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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_6011_Библиотеки_им_академика_М_И_Перельмана.pdf
C H A P T E R 4 1 Structural Kyphoplasty: e StaXx FX System
255
were then put under a preload of 144 N to simulate a recumbent position
during surgery and treated with either KyphX or StaXx. The average cement
volume when using StaXx was 2.50 ml, compared with 7.25 ml with KyphX.
Restoration of vertebral body height was greatest in the anterior portion of the
body and only observed when using the StaXx device. The amount of height
restoration was 5 to 10 mm. The authors observed that the inflatable bone
tamps were able to restore height until they were deflated and removed. At
this time, the compressive preload caused the vertebral body to lose all height
restoration. Treated vertebral bodies were crushed again, and there were no
significant differences in strength or stiffness between the two devices.
11
Patwardhan performed cadaver testing to determine if the StaXx FX
device could restore the vertebral disc pressure adjacent to the fractured endplate to its prefracture values (unpublished company sponsored research).
Restoration of adjacent level disc pressure is believed to decrease anterior
cortical strain and thus reduce the rate of subsequent fractures. Vertebral
height restoration and the reduction in endplate deformity were also studied. Patwardhan used pressure sensors to measure the vertebral disc pressure before fracture, postfracture and posttreatment. Though the results are
still being analyzed, the author’s preliminary report describes that the disc
pressure adjacent to the fractured endplate reduced with StaXx is substantially restored to prefracture values. Clinical data are necessary to determine
if this finding translates to a decrease in the rate of subsequent fractures.
CLINICAL PRESENTATION AND EVALUATION
Patients with vertebral compression fractures typically present with pain
that can be localized to a specific area of the spine. Often, the pain is severe
enough to functionally completely disable the patient. Antiinflammatory
and other pain medication often fail to provide adequate pain relief. A comprehensive evaluation should include sensory, tactile, and reflex assessment.
The physician should also question the patient to determine when the pain
was noticed and the patient’s activity at that time. A comprehensive medical
history will also give insight as to the nature of the pain source. Patients with
known osteoporosis; long-term corticoid steroid use, such as with asthma
inhalers; or a history of cancer are at greater risk for suffering a vertebral
compression fracture. Patients with a history of vertebral compression fractures are likely to present with subsequent fractures.
A standing scoliosis radiographic series should be performed, but at
minimum a standing lateral view and a standing anteroposterior (AP) view
are required. Magnetic resonance imaging (MRI) is imperative visualization to help pinpoint and confirm the location of the pain and visualize the
fracture and it’s configuration. It is important to be aware that radiographs
are of limited utility in determining if the fracture is acute or chronic. Ideally,
a previous radiograph will be available so that a new vertebral fracture can
be distinguished from an existing deformity of the vertebral body. MRI is
particularly well suited for determining if the compression fracture is acute,
because edema will accompany an acute fracture. A T2-weighted image will
show this edema as a brighter area. The specificity of the film can be optimized with an imaging sequence altered to suppress the appearance of fat in
the vertebral body, which also tends to show bright on FSE (fast spin echo)
T2 images (Figure 41-2). The clinician should be aware that outside MRIs
may not be collected with fat suppression and the diagnostic value of the
film may be decreased. Alternatively in those cases, T1-weighted images will
show an edema as a darker area (Figure 41-3). Computed tomography (CT)
scans performed during the initial evaluation provide a better view of the
fractured vertebra and the location of any resulting fragments. If the patient
is not a suitable candidate for an MRI, then the CT scan in conjunction
with nuclear medicine bone scan can also be used to establish fracture age.
With any vertebroplasty or kyphoplasty procedure, endplate restoration and
vertebral height augmentation are more readily achieved on active fractures.
Typically, chronic fractures do not have a great deal of mobility and this may
interfere with the ability to restore the endplate or augment the height of the
vertebral body. In fact, reduction may not be possible on a chronic fracture.
All results should be compared with the patient-reported location, to
determine if the pain is a result of the fractured body. A T-score determination is useful in determining if a patient has osteoporosis or not, especially
with a first-time fracture, and requires bisphosphonate medications to help
prevent further bone loss.
F IG UR E 4 1- 2 A
T2-weighted MRI sequence with
bright edema, indicating an active
fracture. (Images courtesy of Orlando
Ortiz, MD.)
F IG UR E 4 1- 3 A
T1-weighted MRI sequence demonstrates decreased signal in the vertebral body consistent with edema and
active fracture. (Images courtesy of
Orlando Ortiz, MD.)
256
P A R T V Ostteoporotic Surgical Treatment Modalities: Thoracic Spine
A
F IG UR E 4 1- 4 Initial set-up. A, The StaXx structural kyphoplasty procedure begins with the initial fluoroscopy image in the AP view. The vertebral body is
correctly aligned once the inferior endplate is perpendicular to the image, and the spinous process bisects the pedicles. B, After the initial setup image is properly
aligned, then the view is rotated to an en face view or to an oblique view that aligns the anterior aspect of the pedicle to the midline of the vertebra. (Arrow is pedicle
and dotted lines are the margins of the vertebra). (Images courtesy of Wayne Olan, MD.)
B
be placed medial to the rib head, to ensure that the pleural space is not violated, and lateral to the pedicle, to give clearance to the nerve root. Although
the target is smaller in thoracic cases, the landmarks are better defined. The
peripendicular approach is ideal for thoracic cases, in contrast with the
transpedicular approach, because it is parallel to the endplates and facilitates
fracture reduction.
Confirmation of needle placement is observed in the AP and lateral
views (Figure 41-6). The needle stylet is removed, and a Steinmann pin is
advanced to the midline in both the AP and lateral views. This confirms the
proper trajectory and subsequent positioning of the stack in the center of
the vertebral body.
Procedure
A mini-incision (no more than 1.5 cm) is made, and the introducer and
access port assembly is placed over the Steinmann pin and advanced 5 to 10
F IG UR E 4 1 -5 The red box indicates the peripedicular area targeted
during needle placement. (Image courtesy of Wayne Olan, MD.)
OPERATIVE TECHNIQUE
Anesthesia
Structural kyphoplasty procedures are suitable for both general anesthesia and conscious sedation. Choice of anesthesia is at the discretion of the
physician performing the procedure. Regardless, proper assessment to the
patient’s medical history and any preexisting conditions should be considered when selecting the mode of anesthesia.
Position
The patient should be placed in the standard prone position. Placement of
the StaXx Structural Kyphoplasty device is performed under fluoroscopy
using a peripedicular approach. First, the vertebral body is viewed en face
in both AP and lateral images. It’s important that the AP image be square
to the vertebral body and not the patient; thus the C-arm must be rotated
to account for the lateral curvature of the spine. Once the C-arm is properly
oriented for the AP view, the arm should be rotated until the lateral aspect
of the pedicle has moved over about 50% of the vertebral body (Figure
41-4). A perpendicular line should be dropped from the lateral aspect of
the pedicle toward the inferior endplate (Figure 41-5). The target is on
this perpendicular line, 3 to 5 mm superior to the inferior endplate. The
targeting needle should be coincident with the C-arm, similar to looking
down a rifle barrel. This trajectory ensures that the needle will be placed
above Kambin’s triangle, which is a safe area avoiding the exiting nerve
roots below.
The procedure is slightly modified in the thoracic spine because the rib
head must be used as an additional landmark. The targeting needle should
mm into the vertebral body.
The C-arm is then rotated perpendicular (90 degrees) to the instrumentation and fluoroscopy is used to confirm that the introducer and access
port assembly are inserted in the vertebral body, allowing the Steinmann
pin to be removed. The access port assembly is advanced until sufficiently
secured in the cortical wall (Figure 41-7). The introducer is then removed,
leaving the access port. Under perpendicular and lateral fluoroscopic guidance, a depth gauge is used to determine the length across the vertebral body
(Figure 41-8).
After the wafer length is selected, the wafer cartridge is inserted into
the implant delivery gun. The gun and cartridge assembly is primed and
inserted into the access port under perpendicular fluoroscopic guidance
(Figure 41-9). Using lateral fluoroscopic guidance, 1-mm interlocking stackable PEEK wafers are inserted sequentially, allowing for direct control of the
fracture reduction (Figure 41-10).
Fracture reduction, tactile feedback, superior endplate deformation,
or inferior cartridge track deflection are stopping points for wafer insertion. Once the gun has been removed from the access port, still in the
lateral view, a port seal is used to guide the cement needle along the
anterior side of the wafer stack. Bone cement, mixed to a toothpaste
consistency, is injected anterior to the wafer stack for stabilization.
The cement advances up the wafer stack, filling the anterior aspect of
the vertebral body. If the cement does not flow across midline, in the
AP view, additional cement may be placed posterior to the wafer stack
(Figure 41-11).
POSTOPERATIVE CARE
The structural kyphoplasty procedure is generally performed in the out-
patient setting, as is the case with vertebroplasty or balloon kyphoplasty.
The patient is typically discharged home after standard postprocedure
recovery care. Standing radiographs may be obtained before patient
discharge.
C H A P T E R 4 1 Structural Kyphoplasty: e StaXx FX System
F IG UR E 4 1 -6 En face. A,
When performing en face, the lateral
view is used to confirm the targeting
needle insertion point. B, Once targeting has been confirmed in both
the AP and lateral views, the Steinmann pin is advanced. (Images cour-
tesy of Wayne Olan, MD.)
257
A
B
F IG UR E 4 1- 7 Seating of the access port. Once the introducer and access port
are securely fixed in the vertebra, the Steinmann pin is removed. (Image courtesy of Wayne
Olan, MD.)
F I G UR E 4 1 -8 Advancement
of the sizer. A, Through the access
port, the sizer is advanced into the vertebral body. B, The advancement of the
sizer near the far cortex is monitored in
an oblique view. This determines the
size of the implant to be used. (Images
courtesy of Wayne Olan, MD.)
A
B
F IG UR E 4 1- 9 Wafer Insertion. PEEK wafers are sequentially inserted until endplate
fracture reduction is achieved, or endplate deformation occurs, or deflection of the track
to the inferior endplate or tactile feedback from the insertion gun demonstrates excessive
resistance. (Image courtesy of Wayne Olan, MD.)
258
F IG UR E 4 1 -1 0 A small amount of cement is used to secure the StaXx
implant following implantation.
P A R T V Ostteoporotic Surgical Treatment Modalities: Thoracic Spine
COMPLICATIONS AND AVOIDANCE
Kyphoplasty is a relatively safe procedure. Many complications that arise are
a result of the use of bone cement rather than from the actual procedure.
Neurologic injury may occur from malposition of implants in any vertebroplasty or kyphoplasty procedure but are uncommon. The most common,
Stackable
implant
Bone cement
F IG UR E 4 1- 1 1 A CT image shows the cement placed in the anterior
aspect of the vertebral body after the implantation of the StaXx device. (Image
courtesy of Kent Remley, MD.)
nonfatal complications to be anticipated include a transitory fall in blood
pressure, hemorrhage, hematoma, or short-term cardiac conduction
irregularities. Increased pain, rib or vertebra fracture, bone cement allergy,
hematuria, dysuria bladder fistula, and infection are other reported complications. As with any kyphoplasty procedure, users of the StaXx Structural
Kyphoplasty device should monitor for bone cement related events including myocardial infarction, respiratory and cardiac failure, pneumothorax,
abdominal intrusions or ileus, and pulmonary embolism. Care should be
given to assess patients closely for these events, because they are potentially
fatal. The operative suite should have the capacity to immediately treat
these events.
Although structural kyphoplasty uses less cement than the traditional
balloon kyphoplasty, there is still the potential for cement to leak outside of
the vertebral body. Patients should be monitored for signs and symptoms
of soft tissue damage, nerve root pain, cord compression, and neurological
Case Studies
Two case studies are provided. e first is shown in Figure 41-12. is
demonstrates a compression fracture with almost complete loss of anterior
height. e inferior and superior endplates form an angle of 45 degrees.
Following the application of StaXx and cement, much of the anterior height
is restored, and the endplates form an angle of 30 degrees. e reduction
required 11 wafers and 3 ml cement. e second case study is shown in
Figure 41-13. is demonstrates reduction of a two-adjacent-vertebrale
compression fracture. Following reduction, the kyphotic angle had improved
from 38 degrees to just 21 degrees. e cement shows good diffusion
through the both vertebral bodies.
FIGURE 41-12 Case 1. Red dot-
ted lines illustrates height restoration
(Images courtesy of Kent Remley,
MD.)
Pre-op Post-op
C H A P T E R 4 1 Structural Kyphoplasty: e StaXx FX System
Pre-op Post-op
259
FIGURE 41-13 Case 2. Circles
indicate fractures. (Images courtesy
of Kent Remley, M.D.)
impairment. These complications may not always be evident immediately
following the procedures. The physician should assess for these events at
follow-up either in the office or via the phone.
Consideration should be given to prevent complications from a malpositioned or misaligned percutaneous spinal device. Care should be taken to
ensure the structural kyphoplasty device in positioned and implanted correctly to ensure the best possible clinical outcome. Also, as with implantation of any spinal hardware, failure to properly position and implant the
structural kyphoplasty device may result in damage to adjacent neurovascular structures.
CONCLUSIONS AND DISCUSSION
Vertebroplasty and subsequently balloon kyphoplasty were innovative
technologies that enabled physicians to treat a previously untreatable but
disabling condition of the spine. In fact, insufficiency fractures of the spinal vertebra are still a leading cause of progressive morbidity in the elderly
population. Structural kyphoplasty using the StaXx stackable wafer system
provides the latest iteration in therapy and solves many of the problems
associated with the previous technologies. The system enables the physician to have precise control of corrective technology. The positioning of the
wafer stack determines the exact location where the corrective loads will
be applied. The individual 1-mm wafers allow precision in the degree of
correction. The use of the stack as a permanent implant reduces the risk of
subsequent loss of correction. Finally, the wafer stack permits the physician
to control the placement and distribution of the cement.
Ex vivo mechanical testing indicates that injury and deformity of the
endplate is responsible for increasing the risk of fracture of the vertebra
adjacent to the index fracture. Similar testing suggests that the wafer stack
concept provides a more ideal footprint for the correction of endplate deformities. Ultimately, clinical data will be required to prove this point. However, the very promising early experience with this device validates formal
clinical examination in larger series.
References
1. A.G. Hadjipavlou, M.N. Tzermiadianos, P.G. Katonis, et al., Percutaneous vertebroplasty
and balloon kyphoplasty for the treatment of osteoporotic vertebral compression fractures
and osteolytic tumors, JBJS 87-B (12) (2005) 1595–1604.
2. M. Tzermiadianos, A. Hadjipavlou, S. Renner, et al., Altered disc properties after an osteo-
porotic vertebral fracture. Is it a risk factor for adjacent fractures? Journal of Bone and Joint
Surgery - British, Vol. 91-B, Issue (Suppl.1), 108-109.
3. J. Luo, D.M. Skrzypiec, P. Pollintine, et al., Mechanical efficacy of vertebroplasty: influence of
cement type, BMD, fracture severity, and disc degeneration, Bone 40 (4) (2007) 1110–1119.
4. Frankel B and Vandergrift A. The natural history of subsequent adjacent level vertebral com-
pression fractures. Paper #13. Presented at the North American Spine Society 22nd Annual
Meeting, October 23-27, Austin, Texas.
5. B.M. Frankel, T. Monroe, C. Wang, Percutaneous vertebral augmentation: an elevation in
adjacent-level fracture risk in kyphoplasty as compared with vertebroplasty, Spine J. 7 (2007)
575–582.
6. D. Fribourg, C. Tang, P. Sra, et al., Incidence of subsequent vertebral fractures after kypho-
plasty, Spine 29 (20) (2004) 2270–2276.
7. J.S. Harrop, B. Prpa, M.K. Reinhardt, et al., Primary and secondary osteoporosis incidence
of subsequent vertebral compression fractures after kyphoplasty, Spine 29 (19) (2004) 2120–
2125.
8. S.M. Belkoff, J.M. Mathis, D.C. Fenton, et al., An ex vivo biomechanical evaluation of an
inflatable bone tamp used in the treatment of compression fracture, Spine 26 (2) (2001)
151–156.
9. G. Voggenreiter, Balloon kyphoplasty is effective in deformity correction of osteoporotic ver-
tebral compression fractures, Spine 30 (24) (2005) 2806–2812.
10. M.J. Kim, D.P. Lindsey, M. Hannibal, et al., Vertebroplasty versus kyphoplasty: biomechanical behavior under repetitive loading conditions, Spine 31 (18) (2006) 2079–2084.
11. B.B. Pradhan, H.W. Bae, M.A. Kropt, et al., Kyphoplasty reduction of osteoporotic vertebral
compression fractures: correction of local kyphosis versus overall sagittal alignment, Spine 31
(4) (2006) 435–441.
12. S.M. Belkoff, R. Manzi, R.D. Paxson, Mechanical comparison of vertebral body compression
fracture reduction: StaXx FX versus Kyphoplasty. Annual Meeting of Congress of Neurological Surgeons, September 15-20, 2007.
ADVANTAGES AND DISADVANTAGES
Advantages
Directional and controlled correction
Endplate restoration
Permanent implant with sustainable correction
Less cement
Barrier to contain cement
Disadvantages
Requires surgical or radiological expertise
Requires an understanding of anatomy
Crosstrees Percutaneous Vertebral
Augmentation
Philip S. Yuan, Huilin Yang and Dewei Zou
42
k e y p o i n t s
Osteoporosis is typically a silent disease that can first manifest with vertebral
compression fractures (VCFs).
VCFs can lead to kyphosis and functional decline.
Treatment of VCFs with bedrest, bracing, and narcotic medications is often
not effective.
e Crosstrees system for percutaneous vertebral augmentation uses a
removable pod to initially contain the polymethylmethacrylate, allowing for
safer injection and preventing complications from cement extravasation.
e Crosstrees pod also allows for more controlled height restoration and
fracture reduction than that possible with kyphoplasty or vertebroplasty.
INTRODUCTION
Osteoporosis is a major public health problem affecting an estimated 55%
of people over 50 years of age. Every year in the United States more than
700,000 people suffer from vertebral compression fractures (VCFs), with
osteoporosis being the main cause. Osteoporosis, the most common metabolic bone disorder, is typically a silent disease, but has the potential to cause
debilitating back pain when VCFs occur. Other causes of vertebral fracture
include trauma, benign lesions (e.g., hemangioma), and malignant lesions
(e.g., multiple myeloma and metastatic cancer). Osteoporosis is characterized by decreased bone mineral density.
In a normal person, the vertebral bodies are composed of a porous
structure, called trabecular or cancellous bone, encapsulated within a thin
external cap of cortical (dense) bone. In a person with osteoporosis, the
trabeculae that form the central porous bone become thinner and weaker.
When this occurs, the vertebra can fracture and become deformed. This
deformation of the vertebral bodies is classified into three types according to the shape: wedge, biconcave, and crush. As the vertebral bodies collapse, the natural curvature of the spinal column changes. These changes
have mechanical effects on the paraspinal musculature and nerves, resulting in a wide range of symptoms, including pain, decreased sensitivity,
tingling, and weakness. Multiple VCFs can produce kyphotic deformity,
pulmonary dysfunction, loss of appetite, depression, and functional
decline.
Until recently, the options for treatment of vertebral fractures were limited. Patients were confined to bed for prolonged periods and were given
large doses of analgesics. Bracing was used but was usually not well tolerated
by these typically elderly patients and has fallen out of favor. These palliative
treatments do not restore the anatomy of the patient’s vertebral column to
the alignment and morphology it had before the fracture. Treatment success,
defined as relief of pain symptoms, depended on the individual’s capacity to
heal the fracture. This physical change, along with forward angulation, can
cause persistent deformity.
260
The traditional surgical techniques used to treat vertebral fractures or to
maintain spinal stabilization are not as effective in the setting of osteoporosis, because the weakened bone is often not strong enough to support the
metallic rods and screws. Because of the debilitating nature of the disease,
many different procedures have been attempted. Among these, the procedure that has been the most successful is the injection of polymethyl methacrylate (PMMA) bone cement into the vertebral body to stabilize it. This
procedure, known as vertebroplasty or kyphoplasty (when a balloon is first
used to create a space in the vertebra) is performed in patients with painful
fractures that fail to respond to conservative treatment.
A potentially devastating complication of vertebroplasty is the accidental
escape (or leakage) of PMMA from the vertebral body, a problem known as
cement extravasation. This problem can damage the vital structures, such
as the spinal cord, or can contribute to the formation of emboli as a result
of the flow of cement to the venous plexus. This can result in serious neurological complications or even death. Kyphoplasty was developed to help
minimize cement extravasation by first introducing a balloon tamp to create
a space for the cement and compact the surrounding bone. However, cement
leakage is still possible with kyphoplasty, because the cement is only injected
after removal of the balloon.
The Crosstrees PVA (percutaneous vertebral augmentation) pod is
a device designed to percutaneously provide well-controlled delivery of
PMMA during vertebral augmentation. The Crosstrees PVA System
(Crosstrees Medical, Boulder, Colo.) is designed for use with Mendec Spine
PMMA manufactured by Tecres S.p.a. (Verona, Italy), which is marketed
with approved indications for use in the treatment of pathologic vertebral
fracture. The pod device consists of a catheter for administering the cement
into a releasable closed fabric barrier. Following delivery of a known volume
of PMMA and expansion of the pod to a defined size, the fabric barrier is
opened and removed from the vertebral body, leaving only the PMMA within
the bony structure. A final volume of highly viscous PMMA can be added to
the center of the initial bolus to provide additional interdigitation of PMMA
to the cancellous bone. The system is novel in providing the ability to control
the delivery of PMMA to the vertebral body and maintaining fracture reduction without the need for a permanent implant to remain within the patient.
INDICATIONS AND CONTRAINDICATIONS
Surgical treatment of VCFs with the Crosstrees PVA pod is indicated when
debilitating back pain persists despite nonsurgical therapies (Table 42-1). MRI,
the imaging study of choice for diagnosing VCF, typically shows increased signal on short T1 inversion recovery (STIR) sequences when a VCF is acute/
subacute or if there is residual bony edema indicating incomplete healing. A
nuclear medicine study (bone scan) is particularly useful when a MRI cannot
be performed (e.g., when pacemaker is present).
In cases of chronic fracture, vertebral augmentation is not indicated.
Other absolute contraindications to Crosstrees or any other PVA technique
include pregnancy, coagulopathy, osteomyelitis, spinal instability, known
allergy to PMMA, and previous augmentation with PMMA (Table 42-2).
C H A P T E R 4 2 Crosstrees Percutaneous Vertebral Augmentation
TA BL E 42 -1 Relat ive Indications
1. Confirmed acute pain and tenderness over the spine at or near the level of
x-ray compression deformity and positive MRI or bone scan evaluation
2. Not more than three vertebral compression fractures located between T4
and L5
3. Painful fracture with a loss of 0% to 60% of the height of the vertebral body
compared with the height of an adjacent vertebral body that is normal, as
determined by the radiological evaluation
4. Confirmation of fracture by MRI including T1-, T2-, and STIR-weighted
sequences to determine the type and presence of fracture(s); or nuclear
medicine study (bone scan) when MRI cannot be performed (e.g., because
of pacemaker)
5. Adequate vertebral body height and geometry for insertion of the access
instruments of 5.2 mm outside diameter
6. Minimum vertebral body anterior height of 6.0 mm
TA BL E 42 -2 Absolute Contraindications
1. Chronic fracture
2. Spinal instability
3. Known or suspected allergy to PMMA
4. Pregnancy
5. Irreversible coagulopathy or bleeding disorder
6. Active or local infection
7. Previous cement injection or augmentation at the fractured level
TA BL E 42 -3 Relat ive Cont rain dica tions
1. Comminuted or high-energy fracture with extension to posterior wall
2. Burst fracture or pedicle fracture
3. Vertebra plana or significant vertebral collapse, defined as >60% of the
original height of the vertebral body, as measured against the nearest normal
vertebral body
4. Significantly compromised spinal canal or bony retropulsion, especially in
setting of neurologic injury
5. Spinal stenosis
6. Pathologic fractures, both benign and malignant (e.g., myeloma, metastatic
lesions)
7. Presence of more than three acute VCFs
Relative contraindications (Table 42-3) include neurologic deficit (i.e., burst
fracture with significant bony retropulsion, or fracture extending to the posterior cortical wall) and pathologic vertebral fracture related to primary or
metastatic cancer; however, because the Crosstrees pod fully contains the
cement during implantation and has a defined shape, it may be used more
safely in these cases than current vertebroplasty or kyphoplasty techniques.
Another relative contraindication is vertebra plana or greater than 60% loss
of height.
DESCRIPTION OF THE DEVICE
The Crosstrees pod device (Figure 42-1) was developed to provide a percutaneous method of delivering a specific volume of bone cement to the
surgical site in orthopedic procedures. The device is designed such that
261
F IG UR E 4 2- 1 Crosstrees pod device.
F IG UR E 4 2- 2 Crosstrees CDrive cement dispenser.
the woven fabric pod is inserted into the intravertebral space, and a predetermined volume of bone cement is delivered into it, thus reducing the
likelihood of extravertebral cement leakage. The pod expands to a defined
shape with a broad surface area as the cement is injected, elevating the
endplates and restoring height to the fractured vertebra. Following delivery of the bone cement, the pod is opened and withdrawn from the vertebra. Additional cement can be delivered to the center of the cement bolus,
to provide interdigitation with the bone. PMMA is delivered to the pod
by a threaded injection syringe, the Crosstrees CDrive cement dispenser
(Figure 42-2), designed to measure and deliver the volume required for
the selected pod.
PRINCIPLES OF PROCEDURE
The Crosstrees pod device is composed of a woven fabric mounted on the
end of a stainless steel cement delivery shaft. The cement delivery shaft
is housed within an additional stainless steel insertion sleeve which can
be positioned along the axial length of the cement delivery shaft and pod
such that the pod is contained within the insertion sleeve or exposed before
PMMA fill. The proximal end of the delivery shaft is bonded to a Y-adaptor
with Luer connector fittings on each arm of the Y-adaptor.
The pod is designed with a nylon release cord that is attached with a
conventional stitch to the pod. The release cord runs the length of the device
within the delivery shaft and through the straight leg of the Y-adaptor, providing access to the release cord at the proximal end of the device. A polymer
cap is bonded to the proximal end of the release cord and secured by Luer
thread to the Y-adaptor. The cap can be removed from the Y-adaptor and
used to apply tension to the release cord. Following delivery of a defined
volume of PMMA to the pod, tension is applied by the user to the release
cord, pulling the stitch from the wall of the pod, opening the distal pod end.
Using a stylet and 5.2-mm-diameter access cannula, the paraspinal musculature is traversed to access the vertebral body via the pedicle. Either a transpedicular or extrapedicular approach can be used. The stylet and cannula
can be advanced to the bony site and withdrawn slightly to create a location
for placement of the Crosstrees pod within the bony site. As an alternative method, the stylet can be withdrawn from the cannula and a bone drill
advanced through the access cannula into the vertebra and then withdrawn
262
P A R T V Ostteoporotic Surgical Treatment Modalities: Thoracic Spine
creating a space for placement of the Crosstrees pod within the bony site. Often
bone fragments that remain on the drill can be sent for pathologic examination.
The Crosstrees pod is advanced through the lumen of the access cannula
and, under fluoroscopic guidance, placed at the desired location within the
vertebral body. Placement in the bone is confirmed by radiographic imaging.
On confirmation of positioning, the insertion sleeve is withdrawn to expose
the pod. The fabric component of the pod will fill to a known and predictable cubic geometry, aligned such that the maximum surface area is oriented
parallel to the vertebral endplate. This geometry will provide the optimal
surface area for lifting of the compressed bone and restoring vertebral body
height.
Mendec Spine cement (PMMA) is prepared according to manufacturers instructions. The PMMA is loaded into the Crosstrees CDrive and
attached to the pod by Luer taper distal connection fitting. Using fluoroscopic guidance, PMMA is advanced from the CDrive cement dispenser
to the delivery shaft and injected into the pod. PMMA delivery continues until a maximum pod capacity is contained within the pod located
in the bone. After filling to maximum pod capacity, the release cord cap
is removed from the straight leg of the Y-adaptor and tension applied to
the release cord. The release cord is withdrawn from the Crosstrees pod,
removing the stitch from the distal pod end. The release cord is fully withdrawn from the Crosstrees pod assembly. Following removal of the release
cord and opening of the distal pod end, the Crosstrees pod is withdrawn
from the access cannula. The open pod is removed from the patient, leaving no implant other than the specific PMMA. Withdrawal is controlled
by rotation of the threaded extractor mechanism at the proximal end of
the pod assembly, resulting in linear proximal movement of the fabric pod
component to a position within the access cannula. Withdrawal of the pod
will decrease the pod fabric diameter on entry to the access cannula, leaving
the PMMA within the bone. Following removal of the Crosstrees pod, the
access cannula may be used for further access to the bone to deliver a final
PMMA bolus, and it is removed from the patient on completion of the
surgical procedure.
BACKGROUND OF SCIENTIFIC TESTING AND CLINICAL OUTCOMES
It is well established in the published medical literature that the effectiveness of vertebral augmentation is evident almost immediately after the
procedure. Numerous authors have reported significant pain relief within
24 to 48 hours, with stable results preserved at subsequent follow-up in
a majority of patients.
evaluated efficacy principally based on pain relief, because pain is typically the reason patients seek treatment. Pain relief assessment by VAS
is widely reported, with patients reporting significant relief at 24 hours
and later following the procedure. Functional outcomes have also been
reported using multiple assessment methods, but is typically secondary
to evaluation based on pain relief.
outcomes with respect to pain relief post procedure. The study included
117 consecutive subjects undergoing vertebral augmentation procedures.
The authors observed rapid relief in pain, with substantial improvement
within 1 week postprocedure and relatively stable results from 1 through
24 months postoperative.
In a 2006 review, Hulme et al
range of 1% to 2% for osteoporotic fractures and 5% to 10% for metastatic
6
lesions.
Complications specifically related to cement leakage can include
increased local pain, symptomatic pulmonary embolus, radiculopathy, and
cord compression and are estimated to occur in approximately 1% to 3% of
7
cases.
Of the complications potentially associated with vertebroplasty and
kyphoplasty, all but new vertebral fractures occur during or immediately following the procedure. Thus the majority of complications can be identified
within a very short period following the procedure.
Clinical literature in vertebral augmentation reports on the incidence of
additional fractures as the primary focus of longer term follow-up. Leakage
of PMMA from the vertebra has been associated with incidence of new
fracture, with average time to new fracture of 48 days for levels adjacent
to PMMA extravasation and 98 days absent PMMA extravasation.
are reports of the incidence of fracture adjacent to and remote from treated
levels with half of new fractures occurring adjacent to treated levels within
1
Studies in vertebral augmentation have generally
2-4
Ledlie et al5 showed the stability of
4
reported that complication rates are in the
8
There
3 months follow-up. A majority of subsequent vertebral fractures appear to
occur within the first 30 days following a vertebroplasty procedure. Lin et
9
al
reported that in a series of 38 patients treated with vertebroplasty, new
fractures occurred in 14 patients. When cement leakage occurred, the average time to new fracture was 48 days. It was 98 days in patients who did not
have any cement leakage.
The time to observation of cement leakage occurrence is similar across
studies. The existence of cement leakage is generally identified during or
soon after the vertebroplasty procedure. Thus, although cement leakage
appears to be the most commonly occurring complication of vertebroplasty,
the existence of such an event would be identified well within a 30-day
follow-up period.
In addition to evaluation of safety and pain relief, vertebral augmentation studies reported in the literature have often included an assessment of
vertebral body morphology. There is disagreement in the literature on the
efficacy of current treatments in the restoration of vertebral height and the
clinical importance of vertebral height restoration.
4,7
Procedural characteristics including the volume of cement used are also
reported in the literature. Clinical literature reports variability in the volume
of PMMA required for procedure success.
8,10
The Crosstrees system delivers an initial bolus of known volume of PMMA, with device size selection
determined by the investigator, based on vertebral level, degree of vertebral
collapse, and physician assessment of device placement strategy. Pain relief
is often immediate and sustained as noted in the literature review noted
previously. If complications occur, they should become apparent early in the
postoperative period.
OPERATIVE TECHNIQUE
Anesthesia
General anesthesia is usually preferred, because it prevents the patient from
feeling any discomfort and allows a controlled environment for safe passage
of the cannulas down the pedicles. The procedure can be safely performed
using local anesthesia if the patient is medically too unstable to undergo
general anesthesia.
Position
The procedure is always performed with the patient prone on a radiolucent
frame, such as the Jackson table. All attempts should be made to extend
the spine, in an attempt to restore height to the fractured vertebra using
ligamentotaxis.
Surgical Procedure for the Crosstrees System
Position the patient prone on a radiolucent table. Drape and prep according to standard surgical technique. Position two C-arms to achieve biplanar fluoroscopy capability as shown. If only one C-arm is available, the
radiolucent table used must allow the C-arm to freely complete its arc as it
moves from the anteroposterior (AP) to the lateral imaging position and
back again.
Transpedicular Approach
Make a skin incision slightly lateral and superior (varies per level) to the
intersection of the superior and lateral edges of the pedicle as determined
under fluoroscopic guidance. Insert the 11-gauge needle into the incision
and anchor it in bone, gently tapping it with a mallet if necessary. Confirm
its location with fluoroscopy (AP view). Continue tapping the 11-gauge
needle into place, confirming the location of the tip periodically with both
AP and lateral fluoroscopic views. To avoid the spinal canal, make sure the
tip of the needle does not pass medial to the medial border of the pedicle
before entering the posterior vertebral cortex. Once the 11-gauge needle has
crossed the posterior wall of the vertebral body, remove the inner stylet and
replace it with the Indexed Guide Pin. Advance the guide pin anteriorly and
medially into the vertebral body. Use the proximal most visible sizing indicator to select the appropriate size pod. With the guide pin approximately
halfway across the vertebral body on the lateral view, remove the 11-gauge
needle cannula and insert the blunt cannulated assembly over the guide pin.
C H A P T E R 4 2 Crosstrees Percutaneous Vertebral Augmentation
263
Attach the strike plate to the strike plate extension. Insert the tines of the
strike plate into the mating feature of the blunt cannulated stylet and use the
mallet to gently tap the stylet until its tip is just past the posterior vertebral
wall on the lateral view.
Remove the inner stylet and guide pin and leave the access cannula
in place. Note: The wings of the access cannula should be oriented in a
cephalad-caudad position at this point if the primary geometry of the
pod is being used. For an alternate geometry, the cannula wings should be
parallel to the vertebral endplates. Under fluoroscopic guidance, use the
cannulated drill to create a space in the bone before the placement of the
pod and injection of PMMA into the pod. Advance the cannulated drill
under fluoroscopic observation, avoiding contact with the anterior wall of
the vertebra.
Extrapedicular Approach (Usually Recommended in Thoracic Spine)
Make a skin incision a few centimeters lateral and slightly superior to the
intersection of the superior and lateral edges of the pedicle. Insert the
11-gauge needle into the incision and anchor it in bone, gently tapping it
with a mallet if necessary. The correct entry point to the vertebral body is the
costovertebral junction. Confirm the location with fluoroscopy (AP view).
Under fluoroscopic guidance, use the cannulated drill to create a space in
the bone before the placement of the pod and injection of PMMA into the
pod. Advance the cannulated drill under fluoroscopic observation, avoiding
contact with the anterior wall of the vertebra.
Use the laser markings on the drill shaft to confirm drill depth relative to the distal end of the access cannula. Do not drill more than 20 mm
beyond the distal end of the access cannula. Under fluoroscopic guidance,
insert the pod through the access cannula, and slide the extractor collar
connector over the cannula wings to seat. The Y-adaptor will be oriented
laterally and parallel to the vertebral endplates if the primary pod geometry
is being used.
Delivery of PMMA
Remove the insertion sleeve lock from the pod assembly and set aside.
Expose the pod membrane by pulling back on the wings of the device
assembly. Repeat this process on the contralateral side. Under fluoroscopic
guidance, turn the handle on the CDrive to inject spine resin into the pod
membrane. Inject the entire contents of the CDrive by rotating the handle
until it is flush with the CDrive sleeve. Repeat this process on the contralateral side. Confirm PMMA delivery to the pod with fluoroscopy in AP and
lateral views. Remove the luer cap and release cord by withdrawal proximal
from the pod assembly, opening the distal end of the pod fabric. Withdraw
the pod from the vertebra by rotation of the extractor nut wings clockwise
to the limit of the thread travel length. Withdraw the pod assembly from the
cannula. Repeat this process on the contralateral side.
Insert the filler placement cannula (FPC) through the access cannula,
advancing just far enough to place the tip of the FPC into the center of
the cement bolus. Use fluoroscopy and the marks on the FPC cannula to
confirm position. Manually dispense additional PMMA under continuous
fluoroscopic guidance to achieve interdigitation (Table 42-4).
POSTOPERATIVE CARE
Patients usually notice immediate relief of back pain and often do not
require any narcotic medication postoperatively. Patients can be discharged
home the same day or monitored overnight to watch for other medical
comorbidities if necessary. Often these patients are weak because they have
been bedridden and may benefit from the overnight stay and a session with
a physical therapist.
TA BL E 42 -4 Timing for the Prep arat ion and Applica tion
of the PMM A ( Mendec Spine Res in, 68° F )
Operation
(Mendec) Definition
Mixing Mixing of the
Delivery
device filling
Waiting e cement cannot
Working e cement can be
Hardening e cement hard-
ADVANTAGES AND DISADVANTAGES
e Crosstrees device enables controlled implantation of PMMA into a
fractured vertebra, while filling to a known shape and minimizing the chance
of cement leakage. It does not require insertion and removal of a balloon tamp
before the insertion of cement, rather the pod is inserted, reduces the fracture,
and is removed after cement injection and reduction.
Despite the advantages, the Crosstrees procedure may be more technically challenging, because placement of the pod is essential for a good result. e pods
need to be placed near the center of the vertebral body because they will not
necessarily seek the path of least resistance, as in balloon procedures for VCF.
e cement will only fill the pod in a defined shape. With that being said, once
the pod is removed, there is the possibility of back filling additional cement if
so desired, but the risk of leakage is possible if that path is chosen.
components
e dough is
transferred into the
delivery device
be used
delivered
ens and increases
in viscosity and
cannot be delivered
anymore; exothermic reaction takes
place
Function (Crosstrees
pod)
e dough is transferred to the CDrive
Cement delivery,
release cord removal,
pod withdrawal
Manual cement delivery and interdigitation
via filler placement
cannula
Phase
Duration
(sec)
60
60
300
600
360
Both vertebroplasty and kyphoplasty have proved to be effective in
relieving pain related to VCF. A potentially serious complication of these
procedures is cement extravasation. The Crosstrees Medical PVA System
for percutaneous vertebral augmentation consists of instruments designed
to deliver the cement to the vertebral body in a controlled manner preventing extravasation without the requirement for an implant device. This device
is designed to decrease the risk of leakage of bone cement (PMMA) into the
spinal canal and the venous plexus, thereby preventing the complications
associated with extravasation. The Crosstrees pod also has the added benefit of achieving and maintaining fracture reduction during cement injection, whereas in kyphoplasty the balloon tamp can achieve reduction but is
then removed before cement insertion, and reduction is lost in many cases.
The Crosstrees pod adds to the surgeon’s armamentarium for treatment of
VCFs.
CONCLUSIONS AND DISCUSSIONS
In 2005, osteoporosis-related fractures were responsible for an estimated
$19 billion in costs. Osteoporosis is a disease characterized by low bone
mass, leading to bone fragility and an increased susceptibility to fractures,
especially of the spine, hip, and wrist, although any bone can be affected.
VCFs are a frequent cause of pain and disability among the elderly
population.
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264
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