36 Vertebral Body Stenting

Introduction

Vertebral body compression fractures (VBCFs) are the hallmark of osteoporosis, and their incidence increases exponentially with increasing age. VBCFs are related to important morbidity and loss of quality of life comparable to that in hip fractures (Figure 36-1).^1,²

FIGURE 36-1 Survival probability at the age of 75 years for women, comparing the general population with patients after a hip or vertebral fracture. Both groups with fracture show a significant reduction of life expectancy.

The treatment of painful VBCFs with percutaneous cement reinforcement has a long history and appears very effective in a very high percentage of patients treated. There are many case series published that support this treatment, with the most recent publication also providing encouraging long-term results.³^–⁵ Furthermore, there is class A evidence based on a large multicenter Randomized Clinical Trial (RCT) comparing percutaneous cement reinforcement after cavity creation with a balloon against conservative treatment. This study clearly shows a superiority of cement reinforcement for pain, activity level, and pain medication in the first year of treatment.⁶ Although the study is comparing kyphoplasty as a specific technique of reinforcement against conservative treatment, based on several review articles, there is no clinical advantage of kyphoplasty over vertebroplasty.^7,⁸ Most recently, two studies were published comparing vertebroplasty with a sham procedure showing no difference in early outcome. Although the studies show a randomized design with independent assessment, there seems to be a selection bias because the inclusion of patients took several years even though a multicenter study design was used.^9,¹⁰

Although cement reinforcement can stabilize a fracture and therefore decrease pain, height restoration remains an issue, that is not solved yet. Kyphoplasty was introduced initially with the idea to restore vertebral body height. However, the amount of height gain remained very modest, and its clinical impact remains obscure. With the inflation of the balloon, excellent height reduction can be achieved, but after deflation a major amount of the reduction gets lost.¹¹

The consequences of vertebral height loss and increased kyphosis are reported in several epidemiological studies: impaired quality of life and even an increased mortality are documented (see Figure 36-1).^2,^12,¹³

The kyphotic deformity leads to a shift of center of gravity and consecutively to an increased load on the anterior column. Consequently, there is an increased risk for new fractures.^14,¹⁵ Furthermore the increased kyphosis raises the load of the back muscles enormously (Figure 36-2).^16,¹⁷

FIGURE 36-2 Vicious circle of vertebral fractures: The increased kyphosis is related to higher stress of the anterior column. There is the risk of new fractures on the one hand, and it increases the load of the back muscles, which further increases loss of posture on the other hand.

Vertebral Body Stent

How to Restore and Maintain Vertebral Height

The concept of the balloon for height restoration appears most reasonable, because it provides optimal, equal force distribution coupled with a growing surface area. Taking advantage of this principle, the combination of a balloon with an expandable stent appears the optimal solution for restoring and maintaining vertebral body height.

In Vitro Testing

Anatomical data size calculations and Finite Element (FE) modeling allowed the design of a balloon–stent construct strong enough to be expanded and stable enough not to collapse under the elastic load effective in supine position.

Extensive cadaver testing allowed proof of the feasibility of the concept, and in a sophisticated in vitro setup, one could clearly demonstrate the superior potential for height maintenance in comparison to the balloon insertion only with sound significance (Figure 36-3).¹⁸

FIGURE 36-3 A, Comparison of a kyphoplasty procedure and a vertebral body stenting system as assessed in a cadaver model with a preload of 110 N.^21,²² Initial reduction can be achieved equally well with both systems. After deflation of the balloon there is a significant loss of reduction with the kyphoplasty system (∗), whereas the height can be maintained with the VBS (∗∗). B, Summary of twelve pairs of vertebrae tested. Initial height gain is similar in both techniques. Loss of height is observed with both systems, but significantly less with VBS (p = .024), and consequently the overall height restoration is superior with the VBS system (p = .035). (From Wilke HJ, Neef P, Caimi M, Hoogland T, Claes LE. New in vivo measurements of pressures in the intervertebral disc in daily life. Spine 1999;24-8:755-762; and Sato K, Kikuchi S, Yonezawa T. In vivo intradiscal pressure measurement in healthy individuals and in patients with ongoing back problems. Spine 1999;24-23:2468-2474.)