Patent Publication Number: US-2021161682-A1

Title: Methods and devices for spinal correction

Description:
TECHNICAL FIELD 
     The present disclosure relates to spinal correction methods and systems including expandable trial implants and techniques for monitoring the amount of neural spacing achieved and optionally monitoring the amount of disc space distraction and the force on the vertebral endplates. 
     BACKGROUND 
     The human spine is a series of bony vertebral bodies separated by flexible discs called “intervertebral discs.” The discs contain a compressible, flexible jelly-like center called the nucleus pulposus. This flexibility allows the spine to bend and twist. The annulus fibrosus is a tougher, fibrous material that surrounds and contains the nucleus, which otherwise could be extruded into other parts of the body. 
     The human skeleton provides an architectural structure for the human body. The human spine provides not only a mechanical structure for supporting a person&#39;s weight, but also provides passages for the “wires” of the nervous system. The spine provides spacing for the nerves to travel from the brain to other parts of the body. The majority of this spacing is the spinal canal which contains and protects the spinal cord. The spine also defines, at each level of the spine, spacing for nerves roots to branch off from the spinal cord and travel to other parts of the body. Intervertebral discs between the vertebral bodies are critical in providing the appropriate amount of spacing between the vertebral bodies to allow room for these nerve roots. If the discs begin to collapse from their normal height, nerve roots may become compressed and cause pain. 
     The discs also help provide alignment of the vertebral bodies, keeping the spinal canal as a relatively smooth passage for the spinal cord. If the discs become misaligned, the spinal canal may become disjointed and extremely narrowed in portions. If it becomes too narrowed, the spinal cord may become compressed and cause pain. Spondylolysis is an example of one condition which can affect the spacing in the spinal canal. In spondylolysis, one vertebral body slips forward relative to another vertebral body. This can result in a narrowing of the spinal canal and compression of the spinal cord. 
     Other spinal disorders can also result in nerve compression. For example, degenerative disc disease (DDD) can result in a herniated disc. A herniated disc occurs when a portion of the nucleus is extruded from the disc space. This extrusion might impinge on a nerve and cause pain. Also, the extrusion of too much of the nucleus may result in a reduction in the height of the disc, and cause narrowing of the spacing available for nerve roots. 
     A common method of managing these problems is to remove the problematic disc and replace it with a device that restores the disc height and allows for bone growth therethrough. This results in the fusion of two or more adjacent vertebrae. The devices used in this procedure are commonly referred to as “fusion devices” or “fusion cages”. 
     In a fusion procedure, a surgeon first accesses the intervertebral disc space. Next, the surgeon clears out a portion of the intervertebral disc space to make room for the fusion device (or cage). The surgeon may determine the appropriate size fusion cage by using trial implants and “testing” its fit via tactile and visual assessment, often assisted by fluoroscopy. Neuromonitoring can also be used to confirm that there is no significant injury or damage to the neural structures. For example, neuromonitoring can be used to test the response and latency of the nerves which can give an indication of how healthy the nerve is. However, neuromonitoring does not determine if the procedure has created enough “space” (referred to as neural release) to relieve the compression on the nerve. 
     SUMMARY 
     An expandable trial can include an inferior portion, a superior portion, and a middle expanding portion as well as load cells for monitoring the load on the trial. The trial may also include recesses on its lateral sides to provide spacing to accommodate a disc removal tool so tissue can be cleared while monitoring load. In addition, neural foramen spacing can be monitored to provide information about how much neural release has been achieved as the disc is cleaned and the spine is positioned and repositioned. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1 a    is a flow chart of an exemplary embodiment of a method for spinal correction using an expandable trial implant and monitoring the amount of neural spacing achieved. 
         FIG. 1 b    is a system diagram of an exemplary embodiment of a system for spinal correction which may be used in connection with the method of  FIG. 1   a.    
         FIG. 2 a    shows an exemplary embodiment of an image-guided surgery system which may be used in connection with the method of  FIG. 1   a.    
         FIG. 2 b    shows an exemplary embodiment of a mylogram tracking system which may be used in connection with the method of  FIG. 1   a.    
         FIG. 2 c    shows an exemplary embodiment of a direct visualization system which may be used in connection with the method of  FIG. 1   a.    
         FIG. 2 d    shows an exemplary embodiment of an ultrasonic detection system which may be used in connection with the method of  FIG. 1   a.    
         FIG. 2 e    shows an exemplary embodiment of a direct visualization system which may be used in connection with the method of  FIG. 1   a.    
         FIG. 2 f    shows an exemplary embodiment of a dye-based mylogram tracking system which may be used in connection with the method of  FIG. 1   a.    
         FIGS. 3 a  and 3 b    show an exemplary embodiment of an expandable trial implant which may be used in connection with the method of  FIG. 1   a.    
         FIGS. 4 a , 4 b , and 4 c    show exemplary embodiments of a visual display system providing a top view of load information from an expandable trial implant which may be used in connection with the method of  FIG. 1   a.    
         FIGS. 5 a  through 5 h    show an exemplary embodiment of another exemplary embodiment of an expandable trial implant which may be used in connection with the method of  FIG. 1 a      
         FIGS. 6 a  through 6 h    show another exemplary embodiment of an expandable trial implant which may be used in connection with the method of  FIG. 1   a.    
     
    
    
     DETAILED DESCRIPTION OF THE FIGURES 
       FIG. 1 a    is a flow chart of an exemplary embodiment of a method for spinal correction  10  using an expandable trial implant and including monitoring an amount of neural spacing achieved. While various method steps are shown, it is not mandatory for each step to be performed, for example, in some cases an intra-operative baseline may not be determined. Other steps may also be omitted. 
     Spinal correction method  10  may be implemented with a spinal correction system  50  shown in  FIG. 1   b.  As shown in  FIG. 1   b,  spinal correction system  50  includes a neural release system  70 . Neural release system  70  includes a neural spacing monitoring system  72  which determines information representative of an amount of neural spacing achieved. Neural spacing monitoring system  72  may be implemented in various embodiments, such as will be discussed in connection with  FIGS. 2 a    through  2   f.  Neural release system  70  also includes display device  74  and data store  76 . Neural release system  70  can also communicate with data aggregation system  80  which aggregates and evaluates medical data. Data aggregation system  80  may be the system described in any of the following patent applications, each of which are herein incorporated by reference in their entirety: U.S. Patent Application Ser. No. 61/702,073, filed Sep. 17, 2012 and entitled “Systems and Methods for Surgical Planning, Support, and Review”; U.S. Patent Application Ser. No. 61/739,514, filed Dec. 19, 2012 and entitled “Systems and Methods for Surgical Planning, Support, and Review”; and U.S. patent application Ser. No. 13/803,763, filed Mar. 14, 2013 and entitled “Systems and Methods for Surgical and Interventional Planning, Support, Postoperative Follow-Up, and Functional Recovery Tracking.” Data aggregation system  80  may store data from the neural spacing monitoring system  72  and neural release system  70 , along with other post-operative data, and use a combination of data to predict the likelihood of success for fusion and/or pain relief of a future surgery for a particular patient. The prediction of likelihood of success may be based on past outcomes of surgeries on other patients and on information about the particular patient. Data aggregation system  80  may use any of the techniques and algorithms described therein for making such predictions. 
     Spinal correction system  50  includes a pre-operative planning system  60  which may be implemented in various embodiments discussed further below. Spinal correction system  50  also includes load and contact system  65  which determines the load on the expandable trial implant at various portions of the implant and also determines the portions of the trial implant that have contacted the endplates of the vertebral body. While various components are shown, it is not mandatory for spinal correction system  50  to include each component/system. Moreover, while the spinal correction system  50  is shown as including separate physical components, the system  50  could be implemented in one physical component or could be distributed among various components in manners other than as illustrated. 
     Turning back to method  10  of  FIG. 1 a   , as shown at step  100 , pre-operative planning is performed using pre-operative planning system  60 . Pre-operative planning system  60  may include an imaging system (e.g., magnetic-resonance imaging (MRI) systems, x-ray systems, fluoroscopy systems, computed tomography (CT) systems, etc.) to estimate an amount of existing (pre-operative) neural spacing and existing neural compression as well as the amount of disc space achieved by the expandable implant. This information may be communicated to neural release system  70  for determination of a planned amount spinal correction and a planned amount of neural release. The planned amount of spinal correction and the planned amount of neural release may be based on the aggregation of data in data aggregation system  80  which includes historical data on spinal surgeries and their outcomes for pain relief. 
     The existing amount of spinal abnormality and planned amount of spinal correction may be described using various parameters. Pre-operative planning system  60  may calculate an existing pre-operative disc space height (which may include disc space height at various portions of the disc, e.g., posterior, anterior, lateral, central, etc.). Pre-operative planning system  60  may also calculate an existing pre-operative disc space angle (which may include the angle of the superior endplate along various planes, the angle of the inferior endplate along various planes, the angles between both, etc.). This angle may represent the existing pre-operative amount of lordosis, kyphosis, sagittal balance, and coronal balance. The existing pre-operative parameters may be calculated based on images from a CT, MRI, or other non-invasive techniques. 
     Neural release system  70  (or alternatively pre-operative planning system  60  or data aggregation system  80 ) may calculate a planned post-operative disc space height, or change in height, and angle, or change in angle (as well as other parameters such as a desired or planned sagittal and/or anterior-posterior adjustment of one vertebral body relative to another to correct for a spondylolysis). The planned pre-operative parameters may be calculated based on images from a CT, MRI, etc. as well as based on empirical data of previous spine surgeries. The empirical data may include both pre- and post-operative disc space height and angle (and other parameters) as well as data representative of the outcomes of prior surgeries. The outcomes may include post-operative pain data, fusion data, etc. The calculation may be performed by pre-operative planning system  60  with or without information from data aggregation system  80 . 
     In addition to calculating planned or desired post-operative geometries, neural release system  70  (or alternatively pre-operative planning system  60  or data aggregation system  80 ) may calculate a desired or planned post-operative amount of neural release. The planned amount of neural release may take a variety of forms depending on the type of neural release monitoring system to be used intra-operatively. The planned post-operative amount of neural release may be calculated based on images from a CT, MRI, etc. and may be based on empirical data of previous spine surgeries, e.g., using information from data aggregation system  80 . The empirical data may include both pre- and post-operative disc space height and angle and alignment as well as data representative of the outcomes of prior surgeries. The outcomes may include post-operative pain indications, fusion indications, etc. 
     As shown at step  110 , intra-operative baseline measurements are taken and received by neural release system  70 . For example, after the patient is positioned, the surgeon may obtain a baseline of actual neural spacing (e.g., actual neural foramen size, or information representative of neural foramen size such as pressure, size calculations based on direct visualization, etc.). This may be accomplished using neural spacing monitoring system  72 . This information, because it is determined intra-operatively might be more accurate than the information obtained in step  100  which was determined pre-operatively. Neural spacing monitoring system  72  may also determine actual neural compression (e.g., size reduction of the nerve, fluid pressure differential across the neural compression, or other information representative of actual neural compression). Neural release system  70  uses the intra-operative baseline measurements to determine an updated planned amount of neural release. 
     Neural release system  70  may calculate foramen spacing using a variety of algorithms based on intra-operative information provided by neural spacing monitoring system  72  and possibly based on historical and/or empirical information stored, for example, in data aggregation system  80 . Neural release system  70  may calculate foramen spacing using foramen height measurements and foramen width measurements. Neural release system  70  may calculate a foramen area based on the measured height and width. Neural release system  70  may also calculate a foramen area based on multiple measured heights and widths which may be averaged and may provide a more accurate determination of foramen area. Neural release system  70  may further calculate a foramen volume based on the measured height and width along with a measure depth. Neural release system  70  may also calculate a foramen area based on multiple measured heights and widths and depths which may be averaged and may provide a more accurate determination of foramen volume. As another alternative, only foramen height may be used as representative of neural release. 
     Neural release system  70  may calculate a foramen area and/or volume based on geometric information received from imaging systems, e.g., such as with ultrasonic detection system  240  (described in more detail below), or the measurements may be inferred based on measurements that don&#39;t provide geometric information regarding the foramen area and/or volume. For example, neural release system  70  may receive pressure information from pressure system  220  (described in more detail below). Neural release system  70  may calculate or estimate a foramen area or volume based on historical and/or empirical data that relates pressure to foramen area or volume. This information may be stored, for example, in data aggregation system  80 . Rather than converting from pressure information to area and/or volume information, neural release system  70  may use only pressure information which can be representative of foramen geometric information. As discussed in more detail below, for example, neural release system  70  may compare the measured pressure from pressure system  220  to a pressure threshold rather than converting to foramen area and comparing it to an area threshold. 
     Neural release system  70  may also include both pre-operative and intra-operative information in the calculation of foramen area and/or foramen volume or other information representative of foramen area and/or foramen volume (e.g., pressure). For example, neural release system  70  may adjust pre-operative measurements based on intra-operative information. The adjustment may be ratio adjustments or additive or subtractive adjustments to the pre-operative information and may include limits on the magnitude of the overall adjustment, e.g., to protect against erroneous intra-operative measurements. 
     Neural release system  70  may also receive measurements of disc height and use those measurements in determining if the planned or desired neural release has been achieved. Neural release system  70  may include disc height in an overall calculation that represent neural foramen spacing or may treat disc height as a separate parameter with its own separate threshold. Neural release system  70  may use foramen height, width, and depth separately, each with their own separate thresholds. Neural release system  70  may also or alternatively use ratios, such as the ration of foramen height to disc height, again with its own separate threshold. 
     Neural spacing monitoring system  72  may be implemented in a variety of embodiments. For example, neural spacing monitoring system  72  may be an image guided surgery system  210 . As shown in  FIG. 2 a   , image guided surgery system  210  includes markers  212  which are placed on the spinal column at known defined locations with a known defined relationship to the spinal column structure. Image guided surgery system  210  also includes an image guided surgery system receiver  214  that receives signals from markers  212 . Image guided surgery system  210  processes the signals and calculates the spatial position of markers. Image guided surgery system  210  determines an estimated model of the spine based on the spatial position of the markers and the pre-operative planning information which is representative of the structure of the spine. Image guided surgery system  210  then determines information representative of the existing neural foramen spacing prior to insertion of an implant which can be used as a baseline (instead of the pre-operatively estimated amount of neural compression) based on the estimated model of the spine and the locations of the markers. 
     Neural spacing monitoring system  72  may be a pressure system  220 . As shown in  FIG. 2 b   , pressure system  220  includes pressure sensors  222  which are placed on the spinal column on opposite sides of neural compression. Pressure system  220  also includes a receiver  224  that receives signals from pressure sensors  222 . Pressure system  220  processes the signals and calculates the pressure differential across the neural compression. The pressure differential can be used as information representative of the neural foramen spacing prior to insertion of an implant which can be used as a baseline (e.g., a smaller differential represents a larger foramen spacing). Pressure system  220  may also monitor local epidural pressure changes and/or pressure pulses or waves to intraoperatively detect the amount of neural release. 
     Neural spacing monitoring system  72  may be a direct visualization system  230 . As shown in  FIG. 2 c   , direct visualization system  230  includes a steerable camera  232  which is placed in an instrument  236 . Instrument  236  has a proximal end including camera steering controls (not shown) and a distal end including a steerable camera. The distal end of the instrument  236  is designed with open areas for access to visualizing the spine. As shown, instrument  236  includes a relatively flat upper portion  231   a  configured to abut a superior vertebral body and a relatively flat lower portion  231   b  configured to abut an inferior vertebral body (alternatively the upper and lower portions may be shaped with a curve designed to match the shape of an average vertebral body endplate). The spacing between the upper portion  231   a  and the lower portion  231   b  is comparable to the height of the disc space. Multiple instruments may be provided with different spacing to accommodate various disc space heights. The upper portion  231   a  and lower portion  231   b  may be tapered or chamfered to facilitate movement within the disc space. The upper portion  231   a  and lower portion  231   b  are interconnected by walls  233 . Walls  233  are typically narrow to increase viewing area. 
     Direct visualization system  230  also includes an image guided surgery system receiver  234  that receives signals from camera  232 . Direct visualization system  230  determines an estimated model of the spine based on the signal from the camera and the pre-operative planning information which is representative of the structure of the spine. Direct visualization system  230  further determines information representative of the neural foramen spacing based on the video signals and the pre-operative model of the spine. This may be used as a baseline by neural release system  72  instead of the pre-operatively estimated amount of neural compression. 
     Neural spacing monitoring system  72  may be an ultrasonic detection system  240 . As shown in  FIG. 2 d   , ultrasonic detection system  230  includes an ultrasonic probe  242 . Ultrasonic probe  242  is positioned on railing  241  to provide controlled movement of probe  242 . Ultrasonic probe may also be handheld or controlled by various other motion control systems. Ultrasonic detection system  240  also includes an ultrasonic receiver  244  that receives signals from ultrasonic probe  242 . Ultrasonic detection system  240  determines an estimated model of the spine based on the signal from ultrasonic probe  242  and the pre-operative planning information representative of the structure of the spine. Ultrasonic detection system  240  further determines information representative of the neural foramen spacing based on the ultrasonic probe  242  and the pre-operative model of the spine. This may be used as a baseline by neural release system  72  instead of the pre-operatively estimated amount of neural compression. 
     Neural spacing monitoring system  72  may be a conformable balloon system  250 . As shown in  FIG. 2 e   , conformable balloon system  250  includes a conformable balloon  252 . Conformable balloon system  250  also includes a pressure receiver  254  that receives signals from conformable balloon  252 . Conformable balloon system  250  determines information representative of the neural foramen spacing based on the pressure in conformable balloon  252 . This may be used as a baseline by neural release system  72  instead of the pre-operatively estimated amount of neural compression. 
     Neural spacing monitoring system  72  may be a mylogram system  260 . As shown in  FIG. 2 f   , mylogram system  260  includes a fluoroscope  262 . Mylogram system  260  also includes a fluoroscopic receiver  264  that receives signals from fluoroscope  262 . To improve the quality of the fluoroscopic signals, the patient may be injected with contrast agents to assist in determining neural compression and/or constrictions. Mylogram system  260  determines an estimated model of the spine based on the signal from fluoroscope  262  and the pre-operative planning information representative of the structure of the spine. Mylogram system  260  further determines information representative of the neural foramen spacing based on the fluoroscope  262  and the pre-operative model of the spine. This may be used as a baseline by neural release system  72  instead of the pre-operatively estimated amount of neural compression. 
     As shown at step  120 , the surgeon performs initial disc cleaning. Disc cleaning is performed to make room for the fusion cage and to expose the endplates of the vertebral body which is believed to assist with the fusion process. The surgeon may also place a trial in the cleared disc space to get a tactile feel for how well the disc space has been cleared. The trial may also be used to determine whether a particular size implant will fit in the disc space. 
     At step  130 , the surgeon inserts and adjusts an expandable trial implant into the cleaned vertebral disc space while monitoring load and/or contact area. An exemplary expandable trial implant  300  for monitoring load and/or contact area is shown in  FIG. 3 a   . As can be seen in  FIG. 3 a   , the expandable trial implant  300  has recesses  310  located on the lateral sides of the implant. Recesses  310  allow the surgeon to insert additional disc cleaning tools to selectively remove more tissue near either or both of the lateral sides of the implant. Further, the surgeon may selectively remove tissue near the distal and/or proximal portions of the implant. Spinal correction system  50  can assist in determining which area of tissue to remove in order to achieve a planned amount of neural release. 
     The lateral sides of implant may access different portion of the disc depending on the type of procedure performed. For example, in a spinal procedure with lateral access, such as shown in  FIG. 3 a   , the lateral sides of the trial implant would face the anterior and posterior portions of the disc. In a spinal procedure with anterior access, not shown, the lateral sides of the trial implant would face the anterior and posterior portions of the disc. 
       FIG. 3 b    is a top view of expandable trial implant  300 . As shown in  FIG. 3 b   , expandable trial implant  300  includes a relatively flat upper surface  305  configured to abut a superior vertebral body. Expandable trial implant  300  also includes a relatively flat lower surface (not shown) configured to abut an inferior vertebral body. Upper surface  305  and the lower surface may be tapered or contoured to conform to a typical vertebral body endplate. Upper surface  305  and the lower surface may be generally parallel to each other or may be angled in a generally kyphotic or generally lorditoc configuration, again to match typical vertebral body configurations. 
     As shown in  FIG. 3 b   , upper surface  305  includes a plurality of load cells  320 . The lower surface may also include a plurality of load cells (not shown). The load cell may be a pressure sensor, load cell, or any other device capable of sensing pressure or load. Load cells  320  are arranged on the top surface and disposed along the lateral sides of the expandable trial implant  300 . Load cells  320  are also positioned near the proximal and distal ends of the implant. While the load cells  320  are shown as being positioned into rows and columns the load cells  320  may be located at various positions on upper surface  305  and the lower surface. The spacing of the loads cells may be uniform or may be more densely located in areas or more interest to the surgeon, e.g., the spacing may be more dense around the perimeter rather than in the central region of the upper and lower surfaces. 
     Load cells  320  communicate with load and contact system  65  to provide information about the load on expandable trial implant  300  as it is being expanded. Load and contact system  65  may determine whether and when contact is made with the vertebral bodies. Load and contact system  65  may interpret a load greater than some threshold load as an indication that contact has been made with the vertebral bodies. Load and contact system  65  may indicate to the surgeon when contact occurs (visually, audibly, or both, and may be done via neural release system  70  and display  74 ). 
     Alternatively, the upper surface  305  and lower surface may include contact switches or sensors to signal when contact with the vertebral bodies is made. Upper surface  305  and lower surface may alternatively include a film or sheet of sensors for determining contact area/load at various locations on the upper and lower surfaces. 
       FIGS. 4 a  through 4 c    show exemplary embodiments of how display  74  may illustrate the load and contact on the expandable trial implant  300 . As shown in  FIG. 4 a   , graphical view  400  (which may be generated by load and contact system  65  and/or neural release system  70  and displayed on display  74 ) illustrates the load and contact on the superior surface of expandable trial implant  300 . As shown in graphical view  420 , region  402  is indicating a high load, region  403  is indicating a medium load, and region  404  is indicating a low load. The indications can be implemented with color, values, colors and values, may include the ability to zoom in and out of the graphical display for more or less resolution, etc. The load on the inferior surface of expandable trial implant  300  is also illustrated in view  420 . As shown, region  422  is indicating a high load, region  423  is indicating a medium load, and region  424  is indicating a low load. 
     As shown in  FIG. 4 b   , graphical view  430  illustrates the load on the superior surface of expandable trial implant  300 . As shown in graphical view  430 , region  432  is indicating a high load, region  433  is indicating a medium load, and region  434  is indicating a high load. The load on the inferior surface of expandable trial implant  300  is also illustrated in view  440 . As shown, region  442  is indicating a high load, region  443  is indicating a medium load, and region  444  is indicating a high load. 
     As shown in  FIG. 4 c   , graphical view  450  illustrates the load on the superior surface of expandable trial implant  300 . As shown in graphical view  450 , region  452  is indicating a low load, region  453  is indicating a low load, and region  454  is indicating a low load. The load on the inferior surface of expandable trial implant  300  is also illustrated in view  460 . As shown, region  462  is indicating a low load, region  463  is indicating a low load, and region  464  is indicating a low load. 
     Still at step  130 , the surgeon expands the expandable trial implant  300  but stops before the load increases over a predefined threshold which may be for example, a threshold that has been shown to allow for damage to the endplates. Neural release system  70  receives information from load and contact system  65  representing the load and contact area on the superior and inferior surfaces of expandable trial implant  300 . 
     Neural release system  70  may signal, via display  74 , when contact first occurs between the superior and inferior surfaces of expandable trial implant  300  contacts the endplates of the vertebral bodies. Neural release system  70  may also graphically display, via display  74 , when each load cell on the superior and inferior surfaces of expandable trial implant  300  contacts the endplates of the vertebral bodies. Neural release system  70  may also signal, via display  74 , when each of the four corners of the superior and inferior surfaces of expandable trial implant  300  contacts the endplates of the vertebral bodies. 
     Neural release system  70  compares the load information to a predefined threshold. This threshold can warn the surgeon of possible impending endplate damage. The predefined threshold may be a single load threshold which applies to each load cell, may be an average load threshold representing an average of each of the load cells on one or both surfaces of the expandable trial implant  300 , or the predefined threshold may be a combination of single thresholds and an average threshold either of which will trigger a signal to the surgeon. When the predefined threshold is met or exceeded, display  74  or neural release system  70  may visually and/or audibly signal to the surgeon. 
     At step  140 , the surgeon measures the neural foramen release. The surgeon may do this with any of the various neural spacing monitoring systems  72  shown more specifically in  FIGS. 2 a    through  2   f.  Neural spacing monitoring systems  72  sends information to neural release system  70  for processing. If neural release system  70  determines that the measured neural foramen release is equal to or greater than the planned neural foramen release, then at step  150 , neural release system  70  signals, via display  74 , that the foramen is sufficiently released and the surgeon proceeds to step  170  and places the fusion implant into the disc space. Exemplary algorithms for determining whether the desired or planned neural release have been achieved were discussed above. 
     If neural release system  70  determines that the measured neural foramen release has not reached the planned neural foramen release, then at step  150 , neural release system  70  signals that the foramen is not yet sufficiently released and the surgeon proceeds to step  160  and cleans more disc space based on the feedback provided by neural release system  70  and load and contact system  65 . Neural release system  70  may indicate to the surgeon which areas of the disc should be further cleaned. Neural release system  70  may determine the areas based on the measured amount of neural release and the measured loads on expandable trial implant  300 , as well as based upon a determined correlation between the changes in measured load and the resultant change in measured neural release. The correlation may be determined for a single patient, may be based on historical data on multiple patients (e.g., from data aggregation system  80 ), or combinations of both. The neural release system  70  may provide a graphical indication to the surgeon of where to remove more tissue from the disc space, similar to those in  FIGS. 4 a    through  4   c.  As an example, the neural release system  70  may graphically show a vertebral body from a superior view, from a lateral view, and from an anterior view and indicate with color from which regions of the disc, the surgeon should remove more tissue to achieve the planned neural release. 
     After completing step  160 , the method  10  proceeds back to step  130  in which the surgeon will again place the expandable trial implant  300  in the disc space and expand the trial while monitoring the load and contact area. This process is repeated until the planned amount of neural foramen release is achieved, or until other limits are reached such as a maximum amount of disc space retraction, a maximum operative time, measurements of nerve distress, or other such items (not shown in the flow chart). 
       FIGS. 5 a  through 5 h    show an exemplary embodiment another expandable trial implant  500  which may be used in connection with the method of  FIG. 1 a    instead of or in combination with expandable trial implant  300 . Expandable trial implant  500  includes a superior portion  510 , an inferior portion  530 , and an expansion portion  550  located between the superior portion  510  and inferior portion  530 . 
     Superior portion  510  is shaped generally rectangular with an upper surface  511  that is generally flat (but may be shaped generally convexly or otherwise shaped and configured to mate with a typically shaped vertebral body endplate) and is configured to contact a superiorly positioned vertebral body. Superior portion  510  includes load cells  502  located on the upper surface  511 . 
     Superior portion  510  includes a distal portion  514  and a proximal portion  515 . The distal portion  514  of superior portion  510  may be tapered and/or chamfered to allow easier insertion into the disc space. The proximal portion  515  of superior portion  510  may also be tapered and/or chamfered to allow easier removal from the disc space and would typically be less tapered/chamfered that the distal portion  514 . 
     Inferior portion  530  is shaped generally rectangular with a lower surface  531  that is generally flat (but may be shaped generally convexly or otherwise shaped and configured to mate with a typically shaped vertebral body endplate) and is configured to contact an inferiorly positioned vertebral body. Inferior portion  530  includes load cells  502  located on the lower surface  531 . 
     Superior portion  530  includes a distal portion  534  and a proximal portion  535 . The distal portion  534  of superior portion  530  may be tapered and/or chamfered to allow easier insertion into the disc space. The proximal portion  535  of superior portion  530  may also be tapered and/or chamfered to allow easier removal from the disc space and would typically be less tapered/chamfered that the distal portion  534 . 
     Superior portion  510  includes lateral side walls  520  extending generally downward from upper surface  511  and between the distal portion  514  and proximal portion  515 . Inferior portion  530  includes lateral side walls  540  extending generally upward from lower surface  531  and between the distal portion  534  and proximal portion  535 . 
     Rather than being generally flat, side walls  520 ,  540  include a concavely shaped section and together form a C-shape in the lateral portion of expandable trial implant  500 , as best seen in the view of  FIG. 5 f   . This C-shape provides an area  517  on each side of the implant for inserting and using a disc cleaning tool. While expandable trial implant  500  includes generally mirror image and symmetric superior portion  510  and inferior portion  530 , implant  500  may also be non-symmetric. Further, it is not mandatory that each side wall include a concavely shaped section; the concavity may be included only on one portion. Moreover, the concavely shaped section may be any shape that provides a recessed area for a disc removal tool (described in more detail below), such as a rectangular recess, a square recess, or other shapes. 
     Side wall  520  includes a groove  516  extending from the proximal portion  515  to the distal portion  514  (although groove  516  does not have to extend all the way to the distal portion  514 ). Side wall  540  also includes a groove  516  extending from the proximal portion  535  to the distal portion  534  (although groove  536  does not have to extend all the way to the distal portion  534 ). Groove  516  has a rectangular cross section and is sized and configured to mate with a portion of a disc clearing tool to guide and retain the disc clearing tool, described in more detail below. While groove  516  is shown with a rectangular cross section, the cross section may have various shapes to mate with the disc clearing tool, such as a circular shape, square shape, dovetail shape, etc. 
     Expansion portion  550 , which is disposed between superior portion  510  and inferior portion  530 , includes a threaded rod portion  554 , two wedges  552  (that are internally threaded and mate with the threads of rod portion  554 ), and a shaft portion  570  connected to rod portion  554  to rotate rod portion  554 . As shaft portion  570  is rotated, threaded rod portion  554  is also rotated. Expansion portion can also be comprised of other mechanisms for expansion, including balloons, pistons, jacks, shims, etc. 
     Threaded rod portion  554  includes a central circular flange  556  and two oppositely threaded portions  558  and  559  on either side of central flange. Central flange  556  mates with arcuate recesses  525 ,  545  located on the lower side of superior portion  510  and the upper side of inferior portion  530 , respectively. Rotation of threaded rod portion  554  causes wedges  552  to move in opposite directions, i.e., either towards each other or away from each other. As wedge  552  move toward each other, they move along ramps located on the lower side of superior portion  510  and the upper side of inferior portion  530 , causing superior portion  510  and inferior portion  530  to expand apart. 
     Shaft portion  570  includes a driving shaft  571 , an implant mating portion  573 , and a tool guide portion  580 . As best seen in  FIG. 5 f   , tool guide portion  580  includes a shaft mating section  582  and a tool mating section  584 . Shaft mating section  582  extends longitudinally along driving shaft  571  and has a C-shaped cross-section that is sized and configured to snap onto driving shaft  571 . Tool mating section  584  extends longitudinally along shaft mating section  582  and has a C-shaped cross-section that is sized and configured to mate with a disc clearing tool. Shaft portion  570  further includes a camera  586  located between shaft mating section  582  and a tool mating section  584 . Camera  586  is in electrical communication with either load and contact system  65  or neural release system  70  which in turn provides information to display  74  to show camera images of the disc space and assist the surgeon with disc removal. 
     Expandable trial implant  500  may mechanically cooperate with a disc removal tool  590  to allow the surgeon to remove sections of the disc. This can occur, for example, after determination by neural release system  70  that a particular region of disc should be removed, as described above. 
     Disc removal tool  590  includes a shaft  591  and a cutting implement  594 . Cutting implement  594  is shown as a box cutter having four walls forming a square with rounded corners and an aperture therethrough. The walls have sharp edges to cut disc material. Cutting implement  594  may take the shape of any other conventional cutting implement commonly used for disc cutting or removal. 
     Cutting implement  594  is pivotably connected to shaft  591  at hinge  592 . Hinge  592  allows cutting implement  594  to articulate about a pivot point and cut disc from the disc space. Cutting implement  594  can be articulated by interconnected driving shafts or pulleys or any other conventional methods for mechanically producing a pivoting movement. Disc removal tool  590  includes a handle (not shown) and a trigger mechanism (not shown) for the surgeon to control the articulation angle when removing disc material. Cutting implement  594  may also be non-articulating cutting element that is sized and configured to be mate with expandable trial implant  500  described in more detail below. 
     Shaft  591  of disc removal tool  590  is disposed in the C-shaped cross-section of the tool mating section  584  of expandable trial implant  500 , as seen in  FIG. 5 h   . This allows disc removal tool  590  to move longitudinally with respect to expandable trial implant  500 . Shaft  591  includes a longitudinal projection  596  extending along the length of shaft  591 . As shown, longitudinal projection  596  is generally rectangular in cross-section and is sized and configured to mate with and be received in groove  516  in the lateral recess  545  of expandable trial implant  500 . The mating between stabilizes the disc removal tool  590  by limiting the motion of shaft  591  to longitudinal motion and preventing rotational movement. This may provide the surgeon with added stability to assist with removal of disc material. Alternatively, the shaft  591  may not include longitudinal projection  596 , thereby allowing the surgeon the ability to rotate the shaft  591  when appropriate. A kit may be provided with multiple cutting implements, each provided with and without longitudinal projection  596 , thereby providing the surgeon the option of increased stability when appropriate and increased flexibility when appropriate. 
       FIGS. 6 a  through 6 h    show an alternative exemplary embodiment of an expandable trial implant  600  which may be used in connection with the method of  FIG. 1 a    instead of or in combination with expandable trial implant  300  or expandable trial implant  500 . Expandable trial implant  600  includes a superior portion  610 , an inferior portion  630 , and an expansion portion  650  located between the superior portion  610  and inferior portion  630 . 
     Superior portion  610  is shaped generally rectangular with an upper surface  511  that is generally flat (but may be shaped generally convexly or otherwise shaped and configured to mate with a typically shaped vertebral body endplate) and is configured to contact a superiorly positioned vertebral body. Superior portion  610  includes load cells  602  located on the upper surface  611 . 
     Superior portion  610  includes a distal portion  614  and a proximal portion  615 . The distal portion  614  of superior portion  610  may be tapered and/or chamfered to allow easier insertion into the disc space. The proximal portion  615  of superior portion  610  may also be tapered and/or chamfered to allow easier removal from the disc space and would typically be less tapered/chamfered that the distal portion  614 . 
     Inferior portion  630  is shaped generally rectangular with a lower surface  631  that is generally flat (but may be shaped generally convexly or otherwise shaped and configured to mate with a typically shaped vertebral body endplate) and is configured to contact an inferiorly positioned vertebral body. Inferior portion  630  includes load cells  602  located on the lower surface  631 . 
     Superior portion  630  includes a distal portion  634  and a proximal portion  635 . The distal portion  634  of superior portion  630  may be tapered and/or chamfered to allow easier insertion into the disc space. The proximal portion  635  of superior portion  630  may also be tapered and/or chamfered to allow easier removal from the disc space and would typically be less tapered/chamfered that the distal portion  634 . 
     Superior portion  610  includes lateral side walls  620  extending generally downward from upper surface  611  and between the distal portion  614  and proximal portion  615 . Inferior portion  630  includes lateral side walls  640  extending generally upward from lower surface  631  and between the distal portion  634  and proximal portion  635 . 
     Rather than being generally flat, side walls  620 ,  640  include a concavely shaped section and together form a C-shape in the lateral portion of expandable trial implant  600 , as best seen in the view of  FIG. 6 g   . This C-shape provides an area  617  on each side of the implant for inserting and using a disc cleaning tool. While expandable trial implant  600  includes generally mirror image and symmetric superior portion  610  and inferior portion  630 , implant  600  may also be non-symmetric. Further, it is not mandatory that each side wall include a concavely shaped section; the concavity may be included only on one portion. Moreover, the concavely shaped section may be any shape that provides a recessed area for a disc removal tool (described in more detail below), such as a rectangular recess, a square recess, or other shapes. 
     Side wall  620  includes a groove  616  extending from the proximal portion  615  to the distal portion  614  (although groove  616  does not have to extend all the way to the distal portion  614 ). Side wall  640  also includes a groove  616  extending from the proximal portion  635  to the distal portion  634  (although groove  636  does not have to extend all the way to the distal portion  634 ). Groove  616  has a rectangular cross section and is sized and configured to mate with a portion of a disc clearing tool to guide and retain the disc clearing tool, described in more detail below. While groove  616  is shown with a rectangular cross section, the cross section may have various shapes to mate with the disc clearing tool, such as a circular shape, square shape, dovetail shape, etc. 
     Expansion portion  650 , which is disposed between superior portion  610  and inferior portion  630 , includes a distal hinge  651  and a proximal hinge  653  connected by a longitudinal member  652 . Distal hinge  651  is shaped generally as a square but could take any shape and includes two lateral projections  655  extending laterally from opposite sides of the distal hinge  651 . Proximal hinge  653  is shaped generally annular and is disposed around rod  654 . Proximal hinge  653  includes two lateral projections  655  extending laterally from opposite portions of the proximal hinge  653 . 
     Expansion portion  650  is linked to superior portion  610  and inferior portion  630  by a series of four jacks  660  although there could be any number of jacks  660 . As shown in  FIG. 6 c   , each jack  660  includes at least two longitudinal members shown as  660   a  and  660   b  pivotally interconnected to each other at a pivot point and to the projection  655  of distal hinge  651  (or the projection  655  of proximal hinge  653 ). 
     Rod  654  extends from a handle (not shown) towards and through proximal hinge  653 . Rod  654  culminates with two extension flanges  670 . A first extension flange  670  extends upwards toward and through a recess of superior portion  610 . A second extension flange  670  extends downward toward and through a recess of inferior portion  630 . The extension flanges  670  may also function as an over-insertion stop, stopping the surgeon from over-inserting the expandable trial implant  600  too far into the disc space. 
     As proximal hinge  653  is pushed longitudinally with respect to rod  654 , jacks  660  are forced to pivot moving the expandable trial implant  600  from the compressed position (such as shown in  FIG. 6 a   ) and into the expanded position (such as shown in  FIGS. 6 b    and  6   c.    
     As with expandable trial implant  500 , expandable trial implant  600  may include a tool guide portion  580  as shown in  FIGS. 5 b  and 5 c   . Shaft  591  of disc removal tool  590  is disposed in the C-shaped cross-section of the tool mating section  584  of expandable trial implant  600  (not shown). This allows disc removal tool  590  to move longitudinally with respect to expandable trial implant  600 . Shaft  591  includes a longitudinal projection  596  extending along the length of shaft  591 . As shown, longitudinal projection  596  is generally rectangular in cross-section and is sized and configured to mate with and be received in groove  616  in the lateral recess  645  of expandable trial implant  600 . The mating between stabilizes the disc removal tool  590  by limiting the motion of shaft  591  to longitudinal motion and preventing rotational movement. This may provide the surgeon with added stability to assist with removal of disc material. Alternatively, the shaft  591  may not include longitudinal projection  596 , thereby allowing the surgeon the ability to rotate the shaft  591  when appropriate. 
     The above described method can be implemented in a manual, step-wise fashion requiring operator intervention at each step, or certain steps may be automated. Automated steps may be performed by robotic devices which may communicate with neural release system  70  via wired or wireless communication channels. The automated steps may be completely automatic and implemented as a closed loop system with neural release system determining commands to be sent to the robotic devices which may control the expandable trial implant  300  and the cutting implement  594 . The automated steps may be semi-automatic, requiring the surgeon or operator to acknowledge before proceeding with certain robotic steps. 
     Although the present invention has been described with reference to its preferred embodiments, those skillful in the art will recognize changes that may be made in form and structure which do not depart from the spirit of the invention.