Bioactive bone cement as a principal fixture for spinal burst fracture: an in vitro biomechanical and morphologic study

Hybrid kyphoplasty with short-versus intermediate- and long-segment pedicle screw fixations for the management of thoracolumbar burst fractures

BACKGROUND

This study aimed to determine if the hybrid short-segment (HSS) technique is a good alternative to the intermediate-segment (IS) and long-segment (LS) techniques in pedicle screw fixations for acute thoracolumbar burst fractures (TLBFs).

METHODS

In this retrospective evaluation, we examined 43 patients who underwent surgical treatments, including one- or two-level suprajacent (U) and infrajacent (L) pedicle screw fixations, for acute single-level TLBFs with neurological deficits between the T11 and L2 levels from July 2013 to December 2019. Among these patients, 15 individuals underwent HSS (U1L1), 12 received IS (U2L1), and 16 underwent LS (U2L2) fixations. Supplemental kyphoplasty of the fractured vertebral bodies was performed exclusively in the HSS group. Our analysis focused on assessing blood loss and surgical duration. Additionally, we compared postoperative thoracolumbar kyphotic degeneration using the data on Cobb angles on lateral radiographic images acquired at three time points (preoperatively, postoperative day 1, and follow-up). The end of follow-up was defined as the most recent postoperative radiographic image or implant complication occurrence.

RESULTS

Blood loss and surgical duration were significantly lower in the HSS group than in the IS and LS groups. Additionally, the HSS group exhibited the lowest implant complication rate (2/15, 13.33%), followed by the LS (6/16, 37.5%) and IS (8/12, 66.7%) group. Implant complications occurred at a mean follow-up of 7.5 (range: 6-9), 9 (range: 5-23), and 7 (range: 1-21) months in the HSS, IS, and LS groups. Among these implant complications, revision surgeries were performed in two patients in the HSS group, two in the IS group, and one in the LS group. One patient treated by HSS with balloon kyphoplasty underwent reoperation because of symptomatic cement leakage.

CONCLUSIONS

The HSS technique reduced intraoperative blood loss, surgical duration, and postoperative implant complications, indicating it is a good alternative to the IS and LS techniques for treating acute single-level TLBFs. This technique facilitates immediate kyphosis correction and successful maintenance of the corrected alignment within 1 year. Supplemental kyphoplasty with SpineJack® devices and high-viscosity bone cements for anterior reconstruction can potentially decrease the risk of cement leakage and related issues.

Minimally Invasive Approach for Diffuse Idiopathic Skeletal Hyperostosis (DISH)-Related Vertebral Fractures: A Case Report on Combining Vertebral Cement Augmentation and Cement-Augmented Pedicle Screw Instrumentation

Diffuse idiopathic skeletal hyperostosis (DISH)-related vertebral fractures often require surgical intervention due to associated spinal instability and neurological deficits. This study presents a minimally invasive approach that utilizes vertebral cement augmentation and cement-augmented pedicle screw (PS) instrumentation to manage DISH-related vertebral fractures. We present an 87-year-old male patient with a T11 vertebral fracture associated with DISH. Despite the patient's advanced age and comorbidities, he underwent a successful surgical procedure, achieving relatively short-segment fixation by combining vertebral cement augmentation and cement-augmented PS instrumentation. After the surgery, the patient's lower back pain subsided, facilitating a return to normal activities. Radiographic evaluation at the six-month postoperative stage confirmed the maintenance of vertebral body reduction with no indications of implant failure. In DISH-associated vertebral fractures, the combined application of vertebral cement augmentation and cement-augmented PS instrumentation offers a minimally invasive solution that expedites fracture stabilization and enhances patient outcomes. This approach offers the potential for effective fracture stabilization and a significant reduction in postoperative complications, holding promise for managing challenging cases in this patient population.

Long-Segmental Posterior Fusion Combined With Vertebroplasty and Wiring: Alternative Surgical Technique for Kummell's Disease With Neurologic Deficits-A Retrospective Case Series

Purpose

Various surgical methods have been reported for Kummell's disease with neurologic deficits. The aim of this study was to introduce long-segmental posterior fusion (LPF) combined with vertebroplasty (VP) and wiring as an alternative surgical technique.

Material and Methods

We retrospectively analyzed 10 patients undergoing posterior decompression and LPF combined with VP and wiring for Kummell's disease with neurologic deficits from January 2011 to December 2014. The radiologic outcomes included the local kyphotic angle (LKA) and segmental kyphotic angle (SKA). Clinical outcomes, including the visual analog scale (VAS), the Oswestry Disability Index (ODI) and the Frankel grade were assessed. Surgery-related complications were also evaluated.

Results

The mean age of the included patients was 77 ± 8 years with a mean follow-up period of 31.4 ± 4.9 months and a mean bone mineral density of -3.5 ± 0.7 (T-score). The mean operation time was 220 ± 32.3 minutes with a mean blood loss of 555 ± 125.7 mL. The preoperative LKA and SKA were significantly corrected postoperatively (37.9 ± 8.7° vs. 15.3 ± 5.3°, p = 0.005 for LKA; 21.3 ± 5.1° vs. 7.6 ± 2.8°, p = 0.005 for SKA) without a loss of correction at the last follow-up. The VAS and ODI were also significantly improved (7.7 ± 1.1 vs. 3.0 ± 1.6, p = 0.007 for VAS; 90.3 ± 8.9 vs. 49.6 ± 22.7, p = 0.007 for ODI). The Frankel grade of all patients was improved by at least 1 or 2 grades at the last follow-up. Surgery-related complications such as intraoperative cement leakage and implant loosening during the follow-up were not observed.

Conclusions

LPF combined with VP and wiring might be an effective surgical option for Kummell's disease with neurologic deficits, especially for the elderly patients with morbidities.

Level of Evidence

level IV.

Reconstruction of proximal humeral fractures without screws using a reinforced bone substitute

Multi-fragment fractures are still a challenge: current clinical practice relies on plates and screws. Treatment of fractures of the proximal humerus has the intra-operative risk of articular damage when inserting multiple screws. Distal-varus collapse of the head is a frequent complication in osteoporotic patients. The aim of this biomechanical study was to investigate if an Innovative-cement-technique (the screws are replaced by injection of cement) provides the same or better stability of the reconstructed head compared to the Standard-technique (locking screws). A four-fragment fracture was simulated in twelve pairs of humeri, with removal of part of the cancellous bone to simulate osteoporotic "eggshell" defect. One humerus of each pair was repaired either with a Standard-technique (locking plate, 2 cortical and 6 locking screws), or with the Innovative-cement-technique (injection of a partially-resorbable reinforced bone substitute consisting of PMMA additivated with 26% beta-TCP). Cement injection was performed both in the lab and under fluoroscopic monitoring. The reconstructed specimens were tested to failure with a cyclic force of increasing amplitude. The Innovative-cement-technique withstood a force 3.57 times larger than the contralateral Standard reconstructions before failure started. The maximum force before final collapse for the Innovative-cement-technique was 3.56 times larger than the contralateral Standard-technique. These differences were statistically significant. The Innovative-cement-technique, based on the reinforced bone substitute, demonstrated better biomechanical properties compared to the Standard-technique. These findings, along with the advantage of avoiding the possible complications associated with the locking screws, may help safer and more effective treatment in case of osteoporotic multi-fragment humeral fractures.

Novel Surgical Strategy for Treating Osteoporotic Vertebral Fractures with Cord Compression

Objectives

Treatment for osteoporotic vertebral fracture (OVF) with cord compression is challenging and it usually requires surgical interventions to decompress nerves and restore spinal sequences. To describe a novel surgical strategy for treating OVFs with cord compression.

Methods

This is a single‐center retrospective analysis. The inclusion criteria were Frankel grade C‐E, single level T₁₀‐L₂. Between January 2008 and December 2016, a total of 56 OVF patients (47 females and nine males, with an average age of 72 years (66–88 years), comprising of eight grade C, 23 grade D, and 25 grade E patients) were enrolled. The treatment algorithm included preoperative evaluation by MRI, extension CT, and radiography to classify the OVFs as type 1.1 (reducible, stable; n = 13), type1.2 (reducible, unstable; n = 16), type 2 (irreducible; n = 19) or type 2M (modifier; n = 8). Vertebroplasty (VP)/kyphoplasty (KP) was applied in type 1.1. VP/KP with posterior fixation and posterolateral fusion was applied in type 1.2. And additional laminectomy/osteotomy was used in type 2, except in a modifier group (2M) where same procedure as applied for type 1.2 was used. VAS, ODI, Cobb angle, Frankel functional grade, and complications were recorded.

Results

Thirteen cases were classified as type 1.1, 16 cases as type 1.2, 19 cases as type 2, and eight cases as type 2M. The follow‐up period was 38.9 months (range, 24–108 months). All patients were followed‐up in at least 24 months, in which time four patients died, two patients were lost at the last follow‐up, and 50 patients completed the full study. The total VAS and ODI improved from 8 (7, 9) and 75.5% (67.2%, 80.0%) preoperatively to 2 (1, 3) and 31% (24.0%, 37.0%) on conclusion, respectively (P < 0.01). The local kyphotic angle was corrected from 22.3° (17.1°, 33. 8°) preoperatively to 10.4° (6.4°, 15.3°) on conclusion (P < 0.01). Twenty‐three patients had achieved neurological recovery on conclusion (42E, 8D, P < 0.01). Asymptotic cement leakage was observed in 17/56 cases (30.4%), 6/56 in the affected vertebra (10.7%), and 24/330 in the screw trajectory (7.3%). At 2 years postoperatively, 11 new VFs had occurred in nine patients (16.1%), including VFs in nine adjacent segments that all occurred within 1 year after surgery. No cement migration or implant failure was noted.

Conclusion

The novel surgical strategy for treating OVFs with cord compression consists of the most tailored and least invasive treatment for each patient. The positive mid‐ and long‐term clinical and radiological outcomes observed could represent a step forward in devising the proposed algorithm.

Augmentation of a Locking Plate System Using Bioactive Bone Cement-Experiment in a Proximal Humeral Fracture Model

Introduction:

The purpose of this study was to test whether local filling of a novel strontium-containing hydroxyapatite (Sr-HA) bone cement can augment the fixation of a locking plate system in a cadaveric proximal humeral facture model.

Materials and Methods:

Twelve pairs of formalin-treated cadaveric humeri were used. One side in each pair was for cemented group, while the other side was for the control group. The bone mineral density (BMD) of the samples was tested. A 3-part facture model was created and then reduced and fixed by a locking plate system. In the cemented group, the most proximal 4 screw holes were filled with 0.5 mL bone cement. In the control group, the screw holes were not filled by cement. Locking screws were inserted in a standard manner before the cement hardened. X-ray was taken before all the specimens being subjected to mechanical study, in which 6 pairs were used for axial loading (varus bending) test, while other 6 pairs were used for axial rotational test.

Results:

There is no difference in BMD between the cemented side and the control side. The X-ray shows that the implant is in position. Cement filling was noted in the most proximal 4 screws in the cemented group. Better mechanical outcome was seen in the cemented groups, in terms of less maximal displacement per cycle and higher failure point and stiffness in varus bending test. However, no difference was found between the cemented group and the control group in the axial rotation test.

Discussion:

In similarity with the previous studies, our results showed better mechanical results in the cemented group. However, due to the limitations (e.g. sample size, fracture model, testing protocol, etc), we still cannot directly extrapolate current mechanical results to clinical practice at the present moment. Furthermore, it is still unknown whether better primary outcome may lead to better long-term results, even though the local release of strontium may enhance the local bone formation.

Conclusion:

The local filling of Sr-HA bone cement augments the fixation of the locking plate system in current proximal humeral fracture model.

Nanocomposite Porous Microcarriers Based on Strontium-Substituted HA- g-Poly(γ-benzyl-l-glutamate) for Bone Tissue Engineering

Porous microcarriers have aroused increasing attention recently, which can create a protected environment for sufficient cell seeding density, facilitate oxygen and nutrient transfer, and well support the cell attachment and growth. In this study, porous microcarriers fabricated from the strontium-substituted hydroxyapatite- graft-poly(γ-benzyl-l-glutamate) (Sr10-HA- g-PBLG) hybrid nanocomposite were developed. The surface grating of PBLG, the micromorphology and element distribution, mechanical strength, in vitro degradation, and Sr²⁺ ion release of the obtained Sr10-HA- g-PBLG porous microcarriers were investigated, respectively. The grafting ratio and the molecular weight of the grafted PBLG of Sr10-HA- g-PBLG could be effectively controlled by varying the initial ratio of BLG-NCA to Sr10-HA-NH₂. The microcarriers exhibited a highly porous and interconnected microstructure with the porosity of about 90% and overall density of 1.03-1.06 g/cm³. Also, the degradation rate of Sr10-HA-PBLG microcarriers could be effectively controlled and long-term Sr²⁺ release was obtained. The Sr10-HA-PBLG microcarriers allowed cells adhesion, infiltration, and proliferation and promoted the osteogenic differentiation of rabbit adipose-derived stem cells (ADSCs). Successful healing of femoral bone defect was proved by injection of the ADSCs-seeded Sr10-HA-PBLG microcarriers in a rabbit model.

Percutaneous Injection of Strontium Containing Hydroxyapatite versus Polymethacrylate Plus Short-Segment Pedicle Screw Fixation for Traumatic A2- and A3/AO-Type Fractures in Adults

Introduction

Polymethacrylate (PMMA) is commonly used in vertebroplasty and balloon kyphoplasty, but its use has been associated with complications. This study tests three hypotheses: (1) whether strontium hydroxyapatite (Sr-HA) is equivalent to PMMA for restoring thoracolumbar vertebral body fractures, (2) whether the incidence of PMMA leakage is similar to that of Sr-HA leakage, and (3) whether Sr-HAis is resorbed and substituted by new vertebral bone.

Materials and Methods

Two age- and sex-matched groups received short percutaneous pedicle screw fixation plus PEEK implant (Kiva, VCF Treatment System, Benvenue Medical, Santa Clara, CA, USA) filled with either Sr-HA (Group A) or PMMA (Group B) after A2- and A3/AO-type thoracolumbar vertebral body fractures. The Visual Analog Scale (VAS) score and imaging parameters, which included segmental kyphosis angle (SKA), vertebral body height ratios (VBHr), spinal canal encroachment (SCE), bone cement leakage, and Sr-HA resorption, were compared between the two groups.

Results

The average follow-up was 28 months. No differences in VAS scores between Groups A and B were observed at baseline. Baseline back pain in both groups improved significantly three months postoperatively. Anterior, middle, and posterior VBHr did not differ between the two groups at any time point. SKA was improved insignificantly in both groups. SCE decreased insignificantly in both groups on 12-month follow-up using computed tomography (CT). PMMA leakage was observed in one patient, while no Sr-HA paste leakages occurred. Sr-HA resorption and replacement with vertebral bone were observed, and no new fractures were observed.

Conclusions

As all hypotheses were confirmed, the authors recommend the use of Sr-HA instead of PMMA in traumatic spine fractures, although more patients and longer follow-up will be needed to strengthen these results. This trial is registered with NCT03431519.

Stepwise resection of the posterior ligamentous complex for stability of a thoracolumbar compression fracture: An in vitro biomechanical investigation

To quantify the mechanical contribution of posterior ligamentous structures to the stability of thoracolumbar compression fractures.Twelve fresh human T11-L3 spinal specimens were harvested in this study. The 1/3 L1 vertebral body was resected in a wedged shape. After the preinjury had been created, the specimens were subjected to flexion-compression to create a fracture model. Resection of the ligaments was performed in a sequential manner from the bilateral facet capsule ligament (FCL), interspinous ligament, and supraspinous ligament (SSL) to the ligamentum flavum at the T12-L1 level. Then, for the intact specimen, fracture model, and ligament disruption steps, the range of motion (ROM) and neutral zone (NZ) of T12-L1 and L1-L2 were collected for each simulated movement.Sequential transection of the posterior ligamentous complex (PLC), ROM, and NZ were increased in all movements at the T12-L1 segment. In the flexion-extension (FE), the ROM and NZ demonstrated significant increases after the fracture model and resection of SSL and LF. In lateral bending (LB), the ROM increased after the fracture and removal of the LF, while the NZ showed a slight increase. In axial rotation, the fracture model and removal of the LF resulted in a significant increase in the ROM, and the NZ showed a slight change after step reduction. For the L1-L2 segment, resection of the FCL led to an increased ROM in LB.With rupture of SSL or LF, the stability of the segment decreased significantly compared with the intact and fracture model, particularly in FE motion, the function of the PLC was considered to be incompetent.

Therapeutic effects analysis of percutaneous kyphoplasty for osteoporotic vertebral compression fractures: A multicentre study

Background

Percutaneous kyphoplasty (PKP), a minimally invasive treatment, has been widely used for osteoporotic vertebral compression fractures (OVCFs).

Objective

To retrospectively analyse the therapeutic effects of PKP using a series of key techniques in a multicentre study.

Methods

From May 2000 to December 2016, PKP was performed using a series of key techniques (puncture, reduction, and perfusion techniques) for the treatment of 4532 OVCF patients. The pain visual analog scale (VAS) and the Oswestry Disability Index (ODI) questionnaire prior to the operation, at postoperative Day 2, and at the last follow-up were analysed by paired t-test analysis. The leakage of bone cement was evaluated by postoperative radiography and/or computed tomography. Four-year survival was calculated at the last follow-up.

Results

The average follow-up was 63 months (1–116 months). The VAS score decreased from 8.9 (preoperative) to 2.3 (2 days postoperative) to 1.9 (last follow-up). The ODI score of the patients decreased from 86.7 (preoperative) to 31.6 (2 days postoperative) to 25.3 (last follow-up). Both VAS score and ODI score improved significantly. The bone cement leakage rate was 3.5%, with no clinical symptoms. The 4-year survival rate was 77.5%.

Conclusion

This study suggests that PKP with key techniques would be an effective technique to treat OVCF with less risk and better therapeutic effect. Such diagnostic methods and surgical techniques lead to the development and progress of treatment for OVCF.

The translational potential of this article: PKP with key techniques would be an effective technique to treat and lead to the development and progress of treatment for OVCF.

Effects of cement augmentation on the mechanical stability of multilevel spine after vertebral compression fracture

BACKGROUND

Studies on the effects of cement augmentation or vertebroplasty on multi-level spine after vertebral compression fractures are lacking. This paper seeks to establish a 3-vertebrae ovine model to determine the impact of compression fracture on spine biomechanics, and to discover if cement augmentation can restore mechanical stability to fractured spine.

METHODS

Five lumbar spine segments (L1-L3) were obtained from 5-year-old female Merino sheep. Standardized wedge-compression fractures were generated in each L2 vertebra, and then augmented with polymethyl methacrylate (PMMA) cement mixed with 30% barium sulphate powder. Biomechanical pure moment testing in axial rotation (AR), flexion/extension (FE) and lateral bending (LB) was carried out in the intact, fractured and repaired states. Range of motion (ROM) and neutral zone (NZ) parameters were compared, and plain radiographs taken at every stage.

RESULTS

Except for a significant increase in ROM between the intact and fractured states in AR between L1 and L2 (P<0.05), there were no other significant differences in ROM or NZ between the other groups. There was a trend towards an increase in ROM and NZ in all directions after fracture, but this did not reach significance. Normal biomechanics was only minimally restored after augmentation.

CONCLUSIONS

Results suggest that cement augmentation could not restore mechanical stability of fractured spine. Model-specific factors may have had a role in these findings. Caution should be exercised when applying these results to humans.

Cement augmentation in vertebral burst fractures

As a result of axial compression, traumatic vertebral burst fractures disrupt the anterior column, leading to segmental instability and cord compression. In situations with diminished anterior column support, pedicle screw fixation alone may lead to delayed kyphosis, nonunion, and hardware failure. Vertebroplasty and kyphoplasty (balloon-assisted vertebroplasty) have been used in an effort to provide anterior column support in traumatic burst fractures. Cited advantages are providing immediate stability, improving pain, and reducing hardware malfunction. When used in isolation or in combination with posterior instrumentation, these techniques theoretically allow for improved fracture reduction and maintenance of spinal alignment while avoiding the complications and morbidity of anterior approaches. Complications associated with cement use (leakage, systemic effects) are similar to those seen in the treatment of osteoporotic compression fractures; however, extreme caution must be used in fractures with a disrupted posterior wall.

Strontium modified calcium phosphate cements – approaches towards targeted stimulation of bone turnover

Strontium modified calcium phosphate cements can target local bone turnover by stimulating osteoblast proliferation and differentiation (1) as well as bone mineralisation (2), reducing osteoclastogenesis (3) and resorption activity, increase osteoclast apoptosis (4) and affect osteoblast/osteoclast paracrine signalling (5).

Experimental and computational approach investigating burst fracture augmentation using PMMA and calcium phosphate cements

The aim of the study was to use a computational and experimental approach to evaluate, compare and predict the ability of calcium phosphate (CaP) and poly (methyl methacrylate) (PMMA) augmentation cements to restore mechanical stability to traumatically fractured vertebrae, following a vertebroplasty procedure. Traumatic fractures (n = 17) were generated in a series of porcine vertebrae using a drop-weight method. The fractured vertebrae were imaged using μCT and tested under axial compression. Twelve of the fractured vertebrae were randomly selected to undergo a vertebroplasty procedure using either a PMMA (n = 6) or a CaP cement variation (n = 6). The specimens were imaged using μCT and re-tested. Finite element models of the fractured and augmented vertebrae were generated from the μCT data and used to compare the effect of fracture void fill with augmented specimen stiffness. Significant increases (p < 0.05) in failure load were found for both of the augmented specimen groups compared to the fractured group. The experimental and computational results indicated that neither the CaP cement nor PMMA cement could completely restore the vertebral mechanical behavior to the intact level. The effectiveness of the procedure appeared to be more influenced by the volume of fracture filled rather than by the mechanical properties of the cement itself.

Influence of screw augmentation in posterior dynamic and rigid stabilization systems in osteoporotic lumbar vertebrae: a biomechanical cadaveric study

STUDY DESIGN

Biomechanical cadaveric study.

OBJECTIVE

To determine whether augmentation positively influence screw stability or not.

SUMMARY OF BACKGROUND DATA

Implantation of pedicle screws is a common procedure in spine surgery to provide an anchorage of posterior internal fixation into vertebrae. Screw performance is highly correlated to bone quality. Therefore, polymeric cement is often injected through specifically designed perforated pedicle screws into osteoporotic bone to potentially enhance screw stability.

METHODS

Caudocephalic dynamic loading was applied as quasi-physiological alternative to classical pull-out tests on 16 screws implanted in osteoporotic lumbar vertebrae and 20 screws in nonosteoporotic specimen. Load was applied using 2 different configurations simulating standard and dynamic posterior stabilization devices. Screw performance was quantified by measurement of screwhead displacement during the loading cycles. To reduce the impact of bone quality and morphology, screw performance was compared for each vertebra and averaged afterward.

RESULTS

All screws (with or without cement) implanted in osteoporotic vertebrae showed lower performances than the ones implanted into nonosteoporotic specimen. Augmentation was negligible for screws implanted into nonosteoporotic specimen, whereas in osteoporotic vertebrae pedicle screw stability was significantly increased. For dynamic posterior stabilization system an increase of screwhead displacement was observed in comparison with standard fixation devices in both setups.

CONCLUSION

Augmentation enhances screw performance in patients with poor bone stock, whereas no difference is observed for patients without osteoporosis. Furthermore, dynamic stabilization systems have the possibility to fail when implanted in osteoporotic bone.

Biomechanical evaluation of combined short segment fixation and augmentation of incomplete osteoporotic burst fractures

BACKGROUND

Treating traumatic fractures in osteoporosis is challenging. Multiple clinical treatment options are found in literature. Augmentation techniques are promising to reduce treatment-related morbidity. In recent years, there have been an increasing number of reports about extended indication for augmentation techniques. However, biomechanical evaluations of these techniques are limited.

METHODS

Nine thoracolumbar osteoporotic spinal samples (4 FSU) were harvested from postmortem donors and immediately frozen. Biomechanical testing was performed by a robotic-based spine tester. Standardized incomplete burst fractures were created by a combination of osteotomy-like weakening and high velocity compression using a hydraulic material testing apparatus. Biomechanical measurements were performed on specimens in the following conditions: 1) intact, 2) fractured, 3) bisegmental instrumented, 4) bisegmental instrumented with vertebroplasty (hybrid augmentation, HA) and 5) stand-alone vertebroplasty (VP). The range of motion (RoM), neutral zone (NZ), elastic zone (EZ) and stiffness parameters were determined. Statistical evaluation was performed using Wilcoxon signed-rank test for paired samples (p = 0.05).

RESULTS

Significant increases in RoM and in the NZ and EZ (p < 0.005) were observed after fracture production. The RoM was decreased significantly by applying the dorsal bisegmental instrumentation to the fractured specimens (p < 0.005). VP reduced fractured RoM in flexion but was still increased significantly (p < 0.05) above intact kinematic values. NZ stiffness (p < 0.05) and EZ stiffness (p < 0.01) was increased by VP but remained lower than prefracture values. The combination of short segment instrumentation and vertebroplasty (HA) showed no significant changes in RoM and stiffness in NZ in comparison to the instrumented group, except for significant increase of EZ stiffness in flexion (p < 0.05).

CONCLUSIONS

Stand-alone vertebroplasty (VP) showed some degree of support of the anterior column but was accompanied by persistent traumatic instability. Therefore, we would advocate against using VP as a stand-alone procedure in traumatic fractures. HA did not increase primary stability of short segment instrumentation. Some additional support of anterior column and changes of kinematic values of the EZ may lead one to suppose that additive augmentation may reduce the load of dorsal implants and possibly reduce the risk of implant failure.

Traumatic burst fracture with spinal channel involvement augmentation with bioactive strontium-hydroxyapatite cement

In November 2011 a 75-year-old man was admitted to our emergency department with a low back pain caused by a traumatic L1 vertebral collapse with backward projection of posterior wall superior third. The indication for neurosurgical instrumentation was placed, although he refused the treatment. Hence he was treated conservatively without a significant improvement up to January 2012 when, still refusing surgery, he accepted to undergo percutaneous vertebroplasty with a novel bioactive injectable strontium-hydroxyapatite cement. Vertebroplasty was performed without complications. A CT scan, performed the day after the procedure, ruled out extravertebral cement leakage. Pain improvement was significant (preprocedure VAS 10, one-week VAS 4) with a gradual decrease up to three months when it stabilized at 2. CT examination after 1 year showed a good cement osseointegration with osteophytic spurs bridging the superior endplate of the level involved to the inferior one of the level above. The new bone ingrowing property of the strontium-hydroxyapatite containing cement permits to extend the treatment indication also to unstable collapses in which the risk of pseudoarthrosis is very high. In this reported case we evaluated the potential role of percutaneous vertebroplasty in traumatic burst fracture with spinal channel involvement.

Strontium enhances osseointegration of calcium phosphate cement: a histomorphometric pilot study in ovariectomized rats

BACKGROUND

Calcium phosphate cements are used frequently in orthopedic and dental surgeries. Strontium-containing drugs serve as systemic osteoblast-activating medication in various clinical settings promoting mechanical stability of the osteoporotic bone.

METHODS

Strontium-containing calcium phosphate cement (SPC) and calcium phosphate cement (CPC) were compared regarding their local and systemic effects on bone tissue in a standard animal model for osteoporotic bone. A bone defect was created in the distal femoral metaphysis of 60 ovariectomized Sprague-Dawley rats. CPC and SPC were used to fill the defects in 30 rats in each group. Local effects were assessed by histomorphometry at the implant site. Systemic effects were assessed by bone mineral density (BMD) measurements at the contralateral femur and the spine.

RESULTS

Faster osseointegration and more new bone formation were found for SPC as compared to CPC implant sites. SPC implants exhibited more cracks than CPC implants, allowing more bone formation within the implant. Contralateral femur BMD and spine BMD did not differ significantly between the groups.

CONCLUSIONS

The addition of strontium to calcium phosphate stimulates bone formation in and around the implant. Systemic release of strontium from the SPC implants did not lead to sufficiently high serum strontium levels to induce significant systemic effects on bone mass in this rat model.

Gentamicin-loaded strontium-containing hydroxyapatite bioactive bone cement--an efficient bioactive antibiotic drug delivery system

Modified strontium-containing hydroxyapatite (Sr-HA) bone cement was loaded with gentamicin sulfate to generate an efficient bioactive antibiotic drug delivery system for treatment of bone defects. Gentamicin release and its antibacterial property were determined by fluorometric method and inhibition of Staphylococcus aureus (S. aureus) growth. Gentamicin was released from Sr-HA bone cement during the entire period of study and reached around 38% (w/w) cumulatively after 30 days. Antibacterial activity of the gentamicin loaded in the cements is clearly confirmed by the growth inhibition of S. aureus. The results of the amount and duration of gentamicin release suggest a better drug delivery efficiency in Sr-HA bone cement over polymethylmethacrylate bone cement. Bioactivity of the gentamicin-loaded Sr-HA bone cement was confirmed with the formation of apatite layer with 1.836 ± 0.037 μm thick on day 1 and 5.177 ± 1.355 μm thick on day 7 after immersion in simulated body fluid. Compressive strengths of the gentamicin-loaded Sr-HA cement reached 132.60 ± 10.08 MPa, with a slight decrease from the unloaded groups by 4-9%. Bending moduli of Sr-HA cements with and without gentamicin were 1.782 ± 0.072 GPa and 1.681 ± 0.208 GPa, respectively. On the contrary, unloaded Sr-HA cement obtained slightly larger bending strength of 35.48 ± 2.63 MPa comparing with 33.00 ± 1.65 MPa for loaded cement. No statistical difference was found on the bending strengths and modulus of gentamicin-loaded and -unloaded Sr-HA cements. Sr-HA bone cement loaded with gentamicin was proven to be an efficient drug delivery system with uncompromised mechanical properties and bioactivity.

Vertebroplasty-augmented short-segment posterior fixation of osteoporotic vertebral collapse with neurological deficit in the thoracolumbar spine: comparisons with posterior surgery without vertebroplasty and anterior surgery

Object

The surgical approach and treatment of thoracolumbar osteoporotic vertebral collapse with neurological deficit have not been documented in detail. Anterior surgery provides good decompression and solid fusion, but the surgery-related risk is relatively higher than that associated with the posterior approach. In posterior surgery, the major problem after posterior correction and instrumentation is failure to support the anterior spinal column, leading to loss of correction of kyphosis. The aim of this study was to evaluate the efficacy of reinforcing short-segment posterior fixation with vertebroplasty and to compare the outcome with those of posterior surgery without vertebroplasty and anterior surgery, retrospectively.

Methods

The authors studied 83 patients who underwent surgical treatment for a single thoracolumbar osteoporotic vertebral collapse with neurological deficit. Twenty-eight patients treated by posterior surgery combined with vertebroplasty (Group A), 25 patients treated by posterior surgery without vertebroplasty (Group B), and 30 patients treated by anterior surgery (Group C) were followed up for a mean postoperative period of 4.4 years. Neurological outcome, visual analog scale pain score, and radiographic results were compared in the 3 groups.

Results

Postoperative (4–6 weeks) and follow-up neurological outcome and visual analog scale scores were not significantly different among the 3 groups. Postoperative kyphotic angle was significantly reduced in Group B compared with Group C (p = 0.007), whereas the kyphotic angle was not significantly different among the 3 groups at follow-up. The mean ± SD loss of correction at follow-up was 4.6° ± 4.5°, 8.6° ± 6.2°, and 4.5° ± 5.9° in Groups A, B, and C, respectively. The correction loss at follow-up in Group B was significantly higher compared with Groups A and C (p = 0.0171 and p = 0.0180, respectively).

Conclusions

The results suggest that additional reinforcement with vertebroplasty reduces the kyphotic loss and instrumentation failure, compared with patients without the reinforcement of vertebroplasty. Vertebroplasty-augmented short-segment fixation seems to offer immediate spinal stability in patients with thoracolumbar osteoporotic vertebral collapse; the effect seems equivalent to that of anterior reconstruction.

Preliminary biomechanical evaluation of prophylactic vertebral reinforcement adjacent to vertebroplasty under cyclic loading

BACKGROUND CONTEXT

Percutaneous vertebroplasty has become a favored treatment option for reducing pain in osteoporotic patients with vertebral compression fractures (VCFs). Short-term results are promising, although longer-term complications may arise from accelerated failure of the adjacent vertebral body.

PURPOSE

To provide a preliminary biomechanical assessment of prophylactic vertebral reinforcement adjacent to vertebroplasty using a three-vertebra cadaveric segment under dynamic loads that represent increasing activity demands. In addition, the effects of reducing the elastic modulus of the cement used in the intact vertebrae were also assessed.

STUDY DESIGN/SETTING

Three-vertebra cadaveric segments were used to evaluate vertebroplasty with adjacent vertebral reinforcement as an intervention for VCFs.

METHODS

Nine human three-vertebra segments (T12-L2) were prepared and a compression fracture was generated in the superior vertebrae. Vertebroplasty was performed on the fractured T12 vertebra. Subsequently, the adjacent intact L1 vertebra was prophylactically augmented with cement of differing elastic moduli (100-12.5% modulus of the base cement value). After subfailure quasi-static compression tests before and after augmentation, these specimens were subjected to an incrementally increasing dynamic load profile in proportion to patient body weight (BW) to assess the fatigue properties of the construct. Quantitative computed tomography assessments were conducted at several stages in the experimental process to evaluate the vertebral condition and quantify the gross dimensions of the segment.

RESULTS

No significant difference in construct stiffness was found pre- or postaugmentation (t=1.4, p=.19). Displacement plots recorded during dynamic loading showed little evidence of fracture under normal physiological loads or moderate activity (1-2.5x BW). A third of the specimens continued to endure increasing load demands and were confirmed to have no fracture after testing. In six specimens, however, greater loads induced 11 fractures: 7 in the augmented vertebra (2xT12, 5xL5) and 4 in the adjacent L2 vertebra. A strong correlation was observed between the subsidence in the segmental unit and the incidence of fracture after testing (r(Spearman's)=-0.88, p=.002). Altering the modulus of cement in the intact vertebra had no effect on level of segmental compromise.

CONCLUSIONS

These preliminary findings suggest that under normal physiological loads associated with moderate physical activity, prophylactic augmentation adjacent to vertebroplasty showed little evidence of inducing fractures, although loads representing more strenuous activities may generate adjacent and peri-augmentation compromise. Reducing the elastic modulus of the cement in the adjacent intact vertebrae appeared to have no significant effect on the incidence or location of the induced fracture or the overall height loss of the vertebral segment.

Repair of bone segment defects with surface porous fiber-reinforced polymethyl methacrylate (PMMA) composite prosthesis: histomorphometric incorporation model and characterization by SEM

BACKGROUND AND PURPOSE

Polymer technology has provided solutions for filling of bone defects in situations where there may be technical or biological complications with autografts, allografts, and metal prostheses. We present an experimental study on segmental bone defect reconstruction using a polymethylmethacrylate-(PMMA-) based bulk polymer implant prosthesis. We concentrated on osteoconductivity and surface characteristics.

MATERIAL AND METHODS

A critical size segment defect of the rabbit tibia in 19 animals aged 18-24 weeks was reconstructed with a surface porous glass fiber-reinforced (SPF) prosthesis made of polymethylmethacrylate (PMMA). The biomechanical properties of SPF implant material were previously adjusted technically to mimic the properties of normal cortical bone. A plain PMMA implant with no porosity or fiber reinforcement was used as a control. Radiology, histomorphometry, and scanning electron microscopy (SEM) were used for analysis of bone growth into the prosthesis during incorporation.

RESULTS

The radiographic and histological incorporation model showed good host bone contact, and strong formation of new bone as double cortex. Histomorphometric evaluation showed that the bone contact index (BCI) at the posterior surface interface was higher with the SPF implant than for the control. The total appositional bone growth over the posterior surface (area %) was also stronger for the SPF implant than for controls. Both bone growth into the porous surface and the BCI results were related to the quality, coverage, and regularity of the microstructure of the porous surface.

INTERPRETATION

Porous surface structure enhanced appositional bone growth onto the SPF implant. Under load-bearing conditions the implant appears to function like an osteoconductive prosthesis, which enables direct mobilization and rapid return to full weight bearing.

The biomechanical effectiveness of prophylactic vertebroplasty: a dynamic cadaveric study

OBJECT

The purpose of the study was to investigate the segmental effects of prophylactic vertebroplasty under increasingly demanding loading conditions and to assess the effect of altered cement properties on the construct biomechanics.

METHODS

Twelve human cadaveric 3-vertebral functional spinal units (T12-L2) were prepared such that the intact L-1 vertebra was prophylactically augmented with cements of differing elastic moduli (100, 50, 25, and 12.5% modulus of the base cement). These specimens were subjected to quasistatic subfailure compression pre- and postaugmentation to 50% of the predicted failure strength and then cyclic loading in a fatigue rig (115,000 cycles) to characterize the high-stress, short-cycle fatigue properties of the construct. Loading was increased incrementally in proportion to body weight to a maximum of 3.5 x body weight. Quantitative computed tomography assessment was conducted pre- and postaugmentation and following cyclic testing to assess vertebral condition, cement placement, and fracture classification.

RESULTS

Adjacent and periaugmentation fractures were induced in the prophylactically augmented segments. However, it appeared that these fractures mainly occurred when the specimens were subjected to loads beyond those that may commonly occur during most normal physiological activities.

CONCLUSIONS

Lowering the elastic modulus of the cement appeared to have no significant effect on the frequency or severity of the induced fracture within the vertebral segment.

Characteristics and mechanical properties of acrylolpamidronate-treated strontium containing bioactive bone cement

The aim of the present study was to determine the influence of surface treatment on the mechanical properties of strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement. Previously we developed an injectable bioactive cement (SrHAC) system composed of Sr-HA powders and bisphenol A diglycidylether dimethacrylate (Bis-GMA). In this study, the Sr-HA powder was subjected to surface treatment using acrylolpamidronate, a bisphosphonate derivative, which has a polymerizable group, to improve the interface between inorganic filler and organic matrix by binding Sr-HA and copolymerizing into the matrix. After surface treatment, the compression strength, bending strength, and stiffness of the resulting composites were defined by using a material testing machine (MTS) according to ISO 5833. The fracture surface of the bone cement specimen was observed with a scanning electron microscope. Invitro cytotoxicity of surface-treated SrHAC was also studied using a tetrazolium-based cell viability assay (MTS/pms) on human osteoblast-like cells, the SaOS-2 cell line. Cells were seeded at a density of 10(4)/mL and allowed to grow in an incubator for 48 h at 37 degrees C. Results indicated that after surface treatment, the compression strength and stiffness significantly improved by 22.68 and 14.51%, respectively. The bending strength and stiffness of the bioactive bone cement also showed 19.06 and 8.91% improvements via three-point bending test. The fracture surface micromorphology after compression and bending revealed that the bonding between the resin to surface-treated filler considerably improved. The cell viability indicated that the treated particles were nontoxic and did not inhibit cell growth. This study demonstrated a new surface chemistry route to enhance the covalent bonds between inorganic fillers and polymer matrix for improving the mechanical properties of bone cement. This method not only improves the overall mechanical performance but also increases osteoblastic activity.

Effect of weight-bearing on bone-bonding behavior of strontium-containing hydroxyapatite bone cement

The purpose of this study was to investigate and compare the chemical composition and nanomechanical properties at the bone-cement interface under non-weight-bearing and weight-bearing conditions, in order to understand the effect of weight-bearing on the bone-bonding behavior of strontium-containing hydroxyapatite (Sr-HA) cement. In one group, Sr-HA cement was injected into rabbit ilium (under non-weight-bearing conditions). Unilateral hip replacement was performed with Sr-HA cement (under weight-bearing conditions) in the other group. Six months later, scanning electron microscopy (SEM) with energy-dispersive X-ray (EDX) analysis and nanoindentation tests were conducted on the interfaces between cancellous bone and the Sr-HA cement. The nanoindentation results revealed two different transitional behaviors under different conditions. nder weight-bearing conditions, both the Young modulus and hardness at the interface were considerably higher than those at either the Sr-HA cement or cancellous bone. On the contrary, under non-weight-bearing conditions, both the Young modulus and hardness values at the interface were lower than those at the cancellous bone, but were higher than the Sr-HA cement. In addition, EDX results showed that the calcium and phosphorus contents at the interface under weight-bearing conditions were considerably higher than those under non-weight-bearing conditions. The differences in chemical composition and nanomechanical properties at the cement-bone interface under two different conditions indicate that weight-bearing produces significant effects on the bone-bonding behavior of the Sr-HA cement.

Influence of strontia on various properties of surgical simplex P acrylic bone cement and experimental variants

The fact that the composition of acrylic bone cement, as used in cemented primary arthroplasties, is not optimal has been highlighted in the literature. For example: (i) deleterious effects of the radiopacifier (BaSO(4) or ZrO(2) particles in the powder) have been reported; (ii) there is an indication that pre-polymerized poly(methylmethacrylate) (PMMA) beads in the powder may be dispensed with; and (iii) there is a strong consensus that the accelerator commonly used, N,N-dimethyl-p-toluidine (DMPT), is toxic and has many other undesirable properties. At the same time, the effectiveness of drugs that contain a strontium compound in treating the effects of osteoporosis has been explained in terms of the role of strontium in bone formation and resorption. This indicates that strontium compounds may also have desirable effects on osseointegration of arthroplasties. The present study is a detailed evaluation of 24 acrylic bone cement formulations comprising different relative amounts of BaSO(4), strontia (as an alternative radiopacifier), pre-polymerized PMMA beads and DMPT. A large number of properties of the curing and cured cement were determined, including setting time, polymerization rate, fracture toughness and fatigue life. The focus was on the radiopacifier, with the finding being that many properties of formulations that contained strontia were about the same or better than those for cements that contained BaSO(4). Thus, further developmental work on strontia-containing acrylic bone cements is justified, with a view to making them candidates for use in cemented primary arthroplasties.

Vertebral augmentation with a novel Vessel-X bone void filling container system and bioactive bone cement

STUDY DESIGN

Evaluation of a novel, leakage-free vertebroplastic instrumentation by fresh cadaveric studies.

OBJECTIVES

To compare Vessel-X, a novel percutaneous bone void filling container system, with conventional kyphoplasty in restoring strength, stiffness, and height in experimentally induced vertebral compressive fractures and morphologically determine the cement distribution.

SUMMARY OF BACKGROUND DATA

Clinically, both vertebroplasty and kyphoplasty perform well in reinforcement and pain relief. One of the shortcomings, however, is the risk of cement leakage. Vessel-X is a novel bone expander and bone void filler combined instrumentation for vertebral augmentation requiring evaluation.

METHODS

A total of 28 fresh-frozen vertebral specimens were randomly assigned to 4 groups for testing: unipedicular kyphoplasty, bipedicular kyphoplasty, unipedicular Vessel-X, and bipedicular Vessel-X. Compressive fractures were experimentally created on each vertebra after determining the bone mineral density. Kyphoplasty and Vessel-X were performed using bioactive bone cement (SrHAC) under C-arm fluoroscopy and compared by compression testing to measure the effects of augmentation. Morphologic observations were also performed to determine the cement distribution and vertebral height restoration.

RESULTS

There was no significant difference in bone mineral density, initial strength, and stiffness in any of the groups. Furthermore, no significant difference was observed in total cement volume in intragroup comparison within the unipedicular or bipedicular groups. Vessel-X bone filler container could expand well and contain most of the cement. The height restoration ranged from 88.5% to 96.4% in all groups. The augmented strength with unipedicular and bipedicular injections reached 3651.57 N and 4833.73 N, respectively. Stiffness with bipedicular injection was significantly higher than that of unipedicular injection.

CONCLUSION

Vessel-X was comparable to kyphoplasty in restoring the mechanical properties and height of the fractured vertebrae. Interestingly, Vessel-X instrumentation showed considerably less cement leakage and better cement placement in the vertebral body. Therefore, it could be a leakage controllable technique in percutaneous vertebral augmentation.

Biomechanical evaluation of vertebroplasty and kyphoplasty with polymethyl methacrylate or calcium phosphate cement under cyclic loading

STUDY DESIGN

We developed a new method to simulating in vivo dynamic loading as closely as possible, which allows comparison of kyphoplasty and vertebroplasty, as well as augmentation materials.

OBJECTIVE

Special interest was given to calcium phosphate cement, which might fail due to its brittleness.

SUMMARY OF BACKGROUND DATA

Vertebroplasty and kyphoplasty are, with limitations, 2 promising alternative techniques to augment osteoporotic vertebrae with polymethyl methacrylate or calcium phosphate cements. However, little is known about the fatigue characteristics of the treated vertebrae under cyclic loading.

METHODS

Twenty-four intact, osteoporotic bi-segmental human specimens were divided into 4 groups: (1) vertebroplasty with polymethyl methacrylate, (2) kyphoplasty with polymethyl methacrylate, (3) kyphoplasty with calcium phosphate cement, and (4) untreated control group. After augmentation of the middle vertebrae, all specimens underwent 100,000 cycles of eccentric loading during which the specimen revolved around its longitudinal axis. Pre-loading and post-loading radiographs, and subsidence measurements at different sites of the vertebrae were taken. The overall height was additionally determined every 20,000 cycles in the material testing machine. Finally, the specimens were cryosectioned to examine the cements.

RESULTS

Loss of height progressed with strong individual differences in all groups, with an increasing number of load cycles up to median values of 2.8 mm for both augmented groups and 4.2 mm for the nonaugmented group. At the center of the upper endplate, subsidence in kyphoplasty was greater than in vertebroplasty, with little differences with respect to the kind of cement. The cryosections did not show any signs of fatigue in the polymethyl methacrylate, but small cracks were in the calcium phosphate.

CONCLUSIONS

Vertebroplasty and kyphoplasty seem to be equivalent methods in strengthening osteoporotic vertebrae. However, these results cannot be transferred to the treatment of fractures with these methods. A "physiologic" loading situation was achieved by complex motion, including all combinations of flexion/extension with lateral bending during eccentric cyclic loading.

Interfacial behaviour of strontium-containing hydroxyapatite cement with cancellous and cortical bone

The bone-bonding behaviors of various biomaterials have been extensively investigated. However, the precise mechanisms of bone bonding have not yet been clarified, and the differences in interfacial behaviors of biomaterial bonding with cancellous bone and cortical bone have not yet been understood. In this study, strontium-containing hydroxyapatite (Sr-HA) cement, in which 10% calcium ions were substituted by strontium, was performed in a rabbit hip replacement model. Six months later, the morphology and chemical composition of interfaces between Sr-HA cement with cancellous bone and cortical bone were evaluated by field emission scanning electron microscopy (FESEM) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Remarkable differences between these two interfaces were suggested both in morphology and chemical compositions. An apatite layer was found between Sr-HA cement and cancellous bone with a thickness of about 70 microm. However, only a very thin interface (about 1 microm) was formed with cortical bone. As for the cancellous bone/cement interface, high ions intensity of Ca, P, Sr, Na, and O were confirmed by FESEM-EDX and ToF-SIMS. Differences in morphology and chemical component between these two interfaces provided convincing evidences for the proposed dissolution-precipitation coupling mechanism in the formation of biological apatite.

Strontium-containing hydroxyapatite bioactive bone cement in revision hip arthroplasty

Clinical outcome of cemented implants to revision total hip replacement (THR) is not as satisfactory as primary THR, due to the loss of bone stock and normal trabecular pattern. This study evaluated a bioactive bone cement, strontium-containing hydroxyapatite (Sr-HA) bone cement, in a goat revision hip hemi-arthroplasty model, and compared outcomes with polymethylmethacrylate (PMMA) bone cement. Nine months after operation, significantly higher bonding strength was found in the Sr-HA group (3.36+/-1.84 MPa) than in the PMMA bone cement group (1.23+/-0.73 MPa). After detached from the femoral component, the surface of PMMA bone cement mantle was shown relatively smooth, whereas the surface of the Sr-HA bioactive bone cement mantle was uneven, by SEM observation. EDX analysis detected little calcium and no phosphorus on the surface of PMMA bone cement mantle, while high content of calcium (14.03%) and phosphorus (10.37%) was found on the surface of the Sr-HA bone cement mantle. Even higher content of calcium (17.37%) and phosphorus (10.84%) were detected in the concave area. Intimate contact between Sr-HA bioactive bone cement and bone was demonstrated by histological and SEM observation. New bone bonded to the surface of Sr-HA cement and grew along its surface. However, fibrous tissue was observed between PMMA bone cement and bone. The results showed good bioactivity of Sr-HA bioactive bone cement in this revision hip replacement model using goats. This in vivo study also suggested that Sr-HA bioactive bone cement was superior to PMMA bone cement in terms of bone-bonding strength. Use of bioactive bone cement may be a possible solution overcoming problems associated with the use of PMMA bone cement in revision hip replacement.

Strontium-containing hydroxyapatite (Sr-HA) bioactive cement for primary hip replacement: an in vivo study

The purpose of this study was to evaluate the strontium-containing hydroxyapatite (Sr-HA) cement in primary hip replacement, using a rabbit model, and to investigate the histological findings at the cement-implant and bone-cement interfaces under weight-bearing conditions. Unilateral hip replacement was performed with Sr-HA cement or polymethylmethacrylate (PMMA) cement in rabbits and observations were made after 6 months. Good fixation between the Sr-HA cement and implant was observed. Osseointegration of the Sr-HA cement with cancellous bone was widespread. Many multinucleus cells covered the surface of the cement, and resorbed the superficial layer of the cement. By scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, high calcium and phosphorus levels were detected at the interface with a thickness of about 10 microm. Intimate contact was also observed between the Sr-HA cement and cortical bone without fibrous layer intervening. The overall affinity index of bone on Sr-HA cement was (85.06 +/- 5.40)%, which is significantly higher than that on PMMA cement (2.77%+/- 0.49%). On the contrary, a fibrous layer was consistently observed between PMMA cement and bone, and PMMA cement evoked an inflammatory response and foreign body reaction in the surrounding bony tissues. Results suggested good bioactivity and bone-bonding ability of the Sr-HA cement under weight-bearing conditions.

Nano-mechanics of bone and bioactive bone cement interfaces in a load-bearing model

Many bioactive bone cements were developed for total hip replacement and found to bond with bone directly. However, the mechanical properties at the bone/bone cement interface under load bearing are not fully understood. In this study, a bioactive bone cement, which consists of strontium-containing hydroxyapatite (Sr-HA) powder and bisphenol-alpha-glycidyl dimethacrylate (Bis-GMA)-based resin, was evaluated in rabbit hip replacement for 6 months, and the mechanical properties of interfaces of cancellous bone/Sr-HA cement and cortical bone/Sr-HA cement were investigated by nanoindentation. The results showed that Young's modulus (17.6+/-4.2 GPa) and hardness (987.6+/-329.2 MPa) at interface between cancellous bone and Sr-HA cement were significantly higher than those at the cancellous bone (12.7+/-1.7 GPa; 632.7+/-108.4 MPa) and Sr-HA cement (5.2+/-0.5 GPa; 265.5+/-39.2 MPa); whereas Young's modulus (6.3+/-2.8 GPa) and hardness (417.4+/-164.5 MPa) at interface between cortical bone and Sr-HA cement were significantly lower than those at cortical bone (12.9+/-2.2 GPa; 887.9+/-162.0 MPa), but significantly higher than Sr-HA cement (3.6+/-0.3 GPa; 239.1+/-30.4 MPa). The results of the mechanical properties of the interfaces were supported by the histological observation and chemical composition. Osseointegration of Sr-HA cement with cancellous bone was observed. An apatite layer with high content of calcium and phosphorus was found between cancellous bone and Sr-HA cement. However, no such apatite layer was observed at the interface between cortical bone and Sr-HA cement. And the contents of calcium and phosphorus of the interface were lower than those of cortical bone. The mechanical properties indicated that these two interfaces were diffused interfaces, and cancellous bone or cortical bone was grown into Sr-HA cement 6 months after the implantation.

Vertebroplasty by use of a strontium-containing bioactive bone cement

STUDY DESIGN

A review of the laboratory and clinical data for a new strontium-containing hydroxyapatite bioactive bone cement.

OBJECTIVES

To compare the properties of the strontium-containing bioactive bone cement with those of polymethyl methacrylate (PMMA) and hydroxyapatite (HA) bone cements.

SUMMARY OF BACKGROUND DATA

Vertebroplasty and kyphoplasty using conventional PMMA bone cements have been effectively used to treat osteoporotic spine fractures with good short- and medium-term results. However, PMMA has some undesirable properties, including its high setting temperature, lack of osseointegration, and large stiffness mismatch with osteoporotic bone. These properties are responsible for some postoperative complications.

METHODS

Strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement consists of a filler blend of strontium-containing hydroxyapatite, fumed silica and benzoyl peroxide; and a resin blend of bisphenol A diglycidylether methacrylate, triethylene glycol dimethacrylate, poly(ethylene glycol) methacrylate, and N, N-dimethyl-p-toluidine. Its properties, including mechanical strength, setting temperature, biocompatibility, and osseoinduction, were compared with other cements in vitro and in vivo. Early clinical results are presented.

RESULTS

The Sr-HA cement has a setting time of 15 to 18 minutes, a maximum setting temperature of 58 degrees C, a compressive strength of 40.9 MPa, bending strength of 31.3 MPa, and a bending modulus of 1,408 MPa. The bending strength and modulus are closer to human cancellous bone. Sr-HA cement promotes osteoblast attachment and mineralization in vitro and bone growth and osseointegration in vivo. In a pilot study, 23 cases of osteoporotic fractures treated with this cement with a mean follow-up of 18 months suggest that it is as effective as PMMA in relieving pain.

DISCUSSIONS

Oral strontium has been shown to induce new bone formation and is effective in reducing fracture risk in osteoporosis. Our data suggest that strontium delivered locally has the same effect; thus, the combination of strontium with HA in a cement with a low setting temperature, adequate stiffness, and low viscosity makes this a good bioactive cement for vertebroplasty and kyphoplasty.

Estimating the compressive strength of the porcine cervical spine: an examination of the utility of DXA

STUDY DESIGN

The failure strength of porcine spinal units was correlated with vertebral size and bone mineralization. The accuracy of the resulting predictive equations was tested with an independent sample of spinal units.

OBJECTIVES

To determine if dual energy x-ray absorptiometry (DXA)-obtained measures of bone mineralization can be used to accurately predict the compressive tolerance of porcine spinal units.

SUMMARY OF BACKGROUND DATA

Porcine spinal units are often used in place of cadaveric tissues, and normalization is used to improve the transferability of model results. In compressive testing, normalization can be performed to the estimated compressive strength. Bone mineralization measures have been shown to be positively correlated with compressive tolerance and have been used to predict the tolerance of human spinal units. However, the accuracy of these predictive equations has not been assessed with an independent sample.

METHODS

Twenty porcine cervical spinal units were scanned (DXA) to obtain measures of bone mineral content (BMC) and bone mineral density (BMD). The units were compressed to failure, and the failure loads were correlated with the measured bone mineralization and endplate area of the spinal unit. The regression equations were used to predict the compressive tolerance of an independent sample of spinal units.

RESULTS

BMC (P = 0.078) and BMD (P = 0.2834) were not significantly correlated to compressive strength. Endplate area was the most highly correlated variable, with an r of 0.5329. The use of a predictive equation including BMC on the second independent sample resulted in errors of estimation of 1.4 +/- 1.2 kN, corresponding to 13% of the average compressive strength. In comparison, the use of an equation employing endplate area alone resulted in estimation errors of 11%.

CONCLUSIONS

Measures of BMC/BMD did not enhance predictions of compressive strength and will not reduce errors in compressive load normalization in a porcine model. The poor correlations found between BMC and compressive strength may be due to the non-load-bearing anterior processes of the porcine cervical spine.

In vivo cancellous bone remodeling on a strontium-containing hydroxyapatite (sr-HA) bioactive cement

The purpose of this study was to investigate the in vivo bone response to the strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement injected into the cancellous bone. Sr-HA cement was injected into the iliac crest of rabbits for 1, 3, and 6 months. Active bone formation and remodeling were observed after 1 month. Newly formed bone was observed to grow onto the bone cement after 3 months. Thick osteoid layer with osteoblasts formed along the bone and guided over the bone cement surface reflected the stimulating effect of Sr-HA. From scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) analysis, high calcium and phosphorus levels were detected at the interface with a thick layer of 70 microm in width, and fusion of Sr-HA with the bone was observed. Blood vessels were found developing in remodeling sites. The affinity of bone on Sr-HA cement was increased from 73.55 +/- 3.50% after 3 months up to 85.15 +/- 2.74% after 6 months (p < 0.01). In contrast to Sr-HA cement, poly(methyl methacrylate) (PMMA) bone cement was neither osteoconductive nor bioresorbable. Results show that the Sr-HA cement is biocompatible and osteoconductive, which is suitable for use in treating osteoporotic vertebral fractures.

The biomechanics of vertebroplasty: a review

Percutaneous vertebroplasty and kyphoplasty are being used extensively in the United States for the treatment of osteoporotic vertebral compression fractures. Although short-term clinical outcomes appear favourable, long-term data are not yet available and it is becoming increasingly important to understand how the underlying biomechanics of the spine are altered by the procedure. In vitro experimental studies have investigated the effect of cement augmentation on individual vertebra and short spinal segments. For individual vertebra, vertebroplasty appears to increase or return strength to the prefracture level, whereas the stiffness is not always restored. However for multiple-vertebra segments, the strength of the unit as a whole appears to decrease, with failure occurring in the non-augmented vertebrae. Both finite element (FE) and experimental studies have shown that the volume of cement injected affects the restoration of strength and stiffness. The type of cement appears to have less of an effect. Although biomechanical studies of the vertebroplasty process have indicated that the procedure has the potential to restore vertebral strength and stiffness, further work is necessary to understand fully the effects of the augmentation process on the surrounding structures if the treatment is to be fully optimized. This paper is a review of the biomechanical data available on vertebroplasty.

Surface treatment of injectable strontium-containing bioactive bone cement for vertebroplasty

A novel injectable bioactive bone-bonding cement (SrHAC) composed of strontium-containing hydroxyapatite (Sr-HA) as the inorganic filler and bisphenol A diglycidylether dimethacrylate (Bis-GMA) as the organic matrix for vertebroplasty was developed previously. In this study, the Sr-HA powders were surface treated with methyl methacrylate (MMA) to improve the interface integration of the two phases. After surface treatment, the compression strength and Young's modulus, which were tested after immersion in distilled water at 37 degrees C for 24 h according to ISO 5833, were increased by 68.65 % (p <.001) and 31.02% (p <.001), respectively. The bending strength and bending stiffness of the bioactive bone cement were significantly improved by 54.44% (p <.001) and 83.90% (p <.001). In addition, the handling property of the cement was also enhanced. In vitro biomechanical testing showed that the stiffness of the fractured spine recovered to 82.5% (p <.01) of the intact condition after cementation with surface-treated SrHAC. The failure load of the spine cemented with original and MMA-treated SrHAC improved by 14.25% (p <.05) and 46.91% (p <.05) in comparison with the fractured spines. Results from this study revealed that the MMA-treated SrHAC has a better mechanical effect for orthopedic applications.

Ultrastructural study of mineralization of a strontium-containing hydroxyapatite (Sr-HA) cementin vivo

The purpose of this study was to investigate the mineralization leading to osseointegration of strontium-containing hydroxyapatite (Sr-HA) bioactive bone cement injected into cancellous bone in vivo. Sr-HA cement was injected into the ilium of rabbits for 1, 3, and 6 months. The bone mineralization area was found to be largest at 3 months, then at 1 month, and smallest at 6 months (p < 0.01) measured with tetracycline labeling. Osseointegration of Sr-HA cement was achieved at 3 months as observed by scanning electron microscopy. A high calcium and phosphorus area was observed at the interface of bone-Sr-HA cement determined by energy-dispersive X-ray analysis. Transmission electron microscopy gave evidence of the mechanism of bone formation. Dissolution of Sr-HA into debris by the bone remodeling process was thought to increase the concentration of calcium and phosphorus at the interface of bone-Sr-HA cement and stimulate bone formation. Crystalline Sr-HA formed an amorphous layer and dissolved into the surrounding solution, then apatite crystallites were precipitated and formed new bone at 3 months. This young bone then becomes mature bone, which bonds tightly to the Sr-HA cement with collagen fibers inserted perpendicularly after 6 months.

Treatment of Thoracolumbar Burst Fractures with Polymethyl Methacrylate Vertebroplasty and Short-segment Pedicle Screw Fixation

OBJECTIVES

We aimed to evaluate the efficacy of reinforcing short-segment pedicle screw fixation with polymethyl methacrylate (PMMA) vertebroplasty in patients with thoracolumbar burst fractures.

METHODS

We enrolled 70 patients with thoracolumbar burst fractures for treatment with short-segment pedicle screw fixation. Fractures in Group A (n = 20) were reinforced with PMMA vertebroplasty during surgery. Group B patients (n = 50) were not treated with PMMA vertebroplasty. Kyphotic deformity, anterior vertebral height, instrument failure rates, and neurological function outcomes were compared between the two groups.

RESULTS

Kyphosis correction was achieved in Group A (PMMA vertebroplasty) and Group B (Group A, 6.4 degrees; Group B, 5.4 degrees). At the end of the follow-up period, kyphosis correction was maintained in Group A but lost in Group B (Group A, 0.33-degree loss; Group B, 6.20-degree loss) (P = 0.0001). After surgery, greater anterior vertebral height was achieved in Group A than in Group B (Group A, 12.9%; Group B, 2.3%) (P &lt; 0.001). During follow-up, anterior vertebral height was maintained only in Group A (Group A, 0.13 ± 4.06%; Group B, −6.17 ± 1.21%) (P &lt; 0.001). Patients in both Groups A and B demonstrated good postoperative Denis Pain Scale grades (P1 and P2), but Group A had better results than Group B in terms of the control of severe and constant pain (P4 and P5) (P &lt; 0.001). The Frankel Performance Scale scores increased by nearly 1 in both Groups A and B. Group B was subdivided into Group B1 and B2. Group B1 consisted of patients who experienced instrument failure, including screw pullout, breakage, disconnection, and dislodgement (n = 11). Group B2 comprised patients from Group B who did not experience instrument failure (n = 39). There were no instrument failures among patients in Group A. Preoperative kyphotic deformity was greater in Group B1 (23.5 ± 7.9 degrees) than in Group B2 (16.8 ± 8.40 degrees), P &lt; 0.05. Severe and constant pain (P4 and P5) was noted in 36% of Group B1 patients (P &lt; 0.001), and three of these patients required removal of their implants.

CONCLUSION

Reinforcement of short-segment pedicle fixation with PMMA vertebroplasty for the treatment of patients with thoracolumbar burst fracture may achieve and maintain kyphosis correction, and it may also increase and maintain anterior vertebral height. Good Denis Pain Scale grades and improvement in Frankel Performance Scale scores were found in patients without instrument failure (Groups A and B2). Patients with greater preoperative kyphotic deformity had a higher risk of instrument failure if they did not undergo reinforcement with vertebroplasty. PMMA vertebroplasty offers immediate spinal stability in patients with thoracolumbar burst fractures, decreases the instrument failure rate, and provides better postoperative pain control than without vertebroplasty.