Note: Descriptions are shown in the official language in which they were submitted.
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SPECIALIZED CUTTER BLADES
FOR PREPARING INTERVERTEBRAL DISC SPACES
BACKGROUND OF THE INVENTION
[0001] This application builds upon a series of applications filed on behalf
of assignee.
In particular this application extends the innovative work in the area of
manipulating material
in the spine described in co-pending and commonly assigned United States
Patent
Application No. 10/972,077 for Method and Apparatus for Manipulating Material
in the
Spine filed October 22, 2004 and subsequently published as United States
Patent Application
No. US 2005/0149034 Al and United States Provisional Patent Application No.
60/778,035
for Method and Apparatus for Tissue Manipulation and Extraction filed February
28, 2006.
This application claims priority to the `035 application and incorporates by
reference both the
`077 application and the `035 application.
[0002] This application extends the innovative work in the area of spinal
motion
preservation assemblies described in co-pending and commonly assigned United
States
Patent Application No. 11/586,338 for Spinal Motion Preservation Assemblies
filed October
24, 2006 and United States'Patent Application 11/586,486 for Methods and Tools
for
Delivery of Spinal Motion Preservation Assemblies filed October 24, 2006_ This
application
claims priority to and incorporates by reference both `338 and the `486
application.
-20 [0003] While a number of applications have been incorporated by reference
to provide
additional detail it should be noted that these other applications (including
those that have
subsequently issued as patents) were written at an earlier time and had a
different focus from
the present application. Thus, to the extent that the teachings or use of
terminology differ in
any of these incorporated applications from the present application, the
present application
controls.
[0004] 1. Field of the Invention.
[0005] This invention relates generally to improved cutters and methods for
preparing
treafiment sites within the spine, such at the intervertebral space between
two adjacent
vertebral bodies for subsequent therapeutic procedures including therapies
where fusion of
the two adjacent vertebral bodies is not desired such as therapies for the
implantation of
rriotion preservation devices into the spine.
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[0006] Overview
[0007] The present invention is an extension of work in a series of patent
applications
(some now issued patents) with a common assignee. Much of the work is
described in great
detail in the many applications referenced above and incorporated by reference
into this
application. Accordingly, the background of the invention provided here does
not repeat all
of the detail provided in the earlier applications, but instead highlights how
the present
invention adds to this body of work.
[0008] The spinal column is a complex system of bone segments (vertebral
bodies and
other bone segments) which are in most cases separated from one another by
discs in the
intervertebral spaces (sacral vertebrae are an exception). Figure 1 shows the
various
segments of a human spinal column as viewed from the side. In the context of
the present
disclosure, a "motion segment" includes adjacent vertebrae, i.e., an inferior
and a superior
vertebral body, and the intervertebral disc space separating said two
vertebral bodies, whether
denucleated space or with intact or damaged spinal discs. Unless previously
fused (or
damaged), each motion segment contributes to the overall flexibility of the
spine contributes
to the overall ability of the spine to flex to provide support for the
movement of the trunk and
head.
[0009] The vertebrae of the spinal cord are conventionally subdivided into
several
sections. Moving from the head to the tailbone, the sections are cervical 104,
thoracic 108,
lumbar 112, sacral 116, and coccygeal 120. The individual vertebral bodies
within the
sections are identified by number starting at the vertebral body closest to
the head. The trans-
sacral approach is well suited for access to vertebral bodies in the lumbar
section and the
sacral section. As the various vertebral bodies in the sacral section are
usually fused together
in adults, it is sufficient and perhaps more descriptive to merely refer to
the sacrum rather
than the individual sacral components.
[0010] It is useful to set forth some of the standard medical vocabulary
before getting into
a more detailed discussion of the background of the present invention. In the
context of the
this discussion: anterior refers to in front of the spinal column; (ventral)
and posterior refers
to behind the column (dorsal); cephalad means towards the patient's head
(sometimes
"superior"); caudal (sometimes "inferior") refers to the direction or location
that is closer to
the feet. As the present application contemplates accessing the various
vertebral bodies and
intervertebral spaces through a preferred approach that comes in from the
sacrum and moves
towards the head, proximal and distal are defined in context of this channel
of approach.
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Consequently, proximal is closer to the beginning of the channel and thus
towards the feet or
the surgeon, distal is further from the beginning of the channel and thus
towards the head, or
more distant from the surgeon. When referencing tools including cutters,
distal would be the
end intended for insertion into the access channel and proximal refers to the
other end,
generally the end closer to the handle for the tool.
[0011] The individual motion segments within the spinal columns allow movement
within constrained limits and provide protection for the spinal cord. The
discs are important
to cushion and distribute the large forces that pass through the spinal column
as a person
walks, bends, lifts, or otherwise moves. Unfortunately, for a number of
reasons referenced
below, for some people, one or more discs in the spinal column will not
operate as intended.
The reasons for disc problems range from a congenital defect, disease, injury,
or degeneration
attributable to aging. Often when the discs are not operating properly, the
gap between
adjacent vertebral bodies is reduced and this causes additional problems
including pain.
[0012] A range of therapies have been developed to alleviate the pain
associated with
disc problems. One class of solutions is to remove the failed disc and then
fuse the two
adjacent vertebral bodies together with a permanent but inflexible spacing,
also referred to as
static stabilization. One estimate is that in 2004 there were an estimated
300,000 fusion
operations throughout the world. Fusing one section together ends the ability
to flex in that
motion segment. While the loss of the normal physiologic disc function for a
motion
segment through fusion of a motion segment may be better than continuing to
suffer from the
pain, it would be better to alleviate the pain and yet retain all or much of
the normal
performance of a healthy motion segment.
[0013] The Operation of the Spine
[0014] The bodies of successive lumbar, thoracic and cervical vertebrae
articulate with
one another and are separated by the intervertebral spinal discs. Each spinal
disc includes a
fibrous cartilage shell enclosing a central mass, the "nucleus pulposus" (or
"nucleus" herein)
that provides for cushioning and dampening of compressive forces to the spinal
column. The
shell enclosing the nucleus includes cartilaginous endplates adhered to the
opposed cortical
bone endplates of the cephalad and caudal vertebral bodies and the "annulus
fibrosus" (or
"annulus" herein) includes multiple layers of opposing collagen fibers running
circumferentially around the nucleus pulposus and connecting the cartilaginous
endplates.
The natural, physiological nucleus includes hydrophilic (water attracting)
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mucopolysacharides and fibrous strands (protein polymers). The nucleus is
relatively
inelastic, but the annulus can bulge outward slightly to accommodate loads
axially applied to
the spinal motion segment.
[0015] The intervertebral discs are anterior to the spinal canal and located
between the
opposed end faces or endplates of a cephalad and a caudal vertebral bodies.
The inferior
articular processes articulate with the superior articular processes of the
next succeeding
vertebra in the caudal (i.e., toward the feet or inferior) direction. Several
ligaments
(supraspinous, interspinous, anterior and posterior longitudinal, and the
ligamenta flava) hold
the vertebrae in position yet permit a limited degree of movement. The
assembly of two
vertebral bodies, the interposed, intervertebral, spinal disc and the attached
ligaments,
muscles and facet joints is referred to as a "spinal motion segment"
[0016] The relatively large vertebral bodies located in the anterior portion
of the spine
and the intervertebral discs provide the majority of the weight bearing
support of the vertebral
column. Each vertebral body has relatively strong, cortical bone layer forming
the exposed
outside surface of the body, including the endplates, and weaker, cancellous
bone in the
center of the vertebral body.
[0017] The nucleus pulposus that forms the center portion of the
intervertebral disc
consists of 80% water that is absorbed by the proteoglycans in a healthy adult
spine. With
aging, the nucleus becomes less fluid and more viscous and sometimes even
dehydrates and
contracts (sometimes referred to as "isolated disc resorption") causing severe
pain in many
instances. The spinal discs serve as "dampeners" between each vertebral body
that minimize
the impact of movement on the spinal column, and disc degeneration, marked by
a decrease
in water content within the nucleus, renders discs ineffective in transferring
loads to the
annulus layers. In addition, the annulus tends to thicken, desiccate, and
become more rigid,
lessening its ability to elastically deform under load and making it
susceptible to fracturing or
fissuring, and one form of degeneration of the disc thus occurs when the
annulus fissures or is
torn. The fissure may or may not be accompanied by extrusion of nucleus
material into and
beyond the annulus. The fissure itself may be the sole morphological change,
above and
beyond generalized degenerative changes in the connective tissue of the disc,
and disc
fissures can nevertheless be painful and debilitating. Biochemicals contained
within the
nucleus are enabled to escape through the fissure and irritate nearby
structures.
[0018] Various other surgical treatments that attempt to preserve the
intervertebral
spinal disc and to simply relieve pain include a "discectomy" or "disc
decompression" to
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remove some or most of the interior nucleus thereby decompressing and
decreasing outward
pressure on the annulus. In less invasive microsurgical procedures known as
"microlumbar
discectomy" and "automated percutaneous lumbar discectomy", the nucleus is
removed by
suction through a needle laterally extended through the annulus. Although
these procedures
are less invasive than open surgery, they nevertheless suffer the possibility
of injury to the
nerve root and dural sac, perineural scar formation, re-herniation of the site
of the surgery,
and instability = due to excess bone removal. In addition, they generally
involve the
perforation of the annulus.
[0019] Although damaged discs and vertebral bodies can be identified with
sophisticated diagnostic imaging, existing surgical interventions and clinical
outcomes are
not consistently satisfactory. Furthermore, patients undergoing such fusion
surgery
experience significant complications and uncomfortable, prolonged
convalescence. Surgical
complications include disc space infection; nerve root injury; hematoma
formation; instability
of adjacent vertebrae, and disruption of muscle, tendons, and ligaments, for
example.
[0020] As noted previously, the normal nucleus is contained within the space
bounded
by the bony vertebrae above and below it and the annulus fibrosus, which
circumferentially
surrounds it. In this way the nucleus is completely encapsulated and sealed
with the only
communication to the body being a fluid exchange that takes place through the
bone interface
with the vertebrae, known as the endplates.
[0021] The hydroscopic material found in the physiological nucleus has an
affinity for
water (and swells in volume) which is sufficiently powerful to distract (i.e.,
elevate or
"inflate") the intervertebral disc space, despite the significant
physiological loads that are
carried across the disc in normal activities. These forces, which range from
about 0.4x to
about 1.8x body weight, generate local pressure well above normal blood
pressure, and the
nucleus and inner annulus tissue are, in fact, effectively avascular.
[0022] Details of specific advantages and specific motion preservation devices
including
methods for implanting motion preservation devices are described in various
pending
applications including 11/586,338 and 11/586,486 referenced above. The reader
may select
to read these details but there is not a need to repeat that material in its
entirety here.
[0023] While the cutters described below may be used in other surgical
procedures
including spinal surgery that does not approach an intervertebral space via an
axial approach
but comes to the space through an anterior or a posterior approach. The
cutters may be used
in surgical procedures with the motion preservation devices inserted axially
within the spine,
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following either partial or complete nucleectomy and possibly through a
cannula that is
docked against the sacrum, into a surgically de-nucleated disc space, from
said access point
across a treatment zone. In such a procedure, the introduction of the spinal
motion
preservation assembly of the present disclosure is accomplished without the
need to
surgically create or deleteriously enlarge an existing hole in the annulus
fibrosus of the disc.
[0024] Design of cutter blades includes considerations in many cases of the
efficiency
with which the cutter blade prepares the contents of the nucleus for removal
by cutting
(slicing, tearing, or some combination of the two). It is generally desirable
to allow a surgeon
to work quickly and efficiently to reduce the time of surgery which has
benefits in reducing
the use of expensive resources such as the surgical team and the surgical
suite and also
reduces the length of time that a patient is kept under anesthesia.
[0025] A cutter blade that must be replaced frequently may be less desirable
than a cutter
blade with similar characteristics that is more durable and thus may be used
longer without
needing to be replaced.
[0026] A cutter blade that fails in a mode where all the pieces of the failed
cutter blade
may be easily removed from the intervertebral disc space and the patient body
may be
preferred over a similar cutter blade that does not have this characteristic.
SUMMARY OF THE DISCLOSURE
[0027] Disclosed herein are cutter assemblies for use with cutter blades made
of shape
memory materials. The cutter blades may be deployed in the interior of an
intervertebral disc
space and rotated relative to a central axis of the cutter assembly which is
substantially
aligned with a centerline of an axis channel. Rotation of a cutter blade as
part of a cutter
assembly within an intervertebral disc space cuts the material present there
for removal from
the intervertebral disc space. Cutter blades with different attributes (such
as throw length,
cutter blade angle, type and location of blade edges) are adapted to achieve
different
objectives within the intervertebral disc space. Some cutter blades are
adapted to promote
bleeding of cartilage and vertebral body endplates and some cutter blades are
adapted to
avoid causing such bleeding as different therapeutic procedures seek- or seek
to avoid such
bleeding.
[0028] The use of a hollow ground to enhance the cutting action of a blade
edge is
described in connection with the creation of cutter blades.
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[0029] A variety of thin cutter blades are described which may be used in the
interior of a
thin intervertebral disc (having a reduced distance between the endplates of
the adjacent
vertebral bodies).
[0030] Other systems, methods, features and advantages of the invention will
be or will
become apparent to one with skill in the art upon examination of the following
figures and
detailed description. It is intended that all such additional systems,
methods, features and
advantages be included within this description, be within the scope of the
invention, and be
protected by the accompanying claims.
BRIEF DESCRIPTION OF THE FIGURES
[0031] The invention can be better understood with reference to the following
figures.
The components in the figures are not necessarily to scale, emphasis instead
being placed
upon illustrating the principles of the invention. Moreover, in the figures,
like reference
numerals designate corresponding parts throughout the different views.
[00321 FIG. 1 identifies the sections of a human spine.
[0033] FIGS. 2(A)-(C) illustrates an anterior trans-sacral axial access method
of
creating an axial channel in the spine which can be used to prepare an axial
channel in the
spine for use with the present disclosure.
[0034] FIG. 3 shows a cutter assembly inserted into an axial channel with the
cutter
blade in an extended position.
[0035] FIGs 4A-4B are views of a cutter assembly.
[0036] FIG. 5A-5B shows one method for connecting a cutter blade to a cutter
shaft.
[0037] FIG. 6A-6D provides additional views of a cutter assembly including
stops that
limit the range of travel of the cutter sheath.
[0038] FIG. 7 addresses the concept of a series of cutter blades of different
throw
lengths within an intervertebral disc space
[0039] FIGs. 8A-8D shows a series views of a closed loop cutter blade that is
adapted
to scrape away the cartilaginous endplate and roughen the vascularized
vertebral body so as
to cause bleeding.
[0040] FIGs. 9A-9D show four views of a cutter blade of FIG. 8 with a hollow
ground.
[0041] FIG. 10 shows a lateral view of a portion of a human spine.
[0042] FIG. 11 shows an top perspective view of a thin cutter blade for use in
situations such as a thin disc.
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[0043] FIGs. 12A-12D provide additional views of the thin cutter blade of FIG.
11.
[0044] FIG. 13 is a top perspective view of an exploded drawing of thin cutter
blade
shown in FIG. 11.
[0045] FIG. 14 provides a side view of a thin cutter blade that has a 45
degree angle
between the blade arm portion of the proximal arm and the longitudinal portion
of the
proximal arm.
[0046] FIG. 15 shows a thin cutter blade with the cutting edges recessed from
the
exterior surfaces of the thin cutter blade by having adjacent blade edges from
the distal arm
and the proximal arm.
[0047] FIG. 16 shows a "L" cutter blade which used a single arm rather than a
pair of
arms.
[0048] FIG. 17 shows a number of views of an "L" cutter blade that is much
like "L"
cutter blade except that the cutting edges are on the proximal side of the "L"
cutter blade.
[0049] FIGs. 18-19 focus on cutter shafts and the use of cutter shaft
extensions.
[0050] FIG. 20 is the distal end of a cutter shaft.
[0051] FIG. 21 is an enlarged detail of FIG. 20.
[0052] FIG. 22 is a cross section of the distal end of the cutter shaft of
FIG. 20.
[0053] FIG. 23 is the distal end of a cutter shaft.
[0054] FIG. 24 is an enlarged detail of FIG. 23.
[00551 FIG. 25 is a cross section of the distal end of the cutter shaft of
FIG. 23.
[0056] FIGs. 26A-26B are a cutter blade attached to a cutter shaft by a rivet.
[0057] FIG. 26C shows a cutter blade attached to a cutter shaft with a rivet
where.the
cutter shaft has cutter shaft extensions.
DETAIf.,ED DESCRIPTION
[0058] While the inventive cutters described below may be used in other
surgical
procedures, it is useful in context to describe how these cutters could be
adopted for use in a
trans-sacral approach. As noted above there are many advantages associated
with a
minimally invasive, low trauma trans-sacral axial approach. The trans-sacral
axial approach
(described and disclosed in commonly assigned United States Patent Nos.
6,558,386;
6,558,390; 6,575,979; 6,921,403; 7,014,633, and 7,087,058) has a number of
advantages over
other routes for delivery of therapeutic devices to motion segments but there
are logistical
challenges to the preparation of an intervertebral disc space via an axial
access channel. The
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process of addressing these challenges impacts certain aspects of the
cutters'intended for use
in this manner.
[0059] Trans-Sacral Axial Access
[0060] The trans-sacral axial access method illustrated in Figure 2,
eliminates the need
for muscular dissection and other invasive steps associated with traditional
spinal surgery
while allowing for the design and deployment of new and improved instruments
and
therapeutic interventions, including stabilization, motion preservation, and
fixation
devices/fusion systems across a progression-of-treatment in intervention.
[0061] Figure 2 provides an introductory overview of the process with Figure
2(a) and
2(b) showing the process of "walking" a blunt tip stylet 204 up the anterior
face of the
sacrum 116 to the desired position on the sacrum 116 while monitored one or
more
fluoroscopes (not shown). This process moves the rectum 208 out of the way so
that a
straight path is established for the subsequent steps. Figure 2(c) illustrates
a representative
trans-sacral axial channel 212 established through the sacrum 116, the
L5/sacrum
intervertebral space, and into the L5 vertebra 216. If therapy is being
provided to the L4/L5
motion segment then the channel would continue through the L5 vertebra 216
through the
L4/L5 intervertebral space, and into the L4 vertebra 220.
[0062] The discussion of Figure 2 is provided to provide context for the
present
disclosure. Previous applications (some now issued as United States patents)
with common
assignee have included a description of an alternative access method that is a
posterior trans-
sacral axial spinal approach rather than an anterior trans-sacral axial spinal
approach. (See
e.g. United States Patent No. 6,558,386 for Axial Spinal Implant and Method
and Apparatus
for Implanting an Axial Spinal Implant Within the Vertebrae of the Spine as
this patent
'25 describes the anterior trans-sacral axial approach illustrated in Figure 2
and is incorporated by
reference in its entirety.)
[0063] Referring to FIG. 3, a cutter 400 is inserted through the axially
aligned anterior
tract 372 defined by the lumen of the dilator sheath 380 and the axial channel
212 which is
difficult to see as the dilator sheath 380 substantially fills the axial
channe1212 as it passes
through the sacnun 116. (One of skill in the art will appreciate that the
axial channe1212 may
be extended axially by a sequence of steps so that the length of an axial
channel in one Figure
may be different from another Figure such that the axial tract may include
additional
vertebral bodies or intervertebral disc spaces). One of skill in the art will
appreciate that due
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to anatomical differences the axial channel for some therapies may miss the
sacrum and may
enter through another portion of the spine.
[0064] As shown in FIG. 3, motion segment 316 that includes the proximal
vertebra 308
(the sacrum 116), the intervertebral space 312 (in this case the L5-S1 space
with disc 330,
annulus fibrosus 334 and nucleus 338), the distal vertebra 304 (in this case
L5 216). The
cutter 400 comprises a cutting blade (e.g., cutter blade 453 which refers
collectively to any
blade configuration) which is remotely manipulable. The manipulations of the
cutter
blade 453 may include retracting the cutter blade 453 into the cutter assembly
400 so that the
maximum radius of the cutter assembly 400 is reduced and the cutter assembly
with the
retracted blade 453 may be advanced through the axial channel 212. After
reaching the
location where the cutter blade 453 is to be operated, the cutter blade 453
may be extended.
[0065] As shown in FIG. 3, the centerline 262 of the cutter 400 is very close
to the
centerline of the axial channe1212 due to the fit of the dilator sheath 380 in
the axial
channe1212 and the fit of the cutter 400 within the dilator sheath 380. When
the cutter
blade 453 is extended as shown in FIG. 3 the cutter blade is substantially
transverse to the
centerline 262 of the cutter 400. The extended cutter blade 453 is extended
laterally into the
nucleus 338 of the spinal disc 330.
[0066] The cutter shaft 410, cutter sheath 430 (shown in Fig. 4) and the
handle
components are preferably co-configured to enable the cutter blade 453 and the
cutter shaft
410 to which it is attached be able to be "pushed-pulled" so as to retract the
cutter blade 453
into the cutter sheath and then extend the cutter blade 453 from the distal
end of the cutter
sheath as needed. More specifically, the cutter blade edges(s) of the cutter
blade 453 are
retracted into the cutter sheath 430 (Fig. 4) for delivery into the
intervertebral disc space 312.
Once the cutter 400 is in position, the cutter blade 453 is extended distally
and rotated using
the handle to cut tissue within the intervertebral disc space 312. After
completing the cutting
task or until the cutter blade needs replacement, the cutter blade 453 is
again retracted into
the cutter sheath 430 (Fig. 4) for removal of the cutter assembly unit 400
from the axial
channe1212.
[0067] The cutter assembly 400, cutter blade 453 and cutter assembly shaft 410
are
shown schematically in FIGS. 4A-4B and not necessarily to scale to one another
or to the
axial channel 212.
[0068] Cutters can be used to perform nucleectomies via insertion into a disc
space to
excise, fragment and otherwise loosen nucleus pulposus and cartilage from
endplates from
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within the disc cavity and from inferior and superior bone endplate surfaces.
As noted within
this disclosure, damage to or removal of cartilage tends to cause bleeding
within the
intervertebral disc space 312. Bleeding tends to promote bone growth, which
may be desired
in a fusion type therapy but may be undesirable in other therapies, including
therapies that
call for the implantation of a motion preservation device into the motion
segment 316.
[0069] With reference to the exemplary embodiments of FIGS. 4A-B, the cutter
assembly 400 (also referred to as simply a cutter) includes: a cutter shaft
410 with a distal end
412 and a proximal end 414; a cutter blade 453 connected to the distal end 412
of the cutter
shaft 410; a handle 416 connected to the proximal end 414 of the cutter shaft
by an
attachment process such as a set screw or pin; a cutter sheath 430 placed
concentrically over
the shaft 410; and a shaft sleeve 418 (shown in subsequent drawings).
[0070] FIGs. 5A-5B illustrate one method of connecting a cutter blade 453 to a
cutter
shaft 410. Before the pin 409 is inserted, the longitudinal portion 406 of the
cutter blade 453
is placed into a slot 413 near the distal end 412 of the cutter shaft 410. The
cutter blade slot
427 may be aligned with the cutter shaft hole 411 within the shaft slot 413. A
pin 409 may
be placed through a shaft sleeve hole 419 in a shaft sleeve 418 and through a
cutter blade
slot 427 (visible in FIG 5A), a cutter blade hole 407 on the opposite side of
the longitudinal
portion 406 of the cutter blade 453 (best seen in FIG. l0A). The pin passes
through cutter
blade hole 407 and into a cutter shaft hole 411 in a cutter shaft slot 413.
[0071] The shaft slot 413 is dimensioned to accommodate a cutter blade 453.
The width
of the slot 413 is approximately the same as the width of the longitudinal
portion 406 of the
cutter blade 453. The curvature 428 at the distal end of the slot 413
accommodates the
curvature of the cutter blade 453 between the longitudinal portion 406 and the
portion of the
cutter blade that may be extended 402 (also known as the cutter blade arm 402)
(which
defines the reach or throw of the cutter blade 453). The slot 413 provides
torsional support to
the cutter blade arm 402 while the curvature 428 at the distal end of the slot
413 provides
axial support to the cutter blade arm 402 to work in conjunction with cutter
blade edge
geometries to reinforce the cutter blade 453. The cutter shaft extension 480
discussed in
more detail below provides additional support to the cutter blade 453 to
reduce the tendency
of the cutter blade to flex when rotated into tissue.
[0072] The shaft sleeve 418 when pinned, effectively serves to align and fix
the shaft 410
and the longitudinal portion 406 of the cutter blade 453. For purposes of
illustration, the pin
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409 that fixes the cutter blade 453 to the shaft 410 may be approximately 0.06
inches
(1.5 mm) in diameter.
[0073] As cutter blade hole 407 is pinned to the cutter blade shaft 410, the
cutter blade
453 is affixed to the cutter blade shaft 410. The cutter blade slot 427 allows
some relative
motion of the slotted portion of the longitudinal portion 406 relative to the
pinned portion of
the longitudinal portion 406 to accommodate the change of shape of the cutter
blade 453 as it
goes from sheathed to extended and back to sheathed.
[0074] The rest of the cutter 400 components can be fixedly secured to each
other using
any known suitable fixation mechanisms.
[0075] FIGs 6A-6D provides a series of views of a cutter assembly 400. FIG. 6A
is a top
view of the cutter assembly 400. FIG. 6B is a rear view of the cutter assembly
400. FIG. 6C
is a cross section of FIG. 6B. FIG. 6D is a enlarged portion of FIG. 6C.
[0076] As shown an FIGs. 6A and 6D, the slot in the cutter shaft 410 may be
oriented so
that the handle 416 is aligned with the blade arm 402 (when extended). While
not required,
this relationship between the handle and blade is a useful way to allow the
surgeon to keep
track of the position of the extended blade arm 402 by knowing rotational
position of the
handle 416.
[0077] As best seen in Figure 6D, the travel range 440 of the cutter sheath
430 is limited
at the proximal end by a proximal end stop 444 attached to the cutter shaft
410. The travel
range 440 of the cutter sheath 430 is limited at the distal end by a shoulder
448 on the cutter
shaft 410.
[0078] One of skill in the art will appreciate that while the cutter blades
453 are to be
used with a single patient and then disposed, that, certain components such as
the handle 416,
cutter shaft 410, and cutter sheath 430 may be =reusable. The handle and
cutter shaft could be
made as one integral component.
[0079] A sleeve or internal sheath liner (not shown) may be inserted inside
the cutter
sheath to reduce friction. The cutter blade 453 may be formed from a shape
memory alloy
including a nickel-titanium shape memory alloy such as NitinolTM. The cutter
sheath 430
may be made from an appropriate grade of stainless steel. To reduce the
friction between the
cutter blade 453 and the inner surface of the cutter sheath 430, a dry
lubrication such as poly-
tetrafluoroethylene (PTFE) may be used. Alternatively, the sleeve or internal
sheath liner
may be made of a material with a coefficient of fiiction that is lower than
the cutter blade. If
this component is to be reused, it may be chosen for its ability to withstand
multiple
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sterilization cycles. Ultra-high molecular weight polyethylene (UHMWPE) is one
such
material.
[0080] After this introduction to cutters and cutter components, it is useful
to discuss why
a sequence of cutters may be used while preparing the interior of an
intervertebral disc
space 312. FIG. 7 shows a first example. In FIG.7 a motion segment 316
including a distal
vertebral body 304, an intervertebral disc space 312 (with a intervertebral
disc 330 including
an annulus fibrosus 334, and nucleus pulposus 338 and bounded by the
endplates), and a
proximal vertebral body 308 are shown. For purposes of this example, it is not
important
which vertebral bodies are involved beyond the need for them to be adjacent
vertebral bodies.
[0081] FIG. 7 includes the endplate 342 of the distal vertebral body 304 and a
representation of the layer of cartilage 346 located on the endplate 342 which
defines one
portion of the intervertebral disc space 312. Assuming the route of access is
a trans-sacral
axial access, from the point of reference of the intervertebral disc space
312, endplate 342
would be the superior endplate. Likewise FIG. 7 includes the endplate 352 of
the proximal
vertebral body 308 and a representation of the layer of cartilage 356 located
on the
endplate 352 which defines one portion of the intervertebral disc space 312.
Assuming the
route of access is a trans-sacral axial access, from the point of reference of
the intervertebral
disc space 312, endplate 352 would be the inferior endplate.
[0082] One of skill in the art will recognize that the inclusion of the
cartilage layers 346
and 356 is for purposes of discussing the use of cutters and is not intended
to be an
anatomically correct and appropriately dimensioned representation of
cartilage.
[0083] The position of the cutter within the intervertebral disc space may be
visible to the
surgeon under real-time fluoroscopic imaging (possibly both anterior/posterior
and lateral
imaging).
[00841 In order to illustrate a point, FIG. 7 includes representations of
three different
cutter blades 504, 508, and 512 of differing throw lengths. One of ordinary
skill in the art
will appreciate that one method for cutting the nucleus 338 would use a series
of cutter blades
(504, 508, 512, and possibly another longer blade) to gradually cut the
nucleus 338. One of
ordinary skill in the art will understand that these three blades of different
throw lengths
(sometime called reaches) would be used sequentially from shorter to longer
and it is only for
the point of illustration that three different blade lengths are shown
simultaneously in FIG. 7.
To provide context, the reach of a series of cutter blades used in a
particular procedure may
range from 0.40 inches for a small cutter blade to 0.70 inches for a large
cutter blade. One of
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skill in the art will recognize that these ranges are illustrative and could
be different. It will
be understood that the optimum throw for cutter blades depends on several
factors, including
patient anatomy and (axial) entrance point into the disc space, as well as
issues related to
sagittal synunetry of the spinal disc. Moreover, for safety reasons, it may be
desirable to
limit the length of the cutter blade to preclude a throw that is too close to
the disc edge, in
other words to avoid making contact between the cutter blade and the annulus
fibrosus to
preclude compromising the annulus fibrosus.
[0085] Note that the cutter blades 504, 508, and 512 when extended are
transverse to the
centerline of the cutter 262 and parallel to the axis 266 that is
perpendicular to cutter blade
centerline 262. The cutter blades are also close to parallel to the endplates
342 and 352 and
the layers of cartilage 346 and 356.
[0086] In this example, the successively longer cutter blades 504 508, and
512, could be
rotated 360 degrees or more around the centerline 262. Some surgeons may
prefer to work
on one segment at a time by rotating the cutter handle a fraction of 360
degrees (perhaps
approximately 90 degrees) then rotating the cutter handle in the opposite
direction to return to
the position occupied by the cutter. Thus, the process tends to proceed while
working on
radial quadrants. Sometimes this short movement is compared to the movement of
windshield wipers on an automobile.
[0087] In addition to using a series of cutter blades with sequentially
increasing throws,
the surgeon will need to adjust the axial position of the cutter blade by
sliding the cutter
forward (in the direction towards distal) relative to the motion segment so
that the cutter
blade move sequentially closer to the cartilage 346 on the endplate 342 on the
distal vertebral
body 304. The surgeon may opt to create a first space relatively close to the
proximal
vertebral body by using a sequence of cutters of increasing throws then
repeating the process
with the cutter extended further into the nucleus (and repeating the sequence
of blades of
increasing throws).
[0088] Alternatively, the surgeon may choose to use one or more cutters with a
first
throw to create a space approximating a cylinder that is substantially the
height of the space
between the two layers of cartilage and a radius approximately equal to a
first blade throw.
This process may involve the use of a radial cutter blade with a given throw
length followed
by one or more cutter blades at a different blade angle(s) (for example 45
degrees) but the
same throw length. Once the cutting is complete for a given throw length, the
surgeon moves
to cutter blades of a longer throw length starting again with a radial cutter
blade. This
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process may be repeated with cutter blades of increasing blade throws until
the desired
amount of space is created.
[0089] The nature of the therapeutic procedure and the patient anatomy will
determine
the maximum cutter blade throw length required. Certain procedures may tend to
use a
greater number of cutter blade throw lengths to make smaller incremental
increases in throw
length. Other procedures may simply use a small throw length then move to the
maximum
throw length needed to prepare the intervertebral disc space.
[0090] As the nucleus material is cut, the surgeon may periodically remove the
cutter
from the axial channel and use any appropriate tissue extractor tool. United
States Patent
Application No. 10/972,077 (referenced above) describes several retractable
tissue extractors
that may be used for this purpose.
[0091] United States Patent Application No. 10/972,077 (referenced above)
noted that
when preparing a intervertebral disc space for a fusion procedure, it can be
advantageous to
use cutters to scrape away the cartilaginous endplate and roughen the
vascularized vertebral
body so as to cause bleeding, which is desirable in order to facilitate bone
growth and to
promote fusion of the vertebral bodies of the relevant motion segment.
[0092] However, not all therapeutic procedures seek to obtain such bleeding to
promote
fusion. It is unavoidable to disturb the a portion of endplate 352 of the
proximal vertebral
body as the axial channel is created through the endplate 352 and it is
likewise unavoidable to
disturb a portion of the cartilage 356 in the immediate vicinity of the axial
channel (likewise
the endplate 342 and cartilage 346 of the distal vertebral body 304 if the
axial channel 212
(FIG. 2C) is extended into the distal vertebral body 304. However, the
unavoidable
disturbance of a small portion of an endplate and cartilage does not remove
the advantage
within certain procedures of avoiding damage to other portions of the
cartilage and endplate.
[0093] FIG. 8 shows a series views of a closed loop cutter blade 500 that is
adapted to
scrape away the cartilaginous endplate and roughen the vascularized vertebral
body so as to
cause bleeding. Visible are the cutter blade hole 407 and the cutter blade
slot 427. The cutter
blade arm 402 is joined to the longitudinal portions 406 by a pair of
transitional sections 470.
While the precise position is not particularly relevant, in the area where the
two transitional
sections 470 meet the two longitudinal sections 406, the two ends of the
cutter blade meet.
This point of contact could be deemed the place where the loop is closed.
However, it may
be simpler to call the loop closed at 550 which is placed at cutter blade hole
407 and the
currently adjacent portion of cutter blade slot 427 as those two are joined
when the cutter
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blade is attached to the cutter assembly at the blade shaft (See FIG. 5) The
closed loop adds a
safety feature in that in the event of a break in cutter blade 500 while
inserted into an
intervertebral disc space, the cutter blade 500 will remain connected to the
cutter shaft
through either the portion of the cutter blade with the slot 427 (in this case
the distal arm 560
of the cutter blade 500) or the portion of the cutter blade with a hole 407
(in this case the
proximal arm 564 of the cutter blade 500). (One of skill in the art will
recognize that the
distal arm 560 meets the proximal arm 564 at the blade tip 548). As all parts
of the cutter
blade 500 are connected to the cutter shaft such that in the event of a break
in the cutter blade,
the parts can be removed from the intervertebral disc space by prompt removal
of the cutter
assembly.
{0094] Surgeons may note a break in the cutter blade- either by a change in
feel in the
operation of the cutter or by a visible change in the cutter blade as
indicated in the real-time
fluoroscopic imaging. While cutter blades and the process for using cutter
blades are
designed with the intent to avoid breaking cutter blades within the patient's
body, it is useful
to provide this safety feature given the nature of the use of the cutter
blades which come in
contact with vertebral bodies.
10095] Cutter blade 500 can be said to have six different cutting edges 504,
508, 512,
516, 520, 524. Three cutting edges 504, 508, 512 on one side and three cutting
edges 516,
520, 524 on the other side. Edges 504 and 516 are on the proximal portion 536
of the blade
arm 402 of the cutter blade 500, that is the portion of the blade arm that is
closer to the handle
416 (Fig. 4A) than the other portion of the closed loop that is the distal
portion 542 of the
blade arm 402.
[0096] When inserted into the intervertebral disc space, the exterior of the
proximal
portion 536 will generally face the endplate on the proximal vertebral body
(whether or not
the proximal portion is parallel to the endplate). Edges 508 and 520 are on
the distal
portion 542 of the blade arn2 402. When inserted into the intervertebral disc
space, the
exterior of the distal portion 542 will generally face the endplate on the
distal vertebral body
(whether or not the distal portion 542 is parallel to the endplate). Edges 512
and 524 are on
the tip 548 of the cutter blade 500 between the distal portion 542 and the
proximal portion
536 of the blade arm 402 and connecting the distal arm 560 and the proximal
arm 564.
[0097] The cutting edges along the proximal portion 536 and the distal portion
542 of the
blade arm 402 do not extend over the entire blade arm 402. As indicated in
FIG. 7 it is
contemplated that a series of cutter blades of increasing length will be used
so that the cutter
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blade edges do not need to extend over the entire range that was previously
cut by a previous
cutter blade.
[0098] Note that the sides of a cutter blade are not necessarily flat. The
sides (sometimes
called faces) have features that are visible when looking at that side or face
of the object (just
as the indentations on one of the six faces of a single die from a pair of
dice are visible when
looking at that face or side of the die).
[0099] In each case, the six cutting edges are on the outer perimeter 556 of
the closed
loop rather than on the inside perimeter 552 as the outer perimeter 556 is the
better choice for
edge placement in order to contact the cartilage on an endplate. By placing
the cutting edges
on the outer perimeter 556 of the closed loop, the cutter blade 500 is adapted
to maximize the
effectiveness of the cutter blade in cutting either the cartilage 356 (FIG. 7)
on the proximal
endplate 352 (likely to be the inferior endplate when viewed in context of the
intervertebral
disc space 312) or the cartilage 346 (FIG. 7) on the distal endplate 342
(likely to be the
superior endplate when viewed in the context of the intervertebral disc space
312).
[00100] By having cutting edges on both sides of cutter blade 500, the surgeon
may cut
nucleus material while rotating the cutter blade in the clockwise direction
and also while
rotating the cutter blade in the counter-clockwise direction. (Clockwise and
counterclockwise are dependent on orientation. One way of defining clockwise
would be as
viewed from the cutter while looking from proximal towards distal end of the
cutter
assembly. This would match the way the surgeon would view rotation of the
cutter handle.)
.[00101] While being bidirectional is a useful feature, not all cutter blades
must have
cutting edges on both sides. Some cutter blades may have one type of cutting
edge on one
side and a second type of cutter blade on the second side. While it may be
advantageous for
some cutter blades to have blade edges on the tips of the cutter blade, some
cutter blades may
not have a blade edge in the tip or may have a different blade edge type in
the tip 548 than in
the distal portion 542 and proximal portion 536.
[00102] =The cutting blade 500 has a gap 528 within the closed loop that may
allow
material to pass through the gap while the cutter blade 500 is being rotated
within the
intervertebral disc space 312. This may add another aspect to the cutting
action while
reducing the resistance to the cutter blade 500 moving through the
intervertebral disc
space 312. Other cutter blades may have less of a gap between the distal and
proximal
portions or no gap at all.
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[00103] A cutter blade without a gap large enough to allow material to pass
through the
gap in the inside perimeter of the close loop receives benefit from the closed
loop as noted
above in that having the closed loop connected to the cutter shaft provides
two points of
connection for the cutter blade and provides at least one point of connection
from each part of
the cutter blade to the cutter shaft 410 in the event of a break in the cutter
blade.
[00104] Hollow Ground Cutter Blades
[00105] FIG.s 9A-9D show four views of a cutter blade 560 that is similar to
cutter
blade 500 discussed above. These drawings do not show cutter blade holes or
cutter blade
slots as that is not the focus of these drawings and some cutter blades may be
connected to a
cutter shaft with other conventional methods that do not involve a pin or
rivet through a cutter
blade hole or holes or a combination of a cutter blade hole and a cutter blade
slot.
[00][06] What is new in cutter blade 560 over cutter blade 500 is a hollow
ground visible
on the top of the cutter blade 560 as element 564 between blade edges 508 and
520 and as
element 568 between blade edges 524 and 512. While not visible in this set of
figures, the
hollow ground may be added between edge 504 (not visible here) and edge 516 on
the
proximal portion 536 of the blade arm 402.
[00107] FIG. 9D shows a cross section detail A-A of FIG. 9C and shows bevel
angle 576
which for some cutter blades may be in the range of 15 to 60 degrees. FIG. 9D
also shows
that removed materia1580 that is removed to make the hollow ground may range
in this
example from 0.001 inches to 0.020 inches depending in part on the thickness
of the blade
stock but also the extent to which the hollow ground effect is sought in
enhancing the cutting
action of the nearby blade edges. To the extent that the surface of the cutter
blade is recessed
near the blade edges, the blade edges tend to have a more aggressive
interaction with material
such as cartilage or the endplates of the vertebral bodies. This aggressive
interaction tends to
promote the efficiency of the cutter blade when scraping/cutting these
materials and tends to
promote bleeding.
[00108] The use of hollow ground to enhance cutter blades may be used with
cutter blades
using serrated edges in addition to cutter blades such as cutter blade 560
that has a straight
beveled edge.
[00109] Thin Disc Cutter Blades
[00110] FIG. 10 shows a lateral view of portion of a human spine 700. Disc 704
illustrates
a normal healthy disc. Disc 708 is a deteriorating disc. Disc 712 is a bulging
disc. Disc 716
is a herniated disc. Disc 720 is a thinning disc and is noteworthy in that the
space between
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endplates 730 and 734 is greatly reduced in comparison with normal disc 704.
Likewise
discs 724,"rhich are degenerated discs with osteophyte formations are also
thin discs. Closed
loop cutter blades such as cutter blade 453 in FIG. 3 and again in FIG. 5 may
not be
sufficiently thin to operate within a thin disc.
[00111] FIG. 11 shows an top perspective view of a thin cutter blade 800 for
use in
situations such as a thin disc. The thin cutter blade 800 has many features
that are similar to
the cutter blade 500 discussed in connection with FIG. 8_ Thin cutter blade
800 has blade
edges 808 and 820 on the distal arm 860 and blade edges 804 and 816 (not
visible here) on
the proximal arm 864.
[00112] Unlike the closed loop cutter blade 500, there is not a gap between
the distal
ann 860 and the proximal arm 864 in the vicinity of the blade edges. Thus the
thickness of
the cutter blade is on the order of magnitude of only 0.050 inches which is
considerably less
than found in the closed loop cutter blades such as cutter blade 500 in FIG.
8.
[00113] Two rivets 874 are added to retain the flush relationship between the
distal
arm 860 and the proximal arm 864. After the rivets 874 are pressed, the rivets
874 are made
flush with the surface of the distal arm 860 and with the surface of the
proximal arm 864
(lower side of rivets not visible in this view). The tip 848 does not have a
cutting edge but is
rounded or beveled.
[00114] FIGs. 12A-12D provide additional views of thin cutter blade 800. FIG.
12A is a
top perspective view of thin cutter blade 800 much like FIG. 11. As FIG. 12A
shows the
entire thin blade cutter 800 it includes cutter blade slot 427. FIG. 12B, a
front view of thin
cutter blade 800 shows cutter blade slot 427 that is on the proximal arm 864
and visible
through the cutter blade slot 427 is the cutter blade hole 407 that is on
distal arm 860. The
use of a combination of a slot and a hole allows the proximal arm 864 to move
relative to the
distal arm 860 as the thin cutter blade 800 is encircled by the cutter sheath
and thus
constrained to move away from the shape shown in FIG. 12. As the thin cutter
blade 800
changes shape, the curvatures in transitional sections 870 changes. FIG. 12C
is a side view
of thin blade cutter 800 and FIG. 12D is a top view of the thin blade cutter
800
[00115] FIG. 13 is a top perspective view of an exploded drawing of thin blade
cutter 800.
Rivets 874 are visible before insertion and pressing. Distal arm 860 and blade
cutter hole 407
are visible as are proximal arm 864 and blade cutter slot 427.
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[00116] Retaining Film
[00117] FIG. 13 also shows optional element 880 which is a retaining film. The
retaining
film 880 is placed between the proximal arm 864 and the distal arm 860 and is
affixed to
engage each arm. The rivets 874 and the pin or rivet that attaches the thin
cutter blade 800 to
the cutter shaft pass through slits 884 in the retaining film 880. The
retaining film 880 would
come into play if the thin cutter blade 880 were to break both the proximal
arm 864 and the
distal arm 860. The retaining film 880 if operating as intended would not
break and would
retain the broken section in connection with the rest of the thin cutter blade
800 so that the
broken section could be removed from the intervertebral disc space and the
axial channel 212
(FIG.2C).
[00118] The retaining film 880 may be made from a high tensile strength,
dimensionally
stable, biocompatible, sterilizable polymeric film. The retaining film 880 may
be made for
example from a biaxially-oriented polyethylene terephthalate (boPET) polyester
film. In
some instances it may be difficult to adequately adhere the retaining film 880
to a shape
memory alloy such as NitinolTM. However, as the retaining film 880 is
mechanically
connected to the distal arm 860 and the proximal arm 864 through the rivets
874 and the
connection to the cutter shaft, the retaining film 880 may serve a useful
purpose in retaining a
broken section of the thin cutter blade 800 unless the break is between the
last rivet 874 and
the tip 848.
[00119] -The retaining film 880 may range from between about 0.08 mm to about
0.40 mm
in thickness. In addition to retaining broken pieces, the retaining film 880
serves to preclude
the shear and or lateral movement of the distal arm 560 relative to the
proximal arm 564.
[00120] FIG. 14 provides a side view of a thin cutter blade 890 that has a 45
degree angle
between the blade arm 402 portion of the proximal arm 564 and the longitudinal
portion 406
of the proximal arm 564. Thin cutter blades with a range of angles may be
useful for
working in thin discs at the endplates that partially define the
intervertebral disc space (see
endplates 342 and 352 in FIG. 7) where the endplates are not be substantially
perpendicular
with the centerline 262 of the cutter assembly as is the case in FIG. 7. The
angles may range
from 25 to 155 degrees but there may be more demand for angles in the range of
40 to 140
degrees.
[00121] FIG. 15 shows a thin cutter blade 904 with the cutting edges recessed
from the
exterior surfaces of the thin -cutter blade by having adjacent blade edges
from the distal
arm 560 and the proximal arxn 564. While shown with an approximately 90 degree
angle,
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thin cutter blades of this type may be made in a rainge of angles such as from
30 to 120
degrees.
[00122] One of skill in the art will recognize that to the extent that the
cutter blades are
produced in a finite number of nominal cutter blade angles, the actual
measurement of the
precise angle may deviate a few degrees (perhaps 5) from the nominal angle
value. The
actual angle may deviate over cycles of moving from the sheathed to the
extended position.
[00123] In many situations a set of cutter blades of various combinations of
throw lengths
and angles (such as 45 degree, 90 degree, and 135 degree) may be sufficient.
Some surgeons
may feel that they obtain adequate results for some therapies with using just
90 degree and 45
degree cutter blades. Other angles could be used, including angles that
deviate less from 90
such as 60 and 120 degrees, or angles that deviate more from 90 degrees such
as 25 and 155
degrees. Angles even closer to 90 degrees may be useful in some applications
such as an
angle in the vicinity of 105 degrees. Kits could include more than three angle
values for the
cutter blades. For example, a kit might include blades at 25, 45, 60, 90, 105,
120, 135 and
155 degree angles. With this range of blade angles, there is a wide variation
of the extent to
which the extended blades are transverse to the long axis of the cutter
assembly, but in all
these cases the cutter blades are significantly transverse to the long axis of
the cutter
assembly and to the longitudinal portions of the cutter blades.
[00124] Some surgeons may work by initially using a short 90 degree cutter
blade, then
using progressively longer 90 degree cutter blades (one or more longer cutter
blades) to cut as
much material within the intervertebral disc space 312 as can be safely
handled using 90
degree cutter blades. Then the surgeon may want to work with a short 45 degree
cutter blade
then one or more longer 45 degree cutter blades to remove material that would
be difficult to
access using a 90 degree cutter blade. Finally, in some cases, the surgeon may
opt to use a
short 135 degree cutter blade followed by one or more longer 135 degree cutter
blades to cut
nucleus material that is difficult to access using either a 90 degree or a 45
degree cutter blade.
[00125] FIG. 16 shows an "L" cutter blade 910 which used a single arm rather
than a pair
of arms (560 and 564 as in FIG 15). The "L" cutter blade 910 shown in FIG. 16
has a pair of
cutting edges 914 and 918 on the distal surface 922 of the "L" blade 910. The
blade edge
may be cut at a bevel angle of approximately 25 to 80 degrees as indicated in
FIG. 16D. The
"L" cutter blade 910 of FIG. 16 may be used to scrape the cartilage and
endplate on the distal
endplate 730 (See FIG. 10). The advantage of a "L" cutter blade such as 910
over a thin
cutter blade such as 800 shown in FIG. 11 is that the height of the "L" cutter
blade is
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approximately half that of the thin cutter blade 800 as the "L" cutter blade
effectively uses
one arm instead of a stack of two (a proximal arm and a distal arm). Thus an
"L" cutter blade
may be able to work in a thin disc that is too thin for even a thin cutter
blade.
[00126] FIG. 17 shows a number of views of an "L" cutter blade 930 that is
much like
"L" cutter blade 910 except that the cutting edges 934 and 938 are on the
proximal side of the
"L" cutter blade 930. The "L" cutter blade 930 may be used to scrape the
endplate 734 on the
more proximal vertebral body (assumes a trans-axial approach as shown in FIG.
2). The
bevel angles and range of cutter blade angles for "L" cutter blade 930 may be
the same as for
"L" cutter blade 910.
[00127] FIGs. 18 and 19 allow a discussion of a feature in cutter shaft 410
that was visible
in FIGs. 5A and 5B. Cutter shaft 610 receives the longitudinal portion of
cutter blade 600
into a slot and the cutter blade 600 may be pinned to cutter shaft 610 in the
manner discussed
with respect to FIGs. 5A and 5B. However, the cutter shaft 610 differs from
cutter shaft 410
in that it lacks the cutter shaft extensions 480. These cutter shaft
extensions 480 (sometimes
called goal posts) provide additional support to the cutter blade 500. This
additional support
may be desired, in particular, for cutter blades with longer throws.
[00128] When seeking to create cutter assemblies for use with thin cutter
blades or "L"
cutter blades, it may be desirable to use cutter shafts without cutter shaft
extension 480 in
order to minimize the height of the cutter shaft in addition to controlling
the height of the
cutter blade.
[00129] A second reason for using a cutter shaft 610 without cutter shaft
extensions 480 is
when using a short throw cutter blade with a desire to allow more flex in the
blade. In some
instances, additional flex in the shorter throw cutter blades is thought to
help the cutter blade
cut more effectively.
[00130] FIG. 20 is the distal end of a cutter shaft such as cutter shaft 610.
FIG. 21 is an
enlarged detail of FIG. 20. FIG. 22 is a cross section of the distal end of
cutter shaft 610.
Analogous drawings for a cutter shaft 410 with cutter shaft extensions 480 are
shown in
FIGs. 23-25.
[00131] Material choices and other details
[00132] In the context of the present invention, the term "biocompatible"
refers to an
absence of chronic inflammation response or cytotoxicity when or if
physiological tissues are
in contact with, or exposed to (e.g., wear debris) the materials and devices
of the present
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invention. In addition to biocompatibility, in another aspect of the present
invention it is
preferred that the materials comprising the instruments are sterilizable;
visible and/or
imageable, e.g., fluoroscopically.
[00133] The cutter shaft and cutter sheath are typically fabricated from a
metal or metal
alloy, e.g., stainless steel and can be either machined or injection molded.
[00134] Due to limited disc height in certain patients, e.g., where fusion is
indicated due to
herniated or collapsed discs, cutter blades are preferably constructed to have
a lower profile
during extension, use, and retraction.
[00135] In one aspect of the present invention, the separation distance
between the first
and second cutting edges is a controllable variable in manufacturing (that is,
predetermined
during cutter blade formation, through heat treatment of the pinned, preferred
nickel-titanium
shape-memory alloy, e.g., NitinolTM). The separation distance between cutting
edges varies
from about 2 mm to about 8 mm, and, often is about 3 mm to about 4 mm. Some
cutter
blades have a tear drop shape. The maximum separation between cutting edges
may be
located within about the radially outwardly most one third of the total blade
length.
Alternatively, the maximum separation may be positioned within the radially
inwardly most
third of the blade length, or within a central region of the blade length,
depending upon the
desired deployment and cutting characteristics.
[00136] In accordance with one aspect of the embodiments described herein, the
blade
arms and the cutter blades in general can be formed from strip material that
is preferably a
shape memory alloy in its super-elastic or austenitic phase at room and body
temperature and
that ranges in width from about 0.10 inches (2.5 mm) to about 0.20 inches (5
mm) and in
thickness from about 0.015 inches (0.38 mm) to about 0.050 inches (1.3 mm).
Blade arms
formed in accordance with the present embodiment are generally able to be
flexed in excess
of 100 cycles without significant shape loss, and twisted up to one and %2
full turns (about
540 degrees) without breakage. This is twisting of one end of the cutter blade
relative to
another portion of the cutter blade.
[00137] The shape memory feature is useful both in allowing the cutter blade
to resume
the extended position which is in shape memory but the shape memory helps the
cutter blade
resume its intended shape after being distorted while being rotated within the
intervertebral
disc space and receiving uneven resistance to motion.
[00138] In one embodiment, the cutting blade and cutter blade edge is formed
from a
super-elastic, shape memory metal alloy that preferably exhibits
biocompatibility and
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substantial shape recovery when strained to 12%. One known suitable material
that
approximates the preferred biomechanical specifications for cutter blades and
cutter blade
edges and blade arms is an alloy of nickel and titanium (e.g., Ni56_Ti45 and
other alloying
elements, by weight), such as, for example, Nitinol strip material #SE508,
available from
Nitinol Devices and Components, Inc. in Fremont, CA. This material exhibits
substantially
full shape recovery (i.e., recovered elongation when strained from about 6%-
10%, which is
substantially better than the recovered elongation at these strain levels of
stainless steel).
[00139] The shape and length of the formed cutter blade in general varies for
the different
cutting modes. The shape memory material can be formed into the desired cutter
blade
configuration by means of pinning alloy material to a special forming fixture,
followed by a
heat-set, time-temperature process, as follows: placing the Nitinol strip
(with the blade's
cutting edge(s) already ground) into the forming fixture and secured with
bolts; and placing
the entire fixture into the oven at a temperature ranging from about 500 C to
about 550 C
(e.g., where optimum temperature for one fixture is about 525 C) for a time
ranging from
between about 15 to about 40 minutes (e.g., where the optimum time for one
fixture is about
minutes). Flexible cutter blades formed from Nitinol in this manner are
particularly suited
for retraction into a shaft sleeve, and are able to be extended to a right
angle into the disc
space. Moreover, they are able to mechanically withstand a large number of
cutting "cycles"
before failure would occur.
20 1001401 The cutting blade edges are preferably ground with accuracy and
reproducibly.
The angle of the inclined surface of the blade relative to the blade's flat
side surface typically
ranges from about 5 degrees to about 70 degrees, often about 20 degrees to
about 50 degrees.
In one embodiment, the blade angle is approximately 30 degrees relative to the
blade's side
surface.
[00141] In one aspect of the present invention, cutter blades configured with
serrations are
formed by a wire EDM (Electrical Discharge Machining) process to optimize
design profiles.
For higher manufacturing volumes, cutter blades are formed via profile
grinding; progressive
die stamping; machining, or conventional EDM.
[00142] In one embodiment, the shaft of the assembly is formed from solid
stainless steel
or other known suitable material. In one embodiment, the shaft has a diameter
of
approximately 0.25 inches (6.3 mm). The cutter shaft sheath may be formed from
stainless
steel rod or bar or other known suitable material tubing, and has a length of
about 0.7 inches
(17.8 mm).
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[00143] As will be understood by one of skill in the art, certain components
or sub-
assemblies of the assemblies of the present invention may alternatively be
fabricated from
suitable (e.g., biocompatible; sterilizable) polymeric materials, and, for
example, may be
coated (e.g., with PTFE) to reduce friction, where appropriate or necessary.
[00144] For example, the cutter sheath can be fabricated from polymeric
material, stainless
steel, or a combination of stainless steel tubing with a low friction
polymeric sleeve such as
UHMWPE, HDPE, PVDF, PTFE loaded polymer. The sheath typically has an outer
diameter (O.D.) of about 0.31 inches (7 mm) to about 0.35 inches (9 mm).
[00145] ALTERNATIVES
[00146] Alternative method of affixing the blade to the blade shaft.
[00147] ln FIGs 26A-26B, a cutter blade 453 is placed in a shaft slot 413 in a
distal
end 412 of a cutter shaft 410 by a rivet 429 that passes through a cutter
blade slot 427 and
the cutter blade hole (407 but not visible here) and into a cutter shaft hole
411. When using a
rivet, a shaft sleeve (compare element 418 in FIGs 5A and 5B) is not required.
FIG 26C
shows that this method of fixation can be combined with the goal post feature
described
above.
[00148] While the certain cutter blades disclosed above have used a cutter
blade hole 407
on the proximal arm and a cutter blade slot 427 on the distal arm, one of
skill in the art will
appreciate that one could modify the cutter blades and the cutter shaft to
allow the use of the
cutter blade hole on the distal arm and the cutter blade slot on the proximal
arm without
deviating from the spirit of the teachings of the present disclosure.
Likewise, examples
showing the cutter blade hole on the distal arm and the cutter blade slot on
the proximal arm
could be modified to swap the hole and the slot.
[00149] Likewise, one could modify the cutter blades shown above to allow for
at least
some types of cutter blades with holes on both longitudinal portions so that
once pinned there
was not relative motion of one longitudinal portion relative to the other.
Other non-pin
attachment choices could be used that would not allow relative movement. This
alternative
would rely more on the ability of the shape memory material to resume a given
shape as the
pinned longitudinal portions could not move relative to one another to help
with the
transformation.
[00150] Cutter shafts may be specialized to work with specific cutter blades
with specific
blade angles. For example, it may be advantageous to use a cutter shaft for a
45 degree blade
CA 02644160 2008-08-27
WO 2007/100912 PCT/US2007/005403
that allows the 45 degree blade to begin its downward angle while still in
contact with the
cutter shaft. Alternatively, a standard cutter shaft could be used for a range
of cutter blade
angles and the variation in blade angles would be handled in the cutter blades
after the cutter
blade has left contact with the cutter shaft. A combination of both strategies
might call for a
few different cutter shafts such as a 45 degree cutter shaft and a 90 degree
cutter shaft and
using attributes of the cutter blades to provide an expanded range of cutter
blade angles.
[00151] The cutter assemblies described herein may also be used in conjunction
with other
methods, such as hydro-excision or laser to name just two examples to perform
partial or
complete nucleectomies, or to facilitate other tissue manipulation (e.g.,
fragmentation and/or
extraction).
[00152] Alternative Handle
[00153] In accordance with one aspect of the embodiments described herein,
there is
provided a handle configured, for example, as a lever or pistol grip, which is
affixed to the
proximal end of the cutter shaft. Referring to Fig. 4B, the illustrated handle
416 is affixed to
the proximal end 414 of the cutter shaft 410 by a cross-pin or set screw,
which reduces the
risk of handle disengagement from the cutter shaft 410 (unthreading by
rotational
manipulation during cutting). As mentioned, the handle 416 is preferably
affixed so that it is
in rotational positional alignment with the blade arm and serves as a
reference marker for the
blade arm's in situ orientation.
[00154] Alternatively, the handle of the cutter assembly is configured as a
turn knob (not
shown) fabricated from a polymeric material, such as, for example, ABS polymer
or the like,
that is injection moldable and that may be machined, and is affixed to the
cutter shaft by
means of threaded or other engagement to the cutter shaft proximal end.
[00155] Rotational Stops
[00156] In accordance with one aspect of the embodiments described herein,
there are
provided blade arms and cutters that are designed to be rotated and used in
one direction (i.e.,
clockwise or counter-clockwise), i.e., the rotational motion of blade arms in
only one
direction (e.g., clockwise) will initiate severing of nucleus material The
intended motion
during the use of these blades is similar to the back and forth motion of a
windshield wiper -
wherein the excision with respect to these cutters occurs in the sweep that is
clockwise in
direction.
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[00157] In one embodiment (not shown), one or more stops are placed within the
cutter
shaft to control blade arc or range of motion. In another embodiment (not
shown), one or
more stops -are fitted onto the cutter sheath to control the blade arc or
range of motion.
[00158] Kits
[00159] Various combinations of the tools and devices described above may be
provided
in the form of kits, so that all of - the tools desirable for performing a
particular procedure will
be available in a single package. Kits in accordance with the present
invention may include
preparation kits for the desired treatment zone, i.e., provided with the tools
necessary for disc
preparation. Disc preparation kits may differ, depending upon whether the
procedure is
intended to be in preparation for therapy of one or more vertebral levels or
motion segments.
The disc preparation kit may include a plurality of cutters. In a single level
kit, anywhere
from 3 to 7 cutters and, in one embodiment, 5 cutters are provided. In a two
level kit,
anywhere from 5 to 14 cutters may be provided, and, in one embodiment, 10
cutters are
provided. The cutter assemblies will include an assortment of cutter blades.
The assortment
will be different depending on the specific procedure to be performed and
possibly based on
the patient anatomy (which may impact the range of cutter blade throw lengths
needed).
[00160] Typically, a kit will include cutter assemblies with a small radial
cutter blade, a
medium radial cutter blade, and a large radial cutter blade. The kit will
typically also include
three more cutter assemblies with small, medium, and large cutter blades with
a blade angle
of 45 degrees. Kits for specific procedures may include other cutter
assemblies with specific
cutter blades for specific uses for example inclusion of cutter blades chosen
for there ability
to cut into and cause bleeding in either the inferior or superior endplates.
All of the cutters
blades are one-time use, i.e., disposable. Certain other components comprised
within the
cutter assembly may be disposable or reusable.
[00161] The disc preparation kit may (optionally) additionally include one or
more tissue
extraction tools, for removing fragments of the nucleus. In a one level kit, 3
to 8 tissue
extraction tools, and, in one embodiment, 6 tissue extraction tools are
provided. In a two
level disc preparation kit, anywhere from about to 8 to about 14 tissue
extraction tools, and,
in one embodiment, 12 tissue extraction tools are provided. The tissue
extraction tools may
be disposable.
[00162] The two arm thin cutter blades shown above include two rivet
connections in the
blade arm. One of skill in the art will appreciate that a single rivet or more
than two rivets
could be used. Likewise, other mechanical connections could be substituted for
rivets.
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[00163] The cutters described above have been described in the context of use
within an
intervertebral disc space. One of skill in the art will recognize that the
desirable attributes of
the disclosed cutters could be used within other medical procedures that
access material to be
cut (most likely for removal before a subsequent therapeutic procedure) by
delivery of a
cutter blade in a sheathed state to through a lumen before the cutter blade
assumes an
extended position in which the cutter blade has as a shape memory. One of
skill in the art
will recognize that the dimensions of the cutter blade and related components
may need to be
adjusted to meet the relevant anatomic dimensions and the dimension of the
lumen used for
providing access. While there may not be cartilage covered vertebral body
endplates to
preserve or scrape (depending on the desired results) there may be other
anatomic structures
that need to be protected from cutting edges or alternatively need to be
scraped as part of site
preparation, thus making many of the specific teachings of the present
disclosure relevant.
[00164] One of skill in the art will recognize that some of the alternative
implementations
set forth above are not universally mutually exclusive and that in some cases
additional
implementations can be created that employ aspects of two or more of the
variations
described above. For example the hollow ground treatment for enhancing the
cutting ability
of a blade edge while shown in connection with a closed loop cutter blade
could be used in
connection with a thin cutter blade. Likewise, the present disclosure is not
limited to the
specific examples or particular embodimerits provided to promote understanding
of the
various teachings of the present disclosure. Moreover, the scope of the claims
which follow
covers the range of variations, modifications, and substitutes for the
components described
herein as would be known to those of skill in the art.
28
