractures: a case series

BACKGROUND

Complex thoracolumbar fractures require reduction and stabilization. Posterior instrumentation alone and standard cement augmentation may represent undertreatment, while corpectomy has significant morbidity. In a series of unstable thoracolumbar fractures, we assessed the feasibility, safety, and results of 'armed kyphoplasty' (AKP) and surgical posterior stabilization (PS).

METHODS

A total of 24 consecutive patients were treated with combined AKP and PS. Minimally invasive and open surgery techniques were used for PS. AKP was performed with C-arm or biplane fluoroscopic guidance, and screws were placed under navigation or fluoroscopic guidance. A postoperative CT scan and standing plain films were obtained. Patients were followed up according to clinical standards. Kyphosis correction (measured with regional Cobb angle), pain (measured with the Numeric Rating Scale), neurological status (measured with Frankel grade) were assessed.

RESULTS

A total of 25 fractures of neoplastic (40%), traumatic (32%), and osteoporotic (28%) nature were treated. Open surgery and minimally invasive techniques were applied in 16/24 and 8/24 patients, respectively. Decompressive laminectomy was performed in 13 cases. No intraprocedural complications occurred. Two patients (8%) died due to underlying disease complications and three complications (12%) required re-intervention (one surgical site infection, one adjacent fracture, and one screw pull-out) in the first month. The mean Cobb angle was 20.14±6.19° before treatment and 11.66±5.24° after treatment (P<0.0001). No re-fractures occurred at the treated levels.

CONCLUSIONS

Combined AKP and PS is feasible and effective in the treatment of complex thoracolumbar fractures of all etiologies. AKP avoided highly invasive corpectomy. Anterior and posterior support ensured stability, preventing implant failure and re-fracture. The complication rate was low compared with more invasive traditional 360° open surgical approaches.

Risk factors for bone cement dislodgement following balloon kyphoplasty for osteoporotic vertebral compression fracture

OBJECTIVE

The study aimed to determine the incidence and risk factors associated with bone cement dislodgement in patients with osteoporotic vertebral compression fracture following balloon kyphoplasty treatment.

METHODS

A retrospective study was conducted on 203 patients who underwent kyphoplasty in 255 vertebral bodies between January 2017 and December 2021. The patients were categorized into two groups: the bone cement dislodgment group (n = 16) and the non-bone cement dislodgement group (n = 239). Various patient characteristics and radiologic parameters were evaluated. Statistical analysis involved the assessment of the background homogeneity of the group by using independent sample t tests, chi-square tests, and Fisher's exact. Univariate and multivariate logistic regression analyses were performed to explore the impact of background variables on cement dislodgement.

RESULTS

The results revealed that split-type fracture (χ2 = 31.706, p < 0.001), DISH (χ2 = 18.827, p = 0.011), pedicle fracture (χ2 = 22.246, p < 0.001), endplate deficit (χ2 = 14.023, p < 0.001), posterior wall injury (χ2 = 29.124, p < 0.001), and intervertebral vacuum cleft (χ2 = 21.469, p < 0.001) were the factors that significantly differed between the two groups. The multivariate logistic regression analysis revealed posterior wall injury (OR = 12.983, p = 0.025) and intervertebral vacuum cleft (OR = 5.062, p = 0.024) to be independent risk factors.

CONCLUSION

The incidence of bone cement dislodgement in our study was 6.3%. This study underscores the importance of using preoperative radiologic parameters to predict the risk of bone cement dislodgement following balloon kyphoplasty.

Beyond Pain Relief: An In-Depth Review of Vertebral Height Restoration After Balloon Kyphoplasty in Vertebral Compression Fractures

This comprehensive review delves into the intricate landscape of vertebral height restoration after balloon kyphoplasty in cases of vertebral compression fractures. With a comprehensive examination of procedural intricacies, radiological evaluations, clinical outcomes, and influential factors, a nuanced comprehension unfolds. Beyond its immediate alleviation of pain, vertebral height restoration emerges as a linchpin in enhancing spinal alignment, fostering functional recuperation, and augmenting the overall quality of life. This review underscores the pivotal role of balloon kyphoplasty, transcending its mere medical utility to become a conduit for renewed independence and well-being among individuals grappling with vertebral compression fractures. The ongoing advancements in medical science and the continued pursuit of research stand poised to amplify the significance of vertebral height restoration, manifesting a promising horizon for individuals seeking respite from pain, a revitalised capacity for movement, and a life unburdened by its constraints.

Biomechanical analysis of a novel bone cement bridging screw system combined with percutaneous vertebroplasty for treating Kummell's disease

Kummell's Disease (KD) was originally proposed by Dr. Hermann Kummell in 1891 as a type of delayed posttraumatic vertebral collapse, which is a clinical phenomenon. The purpose of this experiment is to compare the strength of bone cement and the novel bone cement bridging screw in the treatment of thoracolumbar Kummell disease (KD) with other treatment methods. Thirty sheep spine specimens were selected. T12 to L2 segments were selected, and a KD intravertebral vacuum cleft model was made at the L1 segment. According to the ways of cement filling, the specimens were divided into percutaneous vertebroplasty (PVP), PVP combined with unilateral percutaneous pediculoplasty (PPP), PVP combined with bilateral PPP, unilateral novel bone cement bridging screw system combined with PVP, and bilateral cement bridging screw system combined with PVP groups. There were two experiments: three-dimensional biomechanical strength test and axial compression test. In the three-dimensional biomechanical strength test, we measured the strength of bone cement in specimens under six motion states, including flexion, extension, left bending, right bending, and left and right axial rotations. In the axial compression test, we detected the maximum axial pressure that the bone cement could withstand when it was under pressure until the bone cement was displaced. The unilateral or bilateral novel bone cement bridging screw with PVP groups had the best strength under flexion, extension, left bending, right bending, and had better biomechanical strength, with a significant difference from the other three groups (p < 0.05). There was no significant difference between the unilateral or bilateral novel bone cement bridging screw with PVP groups (p > 0.05). Unilateral and bilateral novel bone cement bridging screw could achieve similar bone cement strength. Compared with the other three groups, the unilateral or bilateral novel bone cement bridging screw with PVP groups are higher 136.35%, 152.43%; 41.93%, 51.58%; 34.37%, 43.50% respectively. The bilateral novel bone cement bridging screw with PVP could bear the largest pressure under vertical force. To conclude, the novel bone cement bridging screw can increase the strength of bone cement and avoid the loosening and displacement of bone cement in the treatment of KD of the thoracolumbar spine.

Middle column Stent-screw Assisted Internal Fixation (SAIF): a modified minimally-invasive approach to rescue vertebral middle column re-fractures

BACKGROUND

There is limited literature regarding the re-fracture of a previously augmented vertebral compression fracture (VCF). These re-fractures may present as an asymptomatic remodeling of the vertebral body around the cement cast while in other cases they involve the middle column, at the transition zone between the cement-augmented and non-augmented vertebral body. In the latter, a posterior wall retropulsion is possible and, if left untreated, might progress to vertebral body splitting, central canal stenosis, and kyphotic deformity. There is no consensus regarding the best treatment for these re-fractures. There are cases in which a repeated augmentation relieves the pain, but this is considered an undertreatment in cases with middle column involvement, posterior wall retropulsion, and kyphosis.

METHODS

We report four cases of re-fracture with middle column collapse of a previously augmented VCF, treated with the stent-screw assisted internal fixation (SAIF) technique. A modified more postero-medial deployment of the anterior metallic implants was applied, to target the middle column fracture. This modified SAIF allowed the reduction and stabilization of the middle column collapse as well as the partial correction of the posterior wall retropulsion and kyphosis.

RESULTS

Complete relief of back pain with stable clinical and radiographic findings at follow-up was obtained in all cases.

CONCLUSIONS

In selected cases, the middle column SAIF technique is safe and effective for the treatment of the re-fracture with middle column collapse of a previously cement-augmented VCF. This technique requires precision in trocar placement and could represent a useful addition to the technical armamentarium for VCF treatment.

Biomechanical Effects of a Novel Anatomic Titanium Mesh Cage for Single-Level Anterior Cervical Corpectomy and Fusion: A Finite Element Analysis

Background: The traditional titanium mesh cage (TTMC) has become common as a classical instrument for Anterior Cervical Corpectomy and Fusion (ACCF), but a series of complications such as cage subsidence, adjacent segment degeneration (ASD), and implant-related complications by using the TTMC have often been reported in the previous literature. The aim of this study was to assess whether a novel anatomic titanium mesh cage (NTMC) could improve the biomechanical condition after surgery.

Methods: The NTMC model consists of two spacers located on both sides of the TTMC which match the anatomic structure between the endplates by measuring patient preoperative cervical computed tomography (CT) data. The ranges of motion (ROMs) of the surgical segments and the stress peaks in the C6 superior endplates, titanium mesh cage (TMC), screw–bone interface, anterior titanium plate, and adjacent intervertebral disc were compared.

Results: Compared with the TTMC, the NTMC reduced the surgical segmental ROMs by 89.4% postoperatively. The C6 superior endplate stress peaks were higher in the TTMC (4.473–23.890 MPa), followed by the NTMC (1.923–5.035 MPa). The stress peaks on the TMC were higher in the TTMC (47.896–349.525 MPa), and the stress peaks on the TMC were lower in the NTMC (17.907–92.799 MPa). TTMC induced higher stress peaks in the screw–bone interface (40.0–153.2 MPa), followed by the NTMC (14.8–67.8 MPa). About the stress peaks on the anterior titanium plate, the stress of TTMC is from 16.499 to 58.432 MPa, and that of the NTMC is from 12.456 to 34.607 MPa. Moreover, the TTMC induced higher stress peaks in the C3/4 and C6/7 intervertebral disc (0.201–6.691 MPa and 0.248–4.735 MPa, respectively), followed by the NTMC (0.227–3.690 MPa and 0.174–3.521 MPa, respectively).

Conclusion: First, the application of the NTMC can effectively decrease the risks of TMC subsidence after surgery. Second, in the NTMC, the stresses at the anterior screw-plate, bone–screw, and TMC interface are much less than in the TTMC, which decreased the risks of instrument-related complications after surgery. Finally, increases in IDP at adjacent levels are associated with the internal stresses of adjacent discs which may lead to ASD; therefore, the NTMC can effectively decrease the risks of ASD.

Minimally Invasive Stent Screw-Assisted Internal Fixation Technique Corrects Kyphosis in Osteoporotic Vertebral Fractures with Severe Collapse: A Pilot "Vertebra Plana" Series

BACKGROUND AND PURPOSE

Fractures with "vertebra plana" morphology are characterized by severe vertebral body collapse and segmental kyphosis; there is no established treatment standard for these fractures. Vertebroplasty and balloon kyphoplasty might represent an undertreatment, but surgical stabilization is challenging in an often elderly osteoporotic population. This study assessed the feasibility, clinical outcome, and radiologic outcome of the stent screw-assisted internal fixation technique using a percutaneous implant of vertebral body stents and cement-augmented pedicle screws in patients with non-neoplastic vertebra plana fractures.

MATERIALS AND METHODS

Thirty-seven consecutive patients with vertebra plana fractures were treated with the stent screw-assisted internal fixation technique. Vertebral body height, local and vertebral kyphotic angles, outcome scales (numeric rating scale and the Patient's Global Impression of Change), and complications were assessed. Imaging and clinical follow-up were obtained at 1 and 6 months postprocedure.

RESULTS

Median vertebral body height restoration was 7 mm (+74%), 9 mm (+150%), and 3 mm (+17%) at the anterior wall, middle body, and posterior wall, respectively. Median local and vertebral kyphotic angles correction was 8° and 10° and was maintained through the 6-month follow-up. The median numeric rating scale score improved from 8/10 preprocedure to 3/10 at 1 and 6 months (P < .001). No procedural complications occurred.

CONCLUSIONS

The stent screw-assisted internal fixation technique was effective in obtaining height restoration, kyphosis correction, and pain relief in patients with severe vertebral collapse.

Revision balloon kyphoplasty and vertebra-pediculoplasty using cannulated screws for osteoporotic vertebral fractures with cement dislodgement following conventional balloon kyphoplasty

We report the usefulness of revision balloon kyphoplasty (re-BKP) and vertebra-pediculoplasty using cannulated screws (VPCS) for osteoporotic vertebral fractures (OVF) following cement dislodgement of conventional BKP. Between 2015 and 2020, three patients with OVF developed symptomatic cement dislodgement following BKP and underwent re-BKP. All three patients showed a loose cemented mass and spinal instability. Balloon inflation was performed in the gap between the loosened cemented mass and the remaining cortical bone rim, and this extended gap was filled with cement. To prevent re-dislodgement of the cement mass, a cannulated screw was inserted into the cemented mass through the pedicle. All patients achieved early pain relief, and improved vertebral stability of the fractured vertebra and all related symptoms, with no perioperative complications. Re-BKP and VPCS are innovative concepts and could be an effective minimally invasive treatment for OVF following cement dislodgement of conventional BKP treatment.

Biomechanical Effects of Pedicle Screw Positioning on the Surgical Segment in Models After Oblique Lumbar Interbody Fusion: An in-silico Study

Background

Bilateral pedicle screw (BPS) is the “gold standard” of fixation methods for patients with lumbar interbody fusion. Biomechanical deterioration initially triggers complications in the surgical segment. Studies proved that BPS positions and trajectory changes affect the local biomechanical environment. However, no study illustrates the biomechanical effect of insertional screw positions’ change on the surgical segment.

Methods

Oblique lumbar interbody fusion (OLIF) with different BPS insertional positions has been simulated in a well-validated lumbo-sacral model. Fixation stability and stress responses on the surgical segment were evaluated under identical loading conditions.

Results

There is no clear variation tendency for the risk of BPS failure and the change of strain energy density of the grafted bone. However, shifting the insertional screw position close to the surgical segment will increase the range of motions (ROM) in the surgical segment and lead to stress concentration of bony structures, especially in the caudal side of the surgical segment.

Conclusion

Adjusting the insertional position of BPS close to the surgical segment in OLIF models will lead to stress concentration of bony structures and surgical segmental instability. Therefore, reducing BPS’s fixation length was not recommended, which may increase the risk of segmental instability, non-union, and cage subsidence.

Stentoplasty with Resorbable Calcium Salt Bone Void Fillers for the Treatment of Vertebral Compression Fracture: Evaluation After 3 Years

Purpose

The aim of the study is to investigate the clinical and radiological outcomes of vertebral compression fractures treated by stentoplasty with resorbable calcium salt bone void fillers compared with balloon kyphoplasty (BKP).

Methods

This prospective study included patients with fresh mono-thoracolumbar vertebral compression fractures. Patients enrolled were randomly divided into three groups. The patients in group A underwent stentoplasty with calcium sulfate/calcium phosphate (CSCP) composite filler and patients in group B with hydroxyapatite/collagen (HAP/COL) composite filler, while patients in group C underwent BKP with polymethylmethacrylate (PMMA). The clinical outcome was evaluated with visual analogue pain scale (VAS) and Oswestry disability score (ODI). The radiological results were evaluated with anterior height (AH) and Cobb angle of vertebral body. Computed tomography (CT) was used to assess osteogenesis effect.

Results

Each group included 14 patients. The VAS, ODI, Cobb angle and AH were statistically improved compared with preoperative and there was no significant difference between the three groups. However, the AH in group A and group B at 1-year follow-up presented slight loss compared with 1 day after surgery. CT results suggested both group A and group B presented obvious bone trabecula formation and variations of CT value.

Conclusion

The stentoplasty with resorbable calcium salt bone void fillers demonstrated clinical outcomes similar to traditional BKP for vertebral compression fractures. Both HAP/COL and CSCP performed certain osteogenesis. However, stentoplasty with studied fillers showed slight loss of AH within 1 year after surgery.

Biomechanical evaluation of four different posterior instrumentation techniques for single-level transforaminal lumbar interbody fusion: a finite element analysis

This study aims to investigate the fixation strength of unilateral cortical bone trajectory screw fixation (UCBT) and UCBT with contralateral translaminar facet screw fixation (UCBT-TFS) by repeating the verification of three finite element models. Three healthy female models of the lumbosacral spine were constructed. For each of them, four transforaminal lumbar interbody fusion (TLIF) models with the following instruments were created: bilateral traditional trajectory pedicle screw fixation (TT), bilateral cortical bone trajectory screw fixation (CBT), UCBT, and UCBT-TFS. A 150-N compressive load with 10 N/m moments was applied to simulate flexion, extension, lateral bending, and axial rotation. The range of motion (ROM), the stress of the cages, and the stress of the posterior fixations were compared. TT and UCBT-TFS had a similar low ROM compared to the intact models, and CBT showed a higher ROM in lateral bending. UCBT resulted in the highest ROM under all loading conditions, especially in lateral bending (116% and 170% greater than TT in left bending and right bending). UCBT induced a significant increase in the peak stress of cages and instruments, followed by CBT and UCBT-TFS, and the lowest mean values were observed for TT. Among the four different fixation techniques, TT offered the highest fixation strength and lowest implant stress, followed by UCBT-TFS and CBT, while UCBT was the least stable and resulted in increased stress of the screws and cages. UCBT-TFS improved biomechanical stability and appeared to be a less invasive alternative in well-selected patients with single-level TLIF.

The 'armed concrete' approach: stent-screw-assisted internal fixation (SAIF) reconstructs and internally fixates the most severe osteoporotic vertebral fractures

BACKGROUND

The treatment of severe osteoporotic vertebral compression fractures (VCFs) with middle-column (MC) involvement, high fragmentation, large cleft and/or pedicular fracture is challenging. Minimally invasive 'stent-screw-assisted internal fixation' (SAIF) can reduce the fracture, reconstruct the vertebral body (VB) and fix it to the posterior elements.

OBJECTIVE

To assess feasibility, safety, technical and clinical outcome of the SAIF technique in patients with severe osteoporotic VCFs.

METHODS

80 treated vertebrae were analyzed retrospectively. Severe VCFs were characterized by advanced collapse (Genant grade 3), a high degree of osseous fragmentation (McCormack grade 2 and 3), burst morphology with MC injury, pediculo-somatic junction fracture, and/or large osteonecrotic cleft. VB reconstruction was evaluated on postprocedure radiographs and CT scans by two independent raters. Clinical and radiological follow-ups were performed at 1 and 6 months.

RESULTS

SAIF was performed at 28 thoracic and 52 lumbar levels in 73 patients. One transient neurological complication occurred. VB reconstruction was satisfactory in 98.8% of levels (inter-rater reliability 96%, κ=1). Follow-up at 1 month was available for 78/80 levels and at 6 months or later (range 6-24, mean 7.9 months) for 73/80 levels. Significant improvement in the Visual Analog Scale score was noted at 1 and 6 months after treatment (p<0.05). Patients reported global clinical benefit during follow-up (Patient's Global Impression of Change Scale 5.6±0.9 at 1 month and 6.1±0.9 at 6 months). Fourteen new painful VCFs occurred at different levels in 11 patients during follow-up, treated with vertebral augmentation or SAIF. Target-level stability was maintained in all cases.

CONCLUSIONS

SAIF is a minimally invasive, safe, and effective treatment for patients with severe osteoporotic VCFs with MC involvement.

Influence of cement-augmented pedicle screws with different volumes of polymethylmethacrylate in osteoporotic lumbar vertebrae over the adjacent segments: a 3D finite element analysis

Background

Polymethylmethacrylate (PMMA) is commonly used for cement-augmented pedicle screw instrumentation (CAPSI) to improve the fixation stability and reduce the risk of screw loosening in the osteoporotic thoracolumbar spine. Biomechanical researches have shown that various dose of cement (1-3 ml) can be injected to enhance screw stability. To date, there have been no studies on the relationship between adjacent segment degeneration and the volume of PMMA. This study aimed to explore the influence of CAPSI with different volumes of PMMA in osteoporotic lumbar vertebrae over adjacent segments by using finite element analysis.

Methods

Seven different finite element models were reconstructed and simulated under different loading conditions, including (1) an intact model, (2) three single-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml), and (3) three double-level CAPSI models with different volumes of PMMA (1, 1.73, and 2.5 ml). To improve the accuracy of the finite element analysis, the models of the injectable pedicle screw and bone cement were created by using a three-dimensional scanning machine and the CAPSI patient’s CT data, respectively. The range of motion (ROM), the stress of intervertebral discs, and the stress of facet in the adjacent segment were comparatively analyzed among the different models.

Results

The ROMs of the different segments were compared with experimental data, with good agreement under the different load conditions (21.3°, 13.55°, 13.99°, and 6.11° in flexion, extension, bending, and rotation at L3-S1 level, respectively). Compared with the intact model, the ROM, disc stresses, and facet stress in adjacent segments were found to be higher in the six operative models. Otherwise, with a larger volume of PMMA injected, the ROM, disc stresses, and facet stress slightly increased at the adjacent segment. However, the differences were insignificant with the biggest difference less than 3.8%.

Conclusions

CAPSI could increase the incidence of disk degeneration in the adjacent segment, while within a certain range, different volumes of PMMA provided an approximate impact over the adjacent segment degeneration.