Distractor for lumbar insertion instrument

An instrument and method are disclosed for inserting an artificial intervertebral disc implant having upper and lower parts and a pivot element therebetween into an intervertebral space. The instrument has a mounting structure, and an elongated upper arm and elongated lower arms, the arms being pivotally attached to the mounting structure. A distractor separates the upper and lower arms, and hence the upper and lower parts, when moving along the arms so as to permit insertion of the pivot element. The distractor includes a fork arm that extends beyond a main body thereof to engage and support with heads thereof a facing surface of the upper and/or lower part during and following separation of the parts.

FIELD OF THE INVENTION

This invention relates to instruments for inserting intervertebral implants, and more specifically to new and improved instruments and methods for inserting an artificial intervertebral disc implant into an intervertebral space.

BACKGROUND OF THE INVENTION

Currently, when it is necessary to completely remove a disc from between adjacent vertebrae, the conventional procedure is to fuse the adjacent vertebrae together. This “spinal fusion” procedure is a widely accepted surgical treatment for symptomatic lumbar degenerative disc disease. However, reported clinical results vary considerably, and complication rates are considered by some to be unacceptably high.

More recently, there have been important developments in the field of disc replacement, namely disc arthoplasty, which involves the insertion of an artificial intervertebral disc implant into the intervertebral space between adjacent vertebrae, and which allows limited universal movement of the adjacent vertebrae with respect to each other.

The aim of total disc replacement is to remove pain generation (disc), restore anatomy (disc height), and maintain mobility in the functional spinal unit so that the spine remains in an adapted sagittal balance. Sagittal balance is be defined as the equilibrium of the trunk with the legs and pelvis to maintain harmonious sagittal curves. In contrast with fusion techniques, total disc replacement preserves mobility in the motion segment and mimics physiologic conditions.

One such intervertebral implant includes an upper part, or upper plate, That can communicate with a vertebrae, a lower part, or lower plate that can Communicate with the adjacent vertebrae, and a pivot element, or third part, inserted between these two parts. An example of an instrument for this type of implant is disclosed in U.S. Pat. No. 5,314,477. More specifically, tongs are disclosed that can be used, after the insertion of the pivot element between the upper and lower parts of the implant, to move the two vertebrae apart to a distance sufficient for introducing the assembled implant into that space. Additionally, instruments exist for inserting intervertebral implants that move the implant along a longitudinal guide as far as the implant point, and then feed the implant out of the guide and into the intervertebral space. See U.S. Pat. No. 5,571,109. However, both of these instruments are suitable only for inserting complete implants.

An improved instrument is shown in Published Application No. WO 01/01893, published Jan. 11, 2001 and incorporated by reference, and instruments for inserting same are shown in Published Application No. WO 01/19295, published Mar. 22, 2001 and incorporated herein by reference. These applications disclose an arrangement wherein the upper and lower parts of the implant, without the pivot element, are inserted into the intervertebral space, after which the upper and lower parts are separated and the pivot element is inserted therebetween. The terms “separated” and “distracted” are used interchangeably and have the same meaning herein.

In particular, the instrument shown in Published Application No. WO 01/19295 includes: a) an upper arm for engaging an upper part of the implant, b) a lower arm for engaging a lower part of the implant, c) a separate distractor for separating the upper and lower parts from each other after they have been inserted into the intervertebral space, and d) a pusher element for pushing the pivot element along the length of the instrument between the two lower arms and directly into the lower part. After location of the pivot element, the distractor is retracted, allowing the two adjacent vertebrae to come together which urges the upper and lower parts together against the pivot element.

While these and other known instruments and methods represent improvements in the art of artificial intervertebral implant insertion, there exists a continuing need in the art for improvements in the field of instruments and methods for inserting intervertebral implants.

BRIEF SUMMARY OF THE INVENTION

A purpose of the present invention is to provide a new and improved instrument and method for inserting an intervertebral disc implant.

The instruments and methods of the present invention are used to insert various sized artificial intervertebral disc implants at any location along the spine, including especially the lumbar and cervical spine.

An intervertebral implant is normally inserted anteriorly, i.e., from the patient's anterior moving towards the patient's posterior. However, it is to be understood that the implant, the instruments and a method can also be designed and arranged to insert the implant laterally, i.e., from the side or obliquely, from the side-front. To avoid confusion with respect to the patient's anatomy, the invention will be described herein with respect to more simple terminology which relates to instruments and methods themselves. For example, in describing the invention, the terms “front” or “forward” mean the part of the instrument which faces toward the vertebrae or is moving in the direction of movement toward the vertebrae, and the words “back”, “rear”, or “rearward” refer to the end of the instrument furthest from the vertebrae or moving away from the vertebrae. Also, in this application, the words “upper”, “lower”, “uppermost” or “lowermost” or any other words describing orientation of the intervertebral implant or the instruments or methods associated therewith are used only for convenience and are not intended to convey any limitation. More specifically, the parts of the implant, the instrument and/or the methods described in this application with reference to the upper part or plate can in fact be positioned as the superior or inferior part within the patient's vertebrae, with the other of the two parts being the opposite part.

The instrument and the method of the present invention are particularly adapted for use with an artificial intervertebral disc implant having upper and lower parts which undergo limited universal movement with respect to each other, with the upper and lower surfaces of the upper and lower parts engaging the adjacent vertebral surfaces.

For example, the instrument and method of the present invention are used in connection with implant devices that have an upper part or plate and a lower part or plate, and a pivot element therebetween.

In the prior arrangement of WO 01/19295, it has been noted that support of the upper part during a high force distracting movement is not easy. Specifically, in this prior arrangement, the sole engagement of the arms with their respective parts are by way of pins at the end of each of the upper and lower arms engaging apertures in the front of the upper and lower parts. During the exertion of high forces by the distractor to move the upper and lower parts apart, and hence the adjacent vertebrae apart, the posterior portion of the upper part farthest from its engaging pins would have a tendency to move (pivot) into the newly created space.

The present invention improves upon the previous instrument by providing a new and improved distractor element which is constructed and arranged such that it moves the upper and lower parts apart, and hence the adjacent vertebrae, apart. This distractor has a new forward end, or forward arm, which engages and at least supports the upper part along at least the posterior portion thereof, by extending into the space between the upper and lower parts and engaging the interior lower surface of the upper part.

In a preferred arrangement, this forward end of the distractor comprises a pair of fork arms which extend along the bottom of the upper part, offset to one side or the other so as not to interfere with a central portion of the upper part which forms a surface for receiving the pivot element. It will be appreciated that the upper part is always finally engaged at least at the posterior portion thereof by a respective head of each fork arm.

Thus, it is an object of the present invention to provide a new and improved instrument for distracting upper and lower parts of an intervertebral disc implant.

It is another object of the present invention to provide a new and improved method for separating the upper and lower parts of an intervertebral disc implant.

These and other objects of the present invention will become apparent from the detailed description to follow, together with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, like elements are represented by like numerals throughout the several views. As stated above, embodiments of the present invention are directed to instruments and methods for inserting artificial intervertebral disc implants21or the like. As known in the art, prior to inserting of an intervertebral disc implant21, the intervertebral space must be cleaned out with instruments such as elevators and/or chisels. After the intervertebral space has been cleaned out in preparation for receiving intervertebral disc implant21, the next step is to determine the precise size of an inlay protrusion44of a pivot element42(which is located between an upper part22and a lower part32of implant21) which provides a correct overall height for disc implant21for that particular (height) intervertebral space. This determination is accomplished by providing a set of trial implants of different sizes. The operator thus selects by experience the trial implant that the operator believes would be the most appropriate for that particular intervertebral space and disc implant21selected.

Once the correct trial implant has been selected, the next step is to form the cutouts in the adjacent vertebrae using the trial implant. These cutouts are designed to receive raised keels of the upper and lower plates. Typically, a chisel is used to form the required cutouts in the opposed vertebrae. In accordance with the present invention, an insertion instrument50disclosed hereafter is then used to insert intervertebral implant21into the intervertebral space defined by the two vertebrae as explained in detail below.

Typically, examples of intervertebral disc implants21used in connection with the present invention will include those similar to disc implant21depicted in detail inFIGS. 1-2.FIGS. 1-2show disc implant21having upper part22with a raised keel23protruding therefrom, and lower part32with a raised keel33protruding therefrom. Also shown are upper insertion apertures24and one of two lower apertures34. Pivot element42is shown in place between upper part22and lower part32inFIGS. 1 and 2, and in a position to be inserted into the holding space of the lower part32inFIG. 2. Upper part22(as shown inFIGS. 10 and 11) has a domed-shaped concave bearing face26which receives a mating convex inlay protrusion44of pivot element42.

Pivot element42, shown best inFIG. 2, will typically have a substantially rectangular base43which is to be captured in a recess35of lower part32and protrusion44which is to be received in concave domed-shaped bearing face26of upper part22. Lower part32, shown best inFIG. 2, comprises a recess35to snugly receive rectangular base43of pivot element42. Pivot element42can be inserted into recess35from the open side as shown inFIG. 2, allowing opposite edges45of base43to engage lateral grooves37in lower part32so that pivot element42can be inserted and then moved forwardly along grooves37into a fully inserted/captured position in recess35. Other details of implant21are disclosed in WO 01/01893 as noted above and thus need not be discussed here further.

When implanted, as also fully disclosed in WO 01/01893, inlay protrusion44engages concave bearing face26of upper part22, so that upper part22and lower part32are braced on one another via pivot element42and have a pivotal relationship one to the other. Both upper part22and lower part32on a front or anterior face thereof have insertion apertures24,34which are designed to receive mounting pins51of the insertion instrument of the present invention as described below.FIG. 1clearly shows upper part22and lower part32with pivot element42positioned therebetween so that relative pivoting of upper part22and lower part32is permitted.

As shown inFIG. 3and similar to the instrument disclosed in WO 01/01893, insertion instrument50of the present invention has an elongated upper arm57and substantially parallel elongated lower arms52,53. Upper arm57and lower arms52,53engage a mounting structure54, which holds the adjacent ends of arms52,53and57as noted below. The second or free ends of lower arms52,53are each engageable in lower part32of disc implant21while the second or free end of upper arm57is engageable in upper part22. Referring toFIG. 3, these engagements are accomplished by retaining pins51on the associated ends of each arm52,53,57. A holder56is used to attach pins51to upper arm57as broadly described in WO 01/19295, by which upper part22is engaged with upper arm57at a predetermined slight angle to vertical as shown. Mounting structure54includes an opening54A with a spring-loaded ball catch (not shown) therein which receives mounting portion66A of a part of the casing66(seeFIG. 4) to secure the distractor, as discussed in detail below.

In the embodiments of the present invention, lower arms52,53are rotatable about their central, longitudinal axes in order to lock lower arms52,53to lower part32as shown and described in WO 01/19295 and as described below with respect toFIG. 5. As also described in WO 01/19295, upper arm57has pins51of holder56slidably received in apertures24of upper part22as shown inFIG. 6. However, in this embodiment it will be appreciated that holder56is rigid with upper arm57and hence does not pivot relative to upper arm57as does the holder disclosed in WO 01/19295.

As stated above, mounting structure54holds arms52,53,57in pivotable relationship with one another, with lower arms52,53parallel to one another and with upper arm57at a small angle to the plane of lower arms52,53. In the embodiments of the present invention, mounting structure54is spaced apart from the plane defined by the two lower arms52and53. Upper arm57is vertically disposed approximately midway between the two lower arms52and53, so that the free or forward end of upper arm57can, in its lowered position, enter the space between the two parallel lower arms52and53.

As shown inFIG. 6, upper arm57is circular in cross section and on its free end carries U-shaped holder56which receives the free end of upper arm57. Holder56and upper arm57are immovably joined together as noted above.

Instrument50of the present invention further comprises a distractor60, as shown best inFIG. 4, which comprises an elongated arm61with a body62securely attached thereto. At a forward end of body62there are a pair of fork-shaped arms63that extend forward beyond body62substantially parallel to the longitudinal axis of arm61. As shown inFIGS. 4 and 7, body62has a solid wedge portion70which matingly seats with and engages upper arm57as wedge portion70approaches the free end of upper arm57. In addition, as best shown inFIG. 7, fork arms63also have rounded lower seats71which similarly engage the adjacent portions of lower arms52and53. It will be appreciated that distractor60is usable with instruments50having differently spaced lower arms53. Thus, as shown inFIG. 7, the outside portion of seats71are designed to mate against lower arms53(only one of which is partially shown in phantom) where instrument50has widely spaced lower arms53(for larger sized implants21); while the inside portion of seats71are similarly designed to mate against lower arms53′ (only one of which is partially shown in phantom) where instrument50has more closely spaced lower arms53′ (for smaller sized implants21). If only one spacing of lower arms50is usable, then seats71can be designed to mate over the entire surface thereof with the associated lower arm53.

As wedge portion70moves forward along arms52,53and57and approaches disc implant21, wedge portion70forces upper arm57slowly away from lower arms52,53, creating a small starting space between upper part22and lower part32. It will thus be appreciated that wedge portion70serves a function similar to the spreader element (43) disclosed in WO 01/19295. It will also be appreciated that body62includes a protrusion74which also serves a function similar to protrusion44disclosed in WO 01/19295. In particular, protrusion74is used to initially push rectangular base43of pivot element42—whose edges45engage longitudinal grooves55provided along opposing (facing) inner sides of lower arms52,53—forward to a position immediately adjacent implant21and then partially into recess35. The final forward movement of pivot element42is then accomplished using a pushing element80(seeFIG. 10) similar to that described in WO 01/19295, which also engages rectangular base43so that no potentially damaging contact is made with inlay protrusion44.

It will also be appreciated that distractor60of the present invention may further include a leaf spring73provided behind wedge portion70which resiliently mounts a seat72. When distractor60is first located between arms52,53and57and body62is rearward or near mounting structure54, seats71rest loosely on arms52and53but wedge portion70is too far away from upper arm57to have contact therewith (due to the angle of arm57to the plane of lower arms52,53). Thus, at this position it is seat72that resiliently engages arm57to gently hold body62in position between arms52,53and57(working together with mounting structure54as explained below) to assure that protrusion74is in position to engage and hence move pivot element42forward along lower arms52,53as body62is moved toward implant21. Then, as distractor60moves along upper arm57and lower arms52,53adjacent mounting structure54toward disc implant21at the forward end of arms52,53and57, the angle of upper arm57relative to lower arms52,53gradually forces seat72down toward arm61. This movement of seat72is made against the mild force of leaf spring73, so that only a minor reactive force is exerted on arms52,53and57which is insufficient to force upper part22and lower part32of disc implant21apart (so that no significant separating forces are conveyed to upper part22and lower part32). It will be appreciated that seat72does not actually contact arm61during this movement, since wedge portion70is slightly higher than the thickness of seat72so that wedge portion70takes over the holding function of seat72when fork arms63approach implant21—and turns this holding function additionally to a separating function as noted below.

Distractor60engages upper arm57and lower arms52,53in such a way that as distractor60slides forward along between lower arms52,53it rides along the top of lower arms52,53and first seat72of leaf spring73engages upper arm57and then wedge portion70engages upper arm57.FIG. 8shows the position of the upper and lower parts22,32nested together (as described in WO 01/19295) in their closed or initial position before wedge portion70(not shown in this Figure) engages upper arm57and lower arms52,53. With the parts in this position, distractor60, as it moves further forward along upper arm57and lower arms52,53towards disc implant21, will slightly separate upper and lower parts22,32from each other (and hence slightly enlarge the intervertebral space), as wedge portion70of distractor60urges upper arm57upwardly slightly, creating a starting space. This starting space is relatively easy to create, as the intervertebral forces holding upper part22and lower part32adjacent one another are initially small. When this starting space is created, it will be appreciated that protrusion74has caused pivot element42to be located immediately adjacent recess35and thus ready to be pushed forward into recess35as fork arms63move forward between upper part22and lower part32and wedge portion70and/or fork arms63open a space sufficient for receiving pivot element42to pass into (as discussed below).

In the prior art WO 01/19295, further wedging movement of the similar protrusion element was designed to effect a sufficient space so that pivot element42could be easily inserted partially onto lower part32using the protrusion without interference from upper part22. However, as the force required to separate the upper part22from the lower part increased with the increased separation distance (the resistance of the forces trying to close the intervertebral space increased), it would not always be easy to achieve the required spacing and/or the desired orientation of upper part22relative to lower part32was not easily maintained.

In order to make this separation easier, in accordance with the present invention, after the starting space is provided by wedge portion70, further advancement of distractor60causes fork arms63to enter the already created starting space. Entry of heads64of fork arms63into the staring space is facilitated by the tapered front end of each head64. As the heads64of fork arms63enter the starting space between upper part22and lower part32and further forward movement of distractor60occurs, one or both of two reactive forces are exerted to positively force upper part22further away from lower part32in order to provide the needed spacing therebetween. The first force is that of wedge portion70acting on upper part22, while the second force is that of heads64of fork arms63. These forces act in concert in the following manners, which obviously depend on the relative sizes of wedge portion70and heads64of fork arms63(as discussed below with respect toFIGS. 13A-B) as well as the amount of pivoting into the separation space which the posterior end of upper part22experiences as distractor60moves forward.

Typically where there is only some resistance to the distracting movement of upper part22away from lower part32, as where the intervertebral space receiving implant21is large so not much widening is needed, wedge portion70may be sufficient by itself to perform all or most of the needed distracting movement. In this case, heads64of fork arms63may provide no or only a minor effective distracting force. It will be appreciated that where fork arms63provide essentially no distracting force, heads64of fork arms63nonetheless will engage along upper part22and provide a holding or supporting force along upper part22to maintain upper part22in the proper orientation with lower part32(and hence to prevent falling or pivoting of upper part22). Similarly, where heads64of fork arms63provide only a minor distracting force (which distracting force also serves to support or hold), this distracting force of heads64of fork arms63will primarily be exerted as heads64of fork arms63engage along upper part22as wedge portion70does not provide the complete distracting force necessary. Typically when either no distractor force (with supporting/holding occurring) or some distracting force is exerted by heads64of fork arms63, heads64of fork arms63only begin to contact upper part22after passing some of the anterior portion thereof; but this supporting/holding/forcing could occur starting at the anterior portion, but more likely will occur starting near the posterior portion of upper part22at the end of the forward movement of distractor60. In addition, heads64of fork arms63can begin providing only a supporting/holding force and then provide some distracting force, or vice versa or alternately, as forward movement of distractor60occurs.

Typically where there is significant resistance to the distracting movement of upper part22away from lower part32, as where the intervertebral space receiving implant21is small so a more forceful widening may be needed, heads64of fork arms63may perform all or most of the distracting movement after the initial starting space at the anterior end of upper part22is created by wedge portion70. In this case, wedge portion70may provide no or only a minor additional effective distracting force. It will be appreciated that where wedge portion70provides essentially no additional distracting force, wedge portion70may or will nonetheless provide a holding or supporting force at the anterior part of upper part22to help maintain upper part22in the proper orientation with lower part32(and hence to prevent falling or pivoting of upper part22). Similarly, where wedge portion70provides only a minor additional distracting force (which distracting force also serves to support or hold), this distracting force of wedge portion70will primarily be exerted at the anterior portion of upper part22to which upper arm57is directly attached. Typically when either no distracting force (with supporting/holding occurring) or some additional distracting force is exerted by wedge portion70, wedge portion70only effects a supporting/holding and/or distracting force on the anterior part of upper part22as heads64of fork arms63travel further along the posterior half thereof; but this supporting/holding/forcing could occur starting at the beginning of the forward engaging movement of heads64, but more likely will occur starting near the end of the forward movement of heads64(the end of the forward movement of distractor60). In addition, wedge portion70can begin providing only a supporting/holding force and then provide some distracting force, or vice versa or alternately, as the forward movement of distractor60occurs.

While two relative extremes of the two distracting forces of heads64of fork arms63and of wedge portion70have been described above, in practice wedge portion70and heads64will be designed so that in many or even most situations it will be some, possibly changing, combination of the distracting forces of both heads64of fork arms63and wedge portion70which will effect the distracting movement of upper part22away from lower part32. In general, however, as noted above, it is anticipated that where the separation space is more easily produced (a small separating force is needed), wedge portion70will do more of the separating while heads64act more as a support; while where the separation space is less easily produced (a larger separating force is needed), heads64will do more of the separating (and supporting) while wedge portion70does less.

It will be appreciated that the force of heads64of fork arms63acts between lower arms52,53on which body62rests and the engaging portions of heads64of fork arms63on the lower/inner surface of upper part22as shown inFIGS. 10-12. As the attachment of lower part32to lower arms52is strong (relative to the attachment of upper part22to upper arm57), there is no problem with lower part32moving relative to lower arms52. And as the reactive force of heads64of the fork arms63is on the surface of upper part22, this force acts directly to hold/force upper part22away from lower part32.

Where the reactive force of heads64of fork arms63does begin at the anterior end of the facing/inner surface of upper part22, this force moves forward along this surface with only a small distracting force until heads64are moved substantially inward (forward) to the posterior portion as shown inFIGS. 10 and 12. Preferably, the distracting force of heads64begin at about the midway point between the anterior and posterior ends of the surfaces. In this way, there is a more forceful pivoting torque exerted by heads64of fork arms63on the surface of upper part22as fork arms63advance further (as the moment arm length increases, as the moment arm length is measured from the forward end of U-shaped holder56). This is advantageous since generally it is desired to have more separating torque or force at the posterior end of upper part22where a greater resistance to separation is expected.

In addition, it will be appreciated that arm61of distractor60has a stop pin75(FIG. 4) which engages a casing66to signify when distractor61is fully inserted. In particular, pin75is thus specifically positioned on arm61to engage casing66at the point where heads64of fork arms63have advanced fully or forwards sufficiently into the space between upper part22and lower part32to provide the needed spacing for the completion of the insertion of pivot element42(and clearance for inlay protrusion44) by the action of pushing element80(FIG. 10). At this fully inserted position, heads64of fork arms63are at a maximum distance from the anterior end of upper part22so that a maximum pivoting torque can be exerted by heads64(as noted above, where the moment arm is greatest) in case the forces resisting distraction are at their highest (at the maximum displacement of upper part22and lower part32, which is the maximum vertebral spacing).

FIG. 11clearly shows the relationship between distractor60and, as shown in the drawing, the lower/inner surface of upper part22, wherein fork arms63flank domed-shaped bearing face26. This positioning allows pivot element42(not shown inFIG. 11) to be pushed partially into position in recess35as heads64of fork arms63are moved forward to support upper part22in the raised position (where pusher element80, without interference with distractor60, then completes pushing pivot element42into recess35as previously noted).

FIGS. 13A and 13Bshow different bodies62B and62C with protrusions74B and74C and fork arms63B and63C that may be used in connection with distractor60of the present invention. Obviously, the different vertical thicknesses or heights of heads64B and64C of respective fork arms63B and63C provide for the creation of different height insertion spaces between upper part22and lower part32, which would correspond to the different available heights of protrusions44(FIG. 2) typically provided in a set of pivot elements42. In addition, it will be noted that wedge portions70B and70C are respectively vertically thicker or higher in correspondence with the increased thickness of heads64B and64C of fork arms63B and63C. This corresponding thickness is needed to maintain the proper orientation of upper part22to lower part32during use of distractor60. However, if desired or needed, the heights of heads64B and64C could be lowered or raised to effect lesser or greater holding/distracting forces by heads64B and64C relative to wedge portions70B and70C; and similarly but probably less preferably, the heights of wedge portions70B and70C could be lowered or raised to effect lesser or greater holding/distracting forces by wedge portions70B and70C relative to heads64B and64C.

As noted above, and referring toFIGS. 3 and 4, portion66A secures distractor60to mounting structure54via opening54A and the ball catch therein in the much the same manner as the distractor is attached in WO 01/19295. As shown inFIG. 4, distractor60further comprises a hex end67which extends rotatably through casing66and beyond mounting portion66A and which is designed to be engaged by a suitable wrench having a mating hex socket or the like (not shown) if desired. However, in this preferred embodiment, the opposite end from hex end67is provided with a square end or the like (not shown) to which is securely mounted a thumbscrew69. Turning of either thumbscrew69or hex end67results in the turning of a gear wheel (not shown, but inside casing66) which engages a tooth rack65on elongated arm61. This system may be used to carefully and precisely advance distractor60longitudinally Forward towards the second ends of arms52,53and57as noted above and in much the same manner as the distractor is advanced in WO 01/19295—except that a more positive and forceful insertion force can be exerted on tooth rack65by the use of the wrench if such insertion force is needed. As noted above, portion66A secures distractor60to mounting structure54via opening54A and the ball catch therein in the much the same manner as the distractor is attached in WO 01/19295. As shown inFIG. 4, distractor60further comprises a hex end67which extends rotatably through casing66and beyond mounting portion66A and which is designed to be engaged by a suitable wrench having a mating hex socket or the like (not shown) if desired. However, in this preferred embodiment, the opposite end from hex end67is provided with a square end or the like (not shown) to which is securely mounted a thumbscrew69. Turning of either thumbscrew69or hex end67results in the turning of a gear wheel (not shown, but inside casing66) which engages a tooth rack65on elongated arm61. This system may be used to carefully and precisely advance distractor60longitudinally Forward towards the second ends of arms52,53and57as noted above and in much the same manner as the distractor is advanced in WO 01/19295—except that a more positive and forceful insertion force can be exerted on tooth rack65by the use of the wrench if such insertion force is needed.

The insertion instrument described herein comprises a biocompatible metal, such as titanium or a titanium alloy or a stainless steel composite; and may be the same or different material as the upper and lower parts. Pivot element42is also made from a biocompatible material, and is preferably a biocompatible plastic material such as polyethylene. Furthermore, distractor60may comprise a biocompatible coating that assists sliding relative to the arms, or distractor60may comprise a plastic material for the same reason.

Thus, in operation and after suitable preparation as described above and as known in the art, upper part22and lower part32are engaged with upper arm57and lower arms52,53as shown inFIGS. 5 and 6. Lower part32is locked to lower arms52,53by rotation thereof, which causes locking bar protrusions58to engage recesses36of lower part32. Upper and lower parts22,32are then brought to their closest proximity, preferably nested together (as no pivot element is yet present), and inserted into the intervertebral space as shown inFIG. 8.

After insertion of upper and lower parts22,32forwardly into the intervertebral space, pivot element42is inserted between lower arms52adjacent the rear thereof. After mounting of distractor60, pivot element42is then moved forward towards the intervertebral space by distractor60with edges45thereof engaging grooves55formed in lower arms52,53as described in WO 01/19295. As shown inFIGS. 9,10and12, once the starting space is created, further forward advancement of wedge portion70causes heads64of fork arms63to engage the bottom/inner surface of upper part22as noted in detail above, pushing and/or holding upper part22away from lower part32which is held in place by lower arms52,53. With the advancement of arm61, the space between upper part22and lower part32is made large enough to accommodate the similar advancement of pivot element42into lower part32. In the final step, pusher element80is used to complete the insertion of pivot element42into locked engagement with recess35of lower part32as described in WO 01/19295.

Following insertion of pivot element42, pusher element80and distractor60are retracted and upper part22and lower part32are permitted to come together under the force of the adjacent vertebrae which have been displaced, until all parts of intervertebral disc implant21engage one another and attain their final position (as shown inFIG. 1). Finally, by rotation of lower arms52,53about their longitudinal axes, the engagement of locking bar protrusions58is undone and insertion instrument50can be pulled rearwardly off the now properly inserted and completed intervertebral implant21.

While heads64of fork arms63have been described above as only engaging the lower/inner surface of upper part22as fork arms63advance into the intervertebral space provided between upper part22and lower part32, it will be appreciated that engagement of the upper surface of lower part32would be possible as shown inFIG. 14. Thus, a more positive separation of upper part22from lower part32using heads64would be achieved as the separating force would be directly exerted between the facing surfaces of lower part32and upper part22by heads64of fork arms63once heads64of fork arms63completely entered the space provided between upper part22and lower part32. The holding forces of arms52,53and57on upper part22and lower part32in this embodiment would thus not need to be as secure.

Although the invention has been described in considerable detail with respect to preferred embodiments, it will be apparent that the invention is capable of numerous modifications and variations, apparent to those skilled in the art, without departing from the spirit and scope of the claims.