Abstract:
The invention relates to a device for implanting in a human or animal vertebral column, said device comprising a base carrier ( 10 ) that can be fixed to a first vertebral body, an upper carrier ( 14 ) that can be fixed to a second vertebral body, and a spacer element fixed between the base carrier and the upper carrier. The base carrier ( 10 ) and/or the upper carrier ( 14 ) are provided with a cavity ( 18, 24 ) comprising undercuts, for receiving the spacer element in a positively locked manner. The aim of the invention is to economically create one such device that ensures complete freedom of movement of the vertebral column. To this end, the spacer element is embodied as metallic bellows ( 12 ).

Description:
[0001]    DE 203 07 876.4 dated May 19, 2003 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a device for implantation into a human or animal spine according to the preamble of claim  1 . The human spine is formed from various vertebral bodies that are separated from each other by an intervertebral disc (simply called disc in common parlance) acting as a cushion therebetween. These intervertebral discs are made up of a fibrous outer casing that contains a gelatinous liquid. The intervertebral discs are subjected to high forces that may vary from about 780 N to no less than about 2200 N. In particular with age, these high stress forces often cause wear on the intervertebral discs. A once destroyed intervertebral disc cannot heal so that damaged intervertebral discs are usually removed and the adjacent vertebral bodies fused together. The disadvantage thereof is that in this region the spine will be stiff. 
         [0004]    2. Description of the Prior Art 
         [0005]    DE 38 73 566 T2 suggests to separate adjacent vertebral bodies by an implant comprising a spring for keeping the spine mobile in this region. This implant consists of a base carrier and a top carrier that are fixated each on corresponding sides of the vertebral bodies and of an elastic element consisting of two helical springs that is retained on the base carrier and the top carrier. Concurrently, the base carrier and the top carrier are connected together through a common axis in such a manner that both are pivotal about said axis. With this implant, adjacent vertebral bodies remain mobile in the pivoting direction so that a patient provided with such an implant is again capable of stooping. Unfortunately, the rigid pivot axis makes a movement to the right or to the left impossible so that the freedom of movement of a patient provided with such an implant is restricted. 
         [0006]    The implant according to DE 38 73 566 T2 consists of a plurality of individual parts which makes it very costly to produce. Moreover, the many individual parts involve the risk of tissue ingrowth therein, which results in pain or other disabilities. 
         [0007]    From DE 43 15 757 C1 an implant is known that comprises a resilient intermediate element. This intermediate element is composed of a number of substantially cylindrically configured discs that are elastic in the axial direction with the outer wall of the disc being configured to be either concave or convex in order to thus resiliently absorb the forces generated in the axial direction. However, the connections between adjacent discs are hereby subjected to very high loads that may cause damages. Moreover, the implants are made from one piece so that a complete implant must be kept in store for each application case, which results in considerable costs. 
         [0008]    An implant is known from U.S. Pat. No. 5,370,697 that is built in a modular fashion. This implant is composed of an upper and a lower element with a non-elastic tube being insertable therein between to act as a separator in order to span the missing disc or the missing vertebral bone. The elasticity of the spine gets lost in the process. 
       BRIEF SUMMARY OF THE INVENTION 
       [0009]    In view thereof, it is the object of the present invention to provide a device for implantation in a human or animal spine that ensures at low manufacturing cost complete freedom of movement of the spine. 
         [0010]    The technical solution to this object proposed by the invention is a device having the features of claim  1 . Advantageous developed implementations of this device are recited in the subordinate claims. 
         [0011]    A device for implantation in a human or animal spine configured according to this technical teaching has the advantage that the elastic element, which is configured in the form of an undulated bellows, is pivotal in any direction while exhibiting sufficient stiffness to obviate the need for further connection between the base carrier and the top carrier. The undulated bellows further has the advantage that bending may occur in the desired direction without high forces acting thereby onto the base carrier and/or the top carrier. AS a result, the load on the screws fixing the base carrier and/or the top carrier is kept low. 
         [0012]    In a preferred embodiment, undercuts, more specifically in the form of a dovetail joint, are provided in the base carrier and/or in the top carrier on the side turned toward the undulated bellows for interlockingly receiving the parts of the undulated bellows. It is thereby readily possible to for example first introduce the undulated bellows into the base carrier in such a manner that the last undulation is caused to fit the receiving portion. The top carrier may then also be pulled in such a manner over the thus fixated undulated bellows that the crest of the uppermost undulation of the undulated bellows engages the receiving portion. The great advantage of this system is that the base carrier is first screwed to the vertebral body by means of pedicle screws for example before the elastic element, which is configured to be an undulated bellows, is introduced into the receiving portion and before the top carrier is pulled over the undulated bellows. As a result, the device is readily implanted during spine surgery. 
         [0013]    It has thereby been found advantageous to limit the undercuts on one side by an abutment in order to prevent the undulated bellows from inadvertently sliding off at least on this side and above all in order for the surgeon to know how far he can push the undulated bellows into the base or top part. This permits to achieve accurate positioning of the undulated bellows with respect to the base and/or top part. 
         [0014]    In an alternative, preferred embodiment, the base carrier and/or top carrier is connected to the undulated bellows through a bayonet connection. This makes it possible to readily connect the undulated bellows to the base and/or top carrier, even during surgery. 
         [0015]    In another preferred embodiment, a vertically protruding sharp edge is formed on one side of the top carrier that is turned toward the vertebral body. The implanted device is then brought into its final position by this edge that carves into the vertebral body disposed above the top carrier, thus being secured from laterally sliding off. 
         [0016]    In another preferred embodiment, some vertically protruding spikes are attached to the one side of the top carrier and of the base carrier that is turned toward the vertebral body, said spikes penetrating into the respective ones of the vertebral bodies and preventing the device from rotating out of position. 
         [0017]    In still another preferred developed implementation, the top carrier is configured to have a key-shaped cross section in order for this cross section to already accommodate the curvature of the spine so that the undulated bellows may have a substantially rectilinear orientation. 
         [0018]    In still another preferred embodiment, the top carrier is configured to be rectangular in cross section with some undulation troughs and/or undulation crests being configured in the shape of a key in order to achieve, in terms of construction, a curved undulation crest. 
         [0019]    Further advantages of the device of the invention will become apparent from the appended drawing and from the following description of embodiments thereof. Likewise, the invention lies in each and every novel feature or combination of features mentioned above or described herein after. The embodiments discussed herein are merely exemplary in nature and are not intended to limit the scope of the invention in any manner. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0020]    In the drawing: 
           [0021]      FIG. 1  is an exploded side view of a human spine together with a first embodiment of the device of the invention; 
           [0022]      FIG. 2  is an exploded illustration of the device according to  FIG. 1 ; 
           [0023]      FIG. 3  is a front view of the device of  FIG. 1 ; 
           [0024]      FIG. 4  is an exploded side view of a human spine together with a second embodiment of the device of the invention; 
           [0025]      FIG. 5  is a side view of the second embodiment of a device of the invention according to  FIG. 4 ; 
           [0026]      FIG. 6  is a front view of the device of  FIG. 4 ; 
           [0027]      FIG. 7  is a side view of a third embodiment of a device of the invention; 
           [0028]      FIG. 8  is a front view of the device of  FIG. 7 ; 
           [0029]      FIG. 9  is a side view of a fourth embodiment of a device of the invention; 
           [0030]      FIG. 10  is a front view of the device of  FIG. 9 ; 
           [0031]      FIG. 11  is a side view of a fifth embodiment of a device of the invention; 
           [0032]      FIG. 12  is a front view of the device of  FIG. 11 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    The first embodiment of a device of the invention suitable for implantation into a human or animal spine as illustrated in the  FIGS. 1 through 3  includes a base carrier  10  made of a rigid material, an elastic element configured to be an undulated bellows  12  and a top carrier  14 . As best shown in  FIG. 2 , there are provided on the base carrier openings  16  for receiving a bone screw by means of which the base carrier  10  is fastened to the vertebral body. The bone screw is manufactured from a biomaterial that is slowly resorbed over time by the body, with the top carrier  14  and the base carrier  10  having become firmly secured to the vertebral body in the meantime. 
         [0034]    The metallic undulated bellows  12  comprises an undulated outer contour, with discrete undulation troughs  21  and crests  22  annularly surrounding the undulated bellows  12 . This undulated bellows  12  resembles for example an accordion hose. The base carrier  10  further possesses, on its side turned away from the vertebral body, a receiving portion  18  for fastening the undulated bellows  12  to the base carrier  10 . Said receiving portion  18  has a cross section conforming to the contour of an undulation trough  21  and of an undulation crest  22  of the undulated bellows  12  and has two crosspieces  20  that project into the receiving portion  18 . The last undulation crest  22  of the undulated bellows  12  is laterally inserted into the receiving portion  18  where it is positively retained on the base carrier  10  by the crosspieces  20 . On the side of the top carrier  14  that is turned toward the undulated bellows  12 , there is provided a second receiving portion  24  that is configured analogous to the first receiving portion  18 . Again, the undulated bellows  12  can be inserted into the receiving portion  24  by its outer undulation crest  22  in order to be positively retained therein. 
         [0035]    The top carrier  14  is configured to have a key-shaped cross section and has a perpendicularly protruding sharp edge  26  in its center. The sharp edge  26  is oriented normal to the longitudinal direction of the receiving portion  24 . The top carrier  14  and the base carrier  10  are provided with a commercially available coating in order to provide for a quick and good bond between these and the vertebral bone. 
         [0036]    It is understood that the device of the invention is manufactured in various sizes. The size of the top carrier  14  and/or of the base carrier  10  varies so that a specimen of appropriate dimensions is available for each vertebra. The length and the elasticity of the undulated bellows  12  also vary. Only the diameter of the undulated bellows  12  and the corresponding receiving portions  18 ,  24  remain the same in all the devices so that every base carrier  10  may be combined with every undulated bellows  12 . 
         [0037]    The second embodiment of the device of the invention, which is illustrated in the  FIGS. 4 through 6 , is substantially identical with the first embodiment illustrated in the  FIGS. 1 through 3 , and merely differs therefrom by the fact that in this second embodiment the undulated bellows  27  implemented as an accordion hose is configured to be slightly curved and that the top carrier  28  is not configured to be key-shaped but rectangular in cross section. The undulation troughs  29  vary in width in function of the curvature whereas the undulations  22  remain unchanged. 
         [0038]    As a complement to the first embodiment, multiple spikes  32  are formed in this second embodiment on the sides of the top carrier  28  and of the base carrier  30  that are turned toward the vertebral bones, said spikes extending into the respective vertebral bones and preventing the device from rotating out of place. Like the bone screws, said spikes  32  are made from a resorbing biomaterial. 
         [0039]    The third embodiment illustrated in the  FIGS. 7 and 8  differs from the second embodiment illustrated in the  FIGS. 4 through 6  by the fact that in this case the curvature of the undulated bellows  34  is not compensated for by the undulation troughs, but by the undulations  36 . Accordingly, the undulation  36  is implemented to be narrower on the inner side of the curvature than on the outer side of the same. 
         [0040]    The device suitable for implantation in a human or animal spine is utilized whenever an intervertebral disc between two vertebral bodies cannot be repaired and must be removed. In some cases, one or more adjacent vertebral bodies are also weak and need to be completely or partially removed as well. They will then be replaced by the device of the invention. It has been found advantageous to insert the device of the invention in the lumbar spine, in the intervertebral space between the fourth and the second lumbar vertebra, as a stiffened spine is most problematic there. 
         [0041]    To implant the device of the invention, the operating surgeon first fastens the base carrier  10  to the lower vertebral body using for this purpose bone screws that have not been illustrated herein and then laterally inserts the undulated bellows  12  by its last undulation crest  22  into the receiving portion  18 . Then, the top carrier  14  is pulled over the uppermost undulation crest  22  of the undulated bellows  12  and the undulated bellows  12  is bent to allow access. After the device has been assembled in this way, the surgeon pushes the undulated bellows  12  into the desired position with the undulated bellows  12  constituting a connection between the lower portion of the spine and the upper portion of the spine. The sharp edge  26  of the top carrier  14  is thereby brought close to the vertebral body located thereabove so that the sharp edge  26  penetrates into the same. For the rest, the top carrier  14  is fixated using most common methods. 
         [0042]    Implanted in this way, the top carrier  14  and the base carrier  10  grow onto the respective vertebral bone, assisted therein by the coating. At the same time, the body resorbs the bone screws made from biomaterial. 
         [0043]    It is understood that the operating surgeon will insert an undulated bellows  12  having the length and elasticity suited for each specific case. 
         [0044]    As shown in  FIG. 4 , the device of the invention, if dimensioned accordingly, can also be implanted into the cervical spine in the manner described herein above. 
         [0045]    In the fourth embodiment illustrated in the  FIGS. 9 and 10 , an abutment  42  against which the uppermost undulation  44  comes to rest is formed in the receiving portion  24  provided on the top carrier  40 . As a result, the undulated bellows  46  can be accurately positioned and mounting is facilitated since the surgeon is now capable of inserting the undulated bellows  46  into the top carrier  40  or into the base carrier  48  without having to care for other details. The abutment  42  is thereby implemented as a side wall of the top carrier  40  and possesses a receiving portion  24  the contour of which is configured to correspond to the contour of the undulation  44 . 
         [0046]    In a receiving portion  18  provided on the base part  48 , there is also implemented an abutment  42  that corresponds to the abutment  42  of the top carrier  40 . The abutment  42  of the base part  48  is however disposed exactly opposite the abutment of the top carrier  40  so that the two abutments  42  are virtually confronting each other. 
         [0047]    In the fifth embodiment illustrated in the  FIGS. 11 and 12 , two radially protruding pins  56 ,  58  are formed on a respective one of the uppermost and lowermost undulations  52 , of the undulated bellows  50 , said pins being insertable into corresponding recesses  60 ,  62  provided in the top carrier  64  and in the base carrier  66  respectively. The pins  56 ,  58  cooperate with the recesses  60 ,  62  to form a bayonet connection. This bayonet connection allows for fast and easy insertion of the undulated bellows  50  into the top carrier  64  or into the base carrier  66 , with the pins  56 ,  58  being inserted into the recesses  60 ,  62 . By pivoting the elastic element  50 , the pins  56 ,  58  are caused to enter deep into the L-shaped recess  60 ,  62  where they get jammed since the recesses are configured to have a conical taper. By causing the bayonet socket to get jammed in the conical taper of the recesses  60 ,  62 , the undulated bellows  50  is well locked in the top carrier  64  and/or in the base carrier  66  so that the connection is prevented from loosening later. 
       LISTING OF NUMERALS 
       [0000]    
       
         
           
               10  base carrier 
               12  undulated bellows 
               14  top carrier 
               16  opening 
               18  receiving portion 
               20  crosspiece 
               21  undulation trough 
               22  undulation crest 
               24  receiving portion 
               26  sharp edge 
               27  undulated bellows 
               28  top carrier 
               29  undulation trough 
               30  base carrier 
               32  spike 
               34 ,  36  undulated bellows 
               40  top carrier 
               42  abutment 
               44  undulation 
               46  undulated bellows 
               48  base carrier 
               50  undulated bellows 
               52 ,  54  undulation 
               56 ,  58  pins 
               60 ,  62  recess 
               64  top carrier 
               66  base carrier