Abstract:
A system for reconstructing a ligament by fixing at least one graft ligament strand in a bone tunnel is provided. The system a retainer configured for disposition in the bone tunnel, the retainer including a crosshole for receiving a locking pin and a mounting shoulder formed about the crosshole, and a cap removably attached to the retainer for capturing the at least one graft ligament strand by compressing the at least one graft ligament strand between the cap and the retainer, wherein the cap includes at least one locking member configured to engage the mounting shoulder of the retainer to facilitate gripping of the at least one graft ligament strand between the cap and the retainer.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATIONS 
     This patent application claims benefit of: 
     (1) pending prior U.S. Provisional Patent Application Ser. No. 60/602,589, filed Aug. 18, 2004 by Paul Re for METHOD AND APPARATUS FOR RECONSTRUCTING A LIGAMENT; and 
     (2) pending prior U.S. Provisional Patent Application Ser. No. 60/688,588, filed Jun. 8, 2005 by Paul Re et al. for METHOD AND APPARATUS FOR RECONSTRUCTING A LIGAMENT. 
     The two above-identified patent applications are hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to surgical methods and apparatus in general, and more particularly to methods and apparatus for reconstructing a ligament. 
     BACKGROUND OF THE INVENTION 
     A ligament is a piece of fibrous tissue which connects one bone to another. 
     Ligaments are frequently damaged (e.g., detached or torn or ruptured, etc.) as the result of injury and/or accident. A damaged ligament can impede proper motion of a joint and cause pain. 
     Various procedures have been developed to repair or replace a damaged ligament. The specific procedures used depend on the particular ligament which is to be restored and the nature and extent of the damage. 
     One ligament which is frequently damaged as the result of injury and/or accident is the anterior cruciate ligament (ACL) of the knee. Looking now at  FIG. 1 , an ACL  5  is shown extending across the interior of the knee joint, between the top of the tibia  10  and the bottom of the femur  15 . A damaged ACL  5  can cause instability of the knee joint, further damage to other structures, and substantial pain and arthritis. 
     Numerous procedures have been developed to restore a badly damaged ACL through a graft ligament replacement. In general, these ACL replacement procedures involve drilling a bone tunnel  20  ( FIG. 2 ) through tibia  10  and up into femur  15 . Then a graft ligament  25 , consisting of a harvested or artificial ligament or tendon, is passed through the tibial portion of bone tunnel  20  (i.e., the tibial tunnel  30 ), across the interior of the joint, and up into the femoral portion of bone tunnel  20  (i.e., the femoral tunnel  35 ). Then a distal portion of graft ligament  25  is secured in femoral tunnel  35  and a proximal portion of graft ligament  25  is secured in tibial tunnel  30 . 
     There are currently a variety of ways to secure graft ligament  25  in a bone tunnel. 
     One way is to use an interference screw  40  ( FIG. 3 ), such as the Arthrex interference screw (Arthrex, Inc. of Naples, Fla.), to “directly” wedge graft ligament  25  against the sidewall of the bone tunnel. 
     Another way is to use a bearing structure and expansion screw  45  ( FIG. 4 ), such as the Mitek Intrafix system (Depuy Mitek Inc. of Norwood, Mass.), to “indirectly” wedge graft ligament  25  against the sidewall of the bone tunnel. 
     Still another way is to use a fastener device  50  ( FIG. 5 ), such as the Innovasive/Mitek Lynx system (DePuy Mitek Inc. of Norwood, Mass.), to secure graft ligament  25  in the bone tunnel. 
     Yet another way is to use an anchor  55  ( FIG. 6 ), such as the Mitek ligament anchor (DePuy Mitek Inc. of Norwood, Mass.), to suspend graft ligament  25  within the bone tunnel. 
     And another way is to use a suture suspension system  60  ( FIG. 7 ), such as the Acufex/Smith &amp; Nephew Endobutton system (Smith &amp; Nephew, Inc. of Andover, Mass.), to suspend graft ligament  25  in a bone tunnel. 
     And still another way is to use a cross-pinning system  65  ( FIG. 8 ), such as the Arthrex cross-pinning system (Arthrex, Inc. of Naples, Fla.), to suspend graft ligament  25  in the bone tunnel. 
     And yet another way is to pass graft ligament  25  completely through bone tunnel  20  and affix the graft ligament to the outside of the bone with a screw and washer arrangement  70  ( FIGS. 3 ,  7  and  9 ) or a staple (not shown). 
     As noted above, the ACL reconstruction procedure generally involves securing a distal portion of graft ligament  25  in femoral tunnel  35 , and securing a proximal portion of graft ligament  25  in tibial tunnel  30 . Some of the aforementioned ligament reconstruction systems may be effectively and conveniently used in both femoral and tibial fixation, e.g., the Arthrex interference screw. Others of the aforementioned reconstruction systems are generally more appropriate for use in one or the other of the fixations, e.g., the Innovasive/Mitek Lynx system is generally more applicable for femoral fixation, and the screw and washer arrangement is generally more applicable for tibial fixation. 
     In addition to the foregoing, some of the aforementioned reconstruction systems utilize a graft ligament which is harvested so as to include a portion of bone block, e.g., a patellar tendon including a portion of the patella. Others of the aforementioned reconstruction systems utilize a graft ligament which is harvested so as to consist entirely of soft tissue, e.g., a harvested hamstring tendon. 
     In practice, it is generally preferable to harvest graft ligaments consisting entirely of soft tissue, e.g., a hamstring tendon, since this is less painful for the patient and involves less trauma to the donor site. However, graft ligaments consisting entirely of soft tissue are generally more difficult to secure to the host bone than those comprising a bone block, since the soft tissue is physically less rigid and more pliable (e.g., soft and relatively slippery) and the soft tissue tends to be biologically more fragile. 
     SUMMARY OF THE INVENTION 
     The present invention provides a new and improved method and apparatus for securing a graft ligament to a host bone. Significantly, the system may be used for both femoral and tibial fixation, and the system may be used where the graft ligament is formed entirely out of soft tissue (e.g., where the graft ligament comprises a harvested hamstring tendon). 
     More particularly, the present invention comprises the provision and use of a novel retainer which is slidably advanced to a desired fixation position within a bone tunnel, fixed in position within the bone tunnel (preferably by wedging and/or pinning) while applying a lateral force against the graft ligament so as to compressively hold the graft ligament against the sidewall of the bone tunnel, and which then, optionally, has the graft ligament secured thereto with a cap, whereby to secure the graft ligament to the retainer and hence additionally to the host bone. 
     The present invention also comprises the provision and use of a novel retainer which is slidably advanced to a desired fixation position within a bone tunnel so as to apply a lateral force against the graft ligament so as to compressively hold the graft ligament against the sidewall of the bone tunnel, and which is then locked to the host bone as the graft ligament is simultaneously secured to the retainer, whereby to secure the graft ligament to the retainer and hence additionally to the host bone. 
     In one preferred form of the invention, there is provided a system for reconstructing a ligament by fixing at least one graft ligament strand in a bone tunnel, comprising: 
     a retainer for disposition in the bone tunnel, wherein the retainer comprises at least one longitudinally-extending groove formed in the outside surface of the retainer, wherein the groove is configured to seat a graft ligament strand therein, and further wherein the at least one longitudinally-extending groove has a floor which is ramped radially outwardly as the floor extends distally-to-proximally, such that non-rotational advancement of the retainer into the bone tunnel will apply a compressive force to hold the graft ligament strand against the sidewall of the bone tunnel, and wherein the retainer comprises a transverse bore extending therethrough; and 
     a locking pin sized to pass through the transverse bore and into the sidewall of the bone tunnel so as to fix the retainer in place within the bone tunnel. 
     In another preferred form of the invention, there is provided a method for reconstructing a ligament by fixing at least one graft ligament strand in a bone tunnel, comprising: 
     positioning the at least one graft ligament strand in the bone tunnel; 
     providing a retainer in the bone tunnel, wherein the retainer comprises at least one longitudinally-extending groove formed in the outside surface of the retainer, wherein the groove is configured to seat a graft ligament strand therein, and further wherein the at least one longitudinally-extending groove has a floor which is ramped radially outwardly as the floor extends distally-to-proximally, such that non-rotational advancement of the retainer into the bone tunnel will apply a compressive force to hold the graft ligament strand against the sidewall of the bone tunnel, and wherein the retainer comprises a transverse bore extending therethrough; 
     positioning the retainer in the bone tunnel so that the at least one graft ligament strand resides in a longitudinally-extending groove so that the retainer is wedged into place; and 
     passing a locking pin through the transverse bore and into the sidewall of the bone tunnel so as to pin the retainer to the host bone. 
     In another preferred form of the invention, there is provided a system for reconstructing a ligament by fixing at least one graft ligament strand in a bone tunnel, comprising: 
     a retainer for disposition in the bone tunnel; and 
     a cap removably attached to the retainer for capturing the at least one graft ligament strand to the retainer by compressing the at least one graft ligament strand between the cap and the retainer. 
     In another preferred form of the invention, there is provided an inserter for inserting a retainer into a bone tunnel, the inserter comprising: 
     a shaft; 
     an element on the distal end of the shaft for engaging a counterpart element on the retainer, whereby to releasably hold the retainer to the shaft; and 
     an opening formed in the shaft, wherein the opening extends transverse to the longitudinal axis of the shaft, with the opening being aligned with a transverse opening formed in the retainer when the retainer is releasably held to the shaft. 
     In another preferred form of the invention, there is provided a dilator for simultaneously (i) dilating a graft ligament strand extending through a bone tunnel and (ii) dilating the sidewall of the bone tunnel, the dilator comprising: 
     a shaft sized to dilate the sidewall of the bone tunnel when the dilator is inserted into the bone tunnel; and 
     at least one longitudinally-extending groove formed in the side wall of the dilator, wherein the at least one longitudinally-extending groove is configured to seat a graft ligament strand therein, and further wherein the at least one longitudinally-extending groove is sized to dilate the graft ligament strand when the graft ligament strand is seated in the at least one longitudinally-extending groove and the dilator is inserted into the bone tunnel. 
     In another preferred form of the invention, there is provided a method for reconstructing a ligament by fixing at least one graft ligament strand in a bone tunnel, comprising: 
     positioning a retainer in the bone tunnel; and 
     attaching a cap to the retainer so as to capture the at least one graft ligament strand to the retainer by compressing the at least one graft ligament strand between the cap and the retainer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
         FIG. 1  is a schematic side elevational view of a knee joint showing an ACL extending between the tibia and the femur; 
         FIG. 2  is a schematic side elevational view of a knee joint showing a graft ligament extending between the tibia and the femur; 
         FIG. 3  is a schematic side elevational view showing a graft ligament secured in a bone tunnel by an interference screw; 
         FIG. 4  is a schematic side elevational view showing a graft ligament secured in a bone tunnel by a bearing structure and expansion screw; 
         FIG. 5  is a schematic side elevational view showing a graft ligament secured in a bone tunnel by a fastener device; 
         FIG. 6  is a schematic side elevational view showing a graft ligament secured in a bone tunnel by an anchor; 
         FIG. 7  is a schematic side elevational view showing a graft ligament secured in a bone tunnel by a suture suspension system; 
         FIG. 8  is schematic side elevational view showing a graft ligament secured in a bone tunnel by a cross-pinning system; 
         FIG. 9  is a schematic side elevational view showing a graft ligament secured in a bone tunnel by a screw and washer arrangement; 
         FIGS. 10 and 11  are schematic views showing a novel retainer for use in securing a graft ligament in a bone tunnel; 
         FIGS. 12 and 13  are schematic views showing locking pins for securing the retainer of  FIGS. 10 and 11  in a bone tunnel; 
         FIGS. 14 and 15  are schematic views showing the retainer of  FIGS. 10 and 11  with optional locking caps for securing a graft ligament to the retainer of  FIGS. 10 and 11 ; 
         FIGS. 16-24  show a graft ligament being secured in a bone tunnel using the system of  FIGS. 10-15 ; 
         FIGS. 25 and 26  are schematic views showing a second novel retainer for use in securing a graft ligament in a bone tunnel; 
         FIGS. 27-31  show a graft ligament being secured in a bone tunnel using the retainer of  FIGS. 25 and 26 ; 
         FIGS. 32 and 33  are schematic views showing a third novel retainer for use in securing a graft ligament in a bone tunnel; 
         FIGS. 34 and 35  are schematic views showing a fourth novel retainer for use in securing a graft ligament in a bone tunnel; 
         FIGS. 36-38  are schematic views showing a fifth novel retainer for use in securing a graft ligament in a bone tunnel; 
         FIGS. 39 and 40  are schematic views showing additional optional locking caps for use in securing a graft ligament in a bone tunnel; 
         FIG. 41  is a schematic view showing another ligament fixation system formed in accordance with the present invention, wherein the ligament fixation system comprises a retainer, a locking pin and a locking cap; 
         FIG. 41A  is a schematic view showing a sizing wire; 
         FIGS. 42 and 43  are schematic views showing a dilator formed in accordance with the present invention; 
         FIG. 44  is a schematic view showing an inserter formed in accordance with the present invention; 
         FIGS. 45-52  and  52 A- 52 E are schematic views showing further details of the retainer of the ligament fixation system shown in  FIG. 41 ; 
         FIGS. 53-56  are schematic views showing further details of the locking pin of the ligament fixation system shown in  FIG. 41 ; 
         FIGS. 57-61  are schematic views showing further details of the locking cap of the ligament fixation system shown in  FIG. 41 ; 
         FIGS. 62-65  are schematic views showing further details of the inserter shown in  FIG. 44 ; 
         FIGS. 66 and 67  are schematic views showing an alternative form of the inserter; 
         FIGS. 68-81  are a series of views showing how the ligament fixation system of  FIG. 41  may be used to fix a graft ligament in a tibial tunnel; 
         FIGS. 81A and 81B  are schematic views showing an alternative form of the system formed in accordance with the present invention; 
         FIGS. 82-85  are schematic views showing an alternative form of a inserter; 
         FIGS. 86-92  are a series of views showing how the ligament fixation system may be used to fix a graft ligament in a tibial tunnel; and 
         FIGS. 93 and 94  are schematic views showing another alternative form of the system formed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides a new method and apparatus for graft ligament reconstruction. For convenience, the present invention will hereinafter be discussed in the context of its use for ACL tibial fixation; however, it should also be appreciated that the present invention may also be used for femoral fixation, or for fixation of other graft ligaments to other bones. 
     First Ligament Fixation System 
     Looking now at  FIGS. 10-15 , there is shown a ligament fixation system  105 . Ligament fixation system  105  generally comprises a retainer  110 , a locking pin  115  and, optionally, a locking cap  120 . 
     In this form of the invention, as will hereinafter be discussed in further detail, retainer  110  is disposed in tibial tunnel  30 , with graft ligament strands  25  running alongside retainer  110 , whereby the graft ligament strands are compressively secured to the sidewall of tibial tunnel  30 . The locking pin  115  may then be used to pin retainer  110  to the host bone. The locking cap  120  may be secured to retainer  110 , in the process capturing graft ligament strands  25  to retainer  110 , and hence additionally to the host bone. 
     Retainer  110 , locking pin  115  and locking cap  120  are all formed out of one or more biocompatible materials. These biocompatible materials may be non-absorbable (e.g., stainless steel or plastic) or absorbable, or osteoconductive or inductive such as ceramic, allograft or coral. It should be appreciated that it is not necessary for all of the components to be formed out of the same material. In fact, each component is preferably formed out of the material or materials most advantageous for that particular component. Thus, different components may be formed out of different materials, different portions of a single component may be formed out of different materials, etc. 
     Retainer  110  is preferably rigid, or substantially rigid, although it may be to some extent compressive or collapsible so long as it is capable of ultimately maintaining a shape which is consistent with its intended function in the present invention. Thus, while retainer  110  is preferably rigid, or substantially rigid, retainer  110  can have any degree of rigidity which is consistent with the present invention. 
     In one preferred form of the invention, retainer  110  is preferably formed out of an acetyl polymer (e.g., Delrin) or PLA (polylactic acid). 
     In one preferred construction, retainer  110  ( FIGS. 10 ,  11 ,  14  and  15 ) has a generally elongated configuration preferably characterized by a narrowing front end  125 , which gives the retainer  110  a generally wedge-shaped configuration. This preferred wedge-shaped configuration assists in introducing retainer  110  into a bone tunnel and advancing it therein and, in one preferred form of the invention, the wedge-shaped configuration assists in locking retainer  110  within the bone tunnel by wedging it in place, as will hereinafter be discussed in further detail. 
     In addition to the wedge-shaped configuration, retainer  110  also has a plurality of longitudinally extending grooves  130  that extend along retainer  110 . The floors  133  of grooves  130  preferably generally follow the taper of retainer  110 , i.e., the floors  133  of the grooves ramp outward as they extend distal to proximal, so that the groove floors are further from the center axis of the retainer at the proximal ends of the grooves than they are at the distal ends of the grooves. Grooves  130  are sized and shaped to receive strands of graft ligament  25  therein, as will hereinafter be discussed. Preferably four grooves  130  are provided, to accommodate four ligament strands, one in each groove. Grooves  130  are preferably separated from one another by flared fins (or ribs or thickened walls)  135 . 
     In one preferred construction, flared fins  135  define the outer perimeter of retainer  110  along substantially its entire length; in this construction, the outer edges of flared fins  135  define the tapered configuration of retainer  110 . 
     Ribs and/or other protrusions may be formed on the floors  133  of grooves  130 , and/or on flared fins  135 , so as to inhibit longitudinal movement of graft ligament strands  25  relative to retainer  110  when the graft ligament strands are disposed in the retainer&#39;s grooves. 
     Retainer  110  also preferably comprises a threaded recess  140  to facilitate use of the optional locking cap  120  with the retainer. Threaded recess  140  extends distally from the proximal end surface  142  of the retainer  110 . Threaded recess  140  permits the optional locking cap  120  to be releasably secured to retainer  110 , as will also hereinafter be discussed (see  FIGS. 14 ,  15 ,  22  and  23 ). Alternatively, recess  140  can also be configured to accept a ribbed or barbed locking mechanism for securing the optional locking cap  120  to retainer  110 . 
     In one preferred construction, retainer  110  also comprises one or more transverse or oblique bores  145  ( FIGS. 11 ,  14 ,  15  and  18 ) that extend through the proximal end of retainer  110 , with one end of bores  145  opening on the proximal end surface  142  of retainer  110  and the other end of bores  145  opening on the floor  133  of a groove  130  ( FIG. 18 ). In another preferred construction, one end of bores  145  open on the proximal end surface  142  of retainer  110  and the other end of bores  145  open on a flared fin  135 . In still another preferred construction, one end of bores  145  open on the proximal end surface  142  of retainer  110  and the other end of bores  145  open on the floor  133  of a groove  130  and/or on a flared fin  135 . 
     Locking pins  115  ( FIGS. 12 and 13 ) of ligament fixation system  105  comprise a shaft  150  terminating in a pointed distal tip  155 . If desired, an enlarged head  156  can be provided on the proximal end of shaft  150 . Locking pins  115  are used to secure retainer  110  to the host bone, as will hereinafter be discussed. Furthermore, to the extent that locking pins  115  pass through the graft ligament  25 , the locking pins  115  also serve to secure the graft ligament directly to the bone. 
     As noted above, ligament fixation system  105  may, optionally, also comprise locking cap  120 . In one preferred form of the invention, locking cap  120  ( FIGS. 14 and 15 ) comprises a threaded stem  160  (preferably in the form of a screw) and an enlarged cap  165 . Threaded stem  160  is sized to be threadably received in threaded recess  140  of retainer  110 , whereby to releasably secure the locking cap  120  to retainer  110 . Alternatively, threaded stem  160  can also be ribbed or barbed to create an alternative locking mechanism, in which case the retainer&#39;s recess  140  is correspondingly configured. Enlarged cap  165  is preferably sized to have a diameter substantially the same as the proximal end surface  142  of retainer  110  and serves to secure the strands of graft ligament  25  to retainer  110 , as will hereinafter be discussed. If desired, locking cap  165  can include a plurality of distally-projecting fingers  170 . Fingers  170  can be distributed throughout the entire distal surface of enlarged cap  165  or about only the periphery of the distal surface (e.g., such as is shown in  FIGS. 14 and 15 ). Fingers  170  may be of various sizes (see  FIGS. 14 and 15 ) and, if desired, they may be aligned with grooves  130  in retainer  110  ( FIG. 15 ), so as to form a complementary coupling. 
     Ligament fixation system  105  is preferably used as follows. 
     First, tibial bone tunnel  30  and femoral bone tunnel  35  are formed ( FIG. 16 ). In one preferred form of the invention, tibial tunnel  30  is formed with a stepped construction (e.g., such as a bore  30 A and a counterbore  30 B, as shown in  FIG. 16A ), or tibial tunnel  30  is formed with a tapered construction (e.g., such as the bore  30 C shown in  FIG. 16B ), so that the wedge-shaped retainer  110  will advance only a portion of the way down bone tunnel  30  before wedging itself into a locked position within the bone tunnel. The techniques and apparatus for forming such stepped or narrowed bone tunnels are well known in the art. By way of example but not limitation, a stepped bone tunnel may be formed by drilling a bore/counterbore configuration in the bone, and a narrowed bone tunnel may be formed by drilling a smaller tunnel in the bone and then selectively widening that tunnel with a tapered bone dilator instrument. 
     Next, graft ligament strands  25  are fixed to femur  15  in ways well known in the art, with the graft ligament strands  25  extending back through tibia  10  ( FIG. 17 ). 
     Then, with graft ligament strands  25  being tensioned by pulling on the free ends of the strands which extend out the proximal end of tibial tunnel  30 , retainer  110  is advanced into tibial bone tunnel  30 , with graft ligament strands  25  being received in the retainer&#39;s grooves  130  ( FIGS. 18 and 19 ). Retainer  110  may be advanced into tibial tunnel  30  using a variety of techniques, e.g., pushing or pulling. By way of example but not limitation, retainer  110  may be pushed up tibial tunnel  30  using an inserter  171  ( FIG. 18 ) having a pair of fingers  172  for engaging a corresponding pair of holes  173  formed in the proximal end of retainer  110 . As retainer  110  is advanced into tibial tunnel  30 , the ramped floors  133  of grooves  130  progressively force the ligament strands into firm yet atraumatic contact with the sidewall of the bone tunnel (see  FIGS. 19-21 ). 
     As retainer  110  is advanced further and further into tibial tunnel  30 , it will eventually become wedged into position by virtue of the retainer&#39;s geometry (i.e., the ramped floors of grooves  130  and the tapered shape of flared fins  135 ), the stepped or tapered geometry of the tibial tunnel  30 , and the presence of graft ligament strands  25  between retainer  110  and the sidewall of the bone tunnel. In this respect it will also be appreciated that this progressive wedging action is also generally influenced by the typically resilient nature of graft ligament strands  25 , and by the typically softer cancellous bone which forms the sidewall of the intermediate portions of tibial tunnel  30  (and which permits some compression as wedging occurs). This wedging action will effectively lock the graft ligament strands  25  to the sidewall of tibial tunnel  30 , whereby to secure the graft ligament strands to the host bone. 
     When retainer  110  has been advanced a sufficient distance within tibial tunnel  30  (and is preferably wedged into place on account of its tapered shape, including but not limited to the engagement of the flared fins  135  with the sidewall of the stepped or tapered bone tunnel  30 ), a locking pin  115  can be inserted through the transverse or oblique bore  145  ( FIGS. 19-21 ) and into the sidewall of the bone tunnel, whereby to lock retainer  110  to the host bone. By forming transverse bore  145  so that it opens on the proximal end surface  142  of retainer  110  and extends at an oblique angle relative to the longitudinal axis of retainer  110 , locking pin  115  can be introduced to transverse bore  145  from the mouth of tibial tunnel  30  and essentially form a “toe-in” fastening of retainer  110  to the host bone. Furthermore, to the extent that locking pin  115  passes through the graft ligament  25 , the locking pin also serves to secure the graft ligament directly to the bone. 
     Alternatively, and/or additionally, center hole  174  ( FIGS. 10 and 11 ) may be used for a crosspin or cross-screw fixation of retainer  110  to tibia  10 . However, such an arrangement is generally somewhat less convenient, since center hole  174  is concealed within the interior of tibia  10  and systems must be provided to ensure accurate “blind” crosspinning or cross-screwing through the concealed center hole  174 . 
     Thus, in a preferred configuration of the present invention, retainer  110  is prevented from advancing beyond its deployment site by virtue of (1) its wedged engagement with the narrowing wall of tibial tunnel  30 , and (2) locking pin  115 . As noted above, the narrowing of bone tunnel  30  may be formed with a stepped configuration or a narrowing configuration. In some cases the stepped configuration may be preferred, since the stepped tunnel configuration forms a more tortuous path of graft travel, thereby increasing friction and locking of the graft/tunnel/device interface. In general, the stepped tunnel design has a smaller diameter as it approaches the interior of the joint, so as to limit advancement of retainer  110  toward the interior of the joint. 
     At this point the graft ligament fixation may be considered completed, since retainer  110  is compressively securing the graft ligament strands to the sidewall of tibial tunnel  30  and, hence, to the host bone. Furthermore, to the extent that the locking pin  115  passes through the graft ligament, the locking pin also serves to secure the graft ligament directly to the bone. 
     Optionally, and more preferably, however, the locking cap  120  may be used to secure graft ligament strands  25  to retainer  110 . 
     More particularly, after retainer  110  is positioned in tibial tunnel  30 , graft ligament strands  25  are folded over the proximal end surface  142  of retainer  110  ( FIGS. 22 and 23 ). Then locking cap  120  is secured to retainer  110  ( FIGS. 22-24 ), e.g., with a hex driver (not shown) engaging a driver recess  121  ( FIGS. 22-24 ), with the locking cap  120  securing graft ligament strands  25  to retainer  110 , whereby to lock graft ligament strands  25  to retainer  110  and hence to the host bone. 
     Thus, with the use of optional locking cap  120 , graft ligament strands  25  are captured to the host bone by (i) lateral compression created along the length of retainer  110 , as the retainer forces the graft ligament strands outboard against the sidewall of the bone tunnel, and (ii) axial compression created between the underside of locking cap  120  and the proximal end surface  142  of retainer  110  (which is in turn wedged into position in tibial tunnel  30  and pinned into place with locking pin  115 ). Furthermore, to the extent that the locking pin  115  passes through the graft ligament  25 , the locking pin also serves to secure the graft ligament directing to the bone. 
     It should also be appreciated that, inasmuch as graft ligament strands  25  tend to be slightly elastic, and inasmuch as graft ligament strands  25  are secured under tension, upon retainer deployment, graft ligament strands  25  will tend to urge retainer  110  further into the bone tunnel, thereby enhancing the wedging lock to the bone. 
     Thereafter, over time, graft ligament strands  25  and the host bone integrate so as to provide a biologic union. 
     Alternatively, the mouth of the tibial tunnel can be countersunk (at the tibial cortex) to a larger diameter for a short distance. With this arrangement, a larger diameter locking cap can be used to secure graft ligament  25  to the retainer as well as to the annular rim formed at the base of the countersunk hole. This further increases the tortuous path followed by the graft strands and increases the holding strength of the system. 
     Retainer  110  can be formed with various geometries. Thus, for example,  FIGS. 25 and 26  show an alternative retainer  110 A which can be used where only two ligament strands are to be fixed in a bone tunnel. In this arrangement, only two grooves  130 A are provided, with the remainder of retainer  110 A having an arcuate peripheral surface.  FIGS. 27-31  illustrate selected steps in using retainer  110 A to secure graft ligament strands in a bone tunnel. While not shown in  FIG. 27-31 , it will be appreciated that locking cap  120  may, optionally, be used in conjunction with retainer  110 A. 
       FIGS. 32 and 33  illustrate another retainer  110 B. In this case, three grooves  130 B are provided, to accommodate up to three ligament strands. Again, it will be appreciated that, while not shown in  FIGS. 32 and 33 , retainer  110 B is intended to be used with locking pin  115  and, optionally, locking cap  120 . 
       FIGS. 34 and 35  illustrate another retainer  110 C. In this configuration, four grooves  130 C are provided, but they are arranged in retainer  110 C so that bore  145 C opens on a relatively large arcuate surface. Again, it will be appreciated that, while not shown in  FIGS. 34 and 35 , retainer  110 C is intended to be used with locking pin  115  and, optionally, locking cap  120 . 
       FIGS. 36-38  illustrate another retainer  110 D which has a tapered proximal end as well as a tapered distal end. The tapered proximal end can permit better seating of a locking cap to the retainer.  FIGS. 36 and 37  also illustrate how the height of flared fins  135 D (which extend between grooves  130 D) can be varied as desired. Again, it will be appreciated that, while not shown in  FIGS. 36-38 , retainer  110 D is intended to be used, optionally, with locking cap  120 . 
       FIGS. 39 and 40  illustrate alternative locking caps  120 E, where openings  175 E are formed in the locking caps. Openings  175 E permit graft ligament strands  25  to be folded over the proximal end surface  142  of the retainer  110  and then passed through openings  175 E, thereby providing a more tortuous path for the ligament strands so as to help hold graft ligament strands  25  to retainer  110 . Openings  175 E can be positioned between fingers  170 E ( FIG. 39 ), or in alignment with fingers  170 E ( FIG. 40 ), and/or both. 
     Second Ligament Fixation System 
     Looking next at  FIG. 41 , there is shown a ligament fixation system  200 . Ligament fixation system  200  generally comprises a retainer  205 , a locking pin  210  and a locking cap  215 . 
     In this form of the invention, and as will hereinafter be discussed in further detail, retainer  205  is disposed in tibial tunnel  30 , with graft ligament strands  25  running alongside retainer  205 , whereby the graft ligament strands are compressively secured to the sidewall of tibial tunnel  30 . Then locking pin  210  simultaneously pins retainer  205  to the host bone and secures locking cap  215  to retainer  205 , in the process capturing graft ligament strands  25  to retainer  205  and hence additionally to the host bone. 
     Retainer  205 , locking pin  210  and locking cap  215  are all formed out of one or more biocompatible materials. These biocompatible materials may be non-absorbable (e.g., stainless steel or plastic) or absorbable, or osteoconductive or inductive such as ceramic, allograft or coral. It should be appreciated that it is not necessary for all of the components to be formed out of the same material. In fact, each component is preferably formed out of the material or materials most advantageous for that particular component. Thus, different components may be formed out of different materials, different portions of a single component may be formed out of different materials, etc. 
     Retainer  205  is preferably rigid, or substantially rigid, although it may be to some extent compressive or collapsible so long as it is capable of ultimately maintaining a shape which is consistent with its intended function in the present invention. Thus, while retainer  205  is preferably rigid, or substantially rigid, retainer  205  can have any degree of rigidity which is consistent with the present invention. 
     In one preferred form of the invention, retainer  205  is preferably formed out of an acetyl polymer (e.g., Delrin) or PLA (polylactic acid). 
     As will hereinafter also be discussed in further detail, and looking next at FIGS.  68  and  41 A- 44 , ligament fixation system  200  also preferably comprises a sizing wire  218  ( FIG. 41A ), a dilator  220  ( FIGS. 42 and 43 ) and an inserter  225  ( FIG. 44 ). Sizing wire  218  is preferably used to measure the patient&#39;s anatomy and determine the proper size (i.e., length) of retainer  205  to be used in the ligament reconstruction procedure, as will hereinafter be discussed in further detail. Dilator  220  is preferably used to prepare bone tunnel  30  and graft ligament strands  25  prior to deploying retainer  205  in the bone tunnel, as will also hereinafter be discussed. Inserter  225  is preferably used to deploy retainer  205  within bone tunnel  30 , as will also hereinafter be discussed. 
     Retainer  205  of ligament fixation system  200  is shown in further detail in  FIGS. 45-52  and  52 A- 52 E. Retainer  205  generally comprises four longitudinally-extending grooves  227  ( FIGS. 45 and 52 ) for receiving graft ligament strands  25 , a central lumen  230  ( FIG. 49 ) for receiving a portion of inserter  225  as will hereinafter be discussed, a crosshole  235  for receiving locking pin  210 , and a mounting shoulder  240  for seating graft ligament strands  25  and locking cap  215 . 
     In addition to the foregoing, retainer  205  preferably also comprises two main ribs or spines  245  ( FIGS. 45 ,  50  and  52 ), two lateral fins  250  ( FIGS. 45 ,  47 ,  51  and  52 ), a lofted profile  255  to the floors of grooves  227  ( FIGS. 48 and 51 ), a plurality of ribs  257  ( FIGS. 45 ,  46  and  48 ) formed on the floors of the longitudinally-extending grooves  227 , locking profiles  260  formed on the face of mounting shoulder  240  ( FIGS. 45 ,  47  and  50 ), side ribs  265  ( FIGS. 45 and 47 ), internal screw threads  270  formed on the interior of crosshole  235  ( FIGS. 48 and 49 ), recesses  275  formed on the rear end of retainer  205  ( FIGS. 47 ,  48  and  50 ) for engagement by inserter  225 , and stepped pointed tip  280  ( FIGS. 45 and 47 ), each of which are discussed in greater detail below. 
     Main ribs or spines  245  ( FIGS. 45 ,  50  and  52 ) extend down the length of retainer  205  and, when retainer  205  is deployed in the bone tunnel along with a plurality of graft ligament strands, spines  245 : (i) securely seat on the sidewall of the bone tunnel, and (ii) help keep the ligament strands aligned with the longitudinal axis of retainer  205 . 
     Lateral fins  250  ( FIGS. 45 ,  47 ,  51  and  52 ) help, in conjunction with spines  245 , separate graft ligament strands  25  into separately manageable lengths and position those graft ligament strands in the four longitudinally-extending grooves  227  when retainer  205  is introduced into the bone tunnel. To the extent that the graft ligament comprises just two strands rather than four strands (e.g., a tibialis tendon graft), the two lateral fins lie against the two graft ligament strands and apply an additional lateral compressive force. In this respect it should be appreciated that where the system  200  is used with just two ligament strands, dilator  220  prepares those two strands by forming impressions in the strands to receive the lateral fins. 
     Lofted profile  255  ( FIGS. 48 and 51 ) provides a pressure gradient for the graft ligament strands  25  extending alongside the length of retainer  205 . More particularly, lofted profile  255  provides progressively greater compression (in a distal-to-proximal direction) of graft ligament strands  25  against the sidewall of the bone tunnel and, in turn, develops gentle ligament-to-bone contact near the distal end of retainer  205  and more aggressive ligament-to-bone contact near the proximal end of retainer  205 . The increased compression (from the distal end to the proximal end) provides good circumferential ligament coverage around the perimeter of bone tunnel  30  and generates excellent fixation strength. The lofted profile  255 , which provides retainer  205  with a generally tapered configuration, also facilitates insertion of retainer  205  into bone tunnel  30 . 
     Ribs  257  ( FIGS. 45 ,  46  and  48 ) are formed on the floors of the longitudinally-extending grooves  227 , and serve to inhibit longitudinal movement of graft ligament strands  25  relative to retainer  205  when the graft ligament strands are seated in the longitudinally-extending grooves, as will hereinafter be discussed. 
     Locking profiles  260  ( FIGS. 45 ,  47  and  50 ) interact with complementary profiles formed on locking cap  215  (hereinafter discussed) so as to facilitate gripping of graft ligament strands  25  between mounting shoulder  240  ( FIG. 45 ) and the underside of locking cap  215 , as will hereinafter be discussed. 
     Side ribs  265  ( FIGS. 45 and 47 ) provide extra grip for graft ligament strands on the proximal (i.e., non-joint) end of retainer  205 . 
     Internal screw threads  270  ( FIGS. 48 and 49 ) mate with counterpart threads  295  ( FIG. 53 ) formed on locking pin  210 , whereby to facilitate controlled advancement of locking pin  210  through crosshole  235 , as will hereinafter be discussed. 
     Recesses  275  ( FIGS. 47 ,  48  and  50 ) mate with counterpart elements on inserter  225 , as will hereinafter be discussed, whereby to help hold retainer  205  to the inserter. 
     Stepped pointed tip  280  ( FIGS. 45 and 47 ) provides a tortuous path for graft ligament strands  25  as they pass by retainer  205 , so as to help secure graft ligament strands  25  within the bone tunnel. The profile of stepped pointed tip  280  creates additional wedging between retainer  205  and the sidewall of the tapered bone tunnel (i.e., along spines  245 ) in the event that retainer  205  tries to move beyond its intended depth. 
     It should be appreciated that the dimensions of retainer  205  are chosen so that when retainer  205  is disposed in bone tunnel  30  (i.e., after bone tunnel  30  and graft ligament strands  25  are prepared by the dilator  220 ), retainer  205  will wedge firmly into position in bone tunnel  30  against both graft ligament strands  25  and the sidewall of bone tunnel  30 . 
     Locking pin  210  is shown in further detail in  FIGS. 53-56 . Locking pin  210  generally comprises a shaft  285  for insertion through locking cap  215 , retainer  205  and into the host bone, a head  290  for securing locking cap  215  against retainer  205  so as to capture the graft ligament strands  25  to the retainer, and threads  295  for engagement with counterpart internal screw threads  270  on retainer  205  the controlled advancement of locking pin  210  relative to retainer  205 , as will hereinafter be discussed in further detail. Head  290  also preferably comprises a non-circular (e.g., hexagonal, Torx, Phillips, star, etc.) recess  296  for selective mating with a driver (not shown), whereby to facilitate turning of locking pin  210 . 
     Locking pin  210  also preferably comprises a tapered distal tip  300 , one or more shaft enlargements  310 , and a locking cap seat  305  ( FIG. 55 ) located between head  290  and the one or more shaft enlargements  310 , each of which is discussed in greater detail below. 
     Threads  295  are located on shaft  285  and mate with counterpart threads  270  on retainer  205  for controlled advancement of locking pin  210  through crosshole  235  of retainer  205 . In one preferred embodiment, threads  295  on locking pin  210 , and counterpart threads  270  on retainer  205 , are sized so as to protect the user from overtightening locking pin  210  relative to retainer  205 . 
     Tip  300 , at the distal end of shaft  285 , is preferably pointed and smooth so as to facilitate passage of locking pin  210  through crosshole  235  in retainer  205  and into the host bone. 
     Locking cap seat  305  ( FIG. 55 ) is located between head  290  and the one or more shaft enlargements  310 , whereby to permit locking cap  215  ( FIG. 41 ) to slip proximally over the one or more shaft enlargements  310  and then be loosely held to shaft  285  prior to secure tightening of locking pin  210  vis-à-vis retainer  205 , whereby to secure locking cap  215  against the retainer&#39;s mounting shoulder  240 . 
     In one preferred form of the invention, locking pin  210  also includes a plurality of projections  312  ( FIGS. 53 ,  55  and  56 ) for engaging corresponding elements on locking cap  215  whereby to provide an anti-backout feature, as will hereinafter be discussed in further detail. 
     Locking cap  215  is shown in further detail in  FIGS. 57-61 . Locking cap  215  generally comprises a central lumen  315  for receiving shaft  285  of locking pin  210 , locking profiles  320  for interacting with complementary locking profiles  260  ( FIG. 45 ) on retainer  205 , whereby to facilitate gripping graft ligament strands  25  between locking cap  215  and retainer mounting shoulder  240 , and a proximal recess  325  ( FIG. 60 ) for seating head  290  of locking pin  210 . Preferably one or more radial grooves  328  ( FIGS. 60 and 61 ) are provided in recess  325 . Radial grooves  328  comprise a relatively gentle slope  328 A (encountered as moving clockwise in  FIG. 61 ) and a relatively steep slope  328 B (encountered as moving counterclockwise in  FIG. 61 ). Radial grooves  328  interact with projections  312  formed on the locking pin  210  so as to prevent backout of locking pin  210 . In addition, the interaction of projections  312  with radial grooves  328  provide tactile and audible feedback as proper compression is achieved on the graft ligament strands  25 . As seen in  FIGS. 59-61 , the profile of radial grooves  328  allow for positive rotation (i.e., clockwise rotation in  FIG. 61 ) during compressive tightening but prevent backout rotation (i.e., counterclockwise rotation in  FIG. 61 ) of the pin  210 . 
     As noted above, the diameter of central lumen  315  of locking cap  215  is coordinated with locking cap seat  305  ( FIG. 55 ) formed on locking pin  210  so that, prior to locking down locking cap  215  against the retainer&#39;s mounting shoulder  240 , locking cap  215  can freely rotate on shaft  285  while still preventing locking cap  215  from slipping down shaft  285 . As a result, locking cap  215  can be loosely mounted on locking pin  210  and the two members easily manipulated as a unit prior to introducing locking pin  210  into retainer crosshole  235 . 
     Dilator  220  ( FIGS. 42 and 43 ) is preferably used to prepare tibial tunnel  30  and graft ligament strands  25  prior to deploying retainer  205  in the bone tunnel. Dilator  220  essentially (i) compacts the sidewall of the bone tunnel so as to provide a more integral surface for graft ligament engagement, and (ii) compresses the relatively elastic graft ligament strands so as to temporarily reduce their size. Additionally, by dilating the bone tunnel with the graft ligament strands in place, dilator  220  can help mechanically integrate the graft ligament strands with the sidewall of the bone tunnel. Dilator  220  generally comprises a shaft  330  having a distal end  335 . Distal end  335  comprises an atraumatic tip  340  and a plurality of longitudally-extending grooves  345  (matching the number of longitudinal grooves  227  in the retainer  205 ) for receiving graft ligament strands  25 , as will hereinafter be discussed. A handle  350  is formed on the proximal end of shaft  330 . 
     Inserter  225  (FIGS.  44  and  62 - 65 ) is preferably used to deploy retainer  205  in tibial tunnel  30 . Inserter  225  generally comprises a shaft  355  ( FIGS. 44 and 62 ) having a distal tip  360  ( FIGS. 44 ,  62  and  63 ) formed at the distal end of shaft  355  and configured to engage the proximal end of retainer  205 , a handle  365  ( FIG. 44 ) mounted to the proximal end of shaft  355 , and a stylus  370  ( FIGS. 44 and 64 ) for selective insertion through shaft  355  and tip  360  and, when a retainer  205  is mounted to the end of the inserter, through the retainer  205 . Stylus  370  provides additional stability to retainer  205  as retainer  205  is deployed in the host bone with inserter  225 , as will hereinafter be discussed. 
     Inserter  225  also preferably comprises a drill bushing  375  ( FIG. 65 ) for selective attachment to tip  360 , a lumen  380  ( FIG. 62 ) extending through handle  365 , shaft  355  and tip  360  ( FIGS. 44 ,  62  and  63 ), a drill bushing seat  390  ( FIG. 63 ), and fingers  395  ( FIG. 63 ), each of which is discussed in greater detail below. 
     Drill bushing  375  ( FIG. 65 ) comprises a central lumen  396  and a stepped outer profile including a leading nose  397 A, a following shaft  397 B, and a tailing grip  397 C. An annular shoulder  397 D is formed at the intersection of leading nose  397 A and following shaft  397 B. Preferably leading nose  397 A comprises a smooth section  397 E followed by a threaded section  397 F. Drill bushing  375  is selectively mounted to tip  360  by means of drill bushing seat  390  (see below) and is used to accurately drill a crosshole in the host bone, as will hereinafter be discussed in further detail. 
     Lumen  380 , which extend through handle  365 , shaft  355  and tip  360 , accommodates the removable stylus  370 . 
     Drill bushing seat  390  ( FIG. 63 ) comprises a threaded bore  398 A and a partial counterbore  398 B, with an annular shoulder  398 C being formed at the intersection of bore  398 A and counterbore  398 B. Drill bushing seat  390  selectively accommodates drill bushing  375 , with the bushing&#39;s threaded section  397 F received by the seat&#39;s bore  398 A and the bushing&#39;s following shaft  397 B received in the seat&#39;s partial counterbore  398 B, whereby drill bushing  375  may be mounted to tip  360 , with the smooth section  397 E of drill bushing  375  being disposed in and lining the crosshole  235  of the retainer  205  mounted to inserter  225 , as will hereinafter be discussed in further detail. 
     Fingers  395  ( FIG. 63 ) mate with counterpart recesses  275  ( FIG. 48 ) of retainer  205 , whereby to selectively hold retainer  205  on the distal end of inserter  225 . 
     If desired, shaft  355  and tip  360  can be formed as a single member or as a pair of members united during manufacture. 
     If desired, a stylus  370 A ( FIGS. 66 and 67 ) may be used in place of stylus  370 . Stylus  370 A comprises a collet  399 A received in a body  399 B for adjustably gripping of the wire  399 C. 
     Ligament fixation system  200  is preferably used as follows. 
     First, tibial bone tunnel  30  and femoral bone tunnel  35  are formed in ways well known in the art; graft ligament strands  25  are advanced through tibial tunnel  30 , across the knee joint, and into femoral bone tunnel  35  in ways well known in the art; and graft ligament strands  25  are made fast in femoral bone tunnel  35 , with the graft ligament strands  25  extending back across the knee joint, through tibial bone tunnel  30  and out the front of tibia  10 , all in ways well known in the art. 
     Next, and looking now at  FIGS. 68 and 69 , a sizing wire  218  (or other tool) is advanced into tibial bone tunnel  30  to determine the depth of tibial bone tunnel  30 . This is done using the graduation markings formed on sizing wire  218 . The depth of the tibial bone tunnel  30  determines the length of the retainer  205  which is used in the ligament reconstruction. 
     Then sizing wire  218  is removed from tibial bone tunnel  30  ( FIG. 70 ) and, while the free ends of the graft ligament strands  25  are held under tension, the dilator  220  is advanced into tibial bone tunnel  30  ( FIG. 71 ), with the graft ligament strands  25  being received in the dilator&#39;s longtiduinally-extending grooves  345 . As dilator  220  is advanced into tibial bone tunnel  30 , the dilator forces graft ligament strands  25  against the sidewall of tibial bone tunnel  30 , compressing graft ligament strands  25  so as to temporarily remove fluid from the graft ligament strands  25 , compressing the host bone so as to form a more integral bone wall, and mechanically integrating and contouring the graft ligament strands into the host bone. Dilator  220  is advanced to an appropriate depth, using gradation markings formed on the surface of dilator  220  ( FIG. 72 ). Then dilator  220  is removed from tibial bone tunnel  30  ( FIG. 73 ). 
     Next, retainer  205  is loaded onto inserter  225 , with inserter fingers  395  engaging recesses  275  in retainer  205 , and with stylus  370  passing through inserter shaft  355 , inserter tip  360  and retainer  205  ( FIG. 74 ). Then inserter  225  is used to advance retainer  205  to its proper position within bone tunnel  30  ( FIGS. 75 and 76 ). As retainer  205  is inserted into bone tunnel  30 , graft ligament strands  25  (which are held under tension by pulling on their free ends) are received in the retainer&#39;s longitudinally-extending grooves  227  so that the retainer&#39;s lofted profile  255  gently but firmly compresses the graft ligament strands against the sidewall of the bone tunnel. Retainer  205  is advanced until it is properly wedged into position. Once the proper positioning of retainer  205  has been achieved, stylus  370  is removed ( FIG. 77 ). At this point, retainer  205  compressively holds the graft ligament strands  25  against the bone, by virtue of its being wedged into position in the bone tunnel. 
     Next, drill bushing  375  is positioned on drill bushing seat  390  ( FIGS. 78 and 78A , and a drill  400  is used to form a crosshole  405  into the host bone ( FIGS. 79 and 80 ). Once the crosshole  405  has been formed, drill bushing  375  is removed and inserter  225  is removed ( FIG. 80 ). 
     Next, locking pin  210  (with locking cap  215  carried in locking cap seat  305 ), is installed in retainer crosshole  235  and the crosshole  405  drilled into the host bone, with locking cap  215  capturing the graft ligament strands  25  against retainer&#39;s mounting shoulder  240 , so as to simultaneously bind retainer  205  to the host bone and graft ligament strands  25  to retainer  205  ( FIG. 81 ). 
     Thus, with ligament fixation system  200 , graft ligament strands  25  are held to tibia  10  by virtue of the compression provided by retainer  205 ; in addition, the graft ligament strands  25  are secured to retainer  205  by locking cap  215 , with the complete assembly being pinned to the host bone via locking pin  210 . 
     It should also be appreciated that, inasmuch as graft ligament strands  25  tend to be slightly elastic, and inasmuch as graft ligament strands  25  are secured under tension, upon retainer deployment, graft ligament strands  25  will tend to urge retainer  205  further into the bone tunnel, thereby enhancing the wedging lock to the bone. 
     Thereafter, over time, graft ligament strands  25  and the host bone integrate so as to provide a biologic union. 
     If desired, locking pin  210  can have its threads  295  replaced by a ribbed or barbed construction, and retainer  205  can have its threads  270  replaced by a mating geometry so as to form a one-way ratchet mechanism. 
     Furthermore, if desired, locking pin  210  and locking cap  215  can be formed with a singular construction, i.e., with an integral construction. 
       FIGS. 81A and 81B  show an alternative form of the system formed in accordance with the present invention. 
     In one preferred form of the invention, the system is modified so that the crosshole  405  is formed in the tibia after inserter  225  has been withdrawn. 
     More particularly, with this form of the invention, and looking now at  FIGS. 82 and 83 , a modified inserter  225 A is provided. Inserter  225 A includes a modified distal tip  360 A which is generally similar to the tip  360  previously disclosed, except that it omits the drill bushing seat  390 . In addition, and looking now at  FIGS. 84A ,  84 B and  85 , a modified drill bushing  375 A is provided. Drill bushing  375 A comprises a smooth shaft  410 A terminating on its distal end in a smaller smooth shaft  411 A and terminating on its proximal end in a connector  415 A, and including a central bore  420 A. Connector  415 A includes one or more openings  425 A for engagement by a handle  430 A. In this form of the invention, drill bushing  375 A is mounted directly in retainer  205  when forming the bone crosshole  405 , i.e., with smaller smooth shaft  411 A seated in retainer crosshole  235 . 
     More particularly, in this form of the invention, the ligament reconstruction is effected as follows. 
     First, tibial bone tunnel  30  and femoral bone tunnel  35  are formed in ways well known in the art; graft ligament strands  25  are advanced through tibial tunnel  30 , across the knee joint, and into femoral bone tunnel  35  in ways well known in the art; and graft ligament strands  25  are made fast in femoral bone tunnel  35 , with the graft ligament strands  25  extending back across the knee joint, through tibial bone tunnel  30  and out the front of tibia  10 , all in ways well known in the art. 
     Next, the sizing wire  218  (or other tool) is advanced into tibial bone tunnel  30  to determine the depth of tibial bone tunnel  30 . This is done using the graduation markings formed on sizing wire  218 . The depth of the tibial bone tunnel  30  determines the length of the retainer  205  which is used in the ligament reconstruction. 
     Then sizing wire  218  is removed from tibial bone tunnel  30  and, while the free ends of the graft ligament strands  25  are held under tension, the dilator  220  is advanced into tibial bone tunnel  30 , with the graft ligament strands  25  being received in the dilator&#39;s longtiduinally-extending grooves  345 . As dilator  220  is advanced into tibial bone tunnel  30 , the dilator forces graft ligament strands  25  against the sidewall of tibial bone tunnel  30 , compressing graft ligament strands  25  so as to temporarily removed fluid from the graft ligament strands  25 , compressing the host bone so as to form a more integral bone wall, and mechanically integrating and contouring the graft ligament strands into the host bone. Dilator  220  is advanced to an appropriate depth, using gradation markings formed on the surface of dilator  220 . Then dilator  220  is removed from tibial bone tunnel  30 . 
     Next, retainer  205  is loaded onto inserter  225 A, with inserter fingers  395 A engaging recesses  275  in retainer  205 , and with stylus  370 A passing through the inserter shaft  355 A, inserter tip  360 A and retainer  205  ( FIG. 86 ). Then inserter  225 A is used to advance retainer  205  to its proper position within bone tunnel  30  ( FIGS. 87 and 88 ). As retainer  205  is inserted into bone tunnel  30 , graft ligament strands  25  (which are held under tension by pulling on their free ends) are received in the retainer&#39;s longitudinally-extending grooves  227  so that the retainer&#39;s lofted profile  255  gently but firmly compresses the graft ligament strands against the sidewall of the bone tunnel. Retainer  205  is advanced until it is properly wedged into position. Once the proper positioning of retainer  205  has been achieved, inserter  225 A, including stylus  370 A, is removed ( FIGS. 89 and 89A ). In this respect it should be appreciated that inserter  225 A (including stylus  370 A) can be removed without affecting the position of retainer  205  and/or ligament strands  25  inasmuch as retainer  205  has been wedged securely into position. At this point, retainer  205  compressively holds the graft ligament strands  25  against the bone, by virtue of its being wedged into position in the bone tunnel. 
     Next, drill bushing  375 A is positioned in retainer crosshole  235  ( FIG. 90 ), and a drill  400  is used to form a crosshole  405  into the host bone ( FIGS. 90 and 91 ). Once the crosshole  405  has been formed, drill bushing  375 A is removed ( FIG. 91 ). 
     Next, locking pin  210  (with locking cap  215  carried in locking cap seat  305 ) is installed in retainer crosshole  235  and the crosshole  405  drilled into the host bone, with locking cap  215  capturing the graft ligament strands  25  against the retainer&#39;s mounting shoulder  240 , so as to simultaneously bind retainer  205  to the host bone and graft ligament strands  25  to retainer  205  ( FIG. 92 ). Again, with the system using the modified inserter  225 A, graft ligament strands  25  are held to tibia  10  by virtue of the compression provided by retainer  205 ; in addition, the graft ligament strands  25  are secured to retainer  205  by locking cap  215 , with the complete assembly being pinned to the host bone via locking pin  210 . 
     It should also be appreciated that, inasmuch as graft ligament strands  25  tend to be slightly elastic, and inasmuch as graft ligament strands  25  are secured under tension, upon retainer deployment, graft ligament strands  25  will tend to urge retainer  205  further into the bone tunnel, thereby enhancing the wedging lock to the bone. 
     Thereafter, over time, graft ligament strands  25  and the host bone integrate so as to provide a biologic union. 
       FIGS. 93 and 94  show another alternative form of the system formed in accordance with the present invention. 
     Modifications 
     It will be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art while remaining within the principles and scope of the present invention.