MXPA96001079A - Intercorporal fusion device and method for the restoration of anatomy of the columnaverteb - Google Patents

Abstract

The present invention relates to a fusion device for facilitating arthrodesis in the disc space between adjacent vertebrae, characterized in that it comprises: an elongate body having a length and a first end and a second end thereof, and a first diameter in the first end dimensioned to be greater than the space between the adjacent vertebrae, the body further defines a hollow interior dimensioned to receive therein material that promotes bone growth, the body having an outer surface with a pair of opposite cylindrical portions extending to along substantially the entire length of the body and defining the first diameter, and a pair of substantially flat opposed side walls connected between the opposed cylindrical portions, the side walls extending along a substantial portion of the length of the body and external threads defined in the pair of opposite cylindrical portions of the to outer surface and extending along substantially the entire length of the body

Description

INTERCORPORAL FUSION DEVICE AND METHOD FOR THE RESTORATION OF THE ANATOMY OF THE SPINAL COLUMN BACKGROUND OF THE INVENTION The present invention relates to an artificial implant to be placed in the intervertebral space left after the removal of a damaged vertebral disc. Specifically, the invention relates to an implant that facilitates arthrodesis or fusion between adjacent vertebrae, while also maintaining or restoring the normal anatomy of the vertebral column at the particular vertebral level. The number of spinal surgeries to correct the causes of pain in the lower back has steadily increased over the past several years. More frequently, pain in the lower back originates from damage or defects in the vertebral disc between adjacent vertebrae. The disc may be herniated or may suffer from a variety of degenerative conditions, such that in any case, the anatomical function of the disc of the spinal column is interrupted. The most prevalent surgical treatment for these types of conditions has been to fuse the two vertebrae that surround the affected disc. In most cases, the entire disc will be removed, except for the ring, by means of a discoidectomy procedure. Since the damaged disc material has been removed, something must be placed within the intradiscal space, in any other way the space may be compressed resulting in damage to the nerves that extend along the spine. To prevent this disc space from compressing, the intradiscal space is filled with bone or a bone substitute to fuse the two adjacent vertebrae together. In the first techniques, the bone material was simply placed between the adjacent vertebrae, typically in the posterior aspect of the vertebrae and the spine stabilized by a plate or a rod extending over the affected vertebrae. With this technique once the merger occurred, the equipment used to maintain the stability of the segment reaches. be superfluous In addition, the surgical procedures necessary to implement a rod or a plate to stabilize the level during fusion were frequently prolonged and complicated. Therefore, it was determined that a more optimal solution for the stabilization of the excised disc space is to fuse the vertebrae between their respective end plates, more optimally without the need for anterior or posterior plate placement. There have been an extensive number of attempts to develop an acceptable intradiscal implant, which could be used to replace a damaged disc and still maintain the stability of the disk interspace between the adjacent vertebrae, at least until complete arthrodesis is achieved. These "interbody fusion devices" have taken many forms. For example, one of the most prevalent designs takes the form of a cylindrical implant. These types of implant are represented by the Bagby patents, No. 4,501,269; Brantigan, No. 4,878,915; Ray, Nos. 4,961,740 and 5,055,104; and Michelson, No. 5,015,247. In these cylindrical implants, the outer portion of the cylinder can be threaded to facilitate insertion of the interbody fusion device, as represented by the Ray, Brantigan and Michelson patents. In the alternative, some of the fusion implants are designed to be placed in the intradiscos space and the vertebral end plates. These types of devices are represented by the Brantigan patents, Nos. 4,743,256; 4,834,757 and 5,192,327. In each of the patents listed above, the cross section of the implant is constant over its entire length and is usually in the form of a straight circular cylinder. Other implants for interbody fusion have been developed that do not have a constant cross section. For example, McKenna patent No. 4,714,469 shows a hemispherical implant with an elongated protrusion projecting into the vertebral endplate. The Kuntz patent, No. 4,714,469, shows a bullet-shaped prosthesis configured to optimize a friction fit between the prosthesis and the adjacent vertebral bodies. Finally, the Bagby implant, No. 4,936,848 is in the form of a sphere, which is preferably placed between the centers of the adjacent vertebrae. Interbody fusion devices can generally be divided into two basic categories, namely solid implants and implants that are designed to allow inward bone growth. Solid implants are represented by U.S. Patent Nos. 4,878,915; 4,743,256; 4,349,921 and 4,714,469. The remaining patents discussed in the foregoing include some aspect that allows the bone to grow through the implant. It has been found that devices that promote the growth of natural bone achieve a faster and more stable arthrodesis. The device depicted in the Michelson patent is representative of this type of hollow implant, which is typically filled with autologous bone prior to insertion into the intradiscos space. This implant includes a plurality of circular openings, which communicate with the hollow interior of the implant, thereby providing a path for tissue growth between the vertebral endplates and the bone or bone substitute within the implant. In the preparation of the intradiscal space, the end plates are preferably reduced for bone drainage to facilitate this growth into the tissue. During fusion, the metal structure provided by the Michelson implant helps maintain the opening V stability of the movement of the segment to be fused. In addition, once arthrodesis occurs, the implant itself serves as an anchor class for solid bone mass. Many difficulties remain with many interbody fusion devices currently available. Although it is recognized that hollow implants that allow the ingrowth of bone into bone or a bone substitute within the implant, is an optimal technique for achieving fusion, most prior art devices have difficulty in achieving this fusion , at least without the help of some additional stabilization device, such as a rod or a plate. In addition, some of these devices are not structurally strong enough to withstand the heavy loads and bending moments applied to most frequently fused vertebral levels, namely those in the lower lumbar spine.

There has been a need to provide a gap in the interbody fusion device that optimizes the inward growth capabilities of the bone, but still strong enough to support the segment of the spine until arthrodesis occurs. It has been found that openings for inward growth of the bone, play an important role in preventing the tension of the protective plate of the autologous bone impacted within the implant. In other words, if the openings for inward growth are inadequately sized or configured, the autologous bone will not support the load typically found necessary to ensure rapid and complete fusion. In this case, the bone impacted within the implant can be resolved or developed simply into a fibrous tissue, instead of a bone fusion mass, which generally leads to unstable construction. On the other hand, the growth openings in the bone should not be too extensive in such a way that the box provides insufficient support to avoid sinking into the adjacent vertebrae. Another problem that is not considered by the prior art devices relates to the maintenance or restoration of the normal anatomy of the fused spinal segment. Naturally, once the disc is removed, the normal lordotic or kyphotic curvature of the spine is removed. With the above devices, the need to restore this curvature is negligible. For example, in one type of commercial device, the SpineTech BAK device, as represented by the Bagby patent, No. 4,501,269, the adjacent vertebral bodies are widened with a cylindrical stretcher that adjusts the particular implant. In some cases, normal curvature is established before widening and then the implant is inserted. This type of construction is illustrated in FIGURE 1, which reveals the penetration depth of the cylindrical implant into generally healthy vertebrae, adjacent to the instrumental disc space. However this over-widening of the posterior portion is generally not very accepted, due to the removal of the bone that carries the load of the vertebrae and because it is normally difficult to widen through the posterior portion of the lower lumbar segment where the lordosis is older. In most cases, using implants of this type, no effort has been made to restore the lordotic curvature, such that the cylindrical implant is likely to cause a kyphotic deformity as the vertebrae settle around the implant. This phenomenon can often lead to revision surgeries because the spine becomes unbalanced.

In view of these limitations of the above devices, there is a need for an interbody fusion device that can optimize inward growth of the bone, while still maintaining its strength and stability. There is also a need for such an implant that is capable of maintaining or restoring the anatomy of the spine, normal in the instrumented segment. This implant must be strong enough to support and handle heavy loads generated in the spine at the instrumented level, while remaining stable throughout the duration.

BRIEF DESCRIPTION OF THE INVENTION In response to the needs still left unresolved by the above devices, the present invention contemplates a fusion, interbody, threading, hollow device configured to restore the normal angular relationship between adjacent vertebrae. In particular, the device includes an elongated body, tapered substantially along its entire length, defining a hollow interior and having an outer diameter greater than the size of the space between the adjacent vertebrae. The body includes an outer surface with tapered cylindrical portions, opposite and a pair of side surfaces, tapering, flat, opposite between the cylindrical portions. In this way, in an end view, the fusion device gives the appearance of a cylindrical body in which the sides of the body have been truncated along a cord of the outer diameter of the body. The cylindrical portions are threaded for controlled insertion and engagement in the end plates of the adjacent vertebrae. In another aspect of the invention, the outer surface is tapered along its length at an angle corresponding, in one embodiment, to the normal lordotic angle of the lower lumbar vertebrae. The outer surface is also provided with many vascularization openings defined in the flat side surfaces and a pair of opposing, elongate bone growth grooves in the cylindrical portions. The grooves for inward bone growth have a transverse width that is preferably about half the effective width of the cylindrical portions within which the grooves are defined. A conducting tool is provided for inserting the fusion device into the intradiscos space. In one feature, the driving tool includes an axle having a pair of opposing tapered pliers or tongs located at one end. The clamps are connected to the shaft by means of an articulation groove that deflects the clamps to separate them to receive a fusion device between them. In addition, the conductive tool is provided with a sleeve positioned concentrically about the axis and configured to slide along the axis and compress the joint to push the clamps together to hold the fusion device, alternatively, an internal metal expansion ring can be used to Internally maintain the fusion device safely during insertion. In one aspect of the conductive tool, the tapered pliers have an outer surface that takes the form of the tapered cylindrical portions of the fusion device. The tweezers also have a surface that faces inward, flat to correspond to the flat side surfaces of the fusion device. In this way, when the clamps are pressed against the fusion device, the inward facing surfaces of the clamps make contact with the flat sides of the fusion device and the outer surface of the clamps completes the conical shape of the fusion device for facilitate the screwed in the insert. The facing surface inward of the clamps may also be provided as projections for coupling the openings in the fusion device to allow the drive and rotation of the device within the intradiscos space. In another aspect of the invention, methods are provided for implementing the fusion device between the adjacent vertebrae. In one method, the approach is prior and includes the steps of dilating the disc space and piercing the end plates of the vertebra adjacent to the smaller diameter of the threads of the fusion device. A sleeve is inserted to provide a working channel for the piercing step and the subsequent step of implanting the fusion device. The implant is coupled with the conductive tool, inserted through the sleeve and threaded into the prepared hole. The insertion depth of the tapered fusion device determines the amount of angular separation achieved for the adjacent vertebrae. In another inventive method, the insertion site is subsequently prepared, namely, the disc space is dilated and a smaller diameter orifice is punctured in the vertebral endplates. A sleeve is also arranged to provide a working channel for the drilling and insertion stages. The fusion device is inserted into the pierced hole with the flat side walls facing the adjacent vertebrae. The device is then rotated in such a manner that the external threads in the cylindrical portion intersect and engage the adjacent vertebrae. further, since the fusion device is tapered, the tapered outer surface of the device will angularly separate the adjacent vertebrae to restore normal anatomical lordosis.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is an elevation, side view in the sagittal plane of a fusion device of the prior art. FIGURE 2 is an enlarged, perspective view of an interbody fusion device according to an embodiment of the present invention. FIGURE 3 is a cross-sectional, side view of the interbody fusion device shown in FIGURE 2, taken along line 3-3 as seen in the direction of the arrows. FIGURE 4 is an end elevation view of the anterior end of the interbody fusion device shown in FIGURE 2. FIGURE 5 is a top elevation view of the interbody fusion device shown in FIGURE 2.

FIGURE 6 is a side view A-P of the anterior aspect of the spine showing two interbody fusion devices according to FIGURE 2 implanted within the interbody space between L4 and L5. FIGURE 7 is a view in the sagittal plane of the interbody fusion device, implanted between L4 and L5 shown in FIGURE 6. FIGURE 8 is a perspective view of an alternative embodiment of the interbody fusion device, according to FIG. the present invention. FIGURE 9 is a top elevational view of an implant driver in accordance with another aspect of the present invention. FIGURE 10 is an enlarged, perspective view of the end of the implant driver coupled around an interbody fusion device, as shown in FIGURE 2. FIGURE 11 is an enlarged, partial, lateral, cross-sectional view showing the implant driver engaging the interbody fusion device, as shown in FIGURE 10. FIGURE 12 is an enlarged, partial, lateral, cross-sectional view showing an implant impeller of an alternative embodiment, adapted to attach to the device 10 of interbody fusion.

FIGURES 13 (a) - 13 (d) show four stages of a method according to one aspect of the invention for implanting the interbody fusion device, such as the device shown in FIGURE 2. FIGURES 14 (a) - 14 (d) represent the steps of an alternative method for implanting the interbody fusion devices, such as the device shown in FIGURE 2.

DESCRIPTION OF THE PREFERRED MODALITIES For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the modalities illustrated in the drawings and specific language will be used to describe the same. However, it should be understood that no limitation of the scope of the invention is therefore intended, such alterations and other modifications in the illustrated device and such other applications of the principles of the invention as illustrated therein, are contemplated as they are normally intended. it would happen to someone with skill in the technique to which the invention relates. An interbody fusion device 10 according to one aspect of the present invention is shown in FIGURES 2-5. The device is formed by a conical, solid body 11 which is preferably formed of a biocompatible material or inert material. For example, the body 11 can be made of medical grade stainless steel or titanium or other suitable material having suitable strength characteristics set forth herein. The device may also be formed of a biocompatible porous material, such as porous tantalum provided by Implex Corp. For reference purposes, the device 10 has an anterior end 12 and a posterior end 13, which corresponds to the anatomical position of the device. 10 when it is implanted in the intradiscos space. The conical body 11 defines a hollow interior 15, which is joined by a body wall 16 and closed at the rear end 13 by an end wall 17 (see FIGURE 3). The hollow interior of the device 10 is configured to receive autografted bone or a bone substitute material adapted to promote a solid fusion between the adjacent vertebrae and through the intradiscal space. According to the invention, the interbody fusion device 10 is a threaded device configured to be screwed into the end plates of the adjacent vertebrae. In one embodiment of the invention, the conical body 11 defines a series of external, interrupted threads 18 and a complete thread 19 at the front end of the implant. The complete thread 19 serves as an "initiating" thread for screwing the implant into the vertebral end plates in the intradiscal space. the threads 18 and 19 may take various forms known in the art for coupling in the vertebral bone. For example, the threads may have a triangular cross section or a triangular, truncated cross section. Preferably, the threads have a height of 1.0 mm (0.039 inches) to provide adequate support in the vertebral bone, such that the fusion device 10 is not expelled from the intradiscos space by the high loads experienced by the spinal column. Thread spacing in certain specific embodiments may be 2.3 mm (0.091 inches) or 3.0 mm (0.118 inches), depending on the vertebral level at which the device 10 is to be implanted and the amount of thread engagement necessary for keep the implant in position. In one aspect of the invention, the conical body 11 and particularly the body wall 16, includes truncated, parallel side walls 22 shown more clearly in FIGURE 4. The side walls are preferably flat to facilitate insertion of the fusion device between the end plates of the adjacent vertebrae and provide area between them for bone fusion. The truncated side walls extend from the front end 12 of the device to the full threads 19 at the rear end 13. In this way, with the truncated side walls 22, the device 10 gives the appearance in its end view of an incomplete circle in which the sides are cut through a circle cord. In a specific example, the interbody fusion device 10 has a diameter at its leading end of 16.0 mm (0.630 inches). In this specific embodiment, the truncated side walls 22 are formed along parallel string lines approximately 12.0 mm (0.472 inches) apart, such that the arc portion withdrawn from the circle almost subtends 90 ° on each side of the device . Other benefits and advantages provided by the truncated lateral walls 22 of the fusion device 10 will be described in greater detail herein The conical body 11 of the device 10 includes a pair of vascularization openings 24 and 25, defined through each One of the truncated lateral walls 22, these openings 24 and 25 are adapted to be oriented in a lateral direction or in front of the sagittal plane, when the fusion device is implanted within the intradiscos space.The openings are intended to provide a conduit for vascularization occurs between the bone implant material within the hollow interior and the surrounding tissue In addition, some inward growth of bone through these openings may also occur The openings 24 and 25 have been sized to provide a conduit optimal for vascularization to occur, while still retaining a significant amount of structure in the conical body 11 to support the high axial loads that pass through the intradiscos space between adjacent vertebrae. The conical body 11 also defines grooves 27 for inward bone growth, opposite each of which is oriented at 90 ° with respect to the truncated side walls 22. Preferably, these slots 27 are directly adjacent to the vertebral end plates, when the device 10 is implanted. More particularly, as the threads 18 and 19 of the device are screwed into the vertebral end plates, the vertebral bone will partially extend into the slots 27 for contact with the bone implant material contained within the hollow interior of the device 10. As more clearly shown in FIGURE 5, the inwardly growing grooves 27 bone are configured to provide maximum opening for bone inward growth, to ensure complete arthrodesis and a solid fusion. Preferably, the grooves have a lateral width that approximates the effective width of the threaded portions of the body. It has been found that the above devices, which use a plurality of small openings, do not promote rapid and solid arthrodesis of the bone material. Conversely, smaller openings often lead to pseudoarthrosis and the generation of fibrous tissue. Since the inward bone growth grooves 27 of the present invention are directly facing the vertebrae, they need not be located in a portion of the device that is to withstand high loads. On the contrary, the truncated lateral walls 22 will bear the majority of the load that passes between the vertebral end plates through the interrupted threads 18 and through the intradiscos space. In a further feature, the anterior end 12 of the body wall 16 can define a pair of diametrically opposed notches 29, which are configured to engage an implant driving tool as described herein. In addition, the end wall 17 at the rear end 13 of the implant, may be provided with a tool engaging feature (not shown). For example, a hexagonal recess may be provided to accommodate a hexagonal drive tool, as further described herein. In an important feature of the interbody fusion device of the present invention, the body 11 includes a tapered or conical shape. In other words, the outer diameter of the device at its anterior end 12 is larger than the outer diameter at the posterior end 13. As shown in FIGURE 3, the body wall 16 tapers at an angle A around the center line CL of the device 10. The taper of the body wall 16 is adapted to restore the normal relative angle between the adjacent vertebrae. For example, in the lumbar region, the angle A is adapted to restore the normal lordotic angle and curvature of the spine in that region. In a specific example, angle A is 8794 °. It is understood that the implant may have non-tapered portions, with the proviso that the portions do not interfere in any other way with the function of the tapered body. The taper angle A of the implant, coupled with the outer diameter at the anterior and posterior ends of the fusion device 10, defines the amount of angular extension that will occur between the adjacent vertebrae as the implant is placed or screwed into position. This feature is illustrated more clearly in FIGURES 6 and 7 in which a preferred construction employing a pair of fusion devices 10 is shown. In the illustrated construction, the devices 10 are positioned between the lower lumbar vertebrae L4 and L5, with the threads 18 and 19 threaded into the end plates E of the two vertebrae. As shown in FIGURE 7, as the device 10 is threaded into the end plates E, it advances in the direction of the arrow I towards the pivot axis P of the vertebral level. The pivot axis P is nominally the center of the relative rotation between the adjacent vertebrae of the movement segment. As the tapered fusion device 10 is further urged in the direction of the arrow I towards the pivot axis P, the adjacent vertebrae L4 and L5 are extended angularly in the direction of the arrows S. The depth of insertion of the device 10 of fusion will determine the final lordotic angle L achieved between the two vertebrae. In the specific modalities of the implant 10, the outer diameter or diameter of the crests threaded at the end 12 above, can be 16, 18 or 20 mm and the total length of the device can be 26 mm. The dimensioning of the device is directed by the vertebral level within which the device is implanted and the amount of angle that must be developed. In another aspect of the invention, the device 10 is dimensioned in such a way that two such cylindrical bodies 11 can be implanted in a single disk space, as shown in FIGURE 6. This allows the placement of graft material of additional bone between and around the device 10 in si tu. This aspect further promotes fusion through the intradiscal space and also serves to anchor more firmly the devices between the adjacent vertebrae to avoid the expulsion due to the high axial loads at the particular vertebral level. In a specific embodiment of the interbody fusion device 10, the vascularization opening 24 is generally rectangular in shape, having dimensions of 6.0 mm (0.236 inches) by 7.0 mm (0.276 inches). Similarly, the vascularization opening 25 'is rectangular with the dimensions of 4.0 mm (0.157 inches) by 5.0 mm (0.197 inches). Naturally, this opening is smaller because it is placed on the smaller rear end 13 of the device 10. The inwardly growing bone grooves 27 are also rectangular in shape, with a longitudinal dimension of 20.0 mm (0.787 inches) and a width of 6.0 mm (0.236 inches). It has been found that these dimensions of the vascularization openings 24, 25 and the slots 27 provide inward growth of optimal bone and vascularization. In addition, these openings are not so large that they can compromise the structural integrity of the device or allow the bone graft material contained within the hollow interior to be easily ejected during implantation. As can be seen in FIGURE 7, when the device is in position between the vertebrae L4 and L5, the vascularization openings 24 and 25 are lateral, facing the highly vascularized tissue surrounding the vertebrae. Furthermore, as can be seen in FIGURE 6, the grooves 27 for inward bone growth are directed axially, such that they contact the vertebral end plates E. In an alternative embodiment of the invention, shown in FIGURE 8, an interbody fusion device 30 is formed of a conical body 31. The body wall 34 defines a hollow interior 33 as with the fusion device 10 of the previous embodiment. However, in this embodiment the truncated lateral wall 38 does not include any of the vascularization openings. In addition, the grooves 39 for inward bone growth on opposite sides of the device 30 are smaller. This means that the threads 36 interrupted on the outside of the device 30 extend a longer length around the implant. Such a design could be used if a porous material (eg, porous tantalum) is used to provide an additional surface area for inward tissue growth and anchoring to adjacent bone. Also, this intercorporal fusion device 30 of the modality shown in FIGURE 8, can have application at certain vertebral levels, where the risk of expulsion of the device is greater. Accordingly, the amount of contact thread is increased to avoid such expulsion. Prior to insertion, the hollow interior 15 of the fusion device 10 is completely filled with bone or a substitute to facilitate this preload. The interbody fusion device 10 can be implanted using an implant impeller 50, shown in FIGURE 9 in accordance with an aspect of the invention. The implant driver 50 is formed of a shaft 51 and a sleeve 52 positioned concentrically about the shaft. The clamps 54 are formed at one end of the shaft to hold the interbody fusion device 10 for implantation. The clamps include an exterior surface 55tapered, and a flat, opposite, interior surface 56 adapted to engage the truncated lateral walls 22 of the interbody fusion device. The tapered outer surface 55 conforms to the foot diameter of the interrupted threads 18, such that the clamps 54 substantially complete the full cylindrical shape of the body wall 16. The adaptation of the outer, tapered surface of the clamp facilitates the insertion of the screw of the interbody fusion device 10, since the outer surface 55 will be mounted within the threaded hole in the vertebral end plates. Each of the clips is provided with intersubject fingers 58 and a projection 59 extends from the inner surface 56. The function of these components is shown more clearly with reference to FIGURE 11. First with reference to FIGURE 9, the shaft 51 defines an articulated groove 62 that bears each of the pair of grippers 54. The articulated groove 62 is configured as such so that the clips will naturally have a deflected position extending sufficiently far apart to accept the interbody fusion device 10 tapered between them. The shaft 51 defines a conical taper 63 between the articulated groove 62 and each of the clamps 54. This conical taper engages with the conical chamfer 67 defined on the inner wall of the sleeve 52. In this way, as the sleeve 52 the conical chamfer 67 defined on the inner wall of the sleeve 52 is advanced towards the clamps 54. In this way, as the sleeve 52 is advanced towards the clamps 54, the conical chamfer 67 is mounted against the conical taper 63 to close or compress the articulated groove 62. In this form, the clamps 54 are pushed towards each other and pressed into a clamping coupling with the interbody fusion device located between the clamps. The shaft 51 and the sleeve 52 are provided with the threaded interface 65, which allows the sleeve 52 to be threaded up and down the length of the shaft. Specifically, the threaded interface 65 includes external threads on the shaft 51 and internal threads on the sleeve 52, which have the same spacing such that the sleeve can be easily moved up and down the implant driver 50. The shaft 51 is also provided with a pair of detents 69, which restrict backward movement of the sleeve 52 only to the extent necessary to allow the clamps 54 to be spaced a sufficient distance to accept the interbody fusion device 10. The use of the impeller 50 of the implant is shown with reference to FIGURES 10 and 11. As can be seen in FIGURE 10, the outer surface 55 of the clamps 54, resides generally in level with the foot diameter of the interrupted threads 18. As seen in FIGURE 11, the intersubject fingers 58 may be arranged to fit within the vascularization opening 24 in each of the truncated walls 22. In a similar manner, the impulse projections 59 engage the slots 29 of the driving tool at the front end 12 of the conical body 11. The combination of the intersubject fingers 58 and the impulse projections 59 firmly engage the interbody fusion device 10, such that the device can be screwed into a threaded or unthreaded opening in the vertebral bone. An alternative embodiment of the implant driver is shown in FIGURE 12. The driver 90 includes a shaft 91, which is of sufficient length to reach the intradiscos space from the outside of the patient. Attached to the end of the shaft 91 is a head which defines a pair of opposing clamps 93, each of which is configured to make level contact with the flat, truncated lateral walls 22 of the fusion device 10. As in the clamps 54 of the implant driver 50 previously described, the outer surface of the clamps is cylindrical to correspond to the cylindrical threaded portion of the device. Unlike the implant impeller 50, the impeller 90 of the embodiment in FIGURE 12 uses an expansion metal ring assembly to securely hold the fusion device 10 for insertion into the body. Specifically, the head 92 defines a metal ring 94 having a central metal ring hole 95 formed therethrough. The metal ring 94 terminates in an annular projection 96 which at least initially has a diameter slightly larger than the inner diameter of the fusion device 10 at its end 12. An expander shaft 97 slidably extends through the orifice of the metal ring and includes a flared tip 98 located adjacent and extending just behind the annular projection 96. The flared tip 98 of the shaft 97 starts in a diameter sized to slide into the hole 95 of the metal ring and gradually flares to a larger diameter than the hole. The impeller 90 of the implant includes a traction shaft 99 slidably positioned within a hole 100 defined in the shaft 91. The traction shaft 99 has a holding chamber 101 at its end which engages a clamping hub 102 formed at the end of axis 97 expander. Traction shaft 99 projects beyond the end of shaft 91 for access by the surgeon. When the traction shaft 99 is pulled, it pulls the expander shaft 97 away from the annular projection 96 of the metal ring 94, so that the flared tip 98 becomes progressively engaged within the hole 95 of the metal ring. As the tip 98 advances further into the hole 95, the annular projection 96 expands from its initial diameter to a second larger diameter sufficient for the firm clamping contact with the interior of the fusion device 10. With the fusion device coupled in this manner, the implant driver can be used to insert the device 10 into the surgical site, after which the expander shaft can be advanced beyond the hole in the metal ring to release the flared tip and consequently, the fusion device. In accordance with the present invention, two methods for implanting the interbody fusion device 10 are contemplated. First, with reference to FIGURES 12 (a) -12 (d), an earlier approach is shown. As a preliminary step, it is necessary to locate the appropriate starting points to implant the fusion device, preferably bilaterally. In the first stage of the previous approach, a dilator 75 is placed between the vertebral end plates E to dilate the disc space between the vertebrae L4 and L5. (It is understood, of course, that this procedure can be applied to other vertebral levels). In the second stage, shown in FIGURE 12 (b), an outer sleeve 76 is positioned around the disc space. The outer sleeve 76 can be of a known design, ie configured to positively engage the anterior aspect of the vertebral bodies firmly, but temporarily, anchor the outer sleeve 76 in its position. In essence, this outer sleeve 76 functions as a working channel for this laproscopic approach. In this step of FIGURE 12 (b), a known drill or drill 77 extends through the outer sleeve and is used to pierce circular openings in the adjacent vertebral bodies. The openings can be threaded to facilitate the insertion of the screw of the fusion device, although this step is not necessary.

In the next step shown in FIGURE 12 (c), the fusion device 10 is coupled by the implant driver 50 and extends through the outer sleeve 76 until the initiating thread 19 contacts the opening of the bone. The implant driver 50 can then be used to screw the fusion device into the threaded or unthreaded opening formed in the vertebral end plate E. It is understood that at this stage, other suitable impulse tools can be used, such as a screw drive type device for coupling the slots 29 of the impeller tool at the front end 12 of the device 10. As discussed previously, the degree of insertion of the fusion device 10 determines the amount of lordosis added or restored to the vertebral level. In the final stage, the implant driver is removed leaving the fusion device 10 in position. It can be seen that, once implanted, the closed end wall 17 is directed towards the posterior aspect of the vertebrae. The hollow interior 15 is open at its front end, but can be closed by a plastic or metal material, if necessary. In a second inventive method, as shown in FIGS. 13 (a) -13 (d), a subsequent approach is implemented. The first of two stages of the posterior focus, are similar to that of the previous previous approach, except that the dilator 75, the outer sleeve 76 and the perforator 77 are subsequently introduced into the instrumented region. This approach may require the decortication and removal of vertebral bone to accept the outer sleeve 76. In the third step of this method, the fusion device 10 is inserted through the outer sleeve 76 into the expanded disc space. It is understood that the disc space is dilated only to the extension necessary to receive the implant with the side walls 22, truncated directly in front of the vertebral end plates E. In this way, as shown in FIGURE 13 (c), the inwardly growing groove 27 of bone faces laterally, rather than coronally, as expected for its final implanted position. A suitable driving tool 80 can be provided to project the fusion device 10 through the outer sleeve 76 and into the intradiscos space. In one embodiment, the pulse tool 80 includes a projection 81, which is configured to engage a slot opening formed in the end wall 17 at the rear end 13 of the fusion device 10. An internal thread (not shown) can be used to secure the device 10 to the impeller 80. Once the fusion device 10 has been advanced in the intradiscos space to the appropriate depth relative to the pivot axis P of the vertebrae, the Pulse tool 80 is used to rotate the implant in the direction of the rotational arrow R in FIGURE 13 (c). As the drive tool 80 is rotated, the device itself rotates, such that the interrupted threads 18 initiate the cut in the vertebral bone in the end plates E. In this form, the implant functions as a cam to separate the adjacent vertebrae in the direction of the direction of extension of the arrows S in FIGURE 13 (c). This arrangement of the cams provides a slightly easier insertion procedure in which a single rotation is required to hold the implant within the vertebral bone. On the contrary, the technique of screw insertion discussed above requires the continuous threading of the device to leave it in position. With any technique, the position of the fusion device 10 with respect to the adjacent vertebrae can be verified by radiography or other suitable techniques to establish the angular relationship between the vertebrae. Alternatively, the preferred insertion depth of the implant can be determined in advance and measured from the outside of the patient as the implant is placed between the vertebrae. It can be seen that the interbody fusion device 10, the implant impeller 50 and techniques of the present invention provide significant advantages over the above devices and techniques. Specifically, the fusion device 10 provides a threaded implant, bone that maximizes the potential for bone fusion between the adjacent vertebrae, while maintaining the integrity of the implant itself. It is understood that the spinal column bears significant loads along its axial length, which loads must be supported by the fusion device 10 at least until the solid fusion is achieved. The device 10 also provides a means for vascularization and tissue ingrowth to occur, which accelerates the melt index and improves the strength of the resulting fused bone mass. Another significant aspect is that the tapered shape of the implant allows the surgeon to restore and maintain the proper curvature or relative angle between the vertebral bodies. This avoids the significant problems associated with previous devices, in which product deformities occur and the spine is out of balance. Another advantage achieved by the device and its implant driver is the ability for insertion either anteriorly or posteriorly using a laproscopic approach. Depending on the vertebral level, any approach may be preferred, such that it is important that the implant be adapted for insertion from any direction. The controlled insertion of the device is provided by the screwing technique used for the previous insertion (against breaking or crushing) and for the sliding and cam method used for the subsequent technique. Although the invention has been illustrated and described in detail in the drawings and description above, they are to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications to the invention have been made. come to fall within the spirit of the invention you want them to be protected. For example, although the device 10 has been described for use in the spine, the structure and methods of the present invention can also be used in other articulation spaces, such as the ankle, hip and subtalar joints. Further, although the device 10 of the preferred embodiment is shown tapered along its entire length, it is contemplated that a section without taper or inverse taper may be added with the resulting device that still falls within the scope of the invention. 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, property is claimed as contained in the following:

Claims (27)

1. A fusion device for facilitating arthrodesis in the disc space between adjacent vertebrae, characterized in that it comprises: an elongate body having a length and a first diameter at a first end dimensioned to be greater than the space between the adjacent vertebrae, the body further defines a hollow interior sized to receive therein the bone graft material; the body has an outer surface with a pair of opposed cylindrical portions and a pair of opposed side walls, substantially planar between the opposed cylindrical portions, the side walls extend along a substantial portion of the length of the body; and external threads defined in the pair of opposite cylindrical portions of the outer surface and extending along substantially the entire length of the body.

2 . The fusion device according to claim 1, characterized in that the body is tapered along a substantial portion of the length and includes a second diameter at a second end thereof, which is greater than the first diameter.

3. The fusion device according to claim 1, further characterized in that it comprises many openings defined in the opposite side walls for communication with the hollow interior.

4. The fusion device according to claim 3, further characterized by comprising a pair of diametrically opposed slots, through the threads in the cylindrical portion and communicating with the hollow interior, the opposite slots are elongated along the body length and are greater than the number of openings.

5. The fusion device according to claim 1, further characterized in that it comprises a pair of diametrically opposed grooves defined through the threads in the cylindrical portion and communicating with the hollow interior, the opposite grooves are elongated along the length of the body

6. The fusion device according to claim 5, characterized in that the opposed slots are rectangular in configuration and have a width of transverse dimension for the length of the body; and the cylindrical portions have an effective width between the opposite side walls and the opposed slots, wherein the width dimension of the opposed slots is greater than the effective width of the cylindrical portions.

7. The fusion device according to claim 1, characterized in that: the flat side walls end near the first end; and the cylindrical portions and the threads are interrupted by the side walls and circumferentially continuous then at the first end.

8. The fusion device according to claim 1, characterized in that the body is closed at the first end and is open to the hollow interior at a second end opposite the first end.

9. The fusion device according to claim 1, characterized in that the body includes a second end opposite the first end, the second end is open to the hollow interior.

10. The fusion device according to claim 7, characterized in that: the body includes a second end opposite the first end; and the flat side walls end at the second end.

11. The fusion device according to claim 10, characterized in that each of the opposite side walls define a notch in the second end configured to receive a driving tool for implanting the device.

12. A fusion device for facilitating arthrodesis in the disc space between adjacent vertebrae, characterized in that it comprises: an elongated body having a length, a first diameter at a first end and a second greater diameter at a second end opposite the first end, the first and second diameters are configured to be larger than the space between the adjacent vertebrae, the body further defines a hollow interior dimensioned to receive therein the bone graft material; the body has an outer tapered surface from the first diameter to the second diameter with external threads defined thereon and extending substantially completely along the length of the body.

13. The fusion device according to claim 12, further characterized in that it comprises a pair of diametrically opposed grooves defined through the threads on the outer surface and communicating with the hollow interior, the opposite grooves are elongated along the length of the body

14. The fusion device according to claim 12, characterized in that the body is closed at the first end and is open to the hollow interior at the second end.

15. A driving tool for implanting an interbody fusion device in the space between adjacent vertebrae, the fusion device includes a body having a cylindrical outer surface interrupted by opposed, flat side walls, the outer surface having external threads defined thereon, tool is characterized in that it comprises: an elongated shaft; and a pair of opposing clamps connected to one end of the shaft by an articulation, in which the clamps are deflected separating them in relation to one another; each of the clamps has face facing inward surfaces configured for contact with the flat, opposite side walls of the fusing device and the outward facing surfaces configured to conform to the cylindrical outer surface of the fusing device.

16. The pulse tool according to claim 15, characterized in that the fusion device includes defined openings in the flat side surfaces, in which the facing surfaces facing each of the clips includes a finger extending from there and arranged to project into a corresponding opening of the openings in the flat side surface of the fusion device, when the facing surface inwardly contacts the flat lateral surface.

17. The pulse tool according to claim 15, further characterized in that it comprises a sleeve positioned concentrically about the axis and movable axially thereon to compress the joint to push the clamps towards each other, whereby the clamps hold a fusion device placed between the clamps.

18. The pulse tool according to claim 17, characterized in that the sleeve is threadably coupled to the shaft to move axially along the length of the shaft as the sleeve is rotated about the threaded coupling.

19. The pulse tool according to claim 17, characterized in that: the clamps include a tapered surface adjacent to the joint; and the sleeve has a tapered chamfer that is complementary to the tapered surface, such that the tapered chamfer travels along the tapered surface as the sleeve is moved axially towards the clips to compress the joint.

20. The pulse tool according to claim 15, characterized in that the fusion device has a pair of opposed slots defined at one end of the device, wherein the pliers include impulse projections extending from the facing surface towards inside, the impulse projections are configured to engage the opposing slots in the fusion device.

21. A driving tool for implanting an interbody fusion device in the space between the adjacent vertebrae, the hollow fusion device including a body having a cylindrical inner surface and a cylindrical outer surface interrupted by opposed, flat side walls, the outer surface It has external threads defined on it, the tool is characterized because. comprises: an elongated shaft; a pair of opposing clamps connected to one end of the shaft, wherein the clamps are positioned spaced apart from one another to receive the flat, opposite side walls of the fusion device therebetween; and an expansion metal ring assembly connected to the elongated shaft and having a portion expandable from a first diameter small enough to be placed within the interior of the hollow fusion device to a second larger diameter sufficient to hold the interior of the device fusion.

22. The pulse tool according to claim 21, characterized in that the expansion metal ring assembly includes: an integral head with the pair of opposing grippers, the head defining a central hole through it and an annular projection at one end of the head. adjacent and inner hole for the clamps; and an expander shaft slidably disposed within the central bore, the expander shaft has a flared tip from a first diameter small enough to slide into the central bore and a second larger diameter adjacent to the annular projection, when the expander shaft is positioned within the bore. central hole, whereby when the expander shaft is retracted into the central hole, the flared tip progressively expands the annular projection into engagement within the interior of the fusion device.

23. A method for implanting a fusion device in the intradiscal space between the adjacent vertebrae, characterized in that it comprises the steps of: a) providing a hollow fusion device having a cylindrical outer surface, interrupted by flat side walls, the outer surface having threads externally defined on it; b) filling the interior of the fusion device with bone graft material; c) drilling a hole in the bone adjacent to the smaller diameter of the external threads of the fusion device; d) inserting the fusion device into the perforated hole with the flat side surfaces facing the adjacent vertebrae; and e) rotating the fusion device within the hole, such that the external threads engage the adjacent vertebrae.

24. The method according to claim 23, characterized in that: the step of providing a hollow fusion device includes providing a fusion device that is tapered from a first larger end to a second smaller end; and the step of inserting the fusion device includes inserting the device, such that the taper of the device will correspond to the normal anatomical angular relationship between the adjacent vertebrae.

25. The method according to claim 24, characterized in that the drilling and insertion steps are carried out subsequently.

26. The compliance method according to claim 23, characterized in that it comprises the additional step of providing a sleeve in contact with the adjacent vertebrae and aligned with the intradiscos space to provide a working channel for the piercing and insertion steps.

27. A method for implanting a fusion device in the intradiscal space between adjacent vertebrae, characterized in that it comprises the steps of: a) providing a hollow fusion device, having a cylindrical outer surface, tapered with external bony engagement threads; b) drilling a hole in the vertebral end plates on opposite sides of the intradiscos space, the perforated hole having the smaller diameter of the external threads of the fusion device; and c) screwing the fusing device in the bore hole to a predetermined depth within the bore hole, such that the adjacent vertebrae are angularly separated by the tapered outer surface of the fusing device, to restore a predetermined angular relationship between the adjacent vertebrae . SUMMARY OF THE INVENTION An interbody fusion device includes a tapered body defining a hollow interior for receiving bone graft or a bone substitute material. The body defines external threads, which are interrupted in portions of the outer surface of the device. The fusion device defines truncated side walls such that an end view of the body takes a cylindrical shape. The side walls are provided with vascularization openings and the body wall of the device includes grooves for inward bone growth., opposites that extend through the interrupted threaded portion of the body. An implant impeller is provided, which couples the truncated side walls to complete the cylindrical shape of the implant in the foot diameter of the interrupted threads. The impeller facilitates the threaded insertion of the implant into the intradiscal space between adjacent vertebrae. The implant is tapered at a predetermined angle, which generally corresponds to a desired lordotic angle of the spine. The implant is inserted at a predetermined depth in the intradiscal space to restore the normal lordosis of the particular vertebral level. The lordotic angle is restored not only by tapering the implant itself, but also as a function of the depth of insertion of the implant into space. The implant is easily adapted for insertion either from an anterior approach or a posterior focus. In the previous approach, the implant is screwed into the position, while in the posterior approach, the implant functions as a cam to extend the vertebral bodies and separating them at an appropriate lordotic angle.