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Intravertebral Pressure During Vertebroplasty: A Study Comparing Multiple Delivery Systems 2003

Agris JM, Zoarski GH, Stallmeyer MJB. and Ortiz AO*
University of Maryland Medical Center
Baltimore, Maryland
*Winthrop-University Hospital
Mineola, New York

Purpose:
Vertebroplasty has revolutionized the treatment of compression fractures. Claims of enhance safety attributable to “low pressure delivery” with larger bore systems are thus far unsubstantiated. We set out to determine whether intravertebral injection pressure measurements differ substantially between various delivery systems and devices. A simple mathematical model representing the different systems by variable resistance predicts that intravertebral pressure should be the same for a constant rate injection no matter which system is used.

Materials & Methods:
A cadaveric model was designed to measure intravertebral pressure during injection of a standardized poly-methylmethacrylate formulation (Secours, ArthroCare Corporation) through three different delivery systems: an 11-gauge (2.3 mm) disposable bone biopsy needle (Cook, Inc., Bloomington, IN), a 6-gauge (4.1 mm) CDO cannula (American Osteomedix, Irvine, CA), and the (4.0 mm) KyphX Inflatable Bone Tamp system (Kyphon, Inc., Sunnyvale, CA). After vertebral access, the tip of a contralateral 11-gauge needle was placed in close proximity to the tip of the device being tested; a pressure transducer was attached to the second needle. Saline flush confirmed continuity across the system. Intravertebral pressures were monitored during administration of 6cc of poly-methylmethacrylate (Secours, ArthroCare Corporation) at a fixed rate of 4cc/min by power injector (Medrad, Inc. Indianola, PA). Finally, measurements were obtained during manual cement delivery using two different delivery cannulas and blunt stylets (AOM and Kyphon), and a hand crank device (EZflow CDS, ArthroCare Corporation).

Results:
Pressure measurements were acquired over a range of 0-500mm Hg (0-9.8atm). The 11-gauge needle system reached a maximum intravertebral pressure (Pmax) of 170mm Hg (3.3psi). The AOM system reached a Pmax of 290mm Hg (5.7psi). Inflation of the KyphX balloon to a maximum of 225psi generated a Pmax of 100mm Hg (2psi); Pmax during subsequent filling of the cavity with poly-methylmethacrylate was 160mm Hg (3.1psi). Manual cement delivery with the Kyphon BFD generated average peak intravertebral pressures of 261mm Hg (5.1psi). Manual delivery with the EZflow CDS system generated a Pmax of 220mm Hg (4.3psi).
Conclusion: Our results demonstrate little difference in Pmax between the 11-gauge needle and the Kyphon balloon system with constant rate cement delivery. In comparison, the larger bore AOM CDO generated a 75% higher peak intravertebral pressure. Manual cement delivery with the EZflow CDS generated a peak intravertebral pressure which was 29% higher than constant rate delivery using the same 11-gauge needle. If a stylet was used for cement delivery with any system, regardless of size, the Pmax exceeded 500mm Hg (9.8psi). The broad conclusion that larger bore systems provide lower intravertebral pressures during cement delivery is incorrect, and operator training remains essential to the safe performance of percutaneous vertebroplasty. As might be expected, all factors influencing cement delivery in a cadaver cannot be predicted by a simple mathematical model. Additional studies using an acrylic vertebral body model will be performed to minimize variability inherent in cadaveric specimens.

Scientific Paper to be presented by Jacob M. Agris
MS PowerPoint for Windows on CD-ROM
Contact Information:
Jacob M. Agris, M.D., Ph.D.
Division of Neuroradiology
University of Maryland Medical Center
22 S. Greene Street
Baltimore, Maryland 21201
(410) 328-5112 voice
(410) 389-7496 pager