US20040158254A1 - Instrument and method for milling a path into bone - Google Patents

Abstract

An instrument and method for cutting a path in bone are provided. The instrument includes a curved guide member defining a curved opening extending therein, and a bit member positioned within the opening of the guide member. The bit member is adapted to move within the opening of the guide member to cut a path in bone.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• This application claims the benefit of U.S. Provisional Application No. 60/446,963 filed on Feb. 12, 2003. U.S. Provisional Application No. 60/446,963 is herein incorporated by reference for all legitimate purposes.[0001]
BACKGROUND
• The present disclosure relates generally to the field of orthopedics and spinal surgery, and in some embodiments, the present disclosure relates to intervertebral prosthetic joints for use in the total or partial replacement of a natural intervertebral disc, and methods and tools for use therewith.[0002]
• In the treatment of diseases, injuries or malformations affecting spinal motion segments, and especially those affecting disc tissue, it has long been known to remove some or all of a degenerated, ruptured or otherwise failing disc. In cases involving intervertebral disc tissue that has been removed or is otherwise absent from a spinal motion segment, corrective measures are taken to ensure the proper spacing of the vertebrae formerly separated by the removed disc tissue.[0003]
• In some instances, the two adjacent vertebrae are fused together using transplanted bone tissue, an artificial fusion component, or other compositions or devices. Spinal fusion procedures, however, have raised concerns in the medical community that the bio-mechanical rigidity of intervertebral fusion may predispose neighboring spinal motion segments to rapid deterioration. More specifically, unlike a natural intervertebral disc, spinal fusion prevents the fused vertebrae from pivoting and rotating with respect to one another. Such lack of mobility tends to increase stresses on adjacent spinal motion segments.[0004]
• Additionally, several conditions may develop within adjacent spinal motion segments, including disc degeneration, disc herniation, instability, spinal stenosis, spondylosis and facet joint arthritis. Consequently, many patients may require additional disc removal and/or another type of surgical procedure as a result of spinal fusion. Alternatives to spinal fusion are therefore desirable.[0005]
• In particular, this disclosure relates to an instrument that aids in the insertion of alternatives to spinal fusion.[0006]
SUMMARY
• An instrument for cutting a path in bone is provided. The instrument includes a curved guide member defining a curved opening extending therein, and a bit member positioned within the opening of the guide member. The bit member is adapted to move within the opening of the guide member to cut a path in bone.[0007]
• In another embodiment, an instrument for cutting a path in bone is provided. The instrument includes a curved guide member defining a curved opening extending therein, a bit member positioned within the opening of the guide member, a rotatable element operatively connected to the bit member to impart rotational movement to the bit member, and a handle operatively connected to the bit member to impart translational movement to the bit member. The bit member is adapted to cut a curved path into bone via rotational movement in and translational movement through the guide member.[0008]
• In yet another embodiment, a method for cutting a curved path into bone is provided. The method includes providing an instrument having a curved guide member, the curved guide member defining a curved opening therein, positioning a bit member within the opening of the guide member, actuating the instrument to impart rotational movement to the bit member, engaging the bit member with bone, and imparting a translational force to the bit member to cut a curved path in bone.[0009]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a lateral view of a portion of a spondylosed vertebral column.[0010]
• FIG. 2 is a lateral view of a pair of adjacent vertebral endplates of FIG. 1.[0011]
• FIG. 3[0012]ais a lateral view of the pair of adjacent vertebral endplates of FIG. 2 with a rod and screw arrangement.
• FIG. 3[0013]bis a longitudinal, partial sectional view of the pair of adjacent vertebral bodies of FIG. 3a.
• FIG. 4[0014]ais an isometric view of an articulating prosthetic joint for lateral insertion according to one embodiment of the present disclosure.
• FIG. 4[0015]bis an isometric view of an articulating prosthetic joint for lateral insertion according to another embodiment of the present disclosure.
• FIG. 4[0016]cis a front view of the articulating prosthetic joint for lateral insertion of FIG. 4b.
• FIG. 5 is a longitudinal view of the prosthetic joint of FIG. 4[0017]a.
• FIG. 6 is a lateral view of the prosthetic joint of FIG. 4[0018]a.
• FIG. 7 is a lateral, partial sectional view of the prosthetic joint of FIG. 4[0019]adisposed between a pair of spondylosed vertebral endplates.
• FIG. 8 is a lateral, partial sectional view of an alternative articulating prosthetic joint disposed between a pair of vertebral endplates.[0020]
• FIG. 9 is an isometric view of an alternative articulating prosthetic joint according to another embodiment of the present disclosure.[0021]
• FIG. 10 is a lateral, partial sectional view of the prosthetic joint of FIG. 9 disposed between a pair of spondylosed vertebral endplates.[0022]
• FIG. 1I is a lateral, partial sectional view of an alternative articulating prosthetic joint disposed between a pair of vertebral endplates.[0023]
• FIG. 12 is an isometric view of a disc prosthesis according to another embodiment of the present disclosure.[0024]
• FIG. 13 is an isometric view of an alternative disc prosthesis according to another embodiment of the present disclosure.[0025]
• FIG. 14 is an isometric view of an alternative articulating prosthetic joint for anterior insertion according to another embodiment of the present disclosure.[0026]
• FIG. 15 is a longitudinal view of the prosthetic joint of FIG. 14.[0027]
• FIG. 16 is a lateral view of the prosthetic joint of FIG. 14.[0028]
• FIG. 17 is a lateral view of the prosthetic joint of FIG. 14 disposed between a pair of spondylosed vertebral endplates.[0029]
• FIG. 18 is a longitudinal view of an alternative articulating prosthetic joint for anterior insertion according to another embodiment of the present disclosure.[0030]
• FIG. 19 is a longitudinal view of an alternative articulating prosthetic joint for anterior insertion according to yet another embodiment of the present disclosure.[0031]
• FIG. 20 is a longitudinal view of an alternative articulating prosthetic joint for anterior insertion according to yet another embodiment of the present disclosure.[0032]
• FIG. 21 is a longitudinal view of a pair of verterbral endplates having slots for receiving the prosthetic joint of FIG. 18.[0033]
• FIG. 22 is a longitudinal view of a pair of verterbral endplates having slots for receiving the prosthetic joint of FIG. 19.[0034]
• FIG. 23 is a longitudinal view of a pair of verterbral endplates having slots for receiving the prosthetic joint of FIG. 20.[0035]
• FIG. 24 is a lateral, partial sectional view of the prosthetic joint of FIG. 14 disposed between a pair of spondylosed vertebral endplates and an orthopedic implant.[0036]
• FIG. 25 is a lateral, partial sectional view of the prosthetic joint of FIG. 14 disposed between a pair of spondylosed vertebral endplates and a lag screw.[0037]
• FIG. 26 is a schematic top view of the arrangement depicted in FIG. 25.[0038]
• FIG. 27 is a schematic top view of a vertebral body depicting a path for transforaminal insertion.[0039]
• FIG. 28 is an isometric view of an alternative articulating prosthetic joint for transforaminal insertion according to another embodiment of the present disclosure.[0040]
• FIG. 29 is a lateral view of the prosthetic joint of FIG. 28.[0041]
• FIG. 30 is a longitudinal view of the prosthetic joint of FIG. 28.[0042]
• FIG. 31[0043]ais a lateral, partial sectional view of the prosthetic joint of FIG. 28 disposed between a pair of vertebral endplates.
• FIG. 31[0044]bis a longitudinal, partial sectional view of the prosthetic joint of FIG. 28 disposed between a pair of vertebral endplates.
• FIG. 32 is a schematic top view depicting a transforaminal slot formed in a vertebral endplate.[0045]
• FIG. 33 is a schematic top view depicting a milling apparatus shown inserted above a vertebral endplate.[0046]
• FIG. 34[0047]ais a lateral view of the milling apparatus of FIG. 33 shown disposed between a pair of adjacent vertebral endplates.
• FIG. 34[0048]bis a detailed view of a milling tool of the milling apparatus of FIG. 34a.
• FIG. 34[0049]cis a detailed view of an alternative milling tool.
• FIG. 35 is a schematic view of the milling apparatus of FIG. 33.[0050]
• FIG. 36 is an isometric view of an alternative articulating prosthetic joint for transforaminal insertion according to another embodiment of the present disclosure.[0051]
• FIG. 37 is a lateral view of the prosthetic joint of FIG. 36.[0052]
• FIG. 38 is a longitudinal view of the prosthetic joint FIG. 36.[0053]
• FIG. 39 is an isometric view of an alternative articulating prosthetic joint for anterior-oblique insertion according to another embodiment of the present disclosure.[0054]
• FIG. 40 is a longitudinal view of the prosthetic joint of FIG. 39.[0055]
• FIG. 41 is a lateral view of the prosthetic joint of FIG. 39.[0056]
• FIG. 42 is lateral, partial sectional view of the prosthetic joint of FIG. 39 disposed between a pair of vertebral endplates.[0057]
• FIG. 43 is a longitudinal, partial sectional view of the prosthetic joint of FIG. 39 disposed between a pair of vertebral endplates.[0058]
• FIG. 44[0059]ais a top, schematic view depicting a slot formed in a vertebral endplate for receiving the prosthetic joint of FIG. 39.
• FIG. 44[0060]bis a schematic view depicting an alignment process associated with the insertion of the prosthetic joint of FIG. 39.
• FIG. 45 is an exploded view an alternative prosthetic joint according to yet another embodiment of the present disclosure.[0061]
• FIG. 46 is an isometric view of the prosthetic joint of FIG. 45.[0062]
• FIG. 47 is a longitudinal view of the prosthetic joint of FIG. 46.[0063]
• FIG. 48 is a longitudinal view of a pair of adjacent vertebral endplates.[0064]
• FIG. 49[0065]ais a plan view of an articular component of the prosthetic joint of FIG. 45.
• FIG. 49[0066]bis a sectional view of the articular component of FIG. 49ataken along theline49b-49b.
• FIG. 50[0067]ais a plan view of a modular projection member of the prosthetic joint of FIG. 45.
• FIG. 50[0068]bis a sectional view of the modular projection member of FIG. 50ataken along theline50b-50b.
• FIG. 51 is a plan view of the modular projection member of FIG. 50[0069]ainserted into the articular component of FIG. 49a.
• FIG. 52 is a plan view of the modular projection member of FIG. 50[0070]ainserted into the articular component of FIG. 49adepicting the modular projection member in a different position relative to FIG. 51.
DESCRIPTION
• For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments, or examples, illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates. As such, individual features of separately described embodiments can be combined to form additional embodiments. In addition, examples of deformities such as spondylolisthesis are discussed; however, it is understood that the various prosthetic devices described herein can be adapted for use between not only spondylosed vertebrae, but substantially aligned vertebrae as well.[0071]
• I. Lateral Correction[0072]
• In many cases of deformity, such as spondylolisthesis, one or more vertebral bodies can be displaced with respect to other vertebrae or the sacrum. In such a deformity, it is desirable to reduce the extent of displacement, by re-positioning the displaced bodies from their previous position. A spondylolisthesis reduction can be a technically demanding procedure requiring great care to prevent neurological impairment and damage to surrounding soft tissue.[0073]
• Referring now to FIG. 1, shown therein is a lateral view of a portion of a[0074]spinal column10, illustrating a group of adjacent upper and lower vertebrae V1, V2, V3, V4 separated by natural intervertebral discs D1, D2, D3. The illustration of four vertebrae is only intended as an example. Another example would be a sacrum and one vertebrae.
• As shown in the drawing, the vertebrae V[0075]2 is dislocated from the vertebrae V1 in a direction shown byarrow22. Likewise, vertebrae V3 is dislocated in a direction shown byarrow23 and vertebrae V4 is dislocated in a direction shown byarrow direction24. It is desired that the position of vertebrae V2, V3, V4 be corrected by moving them in a direction opposite to thearrows22,23,24, respectively.
• Referring now to FIG. 2, for the sake of further example, two of the displaced vertebrae will be discussed, designated as the lower vertebrae V[0076]_Land the upper vertebrae V_U. In one embodiment, some or all of the natural disc that would have been positioned between the two vertebrae V_L, V_Uis typically removed via a discectomy or a similar surgical procedure, the details of which would be known to one of ordinary skill in the art. Removal of the diseased or degenerated disc results in the formation of an intervertebral space S between the upper and lower vertebrae V_U, V_L.
• In the present embodiment, it is desired to insert a prosthetic joint into the intervertebral space S, similar to the prosthetic joint disclosed in U.S. Ser. No. 10/042,589 filed Jan. 9, 2002, which is incorporated by reference. However, certain changes are required of the above-referenced prosthetic joint. For the following description, the prosthetic joints discussed and described can be identical to those disclosed in the above-referenced patent application, with the exceptions discussed and suggested below.[0077]
• Spondylolisthesis has not heretofore been corrected from the lateral surgical approach. However, in some instances, correction of spondylolisthesis may be desirable from a lateral approach due to the presence of vessels and/or the nervous plexus. In some embodiments, the lateral approach may be particularly pertinent when correcting spondylolisthesis in the lumbar region of the spine, although it will be understood that other regions of the spine are also contemplated.[0078]
• Referring to FIGS. 3[0079]aand3b, correction of spondylolisthesis can be addressed from a lateral approach by, for example, providing a pair of bone screws30,32 for insertion into the vertebrae V_U, V_L, respectively. In one embodiment, the bone screws30,32 are bi-cortical. However, it is understood that the bone screws may alternatively be uni-cortical. Moreover, the bone screws30,32 may be formed of a variety of materials such as any resorbable material, titanium, and PEEK. The PEEK embodiment is advantageous due to the radiotranslucent properties resulting from the use of PEEK material. It is further understood that the bone screws30,32 may alternatively be of any other mechanical structure, and as such, may take the form of pins or rivets, for example. Moreover, the bone screws30,32 are not limited to having threaded portions to engage the vertebrae V_U, V_L.
• The bone screws[0080]30,32 may be linked to one another via arod34, which is configured to rotate about both of the bone screws. It is understood that a variety of connecting members may be used other than therod34. For example, a non-uniform linkage member may be used to link the bone screws30,32. A non-uniform linkage member may provide a plurality of slots and/or grooves that can be engaged in order to aid in its rotation about the bone screws. Therod34 may be connected prior to insertion of the bone screws30,32 into the vertebrae V_U, V_L, or alternatively, may be subsequently connected after placement of the screws. By applying a rotating force to therod34 in the direction ofarrow36, the upper vertebra V_Uis encouraged back into a desired position relative to the lower vertebra V_L. The rotating force can be applied, for example, by a rotatable wrench (not shown) that can be used by a surgeon. It is understood that the upper vertebra V_Umay not reach entirely to a fully corrected position in relation to the lower vertebra V_L, but the displacement can at least be reduced.
• Although not depicted, in another embodiment, it is contemplated that the spondylosed vertebrae V[0081]_U, V_Lcan be addressed from both lateral directions. Thus, a pair of bone screws substantially identical to the bone screws30,32 may be inserted into the vertebrae V_U, V_Lon the opposite side from and in the opposite direction to the bone screws30,32. In such an arrangement, therod34 can be replaced with a ratcheting system that engages each of the bone screw pairs, and as such, the vertebrae V_U, V_Lcan be rotated relative to one another to encourage the vertebrae into a desired position relative to one another.
• Still further, the[0082]rod34 may include any number and type of engagement means to receive any number and type of rotating tools used by a surgeon; For example, a keyed connection may provide more stability when engaging therod34 with a corresponding rotating tool. In other examples, a clamping tool may be used and corresponding clamping notches may be formed in therod34 to receive the clamping tool. Such an arrangement may aid in achieving the force necessary for rotation.
• Moreover,[0083]additional rods34 and bone screws30,32 are contemplated for use in rotating the spondylosed vertebrae V_U, V_Lback into a desired position relative to one another.Additional rods34 and bone screws30,32 may provide additional stability during the procedure.
• Furthermore, although depicted as a substantially lateral insertion, the insertion of the bone screws[0084]30,32 into the vertebrae V_U, V_Lcan be slightly angled relative to the lateral direction. Such angling of the bone screws30,32 during insertion may provide a preferred gripping angle from which the surgeon can begin rotation of the vertebrae V_U, V_Lrelative to one another.
• Referring to FIGS. 4[0085]a,5, and6, shown therein is one embodiment of an offset intervertebral articulating prosthetic joint40 for insertion into the intervertebral space S (FIG. 2) to aid in the correction of spondylolisthesis. The articulating prosthetic joint40 extends generally along a longitudinal axis L and includes a firstarticular component42 and a secondarticular component44. Thearticular components42,44 cooperate to form the prosthetic joint40 which is sized and configured for disposition within the intervertebral space S (FIG. 2) between adjacent vertebral bodies V_U, V_L(FIG. 2).
• The prosthetic joint[0086]40 provides relative pivotal and rotational movement between the adjacent vertebral bodies to maintain or restore motion substantially similar to the normal bio-mechanical motion provided by a natural intervertebral disc. More specifically, thearticular components42,44 are permitted to pivot relative to one another about a number of axes, including lateral or side-to-side pivotal movement about longitudinal axis L and anterior-posterior pivotal movement about a transverse axis T. It should be understood that in one embodiment of the disclosure, thearticular components42,44 are permitted to pivot relative to one another about any axes that lies in a plane that intersects longitudinal axis L and transverse axis T.
• Furthermore, the[0087]articular components42,44 are permitted to rotate relative to one another about a rotational axis R. Although the prosthetic joint40 has been illustrated and described as providing a specific combination of articulating motion, it should be understood that other combinations of articulating movement are also possible, such as, for example, relative translational or linear motion, and such movement is contemplated as falling within the scope of the present disclosure.
• Although the[0088]articular components42,44 of prosthetic joint40 may be formed from a wide variety of materials, in one embodiment of the disclosure, thearticular components42,44 are formed of a cobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However, in alternative embodiments of the disclosure, thearticular components42,44 may be formed of other materials such as titanium or stainless steel, a polymeric material such as polyethylene, or any other biocompatible material that would be apparent to one of ordinary skill in the art.
• The[0089]articular components42,44 each include a bearingsurface46,48, respectively, that may be positioned in direct contact with vertebral bone and is preferably coated with a bone-growth promoting substance, such as, for example, a hydroxyapatite coating formed of calcium phosphate. Additionally, the bearing surfaces46,48 of thearticular components42,44, respectively, may be roughened prior to being coated with the bone-growth promoting substance to further enhance bone on-growth. Such surface roughening may be accomplished by way of, for example, acid etching, knurling, application of a bead coating, or other methods of roughening that would occur to one of ordinary skill in the art.
• [0090]Articular component42 includes asupport plate50 having anarticular surface52 and theopposite bearing surface46.Support plate50 is sized and shaped to substantially correspond to the size and shape of a vertebral endplate of the adjacent vertebral body V_L(FIG. 2). Thesupport plate50 may include one ormore notches54 or other types of indicia for receiving or engaging with a corresponding portion of a surgical instrument (not shown) to aid in the manipulation and insertion of the prosthetic joint40 within the intervertebral space S (FIG. 2) between the adjacent vertebral bodies V_U, V_L(FIG. 2). The surgical instrument (not shown) is preferably configured to hold thearticular components42,44 at a predetermined orientation and spatial relationship relative to one another during manipulation and insertion of the prosthetic joint40, and to release thearticular components42,44 once properly positioned between the adjacent vertebrae.
• In one embodiment of the disclosure, the[0091]articular component42 includes aprojection56 having a convex shape, which may be configured as a spherical-shaped ball (half of which is shown). It should-be understood that other configurations of theprojection56 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. It should also be understood that the remaining portion ofarticular component42 may take on planar or non-planar configurations, such as, for example, an angular or conical configuration extending about theprojection56.
• A flange member or[0092]keel58 extends from the bearingsurface46 and is configured for disposition within a preformed opening in the adjacent vertebral endplate. As with the bearingsurface46, thekeel58 may be coated with a bone-growth promoting substance, such as, for example, a hydroxyapatite coating formed of calcium phosphate. Additionally, thekeel58 may be roughened prior to being coated with the bone-growth promoting substance to further enhance bone on-growth. In one embodiment, thekeel58 extends along the transverse axis T and is substantially centered along the bearingsurface46. However, it should be understood that other positions and orientations of thekeel58 are also contemplated.
• In one embodiment, the[0093]keel58 transversely extends along a substantial portion of thearticular component42. Such an embodiment would accommodate insertion of the prosthetic joint40 using a lateral approach as opposed to, for example, an anterior approach. In a further embodiment, thekeel58 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel58 may be configured as a winged keel, including a lateral portion (not shown) extending across the main body portion ofkeel58.
• In one embodiment, the[0094]keel58 includes threeopenings60 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebral bodies V_U, V_L(FIG. 2). However, it should be understood that any number ofopenings60 may be defined through thekeel58, including a single opening or two or more openings. It should also be understood that theopenings60 need not necessarily extend entirely through thekeel58, but may alternatively extend partially therethrough. It should further be understood that thekeel58 need not necessarily define anyopenings60 extending either partially or entirely therethrough. Additionally, although theopenings60 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings60 are also contemplated.
• In one embodiment, the[0095]articular component44 includes asupport plate70 having anarticular surface72 and theopposite bearing surface48.Support plate70 may be sized and shaped to substantially correspond to the size and shape of a vertebral endplate of the adjacent vertebral body V_U. Thesupport plate70 may include one ormore notches74 or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument, such as discussed above with reference toarticular component42.
• In one embodiment, the[0096]articular surface72 includes arecess76. In one embodiment, therecess76 has a concave shape, and is configured as a spherical-shaped socket. However, it should be understood that other configurations of therecess76 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. The remaining portion of thearticular surface72 can be angled or otherwise configured to facilitate the insertion and/or use of the prosthesis.
• Although the[0097]concave recess76 is illustrated as having a generally smooth, uninterrupted articular surface, it should be understood that a surface depression or cavity may be defined along a portion of therecess76 to provide a means for clearing out matter, such as particulate debris, that is disposed between the abuttingarticular components42,44. In such case, the convex articular surface of theprojection56 may alternatively define a generally smooth, uninterrupted articular surface. In another embodiment, each of theconvex projection56 and theconcave recess76 may define a surface depression to facilitate removal of particulate matter disposed between the abuttingarticular components42,44.
• A flange member or[0098]keel68, configured similar to thekeel58 ofarticular component42, extends from the bearingsurface48. In one embodiment, thekeel68 extends along the transverse axis T and is offset from the center of the bearingsurface48. Such an embodiment would accommodate insertion of the prosthetic joint40 using a lateral approach. However, it should be understood that other shapes, positions and orientations of thekeel68 are also contemplated. For example, in FIGS. 4band4c, thekeels58 and68 may be angled relative to the transverse axis T to aid in the circumvention of veins, arteries, bony portions, or other obstacles that may be in place during insertion of the prosthetic joint40. Also, thekeel68 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel68 may be configured as a winged keel, including a transverse portion extending across the main body portion of thekeel68.
• In one embodiment, and referring to FIG. 5, the[0099]keel68 also includes threeopenings70 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. However, it should be understood that any number ofopenings70 may be defined throughkeel70, including a single opening or two or more openings. It should also be understood that theopenings70 need not necessarily extend entirely through thekeel68, but may alternatively extend partially therethrough. It should further be understood that thekeel68 need not necessarily define anyopenings70 extending either partially or entirely therethrough. Additionally, although theopenings70 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings70 are also contemplated. As discussed above, the bearing surfaces46,48 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface48 and the surface of thekeel68 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebral body V_U. As also discussed above, the bearingsurface48 and the surface ofkeel68 can be roughened prior to application of the hydroxyapatite coating.
• In some embodiments, one or both of the[0100]keels58,68 may include a sharp forward edge, illustrated byedge68aof FIG. 4. By having such an edge, insertion of the keel into the associated vertebral body is facilitated. Also, theedge68acan be of sufficient sharpness that the adjacent vertebral bodies do not require a slot for receiving thekeel68, discussed in greater detail below.
• Referring to FIG. 7, to accommodate insertion of the offset prosthetic joint[0101]40 within a spondylosed intervertebral space, the partially corrected upper and lower vertebrae V_U, V_Lcan be prepared to accept the prosthetic joint40 (shown in section in FIG. 7a) therebetween. Specifically, elongate openings orslots80,82 may be formed along the vertebral endplates of the upper and lower vertebrae V_L, V_U, respectively, at a predetermined width and to a predetermined depth. Theslots80,82 can be laterally offset from each other to accommodate the displaced vertebrae V_Land/or V_U. In one embodiment, theelongate slots80,82 are rectangular-shaped and extend laterally through the vertebrae V_L, V_U, respectively. In a specific embodiment, theslots80,82 are formed by chiseling or curetting. However, other methods of formingslots80,82 are also contemplated as would occur to one of ordinary skill in the art, such as, for example, by drilling or reaming. Furthermore, for some embodiments of the prosthetic joint40, thekeels58 and/or68 can form their owncorresponding slots80,82, respectively.
• Referring to FIG. 8, in one embodiment, the upper and lower vertebrae V[0102]_U, V_Lmay be fully corrected, and thus, an alternative articulating prosthetic joint90 may be used in correcting spondylolisthesis. The articulating joint90 may be substantially similar to the prosthetic joint40 with the exception of the orientation of various elements of the articulating joint90. For example, to accommodate insertion into fully corrected upper and lower vertebrae V_U, V_L, the articulating joint90 may include a laterally-extendingkeel92 that is substantially centered on an upper articulatingcomponent94 of the articulating joint and a laterally-extendingkeel96 that is substantially centered on a lower articulatingcomponent98. Furthermore, the upper articulatingcomponent94 may include arecess100 that is substantially centered to correspond to a substantially centeredprojection102 extending from the lower articulatingcomponent98. In one embodiment, the upper and lower articulatingcomponents94,98 are substantially flush with one another when disposed between fully corrected upper and lower vertebrae V_U, V_L.
• To accommodate insertion of the offset prosthetic joint[0103]90, the fully corrected upper and lower vertebrae V_U, V_Lcan be prepared to accept the prosthetic joint90 therebetween. Specifically, elongate openings orslots104,106 may be formed along the vertebral endplates of the upper and lower vertebrae V_U, V_L, respectively, at a predetermined width and to a predetermined depth. Theslots104,106 can be substantially aligned with each other to accommodate the fully corrected upper and lower vertebrae V_U, V_L. In one embodiment, theelongate slots104,106 are rectangular-shaped and extend laterally through the vertebrae V_U, V_L, respectively. In a specific embodiment, theslots104,106 are formed by chiseling or curetting. However, other methods of formingslots104,106 are also contemplated as would occur to one of ordinary skill in the art, such as, for example, by drilling or reaming. Furthermore, for some embodiments of the prosthetic joint, thekeels92 and/or96 can form their owncorresponding slots104,106, respectively.
• Referring to FIG. 9, in an alternative embodiment, a slidable prosthetic joint[0104]110 can be used to help with the lateral approach for treating spondylolisthesis. The sliding joint110 extends generally along the longitudinal axis L and includes a firstslidable component112 and a secondslidable component114. Theslidable components112,114 cooperate to form the sliding joint110 which is sized and configured for disposition within an intervertebral space between adjacent vertebral bodies.
• The sliding joint[0105]110 provides movement between the adjacent vertebral bodies to maintain or restore some of the motion similar to the normal bio-mechanical motion provided by a natural intervertebral disc. More specifically, theslidable components112,114 are permitted to translate relative to one another in the axial plane.
• Although the[0106]slidable components112,114 of prosthetic joint110 may be formed from a wide variety of materials, in one embodiment, theslidable components112,114 are formed of a cobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However, in alternative embodiments, theslidable components112,114 may be formed of other materials such as titanium or stainless steel, a polymeric material such as polyethylene, or any other biocompatible material that would be apparent to one of ordinary skill in the art. The surfaces of theslidable components112,114 that are positioned in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance, such as, for example, a hydroxyapatite coating formed of calcium phosphate. Additionally, the surface of theslidable components112,114 that are positioned in direct contact with vertebral bone are preferably roughened prior to being coated with the bone-growth promoting substance to further enhance bone on-growth. Such surface roughening may be accomplished by way of, for example, acid etching, knurling, application of a bead coating, or other methods of roughening that would occur to one of ordinary skill in the art.
• [0107]Slidable component112 includes asupport plate116 having aslidable surface118 and anopposite bearing surface120.Support plate116 is preferably sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. Thesupport plate116 can include one ormore notches122 or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument (not shown) to aid in the manipulation and insertion of the prosthetic joint110 within an intervertebral space between adjacent vertebrae. The surgical instrument (not shown) is preferably configured to hold theslidable components112,114 at a predetermined orientation and spatial relationship relative to one another during manipulation and insertion of the prosthetic joint110, and to release theslidable components112,114 once properly positioned between the adjacent vertebrae.
• A flange member or[0108]keel124 extends from the bearingsurface120 and is configured for disposition within a preformed opening in the adjacent vertebral endplate. In one embodiment, thekeel124 extends perpendicularly from the bearingsurface120 and is approximately centrally located along the bearingsurface120. However, it should be understood that other positions and orientations of thekeel124 ate also contemplated.
• In one embodiment, the[0109]keel124 transversely extends along a substantial portion of thesupport plate114. Such an embodiment would accommodate insertion of the prosthetic joint110 using a lateral approach. In a further embodiment, thekeel124 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel124 may be configured as a winged keel, including a transverse portion extending across the main body portion ofkeel124.
• The[0110]keel124 also includesopenings126 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. However, it should be understood that any number ofopenings126 may be defined throughkeel124, including a single opening or three or more openings. It should also be understood that theopenings104 need not necessarily extend entirely through thekeel124, but may alternatively extend partially therethrough. It should further be understood that thekeel124 need not necessarily define anyopenings126 extending either partially or entirely therethrough. Additionally, although theopenings126 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings126 are also contemplated. As discussed above, the surfaces of theslidable component112 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface120 and the surfaces of thekeel124 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface120 and the surfaces ofkeel124 can be roughened prior to application of the hydroxyapatite coating.
• In one embodiment, the[0111]slidable component114 includes asupport plate128 having aslidable surface130 and anopposite bearing surface132.Support plate128 is preferably sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. Thesupport plate128 can include one ormore notches134 or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument, such as discussed above with reference toslidable element112.
• A flange member or[0112]keel136, configured similar to thekeel124 ofslidable component112, extends from the bearingsurface132. In one embodiment, thekeel136 extends perpendicularly from the bearingsurface132 and is offset along the bearingsurface132 to accommodate spondylosed displacements of the vertebrae. Also, the offset position of thekeel136 helps in the circumvention of veins, arteries, bony portions, or other obstacles that may be in place during the insertion of the joint110. It should be further understood that other positions, shapes, orientations, and quantities of thekeel136 are also contemplated. It should also be understood that thekeel136 may also be differently positioned, shaped or oriented, ormore keels136 can be used, for similar or additional reasons.
• In one embodiment, the[0113]keel136 transversely extends along a substantial portion of thesupport plate128. Such an embodiment would accommodate insertion of the prosthetic joint110 using a lateral approach as opposed to another approach such as an anterior approach. In a further embodiment, thekeel136 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel136 may be configured as a winged keel, including a transverse portion extending across the main body portion ofkeel136.
• The[0114]keel136 also includes threeopenings138 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. However, it should be understood that any number ofopenings138 may be defined throughkeel136, including a single opening or three or more openings. It should also be understood that theopenings138 need not necessarily extend entirely through thekeel136, but may alternatively extend partially therethrough. It should further be understood that thekeel136 need not necessarily define anyopenings138 extending either partially or entirely therethrough. Additionally, although theopenings138 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings138 are also contemplated. As discussed above, the surfaces of theslidable component114 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface132 and the surfaces of thekeel136 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface132 and the surfaces ofkeel136 can be roughened prior to application of the hydroxyapatite coating.
• In some embodiments, one or both of the[0115]keels124,136 may include a sharp forward edge, illustrated byedges124a,136a. By having such an edge, insertion of thekeels124,136 into the associated vertebral body is facilitated. Also, theedges124a,136acan be of sufficient sharpness that the vertebral body does not require a slot for receiving thekeels124,136, respectively, discussed in greater detail below.
• Referring to FIG. 10, to accommodate insertion of the prosthetic joint[0116]110 within a spondylosed intervertebral space, the lower and upper vertebrae V_L, V_Ucan be prepared to accept the prosthetic joint110 therebetween. Specifically, elongate openings orslots142,144, may be formed along the vertebral endplates of the lower and upper vertebrae V_L, V_U, respectively, at a predetermined width and to a predetermined depth. Theslots142,144 can be laterally offset from each other to accommodate the displaced vertebrae V_Land/or V_U. In one embodiment of the disclosure, theelongate slots142,144 are rectangular-shaped and extend laterally through the vertebrae V_L, V_U. In a specific embodiment, theslots142,144 are formed by chiseling or curetting. However, other methods of formingslots142,144 are also contemplated as would occur to one of ordinary skill in the art, such as, for example, by drilling or reaming. Furthermore, for some embodiments of the prosthetic joint, thekeels124 and/or136 can form their own corresponding slots.
• Referring to FIG. 11, in one embodiment, the upper and lower vertebrae V[0117]_U, V_Lmay be fully corrected, and thus, an alternative articulating joint150 may be used in correcting spondylolisthesis. The articulating joint150 may be substantially similar to the articulating joint110 with the exception of the orientation of the keel. For example, to accommodate insertion into fully corrected upper and lower vertebrae V_U, V_L, the articulating joint150 may include akeel152 that is substantially centered on an upper articulatingcomponent154 of the articulating joint and akeel156 that is substantially centered on a lower articulatingcomponent158. In one embodiment, the upper and lower articulatingcomponents154,158 are substantially flush with one another when disposed between fully corrected upper and lower vertebrae V_U, V_L.
• To accommodate insertion of the offset prosthetic joint[0118]150, the fully corrected upper and lower vertebrae V_U, V_Lcan be prepared to accept the prosthetic joint150 therebetween. Specifically, elongate openings orslots160,162 are formed along the vertebral endplates of the upper and lower vertebrae V_U, V_L, at a predetermined width and to a predetermined depth. Theslots160,162 can be substantially aligned with each other to accommodate the fully corrected upper and lower vertebrae V_U, V_L. In one embodiment, theelongate slots160,162 are rectangular-shaped and extend laterally through the vertebrae V_U, V_L, respectively. In a specific embodiment, theslots160,162 are formed by chiseling or curetting. However, other methods of formingslots160,162 are also contemplated as would occur to one of ordinary skill in the art, such as, for example, by drilling or reaming. Furthermore, for some embodiments of the prosthetic joint, thekeels152 and/or156 can form their owncorresponding slots160,162, respectively.
• Referring to FIGS. 12 and 13, fusion plates and cages can also be outfitted with one or more keels and laterally inserted, in a manner consistent with the motion-preserving embodiments discussed above and superior to conventional fusion arrangements. Referring specifically to FIG. 12, a[0119]lateral prosthesis170 includes acage172, anupper keel174, and alower keel176. Thecage172 connects to the upper andlower keels174,176 throughsupport plates178,180, respectively. Thecage172 can include many features of the LT-CAGE™ lumbar tapered fusion device provided by Medtronic Sofamor Danek of Memphis, Tenn., and can be used to contain biological material and/or other bone growth promoting materials. Also, the lateral keels174,176 can help to maintain the corrected vertebrae displacement while fusion is occurring.
• Referring to FIG. 13, a[0120]prosthesis190 includes aplate192, anupper keel194, alower keel196, anupper support plate198, and alower support plate200. Theplate192 can be used to maintain a desired distance between the twosupport plates198,200 and promote fusion. Since theplate192 can be relatively thin, the remainder of the disc space can be filled with biological material, bone material, and or other bone growth promoting materials.
• II. Anterior Correction[0121]
• In some instances, correction of spondylolisthesis may be desirable from the anterior approach. Referring to FIGS.[0122]14-16, shown therein is an intervertebral articulating prosthetic joint210 according to an alternative embodiment of the present disclosure. The prosthetic joint210 extends generally along a longitudinal axis L and includes a firstarticular component212 and a secondarticular component214. Thearticular components212,214 cooperate to form the articulating joint210 which is sized and configured for disposition within an intervertebral space between a pair of vertebral bodies, such as the intervertebral space S between the adjacent vertebral bodies V_U, V_L.
• The prosthetic joint[0123]210 provides relative pivotal and rotational movement between the adjacent vertebral bodies V_U, V_Lto maintain or restore motion substantially similar to the normal bio-mechanical motion provided by a natural intervertebral disc. More specifically, thearticular components212,214 are permitted to pivot relative to one another about a number of axes, including lateral or side-to-side pivotal movement about longitudinal axis L and anterior-posterior pivotal movement about a transverse axis T. It should be understood that in one embodiment, thearticular components212,214 are permitted to pivot relative to one another about any axes that lies in a plane that intersects longitudinal axis L and transverse axis T. Additionally, thearticular components212,214 are permitted to rotate relative to one another about a rotational axis R. Although the prosthetic joint210 has been illustrated and described as providing a specific combination of articulating motion, it should be understood that other combinations of articulating movement are also possible, such as, for example, relative translational or linear motion, and are contemplated as falling within the scope of the present disclosure.
• Although the[0124]articular components212,214 of prosthetic joint210 may be formed from a wide variety of materials, in one embodiment, thearticular components212,214 are formed of a cobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However, in alternative embodiments, thearticular components212,214 may be formed of other materials such as titanium or stainless steel, a polymeric material such as polyethylene, or any other biocompatible material that would be apparent to one of ordinary skill in the art. The surfaces of thearticular components212,214 that are positioned in direct contact with vertebral bone may be coated with a bone-growth promoting substance, such as, for example, a hydroxyapatite coating formed of calcium phosphate. Additionally, the surface of thearticular components212,214 that are positioned in direct contact with vertebral bone may be roughened prior to being coated with the bone-growth promoting substance to further enhance bone on-growth. Such surface roughening may be accomplished by way of, for example, acid etching, knurling, application of a bead coating, or other methods of roughening that would occur to one of ordinary skill in the art.
• [0125]Articular component212 includes asupport plate216 having anarticular surface218 and anopposite bearing surface220.Support plate216 may be sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. Thesupport plate216 can include one ormore notches222 or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument (not shown) to aid in the manipulation and insertion of the articulating joint210 within an intervertebral space between adjacent vertebrae. The surgical instrument (not shown) is preferably configured to hold thearticular components212,214 at a predetermined orientation and spatial relationship relative to one another during manipulation and insertion of the articulating joint210, and to release thearticular components212,214 once properly positioned between the adjacent vertebrae.
• In one embodiment, the[0126]articular surface218 includes aprojection224 having a convex shape, which may be configured as a spherical-shaped ball (half of which is shown). It should be understood that other configurations of theprojection224 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. It should also be understood that the remaining portion ofarticular surface218 may take on planar or non-planar configurations, such as, for example, an angular or conical configuration extending about theprojection224.
• In one embodiment, the convex articular surface of the[0127]projection224 is interrupted by a surface depression orcavity226 extending along theprojection224. In one embodiment, thesurface depression226 is configured as a groove. However, it should be understood that other types of surface depressions are also contemplated, including no depression at all. One purpose of thegroove226 is to facilitate the removal of matter disposed between abutting portions of thearticular components212,214. More specifically, thegroove226 may aid in clearing out matter such as, for example, particulate material, that is disposed between the abutting articular surfaces ofcomponents212,214.
• A flange member or[0128]keel230 extends from the bearingsurface220 and is configured for disposition within a preformed opening in the adjacent vertebral endplate. In one embodiment, thekeel230 extends perpendicularly from the bearingsurface220 and is approximately centrally located along the bearingsurface220. However, it should be understood that other positions and orientations of thekeel230 are also contemplated.
• In one embodiment, the[0129]keel230 extends along substantially the entire length of thesupport plate216. Such an embodiment would accommodate insertion of the articulating joint210 using an anterior approach. In a further embodiment, thekeel230 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel230 may be configured as a winged keel, including a transverse portion (not shown) extending across the main body portion ofkeel230.
• The[0130]keel230 also includes a pair ofopenings232 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. However, it should be understood that any number ofopenings232 may be defined throughkeel230, including a single opening or three or more openings. It should also be understood that theopenings232 need not necessarily extend entirely through thekeel230, but may alternatively extend partially therethrough. It should further be understood that thekeel230 need not necessarily define anyopenings232 extending either partially or entirely therethrough. Additionally, although theopenings232 are illustrated as having a circular configuration, it should be understood that other sizes and configurations of theopenings232 are also contemplated. As discussed above, the surfaces of thearticular component212 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface220 and the surfaces of thekeel230 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface220 and the surfaces ofkeel230 can be roughened prior to application of the hydroxyapatite coating.
• In one embodiment, the[0131]articular component214 includes asupport plate240 having anarticular surface242 and anopposite bearing surface244.Support plate240 may be sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. Thesupport plate240 can include one ormore notches246 or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument, such as discussed above with reference toarticular component212.
• In one embodiment, the[0132]articular surface242 includes arecess250, which has a convex shape, such as that of a spherical-shaped socket. However, it should be understood that other configurations of therecess250 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. The remaining portion of thearticular surface242 can be angled or otherwise configured to facilitate the insertion and/or use of the articulating joint210.
• Although the[0133]concave recess250 is illustrated as having a generally smooth, uninterrupted articular surface, it should be understood that a surface depression or cavity may be defined along a portion of therecess250 to aid in clearing out matter, such as particulate debris, that is disposed between the abutting articular surfaces ofarticular components212,214. In such case, the convex articular surface of theball224 may alternatively define a generally smooth, uninterrupted articular surface. In another embodiment, each of theconvex projection224 and theconcave recess250 may define a surface depression to facilitate removal of particulate matter disposed between the abutting articular surfaces.
• A flange member or[0134]keel260, configured similar to thekeel230 ofarticular component212, extends from the bearingsurface244. In one embodiment, thekeel260 extends perpendicularly from the bearingsurface244 and is approximately centrally located along bearingsurface244. However, it should be understood that other positions and orientations of thekeel260 are also contemplated. It should also be understood that thearticular component214 may include two ormore keels260 extending from the bearingsurface244.
• In one embodiment, the[0135]keel260 extends along substantially the entire length of thesupport plate240. Such an embodiment would accommodate insertion of the prosthetic joint210 using an anterior approach. In a further embodiment, thekeel260 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel260 may be configured as a winged keel, including a transverse portion (not shown) extending across the main body portion ofkeel260.
• The[0136]keel260 also includes a pair ofopenings262 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. However, it should be understood that any number ofopenings262 may be defined throughkeel260, including a single opening or three or more openings. It should also be understood that theopenings262 need not necessarily extend entirely through thekeel260, but may alternatively extend partially therethrough. It should further be understood that thekeel260 need not necessarily define anyopenings262 extending either partially or entirely therethrough. Additionally, although theopenings262 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings262 are also contemplated. As discussed above, the surfaces of thearticular component214 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface244 and the surfaces of thekeel260 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface244 and the surfaces ofkeel260 can be roughened prior to application of the hydroxyapatite coating.
• In some embodiments, one or both of the[0137]keels230,260 may include a sharp forward edge, illustrated byedge260aof FIG. 14. By having such an edge, insertion of the keel into the associated vertebral body is facilitated. Also, theedge260acan be of sufficient sharpness that the vertebral body does not require a slot for receiving thekeel260, discussed in greater detail below.
• To work with dislocated vertebrae, such as vertebrae V[0138]1-V5 of FIG. 1 associated with spondylolisthesis, it is recognized that the task of fully correcting and aligning a spondylosed segment may not be achievable or desirable by the surgeon. Therefore, the basic articulation described in co-pending and presently incorporated U.S. Ser. No. 10/042,589 now has an associated displacement to correspond to the vertebrae displacement. That is, for the amount of displacement between two adjacent spondylosed vertebrae, the articulation of the prosthetic joint210 is made to correspond thereto. In some embodiments, such displacement can be effected by positioning one or more of theprojection224 in an offset position on thearticular surface218 of thearticular component212, and positioning one or more of therecess250 in an offset position on thearticular surface242 of thearticular component214. This allows an uncorrected or partially corrected displacement to be mobilized.
• More particularly, and referring to FIGS. 14 and 17, the[0139]projection224 is offset relative to thearticular surface218. For example, when the lower vertebra (V_Lof FIG. 17) is offset in the posterior direction (illustrated by arrow P in FIG. 17), thearticular component212 may be configured such that theprojection224 is offset in the anterior direction relative to thearticular surface218. Continuing this example, the upper vertebra V_Uis therefore offset from the lower vertebra V_Lin the anterior direction (illustrated by arrow A in FIG. 17), and thus, thearticular component214 may be configured such that therecess250 is offset in the posterior direction relative to thearticular surface242. In this manner, thearticular components212,214 can be configured to engage one another via theprojection224 and therecess250, yet be offset from one another to accommodate the spondylosed relationship of the upper and lower vertebrae V_U, V_Lof FIG. 17.
• Referring now to FIG. 16, in another embodiment, the articulating joint[0140]210 may be modified such that thesupport plate216 includes anextended section270 to accommodate a more pronounced displacement relative to FIG. 17 (illustrated by arrow272) and/or provide additional stability against subluxation. Theprojection224 may be positioned on theextended section270 to provide for the more pronounced displacement betweenarticular components212,214.
• Referring to FIGS. 2 and 17, to accommodate insertion of the prosthetic joint[0141]210 within the intervertebral space S, the upper and lower vertebrae V_U, V_Lcan be prepared to accept the prosthetic joint210 therebetween. Specifically, elongate openings orslots280,282 are formed along the vertebral endplates of the upper and lower vertebrae V_U, V_L, respectively, at a predetermined width and to a predetermined depth. In one embodiment, theelongate slots280,282 are rectangular-shaped and extend from ananterior side284 of the vertebrae V_U, V_Ltoward a posterior side. In a specific embodiment, theslots280,282 are formed by chiseling or curetting. However, other methods of forming theslots280,282 are also contemplated as would occur to one of ordinary skill in the art, such as, for example, by drilling or reaming. Furthermore, for some embodiments of the prosthetic joint210, thekeels230 and/or260 can form their owncorresponding slots280,282, respectively. The preparation and example sizes of theslots280,282 are described in further detail in co-pending and presently incorporated U.S. Ser. No. 10/042,589.
• Referring now to FIGS.[0142]18-20, in other embodiments, one or both of thearticular components212,214 may include different numbers of keels and/or modified keels. Referring specifically to FIG. 18, two keels, designated290 and292, extend from the bearingsurface244 and are configured for disposition within preformed openings in the adjacent vertebral endplate. In one embodiment, bothkeels290,292 extend perpendicularly from the bearingsurface244 and are parallel and equally spaced along a central portion of the bearingsurface244.
• Referring specifically to FIG. 19, two keels, designated[0143]294 and296, extend from the bearingsurface224 and are configured for disposition within preformed openings in the adjacent vertebral endplate. In one embodiment, bothkeels294,296 extend perpendicularly from the bearingsurface224 and are parallel and equally spaced along a central portion of the bearingsurface224. It should be understood that other positions and orientations of thekeels290,292,294, and296 are also contemplated.
• Referring specifically to FIG. 20, a[0144]keel298 extends from the bearingsurface244 similar to thekeel260 of FIG. 14, except that thekeel298 includes a laterally-extending or “winged”portion300 opposing the bearingsurface244. Thewinged portion300 can provide several functions, including maintaining the bearingsurface244 tightly against the body V_U, and substantially preventing any longitudinal movement of thearticular component214. Similarly, akeel302 extends from the bearingsurface224 and includes awinged portion304 opposing the bearingsurface224. Thewinged portion304 can provide several functions, including maintaining the bearingsurface224 tightly against the body V_L, and substantially preventing any longitudinal movement of thearticular component212.
• Referring to FIGS.[0145]21-23, to accommodate insertion of the above-described alternativeprosthetic joints210 within the intervertebral space S, the upper and lower vertebrae V_U, V_Lcan be prepared to accept each of the articulatingjoints210 therebetween. Referring specifically to FIG. 21, for the configuration of theprosthetic joint210 of FIG. 18,multiple slots310 and312 are formed along the vertebral endplate of the upper vertebrae V_U, and asingle slot314 is formed along the vertebral endplate of the lower vertebrae V_L. Referring specifically to FIG. 22, for the configuration of theprosthetic joint210 of FIG. 19,multiple slots316,318 and320,322 are formed along the vertebral endplates of the upper vertebrae V_U, and lower vertebrae V_L, respectively. Referring specifically to FIG. 23, for the configuration of theprosthetic joint210 of FIG. 20,winged slots324,326 are formed along the vertebral endplates of the upper vertebrae V_Uand the lower vertebrae V_L, respectively. The preparation of theslots310,312,314,316,318,320,322,324,326 can be accomplished in a similar manner to those discussed above with respect to FIG. 17. For thewinged slots324,326, a standard chisel can be used, or alternatively, a unique wing-shaped chisel can be used.
• Referring to FIG. 24, in addition to the prosthetic joint[0146]210, a wovenorthopedic implant330 can be used to act as an artificial ligament between the two vertebrae V_U, V_L. One embodiment of thewoven implant330 is disclosed in U.S. Ser. No. 10/082,579, which is incorporated by reference. Theimplant330 functions as a natural ligament would function, and helps to stabilize and further secure the two vertebrae V_U, V_Ltogether, and helps to discourage further displacement (or prevent the displacement from returning to the way it was pre-surgery).
• Referring to FIGS. 25 and 26, it is contemplated that a pars fracture, such as is illustrated by a fracture in a[0147]bony element332 that connects a posterior element, such as anarticular process334 to the vertebra V_L, may also be treated during correction of spondylolisthesis from the anterior approach. It is understood that the fracturedbony element332 is exaggerated in the FIG. 25 for the sake of improved clarity. The pars fracture can be repaired by driving alag screw336 having a threadedportion336aand anon-threaded portion336binto anopening338 in the vertebral body V_L, through thebony element332, and into thearticular process334. In some embodiments, all or part of theopening338 can be pre-drilled with a drill or chisel (not shown). Thelag screw336 is inserted and accessed through the anterior direction, and multiple screws can be used to repair multiple processes. By capturing the fractured posterior element and tightening thelag screw336, the vertebrae V_Lis repaired.
• III. Transforaminal Prosthetic Joint[0148]
• In some instances, it is often difficult to approach and clear[0149]4 defective intervertebral disc space due to potential damage to important anatomical structures such as nerve roots, dura, ligamentum flavum and interspinous ligament. For example, preservation of the ligamentous structures is of great importance to restore biomechanical stability of the, segment and its adjacent counterparts. In these situations, a transforaminal approach may allow clearance of the entire intervertebral disc space by opening the neuroforamen on one side. After appropriate clearance, it is possible to achieve further enlargement of the cleared intervertebral compartment by posterior trans-pedicle distraction. While this approach has been used for fusion techniques, such as Transforaminal Lumbar Interbody Fusion, or TLIF, it has not heretofore been used with motion preserving implants.
• Referring to FIG. 27, in a transforaminal approach, the disc V is approached as shown by the[0150]arrow400. The approach is between a posterior approach and a lateral approach, and in some cases, only one side of the disc needs to be exposed (right or left) in order to perform the procedure.
• Referring to FIGS.[0151]28-30, shown therein is an intervertebral articulating prosthetic joint410 according to another form of the present disclosure. The articulating joint410 extends generally along a longitudinal axis L and includes a firstarticular component412 and a secondarticular component414. Thearticular components412,414 cooperate to form the articulating joint410 which is sized and configured for disposition within an intervertebral space between adjacent vertebral bodies.
• The prosthetic joint[0152]410 provides relative pivotal and rotational movement between the adjacent vertebral bodies to maintain or restore motion substantially similar to the normal bio-mechanical motion provided by a natural intervertebral disc. More specifically, thearticular components412,414 are permitted to pivot relative to one another about a number of axes, including lateral or side-to-side pivotal movement about longitudinal axis L and anterior-posterior pivotal movement about a transverse axis T. It should be understood that in one embodiment, thearticular components412,414 are permitted to pivot relative to one another about any axes that lies in a plane that intersects longitudinal axis L and transverse axis T. Additionally, thearticular components412,414 are preferably permitted to rotate relative to one another about a rotational axis R. Although the articulating joint410 has been illustrated and described as providing a specific combination of articulating motion, it should be understood that other combinations of articulating movement are also possible and are contemplated as falling within the scope of the present disclosure. It should also be understood that other types of articulating movement are also contemplated, such as, for example, relative translational or linear motion.
• Although the[0153]articular components412,414 of prosthetic joint410 may be formed from a wide variety of materials, in one embodiment, thearticular components412,414 are formed of a cobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However, in alternative embodiments, thearticular components412,414 may be formed of other materials such as titanium or stainless steel, a polymeric material such as polyethylene, or any other biocompatible material that would be apparent to one of ordinary skill in the art.
• The surfaces of the[0154]articular components412,414 that are positioned in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance, such as, for example, a hydroxyapatite coating formed of calcium phosphate. Additionally, the surface of thearticular components412,414 that are positioned in direct contact with vertebral bone are preferably roughened prior to being coated with the bone-growth promoting substance to further enhance bone on-growth. Such surface roughening may be accomplished by way of, for example, acid etching, knurling, application of a bead coating, or other methods of roughening that would occur to one of ordinary skill in the art.
• [0155]Articular component412 includes asupport plate416 having anarticular surface418 and anopposite bearing surface420.Support plate416 may be sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. In one embodiment, thesupport plate416 is shaped to facilitate a transforaminal insertion approach. As such, thesupport plate416 includescurved side portions422a,422b, which are defined as the generally elongated portions of thesupport plate416 extending betweenarticular surface418 and thebearing surface420. Although not shown, thesupport plate416 can include one or more notches or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument (also not shown) to aid in the manipulation and insertion of the prosthetic joint410 within an intervertebral space between adjacent vertebrae. The surgical instrument (not shown) is preferably configured to hold thearticular components412,414 at a predetermined orientation and spatial relationship relative to one another during manipulation and insertion of the prosthetic joint410, and to release thearticular components412,414 once properly positioned between the adjacent vertebrae.
• In one embodiment, the[0156]articular surface418 includes aprojection424 having a convex shape, which may be configured as a spherical-shaped ball (half of which is shown). It should be understood that other configurations of theprojection424 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. It should also be understood that the remaining portion ofarticular surface418 may take on planar or non-planar configurations, such as, for example, an angular or conical configuration extending about theprojection424.
• A flange member or[0157]keel426 extends from the bearingsurface410 and is configured for disposition within a preformed opening in the adjacent vertebral endplate. In one embodiment, thekeel426 extends perpendicularly from the bearingsurface420 and is approximately centrally located along the bearingsurface420. However, it should be understood that other positions and orientations of thekeel426 are also contemplated.
• In one embodiment, the[0158]keel426 transversely extends along a substantial portion of thesupport plate416. Thekeel426 is curved, generally in a direction similar to thearrow400 of FIG. 27. The degree of curvature of thekeel426 may be substantially similar to and congruous with the degree of curvature of theside portions422a,422b. Such an embodiment would accommodate insertion of the prosthetic joint410 using a transforaminal approach as opposed to the anterior or lateral approaches discussed above. In a further embodiment, thekeel426 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel426 may be configured as a winged keel, including a transverse portion (not shown) extending across the main body portion ofkeel426.
• The[0159]keel426 also includes threeopenings428 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. However, it should be understood that any number ofopenings428 may be defined throughkeel426, including a single opening or three or more openings. It should also be understood that theopenings428 need not necessarily extend entirely through thekeel426, but may alternatively extend partially therethrough. It should further be understood that thekeel426 need not necessarily define anyopenings428 extending either partially or entirely therethrough. Additionally, although theopenings428 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings428 are also contemplated. As discussed above, the surfaces of thearticular component412 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface420 and the surfaces of thekeel426 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface420 and the surfaces ofkeel426 can be roughened prior to application of the hydroxyapatite coating.
• In one embodiment, the[0160]articular component414 includes asupport plate430 having anarticular surface432 and anopposite bearing surface434.Support plate430 may be sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. In one embodiment, thesupport plate430 is shaped to facilitate a transforaminal insertion approach. As such, thesupport plate416 includescurved side portions436a,436b, which are defined as the generally elongated portions of thesupport plate430 extending betweenarticular surface432 and thebearing surface434. Although not shown, thesupport plate430 can include one or more notches or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument, such as discussed above with reference toarticular element412.
• In one embodiment, the[0161]articular surface432 includes arecess440 having a concave shape, which may be configured as a spherical-shaped socket. However, it should be understood that other configurations of therecess440 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. The remaining portion of thearticular surface432 can be angled or otherwise configured to facilitate the insertion and/or use of the prosthesis.
• Although the[0162]concave recess440 is illustrated as having a generally smooth, uninterrupted articular surface, it should be understood that a surface depression or cavity may be defined along a portion of therecess440 to provide a means for clearing out matter, such as particulate debris, that is disposed between the abutting articular surfaces ofcomponents412,414. In such case, the convex articular surface of theball424 may alternatively define a generally smooth, uninterrupted articular surface. In another embodiment, each of theconvex projection424 and theconcave recess440 may define a surface depression to facilitate removal of particulate matter disposed between the abutting articular surfaces.
• A flange member or[0163]keel450, configured similar to thekeel426 ofarticular component412, extends from the bearingsurface434. In one embodiment, thekeel450 can be centrally located, and is positioned directly or parallel in-line with thekeel450. Thekeel450 is curved, in a direction similar to thekeel426 and thearrow400 of FIG. 27. The degree of curvature of thekeel450 may be substantially similar to and congruous with the degree of curvature of theside portions436a,436b. Such an embodiment would accommodate insertion of the prosthetic joint410 using a transforaminal approach as opposed to the anterior or lateral approaches discussed above. In some embodiments, the position of thekeel450 can be offset to help circumvent veins, arteries, bony portions, or other obstacles that may be in place during the insertion of the joint410.
• It should also be understood that the[0164]keel450 may also be differently positioned, shaped or oriented, ormore keels450 can be used, for similar or additional reasons. Also, thekeel450 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel450 may be configured as a winged keel, including a transverse portion (not shown) extending across the main body portion ofkeel450.
• In one embodiment, the[0165]keel450 also includes threeopenings452 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. However, it should be understood that any number ofopenings452 may be defined throughkeel450, including a single opening or three or more openings. It should also be understood that theopenings452 need not necessarily extend entirely through thekeel450, but may alternatively extend partially therethrough. It should further be understood that thekeel450 need not necessarily define anyopenings452 extending either partially or entirely therethrough. Additionally, although theopenings452 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings452 are also contemplated. As discussed above, the surfaces of thearticular component414 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface434 and the surfaces of thekeel450 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface434 and the surfaces ofkeel450 can be roughened prior to application of the hydroxyapatite coating.
• In some embodiments, one or both of the[0166]keels426,450 may include a sharp forward edge, illustrated byedges460,462, respectively, of FIG. 28c. By having such an edge, insertion of the keel into the associated vertebral body is facilitated. Also, theedges460,462 can be of sufficient sharpness that the vertebral bodies do not require a slot for receiving thekeels426,450, discussed in greater detail below.
• Referring to FIGS. 31[0167]aand31b, to accommodate insertion of the prosthetic joint410 within the intervertebral space, the upper and lower vertebrae V_U, V_Lcan be prepared to accept the prosthetic joint410 therebetween. Referring specifically to FIG. 31a, for the configuration of theprosthetic joint410 of FIGS.28-30,multiple slots470,472 are formed along the vertebral endplates of the upper vertebrae V_Uand the lower vertebrae V_L. Theslots470,472 can be created by thekeels426,450 themselves, or can be prepared beforehand.
• Referring also to FIG. 32, it may be desirable to prepare one or more of the[0168]slots470,472 before the prosthetic joint410 is inserted between the upper and lower vertebrae V_U, V_L. Theslots470,472 can be curved, as illustrated by theslot472, in accordance with thecurved keels426,450, to facilitate the movement of the prosthetic joint410 during insertion.
• Referring to FIGS.[0169]33-35, as an alternative to chiseling, which provides only for the cutting of straight slots, amilling guide500 may be used in conjunction with amilling tool502 to cut thecurved slots470,472 (represented by472 in FIG. 32) in the upper and lower vertebral bone V_U, V_L. The millingguide500 andmilling tool502 may be formed of any material including biocompatible materials such as titanium. The millingguide500 includes an elongatedcurved member503, which defines acurved opening504 to correspond to the shape of the desired curve for theslots470,472. Of course, the degree of curvature of themilling guide500, and therefore thecurved opening504, may vary depending on the desired curve of theslots470,472. In one embodiment, the millingguide500 is formed of a pliable material that retains a rigid shape upon reforming such that the degree of curvature of thecurved opening504 may be altered without having to swap out milling guides. The millingguide500, and therefore thecurved opening504, is also of sufficient length so that if theslots470,472 need to be continued through any posterior elements of the vertebrae, such extension of the slots can be accomplished at the same time.
• Referring specifically to FIGS. 34[0170]aand34b, in one embodiment, themilling tool502 includes amilling bit510 that is positioned to be rotated and translated in thecurved opening504. In one embodiment, themilling bit510 is a double fluted routing bit, that may extend simultaneously into the upper and lower vertebrae V_U, V_L.
• The[0171]milling bit510 is also adapted to receive a translational force such that the milling bit can be moved back and forth in thecurved opening504. Referring to FIG. 34b, in one embodiment, a milling bit handle530 is connected in any conventional manner to a housing522 (a portion of which is shown). Thehandle530 extends from thehousing522 and through aslot532 formed in aproximal end534 of themilling guide500 relative to a surgeon (not depicted). As such, thehandle530 can be translated by a surgeon, thereby translating themilling bit510 through thecurved opening504. In this manner, thehandle530 is adapted to impart translational movement to themilling bit510. To accommodate movement of themilling bit510 within thecurved opening504, a pair of bearingassemblies512,514 may be positioned adjacent to thehousing522 to guide themilling bit510 along the curved opening.
• The[0172]housing522 houses a rotation assembly, which, in one embodiment, is a gear assembly524. The gear assembly524 includes adrive gear526 connected to and extending annularly around arotatable shaft528. Theshaft528 is rotatable via an external source represented by power supply516 (FIG. 35). In one embodiment, theshaft528 is housed within thehandle530.
• The gear assembly[0173]524 further includes abit gear531, which is connected to and extends annularly around themilling bit510. Thebit gear531 is positioned on themilling bit510 such that the bit gear is orthogonal relative to and in contact with thedrive gear526. Thus, rotation of theshaft528 imparts rotation to themilling bit510 via the gear assembly524. A pair ofannular shoulders535,536 are also connected to themilling bit510 such that the milling bit can easily move back and forth through thecurved opening504 without slippage in the upper or lower directions as viewed in FIG. 34b. It is understood that the gear assembly524 is merely exemplary of an assembly that may be used to impart rotational motion to themilling bit510. Other types of rotation-imparting assemblies are contemplated as falling within the present disclosure such as pneumatic-type systems.
• Referring to FIG. 34[0174]c, in one such embodiment, apneumatic system538 may be employed to impart rotation to themilling bit510. In one embodiment, a Medtronic Midas Rex® Legend™ motor is used to supply power (represented by P) to the pneumatic system. Aconventional valve539 is used to control the air flow and pressure supplied to rotate themilling bit510. In still other embodiments, manual or combination power supplies are contemplated as being the preferred power supply516 (FIG. 34b) and P (FIG. 34c).
• Referring again to FIGS. 34[0175]aand34b, aguide handle540 is further provided such that the millingguide500 is independently movable relative to themilling bit510. Thus in one embodiment, the millingguide500 can be held via the guide handle540 with one hand while themilling bit510 may be moved within thecurved opening504 via thehandle530 with the other hand. In some embodiments, thehandle530 may extend through the guide handle540 as shown in FIG. 34b. As a result, and referring to FIG. 35, themilling bit510 is adapted to rotate in a direction indicated by arrow R1, and is adapted to be translated through thecurved opening504 in the directions indicated by arrow R2.
• In operation, the milling[0176]guide500 and themilling tool502 can be used to cut a slot, such as theslot472, to prepare the vertebral body V_Lto receive the lower portion of the prosthetic joint410. The surgeon first selects the desired amount of curvature to impart to theslot472 and selects or configures thecorresponding milling guide500. The surgeon then approaches the vertebral body V_Lfrom the transforaminal approach to position the millingguide500 into the disc space between the upper and lower vertebrae V_U, V_Land to abut themilling bit510 against the upper and lower vertebrae V_U, V_L. Upon proper positioning, the surgeon may then actuate themilling tool502 via thepower supply516 to begin cutting into the upper and lower vertebrae V_U, V_Lwith themilling bit510.
• The[0177]milling guide500 may be held by the surgeon or via an external instrument such that the milling guide is stationary during translational movement of themilling bit510 through the milling guide. The curvature of themilling guide500 guides themilling bit510 transforaminally through the upper and lower vertebrae V_U, V_Lto cut a transforaminal slot, such as theslot472 depicted in the lower vertebra V_LFIG. 32, to prepare the upper and lower vertebrae to receive the transforaminal prosthetic joint410.
• In an alternative embodiment, the keels of the prosthetic joint[0178]410 may take alternative shapes and configurations to assist in the curved, transforaminal approach used in inserting the joint. Referring to FIGS.36-38, the keels, designated550 and560, extend from the bearing surfaces434 and420, respectively. Thekeels550,560 are relatively short and thus extend along a short portion of the bearing surfaces434,420, respectively, in comparison to thekeels450,426 of FIGS.28-30. The relative shortness of thekeels550,560 may aid such keels in following theopenings470,472, respectively. In addition, the shortness of thekeels550,560 and the ease with which such keels follow theopenings470,472, respectively, allows the keels to be configured as either straight or curved keels, which increases the design options of the prosthetic joint410. Thekeels550,560 may also be tapered to assist in insertion of the keels into the upper and lower vertebrae V_U, V_L.
• IV. Anterior-Oblique Prosthetic Joint[0179]
• Another approach that can be used to avoid potential damage to important anatomical structures such as nerve roots, dura, ligamentum flavum and interspinous ligament is the anterior oblique approach. For example, the straight anterior approach to the disc space between vertebra L[0180]4 and L5, as well as the superior disc levels, can present high surgical risks during the insertion of a total disc replacement implant because of the attachment of the major vessels to the anterior aspect of the spine.
• Referring to FIGS.[0181]39-41, shown therein is an intervertebral articulating prosthetic joint600 according to another form of the present disclosure. The prosthetic joint600 extends generally along a longitudinal axis L and includes a firstarticular component602 and a secondarticular component604. Thearticular components602,604 cooperate to form the prosthetic joint600 which is sized and configured for disposition within an intervertebral space between adjacent vertebral bodies.
• The prosthetic joint[0182]600 provides relative pivotal and rotational movement between the adjacent vertebral bodies to maintain or restore motion substantially similar to the normal bio-mechanical motion provided by a natural intervertebral disc. More specifically, thearticular components602,604 are permitted to pivot relative to one another about a number of axes, including lateral or side-to-side pivotal movement about longitudinal axis L and anterior-posterior pivotal movement about a transverse axis T. It should be understood that in a preferred embodiment, thearticular components602,604 are permitted to pivot relative to one another about any axes that lies in a plane that intersects longitudinal axis L and transverse axis T. Additionally, thearticular components602,604 may be permitted to rotate relative to one another about a rotational axis R. Although the articulating joint600 has been illustrated and described as providing a specific combination of articulating motion, it should be understood that other combinations of articulating movement are also possible and are contemplated as falling within the scope of the present disclosure. It should also be understood that other types of articulating movement are also contemplated, such as, for example, relative translational or linear motion.
• Although the[0183]articular components602,604 of prosthetic joint600 may be formed from a wide variety of materials, in one embodiment, thearticular components602,604 are formed of a cobalt-chrome-molybdenum metallic alloy (ASTM F-799 or F-75). However, in alternative embodiments of the invention, thearticular components602,604 may be formed of other materials such as titanium or stainless steel, a polymeric material such as polyethylene, or any other biocompatible material that would be apparent to one of ordinary skill in the art. The surfaces of thearticular components602,604 that are positioned in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance, such as, for example, a hydroxyapatite coating formed of calcium phosphate. Additionally, the surface of thearticular components602,604 that are positioned in direct contact with vertebral bone are preferably roughened prior to being coated with the bone-growth promoting substance to further enhance bone on-growth. Such surface roughening may be accomplished by way of, for example, acid etching, knurling, application of a bead coating, or other methods of roughening that would occur to one of ordinary skill in the art.
• [0184]Articular component602 includes asupport plate610 having anarticular surface612 and anopposite bearing surface614.Support plate610 may be sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. In one embodiment, thesupport plate610 is shaped in a triangular-like configuration to facilitate an oblique insertion approach from either the left or right side of the spine, and as such, includes side portions P1, P2 and P3. The side portions P1, P2 and P3 may take a variety of configurations including curved (illustrated by P2) or straight (illustrated by P1 and P3) configurations.
• The[0185]support plate610 can include one ormore notches616 or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument (also not shown) to aid in the manipulation and insertion of the prosthetic joint600 within an intervertebral space between adjacent vertebrae. The surgical instrument (not shown) is preferably configured to hold thearticular components602,604 at a predetermined orientation and spatial relationship relative to one another during manipulation and insertion of the prosthetic joint600, and to release thearticular components602,604 once properly positioned between the adjacent vertebrae.
• In one embodiment, the[0186]articular surface612 includes aprojection620 having a convex shape, which may be configured as a spherical-shaped ball (half of which is shown). It should be understood that other configurations of theprojection620 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. It should also be understood that the remaining portion ofarticular surface612 may take on planar or non-planar configurations, such as, for example, an angular or conical configuration extending about theprojection620.
• A flange member or[0187]keel640 extends from the bearingsurface614 and is configured for disposition within a preformed opening in the adjacent vertebral endplate. In one embodiment, thekeel640 extends perpendicularly from the bearingsurface614 and is approximately centrally located along the bearingsurface614. However, it should be understood that other positions and orientations of thekeel640 are also contemplated. Furthermore, more keels640 can be used, for similar or additional reasons.
• In one embodiment, the[0188]keel640 extends along a substantial portion of thesupport plate610. Thekeel640 is straight, but extends along a direction towards thenotches616 and is parallel with one of the side portions P1 of thesupport plate610. In the present example, thekeel640 is positioned between the transverse axis T and lateral axis L. Such an embodiment accommodates insertion of the prosthetic joint600 using an oblique approach as opposed to the anterior, lateral, or transforaminal approaches discussed above. In a further embodiment, thekeel640 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel640 may be configured as a winged keel, including a transverse portion (not shown) extending across the main body portion ofkeel640.
• The[0189]keel640 also includes a pair ofopenings646 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. Additionally, agap648 may also be formed in thekeel640 to further facilitate bone through-growth. Thegap648 also provides a reference point such that an X-ray can be used to evaluate the positioning and alignment of thesupport plate602 during insertion of the prosthetic joint600. It should be understood that any number ofopenings646 orgaps648 may be defined throughkeel640, including a single opening or gap or several openings and gaps. It should also be understood that theopenings646 andgap648 need not necessarily extend entirely through thekeel640, but may alternatively extend partially therethrough. It should further be understood that thekeel640 need not necessarily define anyopenings646 orgaps648 extending either partially or entirely therethrough. Additionally, although theopenings646 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings646 are also contemplated. As discussed above, the surfaces of thearticular component602 that are in direct contact with vertebral bone may be coated with a bone-growth promoting substance. Specifically, the bearingsurface614 and the surfaces of thekeel640 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface614 and the surfaces ofkeel640 can be roughened prior to application of the hydroxyapatite coating.
• In one embodiment, the[0190]articular component604 includes asupport plate650 having anarticular surface652 and anopposite bearing surface654.Support plate650 may be sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. In one embodiment, thesupport plate610 is shaped in a triangular-like configuration to facilitate an oblique insertion approach from either the left or right side of the spine, and as such, includes side portions P4, P5 and P6. The side portions P4, P5 and P6 may take a variety of configurations including curved (illustrated by P5) or straight (illustrated by P4 and P6) configurations. Thesupport plate650 can include one ormore notches656 or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument, such as discussed above with reference toarticular component602.
• In one embodiment, the[0191]articular surface652 includes arecess660 having a convex shape, which may be configured as a spherical-shaped socket. However, it should be understood that other configurations of therecess660 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. The remaining portion of thearticular surface652 can be angled or otherwise configured to facilitate the insertion and/or use of the prosthesis.
• Although the[0192]concave recess660 is illustrated as having a generally smooth, uninterrupted articular surface, it should be understood that a surface depression or cavity may be defined along a portion of therecess660 to provide a means for clearing out matter, such as particulate debris, that is disposed between the abutting articular surfaces ofcomponents602,604. In such case, the convex articular surface of theball620 may alternatively define a generally smooth, uninterrupted articular surface. In another embodiment of the invention, each of theconvex projection620 and theconcave recess660 may define a surface depression to facilitate removal of particulate matter disposed between the abutting articular surfaces.
• A flange member or[0193]keel670, configured similar to thekeel640 ofarticular component602, extends from the bearingsurface654. In one embodiment, thekeel670 can be centrally located, and is positioned directly or parallel in-line with thekeel640. Thekeel640 is straight, but extends along a direction towards thenotches656 and is parallel with one of the side portions P4 of thesupport plate650. Such an embodiment accommodates insertion of the prosthetic joint600 using an oblique approach as opposed to the anterior, lateral, or transforaminal approaches discussed above. In some embodiments, the position of thekeel670 can be offset to help circumvent veins, arteries, bony portions, or other obstacles that may be in place during the insertion of the joint600.
• It should be further understood that other positions, shapes, orientations, and quantities of the[0194]keel670 are also contemplated. It should also be understood that more keels670 can be used, for similar or additional reasons. Also, thekeel670 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel670 may be configured as a winged keel, including a transverse portion (not shown) extending across the main body portion ofkeel670.
• In one embodiment, the[0195]keel670 also includes a pair ofopenings676 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. Additionally; agap678 may also be formed in thekeel670 to further facilitate bone through-growth. Thegap678 also provides a reference point such that an X-ray can be used to evaluate the positioning and alignment of thesupport plate604 during insertion of the prosthetic joint600. It should be understood that any number ofopenings676 orgaps678 may be defined throughkeel670, including a single opening or gap or several openings or gaps. It should also be understood that theopenings676 andgap678 need not necessarily extend entirely through thekeel670, but may alternatively extend partially therethrough. It should further be understood that thekeel670 need not necessarily define anyopenings676 orgaps678 extending either partially or entirely therethrough; Additionally, although theopenings676 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings676 are also contemplated. As discussed above, the surfaces of thearticular component602 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface654 and the surfaces of thekeel670 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface654 and the surfaces ofkeel670 can be roughened prior to application of the hydroxyapatite coating.
• In some embodiments, one or both of the[0196]keels640,670 may include a sharp forward edge, illustrated byedges680,682. By having such an edge, insertion of thekeels640,670 into the associated vertebral body is facilitated. Also, theedges680,682 can be of sufficient sharpness that the vertebral body does not require a slot for receiving thekeel640,670, discussed in greater detail below.
• Referring to FIGS.[0197]42-44a, to accommodate insertion of the prosthetic joint600 within the intervertebral space, the upper and lower vertebrae V_U, V_Lcan be prepared to accept the prosthetic joint600 therebetween. Referring specifically to FIG. 43, for the configuration of theprosthetic joint600 of FIGS.38-40,multiple slots690,692 are formed along the vertebral endplates of the lower vertebrae V_Land the upper vertebrae V_U, respectively. Theslots690,692 can be created by thekeels640,670 themselves, or can be prepared beforehand by one or more of the methods discussed above. It can be seen from FIGS.42-44, that if one ormore vessels694 are obstructing a straight anterior approach, the oblique approach will allow for an anterior/lateral insertion. Theimplant600 design also ensures a sufficient contact surface for contacting the bony endplates of the vertebrae V_U, V_L.
• Referring to FIG. 44[0198]b, in one embodiment, the prosthetic joint600 can be inserted into the intervertebral space via instrumentation such as the 4-in-1 guide as disclosed in co-pending application U.S. Ser. No. 10/430,473, which is herein incorporated by reference. In one example of an insertion process for inserting the prosthetic joint600, the midline M of the vertebrae V_U, V_Lis located using imaging equipment and apin695 is inserted into the upper vertebra V_Ualong the midline. Anoblique guide member696 is then connected to thepin695 via aflange697 and a handle (not shown) associated with theoblique guide member696 is then adjusted to a proper position. Anoblique pin698 of theoblique guide member696 is then impacted into the upper vertebra V_Uto fix the oblique guide member, thereby indicating the entering reference point and the direction of implant insertion for the prosthetic joint600. The 4-in-1 guide (not shown) can then be used to implant the prosthetic joint600 into the intervertebral space from an anterior-oblique approach, the details of which are more fully discussed in co-pending application U.S. Ser. No. 10/430,473.
• V. Mobile-Bearing Prosthetic Joint[0199]
• In another embodiment, the above-described prosthetic joints can be modified to provide for translational movement as well as rotational movement. For example, referring to FIGS.[0200]45-47, a mobile-bearing prosthetic joint for anterior insertion is generally referred to byreference numeral700. It is understood that the mobile-bearing prosthetic joint700 is described with respect to anterior insertion for the sake of clarity only, and therefore, a variety of insertion directions are contemplated for the mobile-bearing prosthetic joint.
• The prosthetic joint[0201]700 extends generally along a longitudinal axis L and includes a firstarticular component702 and a secondarticular component704. Thearticular components702,704 cooperate to form the prosthetic joint700 which is sized and configured for disposition within an intervertebral space between a pair of vertebral bodies, such as an intervertebral space S1 between adjacent vertebral bodies V_S, V_I(FIG. 48).
• The prosthetic joint[0202]700 provides relative pivotal and rotational movement between the adjacent vertebral bodies V_S, V_Ito maintain or restore motion substantially similar to the normal bio-mechanical motion provided by a natural intervertebral disc but with the added element of translational motion. More specifically, thearticular components702,704 are permitted to pivot relative to one another about a number of axes, including lateral or side-to-side pivotal movement about a longitudinal axis L and anterior-posterior pivotal movement about a transverse axis T. It should be understood that in one embodiment, thearticular components702,704 are permitted to pivot relative to one another about any axes that lies in a plane that intersects longitudinal axis L and transverse axis T. Additionally, thearticular components702,704 are permitted to rotate relative to one another about a rotational axis R. In addition, thearticular components702,704 are permitted to translate relative to one another as will be further described.
• Although the[0203]articular components702,704 of prosthetic joint700 may be formed from a wide variety of materials, in one embodiment, thearticular components702,704 are formed of a cobalt-chrome-molybdenum metallic alloy (ASTM F-799 or-F-75). However, in alternative embodiments, thearticular components702,704 may be formed of other materials such as titanium or stainless steel, a polymeric material such as polyethylene, or any other biocompatible material that would be apparent to one of ordinary skill in the art. The surfaces of thearticular components702,704 that are positioned in direct contact with vertebral bone may be coated with a bone-growth promoting substance, such as, for example, a hydroxyapatite coating formed of calcium phosphate. Additionally, the surface of thearticular components702,704 that are positioned in direct contact with vertebral bone may be roughened prior to being coated with the bone-growth promoting substance to further enhance bone on-growth. Such surface roughening may be accomplished by way of, for example, acid etching, knurling, application of a bead coating, or other methods of roughening that would occur to one of ordinary skill in the art.
• [0204]Articular component702 includes asupport plate706 having anarticular surface708 and anopposite bearing surface710.Support plate706 may be sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. Thesupport plate706 can include one ormore notches712 or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument (not shown) to aid in the manipulation and insertion of the articulating joint700 within an intervertebral space between adjacent vertebrae. The surgical instrument (not shown) is preferably configured to hold thearticular components702,704 at a predetermined orientation and spatial relationship relative to one another during manipulation and insertion of the articulating joint700, and to release thearticular components702,704 once properly positioned between the adjacent vertebrae.
• In one embodiment, and referring to FIGS. 49[0205]aand49b, arecess714 is formed in thearticular surface708. Acircumferential edge716 defining therecess714 along thearticular surface708 is in a concentric relationship with arecess surface718, yet has a smaller diameter relative to the recess surface due to a diverging circular side720 (FIG. 48b) of therecess714. Although described with reference to having a circular shape, it is understood-that therecess714 may take any number of shapes such as square, triangular, or rectangular shapes.
• Referring to FIGS. 50[0206]aand50b, the recess714 (FIG. 49b) is designed to receive a portion of amodular projection member722. Theprojection member722 includes aflange portion724, which is shaped to correspond to the shape of therecess714. As such, theflange portion724 includes a divergingcircumferential side726, which terminates at a substantiallyplanar engagement surface728. Theengagement surface728 is adapted to engage the substantially planar recess surface718 (FIG. 49b). It is understood, however, that although depicted as being substantially planar, theengagement surface728 and therecess surface718 may take any number of corresponding shapes. The diameter of theengagement surface728 is smaller than the diameter of therecess surface718, thereby allowing translation of themodular projection member722 relative to thearticular component702.
• The remaining portion of the[0207]modular projection member722 is defined by aprojection730 having a convex shape, which may be configured as a spherical-shaped ball (half of which is shown). It should be understood that other configurations of theprojection730 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. It should also be understood that the remaining portion ofarticular surface708 may take on planar or non-planar configurations, such as, for example, an angular or conical configuration extending about theprojection224.
• In one embodiment, the convex articular surface of the[0208]projection730 is interrupted by a surface depression orcavity732 extending along theprojection730. In one embodiment, thesurface depression732 is configured as a groove. However, it should be understood that other types of surface depressions are also contemplated, including no depression at all. One purpose of thegroove732 is to facilitate the removal of matter disposed between abutting portions of thearticular components702,704. More specifically, thegroove732 may aid in clearing out matter such as, for example, particulate material, that is disposed between the abutting articular surfaces ofcomponents702,704.
• Referring to FIGS. 45 and 49[0209]b, a flange member orkeel740 extends from the bearingsurface710 and is configured for disposition within a preformed opening in the adjacent vertebral endplate (such as V_Iin FIG. 47). In one embodiment, thekeel740 extends perpendicularly from the bearingsurface710 and is approximately centrally located along the bearingsurface710. However, it should be understood that other positions and orientations of thekeel740 are also contemplated.
• In one embodiment, the[0210]keel740 extends along substantially the entire length of thesupport plate706. Such an embodiment would accommodate insertion of the articulating joint700 using an anterior approach. However, as discussed above, other approaches such as lateral, transforaminal, and anterior-oblique approaches are also contemplated for insertion of the prosthetic joint700. In a further embodiment, thekeel740 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel740 may be configured as a winged keel, including a transverse portion (not shown) extending across the main body portion ofkeel740.
• The[0211]keel740 also includes a pair ofopenings742 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. However, it should be understood that any number ofopenings742 may be defined throughkeel740, including a single opening or three or more openings. It should also be understood that theopenings742 need not necessarily extend entirely through thekeel740, but may alternatively extend partially therethrough. It should further be understood that thekeel740 need not necessarily define anyopenings742 extending either partially or entirely therethrough. Additionally, although theopenings742 are illustrated as having a circular configuration, it should be understood that other sizes and configurations of theopenings742 are also contemplated. As discussed above, the surfaces of thearticular component702 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface710 and the surfaces of thekeel740 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface710 and the surfaces ofkeel740 can be roughened prior to application of the hydroxyapatite coating.
• Referring to FIGS.[0212]45-47, in one embodiment, thearticular component704 includes a support plate750 having anarticular surface752 and anopposite bearing surface754. Support plate750 may be sized and shaped to substantially correspond to the size and shape of the vertebral endplate of an adjacent vertebra. The support plate750 can include one ormore notches756 or other types of indicia for receiving and engaging with a corresponding portion of a surgical instrument, such as discussed above with reference toarticular component702.
• In one embodiment, the[0213]articular surface752 includes a recess758 (FIG. 47), which has a convex shape, such as that of a spherical-shaped socket. However, it should be understood that other configurations of therecess758 are also contemplated, such as, for example, cylindrical, elliptical or other arcuate configurations or possibly non-arcuate configurations. The remaining portion of thearticular surface752 can be angled or otherwise configured to facilitate the insertion and/or use of the articulating joint700.
• Although the[0214]concave recess758 is illustrated as having a generally smooth, uninterrupted articular surface, it should be understood that a surface depression or cavity may be defined along a portion of therecess758 to aid in clearing out matter, such as particulate debris, that is disposed between the abutting articular surfaces ofarticular components702,704. In such case, the convex articular surface of theprojection730 may alternatively define a generally smooth, uninterrupted articular surface. In another embodiment, each of theconvex projection730 and theconcave recess758 may define a surface depression to facilitate removal of particulate matter disposed between the abutting articular surfaces.
• A flange member or[0215]keel760, configured similar to thekeel740 ofarticular component702, extends from the bearingsurface754. In one embodiment, thekeel760 extends perpendicularly from the bearingsurface754 and is approximately centrally located along bearingsurface754. However, it should be understood that other positions and orientations of thekeel760 are also contemplated. It should also be understood that thearticular component704 may include two ormore keels760 extending from the bearingsurface754.
• In one embodiment, the[0216]keel760 extends along substantially the entire length of the support plate750. Such an embodiment would accommodate insertion of the prosthetic joint700 using an anterior approach. However, as discussed above, other approaches such as lateral, transforaminal, and anterior-oblique approaches are also contemplated for insertion of the prosthetic joint700. In a further embodiment, thekeel760 may be angled, tapered, or configured in some other shape to facilitate the functional demands of the keel. In still another embodiment, thekeel760 may be configured as a winged keel, including a transverse portion (not shown) extending across the main body portion ofkeel760.
• The[0217]keel760 also includes a pair ofopenings762 extending therethrough to facilitate bone through-growth to enhance fixation to the adjacent vertebra. However, it should be understood that any number ofopenings762 may be defined throughkeel760, including a single opening or three or more openings. It should also be understood that theopenings762 need not necessarily extend entirely through thekeel760, but may alternatively extend partially therethrough. It should further be understood that thekeel760 need not necessarily define anyopenings762 extending either partially or entirely therethrough. Additionally, although theopenings762 are illustrated as having a circular configuration, it should be understood that other sizes and configurations ofopenings762 are also contemplated. As discussed above, the surfaces of thearticular component704 that are in direct contact with vertebral bone are preferably coated with a bone-growth promoting substance. Specifically, the bearingsurface754 and the surfaces of thekeel760 can be coated with hydroxyapatite to promote bony engagement with the adjacent vertebrae. As also discussed above, the bearingsurface754 and the surfaces ofkeel760 can be roughened prior to application of the hydroxyapatite coating.
• In some embodiments, one or both of the[0218]keels740,760 may include a sharp forward edge, illustrated byedge760aof FIGS. 45 and 46. By having such an edge, insertion of thekeel740,760 into the associated vertebral body is facilitated. Also, theedge760acan be of sufficient sharpness that the vertebral body does not require a slot for receiving thekeel760, discussed in greater detail below.
• Referring to FIG. 45, the mobile-bearing prosthetic joint[0219]700 is assembled by inserting themodular projection722 member into therecess714 formed in thearticular surface708 ofarticular component702. Upon assemblage, the prosthetic joint700 is ready to be inserted into the disc space S1 between adjacent vertebral bodies V_S, V_I(FIG. 48).
• Referring to FIG. 48, to accommodate insertion of the prosthetic joint[0220]700 within the intervertebral space S1, the adjacent vertebral bodies V_S, V_Ican be prepared to accept the prosthetic joint700 therebetween. For the configuration of theprosthetic joint700 of FIGS.45-47,slots770,772 are formed along the vertebral endplates of the vertebrae V_Sand the vertebrae V_I, respectively. Theslots770,772 can be created by thekeels740,760 themselves, or can be prepared beforehand by one or more of the methods discussed above.
• Upon insertion into the disc space S[0221]1, the prosthetic joint700 allows translational movement of thearticular component704 relative to thearticular component702 due to the engagement of themodular projection722 with theconcave recess758 ofarticular component704. For example, in FIG. 51, themodular projection member722 is shown in a posterior position (which would result in movement of thearticular component704 in the posterior direction P), while in FIG. 52, themodular projection member722 is shown in an anterior position (which would result in movement of thearticular component704 in the anterior direction A). FIGS. 51 and 52 are of course only exemplary of the translational movement allowed by the implementation ofmodular projection member722 and thecorresponding recess714, and thus, the amount of translational movement of themodular projection member722, and therefore thearticular component704, relative to thearticular component702 can vary, including in directions other than P and A.
• Furthermore, the positioning of the[0222]modular projection member722 within therecess714 of thearticular component702 allows the modular projection to spin relative to thearticular component702. Thus, in such an embodiment, themodular projection member722 adds the benefit of being able to impart rotation to the articular component704 (via the engagement with the recess758) independent of translational movement imparted to thearticular component704. Such independent relationship between translational and rotational movement adds to the amount of mobility experienced at the prosthetic joint700 relative to prosthetic joints for which translational movement is dependent upon rotational movement and vice versa.
• The present disclosure has been described relative to several preferred embodiments. Improvements or modifications that become apparent to persons of ordinary skill in the art after reading this disclosure are deemed within the spirit and scope of the application. For example, the articulating components of the above-described articulating joints may be reversed without departing from certain aspects of the disclosure. Accordingly, it is understood that several modifications, changes and substitutions are intended in the foregoing disclosure and, in some instances, some features of the disclosure will be employed without a corresponding use of other features. It is also understood that all spatial references, such as “longitudinal” and “transverse,” are for illustrative purposes only and can be varied within the scope of the disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.[0223]

Claims (22)

What is claimed is:

1. A system for simultaneously removing portions of proximate endplates of adjacent vertebral bodies, the system comprising:

a guide member defining an extended opening extending therein, the guide member being configured to fit in a disc space between the two vertebral bodies;

a bit member positioned within the opening of the guide member, the bit member including a superior cutting portion for cutting the end plate of a superior vertebral body, and an inferior cutting portion for cutting the end plate of an inferior vertebral body;

a rotatable element operatively connected to the bit member to impart rotational movement to the superior and inferior cutting portions, and operatively connected to the guide member for moving the bit member along at least a portion of the extended opening.

2. An instrument for cutting a path in bone, comprising a non-linear guide member defining a non-linear opening extending therein, and a bit member positioned within the opening of the guide member, the bit member being adapted to move within the opening of the guide member to cut a path in bone.

3. The instrument ofclaim 2 wherein the bit member comprises at least one bearing assembly disposed adjacent to the guide member to accommodate positioning of the bit member within the opening of the guide member.

4. The instrument ofclaim 2 further comprising at least one rotatable element to accommodate rotational movement of the bit member within the opening of the guide member.

5. The instrument ofclaim 4 wherein the rotatable element is a gear assembly.

6. The instrument ofclaim 2 wherein the bit member extends from a first vertebra to an adjacent second vertebra.

7. The instrument ofclaim 4 further comprising a power source operatively connected to the rotatable element of the bit member for imparting rotational movement to the bit member.

8. The instrument ofclaim 7 further comprising a conduit extending from the guide member for housing a shaft associated with the power source and the rotatable element.

9. The instrument ofclaim 8 wherein the conduit is operatively connected to the bit member and is adapted to impart translational movement to the bit member.

10. The instrument ofclaim 2 wherein the non-linear guide member provides a relatively smooth curvature and a degree of curvature of the curved guide member corresponds to a predetermined cutting path.

11. The instrument ofclaim 10 wherein the predetermined cutting path accommodates a transforaminal approach for cutting vertebral bone.

12. The instrument ofclaim 2 wherein non-linear guide member provides a relatively smooth curvature and a degree of curvature of the guide member is variable.

13. The instrument ofclaim 8 further comprising a handle connected to the guide member.

14. The instrument ofclaim 13 wherein the handle is disposed concentrically about the conduit.

15. An instrument for cutting a path in bone, comprising a curved guide member defining a curved opening extending therein, a bit member positioned within the opening of the guide member, a rotatable element operatively connected to the bit member to impart rotational movement to the bit member, a handle operatively connected to the bit member to impart translational movement to the bit member, wherein the bit member is adapted to cut a curved path into bone via rotational movement in and translational movement through the guide member.

16. The instrument ofclaim 15 wherein the curved path cut into bone corresponds to a transforaminal approach to the bone.

17. The instrument ofclaim 15 further comprising at least one bearing assembly to accommodate positioning of the bit member within the curved opening of the guide member.

18. The instrument ofclaim 15 wherein the degree of curvature of the guide member is variable to correspond to a predetermined cutting path.

19. A method for cutting a curved path into bone, comprising providing an instrument having a curved guide member, the curved guide member defining a curved opening therein, positioning a bit member within the opening of the guide member, actuating the instrument to impart rotational movement to the bit member, engaging the bit member with bone, and imparting a translational force to the bit member to cut a curved path in bone.

20. The method ofclaim 19 wherein the curved cutting path is variable.

21. The method ofclaim 18 wherein actuating the instrument imparts rotational movement to the bit member via a gear assembly.

22. The method ofclaim 18 wherein actuating the instrument imparts rotational movement to the bit member via a pneumatic system.

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