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 ) 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 ) that is insertable into the channel, the locking member comprising a top end ( 81 ) and a bottom end ( 82 ) facing the pressure member; a deformable first portion ( 85 ) and a second portion ( 84 ) provided at the bottom end; wherein, when the locking member is advanced into the channel in the direction of the central axis (C), first the deformable first portion ( 85 ) comes into contact with the pressure member ( 7 ) and is deformed resulting in a load applied to the pressure member that clamps the head, and thereafter the second portion ( 84 ) comes into contact with the rod and clamps the rod.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present disclosure claims the benefit of U.S. Provisional Patent Application Ser. No. 61/654,593, filed Jun. 1, 2012, the contents of which are hereby incorporated by reference in their entirety, and claims priority from European Patent Application EP 12170595.8, filed Jun. 1, 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 element. 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. The polyaxial bone anchoring device further includes a locking member that is insertable into the channel and that has a deformable first portion and a second portion on its side facing the pressure member. When the locking member is advanced into the channel, first the deformable first portion comes into contact with the pressure member and is deformed resulting in a load applied to the pressure member that clamps the head, and thereafter the second portion 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]    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. 
         [0004]    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 
       [0005]    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. 
         [0006]    The object is solved by a polyaxial bone anchoring device according to claim  1 . Further developments are given in the dependent claims. 
         [0007]    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. 
         [0008]    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. 
         [0009]    When the deformable portion of the locking member is elastically deformed, it is possible to perform revisions of the polyaxial anchoring device by removing the locking member and using it again. 
         [0010]    The deformable portion may be designed as a separate part that is fixed to the locking member in order to be able to vary the clamping force by selecting an appropriate deformable portion in view of the material and the shape of the deformable portion. 
         [0011]    The polyaxial bone anchoring device comprises only few parts. The locking member can be used with existing polyaxial bone anchoring devices that allow a separate head and rod fixation. 
     
    
     
       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]    In the drawings: 
           [0014]      FIG. 1 : shows a perspective exploded view of the polyaxial bone anchoring device according to a first embodiment. 
           [0015]      FIG. 2 : shows a perspective view of the polyaxial bone anchoring device of  FIG. 1  in an assembled state. 
           [0016]      FIG. 3 : shows a perspective view from the bottom of the pressure member of the polyaxial bone anchoring device according to the first embodiment. 
           [0017]      FIG. 4 : shows a top view of the pressure member of  FIG. 3 . 
           [0018]      FIG. 5 : shows a cross-sectional view of the pressure member along line A-A in  FIG. 4 . 
           [0019]      FIG. 6 : shows a perspective view from the bottom 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 shown in  FIG. 6 . 
           [0021]      FIG. 8 : shows a cross-sectional view of the locking member along line B-B in  FIG. 7   
           [0022]      FIGS. 9 to 12 : show cross-sectional views of steps of use of the polyaxial bone anchoring device according to the first embodiment, the section taken in a plane perpendicular to the rod axis. 
           [0023]      FIG. 13 : shows an enlarged portion of a detail of  FIG. 12 . 
           [0024]      FIG. 14 : shows a perspective exploded view of the locking member of the polyaxial bone anchoring device according to a second embodiment. 
           [0025]      FIG. 15 : shows a perspective view of the locking member of  FIG. 14  in an assembled state. 
           [0026]      FIGS. 16 to 17 : show cross-sectional views of steps of use of the polyaxial bone anchoring device according to the second embodiment, the section being taken in a plane perpendicular to the rod axis. 
           [0027]      FIG. 18 : shows an enlarged portion of a detail of  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    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 is provided extending from the top end  51  to a predetermined distance from the bottom end  52 . The bore has a first section  53   a  with a first diameter adjacent the top end that goes over with an inclined shoulder in a second section  53   b  with a second diameter smaller than the first diameter. 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. 
         [0029]    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. 
         [0030]    The pressure member  7  is of substantially cylindrical construction with an outer diameter sized so as to allow the pressure member to be introduced into the second portion  53   b  of the bore of the receiving part  5  and to be moved therein in the axial direction. The pressure member  7  has a top end  71  and an opposite bottom end  72  and a longitudinal axis C extending through the two ends being in a mounted state the same as the longitudinal axis C of the receiving part  5 . The pressure element is arranged in the receiving part  5  such that its top end  71  is oriented towards the top end  51  of the receiving part and the bottom end  72  is oriented towards the bottom end  52  of the receiving part. At its top end  71 , the pressure element comprises a substantially U-shaped recess  73  that is configured to receive the rod  6 . When the rod  6  is positioned on the bottom of the recess  73 , the top end  71  of the pressure member  7  is located at a height above the surface of the rod  6 . 
         [0031]    At the top end  71 , the pressure member comprises a collar  77  shaped as two opposite segments of a circle. By the collar, two enlarged surface portions  71   a  are formed at the upper end of the sidewalls of the U-shaped recess  73 . The outer diameter of the pressure element in the region of the collar  77  is enlarged so that the enlarged surface portions  71   a  extend into the first part  53  a of the bore. The enlarged surface portions  71   a  provide an abutment for the locking member described below. 
         [0032]    On its lower side, the pressure member  7  comprises a spherically-shaped recess  74  cooperating with a spherical outer surface portion of the head  3 . Furthermore, a coaxial through-hole  75  is provided in the pressure member that allows access to the recess  4  of the head  3  when the bone anchoring element  1  and the pressure member  7  are mounted in the receiving part  5 . 
         [0033]    The locking member  8  will be described with reference to  FIGS. 1 and 6  to  8 . The locking member  8  in the first embodiment is a monolithic piece. It is formed as a set screw having a top end  81  and a bottom end  82  that faces the pressure member when the locking element is inserted between the legs  57 ,  58  of the receiving part  5 . More in detail, the locking member  8  has adjacent to the top end  81   a  screw portion  83  with an external thread that cooperates with the internal thread of the legs and on the bottom side of the screw portion  83  a cylindrical projection  84  surrounded by a conically outwardly extending portion  85  that is inclined away from the screw portion  83 . The outer diameter of the conical portion  85  is smaller than the outer diameter of the screw portion  83  such that the locking member  8  can be inserted between the legs with its bottom end  82  ahead. 
         [0034]    The cylindrical portion  84  is configured to be a rigid portion, i.e. does not deform under normal operating conditions when it is pressed against the rod, which is described below. The conical portion  85  has a shape similar to a conical washer. It is configured to be a deformable portion that is deformed towards the screw portion  83 , when it is pressed against the pressure member  7  described below. In particular, the conical portion  85  is elastically deformable so that it forms a resilient portion that assumes its original shape when the load is removed. Further, in the original configuration, the conical portion  85  protrudes from the cylindrical portion  87  in the axial direction. It has a size and an elasticity such that when a load is applied to the conical portion  85  in the direction to the top end  81 , the conical portion  85  is bent against the screw portion  83 . In the bent configuration, the cylindrical portion  84  protrudes in an axial direction beyond the conical portion  85 . 
         [0035]    The locking member  8  further comprises a coaxial through-hole  86  with an engagement portion  87 . The engagement portion  87  is the embodiment showing a hexagonal recess. However, it can have any other shape such as a torx-shape or longitudinal grooves or any structure that allows engagement with a tool. The engagement portion needs not to be provided on a through hole. It can be provided as a recess with a depth extending into the locking member from the top end. 
         [0036]    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 PEEK (polyetheretherketone). The parts can be made all of the same or of different materials. 
         [0037]    In use, the receiving part  5  and the anchoring element  1  as well as the pressure member  7  are usually 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. At least two polyaxial bone anchoring devices shall be connected via the rod  6 . After insertion of the bone anchoring elements into the bone, the receiving parts are aligned and the rod is  6  inserted. 
         [0038]    The locking procedure will be explained with reference to  FIGS. 9 to 13 . 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 towards the rod. The locking member is then further screwed-in until an outermost edge of the conical portion contacts the top end surface  71   a  of the pressure member  7  that serves as an abutment. In this position, shown in  FIG. 10 , the conical portion  85  and the cylindrical portion  84  do not contact the rod  6 . Therefore, the rod  6  is freely displaceable in the U-shaped recess of the pressure member that is aligned with the U-shaped recess of the receiving part. When the conical portion  85  contacts the pressure member  7 , pressure is exerted onto the head  3  via the pressure member  7 . This clamps the head  3  in a adjustable angular position with respect to the receiving part and holds the head  3  in this position by means of friction. The clamping force may be precisely adjusted to be higher or lower depending on how far the locking member is screwed-in. 
         [0039]    Further advancement of the locking member towards the rod leads to a deformation of the conical portion  85 . The conical portion  85  is bent towards the screw portion  83  with the top end surface  71   a  of the pressure member  7  acting as an abutment. 
         [0040]    Still further advancement of the locking member towards the rod increases the deformation of the conical portion  85  until the cylindrical portion  84  comes in contact with the surface of the rod  6  as shown in  FIG. 12 . By means of this, the head and the rod are locked. 
         [0041]    It is possible to correct the position of the rod without loosening of the locking of the head. To achieve this, the locking member is screwed-back until the rod becomes displaceable. This is possible due to the resilient property of the conical portion  85 . It may be even possible to fully remove the locking member  8  and to carry out a revision of the complete polyaxial bone anchoring device. 
         [0042]    A second embodiment of the polyaxial anchoring device will be described with reference to  FIGS. 14 to 18 . The second embodiment differs from the first embodiment in the design of the locking member. The locking member  8 ′ according to the second embodiment comprises a conical portion  95 ′ that is a separate member. The conical portion  95 ′ that has a shape similar to a conical washer, i.e. has a coaxial hole  85   a ′, the inner diameter of which is dimensioned such that the conical portion  85 ′ can be placed around the cylindrical portion  84 ′. As shown in  FIG. 14 , the conical portion  85 ′ is mounted from the side of the cylindrical portion  84 ′ onto the locking member  8 ′. It can be press-fit onto the cylindrical portion  84 ′ or crimped, welded or fixed with any other method. In the assembled state as shown in  FIG. 15 , the conical portion  85 ′ is fixed to the screw portion  83  so that the locking member  8 ′ forms a single part. 
         [0043]    The conical portion  85 ′ can be made of a different material compared to the material of the screw portion  83 . Various conical portions  85  can be provided that differ with respect to the material, the cone angle, the thickness, or any other properties to allow an adjustment of the clamping force by selecting an appropriate portion. 
         [0044]    In use, as shown in  FIGS. 16 and 18 , because the conical portion projects from the cylindrical portion, the conical portion comes first into contact with the top end surface  71   a  of the pressure member  7  and begins to clamp the head. Upon further insertion of the locking member  8 ′, the conical portion  85 ′ is deformed and the clamping force onto the head is increased until the head is locked. When the conical portion  85 ′ has been deformed such that the cylindrical portion  84 ′ protrudes, the cylindrical portion  84 ′ comes into contact with the rod and clamps the rod. Final tightening locks the whole assembly. 
         [0045]    Various modifications of the previous embodiments are conceivable. In particular, the deformable portion doesn&#39;t have to be a conical ring-shaped portion. It is sufficient that a deformable portion is located at a position that comes into contact with the top end surface  71   a  of the pressure member. The ring-shaped portion is, however, particularly appropriate for a locking member that is advanced by screwing it between the legs. 
         [0046]    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 a 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 design of the receiving part can be different. As the bone anchoring element, any known bone anchors, such as screws, nails, with or without canulation can be used. 
         [0047]    The connection between the locking member and the receiving part does not necessarily have to be threaded connection. Other connections may be possible, such as, for example, a bayonet connection.