U.S. patent application number 11/299172 was filed with the patent office on 2006-05-04 for expandable preformed structures for deployment in interior body regions.
This patent application is currently assigned to Kyphon Inc.. Invention is credited to Robert M. Scribner, Karen D. Talmadge.
Application Number | 20060095064 11/299172 |
Document ID | / |
Family ID | 22211509 |
Filed Date | 2006-05-04 |
United States Patent
Application |
20060095064 |
Kind Code |
A1 |
Scribner; Robert M. ; et
al. |
May 4, 2006 |
Expandable preformed structures for deployment in interior body
regions
Abstract
An expandable structure made from an elastomer material is
preformed to a desired geometry by exposure to heat and pressure.
The structure undergoes controlled expansion and further distention
in cancellous bone, with controlled deformation and without stress
failure.
Inventors: |
Scribner; Robert M.; (Los
Altos, CA) ; Talmadge; Karen D.; (Palo Alto,
CA) |
Correspondence
Address: |
RYAN KROMHOLZ & MANION, S.C.
POST OFFICE BOX 26618
MILWAUKEE
WI
53226
US
|
Assignee: |
Kyphon Inc.
|
Family ID: |
22211509 |
Appl. No.: |
11/299172 |
Filed: |
December 9, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09837350 |
Apr 18, 2001 |
6979341 |
|
|
11299172 |
Dec 9, 2005 |
|
|
|
09088459 |
Jun 1, 1998 |
|
|
|
09837350 |
Apr 18, 2001 |
|
|
|
Current U.S.
Class: |
606/192 |
Current CPC
Class: |
A61B 2017/00557
20130101; A61M 29/02 20130101; Y10S 606/91 20130101; A61M 25/002
20130101; A61B 17/7097 20130101; A61B 2017/00544 20130101; A61M
25/10 20130101; A61B 2017/0256 20130101; A61M 25/1011 20130101;
A61B 2017/00526 20130101; A61M 2210/02 20130101; A61B 2017/00539
20130101; A61M 2210/1003 20130101; A61B 90/39 20160201; A61B
17/8855 20130101; A61B 17/3472 20130101 |
Class at
Publication: |
606/192 |
International
Class: |
A61M 29/00 20060101
A61M029/00 |
Claims
1. A device for compacting cancellous bone comprising a wall made
from an elastomer material and including a region preformed with a
normally expanded shape outside bone.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of co-pending application
Ser. No. 09/837,350, filed Apr. 18, 2001, which is a continuation
of application Ser. No. 09/088,459, filed Jun. 1, 1998 (now
abandoned), which claims the benefit of application Ser. No.
08/788,786, filed Jan. 23, 1997 (now U.S. Pat. No. 6,235,043),
which is a continuation of application Ser. No. 08/188,224, filed
Jan. 26, 1994 (now abandoned).
FIELD OF THE INVENTION
[0002] The invention relates to expandable structures, which, in
use, are deployed in interior body regions of humans and other
animals.
BACKGROUND OF THE INVENTION
[0003] The deployment of expandable structures, generically called
"balloons," into cancellous bone is known. For example, U.S. Pat.
Nos. 4,969,888 and 5,106,404 disclose apparatus and methods using
expandable structures in cancellous bone for the fixation of
fractures or other osteoporotic and non-osteoporotic conditions of
human and animal bones.
SUMMARY OF THE INVENTION
[0004] When deployed in cancellous bone, expandable structures
should undergo expansion and distention without failure.
Furthermore, such structures, when distended, should generally
match the geometry of the interior bone space in which the
structure is deployed. In addition, such structures should allow
preferential expansion to areas of lowest bone density. Exposure to
cancellous bone also requires materials that exhibit superior
resistance to surface abrasion and tensile stresses.
[0005] It is has been discovered that expandable structures made
from an elastomer material, e.g., polyurethane, which have been
preformed to a desired shape, e.g., by exposure to heat and
pressure, can undergo controlled expansion and further distention
in cancellous bone, without failure, while exhibiting superior
resistance to surface abrasion and puncture when contacting
cancellous bone.
[0006] Features and advantages of the inventions are set forth in
the following Description and Drawings, as well as in the appended
Claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a coronal view of a vertebral body;
[0008] FIG. 2 is a lateral view of the vertebral body shown in FIG.
1;
[0009] FIG. 3 is a plan view of a tool which carries at its distal
end an expandable structure that embodies features of the
invention;
[0010] FIGS. 4A and 4B are enlarged side views of the expandable
structure carried by the tool shown in FIG. 3;
[0011] FIG. 5 is a perspective end view of a tube made of a
polyurethane or elastomer material prior to being formed into the
expandable structure shown in FIG. 4A;
[0012] FIG. 6 is a top perspective view of the tube shown in FIG. 5
positioned in a shape-forming fixture, of which parts are broken
away to permit viewing its interior;
[0013] FIG. 7 is a top perspective view of the shape-forming
fixture shown in FIG. 6, in use applying heat and pressure to a
region of the tube to form a shaped, expandable region;
[0014] FIG. 8 is a coronal view of the vertebral body shown in FIG.
1, with the tool shown in FIG. 3 deployed to compress cancellous
bone as a result of inflating the expandable structure;
[0015] FIG. 9 is a coronal view of the vertebral body shown in FIG.
8, upon removal of the tool, showing the cavity formed by the
compression of cancellous bone by the expandable structure;
[0016] FIG. 10 is a graph which plots the effects of increasing
pressure applied to the interior of the structure to the expanded
volume of the structure;
[0017] FIG. 11 is a coronal view of the vertebral body shown in
FIG. 8, with the tool deployed to compress cancellous bone, and in
which a bendable stylet alters the orientation of the expandable
structure in cancellous bone;
[0018] FIG. 12 is a side view of a complex structure which includes
several expandable segments spaced along its length;
[0019] FIG. 13 is a top perspective view of a shape-forming fixture
used to apply pressure and heat to an extruded or molded tube to
create the structure shown in FIG. 12;
[0020] FIG. 14 is a top view of a kit which holds the tool shown in
FIG. 3 in a sealed, sterile environment prior to use;
[0021] FIG. 15 is an exploded view of the kit shown in FIG. 14;
and
[0022] FIG. 16 is a side view, partly in section, of a composite
expandable structure.
[0023] The invention may be embodied in several forms without
departing from its spirit or essential characteristics. The scope
of the invention is defined in the appended claims, rather than in
the specific description preceding them. All embodiments that fall
within the meaning and range of equivalency of the claims are
therefore intended to be embraced by the claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] The preferred embodiment describes improved systems and
methods that embody features of the invention in the context of
treating bones. This is because the new systems and methods are
advantageous when used for this purpose. However, aspects of the
invention can be advantageously applied for diagnostic or
therapeutic purposes in other areas of the body.
[0025] The new systems and methods will be more specifically
described in the context of the treatment of human vertebra. Of
course, other human or animal bone types can be treated in the same
or equivalent fashion.
[0026] FIG. 1 shows a coronal (top) view of a human lumbar vertebra
12. FIG. 2 shows a lateral (side) view of the vertebra. The
vertebra 12 includes a vertebral body 25, which extends on the
anterior (i.e., front or chest) side of the vertebra 12. The
vertebral body 26 is shaped generally like a marshmallow.
[0027] As FIGS. 1 and 2 show, the vertebral body 26 includes an
exterior formed from compact cortical bone 28. The cortical bone 28
encloses an interior volume of reticulated cancellous, or spongy,
bone 32 (also called medullary bone or trabecular bone).
[0028] The spinal canal 35 (see FIG. 1), is located on the
posterior (i.e., back) side of each vertebra 12. The spinal cord
(not shown) passes through the spinal canal 36. The vertebral arch
40 surrounds the spinal canal 35. Left and right pedicles 42 of the
vertebral arch 40 adjoin the vertebral body 25. The spinous process
44 extends from the posterior of the vertebral arch 40, as do the
left and right transverse processes 46.
[0029] It may be indicated, due to disease or trauma, to compress
cancellous bone within the vertebral body. The compression, for
example, can be used to form an interior cavity, which receives a
filling material, e.g., a flowable material that sets to a hardened
condition, like bone cement, allograft tissue, autograft tissue,
hydroxyapatite, or synthetic bone substitute, as well as a
medication, or combinations thereof, to provide improved interior
support for cortical bone or other therapeutic functions, or both.
The compaction of cancellous bone also exerts interior force upon
cortical bone, making it possible to elevate or push broken and
compressed bone back to or near its original prefracture, or other
desired, condition.
I. Preformed Expandable Structures
[0030] FIG. 3 shows a tool 48 for accessing bone for the purpose of
compacting cancellous bone. The tool 48 includes a catheter tube 50
having a proximal end 52 and a distal end 54. The proximal end 52
carries a handle 14 to facilitate gripping and maneuvering the tube
50. The proximal end 52 also carries a fitting 122 to enable
connection of the tool 48 to external equipment, as will be
described later. The distal end 54 of the tool 48 carries a
structure 55, which, in use, is intended to be expanded in
cancellous bone, e.g., in the vertebral body 26 shown in FIGS. 1
and 2.
[0031] A. Desired Physical and Mechanical Properties
[0032] The material from which the structure 56 is made should
possess various physical and mechanical properties to optimize its
functional capabilities to compact cancellous bone. The three most
important properties are the ability to expand its volume; the
ability to deform in a desired way when expanding and assume a
desired shape inside bone; and the ability to withstand abrasion,
tearing, and puncture when in contact with cancellous bone.
[0033] 1. Expansion Property
[0034] A first desired property for the structure material is the
ability to expand or otherwise increase its volume without failure.
This property enables the structure 55 to be deployed in a
collaD8ed, low profile condition subcutaneously, e.g., through a
cannula, into the targeted bone region. This property also enables
the expansion of the structure 56 inside the targeted bone region
to press against and compress surrounding cancellous bone, or move
cortical bone to a prefracture or other desired condition, or
both.
[0035] The expansion property for the material can be
characterized, e.g., by ultimate elongation properties, which
indicate the greatest degree of expansion that the material can
accommodate prior to failure. An ultimate elongation of at least
about 300% before material failure provides the ability to expand
to the volume necessary to compact cancellous bone, as well as lift
contiguous cortical bone. A material with an ultimate elongation of
less than about 300% is prone to exhibit failure at inflation
volumes short of the desired bone compacting volume.
[0036] 2. Shape Property
[0037] A second desired property for the material of the structure
56 is the ability to predictably deform during expansion, so that
the structure 55 consistently achieves a desired shape inside
bone.
[0038] The shape of the structure 55, when expanded in bone, is
selected by the physician, taking into account the morphology and
geometry of the site to be treated. The shape of the cancellous
bone to be compressed, and the local structures that could be
harmed if bone were moved inappropriately, are generally understood
by medical professionals using textbooks of human skeletal anatomy
along with their knowledge of the site and its disease or injury,
and also taking into account the teachings of U.S. patent
application Ser. No. 08/788,785, filed Jan. 23, 1997, and entitled
"Improved Inflatable Device for Use in Surgical Protocol Relating
to Fixation of Bone," which is incorporated herein by reference.
The physician is also able to select the desired expanded shape
inside bone based upon prior analysis of the morphology of the
targeted bone using, for example, plain film x-ray, fluoroscopic
x-ray, or MRI or CT scanning. The expanded shape inside bone is
selected to optimize the formation of a cavity that, when filled
with a selected material, provides support across the region of the
bone being treated. The selected expanded shape is made by
evaluation of the predicted deformation that will occur with
increased volume due to the shape and physiology of the targeted
bone region.
[0039] In some instances, it is desirable, when creating a cavity,
to also move or displace the cortical bone to achieve the desired
therapeutic result. Such movement is not per se harmful, as that
term is used in this Specification, because it is indicated to
achieve the desired therapeutic result. By definition, harm results
when expansion of the structure 55 results in a worsening of the
overall condition of the bone and surrounding anatomic structures,
for example, by injury to surrounding tissue or causing a permanent
adverse change in bone biomechanics.
[0040] As one general consideration, in cases where the bone
disease causing fracture (or the risk of fracture) is the loss of
cancellous bone mass (as in osteoporosis), the selection of the
expanded shape of the structure 56 inside bone should take into
account the cancellous bone volume which should be compacted to
achieve the desired therapeutic result. An exemplary range is about
30% to 90% of the cancellous bone volume, but the range can vary
depending upon the targeted bone region. Generally speaking,
compacting less of the cancellous bone volume leaves more
uncompacted, diseased cancellous bone at the treatment site.
[0041] Another general guideline for the selection of the expanded
shape of the structure 56 inside bone is the amount that the
targeted fractured bone region has been displaced or depressed. The
controlled deformation diameter expansion of the structure 55
within the cancellous bone region inside a bone can elevate or push
the fractured cortical wall back to or near its anatomic position
occupied before fracture occurred. Generally speaking, inadequate
compaction of cancellous bone results in less lifting of contiguous
cortical bone.
[0042] For practical reasons, it is desired that the expanded shape
of the structure 55 inside bone, when in contact with cancellous
bone, substantially conforms to the shape of the structure 56
outside bone, when in an open air environment. This allows the
physician to select in an open air environment a structure having
an expanded shape desired to meet the targeted therapeutic result,
with the confidence that the expanded shape inside bone will be
similar in important respects.
[0043] An optimal degree of shaping can be achieved by material
selection and by special manufacturing techniques, e.g.,
thermoforming or blow molding, as will be described in greater
detail later.
[0044] 3. Toughness Property
[0045] A third desired property for the material of the structure
56 is the ability to resist surface abrasion, tearing, and puncture
when in contact with cancellous bone.
[0046] This property can be characterized in various ways. For
example, a Taber Abrasion Resistance Value of less than about 90 mg
loss indicates resistance to puncture when contacting cancellous
bone. A Rotating Drum Abrasion Resistance Value of less than 70 mm3
also indicates resistance to puncture when contacting cancellous
bone. This property can further be characterized, e.g., by an
Elmendorf tear strength of greater than about 280 lbf/in, which
indicates resistance to failure caused by cancellous bone abrasion.
This property can also be characterized, e.g., by a Shore Hardness
value of less than about 100 A. This value indicates a degree of
elasticity, flexibility, and ductility.
[0047] Materials with a Taber Abrasion Resistance Value greater
than about 90 mg loss, or a Rotating Drum Abrasion Resistance Value
greater than about 70 mm3, or an Elmendorf tear strength value of
less than about 280 lbf/in, or a Shore Hardness value greater than
about 100 A are not well suited for expansion in cancellous bone,
because failure may occur prior to expansion to the desired
diameter.
[0048] B. Enhanced Expansion and Shape Properties
[0049] The expansion and shape properties just described can be
enhanced and further optimized for compacting cancellous bone by
selecting an elastomer material, which also possess the capability
of being preformed, i.e., to acquire a desired shape by exposure,
e.g., to heat and pressure, e.g., through the use of conventional
thermoforming or blow molding techniques. Candidate materials that
meet this criteria include polyurethane, silicone, thermoplastic
rubber, nylon, and thermoplastic elastomer materials. In a most
preferred embodiment, polyurethane material is used.
[0050] 1. Single Preformed Expandable Structures
[0051] In the embodiment shown in FIG. 4A, the structure 55
comprises an elongated tube 16 made from a polyurethane material.
The tube 15 possesses end regions 18 and 20, each having a first
diameter (designated D1 in FIG. 4A). The tube 16 further includes
an intermediate preformed region 22. The diameter of the preformed
intermediate region 22 has been enlarged by exposure to heat and
pressure to a normally expanded shape having an enlarged diameter
(designated D3 in FIG. 4A) greater than the first diameter D1. The
normally expanded shape D3 exists in an open air environment, prior
to placement inside an interior body region.
[0052] As FIG. 5 shows, the tube 16 is initially formed from
polyurethane (or another preferred) material, for example, by
standard polymer extrusion and molding processes. As FIGS. 5 and 7
show, the shaped region 22 is created by exposing the region 22 to
heat within a fixture or mold 10, while positive interior pressure
is applied to the tube 15 within the region 22. The fixture 10
includes a cavity 24, in which the region 22 rests while heat and
pressure are applied. The cavity 24 has a geometry that the region
22 is intended to assume when inflated with interior pressure in
the fixture 10. In the illustrated embodiment, a generally
spherical shape is envisioned.
[0053] The heat can be applied by coupling the cavity 24 to a
source 120 of heat energy of the fixture 10 itself (as FIG. 7
shows), or conveying a hot air stream or the equivalent into the
cavity 24. The temperature selected is that at which the tube
material will soften and form.
[0054] The range of temperatures in which softening occurs will
depend upon the particular composition of the polymeric material
used. For example, for polyurethane, the softening temperature lays
in the range of about 50.degree. C. to about 190.degree. C. An
operating range of softening temperatures for a given plastic
material can be empirically determined.
[0055] As FIG. 7 shows, while in a heat-softened state and confined
within the cavity 24, one end region 18 is coupled to a source 34
of pressurized fluid. The other end region 20 not coupled to the
source 34 is closed with a cap 122 or otherwise blocked to retain
pressurized fluid in the tube 16. Preferably, the pressurized fluid
is air or an inert gas, designated A in FIG. 7.
[0056] The magnitude of pressure will vary depending upon the wall
thickness and other physical characteristics of the elastomer
material used. The pressure must be less than the burst strength of
the tube material. Typically, air pressure in the range of 5 to
1000 D8i can be used.
[0057] The introduction of pressurized air A into the tube 16
causes the heat-softened region 22 to expand or billow outwardly in
the cavity 24, as FIG. 7 shows. The cavity 24 limits the extent to
which the heat-softened region 22 can expand. The region 22 will,
upon expansion, conform to the geometry of the cavity 24. The
extension of the heat-softened material in the cavity 24 uniformly
relieves material stress in the region 22, as the region 22
acquires a new expanded shape, having the enlarged diameter D3
shown in FIG. 4A.
[0058] The application of heat is terminated, and the region 22 is
allowed to cool, while pressurized fluid is applied to maintain the
enlarged diameter D3. The region 22 can be cooled by an ambient
external air flow, or by a pressurized stream of cooling air.
Alternatively, the cavity 24 can include interior passages through
which a cooling fluid can be circulated. The speed at which cooling
occurs affects the time of the overall process.
[0059] After cooling, the application of pressurized fluid is
terminated. The now preformed structure 56 is removed from the
cavity 24.
[0060] The normally expanded shape characteristics of the structure
55 can be achieved by other techniques. For example, the structure
56 can be formed by dipping, lost wax casting, or injection
molding.
[0061] Upon removal from the fixture 10, the structure 55 is
secured to the distal end 54 of the catheter tube 50. The structure
of the catheter tube 50 can vary and is not critical to the
invention per se. The materials for the catheter tube 50 are
selected to facilitate advancement of the structure 55 into an
interior body region. The catheter tube 50 can be constructed, for
example, using standard flexible, medical grade plastic materials,
like vinyl, nylon, polyethylenes, ionomer, polyurethane, and
polyethylene tetraphthalate (PET). The catheter tube 50 can also
include more rigid materials to impart greater stiffness and
thereby aid in its manipulation. More rigid materials that can be
used for this purpose include Kevlar.TM. material, PEBAX.TM.
material, stainless steel, nickel-titanium alloys (Nitinol.TM.
material), and other metal alloys.
[0062] In the illustrated embodiment (as best shown in FIG. 4A),
the catheter tube 50 includes an interior bore 50, in which an
auxiliary tube 58 is secured. It should be appreciated that the
catheter tube 50 can have more than a single interior lumen, and
can, e.g., have an array of multiple lumens. In the illustrated
embodiment, The auxiliary tube 58 extends through the interior bore
60 and beyond the distal end 54 of the catheter tube 50. One end
region 18 of the tube 16 is secured to the distal end 54 of the
catheter tube 50, while the other end region 20 is secured to the
free extended end 62 of the auxiliary tube 58. The end regions 18
and 20 can be secured, e.g., using adhesive or thermal bonding
processes.
[0063] By drawing a vacuum (i.e., negative pressure) inside the
structure 56, resident air volume is removed, and the diameter of
the region 22 is diminished from its normally expanded shape D3 to
a substantially collaD8ed, and not inflated diameter D2. The
collaD8ed diameter D2 is, due to forming during the heat and
pressure shaping process, still different than the extruded or
molded diameter D1. When substantially collaD8ed or not inflated,
the structure 56 exhibits a low profile, ideal for insertion into
the targeted cancellous bone region. The low profile can be further
reduced to aid insertion, if desired, by enclosing the structure 56
within a constricted introducing sleeve, or by coating the
structure 56 with a lubricious material, such as silicone, or
both.
[0064] As FIGS. 3 and 4 show, the interior bore 60 of the catheter
tube 50 can be coupled (via the fitting 122) to a source 68 of
fluid, for example, sterile saline, or a radiopaque contrast
medium, which permits x-ray visualization of the structure 56. The
interior bore 60 conveys the fluid into the region 22. The increase
of volume within the region up to a given threshold amount
(designated V(D3) in FIG. 10) will return the intermediate region
22 from the collaD8ed diameter D2 to the normal (i.e., enlarged,
but not distended) geometry, having the shape and diameter D3.
[0065] When in its normally enlarged shape D3, the material of the
structure 55 in the region 22 is not significantly stretched or
stressed, because it has been previously expanded in a
stress-relieved condition into this geometry in the cavity 24.
[0066] The magnitude of the radius of expansion (and thus diameter
D3) depends upon the relative increase in diameter in the region 22
brought about by exposure to heat and interior pressure within the
cavity 24. The relative increase between the extruded or molded
tube diameter D1 and diameter D3 should be at least 5% to provide
tube length and geometry of the segment when it expands beyond
diameter D3.
[0067] As FIG. 4B shows, due to expansion of heat-softened material
under pressure in the cavity 24, the wall thickness of the
structure 56 is not uniform. The region 22 has a minimum wall
thickness T3 when in its normally enlarged diameter D3, which is
less than the normal extruded or molded wall thickness (Tl) of the
tube 86.
[0068] Continued volume flow of pressurized fluid into the
structure 56 at the threshold pressure P(t) continues to increase
the interior volume of the structure 56. As its volume increases,
the shaped region 22 of the structure 56 continues to enlarge
beyond the normal diameter D3 toward a distended shape and
geometry, designated D4 in FIG. 4. The threshold pressure P(t)
stays generally constant as volume increases between D3 and D4. As
long as volume is controlled (i.e., so as not to substantially
exceed D4), there is no need for an external pressure regulator.
Volume expansion between D3 and D4 at a substantially constant
pressure occurs because of the material properties of the structure
56, and not because of some external pressure control
mechanism.
[0069] Enlargement of the structure in the region between D3 and D4
stretches the material in the region 22 beyond its stress-relieved
condition. Consequently, the wall thickness T4 at the distended
geometry D4 is less than the minimum wall thickness T3 of the
normally enlarged diameter D3. However, the distended geometry
generally maintains the preformed shape dictated by the cavity 24
(which, in the illustrated embodiment, is spherical).
[0070] In the expansion region between D3 and D4, the addition of
fluid volume at substantially constant P(t) stretches the material,
causing the radius of the structure 55 to increase and the wall
thickness to decrease. Material stress will increase.
[0071] While expanding in the region between D3 and D4, the
structure 56, when inside bone, assumes an increasingly larger
surface and volume, thereby compacting surrounding cancellous bone.
Inflation in cancellous bone may occur at the same threshold
pressure P(t) as outside bone. However, an increase in the
threshold inflation pressure P(t) inside bone may be required, due
to the density of the cancellous bone and resistance of the
cancellous bone to compaction. In this instance, the configuration
of the Pressure vs. Volume curve for a given material sand
structure 56 remains essentially the same as shown in FIG. 10,
except that the generally horizontal portion of the curve between
D3 and D4 is shifted upward on the Y-axis, as shown in phantom
lines in FIG. 10. As a general statement, the threshold pressure
inside bone is determined by the material property of the structure
56 and any added resistance due to the presence of cancellous
bone.
[0072] The distance between D3 and D4, along the x-axis of FIG. 10,
defines the degree to which the wall can elongate at a
substantially constant pressure condition and with increasing
material stress to compact cancellous bone, without failure. As
volume increases at the substantially constant threshold pressure
P(t), wall failure becomes more likely as the diameter of the
structure enlarges significantly further beyond the distended
diameter D4. There comes a point when the structure 56 can no
longer increase its volume as the material elasticity approaches
ultimate elongation, or as material stress approaches ultimate
tensile strength. When either of these ultimate values are reached,
wall failure is likely.
[0073] The distance between D3 and D4 in FIG. 10 during expansion
inside bone is a simultaneous expression of the three physical and
mechanical properties--expansion, shape, and toughness--described
above. For example, a material possessing the requisite elasticity
and shape, but lacking requisite toughness, but may fail short of
the shape D4 due to abrasion and tearing caused by cancellous
bone.
[0074] 2. Complex Preformed Expandable Structures
[0075] Sometimes it can be difficult to achieve a desired
uniformity and area of compaction within a given cancellous bone
region using a expandable body 56 having a single expandable region
22, such as shown in FIG. 4. FIG. 12 shows a complex preformed
structure 80 includes segmented expandable regions 82 and 84 spaced
along its length. The structure 80 provides a longer profile along
which volume can be increased.
[0076] The complex expandable structure 80 is created by extruding
or molding a tube 86 of polyurethane or elastomer material, like
the tube 16 shown in FIG. 5. In the preferred embodiment, the tube
86 is made of a polyurethane material. The tube has a normal
extruded wall thickness (T5) and a normal extruded outside diameter
(D5) (as shown in FIG. 12).
[0077] The segmented shaped regions 82 and 84 are created by
exposing an intermediate region 88 of the tube 86 to heat and
positive interior pressure inside a fixture or mold 90, as shown in
FIG. 13. In the illustrated embodiment, the fixture 90 possesses
two cavity regions 92 and 94 with an intermediate channel 96. The
intermediate region 88 is located in the cavities 92 and 94 and
channel 96.
[0078] The cavity regions 92 and 94 and the channel 95 are exposed
to a source of heat 120, to soften the material of the region 88.
When heat-softened (in the manner previously described), the
interior of the tube 86 is subjected to positive pressure from a
source 34 (as also previously described). The material in the
region 88 expands or extends within the cavities 92 and 94 and the
channel 96 Once cooled and removed from the fixture 90, the
structure 80 can be attached to the distal end of a catheter tube
50 in the same fashion as the structure 56 shown in FIGS. 3 and
4.
[0079] The structure 80 possesses, in an open air environment, a
normal expanded shape, having diameter D7 (shown in phantom lines
in FIG. 12). The normal shape and diameter D7 for the regions 82
and 84 generally correspond with the shape and dimension of the
cavities 92 and 94, respectively.
[0080] When an interior vacuum is drawn, removing air from the
structure 80, the structure 80 assumes a substantially collaD8ed,
and not inflated geometry, shown in phantom lines D6 in FIG. 12.
Due to the application of heat and pressure upon the region 88,
diameter D6 for each region 82 and 84 is larger than the normal
extruded or molded outside diameter D5 of the original extruded
tube 86.
[0081] The regions 82 and 84 are separated by a tubular neck 98,
which segments the structure 80 into two expandable regions 82 and
84. When substantially collaD8ed under vacuum or not inflated, the
structure 80 exhibits a low profile, ideal for insertion into the
targeted cancellous bone region.
[0082] The introduction of fluid volume back into the tube 86 will
cause each region 82 and 84 to return from the collapsed diameter
D5 back to the normal, enlarged, but not distended geometry, having
the shape and diameter shown in phantom lines D7 in FIG. 12.
[0083] In the illustrated embodiment, the first and second shaped
regions 82 and 84 have generally the same radius of expansion and
thus the same non-distended shape and diameter D7. Alternatively,
each region 82 and 84 can have a different radius of expansion, and
thus a different non-distended shape and diameter. Regardless, when
in the normal, non-distended diameter D7, the material of the
structure 80 in the region 88 is not significantly stretched or
stressed, because the regions 82 and 84 have been previously
expanded in a stress-relieved condition into this geometry in the
cavities 92 and 94.
[0084] As before explained in conjunction with the structure 56,
the regions 82 and 84 can be shaped by heat and interior pressure
within different cavities to assume different geometries, e.g.,
cylindrical or elliptical geometry, or a non-spherical,
non-cylindrical, or non-elliptical geometry, with either uniform or
complex curvature, and in either symmetric or asymmetric forms. Of
course, more than two segmented regions 82 and 84 can be formed
along the length of the tube 86.
[0085] Each shaped region 82 and 84 possesses a minimum wall
thickness (designed T7 in FIG. 12) when in the normally enlarged
but not distended geometry D7. Due to expansion of heat-softened
material under pressure in the cavities 92 and 94, the wall
thickness is not uniform, i.e., T7 is less than the normal extruded
or molded wall thickness T5 of the tube 85. The minimum wall
thicknesses T7 for the regions 82 and 84 can be the same or
different.
[0086] When in the enlarged, but not distended geometry, the neck
region 98 has an outside diameter (designated D9 in FIG. 14), which
is equal to or greater than the normal extruded or molded diameter
D5 of the tube 86. The size of the channel 96 in the fixture 90
determines the magnitude of the diameter D9. Due to expansion of
heat-softened material in the adjacent regions 82 and 84 under
pressure in the cavities 92 and 94, the neck region 98 (which
expands under pressure in the channel 96) has a wall thickness
(designated T9 in FIG. 12) which is less than or equal to the
normal extruded or molded wall thickness TE of the tube 86, but
still greater than the minimum wall thickness T7 of either fully
shaped region 82 or 84.
[0087] The formed complex structure 80 thus possesses regions of
non-uniform minimum wall thickness along its length; that is,
T5>T9>T7. The formed complex structure 80 also provides
multiple expandable regions 82 and 84 of the same or different
enlarged outside diameters (D7), segmented by a neck region 98, in
which D6>D5; D7>D6; and D7>D9.
[0088] By continuing to apply fluid volume at a constant pressure
at a threshold amount P(t), and thereby increasing the volume
within the structure 80, the shaped regions 82 and 84 of the
structure 80 will continue to enlarge beyond diameter D7 to a
distended shape and geometry, designated D8 in FIG. 12. The wall
thickness T7 further decreases and approaches T8. As the regions 82
and 84 approach diameter D8, the diameter D9 of the neck region 98
will likewise increase toward diameter D10, as FIG. 12 shows,
providing more uniform, elongated surface contact with cancellous
bone.
[0089] Enlargement of the structure 80 beyond diameter D7 stretches
the material in the regions 82, 84, and 98 beyond their
stress-relieved condition, although the distended geometry of the
regions 82 and 84 will, in important respects, maintain the
preformed shape dictated by the cavities 92 and 94. As before
explained in conjunction with the structure 55, the material in the
regions 82 and 84 has already been stress-relieved in the desired
shape at the normal diameter D7. As previously explained,
enlargement toward the distended diameter D8 occurs at
substantially constant pressure (as FIG. 10 exemplifies), and at
increasing material stress.
[0090] The degree of stretching at a substantially constant
incremental pressure condition can be tailored to achieve a
desired, fully distended diameter D8. The final, fully distended
diameter D8 can be selected to match the dimensions of the targeted
cancellous bone region. The controlled stretching of the segmented
regions 82 and 84 in tandem can provide an equal volume compression
of cancellous bone with a major diameter that is less than a single
non-segmented region (i.e., one without the neck region 98). Stated
another way, segmented regions 82 and 84, when expanded to a given
inflation volume, have a diameter less than a sphere expanded to an
equal inflation volume.
[0091] While expanding in the region between D7 and D8, the
structure 80, like the structure 56, when inside bone, assumes an
increasingly larger surface and volume, thereby compacting
surrounding cancellous bone. Inflation in cancellous bone may occur
at the same threshold pressure P(t) as outside bone. However, an
increase in the threshold inflation pressure P(t) inside bone may
be required, due to the density of the cancellous bone and
resistance of the cancellous bone to compaction.
[0092] 3. Composite Expandable Structures
[0093] In the previous embodiments, the material of the structure
56 or 80 is selected to integrate all desired physical and
mechanical requirements of expansion, shape, and toughness. FIG. 16
exemplifies a composite expandable structure 130, in which the
desired physical and mechanical requirements are segregated by the
use of different materials.
[0094] As shown in FIG. 15, the composite structure 130 includes an
inner expandable body 132 made of a first material that meets one
or more of the desired requirements of expansion and shape. The
composite structure 130 includes an outer expandable body or shell
134, which is made of a second material that meets the desired
requirement of toughness. The shell 134 encaD8ulates and protects
the inner expandable body 132 from surface abrasion, tearing, or
puncture due to contact with cancellous bone.
[0095] The shell 134 can comprise a material applied to the surface
of the inner body by various dipping, painting, or coating
techniques. Alternatively, the shell 134 can comprise a bag or
sock, into which the inner body 132 is placed prior to deployment.
The material for the shell 134 can comprise, e.g., rubber,
silicone, ethylene vinyl acetate, polyurethane, polyethylene, or
multi-filament woven material or fabric or other polymer
material.
[0096] The composite structure 130 makes it possible to isolate the
expansion and shape requirements from the toughness requirement A
material completely or partially failing to meet the toughness
requirement can nevertheless be used for the inner body 132 to
optimize the expansion and shape requirements of the structure 130.
The inner body 132 imparts its optimized expansion and shape
characteristics to cancellous bone, while the shell 134 imparts its
Optimized toughness characteristic to the overall composite
structure 130.
II. Deployment of Preformed Expandable Structures in Bone
[0097] The structure 56 or 80 or 130 can be inserted into bone in
accordance with the teachings of U.S. Pat. Nos. 4,969,888 and
5,108,404, which are incorporated herein by reference. As FIG. 8
shows, access can be accomplished, for example, by drilling an
access portal 64 through a side of the vertebral body 25. This is
called a postero-lateral approach. Alternatively, the access portal
can pass through either pedicle 42, which called a transpedicular
approach.
[0098] A guide sheath or cannula 66 placed into communication with
the access portal 64. The catheter tube 50 is advanced through the
cannula 65 to deploy the structure (FIG. 8 shows structure 55) into
contact with cancellous bone 32. The structure 56 is in its
normally collapsed and not inflated condition (shown as phantom
line diameter D2 in FIG. 8) during deployment. Access in this
fashion can be accomplished using a closed, minimally invasive
procedure or with an open procedure.
[0099] The materials for the catheter tube 50 are selected to
facilitate advancement of the expandable structure 56 into
cancellous bone 32. The catheter tube 50 can be constructed, for
example, using standard flexible, medical grade plastic materials,
like vinyl, nylon, polyethylenes, ionomer, polyurethane, and
polyethylene tetraphthalate (PET). The catheter tube 50 can also
include more rigid materials to impart greater stiffness and
thereby aid in its manipulation. More rigid materials that can be
used for this purpose include stainless steel, nickel-titanium
alloys (Nitinol.TM. material), and other metal alloys.
[0100] As FIG. 8 shows, expansion of the structure 56 to its
enlarged but not distended geometry (phantom line diameter D3 in
FIG. 8), and ultimately to its maximum distended geometry (diameter
D4 in FIG. 8) sequentially compresses cancellous bone 32 in the
vertebral body 26. The compression forms an interior cavity 70 in
the cancellous bone 32. As FIG. 9 shows, subsequent collaD8e and
removal of the structure 56 leaves the cavity 70 in a condition to
receive a filling material, e.g., bone cement. The bone cement,
when hardened, provides improved interior structural support for
cortical bone 32.
[0101] The compaction of cancellous bone 32 shown in FIG. 8 also
exerts interior force upon the surrounding cortical bone 28. The
interior force can elevate or push broken and compressed bone back
to or near its original prefracture, or other desired,
condition.
[0102] In the case of a vertebral body 26, deterioration of
cancellous bone 32 can cause the top and bottom plates (designated
TP and BP in FIG. 2) to compress or move closed together, reducing
the normal physiological height between the plates TP and BP. In
this circumstance, the interior force exerted by the structure 56
as it compacts cancellous bone 32 moves one or both of the top and
bottom plates TP and BP farther apart, to thereby restore a spacing
between them, which is at or close to the normal physiological
distance.
[0103] As shown in FIG. 11, in an alternative embodiment, a
stiffening member or stylet 74 can be inserted through a lumen 72
of the auxiliary tube 58, which is enclosed within the structure
56. The stylet 74 can be made, e.g., from stainless steel or molded
plastic material. The presence of the stylet 74 serves to keep the
structure 55 in the desired distally straightened condition during
passage through the guide sheath 66 into the targeted bone region,
as FIG. 8 shows.
[0104] As further shown in FIG. 11, the stylet 74 can have a
preformed memory, to normally bend its distal region. The memory is
overcome to straighten the stylet 14 when confined within the guide
sheath 56. However, as the structure 56 and preformed stylet 74
advance free of the guide sheath 66 and pass into the targeted
region, the preformed memory bends the stylet 74. The bending
stylet 74 bends the auxiliary tube 58 and thereby shifts the main
axis 78 of the surrounding expandable structure 56 relative to the
axis 78 of the access path (i.e., the guide sheath 66). The prebent
stylet 74, positioned within the interior of the structure 56, aids
in altering the orientation of the structure 56 within targeted
region. It is thereby possible to orient the structure 56 in a more
generally aligned relationship with the natural axes of the
vertebral body 25. A cavity 70, more centrally located within the
bone, e.g., a vertebral body 26, can be established, which provides
more uniform support across the mid region of the vertebral body 26
when filled with bone cement. The capability of the vertebral body
26 to withstand loads is thereby enhanced. The symmetric compaction
of cancellous bone 32 in the interior volume also exerts more equal
and uniform interior forces upon cortical bone 32, to elevate or
push broken and compressed bone.
[0105] There are times when a lesser amount of cancellous bone
compaction is indicated. For example, when the bone disease being
treated is localized, such as in avascular necrosis, or where local
loss of blood supply is killing bone in a limited area, an
expandable structure 56 or 80 or 130 can compact a smaller volume
of total bone. This is because the diseased area requiring
treatment is smaller.
[0106] Another exception lies in the use of an expandable structure
56 or 80 or 130 to improve insertion of solid materials in defined
shapes, like hydroxyapatite and components in total joint
replacement. In these cases, the structure shape and size is
defined by the shape and size of the material being inserted.
[0107] Yet another exception lies in the use of expandable
structures in bones to create cavities to aid in the delivery of
therapeutic substances, as disclosed in copending U.S. patent
application Ser. No. 08/485,394, previously mentioned. In this
case, the cancellous bone may or may not be diseased or adversely
affected. Healthy cancellous bone can be sacrificed by significant
compaction to improve the delivery of a drug or growth factor which
has an important therapeutic purpose. In this application, the size
of the expandable structure 55 or 80 or 130 is chosen by the
desired amount of therapeutic substance sought to be delivered. In
this case, the bone with the drug inside may need to be supported
by standard methods while the drug works and the bone heals.
III. Single Use
[0108] Distention of any one of the expandable structures 56 or 80
or 130 described herein during first use in a targeted body region
generates stress on the material or materials which make up the
structure. The material stress created by operational loads during
first use in a targeted body region can significantly alter the
preformed morphology of the structure, making future performance of
the structure unpredictable.
[0109] For example, expansion within bone during a single use
creates contact with surrounding cortical and cancellous bone.
Regardless of the superior mechanical properties of material, this
contact can in time damage the structure, creating localized
regions of weakness, which may escape detection. Localized areas of
lower density cancellous bone may result in creating areas of
differential expansion and stress on the structure. The existence
of localized regions of weakness or differential stress can
unpredictably cause overall structural failure during a subsequent
use.
[0110] In addition, exposure to blood and tissue during a single
use can entrap biological components on or within the structure or
the associated catheter tube. Despite cleaning and subsequent
sterilization, the presence of entrapped biological components can
lead to unacceptable pyrogenic reactions.
[0111] As a result, following first use, the structure cannot be
consistently relied upon to reach its desired configuration during
subsequent use and may not otherwise meet established performance
and sterilization specifications. The effects of material stress
and damage caused during a single use, coupled with the possibility
of pyrogen reactions--even after resterilization, reasonably
justify imposing a single use restriction upon devices which carry
these expandable structures for deployment in bone.
[0112] To protect patients from the potential adverse consequences
occasioned by multiple use, which include disease transmission, or
material stress and instability, or decreased or unpredictable
performance, the invention also provides a kit 100 (see FIGS. 14
and 15) for storing a single use tool 48 (also shown in FIG. 3)
prior to use. As shown in FIG. 14, the tool 48 carries an
expandable structure. FIG. 14 shows for the purpose of illustration
the structure 56, as described herein. It should be appreciated
that the tool 48 could carry an expandable structure 80 or 130, as
also previously described.
[0113] In the illustrated embodiment (see FIGS. 14 and 15), the kit
100 includes an interior tray 108. The tray 108 holds the tool 48
in a lay-flat, straightened condition during sterilization and
storage prior to its first use. The tray 108 can be formed from die
cut cardboard or thermoformed plastic material. The tray 108
includes one or more spaced apart tabs 110, which hold the catheter
tube 50 and expandable structure 55 in the desired lay-flat,
straightened condition.
[0114] The kit 100 includes an inner wrap 112, which is
peripherally sealed by heat or the like, to enclose the tray 108
from contact with the outside environment. One end of the inner
wrap 112 includes a conventional peal-away seal 114, to provide
quick access to the tray 108 upon instance of use, which preferably
occurs in a sterile environment, such as within an operating
room.
[0115] The kit 100 also includes an outer wrap 116, which is also
peripherally sealed by heat or the like, to enclosed the inner wrap
112. One end of the outer wrap 116 includes a conventional
peal-away seal 118, to provide access to the inner wrap 112, which
can be removed from the outer wrap 116 in anticipation of imminent
use of the probe 102, without compromising sterility of the probe
102 itself.
[0116] Both inner and outer wraps 112 and 116 (see FIG. 15) each
includes a peripherally sealed top sheet 120 and bottom sheet 122.
In the illustrated embodiment, the top sheet 120 is made of
transparent plastic film, like polyethylene or MYLAR.TM. material,
to allow visual identification of the contents of the kit 100. The
bottom sheet 122 is made from a material that is permeable to ETO
sterilization gas, e.g., TYVEK.TM. plastic material (available from
Dupont).
[0117] The sterile kit 100 also carries a label or insert 106,
which includes the statement "For Single Patient Use Only" (or
comparable language) to affirmatively caution against reuse of the
contents of the kit 100. The label 106 also preferably
affirmatively instructs against resterilization of the tool 48. The
label 105 also preferably instructs the physician or user to
dispose of the tool 48 and the entire contents of the kit 100 upon
use in accordance with applicable biological waste procedures. The
presence of the probe 102 packaged in the kit 100 verifies to the
physician or user that tool 48 is sterile and has not been
subjected to prior use. The physician or user is thereby assured
that the expandable structure 55 meets established performance and
sterility specifications, and will have the desired configuration
when expanded for use.
[0118] The label 106 preferably also instructs the physician as to
the use of the expandable structure 56 (or 80 or 130) for
compacting cancellous bone in the manners previously described. For
example, the label 105 instructs the physician to expand the
structure inside bone to compact cancellous bone and form a cavity.
The label 106 can also instruct the physician to fill the cavity
with a material, e.g., bone cement, allograft material, synthetic
bone substitute, a medication, or a flowable material that sets to
a hardened condition.
[0119] The features of the invention are set forth in the following
claims.
* * * * *