Abstract:
A polyaxial bone anchoring device is provided comprising a bone anchoring element ( 1 ) having a shank ( 2 ) to be anchored in the bone and a head ( 3 ); a receiving part ( 5 ) coupled to the shank and configured to pivotably receive the head, and having a channel ( 56 ) for receiving a rod ( 6 ) and a central axis (C); a pressure member ( 7, 7′ ) arranged in the receiving part and configured to exert pressure onto the head to lock the head in the receiving part; a locking member ( 8, 8′ ) that is insertable into the channel, the locking member comprising a top end ( 81 ) and a bottom ( 82 ) end facing the pressure member; wherein the pressure member ( 7, 7′ ) has a deformable portion ( 77, 78; 76′, 107   a,    107   b ); and wherein, when the locking member ( 8, 8′ ) is advanced into the channel in the direction of the central axis (C), first the locking member ( 8, 8′ ) contacts the pressure member ( 7, 7′ ) resulting in a load applied to the pressure member that clamps the head ( 3 ), and thereafter the locking member ( 8, 8′ ) contacts the pressure member ( 7, 7′ ) such that the deformable portion ( 77, 78; 76′, 107   a,    107   b ) is deformed and the locking member comes into contact with the rod and clamps the rod ( 6 ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure claims the benefit of U.S. Provisional Patent Application Ser. No. 61/658,120, filed Jun. 11, 2012, the contents of which are hereby incorporated by reference in their entirety, and claims priority from European Patent Application EP 12171525.4, filed Jun. 11, 2012, the contents of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    The invention relates to a polyaxial bone anchoring device, in particular for use in spinal or trauma surgery. The polyaxial bone anchoring device comprises a bone anchoring element with a shank to be anchored in the bone and a head. The head is pivotably held in a receiving part and can be fixed at an angle by applying pressure onto it via a pressure member. With the receiving part, the bone anchoring element can be coupled to a stabilization rod that is placed into a channel of the receiving part and that can be secured by a locking member. The pressure member comprises a deformable portion. When the locking member is advanced into the channel, first, the locking member contacts the pressure member resulting in a load applied to the pressure member that clamps the head and thereafter the locking member contacts the pressure member such that the deformable portion is deformed and the locking member comes into contact with the rod and clamps the rod. With such a locking member the head and the rod can be fixed in a sequential manner using a tool with a single drive portion that engages the locking member. 
         [0003]    US 2003/0100896 A1 describes a polyaxial bone anchoring device wherein in one embodiment a single piece locking element is used to lock the head and the rod simultaneously when the locking element is tightened. 
         [0004]    U.S. Pat. No. 7,972,364 describes a locking assembly for securing a rod in a rod receiving part of a bone anchoring device that includes a first locking element and a second locking element. With the first locking element and the second locking element the head of the bone anchoring element and the rod can be locked independently using a tool with two drive portions. 
         [0005]    U.S. Pat. No. 8,088,152 B2 describes an orthopaedic retaining system comprising at least one bone screw which has a head part and a threaded shaft pivotably mounted thereon. A clamping element is mounted in the head part, which can be pressed against the threaded shaft from its upper side and, as a result, secure the threaded shaft relative to the head part. A retaining bar is arranged in a receptacle of the head part. Further, a clamping device is provided on the upper side of the head part, by means of which the clamping element and the retaining bar are pressed into the head part such that the threaded shaft and the retaining bar are secured in positions relative to the head part. The clamping device comprises an elastically deformable pressure element which is displaced into a clamping position during actuation of the clamping device. With such a configuration, upon actuation of the clamping device, the pressure element abuts first on the clamping element and thereby secures the pivotable threaded shaft in position on the head part while the retaining bar remains freely displaceable. Only upon further actuation of the clamping device the pressure element is elastically deformed thereby abutting on the retaining bar and securing the retaining bar in position. 
       SUMMARY 
       [0006]    It is the object of the invention to provide an improved polyaxial bone anchoring device that provides for a simplified handling and a reliable fixation of the head and the rod. 
         [0007]    The object is solved by a polyaxial bone anchoring device according to claim  1 . Further developments are given in the dependent claims. 
         [0008]    The polyaxial bone anchoring device allows to lock the head of the bone anchoring element in the receiving part and the rod in a sequential manner using only a single tool with a single drive portion. By this sequential locking mechanism it is possible to first lock or at least preliminarily clamp the head and thereafter clamp the rod and finally lock the rod and the head. Moreover, a full locking of the head and the rod can be carried out and thereafter the fixation of the rod can be loosened to perform adjustments of the rod. 
         [0009]    Because only a single tool with a single drive portion and one-piece loading member is needed for performing these steps, the use of the polyaxial bone anchoring device is facilitated. 
         [0010]    The polyaxial bone anchoring device comprises only few parts. The pressure member and the locking member can be used with existing receiving parts. Hence, existing receiving parts may be upgraded with a sequential locking mechanism to allow an independent head and rod fixation. The number of parts of the polyaxial bone anchoring device that has the sequential locking mechanism is the same as the number of parts of a polyaxial bone anchoring device wherein the head and the rod are locked simultaneously. 
         [0011]    The pressure member and the locking element are relatively easy to manufacture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Further features and advantages of the invention will become apparent from the description of embodiments by means of the accompanying drawings. 
           [0013]      FIG. 1 : shows a perspective exploded view of the polyaxial bone anchoring device according to a first embodiment. 
           [0014]      FIG. 2 : shows a perspective view of the polyaxial bone anchoring device according to the first embodiment in an assembled state. 
           [0015]      FIG. 3 : shows a perspective view from the bottom of the pressure member of the polyaxial bone anchoring device according to the first embodiment. 
           [0016]      FIG. 4 : shows a top view of the pressure member shown in  FIG. 3 . 
           [0017]      FIG. 5   a : shows a cross-sectional view of the pressure member, the section taken along line A-A in  FIG. 4 . 
           [0018]      FIG. 5   b : shows an enlarged view of a portion of  FIG. 5   a.    
           [0019]      FIG. 6 : shows a perspective view from one side of the locking member of the polyaxial bone anchoring device according to the first embodiment. 
           [0020]      FIG. 7 : shows a top view of the locking member of  FIG. 6 . 
           [0021]      FIG. 8 : shows a cross-sectional view of the locking member, the section being taken along line B-B in  FIG. 7 . 
           [0022]      FIG. 9 : shows a cross-sectional view of the polyaxial bone anchoring device with inserted rod, wherein the section is taken in a plane perpendicular to the rod axis in a first configuration of the locking member. 
           [0023]      FIG. 10   a : shows a cross-sectional view of the polyaxial bone anchoring device as in 
           [0024]      FIG. 9 , wherein the locking member is in a second configuration. 
           [0025]      FIG. 10   b : shows an enlarged view of a portion of  FIG. 10   a.    
           [0026]      FIG. 11   a:  shows a cross-sectional view of the polyaxial bone anchoring device as in  FIG. 9  with the locking member in a third configuration. 
           [0027]      FIG. 11   b : shows an enlarged view of a portion of  FIG. 11   a.    
           [0028]      FIG. 12 : shows a perspective exploded view of the polyaxial bone anchoring device according to a second embodiment. 
           [0029]      FIG. 13 : shows a top view of the pressure member of the polyaxial bone anchoring device according to  FIG. 12 . 
           [0030]      FIG. 14   a : shows a cross-sectional view of the pressure member of  FIG. 13  along line C-C in  FIG. 13 . 
           [0031]      FIG. 14   b : shows an enlarged view of a portion of  FIG. 13 . 
           [0032]      FIG. 15 : shows a perspective view from the bottom of the locking member of the polyaxial bone anchoring device according to the second embodiment. 
           [0033]      FIG. 16 : shows a cross-sectional view of the locking member according to the second embodiment. 
           [0034]      FIG. 17 : shows a cross-sectional view of the polyaxial bone anchoring device according to the second embodiment with inserted rod wherein the section is taken in a plane perpendicular to the rod axis and the locking member is in a first configuration. 
           [0035]      FIG. 18   a : shows a cross-sectional view of the polyaxial bone anchoring device according to the second embodiment with the locking member in a second configuration. 
           [0036]      FIG. 18   b : shows an enlarged view of a portion of  FIG. 18   a.    
       
    
    
       [0037]    The polyaxial bone anchoring device according to a first embodiment is shown in  FIGS. 1 and 2 . It comprises an anchoring element  1  having a shank  2  with a threaded portion and a head  3 . The head  3  has a spherically-shaped outer surface portion and, on its side opposite to the shank  2 , a recess  4  for engagement with a tool. A receiving part  5  is provided for coupling the bone anchoring element  1  to a rod  6 . In the receiving part  5 , a pressure member  7  is arranged to exert pressure onto the head  3  of the bone anchoring element. 
       DETAILED DESCRIPTION 
       [0038]    Referring to  FIGS. 1 and 2  as well as  FIGS. 9 to 12 , the receiving part  5  has a top end  51  and a bottom end  52  and is of substantially cylindrical construction with a longitudinal axis C extending through the top end and the bottom end. Coaxially with the longitudinal axis C, a bore  53  is provided extending from the top end  51  to a predetermined distance from the bottom end  52 . At the bottom end  52 , an opening  54  is provided, the diameter of which is smaller than the diameter of the bore  53 . The coaxial bore narrows towards the opening  54 , for example, with a spherically-shaped section  55  that provides a seat for the head  3 . However, the section  55  can have any other shape such as, for example, a conical shape, that ensures the function of the head  3  being pivotably held in the receiving part  5  similar to a ball and socket joint. 
         [0039]    The receiving part  5  further comprises a U-shaped recess  56  starting at the top end  51  and extending in the direction of the bottom end  52 . By means of the U-shaped recess, two free legs  57 ,  58  are formed that are open towards the top end  51  and define a channel for receiving the rod  6 . Adjacent to the top end  51 , a portion with an internal thread  59  is provided at the inner surface of the legs  57 ,  58 . In the embodiment shown, the internal thread  59  is a flat thread having substantially horizontal upper and lower thread flanks. Any other thread form can be used for the internal thread  59 , however, a thread form that reduces or eliminates splaying of the legs is preferable. Below the portion with the internal thread  59  the bore  53  comprises a slightly enlarged portion  53   a  which provides space for the expansion of a portion of the pressure member  7  described below. 
         [0040]    As shown in  FIGS. 1  and  FIGS. 3 to 5 , the pressure member  7  is of a substantially cylindrical construction with a top end  71  and a bottom end  72  and a cylinder axis C extending through the two ends and being in a mounted state of the pressure member the same as the longitudinal axis C of the receiving part  5 . 
         [0041]    The pressure member is arranged in the receiving part such that its top end  71  is oriented towards the top end  51  of the receiving part  5  and the bottom end  72  is oriented towards the bottom end  52  of the receiving part. The pressure member  7  comprises a first cylindrical portion  73  adjacent the bottom end  72  with an outer diameter that is slightly smaller than the inner diameter of the bore  53  of the receiving part so that the pressure member can be introduced into the receiving part  5  from the top end  51  thereof. Adjacent to the bottom end  72 , a spherically-shaped recess  74  is provided that cooperates with a spherical outer surface portion of the head  3  of the bone anchoring element  1 . A coaxial through-hole  75  extends through the pressure member that allows access to the screw head with a tool (not shown). The end of the cylindrical portion  73  opposite to the bottom end  72  has a rim  73   a  from which a substantially cylindrically-shaped recess  76  extends into the direction of the bottom end  72 . The dimension of the recess  76  is such that the rod  6  can be inserted and guided therein. 
         [0042]    Two upstanding walls  77 ,  78  are provided on the rim  73   a  the free end of which form the top end  71  of the pressure member  7 . The walls  77 ,  78  have such a height that together with the recess  76  they form a channel for inserting the rod, wherein the depth of the channel is greater than the diameter of the rod. Hence, when the rod is inserted, the top end  71  of the pressure member extends above the surface of the rod. The walls  77 ,  78  are substantially cylindrically-shaped with the cylinder axis being the cylinder axis of the pressure member  7 . Each wall  77 ,  78  is divided by a longitudinal slit  77   a,    78   a  that is substantially parallel to the cylinder axis C in two wall portions. The outer diameter of the pressure member in the area of the walls  77 ,  78  is slightly smaller than the outer diameter of the pressure member in the cylindrical portion  73 . Hence, when the pressure member is inserted into the bore  53  of the receiving part and the walls  77 ,  78  are located in the section  53   a  of the bore  53 , there is a gap  79  between the inner wall of the bore section  53   a  and the walls  77 ,  78 . The slits  77   a,    78   a  render the walls  77 ,  78  elastically deformable with respect to the cylindrical portion  73  of the pressure member  7 . This means, that the walls  77 ,  78  can be bent radially outward and return elastically to their upright position. Hence, the walls form a deformable portion of the pressure member. Adjacent to the top end  71 , the wall portions  77 ,  78  comprise an inclined inner edge  78   b  that provides an abutment for the locking member to be described below. The inclination may be for example around 45° with respect to the central axis C. 
         [0043]    The locking member  8  will be described with reference to  FIGS. 1 and 6  to  8 . The locking member  8  is a monolithic piece. In the embodiment shown, it is a set screw. The locking member has a top end  81  and a bottom end  82  that faces the pressure member  7 , when the locking member is inserted between the legs  57 ,  58  of the receiving part  5 . An external thread  83  of the locking member cooperates with the internal thread  59  of the receiving part  5 . A coaxial recess  84  is provided at the bottom end  82 . It shall be mentioned, that the recess  84  can be omitted and/or a coaxial through hole can be provided. Adjacent the top end  81 , there is an engagement portion  85  for a tool, which may be, for example, formed as a recess with longitudinal grooves, as a hexagon or other polygon recess, torx-shaped recess or may have any other shape making it suitable as an engagement portion. Hence, with the engagement portion  85 , the locking member  8  has a single drive portion for a drive tool. 
         [0044]    Adjacent the bottom end  82 , there is a cylindrical portion  87  with an outer diameter that is only slightly smaller than the inner diameter of the pressure member between the walls  77 ,  78  so that the cylindrical portion  87  may extend between the walls  77 ,  78 . Between the cylindrical portion  87  and the external thread  83 , there is a conical portion  88  with a cone angle selected such that it corresponds to the angle of inclination of the inclined edge  77   b,    78   b  of the walls  77 ,  78 . The size of the conical portion  88  in axial direction is greater than the size of the inclined edge  77   a,    77   b  of the wall portions  77 ,  78 , so that when the conical portion  88  comes into engagement with the inclined edge  77   b,    78   b,  a movement of the locking member towards the pressure member keeps the inclined edge  77   b,    78   b  and the conical portion  88  in contact over a certain length. 
         [0045]    The parts of the bone anchoring device are made of a bio-compatible material, for example, of a bio-compatible metal or a metal alloy, such as titanium, stainless steel, nickel titanium alloys, such as Nitinol, or made of a bio-compatible plastic material, such as for example PEEK (polyetheretherketone). The parts can be made all of the same or of different materials. 
         [0046]    In use, the receiving part  5  and the anchoring element  1  as well as the pressure member  7  are normally pre-assembled such that the head  3  is pivotably held in the seat  55  of the receiving part  5  and the pressure member  7  is placed onto the head. Usually, at least two polyaxial bone anchoring devices shall be connected via the rod  6 . After insertion of the bone anchoring elements  1  into the bone, the receiving parts  5  are aligned by pivoting the receiving parts relative to the head and then the rod  6  is inserted. 
         [0047]    The locking procedure will be explained with reference to  FIGS. 9 to 11   b . First, as shown in  FIG. 9 , the locking member  8  is inserted into the receiving part with the bottom end  82  of the locking member facing the rod  6 . The locking member  8  is then further screwed-in until its cylindrical portion  87  extends into the space between the walls  77 ,  78  and the conical portion  88  of the locking member abuts against the inclined edge  77   b,    78   b  of the walls  77 ,  78 . Further advancement of the locking member  8  into the receiving part presses the pressure member  7  against the head  3  as shown in  FIGS. 10   a  and  10   b . By means of this, the head  3  is clamped in an adjustable angular position with respect to the receiving part  5  and is held in this position by means of friction. The head may be only slightly clamped or nearly completely locked. 
         [0048]    Then, as shown in  FIGS. 11   a  and  11   b,  the further advancement of the locking member results in a counterforce that the locking member  8  experiences from the pressure member  7 . The walls  77 ,  78  are bent radially outward when the conical portion  88  presses onto the inclined edge  77   b,    78   b  thereby moving the walls  77 ,  78  into the gap  79  that is present between the wall portions and the inner wall of the bore section  53   a  (see arrows in  FIGS. 11   a  and  11   b ). This allows the bottom end  82  of the locking member  8  to move deeper into the channel where the rod is seated and finally contact and lock the rod. By this procedure, the whole polyaxial bone anchoring device is locked. 
         [0049]    It is possible to correct the position of the rod without loosening of the locking of the head. To achieve this, the locking member  8  is screwed-back until the rod  6  becomes displaceable. This is possible due to the resilient property of the deformable walls  77 ,  78  of the pressure member  7 . It may even be possible to fully remove the locking member  8  and to carry out a revision of the complete polyaxial bone anchoring device. 
         [0050]    A second embodiment of the polyaxial bone anchoring device will be described with reference to  FIGS. 12 to 18   b . The second embodiment differs from the first embodiment in the design of the pressure member and of the locking member. Parts and portions that are identical to the first embodiment, have the same reference numerals and the description thereof will not be repeated. 
         [0051]    The pressure member  7 ′ has a top end  71  and a bottom end  72  and a substantially cylindrical portion  73 ′ that extends from the top end  71  to the bottom end  72 . 
         [0052]    A U-shaped recess  76 ′ extends from the top end  71  to a distance from the bottom end  72 . The depth of the U-shaped recess  76 ′ is greater than the diameter of the rod so that when the rod  6  is inserted, the top end  71  of the pressure member extends above the surface of the rod. A small coaxial cylindrical recess  76   a,    76   b  extends from the top end  71  into the sidewalls of the channel formed by the U-shaped recess  76 ′ respectively. The recesses  76   a,    76   b  contribute to rendering the upper portion of the pressure member  7 ′ deformable. At a distance from the top end  71  of both side walls a notch  107   a,    107   b  in the outer surface extending in a transverse or circumferential direction relative to the central axis C is provided. The contour of the notch  107   a,    107   b  is substantially V-shaped, i.e. the width of the notch is increasing towards the outer surface. This renders the upper portion of the pressure member  7 ′ elastically deformable in such a way that compressing the sidewalls of the recess  76 ′ in an axial direction, leads to a reduction of the height of the sidewalls. 
         [0053]    The locking member  8 ′ according to the second embodiment differs from the locking member of the first embodiment in that it comprises only a cylindrical projection  87 ′ that projects away from the threaded portion  83 . The cylindrical projection  87 ′ has a smaller diameter than the threaded portion  83  of the locking member, such that at the end of the threaded portion a ring-shaped abutment  108  is formed that comes into contact with the top end  71  of the pressure member  7 . 
         [0054]    In use, as shown in  FIG. 17 , when the locking member  8 ′ is inserted into the receiving part and advanced towards the pressure member  7 ′, the ring-shaped abutment  108  comes into contact with the top end  71  of the pressure member. Further advancement of the locking member  8 ′ presses the pressure member against the head  3  such that the head  3  is clamped by friction. Due to the counterforce experienced by the locking member  8 ′ from the pressure member when it presses the head  3  into the seat  5 , the further advancement of the locking member  8  presses the abutment  108  against the top end  71  of the pressure member  7 ′. Thereby, the deformable portion formed by the notches  107   a,    107   b  is deformed and the notches are narrowed. Hence, the cylindrical portion  87 ′ of the locking member  8  comes into contact with the surface of the rod  6  and presses onto the rod to fix the rod. 
         [0055]    For a correction of the position of the rod, the locking member can be screwed-back slightly to render the rod displaceable again. Because of the spring function of the deformable portion of the pressure member  7 ′ the pressure onto the head  3  that holds the head  3  in position, is still present and the head remains clamped. Final tightening of the locking member  8  locks the whole assembly. 
         [0056]    Various modifications of the previous embodiments are conceivable. In particular, the deformable portion can be realized also by resilient elements, that are mounted onto the upper end of a pressure member. In such a case, the clamping force can be adjusted by selecting an element with a specific spring force. In addition, features of the different embodiments described can be combined among each other. 
         [0057]    For the polyaxial bone anchoring device any known polyaxial bone anchoring devices can be used that comprise a bone anchoring element that is pivotably received in the receiving part. In particular, bone anchoring devices, wherein the bone anchoring element is introduced from the bottom end of the receiving part into the receiving part, may be used. The head does not need to have a spherical shape. It can also have flattened portions that may be used for restricting the pivoting movement to a single plane. The receiving part may be formed differently in particular inside. It can also have an inclined lower edge to allow an enlarged pivot angle to a specific direction. For the bone anchoring element, any known bone anchors, such as screws, nails, with or without cannulation, can be used. 
         [0058]    The connection between the locking member and the receiving part does not necessarily have to a threaded connection, other connections may be possible, such as for example, a bayonet connection.