U.S. patent application number 12/795914 was filed with the patent office on 2010-09-23 for tissue cavitation device and method.
Invention is credited to Lance Middleton, Laura Middleton.
Application Number | 20100241123 12/795914 |
Document ID | / |
Family ID | 25358709 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100241123 |
Kind Code |
A1 |
Middleton; Lance ; et
al. |
September 23, 2010 |
Tissue Cavitation Device and Method
Abstract
A percutaneous surgical device and method for creating a cavity
within tissue during a minimally invasive procedure. A cavitation
device includes a shaft interconnected to a flexible cutting
element. A flexible cutting element has a first shape suitable for
minimally invasive passage into tissue. The flexible cutting
element has a means to move toward a second shape suitable for
forming a cavity in tissue. When used in bone, the resulting cavity
is usually filled with bone cement or suitable bone replacement
material that is injectable and hardens in situ. The disclosed
cavitation device and methods can be used for the following
applications: (1) treatment or prevention of bone fracture, (2)
joint fusion, (3) implant fixation, (4) tissue harvesting
(especially bone), (5) removal of diseased tissue (hard or soft
tissue), and (6) general tissue removal (hard or soft tissue).
Inventors: |
Middleton; Lance; (Soddy
Daisy, TN) ; Middleton; Laura; (Soddy Daisy,
TN) |
Correspondence
Address: |
FROST BROWN TODD, LLC
2200 PNC CENTER, 201 E. FIFTH STREET
CINCINNATI
OH
45202
US
|
Family ID: |
25358709 |
Appl. No.: |
12/795914 |
Filed: |
June 8, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10818452 |
Apr 5, 2004 |
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12795914 |
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09872042 |
Jun 1, 2001 |
6746451 |
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10818452 |
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Current U.S.
Class: |
606/79 ;
606/92 |
Current CPC
Class: |
A61B 2017/00261
20130101; A61B 17/1668 20130101; A61B 17/1617 20130101; A61B
17/1664 20130101; A61B 17/1671 20130101; A61B 17/8802 20130101;
A61B 17/1635 20130101 |
Class at
Publication: |
606/79 ;
606/92 |
International
Class: |
A61B 17/00 20060101
A61B017/00; A61B 17/58 20060101 A61B017/58 |
Claims
1. A method for treating bone comprising the steps of: forming a
passage in bone; creating a cavity by cutting bone, wherein the
cavity formed by cutting bone is generally spherical and has a
larger diameter than the passage; and expanding the volume of the
cavity by expanding a device within the cavity, thereby reducing a
fracture.
2. The method of claim 1 further comprising the step of filling the
cavity with a material.
3. The method of claim 2, wherein the material is selected from the
group consisting of implant, in-situ curable material, and in situ
hardenable material.
4. The method of claim 2, wherein the material fills the cavity
fully or partially.
5. The method of claim 1, wherein the device is positioned
proximate to cortical bone.
6. The method of claim 1, wherein the device is a medical
balloon.
7. The method of claim 1, wherein the bone is a vertebra.
8. The method of claim 1, wherein the step of separating creating
the cavity by cutting bone uses a tissue cavitation device.
9. A method of reducing a fracture comprising the steps of: forming
a passage in bone; providing a tissue cavitation device, wherein
the tissue cavitation device comprises a deformable cutting
element; separating a portion of bone about the passage with by
rotating the deformable cutting element of the tissue cavitation
device to create a cavity, wherein the diameter of the cavity is
larger than the diameter of the passage; and expanding the volume
of the cavity, thereby reducing the fracture.
10. The method of claim 9, further comprising the step of filling
the cavity with a material selected from the group consisting of
implant material, in-situ curable material, and in situ hardenable
material.
11. The method of claim 9, wherein the step of expanding uses an
expanding device that enlarges the size of the cavity.
12. The method of claim 11, wherein the step of expanding the
volume of the cavity is performed with a medical balloon.
13. The method of claim 9, wherein the tissue cavitation device
comprises a first shape for minimally invasive passage into tissue
and a second shape suitable for forming the cavity.
14. The method of claim 10, wherein the material fills the cavity
fully or partially.
15. The method of claim 10, wherein the material is selected from
the group consisting of permanent, resorbable, penetrating, and
combinations thereof.
16. A method of reducing a fracture comprising the steps of:
forming a passage in bone using a first device along a linear axis;
separating a portion of bone using by rotating a second device to
create a cavity, wherein the cavity is substantially coincident
with the linear axis and has a non-uniform diameter; and expanding
the volume of the cavity with a third device, thereby reducing the
fracture.
17. The method of claim 15, wherein the passage is selected from
the group consisting of intracortical, extracortical,
intrapedicular, extrapedicular, and combinations thereof.
18. The method of claim 15, wherein the second device is a tissue
cavitation device.
19. The method of claim 15, wherein the third device is a medical
balloon.
20. The method of claim 15, further comprising the step of filling
the cavity with a material, wherein the material fills the cavity
fully or partially and is selected from the group consisting of
permanent, resorbable, penetrating, and combinations thereof.
Description
PRIORITY
[0001] The application claims priority to and is a continuation of
U.S. Non-Provisional patent application Ser. No. 10/818,452,
entitled "Tissue Cavitation Device and Method," filed Apr. 5, 2004,
which is a continuation of U.S. Non-Provisional patent application
Ser. No. 09/872,042, entitled "Tissue Cavitation Device and
Method", filed Jun. 1, 2001, now U.S. Pat. No. 6,746,451, the
disclosures of which are herein incorporated by reference in their
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to surgical devices
and methods and, more particularly, to minimally invasive surgical
devices and methods for creating a cavity within hard or soft
tissue.
BACKGROUND OF THE INVENTION
[0003] Surgeons are using minimally invasive surgical techniques on
an increasing basis for the treatment of a wide variety of medical
conditions. Such techniques typically involve the insertion of a
surgical device through a natural body orifice or through a
relatively small incision using a tube or cannula. In contrast,
conventional surgical techniques, typically involve a significantly
larger incision and are therefore sometimes referred to as open
surgery. Thus, as compared with conventional techniques, minimally
invasive surgical techniques offer the advantages of minimizing
trauma to healthy tissue, minimizing blood loss, reducing the risk
of complications such as infection, and reducing recovery time.
Further, certain minimally invasive surgical techniques can be
performed under local anesthesia or even, in some cases, without
anesthesia, and therefore enable surgeons to treat patients who
would not tolerate the general anesthesia required by conventional
techniques.
[0004] Surgical procedures often require the formation of a cavity
within either soft or hard tissue, including bone. Tissue cavities
are formed for a wide variety of reasons, such as for the removal
of diseased tissue, for harvesting tissue in connection with a
biopsy or autogenous transplant, and for implant fixation. To
achieve the benefits associated with minimally invasive techniques,
tissue cavities should be formed by creating only a relatively
small access opening in the target tissue. An instrument or device
can then be inserted through the opening and used to form a hollow
cavity that is significantly larger than the access opening.
Depending on the specific application, the shape of the desired
cavity can be spherical, hemispherical, cylindrical, or any number
of different combinations or variations of such shapes.
[0005] One important surgical application requiring the formation
of a cavity within tissue is the surgical treatment and prevention
of skeletal fractures associated with osteoporosis, which is a
metabolic disease characterized by a decrease in bone mass and
strength. The disease leads to skeletal fractures under light to
moderate trauma and, in its advanced state, can lead to fractures
under normal physiologic loading conditions. It is estimated that
osteoporosis affects approximately 15-20 million people in the
United States and that approximately 1.3 million new fractures each
year are associated with osteoporosis, with the most common
fracture sites being the hip, wrist and vertebrae.
[0006] An emerging prophylactic treatment for osteoporosis involves
replacing weakened bone with a stronger synthetic bone substitute
using minimally invasive surgical procedures. The weakened bone is
first surgically removed from the affected site, thereby forming a
cavity. The cavity is then filled with an injectable synthetic bone
substitute and allowed to harden. The synthetic bone substitute
provides structural reinforcement and thus lessens the risk of
fracture of the affected bone. Without the availability of
minimally invasive surgical procedures, however, the prophylactic
fixation of osteoporosis-weakened bone in this manner would not be
practical because of the increased morbidity, blood loss and risk
of complications associated with conventional procedures. Moreover,
minimally invasive techniques tend to preserve more of the
remaining structural integrity of the bone because they minimize
surgical trama to healthy tissue.
[0007] Other less common conditions in which structural
reinforcement of bone can be appropriate include bone cancer and
avascular necrosis. Surgical treatment for each of these conditions
can involve removal of the diseased tissue by creating a tissue
cavity and filling the cavity with a stronger synthetic bone
substitute to provide structural reinforcement to the affected
bone.
[0008] Existing devices for forming a cavity within soft or hard
tissue are relatively complex assemblies consisting of multiple
components. U.S. Pat. No. 5,445,639 to Kuslich et al. discloses an
intervertebral reamer for use in fusing contiguous vertebra. The
Kuslich et al. device comprises a cylindrical shaft containing a
mechanical mechanism that causes cutting blades to extend axially
from the shaft to cut a tissue cavity as the shaft is rotated. The
shaft of the Kuslich et al. device, however, has a relatively large
diameter in order to house the blade extension mechanism, and
therefore it is necessary to create a relatively large access
opening to insert the device into the body. The complexity of the
device leads to increased manufacturing costs and may also raise
concerns regarding the potential for malfunction.
[0009] U.S. Pat. No. 5,928,239 to Mirza discloses a percutaneous
surgical cavitation device and method useful for forming a tissue
cavity in minimally invasive surgery. The Mirza device comprises an
elongated shaft and a separate cutting tip that is connected to one
end of the shaft by a freely-rotating hinge, as shown in FIG. 1
hereto. The cutting tip of the Mirza device rotates outward about
the hinge, thereby permitting the device to cut a tissue cavity
that is larger than the diameter of the shaft. However, the Mirza
device relies on rotation of the shaft at speeds ranging from
40,000 to 80,000 rpm to cause the cutting tip to rotate outward
about the hinge. Such high rotational speeds can only be produced
by a powered surgical drill and certainly cannot be produced by
manual rotation. Thus, the Mirza device does not permit the surgeon
to exercise the precise control that can be attained through manual
rotation. Moreover, there may be a concern for structural failure
or loosening of the relatively small hinge assembly at such a high
rotational speed when operated in bone. The high rotational speed
of the Mirza device may also generate excessive heat that could
damage healthy tissue surrounding the cavity.
[0010] U.S. Pat. No. 6,066,154 to Reiley et al. discloses an
inflatable, balloon-like device for forming a cavity within tissue.
The Reiley et al. device is inserted into the tissue and then
inflated to form the cavity by compressing surrounding tissue,
rather than by cutting away tissue. The Reiley et al. device,
however, is not intended to cut tissue, and at least a small cavity
must therefore be cut or otherwise formed in the tissue in order to
initially insert the Reiley et al. device.
[0011] Thus, a need continues to exist for a tissue cavitation
device and method that can form tissue cavities of various shapes
that are significantly larger than the access opening in the target
tissue. A need also exists for a cavitation device that is of
relatively simple construction and inexpensive to manufacture, that
can be operated either manually or by a powered surgical drill, and
that, in the case of manual operation, provides the surgeon with
increased control over the size and shape of the cavity formed.
SUMMARY OF THE INVENTION
[0012] The present invention comprises an improved tissue
cavitation device and method that utilizes shape-changing behavior
to form cavities in either hard or soft tissue. The shape-changing
behavior enables the device to be inserted into tissue through a
relatively small access opening, yet also enables the device to
form a tissue cavity having a diameter larger than the diameter of
the access opening. Thus, the invention is particularly useful in
minimally invasive surgery, and can be used for at least the
following specific applications, among others: (1) treatment or
prevention of bone fracture, (2) joint fusion, (3) implant
fixation, (4) tissue harvesting (especially bone), (5) removal of
diseased tissue (hard or soft tissue), and (6) general tissue
removal (hard or soft tissue).
[0013] The cavitation device of the present invention comprises a
rotatable shaft having a flexible cutting element that is adapted
to move between a first shape and a second shape during the process
of forming an internal cavity within tissue. The process of forming
the cavity primarily involves cutting tissue as the shaft is
rotated about its longitudinal axis, but those skilled in the art
will appreciate that the device also can form a cavity by impacting
tissue or displacing tissue as the shaft is either partially or
completely rotated. The internal cavity formed by the device has a
significantly larger diameter than the diameter of the initial
opening used to insert the device into the tissue. The present
invention also comprises flexing means for biasing the flexible
cutting element to move from its first shape to its second shape.
One such means comprises spring bias arising from elastic
deformation of the flexible cutting element. A second such means
comprises bias arising from the behavior of a thermal shape-memory
alloy. A third such means comprises bias arising from centrifugal
force generated as the shaft is rotated. A fourth such means
comprises a tension cable that forcefully actuates the shape change
of the flexible cutting element. The device of the invention can be
operated by conventional surgical drills, and some embodiments also
can be manually operated using a conventional T-handle. When a
T-handle is used to operate the device, the T-handle also can be
adapted to apply tension to the tension cable.
[0014] During minimally invasive surgery, the flexible cutting
element of the cavitation device can be adapted to assume a first
shape for insertion of the device into tissue through a tube placed
percutaneously, thereby creating only a relatively small access
opening in the tissue. Depending on the application and size, the
insertion tube can be a trochar, a cannula, or a needle. As the
device is inserted beyond the distal end of the insertion tube, the
flexible cutting element is adapted to assume a second shape for
forming a cavity in tissue upon rotation of the shaft. When it
assumes the second shape, the flexible cutting element extends or
projects away from the longitudinal axis of the shaft. Thus, the
diameter of the cavity is greater than the diameter of the initial
access opening or pilot hole. In addition to cutting, a flexible
cutting element is capable of displacing and impacting tissue away
from the axis of the shaft.
[0015] According to one method of the present invention, the
periphery of the target tissue, such as bone, can be accessed with
an insertion tube placed percutaneously, and a pilot hole can be
formed in the bone with a standard surgical drill and drill bit.
Next, the cavitation device of the present invention is inserted to
the depth of the pilot hole and rotated. As the flexible cutting
element of the device moves from its first shape to its second
shape, portions of the cutting element forcefully extend away from
the longitudinal axis of the shaft, thereby forming a tissue
cavity. Emulsified bone can be removed through known irrigation and
suction methods. In the case of bone harvesting, the abated bone is
used at another surgical site to promote healing of a bony deficit
or to promote joint fusion. The cavity can then be filled with a
suitable bone substitute that is injectable and hardens in situ. In
the case of removing and replacing osteoporotic bone, the cavity is
filled with structural synthetic bone or bone cement. Since the
device and methods of the present invention are minimally invasive,
they can be used for the prevention of osteoporosis related
fractures in individuals at high risk. Skeletal structures where
osteoporosis related fractures are common include the radius,
femur, and vertebral bodies.
[0016] Surgeons can create cavities of various shapes and sizes
with the device and methods of the present invention. For example,
cavities of various shapes and sizes can be formed by moving the
cavitation device along its axis of rotation or transverse to its
axis of rotation. The size and shape of the cavity also can be
modified by adjusting the insertion angle of the shaft (or the
insertion tube, if one is used) with respect to the tissue angle.
Tissue cavities of various shapes and sizes also can be
interconnected to form more complex shapes.
[0017] The objects and advantages of the present invention include
simplicity, wherein a flexible cutting element eliminates the need
for complex assemblies with numerous moving parts. The
shape-changing behavior of the flexible cutting element enables the
device to be adapted to a shape suitable for minimally invasive
placement in tissue. The inherent outward forces associated with
the shape change of the flexible cutting element assist in the
cutting and displacement of tissue during the process of forming a
cavity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a sectional view of the proximal end of the human
femur and shows the prior art cavitation device disclosed in U.S.
Pat. No. 5,928,239 to Mirza.
[0019] FIG. 2A is a perspective view showing a cavitation device of
the present invention attached to a surgical drill. FIG. 2B is a
detailed view of the distal end of the device depicted in FIG. 2A
and shows a flexible cutting element.
[0020] FIGS. 3A to 3 C are perspective views showing a first
embodiment of the cavitation device of the present invention.
[0021] FIGS. 4A to 4 C are perspective views showing a second
embodiment of the cavitation device of the present invention.
[0022] FIGS. 5A and 5B are perspective views showing a cavitation
device of the present invention having serrations, cutting flutes
and an irrigation passage as additional features.
[0023] FIG. 6 is a perspective view showing a third embodiment of
the cavitation device of the present invention.
[0024] FIGS. 7A and 7B are perspective views showing a fourth
embodiment of the cavitation device of the present invention.
[0025] FIG. 8A is a perspective view showing a fifth embodiment of
the cavitation device of the present invention. FIG. 8B is a
sectional view of the device shown in FIG. 8A.
[0026] FIGS. 9A and 9B are perspective views showing a sixth
embodiment of the cavitation device of the present invention.
[0027] FIG. 10A is a perspective view showing a seventh embodiment
of the cavitation device of the present invention attached to a
T-handle. FIG. 10B is a detailed view showing the flexible cutting
element of the device shown in FIG. 10A.
[0028] FIGS. 11A to 11F are sectional views depicting the method of
using the present invention to form a cavity in bone and filling
the cavity with a bone substitute material.
[0029] FIG. 12A is a sectional view of the proximal end of the
human femur showing a cavitation device of the present invention
creating a cavity to remove osteoporotic bone.
[0030] FIG. 12B shows the cavity of FIG. 12A filled with a
synthetic bone substitute to strengthen the femur.
[0031] FIG. 13A is a schematic sectional view showing a cavitation
device of the present invention creating a cavity between spinal
vertebral bodies. FIG. 13B shows the cavity of FIG. 13A filled with
synthetic bone material to achieve joint fusion.
[0032] FIG. 14A is a sectional view showing a cavitation device of
the present invention creating a generally hemispherical cavity
within osteoporotic bone. FIG. 14B shows the cavity of FIG. 14A
filled with a synthetic bone substitute to strengthen the
attachment of a bone screw.
[0033] FIG. 15 shows a schematic representation of the human pelvis
and the cavitation device of the present invention harvesting bone
from the iliac crest by minimally invasive surgical techniques.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Throughout the following description and the drawings, like
reference numerals are used to identify like parts of the present
invention. FIG. 2A shows a cavitation device 100 of the present
invention attached to a surgical drill 12. Surgical drill 12 is
battery powered and is shown to illustrate one possible means of
operation. There are numerous other options for either powered or
manual operation of cavitation device 100. For powered operation,
the device can be used with a variety of readily available surgical
drills that are pneumatic or electric, such as drills manufactured
by Mathys International, Ltd. For manual operation, the shaft of
the device can be connected to a conventional T-handle, which is a
surgical device that is well known to those skilled in the art. A
supplier of a multi-purpose T-handle is Beere Precision Medical
Instruments.
[0035] As shown in FIG. 2B, cavitation device 100 comprises a
rotatable shaft 110, a flexible cutting element 120, and a cutting
tip 130. Rotatable shaft 110 has a longitudinal axis 111 and
preferably has a generally circular cross-section, but other
cross-sections, such as a generally square cross-section, are
within the scope of the invention. The diameter of rotatable shaft
110 is typically within a range of about 3 to 8 millimeters for
minimally invasive surgery. However, other diameters outside this
range also are within the scope of the invention. Flexible cutting
element 120 is disposed at one of the two ends of rotatable shaft
110 and is preferably formed from the same piece of material as
rotatable shaft 110 for added strength and durability. Those
skilled in the art will appreciate that the integrally formed
construction of rotatable shaft 110 and flexible cutting element
120 also reduces manufacturing costs. Flexible cutting element 120
has a free end 121 and a relatively thin, rectangular
cross-section. Thus, flexible cutting element 120 is consistent
with a machine element known as a leaf spring and also is
consistent with a structural element known as a cantilever beam.
Because of this configuration, flexible cutting element 120 is
adapted to flex between a first shape 122, in which flexible
cutting element 120 is substantially colinear with the longitudinal
axis 111 of rotatable shaft 110, and a second shape 123, in which
flexible cutting element 120 extends or projects away from
longitudinal axis 111 in the general shape of a curvilinear arc, as
shown in FIG. 2B.
[0036] FIGS. 3A to 3 C further illustrate the shape-changing
behavior of cavitation device 100. As shown in FIG. 3A, when
flexible cutting element 120 is in its initial, undeformed state
(i.e., spring unloaded), it extends or projects away from
longitudinal axis 111 of rotatable shaft 110. However, as shown in
FIG. 3B, cavitation device 100 is dimensioned to pass
telescopically through the interior of an insertion tube 14.
Depending on the particular surgical application, insertion tube 14
can be a trochar, a cannula, or a needle. As cavitation device 100
is placed within insertion tube 14, flexible cutting element 120
experiences elastic deformation (i.e., spring loaded) and assumes
first shape 122, in which flexible cutting element 120 is
substantially colinear with longitudinal axis 111. Cutting tip 130
helps to keep flexible cutting element 120 aligned within insertion
tube 14 as it is passed telescopically through insertion tube 14.
Referring now to FIG. 3C, as flexible cutting element 120 extends
past the distal end 15 of insertion tube 14, flexing means, which
in this embodiment is spring bias arising from elastic deformation,
tends to move flexible cutting element 120 from first shape 122
toward second shape 123. Consistent with spring mechanics, flexible
cutting element 120 seeks to return to second shape 123 because it
is a spring unloaded configuration. By reversing the insertion
process, cavitation device 100 can be removed through the insertion
tube 14.
[0037] Cavitation device 100 can be constructed from a wide
spectrum of surgical-grade stainless steels capable of elastic
behavior. Consistent with spring mechanics, it is preferred to have
the shape change of flexible cutting element 120 operate within the
elastic range of the material. Stainless steels are strong,
relatively inexpensive, and their manufacturing processes are well
understood. Another suitable material is the metal alloy Nitinol
(TiNi), a biomaterial capable of superelastic mechanical behavior,
meaning that it can recover from significantly greater deformation
compared to most other metal alloys. The Nitinol metal alloy
contains almost equal parts of titanium and nickel. Nitinol has a
"spring-back" potential ten times greater than stainless steels and
is capable of nearly full recovery from 8% strain levels. Suppliers
of Nitinol include Shape Memory Applications, Inc. and Nitinol
Devices & Components. Alternatively, cavitation device 100 can
be constructed from a polymer, such as nylon or ultra high
molecular weight polyethylene.
[0038] A thermal shape-memory alloy can also be used as a flexing
means for biasing a flexible cutting element to move from a first
shape to a second shape. The most commonly used biomaterial with
thermal shape-memory properties is the Nitinol metal alloy. A
flexible cutting element made from Nitinol can be deformed below a
transformation temperature to a shape suitable for percutaneous
placement into tissue. The reversal of deformation is observed when
the flexible cutting element is heated through the transformation
temperature. The applied heat can be from the surrounding tissue,
or associated with frictional heat generated during operation.
Nitinol is capable of a wide range of shape-memory transformation
temperatures appropriate for the clinical setting, including a
transformation temperature at body temperature of 37.degree. C.
Heat may also be applied by passing electrical current through the
material to cause resistive heating.
[0039] FIGS. 4A to 4C show a second embodiment of the present
invention, cavitation device 200, comprising rotatable shaft 210
and a flexible cutting element 220 having a free end 221 and a
cutting tip 230. Flexible cutting element 220 is formed from a
material, such as Nitinol, which is capable of shape change arising
from thermal shape-memory behavior. Rotatable shaft 210 has a
longitudinal axis 211. FIG. 4A shows cavitation device 200 at rest,
with flexible cutting element 220 deformed below the transformation
temperature to a first shape 222 in which flexible cutting element
220 is substantially colinear with longitudinal axis 211. When
flexible cutting element 220 is in first shape 222, cavitation
device 200 can be easily passed telescopically through the interior
of an insertion tube 14, as shown in FIG. 4B. Referring now to FIG.
4C, as flexible cutting element 220 extends past distal end 15 of
insertion tube 14, applied heat 24 activates the thermal
shape-memory properties of flexible cutting element 220. Applied
heat 24 can be body heat from the patient or operational heat, such
as heat generated from friction. Flexible cutting element 220 has a
bias toward a "remembered" second shape 223, in which flexible
cutting element 220 extends or projects away from longitudinal axis
211 of rotatable shaft 210 in the general shape of a curvilinear
arc, as shown in FIG. 4C. Elastic properties of flexible cutting
element 220 allow removal of cavitation device 200 through the
insertion tube 14.
[0040] It may be advantageous to add additional features to enhance
the performance of a cavitation device of the present invention and
to enhance the process of cavity creation or tissue removal.
Numerous secondary features to aid in tissue cutting include
serrated edges, threads, cutting flutes, abrasive surfaces, and
beveled edges. Variations and different combinations are possible
without departing from the spirit of the present invention.
Referring now to FIGS. 5A and 5B, cavitation device 300 can
comprise serrations 350 to aid in tissue cutting. Similarly,
cutting tip 330 can comprise a cutting flute 360 to aid in tissue
cutting. Cavitation device 300 also can comprise an irrigation
passage 340, which serves as a conduit for tissue irrigation and
removal through rotatable shaft 310.
[0041] Geometric variations, within the spirit of the present
invention, may be developed to enhance or alter the performance of
the dynamic shape behavior. Examples of such variations include the
cross-sectional shape and the length of a flexible cutting element.
For example, the cross-sectional shape of the flexible cutting
element can form a quadrilateral so that the edges formed from the
acute angles of the quadrilateral are adapted to aid in cutting. A
quadrilateral cross-section with a particularly acute angle can
form a knife-edge. Persons skilled in the art will understand that
a flexible cutting element with a quadrilateral cross-section and a
beveled edge would have a substantially quadrilateral cross-section
and that a rectangular cross-section is a substantially
quadrilateral cross-section. Further, the curvature of a flexible
cutting element in the extended position may take a specific shape;
therefore the shape of the tissue cavity need not be limited to
combinations of cylindrical and hemispherical tissue cavities.
Different tissue cavity shapes may be desirable for interfacing
with an implant or to create a region of synthetic bone to match
complex anatomical structures. In addition, a plurality of flexible
cutting elements can be used, rather than a single flexible cutting
element. As an example, FIG. 6 shows a third embodiment of the
present invention, cavitation device 400, comprising a rotatable
shaft 410 having longitudinal axis 411. Cavitation device 400
further comprises flexible cutting element 420 which has a
generally a circular cross-section. Further, as shown in FIG. 7A, a
fourth embodiment of the invention, cavitation device 500,
comprises a rotatable shaft 510 and a plurality of flexible cutting
elements 520. FIG. 7A shows cavitation device 500 with flexible
cutting elements 520 substantially colinear with longitudinal axis
511 of rotatable shaft 510, consistent with a first shape suitable
for minimally invasive placement within tissue. Referring now to
FIG. 7B, flexible cutting elements 520 are shown in a second shape,
in which portions of flexible cutting elements 520 extend or
project away from longitudinal axis 511. Note that flexible cutting
elements 520 form a closed loop that can take a specific shape if
required.
[0042] Another flexing means for biasing a flexible cutting element
to move from a first shape toward a second shape is centrifugal
force arising from rotational velocity of the shaft. Centrifugal
force is the force that tends to impel a thing or parts of a thing
outward from a center of rotation. FIG. 8A shows a fifth embodiment
of the invention, cavitation device 600, comprising rotatable shaft
610 with longitudinal axis 611 and flexible cutting element 620
having a cutting tip 630 and cutting flutes 632. Flexible cutting
element 620 has a generally circular cross-section. FIG. 8B shows
the cross-section of flexible cutting element 620 at the distal end
of shaft 610 and illustrates that flexible cutting element 620 is a
standard cable structure with a uniform helical arrangement of
wires 622 concentrically stranded together. This type of cable
structure has high strength and high flexibility. In additional,
the cable structure has a naturally abrasive quality to aid in
tissue cutting. Continuing to refer to FIG. 8B, flexible cutting
element 620 is shown offset from longitudinal axis 611 to further
encourage outward movement of the flexible cutting element 620
under the influence of centrifugal forces that arise when shaft 610
is rotated at sufficient velocity. Surgical cable made from
stainless steel or titanium alloy is readily available. It is
preferred that cavitation device 600 be driven by a pneumatic
surgical drill capable of rotational velocity greater than about
5,000 revolutions per minute.
[0043] A sixth embodiment of the present invention, cavitation
device 700, is shown in FIGS. 9A and 9B. Referring to FIG. 9A, a
plurality of flexible cutting elements 720 are generally colinear
with the rotatable shaft 710 to form a first shape suitable for
minimally invasive placement of the device within tissue. The
proximal ends of flexible cutting elements 720 are rigidly attached
to rotatable shaft 710, and the distal ends of the flexible cutting
elements 720 are attached to a spindle 730. Referring now to FIG.
9B, when cavitation device 700 is rotated at a sufficient
rotational velocity, flexible cutting elements 720 have a tendency
to bow outward under the influence of centrifugal force. In this
embodiment, the operator can also advance rotatable shaft 710
toward spindle 730 to assist in moving the flexible cutting
elements 720 from the first shape toward a second shape, in which
the flexible cutting elements extend outwardly from the axis of
rotation.
[0044] Additional components may be added to enhance performance in
circumstances requiring a more forceful change in shape of a
flexible cutting element. For example, more force is appropriate
for moving fractured bone to form a tissue cavity and restore the
shape of bone structures, as in the case of treating compression
fractures of vertebral bodies. A cavitation device of the present
invention can be adapted to provide the operator with a means to
directly apply a flexing force to a flexible cutting element. FIGS.
10A and 10B show a seventh embodiment of the invention, cavitation
device 800, comprise a rotatable shaft 810 having longitudinal axis
811 and flexible cutting elements 820. Rotatable shaft 810
additionally has a control passage 812 running substantially along
longitudinal axis 811. A tension cable 870 is connected to flexible
cutting elements 820, preferably at their distal end, and extends
through the control passage 812. The proximal end of cavitation
device 810 is attached to T-handle 880 having a grip 890, with the
proximal end of tension cable 870 being attached to grip 890 such
that rotation of grip 890 about its longitudinal axis 891 applies a
tension force to tension cable 870. Thus, tension cable 870 is a
flexing means for biasing flexible cutting elements 820 to move
from a first shape toward a second shape. As grip 890 is rotated
about its longitudinal axis 891, tension is applied to tension
cable 870, thereby applying compressive and bending forces to
flexible cutting elements 820 and causing them to extend outward
toward a second shape. T-handle 880 also can be rotated manually
about longitudinal axis 811 to form a tissue cavity.
[0045] A cavitation device of the present invention is shown in
FIGS. 11A to 11F forming a cavity in osteoporotic cancellous bone
followed by filling of the cavity with a strengthening synthetic
bone that is injectable and hardens in situ. This method is
generally applicable to all means for shape change behavior of
flexible cutting elements described above. Bone structures are
typically comprised of two types of bone, cortical bone and
cancellous bone. Cortical bone can be considered a rigid, dense
shell, whereas cancellous bone has a high degree of visible
porosity. Cortical bone and cancellous bone combine to form
structures that are strong and lightweight, however, osteoporosis
is a disease that results in a decrease in strength due to a
decrease in bone density.
[0046] Referring specifically to FIG. 11A, through an insertion
tube 14 a standard surgical drill and drill bit are used to create
a pilot hole 46 in bone using established techniques. The bone
structure shown in FIG. 11A includes cortical bone 44 and
cancellous bone 42. A flexible cutting element 120 of cavitation
device 100, shown in FIG. 11B, is in a first shape adapted for
passage through insertion tube 14 to the distal end of pilot hole
46. The cutting tip 130 helps to keep flexible cutting element 120
centered during passage through insertion tube 14 and pilot hole
46. Once placed, the rotatable shaft 110 is used to transmit
torsion to flexible cutting element 120. Referring now to FIG. 11C,
as the rotatable shaft 110 rotates, the flexible cutting element
120 moves toward a second shape during the process of forming a
generally hemispherical tissue cavity 48 with a cavity radius 50.
Thus, the diameter of cavity 48 is twice the size of cavity radius
50. FIG. 11D shows the step of removing ablated tissue from the
tissue cavity 48 with an irrigation tube 18 through established
suction and irrigation techniques. Referring now to FIG. 11E,
cavitation device 100 can be reinserted into the tissue cavity 48
and further advanced and withdrawn to create a larger tissue cavity
48'. The tissue cavity 48' of FIG. 11E is generally cylindrical,
with a cavity radius 50 and a cavity diameter of twice the size of
cavity radius 50. FIG. 11F shows the tissue cavity 48' filled with
an injectable synthetic bone 16 that hardens in situ.
[0047] Polymethylmethacrylate (PMMA), commonly referred to as bone
cement, is a well-known bone synthetic substitute that has been in
use for several decades. Although PMMA has been used effectively,
there continue to be concerns regarding high exothermic
temperatures and potentially toxic fumes produced by PMMA during
curing. Other synthetic bone substitutes have been introduced in
recent years, including resorbable and non-resorbable materials. An
example of a recently introduced resorbable bone substitute is
injectable calcium phosphate, such as the material offered by
Synthes-Stratec, Inc. under the Norian Skeletal Repair System.TM.
brand name. An example of a non-resorbable bone substitute is
injectable terpolymer resin with combeite glass-ceramic reinforcing
particles, such as the material offered by Orthovita, Inc. under
the Cortoss.TM. brand name, which is said to have strength
comparable to human cortical bone.
[0048] Osteoporosis can be a contributing factor to fractures of
bone, especially the femur, radius, and vertebral bodies. There are
several non-invasive methods for determining bone mineral density,
and patients at high risk for fracture can be identified. Patients
with previous fractures related to osteoporosis are at high risk
for re-fracture or initial fractures of other bone structures.
Minimally invasive devices and methods, combined with synthetic
bone substitutes, allow for the strengthening of bone to be
practiced as a preventive treatment for patients at high risk of
fracture.
[0049] The proximal end of the femur, particularly the neck region,
is a common location for osteoporosis-related fractures. Referring
now to FIG. 12A, a cavitation device 100 is first used to create a
generally hemispherical tissue cavity 48 within the cancellous bone
42 in the head 56 of the femur 52 using the methods described
above. Cavitation device 100 is removed from the tissue cavity 48
in preparation for the insertion of a second cavitation device
100'. The cutting radius associated with the second cavitation
device 100' is smaller than the cutting radius of first cavitation
device 100. Continuing to refer to FIG. 12A, a cavitation device
100', is shown creating a second generally cylindrical tissue
cavity 48' within cancellous bone 42 in the neck 54 of a human
femur 52. The resulting interconnecting tissue cavity 48/48' is
filled with a strengthening synthetic bone 16, as shown in FIG.
12B. In addition, the cavitation devices and method shown in FIGS.
12A to 12 B can further be adapted to the treatment of bone
fractures.
[0050] There are numerous situations in orthopaedics where surgical
treatment of a painful joint involves immobilization of the joint
through a process called joint arthrodesis, or joint fusion. The
device and method of the present invention can be used for fusion
of numerous joints, including the spine or sacroiliac joint.
[0051] A spinal motion segment has numerous structures, including
two vertebral bodies 58/58' and an intervertebral disc 62, as shown
schematically in FIG. 13A. Using the methods previously described,
cavitation device 100 is shown in FIG. 13A forming an initial
generally hemispherical tissue cavity 48 that is expanded to form a
generally cylindrical tissue cavity 48'. The cavitation device 100
is cutting in two types of tissue, including the bone of the
vertebral bodies 58/58' and the soft tissue of the intervertebral
disc 62. FIG. 13B shows the tissue cavity 48 filled with synthetic
bone 16 to prevent relative motion of the vertebral bodies 58/58'.
Currently, spinal fusion is typically conducted using open
procedures; however, the present invention allows the process to be
conducted using a less invasive percutaneous surgical
procedure.
[0052] Implants, such as bone screws, anchors, pins and
intramedullary nails are widely used in the orthopaedics. However,
the effectiveness of such implants can be greatly diminished if
their attachment to bone is not secure. Osteoporosis can lead to
excessive porosity that compromises the integrity of the
bone/implant interface. Loose implants are less effective and can
cause additional problems if they migrate from their intended
position. Local strengthening of the bone at the attachment site
would be of tremendous benefit, and the present invention combined
with synthetic bone substitutes addresses this problem.
[0053] Referring now to FIG. 14A, cavitation device 100 is shown
creating a tissue cavity 48 in cancellous bone 42 at a site
designated as an attachment location for a bone screw 22. FIG. 14B
shows the tissue cavity 48 filled with synthetic bone 16, and the
bone screw 22 has been placed substantially within the synthetic
bone 16. An important aspect of the present invention and method is
the preservation of cortical bone 44. The preceding methods and
devices can be part of a planned surgical procedure, or as part of
a salvage procedure when the surgeon experiences unanticipated
stripping of bone during tightening of a bone screw.
[0054] To repair or fuse bone, surgeons often harvest bone from a
second surgical site. Compared to allograft and current bone
substitutes, autogenous bone graft provides all the cells,
proteins, and matrix required to form new bone. Because of the
morbidity associated with open procedures for harvesting bone, the
trend is toward minimally invasive techniques associated with
percutaneous instrumentation. The present invention allows for
minimally invasive access to bone for harvesting. The dynamic shape
behavior of the present invention will allow the technology to move
toward less invasive instruments with smaller working diameters.
Referring now to the FIG. 15, the most common site for bone harvest
is the iliac crest 66 of the pelvis 64. A cavitation device 100 is
shown in the region of the iliac crest 66 creating a tissue cavity
48. Emulsified bone may be removed from the tissue cavity 48 using
known irrigation and suction techniques. The harvested bone will
have a consistency similar to putty, a desirable form for numerous
orthopaedic applications to include the filling of a bone deficit
or joint fusion.
[0055] From the description above, a number of advantages of our
invention become evident. The flexible cutting element of the
invention eliminates the need for complex assemblies with numerous
moving parts. Additionally, the shape-changing behavior of the
flexible cutting element enables percutaneous passage through an
insertion tube. The shape change behavior also improves cutting
efficiency by providing a forceful press of a flexible cutting
element against the tissue during formation of a cavity. The
cavitation device of the present invention can be further adapted
in multi-component configurations to provide the operator with a
means for forcefully actuating a flexible cutting element on
demand. The device and methods of the present invention are
minimally invasive and have many applications, especially in
orthopaedics.
[0056] The preferred embodiments presented in this disclosure are
examples. Those skilled in the art can develop modifications and
variants that do not depart from the spirit and scope of the
disclosed cavitation devices and methods. For example, there are
instances where an insertion tube is not required and a pilot hole
in bone tissue is appropriate for passage to the cavitation site.
Disclosed flexing means for biasing the flexible cuffing elements
to move from a first shape to a second shape include elastic
deformation, thermal shape-memory, centrifugal force, and force
applied through a tension cable. Although these means are
considered in the examples separately, cavitation devices of the
present invention can comprise a combination of two or more of
these means. Those skilled in the art will understand that markings
on the shaft of a cavitation device of the invention can be used
for indicating depth of insertion and that an additional fitting on
the shaft can be used to limit the depth of insertion. Additional
variants, also with the spirit and scope of the invention, include
flexible cutting elements slidably connected to the shaft, such
that the length of a flexible cutting element can be adjusted. Thus
the scope of the invention should be determined by the appended
claims and their legal equivalents, rather than by the examples
given.
* * * * *