Patent Publication Number: US-2005125029-A1

Title: Anatomical interbody implant and gripper for same

Description:
TECHNICAL FIELD  
      The present invention relates to an intersomatic implant for insertion into the disk space defined between two adjacent vertebrae, in order to restore an appropriate height between the vertebrae and in order to allow bone fusion to take place between said adjacent vertebrae.  
      More precisely, the invention provides an intersomatic implant of the cervical type, for insertion into the disk space defined between two adjacent cervical vertebrae.  
     PRIOR ART  
      In the state of the art, it is known to insert an intersomatic implant into the disk space between defined between two adjacent cervical vertebrae. Numerous embodiments of such intersomatic implants are proposed in the prior art. For example, a known cervical intersomatic implant is in the form of a cage comprising two sagittal walls interconnected by a anterior transverse wall and by a posterior transverse wall. Between them, the walls define an open volume for receiving a bone-filler substance for encouraging bone fusion between the two vertebrae.  
      In general, it can be assumed that inserting an implant of the above-described type into the disk space between two adjacent vertebrae is liable to lead to the vertebrae being incorrectly positioned relative to each other. This means that it is not possible to obtain good bone reconstitution between the vertebrae concerned.  
      The invention thus seeks to remedy the above-specified drawbacks by proposing an intersomatic implant adapted to comply better with the anatomy of the spinal column.  
     SUMMARY OF THE INVENTION  
      To achieve such an object, the intersomatic implant is designed to be inserted into the disk space defined between two adjacent vertebrae, namely an overlying vertebra and an underlying vertebra, for the purpose of reestablishing the anatomic space between the vertebrae, the implant being in the form of a cage that is generally in the shape of a rectangular block having at least two sagittal walls substantially parallel to a sagittal plane and interconnected at least by an anterior transverse wall and by a posterior transverse wall extending substantially parallel to a frontal plane, the walls defining between them an open volume for bone filler and presenting rims extending on one surface to define a first transverse face and on the opposite surface to define a second transverse face.  
      According to the invention, the implant comprises: 
          a first transverse face presenting in the sagittal plane a convex profile congruent with the sagittal anatomic profile of an overlying vertebra; and     a second transverse face presenting in the frontal plane a convex profile congruent with the frontal anatomic profile of an overlying vertebra.        

      The invention also seeks to provide an instrument for manipulating such a cage, enabling the drawbacks of known manipulation instruments to be remedied. It is known to provide two holes in the anterior wall of a cage so as to enable two fingers presented by a manipulation instrument to be engaged therein. Unfortunately, while the instrument is manipulating the cage, there is a risk of the cage becoming separated from the instrument, and of it becoming impossible to withdraw the implant after it has been put into place.  
      Another object of the invention is thus to provide an instrument for manipulating a cage in the general sense, regardless of whether it is cervical and/or lumbar, and adapted to hold the implant safely and reliably while it is being put into place or repositioned.  
      To achieve such an object, the manipulation instrument of the invention is a forceps for an implant in the form of a cage generally in the shape of a rectangular block comprising at least two sagittal walls substantially parallel to a sagittal plane and interconnected at least by an anterior transverse wall and by a posterior transverse wall substantially parallel to a frontal plane, the cage being provided with two housings extending substantially facing each other in a frontal direction substantially perpendicularly to the sagittal plane of the cage, the forceps having two branches movable relative to each other and each provided with an insert-engaging jaw.  
      According to the invention, each jaw is provided with a radial stud extending in line with the other radial stud and suitable for being moved towards the other stud so as to be engaged in a respective housing formed in the implant.  
      Various other characteristics appear from the following description given with reference to the accompanying drawings which show embodiments and implementations of the invention as non-limiting examples. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of an embodiment of an implant in accordance with the invention.  
       FIG. 2  is a front view of an implant seen substantially along arrows f 2  of  FIG. 1 .  
       FIG. 3  is a sagittal view of an implant seen substantially along arrow f 3  of  FIG. 1 .  
       FIG. 4  is a plan view of a forceps for manipulating an implant in accordance with the invention.  
       FIGS. 5 and 6  are views on a larger scale respectively from above and from the side showing the implant-engaging jaws of the forceps shown in  FIG. 4 .  
       FIG. 7  is a perspective view showing an intersomatic implant supported by a manipulation forceps in accordance with the invention. 
    
    
     BEST METHOD OF IMPLEMENTING THE INVENTION  
      As can be seen more precisely in FIGS.  1  to  3 , an intersomatic implant in accordance with the invention is in the form of a cage  1  which is generally in the form of a rectangular block and is designed to be inserted in the disk space between two adjacent vertebrae, e.g. cervical vertebrae. The cage  1  has a first sagittal wall  2  and a second sagittal wall  3  extending substantially parallel to each other and to a “sagittal” or “antero-posterior” plane S. The sagittal walls  2  and  3  are interconnected by an “anterior” transverse wall  4  and by a “posterior” transverse wall  5  extending parallel to each other and to a frontal plane F extending perpendicularly to the sagittal plane S.  
      It should be observed that the cage  1  can have one or more intermediate or mid walls extending substantially parallel to the sagittal and/or transverse walls. Preferably, connecting fillets  6  are provided between the sagittal walls and the transverse walls firstly along their internal vertical faces and secondly along their external vertical faces so as to provide a cage  1  having rounded corners on its external and internal vertical faces. For example, the walls  2  to  5  present substantially the same thickness. Similarly, the height of the anterior transverse wall  4  is greater than the height of the posterior transverse wall  5  ( FIG. 3 ).  
      Internally, the cage  1  presents a volume  7  defined by the vertical inside faces of the walls  2  to  5  and designed to be filled with a bone-filler substance for prompting intersomatic fusion. In the example shown, this volume  7  opens out into a first transverse face  8  that is on top and into a second transverse face  9  that is at the bottom. The walls  2  to  5  present, on one surface, rims  10  defining the top transverse face  8 , and on the opposite surface, rims  10 ′ defining the bottom transverse face  9 .  
      The cage  1  has protuberances or projections  11  formed on the rims  10  and  10 ′ of the walls  2  to  5  so as to enable the cage to bite into the underlying and overlying vertebrae. In the preferred example shown, the protuberances  11  are constituted by ridges extending parallel to one another and to the frontal plane F. Naturally, the protuberances can be of different shapes and could be implemented, for example, in the form of individual spikes or by ridges forming chevrons. In general, it should be understood that the top and bottom transverse faces  8  and  9  correspond to the envelope containing the tips of the protuberances  11 .  
      According to a characteristic of the invention which is shown more clearly in  FIG. 3 , the top transverse face  8  has a convex profile C 8  in the sagittal plane S which is congruent with or complementary to the sagittal anatomic profile of an adjacent or overlying vertebra in the example shown. It should be understood that the rims  10  of the walls and more precisely the protuberances  11  defining said top transverse face  8  are arranged to be inscribed in an envelope whose section in the sagittal plane S is rounded or convex in shape.  
      In a preferred embodiment, the top transverse face  8  is defined in the frontal plane F by a straight or rectilinear profile C′ 8  ( FIG. 2 ). The rims  10  of the walls  2  to  5  defining the top transverse face  8  are preferably arranged to be connected to the outside faces of the walls  2  to  5  via connecting fillets  12 .  
      According to another characteristic of the invention which can be seen more clearly in  FIG. 2 , the bottom transverse face  9  presents a convex profile C 9  in the frontal plane F, which profile is congruent with or complementary to the frontal anatomic profile of an adjacent or underlying vertebra in the example shown. The rims  10 ′ of the walls  2  to  5 , and more precisely the protuberances  11  defining said transverse face  9  are arranged to be inscribed in an envelope whose section in the plane S is of rounded shape.  
      Furthermore, it should be observed that the bottom transverse face  9  presents a profile C′ 9  in the sagittal plane that is substantially straight.  
      Advantageously, the above-described cage  1  is adapted to receive at least one, and in the example shown two, radio-opaque markers  13  incorporated over at least a portion of the height of the cage in the anterior and posterior transverse walls  4  and  5 .  
      The above-described cage  1  is particularly adapted to enable it to be manipulated by manipulation forceps  15  of the kind shown in FIGS.  4  to  7 , the forceps having two branches  16  each provided at one end with an insert-engaging jaw  17 .  
      The cage  1  has two housings  20  extending in line with each other and each adapted to receive a radial stud  21  formed on each of the jaws  17  of the forceps. In the example shown, the housings  20  are formed in the sagittal walls  2  and  3 , being in alignment and extending in a frontal direction perpendicular to the sagittal plane S. The housings  20  are preferably located close to the anterior transverse wall  4 . In the example shown, each housing  20  opens out into the two opposite vertical faces of the walls  2  and  3 . Naturally, the housings  20  could be provided in the anterior transverse wall  4  extending in a frontal direction perpendicular to the sagittal plane S. In this embodiment, it can be observed that the two housings  20  can be directly in communication with each other so as to constitute a single bore. The transverse right section of each housing  20  is adapted to receive a radial stud  21 , and, for example, is substantially elliptical in the example shown.  
      In a preferred embodiment, the cage  1  includes antirotation means  23  for co-operating with complementary means  24  provided on the jaws  17  of the manipulation forceps so as to prevent relative rotation between the cage  1  and the forceps  15  when the forceps are engaging the insert. In the example shown, these antirotation means  23  are constituted by a groove formed in each sagittal wall  2 ,  3  to open out into a corresponding housing  20  and extending therefrom to the outside face of the anterior transverse walls  4 . As shown more particularly in  FIG. 3 , each groove  23  is substantially rectangular in right cross-section.  
      As can be seen more clearly in FIGS.  4  to  6 , each insert-engaging jaw  17  is arranged to present complementary antirotation means  24  in the form of an arm or a bar having a free end carrying a radial stud  21  lying substantially in alignment with the other radial stud. Each arm  24  is of cross-section complementary to that of the groove  23  and is designed to be engaged at least in part in the groove  23  formed in a sagittal wall when each of the studs  21  is engaged in a complementary housing  20 . According to a preferred characteristic of the invention, when the studs  21  are engaged in the housings  20  ( FIG. 7 ), the outside faces of the jaws  17 , i.e. the arms  24 , extend substantially in line with the outside faces of the sagittal walls  2  and  3  so as to limit the approach path required for installing the cage.  
      Engaging the studs  21  in the housings  20  ensures that the cage is held securely and prevented from moving in translation, and the co-operation between the arms  24  and the grooves  23  prevents the cage from moving in rotation, in particular in a frontal direction. This ensures that the cage is completely prevented from moving relative to the jaws  17 . It should be observed that the antirotation means  23 ,  24  could be implemented in a different manner. For example, the housings  20  could be prismatic in shape for co-operating with studs of complementary shape.  
      According to a preferred characteristic, each jaw  17  is provided with a stop abutment  27  for coming into contact with the external face of the anterior transverse wall  4  of the cage when the studs  21  are engaged in the housings  20  so as to transmit forces that are exerted axially on the forceps. As can be seen more precisely in  FIG. 4  to  6 , each stop abutment  27  extends radially substantially parallel to the adjacent stud  21  which is connected to the stop abutment  27  via the locking arm  24 . Each stop abutment  27  is preferably arranged on the jaw  17  so as to come into contact with the external face of the anterior wall of the cage substantially in line with the sagittal walls  2  and  3 . Such a disposition provides the advantage of enabling pressure forces exerted on the end  30  of the forceps where the branches  16  join to be transmitted in such a manner as to facilitate insertion of the cage between the vertebrae. The branches  16  of the forceps are preferably made so as to be resilient and urge the jaws  17  permanently towards each other. In this respect, moving the branches  16  towards each other causes the jaws  17  to move apart because the branches cross over, whereas releasing the branches  16  automatically causes the jaws  17  to move towards each other.  
     SUSCEPTIBILITY OF INDUSTRIAL APPLICATION  
      The above-described cage  1  is particularly adapted to complying with the disk space defined between two vertebrae, e.g. cervical vertebrae. Complying with the anatomy of the intervertebral disk that is replaced by the cage  1  serves to encourage bone fusion between the vertebrae and to restore the static configuration of the spine. Furthermore, the cage  1  is made particularly simple to put into place by using the manipulation forceps  15  of the invention. Thus, from an anterior approach path to the cervical spine, resection is performed on the osteophytes, the disk is removed, and then the plane faces of the vertebrae are revivified. Thereafter, a cage  1  can be taken hold of by the forceps  15  by acting on the branches  16  to move the jaws  17  apart, then positioning the studs  21  in the housings  20 , and then by acting on the branches so that the jaws  17  move towards each other, causing the studs  21  to penetrate into the housings  20  and causing the arms  24  to penetrate into the grooves  23 . It should be observed that the grooves  23  are capable of providing a guidance function for the studs  21  which are thus brought up to the housings for insertion purposes. In this position, the cage  1  is held completely securely relative to the forceps by the studs  21  being engaged in the housings  20  and by the arms  24  being engaged in the grooves  23 , and also by the abutments  27  coming into contact against the anterior transverse wall  4 . The cage  1  can be inserted into the disk space, with it being possible to apply thrust force to the end  30  of the forceps, should that be necessary. Pressing the branches  16  together to move the jaws  17  apart enables the studs  21  to be disengaged from the housings  20  so as to allow the forceps to be withdrawn.  
      The invention is not limited to the examples described and shown since numerous modifications can be made thereto without going beyond the ambit of the invention.