María Daniela Vlad

Osteogenic biphasic calcium sulphate dihydrate/iron-modified alpha-tricalcium phosphate bone cement for spinal applications: in vivo study.

In this study, the biocompatibility and the osteogenic features of a new iron-modified alpha-tricalcium phosphate (IM/alpha-TCP) and calcium sulphate dihydrate (CSD) biphasic cement (IM/alpha-TCP/CSD-BC) have been investigated in terms of the in vivo cement resorption, bone tissue formation and host tissue response on sheep animal model. Histological evaluation performed on undecalcified cement-bone specimens assessed the in vivo behaviour. It has been shown that the new IM/alpha-TCP/CSD-BC has the ability to produce firm bone binding in vivo (i.e. bioactivity). Qualitative histology proved cement biocompatibility, osteoconduction and favourable resorption, mainly through a macrophage-mediated mechanism. The results showed that the new cements have biocompatible and osteogenic features of interest as possible cancellous bone replacement biomaterial for minimally invasive spinal surgery applications.

Design and properties of 3D scaffolds for bone tissue engineering.

UNLABELLED In this study, the Voronoi tessellation method has been used to design novel bone like three dimension (3D) porous scaffolds. The Voronoi method has been processed with computer design software to obtain 3D virtual isotropic porous interconnected models, exactly matching the main histomorphometric indices of trabecular bone (trabecular thickness, trabecular separation, trabecular number, bone volume to total volume ratio, bone surface to bone volume ratio, etc.). These bone like models have been further computed for mechanical (elastic modulus) and fluid mass transport (permeability) properties. The results show that the final properties of the scaffolds can be controlled during their microstructure and histomorphometric initial design stage. It is also shown that final properties can be tuned during the design stage to exactly match those of trabecular natural bone. Moreover, identical total porosity models can be designed with quite different specific bone surface area and thus, this specific microstructural feature can be used to favour cell adhesion, migration and, ultimately, new bone apposition (i.e. osteoconduction). Once the virtual models are fully characterized and optimized, these can be easily 3D printed by additive manufacturing and/or stereolitography technologies. STATEMENT OF SIGNIFICANCE The significance of this article goes far beyond the specific objectives on which it is focussed. In fact, it shows, in a guided way, the entire novel process that can be followed to design graded porous implants, whatever its external shape and geometry, but internally tuned to the exact histomorphometric indices needed to match natural human tissues microstructures and, consequently, their mechanical and fluid properties, among others. The significance is even more relevant nowadays thanks to the available new computing and design software that is easily linked to the 3D printing new technologies. It is this transversality, at the frontier of different disciplines, the main characteristic that gives this article a high scientific impact and interest to a broaden audience.

Iron oxide nanoparticles significantly enhances the injectability of apatitic bone cement for vertebroplasty.

Study Design. Experimental study to characterize the setting and the cytocompatibility properties of apatitic bone cement. Objective. To investigate the setting, flowing, and biocompatibility properties of new iron-modified calcium phosphate bone cements. Summary of Background Data. Vertebroplasty and kyphoplasty are efficient procedures for the treatment of painful vertebral compression fractures. Nowadays, calcium phosphate cements are used to treat these fractures mainly due to the similar bone apatitic phase formed after setting. However, clinicians have reported great difficulties in filling the vertebral bodies due to the high pressures needed to inject these materials. Thus, new approaches are needed to improve the initial flowing properties of these cements without affecting or even improving their short-term mechanical stability and their long-term in vivo cement transformation into bone tissue. Methods. Cement setting times were measured by the Gillmore needles method. The evolution of the compressive strength accounted for the cement hardening process. Scanning Electron Microscopy followed the evolution of the cement microstructure with hardening. Radiograph diffraction analysis confirmed the evolution of the crystalline phases underlying the setting and the hardening processes. Injectability tests were performed by using syringes filled with bone cement and recording the evolution of the injection force needed to empty the syringe. Finally, the cytocompatibility was analyzed by culturing human epithelial cells onto the cements and evaluating both the relative cell viability and the adhesion cell density. Results. The modification of the powder phase of an &agr;-tricalcium phosphate cement with iron oxide nanopar-ticles significantly enhanced, at constant liquid to powder cement mixing ratio, the resulting cement injectability by lowering the extrusion force required for cement delivery. For example, 24 wt% iron oxide addition resulted in 83% of cement injected with an extrusion force lower than 25 N. In fact, the setting and the working times of the cement pastes increased with iron oxide addition. Moreover, the new cement pastes showed improved compressive strength in agreement with the crystalline microstructure evolved during hardening. However, iron modification did not produced cytotoxic cements as compare to nonmodified cements. Conclusion. It has been shown that the addition of iron oxide nanoparticles into the powder phase of an &agr;-tricalcium phosphate based cement improved both, the initial injectability and maximum compressive strength of the cement without affecting their physico-chemical setting reactions and their cytocompatibility. These results could be further exploited by designing improved injectable apatitic cements with suitable mechanical properties and in vivo cement transformation ratios into bone tissue by incorporating phases creating porosity.

Injectable iron-modified apatitic bone cement intended for kyphoplasty: cytocompatibility study

In this study, the cytocompatibility of human ephitelial (HEp-2) cells cultured on new injectable iron-modified calcium phosphate cements (IM-CPCs) has been investigated in terms of cell adhesion, cell proliferation, and morphology. Quantitative MTT-assay and scanning electron microscopy (SEM) showed that cell adhesion and viability were not affected with culturing time by iron concentration in a dose-dependent manner. SEM-cell morphology showed that HEp-2 cells, seeded on IM-CPCs, were able to adhere, spread, and attain normal morphology. These results showed that the new injectable IM-CPCs have cytocompatible features of interest to the intended kyphophasty application, for the treatment of osteoporotic vertebral compression fractures.

Characterization and three-dimensional reconstruction of synthetic bone model foams

Sawbones© open-cell foams with different porosity grades are being used as synthetic bone-like models for in vitro mechanical and infiltration experiments. However, a comprehensive characterization of these foams is not available and there is a lack of reliable information about them. For this reason two of these foams (Refs. 1522-505 and -507) have been characterized at the micro architectural level by scanning electron microscopy, computed tomography and image data analysis. BoneJ open software and ImageJ open software were used to obtain the characteristic histomorphometric parameters and the three dimensional virtual models of the foams. The results showed that both foams, while having different macro porosities, appeared undistinguishable at the micro scale. Moreover, the micro structural features resembled those of osteoporotic rather than healthy trabecular bone. It is concluded that Sawbones© foams behave reasonably as synthetic bone-like models. Consequently, their use is recommended for in vitro comparison purposes of both mechanical and infiltration testing performed in real vertebra. Finally, the virtual models obtained, which are available under request, can favour comparisons between future self-similar in vitro experiments and computer simulations.

Potential risks of using cement-augmented screws for spinal fusion in patients with low bone quality

BACKGROUND CONTEXT Dramatic increases in the average life expectancy have led to increases in the variety of degenerative changes and deformities observed in the aging spine. The elderly population can present challenges for spine surgeons, not only because of increased comorbidities, but also because of the quality of their bones. Pedicle screws are the implants used most commonly in spinal surgery for fixation, but their efficacy depends directly on bone quality. Although polymethyl methacrylate (PMMA)-augmented screws represent an alternative for patients with osteoporotic vertebrae, their use has raised some concerns because of the possible association between cement leakages (CLs) and other morbidities. PURPOSE To analyze potential complications related to the use of cement-augmented screws for spinal fusion and to investigate the effectiveness of using these screws in the treatment of patients with low bone quality. STUDY DESIGN A retrospective single-center study. PATIENT SAMPLE This study included 313 consecutive patients who underwent spinal fusion using a total of 1,780 cement-augmented screws. METHODS AND OUTCOME MEASURES We analyzed potential complications related to the use of cement-augmented screws, including CL, vascular injury, infection, screw extraction problems, revision surgery, and instrument failure. There are no financial conflicts of interest to report. RESULTS A total of 1,043 vertebrae were instrumented. Cement leakage was observed in 650 vertebrae (62.3%). There were no major clinical complications related to CL, but two patients (0.6%) had radicular pain related to CL at the S1 foramina. Of the 13 patients (4.1%) who developed deep infections requiring surgical debridement, two with chronic infections had possible spondylitis that required instrument removal. All patients responded well to antibiotic therapy. Revision surgery was performed in 56 patients (17.9%), most of whom had long construction. A total of 180 screws were removed as a result of revision. There were no problems with screw extraction. CONCLUSIONS These results demonstrate the efficacy and safety of cement-augmented screws for the treatment of patients with low bone mineral density.

Advantageous new conic cannula for spine cement injection.

Study Design. Experimental study to characterize the influence of the cannula geometry on both, the pressure drop and the cement flow velocity established along the cannula. Objective. To investigate how the new experimental geometry of cannulas can affect the extravertebral injection pressure and the velocity profiles established along the cannula during the injection process. Summary of Background Data. Vertebroplasty procedure is being used to treat vertebral compression fractures. Vertebra infiltration is favored by the use of suitable: (1) syringes or injector devices; (2) polymer or ceramic bone cements; and (3) cannulas. However, the clinical use of ceramic bone cement has been limited due to press-filtering problems. Thus, new approaches concerning the cannula geometry are needed to minimize the press-filtering of calcium phosphate-based bone cements and thereby broaden its possible applications. Methods. Straight, conic, and combined conic-straight new cannulas with different proximal and distal both length and diameter ratios were drawn with computer-assisted design software. The new geometries were theoretically analyzed by: (1) Hagen-Poisseuille law; and (2) computational fluid dynamics. Some experimental models were manufactured and tested for extrusion in order to confirm and further advance the theoretical results. Results. The results confirm that the totally conic cannula model, having proximal to distal diameter ratio equal 2, requires the lowest injection pressure. Furthermore, its velocity profile showed no discontinuity at all along the cannula length, compared with other known combined proximal and distal straight cannulas, where discontinuity was produced at the proximal-distal transition zone. Conclusion. The conclusion is that the conic cannulas: (a) further reduced the extravertebral pressure during the injection process; (b) showed optimum fluid flow velocity profiles to minimize filter-pressing problems, especially when ceramic cements are used; and (c) can be easily manufactured. In this sense, the new conic cannulas should favor the use of calcium phosphate bone cements in the spine. Level of Evidence: N/A

Analysis of bone cement distribution around fenestrated pedicle screws in low bone quality lumbosacral vertebrae

PurposeTo study the exact distribution of bone cement around augmented fenestrated pedicle screws in both lumbar and sacral vertebrae of patients with low bone quality.MethodsA total of 37 patients with instrumented lumbar fusion were investigated. 3D computed tomography virtual models of the injected cement and screws were obtained. The models were computed for their centroid (i.e. their average mass centre point), and their coordinates (x, y, z) were projected on their respective screw-transversal and screw-longitudinal planes for further analysis.ResultsThe results showed better bone cement homogeneous distribution around the screws in lumbar (L4 and L5) than in sacral (S1) vertebrae. In the lumbar region, the centroids were transversally projected near the transversal centre of symmetry of the screws. On the other hand, in the sacral region, the cement flowed preferentially outside the centre of symmetry of the screws, into the sacral ala.ConclusionsThe results confirm the different flow behaviours of bone cement in lumbar versus sacra vertebrae. The computer methodology followed in this study helps to understand the clinical monitoring observations and lays the foundations for better positioning of the screws and specific vertebrae-oriented screw designs.