MXPA00010777A - Apparatus and method for spinal fusion using implanted devices - Google Patents

Abstract

A spinal implant replaces excised tissue removed during spine surgery. This implant includes fasteners (36) which firmly attach it to vertebrae adjacent to excised tissue so as to transmit tension and torsional loads to and from those vertebrae. The body of the implant has through cavities (34) into which bone growth material is placed during surgery. The body of the implant also has a finite modulus of elasticity in compression so as to share compressive loads with emplaced bone growth material and with new bony growth facilitated by the emplaced material and the load sharing.

Description

APPARATUS AND METHOD FOR THE FUSION OF THE DORSAL SPINE USING DEVICES IMPLANTED FIELD OF THE INVENTION This invention relates, in general, to the treatment of damaged, degenerated or diseased tissue, in the human spine, for example, the intervertebral discs and the vertebrae themselves. It also refers to the removal of the damaged tissue and the stabilization of the remaining spine, by fusing it with another of at least two vertebrae adjacent or closely adjacent to the space left by the surgical removal of the tissue. More particularly, this invention relates to the implantation of devices that can be inserted to occupy the structural place of the disks and vertebrae removed, during healing, and simultaneously share the compression load to facilitate bone fusion by bone growth between adjacent vertebrae, to permanently replace the structural contribution of the removed tissue. This invention is concerned REF .: 124761 in addition to the implantation of devices that do not interfere with the natural lordosis of the spine. This invention also relates to implants that are transradio radiuses to allow monitoring by diagnostic image formation, more accurate.

BACKGROUND OF THE INVENTION For many years a treatment, often a treatment of last resort for serious problems in the back, has been fusion surgery of the spine. This surgery, for example, typically requires the removal of the entire intervertebral disc or part of it. This removal obviously requires the replacement of the structural contribution of the removed disk. The most common sites for this type of surgery, to say those places where the body weight concentrates p incipalmente its load, are the lumbar discs in the intervertebral spaces Ll-2, L2-3, L3-4, L4-5 and L5 -S1. In addition, other damages and conditions such as a tumor in the spine, may require removal not only of the disc, but all (s) or part of one or more vertebrae, creating an even greater need to replace the structural contribution of the tissue. removed. Also, a number of degenerative diseases and other conditions such as scoliosis require correction of the relative orientation of the vertebrae through surgery and fusion. In common daily practice, a surgeon will use one or more procedures commonly known in the art, to fuse the adjacent spinal vertebrae, remnants, with each other, in order to replace the structural contribution of the affected segment of the disc and vertebrae system. In general, for spinal fusions a significant portion of the intervertebral disc is removed, and if necessary, portions of vertebrae, and a stabilizing element, which often includes bone graft material, is packaged in the intervertebral space. Parallel to the bone graft material, instrumentation and additional, external stabilizing devices are typically applied in a method to a series of adjustable pedicle screws and metal rods. The purpose of these devices, among other things, is to prevent the displacement and shock of the vertebrae on the nerves of the spine. However, these bone graft implants and pedicle screws and rods often do not provide enough stability to restrict relative movement between two vertebrae, while the bone grows together to fuse to the adjacent vertebrae. The results of conventional methods to try spinal fusion have been mixed distinctly. For example, the posterior surgical approach of the spine has often been used in the past for conditions such as scoliosis, using Harrington rods and hooks to align and stabilize the spine. In recent years many surgeons have adopted the previous fusion due to the disadvantages of the posterior approach, and the primary problem is that in the posterior approach the surgeon of the spine must intervene beyond the spinal column and its structure of nerves. However, the results of the previous surgery are variable and uncertain because restricting the vertebrae from this side does not address the loads placed on the spine by hyperextension, such as the body swaying in a backward direction. The pedicle screws and rods, always implanted later, tend to loosen either in the bone or in the interface of the screw and the rod, if fusion is not obtained. The fusion percentages for instrumented fusions, post-theoretical, vary from 50% to 90%. It should be noted that X-rays are only accurate at 65% to 70% to determine the state of the fusion, and most studies use this inadequate method to determine the state of the fusion, suggesting that non-union percentages They can be greater than those that are reported. It is also known that posterior pedicle screw systems do not prevent all movement anteriorly, leading to the risk of metal fatigue failure and screw breakage. This continuous movement can also lead to persistent pain, despite the solid posterior bone fusion, if the disc was the original generator of pain. These well-documented failures of pedicle screws have led to extensive litigation in the United States of America. In contrast to the common practice in the United States, using either IBF devices, implanted from the anterior position, or pedicle screws, implanted from the posterior position, in Europe spine surgeons use both the IBF devices and the screws pedicle, in combination, to achieve stability of the spine. These procedures may be more successful in producing the fusion but are much more invasive and expensive and have higher morbidity for the patient. More generally there is much variability in the technique and uncertainty in the result for the different methods that are now in use for spine surgery. For example, Fraser, RD points out in "Interbody, Posterior and Combined Fusions", Spine, V20 (24S): 1675, December 15, 1995, "The analysis of the literature does not indicate that one form of fusion is significantly better than another for degenerative conditions of the lumbar spine. " Fraser did not have the results of recent studies involving the use of metal inter-body cage devices. Ray, Charles D. reported the results of the original IDE study involving his Ray Threaded Fusion Cage (TFC-Ray) in Spine V22 (6): 667, March 15, 1997. Two hundred and eight patients They had two years of follow-up and were reported to have a 96% fusion rate, only 40% excellent results and 25% good or poor results. There are only two reports published regarding the use of the BAK Threaded Interbody Corporal Fusion Cage. The first, published by Hac er, R. J., Spine V22 (6): 660 of March 15, 1997, compares interbody, posterior lumbar fusion, using the BAK device for anterior and posterior fusion with allograft bones. Hacker found that patient satisfaction was equivalent but total costs were less than BAK. Zucherman reported on his first experiences with ALIF assisted 1 aparoscopically, with BAK, but data on the results in these first 17 patients are not presented. Kuslich, S. D. presented the results of the IDE multi-center study of 947 patients who had fusions using the BAK device at the 1996 annual meeting of the North American Spine Society, in Vancouver. This reported a 90.5% fusion rate and some degree of functional improvement in 93% of patients where pain had been eliminated or reduced in 85.6% of patients. The data regarding these threaded boxes are scarce at best. It is clear that the results are better than those for posterior fusion with or without pedicle screw instrumentation, but additional studies are needed. Problems with threaded devices will undoubtedly come to light as they are used under less controlled circumstances in a larger number of patients. John Kostuick, MD, Chief of Spine Surgery at Johns Hopkins Hospital, Baltimore, MD (private communication with James Nicholson, 2nd R. Roy Camille Meeting, Paris, France, January 28, 1998) firmly holds that the merger it can not take place in a metallic IBF device that protects the bone of the load. Dr. Tromanhauser, one of the inventors, in a series of 30 patients who had implants with BAK cages, found that at least 9 patients had continuous pain in the back, with X-rays and CT scanners (Computed Tomography) that were inconclusive to determine the merger. Surgical exploration of these patients revealed continuous movement and non-obvious fusion. All patients were explored at least 6 months after the implantation of the cage, during which time most surgeons would have expected the fusion. The recent unpublished research by Dr. Elsig also indicated that 60% of the cases he reviewed had to be reoperated due to failures in 6 to 8 months after the initial surgery. Therefore there is recognition and belief, especially among the followers of Kostuick, who adhere to the principles of Wolff's law that refer to applying load to the bone during fusion, through the implant device that connects the vertebrae opposite remnants, it would have produced a superior fusion both in resistance and in the duration of the healing time. It is also well proven from the study of bone growth that a load-bearing bone, especially a compression load, tends to grow and becomes stronger. The existing stabilizing implants, in particular the IBF, do not share any compressive load with the new bone growth, possibly protecting, possibly, the new bone growth, from the loads. For example, the BAK cage is promoted because it is so strong that a pair of BAK cages would support the body's total load. It is well known that this protection inhibits the growth of new bone and healing. The greatest limitation in any fusion method, at present, is the nature of the devices available to join the space left by the cutting of diseased or damaged tissue. In particular, the interbody fusion devices (IBF) commonly found on the market in the United States of America do not provide stability in all planes of movement. There is very little evidence to support the biomechanical stability of these devices. These are generally stable under compression (forward flexion) unless the bone is osteoporotic, a condition that could lead to the subsidence of the device within the adjacent vertebral body, with loss of the spatial height of the disc. These can be much less stable under torsion and certainly less stable still under extension where there is no restriction for movement, except for the diseased fibrous annulus that remains intact to provide just that restriction. It is doubtful that a degenerative annulus could provide some long-term "rigidity" and more likely to exhibit the typically expected shift in these fibrocollagenous structures. Another problem that exists with conventional fusion devices and with IBFs is, in particular, the difficulty in monitoring the diagnosis. To assess whether or not fusion between adjacent vertebrae has taken place within the IBF device, simple x-rays are usually obtained that include views under flexion and extension. The usual method (of Cobb) to measure the movement of these X-rays has an error interval of 3 to 5 degrees, well beyond the movement that may be present when the pain is present. It is impossible to see inside a metal IBF with simple X-rays and conclude anything about the state of the fusion. CT scans with reformatted images are being used more and more because of these disadvantages. More recent computer programs for CT scanners have improved the ability to "see" inside the cages, but the metallic artifacts produced by the X-rays are still significant and limit the conclusions that can be formulated. Doctors Tromanhauser and Kant have virtually found no difference in CT scans taken immediately after the operation, with those taken six months later. Accordingly, there is widespread recognition among spine surgeons of the need for a flexible, transparent radio-implant device that can replace degenerated tissue removed and that can be fixed mechanically to the opposing vertebrae. . This device would dramatically increase the likelihood of a successful fusion, because: a) it would significantly eliminate or reduce the relative movement of the adjacent vertebrae and the intervertebral fixation device, both in extension and in torsion, b) therefore reduce or eliminate the need for complementary external fixation, c) by means of the distribution of compression loads, would stimulate the rapid growth of the osseous elements packed inside the intervertebral device causing the osinduction within the bone chips, thereby accelerating the fusion, d) it would allow confirmation that the fusion has been carried out, using standard CT scanning or possibly simple X-rays, and e) it would have the potential to be biologically absorbed, potentially being made from materials such as polylactide D-LPLA or a type collagen two removable, so as not to leave long term matter strange in the intervertebral space. In addition, a flexible implant device can be manufactured entirely or in part, from a human bone autograft or from bone allograft material that is sterilized and processed, automatically matching, roughly, the elastic properties of the patient's bone. . The success rate of the merger, using that approach, exceeds, as anticipated, the success rate of the IBF devices or external fusion devices, only, and at least equals the combined success percentage, of the common combination of the IBF technique and subsequent instrumentation. However, there is currently no known method for mechanically fixing an interbody implant device, such as those known in the art as "cages", to adjacent vertebrae. All the devices of the present simply open, with pressure cat, the intervertebral space, resting on the muscular, ligamentous and annular structures that surround the vertebra, to keep the implants in place. The annulus is always degenerative in these cases and could possibly not work in some predictable way and therefore it could not be trusted that it provides adequate stability for the movement. In addition, the prior art cages are filled with bone chips that are protected from the compression load, by the rigid mechanical cage, preventing the natural inner growth of the bone, through the porous cages, because the new growth bone can not be loaded through the rigid implant. This leads to the lack of fusion, because the bone, according to Wolff's law, seeks to reabsorb due to the protection against stresses offered by the cages. In an effort to overcome this phenomenon, some manufacturers have added bone growth factors to the cage and / or bone graft, in an attempt to "trick" the bone into fusing through the cage. However, there is no method for distributing the compression loads with the material for bone growth and with the new bone growth. The lordosis, which is a pronounced forward curvature of the lumbar spine, is a factor that needs to be taken into account in the design of lumbar implants. It is known in the art that, preserving the natural curvature of the lumbar spine requires the design of a new device such as that of the present invention., with a modest taper, approximately equivalent to the effective angularity of the removed tissue. The restoration of normal anatomy is a basic principle of all orthopedic reconstructive surgery. Therefore, there is a perceived need for a device that joins mechanically in a simultaneous and reliable way to the bone spinal segments, on each side of the removed tissue, to prevent relative movement, in extension (tension) of the spine segments dorsal during healing, which provides spaces in which the material for bone growth can be placed in order to create or improve fusion, and which allows new bone growth and, in a gradually increasing way, if possible, distribute the compression load on the spine, with the material for bone growth and with the new growth, in order to improve the growth and calcification of the bones. The necessary device will require, in some cases, a modest taper to preserve the natural lumbar lordosis of the spine. It will also be extremely useful if a new device minimizes the interference of the imaging of the fusion processes, with X-rays and CTs, or obscures them. In this way, an object of the present invention is to provide a stabilizing device for insertion in the spaces created between the vertebrae during spine surgery. A further object is to create an implantable device, to stabilize the spine by preventing or severely limiting the relative movement between the involved vertebrae, both under tension (extension) loads and under torsional loads, during healing. A further object is to provide a device that promotes bone growth between the adjacent vertebrae, between the space left by the excised material, progressively spreading the compression load, to the bone graft inserted into the device. Still a further object is to provide mechanical stability between the adjacent vertebrae while the bone grows, through a lumen in the implant, and at the same time not to diminish the natural lordosis of the lumbar spine. A further object of the invention is to provide a device that avoids or minimizes interference with various technologies for image formation. Still another object of this invention is to be able to manufacture the device from human bone allograft material.

BRIEF DESCRIPTION OF THE INVENTION The invention described herein consists of a novel implant designed to achieve the preceding objects. The design of the new implant for spinal surgery includes the possibility of manufacturing the device of material that is elastic, especially in response to compression loads, preferably with a compression elasticity that closely matches that of human bone, preferably with the bone of the patient. In particular, the design includes the ability to manufacture the device from bone, human allograft material. The design is also such that the implant mechanically clamps or immobilizes the adjacent vertebrae and stabilizes the involved vertebrae, under tension and under torsion, while transmitting a portion of the vertical compression load, to the associated new bone growth. with the device. This feature of the invention will cause the osteoinduction in the bone chips loaded to the implant and will share a sufficient portion of the load with the existing bone and with the new bone growth, to promote additional bone growth and not interfere with growth for bone fusion Of this invention it can be tapered to preserve the natural lordosis. This invention also minimizes interference with X-ray imaging by virtue of being manufactured wholly or in part from radiolucent materials. The implant of this invention joins two vertebrae by means of a mechanical fixation device, which is hollow to allow matter to be added for bone growth, to one or more spaces communicating with the upper and lower surfaces, for the purpose to promote the merger. The fastening portion of the mechanical fastening device is, in a first embodiment, a fastening arrangement of a mechanical tongue and groove fastener. Other mechanical fasteners commonly used in the wood processing art, such as tack and staple devices, can also be used. The mechanical properties of the device closely coincide with the modulus of elasticity of the bone, in order to promote osteoinduction and rapid bone growth. The devices are, in general, transparent to existing imaging techniques, radiological, in order to allow confirmation of follow-up of the fusion of the adjacent vertebrae. The implant can also be made of materials that are biologically absorbed so as not to leave foreign matter in the body for a long time. The bone allograft material, human, can also be used as the material from which the implaning device is manufactured. In its most general form, the invention consists of an implant for mechanically joining the ends of at least two adjacent vertebrae to a space left by surgically removed spinal tissue, and to promote bone fusion thereof, which comprises a body for distributing loads, comprising a structure having a combination of structural elements manufactured from at least one material having an elastic deformation greater than zero, the combination comprises at least one upper surface and one lower surface; the combination of structural elements establishes for the structure as a whole, a composite elastic deformation, greater than zero, at least under compression and in directions generally axial to the upper surface and the lower surface; the combination of structural elements further comprises at least one cavity communicating with both the upper surface and the lower surface in a suitable configuration such as a receptacle for the bone implant and for the growth material; and on each upper and lower surface, at least one fastener capable of mechanically anchoring the body to the adjacent vertebrae and thereby transmitting the tension and torsional loads, to and from the adjacent vertebrae. In another embodiment, the invention generally consists of an implant for joining the ends of at least two adjacent vertebrae to a space left by surgically removed spinal tissue, and promoting bone fusion thereof, which comprises a structure formed of a single piece of material for bone allograft and having an upper part and a lower part, the structure has an internal cavity communicating with the upper part and with the lower part, to receive the bone implant material, for autograft, and factors of bone growth, the unitary structure has at least one projection of a dovetail tongue, on the upper part and on the bottom part, for the intermediate mechanical immobilization with the adjacent vertebrae, forming a mechanical joint of tongue and groove . Still in a third embodiment, the invention consists of an implant for mechanically joining the ends of at least two adjacent vertebrae to a space left by surgically removed spinal tissue, and to promote bone fusion thereof, which comprises a composite structure made with at least two separate portions of bone allograft material, with different structural properties and having an upper part and a lower part, the structure has an internal cavity communicating with the upper part and with the lower part, to receive the material for autograft bone implant and growth factor, the unitary structure has at least one dovetail tongue on each of the upper and lower surfaces, for intermediate mechanical immobilization with the adjacent vertebrae. An important aspect in the implant procedure is the preparation of the space to receive the implant and the grooves for the dovetail fasteners. A cutting template separates the vertebrae and stabilizes them during preparation and acts as a guide for precise cutting. Special cutting surgical instruments are designed to precisely cut the dovetail and prepare the surface of the endplate. Surgical cutting instruments have a deviation that is provided so that the implant is sized to slide through the template but fits snugly in the space cut in the vertebra, in order to prevent the implant from coming off. Once the cutting template is put in place, an X-ray plate is taken to show that the ends of the separation raberas are clearing the spinal canal. Surgical cutting instruments have depth seals that prevent cutting beyond the separation raberas.

BRIEF DESCRIPTION OF THE DRAWINGS Figure IA is a front view of an implant of this invention, placed between the lumbar vertebrae. Figure IB is a side view of the same implant. Figure 2 is a plan view of the same implant. Figure 3A is a plan view of an implant, showing cavities communicating with the upper and lower surfaces, within which the material for bone growth is placed. Figure 3B is a front view of the same implant, showing the cavities. Figure 3C is a side view of the same implant, showing the cavities. Figure 4A shows, in plan view, a composite implant, with titanium endplates, inserted. Figure 4B is a front view of a composite implant, with titanium endplates, inserted. Figure 4C is a side view of an implant, composite, with inserted titanium endplates. Fig. 5 is an isometric representation of the second embodiment, using a dovetail, tongue and groove, horseshoe-shaped fastener, and showing the retaining pin. Figure 6 shows the implant of Figure 5 inserted between adjacent vertebrae. Figure 7 is an isometric view of a modular implant. Figure 8 is an isometric view of the same modular implant, with the partial representation of the adjacent vertebrae. Figure 9 shows an implant with a retention spike. Figures 10A and 10B represent the handling of the placement instruments, for the preparation of the implant site. Figures 11A and 11B show additional details of a cutting tool or instrument for the preparation of the implant site. Figures 12A and 12B show the operation of the intermediate locking mechanism, for the cutting instrument, for the preparation of the implant site. Figures 13A, 13B and 13C show the cutting instrument, for the preparation of the implant site, with the surgical dovetail cutting instrument, deployed. Figures 14A and 14B show details of the surgical dovetail cutting instrument. Figure 15 is an isometric view of the actuator. Figures 16A and 16B show details of the attachment implement.

DETAILED DESCRIPTION OF THE MODALITIES PREFERRED In preferred embodiments herein, the torsion and tension stability of the spine is provided by fasteners comprising dovetail joints that engage slots cut during surgery, in the vertebrae adjacent to the removed tissue, such that the implant has large surface contact areas. The dovetails transfer the extension and torsion loads between the two vertebrae and the flat contact surface transmits the compression loads. The device further comprises one or more holes through the implant and / or cavities therein, such that the created spaces can be filled with bone graft material which will grow in the healthy vertebral bone and adhere thereto. Optionally, in all modalities tapers can be incorporated, as necessary, to accommodate the natural lumbar lordosis. In this analysis a definition of "elastic deformation" is used for convenience as the elastic displacement per unit of force applied, in other words the reciprocal of stiffness. The composite elastic deformation of the device is selected at a value that promotes the distribution of the compression load with the bone graft and the growth material and the new bone growth. As discussed in greater detail below, in one embodiment, the human bone allograft material is used to fabricate the implant. The new fusion bone will gradually share a growing portion of the compression loads experienced by the spine, because the implant is made of a material, such as a polymer, having a compression module that works in concert with the design of the implant to almost equalize the modulus of elasticity of the bone during deformation under load. The polymer, or in a modality, the material for human bone allograft, has the additional advantage that it is transparent in the formation of X-ray images, allowing easy visualization of the fusion process at the vertebral interface. In a variant of one embodiment, metal retaining clips can be placed on the surface of the implant, both above and below the dovetails, to engage the cortical bone and prevent the implant from moving out of the intervertebral space. The retainers will be generally metallic in order to mark the reference point for the formation of X-ray images for the evaluation of the coupling in ovi 1 i zador. In yet another variation, immobilizing tines will be included on the upper and lower surfaces of the implant, to help secure the implant to adjacent bone surfaces, to minimize detachment. in a second embodiment of the implant, a plurality of dovetail protuberances, or a composite dovetail protrusion, with the approximate configuration of a horseshoe, may be located on the outer portions of the implant, thereby utilizing strength and rigidity of the vertebrae, to support the load of the spine. In this case the device will contain a hollow central core that could be filled with splinters of bone and a biological medium, to accelerate the fusion in the inner ervert space. In the first preferred embodiment, as shown in Figures IA and IB (views in elevation), the vertebrae L4 and L5 (or vertebrae L5 and SI) are mechanically joined by the implant of this invention 3. The device 3 is mechanically clamped to the adjacent vertebrae 1 and 2 by the tongue and groove arrangements 4 , or dovetail. As shown in Figure 2 (in plan view), the implant 3 is positioned so as to provide mechanical support to the spine, both under compression and under tension, but not to enter the space 6 occupied by the bundle. of nerves of the spine. In this preferred embodiment, as shown in Figure 2, the implant 3 will include penetrations or holes 7 the purpose of which is to contain bone growth material to facilitate bone fusion of the adjacent vertebrae. The implant itself can comprise a variety of currently acceptable biocompatible materials, such as Pol i phenolsulphone, Polyaryletherketone (PEEK), Polysulfone, Acetal (Delrin), Ultra-High Molecular Weight Polyethylene, and composite materials, which involve high-strength carbon fibers or REM glass filaments to add tensile and shear strength. As discussed more extensively below, the implant can also be fabricated from bone allograft, human material, autograft material, or bone substitute material, such as coral or calcium phosphate. The implant body may optionally have a modest taper to accommodate the natural lordosis of the lumbar spine. A possible problem with an implant with dovetail fasteners, manufactured from a material such as polysulfone, is that the torque on one vertebra adjacent to the other can exert great stresses on the portions of the vertebrae. angles of the dovetail, thereby causing rupture and cracking of the polysulfone. Thus, a variation in this embodiment comprises a composite implant, made from a plastic material such as polysulfone, for the body, and titanium for the endplates that support the dovetail protrusions. Figures 3A, 3B and 3C show a possible arrangement of this composite structure, with a titanium endplate 8 placed inside the plastic body (and radiotransparent e) 9. Figures 4A to 4C show a variation of this arrangement in where the endplate extends to the lateral margins of the plastic body of the implant 11. Both figures 3 and .4 show a variation of this structure, wherein the titanium endplate 12 is placed inside the plastic body of the implant 9 and 11 in a configuration designed to provide passage spaces or cavities 14 in which the bone growth material can be placed. In these latter configurations, the polysulfone body is inserted molded into the titanium endplates. The dovetail fasteners, titanium, have the tensile strength needed to prevent fracture or cracking, but the body still has the characteristic that "can be seen" from one side to the other, with X-rays and other methods of visualizing the progress of healing. In addition, the holes in the titanium endplates, which are aligned with the cavities for the bone growth material, provide the ability to "see from one side to another" in the vertical direction, to evaluate the growth of new bone. A second preferred embodiment, shown in isometric view in FIG. 5, is inserted between two vertebrae, for example, L4 and L5 or L5 and SI and is mechanically joined by two or more dovetail joints or through a compound of Horseshoe-shaped dovetail, located on each of the upper and lower surfaces of the implant, to the remaining adjacent vertebrae, by means of a compound, tongue and groove mechanism, similar but larger than that used to ensure the implant of the previous modality. In this configuration the implant comprises either a horseshoe-shaped dovetail tongue 33, which in effect creates two dovetail joints, per surface, towards the outer ends of the upper and lower surfaces of the implant, or simply two exterior dovetail tabs, without the upper horseshoe lock. The horseshoe top closure may be substantially curved or it may be substantially straight, with relatively square corners where the dovetail tongue is biased back towards the body of the vertebra. In a variation of this embodiment, within the horseshoe shaped tab of the dovetail tongue 33, the body of the implant is hollow, that is, it contains an opening or cavity 34 communicating with both the upper surface and the lower surface, within which the bone growth material is placed. In this preferred embodiment, as shown further in the isometric view in Figure 6, the implant 35 with a relatively square horseshoe upper closure will have a surface approximately flush with the outer surface of the adjacent vertebrae and will appear to create a dovetail 37 very wide. This embodiment of the implant will also include penetrations or holes in addition to, or alternatives to, those shown in Figure 5, 34, the purpose of which is also to retain the growth material, bone, to facilitate bone fusion of the vertebrae. adjacent. As in the above configuration, the implant 35 is positioned so as to provide mechanical support, both in compression and in tension, to the spine, but not so as to enter the space 6 occupied by the nerve bundle of the spine. The implant in certain cases is further inserted into the remaining segments of tissue 38 of the intervertebral disc. As shown in both Figures 5 and 6, an optional feature of these embodiments is that the implant faces have locking pins 36 to hold the implant in place, between the remaining vertebrae, once it is inserted. This implant, as in the previous embodiment, can itself comprise a variety of currently acceptable implant materials, such as Polyester Ester Ketone (PEEK), Acetyl (delrin), Polysulfone, Ultra-High Molecular Weight Polyethylene (UHMW Poly). , for its acronym in English), and composite materials involving carbon fibers or high strength glass filaments, to add resistance to stress and shear. Again, as discussed further below, the material for human bone allograft can be used to make this device. This mode can also be manufactured with a modest taper to accommodate the natural lordosis. A third preferred embodiment of the lumbar implant, shown in isometric view in Figure 7, comprises three elements, two modular dovetail halves, 41 and 42, which are inserted between the vertebrae L4 and L5 or L5 and SI and mechanically joined together by two dovetail protuberances (similar to those manufactured for the second modality) located on the top and bottom of the implant, in the adjacent vertebrae, by a tongue and groove mechanism similar but larger than that used to secure the previous modalities of the implant. The two modular dovetail halves are held together by a retainer 43. As in the previous configuration, as shown in the isometric view of Figure 8, the implant 35 is positioned in such a way as to provide mechanical support for both under compression as under tension, to the spine, but not as to enter inside the space occupied by the bundle of nerves of the spine. In this preferred modality, as shown in Figure 8, the implant 35 - will include a cavity 39 the purpose of which is to contain the bone growth material, to facilitate bone fusion of the adjacent vertebrae. The open space 39 is packaged with bone growth material and then covered with a retainer 43 designed to press into place there and add stability to the implant and retain the bone growth factor to prevent it from coming out. This implant, as in the above embodiment, can itself comprise a variety of currently acceptable implant materials such as Polyester Ester Ketone (PEEK), Acetyl (delrin), Polysulfone, Ultra-High Molecular Weight Polyethylene (UHMW Poli, for short) in English), and composite materials that involve carbon fibers or high strength glass filaments, to add tension and shear strength. Again, the modular dovetail halves can be tapered to accommodate the lordos is.

Any of the foregoing embodiments may additionally have a feature shown in Figures 5, 6 and 9, especially a retractable prong 36. This prong comprises a wire spring that when deployed engages the adjacent vertebrae to prevent the implant from dislocating . A retraction tool can be inserted into the hole 39 to cause the sigma to retract its tip in the form of a probe, such that the implant disengages from the adjacent vertebra. As previously mentioned, any of the preceding embodiments of the Cor-LokMR intermediate immobilization implant can be fabricated from cadaver bone, which is processed to form the bone allograft material. The grafting of tissues, of living tissue from the same patient, including the bone graft, is well known. The tissue, such as bone, is removed from a part of a body (the donor site) and inserted into the tissue elsewhere (the host site) thereof (or another body). With respect to living bone tissue, in the past it has been desired to be able to remove a piece of graft material from living tissue that is of the exact size and shape necessary for the host site where it will be implanted, but achieving this goal has been shown to be very difficult . On the other hand, the processing of bone material that does not contain living tissue is becoming more and more important. The technique of bone grafts, non-living, has been tried both for autografts and for allografts. For example, US Patent No. 4,678,470 to Nashef, discloses a method for creating a bone graft material, machining a bone block into a particular shape or spraying and grinding it. The graft material is then tanned with glutaraldehyde to sterilize it. This process can produce bone plugs in a desired way. In the Nashef process, the process of spraying or grinding the bone material destroys the structure of the bone tissue. The stage of tanning with glutaraldehyde makes the bone material completely sterile.

In the prior art, the inventors have thought that it is desirable to maintain the graft tissue in a living state during the grafting process. There is no doubt that the use of living tissue in a graft will promote bone healing. But many surgical experiences have shown that healing can be achieved with allografts of non-living bone material that has been processed. In effect, surgeons of the spine express a different preference for these materials, and at least one provider, the Foundation for Musculoskeletal Transplants (MTF, for its acronym in English), has introduced allografts of the femoral ring for surgeries of the spine. Now it is possible to obtain bone for allograft that has been processed, to remove all living material that might exhibit a problem of rejection of the tissue or an infection problem. This processed material preserves much of the structural quality of the original living bone, making it an eoinductor. In addition, it can be shaped according to new and known methods to achieve improved structural behavior.

Research shows that these allografts are very favorable for spinal surgery. According to Brantigan, J. W., Cunningham, B.W., Warden, K., McAfee, P.C., and Steffee, A.D., "Compression Strength Of Donor Bone For Posterior Lumbar Interbody Fusion," Spine, Vol. 18, No. 9, pp. 12113-21 (July 1993): "Many authors have seen donor bone as the equivalent of autologous bone, Nasca et al., Compared fusions in the spine in 62 patients, with autologous bone, and 90 patients with bone preserved cryologically, and found successful arthrodesia in 87% of patients with autologous bone and in 86.6% of patients with allograft ". (Quotations omitted). Also, as previously mentionedRecently sources of material for allograft processed safely have been found available. In the present invention, the allograft bone is reshaped to obtain one of the configurations of Cor-Lok ™ for use as an implant for the spine. Various methods, including Bonutti's, US Patent Nos. 5,662,710 and 5,545,222, may be used to give the allograft material the desired shape. In the first secondary embodiment of this aspect of the present invention, bone material is formed that yields to compression loads on the outer surfaces, without significant degradation of structural, interior properties, such as cancellous or trabecular bone. It is not usual to re-shape the graft tissue in order to obtain the best possible graft. In particular, the bone tissue can be stronger and better able to withstand forces when it is denser and more compact. Compression of allograft bone is desirable from the point of view of general considerations. Generally, bone samples are stronger when they are denser. The compression of allograft bone increases its density and thus generally makes the allograft stronger. The allograft bone also binds better. In addition, recent studies have indicated that the cortex of the vertebral bone is most likely trabecular bone condensed. Mosekilde, L., "Vertebral structure and strength in vivo and in vitro," Cale. Tissue Int. 1993; 53 (Suppl): 121-6; Silva, M.J., Wang, C, Keaveny, T.M., and Hayes, W.C., "Direct and computed tomography thickness measurements of human lumbar vertebral shell and endplate," Bone 1994; 15: 409-14; Vesterby, A., Mosekilde, L., Gunderson, H.J.G., et al., "Biologically meaningful determinations of the intro strength of lumbar vertebrae," Bone 1991; 12: 219-24. Compressing the bone allograft material prior to implantation usually produces a stronger graft. The compression also allows the conversion of larger irregular shapes, in the smallest, desirable form, thereby allowing more different allograft bone sources to be used. By compressing the bone to a certain shape it is possible to configure the allograft to coincide with a container site, preformed and prepared using a contoured cutter to cut a precisely matching cutting space. In particular, this method of training facilitates the formation of dovetail tongue protuberances, on the upper and lower surface of the implant, for the formation of a mechanical tongue and groove joint, with the adjacent vertebrae. In the present invention, a free space is removed from the allograft, cancellous or trabecular bone, and placed in a forming apparatus. The forming apparatus compresses the sample to the desired shape. In particular, this process forms the dovetail tongue protrusions on the upper and lower surface of the implant, for the tongue and groove joint. The cancellous or trabecular material yields on the external surface under pressure, to form a compacted layer around the outside of the allograft form. This compacted layer is not destroyed material but rather substantially forms a structure with properties of the vertebral cortex or a monocoque design, which includes additional structural properties such as improved tensile strength. This improved tensile strength allows the allograft material to perform the same function to resist torsion and extension of the spine as the previously analyzed synthetic materials do. These processes, in general, are able to maintain the homologous property of allograft material. In the second embodiment of this aspect of the present invention, different types of allograft bone are formed as a composite structure to provide the necessary structural properties. Both cancellous or trabecular bone dense, cortical or outer sheath can be compacted into a unified structure. The "tail" of fibrin is very suitable for use as an adhesive in those structures. Fibrin is a component of blood, important for blood clotting. It can be separated or centrifuged from the blood and has the nature of an adhesive gel. Fibrin can be used as an adhesive, either in its natural state or after being compressed, to hold the material together, such as pieces of separate tissue, compressed with each other in a tissue press. In particular, cortical bone from the same source can be used as an outer wrap to provide a composite shape with additional necessary structural properties, such as tensile strength. The cortical bone can also be provided in an outer envelope, quite similarly to known femoral ring implants, to provide the necessary structural properties. In addition, an external envelope is not the only structural element that can be added in this way. In the same way you can include structural elements such as buttresses, bevels, braces and other structural elements. By using these materials, the homologous property of the bone allograft material can be maintained. In another secondary embodiment, a relatively thin outer envelope can be provided, of a synthetic material, to enclose the material for compressed allograft, and provide any additional structural properties needed. After the graft is compressed, the outer wrap is placed around the graft. The outer wrap can be made of a material that expands after it is placed on the spine, thus complementing the intermediate locking properties of the Cor-LokMR mechanical design, providing filling between the allograft and the recipient's site. donation. There are a number of suitable materials that expand when they come in contact with water or other fluids. One is Polyether Ether Ketone (PEEK) (water absorption of about 1.5%). A dried, desiccated biodegradable material or other allograft material may also be used. The expansion can take place in one of two ways. First, the retainer can be compressed, such as with tissue, and then expanded when placed on the body. Second, the retainer can be made of a material that expands when it comes into contact with water or other bodily fluids. It should be noted that the entire allograft implant can be compressed as such, so that it expands when it contacts the water. The expandable outer wrap material can be compressed first with the allograft material, which then expands when placed on the body. It should further be understood that the graft may consist of multiple fragments of tissue, rather than of a composite material. The compression process can be used to compress multiple fragments of bone and form a single larger piece. It should also be understood that the compression process can be used to add additional materials to an allograft material. For example, to the bone tissue can be added tricalcium phosphate, an antibiotic, hydroxyapatite, autografts or polymeric materials. The figures from 10A to 16B represent surgical tools used to install the implant. This apparatus comprises a set of unique tools that will accurately cut a dovetail joint in the bone for the purpose of inserting an implant that immobilizes the adjacent vertebrae with one another.

The guide 44, shown in Figures 10A and 10B, is a tubular tool with raberas 45 extending from one end. The raberas, tapering, 46, to conform to the natural lordosis, are inserted between the vertebrae 47 and separate them to a preferred dimension 48 as shown in Figure 10B. The actuator 68, shown in Figure 5 can be used with a rod extension guide adapter 70, also shown in Figure 15, to urge the guide 44 into place. This stage establishes a fixed reference in relation to the two vertebrae 47 and ensures the vertebrae not to move. The length 49 of the rabbits 45 is consistent with the other tools of the assembly and establishes the degree 49 up to which any tool can penetrate. A lateral X-ray apparatus is used to ensure that the penetration degree 49 is securely away from the spinal canal 50. All other tools have positive catches that contact the depth retainer 51 of the guide, to control the depth of the cut. The extreme cutting tool 52, shown in Figures HA and 11B, is inserted into the guide 44 to make an end cut 52, shown in Figure 11B, for the dovetail. Once fully inserted to the depth retainer 53, a one-piece intermediate locking fastener 54, shown in FIGS. 12A and 12B, which prevents rotation of the blade 55 during insertion, is decoupled from the shaft 56 and then prevents the removal of the end cutting tool 52 from the guide 44. As shown in Figures 12A, and 12B, the intermediate locking latch 54 is held by the spring 57, such that it engages the slot 58 that is find on axis 56, preventing rotation as shown in Figure 12A. When the end cutting tool 52 is inserted into the guide 44 it pushes the intermediate locking latch 54, causing it to rotate out of the slot 58 in the shaft 56, as shown in FIG. 12B. As the intermediate locking latch rotates, it engages guide 44 as shown in FIG. 12B. When the shaft 56 is rotated, as shown in FIG. 12B, the intermediate locking latch 54 can not return to its original position, as shown in FIG. 12A, thereby securing the extreme cutting tool 52. in the guide 44. The intermediate locking latch, in rotation, protects the surgeon from the extreme cutting blade 55 and the removable intermediate locking latch keeps the extreme cutting tool 52 in the guide 44 while the blade 55 is exposed. The surgeon rotates the handle 59 one turn causing the end cutting blade 55 to make extreme cuts 52 as shown in Figure 11B on both vertebrae 47, simultaneously, and return it to the "zero" position in which the end cutting tool 52 can be removed from the guide 44. The dovetail surgical cutting instrument 60, shown in Figure 13A, is inserted into the guide 44 to the point where the blade 61 rests against the vertebrae 47. As shown in Fig. 15, the actuator 68 is placed on the rod extension 62 of the dovetail cutting surgical instrument and operates the dovetail cutting surgical instrument 60, cutting the vertebrae 47, until the depth stop 63 of the dovetail surgical instrument makes contact with the retainer 51 on the guide 44, stopping the blade 61 at the end cut 52, as shown in figure 13 C. The dovetail surgical cutting blade 61, as shown in Figure 14A, has endplate fractures 64, which divide the end plates 65 of the vertebrae (see Figure 13C) into two 66 as shown in FIG. Figure 14B, preventing them from getting stuck in the blade and preparing them for later use. The surgical instrument of cutting 60 of tail of a dove, is removed, and the bone 67 and split vertebral end plate 66 contained in the blade 61 is collected for later use in the implant 33. As shown in Fig. 15, the actuator 68- is a similar pneumatic tool to a miniature pneumatic hammer. The actuator 68 is operated by compressed gas supplied through the inlet tube 69. The actuator 68 receives the rod extension from the guide adapter 70 or the rod extension of the dovetail cutting surgical instrument 62, within a guide hole 71. A piston 72, inside the actuator 68, repeatedly impacts the guide adapter 70 or the rod extension 62 of the dovetail cutting surgical instrument, driving the tool into place. The actuator 68 is activated by the valve 73 that is operated with the finger. The control of the force and speed of the impacts are achieved by modulating the valve 73. The actuator will supply several thousand small impacts instead of a few massive blows from a hammer. The implant 33 of Figure 5 is prepared for insertion by filling the inner portion 34 with collected bone 67 and the split end plates 66, the cuts made by the dovetail surgical instrument, and additional bone and graft material. . The implant 33 then slides in the guide 44 (figure 10) and is pushed to the site by the insertion tool 74, shown in figures 16A and 16B. The insertion tool 74 has a positive retainer 75 which contacts the depth retainer 51 of the guide 44 and ensures the correct positioning of the implant 33, immobilizing the vertebrae 47. The implanting devices, above, contain fixing means that are Well known in the wood processing industry, but not used in Orthopedic Spine Surgery. However, a person skilled in the technique of intervertebral implants would be able, easily, to adapt other fixation devices known in the technique of the transformation of the wood, to the devices for implants in the spine. It will be readily apparent to anyone skilled in the art that there are several means available to attach the bone surfaces to the surfaces of the adjacent implants in order to cause bone anchors to protrude from the surface of the implant and collide and join the vertebrae adjacent to the implant. Staple-like metal clips can be placed between the adjacent vertebrae to join the edges of the vertebrae. Tack and staple configurations can replace the dovetail tongue and groove fasteners. Anchors can also be used for bones in order to join the natural tissue with the adjacent vertebrae, creating an artificial ligament that could form a scar, thus preserving an artificial implant within the disc space while the osteoinduction and the vertebrae are carried out. they merge It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, the content of the following is claimed as property:

Claims (30)

1. An implant for mechanically joining the ends of at least two adjacent vertebrae to a space left by surgically removed spinal tissue, and promoting bone fusion thereof, characterized in that it comprises: a. a body for the distribution of load, which comprises a structure that has: i. a combination of structural elements manufactured from at least one material having an elastic deformation greater than zero, the combination comprises at least one upper surface and one lower surface; ii. the combination of structural elements establishes for the structure as a whole, a composite elastic deformation, greater than zero, at least under compression, in directions generally axial to the upper surface and to the lower surface; iii. the combination of structural elements further comprises at least one cavity communicating with both the upper surface and the lower surface, in a suitable configuration as a receptacle for the bone implant and growth material; and b. in each upper and lower surface, at least one fastener capable of mechanically anchoring the body to the adjacent vertebrae and thereby transmitting the tension and torsional loads to and from the adjacent vertebrae.

2. The implant according to claim 1, characterized in that the at least one fastener on each upper and lower surface comprises a dovetail tongue protrusion, which has a shape such that it coincides with a groove substantially of the same shape, for form a mechanical tongue and groove joint.

3. The implant according to claim 1, characterized in that the at least one fastener on each upper and lower surface, comprises a protrusion of dovetail tongue, in the shape of a horseshoe, with segments on the external portions of the body, the tongue in The dovetail has such a shape to coincide with a groove of substantially equal size and form a mechanical tongue and groove joint.

4. The implant according to claim 1, characterized in that the at least one fastener on each upper and lower surface comprises a plurality of dovetail tongue protuberances, and each of the plurality has a shape to match a slot of substantially equal size, to form a mechanical tongue and groove joint.

5. The implant according to claim 1, characterized in that the at least one fastener on the upper and lower surface comprises at least one tack and staple device.

6. The implant according to claim 1, characterized in that the at least one fastener on each upper and lower surface comprises at least one anchor for the bone

7. The implant according to claim 1, characterized in that the combination of elements comprises an assembly of at least three modular components, the first modular component comprises a right partial separator, the second modular component comprises a left partial separator, and each has a minus one upper surface and one lower surface, and the third modular component comprises a retainer / keeper.

8. The implant according to claim 7, characterized in that the dovetail separator, partial, right, and the partial left dovetail separator, each has, on each upper and lower surface, at least one capable fastener of mechanically anchoring the partial separator to the adjacent vertebrae.

9. The implant according to claim 7, characterized in that the partial separator, right, and the partial separator, left, each has, on each upper and lower surface, at least one fastener, so that together the fasteners form a structure able to mechanically anchor the implant to the adjacent vertebrae.

10. The implant according to claim 1, characterized in that the upper and lower surface are oriented with respect to each other, at an angle such that the implant is able to maintain the lordosis of the spine after insertion.

11. The implant according to claim 1, characterized in that the at least one material having elastic deformation greater than zero, from which the combination of structural elements is manufactured, is selected from the group of the Polyester Ester Ketone (PEEK), Acetyl ( delrin), polysulfone, Ultra-High Molecular Weight Polyethylene (UHMW poly) and composite materials that involve carbon fibers or high-res ist gum glass filaments.

12. The implant according to claim 1, characterized in that the at least one material having an elastic deformation greater than zero, from which the combination of structural elements is manufactured, comprises a material for human bone allograft.

13. The implant according to claim 1, characterized in that it additionally comprises at least one retractable prong on at least one of the upper and lower surfaces, the at least one prong is retractably coupled to the surface of the adjacent vertebra, in order to prevent the implant is dislocated.

14. The implant for mechanically joining the ends and promoting the bone fusion of at least two adjacent vertebrae, to a space left by surgically removed spinal tissue, characterized in that it comprises a structure formed from a single piece of allograft bone material and having a upper and lower part, the structure has an internal cavity communicating with that upper and lower part, to receive an autograft bone material and bone growth factors, the structure has at least one prsion of dovetail tongue on each upper and lower part, for mechanical immobilization with the adjacent vertebrae, forming a mechanical joint of tongue and groove.

15. An implant for mechanically joining the ends of at least two adjacent vertebrae to a space left by surgically removed spinal tissue, and 'promoting bone fusion thereof, characterized in that it comprises a composite structure, fabricated with at least two separate portions of Bone material for allograft and having an upper part and an upper part, that structure has an internal cavity that communicates with the upper part and with the lower part, to receive the bone implant material for autograft and bone growth factors, the The unitary structure has at least one dovetail tongue on both the upper part and the lower part, to mechanically immobilize the adjacent vertebrae by means of tongue and groove joints.

16. The implant according to claim 15, characterized in that the at least two separate portions of the allograft bone material have different structural properties.

17. The implant according to claim 15, characterized in that the at least two separate portions of allograft bone material are bonded together with an adhesive such as the fibrin glue, to form a homologous structure.

18. The implant according to claim 15, characterized in that the at least two separate portions of the allograft bone material, with different structural properties, are bonded together with an adhesive such as the fibrin glue, to form a homologous structure.

19. The implant according to claim 14, characterized in that the structure formed from a single piece of allograft bone material receives the desired shape and structural properties by compression, such that the outer layers of the trabecular or cortical bone, form a compressed layer with structural properties that intensify the structural characteristics of the structure.

20. The implant according to claim 19, characterized in that the outer layers of the bone, trabecular or cortical forming a compressed layer, comprise a structural outer sheath.

21. The method for mechanically joining and promoting bone fusion, of two adjacent vertebrae, in a space left by surgically removed tissue, characterized in that it comprises the implantation of a load-distributing implant that shares the compression loads with the adjacent vertebrae, in order to promote the growth of bone material between the adjacent vertebrae, which is attached to the adjacent vertebrae with fasteners to transmit the shear and tension loads, in order to allow relative movement during and after healing.

22. The method for joining both adjacent vertebrae to a space left by spinal tissue, excised, to an elastic implant comprising an internal cavity filled with bone splinters and / or bone growth medium, designed to promote and accelerate the fusion of the adjacent vertebrae, in such a way that the compression loads are shared with the bone chips and / or the means for the growth of the bones, in order to transmit the stress and torsional loads.

23. A device for separating and holding the adjacent vertebrae, to a space left by spinal tissue, surgically removed, characterized by comprising: a. an elastic body for compression loads and comprising spaces for the placement of material for the growth of bones; and b. fasteners that securely attach to adjacent vertebrae and transmit tension and torsional loads to and from adjacent vertebrae.

24. A device for separating and fixing vertebrae adjacent to a space left by spinal tissue, surgically removed, characterized in that it comprises: a. means for separating adjacent vertebrae while yielding elastically to compression loads; b. means for the placement of a material for the growth of bones; and c. means for securely attaching the device to adjacent vertebrae and transmitting tension and torsional loads to and from the adjacent vertebrae.

25. A surgical, dovetail cutting device that cuts at least two dovetail slots in the bone simultaneously.

26. The dovetail surgical cutting apparatus according to claim 25, characterized in that it comprises at least one axis, a guide and a surgical cutting instrument.

27. A surgical cutting instrument, according to claim 25, characterized in that it additionally comprises an inclined blade that separates the bone removed by the tool, in order to prevent clogging of the tool.

28. A cutting apparatus characterized in that it comprises a single intermediate locking element which prevents the rotation of the shaft outside the guide and which prevents the removal of the tool from the guide while the shaft is rotated.

29. A means consisting of a guide, to stabilize vertebrae adjacent to a space left by spinal tissue, surgically removed, and to establish references for a surgical cutting device.

30. An actuating apparatus of the surgical cutting instrument, capable of providing a plurality of small impacts, axially and sequentially to a device for cutting bone.