Abstract:
A sternum closure device for securing parts of severed sternum, such as a human sternum following surgery. The device includes an anvil, capable of forming staples, a bracket positioned opposite the anvil, an instrument for creating openings in the sternum and a mechanism for feeding, mounting and applying the staples. The bracket is joined with the anvil through a displacement mechanism. The instrument for forming opening is designed as a bit brace having a reducing gear and two chucks, to enable concurrent drilling of openings in both severed parts of the severed sternum. The mechanism for feeding and mounting the staples comprises a ribbed bed, a cartridge containing staples and an instrument for mounting the staples.

Description:
FIELD OF THE INVENTION 
     The present invention relates to medical devices for closure of a severed sternum. In particular, the invention is directed to a sternum closure assemblies and methods for re-approximating split portions of tissue to retain the split portions in adjacent contacting relation to promote healing thereof. 
     BACKGROUND OF THE INVENTION 
     During surgery that involves a median sternotomy, for example, open-heart surgery, the sternum is cut longitudinally to allow access to the organs within the thoracic cavity. A partial or median sternotomy is a procedure by which a saw or other comparable cutting instrument is used to make a midline, longitudinal incision along a portion or the entire axial length of the patient&#39;s sternum, allowing two opposing sternal valves to be separated laterally. Upon completion of the surgery, the sternum is rejoined and closed securely. 
     Traditionally, the sternal halves have been closed with stainless steel wires which are wrapped around or through the sternal halves to engage in face-to-face relationship and compressed together while the sternum heals. For example, in one version, a surgical needle with the metal wire is led via both severed parts of a severed sternum and the free metal wire is cut-off. In another version, the wire tips are further led via openings in special staples, to project outside and the tips are twisted together by tightening the suture, U.S. Pat. No. 4,512,346 and U.S. Pat. No. 5,849,012. However, these devices have certain shortcomings, in that they require significant force, are difficult to maneuver and the sharp wire edges sometimes cause injury and eventually, infection to soft tissues. 
     Other prior art sternum closure assemblies include one or two metal plates, these plates being provided with rows of openings, through which extend the screws, pins, or metal wire, to bring together the severed parts of the sternum. U.S. Pat. No. 4,585,341. These devices have drawbacks in that they are ineffective in fixing the split parts of the severed sternum. Moreover, they are foreign bodies in the thoracic cavity, and they can cause disturbance in blood supply to the osseous tissue, thereby prolonging healing and increasing chances of infection. 
     The strap assemblies known heretofore incorporate clamps, clasps, bands, strips with or without openings and complex locking mechanisms. U.S. Pat. No. 5,356,417; U.S. Pat. No. 5,462,542; and U.S. Pat. No. 6,007,538. The use of compression prevents problems for blood circulation and soft tissues. Other versions of sternum closure devices use tongs, plugs or guns with anvils, to apply staples through the osseous tissue of the sternum. U.S. Pat. No. 4,122,989; and U.S. Pat. No. 4,481,960. However, these devices suffer from several drawbacks, for example, significant force is required to puncture the osseous tissue and insert a staple. In addition, these prior art devices are imprecise in positioning the staples, and do not permit the anvil to bend the staple through 180° angle. Finally, the devices are cumbersome and cause shaking of the organs in the thoraxic cavity. 
     A certain amount of emphasis has also been directed towards the use of appropriate staples which minimize healing time, minimize distortion of the material stapled, minimize damage of material stapled, minimize scar tissue formation and achieve uniform compression of stapled material. U.S. Pat. No. 5,342,396 and U.S. Pat. No. 5,667,527. However, these devices suffer from several of the same drawbacks discussed above for earlier models of the sternum closure devices and systems. 
     It would accordingly be desirable to provide a sternum closure device which is stable in construction and effectively secures the severed parts of sternum or other tissue together, i.e., secures the staples in well defined locations, at a predetermined angle, and at a desirable tension to promote uniform healing of the tissue portions while avoiding complications associated with tissue injury, infection and compression. 
     SUMMARY OF THE INVENTION 
     The present invention provides improved devices and methods of joining with staples, the opposite parts of a severed sternum following a median or partial sternotomy that overcomes the above cited problems inherent in previous sternum closure devices. Generally, the present invention is embodied in an anvil for forming the staples, a bracket positioned opposite the anvil, a means for making openings in the tissue, and a mechanisms for feeding and mounting the staples. 
     According to a first aspect of the invention, a sternum closure device comprises an anvil having an element comprising two slots, said element being used for forming or shaping the staples. A bracket is provided with an additional slot to guide the drilling means and to mount the staples in the sternum. Other improvements to the anvil and bracket include forming elements which facilitate their mounting on the sternum parts. The bracket is provided with a post and a lock, the post having two mutually perpendicular openings and a pin mounted on it, and the lock comprising a housing with a slot, and a spring-actuated locking element with a handle situated in the slot. 
     According to a second aspect of the invention, the bracket is joined with the anvil through a spring-actuated screw having a handle, said screw being positioned in a threaded opening located in the bracket. Two guides are situated between the anvil and the bracket and parallel to the screw, said guides being installed in the openings of the bracket to facilitate displacement of the bracket with respect to the anvil. 
     The sternum closure device of the present invention comprises a bit brace with a reducing gear and two chucks having interchangeable drills for simultaneously drilling openings in both parts of a severed sternum. The reducing gear includes a housing, said housing including a basis with a lug, and a cover. The lug is provided with an opening and a slot. A driving gear wheel is installed on a driving shaft, said driving shaft being joined with a pneumatic drive. Two driven gear wheels are in engagement with the drive wheel gear. The driving wheel is fastened on the driving shafts, and chucks with interchangeable drills are installed on these driven shafts. 
     According to another aspect of the invention, the sternum closure device comprises a mechanism for feeding and mounting the staples, including a carrying element constructed of a bed, said bed having a first and second surface. Two ribs provided with a positive stopper are situated perpendicularly to the bed surface. The bed surface and each rib are provided with slots. The first bed surface is also provided with a lug having a threaded opening and a locking screw. The second and opposite bed surface is designed as a wall having a handle. A sub-assembly used for mounting the staples, is installed on the bed surface, said sub-assembly comprising an L-shaped lever and two spring-actuated posts. Said L-shaped lever has a shaft side and a long side. The two spring-actuated posts are locked on the bed surface and passed through the openings in the shaft side of the L-shape lever. The long side of the L-shaped lever is placed in the slot of the bed surface. 
     A cartridge is placed between the bed ribs, said ribs having an internal sand an external side. The cartridge comprises slots for the staples and a sprelement situated between the cartridge and the face wall of the bed. The spring-wise element presses the cartridge with staples against a plurality of stoppers installed on the internal side of the bed ribs. 
     According to a preferred embodiment of the invention, an instrument for drilling openings is installed on the bracket post along with precise and well-controlled mechanism or means for feeding and mounting staples. A compression spring is situated between the instrument for drilling openings and the mechanism or means for feeding and mounting staples. The instrument for drilling opening may be displaced from the bracket post when necessary. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present invention and the attendant advantages and features thereof will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a side view of a sternum closure device positioned in the state of drilling openings in the sternum. 
     FIG. 2 is a top view of the sternum closure device, taken in the plane of arrow A of FIG.  1 . 
     FIG. 3 is a side view of the sternum closure device when it is in the state of mounting staples. 
     FIG. 4 is a top view of the sternum closure device, taken in the plane of arrow E of FIG. 3 
     FIG. 5 is a front view of the sternum closure device, taken in the plane of arrow B of FIG.  1 . 
     FIG. 6 is a front view of the sternum closure device, taken in the plane of arrow F of FIG.  3 . 
     FIG. 7 is a sectional view of the sternum closure device, which is shown in FIG. 2, in the plane of line C—C; this device is in the state preceding drilling the openings in the sternum. 
     FIG. 7 a  is a sectional view of the sternum closure device, which is shown in FIG. 2, in the plane of line C—C; this device is in the process of drilling the openings in the sternum. 
     FIG. 8 is a sectional view of the sternum closure device, which is shown in FIG. 4 in the plane of line G—G; this device is in the state preceding mounting the staples in the sternum. 
     FIG. 8 a  is a sectional view of the sternum closure device, which is shown in FIG. 4, in the plane of line G—G; this device is in the process of mounting the staples. 
     FIG. 9 is a sectional view in the plane of line D—D of a displacement mechanism, which is shown in FIG.  1 . 
     FIG. 10 is a view following detail  1 , which is shown in FIG.  7 . 
     FIG. 11 is a sectional view of the sternum closure device, which is shown in FIG. 7 a , in the plane of line H—H. 
     FIG. 12 is a sectional view of the sternum closure device, which is shown in FIG. 8 a , in the plane of line K—K. 
     FIG. 13 demonstrates the closed sternum with the set of mounted staples. 
     FIG. 14 demonstrates a second embodiment of the invention having a sliding head instead of a rotating head. 
     FIG. 15 demonstrates the sliding head of the second embodiment which is used both for drilling and stapling. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 to  15 , a sternum closure device  1  is shown to provide a system and method for joining two parts  2  and  3 , of a severed sternum  4 , by means of staples  5 , having legs  6  and  7 , which are inserted through openings  8  and  9  of the severed sternum  4 . 
     A preferred embodiment of the sternum closure device includes an anvil for forming the staples. This anvil is positioned on the internal side of the severed sternum. A bracket is situated on the outer side of the severed sternum, opposite the anvil. The anvil comprises an element for forming the staples. It is designed to have two slots. In addition, the bracket has a third slot which is intended to guide the drills and for mounting the staples on the sternum. The unique feature about the present invention is that the anvil and the bracket are designed with bends such that these bends facilitate their proper mounting on the sternum. 
     The bracket is also provided with a rotatable post and a lock. The post is provided with two mutually perpendicular openings and a pin. The lock comprises of a housing with a slot. A spring-actuated locking element having a handle is situated in the slot in the lock housing. 
     Referring to FIGS. 1, the sternum closure device  1  comprises of an anvil  10  and a bracket  20 , said anvil and said bracket being joined together by a displacement mechanism or means  40 . The sternum closure device  1  further comprises of an instrument  60  which is provided to form openings in the sternum  4 , and a staple feeding mechanism  100 , which is used for feeding and mounting the staples. 
     Referring to FIGS. 1 and 9, anvil  10  is provided with two slots  11  and  12  for the purpose of forming staples  5 , a bend  13  and a through opening  14  used for joining the displacement mechanism  40 . The bracket  20  comprises of a through slot  21 , a bend  22  and a threaded opening  23 , said opening  23  serving to join the displacement mechanism  40 . The bracket  20  further comprises of two through openings  24  and  25 , and a cylindrical post  26 . The cylindrical post  26  is installed on bracket  20  to provide a turning means, the cylindrical post  26  being further provided with two openings  27  and  28  with mutually perpendicular axes, and a pin  29 . A lock  31  is installed traversally to cylindrical post  26  and the lock  31  is fastened on bracket  20 . 
     The bracket is joined to the anvil through a displacement mechanism. This mechanism provides reciprocating displacement of the bracket with respect to the anvil. The displacement mechanism comprises of a spring-actuated screw with a handle. This screw is positioned in the threaded opening in the bracket where it is joined to the anvil. Two guides are situated between the anvil and the bracket. These guides are parallel to the screw and are locked in anvil. The guides are installed in the through openings of the bracket to enable its displacement in the direction of the guides. 
     Referring to FIGS. 1 and 9, the anvil  10  and bracket  20  are joined via the displacement mechanism  40  to enable reciprocating displacement of bracket  20  to and from the anvil  10 . The displacement mechanism  40  comprises of screw  41 , said screw  41  extending into a handle  42 , a compression spring  43  and two guides  44  and  45 . The screw  41  is fastened through a threaded opening  23  in bracket  20 , and is locked rotatably in the through opening  14  of anvil  10 . A spring  43  is installed between the anvil  10  and the bracket  20 , coaxially to the screw  41 . Guides  44  and  45  are locked onto the anvil  10  and are in a parallel position to screw  41 . Guides  44  and  45  are installed in such a way through openings  24  and  25  of bracket  20  to enable displacement of bracket  20  along guides  44  and  45 . 
     Referring to FIG. 10, lock  31  comprises of housing  32 , a locking element  33 , a spring  34  and a handle  35 . The locking element  33  and the spring  34  are introduced partially into housing  32 , and the locking element  33  is prevented from dropping out by the handle  35 , said handle  35  being installed in a slot  36  located in the housing  32 . 
     In a preferred embodiment of the sternum closure device, the instrument for formation of openings in the sternum comprises one of following mechanisms of the group: a menual bit brace, a pneumatic bit brace, a laser perforator or an ultrasound perforator. The bit brace comprises of a reducing gear and two chucks. These chucks have interchangeable drills for simultaneously drilling openings in both parts of the severed sternum, which are to be joined. 
     The reducing gear consists of a housing. The housing includes a basis with a lug and a cover. The lug is provided with a through opening and a slot. A driving gear wheel installed on a driving shaft. A driven gear wheels installed on a driven shafts. The driving shaft is then joined to a pneumatic drive. Chucks with interchangeable drills are nstalled on the driven shafts. 
     Referring to FIGS. 1,  2 ,  5 ,  7  and  7   a , an instrument  60  is provided for formation of openings. The instrument  60  is constructed as a bit brace  61  with a pneumatic drive  62  and two chucks  63  and  64 . The two chucks are provided for mounting interchangeable drills  65  and  66 . The instrument  60  further comprises a reducing gear  71 . Reducing gear  71  is installed over housing  72 , said housing  72  comprising of a basis  73  and a cover  74 . Basis  73  is provided with lug  75 , said lug  75  having an openi 76  and a slot  77 . A driving gear wheel  78  is arranged the space of housing  72 , and installed on a driving shaft  79 . The driving shaft  79  is mounted on basis  73  of housing  72  by means of bearings  80  and  81 . Two driven gear wheels  82  and  83 , engaged with the driving gear wheel  78 , are installed on a driven shafts  84  and  85 . The driven shafts  84  and  85  are mounted on basis  73  of housing  72  by means of bearings  86 ,  87 ,  88  and  89 . The driving shaft  79  is further joined with the pneumatic drive  62 , said drive  62  being designed as a pneumatic motor. Chucks  63  and  64  are installed on driven shafts  84  and  85  and these chucks are used for mounting the interchangeable drills  65  and  66 . 
     Instrument  60  and pin  29  are installed on cylindrical post  26  to enable displacement along the cylindrical post  26 . The pin  29  is locked on cylindrical post  26  via slot  77  of lug  75  of reducing gear  71 . Thus, pin  29  limits the magnitude of displacement of instrument  60  and prevents its turning around post  26 . 
     A mechanism of feeding and mounting the staples is constructed as a bed with two ribs situated perpendicularly to the bed surface. The ribs are provided with a positive stopper. The bed surface and each rib are provided with through slots. One bed surface is provided with a lug, the lug having a threaded through opening and a locking screw in it. The other bed surface is designed as a wall with a handle. 
     Referring to FIGS. 3,  4 ,  6 ,  8 ,  8   a  and  12 , a feeding and staple mounting mechanism  100  comprises of a carrying element constructed as bed  101  having two ribs  102  and  103 . These ribs  102  and  103  are perpendicular to bed  101  and each rib is provided with through longitudinal slots  104  and  105 . Stoppers  106  and  107  are installed on the internal side of each rib  102  and  103 , respectively. Bed  101  is provided with two lugs  108  and  109 , said lugs  108  and  109  in turn are provided with through openings  110  and  111  respectively. Bed  101  is further provided with through slot  112 , said slot  112  being placed in parallel to sides  113  and  114  of bed  101 . Side  113  is provided with lug  115 , which in turn has an opening  116  and a locking screw  117  fastened to the opening  116 . Wall  118 , having an internal side and an external side, is situated in perpendicular to bed  101  on side  114 . Handle  119  is locked to wall  118 . A cylindrical support  120  is further installed on the internal side of wall  118 . 
     Mechanism or means  100  further comprises of a cartridge  131  which is positioned between ribs  102  and  103  of bed  101 , and a spring  132 . Cartridge  131  is designed as a through parallel having slots  133  used for positioning the staples  5 . A bracket  135  having an opening  136  is positioned on face side  134  of cartridge  131 . Cartridge  131  is installed between ribs  102  and  103  and is held inside the bed  101  by two pins  137  and  138 . These two pins  137  and  138  are positioned in slots  104  and  105  of ribs  102  and  103  respectively. Spring  132  is arranged in a cylindrical support  120  of wall  118 . It is further inserted partially in opening  136  of bracket  135 . 
     Mechanism or means  100  further comprises subassembly  141 , used for mounting the staples. The subassembly  141  comprises a pressure L-shaped lever  142 , two posts  143  and  144 , and two springs  145  and  146 . The L-shaped lever  142  has a short side  147 , the short side  147  having two openings  148  and  149 . Posts  143  and  144  pass through openings  148  and  149  respectively. Springs  145  and  146  are installed singly on posts  143  and  144  respectively. The subassembly  141  is installed on bed  101 . The L-shaped lever  142  has a long side  150 , which is introduced in slot  112 . Posts  143  and  144  and springs  145  and  146  are locked through openings  110  and  111  of lugs  108  and  109 , respectively. 
     Mechanism or means  100  is mounted on post  26  perpendicularly to instrument  60  and locked in place by a screw  117 . In addition, spring  161  is installed on post  26  between mechanism  100  and instrument  60 . 
     FIG.  14  and FIG. 15 represent a second prototype of the invention in which instead of having a rotatable head for alternating the two functions of the device—i.e., drilling and stapling, the two functions are carried out by a sliding head  201  which is located at one end of a stream lined instrument  200 . The net effect of this is quicker and simpler alteration of functions and easier handling of the instrument. The cramping of the staples is performed by compressing the ends of the arms of instrument  200  which is easier to do than the rotatable action required in the first embodiment describer earlier. 
     OPERATION OF THE STERNUM CLOSURE DEVICE 
     The mode of operation of the sternum closure device is described herein below. 
     The bracket  20  is moved progressively in direction away from anvil  10  by the displacement mechanism  40  (see FIG.  9 ). The screw  41  is rotated by handle  42 , for example, in an anti-clockwise direction. Bracket  20  moves progressively along guides  44  and  45  in direction away from anvil  10  with releasing spring  43 . This results in greater distance between anvil  10  and bracket  20 . Anvil  10  and bracket  20  are positioned correspondingly from the internal and external sides of parts  2  and  3  of the severed sternum  4 . 
     Bend  13  of anvil  10  and bend  22  of bracket  20  facilitate mounting anvil  10  and bracket  20  on sternum  4 . 
     With rotation of screw  41  by handle  42  in the opposite direction (in this case—in the clock-wise direction), bracket  20  moves progressively along guides  44  and  45  towards anvil  10 . This motion is accompanied with compression of spring  43  and decrease of the distance between anvil  10  and bracket  20  to contact with the internal and external parts  2  and  3  respectively, of the severed sternum  4 . 
     The sternum closure device  1  is arranged in the position of drilling openings in parts  2  and  3  of the severed sternum  4  (FIGS. 1,  2 ,  5 ,  7 ) by lock  31  (FIG.  10 ). 
     In the initial state spring  34  of lock  31  is released and the locking element  33  is placed in one of two mutually perpendicular through openings  27  or  28  of post  26  of bracket  20 . As displacement handle  35  moves along slot  36 , the locking element  33  is removed from the corresponding openings  27  or  28  of post  26  by compression of spring  34 . Then post  26  is released from locking and it turns in bracket  20  until the axis of the through opening  27  is aligned with the axis of the locking element  33  of lock  31 . While descending handle  35 , the compressed spring  34  pushes out the locking element  33  from housing  32 . The locking element is introduced in such a way into the through opening  27  of the post  26 , that it fixes in a position of the drilling openings. 
     Drilling openings  8  and  9  are performed in parts  2  and  3  of the severed sternum  4  (FIGS. 7,  7   a ) by instrument  60  intended for drilling openings. This instrument is installed on post  26  of bracket  20  to allow its reciprocating motion along post  26 . Then the pneumatic motor  62  is switched on. The motor via the driving gear wheel  78  and two driven gear wheels  82  and  83  of reducing gear  71  causes two chucks  63  and  64  to rotate with drills  65  and  66  respectively (FIG.  7 ). By pushing in direction of arrow PUSH onto cover  74  of reducing gear  71  of instrument  60 , the bit brace  61  is displaced along post  26  of bracket  20  toward anvil  10 . This displacement is accompanied by compression of spring  161  and drills  65  and  66 , which pass via slot  21  of bracket  20 . Openings  8  and  9  are drilled simultaneously correspond to two parts  2  and  3  of the severed sternum  4  (FIGS. 7 a ,  11 ). The magnitude of displacement of instrument  60  along post  26  is limited by the length of slot  77  and the limiting pin  29  (FIGS. 7,  7   a ). With completion of drilling opening  8  and  9  (FIG.  11 ), compression on instrument  60  is stopped. It returns to its initial position by release of spring  161  (FIG.  7 ). 
     Then the sternum closure device  1  is transferred in the state of mounting staples  5  in sternum  4  (FIGS. 3,  4 ,  6 ,  8 ) by lock  31  (FIG.  10 ). With displacement of handle  35  of lock  31  along slot  36 , the locking element  36  is removed from the through opening  27  of post  26 , and compresses spring  34 . Then post  26  is released and it is turned in bracket  20  until the axis of the through opening  28  is aligned with the axis of the locking element  33  of lock  31 . With descending handle  35  the compressed spring  34  pushes out the locking element  33  from housing  32 . Then this locking element is introduced into the through opening  28  of post  36  fixings in such a way that it facilitates mounting of the staples. 
     Mounting staples  5  in the through openings  8  and  9  in respective parts  2  and  3  of the severed sternum  4  (FIGS. 8,  8   a ) is performed by mechanism  100  of feeding and mounting staples. This is accomplished by locking mechanism  100  on post  26  of bracket  20 . Cartridge  131  is filled by staples  5  through slots  133 . When mounting the staples  5 , the lomechaniis set above the through slot  21  of bracket  20 . Staples  5  are forced from cartridge  131  onto stoppers  106  and  107  by spring  132  (FIG.  8 ). While pushing in direction of arrow PUSH on the short side  147  of the L-shaped lever  142 , the lever  142  is displaced along two posts  143  and  144  towards anvil  10 . This is accompanied by compression of springs  145  and  146 . The long side  150  of the L-shaped lever  142  passes via the through slot  112  and presses out the first staple  5  from the through slot  133  of cartridge  131 . This staple is introduced via the through slot  21  of bracket  20  by its two legs  6  and  7  corresponding to openings  8  and  9  in parts  2  and  3  respectively, of the severed sternum  4 . With further pushing on the short side  147  of the L-shaped lever  142 , legs  6  and  7  of staple  5  pass via openings  8  and  9 . The form of legs  6  and  7  is changed with bending owing to slots  11  and  12  of anvil  10 , while pulling together parts  2  and  3  of the severed sternum  4  (FIGS. 8 a ,  12 ). 
     The angle in which the two legs of the staple bend is circular and effectively secures the two severed parts of the sternum in a stable grip. The present invention is directed to a sternum closure device which securably retains a plurality of staples around sternum parts to maintain the parts in adjacent engaged relation during healing. The present invention minimizes damage of a tissue stapled and prevents formation of scar tissue. 
     After mounting of staple  5  is completed (FIG. 5) the compression on lever  142  is terminated. It returns to its initial position owing to release of springs  145  and  146  (FIG.  8 ). After egress of the long side  150  of L-shaped lever  142  from the through slot  133  of cartridge  131 , spring  132  is released. The cartridge  131  is displaced through one further step until the next staple  5  is arranged in through slot  133 , with stoppers  106  and  107  (FIGS. 8,  12 ). In order to mount next staples  5 , bracket  20  is displaced progressively away from anvil  10  by the displacement mechanism  40  (FIG.  9 ). Rotation of screw  41  by handle  42  in an anti-clock wise direction allows displacement of bracket  20  progressively along guides  44  and  45  toward anvil  10 . This releases spring  43  and enlarges the distance between anvil  10  and bracket  20 . 
     Then the sternum closure device  1  is made ready for mounting the next staple  5 . This process of mounting displacing and compressing staple  5  is repeated as necessary. 
     When mounting of all required staples  5  is completed (the closed sternum  4  with all mounted staples is shown in FIG.  13 ), the sternum closure device  1  is removed. 
     The present invention provides a relatively simple and less traumatic means to effect sternum closure which can be performed rapidly and effectively by the surgeon. While the above description contains many specifics, these specifics should not be construed as limitations on the scope of the invention, but merely as exemplification of preferred embodiments thereof. Those skilled in the art will envision many other possible variations that are within the scope and spirit of the invention as defined by the claims appended hereto.