Patent Publication Number: US-2013245685-A1

Title: Suture anchor with improved torsional drive head

Description:
CROSS-REFERENCE TO PRIOR APPLICATION 
     This application is a divisional of co-pending application Ser. No. 13/494,395, filed on Jun. 12, 2012, which is a divisional of co-pending application Ser. No. 11/170,419, filed on Jun. 29, 2005 (now U.S. Pat. No. 8,197,509). The entire contents of each are hereby incorporated by reference and for which priority is claimed under 35 U.S.C. §120. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to suture anchors having improved physical properties, more particularly, to biologically compatible suture anchors requiring torsional forces to secure their application within body tissue. 
     BACKGROUND OF THE INVENTION 
     Suture anchors are often used to attach a length of suture to bone in order to use the suture to secure detached soft tissue to the bone. Suture anchors typically have an anchor body, a suture attachment element, and a bone-engaging member for facilitating placement and retaining the suture anchor within bone. The anchor can be inserted into a preformed hole in the bone, and/or the anchor can be self-tapping and thus can include threads for securing the anchor within bone. Oftentimes suture anchors require the application of torsional forces from an insertion tool at one end of the anchor to drive the suture anchor into bone, as with screw-type anchors. Insertion tools are typically formed from an elongate shank having a mating element formed on a distal end thereof for mating with a corresponding mating element formed on or in the drive head of the fixation device. One common type of driver tool includes a hexagonal-shaped or square-shaped socket for receiving a corresponding hexagonal-shaped or square-shaped head of a suture anchor. 
     While conventional suture anchors and their drivers are sufficient, they have some drawbacks. Anchor heads with hexagonal or square shaped cross-sections, for example, tend to have a relatively low stripping strength, meaning that under relatively small torque loads the drive head is permanently damaged and torque transfer is thus inhibited. Additionally, this low stripping strength can be further reduced due to the structural integrity of the anchor head, whose drive interface has been compromised or weakened to some degree by the incorporation of a suture attachment element such as an eyelet used to attach the suture to the anchor head. If the head shape of an attachment element decreases the amount of material on the anchor drive head that interfaces with the driver, then the amount of material that needs to yield or be “stripped” from the drive head is reduced, thus reducing the stripping strength of the head. 
     Conventional suture anchor heads also tend to have a relatively low failure torque, which can result in shearing off of the drive head during insertion. This type of failure is also dependent upon the geometry of the head. In suture anchors, this failure may be exacerbated by the location of the suture attachment element in the head. In particular, if a loop is molded into and embedded within the anchor such that the loop extends outward from the head of the anchor to receive a suture, the entire drive head is relatively weakened and thus has the potential to shear off during insertion. 
     Suture anchors were historically constructed of implantable metals and alloys which afforded sufficiently high tensile and torsional strength to withstand the rigors of insertion, but the implant remained in the body for prolonged periods of time. Polymer, ceramic, or composite material systems, both biodegradable and non-biodegradable, have been developed for similar applications, but typically have lower tensile and torsional strength than metal counterparts, thus increasing the risk of device failure during application of high torque loads during insertion, as described above. More recently, biodegradable composite material systems have been developed that incorporate filler materials within the polymer matrix, such as calcium phosphate particles, which are osteoconductive. These filled systems may have further reduced tensile or torsional properties compared to unfilled polymer systems. Thus there is a need for an improved torsional drive head for suture anchors that have higher torsional resistance to strippage or shearing off. 
     One option to increase the failure torque of an anchor is to increase the size of the drive head. Large anchor heads, however, require a large driver tool, which in turn requires a relatively large tunnel to be formed in the bone. This is particularly undesirable, especially where the tunnel is to be formed in the cancellous bone, and where the procedure is minimally invasive and must traverse through a cannula or arthroscope. Accordingly, most suture anchors are adapted for use with a relatively small driver tool, and thus have relatively small drive heads which can result in a low failure torque and a low stripping strength, particularly in harder bone applications. A drive head of improved torsional strength is desirable to reduce the risk of deformation during insertion. Deformation may cause distortion of the anchor near the suture attachment regions, which can inhibit suture slideability necessary to afford knot tying. Additionally, a torsional drive head more resistant to deformation may make a revision procedure easier, as there are some instances where torque driven anchors need to be backed out and perhaps even reinserted. 
     Accordingly, there remains a need for suture anchors having improved physical properties, and in particular having a high failure torque and a high stripping strength. 
     SUMMARY 
     The present invention provides a suture anchor including an elongate shank that includes proximal and distal ends and defines a longitudinal axis. The shank further includes formed thereon at least one engaging member for facilitating placement of the suture anchor within the bone and securing the suture anchor in the bone once implanted. The suture anchor also includes a drive head having a proximal end, a distal end and a radial cross-sectional geometry; where the distal end is mated to the proximal end of the elongate shank. The drive head includes at least one suture attachment element formed in a portion thereof and at least one anti-rotational member integral therewith, which has a longitudinal cross-sectional geometry. The invention is also directed to suture anchor installation kits containing the suture anchor and a driver tool, as well as methods for attachment of soft tissue to bone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings. 
         FIG. 1A  is a perspective view of a suture anchor of the present invention. 
         FIG. 1B  is another perspective view of the suture anchor shown in  FIG. 1A . 
         FIG. 1C  is top view of the suture anchor shown in  FIG. 1A . 
         FIG. 1D  is another perspective view of a suture anchor of the present invention, showing a suture in place. 
         FIG. 1E  is a cross sectional view of the drive head portion of a suture anchor of the present invention with a suture in place. 
         FIG. 2  is a perspective view of an alternate embodiment of the drive head portion of a suture anchor of the present invention. 
         FIG. 3  is a perspective view of an alternate embodiment of the drive head portion of a suture anchor of the present invention. 
         FIG. 4  is a perspective view of an alternate embodiment of the drive head portion of a suture anchor of the present invention. 
         FIG. 5  is a perspective view of an alternate embodiment of the drive head portion of a suture anchor of the present invention. 
         FIG. 6  is a perspective view of an alternate embodiment of the drive head portion of a suture anchor of the present invention. 
         FIG. 7  is a perspective view of an alternate embodiment of the drive head portion of a suture anchor of the present invention. 
         FIG. 8A  is a side view of one embodiment of a driver tool in accordance with the present invention. 
         FIG. 8B  is an end view of the distal-most end of the driver tool shown in  FIG. 8A . 
         FIG. 9A  is a perspective view of one embodiment of a suture anchor and driver tool where the head of the driver is not mated with the socket of the driver tool. 
         FIG. 9B  is a perspective view of one embodiment of a suture anchor and driver tool of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a suture anchor including an elongate shank defining a longitudinal axis and having at least one engaging member formed therewith to engage bone and facilitate placement of the suture anchor within the bone and to secure the suture anchor in the bone once implanted. The suture anchor also includes a drive head for applying torsion to the elongate shank having a proximal end and a distal end and which is mated to the elongate shank so as to transfer the torsion to the elongate shank, thereby providing for placement of the suture anchor within the bone. The drive head may have a circular or a substantially non-circular radial cross-sectional geometry, for example an oval, and includes at least one anti-rotational member (ARM) formed integral therewith to provide for improved transfer of the torsion to the shank, and a suture attachment element formed in a portion of the drive head for attaching a suture to the suture anchor. As used herein, member is meant to include a structural unit of the shank and/or drive head, respectively, each of which forms a part of the suture anchor. As used herein, element is meant to include a constituent of the drive head for receiving a suture, for example a suture tunnel and/or suture channel. 
     In one embodiment, the suture attachment element comprises a suture tunnel extending through the drive head, either substantially transversely or such that the suture tunnel intersects the longitudinal axis of the suture anchor. The suture tunnel is of sufficient diameter so as to allow a suture of a selected size to pass there through. The suture is passed through the tunnel and looped through such that both suture ends (either with or without a needle) point in the same direction and can then be loaded onto the suture anchor driver. The suture attachment element can also include a longitudinally oriented suture-receiving channel in cooperation with the suture tunnel formed on an outer surface of the drive head. In one embodiment, the suture tunnel is formed proximal to the distal end of the drive head to present a channel-free portion in the drive head. The channel-free portion provides additional structural integrity to the drive head of the suture anchor to minimize the risk of shearing during insertion. In another embodiment, the drive head includes a first suture tunnel having a first pair of opposed suture-receiving channels extending proximally there from, and a second suture tunnel having a second pair of opposed suture-receiving channels extending proximally there from. 
     In one embodiment the suture anchor comprises a drive head of circular or substantially non-circular radial cross-sectional geometry with at least one ARM integral therewith. In a second embodiment, the suture anchor comprises a drive head of circular or substantially non-circular radial cross-sectional geometry with multiple ARMs located on either side of a plane of symmetry for ease of inserter application. The ARMs are of configuration and dimension effective to provide a mating fit with the driver tool in order to ensure efficient transfer of torsion from the drive head to the shank. The presence of the ARMs provides high failure torque and high stripping strength. 
     In other aspects, a suture anchor and installation kit is provided, including at least one suture anchor and a cylindrical driver tool for cooperating with the suture anchor. The suture anchor has a shank with an engaging member formed thereon and defining a longitudinal axis. A drive head is formed on the shank and has a circular or substantially non-circular radial cross-sectional geometry, such as oval, and at least one ARM formed integral therewith. The cylindrical driver tool has a distal end with a socket formed therein having a shape adapted to receive and engage the drive head of the anchor in a mating relationship. The ARM(s) also provide positive mating with the driver tool, such as a key in keyway configuration, to reduce driver slip-off, especially during off-angle insertions. In an exemplary embodiment, the driver tool has an outer diameter that is equal to or less than an outer-most diameter of the engaging member of the anchor. 
     As shown in  FIGS. 1A-1E , where like numbers refer to like features, the present invention generally provides suture anchor  10 , including elongate shank  12  defining longitudinal axis A and having at least one engaging member  20  formed thereon. In the embodiment shown, engaging member  20  is a helical thread. Drive head  30  has proximal end  32  and distal end  34  mated to elongate shank  12  at proximal end  14 . Drive head  30  has a an oval radial cross-sectional geometry, though drive head  30  could have a substantially circular, rectangular, square, hexagonal, or flattened oval radial cross-sectional geometry, and includes at least one suture attachment element  38  formed therein. The radial cross-section is defined as the cross-section perpendicular to longitudinal axis A. Generally, oval is known to include flattened ovals and ovals with flat portions perpendicular to the major X 2  or minor X 1  diameters of drive head  30 . In an exemplary embodiment, minor diameter X 1  of drive head  30  is about three-fourths the size of major diameter X 2 , and major diameter X 2  of drive head  30  is equal to or less than minor diameter d 1  of shank  12 . 
     The configuration of drive head  30  includes at least one ARM  36  protruding from and integral with drive head  30  and extending from distal end  34  towards proximal end  32  of drive head  30 . Additionally, drive head  30  contains at least one suture tunnel  38  and further contains suture-receiving channels  33   a  and  33   b.  ARM  36  is shown here in the plane of suture tunnel  38 , although those skilled in the art, once having the benefit of this disclosure, will realize that ARM  36  and suture tunnel  38  need not align with one another. It may be desirable for such an alignment of ARM  36  with suture tunnel  38  to occur to further strengthen the suture tunnel region, although this is not necessary within the scope of the invention. The configuration of drive head  30  with ARM  36  is particularly advantageous in that it provides suture anchor  10  with improved physical properties, including a high failure torque and high stripping strength. 
     Elongate shank  12  of suture anchor  10  can have a variety of configurations and can include a variety of engaging members  20  formed thereon.  FIG. 1A  illustrates an exemplary embodiment of suture anchor  10  having shank  12  including core  18  with single helical thread  20  extending around core  18  from proximal end  14  to distal end  16  of shank  12 . Thread  20  includes proximal and distal facing flanks  22  and  24 , respectively, that extend between base  26  and substantially flattened crest  28 . Thread  20  defines major diameter d 2  of shank  12 , which can vary along the length of shank  12 , although major diameter d 2  is substantially constant along a substantial portion of shank  12 . Threads  20 , however, can taper at the distal portion of shank  12  to terminate at apex  29  of shank  12 . Core  18  of shank  12  defines minor diameter d 1  that can also be substantially constant, or can vary along the length of shank  12 . As shown in  FIG. 1A , core  18  tapers from proximal end  14  to distal end  16 . Once having the benefit of this disclosure, one skilled in the art will appreciate that shank  12  shown in  FIG. 1A  is merely an exemplary embodiment of shank  12 , and that a variety of shanks having different tissue-engaging members can be used with suture anchor  10  in accordance with the present invention. 
     Drive head  30  of suture anchor  10  is shown in more detail in  FIGS. 1B and 1C , and is attached to, or formed integrally with, shank  12 . The relatively small size of major diameter X 2  of drive head  30 , as compared to major diameter d 2  of shank  12 , is particularly desirable so that drive head  30  will not require a larger tunnel to be formed in the bone than is necessary. Drive head  30  further includes length L h  (shown in  FIG. 1A ) that extends between proximal and distal ends  32  and  34  thereof. Length L h  of drive head  30  can vary, although length L h  of drive head  30  may be optimized to allow the drive head to be received within a driver tool and to be driven into bone without shearing off. Drive head  30  has ARM  36  extending along length L h  between distal end  34  of drive head  30  and the opening of suture tunnel  38 . 
     While a variety of suture attachment elements can be used,  FIGS. 1A-1E  illustrate an exemplary embodiment of suture anchor  10  having suture tunnel  38  that extends through drive head  30  and that allows a length of suture to be disposed there through. Suture tunnel  38  may terminate at a position proximal to distal end  32  of drive head  30  to provide channel-free portion  35  in drive head  30 . Since distal portion  34  of anchor head  30  is typically the part of anchor  10  that is under the most stress during insertion, channel-free portion  35  (shown as shaded area) provides a much stronger, more dense portion of drive head  30  that will minimize the risk of shearing during insertion. 
     Suture anchor  10  can also optionally include longitudinally oriented suture-receiving grooves or channels  33   a  and  33   b  formed therein. Suture-receiving channels  33   a  and  33   b  are formed in the outer surface of drive head  30  and may be spaced equidistant from one another. As shown in  FIG. 1C , two opposed suture-receiving channels  33   a  and  33   b  are positioned along minor diameter X 1  of drive head  30 . 
       FIGS. 1D and 1E  show drive head  30  of the present invention with ARM  36  and suture  11 . Suture  11  is shown passing through drive head  30  by means of suture tunnel  38 . A longitudinal cross-sectional view of drive head  30  with suture  11  passing through suture tunnel  38  and along suture-receiving channels  33   a  and  33   b  is shown in  FIG. 1E . 
       FIG. 2  shows an alternate embodiment of drive head  40  of a suture anchor according to the present invention. In this embodiment, the radial cross-sectional geometry of drive head  40  is substantially oval in shape with ARM  46  thereon that originates at distal end  44  and extends to the opening of suture tunnel  48 . As shown, ARM  46  is tapered from suture tunnel  48  towards distal end  44 . Once having the benefit of this disclosure, those skilled in the art will recognize that ARM  46  may be of other longitudinal cross-sectional geometries, e.g. parabolic, wedge, etc., without deviating from the scope of the invention, and that the ARM may extend only partially from distal end  44  toward proximal end  42 . Additionally, ARM  46  may taper in the opposite orientation, i.e. from distal end  44  towards proximal end  42 . 
     In alternate embodiments, the suture anchor of the present invention may have multiple suture tunnels extending transversely through the anchor, preferably at different positions along the longitudinal axis of the suture anchor so that they would not intersect one another. These suture tunnels may be located in the drive head of the suture anchor and affect the structural integrity of the drive head. 
     As shown in  FIG. 3 , suture tunnels  58   a  and  58   b  and suture-receiving channels  51   a,    51   b,    51   c,  and  51   d  may be positioned along the longitudinal axis of drive head  50 . The position of suture-receiving channels  51   a,    51   b,    51   c,  and  51   d  can also vary, in one embodiment extending through proximal end  53  of drive head  50  and terminate at an opening of the corresponding suture tunnel. For example, suture-receiving channels  51   a  and  51   c  correspond to suture tunnel  58   a  and suture-receiving channels  51   b  and  51   d  correspond to suture tunnel  58   b.  Where the suture tunnels are positioned proximal to distal end  54  of drive head  50 , suture-receiving channels  51   a,    51   b,    51   c,  and  51   d  can also terminate at a position proximal to distal end  54  of drive head  50  to provide a channel-free portion similar to that shown in  FIG. 1B  in the head  30 . Moreover, where two suture tunnels are provided at locations along the length of the drive head  50 , a first pair of opposed suture-receiving channels, e.g., suture-receiving channels  51   b  and  51   d,  can have a length L 1  that is equal to or different than a length L 2  of a second pair of opposed suture-receiving channels, e.g., suture-receiving channels  51   a  and  51   c.  However channels  51   a,    51   b,    51   c,  and  51   d  must have lengths less than L h . In this embodiment, drive head  50  contains ARM  56  thereon. ARM  56  originates at distal end  54  of drive head  50  and terminates at the opening of suture tunnel  58   a.    
     In  FIG. 3 , only one ARM  56  is shown. However, there may be a plurality of ARMs spaced equidistant around the drive head. Multiple ARMs (not shown) may be desirable from a procedural standpoint where the non-circular head geometry possesses a plane of symmetry. In the embodiment shown in  FIG. 3 , the square drive head has two planes of symmetry. With ARMs on either side of a plane of symmetry, rotational alignment of the mating inserter (shown in  FIGS. 8A-9B ) with respect to the implant is further alleviated. Multiple ARMs may also afford further improved physical properties. Once having the benefit of this disclosure, those skilled in the art will recognize other possible configurations with multiple ARMS on either side of a plane of symmetry keeping within the scope of the invention. 
     In  FIG. 4 , an alternate embodiment of drive head  60  is shown. Drive head  60  is circular in radial cross-section and contains ARM  66 , two suture tunnels  61   a  and  61   b  and suture-receiving channels  68   a,    68   b,    68   c,  and  68   d,  where ARM  66  is aligned with suture-receiving channels  68   b  and  68   d.    FIG. 5  shows another alternate embodiment of drive head  70 . This embodiment contains ARM  76 , suture tunnel  71  and suture-receiving channels  78   a  and  78   b,  where ARM  76  is not aligned with suture tunnel  71 . 
       FIG. 6  shows an exemplary embodiment of drive head  80  of suture anchors of the present invention where drive head  80  is substantially oval in radial cross-section and has two ARMs  86   a  and  86   b,  two suture tunnels  81   a  and  81   b  and four suture-receiving channels  88   a,    88   b,    88   c,  and  88   d.    FIG. 7  shows an exemplary embodiment of drive head  90  of suture anchors of the present invention where drive head  90  and two ARMs  96   a  and  96   b,  two suture tunnels  98   a  and  98   b  and four suture receiving channels  91   a,    91   b,    91   c,  and  91   d.    FIG. 6  shows an embodiment where ARMs  86   a  and  86   b  are oriented with the more proximally placed suture tunnel  81   b  and suture-receiving channels  88   b  and  88   d,  while  FIG. 7  shows the opposing embodiment where ARMs  96   a  and  96   b  are oriented with the more distally placed suture tunnel  98   b  and suture-receiving channels  91   b  and  91   d.    
     For placement of suture anchors of the present invention into bone, suture anchors can be driven into bone using a driver tool, such as shown in  FIGS. 8A-8B . Driver tool  100  can have a variety of shapes and sizes, but typically includes elongate shaft  102  having proximal handle portion  104  and distal end  108  having socket  106  formed therein and adapted to seat in mating relationship with the drive head of suture anchors of the present invention. As shown in  FIGS. 8A-8B , socket  106  of driver tool  100  has an overall oval shape and includes opposed ARM-engaging elements  105   a  and  105   b  to engage and cooperate with ARM(s)  112  once the drive head of the suture anchor is placed in cooperation with socket  106  of driver tool  100 . The shape of socket  106  and ARM-engaging elements  105   a  and  105   b  form a close fit with oval-shaped drive head  110  and cooperate with ARM(s)  112  of in such a way as to provide the mated relationship of the drive head within the socket. The size and configuration of the socket in relationship to the drive head and ARMs should be sufficient to provide a secure fit between the drive head and the driver tool, and to prevent rotation of the driver tool with respect to the suture anchor. Driver tool  100  can also contain an inner lumen (not shown) extending there through for receiving free ends of suture. 
     Suitable materials from which suture anchors of the present invention may be formed include biocompatible polymers selected from the group consisting of aliphatic polyesters, polyorthoesters, polyanhydrides, polycarbonates, polyurethanes, polyamides and polyalkylene oxides. The present invention also can be formed from biocompatible metals, glasses or ceramics, or from autograft, allograft, or xenograft bone tissues. Suture anchors can be further comprised of combinations of metals, ceramics, glasses and polymers. 
     The biocompatible materials can be biodegradable or non-biodegradable. Biodegradable materials, such as polymers, readily break down into small segments when exposed to moist body tissue. The segments then either are absorbed by the body, or passed by the body. More particularly, the biodegraded segments do not elicit permanent chronic foreign body reaction, because they are absorbed by the body or passed from the body, such that the body retains no permanent trace or residue of the segment. 
     In one embodiment, the suture anchor comprises biodegradable aliphatic polymer and copolymer polyesters and blends thereof. The aliphatic polyesters are typically synthesized in a ring opening polymerization. Suitable monomers include but are not limited to lactic acid, lactide (including L-, D-, meso and D, L mixtures), glycolic acid, glycolide, epsilon-caprolactone, p-dioxanone (1,4-dioxan-2-one), and trimethylene carbonate (1,3-dioxan-2-one). 
     In another embodiment, the materials comprising the devices will be biodegradable glasses or ceramics comprising mono-, di-, tri-, alpha-tri-, beta-tri-, and tetra-calcium phosphate, hydroxyapatite, calcium sulfates, calcium oxides, calcium carbonates, magnesium calcium phosphates, phospate glasses, bioglasses, and mixtures thereof. 
     In another embodiment, the materials comprising the devices can be combinations of biodegradable ceramics and polymers. Composites are prepared by incorporating biodegradable ceramic reinforcements such as fibers, short-fibers, or particles in a biodegradable polymer matrix. 
     Some particularly useful composites are 30 weight percent beta-tricalcium phosphate particles in 70 weight percent poly(lactic acid), or 30/70 beta-TCP/PLA, and 30 weight percent beta-tricalcium phosphate particles in 70 weight percent poly(lactide)/poly(glycolide) copolymer (mole ratio lactide to glycolyde 85/15), or 30/70 beta-TCP/(85/15 PLGA). 
     In another embodiment of the present invention, the polymers and blends can be used as a therapeutic agent release matrix. To form this matrix, the polymer would be mixed with a therapeutic agent prior to forming the device. The variety of different therapeutic agents that can be used in conjunction with the polymers of the present invention is vast. Therapeutic agents which may be administered via the pharmaceutical compositions of the invention include growth factors, including bone morphogenic proteins (i.e. BMP&#39;s 1-7), bone morphogenic-like proteins (i.e. GFD-5, GFD-7 and GFD-8), epidermal growth factor (EGF), fibroblast growth factor (i.e. FGF 1-9), platelet derived growth factor (PDGF), insulin like growth factor (IGF-I and IGF-II), transforming growth factors (i.e. TGF-beta I-III), vascular endothelial growth factor (VEGF); and other naturally derived or genetically engineered proteins, polysaccharides, glycoproteins, or lipoproteins. 
     Matrix materials for the present invention may be formulated by mixing one or more therapeutic agents with the polymer. Alternatively, a therapeutic agent could be coated on to the polymer, maybe with a pharmaceutically acceptable carrier. Any pharmaceutical carrier can be used that does not dissolve the polymer. The therapeutic agent may be present as a liquid, a finely divided solid, or any other appropriate physical form. Typically, but optionally, the matrix will include one or more additives, such as diluents, carriers, excipients, stabilizers or the like. 
     Methods for using a suture anchor in accordance with the present invention are also provided. In methods for attaching soft tissue to bone according to the present invention, a cavity of sufficient size to receive suture anchors of the present invention may be formed within a bony structure. A suture anchor according to the present invention comprising a suture disposed within the suture attachment element is then attached to a driver tool as shown herein above, and inserted into the bone cavity via the driver tool. In certain embodiments the suture anchor may be placed directly into the bony structure without the need for pre-formation of the cavity. The driver tool is removed and the soft tissue in proximity to the suture anchor is attached to the suture anchor via the suture. 
     The following examples are illustrative of the principles and practice of the present invention, although not limited thereto. 
     Example 1 
     Insertion Torque to Failure Tests 
     Suture anchors with the drive head of the design in  FIG. 7  consisting of two ARM&#39;s, each approximately 0.050″ in height and width, aligned in the plane of the suture eyelets, were subjected to insertion torque to failure tests versus a similar design without the two ARMs. Anchors were machined out of polysulfone. 
     Torque to failure tests were conducted in solid rigid polyurethane foam blocks (Sawbones, 1522-02, Pacific Research Laboratories, Inc., Vashon, Wash.). Torque measurements were recorded in inch-pounds using an Imada (Imada, Inc., Northbrook, Ill.) model DSD-4 Digitial Torque Tester/Screwdriver with mating ¼″ hexagonal drive Jacobs chuck attachment. The mean torque to failure of five anchors with ARMs was 7.0 in-lbs compared to 5.6 in-lbs for anchors designs without ARM&#39;s, representing a 25% increase in torque capacity of the drive head due to the present invention (ARM&#39;s) in polysulfone. 
     Example 2 
     Insertion Torque to Failure Tests 
     Suture anchors with the drive head of the design in  FIG. 6  consisting of two ARM&#39;s, each approximately 0.125″ in height and 0.050″ in width, aligned in the plane of the suture eyelets, were subjected to insertion torque to failure tests versus a similar design without the two ARMs and with the eyelets reversed, thus having the most distal eyelet traverse the long axis of the oval head while the proximal eyelet traverses the short axis of the oval head. Anchors were injection molded from a 30/70 by weight beta-TCP/ (85/15 poly(lactide)/poly(glycolide) composite material (starting Inherent Viscosity of raw polymer approximately 3.0 dl/g measured in chloroform (CHCl3) using the Cannon Automated Viscometer). 
     Torque to failure tests were conducted in solid rigid polyurethane foam blocks (Sawbones, 1522-02, Pacific Research Laboratories, Inc., Vashon, Wash.) under approximately a 6-10 lb compressive load. Torque measurements were recorded in inch-pounds using an Imada (Imada, Inc., Northbrook, Ill.) model DSD-4 Digitial Torque Tester/Screwdriver with mating ¼″ hexagonal drive Jacobs chuck attachment. The mean torque to failure of five anchors with ARMs was 7.8 in-lbs compared to 5.9 in-lbs for anchors designs without ARM&#39;s, representing a 32% increase in torque capacity of the drive head due to the present invention (ARM&#39;s) in the molded composite material.