Patent Publication Number: US-2015088209-A1

Title: Bone anchoring element

Description:
RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 13/617,923, filed Sep. 14, 2012, which is a continuation of U.S. patent application Ser. No. 11/482,374, filed Jul. 7, 2006, now U.S. Pat. No. 8,292,932, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60/697,669, filed Jul. 8, 2005, and claims priority from European Patent Application EP05014839, filed Jul. 8, 2005, the entire disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     The present disclosure relates to a bone anchoring element. A known form of a bone anchoring element is a bone screw having a shaft with a thread for screwing the 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 e.g., in neuro surgery, spinal surgery, pediatric surgery or trauma surgery. 
     EP 0 714 643 A1 discloses a bone fixation device such as a screw or a pin which has a micro-textured contact surface to enhance the installation or gripping characteristics of the device. The micro-textured contact surface includes e.g. angled rasp teeth, which bite or flex to resist movement in one direction and yet flex or slide to allow a relatively easy contact movement in the other direction. 
     DE 198 01 219 A1 discloses a bone nail having rigid barb-like projections being arranged in circumferential rows around the nail. The barb-like projection has a saw-tooth shape which facilitates insertion of the nail as well as prevents loosening of the nail. However, a removal of the nail without destroying the bone is not possible. 
     CH 682450 A5 discloses an anchoring nail for the fixation of orthopedic bone implants. The nail consists of a head part and a shaft part, the shaft having retention elements provided on its outer wall which are arranged along a helical line. The retention elements are wedge-shaped and are provided with cutting edges which allow to screw out and remove the nail from the bone material. However, the core hole which has to be drilled in advance to allow an easy insertion of the nail into the bone and a removal of the nail has to have a precise diameter. In addition, the wedge-shape of the retention elements per se does not allow an easy insertion. 
     In view of the above, there is a need for a bone anchoring element that can remedy one or more of the above described problems associated with current bone anchoring elements. 
     SUMMARY 
     A bone anchoring element according to one or more embodiments of the present disclosure can be inserted into the bone more rapidly, more easily and with less force than conventional bone screws and nails. The bone anchoring element according to one or more embodiments of the present disclosure is versatile and useful in many clinical requirements and is easy to manufacture. The bone anchoring element according to one or more embodiments of the present disclosure does not exert damaging forces on the bone during insertion, provides for secure attachment, and then can be further inserted or can be removed in a screw-like fashion. A method for manufacturing such a bone anchoring element is also disclosed. 
     The bone anchoring element according to one or more embodiments of the present disclosure facilitates rapid and secure anchoring to the bone by pressing the bone anchoring element into a prepared core hole in the bone. The barb elements are arranged on at least on one helical line around the shaft axis of a tubular body part of the shaft of the bone anchoring element. The barb elements provide for a thread-like function, which allows to correct the position of the bone anchoring element in the core hole after inserting it into the core hole, by either positioning it deeper into the bone by means of a screwing-inwards motion or by screwing it backward. The barb elements prevent the bone anchoring element from being pulled out or coming loose. The bone anchoring element can be removed, if required, like a screw by turning it in the opposite or counter-clockwise direction from which it was inserted. 
     The bone anchoring element according to one or more embodiments of the present disclosure is easy to manufacture. If the tubular body of the shaft is made of a shape memory alloy, the shape memory effect can be used in such a way that the barb elements do not project during insertion of the bone anchoring element into the bone and rise up when the bone anchoring element is inserted due to the action of the body heat. The tubular body can also be made of a material having super elastic properties or a spring like behavior. For example a titanium alloy having super elasticity or stainless steel can be used. 
     Further features and advantages of the disclosed embodiments will become apparent and will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective exploded view of a bone anchoring element according to a first embodiment. 
         FIG. 2  shows an enlarged part of a cross-sectional view through the wall of the tubular body of the bone anchoring element of  FIG. 1  in a longitudinal direction. 
         FIG. 3  shows a side view of the bone anchoring element according to  FIG. 1  in an assembled state. 
         FIG. 4  shows an enlarged cross-sectional view of the bone anchoring element according to  FIG. 3  along the line A-A. 
         FIG. 5  shows a schematic view of a first step of the insertion of the bone anchoring element according to  FIGS. 1 to 4 . 
         FIG. 6  shows a schematic view of the inserted state of the bone anchoring element according to  FIG. 5 . 
         FIG. 7  shows a perspective view of a second embodiment of the bone anchoring element. 
         FIG. 8  shows a third embodiment of the bone anchoring element. 
         FIG. 9  shows an exploded view of a fourth embodiment of the bone anchoring element. 
     
    
    
     DETAILED DESCRIPTION 
     A bone anchoring element  1  according to a first embodiment of the disclosure is described with reference to  FIGS. 1 to 4 . The bone anchoring element  1  comprises a shaft  2  with a tip  3  at one end and a head  4  at the other end. The head  4  is spherical segment-shaped and has on its free end a recess  5  for engagement with a screwing-in tool. Between the head  4  and the shaft  2  is a neck portion  6  with a circumferentially projecting shoulder  7  at the side opposite to the spherical head  4 . The shoulder  7  has an outer diameter which is larger than the neck portion  6  and slightly smaller than the diameter of the head  4 . Adjacent to the shoulder  7 , a cylindrical first shaft part  8  is provided. The diameter of the cylindrical first shaft part  8  is smaller than the diameter of the shoulder  7 . At the edge of the shoulder  7 , facing the shaft part  8 , a plurality of U-shaped recesses  9  are provided equidistantly in a circumferential direction which are open towards the side of the cylindrical shaft part  8 . 
     The shaft  2  further consists of a tubular body  10  which has an inner diameter slightly larger than the outer diameter of the cylindrical shaft part  8  so that the tubular body  10  can be placed in a sliding motion onto the cylindrical shaft part  8 . The outer diameter of the tubular body  10  corresponds to the outer diameter of the shoulder  7  so that when the tubular body  10  is placed onto the cylindrical shaft part  8 , the outer surface of the tubular body  10  is flush with the outer surface of the shoulder  7 . On its end facing the head  4 , the tubular body  10  has projections  11  which correspond in their shape and arrangement to the U-shaped recesses  9  provided at the shoulder  7  for engagement when the tubular body  10  is fully placed onto the cylindrical shaft part  8 . In this assembled state, the end of the tubular body  10  abuts the free end of the shoulder  7 . 
     The tubular body  10  comprises a plurality of barb elements  12 . The barb elements  12  are formed by substantially parallelogram-shaped cuts  10   a  being made in the wall of the tubular body  10 . The end base  13  of the parallelogram-shaped cuts  10   a  is not cutout from the tubular body and acts as the attachment and the bending side for the barb elements  12  in the wall of the tubular body  10 . The barb elements  12  are preferably arranged such that when the tubular body  10  is slid onto the cylindrical shaft part  8 , the end base  13  of each barb elements  12  faces the tip  3  while the free end faces the head  4 . As can be seen particularly in  FIG. 3 , the barb elements  12  are arranged on a helical line S around the shaft axis M. The free ends  14  of the barb elements  12  are inclined by an angle α with regard to the circular circumference line U, with the angle α corresponding to the helical angle of the helical line S. Thus, the free ends  14  of the barb element form cutting edges similar to the crest of a screw thread. 
     As can be seen in particular from  FIG. 2 , the barb elements  12  project from the surface of the tubular body  10  by an angle γ, which is selected during the manufacturing process based upon the material used and the actual dimensions of the barb elements  12  so that a desired stiffness of the barb elements  12  is obtained. Due to their configuration and attachment onto the wall of the tubular body  10 , the barb elements  12  are elastically deformable relative to the tubular body  10 . When the barb elements  12  are collapsed or pressed into the cuts, they are pre-tensioned. 
     The axial length of the tubular body  10  corresponds to the length of the cylindrical shaft part  8  so that in an assembled state a free end of the cylindrical shaft part  8  is flush with the free end of the tubular body  10 . The cylindrical shaft part  8  has a cylindrical recess (not shown) at its free end to receive a correspondingly shaped cylindrical projection  15  provided at the tip  3  in a press-fit manner. The outer diameter of the base of the tip  3  corresponds to the outer diameter of the tubular body  10  so that in an assembled state, as shown in  FIG. 3 , the base of the tip  3  is flush with the outer wall of the tubular body  10 . 
     The bone anchoring element  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 tubular body  10  having the barb elements  12  can be made of the same material as the cylindrical shaft part  8 , the head  4  and the tip  3 , or of a different material if a different material is desired to ensure that the barb elements  12  have the necessary elastic properties. 
     Preferably, however, the tubular body  10  with the barb elements  12  can be made of a shape memory alloy having shape memory and/or super elastic characteristics, or can be 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 tubular body  10 . 
     In operation, the bone anchoring element  1  is initially preassembled by sliding the tubular body  10  onto the cylindrical shaft part  8  such that the projections  11  come into engagement with the recesses  9 . Thus, a rotation of the tubular body  10  on the cylindrical shaft part  8  is prevented. Thereafter, the tip  3  is firmly connected with the cylindrical shaft part  8 . 
     In use, as is shown schematically in  FIGS. 5 and 6 , first a core hole  16  is prepared in the bone  17 . The diameter of the core hole  16  corresponds essentially to the outer diameter of the tubular body  10  or it can be slightly larger or smaller, depending upon the desired result or circumstances. The diameter of the core hole  16  is selected depending on the diameter of the tubular body  10  and the flexibility of the barb elements  12  so that the desired resistance is provided by the barb elements  12 . The selected diameter depends also upon the bone quality, for example, it can be selected larger for healthy hard bone and smaller for osteoporotic weak bone. Subsequently, as shown in  FIG. 5 , the bone anchoring element  1  is inserted into the core hole  16 . As the bone anchoring element  1  is being inserted into the core hole  16  of the bone  17 , the barb elements  12  are in a collapsed state and are pressed against or into the cuts due to their elasticity. The sliding motion enables the bone anchoring element  1  to be inserted rapidly and in a smooth way, in contrast to the conventional bone screws using the screwing-in-process. When inserted, the pre-tensioned barb elements  12  expand and rise up and press with their cutting edge  14  outwardly against the wall of the core hole  16 , as is shown in  FIG. 6 . The barb elements  12  prevent the bone anchoring element  1  from being pulled out or from falling out of the core hole  16 . 
     For further and/or final positioning of the bone anchoring element  1  in the core hole  16 , or for positioning of the head  4 , the bone anchoring element  1  is screwed further into the core hole  16  or screwed out therefrom, like a screw, by means of a turning motion with the screwing-in tool engaging the recess  5  of the head  4 . During the final positioning process, the cutting edges  14  of the barb elements  12 , being positioned on the helical line S, act like the crest of a thread. The bone anchoring element  1  can be removed just like a bone screw by turning it in a counter-clockwise direction. 
     In most cases, a conventional bone screw requires not only that the core hole  16  is drilled into the bone, but also that the bone threads are pre-cut into the bone. In all cases, with the insertion of a conventional bone screw, a repeated turning motion is required. Compared to the time required to anchor a conventional bone screw, the time required to insert the bone anchoring element  1  may be substantially shorter due to the fact that the bone anchoring element  1  slides or glides into the core hole  16  without having to encounter the forces of the screw thread on the core hole  16  and the bone  17 . Nonetheless, because of its design and configuration, the bone anchoring element  1  does not fall out of the core hole  16 . Also, when a conventional bone screw is inserted, it cuts with the thread crest in the bone material. 
     A process for manufacturing the bone anchoring element  1  may include providing a cylinder having a diameter corresponding to that of the tubular body  10 , the cylinder being made of a material which is desired for the tubular body  10 , preferably a shape memory alloy or another metallic material or an alloy with flexible properties. In a next step, a coaxial bore is provided in the cylinder such that a tubular body  10  is prepared. Thereafter, the barb elements  12  are generated by means of cutting, for example laser cutting, parallelogram-shaped cuts in the wall of the tubular body  10  in which one side which shall be the base of the barb elements  12  is not cut out. Thereafter the barb elements  12  are bent such that they project to the outside. 
     Modifications of the first embodiment are possible. The head  4  needs not to be spherical segment-shaped but can have another shape, in particular it can have any shape of known screw heads. The recesses  9  and the corresponding projections  11  need not to be U-shaped but can have a different shape. At least one recess  9  and a corresponding projection  11  is necessary to provide securing against rotation. However, it is also possible to prevent rotation by different means. For example, a pin (not shown) which can be inserted into a transverse bore (not shown) provided in the tubular body  10  and the cylindrical shaft part  8  can be used. 
     The barb elements  12  need not have only a parallelogram-shape, but can have another shape, as long as the cutting edges  14  lie on at least one helical line. For example, the barb elements  12  can have a trapezoidal shape. The pitch of the helical line may vary along the length of the tubular body  10 . The barb elements  12  need not to be provided over the whole length of the tubular body  10  but can be provided also only in a section of the tubular body  10 . The distance between the barb elements  12  may also vary. 
     In yet another embodiment of the disclosure, if the tubular body  10  including the barb elements  12  is made from a shape memory alloy, the tubular body  10  is treated before assembly of the bone anchoring element  1  in such a way so that the barb elements  12  project at a body temperature or at an elevated temperature and are in a collapsed position at a lower temperature, e.g. at room temperature. In operation, the bone anchoring element  1  with collapsed barb elements  12  is pressed into the core hole  16 . After the bone anchoring element  1  warms up and equilibrates to the body temperature or is heated through an external device, the barb elements  12  expand to their final position. This provides the advantage that it reduces the amount of force that is required to press the bone anchoring element  1  into the core hole  16  and enables the adjustment of the bone anchoring element  1  to a desired depth by the sliding motion during its insertion as long as the barb elements  12  are in a collapsed state and do not press against the wall of the core hole  16 . If the tubular body  10  has super elasticity in addition to shape memory characteristics, the higher elasticity of the barb elements  12  simplifies the handling and provides additional security in anchoring the bone anchoring element  1  in the bone. 
     In the second embodiment shown in  FIG. 7 , those parts which correspond to the parts of the first embodiment are characterized with the same reference numerals. The bone anchoring element  1  of the second embodiment differs from the bone anchoring element according to the first embodiment in that the tubular body  100  comprises two sections. A first section  101  with barb elements  102  having a first distance from each other in a circumferential direction and having substantially parallelogram-shape, and a second section  103  having barb elements  104  which have a second distance from each other in the circumferential direction which is larger than the first distance of the barb elements  102  in the first section  101 . Hence, the barb elements  104  in section  103  are less densely arranged than the barb elements  102  in section  101 . The barb elements  104  are substantially V-shaped. The bone anchoring element  1  is particularly suitable for application in the spinal column, in particular for anchoring in the vertebra. The second section  103  with the larger distance between the barb elements  104  is provided adjacent to the tip  3  and comes into engagement with the vertebral body. The first section  101  is adjacent to the head and comes into engagement with the pedicle. Thus, due to the larger distance between the barb elements  104  in the vertebral body, any potential damage of the vertebral body can be minimized while providing higher locking forces of the barbs  102  in the pedicle area. 
     In the embodiment shown in  FIG. 7 , the tubular body  100  is made of one single tube. However, the tubular body  100  with sections  101 ,  103  having different characteristics of the barb elements  102 ,  104 , respectively, can be made of two separate tubular bodies. In such a case, it is necessary to prevent rotation between the two tubular bodies. This can be realized, for example, by providing recesses (not shown) at the end of the first tubular body in which projections of the second tubular body engage. 
     Modifications are possible, for example, more than two sections with different characteristics of the barb elements can be provided. 
       FIG. 8  shows a third embodiment of the disclosure. The shaft of the bone anchoring element  1  is not composed of the cylindrical shaft part  8  and the tubular body  10 , but includes a tubular body  200  only. Thus, the shaft is hollow. At its end facing the tip  3 , the tubular body  200  comprises a section with an inner thread  201  which cooperates with an outer thread  202  on the cylindrical projection of the tip  3 . Alternatively, the tip  3  can also be connected in a press-fit manner to the tubular body  200 . The tubular body  200  comprises the barb elements  12  as in the previous embodiments. Different sections with different shapes and/or distances of barb elements  12  can be provided as in the embodiment shown in  FIG. 7 . Also, the pitch of the helical line S can vary along the length of the tubular body  200 . The head  4  is either formed integrally with the tubular body  200  or comprises a projection with an outer thread which can be screwed into the other end of the tubular body  200  which has a corresponding inner thread. Alternatively, the head  4  can be connected in a press-fit manner to the tubular body  200 . The bone anchoring element according to the third embodiment is particularly simple to manufacture. 
       FIG. 9  shows an exploded view of a fourth embodiment of the disclosure. The bone anchoring element  300  according to  FIG. 9  comprises a tip  303 , a tubular body  310  and a shaft  302  provided with a head  4  at one end. The fourth embodiment differs from the above described first embodiment in that barb elements  312  are provided instead of the barb elements  12  of the first embodiment. Further, the fourth embodiment differs from the first embodiment in the structures for connecting the tip  303 , the shaft  302  and the tubular body  310 . 
     First, the barb elements  312  will be described with reference to  FIG. 9 . As can be seen in  FIG. 9 , in top view the barb elements  312  have the contour of an irregular quadrangle which is twisted so that it has a curvature. The free ends  314  of the barb elements  312  lie substantially on a helical line. The width of the free ends  314  of the barb elements  312  is larger than the width of the end base  313  of the barb elements  312 . As a result, the width of the free ends  314  is enlarged as compared to first embodiment which provides a stable construction and an enlarged contact surface of the free ends  314  with the bone into which the bone anchoring element is to be inserted. The free ends  314  of the barb elements form a helical line around the axis of the shaft  302  with the pitch of the helical line enlarged as compared to the first embodiment. The large pitch of the helical line allows fast adjustment of the position of the bone anchoring element in the bone by further screwing-in into the bone or unscrewing from the bone, respectively. 
     As can be seen in  FIG. 9 , a first connecting structure  320  is provided on the projection  315  of tip  303 . This first connecting structure  320  serves to cooperate with the inner bore of the tubular body  310  for establishing a fixation between the tip  303  and the tubular body  310 . Further, a second connecting structure  321  is provided on the shaft  302  on the side directed towards the tip  303 . This second connecting structure  321  cooperates with a corresponding connecting structure (not shown) provided in a concentric inner bore which is provided in the projection  315  of the tip  303  on the side directed towards the shaft  302  and serves to establish a fixation between the tip  303  and the shaft  302 . Furthermore, a third connecting structure  322  is provided on the outer circumference of the shaft  302  on the side of the head  4 . This third connecting structure  322  cooperates with the inner bore of the tubular body  310  on the side directed towards the head  4  in order to establish a fixation between the shaft  302  and the tubular body  310  on the side of the head  4 . 
     In the embodiment shown, the first connecting structure  320  is provided by forming a part of the projection  315  with a substantially square cross-section with rounded edges. When fitted into the inner bore of the tubular body  320 , this shape leads to a distortion-fit connection. The second connecting structure  321  is provided by forming an end of the shaft  302  with a substantially square cross-section with rounded edges. The corresponding connecting structure in the inner bore of the projection  315  is formed by a recess with a substantially square cross-section with rounded edges into which the second connecting structure  321  can be fitted such that positive locking as well as press-fit is achieved. Similar to the first connecting structure  320 , the third connecting structure  322  is provided by forming a part of the shaft  302  on the side of the head  4  with a substantially square outer cross-section with rounded edges so that a distortion-fit connection to the tubular body can be achieved. 
     In the embodiment, the fixation of the tip  303  and the tubular body  310  is achieved by distortion locking, the fixation of the tubular body  310  and the shaft  302  on the side of the head  4  is achieved by distortion locking, and the fixation of the tip  303  and the shaft  302  is achieved by positive locking and frictional locking. 
     By providing the first connecting structure  320 , the second connecting structure  321  and the third connecting structure  322  three sections for transmitting torsional forces are provided in the fourth embodiment. This results in improved properties during insertion into the bone and removal from the bone. 
     The shape of the first, the second and the third connecting structures is not limited to a square shape with rounded edges. For example, hexagonal shapes, octagonal shapes etc. with or without rounded edges are possible as well. 
     In all embodiments described above the diameter of the tubular body can vary over the axial length of the tubular body, for example it can decrease towards the tip so that the tubular body has a conical outer surface. 
     The bone anchoring element  1  can be used together with a plate to establish a bone fixing device or with a receiver part to be connected with a rod to establish a spinal fixation system. Also, all further applications are conceivable in which the bone anchoring element  1  can be used instead of conventional bone screws or instead of conventional pins used in a bone anchoring manner. 
     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.