CN100425214C - Methods and instruments for interbody fusion - Google Patents

Abstract

The invention relates to a driving tool for embedding the body fusion device to the clearance between the adjacent vertebras. The fusion device is provided with a body which is provided with a cylinder outer surface cut by a flat side wall arranged relatively. The outer surface is provided with an outside thread. The tool comprises a lathy axle and a pair of corresponding clamps connected with one end of the axle through an articulated piece. The clamp is separated from each other. Every clamp is provided with a pair of inward surfaces contacting the flat side wall arranged relatively to the fusion device and a pair of outward surfaces coherent to the outer surface of the cylinder of the fusion device.

Description

Drive tool for implanting fusion devices in vivo

This application was submitted on March 26, 1996, the application number is 96105961.3, and the title of the invention is "In vivo fusion device and method for restoring the normal anatomical shape of the spine".

technical field

The present invention relates to an artificial implant for placement between vertebrae in the space left after removal of a damaged intervertebral disc. In particular, the present invention relates to an implant that facilitates arthrodesis or spinal fusion between adjacent vertebrae while maintaining or restoring normal spinal anatomy at a particular vertebral level.

Background technique

Over the past few years, there has been a steady increase in the number of spinal surgeries performed to rule out causes of lower back pain. Most commonly, pain in the lower back is caused by damage or disease to the discs between adjacent vertebrae. These discs may herniate or undergo various degenerations, both of which disrupt the anatomical function of the discs. The most popular surgical approach to these conditions is to fuse the two vertebrae surrounding the diseased disc. In most cases, the entire disc is removed except for the annulus fibrosus through a discectomy. As a result of removing a damaged disc, something has to be put into the space within the disc, or the space can shrink, causing damage to the nerves that run along the spine.

To prevent this intradiscal space from shrinking, it is necessary to fill this space with bone or a bone substitute in order to fuse the two adjacent vertebrae. In earlier techniques, bone material was simply placed between adjacent vertebrae, usually at the back of the vertebrae, and the spine was stabilized using a plate or rod that spanned the affected vertebrae. With this technique, when the fusion is formed, the components used to maintain the stability of the spinal section are redundant. Moreover, the surgical procedures required to stabilize the vertebral level during fusion by implanting rods or plates are often time-consuming and complicated.

It has then been suggested that a better solution to the stability of the intervertebral disc space is to fuse the vertebrae between their respective end plates, preferably without the use of anterior or posterior plates. Considerable effort has been devoted to developing an acceptable intradiscal implant that can both replace a damaged intervertebral disc and maintain the stability of the intradiscal space between adjacent vertebrae at least until complete arthrodesis has developed. into things. These "in vivo fusion devices" come in a variety of forms. For example, one of several more popular designs takes the form of a cylindrical implant. Such implants are described in US Patent No. 4,501,269 to Bagby, US Patent No. 4,878,915 to Brantigan, US Patent Nos. 4,961,740 and 5,055,104 to Ray, and US Patent No. 5,015,247 to Michelson. In these cylindrical implants, as described in the Ray, Brantigan and Michelson patents, the exterior of the cylinder is threaded for insertion into an internal fusion device. Alternatively, certain fusion implants will be tapped into the intradiscal space and vertebral endplates. Devices of this type are described in US Patent Nos. 4,743,256, 4,834,757 and 5,192,327 to Brantigan.

In all of these patents cited above, the cross-section of the implant is constant throughout its length and is generally right-cylindrical. Other implants have also been developed for in vivo fusion that do not have a constant cross-section. For example, US Patent No. 4,714,469 to McKenna shows a hemispherical implant with an elongated protrusion extending into a vertebral endplate. US Patent No. 4,714,469 to Kuntz shows a bullet-shaped prosthesis that optimizes the frictional fit between the prosthesis and the adjacent vertebral body. Finally, the implant of Babgy's US Patent No. 4,936,848 is spherical and is preferably placed between the vertebral bodies of adjacent vertebrae.

Internal fusion devices can generally be divided into two basic types, solid implants and implants with structures that allow bone growth. US Patent Nos. 4,878,915, 4,743,256, 4,349,921 and 4,714,469 describe several solid implants. The remaining patents discussed above have certain technical features that allow bone to grow through the implant. It has been found that faster and more stable joint fixation can be achieved using devices that promote natural bone growth. The device described in the Michelson patent is representative of such hollow implants which are usually filled with autologous bone prior to insertion into the intradiscal space. The implant has circular holes communicating with the hollow lumen of the implant, thereby forming a pathway for tissue growth between the vertebral endplate and the bone or bone substitute located in the implant. When preparing the intradiscal space, it is desirable to reduce the endplates to allow blood supply to the bone, thereby favoring the growth of this tissue. During the fusion process, the metallic structure provided by Michelson's implants helped maintain the patency and stability of the moving segments to be fused. In addition, the implant itself acts as a fixator to the solid body of bone once arthrodesis has been established.

Several difficulties still exist in the many existing in vivo fusion devices. Although hollow implants that allow bone to grow in bone or bone substitutes within the implant are recognized as one of the best technical devices for achieving fusion, most existing devices are difficult to achieve such fusion, at least This fusion is difficult to achieve without the aid of some additional stabilizing means such as rods or plates. Furthermore, some of these devices are not structurally strong enough to withstand the heavy loads and bending movements most frequently imposed on the level of the vertebra being fused, ie, the vertebrae in the lower lumbar region.

There is a need to provide a hollow interbody fusion device that optimizes bone growth capacity yet is strong enough to support a spinal segment until arthrosis is established. The present inventors have found that the opening for bone growth plays an important role in protecting the native bone embedded in the implant from stress. In other words, if the bone growth hole is not the right size or shape, the autogenous bone cannot bear the load that has been found to be necessary to ensure rapid and complete fusion. In such cases, the bone embedded in the implant may resorb or develop into simple fibrous tissue rather than a bony fusion, which would lead to an overall imbalance in the structure. On the other hand, the bone growth hole must not be so large that the shell does not have sufficient support to avoid sinking into the adjacent vertebrae.

Another problem not addressed by the prior devices described above relates to the problem of maintaining or restoring the normal anatomy of the fused spinal segment. Naturally, once the disc is removed, the normal lordotic or kyphotic curvature of the spine disappears. In prior installations, the need to restore this arc was ignored. For example, as represented by Babgy's U.S. No. 4,501,269, in the commercially available, SpineTech BAK device, adjacent vertebral bodies are reamed with a cylindrical reamer equipped with a special implant. In some cases, a normal arc is established prior to reaming prior to insertion of the implant. Such a configuration is illustrated in Figure 1, which shows the depth of insertion of a cylindrical implant into a substantially healthy vertebra adjacent to the intradiscal space in which the implant is installed. However, this method of overreaming the posterior is generally not generally acceptable due to the removal of the load-bearing bone in the spine, and because it is generally difficult to ream the posterior portion of the lower lumbar region where the lordosis is greatest. In most cases where such implants are used, no effort is made to restore the lordotic curvature, so the cylindrical implant is prone to kyphotic deformation as the vertebra stabilizes around the implant. This phenomenon throws the spine out of balance and often leads to reoperation.

Due to these deficiencies of existing devices, there remains a need for an in vivo fusion device that optimizes bone growth capacity while maintaining its strength and stability. There is also a need for such implants to maintain or restore the normal spinal anatomy of the segment in which the implant is placed. Such an implant must be strong enough to support and withstand the heavy loads placed on the spine at the level at which the implant is placed, while remaining stable throughout the procedure.

Contents of the invention

Aiming at the unresolved problems left by the existing devices, the present invention designs a hollow threaded fusion device in the body, which can be used to restore the normal angular relationship between adjacent vertebrae. Specifically, the device has an elongated body that is generally tapered along its entire length and has a hollow lumen with an outer diameter that is greater than the space between adjacent vertebrae. The body has an outer surface having opposed tapered cylindrical portions and a pair of opposed tapered flat side surfaces between the cylindrical portions. Thus, viewed from one end, the fusion device appears as a cylindrical body whose sides are truncated into planes along a chord of the body's outer diameter. The cylindrical portion is threaded to allow the body to be inserted and engaged in a controlled manner to the endplates of adjacent vertebrae.

In another aspect of the invention, the outer surface is tapered along its length at an angle which, in one embodiment, corresponds to the normal lordotic angle of the lower lumbar spine. The outer surface also has openings for blood vessels formed on the flat side surfaces, and a pair of oppositely disposed elongated bone growth grooves formed on the cylindrical portion. The transverse width of the bone growth groove is preferably about half the effective width of the cylindrical portion bounding the groove.

The present invention provides a driving tool for inserting a fusion device into an intradiscal space. In one example, the drive tool includes a shaft having a pair of tapered jaws facing each other at one end of the shaft. The pair of clamps are connected to the shaft by a hinged seam that opens the clamps to hold the fusion device between them. The driver tool also has a sleeve coaxially disposed about the shaft, the sleeve being slidable along the shaft and compressing the hinged seam, thereby pushing the pair of clamps together to grasp the fusion device. Alternatively, an internally expanding elastic collet can be used to tightly support the fusion device from the inside during insertion.

In one aspect of the drive tool, the tapered jaws have an outer surface that is the same shape as the tapered cylindrical portion of the fusion device. The clamp also has a flat medially facing surface corresponding to the flat side surface of the fusion device. Thus, when the clamp is pressed against the fusion device, the inwardly facing surface of the clamp is in contact with the flat side surface of the fusion device, and the outer surface of the clamp combines with the fusion device to form a complete cone for screwing in. Insert the fusion device in the same manner. There may also be several protrusions on the medial facing surface of the jaws to engage holes in the fusion device to drive and rotate the device into the intradiscal space.

In another aspect of the invention, a method of implanting a fusion device between adjacent vertebrae is provided. In one approach, insertion is from the front and includes the steps of dilating the intradiscal space and drilling a hole in the endplate of the adjacent vertebra with a diameter equal to the inner diameter of the fusion device's threads. A sleeve is inserted to form the working channel for the drilling step and the subsequent step of implanting the fusion device. The implant is combined with the driver tool, inserted into the sleeve and screwed into the prepared hole. The depth of insertion of the tapered fusion device determines the angle of separation achieved between adjacent vertebrae.

In another inventive method, the insertion point is prepared posteriorly, ie, the intradiscal space is dilated from the posterior, and an inner diameter hole is drilled in the vertebral endplate. A sleeve is also used to form the working channel for the drilling and insertion steps. Insert the fusion device into the drilled hole with its flat sidewall facing the adjacent vertebrae. The device is then rotated so that the external threads on its cylindrical portion cut into and engage the adjacent vertebrae. Additionally, since the fusion device is tapered, the tapered outer surface of the device will angle the adjacent vertebrae apart, thereby restoring normal lordotic anatomy.

Description of drawings

Fig. 1 is the side view of the sagittal plane of fusion device in the prior art;

Figure 2 is an enlarged perspective view of an intracorporeal fusion device according to one embodiment of the present invention;

Fig. 3 is a side sectional view of the body fusion device shown in Fig. 2 taken along line 3-3 and viewed in the direction of the arrow;

Fig. 4 is an end view of the front end of the body fusion device shown in Fig. 2;

Figure 5 is a top view of the body fusion device shown in Figure 2;

Figure 6 is an A-P side view when viewed from the front of the spine, showing the situation when two internal fusion devices shown in Figure 2 are implanted in the interbody space between L4 and L5;

Figure 7 is a sagittal view of the interbody fusion device shown in Figure 6 implanted between L4 and L5;

Figure 8 is a perspective view of another embodiment of an internal fusion device according to the present invention;

Figure 9 is a top view of an implant driver according to another aspect of the present invention;

Figure 10 is an enlarged perspective view of one end of the implant driver engaged on the internal fusion device shown in Figure 2;

11 is a partially enlarged side cross-sectional view of the implant driver engaged on the internal fusion device shown in FIG. 10;

12 is an enlarged partial side cross-sectional view of another embodiment of an implant driver suitable for engagement with the intracorporeal fusion device shown in FIG. 10;

Figures 13(a)-13(d) illustrate four steps in a method of implanting a fusion device (such as the device shown in Figure 2) in accordance with another aspect of the present invention;

14(a)-14(d) illustrate the four steps of another method of implanting a fusion device such as that shown in FIG. 2 in vivo.

Detailed ways

In order to better understand the principle of the present invention, the present invention will be described below with reference to several embodiments shown in the drawings and using specific language. Nevertheless, it should be understood that this is not meant to limit the scope of the present invention, and those skilled in the art to which the present invention pertains will naturally expect changes and further improvements to the devices shown in the accompanying drawings, as well as those contained therein. Further Applications of the Principles of the Invention.

2-5 illustrate an intracorporeal fusion device 10 according to one aspect of the present invention. The device consists of a rigid conical body 11 preferably made of a biocompatible or inert material. For example, body 11 may be made of medical grade stainless steel or titanium, or other suitable material having suitable strength characteristics as described above. The device can also be made from a biocompatible porous material such as porous tantalum supplied by Implex Corp. For ease of reference, device 10 has a front end 12 and a rear end 13 that correspond to the anatomical position of device 10 when implanted in the intradiscal space. The conical body 11 defines a hollow interior 15 enclosed by body walls 16 and its front end 13 closed by an end wall 17 (see Figure 3). The hollow interior 15 is shaped to receive autograft bone or a bone substitute, promoting strong fusion between adjacent vertebrae and throughout the intradiscal space.

According to the present invention, the interbody fusion device 10 is a threaded device capable of being screwed into the endplates between adjacent vertebrae. In one embodiment of the present invention, the conical body 11 defines a set of interrupted external threads 18 and a full thread 19 at the forward end of the implant. The full thread 19 acts as a "starter" thread for threading the implant onto the vertebral endplate in the intradiscal space. Threads 18 and 19 can have several shapes known in the art for screwing into vertebrae. For example, the threads may have a triangular or truncated triangular cross section. The height of the threads is preferably 1.0 mm (.039 in) in order to provide sufficient engagement force in the vertebrae so that the fusion device 10 is not pushed out of the intradiscal space by the higher loads experienced by the spine. In some specific embodiments, the thread pitch is 2.3mm (0.091in) or 3.0mm (0.118in), depending on the level of the vertebra where the device 10 is to be implanted and the degree of engagement of the threads required to maintain the implant in place. quantity.

In one aspect of the invention, the tapered body 11 , and in particular the body's outer wall 16 , includes a pair of parallel truncated side walls 22 , which are best shown in FIG. 4 . The pair of side walls are preferably flat to facilitate insertion of the fusion device between the endplates of adjacent vertebrae and to form an area for bone fusion. The pair of truncated side walls extend from the front end 12 of the device to a full thread 19 at the rear end 13 . Thus, with the pair of truncated side walls 22, the end of the device 10 is incompletely circular, the sides of which are truncated along a chord of the circle. In a specific embodiment, the diameter of the front end of the intracorporeal fusion device 10 is 16.0 mm (0.630 in). In this particular embodiment, the truncated side walls 22 are formed along a pair of parallel chords approximately 12.0 mm (0.472 in) apart, so that the truncated arc portions on either side of the device are approximately Opposed to an angle of 90°. The benefits and advantages afforded by the truncated sidewall 22 of the fusion device 10 will be described in more detail herein.

The tapered body 11 of the device 10 includes a pair of vascularized openings 24 and 25 defined by respective truncated side walls 22 . When the fusion device is implanted in the intradiscal space, the openings 24 and 25 will be aligned laterally or towards the sagittal plane. This pair of openings will be used to form a passage to enable vascularization between the bone implant in the hollow lumen 15 and the surrounding tissue. In addition, some bone may grow through these openings. The openings 24 and 25 are sized to provide optimal access for vascularization while retaining a substantial amount of structure within the tapered body 11 to withstand relatively high axial loads across the intradiscal space between adjacent vertebrae.

The tapered body 11 also defines a number of opposed bone growth slots 27, all of which are at a 90° angle to the truncated side wall 22. These slots 27 are preferably directly adjacent the vertebral endplates when the device 10 is implanted. More specifically, when the threads 18 and 19 of the device are screwed into the vertebral endplates, the vertebrae will extend partially into the slot 27 to contact the bone implant contained in the hollow lumen 15 of the device 10 . As shown more clearly in Figure 5, in order to ensure complete arthrosis and solid spinal fusion, the bone growth slot 27 is shaped to provide a maximum opening for bone growth. The transverse width of the grooves preferably approximates the effective width of the threaded portion of the body. It has been found that prior art devices employing many small gaps do not promote rapid and firm articulation of bone material. Instead, these small gaps often lead to the formation of pseudarthrosis and the growth of fibrous tissue. Since the bone growth grooves 27 according to the invention are directly facing the vertebrae, they are not located on parts of the device which must be subjected to greater loads. Instead, the truncated side walls 22 will bear most of the load passing between the two end plates of the vertebrae and across the intradiscal space by means of the interrupted threads 18 .

In a further feature, there may be a pair of diametrically opposed notches 29 on the front end 12 of the body 16, the pair of notches 29 being shaped such that they are compatible with the implant drive tools described herein. Furthermore, the end wall 17 of the rear end 13 of the implant may also have a tool-engaging part (not shown). For example, as will be described further herein, a hexagonal recess could be provided to receive a hexagonal driving tool.

An important feature of the intracorporeal fusion device of the present invention is that the body 11 is tapered or conical, in other words, the outer diameter of the front end 12 of the device is greater than the outer diameter of the rear end 13 of the device. As shown in FIG. 3 , body wall 16 tapers at an angle A about a centerline CL of device 10 . The tapered body wall 16 helps to restore the normal relative angle between adjacent vertebrae. For example, in the lumbar area, Angle A helps restore the normal lordotic angle and curvature of the spine in this area. In a specific example, angle A is 8.794°. It will be appreciated that the implant may have some non-tapered portions as long as these do not interfere with the function of the tapered body.

The cone angle A of the implant, combined with the outer diameters of the front and rear ends of the fusion device 10, determine that when the implant is placed or screwed into position it will form between adjacent vertebrae. The amount of angular divergence of . This feature is shown more clearly in FIGS. 6 and 7 , which show a preferred configuration using a pair of fusion devices 10 . In the illustrated configuration, device 10 is placed between lower lumbar vertebrae L4 and L5, with threads 18 and 19 threaded into endplates E of both vertebrae. As shown in Figure 7, when the device 10 is screwed into the endplate E, it advances in the direction of the arrow E towards the pivot P at the vertebral level. The pivot P is nominally the center of relative rotation between adjacent vertebrae of the motion segment. Adjacent vertebrae L4 and L5 angularly diverge in the direction of arrow S as the conical fusion device 10 is advanced further in the direction of arrow I toward pivot P. The insertion depth of the fusion device 10 will determine the final lordotic angle L achieved between two adjacent vertebrae.

In several specific embodiments of the device 10, the outer diameter of the front end 12 or the diameter of the thread crests may be 16, 18 or 20 mm, and the overall length of the device is 26 mm. The size of the device is determined by the level of the vertebra where the device will be implanted and the angle that must be achieved.

In another aspect of the invention, as shown in Fig. 6, the dimensions of the device 10 are such that two such cylindrical bodies 11 can be implanted in one disc space. This enables another bone fusion material to be placed between or around the two devices 10 . This feature also promotes fusion throughout the intradiscal space and secures the device more firmly between adjacent vertebrae, preventing extrusion of the device by higher loads at that particular vertebral level.

In one specific embodiment of the intracorporeal fusion device, the vessel-forming opening 24 is generally rectangular in shape with dimensions of 6.0 mm (0.236 in) by 7.0 mm (0.276 in). Likewise, the vessel-forming opening 25 is also rectangular and measures 4.0 mm (0,157 in) by 5.0 mm (0.197 in). Naturally, this opening is smaller since it is located at the smaller rear end 13 of the device 10 . The bone growth slot 27 is also rectangular, measuring 20.0 mm (0.787 in) long and 6.0 mm (0.236 in) wide. These dimensions of the vascularized openings 24, 25 and grooves 27 have been found to be optimal for bone growth and vascularization. In addition, the size of these openings is not too large, they take into account the structural integrity of the device, or they allow the bone fusion material contained in the hollow lumen 15 to be discharged more easily during implantation.

As shown in Figure 7, when the device is positioned between the L4 and L5 vertebrae, the vascularized openings 24 and 25 are in lateral contact with the richly vascularized tissue surrounding the vertebrae. And, as shown in FIG. 6 , the bone growth groove 27 is oriented in the axial direction, and thus contacts the endplate E of the vertebra.

In another embodiment of the invention shown in FIG. 8 , an interbody fusion device 30 consists of a tapered body 31 . As with the fusion device 10 of the previous embodiments, the body 34 defines a hollow lumen 33 . However, in this embodiment, the truncated side walls 38 do not have openings to form blood vessels. Also, the bone growth channels 34 on opposite sides of the device 10 are relatively small. This means that the interrupted threads 36 on the exterior of the device 30 extend a greater distance around the implant. Such a design can be used if a porous material such as tantalum is used to form an auxiliary surface for tissue growth and fixation to adjacent bone. The internal fusion device 30 of the embodiment shown in Figure 8 can also be applied at certain vertebral levels where the risk of device extrusion is greatest. Therefore, this type of extrusion is prevented by increasing the amount of thread contact. Prior to insertion, the hollow lumen 15 of the device 10 is filled with bone or substitute to facilitate such preloading.

According to one aspect of the present invention, the intracorporeal fusion device 10 can be implanted in the body by using the implant driver 50 shown in FIG. 9 . The implant driver 50 consists of a shaft 51 and a bushing 52 arranged concentrically around the shaft. One end of the shaft carries clamps 54 for holding the internal fusion device 10 for implantation. The clamps have a tapered outer surface 55 and a flat inner surface 56 adapted to mate with the truncated side walls 22 of the intracorporeal fusion device. The tapered outer surface 55 coincides with the root diameter of the interrupted thread 18 so that the clamp 54 substantially fills the entire cylindrical shape of the body wall 16 . The tapered outer surface 55 of the jaws facilitates screwing in of the interbody fusion device 10 as the outer surface 55 will bridge the threaded holes located in the vertebral endplates.

Each clamp has an interlock pin 58 and a drive lug 59 projecting from an inner surface 56 . Figure 11 shows the function of these components more clearly. Referring first to Fig. 9, the shaft 51 has a hinged seam 62 for supporting a pair of clamps 54 thereon. Hinge seam 62 is shaped such that it places the jaws in a naturally deflected position spread far enough apart to receive conical endoconical fusion device 10 between the jaws. Shaft 51 defines a tapered portion 63 between hinge seam 62 and each jaw 54 . This tapered portion mates with a tapered groove 67 on the inner wall of the hub 52 . Thus, when the sleeve 52 is advanced toward the jaw 54 , the tapered groove 67 abuts against the tapered portion 63 , thereby closing or compressing the hinge seam 62 . In this manner, the clamps 54 are pushed towards each other and under pressure clamp the interbody fusion device between the two clamps.

The shaft 51 and sleeve 52 have a threaded interface 65 that enables the sleeve 52 to be threaded onto and unscrewed from the shaft along the length of the shaft. Specifically, the threaded interface 65 includes external threads on the shaft 51 and internal threads on the sleeve 52, the internal and external threads having the same pitch so that the sleeve can be easily removed from the implant driver. Move up and down. The shaft 51 also carries a pair of stop pins 69 which limit the rearward movement of the hub 52 to a range that is only required to allow the jaws 54 to separate a sufficient distance for receiving the interbody fusion device 10 .

Figures 10 and 11 illustrate the use of the implant driver. As shown in FIG. 10 , the outer surface 55 of the clamp 54 is positioned substantially flush with the root diameter of the interrupted thread 18 . As shown in FIG. 11 , two stop pins 58 may be seated in the vessel-forming opening 24 on each truncated side wall 22 . In the same way, the drive lug 59 engages with the drive tool-accommodating recess 29 on the front end 12 of the conical body 11 . Interlock pin 58 and drive lug 59 combine to tightly grip interbody fusion device 10 so that the device can be screwed into tapped or untapped openings in the vertebrae.

Figure 12 shows another embodiment of an implant driver. Driver 90 includes a shaft 91 of sufficient length to allow it to extend from outside the patient's body into the interdiscal space. Attached to the end of the shaft 91 is a head defining a pair of opposing jaws 93 , each jaw being shaped such that they can abut against the flat truncated side walls 22 of the fusion device 10 . As with the two jaws 54 of the implant driver 50 previously described, the outer surface of the jaw 53 is cylindrical so as to conform to the cylindrical threaded portion of the device.

Unlike implant driver 50, driver 90 in the embodiment shown in FIG. 12 utilizes an expandable resilient collet assembly to tightly grip fusion device 10 for insertion into the body. Specifically, head 92 defines a resilient collet 94 having a central bore 95 therethrough. At one end of the resilient collet 94 is an annular flange 96 having a diameter, at least initially, slightly smaller than the inner diameter of the end 12 of the fusion device 10 . An expander shaft 97 slidably extends through the bore and has an enlarged end portion 98 adjacent to and just beyond the annular flange 96 . The enlarged end 98 of the expander shaft 97 has a smaller diameter at its starting end to enable it to slide in the bushing 95, from which end the diameter of the end 98 gradually increases to be larger than said bushing diameter of.

Implant driver 90 includes a removal tool shaft 99 slidably disposed within a bore 100 defined by shaft 91 . At the end of the removal tool shaft 99 there is a locking cavity 101 which engages a locking hub 102 on the end of the expander shaft 97 . The removal tool shaft 99 extends beyond the end of the shaft 91 for the surgeon to hold. As the removal tool shaft 99 is pulled out, it pulls the expander shaft 97 outwardly from the annular flange 96 of the sleeve 94 so that the widened end 98 gradually engages in the sleeve bore 95 . As end 98 is advanced further into collar 95 , annular flange 97 expands from an initial diameter to a second, larger diameter sufficient to tightly grip the lumen of fusion device 10 . By engaging the implant driver with the fusion device in this manner, the device 10 can be inserted into the surgical field, and the reamer shaft can then be pushed out of the cannula to release the oversized end, thereby releasing the fusion device .

The present invention contemplates two methods of implanting the fusion device 10 in vivo. First, Figures 13(a)-13(d) illustrate the front insertion method. In a preliminary step, a suitable, preferably bilateral, starting point for implantation of the fusion device needs to be determined. In the first step of this anterior insertion, a dilator 75 is first placed between the two endplates E of the vertebra to dilate the disc space between L4 and L5. (Of course, it should be understood that this procedure can be used at other vertebral levels as well). In a second step shown in Figure 13(b), a sleeve 76 is placed around the disc gap. Sleeve 76 may be shaped in known manner to positively engage the anterior portion of the vertebral body to securely, but temporarily, position sleeve 76 . In essence, the sleeve 76 functions as a working channel in this laproscopic implantation method. In this step shown in Figure 13(b), a well known drill bit 77 is inserted into the sleeve and is used to drill holes in the two adjacent vertebrae. Threads can also be tapped in these holes to facilitate screwing the fusion device in, although this step is not essential.

In the next step shown in Figure 13(c), the fusion device 10 is held by the implant driver 50 and inserted into the sleeve 76 until the activation thread 19 contacts the opening in the bone. The implant driver 50 may then be used to screw the fusion device 10 into the tapped or untapped hole made in the vertebral endplate. It should be understood that other suitable driving tools, such as screw driver type devices, which engage the driving tool recess 29 at the front end 12 of the device 10 may also be utilized in this step. As previously stated, the degree of insertion of the fusion device 10 determines the amount of lordosis added to, or restored to, this spinal level. In a final step, the implanted driver is removed, leaving the fusion device 10 in place. It can be seen that once implanted, the closed end wall 17 is towards the posterior end of the vertebra. The hollow inner cavity 15 positioned at the front end is open, but it can be closed with metal or plastic material if necessary.

In the second inventive method, Figures 14(a)-14(d) show the rear insertion method. The first two steps of the posterior approach are similar to the anterior approach, except that the dilator 75, sleeve 76, and drill 77 are placed posteriorly into the region where the implant will be placed. This insertion method may require the vertebrae to be stripped or removed in order to receive the sleeve 76 . In the third step of the method, fusion device 10 is inserted through sleeve 76 into the expanded disc space. It should be understood that the disc space need only be expanded to the extent necessary to receive an implant having a truncated side wall 22 directly facing the vertebral endplate E. Therefore, as shown in Figure 14(c), the bone growth groove 27 is oriented laterally, rather than laterally, consistent with its intended implantation location. A suitable driving tool 80 can be used to extend the fusion device 10 through the sleeve 76 and into the intradiscal space. In one embodiment, the driving tool 80 has a protrusion 81 that is shaped to conform to a notch formed in the end wall 17 of the rear end 13 of the fusion device 10 . Device 10 may also be secured to driver 80 using external threads (not shown).

Once the fusion device 10 has been pushed into the intradiscal space and to the appropriate depth relative to the pivot P of the vertebrae, the implant can be rotated in the direction indicated by arrow R in Figure 14(c) using the driving tool 80. As the driving tool 80 is rotated, the device itself is rotated, causing the interrupted threads 18 to begin cutting into the vertebrae at the endplate E. In this manner, the implant acts like a cam to separate adjacent vertebrae along the direction of divergence indicated by arrow S in Figure 14(c). This cammed insertion is somewhat easier to insert because only one rotation is needed to lock the implant into the vertebrae. In contrast, the previously discussed threaded insertion technique requires continuous screwing of the device into its position.

Using either of these techniques, the position of the fusion device 10 relative to its adjacent vertebrae can be verified using X-rays or other suitable technique to establish the angular relationship between the vertebrae. Alternatively, the preferred implant insertion depth can be predetermined and measured from outside the patient's body while the implant is placed between the vertebrae.

It can be seen that the intracorporeal fusion device 10, the implant driver 50 and the method of the present invention have significant advantages over the existing devices and techniques. Specifically, fusion device 10 is a threaded hollow insert that maximizes the potential for bony fusion between adjacent vertebrae while maintaining the integrity of the implant itself. It should be understood that the spine is subject to considerable loads in its axial direction which must be carried by the fusion device 10 at least until solid fusion is achieved. The device 10 also has components for vascularization and tissue growth which accelerate the rate of fusion and increase the strength of the resulting bone mass. Another notable aspect is that the tapered shape of the implant enables the surgeon to restore and maintain the proper curvature or relative angle between the vertebral bodies. This avoids the serious problems associated with existing devices such as product deformation, spine loss of balance, and the like. Another advantage of the device and implant driver of the present invention is that it can be inserted both anteriorly and posteriorly using a laparoscopic insertion method. Depending on the vertebral level, both methods of insertion are advisable, so it is important that the implant is suitable for insertion from both directions. In the anterior insertion method, the insertion of the device is controlled using a screw-in technique (as opposed to knocking in), and in the posterior insertion method, the insertion of the device is controlled by a slide-in and cam-type method.

While the invention has been shown and described with reference to the drawings and foregoing description, such drawings and description are illustrative only and not restrictive, and it is to be understood that the foregoing has shown and described preferred embodiments, which fall within the scope of this disclosure. All changes and improvements within the conceptual scope of the invention should be protected. For example, although the device 10 is disclosed for use in the spine, the structures and methods of the present invention may also be used in other joint spaces, such as the ankle, wrist, and subtalar joints. Furthermore, although the device 10 is shown as being tapered throughout its entire length in the preferred embodiment, it is still within the scope of the invention to add non-tapered or inverted tapered portions to the resulting device. .

Claims (8)

1. A driving tool for implanting an internal fusion device into a space between adjacent vertebrae, said fusion device having a main body having a section interrupted by oppositely disposed straight side walls The cylindrical outer surface of said outer surface has external threads, and said driving tool comprises: an elongated shaft; and a pair of opposing jaws attached to one end of said shaft by a hinge, said jaws being offset from each other; Each of the jaws has a pair of inwardly facing surfaces shaped to contact oppositely disposed straight side walls of the fusion device and a pair of outer cylindrical surfaces shaped to conform to the fusion device. outward facing surface. 2. The driving tool as claimed in claim 1, wherein the fusion device has an opening on a straight side surface, wherein each of said inwardly facing surfaces of said jaws has an opening from a pin protruding from the surface, said pin extending into one of the plurality of openings on the flat side surface of the fusion device when said inwardly facing surface is in contact with said flat side surface . 3. The driving tool as claimed in claim 1, wherein the driving tool further comprises a sleeve coaxially arranged around the shaft, the sleeve can slide on the shaft, The hinge is thereby squeezed to push the jaws closer to each other, whereby the jaws clamp the fusion device between the jaws. 4. The driving tool as claimed in claim 3, wherein said bushing is threadedly engaged on said shaft, so that when said bushing is rotated around the threaded joint, said bushing The bushing moves axially along the length of the shaft. 5. The driving tool as claimed in claim 3, characterized in that: said clamp has a tapered surface adjacent said hinge; and There is a tapered groove on the inner surface of the sleeve, the tapered groove is complementary to the tapered surface, so that when the sleeve moves axially towards the clamp When the hinge is squeezed, the tapered groove also moves along the tapered surface. 6. The driving tool of claim 1, wherein said fusion device has a pair of oppositely disposed notches cut into one end thereof, wherein said jaws have some openings from said inwardly facing surface The protruding driving protrusion can be engaged with the oppositely arranged notch in the fusion device. 7. A driving tool for implanting an internal fusion device into the space between adjacent vertebrae, said fusion device being hollow, said fusion device having a main body, said main body having a cylindrical inner surface and a cylindrical outer surface interrupted by opposite straight sidewalls, said outer surface has external threads, said driving tool comprises: an elongated shaft; and a pair of opposing jaws attached to one end of the shaft, the jaws being offset from each other to receive the oppositely disposed straight sidewalls of the fusion device therebetween; and an expandable elastomeric collet assembly connected to said elongated shaft, said expandable elastomeric collet assembly having a portion capable of growing from a small enough to fit within the hollow fusion The first diameter in the lumen of the device expands to a second, larger diameter enabling it to grip the lumen of the fusion device. 8. The driving tool according to claim 7, wherein said expandable elastic collet assembly comprises: a head integral with said pair of opposing jaws, said head having a central bore extending therethrough and an end adjacent said jaws at one end of said central bore; an annular flange on the inside of the clamp; and an expander shaft slidably disposed in the center hole, the expander shaft has an end, when the expander shaft is placed in the center hole, the the end portion expands from a first diameter small enough to slide within said central bore to a second larger diameter adjacent said annular flange, Thus, when the expander shaft is retracted into the central bore, the enlarged end gradually expands the annular flange to the extent of engaging the lumen of the fusion device.

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