Introduction

Percutaneous treatment of vertebral compression fractures (VCFs) was first performed in France in 1984 by Galibert and Deramond.¹ The two most commonly performed minimally invasive VCF procedures are known as vertebroplasty and kyphoplasty. The primary difference is that in kyphoplasty, commonly referred to as percutaneous vertebral augmentation, a cavity using a mechanical device is created before cement delivery.^∗ Both procedures have been shown to provide dramatic pain relief in vertebral body fractures associated with underlying osteoporosis or malignancy, and have been successfully applied in cases in which conservative management has failed and surgery is undesirable.¹–⁷, ¹⁰–¹⁴ Because they have a higher incidence of osteoporosis, most patients referred for this procedure are women. However, men with vertebral body fractures from osteoporosis also present for treatment. Many of the characteristics of the male population with osteoporotic vertebral body fractures have recently been described.^4,7 Vertebral body fractures are the most common osteoporotic fractures in men. Like those in women, they are associated with significant morbidity and restriction of activities of daily living.⁸ The economic impact of osteoporotic fractures was estimated at nearly $2.7 billion in 1995 for men alone,⁹ making this a substantial health care problem from the standpoint of both cost and morbidity.

Minimally invasive treatment of vertebral compression fractures requires the image-guided insertion of a needle or working cannula through or adjacent to the pedicle into the vertebral body. Acrylic or calcium phosphate bone cement is then injected into the vertebral body (either with or without performing cavity creation) where it solidifies, providing structural support and preventing the movement associated with pain.^3,14

In 2002 there were approximately 38,000 vertebroplasties and 16,000 kyphoplasties performed in the United States. By 2007 this grew to approximately 80,000 vertebroplasties and 50,000 kyphoplasties in 2007. As the use of both modalities for the treatment of vertebral compression fractures has increased, so have questions regarding safety and efficacy and the need for greater control of cement delivery. A desire for restoration of height (in mobile fractures) and a minimalist approach to the procedure has lead to interest in convergence and evolution in the field of minimally invasive treatment of VCF, just as the Montgolfier brothers and the Wright brothers competed in some ways. Although both procedures are largely safe, U.S. Food and drug Administration (FDA) data have highlighted two main concerns: venous extravasation resulting in cord compression and pulmonary emboli leading in some cases to paralysis.

Although both vertebroplasty and kyphoplasty are largely safe and provide similar rates of pain relief, the added complexity and possible radiation exposure of multiple steps associated with conventional (balloon-assisted) kyphoplasty have been considered by some as warranted because it offers the possibility of restoring vertebral height and it carries lower rates of cement leakage than vertebroplasty. The value of controlling cement delivery and potential for height restoration, when possible, are universally accepted. Cement control in a clinical environment can be modified in two ways—the viscosity at the time of delivery and the amount of time (working time) the cement can be delivered. Numerous emerging technologies are focused on providing physicians promising new therapies for managing vertebral compression fractures of the spine in a minimalist, safe way, while providing patients with much needed pain relief. Since 2006, technology has evolved so extensively that the traditional use of the procedural term kyphoplasty has been expanded to incorporate the use of other technologies. Initially, kyphoplasty was defined as the “balloon procedure.” Today there are additional technologies designed for minimally invasive, cavity creating VCF treatment. Consequently, procedure terminology has evolved, as evidenced by Centers for Medicare and Medicaid Services (CMS) 2009 fiscal year International Classification of Diseases (ICD-9) code title for “Kyphoplasty” being replaced with “Percutaneous Vertebral Augmentation,” and “conventional” balloon-assisted procedures being listed as an example of vertebral augmentation procedures.

The StabiliT Vertebral Augmentation System (DFine Inc., San Jose, CA, USA) is a novel product intended for the treatment of VCFs associated with osteoporotic fractures and tumors of the spine in a procedure known as radiofrequency (RF) kyphoplasty. RF kyphoplasty is designed to minimize leakage, enable height restoration of mobile fractures, and provide pain relief through fracture stabilization by way of site- and size-specific cavity creation and extended, controlled delivery of an ultrahigh viscosity cement. This new percutaneous vertebral augmentation system combines the following unique attributes: navigational cavity creation device; RF energy modulated, ultra-high viscosity cement; unique, hydraulic delivery system; and a remotely controlled delivery mechanism to offer additional control to the physician in treatment of a VCF. The use of RF energy to modulate bone cement polymerization immediately before entering the patient permits the system to maintain cement in a reservoir at ambient temperature with a very long working time, yet deliver cement of a viscosity many times higher than conventionally delivered polymethyl methacrylate (PMMA) cement. This control during the cement delivery results in the potential for reduced venous extravasation and yet retains the ability to move bone fragments and restore height.

This chapter reviews the novel StabiliT Vertebral Augmentation System and the initial cadaver and clinical experience in which the system was used to perform the RF kyphoplasty. The potential ability of the StabiliT Vertebral Augmentation System in performing RF kyphoplasty to restore vertebral height is comparable to that of conventional vertebroplasty and conventional balloon kyphoplasty procedures in a cadaver model. The early clinical experience, generated by interventional neuroradiologists, orthopedic surgeons, and neurosurgeons, is compared with clinical results previously reported for conventional vertebroplasty and balloon kyphoplasty. To date, over 1200 patients have been treated with the StabiliT Vertebral Augmentation System without symptomatic cement extravasation.

Materials and Methods

The StabiliT Vertebral Augmentation System

The StabiliT Vertebral Augmentation System is a unique RF controlled cement delivery system for the treatment of vertebral compression fractures. It has been cleared for use in the United States for percutaneous delivery of StabiliT ER (Energy Responsive) Bone Cement in kyphoplasty procedures in the treatment of painful vertebral compression fractures, which may result from osteoporosis, benign lesions (hemangioma), and malignant lesions (metastatic cancers, myeloma). It contains the following components: a proprietary energy-responsive PMMA bone cement (StabiliT ER Bone Cement); a unique vacuum saturation cement mixing system (Saturate Mixing System); a controller (Mulitplex Controller) that contains both a radiofrequency generator and a hydraulic drive; introducer/working cannulae for access to the vertebral body; straight and navigational cavity creation devices to permit specificity of the site and size of the cavity; a PFA (Teflon-like)-lined heating element (Activation Element) and delivery cannulae to permit the delivery of uniquely high viscosity PMMA cement; and a 3-m-long cable to permit remote-control delivery of the cement, thereby controlling the operator’s radiation exposure (Figure 40-1). Following cavity creation using the articulated arm of the MidLine Osteotome, the StabiliT System (DFine Inc., San Jose, CA, USA) preferentially delivers cement to the cavity but further permits interdigitation of the ultra-high viscosity cement into the adjacent trabecular beds (Figure 40-2).

FIGURE 40-1 A, StabiliT Vertebral Augmentation System for radiofrequency kyphoplasty. B, Cement in the reservoir before passing through the Activation Element and delivery cannula has extended working time.

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