Abstract:
An improved suture anchor has one or more channels formed into the exterior surface of the anchor body. The channels may be used to inject a compound, such as filler material or an adhesive, into the implant site. Preferably, the channels connect to a retainer in the anchor body for a suture to pass through, preventing the suture from being compressed and allowing removal and adjustment of a suture retained by the anchor after the anchor is installed in a bone. The retainer is preferably a slot formed into the distal end of the anchor body. In a method of securing tissue to bone, an insertion tool is used to insert the suture into the anchor and install the anchor into an implant site in the bone. If the suture later fails, the channels may be used to fill the implant site with bone cement for redrilling. Preferably, the suture anchor is made of human cortical bone or a similarly bioabsorbable and osteoconductive material.

Description:
FIELD OF INVENTION 
       [0001]    This invention relates to methods and devices for attaching tissue to bone. This invention relates particularly to a suture anchor that is installed in bone. 
       BACKGROUND 
       [0002]    The field of orthopedic surgery addresses the need to reattach tissue, particularly connective tissue such as tendons and ligaments, to bone following detachment due to injury or surgery. One approach that is commonly used is to install an implant in the bone at the reattachment site. The tissue is then tied to the implant with one or more lengths of suture. Eventually, the tissue heals by reconnecting to the bone. The implant, known as an anchor, and the sutures may be left in the body or removed. 
         [0003]    There are several drawbacks to this procedure. Commonly-used materials for an anchor include metals, plastics, and other nonorganics that may cause adverse biochemical reactions in the body, such as bone and tissue necrosis and other damage, rejection of the implant by the body, and release of toxins into healthy tissue, bone marrow, or the blood stream through degradation of the implant. Additionally, these materials are not bioabsorbable or osteoconductive, so their permanent implantation may prevent the bone from fully healing. It would be advantageous to develop a suture anchor that has more favorable biochemical properties. 
         [0004]    Another drawback with most existing anchors relates to securely fastening the anchor, and thereby the suture, to the bone. Some anchors are threaded like a screw and therefore are screwed into the bone, with the threads essentially cutting into the bone to secure the anchor. This can traumatize or otherwise damage the living bone when inserted and removed. Additionally, most anchors are loaded with suture before insertion. If the anchor must be twisted to seat it in the bone, pre-loaded suture will also be twisted, potentially damaging the suture. Other anchors are ribbed and are forced into a hole in the bone that is slightly smaller in diameter than the ribs. While this design may not twist the suture, it may still traumatize or otherwise damage the surrounding bone, and may also damage the anchor due to the force required to fully insert the anchor. 
         [0005]    Push-in anchors are known to be substantially the same size as the hole into which they are inserted. Most such anchors are then secured by an adhesive. Using an adhesive, however, is potentially messy and expensive, requires an additional step, and may not be an option at all if the anchor is a temporary implant. An anchor that can be secured in place without these problems is needed. 
         [0006]    These problems have been recently addressed using suture anchors made of bioabsorbable, osteoconductive material, including human cortical bone. These materials are absorbed by the living bone as new bone tissue develops around the implant and into its porous body. Additionally, these materials do not damage the living bone or tissue, do not release toxins, are far less likely than nonorganic materials to be rejected by the body, and allow the bone to fully heal. Typically, cortical bone material is pulverized and used as an additive in molding the anchor, but certain anchor designs made from whole cortical bone are known. For example, the Musculoskeletal Transplant Foundation produces the ALLOFIX® line of biologic suture anchors, which are machined from cortical bone of the tibia or femur of a human cadaver. It has been shown that the ALLOFIX® suture anchors are fully incorporated into the surrounding live bone and are no longer visible on x-ray films within four months of implantation. Further, it has been shown that allogenic cortical bone will naturally expand by about 3% of its size when it is inserted and contacts living bone. The mechanism of this expansion is not fully understood, but is believed to be caused largely by hydrolysis, due to the porosity of the cortical bone. The expansion of the anchor is sufficient to secure it in place, so that a push-in anchor may be used without adhesive. The expansion also encourages osteoconduction from the living bone to the anchor. 
         [0007]    While these relatively new implants exhibit improved biochemical properties over nonorganic designs, they continue to suffer from other design drawbacks. One problem involves the use of an eyelet attached to or passing through the anchor for securing the suture to the anchor. Some anchors have eyelets attached at the top of the anchor, much like the head of a needle. These eyelets are prone to breaking off, and otherwise prevent insertion of the anchor so it is flush with the bone, because the eyelet protrudes. In other anchors, such as the ALLOFIX® anchors, the eyelet is a tunnel through the anchor body. These anchors secure the suture in place by wedging it between the anchor and the bone during insertion, a process known as interference fit. Interference overcomes the problems with protruding eyelets, but unfortunately creates a potentially more hazardous problem in “pinching” the suture. Specifically, the tensile strength of the suture may be dramatically reduced where it is pinched, and some sutures may be observably damaged when pinched due to their thickness or composition. Another drawback is the difficulty, and often impossibility, of repositioning a suture or removing a broken suture without removing the anchor. An anchor that securely retains the suture and accommodates all types of sutures without reducing the tensile strength of the suture is needed. 
         [0008]    Through all approaches to suture anchors, a key design element is the anchor&#39;s resistance to the high tensile forces often imparted by connective tissue. The most problematic anchor susceptibilities are referred to as bending, which is the anchor&#39;s resistance to becoming concave or convex; shear, which is the anchor&#39;s resistance to lateral breakage; and pullout, which is the anchor&#39;s resistance to being withdrawn from the insertion hole. A suture anchor that addresses the drawbacks of existing anchors while maintaining acceptable resistances is desired. 
         [0009]    Therefore, it is an object of this invention to provide an apparatus to reattach tissue that has become detached from bone. It is a further object that the device be composed of a material that is not harmful to the body. Another object of this invention is to provide an attachment device that does not damage the bone as it is inserted. A further object is to provide a suture anchor that may be used with any suture. A further object is that the suture anchor allows easy repositioning and removal of an attached suture. Another object is that the suture anchor does not reduce the tensile strength of the suture when inserted. Another object is to provide a method of attaching tissue to bone using a bioabsorbable suture anchor without reducing the tensile strength of the suture. 
       SUMMARY OF THE INVENTION 
       [0010]    A suture anchor is installed in bone and receives a suture which is in turn attached to tissue, such as a tendon, capsule, or ligament, creating a temporary or permanent attachment of the tissue to the bone. The anchor is preferably cylindrical, most preferably having planar ends. The anchor is preferably made out of a bioabsorbable material, most preferably human cortical bone, or another osteoconductive material capable of incorporation with the living bone to which it is anchored. Chemical reactions from direct contact with the living bone cause the anchor to expand, securing the anchor in place until the anchor is incorporated into the living bone. 
         [0011]    The anchor has a retainer formed into the anchor body. The retainer receives a suture and holds the suture in place. In the preferred embodiment, the retainer is a slot formed into the end of the anchor body that goes into the bone, so that the suture is retained behind the anchor when the anchor is installed. One or more channels are formed into the anchor body, running substantially parallel to the axis of the anchor body and connecting to the retainer. The suture may pass through these channels and out of the bone, so that the tensile strength of the suture is not affected by compression forces, such as in interference fit. The channels may be used to adjust the placement of a loaded suture by pulling one of the loose ends. Additionally, the channels may be used to deliver filling material into the hole behind the anchor as needed. In an alternative embodiment, the retainer may be an eyelet through the anchor body, and the channels connect to the eyelet. 
         [0012]    To attach the tissue to the bone, a hole may be drilled in the bone to receive the anchor. An insertion tool may be used to load the suture into the anchor and then insert the anchor into the hole. The sutures may be repositioned through the channels in the anchor, and are then attached to the tissue by conventional means. A broken suture may be removed by pulling it through the channels, and the channels and retainer may be filled with bone cement or another compound so that the insertion site may be reused for anchoring if needed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a side perspective view of a first embodiment of a suture anchor with a length of suture loaded in the anchor. 
           [0014]      FIG. 2  is a right side view of the suture anchor of  FIG. 1 . 
           [0015]      FIG. 3  is a top view of the suture anchor of  FIG. 1 . 
           [0016]      FIG. 4  is a side perspective view of the preferred embodiment of the suture anchor with a length of suture loaded in the anchor. 
           [0017]      FIG. 5  is a right side view of the suture anchor of  FIG. 4 . 
           [0018]      FIG. 6  is a bottom view of the suture anchor of  FIG. 4 . 
           [0019]      FIG. 7  a top perspective view of an insertion tool used in the surgical system. 
           [0020]      FIG. 8  is a bottom view of the insertion tool of  FIG. 7   
           [0021]      FIGS. 9A-9B  illustrate a front view of using the insertion tool of  FIG. 7  to load a suture into the preferred anchor, with the anchor shown in cross-section taken along line  4 - 4  of  FIG. 4 , and the shaft and handle of the insertion tool shown in cross-section taken along line  7 - 7  of  FIG. 7 . 
           [0022]      FIGS. 10A-10C  are partial cross-sectional side views of a method of implanting the preferred suture anchor in a human calcaneus. 
           [0023]      FIGS. 11A-11B  are cross-section side views of a method of filling a bone void behind the preferred suture anchor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring to  FIGS. 1-6 , there is illustrated the preferred embodiment of the present invention, designated generally as  10 , which is a suture anchor that is implanted in a living bone so that one or more retained sutures  40  may be used to attach tissue to the bone. The anchor  10  comprises an anchor body  11  having a proximal end  12  and a distal end  13 . The anchor  10  is inserted into the bone distal end  13  first. The anchor  10  may be any size and shape that is capable of anchoring the target tissue to the target bone, including cylindrical, prism-shaped with any two-dimensional shaped base, pyramidal, conal, or a combination of such shapes. For example, in a first embodiment illustrated in  FIGS. 1-3 , the anchor body  11  is substantially bullet-shaped, having a cylindrical portion starting at the proximal end  12  and tapering from a first diameter D to a second diameter D′ at the distal end  13 . Preferably, the anchor body is cylindrical with planar ends  12 ,  13  that are orthogonal to the axis A-A of the cylinder. See  FIGS. 4-6 . The exterior surface of the anchor body  11 , being the surface that contacts the living bone on insertion, is preferably substantially smooth, but may comprise projections designed to secure the anchor  10  to the living bone, such as ribs or threads. In other embodiments, one or both of the proximal end  12  and distal end  13  may be non-planar, such as concave, convex, or tapered. Further, if one or both of the proximal end  12  and distal end  13  are planar, the plane of each planar end may be non-orthogonal to the axis A-A of the anchor body  11 , to a degree that is beneficial for the implementation. 
         [0025]    The proximal end  12  may have an insertion guide  17  formed into its surface. The insertion guide  17  helps a physician position an insertion tool properly on the proximal end  12  to insert the anchor  10  into the bone. In the embodiment shown, the insertion guide  17  is a set of orthogonal grooves formed into the proximal end  12 . The insertion tool for this embodiment has corresponding projections formed into the surface that contacts the anchor  10  for insertion. The insertion guide  17  may have any desirable configuration, including a configuration that is specific to a certain model of insertion tool, or a configuration that is usable by several different insertion tools. The preferred insertion guide  17  corresponds to the insertion tool  50  described below. 
         [0026]    A retainer  14  is formed into the anchor body  11  and configured to retain one or more sutures  40  in place when the anchor  10  is implanted. The retainer  11  may be formed through the anchor body  11 , or may be formed into the distal end  13  of the anchor body  11 . Referring to  FIGS. 1-3 , a retainer  14  that passes through the anchor body  11  is loaded with suture  40  by threading a loose end of the suture  40  through the retainer  14  and pulling the end until the desired length of suture  40  is played out on either side of the anchor  10 . Preferably, however, the retainer  14  is a suture slot formed into the distal end  13  and spanning the diameter of the anchor body  11 . See  FIGS. 4-6 . This embodiment of the anchor  10  is easier to load because threading of the suture  40  through the retainer  14  is not necessary; rather, the suture  40  is inserted into the slot at the desired point along the length of the suture  40 . 
         [0027]    The size and shape of the retainer  14  and its location on the anchor body  11  may depend on the number, length, and type of sutures  40  used, and may further depend on certain properties of the anchor  10 , including the anchor&#39;s  10  size, shape, and composition. A retainer  14  that passes through the anchor body  11 , as in  FIG. 1 , may have a circular, ovular, triangular, square, or otherwise polygonal profile, and may be uniform or variable. Such a retainer  14  may be positioned between the proximal end  12  and the distal end  13 , at a distance from the proximal end  12  that is favorable to the intended use of the anchor. Specifically, positioning the retainer  14  close to the proximal end  12  increases the ease of loading the anchor  12  with sutures  40  after implantation because a shorter length must be played out before the loose end of the suture  40  emerges from the opposite end of the retainer  14 . On the other hand, positioning the retainer  14  further from the proximal end  12  increases the anchor&#39;s resistance to tensile forces and better protects against the suture tearing through the anchor  10  because there is more material between the suture  40  and the proximal end  12 . 
         [0028]    Referring again to  FIGS. 4-6 , a retainer  14  that is formed into the distal end  13  may have a concave, triangular, square, or rectangular profile, or another similar shape. Preferably, the retainer  14  has a rectangular profile and is wide enough to allow insertion of multiple sutures  40 . Preferably, the width W of the retainer  14  is between 10% and 33% of the diameter D of the anchor  10 , and is most preferably 33%. The preferred depth P may be referred to as a percentage of the length of the anchor body  11 , and may be as long as 80% of the length of the anchor body  11 . A deeper retainer  14  provides shorter channels  15 ,  16 , and so less of the suture  40  contacts the anchor  10 . However, the anchor&#39;s  10  resistance to pullout decreases as the proximity of the suture  40  to the proximal end  12  increases. The depth P is therefore preferably in the range of. 10% to 25% of the length of the anchor body  11 , which is deep enough to retain sutures  40  while keeping a substantial portion of the anchor body  11  above the suture  40  to prevent pullout. 
         [0029]    One or more channels  15 ,  16  may be formed into the exterior surface of the anchor body  11 , the exterior surface being the surface that contacts the living bone on insertion. The channels  15 ,  16  provide access to the implant site to perform one or more functions as described below. The channels  15 ,  16  preferably connect the retainer  14  to the proximal end  12 . In some embodiments, the channels  15 ,  16  may extend past the retainer  14 , and may further extend to the distal end  13 . Preferably, the channels  15 ,  16  are straight, and most preferably are formed substantially parallel to the axis A-A of the anchor body  11 . Alternatively, one or more of the channels may be curved or zigzagged or otherwise askew. 
         [0030]    The channels  15 ,  16  may have multiple functions. One function is to inject a compound, such as filler material or an adhesive, into any empty space behind the anchor  10  once the anchor  10  is implanted. For this function it is not necessary to have multiple channels  15 ; a single channel  15  that extends from the proximal end  12  to the distal end  13  is sufficient. Additionally, it is not necessary that the channel  15  connect to the retainer  14  if the sole purpose of the channel  15  is to inject a compound. For this function, the channel  15  is shaped to accommodate an injecting tool, such as a syringe. See  FIGS. 8A-B  and the description below. 
         [0031]    Another function of the channels  15 ,  16  is to form, essentially, a passage from the proximal end  12  of the anchor body  11  down into the implant site, through the retainer  14 , and back to the proximal end  12 . See  FIGS. 1-6 , where the passage is formed by a first channel  15  connecting to one end of the retainer  14 , and a second channel  16  connecting to the other end of the retainer  14 , with both channels  15 ,  16  extending to the proximal end  12 . The passage may be used to maintain the sutures  40  while the anchor  10  is implanted, without removing the anchor  10 . Maintaining the sutures  40  may include removing a damaged or unwanted suture  40 , and adjusting the position of a suture  40  in the retainer  14 . The channels  15 ,  16  therefore have a width, and depth relative to the surface of the anchor body  11 , that can accommodate the desired number and width of sutures  40 . As illustrated, the channels  15 ,  16  are preferably concave. Alternatively, the channels  15 ,  16  may have a triangular, rectangular, or other polygonal profile. In the preferred embodiment, there are two channels  15 ,  16  positioned opposite, or 180 degrees from each other on the anchor body  11 . 
         [0032]    The anchor body  11  may be made of any material now known or later developed to be used for bone implants, including metal, polymers such as polylactic acid, bioabsorbable compounds, compounds comprising processed cortical bone, and machined cortical bone. Preferably, the anchor body  11  is machined from a single piece of cortical bone sourced from a human cadaver. Once implanted, it is expected that the preferred anchor  10  will expand by about 3% of its size, which is sufficient to secure the anchor  10  in place by interference fit. Additionally, new bone tissue from the living bone forms on the surface and into the porous structure of the anchor  10 . It is further theorized that additional chemical bonds form between the living bone and the anchor  10  along the contacting surfaces, further holding the anchor  10  in place and absorbing the anchor  10 . 
         [0033]    It is contemplated in the present invention to provide the inventive channels and slot-shaped retainer  14  to existing and future-developed suture anchor designs. Because a suture anchor may be used at substantially any location in the body, the properties of the anchor  10 , including the size, shape, and composition of the anchor body  11 , retainer  14 , and one or more channels  15 ,  16 , may depend on the intended use of the anchor  10 . The intended use may be defined by one or more of: the bone into which the anchor  10  will be implanted; the condition of the bone; the location, entry angle, width, and depth of the hole into which the anchor  10  will be inserted; whether the anchor  10  is replacing a failed implant; the tissue to which the suture  40  is to be attached, and the properties and condition of that tissue; the number, width, and composition of the sutures  40 , and the desired performance characteristics of the anchor  10 . The present inventive anchor  10  may be implanted into any bone and used to reattach any tissue. 
         [0034]    Preferably, the anchor  10  is loaded with suture  40  and installed into the implantation site using an insertion tool  50 . Referring to  FIGS. 7 ,  8 , and  9 A-B, the insertion tool  50  has a shaft  51  with a handle  52  attached to its proximal end. The face  53  of the distal end of the shaft  51  contacts the proximal end  12  of the anchor  10 . Preferably, the face  53  comprises a protruding alignment guide  54  that cooperates with the insertion guide  17  on the anchor  10 . A reel duct  55  passes through the shaft  51  substantially orthogonally to the axis of the shaft  51 , and a pin duct  56  is positioned substantially coaxially with the shaft  51 , passing through the handle  52  and extending into the shaft  51 , intersecting the reel duct  55  and terminating at a point that is distal of the reel duct  55 . The reel duct  55  receives a reel  57  that is slightly smaller than the diameter of the reel duct  55  so it may rotate freely in the reel duct  55 . The reel  57  has a plurality of locking holes  59  passing through the reel  57  and aligned with the pin duct  56 . Preferably, the locking holes  59  are spaced uniformly around the reel  57  so that each locking hole  59  has a diametrically opposed locking hole  59 . A pin  60  having a pin shaft  61  and a pin head  62  fits into the pin duct  56  such that the head  62  contacts the top of the handle  52  when the pin  60  is fully inserted. The pin  60  passes through diametrically opposed locking holes  59  to prevent the reel  57  from rotating. 
         [0035]    Referring to  FIGS. 9A and 9B , the insertion tool  50  is configured to retain the anchor  10  in a desired alignment and hold the suture  40  under slight tension in the retainer  14  and along the channels  15 ,  16  for installation. The alignment guide  54  cooperates with the insertion guide  17  to align the channels  15 ,  16  with the reel  57 . The suture  40  is loaded by inserting it into the retainer  14  at the desired point along the length of the suture, typically the midpoint. The loose ends, which may be attached to suture needles as is known in the art, are then wrapped at least once around the reel  57 . The ends may be wrapped by hand, but preferably the ends are wrapped around the reel ends  58  and the reel  57  is rotated to take up the slack in the suture  40 . The suture  40  is wrapped until slight tension retains the suture  40  in the retainer  14  and at least partially within the channels  15 ,  16 . Then, the pin  60  is inserted into the pin duct  56 , passing through a pair of diametrically opposed locking holes  59  to lock the reel  57  in place. Once the anchor  10  is installed in the implantation site, the pin  60  is pulled out, unlocking the reel  57 . The insertion tool  50  is then withdrawn, and as it is withdrawn the suture  40  unspools from the reel  57 , leaving the loose ends available for tying to the tissue. 
         [0036]    By example, there is illustrated in  FIGS. 10A-C  a method of using the preferred anchor  10  in a human ankle reconstructive surgery.  FIG. 10A  illustrates the calcaneal tendon  71  having been severed from its attachment point to the calcaneus  70 , which is illustrated in partial cross-section. The preferred anchor  10  is used to reattach the tendon. In this example, the preferred anchor  10  has a diameter of 6 mm and a length of 12 mm. First, as shown in  FIG. 10A , a hole  72  is drilled into the calcaneus  70  so that the axis of the hole  72  is at an angle of between 90 and 135 degrees from the suture  40  when it is tied in place. This angle is in accordance with the “deadman” theory developed by Burkhart. Parisien 8:76 (Third Edition). The hole  72  is substantially the same diameter and length as the anchor  10 . 
         [0037]    Then, the anchor  10  is loaded with a size 2-0 suture  40 , which has a diameter of 0.3 mm, using the insertion tool  50  as shown in  FIGS. 9A-B  and described above. Once the anchor  10  is loaded and positioned on the insertion tool  50 , the distal end  13  is placed at the mouth of the hole  72 . The physician applies pressure to the handle  52 , pushing the anchor  10  into the hole  72 . Referring again to  FIG. 10B , when the proximal end  12  of the anchor  10  is substantially flush with the surface of the calcaneus  70 , the pin  60  is pulled from the locked position and the insertion tool  50  is withdrawn, spooling the suture off of the reel  57 . The suture  40  passes out of the channels  15 ,  16 , leaving the loose ends to be attached to the tendon  71  as is known in the art. The anchor  10  expands, securing itself in the hole  72 . Then, as shown in  FIG. 10C , the tendon  71  is positioned so it may be sewn into place with the suture  40 . 
         [0038]    If the suture  40  must be removed due to breakage, damage, or poor placement of the anchor  10 , the physician can detach the suture  40  from one or both suture needles and pull the suture  40  out of the tendon  71  and out of the anchor  10  through the channels  15 ,  16 . Referring to  FIGS. 11A-B , the physician may then fill in any bone voids in the implantation site, such as a drill tip void  81  left from drilling the hole  72 . The channels  15 ,  16  themselves may also be filled. In  FIG. 11A , a needle  83  of a syringe  82  filled with bone cement  84  is inserted into the channel  15 . Depressing the plunger fills the drill tip void  81  with bone cement  84 , and the bone cement  84  also fills the second channel (not shown) and, finally, the first channel  15  as the needle  83  is withdrawn. This completely fills the implantation site. See  FIG. 11B . Once the bone cement  84  has set, the implantation site may be redrilled for a new anchor  10  if desired. 
         [0039]    While there has been illustrated and described what is at present considered to be the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the invention. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.