Abstract:
A graft ligament anchor comprises a graft ligament engagement member disposed in an opening in a bone, the graft ligament engagement member being arranged to receive a graft ligament alongside the engagement member, and a locking member for disposition in the opening, and at least in part engageable with the graft ligament engagement member. Movement of the locking member in the opening causes the locking member to urge the engagement member, and the graft ligament therewith, toward a wall of the opening, to secure the graft ligament to the wall of the opening. A method for attaching a graft ligament to a bone comprises providing an opening in the bone, inserting the graft ligament and a graft ligament engagement member in the opening, with the graft ligament disposed alongside a first portion of the engagement member, and inserting a locking member in the bone alongside a second portion of the engagement member, the locking member being separated from the graft ligament by the graft ligament engagement member. The method further comprises moving the locking member to cause the locking member to engage the graft ligament engagement member to urge the graft ligament engagement member, and the graft ligament therewith, toward a wall of the opening to secure the graft ligament to the wall of the opening.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to medical apparatus and methods in general, and more particularly to apparatus and methods for reconstructing ligaments.  
         BACKGROUND OF THE INVENTION  
         [0002]    Ligaments are tough bands of tissue which serve to connect the articular extremities of bones, or to support or retain organs in place within the body. Ligaments are typically composed of coarse bundles of dense white fibrous tissue which are disposed in a parallel or closely interlaced manner, with the fibrous tissue being pliant and flexible, but not significantly extensible.  
           [0003]    In many cases, ligaments are torn or ruptured as a result of accidents. As a result, various procedures have been developed to repair or replace such damaged ligaments.  
           [0004]    For example, in the human knee, the anterior and posterior cruciate ligaments (i.e., the ACL and PCL) extend between the top end of the tibia and the bottom end of the femur. The ACL and PCL cooperate, together with other ligaments and soft tissue, to provide both static and dynamic stability to the knee. Often, the anterior cruciate ligament (i.e., the ACL) is ruptured or torn as a result of, for example, a sports-related injury. Consequently, various surgical procedures have been developed for reconstructing the ACL so as to restore normal function to the knee.  
           [0005]    In many instances, the ACL may be reconstructed by replacing the ruptured ACL with a graft ligament. More particularly, with such procedures, bone tunnels are typically formed in the top end of the tibia and the bottom end of the femur, with one end of the graft ligament being positioned in the femoral tunnel and the other end of the graft ligament being positioned in the tibial tunnel. The two ends of the graft ligament are anchored in place in various ways known in the art so that the graft ligament extends between the femur and the tibia in substantially the same way, and with substantially the same function, as the original ACL. This graft ligament then cooperates with the surrounding anatomical structures so as to restore normal function to the knee.  
           [0006]    In some circumstances the graft ligament may be a ligament or tendon which is harvested from elsewhere in the patient; in other circumstances the graft ligament may be a synthetic device. For the purposes of the present invention, all of the foregoing can be collectively referred to as a “graft ligament”, “graft material” or “graft member.”  
           [0007]    As noted above, the graft ligament may be anchored in place in various ways. See, for example, U.S. Pat. No. 4,828,562, issued May 9, 1989 to Robert V. Kenna; U.S. Pat. No. 4,744,793, issued May 17, 1988 to Jack E. Parr et al.; U.S. Pat. No. 4,755,183, issued Jul. 5, 1988 to Robert V. Kenna; U.S. Pat. No. 4,927,421, issued May 22, 1990 to E. Marlowe Goble et al.; U.S. Pat. No. 4,950,270, issued Aug. 21, 1990 to Jerald A. Bowman et al.; U.S. Pat. No. 5,062,843, issued Nov. 5, 1991 to Thomas H. Mahony, III; U.S. Pat. No. 5,147,362, issued Sep. 15, 1992 to E. Marlowe Goble; U.S. Pat. No. 5,211,647, issued May 18, 1993 to Reinhold Schmieding; U.S. Pat. No. 5,151,104, issued Sep. 29, 1992 to Robert V. Kenna; U.S. Pat. No. 4,784,126, issued Nov. 15, 1988 to Donald H. Hourahane; U.S. Pat. No. 4,590,928, issued May 27, 1986 to Michael S. Hunt et al.; and French Patent Publication No. 2,590,792, filed Dec. 4, 1985 by Francis Henri Breard.  
           [0008]    Despite the above-identified advances in the art, there remains a need for a graft ligament anchor which is simple, easy to install, and inexpensive to manufacture, while providing secure, trouble-free anchoring of the graft ligament, typically in the knee joint of a mammal.  
         OBJECTS OF THE INVENTION  
         [0009]    Accordingly, one object of the present invention is to provide an improved graft ligament anchor which is relatively simple in construction and therefore inexpensive to manufacture, relatively easy to handle and install, and reliable and safe in operation.  
           [0010]    Another object of the present invention is to provide an improved method for attaching a graft ligament to a bone.  
         SUMMARY OF THE INVENTION  
         [0011]    These and other objects of the present invention are addressed by the provision and use of a novel graft ligament anchor comprising graft ligament engagement means for disposition in an opening in a bone, such that a wall of the graft ligament engagement means resides adjacent to at least one graft ligament disposed in the opening, and locking means for disposition in the opening in the bone and at least partially engageable with the graft ligament engagement means. The elements of the graft ligament anchor are adapted such that movement of the locking means in the opening in the bone causes at least a part of the locking means to engage the graft ligament engagement means so as to urge the graft ligament engagement means, and hence the portion of the graft ligament disposed adjacent thereto, toward a wall of the opening in the bone, whereby to secure the graft ligament to the wall of the opening.  
           [0012]    In use, an opening is made in the bone, and the graft ligament and the graft ligament engagement means are inserted into the opening, with a portion of the graft ligament being disposed alongside a wall of the graft ligament engagement means. In accordance with the present invention, the locking means are also positioned in the opening in the bone, alongside the graft ligament engagement means, with the locking means being separated from the graft ligament by a portion of the graft ligament engagement means. The method further includes moving the locking means in the opening in the bone so as to cause at least a portion thereof to urge the graft ligament engagement means, and hence the portion of the graft ligament disposed adjacent thereto, toward a wall of the opening, whereby to secure the graft ligament to the wall of the opening.  
           [0013]    In one aspect of the invention, a graft fixation device for fixing a graft member within a bone tunnel includes a radially expandable sheath having a side wall with at least one structurally weakened fracture region extending longitudinally along a length of the sheath in the side wall. The radially expandable sheath is sized to fit within a bone tunnel so that a graft member may be accommodated between a wall of a bone tunnel and an outer surface of the radially expandable sheath. A sheath expander is disposable in a central lumen of the radially expandable sheath to radially expand the sheath so as to fix the graft member within the bone tunnel. The structurally weakened fracture region is adapted to fracture upon radial expansion of the sheath to allow varying amounts of radial expansion.  
           [0014]    In specific embodiments of this aspect of the invention, a number of longitudinal side wall segments can be provided, the segments being connected by longitudinal fracture regions. The side wall segments can also have concave outer surfaces so that each segment can capture a portion of graft material between its outer surface and the bone tunnel wall. In a further embodiment, the segments can be longitudinally divided into subsegments connected by longitudinal flexion regions.  
           [0015]    In another aspect of the invention, a graft fixation device for fixing a graft member within a bone tunnel includes a radially expandable sheath having a side wall comprising a plurality of longitudinal side wall segments separated by convex longitudinal flex regions having convex outer surfaces, the radially expandable sheath being sized to fit within a bone tunnel and defining a central lumen. In this aspect, the side wall segments are flexible and have a concave outer surface adapted to enclose a graft member between the concave outer surface and a bone tunnel wall. A sheath expander is disposable in the central lumen of the radially expandable sheath to flex the convex longitudinal flex regions and the flexible concave wall segments to radially expand the sheath so as to fix a graft member within a bone tunnel.  
           [0016]    In specific embodiments of this aspect, the side wall segments may include rigid longitudinal subsegments connected by longitudinal flex regions to provide flexing within the segments. In addition, convex longitudinal flex regions may be configured to flex, but then fracture to allow further radial expansion of the sheath.  
           [0017]    Graft fixation devices of the invention allow a wider variety of materials to be used to form the radially expanding sheath and can also allow a single sized sheath to be used with a larger variety of bone tunnel and expander sizes. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    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 are to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein:  
         [0019]    [0019]FIG. 1 is a diagrammatic sectional view of one form of graft ligament anchor made in accordance with the present invention;  
         [0020]    [0020]FIG. 2 is similar to FIG. 1, but shows the graft ligament anchor components in different operating positions;  
         [0021]    [0021]FIG. 3 is similar to FIG. 1, but shows an alternative embodiment of the present invention;  
         [0022]    [0022]FIG. 4 is a diagrammatic sectional view of another form of graft ligament anchor made in accordance with the present invention;  
         [0023]    [0023]FIG. 5 is similar to FIG. 4, but shows the graft ligament anchor components in different operating positions;  
         [0024]    [0024]FIG. 6 is a diagrammatic sectional view of another form of graft ligament anchor made in accordance with the present invention;  
         [0025]    [0025]FIG. 7 is a diagrammatic sectional view of still another form of graft ligament anchor made in accordance with the present invention;  
         [0026]    [0026]FIG. 8 is a diagrammatic sectional view of yet another form of graft ligament anchor made in accordance with the present invention;  
         [0027]    [0027]FIG. 9 is a perspective view of one of the components of the graft ligament anchor shown in FIG. 8;  
         [0028]    [0028]FIG. 10 is a diagrammatic sectional view of still another form of graft ligament anchor made in accordance with the present invention;  
         [0029]    [0029]FIG. 11 is a diagrammatic view of still another form of graft ligament anchor made in accordance with the present invention;  
         [0030]    [0030]FIG. 12 is a diagrammatic sectional view of yet another form of graft ligament anchor made in accordance with the present invention;  
         [0031]    [0031]FIG. 13 is similar to FIG. 12, but shows the graft ligament anchor components in different operating conditions;  
         [0032]    [0032]FIG. 13A is a diagrammatic sectional view of still another form of ligament anchor made in accordance with the present invention;  
         [0033]    [0033]FIG. 14 is a top plan view of still another form of graft ligament anchor made in accordance with the present invention;  
         [0034]    [0034]FIG. 15 is a side view, in section, of the graft ligament anchor shown in FIG. 14;  
         [0035]    [0035]FIG. 16 is a side view showing the graft ligament anchor of FIGS. 14 and 15 securing a graft ligament to a bone;  
         [0036]    [0036]FIG. 17 is similar to a portion of FIG. 16, but showing components of the graft ligament anchor and graft ligament of FIG. 16 in alternative positions;  
         [0037]    [0037]FIG. 18 is a top plan view of yet another form of graft ligament anchor made in accordance with the present invention;  
         [0038]    [0038]FIG. 19 is a side view, in section, of the graft ligament anchor shown in FIG. 18;  
         [0039]    [0039]FIG. 20 is a diagrammatic sectional view of still another form of graft ligament anchor made in accordance with the present invention;  
         [0040]    [0040]FIG. 21 is a perspective view of a component of the graft ligament anchor shown in FIG. 20;  
         [0041]    [0041]FIG. 22 is a diagrammatic sectional view of still another form of graft ligament anchor made in accordance with the present invention;  
         [0042]    [0042]FIG. 23 is a perspective view of components of the graft ligament anchor of FIG. 22;  
         [0043]    [0043]FIG. 24 is a perspective view of a radially expandable sheath in accordance with a further embodiment of the invention;  
         [0044]    [0044]FIG. 25A is a side view of the sheath of FIG. 24;  
         [0045]    [0045]FIG. 25B is a cross-sectional view of the sheath of FIG. 25A taken along line A-A′ in an unexpanded state;  
         [0046]    [0046]FIG. 26 is an exploded view of the radially expandable sheath of FIG. 24 and a sheath expander;  
         [0047]    [0047]FIG. 27 is a cross-sectional view of the radially expandable sheath of FIG. 24 with graft material placed in a bone tunnel prior to fixation; and  
         [0048]    [0048]FIG. 28 is a cross-sectional view of the sheath and graft material of FIG. 27 in after fixation within the bone tunnel. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0049]    Referring first to FIG. 1, it will be seen that one illustrative embodiment of the present invention includes a graft ligament engagement means  20  comprising a deformable sleeve  22 , preferably formed out of metal or plastic, and adapted to be inserted into an opening  24  formed in a bone B. One or more graft ligaments  28  are disposed alongside an interior wall  30  of sleeve  22 .  
         [0050]    The embodiment illustrated in FIG. 1 further includes locking means  32 , which may be a pivotally movable rocker arm  34 , which may be provided with a slot  36  for receiving a key member (not shown) for turning rocker arm  34 .  
         [0051]    Referring to FIG. 2, it will be seen that turning rocker arm  34  enables a portion of the rocker arm to impinge upon an exterior surface  40  of sleeve  22  so as to force sleeve  22 , and hence graft ligaments  28  contained therein, toward sidewall  38  of opening  24 , whereby to secure sleeve  22  and graft ligaments  28  between opening sidewall  38  and locking means  32 .  
         [0052]    In operation, opening  24  is first made in bone B and then graft ligaments  28  and graft ligament engagement means  20  are inserted into opening  24 , with graft ligaments  28  being disposed alongside a first wall, i.e., the interior wall  30 , of sleeve  22 . Locking means  32  are inserted into opening  24  alongside the exterior surface  40  of sleeve  22 . Locking means  32  are thus separated from graft ligaments  28  by graft ligament engagement means  20 , i.e., sleeve  22 . As noted above, movement of locking means  32  causes at least a portion thereof to engage sleeve  22  and to crimp the sleeve inwardly upon graft ligaments  28 , and to push both sleeve  22  and graft ligaments  28  against sidewall  38  of opening  24 .  
         [0053]    If it is desired to thereafter release graft ligaments  28 , rocker arm  34  may be moved back to the position shown in FIG. 1. To this end, graft ligament engagement means  20  preferably are formed out of a resilient material, whereby engagement means  20  can return to substantially the same position shown in FIG. 1 when locking means  32  return to the position shown in FIG. 1.  
         [0054]    If desired, substantially all of sleeve  22  can be formed so as to be deformable; alternatively, some of sleeve  22  can be formed so as to be rigid. By way of example, the portion of sleeve  22  contacted by locking means  32  can be formed so as to be substantially rigid.  
         [0055]    Graft ligaments  28  may comprise natural or synthetic graft ligament material, and the anchor can be used to attach natural or synthetic graft ligaments and/or tendons to bone. Sleeve  22  preferably is provided with inwardly-extending protrusions  42 , such as spikes  44 , for securely retaining graft ligaments  28  therein.  
         [0056]    Locking means  32  may be a rocker arm type, such as the rocker arm member  34  shown in FIGS. 1 and 2, or a generally conically-shaped expansion plug  46 , as shown in FIG. 3, with the expansion plug preferably being threaded such that as the plug is screwed into place, an increasing diameter of the plug engages sleeve  22  in a wedge-like manner so as to force the sleeve against interior wall  38  of opening  24 .  
         [0057]    In FIG. 4, there is shown an alternative embodiment in which graft ligaments  28  are disposed alongside exterior wall  40  of sleeve  22 , and locking means  32  is disposed within sleeve  22 . With this embodiment, locking means  32  operate to engage interior wall  30  of the sleeve (FIG. 5), whereby to force graft ligaments  28  against sidewall  38  of opening  24 . Again, locking means  32  may be a rocker arm type, such as the rocker arm member  34  shown in FIGS. 4 and 5, or may be an expansion plug  46 , preferably threaded, of the sort shown in FIG. 3. With the embodiment shown in FIGS. 4 and 5, sleeve  22  may be provided with protrusions  42  (in the form of spikes  44 , for example) on the exterior wall  40  thereof for engagement with graft ligaments  28 . In many instances, it is beneficial to provide at least two discrete graft ligaments  28  and, in such cases, it is preferable that the graft ligaments be disposed on substantially opposite diametric sides of the sleeve, as shown in FIGS. 4 and 5.  
         [0058]    In FIG. 6, there is shown an embodiment similar to that shown in FIGS. 4 and 5, but provided with an expandable sleeve  22 A, rather than a deformable metal or plastic sleeve  22  as shown in FIGS.  1 - 5 . Sleeve  22 A may be formed out of an elastomeric material, and it is expanded radially outwardly by engagement with a centrally disposed locking means  32  (preferably in the form of a threaded expansion plug  46 ) so as to force graft ligaments  28  outward into a secured position between sleeve  22 A and opening sidewall  38 .  
         [0059]    In operation, the embodiments shown in FIGS.  4 - 6  function similarly to the embodiments shown in FIGS.  1 - 3  in attaching graft ligaments  28  to bone B. Opening  24  is first made in bone B. Graft ligaments  28  and graft ligament engagement means  20  (in the form of sleeve  22  or sleeve  22 A) are inserted into opening  24 , with graft ligaments  28  disposed alongside exterior wall  40  of the graft ligament engagement means, i.e., alongside the exterior wall  40  of sleeve  22  or sleeve  22 A. Locking means  32  (in the form of a rocker arm member  34  or a threaded expansion plug  46 ) are inserted axially into the sleeve, alongside interior wall  30  of the sleeve. Locking means  32  are thus separated from the graft ligaments  28  by the sleeve ( 22  or  22 A). Then locking means  32  are manipulated so as to engage the sleeve ( 22  or  22 A) and thereby urge the sleeve, and hence graft ligaments  28 , toward opening sidewall  38 , whereby to secure the sleeve and graft ligaments to the wall of the opening.  
         [0060]    If and when it is desired to adjust tension on graft ligaments  28 , locking means  32  may be backed off, that is, if locking means  32  comprise the rocker arm type cam member  34 , the arm need only be rotated 90° from the positions shown in FIGS. 2 and 5, to return to the positions shown, respectively, in FIGS. 1 and 4; if, on the other hand, locking means  32  comprise expansion plug  46 , the plug need only be unscrewed or otherwise axially withdrawn so as to release the securing of the graft ligaments.  
         [0061]    Referring next to FIG. 7, it will be seen that in an alternative embodiment, graft ligament engagement means  20  comprises plate means  48  which are movable transversely within the bone opening. As in the embodiments previously described, graft ligaments  28  are disposed alongside a wall  50  of graft ligament engagement means  20 , which in this instance is a first major surface of plate means  48 . Graft ligament engagement means  20  are disposed between graft ligaments  28  and locking means  32 . Locking means  32  may be, as in the above-described embodiments, an expansion plug  46  (as shown in FIG. 7), or locking means  32  may be a rocker arm type of cam member  34  (of the sort shown in FIGS. 1, 2,  4  and  5 ). Locking means  32  are adapted to impinge upon a second major surface  52  of plate means  48 . Plate means  48 , in the embodiment shown in FIG. 7, comprises a single plate  54  having, on first major surface  50  thereof, one or more concavities  56  for nesting one or more graft ligaments  28 , respectively.  
         [0062]    In the attachment of one or more graft ligaments  28  to a bone B, using the embodiment of FIG. 7, locking means  32  are manipulated so as to bear against plate  54  so as to move plate  54  into engagement with graft ligaments  28 , and thence to further move plate  54  so as to secure the graft ligaments against sidewall  38  of opening  24 .  
         [0063]    Referring next to FIG. 8, it will be seen that locking means  32  may comprise the threaded expansion plug  46  deployed partly in opening  24  and threaded partly into bone B, thus serving as a so-called interference screw. With this arrangement, plug  46  is thereby (i) in part along its length disposed in opening  24 , protruding into the opening from opening wall  38 , and (ii) in part along its length threadedly engaged with bone B. Screwing in plug  46  causes the plug to engage plate  54  which, in turn, compacts one or more graft ligaments  28  against wall  38  of opening  24 .  
         [0064]    In lieu of, or in addition to, the aforementioned concavities  56  shown in FIG. 7, plate  54  may be provided with gripper ribs  58  for engaging graft ligaments  28 , as shown in FIGS. 8 and 9.  
         [0065]    In FIG. 10, it is shown that plate means  48  may include first and second plates  60 ,  62 , each having a wall  50  facing one or more graft ligaments  28 , and a wall  52  facing locking means  32 . Plates  60 ,  62  may be joined together by a link  64  which may be molded integrally with plates  60 ,  62  so as to form a so-called “living hinge” link. Locking means  32  are depicted in FIG. 10 as a rocker arm type of cam member  34 , but it will be appreciated that an expansion plug type of locking means (e.g., a plug  46  such as that shown in FIGS. 3, 6 and  7 ) might also be used.  
         [0066]    In operation, rotative movement of rocker arm  34  (or axial movement of expansion plug  46 ) causes plates  60 ,  62  to move outwardly from each other so as to urge graft ligaments  28  against wall  38  of opening  24 . Walls  50  of plates  60 ,  62  may be provided with concavities  56 , as shown in FIG. 10, or with ribs  58  of the sort shown in FIG. 9, or both.  
         [0067]    Referring next to FIG. 11, it will be seen that still another embodiment of the present invention includes, as graft ligament engagement means  20 , a V-shaped strip  94 , preferably made out of a resilient metal or plastic material. An end portion  96  of a graft ligament  28  is disposed between first and second leg portions  98 ,  100  of V-shaped strip  94 , and graft ligament  28  extends alongside an exterior surface  102  of second leg portion  100 . Locking means  32  comprise a threaded expansion plug  46  disposed partly in opening  24  and partly in bone B, along sidewall  38  of opening  24 , in a manner similar to the disposition of threaded expansion plug  46  shown in FIG. 8.  
         [0068]    Upon screwing in expansion plug  46 , the expansion plug engages first leg  98  of graft ligament engagement means  20  (i.e., the V-shaped strip  94 ) to force first leg  98  to close upon second leg  100  with the graft ligament end portion  96  sandwiched therebetween and, upon further screwing in of threaded expansion plug  46 , to force graft ligament engagement means  20  and graft ligament  28  against wall  38  of opening  24 . To release graft ligament  28 , an operator need only back out expansion plug  46 .  
         [0069]    When attaching a graft ligament to a bone with the graft ligament anchor shown in FIG. 11, an opening is first drilled, or otherwise made, in the bone. Then the V-shaped strip  94  is inserted into the opening, with a nose portion  104  thereof pointed inwardly of the bone. Next, end portion  96  of graft ligament  28  is inserted between first and second leg portions  98 ,  100  of V-shaped strip  94 . Threaded expansion plug  46  is then inserted into opening wall  38  such that a first portion  106  of the lengthwise extent of plug  46  is disposed in opening  24 , and second portion  108  of the lengthwise extent of plug  46  is threadedly engaged with bone B. Expansion plug  46  is then screwed further down so as to cause plug  46  to engage first leg  98  of V-shaped strip  94  so as to secure graft ligament end portion  96  in V-shaped strip  94 , and then screwed down further to wedge strip  94  and graft ligament  28  against wall  38  of opening  24 .  
         [0070]    Still referring to FIG. 11, it is to be appreciated that bone opening  24  may be formed with a constant diameter throughout its length or, if desired, may be formed with two different diameters along its length, in the manner shown in FIG. 11, so as to form an annular shoulder  110  within the bone opening. The provision of an annular shoulder  110  can be very helpful in ensuring that the graft ligament anchor is prevented from migrating further into bone B, even if graft ligament  28  should thereafter be subjected to substantial retraction forces.  
         [0071]    In a modification (not shown) of the FIG. 11 embodiment, the expansion plug  46  may be entered alongside graft ligament  28  and second leg portion  100  of strip  94 . In this modified version, the expansion plug  46  operates as described above, except that expansion plug  46  engages graft ligament  28  and forces strip first leg  98  against wall  38  of opening  24 .  
         [0072]    Looking next at FIGS. 12 and 13, yet another form of graft ligament anchor is disclosed. This graft ligament anchor is similar to the embodiment shown in FIG. 6, except that the expandable sleeve  22 B is in the form of a cylindrical coil. Sleeve  22 B is formed out of an elastomeric material and is expanded radially outwardly by engagement with a centrally disposed locking means  32  (preferably an axially-movable threaded expansion plug  46 ) so as to force graft ligament  28  outward into a secured position between sleeve  22 B and bone B.  
         [0073]    In FIG. 13A there is shown an embodiment similar to that shown in FIG. 10, but in which the first and second plates  60 ,  62  are discrete plates and not connected to each other. With this arrangement, locking means  32  is inserted into a central recess  74  defined by plate walls  52 , and may comprise either an expansion plug  46  of the type shown in FIGS. 6 and 7 or a rocker arm type of cam member  34  of the type shown in FIGS. 1 and 2.  
         [0074]    Looking next at FIGS. 14 and 15, another graft ligament anchor  200  is shown. Anchor  200  includes graft ligament engagement means  20  comprising a flat plate  201 , a pair of through-holes  202 ,  204  and a threaded through-hole  206 . In use, and looking now at FIGS. 14, 15 and  16 , the free end  96  of graft ligament  28  is passed downward through hole  202  and then back upward again through hole  204 , and then a screw  208  is used to secure anchor  200  to the wall  210  of the bone opening by threading the shank of screw  208  through hole  206 , through graft ligament  28 , and into bone B. This will cause screw  208  and plate  201  to securely attach graft ligament  28  to bone B.  
         [0075]    As shown in FIG. 17, alternatively, graft ligament  28  may be passed upwardly through hole  202  and downwardly through hole  204 . Screw  208  is then threaded through hole  206  and graft ligament  28  and into bone B. Thus, as in the embodiment shown in FIG. 16, screw  208  and plate  201  secure graft ligament  28  to bone B.  
         [0076]    [0076]FIGS. 18 and 19 show another graft ligament anchor  200 A. Graft ligament anchor  200 A is similar to graft ligament anchor  200 , except that it includes a plurality of spikes  212  for projecting into wall  210  (FIG. 16) of bone B when the graft ligament anchor is deployed against the bone. Also, graft ligament anchor  200 A has an enlarged configuration  214  in the region of through-hole  206 A, as shown in FIG. 18.  
         [0077]    Referring next to FIG. 20, there is shown a still further alternative embodiment of graft ligament anchor, similar to that shown in FIG. 7, wherein graft ligament engagement means  20  comprises plate means  48  formed in a U-shaped configuration (FIG. 21) movable transversely within bone opening  24 . At least one graft ligament  28  is disposed alongside wall  50  of graft ligament engagement means  20 , which in this instance is a first major surface of plate means  48 . Graft ligament engagement means  20  is disposed between graft ligament  28  and locking means  32 . Locking means  32  may be an expansion plug  46 , as shown in FIG. 20 and in FIG. 7, or a rocker arm type cam member  34 , as shown in FIG. 1, or an interference screw type expansion plug  46 , as shown in FIG. 11, or a transverse screw  208 , as shown in FIG. 16.  
         [0078]    In attachment of one or more graft ligaments  28  to a bone B, using the embodiment of FIG. 20, locking means  32  is manipulated so as to bear against a second major surface  52  of plate means  48  and thereby move plate means  48  into engagement with graft ligament  28 , and thence to drive free ends  49  of plate means  48  into sidewall  38  of opening  24  so as to fasten graft ligament  28  to sidewall  38  and, thereby, to bone B.  
         [0079]    Referring to FIGS. 22 and 23, there is shown still another alternative embodiment of graft ligament anchor including a tubular member  300 , open at first and second ends  302 ,  304  and having an opening  306  in the sidewall thereof. Otherwise, the graft ligament anchor of FIG. 22 is similar to the graft ligament anchor of FIG. 20, described hereinabove.  
         [0080]    In attachment of one or more graft ligaments  28  to a bone, using the embodiment of FIGS. 22 and 23, locking means  32  are manipulated to bear against second major surface  52  of plate means  48  so as to move plate means  48  through tubular member opening  306  and into engagement with graft ligament  28 , and thence further to drive free ends  49  of plate means  48  into sidewall  38  of opening  24 , whereby to fasten tubular member  300  and graft ligament  28  to sidewall  38  and, thereby, to bone B. In this embodiment, and in the embodiments shown in FIGS.  1 - 3 , an operator may fasten the graft ligament to the bone without the graft ligament contacting the bone. The tubular member  300  preferably is of a plastic or metallic material and the plate means  48  is of a plastic or metallic material. In the embodiments shown in FIGS. 20 and 22, the plate means  48  may be provided with interior teeth  47  for gripping graft ligament  28 .  
         [0081]    A further embodiment of the present invention is illustrated in FIG. 24-FIG. 28. FIG. 24 shows a perspective view of a selectively radially expandable sheath  400  having a side wall  401  and defining a central lumen  450 . As illustrated in FIG. 27, sheath  400  is sized to fit within a bone tunnel  600  (FIG. 27) while capturing graft material  28  between an outer surface of the sheath and an inner wall of bone tunnel  600 . Central lumen  450  is sized to accept a sheath expanding element (such as sheath expanding element  700  (FIG. 26) or locking means  32  (see, e.g., FIG. 10)) that expands the sheath radially to fix graft material  28  within bone tunnel  600  as illustrated in FIG. 28.  
         [0082]    Referring again to FIG. 24, sheath  400  can include a proximal or “sheath expander lead-in” end region  403  that is tapered to ease insertion of a sheath expander into central lumen  450 . Lead-in region  403  may have proximal cut-out areas  406  to facilitate radial expansion in the proximal cross-section of sheath  400 . Central lumen  450  may also include female threads  407  on an inside surface  408  of side wall  401  to facilitate a threaded engagement with a threaded sheath expander (such as tapered screw sheath expander  700  (FIG. 26)) in central lumen  450 . Lead-in region  403  of sheath  400  can also include a tab  1000  which may serve as a stop to prevent any overinsertion of sheath  400  into a bone tunnel. The outer diameter of side wall  401  may also taper from a larger diameter in lead-in region  403  to a smaller diameter at distal tip  409  to provide a gradual transition in the amount of ultimate compressive load being applied to graft members  28  during insertion. As with lead-in region  403 , distal tip  409  may have cut-out areas  452  to facilitate radial expansion in the distal cross-section of sheath  400 . A portion of the outside surface of side wall  401  may include ribs  402 , protrusions or other similar features which roughen the outside surface and engage with either or both the wall  600  (FIGS. 27 and 28) of a bone tunnel and graft material  28  when sheath  400  is expanded.  
         [0083]    As illustrated in the cross-sectional view of FIG. 25B, side wall  401  of sheath  400  is divided into four londitudinal side wall segments  405 , each having concave outer surfaces which provide regions  410 ,  420 ,  430 , and  440  where graft material may be disposed between the side wall segments and bone tunnel wall  600  (as further illustrated in FIG. 27). In accordance with the principles of the invention, a sheath expander (such as tapered screw sheath expander  700 ) may be inserted into central lumen  450  of sheath  400  to deform non-circular side wall  401  toward a circular geometry to conform with an outer diameter of expander  700 . Sheath  400  includes a number of features configured to accommodate this deformation.  
         [0084]    In particular, sheath  400  can include one or more structurally weakened fracture regions  490  extending longitudinally along a length of side wall  401 . As used herein, structurally weakened refers to a feature that can allow flexion and/or fracture side wall  401 , in some instances allowing the wall to flex as if it were hinged (and it is further contemplated that a hinge of any type could be a structurally weakened region). In a preferred embodiment, fracture regions  490  extend substantially along or entirely along the length of side wall  401  and may incorporate proximal and distal cut outs  406  and  452 . Further, fracture regions  490  may be configured to flex to allow some radial expansion of the sheath before fracturing to allow even further radial expansion of sheath  400  (post fracture expansion is illustrated in FIG. 28). Fracture regions  490  may be formed by thinning the material of side wall  401  longitudinally in the region of desired fracture, and in one embodiment, may be a longitudinal groove cut into side wall  401 .  
         [0085]    In the illustrative embodiment of FIG. 25B, sheath  400  comprises four longitudinal side wall segments  405  that circumscribe central lumen  450 , each of the longitudinal side wall segments being connected to its neighbors by the four structurally weakened longitudinal fracture regions  490 . While this configuration may be preferred in the situation that the graft material being fixed to a bone tunnel can easily be separated into four components, a person of ordinary skill in the art will recognize that more or fewer side wall segments and structurally weakened regions can be provided to adapt sheath  400  to different fixation requirements. In addition, central lumen need not be fully circumscribed by side wall segments having concave outer surfaces. For example, half of side wall  401  could take the form of one half of a cylinder generally conforming to the shape of the bone tunnel, while the other half of side wall  401  could comprise two or more side wall segments  405  having concave outer surfaces, the side wall segments  405  being connected to each other and to the half cylinder portion by longitudinal fracture regions. Such a configuration may be preferable where a surgeon wishes to fix the graft material to one side of a bone tunnel (such as an anterior or posterior side) at the expense of fixation to the opposed side.  
         [0086]    Concave side wall segments  405  may also include longitudinal flexion regions  480  to aid in allowing the wall segments to expand radially outward to fix graft material to a bone tunnel wall. As with fracture regions  490 , flexion regions can extend substantially along or entirely along the length of side wall  401 . Flexion regions  480  may also be formed by thinning the material of side wall  401  longitudinally in the region of desired flexion, and in one embodiment, may be a longitudinal groove cut into side wall  401 .  
         [0087]    In the illustrated embodiment, each concave side wall segment  405  includes two longitudinal flexion regions  480  which divide the wall segments into three relatively rigid longitudinal subsegments connected by the two longitudinal flexion regions. A person of ordinary skill in the art will recognize that a sheath of the invention could be formed using only one flexion region within a wall segment or by using more than two such flexion regions within the spirit of the invention.  
         [0088]    In one embodiment of the invention, longitudinal fracture regions  490  (which preferably flex before fracturing) have a convex outer surface and act as “outer hinges,” while longitudinal flexion regions  480  act as “inner hinges” to allow a first measure of radial expansion toward a circular geometry by flexing of these inner and outer hinges. This first measure of radial expansion can be followed by fracture of one or more of the longitudinal fracture regions  490  to provide a second measure of radial expansion beyond the first measure.  
         [0089]    The provision of inner  480  and outer  490  hinges in sheath  400  provides resiliency and malleability to side wall  401  and allows for the option of using stiffer, stronger starting stock for sheath  400  than would otherwise be possible. Both inner hinge flexion regions  480  and outer hinge fracture regions  490  serve as concentrated bending areas. However, fracture regions  490  are preferably configured to act as regions of maximum stress as there is less or no graft material  28  to counterbalance radial stresses. If side wall  401  is to fail at any location for lack of ductility or strength, this embodiment allows for breakage to occur at fracture regions  490 , further illustrated in FIG. 28 after fracture as edges  500 . Flexion regions  480 , as thinned regions, are preferably configured to add flexibility to side wall segments  405  and to facilitate increase of the radius of curvature of the concave outer surface of segments  405  without undue risk of breakage on segments  405  which must carry a compressive load to graft material  28 . Accordingly, fracture regions  490  would preferably have a geometry such that the local material stresses during expansion of sheath  400  are always greater than the local stresses at flexion regions  480  so that material rupture will always be directed along the path of fracture regions  490 . This means of controlled rupture ensures that sheath  400  will remain biomechanically functional since the rupture will then occur away from ligament accommodating regions  410 ,  420 ,  430 ,  440 .  
         [0090]    Further, such controlled rupture along fracture regions  490  facilitates use of a wider variety of expander sizes, including the use of expanders having an outer diameter or circumference at least as large as the diameter or circumference of sheath  400 . In this way, a single sheath size may be stocked for a wide variety of procedures and intended bone tunnel sizes. In one embodiment, sheath  400  may be provided in a kit to surgeons in which a plurality of expanders having different sizes are provided for use with a single size sheath.  
         [0091]    The inclusion of fracture regions  490  and/or flexion regions  480  widen the choice of available sheath materials to include, for example, biocompatible bioabsorbable polymers selected from the group consisting of aliphatic polyesters, polyorthoesters, polyanhydrides, polycarbonates, polyurethanes, polyamides and polyalkylene oxides. Sheath  400  may also be formed from absorbable glasses and ceramics (possibly comprising calcium phosphates and other biocompatible metal oxides (i.e., CaO)). Sheath  400  may also be formed from metals; it can comprise combinations of metals, absorbable ceramics, glasses or polymers.  
         [0092]    In further embodiments, the expandable sheath may be fabricated from aliphatic polymer and copolymer polyesters and blends thereof. Suitable monomers include but are not limited to lactic acid, lactide (including L-, D-, meso and D,L mixtures), glycolic acid, glycolide, E-caprolactone, p-dioxanone (1,4-dioxan-2-one), trimethylene carbonate (1,3-dioxan-2-one), delta-valerolactone, beta-butyrolactone, epsilon-decalactone, 2,5-diketomorpholine, pivalolactone, alpha, alpha-diethylpropiolactone, ethylene carbonate, ethylene oxalate, 3-methyl-1,4-dioxane-2,5-dione, 3,3-diethyl-1,4-dioxan-2,5-dione, gamma-but yrol act one, 1,4-dioxepan-2-one, 1,5-dioxepan-2-one, 6,6-dimethyl-dioxepan-2-one, 6,8-dioxabicycloctane-7-one and combinations thereof. These monomers generally are polymerized in the presence of an organometallic catalyst and an initiator at elevated temperatures. The organometallic catalyst may be tin based, (e.g., stannous octoate), and may be present in the monomer mixture at a molar ratio of monomer to catalyst ranging from about 10,000/1 to about 100,000/1. The aliphatic polyesters are typically synthesized in a ring-opening polymerization process. The initiator is typically an alkanol (including diols and polyols), a glycol, a hydroxyacid, or an amine, and is present in the monomer mixture at a molar ratio of monomer to initiator ranging from about 100/1 to about 5000/1. The polymerization typically is carried out at a temperature range from about 80° C. to about 240° C., preferably from about 100° C. to about 220° C., until the desired molecular weight and viscosity are achieved.  
         [0093]    It is to be understood that the present invention is by no means limited to the particular constructions and methods herein disclosed and/or shown in the drawings, but also comprises any modifications or equivalents within the scope of the claims