U.S. patent application number 12/892597 was filed with the patent office on 2011-01-20 for implants with helical supports and methods of use for spacing vertebral members.
This patent application is currently assigned to Warsaw Orthopedic, Inc.. Invention is credited to Jonathan M. Dewey, Anthony J. Melkent.
Application Number | 20110015746 12/892597 |
Document ID | / |
Family ID | 39585089 |
Filed Date | 2011-01-20 |
United States Patent
Application |
20110015746 |
Kind Code |
A1 |
Melkent; Anthony J. ; et
al. |
January 20, 2011 |
Implants with Helical Supports and Methods of Use for Spacing
Vertebral Members
Abstract
The present application is directed to implants with inner and
outer members positioned in a telescoping arrangement. The members
may include helical supports to selectively adjust the height of
the implant. The helical supports offer a large contact surface to
prevent inadvertent reduction of the length due to application of a
compressive force. In some embodiments, the helical support members
may be shaped to facilitate movement of the members to increase the
height. The shape may further prevent movement that would decrease
the height. Some embodiments may also prevent relative rotation of
the members. In use, the inner and outer members are moved apart to
adjust the height of the implant to space apart the vertebral
members. The members may further be constructed to prevent the
members from moving together after insertion between the vertebral
members.
Inventors: |
Melkent; Anthony J.;
(Memphis, TN) ; Dewey; Jonathan M.; (Memphis,
TN) |
Correspondence
Address: |
MEDTRONIC;Attn: Noreen Johnson - IP Legal Department
2600 Sofamor Danek Drive
MEMPHIS
TN
38132
US
|
Assignee: |
Warsaw Orthopedic, Inc.
Warsaw
IN
|
Family ID: |
39585089 |
Appl. No.: |
12/892597 |
Filed: |
September 28, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11549791 |
Oct 16, 2006 |
7815683 |
|
|
12892597 |
|
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|
|
Current U.S.
Class: |
623/17.16 |
Current CPC
Class: |
A61F 2002/3055 20130101;
A61F 2002/30224 20130101; A61F 2230/0021 20130101; A61F 2002/30593
20130101; A61F 2/44 20130101; A61F 2220/0091 20130101; A61F
2002/30522 20130101; A61F 2002/30405 20130101; A61F 2220/0025
20130101; A61F 2230/0023 20130101; A61F 2002/30471 20130101; A61F
2002/30601 20130101; A61F 2002/30154 20130101; A61F 2002/30841
20130101; A61F 2002/30156 20130101; A61F 2002/30594 20130101; A61F
2230/0069 20130101 |
Class at
Publication: |
623/17.16 |
International
Class: |
A61F 2/44 20060101
A61F002/44 |
Claims
1. An implant for spacing apart vertebral members comprising: an
outer member having an inner surface; a first helical support that
wraps around the inner surface of the outer member; an inner member
positioned within the outer member and having an outer surface; a
second helical support that wraps around the outer surface of the
inner member; the outer and inner members being in telescoping
arrangement with the first and second helical supports engaging
together; at least one of the first and second helical supports
includes a plurality of teeth that are spaced apart by cuts, the
plurality of teeth extend radially outward beyond a floor of the
cuts.
2. The implant of claim 1, wherein each of the inner and outer
members are cylindrical with circular cross-sectional shapes.
3. The implant of claim 1, wherein both of the first and second
helical supports include a plurality of teeth.
4. The implant of claim 1, wherein one of the inner and outer
members includes an additional helical support that wraps around
the member in an opposite direction.
5. The implant of claim 1, wherein the plurality of teeth each
include a diamond shape with four straight sides.
6. The implant of claim 5, wherein the plurality of teeth each
include an angle of incidence of about 45.degree. formed between a
superior side and a horizontal line that extends through the
tooth.
7. The implant of claim 5, wherein the plurality of teeth include a
flat top surface.
8. The implant of claim 1, wherein the outer member includes a
longitudinal slot that extends inward from an end, the slot
includes a pair of side walls and a back wall opposite from the
end.
9. The implant of claim 1, wherein the plurality of teeth each
include a superior side and an inferior side with the superior side
extending radially outward at a different angle than the inferior
side.
10. The implant of claim 1, wherein the inner and outer members
include a common cross-sectional shape.
11. The implant of claim 1, wherein the outer member is formed from
at least two separate pieces.
12. An implant for spacing apart vertebral members comprising: an
outer member comprising a first helical support that extends along
an inner side of the outer member; an inner member positioned in an
interior of the outer member, the inner member comprising a second
helical support that extends along an outer side of the inner
member; each of the outer and inner members including opposing ends
and one or more side walls that extend between the ends, at least
one of the side walls of each of the outer and inner members being
flat; the inner and outer members being axially movable to adjust a
height of the implant with the first and second helical supports
engaging together to maintain the height.
13. The implant of claim 12, wherein at least one of the first and
second helical supports comprises a plurality of teeth that are
separated by one or more cuts, the plurality of teeth extending
radially outward beyond a floor of the cuts.
14. The implant of claim 12, wherein the outer member and the inner
member have a common cross-sectional shape.
15. An implant for spacing apart vertebral members comprising: an
outer member having an inner surface; a first helical support on
the inner surface of the outer member; an inner member positioned
in the outer member and having an outer surface; a second helical
support on the outer surface of the inner member; the outer and
inner members being in a telescoping arrangement with the first and
second helical supports engaged together; the first and second
helical supports shaped to prevent relative rotation between the
inner and outer members.
16. The implant of claim 15, wherein at least one of the first and
second helical supports includes a plurality of teeth that are
spaced apart by cuts, the plurality of teeth extending radially
outward beyond a floor of the cuts.
17. The implant of claim 15, wherein each of the inner and outer
members are cylindrical with circular cross-sectional shapes.
18. The implant of claim 15, wherein one of the inner and outer
members includes an additional helical support that wraps around
the member in an opposite direction.
19. The implant of claim 15, wherein the outer member includes a
longitudinal slot that extends inward from an end of the outer
member, the slot having a pair of side walls and a back wall
opposite from the end.
20. The implant of claim 15, wherein the plurality of teeth each
include a superior side and an inferior side with the superior side
extending radially outward at a different angle than the inferior
side.
Description
RELATED APPLICATION
[0001] This application is a continuation of co-pending application
Ser. No. 11/549,791, filed on Oct. 16, 2006, and herein
incorporated by reference in its entirety.
BACKGROUND
[0002] The present application is directed to devices and methods
for spacing vertebral members, and more particularly, to
intervertebral implants with inner and outer members each with one
or more helical supports to selectively adjust the height of the
implant.
[0003] The spine is divided into four regions comprising the
cervical, thoracic, lumbar, and sacrococcygeal regions. The
cervical region includes the top seven vertebral members identified
as C1-C7. The thoracic region includes the next twelve vertebral
members identified as T1-T12. The lumbar region includes five
vertebral members L1-L5. The sacrococcygeal region includes nine
fused vertebral members that form the sacrum and the coccyx. The
vertebral members of the spine are aligned in a curved
configuration that includes a cervical curve, thoracic curve, and
lumbosacral curve. Intervertebral discs are positioned between the
vertebral members and permit flexion, extension, lateral bending,
and rotation.
[0004] Various conditions may lead to damage of the intervertebral
discs and/or the vertebral members. The damage may result from a
variety of causes including a specific event such as trauma, a
degenerative condition, a tumor, or infection. Damage to the
intervertebral discs and vertebral members can lead to pain,
neurological deficit, and/or loss of motion.
[0005] Various procedures include replacing the entirety or a
section of a vertebral member, the entirety or a section of an
intervertebral disc, or both. One or more replacement implants may
be inserted to replace the damaged vertebral members and/or discs.
The implants reduce or eliminate the pain and neurological deficit,
and increase the range of motion.
SUMMARY
[0006] The present application is directed to implants for spacing
apart vertebral members. The implants may include an outer member
having an inner surface. A first helical support may wrap around
the inner surface of the outer member. An inner member may be
positioned within the outer member and have an outer surface. A
second helical support may wrap around the outer surface of the
inner member. The outer and inner members may be in telescoping
arrangement with the first and second helical supports engaging
together. At least one of the first and second helical supports may
include a plurality of teeth that are spaced apart by cuts with the
plurality of teeth extending radially outward beyond a floor of the
cuts.
[0007] The implants may also include an outer member having a first
helical support that extends along an inner side of the outer
member. An inner member may be positioned in an interior of the
outer member. The inner member may include a second helical support
that extends along an outer side of the inner member. Each of the
outer and inner members may include opposing ends and one or more
side walls that extend between the ends. At least one of the side
walls of each of the outer and inner members may be flat. The inner
and outer members may be axially movable to adjust a height of the
implant with the first and second helical supports engaging
together to maintain the height.
[0008] The implants may also include an outer member having an
inner surface with a first helical support on the inner surface of
the outer member. An inner member may be positioned in the outer
member and have an outer surface. A second helical support may be
on the outer surface of the inner member. The outer and inner
members may be in a telescoping arrangement with the first and
second helical supports engaged together. The first and second
helical supports may be shaped to prevent relative rotation between
the inner and outer members.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a perspective view of an implant according to one
embodiment.
[0010] FIG. 2 is a perspective view of an implant according to one
embodiment.
[0011] FIG. 3 is a perspective view of an implant according to one
embodiment.
[0012] FIG. 4 is a perspective view of an outer member according to
one embodiment.
[0013] FIG. 5 is a perspective view of an outer member according to
one embodiment.
[0014] FIG. 6 is a perspective view of an outer member according to
one embodiment.
[0015] FIG. 7 is a side view of an inner member according to one
embodiment.
[0016] FIG. 8 is a perspective view of an inner member according to
one embodiment.
[0017] FIG. 9 is a section view of an outer member according to one
embodiment.
[0018] FIG. 10A is a perspective view of an inner member according
to one embodiment.
[0019] FIG. 10B is a detail view of a portion of the inner member
of FIG. 10A.
[0020] FIG. 11 is a cut-away view of an inner member within an
outer member according to one embodiment.
[0021] FIGS. 12A, 12B, and 12C are side schematic views
illustrating relative positions of inner and outer members
according to one embodiment.
[0022] FIG. 13 is a partial schematic view of helical supports
according to one embodiment.
[0023] FIG. 14 is a side view of an extension positioned within
mating slots according to one embodiment.
[0024] FIG. 15 is a side view of an extension according to one
embodiment.
DETAILED DESCRIPTION
[0025] The present application is directed to implants and methods
of spacing apart vertebral members. The implants may be used for
replacement of a vertebral member such as during a corpectomy
procedure, replacement of an intervertebral disc during a
discectomy procedure, or replacement of both a vertebral member and
intervertebral disc. The implants are constructed of inner and
outer members that include helical supports for relative movement
in a first direction to selectively adjust a height of the implant.
The supports engage together to prevent the relative movement of
the members in a second direction after insertion within the
patient that would decrease the height of the implant.
[0026] FIG. 1 illustrates one embodiment of an implant 10. The
implant 10 includes inner and outer members 20, 30 arranged in a
telescoping configuration. Helical supports are positioned on the
exterior of the inner member 20 and interior of the outer member
30. The helical supports maintain the height H of the implant 10
after insertion within the patient. The supports also provide for
relative movement of the members 20, 30 in an outward direction to
increase the height H, and prevent or restrict relative movement of
the members 20, 30 in an inward direction that would decrease the
implant height.
[0027] Members 20, 30 may include a variety of different
cross-sectional shapes and sizes. The shapes and sizes of the
members 20, 30 provide for relative axial movement to adjust the
height H, and also for the helical supports to engage together.
FIG. 1 illustrates an embodiment with tubular members 20, including
a circular cross-sectional shape. FIG. 2 illustrates an embodiment
with a rectangular cross-sectional shape, and FIG. 3 includes a
triangular cross-sectional shape. In these embodiments, the
cross-sectional shapes of the members 20, 30 are the same. In other
embodiments, the shapes may be different provided they allow for
axial movement and for engagement of the helical supports.
[0028] One or both members 20, 30 may be constructed as a single
piece such as illustrated in FIG. 1. Members 20, 30 may also be
constructed from multiple pieces as illustrated in FIG. 4. In this
embodiment, member 30 comprises first and second sections 130, 131
connected together with one or more fasteners 132. Each of the
members 130, 131 are semi-cylindrical and connect together to form
the overall cylindrical member 30. The connection may provide for
the members 130, 131 to pivot about the fastener(s) 132 to provide
ratcheting action during axial movement of the members 20, 30 as
will be explained in detail.
[0029] One or more bands 86 may also attach multiple sections of
the members 20, 30 together. FIG. 5 includes a pair of bands 86
that extend around sections 120, 121, and 122 to form member 20.
Bands 86 may be constructed of flexible or inflexible
materials.
[0030] Outer member 30 includes a body 31 with a hollow interior
32. One or more slots 33 may extend along a longitudinal length of
the body 31. The slots 33 allow the body 31 to move radially in a
ratcheting manner during movement of the members 20, 30 as will be
explained below. In the embodiment of FIG. 6, two slots 33 extend
axially along a section of the length and are positioned on
opposing sides of the body 31. A hinge 39 may be positioned at the
end of the slots 33. Hinge 39 may include an enlarged opening
integral with the slot 33 for ratcheting motion of the slotted
body. In some embodiments as illustrated in FIGS. 2 and 3, slots 33
are positioned in the corners of the polygonal outer members
30.
[0031] Inner member 20 is sized to fit within the outer member 30.
Timer member 20 includes a body 21 with a hollow interior 22. A
centerline of the inner member 20 is substantially aligned with a
centerline of the outer member 30. Inner member 20 may be the same
or different height as the outer member 30.
[0032] Endplates 50 may be positioned on one or more of the members
20, 30 to contact the vertebral members as illustrated in FIG. 1.
The endplates 50 may include a variety of shapes and sizes
depending upon the context of use. In one embodiment, an opening 51
is positioned on one or both endplates 50. Opening 51 leads into
the interiors 22, 32 of the members 20, 30. Graft material may be
placed within the center of the implant 10 to facilitate bone
growth and fusion with the vertebral members. In another
embodiment, the members 20, 30 directly contact the vertebral
members (i.e., no endplates 50). The outer surfaces of the
endplates 50 or members 20, 30 may include teeth to bite into the
vertebral members and maintain the position of the implant 10.
Teeth may include a variety of shapes and sizes. The outer surfaces
may also include a roughened surface to facilitate contact with the
vertebral member.
[0033] Helical supports 40 extend from the exterior of the inner
member 20 and the interior of the outer member 30. The helical
supports 40 engage together to maintain the height H of the implant
10 under a compressive load. The helical supports 40 may also allow
for outward axial movement of the members 20, 30 to enlarge the
height as necessary. Helical supports 40 may include a variety of
shapes and sizes. The helical supports on the members 20, 30 may be
the same or different, may continuously extend around the members
20, 30, or may be discontinuous comprising one or more discrete
sections. Further, multiple helical supports 40 may be positioned
on one or both members 20, 30.
[0034] FIG. 7 illustrates one embodiment of a helical support 40
extending around the inner member 20. Support 40 includes a helical
spline 41. Wraps of the spline 41 are separated by a cut 42. Spline
41 includes a thickness t defined between superior and inferior
sides 43, 44. The distance between wraps of the spline 41, and the
angle of the spline 41 may vary depending upon the context. FIG. 8
illustrates a similar embodiment with a helical spline 41 separated
by a cut 42. The thickness t of the spline 41 is greater and the
cut 42 is narrower than that of FIG. 7.
[0035] Multiple helical supports 40 may extend around the members
20, 30. FIG. 9 includes a first helical spline 41a extending in a
first direction, and second helical spline 41b in a second
direction. Each spline 41a, 41b includes a superior side 43 and an
inferior side 44. Cuts 42 are positioned between the splines 41a,
41b. In this embodiment, splines 41a, 41b are substantially the
same shape and size. In other embodiments, the splines 41a, 41b may
be different.
[0036] Helical supports 40 may also include teeth 45 as illustrated
in FIGS. 10A and 10B. Teeth 45 each include one or more superior
sides 43 and inferior sides 44. Cuts 42 are positioned adjacent to
each of the sides 43, 44. Teeth 45 may further include an outer
surface that in this embodiment is substantially smooth. The teeth
45 and cuts 42 are spaced in helical patterns along the body 21.
The teeth 45 and cuts 42 generally form a first helical spline that
wraps around the body 21 in a first direction, and a second helical
spline that wraps around the body in a second direction.
[0037] In some embodiments, the helical supports 40 are the same on
each of the members 20, 30. By way of example, each of the members
20, 30 may include a plurality of teeth 45. Alternatively, the
helical supports 40 may be different. FIG. 11 illustrates an
embodiment with the members 20, 30 including different helical
supports 40 with the inner member 20 including teeth 45 that engage
with splines 41a, 41b of the outer member 30.
[0038] Movement of the inner member 20 relative to the outer member
30 adjusts the height H of the implant 10. FIGS. 12A-12C illustrate
one embodiment of this movement that expands the height of the
implant 10 from H to H'. In this embodiment, the inner member 20
includes teeth 45 and the outer member 30 includes a pair of
splines 41. As illustrated in FIG. 12A, implant 10 includes a first
height H. The splines 41 and teeth 45 are engaged together to
maintain the first height H with the inferior sides 44 of the
splines 41 in contact against the superior sides 44 of the teeth
45.
[0039] The sides 43, 44 of the helical supports 40 may be
configured to facilitate outward movement, and prevent inward
movement. The inferior sides 44 of the splines 41 and superior
sides 43 of the teeth 45 are disposed at a steep angle that
prevents inward movement when a compressive load is applied to the
implant 10. In this embodiment, sides 44, 45 each extend outward
from their respective bodies at substantially 90.degree.. In
another embodiment, the sides 44, 45 are undercut to engage
together and prevent inward movement.
[0040] An increase in height is accomplished by applying an outward
distraction force along the line C. The force causes the outer
member 30 to move outward relative to the inner member 20 and
helical support members 40 to slide across each other as
illustrated in FIG. 12B. Specifically, the splines 41 and teeth 45
move from the opposing cuts 42 and slide across each other. This
outward movement of the support members 40 is facilitated by the
superior sides 43 of the splines 41 and inferior sides 44 of the
teeth 45 being disposed at a shallow angle. The movement further
causes the outer surface of the splines 41 to slide along the
surfaces of the teeth 45. In one embodiment, each of the outer
surfaces is substantially smooth to facilitate the sliding
movement.
[0041] The outward movement may further be assisted by the
expansion of the body 31. This expansion may be caused by the
flexibility of one or both of the members 20, 30. Expansion may
also be caused by a radial expansion of the outer member 30 due to
the one or more longitudinal slots 33. The slots 33 provide for the
outer member 30 to radially expand thus allowing the helical
support member 40 on the outer member 30 to engage and disengage
with the inner member 20. In large expansion movements, the outer
member 30 moves in a ratcheting motion as the support member 40
moves past the opposing support member 40 on the inner member 20.
Using FIG. 12B as an example, the ratcheting motion is caused as
the splines 41 slide past the multiple teeth 45 and cuts 42. The
movement of the support members 40 may further provide tactile
feedback to the surgeon to determine the expansion of the implant
10.
[0042] FIG. 12C illustrates the outer member 30 attached at a
higher location along the inner member 20 with the implant 10 now
including a greater height H'. The splines 41 are again engaged
within the teeth 45 to prevent inward movement.
[0043] Slots 33 may be positioned on the outer member 30 for
outward radial movement as described in FIGS. 12A-12C. In another
embodiment, one or more slots 33 may be positioned along the
longitudinal length of the inner member 20. Slots 33 cause the
inner member 20 to move radially inwardly thus allowing for the
helical supports 40 to slide past one another.
[0044] The helical supports 40 may not extend along sections of the
members 20, 30 that are not slotted. As illustrated in FIG. 9, the
splines 41a, 41b extend from a lower edge of the body to the hinges
39. The section above the hinges 39 may not allow for radial
movement. Helical supports 40 positioned in this non-slotted
section may not be able to become disengaged from the corresponding
helical supports 40 and therefore prevent axial expansion of the
implant 10.
[0045] The implant 10 may also prevent the relative rotation of the
members 20, 30. In one embodiment, rotation is prevented due to the
shape of the inner members 20, 30. FIGS. 2 and 3 illustrate
embodiments with the shapes of the members 20, 30 preventing
rotation.
[0046] One embodiment includes one or more extensions 60 that
extend between the members 20, 30. Extensions 60 fit within a slot
33 to prevent rotation and allow for axial movement. FIG. 6
illustrates one embodiment with the extension 60 extending inward
into the interior 32 of the outer member 30. The extension 60 is
sized to fit within a longitudinal slot 33 in the inner member 20
such as a slot 33 illustrated in FIG. 8. The extension 60 may
include a variety of shapes and sizes to fit within the slot 33.
Extensions 60 may extend from either of the members 20, 30 to fit
within opposing slots 33. Further, multiple extensions 60 may be
positioned along the members 20, 30 to fit within one or more slots
33.
[0047] In another embodiment as illustrated in FIG. 14, extension
60 is a separate member that fits within slots 33a, 33b. The
extension 60 may move axially within the combined slots 33a, 33b.
Extension 60 allows for axial movement of the members 20, 30, yet
prevents rotation. FIG. 15 illustrates an embodiment of the
extension 60 that includes a core 87 and opposing wings 86. Core 87
is sized to move along the slots 33a, 33b, while the wings 86
prevent escape.
[0048] The members 20, 30 may include a stop mechanism to control
the extent of axial movement in the outward direction. In one
embodiment, each member 20, 30 includes a rim that contact together
and prevent further axial movement.
[0049] Rotation prevention may also be caused by multiple helical
supports 40 that wrap in different directions around one of the
members 20, 30. The opposing helical supports 40 bind together to
prevent relative rotation.
[0050] The angle of incidence .alpha. is formed between a superior
side 43 and a horizontal line that extends through the helical
support 40 as illustrated in FIG. 10B. The angle of incidence
.alpha. of the helical supports 40 may vary depending upon the
context. In one embodiment, the angle .alpha. is about
45.degree..
[0051] One or more fasteners 92 may be inserted within the members
20, 30 to lock the implant height as illustrated in FIG. 12C.
Fasteners 92 are inserted through the outer member 30 to contact
the inner member 20. The fasteners 92 may contact the outer surface
of the inner member 20, or extend into an aperture in the body 21.
Fasteners 92 may include a variety of configurations including but
not limited to screws, rivets, pins, and clips.
[0052] In one embodiment as illustrated in FIG. 10A, helical
supports 40 are positioned about the entirety of the members 20,
30. In other embodiments, the inner member 20 may include areas on
the members 20, 30 that do not include helical supports 40. The
size of these areas may vary depending upon the context of use.
[0053] The shapes and orientations of the superior and inferior
sides 43, 44 may vary. In one embodiment as illustrated in FIGS.
12A-12C, inferior edges 44 of the teeth 45 and superior edges 43 of
the splines include a shallow angle. In another embodiment as
illustrated in FIG. 13, each side 43, 44 extends outward from the
respective body 21, 31 at a substantially perpendicularly angle.
This configuration may provide a more secure engagement between the
supports 40, but may require more axial force to adjust the
height.
[0054] The implants 10 may be inserted into the spine from a
variety of approaches. One embodiment includes accessing the spine
from an anterior approach. Other applications contemplate other
approaches, including posterior, postero-lateral, antero-lateral
and lateral approaches to the spine. Further, the implants 10 may
be used with the various regions of the spine, including the
cervical, thoracic, lumbar and/or sacral regions.
[0055] In one embodiment as illustrated in FIG. 1, the outer member
30 extends completely around the inner member 20. In another
embodiment, the outer member 30 may extend around a section of the
inner member 20. A slot 33 may extend the length of the outer
member 30 from a top edge to a bottom edge thereby forming an open
section.
[0056] Spatially relative terms such as "under", "below", "over",
"inferior", "superior", and the like, are used for ease of
description to explain the positioning of one element relative to a
second element. These terms are intended to encompass different
orientations of the device in addition to different orientations
than those depicted in the figures. Further, terms such as "first",
"second", and the like, are also used to describe various elements,
regions, sections, etc and are also not intended to be limiting.
Like terms refer to like elements throughout the description.
[0057] As used herein, the terms "having", "containing",
"including", "comprising" and the like are open ended terms that
indicate the presence of stated elements or features, but do not
preclude additional elements or features. The articles "a", "an"
and "the" are intended to include the plural as well as the
singular, unless the context clearly indicates otherwise.
[0058] The present invention may be carried out in other specific
ways than those herein set forth without departing from the scope
and essential characteristics of the invention. In the embodiments
described above, the inner member 20 and the outer member 30 are
substantially straight. Members 20, 30 may also be curved. The
present embodiments are, therefore, to be considered in all
respects as illustrative and not restrictive, and all changes
coming within the meaning and equivalency range of the appended
claims are intended to be embraced therein.
* * * * *