as will be apparent from the drawings , in particular , from fig1 a , 1 b and 4 , an intervertebral disc 3 is arranged between two vertebrae 1 , 2 . the intervertebral disc 3 consists of the central nucleus 4 and the annulus fibrosus 5 surrounding it . the upper vertebra 1 is omitted in fig4 for the sake of clarity . it shall , however , be understood that this upper vertebra 1 rests with its lower end plate 6 in a surface - to - surface manner in the same way as the lower vertebra 2 with its upper end plate 7 against the intervertebral disc 3 . fig4 shows schematically how through an opening 8 in the annulus fibrosus , for example , in the form of a tear , nucleus material 9 leaks out from the nucleus 4 . this leaking material can bear on adjacent nerve roots and cause pain . to repair this injury , the nucleus material 9 leaking from the opening 8 is removed in a surgical operation . this may be carried out with , for example , a forceps - like instrument 10 with which the jelly - like nucleus material 9 is cut off and the opening 8 may also be enlarged and its edges smoothed ( fig5 ). the thus removed nucleus material 9 may be used for growing a culture of the patient &# 39 ; s own body cells . in this way , it is possible to produce , for example , within two weeks a cell culture which may then be used in the manner described hereinbelow . the opening 8 must be closed in a further surgical step . for this purpose , a test implant 11 is first inserted into the opening 8 . the test implant 11 consists , for example , of a biocompatible metal and is selected in relation to the size of the opening 8 such that upon introducing the test implant 11 into the opening 8 , the latter is not unnecessarily enlarged . the test implant 11 may have , for example , the shape of a relatively narrow rectangular parallelepiped . the test implant 11 is connectable ( fig6 ) by a rod 12 to a handle , not shown in the drawings , and has projections 13 at the sides , which delimit the penetration depth into the opening 8 . on its upper face and on its lower face , the test implant 11 has a central groove 14 extending parallel to the rod 12 . the groove 14 forms a guide groove for a chisel 15 . this chisel 15 is held at the end of a tubular shaft 16 , which after removal of the handle from the rod 12 , can be pushed over the rod 12 ( fig7 ). the chisel 15 is guided in the groove 14 and protrudes from it with a cutting edge 17 . when the chisel 15 is advanced along the rod 12 , it cuts with its cutting edge 17 a groove 18 in the adjacent end plate 6 of the vertebra 1 . this groove then extends parallel to the groove 14 in the test implant 11 . this procedure may be carried out in the same way at the lower face of the test implant 11 . in this way , a corresponding groove 19 is made there in the end plate 7 of the vertebra 2 . after removal of the test implant 11 , an implant 20 may be inserted in the opening 8 in order to close it . in the embodiment shown in fig8 , the implant 20 has the shape of a rectangular parallelepiped which carries webs or ribs 21 , 22 extending at the center of its upper face and its lower face and running parallel to the edges of the implant 20 . the implant 20 is pushed into the opening 8 using a suitable insertion instrument 23 which releasably grips the implant 20 . the direction of advance extends parallel to the longitudinal direction of the ribs 21 , 22 which enter the grooves 18 and 19 , respectively , during the insertion . once the implant 20 has been pushed fully into the opening 8 , the insertion instrument may be released and removed . as will be apparent from the illustration in fig9 , the implant 20 now closes the opening 8 and is supported at its upper face on the end plate 6 of the vertebra 1 and at its lower face on the end plate 7 of the vertebra 2 . the ribs 21 and 22 engage the grooves 18 and 19 , respectively , and thereby fix the implant 20 in this position . the implant 20 consists of a resorbable material and is porous . the size of the pores lies between 150 μm and 200 μm . the material of the plug - shaped implant 20 is flexible and elastic , so that it adapts optimally to the contour of the opening 8 and also easily follows the movements of the material of the annulus fibrosus . the ribs 21 and 22 , on the other hand , are rigid , i . e ., considerably harder and not deformable or elastic in the same way as the rest of the material of the implant 20 . this results in a rigid connection in the area in which the implant 20 is fixed to the adjacent vertebrae 1 , 2 , but in between the material of the implant 20 adapts to the movability of the material of the annulus fibrosus and reliably closes the opening 8 . in this way , the entire material of the plug between the ribs 21 , 22 may be flexible or elastic , but it is also possible for the material of the plug to become progressively firmer towards the ribs 21 , 22 . for example , the upper face and the lower face of the plug could be rigid in a way similar to the ribs 21 , 22 , so that they form rigid contact surfaces at the end plates of the vertebrae . it is merely important that the material of the plug should be flexible and elastic in the central area thereof so as to ensure adaptation to the movability of the annulus fibrosus tissue . when the opening 8 in the annulus fibrosus 5 has been closed in this way , the cell material grown outside of the body can be introduced into the interior of the intervertebral disc 3 . as a rule , this is carried out approximately two weeks after the surgical operation described above . the introduction may be carried out using an injection needle 24 ( fig1 ) which is inserted through the implant 20 into the interior of the intervertebral disc 3 and injects the material into both this interior and the porous area of the implant 20 . the injected body cells grow in the interior of the intervertebral disc 3 and in the implant 20 and finally close the opening 8 reliably , so that the opening also remains closed when the implant 20 gradually disintegrates and is resorbed by the body . in the embodiment shown in fig1 to 10 , the implant 20 has substantially the shape of a cube or a rectangular parallelepiped and carries on its upper face and on its lower face a web arranged at the center of each of these . in the modified embodiment of fig3 , the implant 20 also has substantially the shape of a rectangular parallelepiped but is broader , and , therefore , two parallel ribs 21 and 22 , respectively , are arranged on the upper face and the lower face , respectively . the ribs 21 and 22 are spaced from the side surfaces of the implant 20 , so that in the area of the side surfaces the implant can adapt optimally to the tissue of the annulus fibrosus owing to the flexible and elastic structure , while the implant 20 is fixed by the parallel ribs 21 , 22 in corresponding double grooves 18 , 19 in the end plates of the vertebrae . instead of the ribs 21 , 22 , several pin - shaped projections lying alongside one another in a line could be provided . furthermore , with a view to better fixing of the implant in the vertebrae , it is also possible to provide the ribs or projections with a toothing which engages in the side walls of the grooves 18 , 19 . on its outer side , the implant 20 may be covered with a membrane which is impervious and seals the porous implant 20 off from the outside . this membrane may also consist of resorbable material . this material preferably decomposes more slowly than the material of the rest of the implant 20 and is , therefore , resorbed later . furthermore , an anti - adhesion layer , not shown in detail in the drawings , may be applied to this area . this may consist , for example , of a gelatin - containing gel or spray . post - operative formation of scar tissue may thereby be prevented .
in an implant in the form of a plug for closing an opening in the annulus fibrosus , in order to ensure as reliable a fixing of the plug as possible and a secure closure , it is proposed that the plug have rigid anchoring elements for the end plates of adjacent vertebrae on its upper face and on its lower face , and a deformable structure in the area between upper face and lower face .