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

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.)

Clinical Application

Indications

The use of the vertebral body stent (VBS) is indicated in acute and subacute painful VBCFs with at least 15% of height loss and kyphotic deformity with the potential of reducibility. In consolidated and fixed fractures, the use of a stent is no longer indicated.

Surgical Technique

Preferably the procedure is performed under general anesthesia, with the patient placed in hyperextension. Based on the preoperative imaging (either CT scan or MRI and conventional x-rays), the placement of the working cannula and the stent is planned in order to achieve an optimal effect for the fracture reduction (Figure 36-4, A). Intraoperatively this placement is navigated by biplanar C-arm control. The crucial landmarks to be respected are the medial border of the pedicle and the posterior wall of the vertebral body. Depending on the individual anatomical situation, the working cannula is placed transpedicular or parapedicular (Figure 36-4, B).

FIGURE 36-4 A, Principles of surgical technique: The optimal placement of the stent is assessed and planned preoperatively based either on a CT scan or MRI investigation. The stents should be located in order to achieve optimal effect, which is about 5 mm below the endplate and in the area of maximal compression. White line are antero posterior vertebral body dimension; arrow is trajectory of trocar placement; white circles are pedicles. B, Intraoperative orientation is based on anteroposterior and lateral C-arm projections. The crucial landmarks to be respected are the medial border of the pedicle in the anteroposterior view and the posterior wall of the vertebral body in the lateral view. The tip of the guide wire must not breach the medial border of the pedicle before it reaches the level of the posterior wall. Arrows illustrate angulation (top and bottom left pictures) and inclination (top right picture) of trocar placement; red line is medial border (top left picture) of pedicle and posterior edge (top right and bottom picture) of vertebral body.

Once the working cannula is positioned, the space for the stent is prepared and its size determined and confirmed with the reamer. Then the stents are placed and the appropriate position is monitored in both planes. Make sure that the stents are outside the working cannula but fully inside the vertebral body and that they do not interfere at the tip. Do not start expansion before this check. Then a stepwise symmetrical filling of the balloon stent is performed under pressure, volume, and visual control by imaging. Once the maximal filling or height restoration is achieved, the balloons are deflated and removed. The filling is performed with high viscosity polymethylmethacrylate (PMMA). The cement should fill the void of the stent and infiltrate the surrounding bone. If there is any leakage, cement injections must be stopped immediately, wait for at least 45 seconds and then cautiously continue with the injection (Figure 36-5). Once the cement is cured remove the filling cannulas.

FIGURE 36-5 A, A 56-year-old woman after a minor car accident. The patient shows an atypical compression fracture of the lower endplate on the right hand side. When standing, the patient complains about L4 nerve root pain. The treatment consisted of a percutaneous reduction with a stent implantation (B to G). B, The working cannulas are placed bilaterally with slightly increased convergence of the left side. The trajectories give an idea of the final position of the stents The red dotted lines represent trajectory of trocar placement. C, After reaming, the stents are placed bilaterally. Top: Stent applicator and pressure manometer; Top Left: AP view of stent placement prior to stent expansion; Top Right: Lateral view of stent placement prior to stent expansion. D, The stent is expanded stepwise until maximal reduction is achieved or the maximal volume has been reached. E, After deflation and removal of the balloon, the stents remain expanded and the reduction is maintained. Left side pictures are AP views of stent after expansion and right side pics are lateral views of stent after expansion. F, Cement reinforcement with PMMA is performed with filling of the stents and infiltration of the surrounding bone. G, H, Comparison of the preoperative and postoperative CT scan demonstrating the amount of reduction and the ideal cement filling (left to right). I, Follow-up standing x-ray after 6 months.

The after-treatment remains the same as for vertebroplasty. Patients can be mobilized and be active as tolerated immediately after the procedure.

Clinical Experience

Since conformité européenne (CE) registration of the VBS in November, 2008, we have treated 49 patients with the system and documented these patients in a prospective study. The parameters that were assessed included technical aspects, surgical complications, and potential of height restoration.

Results

In our series of 49 patients, we treated 32 patients with osteoporotic compression fractures, 12 patients with traumatic fractures of the thoracolumbar spine, and 5 patients with fractures related to myeloma. The average age was 67 years (range, 27 to 85), and there were 31 women and 18 men.

Technical failures included rupture of the balloon, which was observed in three cases. These failures were observed in cases when the stent showed an eccentric expansion, and the edge of the stent most likely provoked the failure. In one case, a bony spica was the most likely cause. Balloon ruptures were observed at the end of the expansion. These did not lead to further problems, because the balloons could be completely removed with ease and the cementing afterwards was uneventful. In five cases it was not possible to expand the stent because of the already healed fracture. The pressure pump with its built-in peak pressure limit failed at 32 bars in all cases. In two occasions, the stent was removed again with the balloon. In the other cases it remained in place. In all these cases it was possible to inject some cement.

The amount of reduction that was achieved in the cases with still mobile fractures (n = 40) was measured by the segmental kyphosis (Figure 36-6, C). The average kyphosis angle preoperatively was 23 degrees (13 to 32 degrees) and could be corrected to 12 degrees (0 to 16 degrees) postoperatively. Height restoration was assessed semiquantitatively in the cases where the deformity was not mainly the kyphosis. The amount was graded from 0 to 3, where 0 meant no reduction possible and 3 meant complete restoration. There were 9 cases with grade 0. We have seen 18 cases with a reduction of grade 1, which means 50% height gain (see Figure 36-5); 15 cases with grade 2, which is 75% of height gain (Figure 36-7); and 7 cases with complete height restoration (Figure 36-8).

FIGURE 36-6 A, A 72-year-old woman with pain history of 8 weeks. The first x-rays show a complete collapse of L1 with severe kyphosis. B, Combining the closed reduction techniques of lordoplasty²³ and VBS allows a nearly complete height restoration. (From Orler R, Frauchiger LH, Lange U, Heini PF. Lordoplasty: report on early results with a new technique for the treatment of vertebral compression fractures to restore the lordosis. Eur Spine J, 15(2) 1769-1775, 2006.) C, Comparison of preoperative standing film and follow-up x-ray after 6 months. The vertebral height is well restored and maintained and the kyphosis nearly completely corrected (D and E).

FIGURE 36-7 A 78-year-old man with severe compression fractures of L1 after simple fall. Known osteoporosis due to steroid medication. Refractory immobilizing pain despite 10 days of hospital stay. A, CT scans depict severe vertebral body compression with posterior wall displacement and cleft formation. B, Based on the CT scan, preoperative planning of feasibility and possible stent dimension is performed. The minimal height for stent placement is about 8 mm. C to E, Intraoperative pictures of the surgical procedure: stent placement, expansion, balloon removal. Arrows in the image indicate the fractures. F, Standing x-ray images at 4 months postoperative with well-maintained vertebral height. The adjacent vertebrae were reinforced in a prophylactic sense.

FIGURE 36-8 A, Male patient, 41 years old, presents after a skiing accident with a burst split fracture of L1 (AO 3.2). B, The stent restored L1 to its former height. Ligamentotaxis provides realignment of the fragments, the cement then provides stability that allows immediate weight bearing. Reservations against using PMMA in young people are justified; however, alternative material is lacking and histologic workup of a postmortem specimen depicts no adverse effects around the cement, as demonstrated in the MRI taken 1 month after the intervention.²⁴ (From Braunstein V, Sprecher CM, Gisep A, Benneker L, Yen K, Schneider E, Heini P, Milz S. Long-term reaction to bone cement in osteoporotic bone: new bone formation in vertebral bodies after vertebroplasty. J Anat 2008;212-5:697-701.)

Cement leakage was observed in 9 out of 49 patients. These leaks were observed in the paravertebral tissue in 6 cases; in 2 cases, vascular leaks were present; and in 1 case, leakage into the foramen occurred. None of these leaks were clinically symptomatic.

The best potential for height gain was observed in our series of fresh traumatic fractures (n = 12). The healthy bone provides an optimal counterforce for the application of the reduction forces by the stent.

Discussion

Vertebral body stents permit restoration and maintenance of vertebral body height in vitro, and clinically it is possible to restore height in acute and subacute fractures. In addition the stent allows the clinician to overcome the limitations of the balloon-only principle. The balloon is optimal in the sense that it provides the best load distribution over the maximum possible area, but it is not able to maintain it after deflation.

So far the feasibility of the system can be demonstrated. Its use and application appears safe and reliable. The surgical procedure is more demanding in comparison to a simple vertebroplasty. Correct stent placement appears crucial in order achieve an optimal effect. For a controlled filling, the use of highly viscous cement with a long working time appears mandatory (i.e., Vertecem).

The clinical impact of height restoration needs to be demonstrated. Based on clinical comparison the impact of the fracture kyphosis seems to be more important than the overall kyphosis regarding balance problems of the spine.¹⁹ Biomechanical calculations suggest that the increase of kyphosis is related to an increase of the pressure on the anterior column on one hand, and, more importantly, a massive increase on the muscle load posteriorly.^14,20 This may be the cause of a vicious circle that ends up in this so-called sagittal plane decompensation.¹⁷ Therefore there is a rationale for height restoration and maintenance of spinal alignment. Further clinical studies are needed to demonstrate how vertebral body stenting is able to contribute to this.