PROSTHESIS FOR ARTHRODESIS OF INTER-VERTEBRAL DISC SPACE FOR ANTERIOR-POSTERIOR APPRAOCH

Abstract: Prosthesis for the arthrodesis of a human spine's segment of anterior and posterior (PLIF-ALIF) approach, consisting of two parts that are assembled during their implantation to the patient, interbody space after disc removal. For the anterior approach a conical threaded cage and conical forked cage, for the posterior appraoch a cylindrical threaded cage and two simple rectangular cages are used. Our prosthesis achieves the desired outcome when we tie two vertebrae, (arthrodesis), by distracting the space efficiently and stabilizing it with the screwing treaded cage, then enlarging the prosthesis surface by assembling the rectangular one. No need for further support with pedicle screws, as the previous techniques. Our prosthesis which combines both types has the characteristic that nullifies the disadvatages that existed on each type separately, that is migration, subsidence and abolishes the need for use of other support systems. Speed is also gained through simple positioning, avoiding errors and the dangers much than the previous techniques, while we expect a perfect outcome.

Description: Title Prosthesis for arthrodesis of inter-vertebral disc space for anterior-posterior approach. Description Terms used Human Spine (H.S.), Arthrodesis of H.S., PLIF (Posterior Lumbar Interbody Fusion, ALIF (Anterior Lumbar Interbody Fusion), end-plate, forked trapezium cage, simple parallelogram cage, cylindrical threaded cage, conical threaded cage, spongiosa bone. B) TECHNICAL FIELD Degenerative, diseases of the H.S dealing with pain relief, mobilization and possibility of return to work are nowadays dealt with more advanced methods and very good results compared to those of the recent past. The technology of the cages, that is of the prosthesis' for interbody fusion in between two vertebrae as well as other materials and spine implants, that aim at stabilizing and tying the H.S., helped towards this evolution. The two types of arthrodesis cages of today's existing techniques are of two main categories: a) cylindrical shaped ones that are screwed in the inter-vertebral space and b) rectangular trapezium or parallelogram shaped ones, which are inserted in the implantation site through impaction. There is also a third category which combines the properties of both and obtains distraction by the forked rectangular cage impaction, then stabilizing by screwing at its inner side the threaded one, only for anterior approach. Our new prosthesis uses the technique of the two main types, of today's existing technology and therefore combines the characteristic advantages of both. Our prosthesis obtains arthrodesis either by posterior or anterior approach and consists of threaded screwing cage of conical shape, and a trapezium forked cage, assembled in the in-between space of two vertebrae of the H.S. for anterior approach and fusion. For posterior approach, two cylindrical, not conical screwing cages are used laterally and two rectangular ones (not forked) at the interior side. The scope is to 1) successfully restore the inter- vertebral space's height, 2) reduce the possibilities of the prosthesis' s migration or subsidence in the vertebral bodies. 3) succeed in immediate immobilization of the segment, and 4) arthrodesis and creation of the best conditions, permanent ossification and creation of bone bridge connecting the two vertebral bodies and the prosthesis which is filled with allograft or autograft. 5) The most important success of the new prosthesis is to nullify the need for additional fusion with pedicle screws. The current technology of inter- vertebral prosthesis' s presents large percentages of failure, in case it is not combined with posterior fusion systems with pedicle screws, due to the increased danger that they present or migration of the rectangular ones, or subsidence into the vertebral bodies of the screwing ones (collapsus), when they are implanted alone. C EVALUATION AND DESCRIPTION OF THE PREVIOUS TECHNIQUE The need for arthrodesis in the Human Spine is widely mentioned in international bibliography and mostly in case of instability, degeneration of inter- vertebral disc, spondylolisthesis, etc. The established methods usually involve insertion of autograft between the vertebral bodies with or without posterior support with pedicle screws or other fusion materials. The introduction of new methods during the last decade with the cages' technology, has further improved the results of these operations. However even the new prosthesis, present many and serious problems, either during positioning or post-operatively. The screwing hollow titanium cages demand use and very precise handling of a series of sharp and dangerous instruments which work only a few millimeters away or even touch vital tissues for the patient's safety, such as the aorta, the nerves' roots, the esophagus and other, without easy control of the instruments position and direction during the operations. Due to this fact, there is a plethora of complications, hemorrhages, injuries, implantation in wrong place, or loose implantation without the desired stabilization forces between the vertebral bodies. Generally, with the existing technology and according to international bibliography there is a 20% of complications.. ^Referred disadvantages of threaded cages include loss of stability without pedicle screws, subsidence, loss of bone stock, pseydarthrosis difficulty in achieving lordosis, etc. Conclusion: smaller cages with pedicle screws that can be found in many published studies are more effective. The technical procedure of insertion of implants of the same type such as Ray, BAK- L, etc., requires 'ground' preparation (bone bed) of the vertebral bodies, of the end- plates with the use of very sharp instruments, such as reamers, taps, etc., which pass through cylindrical guides that carry teeth that secure them on the upper and lower body by impacting them lightly, having previously distracted the space's height with metal distractors of cylindrical or conical shape that are removed after positioning of the cylindrical toothed guide which preserves the desired height after the distractor's removal, but only via the guide's teeth. Then, through this cylindrical guide, pass the tap, the reamer, and finally screw the cylindrical or conical-cylindrical shaped cage. During the instruments' handling, control of the preservation of the guide's direction is difficult, because the guide easily changes direction due to the required force which is mostly exercised during taping of the end-plates and leads to movement of 2-3 teeth that hold the guide in its position, resulting in unequal cut of the upper and lower end- plates, or creating two not parallel holes and increasing the possibilities for wrong implantation of the two cages demanded. The wrong direction can occur either on the sagital or on the transverse axis of the disc. There are other types of cylindrical guides-distractors (paddle tube type) which are oriented more easily and follow the parallel direction of the end-plates while employing the same technique, that is use of taps and reamers, etc. Thus, there are disadvantages due to insufficient control of the guide and due to use of many instruments since their manipulation creates conditions for not safe implantation, while the procedure as a whole is complicated and seriously increases dangers that can lead to injuries or failures. Due tς the difficulties described above, we can lose the correct direction and prepare incorrectly the hole for the implant's insertion. The drilling-cut of the spongiosa bone step, for bone bed preparation evokes mass bleeding and makes the continuity of the operation difficult because of poor view of the operating field and forces the surgeon to speed up the procedure, therefore increasing the possibility of error. Hence, one of the operation's risks is the need for revision of the procedure as a whole in order to correct the implant's insertion hole which is only done by choosing an implant of larger size, having previously employed again reamer, tap, etc. of the next larger size, keeping in mind that this might not be feasible in all cases. The usual cases of failure occur when the implant is not equally screwed in the upper and lower body, or when it is only screwed into one and while simply touches the other, because the reamer cuts unequally into the upper and lower vertebral bodies, which can affect the implantation's stability. This is necessary in order to stop the pain, and of course speeds up the final fusion and arthrodesis. Another disadvantage of the previous technique is that the use of sharp drills destroys the structure of the end-plates and their resistance along the created hole, the whole situation worsens if two continuous levels are to be operated, since this can reduce the resistance of the rest of the spongiosa bone tissue between the two adjacent disc spaces, resulting in post-operative failures such as vertebrae fractures or intrusion of the prosthesis in the soft spongiosa bone. There also exist rectangular not screwing cages that are inserted between two vertebrae by wedging them in through impaction and many H.S. surgeons prefer them, in order to avoid the above mentioned complications and difficulties since their implantation is easy, without use of dangerous instruments, dangers that characterize the screwing cage's implantation, or its post-operative complications. However, these cages present big risk of migration, and this is why it is totally necessary for additional stabilization with pedicle screws. There are also combinations of screwing and flat cages assembled, but with different implantation steps. D ADVANTAGES OF OUR INVENTION Our prosthesis can be used not only for anterior interbody fusion (ALIF) but also for posterior interbody fusion (PLIF), unlike the others as WO A 9848738 (CROZET YVES; DIMSO S A (FR) or EP A 0 716 840 (SURGICAL DYNAMICS) or WO A 98 02117 (AESCULAP AG ET ALL). The cages' up today technology, is separated into two categories. The screwing ones that are implanted by screwing, and the inserting ones that are implanted through light impaction wedging. Our prosthesis combines both types, that is, its one part is screwed and the other one is inserted and connected to the first one. Our prosthesis consists of two parts, the conical threaded cage which is forwarded by screwing, without previous use of reamer or tap, onto which we then apply a forked trapezium, conical rectangular cage which is secured on it for the anterior fusion or a simple rectangular one for the posterior one. This combination succeeds in presenting the positive properties of both types, because the implantation is very stable and migration is unlikely to occur, while leaving 50% of the implantation's length on the end-plates unharmed, since there is no use of drills that cut the end-plate in all the length of the implantation site, thus reducing its endurance. Generally speaking, the use of drill in the other techniques, destroys the architectural structure of the vertebral body and its endurance, increases the danger for subsidence, can cause fracture and is a serious drawback of the screwing cages' technique. Aim of the combination of the new prosthesis' s advantages is avoidance of use of pedicle screws which are implanted in order to avoid complications of migration, and subsidence. Hence, we have less operation time, less instruments, less dangers, reduction of cost and generally less bleeding, less complications not only during the operation but also afterwards, no need for additional posterior stabilization with rods and screws, which is considered necessary, for the protection of the screwing cages from subsidence and the inserted ones that are wedged from movement and migration. Simplification of the implantation's technique through nώiimization of the demanded steps, since neither drill nor reamer is used due to the fact that our cage has self- cutting threads so that it is screwed on its own, while the distractor which stays steadily in its position also serves as a guide. The danger of false implantation of the implant is drastically minimized due to the fact that it carries self-cutting threads that allow it to be screwed passing over the distractor-guide, in the direction that it's been given. The screwing cage is of cylindrical shape and carries saw-like teeth on its perimeter with the aid of which it is forwarded, as the external self-cutting threads start to rotate, helping the implant to be forwarded towards its final location that can differ according to the method of approach that is being followed (anterior or posterior). A major simplification step is that the implant itself is used as an instrument able to prepare the insertion site while it is being forwarded at the same time, it is screwed cutting at the bone at the same time, destroying at least 50% less of the end-plate structure, in contrast to the other screwing cages, which use sharp reamers. After partial or total removal of the inter- vertebral disc material, by use of disc ronguers and curettes and the revelation of the end-plates at the insertion site, only two instruments are used for the final implantation. The stemmed distractor-guide and the T - driver of the threaded cage. The new guide employed in our technique has an advantage because it cannot move thus changing angle or direction during implantation, compared to the tubular ones with fixation teeth of the old techniques that can easily move and loose direction. Our distractor - guide obtains a first small distraction of the disc space, which then is accomplished at his final height by screwing the self taping, hollow conical for ALIF or cylindrical for PLIF cage. This is a basic advantage of the new method which requires less steps and reduces time. In older techniques the use of many dangerous instruments which pass or even come in contact with vital tissues such as the aorta, nerve roots, the dura etc, increased their injury danger. The implantation of our prosthesis can be achieved in less time and with safe manipulations, without mistakes regarding the direction thus increasing the possibilities of a good result. Besides avoiding the reaming of end plates, we have no bleeding, or weakness of the endurance of the vertebral body. By adding the forked trapezium cage we increase the prosthesis' s final contact surface, thus achieving the combination of the stable implantation, a property of the screwing cages that do not migrate easily and a property of the rectangular or trapezium cages which increases the contact surface and does not allow subsidence of the prosthesis in the adjacent vertebral bodies. Unlike other techniques of combined flat and screwing cages, the better stability of our system, is obtained thanks to the implantation steps. In our system we screw first the cylindrical cage, thus obtaining distraction and stabilization and then we just add laterally for anterior and unilaterally for posterior of the cylindrical cage a rectangular one, conical and forked (forked) for ALIF and simple for PLIF, without applying any force. So, we pay special attention to choose the right height of rectangular cages in order to avoid any further distraction already obtained by the cylindrical one, because doing that we will have a risk of loosening it from its position. Another problem of the old technique was the preparation of the hole in the end plates with reamer, where threads would be shaped with the use of tap. The prepared depth was some times less than the implant's length preventing it from going deeper and the implant was screwed falsely or even destroyed the threads due to the surgeon's effort to screw it beyond the prepared depth, resulting in it being loose and this led to revision of the whole procedure and the implantation of an implant of larger size. In conclusion the advantages are speed, safety, stable implantation and significantly reduced risk of subsidence and migration. The existing combination of flat and screwing cages uses adverse implantation steps, by inserting first the flat cage and distracting the space by impaction of the flat cage, then screwing the threaded cage on a prepared by reamer bone bed. E) REVELATION Fig. 1 shows the front view of the forked trapezium cage, fig.2 shows its lateral view, and fig. 3 the overview fig. 4 the threaded-cage that is screwed in the opening where the destroyed disc was. Fig. 5 shows the cage laterally and the driver's application notch. Fig.6 shows the prosthesis assembled, which is an aspect of the threaded cage and the forked trapezium cage, fig. 7 and fig. 8 the prosthesis assembled from another angle. Fig. 9 shows the three parts that compose the prosthesis and fig. 10 the positioning order in the inter-vertebral space. Fig. 11 shows the posterior approach and arthrodesis prosthesis, which carries instead of a forked cage, a simple externally rectangular, one for each cylindrical threaded cage. In fig. 12 the structure of the self-cutting threaded cage can be seen and on fig. 13 the role of the distractor-guide' s and the way that it leads the threaded cage in the inter-vertebral space above it. The arthrodesis prosthesis for inter-vertebral space, consists of a cylindrical-conical threaded cage, fig. 12, fig. 4, fig. 5 with external threads, constructed of titanium alloy special for implants or carbon fibers, and other materials which will be biocompatible and of specific ruggedness so that they withstand the loads and forces exercised, and a forked one, also conical trapezium cage, fig.l, 2, 3 constructed of the same material, for anterior approach, or a simple rectangular one, fig. 14 for posterior approach. The threaded cage fig. 12 bears three teeth 1 on its front part, saw-like, that cut the bone where it is implanted with application of relative pressure and screwing. Self-cutting threads 2 are an immediate continuity of the external teeth that allow easy forwarding through rotation and with the exercise of light pressure. Hence, the threaded cage with its saw-like front part and the threads immediately following, succeeds in its easy implantation since it cuts and at the same time is being screwed in the bone. The internal part of the threaded cage is hollow of equal diameter to all its length, for each size of the prosthesis, proportional to the size of the vertebrae. For each size there exists a distractor of equal diameter to the diameter of the internal opening of the threaded cages. For the Cervical Spine distractors of smaller diameter are employed and generally a threaded cage with forked trapezium cage. On the other hand, for the posterior Lumbar approach two threaded cages of small diameter are used in combination with two simple rectangular cages, fig. 14 and fig. 11. The threaded cages have an external diameter larger to the distractor' s diameter by 2 millimeters which is based on the dimensions and the size of the threaded cage's implant. All threaded cages independently of their size carry slots- openings 3 fissures 4 on their periphery in order to collect the bone that they cut without losing their cutting abilities and also notch 5 into which the driver is attached. The securing forked cage, fig. 1, 2, 3, carries in its center opening 10. The simple rectangular, fig. 14 carries proportional opening 10 through which the safety 11 is secured, fig. 9 and connects the rectangular cage and the threaded cage. The trapezium's forked or the rectangular simple cage's height is lower then the threaded cage's diameter by 2,5-3mm, so that it is easily inserted and secured next to the threaded cage, fig. 6. The forked cage's height on its front part (on the point where it is connected to the threaded cage) is taller by 4 degrees so that it fits the anatomical characteristics of the space, which is taller at the front and lower at the back, as there is also a difference in height from the center towards the sides, that is the edges 1 are larger than the 2 (fig. 6, fig. 7), so that there is an inclination of about 4 degrees. The fissures-openings 3 of the threaded cage fig. 5, and the notch 8 fig. 3 and fig. 14 allow the secondary development of bone tissue and the bridging of the upper and lower vertebral bodies with bone bridge. The threaded cage also carries fissures 4, fig. 5 and fig. 12 on its front part into which the cut bone which is the result of the screwing is gathered thus not preventing its further screwing. The unique preparation demanded is the positioning of the distractor-guide 20, on opening that has been created on the inter-vertebral disc fig. 13, with drill 6-8mm, or removal of the disc with curettes or laminectomy rongeurs until the end-plates of the upper and lower body are removed. The use of distractors is common in all preexisting techniques, due to the need for distraction of the lost height of the inter- vertebral space and also for the creation of opposite stabilization forces that come into existence with their insertion. The advantages of our technique start from this common point and beyond since the distractor remains in its position up until the hollow threaded cage fig. 4, 5, and 13 which passes over it is screwed, and only then is removed. The threaded cage is now steadily screwed in the inter- vertebral space and the next step is the addition and securing of the forked trapezium cage fig. 3 or fig. 2 for anterior and fig. 14 . for posterior, of appropriate height which increases the total contact surface where loads are exercised and generally we have existence of the advantages of both types of cages, that are conical or cylindrical screwing and the rectangular ones. During positioning, the distractor 20 is not removed but remains in its position and serves as a guide up until about 50% of the threaded cage's length which passes over it is screwed. The threaded cage 5 passes over the guide 20, is connected to the driver 9 of T shape, fig. 13 and is easily screwed following the root of guide 20. For the anterior approach we apply with light pressure the trapezium forked cage, fig. 1, 2, 3 and secure with safety 11. In posterior Lumbar approach (PLIF), fig. 11 after laminectomy as can be seen on fig. 11 the dotted part 30 and revelation of the spinal cord and the dura 40, we screw two threaded cages 5 of small diameter as much as we can close to the sides and as much outwards as possible, having previously removed disc material, and then pass each of the two simple rectangular cages from the internal side while slightly pushing aside the dura fig. 14, and secure again with safety 11 fig. 9, through hole 10 fig. 14 and fig. 11. EXAMPLE OF THE INVENTION'S APPLICATION On a patient that has been suffering from back pain for a period of over 6 months and after clinical and laboratory examination with indications for surgery, due to pressure on the roots of O5 and due to loss of height of the inter-vertebral space O5-I1, so that pain he is relieved from pain and the functionality is restored arthrodesis is decided to be performed with anterior approach. Postero-peritoneal opening with retroperitoneal incision is attempted and after the space O5-I1 is prepared, we remove the disc with laminectomy rongeurs and curettes in such a depth and width so that our prosthesis fits. Afterwards, we wedge the distractor 20 by impaction up to a depth of about 2,5 centimeters and we pass the conical threaded cage over it until its front teeth come in contact with the end-plates of O5 and II. Then with the aid of the T shaped driver we screw up until 50% of the threaded cage's length, remove the guide which is no longer needed and screw the rest of the threaded cage. We fill its hollow part with autograft or allograft and then choose a trapezium forked cage of appropriate height which we forward and wedge so that the two legs pass to the right and left of the threaded cage, without application of force since it will loosen the threaded cage's screwing. Positioning of the trapezium cage is also done after it filled with graft. Finally, the two cages are safely connected. The positioning is simple, without use of many or dangerous and sharp instruments, the expected result is compared to that of double fusion, anterior-posterior.

Claims: CLAIMS 1. Prosthesis for arthrodesis of the inter-vertebral space of anterior and posterior approach consisting of, a hollow conical threaded cage, fig. 4 and a conical- trapezium forked cage, for the anterior approach, fig. 2, fig. 3, that are assembled together, with the aid of safety 11, fig. 9, which conical threaded cage is characterized from its narrow front part and the external self-cutting threads to all its length, whose cage's the dimensions and sizes depend on the segment level of the spine we fuse, thus it is longer and of larger diameter for the Lumbar Spine and smaller for the corresponded Thoracic, and Cervical, of 1 millimeter thickness, which threaded cage carries 3 fissures, that start on its front and narrow part where they form sharp ends 1, fig. 12, which is internally hollow with opening of the same diameter to all its length so that the distractor-guide 20 that is of same diameter can pass through, preserving the position and direction during screwing 50% of the threaded cage's length, where after screwing it, we insert the forked anatomically conical-trapezium cage fig. 10 and fig. 7, whose two legs 8 fig. 3, lean right and left of the threaded cage and are of less height than it, fig. 6, so that when it is positioned it does not raise nor distract more the inter-vertebral space than the distraction accomplished by the distractor 20 fig. 13 and the final screwing of the threaded cage. For the implantation of which the only preparation for the insertion ground is removal of the disc material, so that the end-plates are exposed, in between which the threaded cage is screwed and the forked trapezium conical cage sits into, so that the assembled prosthesis withstands the shearing forces that tend to move it, and also the increased contact surface with the end- plates minimizes the possibility of subsidence of the prosthesis inside the vertebral bodies. In posterior approach, where the existence of the spinal cord that does not allow insertion of forked cage, we use two cylindrical ones instead of one conical threaded cage, that are positioned after laminectomy as much outwards as possible, while instead of a forked conical cage we put two simple rectangular ones 8 fig. 14, fig.11, pushing aside the less possible the .dura. 2. Prosthesis for arthrodesis of the inter-vertebral space of anterior and posterior approach, as in claim 1, where the conical threaded cage and the forked cage for the anterior approach, have a height difference of about 4 degrees, the back from the front part, so that they fit the anatomic characteristics of the inter-vertebral space which is higher at the front and lower at the back. The forked cage has also a height difference from its center to its lateral sides, which are defined by edges 1 fig. 6 and fig. 7 that are larger from edges 2, so that they create a slope more than 3-4 degrees, both on the upper and lower part of the prosthesis. 3. Prosthesis for arthrodesis of the inter- vertebral space of anterior and posterior approach, as in claim 1, whose threaded cage is a cylindrical cage carrying fissures that form saw-like teeth, that aid an easy screwing. 4. Prosthesis for arthrodesis of the inter-vertebral space of anterior and posterior approach, as in claim 1, whose external threads start immediately after the teeth creating a threaded cage which carries threads to all its length. 5. Prosthesis for arthrodesis of the inter-vertebral space of anterior and posterior approach, as in claim 1, in various sizes determined by the diameter of the hollow section of the threaded cage through which the distractor-guide 20 passes, for whom each increase of the diameter by 1 millimeter is proportional to a 2 millimeters increase of the external diameter of the threaded cage. 6. Prosthesis for arthrodesis of the inter-vertebral space of anterior and posterior approach, as in claim 1, whose conical or cylindrical threaded cages, carry on the posterior part, two notches where the T shaped holder is attached, fig. 13. 7. Prosthesis for arthrodesis of the inter-vertebral space of anterior and posterior approach, as in claim 1, whose threaded cages have openings 5 on their upper and lower as well as on their lateral sides, that allow communication with the upper and lower vertebral bodies, so that creation of bone bridge is facilitated. 8. Prosthesis for arthrodesis of the inter-vertebral space, of anterior and posterior approach, as in claim 1, whose securing cages, forked trapezium or simple, carry openings holes to all their length so that they allow and facilitate the creation of bone bridge. 9. Prosthesis for arthrodesis of the inter- vertebral space of anterior and posterior approach, as in claim 1, whose forked inserting or simple cages are secured on the threaded cages safely with safety 11 through hole 10 having previously screwed the threaded cage. 10. Prosthesis for arthrodesis of the inter-vertebral space of anterior and posterior approach, as in claim 1, whose forked rectangular cage fig. 6 has height at the edge 1 fig. 6, fig. 7 of 2-3 millimeters less than the height (diameter) of the threaded cage and is lowered more at its tow ends of the edge 2, fig. 6, fig. 7, so that it fits to the anatomy of the inter- vertebral space of lateral oval shape which is taller in the middle and lower at the ends, thus shaping the anatomy of the inter vertebral disc space, thus being anatomical. AMENDED CLAIMS [received by the International Bureau on 26 April 2002 (26.04.02); original claims 1, 2 and 5 replaced by new claims 1, 2 and 5; remaining claims unchanged (2 pages)] 1. Prosthesis for arthrodesis of the inter-vertebral space, consisting of one hollow conical threaded cage Fig.4, assembled with one forked anatomical plate, Fig.3, FiglO, for the anterior fusion of the Lumbar, Thoracic or Cervical spine and one hollow cylindrical threaded cage Fig 5 assembled with one simple plate Fig.14 for the posterior fusion of the Lumbar spine. The two part's prosthesis, either conical hollow threaded screw, or cylindrical hollow screw, are assembled with the corresponded plates, forked for anterior and simple for posterior, then securing with a safety pin. The dimensions and sizes depend on the segment level of the spine we fuse, thus it is longer and of larger diameter for the Lumbar Spine and smaller for the corresponded Thoracic, and Cervical, of 1 millimeter thickness of its wall, which threaded cage carries 3 fissures, that start on its front and narrow part where they form sharp ends 1, fig. 12, which is internally hollow with opening of the same diameter to all its length so that the distractor-guide 20 that is of same diameter can pass through, preserving the position and direction during screwing. For the posterior approach, where the existence of the spinal cord does not allow insertion of forked plate, we use two simple plates Fig.14, which are assembled on the cylindrical hollow screws Fig. 5, that are positioned after laminectomy as much outwards as possible, thus leaving enough space for the plate's accommodation. 2. Prosthesis for arthrodesis of the inter-vertebral space for anterior and posterior approach as in claim 1, whose forked plate for the anterior approach, fig. 2, fig. 3, is assembled with the threaded conical screwing gage Fig.4 with the aid of safety 11, fig. 9, which conical threaded cage is characterized from its narrow front part and the external self-cutting threads to all its length, where the conical threaded cage and the forked plate for the anterior approach, have a height difference resulting from about 4 degrees slop, thus being higher at the front end than the back side, so that they fit the anatomic characteristics of the inter-vertebral space which also is higher at the front and lower at the back. The forked plate has also a height difference from its center to its lateral sides, which are defined by edges 1 fig. 6 and fig. 7 that are larger from edges 2, so that they create a slope more than 3-4 degrees, both on the upper and lower part of the prosthesis. 3. Prosthesis for arthrodesis of the inter- vertebral space for anterior and posterior approach, as in claim 1, whose threaded cage is a cylindrical cage carrying fissures that form saw-like teeth, that aid an easy screwing. 4 "Prosthesis for arthrodesis of the inter-vertebral space for anterior and posterior approach, as in claim 1, whose external threads start immediately after the teeth creating a threaded cage which carries threads to all its length. 5. Prosthesis for arthrodesis of the inter-vertebral space for anterior and posterior approach, as in claim 1, which positioning and application method is determined by the diameter of the hollow section of the threaded cage through which for each one implant size one distractor-guide 20 of same diameter (thickness) passes, for whom each increase of the diameter by 1 millimeter is proportional to a 2 millimeters increase of the external diameter of the threaded cage, where after screwing it we obtain reduction of the disc height, and then we insert the forked anatomically conical-trapezium plate fig. 10 and fig. 7, whose two legs 8 fig. 3 lean right and left of the threaded cage and are of less height than it, fig. 6, so that when it is positioned it does not raise nor distract more the inter- vertebral space than the distraction accomplished by the distractor 20 fig. 13 and the final screwing of the threaded cage. 6. Prosthesis for arthrodesis of the inter-vertebral space for anterior and posterior approach, as in claim 1, whose threaded cages have openings 5 on their upper and lower as well as on their lateral sides, that allow communication with the upper and lower vertebral bodies, so that creation of bone bridge is facilitated. 7. Prosthesis for arthrodesis of the inter-vertebral space for anterior and posterior approach, as in claim 1, whose securing plates, forked trapezium or simple, carry openings holes 8 to all their length so that they allow and facilitate the creation of bone bridge. 8. Prosthesis for arthrodesis of the inter-vertebral space for anterior and posterior approach, as in claim 1, whose forked or simple plates are secured on the threaded cages safely with safety 11 through hole 10 having previously screwed the threaded cage. 9. Prosthesis for arthrodesis of the inter-vertebral space for anterior and posterior approach, as in claim 1, whose forked rectangular plate fig. 6 has height at the edge 1 fig. 6, fig. 7 of 2-3 millimeters less than the height (diameter) of the threaded plate and is lowered more at its tow ends of the edge 2, fig. 6, fig. 7, so that it fits to the anatomy of the inter-vertebral space of lateral oval shape which is taller in the middle and lower at the ends, thus shaping the anatomy of the inter vertebral disc space, thus being anatomical.

Inventors: KALAITZIS CHRISTOS, KARAVELIS ANTONIOS, KALAITZIS, CHRISTOS, KARAVELIS, ANTONIOS
Applicants: KALAITZIS CHRISTOS, KARAVELIS ANTONIOS, KALAITZIS, CHRISTOS, KARAVELIS, ANTONIOS
Application year: 2001
Main classification: A61F2
IPC codes: A61B17, A61F2