U.S. patent application number 13/535197 was filed with the patent office on 2013-12-12 for mems micro debrider devices and methods of tissue removal.
This patent application is currently assigned to MICROFABRICA INC.. The applicant listed for this patent is Richard T. Chen, Gregory P. Schmitz, Arun Veeramani, Ming-Ting Wu. Invention is credited to Richard T. Chen, Gregory P. Schmitz, Arun Veeramani, Ming-Ting Wu.
Application Number | 20130331878 13/535197 |
Document ID | / |
Family ID | 47439108 |
Filed Date | 2013-12-12 |
United States Patent
Application |
20130331878 |
Kind Code |
A2 |
Schmitz; Gregory P. ; et
al. |
December 12, 2013 |
MEMS MICRO DEBRIDER DEVICES AND METHODS OF TISSUE REMOVAL
Abstract
Medical devices for shearing tissue into small pieces are
provided. One exemplary device includes oppositely rotating first
and second rotatable members, each located at least partially
within a distal housing. The device also includes first and second
circular axle portions, and first and second blades that are
directly adjacent to one another and positioned to partially
overlap such that tissue may be sheared between the first and
second blades, between the first blade and the second axle portion
and between the second blade and the first axle portion. The
rotatable members are configured to engage tissue from a target
tissue site with teeth of the first and second blades, rotate
towards one another and inwardly to direct tissue from the target
tissue site through a tissue engaging opening and into an interior
portion of the distal housing. Methods of fabricating and using the
above device are also disclosed.
Inventors: |
Schmitz; Gregory P.; (Los
Gatos, CA) ; Wu; Ming-Ting; (Northridge, CA) ;
Chen; Richard T.; (WoodlandHills, CA) ; Veeramani;
Arun; (Woodland Hills, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schmitz; Gregory P.
Wu; Ming-Ting
Chen; Richard T.
Veeramani; Arun |
Van Nuys
Van Nuys
Van Nuys
Van Nuys |
CA
CA
CA
CA |
US
US
US
US |
|
|
Assignee: |
MICROFABRICA INC.
Van Nuys
CA
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20130012975 A1 |
January 10, 2013 |
|
|
Family ID: |
47439108 |
Appl. No.: |
13/535197 |
Filed: |
June 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13007578 |
Jan 14, 2011 |
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13535197 |
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12490295 |
Jun 23, 2009 |
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13007578 |
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13007578 |
Jan 14, 2011 |
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12490295 |
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12490301 |
Jun 23, 2009 |
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13007578 |
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61408558 |
Oct 29, 2010 |
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61075006 |
Jun 23, 2008 |
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61164864 |
Mar 30, 2009 |
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61164883 |
Mar 30, 2009 |
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61075006 |
Jun 23, 2008 |
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61164864 |
Mar 30, 2009 |
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61164883 |
Mar 30, 2009 |
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Current U.S.
Class: |
606/179 |
Current CPC
Class: |
A61B 2017/22044
20130101; A61B 2017/22077 20130101; A61B 17/221 20130101; A61B
17/32002 20130101; A61B 2017/32006 20130101; A61B 2017/003
20130101; A61B 17/1671 20130101; A61B 17/14 20130101; A61B
2017/320775 20130101; A61B 2017/320032 20130101; A61B 17/16
20130101; A61B 2017/32004 20130101; A61B 2017/22039 20130101; A61B
2017/00261 20130101; A61B 2017/2927 20130101; A61B 2017/1602
20130101; A61B 90/361 20160201; A61B 2017/320048 20130101; A61B
17/22031 20130101 |
Class at
Publication: |
606/179 |
International
Class: |
A61B 17/14 20060101
A61B017/14 |
Claims
1. A medical device for removing tissue from a subject, comprising:
a distal housing configured with at least one tissue engaging
opening; an elongate member coupled to the distal housing and
configured to introduce the distal housing to a target tissue site
of the subject; a first rotatable member located at least partially
within the distal housing and configured to rotate about a first
axis, the first rotatable member comprising a first disc-shaped
blade having a series of teeth along an outer circumference of the
blade, the first blade lying in a first plane; the first rotatable
member further comprising a circular first axle portion lying in a
second plane that is offset from, parallel and adjacent to the
first plane, the first axle portion having an outer circumference
that is smaller than that of the first blade, and a second
rotatable member located at least partially within the distal
housing and configured to rotate about a second axis parallel to
and radially offset from the first axis, the second rotatable
member configured to rotate in a direction opposite of a direction
of rotation of the first rotatable member, the second rotatable
member comprising a second disc-shaped blade having a series of
teeth along an outer circumference of the blade, the second blade
lying in the second plane, the second rotatable member further
comprising a circular second axle portion lying in the first plane,
the second axle portion having an outer circumference that is
smaller than that of the second blade, wherein the first and second
blades are directly adjacent to one another and positioned to
partially overlap such that tissue may be sheared between the first
and second blades, between the first blade and the second axle
portion and between the second blade and the first axle portion,
the rotatable members configured to engage tissue from the target
tissue site with the teeth of the first and second blades, rotate
towards one another and inwardly to direct tissue from the target
tissue site through the tissue engaging opening and into an
interior portion of the distal housing.
2. The medical device of claim 1, wherein the first rotatable
member further comprises a third disc-shaped blade having a series
of teeth along an outer circumference of the blade, the third blade
lying in a third plane that is offset from, parallel and adjacent
to the second plane, the second rotatable member further comprising
a circular third axle portion lying in the third plane, the third
axle portion having an outer circumference that is smaller than
that of the third blade, wherein the second and third blades are
directly adjacent to one another and positioned to partially
overlap such that tissue may be sheared between the second and
third blades and between the third blade and the third axle
portion, the rotatable members configured to engage tissue from the
target tissue site with the teeth of the first, second and third
blades, rotate towards one another and inwardly to direct tissue
from the target tissue site through the tissue engaging opening and
into an interior portion of the distal housing.
3. The medical device of claim 1, wherein the distal housing
further comprises a tissue cutting portion lying in a third plane
that is offset from, parallel and adjacent to the second plane,
wherein the tissue cutting portion and the second blade are
directly adjacent to one another and positioned to partially
overlap such that tissue may be sheared between the tissue cutting
portion of the distal housing and the second blade.
4. The medical device of claim 1, wherein the first and second
blades are no more than 30 microns apart where they partially
overlap.
5. The medical device of claim 1, wherein the outer circumference
of the first blade is no more than 30 microns apart from the outer
circumference of the second axle portion, and the outer
circumference of the second blade is no more than 30 microns apart
from the outer circumference of the first axle portion.
6. The medical device of claim 1, where the first and the second
blades and the first and the second axle portions each have a
thickness of less than 1 mm.
7. The medical device of claim 1, wherein the first and the second
rotation axes are generally perpendicular to a longitudinal axis of
the elongate member.
8. The medical device of claim 1, wherein the rotations of the
first and the second rotatable members are synchronized such that a
first trough associated with one of the teeth located along the
outer circumference of the first blade and a second trough
associated with one of the teeth located along the outer
circumference of the second blade simultaneously engage a single
fiber or single bundle of fibers from the target tissue site.
9. The medical device of claim 8, wherein the first and the second
troughs cooperate to compress portions of the single fiber or
single bundle of fibers as the first and the second rotatable
members rotate toward one another, thereby reducing the volume of
the tissue entering the distal housing.
10. The medical device of claim 1, wherein the rotations of the
first and the second rotatable members are configured to
alternately rotate in and out of phase with one another.
11. The medical device of claim 1, wherein the first and the second
rotatable members are independently driven.
12. The medical device of claim 1, wherein the first and the second
rotatable members are configured to periodically reverse direction
of rotation during tissue cutting.
13. The medical device of claim 12, wherein the rotations of the
first and the second rotatable members are configured to reverse
direction at least once per second.
14. The medical device of claim 12, wherein the device is
configured to provide a dwell time of at least about 50
milliseconds when the first and the second rotatable members
reverse direction.
15. A method of fabricating the device of claim 1, comprising
fabricating the first blade and the second axle portion together in
a first material deposition process step and fabricating the second
blade and the first axle portion together in a second material
deposition process step.
16. A method of using the device of claim 1, comprising urging the
distal housing of the device against a target tissue site of a
subject and extracting cut tissue pieces from a proximal end of the
elongate member.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation-In-Part of U.S.
application Ser. No. 13/007,578 filed Jan. 14, 2011, which claims
the benefit of U.S. Provisional Application No. 61/408,558 filed
Oct. 29, 2010; and which is a Continuation-In-Part of U.S.
application Ser. No. 12/490,295 filed Jun. 23, 2009, which claims
priority to: U.S. Provisional Application No. 61/075,006 filed Jun.
23, 2008; U.S. Provisional Application No. 61/164,864 filed Mar.
30, 2009; and U.S. Provisional Application No. 61/164,883 filed
Mar. 30, 2009. This application is a Continuation of U.S.
application Ser. No. 13/007,578 filed Jan. 14, 2011, which is also
a Continuation in Part of U.S. application Ser. No. 12/490,301
filed Jun. 23, 2009 which claims priority to: U.S. Provisional
Application No. 61/075,006 filed Jun. 23, 2008; U.S. Provisional
Application No. 61/164,864 filed Mar. 30, 2009; and U.S.
Provisional Application No. 61/164,883 filed Mar. 30, 2009. Each of
these applications is incorporated herein by reference as if set
forth in full herein.
INCORPORATION BY REFERENCE
[0002] All publications and patent applications mentioned in this
specification are herein incorporated by reference to the same
extent as if each individual publication or patent application was
specifically and individually indicated to be incorporated by
reference.
FIELD OF THE INVENTION
[0003] Embodiments of the present disclosure relate to micro-scale
and millimeter-scale tissue debridement devices that may, for
example, be used to remove unwanted tissue or other material from
selected locations within a body of a patient during a minimally
invasive or other medical procedure and in particular embodiments
multi-layer, multi-material electrochemical fabrication methods are
used to, in whole or in part, form such devices.
BACKGROUND OF THE INVENTION
[0004] Debridement is the medical removal of necrotic, cancerous,
damaged, infected or otherwise unwanted tissue. Some medical
procedures include, or consist primarily of, the mechanical
debridement of tissue from a subject. Rotary debrider devices have
been used in such procedures for many years.
[0005] Some debrider devices with relatively large dimensions risk
removing unintended tissue from the subject, or damaging the
unintended tissue. There is a need for tissue removal devices which
have small dimensions and improved functionality which allow them
to more safely remove only the desired tissue from the patient.
There is also a need for tissue removal devices which have small
dimensions and improved functionality over existing products and
procedures which allow them to more efficiently remove tissue from
the patient.
[0006] Prior art tissue removal devices often remove tissue in
large pieces, having dimensions well over 2 mm. The tissue pieces
are removed through an aspiration lumen typically 3.5 to 5 mm in
diameter. Since the tissue pieces being removed commonly have
dimensions that are 1 to 2 lumen diameters in length, the tissue
pieces can often clog the tissue removal lumen.
[0007] One portion of the body in which tissue can be removed to
treat a variety of conditions is the spine area. Tissue removal
devices for the spine are needed that can be produced with
sufficiently small dimensions and/or that have increased
performance over existing techniques. For example, a herniated disc
or bulging disc can be treated by performing a discectomy, e.g. by
removing all or part of the nucleus pulposus of the damaged disc.
Such procedures may also involve a laminotomy or laminectomy
wherein a portion or all of a lamina may be removed to allow access
to the herniated disc. Artificial disc replacement (total or
partial) is another example of a procedure which requires the
removal of all or a portion of the disc, which is replaced with an
artificial device or material.
[0008] Tissue removal devices are needed which can be produced with
sufficient mechanical complexity and a small size so that they can
both safely and more efficiently remove tissue from a subject,
and/or remove tissue in a less invasive procedure and/or with less
damage to adjacent tissue such that risks are lowered and recovery
time is improved.
SUMMARY OF THE DISCLOSURE
[0009] According to some aspects of the disclosure, a medical
device for removing tissue from a subject is provided. One
exemplary device includes a distal housing, an elongate member, a
first rotatable member and a second rotatable member. The distal
housing is configured with at least one tissue engaging opening.
The elongate member is coupled to the distal housing and configured
to introduce the distal housing to a target tissue site of the
subject. The first rotatable member is located at least partially
within the distal housing and is configured to rotate about a first
axis. The first rotatable member comprises a first disc-shaped
blade having a series of teeth along an outer circumference of the
blade. The first blade lies in a first plane. The first rotatable
member further includes a circular first axle portion lying in a
second plane that is offset from, parallel and adjacent to the
first plane. The first axle portion has an outer circumference that
is smaller than that of the first blade. The second rotatable
member is also located at least partially within the distal housing
and is configured to rotate about a second axis parallel to and
offset from the first axis. The second rotatable member is
configured to rotate in a direction opposite of a direction of
rotation of the first rotatable member. The second rotatable member
includes a second disc-shaped blade having a series of teeth along
an outer circumference of the blade. The second blade lies in the
second plane. The second rotatable member further includes a
circular second axle portion lying in the first plane. The second
axle portion has an outer circumference that is smaller than that
of the second blade. The first and second blades are directly
adjacent to one another and positioned to partially overlap such
that tissue may be sheared between the first and second blades,
between the first blade and the second axle portion and between the
second blade and the first axle portion. The rotatable members are
configured to engage tissue from the target tissue site with the
teeth of the first and second blades, rotate towards one another
and inwardly to direct tissue from the target tissue site through
the tissue engaging opening and into an interior portion of the
distal housing.
[0010] In some embodiments, the first rotatable member further
includes a third disc-shaped blade having a series of teeth along
an outer circumference of the blade. In these embodiments, the
third blade lies in a third plane that is offset from, parallel and
adjacent to the second plane. The second rotatable member further
includes a circular third axle portion lying in the third plane.
The third axle portion has an outer circumference that is smaller
than that of the third blade. The second and third blades are
directly adjacent to one another and positioned to partially
overlap such that tissue may be sheared between the second and
third blades and between the third blade and the third axle
portion. The rotatable members are configured to engage tissue from
the target tissue site with the teeth of the first, second and
third blades, rotate towards one another and inwardly to direct
tissue from the target tissue site through the tissue engaging
opening and into an interior portion of the distal housing.
[0011] In some embodiments, the distal housing further includes a
tissue cutting portion lying in a third plane that is offset from,
parallel and adjacent to the second plane. In these embodiments,
the tissue cutting portion and the second blade are directly
adjacent to one another and positioned to partially overlap such
that tissue may be sheared between the tissue cutting portion of
the distal housing and the second blade.
[0012] In some embodiments, the first and second blades are no more
than 30 microns apart where they partially overlap. In some
embodiments, the outer circumference of the first blade is no more
than 30 microns apart from the outer circumference of the second
axle portion, and the outer circumference of the second blade is no
more than 30 microns apart from the outer circumference of the
first axle portion. The first and the second blades and the first
and the second axle portions may each have a thickness of less than
1 mm. The first and the second rotation axes may be generally
perpendicular to a longitudinal axis of the elongate member.
[0013] In some embodiments, the rotations of the first and the
second rotatable members are synchronized such that a first trough
associated with one of the teeth located along the outer
circumference of the first blade and a second trough associated
with one of the teeth located along the outer circumference of the
second blade simultaneously engage a single fiber or single bundle
of fibers from the target tissue site. In these embodiments, the
first and the second troughs cooperate to compress portions of the
single fiber or single bundle of fibers as the first and the second
rotatable members rotate toward one another, thereby reducing the
volume of the tissue entering the distal housing.
[0014] In some embodiments, the rotations of the first and the
second rotatable members are configured to alternately rotate in
and out of phase with one another. The first and the second
rotatable members may be independently driven. The first and the
second rotatable members may be configured to periodically reverse
direction of rotation during tissue cutting, and may be configured
to reverse direction at least once per second. The device may be
configured to provide a dwell time of at least about 50
milliseconds when the first and the second rotatable members
reverse direction.
[0015] According to aspects of the disclosure, methods of
fabricated the above devices are disclosed. In some embodiments,
the method includes fabricating the first blade and the second axle
portion together in a first material deposition process step and
fabricating the second blade and the first axle portion together in
a second material deposition process step.
[0016] According to aspects of the disclosure, methods of using the
above devices are disclosed. In some embodiments, the method
includes urging the distal housing of the device against a target
tissue site of a subject and extracting cut tissue pieces from a
proximal end of the elongate member.
[0017] Other aspects of the disclosure will be understood by those
of skill in the art upon review of the teachings herein. Other
aspects of the disclosure may involve combinations of the above
noted aspects of the disclosure. These other aspects of the
disclosure may provide various combinations of the aspects
presented above as well as provide other configurations,
structures, functional relationships, and processes that have not
been specifically set forth above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIGS. 1-3 illustrate an exemplary embodiment of a working
end of a tissue removal device.
[0019] FIGS. 4A-4G illustrate exemplary embodiments of drive
mechanisms which can power the drive trains in the working end of
tissue removal devices.
[0020] FIGS. 5A-5C show another exemplary embodiment of a tissue
removal device.
[0021] FIGS. 6A-6C show an exemplary cutter head assembly 5332 that
may be used with debriding device 5310, shown in FIGS. 5A-5C.
[0022] FIGS. 7A-7F show details of an exemplary rotor housing
assembly 5420'.
[0023] FIGS. 8A-8C show tissue shearing details of an exemplary two
blade device.
[0024] FIGS. 9A-9C show tissue shearing details of an exemplary
three blade device.
[0025] FIGS. 10A-10C show further tissue shearing details.
DETAILED DESCRIPTION
[0026] FIGS. 1-3 illustrate an exemplary embodiment of a working
end of a tissue removal device, which can be fabricated wholly or
in part by electrochemical fabrication techniques, such as those
described or referenced herein. Tissue removal device working end
100 has a distal region "D" and proximal region "P," and includes
housing 101 and blade stacks 102 and 104. Blade stacks 102 and 104
include a plurality of blades 102A-102C and 104A-104C,
respectively. Three blades are shown in each stack, although the
blade stacks can have one or more blades. Each of the blades
includes a plurality of teeth 106 (see FIG. 3), some of which are
shown projecting from housing 101 and configured to engage and
process tissue. Processing tissue as used herein includes any of
cutting tissue, shredding tissue, capturing tissue, any other
manipulation of tissue as described herein, or any combination
thereof. The working end of the device generally has a length L,
height H, and width W. Housing 101 can have a variety of shapes or
configurations, including a generally cylindrical shape.
[0027] In this embodiment both blade stacks are configured to
rotate. The blades in blade stack 102 are configured to rotate in a
direction opposite that of the blades in blade stack 104, as
designated by the counterclockwise "CCW" and clockwise "CW"
directions in FIG. 1. The oppositely rotating blades direct
material, such as tissue, into an interior region of housing 101
(described in more detail below). In some embodiments, the blades
can be made to be rotated in directions opposite to those
indicated, e.g. to disengage from tissue if a jam occurs or to
cause the device to be pulled distally into a body of tissue when
given appropriate back side teeth configurations.
[0028] Housing 101 also includes a drive mechanism coupler 105,
shown as a square hole or bore, which couples a drive train
disposed in the housing to a drive mechanism disposed external to
the housing. The drive mechanism, described in more detail below,
drives the rotation of the drive train, which drives the rotation
of the blades. The drive train disposed in the housing can also be
considered part of the drive mechanism when viewed from the
perspective of the blades. Drive mechanism coupler 105 translates a
rotational force applied to the coupler by the drive mechanism (not
shown) to the drive train disposed within housing 101.
[0029] FIG. 1 also shows release holes 111-115 which allow for
removal of sacrificed material during formation of the working
end.
[0030] FIG. 2 shows a perspective view of the proximal end of
tissue removal device working end 100. Material directed into
housing 101 by the rotating blades is directed into chamber 103,
wherein it can be stored temporarily or directed further
proximally, as described below. A first gear train cover 121
provides for a first surface of chamber 103, while a second gear
train cover 122 provides a second surface of chamber 103. FIG. 2
also shows drive mechanism coupler cover 123.
[0031] In some embodiments in which the working end 100 includes a
storage chamber, the chamber may remain open while in other
embodiments it may be closed while in still other embodiments it
may include a filter that only allows passage of items of a
sufficiently small size to exit.
[0032] FIG. 3 shows a perspective view of the distal end of the
working end 100. In this embodiment the blades in stack 102 are
interdigitated with the blades in stack 104 (i.e. the blade ends
are offset vertically along dimension H and have maximum radial
extensions that overlap laterally along the width dimension W. The
blades can be formed to be interdigitated by, e.g. if formed using
a multi-layer, multi-material electrochemical fabrication
technique, forming each blade in stack 102 in a different layer
than each blade in stack 104. If during formation portions of
separately moveable blade components overlap laterally, the
overlapping blades should not just be formed on different layers
but should be formed such an intermediate layer defines a vertical
gap between them. For example, the bottom blade in stack 102 is
shown formed in a layer beneath the layer in which the bottom blade
in stack 104 is formed.
[0033] When manufacturing tissue removal devices of the various
embodiments set forth herein using a multi-layer multi-material
electrochemical fabrication process, it is generally beneficial if
not necessary to maintain horizontal spacing of component features
and widths of component dimensions remain above the minimum feature
size. It is important that vertical gaps of appropriate size be
formed between separately movable components that overlap in X-Y
space (assuming the layers during formation are being stacked along
the Z axis) so that they do not inadvertently bond together and to
ensure that adequate pathways are provided to allow etching of
sacrificial material to occur. For example, it is generally
important that gaps exist between a gear element (e.g. a tooth) in
a first gear tier and a second gear tier so that the overlapping
teeth of adjacent gears do not bond together. It is also generally
important to form gaps between components that move relative to one
another (e.g., gears and gear covers, between blades and housing,
etc.). In some embodiments the gaps formed between moving layers is
between about 2 um and about 8 um.
[0034] In some embodiments, it is desired to define a shearing
thickness as the gap between elements has they move past one
another. Such gaps may be defined by layer thickness increments or
multiples of such increments or by the intralayer spacing of
elements as they move past one another. In some embodiments,
shearing thickness of blades passing blades or blades moving past
interdigitated fingers, or the like may be optimally set in the
range of 2-100 microns or some other amount depending on the
viscosity or other parameters of the materials being encountered
and what the interaction is to be (e.g. tearing, shredding,
transporting, or the like). For example for shredding or tearing
tissue, the gap may be in the range of 2-10 microns, or in some
embodiments in the range of 4-6 microns.
[0035] FIGS. 4A-4G illustrate an example a of a side tissue removal
working end. FIG. 4A is a top sectional view with a top portion of
the housing removed, which shows working end 290 comprising housing
298 and four tissue removal elements 294-297, which are shown as
blade stacks. Blade stacks 294 and 295 process tissue along one
side of the housing by directing tissue in the direction of arrow
292. Blade stacks 296 and 297 process tissue along a second side of
the housing by directing tissue in the direction of arrow 293. As
shown in FIGS. 4A-B, blade stacks 294 and 297 each have two blades,
while blade stacks 295 and 296 each have three blades.
[0036] FIG. 4C shows a perspective view without housing 298
illustrating the drive mechanism for the side tissue removal device
290. The drive mechanism includes belt 299, distal pulley 300, and
side pulleys 301-304. The side pulleys are coupled to the blade
stacks and rotation of the side pulleys rotates the blade stacks.
The belt is disposed through side pulleys 301 and 302 and around
distal pulley 300 before returning through side pulleys 303 and
304. Actuating of belt 299 therefore activates all four blade
stacks. In some embodiments the belt is a nitinol wire, but can be
any other suitable material. FIG. 4D is a view with the top portion
of the housing removed to show the internal drive mechanism. FIG.
4E shows the same view with the top on the housing. FIGS. 4F and 4G
show top views of the working end shown in FIGS. 4D and 4E,
respectively. Vacuum, irrigation, or a combination of the two may
be used to send extracted tissue from the interior of the working
end, proximally to a storage reservoir (e.g. within the working end
or located outside the body of the patient on which a procedure is
being performed).
[0037] FIGS. 5A-5C show another exemplary embodiment of a tissue
removal device. Device 5310 may employ any of the cutting heads
described herein, or other suitable cutting heads. In some
embodiments, a double rotor shredding head is employed at the
distal end of device 5310 to selectively debride tissue down to the
cellular level.
[0038] In this exemplary embodiment, handheld device 5310 includes
a stepper motor 5312 at its proximal end. In other embodiments,
other types of electric, pneumatic or hydraulic motors, servos, or
other prime movers may be used. The proximal end of motor 5312 may
be provided with a manually turnable thumbwheel 5314, as shown. In
this embodiment, the distal output end of motor 5312 is provided
with a housing 5316, which is made up of a front cover 5318 and a
rear cover 5320. Located distally from housing 5316 are an outer
shaft housing 5322, an outer shaft lock seal 5324, and a support
clamp 5326. A non-rotating, outer support tube 5328 extends from
within the proximal end of device 5310 towards the distal end of
the device. Within support tube 5328, a rotating drive tube 5330
(best seen in FIGS. 5B and 5C) also extends from within the
proximal end of device 5310 towards the distal end of the device.
The support tube 5328 and inner drive tube 5330 may collectively be
referred to as an introducer. A cutter head assembly 5332,
subsequently described in detail, is attached to the distal end of
support tube 5328.
[0039] As best seen in FIG. 5B, other components of device 5310
include motor shaft drive axle 5334, motor dog 5335, four bearings
5336, drive gear 5338, driven gear 5340, inner drive shaft axle
5342, inner shaft lock seal 5344, vacuum gland disk 5346, vacuum
seal lock housing 5348, vacuum seal lock 5350, vacuum hose barb
5352, irrigation fluid hose barb 5354, outer tube o-ring 5356, and
two vacuum gland o-rings 5358. Various other pins, dowels,
fasteners, set screws, ball detents, shims and wave disc springs
are shown in the figures without reference numerals. As will be
appreciated by those skilled in this art, these non-referenced
components serve to align, retain and ensure the proper functioning
of the other components of exemplary device 5310.
[0040] The two rotors of cutter head assembly 5332 located at the
distal end of device 5310 are driven by motor 5312 through drive
tube 5330 and other drive components of device 5310, as will now be
described in more detail. As best seen in FIGS. 5B and 5C, a motor
dog 5335 is attached to the output shaft of motor 5312. Motor dog
5335 is coupled to motor shaft drive axle 5334, which is rotatably
mounted in housing 5316 with two bearings 5336. Drive gear 5338 is
rigidly fixed to motor shaft drive axle 5334, and drives driven
gear 5340. Driven gear 5340 is rigidly fixed to inner drive shaft
axle 5342, which is rotatably mounted in housing 5316 with two
bearings 5336. Inner rotating drive tube 5330 passes through the
center of inner drive shaft axle 5342 and is rotatably fixed
thereto. Drive tube 5330 extends from the proximal end of device
5310 to the distal end of the device through the non-rotating outer
support tube 5328. The distal end of drive tube 5330 (or a separate
tube 5330' attached thereto) is provided with crown teeth around
its periphery, as shown in FIGS. 6B and 6C, for meshing with drive
gear 5410. As drive tube 5330 is rotated about a longitudinal axis
of device 5310 by motor 5312 through the above-described drive
train components, it drives drive gear 5410 about an axis that is
perpendicular to the longitudinal axis, as can be appreciated by
viewing FIG. 6. Drive gear 5410 in turn drives other components of
the cutter head assembly, and as is subsequently described in more
detail.
[0041] In some embodiments motor 5312 is provided with feedback
control for rotational velocity and torque. These two parameters
can be used for controlling and monitoring changes in rotational
velocity and the torque load. For measuring rotational velocity, an
encoder may be located at one or more of the cutter rotors, at the
drive motor, or at another location along the drive train between
the drive motor and cutter rotors. In some embodiments, the encoder
is located at or close to the rotors to avoid backlash associated
with the drive train, thereby making the velocity monitoring more
responsive and accurate. Encoder technologies that may be used
include optical, resistive, capacitive and/or inductive
measurement. To sense torque load, one or more strain gages may be
located at the cutter rotors, at the drive motor, or at another
location along the drive train between the drive motor and cutter
rotors. Torque load may also be sensed by monitoring the current
being drawn by the motor. By sensing changes in velocity and/or
torque, a controller associated with device 5310 can determine that
the cutter rotors are passing from one tissue type to another and
take appropriate action. For example, the controller can sense when
the cutter elements are passing from soft to hard tissue, from hard
to medium density tissue, or from a cutting state to non-cutting
state. In response to these changes, the controller and/or device
5310 can provide audio, visual and/or tactile feedback to the
surgeon. In some embodiments, the controller can change the
velocity, direction or stop cutter rotors from rotating in response
to velocity and/or torque feedback. In one embodiment of the
invention, a typical cutting rotor speed is on the order of 100 to
20,000 rotations per minute, and a typical torque load is on the
order of 0.25 to 150 mN-meter. Other sensors, such as a pressure
sensor or strain sensor located at the distal tip of device 5310,
may also be utilized to provide feedback that tissue cutting
elements are moving from one tissue type to another. In some
embodiments, an impendence sensor may be located at the distal tip
of the device, to sense different tissue types or conditions, and
provide corresponding feedback for tissue cutting control when the
tissue being cut by the cutter head changes. Such a pressure sensor
feedback control arrangement can be used with types of cutting
devices other than those disclosed herein.
[0042] Referring now to FIG. 5C, irrigation fluid hose barb 5354 is
provided on the lower side of outer shaft housing 5322 of exemplary
device 5310. Hose barb 5354, or a similar fluid line coupling, may
be connected to a supply of irrigation fluid. The lumen of hose
barb 5354 is in fluid communication with an internal irrigation
fluid cavity 5360. Fluid cavity 5360 surrounds internal drive tube
5330, and is bounded on its proximal end by o-ring seal 5358 around
drive tube 5330. Fluid cavity 5360 is bounded on its distal end by
o-ring seal 5356 around outer support tube 5328. This arrangement
allows drive tube 5330 to rotate, but constrains irrigation fluid
delivered from hose barb 5354 to travel only through the annular
space defined by the outer surface of drive tube 5330 and the inner
surface of support tube 5328. Irrigation fluid may thus flow
distally through the annular space to the distal end of device
5310.
[0043] As shown in FIG. 6B, one or more drive aligner rings 5412
may be provided between outer support tube 5328 and inner drive
tube 5330 along their lengths to support drive tube 5330 as it
rotates. In order to allow the flow of irrigation fluid between the
tubes 5328 and 5330, rings 5412 may be provided with one or more
channels 5414 as shown. When the distal flow of irrigation fluid
reaches the cutter head assembly 5332, it continues to flow
distally into lug 5416. To enable the fluid flow, lug 5416 is
provided with fluid channels 5418 located along the outer walls of
its central bore, as best seen in FIG. 6C. In this embodiments,
irrigation fluid passes distally between inner drive tube 5330 and
lug 5416 through channels 5418 (only one channel shown in FIG. 6C).
Irrigation fluid flowing distally through channels 5418 may be
directed toward the outside portions of cutting elements. In this
embodiment, the outside portions of cutting elements are rotating
distally, away from the fluid flow, while the inside portions of
cutting elements are rotating proximally, toward the center of lug
5416 and drive tube 5330.
[0044] In some embodiments, the irrigation fluid serves multiple
functions. The irrigation fluid can serve to lubricate the cutting
elements, drive gears, journal bearings and other components as the
parts rotate. The irrigation fluid can also serve to cool the
cutting elements and/or the tissue being cut, absorbing heat and
carrying it away as the irrigation fluid is removed from the
patient. The fluid can serve to flush tissue particles from the
moving parts to prevent them from becoming clogged. The fluid can
also serve to carry away the tissue portions being cut and remove
them from the target tissue site. In some embodiments, the
irrigation fluid is discharged from the cutting device and may be
removed from the target tissue site with other, traditional
aspiration means. With the current exemplary cutting device 5310,
however, the irrigation fluid and/or other bodily fluids may be
removed from the target tissue site by the cutting device 5310, as
will now be described in detail.
[0045] As previously described, irrigation fluid may be delivered
to cutting elements and/or a target tissue site through device
5310. Exemplary device 5310 is also constructed to remove the
irrigation fluid and tissue portions cut from the target tissue
site through the shaft of device 5310. As can be appreciated by
viewing FIG. 7F, the two interleaving stacks of cutting elements,
also referred to as rotors 5610 and 5612, have an overlapping
section 5614 in the center of cutter head assembly 5332. The two
rotors 5610 and 5612 may be rotated in opposite directions such
that each rotor engages target tissue and pulls it towards the
central overlapping section 5614. In overlapping section 5614, the
tissue is shredded into small pieces by the interdigitated cutting
elements, as is subsequently described in more detail. The small
tissue portions are generally propelled in a proximal direction by
rotors 5610 and 5612, away from the target tissue site and into the
cutter head assembly 5332. As can be appreciated by viewing FIG.
7F, the shredded tissue portions emerge from rotors 5610 and 5612
substantially along the central axis of lug 5416 (and therefore
also the central axis of drive tube 5330. With sufficient
irrigation fluid being supplied to the tissue cutting area, and
sufficient aspiration being provided from the proximal end of the
device, irrigation fluid around rotors 5610 and 5612 carries the
cut tissue particles proximally down the center of drive tube 5330.
As shown in FIG. 5C, the proximal end of drive tube 5330 is in
fluid communication with hose barb 5352 located at the proximal end
of device 5310. A traditional aspiration device or other suction
source may be attached to device 5310 through hose barb 5352 or
other suitable fluid coupling to collect the spent irrigation fluid
and cut tissue portions.
[0046] In some embodiments, the cut tissues portions emerging from
hose barb 5352 may be collected for testing. The tissue portions
may be separated from the irrigation fluid, such as by centrifugal
force, settling and/or filtering. The tissue portions may be
measured to precisely determine the mass and/or volume of tissue
removed. The pathology of some or all of the tissue portions may
also be determined. In some embodiments, the above testing may be
performed during a surgical procedure so that results of the
testing may be used to affect additional stages of the
procedure.
[0047] According to aspects of the invention, the inside diameter
of drive tube 5330 may be much larger than the maximum dimension of
the tissue portions traveling through it. In some embodiments, the
maximum tissue dimension is less than about 2 mm across. In one
exemplary embodiment, the inside diameter of drive tube 5330 is
about 3 mm, the outside diameter of the support tube 5328 is about
5.6 mm, and the maximum dimension of the tissue portions is about
150 microns. In another exemplary embodiment, the inside diameter
of drive tube 5330 is about 1.5 mm, the outside diameter of the
support tube 5328 is about 2.8 mm, and the maximum dimension of the
tissue portions is about 75 microns. In other embodiments, the
inside diameter of drive tube 5330 is between about 3 mm and about
6 mm. In some embodiments, the maximum dimension of the tissue
portions is at least one order of magnitude less than a diameter of
the tissue removal lumen. In other embodiments, the maximum
dimension of the tissue portions is at least twenty times less than
a diameter of the tissue removal lumen. In some embodiments, the
maximum dimension of the tissue portions is less than about 100
microns. In other embodiments, the maximum dimension of the tissue
portions is about 2 microns.
[0048] Referring now to FIGS. 6A-6C, an exemplary cutter head
assembly 5332 is described in more detail. Cutter head assembly
5332 may be used with debriding device 5310, shown in FIGS. 6A-6C.
As best seen in FIG. 6B, cutter head assembly 5332 includes lug
5416, drive gear 5410, rotor housing assembly 5420, aligner pin
5422, and aligner cap 5424. Lug 5416 is provided with a cutout on
its distal end for receiving rotor housing assembly 5420. Beneath
the rotor housing cutout, lug 5416 has a circular recess for
receiving drive gear 5410. A bore is provided in the bottom of lug
5416 for receiving the head of aligner pin 5422. When cutter head
5332 is assembled, the shank of aligner pin 5422 passes through the
bore of lug 5416, through a square aperture in the center of drive
gear 5410, through a bore in the proximal end of rotor housing
assembly 5420, and into a large diameter bore through the top of
lug 5416. Aligner cap 5424 is received with the large diameter bore
in the top of lug 5416, and is fastened to aligner pin 5422 by a
press fit, weld, threads, a separate fastener, or other suitable
means. In this assembled arrangement, pin 5422 and cap 5424 retain
rotor housing 5426 from moving longitudinally relative to the
central axis of the instrument, and rotor housing 5426 and drive
gear 5410 retain pin 5422 and cap 5424 from moving radially
relative to the central axis of the instrument. Pin 5422 and cap
5424 spin together as a unit relative to lug 5416, and serve to
align drive gear with the distal end of drive tube 5330', as
previously described. Pin 5422 also serves to transmit torque from
drive gear 5410 to gear 5616, which resides inside the rotor
housing directly above drive gear 5410. Lug bearing 5416 forms the
base of cutter head assembly 5332, shown in FIGS. 6A-6C. As
subsequently described in further detail, various different cutter
heads may alternately be inserted into and secured within the slot
shaped opening in the distal end of the lug bearing.
[0049] FIGS. 7A-7F show further details of an exemplary rotor
housing assembly 5420'. Assembly 5420' is constructed and operates
in a manner similar to assembly 5420 as previously described in
reference to FIGS. 6A-6C, but has a different blade configuration.
As shown in FIG. 7A, rotor housing assembly 5420' includes a pair
of rotors 5610' and 5612', each rotatably mounted in rotor housing
5426 by an axle 5618. In this embodiment, rotors 5610' and 5612'
are configured to rotate in opposite directions to draw tissue into
a center, overlapping region where the tissue is shredded.
[0050] Referring to FIGS. 7B and 7C, the components of rotor
housing assembly 5420' are shown. Assembly 5420' includes housing
5426, a pair of axles 5418, and gears 5410, 5620 and 5622, as
previously described. Rotor 5610' includes two blades 5710
interspersed with three spacer rings 5714 on first axle 5418. Rotor
5612' includes three blades 5712 interspersed with two spacer rings
5716 on second axle 5418.
[0051] It should be noted that while rotor housing assembly 5420'
is shown in an exploded format for clarity in FIGS. 7B and 7C,
suggesting that the components are fabricated separately and then
assembled using traditional assembly processes, this may or may not
be the case, depending on the embodiment. In some embodiments,
rotor assembly 5420' is assembled this way. In other embodiments,
assembly 5420' may be built in layers, such as by using a MEMS
fabrication processes. For example, after portions of housing 5426
and gears 5410, 5620 and 5622 are built up in layers, bottom blade
5712, bottom spacer 5714, and housing fin 5624 are formed together
in one or more layers. Following this layer, bottom blade 5710,
bottom spacer 5716, and bottom housing fin 5626 may be formed
together in one or more layers. The process may be repeated until
the entire rotors 5610' and 5612' and surrounding components are
formed. A thin sacrificial layer may be formed between adjacent
layers of components to separate the components from one layer from
components of adjacent layers. Sacrificial material may also be
formed in portions of each non-sacrificial layer to separate
components on that layer, create desired voids in the finished
assembly, and to provide a substrate for forming components in
subsequent layers above. With such a fabrication technique, rotor
5610' may be formed as a single unitary structure interleaved with
portions of rotor housing 5426, rather than separate components
(i.e. axle 5418, spacers 5714, blades 5710, and gear 5620.)
Similarly, rotor 5612' may be formed as a single unitary structure
interleaved with portions of rotor housing 5426, rather than
separate components (i.e. axle 5418, blades 5712, spacers 5716, and
gear 5622.) In some embodiments, combinations of fabrication and
assembly techniques may be used to create the rotor housing and/or
cutter head assemblies.
[0052] Referring to the top view shown in FIG. 7D, it can be seen
that in this embodiment the axle 5418 of rotor 5612' is more
distally located than axle 5418 of rotor 5610'. It can also be seen
that while a top plate portion of rotor housing 5426 covers most of
rotor blades 5710 and 5712, the blades protrude less from a middle
and bottom plate portion of housing 5426. Further details of
protruding blades and rotor characteristics are subsequently
discussed in reference to FIG. 7F.
[0053] A front or distal end view is shown in FIG. 7G. As depicted
in FIG. 7G, very small gaps or interference fits 5717 between
overlapping blades 5710 and 5712 are desirable in some embodiments.
Similarly, very small gaps or interference fits 5719 between blades
5712 and adjacent portions of rotor housing 5426 are desirable in
some embodiments, as will be subsequently described in more
detail.
[0054] Referring to the cross-sectional plan view of FIG. 7F, the
bottom two blades 5712 of rotor 5612' and the bottom blade 5710 of
rotor 5610' are shown. As shown, blades 5710 have a larger outer
diameter than that of blades 5712. But because axle 5418 of rotor
5612' is located more distally than axle 5418 of rotor 5610',
blades 5712 protrude more distally from the bottom of rotor housing
5426 than do blades 5710 of rotor 5610'. It can also be seen that
teeth 5718 and associated troughs 5720 of blades 5712 are
configured to be rotationally out of phase with those of other
blades 5712 of rotor 5612'. As will subsequently be discussed in
more detail, this arrangement can tune rotors 5612 to selective cut
certain types of tissue and avoid cutting other types of
tissue.
[0055] Various rotor gaps can be seen in FIG. 7F. For example, gap
5722 is shown between the tips of blade teeth 5718 of rotor 5612'
and spacer ring 5714/axle 5418 of opposing rotor 5610'. Gap 5724 is
also shown, between the tips of blade teeth 5718 of rotor 5612' and
the adjacent portion of housing 5426. Gap 5726 is also shown,
between spacer ring 5714/axle 5418 of rotor 5610' and the adjacent
portion of housing 5426. In some embodiments, it is desirable to
keep gaps 5722, 5724 and 5726 very small, to ensure that tissue
portions/particles that pass through rotors 5610' and 5612' are
first cut to a very small size, and to avoid jamming or clogging
rotors 5610' and 5612'. In some embodiments, these gaps are
fabricated as small interferences between the adjacent parts so
that when the rotors are first rotated, the adjacent parts hit each
other and wear down or burnish each other. In this manner, after a
break in period, smaller interference or zero clearance fits are
created between the adjacent moving parts. Gap distances that
applicants believe are advantageous include less than about 20
microns, less than about 10 microns, less than about 5 microns,
less than about 1 micron, substantially zero, an initial
interference fit of at least 2 microns, and an initial interference
fit of about 5 microns.
[0056] In operation, the cutter elements of rotor housing assembly
shown in FIGS. 7A-7F serve to grab tissue from a target source,
draw the tissue towards a central region between the blades, cut
the tissue from the source, and morcellate the tissue in small
pieces for transport away from the body. In other embodiments,
separate cutter elements may be used for these various functions.
For example, one blade or blades may be used to cut tissue from the
source, while another blade or set of blades may be used to
morcellate the cut tissue.
[0057] Components of cutter head assembly 5332, including rotor
housing assemblies 5420 and 5420', may be fabricated using
processes such as laser cutting/machining, photo chemical machining
(PCM), Swiss screw, electro-discharge machining (EDM),
electroforming and/or other processes for fabricating small parts.
Wafer manufacturing processes may be used to produce high precision
micro parts, such as EFAB, X-ray LIGA (Lithography, Electroplating,
and Molding), and/or UV LIGA. An electrochemical fabrication
technique for forming three-dimensional structures from a plurality
of adhered layers is being commercially pursued by applicant
Microfabrica.RTM. Inc. (formerly MEMGen Corporation) of Van Nuys,
California under the name EFAB.RTM.. Such a technique may be
advantageously used to fabricate components described herein,
particularly rotors and associated components.
[0058] In some embodiments, the shredder's ability to selectively
remove tissue is attributed to the protrusion of the rotating
cutters from the housing and the design of a tooth pitch (space
between the tips of adjacent teeth) of each rotor. In some
embodiments, the protrusion sets the depth of the inward cut for
the tips of the rotor. This inward depth controls the thickness of
tissue being removed. The tooth pitch or number of teeth
circumferentially about the rotor diameter provides an opening for
individual tissue fibers and/or fiber bundles to be hooked,
tensioned and drawn between the cutters.
[0059] From the point of view of the selected tissue, the tooth
pitch and protrusion may be designed to grasp the smallest fibers
or fiber bundles that are to be removed. From the point of view of
the non-selected tissue, the tooth pitch may be many times smaller
than the fiber or fiber bundle, and the protrusion may also be
equally smaller than the fiber/bundle diameter.
[0060] As previously described, FIG. 7D shows the exemplary
protrusion of blades 5710 and 5712 as viewed from the top of a
rotor housing assembly 5420'. In some embodiments, the protrusion
is more exposed on the top side than the bottom. In other
embodiments, the cutter device has the same protrusion for both
sides. Biasing the protrusion more on one side than the other can
provide advantages such as cutting/shredding directionality and/or
additional safety. Blade protrusion distances that applicants
believe are advantageous include less than about 100 microns, less
than about 10 microns, substantially flush with the housing,
recessed a minimum of about 5 microns, and recessed a minimum of
about 10 microns.
[0061] Tooth pitch is the distance from one tooth tip to the next
tooth tip along an imaginary circle circumscribing the outer
circumference of the blade. The trough diameter or depth generally
is the distance between the tooth tip and the low point between the
tooth tips. In many embodiments, the trough is a critical geometry
component that enables tissue selectivity. Additionally, the trough
opening (i.e. the distance from tooth tip to the tooth back of an
adjoining tooth) can deter nine the size of the "window" for
capturing a fiber or fiber bundle diameter.
[0062] In some embodiments, the target tissue being cut is hydrated
and generally has a nominal fiber diameter of about 6 to about 9
microns. In some embodiments, the target tissue being cut is dry
and generally has a nominal fiber diameter of about 5 to about 6
microns. In some embodiments, the tissue fibers are connected
together in bundles having a nominal diameter of about 250
microns.
[0063] Typical dimensions in some embodiments include: [0064]
Housing diameter: 6 mm or less [0065] Blade diameter range: 0.75 mm
to 4 mm [0066] Tip to Tip range: 0.2 mm to 1 mm [0067] Trough
diameter range: 2 microns to 0.5 mm [0068] Blade protrusion range:
2 microns to 2 mm The tip to tip distance is typically at least two
times the trough diameter for hook type teeth.
[0069] The tissue cutting devices disclosed herein may be
configured for use in a variety of procedures. An example of a
cardiac application is using the inventive devices to selectively
remove endocardium, with the cutting device configured to leave the
underlying myocardium uncut. An example of a tissue removing
application involving the esophagus includes selectively removing
mucosa, leaving the submucosa. Such a therapy would be useful for
treating Barrett's disease. Examples in the spinal area include
selectively removing flavum, with the cutting device configured to
stop removing tissue when dura is reached, leaving the dura intact.
Selective removal of flavum but not nerve root is another
embodiment. A cutting device constructed according to aspects of
the invention can also be configured to remove flavum without
cutting bone. In this embodiment, the rotor velocity could be
changed and/or the cutting elements could be changed after the
flavum is removed such that some bone tissue could then be removed.
Examples in the neurovascular area include selectively removing
cancerous tissue while not cutting adjacent blood vessel tissue or
nerve tissue. In the rheumatology field, tears in labral target
tissue may be selectively removed while preserving adjacent
non-target tissue, such as in the hips, shoulders, knees, ankles,
and small joints. In some embodiments, small teeth on the rotors
can interact with micron scale fibers of cartilage, removing tissue
in a precise way, much like precision machining of materials that
are harder than tissue. Other target tissues that may be
selectively removed by the inventive devices and methods described
herein include cartilage, which tends to be of a medium density,
periosteum, stones, calcium deposits, calcified tissue, cancellous
bone, cortical bone, plaque, thrombi, blood clots, and emboli.
[0070] It can be appreciated by those skilled in the art of tissue
removal that soft tissue is much more difficult to remove in a
small quantities and/or in a precise way than harder tissue such as
bone that may be grinded or sculpted, since soft tissue tends to
move or compress when being cut, rather than cut cleanly. Cutting
tissue rather than removing it with a laser or other high energy
device has the advantage of not overheating the tissue. This allows
the tissue to be collected and its pathology tested, as previously
described.
[0071] In some embodiments of the invention, the selective tissue
cutting tool may be moved laterally along a tissue plane, removing
thin swaths of tissue with each pass until the desired amount or
type of tissue is removed. In some embodiments, the tool may be
plunged into the target tissue in a distal direction, until a
desired depth or type of tissue is reached. In any of these
embodiments, the tool may cut a swath or bore that is as large as
or larger than the width of the tool head. In some embodiments, the
cutting elements are distally facing, laterally facing, or
both.
[0072] Referring to FIGS. 8A-10C, further details of exemplary
tissue cutting devices are depicted. For clarity of illustration
and explanation, the rotors depicted in these figures are shown
with only one or two blades each, and some of the blades include
only a single hook-shaped tooth. Functional surgical instruments
may be fabricated with these simplified constructs. However, the
concepts being discussed relative to these embodiments may be
equally applied to the other embodiments disclosed herein (e.g.,
rotors having many blades and/or multi-toothed blades.)
Additionally, various portions of the rotors depicted in these
figures may be shown as separate components for clarity. In some
embodiments, these portions may be fabricated as separate
components, while in other embodiments they may be integrally
formed into unitary rotors.
[0073] Referring first to FIG. 8A, a tissue cutting device 800
having two overlapping or interdigitated rotatable members 802 and
804 is shown. First rotatable member 802 comprises a first
hook-shaped blade 806 having a first tooth 808, and a first axle
portion 810. First rotatable member 802 is rotatably mounted to
housing 812 such that it rotates about a first axis 814. Second
rotatable member 804 comprises a second hook-shaped blade 816
having a second tooth 818, a second axle portion 820, and a third
axle portion 822. Second rotatable member 804 is rotatably mounted
to housing 812 such that it rotates about a second axis 824 that is
parallel and offset from first axis 814. A portion of housing 812
resides directly adjacent to second blade 816 (shown above second
blade 816 in FIG. 8A.)
[0074] First blade 806 and second axle portion 820 both lie in a
first plane 826, and may be fabricated in the same
layer(s)/processing step(s), for example if a MEMS fabrication
process is used. Similarly, second blade 816 and first axle portion
810 both lie in a second plane 828, and may be fabricated in the
same layer(s)/processing step(s). Additionally, third axle portion
820 and housing portion 812 both lie in a third plane 830, and may
be fabricated in the same layer(s)/processing step(s). Regardless
of whether a MEMS fabrication process is used, first blade 806 and
first axle portion 810 of first rotatable member 802 may be formed
as separate, discrete components or may be formed to create an
integrated, monolithic structure. Similarly, second blade 816,
second axle portion 820 and third axle portion 822 of second
rotatable member 804 may be formed as separate, discrete components
or may be formed to create an integrated, monolithic structure.
[0075] As can be seen in FIGS. 8A and 8B, there is a region of
overlap 832 that generally lies between first axis 814 and second
axis 824 in which first blade 806 and second blade 816 overlap one
another. In some embodiments, first blade 806 and second blade 816
are always overlapping. In other embodiments, such as shown in
FIGS. 8A-8C, first blade 806 and second blade 816 only overlap
during one or more portions of their rotations, such as when first
tooth 808 and second tooth 818 both rotate into the region of
overlap 832 simultaneously. In this embodiment, first rotatable
member 802 and second rotatable member 804 rotate at the same
angular velocity and are synchronized so that first tooth 808 and
second tooth 818 overlap one another each time they pass through
the region of overlap 832. Additionally, housing portion 812
overlaps second blade 816, at least in the region of overlap 832
when second tooth 818 passes through.
[0076] Referring to FIGS. 8B and 8C, the overlapping relationship
between first blade 806, second blade 816 and housing portion 812
can be seen. A small gap 834 is provided between first blade 806
and second blade 816. Similarly, a small gap 836 is provided
between second blade 816 and housing portion 812. The outer
circumference of first blade 806 and the diameter of second axle
portion 820 are selected relative to the spacing of first rotation
axis 814 and second rotation axis 824 such that a small gap 838 is
provided between the tip of first tooth 808 and second axle portion
820. Similarly, the outer circumference of second blade 816 and the
diameter of first axle portion 810 are selected relative to the
spacing of first rotation axis 814 and second rotation axis 824
such that a small gap 840 is provided between the tip of second
tooth 818 and first axle portion 810. A gap 842 is also provided
between third axle portion 822 and housing portion 812.
[0077] Gap 834 is kept small so that tissue can be efficiently
sheared between first tooth 808 and second tooth 818. Similarly,
gap 836 is kept small so that tissue can be efficiently sheared
between second tooth 818 and housing portion 812. Gap 838 is kept
small so that tissue can be efficiently sheared between the tip of
first tooth 808 and second axle portion 820. Gap 840 is kept small
so that tissue can be efficiently sheared between the tip of second
tooth 818 and first axle portion 810. Gap 842 is kept small so that
tissue can be efficiently sheared between third axle portion 822
and housing portion 812.
[0078] What is meant by "small gap" is a tight interface between
mating surfaces or edges, which in some embodiments is essentially
no gap at all. In these embodiments, mating parts may be configured
such that the gap is so small that it is not measurable. This may
be accomplished by creating a sliding fit between the mating parts,
or creating a small interference fit. With an interference fit, the
parts may be designed to flex away from each other so they do not
bind. In some embodiments, an interference fit can be reduced to a
zero gap fit by driving the rotors with high torque during a
break-in period to allow the surfaces to wear or burnish against
each other to remove a small amount of material. In some
embodiments, at least one of the gaps 834 and 836 is no more than
30 microns. In some embodiments, at least one of the gaps 838, 840
and 842 is no more than 30 microns. In some embodiments, all of the
gaps 834, 836, 838, 840 and 842 are no more than 30 microns.
[0079] The combination of the five tissue shearing interfaces
provided around a blade as just described allows tissue to be
sheared more quickly, efficiently and predictably. When all gaps
are kept very small, tissue may be efficiently sheared into small
pieces (as will be subsequently described in more detail) around
all surfaces of the blade, with a reduced risk of the rotatable
members getting clogged or jammed.
[0080] Referring to FIGS. 9A-9C, another embodiment similar to that
shown in FIGS. 8A-8C will be described. In this embodiment, one of
the rotatable members has more than one blade.
[0081] Referring first to FIG. 9A, a tissue cutting device 900
having two overlapping or interdigitated rotatable members 902 and
904 is shown. First rotatable member 902 comprises a first
hook-shaped blade 906 having a first tooth 908, a first axle
portion 910, and a third hook-shaped blade 911 having a third tooth
913. First rotatable member 902 is rotatably mounted to a housing
(not shown) such that it rotates about a first axis 914. Second
rotatable member 904 comprises a second hook-shaped blade 916
having a second tooth 918, a second axle portion 920, and a third
axle portion 922. Second rotatable member 904 is rotatably mounted
to the housing such that it rotates about a second axis 924 that is
parallel and offset from first axis 914.
[0082] First blade 906 and second axle portion 920 both lie in a
first plane 926, and may be fabricated in the same
layer(s)/processing step(s), for example if a MEMS fabrication
process is used. Similarly, second blade 916 and first axle portion
910 both lie in a second plane 928, and may be fabricated in the
same layer(s)/processing step(s). Additionally, third blade 911 and
third axle portion 920 both lie in a third plane 930, and may be
fabricated in the same layer(s)/processing step(s). Regardless of
whether a MEMS fabrication process is used, first blade 906, first
axle portion 910, and third blade 911 of first rotatable member 902
may be formed as separate, discrete components or may be formed to
create an integrated, monolithic structure. Similarly, second blade
916, second axle portion 920 and third axle portion 922 of second
rotatable member 904 may be formed as separate, discrete components
or may be formed to create an integrated, monolithic structure.
[0083] As can be seen in FIGS. 9A and 9B, there is a region of
overlap 932 that generally lies between first axis 914 and second
axis 924 in which first blade 906, second blade 916 and third blade
911 overlap one another. In some embodiments, first blade 906,
second blade 916 and third blade 911 are always overlapping. In
other embodiments, such as shown in FIGS. 9A-9C, first blade 906,
second blade 916 and third blade 911 only overlap during one or
more portions of their rotations, such as when first tooth 908,
second tooth 918 and third tooth 913 all rotate into the region of
overlap 932 simultaneously. In this embodiment, first rotatable
member 902 and second rotatable member 904 rotate at the same
angular velocity and are synchronized so that first tooth 908,
second tooth 918 and third tooth 913 overlap one another each time
they pass through the region of overlap 932.
[0084] Referring to FIGS. 9B and 9C, the overlapping relationship
between first blade 906, second blade 916 and third blade 911 can
be seen. A small gap 934 is provided between first blade 906 and
second blade 916. Similarly, a small gap 936 is provided between
second blade 916 and third blade 911. The outer circumference of
first blade 906 and the diameter of second axle portion 920 are
selected relative to the spacing of first rotation axis 914 and
second rotation axis 924 such that a small gap 938 is provided
between the tip of first tooth 908 and second axle portion 920.
Similarly, the outer circumference of second blade 916 and the
diameter of first axle portion 910 are selected relative to the
spacing of first rotation axis 914 and second rotation axis 924
such that a small gap 940 is provided between the tip of second
tooth 918 and first axle portion 910. Additionally, the outer
circumference of third blade 911 and the diameter of third axle
portion 922 are selected relative to the spacing of first rotation
axis 914 and second rotation axis 924 such that a small gap 942 is
provided between the tip of third tooth 913 and third axle portion
922.
[0085] Gap 934 is kept small so that tissue can be efficiently
sheared between first tooth 908 and second tooth 918. Similarly,
gap 936 is kept small so that tissue can be efficiently sheared
between second tooth 918 and third tooth 911. Gap 938 is kept small
so that tissue can be efficiently sheared between the tip of first
tooth 908 and second axle portion 920. Gap 940 is kept small so
that tissue can be efficiently sheared between the tip of second
tooth 918 and first axle portion 910. Gap 942 is kept small so that
tissue can be efficiently sheared between third tooth 913 and third
axle portion 922.
[0086] What is meant by "small gap" is a tight interface between
mating surfaces or edges, which in some embodiments is essentially
no gap at all. In these embodiments, mating parts may be configured
such that the gap is so small that it is not measurable. This may
be accomplished by creating a sliding fit between the mating parts,
or creating a small interference fit. With an interference fit, the
parts may be designed to flex away from each other so they do not
bind. In some embodiments, a "negative gap" or interference fit can
be reduced to a zero gap fit by driving the rotors with high torque
during a break-in period to allow the surfaces to wear or burnish
against each other to remove a small amount of material. In some
embodiments, at least one of the gaps 934 and 936 is no more than
30 microns. In some embodiments, at least one of the gaps 938, 940
and 942 is no more than 30 microns. In some embodiments, all of the
gaps 934, 936, 938, 940 and 942 are no more than 30 microns.
[0087] Additional blades may be added to rotatable members 902 and
904 such that each member has three or more blades, with the blades
of the first rotatable member 902 interdigitated with the blades of
the second rotatable member 902. With all gaps between the blades,
axle portions and housing kept small (no more than 30 microns in
some embodiments), tissue may be drawn into the housing and
efficiently sheared into small pieces with a reduced risk of the
rotatable members getting clogged or jammed.
[0088] Referring to FIGS. 10A-10C, additional details of the tissue
shearing process of some embodiments will be described. The
exemplary embodiment shown in these figures includes a first blade
1000 having a first tooth 1002, and a second blade 1004 having a
second tooth 1006. First blade rotates about a first axis 1008, and
second blade 1004 rotates about a second axis 1010 that is parallel
to and radially offset from first axis 1008. First blade 1000
partially overlaps with second blade 1004 in an overlap region
1012. First blade 1000 lies in a plane directly above second blade
1004 with a small gap therebetween, as with previously described
embodiments. First blade 1000 has a first axle portion 1014
directly below it, in the same plane as second blade 1004.
Similarly, second blade 1004 has a second axle portion 1016
directly above it, in the same plane as first blade 1000.
[0089] FIGS. 10A-10C show a progression of steps that occur when
the first and second blades cut tissue 1018 into small pieces. As
shown in FIG. 10A, first tooth 1002 and second tooth 1006 initially
engage the target tissue 1018 when the teeth are near the outer
reach of their orbits closest to the tissue. Teeth 1002 and 1006
grab the tissue and start to compress it as they travel toward each
other. As shown in FIG. 10A, a heart-shaped volume of tissue 1020
is engaged by the teeth. As teeth 1002 and 1006 travel closer
together as shown in FIG. 10B, the heart-shaped volume of tissue is
further compressed into a generally circular shaped piece of tissue
1022. As the tips of the teeth come closer together, this circular
volume 1022 is separated from the main tissue mass 1018. As shown
in FIG. 10C, tooth 1002 of first blade 1000 passes over second
blade 1004 and shears the compressed, circular tissue volume in
half against the second blade 1004, forming a first thin disc of
tissue 1024. The outer tip of first tooth 1002 comes close to the
outer diameter of second axle portion 1016 (within 30 microns or
less in some embodiments, as previously described.) Any portion of
tissue disc 1024 that may be hanging over the tip of the first
tooth 1002 is then sheared between the tip and second axle portion
1016. In a similar manner, tooth 1006 of second blade 1004 passes
over first blade 1000 and shears the compressed, circular tissue
volume in half against the first blade 1000, forming a second thin
disc of tissue 1026. The outer tip of second tooth 1006 comes close
to the outer diameter of first axle portion 1014 (within 30 microns
or less in some embodiments, as previously described.) Any portion
of tissue disc 1026 that may be hanging over the tip of the second
tooth 1006 is then sheared between the tip and first axle portion
1014. As teeth 1002 and 1006 continue to rotate past the overlap
region 1012, tissue discs 1024 and 1026 and other smaller pieces of
tissue are expelled into the center of the housing, in the
direction of Arrow A. It can be appreciated that when many blades
are stacked up and interdigitated like the two blades shown in
FIGS. 10A-10C, a target tissue volume 1018 may be quickly rendered
into many small discs of tissue.
[0090] In some embodiments, the diameter of tissue discs 1024 and
1026 is no larger than about 3000 microns. In other embodiments,
the diameter of tissue discs 1024 and 1026 is no larger than about
750 microns. In other embodiments, the diameter of tissue discs
1024 and 1026 is no larger than about 150 microns. In some
embodiments, the thickness of tissue discs 1024 and 1026 is no
larger than about 1000 microns. In other embodiments, the thickness
of tissue discs 1024 and 1026 is no larger than about 250 microns.
In other embodiments, the thickness of tissue discs 1024 and 1026
is no larger than about 50 microns. In some embodiments, the small
pieces of tissue expand as they are released from teeth 1002 and
1006. In other embodiments, the small pieces of tissue have had
liquid compressed out of them and do not expand appreciably. It can
be appreciated that when the profiles of first tooth 1002 and
second tooth 1006 are modified, the shape of the tissue pieces that
emerge may be other than disc shaped.
[0091] While exemplary embodiments have been shown having teeth on
opposing rotatable members that rotate in sync with one another, in
other embodiments the teeth may be arranged so that they are out of
sync with one another. In other words, a tooth from one blade may
shear tissue with a portion of an opposing blade where there is no
tooth, and vice versa. In some embodiments, the rotations of the
first and the second rotatable members are configured to
alternately rotate in and out of phase with one another. This may
be accomplished, for example, by independently driving the
rotatable members with separate motors and/or drive trains, by
driving two similar rotatable members at different speeds, or
driving two dissimilar rotatable members at the same speed.
[0092] In some embodiments the first and the second rotatable
members are configured to periodically reverse direction of
rotation during tissue cutting. This may be done to ensure the
tissue cutting head does not clog, to disengage the cutting head
from the target tissue, or to engage a different portion of the
target tissue, for example. Cutting teeth may be provided that cut
equally well in both directions, or are optimized for cutting in a
single direction. The rotations of the first and the second
rotatable members may be configured to reverse direction at least
once per second. In some embodiments the device is configured to
provide a dwell time of at least about 50 milliseconds when the
first and the second rotatable members reverse direction.
[0093] In view of the teachings herein, many further embodiments,
alternatives in design and uses of the embodiments of the instant
invention will be apparent to those of skill in the art. As such,
it is not intended that the invention be limited to the particular
illustrative embodiments, alternatives, and uses described above
but instead that it be defined by the claims presented
hereafter.
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