Abstract:
A bone anchoring device for anchoring in a bone comprises a hollow shaft having an outer surface including a first portion and a threadless second portion, the second portion having a larger outer diameter and a shorter axial length than the first portion; and a barb carrier having at least two barb elements. The shaft and the barb carrier can be moved relative to each other in such a manner that in a first configuration the barb elements of the barb carrier project beyond an outer surface of the shaft by a distance d 1 , and in such a manner that in a second configuration the barb elements of the barb carrier project beyond the outer surface of the shaft along the second portion of the shaft by a distance of d 2 , wherein d 2 &gt;d 1 .

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/535,290, filed Sep. 15, 2011, the contents of which are hereby incorporated by reference in their entirety, and claims priority to European Patent Application EP 11 181 525.4, filed Sep. 15, 2011, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a bone anchoring device, in particular for application to the femur for anchoring in a bone. The bone anchoring devices includes a hollow shaft having an outer surface and a barb carrier having a plurality of barb elements. The shaft and the barb carrier can be moved relative to each other in such a manner that in a first configuration the barb elements of the barb carrier do not project beyond an outer surface of the shaft and in such a manner that in a second configuration the barb elements of the barb carrier project beyond the outer surface of the shaft. The moving direction of the barb carrier from the first to the second configuration is against the insertion direction of the bone anchoring device, wherein the bone anchoring device is threadless. The bone anchoring device may be applied, for example, to an osteoporotic femur. 
         [0003]    A known form of a bone anchoring device is a bone screw comprising a shaft with a thread for screwing a screw into a bone. The bone screw is manually inserted into the bone by means of a screw driver, which is a time-consuming and force-requiring process. Moreover, during the process in which the screw is inserted into the bone, high pressure forces may be acting on the bone itself, which is undesirable in certain clinical applications such as in neurosurgery, spinal surgery, pediatric surgery or trauma surgery. In particular, referring to osteoporosis, such high pressure forces acting on the surrounding bone structure are highly problematic. 
       DESCRIPTION OF RELATED ART 
       [0004]    US 2001/0000186 A1 discloses a surgical fastener assembly for coupling first and second bone portions across a fracture therebetween having a thread and a hollow portion with four openings for guiding four elongated pins hold by an insert which is movable within the hollow portion. These pins engage with the bone structure when the insert is axially pulled back by means of a tool. 
       SUMMARY 
       [0005]    It is an object of the invention to provide a bone anchoring device, which can be inserted into the bone more rapidly, more easily and with less force than conventional bone screws and nails and can also be removed easily from the bone. 
         [0006]    The bone anchoring device according to an embodiment of the invention facilitates rapid and secure anchoring in the bone by pressing the bone anchoring device into a prepared bore hole in the bone. During the insertion of the bone anchoring device, barb elements of an insert, which forms a barb carrier, extend into the openings of a hollow shaft of the bone anchoring device not farther than an outer surface of the shaft. After insertion of the bone anchoring device, the barb carrier and the shaft are moved relative to each other in such a manner that the barb elements of the barb carrier are spread and project through the openings of the hollow shaft beyond the outer surface of the shaft. Therefore, the barb elements prevent the bone anchoring device from being pulled out or coming loose. The bone anchoring device of the present invention can be easily removed, if required, by just moving again the hollow shaft and the barb carrier relative to each other in such a manner that the barb elements of the insert only extend into the openings maximally as far as the outer surface of the shaft, i.e. in this configuration the barb elements do not project beyond the outer surface of the shaft. In this configuration there is no barb effect, because the barb elements do not engage with the surrounding bone structure. 
         [0007]    The barb elements may be flexible and are made of any flexible material, for example of Nitinol. It is one advantage of Nitinol that a deformation of the barb elements made of this material is completely reversible. 
         [0008]    By this reversible barb connection, the threadless bone anchoring device does not exert damaging forces on the bone during insertion and provides for secure attachment. Therefore, the present invention is especially suitable for osteoporosis patients, because there is no damaging by a thread or a screw which directly acts on the surrounding bone structure. The barb elements penetrate the bone structure wherein this penetration is more gentle as for example an expanding or swinging-out of the barb elements which would destroy more surrounding bone structure. Furthermore, the implanting process of the bone anchoring device according to the present invention is very fast, since it is not necessary to screw it in but only to insert it. The bone anchoring device according to the invention is also easily to manufacture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Further features and advantages of the invention will become apparent and will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings. 
           [0010]      FIG. 1   a  shows a perspective view of a bone anchoring device in a first configuration according to a first embodiment which is attached to a bone plate. 
           [0011]      FIG. 1   b  shows a perspective view of the bone anchoring device in a second configuration according to the embodiment shown in  FIG. 1   a  which is attached to the bone plate. 
           [0012]      FIG. 2  shows a perspective view of the bone anchoring device in the first configuration according to the embodiment shown in  FIG. 1   a.    
           [0013]      FIG. 3  shows a perspective view of the bone anchoring device in the first configuration according to the embodiment shown in  FIG. 1   a  together with a connection screw. 
           [0014]      FIG. 4  shows a perspective exploded view of the bone anchoring device shown in  FIG. 3 . 
           [0015]      FIG. 5   a  shows a perspective view of an enlarged portion of the bone anchoring device shown in  FIG. 1   a.    
           [0016]      FIG. 5   b  shows a perspective view of an enlarged portion of the bone anchoring device shown in  FIG. 1   b.    
           [0017]      FIG. 6   a  shows a side view of the bone anchoring device in the first configuration according to the embodiment shown in  FIG. 1   a.    
           [0018]      FIG. 6   b  shows a cross-sectional view of the bone anchoring device in the first configuration according to the embodiment shown in  FIG. 1   a.    
           [0019]      FIG. 6   c  shows a side view of the bone anchoring device in the second configuration according to the embodiment shown in  FIG. 1   b.    
           [0020]      FIG. 6   d  shows a cross-sectional view of the bone anchoring device in the second configuration according to the embodiment shown in  FIG. 1   b.    
           [0021]      FIG. 7   a  shows a cross-sectional view of a front portion of the bone anchoring device in the first configuration according to the embodiment shown in  FIG. 1   a  inserted into a bone. 
           [0022]      FIG. 7   b  shows a cross-sectional view of a front portion of the bone anchoring device in the second configuration according to the embodiment shown in  FIG. 1   b  inserted into the bone. 
           [0023]      FIG. 8   a  shows a perspective view of a barb carrier in a manufacturing configuration according to a second embodiment. 
           [0024]      FIG. 8   b  shows a perspective view of the barb carrier in a first configuration according to the embodiment shown in  FIG. 8   a.    
           [0025]      FIG. 8   c  shows a perspective view of the barb carrier in a second configuration according to the embodiment shown in  FIG. 8   a.    
           [0026]      FIG. 9   a  shows a perspective view of an enlarged portion of a bone anchoring device in the first configuration according to the embodiment shown in  FIG. 8   b.    
           [0027]      FIG. 9   b  shows a perspective view of an enlarged portion of the bone anchoring device according to the second embodiment in the configuration shown in  FIG. 8   c.    
           [0028]      FIG. 10   a  shows a side view of the bone anchoring device in the first configuration according to the embodiment shown in  FIG. 8   b.    
           [0029]      FIG. 10   b  shows a cross-sectional view of the bone anchoring device in the first configuration according to the embodiment shown in  FIG. 8   b.    
           [0030]      FIG. 10   c  shows a side view of the bone anchoring device in the second configuration according to the embodiment shown in  FIG. 8   c.    
           [0031]      FIG. 10   d  shows a cross-sectional view of the bone anchoring device in the second configuration according to the embodiment shown in  FIG. 8   c.    
       
    
    
     DETAILED DESCRIPTION 
       [0032]    A bone anchoring device  1  according to a first embodiment of the invention is described with reference to  FIGS. 1 to 7   b . As can be seen from  FIGS. 1   a  and  1   b , the threadless bone anchoring device  1 , in particular a femur anchor  1 , can be connected to a bone plate  100  which comprises a plate-like body which is fixed to a bone by screws for example and a tube-like body which can accommodate a portion of the bone anchoring device  1 , wherein the plate-like body and the tube-like body may be connected integrally to each other in an angled manner as can be seen from  FIGS. 1   a  and  1   b.    
         [0033]      FIG. 2  shows the bone anchoring device  1  having a shaft which comprises a substantially cylindrical hollow shaft portion  2  and a substantially cylindrical hollow head portion  3 . The shaft portion  2  has a first end  23 , a second end  24  and at least one coaxial groove  21 , wherein the groove  21  extends from the first end  23  to a predetermined distance from the second end  24 . The groove  21  comprises a hole  22  at a distance to the second end  24  of the shaft  2  portion. The shaft portion  2  and the head portion  3  are formed integrally and the outer diameter of the head portion  3  is larger than the outer diameter of the shaft portion  2 . It is also possible to provide the shaft portion  2  and the head portion  3  as separate parts and/or to provide them with the same diameter. 
         [0034]    In  FIGS. 3 and 4  a locking screw  4  is shown by which the bone anchoring device  1  can be fixed to the bone plate  100  via an inner thread  25 , shown in  FIGS. 6   b ,  6   d . As can be seen in  FIG. 4 , the bone anchoring device  1  further comprises a sleeve  7  having a pin  71  which is configured to cooperate with the hole  22  of the groove  21  of the shaft  2  portion. The pin  71  can be a snap fastener, for example, which can be pushed inside the sleeve  7  against a spring force, for example (not shown). The sleeve  7  fits into the hollow shaft  2  portion, i.e. the outer diameter of the sleeve  7  is the same or slightly smaller than the inner diameter of the hollow shaft portion  2 , which can be seen, for example, in  FIGS. 6   b  and  6   d . The pin  71  fits into the hole  22  of the groove  21  of the shaft portion  2  and can snap into or engage with the hole  22  from the inside of the shaft portion  2 . By this, the sleeve  7  works as a stop for a head of a screw  6  which is also insertable into the hollow shaft portion  2 . By the sleeve  7 , the screw  6  is prevented from moving towards the first end  23  of the shaft portion  2 . For preventing the screw  6  from moving in the direction of the second end  24 , an abutment portion  26 , shown in  FIGS. 6   b ,  6   d , is provided integrally with the shaft portion  2  which forms an abutment for the head of the screw  6 . Because of this abutment, the screw  6  can only be inserted into the shaft portion  2  from the first end  23 . 
         [0035]    Furthermore, a barb carrier  5  in the form of an insert is provided having a first end  55 , a second end  56 , a shaft member  53 , a head member  51  and a plurality of barb elements  52  which are connected to the shaft member  53 . The head member  51  of the barb carrier  5  comprises a cylindrical portion and a cone-shaped portion which forms a tip. 
         [0036]    As can be seen from  FIG. 5   a , the head portion  3  comprises an outer surface  31  that has a plurality of circumferential grooves  33 . In  FIG. 5   a  three grooves  33  are shown. The grooves  33  have a circle-segment-shaped cross-section. On the ground of each groove  33  openings  32  are provided which are circumferentially distributed with the same distance to one another and extend through the wall of the hollow head portion  3  for guiding the barb elements  52  in operation. In.  FIG. 5   a , four openings  32  are shown in each groove  33 . That means that the openings  32  are positioned in a 90° angular orientation to each other. It is also possible to provide more or fewer grooves  33 , more or fewer openings  32  or to arrange the openings  32  in different ways referring to their angular orientation. As can be seen from  FIGS. 5   a ,  5   b  the head  51  of the barb carrier  5  forms a tip of the bone anchoring device  1 . 
         [0037]    As can be seen from  FIGS. 6   a  and  6   b , the bone anchoring device  1  in a first configuration is shown. The bone anchoring device  1  comprises an inner thread  25  on its first end  23  which can cooperate with the locking screw  4  shown in  FIG. 4  to fix the bone anchoring device  1 , for example to the bone plate  100 . The sleeve  7  is provided within the hollow shaft portion  2  and forms a stop for the screw  6  having an engagement structure  63  for engaging with a tool (not shown) for rotating the screw  6 . The barb carrier  5  is provided partly within the head portion  3  and partly within the shaft portion  2 . Adjacent to the first end  55  of the barb carrier  5 , the shaft member  53  has a threaded hole with an inner thread  54  for engaging an outer thread of the screw  6 . 
         [0038]    In the first configuration the cone-shaped portion of the head  51  of the barb carrier  5  is flush with the outer circular edge of the head portion  3 . By this, the cone-shaped portion of the head  51  forms the tip for the bone anchoring device  1  in this first configuration. Referring to the relative position of the shaft portion  2  and the barb carrier  5 , there is a first distance between the abutment portion  26  and the first end  55  of the barb carrier  5 . Furthermore, the barb elements  52  which are connected to the shaft element  53  of the barb carrier  5  extend into the openings  32  of the head portion  3  not farther than an outer surface  31  of the head portion  3 . In this first configuration the barb elements  52  do not project over the outer surface  31  of the head portion  3 . Therefore, in the first configuration the bone anchoring device  1  can be easily introduced into a hole which was drilled into a bone, which can be seen from  FIG. 7   a.    
         [0039]    In a second configuration shown in  FIGS. 6   c  and  6   d  the barb carrier  5  is positioned closer to the screw  6  and the sleeve  7  as compared to the first configuration shown in  FIGS. 6   a  and  6   b . Further referring to the relative position of the shaft portion  2  and the barb carrier  5 , there is a second distance between the abutment portion  26  and the first end  55  of the barb carrier  5 , wherein the first distance in the first configuration is larger than the second distance in the second configuration. It is possible that the second distance is nearly zero. In this configuration the barb elements  52  of the insert  5  are bent and project through the openings  32  beyond the outer surface  31  of the head portion  3 . In this configuration, the bone anchoring device  1  is fixed in the bone, as can be seen from  FIG. 7   b . This fixing is reversible. For preventing the barb elements  52  from overloading or shearing, the relative position of the of the shaft portion  2  and the barb carrier  5  to one another, in the second configuration the movement and therefore the deformation of the barb elements  52  is limited by dimensioning the drilling depth of the inner thread  54  such that the screw  6  is completely screwed in with obtaining the second configuration. Between the first and the second configuration, many intermediate configurations exist because of the stepless movement of the barb carrier  5  relative to the shaft  2 . 
         [0040]    As can be seen in particular from  FIGS. 6   b  and  6   d , the barb elements  52  project from the surface of the shaft member  53  of the barb carrier  5  by an angle which is selected during the manufacturing process based upon the material used and the actual dimensions of the barb elements  52  so that a desired stiffness of the barb elements  52  is obtained. The barb elements  52  are attached to the shaft member  53  of the barb carrier  5  by drilling in bore holes into which the barb elements, which can be designed as short pins having a substantially circular cross-section, be inserted by means of a press fit connection. It is also possible to attach the barb elements  52  in different ways to the barb carrier  5 , for example by adhesive bonding. Due to their configuration and attachment, the barb elements  52  are elastically deformable relative to the barb carrier  5  and also relative to the openings  32  of the head portion  3  by which they are guided. The barb elements  52  are arranged in an arrow-like, pinfeather-like or fir tree-like configuration, wherein the “arrows” are directed towards the tip  51 . 
         [0041]    The bone anchoring device  1  can be made of any body-compatible material. Preferably, a body-compatible metal, such as titanium, stainless steel and their alloys, or a body-compatible plastic material can be used. The shaft portion  2  and the head portion  3  can be made of the same material as the barb carrier  5  or of a different material, if a different material is desired to ensure that the barb elements  52  have the necessary elastic properties. Preferably, however, the barb carrier  5  and/or the barb elements  52  are made of a shape-memory alloy having shape-memory and/or super elastic characteristics or are made of a material having spring-like characteristics like stainless steel or titanium alloys. For example, nickel-titanium alloys such as Nitinol are suitable for use for the barb elements  52 . 
         [0042]    The bone anchoring device is assembled as follows. First, the screw  6  is inserted into the shaft portion  2  from the first end  23  (in  FIGS. 6   a - d  from above). The abutment portion  26  holds the screw  6  in its position. After that the sleeve  7  is inserted into the shaft portion  2  from the first end  23  and the pin  71  snaps into or engages with the hole  22 . By this the screw head is now axially fixed between the sleeve  7  and the abutment portion  26  and can only rotate by this guiding structure. Then, the barb carrier  5  is inserted into the head portion  3  from the head portion  3  (in  FIG. 6   a -d from the bottom) in such a manner that the barb elements  52  extend into the openings  32 , but do not project beyond the outer surface  31 . The screw  6  is screwed into the inner thread  54  of the barb carrier  5  by means of a tool (not shown) which is inserted from the first end  23  of the shaft portion  2  through the sleeve  7  into the engagement structure  63  of the screw  6 . 
         [0043]    In use, the bone anchoring device  1  is inserted into a drilled bore hole provided in a bone. Then the screw  6  is rotated by means of the tool (not shown) which moves the barb carrier  5  in the direction of the first end  23  of the shaft portion  2  by the screw and nut connection. By this the barb elements  52  start to move further through the openings  32  of the head  3  and project beyond the surface  31  of the head portion  3 . By this, the bone anchoring device  1  is fixed in the bone. Because of their flexibility and because of the shape of the openings  32 , the barb elements  52  bend in a direction perpendicular to the longitudinal axis of the bone anchoring device. By this bending the barb elements  52  penetrate the surrounding bone structure. The barb elements  52  expand in the created channel which results in a minimal damaging of the surrounding bone structure. It is possible to provide barb elements  52  with sharpened tips. 
         [0044]    In  FIGS. 8   a  to  10   d  a second embodiment of the bone anchoring device is shown. The function of the system and the device as such is the same as described under the first embodiment of the invention; only the construction of the barb carrier is different. 
         [0045]    In  FIGS. 8   a  to  8   c  a barb carrier  5 ′ according to the second embodiment is shown comprising a substantially cylindrical hollow sleeve-like main body having barb elements  52 ′. The barb elements  52 ′ having a substantially rectangular cross-section are cut out of the wall of the cylindrical body, for example by laser cutting. Preferably, the barb carrier  5 ′ is made of a shape memory material, for example of Nitinol. In  FIG. 8   a  the barb carrier  5 ′ is shown in its manufacturing configuration where the barb elements  52 ′ are not spread but are flush with the rest of the surface of the cylindrical body of the barb carrier  5 ′. In  FIG. 8   b  the barb carrier  5 ′ is shown in a first configuration where the barb elements  52 ′ are spread partly. In  FIG. 8   c  the barb carrier  5 ′ is shown in its second configuration where the barb elements  52 ′ are spread completely. 
         [0046]      FIGS. 9   a  and  9   b  correspond to  FIGS. 5   a  and  5   b  showing the bone anchoring device  1 ′ comprising a shaft portion  2 ′ having a groove  21 ′ and a head portion  3 ′ having a plurality of grooves  32 ′ and an outer surface  31 ′ and a tip  51 ′. 
         [0047]    As can be seen from  FIGS. 10   a  and  10   b  the barb carrier  5 ′ is clamped between the tip  51 ′ and a shaft member  53 ′ having a first end  55 ′ and a second end  56 ′. The tip  51 ′ comprises an inner thread  511  and the second end  56 ′ of the shaft member  53 ′ forms an outer thread, which is configured to engage the inner thread  511  of the tip  51 ′ to clamp the barb carrier  5 ′. The wall of the barb carrier  5 ′ is supported by a circumferential portion of the shaft member  53 ′ and a circumferential portion of the tip  51 ′, wherein the outer diameters of the supporting circumferential surfaces and the outer diameter of the barb carrier  5 ′ are substantially the same such as the whole construction is insertable into the head portion  3 ′ of the bone anchoring element  1 ′. 
         [0048]    The movement of the shaft portion  2 ′ and the head portion  3 ′ relative to the barb carrier  5 ′ takes place as in the first embodiment. The shaft member  53 ′ comprises an inner thread  54 ′ on its first end  55 ′ which cooperates with a screw  6 ′. The screw  6 ′ is fixed between an abutment portion  26 ′ and a sleeve  7 ′ and can only perform a rotational movement for moving the barb carrier  5 ′ relative to the shaft portion  2 ′ and the head portion  3 ′ as in the first embodiment. 
         [0049]      FIGS. 10   a  and  10   b  show the bone anchoring device  1 ′ in the first configuration which is the same as the first configuration described referring to the first embodiment and  FIGS. 10   c  and  10   d  show the bone anchoring device  1 ′ in the second configuration which is the same as the second configuration described referring to the first embodiment. 
         [0050]    The bone anchoring device according to the invention and in particular the femur anchor can be used together with a bone plate as shown in  FIGS. 1   a  and  1   b , especially for use in osteoporotic bones. Also all further applications are conceivable in which the bone anchoring device can be used instead of conventional bone screws or instead of conventional pins used in a bone anchoring manner. It is also possible to provide rigid barb elements. In such a case the openings should be configured as long holes or recesses for guiding the barb elements. 
         [0051]    Furthermore instead of the sleeve for supporting the screw together with the abutment portion other elements could be used which support the screw and allow the passing of the tool and the engagement with the engagement structure of the screw. For example, a snap ring could be. used.