Abstract:
A knotless bone anchor and method for securing soft tissue, such as tendons, to bone, includes a plurality of discrete components. In one variation of the invention, the bone anchor includes a proximal toggle component, an intermediate plug component, and a distal sleeve component. Suture is looped around the plug component and once the anchor is actuated, the suture is compressed between the plug and the sleeve components. Advantageously, one or more of the components may be made of a biocompatible polymer. The polymeric components may be detachably joined to a drive shaft using a plurality of sacrificial fills. The sacrificial fills are broken or severed during deployment of the anchor. Related instruments and methods are also described.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/913,985 filed Apr. 25, 2007, the complete disclosure of which is incorporated herein by reference for all purposes. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates generally to methods and apparatus for attaching soft tissue to bone, and more particularly to anchors and methods for securing connective tissue, such as ligaments or tendons, to bone. The invention has particular application to arthroscopic surgical techniques for reattaching the rotator cuff to the humeral head, in order to repair the rotator cuff. 
     BACKGROUND 
     It is an increasingly common problem for tendons and other soft, connective tissues to tear or to detach from associated bone. One such type of tear or detachment is a “rotator cuff” tear, wherein the supraspinatus tendon separates from the humerus, causing pain and loss of ability to elevate and externally rotate the arm. Complete separation can occur if the shoulder is subjected to gross trauma, but typically, the tear begins as a small lesion, especially in older patients. 
     To repair a torn rotator cuff, the typical course today is to do so surgically, through a large incision. This approach is presently taken in almost 99% of rotator cuff repair cases. There are two types of open surgical approaches for repair of the rotator cuff, one known as the “classic open” and the other as the “mini-open”. The classic open approach requires a large incision and complete detachment of the deltoid muscle from the acromion to facilitate exposure. The cuff is debrided to ensure suture attachment to viable tissue and to create a reasonable edge approximation. In addition, the humeral head is abraded or notched at the proposed soft tissue to bone reattachment point, as healing is enhanced on a raw bone surface. A series of small diameter holes, referred to as “transosseous tunnels”, are “punched” through the bone laterally from the abraded or notched surface to a point on the outside surface of the greater tuberosity, commonly a distance of 2 to 3 cm. Finally, the cuff is sutured and secured to the bone by pulling the suture ends through the transosseous tunnels and tying them together using the bone between two successive tunnels as a bridge, after which the deltoid muscle must be surgically reattached to the acromion. Because of this maneuver, the deltoid requires postoperative protection, thus retarding rehabilitation and possibly resulting in residual weakness. Complete rehabilitation takes approximately 9 to 12 months. 
     The mini-open technique differs from the classic approach by gaining access through a smaller incision and splitting rather than detaching the deltoid. Additionally, this procedure is typically performed in conjunction with arthroscopic acromial decompression. Once the deltoid is split, it is retracted to expose the rotator cuff tear. As before, the cuff is debrided, the humeral head is abraded, and the so-called “transosseous tunnels”, are “punched” through the bone or suture anchors are inserted. Following the suturing of the rotator cuff to the humeral head, the split deltoid is surgically repaired. 
     The above described surgical techniques are associated with a great deal of patient discomfort and a lengthy recovery time, ranging from at least four months to one year or more. It is the above described manipulation of the deltoid muscle together with the large skin incision that causes the majority of patient discomfort and an increased recovery time. 
     Various less invasive arthroscopic techniques are beginning to be developed in an effort to address the shortcomings of open surgical repair. Working through small trocar portals that minimize disruption of the deltoid muscle, a few surgeons have been able to reattach the rotator cuff using various bone anchor and suture configurations. The rotator cuff is sutured intracorporeally and an anchor is driven into bone at a location appropriate for repair. Rather than thread the suture through transosseous tunnels which are difficult or impossible to create arthroscopically using current techniques, the repair is completed by tying the cuff down against bone using the anchor and suture. Early results of less invasive techniques are encouraging, with a substantial reduction in both patient recovery time and discomfort. 
     Unfortunately, the skill level required to facilitate an entirely arthroscopic repair of the rotator cuff is inordinately high. Intracorporeal suturing is clumsy and time consuming, and only the simplest stitch patterns can be utilized. Extracorporeal knot tying is somewhat less difficult, but the tightness of the knots is difficult to judge, and the tension cannot later be adjusted. Also, because of the use of bone anchors to provide a suture fixation point in the bone, the knots that secure the soft tissues to the anchor by necessity leave the knot bundle on top of the soft tissues. In the case of rotator cuff repair, this means that the knot bundle is left in the shoulder capsule where it can be felt by the patient postoperatively when the patient exercises the shoulder joint. So, knots tied arthroscopically are difficult to achieve, difficult or impossible to adjust, and are located in less than optimal areas of the shoulder. Suture tension is also impossible to measure and adjust once the knot has been fixed. Much skill is required to both place the sutures in the soft tissues, and to tie knots while working through a trocar under endoscopic visualization. 
     There have been attempts to solve the problem of placing sutures in soft tissues and tying knots in an endoscopic environment, and there have been attempts to address the problem and to simplify the process of suture fixation. One such approach is disclosed in U.S. Pat. No. 5,383,905 to Golds et al. The patent describes a device for securing a suture loop about bodily tissue that includes a bead member having a longitudinal bore and an anchor member adapted to be slidably inserted within the bore of the bead member. The anchor member includes at least two axial compressible sections which define a passageway to receive two end portions of a suture loop. The axial sections collapse radially inwardly upon insertion of the anchor member within the bore of the bead member to securely wedge the suture end portions received within the passageway. 
     Although the Golds et al. patent approach utilizes a wedge-shaped member to lock the sutures in place, the suture legs are passing through the bore of the bead only one time, in a proximal to distal direction, and are locked by the collapsing of the wedge, which creates an interference on the longitudinal bore of the anchor member. Also, no provision is made in this design for attachment of sutures to bone. The design is primarily suited for locking a suture loop, such as is used for ligation or approximation of soft tissues. 
     An approach that includes bone attachment is described in U.S. Pat. No. 5,584,835 to Greenfield. In this patent, a two part device for attaching soft tissue to bone is shown. A bone anchor portion is screwed into a hole in the bone, and is disposed to accept a plug that has been adapted to receive sutures. In one embodiment, the suture plug is configured so that when it is forced into its receptacle in the bone anchor portion, sutures that have been passed through an eyelet in the plug are trapped by friction between the wall of the anchor portion and the body of the plug portion. 
     Although there is some merit to this approach for eliminating the need for knots in the attachment of sutures to bone, a problem with being able to properly set the tension in the sutures exists. The user is required to pull on the sutures until appropriate tension is achieved, and then to set the plug portion into the bone anchor portion. This action increases the tension in the sutures, and may garrotte the soft tissues or increase the tension in the sutures beyond the tensile strength of the material, breaking the sutures. In addition, the minimal surface area provided by this anchor design for pinching or locking the sutures in place will abrade or damage the suture such that the suture&#39;s ability to resist load will be greatly compromised. 
     A disclosure that incorporates bone attachment and eliminates knot tying is set forth in U.S. Pat. No. 5,702,397 to Goble et al. One embodiment, in particular, is shown in FIG. 23 of that patent and includes a bone anchor that has a threaded body with an inner cavity. The cavity is open to one end of the threaded body, and joins two lumens that run out to the other end of the threaded body. Within the cavity is disposed a gear, journaled on an axle. A length of suture is threaded through one lumen, around the gear, and out through the other lumen. A ball is disposed within the cavity to ride against a tapered race and ostensibly lock the suture in place. What is not clear from the patent disclosure is how the force D shown as the tension in the suture would lock the ball into the race. Although this embodiment purports to be a self-locking anchor adapted for use in blind holes for fixing sutures into bone, the construct shown is complicated, and does not appear to be adequate to reliably fixate the suture. 
     Another approach for repairing the rotator cuff or fixing other soft tissues to bone, wherein suture tension can be adjusted, the suture anchor resides completely below the cortical bone surface, and there is no requirement for the surgeon to tie a knot to attach the suture to the bone anchor is disclosed in U.S. Pat. Nos. 6,770,076; 7,083,638; and 6,780,198 assigned to Opus Medical, and now assigned to ArthroCare Corporation. These patents disclose, amongst other things, a knotless anchor system comprising a bone anchor and insertion instrument that affixes an anchor in a bone passageway with a toggling structure, semi-automatically tensions the suture until the tissue is in a desired location, and immobilizes the suture by compressing the suture between various components of the anchor. Despite these patents setting forth various techniques for arthroscopically attaching tissue and generally overcoming many of the shortcomings identified above, enhanced anchoring and deployment systems are still desirable. 
     A significant number of surgeons prefer that the bone anchors they use in the performance of, for example, a rotator cuff repair be constructed of materials that are non-metallic. This allows for easier post operative imaging using MRI. Also, in the event of a revision to the initial surgery, non metallic anchors are easier to work around or drill through. Therefore, it is desirable, for example, to provide an anchoring system having a robust polymeric suture guide that is capable of holding a suture in place while withstanding the forces imposed on it during suture tensioning; to provide an anchoring system made of a wide variety of materials having varying degrees of strength; to provide an improved insertion instrument that can be conveniently actuated to deploy and detach one or more anchor components from the insertion instrument; and to provide an improved bone preparation instrument that can create spaces for the above described devices. 
     SUMMARY OF THE INVENTION 
     One embodiment of the present invention is a bone anchor for attaching tissue to a bone. The anchor has multiple separate or discrete components including a bone affixing component, a suture guide component, and a suture locking component. The bone affixing component serves to hold the anchor in a bone tunnel, the suture guide component serves to hold the suture during tensioning, and the suture locking component serves to immobilize the suture. 
     In another embodiment of the present invention, the bone affixing component is an oval-shaped disc. The disc has a first, low profile, insertion orientation and a second, radially enlarged, deployed orientation. The enlarged cross section of the deployed orientation securely affixes the anchor in a bone tunnel. 
     In another embodiment of the present invention, the suture guide component has a plug or bullet shape. The suture is looped around the plug and is held in position along a path by the suture guide. The plug, due to its robust monolithic design, may be made of a polymer or another material known to have less mechanical strength than various metals such as stainless steel. The plug is positioned distal to the affixation structure such that when a suture is tensioned around the plug member, a proximal surface of the plug abuts a distal surface of the bone affixation structure, thus providing a fixed point to which the soft tissues being repaired may be referenced. The plug member around which the suture is passed is immobile relative to the surface of the bone, and provides a means by which the soft tissues may be held in apposition to the bone at a desired tension. 
     In another embodiment of the present invention, the sleeve component includes an internal cavity or lumen that is sized to accept the plug component therein. The size of the internal lumen or cavity is such that there is a gap between the inner suture guide member and wall of the internal lumen. However, when a suture is present in the suture guide or channel of the plug component, and the sleeve component is positioned coaxially to the plug, the suture is compressed and therefore immobilized by frictional forces developed between the suture limbs, the plug, and the sleeve. 
     One or more of the components of the bone anchor may be detachably joined to a driver shaft. The anchor components may be joined to the driver shaft by one or more sacrificial fills. The sacrificial fill may be severed or broken to deploy the individual component, and separate the anchor component from the shaft upon actuation of the driver instrument. In one embodiment, an elongate die tube and driver shaft are concentric. The die tube is disposed exteriorly and includes a distal abutment surface. As the inner drive shaft is pulled proximally, one or more of the anchor components abuts the distal end of the die shaft and is forced off the drive shaft. In this manner the sacrificial fills securely hold the anchor on the shaft during insertion and until deployment is desired. 
     In another embodiment of the present invention, the sacrificial fills are sized differently from one another. The sacrificial fills corresponding to the toggle have a different size than those corresponding to the plug. In one embodiment, the sacrificial fills corresponding to the toggle member include a set of sacrificial fills that are smaller in diameter than a set of sacrificial fills corresponding to the plug member, or the sleeve member. 
     In another embodiment of the present invention a method for securing a soft tissue to a bone body includes placing a stitch in the soft tissue to obtain at least one free suture end; threading a bone anchor with the free suture end; inserting the anchor into a bone tunnel; actuating a first component of the anchor to affix the anchor in the bone tunnel; tensioning the suture until the tissue is held under tension in a desired location subsequent to the actuating step; and locking the suture wherein the anchor is detached from the drive member by severing the sacrificial fills. The sacrificial fills join the anchor to the drive shaft and may be made of polymer. Additionally, the actuating step may be carried out by toggling the first anchor component. The method may further be limited to attaching specific tissue such as the rotator cuff. The anchor may comprise a suture guide or channel component including a plug-shaped body having an external groove disposed about an exterior surface. The locking step may be carried out by compressing the suture between a plug component and a sleeve component. 
     In another embodiment of the present invention, a bone tunnel preparation instrument is adapted to undercut a subcortical tissue mass along a bone passageway or socket. The instrument includes a distal end section and a lateral window in the distal end section that houses a punch member. The punch member has at least one cutting edge and is operatively connected to a manual trigger. Upon actuation of the trigger, the cutting edge of the punch protrudes from the window to the extent that the trigger is actuated thereby modifying and cutting out subcortical tissue in the vicinity of the window. 
     The punch shape in one embodiment includes a trailing cutting edge that is opposite the leading cutting edge and a tissue capture area that engulfs tissue as the punch sweeps out from the window. The punch may be pivotally mounted within the window so as to pivot when it is actuated. In one embodiment of the present invention, the punch sweeps a tissue area matching that of a bone anchor to be deployed in the bone tunnel. In another embodiment, a distance between the cutting leading edge and a fixed stop along the instrument shaft remains constant as the cutting edge sweeps through tissue. 
     Still other embodiments of the present invention shall become apparent to the reader upon reading the following disclosure with reference to the appended figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1E  are partial sectional views illustrating the steps to carry out attaching soft tissue to bone in accordance with one embodiment of the present invention; 
         FIGS. 2A-2B  are enlarged sectional views illustrating locking a suture in an anchor to reattach a rotator cuff tendon; 
         FIG. 3A  is a partial perspective view of an anchor positioned on a distal end of a delivery instrument in accordance with the present invention; 
         FIG. 3B  is a partial perspective view of the distal end of the delivery instrument shown in  FIG. 3A  excluding the anchor; 
         FIGS. 4A-4C  are partial sectional views illustrating the steps to carry out preparation of a bone passage or tunnel using a punch instrument in accordance with one embodiment of the present invention; 
         FIG. 5A  is a side view of the bone tunnel preparation instrument in a low profile delivery or insertion configuration; 
         FIG. 5B  is an enlarged view of the distal end section of the instrument shown in  FIG. 5A ; 
         FIG. 6A  is a side view of the bone tunnel preparation instrument in a large profile or actuated configuration; 
         FIG. 6B  is an enlarged view of the distal end section of the instrument shown in  FIG. 6A . 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides an improved knotless suture anchor apparatus for anchoring a length of suture with respect to a body cavity. In the exemplary embodiment described herein, the apparatus is used to anchor a length of suture to a bone structure, for example, the humeral bone of the human shoulder. The length of suture is desirably looped through soft tissue, such as a rotator cuff tendon, to approximate and fix the soft tissue with respect to the body cavity (e.g., bone structure). It should be understood, however, that the suture anchor apparatus may be utilized to secure a length of suture to body cavities other than in a bone structure, and may even be used to anchor the suture outside of a body cavity, merely to a predetermined location within the body. In this regard, the preferred apparatus includes one or more anchor components within which the length of suture may be anchored without knots. The anchor also includes one or more components or structures to affix the anchor in a bone passageway. 
     As mentioned herein, the present invention is particularly well-suited for repairing rotator cuff injuries by re-attaching the rotator cuff tendon to the outside of the humeral head. The invention permits minimally invasive surgeries on such injuries and greatly facilitates rapid and secure fixation of the rotator cuff tendon to the humeral head. It should be understood that the same principles described herein apply to the repair of other injuries in which soft tissue is to be re-attached to a bone structure. 
       FIGS. 1A-1E  show a procedure for repairing a rotator cuff tendon injury in accordance with the present invention. Referring first to  FIG. 1A , a partial cross-sectional view through the left shoulder of a human as viewed from the front is illustrated. The rotator cuff tendon  40  is shown in its natural position overlying the bulbous humeral head  42  of the humerus bone. In rotator cuff injuries, the tendon  40  partially or completely separates from its attachment point to the humeral head  42 , which point of attachment is typically located along an angled shelf, the greater tuberosity. In minimally invasive surgeries to repair the rotator cuff injury, the surgeon threads one or more sutures  28  through the rotator cuff tendon  40  and anchors them to the greater tuberosity. The suture anchor system, as will be described below, facilitates this latter step of anchoring the sutures to the greater tuberosity. 
       FIG. 1A  shows a generally tubular trocar  50  that provides a conduit through the soft tissue of the shoulder. Typically, the surgeon makes an incision or stab wound through the outer dermal layers of sufficient size to permit passage of the trocar  50  through the skin and the deltoid muscle into proximity with the humeral head  42 . Various trocars and techniques for creating the approach passageway are known and may be utilized with the present invention. In addition, more than one incision and conduit may be necessary to perform the several suturing and anchoring steps. 
     After establishing one or more direct conduits to the humeral head  42 , the surgeon passes a length of suture through the soft tissue of the rotator cuff tendon  40  so that a loop  34  of suture material is embedded therein, as seen in  FIG. 1A . The two free ends  33   a ,  33   b  of the length of suture are withdrawn from the patient and coupled to a suture anchor system. The anchor may be threaded with the suture  28  by hand, with a tool, or perhaps with a snare or wire loop as described in U.S. Pat. No. 6,780,198 the entirety of which is incorporated by reference. 
       FIG. 1B  shows a suture anchor  120  inserted in the bone tunnel or cavity  52 . Next, as shown in  FIG. 1C , the anchor is affixed to the bone using an anchoring structure or component  130  located on the proximal end of the suture anchor  120 . The anchoring structure  130  functions as a toggle member, and rotates from a low profile insertion position to a radially enlarged deployed position. The anchoring component  130  is deployed distal to the hard cortical bone layer  46 . In this manner, the suture anchor  120  is prevented from being removed from the tunnel  52  once the anchoring structure  130  is deployed. Although the present invention illustrates a particular anchoring structure  130 , any similar expedient will work. Examples of other suitable anchoring structures include those shown in U.S. Pat. Nos. 6,770,076 and 6,582,453, the disclosures of which are hereby incorporated by reference in their entirety. Alternatively, an anchoring structure that expands into contact with or is screwed into the cancellous matter  48  may be used. In short, the present invention includes various anchoring structures except where expressly excluded in the appended claims. 
       FIG. 1D  shows the anchoring system in an unlocked position subsequent to tension being applied to the suture. Tensioning of the tissue may be carried out by hand by simply pulling on the sutures or, more preferably, with a semiautomatic or tensioning mechanism as described in U.S. Pat. No. 6,780,198 the disclosure of which is hereby incorporated by reference in its entirety. In this manner, the suture may be tensioned until the tissue is positioned in a target location. 
       FIG. 1E  shows the step of locking or immobilizing the suture between two components of the anchor without the use of knots. In particular, the suture is compressed between plug  140  and sleeve  150 . Locking the suture between multiple components is also described in U.S. Pat. No. 7,083,638 the disclosure of which is hereby incorporated by reference in its entirety. 
     Although not shown, the remaining steps in the procedure involve withdrawing the instruments from the surgical site and severing the free ends  33   a ,  33   b  close to the suture anchor. 
       FIGS. 2A-2B  illustrate additional details of the suture anchor  120  in operation. In particular,  FIG. 2A  illustrates the anchor  120  affixed in a bone tunnel subsequent to the suture  28  being tensioned with a force F suture . The tissue  40  is positioned at a desired location adjacent the bone body.  FIG. 2B  illustrates the anchor  120  affixed in the bone tunnel subsequent to locking the suture between plug  140  and sleeve  150 . In this embodiment of the present invention, the suture extends along a suture guide on an exterior surface of the plug  140 , across a distal surface of the plug  140 , and returns in the proximal direction to exit the anchor and the bone tunnel. Sleeve  150  is shown as a tubular shaped component having a lumen or cavity that is adapted to receive the plug. A small gap exists between the exterior surface of the plug and the interior surface of the cavity or sleeve such that there is no interference or compression fit between the plug and the sleeve. The gap is less than the thickness of the suture(s) so that the suture is squeezed when the sleeve is urged or pulled over the plug. Indeed, the suture becomes immobilized or locked once the sleeve surrounds the plug. This permanently attaches tissue  40  to the bone. 
     Although  FIGS. 2A-2B  show a particular design, the shapes of the anchor components may vary. The plug  140  may have, for example, a bullet shape, cylindrical, spherical, elongate, tapering, or solid shape. Preferably the plug is substantially robust so as to serve at least two functions 1) provide enough force to squeeze and lock the suture, and 2) provide a suture guide that can withstand forces arising from the above mentioned tensioning step. Additionally, although a simple pin, pulley or cross bar may be sufficient when the plug is made of a metal, a more robust shape such as that shown in  FIGS. 2A-2B  is preferred for materials having less strength such as certain polymers including for example polyetheretherketone (PEEK). Other biocompatible, bioabsorbable or bioactive materials may be incorporated into the design as well. 
       FIG. 3A  shows an enlarged perspective partial view of an undeployed anchor  120 , suture  28 , and distal end section of a driver  200 . Each of the components of the anchor are shown connected to drive shaft  210 . In particular, toggle member  130  is proximal to plug  140 . Plug  140  is proximal to sleeve  150 . Additionally, a space is present between each of the components such that the anchor components are separated, disconnected, or, in a sense, “free floating”. But for the drive shaft  210  and the anchor&#39;s detachable connection to the drive shaft as shall be explained in more detail below, the anchor components would be unconstrained and allowed to fall out of position. 
     In one embodiment of the present invention, as described above, the anchor is affixed in the bone. To this end, an anchoring component such as toggle  130  is moved perpendicular to the longitudinal axis of the shaft. This deployment may be achieved by providing relative opposite motion between drive shaft  210  and driver die  220  such that the die surface forces the toggle to rotate to a transverse direction. 
     Though not fully shown in these Figures, the driver preferably includes a handle, elongate shaft, and actuation lever or trigger. The actuator member serves to deploy the bone affixing structure, tension the suture, and/or lock the suture in place. An example of a driver instrument is illustrated in U.S. Pat. No. 6,780,198 which is incorporated by reference in its entirety. 
       FIG. 3B  shows an example of a distal end section of a driver instrument  200 . Driver shaft  210  is shown having a generally tubular shape and terminating in two arms or ribbons  236   a,b , that extend longitudinally. A plurality of holes are arranged on the driver shaft including toggle holes, plug holes, and sleeve holes. Each hole accepts, receives, or is filled with a sacrificial fill or link extending from the anchor. A purpose of the sacrificial fills is to securely hold the anchor components on the shaft until the surgeon desires to actuate and deploy the components. When the surgeon desires to actuate and detach the components from the shaft, relative motion between the drive shaft and the driver die  220  causes the distal surface of the die to push the anchor off the drive shaft. The sacrificial fills shear or break as the drive die  220  pushes the anchor  120 . As discussed further below, the sacrificial fills may be designed to control the order in which the anchor components are actuated (or detached). Additionally, the anchor and sacrificial fills may be conveniently inserted molded onto the shaft so that the anchor is formed on the shaft and the plurality of holes are filled with molten polymer. When the polymer solidifies, the sacrificial fills are created. 
       FIG. 3B  shows the holes increasing in diameter along the length of the driver shaft. This design encourages the most proximal fills to break first, and to encourage the more distal fills along the length of the driver ribbons  236   a,b  to break last. In particular, the sleeve holes  252  have a larger diameter than the plug holes  242 , and the toggle holes  232 . Similarly, sleeve holes have a progression of increased diameter. Selection of the diameter, location, shape, and number of holes affects the holding strength of the anchor component to the drive shaft. In this embodiment, the anchor affixation or toggle member is actuated and detached from the shaft first. The toggle holes  232  are less numerous and may be smaller than the other fill holes. The sleeve holes  252   a  are the largest and require the most force to break. The sleeve therefore is the last anchor component to be detached or break from the shaft  210 . This sequence is desired because the suture locking step is the final step. 
     Walking through the sequence of operation again, and referring to  FIGS. 3A-3B , when the delivery system pulls on the driver tube  210 , the toggle  130  is forced against the driver die  220 , breaking the attachments created by the holes  232  and turning the toggle perpendicular to the axis of the anchor. The suture is then tightened, and when the user is satisfied with the suture tension and is ready to lock the suture  28  in place, the delivery system then urges the driver  210  further proximal. A flange  142  abuts the lower (distal) surface  134  of the toggle  130 , which places the bonds created between plug holes  242  and the plug  140  in shear. The sacrificial fills break, freeing the plug  140  from the driver ribbons  236 , and allow the sleeve  150  to begin to travel proximally as well. The sleeve  150  slides up over the plug  140 , trapping the suture in place. When tabs  152  on the sleeve  150  abut the flange  142  on the plug  140 , the sacrificial fills or bonds formed between the sleeve holes  252  and the sleeve  150  are placed in shear. The bonds break, allowing the driver ribbons  236   a,b  to be withdrawn from the bone anchor  120 , completing the deployment. 
     Once deployed, the free floating components are held or bound together by virtue of the suture, extending from the anchor, looping through the tissue, and returning to the anchor. The tension on the suture holds the components together and against the cortical bone shelf. In this manner, this multi-component embodiment provides an elegant solution for attaching tissue to bone. 
       FIGS. 4A-4C  show another embodiment of the present invention comprising preparing a bone tunnel  300  for accepting an expanding anchor (not shown). In particular, an enlarged subcortical space  310  is created in this embodiment along the bone tunnel or cavity. Referring first to  FIG. 4A , a tunnel  300  is created using a drill, punch, or another instrument  302 . 
     Next, an undercut tool or punch  304  is inserted into the bone tunnel  300  and gradually actuated to modify and create a radially enlarged space  310  in a subcortical layer of bone  322 . As shown in  FIG. 4B , a cutting edge  350  extends from a window  352  of the punch  304  to carve out, cut, or capture tissue. 
       FIG. 4C  shows the enlarged subcortical space  310  with the undercut punch  304  removed. The enlarged subcortical space  310  is intended to mimic the shape of the volume that is swept or created by the toggle component, described above, during the bone anchor deployment. The creation of an enlarged subcortical space along the bone tunnel is particularly useful when anchors are to be deployed that have a relatively weak, atraumatic, brittle, or flexible bone affixation structure (e.g., toggle ring) because such structures may not consistently or reliably displace bone tissue and achieve a suitable bone lock. It is thus desirable to pre-treat the tunnel and create a subcortical space to receive the bone-affixation structure (e.g., a toggle) such that the anchor may safely lock. 
       FIGS. 5A-5B  show a side view of an undercut punch  304  in a low profile (or insertion) mode. Punch  304  is shown having an elongate shaft  306  connected to a handle  308   a . A trigger or actuator  308   b  is joined to the handle to cause the recessed blade  350  to extend beyond the window and sweep or capture tissue.  FIG. 5B  is an enlarged view of the distal section of the elongate shaft  306 . In particular, distal section includes an inner drive shaft  362 , a die shaft  364 , and a blade  350  recessed in a window  352 . The blade or punch rotates about a pin  356  as the trigger is actuated. Additionally, the punch includes a tip  360  shown at a first distance A 1  from the end of the drive die  364 . The tip is shown having a rounded, atraumatic end. Additionally, the leading edge of blade  350  is spaced D from the drive die. 
       FIGS. 6A-6B  show a side view of the undercut punch  304  after it has been actuated. In particular, actuation member  308   b  is shown compressed or manipulated towards handle  308   a . This relative motion between the handle and trigger urges the inner drive shaft  362 , and tip  360  proximally such that distance A 2  is less than A 1 . 
     A link member  358  pivotally connects to blade  350  and holds the blade a fixed distance D from the drive die  364 . The blade leading edge  350  thus tends to move laterally during its travel and not longitudinally. This substantially lateral or transverse sweep ensures that the blade&#39;s sweep mimics the path of the anchor&#39;s toggle component, described above. 
     Additionally, the trailing edge  354  pivots in a direction opposite to the leading edge  350 . The trailing edge is shown having a tissue capturing area as well as a plurality of teeth. It is to be understood that the blade may comprise a number of blade surfaces, tissue capture areas, teeth, and other features to sweep tissue and prepare the tunnel for accepting a bone anchor device. 
     Accordingly, although an exemplary embodiment of the invention has been shown and described, it is to be understood that all the terms used herein are descriptive rather than limiting, and that many changes, modifications, combinations, and substitutions may be made by one having ordinary skill in the art without departing from the spirit and scope of the invention. In particular, it is noted that the procedures, while oriented toward the arthroscopic repair of the rotator cuff, are applicable to the repair of any body location wherein it is desired to attach or reattach soft tissue to bone, particularly using an arthroscopic procedure.