Patent Description:
At times, the source of a patient's back pain may not be clear. Among possible causes for such pain are disease, degradation and/or injury to the spinal bones and/or discs of the spine, as well as to various ancillary structures such as the lamina and/or associated facet joints. While spinal fusion and/or disc arthroplasty procedures have been successful in treating spinal joints to reduce pain, such treatments are often limited in their efficacy, often fuse or immobilize portions or a patient's spine, and are often unable to address and/or correct severe spinal deformities, including spinal dislocations and/or curvature abnormalities such as juvenile and/or adult scoliosis. Therefore, a motion preserving joint replacement system is needed that can reduce and/or correct severe spinal deformities while replacing all or part of the function of the spinal disc and/or associated spinal structures. <CIT> discloses a spinal implant for insertion between adjacent vertebrae to function as a disc prosthesis. The prosthesis is formed from two plates fastened to adjacent vertebrae facing each other. The facing sides of the plates have a donut shaped cushioning coupler to replicate the displaced disc material. Stabilizing links are positioned along the edge of the plates to prevent over compression of the shaped cushioning coupler in a bending moment. Adjustable mounting brackets are used to secure the implant to the spine. <CIT> discloses a prosthesis comprising a pair of connection plates for connection with adjacent vertebral objects, and a hinge core forming a hinge having concave hinge surface and complementary convex hinge surface, with one of the connection plates. The concave hinge surface encloses the convex hinge surface within a solid angle of <NUM> degrees, such that the convex hinge surface lies within a recess surrounded by edges. <CIT> discloses an apparatus and method is provided relating to artificial discs. An artificial disc is provided that facilitates simultaneous and independent articulation of flexion/extension, lateral bending, anterior/posterior translation, and axial rotation. The artificial disc provides these four simultaneous and independent articulations by independently addressing each type of articulation in the design of the artificial disc. In one example, an artificial disc is comprised of a bearing disposed between first and second end plates. The bearing is movable relative to each end plate, independent of the other end plate. The end plates are affixed to adjacent vertebrae. <CIT> discloses a metal composite orthopaedic device such as an articulating spinal spacer. The device can comprise a metallic substrate cladded or joined to one or more metallic layer(s). The substrate and metallic layer(s) can be selected of different metals and metal alloys to provide desired wear performance, imaging characteristics and optionally to serve as a reservoir for therapeutic agents. <CIT> discloses systems, devices, methods and surgical procedures for altering and/or correcting the alignment of adjacent bones, including bones of the spine.

The present invention relates to a prosthetic system as claimed hereafter. Preferred embodiments of the invention are set forth in the dependent claims. In various embodiments, surgical methods (not claimed) and techniques are described wherein portions of a patient's spinal bones may be shaped, shaved, resected and/or removed, including portions of a vertebral endplate and/or pedicular portion(s) (and/or associated structures), with at least one or more portions of the pedicle being retained to provide at least partial support for a prosthetic system that is implanted between the upper and lower vertebrae.

In various embodiments, the prosthetic system can comprise a pair of independent joint components, each of the independent joint component pairs comprising an upper joint component and a lower joint component. The upper joint component can comprise an upper contact surface and an upper articulation surface, and the lower joint component can comprise a lower contact surface and a lower articulation surface configured to movably engage the upper articulation surface to form an articulating joint pair, with two articulating joint pairs implanted into an intervertebral space between adjacent vertebrae to form an articulating joint. The articulating joint is adapted for implantation within a disc space between the upper and lower vertebrae, allowing the upper and lower vertebrae to move relative to one another. The lower joint components will also each desirably include supports or bridge components extending posteriorly from the disc space, with at least a portion of each bridge component including an outer surface which abuts and/or engages with at least a portion of a pedicle and/or portions of the vertebral arch of the lower vertebral body.

In various embodiments, the individual components of the articulating joint, specifically the various upper and lower joint components of the two articulating joint pairs, are configured such that these components can assume a variety of differing positions and/or orientations (i.e., relative to each other and/or relative to the vertebral bodies in which they are implanted) while maintaining a capacity to articulate in a desired manner. Such design features allow the use of similar and/or identical joint components at all levels of the spine, even if patient injuries and/or anatomical constraints require modification of component positioned at differing levels of the spine.

In an example not in accordance with the claimed invention, a surgical method comprises non-invasively imaging at least upper and lower vertebral bodies of a patient's spine, and then preoperatively planning the surgical removal of some portions of an endplate and one or more pedicles of the lower vertebral body to alter, restore and/or correct the alignment between the upper and lower vertebral bodies to a desired and/or more anatomically correct alignment. Surgical removal according to the preoperative plan can be accomplished, which can include removal of the endplate and/or a portion of one or more pedicles of the lower vertebral body, and then insertion of a prosthetic system between the upper and lower vertebrae, wherein the system comprises an upper joint component and a lower joint component, with the lower joint component including a support extending posteriorly from the lower joint component, the posterior support including a surface adapted and configured to fit within at least a remaining portion of one or more pedicles of the lower vertebral body.

In the various examples described herein and not forming part of the invention, the planning and surgical corrections to the spinal alignment can include alterations to the lordotic curvature of the patient's spine, alterations to the lateral curvature of the patient's spine (i.e., to address scoliosis, for example), and/or various combinations thereof. If desired, a surgical correction to a specific region of the spine may result in a more-normal anatomical alignment of the affected segment, or the surgical correction may result in an alignment that is further away from the natural alignment (such as where the treated segment desirably compensates for other misaligned levels that may not be surgically treated). In various examples, the anatomical imaging, analysis, approach, vertebral preparation, implant preparation and/or placement can be accomplished with the aid of surgical navigation and/or robotic guidance. Due to the complex nature of the preoperative planning and/or execution, these tools may be particularly well suited for the present invention to allow execution of the plan in the operative environment. While the implantation, planing and surgical methods described herein do not form part of the invention, they are disclosed as they represent useful background for understanding the invention.

The foregoing and other objects, aspects, uses, features, and advantages of embodiments will become more apparent and may be better understood by referring to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings, wherein:.

Various features of the present invention include the recognition of a need for a more effective and versatile system of addressing spinal disease and deformities, including the correction and/or alteration of spinal levels using a motion preserving construct. A variety of configurations, sizes and shapes of such components and associated tools can be utilized in diverse anatomical regions, including use in spinal surgery as well as other anatomical locations. In various medical applications, the disclosed components and related surgical tools and techniques can desirably facilitate the treatment of various types of bone disease and/or damage by surgeons, which can be important to achieve the most accurate and best implant performance and/or fit, as well as facilitate patient recovery.

This specification describes novel systems, devices and methods (not claimed) to treat spinal fractures. Aspects of the present invention will be described with regard to the treatment of vertebral bodies at the lumbar and/or thoracic levels. It should be appreciated, however, that various aspects of the present invention may not limited in their application to thoracic or lumbar injuries. The systems and methods (not claimed) may be applicable to the treatment of fractures in diverse bone types. Embodiments will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It should be understood that the figures are not necessarily to scale.

The present disclosure relates generally to systems and methods (not claimed) for spinal surgery and, more particularly in some embodiments, to spinal arthroplasty systems and methods (not claimed) for posterior implantation. For the purposes of promoting an understanding of the principles of the invention, reference will now be made to embodiments or examples illustrated in the drawings, and specific language will be used to describe the same. Any alteration 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 disclosure relates.

Various embodiments disclosed herein can be utilized in conjunction with various devices, tools and/or surgical techniques described in co-pending <CIT> and entitled "Spinal Osteotomy".

Referring first to <FIG>, a sagittal view of a vertebral column <NUM> is shown, illustrating a sequence of vertebrae V1, V2, V3, V4 separated by natural intervertebral discs D1, D2, D3, respectively. Although the illustration generally depicts a lumbar section of a spinal column, it is understood that the devices, systems, and methods (not claimed) of this disclosure may also be applied to all regions of the vertebral column, including thoracic and cervical regions.

Referring now to <FIG>, a vertebral joint <NUM> of the vertebral column <NUM> includes the adjacent vertebrae V1, V2 between which the intervertebral disc D1 extends. The vertebra V1 includes a generally cylindrical vertebral body portion <NUM>, an inferior articular process <NUM>, and an inferior endplate <NUM>. The vertebra V2 includes a generally cylindrical vertebral body portion <NUM>, a superior articular process <NUM>, and a superior endplate <NUM>. For reference purposes, a longitudinal axis <NUM> extends through the centers of the cylindrical vertebral body portions <NUM>, <NUM>. A pedicle <NUM> extends between the vertebral body portion <NUM> and superior articular process <NUM>. The inferior articular process <NUM> and the superior articular process <NUM> form a facet or zygapophyseal joint <NUM>. The facet joint <NUM> has a fluid filled capsule and cartilage to provide articulating surfaces for the articular processes <NUM>, <NUM>. Both the disc D1 and the facet joint <NUM> permit motion between adjacent bone surfaces, allowing the total vertebral joint <NUM> a normal range of flexion/extension, lateral bending, and rotational motion. As the disc D1 and/or the facet joint <NUM> deteriorate due to aging, injury, disease, or other factors, all or portions of the disc, the facet joint, and/or the articular processes <NUM>, <NUM> may be removed and replaced by a prosthetic device which may preserve motion in the spinal joint <NUM>. Although not described in detail, a second bilateral prosthetic device may also be used to replace a portion of the function of disc D1 and/or the function of a second facet joint opposite the facet joint <NUM>.

<FIG> depicts a side view of one exemplary spinal motion unit <NUM> that is undergoing a surgical procedure in accordance with an example of the present disclosure. In this example, preoperative image data of the spinal motion unit has been obtained, and a surgical plan to alter the alignment of the spinal motion has being proposed. In this example, a proposed lower component alignment path <NUM> has been presented, which will desirably result in the surgical removal of a "wedge" of bony material from the lower vertebral body <NUM> and/or one or both pedicles <NUM>, which is represented by the shaded triangle "T" of <FIG> (involving removal of bony material at or below the anatomical alignment line <NUM> up to the revised alignment line of <NUM>). Desirably, this surgical plan will allow some and/or all of at least the bottom of the pedicles to be preserved during such removal, such that the remaining portions of the pedicle are attached to the vertebral body, to provide additional stability to lower surfaces of the implant. If desired, the resection may be symmetrical on each side of the vertebral body, or the resection may be asymmetrical in some fashion.

Because of various anatomical differences between vertebral levels, some vertebral levels will typically accommodate a greater degree of osteotomy correction than others. For example, at the L1/L2 level, an osteotomy angle α of up to <NUM> degrees (i.e., a correction of from zero to <NUM> degrees) can be accomplished on one or both sides of a treated lower vertebral body, while retaining sufficient pedicular structure underneath the implant to maintain adequate implant support. At the L2/L3 level, an osteotomy angle α of up to <NUM> degrees (i.e., a correction of from zero to <NUM> degrees) can be accomplished on one or both sides of a treated lower vertebral body, while retaining sufficient pedicular structure underneath the implant to maintain adequate implant support. At the L3/L4 level, an osteotomy angle α of up to <NUM> degrees (i.e., a correction of from zero to <NUM> degrees) can be accomplished on one or both sides of a treated lower vertebral body, while retaining sufficient pedicular structure underneath the implant to maintain adequate implant support. At the L4/L5 level, an osteotomy angle α of up to <NUM> degrees (i.e., a correction of from zero to <NUM> degrees) can be accomplished on one or both sides of a treated lower vertebral body, while retaining sufficient pedicular structure underneath the implant to maintain adequate implant support. At the L5/S1 level, an osteotomy angle α of up to <NUM> degrees (i.e., a correction of from zero to <NUM> degrees) can be accomplished on one or both sides of a treated lower vertebral body, while retaining sufficient pedicular structure underneath the implant to maintain adequate implant support. Such a significant degree of surgical correction in a procedure utilizing a motion preserving implant is heretofore unheard of in spinal surgery, and such dramatic corrections are even infrequent using fusion implants and/or during other corrective surgeries.

In various examples, the use of robotics and/or computer guided surgical platforms (and/or computer-aided navigation) are contemplated herein, including in the planning and/or execution stages of the surgery.

<FIG> depicts a posterior view of the exemplary spinal motion unit <NUM>, where an asymmetrical resection is being planned to desirably correct an undesirable medial/lateral curvature of the spine. In this embodiment, more material will be resected from right side of the spinal motion unit than from the left side, which will desirably induce a slight medial curvature to the patient's spine (i.e., providing a desired coronal plan correction). In addition, as previously noted, the surgical plan will desirably allow some and/or all of at least the bottom of the pedicles to be preserved during such removal, such that the remaining portions of the pedicle are attached to the vertebral body, to provide additional stability to lower surfaces of the implant.

<FIG> depicts a top view of a vertebral body of the surgical plan on <FIG>, in which the proposed bone "wedges" are shown in shadow as planning boxes <NUM> and <NUM>. In this example, the wedges could be taken from both sides for sagittal correction, or both side asymmetrically or unilaterally for combined coronal and sagittal correction.

<FIG> depict one exemplary lordotic correction that could be obtained using the teachings of the present disclosure. In this example, a vertebral body <NUM> is imaged, and a surgical resection plan is proposed (indicated as the shaded triangle). <FIG> shows the vertebral body <NUM> after resection, and <FIG> depicts the new orientation of the vertebral body <NUM> after resection is complete, which could represent an increased lordotic curvature of the lumbar spine when accomplished at the lumbar level. <FIG> depicts the resulting correction to the functional spinal unit, wherein a negative <NUM> degree curvature was altered and stabilized to a positive <NUM> degree curvature using the techniques and implants described herein. In various examples, a surgical correction can also address medial/lateral correction, such as where one side of a vertebral body (i.e., the left side) is altered to a different degree than the opposite side (i.e., right side) of a single vertebral body. In such a case, the curvature of the spine may be altered to the left or right side of the patient, which may have particular utility in correcting scoliotic curvature and/or the like.

In preparing the vertebral body of <FIG>, it is contemplated that a power reciprocating tool, rasp or similar surgical tool or drill can be utilized to prepare at least the lower vertebral surface, such as the rasps depicted in <FIG>. In this example, a rasp may be introduced into the surgical field, with a forward portion of the rasp located on the endplate of the lower vertebral body, near an anterior portion of the vertebral body, and when actuated the rasp can be pushed downward into the vertebral body along a curving path, which desirably provides increased pressure on a posterior section of the rasp - which cuts the posterior vertebral body more quickly and/or aggressively than the anterior portion of the endplate or vertebral body, desirably creating a wedge or channel extending through the posterior vertebral body and/or pedicle. Depending upon the desired depth and/or angle of cut, the rasp may be utilized to cut completely through the cortical bone of the upper endplate and/or posterior cortical ring of the vertebral body, including portions of the pedicle, which may be accomplished with and/or without complete removal of the cortical bone on an anterior portion of the treated endplate.

<FIG> depicts a lateral view of an exemplary lower spinal segment <NUM>, with typical lumbar lordotic angular variance across various spinal levels indicated by dotted lines. In general, a surgical procedure to repair a particular vertebral level will often seek to approximate the relevant lordotic angles depicted herein, although normal anatomical variance across a normal patient population may cause a surgeon to alter these angles somewhat in their surgical repair. In addition, where a pre-existing injury has significantly altered the dynamics and/or kinematics of a patient's spine, a surgeon may opt for surgical repairs that attempt to restore and/or approximate the overall natural lordotic curvature of the patient's spine, even where such correction might alter a single level or group of levels to less desirable and/or non-desirable angles (i.e., in an attempt to restore a more natural anatomical curvature to the spine as a whole). For example, as discussed in "<NPL>, as compared to the sacral angle <NUM>, L1 normally has a typical angular range of <NUM> degrees to -<NUM> degrees (<NUM>: <NUM>°:-<NUM>°), L2 has a typical angular range of <NUM> degrees to -<NUM> degrees (<NUM>: <NUM>°:-<NUM>°), L3 has a typical angular range of <NUM> degrees to - <NUM> degrees (<NUM>: <NUM>°/-<NUM>°), L4 has a typical angular range of <NUM> degrees to -<NUM> degrees (<NUM>: <NUM>°:-<NUM>°) and L5 has a typical angular range of <NUM> degrees to -<NUM> degrees (<NUM>: <NUM>°:-<NUM>°).

<FIG> depicts an anterior-posterior (A/P) view of the spinal segment of <FIG>, showing typical facet joint angles for each lower spinal level. Because the facets and related spinal structures of each vertebral level are typically angled somewhat differently, and the implants of the current invention desirably utilize some portion of the pedicular support structures of a given level to improve implant stability and durability, the implant components will desirably accommodate these angular differentials, which in the disclosed figures are. As best seen in <FIG> and <FIG>, one exemplary angle θS1 (referred to as the transverse pedicle angle) for the S1 pedicles (relevant to an implant in the L5-S1 level) is approximate <NUM> degrees from midline, or a "toe-in" angle (between the two pedicles of the vertebral body) of approximately <NUM>° therebetween. <FIG> and <FIG> depict an exemplary pedicle angle θL5 for L5 (relevant to an implant in the L4-L5 level) of approximately <NUM> degrees from midline, or a "toe-in" angle of approximately <NUM>° therebetween. <FIG> and <FIG> depict an exemplary pedicle angle θL4 for L4 (relevant to an implant in the L3-L4 level) of approximately <NUM> degrees from midline, or a "toe-in" angle of approximately <NUM>° therebetween. <FIG> and <FIG> depict an exemplary pedicle angle θL3 for L3 (relevant to an implant in the L2-L3 level) of approximately <NUM> degrees from midline, or a "toe-in" angle of approximately <NUM>° therebetween. <FIG> and <FIG> depict an exemplary pedicle angle θL2 for L2 (relevant to an implant in the L1-L2 level) of approximately <NUM> degrees from midline, or a "toe-in" angle of approximately <NUM>° therebetween. <FIG> depicts an exemplary pedicle angle θL1 for L1 (relevant to an implant in the T12-L1 level) of approximately <NUM> degrees from midline, or a "toe-in" angle of approximately <NUM>° therebetween. Of course, it should be understood that the vertebral bodies herein are depicted in an "idealized" fashion, as natural anatomical variations within the patient population and injury and/or degradation of an individual patient's vertebral bodies will result in vertebral bodies that are generally non-symmetrical - that is, the left and right pedicles of an actual vertebral body are unlikely to be perfectly symmetrical and/or uniform as measured from the vertebral midline.

In various embodiments, the devices disclosed herein can be utilized in a variety of positions and/or placements, including those previously discussed. In various additional exemplary embodiments, implant component pairs such as those described herein can be utilized at multiple vertebral levels of the spine, including placement at a transverse pedicle angle θS1 of from <NUM> degrees to <NUM> degrees, θL5 of from <NUM> degrees to <NUM> degrees, θL4 of <NUM> degrees to <NUM> degrees, θL3 of <NUM> degrees to <NUM> degrees, θL2 <NUM> degrees to <NUM> degrees and/or θL1 of zero degrees to <NUM> degrees.

<FIG> depicts a cephalad-caudad view of an S1 vertebral body, with a pair of intervertebral implants <NUM> and <NUM> implanted therein. In this embodiment, each of the intervertebral implants <NUM> and <NUM> are desirably aligned along a respective right and left pedicle of the vertebral body, which results in an intervertebral construct having a toe-in angle αS1 of approximately <NUM> degrees. This first component arrangement will desirably provide a significant resistance to shear loading of the implants and the spinal level, as such high shear loading is common in this spinal level. In contrast, <FIG> depicts a cephalad-caudad view of a L1 vertebral body, with a pair of intervertebral implants <NUM> and <NUM> implanted therein. In this embodiment, each of the intervertebral implants <NUM> and <NUM> are desirably aligned along a respective right and left pedicle of the vertebral body, which results in an intervertebral construct having a toe-in angle αL1 of approximately <NUM> degrees. This second component arrangement allows for less resistance to shear loading of the implants at this level, as high shear loading is much less likely to occur at this spinal level. However, the unique design of the implant components described herein allow for implantation at multiple levels of the spine, as it is highly desirable to have a single intervertebral implant design that can accommodate a wide range of variations in pedicle angles and/or lordotic angles of the vertebral bodies in which they are implanted.

In addition to being capable of use at multiple levels of the spine, the disclosed implants further allow significant alignment variations with little no effect on the functionality of the construct. For example, as depicted in <FIG>, the component pairs <NUM> and <NUM> can be implanted in a vertebral levels with a significant variation ρC in coronal plane alignment (in some embodiments up to <NUM> degrees out of alignment in the coronal plane) and still function to allow a desired amount of flexion and/or extension for the treated vertebral level. <FIG> depicts the component pairs <NUM> and <NUM> implanted in a vertebral levels with a significant variation ρS in sagittal plane alignment (in some embodiments up to <NUM> degrees out of alignment in the coronal plane) and still function to allow some amount of flexion and/or extension for the treated vertebral level.

<FIG> and <FIG> depict exploded and fully assembled perspective view of an intervertebral implant <NUM> which provides for significant resection of a vertebral body and/or pedicle (including resection of a superior endplate and/or cortical rim portion of an inferior vertebral body, as well as optionally preparation of only part of a pedicle) and associated spinal structures, while still preserving stability and/or motion in the spinal joint. The intervertebral implant <NUM> can include an upper joint component <NUM> and a lower joint component <NUM>. The upper joint component <NUM> desirably includes an articulation surface <NUM>, which may be smooth, concave, and/or generally spherical in shape. The lower joint component <NUM> can similarly include an articulation surface <NUM>, which may be smooth, convex, and/or generally spherical in shape. As assembled, the articulation surface <NUM> may engage the articulation surface <NUM> to produce a ball-and-socket style anterior joint.

As defined herein, a "spherical" shaped surface could include any curved surface having a uniform radius of curvature and may refer to a spherical cap or a segment of a sphere. In various alternative embodiments, non-spherical curved surfaces may function as articulation surfaces to impart specific limits to the range of motion of the prosthetic device. In still another alternative embodiment, the joint may be inverted with the upper articulation surface having a convex shape and the lower articulation surface having a concave articulation surface.

As best seen in <FIG> and <FIG>, the upper joint component <NUM> can include an upper joint body <NUM> and an articulating insert <NUM> (depict as transparent in <FIG> and solid in <FIG>). In this embodiment, the articulating insert <NUM> can be formed from a durable, flexible material such as ultra-high-molecular-weight polyethylene (UHMWPE) or similar material, while the upper joint body <NUM> can comprise a metallic component to which the insert <NUM> is attached. A corresponding articulating surface <NUM> of the lower joint component <NUM> can desirably be formed from metal (i.e., chrome cobalt) or a ceramic material, such that one bearing component (i.e., the upper bearing component) is significantly more compliant than the other bearing component (i.e., the lower bearing component). This arrangement can provide a better performing joint which experiences less wear and/or generates less wear debris than many other implant designs, as the concave UHMWPE "cup" can easily conform to or otherwise accommodate the harder ball or other convex surface, providing better wear performance and reducing the potential for stress concentrations and/or point loading of the joint.

In the present invention, various embodiments of these disclosed spinal implants may perform better, experience less wear and/or generate less wear debris if the "softer" component is on the concave side of the bearing couple (including spherical ball-in-cup type bearing couples as well as non-spherical and/or curved bearing couples) and the "harder" component is on the convex side. Such an arrangement can allow the cup or other concave receiving surface to "conform to" or otherwise accommodate the harder ball or other convex surface, providing better wear performance and reducing the potential for stress concentrations and/or point loading. In contrast, the existing configurations of many implants in the prior art allow for a variety of suboptimal effects, including the potential for rim loading of surfaces within the bearing, which can greatly accelerate wear and/or failure of the bearing couple.

While various examples disclosed herein can include bearing couples of identical and/or similar materials (not claimed), In other embodiments a spinal joint replacement can incorporate one or more bearing couples having dissimilar bearing surface materials (i.e., the dissimilar materials having dissimilar hardness or durometer measures in various embodiments), which in at least one embodiment includes a metal component that engages with a non-metallic component such as an ultra-high-molecular-weight polyethylene (UHMWPE) component or similar material, where one bearing component is significantly more compliant than the other. In various embodiments, the present invention can be utilized with a lumbar or cervical disc replacement implant, where the bearing surfaces can be arranged and configured in the disclosed manner. If desired, a posterior lumbar joint replacement can be provided, wherein the upper concave UHMWPE structure and/or surface may be fixed within a bone ingrowth shell of 3D printed or similar porous titanium to transmit stress and desirably in-grow biologically to the upper end plate of the upper vertebrae, and a 3D printed or similar titanium inferior component can be provided with a tail that travels down the axis of the pedicle, to transmit loads and biologically fix to the lower end plate and/or cortical/cancellous bone of the lower vertebrae. If desired, the lower component could optionally have a Cobalt Chrome (CoCr) or similar bearing cap to wear against and/or articulate with the upper UHMWPE component.

In addition to the polyethylene articulation surface <NUM>, the insert can also incorporate various peripheral structures such as retention surfaces <NUM>, <NUM> and motion limiters or bumpers <NUM> and <NUM>, which in this embodiment are depicted as recessed surfaces and shoulders. As best seen in <FIG>, the lower joint component <NUM> can also include retention surfaces <NUM>, <NUM> and bumpers or motion limiters <NUM>, 875a which in this embodiment are corresponding recessed surfaces and upwardly protruding extensions, which are spaced apart from the articulation surface <NUM>. As will be described in greater detail below, the pairs of motion limiters <NUM>, <NUM> and <NUM>, 875a and the retention surfaces <NUM>, <NUM>, <NUM> and <NUM> desirably allow significant range of motion between the upper and lower joint components <NUM> and <NUM> in a variety of orientations, while constraining and/or limiting movement to a desirable range, thereby preventing or limiting the dislocation of the joint formed by the implant components. Because these structures are formed from polyethylene on the insert, however, the polymeric material helps to absorb and/or dissipate the impact on the metallic surfaces to some degree, thereby reducing peak loading of the implant and/or the various bone anchors securing the implant to the patient's anatomy.

In various exemplary embodiments, the lower joint component <NUM> includes a bridge component <NUM> (see <FIG>), which extends posteriorly from the intervertebral disc space between the vertebral bodies, with a lower surface that abuts and/or engages with at least a portion of a pedicle of the vertebral body to a distal end <NUM> of the lower joint component <NUM>.

The distal end <NUM> of the bridge <NUM> includes a connection component <NUM>, which in this embodiment is a passage for accepting a pedicle screw-type fastener. In this embodiment, the fastener can be a bone screw, however in alternative embodiments, fasteners such as nails, staples, or other mechanical or chemical fasteners may be suitable. The orientation of the connection component <NUM> desirably permits the fastener to become inserted along and/or parallel to a pedicle (i.e., extrapedicularly), such that the screw may travel a path obliquely angled or skewed away from a central axis defined through a pedicle. The fastener may be threaded across a portion of the pedicle and into the vertebral body. Extrapedicular fixation may be any fixation into the pedicle that does not follow a path down a central axis defined generally posterior-anterior through the pedicle. In this embodiment, the screw passes through a wall portion of the pedicle, whereby it may achieve strong cortical fixation. In all embodiments, the fasteners may be at least partially recessed so as not to interfere with articulations, soft tissues, and neural structures.

As installed, the bridge <NUM> and the fastener may limit excessive movement of the device, particularly during flexion/extension motions. Additionally, the bridge may distribute the loads on the lower vertebra and/or cortical bone of the pedicle, thereby reducing any opportunity for subsidence of the lower joint component into the vertebral body, even where the anterior portions of the implant may be primarily supported by cancellous bone exposed by removal of the endplate material.

If desired, the connection component <NUM> may further include an optional locking clip <NUM> (see <FIG>), which in this embodiment is an elastically deformable C-shaped structure which holds a fastener <NUM> in place, resisting any backward disengagement of the fastener <NUM>, particularly when the joint is in motion. It is understood that in alternative embodiments, the locking clip may be a cap, a clamp, an adhesive, or other suitable mechanical or chemical systems for limiting movement of the fastener.

As best seen in <FIG>, in various embodiments the upper and lower joint components will desirably provide at least <NUM> degrees of flexion βF, and at least <NUM> degrees of extension βE along the articulating surfaces before the motion limiters or bumpers on the upper and lower joint components come into respective contact. In at least one exemplary embodiment, these bumper surfaces can desirably be gently curved surfaces which are angled and/or tilted relative to a neutral axis of the upper and lower joint components, such that the plane of the bumper surface is offset and parallel to a plane passing through the axes of revolution between the upper and lower joint components, which is best depicted in <FIG> for flexion and <FIG> for extension.

<FIG> depict examples of how the upper and lower joint components of the present invention are designed to allow for a desired range of flexion and extension, regardless of the pedicle angle in which they are implanted. In the embodiment of <FIG>, flexion (i.e., forward) movement and extension (i.e. backward) movement of the implant occurs along the longitudinal axis L of the implant (in the directions of the movement axis indicated by the arrow). In this embodiment, this movement causes the center of the bumpers of the upper and lower joint components (i.e., front bumpers for flexion and rearward bumpers for extension) to eventually come into contact and generally constrain further movement of the implant at its rotation limits (which may include contact between the entirety of the upper and lower bumpers in some embodiments). In <FIG>, flexion and extension occur at a more narrow angle α to the longitudinal axis L of the implant, which generally induces the more leftward sides of the front bumpers to contact in flexion, and the more rightward sides of the rear bumpers to contact and generally constrain movement of the implant at its rotation limits. In <FIG>, flexion and extension occur at a greater angle α to the longitudinal axis L of the implant, which generally causes the most extreme leftward sides of the front bumpers to contact in flexion, and the most extreme rightward sides of the rear bumpers to contact and generally constrain movement of the implant at its rotation limits.

<FIG> depict how the disclosed implant components can accommodate component misalignment and/or movement, yet still function in a normal manner. As best seen in <FIG>, the upper and lower components can move along axis M in a desired manner, where the implant components are aligned. However, <FIG> shows that a similar range of motion of the upper and lower components can still be achieved where the upper and lower components are not fully aligned, such as where the upper component may be rotated clockwise relative to the lower components. While one objective of the disclosed surgical procedure is to desirably align the upper and lower components during device implantation, it is possible that anatomical constraints will obviate the surgeon's ability to make such parallel alignment during implantation, or post-surgical migration, rotation and/or subsidence of an individual implant component and/or component pair will alter such alignment over time. In such a case, the implant will desirably accommodate such changes and will continue to provide a desired degree of motion to the treated spinal level.

<FIG> depicts a cephalad view of pair of implant component pairs <NUM> and <NUM> in a vertebral body <NUM>, where a toe-in angle of the implant component pair <NUM> at the right side of the vertebral body is significantly greater than a toe-in angle of the implant component pair <NUM> at the left side of the vertebral body, with <FIG> depicting the implant component pairs <NUM> and <NUM> of <FIG> from an anterior-posterior (A/P) viewpoint during a flexion motion. It should be understood that such differences in toe-in angles in a given vertebral body can be quite common, due to a variety of factors (including those already discussed). However, regardless of implant positioning and/or alignment, the present inventions will desirably provide an adequate range of motion to the treated spinal level. As best seen in <FIG>, the cooperation between the component pairs allows for flexion and/or extension of the treated vertebral level in a desired anterior-posterior direction, with the implant component pair <NUM> having the greater toe-in angle providing for bumper impingement towards a side of implant (in a region indicated by the black arrow), while the implant component pair <NUM> having the lesser toe-in angle provides for bumper impingement closer towards a central region of the implant (in a region indicated by the white arrow). In this manner, therefore, the various implant components described herein can provide a desired range of motion for a treated spinal level, regardless of implant alignment and/or natural anatomical variation. In one exemplary embodiment, shown in Table <NUM> below, the implant can allow significant flexion and/or extension to an individual construct pair for a variety of toe-in angulations.

If desired, the motion allowed by one or more motion limiters and/or bumpers of one of more of the implant components may be shaped to provide a greater or lesser range of flexion/extension motion. For example, a surface on the motion limiter angled away from the articulation surface may permit greater flexion motion than would a motion limiter surface parallel to an axis of the spine.

<FIG> depicts a side view of an upper joint component <NUM> having an outer contact surface <NUM> for interfacing with a vertebral endplate (not shown). The upper joint component <NUM> may further include an upper keel <NUM> extending from the outer contact surface <NUM> and comprising a tapered leading edge <NUM>, an elongated portion <NUM> and a posterior tab <NUM>. The elongated portion <NUM> can provide the prosthetic device with greater stability in a portion of the hard cortical bone of the outer wall of a vertebral body, and can extends to the posterior edge of the upper joint component to provide additional stability where it meets with the posterior tab <NUM>. The posterior tab <NUM> can desirably extending upward from a posterior edge of the outer contact surface <NUM>. In this embodiment, the tab <NUM> may be generally perpendicular or slightly acutely angled relative to the contact surface. The tab <NUM> may be integrally formed with or otherwise abut the posterior end of the upper keel <NUM>. If desired, the posterior tab may serve as a stop to prevent the device from being inserted too far anteriorly into the intervertebral disc space. The position of the tab may be monitored with fluoroscopy or other visualization methods during surgery to determine the progress of the implantation and to confirm when the device has been completely implanted with the posterior tab in contact with a posterior wall of the vertebral body. Because the position of the posterior tab may be fixed relative to a center of rotation of the joint formed by the various articulation surfaces, the location of the posterior tab may serve as an indicator of the location of the center of rotation. After the surgeon has determined the desired location for the center of rotation, the upper joint component may be selected so that as the posterior tab is positioned against the posterior wall of the vertebral body, the center of rotation is moved into the desired predetermined location. In various alternative embodiments, the upper keel may be longer or shorter to achieve desired stability. If desired, the lower joint component may similarly include a lower keel extending from an outer contact surface, if desired. In various alternative embodiments, the width of the keel may vary. For example, the keel may taper or have an undulating wave form. In still another alternative, the keel may be perforated or porous to promote bone ingrowth.

<FIG> depict an upper joint component <NUM> with a lower engagement surface <NUM>, which in these figures desirably engages with an articulating insert (which is not installed in these figures). The lower engagement surface <NUM> desirably includes a peripheral ridge <NUM> and ridge groove <NUM>. In this embodiment, the articulating surface can comprise an ultra-high-molecular-weight polyethylene (UHMWPE) or similar material, which is desirably over-molded onto the lower engagement surface <NUM> of the upper joint component <NUM> (to desirably create the implant of <FIG>). In various embodiments, the polyethylene material will desirably over mold and be engaged with the peripheral ridge <NUM> and ridge groove <NUM>, such that when the polyethylene cools and shrinks slightly during the molding and/or cross-linking processes, the polyethylene will become more tightly engaged with and secured onto the peripheral ridge <NUM> and ridge groove <NUM>.

The size and shape of the various joint components described herein may be limited by the constraints of a posterior surgical approach. For example, the upper and lower joint components may be configured to cover a maximum vertebral endplate area to dissipate loads and reduce subsidence while still fitting through the posterior surgical exposure, Kambin's triangle, and other neural elements. To achieve maximum surface coverage, the material of the anterior joint components may extend anteriorly from the articulation surfaces, respectively. The width of the upper and lower joint components may also be selected to desirably pass through Kambin's triangle and to co-exist with the neural elements, yet provide sufficient cross-sectional area to the pedicle structures for additional support.

In alternative embodiments, the upper and lower joint components may be provided in various heights. For example, the height of the upper component may be increased by manufacturing the component with a thickened contact surface. Likewise, material may be added to increase the overall height of the lower component. Providing the components in a variety of selectable heights may allow the surgeon to create the appropriate tension within the joint to both promote bone growth into the upper and lower components and to achieve a desired range of motion. In still other alternative embodiments, the heights of the upper and lower joint components may increase or decrease along the length of the component to create a desired lordosis or kyphosis. The ability to modify the resulting angle between the upper and lower vertebral contact surfaces may allow the surgeon to address variations among patient anatomies or between levels of the vertebral column, such as at the lumbosacral joint (L5-S1). Allowing the surgeon to vary the height, angulation, and performance of the prosthetic device based on the vertebral level or the patient's anatomy may ensure a better fit and a better prognosis for the patient.

For all of the embodiments described herein, the prosthetic device may be formed of any suitable biocompatible material including metals such as cobalt-chromium alloys, titanium alloys, nickel titanium alloys, and/or stainless steel alloys. Ceramic materials such as aluminum oxide or alumina, zirconium oxide or zirconia, compact of particulate diamond, and/or pyrolytic carbon may also be suitable. Polymer materials may also be used, including any member of the polyaryletherketone (PAEK) family such as polyetheretherketone (PEEK), carbon-reinforced PEEK, or polyetherketoneketone (PEKK); polysulfone; polyetherimide; polyimide; ultra-high molecular weight polyethylene (UHMWPE); and/or cross-linked UHMWPE. The various components comprising the prosthetic device <NUM> may be formed of different materials thus permitting metal on metal, metal on ceramic, metal on polymer, ceramic on ceramic, ceramic on polymer, or polymer on polymer constructions.

In any one of the described embodiments, the bone contacting surfaces of the prosthetic device including contact surfaces, keels, and/or any bridge surfaces may include features or coatings which enhance the fixation of the implanted prosthesis. For example, the surfaces may be roughened such as by chemical etching, bead-blasting, sanding, grinding, serrating, and/or diamond-cutting. All or a portion of the bone contacting surfaces of the prosthetic device may also be coated with a biocompatible and osteoconductive material such as hydroxyapatite (HA), tricalcium phosphate (TCP), and/or calcium carbonate to promote bone in growth and fixation. Alternatively, osteoinductive coatings, such as proteins from transforming growth factor (TGF) beta superfamily, or bone-morphogenic proteins, such as BMP2 or BMP7, may be used. Other suitable features may include spikes, ridges, and/or other surface textures.

The prosthetic device may be installed between adjacent vertebrae as described herein. The prosthetic device may be implanted into a patient using a posterior transforaminal approach similar to the known TLIF (transforaminal lumbar interbody fusion) or PLIF (posterior lumbar interbody fusion) procedures. PLIF style approaches are generally more medial and rely on more retraction of the traversing root and dura to access the vertebral disc space. The space between these structures is known as Kambin's triangle. TLIF approaches are typically more oblique, requiring less retraction of the exiting root, and less epidural bleeding with less retraction of the traversing structures. It is also possible to access the intervertebral space using a far lateral approach, above the position of the exiting nerve root and outside of Kambin's triangle. In some instances, it may be possible to access the intervertebral space via the far lateral without resecting the facets. Furthermore, a direct lateral approach through the psoas is known. This approach avoids the posterior neural elements completely. Embodiments of the current disclosure may adopt any of these common approaches or combinations thereof.

In various examples, some or all of the affected disc and surrounding tissue may be removed via the foramina. The superior endplate of the vertebra may be milled, rasped, or otherwise resected to match the profile of the outer contact surface of the lower joint component to normalize stress distributions on the endplate, and/or to provide initial fixation prior to bone ingrowth. The preparation of the endplate of vertebra may result in a flattened surface or in surface contours such as pockets, grooves, or other contours that may match corresponding features on the outer contact surface. The inferior endplate of the vertebra may be similarly prepared to receive the upper joint component to the extent allowed by the exiting nerve root and the dorsal root ganglia. In various examples, the natural facet joint and the corresponding articular processes can be rasped and/or prepared to accommodate and/or support an outer surface of the bridge component.

<FIG> and <FIG> depict a perspective and exploded view of an insertion tool (not claimed) <NUM> for implanting a prosthetic device of the present invention. In this embodiment, the tool <NUM> includes a central shaft <NUM> with a threaded distal tip that is threadably engaged with a lower component tool <NUM>, and an upper component tool <NUM> which slides longitudinally along a pin <NUM> in the central shaft <NUM> in response to rotation of a rotatable handle <NUM>. The tool also includes a proximal handle <NUM> which is secured to the central shaft <NUM> by a pin <NUM>.

<FIG> depict partial perspective and exploded views of a distal tip of an insertion tool <NUM> with an upper component <NUM> and a lower component <NUM> secured thereupon. In use, the insertion tool can retain both the upper and lower components for simultaneous insertion in a fully assembled fashion, and further allow a fixation element such as a screw (not shown) to be introduced through an opening in the lower component to secure the device in a desired position and/or orientation. Once the implant is secured to the vertebral body in a desired fashion, the insertion tool <NUM> can release the upper and lower components and be removed from the patient.

According to an example, a first surgical incision for providing access via a bilateral approach is made in the patient's back, and a decompression of the posterior vertebral elements on a first posterior side of the spinal motion unit (i.e., removal of portions of the upper and/or lower facets on the medial side, for example) or other standard bilateral decompression can be accomplished to provide access to the intervertebral disc space. A discectomy can then be accomplished through the access, and a distractor/trial can be placed between the vertebral bodies, with the overlying skin and tissues allowed to relax. A second surgical incision is made to provide access to the opposing (i.e., lateral) side of the spinal motion unit, and then a similar decompression and discectomy can be accomplished through the lateral access.

The surgeon can then rasp, resect and/or otherwise remove portions of the vertebral body, the pedicle and/or other posterior structures of the vertebral body, including portions of the upper endplate of the lower vertebral body, in accordance with the preoperative surgical plan. In various examples, the rasp may be operated manually, although the employed of a powered rasp tool may be particularly desirous, especially where significant bony material from the endplate, the cortical rim and/or one or more pedicles is being removed to alter the lordotic angle or other alignment(s) of one or more vertebral bodies.

In various examples, various types of flat rasps <NUM> or <NUM> (see <FIG> and <FIG>) can be utilized to remove and prepare the upper surface of the lower vertebral body and pedicle, and such rasps may be similarly used on the lower endplate of the upper vertebral body, such as to flatten or otherwise prepare the top of the disc space and/or to cut down through pedicles and/or other posterior structures where a significant osteotomy is being performed. Once the upper surface of the lower vertebral body has been prepared using the flat rasp, a keel rasp <NUM> (see <FIG>) can be utilized to prepare a keel slot or similar feature in the vertebral body and/or pedicle. Once the keel slot of prepared in the lower vertebral body, an indexed rasp <NUM> (See <FIG>) can be used, which desirably includes a non-cutting index <NUM> to align with the keel slot to create a top keel and align it with the cut along the pedicle - and the top keel groove can then be formed in the upper vertebral body.

Once one side of the vertebral body and disc space have been prepared in this fashion, a spacer or trial may be placed into the disc space to ensure the vertebral bodies have been properly prepared (if desired) - such as to ensure that a desired angular correction has been established, and/or that a desired tension of the lateral annulus will be achieved once the final implant has been emplaced. If the trial/spacer appears to properly fit, then the trial/spacer can be removed and replaced with the assembled implant. Once the assembled implant is in a desired position, an anchoring screw or other anchoring device can be inserted through the connection component and secured to the lower vertebral body.

In various examples, the flat rasp(s) or other surgical tool(s) could be attached to a surgical guidance system, allowing a surgeon to view the predicted and/or actual path of the rasp/tool on the targeted anatomy. Various additional steps of the procedure as outlined could be accomplished using a surgical guidance system, with at least one benefit of surgical guidance potentially reducing radiation exposure to the patient and/or operative room personnel while enhancing the accuracy and/or fidelity of the anatomical preparation by matching the preoperative plan with the intraoperative execution in three dimensions.

In other alternative examples, the various steps described herein could be accomplished with the aid of a surgical robot, with or without surgical navigation. In one example, the surgical robot could provide haptic feedback to the surgeon, which might desirably notify the surgeon of approaching soft tissues and/or other surgical boundaries. In another example, the robot could provide rigid limits for surgeon activity (i.e., to prevent cutting into delicate tissues, for example). In a third example, the surgical robot could complete surgical steps autonomously (i.e., with or without surgeon intervention). The employment of surgical robots as outlined could potentially reduce radiation exposure to the patient and/or operative room personnel while enhancing the accuracy and/or fidelity of the anatomical preparation by matching the preoperative plan with the intraoperative execution in three dimensions.

Claim 1:
A prosthetic system (<NUM>) for implantation between upper and lower vertebrae, the system comprising:
an upper joint component (<NUM>) comprising a metallic upper contact surface and a polyethylene upper articulation surface (<NUM>);
a lower joint component (<NUM>) comprising a first lower contact surface for engaging a cancellous bone surface exposed by resection of one or more endplate surfaces of the lower vertebrae and a metallic lower articulation surface (<NUM>) configured to movably engage the polyethylene upper articulation surface to form an articulating joint, wherein the articulating joint is adapted for implantation within a disc space between the upper and lower vertebrae and aligned along a transverse pedicle angle, allowing the upper and lower vertebrae to move relative to one another; and
a bridge component (<NUM>) extending posteriorly from the lower joint component (<NUM>) and from the disc space, the bridge component (<NUM>) having a second lower contact surface configured for engaging a resected bone surface of a pedicle of the lower vertebrae, wherein the distal end of the bridge component comprises a connection component (<NUM>) adapted to receive a fastener (<NUM>).