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C H A P T E R 3 9 Directed Cement Flow Kyphoplasty for Treatment of Osteoporotic Vertebral Compression Fractures
3500
Vertebroplasty
3000
Shield
21,000
29,275
32,063
245
2500
2000
1500
Load (N)
42,000
315
3
25
1635
335
835
855
6
29,000
600
8,635
1000
500
0
Vertebroplasty specimen not tested
Pair 1 Pair 2 Pair 3 Pair 4 Pair 5 Pair 6 Pair 7 Pair 8
F IG UR E 3 9- 4 Summary of cyclic testing results for treated vertebral body specimens. Testing was performed on specimen pairs, obtained from adjacent
levels from the same donor spine. For 6 of 8 pairs, vertebral bodies treated with the Shield Kyphoplasty System withstood a greater number of loading cycles and
failed at higher load levels as compared to specimens treated with vertebroplasty.
A
F IG UR E 3 9 - 5 Blunt tip wire verifies medial needle placement in A/P (A) and lateral (B) fluoroscopic images. (Images provided by Dr. G. C. Anselmetti, Insti-
tute for Cancer Research and Treatment, Torino, Italy.)
B
F IG UR E 3 9- 6 The working channel cannula is placed over the wire and
advanced into the vertebral body 3 to 5 mm beyond the posterior cortical wall.
Medial marking is oriented toward the patient’s spine.
246
P A R T V Osteoporotic Surgical Treatment Modalities: Thoracic Spine
A
F IG UR E 3 9- 7 Fluoroscopic images of the drill advancing along a curved path (A, AP view). Drilling is complete when the contralateral pedicle is reached.
The blade is deflected and a 10-mm diameter cavity is created as the instrument is counterrotated (B, lateral view). (Images provided by Dr. G. C. Anselmetti, Institute
for Cancer Research and Treatment, Torino, Italy.)
A
F IG UR E 3 9- 8 Axial (A), lateral (B), and AP (C) CT images of the cement mantle created by the Shield implant. Cement fills the implant, flows through the
holes and is directed to the anterior, superior and inferior regions of the vertebral body. Flow in the posterior direction is limited, reducing the risk of posterior leakage. (Images provided by Dr. G. Stender, Groenemeyer-Institute, Bochum, Germany)
B C
THE SHIELD KYPHOPLASTY SYSTEM SURGICAL TECHNIQUE
The percutaneous needle approach used for the Shield Kyphoplasty Sys-
tem is similar to the original kyphoplasty procedure widely used to treat
vertebral compression fractures. However, only a single needle placement
targeting the anterior sagittal midline is required for the Shield system for all
levels of the spine. The approach angle and needle position is verified with
anteroposterior (AP) and lateral fluoroscopy, as shown in Figure 39-5. Once
angular orientation has been established, the needle is advanced into the
vertebral body beyond the posterior cortical wall. The stylet of the needle is
removed and replaced with a blunt tipped wire. The needle is then retracted
leaving the wire in place. A 4-mm outer diameter working channel cannula
B
cement fill portal. The Shield Kyphoplasty System includes a bone cement
mixing and injection device that mates with the delivery system. The injection system is capable of injecting high viscosity cement. Cement injection
should be performed under biplanar fluoroscopic imaging. The materials
used in the construction of the Shield cement director allow visualization of
the cement while it fills the implant and flows into the anterior, superior, and
inferior regions of the cancellous bone, as shown in Figure 39-8.
Postoperatively, patients treated with the Shield Kyphoplasty System
require the same care as given following standard vertebroplasty and kyphoplasty procedures. Potential complications are also similar to these procedures and include possible cement leakage, pulmonary embolus, neuropathy.
and endplate fracture.
is then placed over the wire to a depth of 5 mm anterior to the posterior
cortical wall, as depicted in Figure 39-6. Proper placement of the working
channel cannula includes orienting the key slot in the medial direction. This
ensures that all subsequent invasive steps in the procedure involving bone
cutting will have the proper medial orientation.
The Shield Kyphoplasty System cavity cutter is inserted within and
locked to the working channel. The cutting device is designed to drill along a
curved path projecting anteriorly and medially from the end of the working
channel. The surgeon advances the drill by manually rotating in the clockwise direction while stabilizing the working channel with the other hand. It
is recommended that drilling be ceased once the blade tip has reached the
medial border of the contralateral pedicle, as shown in Figure 39-7. Once
the path is complete, the blade is deflected to 10 mm. A cylindrical cavity
is created as the blade rotates and translates along the original path in the
proximal direction. After several turns, the blade is retracted at a predetermined point on the proximal end of the path to create a cavity that is the
same length as the selected implant: 15 mm, 20 mm, or 25 mm.
The appropriate size delivery system with a preloaded Shield implant
is then inserted into the working channel. The delivery system is curved,
allowing the Shield implant to be deployed precisely within the central
cavity. Removal of an internal wire exposes a luer connector, which is the
CLINICAL OUTCOMES
The clinical performance of the Shield Kyphoplasty System has been evalu-
ated in a 1-year, multicenter, prospective, 2:1 randomized controlled study
comparing pain relief, cement leakage rates, and leak locations for the Shield
and conventional percutaneous vertebroplasty.
this study consisted of adults at least 50 years old with osteoporosis and
painful benign vertebral compression fractures at one to three levels between
T4 and L5. A total of 77 patients and 104 levels were treated, 49 patients (65
levels) with the Shield Kyphoplasty System and 28 patients (39 levels) with
conventional vertebroplasty. The Shield procedure was performed using a
unilateral transpedicular or extrapedicular approach, whereas the vertebroplasty procedure was performed using a standard bipedicular approach.
Pain was assessed using a 10-point visual analog scale (VAS) at 24 hours
postoperatively, 3 months, and again at 1 year. To evaluate and compare
cement leakage rates, plain radiographs (AP and lateral) and CT scans were
obtained within 24 hours of the procedure. Cement leakage was assessed
by the operating surgeon (radiographs) and an independent reviewer (CT
images). The increased resolution of the CT images allowed small leaks
to be identified that would have been overlooked on radiographic images.
4
The patient population for
C H A P T E R 3 9 Directed Cement Flow Kyphoplasty for Treatment of Osteoporotic Vertebral Compression Fractures
Mean pain score (VAS)
247
F IG UR E 39 -9 Pain scores for multicenter randomized 1-year clinical
study comparing treatment of painful osteoporotic compression fractures with
the Shield Kyphoplasty System and conventional vertebroplasty. Pain scores
dropped substantially 24 hours postoperatively, and pain relief was sustained
through the 12-month follow-up period.
10.0
9.0
8.0
7.0
6.0
5.0
4.0
3.0
2.0
1.0
0
F IG UR E 3 9- 10 Pain scores for pilot study of the Shield Kyphoplasty
System. Pain relief was maintained throughout the 2-year follow-up period.
Cement leaks were classified as follows: Type B—through the basivertebral
vein, Type C—through a cortical bone defect (including endplates), and
Type S—through a segmental vein.
Significant pain relief was achieved immediately following treatment
with both the Shield Kyphoplasty System and conventional vertebroplasty,
as shown in Figure 39-9. Mean preoperative pain scores were 8.31 ± 1.12
and 8.49 ± 1.18 for the Shield and vertebroplasty groups, respectively. The
mean pain scores decreased by more than 6 points for both groups at 24
hours post-op, and pain relief was sustained during the 12 month follow-up
period. The results of a single arm, two-year pilot study (20 patients) further demonstrate that long-term pain relief is achieved in patients treated
with the Shield Kyphoplasty System, as shown in Figure 39-10.
In the randomized clinical study, cement leaks were identified and classified from both plain radiographic images and CT reconstructions. Leakage
rates reported in the literature are highly variable, ranging from 7% to 90% for
vertebroplasty and 0% to 33% for kyphoplasty.
to interpret because different methods are used to assess leak rates, and the
resolution can vary among the methods and among institutions. In general,
studies that use CT imaging to quantify cement leaks report much greater
leakage rates than studies that rely on routine radiographic interpretation.
The overall leakage rate for patients treated with the Shield Kyphoplasty
System was substantially lower than the leakage rate for patients treated
n = 20
n = 20
Pre-op Post-op 3 mos. 12 mos.6 mos.6 wks. 24 mos.
n = 20
n = 19
5
n = 18
6
This data is often difficult
n = 17
n = 17
TA BL E 39 -1 Cement L eakage Rates (L eaks/ Trea ted
Shield Kyphoplasty
System
Vertebroplasty 10/39 (25.6%) 54/39 (138.5%)
*
Some levels exhibited multiple leaks.
TA BL E 39 -2 Lea k C lassifi cati on (Leak s/Trea ted Levels)
Shield Kyphoplasty
System
Vertebroplasty 12/39 (30.8%) 22/39 (56.4%) 20/39 (51.3%)
*
Some levels exhibited multiple leaks.
*
Levels)
Radiographs CT Images
8/65 (12.3%) 42/65 (64.6%)
Type B Type C Type S
8/65 (12.3%) 15/65 (23.1%) 19/65 (29.2%)
*
with conventional vertebroplasty, as shown in Table 39-1. Eight levels in the
Shield group and 14 levels in the control group exhibited multiple leaks and
in these instances, each leak was counted and classified separately. The leakage rate for all types of leaks was decreased for the Shield treatment group,
as compared to the vertebroplasty treatment group shown in Table 39-2.
The Type B leakage rate, involving cement leakage into the basivertebral vein,
was markedly decreased for patients treated with the Shield system and was
the lowest leakage rate observed overall. This result confirms that anteriorly
directed cement flow is effectively achieved by using the Shield implant.
CONCLUSIONS
The Shield Kyphoplasty System provides new direction and control capabilities for treatment of osteoporotic vertebral compression fractures. This system
can be used to effectively treat painful fractures of the thoracic and lumbar
spine from a unilateral approach. The unique curved cavity creation instrument provides minimally invasive access to the center of the vertebral body,
allowing the Shield cement-directing implant to be reproducibly positioned
and oriented. Bone cement is injected into the implant, which guides cement
flow in the anterior, superior and inferior directions. Mechanical testing demonstrates that the cement mantle formed by the Shield implant interdigitates
with the intact bone structure, stabilizes the fracture, and provides enduring
biomechanical reinforcement. Good long-term clinical outcomes have been
obtained for the Shield system, as compared to bipedicular vertebroplasty. Pain
relief is immediate and sustained for at least 2 years postoperatively. Directed
cement flow additionally reduces leakage rates and the risk of leakage-related
complications, potentially improving the safety of the procedure.
References
1. D. Wardlaw, S.R. Cummings, J. Van Meirhaeghe, L. Bastian, J.B. Tillman, J. Ranstam, R.
Eastell, P. Shabe, K. Talmadge, S. Boonen, Efficacy and safety of balloon kyphoplasty compared with non-surgical care for vertebral compression fracture (FREE): a randomised controlled trial, Lancet 373 (9668) (2009 Mar 21) 1016–1024.
2. A. Hiwatashi, R. Sidhu, R.K. Lee, R.R. deGuzman, D.T. Piekut, P.L. Westesson, Kyphoplasty
versus vertebroplasty to increase vertebral body height: a cadaveric study, Radiology 237 (3)
(2005) 1115–1119.
3. B.B. Pradhan, H.W. Bae, M.A. Kropf, V.V. Patel, R.B. Delamarter, Kyphoplasty reduction of
osteoporotic vertebral compression fractures: correction of local kyphosis versus overall sagittal
alignment, Spine 31 (4) (2006 Feb 15) 435–441.
4. R . Pflugmacher, J. Hierholzer, G. Stender, R. Hammerstingl, E. Truumees, A.K. Wakhloo,
M.J. Gounis, T.J. Vogl, Evaluation of leakage rates for a cement directing kyphoplasty system,
Presented at the 25th Annual Meeting of the North American Spine Society, San Francisco
CA, Nov. 10-14, 2009.
5. J.S. Yeom, W.J. Kim, W.S. Choy, C.K. Lee, B.S. Chang, J.W. Kang, Leakage of cement in percutaneous transpedicular vertebroplasty for painful osteoporotic compression fractures, J. Bone
Joint. Surg. Br. 85 (1) (2003 Jan) 83–89.
6. P.A. Hulme, J. Krebs, S.J. Ferguson, U. Berlemann, Vertebroplasty and kyphoplasty: a systematic review of 69 clinical studies, Spine 31 (17) (2006 Aug 1) 1983–2001.
Radiofrequency Kyphoplasty:
A Novel Approach to Minimally
Invasive Treatment of Vertebral
Compression Fractures
Kieran Murphy
40
k e y p o i n t s
In-line use of radiofrequency (RF) energy to warm cement immediately
before being delivered permits extended working time for consistent delivery
of an ultra-high viscosity cement.
A navigational osteotome device permits site- and size-specific cavity creation
before cement augmentation, increasing the potential for uniportal treatment
of vertebral compression fractures.
Remote-controlled cement delivery system provides potential for reduced
radiation exposure.
RF kyphoplasty provides pain relief and reduction in vertebral compression
fracture–related disability similar to that reported for conventional balloon
kyphoplasty and vertebroplasty.
INTRODUCTION
Percutaneous treatment of vertebral compression fractures (VCFs) was first
performed in France in 1984 by Galibert and Deramond.
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.
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.
porosis, 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.
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.
at nearly $2.7 billion in 1995 for men alone,
care problem from the standpoint of both cost and morbidity.
*AMA Current Procedural Terminology (CPT) 2009 for Vertebral Augmentation Procedures
reads: “Percutaneous vertebral augmentation, including cavity creation (fracture reduction and
bone biopsy included when performed) using mechanical device, one vertebral body, unilateral
or bilateral cannulation (e.g., kyphoplasty)”. ICD-9-CM procedure code addendum (ICD-9 CM
2009 Volumes 1 & 2) for Percutaneous Vertebral Augmentation reads: Insertion of inflatable
balloon, bone tamp, or other device displacing (removing) (compacting) bone to create a space
(cavity) (void) prior to the injection of bone void filler (cement) (polymethylmethacrylate)
(PMMA) or other substance.
8
The economic impact of osteoporotic fractures was estimated
1-7,10-14
Because they have a higher incidence of osteo-
4,7
9
making this a substantial health
1
The two most
*
Both procedures
Vertebral body fractures
248
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.
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
3,14
C H A P T E R 4 0 R adiofrequency Kyphoplasty
249
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 Mid-
Line 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).
In Vitro Evaluation of Height Restoration and Intravertebral Pressure in Three Minimally Invasive Procedures Using an Osteoporotic Cadaver Bone Model
The potential to restore height in mobile vertebral compression fractures
and the possible impact on intravertebral pressure have been reported in
various studies.
87 years of age were used. The specimens in each study had bone mineral
densities (BMDs) of 0.687 ± 0.136 g/cm
tively. Individual vertebral bodies (VBs) were prepared by transecting the
pedicles and removing all disc material from the endplates. Cephalac and
caudal surfaces of each vertebral body were rigidly embedded in a urethane
potting compound (Smooth ON, Easton, Penn.).
Each vertebral body was mounted in a custom semiconstrained fixture and
rigidly attached to a servohydraulic load frame (8521S, Instron Corp, Canton,
Mass.). A 500-N offset load was applied to the specimen and a radiograph
taken to determine prefracture anterior vertebral body height (GE OEC Diasonics Model 9000, Fairfield, Conn.). Offset loads were applied at a displacement rate of 5 mm/min with a data acquisition rate of 20 Hz. Monotonic
testing was performed until the height of the vertebral body had been
17,18
Cadaver spines obtained from women between 66 and
3
and 0.707 ± 0.136 g/cm3 respec-
F IG UR E 4 0 -1 A, StabiliT Ver-
tebral Augmentation System for radiofrequency kyphoplasty. B, Cement in
the reservoir before passing through the
Activation Element and delivery cannula
has extended working time.
A
F IG UR E 4 0- 2 Navigational Osteotome permits site-specific cavity creation and interdigitation of ultra-high viscosity cement.
B
250
P A R T V Ostteoporotic Surgical Treatment Modalities: Thoracic Spine
reduced by 30%. Postfracture height was determined using radiographic
images under a 500-N compressive offset loads. Each treatment, conventional
balloon kyphoplasty (BKP) (KyphX, Medtronic Inc., Memphis, Tenn.) , RF
kyphoplasty (RFK) (StabiliT Vertebral Augmentation System) and vertebroplasty (Vertebroplastic, DePuy Spine Inc., Raynham, Mass.), was performed
on randomly assigned vertebral bodies.
All three procedures (BKP, RFK, and vertebroplasty) were utilized by
physicians skilled in these minimally invasive techniques. Standard bipedicular technique was used in the BKP specimen. RFK was performed using
a unipedicular technique and the MidLine Osteotome. A total of 6 ml bone
cement was used in all specimens. After each treatment, vertebral bodies
were incubated in a 37° C water bath for a minimum of 2 hours before posttreatment radiographic evaluation. Posttreatment radiographs were taken
while a 500-N offset load was applied to the specimen. Anterior height was
measured from the prefracture, postfracture, and posttreatment radiographs
using Photoshop (Adobe Systems, Inc., San Jose, Calif.). Each measurement
was done by five different individuals blinded to the treatment performed on
the specimens (Figure 40-3). Statistical comparisons between the treatment
groups were performed, and statistical significance was defined as p < .05. In
one of the studies, a pressure transducer was placed into the venous plexus
through the posterior cortex to measure the intravertebral pressure during
cement delivery.
RESULTS
A significant difference in height was found between the prefracture and
postfracture specimens for all three groups. Mechanical VCF height elevation equivalent to that observed in BKP was achieved using RFK. In contrast, conventional vertebroplasty procedure, in which cement simply fills
existing VCF voids before extravasation via the path of least resistance,
was unable to restore comparable height. The mean anterior height restorations for the conventional BKP, RFK, and vertebroplasty systems were
74.8 ± 9.4%, 83.7 ± 17.5%, and 32.8 ± 8.1%, respectively.
significant difference between the BKP and RFK groups (p = .40). The
BKP and RFK procedures both restored significantly more height than that
achieved with the vertebroplasty procedure (p ≤ .001 and p ≤ .002 respectively). The mean maximum intravertebral pressures recorded during RFK,
BKP, and vertebroplasty were 9.8 ± 0.1 kPa, 9.8 ± 0.0 kPa, and 14.7 ± 9.7
kPa, respectively. Wilcoxon signed rank tests did not yield any significant
differences between the RF kyphoplasty and vertebroplasty (p = .5), balloon
kyphoplasty, and vertebroplasty (p = 1.0) or RF kyphoplasty and balloon
kyphoplasty (p = 1.0) treatment groups.
16
These data demonstrate that the
use of an ultra-high viscosity cement and an appropriate delivery system can
provide an alternative to currently available methods to restore height in a
VCF without adverse increases in intravertebral pressure.
17
There was no
A
C
E
B
D
F
F IG UR E 4 0 -3 Images of postfracture (on left) and posttreatment (on right) vertebral bodies vertebroplasty (A, B), conventional balloon kyphoplasty (C, D),
and radiofrequency kyphoplasty (E, F).
C H A P T E R 4 0 R adiofrequency Kyphoplasty
251
A
C
F IG UR E 4 0- 4 Intraoperative images demonstrating site-specific cavity creation and ultra-high viscosity cement augmentation. Pre injection xrays: with single
cannula (A and B) and double cannulas (C and D); Post injection xrays (E, F, G and H). (Courtesy of Dr. Florian Elgeti, Charité-Universitätsmedizin Berlin.)
B
D
RF KYPHOPLASTY CLINICAL EXPERIENCE WITH THE StabiliT VERTEBRAL AUGMENTATION SYSTEM
To date, over 2000 vertebral levels and 1200 RF kyphoplasty cases have been
performed using the StabiliT Vertebral Augmentation System. No cementrelated symptomatic adverse events have been reported to date. The proce-
E
G
TA BL E 40 -1 Cl inic al Resu lts f rom the Europe an
Pro spec tive Clin ical Trial w ith t he St abiliT Ve rteb ral
Aug ment atio n Syst em Comp are Favorab ly with Previ ously
Documente d Pain Relief an d Fu nctional Scores for
Convent ional Balloon Kyphoplasty and Vert ebroplasty
dure involves a site-specific cavity creation using the MidLine Osteotome
under fluoroscopic guidance, followed by controlled delivery of an ultra high
viscosity cement (Figure 40-4). The ultra-high viscosity cement preferen-
Procedure
F
H
VAS score (n) ODI Score (n)
Pre 3 mo Pre 1 mo 3 mo
tially fills the site-specific cavity before driving into the fracture planes and
interdigitating into the adjacent trabeculae. Because only the cement that is
delivered into the patient is exposed to RF energy, cement delivery can be
delayed for extended periods of time if need be to minimize extravasation in
cases of large fractures planes or lytic lesions. The initial clinical experience
Balloon kyphoplasty*
Vertebroplasty
RF kyphoplasty 7.2 2.4 55 33 26
,†
6.2 2.8 46 30 ND
‡,§
7.5 3.5 75 ND 38.7
included a prospective controlled clinical trial performed under an Ethics
Committee–approved protocol at three sites in two countries (Hungary
and Austria) and performed by physicians of three disciplines: neurosurgery, interventional radiology, and orthopedic surgery. Patients in this study
(SPACE—Spinal Augmentation with Cement and Energy) were eligible
ND, Not done.
*
I. Lieberman and M.K. Reinhardt. CORR 415S (2003) s176–s186.
†
From S. Garfin et al. SPINE vol. 31 19(2006) 2213–2220.
‡F. McKiernan, T. Faciszewski, R. Jensen. JBJS vol. 86A 12 (2004) 2600–2606.
§
K.-Y. Ha et al. JBJS (Br), 88 (B) (2006) 629–633
for enrollment if they had one to three vertebral fractures from T7 through
L5. Clinical results of the first 104 fractures in 73 patients treated to date
with the StabiliT system were reported in the 2009 Scientific Meeting of
the Society for Interventional Radiology.
relief (measured by visual analogue scale [VAS]) and improved function
(measured by Oswestry Disability Index [ODI]) consistent with published
data for conventional balloon kyphoplasty and vertebroplasty (Table 40-1).
As has been reported for conventional balloon kyphoplasty and vertebroplasty, RF kyphoplasty reduced pain scores greater than 50% when measured by the VAS, a validated instrument.
Additionally, in a series of 20 VCFs in 14 patients, Elgeti reported
height restoration and kyphosis correction in 50% of the fractures, with an
averageheight restoration of 4 mm and kyphosis correction of 5.6 degrees
(Figure 40-5).
18
17
The study demonstrated pain
Site-specific cavity creation and ultra-high viscosity cement delivery
with a unique hydraulic delivery system has been shown to enable mechanical VCF height elevation equivalent to that observed in balloon-assisted
kyphoplasty without committing the physician to filling large cavities created by balloon inflation. Control in where and how much cement is used to
augment VCFs may prove invaluable in providing the physician with a new
means of stabilizing fractures and, in mobile fractures, reducing the height
without long-term fear of stress shielding.
Since 1984, technology has converged in a way that impacts the traditional use of the term kyphoplasty. Initially kyphoplasty was defined
as the “balloon procedure.” Today, there are additional technologies
designed for minimally invasive, cavity creating VCF treatment. Con-
DISCUSSION
The StabiliT Vertebral Augmentation System has been cleared for use in
the United States for percutaneous delivery of StabiliT ER Bone Cement
in kyphoplasty procedures in the treatment of pathological fractures of the
vertebrae. Painful vertebral compression fractures may result from osteoporosis, benign lesions (hemangioma), and malignant lesions (metastatic
cancers, myeloma).
sequently, procedure terminology has evolved, as evidenced by CMS
recently replacing the ICD-9 code title of “Kyphoplasty” with “Percutaneous Vertebral Augmentation,” with examples of this procedure
category including conventional kyphoplasty and other various technologies commercially available at the time of publishing, included in
the description. High viscosity cement has the ability to combine the
minimalism of vertebroplasty with the mechanical potential benefits
of a vertebral implant or balloon. Our data show an ability to deliver
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P A R T V Ostteoporotic Surgical Treatment Modalities: Thoracic Spine
A
B
F IG UR E 40 -5 Preoperative (A and B) and postoperative (C and D) radiographs of a 3-week-old T9 osteoporotic vertebral compression fracture demon-
strating 4-mm height restoration (19% reduction in compression) and 8-degree correction of kyphotic angle (12 degrees preoperative vs 4 degrees postoperative)
following radiofrequency kyphoplasty. (Courtesy of Dr. Florian Elgeti, Charité-Universitätsmedizin, Berlin).
cement in a more controlled manner and to create height-restorative
forces based on location and the cohesive properties of the cement. Ultimately this new method will find its place in a modern buffet of options
for repair of these VCFs with benefits for the patient and simplicity for
the physician.
References
1. P. Galibert, H. Deramond, P. Rosat, et al., Preliminary note on the treatment of vertebral angioma by percutaneous acrylic vertebroplasty, Neurochirurgie 33 (2) (1987) 166–168. French.
2. G.H. Zoarski, P. Snow, W.J. Olan, et al., Percutaneous vertebroplasty for osteoporotic compression fractures: quantitative prospective evaluation of long-term outcomes, J. Vasc. Interv.
Radiol. 13 (2002) 139–148.
3. A. Weill, J. Chiras, J.M. Simon, et al., Spinal metastases: indications for and results of percutaneous injection of acrylic surgical cement, Radiology 199 (1996) 241–247.
4. A. Cotton, F. Dewatre, B. Cortet, et al., Percutaneous vertebroplasty for osteolytic metastases
and myeloma: effects of the percentage of lesion filling and the leakage of methyl methacrylate at clinical follow-up, Radiology 200 (1996) 525–530.
5. J.K. McGraw, J.A. Lippert, K.D. Minkus, et al., Prospective evaluation of pain relief in 100
patients undergoing percutaneous vertebroplasty: results and follow-up, J. Vasc. Interv.
Radiol. 13 (2002) 883–886.
6. A.J. Evans, M.E. Jensen, K.E. Kip, et al., Vertebral compression fractures: pain reduction
and improvement in functional mobility after percutaneous polymethylmethacrylate vertebroplasty retrospective report of 245 cases, Radiology 226 (2) (2003) 366–372.
7. C. Vasconcelos, P. Gailloud, N.J. Beauchamp, et al., Is percutaneous vertebroplasty without
pretreatment venography safe? Evaluation of 205 consecutive procedures, AJNR Am. J. Neuroradiol. 23 (6) (2002) 913–917.
C
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8. T.W. O’Neill, D. Felsenberg, J. Varlow, et al., The prevalence of vertebral deformity in European men and women: the European vertebral osteoporosis study, J. Bone Miner. Res. 11
(1996) 1010–1018.
9. N.F. Ray, J.K. Chan, M. Thamer, et al., Medical expenditures for the treatment of osteoporotic fractures in the United States in 1995: report from the National Osteoporosis Foundation, J. Bone Miner. Res. 12 (1997) 24–35.
10. M.J. McGirt, S.L. Parker, et al., Vertebroplasty and kyphoplasty for the treatment of vertebral compression fractures: an evidenced-based review of the literature. Spine J. 9 (2009)
501–508.
11. I.H. Lieberman, S. Dudeney, M.K. Reinhardt, et al., Initial outcome and efficacy of “kyphoplasty” in the treatment of painful osteoporotic vertebral compression fractures, Spine 26
(14) (2001) 1631–1638.
12. S.R. Garfin, H.A. Yuan, M.A. Reiley, Kyphoplasty and vertebroplasty for the treatment of
painful osteoporotic compression fractures, Spine 26 (2001) 1511–1515.
13. E. Truumees, A. Hilibrand, A.R. Vaccaro, Percutaneous vertebral augmentation, Spine J. 4
(2004) 218–229.
14. D.K. Resnick, S.R. Garfin, Vertebroplasty and kyphoplasty, Thieme, New York, 2005.
15. K. Murphy, E.Wong, R. Poser, et al., Comparison of intravertebral pressure and height restoration in three minimally invasive treatments of vertebral compression fractures. 2009 SIR
Annual Scientific Meeting, Abstract #34.
16. T. Raley, R . Poser, A. Kohm. Comparative Height restoration of three vertebral augmentation systems for treatment of vertebral compression fractures. 55th Annual Meeting of the
Orthopedic Research Society (2009), 0639.
17. L. Miko, I. Szikora, J. Grohs, et al., Initial clinical experience with radio-frequency based
vertebral augmentation in treatment of vertebral compression fractures. 2009 SIR Annual
Scientific Meeting, Abstract #35.
18. Fourth Symposium Vertebroplastie/Kyphoplastie. 26 September 2009. Potsdam, Germany.
Structural Kyphoplasty:
The StaXx FX System
Harvinder S. Sandhu and Wayne J. Olan
41
k e y p o i n t s
e StaXx FX system is an alternative to balloon kyphoplasty or
vertebroplasty for the treatment of vertebral compression fractures.
e StaXx FX system involves the progressive application of permanent
individual Polyetheretherketone (PEEK) wafers to reduce the fracture
and provide sustained support to the endplate. After implantation into the
vertebral body, the wafers are embedded in bone cement.
e amount of cement used with the StaXx system is less than with either
kyphoplasty or vertebroplasty, thereby reducing the risk of cement-related
complications.
Preliminary biomechanical data collected on the StaXx FX device suggest
a substantial restoration of normal disc pressure and lower stresses on the
anterior cortical shell of the treated vertebral body.
Although clinical data are required to confirm this, the restoration of normal
disc pressure may reduce the rate of adjacent level fractures after treatment
with the StaXx FX device.
INTRODUCTION
The goal of percutaneous vertebroplasty and kyphoplasty is to provide relief
to patients presenting with painful osteoporotic vertebral compression fractures. Vertebroplasty was introduced as a means of stabilizing these insufficiency fractures by injecting high-pressure, low-viscosity cement directly
into the fractured vertebra. The short-term effect of the intervention is to
also alleviate the disabling pain associated with the vertebral injury. There
are a number of drawbacks associated with traditional vertebroplasty. These
include extravasation of cement from the vertebral body and an inability
to correct the deformity or reduce the fracture. Balloon kyphoplasty was
developed as an attempt to address these issues. In balloon kyphoplasty, an
inflatable bone tamp is used to create a void in the fractured vertebra, which
is then filled with cement.
Hadjipavlou et al
for these procedures. The reported success rates for these procedures is
consistently above 80% (defined as patient-reported good to excellent pain
response) with risk for certain complications. These complications include
a transient increase in pain, infection, leakage of cement, and secondary
vertebral compression fractures. With kyphoplasty, there have been a small
number of reports of balloon rupture, but the failed balloons were withdrawn without incident. Cement leakage is the most common cause of pulmonary or neurological complications. The comparison of cement leakage
risk between kyphoplasty and vertebroplasty remains controversial. Some
reports suggest a clinically insignificant difference in risk, whereas others
suggest that kyphoplasty is associated with less leakage.
Both vertebroplasty and kyphoplasty may increase the risk of subsequent
vertebral fractures, particularly at the adjacent level. Some have hypothesized
that this may be due to changes in load distribution across the endplate that
occur when disc is pressure lost after endplate fracture. Fracture of the endplate
1
provided a thorough review of the existing literature
increases the volume for the nucleus pulposus and reduces its ability to
hydrostatically resist compressive load. In flexion, the reduced load on the
nucleus causes greater load on the annulus and the anterior cortex of the
vertebral body adjacent to the fractured endplate. This mechanism is being
investigated by Patwardhan et al.
cement to the vertebral body increases the stiffness of the vertebral body and
that this may play a role in subsequent fractures. The effect of cement on the
treated and adjacent levels is still being studied, but it appears that this effect
is small compared to bone mineral density.
Advocates of kyphoplasty believe that the procedure actually reduces the
rate of adjacent level fractures, compared to vertebroplasty, because it more
effectively reduces the fracture. However, no randomized studies have been
conducted to compare the two techniques, and the natural history of adjacent level fractures has been difficult to quantify. Frankel and Vandergrift
reviewed the results of 2,000 patients enrolled in a trial evaluating bisphosphonate in patients with vertebral compression fractures. The authors noted
that the rates of new fractures were 7.9% and 15% in patients treated with
bisphosphonate and placebo, respectively. Moreover, in the bisphosphonate
group, only 3.4% of new vertebral compression fractures were at the adjacent level, compared to 7.1% in the placebo group.
review of the literature found the rates of subsequent adjacent level fractures
following kyphoplasty to be 13% compared to 10% with vertebroplasty, suggesting that cement implantation with both of these techniques increased
the risk of subsequent fractures compared to natural history.
Frankel et al5 compared outcomes in a series of 17 patients (20 fractures) undergoing kyphoplasty and 19 patients (26 fractures) undergoing
vertebroplasty. The authors reported an average of 4.65 ml and 3.78 ml of
cement per vertebral body with kyphoplasty and vertebroplasty, respectively.
There were five adjacent level fractures in three kyphoplasty patients (3/17
[18%]) and none in the vertebroplasty group.
retrospective review of 38 patients (47 fractures) treated with kyphoplasty.
Patients received between 1.5 and 6.0 ml cement per vertebral body. The
authors reported that 10 patients (26%) had a subsequent fracture during
the follow-up period (average 8 months), and 8 of those patients had a subsequent fracture within 2 months. The 8 patients with early “new fractures”
all had a fracture at the adjacent level and the 2 patients with later “new fractures” all had fractures that were not adjacent to the index fracture.
A larger study was performed by Harrop et al6 in which 115 patients
were treated with kyphoplasty. All patients had at least 3 months follow-up.
In this group, 26 patients (22.6%) developed 34 new compression fractures.
The authors then classified patients as having primary osteoporosis (80
patients) or secondary steroid-induced osteoporosis (35 patients) and calculated at the rate of subsequent fractures in each group. They reported that
the incidence of postkyphoplasty compression factures in primary osteoporosis patients was 11%, and the incidence in the steroid-induced osteoporosis group was 49% (p < .00001).
bisphosphonates in these patients.
The Frankel
phonates and steroids have a significant effect on bone quality and
should be considered in any analysis of adjacent-level fractures following
4,5
and Harrop7 papers demonstrate that both bisphos-
2
Some have speculated that the addition of
3
4
Frankel and vandergrift
4
5
Fribourg et al6 published a
6
7
There was no mention of the use of
253
4
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P A R T V Ostteoporotic Surgical Treatment Modalities: Thoracic Spine
vertebroplasty or kyphoplasty. Each of these papers reported subsequent
fractures in 18% to 26% of patients, with the best case being 11% in
patients specifically with primary osteoporosis. Because the natural history of adjacent level fractures is likely between 8% and 15%, standard
vertebroplasty and balloon kyphoplasty may actually increase the risk
of subsequent compression fractures, despite the success in reducing a
patient’s pain from the index fracture.
4-7
Cadaver testing has been used to test the hypothesis that kyphoplasty
is more efficacious for deformity correction than standard vertebroplasty.
Belkoff et al
8
experimentally created compression fractures in 16 osteoporotic vertebral bodies and treated them with either balloon kyphoplasty
or vertebroplasty. The vertebral bodies were compressed to 25% of their
initial height; however, there was an initial elastic recovery of about 15%.
The authors measured the change in height with the application of cement
and then subjected those vertebral bodies to compressive failure. The
authors reported that 97% of the height loss was regained with kyphoplasty, whereas only 30% of height loss was regained with vertebroplasty.
These results may not reflect the in vivo situation, because muscle forces
and body weight will resist height restoration, as measured clinically by
Voggen reiter.8 The vertebral bodies in both groups were found to be stronger after the application of cement. However, those treated with kyphoplasty were found to return to their initial stiffness, whereas those treated
with vertebroplasty did not.
9
Kim et al10 performed a similar cadaver
evaluation with the addition of cyclic loading to determine how vertebral
fracture correction was maintained over time. They reported that balloon
kyphoplasty was able to restore vertebral height, but there was significant
loss of height over 100,000 cycles of compressive load. Vertebroplasty was
better able to maintain height under dynamic loading. Ultimately, after
the cyclic testing regimen, the vertebrae treated with kyphoplasty had less
height than those treated with vertebroplasty.
10
In contrast to Belkoff,8
the vertebral bodies treated with vertebroplasty were more stiff than with
kyphoplasty.
Cadaver studies of isolated vertebral bodies cannot capture the interaction
between vertebral bodies or in vivo loads. Clinical data are necessary to realistically measure the ability to achieve reduction of a vertebral compression fracture. Pradham et al
11
evaluated a series of 65 consecutive patients treated with
kyphoplasty between 1 to 3 levels. Kyphoplasty reduced the local kyphotic
deformity by an average of 7.3 degrees (63% of preoperative kyphosis), but
this did not translate into a similar correction of overall sagittal alignment.
Angular correction decreased to 2.4 degrees when measured from the level
above to the level below. Similarly, the reductions decreased to 1.5 and 1.0
degree at spans of 2 and 3 levels above and below the index level, respectively.
The authors concluded that it was unrealistic to expect a 1- or 2 -level kyphoplasty to significantly improve sagittal alignment after vertebral compression
11
fracture.
The StaXx FX Structural Kyphoplasty System (Spine Wave, Inc.,
Shelton, Conn.) was introduced to allow the physician to reduce the vertebral fracture and to correct the kyphotic deformity with a system of progressively stacked wavers made from PEEK (Figure 41-1). The permanent
implant system allows controlled vertical expansion in situ and eliminates
the intraoperative height loss that may occur after deflation of a balloon.
Pradhan et al
11
remarked that using balloons to reduce the fracture is
not ideal, because the balloon and subsequently inserted cement follow
a path of least resistance, resulting in localized stresses on the endplate.
These localized stresses compromise the endplate’s ability to maintain an
improvement in the spine’s overall sagittal alignment. The geometry of the
StaXx system includes a wide, flat surface to support the endplate, which
encourages hydrostatic compression of the nucleus and normalization
of load across the disc. This endplate support may enable the system to
reduce the number of adjacent level fractures following treatment of an
initial compression fracture. Tactile feedback and manual wafer implantation provide greater physician control and directed axial expansion to
reduce the fractured endplate.
The StaXx FX Structural Kyphoplasty System requires only a small
amount of cement, because the PEEK wafers occupy much of the volume
created during reduction. This may reduce the incidence of cement-related
pulmonary complications compared to kyphoplasty. The device itself
impedes the flow of cement when placed anteriorly, thereby reducing the
risk of posterior cement extravasation.
8
F IG UR E 4 1- 1 Stackable PEEK wafers of the StaXx FX Structural
Kyphoplasty device allow the physician to have controlled repair of a vertebral
compression fracture.
INDICATIONS AND CONTRAINDICATIONS
The intended use of The StaXx FX Structural Kyphoplasty System is for
the reduction of spinal fractures. The device is contraindicated in patients
presenting with markedly displaced bony fragments or retropulsion of one
or more fragments that compromise the spinal canal. The physician should
also evaluate the patient’s medical history for such conditions as inability to
tolerate anesthesia, morbid obesity, active infections, fever, leukocytosis, or
factors inhibiting proper claudication. Attention should also be given to the
spinal anatomy and morphology. Safe surgical access and appropriate size
implant components are paramount for a successful procedure.
DESCRIPTION OF THE DEVICE
The StaXx FX Structural Kyphoplasty System is a novel device to be used
in kyphoplasty procedures. Unlike traditional balloon kyphoplasty, structural kyphoplasty allows for physician-controlled fracture reduction. This
device is implanted in the fractured vertebra via a percutaneous, peripedicular surgical approach. StaXx wafers are 1 mm thick and made from PEEK
Optima. Wafers are inserted one at a time, using a wedge action to create
vertical lift and reduce the fractured vertebral body. The first wafer, or base
wafer, acts as a terminus for subsequently inserted wafers and is the foundation of the wafer stack. Once the StaXx wafers are inserted, bone cement
is injected into the vertebral body for further stabilization. A small volume
of cement is injected anteriorly at the base of the wafer stack, securing the
anterior column. Interventional radiologists, neurosurgeons, and orthopedists may perform this procedure.
BACKGROUND OF SCIENTIFIC TESTING AND CLINICAL OUTCOMES
The StaXx FX Structural Kyphoplasty System was introduced to the Euro-
pean market in 2006. It was cleared for the U.S. market via the 510(k) pathway in April 2007, and the first surgery was in August of that year. Although
clinical experience thus far is limited to only a few hundred cases, results are
very promising. No neurological complications related to the device or surgical procedure have been reported. Cement use is greatly decreased, averaging 2.5 ml per level in preliminary registries of patients. In relatively acute
fractures, physicians have reported extreme satisfaction in the ability of the
StaXx FX Structural Kyphoplasty System to correct endplate deformities.
Cadaveric testing by Dr. Stephen M. Belkoff has shown similarities in
both strength and stiffness between balloon kyphoplasty and structural
kyphoplasty (presented at the Annual Meeting of Congress of Neurological
Surgeons, September 15-20, 2007).
Kyphon Bone Tamp (KyphX) and unilateral StaXx FX Structural Kyphoplasty (Spine Wave Shelton, CT USA). Vertebral bodies were preconditioned
with a preload of 89 N and then subjected to compressive loading at a displacement rate of 5 mm/min until the body had lost half its height. The fractures
12
The study methods compared bilateral