Medical installation tool

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This applicationMore than one reissue application has been filed for the reissue of U.S. Pat. No. 6,755,841. This application is a continuation reissue of U.S. patent application Ser. No. 11/397,887, filed on Mar. 29, 2006, now U.S. Pat. No. Re. 43,317, which is a reissue of U.S. patent application Ser. No. 10/011,264, filed on Dec. 7, 2001, now U.S. Pat. No. 6,755,841, which is a continuation-in-part of U.S. patent application Ser. No. 09/566,514, filed on May 8, 2000, now U.S. Pat. No. 6,478,800 entitled “Medical Installation Tool,” the entire contents of each of which is hereby expressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

0002The invention relates to a tool for inserting prostheses within the body, and more particularly to tools for inserting prostheses, such as artificial discs and cages, within an intervertebral space.

0003Spinal surgery involves many challenges as the long-term health and mobility of the patient often depends on the surgeon's technique and precision. One type of spinal surgery involves the removal of the natural disc tissue that is located between adjacent vertebral bodies. Procedures are known in which the natural, damaged disc tissue is replaced with an interbody cage or fusion device, or with a disc prosthesis.

0004The insertion of an article, such as an artificial disc prosthesis, presents the surgeon with several challenges. The adjacent vertebral bodies collapse upon each other once the natural disc tissue is removed. These bodies must be separated to an extent sufficient to enable the placement of the prosthesis. However, if the vertebral bodies are separated, or distracted, to beyond a certain degree, further injury can occur. The disc prosthesis must also be properly positioned between the adjacent vertebral bodies. Over-insertion, or under-insertion of the prosthesis can lead to pain, postural problems and/or limited mobility or freedom of movement.

0005Specialized tools have been developed to facilitate the placement of devices, such as disc prosthesis, between adjacent vertebral bodies of a patient's spine. Among the known tools for performing such procedures are separate spinal distractors and insertion devices. The use of separate tools to distract the vertebral bodies and insert a disc prosthesis or graft can prove cumbersome. Further, the use of some distractors can cause over-distraction of the vertebral bodies.

0006Exemplary devices for installing prosthesis and/or grafts between vertebral bodies are disclosed in U.S. Pat. Nos. 5,431,658 and 5,505,732. U.S. Pat. No. 5,431,658 discloses a facilitator device for the insertion of bone grafts between two adjacent vertebrae. The disclosed tool has two flat, tong-like guides that distract the vertebrae as a screw-type inserter forces the graft between the distracted vertebrae. U.S. Pat. No. 5,505,732 discloses an apparatus and a method of inserting spinal implants. The intervertebral space is first distracted and a hollow sleeve having teeth at one end is then driven into the vertebrae that are adjacent the disc space. A drill is then passed through the hollow sleeve, removing the disc and the bone in preparation for receiving the spinal implant, which is then inserted through the sleeve.

0007Despite existing tools and technologies, there remains a need to provide a device to facilitate the proper and convenient insertion of an object, such as a disc prosthesis, between adjacent vertebral bodies while minimizing the risk of further injury to the patient.

SUMMARY OF THE INVENTION

0008The present invention provides a device useful for implanting prostheses, such as artificial spinal discs and cages, within a patient in a safe and efficient manner. The installation tool of the invention generally includes a pair of opposed levers, each of which has a proximal handle portion and a distal portion. A fulcrum is disposed between the two levers to enable proper operation of the tool. The tool further includes a pusher block that is positioned between the two levers and is selectively movable between an initial location distal of the fulcrum and a final location adjacent the distal end of the levers. The pusher block includes a proximal end, a distal end, and a bore extending at least partially therethrough. A pusher rod, which facilitates movement of a pusher block, has a distal end extending into the bore in the pusher block and a proximal, handle end.

0009The pusher rod and/or pusher block can be adapted to mate to a variety of prosthesis devices. In one embodiment, the pusher block can include a blind bore and a distal end of the pusher rod can mate with the blind bore in the pusher block. The pusher block can thus include a distally facing surface having surface features adapted to conform to or mate with complementary surface features on a prosthesis. In another embodiment, the bore can extend entirely through the pusher block to allow a distal end of the pusher rod to extend through the bore in the pusher block. The pusher rod can thus include a distal tip that is effective to mate to a prosthesis.

0010In yet another embodiment, the rod can include a first externally threaded distal portion and a second externally threaded distal portion. The second distal portion is positioned proximal to the first distal portion, and has a diameter greater than a diameter of the first distal portion. The bore of the pusher block can include a threaded proximal opening, a distal opening, and a chamber formed therebetween. The proximal opening is threadingly matable with the second distal portion of the rod to allow the second distal portion of the rod to be threadingly inserted through the proximal opening and positioned within the chamber. The diameter of the distal opening of the pusher block should be less than the diameter of the proximal opening of the pusher block to prevent the second threaded portion of the rod from extending through the distal opening in the pusher block. The threaded second distal portion is preferably freely rotatable within the chamber of the pusher block. The threaded first distal portion of the rod extends through the distal opening in the pusher block and includes a distal tip which is adapted to mate to a prosthesis.

0011In other aspects of the invention the bore extends entirely through the pusher block and a distal tip of the pusher rod is adapted to extend through the bore in the pusher block. The distal tip of the pusher rod is further adapted to mate to a grasping element effective to releasably engage a prosthesis. The grasping element can include an elongate proximal portion with a bore formed therein and a distal portion that is effective to releasably engage a prosthesis. The proximal portion has an outer diameter that is adapted to fit within the bore of the distal end of the pusher block. The distal portion of the grasping can include opposed first and second components that are movable between a first, open position, and a second, closed position that is effective to engage a prosthesis. In use, the distal end of the rod threadingly engages the bore of the grasping element. Rotation of the rod in a first direction is effective to cause the elongate proximal portion of the grasping element to move proximally within the bore of the pusher block, thereby moving the first and second components to the second, closed position. Rotation of the rod in a second, opposed direction is effective to cause the elongate proximal portion of the grasping element to move distally out of the bore of the pusher block and move the first and second components to the first, open position. The first and second components can optionally include at least one surface feature effective to engage a prosthesis.

0012In yet another embodiment, a medical device installation kit can be provided having a pair of opposed levers, a fulcrum disposed between the levers for allowing pivotal movement of the levers with respect to each other, and a plurality of prosthesis installation assemblies. Each assembly is adapted to be slidably disposed between the levers and movable between a first, proximal position and a second, distal portion. A handle portion can be provided on each assembly for moving the prosthesis installation assembly between the first and second positions. Each assembly further includes a distal prosthesis effecting element adapted to place a prosthesis between adjacent bone structures.

0013In one embodiment, one of the prosthesis installation assemblies includes a pusher block having a proximal end, a distal end, and a bore extending therethrough, a pusher rod slidably disposed between the levers and extending through the bore in the pusher block, and a grasping element effective to releasably engage a prosthesis. In another embodiment, one of the prosthesis installation assemblies includes a pusher rod having a proximal handle portion and a distal portion having a distal tip adapted to positively engage a prosthesis. A pusher block can be provided having a bore extending therethrough and adapted to receive a distal portion of the pusher rod. In yet another embodiment, one of the prosthesis installation assemblies can include a pusher rod having an externally threaded first distal portion and an externally threaded second distal portion. The second distal portion has a diameter greater than the first distal portion, and is positioned proximal to the first distal portion. The assembly further includes a pusher block having a bore extending entirely therethrough having a threaded proximal opening that is threadingly matable with the second distal portion of the rod, and a distal opening having a diameter less than the diameter of the second distal portion of the rod. A chamber having a diameter greater than the diameter of the second distal portion of the pusher rod is disposed between the first and second openings of the pusher block. In other aspects, one of the prosthesis installation assemblies can include a pusher block having a bore extending therethrough, a pusher rod extending through the bore in the pusher block, and a plurality of connector elements having a proximal portion adapted to mate to a distal tip of the pusher rod, and a distal portion adapted to mate to a prosthesis.

0014The installation tool of the invention can be used in the following manner. Once the natural, damaged disc tissue is removed from a patient and the area is prepared to receive an artificial prosthesis, such as an artificial disc, the artificial disc is loaded between the levers of the installation tool so that a posterior side of the disc abuts a distal end of the pusher block. The distal tip of the levers is then positioned between the vertebral bodies such that the outwardly facing surfaces of each lever contacts opposed vertebral bodies. Once this position is achieved, the pusher rod is advanced distally, causing the pusher block and the artificial disc to likewise move distally along the inner surfaces of the levers. As the artificial disc and the pusher rod move distally, or forward, the levers separate and also cause vertical separation of the adjacent vertebral bodies. To achieve the proper position of the artificial disc, the distal facing surfaces of the pusher block should contact the vertebral bodies. Once such contact is achieved between the distal facing surfaces of the pusher block and the vertebral bodies, the artificial disc is properly positioned. This tool thus enables the proper positioning of the artificial disc between the vertebral bodies, without over-insertion or under-insertion of the artificial disc, while minimizing the degree of distraction of the vertebrae. To remove the tool, a slaphammer or similar device can be used to apply a proximally directed force to the tool to extract the blade tips without removing the implant.

BRIEF DESCRIPTION OF THE DRAWINGS

0015The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

0016<figref idref="DRAWINGS">FIG. 1</figref> is a perspective view of an installation tool according to the present invention;

0017<figref idref="DRAWINGS">FIG. 2</figref> is a side, elevation view of the tool shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0018<figref idref="DRAWINGS">FIG. 3</figref> is a top view of the tool shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0019<figref idref="DRAWINGS">FIG. 3A</figref> is a perspective view of an installation tool having curved distal blade tips according to another embodiment of the present invention;

0020<figref idref="DRAWINGS">FIG. 3B</figref> is a side view illustration of another embodiment of an installation tool according to the present invention;

0021<figref idref="DRAWINGS">FIG. 4</figref> is a sectional view of the tool shown in <figref idref="DRAWINGS">FIG. 2</figref>, at line <b>4</b>-<b>4</b>;

0022<figref idref="DRAWINGS">FIG. 5</figref> is a top view of a portion of the tool shown in <figref idref="DRAWINGS">FIG. 2</figref>, at line <b>5</b>-<b>5</b>;

0023<figref idref="DRAWINGS">FIG. 6</figref> is an exploded view of a proximal portion of the tool shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0024<figref idref="DRAWINGS">FIG. 7</figref> is an exploded view of a portion of the tool shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0025<figref idref="DRAWINGS">FIG. 7A</figref> is an enlarged view of another embodiment of a pusher block of the tool shown in <figref idref="DRAWINGS">FIGS. 1-3B</figref>;

0026<figref idref="DRAWINGS">FIG. 8</figref> is a side view of a portion of a medical installation tool according to yet another embodiment;

0027<figref idref="DRAWINGS">FIGS. 8A-8D</figref> illustrate, sequentially, the operation of the installation tool according to the present invention during the installation of an artificial disc;

0028<figref idref="DRAWINGS">FIG. 9</figref> is a side-elevation view of one embodiment of an installation tool according to the present invention in an initial, unlocked position;

0029<figref idref="DRAWINGS">FIG. 10</figref> is a side view of the installation tool of <figref idref="DRAWINGS">FIG. 9</figref> in a final, locked position;

0030<figref idref="DRAWINGS">FIG. 11</figref> is a sectional view of the tool shown in <figref idref="DRAWINGS">FIG. 9</figref>, at line <b>11</b>-<b>11</b>;

0031<figref idref="DRAWINGS">FIG. 12</figref> is perspective view of a pusher block useful with the tool of the present invention;

0032<figref idref="DRAWINGS">FIG. 13</figref> is a perspective view of a further embodiment of an installation tool according to the present invention;

0033<figref idref="DRAWINGS">FIG. 14</figref> is an exploded, perspective view of a portion of the installation tool shown in <figref idref="DRAWINGS">FIG. 13</figref>;

0034<figref idref="DRAWINGS">FIG. 15A</figref> is a side, elevation view of a portion of the distal end of the installation tool of <figref idref="DRAWINGS">FIG. 13</figref> in a first position;

0035<figref idref="DRAWINGS">FIG. 15B</figref> is a side, elevation view of a portion of the distal end of the installation tool of <figref idref="DRAWINGS">FIG. 13</figref> in a second position;

0036<figref idref="DRAWINGS">FIG. 16</figref> is an exploded side, perspective view of one embodiment of a connector element for use with a medical installation tool;

0037<figref idref="DRAWINGS">FIG. 17</figref> is an exploded perspective view of a slaphammer instrument for use with a medical installation tool of the present invention;

0038<figref idref="DRAWINGS">FIG. 18</figref> is a side view illustration of a portion of a pusher rod for use with a medical installation tool according to the present invention;

0039<figref idref="DRAWINGS">FIG. 19A</figref> is a cross-sectional side view of a pusher block component of the medical installation tool shown in <figref idref="DRAWINGS">FIG. 8</figref>; and

0040<figref idref="DRAWINGS">FIG. 19B</figref> is a plan view of the proximal end of the pusher block of <figref idref="DRAWINGS">FIG. 19A</figref>.

DETAILED DESCRIPTION OF THE DRAWINGS

0041The present invention provides an installation tool that is useful for the efficient and effective placement of an article, such as an artificial disc or cage, between adjacent vertebral bodies. The installation tool can be provided as a kit having modular components which allow the surgeon to select from among a variety of components to assemble an installation tool that is optimized for its intended use. Although the invention is described primarily with reference to being used to install an artificial disc between adjacent vertebral bodies, it is understood that the installation tool of the invention can be used to place other elements between vertebral bodies, or in other locations within a patient's body. Exemplary elements that can be placed between vertebral bodies include, but are not limited to interbody cages, fulsion devices, spacers, grafts, and the like.

0042As shown in <figref idref="DRAWINGS">FIGS. 1-3B</figref>, the installation tool <b>10</b> of the invention includes opposed levers <b>12</b>, <b>14</b>, each having a distal portion <b>12</b>A, <b>14</b>A and a proximal, handle portion <b>12</b>B, <b>14</b>B. Disposed between the levers <b>12</b>, <b>14</b> is a fulcrum <b>16</b> and pusher block <b>18</b>, which is disposed distally of the fulcrum <b>16</b>. The pusher block <b>18</b> includes a bore extending at least partially therethrough and it is selectively movable from an initial position distal of the fulcrum <b>16</b> to a final location adjacent a distal end of the levers. A pusher rod <b>20</b>, which facilitates selective movement of the pusher block, has a proximal handle end <b>20</b>B and a distal end <b>20</b>A extending into the bore in the pusher block. Although not part of the invention, a prosthesis, such as an artificial disc <b>24</b>, is positioned between the levers, distal of the pusher block <b>18</b>.

0043Preferably the levers <b>12</b> and <b>14</b> are elongate elements that are mirror images of each other. There is no absolute top or bottom of the tool <b>10</b> since it is possible to use either surface as a “top” surface. For ease of reference, however, levers will sometimes be described herein with reference to an illustrated orientation. For example, lever <b>12</b>, and components thereof, may sometimes be referred to as the top, upper, or superior lever while lever <b>14</b> may sometimes be referred to as the bottom, lower, or inferior lever.

0044With further reference to <figref idref="DRAWINGS">FIGS. 1-3B</figref>, the levers <b>12</b>, <b>14</b> include distal <b>12</b>A, <b>14</b>A and proximal <b>12</b>B, <b>14</b>B ends. The proximal end <b>12</b>B, <b>14</b>B of each lever may be of a shape that facilitates convenient grasping and handling of the tool. The proximal end of each lever may comprise approximately one-half of the length of each lever. In one embodiment, a shoulder <b>26</b> marks the end of the proximal portion of the tool and the beginning of the distal portion of the tool. As shown in <figref idref="DRAWINGS">FIGS. 1 and 3</figref>, the proximal portion of each lever preferably has a width (W_p) that is greater than the width (W_d) of the distal portion of each lever.

0045The proximal portion <b>12</b>B of each lever may include an indented region <b>28</b> for receiving the fulcrum <b>16</b>. As shown in <figref idref="DRAWINGS">FIGS. 1 and 6</figref>, the indented region <b>28</b> is in the form of a substantially rectangular cut-out formed on both sides of levers <b>12</b>B, <b>14</b>B. This indented region <b>28</b> enables the levers to conveniently seat the fulcrum <b>16</b>, as described below. The recessed region <b>28</b> is preferably formed slightly proximally of the shoulder <b>26</b>. In one embodiment the distal portion of the recessed region <b>28</b> begins approximately 10 to 100 mm proximally of shoulder <b>26</b>. The recessed region <b>28</b> generally has a length in the range of about 10 to 40 mm and is recessed by about 1 to 40 mm.

0046The proximal region of each lever <b>12</b>B, <b>14</b>B may also include a bore <b>30</b>A, <b>30</b>B which is adapted to seat a bolt <b>32</b> that enables control of the spacing between levers so that the pusher block accurately engages the metal portion of the artificial disc. As shown in <figref idref="DRAWINGS">FIG. 6</figref>, bolt <b>32</b> includes a head <b>34</b> and shaft <b>35</b> having a threaded region <b>36</b>. Preferably, internal threads <b>36</b> are formed within bore <b>30</b>A.

0047The distal portion of each lever <b>12</b>A, <b>14</b>A features side surfaces <b>46</b>, <b>48</b>, outwardly facing surfaces <b>38</b>, <b>40</b> (illustrated as top and bottom surfaces in <figref idref="DRAWINGS">FIG. 6</figref>, respectively), and inwardly facing surfaces <b>42</b>, <b>44</b> upon which the artificial disc <b>24</b> can ride during an installation procedure. The outwardly and inwardly facing surfaces of the lever preferably are substantially smooth. The inwardly facing surfaces <b>42</b>, <b>44</b> can, however, include surface features effective to mate to complementary surface features formed on the implant. For example, each lever <b>12</b>, <b>14</b> can include a rail (not shown) formed in the inwardly facing surface <b>42</b>, <b>44</b> that is effective to be slidably disposed within a corresponding groove or channel formed in the implant. As a result of the surface features formed on the inwardly facing surfaces <b>42</b>, <b>44</b> of the levers <b>12</b>, <b>14</b>, the width (W_d) of the distal portion of each lever can be substantially the same as or even greater than the width (W_p) of the proximal portion of each lever.

0048The distal portions <b>12</b>A, <b>14</b>A of the levers <b>12</b>, <b>14</b> can also have blade tips <b>50</b>A, <b>50</b>B formed at the distal ends of the levers. The blade tips are sized and configured to facilitate their placement between vertebral bodies <b>201</b>, <b>202</b>. The outwardly facing surfaces <b>52</b>A, <b>52</b>B of blade tips may be configured to have surfaces that are beveled or radiused. In one embodiment illustrated in <figref idref="DRAWINGS">FIG. 3A</figref>, the blade tips <b>12</b>_cC, <b>14</b>_cC can be substantially curved or angled in a superior or inferior direction to facilitate placement of the blade tips <b>12</b>_cC, <b>14</b>_cC between adjacent vertebrae. In the illustrated embodiment, the distal tip of the rod <b>20</b>_cincludes a spring <b>2</b> which allows the distal portion of the rod <b>20</b>_cto conform or bend to the shape of the curved blade tips <b>50</b>A, <b>50</b>B. The proximal end <b>4</b> of the spring <b>2</b> can be threadingly mated to or otherwise attached to the distal end of the rod <b>20</b>_c, and the end <b>6</b> of the spring <b>4</b> can be attached to the proximal end of the pusher block <b>18</b>_c. Preferably, the pusher block <b>18</b>_cincludes a protrusion adapted to extend into the bore in the spring <b>4</b> to mate the pusher block <b>18</b>_cto the spring <b>4</b>.

0049The thickness of the levers, measured at the blade tips when the tool is closed, as shown in <figref idref="DRAWINGS">FIG. 1</figref>, can be considerably less than the thickness of the levers measured near the fulcrum between outwardly facing surfaces <b>38</b>, <b>40</b> when the tool is in the closed position. Preferably, the thickness measured at the blade tips is in the range of about 0.5 to 2 mm. A portion of each lever <b>12</b>A, <b>14</b>A, disposed adjacent a proximal end of the blade tips <b>50</b>A, <b>50</b>B, can include a stop surface <b>54</b>. The stop surface <b>54</b>, which is substantially vertically oriented and distally facing, is adapted to abut a vertebral body during a surgical procedure for installing an element, such as an artificial disc, between adjacent vertebral bodies. The stop surface <b>54</b> may assume a variety of configurations. In one embodiment, shown in FIGS. <b>2</b> and <b>8</b>A-<b>9</b>, the stop surface has a substantially concave profile when viewed in the vertical plane.

0050As shown in <figref idref="DRAWINGS">FIGS. 6-7</figref> the side surfaces of the distal portions <b>12</b>A, <b>14</b>A of the levers <b>12</b>, <b>14</b> may have opposed rails <b>56</b>, <b>58</b>, with a recessed track <b>60</b> disposed therebetween. The formation of such recessed tracks <b>60</b> within the distal side walls of levers <b>12</b>, <b>14</b> causes these elements to have a profile that, as shown in <figref idref="DRAWINGS">FIGS. 4 and 7</figref>, is substantially I-shaped or T-shaped. The rails <b>56</b>, <b>58</b> and track <b>60</b>, as discussed below, can be effective to facilitate smooth and efficient movement of the pusher block.

0051One of ordinary skill in the art will appreciate that the size and shape of the levers may vary. Generally, however, the overall length of the levers is about 200 to 400 mm, with proximal portion <b>12</b>B, <b>14</b>B (proximal end to shoulder <b>26</b>) having a length of about 100 to 300 mm and the distal portion <b>12</b>A, <b>14</b>A (shoulder <b>26</b> to blade tips) having a length of about 100 to 300 mm.

0052In one embodiment, illustrated in <figref idref="DRAWINGS">FIGS. 1-3</figref> and <b>6</b>, the fulcrum <b>16</b> is substantially a block-like object having substantially vertical side walls <b>62</b>. The upper and lower surfaces <b>64</b>, <b>66</b> of fulcrum <b>16</b> include recesses or grooves <b>68</b>, each of which is defined by a base wall <b>70</b>, <b>72</b> and opposed inner side walls <b>74</b>. A core section <b>78</b> lies between the base walls <b>70</b> and <b>72</b>. The core section <b>78</b> preferably includes a central bore <b>80</b> to allow passage of pusher rod therethrough. In an exemplary embodiment each base wall <b>70</b>, <b>72</b> includes a mounting post <b>82</b>. As shown in <figref idref="DRAWINGS">FIG. 6</figref>, a biasing element <b>84</b>′, such as a coil spring, may be placed upon each of mounting posts <b>82</b> and the mounting posts, in turn, positioned within the bores <b>31</b>A, <b>31</b>B of levers <b>12</b>, <b>14</b>.

0053The fulcrum <b>16</b> may assume virtually any size and shape that is able to render it effective to separate a substantially intermediate portion of levers while allowing the proximal, handle portion <b>12</b>B, <b>14</b>B to be closed together and result in the opening or separation of the distal portion <b>12</b>A, <b>14</b>A. Generally, the height of the vertical side walls <b>62</b> is in the range of about 20 to 70 mm while the height of the core section <b>78</b> (shown in <figref idref="DRAWINGS">FIG. 7</figref>) is in the range of about 5 to 30 mm. The length of the core section <b>78</b> may be about 5 to 40 mm.

0054One of ordinary skill in the art will further appreciate that the fulcrum may take on a variety of other shapes, sizes and mounting configurations. The embodiment described above is intended to represent one exemplary fulcrum design and mounting configuration.

0055The bolt <b>32</b>, as noted above, can be used to adjust the height/spacing of the levers. One of bores <b>30</b>A, <b>30</b>B, has internal threads <b>37</b> that mate with threaded portion <b>36</b> of bolt <b>32</b>. Tightening or loosening of the bolt will result in increasing or decreasing the spacing/distance between the levers.

0056The pusher block <b>18</b>, as illustrated in <figref idref="DRAWINGS">FIG. 7</figref>, may be in the form of a substantially block-like object having vertical side walls <b>84</b> that define upper and lower recesses <b>86</b>, <b>88</b> wherein each recess is defined by a base wall <b>90</b> and opposed inwardly facing side walls <b>92</b>. Each inwardly facing side wall <b>92</b> preferably includes a guide post <b>94</b> that is matable within recessed tracks <b>60</b> formed in the distal portion of levers <b>12</b>A, <b>14</b>A.

0057In another embodiment, shown in <figref idref="DRAWINGS">FIG. 7A</figref>, each inwardly facing side wall <b>92</b>′ of pusher block <b>18</b>_aincludes a rail <b>95</b> extending from the proximal end to the distal end of the pusher block <b>18</b>_a. Each rail <b>95</b> forms a groove or track <b>97</b> that is matable with rail <b>56</b> or rail <b>58</b> of each lever <b>12</b>, <b>14</b>. The rail <b>95</b> and track <b>97</b> of top and bottom sides of the pusher block <b>18</b>_alimit movement of the levers <b>12</b>, <b>14</b> with respect to each other. In use, proximal movement of the pusher block <b>18</b>_ais effective to cause the blade tips <b>50</b>A, <b>50</b>B to move to the closed position, and to cause the proximal portion of the levers <b>12</b>, <b>14</b> to be fully disposed within the recesses <b>68</b> (<figref idref="DRAWINGS">FIG. 6</figref>) of the fulcrum <b>16</b>. Once the pusher block <b>18</b> is positioned just distal to the fulcrum <b>16</b>, the levers <b>12</b>, <b>14</b> are in effect locked in the closed position.

0058Referring back to <figref idref="DRAWINGS">FIG. 7</figref>, the core section <b>91</b> of the pusher block <b>18</b> is disposed between upper and lower base walls <b>90</b> and includes a proximally facing wall <b>96</b> and a distally facing wall <b>97</b>. In one embodiment, the height of the core section <b>91</b> is less than the height of the prosthesis to be installed, thus enabling inwardly facing surfaces <b>42</b>, <b>44</b> of levers <b>12</b>, <b>14</b> to contact the prosthesis. Alternatively, as shown in <figref idref="DRAWINGS">FIG. 8</figref>, the core section <b>91</b> can have a height h_cthat is slightly greater than the height of the prosthesis <b>24</b>_bto prevent the prosthesis <b>24</b>_bfrom contacting the inwardly facing surface <b>42</b>, <b>44</b> of each lever <b>12</b>_b, <b>14</b>_b. Thus, the prosthesis <b>24</b>_bis spaced apart from the levers <b>12</b>_b, <b>14</b>_bwhen mated to the pusher block <b>18</b>_bor pusher rod <b>20</b>_b. The distally facing wall of the pusher block <b>18</b> can have a shape which conforms to the shape of a prosthesis. In an exemplary embodiment, several pusher blocks <b>18</b>, <b>18</b>_a, <b>18</b>_bcan be provided, each having a different size and/or shape that is optimized for use with a particular prosthesis or patient.

0059As noted above, a pusher rod <b>20</b> may be utilized to actuate pusher block <b>18</b>. The pusher rod <b>20</b> is preferably an elongate, cylindrical member having a proximal end <b>20</b>B and a distal end <b>20</b>A. The rod is adapted to be positioned between the proximal ends <b>12</b>B, <b>14</b>B of the levers <b>12</b>, <b>14</b> so that it extends into or through the bore <b>80</b> in fulcrum <b>16</b>. The rod <b>20</b> can be adapted to mate to the pusher block <b>18</b> such that forward and rearward movement of the pusher rod will directly move the pusher block. Alternatively, the pusher block <b>18</b> can include a bore extending entirely therethrough, and the rod <b>20</b> can be disposed through the bore to mate directly to a prosthesis, or to mate to a connector element which, in turn, mates to a prosthesis.

0060The pusher rod <b>20</b> can optionally include a stop feature to prevent the levers <b>12</b>, <b>14</b> from being removed from the recessed formed in the pusher block. As shown in <figref idref="DRAWINGS">FIGS. 3A and 3B</figref>, the rod <b>20</b>, <b>20</b>_ccan include a stop surface <b>17</b> which abuts the proximal opening of the bore <b>80</b> in the fulcrum <b>16</b>, thereby preventing proximal movement of the levers <b>12</b>, <b>14</b> and fulcrum <b>16</b>. The stop surface <b>17</b> can be formed by a change in diameter of the pusher rod <b>20</b>, <b>20</b>_c, such that the proximal portion of the rod has a diameter greater than the distal portion of the rod <b>20</b>, <b>20</b>_c, and greater than the bore in the pusher block <b>18</b>. Alternatively, the stop surface <b>17</b> can be formed from an annular flange or similar protruding structure.

0061The pusher block <b>18</b> and pusher rod <b>20</b> can include a variety of features, e.g. connector elements, for joining the block <b>18</b> to the rod <b>20</b>, or for mating the rod <b>20</b> and/or the block <b>18</b> to a prosthesis <b>24</b>. By way of non-limiting example, <figref idref="DRAWINGS">FIG. 7</figref> illustrates one embodiment in which the proximal end of the pusher block <b>18</b> facing wall includes a blind bore <b>98</b> having internal threads <b>100</b>. The threads are adapted to mate with complimentary threads <b>102</b> formed on a distal end <b>20</b>A of the pusher rod <b>20</b>, thereby allowing the pusher rod <b>20</b> to positively engage the pusher block <b>18</b>. The distal facing wall <b>97</b> of the pusher block may include a recessed region <b>104</b> that is adapted to nest artificial disc <b>24</b>. As illustrated, the recessed region <b>104</b> has dimensions that enable the artificial disc to fit loosely therein. One of ordinary skill in the art will appreciate that the recessed area should have dimensions slightly greater than the dimensions of the disc so as to avoid a frictional fit that may inhibit free release of the disc from the tool. <figref idref="DRAWINGS">FIG. 12</figref> illustrates one embodiment of a recessed region <b>104</b> having a contact wall <b>106</b> that has a generally arcuate shape. Preferably, contact wall <b>106</b> is substantially concave and well suited to maintaining contact over a substantial surface area of a generally curved (convex) posterior surface of an artificial disc <b>24</b>.

0062<figref idref="DRAWINGS">FIGS. 8</figref>, and <b>18</b>-<b>19</b>B illustrate another embodiment of a connector element for joining the pusher rod <b>20</b>_bto the pusher block <b>18</b>_b, and optionally to a prosthesis <b>24</b>_b. As shown in <figref idref="DRAWINGS">FIGS. 19A and 19B</figref>, the pusher block <b>18</b>_bincludes a bore <b>401</b> having a proximal opening <b>406</b>, a distal opening <b>405</b>, and a chamber <b>408</b> extending therebetween. The proximal and distal openings <b>406</b>, <b>405</b> preferably each have substantially the same diameter, and preferably each have a diameter less than the diameter of the chamber <b>408</b>. As shown in <figref idref="DRAWINGS">FIG. 19B</figref>, the proximal opening <b>406</b> includes a threaded region <b>403</b> which mates to a corresponding threaded region <b>411</b> formed on the rod <b>20</b>_b(<figref idref="DRAWINGS">FIG. 18</figref>). The proximal opening <b>406</b> can, however, include a variety of engagement elements such as, for example, an o-ring which mates to a corresponding groove formed on the rod <b>20</b>_b. The distal opening <b>405</b> does not include threads, and thus is effective to prevent the threaded portion of the rod <b>20</b>_bfrom being threaded through the distal opening <b>405</b>. The proximal opening <b>406</b> can also include a tapered portion <b>409</b> for abutting a corresponding tapered portion <b>410</b> formed on the rod <b>20</b>_b.

0063<figref idref="DRAWINGS">FIG. 18</figref> illustrates a pusher rod <b>20</b>_bthat is suitable for use with the embodiment of pusher block <b>18</b>_bshown in <figref idref="DRAWINGS">FIGS. 19A and 19B</figref>. Pusher rod <b>20</b>_bincludes a distal tip <b>413</b>, a connector segment <b>412</b> extending proximally from the distal tip <b>413</b>, and an annular flange <b>411</b> having a distal end <b>418</b> integral with the connector segment <b>412</b> and a proximal end <b>416</b> mated to the rod <b>20</b>. The proximal and distal ends <b>416</b>, <b>418</b> can be tapered to facilitate insertion and removal of the rod <b>20</b>_bfrom the pusher block <b>18</b>. The distal tip <b>413</b> of the rod <b>20</b>_bcan mate to a prosthesis, and thus can include an engagement element. As shown in <figref idref="DRAWINGS">FIG. 18</figref>, the distal tip <b>413</b> is threaded <b>415</b> to mate with corresponding threads formed in a bore in a prosthesis.

0064In use, the rod <b>20</b>_bis inserted into the proximal opening <b>406</b> of the pusher block <b>18</b>. The distal tip <b>413</b> and connector segment <b>412</b> can be inserted through the bore until the threaded annular flange <b>411</b> engages the threaded region <b>403</b> of the pusher block <b>18</b>_b. The flange <b>411</b> can then be rotated and thus threaded through the bore <b>403</b> to position the flange <b>411</b> in the chamber <b>408</b>. Further distal movement of the rod <b>20</b>_bwill insert the distal tip <b>413</b> and a substantial portion of the connector rod <b>412</b> through the distal opening <b>405</b> of the pusher block <b>18</b>_b. The lack of threads, and the size differential, in the distal opening <b>405</b> will, however, prevent the annular flange <b>411</b> from exiting the chamber. Once the annular flange <b>411</b> is positioned in the chamber, the rod <b>20</b>_bis free to rotate. The rod <b>20</b>_bcan then be rotated to positively engage a prosthesis, or to detach the rod from a prosthesis. In an exemplary embodiment, the threads formed on the annular flange <b>411</b> are oriented in a direction opposite to the threads <b>415</b> formed on the distal tip <b>413</b>. This allows the rod <b>20</b>_bto be detached from a prosthesis without allowing the rod <b>20</b>_bto be threadingly removed through the proximal opening <b>406</b>.

0065A person having ordinary skill in the art will appreciate that the annular flange <b>411</b>, and the distal tip <b>413</b> can employ a variety of engagement elements other than threads. For example, other locking elements include snap-fit engagements, frictional engagements, bayonet-type locks, leur locks, or any other type of connector.

0066<figref idref="DRAWINGS">FIG. 16</figref> illustrates another embodiment of a connector element for joining the pusher block <b>18</b>_dto a prosthesis <b>600</b>. As shown, a grasper element <b>500</b> is provided for grasping a prosthesis <b>600</b>. The grasper <b>500</b> includes a proximal portion <b>502</b> and a distal portion <b>504</b>. The proximal portion <b>502</b> is elongate, having a substantially cylindrical cross-section with an outer diameter d, and a bore <b>506</b> extending therethrough along the longitudinal axis l of the instrument. The bore <b>506</b> is adapted to matingly engage the distal end <b>20</b>A of the rod <b>20</b>, and thus can include internal threads that threadingly receive the threaded distal end <b>20</b>A of the rod <b>20</b>. A person having ordinary skill in the art will appreciate that a variety of alternative engagement mechanisms can be provided for mating the grasper <b>500</b> to the rod <b>20</b>. The outer diameter d of the cylindrical proximal portion <b>502</b> should be less than the diameter of the bore <b>80</b>_din the pusher block <b>18</b>_dto allow the proximal portion <b>502</b> to be inserted into the bore <b>80</b>_d. The proximal portion <b>502</b> preferably includes a tapered region <b>505</b> which increases toward the distal portion <b>504</b>.

0067The distal portion <b>504</b> of the grasper <b>500</b> is oriented to extend in a direction substantially transverse to the longitudinal axis l of the instrument and includes first and second wing-like components <b>508</b>, <b>509</b>, each positioned on opposed sides of the longitudinal axis l, and separated from one another by a gap <b>513</b>. The first and second components <b>508</b>, <b>509</b> are not attached to each other, but include a proximally extending portion <b>510</b>, <b>511</b> which mates to the proximal portion <b>502</b>. The proximally extending portions <b>510</b>, <b>511</b> taper inwardly toward the proximal portion <b>502</b>. As a result, the grasper <b>500</b> incrementally increases in diameter d toward the distal portion <b>504</b> of the grasper <b>500</b>. In an exemplary embodiment, the gap <b>513</b> allows the first and second components <b>508</b>, <b>509</b> to be pinched together.

0068The first and second components <b>508</b>, <b>509</b> each include a distally facing wall <b>520</b>, <b>521</b>. The walls <b>520</b>, <b>521</b> can have a shape that conforms to the shape of a prosthesis, and preferably the walls are slightly concave to fit around a substantially cylindrical or disc-shaped prosthesis <b>600</b>, as shown. Each component <b>508</b>, <b>509</b> can include a protruding element <b>515</b>, <b>516</b> disposed on the distally facing wall <b>520</b>, <b>521</b> that is effective to engage a prosthesis <b>600</b>. The protruding elements <b>515</b>, <b>516</b> can be, for example, triangle-shaped, diamond shaped, or hook-like members which, when placed into openings <b>518</b> formed in the prosthesis <b>600</b>, are effective to engage the prosthesis <b>600</b>.

0069In use, the grasper <b>500</b> is inserted into the bore <b>80</b>_din the pusher block <b>18</b>_dand it is mated to the rod <b>20</b>. The protruding elements <b>515</b>, <b>516</b> are inserted into the openings <b>518</b> formed in the prosthesis <b>600</b>, and the rod <b>20</b> is rotated to engage the grasper <b>600</b>, thereby moving the grasper <b>600</b> proximally. As the grasper <b>600</b> is pulled in a proximal direction by the rod <b>20</b>, the tapered portion of the grasper <b>500</b> is pulled into bore <b>80</b>_d, thereby causing the first and second components <b>508</b>, <b>509</b> to be pinched together. As a result, the protruding elements <b>515</b>, <b>516</b> grasp and retain the prosthesis <b>600</b>. The prosthesis <b>600</b> can then be positioned between adjacent vertebrae and, once positioned, the rod <b>20</b> can be rotated in the opposite direction to release the grasper <b>500</b>, thereby allowing the first and second components <b>508</b>, <b>509</b> to return to their separated state, thus releasing the prosthesis <b>600</b>.

0070In an exemplary embodiment, the pusher block <b>18</b>_dincludes a recessed region <b>19</b> formed in each of the side walls of the pusher block <b>18</b>_dto allow the grasper <b>500</b> to be inserted into the bore <b>80</b>_d. The first and second components <b>508</b>, <b>509</b>, when mated to the pusher block <b>18</b>_d, sit within the recessed region <b>19</b>. The rod <b>20</b> preferably includes a stop surface (not shown) to prevent further insertion of the rod <b>20</b> through the bore <b>80</b>_din the pusher block <b>18</b>_d. The stop surface should be positioned to allow a distal portion of the rod <b>20</b> to extend through the bore <b>80</b>_dto engage the grasper <b>500</b>.

0071The depth of insertion of the cage <b>600</b> between the vertebral bodies is dependant on the length of the grasper <b>500</b> and the depth of the recessed portion <b>19</b>. For example, the length of the grasper <b>500</b> and the depth of the recessed portion <b>19</b> can be substantially the same such that the distal end of the pusher block is aligned with the distal end of the grasper. In use, the distal ends of the pusher block and the grasper align with the outer edge of the adjacent vertebrae. As a result, the implanted disc is substantially aligned with the outer edge of the adjacent vertebrae. Alternatively, the grasper <b>500</b> can have a length greater than the depth of the recessed portion <b>19</b> such that the depth of insertion of the disc is substantially equal to the different between the length of the grasper <b>500</b> and the depth of the recessed portion <b>19</b>.

0072<figref idref="DRAWINGS">FIGS. 9 and 10</figref> illustrate an alternative embodiment in which installation tool <b>10</b>′ includes a locking mechanism <b>108</b> in the proximal, handle portion <b>12</b>B′, <b>14</b>B′ of levers <b>12</b>′, <b>14</b>′. The locking mechanism, which may comprise a latch and groove, simply secures the proximal handle portion of levers in a desired position and prevents complete separation of these elements. <figref idref="DRAWINGS">FIG. 9</figref> illustrates the tool <b>10</b>′ in a position in which the proximal portion <b>12</b>B′, <b>14</b>B′ of the levers is open or unactuated. The locking mechanism <b>108</b> prevents further opening or separation of the proximal portions <b>12</b>B′, <b>14</b>B′ of the levers. However, as shown in <figref idref="DRAWINGS">FIG. 10</figref>, the locking mechanism still allows the handles <b>12</b>B′, <b>14</b>B′ to be actuated or closed together in order to operate the tool and install a prosthesis, such as artificial disc <b>24</b>. One benefit of the locking mechanism <b>108</b> is that the disc is less likely to become inadvertently dislodged from the tool during pre-surgical installation manipulation of the tool.

0073<figref idref="DRAWINGS">FIG. 13</figref> illustrates an embodiment of the invention in which installation tool <b>300</b> includes a plurality protrusions <b>302</b>, <b>304</b> formed on proximal or handle portions <b>312</b>B, <b>314</b>B of levers <b>312</b>, <b>314</b>. Preferably, the protrusions <b>302</b>, <b>304</b> are formed on lateral surfaces of the handle portions. In an exemplary embodiment two protrusions are formed on each of the top and bottom levers <b>312</b>, <b>314</b>. Although illustrated as being substantially cylindrical in shape, it is understood that protrusions <b>302</b>, <b>304</b> may take virtually any shape. Referring back to <figref idref="DRAWINGS">FIG. 3B</figref>, for example, the proximal end <b>12</b>B, <b>14</b>B of the handles <b>12</b>, <b>14</b> can have a T-shape. The T-shape, or the protrusions, may be useful to facilitate extraction of the blade tips <b>350</b>A, <b>350</b>B using a tool such a slaphammer <b>800</b> or a slap fork (shown in <figref idref="DRAWINGS">FIG. 17</figref>) The slap hammer <b>800</b> is positioned around the levers <b>12</b>, <b>14</b>, and slid proximally to apply a proximally directed force to the T-shaped handles, or to the protrusions <b>302</b>, <b>304</b>. The dimensions of T-shaped handles or the protrusions <b>302</b>, <b>304</b> may vary within a wide range. Generally, however, the T-shaped handles or protrusions <b>302</b>, <b>304</b> extend from the lateral surfaces of levers <b>312</b>, <b>314</b> by a distance of about 3 mm to 50 mm.

0074Although T-shaped handles and protrusions <b>302</b>, <b>304</b> are illustrated, one of ordinary skill in the art will readily appreciate that the handles can have a variety of configurations for allowing use of a slap hammer with the instrument.

0075With reference to <figref idref="DRAWINGS">FIGS. 13-15B</figref>, the installation tool <b>300</b> may also include a feature which permits selective adjustment of blade tip length (i.e., the distance between the distal end <b>306</b> of blade tips <b>350</b>A, B and stop surface <b>354</b>). In such an embodiment the distal portion of each of the levers <b>312</b>A, <b>314</b>A has a stop member component <b>307</b> and a blade member component <b>308</b>, which are longitudinally separable with respect to each other. The separability of components <b>307</b> and <b>308</b> permits the blade tip length to be adjusted by varying the relative positions of components <b>307</b>, <b>308</b>.

0076As shown in <figref idref="DRAWINGS">FIGS. 13 and 14</figref> tool <b>300</b> includes a junction box <b>309</b> which houses and secures the components <b>307</b>, <b>308</b>. A portion <b>307</b>A of the stop member component <b>307</b>, which mates with the inner surface of the cover <b>320</b> of the junction box <b>309</b>, includes a series of grooves <b>310</b> separated by raised ridges <b>311</b>. Similarly, the abutting, inner surface of the cover <b>320</b> of the junction box <b>309</b> includes grooves and ridges <b>310</b>, <b>311</b> as well. As further illustrated, the cover <b>320</b> is secured to levers <b>312</b>, <b>314</b> by suitable fasteners, such as screws <b>322</b>. Biasing elements, such as compression springs (not shown) are preferably used to bias the junction box to a position such that the grooves and ridges <b>310</b>, <b>311</b> of the cover <b>320</b> and the stop member component <b>307</b> mate with and remain firmly secured to one another. As shown in <figref idref="DRAWINGS">FIG. 14</figref>, suitable indicia <b>325</b> may be present on the stop member component <b>307</b> to indicate the position of the stop member component <b>307</b> with respect to the blade member component. Although <figref idref="DRAWINGS">FIG. 14</figref> only illustrates, in detail, the configuration of lever <b>12</b>, it is understood that the same construction is used for lever <b>14</b>.

0077The result of this selective adjustability is shown in <figref idref="DRAWINGS">FIGS. 15A and 15B</figref>, in which the blade tip length is greater in <figref idref="DRAWINGS">FIG. 15A</figref> than in <figref idref="DRAWINGS">FIG. 15B</figref>.

0078FIGS. <b>1</b> and <b>8</b>A-<b>8</b>D sequentially illustrate the use of tool <b>10</b> for the installation of an artificial disc <b>24</b>. The tool is first assembled as shown in <figref idref="DRAWINGS">FIG. 1</figref>, and with pusher block <b>18</b> positioned in its initial position such that its proximally facing wall <b>96</b> abuts shoulder <b>26</b>, the posterior surface <b>27</b> of the disc is placed against the distal facing wall <b>97</b> of the pusher block. With the handles <b>12</b>B, <b>14</b>B in the open position and the blade tips <b>50</b>A, B closed, the blade tips are wedged between adjacent vertebral bodies <b>201</b>, <b>202</b> to effect slight separation between at least the anterior portions of the vertebral bodies. The blade tips <b>50</b>A, B should be fully inserted between the vertebral bodies, as shown in <figref idref="DRAWINGS">FIG. 8A</figref>, so as to enable the vertebral stop surface <b>54</b> to abut the posterior side <b>204</b> of the vertebral bodies <b>201</b>, <b>202</b>. The pusher rod <b>20</b> is then pushed forward, causing distal movement of the pusher block <b>18</b> and artificial disc <b>24</b>. The forward or distal movement of pusher block <b>18</b> and the artificial disc <b>24</b> also causes further separation of the blade tips <b>50</b>A, B and thus further separation of the vertebral bodies <b>201</b>, <b>202</b> as shown in <figref idref="DRAWINGS">FIG. 8B</figref>. Advancement of the pusher block <b>18</b> and the artificial disc <b>24</b> continues until, as shown in <figref idref="DRAWINGS">FIG. 8C</figref>, the disc is properly installed between adjacent vertebral bodies. <figref idref="DRAWINGS">FIGS. 8B and 8C</figref> illustrate that at all times separation of the vertebral bodies is only effected to the extent necessary to insert the disc. Excessive distraction or separation of the vertebral bodies does not occur because the separation of vertebral bodies is caused by the height of the pusher block.

0079The installation tool of the present invention can also be provided as a kit having modular components which allow the surgeon to select from among a variety of components to assemble an installation tool that is optimized for its intended use. The kit preferably includes several different rods, pusher blocks, and connectors elements, such as grasper <b>500</b>, each adapted to be used with a particular implant. For example, the kit can include three types of pusher blocks, each adapted to mate with a particular prosthesis. As shown in <figref idref="DRAWINGS">FIG. 16</figref>, the pusher block <b>18</b>_dcan be used in combination with grasper <b>500</b> to insert a cage-type spacing prosthesis. Alternatively, as shown in <figref idref="DRAWINGS">FIG. 1</figref>, pusher block <b>18</b> can be provided for inserting an artificial disc. A person having ordinary skill in the art will appreciate that the installation tool can include a variety of components having a combination of different features. Moreover, the components can be adapted for use with particular types of prosthesis, or for use with other components.

0080One of ordinary skill in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publication and references cited herein are expressly incorporated herein by reference in their entity.