U.S. patent application number 14/829787 was filed with the patent office on 2015-12-10 for process for producing roughened surface patterns on surface of interbody devices.
The applicant listed for this patent is Titan Spine, LLC. Invention is credited to Chad J. Patterson, Peter F. Ullrich, JR..
Application Number | 20150351929 14/829787 |
Document ID | / |
Family ID | 47292257 |
Filed Date | 2015-12-10 |
United States Patent
Application |
20150351929 |
Kind Code |
A1 |
Ullrich, JR.; Peter F. ; et
al. |
December 10, 2015 |
PROCESS FOR PRODUCING ROUGHENED SURFACE PATTERNS ON SURFACE OF
INTERBODY DEVICES
Abstract
Processes for producing interbody spinal implants having a body
with a top surface, a bottom surface, opposing lateral sides,
opposing anterior and posterior portions, a substantially hollow
center, and a single vertical aperture; and optionally, one or two
integration plates affixed to the body. The processes include
applying an additive process, a subtractive process, or both
processes to at least one surface of the interbody spinal implant
to form a roughened surface topography having a regular repeating
pattern. The roughened surface topography is specifically designed
to provide certain frictional characteristics, load dispersion, and
to influence the biological responses that occur during bone
healing and fusion.
Inventors: |
Ullrich, JR.; Peter F.;
(Neenah, WI) ; Patterson; Chad J.; (Port
Washington, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Titan Spine, LLC |
Mequon |
WI |
US |
|
|
Family ID: |
47292257 |
Appl. No.: |
14/829787 |
Filed: |
August 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13566357 |
Aug 3, 2012 |
9125756 |
|
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14829787 |
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|
12151198 |
May 5, 2008 |
8262737 |
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13566357 |
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11123359 |
May 6, 2005 |
7662186 |
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12151198 |
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Current U.S.
Class: |
427/2.24 ;
204/192.15 |
Current CPC
Class: |
A61F 2002/30405
20130101; A61F 2002/30838 20130101; A61F 2002/30836 20130101; A61F
2002/2817 20130101; A61F 2310/00047 20130101; Y10T 29/49995
20150115; A61F 2/4455 20130101; A61F 2310/00023 20130101; A61F
2002/30892 20130101; A61F 2002/3093 20130101; C23C 14/35 20130101;
A61F 2310/00131 20130101; A61F 2002/30133 20130101; A61F 2002/30507
20130101; A61F 2002/30789 20130101; A61F 2002/4629 20130101; A61F
2310/00053 20130101; A61F 2002/30925 20130101; A61F 2002/30321
20130101; A61F 2002/30772 20130101; A61F 2002/30785 20130101; A61F
2310/00407 20130101; C23C 14/3485 20130101; A61F 2002/30014
20130101; Y10T 29/49888 20150115; A61F 2002/30481 20130101; A61F
2002/30774 20130101; A61F 2002/30011 20130101; A61F 2/30965
20130101; A61F 2002/30769 20130101; A61F 2/4465 20130101; A61F
2002/30451 20130101; A61F 2002/2835 20130101; A61F 2002/30985
20130101; A61F 2002/30779 20130101; A61F 2002/30906 20130101; A61F
2002/30273 20130101; A61F 2310/00017 20130101; C23C 14/34 20130101;
A61F 2002/30604 20130101; A61F 2002/30973 20130101; A61F 2002/30787
20130101; A61F 2002/30469 20130101; A61F 2002/30593 20130101; A61F
2002/30433 20130101; A61F 2002/3097 20130101; A61F 2002/305
20130101; A61F 2002/3084 20130101; A61F 2002/448 20130101; A61F
2/4611 20130101 |
International
Class: |
A61F 2/44 20060101
A61F002/44; C23C 14/35 20060101 C23C014/35; C23C 14/34 20060101
C23C014/34 |
Claims
1. A process of producing an interbody spinal implant having a
roughened surface pattern, comprising providing an interbody spinal
implant comprising a body that is generally oval-shaped in
transverse cross section, and comprises a top surface, a bottom
surface, opposing lateral sides, opposing anterior and posterior
portions, a sharp edge at the junction of the anterior portion and
the top surface and at the junction of the anterior portion and the
bottom surface to resist pullout of the implant once inserted in
the intervertebral space, a substantially hollow center, and a
single vertical aperture-extending from the top surface to the
bottom surface, having maximum width at its center, and defining a
transverse rim on the top surface and on the bottom surface, said
transverse rim having a posterior thickness greater than an
anterior thickness, and having a blunt and radiused portion along
the top of each lateral side and the top of the posterior portion,
and depositing a roughened surface pattern onto the portion of the
transverse rim that is not blunt and radiused, but not onto the
blunt and radiused portion of the transverse rim.
2. The process of claim 1, further comprising applying a protective
maskant to each surface of the implant except for the portion of
the transverse rim that is not blunt and radiused prior to the
depositing step.
3. The process of claim 1, wherein the depositing comprises sputter
depositing, vacuum depositing, physical vapor depositing, chemical
vapor depositing, or spin coating.
4. The process of claim 3, wherein the sputter depositing comprises
direct current (DC) sputtering, DC magnetron sputtering,
alternating current (AC) sputtering, pulse DC sputtering, or radio
frequency (RF) sputtering.
5. The process of claim 3, wherein the depositing step is carried
out using an ink jet printer.
6. The process of claim 1, wherein the roughened surface pattern
comprises an array.
7. The process of claim 6, wherein the array comprises an array of
dots, spheres, or semi-spheres.
8. The process of claim 6, wherein the array comprises an array of
amorphous shapes.
9. The process of claim 1, wherein the roughened surface pattern is
oriented in a direction opposite to the direction of biologic
forces.
10. The process of claim 1, wherein the roughened surface pattern
is oriented in a direction opposite to the direction in which the
implant is inserted into the intervertebral space.
11. The process of claim 1, wherein the roughened surface pattern
promotes bone growth, fusion, and healing.
12. The process of claim 1, wherein the roughened surface pattern
comprises a roughness average amplitude, Ra, of about 1-200.
13. The process of claim 1, wherein the body comprises poly ether
ether ketone (PEEK).
14. The process of claim 13, wherein the roughened surface pattern
comprises titanium or a titanium alloy.
15. The process of claim 1, wherein the body comprises titanium or
a titanium alloy.
16. The process of claim 1, wherein the single vertical aperture of
the body has a size and shape predetermined to maximize the surface
area of the top surface and the bottom surface available proximate
the anterior and posterior portions.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 13/566,357, filed on Aug. 3, 2012, which is a
continuation-in-part of U.S. patent application Ser. No.
12/151,198, filed on May 5, 2008, and issued as U.S. Pat. No.
8,262,737, which is a continuation-in-part of U.S. patent
application Ser. No. 11/123,359, filed on May 6, 2005, and issued
as U.S. Pat. No. 7,662,186. The contents of all prior applications
are incorporated by reference into this document, in their entirety
and for all purposes.
TECHNICAL FIELD
[0002] The present invention relates generally to improved
processes of making interbody spinal implants and, more
particularly, to processes of producing spinal implants having
regular repeating patterns on integration surfaces of the
implants.
BACKGROUND OF THE INVENTION
[0003] In the simplest terms, the spine is a column made of
vertebrae and discs. The vertebrae provide the support and
structure of the spine while the spinal discs, located between the
vertebrae, act as cushions or "shock absorbers." These discs also
contribute to the flexibility and motion of the spinal column. Over
time, the discs may become diseased or infected, may develop
deformities such as tears or cracks, or may simply lose structural
integrity (e.g., the discs may bulge or flatten). Impaired discs
can affect the anatomical functions of the vertebrae, due to the
resultant lack of proper biomechanical support, and are often
associated with chronic back pain.
[0004] Several surgical techniques have been developed to address
spinal defects, such as disc degeneration and deformity. Spinal
fusion has become a recognized surgical procedure for mitigating
back pain by restoring biomechanical and anatomical integrity to
the spine. Spinal fusion techniques involve the removal, or partial
removal, of at least one intervertebral disc and preparation of the
disc space for receiving an implant by shaping the exposed
vertebral endplates. An implant is then inserted between the
opposing endplates.
[0005] Spinal fusion procedures can be achieved using a posterior
or an anterior approach, for example. Anterior interbody fusion
procedures generally have the advantages of reduced operative times
and reduced blood loss. Further, anterior procedures do not
interfere with the posterior anatomic structure of the lumbar
spine. Anterior procedures also minimize scarring within the spinal
canal while still achieving improved fusion rates, which is
advantageous from a structural and biomechanical perspective. These
generally preferred anterior procedures are particularly
advantageous in providing improved access to the disc space, and
thus correspondingly better endplate preparation.
[0006] There are a number of problems, however, with traditional
spinal implants including, but not limited to, improper seating of
the implant, implant subsidence (defined as sinking or settling)
into the softer cancellous bone of the vertebral body, poor
biomechanical integrity of the endplates, damaging critical bone
structures during or after implantation, and the like. In summary,
at least ten, separate challenges can be identified as inherent in
traditional anterior spinal fusion devices. Such challenges
include: (1) end-plate preparation; (2) implant difficulty; (3)
materials of construction; (4) implant expulsion; (5) implant
subsidence; (6) insufficient room for bone graft; (7) stress
shielding; (8) lack of implant incorporation with vertebral bone;
(9) limitations on radiographic visualization; and (10) cost of
manufacture and inventory.
[0007] With regard to manufacturing of such implants, there are
traditionally many steps necessary to produce a high quality
implant. For example, the manufacturing process may require a
series of steps including, but not necessarily limited to, cutting
the basic implant shape from raw materials and adding features by
removing material from the initial basic shape. Conventional
processes may include numerous steps of holding and releasing the
part until the finished implant is completed. The part also may
undergo subsequent surface processing to provide surface features
on the completed implant--although certain surface features, such
as grossly textured surfaces with undercuts or sharp edges, can
work detrimentally in the healing process. In particular, undercuts
or sharp edges can compound the load induced stresses imparted
between the implant and the opposing bones, and the long term
result can include degeneration of the bone structures.
SUMMARY OF THE INVENTION
[0008] The present invention provides for processes of producing
interbody spinal implants having specifically designed surface
features intended to influence the biological processes that occur
during bone healing and fusion. In particular, the surface features
of the implants may be produced by subtractive or additive
processes that may be automated to produce desired surface
patterns. In the case of a subtractive process, a mask may be used
to provide the desired patterns and the automation provides for
high mask location accuracy and uniform dispensing of the mask
material. In the case of an additive process, the automation
provides for uniform and accurate patterns applied to and
protruding from the surface. In both cases, the implants have
special surface features that may be produced rapidly with complex
patterns designed to achieve a balanced surface having frictional
characteristics and load dispersion over the cumulative surface
area. The process also is designed so as not to constrain
subsequent processes or degrade the previous process steps.
[0009] In one embodiment, the present invention provides a process
of producing an interbody spinal implant having a regular repeating
pattern including applying at least one additive process or
subtractive process to at least one base surface of an interbody
spinal implant to form a regular repeating pattern. The interbody
spinal implant includes a body having a top surface, a bottom
surface, opposing lateral sides, opposing anterior and posterior
portions, a substantially hollow center, and a single vertical
aperture; and optionally, at least one of a first integration plate
affixed to the top surface of the body and a second integration
plate affixed to the bottom surface of the body, where the first
integration plate and the second integration plate each have a top
surface, a bottom surface, opposing lateral sides, opposing
anterior and posterior portions, and a single vertical aperture
extending from the top surface to the bottom surface and aligning
with the single vertical aperture of the body. In other words, the
implant may comprise a solid-body implant or a composite
structure.
[0010] The regular repeating pattern may be applied as an additive
process or a subtractive process. In an additive process, a pattern
is applied (e.g., an array of specs, dots, strips, or the like) to
a base surface of the implant, for example, through deposition,
welding, impacting, injection, or the like, to provide protrusions,
extensions, or projections from the base surface. In a subtractive
process, on the other hand, the pattern may be formed by making
cuts, recesses, or removing portions of the base surface of the
implant. For example, one or more patterns of maskant may be
applied to the base surface (e.g., in an array of specs, dots,
strips, or the like). Then, a chemical etchant (e.g., an acid etch)
may be applied to remove the material in the regions not protected
by the maskant to provide recesses, cuts, or holes in the base
surface. The chemical etchant may be applied using any suitable
technique (e.g., by spraying, immersion, or the like) to the
unmasked surfaces. After etching, a single time or repeatedly, the
maskant may then be removed to reveal the pattern. In both cases,
complex patterns with highly accurate and specifically designed
shapes may be obtained. The process may also include some
combination of additive and subtractive techniques.
[0011] In another embodiment, a process of producing an interbody
spinal implant having a regular repeating pattern includes
obtaining an interbody spinal implant (e.g., by machining the
implant from a blank or raw material) and repeatedly (e.g., more
than once) applying an additive process to at least one base
surface of the interbody spinal implant to form a roughened surface
topography having a regular repeating pattern. The additive process
(e.g., deposition) may be applied sequentially, for example, to
provide an array of shapes or structures protruding from the base
surface.
[0012] In another embodiment, a process of producing an interbody
spinal implant having a regular repeating pattern includes
obtaining an interbody spinal implant and repeatedly applying a
subtractive process to at least one base surface of the interbody
spinal implant to form a roughened surface topography having a
regular repeating pattern. The repeated process may include, for
example, applying a first maskant; then applying a first chemical
etchant; subsequently applying a second maskant; and then applying
a second chemical etchant, in a repeated manner. Alternatively, the
process may include applying a first maskant, applying a second
maskant, and so on; and then applying a first chemical etchant,
optionally, applying a second chemical etchant, and so on. The
subtractive process (e.g., acid etching) may be applied
sequentially, for example, to provide an array of shapes or
structures recessed into the base surface.
[0013] The regular repeating pattern in the subtractive or additive
processes may form a roughened surface topography. The roughened
surface topography may help to promote bone growth, fusion, and
healing responses and may be oriented in opposition to the biologic
forces on the interbody spinal implant and to an insertion
direction.
[0014] The regular repeating pattern may be applied to at least one
surface of the implant. Preferably, the pattern is applied to the
integration surface or surfaces of the implant. In the case of a
solid-body implant, the integration surface includes the top
surface, bottom surface, or both surfaces of the implant. In the
case of a composite implant with a single integration plate, the
integration surfaces include the top surface of the integration
plate and the top surface of the body of the implant or the top
surface of the integration plate and the bottom surface of the body
of the implant. In the case of a composite implant with two
integration plates, the integration surface may include the top
surface of both integration plates (i.e., the outer surfaces).
[0015] The resulting implant, for a solid-body implant or a
composite implant, comprises at least one integration surface
having a roughened surface topography where the entire implant or
the integration plate was produced by such a process that at least
the integration surfaces of the implant comprise a selective
pattern of high accuracy.
[0016] Various implant body shapes are provided to allow for
implantation through various access paths to the spine through a
patient's body. The structures and surfaces are designed to work in
concert to preserve endplate bone structures, provide for
sufficient bioactivity in each respective location, and provide
stability within the disc space and the graft containment axial
column. In particular, the shapes and textures of the bioactive
surfaces vary based on the implant insertion path, location within
the disc space, and frictional characteristics of the surfaces.
BRIEF DESCRIPTION OF THE DRAWING
[0017] The invention is best understood from the following detailed
description when read in connection with the accompanying drawing.
It is emphasized that, according to common practice, the various
features of the drawing are not to scale. On the contrary, the
dimensions of the various features are arbitrarily expanded or
reduced for clarity. Included in the drawing are the following
figures:
[0018] FIG. 1 shows an example of a first step of a subtractive
process where rows of maskant are applied in an array to a surface
of an implant;
[0019] FIG. 2 shows an example of a second step of the subtractive
process where a second overlapping layer of maskant is applied to
the surface of the implant shown in FIG. 1;
[0020] FIG. 3 shows an example of a third step of the subtractive
process where a third overlapping layer of maskant is applied to
the surface of the implant shown in FIG. 2;
[0021] FIGS. 4A-4C show an example of a pattern of cuts formed by a
three step process in the surface of the implant;
[0022] FIG. 5 shows Ra, Rmax, and Sm for a roughened surface
topography;
[0023] FIG. 6 shows an example of a first step of a subtractive
process where strips of maskant are applied to a surface of the
implant;
[0024] FIG. 7 shows an example of a second step of the subtractive
process where overlapping strips of maskant are applied to the
surface of the implant shown in FIG. 6;
[0025] FIG. 8 shows an example of an additive process where a
patterned array of squares is applied to the surface of the
implant;
[0026] FIG. 9 shows an example of a surface of the implant
following two additive processes with a patterned array;
[0027] FIG. 10 shows an example of an abraded surface detail that
may be produced by an additive or subtractive process;
[0028] FIG. 11A shows a perspective view of an embodiment of the
interbody spinal implant having a generally oval shape and
roughened surface topography on the top surface;
[0029] FIG. 11B shows a top view of the embodiment of the interbody
spinal implant illustrated in FIG. 11A;
[0030] FIG. 12 shows an exploded view of a generally oval-shaped
implant with an integration plate;
[0031] FIG. 13 shows an anterior view of an embodiment of the
interbody spinal implant having two integration plates, which
sandwich the body of the implant;
[0032] FIG. 14 shows an exploded view of a curved implant with an
integration plate;
[0033] FIG. 15 shows an exploded view of a posterior implant with
an integration plate;
[0034] FIG. 16 shows an exploded view of a lateral lumbar implant
with an integration plate;
[0035] FIG. 17 shows an exploded view of a generally oval-shaped
anterior cervical implant with an integration plate;
[0036] FIG. 18 illustrates one set of process steps that can be
used to form macro, micro, or nano processes;
[0037] FIG. 19 graphically represents the average amplitude,
Ra;
[0038] FIG. 20 graphically represents the average peak-to-valley
roughness, Rz;
[0039] FIG. 21 graphically represents the maximum peak-to-valley
height, Rmax;
[0040] FIG. 22 graphically represents the total peak-to-valley of
waviness profile; and
[0041] FIG. 23 graphically represents the mean spacing, Sm.
DETAILED DESCRIPTION OF THE INVENTION
[0042] The present invention provides for interbody spinal
implants, including solid-body implants and composite implants,
having surfaces with a specific pattern designed to influence, for
example, healing and fusion responses and provide a balanced
friction inducing load dispersing surface.
[0043] Accordingly, in one embodiment of the present invention, a
process of producing an interbody spinal implant includes applying
at least one additive process or subtractive process to at least
one base surface of an interbody spinal implant to form a regular
repeating pattern (e.g., a roughened surface topography).
[0044] The implant may be obtained or produced, for example, by
machining the implant from a raw material, and once the implant is
produced, then applying surface processing to the surfaces
requiring such treatment. For example, the raw material may be
obtained from a supplier, and machined (e.g., milled or turned)
into the basic implant shape and having certain features (e.g.,
apertures). After machining the implant, certain surface features
may be applied to desired surfaces. For example, a protective
maskant may be applied to protect the surfaces of the implant where
those protected surfaces will not undergo any surface treatment.
The protective mask may be applied to the entire implant (e.g., by
immersion in the maskant) or a portion of the implant. Then, a
portion of the protective mask may be removed to expose the area of
the implant which requires a special surface treatment (e.g., the
integration surfaces). A protective maskant may or may not be
required depending on the process employed.
[0045] Creating the Pattern
[0046] Once the given area of the surface is prepared (e.g.,
exposed and unmasked) for a surface treatment, at least one
additive process or subtractive process may be applied to the base
surface. As used in this document, the "base surface" includes the
original surface of the implant. In other words, the base surface
includes any of the surfaces which define the implant before
undergoing surface processing. The base surface may also include,
however, a modified original surface, for example, a base surface
that has previously undergone at least one subtractive process,
additive process, or both processes (e.g., exposing new surfaces
from the original surface or providing new surfaces on to the
original surface).
[0047] The shapes of the frictional surface protrusions or recesses
provided by the subtractive process, additive process, or both
processes form a roughened surface topography on at least one
surface of the implant. The roughened surface topography preferably
includes a predetermined repeating pattern. As used in this
document, "predetermined" means determined beforehand, so that the
predetermined characteristic must be determined, i.e., chosen or at
least known, before use of the implant. The pattern may consist of
an array of shapes or structures. The array may include a
systematic arrangement of objects (e.g., dots, circles, ovals,
squares, or strips) in rows, columns, or both.
[0048] The shapes may be formed using processes and methods
commonly applied to remove material (e.g., subtractive techniques)
during fabrication of implantable devices such as cutting and
removal processes, machining, chemical etching, abrasive media
blasting, and others known in the art. Alternatively or in
addition, the shapes may be formed using methods commonly applied
to add material (e.g., additive processes) to a surface such as
coating, sputtering, printing, and other additive processes known
in the art.
[0049] (a) Subtractive Process
[0050] A subtractive process may be applied to at least one surface
of the implant. As used in this document, "subtractive process" is
intended to encompass any process which removes material (e.g.,
metal or plastic) from a surface of the implant. Suitable
subtractive techniques may include, but are not limited to,
machining (e.g., milling, turning, or both techniques may be
performed using machine tools, such as saws, lathes, milling
machines, drill presses, or other equipment used with a sharp
cutting tool to physically remove material to achieve a desired
geometry); unmasked or masked etching (e.g., portions of the
surface are protected by a masking material which resists etching
and an etching substance is applied to unmasked portions);
chemical, photo, electrical, electrochemical, plasma, or laser
etching; cutting and removal processes; casting; forging;
machining; drilling; grinding; shot peening; abrasive media
blasting (such as sand or grit blasting); and combinations of these
subtractive processes.
[0051] The subtractive process may include applying a temporary
patterned mask before the subtractive process is performed. In
other words, a mask may be applied to the desired surface, for
example, to produce a desired pattern before implementing the
subtractive technique. The pattern may include a designed
configuration or array of dots, circles, semi-circles, squares,
triangles, lines, strips, amorphous shapes, or any suitable pattern
designed to provide frictional contact with opposing bones,
dispersion loading, and to promote bone healing and fusion.
Referring to the drawing, in which like reference numbers refer to
like elements throughout the various figures that comprise the
drawing, FIG. 1 depicts an embodiment of the invention where rows
of maskant are applied in a first pattern 103 (e.g., dots or
circles) on an original surface 104 of the implant 1.
[0052] The maskant may be applied using any suitable techniques
known in the art, such as deposition (e.g., sputter deposition,
vacuum deposition, physical vapor deposition, chemical vapor
deposition, and spin coating), evaporation (e.g., electron beam
evaporation, thermal evaporation, and plasma assisted thermal
evaporation), and the like. The sputtering may include, for
example, DC sputtering, DC magnetron sputtering, AC sputtering,
pulse DC sputtering, RF sputtering, etc. In an exemplary
embodiment, the maskant is applied automatically in a regular
repeating pattern (e.g., an array) using a sputtering technique.
Preferably, the maskant is applied automatically using an ink jet
printing apparatus or system (e.g., digital ink jet technology).
For example, a moving injector may pass rapidly over the surface
and dispense (e.g., under pressure) small amounts of the maskant
onto the surface in the pattern. As shown in FIG. 1, an array of
maskant may be applied in a first pattern 103, for example, by a
printing system.
[0053] A suitable maskant may be selected by one of ordinary skill
in the art depending on the subtractive process employed. The
maskant may include, for example, polymeric masks or inorganic
masks (e.g., SiO.sub.2, W, hydrogen silsesquioxane). The mask may
also include photosensitive masks. If necessary, the mask may be
cured, for example, at room temperature or under heating before
applying the subtractive process (e.g., acid etching). Preferably,
the maskant should be selected to be able to withstand the
subtractive process and any further processing of the implant.
[0054] The subtractive process may include a single subtractive
step or multiple subtractive steps. The subtractive process may be
applied sequentially, for example, to provide an array of shapes or
structures recessed into the base surface. In an exemplary
embodiment, the process is repeated (occurs more than once) and may
include, for example, (1) applying a first maskant and then
applying a first chemical etchant; and (2) subsequently applying a
second maskant and then applying a second chemical etchant. Steps
(1) and (2) may continue repeatedly until the desired pattern is
obtained. In the alternative or in addition, the process may
include, for example, (1) applying a first maskant, applying a
second maskant, and applying as many additional masks as are
necessary to produce the desired pattern; and (2) then applying a
first chemical etchant, optionally, applying a second chemical
etchant, and so on to produce the required degree of etching.
[0055] FIGS. 1-3 show an example of a three step process of
applying maskant to an original surface 104 of an implant. In a
first step shown in FIG. 1, an array of maskant is applied in a
first pattern 103 (e.g., dots or circles) on an original surface
104 of the implant 1. In a second step shown in FIG. 2, another
layer of maskant is applied in a second pattern 105 (e.g., dots or
circles) at least partially overlapping the first pattern 103. In a
third step shown in FIG. 3, another layer of maskant is applied in
a third pattern 107 (e.g., dots or circles) at least partially
overlapping the first pattern 103, the second pattern 105, or both
patterns. More layers of maskant may be applied if necessary to
form the desired pattern. After the pattern of maskant is applied
to the original surface, then a chemical etchant may be applied to
the portions of the original surface that are unprotected by
maskant. For example, the surface may be subjected to acid etching,
with a strong acid, such as hydrochloric acid (HCl), hydroiodic
acid (HI), hydrobromic acid (HBr), hydrofluoric (HF), perchloric
acid (HClO.sub.4), nitric acid (HNO.sub.3), sulfuric acid
(H.sub.2SO.sub.4), and the like. The acid etching may also be
repeated, if desired, to obtain the predetermined pattern of
recesses.
[0056] FIGS. 4A-4C depict an alternative embodiment where the
pattern array is directly cut, for example, by etching. Therefore,
a mask may be applied to areas of the original surface which are
not part of the cut pattern. In a three-step process, for example,
the subtractive process may form a first cut pattern 103a, second
cut pattern 105a, and third cut pattern 107a, respectively.
[0057] FIGS. 6 and 7 depict an alternative embodiment where the
first pattern 103 includes rows of maskant applied in a pattern of
strips on the original surface 104. The strips of maskant are
applied in a series of equal parallel intervals. Then, a second
pattern 105, also applied as strips of maskant in a series of equal
parallel intervals, is aligned perpendicularly to the first pattern
103, for example, to form a lattice or basket pattern. It is also
envisioned that other angles (e.g., between 0.degree. and
90.degree.) may be produced in the overlapping patterns. After the
pattern of maskant is applied, then an etchant may be applied, for
example, to the portions of the original surface that are
unprotected by the maskant.
[0058] Once the subtractive process is complete and the pattern has
been formed and cut into the implant, any mask used in the process
may be removed using suitable mechanisms known in the art. For
example, the mask may be peeled or scraped, removed by a solvent or
heat, dissolved by light, etc.
[0059] (b) Additive Process
[0060] An additive process may be applied to at least one surface
of the implant. As used in this document, "additive process" is
intended to encompass any process which adds material to a surface
of the implant. The additive process may form protrusions,
projections, extensions, or the like extending outwardly from the
base surface in a three dimensional manner. Preferably, however,
the added features do not comprise teeth or other sharp
projections. Suitable additive techniques may include, but are not
limited to, sputtering, printing, welding, coating, depositing
molten material, impacting, injecting, optical melt additive
processes, and other additive processes known in the art. Additive
processes typically do not require a maskant to be applied to form
a pattern, but a mask may be applied, for example, to protect
certain surfaces.
[0061] The additive process may include applying the pattern
directly to the surface. The pattern may include a designed
configuration or array of lines, strips, dots, spherical shapes
(e.g., spheres, semi-spheres), quadrilateral shapes (e.g., cubes,
polyhedral pyramids), or amorphous or irregular shapes including
any suitable pattern designed to provide frictional contact with
opposing bones, dispersion loading, and to promote bone healing and
fusion. FIG. 8 depicts an embodiment of the invention where
protruding rows of material are applied in a first pattern 103
(e.g., squares or cubes) on an original surface 104 of the implant
1.
[0062] The pattern may be applied using any suitable techniques
known in the art, such as deposition (e.g., sputter deposition,
vacuum deposition, physical vapor deposition, chemical vapor
deposition, and spin coating), evaporation (e.g., electron beam
evaporation, thermal evaporation, and plasma assisted thermal
evaporation), and the like. The sputtering may include, for
example, DC sputtering, DC magnetron sputtering, AC sputtering,
pulse DC sputtering, RF sputtering, etc. In an exemplary
embodiment, the pattern is automatically applied to the surface in
a regular repeating pattern (e.g., an array) using a sputtering
technique. Preferably, the pattern is directly applied to the
surface using an ink jet printing apparatus. As shown in FIG. 8, an
array of material may be applied in a first pattern 103, for
example, by a printing system.
[0063] The additive features may contain any suitable material,
which may be the same or a different material then the surface
being treated. Suitable materials may be selected by one of
ordinary skill in the art depending on the additive process
employed. The material may include, for example, polymeric or
inorganic materials (e.g., titanium) including any of the materials
used to form the implant 1. The added material may be selected to
be able to withstand any further processing of the implant. It may
also be desired, however, that the added material is at least
partially removed by subtractive techniques. In one embodiment, the
surface undergoes an additive process and a subtractive process
(e.g., etching) which removes at least a portion of the features
added in the additive process.
[0064] The additive process may include a single additive step or
multiple additive steps. The additive process may be applied
sequentially, for example, to provide an array of shapes or
structures protruding from the base surface. In an exemplary
embodiment, the process is repeated (occurs more than once) and may
include, for example, applying a first pattern of protrusions and
then applying a second pattern of protrusions. In another
embodiment, the process includes applying a first pattern of
protrusions and then applying a pattern of recesses using a
subtractive process.
[0065] FIG. 9 shows an example of a two-step additive process on a
surface of the implant 1. In a first step, a first pattern 103 is
applied in an array of protruding squares or cubes on the original
surface 104 of the implant 1. In a second step, a second pattern
105 of dots is applied to the areas not covered by the first
pattern 103. In the alternative, the second pattern 105 may also at
least partially overlap the first pattern 103.
[0066] FIG. 10 shows an alternative example depicting an abraded
surface detail which may be produced in an additive process, a
subtractive process, or both processes. The three patterns may be
applied simultaneously or sequentially to form a first pattern 103,
a second pattern 105, and a third pattern 107 recessed into or
projecting from the original surface 104. For example, the three
patterns may form an overall repeating pattern on the surface of
the implant 1.
[0067] Surface Topography
[0068] The subtractive process, additive process, or both processes
may form a roughened surface topography 80 from macro processing,
micro processing, nano processing, or any combination of the three.
The term "macro" typically means relatively large; for example, in
the present application, dimensions measured in millimeters (mm).
The term "micro" typically means one millionth (10.sup.6); for
example, in the present application, dimensions measured in microns
(.mu.m) which correspond to 10.sup.-6 meters. The term "nano"
typically means one billionth (b 10.sup.-9); for example, in the
present application, dimensions measured in nanometers (nm) which
correspond to 10.sup.-9 meters.
[0069] FIG. 18 illustrates one set of process steps that can be
used to form macro, micro, or nano processes. As illustrated, there
may be some overlap in the processes that can be applied to form
each of the three types of features (macro, micro, and nano). For
example, acid etching can be used to form the macro features, then
the same or a different acid etching process can be used to form
the micro features. The features may be provided in a random design
or a predetermined pattern (e.g., a repeating pattern).
[0070] (a) Macro Features
[0071] The macro features of the roughened surface topography 80
are relatively large features (e.g., on the order of millimeters).
The macro features may be formed from subtractive techniques (e.g.,
mechanical or chemical bulk removal, for example) or additive
techniques (e.g., deposition or sputtering) as described above. The
patterns may be organized in regular repeating patterns and
optionally overlapping each other. In one embodiment, the macro
features may be formed in three, sequential steps.
[0072] FIG. 4A illustrates the result of one step or a first step
in forming macro features. Specifically, a first cut pattern 103a
of the macro features is formed in a surface (e.g., the top surface
81 of an integration plate 82). The "cut 1" features of the first
cut pattern 103a may cover about 20% of the total area of the
surface, for example, leaving about 80% of the original surface 104
remaining The range of these percentages may be about .+-.20%,
preferably .+-.10%, and more preferably about .+-.5%. The "cut 1"
features of the first cut pattern 103a do not have any undercuts.
In one embodiment, these "cut 1" features have the smallest
diameter and greatest depth of the macro features that are formed
during the sequential steps.
[0073] FIG. 4B illustrates the result of a second step in forming
macro features. Specifically, a second cut pattern 105a of the
macro features is formed in the surface. Together, the "cut 1"
features of the first cut pattern 103a and the "cut 2" features of
the second cut pattern 105a may cover about 85% of the total area
of the surface, for example, leaving about 15% of the original
surface 104 remaining The range of these percentages may be about
.+-.10% and preferably .+-.5%. In an embodiment of the invention,
these "cut 2" features have both a diameter and a depth between
those of the "cut 1" and "cut 3" features of the macro features
that are formed during the first and third steps of the process of
forming the macro features of the roughened surface topography
80.
[0074] FIG. 4C illustrates the result of the third step in forming
macro features. Specifically, a third cut pattern 107a of the macro
features may be formed in the surface. Together, the "cut 1"
features of the first cut pattern 103a, the "cut 2" features of the
second cut pattern 105a, and the "cut 3" features of the third cut
pattern 107a cover about 95% of the total area of the surface, for
example, leaving about 5% of the original surface 104 remaining The
range of these percentages may be about .+-.1%. In an embodiment of
the invention, these "cut 3" features may have the largest diameter
and least depth of the macro features that are formed during the
sequential process steps. Following completion of the three,
sequential processing steps, the finished macro features may
comprise multiple patterns of the three, overlapping cuts: the
first cut pattern 103a, the second cut pattern 105a, and the third
cut pattern 107a.
[0075] (b) Micro Features
[0076] The micro features may also be formed from subtractive
techniques (e.g., mechanical or chemical bulk removal, for example)
or additive techniques (e.g., deposition or sputtering) described
above.
[0077] In an exemplary embodiment, the micro features are removed
by masked or unmasked etching, such as acid etching. For example,
portions of the surface may be exposed to a chemical etching. In an
exemplary embodiment, the micro process includes an acid etching,
with a strong acid, such as hydrochloric acid (HCl), hydroiodic
acid (HI), hydrobromic acid (HBr), hydrofluoric (HF), perchloric
acid (HClO.sub.4), nitric acid (HNO.sub.3), sulfuric acid
(H.sub.2SO.sub.4), and the like. The etching process may be
repeated a number of times as necessitated by the amount and nature
of the irregularities required for any particular application.
Control of the strength of the etchant material, the temperature at
which the etching process takes place, and the time allotted for
the etching process allow fine control over the resulting surface
produced by the process. The number of repetitions of the etching
process can also be used to control the surface features. For
example, the roughened surface topography 80 may be obtained via
the repetitive masking and chemical or electrochemical milling
processes described in U.S. Pat. No. 5,258,098; U.S. Pat. No.
5,507,815; U.S. Pat. No. 5,922,029; and U.S. Pat. No. 6,193,762,
the contents of which are incorporated by reference into this
document, in their entirety, and for all purposes.
[0078] By way of example, an etchant mixture of at least one of
nitric acid and hydrofluoric acid may be repeatedly applied to a
titanium surface to produce an average etch depth of about 0.53 mm.
In another example, chemical modification of a titanium surface can
be achieved using at least one of hydrofluoric acid, hydrochloric
acid, and sulfuric acid. In a dual acid etching process, for
example, the first exposure is to hydrofluoric acid and the second
is to a hydrochloric acid and sulfuric acid mixture. Chemical acid
etching alone may enhance osteointegration without adding
particulate matter (e.g., hydroxyapatite) or embedding surface
contaminants (e.g., grit particles).
[0079] The micro features may also be created by abrasive or grit
blasting, for example, by applying a stream of abrasive material
(such as alumina, sand, and the like) to the surface. In an
exemplary embodiment, the micro features are created, at least
partially, with an aqueous hydrochloric acid etching step and at
least partially with an AlO.sub.2 blasting step. Patterns may be
organized in regular repeating patterns and optionally overlapping
each other. After the micro features are formed, it is possible
that less than about 3% of the original surface 104 remains. The
range of that percentage may be about .+-.1%.
[0080] (c) Nano Features
[0081] The nano features may also be formed from subtractive
techniques (e.g., mechanical or chemical bulk removal, for example)
or additive techniques (e.g., deposition or sputtering) described
above.
[0082] In an exemplary embodiment, the nano features are removed by
masked or unmasked etching. For example, portions of the surface,
optionally including portions of the surface exposed by the macro
and micro steps described above, may be exposed to a chemical
etching. In an exemplary embodiment, the nano process also includes
an acid etching, with a strong or weak acid, such as hydrochloric
acid (HCl), hydroiodic acid (HI), hydrobromic acid (HBr),
hydrofluoric (HF), perchloric acid (HClO.sub.4), nitric acid
(HNO.sub.3), sulfuric acid (H.sub.2SO.sub.4), and the like. The
acid etching process for the nano step is preferably less
aggressive than the acid etching process in the micro step. In
other words, a less acidic, milder, or more diluted acid may be
selected. In an exemplary embodiment, the nano features are
created, at least partially, with an aqueous hydrochloric acid
etching step.
[0083] The acid solution may be prepared using any suitable
techniques known in the art. For example, the acid solution may be
prepared by combining hydrochloric acid and water, simultaneously
or sequentially. The acid solution may be applied to the implant 1
using any suitable mechanism or techniques known in the art, for
example, immersion, spraying, brushing, and the like. If desired,
certain areas of the implant 1 may be masked in patterns or to
protect certain portions of the implant 1. After the acid solution
is applied, the acid solution may be removed, for example, by
rinsing with water (e.g., deionized water).
[0084] It is contemplated that the nano features may also be
created by the abrasive or grit blasting, for example, described
for the micro processing step. Patterns may be organized in regular
repeating patterns and optionally overlapping each other. The nano
features may also be achieved by tumble finishing (e.g., tumbling)
the part or the implant 1. Suitable equipment and techniques can be
selected by one of ordinary skill in the art. For example, a barrel
may be filled with the parts or implants 1 and the barrel is then
rotated. Thus, the part or implants 1 may be tumbled against
themselves or with steel balls, shot, rounded-end pins, ballcones,
or the like. The tumbling process may be wet (e.g., with a
lubricant) or dry. After the nano features are formed, it is
possible that less than about 1% of the original surface 104
remains. For example, after the nano features are formed, the
roughened surface topography 80 may cover substantially the entire
surface.
[0085] As should be readily apparent to a skilled artisan, the
processes described in this document can be adjusted to create a
mixture of depths, diameters, feature sizes, and other geometries
suitable for a particular implant application. The orientation of
the pattern of features can also be adjusted. Such flexibility is
desirable, especially because the ultimate pattern of the roughened
surface topography 80 should be oriented in opposition to the
biologic forces on the implant 1 and to the insertion direction. In
one particular embodiment, for example, the pattern of the
roughened surface topography 80 may be modeled after an S-shaped
tire tread.
[0086] The subtractive process and the additive process form a
roughened surface topography 80. The resulting surfaces preferably
have repeating patterns in the shape and location of the features.
These patterns allow for the design and production of surfaces that
resist motion induced by loading in specific directions that are
beneficial to the installation process and resist the opposing
forces that can be the result of biologic or patient activities
such as standing, bending, or turning or as a result of other
activities. The shapes of the surface features work to increase the
surface contact area but do not result in undercuts that generate a
cutting or aggressively abrasive action on the contacting bone
surfaces.
[0087] Integration Surface
[0088] In an exemplary embodiment, the subtractive or additive
process is applied to at least one of the surfaces which form the
integration surfaces of the implant. As used in this document, the
integration surface is the surface at least partially in contact
with the vertebral or bone structure. In particular, the
subtractive or additive process may be applied to the top surface
of the implant, the bottom surface of the implant, or both
surfaces. The subtractive or additive process may be applied to the
entire surface or a portion of the integration surface.
[0089] The integration surfaces on the implant preferably have
predefined surface features that (a) engage the vertebral endplates
with a friction fit and, following an endplate preserving surgical
technique, (b) attain initial stabilization, and (c) benefit
fusion. The composition of the endplate is a thin layer of
notch-sensitive bone that is easily damaged by features (such as
teeth) that protrude sharply from the surface of traditional
implants. Avoiding such teeth and the attendant risk of damage, the
roughened surface topography 80 of the integration surface(s) does
not have teeth or other sharp, potentially damaging structures;
rather, the roughened surface topography 80 may have a pattern of
repeating features of predetermined sizes, smooth shapes, and
orientations.
[0090] These designed surfaces are composed of various sizes of
features that, at the microscopic level, interact with the tissues
and stimulate their natural remodeling and growth. At a larger
scale these features perform the function of generating
non-stressful friction that, when combined with a surgical
technique that retains the most rigid cortical bone structures in
the disc space, allows for a friction fit that does not abrade,
chip, perforate, or compromise the critical endplate structures.
The features may be divided into three size scales: nano, micro,
and macro. The overlapping of the three feature sizes can be
achieved using manufacturing processes that are completed
sequentially and, therefore, do not remove or degrade the previous
process.
[0091] Implant Structure
[0092] FIG. 11A shows a perspective view of an interbody spinal
implant 1, which is especially well adapted for use in an Anterior
Lumbar Interbody Fusion (ALIF) procedure. The interbody spinal
implant 1 includes a top surface 10, a bottom surface 20, opposing
lateral sides 30, and opposing anterior 40 and posterior 50
portions. The interbody spinal implant 1 may include implants made
of a single piece of material or composite implants.
[0093] Interbody spinal implants 1 made of a single piece of
material or solid-body implants do not include integration plates
82. The integration surface may include the top surface 10 of the
implant 1, the bottom surface 20 of the implant 1, or both
surfaces. The integration surface has a roughened surface
topography 80, without sharp teeth that risk damage to bone
structures, which was formed in the subtractive process or additive
process described above.
[0094] Composite implants include at least a body 2 and one or two
integration plates 82, which may be formed from the same or
different materials. As depicted in FIG. 12, the implant 1 includes
a first integration plate 82 affixed to the top surface 10 of the
body 2 and an optional second integration plate 82 (shown in FIG.
13) affixed to the bottom surface 20 of the body 2. The first
integration plate 82 and optional second integration plate 82 each
have a top surface 81, a bottom surface 83, opposing lateral sides,
opposing anterior portion 41 and posterior portion 51, and a single
vertical aperture 61 extending from the top surface 81 to the
bottom surface 83 and aligning with the single vertical aperture 60
of the body 2.
[0095] When present, the integration plate(s) 82 comprise an
integration surface (e.g., the top surface 81 of the integration
plate 82), which is adapted to grip bone through friction generated
when the implant 1 is placed between two vertebrae and to inhibit
migration of the implant 1 once implanted. The integration surfaces
may also have a fusion and biologically active surface geometry. In
other words, at least a portion of the top surface 81 of the first
integration plate 82 (e.g., a first integration surface) and
optionally a top surface 81 of a second integration plate 82 (e.g.,
a second integration surface) has a roughened surface topography
80, without sharp teeth that risk damage to bone structures. The
roughened surface topography 80 preferably includes micro features
of a regular repeating pattern, formed during the subtractive or
additive process, which may promote biological and chemical
attachment or fusion with the bone structure.
[0096] The body 2 and at least one integration plate 82 are
preferably compatibly shaped, such that the implant 1 having the
body 2 and integration plate(s) 82 joined together may have a
generally oval shape, a generally rectangular shape, a generally
curved shape, or any other shape described or exemplified in this
specification. Thus, for example, the body 2 and the integration
plate(s) 82 may be generally oval-shaped in transverse
cross-section. The body 2 and the integration plate(s) 82 may be
generally rectangular-shaped in transverse cross-section. The body
2 and the integration plate(s) 82 may be generally curved-shaped in
transverse cross-section.
[0097] The body 2 and integration plate(s) 82 of the implant 1 may
be the same material or may be different. The body 2 and the
integration plate(s) 82 may be composed of a suitable biocompatible
material. In an exemplary embodiment, the body 2 and optional
integration plate(s) 82 are formed of metal, which may be coated or
not coated. Suitable metals, such as titanium, aluminum, vanadium,
tantalum, stainless steel, and alloys of the metals, may be
selected by one of ordinary skill in the art. In a preferred
embodiment, however, the metal is at least one of titanium,
aluminum, and vanadium, without any coatings. In a more preferred
embodiment, the body 2 and optional integration plate(s) 82 are
comprised of titanium or a titanium alloy. An oxide layer may
naturally form on a titanium or titanium alloy.
[0098] Alternatively, the body 2 may be composed of a non-metal
biocompatible material. In one embodiment, the body 2 of the
implant 1 is formed of a plastic, polymeric, or composite material.
For example, suitable polymers may comprise silicones, polyolefins,
polyesters, polyethers, polystyrenes, polyurethanes, acrylates, and
co-polymers and mixtures of the polymers. Certain embodiments of
the present invention may be comprised of a biocompatible,
polymeric matrix reinforced with bioactive fillers, fibers, or
both. Certain embodiments of the present invention may be comprised
of urethane dimethacrylate (DUDMA)/tri-ethylene glycol
dimethacrylate (TEDGMA) blended resin and a plurality of fillers
and fibers including bioactive fillers and E-glass fibers. In
another embodiment, the body 2 comprises polyetherether-ketone
(PEEK), hedrocel, or ultra-high molecular weight polyethylene
(UHMWPE). Hedrocel is a composite material composed of carbon and
an inert metal, such as tantalum. UHMWPE, also known as
high-modulus polyethylene (HMPE) or high-performance polyethylene
(HPPE), is a subset of the thermoplastic polyethylene, with a high
molecular weight, usually between 2 and 6 million.
[0099] Certain embodiments of the interbody spinal implant 1 are
substantially hollow and have a generally oval-shaped transverse
cross-sectional area. Substantially hollow, as used in this
document, means at least about 33% of the interior volume of the
interbody spinal implant 1 is vacant. Still further, the
substantially hollow portion may be filled with cancellous
autograft bone, allograft bone, demineralized bone matrix (DBM),
porous synthetic bone graft substitute, bone morphogenic protein
(BMP), or combinations of those materials.
[0100] Certain embodiments of the present invention may be
especially suited for placement between adjacent human vertebral
bodies. The implants of the present invention may be used in
procedures such as Anterior Lumbar Interbody Fusion (ALIF),
Posterior Lumbar Interbody Fusion (PLIF), Transforaminal Lumbar
Interbody Fusion (TLIF), and cervical fusion. Certain embodiments
do not extend beyond the outer dimensions of the vertebral
bodies.
[0101] The ability to achieve spinal fusion is directly related to
the available vascular contact area over which fusion is desired,
the quality and quantity of the fusion mass, and the stability of
the interbody spinal implant. Interbody spinal implants, as now
taught, allow for improved seating over the apophyseal rim of the
vertebral body. Still further, interbody spinal implants, as now
taught, better utilize this vital surface area over which fusion
may occur and may better bear the considerable biomechanical loads
presented through the spinal column with minimal interference with
other anatomical or neurological spinal structures. Even further,
interbody spinal implants, according to certain aspects of the
present invention, allow for improved visualization of implant
seating and fusion assessment. Interbody spinal implants, as now
taught, may also stimulate osteointegration (e.g., formation of a
direct structural and functional interface between the artificial
implant and living bone or soft tissue) with the surrounding living
bone.
[0102] It is generally believed that the surface of an implant
determines its ultimate ability to integrate into the surrounding
living bone. Without being limited by theory, it is hypothesized
that the cumulative effects of at least implant composition,
implant surface energy, and implant surface roughness play a major
role in the biological response to, and osteointegration of, an
implant device. Thus, implant fixation may depend, at least in
part, on the stimulation and proliferation of bone modeling and
forming cells, such as osteoclasts and osteoblasts and
like-functioning cells upon the implant surface. Still further, it
appears that these cells attach more readily to relatively rough
surfaces rather than smooth surfaces. In this manner, a surface may
be bioactive due to its ability to stimulate cellular attachment
and osteointegration. The roughened surface topography 80 described
in this document may better promote the osteointegration of certain
embodiments of the present invention. The roughened surface
topography 80 may also better grip the vertebral endplate surfaces
and inhibit implant migration upon placement and seating.
[0103] Several separate parameters can be used to characterize the
roughness of an implant surface. Among those parameters are the
average amplitude, Ra; the maximum peak-to-valley height, Rmax; and
the mean spacing, Sm. Each of these three parameters, and others,
are explained in detail below. Surface roughness may be measured
using a laser profilometer or other standard instrumentation.
[0104] In addition to the parameters Ra, Rmax, and Sm mentioned
above, at least two other parameters can be used to characterize
the roughness of an implant surface. In summary, the five
parameters are: (1) average amplitude, Ra; (2) average
peak-to-valley roughness, Rz; (3) maximum peak-to-valley height,
Rmax; (4) total peak-to-valley of waviness profile, Wt; and (5)
mean spacing, Sm. Each parameter is explained in detail as
follows.
[0105] 1. Average Amplitude Ra
[0106] In practice, "Ra" is the most commonly used roughness
parameter. It is the arithmetic average height. Mathematically, Ra
is computed as the average distance between each roughness profile
point and the mean line. In FIG. 19, the average amplitude is the
average length of the arrows.
[0107] In mathematical terms, this process can be represented
as
Ra = 1 n i = 1 n y i ##EQU00001##
[0108] 2. Average Peak-to-Valley Roughness Rz
[0109] The average peak-to-valley roughness, Rz, is defined by the
ISO and ASME 1995 and later. Rz is based on one peak and one valley
per sampling length. The RzDIN value is based on the determination
of the peak-to-valley distance in each sampling length. These
individual peak-to-valley distances are averaged, resulting in the
RzDIN value, as illustrated in FIG. 20.
[0110] 3. Maximum Peak-to-Valley Height Rmax
[0111] The maximum peak-to-valley height, Rmax, is the maximum
peak-to-valley distance in a single sampling length--as illustrated
in FIG. 21.
[0112] 4. Total Peak-to-Valley of Waviness Profile Wt
[0113] The total peak-to-valley of waviness profile (over the
entire assessment length) is illustrated in FIG. 22.
[0114] 5. Mean Spacing Sm
[0115] The mean spacing, Sm, is the average spacing between
positive mean line crossings. The distance between each positive
(upward) mean line crossing is determined and the average value is
calculated, as illustrated in FIG. 23.
[0116] The parameters Sm, Rmax, and Ra can be used to define the
surface roughness following formation of each of the three types of
features: macro, micro, and nano.
[0117] If present, the following preferred ranges (all measurements
in microns) are as follows for the macro features for each of the
three parameters. The mean spacing, Sm, is between about 400-2,000,
with a range of 750-1,750 preferred and a range of 1,000-1,500 most
preferred. The maximum peak-to-valley height, Rmax, is between
about 40-500, with a range of 150-400 preferred and a range of
250-300 most preferred. The average amplitude, Ra, is between about
8-200, preferably, 20-200, more preferably 50-150, and most
preferably 100-125.
[0118] If present, the following preferred ranges (all measurements
in microns) are as follows for the micro features for each of the
three parameters. The mean spacing, Sm, is between about 20-400,
with a range of 100-300 preferred and a range of 200-250 most
preferred. The maximum peak-to-valley height, Rmax, is between
about 2-40, with a range of 2-20 preferred and a range of 9-13 most
preferred. The average amplitude, Ra, is between about 1-20,
preferably 2-15, more preferably 4-10, even more preferably 2-8,
and most preferably 2-6.
[0119] If present, the following preferred ranges (all measurements
in microns) are as follows for the nano features for each of the
three parameters. The mean spacing, Sm, is between about 0.5-20,
with a range of 1-15 preferred and a range of 5-12 most preferred.
The maximum peak-to-valley height, Rmax, is between about 0.2-2,
with a range of 0.2-1.8 preferred and a range of 0.3-1.3 most
preferred. The average amplitude, Ra, is between about 0.01-2,
preferably 0.01-1, more preferably, 0.02-0.8, and most preferably
0.03-0.6.
[0120] An example of such data is provided in Table 2 below.
TABLE-US-00001 TABLE 2 EXAMPLE DATA BY PROCESS STEP Size (Sm) Depth
(Rmax) Roughness (Ra) Surface Feature Size and Roughness (Metric):
Macro (.mu.m) Max. 2,000 500 200 Min. 400 40 20 Avg. 1,200 270 110
Surface Feature Size and Roughness (Metric): Micro (.mu.m) Max. 400
40 20 Min. 20 2 1 Avg. 210 11 5.5 Surface Feature Size and
Roughness (Metric): Nano (.mu.m) Max. 20 2 1 Min. 0.5 0.2 0.01 Avg.
10.25 1.1 0.505
[0121] Integration Plate(s)
[0122] In the case of a composite implant 1, 101, 101a, 201, and
301, the integration plate, shown in the drawing as component 82
(FIGS. 12 and 13), 182a (FIG. 14), 182 (FIG. 15), 382 (FIGS. 16),
and 282 (FIG. 17), respectively, includes the roughened surface
topography 80, 180, 180a, 280, and 380 for the integration surface,
and is connectable to either or both of the top surface 10, 110,
110a, 210, and 310 or bottom surface 20, 120, 120a, 220, and 320.
The integration plate 82, 182, 182a, 282, and 382 includes a top
surface 81, 181, 181a, 281, and 381; a bottom surface 83, 183,
183a, 283, and 383; an anterior portion 41, 141, 141a, 241, and
341; a posterior portion 51, 151, 151a, 251, and 351; and at least
one vertical aperture 61, 161, 161a, 261, and 361. The anterior
portion 41, 141, 141a, 241, and 341 preferably aligns with the
anterior portion 40, 140, 140a, 240, and 340 of the main body 2 of
the implant 1, 101, 101a, 201, and 301, respectively, and the
posterior portion 51, 151, 151a, 251, and 351 aligns with the
posterior portion 50, 150, 150a, 250, and 350 of the main body 2 of
the implant 1, 101, 101a, 201, and 301, respectively. The vertical
aperture 61, 161, 161a, 261, and 361 preferably aligns with the
vertical aperture 60, 160, 160a, 260, and 360 of the main body 2 of
the implant 1, 101, 101a, 201, and 301, respectively. Thus, the
integration plate vertical aperture 61, 161, 161a, 261, and 361 and
the body vertical aperture 60, 160, 160a, 260, and 360 preferably
comprise substantially the same shape.
[0123] The integration plate 82, 182, 182a, 282, and 382 may be
attached or affixed to the main body of the implant 1, 101, 101a,
201, and 301 using any suitable mechanisms known in the art. For
example, the bottom surface 83, 183, 183a, 283, and 383 of the
integration plate 82, 182, 182a, 282, and 382 may comprise a
reciprocal connector structure, such as a plurality of posts 84,
184, 184a, 284, and 384 that align with and insert into a
corresponding connector structure such as a plurality of holes 12,
112, 112a, 212, and 312 on the top surface 10, 110, 110a, 210, and
310 and/or bottom surface 20, 120, 120a, 220, and 320 of the main
body 2 of the implant 1, 101, 101a, 201, and 301, respectively, and
thus facilitate the connection between the integration plate 82,
182, 182a, 282, and 382 and the main body 2 of the implant 1, 101,
101a, 201, and 301. Thus, integration plates 82, 182, 182a, 282,
and 382 with different sizes, shapes, or features may be used in
connection with the implant 1, 101, 101a, 201, and 301, for
example, to accommodate attributes of the spine of the patient in
to which the implant 1, 101, 101a, 201, and 301 is to be implanted.
Among these different sizes, shapes, and features are lordotic
angles; anti-expulsion edges 8, 108, 108a, 208, and 308; and
anti-expulsion angles as described throughout this
specification.
[0124] The implant 1, 101, 101a, 201, and 301 is configured to
receive the integration plate 82, 182, 182a, 282, and 382,
respectively. Thus, for example, the top surface 10, 110, 110a,
210, and 310 and/or bottom surface 20, 120, 120a, 220, and 320 of
the implant 1, 101, 101a, 201, and 301 may be optionally recessed,
and comprise a plurality of holes 12, 112, 112a, 212, and 312 that
mate with the plurality of posts 84, 184, 184a, 284, and 384 on the
bottom surface 83, 183, 183a, 283, and 383 of the integration plate
82, 182, 182a, 282, and 382. Thus, the plurality of posts 84, 184,
184a, 284, and 384 are inserted into the plurality of holes 12,
112, 112a, 212, and 312.
[0125] FIG. 12 shows that the top surface 10 is recessed and
comprises a plurality of holes 12, but the recessed bottom surface
20 and its holes 12 are not shown. FIG. 14 shows that the top
surface 110a is recessed and comprises a plurality of holes 112a,
but the recessed bottom surface 120a and its holes 112a are not
shown. FIG. 15 shows that the top surface 110 is recessed and
comprises a plurality of holes 112, but the recessed bottom surface
120 and its holes 112 are not shown. FIG. 16 shows that the top
surface 310 is recessed and comprises a plurality of holes 312, but
the recessed bottom surface 320 and its holes 312 are not shown.
FIG. 17 shows that the top surface 210 is recessed and comprises a
plurality of holes 212, but the recessed bottom surface 220 and its
holes 212 are not shown. The recess may be at a depth D, and the
recess depth D preferably is uniform throughout the top surface 10,
110, 110a, 210, and 310 and/or bottom surface 20, 120, 120a, 220,
and 320.
[0126] The recess depth D preferably corresponds to a thickness T
of the integration plate 82, 182, 182a, 282, and 382. Thus, in some
aspects, the depth D and thickness T are the same so that once the
integration plate 82, 182, 182a, 282, and 382 and body of the
implant 1, 101, 101a, 201, and 301, respectively, are placed
together, the top surface 10, 110, 110a, 210, and 310 and/or bottom
surface 20, 120, 120a, 220, and 320 of the implant 1, 101, 101a,
201, and 301 is substantially even, at least at the seam/junction
between the integration plate 82, 182, 182a, 282, and 382 and the
top surface 10, 110, 110a, 210, and 310 or bottom surface 20, 210,
120a, 220, and 320. In some embodiments, the posterior portion 51,
151, 151a, 251, and 351 and the anterior portion 41, 141, 141a,
241, and 341 of the integration plate 82, 182, 182a, 282, and 382
have different thicknesses such that the anterior portion 41, 141,
141a, 241, and 341 has a greater thickness than the thickness of
the posterior portion 51, 151, 151a, 251, and 351.
[0127] The recess depth D and the thickness T may each
independently be from about 0.1 mm to about 10 mm. In preferred
aspects, the recess depth D and the thickness T may each
independently be from about 1 mm to about 5 mm. Thus, for example,
the recess depth D or the thickness T may be selected from about
0.1 mm, about 0.25 mm, about 0.5 mm, about 0.75 mm, about 1 mm,
about 1.25 mm, about 1.5 mm, about 1.75 mm, about 2 mm, about 2.25
mm, about 2.5 mm, about 2.75 mm, about 3 mm, about 3.25 mm, about
3.5 mm, about 3.75 mm, about 4 mm, about 4.25 mm, about 4.5 mm,
about 4.75 mm, about 5 mm, 5.5 mm, about 6 mm, about 6.5 mm, about
7 mm, about 75 mm, or about 8 mm.
[0128] Recessing the top surface 10, 110, 110a, 210, and 310 or
bottom surface 20, 120, 120a, 220, and 320 exposes a ridge 11, 111,
111a, 211, and 311 against which the anterior portion 41, 141,
141a, 241, and 341; posterior portion 51, 151, 151a, 251, and 251;
or lateral side of the integration plate 82, 182, 182a, 282, and
382 may be seated when brought together with the implant 1, 101,
101a, 201, and 301.
[0129] The integration plate 82, 182, 182a, 282, and 382 may be
used with an implant suitable for ALIF (e.g., implant 1,
integration plate 82), PLIF (e.g., implant 101, integration plate
182), or TLIF fusion (e.g., implant 101a, integration plate 182a);
may be used with an implant suitable for cervical fusion (e.g.,
implant 201, integration plate 282); and may be used with an
implant suitable for lateral lumbar insertion (e.g., implant 301,
integration plate 382).
[0130] The reciprocal connector such as the post 84, 184, 184a,
284, and 384 preferably is secured within the connector of the body
such as the hole 12, 112, 112a, 212, and 312 to mediate the
connection between the integration plate 82, 182, 182a, 282, and
382 and the implant 1, 101, 101a, 201, and 301. The connection
should be capable of withstanding significant loads and shear
forces when implanted in the spine of the patient. The connection
between the post 84, 184, 184a, 284, and 384 and the hole 12, 112,
112a, 212, and 312 may comprise a friction fit. In some aspects,
the reciprocal connector such as the post 84, 184, 184a, 284, and
384 and the connector of the body such as the hole 12, 112, 112a,
212, and 312 have additional compatible structures and features to
further strengthen the connection between the integration plate 82,
182, 182a, 282, and 382 and the implant 1, 101, 101a, 201, and
301.
[0131] The structures and features may be on either or both of the
integration plate 82, 182, 182a, 282, and 382 and the main body 2
of the implant 1, 101, 101a, 201, and 301. In general, the
structures include fasteners, compatibly shaped joints, compatibly
shaped undercuts, and/or other suitable connectors having different
shapes, sizes, and configurations. For example, a fastener may
include a pin, screw, bolt, rod, anchor, snap, clasp, clip, clamp,
or rivet. In some aspects, an adhesive may be used to further
strengthen any of the integration plate 82, 182, 182a, 282, and 382
and implant 1, 101, 101a, 201, and 301 connections described in
this specification. An adhesive may comprise cement, glue, polymer,
epoxy, solder, weld, or other suitable binding materials.
[0132] The integration plate 82, 182, 182a, 282, and 382 may
comprise one or more reciprocal connectors (not shown), such as one
or more posts, each having a bore, extending through a horizontal
plane. The post may be inserted into a connector such as a hole
through the implant 1, 101, 101a, 201, and 301. A fastener (not
shown), such as a pin, may be inserted through the bore thereby
preventing the post from being disengaged from the hole. In some
aspects, the pin may be threaded through a second bore that passes
through the walls of the implant 1, 101, 101a, 201, and 301 itself;
although it is preferable that the implant 1, 101, 101a, 201, and
301 does not include a second bore through its walls and that the
bore is accessible from the space inside of the implant.
Alternatively, the integration plate 82, 182, 182a, 282, and 382
may comprise a plurality of bores (not shown) present on and having
openings accessible from the bottom of the integration plate 82,
182, 182a, 282, and 382. The bores may mate with a plurality of
fasteners, which may comprise rods integral with or otherwise
attached to the top surface or bottom surface of the implant 1,
101, 101a, 201, and 301. For example, the rods may be molded as
upward-facing extensions or snap-fit into the bores. In some
aspects, for example, where the body 2 of the implant 1, 101, 101a,
201, and 301 is comprised of a plastic or polymeric material, the
hole 12, 112, 112a, 212, and 312 may not be present, and the screw
or bolt (not shown) may be screwed directly into the plastic or
polymeric material, with the screw threads tightly gripping the
plastic or polymeric material to form the connection.
[0133] It is also contemplated that the bottom surface 83, 183,
183a, 283, and 383 of the integration plate 82, 182, 182a, 282, and
382 may comprise undercuts (not shown) in shapes that form a tight
junction with compatible shapes on the implant 1, 101, 101a, 201,
and 301. For example, the bottom surface 83, 183, 183a, 283, and
383 may comprise a dovetail joint, bevel, or taper that fits with a
counterpart dovetail joint, bevel, or taper on the body 2 of the
implant 1, 101, 101a, 201, and 301.
[0134] An adhesive (not shown) may directly join the integration
plate 82, 182, 182a, 282, and 382 and the body 2 of the implant 1,
101, 101a, 201, and 301 together, with or without other connecting
features. For example, the adhesive may be applied to the bottom
surface 83, 183, 183a, 283, and 383 of the integration plate 82,
182, 182a, 282, and 382. Alternatively, the adhesive may be applied
to the top surface 10, 110, 110a, 210, and 310 or bottom surface
20, 120, 120a, 220, and 320 or both surfaces of the implant 1, 101,
101a, 201, and 301.
[0135] The foregoing describes various non-limiting examples of how
the one or two integration plates 82, 182, 182a, 282, and 382 may
be joined together with the implant 1, 101, 101a, 201, and 301.
[0136] Other Implant Features
[0137] The implant 1 may be machined to comprise some or all of the
following implant features, for example. In some aspects, the
interbody spinal implant 1 is substantially hollow and has a
generally oval-shaped transverse cross-sectional area with smooth,
rounded, or both smooth and rounded lateral sides 30 and
posterior-lateral corners. The implant 1 includes at least one
vertical aperture 60 that extends the entire height of the implant
body 2. The vertical aperture 60 defines an interior surface or
hollow cavity within the implant 1, which may be filled with bone
growth inducing materials. The vertical aperture (a) extends from
the top surface to the bottom surface, (b) has a size and shape
predetermined to maximize the surface area of the top surface and
the bottom surface available proximate the anterior and posterior
portions while maximizing both radiographic visualization and
access to the substantially hollow center, and (c) optionally
defines a transverse rim. The vertical aperture 60 may further
define a transverse rim 100 having a greater posterior portion
thickness 55 than an anterior portion thickness 45.
[0138] In at least one embodiment, the opposing lateral sides 30
and the anterior portion 40 have a rim thickness 45 of about 5 mm,
while the posterior portion 50 has a rim thickness 55 of about 7
mm. Thus, the rim posterior portion thickness 55 may allow for
better stress sharing between the implant 1 and the adjacent
vertebral endplates and helps to compensate for the weaker
posterior endplate bone. In some aspects, the transverse rim 100
has a generally large surface area and contacts the vertebral
endplate. The transverse rim 100 may act to better distribute
contact stresses upon the implant 1, and hence minimize the risk of
subsidence while maximizing contact with the apophyseal supportive
bone. It is also possible for the transverse rim 100 to have a
substantially constant thickness (e.g., for the anterior portion
thickness 45 to be substantially the same as the posterior portion
thickness 55) or for the posterior portion 50 to have a rim
thickness 55 less than that of the opposing lateral sides 30 and
the anterior portion 40.
[0139] The implant 1 may be shaped to reduce the risk of
subsidence, and improve stability, by maximizing contact with the
apophyseal rim of vertebral endplates. Embodiments may be provided
in a variety of anatomical footprints having a medial-lateral width
ranging from about 32 mm to about 44 mm. An interbody spinal
implant 1 generally does not require extensive supplemental or
obstructive implant instrumentation to maintain the prepared disc
space during implantation. Thus, the interbody spinal implant 1 and
associated implantation methods allow for larger-sized implants as
compared with other size-limited interbody spinal implants known in
the art. This advantage allows for greater medial-lateral width and
correspondingly greater contact with the apophyseal rim.
[0140] As illustrated in FIGS. 12 and 13, the implant 1 has an
opening 90 in the anterior portion 40. In one embodiment, the
posterior portion 50 may have a similarly shaped opening 90 (not
shown). In some aspects, only the anterior portion 40 has the
opening 90 while the posterior portion 50 has an alternative
opening 92 (which may have a size and shape different from the
opening 90). The opening 92 defines an interior surface or hollow
cavity, which may be filled with bone growth inducing
materials.
[0141] The opening 90, 290, and 390 has a number of functions. One
function is to facilitate manipulation of the implant 1, 201, and
301 by the caretaker. Thus, the caretaker may insert a surgical
tool into the opening 90, 290, and 390 and, through the engagement
between the surgical tool and the opening 90, 290, and 390,
manipulate the implant 1, 201, and 301. The opening 90, 290, and
390 may be threaded to enhance the engagement. A suitable surgical
tool, such as a distractor (not shown), may be selected by one of
ordinary skill in the art.
[0142] As best shown in FIGS. 14 and 15, the anterior portion 140,
140a may have a tapered nose 142, 142a to facilitate insertion of
the implant 101.
[0143] The implant 1 may further include at least one transverse
aperture 70 that extends the entire transverse length of the
implant body. The transverse aperture 70 defines an interior
surface or hollow cavity, which may be filled with bone growth
inducing materials. The at least one transverse aperture 70 may
provide improved visibility of the implant 1 during surgical
procedures to ensure proper implant placement and seating, and may
also improve post-operative assessment of implant fusion. The
transverse aperture 70 may be broken into two, separate sections by
an intermediate wall. Suitable shapes and dimensions for the
transverse aperture 70 may be selected by one of ordinary skill in
the art. In particular, all edges of the transverse aperture 70 may
be rounded, smooth, or both. The intermediate wall may be made of
the same material as the remainder of the body 2 of the implant 1
(e.g., plastic), or it may be made of another material (e.g.,
metal). The intermediate wall may offer one or more of several
advantages, including reinforcement of the implant 1 and improved
bone graft containment.
[0144] The implant 1 may be provided with a solid rear wall (not
shown). The rear wall may extend the entire width of the implant
body and nearly the entire height of the implant body. Thus, the
rear wall can essentially close the anterior portion 40 of the
implant 1. The rear wall may offer one or more of several
advantages, including reinforcement of the implant 1 and improved
bone graft containment. In the cervical application, it may be
important to prevent bone graft material from entering the spinal
canal.
[0145] The implant 1 may also have a lordotic angle to facilitate
alignment. The anterior portion 40 is preferably generally greater
in height than the opposing posterior portion 50. Therefore, the
implant 1 may better compensate for the generally less supportive
bone found in certain regions of the vertebral endplate. As much as
seven degrees of lordosis (or more) may be built into the implant 1
to help restore cervical balance.
[0146] To enhance movement resistance and provide additional
stability under spinal loads in the body, the implant 1, 101, 101a,
201, and 301 may comprise one or more anti-expulsion edges 8, 108,
108a, 208, and 308 that tend to "dig" into the end-plates slightly
and help to resist expulsion. The anti-expulsion edges 8, 108,
108a, 208, and 308 may be present on the top surface 81 of the
integration plate 82 affixed to the top surface 10, 110, 110a, 210,
and 310; the bottom surface 20, 120, 120a, 220, and 320; or both
surfaces of the implant 1, 101, 101a, 201, and 301. Alternatively,
the anti-expulsion edges 8, 108, 108a, 208, and 308 may be present
on the top surface 10, 110, 110a, 210, and 310; the bottom surface
20, 120, 120a, 220, and 320; or both surfaces of the body of the
implant 1, 101, 101a, 201, and 301.
[0147] By way of example, FIG. 12 shows an anti-expulsion edge 8 on
the top surface 81 of the integration plate 82 and the bottom
surface 20 of the anterior face 40 of the implant 1. Each
anti-expulsion edge 8 may protrude above the plane of the top
surface 81 of the integration plate 82 and bottom surface 20, with
the amount of protrusion increasing toward the anterior face 40 and
the highest protrusion height P at the anterior-most edge of the
top surface 81 of the integration plate 82 or bottom surface
20.
[0148] An anti-expulsion edge 8, 108, 108a, 208, and 308 may be
oriented toward the anterior portion 40, 140, 140a, 240, and 340,
or the posterior portion 50, 150, 150a, 250, and 350, or either of
the opposing lateral sides 30, 130, 130a, 230, and 330. The
orientation of the anti-expulsion edge 8, 108, 108a, 208, and 308
may depend on the intended orientation of the implant 1, 101, 101a,
201, and 301 when it has been implanted between vertebrae in the
patient.
[0149] Example Surgical Methods
[0150] The following examples of surgical methods are included to
more clearly demonstrate the overall nature of the invention. These
examples are exemplary, not restrictive, of the invention.
[0151] Certain embodiments of the invention are particularly suited
for use during interbody spinal implant procedures currently known
in the art. For example, the disc space may be accessed using a
standard mini open retroperitoneal laparotomy approach. The center
of the disc space is located by AP fluoroscopy taking care to make
sure the pedicles are equidistant from the spinous process. The
disc space is then incised by making a window in the annulus for
insertion of certain embodiments of the spinal implant 1, 101,
101a, 201, and 301 (a 32 or 36 mm window in the annulus is
typically suitable for insertion). The process according to the
invention minimizes, if it does not eliminate, the cutting of bone.
The endplates are cleaned of all cartilage with a curette, however,
and a size-specific rasp (or broach) may then be used.
[0152] Use of a rasp preferably substantially minimizes or
eliminates removal of bone, thus substantially minimizing or
eliminating impact to the natural anatomical arch, or concavity, of
the vertebral endplate while preserving much of the apophyseal rim.
Preservation of the anatomical concavity is particularly
advantageous in maintaining biomechanical integrity of the spine.
For example, in a healthy spine, the transfer of compressive loads
from the vertebrae to the spinal disc is achieved via hoop stresses
acting upon the natural arch of the endplate. The distribution of
forces, and resultant hoop stress, along the natural arch allows
the relatively thin shell of subchondral bone to transfer large
amounts of load.
[0153] During traditional fusion procedures, the vertebral endplate
natural arch may be significantly removed due to excessive surface
preparation for implant placement and seating. This is especially
common where the implant 1, 101, 101a, 201, and 301 is to be seated
near the center of the vertebral endplate or the implant 1, 101,
101a, 201, and 301 is of relatively small medial-lateral width.
Breaching the vertebral endplate natural arch disrupts the
biomechanical integrity of the vertebral endplate such that shear
stress, rather than hoop stress, acts upon the endplate surface.
This redistribution of stresses may result in subsidence of the
implant 1, 101, 101a, 201, and 301 into the vertebral body.
[0154] Preferred embodiments of the surgical method minimize
endplate bone removal on the whole, while still allowing for some
removal along the vertebral endplate far lateral edges where the
subchondral bone is thickest. Still further, certain embodiments of
the interbody spinal implant 1, 101, 101a, 201, and 301 include
smooth, rounded, and highly radiused posterior portions and lateral
sides which may minimize extraneous bone removal for endplate
preparation and reduce localized stress concentrations. Thus,
interbody surgical implant 1, 101, 101a, 201, and 301 and methods
of using it are particularly useful in preserving the natural arch
of the vertebral endplate and minimizing the chance of implant
subsidence.
[0155] Because the endplates are spared during the process of
inserting the spinal implant 1, 101, 101a, 201, and 301, hoop
stress of the inferior and superior endplates is maintained. Spared
endplates allow the transfer of axial stress to the apophasis.
Endplate flexion allows the bone graft placed in the interior of
the spinal implant 1, 101, 101a, 201, and 301 to accept and share
stress transmitted from the endplates. In addition, spared
endplates minimize the concern that BMP might erode the cancellous
bone.
[0156] Interbody spinal implant 1, 101, 101a, 201, and 301 is
durable and can be impacted between the endplates with standard
instrumentation. Therefore, certain embodiments of the invention
may be used as the final distractor during implantation. In this
manner, the disc space may be under-distracted (e.g., distracted to
some height less than the height of the interbody spinal implant 1)
to facilitate press-fit implantation. Further, certain embodiments
of the current invention having a smooth and rounded posterior
portion (and lateral sides) may facilitate easier insertion into
the disc space. Still further, the surface roughened topography 80
may lessen the risk of excessive bone removal during distraction as
compared to implants having teeth, ridges, or threads currently
known in the art even in view of a press-fit surgical distraction
method. Nonetheless, once implanted, the interbody surgical implant
1, 101, 101a, 201, and 301 may provide secure seating and prove
difficult to remove. Thus, certain embodiments of the interbody
spinal implant 1, 101, 101a, 201, and 301 may maintain a position
between the vertebral endplates due, at least in part, to resultant
annular tension attributable to press-fit surgical implantation
and, post-operatively, improved osteointegration.
[0157] Surgical implants and methods according to embodiments of
the invention tension the vertebral annulus via distraction. These
embodiments may also restore spinal lordosis, thus improving
sagittal and coronal alignment. Implant systems currently known in
the art require additional instrumentation, such as distraction
plugs, to tension the annulus. These distraction plugs require
further tertiary instrumentation, however, to maintain the lordotic
correction during actual spinal implant insertion. If tertiary
instrumentation is not used, then some amount of lordotic
correction may be lost upon distraction plug removal. Interbody
spinal implant 1, 101, 101a, 201, and 301, according to certain
embodiments of the invention, is particularly advantageous in
improving spinal lordosis without the need for tertiary
instrumentation, thus reducing the instrument load upon the
surgeon. This reduced instrument load may further decrease the
complexity, and required steps, of the implantation procedure.
[0158] Certain embodiments of the spinal implant 1, 101, 101a, 201,
and 301 may also reduce deformities (such as isthmic
spondylolythesis) caused by distraction implant methods.
Traditional implant systems require secondary or additional
instrumentation to maintain the relative position of the vertebrae
or distract collapsed disc spaces. In contrast, interbody spinal
implant 1, 101, 101a, 201, and 301 may be used as the final
distractor and thus maintain the relative position of the vertebrae
without the need for secondary instrumentation.
[0159] Certain embodiments collectively comprise a family of
implants, each having a common design philosophy. These implants 1,
101, 101a, 201, and 301 and the associated surgical technique have
been designed to address at least the ten, separate challenges
associated with the current generation of traditional anterior
spinal fusion devices listed above in the Background section of
this document.
[0160] After desired annulotomy and discectomy, embodiments of the
invention first adequately distract the disc space by inserting
(through impaction) and removing sequentially larger sizes of very
smooth distractors, which have been size matched with the size of
the available implant 1, 101, 101a, 201, and 301. Once adequate
distraction is achieved, the surgeon prepares the end-plate with a
rasp. There is no secondary instrumentation required to keep the
disc space distracted while the implant 1, 101, 101a, 201, and 301
is inserted, as the implant 1, 101, 101a, 201, and 301 has
sufficient mechanical strength that it is impacted into the disc
space. In fact, the height of the implant 1, 101, 101a, 201, and
301 is preferably about 1 mm greater than the height of the rasp
used for end-plate preparation, to create some additional tension
in the annulus by implantation, which creates a stable implant
construct in the disc space.
[0161] The implant geometry has features which allow it to be
implanted via any one of an anterior, antero-lateral, or lateral
approach, providing tremendous intra-operative flexibility of
options. The implant 1, 101, 101a, 201, and 301 has adequate
strength to allow impact, and the sides of the implant 1, 101,
101a, 201, and 301 may have smooth surfaces to allow for easy
implantation and, specifically, to prevent binding of the implant
1, 101, 101a, 201, and 301 to soft tissues during implantation.
[0162] The invention encompasses a number of different implant 1,
101, 101a, 201, and 301 configurations, including a composite
implant 1, 101, 101a, 201, and 301 formed of top and optional
bottom plates (components), for example, made out of titanium. The
integration surfaces exposed to the vertebral body have a roughened
surface topography 80 to allow for bony in-growth over time, and to
provide resistance against expulsion. The top and bottom titanium
plates may be assembled together with the implant body 2. The net
result is a composite implant 1, 101, 101a, 201, and 301 that has
engineered stiffness for its clinical application. The axial load
may be borne by the polymeric component of the construct.
[0163] It is believed that an intact vertebral end-plate deflects
like a diaphragm under axial compressive loads generated due to
physiologic activities. If a spinal fusion implant 1, 101, 101a,
201, and 301 is inserted in the prepared disc space via a procedure
which does not destroy the end-plates, and if the implant 1, 101,
101a, 201, and 301 contacts the end-plates only peripherally, the
central dome of the end-plates can still deflect under physiologic
loads. This deflection of the dome can pressurize the bone graft
material packed inside the spinal implant, hence allowing it to
heal naturally. The implant 1, 101, 101a, 201, and 301 designed
according to certain embodiments allows the vertebral end-plate to
deflect and allows healing of the bone graft into fusion.
[0164] Although illustrated and described above with reference to
certain specific embodiments and examples, the present invention is
nevertheless not intended to be limited to the details shown.
Rather, various modifications may be made in the details within the
scope and range of equivalents of the claims and without departing
from the spirit of the invention. It is expressly intended, for
example, that all ranges broadly recited in this document include
within their scope all narrower ranges which fall within the
broader ranges. In addition, features of one embodiment may be
incorporated into another embodiment.
* * * * *