Patent Publication Number: US-2017360492-A1

Title: Bone anchor with plug member and tool for inserting the plug member into the bone anchor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/991,822, filed Jan. 8, 2016, which is a continuation of U.S. patent application Ser. No. 14/188,391, filed Feb. 24, 2014, now U.S. Pat. No. 9,265,539, which is a continuation of U.S. patent application Ser. No. 12/494,107, filed Jun. 29, 2009, now U.S. Pat. No. 8,690,930, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/077,377, filed Jul. 1, 2008, the contents of which are hereby incorporated by reference in their entirety, and claims priority from European Patent Application EP 08 011 874.8, filed Jul. 1, 2008, the contents of which are hereby incorporated by reference in their entirety. 
    
    
     SUMMARY 
     The application relates to a bone anchor with a cannulated shaft and a plug member which is insertable into the shaft for closing the shaft at one end. The application also relates to a tool for introducing the plug member. 
     WO 01/26568 A1 describes a bone anchor in the form of a bone screw with a screw head and a threaded shaft which includes an axial bore and a plurality of radial bores. The axial bore is open at the screw head side and closed at the free end of the screw shaft. The known bone screw can be anchored in the bone through injecting bone cement into the shaft. This leads to a permanent and safe fixation of the bone anchor. 
     A bone anchor in the form of a bone screw with a cannulated shaft is also known from U.S. Pat. No. 5,047,030. The interior of the bone screw has a continuous longitudinal canal with several radially extending transverse canals which contact the longitudinal canal. The longitudinal canal is open at both ends of the screw, and it is possible to connect a vacuum pump via a tube in the area around the screw head to apply a vacuum to suck blood or other material. 
     WO 02/38054 A2, US 2004/0122431 A1 and US 2004/0147929 A1 disclose bone screws with a tubular threaded portion and a tip portion which can be connected to the tubular threaded portion. The tubular threaded portion has a number of recesses in its wall. It is possible to fill the tubular threaded portion with bone cement. 
     Minimally invasive surgery is applied in an increasing number of cases. With minimally invasive surgery in some cases guide wires are used to place an implant at the implantation site. A minimally invasive access is usually made percutaneously through the skin. 
     Based on the foregoing, there is a need for a bone anchor which has a broad range of application, for example which is suitable for being placed at the implantation site with minimally invasive surgery and which can be filled with a bone cement or another substance. 
     SUMMARY 
     The bone anchor according to the disclosure can be used in both, conventional surgery and minimally invasive surgery. It is possible to provide plug members for existing cannulated bone screws to render them suitable for minimally invasive surgery. 
     The bone anchor with the plug member prevents leaking of injected bone cement at the tip of the bone anchor. This reduces possible damages of vascular structures. 
     Further features and advantages will become apparent from the description of embodiments of the invention by means of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exploded perspective view of the bone anchor according to one embodiment. 
         FIG. 2  shows the bone anchor of  FIG. 1  in an assembled state when the rod is fixed. 
         FIG. 3  shows a sectional view of the bone anchor of  FIG. 2 , the section being taken along a plane containing the rod axis. 
         FIG. 4  shows a top view of the plug member used in the bone anchor of  FIGS. 1 to 3 . 
         FIG. 5  shows a perspective view of the plug member of  FIG. 4 . 
         FIG. 6  shows a side view of the plug member. 
         FIG. 7  shows a sectional view of the plug member. 
         FIG. 8  shows an enlarged sectional view of the plug member of  FIGS. 4 to 7  being inserted into the bone anchor. 
         FIG. 9  shows an enlarged sectional view of a second embodiment of the bone anchor with another plug member. 
         FIG. 10  shows an enlarged sectional view of a third embodiment of the bone anchor with a further plug member. 
         FIG. 11  shows an exploded view of a first embodiment of a tool for inserting the plug member into the bone anchor. 
         FIG. 12  shows a perspective view of the bone anchor with the tool of  FIG. 11  assembled with the plug member. 
         FIG. 13  shows a perspective view of the bone anchor with a second embodiment of a tool in a position of injecting bone cement. 
         FIG. 14  shows the bone anchor with the second embodiment of the tool in an exploded view. 
         FIG. 15  shows steps of using the bone anchor in minimally invasive surgery. 
         FIGS. 16 a   - to  16   c  show steps of using the bone anchor in minimally invasive surgery. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 to 8  show a first embodiment of a bone anchor according to the disclosure. A bone anchoring device  1  includes the bone anchor  2  for anchoring in the bone, a receiving part  3  for receiving a rod  4 , a pressure element  5  acting onto the bone anchor  2  and a securing element  6 . The bone anchoring device  1  according to the embodiment described is a polyaxial bone screw where the bone anchor  2  is held pivotably in the receiving part  3  which couples the bone anchor to the spinal rod  4 . The angular position of the bone anchor relative to the rod can be fixed with the securing element  6 . 
     As shown in particular in  FIG. 3 , the bone anchor  2  includes a shaft  7  with a head  8  at a first end and a free second end  9  which may be shaped as a tip. In the embodiment shown the head  8  has a shape of a spherical segment. Further, a bone thread  10  is provided on at least a portion of the outer surface of the shaft  7 . 
     The bone anchor  2  is cannulated. The bone anchor  2  includes a substantially coaxial bore  11  which extends from the first end through the head  8  and the shaft  7  up to the second end  9 . In a portion  12  adjacent to the second end  9  the diameter of the bore is smaller than in the main part of the shaft  7 , thereby producing a shoulder  13  inside the shaft  7 . At the free end of the head  8  an engagement structure  14  is provided for engagement with a tool. In the wall of the shaft  7  a plurality of openings  15  are provided which connect the bore  11  with the outside. The number, the size and the arrangement of the openings  15  is designed according to the overall dimension of the bone anchor  2  for the purpose of forming outlets for bone cement or pharmaceutical substances to be introduced into the bone anchor. 
     The diameter of the bore  11  and in particular of the portion  12  is designed such that a guide wire which is commonly used for minimally invasive surgery can be guided through the bone anchor  2 . 
     The receiving part  3  is, as shown in particular in  FIGS. 1 to 3 , substantially cylindrically shaped with a first end  3   a  and an opposite second end  3   b . The receiving part  3  includes a coaxial bore  16  extending from the first end in the direction to the second end and tapering towards the second end  16  so that the head  8  of the bone anchor is pivotably held in the receiving part  3 . Further, the receiving part has a substantially U-shaped recess  17  starting from the first end  3   a  and extending into the direction of the second end  3   b  by means of which two free legs  18   a ,  18   b  are formed. An internal thread  19  is provided at a portion of said free legs  18   a ,  18   b  for screwing in the securing element  6 . In the embodiment, the securing element  6  is an inner screw. 
     The pressure element  5  serves for exerting pressure onto the head  8  of the bone anchor when the inner screw  6  is tightened so that it presses onto the rod  4 . The pressure element  5  is designed such that it can be introduced into the coaxial bore  16  and moved therein in an axial direction. The pressure element  5  includes on its side facing the head  8  a substantially spherical recess  20  in order to distribute the pressure onto head  8  and on its opposite side a substantially cylindrical recess  21  for receiving the rod  4 . The pressure element  5  also includes a coaxial bore  22  for guiding a guide wire or a screw tool therethrough. 
     As shown in  FIGS. 4 to 8  the bone anchor further includes a plug member  30  for closing the bore  11  of the shaft  7  at the end portion  12  of the free second end  9 . The plug member  30  is a separate part which can be introduced into the bore  11 . In the embodiment shown in  FIGS. 4 to 8  the plug member  30  includes a first cylindrical portion  31  the diameter of which is such that it fits into the portion  12  of the shaft  7 . At the free end of the first cylindrical portion  31  a chamfered portion  32  may be provided for facilitating introduction of the plug member. Opposite to chamfered portion  32  the plug member includes a second cylindrical portion  33  the diameter of which is such that it fits to the inner diameter of the bore  11 . A transitional portion  34  between the first cylindrical portion  31  and the second cylindrical portion  33  is provided which can be shaped so as to match the shape of the shoulder  13  between the main portion of the bore  11  and the end portion  12  having the reduced diameter. Hence, the shoulder  13  forms a stop for the introduction of the plug member. 
     At the free end of the second cylindrical portion  33  a plurality of upstanding holding springs  35  are provided. The holding springs  35  are arranged in a circle with a diameter smaller than that of the second cylindrical portion  33  and have elasticity so as to be resiliently movable outwards and/or inwards. At their free ends, the holding springs  35  comprise catches  36 , respectively, for a detachable engagement with a tool described later. The holding springs  35  are arranged in such a manner that their outer portions of the catches  36  do not project outside the diameter of the second cylindrical portion  33 . 
     As shown in  FIG. 8 , when the plug member  30  is fully inserted into the bore  11  it closes the bore at the second portion  12  so that any bone cement or pharmaceutical substance which is introduced into bore  11  cannot escape through the second end  9 . 
     The material from which the bone anchor, the receiving part, the pressure element and the securing screw are made can be any material which is usual for these kind of devices, in particular, a body compatible metal, such as, for example, titanium or stainless steel or a metal alloy or any body compatible plastics, such as, for example, PEEK. The rod can be made of metal or plastics, depending on the application, i.e. whether the rod shall provide pure fixation or dynamic stabilisation. The material of the plug member can be the same as the material of the anchor or can be a different material. Suitable materials for the plug member are in particular titanium and titanium alloys, stainless steel used for implants and PEEK. 
     A second embodiment of the plug member is shown in  FIG. 9 . The plug member  40  is ball-shaped with a diameter of the ball which is larger than the inner diameter of the bore  11  in the second portion  12  and smaller than the inner diameter of the bore  11  in the main portion the shaft  7 . The ball-shaped plug member  40  is made advantageously of a material with a high specific weight, such as metal, so that the plug member  40  can be introduced and falls down by its own weight. 
       FIG. 10  shows a third embodiment of the bone anchor with a plug member  41  which differs from the plug member  30  only in that it does not have the holding springs  35  and that instead of the holding springs  35 , a recess  42  is provided in the second cylindrical portion which serves for engagement with a tool. All other portions are identical to the plug member  30 . 
     Although a polyaxial bone screw has been shown as a bone anchoring device including the bone anchor, any other bone anchor is encompassed by the disclosure. For example, a monoaxial bone screw wherein the head of the bone anchor  2  is shaped so as to receive the rod can be used. The bone anchor further does not need to have a bone thread provided on the shaft. It can also be designed as a push and turn anchor having barb elements for retention in the bone. The bone anchor also can be designed as a bone nail with smooth outer surface. 
     Other modifications of the plug member are also conceivable. For example, the plug member can be disk-shaped, cone-shaped or can have any other shape. 
     A first embodiment of a tool for inserting the plug member into the bone anchor is now described with reference to  FIGS. 11 and 12 . The tool  50  is particularly suitable for inserting the plug member of the type shown in  FIGS. 4 to 8 . The tool  50  includes a handle  51  for gripping and an insertion tube  52  extending through the handle  51 . The insertion tube  52  is hollow and has a length which is at least as long as the length of the shaft so as to be able to position the plug member  30  at the end of the bore  11 . The inner diameter of the tube  52  is such that the tube  52  can be placed onto the holdings  35  of the plug member so that the holding springs with the catches  36  are moved inwards to a certain extent. In this manner they are gripped at the end of the tube  52 . The insertion tube  52  may have at its end inside a recess cooperating with the catches  36 . The outer diameter of the tube  52  is slightly smaller than the inner diameter of the bore  11 , so that the insertion tube  52  can be introduced into bore  11 . The insertion tube  52  extends through the handle  51  so that the open end  53  of the tube  52  is substantially flush with the end portion of the handle  51 .  FIG. 11  shows the anchor  2 , the plug member  30  and the tool  50  in an exploded view. In the representation of  FIG. 12  the plug member  30  is gripped by the tool  50 . Since the tube  52  extends through the handle  51  it is possible to guide a guide wire through the open end  53  into the tube portion. 
       FIGS. 13 and 14  show two positions of a second embodiment of the tool with respect to the bone anchor. 
     The tool  60  according to this embodiment is formed by a syringe  60 . The syringe  60  is particularly suitable for injection of bone cement or pharmaceutical substances into the bone anchor  2 . The syringe  60  includes a barrel with a handle  61  for gripping and a plunger  62  for pushing the bone cement or the substance into a needle or tube  63 . The needle or tube  63  is designed so as to be able to grip the plug member  30  or to engage into the recess  42  of the plug member  41 . The needle or tube  63  is long enough so that the plug member can be placed at the end of the bore  11 . 
     Modifications of these tools are also conceivable. For example, the insertion tubes  52  or  63  can be flexible so as to be adaptable to non-straight channels in the bone anchor. Any other gripping mechanism with, for example, release function for gripping and releasing the plug member is possible. 
     Use of the bone anchor is now described with respect to  FIGS. 15 and 16 .  FIGS. 15 and 16  show the implantation of the bone anchor with minimally invasive surgery. In a first step, a guide wire  100  is placed percutaneously through the skin  101  to the final position of the bone anchor in a vertebra  102  of the vertebral column. The plug member is not inserted into the bone anchor as this stage of the procedure. Thereafter, the bone anchor  2  or, as shown in  FIG. 15 , the bone anchor preassembled with the receiving part  3  and the pressure element  5  is provided and the guide wire  100  is guided through the bone anchor and the receiving part  3  from the first end  9  of the bone anchor. Next, the bone anchoring device  1  is guided along the guide wire  100  to the vertebra  102  which is the final implantation site and is finally screwed into the pedicle. Thereafter, the guide wire is removed. 
       FIGS. 16 a  to 16 c    show the steps of introducing the plug member. As shown in  FIG. 16 a   , the tool  50  is used to introduce the plug member  30  into the bone anchor  2 .  FIG. 16   b  shows a side view and  FIG. 16 c    a sectional view of an enlarged portion of the anchor  2  with the plug member  30  inserted by the tube  52 . The plug member  30  is gripped by the tube  52  of the tool  50  and the tube  52  is introduced into the bone anchor. The plug member  30  is then detached from the tool by inserting the guide wire  100  (not shown) and pushing the guide wire  100  against the plug member so that the plug member finally rests on the shoulder  13  and closes the bone anchor. Thereafter, bone cement or a pharmaceutical substance is injected which exits through the openings  15  into the surrounding bone material. It cannot exit through the free end  9  of the bone anchor since the free end  9  is closed by the plug member. This results in a safe fixation, since there is no leakage of bone cement at the free end  9  which could loosen the anchor or damage vascular structures. 
     In case of the plug member  40  which is ball-shaped, the plug member  40  is only introduced into the upper portion of the bore  11  so that it falls down by its own weight and closes the free end  9 . 
     In an alternative manner the plug member  30  or  41  is gripped by the needle  63  of the syringe  60  containing the bone cement or the pharmaceutical substance and the plug member is injected through injection of the bone cement or the pharmaceutical substance into bore  11  until it closes the free end. 
     After at least two bone anchors are anchored, the rod  4  is inserted and fixed by means of the securing element. 
     While a particular form of the disclosure has been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, it is not intended that the disclosure be limited, except as by the appended claims.