Abstract:
A graft fixation system for fixing graft material in a bone tunnel includes an expandable fixation member having a graft receiving eyelet disposed proximate its distal end, opposed bone engaging elements disposed about its periphery, and an expansion plug receiving opening defined in its proximal end. The system also includes an expansion plug having a diameter greater than the diameter of the expansion plug receiving opening so that forceble insertion of the expansion plug into the expansion plug receiving opening causes an expansion of the expandable fixation member driving the opposed bone engaging elements apart so as to fix the bone engaging elements, as well as the graft material, in a bone tunnel.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 11/299,493, filed on Dec. 9, 2005, now U.S. Pat. No. 7,901,456, issued Mar. 8, 2011, which is a continuation of U.S. patent application Ser. No. 11/098,199, filed on Apr. 4, 2005, now U.S. Pat. No. 7,008,451, issued Mar. 7, 2006, which is a continuation of U.S. patent application Ser. No. 09/966,737, filed on Sep. 28, 2001, now U.S. Pat. No. 6,887,271, issued May 3, 2005. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to systems and methods for locking and integrating soft tissue with bone. More specifically, systems and methods for use in conjunction with ligament replacement surgery are described. 
     BACKGROUND OF THE INVENTION 
     The complete or partial detachment of ligaments, tendons or other soft tissues (hereinafter “ligamentary material”) from the bones with which they are associated are commonplace, particularly among athletes. Such injuries usually result from excessive stress being applied on these tissues. Some degree of tissue detachment may occur, for instance, as the result of an accident, overexertion during a work-related activity, stress during the course of an athletic event, or in conjunction with numerous other situations and activities. If, however, ligamentary material is completely detached from its associated bone(s) or is severed, partial or permanent disability may result. 
     Fortunately, there are numerous surgical techniques known and used in the art for reattaching detached tissues and/or completely replacing ligamentary material. One such technique involves the use of “traditional” fasteners (e.g. metal staples, cancellous bone screws.) Such fasteners have also been used to attach tendon or ligament substitutes (often formed of autogenous tissue harvested from elsewhere in the body, collectively referred to herein as “grafts” or “graft material”) to the desired bone(s). A common surgery involves replacing or repairing the anterior cruciate ligament (ACL) in a human knee. Bone tunnels are appropriately aligned and formed in both the proximal tibia and the distal femur during the course of this surgery. Graft material is somehow rigidly coupled, usually with bone blocks to be inserted into these tunnels, to fix the material in a proper position for long term use in the body. 
     Such ligament fixation schemes have not been entirely successful. For example, rigid attachment using “traditional” attachment devices such as staples, sutures and screws often cannot be maintained even under normal tensile loads. Also, the use of sharp screws to create a locking interference fit between a bone plug/block and a bone tunnel may be problematic. For instance, there is always the possibility of damaging the ligament during insertion of the screw. In addition, it may be difficult to maintain the desired tension on the graft material during insertion of the screw. Alternative, non-rigid fixation schemes (such as suspending a ligament graft from a suture button) also have drawbacks. Because the graft structure is not, in such schemes, rigidly fixed within the bone tunnels, movement of the graft structure may disrupt the healing process. It is known that intimate contact between the graft material and the walls of the bone tunnels aids in ensuring an effective, efficient healing process. 
     Another potential problem may arise even where the graft material appears to be successfully fixed within the bone tunnel. Bone tunnels are usually drilled for a considerable length into the femur for fixation of the graft material in ACL replacement procedures. Where exactly within the tunnel the graft is fixed often depends on the manner of fixation and tensioning of the graft material, but often the site for fixation is chosen as the place where the fixation device best allows fixing. Where the fixation takes place inside the bone tunnel apart from the bone tunnel edge at the distal end of the femur, the graft material that extends from the fixation point to the edge of the bone tunnel often moves or slides within this remaining portion of the tunnel. This phenomenon is known to some surgeons as the “windshield wiper” effect. As noted above, movement tends to prevent healing and fixation of the soft tissue to bone, so where the windshield wiper effect occurs, the portion of the graft that moves when the patient uses the reconstructed joint may never heal completely in the region near the edge of the bone tunnel. This potential problem defeats the goal of most surgeons which is to have the graft material fix as close as possible to its natural fixation point before being damaged by injury or disease. This natural fixation point is generally at the edge of the bone tunnel, where the graft will not fix if the windshield wiper effect is present. 
     Accordingly, there is a need for ligament graft fixation devices that reliably provide fixation of graft material in the region closest to the natural fixation point of the ligamentary material being replaced. 
     SUMMARY OF THE INVENTION 
     The present invention provides a ligament graft fixation system for fixing ligament graft material within a bone tunnel in a way that better approximates the natural fixation point of the ligamentary material that is being replaced. The system of the invention includes an expandable fixation member having a graft receiving eyelet disposed proximate its distal end, opposed bone engaging elements disposed about its periphery, and an expansion plug receiving opening defined in its proximal end. The system also includes an expansion plug having a diameter greater than the diameter of the expansion plug receiving opening so that forcible insertion of the expansion plug into the expansion plug receiving opening causes an expansion of the expandable fixation member to drive the opposed bone engaging elements apart so as to fix the bone engaging elements, as well as the graft material, in a bone tunnel. The fixation system of the invention allows for fixation at the proximal end of the fixation member, which can be placed proximate to the edge of the bone tunnel to fix the graft as close to the anatomically correct position as desired. 
     Specific embodiments of the fixation system of the invention include those having graft receiving grooves extending distally from the eyelet, including embodiments where the grooves are asymmetrically placed to allow anterior or posterior fixation at the surgeon&#39;s discretion. Expansion slots can also be provided to specifically direct the expansion of the fixation member so that the expansion can not only engage the bone engaging elements with the wall of the bone tunnel, but also urge the graft material into closer association with the bone tunnel wall. 
     In still other embodiments, the graft receiving eyelet can be provided on a separate tip that includes a proximal expansion plug that can forcibly mate with a distal plug receiving opening on the fixation member. In this embodiment, proximal and distal expansion slots can be provided, and in some cases, the proximal and distal expansion slots can encourage expansion in different directions. For example, one or more distal slots can be employed to encourage expansion in a direction that will drive the opposed bone engaging elements apart so as to fix the fixation member to bone, while the one or more proximal slots can encourage expansion in a direction that will urge the graft material into closer contact with the bone tunnel walls. In this embodiment, it may be desirable to size the plugs and plug receiving openings to allow the proximal plug to enter the distal plug receiving opening first upon compressing the system to forcibly engage the plugs so that the graft material does not bunch up upon fixation. This specific embodiment provides still more proximal fixation which can be provided near the edge of a bone tunnel as desired. 
     Insertion and activation elements can also be provided. In any of the previously mentioned embodiments, a pull rod can extend through the expansion plug and engage the distal-most element of the system while a cannulated push tube can slide over the pull rod to engage the expansion plug. Relative movement between the pull rod and the push tube can then forcibly engage the elements. 
     In a method of the invention, a bone tunnel can first be formed, then a fixation system as described above can be loaded with graft material through the eyelet, and the fixation system and graft material can be inserted into the bone tunnel. Insertion into the bone tunnel can stop when the proximal end of the fixation member is substantially even with or slightly inside the edge of the bone tunnel. The fixation system can then be actuated to fix the fixation member and the graft proximate to the edge of the bone tunnel in the desired anatomically correct position. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a side view of a graft fixation system of the invention loaded with graft material and mounted on an insertion member; 
         FIGS. 2 ,  2 A and  2 B are perspective, end and cross-sectional views of an expanding fixation member of the graft fixation system of  FIG. 1 ; 
         FIG. 3  is an exploded view of the graft fixation system of  FIG. 1  including an expanding fixation member, an expansion plug and a pull rod; 
         FIG. 4  is a side view of the graft fixation system of  FIG. 1  without graft material; 
         FIG. 5  is a side view of a graft fixation system of the invention having a separate distal tip; 
         FIG. 6  is a plan view of graft fixation system of  FIG. 5 ; and 
         FIG. 7  is a schematic view of an actuation device suitable for use with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a device, system, and method useful for fixing soft tissue graft material within a bone tunnel to replace damaged ligamentary material and restore function to the portion of a patient&#39;s body in which the damaged ligamentary material was located.  FIG. 1  provides an illustration of one such system of the invention having a fixation member  20 , an expansion plug  21  positioned at a proximal end  110  of the fixation member, and a graft material holding element in the form of an eyelet  24  located proximate to a distal end  112  of the fixation member. Graft material  200  can be passed through eyelet  24  so that two ends  201  of the graft trail fixation member  20  proximally. An insertion element  114  mates with fixation member  20  and expansion plug  21  and extends proximally. In use, a surgeon inserts fixation member  20  along with graft material  200  into a prepared bone tunnel using insertion element  114  until the graft and fixation member are in the desired position for graft fixation within the tunnel. Insertion element  114  can then be actuated or manipulated by the surgeon to force expansion plug  21  distally into fixation member  20  to cause the fixation member to expand and thereby fix the graft material to the interior of the bone tunnel. Further details of this and other embodiments of the invention are provided by reference to further FIGS. below. 
     As can be seen in  FIGS. 2 ,  2 A and  2 B (which illustrate a side view, a proximal end view, and a lengthwise cross-section, respectively, of fixation member  20 ), fixation member  20  includes cut out passages or grooves  23  extending proximally along the fixation member from each of the two opposed sides of eyelet  24 . In general, fixation member  20  will be sized to fit closely into a bone tunnel of predetermined size. Typical grafts used to replace ligamentary material are compressible, and grooves  23  will be sized so that the graft material will be snugly pressed between the walls of the bone tunnel and grooves  23  upon insertion of the fixation system into the tunnel. 
     Fixation member  20  also includes a proximal expansion plug receiving opening  22  which extends distally within the body of the fixation member. Opening  22  is threaded in the illustrated embodiment in two regions. A first threaded region  120 , close to proximal end  110  of fixation member  20 , is threaded so as to engage expansion plug  21  when the plug is forced into the fixation member and lock the plug in place. A second threaded region  122 , distal to region  120 , is threaded to engage a pull rod  1002  (further described with respect to  FIG. 3  below) that may be provided as part of insertion element  114 . 
     On its external surfaces, fixation member  20  has a rounded or bullet shaped distal end to aid the surgeon in directing the fixation member into a bone tunnel. In addition, about its outer circumference (and generally not within grooves  23 ), fixation member  20  includes a series of opposed bone engaging elements  11 ,  12 . As illustrated, bone engaging elements  11 ,  12  are fins that are angled proximally so that while they can slide into a bone tunnel relatively easily, it will be more difficult to pull fixation member  20  from a bone tunnel after insertion as the fins will dig into the walls of the bone tunnel (especially after expansion of the fixation element). While bone engaging elements  11 ,  12  in this illustrated embodiment are angled fins, a person of ordinary skill in the art will recognize that other bone engaging elements known in the art, including for example asymmetric wedges, nitinol arcs, or mechanical elements that spring into cancellous bone, may be used as bone engaging elements on fixation member  20  within the spirit of the invention. 
     One or more expansion slots  124  are also provided (two such slots  124  are illustrated in  FIG. 2 ) on fixation member  20  beginning at the proximal end  110  of the fixation member and extending distally through threaded region  120 , generally extending at least as far as expansion plug  21  will be inserted into the fixation member. Slots  124  preferably do not extend through the entirety of threaded region  122  to which a pull tool may be attached as such an extension of slots  124  might weaken the engagement between the pull tool and the fixation member. A person of ordinary skill in the art will recognize that the number and position of the one or more expansion slots  124  can be varied from the number (two) and positions illustrated in  FIG. 2  within the spirit of the invention to allow fixation member  20  to expand upon insertion of expansion plug  21  so as to fix graft material to a bone tunnel wall. In particular, slot or slots  124  should be placed so as to result in an expansion of fixation member  20  so that bone engaging elements  11  and  12  move in opposed directions to force the bone engaging elements into engagement contact with the bone tunnel wall to lock the fixation member in place within the bone tunnel. It may also be desirable to place the slot or slots  120  so that fixation member  20  expands so as to force graft material pressed between grooves  23  and the bone tunnel wall into even more intimate contact therewith. 
     As can be seen in  FIGS. 2 and 2A , bone engaging elements  11 ,  12  have different lengths about the circumference of fixation member  20 , with bone engaging elements  11  being larger and having a greater fixation region than bone engaging elements  12 . This difference in size results from an asymmetric placement of grooves  23 . Each of the two grooves  23  are specifically displaced in a direction toward bone engaging elements  12  as the grooves extend generally proximally from graft eyelet  24 . This asymmetry allows a surgeon to select a preferred direction for fixation of graft material within a bone tunnel. For example, for an ACL replacement surgery requiring graft fixation in a bone tunnel formed in a patient&#39;s distal femur, the surgeon, for reasons of preference or owing to a specific fixation scheme, may wish to have a more anterior or more posterior fixation of the graft material. Because graft material will be captured between grooves  23  and the walls of the bone tunnel, and because in the illustrated embodiment the grooves are asymmetrically placed, the surgeon may choose to insert the graft/fixation member system so that more of the graft material is captured against the bone tunnel in an anterior or posterior direction. 
     In addition to asymmetric sizing of bone engaging elements  11 ,  12 , asymmetric placement of grooves  23  can result in asymmetric placement of proximal opening  22 . Proximal opening  22  must be placed so that sufficient fixation member  20  material exists to provide strength for threads in threaded region  120  and particularly in threaded region  122  which may be used to securely attach fixation member  20  to a pull tool. Where grooves  23  are displaced toward bone engaging elements  12 , this requirement can best be met by placing proximal opening  22  closer to bone engaging elements  11 . 
     Turning now to  FIG. 3  (showing an exploded view) and  FIG. 4  (showing an assembled fixation assembly of the invention ready for graft placement and fixation), assembly and activation of a system of the invention will be described.  FIG. 3  illustrates a fixation member  20 , an expansion plug  21 , and a pull rod  1002  in exploded view and ready for assembly. As shown in  FIG. 3 , expansion plug  21  is larger in diameter than proximal plug receiving opening  22  of expansion member  20  so that, upon forcible insertion of expansion plug  21  into opening  22 , a forced expansion of fixation member  20  is achieved as described above. 
     Expansion plug  21  includes external threads  126  which, although larger in diameter than threads in threaded region  120  of opening  22 , are preferably of the same pitch as the threads in threaded region  120  so that when the expansion plug has been forced into the opening, threads  126  will engage threaded region  120  to lock expansion plug in place within opening  22 . While providing threads  126  and threaded region  120  as elements for locking expansion plug  21  into opening  22  may be convenient for reasons of manufacture, a person of ordinary skill in the art will recognize that a number of other locking elements could be provided such as, for example, expanding locking elements provided on one of the plug or the opening that engage complimentary recesses provided on the other of the plug or the opening, or a pin could be provided on one of the plug or the opening to fit into an L-shaped recess on the other of the plug or the opening so that following insertion and expansion, twisting of one component relative to the other would create a locking relationship that would prevent the plug from backing out of the opening. 
     Expansion plug  21  may also include a tapered distal  128  configured to ease entry of the expansion plug into opening  22 . In addition, the distal end of expansion plug  21  can include a removal tool engaging element such as female hex  25 . In the event that threaded expansion plug  21  (which is cannulated as described below) should need to be removed from fixation member  20 , a removal tool having a male hex head could be inserted through the plug cannula to engage female hex  25  to “unthread” a plug that would otherwise be locked into place. 
     In one exemplary embodiment intended for use in fixing graft material in a bone tunnel in a patient&#39;s distal femur for replacing a damaged ACL, fixation member  20  can have an overall length of approximately 0.995 inches (with bone engaging elements  11 ,  12  extending along a length of about 0.390 inches) and a diameter from bone engaging elements  11  to bone engaging elements  12  of about 0.310 inches. Expansion plug  21  can have a major diameter of approximately 0.180 inches and a minor diameter of about 0.160 inches while opening  22  can have a minor diameter of about 0.102 inches and a major diameter of about 0.113 inches. In this same exemplary embodiment, expansion plug  21  can have a length of approximately 0.375 inches while expansion slots  124  can have a length of approximately 0.450 inches. A person of ordinary skill in the art will recognize that these dimensions are provided only to give guidance as to the construction of one embodiment of the invention, and that parts described herein could have other dimensions, especially if tailored to different end uses. The component elements of the invention can be made from a variety of polymers and bio-absorbable polymers known to be useful for implantable medical devices. In one embodiment, each component is formed from Delrin. 
     Also illustrated in  FIG. 3  is pull rod  1002  which is part of insertion element  114  ( FIG. 1 ). Pull rod  1002  is sized pass through cannulated expansion plug  21  and into opening  22  in fixation element  20  where distal threads  1001  are configured to threadedly engage at least threaded portion  122  ( FIG. 2B ) within opening  22  so as to be releasably engaged to fixation member  20 . As further shown in  FIG. 4 , assembly of the fixation system to insertion element  114  involves sliding expansion plug  21  distally along pull rod  1002  until distal taper region  128  on the plug engages opening  22  on fixation element  20 , and sliding push tube  1003  over pull rod  1002  so that a distal end  1005  of the push tube abuts a proximal end of expansion plug  21 . In order to provide better surface contact between push tube  1003  and expansion plug  21 , a tapered or flared element  1004  may be provided adjacent the distal end of the push tube. So assembled, the fixation system of the invention may be actuated by providing relative movement between pull rod  1002  and push tube  1003  to force expansion plug  21  into opening  22  in fixation element  20  to thereby lock the fixation element into a bone tunnel and fix graft material to the tunnel wall. 
     In use in ACL replacement surgery, a surgeon would loop graft material  200  through eyelet  24  to result in the configuration illustrated in  FIG. 1 . The surgeon would next insert fixation element  20  (with attached graft material  200 ) into a prepared bone tunnel in the distal end of a patient&#39;s femur. Fixation element  20  is preferably inserted into the bone tunnel to such a depth that proximal end face  110  of the fixation element is substantially even with or slightly inside the edge of the bone tunnel. The system can then be actuated by holding pull rod  1002  to prevent distal movement of fixation element while pushing on push tube  1003  to force expansion plug  21  into opening  22  of fixation element  20 , thereby expanding fixation element to fix the graft within the tunnel. By fixing the graft material in this way, with the fixation element fixing the graft material right to its proximal end  110  and placing the proximal end near the edge of the bone tunnel, the graft will be fixed at or near the edge of the bone tunnel and the “windshield wiper” effect will be reduced or eliminated. 
     A further embodiment of the fixation system of the invention is illustrated in  FIGS. 5 and 6 . In this embodiment, a distal tip  54  having graft receiving eyelet  24  is not integral with fixation member  50 . Rather, tip  51  includes a curved or bullet shaped distal end  112 , eyelet  24  near the distal end, and a proximal plug  310  that engages fixation member  50 . Like expansion plug  21 , proximal plug  310  on tip  51  includes threads that are larger in diameter than a distal threaded opening  350  on fixation member  50 , but which have the same thread pitch as the threaded opening  350  so that, upon forcible insertion, proximal plug  310  will cause fixation member  50  to expand near its distal end  130  and the threads will lock the tip to the fixation member. Proximal plug  310  can also include an internal threaded region  311  to allow the tip to be fixed to pull rod  1002  so that fixation element  50  may be actuated in the same manner as fixation member  20 . 
     Like fixation member  20  of the previously described embodiment, fixation member  50  has opposed bone engaging elements  11 ,  12  and asymmetrically placed graft placement grooves  23 . Tip  51  can also define a portion of grooves  23  distally from fixation member  50  to eyelet  24 . Fixation member  50  also includes a proximal threaded opening  55  for receiving expansion plug  52  in substantially the same way that fixation member  20  receives expansion plug  21 . 
     Fixation member  50  further includes two separate pairs of expansion slots with slots  360  provided proximally to allow expansion from insertion of expansion plug  52  and expansion slots  370  provided distally to allow expansion from insertion of proximal plug  310  of tip  51 . As is apparent in the embodiment illustrated in  FIG. 6 , expansion slots  360 ,  370  are provided in different orientations to provide differing expansion of fixation member  50  from the insertion of the differing plugs  52 ,  311 , respectively. Distal expansion slots  370  are oriented to allow maximum expansion in a direction to allow bone engaging elements  11 ,  12  to expand to lock fixation member  50  to a bone tunnel. Proximal expansion slots  360  are oriented to allow maximum expansion in the general direction of grooves  23  so as to force graft material located in the grooves into tighter engagement with the bone tunnel wall near the proximal portion of the fixation element where fixation is most desired. 
     As is further clear from the embodiment illustrated in  FIG. 6 , distal threaded opening  350  can have a larger diameter that proximal threaded opening  55 . Where proximal plug  310  on tip  51  and expansion plug  52  have approximately the same diameter, this will cause proximal expansion plug  310  to enter distal threaded opening  350  before expansion plug  52  enters proximal threaded opening  55 . This can be advantageous where, as here, the distal portion of fixation member  50  expands primarily to lock bone engaging elements  11 ,  12  into the bone tunnel wall. In this way, fixation member  50  can lock within the tunnel, proximal ends  201  of graft material  200  can be pulled taught by the surgeon, and actuation can continue with expansion plug  52  expanding a proximal portion of fixation member  50  to press the graft material against the bone tunnel wall for optimal fixation. The system of  FIGS. 5 and 6  can be inserted and actuated in the same manner as the embodiment of  FIGS. 1 to 4 . 
       FIG. 7  illustrates a schematic of a delivery device or handle assembly  500  suitable for coupling to pull rod  1002  and push tube  1003  to actuate the illustrated embodiments of the present invention. Handle assembly  500  comprises a body having a handle grip  502 . A trigger  505 , having a plurality of fingers  507 , is pivotally connected to body  501 . Body  501  also comprises a bore  508  opening on the body&#39;s distal end, and a counterbore  509  opening on the body&#39;s proximal end. A shoulder  509 A is formed at the intersection of bore  508  and counterbore  509 . 
     Handle assembly  500  also comprises a hollow ram  515 . Ram  515  is sized so that it can slidably accommodate pull rod  1002  within its inner diameter and so that it can be coupled to a proximal end of push tube  1003 . Ram  515  comprises a narrower distal portion  520  terminating in a distal tip  510 , and a wider proximal portion  525  including a plurality of teeth  530 . A shoulder  535  is formed at the intersection of narrower distal portion  520  and wider proximal potion  525 . A slot  540  extends through the side wall of narrower distal portion  520 . 
     Ram  515  is mounted in body  510  so that (1) the ram&#39;s narrower distal portion  520  extends through, and protrudes from, the body&#39;s bore  508 , (2) the ram&#39;s wider proximal portion  525  is disposed in the body&#39;s counterbore  509 , and (3) the trigger&#39;s fingers  507  engage the ram&#39;s teeth  530 . As a result of this construction, moving trigger  505  will cause ram  515  to move relative to body  501 . A spring  545  is positioned in body  501 , between body shoulder  509 A and ram shoulder  535 , so as to bias ram  515  in a proximal direction. A stop pin  550  extends into counterbore  509  So as to limit proximal movement of ram  515 . 
     Handle assembly  500  also comprises a gate  555  which includes an opening  560  therein. Opening  560  defines a bottom wall  565  thereof. Gate  555  is disposed in an opening  570  formed in body  501 . A spring  575  biases gate  555  against a locking pin  580 , which extends through an oversized hole  585  formed in gate  555 . Gate  555  is disposed in body  501  so that the gate&#39;s bottom wall  565  normally protrudes, via ram slot  540 , into the interior of ram  515 ; however, pressing gate  555  downward against the power of spring  575  will permit the gate&#39;s bottom wall  565  to be removed from the interior of ram  515 . 
     In use handle assembly  500  is loaded over a proximal end of shaft pull rod  1002 , and moved proximally down the shaft until the gate&#39;s bottom wall  565  starts to engage the ribs  1008  (see  FIG. 5 ) of pull rod  1002 . As this occurs, inclined proximal surfaces of ribs  1008  will allow the handle assembly  500  to be moved distally along pull rod  1002  to the extent desired. However, by providing inclined surfaces on only the proximal sides of ribs  1008 , the geometry of the ribs can prevent handle assembly  500  from moving back proximally along the shaft, unless, gate  555  is pressed downward against the power of spring  575  so as to move the gate&#39;s bottom wall  565  out of engagement with ribs  1008 . Handle assembly  500  is moved down pull rod  1002  until the ram&#39;s distal end surface  510  engages, or substantially engages, the proximal end  1010  of push tube  1003 . Thereafter, pulling of the handle assembly&#39;s trigger  505  will cause ram  515  to move distally along pull rod  1002 , whereby push tube  1003  can drive expansion plug  21 ,  52  into fixation member  20 ,  50 , respectively, so as to fix fixation member  20 ,  50 , and thus graft material  200  in a bone tunnel. 
     The use of handle assembly  500  in conjunction with pull rod  1002  is often preferred, since it permits pull rod  1002  to be held in place while ram  515  is advanced down pull rod  1002 . More particularly, inasmuch as handle assembly  500  is releasably secured to pull rod  1002  via the engagement of handle gate  555  with pull rod ribs  1008 , handle assembly  500  can stabilize pull rod  1002  even as the handle&#39;s ram  515  is advancing down pull rod  1002 . This has been found to be advantageous in many circumstances. Further details regarding the configuration and use of handle assembly  500  may be found in co-pending application Ser. No. 09/510,770, filed Feb. 23, 2000, which is hereby incorporated by reference. 
     One of ordinary skill in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publication and references cited herein are expressly incorporated herein by reference in their entirety.