Abstract:
An apparatus for leading a cerclage member along a desired path through a portion of bone, comprises a guide strip extending from a proximal end to a sharpened distal end, at least a portion of the guide strip being biased to assume a shape corresponding to a portion of a desired path along which the cerclage member is to pass through a portion of bone and a delivery cannula including a lumen sized to slidably receive the guide strip therein, the cannula maintaining the guide strip in a substantially straight configuration until the guide strip is extended distally out of the lumen.

Description:
PRIORITY CLAIM 
       [0001]    The present application claims priority to U.S. Provisional Application Ser. No. 61/179,881 entitled “Peri-Prosthetic Fixation Implant and Method” filed on May 20, 2009 to Konrad Schaller, Tom Overes and Robert Frigg, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    Fractures are often treated by wrapping a wire or other cable around a target portion of bone to stabilize the bone. The cable is typically looped around the target bone and locked at a desired tension therearound to hold portions of bone in a desired spatial relation to one another. Known cables for this purpose are generally formed with bulky heads that lockingly engage elongated portions thereof to maintain the cable looped around a target portion of bone with a desired tension. However, the large profile of these locking heads often requires that they project away from the bone and associated medical device (e.g., bone screw, bone plate, etc.) irritating ligaments, nerves and other adjacent tissue. Furthermore, once implanted, such cables often loosen and slide along an outer perimeter of the bone reducing the mechanical stability of the treated bone and increasing the possibility of further fractures. Bone defects such as osteoporosis further increase the likelihood of such fractures. Such loosening and movement of a cable may also result in misalignment, stiffness, nonunion, abnormal joint mechanics, healing impairment, etc 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention is directed to an apparatus for leading a cerclage member along a desired path through a portion of bone, comprising a guide strip extending from a proximal end to a sharpened distal end, at least a portion of the guide strip being biased to assume a shape corresponding to a portion of a desired path along which the cerclage member is to pass through a portion of bone in combination with a delivery cannula including a lumen sized to slidably receive the guide strip therein, the cannula maintaining the guide strip in a substantially straight configuration until the guide strip is extended distally out of the lumen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  shows a first perspective view of a system according to a first embodiment of the present invention; 
           [0005]      FIG. 2  shows a first partial cross-sectional view of an exemplary method for the system of  FIG. 1 ; 
           [0006]      FIG. 3  shows a second partial cross-sectional view of an exemplary method for the system of  FIG. 1 ; 
           [0007]      FIG. 4  shows a third partial cross-sectional view of an exemplary method for the system of  FIG. 1 ; 
           [0008]      FIG. 5  shows a fourth partial cross-sectional view of an exemplary method for the system of  FIG. 1 ; 
           [0009]      FIG. 6  shows a fifth partial cross-sectional view of an exemplary method for the system of  FIG. 1 ; and 
           [0010]      FIG. 7  shows a partial cross-sectional view of a system according to a fifth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The present invention relates generally to methods and devices for the stabilization and fixation of fractured bones and bone fragments via cerclage. Specifically, the present invention relates to a cable tie that is configured to lock the cable in a desired position about a target bone, with dimensions of the cable tie being selected to minimize or prevent the irritation of adjacent tissues. An exemplary cable tie according to the present invention is formed with self-locking notches formed on a body thereof to permit the cable tie to lock in place when positioned around a target portion of bone. In an exemplary method of use, a cable including a cable tie according to the present invention may be passed through a portion of the target bone via a first hole predrilled into a portion of the target bone, around a periphery of a previously implanted bone fixation device and out of the bone via a second predrilled hole substantially parallel to the first hole. A distal portion of the cable may be formed to assume a predefined shape corresponding to a path along which it is to travel around the implanted bone fixation device from the first hole to the second hole with a distal end thereof sharpened to facilitate the penetration of intervening bone. The distal end may then be inserted into a head of the cable tie so that a first locking feature of the distal end of the cable lockingly engages a corresponding second locking feature of the head to lock the cable at a desired tension around the bone fixation device and a portion of bone between external openings of the first and second holes (i.e., openings to these holes at the surface of the bone). Embodiments of the present invention may be employed with any of a plurality of procedures involving cerclage including peri-prosthetic bone fixation procedures and trolley spine procedures, as those skilled in the art will understand. It is noted that although embodiments of the present invention are directed to the treatment of long bones, the exemplary system and method can be applied to any bone fixation procedure without deviating from the spirit and scope of the present invention. As used in this application, the terms proximal and distal refer to directions along the cable tie with a distal end including the sharpened tip which forms the leading end of the cable as it is inserted into the bone. The cable extends proximally from this end. 
         [0012]    As shown in  FIGS. 1-6 , a system  100  and method according to a first embodiment of the invention include a cable tie  102  configured for insertion through a portion of bone to anchor a bone plate  104  or other item at a desired position on a bone  112 . The cable tie  102  is formed with a longitudinal section  126  extending distally from a head  124  at a proximal end thereof to a distal end  128 . The longitudinal section  126  includes a ribbed portion (not shown) configured to engage a tab (not shown) formed in the head  124 , as those skilled in the art will understand. A length of the cable tie  102  is chosen, for example, from any of a plurality of standard lengths known in the art and appropriate for a procedure to be performed. The cable tie  102  may be formed of any flexible yet durable material including, but not limited to, a compound plastic, polyaryletheretherketone (“PEEK”), or any other biocompatible plastic wherein the selected material may, for example, be chosen based on the expected load to be applied thereto during and after insertion to a target portion of bone. In a first operative configuration, the distal end  128  of the cable tie  102  is temporarily attached to a proximal end  136  of a guide strip  134 . The guide strip  134  extends from the proximal end  136  to sharpened distal end  138 . A predetermined length of the distal end of the guide strip  134  is biased to assume a preformed curvature corresponding to a desired path of the cable tie  102  through a portion of the bone  112 , as will be described in greater detail hereinafter. The guide strip  134  may be formed, for example, of Nitinol which has shape-memorizing properties permitting memorization of the predetermined curvature  340  or any other suitable material, as those skilled in the art will understand. 
         [0013]      FIGS. 2-6  sequentially depict the process by which the system  100  and guide strip  134  may be used to lock the bone plate  104  to the target bone. The bone  112  may, for example, be a fractured long bone or any other bone in a living body. Those skilled in the art will understand that, in some cases or locations, the use of bone screws may not be desirable due to potential interference with a previously inserted bone fixation device such as a stem, rod or shaft  108 . In addition, cables used to anchor fixation devices (e.g., bone plates) on long bones may sometimes slide along the bone away from a desired position. The following exemplary method permits the attachment of a bone fixation device such as a bone plate  104  to the bone  112  using a cable tie inserted through the bone  112  around a periphery of a shaft  108  of a previously inserted bone fixation device. The bone plate  104  may be a trauma plate or any other known bone fixation device and may further comprise any number of plate holes  106  extending therethrough.  FIGS. 5-9  depict a partial cross-sectional view of the target bone  112 . Although the bone  112  is shown without any fractures, in practice, the bone  112  may include any number and arrangement of fractures treatable by the bone plate  104 . 
         [0014]    In a first exemplary step, the bone plate  104  is placed against the target bone  112  in a desired orientation and temporarily held in place by, for example, fixation screws inserted into smaller plate holes  107  located on ends thereof. Alternatively, any other means known in the art may be used to temporarily maintain a desired position of the bone plate  104  relative to the bone  112 . As shown in  FIG. 2 , first and second holes  142  and  144  are then drilled into the bone  112  at locations adjacent to a portion of the bone plate  104  to be anchored by the cable tie  102 . For example, as described below in this embodiment, the cable tie  102  is locked in place by threading the distal end  128  of the cable tie  102  through a hole  106  in the bone plate  104  and then passing the distal end through a locking mechanism in the head  124  of the cable tie  102 . The locking mechanism may, for example, be a projection within a channel of the head  124  which locks in a ratchet fashion with a ribbed portion (e.g., a series of angled teeth) on a face of the cable tie  102 . Thus the holes will be drilled in a position corresponding to the hole  106  through which the cable tie is to extend. In another embodiment of the present invention (not shown), the bone plate  104  may be equipped with an integrated locking feature to permit ratcheted locking of the cable tie  102  therewith. The locking feature may be constructed substantially similarly to the head  124  with a projection extending into an opening thereof, the projection engaging a ribbed portion of the cable tie  102  when inserted through the opening. In yet another embodiment, the bone plate  104  may comprise a locking feature (not shown) insertable into a plate hole thereof, the locking feature also permitting ratcheted locking of the cable tie  102  therein in accordance with the system and method discussed earlier. 
         [0015]    The drill (not shown) may be guided into the bone  112  under an imaging technique known in the art or by preoperative planning as would be understood by those skilled in the art. The first and second holes  142 ,  144  are drilled into the bone  112  at an angle substantially perpendicular to a plane of the bone plate  104  separated by a distance selected to achieve a desired separation of the ends of the cable tie  102  passed therethrough around the bone plate  104  so that ends thereof lie substantially adjacent the shaft  108 . In a preferred embodiment, the first and second holes  142 ,  144  are parallel to one another although different angles may be used to bypass a prosthetic implant or other bone fixation element previously implanted in the bone, as those skilled in the art will understand. A guiding instrument  148  is then inserted into the first hole  142  until a distal end thereof engages an end of the first hole  142 . The guiding instrument  148  has a diameter substantially equivalent to or smaller than a diameter of the first and second holes  142 ,  144 . 
         [0016]    As shown in  FIG. 3 , the guide strip  134  is then advanced out of the guiding instrument  148 . As noted earlier, the guide strip  134  is formed of a shape-memory material and will thus automatically assume a memorized shape once confining forces are removed therefrom. Insertion into the guiding instrument  148  straightens the guide strip  134 . Accordingly, as the guide strip  134  exits the guiding instrument  148 , the second end  138  follows a path dictated by the shape-memorized curve  140 . As noted earlier, a curvature of the curve  140  is selected to permit the second end  138  to mate with the second hole  144 . By applying a stepped force to the first end  136 , the sharpened second end  138  of the guide strip  134  penetrates the bone  112  in a direction extending around the shaft  108  to open into the second hole  144 , defining a third curved hole  146  between the first and second holes  142 ,  144 . 
         [0017]    A catching instrument  150  is then inserted into the second hole  144  so that a hook  152  formed on a distal end thereof engages the second end  138  of the guide strip  134 . A force D is then applied to the catching instrument  150  in conjunction with a force C being applied to the guiding instrument  148  to guide the guide strip  134  completely through the first, second and third holes  142 ,  144 ,  146 . As noted earlier, a first end  136  of the guide strip  134  is attached to a distal end  128  of the cable tie  102 . Thus, the cable tie  102  follows the path of the guide strip  134  through the first, second and third openings  142 ,  144 ,  146 . The catching instrument  150  is an optional component of the system  100  and, in an alternate embodiment, the guide strip  134  may be traversed through the first, second and third openings  142 ,  144 ,  146  solely by applying the force C to the guiding instrument  148 . The cable tie  102  is advanced to the position shown in  FIG. 4 . The free distal end  128  is then disengaged from the guide strip  134  and is woven through a first one of the plate holes  106  and subsequently through the head  124  of the cable tie  102 . The cable tie  102  can then be tightened so the head  124  lies adjacent the opening  106  to lock a position of the bone plate  104  against the bone  112 . If desired, additional cable ties  102  may be inserted in the bone  112  in accordance with the procedure outlined above. 
         [0018]    Various modifications may be made to the system  100  without deviating from the spirit and scope of the present invention. For example, the cable tie  102  may be replaced with a standard cerclage wire, a strap, a retainer or another wire securement mechanism known in the art. 
         [0019]      FIG. 7  depicts a system  200  according to another embodiment of the present invention. The system  200  is directed to the fixation of a peri-prosthetic fracture of a bone  212 . The system  200  is formed substantially similarly as the system  100  with the exception of the depth of first and second predrilled holes  242  and  244 . Specifically, the predrilled holes  242 ,  244  of system  200  extend completely through the bone  212  along opposite sides of a bone implant  208 . The first and second predrilled holes  242 ,  244  are parallel to one another and are equidistant from the bone implant  208  in order to provide an equal force distribution to the bone  212 , as those skilled in the art will understand. 
         [0020]    In accordance with an exemplary method for the system  200 , a bone plate  204  is first positioned so that first and second plate holes  232 ,  234  thereof are aligned with the predrilled holes  242 ,  244 . A free distal end (not shown) of a cable  202  is inserted through the first plate hole  232  extending through the bone plate  204 , through the first opening  242  extending through the bone  212  and out of an end thereof. The free distal end (not shown) is then inserted into the second opening  244  and advanced therethrough to exit out of the second plate hole  234  aligned therewith. The free end of the cable tie  202  is then inserted through a head  224  of the cable tie  202  so that locking features (not shown) formed on a shaft  226  engage locking features formed within the head  224 , as described in greater detail earlier. The cable tie  202  is then tightened to lock the bone plate  204  against an outer periphery of the bone  212  and bone plate  204 . 
         [0021]    It will be apparent to those skilled in the art that various modifications and variations may be made in the structure and the methodology of the present invention, without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations of the invention provided that they come within the scope of the appended claims and their equivalents.