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
Novel conic cannulas further reduce the extravertebral pressure during cement injection in vertebroplasty. The velocity profiles established along the conic cannulas were continuous compared with the straight cannulas; these profiles should minimize filter pressing of biphasic calcium phosphate bone cements.
*Interdepartment Research Group for the Applied Scientific Collaboration (IRGASC), Division of Biomaterials & Bioengineering, Technical University of Catalonia (UPC), Barcelona, Spain; and
†Faculty of Medical Bioengineering, “Gr. T. Popa” University of Medicine and Pharmacy, Iasi, Romania.
Address correspondence and reprint requests to Enrique Fernandez Aguado, PhD, Department of Materials Science and Metallurgical Engineering, Technical University of Catalonia (UPC), Avda. Diagonal 647, E-08028-Barcelona, Spain; E-mail: firstname.lastname@example.org
Acknowledgment date: February 27, 2014. Acceptance date: May 28, 2014.
The manuscript submitted does not contain information about medical device(s)/drug(s).
Ministerio de Economia y Competitividad, Gobierno de Espana (public funding received through project MAT2010-19431) funds were received to support this work.
No relevant financial activities outside the submitted work.