fig1 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 fig1 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 . 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 fig2 , 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 . 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 . fig3 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 . fig4 a 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 ( fig4 a ). 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 ( fig4 b ). 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 . rotation is approximately 90 degrees and can occur by applying tension to the trailing line 28 ( fig4 c ). 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 ( fig4 d ). 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 . 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 %. 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 fig1 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 fig5 and 6 the flipping distance was reduced to 2 mm . 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 . fig5 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 fig6 ). the two - piece construction eases assembly . the fixation device 10 of fig1 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 . 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 . 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 . fig7 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 fig8 a to 8d like parts have like part numbers with a subscript corresponding the figure number . in fig8 a 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 fig8 a to 8d ) and hold it in place . fig8 b 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 . fig8 c works similarly , but the slots 112 c have a sharp inward transition 118 at the midpoint 116 c . in fig8 d 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 . 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 . 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 .