Patent Publication Number: US-2022211422-A1

Title: Bone anchor, kit and method of use

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/630,506 filed Jan. 13, 2020, which is the US national phase application of PCT Application No. PCT/IL2018/050768 (published as WO 2019/012540), filed Jul. 12, 2018, which claims the benefit of priority to U.S. Provisional Patent Application No. 62/531,399, filed Jul. 12, 2017. The contents of the above-referenced U.S. Provisional Patent Application are all incorporated by reference as if fully set forth herein in its entirety. 
    
    
     FIELD AND BACKGROUND OF THE INVENTION 
     The present invention, in some embodiments thereof, relates to bone anchors and, more particularly, but not exclusively, to self-tapping bone anchors. 
     Fixation devices such as screws, pins or similar are commonly used to fix implants and support devices (e.g., bone plates) to bone and may also be used alone, as implants, around joints to hold cancellous bone fragments together e.g., in compound fractures. 
     Commonly such fixation devices may be subject to high stress such as compression and shearing forces, bending forces, torque or a combination of all resulting from a shift of load-bearing articulating surfaces during movement of the articulating bones such as during walking or in load bearing surfaces e.g., on a tooth implant while chewing, bringing about loosening of the fixation device. 
     SUMMARY OF THE INVENTION 
     According to an aspect of some embodiments there is provided a bone anchor including an elongated core having a tip at a distal end and coupled to a head at a proximal end, and a segmented helical thread defining one or more gaps therein, each gap defining at least a trailing wall, the trailing wall having a cutting surface including at least one cutting edge; the bone cutting surface and the cutting edge configured to cut bone and guide bone fragments radially inwards. 
     According to some embodiments, the gap defines at least a leading wall being more distal along the helical thread in respect to the trailing wall. 
     According to some embodiments, a major radius (r 2 ) of a following second wing is greater than a major radius (r 1 ) of a preceding first wing by at least one dimension (X), expressed by the formula [X=(r 2 )−(r 1 )] and each subsequent wing expands a major radius of a female thread in bone formed by a preceding wing by at least the dimension (X). According to some embodiments, the bone is cortical bone. According to some embodiments, at least the dimension (X) and a number of turns of the anchor in bone defines the quantity of bone fragments that accumulates in the gap. 
     According to some embodiments, upon rotation of the anchor, the wings continuously cut bone. 
     According to some embodiments, the cutting surface area is sized and shaped to, upon rotation of the anchor, push the bone fragments accumulated in the gap along a female thread formed by at least one preceding wing. 
     According to some embodiments, at least one cutting edge is oriented within 30 degrees of parallel to a thread axis. According to some embodiments, at least one cutting edge is oriented perpendicular to a helix angle of the helical thread. 
     According to some embodiments, the core has cylindrical geometry. According to some embodiments, the wing is attached to the core along at least one third of the circumference of the shaft. 
     According to some embodiments, the trailing wall is disposed along a plane that extends radially from a longitudinal axis of the core. 
     According to some embodiments, the trailing wall is disposed along a plane disposed within 30 degrees from a parallel to a thread axis. According to some embodiments, the trailing wall is concave. 
     According to some embodiments, at least one of the wings includes a proximally facing surface and a bone facing surface and the proximally facing surface and the bone facing surface are equidistant from each other. 
     According to some embodiments, a first border of the trailing wall is coupled to a trailing edge of the proximally facing surface to form a cutting. According to some embodiments, a second border of the trailing wall is coupled to a trailing edge of the bone facing surface to form a cutting edge. 
     According to some embodiments, at least one of the wings includes a circumferential surface parallel to a longitudinal axis of the core and disposed along a major diameter of the wing. According to some embodiments, the circumferential surface and the trailing wall meet at the cutting edge. According to some embodiments, the circumferential surface and the trailing wall meet at an angle between 30 and 90 degrees. 
     According to some embodiments, circumferential surfaces of a plurality of wings form an imaginary cone. 
     According to some embodiments, the wing includes a square or rectangular cross section at any point along its length. 
     According to some embodiments, the cutting surface and cutting edge of the trailing wall are disposed along a radius of the core. 
     According to some embodiments, the cutting surface and cutting edge of the trailing wall are angled in respect to a radius of the core such that the cutting edge is disposed more distally along the thread that an edge of the cutting surface attached to the core. According to some embodiments, the trailing wall is angled between 0 and 30 degrees in respect to the radius. 
     According to some embodiments, the head includes a first surface coupled to the core and a second surface facing away from the core. According to some embodiments, a distance between the surface coupled to the core and a most proximal portion of a most proximal wing is between 1 and 3 mm. 
     According to some embodiments, a major diameter of at least one wing is at least equal to twice the diameter of the core. 
     According to some embodiments, the anchor includes a distal wingless portion having at least one flute, wherein the distal wingless portion extends between 20 and 40 percent of the core length. 
     According to some embodiments, the distal wingless portion extends more than 2 mm from the distal tip. 
     According to an aspect of some embodiments there is provided a drill guide for the bone anchor as recited elsewhere herein including a handle coupled to a body including a bone contacting surface and a bore sized to receive a bone drill, and the bone contacting surface including a wedge extending radially outwards from a rim of the bore and projecting away from the surface. 
     According to some embodiments, the wedge is shaped to form a recess extending from a rim of a bore drilled in a bone, shaped and sized to receive at least a portion of one of the radially extending wings. According to some embodiments, the drill guide includes a handle; coupled to a body including a bone contacting surface and a bore sized to receive a bone drill and the bone contacting surface including a wedge extending radially from a rim of the bore and projecting away from the surface. 
     According to an aspect of some embodiments there is provided a bone anchor kit including at least one bone anchor including a head, a core and a segment helical thread defining one or more gaps therein, each gap defining at least a trailing wall the trailing wall having a cutting surface including at least one cutting edge; the bone cutting surface and the cutting edge configured to cut bone and guide bone fragments radially inwards, at least one bone anchor driving tool and at least one bone anchor dedicated drill guide. 
     According to an aspect of some embodiments of the invention, there is provided a clawed plate having at least one aperture on one end and at least one claw on the opposite end. In some embodiments, the claw is curved in respect to the surface of the plate. In some embodiments, the aperture is sized to accommodate at least a bone anchor. In some embodiments, the aperture comprises a step sized to accommodate art least a shoulder of the bone anchor head. 
     According to an aspect of some embodiments there is provided a method for implanting a bone anchor in bone including drilling a bore in a cortical layer of the bone, forming a notch in a surface of the bone, placing in the bore a bone anchor including a core and a segment helical thread defining one or more gaps therein, each gap defining at least a trailing wall the trailing wall having a cutting surface including at least one cutting edge such that at least a portion of the cutting edge is positioned inside the slot, rotating and driving the anchor into the bone and cutting bone and guiding bone fragments radially inwards. 
     According to some embodiments, the notch extends radially from a rim of the bore. According to some embodiments, a diameter of the bore is sized to snuggly accommodate the core. 
     According to some embodiments, the method further includes placing a fixation device against the bone and placing the bone anchor through an opening in the fixation device into the drilled bore. 
     According to some embodiments, the method further includes forming a female thread in bone in which a major diameter (Ø MD1 ) of the female thread behind a first wing is smaller than a major diameter (Ø MD2 ) of said female thread behind a following second wing. 
     Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced. 
       In the drawings: 
         FIG. 1A  is a pictorial view illustration of a commonly used cancellous bone screw and a cross-section view illustration of an interaction of a cancellous bone screw thread with cancellous bone; 
         FIG. 1B  is an in Vivo Evaluation of immediately loaded stainless steel and titanium orthodontic screws in a growing bone; 
         FIGS. 2A, 2B, 2C, 2D and 2E  are side view and cross-section view simplified illustrations of a bone anchor and operation thereof in accordance with some embodiments of the present invention; 
         FIGS. 3A, 3B, 3C and 3D  are a side and bottom view simplified illustrations of a bone anchor; 
         FIGS. 4A, 4B, 4C and 4D  are bottom view simplified illustrations of a bone anchor; 
         FIGS. 5A, 5B, 5C, 5D and 5E  are pictorial simplified illustrations of the modus operandi of a bone anchor; 
         FIG. 6  is a pictorial view simplified illustration of an implanted bone anchor; 
         FIGS. 7A and 7B  are pictorial view simplified illustrations of an exemplary embodiment of a bone anchor; 
         FIG. 8  is a pictorial view simplified illustration of an exemplary embodiment of a bone anchor; 
         FIG. 9  is a pictorial view simplified illustration of an exemplary embodiment of a bone anchor; 
         FIG. 10  is a pictorial view simplified illustration of an exemplary embodiment of a bone anchor; 
         FIG. 11  is a pictorial view simplified illustration of an exemplary embodiment of a bone anchor; 
         FIGS. 12A, 12B, 12C and 12D  are cross-section view simplified illustrations of bone anchor wings in accordance with some embodiments of the current invention; 
         FIGS. 13A, 13B, 13C, 13D and 13E  are pictorial view simplified illustrations of a dedicated drill guide for a bone anchor; 
         FIGS. 14A, 14B, 14C and 14D  are pictorial view simplified illustrations of employment of a dedicated drill guide for a bone anchor; 
         FIGS. 15A, 15B, 15C and 15D  are cross-section view simplified illustrations of positioning of a bone anchor in a bore drilled through a cortical bone layer; 
         FIG. 16  is a cross-section view simplified illustration of a drilled bore and a notch made in bone; 
         FIG. 17  is a pictorial view and partial diagrammatic view simplified illustration of an embodiment of a bone anchor kit; 
         FIGS. 18A, 18B, 18C and 18D  are a perspective view and a plan view simplified illustrations of an embodiment of a clawed bone plate in accordance with some embodiments of the invention; 
         FIGS. 19A, 19B and 19C  are a perspective view and a plan view simplified illustrations of implementation of a clawed bone plate in accordance with some embodiments of the invention; and 
         FIG. 20  is a flow chart of an exemplary method of implanting a bone anchor in bone. 
     
    
    
     DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION 
     The present invention, in some embodiments thereof, relates to bone anchors and, more particularly, but not exclusively, to self-tapping bone anchors. 
     For purposes of better understanding some embodiments of the present invention, as illustrated in  FIGS. 2A to 20  of the drawings, reference is first made to the construction and operation of a commonly used cancellous bone screw as illustrated in  FIGS. 1A and 1B . 
     Shown in  FIG. 1A  is a commonly used cancellous bone screw  102  and a cross-section view simplified illustration of a thread  104  of a cancellous bone screw interacting with cancellous bone. Threads  104  of a commonly used cancellous bone screws are typified by having sharp tapered edges  106  along the major diameter of the thread configured to cut into cancellous bone and tap a female thread  108  in which the screw will eventually become embedded. The screw thread  104  cuts into the bone and in some instances may form bone debris that may create binding or wedging during insertion. The binding or wedging during insertion may provide a feel to the surgeon of a solid attachment, but may disappear as pulverized material is resorbed, or further crushed. Some pulverized material may also be lost into crevices and caverns of the cancellous bone. This phenomenon may be seen in  FIG. 1B , which is an in Vivo Evaluation of Immediately Loaded Stainless Steel and Titanium Orthodontic Screws in a Growing Bone taken from Kerstin Gritsch, Norbert Laroche, Jeanne-Marie Bonnet, Patrick Exbrayat, Laurent Morgon, Muriel Rabilloud, Brigitte Grosgogeat/Published: Oct. 4, 2013, https://doi(dot)org/10(dot)1371/journal(dot)pone(dot)0076223. Sharp tapered edges  106  commonly compress and crush surrounding bone and force pulverized material in a radially outward direction. Additionally, tapered thread edges often result in the screw placing the bone in a highly stressed condition, with the result that a sharp impact might easily cause the bone to crack. 
     As a result and as shown in  FIG. 1B , several weeks after implantation only a portion of the screw  110  remains in contact with bone  112  while along other portions of the screw thread the bone has been resorbed and replaced by fibrous tissue  114 . Fibrous tissue, being weaker than bone, allows for movement of the screw, succumbing to applied pressures and forces leading eventually to loosening and the pulling out of the screw and implant. 
     Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. 
     As used herein, the term “Proximal” or “Proximally” means close to or in the direction of the anchor head. The term “Distal” or “Distally” means close to or in the direction of the anchor tip and away from the anchor head. As used herein, the term “Leading” refers to a portion of the anchor (e.g., a wall of a gap between a pair of wings) that is more distal along the anchor thread. The term “Trailing” refers to a portion of the anchor (e.g., a wall of a gap between a pair of wings) that is more proximal. In some embodiments, for example, a trailing wall of a gap comprises a leading cutting surface of the wing proximal to the gap. 
     A “Leading Portion” or “Leading Edge” becomes a corresponding “Trailing Portion” or “Trailing Edge” when the direction of rotation of the anchor is reversed. 
     The term “Major Radius (r)” as used herein means half of a “Major Diameter (Ø)” of the anchor at the measured level. 
     An aspect of some embodiments of the invention relates to a bone anchor comprising a core disposed between an anchor head at one end and a tip at an opposite end and wings that form a thread around the core. In some embodiments, the thread comprises a segmented helical thread defining one or more gaps therein. In some embodiments, each gap defines at least a trailing wall having a cutting surface including at least one cutting edge. In some embodiments, the bone cutting surface and cutting edge are configured to cut bone and guide bone fragments radially inwards. In some embodiments, the gap defines at least a leading wall being more distal along the helical thread in respect to the trailing wall. 
     In some embodiments, the gap trailing wall is operative to push bone fragments accumulated in the gap along a female thread formed by at least one preceding wing. In some embodiments, the gap leading wall is configured to trap and collect bone fragments accumulated in the gap during insertion of the anchor into an implantation site. The bony fragments serve as autografts and promote bone regeneration during the healing process. 
     In some embodiments, the anchor comprises an elongated core or a stem disposed between and coupled to a head at a proximal end and a tip at a distal end. In some embodiments, the core comprises at least two radially extending wings. In some embodiments, at least one wing comprises a leading portion and a trailing portion. In some embodiments, the leading portion of at least one wing comprises a bone cutting surface having at least one bone cutting edge. In some embodiments, the trailing portion of at least one wing comprises a trailing wall. In some embodiments, the leading bone cutting surface is disposed along a plane parallel to a longitudinal axis of the core and extends radially from the longitudinal axis with an inner border coupled to the core and an outer border at a major diameter of the thread. 
     In some embodiments, the wings form a segmented helical thread along at least a portion of the core. In some embodiments, the wings are arranged in subsequence so that one wing is followed (but is not in contact with) a subsequent wing along a helical path. In some embodiments, every pair of subsequently arranged wings trap and collect bone fragments in a space disposed in between the wings. In some embodiments, the wings are coupled to and wrap around the core. In some embodiments, the wings wrap around the core along a helical path extending longitudinally along the core from the head of the anchor to the tip. 
     In some embodiments, the wing comprises at least one proximally facing surface facing the head of the anchor. In some embodiments, the wing comprises at least one distally facing surface facing the tip of the anchor. In some embodiments, the proximally facing and distally facing surfaces are equidistant. In some embodiments, a circumferential surface is coupled at a distal margin to a circumferential edge of the distal surface at a major diameter (Ø) of the wing and at a proximal margin to a circumferential edge of the proximal surface at a major diameter (Ø) of the wing. In some embodiments, the circumferential surface is perpendicular to the proximal and/or distal surfaces. In some embodiments, for any wing  210  a major diameter (Ø MD ) is at least twice the diameter of the core (Ø md ). In some embodiments, for any wing a major diameter (Ø MD ) is between 1.5 and 4 times, 2.5 and 3.5 times, less than twice or more than  4  times the diameter of the core (Ø md ). 
     In some embodiments, at least the leading portion bone cutting surface is defined by a radially extending surface. In some embodiments, edges of the bone cutting surface are coupled at an angle to leading edges of the proximal, distal and circumferential surfaces of the wings and the outer surface of the core. In some embodiments, a surface of the bone cutting surface is angled at an angle (α) in respect to a radius (r) of the anchor core at the point of contact of the surface with the anchor core. In some embodiments, angle (α) is between 0 and 50 degrees. In some embodiments, angle (α) is between 0 and 50 degrees 10 and 40 degrees, 20 and 30 degrees more than 50 or less than 0 degrees. 
     In some embodiments, at least one of coupled edges of the bone cutting surface of the leading portion and the leading edges of the proximal, distal and circumferential surfaces forms a cutting edge. In some embodiments, the bone cutting surface is flat. In some embodiments, the bone cutting surface is at least partially curved. In some embodiments, the bone cutting surface forms concave spoon geometry. In some embodiments, the cutting edge coupling the bone cutting surface and the leading edge of the circumferential surface is positioned further along (down) the thread than the bone cutting surface edge coupled to the core forming an angle between the bone cutting surface and a radius extending through the bone cutting surface edge coupled to the core. In some embodiments, the bone cutting surface angle in respect to a radius extending from the core extending through the bone cutting surface edge coupled to the core is less than 45 degrees, between 0 and 45 degrees, 5 and 30 degrees, 10 and 20 degrees, less than 5 degrees or more than 45 degrees. 
     In some embodiments, at least the trailing edge comprises a surface defining a radially extending bone cutting surface. In some embodiments, edges of the bone cutting surface are coupled at an angle to trailing edges of the proximal, distal and circumferential surfaces and the outer surface of the core. In some embodiments, the angle is 90 degrees or less. In some embodiments, the angle is between 30 and 90 degrees, 45 and 60 degrees more than 90 or less than 30 degrees. In some embodiments, at least one of coupled edges of the surface of the trailing edge and the trailing edges of the proximal, distal and circumferential surfaces forms a cutting edge. In some embodiments, the bone cutting surface is flat. In some embodiments, the bone cutting surface is at least partially curved. In some embodiments, the bone cutting surface forms concave spoon geometry. In some embodiments, the bone cutting surface edge coupled to the core is positioned further along (down) the thread than the cutting edge coupling the bone cutting surface and the trailing edge of the circumferential surface, forming an angle between the bone cutting surface and a radius extending through the bone cutting surface edge coupled to the core. In some embodiments, the bone cutting surface angle in respect to a radius extending from the core extending through the bone cutting surface edge coupled to the core is less than 45 degrees, between 0 and 45 degrees, 5 and 30 degrees, 10 and 20 degrees, less than 5 degrees or more than 45 degrees. 
     In some embodiments, the leading portion and trailing portion are defined by a direction of rotation of the anchor. In some embodiments, the trailing portion of one wing and a leading portion of a following wing define a gap between them operative to trap bone fragments carved from the bone during rotation of the anchor by at least one cutting edge of the leading portion of a following wing. 
     In some embodiments, a major diameter (Ø) of each wing is larger than a major diameter of a subsequently preceding wing. In some embodiments, a single wing extends along any 360 degree full circumference of the core at any wing populated level. In some embodiments, a transverse cross-section of the anchor at a level of any wing transects the core and at least a portion of a single wing. In some embodiments, the heads comprises at least one distally facing surface. In some embodiments, a proximal end of the core is coupled to the distally facing surface of the head. In some embodiments, a distance between the distally facing surface of the head and a most proximal aspect of the most proximal wing equals a thickness of the bone cortex at the point of insertion of the anchor. 
     An aspect of some embodiments of the invention relates to a drill guide for a bone anchor. In some embodiments, the drill guide comprises a handle and a body having a bore sized and fitted to receive a drill bit. In some embodiments, the bore is centrally located. In some embodiments, the body comprises a distally facing surface comprising at least one wedge. In some embodiments, the wedge projects distally from the distally facing surface of the drill guide body. In some embodiments, the wedge has flat geometry, comprising a sharp distal ridge extending radially outwardly from the bore. In some embodiments, the drill guide body comprises a flat proximally facing surface operative to receive a hammer strike. 
     An aspect of some embodiments of the invention relates to a combination bone anchor operative to tap a female thread in bone and trap and collect bone fragments during insertion. 
     In some embodiments, the anchor comprises a core or a stem disposed between and coupled to a head at a proximal end and a tip at a distal end. In some embodiments, the core comprises at least two radially extending wings. In some embodiments, at least a distal portion of the core comprises a cancellous bone driving thread. 
     In some embodiments, the wings form a segmented helical thread along at least a portion of the core. In some embodiments, the wings are arranged in subsequence so that one wing is followed (but is not in contact with) a subsequent wing along a helical path. In some embodiments, every pair of subsequently arranged wings collect bone fragments in a space disposed in between the wings. In some embodiments, the wings are coupled to and wrap around the core. In some embodiments, the wings wrap around the core along a helical path extending longitudinally along the core from the head of the anchor to the tip. In some embodiments, the most distal wing, closest to the tip has hatchet blade geometry comprising a sharp edge and a trailing wall. In some embodiments, the most distal wing, closest to the tip comprises a regular cancellous bone thread blade and a trailing surface  240 . 
     In some embodiments, all gaps have the same size (volume, length and/or width). In some embodiments, the gaps differ in size. In some embodiments sizes of the gaps (e.g., volume, length and/or width) are in inverse proportion in respect to the major diameter of the wings defining the gap. The greater the major diameter—the smaller the gap is. In some embodiments, the closer the gap is to the anchor head, the smaller the gap is. 
     An aspect of some embodiments of the invention relates to a bone anchor kit for a bone anchor operative to tap a female thread in bone and collect and preserve bone fragments during insertion. 
     In some embodiments, the kit comprises at least one bone anchor and at least one bone drill guide. In some embodiments, the kit comprises at least one ratchet operative to drive the anchor into bone. In some embodiments, the anchor comprises a core or a stem disposed between and coupled to a head at a proximal end and a tip at a distal end. In some embodiments, the core comprises at least two radially extending wings. In some embodiments, the wings form a segmented helical thread along at least a portion of the core. In some embodiments, the wings are arranged in subsequence so that one wing is followed (but is not in contact with) a subsequent wing along a helical path. In some embodiments, every pair of subsequently arranged wings collect bone fragments in a space disposed in between the wings. 
     In some embodiments, the kit comprises a plurality of bone anchors having a variety of sizes. In some embodiments, the kit comprises a plurality of bone anchors having varying distances between a distally facing surface of the head and a most proximal aspect of the most proximal wing that equal various thicknesses of the bone cortex at various points of insertion of the anchor. 
     In some embodiments, the kit comprises a plurality of bone anchors comprising varying numbers of wings corresponding to the length of the anchor, specific bone and site of insertion into bone. 
     In some embodiments, the kit comprises at least one combination bone anchor operative to tap a female thread in bone and collect and preserve bone fragments during insertion. 
     In some embodiments, the anchor comprises a core or a stem disposed between and coupled to a head at a proximal end and a tip at a distal end. In some embodiments, the core comprises at least two radially extending wings. In some embodiments, at least a distal portion of the core comprises a wingless portion. 
     In some embodiments, the kit comprises at least one bone drill, at least one drill bit, at least one hammer and at least one anchor driver. In some embodiments, the anchor driver comprises a ratchet. 
     An aspect of some embodiments of the invention relates to a method of securing an implant to bone. In some embodiments, the method comprises driving into bone a bone anchor operative to tap a female thread in bone and collect and preserve bone fragments during insertion. In some embodiments the method comprises placing a drill guide on a surface of bone and forming a notch in the bone. In some embodiments, the method comprises drilling a bore in a surface of a bone, the bore being in continuum with the notch. In some embodiments, the method comprises placing an implant against the bone and placing the bone anchor comprising a stem and at least two radially extending wings coupled to and arrange subsequently to wrap said stem forming a segmented helical thread along at least a portion of said stem through an opening in the implant and into the drilled bore in the bone. In some embodiments, the method comprises rotating the anchor and inserting a distal edge of the most distal wing into the notch formed in the bone and driving the anchor into the bone. In some embodiments, the method comprises collecting bone fragments between at least two subsequent wings during rotation of the anchor. 
     Bone Anchor Structure 
     Reference is now made to  FIGS. 2A, 2B, 2C, 2D and 2E , which are side view and cross-section view simplified illustrations of a bone anchor and operation thereof in accordance with some embodiments of the present invention. As shown in the exemplary embodiment in  FIG. 2A , bone anchor  202  comprises an elongated core or stem  204  disposed between and coupled to a head  206  at a proximal end and a sharp tip  208  at a distal end. In some embodiments, head  206  is similar to the anchor head described in detail in international patent application publication WO2015/186123 which is incorporated herein in its entirety, the description of which will therefore not be repeated. 
     In some embodiments, head  206  comprises at least one distally facing surface  238 . In In some embodiments, core  204  comprises at least two radially extending wings  210 . In some embodiments, and as shown elsewhere herein, wings  210  form a segmented helical thread  212  along at least a portion of core  204 . In some embodiments, wings  210  are arranged in subsequence so that one wing (e.g.,  FIG. 2D , wing  210 - 1 ) is followed (but is not in contact with) a subsequent wing (e.g.,  FIG. 2D , wing  210 - 2 ) along the helical path. In some embodiments, each pair of subsequently arranged wings  210  form a gap  214  in them along the thread in which bone fragments  290  carved out of the bone are trapped and collected as anchor  202  is rotatingly driven into the bone and will be explained in greater detail elsewhere herein. The trapped and collected bone fragments serve as bony autografts that promote regeneration of bone during the healing process as explained in greater detail elsewhere herein. In some embodiments, wings  210  are coupled to and wrap around core  204  to form thread  212 . In some embodiments, helical path  212  extends longitudinally along core  204  from head  206  of anchor  202  to tip  208 . 
     A potential advantage of the structure of anchor  202  is in that only the cortical bone requires drilling. No drilling is required in cancellous bone since the wings are self-tapping and carve their own female thread path through cancellous bone as they are rotatingly driven into the site of implantation. 
     In some embodiments, at least one wing  210  has ledge geometry. In some embodiments, wing  210  comprises at least one proximally facing surface  216  facing head  206  of the anchor and at least one distally facing surface  218  facing tip  208 . In some embodiments, proximally facing surface  216  and distally facing surface  218  are equidistant. In some embodiments, a wing comprises a circumferential surface  220  along a major diameter of wing  210  and parallel to a longitudinal axis of core  204 . In some embodiments, a distal edge of circumferential surface  220  is coupled at least at a major diameter (Ø) of wing  210  to a circumferential edge  222  of distal surface  218  and a proximal edge of circumferential surface  220  at least at a major diameter (Ø) of wing  210  to a circumferential edge  224  of proximal surface  216 . In some embodiments, circumferential surface  220  is perpendicular to proximal and/or distal surfaces  216 / 218 . 
     In some embodiments, as shown in the exemplary embodiment depicted in  FIG. 2C  and explained in greater detail elsewhere herein, any wing  210  comprises a rectangular or square transverse cross-section taken along a radius (e.g.  FIG. 2B , r 1 /r 2 /r 3 ) anywhere along wing  210 . 
     In some embodiments, at least one wing  210  comprises a leading portion  226  and a trailing portion  228 . In some embodiments, at least the leading portion  226  comprises a surface defining a radially extending bone cutting surface  230 . In some embodiments and as shown in  FIG. 2B , bone cutting surface  230  is flat. In some embodiments and as shown in  FIG. 2D , bone cutting surface  230  is curved (concave) in a radial dimension. In some embodiments and as shown in  FIG. 2E , bone cutting surface  230  is curved (concave) in both a radial dimension and longitudinal dimension forming a spooned shaped. In some embodiments, meeting edges of bone cutting surface  230  with a leading edge of proximal surface  216 , a leading edge of distal surface  218  and/or a leading edge of circumferential surface  220  form one or more bone corresponding cutting edges  232 ,  234  and  236 . In some embodiments, the trailing portion of at least one wing  210  comprises a trailing surface  240 . 
     As explained in greater detail elsewhere herein, as the anchor is turned while being driven into bone, cutting edges  232 ,  234  and  236  carve bone forming a channel spiraling down along core  204 . Carved bone fragments are collected by bone cutting surface  230  and the collected fragments are trapped and built up within gap  214  between a trailing portion of a wing  210  and a leading portion of a following wing  210 . 
     Reference is now made to  FIGS. 3A, 3B, 3C and 3D  which are a side and bottom view simplified illustrations of a bone anchor. 
     As depicted in the exemplary embodiment shown in  FIG. 3A , wings  210  of anchor  202  form a segmented thread  212  over at least as portion of core  204 . In some embodiments, core  204  is cylindrical, having a constant minor diameter along at least a portion of core  204 . Hence and as shown in the example depicted in  FIG. 3C , wings  210  comprise a constant minor diameter along at least a portion of core  204  and in some embodiments, an increasing major diameter from tip  208  towards head  206 . In some embodiments, for any wing  210  a major diameter (Ø MD ) of the wing is at least twice the diameter of core  204  (Ø MD ). In some embodiments, for any wing  210  a major diameter (Ø MD ) is between 2 and 4 times, 2.5 and 3.5 times, less than twice or more than  4  times the diameter of core  204  (Ø md ). 
     As used herein, the term “Major Diameter” is the larger of two extreme diameters delimiting the height of a thread profile, as a cross-sectional view is taken in a plane containing the axis of the threads and the term “Minor Diameter” is the lower extreme diameter of the thread. 
     As shown in the example in  FIG. 3A , a major diameter (Ø 8 ) of wing  210  closest to head  206  is much greater than a major diameter (Ø 1 ) of wing  210  closest to tip  208 . In some embodiments, major diameter (Ø 8 ) is between 2 and 8 times major diameter (Ø 1 ), between 3 and 6 times major diameter (Ø 1 ), between 4 and 5 times major diameter (Ø 1 ), less than twice major diameter (Ø 1 ) or more than 8 times major diameter (Ø 1 ). 
     The increase in the major diameter (Ø) of wings  210  the closer they are to head  206  is also shown in  FIG. 3B , which is a longitudinal sectional simplified illustration of a portion of the exemplary embodiment shown in  FIGS. 2A-E , taken along axis A-A. As shown in the example depicted in  FIG. 3B , the major diameter (Ø) of wing  210 - 18  (i.e., 2*r 3 ) is greater than the major diameter (Ø) of wing  210 - 16  (i.e., 2*r 2 ), which in turn is greater than the major diameter (Ø) of wing  210 - 14  (i.e., 2*r 1 ). The effective cutting portion  250 - 18  of the surface of a leading bone cutting surface  230  for wing  210 - 18  would therefore be the thickness/height (h 18 ) of the wing multiplied by the difference (r 3 −r 2 ) between the radius (i.e., half major diameter) of  210 - 18  and the radius of wing  210 - 16  preceding wing  210 - 18  along the thread. Hence, in some embodiments, each wing  210  cuts a fragment of bone (e.g., cortical bone) having at least one dimension (X) equal, for example, to (r 2 ) less (r 1 ), i.e., X=(r 2 )−(r 1 ). Accordingly, the effective cutting portion  250 - 16  of the surface of a leading bone cutting surface  230  for wing  210 - 16  would therefore be the thickness/height (h 16 ) of the wing multiplied by the difference (r 2 −r 1 ) between the radius (i.e., half major diameter) of  210 - 16  and the radius of wing  210 - 14  preceding wing  210 - 16  along the thread. In  FIG. 3B , only wings  210 - 15 / 210 - 17  and  210 - 19  have been ignored for the purpose of simplifying the explanation however it should be noted that as explained elsewhere herein, the major diameter (2*r) of each wing  210  increases in accordance with the progression of wing reference numerals from  210 - 14  to  210 - 19 . 
     In some embodiments, at least the dimension (X) and a number of turns of the anchor in the bone define the quantity of bone fragments that accumulates in the gap. Hence, once the anchor is fully inserted in bone, the number of the fragments in gaps  214  will depend on the axial location of the gap. The more distal the gap—the greater will be the quantity of bone fragments in gap  214 . Hence, in more distal gaps  214  the quantity of accumulated bone may exceed the volume of gap  214  and bring about radially inward compression of the bone fragments. 
     In some embodiments, the thicknesses of the wings are the same. In some embodiments, the thicknesses of the wings vary. 
     The arrangement of the wings in a growing major diameter order is set to provide each wing  210  with a bite off a fragment of cortical bone  302  before entering cancellous bone. The fragment of cortical bone together with cancellous bone fragments collected while anchor  202  is driven into the bone serve as boney autografts that promote bone tissue regeneration during the healing process. In  FIG. 3A , several cortical layers  302  are drawn (each next to each wing  210 ) for explanatory reasons only, to demonstrate the progressively growing size of bites taken by wings  210  from cortical bone layer  302  as each wing is driven through cortical layer  302  and as the major diameter of the wing increases in size the closer the wing  210  is to head  206 . This is also shown in  FIG. 3B , which is a bottom view simplified illustration of bone anchor  202  viewed in the direction indicated by arrow  350  of  FIG. 3A . As shown in  FIG. 3B , four tangential lines T 1 , T 2 , T 3  and T 4  are drawn tangent to a major diameter of four subsequent wings  210 :  210 - 1 ,  210 - 2 ,  210 - 3  and  210 - 4  wherein  210 - 1  is the most distal wing and  210 - 4  is the most proximal wing. As illustrated in  FIG. 3B , the major diameter (Ø 1 ) of wing  210 - 1  being twice radius (r 1 ) at point of tangent T 1  is much smaller than the major diameter (Ø 4 ) of wing  210 - 4  being twice radius (r 4 ) at point of tangent T 4 . 
     Wing  210 - 5  being closest to a head  206  comprises the same diameter as a shoulder  370  of head  206  so that to prepare a bore in the cortical bone that will tightly and precisely accommodate shoulder  370  and help prevent “rocking” of anchor  202  after insertion as described in greater detail in the related International Application Publication WO2015/186123 incorporated by reference herein in its entirety. 
     Reference is now made to  FIGS. 4A, 4B, 4C and 4D  which are bottom view simplified illustrations of anchor  202  viewed from a direction indicated by arrow  350  of  FIG. 3A . In  FIG. 4A , the direction of rotation of anchor s defined by a curved arrow  450 . The direction of rotation defines for each wing  210  a leading portion  402  comprising a cutting surface  404  and a trailing portion  406 . As described elsewhere herein, the leading and trailing portions  402 / 406  respectively are defined by the direction of rotation indicated by arrow  450 . However, reversal of the direction of rotation redefines leading portion  402  as a trailing portion and trailing portion  406  as a leading portion having a cutting edge  408 . 
     In some embodiments and as shown in  FIG. 4A , the surface of a bone cutting surface, for example bone cutting surface  404 - 1  of wing  210 - 6 , is at an angle (α) in reference to a radius (r) of anchor  202  at the point of contact of the surface of surface  404  with core  204  and with respect to the direction of rotation indicated by arrow  450 . In this configuration, the edge of surface  404  at the major diameter of wing  210 - 6  is more advanced in reference to the direction of rotation of anchor  202  than the edge of the surface of wall  404 - 1  coupled to core  204 . In some embodiments, angle (α) is between 0 and 50 degrees. In some embodiments, angle (α) is between 0 and 50 degrees 10 and 40 degrees, 20 and 30 degrees more than 50 or less than 0 degrees. As shown in  FIG. 4B , the surface of a bone cutting surface, for example a bone cutting surface  404 - 2  of wing  210 - 7 , is disposed along a radius (r) of anchor  202 , at an angle (α) of 0 (zero) degrees in reference to a radius (r) of anchor  202  at the point of contact of the surface of wall  404 - 2  with core  204 . As shown in  FIG. 4B , the surface of a bone cutting surface, for example a bone cutting surface  404 - 2  of wing  210 - 7 , is at a negative angle (α) in reference to a radius (r) of anchor  202  at the point of contact of the surface of surface  404 - 2  with core  204  and with respect to the direction of rotation indicated by arrow  450 . 
     A potential advantage of an angled bone cutting surface  404  is in that the angle provides surface  404  with a greater cutting surface area than a surface aligned with the anchor radius. 
     Another potential advantage of an angled bone cutting surface  404  is in that the angle enables surface  404  to push bone fragments along female thread  412  while guiding the bone fragments radially inwards urging the fragments centrally, closer to core  204 . 
     As explained elsewhere herein, a potential advantage of a concavity of the surface of leading bone cutting surface  230  is in that it enables surface  230  to cup bone fragments and better keep the fragments from being pulverized ands or urged radially outward into crevices and caverns of the cancellous bone. 
     One or more leading edges of circumferential surface  220  form one or more bone corresponding cutting edges  232 ,  234  and  236 . In some embodiments, the trailing portion of at least one wing  210  comprises a trailing surface  240 . 
     As explained in greater detail elsewhere herein, as the anchor is turned while being driven into bone, cutting edges  232 ,  234  and  236  carve bone forming a channel spiraling down along core  204 . Carved bone fragments are collected by bone cutting surface  230  and the collected fragments are trapped and built up within gap  214  between a trailing portion of a wing  210  and a leading portion of a following wing  210 . 
     The exemplary embodiment depicted in  FIG. 4D  demonstrates an example of a female thread  412  carved out of the bone by anchor  202  wings  210 . A circumferential surface  410  of female thread  412 , mirroring circumferential surface  220  along great diameter (Ø MD ) of anchor  202 , is blunt. 
     A potential advantage of female thread having a blunt circumferential surface is in that such a surface minimizes compression and crushing of surrounding bone and the associated driving of pulverized material in a radially outward direction as seen in commonly used cortical bone screws and explained elsewhere herein. 
     Bone Anchor Wings Operation 
     Reference is now made to  FIGS. 5A, 5B, 5C, 5D and 5E  which are pictorial simplified illustrations of the modus operandi of bone anchor  202 . Wings  210  of anchor  202 , when driven into bone, tap or cut bone fragments from the bone and collect, preserve and drive the bone fragments along with anchor  202 . 
     A potential advantage of collecting and preserving the bone fragments is in that the fragments become centers for bone tissue regeneration in contact with bone anchor  202  stem  204  and wings  210 . For all practical purposes, anchor  202  performs autogenous bone tissue transplantation as it is implanted in to the bone tissue. 
     As shown in  FIG. 5A , as anchor  202  is driven into bone tissue, wings  210  first encounter a layer  525  of cortical bone. At the cortical bone level, each wing  210  breaks off a fragment  502  of cortical bone as illustrated in  FIG. 5B . As anchor  202  is rotated and wings  210  are advanced along a previously formed female thread  412 , wings  210  are driven into cancellous bone. At the cancellous bone level and as shown in the exemplary embodiment depicted in  FIG. 5C , each wing  210  taps a new female thread  412  in the cancellous bone having a major diameter (Ø MD ) than thread  412  tapped by the preceding wing  210 . Cancellous bone fragments  504  broken off the previously tapped boney thread, together with cortical bone fragments  502  are pushed along female thread  412  by cutting surface  404 , as indicated by a broken arrow  550  and accumulated, as shown in  FIG. 5D , in gap  214  between trailing surface 240  of wing  210 - 9  and leading bone cutting surface  230  of wing  210 - 10 . 
       FIG. 5E  illustrates anchor  220  in a final state of implantation in which all gaps  214  are filled with cortical and cancellous bone fragments  402 / 404  respectively forming a continuous fill of female bone thread  412  with alternating anchor  202  wings  210  and bone fragments  502  and  504 . As described elsewhere herein, bone fragments  502  and  504  trapped in gap  214  promote bone regeneration locking wings  210  in regenerated bone. 
     As depicted in  FIG. 5E , the farther the gap is from anchor head  206 , e.g., gap  506 , the fuller it becomes with bone fragments and debris. This is because cutting surfaces of leading walls of consecutive wings defining gap  506  continuously cut bone as anchor  202  is rotated, by at least a dimension (X) as explained in greater detail elsewhere herein and have turned more times than those defining gaps e.g., gap  508  closer to head  206 , and have therefore traveled a greater distance along the female thread and accumulated more bone fragments and debris. In some embodiments, all gaps in a bone anchor comprise the same size. In some embodiments, a bone anchor comprises gaps of varying sizes e.g., volume, length and/or width. For example, in some embodiments, gaps between consecutive wings do not necessary fill completely with fragments of bone tissue to allow growth of the accumulated bone tissue just as does an implanted bone graft. Alternatively, and optionally, gaps between consecutive wings located distally may extend along a greater length of the anchor thread, e.g., 1.25, 1.5, 2, 2.25, 2.5, 3 times longer, less than 1.25 times longer, more than 3 times longer or any value in between, than gaps between consecutive wings located more proximally. This is since gaps that have “traveled” a longer distance (i.e., more anchor rotations) accumulate more debris than gaps that have “traveled” a shorter distance (i.e., less anchor rotations). The more distally located is the gap, the more distance (i.e., rotations) it “travels”. 
     However, in some embodiments, sizes of the gaps (e.g., volume, length and/or width) are in inverse proportion in respect to the major diameter of the wings defining the gap, e.g., the greater the major diameters of the consecutive wings defining the gap the smaller the gap size. For example, in short screws, the gap between consecutive wings especially close to the anchor head  206  such as gap  508  may be too large for the expected amount of bone tissue fragments expected to accumulate in the gap. Hence, a distance between a trailing surface of a first wing and a leading surface of a following wing defining a length of the gap in between may be shorter the closer the gap is to anchor head  206 . In such embodiments, gap  506  may be larger in volume, length and/or width than the following gap and so on up to gap  508  which is the smallest. 
     Reference is now made to  FIG. 6 , which is a pictorial view simplified illustration of an implanted anchor  202 . As shown in the exemplary embodiment depicted in  FIG. 6 , anchor  202  is shown to be fixing a support device  602  (e.g., a bone plate) to bone. In some embodiments, the most proximal wing  210 - 11  is located at a distance (d 1 ) from head  206  distally facing surface  238 . In some embodiments, distance (d 1 ) corresponds to a thickness (d CT ) of a cortical bone layer  525  at the site of anchor  202  implantation. In some embodiments, (d 1 ) is between 1 and 10 mm, 2 and 8 mm, 3 and 6 mm, 4 and 5 mm, less than 2 mm or more than 10 mm. 
     A potential advantage in a distance (d 1 ) between the most proximal wing  210 - 11  and distally facing surface  238  is in that cortical bone regeneration inwards, into the gap between the most proximal wing  210 - 11  and distally facing surface  238  and encloses on core  204  providing added stability to anchor  202  by reducing “rocking” movement of the anchor as well as increasing resistance to pullout forces acting on anchor  202 . 
       FIGS. 7A and 7B  are pictorial view simplified illustrations depicting an exemplary embodiment of an anchor  702 . Anchor  702  comprises a wingless distal portion  704 . In some embodiments, wingless distal portion  704  includes a cutting flute  708 . In some embodiments, flute  708  is parallel to a longitudinal axis of core  204 . As described elsewhere herein, only the cortical bone layer  525  requires drilling that provides a directional guiding bore for insertion of wingless distal portion  704  of anchor  702 . Hence, wingless distal portion  704  extends proximally from tip  208  for a distance (d 2 ) that corresponds to a thickness of the cortical bone layer  525  at the site of implantation. In some embodiments, (d 2 ) is equal to, greater or smaller than the thickness (c CT ) of cortical bone layer  525 . In some embodiments, (d 2 ) is between 1 and 10 mm, 2 and 8 mm, 3 and 6 mm, 4 and 5 mm, less than 2 mm or more than 10 mm. 
     A potential advantage in the structure of anchor  702  is in that penetration of wingless distal portion  704  of anchor  202  core  204  into cancellous bone  706  displaces and compresses cancellous bone  706 - 1  radially outward along stem  204  as indicated by arrows designated reference numeral  750 . Further rotational insertion of anchor  702  into cancellous bone  706  drives wings  210  to carve the already compressed cancellous bone  706  and collect a greater volume of fragments than in a configuration in which cancellous bone  706  not been previously compressed. 
     Reference is now made to  FIGS. 8, 9 and 10  which are pictorial view simplified illustrations of exemplary embodiments of a bone anchor. As shown in  FIGS. 8-10 , a bone anchor  802 / 902 / 1002  has two or more pairs of wings  210  and varying lengths of core  204 . 
     In some orthopedic situations and in some embodiments, two pairs (four wings) comprise a combined surface area (e.g., combined surface area of proximally facing surfaces  216  of wings  210 ) to prevent “rocking” motion and pullout of anchor  802 / 902  after implantation. For example, anchor  902 , having a short core  204  may be suitable for implantation in areas having limited bone depth such as in infant bones in pediatric orthopedics or dental surgical procedures. A length of an anchor such as the example illustrated in  FIG. 9  for dental procedures may be between 3 and 20 mm, 5 and 15 mm, 8 and 12 mm, less than 3 mm or more than 12 mm. 
     In some embodiments, stress calculations may show an increased requirement for wing surface area with limited depth of bone.  FIG. 10  depicts an exemplary embodiment in which, with respect to bone anchor  902  of  FIG. 9 , wings  1010  have a greater major diameter than wings  210  of  FIG. 9  and therefore an increased surface area of, for example, combined surface area of proximally facing surfaces  1016  of wings  1010  that prevent “rocking” motion and pullout of anchor  1010  after implantation despite the limited available bone depth. 
       FIG. 11 , which is a side view simplified illustration of an exemplary embodiment of a bone anchor, depicts an anchor  1102  similar to anchors described elsewhere herein comprising one or more notches or perforations  1150  in core  1104 . Notches or perforations  1104  promote growth of bone tissue into the pores or notches increasing stability and fixation of anchor  1102  in the bone. In some embodiments, bone anchor  202 ,  702 ,  802 ,  902 ,  1002 ,  1102 ,  1202 ,  1222 ,  1402  and  1452  are coated with an anti-loosening coating such as Trabecular Structures™ (Manufactured by Arcam AB, Headquarters Krokslatts Fabriker 27ASE-431 37 Molndal, Sweden). 
       FIGS. 12A, 12B, 12C and 12D , which are cross-section view simplified illustrations of bone anchor  202  wings  210  illustrate examples of proximally facing and/or distally facing surfaces  216 / 218  respectively of wings  210  comprising greater surface areas than square or rectangle cross-sections of wings  210 . The cross-sections are taken along a radius extending from core  204  radially outwards as shown and discussed elsewhere herein. 
     In the example shown in  FIG. 12A , a proximally facing surface  216  is angled and slants radially inwards (from circumferential surface  220  towards core  204 ). Angled surface  216  does not only provide greater resistance to pullout but also helps maintain bone fragments close to core  204  and preventing such fragments from moving radially outwards. 
       FIG. 12B  shows an exemplary embodiment similar to that depicted in  FIG. 12A  in which distally facing surface  218  is angled and slants radially inwards (from circumferential surface  220  towards core  204 ) similarly to proximally facing surface  216 . The increased surface area of distally facing surface  218  provides greater resistance to further advancement of anchor  1002  succumbing to longitudinal forces resulting from, for example, chewing. 
       FIGS. 12C and 12D  comprise convex proximally facing and/or distally facing surfaces  216 / 218  respectively of wings  210 . Similar to the exemplary embodiments depicted in  FIGS. 12A and 12B , concave surfaces  216  do not only provide greater resistance to pullout but also help maintain bone fragments close to core  204  and prevent such fragments from moving radially outwards. Similarly, an increased surface area of distally facing surfaces  218  provides greater resistance to further advancement of anchor  1002  succumbing to longitudinal forces resulting from, for example, chewing. 
     Dedicated Drill Guide 
     Reference is now made to  FIGS. 13A, 13B, 13C, 13D and 13E , which are pictorial view and partially sectional view simplified illustrations of a dedicated drill guide  1202  for a bone anchor as described elsewhere herein. In some embodiments, drill guide  1202  comprises at least one handle  1204  and a body  1206  having a bore  1208  sized and fitted to receive a drill bit (not shown). In some embodiments, bore  1208  is centrally located. Optionally, a longitudinal axis of handle  1204  is angled at an angle (β) in respect to the longitudinal axis of bore  1208  so that the hand of the surgeon does not contact tissue when placing body  1206  against bone. Optionally, angle (β) is between 10 and 45 degrees, 15 and 40 degrees, 20 and 35 degrees, less than 10 degrees or more than 45 degrees. 
     In some embodiments, body  1206  comprises a protrusion  1210  on a bone facing aspect of body  1206 , sized and fitted to be received by a bone anchor head  206  receiving opening in an implant  1230 . For example, such an implant can be a bone plate or a cementless joint resurfacing system as described in International Patent Application No. PCT/IL2016/050818 to the same inventor and is hereby incorporated herein in its entirety. 
     In some embodiments, protrusion  1210  is cylindrical. In some embodiments and as shown in  FIG. 13D , body  1206  protrusion  1210  is sized and fitted to be received by a bone anchor head  206  receiving opening  1228  in an implant  1230  surface, e.g., a bone plate. In some embodiments, the diameter of protrusion  1210  is sized to snugly fit inside opening  1228  in an implant  1230 . This is to ensure that drill guide bore  1208  is centered correctly in respect to implant  1230 . In some embodiments, body  1206  comprises a bone facing surface  1212  and a surface  1212  facing away from bone. In some embodiments, bone facing surface  1212  is flat. In some embodiments, bone facing surface  1212  is curved and/or angled. 
     In some embodiments, body  1206  bone facing surface  1212  comprises at least one sharp wedge  1214 . In some embodiments, wedge  1214  projects distally from bone facing surface  1212  of drill guide body  1206 . In the exemplary embodiment depicted in  FIGS. 13A-13D  wedge  1214  comprises flat elongated blade-like geometry, having a sharp ridge  1216  and extending radially outwardly from bore  1208 . In some embodiments, drill guide body  1206  comprises a flat proximally facing surface  1218  operative to receive a hammer strike. 
     In some embodiments, and as shown in  FIG. 13E  walls of drill guide  1222  body  1226  are curved so that drill guide  1222  specifically fits between teeth  1250  to contact bone  1252 . 
     In  FIGS. 14A-14D, 15A-15D and 16 , bone implant  1230  has been removed to simplify the explanation. 
     Referring now to  FIGS. 14A, 14B and 14C , which are pictorial view simplified illustrations of employment of drill guide  1202  in drilling a bore in cortex of a bone in preparation for implantation of a bone anchor, viewed from a direction indicated in  FIG. 12A  by an arrow  1275 . 
     As shown in  FIG. 14A , drill guide  1202  is placed on surface of a bone at a site of anchor implantation such that sharp ridge  1216  of wedge  1214  engages surface  1302  of bone cortex  525 . Once in place, a hammer  1304  is used to tap proximal surface  1218  of body  1206  in a direction indicated by an arrow  1350  and drive wedge  1214  at least partially into cortical bone layer  525 . As shown in the exemplary embodiment depicted in  FIG. 14B , wedge  1214  is driven into cortical bone  525  until at least a portion of bone facing surface  1212  engages surface  1302  of cortical bone  525 . Once body  1206  of drill guide  1202  is firmly placed against surface  1302  of cortical bone  525 , a drill bit  1355  may be inserted into bore  1208  and a bore  1306  drilled through cortical layer  525  as shown in  FIG. 14C . As explained elsewhere herein, no drilling is necessary in cancellous bone. 
     At this stage, drill  1306  and drill guide  1202  are removed. In some embodiments, drill guide  1202  may be made of disposable materials and may be disposed of at this stage. 
       FIG. 14D , shows surface  1302  of cortical bone  525  viewed from a direction indicated in  FIG. 14B  by an arrow  1360  once drill guide  1202  and drill bit  1355  have been removed. Bore  1306  extends the full thickness of cortical bone layer  525  and a notch  1308  extending superficially radially outward from bore  1306 . In the example depicted in  FIG. 14D , notch  1308  has slot geometry with a depth equivalent to the height (h) of wedge  1214  from bone facing surface  1212 . In some embodiments, height (h) may be between 0.1 and 1 mm, 0.2 and 0.8 mm, 04 and 0.6 mm, less than 0.1 or more than 1 mm. 
     Reference is now made to  FIGS. 15A, 15B, 15C and 15D , which are cross-section view simplified illustrations of positioning of an anchor  202  in a bore  1306  drilled through cortical bone layer  525  with or without a notch  1308  and exemplary embodiments of anchor  202  distal ends and tips. As shown in the exemplary embodiment depicted in  FIG. 15A , cortical bone layer  525  comprises a drilled bore  1306  with no notch in surface  1302 . Tip  208  of anchor  202  is placed inside bore  1306 , however, anchor  202  is positioned at an angle in respect to surface  1302  of cortical bone layer  525 . The angle may be created by positioning distally facing surface  218  of wing  210 - 12  against surface  1302  of the bone providing a surgeon with a false feeling of a close fit of anchor  202  in bore  1306 . 
     In the exemplary embodiment shown in  FIG. 15B , cortical bone layer  525  comprises both a drilled bore  1306  and a notch  1308  in surface  1302  of the bone. In this configuration, tip  208  of anchor  202  is placed inside bore  1306  and at least a portion of leading portion  226  of wing  210 - 12  is received within notch  1308  and allows the correct positioning of anchor  202  in respect to surface  1302 . 
     A potential advantage in notching the surface  1302  of cortical bone layer  525  is in that it allows correct positioning of anchor  202  in respect to surface  525 . 
     A potential advantage in notching the surface  1302  of cortical bone layer  525  is in that notch  1308  provides an initial grip of a portion of cortical bone for bone cutting surface  230  when anchor  202  is rotated. This is shown in  FIG. 16 , which is a cross-section view simplified illustration of a drilled bore and notch made in bone taken along broken line Q-Q in  FIG. 15B  and viewed from a direction indicated by an arrow  1460 . As shown in  FIG. 16 , a leading portion  226  of wing  210 - 12  is inserted inside notch  1308  and engaged against and gripping at least a portion of a wall  1310  of notch  1308 . 
       FIGS. 15C and 15D  illustrate exemplary embodiments of distal tips of anchors  1402  and  1452  suitable for insertion in notch  1308  and provide anchor  202  with a correct spatial orientation in respect to the surface of cortical bone  525 . In the embodiment shown in  FIG. 15C , the most distal wing  1404  has hatchet blade geometry comprising a sharp edge  1406  and a trailing surface  240 . In the exemplary embodiment depicted in  FIG. 15D , bone cutting surface  230  of the most distal wing  1408  has been replaced with a regular cancellous bone thread blade  1410  but maintains trailing surface  240 . 
     Bone Anchor Kit 
     In some embodiments and as shown in  FIG. 17 , which is a pictorial view and partial diagrammatic view simplified illustration of an embodiment of a bone anchor kit, a bone anchor kit  1602  comprises a plurality of bone anchors having varying distances between a distally facing surface  238  of head  206  and a most proximal aspect of the most proximal wing  210  some examples include one or more bone anchors  202 ,  1604 ,  702 ,  802  and/or  902  or any other types of bone anchors as described elsewhere herein, and a bone anchor dedicated drill guide. In some embodiments, bone anchor kit includes one or more drill bits  1355 , one or more hammers  1304  and a bone anchor driving tool  1606 . In some embodiments, one or more anchors  202 ,  1604 ,  702 ,  802  and/or  902  have heads comprising hexagonal bores sized and fitted to receive a hexagonal screw driver such as that commonly found in orthopedic surgical suites. 
     A bone anchor kit  1602  can be set for specific orthopedic or dental surgical procedures and contain specific anchors and associated tools for the intended procedure. Such kits may include dental surgical procedure kits, pediatric orthopedic surgical kits, and others. In some embodiments, a bone anchor kit may be combined with other orthopedic surgical kits such as knee resurfacing or total knee replacement kits, hand orthopedic surgery kits, jaw reconstructive surgical kits and similar. 
     Clawed Bone Plate 
     Reference is now made to  FIGS. 18A, 18B and 18C , which are perspective view and plan view simplified illustrations of a clawed bone plate to be used with a bone anchor as described elsewhere herein and in accordance with an aspect of some embodiments of the invention. 
     The rotator cuff is a general term including shoulder complex muscles that predominantly stabilize the glenohumeral joint, but also contribute significantly to movement. The rotator cuff muscles include the Supraspinatus, Infraspinatus, Teres Minor and Subscapularis muscles. The tendons of these muscles coalesce to form the rotator cuff. 
     Rotator cuff tears are relatively common, and their repair entails surgery to repair a torn tendon in the shoulder. The procedure can be done with a large (open) incision or with shoulder arthroscopy, which uses smaller incisions. The tendons are re-attached to the bone using small rivets (called suture anchors) made of metal or an absorbable material. Sutures are attached to the anchors that tie the tendon back to the bone. Tears in the rotator cuff tendons can be partial or full where the tendon is approximated to the head of the Humerus bone prior to fixation. 
     In some embodiments, a bone anchor kit e.g., bone anchor kit  1602  comprises a set for specific orthopedic procedures e.g., rotator cuff tendon rupture repair. 
     In some embodiments, a rotator cuff repair kit is similar to bone anchor kit  1602  as explained elsewhere herein and comprises at least one clawed bone plate  1800  as depicted in  FIGS. 18A, 18B, 18C and 18D .  FIGS. 18A and 18B  are a perspective view and a plan view simplified illustrations of an embodiment of a clawed bone plate in accordance with some embodiments of the invention.  FIG. 18B  is a plan view of the clawed bone plate in  FIG. 18A  viewed from a direction indicated by arrow  1810 . In some embodiments, clawed bone plate  1800  comprises a generally flat or slightly curved body  1802  having at least one aperture  1804  on one end and one or more claws  1806  on the opposite end. In some embodiments, tips  1822  of claws  1806  are blunt. In some embodiments, tips  1822  of claws  1806  are sharp. 
     In some embodiments, one or more claws  1806  are angled in respect to body  1802  of clawed bone plate  1800  so that to protrude from a bone-facing surface  1808  of clawed bone plate  1800 . In some embodiments, aperture  1804  is sized to accommodate at least a bone anchor  202 . In some embodiments, aperture  1804  comprises a step  1820  sized to accommodate at least a shoulder  370  of the bone anchor  202  head  206 . In some embodiments, at least two claws  1806  share a common generally flat surface  1814  along before joining body  1802  of clawed bone plate  1800 . 
       FIGS. 18C and 18D  are a perspective view and a plan view simplified illustrations of a clawed bone plate  1850  in accordance with some embodiments of the invention.  FIG. 18D  is a plan view simplified illustration of clawed bone plate  1850  viewed from a direction indicated by arrow  1830 . As shown in  FIGS. 18C and 18D , a body  1852  of clawed bone plate  1850  forms clefts  1854  at one end  1818  that define individual claws  1806 . In some embodiments, an aperture  1856  at an end of body  1852  opposite to clefted end  1818  comprises a step  1820  sized to accommodate at least a shoulder  370  of the bone anchor  202  head  206 . 
     In some embodiments, clawed bone plate  1800 / 1850  is made of commonly used bone plate materials such as stainless steel and titanium or any other suitable biocompatible material. 
     Referring now to FIGS. 19 A,  19 B and  19 C, collectively referred to as  FIG. 19 , which are a perspective view and side view simplified illustrations of implementation of the clawed bone plate in accordance with some embodiments of the invention. As shown in the exemplary embodiment depicted in  FIG. 19 , for correction of a partial or full tear of a rotator cuff tendon  1950 , clawed bone plate  1800 / 1850  is applied to the torn tendon so that tips  1822  of individual claws  1806  are in contact with a portion of tendon  1950  extending from a rotator cuff muscle. The aperture  1804 / 1856  end of clawed bone plate  1800 / 1850  respectively is positioned over an exposed surface of a head of the Humerus bone  1952 . In some embodiments, the torn portion of tendon  1950  is approximated if necessary (e.g., in cases of a full tear). 
     As shown in the exemplary embodiment depicted in  FIG. 19  anchor  202  is driven through aperture  1804 / 1856  and into the head of the Humerus bone  1952 , urging clawed bone plate  1800 / 1850  against the head of the Humerus bone  1952  and driving claws  1806  into tendon  1950  tissue. In some embodiments, claws  1806  at least partially bite into tendon  1950  and/or surface of the head of the Humerus bone  1952 . 
     A potential advantage in the clawed bone plate  1800 / 1850  is in that rotator cuff partial or full tear is repaired without the use of sutures and requires only fixation of clawed bone plate  1800 / 1850  to the head of the Humerus bone  1952  and tendon  1950  using anchor  202 . 
     A potential advantage in the clawed bone plate  1800 / 1850  is in that the procedure is time sparing and simple to execute. 
     A Method of Use of a Bone Anchor and a Kit Comprising a Bone Anchor 
     Reference is now made to  FIG. 20 , which is a flow chart of an exemplary method of implanting a bone anchor in bone. In some embodiments, at  1702  the method comprises optionally placing a dedicated drill guide  1202  against surface of a bone at a site of anchor implantation. Optionally, at  1704  tapping drill guide  1202  to form a notch  1308  in surface  1302  of the bone. At  1706  a bore  1306  is drilled in cortical bone layer  525  and a fixation device is optionally placed against the surface  1302  of the bone at  1708 . In some embodiments, a fixation device is a bone plate. In some embodiments, a fixation device is a knee resurfacing device or any other suitable device. At  1710  a bone anchor (e.g., anchor  202 ) is placed in the drilled bore  1306 , optionally through an opening in the fixation device. Optionally, at least a portion of a wing  210  is placed in notch  1308  at  1712 . At  1714  rotating the bone anchor and collecting at  1716  bone fragments between every two subsequent wings  210  as the anchor is driven deeper into the bone. 
     The terms “comprises”, “comprising”, “includes”, “including”, “has”, “having” and their conjugates mean “including but not limited to”. 
     Throughout this application, embodiments of this invention may be presented with reference to a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as “from 1 to 6” should be considered to have specifically disclosed subranges such as “from 1 to 3”, “from 1 to 4”, “from 1 to 5”, “from 2 to 4”, “from 2 to 6”, “from 3 to 6”, etc.; as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range. 
     Whenever a numerical range is indicated herein (for example “10-15”, “10 to 15”, or any pair of numbers linked by these another such range indication), it is meant to include any number (fractional or integral) within the indicated range limits, including the range limits, unless the context clearly dictates otherwise. The phrases “range/ranging/ranges between” a first indicate number and a second indicate number and “range/ranging/ranges from” a first indicate number “to”, “up to”, “until” or “through” (or another such range-indicating term) a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numbers therebetween. 
     Unless otherwise indicated, numbers used herein, and any number ranges based thereon are approximations within the accuracy of reasonable measurement and rounding errors as understood by persons skilled in the art. 
     It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.