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C H A P T E R 3 5 Vertebroplasty
215
After a careful history, physical examination, and assessment of radiographic imaging, the physician must then determine not only that the source
of the patient’s pain is indeed a VCF, but also that this fracture is amenable
to vertebroplasty. The primary indication for vertebroplasty is the alleviation of pain associated with a VCF due to osteoporosis or tumor. Repeated
studies have demonstrated superior pain relief with treatment of acute or
subacute fractures. Perhaps most notable is the non–industry-sponsored,
double-cohort by Alvarez et al
erative treatment for VCFs. He found statistically significant differences
at 3 months follow-up. Wardlaw et al
trial comparing balloon kyphoplasty with nonsurgical care for VCFs. He
too demonstrated a significant improvement in the intervention group at 1
month. Some now advocate the treatment of VCF within days of injury if
the pain is so severe as to require parenteral narcotics and hospitalization.
Late treatment, 6 months to years after the initial injury, is less likely to
completely relieve pain, but symptomatic improvement has been noted in
some studies.
3
, which compared vertebroplasty to nonop-
4
published a randomized controlled
Absolute Contraindications
As the primary indication for vertebroplasty is pain, it follows that an
asymptomatic stable vertebral compression fracture is a contraindication
for the procedure. Similarly, a painful osteoporotic fracture that is steadily
improving with conservative medical treatment should not be treated with
vertebroplasty. At this point, as there are no data to suggest that there is a
benefit to the stabilization of vertebrae “at high risk of impending fracture”
in the osteoporotic patient, a vertebroplasty should not be performed in
the absence of radiographic evidence of a VCF. Because a VCF in a young
patient with normal bone density should heal without complication, acute
traumatic fractures in this population should be treated conservatively.
There is evidence to suggest that PMMA may interfere with bone healing in
normal bone. Osteomyelitis of the target vertebra, uncorrectable coagulopathy or hemorrhagic diasthesis, and an allergy to any component required
for the procedure all also are considered contraindications to vertebroplasty.
Relative Contraindications
While not an absolute contraindication, patients with radiculopathy localized to the level of the VCF should be warned that vertebroplasty may not
improve all their symptoms, and may even worsen the pain. Also, fractures
with either significant retropulsion or tumor extension into the epidural
space are cases that necessitate significant preoperative planning. A preprocedure CT scan is indicated to visualize the fracture morphology and
potential cord compression. Even a small amount of cement extravasation
or displacement of tumor into the spinal canal could worsen symptoms and
make decompressive surgery more technically challenging. In these cases,
there should at least be consideration for decompression prior to vertebroplasty. VCFs with greater than 70% loss of vertebral body height are technically challenging, and true vertebra plana may be technically impossible. A
preoperative CT scan with coronal and sagittal reconstructions may help to
identify areas of the vertebra with adequate residual height. Typically height
is better preserved along the lateral aspect of the vertebral body; this may be
a target for vertebroplasty. Due to the risk of toxicity from PMMA monomers or fat emboli, treatment of more than three levels at a single setting is
not suggested. Finally, as evidence suggests poorer outcomes with chronic
fractures, a stable, chronic asymptomatic fracture is also a relative contraindication.
TECHNIQUE
As with any procedure, the process begins with proper patient selection (as
discussed earlier) and the procurement of informed consent. A thorough
discussion of the risks and benefits of the procedure is not only an ethical
necessity, but it also helps to assess and modulate the patient’s expectations
of clinical results.
Prior to the procedure, a thorough review of the patient’s medical history
(to allow the identification of potentially complicating disease processes),
medications (to assess for anticoagulants), and physical examination allows
for necessary procedural modifications to ensure the safety of the patient.
Once optimized, the patient may be brought to the procedure suite. Preoperative antibiotics, typically one gram of cefazolin, should be given 30 minutes prior to the commencement of the procedure.
Anesthesia for vertebroplasty is commonly a combination of conscious
sedation and a local anesthetic. It is often advantageous to administer partial
doses of sedation prior to positioning to decrease patient discomfort and
anxiety. General anesthesia may be used if the patient is unable to tolerate
prone positioning with only sedation due to pain or psychological disability;
however, this adds risk and substantial cost to the procedure. Once secured
in the prone position, radiographic imaging must be properly aligned. Fluoroscopy is the most commonly used modality. While biplanar fluoroscopy
machines are now available, allowing fast real-time visualization of the procedure, these are expensive and are not readily available to many physicians.
If single-plane imaging is used, it is imperative to obtain orthogonal projections to allow reliable assessment of needle positioning. CT scanning may
be used as an adjunct to fluoroscopy: however, alone it does not allow for
real-time monitoring of needle placement or cement injection. Also, it may
require general anesthesia to limit patient movement. Indications for CT
scan use include cervical or high-thoracic fractures necessitating the visualization of the carotid/jugular complex and vertebral vessels, sacral insufficiency fractures, and pathological fractures with risk of tumor displacement.
In these cases, if fluoroscopy is not used, then cement must be injected in
very small aliquots and scans should be performed frequently to assess for
leakage.
The approach should be determined preoperatively based on the location
of the lesion and its etiology. Preoperative CT scanning may be employed to
help make this assessment.
Transpedicular Approach
This is the classic approach employed by most physicians for standard thoracic and lumbar fractures, as it provides a discrete anatomic target for needle placement. Also, it has a safe entry point that permits easy compression
of overlying soft tissues postoperatively to lessen the chance of hematoma
formation. This approach is also effective for biopsy of the lesion, should
this be needed as part of a diagnostic workup.
Parapedicular (Transcostovertebral) Approach
The needle is inserted lateral to the pedicle, and approaches the vertebra
from above the transverse process. This approach is useful when the pedicle
is deformed, absent, or too small to accept the appropriate needle. Risks
associated with this approach include a low incidence of pneumothorax and
paraspinal hematoma.
Posterolateral Approach
This approach is primarily of historical importance. It was used most in
patients with small pedicles, in whom a transpedicular approach would be
dangerous. Utilizing a more lateral starting point, a small needle traverses
the lateral process and thus reaches the vertebral body at a more anterior
position than with other approaches. However, as the needle passes below
the pedicle, the nerve is placed at risk. In the thoracic region, there is a high
potential for pneumothorax if the operator lacerates the pleura.
Anterolateral Approach
This approach is used for cervical or high-thoracic fractures where small
pedicles and the orientation of the pedicles make a transpedicular approach
difficult. It is imperative to avoid the carotid/jugular complex, the vertebral
arteries, and the esophagus. A right-sided approach, opposite the esophagus,
allows the operator to manually push the carotid out of the way. A CT scan
may be used to better visualize these structures.
Procedure
Once the approach has been chosen, local anesthesia should be injected into
the skin and subcutaneous tissue along the expected needle tract; The periosteum of the bone at its entry site should also be injected. Next, a small
216
P A R T V Osteoporotic Surgical Treatment Modalities: Thoracic Spine
skin incision is made. The trocar and cannula are then introduced through
the skin incision and worked through the subcutaneous tissues down to
the level of the periosteum. The cannula and trocar should then be passed
into the bone. In osteoporotic bone, this can usually be done manually. In
neoplastic disease, the normal bone may be dense, necessitating the use of
a mallet for appropriate placement. Ultimately the tip of the needle should
be positioned beyond the midpoint of the vertebral body as viewed on the
lateral projection.
Some operators advocate for the placement of two transpedicular needles in the routine case. This allows for a larger margin of safety, increases
the chance of completing filling in a single batch of cement, and minimizes
leaks. A single needle may be used, and is successful in most cases. Historically, some operators have utilized venography to identify potential leak
sites. However, it was shown to have a low predictive value and has been
abandoned.
Once all needles have been properly placed as confirmed by imaging, the
cement may be prepared in a sterile vacuum device as recommended by the
manufacturer. The cement is then injected through the cannula using small
syringes for easy control. Cementing should be conducted either in real time
or after injection of small amounts (0.1-0.2 ml aliquots). Any evidence of
cement leakage outside of the vertebral body should prompt a pause. After
waiting several minutes, reinjection of cement through the same needle may
be attempted. If no additional leaks are visualized, continued injection may
continue. However, if there is evidence of persistent leakage, a second, contralateral needle should be used for further injection. The amount of cement
necessary for optimal results varies in each case. Generally, 50% to 70% of
the visualized volume of the compressed vertebra should be filled. A twist
of the cannula can help to break the cement at the tip and the cannula may
be removed.
To decrease the risk of hematoma formation, local pressure should be
applied for 3 to 5 minutes after withdrawing the cannula. The entry site
should then be dressed in sterile fashion. Once moved from the procedure
table, the patient should remain recumbent for 1 to 2 hours, while being
monitored for any neurological changes or other adverse events. If there
is no evidence of complication, the patient may be discharged home, but
should remain on bed rest, or at least with minimal activity, for 24 hours.
INJECTION MATERIALS
The ideal filler material for use in vertebroplasty and kyphoplasty must
demonstrate good biocompatibility, adequate biomechanical strength and
stiffness, and radiopacity for use in fluoroscopically guided procedures.
Additionally, the material must be amenable to easy preparation, and possess appropriate flow and polymerization or crystallization characteristics.
In the first vertebroplasty procedures, PMMA bone cement mixed with
a contrast agent, typically barium sulfate, was injected into vertebral bodies under image guidance.
PMMA bone cements have been used by orthopedic surgeons for the fixation of both plastic and metal components in joint replacement and, less
often, in the stabilization of pathological fracture. Early studies showed
maintenance of the bond between the prosthesis and the PMMA with no
evidence of harmful systemic effects. Thus, PMMA is now widely used
throughout orthopedics.
Advantages to PMMA include its familiarity for operating physicians,
its ease of handling, and its cost-effectiveness. Also, PMMA shows good
biomechanical strength and stiffness and evidence that it is relatively bioinert. For this reason, as of April 2004, the FDA has approved the labeling
of certain brands of PMMA for the treatment of pathological fractures of
the vertebral body resulting to osteoporosis and tumor. However, several
disadvantages to PMMA have become apparent. Perhaps most notable is
PMMA’s lack of osteoconductivity. As such, there is no potential for remodeling or integration into the surrounding bone. Histologic studies have
reported a thin fibrous membrane surrounding the PMMA injected into
vertebral bodies, providing further evidence of the lack of osseous integration. Therefore, PMMA relies solely on the bulk effect of injected cement
for strength and stability. Additionally, there have been theoretical concerns
regarding the high polymerization temperature of PMMA, though to date
there has been no clear evidence to support this. Finally, as is well documented in the arthroplasty literature, PMMA is associated with potential
5
Since Charnley first reported its use in 1960,
monomer toxicity. The molecule is known to be arrhythmogenic and cardiotoxic at the volumes used in knee and hip replacement. For this reason,
many authors recommend limiting vertebroplasty or kyphoplasty to two or
three levels at any surgical setting.
The limitations of PMMA cement have led researchers to seek alternative filler materials. The primary characteristic of these novel products is
their osteoconductivity. The best studied of these synthetic bone substitutes
is the class of calcium phosphate cements. As osteoconductive agents, these
possess the potential for resorption of cement and replacement with new
bone, effectively restoring vertebral body bone mass. Studies have shown
evidence of osteoclastic resorption of the cement and fragmentation with
vascular invasions and bony ingrowth.
6
Histologic results show direct bone
apposition suggestive of remodeling. Like PMMA, calcium phosphate fillers
initially function as bulk-filling agents. However, due to their osteoconductive capabilities, their strength is gradually reinforced by new bone formation. Biomechanical testing of calcium phosphate cements has verified their
ability to restore the mechanical integrity of the vertebral body.
Calcium sulfate, also known as plaster of Paris, has been investigated as a
potential filler material. Long used as a bone graft substitute, calcium sulfate
is injectable, osteoconductive, and cures with a limited exothermic reaction.
Histologic and radiographic analysis has shown progressive resorption of
the cement and osteoblastic rimming of the newly woven bone. However,
there is concern that the material is too rapidly resorbed, leading to lack of
stability during the remodeling process.
Calcium phosphate and calcium sulfate cements share several common
problems. Both materials have a low viscosity as well as handling characteristics that are different from PMMA and thus are unfamiliar to most
orthopedic surgeons. The cost of these products is also well above that of
PMMA. Finally, these products, as ion suspensions, have thixotropic properties. Thus, the material is susceptible to separation within the delivery
tube, making injection difficult.
Finally, novel composite materials, such as the cross-linked resin and
glass ceramic particles of Cortoss, by Orthovita, have been approved by the
FDA as potential alternative fillers. Proposed advantages of these materials
include constant flow characteristics, inherent radiopacity, lower polymerization temperature, and mechanical strength properties that exceed those
of PMMA. Animal studies have demonstrated its osteoconductive capacity.
The potential for these composite fillers is still being defined.
COMPLICATIONS
In a patient with an osteoporotic VCF treated by percutaneous vertebroplasty, the incidence of complication necessitating surgical intervention is
estimated to be less than 1%.
will require surgery to manage a complication of vertebroplasty. In this population, less significant complications are estimated to occur in up to 10%
of patients. This increased risk is likely due to an increased risk of cement
extravasation due to cortical breaks in the vertebral body.
The most common complication of vertebroplasty is approximately 72
hours of mild local tenderness. More severe pain localized to the needle site
may be due to hematoma or bruising. This can be minimized with 5 minutes of manual compression after removal of the cannula. More common in
patients with an underlying malignancy, is dermatomal or radicular pain.
Typically, no specific treatment is needed and NSAIDs are used to treat
pain. Occasionally, a brief course of either oral or local steroid injections
may be necessary to relieve the pain. Such complications may be monitored
and treated conservatively so long as there are no associated motor deficits
or bladder or bowel incontinence. The etiology of radicular pain may be
from spinal cord or nerve root compression due to retropulsion of tumor
fragments or extravasation of cement. At its worst, paraplegia may occur by
this mechanism.
Extravasation of cement into the epidural veins can cause a cement
embolism to the lung. As in hip and knee arthroplasty, the pressurized
injection of cement into the vertebral body can also cause a fat embolism.
While the majority of these emboli are asymptomatic, they can be particularly problematic in patients with pre existing pulmonary conditions, such
as COPD. Further respiratory complications can be induced by inaccurate
placement of the needle, which can cause a pneumothorax. As in all invasive procedures, there is a risk of bleeding, which is more common in the
7
In patients with neoplastic VCF, 2.7% to 5.4%
C H A P T E R 3 5 Vertebroplasty
217
parapedicular approach due to the large paraspinous vessels. Infection is
exceedingly rare. Finally, there have been reports of deaths attributed to vertebroplasty and kyphoplasty. These seem to be due to severe cement allergy
or pulmonary failure in patients with preoperative pulmonary compromise.
NEJM RANDOMIZED CONTROLLED TRIALS
The August 6, 2009 issue of the New England Journal of Medicine presented
two randomized studies seeking to assess the efficacy of vertebroplasty for
pain relief in osteoporotic vertebral fractures. In Buchbinder et al,
8
enrolled
patients with one or two painful osteoporotic VCFs less than 12 months
old and unhealed, as confirmed by MRI, were randomized to either vertbroplasty or a sham procedure. Outcomes were assessed up to 6 months.
They concluded that there was “no beneficial effect of vertebroplasty over
a sham procedure at 1 week or at 1, 3, or 6 months among patients with
painful osteoporotic vertebral fractures.” Kallmes et al
9
randomly assigned
131 patients with one, two, or three painful osteoporotic VCFs thought
to be less than 1 year old to either vertebroplasty or a similar sham procedure. Outcomes were assessed up to 3 months. Of note, MRI was only
employed if the age of the fracture was “unknown.” This study concludes
that “improvements in pain and pain-related disability associated with
osteoporotic compression fractures in patients treated with vertebroplasty
were similar to improvements in a control group.”
Upon further examination of these studies, several important criticisms
have been raised.
10
These are discussed below.
Fracture Acuity
The natural history of a VCF is approximately 6 to 8 weeks, at which point
most fractures will be healed. Buchbinder did use MRI assessment (edema
or presence of a fracture line) as part of her inclusion criteria. However,
Kallmes only employed MRI if the age of the fracture was unknown, leaving
the possibility of enrolled patients with healed or chronic fractures. Only
32% of Buchbinder’s cohort consisted of fractures less than 6 weeks old;
44% of Kallmes’ group was composed of fractures less than 6 weeks old.
Additionally, both groups included fractures up to 12 months old. Again,
this extends well beyond the typical natural history of the fracture and
therefore may include back pain due to other causes and the most refractory VCFs.
Enrollment
As in any study, there is an inherent selection bias. Patients with the most
severe pain due to VCF are those patients most likely to benefit from vertebroplasty. However, these patients are less likely to enroll in a study where
they may receive a sham treatment. Kallmes enrolled only 131 of 1812
patients; the most common reason for not entering was patient refusal.
In Buchbinder’s group, 141 patients who met all inclusion criteria did not
enroll. This has led to an unquantifiable selection bias that limits the applicability of the results.
a plausible mechanism for relief of back pain, albeit not fracture pain, from
such common etiologies as facet arthropathy.
Crossover
Kallmes reported a 12% versus 43% crossover between his treatment and
control groups. This difference suggests a patient dissatisfaction with the
control procedure that was not fully captured by the reported pain scales.
Additionally, the intention-to-treat analysis probably underestimated the
true treatment effect.
CONCLUSION
The introduction of vertebroplasty, and now kyphoplasty, has provided
physicians with additional options for the treatment of VCFs. Specifically,
vertebroplasty has been shown to be indicated for the acute and subacute
treatment of VCFs due to osteoporosis and malignancy. Contraindications to the procedure include asymptomatic VCFs; painful VCFs that
are improving with conservative medical treatment; traumatic VCFs in the
young, nonosteoporotic patient; and patients with osteomyelitis, an uncorrectable coaguloapthy, or an allergy to any component of the procedure.
While the technique and its indications are continuing to evolve, numerous studies, including Alvarez et al, have suggested that vertebroplasty is a
successful and safe procedure to alleviate the pain associated with acute and
subacute osteoporotic or neoplastic VCFs. The recent Kallmes and Buchbinder articles do not support the previous robust benefits demonstrated
in other studies; however, their efficacy must be questioned in light of the
numerous criticisms stated above, most notably the use of a local anesthetic
injection as an unproven sham procedure.
References
1. O. Johnell, J.A. Kanis, An estimate of the worldwide prevalence and disability associated with
osteoporotic fractures, Osteoporos. Int. 17 (2006) 1726–1733.
2. P. Galibert, H. Deramond, et al., Preliminary note on the treatment of vertebral hemangioma
by percutaneous acrylic vertebroplasty, Neurochirurgie 33 (2) (1987) 166–168.
3. L. Alvarez, M. Alcaraz, et al., Percutaneous vertebroplasty: functional improvement in
patients with osteoporotic compression fractures, Spine 31 (10) (2006) 1113–1118.
4. D. Wardlaw, S.R. Cummings, et al., Efficacy and safety of balloon kyphoplasty compared
with non-surgical care for vertebral compression fracture: a randomized controlled trial,
Lancet 373 (9668) (2009) 1016–1024.
5. I.H. Lieberman, D. Togawa, M.M. Kayanja, Vertebroplasty and kyphoplasty: filler materials,
Spine J. 5 (6 Suppl) (2005) 305S–316S.
6. T.M. Turner, et al., Vertebroplasty comparing injectable calcium phosphate cement compared
with polymethylmethacrylate in a unique canine vertebral body large defect model, Spine J. 8
(3) (2008) 482–487.
7. J.M. Mathis, H. Deramond, S.M. Belkoff, Percutaneous vertebroplasty and kyphoplasty,
ed 2, Springer, New York, 2006.
8. R. Buchbinder, R.H. Osborne, et al., A randomized trial of vertebroplasty for painful osteo-
porotic vertebral fractures, N. Engl. J. Med. 361 (6) (2009) 557–568.
9. D.F. Kallmes, B.A. Comstock, et al., A randomized trial of vertebroplasty for osteoporotic
spinal fractures, N. Engl. J. Med. 361 (6) (2009) 569–579.
10. North American Spine Society: Newly released vertebroplasty RCTs: a tale of two trials:
www.spine.org/Documents/NASSComment_on_Vertebroplasty.pdf. Accessed May 5,
2010.
Control Group as an “Alternative Intervention”
Both Buchbinder and Kallmes utilized a sham surgery consisting of the
injection of an anesthetic into the skin, subcutaneous tissues, and facet capsule/periosteum. In reality, it may not be a placebo at all. This may constitute
Vertebral Body Stenting
Survival probability
Paul F. Heini
36
INTRODUCTION
Vertebral body compression fractures (VBCFs) are the hallmark of osteo-
porosis, 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).
ment 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 longterm results.
ticenter 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.
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.
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.
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.
reported in several epidemiological studies: impaired quality of life and even
an increased mortality are documented (see Figure 36-1).
tively to an increased load on the anterior column. Consequently, there is an
218
k e y p o i n t s
Vertebral body compression fractures are the hallmark of osteoporosis and
often represent the starting point for the vicious circle of progressive collapse
and further fractures.
Cement reinforcement for painful osteoporotic compression fractures
provides substantial pain relief and can prevent further collapse. However, it
does not allow active height restoration and correction of the spinal alignment.
Vertebral body stenting provides effective and improved height restoration
potential in comparison to a kyphoplasty procedure.
e first clinical application of vertebral body stenting shows its feasibility
and safety. Height restoration and maintenance is possible in mobile fractures.
e impact of height restoration is not clear yet and needs to be assessed further.
1,2
The treatment of painful VBCFs with percutaneous cement reinforce-
3-5
Furthermore, there is class A evidence based on a large mul-
9,10
Although cement reinforcement can stabilize a fracture and therefore
11
The consequences of vertebral height loss and increased kyphosis are
2,12,13
The kyphotic deformity leads to a shift of center of gravity and consecu-
increased risk for new fractures.
14,15
Furthermore the increased kyphosis
raises the load of the back muscles enormously (Figure 36-2).
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
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.
6
7,8
1.0
0.8
0.6
0.4
0.2
0
0 5 10 15
Women
General population
Hip fracture
Vertebral fracture
Major fracture
Minor fracture
Log-rank P < .001
Years
F IG UR E 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.
16,17
C H A P T E R 3 6 Vertebral Body Stenting
5
Consequences of vertebral height loss
219
F IG UR E 3 6- 2 Vicious circle of verte-
bral 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.
Shift of center of gravity (G)
Increased bending moment
Increased loading on muscles
and ligaments
Increased compression stress
anterior column
110 N
G
CG
110 N
Kyphoplasty
A
VBS
4
3
2
1
0
–1
Height gain/loss (mm)
–2
–3
–4
B
Height gain
reposition
N = 24 (12 each)
Height loss
deflation
Final height
gain
110 N
BKP
VBS
F IG UR E 3 6 - 3 A, Comparison of a kyphoplasty procedure and a ver-
tebral body stenting system as assessed in a cadaver model with a preload of
21,22
110 N.
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.)
Initial reduction can be achieved equally well with both systems.
110 N
220
P A R T V Osteoporotic Surgical Treatment Modalities: Thoracic Spine
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).
22.0 mm
21.2 mm
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
A
B
F IG UR E 3 6 -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.
C H A P T E R 3 6 Vertebral Body Stenting
221
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.
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 (Fig-
ure 36-6, C). The average kyphosis angle preoperatively was 23 degrees
A
B
FIGURE 36-5 A, A 56-year-old woman after a minor car accident. The patient shows an atypical compression frac-
ture 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.
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P A R T V Osteoporotic Surgical Treatment Modalities: Thoracic Spine
C
F IG UR E 36 -5 , c o nt ’ d 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.
(13 to 32degrees) 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);
15cases with grade 2, which is 75% of height gain (Figure 36-7); and 7 cases
with complete height restoration (Figure 36-8).
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
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C H A P T E R 3 6 Vertebral Body Stenting
223
D
E
F IG UR E 3 6- 5 , c o nt ’d 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.
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P A R T V Osteoporotic Surgical Treatment Modalities: Thoracic Spine
F
G
F IG UR E 3 6- 5, c on t’d 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).