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Study Design: Low elastic modulus expandable pedicle screw (L-EPS) was inserted into osteoporotic sheep. Biomechanical tests, micro-CT analysis and histologic observation were performed., Objective: To find out whether the L-EPS can further improve fixation strength compared to the expandable pedicle screws (EPS) in osteoporotic sheep spine. The screw-bone interface is also detected by micro-computed tomography (CT) and histologic techniques., Summary of Background Data: There are some studies on EPS in vivo; however, no earlier study has focused on the elastic modulus of EPS, especially in osteoporosis., Methods: Twelve months after ovariectomy, bilateral pedicles of lumbar vertebrae (L1 to L5) of 4 female sheep were fixed with EPSs. The L-EPS and EPS were randomly placed into each pedicle and then were expanded. Six months later, the sheep were sacrificed and biomechanical tests, micro-CT analysis, and histologic observation were conducted on the isolated specimen vertebrae., Results: Twelve months after ovariectomy, animal model of osteoporosis was established successfully. The axial pull-out strength in L-EPS group was significantly enhanced compared with that in the EPS group (P < 0.05). Micro-CT reconstruction and analysis showed that there was more bone around the L-EPS group compared with those in EPS group (P < 0.05), meanwhile the more homogeneous bone formation distribution around the screws was found in the L-EPS group. Histologic observation showed that newly formed bone extended along the expandable fissures and grew into the center of EPS; meanwhile, the more direct contact and the less fibrous tissue on the screw-bone interface were observed in the L-EPS group., Conclusions: The L-EPS can further improve the biomechanical fixation strength of EPS in the osteoporotic sheep. The screw elastic matching with surrounding bone is helpful to distribute stress uniformly, relieve the stress shielding effect, and strengthen the screw-bone interface. Although the experience with the L-EPS is very limited and preliminary, results to date indicate that it is of value in treating patients with osteoporosis and warrants further study.

Study Design: Augmentation of pedicle screws with calcium sulfate cement (CSC) was performed in osteoporotic sheep. Biomechanical tests, micro-computed tomography (CT) analysis, and histological observation were performed., Objective: To investigate the long-term biomechanical performance of pedicle screws augmented with CSC in vivo and evaluated the screw-bone interfacial bonding with micro-CT and histological techniques., Summary of Background Data: There is little information on the long-term biomechanical performance and screw-bone interfacial bonding of pedicle screws augmented with CSC in osteoporosis in vivo., Methods: Twelve months after ovariectomy, bilateral pedicles of lumbar vertebrae (L1 to L5) of 6 female sheep were fixed with pedicle screws. One pedicle of each vertebral body was treated with a screw augmented with CSC (CSC group) and the contralateral pedicle was treated with a screw without any augmentation (control group). Three months later, the sheep were killed and biomechanical tests, micro-CT analysis, and histological observation were conducted on the isolated specimen vertebrae., Results: Twelve months after ovariectomy, animal model of osteoporosis was established successfully. Both the axial and vertical stabilities of the pedicle screws in CSC group were significantly enhanced compared with those in the control group (P<0.05). Micro-CT reconstruction and analysis showed that there were more bone trabeculae around the screws in CSC group compared with those in control group (P<0.05), and the bone trabeculae were significantly denser than those in control group (P<0.05). Histological observation showed that CSC was completely degradated and bone trabeculae around the screws in CSC group were more and denser than that in the control group. Bone trabeculae held the screws tightly without any interspaces between screw and bone, which formed strong bonding between bone and screw., Conclusions: CSC can significantly improve screw-bone interfacial bonding and strengthen the long-term stability of pedicle screws in osteoporotic sheep. Augmentation with CSC may be a potentially useful method to increase the stability of pedicle screws in patients with osteoporosis.

Objective: The purpose of this study was to analyze the local treatment effects of rhBMP-2 combined with fibrin sealant (FS) on bone mineral density, microarchitectural and mechanical properties in osteoporotic ovine spine., Materials and Methods: Postmenopausal osteoporosis was induced in eight sheep through ovariectomy (OVX) and a low-calcium diet for a period of 12 months. According to the Latin square design, L3-L6 vertebrae were randomly assigned to four treatment groups: A (rhBMP-2/FS), B (rhBMP-2), C (FS) and D (blank control). All materials were injected into the assigned vertebra transpedicularly. All animals were euthanized 3 months after treatment. Bone mineral density (BMD), microarchitectural and mechanical properties were assessed. ANOVA analysis of variance was used to determine effects of rhBMP-2/FS (α = 0.05)., Results: The BMD in group A (rhBMP-2/FS) was 18.8, 30.4 and 27.9% higher than that in group B, C and D, respectively. Analysis of bone structure by micro-CT revealed higher trabecular bone volume (BV/TV), trabecular thickness (Tb.Th) and trabecular number (Tb.N) in the rhBMP-2/FS group (P < 0.01). In addition, vertebrae treated with rhBMP-2/FS exhibited higher yield stress, ultimate stress, energy absorption and bone modulus compared to the control groups., Conclusions: Local administration of rhBMP-2/FS showed a positive trend in improving BMD, microarchitectural parameters and mechanical strength of osteoporotic vertebra. Slow release of rhBMP-2 using FS appeared to be an effective method of protein delivery. The local treatment of osteoporosis in the spine can increase bone strength and reduce fracture risk quickly.

Purpose: To investigate the clinical abstract and radiographic outcome of multi-axial expandable pedicle screws (MEPS) in patients with osteoporosis., Methods: One hundred and twenty-five consecutive patients received MEPS from the UPASS spinal fixation system to obtain thoracolumbar or lumbosacral stabilization. All patients underwent bone mineral density (BMD) scans. The indications for use of the MEPS were spinal diseases with severe osteoporosis (degenerative diseases 46 cases, compression fractures 28 cases, lumbar tuberculosis 27 cases and revision spine surgery 24 cases). The pre-operative and three months post-operative functional evaluations were graded with JOA and VAS scoring system. One week, six months and 12 months after surgery, plain film and three-dimensional CT scans were obtained to evaluate the spinal fusion and fixation effectiveness of MEPS., Results: The mean follow-up period was 18 months (ranged from 6 to 33 months). All patients suffered from severely osteoporosis with a decrease of 25.3% in BMD. The pre-operative JOA and VAS scores were 11.3±3.0 and 6.7±1.8 mm, respectively. Three months after operation, the JOA and VAS scores were 25.2±2.0 and 2.3±1.7 mm. The recovery rate was 78.1±11.5％ and the clinical results were satisfying. There were no instances of screw loosening or pullout of the MEPS and the screw-bone interface was excellent. The radiographic results showed that bone healing, both around the screws and inter-vertebral, was achieved., Conclusion: In osteoporosis spine surgery, excellent bone-screw interface and fixation strength can be achieved by using MEPS. MEPS are a novel approach to increase the pedicle screw fixation in osteoporotic and revision spine surgeries.

Background: Epidural leaks or canal intrusion are often found in vertebroplasty, which can lead to several complications. To the best of our knowledge, this is the first report on using two-stage injection procedure in vertebroplasty to reduce cement leakage rate., Materials and Methods: Fifty cadaveric vertebrae (L1-L5) were harvested from 10 osteoporotic lumbar spines. The age of the female donors ranged from 60 to 72 y; the bone mineral density (BMD) of the vertebrae ranged from 0.226 to 0.631 g/cm(2). Polymethylmethacrylate (PMMA) was injected into vertebral bodies by either novel two-stage injection (1 mL cement was injected at first stage and another 4 mL cement was injected at second stage after the cement solidified) or standard conventional injection procedure. After injection, all vertebral bodies (VBs) were checked for cement leakage into spinal canal by vision and fluoroscopy. Cement leakage rates were recorded., Results: The two-stage injection procedure resulted in a significant decrease in the epidural or canal leakage rate (P = 0.032). In addition, the paravertebral leakage rate was significantly higher in two-stage injection procedure group (48%) than in conventional injection procedure group (16%). However, no significant difference was found for the total cement leakage rate between the two groups., Conclusion: Compared with conventional procedure, the two-stage injection procedure in vertebroplasty decreased incidence of epidural and canal leaks. The first-stage injecting PMMA can be a barrier to the epidural extravasation of cement during vertebroplasty. Further in vivo and clinical researches are needed to evaluate the new procedure., (Crown Copyright © 2010. Published by Elsevier Inc. All rights reserved.)

Osteoporotic/osteopenia fractures occur most frequently in trabeculae-rich skeletal sites. The purpose of this study was to use a high-resolution micro-computed tomography (micro-CT) and dual energy X-ray absorptionmeter (DEXA) to investigate the changes in micro-architecture and bone mineral density (BMD) in a sheep model resulted from ovariectomy (OVX). Biomechanical tests were performed to evaluate the strength of the trabecular bone. Twenty adult sheeps were randomly divided into three groups: sham group (n=8), group 1 (n=4) and group 2 (n=8). In groups 1 and 2, all sheep were ovariectomized (OVX); in the sham group, the ovaries were located and the oviducts were ligated. In all animals, BMD for lumbar spine was obtained during the surgical procedure. BMD at the spine, femoral neck and femoral condyle was determined 6 months (group 1) and 12 months (group 2) post-OVX. Lumbar spines and femora were obtained and underwent BMD scan, micro-CT analysis. Compressive mechanical properties were determined from biopsies of vertebral bodies and femoral condyles. BMD, micro-architectural parameters and mechanical properties of cancellous bone did not decrease significantly at 6 months post-OVX. Twelve months after OVX, BMD, micro-architectural parameters and mechanical properties decreased significantly. The results of linear regression analyses showed that trabecular thickness (Tb.Th) (r=0.945, R2=0.886) and bone volume fraction (BV/TV) (r=0.783, R2=0.586) had strong (R2>0.5) correlation to compression stress. In OVX sheep, changes in the structural parameters of trabecular bone are comparable to the human situation during osteoporosis was induced. The sheep model presented seems to meet the criteria for an osteopenia model for fracture treatment with respect to morphometric and mechanical properties. But the duration of OVX must be longer than 12 months to ensure the animal model can be established successfully.

Objective: To investigate the properties of screw-bone interface of expansive pedicle screw (EPS) in osteoporotic sheep by micro-CT and histological observation., Methods: Six female sheep with bilateral ovariectomy-induced osteoporosis were employed in this experiment. After EPS insertion in each femoral condyle, the sheep were randomly divided into two groups: 3 sheep were bred for 3 months (Group A), while the other 3 were bred for 6 months (Group B). After the animals being killed, the femoral condyles with EPS were obtained, which were three-dimensionally-imaged and reconstructed by micro-CT. Histological evaluation was made thereafter., Results: The trabecular microstructure was denser at the screw-bone interface than in the distant parts in expansive section, especially within the spiral marking. In the non-expansive section, however, there was no significant difference between the interface and the distant parts. The regions of interest (ROI) adjacent to EPS were reconstructed and analyzed by micro-CT with the same thresholds. The three-dimensional (3-D) parameters, including tissue mineral density (TMD), bone volume fraction (BVF, BV/TV), bone surface/bone volume (BS/BV) ratio, trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp), were significantly better in expansive sections than non-expansive sections (P less than 0.05). Histologically, newly-formed bony trabeculae crawled along the expansive fissures and into the center of EPS. The newly-formed bones, as well as the bones at the bone-screw interface, closely contacted with the EPS and constructed four compartments., Conclusions: The findings of the current study, based on micro-CT and histological evaluation, suggest that EPS can significantly provide stabilization in osteoporotic cancellous bones.

Objective: To investigate the properties of screw-bone interface of expansive pedicle screw (EPS) in osteoporotic sheep using micro-CT and histology., Methods: Six female sheep with bilateral ovariectomy-induced osteoporosis were employed in this experiment and were randomly assigned into 2 groups: A and B. After EPS insertion in each femoral condyles, sheep in group A were bred for 3 months, while those in group B 6 months. Femoral condyles with EPS were 3D-imaged and reconstructed by micro-CT. Histology was evaluated thereafter., Results: The trabecular microstructure was denser at the screw-bone interface than in the distant parts in expansive section, especially within spiral marking. In the non-expansive section, however, there was no significant difference between the interface and the distant parts. The regions of interest (ROI) adjacent to EPS were reconstructed and analyzed by micro-CT using the same thresholds. The 3D-parameters generated, including tissue mineral density (TMD), bone volume fraction (BVF, BV/TV), bone surface/bone volume (BS/BV) ratio, trabecular thickness (Tb.Th), and trabecular separation (Tb.Sp), were significantly better in expansive than in non-expansive sections (P < 0.05). Histologically, newly formed bone trabeculae crawled along the expansive fissures and into the center of EPS. The newly formed bones, as well as the bone at the bone-screw interface, closely contacted the EPS and constructed four compartments., Conclusions: Based on micro-CT and histological evaluation, the study suggest that EPS can significantly provide stabilization in osteoporotic cancellous bone.