Patent Publication Number: US-2023134446-A1

Title: Knotless anchor drive system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. provisional application Ser. No. 63/275,661 filed Nov. 4, 2021, titled ‘KNOTLESS ANCHOR DRIVE SYSTEM,” which is incorporated by reference herein, it its entirety. 
    
    
     FIELD 
     The present disclosure relates to a low-profile knotless anchor drive system. 
     BACKGROUND 
     Anchors and their associated systems provide useful fixation devices for tissue repair, such as for repairing tendons or ligament to bone. Anchors may also be used to augment a repair, such as systems disclosed in U.S. patent application Ser. No. 17/470,509 titled “JOINT REPAIR AUGMENTATION”, commonly owned and herein incorporated by reference in its entirety. Anchors may be inserted using an anchor inserter, either by pounding the anchor into the bone with or without a prepared bone hole. The anchor can be configured as a screw mechanism or an interference fit device and may be made of metal, plastic or bioabsorbable material (which dissolves in the body over time). 
     During operation of the anchor, a portion of the anchor may be rotated, and therefore torsional forces may be applied to the anchor via the insertion instrument. For example, the anchor may include a threaded external surface and insertion may include rotatingly advancing the anchor into the tissue, like a screw-type anchor, known in the art. In another example, an anchor may include a means of trapping a suture coupled thereto, and thereby knotlessly locking a suture with an anchor. The term suture may include equivalent flexible members such as suture tape, wire, cable, ribbon or grafts. Knotlessly locking the suture may include axially advancing a threaded plug along an anchor body lumen to trap the suture between the plug and anchor body lumen. Axially advancing the plug may include holding the anchor body stationary, while rotating the plug relative to the anchor body. Stated another way, axially advancing the plug may include rotating the plug while holding the anchor in a manner that resists concomitant rotation. 
     Means of applying a torsional force to a portion of the anchor, either to rotate the anchor itself or resist rotation while other elements are rotated may add features and size to the anchor body and associated system. An example existing anchor system is disclosed in U.S. Pat. No. 10,617,406, commonly owned and herein incorporated by reference. This existing anchor systems add a shaped bore in the proximal end of the anchor, that may be square shaped. A shaped bore may receive a mating inserter end therein with a corresponding cross section. In this example the bore inner diameter engages and surrounds the outer peripheral surface of the mating inserter end. In this example anchor, torsional forces are applied to the anchor to advance a plug into the distal eyelet, while the anchor body is held stationary. A shaped anchor bore, and inserter distal end together have an inherent volume of material and therefore may add profile or size to the anchor. A larger anchor may require excessive removal of bone tissue, which in some parts of the body, such as the extremities, may not always be available. Non-limiting example bones of the extremities include bones in the foot, ankle, wrist or hand. Therefore, there is a need to provide an anchor with a transmission mechanism that may apply a torsional force to a portion of an anchor, that has a minimal profile. There is a need for a transmission mechanism for small knotless anchor systems, and thereby small in profile, that allows torsional forces to be applied to the anchor to keep the anchor stationary, while allowing for rotation of a knotless mechanism to advance through the transmission mechanism. 
     SUMMARY 
     Described herein is a knotless anchor system that is streamlined to reduce the profile of the knotless anchor system, which may be particularly advantageous where space or target tissue is limited. Knotless anchor system may include an anchor body, an inserter and a plug spanning therebetween. Inserter and anchor body are coupled in a low-profile manner to insert the anchor body into a tissue, and rotationally stabilize the anchor body while advancing the plug. The anchor system provides a transmission mechanism for small knotless anchors that incorporates a puzzle cut to rotationally stabilize the anchor body while allowing torsional forces to be applied to a plug, adding minimal profile or outermost diameter of the anchor body. The transmission mechanism includes an inserter sleeve and anchor body that is axially coincident and each share both an outer diameter and inner diameter along the transmission mechanism. 
     Disclosed herein is an example suture anchor system that includes an anchor body, a plug and an insertion instrument. The anchor body is configured to anchor within a target tissue and may include externally disposed bone engaging members. The anchor body generally includes a proximal portion, a distal tip that may be tapered and an outer surface extending therebetween. The anchor body may be a rigid tubular body formed of a metal or polymer material. The anchor body may be formed of PEEK. The anchor body may include an eyelet extending therethrough for receiving at least one flexible member such as a suture therethrough. The anchor body also includes a cavity extending axially from the eyelet and up to and including the proximal open end of the anchor body. The anchor body also includes an annular projection extending from the proximal end defining a lumen continuous and coaxial with the cavity, the annular projection having an annular slot extending axially therealong. The plug is configured to move axially along both the anchor body cavity and annular projection lumen and moves to knotlessly lock the flexible member that extends through the eyelet with the anchor body. The insertion instrument may have a sleeve at the distal end that houses a portion of the plug as the system is obtained. The sleeve has an annular tab extending axially from the sleeve distal end, the tab continuous with the sleeve outer surface. The annular slot of the anchor body is sized and shaped to slidingly receive the annular tab therein to interdigitate when the insertion instrument and anchor body are linked. When coupled in this way this forms an annular connecting portion that includes an inner-lumen surface and an external surface that both include the annular projection and the annular tab. The annular connecting portion allows torsional forces to be applied to the plug to axially advance it, while keeping the anchor body stationary, with minimal added profile to the system. 
     In some example systems the annular tab has a threaded inner surface for threadingly engaging external threads on the plug. The sleeve distal end may also include internal threads to threadingly engage threads on the plug. The anchor body cavity may also include threads such that, as obtained the plug is threadingly engaged with the anchor body cavity and the sleeve distal end internal threads. This helps retain the anchor plug and instrument coupled during use. In some example systems, the anchor body annular projection is absent threads, and the annular tab inner surface is threaded to also threadingly engage threads of the plug. In this example, the annular connecting portion inner-lumen surface therefore includes a segment that is threaded and a segment that is not threaded. The annular projection may define a first annular segment length, and the annular tab may define a second annular segment length and wherein the first annular segment length may be greater than and may be at least double that of the second annular segment length. The greater first annular segment length may compensate for the weaker or less rigid materials of the anchor body relative to the inserter tabs. In some example embodiments the eyelet may traverse the anchor body, defining an entrance and exit aperture, and the exit and entrance apertures may align with the annular projection so that that suture extends along a channel and over a smooth annular project rather than over the discontinuity of the slot and tabs. The eyelet may traverse the anchor body, defining an entrance and exit aperture, and wherein the exit and entrance apertures may be circumferentially offset from the annular slot. 
     An example embodiment of a knotless suture anchoring system is disclosed, including an anchor body and an insertion instrument. The anchor body anchor within a target tissue and includes a tubular body, a means of engaging the target tissue and proximal connecting portion for functionally linking with the insertion instrument. The insertion instrument inserts the anchor body within the target tissue and includes a distally disposed instrument connecting portion at a distal end of an insertion instrument sleeve. The anchor body connecting portion and the insertion instrument connecting portion are configured to interlink or assemble such that they axially overlap and interdigitate to form a tubular connecting portion with a shared inner diameter and a shared outer diameter. 
     In some example embodiments, the system also includes a plug, that is moved axially along a cavity of the anchor body via actuation means of the insertion instrument. The plug also axially advances along a tubular connecting portion lumen defined by the shared inner diameter. The plug moves into the anchor body to knotlessly lock a suture or equivalent flexible member with the anchor body. The plug may be rotated while moving axially and the tubular connecting portion is configured to inhibit anchor body rotation while rotating the plug. The anchor body proximal connecting portion may define an annular projection with two annular slots therethrough and the insertion instrument connecting portion may include two annular tabbed projections on opposing sides to each other of the sleeve, the two annular tabbed projections configured to be received by, one each, the two annular slots to define the tubular connecting portion. The instrument connecting portion may be threaded to threadingly engage threads of the plug and the anchor body proximal connecting portion may be absent threads, so that the shared inner diameter of the tubular connecting portion includes a segment that is threaded and a segment that is absent threads. The proximal connecting portion may define a first circumferential segment length of the tubular connecting portion and the instrument connecting portion defines a second circumferential segment length of the tubular connecting portion and wherein the first circumferential segment length is greater than the second circumferential segment length. The anchor body may also include an eyelet through the anchor body, having an entrance and exit aperture for receiving a suture therethrough, and the exit and entrance apertures may be circumferentially offset from the two annular slots of the anchor body connecting portion. 
     An example method of knotless locking a tissue repair is also disclosed, including obtain a suture anchor system as disclosed herein. A suture may then be inserted through the eyelet and then tensioned to a target tension. The plug may be rotated to axially advance it through the annular connecting portion and into the anchor body cavity and while rotating, the anchor body may be held static via the annular connecting portion. A distal terminus of the plug may engage with the suture to knotless locking the suture. 
     In some example methods, the plug may be threaded, and a portion of the annular connecting portion may also be threaded to threadingly engage the plug. The insertion instrument may be removed after the suture has been knotlessly locked. Inserting the suture may also include extending the suture from the eyelet along the anchor body and along the annular projection, at a location circumferentially spaced away from the annular slot. 
     These and other features and advantages will be apparent from a reading of the following detailed description and a review of the associated drawings. It is to be understood that both the foregoing general description and the following detailed description are explanatory only and are not restrictive of aspects as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be more fully understood by reference to the detailed description, in conjunction with the following figures, wherein: 
         FIG.  1    illustrates a knotless anchor system with a puzzle cut connecting portion, in accordance with this disclosure; 
         FIG.  2    illustrates a distal end of the knotless anchor system with a puzzle cut connecting portion, in accordance with this disclosure; 
         FIG.  3 A  illustrates a perspective view of an anchor body of the knotless anchor system of this disclosure; 
         FIG.  3 B  illustrates a side view of the anchor body of the knotless anchor system of this disclosure; 
         FIG.  3 C  illustrates another side view of the anchor body of the knotless anchor system of this disclosure; 
         FIG.  3 D  illustrates a cross section view of the anchor body of the knotless anchor system of this disclosure; 
         FIG.  4    illustrates an exploded view of the anchor body and inserter of the knotless anchor system, with a plug and driver removed, in accordance with this disclosure; 
         FIGS.  5 A and  5 B  illustrate cross sections of the distal end of the knotless anchor system with a puzzle cut connecting portion, in accordance with this disclosure; 
         FIG.  6    illustrates a cross section through the puzzle cut connecting portion of the knotless anchor system, in accordance with this disclosure; and 
         FIGS.  7 A and  7 B  illustrate various views of another example embodiment of an anchor body of a knotless anchor system with a puzzle cut connecting portion. 
     
    
    
     DETAILED DESCRIPTION 
     In the description that follows, like components have been given the same reference numerals, regardless of whether they are shown in different examples. To illustrate example(s) in a clear and concise manner, the drawings may not necessarily be to scale and certain features may be shown in somewhat schematic form. Features that are described and/or illustrated with respect to one example may be used in the same way or in a similar way in one or more other examples and/or in combination with or instead of the features of the other examples. 
     As used in the specification and claims, for the purposes of describing and defining the invention, the terms “about” and “substantially” are used to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The terms “about” and “substantially” are also used herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue. “Comprise,” “include,” and/or plural forms of each are open ended and include the listed parts and can include additional parts that are not listed. “And/or” is open-ended and includes one or more of the listed parts and combinations of the listed parts. Use of the terms “upper,” “lower,” “upwards,” and the like is intended only to help in the clear description of the present disclosure and are not intended to limit the structure, positioning and/or operation of the disclosure in any manner. 
       FIG.  1    illustrates an anchoring system  100  including an inserter  120  and anchor body  150 . Inserter  120  may include a handle  122  at a proximal end with actuator  123 , a shaft  125  and shaft distal end  124 . Anchor body  150  is coupled to inserter  120  at distal end  124 . In some embodiments, a suture (or equivalent flexible member) may be coupled to the anchor body  150  and then to a tensioning member  128  for controlling a tension on the suture. This may be used when system  100  is part of a ligament augmentation system, for example, similar to that disclosed in commonly owned patent application Ser. No. 17/470,509 titled “JOINT REPAIR AUGMENTATION”, herein incorporated by reference. 
       FIG.  2    illustrates the anchor body  150  coupled to inserter distal end  124  defining a connecting portion  200 . Connecting portion  200  includes axially overlapping portions of both the inserter shaft distal end  124  and anchor body proximal end in a circumferentially arranged finger-joint style interlock. 
       FIGS.  3 A- 3 D  illustrate a variety of views of anchor body  150 . Anchor body  150  may be an elongate tubular body, with a proximal end  155  and a closed tapered distal end  160 . The anchor body  150  may also have an eyelet  156 , extending transversely through a longitudinal axis of the anchor body  150 , and dimensioned to receive one or more sutures (or equivalent) therethrough (sutures not shown). The anchor body  150  further includes a cannulation  158  formed within the anchor body  150  and intersecting the eyelet  156 . Anchor body  150  includes at least one bone engaging member  153 , extending radially from the body  150 . As illustrated, anchor body  150  may include two rows of axially spaced bone engaging members  153 , the two rows extending from opposite sides of the body  150  from each other. The bone engaging members  153  may be barbs or wings for example. An external channel  154  may extend axially along an outer surface of body  150  from eyelet  156  to proximal end  155 , for guiding and receiving a length of suture therealong. The external channel  154  may define a circumferential spacing between the two rows of axially spaced bone engaging members  153 . A path  154   a  is shown illustrating a suture path from eyelet  156  along external channel  154 . A second channel and corresponding path that may be diametrically opposite path  154   a  may also extend along the body  150  on the opposing side. 
     Proximal end  155  of anchor body  150  defines an anchor portion of the connecting portion  200 . Proximal end  155  includes two axially extending prongs  180   a ,  180   b . Connecting portion  200  may define circumferentially arranged finger-joint style interlock, to define a cylindrical shape when the inserter and anchor body are coupled. Prongs  180   a ,  180   b  define annular segments of cylindrical shaped connecting portion  200  (transmission mechanism) between the anchor body  150  and inserter distal end  124 . An axially moving plug (shown later) is disposed within and along connecting portion  200  and also within cannulation  158 . Prongs  180   a ,  180   b  may include smooth inner diameter walls  181   a ,  181   b . Prongs  180   a ,  180   b  may extend axially and circumferentially and define annular gaps  182   a ,  182   b  that are configured to receive axially extending prongs of shaft distal end  124  (shown later). Prongs  180   a ,  180   b  may define annular gaps  182   a ,  182   b , the gaps circumferentially offset from channels  154 . Gaps  182   a ,  182   b  may be axially aligned with the rows of axially spaced bone engaging members  153 . Prongs  180   a ,  180   b  may be on the same circumferential side and axially continuous with eyelet opening and channel(s)  154 , such that a suture may extend from the eyelet  156  axially along channel(s)  154  linearly along and parallel to the anchor body longitudinal axis, and also over a smooth outer surface of a prong ( 180   a ,  180   b ). Circumferential ends of the bone engaging members  153  may help retain suture within the channel(s)  154 . 
     Illustrated in  FIG.  3 B  is one of the rows of axially spaced bone engaging members  153 , including members  153   a ,  153   b  and  153   c . At least some of the members  153   a ,  153   b  may include a concave recess  353   a ,  353   b , that is arranged on a proximal edge of the member and also centered along each of the bone engaging member  153   a ,  153   b . The recess  353   a ,  353   b  may improve flexibility of the member  153   a ,  153   b  as they flex during insertion into the target bone. Concave recess  353   a ,  353   b  may be tapered along a length of each bone engaging member, to define a smooth contoured concave external surface  354   a ,  354   b . Concave recesses  353   a ,  353   b  may axially align with one of the annular gaps  182   a  or  182   b . Also shown in  FIG.  3 B , a proximal most bone engaging member  153   c  may be split, the split extending circumferentially and approximately matching a circumferential extent of one of the adjacent annular gaps ( 182   a ,  182   b ). This proximal most bone engaging member  153   c  may be larger than the other members  153   a ,  153   b , in both volume and radial extent (also shown in  FIG.  3 D ). The proximal most bone engaging member  153   c  may provide the strongest fixation. The added volume may increase rigidity of the member  153   c  and the radial extension may encroach further into the bone tissue. 
       FIG.  3 D  illustrates a cross sectional views of anchor  150 . Cannulation  158  may include internal threads therealong, for threadingly engaging the plug. 
       FIG.  4    illustrates an exploded view of the inserter distal end  124  and anchor body  150 , with the plug and plug driver removed for clarity of the figure. Prongs  180   a ,  180   b  define annular gaps  182   a ,  182   b , for receipt of inserter tabs  130   a ,  130   b  therein. This puzzle cut coupling rotationally stabilizes the anchor body  150  relative to the inserter  120 , while keeping a low profile. When prongs  180   a ,  180   b  interdigitate with tabs  130   a ,  130   b , they form a tubular construct that shares both an outer and inner diameter therealong. The outer circumferential surface of the resulting tubular interlinking joint (connecting portion  200 ) is formed by both the prongs  180   a ,  180   b  and tabs  130   a ,  130   b . The inner circumferential surface of the resulting tubular interlinking joint (connecting portion  200 ) is formed by both the prongs  180   a ,  180   b  and tabs  130   a ,  130   b . Inserter tabs  130   a ,  130   b  may define a threaded inner diameter surface  133   a ,  133   b  that threadingly engages a plug. Prongs  180   a ,  180   b  and tabs  130   a ,  130   b  may have an axial length sufficient to counter any rotation and stably hold the anchor body. Prongs  180   a ,  180   b  and tabs  130   a ,  130   b  may be between 2-5 mm in length. While two prongs and tabs are shown, circumferentially arranged symmetrically around the connecting portion  200 , other numbers are envisioned. In some embodiments there may be only one prong and one tab. In other embodiments there may be three of each, circumferentially arranged relative to each other. 
       FIGS.  5 A and  5 B  illustrate longitudinal cross sections of the system distal end, including anchor body  150 , plug  300 , plug actuation rod (plug driver)  310  and inserter distal end  124 . The plug  300  may be a generally elongated, tubular threaded rod with a cannulation adapted to receive a distal end of the rod  310 . Plug  300  and rod  310  may be similar to and be operated in a similar fashion the commonly owned U.S. Pat. No. 10,617,406, herein incorporated in its entirety by reference. Axially advancing plug, via actuation of rod  310  may advance the plug  300  to as to engage and knotlessly lock a suture extending through eyelet  156 . 
       FIGS.  5 A and  5 B  both illustrate the assembly without a suture. In both  FIGS.  5 A and  5 B , the plug  300  is also shown in a proximal location, threadingly coupled to both the anchor body  150  and inserter distal end  124 . This provides stability while inserting the anchor  150  into the tissue. The system  100  may be provided with the plug  300  in this location. As provided the plug  300  is proximally spaced from eyelet  156  so that any suture or equivalent flexible member may be threaded through and slid through eyelet  156  of anchor body  150 . Plug  300  may be axially advanced to knotless lock the suture (not shown) via rod  310 . Rod  310  may be operatively coupled to an actuator  123  on the handle  122 , and rotation of rod  310  may axially advance the plug  300  while the connection portion  200  holds the anchor body  150  stationary. In  FIG.  5 A  the connecting portion  200  is shown with a cross section that includes only the anchor prongs  180   a ,  180   b . Prongs  180   a ,  180   b  may have a smooth (non-threaded) inner circumferential surface and may define an inner diameter than provide clearance for the threaded plug  300  to axially advance through. In  FIG.  5 B  the cross section shown extends through the inserter sleeve tabs  130   a ,  130   b . Tabs  130   a ,  130   b  may define a threaded inner surface, that threadingly engages the threaded plug  300 . Therefore, the inner circumferential surface of the connecting portion  200  may include at least one annular segment that is threaded and at least one segment that is non-threaded. 
       FIG.  6    illustrates a transverse cross section of the connecting portion  200 , at the location shown in  FIG.  2    (illustrated with the number “ 6 ”). Threaded plug  300  is shown with rod  310 . Plug cannulation  305  may be shaped to receive a rod  310 , that may be configured to rotate plug  300 . Cannulation  305  and rod cross section may have a cross section that is triangular as shown. Other non-limited examples may be square, rectangular or hexagonal. Cross section of connecting portion  200  is shown, including both anchor prongs  180   a ,  180   b  and inserter tabs  130   a ,  130   b . All prongs and tabs may be curved to define an approximate tubular shape along the connecting portion  200 , as interlinked. The discontinuities are due to internal threads on the tabs  130   a ,  130   b . Connecting portion  200 , when interlinked defines an inner diameter surface  205  that may include discontinuities due to threads on the tabs  130   a ,  130   b . A least a portion of inner diameter surface  205  may engage plug  300 , such as threaded inner surfaces  133   a  of inserter tab  130   a . In other embodiments inner diameter surface  133   a ,  133   b  may be smooth (non threaded). Inserter prongs  130   a ,  130   b  may therefore extend slightly further radially inward, to accommodate the threads. Anchor body prongs  180   a ,  180   b  may define longer segment lengths than tabs  130   a , 130   b , which may balance the offset in materials and relative structural integrity between the anchor body  150  and inserter distal end  124 . Anchor body  150  may be fabricated from a polymer that may be bioabsorbable, while the anchor inserter distal end  124  may be include metal, and therefore inherently a mismatch in structural integrity may exist therebetween. In cross section, therefore, the annular cross section may define a 360-degree bounded cannulation when interlinked. The boundary of the 360-degree bounded cannulation may include an annular segment or plurality of annular segments formed by the anchor prongs  180   a ,  180   b , and an annular segment or plurality of annular segments formed by the inserter tabs  130   a ,  130   b . In some embodiments the annular segment or plurality thereof formed by the anchor prongs  180   a ,  180   b  may define substantially more of the 360-degree boundary than the annular segment or plurality thereof formed by the inserter tabs  130   a ,  130   b . For example, in some embodiments the segment or plurality of segments formed by the anchor prongs  180   a ,  180   b  may define at least double the boundary length relative to the segment or plurality of segments formed by the inserter tabs  130   a ,  130   b . For example, in some embodiments the segment or plurality of segments formed by the anchor prongs  180   a ,  180   b  may define double the boundary length relative to the segment or plurality of segments formed by the inserter tabs  130   a ,  130   b.    
       FIGS.  7 A and  7 B  illustrates another example embodiment of an anchor body  750 , anchor body  750  like anchor body  150  except where described. Same or essentially similar elements are given the same label numbers. Anchor body  750  may couple to inserter  120  at shaft distal end  124 . A suture (or equivalent flexible member) may be coupled to the anchor body  750  and then to a tensioning member  128  for controlling a tension on the suture. Anchor body  750  may couple to inserter distal end  124  defining a connecting portion similar to that shown in  FIG.  2   . Connecting portion includes axially overlapping portions of both the inserter shaft distal end  124  and anchor body proximal end  755  in a circumferentially arranged finger-joint style interlock. 
     Anchor body  750  may be an elongate tubular body, with a proximal end  755  and a closed tapered distal end  160 . The anchor body  750  may also include eyelet  156  and cannulation  158  formed within the anchor body  750  and intersecting the eyelet  156 . Anchor body  750  includes at least one bone engaging member  753   a ,  753   b ,  753   c ,  753   d , extending radially from the body  750 . As illustrated, anchor body  750  may include two rows of axially spaced bone engaging members, the two rows extending from opposite sides of the body  750  from each other. The bone engaging members may be barbs or wings for example. An external surface  754  may extend axially along an outer surface of body  750  from eyelet  156  to proximal end  755 , for guiding and receiving a length of suture therealong. The external channel  754  may define a circumferential spacing between the two rows of axially spaced bone engaging members  753   a ,  753   b ,  753   c ,  753   d . A path  754   a  is shown illustrating a suture path from eyelet  756  along external channel  754 . A second channel and corresponding path that may be diametrically opposite path  754   a  may also extend along the body  750  on the opposing side. 
     Proximal end  755  of anchor body  750  defines an anchor portion of connecting portion that is similar to connecting portion,  200  except as noted. Proximal end  755  includes two axially extending prongs  780   a ,  780   b , similar to prongs  180   a ,  180   a , in that they define circumferentially arranged finger-joint style interlock, to define a cylindrical shape when the inserter and anchor body are coupled. Prongs  780   a ,  780   b  are similar to prongs  180   a ,  180   a  except that they include internal threaded surfaces  781   a ,  781   b . As obtained, plug may be disposed along connecting portion  200  including threadingly engaging prong threaded surfaces  781   a ,  781   b . Prong threaded surfaces  781   a ,  781   b  may define continuous threads with threaded inner lumen surface of cavity  158 , such that external threads of plug  300  threadingly engage both threaded surface  781   a ,  781   b  and also the threaded inner lumen surface of cavity  158  as obtained. A threaded engagement between plug  300  and surfaces  781   a ,  781   b  may improve the general stability and hold between the inserter  120 , plug  300  and anchor  750  during insertion and general manipulation of the system 
     Illustrated in both  FIG.  7 A  and  FIG.  7 B  each row of axially spaced bone engaging members may include four members  753   a ,  753   b ,  753   c  and  753   d . Each of the four members  753   a ,  753   b ,  753   c  and  753   d  may define radially projecting members that are different from each other. The distal most member  753   a  may be the smallest and most tapered. The distal most member  753   a  may extend the least radially from the body  750  relative to the other members,  753   b ,  753   c  and  753   c . Each member  753   a ,  753   b ,  753   c  and  753   d  may increase in both rigidity and radial extension the further proximally disposed the member is along the row. Each member  753   a ,  753   b ,  753   c  and  753   d  may define a projection that is different from the others. This may provide for easier insertion, as the distal most member  753   a , the most flexible and radially closest of the members enters the bone opening first, the insertion force, and thereby fixation force gradually increasing as each successive member ( 753   b ,  753   c ,  753   d ) enters the bone opening. 
     Anchor body  750  may also include rows of external cavities  754   a ,  754   b ,  754   c , directly adjacent a corresponding member  753   a ,  753   b  and  753   c , as clearance for members  753   a ,  753   b  and  753   c  as they flex during anchor insertion. Cavities  754   a ,  754   b ,  754   c  may therefore be sized to receive a portion of their corresponding fixation member  753   a ,  753   b  and  753   c.    
     A method of knotless securing a suture (or equivalent) within bone tissue may include obtaining system  100 , the system  100  including an inserter  120  and an anchor body ( 150  or  750 ) with an eyelet  156  extending therethrough. At least one suture may be obtained and threaded through the eyelet  156 . The suture may then be tensioned. The suture may be operatively coupled to a tensioning wheel  128  of the inserter  200  to tension the suture. The system  100  may be obtained with a threaded tubular plug  300  threadingly coupled to both the anchor body ( 150  or  750 ) and inserter  120 . The threaded plug may extend and directly threadingly engage a threaded cannulation  158  of the anchor body  150  or  750  and a threaded cannulation of the inserter distal end  124 . In this location, the threaded plug  300  may extending along a lumen of a connecting portion  200 , the lumen boundary shared by both the anchor body ( 150 ,  750 ) and inserter distal end  124 . The connection portion may include an annular segment that includes threads, to threadingly engage the plug  300 . 
     Once the desired tension has been achieved on the suture, the threaded plug  300  may be axially advanced further into the anchor body ( 150 ,  750 ) to knotlessly lock the suture with the anchor body ( 150 ,  750 ). Axially advancing may include rotating the plug  300  while holding the anchor body ( 150 ,  750 ) stationary. The connecting portion defines an annular interlinking joint that holds the anchor body stationary while the plug rotates. A distal terminus of the plug  300  may move from a first axial position to a second axial position; wherein, in the first axial position, the plug  300  engages both the anchor body ( 150 ,  750 ) and the threaded distal end of the inserter  120  and a distal terminus of the plug  300  is proximal to the eyelet; and wherein, while moving to the second axial position, the plug advances further into the anchor body ( 150 ,  750 ) threadingly disengages from the inserter  120  and may also covers at least a portion of the eyelet  156  so as to secure the suture between a distal terminus of the plug  300  and distal bottom end of the anchor cannulation  158 . In the second axial position, the plug  300  may be entirely recessed from the body proximal end  155 ,  755 . The inserter may now be removed, leaving the plug and anchor within the bone tissue. 
     One skilled in the art will realize the disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing examples are therefore to be considered in all respects illustrative rather than limiting of the disclosure described herein. Scope of the disclosure is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.