Patent Publication Number: US-2010114168-A1

Title: Anchor with non-threaded securing mechanism to attach an elongated member to a bone

Description:
RELATED APPLICATION 
     Co-pending U.S. patent application Ser. No. 12/260,823 is directed to an anchor with a two member securing mechanism for attaching an elongated member to a bone. 
    
    
     BACKGROUND 
     The present application relates to anchors for attaching an elongated member to a bone, and more particularly to anchors with a non-threaded securing mechanism to capture the elongated member. 
     Elongated members such as but not limited to rods, wires, and tethers, are used in a variety of different surgical applications. The elongated members are attached to a bone in a patient and may provide a corrective force, support, or positioning for the bone and other adjacent bones. The elongated members are attached to the bone by anchors that include a receiver and a shaft. The receiver is configured to receive the elongated member, and the shaft is configured to attach to the bone. Many previous anchors include a set screw that is threaded onto the receiver to capture the elongated member. The threaded set screw design may include several drawbacks. 
     One drawback is the set screw may be threaded improperly onto the receiver. This may cause the threads to be stripped on the receiver and/or set screw. The set screw may bind within the receiver preventing further tightening of the set screw to fully engage the elongated member. Alternatively, the set screw is thereafter removed from the receiver but the threads on the receiver are stripped requiring removal and replacement. Another issue may be the false impression that the set screw is fully tightened in the receiver and engaged with the elongated member. At some point thereafter, the improperly threaded set screw loosens in the receiver requiring a revision procedure. 
     Another drawback is the set screw may cause the arms of the receiver to splay apart. The set screw may apply an outward force on the arms of the receiver as it is threaded onto the receiver. This force may cause the arms to move apart which may cause the set screw to become loosely attached to the receiver. Again, this may result in the set screw not fully engaging the elongated member, and/or the set screw becoming loose which would require correction during a revision procedure. 
     SUMMARY 
     The present application is directed a device to attach an elongated member to a bone in a patient. The device may include 
     Other aspects of various embodiments of the anchor are also disclosed in the following description. The various aspects may be used alone or in any combination, as is desired. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an anchor attaching an elongated member to a bone according to one embodiment. 
         FIG. 2  is an exploded perspective view of an anchor for attaching an elongated member to a bone according to one embodiment. 
         FIG. 3  is a perspective view of a base according to one embodiment. 
         FIG. 4  is a sectional view cut along line IV-IV of  FIG. 3  of the base. 
         FIG. 5  is a sectional view of a base according to one embodiment. 
         FIG. 6  is a perspective view of an insert according to one embodiment. 
         FIG. 7  is a sectional view cut along line VII-VII of  FIG. 6  of the insert. 
         FIG. 8  is a sectional view of an insert according to one embodiment. 
         FIG. 9  is a sectional view of an insert attached to a base according to one embodiment. 
         FIG. 10  is a side view of an insert attached to a base according to one embodiment. 
         FIG. 11  is a sectional view of an anchor attaching an elongated member to a bone according to one embodiment. 
         FIG. 12  is a sectional view of an anchor attaching an elongated member to a bone according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present application is directed to an anchor with a non-threaded securing mechanism for attaching an elongated member to a bone.  FIG. 1  illustrates one embodiment of an anchor  10  securing an elongated member  100  to a bone  110 . The anchor  10  includes a receiver  50 , shaft  60 , and securing mechanism  20 . The receiver  50  includes spaced-apart arms  52  that form a channel  51  sized to receive the elongated member  100 . The shaft  60  extends from the receiver  50  and is configured to engage with the bone  110 . The securing mechanism  20 , including a base  30  and an insert  40 , attaches to the receiver  50  to capture the elongated member  100  in the channel  51 . The base  30  is configured to attach to the arms  52  and includes an aperture  31  that receives the insert  40 . The insert  40  extends through the aperture  31  and may contact against the elongated member  100 . The securing mechanism  20  does not include threads and attaches to the receiver  50  in a manner to prevent splaying of the arms  52 . 
     As illustrated in  FIG. 2 , the receiver  50  includes the arms  52  and a body  53  that form the channel  51 . The receiver  50  also includes a first end  54  and a second end  55 . A receiving surface  56  of the channel  51  may be shaped to match the size and shape of the elongated member  100 . Extensions  57  are positioned on the outer surface of the arms  52 . The extensions  57  include a ramped surface  58  and a contact surface  59 . The contact surface  59  may be substantially perpendicular to a longitudinal axis of the receiver  50 . The extensions  57  may include a width that is greater than the remainder of the arms  52 . Further, the width of the extensions  57  increases away from the second end  55  of the receiver  50 .  FIG. 2  illustrates the extensions  57  positioned at the second end  55  of the arms  52 . Extensions  57  may also be positioned along the arms  52  away from the second end  55 . Further, multiple extensions  57  may be spaced along the arms  52 . 
     The shaft  60  is configured to attach to the bone  110 . The shaft  60  may include threads  61  that engage with the bone  110 . Shaft  60  may also include a hook or other shape to engage with the bone  110   
     The receiver  50  and shaft  60  may be formed as a single piece or as separate pieces that attach together as illustrated in  FIG. 2 . The two piece construction provides for the receiver  50  to be movable relative to the shaft  60  to accommodate the elongated member  100  at various angular positions.  FIG. 2  includes an embodiment with the body  53  of the receiver  50  including a hollow interior sized to receive a head  62  of the shaft  60 . A crown  70  may be positioned on the head  62  to facilitate placement and movement of the anchor  60  relative to the receiver  50 . U.S. patent application Ser. No. 12/038,572 discloses embodiments of two piece construction and is herein incorporated by reference. 
     The base  30  includes an aperture  31  with a width Y to receive the insert  40 . Base  30  also includes apertures  32 ,  33  shaped and sized to receive the arms  52  and attach to the receiver  50 . The base  30  may include various shapes, such as but not limited to a circular shape as illustrated in  FIG. 2  and a rectangular shape as illustrated in  FIG. 3 . The base  30  may include various thicknesses measured between the first side  34  and the second side  35 . Further, the thickness of the base  30  may vary across the length and width. 
     As illustrated in  FIG. 4 , the apertures  32 ,  33  that receive the arms  52  include opposing surfaces  36 ,  37  when viewed in cross-section. The surfaces  36 ,  37  are positioned for a width of the apertures  32 ,  33  to be larger at the first side  34  than at the second side  35 . In this specific embodiment, surfaces  36  are substantially parallel to a centerline A of the base  30 , and surfaces  37  are positioned at a non-parallel and non-perpendicular angle to the centerline A. If extended outward, the surfaces  36 ,  37  would form an acute angle and intersect at a point above the second side  35 . The decreasing widths of the apertures  32 ,  33  from the first side  34  towards the second side  35  facilitate attachment to the arms  52  as will be explained in detail below.  FIG. 5  includes a base  30  with aperture  32  including a substantially constant width, and aperture  33  including a width that narrows from the first side  34  to the second side  35 . 
     The insert  40  is sized to move along the aperture  31  of the base  30 . The insert  40  includes a first side  41  and an opposing second side  42 . The insert  40  may be solid, or may include a bore that extends through an interior section from the first side  41  to the second side  42 . The insert  40  may also be substantially solid with a cavity that extends inward from one or both sides  41 ,  42 . An extension  43  is positioned between the first and second sides  41 ,  42 . As illustrated in  FIG. 6 , the extension  43  includes a contact surface  44  that is substantially perpendicular with a longitudinal axis B of the insert  40 , and an angled surface  45  that is at a non-parallel and non-perpendicular orientation relative to the longitudinal axis B. The extension  43  may extend continuously around the insert  40 , or may include one or more discrete sections. 
     The extension  43  includes a width X that is greater than the aperture width Y. The extension  43  is constructed to be compressible to fit into the aperture  31 . The insert  40  may be constructed in various manners to allow for compression.  FIG. 7  includes an embodiment with the extension  43  constructed of a material that compresses while in the aperture  31 . A main body  46  of the insert  40  may be constructed of a different material that may or may not compress. If the material does not compress, then the width of the main body  46  is less than the width Y of the aperture  31 . In another embodiment, the entire insert  40  is constructed of one or more compressible materials.  FIG. 8  includes one or more slots  47  that extend inward from the first end  41  and include opposing sidewalls and an interior end. The slots  47  provide for the extension  43  to compress inward while positioned in the aperture  31 . The various embodiments provide for the extension  43  to rebound outward away from the longitudinal axis B when the extension  43  is away from the aperture  31 . 
     The insert  40  may be operatively connected to the base  30  prior to attachment of the base  30  to the receiver  50 . This facilitates attachment of the securing mechanism  20  to the receiver  50  by forming a larger overall structure that may be easier to handle by the surgeon during the surgical procedure.  FIG. 9  includes an embodiment with the expansion force of the compressed extension  43  against the surface of the aperture  31  being adequate for attachment.  FIG. 10  includes a groove  38  positioned in the sidewall of the aperture  31 . The groove  38  is sized to receive the extension  43  to attach the insert  40  to the base  30 . The groove  38  may include various shapes and sizes to receive the extension  43 . Further, the groove  38  may be located at various locations along the aperture  31  between the first and second sides  34 ,  35 . 
     The anchor  10  may be constructed of various materials. Examples include but are not limited to titanium, PEEK, polyurethane, polypropylene, or polyethylene, and UHMWPE. 
     One method of using the anchor  10  includes attaching the receiver  50  and shaft  60  to the bone  110  at the appropriate position to receive the elongated member  100 . Once the elongated member  100  is in the channel  51 , the securing mechanism  20  is attached to receiver  50  to secure the elongated member  100 . Initially, the base  30  is attached to the receiver  50 . In one method, the apertures  32 ,  33  on the base  30  are aligned with the arms  52  on the receiver  50 . As illustrated in  FIG. 11 , angled second surface  37  of apertures  32 ,  33  are aligned with the angled surfaces  58  of the extensions  57 . A downward force is applied to the base  30  to force the base  30  over the arms  52  with the apertures  32 ,  33  moving over the extensions  57  and the base  30  attaching to the receiver  50 . The downward force causes the angled aperture surfaces  37  to slide along the angled extension surfaces  58 . The force may cause the arms  52  of the receiver  50  to move together and/or the apertures  32 ,  33  to elongate to allow the base  30  to move beyond the contact surfaces  59  of the extensions  57 . The contact surfaces  59  move over the second side  35  and prevent removal of the base  30  once the second side  35  of the base  30  is moved beyond the angled surfaces  58 . 
     After the base  30  is attached to the receiver  50 , the insert  40  is moved towards the elongated member  100 . A downward force is applied to the insert  40  to move the extension  43  through the aperture  31 . The extension  43  is in a compressed state with a reduced width as it moves through the aperture  31 . As illustrated in  FIG. 11 , the width of the extension  43  increases to a width greater than the aperture  31  after moving beyond the first side  34  of the base  30 . This enlarged size prevents the insert  40  from beyond removed from the base  30 . As illustrated in  FIG. 11 , the first side  41  of the insert  40  may contact against the elongated member  100 . Alternatively, the first side  41  may be spaced from the elongated member  100 . The first side  34  of the base  30  may also spaced away from the elongated member  100  when the base  30  is attached to the receiver  50 . 
     The second side  42  of the insert  40  may be flush with the second side  55  of the receiver  50  upon final deployment. Alternatively, the second side  42  may be recessed below the second side  55 , or may extend outward beyond the second side  55 . 
     The force applied to the base  30  and insert  40  may be directly applied by the surgeon. The surgeon may use their finger and/or hand to directly contact against the base  30  and insert. Alternatively, the second sides  35 ,  42  may include receptacles to receive a tool that is handled by the surgeon and applies the force to the base  30  and/or insert  40 . 
       FIG. 12  includes an embodiment with the extensions  43  on the insert  40  positioned away from the first side  41 . The insert  40  is attached to the base  30  when the extensions  43  extend into the grooves  38  as illustrated in  FIG. 12 . In this position, the first side  41  of the insert  40  extends outward into the channel  51  beyond the first side  34  of the base  30 . The first side  41  may contact against or be spaced away from the elongated member  100 . 
     The cross-sectional shapes of the insert  40  and aperture  31  may substantially match to facilitate axial movement of the insert  40  relative to the base  30 . The insert  40  and aperture  31  may include various shapes, including but not limited to circular, square, rectangular, triangular, oval, and octagonal. 
     The elongated member  100  may include a variety of configurations, including but not limited to a rod, wire, and tether. The elongated member  100  may be made from a suitably strong rigid material known in the art, such as titanium, or from a semi-rigid material such as PEEK, polyurethane, polypropylene, or polyethylene. The elongated member  100  may include a variety of cross-sectional shapes including but not limited to circular, rectangular, square, and oval. Depending upon the context of use, the elongated member  100  may be linear or non-linear. 
     The elongated member  100  provides a force to the bone  110 . One application includes the elongated member  100  being applied to the spine of a patient with the bone  110  being a vertebral member. In one specific embodiment, the anchor  10  is attached to a pedicle of a vertebral member. Other applications include but are not limited to attachment to the femur, fibula, tibia, humerus, and mandible. 
     The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. Further, the various aspects of the disclosed device and method may be used alone or in any combination, as is desired. The disclosed embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.