Abstract:
The invention relates to an implant for supporting a vertebral column, including at least one attachment element ( 300 ) and a connecting rod. Such an attachment element ( 300 ) includes an anchoring member ( 13 ) in a vertebral body, as well as a head ( 14 ) in which a passage opening ( 15 ) is provided that is conducive to receiving a connecting rod ( 12 ), the attachment element ( 300 ) being remarkable in that it comprises a means ( 316 ) for centering said rod, said rod-centering means being mounted on a spring-back means ( 317 ) placed in said head ( 14 ), said centering means ( 316 ) and said head ( 14 ) being movable relative to each other. A connecting rod ( 12 ) capable of being inserted into a passage opening ( 15 ) of an attachment element ( 300 ) includes at least one second centering surface ( 19 ). The attachment element ( 300 ) and the connecting rod ( 12 ) engage to form an implant in which said rod is rotatably and/or translatably movable relative to the anchoring member ( 13 ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of vertebral column surgery on the human or animal body, and more particularly implants for stabilizing part of the vertebral column. 
       BACKGROUND 
       [0002]    The vertebral column plays a key role in many respects for the human or animal body and in particular, it must be able to absorb mechanical stresses due to movements of the body. The vertebral column may, however, no longer be able to correctly perform its functions, for example, following a trauma or for reasons related to age or illness that can cause wear, or degeneration of one or more vertebral articulations: these are referred to as instabilities. Such instabilities are very often a source of pain and can be treated using medication, rehabilitation, or surgery with or without instrumentalization. 
         [0003]    The instrumentalization of the vertebral column consists of consolidating the stability of the vertebral column by placing an implant connecting the vertebral bodies of at least two consecutive vertebrae. Traditionally, such an implant comprises two elements connected to the vertebral bodies of the screw, hook, or cable type and are connected to each other by bar or plate-type elements. For clinical reasons, it is desirable for such an implant to have a certain flexibility and to absorb shocks or deform and avoid traumatizing the vertebral column. In this way, U.S. Pat. No. 6,966,910 describes an intervertebral bridge having two screws connected by a connection element whereof the geometric shape is conducive to bending in case of excessive stress. Such an intervertebral bridge does not, however, have all of the flexibility needed to avoid hindering the mobility of the part of the vertebral column thus treated. In order to impart greater mobility to the implanted part of a vertebral column, patent application US 2004/0049190 describes a dynamic device  1 , shown in the appended  FIG. 1 , including two anchor elements  2  intended to be attached to vertebrae  3  connected by a bar  4  slidingly mounted to allow movement in the direction of the double arrow. An elastic means  5  is arranged on the bar  4 , in the space  6  between the two anchor elements  2 , symbolized by the square zone in broken lines, in order to exert a force in the direction of the longitudinal axis of the bar  4 . Such a dynamic device  1  allows acceptable mobility of the treated part of the vertebral column, but is, however, bulky and cannot be used to correct all defects of the vertebral column. In fact, seen from the front or back, a healthy vertebral column is substantially rectilinear. However, in a sagittal plane, the vertebral column has four curves that, from bottom to top, are called sacral curve, lumbar lordosis, dorsal kyphosis and cervical lordosis. However, at the lumbar lordosis, the spaces between the vertebral bodies are particularly reduced and therefore a dynamic device  1  like that described in patent application U.S. 2004/0049190 cannot be positioned there due to the bulk of its elastic means  5 . Furthermore, such a dynamic device  1  does not allow a dynamic control of the rotational movement of the bar  4  relative to the anchor elements  2 . 
       BRIEF SUMMARY 
       [0004]    The present invention aims to resolve all or some of the aforementioned drawbacks. In this technical context, one aim of the present invention is to provide an implant to stabilize a vertebral column allowing translational and/or rotational mobility of the treated part of the vertebral column. More particularly, the present invention aims to obtain an implant able to be implanted at a lumbar lordosis or on part of a vertebral column whereof the vertebrae are not very spaced apart. 
         [0005]    To that end, the present invention relates to an attachment element for a maintenance implant of part of a human or animal vertebral column, comprising, on the one hand, an anchor member intended to attach the element in a vertebral body and, on the other hand, a head in which a passage opening is formed conducive to receiving a connecting rod, this element being remarkable in that it includes means for centering said connecting rod mounted on a spring-back means arranged in said head, said centering means and said head being mobile relative to each other. 
         [0006]    The present invention also relates to a connecting rod for a maintenance implant for a human or animal vertebral column, able to be inserted into a passage opening of an attachment element and comprising at least one second centering surface including a notch and/or a protrusion. 
         [0007]    In this way, an attachment element according to the invention, in cooperation with a connecting rod according to the invention, makes it possible to obtain an implant according to the invention, as described below, offering suitable mobility and allowing dynamic control of the movement of the vertebrae of part of a vertebral column connected by said implant: in fact, during a relative movement of two vertebrae connected by an implant according to the invention, the connecting rod and the attachment element according to the invention can move translationally and/or rotationally relative to each other, said centering means tending to return the connecting rod and the attachment element in a predefined position, owing to the return forces exerted by the spring-back means. The spring-back means being arranged on the head of the attachment element, this allows the implant according to the invention to be positioned at a lumbar lordosis of a vertebral column: in fact, unlike a traditional device, it is not necessary to provide a space like the space usually required for the spring-back means of a dynamic device according to the prior art. 
         [0008]    In one embodiment of the invention, the relative movement of the centering means is done along an axis transverse, in particular perpendicular, to the axis of the passage opening. An axis transverse to the axis of the opening makes it possible to reduce the minimum space needed between two vertebrae so they can be connected by an implant according to the present invention. 
         [0009]    In one embodiment of the invention, said spring-back means tend to push said centering means towards the inside of the passage opening. The centering means pushed towards the inside of the passage opening are intended to bear on the connecting rod and minimize the functional play between the attachment element and said rod. 
         [0010]    In one embodiment of the invention, said head also has a housing emerging in the passage opening inside which the spring-back means and the centering means are housed. 
         [0011]    In one embodiment of the invention, said attachment element also comprising a bolt intended to close the housing made to emerge outside said head, the bolt comprising the spring-back means and the centering means. A bolt comprising the spring-back means and the centering means makes it possible to simplify the assembly of the attachment element. 
         [0012]    In one embodiment of the invention, the bolt has flexible fins intended to cooperate with a stop formed in the surface of the housing. The fins are simple to make and can be molded with the bolt or can be machined on the bolt: this makes it possible to simplify the assembly, the number of pieces necessary for the assembly, and the production costs of the attachment element according to the invention. 
         [0013]    In one embodiment of the invention, the centering means is secured to the anchor member, said spring-back means being mounted between the head and said anchor member. The spring-back means can then for example be formed by an inexpensive annular seal. 
         [0014]    In one embodiment of the invention, the head and the anchor member are translationally and/or rotationally mobile relative to each other. Thus, an implant made using an attachment element according to the invention has increased mobility. 
         [0015]    In one embodiment of the invention, the spring-back means is designed so as to exert a rotational return torque between the head and the anchor member. Thus, an attachment element according to the invention allows a dynamic control during translational and/or rotational movements of the vertebrae. 
         [0016]    In one embodiment of the invention, said centering means includes a first centering surface opposite the passage opening having at least one slope, in particular planar or curved. 
         [0017]    In one embodiment of the invention, the first centering surface has a notch. 
         [0018]    In one embodiment of the invention, the first centering surface has a boss. 
         [0019]    In one embodiment of the invention, at least part of the surface delimiting the passage opening has an additional centering surface having a boss and/or a notch. 
         [0020]    In one embodiment of the connecting rod according to the invention, each second centering surface is formed near one of the ends of the connecting rod. 
         [0021]    Lastly, the present invention relates to an implant for stabilizing a vertebral column in the human or animal body having at least one attachment element according to the invention and at least one connecting rod according to the invention inserted into the passage opening of said attachment element, the centering means being designed to cooperate with said second centering surface. 
         [0022]    Preferably, said connecting rod is rotationally and/or translationally mobile relative to the anchor member, said first and second centering surfaces being designed to cooperate so as to move said connecting rod rotationally and/or translationally relative to the anchor member. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The invention will be better understood using the detailed description below in light of the appended drawings, in which: 
           [0024]      FIG. 1  shows a diagrammatic view of a dynamic device according to the prior art, as mentioned in the preamble of the present description; 
           [0025]      FIG. 2  shows a diagrammatic view of an implant according to the invention; 
           [0026]      FIGS. 3   a  and  3   b  show longitudinal diagrammatic cross-sectional views of an attachment element according to a first embodiment of the invention and part of a connecting rod according to the invention; 
           [0027]      FIGS. 4   a  to  4   c  show longitudinal diagrammatic cross-sectional views of an attachment element according to a second embodiment of the invention and part of a connecting rod according to the invention; 
           [0028]      FIGS. 5   a  and  5   b  respectively show longitudinal diagrammatic cross-sectional views of an attachment element according to a third embodiment of the invention and part of a connecting rod according to the invention; 
           [0029]      FIGS. 6   a  to  6   c  show perspective ( 6   a,    6   b ) and longitudinal cross-sectional ( 6   c ) diagrammatic views of an attachment element according to a fourth embodiment of the invention and part of a connecting rod according to the invention; 
           [0030]      FIGS. 7   a  to  7   f  show diagrammatic perspective views of details of second centering surfaces of the connecting rod according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    An implant  10  according to the invention, as shown diagrammatically in 
         [0032]      FIG. 2 , has at least one attachment element  11  according to the invention intended to be anchored in a vertebra  3  and at least one connecting rod  12  according to the invention. The attachment element  11  includes an anchor member  13  intended to attach said attachment element  11  in the vertebral body of a vertebra  3 . The attachment element  11  also has a head  14  in which a passage opening  15  is formed conducive to receiving the connecting rod  12 , so that the latter can slide inside said passage opening  15  at least in the direction symbolized by the double arrow. In the head  14  of the attachment element  11 , a means  16  for centering the connecting rod  12  is arranged mounted on a spring-back means  17 . The centering means  16  has a first centering surface  18  opposite the passage opening  15  and having at least one planar or curved slope, said first centering surface  18  forming a boss and/or a notch. The spring-back means  17  exerts forces on the centering means  16  so as to push said first centering surface  18  towards the inside of the passage opening  15 . 
         [0033]    The connecting rod  12  has, at one of its ends intended to be inserted into the passage opening  15 , a second centering surface  19  also having a notch and/or a protrusion. At the other end of the connecting rod  12 , a traditional anchor screw  20  is for example attached, intended to attach the implant  10  according to the invention in a second vertebra  3 . 
         [0034]    When the connecting rod  12  is inserted into the passage opening  15 , the first and second centering surfaces ( 18 ,  19 ) cooperate, as detailed later, to move said connecting rod  12 , rotationally and/or translationally, relative to the anchor member  13 . 
         [0035]    Incorporating a spring-back means  17  inside the head  14  makes it possible to free the space occupied by the spring-back means  5  on the bar  4  of a traditional dynamic device  1 . In this way, the space  21 , symbolized by the square zone in dotted lines in  FIG. 2 , situated between the fastening element  11  and the anchor screw  20  of the implant  10  of  FIG. 2 , is more limited than the space  6  occupied by the elastic means  5  of a traditional dynamic device  1  shown in  FIG. 1 . Moreover, the relative movement of the centering means  16  along an axis A transverse to the axis B of the passage opening  15  makes it possible to position the centering means  16  outside the space  21  and therefore to further reduce the latter. The bulk of the space  21  by the centering means  16  is minimal when the transverse axis A is perpendicular to the axis B of the passage opening  15 . 
         [0036]    Such a limited space  21  makes it possible to position an implant  10  according to the invention on two consecutive vertebrae  3  situated in a zone of the vertebral column, such as the lumbar lordosis, when a traditional dynamic device  1  cannot be positioned because it is too bulky. 
         [0037]    In the continuation of the description, and in order to simplify the reading thereof, elements similar or identical to the various attachment elements may keep the same numbering. 
         [0038]      FIGS. 3   a  and  3   b  are longitudinal cross-sectional views of an attachment element  100  according to a first embodiment of the invention, in the passage opening  15  in which a connecting rod  12  according to the invention is inserted. The attachment element  100  has a head  14  integral with the anchor member  13  for example formed by a screw  113 . In this embodiment, the head  14  has a housing  22 , emerging inside the passage opening  15 , in which the spring-back means  17 , in this case formed by a helical spring  117 , and the centering means  17  then made up of a centering block  116  mounted on the helical spring  117 , on the other hand, are arranged. The centering block  116  can move along an axis parallel to the longitudinal axis of the screw  113  and the helical spring  117  pushes the centering block  116  towards the inside of the passage opening  15  by freeing a space  23  between the centering block  116  and the bottom of the housing  22 . 
         [0039]    The centering block  116  has a first centering surface  18 , for example a spherical notch  118 , situated opposite the passage opening  15 . Advantageously, an additional centering surface  24  delimiting the passage opening  15 , and opposite the first centering surface  18 , also has a boss or a notch. In the embodiment of the invention shown in  FIG. 3   a , the recess  22  extends through the passage opening  15  and emerges outside the head  14 . Such a recess  22  is easy to produce and can be closed by a bolt  125 . The additional centering surface  24  is, for example, the face of a bolt  125  intended to arrive opposite the passage opening  15 . 
         [0040]    The connecting rod  12  according to the invention has a second centering surface  19  shown in this embodiment by a rounded boss  26 . The first and second centering surfaces ( 18 ,  19 ) are kept in contact owing to the helical spring  117 . In the absence of stress of the connecting rod  12  and/or the attachment element  100 , and owing to the complementary shapes of the rounded boss  26  and the spherical notch  118 , the connecting rod  12  occupies a predefined position as shown in  FIG. 3   a.    
         [0041]    When a force is applied on the implant  10  according to the invention, for example when the vertebrae  3  supporting the implant  10  move relative to each other, the connecting rod  12  and the attachment element  100  can be made to move relative to each other. During such movement, the first and second centering surfaces ( 18 ,  19 ) slide one on the other and are kept in contact owing to the pressure exerted by the helical spring  117 . During the translational movement of the connecting rod  12  in the passage opening  15 , the rounded boss  26  forces the centering block  116  into a translational movement in the housing  22 . In this way, when the connecting rod  12  moves away from the predefined position shown in  FIG. 3   a , the rounded boss  26 , given the shape of the spherical notch  118 , pushes the centering block  116  so as to compress the helical spring  117  by reducing the space  23  between the centering block  116  and the bottom of the housing  22 , as shown in  FIG. 3   b . The compression of the helical spring  117  then opposes, in this case, the relative movement of the connecting rod  12  in the passage opening  15 . Thus, when the connecting rod  12  and/or the attachment element  100  are no longer long subjected to an outside force involving their relative movement, as the first and second centering surfaces ( 18 ,  19 ) are in contact, these sliding one on the other so as to relax the helical spring  117 . Such a sliding results in returning the connecting rod  12  towards the predefined position shown in  FIG. 3   a.    
         [0042]    The centering block  116 , pushed by the helical spring  117 , exerts a force on the connecting rod  12 , which is kept pressed against the additional centering surface  24 . This additional centering surface  24 , in the same way as the first centering surface  18 , participates in guiding the connecting rod  12  towards the predefined position of  FIG. 3   a , owing to its adapted shape complementary to the rounded boss  26 . 
         [0043]      FIGS. 4   a ,  4   b  and  4   c  are longitudinal cross-sectional views of an attachment element  200  according to a second embodiment of the invention, in the passage opening  15  in which a connecting rod  12  is introduced similar to that already described in  FIGS. 3   a  and  3   b , for example. The attachment element  200  has a head  14  and an anchor member  13 , for example comprising a screw  213 , able to move translationally and/or rotationally relative to each other. In this embodiment, the head  14  has a housing  22 , emerging inside the passage opening  15 . In this embodiment, the housing  22  is a through housing, along an axis A substantially perpendicular to the axis B of the passage opening  15 . One of the openings of the housing  22  has a rim  27  and the other opening is intended to be closed by a bolt  225 . In this attachment element  200 , the centering means  16  is secured to the anchor member  13  and forms one of the ends  216  of said screw  213 . The anchor member  13  and the rim  27  are designed so that the screw  213  can extend through the opening of the housing  22  including said rim  27  and so as to prevent the passage of the centering means  16 . According to this embodiment, the spring-back means  17  has an elastically deformable annular seal  217  arranged inside the housing  22  and resting on the rim  27 , the annular seal  217  being arranged to be inserted between said rim  27  and the centering means  16 . Advantageously, the annular seal  217  is arranged to exert a rotational return torque between the anchor member  13  and the head  14 , towards an aligned position of these two members along the transverse axis A: such a return torque is due to the elasticity of the seal  217 , stuck between the housing  22  on the one hand and the centering means  16  on the other hand. The annular seal  217  being elastically deformable, it also allows, in addition to a rotational movement, a translational movement of the end  216  of the screw  213  relative to the head  14  when it undergoes elastic crushing. 
         [0044]    The end  216  comprises a first centering surface  18  formed, according to this embodiment, by a centering rim  218  formed at the end  216  of the anchor member  13  intended to be opposite the passage opening  15 . When the connecting rod  12  is introduced into the passage opening  15 , it can occupy a predefined and privileged position, as shown in  FIG. 4   a , in which the centering rim  218  and the rounded boss  26  are in contact, and in which the walls of the passage opening  15  and/or the end of the bolt  215  opposite the passage opening  15  are also in contact with the rounded boss  26 . In this predefined position, the annular joint  217  does not undergo dissymmetrical crushing relative to the axis A. 
         [0045]    In the case of a relative movement of the connecting rod  12  and the attachment element  200 , the rounded boss  26  in contact with the centering rim  218  imposes an elastic deformation on the annular seal  217 , visible in particular in  FIG. 4   c , which creates an elastic effort tending to return the connecting rod  12  and the attachment element  200  to a predefined position as described in Figure  4   a.  The annular seal  217  has the advantage of allowing a great freedom of relative movement between the head  14 , the screw  213 , and the connecting rod  12 , rotationally and/or translationally. In particular, the annular seal  217  allows one of the screw  213  and the connecting rod  12  as shown in  FIG. 4   c  via the axes A and B. 
         [0046]    According to a third embodiment, as shown in  FIGS. 5   a  and  5   b , an attachment element  300  differs from the attachment element  100  in that a housing  29  is formed in a bolt  325 , said housing forming a continuation of the housing  22  that the bolt  325  is meant to close. The bolt  325  is, for example, attached to the head  14  using a screw pitch formed in the wall of the housing  22 . This housing  29  receives a helical spring  317  and a centering block  316  mounted on said helical spring  317 , the centering block  316  protruding from said housing  22  into the passage opening  15 , when the bolt  325  is positioned in the housing  22 . This centering block  316 , like the centering block  116  of the first embodiment described in  FIGS. 3   a  and  3   b , constitutes the centering means  16 . The first centering surface  18  making up the face of the centering block  316  opposite the passage opening  15  is for example a rounded boss  318 . In that case, the second centering surface  19  formed in the connecting rod  12  adapted to said attachment element  300  is a rounded notch  28 . As for the attachment element  100  of the first embodiment, a relative movement of the connecting rod  12  relative to the head  14  of the attachment element  300  involves a compression of the helical spring  317 , as shown in  FIG. 5   b , which then exerts a force on the centering block  316 , transmitted to the connecting rod  12  via the sliding contact between the first centering surface  18  and the second centering surface  19 . This force tends to return the connecting rod  12  to the predefined position as shown in  FIG. 5   a.    
         [0047]    According to a fourth embodiment, like that shown in  FIGS. 6   a  to  6   c , an attachment element  400  has an anchor member  13  made up of a screw  413  extended by a U-shaped head  414 , the space situated between the branches of the “U” constituting the housing  22  and the passage opening  15 . In this embodiment, the housing  22  has at least one stop  30  formed in the surface of said housing  22 , i.e. on the branches of the “U.” The attachment element  400 , shown in  FIGS. 6   a  to  6   c , has two stops  30  arranged opposite each other and protruding in the housing  22 . According to an alternative of the invention that is not shown, a stop is for example a screw pitch portion. 
         [0048]    A bolt  425  intended to close the housing  22  has at least two flexible fins  31  intended to cooperate with said stops  30  in order to allow the bolt  425  to be fastened on the head  414 . The bolt  425  has a first centering surface  18  formed by a rounded notch  418 , visible in  FIG. 6   c , situated on the face of the bolt  425  intended to be placed opposite the passage opening  15 . 
         [0049]    The assembly of the implant  10  done using an attachment element  400  is particularly easy since a connecting rod  12 , like that previously described with the first and second embodiments of the attachment element ( 100 ,  200 ), is inserted between the branches of the U-shaped head  414 , as shown in  FIG. 6   a , then the bolt  425  is screwed on the head  414  to make the fins  31  cooperate with the stops  30  in order to retain the connecting rod  12 . Once the bolt  425  is positioned and retained by the fins  31  and the stops  30 , the first and second centering surface ( 18 ,  19 ) ensure the centering using the fins  31 . The latter parts act as spring-back means  16  owing to their flexibility, in addition to their fastening function of the bolt  425 . Thus, upon a relative movement of the connecting rod  12  in relation to the attachment element  400 , the sliding of the rounded boss  26  along the rounded notch  418  causes a movement of the bolt  425 . This movement of the bolt is done along an axis parallel to the branches of the “U” of the head  414  owing to an elastic deformation of the fins  31 , as shown in  FIG. 6   c . These elastic deformations of the fins  31  create a spring-back force opposing the movement of said bolt  425  and the connecting rod  12 , tending to return said connecting rod  12  by sliding of the first and second centering surfaces ( 18 ,  19 ) into a predefined position described in  FIGS. 6   a  and  6   b . In this predefined position, the fins  31  do not undergo any elastic deformation. 
         [0050]    The connecting rod  12  according to the invention, used in cooperation with an attachment element  100 ,  200 ,  300 ,  400  according to the invention, has, near one  32  of its ends, a second centering surface  19  such as a rounded boss  26 , described in  FIGS. 3   a ,  3   b ,  4   a ,  4   b ,  4   c ,  6   a ,  6   b  and  6   c , or a rounded notch  28  as shown in  FIGS. 5   a  and  5   b . The second centering surface  19  is not, however, limited to these shapes and can, for example, assume various shapes like those shown in  FIGS. 7   a  to  7   f . One skilled in the art will then know how to adapt the shape of the first centering surface to ensure adequate cooperation between the connecting rod and the attachment element. This results in the rounded boss  26  shown in  FIG. 7   d  and the rounded notch  28  of  FIG. 7   a . A boss can also have non-curved slopes such as, for example, the boss  33  of  FIG. 7   e . Likewise, a notch can have non-rounded slopes like those of the notch  34  shown in  FIG. 7   b.    
         [0051]    Moreover, the notch or the boss can be asymmetrical like the notch  35  shown in  FIG. 7   c , which has a wall  36  forming a stop. Such a notch  35  can be interesting to prevent the relative movement in a direction of the connecting rod  12  with the associated attachment element, owing to the wall  36  forming the stop: the wall  36  forming the stop prevents the movement of the attachment element towards the end  32  of said connecting rod  12 . 
         [0052]    Furthermore, the second centering surface  19  can also be formed by a ring  37  attached on the connecting rod  12  according to the invention as is the case of the connecting rod  12  shown in  FIG. 7   f.    
         [0053]    Of course, the embodiments mentioned above are in no way limiting and other details and improvements can be made to an attachment element  100 ,  200 ,  300 ,  400  or to a connecting rod  12  according to the invention, without going beyond the scope of the invention where other shapes of an attachment element or a connecting rod can be made: in particular, aside from the shapes detailed in the Figures, the first and second centering surfaces ( 18 ,  19 ) can include rotational centering elements, not shown, able to impart a rotational movement so as to return the connecting rod to a predefined position.