Abstract:
Methods for anterior-to-posterior talus-calcaneus screw insertion through an ankle arthrodesis nail according to embodiments of the present invention include coupling a first jig to the nail, aligning a drill bit with a first aperture of the nail by inserting it through a second aperture in the first jig, drilling a first hole through a tibia aligned with the first aperture, fixing the nail to the tibia with a screw through the first hole into the first aperture, coupling a second jig to the first jig, aligning the drill bit with a third aperture in the nail by inserting the drill bit through a fourth aperture in the second jig, drilling a second hole through a talus and a calcaneus aligned with the third aperture; and fixing the nail to the talus and calcaneus by inserting a screw through the second hole into the third aperture in an anterior-to-posterior direction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/332,091, filed on May 6, 2010, which is incorporated herein by reference in its entirety for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments of the present invention relate generally to ankle arthrodesis, and more specifically to systems and methods for anterior-to-posterior talus-calcaneus screw insertion through an arthrodesis nail. 
       BACKGROUND 
       [0003]    Current talus-calcaneus screw insertion systems and methods involve a strictly posterior approach, which requires screws to be inserted posteriorly into the calcaneus, through an arthrodesis nail, and into the talus. Current jigs for such surgical procedures permit only posterior insertion of such screws. 
       SUMMARY 
       [0004]    A surgical apparatus according to embodiments of the present invention facilitates anterior-to-posterior insertion of screws through the talus, arthrodesis nail, and calcaneus, or through the calcaneus and the tibia. Such apparatus may include two jigs: a first jig configured for rigid attachment to an arthrodesis nail and/or to an intermediate piece extending from the arthrodesis nail, and a second jig configured for attachment to the first jig, according to embodiments of the present invention. When the first jig is coupled to the arthrodesis nail, and the second jig coupled to the first jig, holes in the second jig are aligned with holes in the arthrodesis nail, to permit drilling and/or insertion of fixation screws from anterior to posterior into the talus, through the nail, and through the calcaneus. According to embodiments of the present invention, the second jig may be removed from the first jig and flipped and/or reconfigured to permit a posterior insertion of the screws, using the same first jig and the same second jig. 
         [0005]    A surgical method according to embodiments of the present invention includes attaching a first jig to an ankle arthrodesis nail, placing drill guides through holes in the first jig to drill holes through the tibia aligned with holes in the nail, inserting screws through the tibia holes and through the nail, coupling a second jig with the first jig, placing drill guides through holes in the second jig to drill holes through the talus and/or calcaneus aligned with holes in the nail, and inserting screws from anterior to posterior through the talus, through the holes in the nail, and into the calcaneus. According to embodiments of the present invention, the second jig is removed from the first jig, flipped and/or reoriented, and reattached to the first jig to permit a posterior approach using the same first and second jig. 
         [0006]    While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  illustrates a medio-anterior perspective view of an ankle with an arthrodesis nail and a tibial jig coupled to the arthrodesis nail, according to embodiments of the present invention. 
           [0008]      FIG. 2  illustrates a perspective view of an arthrodesis nail, a nail connector, and a base tool, according to embodiments of the present invention. 
           [0009]      FIG. 3  illustrates a medio-anterior perspective view of an ankle with an arthrodesis nail, a tibial jig coupled to the arthrodesis nail, and a talus-calcaneus jig coupled to the tibial jig in an anterior insertion position, according to embodiments of the present invention. 
           [0010]      FIG. 4  illustrates a perspective view of a talus-calcaneus jig, according to embodiments of the present invention. 
           [0011]      FIG. 5  illustrates a perspective view of the talus-calcaneus jig of  FIG. 4  coupled to a tibial jig, according to embodiments of the present invention. 
           [0012]      FIG. 6  illustrates another perspective view of a talus-calcaneus jig according to embodiments of the present invention. 
           [0013]      FIG. 7  illustrates the medio-anterior perspective view of  FIG. 3 , with talus-calcaneus guides placed on the talus-calcaneus jig, according to embodiments of the present invention. 
           [0014]      FIG. 8  illustrates a latero-posterior perspective view of the arthrodesis nail, tibial jig, and talus-calcaneus jig of  FIGS. 1 ,  3 , and  7  with the talus-calcaneus jig in a posterior insertion position, according to embodiments of the present invention. 
           [0015]      FIG. 9  illustrates a front partial cross-sectional view of a right ankle joint with an ankle arthrodesis nail secured to the tibia with tibial screws and secured to the talus and calcaneus with screws applied anteriorly, according to embodiments of the present invention. 
           [0016]      FIG. 10  illustrates a bottom partial cross sectional view of a right ankle joint with an ankle arthrodesis nail secured to the talus and calcaneus with screws applied anteriorly, according to embodiments of the present invention. 
           [0017]      FIG. 11  illustrates a latero-anterior perspective view of the ankle joint of  FIG. 9 , according to embodiments of the present invention. 
           [0018]      FIG. 12  illustrates a perspective view of an ankle arthrodesis jig system with a talus-calcaneus jig in a posterior-to-anterior insertion position, according to embodiments of the present invention. 
           [0019]      FIG. 13  illustrates a perspective view of the ankle arthrodesis jig system of  FIG. 12  with the talus-calcaneus jig in an anterior-to-posterior insertion position, according to embodiments of the present invention. 
           [0020]      FIG. 14  illustrates a perspective view of an ankle with an alternative ankle arthrodesis system in a proximal fixation position, according to embodiments of the present invention. 
           [0021]      FIG. 15  illustrates a perspective view of an ankle with the alternative ankle arthrodesis system of  FIG. 14  in an anterior-to-posterior screw insertion position, according to embodiments of the present invention. 
           [0022]      FIG. 16  illustrates a perspective view of an ankle with the alternative ankle arthrodesis system of  FIGS. 14 and 15  in a posterior-to-anterior screw insertion position, according to embodiments of the present invention. 
       
    
    
       [0023]    While the invention is amenable to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and are described in detail below. The intention, however, is not to limit the invention to the particular embodiments described. On the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0024]      FIG. 1  illustrates a medio-anterior perspective view of an ankle with an arthrodesis nail  110  and a tibial jig  101  coupled to the arthrodesis nail  110 , according to embodiments of the present invention.  FIG. 2  illustrates a perspective view of arthrodesis nail  110 , nail connector  102 , and a base tool  206 , according to embodiments of the present invention. The ankle joint includes several bones, including a tibia  108 , a calcaneus  104 , and a talus  106 . According to embodiments of the present invention, the nail  110  has a slot, such as a female slot  202 , that interfaces with a stem, such as a male stem  204 , of the nail connector  102 . According to some embodiments of the present invention, the connection between slot  202  and stem  204  prevents the nail connector  102  from rotating with respect to the nail  110 ; according to other embodiments, such connection prevents the nail connector  102  from moving at all with respect to the nail  110 . A base tool  206  (see  FIG. 2 ) may be removably coupled with the bottom of the nail connector  102 ; base tool  206  may assist the surgeon in placing and/or rotating the nail  110 , according to embodiments of the present invention. 
         [0025]    As illustrated in  FIG. 1 , once a hole has been drilled for the arthrodesis nail  110 , and the nail  110  placed through the bottom of the ankle and up into the tibia  108 , the tibia  108  is then secured to a proximal end of the nail  110 , according to embodiments of the present invention. A tibial jig  101  may include a collar  114  on its bottom end, and the collar  114  may be configured to fit over and/or otherwise interface with the nail connector  102 . A pin  112  may extend through collar  114  and into the nail connector  102  to couple the tibial jig  101  with the nail connector  102 . Such a coupling creates a rigid connection of the arthrodesis nail  110  to the tibial jig  101 , such that the tibial jig  101  cannot rotate and/or move with respect to the arthrodesis nail  110  after the pin  112  has secured the collar  114  to the nail connector  102 , according to embodiments of the present invention. Based on the disclosure provided herein, one of ordinary skill in the art will appreciate the various other ways in which the tibial jig  101  may be coupled to the arthrodesis nail to prevent rotation and/or other movement of the tibial jig  101  with respect to the arthrodesis nail  110 , according to embodiments of the present invention. The arthrodesis nail  110  may further include talus-calcaneus screw holes  208 ,  210 , according to embodiments of the present invention. 
         [0026]    The slot  202  and stem  204  interface may be configured to permit the nail connector  102  to couple with the nail  110  only at a predetermined rotational angle, and the nail connector  102  may include a slot or other indexing mechanism configured to interact with the pin  112  to permit the tibial jig  101  to couple with the nail connector  102  only at a predetermined angle, according to embodiments of the present invention. In this fashion, once the tibial jig  101  has been properly coupled to the arthrodesis nail  110 , the surgeon will be able to rely on the fact that tibial guide holes  116 ,  118  on the tibial jig  101  will align with tibial screw holes  128 ,  130  on the arthrodesis nail  110 , even though the surgeon will be unable to see the tibial screw holes  128 ,  130  after insertion of the arthrodesis nail  110 , according to embodiments of the present invention. 
         [0027]    In other words, when the tibial jig  101  is coupled to the nail  110  (e.g. via nail connector  102 ), a line drawn through tibial guide hole  116  intersects tibial screw hole  128  in the nail  110 , and a line drawn through tibial guide hole  118  intersects tibial screw hole  130 , according to embodiments of the present invention. According to embodiments of the present invention, an axial centerline of tibial guide hole  116  intersects tibial screw hole  128 , and an axial centerline of tibial guide hole  118  intersects tibial screw hole  130 . 
         [0028]    Guides  120 ,  122  (e.g. trocars) may be inserted into tibial guide holes  116 ,  118 . Guides  120 ,  122  may serve as drill guides, such that a hole drilled through guide  120  and tibia  108  will align with hole  128  in the nail  110 , and a hole drilled through guide  122  and tibia  108  will align with hole  130  in the nail, according to embodiments of the present invention. Guides  120 ,  122  may also serve as screw insertion or driving guides, such that a tibial screw  124  inserted through guide  120  with a driving element will be aligned with and then driven into tibial screw hole  128 , and a tibial screw  126  inserted through guide  122  will be aligned with and then driven into tibial screw hole  130 , according to embodiments of the present invention. Tibial screws  124 ,  126  serve to fix the position of the arthrodesis nail  110  with respect to the tibia  108 , according to embodiments of the present invention. 
         [0029]    A flange  250  on the nail connector  102  permits compression applied to the plantar surface of the calcaneus  104  to compress the calcaneus  104  and talus  106  against the tibia  108 ; this may be done after fixation of the arthrodesis nail  110  to the tibia  108  via one or more screws  124 ,  126 , according to embodiments of the present invention. According to some embodiments of the present invention, compression of the calcaneus  104  and/or talus  106  is achieved manually or in another way, and is not required for screw positioning. 
         [0030]      FIG. 3  illustrates a medio-anterior perspective view of an ankle with an arthrodesis nail  110 , a tibial jig  101  coupled to the arthrodesis nail  110 , and a talus-calcaneus jig  301  coupled to the tibial jig  101  in an anterior insertion position, according to embodiments of the present invention.  FIG. 4  illustrates a perspective view of a talus-calcaneus jig  301 , according to embodiments of the present invention. Once the arthrodesis nail  110  has been secured to the tibia  108 , the nail  110  is then fixed to the talus  106  and calcaneus  104 , according to embodiments of the present invention.  FIG. 5  illustrates a perspective view of the talus-calcaneus jig  301  of  FIG. 4  coupled to a tibial jig  101 , according to embodiments of the present invention.  FIG. 6  illustrates another perspective view of a talus-calcaneus jig  301  according to embodiments of the present invention. A talus-calcaneus jig  301  may be coupled to the tibial jig  101  for this purpose, according to embodiments of the present invention. The talus-calcaneus jig  301  may include one or more pegs  408 ,  410  rigidly affixed to the jig  301 . Pegs  408 ,  410  may be configured for placement or insertion into holes  132 ,  134  in the tibial jig  101 . 
         [0031]    The pegs  408 ,  410  and holes  132 ,  134  are configured to position the talus-calcaneus jig  301  with respect to the tibial jig  101  (and thus with respect to the nail  110 ), such that when peg  408  is inserted into hole  132  and peg  410  is inserted into hole  134 , a line drawn through hole  304  intersects hole  208  and a line drawn through hole  306  intersects hole  210 , according to embodiments of the present invention. When peg  408  is inserted into hole  132 , and peg  410  is inserted into hole  134 , an axial centerline of hole  304  intersects hole  208  of the nail  110 , and an axial centerline of hole  306  intersects hole  210  of nail, according to embodiments of the present invention. A screw  302  may be inserted through a hole in the talus-calcaneus jig  301  and into threaded engagement with a threaded hole  136  in the tibial jig  101 , in order to rigidly couple the talus-calcaneus jig  301  to the tibial jig  101 , according to embodiments of the present invention. 
         [0032]    According to an alternative embodiment of the present invention, the pegs  408 ,  410  may be included by the tibial jig  301  and holes  132 ,  134  may be included by the talus-calcaneus jig  301 . Based on the disclosure provided herein, one of ordinary skill in the art will appreciate the various ways in which the talus-calcaneus jig  301  may be coupled to the tibial jig  101  at a desired angle in order to permit alignment of the one or more holes  304 ,  306  with the one or more holes  208 ,  210  in the arthrodesis nail  110 , according to embodiments of the present invention. 
         [0033]    The talus-calcaneus jig  301  may include a guide arm  401  and a connection arm  402 , and the guide arm  401  may be coupled with the connection arm at an approximate right angle (e.g. approximately ninety degrees), according to embodiments of the present invention. 
         [0034]      FIG. 7  illustrates the medio-anterior perspective view of  FIG. 3 , with talus-calcaneus guides  706 ,  708  placed on the talus-calcaneus jig  301 , according to embodiments of the present invention. Guides  706 ,  708  (e.g. trocars) may be inserted into talus-calcaneus guide holes  306 ,  304 . Guides  706 ,  708  may serve as drill guides, such that a hole drilled through guide  706  and talus  106  will align with hole  208  in the nail  110 , and a hole drilled through guide  708  and talus  106  will align with hole  210  in the nail  110 , according to embodiments of the present invention. Guides  706 ,  708  may also serve as screw insertion or driving guides, such that a talus-calcaneus screw  702  inserted through guide  706  with a driving element will be aligned with and then driven into talus-calcaneus screw hole  208 , and a talus-calcaneus screw  704  inserted through guide  708  will be aligned with and then driven into talus-calcaneus screw hole  210 , according to embodiments of the present invention. Talus-calcaneus screws  702 ,  704  serve to fix the position of the arthrodesis nail  110  with respect to the talus  106  and calcaneus  104 , according to embodiments of the present invention. 
         [0035]    Although holes  304 ,  306  are described as being aligned with holes  208 ,  210 , the same is true for apertures passing through guides  706 ,  708 , according to embodiments of the present invention. And although holes  116 ,  118  are described as being aligned with holes  128 ,  130 , the same is true for apertures passing through guides  120 ,  122 , according to embodiments of the present invention. 
         [0036]    According to embodiments of the present invention, the talus-calcaneus jig  301  is removably coupled to the tibial jig  101 , to permit the talus-calcaneus jig  301  to be switched between an anterior-to-posterior talus-calcaneus screw insertion position and a posterior-to-anterior talus-calcaneus screw insertion position. For example, screw  302  may be loosened and/or unthreaded from hole  136  to release the talus-calcaneus jig  301  from the tibial jig  101 , by removing pegs  408 ,  410  from holes  132 ,  134 . Then, peg  410  may be placed through hole  132  and peg  408  may be placed through hole  134 , and talus-calcaneus jig  301  may again be attached to tibial jig  101  via screw  302 , according to embodiments of the present invention.  FIG. 8  illustrates a latero-posterior perspective view of the arthrodesis nail  110 , tibial jig  101 , and talus-calcaneus jig  301  of  FIGS. 1 ,  3 , and  7  with the talus-calcaneus jig  301  in a posterior-to-anterior insertion position, according to embodiments of the present invention. 
         [0037]      FIG. 8  illustrates that the same talus-calcaneus jig  301  and tibial jig  101  combination can be used for both anterior-to-posterior and posterior-to-anterior arthrodesis screw insertion, according to embodiments of the present invention. As illustrated in  FIGS. 4-6 , the guide section  401  of the talus-calcaneus jig  301  may include multiple sets of holes. One set of holes  304 ,  306  may be configured to receive guides  706 ,  708  in order to guide drilling and screw  702 ,  704  insertion when the talus-calcaneus jig  301  is in the anterior-to-posterior screw insertion position of  FIG. 7 , according to embodiments of the present invention. The guide section  401  may include another set of holes  404 ,  406  configured to receive guides  706 ,  708  in order to guide drilling and screw  702 ,  704  insertion when talus-calcaneus jig  301  is in the posterior-to-anterior screw insertion position of  FIG. 8 , according to embodiments of the present invention. According to embodiments of the present invention, the talus-calcaneus jig  301  includes visual markings  502 ,  504  (see  FIG. 5 ) indicating to the surgeon which holes are for anterior-to-posterior screw insertion and which holes are for posterior-to-anterior screw insertion. According to embodiments of the present invention, such visual markings  502 ,  504  include one or more of a color code, a word, a number, a pattern, a line, a notch or groove, and/or a protrusion. For example, the visual markings  502 ,  504  may include the letters “AP” connected by lines to the two holes corresponding to anterior-to-posterior screw insertion, and the letters “PA” connected by lines to the two holes corresponding to posterior-to-anterior screw insertion. 
         [0038]    According to embodiments of the present invention, the talus-calcaneus jig is U-shaped and includes talus-calcaneus screw insertion holes on opposing ends, such that either anterior-to-posterior or posterior-to-anterior screw insertion may be accomplished using the same talus-calcaneus jig and without changing the position of the talus-calcaneus jig with respect to the tibial jig  101 . 
         [0039]    Embodiments of the present invention permit a surgeon to decide, during the surgical ankle arthrodesis procedure, whether to use an anterior-to-posterior screw insertion approach or a posterior-to-anterior screw insertion approach. Due to the ease of changing the position of the talus-calcaneus jig  301  with respect to the tibial jig  101 , and due to the fact that the same tibial jig  301  piece of hardware may be used with the same tibial jig  101  for both approaches, a surgeon is provided with more flexibility both before and especially during the arthrodesis procedure. The surgeon may want to place the talus-calcaneus screws via an anterior-to-posterior method in order to limit the number of incisions, secure a bone graft in the talus with a screw, and/or in order to make the operation faster. Also, embodiments of the present invention permit a surgeon to decide between the anterior-to-posterior and posterior-to-anterior approaches based on an observation of the bone quality during surgery; for example, if a surgeon were initially planning an anterior-to-posterior insertion approach, and during surgery discovered the bone quality of the talus to be poor or not as suitable to accept the drilling and/or screw insertion, then the surgeon could simply change the configuration of the talus-calcaneus jig  301  without removing or adjusting the tibial jig  101  to implement a posterior-to-anterior approach. 
         [0040]    When the talus-calcaneus jig  301  is in the posterior-to-anterior screw insertion position of  FIG. 8 , a line through hole  404  intersects hole  208  in the arthrodesis nail  110 , and a line through hole  406  intersects hole  210  in the nail  110 , according to embodiments of the present invention. According to embodiments of the present invention, an axial centerline of hole  404  intersects hole  208  and an axial centerline of hole  406  intersects hole  210 . Guides  706 ,  708  (e.g. trocars) may be inserted into talus-calcaneus guide holes  404 ,  406 . Guides  706 ,  708  may serve as drill guides, such that a hole drilled through guide  706  (e.g. a hole drilled using guide  706  as a guide) and calcaneus  104  will align with hole  208  in the nail  110 , and a hole drilled through guide  708  and calcaneus  104  will align with hole  210  in the nail  110 , according to embodiments of the present invention. Guides  706 ,  708  may also serve as screw insertion or driving guides, such that a talus-calcaneus screw  702  inserted through guide  706  with a driving element will be aligned with and then driven into talus-calcaneus screw hole  208 , and a talus-calcaneus screw  704  inserted through guide  708  will be aligned with and then driven into talus-calcaneus screw hole  210 , according to embodiments of the present invention. Talus-calcaneus screws  702 ,  704  serve to fix the position of the arthrodesis nail  110  with respect to the talus  106  and calcaneus  104 , according to embodiments of the present invention. 
         [0041]    Although a screw  302  is illustrated as providing the releasable coupling between the talus-calcaneus jig  301  and the tibial jig  101 , one of ordinary skill in the art, based on the disclosure provided herein, will appreciate the numerous other ways in which the talus-calcaneus jig  301  may be releasably coupled with the tibial jig  101 , according to embodiments of the present invention. For example, a quick-release and/or spring-loaded coupling mechanism may be employed, to permit the talus-calcaneus jig  301  to be pulled away from tibial jig  101  a sufficient distance to permit pegs  408 ,  410  to be removed from holes  132 ,  134 , and then turned to the opposite configuration and released, permitting the pegs  408 ,  410  to re-engage opposite holes, according to embodiments of the present invention. Other types of quick-release and/or spring-loaded and/or slot-based mechanisms may be used, according to embodiments of the present invention. 
         [0042]    Although guide members  120 ,  122 ,  706 ,  708  are described, the apertures  116 ,  118 ,  304 ,  306 ,  404 ,  406  may themselves be used to guide drill bits and/or screw insertion and/or screw driving, according to embodiments of the present invention. 
         [0043]      FIG. 9  illustrates a front partial cross-sectional view of a right ankle joint with an ankle arthrodesis nail secured to the tibia with tibial screws and secured to the talus and calcaneus with screws applied anteriorly, according to embodiments of the present invention.  FIG. 10  illustrates a bottom partial cross sectional view of a right ankle joint with an ankle arthrodesis nail secured to the talus and calcaneus with screws applied anteriorly, according to embodiments of the present invention.  FIG. 11  illustrates a latero-anterior perspective view of the ankle joint of  FIG. 9 , according to embodiments of the present invention. 
         [0044]      FIG. 12  illustrates a perspective view of an ankle arthrodesis jig system  100  with a talus-calcaneus jig  301  in a posterior-to-anterior insertion position, according to embodiments of the present invention.  FIG. 13  illustrates a perspective view of the ankle arthrodesis jig system  100  of  FIG. 12  with the talus-calcaneus jig  301  in an anterior-to-posterior insertion position, according to embodiments of the present invention. 
         [0045]    A jig according to some embodiments of the present invention does not include a talus-calcaneus element; instead, a single lateral jig may be coupled to the arthrodesis nail and rotated ninety degrees to the front and/or ninety degrees to the back, in order to insert screws in an anterior-to-posterior direction or in a posterior-to-anterior direction using the same single lateral jig. For example,  FIGS. 14-16  illustrate such a jig  1700 . Jig  1700  couples, for example rotatably couples, with the arthrodesis nail  110 , according to embodiments of the present invention. Jig  1700  may be oriented in one of three discrete locked positions, according to embodiments of the present invention. In a “zero degree” lock position, as illustrated in  FIG. 14 , one or more tibial screw holes  1702  on jig  1700  are aligned with one or more holes  128 ,  130  of the nail  110  for fixation of the tibia with respect to the nail  110 , according to embodiments of the present invention. In a “+90° lock position,” one or more anterior-to-posterior insertion holes  1704  are aligned with one or more holes  208 ,  210  in nail  110 , as illustrated in  FIG. 15 , according to embodiments of the present invention. In a “−90° lock position,” one or more posterior-to-anterior insertion holes  1706  are aligned with one or more holes  208 ,  210  in nail  110 , as illustrated in  FIG. 16 , according to embodiments of the present invention. Thus, the sets of one or more holes  1702 ,  1704 ,  1706  may be formed in a single rigid jig  1700  that is rotatable between two or more positions about the nail  110 , according to embodiments of the present invention. For example, in one embodiment, jig  1700  rotates between the position of  FIG. 14  and the position of  FIG. 15 , but not to the position of  FIG. 16 . In another embodiment, jig  1700  is rotatable between all three discrete locked positions of  FIGS. 14-16 . Various modifications and additions can be made to the exemplary embodiments discussed without departing from the scope of the present invention. For example, while the embodiments described above refer to particular features, the scope of this invention also includes embodiments having different combinations of features and embodiments that do not include all of the described features. Accordingly, the scope of the present invention is intended to embrace all such alternatives, modifications, and variations as fall within the scope of the claims, together with all equivalents thereof.