Patent Abstract:
A threaded suture anchor formed of a material comprising polyether-ether ketone (PEEK) has a suture loop that is disposed internally within the suture anchor. The suture loop can extend through a substantial length of the anchor body with the ends of the suture loop secured at the distal end of the anchor and the proximal end of the loop being flush with or recessed just below the proximal surface of the proximal end of the anchor. The anchor body can be threaded and have a tapered distal portion.

Full Description:
FIELD OF THE INVENTION 
   The present invention relates to an apparatus for anchoring surgical suture to bone. More specifically, the present invention relates to a threaded suture anchor formed of polyether-ether ketone (PEEK) having an internal suture loop for receiving one or more strands of suture to anchor the suture to bone during arthroscopic surgery. 
   BACKGROUND OF THE INVENTION 
   When soft tissue tears away from bone, reattachment becomes necessary. Various devices, including sutures alone, screws, staples, wedges, and plugs have been used in the prior art to secure soft tissue to bone. 
   Recently, various types of threaded suture anchors have been developed for this purpose. Some threaded suture anchors are designed to be inserted into a pre-drilled hole. Other suture anchors are self-tapping. 
   U.S. Pat. No. 4,632,100 discloses a cylindrical threaded suture anchor. The suture anchor of the &#39;100 patent includes a drill bit at a leading end for boring a hole in a bone, followed by a flight of threads spaced from the drill bit for securing the anchor into the hole created by the drill bit. 
   U.S. Pat. No. 5,370,662 discloses a suture anchor having threads which extend to the tip of the anchor. U.S. Pat. No. 5,156,616 discloses a similar suture anchor having an axial opening for holding a knotted piece of suture. 
   All of the above-noted suture anchors include structure for attaching the suture to the anchor. U.S. Pat. No. 4,632,100, for example, discloses a press-fitted disc and knot structure which secures the suture to the anchor. In other suture anchors, such as those disclosed in U.S. Pat. No. 5,370,662, the suture is passed through an eyelet located on the proximal end of the anchor. In the case of a bioabsorbable suture anchor, the suture may be insert molded into the anchor, as disclosed in U.S. Pat. No. 5,964,783. However, the materials used to make such suture anchors can impose limitations on their use. For example, suture anchors made of metal or certain polymers are not radiolucent or radioopaque and thus are not visible on magnetic resonance imaging (“MRI”) scans. In addition, such suture anchors may not be revisable once implanted in the bone. 
   Problems can also arise if the structure for attaching the suture fails, allowing the suture to become detached from the anchor. Also, the suture often is exposed to abrasion or cutting by sharp or rough areas along the walls of the bone canal into which the anchor is inserted. 
   Moreover, the eyelet or, in the case of U.S. Pat. No. 4,632,100, the axial opening for receiving the disc to which the suture is knotted, is formed as part of the drive head of the known suture anchors. Combining these two functions in one structure often tends to weaken the drive head. 
   In addition, various other modifications to the drive head often are employed in connection with suture attachment. For example, recessed grooves may be formed on opposite sides of the drive head to receive and protect the suture from abrasive areas of the suture anchor tunnel or to facilitate mating between the anchor to the driver. In such cases, the drive head often must be made of a larger diameter to recover the mechanical strength lost from the removal of material relating to the suture-attachment or suture-protection modifications. 
   Further, the prior art suture anchors having eyelets extending from the proximal ends require countersinking of the eyelet below the bone surface to avoid having the patient&#39;s tissue abrade against the exposed eyelet. As a result, suture attached to the eyelet is vulnerable to abrasion by the bony rim of the countersunk hole into which the suture anchor is installed. In addition, in biodegradable suture anchors, the suture eyelet can degrade rapidly, causing the suture to become detached from the anchor prematurely. 
   Accordingly, there is a need for a threaded suture anchor to which suture is secured effectively so as to prevent detachment of the suture. It is further desirable for such suture anchors to have eyelets that will not abrade tissue and which do not require countersinking. In addition, a need exists for a suture anchor or implant formed by a material which is visible on MRI scans and is revisable following implantation. 
   BRIEF SUMMARY OF THE INVENTION 
   The suture anchor of the present invention overcomes the disadvantages of the prior art discussed above by providing a threaded suture anchor having a suture loop disposed inside the body of the suture anchor. In one embodiment, the suture anchor is formed from a material comprising polyether-etherketone (“PEEK”). The advantages of PEEK are described in a white paper entitled, “New Materials in Sports Medicine,” Arthrex, Inc. 2005, the disclosure of which is herein incorporated by reference. 
   The proximal end surface of the threaded suture anchor of the present invention is preferably smooth and rounded to minimize suture abrasion, while the distal portion of the anchor is tapered to an elongated point to enable the anchor to be self-tapping. The proximal end portion of the suture anchor body has a hexagonally shaped opening to accept a hexagonal drive head. 
   The internal suture loop extends through a substantial length of the anchor body with the ends of the suture loop secured onto the distal end portion of the anchor and the proximal end of the loop being flush with or recessed just below the plane across the proximal face of the anchor. 
   Advantageously, suture attached to the anchor through the suture loop exits the suture anchor through a central bore in the anchor, which prevents suture abrasion by the wall of the bone tunnel into which the anchor is inserted. 
   Other features and advantages of the present invention will become apparent from the following description of the invention, which refers to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a first preferred embodiment of a suture anchor according to the present invention; 
       FIG. 2  is a side elevational view of the suture anchor shown in  FIG. 1 ; 
       FIG. 3  is a longitudinal sectional view of the suture anchor shown in  FIG. 2  through the plane  3 - 3  indicated therein; 
       FIG. 4  is a cross sectional view of the suture anchor of  FIG. 1  showing the internal suture loop therein, and having suture strands attached to the suture anchor through the internal suture loop. 
       FIG. 5  is a cross sectional view through the suture anchor and suture loop of  FIG. 4  through the plane  6 - 6  indicated therein. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2  illustrate a suture anchor according to a first preferred embodiment of the present invention, indicated generally by reference numeral  110 . In the preferred embodiment, body  108  of anchor  110  has a length of about 0.55 in., a major diameter “a” of about 0.21 in., and a minor diameter “b” of about 0.14 in. Suture anchor body  108  generally tapers to a narrow point  114  at the distal end thereof. In particular, the major diameter of the anchor body is generally constant along about two-thirds of the length of the body, whereupon the diameter of the anchor then tapers to a relatively sharp point, e.g., approximately 16 degrees. In one embodiment, the relatively sharp distal tip of anchor  110  enables the anchor to be installed without having to first drill a hole in the bone where the anchor  110  is to be installed. 
   Although such tapering is preferred, suture anchor  110  may be formed to have a less tapered shape, or even cylindrical shape, to accommodate different preferences of the surgeon and/or the application of the suture anchor. For example, the tapered distal end of the anchor may be formed to be more blunt, in which case it is necessary to provide a pre-formed hole in the bone prior to insertion of the suture anchor. 
   A continuous thread  116  wraps around the body  108  in a clockwise direction, as shown. Anchor  110  has about six flights of thread, with the angle of the proximal surface  128  of each thread being approximately one-third the angle of the distal surface  130  of each thread relative to the horizontal direction perpendicular to the longitudinal axis of the anchor, e.g., 15 degrees versus 45 degrees. 
   As can be seen more clearly with reference to  FIG. 3 , the proximal end portion of the anchor has a hexagonally shaped bore  132  having an opening  120  at the proximal end of anchor body  108  and extending into the anchor body approximately one-fourth of the length thereof. Prior art anchors have sharp edges around the drive opening, which is problematic in that sutures passing through the central opening at the proximal end of the anchor can be abraded by the sharp edges, thereby compromising the strength of the sutures. In one embodiment of the suture anchor of the present invention, the peripheral edges defining hexagonally shaped opening  120  is smooth and rounded outwardly with no sharp edges. Preferably, the opening  120  forms a slight lip curving around the diameter of the bore  132 . Thus, sutures threaded through the anchor  110 , as will be discussed below, will not become frayed upon being pressed or rubbed against the anchor at the proximal opening  120 . 
   A cylindrical bore  136  having a diameter smaller than that of the hexagonally shaped bore  132  extends from the distal end of the hexagonally shaped bore  132  to a position roughly one quarter along the length of anchor body  108 . The transition between hexagonally shaped bore  132  and cylindrical bore  136  forms an annular shoulder  134 , against which the distal end of a hex driver abuts when inserted into the hexagonally shaped bore  132  to drive the anchor into bone. 
   Two longitudinal passageways  126  are formed in anchor body  108  distally to the cylindrical bore  136 , extending from the distal end of bore  136  to two corresponding apertures  118  formed opposite to each other in an offset manner through the angled distal portion of suture anchor  110 . Referring to the cross-sectional view shown in  FIG. 5 , the preferred distance “c” between the centers of the two passageways  126  is about 0.55 in. 
   Apertures  118  each have an inner opening  117  defining the exit from the respective passageway  126 , and widen to a larger, exterior opening  119  along the radial surface of anchor body  108 . As can be seen in  FIG. 2 , apertures  118  are disposed between the threads  116  around anchor body  108 . Due to the shape of apertures  118  and the angle at which apertures  118  intersect passageways  126 , inner openings  117  are slightly oblong and may have an angle along the periphery thereof. Preferably, the peripheral edges defining the inner openings  117  of the suture anchor are smoothed and rounded (e.g., during the manufacturing process) so as to not abrade the suture knots which will be affixed therein (described below). 
   An eyelet formed of a loop of suture  122  is disposed inside the body of suture anchor  110 . The ends of the suture strand forming the loop can be threaded through the longitudinal passageways  126  from the proximal opening  120  and pass into the apertures  118 . Threading the ends of the suture through the passageways  126  and the apertures  118  may be facilitated by coating the ends of the suture (having a length longer than the length of the passageways  126 ) with a stiffening agent. 
   The proximal-most surface of the suture loop  122  is flush with or slightly recessed from the proximal opening  120 , so that the suture loop does not project outside the body  108  of suture anchor  110 . Preferably, the suture loop  122  is recessed between 0.05 to 0.14 in. from the plane across the suture anchor  110  at the proximal opening  120  thereof, as measured from the underside of the proximal-most point of the loop  122 . The underside position corresponds to the depth into the bore  132  at which a suture strand inserted through the loop  122  would be attached to anchor  110 . 
   To secure the suture loop onto anchor body  108 , the ends of suture loop  122  are each tied in a knot  125 , e.g., an overhand knot, and sealed with a biocompatible adhesive to permanently affix the knot. As illustrated in  FIG. 4 , knots  125  are then respectively inserted into the apertures  118  so that the knots are substantially entirely fitted within the space of the apertures  118 . As shown in  FIG. 4 , knots  125  are asymmetrically disposed in their respective apertures  118  relative to a most proximal end  113  of the anchor body  108 . The smaller diameter of inner openings  117  of apertures  118  prevent the knots  125  from being pulled through into the interior of the anchor  110 . Affixed in this manner, suture loop  122  has a pullout strength of 45 lbs. from the suture anchor  110 . 
   Preferably, the suture anchor  110  is formed from a material comprising PEEK. A suture anchor formed from a material comprising PEEK has several advantageous properties. First, PEEK is radiolucent. PEEK does not contain metal and therefore no metallic scatter occurs during magnetic resonance imaging (MRI) scans. 
   In addition, suture anchors formed by PEEK have significantly reduced notch sensitivity resulting in a more stable and resilient suture anchor. The term “resilient” as used herein is not meant to imply that PEEK material is deformable and recovers its size and shape after deformation, rather is intended to mean that PEEK is capable of withstanding shock and other outside forces without deterioration. Specifically, the term “resilient” is taken from the PEEK-Optima Polymer brochure of Invibio Ltd., UK, 2004, where it is stated that PEEK is “resilient and enduring” in the sense that PEEK is “characterized by its high strength. extreme resistance to hydrolysis and resistance to the effects of ionizing radiation. Therefore, PEEK-OPTIMA can be repeatedly sterilized . . . without significant deterioration of mechanical properties.” The construction of an anchor body formed from a material comprising PEEK provides both stable fixation and revisability. Previously available suture anchors may require “wings” or “arms” to provide fixation. In contrast, the threading of the PEEK unibody construction shown in  FIGS. 1-5  provide stable fixation without requiring additional structural features. Furthermore, PEEK suture anchors are revisable, for example, by drilling out the anchor. 
   The mechanical properties of PEEK closely match the mechanical properties of bone: tensile yield strength, shear strength, and modulus. These properties are not significantly degraded by gamma-irradiation, steam-sterilization (water environment), or oxidation (aging). The material is also resistant to heat and requires no special accommodations for shipping and handling. 
   Preferably, the material forming the suture loop  122  is a #5 USP braided polyester suture or #2 FiberWire™, a high strength suture formed of a braid of polyester and ultrahigh molecular weight polyethylene, coated with silicone, and sold by Arthrex, Inc. of Naples, Fla. However, any suitable coated or uncoated suture material can be used with the suture anchor of the invention. 
   The suture anchor according to the present invention need not be formed as a threaded device, but can also be formed as a tap-in type anchor. Also, the measurements, angles and ratios between the dimensions of the suture anchor may be varied from those described above so as to be suitable for the conditions and applications in which the suture anchor is to be used. 
   In manufacturing the suture anchor  110  in accordance with the present invention, the anchor body  108  is machined, with the bores, passageways and apertures described above either being formed during the machining process or formed afterwards. If necessary, the distal tip  114  of the anchor  110  is trimmed to the desired length and the surfaces of the anchor are polished to the desired finish. Alternatively, the anchor body  108  can be cast in a die with the bores, passageways and apertures described above either being formed during the casting process or formed afterwards. 
   Preferably, the suture anchors according to the present invention are distributed to surgeons with one or more strands of suture  138  already threaded through the suture loop. Such sutures attached to the suture anchor through the internal suture loop must be able to slide smoothly through the slightly recessed loop. Sutures suitable for use in conjunction with the suture anchor and internal suture loop discussed herein include #2 FiberWire™ and #2 braided polyester. If more than one suture strand is provided through the suture loop, each strand is preferably a different color, e.g., green, white, blue, etc., or may be provided with color contrasting strands. 
   Optionally, or if it becomes necessary due to the pre-threaded suture strands being accidentally removed from the suture loop, the user may be required to thread or re-thread the suture strands through the suture loop. In this case, threading a strand of suture through the suture loop may be facilitated if the ends of the suture strand are coated with a stiffening agent. Alternatively or additionally, a tool may be used to thread the suture strands and/or grasp the end of the suture after passing through the suture loop. 
   As mentioned above, the suture anchor of the present invention may be installed in the bone without the need to pre-drill a hole in the bone. The suture anchor is installed using a driver having a shaft having a hexagonal cross-section for at least a length equal to the length of the hexagonal bore  132 ,  232  from proximal opening  120 ,  220  to the shoulder  134 ,  234  inside the anchor  110 ,  210 . The driver has a cannula extending through the entire length thereof, with openings at the proximal and distal ends thereof. The outer diameter of the hexagonal shaft can be sized to fit inside the hexagonal bore in the anchor so as to be enabled to drive the same. 
   With the desired number of suture strands threaded through the suture loop in the suture anchor, the ends of the suture strands are threaded through the cannula in the hex driver from the distal end thereof and exiting from the proximal opening thereof. The distal end of the hexagonal shaft of the driver can be inserted into the proximal end of the anchor while the suture loop is inserted into the distal end opening of the driver. With the distal end of the driver abutting shoulder  134  and the anchor positioned at the location at which it is to be installed, the hex driver is rotated to drive the anchor into the bone until the proximal surface of the anchor is flush with the surface of the bone. 
   Since it is not necessary for the proximal end of the anchor to be countersunk below the bone surface to prevent tissue abrasion by an exposed suture loop, as is required with prior art devices, the suture anchor of the present invention does not need to be inserted as far as the prior art anchors, while also avoiding abrasion of the sutures by the rim of the bone. 
   The suture anchor of the present invention provides greater pull-out strength of the suture loop than prior suture anchors. In addition, the suture loop of the present invention, being disposed inside the suture anchor, is protected from abrasion and degradation. 
   Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. Therefore, the present invention is to be limited not by the specific disclosure herein, but only by the appended claims.

Technology Classification (CPC): 0