Patent Publication Number: US-2017367841-A1

Title: Spinal Cages and Instruments for Inserting Same

Description:
The invention relates to different embodiments of spinal cages having associated insertion instruments. A spinal cage shall be construed to mean a spinal implant that may be used as a spinal disc replacement for fusing vertebrae. 
     Spinal cages for fusing vertebrae are known. Their geometry is adapted to the anatomy of the human vertebra, they are disposed between two vertebrae, and they replace all or part of the disc. 
     Typically, due solely to their mechanical properties, in a first phase of their disposition in the human body they hold the vertebrae at a distance and thus in an anatomically correct position. In a second phase they promote fusing of, and thus the growth of, the two vertebrae surrounding them. 
     Known components for fusing vertebrae are based on metal materials such as e.g. tantalum or titanium, plastics such as e.g. highly crosslinked PE materials (polyethylene) or PEEK (polyether ether ketone), or silicon nitride. 
     The underlying object of the invention is to improve a spinal implant according to the preamble to claim  1  such that while implanted no wear and no abrasion occur and said implant in-grows into the tissue better. 
     According to the invention, this object is attained using the features of claim  1 . 
     Since the spinal implant comprises a ceramic material and carries a porous ceramic foam, at least in sub-sections, when implanted there is no wear and no abrasion and said implant in-grows into the tissue better. 
     The engaging elements are preferably teeth, grooves, or edges so that the implant anchors better. 
     Arranged on the anterior wall is at least one longitudinal hole that connects the inner lateral wall to the outer lateral wall. This longitudinal hole is the insertion opening for an insertion instrument. It is also possible for two longitudinal holes, spaced apart from one another, to be arranged on the anterior wall. 
     The two longitudinal holes are preferably arranged the same distance from the depth axis and are arranged on either side of said depth axis. This facilitates insertion with an insertion instrument, i.e., there is no jamming. 
     The two longitudinal holes preferably converge, i.e. they are arranged at an acute angle to the depth axis. The insertion instrument can grip the implant better because of this. 
     In one preferred embodiment, the upper end plate and the lower end plate run parallel to one another or the upper end plate and the lower end plate are at an angle to the center plane and the end plates drop continuously from the anterior wall to the posterior wall with respect to the center plane. Because of this the implant is better adapted to the natural shape of the vertebrae. 
     In one embodiment, the upper end plate and the lower end plate are arranged at an angle between 0° and 10°, preferably 2° to 5°, with respect to the center plane. 
     In one embodiment, the upper end plate runs at an angle to the center plane that is half as big as the angle between the lower end plate and the center plane. This facilitates better anchoring between the vertebrae. 
     The upper end plate preferably runs at an angle of 4° to the center plane, and the lower end plate at an angle of 2° to the center plane. Because of this the implant is better adapted to the natural shape of the vertebrae. 
     In a spinal implant having a longitudinal axis, a depth axis, and a width axis, wherein the depth axis and the width axis intersect the longitudinal axis, the spinal implant is preferably embodied essentially in a rectangle from the anterior wall to the width axis and from the width axis to the posterior wall the two lateral walls turn from the width axis at an angle between 60° and 70°. 
     Preferably present on the spinal implant are indentations that are filled with the ceramic foam and/or the ceramic foam is applied directly to the surfaces of the spinal implant. The indentations form a receiving space for the ceramic foam. 
     Preferably an L-shaped indentation that reaches to the anterior wall is disposed on each of the two longitudinal walls. These indentations are also contact points for the insertion instrument. 
     In one embodiment, the indentations are arranged on the upper end plate and on the lower end plate, and engaging elements, preferably edges, are disposed between the indentations. Due to this, both indentations and edges are arranged. The edges facilitate anchoring immediately following implantation until the implant is in-grown due to the ceramic foam. 
     In one embodiment, the upper end plate is arched. 
    
    
       FIGS. 1 a  and 1 b    depict a first embodiment of an inventive spinal cage  1 . This spinal cage  1  is embodied in a trapezoidal shape with a planar upper end plate  2  and a planar lower end plate  3  that are connected by lateral walls  4 . Disposed adjacent to the outer edge  5  of the two end plates  2 ,  3  are teeth  6  that project from the end plates  2 ,  3  and facilitate better anchoring with the human vertebrae. These teeth  6  may also be arranged at different sites on the end plate  2 ,  3  and with a different quantity of teeth. Other structures, such as e.g. grooves or edges, may also be used instead of the teeth  6 . 
     The lateral walls  4  are divided into an anterior wall  4   a,  posterior wall  4   b,  and two longitudinal walls  4   c.  A longitudinal hole  7  is disposed in the center of the anterior wall  4   a.  This longitudinal hole  7  is provided for the insertion of an explantation instrument, which shall be described later. 
     An L-shaped indentation  8  for engaging with an insertion instrument, which shall be described later, is disposed on each of the two longitudinal walls  4   c.  The indentation  8  leads to the anterior wall  4   a,  so that the insertion instrument does not project out of the indentation  8  when inserted. 
       FIG. 1 c    depicts the described spinal cage  1  from above. The depth axis  10  and the width axis  11  lead through the longitudinal axis  9 . The spinal cage  1  is essentially embodied in a rectangular shape from the anterior wall  4   a  to the width axis  11 . From the width axis  11  to the posterior wall  4   b,  the two lateral walls  4   c  turn from the width axis  11  at an angle between 60° and 70°. Optional chamfers  12  are disposed on the edge of the end plates  2 ,  3  from the width axis  11  to the posterior wall  4   b.  The teeth are not shown in this figure or in the following  FIG. 1   d.    
       FIG. 4 d    is a schematic depiction of a longitudinal side  4   c,  with no indentation. The upper end plate  2  runs at an angle of 4° to the center plane  13  and the lower end plate  3  runs at an angle of 2° to the center plane  13 . Angles between 0° and 10°, preferably between 2° to 5°, are possible. The end plates  2 ,  3  thus drop continuously from the anterior wall  4   a  to the posterior wall  4   b  with respect to the center plane  13 . 
     The trapezoidal shape is consistent with anatomy (uncinate processes). The total angle is divided asymmetrically (4° and 2°, in this case), but may also be divided symmetrically (e.g., 3° and 3°). This preferably applies for planar end plates  2 ,  3 . 
       FIG. 2  depicts a variant of an inventive spinal cage  1  having a curved upper end plate  2 , depicted schematically. This is an adaptation to the natural curvature of the lower vertebral end plate. 
       FIG. 3 a    depicts a segment from a lateral wall  4 . Present on it is an indentation  14  that is filled with a ceramic foam  15 . In this way, a porous surface that effects better in-growth of the bone is obtained. The indentation  14  and thus the ceramic foam  15  are preferably arranged circumferentially on the lateral walls  4 . 
       FIG. 3 b    depicts a segment from a lateral wall  4 . No indentation is present thereon, but instead the ceramic foam  15  is applied directly to the planar surface. In this way, as well, a porous surface is obtained that effects better in-growth of the bone. The ceramic foam  15  is preferably arranged circumferentially on the lateral walls  4 . 
     Additional spinal cages and insertion instruments shall be described in the following. 
       FIG. 4  depicts the spinal cage  1  according to  FIG. 1  and an associated insertion instrument  16 . The insertion instrument  16  has fork tines  17  that engage in the indentations  8  (see  FIG. 1 ) and in the lateral channels. The fork tines are stressed, so that a non-positive connection is created using the channels or V-channels (V-belt principle). Because of this the insertion instrument  16  does not catch when it is retracted. High leveraging forces may be transmitted using the interface, which is disposed far to the outside. The limited tensile forces are a drawback. An adapted insertion instrument  16  is required for each cage width. The view of the spinal cage  1  is also limited. The insertion instrument  16  covers the anterior wall  4   a  of the spinal cage  1 . 
       FIGS. 5 a , 5 b , 5 c , 5 d , 5 d    depict another inventive spinal cage  1 .  FIGS. 5 a , 5 b    depict the spinal cage  1  in two perspective elevations.  FIG. 5 c    is a view from the front, i.e., onto the anterior wall  4   a,  and  FIG. 5 d    is a section along the center plane  13 .  FIG. 5 e    depicts this spinal cage  1  together with the appropriate insertion instrument  19 . 
     In contrast to the spinal cage  1  from  FIG. 1 , the spinal cage  1  does not have any lateral indentations  8 , nor does it have a center longitudinal hole  7 . Otherwise, except from two oval longitudinal holes  18 , it is identical to the spinal cage  1  from  FIG. 1 . 
     These longitudinal holes  18  are disposed, spaced apart from one another, in the anterior wall  4   a.  An important feature is that these two longitudinal holes  18  converge, i.e., they are arranged at an acute angle to the depth axis  10 . The depth axis  10  and the width axis  11  intersect the longitudinal axis  9 . 
       FIG. 5 e    depicts this spinal cage  1  together with the gripper or the tong-like insertion instrument  19 . The insertion instrument  19  has two spreading arms  20  that engage in the longitudinal holes  18  and are then spread. The two spreading arms  20  are preferably adapted to the longitudinal holes  18  and also converge like them. This creates a positive fit. The longitudinal hole  18  and spreading arm  20  interface is independent of the size of the spinal cage  1 . Only the limited contact surface between the spreading arms  20  and the longitudinal hole  18  is disadvantageous. The spinal cage  1  from  FIG. 5 e    is only shown schematically. 
       FIG. 6  depicts another embodiment of the inventive spinal cage  1 . This spinal cage  1  is distinguished from the spinal cages  1  described in the foregoing by the shape of the longitudinal holes  18  and a recess arranged between the longitudinal holes. 
     In contrast to the spinal cage  1  in  FIG. 1 , the spinal cage  1  does not have any lateral indentations  8 , nor does it have any center longitudinal hole  7 . In this embodiment, it is important that the longitudinal holes are embodied in a V shape. This has the advantage that there is a larger support surface for the insertion instrument and thus better force transmission is possible. A recess  21  like an arrow may optionally be provided between the longitudinal holes  18 . The arrow or the recess  21  indicates to the surgeon the direction of insertion and also acts as an engaging element for an insertion instrument. 
       FIG. 7  depicts another embodiment of an inventive spinal cage  1 .  FIG. 7 a    is a perspective elevation of the spinal cage  1 . It is easy to see that this spinal cage  1  does not have any lateral indentations  8 , nor does it have a center longitudinal hole  7 . What is important in this embodiment is that the longitudinal holes  18  are embodied in a trapezoidal shape (asymmetrically). Because of this, the wall of the longitudinal hole  18  that faces the lower end plate  3  is longer, i.e., has an even larger support surface for the tool. A clear orientation of the spinal cage  1  on the instrument is attained due to the recess  21 . In addition, due to the embodiment of the longitudinal hole  18  as a trapezoid, it is not possible to insert the insertion instrument  18  incorrectly. 
       FIG. 7 b    depicts the spinal cage  1  from the side. It may be seen that the upper end plate  2  is arched. On the other hand, the lower end plate  3  is embodied flat. As  FIG. 7 b    depicts, teeth  6  are arranged on the end plates  2  here, as well. 
       FIG. 7 c    depicts the spinal cage  1  from the anterior side with the trapezoidal longitudinal holes  18  and the recess  21 .  FIG. 7 d    depicts the upper end plate  2  with the teeth  6 .  FIG. 7 e    depicts the spinal cage  1  from the posterior side. 
       FIG. 8  depicts the spinal cage  1  according to  FIG. 1  together with an explantation instrument  22 . This explantation instrument  22  is provided with a hammer head  23  and is inserted into the longitudinal hole  7  or the longitudinal holes  18  and locked by rotating 90°. Then it is simple to explant the spinal cage  1 .  FIG. 8 a    depicts the explantation instrument  22  inserted in the spinal cage  1  and not yet locked.  FIG. 8 b    depicts the explantation instrument  22  inserted into the spinal cage  1  and locked. 
       FIG. 9 a    depicts a spinal cage  1  having a circumferential groove  24  added to the upper end plate  2 . As also described for  FIG. 3 , this groove  24  may be filled with a ceramic foam (not depicted in  FIG. 9 ). This filling would look like that in  FIG. 3 .  FIG. 9 b    depicts the spinal cage  1  from the anterior side with the longitudinal holes  18  and the recess  21  and  FIG. 9 c    depicts the spinal cage  1  from the posterior side. 
       FIGS. 10 a , 10 b , and 10 c    depict an inventive spinal cage  1 . This spinal cage  1  is embodied in a trapezoidal shape having an upper end plate  2  and a lower end plate  3  that are connected by lateral walls  4 . Disposed adjacent to the outer edge  5  of both end plates  2 ,  3  are teeth  6  that project from the end plates  2 ,  3  and facilitate better anchoring with the human vertebrae. These teeth  6  may also be arranged at different sites on the end plates  2 ,  3  and with a different quantity of teeth. Other structures, such as e.g. grooves or edges, may also be used instead of the teeth  6 . 
       FIG. 10 a    is a perspective elevation of the spinal cage  1 ,  FIG. 10 b    depicts a view onto one side  4 , and  FIG. 10 c    depicts a view from above onto the upper end plate  2 . The surfaces between the teeth  6  are provided with grooves  26  that may be filled with a ceramic foam (not shown in  FIG. 10 ). 
     The lateral walls  4  are also provided with grooves  26  that may be filled with a ceramic foam (not shown in  FIG. 10 ).