Vertebral compression fractures are one of the more common sequelae of osteoporosis. Untreated VCFs predispose patients to subsequent vertebral and hip fractures, precipitating a progressive, downward spiral of deformity and disability, and elevating the risk of mortality.
(Lindsay et al., 2001; Melton, Atkinson, Cooper, O’Fallon, & Riggs, 1999; Black, Arden, Palermo, Pearson, & Cummings, 1999)
Non-surgical management with bed rest, pain medication, braces, and physical therapy was once the preferred approach to VCF treatment, chiefly because the risks of open back surgery outweighed its benefits. However, the advent of minimally invasive approaches to vertebral body augmentation has improved the outlook for patients with VCF.(Korovessis, Vardakastanis, Repantis, & Vitsas, 2014; Tutton & The KAST Investigators, 2014; Otten et al., 2013; Korovessis, Vardakastanis, Repantis, & Vitsas, 2013; Van Meirhaeghe et al., 2013; Boonen et al., 2011; Wardlaw et al., 2009) Modern evidence clearly shows a morbidity and survival benefit for patients treated with minimally invasive VBA, compared to conservative management. (Chen, Cohen, & Skolasky, 2013; Edidin, Ong, Lau, & Kurtz, 2011)
The field of VBA is evolving, and recent product introductions have brought more potential options to treating physicians. The strengths and weaknesses of the three current and most popular approaches to VBA, all currently cleared for use in the United States, are summarized here.
Traditional vertebroplasty (needle and cement): The least complex approach to minimally invasive repair of VCF is to inject polymethyl methacrylate bone cement into the fracture using a spinal needle. This approach works well for simple fixation and pain relief, and has dramatically improved quality of life for many patients. However, the procedure does not technically achieve augmentation, since it is unable to reduce the fracture, provide the structural support necessary to correct the kyphotic angle, or otherwise address the progressive deformity associated with VCF. Indeed, it is also an unfortunate reality that the relative stiffness of PMMA compared to osteoporotic bone may put patients at risk of subsequent, adjacent-level fractures and progression of kyphosis. (Boonen et al. et al., 2011; Wardlaw et al. et al., 2009) Further, extravasation of the cement, although a rare complication, is most common using this technique, in part due to the relatively poor control over cement deployment during the procedure.
Balloon kyphoplasty: Over the past decade, the balloon kyphoplasty system from Medtronic Inc. has become so widely accepted that it is viewed as almost synonymous with minimally invasive VBA. Two small balloons are inserted transpedicularly into the body of the fractured vertebra, and then expanded to create a cavity within the vertebral body for placement of injected bone cement. When BKP was first developed, the goal was to achieve the rapid fixation and pain reduction, while also restoring vertebral height, reducing kyphosis, limiting the occurrence of adjacent-level fractures, and controlling leakage.
Unfortunately, real-world results have been mixed. Without a doubt, VCF patients treated with BKP fare better in terms of pain reduction, quality of life, function, and mobility than those managed conservatively. (Wardlaw et al. et al., 2009; Van Meirhaeghe et al. et al., 2013) Incidence of cement extravasation may also be somewhat lower with BKP than with traditional needle approaches, although a non-zero risk of this complication still exists. (Ren et al., 2010) However, other hoped-for benefits of BKP have never been proven definitively. In particular, significant room for improvement remains in the ability to correct the kyphotic angle and control cement deployment. It is also troubling that BKP has proven unable to overcome the problem of new fractures that may be exacerbated by the relative stiffness of the cement compared to cortical bone.(Boonen et al. et al., 2011; Wardlaw et al. et al., 2009)
Implant-based minimally invasive VBA: In 2014, a novel, implant-based approach to VBA known as the Kiva VCF Treatment System by Benvenue Medical, Inc. received 510(k) clearance for use in the reduction and treatment of spinal fractures in the thoracic and/or lumbar spine from T6 through L5. It is intended to be used in combination with the Benvenue Vertebral Augmentation Cement Kit. Briefly, a continuous-loop implant is inserted into the body of the fractured vertebra using a transpedicular approach, over a nitinol, coiled guidewire. As the implant is introduced over the wire into the vertebral body, it forms a stacked coil structure, providing angle correction that can be controlled by varying the number of loops deployed. Once the physician is satisfied with the correction, the guidewire is removed and cement is introduced into the lumen of the device. The defined structure of the implant contains the cement peripherally and guides it centrally and toward the endplates, reducing the total volume of cement required.
The implant itself is made from the flexible medical polymer, polyether ether ketone or PEEK. When filled with hardened PMMA, the implant exhibits less than 50 percent of the stiffness of PMMA alone and more closely approximates the physiologic characteristics of cortical bone, lending flexible structural support to the fracture. The goal of these structural features are to address the unmet goals of VBA: more reliable restoration of anatomy, elevation of the endplate, marked improvement in kyphosis and reduction in the incidence of cement extravasation.
Multiple clinical studies have shown that the implant-based system meets or exceeds performance of BKP. Most recently, KAST (Kiva System as a Vertebral Augmentation Treatment – A Safety and Effectiveness Trial) evaluated the implant versus BKP in 300 patients at 21 centers in the United States, Canada, Belgium, France and Germany, making it one of the largest randomized, multicenter studies in this space to date. (Tutton et al., 2014) The KAST study met its primary endpoint, a composite of pain improvement, function and safety, showing the implant to be non-inferior to BKP at 12 months post-procedure. It also met several key secondary endpoints, with a site-reported 34 percent lower rate of cement extravasation and 44 percent reduction in cement volume compared to BKP. Although the study was not sufficiently powered to prove statistical significance in the secondary endpoint of reduction in adjacent-level fractures, a clinically important 30 percent reduction in this endpoint suggests promising direction for future study.
In an independent, randomized, single-center trial of 168 patients, the implant system was associated with statistically significant reductions in cement volume and leakage, and improvement in kyphotic angle restoration compared to BKP. (Korovessis et al., 2013) Another independent, single-center study compared the implant system to BKP in 52 patients. Results showed that the implant system reduced pain and the rate of new adjacent-level fractures, with less leakage of cement compared to BKP. (Otten et al. et al., 2013) Other peer-reviewed clinical evidence supports use of the implant-based system for VCFs caused by malignant tumors and trauma. (Anselmetti et al., 2013; Korovessis et al., 2014)
Together, the results of these combined studies demonstrate that the implant-based system is associated with a reduced rate of adjacent-level fractures even in high-risk populations, improved restoration of the kyphotic angle, reduced cement volume used and reduced rate of cement extravasation. Further, timely treatment is generally possible—subject to reimbursement guidance within 2 weeks after onset of VCF pain—and improvement in pain is routinely immediate.
To date, the drawbacks of the implant system are the relatively minor adaptations in technique that new operators will have to address. For example, placement of the introducer and the device, although made through the well-defined and safe transpedicular approach, requires greater precision and closer operator attention than with BKP because the implant must be positioned more exactly within the vertebral body than a kyphoplasty balloon. However, this is offset by the need to access the vertebral body only once — versus twice with BKP — since the approach is unipedicular. The other point requiring a change in operator mindset is to become comfortable with the use of lower volumes of less viscous cement. Over the course of BKP development, many operators have become accustomed to the thicker bone cements that were developed in an effort to mitigate extravasation. This is not necessary with the implant, because injected cement is directed to flow centrally into the vertebral body through small slots in the implant. Neither of these considerations makes for a particularly difficult learning curve.
Discussion and Conclusions
Much progress has been made in the field of minimally invasive VBA over the last decade, spurred by a more comprehensive understanding of the serious consequences of un- or under-treated VCF. In some patients, VBA can completely restore a patient’s functionality while in others there remains a need for a comprehensive program of pain management, osteoporosis management and physical and functional therapy. The ability to provide additional structural support for the healing vertebra while minimizing the risk of new adjacent-level fractures may aid in negating the vicious cycle of disability associated with VCF, instead promoting a virtuous cycle of recovery.
References
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