Abstract:
A buckle useful for cortical fixation has a graft retention loop slidably affixed thereto for movement from a first position adjacent a first end of the buckle to a second position at about the midpoint of the buckle. The buckle, with a graft over the loop, is drawn up lengthwise through a bone tunnel through a tibia and then flipped sideways to rest against the surface of the bone with the loop and graft depending back into the tunnel. The sliding attachment of the loop permits flipping of the buckle minimizes the flipping distance, which is the excess amount of the loop which must be pulled free of the tunnel to allow the buckle to be flipped sideways.

Description:
BACKGROUND 
       [0001]    This application relates to graft fixation, and more particularly to graft tissue fixation employing flipping-type fixation devices. 
         [0002]    Flipping-type fixation devices, such as disclosed in U.S. Pat. Nos. 5,306,301 and 5,645,588 incorporated herein by reference, allow a simple procedure to be used for fixing tissue such as in an Anterior Cruciate Ligament (ACL) reconstruction. Such device comprises an elongated bar having a central suture loop depending therefrom. A tunnel is prepared in the femur from a position at or near the patellar surface up through a portion of the femur and exiting through the side of the femur at a superior location. A graft is looped over the loop attached to the elongated bar. The bar is able to pass in one direction up through the tunnel. After exiting the superior end of the tunnel, the bar is flipped approximately 90 degrees so that it will not pass back through the tunnel and is positioned against the femur with the loop and graft hanging down into the tunnel therefrom. Tension on the graft keeps the bar in place against the bone surface. 
         [0003]    To initiate the flipping, however, the bar must be passed completely outside of the tunnel. When it is then placed down against the bone the suture loop falls back into the tunnel by the amount that it was pulled free of the tunnel, about 50% of the length of the bar. This decreases the contact of the graft with the bone in the tunnel. Also, longer loop lengths have the potential to increase motion of the graft within the tunnel, thus potentially slowing the healing process in which the graft attaches to the bone. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention overcomes these and other limitations of the prior art in a simple and elegant design. 
         [0005]    A method according to the present invention provides for fixing a graft ligament into a bone tunnel. The method comprises the steps of: a) forming a graft construct by draping the graft ligament over a loop depending from a fixation buckle, the buckle having a length along a longitudinal axis which is at least twice a maximum lateral dimension, the tunnel having an exit where it exits the bone and the length also being larger than a maximum width of exit; b) pulling the graft construct up through the bone tunnel with the buckle traveling lengthwise through the tunnel with the loop depending from the buckle from a first position located below a midpoint of the length of the buckle; c) pulling the buckle out of the tunnel through the exit and rotating it so that its longitudinal axis is sufficiently out of alignment with the tunnel to prevent the buckle from passing back into the tunnel; d) moving the loop from the first position to a second position along the buckle, the second position being at about the midpoint of the buckle; and e) engaging the buckle against the bone at the exit with the loop depending into the tunnel from the second position on the buckle. 
         [0006]    Preferably, the loop is received through at least one elongated slot on the buckle and moves from the first position to the second position by sliding along the at least one elongated slot. Preferably, the at least one slot has an end at about the midpoint of the buckle and the loop is engages with the end of the slot as it is moved into the second position. 
         [0007]    Preferably, the loop slides along a surface of the buckle between the first position and the second position and that surface slopes downwardly as it approaches the midpoint of the buckle. 
         [0008]    After step e) the loop depends into the tunnel by a first length and preferably, during step c) the loop depends into the tunnel by a second length that is less than the first length. While performing of step c) the second length is never less than the first length by more than 3.5 mm. 
         [0009]    In one aspect of the invention, the graft ligament is an ACL replacement and the bone tunnel is formed through a tibia. 
         [0010]    A graft retention device according to the present invention comprises an elongated body having a first end and a second end and a midpoint therebetween. A graft retention loop slidably affixes to the elongated body for movement along the elongated body from a first position adjacent the first end and a second position at about the midpoint. A stop on the elongated body prevents the loop from sliding past the second position toward the second end. 
         [0011]    In one aspect of the invention, a leading line releasably attaches to the elongated body at its second end. Further, a trailing line may be releasably attached to the elongated body at its first end. 
         [0012]    Preferably, the elongated body comprises a pair of elongated slots extending from adjacent the first end to about the midpoint and which define a tang therebetween, the loop passing through the slots and over the tang. In one aspect of the invention, the elongated bar has an upper surface, the tang has an upper surface and the upper surface of the tang slopes downwardly away from the upper surface of the buckle as the tang approaches the midpoint. 
         [0013]    Preferably, the elongated body and the loop are sterile and formed from biocompatible implantable materials. 
         [0014]    Preferably, the second position is located within a central 25% of a length of the elongated bar between its first end and its second end. 
         [0015]    In one aspect of the invention, a retainer on the elongated body discourages movement of the loop out of the second position. The retainer can comprise one or more barbs. 
         [0016]    A graft retention device according to the present invention comprises an elongated body having a first end and a second end. A graft retention loop slidably affixes to the elongated body for movement along the elongated body from a first position adjacent the first end and a second position at about the midpoint. The loop depends downwardly from the elongated body and is from the first position to the second position along a sliding surface. The sliding surface is lower at the second position than at the first position whereby to encourage the loop to move toward the second position. 
         [0017]    In one aspect of the invention, a leading line releasably attaches to the elongated body at its second end. A trailing line can releasably attach to the elongated body at its first end. 
         [0018]    Preferably, the elongated body and the loop are sterile and formed from biocompatible implantable materials. 
         [0019]    Preferably, the elongated body comprises a pair of elongated slots extending from adjacent the first end to about the midpoint and which define a tang therebetween, the loop passing through the slots and over the tang, the tang forming the sliding surface. 
         [0020]    In one aspect of the invention, a retainer on the elongated body discourages movement of the loop out of the second position. The retainer can comprise one or more barbs. The retainer can comprise a narrowing of the tang between the slots at the midpoint. The retainer can comprise a hollow in the upper surface of the tang defined at least in part by a transition which transition restricts sliding of the loop out of the hollow. 
         [0021]    Preferably, the graft retention device has a flipping distance of no greater than 3.5 mm and more preferably no greater than 2 mm. Preferably, the graft retention device has a flipping distance no greater than ⅓ of a maximum length of the body and more preferably no greater than ¼ of the maximum length. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a perspective view of a fixation device buckle according to the present invention; 
           [0023]      FIG. 2  is a side elevation view of a fixation device according to the present invention employing the buckle of  FIG. 1 ; 
           [0024]      FIG. 3  is a side elevation view in cross-section of a ACL repair in a knee employing the fixation device of  FIG. 2 ; 
           [0025]      FIGS. 4A to 4D  are side elevation views in cross-section of an ACL repair procedure employing the fixation device of  FIG. 2 ; and 
           [0026]      FIG. 5  is a top perspective view of an alternative embodiment of a buckle according to the present invention, showing the loop seated at the midpoint; 
           [0027]      FIG. 6  is an underside perspective view of the buckle of  FIG. 5 , shown without the loop attached; 
           [0028]      FIG. 7  is a side elevation view of an alternative embodiment of a buckle according to the present invention, having a hollow for capturing the loop at the midpoint; 
           [0029]      FIG. 8A  is a top plan view of an alternative embodiment of a buckle according to the present invention having slots which narrow toward the midpoint of the buckle; 
           [0030]      FIG. 8B  is a top plan view of an alternative embodiment of a buckle according to the present invention having slots which get closer together toward the midpoint of the buckle; 
           [0031]      FIG. 8C  is a top plan view of an alternative embodiment of a buckle according to the present invention having slots which turn inwardly towards each other at the midpoint of the buckle; and 
           [0032]      FIG. 8D  is a top plan view of an alternative embodiment of a buckle according to the present invention having a single slot. 
       
    
    
     DETAILED DESCRIPTION 
       [0033]      FIGS. 1 and 2  show an illustrative embodiment of a graft fixation device  10  according to the present invention. It comprises an elongated bar or buckle  12  having a graft receiving loop  14  depending therefrom. The buckle  12  comprises a first end  16  and second end  18 , and an upper surface  20  and lower surface  22 . (The terms “upper” and “lower” and related terms such as “upwards” are used herein with reference to the surfaces of the buckle  12  just defined, with the lower surface  22  being that surface which will face a bone—not shown in FIGS.  1  and  2 —when the buckle  12  is employed.) First and second holes  24  and  26  penetrate the buckle  12  at the first and second ends  16  and  18  respectively, passing from the upper surface  20  to the lower surface  22 . The first hole  24  receives a trailing line  28  and the second hole  26  a leading line  30 . The trailing line  28  and leading line  30  are preferably formed of ORTHOCORD #2 suture available from Ethicon, Inc. of Somerville, N.J. The leading line  30  may experience higher stress than the trailing line  28  while placing the fixation device  10  as will become apparent as the placement procedure is described. The second hole  26  is shown slightly larger than the first hole  24  (although they could be made the same size) and the leading line  30  can be a higher strength suture such as with a larger diameter than the trailing line  28 . This difference can be used to differentiate the leading line  30  and trailing line  28 . They can also be differentiated in some other fashion such as via varying colors or visual patterns. 
         [0034]    A pair of longitudinal slots  32  penetrate the buckle  12  from the upper surface  20  to the lower surface  22  and extend from a first end  34  adjacent the first hole  24  to a second end  36  at a midpoint  38  of the buckle  12 . The slots  32  define a retention tang  40  therebetween. An upper surface  42  of the retention tang slopes downwardly from the first end  34  of the slots  32  to the second end  36  to encourage the loop  14  to migrate toward the midpoint  38  at implantation. The loop  14  is threaded through the slots  32  and slides along the retention tang upper surface  42 . Preferably, the vertical dimension of the retention tang  40 , as viewed in  FIG. 2 , is constant from the first end  34  to second end  36  to enhance its strength and rigidity, with the retention tang  40  thus depending slightly below the buckle lower surface  22  at the midpoint  38 . The tang  40  is shown with a slope below the upper surface  20  of 13.6 degrees but could be anywhere from zero to about 45 degrees. It could also vary in slope, such as getting progressively steeper toward the midpoint  38  to encourage the loop to stay at the midpoint  38  after implantation. 
         [0035]    Preferably, for an ACL repair the buckle  12  is approximately 12 mm long, 4 mm wide and 1.5 to 2.5 mm thick, with the thickest portion being the midpoint  38  where the tang  40  depends. The tang  40  is approximately 1.5 mm thick. The buckle  12  is preferably formed of a biocompatible material such as 6A1-4V Ti alloy. Preferably, the loop  14  is woven of ultra-high molecular weight polyethylene, such as DYNEEMA, and polyester. The material of the loop  14  is preferably about 2 mm in diameter, preferably being in a range of from #2-0 up through about 4 mm, and the loop  14  is preferably between about 8 mm and 60 mm long. The loop  14  can be woven onto the buckle  12  to form a continuous loop without knots. U.S. Pat. No. 6,352,603 to Bryant, incorporated herein by reference, illustrates one method for achieving such a construct. 
         [0036]      FIG. 3  illustrates a graft construct  44 , comprising a tissue graft  46  looped over the loop  14  of the fixation device  10 , in place in a patient&#39;s leg  48 . A tunnel  50  in the leg&#39;s femur  52  comprises a larger diameter inferior portion or socket  54  sized to accommodate the graft  46  and a smaller diameter superior portion or passing channel  56  sized to accept the buckle  12  in a lengthwise orientation. The buckle  12  sits against the femur  52  in a sideways orientation with the loop  14  depending down through the passing channel  56  and into the socket  54  in which is placed the graft  46 . An opposite end of the graft  46  is placed into a tibial tunnel  58  in the leg&#39;s tibia  60  and held in place with an anchor  62  such as the INTRAFIX® anchor available from DePuy Mitek Inc. of Raynham, Mass. 
         [0037]      FIGS. 4A to 4D  illustrate the process of passing the buckle  12  up through the tunnel  50 . At the start of the procedure, the graft tissue  46  is threaded through the loop  14 . A longitudinal axis  60  of the buckle  12  is oriented coaxially with a longitudinal axis  62  of the tunnel  50 , with the loop  14  depending from the first end  34  of the slots  32  ( FIG. 4A ). Tension on the leading line  30  pulls the second end  18  of the buckle  12  upwardly out of the tunnel  50  until the first end  16  is free of the tunnel ( FIG. 4B ). Preferably, the loop  14  and the passing channel  56  are dimensioned so that if the graft construct  44  is pulled up until the graft tissue  46  abuts the end of the socket  54  the first end  16  of the buckle  12  has just cleared the end of the tunnel  50  thus providing tactile feedback to the surgeon that the buckle  12  is properly positioned to be rotated. 
         [0038]    Rotation is approximately 90 degrees and can occur by applying tension to the trailing line  28  ( FIG. 4C ). The final orientation depends upon the angle at which the tunnel  50  penetrates the femur  52 . As the buckle  12  is rotated, opposing tension supplied by the graft tissue  46  tends to cause the loop  14  to slide along the retention tang  40  leaving it depending down into the tunnel  50  from the midpoint  38  of the buckle  12 . This occurs with a distinct snapping motion that can be felt by the surgeon through the trailing line  28  to provide tactile feedback that the migration has occurred properly. The trailing line  28  and leading line  30  are then removed and tension from the graft tissue  46  pulls the buckle  12  lower surface  22  firmly against the femur  52  ( FIG. 4D ). The crosswise orientation of the buckle  12  versus the tunnel  50  and the loop  14  depending from the midpoint  38  of the buckle  12  prevent the buckle from migrating back into the tunnel  50  thus providing secure fixation of the graft tissue  46 . 
         [0039]    The slope of the tang upper surface  42  assists in urging the loop  14  toward the midpoint  38 . Its angle on the femur  52  versus the tunnel  50  also tends to pull the loop  14  across the buckle  12  to sit at the slot second ends  36  and the buckle  12 . Locating the ends  36  at the midpoint  38  thus helps keep the loop  14  seated at the midpoint  38 . In terms of final seating of the loop  14  the term “midpoint” can be broadly construed. Seating at the exact middle of the buckle  12  provides an equal amount of buckle to each side thereof to minimize any chance that the buckle  12  can slip along the bone in such a fashion that and end thereof could fall back into the tunnel  50 . In practical terms the loop  14  can be seated in other locations yet still be safely situated to prevent the buckle  12  from falling back into the tunnel  50 . Preferably, the loop  14  is seated somewhere in the middle 50% of the length of the buckle  12  and more preferably within the middle 25%. 
       EXAMPLE 1 
       [0040]    The gap which exists between the graft  46  and the end of the socket  54  can be reduced by the present invention. To evaluate this advantage similarly sized buckles were compared. Buckle A was a commercially available product similar to that described in the &#39;301 Patent and Buckle B is the buckle  12  depicted in  FIG. 1  herein. Each was 12.2 mm long, 4.0 mm wide, and 1.4 mm thick, with Buckle B being 2.5 mm thick at its midpoint due to the bottom of the tang depending below the lower surface. The buckles were threaded with loops of similar thickness and construction to each other; with the tests performed using loop lengths of between 15 and 30 mm. Caliper measurements were performed of the loop from the buckle to the furthest inside portion of the loop in two configurations: 1) the loop stretched downwardly from and perpendicular to the buckle as representative of the final fixation position, and 2) the loop stretched from the trailing end of the buckle and parallel to the buckle as representative of the position as the buckle is being pulled up through the tunnel immediately prior to being flipped. The differences in these measurements represent the flipping distance and for Buckle A were 6.6 mm. For Buckle B they were 3.2 mm. In a subsequent test employing a buckle design similar to that of  FIGS. 5 and 6  the flipping distance was reduced to 2 mm. 
         [0041]    The flipping distance is representative of the gap between the graft  46  and the end of the socket  54 . Ideally this gap is zero and the graft  46  extends all the way to the end of the socket  54 . Buckle B substantially reduced the flipping distance. 
         [0042]      FIGS. 5 and 6  illustrate another fixation buckle  60  according to the present invention that incorporates a similar shape and function to the buckle  12 , but further comprises a two-piece construction comprising an outer frame  62  and an insert  64 . The frame  62  has a first flange  65  at a first end  66  and a second flange  68  at a second end  70 . The insert  64  fits within the frame  62  and has rabbets  71  that mate with the flanges  65  and  68 . The insert  64  incorporates a first hole  72  at a first end  74  and a second hole  76  at a second end  78  plus a retention tang  80 . A sidewall  82  of the frame  62  can be slightly thinner adjacent the retention tang  80  to accommodate a loop  83  (not shown in  FIG. 6 ). 
         [0043]    The two-piece construction eases assembly. The fixation device  10  of  FIG. 1  is preferably formed by weaving the loop  14  around the retention tang  40  to form the loop  14 . This potentially complicates the weaving process. With the buckle  60 , the loop  83  can be woven separately, and then threaded over the retention tang  80  prior to fitting the insert  64  into the frame  62 . The insert  64  can be held in the frame  62  by a friction fit, an interference fit, by welding or other appropriate means. The interaction between the flanges  65  and  68  and the insert  62  provides structural integrity against forces applied downwardly upon the retention tang  80 . 
         [0044]    Refinements and variations to the buckle  12 , and as well to the buckle  60 , could include slots  32  which extend to both sides such that the second side mirrors the first, and the retention tang  40  sloping down from both ends toward the center. This would allow a surgeon to pull the buckle  12  up through the tunnel  50  by either end. Also, the upper surface  42  of the retention tang  40  could be rounded to provide a better surface for the loop  14  to ride over and lessen chafing of the loop  14 . 
         [0045]    Provision can be made to discourage the loop  14  from moving away from the midpoint  38 , such as by providing barbs (not shown) along the upper surface  42  or other areas of the buckle  12  where they may engage the loop  14  as it slides along the slots  32 .  FIG. 7  shows a buckle  100  having a tang  102  will a pronounced dip  104  to capture and retain the loop  14  at a midpoint  106 . In  FIGS. 8A to 8D  like parts have like part numbers with a subscript corresponding the figure number. In  FIG. 8A  a buckle  110   a  has a pair of slots  112   a  which define a tang  114   a  sloping downwardly toward and terminating at a midpoint  116   a.  The slots  112   a  get narrower toward the midpoint  116   a  so as to pinch the loop  14  (not shown in  FIGS. 8A to 8D ) and hold it in place.  FIG. 8B  illustrates a buckle  110   b  in which the slots  112   b  get closer together towards the midpoint  116   b.  The tension on the loop  14  would encourage the loop  14  to close laterally and stay at the midpoint  116   b.  A series of barbs  117  are also shown which are intended to discourage the loop  14  to move away from the midpoint  116   b.    FIG. 8C  works similarly, but the slots  112   c  have a sharp inward transition  118  at the midpoint  116   c.  In  FIG. 8D  rather than a pair of slots, there is one slot  112   d  and an aperture  120  through which the loop  14  would thread and thus only one portion of the loop  14  would slide along a surface  122  which slopes downwardly toward the midpoint  116   d  of the buckle  110   d.    
         [0046]    The configuration of slots  32  forming the tang  40  for attaching the loop  14  to the buckle and allowing its movement is preferred due to its simplicity, strength and economy of material in construction. However, other attachments techniques which allow movement of the loop from a position near the first end of the buckle  12  to a position near the midpoint of the buckle  12  are contemplated and within the scope of the present invention. The buckle is particularly suited to ACL repair, but can be useful in other repairs such as for example reattachment of a biceps brachii tendon. 
         [0047]    The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.