Patent ID: 12232974

DETAILED DESCRIPTION

As discussed above, the disclosed invention relates to artificial IVD joints. In particular, the invention relates to artificial implantable IVD joints with a “floating” COR, including artificial IVD joints with controls for adjusting the COR position.

Total disc replacement (“TDR”) devices are available for treatment of patients with a wide variety of severe inflammatory and degenerative conditions of the cervical IVD, including but not limited to spondylolisthesis, degenerative disc disease, spinal cord nerve compression, and trauma. Motion-preserving TDR procedures for cervical IVD are available for patients. The spine surgeon may choose and favor a TDR implant device based on the patient's anticipated postoperative activity level and to minimize adjacent segment disease (“ASD”). Commonly employed TDR implant devices use a ball-and-socket or similar design with a fixed COR and rotation-coupled translation. With constrained motion about a fixed COR, the positioning of the TDR implant device intraoperatively may, therefore, affect resulting postoperative kinematics.

In vivo, the intervertebral axis of rotation is affected by physiologic conditions. With reference to mechanics, the instantaneous COR of a rigid plane moving within a plane is a centrode. Fixed-position TDR devices are typically implanted intraoperatively by centering the TDR endplates in the midline of the vertebral bodies, creating a fixed COR. The patient's natural COR, however, is not fixed, but changes with spinal motion. The axis of rotation of two vertebral bodies separated by an IVD is dynamic, describing a centrode. This dynamic axis of rotation, however, is not duplicated by currently available TDR devices. In current TDR devices, the axis of rotation is fixed and translation is allowed only when coupled with rotation.

Ideally, vertebral endplate positioning of a TDR device should not necessarily be centered over the COR of the vertebral bodies, which is not fixed, but rather be determined based upon the biomechanical consequences of anterior-posterior (“A/P”) and lateral variations of the vertebral endplate positioning of the TDR device. The biomechanics may be defined and consequences of various TDR endplate positions predicted by measuring changes in facet loading and the instantaneous axis of rotation (“IAR”) with flexion and extension, lateral bending, and rotation at various levels following TDR. One way to obtain these measurements is by performing TDR in fresh human cadaver spines and then taking the measurements directly in various states of A/P flexion/extension, lateral bending, and axial rotation.

Because of the fixed nature of currently available TDR devices, the endplate placement position on the vertebral body affects the IAR, the overall range of motion (“ROM”), the facet joint load distribution, and vertebral coupling—combination of lateral bending with axial rotation depending upon the anatomic characteristics of the intervertebral and facet joints at a given level of the spine. To replicate the moving non-fixed nature of the COR in the centrode, a biasing member may be used, a non-limiting example being a spring, to control the travel of an adjustable body coupled to an articular surface. For example, a stiff spring would allow less movement of the adjustable body (small centrode envelope) compared to a relatively less-stiff spring (large centrode envelope).

Embodiments of the invention address this and other limitations by providing a TDR device which allows for adjusting the COR by partially replicating the natural “floating” COR. A total IVD replacement device may be adjusted based upon force distribution across the intervertebral and facet joint surfaces during rotation and IAR characteristics with flexion/extension, lateral bending, and axial rotation. Adjustable positioning allows the spine surgeon to optimize load distribution and stability, providing optimal performance based upon the physical parameters, age, and activity requirements of the individual patient. Embodiments of the invention selectively position prosthetic IVD joint articular surfaces between opposing vertebral end plates to account for the non-fixed nature of the COR, or centrode, of the natural IVD joint.

FIG.1(A)shows an total IVD replacement total IVD replacement device100. Total IVD replacement device100, in some embodiments, is surgically implanted in the operating room under general anesthesia to replace a diseased or damaged IVD.FIG.1(C)andFIG.1(D)show a front perspective and front view respectively of an example embodiment of total IVD replacement device100implanted between the fifth cervical vertebra and the sixth cervical vertebra of a human cervical spine. The various embodiments of total IVD replacement device100may be sized and otherwise configured appropriately for implantation at cervical spinal levels in some embodiments, at thoracic spinal levels in some embodiments, and at lumbar spinal levels in some embodiment. In some embodiments, implantation requires substantial removal of the IVD, including some or all of the annulus and some or all of the nucleus pulposis. In some embodiments, a portion of the vertebral body above and below the disc space is also removed as necessary to create a space for insertion of total IVD replacement device100without substantially altering the length of and/or transmitting a compressing or distracting force to other levels of the spinal column. This may be somewhat appreciated by the embodiment shown inFIG.1(D). An anterior surgical approach for implantation of total IVD replacement device100is preferable, in some embodiments. In some embodiments, a lateral surgical approach may be used to expose the adjoining vertebral bodies for IVD replacement. In some embodiments, still other surgical approaches may be used.

As shown in the embodiment illustrated inFIG.1(A)andFIG.1(B), total IVD replacement device100comprises two primary components: a cranial member120and a caudal member140. Cranial member120and caudal member140are each an assembly of components (see exploded views inFIG.8-FIG.10.) In the example embodiment shown in the drawing figures, and in some other embodiments, cranial member120and caudal member140are the same, wherein caudal member140is merely an upside-down cranial member120. In no way, however, is this intended to be limiting. Some embodiments of the invention employ, for example, different shapes, articular surfaces, actuator means, adjustable body-base body coupling means, and other aspects distinguishing cranial member120and caudal member140from one another.

Cranial member120and caudal member140each, in some embodiments, comprise a base body and an adjustable body coupled to an articular surface, wherein the adjustable body is moveable in relation to the base body. In some embodiments, the adjustable body is moveable along an anteroposterior axis AP, as shown inFIG.1(A). In some embodiments, the adjustable body is movable along a lateral axis L, as shown inFIG.1(A). In some embodiments, the adjustable body is movable along both anteroposterior axis AP and lateral axis L. In some embodiments, the adjustable body position is controlled by a biasing member acting along anteroposterior axis AP. In some embodiments, the adjustable body is controlled by a biasing member acting along lateral axis L. In some embodiments, the adjustable body is positioned by an actuator, wherein a spine surgeon or other healthcare provider may adjust the position of the adjustable body with respect to its respective base body. These example embodiments are discussed in detail herein below.

FIG.1also shows a cranial base body122that, when implanted in a patient, attaches to the caudal aspect of the vertebral body immediately cranial to the IVD replacement level. For example, in an IVD replacement at C5-C6, cranial base body122attaches to the caudal aspect of the fifth cervical vertebral body. Also in this example, and as suggested byFIG.1(D), a caudal base body142attaches to the cranial aspect of the sixth cervical vertebral body.

Cranial base body122, caudal base body124, and other components of total IVD replacement device100are constructed from non-toxic, biocompatible substances, such as those known in the art and currently used in other prosthetic devices. Examples include polyethylene for articular surfaces. Cobalt-chromium alloys, titanium, titanium allows, tantalum, zirconium and its alloys, and polyethylene may be used for the base bodies, adjustable bodies, and other components of total IVD replacement device100. There materials are listed by way of example only. Other non-toxic, corrosion-resistant, biocompatible materials are be used, in some embodiments.

In some embodiments, a cranial attachment apparatus110couples cranial base body122to a caudal aspect of a cranial vertebral body and a caudal attachment apparatus couples caudal base body142to the cranial aspect of a caudal vertebral body. In some embodiments, such as the embodiment shown inFIG.1(D), cranial attachment apparatus110comprises a cranial screw strut111and a cranial bone screw112. Two cranial bone screws112engaging cranial base body122through a pair of cranial screw struts111and two caudal bone screws162engaging caudal base body142through a pair of caudal screw struts161are shown in the embodiment illustrated inFIG.1(D). This is not meant to be limiting, other suitable mechanical attachment apparatuses can be employed. Another apparatus attaching a base body to an adjacent vertebral body is a biocompatible bone cement coupled to a cranial adhesive surface113or a caudal adhesive surface163. Examples of bone cement include, but are not limited to, synthetic self-curing compounds such as polymethyl methacrylate (“PMMA”) and methyl methacrylate (“MMA.”) The mechanical attachment apparatuses may comprise bone screw(s) biocompatible adhesive, or a combination of bone screw(s)102and biocompatible adhesive. Other fasteners, cements, or alternative attachment or coupling apparatuses are employed in some embodiments to maintain total IVD replacement device100coupled to adjacent vertebral bodies, including natural in-vivo anatomic structures and forces, in some embodiments.

As shown by the various exploded, views in the drawing figures referenced above and further discussed below, cranial member120and caudal member140also comprise an example of a total IVD replacement device100wherein the respective adjustable bodies are movably coupled to the respective base bodies, in some embodiments. Cranial member120and caudal member140each comprise an articular surface; cranial adjustable body127of cranial member120comprises a cranial articular surface129and caudal adjustable body147of caudal member140comprises a caudal articular surface149.

Cranial articular surface129and caudal articular surface149moveably engage one another to form an artificial joint interface of total IVD replacement device100and reconstruct the motion, load-bearing, and force distribution characteristics of the replaced IVD. Cranial articular surface120and caudal articular surface140are shown inFIG.2-FIG.10as flat, planar surfaces. This is not meant to be limiting, but rather to offer a simple example for clarity. Cranial articular surface129and caudal articular surface140may be fashioned into any manner of complimentary shapes that moveably engage one-another to allow for motion across the total IVD replacement device100. One example of such complimentary shapes is a partial ball-and-socket configuration, as in the embodiment of total IVD replacement device100shown inFIG.1(C)andFIG.1(D). These two figures show an embodiment of total BID replacement device100wherein caudal articular surface149is a partial convexity, as shown byFIG.1(C), and cranial articular surface129is a corresponding partial concavity (incompletely shown by the figure.) In alternative embodiments, the convexity may be on cranial articular surface120and the concavity on caudal articular surface149. Other shapes and examples are possible for cranial articular surface120and caudal articular surface149. In some embodiments, the artificial joint interface is a surface allowing only flexion-extension.

In the example embodiment shown inFIG.1(B), caudal articular surface149is coupled to a caudal adjustable body147of caudal member140. In the embodiment shown inFIG.1(A)andFIG.1(B), caudal base body147comprises a second recess157defining an inner volume having a perimeter. Second adjustable body147is coupled within second recess157and moveable within the perimeter of second recess157. Caudal adjustable body147extends from the inner volume of second recess157. In some embodiments, a first caudal actuator144engages caudal adjustable body147. In some embodiments, a second caudal actuator145engages caudal adjustable body147. In the embodiments shown, caudal adjustable body147moves parallel to anteroposterior line AP (shown inFIG.1(A)). In some embodiments, caudal adjustable body147moves parallel to lateral line L, perpendicular to anteroposterior line AP. In some embodiments, caudal adjustable body147moves two-dimensionally in a plane wherein anteroposterior line AP and lateral line L are coplanar, defining a plane wherein the instantaneous COR of caudal adjustable body147is located within the plane. In some embodiments, first caudal actuator144engages caudal adjustable body147and controls movement of caudal adjustable body147in a direction parallel with anteroposterior line AP. In some embodiments, second caudal actuator145engages caudal adjustable body147and controls movement of caudal adjustable body147in a direction parallel with lateral line L. In some embodiments, caudal adjustable body147remains in a non-fixed position, moving in the plane defined by the coplanar lines line AP and line L.

In some embodiments, caudal adjustable body147is adjusted to a non-fixed position or partially fixed position with an instantaneous COR located on a plane defined by the A/P axis and the lateral axis. In these and some other embodiments, second actuator activates caudal adjustable body147so as to control motion along the A/P axis, the lateral axis, or a combination of both the A/P and the lateral axes.

Similar to caudal member140, cranial member120, in some embodiments, comprises a cranial adjustable body127comprising a cranial articular surface129. Cranial base body122comprises a first recess137defining an inner volume having a perimeter. Cranial adjustable body127is coupled within first recess137and moveable within the perimeter of first recess137. Cranial adjustable body127extends from the inner volume of first recess137. In some embodiments, a first cranial actuator124engages cranial adjustable body127. In some embodiments, first cranial actuator124or second cranial actuator125control movement of cranial adjustable body127in scope and manner similar to the activation and control of caudal adjustable body147by first caudal actuator144and second caudal actuator145of caudal member140, discussed above. In some embodiments, the motion of first adjustable body127is controlled by first cranial actuator124or second cranial actuator125in scope and manner substantially different than the control of second adjustable body147by first caudal actuator144or second caudal actuator145. In some embodiments, the manner of activation employed by first cranial actuator124, second cranial actuator125, first caudal actuator144, and second caudal actuator145is substantially the same. In some embodiments, first cranial actuator124or first caudal actuator144is a unitary actuator, wherein either first cranial actuator124or first caudal actuator144positions both cranial adjustable body127and caudal adjustable body147simultaneously along line AP. In some embodiments, second cranial actuator125or second caudal actuator145is a unitary actuator, wherein either second cranial actuator125or second caudal actuator144positions both cranial adjustable body127and caudal adjustable body147simultaneously along line L.

In some embodiments, adjustments are performed non-surgically by remotely adjusting any one or more of first cranial actuator124, second cranial actuator125, first caudal actuator144, or second caudal actuator145in any combination based upon data generated from an internal cranial stress monitoring device (not shown in the Figures), an internal caudal stress monitoring device (not shown in the Figures), or data generated from both the internal cranial stress monitoring device and the internal caudal stress monitoring device. In some embodiments, either or both the internal cranial stress monitoring device and the internal caudal stress monitoring device are coupled to IVD replacement device100. In some embodiments, either or both the internal cranial stress monitoring device and the internal caudal stress monitoring device are not coupled to IVD replacement device. Either or both of the internal cranial stress monitoring device and the internal caudal stress monitoring device may be mechanically coupled to an intervertebral disc, a vertebral body, an intervertebral facet joint, a vertebral lamina, a vertebral pedicle, or any other vertebral or intervertebral anatomic structure adjacent to or remote from the spinal level of total IVD replacement device100insertion, without limitation. This use of stress monitoring devices for internal stress monitoring, in some embodiments, directs and allows for non-surgical adjustments of cranial adjustable body127or caudal adjustable body147to be performed at any time, according to changes in force distribution along the anterior or posterior spinal columnar elements to create and maintain a favorable distribution of forces within the spinal column.

FIG.2is a left side view of total IVD replacement device100. As shown inFIG.2, cranial member120contacts caudal member140at the interface between cranial articular surface129and caudal articular surface149. Also shown inFIG.2is a cranial screw strut123of cranial base member122and a caudal screw strut143of caudal base member142. Cranial screw strut123and caudal screw strut143in the embodiment shown direct a bone screw into a vertebral body at an angle suitable to create a force component tending to secure each base member upward or downward (i.e. cranially or caudally) against its corresponding vertebral body.

FIG.2shows the small portion of cranial adjustable body127and caudal adjustable body147extending from a cranial base body122and caudal base body142respectively. In the embodiment shown in the figures, this exposed portion of each adjustable body comprises a flange which contacts a sliding surface of the corresponding base body. Cranial adjustable body127comprises a cranial flange128and second adjustable body147comprises a caudal flange148. The full shape of cranial adjustable body127and caudal adjustable body147, including cranial flange128and caudal flange148, is shown in the exploded drawing figures (FIG.8-FIG.10) discussed herein below.

FIG.2also shows first cranial actuator124and first caudal actuator144partially engaged within cranial base member122and caudal base member142respectively. First actuator124and second actuator144are shown fully engaged within the corresponding base members122and142byFIG.1(D). In this and some other embodiments, first cranial actuator124and first caudal actuator144are bolts which are accessed from an anterior (front-side) position. This facilitates activating the corresponding adjustable body in the A/P axis. Some embodiments may employ first actuator124, second actuator144, or both accessed from a lateral position to facilitate activating the corresponding adjustable body on the lateral axis. Other actuator apparatuses may be used, such as, for example, cams, levers, cantilevered members, an apparatus comprising a solenoid, other electronic apparatus, or a hydraulic apparatus. Any suitable apparatus for causing movement of an adjustable body, controlling movement of an adjustable body, or simultaneously both causing and controlling movement of cranial adjustable body127or caudal adjustable body147within a base body122or a base body142respectively are used in some embodiments of the invention.

FIG.3is a right side view of total IVD replacement device100, corresponding to the left side view shown inFIG.2and described above. In the embodiments shown by the figures, there is left-right symmetry. This is not meant to be limiting. In some embodiments, asymmetry between the left side and the right side of total IVD replacement device100may be present. Additionally,FIG.3shows anteroposterior axis line AP.

FIG.4is a front (anterior) view of total IVD replacement device100. A corresponding view of an implanted total IVD replacement device100mentioned above is shown byFIG.1(D). In the embodiment shown byFIG.4, total IVD replacement device100projects backward (posteriorly) into the intervertebral space, replacing the excised IVD, at the level where total IVD replacement device100is implanted in the spinal column. First cranial actuator124and first caudal actuator144are shown, along with the midline positioning of each actuator in the illustrated embodiment. Also shown inFIG.4are caudal screw struts161oriented at an angle for engaging cranial bone screws112. First flange128of cranial adjustable body127and second flange148of caudal adjustable body147are also shown.

FIG.5shows a back (posterior) view of total IVD replacement device100. In the embodiment shown inFIG.5, with the exception of cranial screw struts123and caudal screw struts161, all visible surfaces of the device in the figure are contained within the intervertebral space, cranial vertebral body, and caudal vertebral body when total IVD replacement device100is implanted in a spinal column. Additionally,FIG.5shows lateral axis line L.

FIG.6shows a top view of total IVD replacement device100. Cranial base body122, cranial screw struts123and first cranial actuator124are the only designated structures seen in this view. Of note, cranial base member122comprises cranial adhesive surface113. Cranial adhesive surface113and caudal adhesive surface163shown inFIG.7, each present a broad, flat surface for contacting the caudal aspect or cranial aspect respectively of a vertebral body when implanted into the resected IVD space. In some embodiments, cranial base body122, caudal base body142, or both elements are formed from a sufficiently porous material, such as tantalum or tantalum-ceramic, for example, to enhance penetration of bone cement and/or ingrowth of bone. In some embodiments, the combination of porous material and a relatively large surface area contributes to stable and durable fixation of cranial base body122and caudal base body142to the corresponding vertebral bodies.

FIG.7shows a bottom view of total IVD replacement device100. As shown byFIG.6andFIG.7, some embodiments of total IVD replacement device100present a similar profile from the top or the bottom.

Exploded views ofFIG.8-FIG.10demonstrate elements of one non-limiting example embodiment for positioning (moving and/or fixing in position) an adjustable body of total IVD replacement device100wherein the components shown have been discussed with regard toFIGS.1-7. The listed elements comprising caudal member140, or cranial member120, comprise a system wherein a dynamic COR is created. The joint interface between cranial articular surface129and caudal articular surface149is movable such that the natural distribution of forces during antero-posterior flexion, lateral bending, and axial rotation of the vertebral bodies along the spinal axis on either side of the implanted total IVD replacement device100is preserved.

Different embodiments of total IVD replacement device100create a dynamic COR in slightly different ways, according to the movement characteristics and forces present at the IVD joint replacement level in the spinal column. For example, in some embodiments, the position of caudal adjustable body147relative to caudal base body142adjusts by moving along a first caudal track150in the caudal axis AP. In some embodiments, the position of caudal adjustable body147relative to caudal base body142additionally adjusts by moving along a second caudal track in the caudal axis L, wherein caudal adjustable body147“floats” in a plane formed by the two coplanar lines caudal axis AP and caudal axis L. First caudal track150may be any track, such as a pin-track as shown inFIG.7andFIG.8. Alternatively, first caudal track may be a groove in caudal base body142that engages with a shape corresponding to a tongue on caudal adjustable body147. In some embodiments, the groove is located on caudal adjustable body147and the shape comprises caudal base body142. In some embodiments, other pin-and-groove track mechanisms are used.

A similar arrangement of elements comprises cranial member120, such cranial adjustable body127moves in relation to cranial base body122causing the position of cranial articular surface129of cranial adjustable body127to correspond with caudal articular surface140of caudal adjustable body147. In some embodiments, cranial member120comprises a first cranial actuator124that adjusts a position of cranial adjustable body127along cranial axis AP by controlling movement along cranial axis AP or fixing the position of cranial adjustable body127along cranial axis AP. In some embodiments, cranial member120comprises a second cranial actuator125that adjusts a position of cranial adjustable body127along cranial axis L by controlling movement along cranial axis L or fixing the position of cranial adjustable body127along cranial axis L. In some embodiments, a first cranial biasing member131biases cranial adjustable body127against first cranial actuator124. First cranial biasing member131may be a compression spring, in some embodiments. In some embodiments, first cranial biasing member131may be a mechanical biasing member other than a compression spring. In some embodiments, first cranial biasing member131may be a solenoid or similar electrically-activated magnetic biasing device.

In some embodiments, a first caudal actuator144controls movement of caudal adjustable body147in one direction along caudal axis AP. In some embodiments, first caudal actuator144fixes caudal adjustable body147in a fixed position, wherein adjustment of first caudal actuator144determines the position of fixation of caudal adjustable body147along caudal axis AP. In some embodiments, a first caudal biasing member151biases caudal adjustable body147against first caudal actuator144. First caudal biasing member151may be a compression spring, in some embodiments and in the embodiment shown inFIG.8andFIG.9. In some embodiments, first caudal biasing member151may be a mechanical biasing member other than a compression spring. In some embodiments, first caudal biasing member151may be a solenoid or similar electrically-activated magnetic biasing device.

Such elements may comprise caudal member140, cranial member120, both, or neither in embodiments of the invention. In some embodiments, a positioning/fixing, apparatus other than shown in the drawing figures may be used. Different or similar elements may comprise caudal member140and cranial member120in some embodiment of the invention. In some embodiments, adjustment of any one actuator, such as first cranial actuator124, second cranial actuator125, first caudal actuator144, or second caudal actuator145simultaneously and correspondingly adjusts, limits, or fixes the position of both cranial articular surface129of cranial adjustable body127and caudal articular surface149of caudal adjustable body147. In some embodiments, adjustment of any two actuators correspondingly adjusts, limits, or fixes the position of both cranial articular surface129of cranial adjustable body127and caudal articular surface149of caudal adjustable body147.

In the embodiment shown inFIG.8, and some other embodiments, caudal adjustable body147comprises a caudal rib153coupled to caudal flange148opposite caudal articular surface149. When assembled, caudal rib153is enveloped within caudal base body142. Caudal flange128engages a caudal sliding surface141of caudal base body142; correspondingly, cranial flange128engages a cranial sliding surface134of cranial base body122. In the embodiments shown inFIG.8and other drawing figures, caudal rib153comprises a caudal track guide152. In some embodiments, two caudal track guides152each engage a corresponding caudal track150. Caudal track150is coupled to caudal base body142. In some embodiments, a first cranial track130is similarly coupled to cranial base body142. In the embodiment shown inFIG.8, first caudal biasing member151also engages first caudal track150, although this is not meant to be limiting. When assembled, first caudal track150and first caudal biasing member151are located within an inner volume of caudal base body141such that first caudal biasing member151is constrained and partially compressed between first caudal blocking surface154and second rib153. A similar mechanism for cranial member120comprising a first cranial track130, a first cranial biasing member131, cranial base body122, a first cranial blocking surface134, and a first cranial rib133. First cranial actuator124or first caudal actuator144engage cranial rib133or caudal rib153opposite first cranial biasing member131or first caudal biasing member151respectively such that first cranial actuator124or first caudal actuator144and first cranial actuator131or first caudal actuator151exert opposing forces against cranial rib133or caudal rib153respectively. These opposing forces operate to stabilize cranial adjustable body127or caudal adjustable body147in a position governed by the position of first cranial actuator124or first caudal actuator144respectively. The foregoing example of an apparatus for positioning an adjustable body of total IVD replacement device100is not meant to be limiting. Any similar or alternative but suitable means for adjusting the position of cranial articular surface129or caudal articular surface149relative to cranial base body122or caudal base body142respectively of total IVD replacement device100can be used.

FIG.9is a bottom (caudal) view of elements of a disassembled cranial member of a total IVD replacement device.FIG.9shows cranial base body122and cranial adjustable body127, two first cranial tracks130, first cranial biasing member131and first cranial actuator124, in a non-limiting example embodiment.

FIG.10is an additional exploded perspective view of a caudal member of a total IVD replacement device. Similar toFIG.8discussed in detail herein above,FIG.10shows elements comprising caudal member140, including first caudal track150and first caudal track guide152, wherein caudal adjustable body147moves along caudal axis AP (as illustrated inFIG.1(A). First caudal biasing member151is not shown in this figure.

FIG.11is a flowchart diagram of a method200of surgically inserting an total IVD replacement device into a patient. Method200comprises an excising step210, a coupling step220, and an articulating step230. Excising step210comprises surgically removing the IVD from an intervertebral space, using established surgical techniques known in the art. In some embodiments, excising step additionally comprises excising a portion of each vertebral body bounding the excises IVD intervertebral space cranially and caudally to increase the space available for insertion of the total IVD replacement device.

Coupling step220comprises coupling a total IVD replacement device to a vertebral body. In some embodiments, coupling step comprises utilizing a commercially available bone screw designed for fixing a hardware device to a vertebral body to fix a cranial base body or a caudal base body of the total IVD replacement device to the corresponding vertebral body. In some embodiments, coupling step220comprises the use of a biocompatible adhesive bone cement, such as polymethyl-methacrylate, or the like. In some embodiments, coupling step220comprises both the use of a bone screw and an adhesive. In some embodiments, coupling step220comprises the use of an alternative orthopedic fixation device other than a bone screw.

Articulating step220of method200comprises articulating a cranial articular surface and a caudal articular surface of a total IVD replacement device. In some embodiments, articulating step220is performed prior to coupling step220. In some embodiments, articulating step220is performed following coupling step220, with or without execution of additional intervening steps, in some embodiments.

FIG.12is a flowchart diagram an alternative embodiment of method200.FIG.12shows an additional radiographing step240. Radiographing step240comprises radiographing the position of the total IVD replacement device following coupling step220and articulation step230. Radiographing step240is performed utilizing established techniques known in the art and is useful to confirm proper positioning of total IVD replacement device100in the patient, prior to completing the surgical procedure.

FIG.13is a flowchart diagram of an additional alternative embodiment of method200.FIG.13shows an additional fluoroscoping step250. Fluoroscoping step250comprises dynamically intraoperatively fluoroscoping the position of the total IVD replacement device. The use of intraoperative fluoroscopy is important, in some embodiments, to evaluate how the position of coupled total IVD replacement device100affects movement of intervertebral joints through the spinal column above and below inserted total IVD replacement device100. Evidence of asynchronous motion, asymmetrical motion, and unbalanced force distribution caused by an sub-optimally positioned or maladjusted total IVD replacement device is visible upon fluoroscopic evaluation during flexion-extension, lateral bending, and axial rotation, in some embodiments. The surgeon is then able to discover sub-optimal positioning or adjustment of the total IVD replacement device and attempt to correct the position or adjustment while the patient remains under anesthesia in the operating room.

FIG.14is a flowchart diagram yet another alternative embodiment of method200.FIG.14shows an additional adjusting step260. Adjusting step260comprises adjusting the position of an articular surface of the coupled total IVD replacement device. In some embodiments, adjusting step260comprises adjustment of an actuator to adjust, move, or fix the position of the articular surface. In some embodiments, adjusting step260is performed following radiographing step240or fluoroscoping step250. In some embodiments, adjusting step260and fluoroscoping step215are alternatively and repeatedly performed until the position of the articular surface is optimized by the operating surgeon.

In some embodiments, adjusting step260is performed at a time after the patient leaves the operating room. In some embodiments, adjusting step260is performed by a healthcare provider other than the operating surgeon, in a remote place and at a remote time from the surgical procedure performed in a hospital to insert total IVD replacement device100in the patient. For example, in some embodiments, adjustments are performed non-surgically by remotely adjusting any one or more of first cranial actuator124, second cranial actuator125, first caudal actuator144, or second caudal actuator145in any combination based upon data generated from an internal cranial stress monitoring device (not shown in the Figures), an internal caudal stress monitoring device (not shown in the figures), or date generated from both the internal cranial stress monitoring device and the internal caudal stress monitoring device.

EXPERIMENTAL EXAMPLE AND RESULTS

In the course of developing various embodiments of the invention, experiments were undertaken to determine the biomechanical effects of cervical fixed-COR TDR device position variations on inter-vertebral body motion and vertebral load sharing. To develop and test a working prototype of some embodiments of the invention, an experimental model was used. In this model, TDR was performed in fresh cadaveric human donor spines at the C5-C6 position. A commercially available 5 mm M TDR device coupled to an embodiment of the invention was implanted. Implantation required a full C5-C6 disc In this and other embodiments, the A/P endplate position is adjustably controlled with a center set screw, wherein two full screw rotations translates the endplate position by 1 mm in the A/P plane.

In one experimental example, fresh, un-embalmed cadaver spine specimens comprising integrated segments C3-T1 from five human donors (three male and two female, mean age±standard deviation of 49.2±11.2 years) were used. Stain gauges were attached to the right and left lamina of C5 to monitor vertebral load sharing across the C5/C6 facet joints immediately above the TDR index level (C5-C6). The specimens were tested quasi-statically using pure moments (1.5 Newton-meters) in flexion-extension (“FE”), right and left axial rotation (“AR”), and right and left lateral bending (“LB”) in the following configurations: 1) normal/intact (no TDR); 2) centered TDR; 3) TDR positioned 2 millimeters (“MM”) anteriorly; and 4) TDR positioned 2 mm posteriorly. The testing order in configurations 2, 3, and 4 above was randomized among the specimens. Anteroposterior (“A/P”) device positions were controlled on custom designed and fabricated inferior and superior implant base plates with implant positions verified using X-ray fluoroscopic A/P and lateral views. Collected data included range of motion (“ROM”), lax zone/stiff zone, location of COR, angular coupling, and changes in surface strain indicating changes in load sharing across the anterior (vertebral bodies/IVD joints) and posterior (facet joints) elements of the vertebral column. The effects of TDR position variations were analyzed by comparing the changes from normal and using RM-ANOVA with a p-value of 0.05.

Results showed that the A/P TDR position variations had a greater effect on the ROM during FE than during LB and AR, however the changes were not statistically significant in any direction of motion. The effects of TDR position variations on coupled motion, including AR during LB and LB during AR, were not significant. The axis of rotation shifted in the direction of the changed TDR position.

There were, however, notable changes in laminar strains, indicating changes in facet loads within the posterior column. These results were interpreted to show that although A/P position variations of greater than 2 mm of a cervical TDR at the C5-C6 level have a fixed COR not significantly affected by the ROM or coupled motion, IAR and laminar strains show significant load-sharing changes between the anterior and posterior spinal columns via the facet joints.

An total IVD replacement device has been described. Preliminary testing of a prototype of some embodiments of the invention suggests the total IVD replacement device performs well in the experimental model and provides superior versatility compared to TDR devices currently available and described in the art. The total IVD replacement device is surgically implanted to replace an IVD damaged by disease, trauma, or other degenerative process. Elements of the invention enable adjustment of the relative positions of the joint's articular surfaces, allowing for optimization of load distribution between the anterior and posterior spinal elements, thus increasing stability and providing optimal performance specific to the age, physical parameters, and activity requirements of an individual patient.

The embodiments and examples set forth herein were presented in order to best explain the present invention and its practical application and to thereby enable those of ordinary skill in the art to make and use the invention. However, those of ordinary skill in the art will recognize that the foregoing description and examples have been presented for the purposes of illustration and example only. The description as set forth is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the teachings above without departing from the spirit and scope of the forthcoming claims.