Abstract:
Apparatus for compression, comprising: a compression plate comprising first and second opposing regions connected together by an elastic bridge member, wherein the elastic bridge member has a non-linear configuration in its unbiased condition but is capable of being elastically deformed to a more linear configuration upon application of force to the elastic bridge member, and an opening formed in each of the first and second opposing regions, wherein the opening in each of the first and second opposing regions is configured to receive a fastener; such that the openings in the first and second opposing regions are separated by a first distance when the elastic bridge member is in its non-linear configuration, and openings in the first and second opposing regions are separated by a second distance when the elastic bridge member is in its more linear configuration, and wherein the second distance is greater than the first distance.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATION 
       [0001]    This patent application claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/952,524, filed Mar. 13, 2014 by MX Orthopedics, Corp. and Matthew Fonte et al. for SHAPE MEMORY COMPRESSION PLATE—ENHANCED COMPRESSION AT FRACTURE SITE (Attorney&#39;s Docket No. FONTE-38 PROV), which patent application is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to plates for generating, applying, and maintaining compression to a site in a human or animal body in order to facilitate healing of diseased or damaged tissue. The invention finds particular utility in the field of orthopedics and specifically for reducing fractures and maintaining compression between bone fragments. While the invention has application throughout the body, its utility will be illustrated herein in the context of the repair of fractured or displaced bone tissue, such as during a Calcaneal-Cuboid Arthrodesis, Metatarsal Shortening and/or Distal Radius Fixation. The present invention also finds utility as a cervical compression plate, and/or as other spinal compression plates. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the field of orthopedic surgery it is common to rejoin broken bones. The success of the surgical procedure often depends on the ability to reapproximate the bone fragments, the amount of compression achieved between the bone fragments, and the ability to sustain that compression over a period of time. If the surgeon is unable to bring the bone fragments into close contact, a gap will exist between the bone fragments and the bone tissue will need to fill that gap before complete healing can take place. Furthermore, gaps between bone fragments that are too large allow motion to occur between the bone fragments, disrupting the healing tissue and thus slowing the healing process. Optimal healing requires that the bone fragments be in close contact with each other, and for a compressive load to be applied and maintained between the bone fragments. Compressive strain between bone fragments has been found to accelerate the healing process in accordance with Wolf&#39;s Law. 
         [0004]    Broken bones can be rejoined using plates. These plates are generally formed from a sheet or ribbon of material with a plurality of holes formed therein. The plates are typically manufactured from either stainless steel alloys or titanium alloys. The plates are placed adjacent to a fracture so that the plate spans the fracture line, and then screws are inserted through the holes in the plate and into the bone fragments on either side of the fracture site so as to stabilize the bone fragments relative to one another. 
         [0005]    While these plates are designed to stabilize a fracture, they do not always succeed in generating a compressive load between the bone fragments. It is widely reported that the compressive load of plates dissipates rapidly as the bone relaxes and remodels around the screws which hold the plate to the bone. 
         [0006]    Thus there exists a clinical need for new and improved compression plates which are able to bring bone fragments into close proximity with each other, generate a compressive load, and maintain that compressive load for a prolonged period of time while healing occurs. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a novel compression plate which is able to bring bone fragments into close proximity with each other, generate a compressive load, and maintain that compressive load for a prolonged period of time while healing occurs. 
         [0008]    Among other things, the present invention comprises the provision and use of a novel compression plate which is manufactured from a single piece of shape memory material (e.g., a material capable of exhibiting superelasticity and/or a temperature-induced shape change). The shape memory material may be a metal alloy (e.g., Nitinol) or a polymer (e.g., appropriately processed PEEK). The novel compression plate is designed to reduce fractures and generate and maintain more uniform compression between the cortical bone and cancellous bone of the bone fragments so as to aid in fracture healing. 
         [0009]    In one form of the invention, the novel compression plate comprises two opposing regions joined together by a pair of elastic bridge members, and an opening in each of the two opposing regions for receiving screws. In the un-restrained state, the two elastic bridge members are bowed outwardly. Prior to implantation, the two elastic bridge members can be reversibly strained inwardly so that the two elastic bridge members are nearly parallel (i.e., the two elastic bridge members are stretched laterally inwardly). A delivery device may be used to accomplish this straining of the compression plate and to hold the compression plate in this strained state prior to implantation. Upon implantation, the constraint on the two elastic bridge members is removed, whereupon the two elastic bridge members attempt to return to their original unrestrained state, thereby generating a compressive load and maintaining that compressive load for a prolonged period of time while healing occurs. 
         [0010]    In one preferred form of the invention, there is provided apparatus for providing compression within a body, said apparatus comprising: 
         [0011]    a compression plate comprising first and second opposing regions connected together by at least one elastic bridge member, wherein said at least one elastic bridge member has a non-linear configuration when it is in its unbiased condition but is capable of being elastically deformed to a more linear configuration upon the application of force to said at least one elastic bridge member, and at least one opening formed in each of said first and second opposing regions, wherein said at least one opening in each of said first and second opposing regions is configured to receive a fastener; 
         [0012]    such that said openings in said first and second opposing regions are separated by a first distance when said at least one elastic bridge member is in its said non-linear configuration, and said openings in said first and second opposing regions are separated by a second distance when said at least one elastic bridge member is in its said more linear configuration, and further wherein said second distance is greater than said first distance. 
         [0013]    In another preferred form of the invention, there is provided a compression plate for providing compression to first and second bone fragments across a fracture line, said compression plate comprising: 
         [0014]    first and second opposing regions connected together by at least one elastic bridge member, wherein said at least one elastic bridge member has a non-linear configuration when it is in its unbiased condition but is capable of being elastically deformed to a more linear configuration upon the application of force to said at least one elastic bridge member; and 
         [0015]    at least one opening formed in each of said first and second opposing regions, wherein said at least one opening in each of said first and second opposing regions is configured to receive a fastener; 
         [0016]    such that when said at least one elastic bridge member is elastically strained into its said more linear configuration, and said compression plate is positioned against bone so that one of said openings is positioned over the first bone fragment and one of said openings is positioned over the second bone fragment, with said at least one elastic bridge member spanning the fracture line, and when a fastener is passed through one opening and into the first bone fragment and another fastener is passed through the other opening and into the second bone fragment, and the strain on said at least one elastic bridge member is thereafter released, said compression plate will apply a compressive force across the fracture line. 
         [0017]    In another preferred form of the invention, there is provided a method for applying compression to first and second bone fragments across a fracture line, said method comprising: 
         [0018]    providing apparatus for providing compression within a body, said apparatus comprising:
       a compression plate comprising first and second opposing regions connected together by at least one elastic bridge member, wherein said at least one elastic bridge member has a non-linear configuration when it is in its unbiased condition but is capable of being elastically deformed to a more linear configuration upon the application of force to said at least one elastic bridge member, and at least one opening formed in each of said first and second opposing regions, wherein said at least one opening in each of said first and second opposing regions is configured to receive a fastener;   such that said openings in said first and second opposing regions are separated by a first distance when said at least one elastic bridge member is in its said non-linear configuration, and said openings in said first and second opposing regions are separated by a second distance when said at least one elastic bridge member is in its said more linear configuration, and further wherein said second distance is greater than said first distance;       
 
         [0021]    elastically straining said at least one elastic bridge member into its said more linear configuration, and positioning said compression plate against the first and second bone fragments so that one of said openings is positioned over the first bone fragment and one of said openings is positioned over the second bone fragment, with said at least one elastic bridge member spanning the fracture line, and passing a fastener through one opening and into the first bone fragment and passing another fastener through the other opening and into the second bone fragment; and 
         [0022]    releasing the strain on said at least one elastic bridge member so that said compression plate will apply a compressive force across the fracture line. 
         [0023]    In another preferred form of the invention, there is provided a compression plate comprising: 
         [0024]    first and second opposing regions connected together by at least one bridge member; and 
         [0025]    at least one opening formed in each of said first and second opposing regions, wherein said at least one opening in each of said first and second opposing regions is configured to receive a fastener; 
         [0026]    wherein said at least one bridge member is formed out of austenite but capable of forming stress-induced martensite; 
         [0027]    and further wherein at least one of said opposing regions is formed out of fully annealed Nitinol or martensitic Nitinol with an austenite start temperature greater than body temperature. 
         [0028]    In another preferred form of the invention, there is provided apparatus for providing distraction within a body, said apparatus comprising: 
         [0029]    a distraction plate comprising first and second opposing regions connected together by at least one elastic bridge member, wherein said at least one elastic bridge member has a more linear configuration when it is in its unbiased condition but is capable of being elastically deformed to a less linear configuration upon the application of force to said at least one elastic bridge member, and at least one opening formed in each of said first and second opposing regions, wherein said at least one opening in each of said first and second opposing regions is configured to receive a fastener; 
         [0030]    such that said openings in said first and second opposing regions are separated by a first distance when said at least one elastic bridge member is in its said more linear configuration, and said openings in said first and second opposing regions are separated by a second distance when said at least one elastic bridge member is in its said less linear configuration, and further wherein said first distance is greater than said second distance. 
         [0031]    In another preferred form of the invention, there is provided a method for applying distraction to first and second bone segments, said method comprising: 
         [0032]    providing apparatus for providing distraction to first and second bone segments, said apparatus comprising:
       a distraction plate comprising first and second opposing regions connected together by at least one elastic bridge member, wherein said at least one elastic bridge member has a more linear configuration when it is in its unbiased condition but is capable of being elastically deformed to a less linear configuration upon the application of force to said at least one elastic bridge member, and at least one opening formed in each of said first and second opposing regions, wherein said at least one opening in each of said first and second opposing regions is configured to receive a fastener;   such that said openings in said first and second opposing regions are separated by a first distance when said at least one elastic bridge member is in its said more linear configuration, and said openings in said first and second opposing regions are separated by a second distance when said at least one elastic bridge member is in its said less linear configuration, and further wherein said first distance is greater than said second distance;       
 
         [0035]    elastically straining said at least one elastic bridge member into its said less linear configuration, and positioning said distraction plate against the first and second bone segments so that one of said openings is positioned over the first bone segment and one of said openings is positioned over the second bone segment, and passing a fastener through one opening and into the first bone segment and passing another fastener through the other opening and into the second bone segment; and 
         [0036]    releasing the strain on said at least one elastic bridge member so that said distraction plate will apply a distraction force to the first and second bone segments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]    These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
           [0038]      FIG. 1  is a schematic view of a novel compression plate formed in accordance with the present invention, wherein the compression plate comprises a pair of bridge members which are capable of being elastically strained, two openings for receiving screws, and further wherein the compression plate is shown in its unstrained condition; 
           [0039]      FIG. 2  is a schematic view of the novel compression plate shown in  FIG. 1 , wherein the pair of elastic bridge members of the compression plate have been elastically strained to a near-parallel condition; 
           [0040]      FIG. 3  is a schematic view showing how the elastically strained compression plate of  FIG. 2  will foreshorten when the strain on the compression plate is removed; 
           [0041]      FIG. 4  is a schematic view of another novel compression plate formed in accordance with the present invention, wherein the compression plate comprises a pair of bridge members which are capable of being elastically strained, wherein each of the opposing regions of the compression plate comprises two openings for receiving screws, and further wherein the compression plate is shown in its unstrained condition; 
           [0042]      FIG. 5  is a schematic view of the novel compression plate shown in  FIG. 4 , wherein the two elastic bridge members of the compression plate have been elastically strained to a near-parallel condition; 
           [0043]      FIG. 6  is a schematic view showing how the elastically strained compression plate of  FIG. 5  will foreshorten when the strain on the compression plate is removed; 
           [0044]      FIG. 7  is a schematic view of another novel compression plate formed in accordance with the present invention, wherein the compression plate comprises a single “S-shaped” bridge member which is capable of being elastically strained, two openings for receiving screws, and further wherein the compression plate is shown in its unstrained (i.e., unstretched) condition; 
           [0045]      FIG. 8  is a schematic view of the novel compression plate shown in  FIG. 7 , wherein the single “S-shaped” elastic bridge member of the compression plate has been elastically strained (i.e., longitudinally stretched); 
           [0046]      FIG. 9  is a schematic view showing how the elastically strained compression plate of  FIG. 7  will foreshorten when the strain on the compression plate is removed; 
           [0047]      FIGS. 10A-10F  are schematic views showing other novel compression plates formed in accordance with the present invention—these compression plates may be used when a more tailored anatomical fixation is required (e.g., for Cranio-Maxillofacial fracture fixation); 
           [0048]      FIG. 11  is a schematic view of a screw system which can be used to attach the novel compression plate of the present invention to bone—in this embodiment, the screw is a snap-off screw that detaches from the driver when the screw has been fully seated in the bone; 
           [0049]      FIG. 12  is a schematic view showing snap-off screws being used to attach the novel compression plate to the bone; 
           [0050]      FIG. 13  is a schematic view showing a delivery device which may be used with the novel compression plate shown in  FIG. 4  to elastically strain (i.e., stretch) the two elastic bridge members of the compression plate so as to make them parallel (or at least more parallel than their unconstrained state); 
           [0051]      FIG. 14  is a schematic view showing how the delivery device shown in  FIG. 13  engages the novel compression plate shown in  FIG. 4 ; 
           [0052]      FIG. 15  is a schematic cross-sectional view of the delivery device showing in  FIG. 13 ; 
           [0053]      FIG. 16  is a schematic view of an alternative delivery device which may be used with the novel compression plate shown in  FIG. 2 ; 
           [0054]      FIGS. 17 and 18  are schematic views showing how the novel compression plate shown in  FIGS. 4 and 5  may be used to provide compression across a bone fracture; 
           [0055]      FIG. 19  is a schematic view of another novel compression plate formed in accordance with the present invention, wherein the compression plate is contoured so as to allow for multiple compression plates to be assembled together into a custom plate configuration, and further wherein the two elastic bridge members of the compression plate can be elastically strained to a near-parallel condition; 
           [0056]      FIG. 20  is a schematic view of a multi-member compression plate configuration made up of a plurality of the compression plates shown in  FIG. 19 ; 
           [0057]      FIG. 21  is a schematic view of the lap joint which is created when two of the compression plates of  FIG. 19  are assembled together; 
           [0058]      FIG. 22  is a schematic view of another novel compression plate formed in accordance with the present invention, wherein areas of the compression plate (e.g., the two opposing regions of the compression plate) have been selectively treated so as to allow for plastic deformation to occur in those areas, and elastic strain to occur in other areas of the compression plate (e.g., the two elastic bridge members of the compression plate); 
           [0059]      FIGS. 23-25  are schematic views showing plastic threaded inserts disposed between the openings of the compression plate and the fixation screws which are used to hold the compression plate to bone; and 
           [0060]      FIG. 26  is a schematic view of a novel distraction plate formed in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Novel Compression Plate Comprising Elastic Bridge Members 
       [0061]    Looking first at  FIG. 1 , there is shown a novel compression plate  5  which is able to bring bone fragments into close proximity with each other, generate compressive load across the fracture line (i.e., between the cortical bone and the cancellous bone of the bone fragments), and maintain that compressive load for a prolonged period of time while healing occurs. 
         [0062]    Novel compression plate  5  is preferably a structure manufactured from a single piece of shape memory material (e.g., a material capable of exhibiting superelasticity and/or a temperature-induced shape change). The shape memory material may be a metal alloy (e.g., Nitinol) or a polymer (e.g., appropriately processed PEEK). Compression plate  5  is designed to reduce fractures and generate and maintain compression between bone fragments in order to aid in fracture healing. Compression plate  5  generally comprises two opposing regions  10  joined together by a pair of elastic bridge members  15 , and at least one opening  20  formed in each of the two opposing regions  10  for receiving fixation screws. Openings  20  may have a countersunk feature (e.g., a bore-counterbore configuration) so as to allow the heads of the fixation screws to sit substantially flat with the top surface of compression plate  5 . Additionally, openings  20  may be threaded so as to allow for positive engagement between the openings and the threaded fixation screws. In the un-restrained state, elastic bridge members  15  are bowed outwardly, such as in the manner shown in  FIG. 1 . 
         [0063]    Prior to implantation, elastic bridge members  15  of compression plate  5  can be reversibly strained inwardly (i.e., bent laterally inwardly), thus increasing the distance  25  ( FIG. 3 ) between opposing regions  10  (and hence openings  20 ) of compression plate  5  ( FIG. 2 ). Note that where compression plate  5  is formed out of Nitinol, elastic deformations of up to approximately 8% are achievable. A delivery device (see below) can be used to strain elastic bridge members  15  so as to bring elastic bridge members  15  to a substantially parallel state. 
         [0064]    During implantation, the strained (i.e., elongated) compression plate  5  is positioned against the bone fragments and secured to those bone fragments by passing fixation screws through openings  20  and into the bone fragments. 
         [0065]    Removal of the induced strain on compression plate  5  (provided by the delivery device, see below) results in compression plate  5  attempting to return to its original un-restrained state ( FIG. 3 ), thereby generating a compressive load on the bone (i.e., through elastic bridge members  15 , openings  20  and fixation screws extending through openings  20 ) and maintaining that compressive load on the bone for a prolonged period of time while healing occurs. 
         [0066]      FIGS. 4-6  show another compression plate  5  which is generally similar to the compression plate  5  shown in  FIGS. 1-3 , except that the opposing regions  10  of the compression plate shown in  FIGS. 4-6  each has two openings  20  for receiving fixation screws. 
         [0067]      FIGS. 7-9  show another novel compression plate  5  also formed in accordance with the present invention. More particularly, the novel compression plate  5  of  FIGS. 7-9  is generally similar to the compression plate  5  shown in  FIGS. 1-3 , except that the compression plate  5  of  FIGS. 7-9  has only one elastic bridge member  15 , and that elastic bridge member  15  has an “S” configuration. It will be appreciated that the “S” configuration of elastic bridge member  15  of  FIGS. 7-9  allows the elastic bridge member to be strained so as to move openings  20  further apart, and thereafter relaxed so as to cause a foreshortening of the distance between openings  20 . As a result, when compression plate  5  of  FIGS. 7-9  is strained so as to move openings  20  further apart, and fixation screws are thereafter passed through openings  20  of the strained compression plate and advanced into bone, and the strain on elastic bridge member  15  is thereafter released, the compression plate and fixation screws will apply a compressive force to the bone. 
         [0068]      FIGS. 10A-10F  are schematic views showing additional novel compression plates  5  also formed in accordance with the present invention—these compression plates may be used when more tailored anatomical fixation is required (e.g., for Cranio-Maxillofacial fracture fixation). 
         [0069]    Thus it should be appreciated that compression plate  5  may be formed in a variety of linear and non-linear configurations, and may include two or more opposing regions  10  and one or more elastic bridge members  15 . Thus, for example, in one form of the invention, compression plate  5  may comprise a linear configuration having two opposing regions  10  connected together by one or more elastic bridge members  15 . In another form of the invention, compression plate  5  may comprise a linear configuration having three or more opposing regions  10 , each pair of opposing regions being connected together by one or more elastic bridge members  15 . In still another form of the invention, compression plate  5  may comprise a non-linear configuration (e.g., a curved configuration) having two opposing regions  10  connected together by one or more elastic bridge members  15 . In still another form of the invention, compression plate  5  may comprise a non-linear configuration (e.g., a triangular configuration, a L-shaped configuration, etc.) having three or more opposing regions  10 , each pair of opposing regions being connected together by one or more elastic bridge members  15 . It will be appreciated that compression plate  5  may also comprise still other configurations, e.g., square, circular, etc., all of which are considered to be within the scope of the present invention. 
         [0070]    It will be appreciated that the fixation screws used with compression plate  5  may be conventional fixation screws of the sort well known in the field of fracture fixation. 
         [0071]    By way of example but not limitation, and looking now at  FIG. 11 , there is shown a snap-off screw system  100  of the sort well known in the art. This snap-off screw system can be used to secure compression plate  5  to bone. The snap-off screw system  100  has a shaft  105  to engage a rotary driver (not shown), a drive head  110  to engage a screw driver (not shown), a preferred shear location  115 , and a fixation screw  120  provided with a screw head  125  and screw threads  130 . Screw head  125  may have external threads (not shown) to engage mating threads on opening  20  of compression plate  5 , so that fixation screw  120  may function as a locking screw. 
         [0072]      FIG. 12  shows compression plate  5  with snap-off screw system  100  being used to deploy fixation screws  120  through openings  20  and into bone. Note that in  FIG. 12 , compression plate  5  is shown with its elastic bridge members  35  strained inwardly, although the delivery device (which bends elastic bridge members  15  inwardly) has been omitted for clarity of illustration. 
         [0073]    It will be appreciated that various delivery devices may be used to deploy compression plate  5  in the body. 
         [0074]    By way of example but not limitation, and looking now at  FIGS. 13-15 , there is shown an exemplary delivery device  200  which may be used to strain (i.e., compress) elastic bridge members  15 . Delivery device  200  generally comprises an outer body  205 , a central screw  210 , a nut  215  and a wedge assembly  220 . Plate  5  is engaged by wedge assembly  220  which is movably disposed in a wedge-shaped recess  225  formed in outer body  205 . Wedge assembly  220  comprises two individual wedges  230  that ride in wedge-shaped recess  225  (formed in outer body  205 ) and engage screw  210 . The distal end of each individual wedge  230  has two pins  235  that engage elastic bridge members  15  of compression plates  5 . When screw  210  is a conventional right-handed thread, loosening nut  215  causes wedge assembly  220  to move downward in wedge-shaped recess  225  of outer body  205 , thereby reducing the distance between pins  235 . This causes elastic bridge members  15  of compression plate  5  to elastically deform to a near-parallel (or at least to a more parallel) condition. Tightening nut  215  causes wedge assembly  220  to move upward in wedge-shaped recess  225  of outer body  205 , thereby increasing the distance between pins  235 . This releases the strain on elastic bridge members  15  of compression plate  5 , thereby allowing the elastic bridge members  15  to return to their original, outwardly-bowed shape. 
         [0075]      FIG. 16  shows another delivery device  240  which may be used to deploy compression plate  5 . The delivery device  240  shown in  FIG. 16  is essentially hemostat pliers, with the working tips  245  of the hemostat pliers applying the strain on elastic bridge members  15  of compression plate  5 . 
       Novel Method for Applying Compression to a Fracture Using the Novel Compression Plate 
       [0076]    Now next at  FIGS. 17 and 18 , there is shown one preferred method for treating a fracture  300  formed between two bone fragments  305  using novel compression plate  5 . 
         [0077]    First, compression plate  5  is loaded onto the delivery device (e.g., delivery device  200  discussed above) and elastic bridge members  15  are compressed so that they are near-parallel (or at least more parallel). The constrained compression plate  5  is then placed over the fracture line  300  and holes  310  are drilled through openings  20 . Screws (e.g., snap-off screws  120  of snap-off screw system  100 ) are installed (i.e., they are advanced through openings  20  and into bone fragments  305 ), thereby fixing compression plate  5  to the bone fragments  305 . The constraining delivery device (e.g., delivery device  200 ) is then removed and the compression plate  5  is allowed to attempt to regain its original unconstrained shape, thereby generating and maintaining compression across the fracture site. 
         [0078]      FIGS. 19-21  show another novel compression plate  5  formed in accordance with the present invention. More particularly, in this form of the invention, compression plate  5  is configured so as to allow multiple compression plates  5  to be assembled together as a modular plating system  400 . If desired, one or both of the two opposing regions  10  of each compression plate  5  may be formed with a height equal to one-half of the height of the two elastic bridge members  15  and, if desired, an opposing region  10  may be aligned with the top surface of the elastic bridge members  15 , or the opposing region  10  may be aligned with the bottom surface of the elastic bridge member  15 . In this way, adjacent regions  10  can be combined so as to form a lap joint which receives a fixation screw  120 . 
         [0079]      FIG. 22  shows a novel compression plate  5  that has had areas of the compression plate selectively processed (e.g., heat treated) so as to create plastic areas (e.g., opposing regions  10 ) which can be bent to take a set. This construction allows the compression plate to be contourable to the patient&#39;s anatomy (using the areas of plastic deformation) while also generating and maintaining compression across fracture sites (using the areas of elastic deformation). In one preferred form of the invention, compression plate  5  is formed out of Nitinol; the plastic areas of compression plate  5  (e.g., opposing regions  10 ) are formed out of fully annealed Nitinol or martensitic Nitinol with an austenite start temperature greater than body temperature; and the elastic areas of compression plate  5  (e.g., elastic bridge members  15 ) are formed out of austenitic Nitinol but capable of forming stress-induced martensite. 
         [0080]    Note that compression plate  5  is configured so that the force which is generated as compression plate  5  reconfigures (i.e., as elastic bridge members  15  return outwardly) is less than the “tear through” force of the bone which receives screws  120 , i.e., compression plate  5  is specifically engineered so as to not “tear through” the bone tissue when attempting to reconfigure to its original foreshortened configuration. The compressive forces of compression plate  5  can be controlled by (i) modulating the material properties of the compression plate, and/or (ii) varying the geometry of the compression plate. 
         [0081]    The percentage of cold work in the shape memory material forming compression plate  5  affects the compressive force generated by the reconfiguring compression plate. As the percentage of cold work increases, the compression force declines. A Nitinol compression plate should, preferably, have between about 15% and 55% cold work to control the recovery force of the compression plate; however, other degrees of cold work may be used, and/or the material may not be cold worked at all. 
         [0082]    Another material property that affects the plate&#39;s compression force is the temperature differential between the body that the compression plate will be implanted into (assumed to be 37° C., which is the temperature of a human body) and the austenite finish temperature of the shape memory material forming compression plate  5 . A smaller temperature differential between the two will result in the compression plate generating a smaller compressive load; conversely, a larger temperature differential between the two will result in the compression plate generating a larger compressive load. When the compression plate is made out Nitinol, the compression plate should, preferably, have an austenite finish temperature of greater than about −10° C., resulting in a temperature differential of about 47° C. when the compression plate is implanted (assuming that the compression plate is implanted in a human body). 
         [0083]    Plate geometry also affects the compression forces which are generated by the reconfiguring plate. More particularly, the cross-sectional area of elastic bridge members  15  affects the compression forces generated by the reconfiguring plate. As the cross-sectional areas increase, so do the compression forces that the reconfiguring plate will generate. It should be appreciated that the force generated as an elastic bridge member  15  attempts to recover from the constrained linear configuration ( FIG. 2 ) to the bowed outward configuration ( FIG. 1 ) is less than the force which would be generated were the plate to be constructed with linear elastic bridge members that are stretched longitudinally in tension. A plate with linear elastic bridge members that are stretched longitudinally in tension may recover with a force that exceeds the pull-out force in bone. 
         [0084]    In one preferred form of the invention, compression plate  5  and delivery device  200  are provided in the form of a sterilized kit. The kit may include additional instruments to aid in the implantation of the compression plate (e.g., k-wire, drill bit, plate size guide, screws, etc.). In one preferred form of the invention, compression plate  5  is provided with an associated delivery device (e.g., delivery device  200 ) in a sterile package, with elastic bridge members  15  being pre-constrained (e.g., so that elastic bridge members  15  are substantially straight, or at least more straight than when the elastic bridge members are in their unconstrained condition) in the sterile package by the delivery device (e.g., delivery device  200 ). 
       Test Data 
       [0085]    Static Elastic Bending: 25 mm interaxis width compression plates were tested. A 4-point bending load was applied on a tensile testing machine at a rate of 25.4 mm/min. Bending stiffness was calculated as the initial slope of load vs. displacement. The novel compression plate  5  had comparable Bending Strengths (16.33N/mm vs. 15.86N/mm p=0.818) to conventional fracture fixation plates. 
         [0086]    Compression Force: Greater interfragmentary compression has been found to enhance the healing of fractured bones. The compression plates of the present invention utilize the unique superelastic properties of Nitinol to enhance and sustain compression across the fracture plane. The compressive force generated by the novel compression plates of the present invention generate and maintain 180N of compression over nearly 1 mm of bone resorption. 
       Use of Plastic Threaded Inserts Between the Openings of the Compression Plate and the Fixation Screws 
       [0087]    If desired, and looking now at  FIGS. 23-25 , a plastic threaded insert  450  (with a central hole  455  and external threads  460 ) can be inserted into mating threaded holes  20  on compression plate  5 . Threaded plastic inserts  450  can accept a fixation screw (e.g., a fixation screw  120 ) with appropriate locking threads on the head of the fixation screw. The threads on the head of the fixation screw are able to cut threads into plastic threaded insert  450 , locking the fixation screw to compression plate  5  via the intervening plastic threaded insert  450 . Note that the fixation screws can be inserted on an angle (e.g., up to 15 degrees) off the center axis of threaded holes  20 , allowing for polyaxial fixation of compression plate  5 . 
         [0088]    Additionally, it should be appreciated that plastic threaded insert  450  insulates the metallic fixation screw from compression plate  5 , thereby limiting galvanic corrosion between the compression plate  5  and the metallic fixation screws. 
       Use of Other Types of Fasteners with the Novel Compression Plate 
       [0089]    In the foregoing disclosure, compression plate  5  is secured to bone fragments using threaded fixation screws. However, if desired, other types of fasteners may also be used to secure compression plate  5  to bone fragments. By way of example but not limitation, pins may be used to secure compression plate  5  to bone fragments. 
       Applying Distraction to Bone Using a Novel Distraction Plate 
       [0090]    In the foregoing disclosure, compression plate  5  has been discussed in the context of providing compression across a fracture. However, it should also be appreciated that, if desired, the apparatus can be modified so as to provide a distraction force to bone (e.g., to separate two bones or bone fragments, or to induce bone growth in a single bone, etc.). 
         [0091]    By way of example but not limitation, and looking now at  FIG. 26 , there is shown a novel distraction plate  505  formed in accordance with the present invention. Distraction plate  505  generally comprises two opposing regions  510  joined together by a pair of elastic bridge members  515 , and at least one opening  520  formed in each of the two opposing regions  510  for receiving fixation screws. Openings  520  may have a countersunk feature (e.g., a bore-counterbore configuration) so as to allow the heads of the fixation screws to sit substantially flat with the top surface of distraction plate  505 . Additionally, openings  520  may be threaded so as to allow for positive engagement between the openings and the threaded fixation screws. In the un-restrained state, elastic bridge members  515  are linearly aligned, such as in the manner shown in  FIG. 26 . Note that this is the inverse of the configuration of compression plate  5 , where elastic bridge members  15  are bowed outwardly when in their un-restrained state. 
         [0092]    Prior to implantation, elastic bridge members  515  of distraction plate  505  can be reversibly strained outwardly (i.e., forced outwardly), thus decreasing the distance  525  between opposing regions  510  (and hence openings  520 ) of distraction plate  505 . A delivery device can be used to strain elastic bridge members  515  so as to force elastic bridge members  515  outwardly, e.g., a delivery device generally similar to the delivery device  200 , or the delivery device  240 , discussed above, except that the delivery device is configured to force elastic bridge members  515  apart when appropriate. 
         [0093]    During implantation, the strained (i.e., the forcibly foreshortened) distraction plate  505  is secured to bone by passing fixation screws through openings  520  and into the bone. 
         [0094]    Removal of the induced strain on distraction plate  505  (provided by the aforementioned delivery device) results in distraction plate  505  attempting to return to its original un-restrained state (i.e., with elastic bridge members  515  linearly aligned), thereby generating a distraction load on the bone to which distraction plate  505  is secured (i.e., through elastic bridge members  515 , openings  520  and fixation screws extending through openings  520 ), and maintaining that distraction load on the bone for a prolonged period of time while healing occurs. 
       Modifications of the Preferred Embodiments 
       [0095]    It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.