Cement distribution, volume, and compliance in vertebroplasty: some answers from an anatomy-based nonlinear finite element study

Unilateral Dual-Plane Puncture Percutaneous Vertebroplasty Reduces Re-Collapse in Osteoporotic Vertebral Compression Fractures by Advancing Cement Delivery

PURPOSE

Evaluate the efficacy of a novel unilateral dual-plane puncture technique in improving bone cement distribution and reducing vertebral re-collapse following percutaneous vertebroplasty (PVP) for osteoporotic vertebral compression fractures (OVCFs). By introducing the novel unilateral dual-plane puncture technique, this study aims to improve cement distribution, reduce the incidence of re-collapse, and enhance long-term clinical outcomes for patients suffering from OVCFs.

METHODS

This is a randomized trial conducted from April 2021 to December 2022, enrolling 145 patients diagnosed with OVCFs. Patients were allocated into either traditional or unilateral dual-plane puncture groups. Bone cement distribution, vertebral height, and segmental kyphotic angle were measured through postoperative x-ray, while clinical outcomes were evaluated using the Visual Analog Scale (VAS) and the Oswestry Disability Index (ODI). Statistical analysis was performed using the Mann-Whitney U test and independent samples t test for continuous variables, and chi-square or Fisher's exact test for categorical variables.

RESULTS

The unilateral dual-plane puncture technique notably augmented bone cement contact with both superior and inferior endplates compared to conventional methods, achieving rates of 64.86% versus 40.85% (p < 0.001). This contributed to a significant reduction in the incidence of vertebral re-collapse within the first year post-operation: 18.92% in the unilateral dual-plane group as opposed to 42.25% in the traditional group (p < 0.001). Furthermore, the unilateral dual-plane group exhibited markedly superior long-term efficacy, evidenced by mean VAS and ODI scores of 1.26 and 28.58, respectively, in comparison to 2.03 and 32.45 in the traditional group.

CONCLUSIONS

The unilateral dual-plane puncture technique advances bone cement distribution within the vertebra, thereby reducing the risk of vertebral re-collapse following PVP surgery and improving long-term clinical outcomes for patients with OVCFs.

An imaging anatomical study on percutaneous vertebral augmentation for thoracic spine via the unilateral transverse process-pedicle approach

BACKGROUND

Percutaneous vertebral augmentation (PVA) via the unilateral transverse process-pedicle approach (UTPPA) has shown promise for treating painful osteoporotic vertebral compression fractures (OVCFs). This study aimed to investigate the anatomical parameters of PVA for thoracic spine via the UTPPA using a three-dimensional computed tomography (3D CT) database.

METHODS

PVA was simulated through the UTPPA on 3D CT scans on 100 patients (50 men and 50 women), involving a total of 1200 thoracic vertebral bodies (T1-T12). Anatomical parameters, including the distance between the bone entry puncture point and the midline of the vertebral body (DEM), the puncture inner inclination angle (PIA), the maximum PIA (Amax), the middle PIA (Amid), the minimum PIA (Amin), the safe range of the PIA (SRA), and the minimum transverse pedicle width (MTPW), were measured and compared.

RESULTS

The mean DEM ranged from 17.60 ± 2.63 mm to 22.71 ± 4.07 mm, and the Amid ranged from 24.27° ± 2.21° to 40.77° ± 6.11°. The mean left DEM was significantly larger than the right (p < 0.001). The right SRA was significantly larger than the left (p < 0.001). The mean DEM, SRA and MTPW were significantly larger in men than in women (p < 0.001).

CONCLUSION

In PVA for thoracic spine treatment using UTPPA, our study demonstrated that selecting this approach in men and puncturing from the right side in the thoracic vertebrae could be safer.

Predictors for vertebral height deterioration in fractured vertebrae operated by percutaneous vertebroplasty

BACKGROUND

Vertebral height loss of fractured vertebrae treated by percutaneous vertebral augmentation (PVA) for osteoporotic vertebral compression fracture (OVCFs) during follow-up had been reported. Mostly, vertebral height loss and its relevant terms (e.g., "recompression", "recollapse" and "refracture") were defined according to immediate postoperative vertebral height as the baseline in published studies. By contrast, vertebral height deterioration (VHD) was defined according to preoperative vertebral height as the baseline in the present study. The aim of the study was to reveal predictors for VHD in fractured vertebrae operated by percutaneous vertebroplasty (PVP), with a specific focus on surgical factors.

METHODS

All patients with OVCFs treated by PVP between April 2016 and September 2018 were retrospectively reviewed. Patients were followed up for at least 12 months after procedure according to treatment protocol. VHD was defined as the presence of a decrease of vertebral height at final follow-up compared to preoperative. Clinical, radiological and surgical factors that might affect occurrence of VHD were assessed using univariate and multivariate analyses.

RESULTS

A total of 543 patients (females 80%, age 73.2 ± 8.1 years) with 681 fractured vertebrae who underwent PVP were enrolled. Mean follow-up time was 28.9 ± 13.4 months (range, 12-59 months). Incidence of VHD in fractured vertebrae was 48.9% (333/681). One clinical factor and four radiological factors, including fracture age (OR = 0.513, 95% CI 0.385-0.683, p = 0.000), fracture location (OR = 2.878, 95% CI 1.994-4.152, p = 0.000), fracture severity (OR = 0.521, 95% CI 0.386-0.703, p = 0.000), cortical defect on lateral wall (OR = 2.535, 95% CI 1.351-4.758, p = 0.004) and intravertebral cleft (OR = 2.362, 95% CI 1.488-3.750, p = 0.000), were independent predictors for VHD. However, all the surgical factors evaluated were not significant in final model analysis.

CONCLUSIONS

Surgical factors might play a negligible effect on VHD. VHD might be due to natural course of fracture/osteoporosis.

Impact of Cement Distribution on the Efficacy of Percutaneous Vertebral Augmentation for Osteoporotic Fractures: Assessment with an MRI-Based Reference Marker

BACKGROUND

No studies have evaluated the impact of the cement distribution as classified on the basis of the fracture bone marrow edema area (FBMEA) in magnetic resonance imaging (MRI) on the efficacy of percutaneous vertebral augmentation (PVA) for acute osteoporotic vertebral fractures.

METHODS

The clinical data of patients with acute, painful, single-level thoracolumbar osteoporotic fractures were retrospectively analyzed. The bone cement distribution on the postoperative radiograph was divided into 4 types according to the distribution of the FBMEA on the preoperative MRI. The primary outcomes were the postoperative visual analog scale (VAS) for pain and Oswestry Disability Index (ODI) scores. Cement leakage, adjacent vertebral fractures (an important concern in complications after vertebroplasty and a subset of new fractures), and recollapse of the treated vertebra were also evaluated.

RESULTS

A total of 128 patients, 80.5% of whom were female, were included and had follow-up for 24 months. The mean patient age (and standard deviation) was 74.2 ± 8.6 years. The cement distribution was classified as Type I in 18 patients, Type II in 26, Type III in 46, and Type IV in 38. At the primary time point (6 months), there was a significant difference in the ODI score favoring the Type-III and Type-IV groups compared with the Type-I and Type-II groups (adjusted 95% confidence interval [CI]: Type I versus Type II, -2.40 to 4.50; Type I versus Type III, 1.35 to 7.63; Type I versus Type IV, 1.27 to 7.92; Type II versus Type III, 0.67 to 6.21; Type II versus Type IV, 0.63 to 6.46; adjusted p < 0.0083), whereas no significant differences were found between the 4 groups in the VAS pain score. The Type-II and Type-IV groups had a higher incidence of cement leakage, and the Type-III and Type-IV groups had a lower incidence of vertebral recollapse.

CONCLUSIONS

An adequate distribution of bone cement is advantageous for functional improvement, short-term pain relief, and a lower rate of vertebral recollapse. The FBMEA appears to be a feasible reference marker for evaluating the performance of the PVA procedure.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

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%.

Percutaneous kyphoplasty through unilateral puncture on the convex side for the treatment of painful osteoporotic vertebral compression fracture with scoliosis

PURPOSE

To assess the clinical safety, accuracy, and efficacy of percutaneous kyphoplasty (PKP) surgery using an enhanced method of unilateral puncture on the convex side for the treatment of painful osteoporotic vertebral compression fractures (P-OVCF) with scoliosis.

METHODS

Clinical and radiographic data of P-OVCF patients with scoliosis who underwent PKP via unilateral puncture on the convex side from January 2018 to December 2021 were retrospectively analyzed. This technique's detailed surgical steps and tips were described. The local kyphosis angle (LKA), scoliosis Cobb angle (SCA), and local scoliosis Cobb angle (LSCA) were measured using X-ray and compared at pre-operation, post-operation, and the last follow-up. The width of pedicle (POW), inner inclination angle (IIA), lateral distance (LD), and puncture course length (PCL) were measured on the axial computed tomography image and compared between two sides. Postoperative computed tomography was employed to evaluate the condition of cement distribution and puncture. Clinical outcomes were evaluated using the Oswestry Disability Index (ODI) and Visual Analog Scale (VAS) for back pain (BP).

RESULTS

Thirty-six patients, 23 women and 13 men, with an average age of 76.31 ± 6.28 years were monitored for 17.69 ± 4.70 months. The median surgical duration of single vertebrae was 35 min. The volume of bone cement for single vertebrae was 3.81 ± 0.87 ml and the proportion of sufficient cement distribution of the patients was 97.22. LKA was considerably improved from pre-operation to post-operation and sustained at the last follow-up. SCA and LSCA were not significantly modified between these three-time points. IIA, PCL, and LD were lower on the convex side than on the concave side. POW was considerably wider on the convex side. The ODI and VAS-BP scores were significantly improved after surgery and sustained during the follow-up.

CONCLUSIONS

Combining with the proper assessment of the pre-injured life status of patients, PKP surgery using unilateral puncture on the convex side for the treatment of P-OVCF with scoliosis can achieve safe, excellent clinical, and radiographic outcomes.

Percutaneous Curved Vertebroplasty Decrease the Risk of Cemented Vertebra Refracture Compared with Bilateral Percutaneous Kyphoplasty in the Treatment of Osteoporotic Vertebral Compression Fractures

Purpose

The purpose of this study is to compare the refracture rate of the cemented vertebral body of percutaneous curved vertebroplasty (PCVP) and bilateral percutaneous kyphoplasty (PKP) in the treatment of osteoporotic vertebral compression fractures (OVCF).

Methods

Ninety-four patients with single segment thoracolumbar OVCF were randomly divided into two groups (47 patients in each) and underwent PCVP or bilateral PKP surgery, respectively. Refracture of cemented vertebral body, bone cement injection volume and cement pattern, cement leakage rate, total surgical time, intraoperative fluoroscopy time, preoperative and postoperative Cobb angles and anterior vertebral height, Oswestry disability index questionnaire (ODI) and visual analog scales (VAS) were recorded.

Results

The PCVP group had significantly lower refracture incidence of the cemented vertebral than the bilateral PKP group (p<0.05). There was a significant postoperative improvement in the VAS score and ODI in both group (p<0.01), and no significant difference was found between two groups. The operation time and intraoperative fluoroscopy times were significantly less in the PCVP group than in the bilateral PKP group (p<0.01). The mean kyphosis angle correction and vertebral height restoration in the PCVP group was significantly less than that in the bilateral PKP group (p<0.01).

Conclusion

Both PCVP and PKP were safe and effective treatments for OVCF. The PCVP had lower refracture rate of the cemented vertebral than the bilateral PKP group, and PCVP entailed less exposure to fluoroscopy and shorter operation time than bilateral PKP.

Comparison of percutaneous vertebroplasty and conservative treatment for one level thoracolumbar osteoporotic compression fracture in a 3-year study

The efficacy of Mesh optimized versus standard percutaneous vertebroplasty (PVP) for osteoporotic vertebral compression fractures. Grid optimization (102 cases; 38 men, 64 women aged 67.3 ± 8.5) and traditional PVP groups (94 cases) were identified from 196 PVP patients treated from May 2016 to 2019. The optimal puncture site and angle forced bone cement into both groups before surgery. The main indexes were operation time, X-ray fluoroscopy times, bone cement injection volume, leakage, VAS, and injured vertebrae height. Preoperative general data were equivalent between groups (P > 0.05). All patients survived surgery without spinal cord injury, incision infection, pulmonary embolism, or death. The mesh optimization group had improved operation time (34.8 ± 6.5 min), fluoroscopy times (29.5 ± 5.5), bone cement injection volume (5.3 ± 2.1 ml), and bone cement permeability greater (3.9 percent; 4/98) than the standard PVP group (P < 0.05). Similarly, the grid optimization group had superior VAS scores (1.1 ± 0.6; 1.0 ± 0.3; and 0.9 ± 0.2) than the standard PVP group at 3 days, 3 months, and the last follow-up visit (P < 0.05). On day three after surgery, both had similar heights of injured vertebra's anterior and middle edges (P > 0.05). However, in the mesh optimization group, measurements improved to 1.8 ± 0.4 mm and (1.8 ± 0.3) mm by month three and to 1.7 ± 0.3 mm at last follow-up (P < 0.05). Mesh-optimized PVP with a mesh locator treats osteoporotic vertebral compression fractures more safely and effectively than regular PVP.

A nomogram for predicting the risk of new vertebral compression fracture after percutaneous kyphoplasty

BACKGROUND

New vertebral compression fractures (NVCFs) are common adverse events in percutaneous kyphoplasty (PKP). The present study aimed to investigate the risk factors for NVCFs in patients after PKP and to construct a nomogram for the prediction of the risk of re-fracture.

METHODS

We retrospectively analyzed the medical records of patients after PKP surgery between January 2017 and December 2020. Patients were divided into an NVCF group (n = 225) and a control group (n = 94) based on the presence or absence of NVCFs, respectively, at follow-up within 2 years after surgery. Lasso regression was used to screen for risk factors for re-fracture. Based on the results, a Lasso-logistic regression model was developed, and its prediction performance was evaluated using receiver operating characteristic curves, calibration, and decision curve analysis. The model was visualized, and a nomogram was constructed.

RESULTS

A total of eight potential predictors were obtained from Lasso screening. Advanced age, low body mass index, low bone mineral density, lack of anti-osteoporosis treatment, low preoperative vertebral body height, vertebral body height recovery ≥ 2, cement leakage, and shape D (lack of simultaneous contact of bone cement with the upper and lower plates) were included in the logistic regression model.

CONCLUSIONS

A nomogram for predicting postoperative NVCF in PKP was developed and validated. This model can be used for rational assessment of the magnitude of the risk of developing NVCFs after PKP, and can help orthopedic surgeons make clinical decisions aimed at reducing the occurrence of NVCFs.

Clinical outcomes with second injection after insufficient bone cement distribution in unilateral kyphoplasty for osteoporotic vertebral compressive fracture: a cohort retrospective study

BACKGROUND

Bone cement distribution is an important factor affecting pain relief and long-term prognosis of osteoporotic vertebral compression fracture (OVCF) treated with vertebral augmentation. Unilateral percutaneous kyphoplasty (PKP) is the most common procedure, and insufficient bone cement distribution is more common than bilateral PKP. However, effective remedies are remain lack. In this study, sufficient cement distribution was achieved by adjusting the working channel followed by second cement injection as a remedy in cases with insufficient cement distribution, and the purpose was to evaluate the clinical outcomes by a retrospective cohort study.

METHODS

From July 1, 2017 to July 31, 2020, OVCF patients treated with unilateral PKP were included in this retrospective cohort study. According to the bone cement distribution (insufficient cement distribution was confirmed when the cement did not exceed the mid line of the vertebral body in frontal film or/and the cement did not contact the upper/lower vertebral endplates in the lateral film.) and whether second injection was performed during surgery, the patients were divided into three groups. Insufficient group: patients with insufficient cement distribution confirmed by fluoroscopy or postoperative x-ray. Second injection group: patients with insufficient cement distribution was found during the procedure, and second injection was performed to improve the cement distribution.

CONTROL GROUP

patients with sufficient cement distribution in one injection. The Primary outcome was cemented vertebrae re-collapse rate. The secondary outcomes included operative time, radiation exposure, cement leakage rate, VAS, ODI, and adjacent vertebral fracture rate.

RESULTS

There are 34 cases in insufficient group, 45 cases in second injection group, and 241 cases in control group. There was no significant difference in baseline data and follow-up time among the three groups.

PRIMARY OUTCOME

The injured vertebrae re-collapse rate of insufficient group was significantly higher than that of second injection group (42.22% vs 20.59%, P = 0.000) and control group (42.22% vs. 18.26%, P = 0.000). Kaplan-Meier survival analysis showed that there was no significant difference in the survival time between second injection group and control group (P = 0.741, Log-rank test), both of which were significant less than that in insufficient group (P = 0.032 and 0.000, respectively).

SECONDARY OUTCOMES

There was no significant difference in VAS score and ODI after operation between second injection group and control group, both of which were superior to those in insufficient group (P = 0.000). At the final follow-up, there was no significant difference in VAS and ODI among the three groups (P > 0.05). The operation time of second injection group was significantly higher than that of insufficient group (53.41 ± 8.85 vs 44.18 ± 7.41, P = 0.000) and control group (53.41 ± 8.85 vs 44.28 ± 7.22, P = 0.000). The radiation exposure of the second injection group was significantly higher than that of insufficient group (40.09 ± 8.39 vs 30.38 ± 6.87, P = 0.000) and control group (40.09 ± 8.39 vs 31.31 ± 6.49, P = 0.000). The cement leakage rate of second injection group (20.59%) was comparable with that of insufficient group (24.44%) and control group (21.26%) (P = 0.877). The length of hospital stay of the second injection group (4.38 ± 1.72) was comparable with that of insufficient group (4.18 ± 1.60) and control group (4.52 ± 1.46) (P = 0.431).

CONCLUSIONS

When cement distribution is insufficient during unilateral PKP, second injection may relieve early pain, reduce the incidence of cemented vertebral re-collapse and adjacent vertebral fracture, without increasing the cement leakage rate, although this procedure may increase the operation time and radiation exposure.

Risk assessment for sandwich vertebral fractures in the treatment of osteoporosis vertebral compression fractures using two methods of bone cement reinforcement

PURPOSE

Bone cement augmentation surgery includes percutaneous vertebroplasty (PVP) and percutaneous kyphoplasty (PKP). In this study, we aimed to investigate the risk of sandwich vertebral fractures in the treatment of osteoporotic vertebral compression fractures via PVP and PKP.

METHODS

We performed a retrospective analytical study and included 61 patients with osteoporotic vertebral compression fractures who underwent PVP and PKP at the Spinal Surgery Department of The Second Hospital of Liaocheng Affiliated with Shandong First Medical University from January 2019 to January 2022. These patients were divided into the following two groups by simple random sampling: group A (N = 30) underwent PVP treatment and group B (N = 31) underwent PKP treatment. The surgical time, fluoroscopy frequency, visual analog scale (VAS) score, amount of bone cement, the leakage rate of bone cement in intervertebral space, Cobb angle, and the incidence of fractures in both groups of sandwich vertebral were recorded after 1 year of follow-up.

RESULTS

No statistically significant difference was found in terms of surgical time, fluoroscopy frequency, and VAS score between the two groups (P > 0.05). However, a statistically significant difference was found in terms of the amount of bone cement, the leakage rate of bone cement intervertebral space, Cobb angle, and the incidence of vertebral body fractures in both groups (P < 0.05). The amount of bone cement, the leakage rate of bone cement in intervertebral space, Cobb angle, and sandwich vertebral fractures were higher in Group A than in Group B.

CONCLUSIONS

When PVP and PKP were performed to treat osteoporotic vertebral compression fractures, the sandwich vertebral exhibited a risk of fracture. PVP exhibited a greater relative risk than PKP, which may be due to the relatively larger amount of bone cement, higher rate of bone cement leakage in the intervertebral space, and larger Cobb angle.

Pedicle screw augmentation in posterior constructs of the thoracolumbar spine: How many pedicle screws should be augmented?

BACKGROUNDS

To evaluate the effects of different pedicle screw augmentation strategies on screw loosening and adjacent segment collapse at the proximal end of long-segment instrumentation.

METHODS

Eighteen osteoporotic (9 male, 9 female donors; mean age: 74.7 ± 10.9 [SD] years) thoracolumbar multi-segmental motion segments (Th11 - L1) were assigned as follows: control, one-level augmented screws (marginally), and two-level augmented screws (fully augmented) groups (3 × 6). Pedicle screw placement was performed in Th12 and L1. Cyclic loading in flexion started with 100-500 N (4 Hz) and was increased by 5 N every 500 cycles. Standardized lateral fluoroscopy images with 7.5 Nm loading were obtained periodically during loading. The global alignment angle was measured to evaluate the overall alignment and proximal junctional kyphosis. The intra-instrumental angle was used to evaluate screw fixation.

FINDINGS

Considering screw fixation as a failure criterion, the failure loads of the control (683 N), and marginally (858 N) and fully augmented (1050 N) constructs were significantly different (ANOVA p = 0.032).Taking the overall specimen alignment as failure criteria, failure loads of the three groups (control 933 ± 271.4 N, marginally 858 N ± 196 N, and full 933 ± 246.3 N were in the same range and did not show any significance (p = 0.825).

INTERPRETATION

Global failure loads were comparable among the three groups and unchanged with augmentation because the adjacent segment and not the instrumentation failed first. Augmentation of all screws showed significant improved in screw anchorage.

Comparative evaluation of an innovative deflectable percutaneous kyphoplasty versus conventional bilateral percutaneous kyphoplasty for osteoporotic vertebral compression fractures: a prospective, randomized and controlled trial

BACKGROUND CONTEXT

Osteoporotic vertebral compression fractures (OVCFs) can be treated with percutaneous kyphoplasty (PKP). In contrast to conventional PKP, the novel deflectable percutaneous kyphoplasty (DPKP), is a unilateral transpedicular approach procedure allowing a similar bilateral puncture effect, which owes to the deflectable curved bone expander creating a transcentral line cavity to achieve uniform distribution of cement and biomechanical balance while reducing operative time and radiation exposure.

PURPOSE

The purpose of this study was to prospectively compare and evaluate an innovative surgical procedure, DPKP, versus conventional bilateral percutaneous kyphoplasty (BPKP).

STUDY DESIGN

This is a prospective randomized controlled trial (RCT).

SAMPLE

The totality of the participants (n=90) suffering from OVCFs between May 2019 and October 2020, were randomized by SAS 9.3 to generate a block randomization sequence, which was utilized to randomize the groups in a 1:1 ratio, assigned to the DPKP group (n=45) and the BPKP group (n=45) to undergo accordingly procedures.

OUTCOME MEASURES

The primary outcome was the total operative time. The secondary outcomes included: comparative assessment of visual analog scale (VAS) scores, Oswestry disability index (ODI), kyphosis angle (KA), anterior border height (AH) of the injured vertebra, frequency of intraoperative X-ray fluoroscopy, the injection volume, distribution pattern and leakage rate of bone cement.

METHODS

All subjects underwent assessment by at least one senior orthopedist and radiologist for the VAS scores, ODI, KA, AH of the injured vertebra, total operative time, the injection volume, distribution pattern, leakage rate of bone cement at preoperative and 24 hours, 6 months, and 1 year postoperatively. Inclusion criteria for subjects in this prospective study were as follows: (1) 60 < age < 80 years old; (2) preoperative spinal X-ray, CT, and MRI confirmed as single-segment, fresh thoracolumbar OVCFs (T5-L5, 15% < collapse < 80%); MRI shows low signal on T1-WI and high signal on T2-WI, especially with STIR high signal characterized by vertebral edema; (3) painful OVCFs refractory to medical treatment, 2 weeks < Symptom duration < 3 months;(4) With significant physical signs of local tenderness; (5) T score of bone mineral density (BMD) < -2.5.

RESULTS

The total operative time was significantly reduced in the DPKP group (43.3±19.58 minutes, 95% CI: 37.23-49.37) compared to the BPKP group (55.16±11.56 minutes, 95% CI: 51.78-58.54) (p<.001). Compared to the BPKP group (frequency of intraoperative X-ray fluoroscopy: 43.42±8.64, 95% CI: 40.90-45.95; the volume of bone cement injected: 5.56±0.85 mL, 95% CI: 5.31-5.81), the frequency of intraoperative X-ray fluoroscopy (30.05±17.41, 95% CI: 24.66-35.45) and volume of bone cement injected (5.08±0.97 mL, 95% CI: 4.78-5.38) significantly reduced in the DPKP group compared to the (p<.001). In addition, compared to the preoperative period, both groups showed significant improvements in the postoperative VAS scores, ODI, KA, and AH (p<.001), but there was no statistical difference between the DPKP and BPKP groups (p>.05) at any time-point. Interestingly, although without statistical differences, a tendency towards a lower rate of bone cement leakage was observed in the DPKP group.

CONCLUSION

Our study results indicate that the innovative DPKP is as safe and effective as BPKP in relieving pain, improving the patient's quality of life, and reconstructing vertebral body height. Particularly, DPKP did reduce operative time and radiation exposure compared to BPKP, which correlated with unilateral and bilateral exposure procedures. Moreover, the final cement distribution was less predictable in DPKP, and further studies are warranted to clarify the advantages of DPKP versus conventional unilateral percutaneous kyphoplasty (UPKP) and BPKP.

Effect of cement distribution type on clinical outcome after percutaneous vertebroplasty for osteoporotic vertebral compression fractures in the aging population

Objective

The study aimed to investigate the effect of the type of bone cement distribution on clinical outcomes following percutaneous vertebroplasty (PVP) for osteoporotic vertebral compression fractures (OVCF) in the elderly.

Methods

Retrospective analysis of 160 patients diagnosed with OVCF who underwent PVP treatment from March 2018 to December 2020. Based on the kind of postoperative bone cement distribution, bone cement was classified as types I, II, III, IV, and V. Visual Analog Scale (VAS), Oswestry Disability Index (ODI), Cobb angle, anterior vertebral height ratio, refracture rate of injured vertebrae, and incidence of adjacent vertebral fractures were compared for the five types before and after three days, and one year of operation.

Results

VAS and ODI at three days and one year postoperative were significantly lower than those preoperative (P < 0.05) for all five distribution types. VAS and ODI for types I, II, and III were lower at one year postoperatively than for types IV and V (P < 0.05). There was no significant difference in Cobb angle and anterior vertebral body height ratio between preoperative and three days postoperative groups (P < 0.05); however, there were significant differences between three days and one-year postoperative and preoperative groups (P < 0.05). Following one year of surgery, the Cobb angle and the anterior vertebral height ratio of types IV and V were significantly different from those of types I, II, and III (P < 0.05), and there was a statistically significant difference between types IV and V (P < 0.05). In terms of the incidence of injured vertebral refractures and adjacent vertebral fractures, the evenly distributed types I, II, and III were significantly lower than the unevenly distributed types IV and V, and the incidence of type V was higher (P < 0.05).

Conclusions

The clinical efficacy of cement distribution following PVP of types I, II, and III is better than that of types IV and V, which can better relieve pain with long-lasting efficacy and minimize the occurrence of refractures of injured vertebrae and adjacent vertebral body fractures.

An anatomical feasibility study using CTA reconstruction for modified percutaneous lumbar vertebroplasty

Background

Lumbar vertebroplasty via several different types of extrapedicular approach has been reported with acceptable clinical results yet the anatomical basis for its safety is not fully explored. Injury to the lumbar arteries (LAs) is one of the most important potential complications. However, anatomical research on the course and variability of this structure is lacking. To investigate the anatomical feasibility of percutaneous vertebroplasty for lumbar osteoporotic vertebral compression fractures via a unilateral Extrapedicular approach.

Methods

A total of 300 LAs of 30 patients with non-spinal disorders were retrospectively analyzed by computed tomographic angiography (CTA). The lateral aspect of the vertebral body was divided into 9 zones of approximately equal area. The anatomy and orientation of LAs were analyzed in detail.

Results

LAs were most commonly found in the middle third of the body (zones 4, 5, and 6); the upper 1/3 of the vertebral body had LAs distributed only anteriorly and laterally (zones 1 and 2). No arteries were observed in the postero-superior segment (zone 3). From L1 to L3 an arched pattern predominated. At L4 an inferior oblique pattern (antero-superior to postero-inferior) predominated. Limited CTA visualization at L4 and particularly L5 as well as greater anatomical variation means that there is more uncertainty at these levels.

Conclusion

From L1 to L3, the posterior superior segment (zone 1) of the vertebral body appears to be a safe area with low risk of arterial injury. This has relevance for design of a safe lumbar vertebral extrapedicular approach.

Interventional Radiology in the Management of Metastases and Bone Tumors

Interventional Radiology (IR) has experienced an exponential growth in recent years. Technological advances of the last decades have made it possible to use new treatments on a larger scale, with good results in terms of safety and effectiveness. In musculoskeletal field, painful bone metastases are the most common target of IR palliative treatments; however, in selected cases of bone metastases, IR may play a curative role, also in combination with other techniques (surgery, radiation and oncology therapies, etc.). Primary malignant bone tumors are extremely rare compared with secondary bone lesions: osteosarcoma, Ewing sarcoma, and chondrosarcoma are the most common; however, the role of interventional radiology in this fiels is marginal. In this review, the main techniques used in interventional radiology were examined, and advantages and limitations illustrated. Techniques of ablation (Radiofrequency, Microwaves, Cryoablation as also magnetic resonance imaging-guided high-intensity focused ultrasound), embolization, and Cementoplasty will be described. The techniques of ablation work by destruction of pathological tissue by thermal energy (by an increase of temperature up to 90 °C with the exception of the Cryoablation that works by freezing the tissue up to -40 °C). Embolization creates an ischemic necrosis by the occlusion of the arterial vessels that feed the tumor. Finally, cementoplasty has the aim of strengthening bone segment weakened by the growth of pathological tissue through the injection of cement. The results of the treatments performed so far were also assessed and presented focused the attention on the management of bone metastasis.

A digital twin for simulating the vertebroplasty procedure and its impact on mechanical stability of vertebra in cancer patients

We present the application of ReconGAN, introduced in a previous study, for simulating the vertebroplasty (VP) operation and its impact on the fracture response of a vertebral body. ReconGAN consists of a Deep Convolutional Generative Adversarial Network (DCGAN) and a finite element based shape optimization algorithm to virtually reconstruct the trabecular bone microstructure. The VP procedure involves injecting shear-thinning liquid bone cement through a needle in the trabecular region to reinforce a diseased or fractured vertebra. To simulate this treatment modality, computational fluid dynamics (CFD) is employed to predict the morphology of the injected cement within the bone microstructure. A power-law equation is utilized to characterize the non-Newtonian shear-thinning behavior of the polymethyl methacrylate (PMMA) bone cement during injection simulations. The CFD model is coupled with the level-set method to simulate the motion of the interface separating bone cement and bone marrow. After predicting the cement morphology, a data co-registration algorithm is employed to transform the CFD model to a high-fidelity continuum damage mechanics (CDM) finite element model of the augmented vertebra for predicting the fracture response. A feasibility study is presented to demonstrate the ability of this CFD-CDM framework to investigate the effect of VP on the mechanical integrity of the vertebral body in a cancer patient with a lytic metastatic tumor.

Comparison of Unipedicular and Bipedicular Percutaneous Kyphoplasty for Kummell's Disease

Objective

To compare the clinical efficacy of unipedicular and bipedicular percutaneous kyphoplasty (PKP) for Kummell's disease.

Methods

A retrospective study was performed to review 40 patients with stage I and II Kummell's disease who underwent PKP in our hospital from January 2015 to June 2018. Based on the transpedicular approach of PKP, those patients were randomly divided into unipedicular group (n = 19) and bipedicular group (n = 21). Operative time, bone cement injection volume and cement leakage rate were compared in the two groups. Pre- and post-operative visual analogue score (VAS), local kyphotic angle and average vertebral height were also evaluated.

Results

All patients underwent surgery successfully. Compared with preoperative condition, VAS was significantly decreased at 1 day after operation and the last follow-up in both groups (P < .05), and local kyphotic angle and average vertebral height were restored markedly (P < .05). Operative time of both groups had no significant difference (P > .05). Bone cement injection volume was larger in bipedicular group (P < .05). At 1 day after operation and the last follow-up, the local kyphotic angle and average vertebral height in bipedicular group were restored better than those in unipedicular group (P < .05). There were 4 cases of cement leakage in both groups, with leakage rates of 21.1% and 19.0%, respectively, and the difference was not significant (P > .05).

Conclusion

Both unipedicular and bipedicular PKP are effective for treating patients with stage I and II Kummell's disease, while postoperative pain relief and imaging results in bipedicular group were better than those in unipedicular group.

A Three-Dimensional Cement Quantification Method for Decision Prediction of Vertebral Recompression after Vertebroplasty

Objective

Proposing parameters to quantify cement distribution and increasing accuracy for decision prediction of vertebroplasty postoperative complication.

Methods

Finite element analysis was used to biomechanically assess vertebral mechanics (n = 51) after percutaneous vertebroplasty (PVP) or kyphoplasty (PKP). The vertebral space was divided into 27 portions. The numbers of cement occupied portions and numbers of cement-endplate contact portions were defined as overall distribution number (oDN) and overall endplate contact number (oEP), respectively. And cement distribution was parametrized by oDN and oEP. The determination coefficients of vertebral mechanics and parameters (R 2) can validate the correlation of proposed parameters with vertebral mechanics.

Results

oDN and oEP were mainly correlated with failure load (R 2 = 0.729) and stiffness (R 2 = 0.684), respectively. oDN, oEP, failure load, and stiffness had obvious difference between the PVP group and the PKP group (P < 0.05). The regional endplate contact number in the front column is most correlated with vertebral stiffness (R 2 = 0.59) among all regional parameters. Cement volume and volume fraction are not dominant factors of vertebral augmentation, and they are not suitable for postoperative fracture risk prediction.

Conclusions

Proposed parameters with high correlation on vertebral mechanics are promising for clinical utility. The oDN and oEP can strongly affect augmented vertebral mechanics thus is suitable for postoperative fracture risk prediction. The parameters are beneficial for decision-making process of revision surgery necessity. Parametrized methods are also favorable for surgeon's preoperative planning. The methods can be inspirational for clinical image recognition development and auxiliary diagnosis.

Effects of Location and Volume of Intraosseous Cement on Adjacent Level of Osteoporotic Spine Undergoing Kyphoplasty: Finite Element Analysis

OBJECTIVE

Kyphoplasty (KP) is a surgery used to reduce pain and increase stability by injecting medical bone cement into broken vertebrae. The purpose of this study was to determine the ideal amount of cement and injection site by analyzing forces with the finite element method.

METHODS

We modeled the anatomical structure of the vertebra and injected the cement at T12. By increasing the amount of cement from 1 cc to 22 cc, stress applied to T11 and L1 cortical was calculated. In addition, stress applied to the adjacent KP level was calculated with different injection sites (medial, anterosuperior, posterosuperior, anteroinferior, and posteroinferior). After 5 cc cement was inserted, adjacent end plate stress was analyzed.

RESULTS

In this study, break point adjacent bone stress according to the capacity of cement was bimodal. Flexion/extension and lateral bending conditions showed similar break points (11.5-11.7 cc and 18.5-18.6 cc, respectively). When cement injection was changed, front under and back under had the highest stress values among various parts, whereas the center position showed the lowest stress value.

CONCLUSIONS

With increasing amount of bone cement, stress on the upper and lower end plates of the cemented segment increased significantly. Thus, increasing cement amount to be more than 11.5 cc has a potential risk of adjacent fracture. Centrally injected bone cement can lower the risk of adjacent fracture after percutaneous KP.

Clinical Outcomes of Fracture Haemorrhage Aspiration for Percutaneous Vertebroplasty in Treating Osteoporotic Vertebral Compression Fractures

Background

A retrospective study aimed to introduce a new method for improving the diffusion degree of bone cement and to observe its clinical efficacy in percutaneous vertebroplasty treating osteoporotic vertebral compression fractures (OVCFs).

Methods

From January 2019 to March 2020, a total of 83 patients were enrolled and reviewed. The patients were divided into two groups according to the operation method. The clinical and radiographic parameters were recorded and compared between these two groups. Those who received percutaneous vertebroplasty with haemorrhage aspiration were recorded as group A (n=42). In group A, the haemorrhage in the vertebral fracture was aspirated compared with conventional percutaneous vertebroplasty. Patients who underwent conventional percutaneous vertebroplasty were classified as group B (n=41).

Results

Visual analogue scale (VAS) values and Oswestry Disability Index (ODI) scores showed no significant difference between the two groups preoperatively, postoperatively or at the final follow-up (FU) (P>0.05). The intraoperative VAS score (bone cement injection) in group A was significantly lower than that in group B (3.83±0.79 vs 5.44±1.32, P < 0.01). The local kyphotic angle (LKA) (final follow-up), LKA loss, fractured vertebral anterior height loss (FVAHL) and anterior vertebral height loss ratio (AVHLR) were significantly lower in group A than in group B. The anterior vertebral height ratio (AVHR) at the final FU in group A was higher than that in group B (P=0.013). The distribution of bone cement was significantly different (P=0.034). By analysing the distribution pattern of bone cement, it was found that the values of LKA loss, FVAHL and AVHLR were superior in the type A bone cement distribution to those in types B and C.

Conclusion

Compared with traditional surgical methods, bone haemorrhage aspiration could improve the diffusion degree of bone cement and reduce the height loss and deformity of injured vertebrae. This method provides a feasible new scheme for improving the dispersion of bone cement.

Development and validation of a nomogram for predicting the probability of new vertebral compression fractures after vertebral augmentation of osteoporotic vertebral compression fractures

INTRODUCTION

New vertebral compression fractures (NVCFs) are adverse events after vertebral augmentation of osteoporotic vertebral compression fractures (OVCFs). Predicting the risk of vertebral compression fractures (VCFs) accurately after surgery is still a significant challenge for spinal surgeons. The aim of our study was to identify risk factors of NCVFs after vertebral augmentation of OVCFs and develop a nomogram.

METHODS

We retrospectively reviewed the medical records of patients with OVCFs who underwent percutaneous vertebroplasty (PVP) or percutaneous kyphoplasty (PKP). Patients were divided into the NVCFs group and control group, base on the patients with or without NVCFs within 2 years follow-up period after surgery. A training cohort of 403 patients diagnosed in our hospital from June 2014 to December 2016 was used for model development. The independent predictive factors of postoperative VCFs were determined by least absolute shrinkage and selection operator (LASSO) logistic regression, univariate analysis and multivariate logistic regression analysis. We provided a nomogram for predicting the risk of NVCFs based on independent predictive factors and used the receiver operating characteristic curve (ROC), calibration curve, and decision curve analyses (DCA) to evaluated the prognostic performance. After internal validation, the nomogram was further evaluated in a validation cohort of 159 patients included between January 2017 and June 2018.

RESULTS

Of the 403 patients in the training cohort, 49(12.16%) were NVCFs at an average of 16.7 (1 to 23) months within the 2 years follow-up period. Of the 159 patients in the validation cohort, 17(10.69%) were NVCFs at an average of 8.7 (1 to 15) months within the 2 years follow-up period. In the training cohort, the proportions of elderly patients older than 80 years were 32.65 and 13.56% in the NVCFs and control group, respectively (p = 0.003). The percentages of patients with previous fracture history were 26.53 and 12.71% in the NVCFs and control group, respectively (p = 0.010). The volume of bone cement were 4.43 ± 0.88 mL and 4.02 ± 1.13 mL in the NVCFs and Control group, respectively (p = 0.014). The differences have statistical significance in the bone cement leakage, bone cement dispersion, contact with endplate, anti-osteoporotic treatment, post-op Cobb angle and Cobb angle restoration characteristics between the two groups. The model was established by multivariate logistic regression analysis to obtain independent predictors. In the training and validation cohort, the AUC of the nomogram were 0.882 (95% confidence interval (CI), 0.824-0.940) and 0.869 (95% CI: 0.811-0.927), respectively. The C index of the nomogram was 0.886 in the training cohort and 0.893 in the validation cohort, demonstrating good discrimination. In the training and validation cohort, the optimal calibration curves demonstrated the coincidence between prediction and actual status, and the decision curve analysis demonstrated that the full model had the highest clinical net benefit across the entire range of threshold probabilities.

CONCLUSION

A nomogram for predicting NVCFs after vertebral augmentation was established and validated. For patients evaluated by this model with predictive high risk of developing postoperative VCFs, postoperative management strategies such as enhance osteoporosis-related health education and management should be considered.

Clinical observation of two bone cement distribution modes after percutaneous vertebroplasty for osteoporotic vertebral compression fractures

Background

Current findings suggest that percutaneous vertebroplasty(PVP) is a suitable therapeutic approach for osteoporotic vertebral compression fractures (OVCFs). The present retrospective study aimed to investigate the differences in clinical efficacy and related complications between the two bone cement distribution modes.

Methods

We retrospectively reviewed the medical records of the patients with single-segment OVCFs who underwent bilateral percutaneous vertebroplasty. Patients were divided into blocky and spongy group according to the type of postoperative bone cement distribution. Clinical efficacy and related complications was compared between the two bone cement distribution modes on 24 h after the operation and last follow-up.

Results

A total of 329 patients with an average follow up time of 17.54 months were included. The blocky group included 131 patients, 109 females(83.2 %) and 22 males(16.8 %) with a median age of 72.69 ± 7.76 years, while the Spongy group was made up of 198 patients, 38 females(19.2 %) and 160 males(80.8 %) with a median age of 71.11 ± 7.36 years. The VAS and ODI after operation improved significantly in both two groups. The VAS and ODI in the spongy group was significantly lower than that in the blocky group, 24 h postoperatively, and at the last follow-up. There were 42 cases (12.8 %) of adjacent vertebral fractures, 26 cases (19.8 %) in the blocky group and 16 cases (8.1 %) in the spongy group. There were 57 cases (17.3 %) of bone cement leakage, 18 cases (13.7 %) in blocky group and 39 cases (19.7 %) in the spongy group. At 24 h postoperatively and at the last follow-up, local kyphosis and anterior vertebral height were significantly corrected in both groups, but gradually decreased over time, and the degree of correction was significantly higher in the spongy group than in the block group. The change of local kyphosis and loss of vertebral body height were also less severe in the spongy group at the last follow-up.

Conclusions

Compared with blocky group, spongy group can better maintain the height of the vertebral body, correct local kyphosis, reduce the risk of the vertebral body recompression, long-term pain and restore functions.

A Multiscale Finite Element Analysis of Balloon Kyphoplasty to Investigate the Risk of Bone-Cement Separation In Vivo

BACKGROUND

During the past decade there has been a significant increase in the number of vertebral fractures being treated with the balloon kyphoplasty procedure. Although previous investigations have found kyphoplasty to be an effective treatment for reducing patient pain and lowering cement-leakage risk, there have been reports of vertebral recollapse following the procedure. These reports have indicated evidence of in vivo bone-cement separation leading to collapse of the treated vertebra.

METHODS

The following study documents a multiscale analysis capable of evaluating the risk of bone-cement interface separation during lying, standing, and walking activities following balloon kyphoplasty.

RESULTS

Results from the analysis found that instances of reduced cement interlock could initiate both tensile and shear separation of the interface region at up to 7 times the failure threshold during walking or up to 1.9 times the threshold during some cases for standing. Lying prone offered the best protection from interface failure in all cases, with a minimum safety factor of 2.95.

CONCLUSIONS

The results of the multiscale analysis show it is essential for kyphoplasty simulations to take account of the micromechanical behavior of the bone-cement interface to be truly representative of the in vivo situation after the treatment. The results further illustrate the importance of ensuring adequate cement infiltration into the compacted bone periphery during kyphoplasty through a combination of new techniques, tools, and biomaterials in a multifaceted approach to solve this complex challenge.

The effect of bone cement distribution on the outcome of percutaneous Vertebroplasty: a case cohort study

Background

To analyze the effect of different types of bone cement distribution after percutaneous vertebroplasty (PVP) in patients with osteoporotic vertebral compression fracture (OVCF).

Methods

One hundred thirty seven patients with single level OVCF who underwent PVP were retrospectively analyzed. The patients were divided into two groups according to bone cement distribution. Group A: bone cement contacted both upper and lower endplates; Group B: bone cement missed at least one endplate. Group B was divided into 3 subgroups. Group B1: bone cement only contacted the upper endplates; Group B2: bone cement only contacted the lower endplates; Group B3: bone cement only located in the middle of vertebral body. The visual analogue scale (VAS) score at 24 h post operation and last follow-up, anterior vertebral height restoration ratio (AVHRR), anterior vertebral height loss ratio (AVHLR), local kyphotic angle change and vertebral body recompression rate were compared.

Results

24 h post operation, the pain of all groups were significantly improved. The average follow-up time was 15.3 ± 6.3 (6–24) months. At last follow-up, the VAS score of group A was lower than that of group B. There were 14 cases (10.2%) of adjacent vertebral fracture, 5 cases (8.6%) in group A and 9 cases (11.4%) in group B. There were 9 cases (6.6%) of cement leakage, 4 cases (6.9%) in group A and 5 cases (6.3%) in group B. At last follow-up, there were 16 cases (11.7%) of vertebral body recompression, including 3 cases (5.2%) in group A and 13 cases (16.5%) in group B. There was no significant difference in AVHRR between two groups. Local kyphotic angle change was significant larger in group B. At last follow-up, AVHLR in group B was higher than that in group A. Analysis in subgroup B revealed no significant difference in VAS score, local kyphotic angle change, vertebral recompression rate, AVHRR or AVHLR.

Conclusions

If the bone cement fully contacted both the upper and lower endplates, it can better restore the strength of the vertebral body and maintain the height of the vertebral body, reduce the risk of the vertebral body recompression and long-term pain.

Optimizing computational methods of modeling vertebroplasty in experimentally augmented human lumbar vertebrae

Vertebroplasty has been widely used for the treatment of osteoporotic compression fractures but the efficacy of the technique has been questioned by the outcomes of randomized clinical trials. Finite-element (FE) models allow an investigation into the structural and geometric variation that affect the response to augmentation. However, current specimen-specific FE models are limited due to their poor reproduction of cement augmentation behavior. The aims of this study were to develop new methods of modeling the vertebral body in both a nonaugmented and augmented state. Experimental tests were conducted using human lumbar spine vertebral specimens. These tests included micro-computed tomography imaging, mechanical testing, augmentation with cement, reimaging, and retesting. Specimen-specific FE models of the vertebrae were made comparing different approaches to capturing the bone material properties and to modeling the cement augmentation region. These methods significantly improved the modeling accuracy of nonaugmented vertebrae. Methods that used the registration of multiple images (pre- and post-augmentation) of a vertebra achieved good agreement between augmented models and their experimental counterparts in terms of predictions of stiffness. Such models allow for further investigation into how vertebral variation influences the mechanical outcomes of vertebroplasty.

The effect of bone cement distribution on clinical efficacy after percutaneous kyphoplasty for osteoporotic vertebral compression fractures

To evaluate the influence of various distributions of bone cement on the clinical efficacy of percutaneous kyphoplasty (PKP) in treating osteoporotic vertebrae compression fractures.A total of 201 OVCF patients (30 males and 171 females) who received PKP treatment in our hospital were enrolled in this study. According to the characteristic of cement distribution, patients were divided into 2 groups: group A ("H" shaped group), the filling pattern in vertebral body were 2 briquettes and connected with / without cement bridge; and group B ("O" shaped group), the filling pattern in vertebral body was a complete crumb and without any separation. Bone mineral density, volume of injected cement, radiographic parameters, and VAS scores were recorded and analyzed between the 2 groups.All patients finished at least a 1-year follow-up and both groups had significant improvement in radiographic parameters and clinical results. No significant differences in BMD, operation time, bleeding volume, or leakage of cement were observed between the 2 groups. Compared with group B, group A had a larger use of bone cement, lower proportion of unipedicular approach, and better VAS scores at 1 year after surgery.Both "H" and "O" shaped distribution pattern can improve radiographic data and clinical outcomes effectively. However, "H" shaped distribution can achieve better clinical recovery at short-term follow-up.

Postoperative Clinical Outcomes of Balloon Kyphoplasty Treatment: Would Adherence to Indications and Contraindications Prevent Complications?

Study Design

We retrospectively assessed the postoperative clinical outcomes of balloon kyphoplasty (BKP).

Purpose

To evaluate the risk factors for complications and to reconfirm the indications and contraindications for BKP.

Overview of Literature

In Japan, BKP is indicated for cases of osteoporotic vertebral fractures when pain is not improved even after an adequate period of conservative treatment. Contraindications to BKP include pedicle fracture, fracture of a flat vertebra, or fracture of the posterior wall of the vertebral body diagnosed on computed tomography.

Methods

Seventy-five patients who underwent BKP in our institution participated in this study; 49 provided follow-up data. Those with complications and persistent pain were assigned to the “eventful” group; the others, to the “uneventful” group. We evaluated risk factors for complications and persistent pain, including the presence or absence of severe posterior wall injury/pedicle fracture, the shape of the vertebral body, and the time period from onset of pain to BKP.

Results

The incidences of severe posterior wall injury, pedicle fracture, and flattened vertebral body did not differ significantly between the uneventful and eventful groups. However, there was a significant difference in disease duration between those with and those without adjacent vertebral fractures (AVFs): The incidence of AVF was lower among patients with disease of less than 8 weeks’ duration.

Conclusions

Disease duration is a possible risk factor for developing AVF, whereas other characteristics were not risk factors for complications after BKP. Although it has been suggested that BKP treatment in the early phase after injury results in a good outcome, the indications should be determined according to prognosis that is based on findings obtained with tools such as imaging examinations.

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

Vertebral compression fractures are one of the most relevant clinical consequences caused by osteoporosis: one of the most common treatment for such fractures is vertebral augmentation through minimally invasive approaches (vertebroplasty or balloon-kyphoplasty). Unfortunately, these techniques still present drawbacks, such as re-fractures of the treated vertebral body with subsidence of the non-augmented portions or re-fracture of the non-augmented middle column at the junction with the augmented anterior column. A novel minimally-invasive augmentation technique, called Stent-Screw Assisted Internal Fixation, has been recently proposed for the treatment of severe osteoporotic and neoplastic fractures: this technique uses two vertebral body stents and percutaneous cannulated and fenestrated pedicular screws, through which cement is injected inside the expanded stents to achieve optimal stents' and vertebral body's filling. The role of the pedicle screws is to anchor the stents-cement complex to the posterior column, acting as a bridge across the middle column and preserving its integrity from possible collapse. In order to evaluate the potential of the new technique in restoring the load bearing capacity of the anterior and middle spinal columns and in reducing bone strains, a Finite Element model of an osteoporotic lumbar spine has been developed. Both standard vertebroplasty and Stent-Screw Assisted Internal Fixation have been simulated: simulations have been run taking into account everyday activities (standing and flexion) and comparison between the two techniques, in terms of strain distribution on vertebral endplates and posterior and anterior wall, was performed. Results show that Stent-Screw Assisted Internal Fixation significantly decrease the strain distribution on the superior EP and the cortical wall compared to vertebroplasty, possibly reducing the re-fracture risk of the middle-column at the treated level.

Percutaneous Vertebral Body Augmentations: The State of Art

Osteoporotic compression fractures of the vertebral body can result in pain and long-term morbidity, including spinal deformity, with increased risk of mortality resulting from associated complications. Conservative management includes opioids and other analgesics, bed rest, and a back brace. For patients with severe and disabling pain, vertebral augmentation (vertebroplasty and kyphoplasty) is often considered, with these procedures endorsed by multiple professional societies, and provides immediate structural support, and stabilizes and reinforces the weakened bone structure. The purpose of this article is to review the vertebral biomechanics, indications and contraindications, and techniques of performing successful vertebral augmentation.

Influence of the distribution of bone cement along the fracture line on the curative effect of vertebral augmentation

Objective

The present study was performed to evaluate the effect of different bone cement distributions along the fracture line on clinical and imaging outcomes of vertebral augmentation.

Methods

In total, 84 patients who underwent vertebral augmentation for a single osteoporotic vertebral compression fracture from January 2016 to August 2018 were retrospectively reviewed. These patients were divided into two groups according to the relationship between the bone cement distribution and the fracture line: the unilateral group (n = 23) and the bilateral group (n = 61). Postoperative clinical and imaging parameters were compared between the two groups.

Results

Statistical analyses showed no significant difference in postoperative pain relief, bone cement leakage, nerve injury, or new vertebral fracture between the two groups. Significant recovery from vertebral compression was observed in the bilateral group after surgery, but there was no significant difference in vertebral compression after surgery in the unilateral group.

Conclusions

Pain relief was similar for different types of cement distributions along the fracture line, but a bilateral cement distribution exhibited better recovery from vertebral compression and did not increase bone cement leakage in the vertebral augmentation procedure.

Kyphoplasty of Osteoporotic Fractured Vertebrae: A Finite Element Analysis about Two Types of Cement

If conservative treatment of osteoporotic vertebral compression fractures fails, vertebro- or kyphoplasty is indicated. Usually, polymethylmethacrylate cement (PMMA) is applied coming along with many disadvantageous features. Aluminum-free glass-polyalkenoate cement (GPC) appears to be a benefit alternative material. This study aimed at comparing the mean stress values in human vertebrae after kyphoplasty with PMMA and GPC (IlluminOss™) at hand of a finite element analysis. Three models were created performing kyphoplasty using PMMA or IlluminOss™, respectively, at two native, human lumbar vertebrae (L4) while one remains intact. Finite element analysis was performed using CT-scans of every vertebra. Moreover the PMMA-treated vertebra was used as a model as analyses were executed using material data of PMMA and of GPC. The unimpaired, spongious bone showed potentials of 0.25 MPa maximally. After augmentation stress levels showed fivefold increase, rising from externally to internally, revealing stress peaks at the ventral border of the spinal canal. At central areas of cement 1 MPa is measured in both types of cement. Around these central areas the von Mises stress decreased about 25-50% (0.5-0.75 MPa). If workload of 500 N was applied, the stress appeared to be more centralized at the IlluminOss™-model, similar to the unimpaired. Considering the endplates the GPC model also closely resembles the unimpaired. Comparing the PMMA-treated vertebral body and the GPC-simulation, there is an obvious difference. While the PMMA-treated model showed a central stress peak of 5 MPa, the GPC-simulation of the same vertebral body presents lower stress of 1.2-2.5 MPa. Finite element analysis showed that IlluminOss™ (GPC), used in kyphoplasty of vertebral bodies, creates lower level stress and strain compared to standardly used PMMA, leading to lower stress concentrations on the cranial and caudal vertebral surface especially. GPC appears to own advantageous biological and clinical relevant features.

Distribution Pattern Making Sense: Patients Achieve Rapider Pain Relief with Confluent Rather Than Separated Bilateral Cement in Percutaneous Kyphoplasty for Osteoporotic Vertebral Compression Fractures

BACKGROUND

It has been reported the distribution of bone cement in percutaneous kyphoplasty (PKP) has an impact on the curative effect. No studies have compared between confluent and separated cement pattern of bilateral bone cement in PKP for patients with osteoporotic vertebral compression fractures.

METHODS

Between 2010 and 2016, 1341 patients were enrolled and divided into 2 groups. Group A (n = 723), bilateral cement was confluent; Group B (n = 618), bilateral cement was separated. The visual analogue scale (VAS), Oswestry Disability Index (ODI), anterior vertebral height (AVH), and local kyphotic angle (LKA) were obtained preoperatively, 2 days after surgery, and at the final follow-up to assess the functional and radiographic efficacy of the surgery.

RESULTS

The VAS, ODI, AVH, and LKA 2 days after operation and at the final follow-up were significantly improved compared with the preoperative for both groups (P < 0.05). There existed no significant difference between groups at various time point in ODI, AVH, and LKA (P > 0.05). Group A showed better VAS than group B 2 days after surgery (1.91 ± 0.98 vs. 2.35 ± 0.78, P < 0.001), also with better pre-postoperative VAS change (6.23 ± 0.76 vs. 5.75 ± 1.02, P < 0.001). Multiple linear regression for pain relief degree revealed group A (P < 0.001), older age (P < 0.001), and more cement volume (P < 0.001) contribute to rapid improvement of back pain. The cement leakage rate was 3.7% in group A and 2.9% in group B, with no significant difference (P = 0.405).

CONCLUSIONS

Patients achieved rapider pain relief with confluent rather than separated bilateral bone cement pattern in PKP for osteoporotic vertebral compression fracture.

Prophylactic vertebroplasty versus kyphoplasty in osteoporosis: A comprehensive biomechanical matched-pair study by in vitro compressive testing

Vertebroplasty and kyphoplasty are alternative augmentation techniques of osteoporotic vertebral compression fractures. However, shortly after augmentation, new vertebral compression fractures may occur, mostly in the adjacent vertebrae. To prevent this, prophylactic cement injection can be applied to the neighboring vertebral bodies. Although there are many evidence-based clinical studies on the potential hazards of vertebroplasty and kyphoplasty, there are only few studies comparing the prophylactic potential of the two treatments. In this matched-pair experimental biomechanical study, the two treatments were compared via destructive compressive testing of 76 non-fractured osteoporotic human lumbar vertebral bodies from 24 cadavers, augmented pair-wise with vertebroplasty or kyphoplasty. Strength, stiffness and deformability were analyzed in terms of donor age, CT-based bone density, vertebral morphometry, and cement-endplate contacts. These were investigated in a paired analysis and also in terms of the number of cement-endplate contacts. Vertebroplasty resulted in significantly, but only 19% larger stiffness, approximately equal failure load and smaller failure displacement compared to kyphoplasty. Cement-endplate contacts affect augmentation differently for the two techniques, namely, strength significantly increased with increasing number of contacts in vertebroplasty, but decreased in kyphoplasty. The reasons for these contrasting behavior included the fundamentally different augmentation method, the resulting different construction and location of cement clouds and the different form and location of failure. These results indicate that both prophylactic vertebroplasty and kyphoplasty of non-fractured adjacent vertebrae may be advantageous to avoid subsequent fractures after post-fracture vertebroplasty and kyphoplasty, respectively. However, cement bridging in vertebroplasty and central cement placement in kyphoplasty are advantageous in prevention.

Case-specific non-linear finite element models to predict failure behavior in two functional spinal units

Current finite element (FE) models predicting failure behavior comprise single vertebrae, thereby neglecting the role of the posterior elements and intervertebral discs. Therefore, this study aimed to develop a more clinically relevant, case-specific non-linear FE model of two functional spinal units able to predict failure behavior in terms of (i) the vertebra predicted to fail; (ii) deformation of the specimens; (iii) stiffness; and (iv) load to failure. For this purpose, we also studied the effect of different bone density-mechanical properties relationships (material models) on the prediction of failure behavior. Twelve two functional spinal units (T6-T8, T9-T11, T12-L2, and L3-L5) with and without artificial metastases were destructively tested in axial compression. These experiments were simulated using CT-based case-specific non-linear FE models. Bone mechanical properties were assigned using four commonly used material models. In 10 of the 11 specimens our FE model was able to correctly indicate which vertebrae failed during the experiments. However, predictions of the three-dimensional deformations of the specimens were less promising. Whereas stiffness of the whole construct could be strongly predicted (R²  = 0.637-0.688, p < 0.01), we obtained weak correlations between FE predicted and experimentally determined load to failure, as defined by the total reaction force exhibiting a drop in force (R²  = 0.219-0.247, p > 0.05). Additionally, we found that the correlation between predicted and experimental fracture loads did not strongly depend on the material model implemented, but the stiffness predictions did. In conclusion, this work showed that, in its current state, our FE models may be used to identify the weakest vertebra, but that substantial improvements are required in order to quantify in vivo failure loads. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodical, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 36:3208-3218, 2018.

Percutaneous Vertebral Augmentation for Osteoporotic Vertebral Compression Fracture in the Midthoracic Vertebrae (T5-8): A Retrospective Study of 101 Patients with 111 Fractured Segments

OBJECTIVE

Data reporting percutaneous vertebroplasty (PVP) or percutaneous balloon kyphoplasty (PKP) application to the midthoracic vertebrae remain limited. This study aimed to summarize our experiences and explore the efficacy and safety of PVP or PKP in dealing with osteoporotic vertebral compression fracture (OVCF) in the midthoracic vertebrae.

METHODS

Patients receiving PVP or PKP for midthoracic OVCF in our institution from January 2015 to January 2018 were retrospectively enrolled. All patients were grouped according to cement augmentation procedure types, surgical approaches, and puncture routes. All patients underwent a postoperative follow-up of 2-36 months. Visual analog scale (VAS) and ECOG Scale of Performance Status scores were evaluated pre- and postoperatively. Cement distribution and rate of cement leakage were assessed by radiographs. Associations of these variables and clinical scores and radiographic indices were analyzed.

RESULTS

A total of 101 consecutive patients with 111 fractured centrums were enrolled. Both VAS and ECOG Scale of Performance Status scores of all patients decreased significantly after the operation, and progressively decreased at the final follow-up. The cement distribution of the bipedicular group was significantly better than the unipedicular group, but the total leakage rate of the former (71.7%) was significantly higher than the latter (43.1%). The rate of epidural cement leakage in the PKP group (5.4%) was significantly lower than that of the PVP group (20.3%), whereas the left puncture group (28.6%) was significantly higher than that of the right puncture group (2.7%).

CONCLUSIONS

PKP and a bipedicular approach can help improve cement distribution and reduce the epidural cement leakage rate and therefore should be preferred over PVP or a unipedicular approach in OVCF of the midthoracic vertebrae.

Fracture generation in human vertebrae under compression loading: The influence of pedicle preservation and bone mineral density on in vitro fracture behavior

BACKGROUND

Fractured vertebral bodies are a common and wide spread health issue.

OBJECTIVE

The purpose of this study was to develop a standardized method to experimentally generate compression fractures in vertebral bodies. The influence of the pedicles has been investigated with regards to the fracture behavior. The correlation between bone mineral density (BMD), the cause of fractures and the fracture behavior was investigated.

METHODS

Twenty-one fresh frozen human lumbar spines were examined for bone mineral density (BMD) by means of quantitative computed tomography (qCT). All soft tissue was removed, vertebrae were carefully separated from each other and the exposed cranial and caudal endplates were covered with a thin layer of resin to generate a plane and homogeneous surface. A total of 80 vertebral bodies were tested until fracture.

RESULTS

A good positive correlation was found between BMD, fracture compression force and stiffness of the vertebral body. No significant differences were found between the fractures generated in vertebral bodies with and without pedicles, respectively.

CONCLUSIONS

Our model represents a consolidation of already existing testing devices. The comparative measurement of the BMD and the fracture behavior shows validity. In contrast to other authors, the force was applied to the whole vertebral body. Furthermore the upper and lower plates were not parallelized and therefore the natural anatomic shape was imitated. Fracture behavior was not altered by removing the pedicles.

Coronal Imaging Changes Associated with Recollapse of Injured Vertebrae After Percutaneous Vertebroplasty or Percutaneous Kyphoplasty Treatment for Osteoporotic Thoracolumbar Fracture

OBJECTIVE

To observe coronal imaging changes associated with recollapse of injured vertebrae after percutaneous vertebroplasty or percutaneous kyphoplasty for osteoporotic thoracolumbar fracture (OTLF).

METHODS

Fifty-four cases were retrospectively divided into 2 groups according to the Arbeitsgemeinschaft für Osteosynthesefragen/Association for the Study of Internal Fixation (AO/ASIF) classification of thoracolumbar fracture: group A, type A1 fracture (n = 26); group B, type A3.1 fracture (n = 28). Visual analog scale, Oswestry Disability Index, local scoliotic Cobb angle, and coronal wedge angle of the injured vertebrae were observed preoperatively, on postoperative day 3, and at final follow-up.

RESULTS

The average follow-up time was 19.17 ± 6.30 months. At final follow-up, the visual analog scale score and the Oswestry Disability Index score were significantly greater in group B than in group A (both P < 0.05). At final follow-up, loss of correction of scoliotic Cobb angle and coronal wedge angle was significantly higher in group B than in group A (P < 0.05).

CONCLUSIONS

Percutaneous vertebroplasty or percutaneous kyphoplasty was effective in both type A1 and type A3.1 OTLF. However, coronal imaging changes after percutaneous vertebroplasty or percutaneous kyphoplasty were more obvious in type A3.1 OTLF than in type A1. Moreover, clinical outcomes in type A3.1 OTLF were slightly inferior to those in type A1.

Glass -polyalkenoate cement: An alternative material for kyphoplasty in osteoporotic vertebral compression fractures - An ex vivo study

Adjacent vertebral body fracture is described as a risk after vertebroplasty and kyphoplasty. It may be true that this phenomenon is caused precisely because of the frequently used polymethylmethacrylate cement (PMMA), which shows a higher level of stiffness than bone material and may ultimately lead to shifting stress levels within the entire spine. The goal of the present study was to evaluate and compare the pressure distribution in the endplate of human vertebrae after kyphoplasty with PMMA and aluminum-free glass-polyalkenoate cement (gpc). For the present study, 8 fresh frozen human cadaveric vertebral bodies from the thoracolumbar junction were used. All vertebrae were augmented transpedicularly on one side with gpc and on the other side with PMMA. A loading of 600 N, 800 N and 1000 N was applied. In the data processing an individual region of interest (roi) was generated for each vertebra. The following parameters were determined for each roi: maximum force [N], maximum pressure [kPa], mean pressure [kPa], roi area [cm²]. We found significantly higher mean pressure values in the areas of the vertebrae augmented with PMMA, compared to the ones after augmentation with gpc (p = 0.012) when applying 1000 N. In the groups with lower forces there were no statistical relevant differences. The pressure distribution shows an advantage for gpc. A material, which does not create load concentration onto the cranial and caudal vertebral surface, could have major advantages concerning the risk of adjacent vertebral fractures. Thus the results of the 1000 N loading protocol suggest gpc being a possible alternative to ordinary PMMA cement, regarding its influence on stiffness in kyphoplasty. These and other general aspects like incorporation should be addressed and elaborated more detailed in further studies.

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.

A REVIEW ON BIOMECHANICAL ASPECTS OF VERTEBROPLASTY AND KYPHOPLASTY USING FINITE ELEMENT MODELING-BASED METHODS

The vertebroplasty (VP) and kyphoplasty (KP) are two minimally invasive surgeries using cement augmentation to treat the osteoporotic vertebrae in elderlies in order to relieve pain and prevent the continuation of microfractures. Biomechanists have always tried to assess the mechanical behavior of vertebrae after cement augmentation by using both the experimental and theoretical methods such as finite element modeling (FEM).

In this study, 31 related articles using FEM in analyzing the VP and KP have been reviewed. This study included two main categories of spinal load distribution and tension in vertebrae after the VP and KP operations. This could be obtained by conducting FEM on the whole spine or other sectors of it such as intervertebral disc (IVD) or end plates (EPs). This study also referred to articles predicting the probability of adjacent fractures following VP and KP. The most common software employed in FEM was ABAQUS, applied for static and dynamic loads’ analyses.

It was found that most of the reviewed articles adopted reverse engineering techniques by converting 2D computed tomography (CT) scan images into 3D reconstructed models. The material properties were generally taken from the literature. In more than 80% of studies, the model geometry was based on CT data of the spine. Almost 45% of the studies have attempted to compare the simulated vertebra after augmentation with experimental results taken from the literature (5% of the reviewed articles) or their own experimental tests (40% of the reviewed articles).

Computational modeling of long-term effects of prophylactic vertebroplasty on bone adaptation

Cement augmentation in vertebrae (vertebroplasty) is usually used to restore mechanical strength after spinal fracture but could also be used as a prophylactic treatment. So far, the mechanical competence has been determined immediately post-treatment, without considering long-term effects of bone adaptation. In this work, we investigated such long-term effects of vertebroplasty on the stiffness of the augmented bone by means of computational simulation of bone adaptation. Using micro-finite element analysis, we determined sites of increased mechanical stress (stress raisers) and stress shielding and, based on the simulations, regions with increased or decreased bone loss due to augmentation. Cement volumes connecting the end plates led to increased stress shielding and bone loss. The increased stiffness due to the augmentation, however, remained constant over the simulation time of 30 years. If the intervention was performed at an earlier time point, it did lead to more bone loss, but again, it did not affect long-term stability as this loss was compensated by bone gains in other areas. In particular, around the augmentation cement, bone structures were preserved, suggesting a long-term integration of the cement in the augmented bone. We conclude that, from a biomechanical perspective, the impact of vertebroplasty on the bone at the microstructural level is less detrimental than previously thought.

Effect of the In Vitro Boundary Conditions on the Surface Strain Experienced by the Vertebral Body in the Elastic Regime

The vertebral strength and strain can be assessed in vitro by both using isolated vertebrae and sets of three adjacent vertebrae (the central one is loaded through the disks). Our goal was to elucidate if testing single-vertebra-specimens in the elastic regime provides different surface strains to three-vertebrae-segments. Twelve three-vertebrae sets were extracted from thoracolumbar human spines. To measure the principal strains, the central vertebra of each segment was prepared with eight strain-gauges. The sets were tested mechanically, allowing comparison of the surface strains between the two boundary conditions: first when the same vertebra was loaded through the disks (three-vertebrae-segment) and then with the endplates embedded in cement (single-vertebra). They were all subjected to four nondestructive tests (compression, traction, torsion clockwise, and counterclockwise). The magnitude of principal strains differed significantly between the two boundary conditions. For axial loading, the largest principal strains (along vertebral axis) were significantly higher when the same vertebra was tested isolated compared to the three-vertebrae-segment. Conversely, circumferential strains decreased significantly in the single vertebrae compared to the three-vertebrae-segment, with some variations exceeding 100% of the strain magnitude, including changes from tension to compression. For torsion, the differences between boundary conditions were smaller. This study shows that, in the elastic regime, when the vertebra is loaded through a cement pot, the surface strains differ from when it is loaded through the disks. Therefore, when single vertebrae are tested, surface strain should be taken with caution.

Using side-opening injection cannulas to prevent cement leakage in percutaneous vertebroplasty for osteoporotic vertebral compression fractures, does it really work?

BACKGROUND

Percutaneous vertebroplasty has been widely applied in the treatment of osteoporotic vertebral compression fractures over the past two decades. However as one of the major complications, the rate of cement leakage seems not to be decreased significantly. In this study, the rate of cement leakage was compared between two groups using two different cement injection cannulas. The purpose was to determine the efficacy of side-opening cannula on preventing cement leakage in vertebroplasty for the treatment of osteoporotic vertebral compression fractures.

METHODS

A retrospective study was conducted from January 2013 to December 2015. Totally 225 patients who received bilateral vertebroplasty due to osteoporotic vertebral compression fractures were included in the study. The patients were divided into test group who received vertebroplasty with side-opening cannulas and control group who received vertebroplasty with front-opening cannulas. The patients' medical records were reviewed to determine the bone marrow density, preoperative vertebral compression ratio, preoperative and postoperative VAS, operation time, volume of injected bone cement, rate of cement leakage. Post-operative X-rays and CT scans were utilized to assess the degree of Cement leakage. Comparisons between groups and clinical results on VAS in each group were analyzed with appropriate test.

RESULTS

All the patients were performed successfully without symptomatic complications. The back pain was significantly relieved after operation in both groups (P < 0.05). At 6 days and 6 months follow-up, there was no significant difference in the mean VAS score between the two groups (P > 0.05). The rate of cement leakage in the test group was significantly lower than that in the control group (P < 0.05).

CONCLUSION

Percutaneous vertebroplasty with side-opening cannula is a safe and effective minimally invasive method in the treatment of osteoporotic vertebral compression fractures, the rate of cement leakage can be significantly reduced by redirecting the cement flow.

How are adjacent spinal levels affected by vertebral fracture and by vertebroplasty? A biomechanical study on cadaveric spines

BACKGROUND CONTEXT

Spinal injuries and surgery may have important effects on neighboring spinal levels, but previous investigations of adjacent-level biomechanics have produced conflicting results. We use "stress profilometry" and noncontact strain measurements to investigate thoroughly this long-standing problem.

PURPOSE

This study aimed to determine how vertebral fracture and vertebroplasty affect compressive load-sharing and vertebral deformations at adjacent spinal levels.

STUDY DESIGN

We conducted mechanical experiments on cadaver spines.

METHODS

Twenty-eight cadaveric spine specimens, comprising three thoracolumbar vertebrae and the intervening discs and ligaments, were dissected from fourteen cadavers aged 67-92 years. A needle-mounted pressure transducer was used to measure the distribution of compressive stress across the anteroposterior diameter of both intervertebral discs. "Stress profiles" were analyzed to quantify intradiscal pressure (IDP) and concentrations of compressive stress in the anterior and posterior annulus. Summation of stresses over discrete areas yielded the compressive force acting on the anterior and posterior halves of each vertebral body, and the compressive force resisted by the neural arch. Creep deformations of vertebral bodies under load were measured using an optical MacReflex system. All measurements were repeated following compressive injury to one of the three vertebrae, and again after the injury had been treated by vertebroplasty. The study was funded by a grant from Action Medical Research, UK ($143,230). Authors of this study have no conflicts of interest to disclose.

RESULTS

Injury usually involved endplate fracture, often combined with deformation of the anterior cortex, so that the affected vertebral body developed slight anterior wedging. Injury reduced IDP at the affected level, to an average 47% of pre-fracture values (p<.001), and transferred compressive load-bearing from nucleus to annulus, and also from disc to neural arch. Similar but reduced effects were seen at adjacent (non-fractured) levels, where mean IDP was reduced to 73% of baseline values (p<.001). Vertebroplasty partially reversed these changes, increasing mean IDP to 76% and 81% of baseline values at fractured and adjacent levels, respectively. Injury also increased creep deformation of the vertebral body under load, especially in the anterior region where a 14-fold increase was observed at the fractured level and a threefold increase was observed at the adjacent level. Vertebroplasty also reversed these changes, reducing deformation of the anterior vertebral body (compared with post-fracture values) by 62% at the fractured level, and by 52% at the adjacent level.

CONCLUSIONS

Vertebral fracture adversely affects compressive load-sharing and increases vertebral deformations at both fractured and adjacent levels. All effects can be partially reversed by vertebroplasty.

Prophylactic vertebroplasty procedure applied with a resorbable bone cement can decrease the fracture risk of sandwich vertebrae: long-term evaluation of clinical outcomes

A sandwich vertebra is formed after multiple osteoporotic vertebral fractures treated by percutaneous vertebroplasty, which has a risk of developing new fractures. The purpose of our study was to (i) investigate the occurrence of new fractures in sandwich vertebra after cement augmentation procedures and to (ii) evaluate the clinical outcomes after prophylactic vertebral reinforcement applied with resorbable bone cement.

From June 2011 to 2014, we analysed 55 patients with at least one sandwich vertebrae and treated with percutaneous vertebroplasty. Eighteen patients were treated by prophylactic vertebroplasty with a resorbable bone cement to strengthen the sandwich vertebrae as the prevention group. The others were the non-prevention group. All patients were examined by spinal radiographs within 1 day, 6 months, 12 months, 24 months and thereafter.

The incidence of sandwich vertebra is 8.25% (55/667) in our study. Most sandwich vertebrae (69.01%, 49/71) are distributed in the thoracic–lumbar junction. There are 24 sandwich vertebrae (18 patients) and 47 sandwich vertebrae (37 patients) in either prevention group or non-prevention group, respectively. No significant difference is found between age, sex, body mass index, bone mineral density, cement disk leakage, sandwich vertebrae distribution or Cobb angle in the two groups. In the follow-up, 8 out of 37 (21.6%) patients (with eight sandwich vertebrae) developed new fractures in non-prevention’ group, whereas no new fractures were detected in the prevention group. Neither Cobb angle nor vertebral compression rate showed significant change in the prevention group during the follow-up. However, in the non-prevention group, we found that Cobb angle increased and vertebral height lost significantly (P < 0.05).

Prophylactic vertebroplasty procedure applied with resorbable bone cement could decrease the rate of new fractures of sandwich vertebrae.

Finite Element-Based Mechanical Assessment of Bone Quality on the Basis of In Vivo Images

Beyond bone mineral density (BMD), bone quality designates the mechanical integrity of bone tissue. In vivo images based on X-ray attenuation, such as CT reconstructions, provide size, shape, and local BMD distribution and may be exploited as input for finite element analysis (FEA) to assess bone fragility. Further key input parameters of FEA are the material properties of bone tissue. This review discusses the main determinants of bone mechanical properties and emphasizes the added value, as well as the important assumptions underlying finite element analysis. Bone tissue is a sophisticated, multiscale composite material that undergoes remodeling but exhibits a rather narrow band of tissue mineralization. Mechanically, bone tissue behaves elastically under physiologic loads and yields by cracking beyond critical strain levels. Through adequate cell-orchestrated modeling, trabecular bone tunes its mechanical properties by volume fraction and fabric. With proper calibration, these mechanical properties may be incorporated in quantitative CT-based finite element analysis that has been validated extensively with ex vivo experiments and has been applied increasingly in clinical trials to assess treatment efficacy against osteoporosis.

Bone cement flow analysis by stepwise injection through medical cannulas

Cement leakage is a serious adverse event potentially occurring during vertebroplasty. Pre-operative in-silico planning of the cement filling process can help reducing complication rates related to leakage. This requires a better understanding of the cement flow along the whole injection path. Therefore, the aim of the present study was to analyze bone cement flow behavior by stepwise injections through medical cannulas. Sixteen cannulas were assigned to four groups for stepwise injection of differently colored cement portions of 1ml volume. Each group differed in the amount of injected cement portions with a range of 1-4ml. After cement curing longitudinal cross-sections of the cannulas were performed and high-resolution pictures taken. Based on these pictures, quadratic polynomial interpolation was applied to the marked intersections between the last two injected cement portions to calculate the leading coefficients. Leading coefficients in the groups with three cement portions (0.287 ± 0.078), four portions (0.243 ± 0.041) and two portions (0.232 ± 0.050) were comparable and significantly higher than the group with one cement portion (0.0032 ± 0.0004), p ≤ 0.016. Based on these findings, cement flow through medical cannulas can be considered as predictable and can therefore be excluded as a source of risk for possible cement leakage complications during vertebroplasty procedures.

A PRELIMINARY IN VITRO BIOMECHANICAL EVALUATION OF PROPHYLACTIC CEMENT AUGMENTATION OF THE THORACOLUMBAR VERTEBRAE

In this paper, the biomechanical effectiveness of prophylactic augmentation in preventing fracture was investigated. In vitro biomechanical tests were performed to assess which factors make prophylactic augmentation effective/ineffective in reducing fracture risk. Nondestructive and destructive in vitro tests were performed on isolated osteoporotic vertebrae. Five sets of three-adjacent-vertebrae were tested. The central vertebra of each triplet was tested in the natural condition (control) non-destructively (axial-compression, torsion) and destructively (axial-compression). The two adjacent vertebrae were first tested nondestructively (axial-compression, torsion) pre-augmentation; prophylactic augmentation (uni- or bi-pedicular access) was then performed delivering 5.04[Formula: see text]mL to 8.44[Formula: see text]mL of acrylic cement by means of a customized device; quality of augmentation was CT-assessed; the augmented vertebrae were re-tested nondestructively (axial-compression, torsion), and eventually loaded to failure (axial-compression). Vertebral stiffness was correlated with the first-failure, but not with ultimate failure. The force and work to ultimate failure in prophylactic-augmented vertebrae was consistently larger than in the controls. However, in some cases the first-failure force and work in the augmented vertebrae were lower than for the controls. To investigate the reasons for such unpredictable results, the correlation with augmentation quality was analyzed. Some augmentation parameters seemed more correlated with mechanical outcome (statistically not-significant due to the limited sample size): uni-pedicular access resulted in a single cement mass, which tended to increase the force and work to first- and ultimate failure. The specimens with the highest strength and toughness also had: at least 25% cement filling, cement mass shifted anteriorly, and cement-endplate contact. These findings seem to confirm that prophylactic augmentation may aid reducing the risk of fracture. However, inadequate augmentation may have detrimental consequences. This study suggests that, to improve the strength of the augmented vertebrae, more attention should be dedicated to the quality of augmentation in terms of amount and position of the injected cement.