Adjustable cutting of cutout in vertebral bone

An instrument, instrument system and method for cutting a cutout in a vertebral bone adjacent an intervertebral space are provided which make use of a cutting blade. The cutting blade is mounted on a support structure for movement toward and cutting into the vertebral bone. A stop arrangement is also mounted on the support structure and is movable relative to the cutting blade to a position to limit movement of the cutting blade into the vertebral bone. Typically, the limited movement cutting is made after two cutouts are provided in adjacent vertebral bones using a trial implant.

BACKGROUND OF THE INVENTION

This invention relates to intervertebral implants; and more specifically, it relates to new and improved instruments and methods for preparing an intervertebral space for receiving an artificial intervertebral disc implant (sometimes referred to below simply as an implant).

When it is necessary to completely remove a disc from between adjacent vertebrae, the conventional procedure is to fuse the adjacent vertebrae together. More recently, there have been important developments in the field of disc replacement, namely disc arthroplasty. Disc arthroplasty involves the insertion of an artificial intervertebral disc implant into the intervertebral space between adjacent vertebrae, thereby allowing limited universal movement of the adjacent vertebrae with respect to each other.

Some instruments have been developed to date for preparing an intervertebral space for receiving an artificial disc implant. These instruments include a set of different sizes of trial implants, different ones of which are inserted into a cleaned out intervertebral space until the correct size trial implant has been determined, thereby determining the size of the actual implant to be inserted. The trial implant may have a fixed stop member in the form of a pin fixed to the rear end of the trial implant and extending vertically for engaging the vertebrae to limit movement of the trial implant into the intervertebral space. Some implants have a raised keel which requires that a cutout or slot be formed in the vertebrae adjacent the intervertebral space for receiving these raised keels. One known arrangement for forming these cutouts is a chisel which can be mounted with chisel portions movable along guiding slots in the top and bottom of the selected trial implant as the chisel portions cut into the adjacent vertebrae to form the two cutouts.

One known artificial disc implant is shown in Published application No. WO 01/01893, published Jan. 11, 2001, and instruments for inserting same are shown in Published application No. WO 01/19295, published Mar. 22, 2001. Another disclosure of artificial disc implants and apparatus associated therewith is contained in U.S. Ser. No. 10/423,879 filed Apr. 28, 2003. The teachings of these three references are hereby incorporated by reference.

While these known instruments and methods represent a substantial improvement in the art, there exists a continuing need for improvements in the field of instruments and methods for preparing an intervertebral space for receiving an artificial intervertebral disc implant.

BRIEF SUMMARY OF THE INVENTION

A purpose of the present invention is to provide new and improved instruments and related methods for preparing an intervertebral space for receiving an artificial intervertebral disc implant, particularly where a cutting tool has been used in conjunction with a trial implant to provide first and second opposed (paired) cutouts in the vertebrae located on opposite sides of a trial implant. When such paired cutouts are prepared, they are usually substantially identical in both width, height, and depth (length). However, in some situations, it may be desired for one cutout to have a different depth than the other cutout.

The instrument of the present invention may be used to prepare the intervertebral space at any location along the spine, including especially the lumbar and cervical spines. However, since the cervical vertebrae are so small relative to the lumbar vertebrae, i.e., about 20% of the area of the lumbar spine vertebrae, some instruments may be more suited than others for the cervical spine.

While the trial implant as well as the intervertebral implant is normally inserted from the patient's anterior moving towards the patient's posterior, it is to be understood that the implant, the instruments and the method can also be designed and arranged to insert the implant laterally or obliquely, i.e., from the side, in which case the keels thereof will be oriented on the implant for such lateral movement and the cutouts in the adjacent vertebrae will be opened toward a lateral side to receive the keels. 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 the 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, while the words “back”, “rear” or “rearward” refer to the end of the instrument farthest from the vertebrae or moving away from the vertebrae. Also, in this application, the words “upper” or “lower” or “uppermost” or “lowermost” or any other words describing the orientation of the intervertebral implant or the instruments or methods associated therewith are used only for convenience of description and are not intended to convey any limitation. More specifically, the parts of the implant, the instruments and/or the methods described in this application with reference to the upper part 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.

It is thus an object of the present invention to provide new and improved instruments for preparing an intervertebral space for receiving an artificial intervertebral disc implant.

The instruments and the methods of the present invention are particularly adapted for the ultimate implantation of 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 as well known in the art. These instruments and methods of the present invention are particularly for use where the implant has a keel extending from the vertebrae engaging surfaces into slots or cutouts formed in the adjacent vertebrae.

In accordance with a first aspect of the present invention, there is provided an instrument, instrument system and method for cutting a slot or cutout in a vertebral bone, or for lengthening an already formed cutout.

In accordance with an illustrative embodiment of the present invention, an instrument or instrument system for further cutting an already formed cutout, or even for initially cutting a cutout, into a first vertebral bone located adjacent a trial implant is provided. A trial implant is located in an intervertebral space between the first vertebral bone and a second vertebral bone, which trial implant has a holding device for holding the trial implant in the intervertebral space. The holding device includes a shaft which engages the trial implant and which extends rearwardly therefrom. Then a cutting instrument is provided in accordance with the present invention which has a cutting tool for creating or lengthening one cutout. This cutting instrument also includes a stop which limits forward movement of the cutting tool. The position of this stop is adjustable, to adjust the depth of cut of the cutting tool, and hence the length or increased length of the cutout.

In accordance with the present invention, a method for increasing by a predetermined distance a depth of a first cutout cut into a first vertebral bone located adjacent a trial implant is disclosed. In this method, a first cutout is initially cut in the first vertebral bone and a second cutout in the second vertebral bone. This is accomplished using a first cutting tool with first and second chisel portions which cut the first and second cutouts simultaneously. Then, after removing the first cutting tool from the shaft, a second cutting tool is placed on the shaft. This second cutting tool has a single chisel portion which is received all of the way into the first cutout (the cutout to be extended). An adjustable stop on the second cutting tool is then or previously adjusted to have a predetermined offset distance away from an adjacent surface of the trial implant (or in other words, away from the tip of the chisel portion), with this predetermined offset distance being equal to the predetermined distance of depth increase desired. The second cutting tool is then advanced forward until the adjustable stop contacts the adjacent surface of the trial implant, which forward advancement effects a cutting of the vertebral bone and hence an increase in depth of the first cutout by the predetermined distance. After that, the second cutting tool is removed from the shaft.

Thus, it is an object of the present invention to provide new and improved instruments for preparing an intervertebral space for receiving an artificial disc implant, particularly where a first cutout for receiving a keel of the artificial disc implant must be longer than a second cutout for the opposite keel of the artificial disc implant.

It is another object of the present invention to provide new and improved methods for preparing an intervertebral space for receiving an artificial disc implant, particularly where a first cutout for receiving a keel of the artificial disc implant must be longer than a second cutout for the opposite keel of the artificial disc implant.

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

DETAILED DESCRIPTION OF THE INVENTION

Initially, it will be noted that the instruments and methods described herein are applicable for preparing an intervertebral space for subsequent insertion of a wide range of artificial disc implants. And while the instruments and methods described herein include the concept of forming cutouts to receive raised keels, it will be appreciated that these instruments and methods are adaptable for preparing a space where any artificial implant having such keels is used.

With reference now to the drawings in which like numerals represent like elements throughout the views, a presently preferred instrument10in accordance with the present is depicted inFIGS. 1-4. As best shown inFIG. 4, instrument10is part of an instrument system12, where instrument system12is typically used for finishing the preparation of an intervertebral space14located between a first vertebral bone16and a second vertebral bone18. The initial preparation of intervertebral space14is performed with any of many instruments known in the art, with the preparation typically ending where a two pronged chisel instrument produces two identical cutouts20and22in vertebral bones16and18with the guidance of a trial implant24. It will be appreciated that cutout20is identical with the side profile of the chisel part of instrument10received therein and thus cutout20is shown inFIG. 4without separation from the chisel part. It will also be appreciated that instrument10can be used to initially provide a single cutout in either vertebral bone16or18if desired, and then to provide the other cutout with a different depth if desired and in a manner which will be evident subsequently.

As an alternative-to the angled (relative to the guiding surface of implant24) cutout20depicted inFIG. 4, and perhaps more typically as depicted inFIG. 5, the initial cutout20A (and similar cutout on the opposite side not depicted) can be parallel to implant24. In this case, it is only the overall length of cutout20A, and not the height as well as in the embodiment ofFIG. 4, which is extended by instrument10to, for example, the length of cutout24B as schematically depicted. If desired, of course, the chisel as depicted inFIG. 4could be used with cutout20A, to increase both the length of cutout20A as well as the height.

As also known in the art, trial implant24includes a holding device26having a shaft28which is brazed (or alternatively, threadably received) onto trial implant24and which extends rearwardly therefrom. Holding device26is used to insert trial implant24into a cleaned intervertebral space14up to the position where an implant stop30attached to one lateral side of trail implant24contacts bones16and18as shown. Conveniently, shaft28has a handle29on the distal end to facilitate insertion of trial implant24into place, which handle is then removed from shaft28so as not to interfere with the remaining procedures involving trial implant24(as described below). Implant stop30thus acts to properly place trail implant24in intervertebral space14, and to maintain trial implant24at this position when identical cutouts20and22are cut by the two pronged chisel instrument as it moves forward along shaft28as well appreciated by those of ordinary skill. Located along a top side (and typically-along the bottom side as well where the two pronged chisel instrument is used) of trial implant24is a groove32in which the mating chisel part of instrument10is slidably guided during cutting of bone16as the chisel instrument is advanced along shaft28.

As shown best inFIGS. 1-3, instrument10of the present invention includes a cutting tool40having an elongate cutting shank42. Cutting shank42includes a front end44and a rear end46at which a lateral extending flange48is located. Cutting shank42is preferably a hollow generically cylindrical tube. From flange48forward, cutting shank42is provided with flats50A and50B on opposite lateral sides from one another as shown. By use of flats50A and50B, a similarly shaped slotted (U-shaped) hammer (not shown, but as known in the art) can be easily positioned around cutting shank42to provide an axially rearward impact against flange48to move cutting tool40backwards and away from vertebral bones16and18if desired. It will be appreciated that flats50A and50B can be omitted (so that cutting shank42is circular throughout its length) if the slot of the hammer is larger than the diameter of cutting shank42.

Provided at front end44of cutting shank42is a chisel52which is attached to cutting shank42by silver soldering or the like of the mating surfaces. Chisel52includes a blade portion54located to be extending forward from an upper portion of front end44. As best shown inFIG. 1, chisel.52includes flats55A and55B which are matingly aligned with flats50A and50B of cutting shank42so that the axial (or frontal) profile of cutting shank42including flats50A and50B is about the same as that of chisel52including flats55A and55B. It will be appreciated that chisel52is configured so that chisel52does not extend vertically into a bottom half of the axial profile of cutting shank42(that is, chisel52is located within the top half of the axial profile of cutting shank42); and so that chisel52does not extend laterally beyond the cross sectional profile of cutting shank42.

Chisel52has a lower guiding section56which is received in groove32for guided sliding movement along the top of trial implant24, in the same manner as noted above for the prior art two pronged chisel instrument. Blade portion54of chisel42includes a tip58and holes or fenestrations60therealong in which bits of cut bone or the like can gather so as not to interfere with the cutting action of blade portion54as cutting shank42is moved in a cutting motion from front to back (as discussed subsequently). With this configuration at front end44of cutting shank42, front end44including chisel52easily fits past stop30of trial implant24(no matter whether chisel52is up or down).

Provided at a rear end46of cutting shank42is an impact portion formed as a cage62. Cage62is securely attached to rear end46via a pin64which is snugly received in mating holes in cage62and rear end46as shown. When cage62is secured to rear end46, the front portion of cage62is engaged with flange48so that the rear portion of cage62serves as a relatively flat impact surface against which a suitable hammer or the like can be struck to impart a forward movement to cutting shank42and hence to chisel52to cut vertebral bone16.

Located along flat50A of cutting shank42, but close to rear end46, is a window slot66which extends to the interior hollow portion of cutting shank42. Circumferentially about cutting shank42at the location of window slot66is a reference scale68. Scale68is formed by a series of concentric and equally spaced marks or cuts about cutting shank42, conveniently spaced in millimeter increments or the like as desired.

Cutting instrument10also includes a stop70which serves to limit a forward movement of cutting tool40during cutting with chisel52. Stop70includes a stop shank72having a front end74and a rear end76. Stop shank72is preferably a hollow generally cylindrical tube which is internally sized to be slidably received on shaft28of holding device26with little play so that sliding movement of stop shank72relative to shaft28is smooth and precise. In addition, the outside diameter or dimensions of stop shank72are sized so that cutting shank42is slidably received on stop shank72with little play so that a sliding movement of cutting shank42relative to stop shank72is smooth and precise and hence there is a sliding movement of cutting shank42relative to shaft28as well. As shown, stop shank72is conveniently formed of two pieces silver soldered together at their mating surfaces.

As shown best inFIG. 1, front end74includes a stop member78which is shaped to extend forward from a lower portion of front end74and which terminates with a stop surface80. Stop member78has a vertical profile which fits within the profile of chisel52which is immediately thereabove, so that like chisel52, stop member78can also move past stop30of trial implant24. As explained subsequently, as stop member78moves past stop30, stop surface80engages or presses against trial implant24as shown inFIG. 4. While stop member78has been shown with the particular flattened shape in order to move past stop30, stop member78could just continue the cylindrical shape of stop shank72if this were to necessary. Stop70also includes a reference mark82on the outer surface of stop shank72adjacent to rear end76. Reference mark82is positioned and designed to be viewable through window slot66of cutting shank42and is used in conjunction with reference scale68adjacent window slot66in a manner to be described subsequently.

Cutting tool10further includes an adjustment mechanism90which is used to adjustably connect stop member78relative to cutting tool40, whereby a longitudinal position of stop member78relative to tip58of chisel52is likewise adjustable. Thus, by proper adjustment, when stop surface80of stop member78engages trial implant24, tip58can be determined to have cut into bone16by a predetermined and desired distance. It will be appreciated that reference mark82as seen through window slot66and relative to reference scale68can be used in determining the predetermined distance and length of cut as will be discussed subsequently.

In this preferred embodiment, adjustment mechanism90includes a threaded interconnection between cutting shank42and stop shank72so that relative rotation of one threaded connection with respect to the other causes cutting shank42to move relative to stop shank72. In particular, stop shank72includes external/male threads92at rear end76thereof, while cutting shank42includes a reaction bolt94having internal/female threads96which are matingly received by threads92. In order to achieve relative movement of threads92and96, reaction bolt94includes a head98which rotatably abuts against the adjacent inside end of the opening of cage62. In addition, reaction bolt96is pressed into an outer shell or rotation member102and then reaction bolt96is positively prevented from rotation by securing pins100which pass into outer shell102. Shell102extends radially out beyond cage62so that reaction bolt96is easily rotated within cage62by engagement with shell102. It will be appreciated that the position of the male and female threads could be reversed and the operation would be the same.

In order to prevent stop shank72from rotating together with shell102and reaction bolt96, and in order to align cutting shank42circumferentially relative to stop shank72and hence to keep stop70properly aligned in use, adjustment mechanism90also includes an aligning means104. Aligning means104includes an axial slot106provided adjacent rear end76of stop shank72(or elsewhere along stop shank72if desired) together with a pin108which is secured in cutting shank42and which is slidably received in axial slot106. It will thus be appreciated that by rotation of shell102(and hence rotation of male threads96), the axial position of stop shank72, and hence the axial position of stop surface80, is adjusted relative to cutting shank42and hence relative to tip58of chisel52.

In operation, instrument10has the following method of use and instrument system12functions in the following manner. Initially, after intervertebral space14is suitably prepared (as well known in the art), trial implant24is inserted therein. Trial implant24is properly positioned by holding device26, especially by the manipulation of shaft28extending rearwardly therefrom and which is accessible by the user. Typically, a two-pronged or dual chisel cutting chisel device (not shown) is selected by the user according to a predetermined desired length of cut into vertebral bones16and18. This dual chisel device is positioned by the user on shaft28, and moved forward onto trial implant24with corresponding guiding portions of each chisel portion located in a corresponding guiding groove32of trial implant24. As the dual chisel device is moved (by impacts) from front to back, two opposite cutouts are made in the adjacent vertebral bones16and18. The dual chisel device has a central bridging portion between the chisel portions so that the cutting of the cutouts continues until the central portion of the dual chisel device engages trial implant24, at which time two opposite and desired length cuts20and22are made in vertebral bones16and18as shown inFIG. 4. The dual chisel device is then removed from about shaft28, typically followed by a subsequent implanting of the permanent and corresponding sized artificial implant.

While the above procedure has been satisfactory in most situations, in certain situations such as where there is a large lordosis angle or retrolisthesis, one of the cutouts formed by the dual chisel may be too short (not deep enough for the keel of the permanent implant). In such a situation, extension of only one cutout is needed, which is here depicted as the top cutout20inFIG. 4or top cutout20A inFIG. 5. Thus, cutting instrument10is used to extend top cutout20by an amount which is predetermined by fluoroscopy or the like prior to cutting with instrument10.

To determine the extra length needed for cutout20, it would be possible to view cutout20while the dual chisel device is in place and to then determine that cutout20needs to be extended by, for example, 2 mm. Alternatively, it would be possible to view cutout20after removal of the dual chisel to make this determination. Thus, with instrument10located in other than a cutting position (either outside of the body of the patient or positioned on shaft28away from vertebral bone16), stop surface80can be adjusted using shell102and reference mark82so that it is further by 2 mm from tip58than the central bridging portion of the dual chisel was from the corresponding tip (that is, the depth of cut of the dual chisel plus the predetermined distance). Such an adjustment of stop surface80can also be accomplished with reference to the dual chisel itself (or rather the top chisel part thereof and the bridge). Thus, where the dual chisel is used as a guide for the length of cut already made, direct comparison or measurement is made of the tip to bridge portion distance. Reference mark82and reference scale68can also be used to precisely adjust the extra length of cut if desired rather than relying on additional measurements.

Alternatively and preferably when usable, instrument10is moved along shaft28until blade portion54is all of the way in top cutout20, and the user can then decide using an active fluoroscopy how much further cutout20should be extended (e.g., 2 mm). Then, stop surface80is correspondingly adjusted using shell102, with attention to reference mark82and reference scale68if desired. Of course, the user can simply look at blade portion54in place using the active fluoroscopy and then back stop surface80away from trial implant24(and hence away from chisel tip58) by an amount which looks sufficient (e.g., about 2 mm).

Once stop surface80is positioned as desired and instrument10is in place, the impact surface of cage62is impacted by a suitable hammer or the like to move cutting shank42forward to cut vertebral bone16until stop surface80engages trial implant24. At this time, further advance of chisel52is not possible, and hence chisel52has been driven forward a sufficient amount to effect the predetermined extension of cutout20, such as shown by extended cutout20′ shown inFIG. 4by a chained line.

As noted above, in the more typical case, it will only be desired to extend the depth of cut of the cutout provided by the dual chisel and this is shown inFIG. 5. Thus, blade portion54A of chisel52A is used in the same manner as described above for chisel52to extend the depth of cut of cutout20A to cutout20B. However, as the top of blade portion54A is parallel to implant24, no additional height is cut, only the additional length is cut when instrument10is used therewith.

While the present invention has been described above primarily with an application to extending the length of a cutout which had already been cut together with a similar cutout on the opposite vertebral bone, it will be appreciated that instrument10can also be used with a trial implant to make an initial cutout of a predetermined length on one side of the trial implant in one vertebral bone, and then by reversing the position of instrument10, instrument10can make a second cutout of a different or same predetermined length in the opposite vertebral bone.

It will also be appreciated that if desired a suitable ball plunger or other tactile or auditory mechanism could be used in conjunction with cage62to provide an indication to the user every time that cage62is turned a certain amount, such as a tenth of a millimeter. This would make it easier to judge how far cage62should be rotated to move stop surface80of stop member78as desired.

It will further be appreciated that the location of stop shank72inside of cutting shank42and about shaft28could be reversed, so that cutting shank42is located inside of stop shank72and about shaft28.

Although the invention has been described in considerable detail with respect to preferred embodiments thereof, it will be apparent that the invention is capable of numerous modifications and variations, apparent to those skilled in the art.