U.S. patent application number 10/285723 was filed with the patent office on 2004-05-06 for laterally expandable cage.
Invention is credited to Berry, Bret.
Application Number | 20040088054 10/285723 |
Document ID | / |
Family ID | 32069418 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040088054 |
Kind Code |
A1 |
Berry, Bret |
May 6, 2004 |
LATERALLY EXPANDABLE CAGE
Abstract
A laterally expandable spinal implant includes a central body
and two wings that are adapted to be received within an inner
chamber formed within the central body. The wings have guide rails
that fit into grooves defined in the central body. To ensure that
the implant is properly secured, each guide rail has an outer end
with a cutting surface that cuts into vertebral end plates when the
wings are extended. The two wings are connected together through a
central turnbuckle shaft that has geared teeth and threading on
both ends that engage threaded cavities in the wings. Through the
gear teeth, the turnbuckle shaft is able to be rotated so as to
laterally extend the wings from the central member. A locking
mechanism locks the turnbuckle shaft to prevent the wings from
retracting.
Inventors: |
Berry, Bret; (Cordova,
TN) |
Correspondence
Address: |
Woodard, Emhardt, Naughton,
Moriarty and McNett LLP
Bank One Center/Tower
111 Monument Circle, Suite 3700
Indianapolis
IN
46204-5137
US
|
Family ID: |
32069418 |
Appl. No.: |
10/285723 |
Filed: |
November 1, 2002 |
Current U.S.
Class: |
623/17.11 |
Current CPC
Class: |
A61F 2002/30845
20130101; A61F 2002/30571 20130101; A61F 2002/4627 20130101; A61F
2002/30387 20130101; A61F 2/447 20130101; A61F 2002/30579 20130101;
A61F 2002/30593 20130101; A61F 2220/0025 20130101; A61F 2002/30883
20130101; A61F 2/4455 20130101; A61F 2002/30904 20130101; A61F
2002/30411 20130101; A61F 2002/30556 20130101; A61F 2002/3039
20130101; A61F 2250/0009 20130101; A61F 2/442 20130101; A61F 2/4611
20130101; A61F 2002/30523 20130101; A61F 2002/30525 20130101 |
Class at
Publication: |
623/017.11 |
International
Class: |
A61F 002/44 |
Claims
What is claimed is:
1. A spinal implant, comprising: a cage defining an interior
cavity; an expansion mechanism received in said cavity of said
cage; a pair of wings operatively coupled to said expansion
mechanism, said wings each having opposing vertebrae engaging
surfaces that are configured to engage opposing vertebrae; and
wherein said expansion mechanism is operable to laterally move said
wings between the vertebrae from a compact configuration in which
at least a majority of said wings are received in said cavity of
said cage to an expanded configuration in which said wings extend
from said cage with said vertebrae engaging surfaces on each of
said wings engaging the vertebrae.
2. The implant of claim 1, wherein said expansion mechanism
includes a shaft having threaded portions on opposite ends that
threadedly engage said wings.
3. The implant of claim 2, wherein said shaft includes a gear
positioned between said threaded portions for rotating the
shaft.
4. The implant of claim 2, wherein said threaded portions are
oppositely threaded and have equal thread pitch.
5. The implant of claim 2, further comprising a lock mechanism
operable to lock said wings in said expanded configuration.
6. The implant of claim 5, wherein: said lock mechanism includes
lock cavities defined in said wings; and said lock cavities are
configured to prevent rotation of said shaft when said shaft is
positioned within said lock cavities.
7. The implant of claim 6, wherein only a portion of each of said
lock cavities is threaded.
8. The implant of claim 5, wherein said lock mechanism includes a
leaf spring engaged to said cage, said leaf spring being operable
to at least prevent rotation of said shaft in one direction.
9. The implant of claim 8, wherein said shaft includes a gear
engageable with said leaf spring.
10. The implant of claim 1 further comprising a lock mechanism to
lock said wings in an expanded configuration.
11. The implant of claim 10, wherein said lock mechanism included
lock cavities constructed and arranged to lock said wings in said
expanded configuration.
12. The implant of claim 10, wherein said lock mechanism includes a
leaf spring coupled to said cage.
13. The implant of claim 1, wherein said cage has a generally
rectangular cross-sectional shape.
14. The implant of claim 1, wherein said cage defines a tool
opening for providing access to said cavity.
15. The implant of claim 1, wherein said cage defines wing openings
on opposite sides of said cage in which said wings are slidably
received.
16. The implants of claim 15, wherein: at least one of said wing
openings defines a guide channel; and at least one of said wings
has a guide member slidably received in said guide channel.
17. The implants of claim 16, wherein said guide member has a
dovetail cross-sectional shape.
18. The implant of claim 17, wherein said guide member has a
cutting edge operable to cut one of the vertebrae during extension
of said wings.
19. The implant of claim 16, wherein said guide member has a
cutting edge operable to cut one of the vertebrae during extension
of said wings.
20. The implant of claim 1, wherein: the vertebrae have apophyseal
rings; and said wings have a generally arcuate shape to coincide
with the shape of the apophyseal rings of the vertebrae.
21. The implant of claim 1, wherein said cage has opposing surfaces
configured to engage the vertebrae.
22. The implant of claim 21, wherein said opposing surfaces are
textured surfaces to prevent expulsion of said implant.
23. The implant of claim 22, wherein said textured surfaces include
ridges.
24. The implant of claim 1, wherein said vertebrae engaging
surfaces of said wings are contoured to correspond in shape to the
vertebrae.
25. The implant of claim 1, wherein at least one of said wings has
a guide rail received in a guide rail channel defined in said
cage.
26. The implant of claim 25, wherein said guide rail has a dovetail
cross-sectional shape.
27. The implant of claim 25, wherein said guide rail has an outer
cutting edge constructed and arranged to cut the vertebrae during
extension of said wings.
28. The implant of claim 1, wherein said cage has oppositely facing
vertebrae engagement surfaces and said interior cavity extends
between said vertebrae engagement surfaces of said cage.
29. The implant of claim 1, wherein wings define an access opening
for allowing access to said expansion mechanism when said wings are
in said compact configuration.
30. A fusion device for implanting between opposing vertebrae that
define a disc space, comprising: a central member; at least one
pair of lateral members slidably coupled to said central member;
and means for extending said lateral members from said central
member into the disc space between the vertebrae with each of said
lateral members engaging both of the vertebrae.
31. The fusion device of claim 30, wherein said means for extending
said lateral members includes a shaft with threaded portions
coupled to said lateral members.
32. An apparatus, comprising: a spinal implant including a central
member defining an interior cavity and a pair of openings defined
on opposite sides of said central member that open into said
interior cavity, a pair of wings slidably received in said openings
in said central member, and a shaft coupled to said wings, said
shaft having at least one threaded portion threadedly engaging at
least one of said wings.
33. The apparatus of claim 32, wherein: said openings have guide
channels; and said wings have guide rails slidably received in said
guide channels.
34. The apparatus of claim 32, wherein said at least one threaded
portion has a pair of oppositely threaded portions at opposite ends
of said shaft.
35. The apparatus of claim 32, further comprising an inserter
engaged with said implant to extend said wings.
36. The apparatus of claim 35, wherein said shaft on said spinal
implant includes a gear.
37. The apparatus of claim 36, wherein said inserter includes: an
actuation knob; a drive shaft coupled to said knob; a drive gear
coupled to said drive shaft; and an intermediate gear engaging said
drive gear and said gear on said shaft of said spinal implant.
Description
BACKGROUND
[0001] The present invention generally concerns spinal implants,
and more specifically, but not exclusively, concerns a laterally
expandable vertebral implant.
[0002] A major cause of persistent, often disabling, back pain can
arise by disruption of the disc annulus, chronic inflammation of
the disc, or relative instability of vertebral bodies surrounding a
given disc, such as might occur due to a degenerative disease. In
the more severe cases, some form of mechanical limitation to the
movement of the vertebrae on either side of the subject disc is
necessary. In such cases, the disc tissue is irreparably damaged,
thereby necessitating removal of the entire disc. However, when the
disc nucleus is removed without subsequent stabilization the same
disabling back pain often reoccurs due to persistent inflammation
and/or instability.
[0003] Various approaches have been developed to stabilize the
adjacent vertebral bodies following excision of this material. In
one approach, two adjacent vertebrae are fused together through a
fusion device that is implanted between the vertebrae. Many of
these existing implant designs have drawbacks that lower the spinal
fusion rates. Among these design drawbacks, one such flaw is that
the implants subside into the vertebral end plates, thereby
reducing the spacing between the vertebral bodies. With prior
fusion devices, and even some prosthetic devices, a large portion
of the load is placed against the weakest part of the vertebral
body, which can lead to cavitation of the device into the
surrounding vertebral endplates with subsequent collapse of the
inner discal space and even damage of the vertebrae itself. Another
frequent cause for subsistence is created by having a small area of
contact between the implant and the endplates. As one should
appreciate, the less surface area of contact between the implant
and the end plates, the greater the risk of subsistence.
[0004] Another flaw of many implants is the lack of stability
created after implantation. Stability is crucial to the success of
a fusion. The implant must be securely fixated to the vertebral
bodies in order to ensure that no movement occurs between the two.
If movement does occur between the vertebral bodies and the
implant, the bone may not properly fuse, thereby creating stability
problems. Moreover, some designs limit the amount of graft
material, which may be able to be used with the implant. The larger
area of graft material that is able to contact the endplates, the
better chances of a good, solid bone growth between the two
vertebrae.
[0005] Some designs have created implants in which the majority of
the implant is positioned over the harder cortical bone of the
apophyseal ring of the vertebrae in order to reduce the chances of
subsistence. However, with these designs, the implant is made from
multiple separate components that are individually assembled
together within the disc space. Each component is implanted
separately and then attached to one another within the disc space.
As should be appreciated, assembling such an implant in the disc
space can be rather difficult. Such implants also tend to lack a
stiff central body, which is essential to the stability of the
implant as well as entire fusion construct. Moreover, such implants
have no mechanism to fix the implant to the vertebral body.
Typically, one has to use bone screws to secure the implant to the
vertebral bodies, which makes the implantation process more
complicated and difficult. In addition, such implants generally
have a single lateral width, and therefore, it is generally very
difficult, if not impossible, to adjust for differently sized
vertebrae. Another flaw is that these designs typically do not
provide a mechanism for ensuring that the spacers are properly
positioned. Since the lateral spacers of these types of implants
are independently assembled within the disc space, the lateral
members can be positioned at unequal positions along the apophyseal
ring, thereby increasing the risk that the implant will subside
into the vertebral end plates.
SUMMARY
[0006] In one aspect, a spinal implant includes a cage defining an
interior cavity and an expansion mechanism received in the cavity
of the cage. A pair of wings are operatively coupled to the
expansion mechanism, and the wings each have opposing vertebrae
engaging surfaces that are configured to engage opposing vertebrae.
The expansion mechanism is operable to laterally move the wings
between the vertebrae from a compact configuration in which at
least a majority of the wings are received in the cavity of the
cage to an expanded configuration in which the wings extend from
the cage with the vertebrae engaging surfaces on each of the wings
engaging the vertebrae.
[0007] Another aspect concerns a fusion device for implanting
between opposing vertebrae that define a disc space. The device
includes a central member and at least one pair of lateral members
slidably coupled to the central member. The device further includes
means for extending the lateral members from the central member
into the disc space between the vertebrae with each of the lateral
members engaging both of the vertebrae.
[0008] In a further aspect, an apparatus includes a spinal implant.
The spinal implant includes a central member defining an interior
cavity and a pair of openings defined on opposite sides of the
central member that open into the interior cavity. A pair of wings
are slidably received in the openings in the central member. A
shaft is coupled to the wings, and the shaft has at least one
threaded portion threadedly engaging at least one of the wings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a top perspective view of a spinal implant
according to one embodiment in an expanded configuration.
[0010] FIG. 2 is an exploded view of the FIG. 1 implant.
[0011] FIG. 3 is a top perspective view of the FIG. 1 implant in a
compact configuration.
[0012] FIG. 4 is an end view of the FIG. 1 implant in a compact
configuration.
[0013] FIG. 5 is a top perspective view of the FIG. 1 implant in an
expanded configuration.
[0014] FIG. 6 is an end view of the FIG. 1 implant in an expanded
configuration.
[0015] FIG. 7 is a perspective view of the FIG. 1 implant attached
to an inserter tool.
[0016] FIG. 8 is an enlarged, perspective view of the FIG. 1
implant coupled to the FIG. 7 tool.
[0017] FIG. 9 is a partial cross-sectional view of the FIG. 1
implant positioned in an interdiscal space in an expanded
configuration.
[0018] FIG. 10 is a side view of the FIG. 1 implant in the
interdiscal space.
[0019] FIG. 11 is a top view of the FIG. 1 implant in the
interdiscal space.
[0020] FIG. 12 is a perspective view of a spinal implant according
to another embodiment.
DETAILED DESCRIPTION
[0021] For the purposes of promoting an understanding of the
principles of the present invention, reference will now be made to
the embodiments illustrated in the drawings, and specific language
will be used to describe the same. It will nevertheless be
understood that no limitation of the scope of the invention is
intended thereby. Any alterations and further modification in the
described processes, systems, or devices, and any further
applications of the principles of the invention as described herein
are contemplated as would normally occur to one skilled in the art
to which the invention relates. Some embodiments of the invention
are shown in great detail, although it will be apparent to those
skilled in the relevant art that some of the features may not be
shown for the sake of clarity.
[0022] A laterally expandable spinal implant 100 according to one
embodiment of the present invention will now be described with
reference to FIGS. 1-6. As shown in FIGS. 1 and 2, the implant 100
includes a central member or cage 102, a pair of lateral members or
wings 104 that are adapted to laterally extend from the cage 102,
and an expansion mechanism 106 (or means) that is operable to
extend the wings 104. In the illustrated embodiment, the expansion
mechanism 106 includes a turnbuckle or threaded shaft 108 that
connects the wings 104 together. In other embodiments, the
expansion mechanism can include hydraulic pistons, mechanical
linkages, and the like. The shaft 108 includes a gear 110 that is
centrally located on the shaft 108 between opposing threaded
portions 112 and 114. In one embodiment, threads 116 on the
threaded portions 1 12 and 114 are oppositely threaded (i.e., one
is a left handed thread and the other is a right handed thread.) In
one form of the present invention, the threads 116 of the threaded
portions 112 and 114 have an equal pitch such that the wings 104
are able to extend from the central member 102 at the same rate.
This ensures that the implant 100 has a symmetrical configuration,
which in turn aids in centering the implant 100 over the vertebrae.
The threaded portions 112 and 114 threadedly engage threaded
openings 118 that are defined in each of the wings 104. In another
embodiment, only one end of the shaft 108 is threaded, while the
other end of the shaft 108 is unthreaded. With this embodiment, the
wings 104 are still extended by rotating the shaft 108.
[0023] Implant 100 further includes a lock mechanism 120 that is
used to lock the wings 104 in an expanded configuration in which
the wings 104 laterally extend from the cage 102. In the embodiment
illustrated in FIG. 1, the lock mechanism 120 includes lock
cavities 122 that are defined in each of the wings 104 next to the
threaded openings 118. As illustrated in FIG. 2, the lock cavities
122 open into the threaded opening 118 in the wings 104. In one
embodiment, each lock cavity 122 is only partially threaded such
that once the wings 104 are in the expanded configuration, the
shaft 108 can be slid from the threaded opening 118 into the lock
cavity 122. By being only partially threaded near the entrance of
the cavity 122, the shaft 108 is unable to rotate such that the
wings 104 are unable to be retracted. In another embodiment, the
lock cavity 122 is unthreaded, but has a depth shallower than the
threaded openings 118 so as to keep the wings 104 in the expanded
configuration, when the shaft is moved into the lock cavities
122.
[0024] Referring to FIG. 2, each wing 104 includes opposing
vertebrae engaging surfaces 202 that are configured to engage
opposing vertebrae, as well as medial 204 and lateral 206 side
surfaces. As shown, the wings 104, according to the illustrated
embodiment, have a generally tapered shape so as to coincide with
the vertebral endplate geometry. The vertebrae engaging surfaces
202 generally taper from the medial sides 204 to the lateral sides
206. To further reduce trauma upon insertion of the implant 100,
the wings 104 have beveled edges 208 between the vertebrae engaging
surfaces 202 and the lateral surfaces 206. In the illustrated
embodiment, the medial sides of the wings 104 are generally flat so
as to allow the wings 104 to contact one another in a compact state
when the wings 104 are retracted within the cage 102. The medial
sides 204 of the wings 104 define access channels 210 around the
threaded opening 114 and the lock cavity 122. In one form, access
channel 210 is sized to receive the gear 110 on the shaft 108. The
access channel 210 has an opening 212 that allows the physician to
gain access and rotate the gear 110 so as to expand the implant
100. In the illustrated embodiment, the lateral sides 206 have a
generally curved shape in order to coincide with the shape of the
apophyseal ring of the vertebrae.
[0025] With continued reference to FIG. 2, the cage 102 has a
proximal or tool engaging end wall portion 214, an opposite distal
end wall portion 216, and a pair of opposing lateral wall portions
218 that together define an interior cavity 220. The cage 202
further has a pair of opposing vertebrae engaging surfaces 222 that
are configured to engage opposing vertebrae. To coincide with
vertebrae geometry, surfaces 222 in the illustrated embodiment are
tapered such that surfaces 222 angle towards one another from the
proximal end wall portion 214 to the distal end wall portion 216.
As shown, the interior cavity 220 extends through both vertebrae
engaging surfaces 222. In the illustrated embodiment, the cage 102
has a generally rectangular shape. The vertebrae engaging surfaces
222 can include texturing so as to prevent expulsion of the implant
100 from the vertebrae. For instance, the vertebrae engaging
surfaces 222 in the illustrated embodiment have ridges 224 that aid
in preventing expulsion of the implant 100. As should be
appreciated, in other forms of the present invention, the vertebrae
engaging surfaces 222 can include other types of texturing for
preventing expulsion of the implant 100. The proximal end wall
portion 214 defines a tool opening 226 through which an insertion
tool can be inserted into the interior cavity 220, and lateral
walls 218 define wing openings 228 through which the wings 104 are
slidably received into the interior cavity 220.
[0026] FIGS. 3 and 4 illustrate the implant 100 when in a compact
state in which the wings 104 are retracted inside the interior
cavity 220. As shown in FIG. 3, the wings 104 have one or more
guide rails 302 that engage corresponding guide channels 304 formed
around the wing openings 228. In the illustrated embodiment, each
wing 104 has four guide rails, with a pair positioned along each
opposing vertebrae engaging surface 202 of the wing 104. In order
to provide further stability, the guide rails 302 and the
corresponding channels 304 in the illustrated embodiment have a
general dovetail shape. Moreover, as discussed in further detail
below, the dovetail shape of the guide rails 302 ensure that the
wings 104 remain secure in the vertebrae once implanted. When the
implant 100 is in a compact state, the majority of the wings 104
are received in the interior cavity 220 of the cage 102. In the
compact state, the medial sides 204 contact each other and the
entrances 212 of the access channels 210 define an access opening
306 through which an insertion tool can gain access to gear 110 on
shaft 108 in order to rotate the shaft 108.
[0027] As previously mentioned, the gear 110 is used to rotate the
shaft 108, thereby causing the wings 104 to extend from the cage
102. FIGS. 5 and 6 show the implant 100 with the wings 104 in a
laterally expanded state in which the wings 104 extend from the
cage 102. As should be appreciated, the expansion mechanism 106
allows the wings 104 to extend at varying distances from the cage
102 such that the size of the implant 100 can be adjusted to
correspond to the size of the selected vertebrae. As shown in FIG.
6, outer lateral ends 402 of the guide rails 302 define an inward
notch 404 such that the outer lateral ends 402 form cutting edges
406. As the wings 104 are extended, the cutting edges 406 cut
channels into the vertebrae. The cutting edges 406 act like spikes
to embed the wings 104 into the vertebral endplates. Once the wings
104 are extended, the dovetail shape of the guide rails 302 help to
ensure that the wings 104 are firmly secured to the vertebrae. Once
the wings 104 are in the desired extended position, the shaft 108
is then slid into the lock cavity 122 (FIG. 2) in order to lock the
wings 104 in the desired extended position. After implantation,
bone graft material can be packed into the interior cavity 220 via
tool opening 226 to promote fusion of the vertebrae. With the wings
104 slightly extended, bone graft material can even be packed
before implantation. Following implantation, the interior cavity
220 provides a large area in which a fusion mass can be formed
between the vertebrae.
[0028] An implant inserter assembly 700 that includes the implant
100 coupled to an inserter 702 according to one embodiment of the
present invention is illustrated in FIGS. 7 and 8. The inserter 702
includes a driving handle 704, an actuation knob 706, a shaft
portion 708, a gripping knob 710 and a head portion 712. In the
illustrated embodiment, the handle portion 704 is solid and
includes an impaction surface 714 against which a hammer or the
like can strike to drive implant 100 between the vertebrae. The
actuation knob 706 is connected to a drive shaft 802, which extends
from the actuation knob 706, through the shaft 708, and through the
head 712. When the implant 100 engages the inserter 702, the
actuation knob 706 is able to extend the wings 104. As shown in
FIG. 8, the drive shaft 804 has at one end a drive gear 804 with
teeth 806 that engage an intermediate gear 808 that is coupled to
the head 712 through a carrier member 810. During implantation, the
intermediate gear 808 engages gear 110 on the shaft 108 of the
implant 100. As the actuation knob 706 is rotated, the drive shaft
802 rotates drive gear 804. In turn, the drive gear 804 rotates the
intermediate gear 808, which then is used to rotate the shaft 108
in order to extend the wings 104. The gripping knob 710 is rotated
in order to extend gripping fingers 812 inside the interior cavity
220 such that the inserter 702 engages the tool opening 226 of the
implant 100. The gripping knob 710 and the gripping fingers 812 can
be optional, such that in one embodiment knob 710 and fingers 812
are not included. To provide a large surface area for impaction,
the head 712 has a generally rectangular shape to generally
coincide with the shape of the proximal end wall portion 214 of the
implant 100.
[0029] FIGS. 9, 10 and 11 show various views of the implant 100
when implanted between adjacent vertebrae 902 and 904. Before
implantation, a portion of the annulus is removed to create a
larger disc space for the implantation of the implant 100. The
vertebral end plates are prepared by removing cartilaginous
material connected to them. A window 906, which generally
corresponds in shape and size to the cage 102, is formed in both
vertebrae 902 and 904. Before implantation, the wings 104 are
positioned in their retracted position inside the interior cavity
220 of the implant 100, and the implant 100 is attached to the
inserter 702 in the manner as illustrated in FIG. 7. The implant
100 is then impacted into the window 906 formed between vertebrae
902 and 904. Rotation of the actuation knob 706 on the inserter 702
causes the shaft 108 on the implant 100 to rotate, thereby
expanding the implant 100. As previously mentioned, this causes the
wings 104 to laterally expand from the cage 102 between the
vertebrae. In one embodiment, the wings 104 are extended from the
cage 102 at the same rate to ensure that the implant 100 remains
centered between the vertebrae 902 and 904. As the wings 104
extend, the cutting edges 406 of the guide rails 302 cut into the
vertebrae 902 and 904, thereby ensuring that the implant is
securely fastened to the vertebrae 902 and 904. The wings 104 are
expanded until they are positioned over the apophyseal ring, which
contains the harder cortical bone. As shown in FIG. 9, the shape of
the wings 104 generally correspond to the geometry of the end
plates of vertebrae 902 and 904. Due to the large surface area
provided by the implant 100 and by being supported on the harder
cortical bone of the apophyseal ring, the risk of subsidence of the
implant 100 into the vertebrae 902 and 904 is reduced. Moreover,
the construction of implant 100 allows for the implant to have
variable dimensions such that the implant 100 can accommodate
vertebrae of varying sizes. Once the implant 100 has been expanded
to the desired expansion configuration, the turnbuckle 108 can be
moved into the block cavity 122 such that the wings 104 are locked
into position.
[0030] Referring to FIG. 12, an implant 1200 according to another
embodiment of the present invention incorporates a number of the
same features described above, with the exceptions noted below. As
should be appreciated, the locking mechanism 120 in this embodiment
differs from the one described above. In the embodiment illustrated
in FIG. 12, the locking mechanism 120 includes a leaf spring 1202
that is attached to the distal end wall portion 216 of the cage
102. As shown, the leaf spring 1202 engages the gear 110 on the
shaft 108. The leaf spring 1202 is positioned such that the shaft
108 can only be rotated in one direction so that the wings 104 can
only move in a laterally expanding direction. The spring 1202
resists rotation of the shaft in the opposite direction, so that
once the wings 104 are extended to the desired location the spring
1202 locks the wings 104 into position.
[0031] While specific embodiments of the invention have been shown
and described in detail, the breadth and scope of the present
invention should not be limited by the above described exemplary
embodiments, but should be defined only in accordance with the
following claims and their equivalents. It is understood that only
selected embodiments have been shown and described and that all
changes and modifications that come within the spirit of the
invention are desired to be protected.
* * * * *