Expandable spinal implant and surgical method

An expandable spinal implant is disclosed. The implant includes a plurality of ribs which are deformable between first and second states. In the first state, the ribs present a generally cylindrical implant. In the expanded second state, the ribs are arced outwardly to define a generally spherical implant. A tie mechanism is provided for urging the ribs between the first and second states and for holding the ribs in the expanded state. A novel surgical method is disclosed for stabilizing the spine by inserting the implant in the first state between opposing vertebrae and expanding the implant to the second state.

II. BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention pertains to a surgical procedure for stabilizing the spine. 
The procedure includes the use of a novel implant. More particularly, this 
invention pertains to a novel expandable spinal implant and a novel 
surgical method utilizing the implant. 
2. Description of the Prior Art 
Chronic low back pain is one of the most common and perplexing problems 
facing the field of orthopedic surgery. In addition to patient discomfort, 
chronic low back pain has severe adverse societal impacts, including lost 
income and possible chronic dependence on drugs, alcohol and public relief 
programs. 
In many cases, low back pain can be avoided by preventing relative motion 
between spinal vertebrae. This treatment is commonly referred to as 
intervertebral stabilization. To abate low back pain, stabilization is 
directed to stabilizing contiguous vertebrae in the lumbar region of the 
spine. 
Surgical techniques are known for use in spinal stabilization. These 
techniques seek to rigidly join vertebrae which are separated by a 
degenerated disk. Ideally, the surgery effectively replaces the 
vertebra-disk-vertebra combination with a single rigid vertebra. Various 
surgical techniques have been developed which attempt to approach or 
approximate this ideal. 
One technique known in the art is to partially remove a degenerated disk 
and insert a bone graft into the void formed by the removed disk. Other 
techniques involve the use of an implant which, acting along or in 
combination with bone fragments, replace the use of bone grafts. An 
example of such an implant is shown in U.S. Pat. No. 4,501,269 to Bagby 
dated Feb. 26, 1989. In Bagby, a large, cylindrical basket is driven into 
a hole formed between bones which are to be joined. The basket is hollow 
and is filled with bone fragments which are produced during a boring step. 
Bone-to-bone fusion is achieved through and about the basket. In Bagby, 
the hole for the basket is slightly smaller than the diameter of the 
basket. This structure results in the spreading of the opposing bone 
segments upon insertion of the basket. This results in taughtness, which 
provides initial stabilization. Eventual fusion of the opposing bone 
segments results from bone growth through the basket. 
Implants such as those shown in U.S. Pat. No. 4,501,269 are promising. 
However, improved implant design is necessary to enhance patient safety 
and the probability of a satisfactory recovery. 
III. SUMMARY OF THE INVENTION 
According to a preferred embodiment of the present invention, and implant 
for insertion into a bore formed between opposing vertebrae of an animal's 
spine is disclosed. The implant includes an expandable body and a 
mechanism for expanding the body between a first state and a second state. 
The body includes a plurality of ribs which are deformable between first 
and second shapes. The exterior dimensions of the body is larger in the 
second shape than in the first shape. The preferred embodiment also 
discloses a novel surgical method involving use of the implant. In the 
novel method, an entrance bore is formed into the degenerated disk area of 
a spine. An enlarged chamber is formed between opposing vertebrae to be 
fused, with the enlarged chamber communicating through the exterior of the 
spine via the entrance bore. The vertebra implant in the first state is 
inserted through the entrance bore into the chamber and expanded into the 
second shape.

V. DESCRIPTION OF THE PREFERRED EMBODIMENT 
A. General 
Reference is now directed to the various figures in which identical 
elements are numbered identically throughout. FIG. 1 is a perspective view 
of an implant 10 according to a preferred embodiment of the present 
invention. Implant 10 includes a body 12 and an expander 14. The expander 
14 includes a tie rod 16 and an attachable end cap 18. 
Shown best in FIG. 3, body 12 has a rest (or first) state in which body 12 
is generally cylindrical. As will be more fully described, through 
application of expander 14, body 12 may be deformed to an expanded (or 
second) state such as that shown in FIGS. 1 and 2. 
B. Implant Body 
The body 12 includes an inner structure 20 (conveniently referred to as a 
matrix) and an outer structure 22 (conveniently referred to as a shell). 
Shell 22 is a hollow, cylindrical tube. The tubular shell 22 has a 
plurality of longitudinally extending slots 24. Slots 24 are angularly 
displaced around the circumference of tubular shell 22 and extend through 
the entire thickness of tubular shell 22. However, the slots 24 do not 
extend the entire length of shell 22, such that the terminal ends of shell 
22 (designated by number 23) are solid rings 23 through which slots 24 do 
not extend. 
The material of outer structure 22 between slots 24 defines a plurality of 
outer ribs 26. As shown in FIG. 3, the ribs 26 are arranged in a generally 
cylindrical array, with the rings 23 holding the ribs 26 in the 
cylindrical array. 
The inner structure or matrix 20 of body 12 includes a plurality of inner 
ribs 28, with each of ribs 28 disposed on an inner surface of each of 
outer ribs 26. A plurality of circumferential grooves 30 are cut into the 
inner surface of each of inner ribs 28 and spaced at intervals along the 
longitudinal length of ribs 28. As shown in FIG. 4, each of grooves 30 are 
V-shaped in cross-section, with a wide end of the grooves 30 at the inner 
surface of the inner ribs 28. The grooves 30 are closely spaced from, but 
do not extend all the way to, the outer surface of inner ribs 28. The 
grooves 30 divide the ribs 28 into a plurality of block segments 29. 
C. Implant Expander 
As previous indicated, the includes tie rod 16 and an attachable end cap 
18. Shown best in FIG. 5, tie rod 16 includes an integrally molded end cap 
32 having a disk-shaped force transmitting plate 34 and a frusto-conical 
shaped support disk 36. An annular groove 38 is formed in cap 32 between 
plate 34 and support disk 36. 
A tie rod post 40 extends axially from disk 36 and terminates at a distal 
end 42. Adjacent distal end 42, post 40 is provided with a plurality of 
barbs 44. 
As shown in FIGS. 6 and 7, attachable end cap 18 is similar to cap 32 in 
that cap 18 has an outer disk-shaped force transmitting plate 46 and an 
inner, frusto-conical support disk 48. Plate 46 and disk 48 are separated 
by an annular groove 50. Formed through an axis of attachable end cap 18 
is a notched bore 52 with notches 54 complementarily sized to receive 
barbs 44 of tie rod 16. 
D. Cooperative Assembly of Body 12 and Expander 14 
Tie rod 16 and end cap 18 are sized to cooperate to exert a deforming force 
on the axially opposite ends 23 of body 12. Specifically, plates 34 and 46 
of caps 32 and 18, respectively, are sized to oppose and abut ring ends 23 
of body 12. Frusto-conical disks 36, 48 are sized to be received within 
shell 22, with disks 36, 48 opposing inner ribs 28. 
Tie rod 16 is aligned to pass through bore 52, with barbs 44 captured 
within notches 54. By drawing on free end 42 through any suitable drawing 
means, tie rod 16 is urged through bore 52. The barbs 44 incrementally 
advance through notches 54 to draw caps 32 and 18 together while 
preventing separation of caps 32, 18 when the drawing force is removed 
from free end 42. 
With plates 34, 46 sized to abut ring ends 23, the force which urges end 
caps 18, 32 together creates a compressive force on the axially opposite 
ends 23 of body 12. This force causes ribs 26, 28 to arc outwardly to the 
shape shown in FIGS. 1 and 2. 
As shown in FIGS. 1 and 2, the inner ribs 28 curve outwardly to a point 
where the opposing notch-defining surfaces of notches 30 have collapsed 
onto one another so that grooves 30 are closed as shown in FIGS. 1 and 2. 
Best shown in FIG. 2, frusto-conical disks 36, 48 are shaped to oppose and 
abut the ends of inner ribs 28 when ribs are fully arched. Grooves 38, 50 
are sized to receive rings 23 as the shell 22 deforms to the expanded 
shape of FIG. 2. 
As shown best in a comparison between FIGS. 2A and 2B, the ribs 28 are 
shown expanded between the first shape (FIG. 2A) and the second shape 
(FIG. 2B). In the first shape, the ribs 28 are generally straight with the 
opposing surfaces of contiguous block segments 29 being spaced apart. In 
the expanded shape of FIG. 2B, the opposing surfaces of the block segments 
29 are touching. As a result, the arch shaped rib 28 is now load bearing. 
The structural integrity of the arched rib 28 (as shown in FIG. 2B) is 
similar to the load bearing characteristics of stone arches in 
architecture. The shape of the block segments 29 is voussoir-shaped. 
("Voussoir" being recognized as the wedged shaped stones which comprise 
architectural arches.) With each of the blocks at least partially 
touching, the load bearing integrity of the arched rib 28 is maintained. 
E. Preferred Materials of Construction 
The preferred embodiment, described above, illustrates body 12 as being a 
composite of an inner structure (or matrix) 20 and an outer structure (or 
shell) 22. This composite structure is selected so that materials of 
different properties can be used for forming inner ribs 28 and outer ribs 
26. 
Preferably, outer ribs 26 are formed of a material which is highly 
resistant to tensile forces. On the other hand, inner ribs 28 are formed 
from a material which is highly resistant to compressive forces. The high 
resistance to compressive forces of inner ribs 28 requires the formation 
of grooves 30, which are closed as inner ribs 28 are bent to the fully 
arched position shown in FIGS. 1 and 2. 
As will be described, it is anticipated that the implant 10 will be 
preferably used in surgery in spines of humans as well as other animals. 
Accordingly, the material of inner structure 20, outer structure 22, and 
expander 14 should be biocompatible. Often, it is preferable that the 
material of these elements be radiolucent so that they will not interfere 
with X-ray examination of a patient's recovery. A preferred material for 
expander 14 (including tie rod 16, cap 18 and cap 32) is polyethylene. 
This material is biocompatible, radiolucent, and has sufficient 
flexibility for barbs 44 to be advanced through notched bore 52 in one 
direction in response to a drawing force on end 42, but maintain a fixed 
position in the absence of the force 42. 
A preferred material for the outer structure 22 is carbon fiber. This 
material should permit the outer structure 22 to bend, but not stretch. 
Accordingly, the outer structure 22 and outer ribs 26 hold the inner ribs 
28 in place and prevent breakage of ribs 28. Carbon fiber is known to be 
biocompatible and radiolucent. 
The material of the inner ribs 28 is preferably polymethyl methacrylate. 
This material is rigid and resistant to compression. From widespread use 
as a bone cement and joint replacement, this material is known to be 
biocompatible and radiolucent. With the combination of materials, the 
expanded implant 10 is a rigid ball-like structure which is resistant to 
compression. 
As a result of the structure of the present invention, the expander ribs 28 
are straight in a rest position but assume an arch shape when expanded. 
The arch is a combination of individual building blocks of compression 
resistant material. The building blocks are the material between grooves 
30. An arch formed of blocks of compression resistant material is highly 
resistant to forces acting to collapse the arch. 
It will be appreciated that the foregoing recitation of materials is to 
illustrate a presently preferred construction. It is not an intent to 
limit the present application to the disclosed materials. For example, it 
may be desirable to form elements of the implant from resorbable material. 
For example, the outer ribs 26 could be formed of tightly woven suture 
material such as polyglycolic acid. Inner ribs 28 could be formed of any 
biocompatible ceramic such as hydroxyapatite or tricalcium phosphate. 
F. Method of Construction 
With best reference to FIGS. 4 and 8-18 of the drawings, the method of 
construction of body 12 will now be described. As shown in FIGS. 4 and 
8-10, the starting materials of the construction include a cylindrical 
outer structure 22 (FIGS. 8 and 9) and a cylindrical inner structure 20 
(FIGS. 10 and 11). 
As previously indicated, tubular outer structure 22 is a tube of carbon 
fiber. Tubular inner structure 20 is a tube of polymethyl methacralate. 
Inner structure 20 is sized to be axially received within outer structure 
22, with a close tolerance between structures 20 and 22. The axial length 
of inner structure 20 is sized to be slightly less than the axial length 
of the outer structure 22. 
Structures 20 and 22 are joined into a completed assembly 60, as shown in 
FIG. 13. Assembly 60 is formed by sliding inner structure 20 into outer 
structure 22 as shown in FIG. 12. Inner structure 20 is adhered to the 
inner surface of outer structure 22 through any suitable mean, such as 
adhesives or the like. 
With assembly 60 formed as shown in FIG. 13, circumferential grooves 30 may 
now be cut into the inner matrix 20. A preferred tool 62 for cutting 
grooves 30 is shown in FIGS. 14-17. 
Tool 62 includes a pair of blade support rods 64 (only one of which is 
shown in FIG. 17). Each of rods 64 carries a row of V-shaped cutting teeth 
66. The shape of teeth 66 is selected so that the teeth 66 will cut 
V-shaped grooves 30. 
Rods 64 and teeth 66 are selected so that rods 64 may be placed together 
(as shown in FIG. 15) with the points of teeth 66 just beginning to cut 
into matrix 20 when the rods 64 are axially positioned within matrix 20 
and rotated about the axis. 
As shown best in FIG. 16, grooves 30 are cut by simultaneous rotation of 
tool 62 about the axis of assembly 60 (i.e., rotation in the direction of 
arrow A) and separation of rods 64 in the direction of arrows B. 
Accordingly, as the tool 62 is rotated and separated, the teeth 66 cut 
grooves 30 of progressively increasing depths until the teeth 66 are 
cutting close to, but not through, the outer surface of matrix 20. FIG. 18 
shows the partially-completed body 12 where grooves 30 are formed in 
matrix 20, but without axial slots 24 having been cut through the assembly 
60. 
With the assembly 60 as formed in FIG. 18, the body 12 may be completed by 
cutting axial slots 24 through both the inner matrix 20 and the outer 
shell 22. The slots 24 may be cut through any suitable means, and are best 
shown in FIG. 4 as having been cut completely through the thickness of 
inner matrix 20 and outer shell 22. The length of slots 24 are selected so 
that they cut through the entire axial length of matrix 20 but do not cut 
through the entire length of outer shell 22. With the method of 
construction thus described, the entire body 12 is completed. 
G. Novel Surgical Method 
1. Formation of Entrance Bore 
As indicated, the implant 10 is preferably used in spinal stabilization 
surgery. FIG. 2 of the drawings shows vertebrae 100 and 110 separated by 
disk material 112. 
After identifying a diseased disk 112, the surgeon forms a bore 114 through 
the disk layer 112. The bore 114 is formed through any conventional means 
by using a surgical drill bit (not shown). The bit is sized such that the 
diameter of the bore 114 is approximately sized to be the external 
diameter of the implant body 12 when in the relaxed or first state as 
shown in FIG. 3. The depth of the bore 114 is controlled so that the axial 
length of the body 12 may be fully inserted within the bore, with the body 
12 fully located between opposing vertebrae 100, 110. 
While the diameter of body 12 and bore 114 will vary from patient to 
patient, there is a practical maximum size of the diameter of bore 114 for 
any given patient. This maximum is attributed to the fact that too large 
of a drill bit cannot be passed through the patient's body and placed 
against disk tissue 112. If too large a drill bit is used, the size of the 
bit will interfere and possibly damage other anatomical parts, such as 
important blood vessels, nerves, etc. 
A typical selected diameter of body 12 (when in the first state) and bore 
114 is preferably about 12 mm. This diameter is selected for bore 114 to 
cut through disk material separating the fourth and firth lumbar vertebrae 
in a human spine in a typical adult human male. The depth of the 
intervertebral space between the fourth and fifth lumbar vertebrae in an 
adult human male (measured as the anterior-posterior dimension of the 
vertebrae) is commonly about 35 mm. As a result, a preferred length of 
body 12 will be about 25 mm so that the body 12 may be fully received 
within and between opposing vertebrae. 
It will be appreciated that the foregoing dimensions and descriptions have 
been given with respect to a particular vertebrae location in the spine of 
an adult human male. It is anticipated the present implant and method 
could be used on any animal spine. Accordingly, the dimensions of the 
implant 10 and entrance bore 114 will vary proportionately with increases 
or decreases in spinal anatomy between different animal types. Also, in 
humans, the dimension will vary with numerous factors, including anatomic 
region of the spine, age and sex. For example, the implant and surgical 
method is not limited to the lumbar region, and may be utilized in other 
regions of the spine where vertebrae dimensions may be different than 
those described. Therefore, several different sizes of the implant 10 are 
anticipated so a surgeon can select the optimum implant 10 for a given 
patient. 
2. Formation of Enlarged Chamber 
With the entrance bore 114 formed as described, the surgeon then cuts a 
hollow spherical chamber 116 between the opposing vertebrae 100 and 110. 
The chamber 116 is sized to be complementary to the exterior dimensions of 
the implant 12 in the enlarged state. 
Since the chamber 116 has greater volume than a bore 114, the cutting of 
chamber 116 removes greater amounts of disk material and exposes a greater 
surface area of the opposing vertebrae bone material. The exposure of the 
additional surface area increases the probability of successful grafting 
between the opposing vertebrae 100, 110. 
The formation of the enlarged spherical chamber 116 can be formed through 
any suitable technique. Preferably, the chamber 116 is formed through the 
use of an intervertebral reamer such as that shown and described in U.S. 
Pat. No. 5,015,255 and copending U.S. Pat. application Ser. No. 
07/350,050, filed on May 10, 1989, which names myself and James D. Corin 
as joint inventors. 
The diameter of the chamber 116 (and hence, the maximum allowable diameter 
of the expanded implant 10) is selected to provide a clearance so that the 
chamber 116 is not cut through the sides of the vertebrae. This diameter 
will vary from patient to patient, and between locations in the spine. 
However, to provide a clearance of about 11 mm of the sides of the 
vertebrae, the chamber is preferably held to a maximum diameter of about 
22 mm. 
3. Insertion and Expansion of Implant 
With the enlarged chamber 116 so formed, the surgeon places implant 10 in 
the unexpanded state into bore 114, the molded end cap 32 is adjacent the 
anterior side of the spine. The free end 42 of the rod 16 is exposed to 
the surgeon. 
In FIG. 2A, an unexpanded implant 10 is shown inserted within an enlarged 
chamber 116. In the position shown in FIG. 2A, the implant 10 is not 
urging vertebra 100, 110 apart. Accordingly, the annulus (the fibrous 
outer circumferential portion of disk 112) connecting the vertebra 100, 
110 is shown in a relaxed or unstretched state. 
With the implant 10 so inserted, the surgeon then draws on tie rod 16 to 
force implant 10 to expand to the second shape as shown in FIG. 2. The 
mechanism by which the surgeon applies the compressive force to the 
implant 10 may be any suitable method. In FIG. 2, the surgeon is shown 
using a ratchet gun 119 for applying the compressive force. Ratchet guns 
are well known and form no part of this invention per se. 
The gun 119 has a barrel end 118 which is sized to be received within bore 
114. A free end 120 of barrel end 118 abuts plate 46 of attachable cap 18. 
The barbed rod 40 passes through barrel 118. The barbs 44 are advanced 
through a ratchet mechanism (not shown) actuated by the surgeon's 
operation of a ratchet gun trigger 122. 
The surgeon continues to draw the barbed end of the tie rod 16 through the 
ratchet gun 119 until the implant 10 is expanded to the fully expanded 
state. As it expands, the outer surfaces of the implant 10 abut against 
the opposing surfaces of the vertebrae 100, 110. Continued expansion of 
the implant 10 causes the vertebrae 100, 110 to stretch apart slightly. 
This stretching acts to tighten the annulus of disk 112, which has not 
been removed through the formation of bore 114 and chamber 116. Those 
skilled in the art will recognize the annulus as being the fibrous outer 
circumferential portion of the disk 112. The stretching and tightening of 
the annulus provides initial stabilization between the opposing vertebrae. 
So that stretching will occur, the external dimensions of chamber 116 are 
preferably sized to be about 3 mm less than the external dimensions of the 
implant 10 measured in the fully expanded state. 
With the implant 10 fully expanded, the surgeon removes the ratchet gun and 
severs the excess barbed end of the tie rod 16. 
4. Use of a Graft Medium 
While the patient may now be closed, it is preferable that the chamber 116 
be filled with a graft medium to facilitate fusion between the opposing 
vertebrae 100, 110. The preferred graft medium would be finely chopped 
cortical or cancellous bone chips. 
FIG. 2B shows a preferred method for admitting the graft medium into 
chamber 116. As shown in FIG. 2B, the entrance bore 114 is drilled to the 
side of the anterior-posterior axis (A-P) of the patient. An access bore 
160 is formed through the vertebra 100 on the opposite side of the axis 
(A-P). The surgeon can then impact bone chips into chamber 116 through 
bore 160. The bone chips are admitted into the chamber 116 by passing them 
through opposing ribs 26 of the expanded implant body 12. 
An alternative method of admitting bone chips into chamber 116 is to fill 
the chamber 116 with a bone chip slurry before inserting the implant 10 
into the chamber 116. Also, the implant 10 could also be impregnated with 
a bone chip slurry before being passed into the chamber 116. 
With the graft medium in place, the surgeon can then close the patient 
through any suitable technique. 
The grafting of bone chips results in a fusion between the vertebrae bodies 
100, 110. While the fusion process is taking place, the surgeon can 
readily monitor the patient's progress since the preferred materials of 
the implant 10 are radiolucent and will not interfere with X-ray 
examination. Also, during the fusion process, the implant 10 is 
self-retaining in a rigid, generally spherical shape. The rigidity of the 
enlarged implant 10, together with the stretching of the annulus, provides 
stabilization between vertebrae 100, 110 during the fusion process. 
H. Alternative Embodiments 
1. Expanded Implant with Netting 
Referring now to FIGS. 19-22, an alternative embodiment of the present 
invention is shown. In the alternative embodiment a netting 200 is 
provided surrounding the implant body 12. Except for the addition of the 
netting 200, the implant is identical to that shown in FIG. 1 and similar 
elements will be numbered identically. 
In use of the embodiment of FIG. 1, there is a concern that the ribs 26 
could sink into soft bone material of the patient's vertebra. To prevent 
this, a fiber netting 200 (preferably of nylon or polyethylene) surrounds 
the body portion 12. In a preferred embodiment, the netting 200 presents 
openings of about 1 millimeter in size. The netting is bonded through any 
suitable means (such as adhesive or heat bonding) to the outer surface of 
the ribs 26. The size of the netting 200 is selected such that when the 
implant 10 is expanded to its fully expanded position (as shown in FIGS. 
19 and 21) the netting is taut resulting in a hard ball shape which 
prevents sinking into the bone tissue. 
As shown in FIGS. 20 and 22, in the unexpanded shape, the netting between 
the ribs 26 is forced downwardly into the implant body 12 through opposing 
ribs 26 to define a plurality of inwardly projecting pleats 202. As a 
result, in the unexpanded shape, the netting does not interfere with the 
exterior dimensions of the implant body 12. Accordingly, the implant body 
12 may be readily inserted into the bore 114 formed between opposing 
vertebra (as shown in FIGS. 1 and 2A). 
The reader will recall that the outer ribs 26 retain the inner ribs 28 
while the inner ribs are being deformed to the arch shape. A further 
alternative embodiment (not shown) could be the elimination of the outer 
rib material 26 with the netting 200 bonded directly to the inner ribs 28 
to hold them in place as they are being expanded to the arch shape. 
Above, the preferred material of the netting 200 was identified as nylon or 
polyethylene. An alternative material would be any resorbable material 
such as loose woven suture material (e.g. polyglycolic acid). 
2. Ball and Socket Connection 
As shown in FIGS. 4, 5 and 7, the inner rib 28 includes a plurality of cuts 
30 which separate the rib 28 into a plurality of blocks 29 having flat 
opposing surfaces. The flat opposing surfaces will abut flat surfaces such 
as surface 48 of end cap 18 (see FIG. 7). 
To ensure maximum load transmission between the ribs 28 and the end caps 
32, 18, a second alternative embodiment provides for hemispherical concave 
indents 210 formed on the frusto-conical disks 36, 48. Correspondingly, 
the end portions of the ribs 28 are provided with convex hemispherical 
surfaces 212. Surfaces 212 are sized to be complimentarily received within 
detents 210. As a result, as the ribs 28 are expanding to the arched 
position (shown in FIG. 23), surfaces 212 are freely sliding within 
detents 210. This ensures maximum surface area contact between the ribs 28 
and the surfaces 36, 48. 
An alternative to the spherical ball and socket geometry would be a 
cylindrical geometry (not shown). Namely, convex cylindrical rounded ends 
of ribs 28 could be received in concave and complementary cylindrical 
rounded detents in disks 36, 48. With cylindrical axis being transverse to 
the longitudinal dimension of the implant, the cylindrical geometry will 
prevent lateral motion while accommodating the arching of the ribs 28. 
From the foregoing, it can be seen how the present invention has been 
attained in a preferred manner. Modifications and equivalents of the 
disclosed concepts while readily occur to those skilled in the art are 
intended to be included within the scope of the invention. Thus, the scope 
of the invention is intended to be limited only by the scope of the claims 
which, are, or may hereafter be, appended hereto.