Abstract:
An artificial spinal implant for placement between adjacent vertebrae to replace disk material and to stabilize the involved vertebrae is described. The artificial disk may be disassembled for installation and/or removal for repair, replacement or adjustment, and may be assembled from the front of the spine as individual component parts, thereby permitting alignment of the spine during the assembly process, and the stabilization of the involved vertebrae once assembly has been completed. Further, the components may be chosen from a set of similar components having different sizes, thereby enabling the implant to be tailor fit to the requirements of the patient.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to orthopedic surgery and, more particularly, to artificial spinal implants for insertion between spinal vertebrae which may be used to replace ruptured or excised spinal disks and to stabilize the spine. 
     BACKGROUND OF THE INVENTION 
     It is known that spinal musculature does little to stabilize facet joint articulation in the spine. This function is provided by the ligament structure. Most artificial disk replacements today are for degenerate disks which are causing pain. The bone, muscle and the ligaments are all intact, and the spine itself is stable. When a spine is unstable and the bones and ligaments allow the spine to move out of alignment, rods and screws are used to provide stability. In some situations a spinal fusion is performed. 
     Spinal prostheses for replacement of missing or excised disk material that replicate the functions of the missing tissue have been sought. The CHARITÉ® Artificial Disc was developed at the CHARITÉ University Hospital in Berlin, Germany in the mid-1980s. Further refinements to the design were incorporated with the cooperation of the staff at Waldemar Link GmbH. The basic device includes a sliding core made from a medical grade plastic, sandwiched between two metal endplates made from medical grade cobalt chromium alloy. The endplates support the core and have small teeth which secure them to the vertebrae above and below the disk space. In a clinical study, patients were observed to have motion between 0° and 21° while bending forward and backward. U.S. Pat. No. 4,759,766 for “Intervertebral Disc Endoprosthesis” which issued to Karin Büttner-Janz et al. on Jul. 26, 1988; U.S. Pat. No. 5,401,269 for “Intervertebral Disc Endoprosthesis” which issued to Karin Büttner-Janz et al. on Mar. 28, 1995; and U.S. Pat. No. 5,556,431 for “Intervertebral Disc Endoprosthesis” which issued to Karin Büttner-Janz on Sep. 17, 1996 represent several embodiments of this disk. 
     U.S. Pat. No. 5,683,465 for “Artificial Intervertebral Disk Prosthesis” which issued to Gary Lee Shinn et al. on Nov. 4, 1997 includes a first disk half having a portion of a socket attached to a first plate, a second disk half having a portion of a ball attached to a second plate, the socket further having a plurality of expansion slots which expand to allow the portion of a ball to be inserted into the socket such that the expansion slots expand around the portion of a ball to be inserted into the socket and then contract to retain the portion of a ball therein. The disk is fastened to the vertebrae by pins, tabs or by a first annulus or second annulus, each of which extend from the disk. A flexible substantially toroidal enclosure is attached to the perimeter of the first plate and to the perimeter of the second plate when desired to form a barrier between the disk and any proximal organic material. 
     U.S. Pat. No. 7,195,644 for “Ball And Dual Socket Joint” which issued to Robert Diaz et al. on Mar. 27, 2007, U.S. Patent Application Publication 2006/0190084 (Aug. 24, 2006) for “Interior Insert Ball And Dual Socket Joint” by Robert Doubler et al., and U.S. Patent Publication No. 2007/0162133 (Jul. 12, 2007) by Robert Doubler et al. teach a spinal implant inserted between adjacent vertebrae to function as a disk prosthesis which includes two plates fastened to adjacent vertebrae facing each other, the facing sides of the plates each having a depending skirt formed as concentric arcs and bowed or tapered in the axial direction. Depressions are centrally located between the arcs of the plates and a ceramic ball is universally movable in the depressions. 
     U.S. Pat. No. 7,282,065 for “Disk Augmentation System And Method” which issued to David Louis Kirschman on Oct. 16, 2007 describes a retainer including artificial supports posterior to or exterior of a spinal column and a spinal column axis for receiving and securing at least one artificial compression body in a supported relationship to facilitate reducing the load on one or more natural disks of a patient. 
     With the exceptions of the &#39;065 and the &#39;644 patents, the above patents and patent applications provide no stability to the spine in the situation where stability is not provided by existing ligaments. The &#39;065 patent does not permit significant movement of the vertebrae involved. The &#39;644 patent teaches that the facing sides of the plates each have a depending skirt formed as concentric depending and upstanding arcs of about 90 degrees, such that each interrupted skirt may be oriented whereby depending opposed arcs are aligned with upstanding opposed arcs, thereby interlocking the plates in a movable joint that cannot be separated axially. The contacting surfaces are spherical or bowed from the plate at least to the height of the diameter of the ball. This design does not permit lateral movement between the plates. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an artificial spinal disk for stabilizing spinal vertebrae. 
     Another object of the invention is to provide an artificial spinal disk for stabilizing spinal vertebrae while permitting significant motion of the stabilized vertebrae. 
     Still another object of the invention is to provide an artificial spinal disk for stabilizing spinal vertebrae while permitting significant motion of the stabilized vertebrae in situations where there is little muscle, ligament or bone structure to support the vertebrae. 
     Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     To achieve the foregoing and other objects, and in accordance with the purposes of the present invention, as embodied and broadly described herein, the artificial spinal disk for placement between adjacent spinal vertebrae to replace disk material, hereof, includes in combination: a first flat plate for attaching to the endplate of a first vertebral body the first flat plate having a first surface and an opposing second surface, a front wall, and a slot opening through the second surface and through the front wall; a second flat plate having a first surface and an opposing second surface, adapted to slide into the slot in the first plate; a post having a first end, and a second end perpendicularly attached to the second surface of the second plate and extending through the slot opening in the second surface of the first plate; a ball mounted on the first end of the post; means for rigidly affixing the second plate to the first plate; a third flat plate for attaching to the endplate of a second vertebral body, the endplate of the second vertebral body opposing the endplate of the first vertebral body, the third flat plate having a first surface and an opposing second surface, a front wall, and a slot opening through the second flat surface and through the front wall; a fourth member having a first surface, an opposing second surface and a front wall, and adapted to slide into the slot in the third plate, the fourth member having a slot therein opening through the second surface and through the front wall thereof and a first channel within the slot opening through the front wall of the fourth member adapted to slidably and rotatably receive the ball; means for rigidly affixing the fourth member to the third plate; a fifth member having a first surface, an opposing second surface, and a rear wall, and adapted to slide into the slot in the fourth member, the second surface having a second channel therein adapted to slidably and rotatably receive the ball and the post, and opening through the rear wall; and means for rigidly affixing the fifth member to the fourth member, whereby the channel in the fifth member and the channel in the fourth member are opposing, parallel channels wherein the ball may rotate and slide a chosen distance therein. 
     In another aspect of the invention and in accordance with its objects and purposes, the artificial spinal disk for placement between adjacent spinal vertebrae to replace disk material, hereof, includes in combination: a first flat plate for attaching to the endplate of a first vertebral body, the first flat plate having a first surface and an opposing second surface, a front wall, and a slot opening through the second surface and through the front wall; a second flat plate having a first surface and an opposing second surface, and adapted to slide into the slot in the first plate; a post having a first end, and a second end perpendicularly attached to the second surface of the second plate and extending through the slot opening in the second flat surface of the first plate; a ball mounted on the first end of the post; means for rigidly affixing the second plate to the first plate; a third member having a first surface, an opposing second surface, and a front wall, the first surface being adapted to be attached to the endplate of a second vertebral body opposing the endplate of the first vertebral body, the third member having a slot therein opening through the second surface and through the front wall thereof and a first channel within the slot opening through the front wall of the third member adapted to slidably and rotatably receive the ball; a fourth member having a first surface, a second opposing surface, and a rear wall, and adapted to slide into the slot in the third member, the second surface having a second channel therein adapted to slidably and rotatably receive the ball, and opening through the rear wall; and means for rigidly affixing the fourth member to the third member, whereby the channel in the third member and the channel in the fourth member form opposing, parallel channels, wherein the ball may rotate and slide a chosen distance therein. 
     In yet another aspect of the invention and in accordance with its objects and purposes, the artificial spinal disk for placement between adjacent spinal vertebrae to replace disk material, hereof, includes in combination: a first flat plate for attaching to the endplate of a first vertebral body the first flat plate having a first surface and an opposing second surface; a post having a first end, and a second end perpendicularly attached to the second surface of the first plate; a ball mounted on the first end of the post; a second flat plate for attaching to the endplate of a second vertebral body the endplate of the second vertebral body opposing the endplate of the first vertebral body, the second flat plate having a first surface and an opposing second surface, a front wall, and a slot opening through the second surface and through the front wall; a third member having a first surface, an opposing second surface and a front wall, and adapted to slide into the slot in the second plate, the third member having a slot therein opening through the second surface and through the front wall thereof and a first channel within the slot opening through the front wall of the third member adapted to slidably and rotatably receive the ball; means for rigidly affixing the third member to the second plate; a fourth member having a first surface, an opposing second surface, a rear wall, and adapted to slide into the slot in the third member, the second surface having a second channel therein adapted to slidably and rotatably receive the ball, and opening through the rear wall; and means for rigidly affixing the third member to the fourth member, whereby the channel in the third member and the channel in the fourth member are opposing, parallel channels, wherein the ball may rotate and slide a chosen distance therein. 
     In still another aspect of the invention and in accordance with its objects and purposes, the artificial spinal disk for placement between adjacent spinal vertebrae to replace disk material, hereof, includes in combination: a first flat plate for attaching to the endplate of a first vertebral body the first flat plate having a first surface and an opposing second surface; a post having a first end, and a second end perpendicularly attached to the second surface of the first plate; a ball mounted on the first end of the post; a second member having a first surface, an opposing second surface, and a front wall, the first surface adapted to be attached to the endplate of a second vertebral body opposing the endplate of the first vertebral body, the second member having a slot therein opening through the second surface and through the front wall thereof and a first channel within the slot opening through the front wall of the second member adapted to slidably and rotatably receive the ball; a third member having a first surface, an opposing second surface, and a rear wall, and adapted to slide into the slot in the second member, the second surface having a second channel therein adapted to slidably and rotatably receive the ball, and opening through the rear wall; and means for rigidly affixing the third member to the second member, whereby the channel in the second member and the channel in the third member form opposing, parallel channels wherein the ball may rotate and slide a chosen distance therein. 
     Benefits and advantages of the present invention include, but are not limited to, providing an artificial spinal disk for insertion between two adjacent spinal vertebrae, portions of which may be removed for repair or replacement without damaging the spinal vertebrae. Additionally the spinal implant hereof may be assembled from the front of the spine as individual component parts, thereby permitting alignment of the spine during the assembly process, and the stabilization of the involved vertebrae once assembly has been completed. Further, the components may be chosen from a set of similar components having different sizes, thereby enabling the implant to be tailor fit to the requirements of the patient. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1  is a schematic representation of an exploded perspective view of one embodiment of the artificial spine implant of the present invention illustrating first and third flat plates adapted to attach to opposing vertebral bodies; a second plate to which a post having a ball mounted thereon may be attached, the second plate being reversibly received by the first plate; and two members when combined forming a channel for slidably and rotatably restraining the ball and post, one of the two members being reversibly received by the third plate. 
         FIG. 2  is a schematic representation of a perspective assembled view of the embodiment of the artificial spine implant illustrated in  FIG. 1  hereof. 
         FIG. 3  is a schematic representation of a side view of the embodiment of the artificial spine implant illustrated in  FIG. 1  hereof. 
         FIG. 4  is a schematic representation of the front view of the embodiment of the artificial spine implant illustrated in  FIG. 1  hereof, showing the implant in place and attached to each of two opposing vertebral bodies. 
         FIG. 5  is a schematic representation of an exploded perspective view of a four-piece embodiment of the artificial spinal disk hereof including a first flat plate effective for attachment to a first vertebral body; a second plate to which a post having a ball mounted thereon is attached, wherein the second plate may be reversibly received by the first plate; and two members when combined forming an enclosed channel for slidably and rotatably restraining the ball and post, one of the two members being attached to a second vertebral body opposing the first vertebral body. 
         FIG. 6  is a schematic representation of an exploded perspective view of a second four-piece embodiment of the artificial spinal disk hereof including a first flat plate effective for attachment to a first vertebral body, and to which a post having a ball mounted thereon is attached; and two members when combined forming an enclosed channel for slidably and rotatably restraining the ball and post, the two members being reversibly attached to a third plate effective for attachment to a second vertebral body opposing the first vertebral body. 
         FIG. 7  is a schematic representation of an exploded perspective view of a three-piece embodiment of the artificial spinal disk hereof including a first flat plate effective for attachment to a first vertebral body and to which a post having a ball mounted thereon is attached; and two members when combined forming an enclosed channel for slidably and rotatably restraining the ball and post, one of the two members being attached to a second vertebral body opposing the first vertebral body. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Briefly, the present invention includes an artificial spinal implant for placement between adjacent vertebrae to replace disk material and stabilize vertebrae involved. The component parts of the implant may be assembled in the space between the vertebrae during surgery as individual components which permits each implant to be tailored to the requirements of the patient. This also permits the spine to be aligned during assembly of the components, the involved vertebrae being stabilized when the assembly is complete. The assembled implant allows controlled anterior/posterior motion of the vertebrae as well as relative rotation thereof and bending therebetween. 
     Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. In the Figures, similar structure will be identified using identical reference characters. Turning now to  FIG. 1 , a schematic representation of an exploded view of one embodiment of the artificial spine implant,  10 , hereof is shown. First flat plate,  12 , adapted for attachment to the endplate of a first vertebral body may have first flat surface,  14 , second flat surface,  16 , parallel thereto, front wall,  18 , and rear wall,  20 , slot,  22 , opening through second flat surface  16  and at least through front surface  16 , and means,  24 , for attaching plate  12  to the first vertebral body. Beneficially, one example of slot  22  may have a dovetail cross section. However, in what follows, hereinbelow, slots such as slot  22  may have other shapes; rectangular, as an example. One example of attaching means  24  is illustrated as tabs,  24   a  and  24   b , having screw holes,  26   a  and  26   b , therein each adapted for receiving a screw body therethrough effective for affixing plate  12  to the front side of the first vertebral body. 
     Second flat plate,  28 , having first flat surface,  30 , and second flat surface,  32 , parallel thereto, is adapted to slide into dovetail slot  22  in first plate  12 . Post,  34 , having first wall,  36 , and second wall,  38 , is perpendicularly attached to second surface  32  of second plate  28  and extends through the opening of slot  22  in second surface  16  of first plate  12 . Ball,  40 , is attached to post  34  in the vicinity of second end  38  thereof. Ball  40  may be reversibly attached to post  34 . Means,  42 , are provided for rigidly affixing second plate  28  to first plate  12  after second plate  28  has been received by first plate  12 . As shown in  FIG. 1 , means  42  may include tab,  42 , perpendicularly attached to front end,  44 , of second plate  28 , and having at least one hole,  46 , adapted for permitting a screw body (not shown in  FIG. 1 ) to pass therethrough such that the screw may be screwed into at least one threaded hole,  48 , in front face  18  of plate  12  once plate  28  is slid into slot  22  of plate  12 , thereby securing plate  28  to plate  12 . Tab  42  may also include hole,  50 , adapted for receiving a screw body therethrough effective for affixing plate  28  to the front side of the first vertebral body. 
     Surface  14  of plate  12  may have at least one longitudinal ridge,  52 , protruding therefrom to assist in stabilizing plate  12  on the endplate of the first vertebral body. Surface  14  may also be roughened such that bone from the endplate may grow thereinto for further stabilization of plate  12  on the endplate. 
     Third flat plate,  54 , adapted for attachment to the endplate of an opposing second vertebral body may have first flat surface,  56 , second flat surface,  58 , parallel thereto, front wall,  60 , and rear wall,  62 , slot,  64 , opening through second flat surface  58  and at least through front wall  60 , and means,  66 , for attaching plate  54  to the second vertebral body. Beneficially, one example of slot  64  may have a dovetail cross section. One example of attaching means  66  is illustrated as tabs,  66   a  and  66   b , having screw holes,  68   a  and  68   b , therein for affixing plate  54  to the front side of the second vertebral body. 
     Fourth member,  70 , having first flat surface,  72 , second flat surface,  74 , parallel thereto, front wall,  76 , and rear wall,  78 , first surface  72  being adapted to slide into slot  64  in third plate  54 . Shown in  FIG. 1  is that first flat surface  72  has a dovetail cross section,  80 . Fourth member  70  also has slot,  82 , therein opening through second flat surface  74  and through front wall  76  thereof, and first channel,  84 , opening into slot  82  and also opening through front wall  76 . First channel  84  is adapted to slidably and rotatably receive ball  40 . Beneficially, channel  84  is circular in cross section, although other shapes may be envisioned. In what follows, hereinbelow, channels such as channel  84  may be oval or diamond-shaped, as examples. Means,  86 , are provided for attaching fourth member  70  to the front of the second vertebral body, and is illustrated in  FIG. 1  as a tab disposed perpendicularly to first surface  72 , and having hole  88  therein adapted for permitting the body of a screw to pass therethrough and into the vertebral body. Means,  90 , are provided for rigidly affixing fourth member  70  to third plate  54  after fourth member  70  has been received by the third plate, and are shown in  FIG. 1  as at least one hole  90  adapted for permitting the body of a screw to pass therethrough and into at least one threaded hole,  92 , in plate  54 . 
     Fifth member,  94 , having first flat surface,  96 , second flat surface,  98 , parallel thereto, front wall,  100 , and rear wall,  102 , is adapted to slide into slot  82  in fourth member  70 , first surface  96  having second channel,  104 , therein and opening through rear wall  102  and through second flat face  98 . Second channel  104  is adapted to slidably and rotatably receive ball  40 , while post  34  slidably fits through opening,  106 , in second surface  98 . Beneficially, channel  104  is circular in cross section, although other shapes may be envisioned. In what follows, hereinbelow, channels such as channel  104  may be oval or diamond-shaped, as examples. Means,  108 , shown in  FIG. 1  as flange  108  having at least one hole,  110 , are provided for rigidly affixing fifth member  94  to fourth member  70 , hole  110  being adapted such that the body of a screw may pass therethrough and into at least one matching threaded hole,  112 , in fourth member  70 .  FIG. 1  shows the cross section,  114 , of fifth member  94  as having a dove tail configuration to match slot  82  in fourth member  70 . When fifth member  94  is inserted into fourth member  70 , channel  104  in fifth member  94  and channel  84  in fourth member  70  form opposing, parallel channels wherein ball  40  may rotate and slide a chosen distance therein as determined by the length of opening  106  from the inside surface of wall,  116 , in fourth member  70 . 
     Surface  56  of plate  54  may have at least one longitudinal ridge,  118 , protruding therefrom to assist in stabilizing plate  54  on the endplate of the second vertebral body. Surface  56  may also be roughened such that bone from the endplate may grow thereinto for further stabilization of plate  54  on the endplate. 
     Parallel, rotation limiting stubs,  120   a  and  120   b , affixed to flange  108  of fifth member  94  and perpendicular to surface  98  thereof engage stub,  122 , affixed to tab  42  of second plate  28  and perpendicular to surface  32  thereof, in such a manner that ball  40  is limited in the amount of rotation when capture in cooperating channels  84  and  104 . 
     Components of artificial spinal implant  10 , including screws, may be fabricated from non-ferromagnetic metals including titanium and titanium alloys in order to avoid interference with MRI investigations. Surfaces where metal-to-metal contact occurs, such as ball  40  in channels  84  and  104 , may have metal surfaces coated with suitable polymers as is known in the medical arts, in order to avoid wear debris. The distance between surface  14  of plate  12  and surface  56  of plate  54  may be about 0.5 in. for cervical spinal implants, and about 1 in. for lumbar spinal implants for male adults, with correspondingly smaller implants for women and children. 
     It should be mentioned that other forms of attachment of the various components to one another may be envisioned. For example, the plates may be screwed together rather than requiring cooperating rectangular or dovetailing slots. Spring-loaded latches or spring devices utilizing rods or pins may be employed for attaching the plates, as examples, in place of screws. Further, although the plates and members hereof are illustrated as being rectangular in shape and having generally parallel surfaces, other shapes and orientations of the surfaces may be envisioned. Additionally, implant  10  hereof may also be utilized such that the plate attached to the upper spinal vertebra may be attached to the lower vertebra, and the implant effectively rotated by 180°. 
       FIG. 2  is a schematic representation of a perspective assembled view of the embodiment of the artificial spine implant illustrated in  FIG. 1  hereof, clearly showing space,  124 , between first plate  12  and fourth member  70  resulting from post  36  and ball  40  resting in cooperating channels  84  and  104 . 
       FIG. 3  is a schematic representation of a side view of the embodiment of the artificial spine implant illustrated in  FIG. 1  hereof, illustrating the deployment of artificial spinal disk  10  between upper vertebral body,  126 , and lower vertebral body,  128 . It should be mentioned that artificial spinal disk  10  may also be mounted such that first plate  12  is in contact with lower vertebral body  128  and third plate  54  is in contact with upper vertebral body  126 . 
       FIG. 4  is a schematic representation of the front view of the embodiment of the artificial spine implant illustrated in  FIG. 1  hereof, showing the implant in place and attached to each of two opposing vertebral bodies. Screws,  130   a - 130   c , are shown as fastening plates  12  and  28  to upper vertebral body  126 , while screws,  132   a - 132   c , are shown fastening plate  54  and member  70  to lower vertebral body  128 . Screws,  134   a  and  134   b , fasten plate  28  to plate  12 , screws,  136   a  and  136   b , fasten member  70  to plate  54 , and screws,  138   a  and  138   b , attach member  94  to member  70 . 
       FIG. 5  is a schematic representation of an exploded perspective view of another embodiment of the artificial spinal disk  10  hereof showing a four-piece version thereof, including first flat plate  12  effective for attachment to a first vertebral body; a second plate  28  to which post  34  having ball  40  mounted thereon is attached, wherein plate  28  is reversibly attached to plate  12 , as described above; and two members,  140  and  142 , which are similar to members  70  and  94 , respectively, in  FIG. 1  hereof, forming an enclosed channel for slidably and rotatably restraining ball  40 , in a manner similar to that described above for members  70  and  94 , member,  140 , being attached to a second vertebral body opposing the first vertebral body. 
       FIG. 6  is a schematic representation of an exploded perspective view of a second, four-piece embodiment of the artificial spinal disk  10  hereof, including first flat plate,  144 , effective for attachment to a first vertebral body, and to which post  34  having ball  40  mounted thereon is attached in a similar manner to plates  12  and  28  in  FIG. 1  hereof when combined as described hereinabove; and two members  70  and  94  when combined forming an enclosed channel for slidably and rotatably restraining ball  40  and post  34 , members  70  and  94  being reversibly attached to second plate  54  effective for attachment to a second vertebral body opposing the first vertebral body, as also described hereinabove. Ball  40  may be reversibly attached to post  34  using threaded member,  146 , which is adapted to be screwed into a threaded hole in ball  40  (not shown in  FIG. 6 ). 
       FIG. 7  is a schematic representation of an exploded perspective view of a three-piece embodiment of the artificial spinal disk  10  hereof including first flat plate  144  effective for attachment to a first vertebral body and to which post  34  having ball  40  mounted thereon is attached in a similar manner to plates  12  and  28  in  FIG. 1  hereof when combined as described hereinabove; and two members,  140  and  142 , which are similar to members  70  and  94 , respectively, in  FIG. 1  hereof, forming an enclosed channel for slidably and rotatably restraining ball  40  and post  34 , in a manner similar to that described above for members  70  and  94 , member,  140 , being attached to a second vertebral body opposing the first vertebral body. As stated above, ball  40  may be reversibly attached to post  34  using threaded member,  146 , which is adapted to be screwed into a threaded hole in ball  40  (not shown in  FIG. 7 ). 
     The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.