Abstract:
An instrument for holding an intervertebral spacer, the instrument comprising a shaft having a proximal end and a distal end, the proximal end forming a handle and the distal end forming a spacer engaging subassembly, the spacer engaging subassembly comprising at least one selectively expanding and contracting enclosure into which at least a portion of the spacer is introduced when the engaging subassembly is expanded and an actuating mechanism, extending from the proximal end to the distal end, by which the spacer member engaging subassembly may be selectively expanded and contracted.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 10/771,597, filed on Feb. 4, 2004, which is a continuation of U.S. application Ser. No. 09/906,127, filed on Jul. 16, 2001, the disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to a treatment for scoliosis and more specifically to the instruments, implants, distracting trial spacers, and surgical methodology used in the treatment and correction of scoliosis. 
       BACKGROUND OF THE INVENTION 
       [0003]    The bones and connective tissue of an adult human spinal column consists of more than 20 discrete bones. These more than 20 bones are anatomically categorized as being members of one of four classifications: cervical, thoracic, lumbar, or sacral. They are coupled sequentially to one another by tri-joint complexes that consist of an anterior intervertebral disc and the two posterior facet joints. The anterior intervertebral discs of adjacent bones are cushioning cartilage spacers. 
         [0004]    The spinal column of bones is highly complex in that it includes these 20 bones coupled to one another (and others), and it houses and protects critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. In spite of these complications, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction. 
         [0005]    Genetic, congenital and/or developmental irregularities are the principle causes that can result in spinal pathologies in which the natural curvature of the spine lost. Scoliosis is a very common one of these types of irregularities, resulting in a sequential misalignment of the bones and intervertebral discs of the spine. Major causes of scoliosis are idiopathic (i.e., unknown cause), congenital developmental anomalies and neuromuscular disorders such as cerebral palsy. The misalignment usually manifests itself in an asymmetry of the vertebral bodies, such that, over a sequence of spinal bones, the spine twists and/or bends to one side. In severe cases, neurological impairment and/or physiological disability may result. 
         [0006]    The present surgical technique for treating scoliosis (as well as other spinal conditions) includes the implantation of a plurality of hooks and/or screws into the spinal bones, connecting rods to these elements, physically bracing the bones into the desired positions, and permitting the bones to fuse across the entire assembly. This immobilization often requires anterior plates, rods and screws and posterior rods, hooks and/or screws. Alternatively, spacer elements are positioned between the sequential bones, which spacers are often designed to permit fusion of the bone into the matrix of the spacer from either end, hastening the necessary rigidity of the developing bone structure. Spacers allow bone fusion to grow into or around them. There are two classes of intervertebral spacers: horizontal cages such as the BAK™ and Ray cages, as described and set forth in exemplary U.S. Pat. Nos. 5,015,247 to Michelson and 5,026,373 to Ray et al., respectively, and vertical cages such the Harms cages, as described and set forth in exemplary U.S. Pat. No. 4,820,305. 
         [0007]    Similar techniques have been employed in other spinal infirmities, including collapsed disc spaces (failure of the intervertebral disc), traumatic fractures, and other degenerative disorders. While the present invention has many applications, such applications include the treatment of any spinal disorder in which the space between vertebral bones needs to be surgically separated (the bones distracted), realigned and then fused to one another. 
         [0008]    A variety of systems have been disclosed in the art which achieve immobilization and/or fusion of adjacent bones by implanting artificial assemblies in or on the spinal column. The region of the back that needs to be immobilized, as well as the individual variations in anatomy, determine the appropriate surgical protocol and implantation assembly. With respect to the failure of the intervertebral disc, and the insertion of implants and/or height restorative devices, several methods and devices have been disclosed in the prior art. 
         [0009]    Restoring the appropriate height and orientation of the vertebral bones and the intervertebral space is the first step in the surgical strategy for correcting this condition. Once this is achieved, one class of surgical implantation procedures involves positioning a device into the intervening space. This may be done through a posterior approach, a lateral approach, or an anterior approach. Various implant devices for this purpose include femoral ring allograft, cylindrical metallic devices (i.e., cages), and metal mesh structures that may be filled with suitable bone graft materials. Some of these implant devices are only suitable for one direction of approach to the spine. All of these devices, however, are provided with the intention that the adjacent bones will, once restored to their appropriate alignment and separation, then grow together across the space and fuse together (or at least fuse into the device implanted between the bones). 
         [0010]    Most recently, the development of non-fusion implant devices, which purport to permit continued natural movement in the tri-joint complex have provided great promise. The instrumentation and methods for the implantation of these non-fusion devices, as well as the implantation of the fusion devices catalogued previously, therefore should integrate the functions of restoring proper anatomical spacing and easy insertion of the selected device into the formed volume. 
         [0011]    It is, therefore, an object of the present invention to provide a new and novel treatment for scoliosis, as well as for the treatment of spinal pathologies in general. 
         [0012]    It is, correspondingly, another object of the present invention to provide an intervertebral distraction trial tool which more accurately and easily separates collapsed intervertebral spaces. 
         [0013]    It is further an object of the present invention to provide an intervertebral distraction trial tool which more can be used to correct scoliosis and/or restore normal alignment to the spine. 
         [0014]    It is further an object of the present invention to provide an instrument that proficiently and simply manages the insertion, rotation, and removal of the intervertebral distraction trial tools. 
         [0015]    It is further an object of the present invention to provide an implantable spacer device that permits more anatomically appropriate and rapidly osteogenic fusion across the intervertebral space. 
         [0016]    Other objects of the present invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter. 
       BRIEF SUMMARY OF THE INVENTION 
       [0017]    The present invention is directed to a method of treatment of scoliosis and other spinal disorders. This method of treatment further includes several new and novel instruments, implantable trial distraction elements, and intervertebral spacer implants. Inasmuch as the description of the new and novel method cannot be complete without a description of each of these integral members, the following includes ample explanation of these elements as well as description of the surgical techniques. 
         [0018]    First, the patient spine is exposed through an anterior approach (i.e., the surgeon creates an access hole which permits direct interaction with the anterior and/or anterio-lateral portion of the intervertebral bodies). In the case of scoliosis, as well as in other disorders in which the intervertebral space requires distraction and/or repositioning, the surgeon removes the intervertebral disc material, usually leaving some portion of the annulus (the cylindrical weave of fibrous tissue which normally surrounds and constrains the softer cartilage cushion of the disc material). The surgeon then, in succession, inserts a series of intervertebral trial spacers of defined width. Each of the series of spacers is of a progressively wider thickness, resulting in the continual widening of the space until restoration of the proper disc height has been achieved. Proper disc height restoration is determined by surgical experience, and by observation of the annulus. (Often, the tightening of the annulus indicates that the proper disc height has been reached, inasmuch as the annulus is much less likely to be distorted by the same disruption that caused the intervertebral disc to collapse in the first place.) 
         [0019]    More particularly, with respect to the specific instruments disclosed herein, a series of solid trial spacer elements and an instrument for their insertion and removal is now provided. Each trial spacer is a generally cylindrical disc having a deep annular groove at its midpoint, which forms a central trunk and radial flanges at each end of the trunk. Stated alternatively, two cylindrical upper and lower halves of the disc are held in a closely coaxial spaced apart association by the central trunk, which forms a coaxial bridge between the upper and lower halves. The annular groove is particularly useful for holding the spacer using the spacer insertion instrument of the invention, described below, in that the holding end of the insertion instrument fits within the groove. 
         [0020]    A variety of features of embodiments of the trial spacer elements are disclosed. In some embodiments, such as the first and second embodiments described below, support portions (the portions that are in contact with the adjacent vertebral bodies when the spacer is disposed between the bodies) of the top and bottom surfaces are parallel. Spacers having this feature are generally described herein as “constant thickness” trial spacers. In other embodiments, such as the third and fourth embodiments described below, the support portions are not parallel, providing an overall taper to the spacer at an angle. Spacers having this feature are generally described herein as “tapered thickness” trial spacers. The tapered thickness trial spacers are particularly useful for treating scoliosis, as described below. 
         [0021]    Other features of embodiments of the trial spacer elements include beveled flanges and non-parallel annular groove walls. More specifically, in some embodiments, such as the second and fourth embodiments described below, the flanges are radially beveled in that an outer edge of the top surface of the disc is tapered toward an outer edge of the bottom surface of the disc. In other embodiments, such as the first and third embodiments described below, the flanges are not radially beveled in this manner. The radial beveling feature can be particularly useful for easing the insertion of the spacer in between collapsed vertebral bodies, as described below. Further, in some embodiments, such as the first and third embodiments described below, the walls of the annular groove are parallel, such that the floor of the groove is as wide as the opening of the groove. In other embodiments, such as the second and fourth embodiments described below, the walls of the annular groove are tapered toward one another with the increasing depth of the groove, such that the floor of the groove is narrower than the opening of the groove. Each type of annular groove is useful, depending on the particular surgical application and on the particular embodiment of the spacer insertion instrument that is used to insert the spacer. 
         [0022]    Collections of trial spacer elements are provided by the invention. Preferably, each spacer in a particular set maintains the same diameter as the other spacers in the set. (It shall be understood that different collections of spacers may be provided such that the diameter of the selected collection of trial spacers is appropriate for the specific patient being treated.) Also preferably, each spacer in a particular set has a predetermined depth that differs from the depth of the other spacers in the set. The predetermined depth is provided in that while each spacer in the set shares the same annular groove dimensions (so that each can be held by the same insertion instrument), each spacer has a different flange thickness (in sets where the spacers are constant thickness spacers). For sets of tapered thickness spacers, the predetermined maximum depth and predetermined minimum depth (the two depths providing the overall taper) are provided in that while each spacer in the set shares the same annular groove dimensions (so that each can be held by the same insertion instrument), each spacer has a different maximum flange thickness and a different minimum flange thickness. Preferably in sets of tapered thickness spacers, the overall taper angle is the same for each spacer in the set. The usefulness of providing sets of spacers similar in most respects except for the depth dimension will be described in greater detail below. 
         [0023]    With regard to the instrument for the insertion and removal of the trial spacer elements, a first embodiment (particularly useful for inserting constant thickness trial spacers) of a spacer insertion tool includes an elongated shaft and a handle at one end of the shaft. The distal end of the shaft includes semi-circular hook that is adapted to hold a trial spacer within an enclosure formed by the hook. The angle swept out by the hook is slightly greater than 180 degrees, but the inner diameter of the hook is only slightly larger than the central trunk of the trial spacer. Therefore, the trial spacer may be snapped into the enclosure, but maintains complete rotational freedom within its grasp. A loading tool may be provided to assist in the loading and unloading of the trial spacer from the trial spacer insertion instrument of this embodiment. This loading tool comprises a forked hook having two curved tines separated by a notch that engages the shaft of the insertion tool as the tines engage the flanges of the trial spacer, to force the trial spacer into the enclosure. Alternatively and/or additionally, the same device may be utilized to remove the spacer from the enclosure, by reversing the position of the forked hook relative to the insertion tool and the spacer. 
         [0024]    The insertion tool of this embodiment can be used to insert a series of constant thickness trial spacers (some of which may have beveled flange edges for easing the insertion between the collapsed bones and into the space to be distracted). More specifically, thinner trial spacers can initially be inserted into the spacer, followed successively by thicker trial spacers until the desired spacing is achieved. Once the appropriate spacing has been achieved, immobilization of the spine by fixation, fusion, or non-fusion techniques and devices, such as those set forth in co-pending U.S. patent application Ser. Nos. 09/906,117 and 09/906,118, entitled “An Intervertebral Spacer Device Having a Wave Washer Force Restoring Element” and “An Intervertebral Spacer Device Having a Spiral Wave Washer Force Restoring Element”, respectively, as well as U.S. Pat. No. 5,989,291, entitled “An Intervertebral Spacer Device”, may be desirable. 
         [0025]    While simple distraction to a constant height across the intervertebral space is appropriate for standard disc compression pathologies, in the case of scoliosis, simple constant thickness distraction is insufficient to remediate the pathological condition. What is necessary is the distraction of the sequence of spaces, each to an appropriate angle and height, such that the overall spinal configuration is anatomically correct. Tapered trial spacers, such as those disclosed in the present application, are the first such distraction tools to provide such a tailored correction of the misangulation of the spinal bones. 
         [0026]    More particularly, the surgeon inserts the tapered trial spacers into the intervertebral space (presumably from the anterior, or anterio-lateral, approach) with the narrow edge of the trial spacer forming a wedge and sliding between the adjacent bones. By utilizing either a second or third embodiment of the spacer insertion tool, described more fully below, the surgeon may turn the spacer around its axis within the intervertebral space to find the most appropriate rotational position (corresponding to the most desirable straightening effect on the spinal column). Stated alternatively, each of the tapered trial spacers has an overall wedge shape that generally corresponds to the pathological tapering of the adjacent bones that characterizes scoliosis. By rotating the wedge-shaped spacer after it has been placed between the adjacent bones, the overall disc alignment may be compensated, restoring appropriate anatomical status. It should be understood that additional rotation of the spacer may restore lordosis to the spine, and that over-rotation (if the particular spine is flexible enough) of the spacer would result in a pathological curvature in the opposite direction. 
         [0027]    This second embodiment of the spacer insertion tool includes a handle and an elongated dual shaft, the dual shaft culminating in a trial spacer grasping pincer, rather than the simple hook of the first embodiment. This pincer differs from the hook of the first embodiment of the trial spacer insertion tool described above, inasmuch as the dual shaft includes a fixed shaft and a selectively engagable shaft which, together, form pincer. More specifically, the fixed shaft includes a semicircular hook portion of the pincer at its distal end, having an enclosure within which a trial spacer can be placed. The selectively engagable shaft includes the complementary portion of the pincer, which moves toward the hook portion to grasp and hold the trial spacer when the engagable shaft is engaged, and moves away from the hook portion to release the trial spacer when the engagable shaft is disengaged. (The spacer can be unloaded and loaded when the engagable shaft is disengaged.) The engagement action prevents the spacer from moving relative to the tool, and therefore permits the surgeon to rotate the tapered spacer in between the vertebral bodies (by contrast, the first embodiment of the trial spacer insertion instrument permitted the spacer to rotate freely in the enclosure of the hook). There are alternative insertion and rotating instruments that may be designed, so long as they selectively and alternatingly release or hold the trial spacer securely against rotation (the spacer cannot be permitted to rotate freely if it must be turned in the intervertebral space). The tapered trial spacers themselves can include angle markers that clearly indicate to the surgeon the amount of rotation that was necessary for the correction of the spinal deformity. Such angle markers can also serve as a guide for the implantation of a secondary bone graft (e.g., a femoral ring) or another intervertebral spacer device. 
         [0028]    Once the surgeon has determined the appropriate geometry for the surgical implants via the trial spacers, he or she is ready to immobilize the spine in that position. While multiple ways for immobilizing the spine are disclosed in the prior art, any one of which and others may be suitable for the specific surgical patient&#39;s treatment, three alternative ways are herein described. 
         [0029]    First, the trial spacers may be left in the patient while rod fixation apparatuses (anterior or posterior) are mounted to the spine, thereby holding the spine in its desired orientation even after the trial spacers are subsequently removed. Alternatively, surface plating and/or intervertebral cage devices may be mounted to the spine to promote fusion without the need for bulky rod assemblies. (While this approach may seem more surgically desirable, questions regarding the long term stability of these constructs have led some surgeons to chose combinations of rodding and cages.) 
         [0030]    A third approach to immobilizing the corrected spine is to insert a shaped bone graft, or suitably contoured porous metal spacer, into the properly distracted intervertebral space, and either plating or using rod fixation to hold the construct stable as the spine fuses. The insertion of a femoral ring allograft, or porous metal implant, into an intervertebral space is described more fully in co-pending U.S. patent application Ser. Nos. 09/844,904 and 09/906,123, respectively entitled “A Porous Interbody Fusion Device Having Integrated Polyaxial Locking Interference Screws” and “Porous Intervertebral Distraction Spacers”. 
         [0031]    The tapered trial spacers may also serve as precursors (measuring instruments) for another spacer (e.g., a porous metal spacer), similarly shaped, which is inserted into the intervertebral space by the same instrument. 
         [0032]    Therefore, the present invention, in its many embodiments and components, is directed to a surgical treatment for restoring a proper anatomical spacing and alignment to vertebral bones of a scoliosis patient. In one desired embodiment, the present invention comprises a surgical method, which in a first embodiment, comprises: 1. determining an angular misalignment associated with at least one pair of adjacent vertebral bones; 2. sequentially inserting and removing a series of progressively wider cylindrical spacer elements into the corresponding intervertebral space between said at least one pair of adjacent vertebral bones until the proper anatomical spacing between the pair of adjacent vertebral bones is restored; 3. for each intervertebral space, inserting a diametrically tapered cylindrical spacer element into the intervertebral space between said corresponding pair of adjacent vertebral bones; and 4. rotating said diametrically tapered cylindrical spacer element such that the rotational orientation of the tapered cylindrical spacer element introduces the appropriate counter offset to the intervertebral space of the previously misaligned scoliotic vertebral bones, thereby restoring the proper anatomical alignment of the vertebral bones. 
         [0033]    It shall be understood that each of said progressively wider cylindrical spacer elements includes substantially parallel upper and lower surfaces. The method may also include the additional step of affixing immobilizing instrumentation to the vertebral bones of the patient to hold the restored vertebral bones rigidly in position to facilitate fusion, and positioning bone fusion material adjacent to the restored vertebral bones. It shall be understood that other equivalent (or alternatively efficacious) means for facilitating healing, such as including positioning a non-fusion intervertebral spacer device between the restored vertebral bones so that a proper anatomical motion may be possible. 
         [0034]    The surgical treatment set forth above should be further refined inasmuch with respect to the diametrically tapered cylindrical spacer elements, such that each has a width along its central cylindrical axis substantially equivalent to the axial width of the final cylindrical spacer element utilized in the step of sequentially inserting and removing the series of progressively wider cylindrical spacer elements to restore the proper anatomical spacing between the pair of adjacent vertebral bones. 
         [0035]    It shall be understood that each progressively wider cylindrical spacer element and/or diametrically tapered cylindrical spacer element may comprise solid or porous metal, or a porous or non-porous organic implantable material. 
         [0036]    For clarity, this embodiment of the surgical method includes exposing an intervertebral space between adjacent vertebral bones, distracting the space by sequentially inserting therein and subsequently removing therefrom a plurality of intervertebral spacers, each having a pre-determined thickness, the thicknesses incrementally increasing from one spacer to another at an increment acceptable for safely distracting the space to a desired distance, and when adjustment of an angular misalignment of the adjacent vertebral bones is necessary, inserting, and when necessary rotating, in the intervertebral space, at least one diametrically tapered intervertebral spacer having a thickness along its central cylindrical axis sufficient to maintain the desired distance between the adjacent vertebral bones, and a diametrical angle sufficient to reorient the adjacent bones to the desired configuration, when rotational adjustment of the angular misalignment is necessary, rotating said tapered intervertebral spacer within the space until the desired alignment is established. 
         [0037]    In an alternative embodiment, in which porous spacers are utilized, the surgical method of the present invention may comprise: determining an angular misalignment associated with at least one pair of adjacent vertebral bones; sequentially inserting and removing a series of progressively wider cylindrical spacer elements into the corresponding intervertebral space between said at least one pair of adjacent vertebral bones until the proper anatomical spacing between the pair of adjacent vertebral bones is restored; for each intervertebral space, inserting a diametrically tapered cylindrical porous spacer element into the intervertebral space between said corresponding pair of adjacent vertebral bones; rotating said diametrically tapered cylindrical porous spacer element such that the rotational orientation of the tapered cylindrical porous spacer element introduces the appropriate counter offset to the intervertebral space of the previously misaligned scoliotic vertebral bones, thereby restoring the proper anatomical alignment of the vertebral bones; and stabilizing the pair of adjacent vertebral bones to permit infused growth of bone into the diametrically tapered cylindrical porous spacer element. 
         [0038]    As shall be readily understood, in its most basic form, the method of the present invention principally consists of sequentially inserting and removing a series of progressively wider cylindrical spacer elements into the intervertebral space between adjacent vertebral bones until the distance between the vertebral bones is anatomically appropriate. 
         [0039]    More particularly, with respect to the various spacers of the present invention, in its most basic form, the spacers comprise a plurality of sequentially axially wider disc spacer elements, the sequential insertion and removal of which, into an intervertebral space effects a widening of the intervertebral space, such that a desired anatomical spacing of adjacent vertebral bones may be restored. These spacers may include beveled upper and lower circumferential radial edges which facilitate the application of the desired spreading force to the adjacent vertebral bones. For the ease of surgical use, these spacers may each include an engagement locus which couples with a corresponding insertion and removal tool to facilitate the same. This locus comprises an axially medial groove into which said insertion and removal tool can be seated. In two alternative embodiments, the medial groove may comprises a constant width, such that each disc spacer element may rotate freely within the corresponding insertion and removal tool. Alternatively, the groove may be a radially widening groove, such that each disc spacer element may be prevented from rotating freely with respect to the corresponding insertion and removal tool by a clamping action thereof, thereby permitting the controlled rotation of the corresponding disc spacer element within the intervertebral space by manipulation of the insertion and removal tool. 
         [0040]    Tapered spacers, for use in reorienting as well as distracting the alignment of the adjacent vertebral bones may be used. These tapered spacers comprise diametrically tapered upper and lower surfaces. Ideally, for surgeon measurement purposes, each of the disc spacer elements includes at least two relative angle designation marks on at least one of said upper and lower surfaces such that a surgeon user may readily visually determine the rotational angle of said disc spacer element relative to a known reference. 
         [0041]    It shall be understood that the intervertebral spacers each have a unique axial thickness, the thicknesses increasing sequentially from one spacer to another, the increasing thicknesses increasing incrementally, said plurality of spacers being particularly useful for gradually distracting adjacent vertebral bones in an anatomically appropriate manner. 
         [0042]    A critical feature of the present invention is the potential for using porous spacers to distract and potentially reorient the spine, and that the spacers may be implanted permanently into the space between the vertebral bones such that bone ingrowth and solid fusion may occur across the intervertebral space. 
         [0043]    As introduced above, insertion tools are additional components of the present invention. In a first embodiment, the instrument for inserting and removing an intervertebral spacer into and out from an intervertebral space between adjacent vertebral bones, the spacer having a trunk portion having a longitudinal axis and flange portions at each longitudinal end of the trunk, the instrument comprises: a shaft having a proximal end and a distal end; said proximal end including a handle; and a holding structure provided at the distal end, which holding structure includes an enclosure within which the trunk of the spacer may be selectively introduced and maintained therein, the holding structure having an opening leading to the enclosure and through which opening the trunk of the spacer may be selectively passed to when forced therethough. More specifically, the trunk of the spacer has a first width, the opening has a second width which is incrementally smaller than the first width, and the enclosure has a third width which accommodates the first width, such that selective introduction of the trunk through the opening and into the enclosure requires a force to elastically widen the opening such that the trunk may pass through the opening and into the enclosure, the restoration of the opening providing an occlusion which maintains the trunk within the enclosure. As suggested above, the trunk is generally cylindrical and, therefore, the holding structure includes a hook having a curvate extent which forms a partial-circular enclosure, and which curvate extent fits between the flanges when the trunk is maintained within the enclosure. 
         [0044]    In such an embodiment, the intervertebral spacer is selectively snapped into and out of the enclosure through the opening, and such that the intervertebral spacer may be rotationally freely held within the enclosure. In order to snap the spacer into and out of the enclosure, a second element is often utilized. This second helper tool comprises a handle portion at one end, and a bifurcated pair of spaced apart curvate hook-shaped tines at the other. The times have a radius of curvature greater than that of each of the spacers, such that when the first and second elements engage one another (at a fulcrum point at the point of bifurcation of the spaced apart curvate hook-shaped tines and a point between the handle and enclosure ends of the first element), the introduction and removal of the distraction member from the enclosure is facilitated. 
         [0045]    In a second embodiment, which is more suited for the insertion, rotation and removal of the tapered spacers, the tool comprises a shaft having a proximal end and a distal end, said proximal end forming a handle and the distal end forming a spacer member engaging subassembly; said spacer member engaging subassembly including at least one selectively expanding and contracting enclosure into which the central core may be introduced when the engaging subassembly is in the expanded state, and which holds the spacer member so that it cannot move when the selectively expanding and contracting enclosure is rendered into the contracted state; and an actuating mechanism, extending from the proximal end to the distal end, by which the spacer member engaging subassembly may be selectively expanded and contracted. More specifically, the spacer member engaging subassembly comprises a fixed curvate hook defining a portion of the enclosure, a second, selectively advanceable and retractable, portion adjacent the fixed hook portion and said first and second portions forming said selectively expanding and contracting enclosure. Stated alternatively, the selectively expanding and contracting enclosure is formed by at least two members which are maintained in selectively slideable association with each other, at least one of said at least two members including a tapered edge thereof. 
         [0046]    The instrument of this embodiment includes an actuating mechanism including a trigger element disposed in the handle portion, which trigger is actionably coupled to advancing and retracting cams which are coupled to the second portion to advance and retract the second portion in accordance with selective manipulation of the trigger. In more detail, the spacer member engaging subassembly comprises a fixed member and a selectively moveable member which, together, form said selectively expanding and contracting enclosure, and wherein said actuating mechanism comprises a trigger which is mechanically coupled to said selectively moveable member, the mechanical coupling including a rod, a plate having a protrusion, and a lever having a slot, the rod being connected at one end to the selectively moveable member and at another end to the plate, the protrusion engaging the slot, the lever being attached to the trigger, so that when the trigger is engaged, the lever pulls the plate protrusion by the slot, the plate pulls the rod, and the rod moves the selectively moveable member toward the fixed member. 
         [0047]    In a third embodiment, the tool comprises a shaft having a proximal end forming a handle, and a distal end forming a claw subassembly for holding said spacer, said claw subassembly including a first pincer which is fixed at the distal end of the shaft and a second pincer which is selectively rotateable into and out of spacer holding association with said first pincer to hold and release, respectively, the spacer; and an actuation mechanism for selectively rotating the second pincer. The second pincer is rotateably mounted to the shaft and is spring biased away from the first pincer. 
         [0048]    In this embodiment the actuation mechanism comprises a sliding member mounted to the shaft which is selectively moveable in the distal direction by a force sufficient to overcome the bias of the spring, the distally directed movement of the sliding member thereby causing the second pincer to move toward the fixed first pincer, and the subsequent retraction of the sliding member in a proximal direction causes the sliding member to disengage the second pincer and the permits the pincers to separate under the bias of the spring. In order to facilitate this action, the second pincer includes a tapered surface which is engaged by a corresponding surface of the sliding member, said engagement causes the second pincer to rotate relative to the first pincer. 
         [0049]    More specifically, the intervertebral spacer comprises a cylindrical member having an annular groove defining a central axial core portion and a pair of flange portions at opposing ends thereof; and the claw subassembly engages the spacer at the central axial core. 
         [0050]    Stated alternatively, this third embodiment comprises a pair of pincers, a first of this pair being fixed, and a second being coupled to the first in open-biased opposition thereto, and a sliding element which may be selectively translated into and out of engagement with said second pincer to close and open the pair of pincers, respectively. The pair of pincers define an intervertebral spacer grasping enclosure having an access opening through which the intervertebral spacer can be passed for placement into the enclosure when the sliding element is out of engagement with the second pincer, and the spacer is securely maintained between the first and second pincers when the sliding element has been translated into engagement with the second pincer. Ideally, the first and second pincers are mounted at the distal end of a common shaft, and the sliding element is translateable along said shaft; and wherein the second pincer has a portion thereof which is engaged by the sliding element to close the pair of pincers. In addition, the second pincer is mounted to the common shaft by a pivot joint, and the portion of the second pincer which is engaged by the sliding element is a tapered surface, the angle of which tapered surface, when engaged by the sliding element, causes the second pincer to rotate about the pivot joint, closing the first and second pincers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0051]      FIGS. 1   a - c  illustrates a first embodiment of an intervertebral trial spacer of the invention is illustrated in side, top and side cutaway views, respectively. 
           [0052]      FIG. 1   d  illustrates a first set of intervertebral spacers of the invention in a side view. 
           [0053]      FIGS. 2   a - c  illustrate a second embodiment of an intervertebral spacer of the invention in side, top and side cutaway views, respectively. 
           [0054]      FIG. 2   d  illustrates a second set of intervertebral spacers of the invention in a side view. 
           [0055]      FIGS. 3   a - c  illustrate a third embodiment of an intervertebral spacer of the invention in side, top and side cutaway views, respectively. 
           [0056]      FIG. 3   d  illustrates a third set of tapered intervertebral spacers of the invention in a side view. 
           [0057]      FIGS. 4   a - c  illustrate a fourth embodiment of an intervertebral spacer of the invention in side, top and side cutaway views, respectively. 
           [0058]      FIG. 4   d  illustrates a fourth set of tapered intervertebral spacers of the invention in a side view. 
           [0059]      FIG. 5   a  illustrates a first embodiment of a spacer insertion tool  500  of the invention in a side view. 
           [0060]      FIG. 5   b  is a cutaway view of the insertion tool of  FIG. 5   a  holding the spacer of  FIGS. 1   a - c.    
           [0061]      FIG. 6   a - b  illustrates an embodiment of a loading accessory for a spacer insertion tool of the invention in side and top views, respectively. 
           [0062]      FIG. 6   c  shows the loading accessory of  FIGS. 6   a - b  in operation to load the spacer of  FIG. 1   a - c  into the spacer insertion tool of  FIG. 5   a.    
           [0063]      FIG. 6   d  shows the loading accessory of  FIGS. 6   a - b  in operation to unload the spacer the spacer insertion tool of  FIG. 5   a.    
           [0064]      FIG. 7   a  illustrates another embodiment of a spacer insertion tool of the invention in a side view. 
           [0065]      FIG. 7   b  is a cutaway view of the insertion tool of  FIG. 7   a  holding the spacer of  FIGS. 4   a - c.    
           [0066]      FIGS. 8   a - b  illustrates yet another embodiment of a spacer insertion tool of the invention in open and closed side views, respectively. 
           [0067]      FIG. 8   c  is a cutaway view of the insertion tool of  FIGS. 8   a - b  holding the spacer of  FIGS. 4   a - c.    
       
    
    
     DETAILED DESCRIPTION 
       [0068]    While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which particular embodiments and methods of implantation are shown, it is to be understood at the outset that persons skilled in the art may modify the invention herein described while achieving the functions and results of this invention. Accordingly, the descriptions which follow are to be understood as illustrative and exemplary of specific structures, aspects and features within the broad scope of the present invention and not as limiting of such broad scope. Like numbers refer to similar features of like elements throughout. 
         [0069]    First, the patient spine is exposed through an anterior approach (i.e. the surgeon creates an access hole which permits direct interaction with the anterior and/or anterio-lateral portion of the intervertebral bodies). In the case of scoliosis, as well as in other disorders in which the intervertebral space requires distraction and/or repositioning, the surgeon removes the intervertebral disc material, usually leaving some portion of the annulus (the cylindrical weave of fibrous tissue which normally surrounds and constrains the softer cartilage cushion of the disc material). The surgeon then, in succession, inserts a series of intervertebral trial spacers of defined width. Each of the series of spacers is of a progressively wider thickness, resulting in the continual widening of the space until restoration of the proper disc height has been achieved. Proper disc height restoration is determined by surgical experience, and by observation of the annulus. (Often, the tightening of the annulus indicates that the proper disc height has been reached, inasmuch as the annulus is much less likely to be distorted by the same disruption that caused the intervertebral disc to collapse in the first place.) 
         [0070]    More particularly, with respect to the specific instruments disclosed herein, a series of solid trial spacer elements and an instrument for their insertion and removal is now provided. Each trial spacer is a generally cylindrical disc having a deep annular groove at its midpoint, which forms a central trunk and radial flanges at each end of the trunk. Stated alternatively, two cylindrical upper and lower halves of the disc are held in a closely coaxial spaced apart association by the central trunk, which forms a coaxial bridge between the upper and lower halves. The annular groove is particularly useful for holding the spacer using the spacer insertion instrument of the invention, described below, in that the holding end of the insertion instrument fits within the groove. 
         [0071]    A variety of features of embodiments of the trial spacer elements are disclosed. In some embodiments, such as the first and second embodiments described below, support portions (the portions that are in contact with the adjacent vertebral bodies when the spacer is disposed between the bodies) of the top and bottom surfaces are parallel. Spacers having this feature are generally described herein as “constant thickness” trial spacers. In other embodiments, such as the third and fourth embodiments described below, the support portions are not parallel, providing an overall taper to the spacer at an angle. Spacers having this feature are generally described herein as “tapered thickness” trial spacers. The tapered thickness trial spacers are particularly useful for treating scoliosis, as described below. 
         [0072]    Other features of embodiments of the trial spacer elements include beveled flanges and non-parallel annular groove walls. More specifically, in some embodiments, such as the second and fourth embodiments described below, the flanges are radially beveled in that an outer edge of the top surface of the disc is tapered toward an outer edge of the bottom surface of the disc. In other embodiments, such as the first and third embodiments described below, the flanges are not radially beveled in this manner. The radial beveling feature can be particularly useful for easing the insertion of the spacer in between collapsed vertebral bodies, as described below. Further, in some embodiments, such as the first and third embodiments described below, the walls of the annular groove are parallel, such that the floor of the groove is as wide as the opening of the groove. In other embodiments, such as the second and fourth embodiments described below, the walls of the annular groove are tapered toward one another with the increasing depth of the groove, such that the floor of the groove is narrower than the opening of the groove. Each type of annular groove is useful, depending on the particular surgical application and on the particular embodiment of the spacer insertion instrument that is used to insert the spacer. 
         [0073]    Collections of trial spacer elements are provided by the invention. Preferably, each spacer in a particular set maintains the same diameter as the other spacers in the set. (It shall be understood that different collections of spacers may be provided such that the diameter of the selected collection of trial spacers is appropriate for the specific patient being treated. For example, the diameters of the trial spacers in a collection that is suitable for use with pediatric patients would be smaller than the diameters of the trial spacers in a collection that is suitable for use with adult patients.) Also preferably, each spacer in a particular set has a predetermined depth that differs from the depth of the other spacers in the set. The predetermined depth is provided in that while each spacer in the set shares the same annular groove dimensions (so that each can be held by the same insertion instrument), each spacer has a different flange thickness (in sets where the spacers are constant thickness spacers). For sets of tapered thickness spacers, the predetermined maximum depth and predetermined minimum depth (the two depths providing the overall taper) are provided in that while each spacer in the set shares the same annular groove dimensions (so that each can be held by the same insertion instrument), each spacer has a different maximum flange thickness and a different minimum flange thickness. Preferably in sets of tapered thickness spacers, the overall taper angle is the same for each spacer in the set. The usefulness of providing sets of spacers similar in most respects except for the depth dimension will be described in greater detail below. 
         [0074]    Referring now to  FIGS. 1   a - c , a first embodiment of an intervertebral trial spacer  100  of the invention is illustrated in side, top and side cutaway views, respectively. The spacer  100  is a cylindrical disc with an annular groove  102  that forms a central trunk  103  and radial flanges  104 , 106  at each end of the trunk  102 . In this embodiment, support portions  108 , 110  of the top and bottom surfaces  112 , 114  of the disc are parallel. Further in this embodiment, the walls  120 , 122  of the annular groove  102  are parallel, such that the floor  124  of the groove  102  is as wide as the opening  126  of the groove  102 . Further in this embodiment, the spacer  100  has a central bore  128 . 
         [0075]    Referring now to  FIG. 1   d , a set of intervertebral spacers  100   a - l  of the invention are illustrated in a side view. Each spacer  100   a - l  is formed generally similarly to the intervertebral spacer  100  of  FIGS. 1   a - c , except that each spacer  100   a - l  has a predetermined depth (denoted by the preferred dimension identified adjacent each spacer) provided in that while each spacer  100   a - l  shares the same annular groove dimensions as the other spacers, each spacer  100   a - l  has a different flange thickness dimension. For example, the flanges  104   l , 106   l  are thicker than the flanges  104   a , 106   a.    
         [0076]    Referring now to  FIGS. 2   a - c , a second embodiment of an intervertebral spacer  200  of the invention is illustrated in side, top and side cutaway views, respectively. Similarly to the spacer  100 , the spacer  200  is a cylindrical disc with an annular groove  202  that forms a central trunk  203  and radial flanges  204 , 206  at each end of the trunk  202 . However, in this embodiment, the flanges  204 , 206  are radially tapered in that support portions  208 , 210  of the top and bottom surfaces  212 , 214  of the disc are parallel, while an outer edge  216  of the top surface  212  is tapered toward an outer edge  218  of the bottom surface  214 . Further in this embodiment, in contrast to the spacer  100 , the walls  220 , 222  of the annular groove  202  are tapered toward one another with the increasing depth of the groove  202 , such that the floor  224  of the groove  202  is more narrow than the opening  226  of the groove. Further in this embodiment, the spacer  200  has a central bore  228 . 
         [0077]    Referring now to  FIG. 2   d , a set of intervertebral spacers  200   a - l  of the invention are illustrated in a side view. Each spacer  200   a - l  is formed generally similarly to the intervertebral spacer  200  of  FIGS. 2   a - c , except that each spacer  200   a - l  has a predetermined depth (denoted by the preferred dimension identified adjacent each spacer) provided in that while each spacer  200   a - l  shares the same annular groove dimensions as the other spacers, each spacer  200   a - l  has a different flange thickness dimension. For example, the flanges  204   l , 206   l  are thicker than the flanges  204   a , 206   a.    
         [0078]    With regard to the instrument for the insertion and removal of the trial spacer elements, a first embodiment (particularly useful for inserting constant thickness trial spacers) of a spacer insertion tool includes an elongated shaft and a handle at one end of the shaft. The distal end of the shaft includes semi-circular hook that is adapted to hold a trial spacer within an enclosure formed by the hook. The angle swept out by the hook is slightly greater than 180 degrees, but the inner diameter of the hook is only slightly larger than the central trunk of the trial spacer. Therefore, the trial spacer may be snapped into the enclosure, but maintains complete rotational freedom within its grasp. A loading tool may be provided to assist in the loading and unloading of the trial spacer from the trial spacer insertion instrument of this embodiment. This loading tool comprises a forked hook having two tines separated by a notch that engages the shaft of the insertion tool as the tines engage the flanges of the trial spacer, to force the trial spacer into the enclosure. Alternatively and/or additionally, the same device may be utilized to remove the spacer from the enclosure, by reversing the position of the forked hook relative to the insertion tool and the spacer. 
         [0079]    Referring now to  FIG. 5   a , a first embodiment of a spacer insertion tool  500  of the invention is illustrated in a side view. The insertion tool  500  includes an elongated shaft  502  and a handle  503  at one end of the shaft  502 . At the other end of the shaft  502 , the insertion tool  500  includes a semi-circular hook  504  that is adapted to hold an intervertebral spacer of the invention within an enclosure  506  of the hook  504 . The central trunk of the spacer can be snapped into the enclosure  506  of the hook  504  so that the extent of the hook  504  fits loosely within the annular groove of the spacer and is flanked by the flanges of the spacer. The central trunk of the spacer can also be snapped out of the enclosure  506 . 
         [0080]    In this regard, the hook  504  has an opening  508  that temporarily expands when the central trunk of the spacer is forced through the opening  508 . That is, the outer diameter of the central trunk is greater than the width of the opening  508 , so that the central trunk cannot pass through the opening  508  without force. The application of a force sufficient to cause the opening  508  to expand when confronted with the central trunk causes the central trunk to pass through the opening  508 . After the central trunk has cleared the opening  508 , the opening  508  will contract. The temporary expansion in this embodiment is provided by the hook  504  being formed of a material having a low elasticity and the hook  504  being provided with a stress notch  510  on the extent (preferably located opposite the opening  508  for maximum efficiency) to ease the expansion. 
         [0081]    Once the spacer is loaded into the enclosure, the opening  508 , having contracted back to its resting width, prevents the central trunk from exiting the enclosure radially through the opening, because, as stated above, the outer diameter of the central trunk is greater than the width of the opening  508 . Further, by flanking the extent of the hook  504 , the flanges of the spacer prevent the spacer from exiting the enclosure laterally. The hook  504  therefore holds the spacer loosely in the enclosure so that the spacer can rotate about the cylindrical axis of the central trunk while being held by the hook  504 . 
         [0082]    Referring now to  FIG. 5   b , a cutaway view of the insertion tool  500  of  FIG. 5   a  holding the spacer  100  of  FIGS. 1   a - c  shows the extent of the hook  504  in cross-section and fitting within the annular groove of the spacer. It can be seen that to enable the spacer  100  to be loosely held in the enclosure, the width of the extent is smaller than the width of the annular groove, and the depth of the extent is less than the depth of the annular groove if it is desirable for the flanges to fully flank the extent. Preferably, as shown, the outer diameter of the hook  504  is substantially equal to the outer diameter of the spacer  100 . 
         [0083]    Referring now to  FIG. 6   a - b , an embodiment of a loading accessory  600  for a spacer insertion tool of the invention is illustrated in side and top views, respectively. The loading accessory  600  can be used to ease the passing of the central trunk of the spacer through the opening of the spacer insertion tool, both for loading the spacer into the enclosure and unloading the spacer from the enclosure. The loading accessory  600  includes an elongated shaft  602  and a forked hook  604  at an end of the shaft  602 . A notch  606  having a base  608  separates the tines  610 , 612  of the forked hook  604 . 
         [0084]    The width of the notch  608  separating the tines  610 , 612  is wide enough to accommodate the width of the hook  504  of the insertion tool  500  and the width of the shaft  502  of the insertion tool  500 , but narrow enough so that the tines  610 , 612  can engage the edges of the flanges of the spacer. Preferably, as shown, the curvature of the tines  608 , 610  follows the curvature of the edges of the flanges. 
         [0085]    Referring now to  FIG. 6   c , the loading accessory  600  of  FIGS. 6   a - b  is shown in operation to load the spacer  100  of  FIG. 1   a - c  into the spacer insertion tool  500  of  FIG. 5   a . Initially, the spacer  100  is positioned adjacent the opening  508  of the insertion tool  500 . Then, the tines  610 , 612  of the loading accessory  600  are passed on either side of the shaft  502  of the insertion tool  500  such that the notch  606  accommodates the shaft  502  and until the base  608  of the notch  606  contacts the shaft  502 . Then, the loading accessory  600  is rotated, using the contact between the shaft  502  and the base  608  as a fulcrum, to cause the tines  610 , 612  to engage the flanges  104 , 106  of the spacer  100  and push them into the enclosure  506  of the tool  500 . Applying a force to the rotation, sufficient to cause the opening  508  of the tool  500  to expand when confronted with the central trunk of the spacer, causes the central trunk to pass through the opening  508 . 
         [0086]    Referring now to  FIG. 6   d , the loading accessory  600  of  FIGS. 6   a - b  is shown in operation to unload the spacer  100  of  FIG. 1   a - c  from the spacer insertion tool  500  of  FIG. 5   a . Initially, with the spacer  100  held by the tool  500 , the tines  610 , 612  of the loading accessory  600  are passed on either side of the shaft  502  of the insertion tool  500  such that the notch  606  accommodates the shaft  502  and until the base  608  of the notch  606  contacts the shaft  502 . Then, the loading accessory  600  is rotated, using the contact between the shaft  502  and the base  608  as a fulcrum, to cause the tines  610 , 612  to engage the flanges  104 , 106  of the spacer  100  and push them out of the enclosure  506  of the tool  500 . Applying a force to the rotation, sufficient to cause the opening  508  of the tool  500  to expand when confronted with the central trunk of the spacer, causes the central trunk to pass through the opening  508 . The width of the notch  606  accommodates the width of the hook  504  as the spacer  100  is being pushed out of the enclosure  506 . 
         [0087]    The insertion tool of this first embodiment can be used to insert a series of constant thickness trial spacers (some of which may have beveled flange edges for easing the insertion between the collapsed bones and into the space to be distracted). More specifically, thinner trial spacers can initially be inserted into the spacer, followed successively by thicker trial spacers until the desired spacing is achieved. Once the appropriate spacing has been achieved, immobilization of the spine by fixation, fusion, or non-fusion techniques and devices, such as those set forth in co-pending U.S. patent application Ser. Nos. 09/906,117 and 09/906,118, entitled “An Intervertebral Spacer Device Having a Wave Washer Force Restoring Element” and “An Intervertebral Spacer Device Having a Spiral Wave Washer Force Restoring Element”, respectively, as well as U.S. Pat. No. 5,989,291, entitled “An Intervertebral Spacer Device”, may be desirable. 
         [0088]    While simple distraction to a constant height across the intervertebral space is appropriate for standard disc compression pathologies, in the case of scoliosis, simple constant thickness distraction is insufficient to remediate the pathological condition. What is necessary is the distraction of the sequence of spaces, each to an appropriate angle and height, such that the overall spinal configuration is anatomically correct. Tapered trial spacers, such as those disclosed in the present application, are the first such distraction tools to provide such a tailored correction of the misangulation of the spinal bones. 
         [0089]    More particularly, the surgeon inserts the tapered trial spacers into the intervertebral space (presumably from the anterior, or anterio-lateral, approach) with the narrow edge of the trial spacer forming a wedge and sliding between the adjacent bones. By utilizing either a second or third embodiment of the spacer insertion tool, described more fully hereinafter with respect to  FIGS. 7   a - c  and  8   a - c  respectively, the surgeon may turn the spacer around its axis within the intervertebral space to find the most appropriate rotational position (corresponding to the most desirable straightening effect on the spinal column). Stated alternatively, each of the tapered trial spacers has an overall wedge shape that generally corresponds to the pathological tapering of the adjacent bones that characterizes scoliosis. By rotating the wedge-shaped spacer after it has been placed between the adjacent bones, the overall disc alignment may be compensated, restoring appropriate anatomical status. It should be understood that additional rotation of the spacer may restore lordosis to the spine, and that over-rotation (if the particular spine is flexible enough) of the spacer would result in a pathological curvature in the opposite direction. 
         [0090]    Referring now to  FIGS. 3   a - c , a third embodiment of an intervertebral spacer  300  of the invention is illustrated in side, top and side cutaway views, respectively. Similarly to the spacer  100 , the spacer  300  is a cylindrical disc with an annular groove  302  that forms a central trunk  303  and radial flanges  304 , 306  at each end of the trunk  303 . However, in this embodiment, support portions  308 , 310  of the top and bottom surfaces  312 , 314  of the disc are not parallel, providing an overall taper to the spacer  300  at an angle. Still, similarly to the spacer  100 , the walls  320 , 322  of the annular groove  302  are parallel, such that the floor  324  of the groove  302  is as wide as the opening  326  of the groove  302 . Further in this embodiment, the spacer  300  has a central bore  328 . 
         [0091]    Referring now to  FIG. 3   d , a set of tapered intervertebral spacers  300   a - j  of the invention are illustrated in a side view. Each spacer  300   a - j  is formed generally similarly to the intervertebral spacer  300  of  FIGS. 3   a - c , except that each spacer  300   a - j  has a predetermined maximum depth (denoted by the preferred maximum depth dimension identified adjacent each spacer) and a predetermined minimum depth (denoted by the preferred minimum depth dimension identified adjacent each spacer), each provided in that while each spacer  300   a - j  shares the same annular groove width dimension as the other spacers, each spacer  300   a - j  has a different maximum flange thickness dimension and a different minimum flange thickness dimension. For example, the flanges  304   j , 306   j  have a thicker maximum flange thickness dimension and a thicker minimum flange thickness dimension than the flanges  304   a , 306   a.    
         [0092]    Referring now to  FIGS. 4   a - c , a fourth embodiment of an intervertebral spacer  400  of the invention is illustrated in side, top and side cutaway views, respectively. Similarly to the spacer  200 , the spacer  400  is a cylindrical disc with an annular groove  402  that forms a central trunk  403  and radial flanges  404 , 406  at each end of the trunk  403 . However, in this embodiment, support portions  408 , 410  of the top and bottom surfaces  412 , 414  of the disc are not parallel. Still, similarly to the spacer  200 , the flanges  404 , 406  are radially tapered in that an outer edge  416  of the top surface  412  is tapered toward an outer edge  418  of the bottom surface  414 . Further in this embodiment, similarly to the spacer  200 , the walls  420 , 422  of the annular groove  402  are tapered toward one another with the increasing depth of the groove  402 , such that the floor  424  of the groove  402  is more narrow than the opening  426  of the groove. Further in this embodiment, the spacer  400  has a central bore  428 . 
         [0093]    Referring now to  FIG. 4   d , a set of tapered intervertebral spacers  400   a - j  of the invention are illustrated in a side view. Each spacer  400   a - j  is formed generally similarly to the intervertebral spacer  400  of  FIGS. 4   a - c , except that each spacer  400   a - j  has a predetermined maximum depth (denoted by the preferred maximum depth dimension identified adjacent each spacer) and a predetermined minimum depth (denoted by the preferred minimum depth dimension identified adjacent each spacer), each provided in that while each spacer  400   a - j  shares the same annular groove width dimension as the other spacers, each spacer  400   a - j  has a different maximum flange thickness dimension and a different minimum flange thickness dimension. For example, the flanges  404   j , 406   j  have a thicker maximum flange thickness dimension and a thicker minimum flange thickness dimension than the flanges  404   a , 406   a.    
         [0094]    It should understood that the various features of the different embodiments of the intervertebral spacer of the invention discussed above can be used in various combinations and permutations to form the illustrated embodiments and other embodiments of the intervertebral spacer of the invention. In some embodiments, the walls of the annular groove are parallel. In other embodiments, they are not parallel. In some embodiments where they are not parallel, they are tapered toward one another with the increasing depth of the groove. In other embodiments where they are not parallel, they are tapered toward one another with the decreasing depth of the groove. In some embodiments, the support portions of the top and bottom surfaces are parallel. In other embodiments, they are not parallel. In some embodiments, the flanges are radially tapered in that the outer edge of the top surface is tapered toward an outer edge of the bottom surface. In other embodiments, the flanges are not radially tapered. In some embodiments, the spacer has a central bore. In other embodiments, the spacer does not have a central bore. 
         [0095]    It should be understood that while in the illustrated embodiments where spacers in a set have an overall taper, the angle of the overall taper of each spacer in the set is the same as the angle of the overall taper of the other spacers in the set, the invention encompasses a set of spacers in which the angle of the overall taper of each spacer in the set is different than the angle of the overall taper of at least one other spacer in the set. 
         [0096]    It should be understood that while in the illustrated embodiments where the spacer has an overall taper, the angle of the overall taper can be predetermined, such that the maximum flange thickness and the minimum flange thickness can be selected to achieve a desired overall taper angle. 
         [0097]    It should be understood that while in the illustrated embodiments the spacers are shown as having a cylindrical shape, it should be understood that in other embodiment, the spacers can have oval, square, or rectangular cross-sections, or cross-sections of other shapes, provided that any corners are rounded as necessary to prevent damage to surrounding tissue. 
         [0098]    As suggested previously, the insertion, rotation and removal of the tapered trial intervertebral spacers requires an alternate spacer insertion tool. This second embodiment of the spacer insertion tool includes a handle and an elongated dual shaft, the dual shaft culminating in a trial spacer grasping pincer, rather than the simple hook of the first embodiment. This pincer differs from the hook of the first embodiment of the trial spacer insertion tool described above, inasmuch as the dual shaft includes a fixed shaft and a selectively engagable shaft which, together, form pincer. More specifically, the fixed shaft includes a semicircular hook portion of the pincer at its distal end, having an enclosure within which a trial spacer can be placed. The selectively engagable shaft includes the complementary portion of the pincer, which moves toward the hook portion to grasp and hold the trial spacer when the engagable shaft is engaged, and moves away from the hook portion to release the trial spacer when the engagable shaft is disengaged. (The spacer can be unloaded and loaded when the engagable shaft is disengaged.) The engagement action prevents the spacer from moving relative to the tool, and therefore permits the surgeon to rotate the tapered spacer in between the vertebral bodies (by contrast, the first embodiment of the trial spacer insertion instrument permitted the spacer to rotate freely in the enclosure of the hook). 
         [0099]    Referring now to  FIG. 7   a , another embodiment of a spacer insertion tool  700  of the invention is illustrated in a side view. The insertion tool  700  includes an elongated shaft  702  and a handle  704  at one end of the shaft  702 . The insertion tool  700  further includes a compression assembly that is adapted to hold an intervertebral spacer of the invention at the other end of the shaft  702  so that the spacer cannot move when held. The insertion tool  700  further includes a release assembly that is adapted to release the spacer from being held. 
         [0100]    The compression assembly includes a semicircular hook  706  at the other end of the shaft  702  and a compression surface  708  adjacent the hook  706 . The hook  706  has an enclosure  709  defined by the extent of the hook  706  and an opening  710  through which the central trunk can pass freely to be placed into the enclosure  709 . That is, the width of the opening  710  is greater than the diameter of the central trunk. When the central trunk is placed within the enclosure  709 , the extent of the hook  706  fits loosely within the annular groove of the spacer. 
         [0101]    The compression assembly further includes a compression trigger  712  mechanically connected to the hook  706  such that as the compression trigger  712  is placed in an engaged position, the hook  706  is pulled toward the compression surface  708 . The mechanical connection includes a rod  714  connected at one end to the hook  706  and at the other end to a plate  716 . A rod  718  protruding from the plate  716  is engaged by a slot  720  in a lever  722  attached to the compression trigger  712 . When the compression trigger  712  is engaged, the rod  714  of the lever  722  pulls the plate  716  by the slot  720 . The plate  716  in turn pulls the rod  714 , which in turn pulls the hook  704  toward the compression surface  708 . 
         [0102]    When the hook  706  is pulled toward the compression surface  708  when the central trunk of the spacer is in the enclosure  709 , the central trunk is compressed within the enclosure  709  between the hook  706  and the compression surface  708  so that the spacer cannot move. 
         [0103]    The release assembly includes a spring  724  biasing the compression trigger  712  to a disengaged position. Therefore, after the compression trigger  712  is released, it moves to the disengaged position. However, so that the central trunk remains compressed within the enclosure even after the compression trigger  712  is released (e.g., so that the surgeon does not need to continue holding the compression trigger  712  to effect the compression), the compression assembly further includes teeth  726  on the rod  714  and corresponding teeth  730  that confront the rod teeth  726  to prevent the rod  714  from retreating, to maintain the compression. 
         [0104]    The release assembly further includes a release trigger  732  that can be engaged to release the rod teeth  726  from the corresponding teeth  730  to allow the rod  714  to return to its rest position, thereby alleviating the compression. More specifically, the release trigger  732  has the corresponding teeth  730  and the release assembly further includes a spring  734  that biases the release trigger  732  toward a position in which the corresponding teeth  730  engage the rod teeth  726 . This arrangement allows the release trigger  732  to be engaged by pressing the release trigger  732  with a force great enough to overcome the bias of the spring  734 , so that the corresponding teeth  730  are disengaged from the rod teeth  726 . Therefore, when the release trigger  732  is pressed, the compression is alleviated, and the central trunk of the spacer can be freely passed through the opening  710  to be taken out of the enclosure  709 . 
         [0105]    Referring now to  FIG. 7   b , a cutaway view of the insertion tool  700  of  FIG. 7   a  holding the spacer  400  of  FIGS. 4   a - c  shows the extent of the hook  706  in cross-section and fitting within the annular groove of the spacer as the spacer is compressed between the compression surface  708  and the hook  706 . It can be seen that the width of the extent of the hook  706  is smaller than the width of the annular groove, and the depth of the extent is less than the depth of the annular groove if it is desirable for the flanges to fully flank the extent. Preferably, as shown, the outer diameter of the hook  706  is substantially equal to the outer diameter of the spacer  400 . 
         [0106]    Referring now to  FIGS. 8   a - b , yet another embodiment of a spacer insertion tool  800  of the invention is illustrated in open and closed side views, respectively. The insertion tool  800  includes an elongated shaft  802  and a handle  804  at one end of the shaft  802 . The insertion tool  800  further includes a compression assembly that is adapted to hold an intervertebral spacer of the invention at the other end of the shaft  802  so that the spacer cannot move when held. The insertion tool  800  further includes a release assembly that is adapted to release the spacer from being held. 
         [0107]    The compression assembly includes a claw  806  at the other end of the shaft  802  having opposing pincers  807   a ,  807   b , each providing one of opposing compression surfaces  808   a ,  808   b . The claw  806  has an enclosure  809  defined by the extents of the pincers  807   a ,  807   b  and an opening  810  through which the central trunk can pass freely to be placed into the enclosure  809  when the claw  806  is open (i.e., when the opposing pincers  807   a ,  807   b  are separated). That is, the width of the opening  810  is greater than the diameter of the central trunk when the claw  806  is open. When the central trunk is placed within the enclosure  809 , the extents of the pincers  807   a ,  807   b  fit loosely within the annular groove of the spacer. 
         [0108]    The compression assembly further includes a compression slide  812  that when moved to an engaged position (here, a forward position shown in  FIG. 8   b ) closes the claw  806 . The closure of the claw  806  by the compression slide  812  is effected as follows. One of the pincers  807   a  is in a fixed position relative to the elongated shaft  802  whereas the other pincer  807   b  is adapted to rotate about an axis transverse to the shaft  802 . In this embodiment, the rotation is provided by a pin  813  passing through each pincer at a rotation point along the transverse axis. One position of the movable pincer  807   b  along the rotation path (shown in  FIG. 8   a ) defines the opened claw  806  in that the pincers  807   a ,  807   b  are separated. Another position of the movable pincer  807   b  along the rotation path (shown in  FIG. 8   b ) defines the closed claw  806  in that the pincers  807   a ,  807   b  are brought together. When the pincers  807   a ,  807   b  are separated, an engagement surface  814  of the movable pincer  807   b  is placed in an available compression path of an engagement surface  816  of the compression slide  812 . The engagement surface  814  is tapered so that when the compression slide  812  is moved to the engaged, the engagement surface  816  of the compression slide  812  moves along the available compression path and engages the tapered surface  814  to push the surface  814  aside and thereby cause a rotation of the movable pincer  807   b  to the position defining the closed claw  806 . 
         [0109]    When the pincers  807   a ,  807   b  are thereby brought together to close the claw  806  when the central trunk of the spacer is in the enclosure  809 , the compression surfaces  808   a ,  808   b  come to bear on the central trunk to compress it within the enclosure  809  so that the spacer cannot move. 
         [0110]    The release assembly includes a spring  818  biasing the movable pincer  807   b  to the rotation path position defining the open claw  806 . Therefore, when the compression slide  812  is moved to a disengaged position (here, a backward position), the engagement surface  816  of the compression slide  812  moves along an available release path (here, a backtracking along the compression path) and frees the engagement surface  814  of the movable pincer  807   b  to allow the engagement surface  814  to return to a place in the available compression path by the biasing action of the spring  818 . When the claw  806  is open, the compression is alleviated and the central trunk of the spacer can be freely passed through the opening  810  to be taken out of the enclosure  809 . 
         [0111]    The release assembly further includes at least one barrier  820   a ,  820   b  that limits the biasing action of the spring  818  by preventing the movable pincer  807   b  from rotating beyond the position that places the engagement surface  814  in the available compression path. In this embodiment, confrontation surfaces  822   a ,  822   b  on the movable pincer  807   b  confront the barriers  820   a ,  820   b  as the pincer  807   b  rotates toward the rotation path position defining the open claw  806  under the biasing force of the spring  818 . When the engagement surface  814  is returned to the place in the available compression path, the barriers  820   a ,  820   b  prevent the confrontation surfaces  822   a ,  822   b  from advancing further. The spring  818  and the barriers  820   a ,  820   b  maintain the movable pincer  807   b  in this position until the compression slide  812  is advanced toward the engaged position by a force great enough to overcome the biasing force of the spring  818 . 
         [0112]    Referring now to  FIG. 8   c , a cutaway view of the insertion tool  800  of  FIGS. 8   a - b  holding the spacer  400  of  FIGS. 4   a - c  shows the extents of the pincers  807   a ,  807   b  in cross-section and fitting within the annular groove of the spacer as the spacer is compressed between the compression surfaces  808   a ,  808   b . It can be seen that the width of each extent is smaller than the width of the annular groove, and the depth of each extent is less than the depth of the annular groove if it is desirable for the flanges to fully flank the extents. Preferably, as shown, the outer diameter of the claw  806  is substantially equal to the outer diameter of the spacer  400 . 
         [0113]    There are alternative insertion and rotating instruments that may be designed, so long as they selectively and alternatingly release or hold the trial spacer securely against rotation (the spacer can&#39;t rotate freely if it is to be turned in the intervertebral space). The tapered trial spacers themselves can include angle markers that clearly indicate to the surgeon the amount of rotation that was necessary for the correction of the spinal deformity. Such angle markers can also serve as a guide for the implantation of a secondary bone graft (e.g., a femoral ring) or another intervertebral spacer device. 
         [0114]    Once the surgeon has determined the appropriate geometry for the surgical implants via the trial spacers, he or she is ready to immobilize the spine in that position. While multiple ways for immobilizing the spine are disclosed in the prior art, any one of which may be suitable for the specific surgical patient&#39;s treatment, three alternative ways are herein described. 
         [0115]    First, the trial spacers may be left in the patient while rod fixation apparatuses (anterior or posterior) are mounted to the spine, thereby holding the spine in its desired orientation even after the trial spacers are subsequently removed. Alternatively, surface plating and/or intervertebral cage devices may be mounted to the spine to promote fusion without the need for bulky rod assemblies. (While this approach may seem more surgically desirable, questions regarding the long-term stability of these constructs have led to some surgeons to choose combinations of rodding and cages.) 
         [0116]    A third approach to immobilizing the corrected spine is to insert a shaped bone graft, or suitably contoured porous metal spacer, into the properly distracted intervertebral space, and either plating or using rod fixation to hold the construct stable as the spine fuses. The insertion of a femoral ring allograft, or porous metal implant, into an intervertebral space is described more fully in co-pending U.S. patent application Ser. Nos. 09/844,904 and 09/906,123, entitled “A Porous Interbody Fusion Device Having Integrated Polyaxial Locking Interference Screws” and “Porous Intervertebral Distraction Spacers”. 
         [0117]    The tapered trial spacers may also serve as precursors (measuring instruments) for another spacer (e.g., a porous metal spacer), similarly shaped, which is inserted into the intervertebral space by the same instrument. 
         [0118]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.