Abstract:
The present invention related to an implant (1) for an intervertebral space consists of a frame (2) which is closed at the sides but open without restriction at the top and bottom and provided with an anterior lead-in face (3) and a posterior manipulation face (4). The upper (5) and lower boundary (6) of the frame (2) is convex, so that the implant (1) has an overall lens shape in the midplane (8) of the frame (2) containing the longitudinal axis (7) of the implant (1). The inner cavity (15) which is open without restriction at the top and bottom can be filled with a compressible material. The posterior manipulation face (4) of the frame (2) is provided with an aperture (9) to allow the introduction of a compression element (10) with which the compressible material can be forced out of the inner cavity (15).

Description:
TECHNICAL FIELD 
     The invention relates to an implant, especially for insertion into a intervertebral space. Such implants are primarily intended to promote bone bridges on vertebral bodies, and they are attached between the vertebral body and the spinal column after resection of a disk or intervertebral disk. 
     BACKGROUND ART 
     It is known that a damaged intervertebral disk can be removed, and that the resulting space can be filled with cortico-spongious bone. 
     In this method, the vertebral bodies are first stretched apart as much as possible by means of spreaders. A special technique consists in inserting wedge-shaped elements--so-called dilators--between the two vertebral bodies, so as to spread them apart step-by-step. Dilators, each with a 1 mm larger diameter, in alternation left and right, are here attached posteriorly. After the maximum possible spread has been reached, the dilators are replaced by the above-mentioned cortico-spongious bone. 
     This known technique has the disadvantage that the bone is difficult to handle and to bring into the proper position, corrections being nearly impossible. Another disadvantage of this technique is that a rectangular or cylindrical recess must be punched and/or milled out of the intervertebral space, so that the bone plugs can be inserted between the originally concave sides of the adjoining vertebral bodies. This is complicated and furthermore results in damage to the vertebral body. 
     WO89/12431 discloses an implant for the intervertebral space. This implant has the shape of a hollow cylinder and is perforated on all sides. It can be closed from the manipulation side by means of a screw cover. Bone mass which may possibly be inserted into the cylinder cavity cannot be compressed and, in addition, the small perforations--intended only for the bone to grow in--would make pressing out the bone mass impossible. 
     WO90/000037 discloses a square implant, perforated on all sides, for the intervertebral space. It has a screw/wedge mechanism mounted in its interior, by means of which four claws can be run out both on the top and on the bottom. So that bone mass can be filled into this implant pre-operatively, the screw/wedge mechanism first must be unmounted and then must be remounted again, which would be very complicated. But even in such a case, the bone mass could not exit from the implant because, on the one hand, the existing, relatively large slits would be closed by the run-out claws and, on the other hand, the small perforations are unsuited for this. 
     PCT/CH94/00184 to BECKERS describes an implant whose specific shape and mode of insertion makes possibly an extremely stable clamping between the vertebral bodies, without thereby damaging the surface of the bony cover plate of the vertebral bodies. 
     The starting point of this implant is a certain shape of the cover plates which belong to the two adjoining vertebra and which bound the intervertebral space. However, in reality the geometry of the cover plate varies from patient to patient. As a result, the contact between th e bone material pt into the implant and the cover plates is not always optimal. Depending on circumstances, this can delay bone healing. The invention provides a remedy for this. 
     SUMMARY OF THE INVENTION 
     It is the object of the invention to provide an implant for the intervertebral space, such that the bone mass introduced therein--after implantation--can be compressed and can be pressed out against the treated cover plates of the adjoining vertebra, whose cartilage has been re moved. In this way, the cavity resulting from an anatomical mismatch is filled up with bone mass. 
     The invention achieves its set objective by means of ar implant which has the features a frame which is closed at the side but is open without restriction on the top and bottom, and which has an anterior lead-in face and a posterior manipulation face, with upper and lower boundaries of the frame being convex in shape, so that the implant has a overall lens shape. The inner cavity of the implant is open without restriction on the top and bottom, and is filled with a compressible material. Also, the posterior manipulation face includes an aperture which allows the introduction of a compression element which is used to force the compressible material out from the cavity. This implant can be manipulated by use of an instrument having a sleeve which includes means for exerting torque on the implant, and two inserts which engage each other concentrically and which are connected to the compression element in such a fashion that forces are exerted in the direction of the longitudinal axis of the implant by one insert, and about the longitudinal axis by the other insert. 
     The compression element which can be inserted into the inventive implant can be gripped by a tool, so that, if the implant is appropriately designed, an external force and a torque can be exerted on the implant relatively easily, by way of the compression element. This makes it possible to insert the implant, together with the compression element, into the intervertebral space, to remove them, aid to manipulate them individually or jointly. 
     The apparatuses which allow a tool to exert a grip can be designed as attachment points in such a fashion that a rotational force and/or an axial force and/or a lateral force can be exerted on the compression element and through this on the implant itself. 
     In an advantageous embodiment of the compression element and of the implant in an appropriately designed instrument, these attachment points are constructed at least in such a way that they make it possible to exert a rotational force on the compression element and on the implant itself. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     To elucidate the invention better, several examples of advantageous embodiments will be described below, with reference to the appropriate drawings, but the invention is not limited to these drawings wherein: 
     FIG. 1 shows a a perspective view of the implant with its compression element. 
     FIG. 2 shows an exploded view of an instrument suited for manipulating the implant of FIG. 1. 
     FIG. 3 shows a a perspective view, of the instrument of FIG. 2. 
     FIG. 4 shows a partial longitudinal section through the instrument of FIG. 3, in the transition region between the instrument and the compression element of the implant. 
     FIG. 5 shows a longitudinal section through an implant of FIG. 1, inserted into the intervertebral space, before the bone mass has been compressed. 
     FIG. 6 shows a longitudinal section of an implant according to FIG. 1, inserted into the intervertebral space, after the bone mass has been compressed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention and modifications thereof will be explained in more detail below by means of partially schematic representations of several embodiments. 
     The implant 1 shown in FIG. 1 essentially consists of a frame 2, which is laterally closed but which is open without restriction on the top and bottom, and which has an anterior insertion face 3 and a posterior manipulation face 4. 
     The longitudinal axis 7 of the implant 1 is the mid-perpendicular on the anterior insertion face 3 and the posterior manipulation face 4. The mid-plane 8 of the implant 1 is defined by the longitudinal axis 7 of the implant 1 and the mid-perpendicular to the lateral faces 19a, 19b of the frame 2. 
     The posterior manipulation face 4 of the frame 2 has an aperture 9, into which a compression element 10 can be inserted. The compression element 10 preferably is a screw with a thread 11 and a hexagon socket 13. This screw is inserted into the aperture 9, thread 11 mating with internal thread 12 of aperture 9, before the implant 1 is inserted into the intervertebral space. 
     The frame 2, which is formed by the faces 3, 4 and the lateral walls 19a, 19b, encloses a cavity 15, which can be filled with a compressible mass, preferably consisting of autologous bone material, and which can be compressed in situ by means of the compression element 10, after the implant 1 has been inserted into the intervertebral space. 
     Implant 1 has a P value of about 0.5 to 1.5 mm, wherein P is defined as FT/O, where F is the cross sectional area F of the aperture 9, T is the maximum possible penetration depth of the compression element 10 into the inner cavity 15, and O is the reciprocal of the sum of the areas of the two openings 18a, 18b in the upper and lower boundaries 5, 6 of the frame 2. Preferably, the P value is between 0.6 and 0.9 mm. 
     The lateral walls 19a, 19b of the implant 1 shown in FIG. 1 have perforations 14, through which the bone can grow into the implant 1. The upper and lower boundaries 5, 6 of the frame 2 are provided with apertures 18a, 18b. The area of the apertures 18a, 18b preferably represents 40 to 60%, and most preferably 45 to 55%, of the entire cross sectional area of the implant 1. 
     The transverse slot 16, which is situated in the posterior manipulation face 4, serves as an apparatus for gripping the implant 1 by an instrument. The transverse slot 16 shown here makes it possible to apply a rotational torque, via the instrument, directly on the implant 1. 
     FIG. 2 shows the implant 1 together with the compression element 10 and the instrument 20. The instrument 20 makes it possible to manipulate simultaneously the implant 1 and the compression element 10. The instrument 20 essentially consists of a sleeve 21, a tube-like insert 23, a handle 24, and another insert 25. The sleeve 21 has an apparatus 27 which fits into the slot 16 of the implant 1. This slot 16 makes it possible to transmit a torque from the instrument 20 directly to the implant 1. The insert 23 is pushed into the sleeve 21 and is connected thereto in a rotationally stable fashion. Its front end has an apparatus 22 so as to connect it to the compression screw 10 in a manner that is resistant to tension and compression (see FIG. 4). The posterior end 28 of the insert 23 has a geometry which makes possible a rotation-, tension-, and compression-stable connection between the insert 23 and the handle 24. Rotational stability is assured by the two faces 28a. Two co-lateral balls, situated in the handle 24, are pressed into the co-lateral bores 28b when the handle 24 is pushed on the insert 23, and they thus make it possible to apply stretching and compressing forces, via the compression element 10, to the implant 1. The second insert is pushed on only after the apparatus 22 has already clicked into the compression element 10. It presses the apparatus 22 apart, and in this way prevents the connection from loosening up when forces appear in the longitudinal axis of the implant 1. The second insert 25, shown in FIG. 2, has a hexagon bolt 26 in front, which is inserted into the hexagon socket of the compression element 10. This hexagon bolt 26 makes it possible to turn the compression element 10 in and out, since it is designed as a screw, and thus makes it possible to compress the fill mass in the implant 1. The insert 25 is operated by a small hand wheel 29, shown in FIG. 3 
     FIG. 3 shows the instrument 20, in its mounted state, with the insert 25 in the grip and with the mounted hand wheel 29. 
     FIG. 4 shows the lower part of the instrument 20 directly before its end 23 is clicked into the compression element 10. The end 23 resembles a collet chuck and has at least one slot. After it has been clicked in, the insert 25 is pushed into the insert 23 far enough so that the hexagon bolt 26 penetrates completely into the hexagon socket 13 of the compression element 10. In this position, the insert 25 prevents the collet chuck 22 from being compressed Due to the flange 17, the connection between the instrument 20 and the compression element 10 can now accept forces in the longitudinal direction of the implant 1. Once it is connected to the instrument 20, the compression element 10 can be turned relative to the instrument 20 by means of the insert 25. As already mentioned, the instrument 20 is itself connected to the implant 1 by means of the apparatus 27, in a rotationally stable manner. This now makes it possible to turn the compression element 10 into the implant 1 by means of the insert 25, and thus to compress the fill mass and to press it through the apertures 18a, 18b in the upper and lower convex boundaries 5, 6 of the frame 2, against the cover plates 130 of the upper and lower adjoining vertebral bodies 100. 
     The connection between the instrument 20, shown in FIGS. 2 and 3, and the implant 1, shown in all the figures, is made as follows: 
     Clicking the collet chuck 22 into the compression element 10 
     Pushing in the insert 25 until its hexagonal bolt 26 has completely disappeared in the hexagonal socket 13 of the implant 1 
     Inserting the apparatus 27 of the instrument 20 in to the apparatus 16 of the implant 1 
     Inserting the compression element 10 into the implant 1 until its most forward part is flush with the in side of the frame 2 of the implant 1. 
     The implant 1 or the compression element 10 can now be manipulated with the instrument 20 as needed: insertion, rotation, and compression. The connection is designed in such a way that especially torques about and forces along the longitudinal axis 7 can be exerted on the compression element 10 through the instrument 20 and can be exerted on the implant 1 through the compression element 10. The mass, preferably consisting of autologous bone, is filled in only after the instrument 20 has been connected to the implant 1 and before the implant 1 has been inserted into the intervertebral space. 
     It will now be explained, with reference to FIGS. 5 and 6, how the fill mass is compressed and is pressed into the cavity between the implant 1 and the bone. As a preliminary, the implants 1, in transverse position, are inserted from posterior left and right, past the dura 110, by means of the instrument 20 (two implants per vertebral segment that is to be fused). They are then set upright about their longitudinal axis 7. Toward anterior, they are held by the remaining annulus 120 of the intervertebral disk. Toward posterior, they are generally stabilized by an additional posterior pedicle fixation system. FIGS. 5 and 6 show one of these two implants 1 after it has been inserted and set upright, The compression element 10 in FIG. 5 is still in its initial position, i.e. it is still turned in so far that the implant 1 can be manipulated through the compression element 10, by means of the instrument 20, without already compressing the fill mass. For the sake of clarity, the instrument 20, which is fixedly connected to the implant 1, has not been shown in the drawing. The anatomical structures shown in FIGS. 5 and 6 show a certain discrepancy between the upper and lower boundary 5 and 6 of the implant 1 and the cover plates 130 of the adjoining vertebral bodies 100. The objective now is to turn in the compression element by means of the insert 25 until the fill mass 82, emerging on the top and bottom, has filled up the cavity 81 between the implant 1 and the bone. 
     FIG. 6 shows the implant 1 after the compression element 10 has been turned in. The cavity 81 is filled completely with the emerging fill mass 82.