Abstract:
A sternum fixation device for securing parts of a sternum includes first and second removably associated plates. The first plate has an upper surface and a sternum-contacting surface, and at least one hole passing through both of these surfaces for receiving a fastener head. The second plate has at least one attachment member for fixation to the sternum. A release member holds the first and second plates together, and is movably associated with at least one of the first and second plates such that it may be moved to allow separation of the two parts of the sternum.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The benefit of Provisional Application No. 60/270,620, filed Feb. 23, 2001 is claimed under 35 U.S.C. §119(e). 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to surgical devices, and more particularly, to devices for reapproximating two or more parts of a patient&#39;s sternum. 
     BACKGROUND OF THE INVENTION 
     Many surgical procedures require two or more parts of a sternum to be reapproximated, or fixed together, such as sternal reconstruction and repair of sternal trauma. In addition, various types of surgical procedures are currently performed to investigate, diagnose, and treat diseases involving tissues or organs located in a patient&#39;s thoracic cavity, such as the heart and lungs. These procedures typically require a partial or median sternotomy to gain access to the patient&#39;s thoracic cavity. A partial or median sternotomy is a procedure by which a saw or other appropriate 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 halves to be separated laterally. A large opening into the thoracic cavity is thus created, through which a surgeon may directly visualize and operate upon the heart and other thoracic organs, vessels, or tissues. Following the surgical procedure within the thoracic cavity, the two severed sternal halves must be reapproximated. 
     Sternum fixation has traditionally has been performed using stainless steel wires that are wrapped around or through the sternal halves and then twisted together, so as to compress the two halves together. Other methods of sternum fixation include the use of band or strap assemblies. Such assemblies typically include a locking mechanism, which secures a strap in a closed looped configuration around the sternum halves. While utilization of steel wires and strap assemblies have been widely accepted for sternum fixation, these devices present a number of disadvantages. For example, steel wires are susceptible to breakage, are difficult to maneuver and place around the sternum, and often have sharp ends that can pierce through the surgeon&#39;s gloves or fingers. Steel wire and band assemblies also provide insufficient or non-uniform clamping force on the sternal halves, thus resulting in sternal nonunion. The steel wire and band assemblies also provide insufficient clamping forces in all three planar directions, thus leading to healing problems caused by unwanted bone movements leading to raking and rubbing of the surrounding tissue or bone. 
     Several other techniques of sternal fixation have been developed for reapproximating the sternal halves. One technique uses plates that are located on both sternal halves across the sternotomy and are fixed thereto by means of screws through the bone on either side of the sternotomy. This technique, however, is not optimal because it requires direct fixation of the plates to the bone with screws, making reentry into the thoracic cavity through the sternotomy extremely difficult in case of a medical emergency. 
     Another technique uses a sternal clamp having a pair of opposed generally J-shaped clamp members which are laterally adjustable relative to one another but can be rigidly joined with a set of machine screws. Similar to the use of plates, discussed above, this technique does not provide quick access to the organs and/or tissues within the patient&#39;s thoracic cavity. 
     Yet another fixation device comprises a pair of hook-shaped clamps that slide together and lock in position with respect to one another using a ratchet assembly. The ratchet assembly provides quickened accesses to the thoracic cavity, but is cumbersome to use and is limited to the hook-shaped clamp members disclosed. 
     Therefore, it is desirable to provide a sternum fixation device that stabilizes the sternum in all three planar directions, has a fast and easy to use quick-release feature, and works in several different configurations. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a sternum fixation device for securing parts of a sternum. The sternum fixation device includes a first plate and a second plate. The first plate has an upper surface and a sternum-contacting surface, at least one hole passing through the upper and sternum-contacting surfaces for receiving a fastener head of a bone fastener, and a first longitudinal bore defining an axis oriented substantially transversely to the at least one hole. The at least one hole may be threaded to receive a threaded fastener head. The second plate has an upper surface and a sternum-contacting surface, an attachment member for fixation to the sternum, and a second longitudinal bore. The first and second plates are dimensioned to mate with one another such that the first and second longitudinal bores are aligned to receive the release member, and removal of the release member from the first and second longitudinal bores allows separation of the two parts of the sternum. The first and second plates mate with one another such that they cannot rotate with respect to one another about the release member. 
     According to one aspect of the present invention, the release member is a pin, which may be a single pronged pin. The pin may have a splayed apart tip portion. Alternatively, the release member is a two pronged pin, which may be angled with respect to a mating line between the first and second plates. The release member may also be a cam or quarter-turn fastener, and the first and second plates may be provided with matching sets of ratchet teeth that cooperate with the release member to allow the distance between the first and second plates to be varied. 
     The attachment member may be a threaded through hole that passes through the second plate upper and sternum-contacting surfaces for receiving a threaded fastener head. To increase pull-out resistance of the fastener, the at least one threaded hole may be angled away from the second plate. 
     According to another embodiment of the present invention, the attachment member is a hook member for engaging an intercostal space portion of the sternum. Preferably, the attachment member comprises at least two hook members that are spaced apart by an adjustable lateral distance. Alternate embodiments include multiple combinations of fastener and hook-shaped attachment members. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a first embodiment of a sternum fixation device according to the present invention; 
         FIG. 2  is an exploded perspective view of the sternum fixation device of  FIG. 1 ; 
         FIG. 3  is a perspective view of the sternum fixation device of  FIG. 1 , having a U-shaped release member; 
         FIG. 4  is an exploded perspective view of the sternum fixation device of  FIG. 3 ; 
         FIG. 5  is a perspective view of the sternum fixation device of  FIG. 1 , having differently shaped first and second mating portions; 
         FIGS. 6-7  are exploded perspective views of the sternum fixation device of  FIG. 5 , showing variations of the first and second mating portions and release member; 
         FIG. 8  is an elevational view of the sternum fixation device of  FIG. 5 , wherein the release member is angled with respect to a mating line between the first and second plates; 
         FIG. 9  is a perspective view of the sternum fixation device of  FIG. 1 , having differently shaped first and second mating portions; 
         FIGS. 10-12  are elevational views of the sternum fixation device of  FIG. 5 , having additional first and second attachment members; 
         FIG. 13  is a perspective view of the sternum fixation device of  FIG. 5 , having additional first and second attachment members; 
         FIG. 14  is a perspective view of a sternum fixation device of  FIG. 1 , having an alternate embodiment of the release member of  FIG. 1 ; 
         FIG. 15  is a perspective view of a second embodiment of a sternum fixation device according to the present invention, having hook-shaped attachment members; 
         FIG. 16  is a perspective view of the sternum fixation device of  FIG. 15 , having adjustably spaced-apart hook members; 
         FIG. 17  is a perspective view of the sternum fixation device of  FIG. 15 , having first and second attachment members including a combination of hooks and threaded fastener holes; 
         FIG. 18  is a perspective view of the sternum fixation device of  FIG. 15 , having an alternate embodiment of the release member; and 
         FIG. 19  is an elevational view of a bone fastener having a threaded head portion for use with one embodiment of the first and second attachment members according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show a first illustrative embodiment of a sternum fixation device according to the present invention, shown as sternum fixation device  10 . Sternum fixation device  10  includes first and second mating plates  12 ,  14  attached to one another by a release member  16 . First plate  12  and second plate  14  may be used to reapproximate, or secure together, two or more parts of a sternum by attaching each plate to a part of the sternum. Sternum fixation device  10  may be constructed from any suitable bio-compatible material including, but not limited to, bioresorbable materials, radio-translucent materials, allograft materials, stainless steel and titanium 
     First plate  12  includes an upper surface  18  and a sternum-contacting surface  20 , and a first attachment member  22  for attachment to the sternum. First attachment member  22  is shown as a plurality of threaded holes that are configured to receive a threaded head portion  44  of a fastener, such as a bone screw  42 , shown in FIG.  19 . The fastener may alternatively have an elongated shaft with barbs formed thereon that anchor the fastener in the bone. Second plate  14  includes an upper surface  24  and a sternum-contacting surface  26 , and a second attachment member  28 , also shown as a plurality of threaded holes for receiving a threaded head portion of a bone screw  42 . Alternatively, the holes of the first and second attachment members  22 ,  28  may not have threads and receive a non-threaded head portion of a fastener. Sternum-contacting surfaces  20 ,  26  may be scalloped, or provided with various other surface treatments that are known by one of ordinary skill in the bone plating art to minimize the contact area between the first and second plates  12 ,  14  and the respective parts of the sternum. 
     First plate  12  further includes a series of first joining portions  30  that inter-digitate with corresponding second joining portions  32  on second plate  14 . A first longitudinal bore  34  extends through the first joining portions  30  and a second longitudinal bore  36  extends through the second joining portions  32  such that when first plate  12  and second plate  14  are positioned adjacent one another with the first and second joining portions  30 ,  32  inter-digitated, the first and second longitudinal bores  34 ,  36  are substantially aligned and may receive release member  16 . Alternatively, the first and second joining portions  30 ,  32  could be provided with multiple sets of aligned longitudinal bores to allow the distance between the first and second attachment members  22 ,  28  to be varied to accommodate a range of sternum sizes. 
     As shown in  FIGS. 1 and 2 , release member  16  is shown as an elongated pin having a curved grip portion  35 . Release member  16  could alternatively have a T-shaped grip portion. When inserted into aligned first and second longitudinal bores  34 ,  36 , release member  16  secures the first and second plates  12 ,  14  together. As shown in  FIG. 2 , when the release member  16  is removed from the first and second longitudinal bores  34 ,  36 , the first and second plates  12 ,  14  are allowed to separate. Thus, release member  16  can be removed from the first and second longitudinal bores  34 ,  36  to quickly and conveniently gain access to the thoracic cavity. This quick release mechanism can be useful, for example, in the case of a medical emergency. 
     According to one aspect of the present invention, first and second joining portions  30 ,  32  may be configured such that the first and second plates  12 ,  14  cannot rotate with respect to one another about the release member  16 , thus providing increased stabilization of the two parts of the sternum. As shown in  FIG. 2 , the first and second joining portions  30 ,  32  overlap as well as inter-digitate, thus fixing the plates together such that they do not rotate with respect to one another. As an alternative to overlapping the joining portions, release member  16  may be configured to prevent relative rotation between the first and second plates  12 ,  14 . For example, release member  16  and the first and second longitudinal bores  34 ,  36  may have matching polygonal cross-sections, such as rectangular, square, or triangular, which prevent rotation of either of the plates  12 ,  14  relative to the release member  16  and consequently, relative to one another. The matching cross-sections may also be ovular. Alternatively, release member  16  may be a multi-pronged pin and the first and second joining portions  30 ,  32  may be provided with multiple sets of aligned longitudinal bores. One of ordinary skill in the bone plating art, however, will know and appreciate than any number of configurations may be used to prevent rotation between the first and second plates  12 ,  14 . 
     Referring to  FIGS. 3 and 4 , a variation of sternum fixation device  10  is shown with release member  16  in the form of a U-shaped pin having spaced apart leg portions  37 ,  39 . The first and second plates  12 ,  14  have first and second joining portions  30 ,  32  that are spaced apart such that a central opening  33  is defined between the first and second plates  12 ,  14 . Central opening  33  serves to minimize the amount of implanted material that contacts the sternum. A third longitudinal bore  38  extends through the first mating portion  30  and a fourth longitudinal bore  40  extends through the second mating portion  32 . The third and forth longitudinal bores  38 ,  40  are located such that when the first plate  12  and second plate  14  are positioned adjacent one another with the first and second joining portions  30 ,  32  inter-digitated, the first and second longitudinal bores  34 ,  36  are substantially aligned, as are the third and forth longitudinal bores  38 ,  40 . Thus, each of the release member leg portions  37 ,  39  may be received in one of the aligned pairs of bores to secure the first and second plates  12 ,  14  together. The spaced apart relationship of leg portions  37 ,  39  and the respective sets of aligned longitudinal bores prevents the first and second plates  12 ,  14  from rotating with respect to one another about the release member  16 , thus stabilizing the sternum fixation device  10 . 
     Still referring to  FIGS. 3 and 4 , the first and second attachment members  22 ,  28  are in the form of a plurality of threaded holes configured to receive a threaded head  44  of a bone screw  42 . To reduce the tendency of the bone screws  42  to pull out of the sternum, the threaded holes of the first attachment member  22  and the second attachment member  28  may be angled such that the threaded tip portions  46  of opposing bone screws, for example, bone screws  42   a  and  42   b , are angled towards one another. 
       FIGS. 5-12  show several additional variations of sternum fixation device  10 . In each of the variations shown, first and second plates  12 ,  14  are reduced in size so that they outline the first and second attachment members  22 ,  28 , thereby reducing the amount of material that contacts the sternum. Referring to  FIGS. 5 ,  6  and  7 , the first and second joining portions  30 ,  32  may each have protrusions and/or indentations formed thereon to prevent them from rotating with respect to one another. As shown in  FIG. 6 , second joining portion  32  includes transverse tabs  48  and groove  50 , and first joining portion  30  has mating grooves  52  and tab  54  formed thereon, which cooperate to prevent rotation between the first and second plates  12 ,  14 . Release member  16  has a resiliently expanded, or splayed, tip portion  56  that provides resistance against the release member  16  coming out of first and second longitudinal bores  34 ,  36 . Release member  16  may alternatively be a taper pin. As shown in  FIG. 7 , tabs  48  and grooves  52  may be oriented parallel to the joining portions, however, one of ordinary skill in the bone plating art will know and appreciate that any number of configurations of mating protrusions and/or indentations may be formed on the first and second mating portions  30 ,  32  to prevent rotation between them. 
       FIG. 8  shows a variation of sternum fixation device  10  wherein the first and second longitudinal bores  34 ,  36  are oriented at an angle  58  to the intersection  57  of first and second plates  12 ,  14 . When release member  16  is received in aligned first and second longitudinal bores  34 ,  36  (hidden in FIG.  8 ), the skewed orientation of release member  16  with respect to intersection  57  prevents rotation between the first and second plates  12 ,  14 .  FIG. 9  shows another variation of sternum fixation device  10  having a release member  16  in the form of a U-shaped pin, as discussed above with respect to  FIGS. 3 and 4 . Release member  16  could alternatively be a V-shaped pin, a T-shaped pin, or any other shape known to one of ordinary skill in the art.  FIG. 10  shows a variation of sternum fixation device  10  having first and second attachment members  22 ,  28  comprising three threaded fastener or screw holes each, and a skewed release member  16 .  FIG. 11  shows another variation having a U-shaped release member  16  with an enlarged ring-shaped grip portion  35 .  FIG. 12  shows yet another variation where first attachment member  22  and second attachment member  28  each comprise six threaded fastener or screw holes for receiving a threaded head  44  of a bone fastener or bone screw  42 .  FIG. 13  shown a variation where the first attachment member  22  and the second attachment member  28  are arranged in a H-shaped pattern. One of ordinary skill in the bone plating art will know and appreciate that any of the features and variations described above may be combined to produce a sternum fixation device according to the present invention. 
       FIG. 14 , shows an alternate embodiment of a release member  116  according to the present invention, which comprises a pair of quarter-turn fasteners or screws, or other cam-type screws known by one of ordinary skill in the art. The first joining portions  130  each have a countersunk bore  134  for receiving a head  135  of the release member  116 , and the second joining portions  132  each have a threaded bore, or cam surface  136  (hidden in FIG.  14 ), for receiving a threaded or cam portion  137  (hidden in  FIG. 14 ) of the release member  116 , or vice versa. The first joining portions  130  overlap the second joining portions  132 , or vice versa, such that the release member  116  can be inserted through the countersunk bore  134  and be received by cam surface  136  to secure the first and second plates  12 ,  14  together. To separate the first and second plates  12 ,  14  the release member  116  is rotated through a predetermined angle preferably of less than 360 degrees, such as, for example ninety degrees, to release the cam portion  137  of the release member  116  from the cam surface  136  and allow the first and second plates  12 ,  14  to come apart. 
     Referring to  FIGS. 14-17 , a second embodiment of the present invention is shown as sternum fixation device  210 . Sternum fixation device  210  includes first and second plates  212 ,  214  attached to one another by release member  216 . First plate  212  includes an upper surface  218  and a sternum-contacting surface  220 , and first attachment member  222 . As will be discussed in more detail below, first attachment member  222  is a plurality of hooks that are configured and dimensioned to engage the sternum between the intercostal spaces. Second plate  214  includes an upper surface  224  and a sternum-contacting surface  226 , and second attachment member  228 . Second attachment member  228  is a plurality of holes for receiving a bone fastener or screw  242 , which holes are preferably threaded to receive a threaded head  244  of the bone screw  242 . 
     First plate  212  further includes a first joining portion  230  that overlaps with corresponding second joining portion  232  on second plate  214 . An elongated slot  234  extends through the second joining portion  232  and is dimensioned to receive release member  216 , which is a cam, as shown in  FIGS. 14 and 15 , or quarter-turn fastener or screw, as shown in FIG.  16 . As shown in  FIGS. 14 and 15 , release member  216  may be a generally rectangular cam that is rotatable between a locking position and a releasing position and has a first dimension  260  that can pass through the slot  234  when it is oriented parallel thereto, but can not pass through the slot  234  when it is substantially transverse thereto. Thus, when release member  216  is in the locking position, the first dimension  260  is oriented substantially transverse to the elongated slot  234  and locks the first and second plates  212 ,  214  together. When release member  216  is rotated into the releasing position, the first dimension  260  is in alignment with the elongated slot  234  and allows separation of the first and second plates.  FIG. 16  shows release member  216  as a quarter-turn screw having a head  235  and a threaded portion  237  (hidden). Threaded portion  237  passes through elongated slot  234  and engages a threaded bore  236  (hidden) in first joining portion  230 , and head  235  engages the upper surface  224  of second joining portion  232  to lock the first and second plates  212 ,  214  together. According to either configuration of release member  216 , cam or quarter-turn screw, the first and second plates  212 ,  214  may be separated by rotating release member  216  through a predetermined angle preferably of less than 360 degrees, such as, for example, ninety degrees, to free release member  216  from elongated slot  234  and allow the first and second plates  212 ,  214  to separate. One of ordinary skill in the art will know and appreciate that any number of cam or quarter-turn screw configurations may be used to releasably lock the first and second plates  212 ,  214  together. 
     Referring to  FIGS. 14-16 , first and second joining portions  230 ,  232  may each have a series of transverse ratchet teeth  262 ,  264  defined thereon that cooperate to lock first and second plates  212 ,  214  together. The position of second joining portion  232  may be varied incrementally with respect to first joining portion  232 , provided that release member  216  is maintained within the boundaries of elongated slot  234 , which position may be locked by the cooperation of transverse ratchet teeth  262 ,  264 , which are pressed together by release member  216 . Thus, first and second plates  212 ,  214  can be locked together at varying distances apart from one another, allowing sternum fixation device  210  to be used with sternums of different sizes. 
       FIG. 18  shows a variation of sternum fixation device  210  where release member  216  is a U-shaped pin that is received in sets of substantially aligned longitudinal bores  234  (hidden),  236  and  238  (hidden),  240  disposed in inter-digitated first and second joining portions  230 ,  232 , as described above with respect to sternum fixation device  10 . One of ordinary skill in the art will appreciate that all the configurations of the release member  16  and the first and second joining portions  30 ,  32 , as described above with respect to sternum fixation device  10 , may also be used with sternum fixation device  210 . 
     Referring back to  FIG. 15 , first attachment member  222  is shown as a pair of laterally spaced-apart, generally curved hooks for engaging the intercostal spaces of a patient&#39;s sternum. First attachment member  222  may have C-shaped, J-shaped, L-shaped, or any other shaped hooks known in the art to be suitable for engaging the intercostal spaces of a sternum. One of ordinary skill in the art will appreciate that first attachment member  222  may have any number of hooks configured for engaging any respective number of intercostal spaces. In addition, first attachment member  222  can be made having various different dimensions, such as the size of the hooks and the lateral spacing therebetween, to accommodate sternums having different sizes and proportions.  FIG. 16  shows a variation of first attachment member  222  where the number of hooks  270  and the lateral distance between them is adjustable. First plate  212  has a longitudinal array of mounting apertures  272  defined therein for receiving mounting bolts  274  that secure the hooks to the first plate  212 , thus allowing the mounting position of the hooks to be adapted to conform to varying distances between intercostal spaces. Mounting bolts  274  are preferably recessed into mounting apertures  272 , for example, by countersinking or counterboring the apertures  272 , to reduce the amount of material protruding above upper surface  218 . Referring to  FIGS. 17 and 18 , the first attachment member  222  can have pointed, self-dissecting tip portions  276  that aid in inserting the hooks through soft tissue and muscle that is found in the intercostal spaces. First attachment member  222  can additionally have apertures  278  (shown in  FIG. 17 ) defined therein for receiving pins that may be used to stabilize attachment member  222  in the intercostal space. 
     While it is apparent that the illustrative embodiments of the invention herein disclosed fulfil the objectives stated above, it will be appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. For example, as shown in  FIG. 17 , sternum fixation device  210  may further include third attachment member  280 , a threaded hole for receiving a threaded head portion  244  of a bone fastener or screw  242 , and fourth attachment member  282 , an intercostal space hook. One of ordinary skill in the art will appreciate that sternum fixation device  210  may include any number and combination of attachment members, such as hooks and bone screws, and release members, such as pins, U-shaped pins, and cam members. Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments which come within the spirit and scope of the present invention.