Patent Application
20210045649
The present invention relates to a system and methods generally aimed at surgery. More particularly, the present invention is directed at a system and related methods for performing surgical procedures and assessments involving the use of neurophysiologic recordings.
Neurophysiology monitoring has become an increasingly important adjunct to surgical procedures where neural tissue may be at risk. Spinal surgery, in particular, involves working close to delicate tissue in and surrounding the spine, which can be damaged in any number of different ways. For example, an exiting nerve root may be comprised if surgical instruments have to pass near or close to the nerve while accessing the surgical target site in the spine. A spinal nerve and/or exiting nerve root may also be compromised if a pedicle screw, used often to secure fixation of multiple vertebra relative to each other, breaches the cortical layer of the pedicle. Surgeries targeting the spine may also require the retraction of nerve and/or vascular tissue out of the operative corridor. While doing so is necessary, there is a possibility of damaging nerve tissue through over retraction and/or a decreased supply of blood reaching the tissue due to the impingement of the retractor against the vascular tissue. Various neurophysiological techniques have been attempted and developed to monitor delicate nerve tissue during surgery in attempts to reduce the risk inherent in spine surgery (and surgery in general). Because of the complex structure of the spine and nervous system no single monitoring technique has been developed that may adequately assess the risk to nervous tissue in all situations and complex techniques are often utilized in conjunction one or more other complex monitoring techniques. EMG monitoring, for example, may be used to detect the presence of nerve roots near a surgical instrument or a breach formed in a pedicle wall. EMG monitoring is not, however, very effective when spinal cord monitoring is required.
When spinal cord monitoring is required, either or both motor evoked potential (MEP) or somatosensory evoked potential (SSEP) monitoring are often chosen. While both MEP and SSEP monitoring can be quite effective at detecting changes in the health of the spinal cord, MEP is limited because it only monitors the ventral column of the spinal cord and SSEP is limited because it only monitors the dorsal column of the spinal cord. Danger to nerve tissue that might then be detected using one these methods may be missed by the other, and vice versa. Thus, it may be most effective to use both MEP and SSEP monitoring during the same procedure, while still potentially needing EMG monitoring as well.
EMG, MEP, and SSEP involve complex analysis and specially trained neurophysiologists are generally called upon to perform the monitoring. Even though performed by specialists, interpreting the complex waveforms in this fashion is nonetheless disadvantageously prone to human error and can be disadvantageously time consuming, adding to the duration of the operation and translating into increased health care costs. Even more costly is the fact that the neurophysiologist is required in addition to the actual surgeon performing the spinal operation. Putting the difficulties associated with human interpretation of EMG, MEP, and SSEP monitoring aside, combining such testing in the OR generally requires multiple products to accommodate the differing requirements of each. This is disadvantageous when space is often at such a premium in the operating rooms of today. The present invention is directed at eliminating, or at least reducing the effects of, the above-described problems with the prior art.
The present invention includes a system and methods for avoiding harm to neural tissue during surgery. According to a broad aspect, the present invention includes instruments capable of stimulating either the peripheral nerves of a patient, the spinal cord of a patient, or both, additional instruments capable of recording the evoked somatosensory responses, and a processing system. The instrument is configured to deliver a stimulation signal preoperatively, perioperatively, and postoperatively. The processing system is programmed with a set of at least three threshold ranges and configured to receive first stimulation signal to said instrument at a first magnitude. The first magnitude corresponds to a boundary between the pair of ranges. The processing system further receives a second stimulation signal at a second magnitude corresponding to a boundary between a different pair of the ranges. The processing unit is still further programmed to and measure the response of nerves depolarized by said stimulation signals as received by the somatosensory cortex to indicate spinal cord health.
According to another broad aspect, the present invention includes a control unit, a patient module, and a plurality of surgical accessories adapted to couple to the patient module. The control unit includes a power supply and is programmed to receive user commands, activate stimulation in a plurality of predetermined modes, process signal data according to defined algorithms, display received parameters and processed data, and monitor system status. The patient module is in communication with the control unit. The patient module is within the sterile field. The patient module includes signal conditioning circuitry, stimulator drive circuitry, and signal conditioning circuitry required to perform said stimulation in said predetermined modes. The patient module includes a processor programmed to perform a plurality of predetermined functions including at least two of static pedicle integrity testing, dynamic pedicle integrity testing, nerve proximity detection, neuromuscular pathway assessment, manual motor evoked potential monitoring, automatic motor evoked potential monitoring, manual somatosensory evoked potential monitoring, automatic motor evoked potential monitoring, non-evoked monitoring, and surgical navigation.
According to still another broad aspect, the present invention includes an instrument and a processing system. The instrument is in communication with the processing unit. The instrument is capable of advancement to a surgical target site and is configured to deliver a stimulation signal at least one of while advancing to said target site and after reaching said target site. The processing unit is programmed to perform a plurality of predetermined functions using said instrument including at least two of static pedicle integrity testing, dynamic pedicle integrity testing, nerve proximity detection, neuromuscular pathway assessment, manual motor evoked potential monitoring, automatic motor evoked potential monitoring, manual somatosensory evoked potential monitoring, automatic somatosensory evoked potential monitoring, non-evoked monitoring, and surgical navigation. The processing system has a pre-established profile for at least one of said predetermined functions so as to facilitate the initiation of said at least one . predetermined function.
Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein:
Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The systems disclosed herein boast a variety of inventive features and components that warrant patent protection, both individually and in combination. It is also expressly noted that, although described herein largely in terms of use in spinal surgery, the surgical system and related methods described herein are suitable for use in any number of additional procedures, surgical or otherwise, wherein assessing the health of the spinal cord and/or various other nerve tissue may prove beneficial.
A surgeon operable neurophysiology system 10 is described herein and is capable of performing a number of neurophysiological and/or guidance assessments at the direction of the surgeon (and/or other members of the surgical team). By way of example only,
In one embodiment, the neurophysiology system 10 may be configured to execute any of the functional modes including, but not necessarily limited to, static pedicle integrity testing (“Basic Stimulated EMG”), dynamic pedicle integrity testing (“Dynamic Stimulated EMG”), nerve proximity detection (“XLIF®”), neuromuscular pathway assessment (“Twitch Test”), motor evoked potential monitoring (“MEP Manual” and “MEP Automatic”), somatosensory evoked potential monitoring (“SSEP Manual” and “SSEP Automatic”), non-evoked monitoring (“Free-run EMG”) and surgical navigation (“Navigated Guidance”). The neurophysiology system 10 may also be configured for performance in any of the lumbar, thoracolumbar, and cervical regions of the spine.
Before further addressing the various functional modes of the surgical system 10, the hardware components and features of the system 10 will be describe in further detail. The control unit 12 of the neurophysiology system 10, illustrated by way of example only in
The patient module 14, shown by way of example only in
With reference to
As soon as a device is plugged into any one of ports 50, 52, 56, or 58, the neurophysiology system 10 automatically performs a circuit continuity check to ensure the associated device will work properly. Each device forms a separate closed circuit with the patient module such that the devices may be checked independent of each other. If one device is not working properly the device may be identified individually while the remaining devices continue indicate their valid status. An indicator LED is provided for each port to convey the results of the continuity check to the user. Thus, according to the example embodiment of
To connect the array of recording electrodes 24 and stimulation electrodes 22 utilized by the system 10, the patient module 14 also includes a plurality of electrode harness ports. In the embodiment shown, the patient module 14 includes an EMG/MEP harness port 72, SSEP harness port 74, and an Auxiliary harness port 76 (for expansion and/or custom harnesses). Each harness port 72, 74, and 76 includes a shaped socket 78 that corresponds to a matching shaped connector 82 on the appropriate electrode harness 80. In addition, the neurophysiology system 10 may preferably employ a color code system wherein each modality (e.g. EMG, EMG/MEP, and SSEP) has a unique color associated with it. By way of example only and as shown herein, EMG monitoring (including, screw tests, detection, and nerve retractor) may be associated with the color green, MEP monitoring with the color blue, and SSEP monitoring may be associated with the color orange. Thus, each harness port 72, 74, 76 is marked with the appropriate color which will also correspond to the appropriate harness 80. Utilizing the combination of the dedicated color code and the shaped socket/connector interface simplifies the setup of the system, reduces errors, and can greatly minimize the amount of pre-operative preparation necessary. The patient module 14, and especially the configuration of quantity and layout of the various ports and indicators, has been described according to one example embodiment of the present invention. It should be appreciated, however, that the patient module 14 could be configured with any number of different arrangements without departing from the scope of the invention.
As mentioned above, to simplify setup of the system 10, all of the recording electrodes 24 and stimulation electrodes 22 that are required to perform one of the various functional modes (including a common electrode 23 providing a ground reference to pre-amplifiers in the patient module 14, and an anode electrode 25 providing a return path for the stimulation current) are bundled together and provided in single electrode harness 80, as illustrated, by way of example only, in
At one end of the harness 80 is the shaped connector 82. As described above, the shaped connector 82 interfaces with the shaped socket 72, 74, or 76 (depending on the functions harness 80 is provided for). Each harness 80 utilizes a shaped connector 82 that corresponds to the appropriate shaped socket 72, 74, 76 on the patient module 14. If the shapes of the socket and connector do not match the harness 80, connection to the patient module 14 cannot be established. According to one embodiment, the EMG and the EMG/MEP harnesses both plug into the EMG/MEP harness port 72 and thus they both utilize the same shaped connector 82. By way of example only,
To facilitate easy placement of scalp electrodes used during MEP and SSEP modes, an electrode cap 81, depicted by way of example only in
In addition to or instead of color coding the electrode lead wires to designated intended placement, the end of each wire lead next to the electrode connector 102 may be tagged with a label 86 that shows or describes the proper positioning of the electrode on the patient. The label 86 preferably demonstrates proper electrode placement graphically and textually. As shown in
As mentioned above, the neurophysiology monitoring system 10 may include a secondary display, such as for example only, the secondary display 46 illustrated in
Having described an example embodiment of the system 10 and the hardware components that comprise it, the neurophysiological functionality and methodology of the system 10 will now be described in further detail. Various parameters and configurations of the neuromonitoring system 10 may depend upon the target location (i.e. spinal region) of the surgical procedure and/or user preference. In one embodiment, upon starting the system 10 the software will open to a startup screen, illustrated by way of example only, in
Selecting a profile configures the system 10 to the parameters assigned for the selected profile (standard or custom). The availability of different function modes may depend upon the profile selected. By way of example only, selecting the cervical and thoracolumbar spinal regions may automatically configure the options to allow selection of the SSEP Manual, SSEP Automatic, MEP Manual, MEP Automatic, Twitch Test, Basic Stimulated EMG, Dynamic Stimulated EMG, XLIF, Free-Run EMG, and Navigated Guidance modes, while selecting the lumbar region may automatically configure the options to allow selection of the Twitch Test, Basic, Difference, and Dynamic Stimulated EMG Tests, XLIF®, and Nerve Retractor modes. Default parameters associated with the various function modes may also depend on the profile selected, for example, the characteristics of the stimulation signal delivered by the system 10 may vary depending on the profile. By way of example, the stimulation signal utilized for the Stimulated EMG modes may be configured differently when a lumbar profile is selected versus when one of a thoracolumbar profile and a cervical profile.
As previously described above, each of the hardware components includes an identification tag that allows the control unit 12 to determine which devices are hooked up and ready for operation. In one embodiment, profiles may only be available for selection if the appropriate devices (e.g. proper electrode harness 80 and stimulation accessories) are connected and/or ready for operation. Alternatively, the software could bypass the startup screen and jump straight to one of the functional modes based on the accessories and/or harnesses it knows are plugged in. The ability to select a profile based on standard parameters, and especially on customized preferences, may save significant time at the beginning of a procedure and provides for monitoring availability right from the start. Moving on from the startup screen, the software advances directly to an electrode test screen and impedance tests, which are performed on every electrode as discussed above. When an acceptable impedance test has been completed, the system 10 is ready to begin monitoring and the software advances to a monitoring screen from which the neurophysiological monitoring functions of the system 10 are performed.
The information displayed on the monitoring screen may include, but is not necessarily limited to, alpha-numeric and/or graphical information regarding any of the functional modes (e.g. SSEP Manual, SSEP Automatic, MEP Manual, MEP Automatic, Twitch Test, Basic Stimulated EMG, Dynamic Stimulated EMG, XLIF, Free-Run EMG, and Navigated Guidance), attached accessories (e.g. stimulation probe 16, stimulation clip 18, tilt sensor 54), electrode harness or harnesses attached, impedance test results, myotome/EMG levels, stimulation levels, history reports, selected parameters, test results, etc. . . . In one embodiment, set forth by way of example only, this information displayed on a main monitoring screen may include, but is not necessarily limited to the following components as set forth in Table 6:
From a profile setting window 160, illustrated by way of example only in
Various features of the monitoring screen 200 of the GUI will now be described. The patient module 14 is configured such that the neurophysiology system 10 may conduct an impedance test under the direction of the control unit 12 of all electrodes once the system is set up and the electrode harness is connected and applied to the patient. After choosing the appropriate spinal site upon program startup (described below), the user is automatically directed to an electrode test.
The functions performed by the neuromonitoring system 10 may include, but are not necessarily limited to, the Twitch Test, Free-run EMG, Basic Stimulated EMG, Dynamic Stimulated EMG, XLIF®, Nerve Retractor, MEP Manual, MEP Automatic, and SSEP Manual, SSEP Automatic, and Navigated Guidance modes, all of which will be described briefly below. The Twitch Test mode is designed to assess the neuromuscular pathway via the so-called “train-of-four test” to ensure the neuromuscular pathway is free from muscle relaxants prior to performing neurophysiology-based testing, such as bone integrity (e.g. pedicle) testing, nerve detection, and nerve retraction. This is described in greater detail within PCT Patent App. No. PCT/US2005/036089, entitled “System and Methods for Assessing the Neuromuscular Pathway Prior to Nerve Testing,” filed Oct. 7, 2005, the entire contents of which is hereby incorporated by reference as if set forth fully herein. The Basic Stimulated EMG Dynamic Stimulated EMG tests are designed to assess the integrity of bone (e.g. pedicle) during all aspects of pilot hole formation (e.g., via an awl), pilot hole preparation (e.g. via a tap), and screw introduction (during and after). These modes are described in greater detail in PCT Patent App. No. PCT/US02/35047 entitled “System and Methods for Performing Percutaneous Pedicle Integrity Assessments,” filed on Oct. 30, 2002, and PCT Patent App. No. PCT/US2004/025550, entitled “System and Methods for Performing Dynamic Pedicle Integrity Assessments,” filed on Aug. 5, 2004 the entire contents of which are both hereby incorporated by reference as if set forth fully herein. The XLIF mode is designed to detect the presence of nerves during the use of the various surgical access instruments of the neuromonitoring system 10, including the pedicle access needle 26, k-wire 42, dilator 44, and retractor assembly 70. This mode is described in greater detail within PCT Patent App. No. PCT/US2002/22247, entitled “System and Methods for Determining Nerve Proximity, Direction, and Pathology During Surgery,” filed on Jul. 11, 2002, the entire contents of which is hereby incorporated by reference as if set forth fully herein. The Nerve Retractor mode is designed to assess the health or pathology of a nerve before, during, and after retraction of the nerve during a surgical procedure. This mode is described in greater detail within PCT Patent App. No. PCT/US2002/30617, entitled “System and Methods for Performing Surgical Procedures and Assessments,” filed on Sep. 25, 2002, the entire contents of which are hereby incorporated by reference as if set forth fully herein. The MEP Auto and MEP Manual modes are designed to test the motor pathway to detect potential damage to the spinal cord by stimulating the motor cortex in the brain and recording the resulting EMG response of various muscles in the upper and lower extremities. The SSEP function is designed to test the sensory pathway to detect potential damage to the spinal cord by stimulating peripheral nerves inferior to the target spinal level and recording the action potential from sensors superior to the spinal level. The MEP Auto, MEP manual, and SSEP modes are described in greater detail within PCT Patent App. No. PCT/US2006/003966, entitled “System and Methods for Performing Neurophysiologic Assessments During Spine Surgery,” filed on Feb. 2, 2006, the entire contents of which is hereby incorporated by reference as if set forth fully herein. The Navigated Guidance function is designed to facilitate the safe and reproducible use of surgical instruments and/or implants by providing the ability to determine the optimal or desired trajectory for surgical instruments and/or implants and monitor the trajectory of surgical instruments and/or implants during surgery. This mode is described in greater detail within PCT Patent App. No. PCT/US2007/11962, entitled “Surgical Trajectory Monitoring System and Related Methods,” filed on Jul. 30, 2007, and PCT Patent App. No. PCT/US2008/12121, the entire contents of which are each incorporated herein by reference as if set forth fully herein. These functions will be explained now in brief detail.
The neuromonitoring system 10 performs assessments of spinal cord health using one or more of MEP Auto, MEP Manual, SSEP Auto, and SSEP manual modes.
In the SSEP modes, the neuromonitoring system 10 stimulates peripheral sensory nerves that exit the spinal cord below the level of surgery and then measures the electrical action potential from electrodes located on the nervous system superior to the surgical target site. Recording sites below the applicable target site are also preferably monitored as a positive control measure to ensure variances from normal or expected results are not due to problems with the stimulation signal deliver (e.g. misplaced stimulation electrode, inadequate stimulation signal parameters, etc.). To accomplish this, stimulation electrodes 22 may be placed on the skin over the desired peripheral nerve (such as by way of example only, the left and right Posterior Tibial nerve and/or the left and right Ulnar nerve) and recording electrodes 24 are positioned on the recording sites (such as, by way of example only, C2 vertebra, Cp3 scalp, Cp4 scalp, Erb's point, Popliteal Fossa) and stimulation signals are delivered from the patient module 14.
Damage in the spinal cord may disrupt the transmission of the signal up along the spinothalamic pathway through the spinal cord resulting in a weakened, delayed, or absent signal at the recording sites superior to the surgery location (e.g. cortical and subcortical sites). To check for these occurrences, the system 10 monitors the amplitude and latency of the evoked signal response. According to one embodiment, the system 10 may perform SSEP in either of two modes: Automatic mode and Manual mode. In SSEP Auto mode, the system 10 compares the difference between the amplitude and latency of the signal response vs. the amplitude and latency of a baseline signal response. The difference is compared against predetermined “safe” and “unsafe” levels and the results are displayed on display 34. According to one embodiment, the system may determine safe and unsafe levels based on each of the amplitude and latency values for each of the cortical and subcortical sites individually, for each stimulation channel. That is, if either of the subcortical and cortical amplitudes decrease by a predetermined level, or either of the subcortical and cortical latency values increase by a predetermined level, the system may issue a warning. By way of example, the alert may comprise a Red, Yellow, Green type warning associated with the applicable channel wherein Red indicates that at least one of the determined values falls within the unsafe level, the color green may indicate that all of the values fall within the safe level, and the color yellow may indicate that at least one of the values falls between the safe and unsafe levels. To generate more information, the system 10 may analyze the results in combination. With this information, in addition to the Red, Yellow, and Green alerts, the system 10 may indicate possible causes for the results achieved. In SSEP Manual mode, signal response waveforms and amplitude and latency values associated with those waveforms are displayed for the user. The user then makes the comparison between a baseline the signal response.
Selecting one of the stimulation site tabs 264 will open a control window 265, seen in
In order to monitor the health of the spinal cord with SSEP, the user must be able to determine if the responses to the stimulation signal are changing. To monitor for this change a baseline is determined, preferably during set-up. This can be accomplished simply by selecting the “set as baseline” button 298 next to the “start stim” button 284 on the setting screen illustrated in
During SSEP modes (auto and manual), a single waveform response is generated for each stimulation signal run (for each stimulation channel). The waveforms are arranged with stimulation on the extreme left and time increasing to the right. By way of example, the waveforms are captured in a 100 ms window following stimulation. The stimulation signal run is comprised of a predefined number of stimulation pulses firing at the selected stimulation frequency. By way of example only, the stimulation signal may include 300 pulses at a frequency of 4.7 Hz. A 100 ms window of data is acquired on each of three SSEP recording channels: cortical, subcortical, and peripheral. With each successive stimulation on the same channel during a stimulation run, the three acquired waveforms are summed and averaged with the prior waveforms during the same stimulation run for the purpose of filtering out asynchronous events such that only the synchronous evoked response remains after a sufficient number of pulses. Thus, the final waveform displayed by the system 10 represents an averaging of the entire set (e.g. 300) of responses detected.
With each subsequent stimulation run, waveforms are drawn slightly lower each time, as depicted in
According to one example, the baseline and the latest waveforms may have markers 314, 316 placed indicating latency and amplitude values associated with the waveform. The latency is defined as the time from stimulation to the first (earliest) marker. There is one “N” 314 and one “P” 316 marker for each waveform. The N marker is defined as the maximum average sample value within a window and the P value is defined as the minimum average sample value within the window. The markers may comprise cross consisting of a horizontal and a vertical line in the same color as the waveform. Associated with each marker is a text label 317 indicating the value at the marker. The earlier of the two markers is labeled with the latency (e.g. 22.3 ms). The latter of the two markers is labeled with the amplitude (e.g. 4.2 uV). The amplitude is defined as the difference in microvolts between average sample values at the markers. The latency is defined as the time from stimulation to the first (earliest) marker. Preferably, the markers are placed automatically by the system 10 (in both auto an manual modes). In manual mode, the user may select to place (and or move) markers manually.
Further selecting one of the channel windows 294 will zoom in on the waveforms contained in that window 294.
Referencing
In Automatic mode, the surgical system 10 also includes a timer function which can be controlled from the setup screen. Using the timer drop down menu 326, the user may set and/or change a time interval for the timer application. There are two separate options of the timer function: (1) an automatic stimulation on time out which can be selected by pressing the auto start button 322 labeled (by way of example only) “Auto Start Stim when timed out”; and (2) a prompted stimulation reminder on time out which can be selected by pressing the prompt stimulation button 324 labeled (by way of example only) “Prompt Stim when timed out”. After each SSEP monitoring episode, the system 10 will initiate a timer corresponding to the selected time interval and, when the time has elapsed, the system will either automatically perform the SSEP stimulation or a stimulation reminder will be activated, depending on the selected option. The stimulation reminder may include, by way of example only, any one of, or combination of, an audible tone, voice recording, screen flash, pop up window, scrolling message, or any other such alert to remind the user to test SSEP again. It is also contemplated that the timer function described may be implemented in SSEP Manual mode.
With reference to
In addition to alerting the user to any changes in the amplitude and/or latency of the SSEP signal response, it is further contemplated that the neuromonitoring system 10 may assess the data from all the recording sites to interpret possible causes for changes in the SSEP response. Based on that information, the program may suggest potential reasons for the change. Furthermore, it may suggest potential actions to be taken to avoid danger. It is still further contemplated that the neurophysiology system 10 may be communicatively linked with other equipment in the operating room, such as for example, anesthesia monitoring equipment. Data from this other equipment may be considered by the program to generate more accuracy and or better suggestions. By way of example only, Table 7 illustrates the SSEP illustrates various warnings that may be associated with particular SSEP results and result combination, and show to the user. For example, if in response to stimulation of the left ulnar nerve, the peripheral response from Erb's Point showed no change in amplitude or latency, the subcortical response showed a decrease in amplitude, and the cortical response showed a decrease in amplitude, the event box 206 (shown in
As mentioned above, the system 10 may employ an automated tests to quickly select the optimal stimulus parameters for conducting SSEP testing on each active stimulation channel. This can be done according to any number of algorithms that automatically adjust various parameters until a combination resulting in the most desirable result is achieved. By way of example, the system 10 may utilize an algorithm similar to the hunting algorithm described below for finding Ithresh for EMG and MEP modalities. According to this example, the desired stimulation parameters are determined by first finding the lowest Ithresh (that is the lowest stimulation signal intensity that results in a waveform having a predetermined amplitude, Vthresh) for each stimulation site (e.g., left posterior tibial nerve (LPTN), right posterior tibial nerve (RPTN), left ulnar nerve (LUN), and right ulnar nerve (RUN)). By way of example only, to determine the Ithresh for a LPTN, using polarity A (cathode proximal to the surgical site), an initial, predetermined stimulus intensity is applied transcutaneously to the left PTN stimulation site. If no response is obtained from recording electrodes at the left popliteal fossa with a Vpp greater or equal to Vthresh, polarity B is used (anode proximal to the surgical site), and the same stimulus intensity is applied. If no response is obtained at the first stimulus level for either polarity, the polarity is again switched and the stimulation intensity is doubled. Thus, using polarity A, a second stimulus intensity is applied. If there is no response recorded from the left. popliteal fossa, the polarity is reversed and a stimulus of the same second intensity is applied. If there is still no response that recruits (results in a Vpp at or above Vthresh), the stimulus intensity is again doubled until there is an evoked potential with a Vpp greater or equal to Vthresh. The polarity setting from which the first evoked potential recorded in the left popliteal fossa that achieves Vthresh, is set as the polarity for this stimulation site. The first stimulation intensity to achieve Vthresh and the immediately previous stimulation intensity form an initial bracket.
After the threshold current Ithresh has been bracketed, the initial bracket is successively reduced via bisection to a predetermined width. This is accomplished by applying a first bisection stimulation current that bisects (i.e. forms the midpoint of) the initial bracket. If this first bisection stimulation current recruits, the bracket is reduced to the lower half of the initial bracket. If this first bisection stimulation current does not recruit, the bracket is reduced to the upper half of the initial bracket. This process is continued for each successive bracket until Ithresh is bracketed by stimulation currents separated by the predetermined width. Once Ithresh is determined for a particular stimulation channel, the stimulus intensity is set as the value 20% greater than the detected threshold. This is repeated for each stimulation channel until the optimal stimulation signal is set for each. The optimal stimulation signal may be determined for each stimulation channel in sequence, or, simultaneously (by proceeding in similar fashion to the multi channel threshold detection algorithm described below. The determined stimulation values will then preferably be used throughout the monitoring procedure.
The threshold hunting algorithm for optimizing SSEP stimulation parameter is further described with reference to
With reference to
The neuromonitoring system 10 performs neuromuscular pathway (NMP) assessments, via Twitch Test mode, by electrically stimulating a peripheral nerve (preferably the Peroneal Nerve for lumbar and thoracolumbar applications and the Median Nerve for cervical applications) via stimulation electrodes 22 contained in the applicable electrode harness and placed on the skin over the nerve or by direct stimulation of a spinal nerve using a surgical accessory such as the probe 116. Evoked responses from the muscles innervated by the stimulated nerve are detected and recorded, the results of which are analyzed and a relationship between at least two responses or a stimulation signal and a response is identified. The identified relationship provides an indication of the current state of the NMP. The identified relationship may include, but is not necessarily limited to, one or more of magnitude ratios between multiple evoked responses and the presence or absence of an evoked response relative to a given stimulation signal or signals. With reference to
It should be appreciated that while
The neuromonitoring system 10 may test the integrity of pedicle holes (during and/or after formation) and/or screws (during and/or after introduction) via the Basic Stimulation EMG and Dynamic Stimulation EMG tests. To perform the Basic Stimulation EMG a test probe 116 is placed in the screw hole prior to screw insertion or placed on the installed screw head and a stimulation signal is applied. The insulating character of bone will prevent the stimulation current, up to a certain amplitude, from communicating with the nerve, thus resulting in a relatively high Ithresh, as determined via the basic threshold hunting algorithm described below. However, in the event the pedicle wall has been breached by the screw or tap, the current density in the breach area will increase to the point that the stimulation current will pass through to the adjacent nerve roots and they will depolarize at a lower stimulation current, thus Ithresh will be relatively low. The system described herein may exploit this knowledge to inform the practitioner of the current Ithresh of the tested screw to determine if the pilot hole or screw has breached the pedicle wall.
In Dynamic Stim EMG mode, test probe 116 may be replaced with a clip 18 which may be utilized to couple a surgical tool, such as for example, a tap member 28 or a pedicle access needle 26, to the neuromonitoring system 10. In this manner, a stimulation signal may be passed through the surgical tool and pedicle integrity testing can be performed while the tool is in use. Thus, testing may be performed during pilot hole formation by coupling the access needle 26 to the neuromonitoring system 10, and during pilot hole preparation by coupling the tap 28 to the system 10. Likewise, by coupling a pedicle screw to the neuromonitoring system 10 (such as via pedicle screw instrumentation), integrity testing may be performed during screw introduction.
In both Basic Stimulation EMG mode and Dynamic Stimulation EMG mode, the signal characteristics used for testing in the lumbar testing may not be effective when monitoring in the thoracic and/or cervical levels because of the proximity of the spinal cord to thoracic and cervical pedicles. Whereas a breach formed in a pedicle of the lumbar spine results in stimulation being applied to a nerve root, a breach in a thoracic or cervical pedicle may result in stimulation of the spinal cord instead, but the spinal cord may not respond to a stimulation signal the same way the nerve root would. To account for this, the surgical system 10 is equipped to deliver stimulation signals having different characteristics based on the region selected. By way of example only, when the lumbar region is selected, stimulation signals for the stimulated EMG modes comprise single pulse signals. On the other hand, when the thoracic and cervical regions are selected the stimulation signals may be configured as multipulse signals.
Stimulation results (including but not necessarily limited to at least one of the numerical Ithresh value and color coded safety level indication) and other relevant data are conveyed to the user on at least main display 34, as illustrated in
The neuromonitoring system 10 may perform nerve proximity testing, via the XLIF mode, to ensure safe and reproducible access to surgical target sites. Using the surgical access components 26-32, the system 10 detects the existence of neural structures before, during, and after the establishment of an operative corridor through (or near) any of a variety of tissues having such neural structures which, if contacted or impinged, may otherwise result in neural impairment for the patient. The surgical access components 26-32 are designed to bluntly dissect the tissue between the patient's skin and the surgical target site. Dilators of increasing diameter, which are equipped with one or more stimulating electrodes, are advanced towards the target site until a sufficient operating corridor is established to advance retractor 32 to the target site. As the dilators are advanced to the target site electrical stimulation signals are emitted via the stimulation electrodes. The stimulation signal will stimulate nerves in close proximity to the stimulation electrode and the corresponding EMG response is monitored. As a nerve gets closer to the stimulation electrode, the stimulation current required to evoke a muscle response decreases because the resistance caused by human tissue will decrease, and it will take less current to cause nervous tissue to depolarize. Ithresh is calculated, using the basic threshold hunting algorithm described below, providing a measure of the communication between the stimulation signal and the nerve and thus giving a relative indication of the proximity between access components and nerves. An example of the monitoring screen 200 with XLIF mode active is depicted in
The neuromonitoring system 10 may also conduct free-run EMG monitoring while the system is in any of the above-described modes. Free-run EMG monitoring continuously listens for spontaneous muscle activity that may be indicative of potential danger. The system 10 may automatically cycle into free-run monitoring after 5 seconds (by way of example only) of inactivity. Initiating a stimulation signal in the selected mode will interrupt the free-run monitoring until the system 10 has again been inactive for five seconds, at which time the free-run begins again. An example of the monitoring screen 200 with Free-run EMG active is depicted in
The neuromonitoring system 10 may also perform a navigated guidance function. The navigated guidance feature may be used by way of example only, to ensure safe and reproducible pedicle screw placement by monitoring the axial trajectory of surgical instruments used during pilot hole formation and/or screw insertion. Preferably, EMG monitoring may be performed simultaneously with the navigated guidance feature. To perform the navigated guidance and angle-measuring device (hereafter “tilt sensor”) 54 is connected to the patient module 14 via one of the accessory ports 62. The tilt sensor measures its angular orientation with respect to a reference axis (such as, for example, “vertical” or “gravity”) and the control unit displays the measurements. Because the tilt sensor is attached to a surgical instrument the angular orientation of the instrument, may be determined as well, enabling the surgeon to position and maintain the instrument along a desired trajectory during use. In general, to orient and maintain the surgical instrument along a desired trajectory during pilot hole formation, the surgical instrument is advanced to the pedicle (through any of open, mini-open, or percutaneous access) while oriented in the zero-angle position. The instrument is then angulated in the sagittal plane until the proper cranial-caudal angle is reached. Maintaining the proper cranial-caudal angle, the surgical instrument may then be angulated In the transverse plane until the proper medial-lateral angle is attained. Once the control unit 12 indicates that both the medial-lateral and cranial caudal angles are matched correctly, the instrument may be advanced into the pedicle to form the pilot hole, monitoring the angular trajectory of the instrument until the hole formation is complete.
The control unit 12 may communicate any of numerical, graphical, and audio feedback corresponding to the orientation of the tilt sensor in the sagittal plane (cranial-caudal angle) and in the transverse plane (medial-lateral angle). The medial-lateral and cranial-caudal angle readouts may be displayed simultaneously and continuously while the tilt sensor is in use, or any other variation thereof (e.g. individually and/or intermittently).
To obtain Ithresh and take advantage of the useful information it provides, the system 10 identifies and measures the peak-to-peak voltage (Vpp) of each EMG response corresponding to a given stimulation current (IStim). Identifying the true Vpp of a response may be complicated by the existence of stimulation and/or noise artifacts which may create an erroneous Vpp measurement. To overcome this challenge, the neuromonitoring system 10 of the present invention may employ any number of suitable artifact rejection techniques such as those shown and described in full in the above referenced co-pending and commonly assigned PCT App. Ser. No. PCT/US2004/025550, entitled “System and Methods for Performing Dynamic Pedicle Integrity Assessments,” filed on Aug. 5, 2004, the entire contents of which are incorporated by reference into this disclosure as if set forth fully herein. Upon measuring Vpp for each EMG response, the information is analyzed relative to the corresponding stimulation current (Istim) in order to identify the minimum stimulation current (IThresh) capable of resulting in a predetermined Vpp EMG response. According to the present invention, the determination of IThresh may be accomplished via any of a variety of suitable algorithms or techniques.
Additionally, in the “dynamic” functional modes, including, but not necessarily limited to Dynamic Stimulation EMG and XLIF, the system may continuously update the stimulation threshold level and indicate that level to the user. To do so, the threshold hunting algorithm does not repeatedly determine the Ithresh level anew, but rather, it determines whether stimulation current thresholds are changing. This is accomplished, as illustrated in
In an alternative embodiment, rather than beginning by entering the bracketing phase at the minimum stimulation current and bracketing upwards until Ithresh is bracketed, the threshold hunting algorithm may begin by immediately determining the appropriate safety level and then entering the bracketing phase. The algorithm may accomplish this by initiating stimulation at one or more of the boundary current levels. By way of example only, and with reference to
For some functions, such as (by way of example) MEP, it may be desirable to obtain Ithresh for each active channel each time the function is performed. This is particularly advantageous when assessing changes in Ithresh over time as a means to detect potential problems (as opposed to detecting an Ithresh below a predetermined level determined to be safe, such as in the Stimulated EMG modes). While Ithresh can be found for each active channel using the algorithm as described above, it requires a potentially large number of stimulations, each of which is associated with a specific time delay, which can add significantly to the response time. Done repeatedly, it could also add significantly to the overall time required to complete the surgical procedure, which may present added risk to the patient and added costs. To overcome this drawback, a preferred embodiment of the neuromonitoring system 10 boasts a multi-channel threshold hunting algorithm so as to quickly determine Ithresh for each channel while minimizing the number of stimulations and thus reduce the time required to perform such determinations.
The multi-channel threshold hunting algorithm reduces the number stimulations required to complete the bracketing and bisection steps when Ithresh s being found for multiple channels. The multi-channel algorithm does so by omitting stimulations for which the result is predictable from the data already acquired. When a stimulation signal is omitted, the algorithm proceeds as if the stimulation had taken place. However, instead of reporting an actual recruitment result, the reported result is inferred from previous data. This permits the algorithm to proceed to the next step immediately, without the time delay associated with a stimulation signal.
Regardless of what channel is being processed for Ithresh, each stimulation signal elicits a response from all active channels. That is to say, every channel either recruits or does not recruit in response to a stimulation signal (again, a channel is said to have recruited if a stimulation signal evokes an EMG response deemed to be significant on that channel, such as Vpp of approximately 100 uV). These recruitment results are recorded and saved for each channel. Later, when a different channel is processed for Ithresh the saved data can be accessed and, based on that data, the algorithm may omit a stimulation signal and infer whether or not the channel would recruit at the given stimulation current.
There are two reasons the algorithm may omit a stimulation signal and report previous recruitment results. A stimulation signal may be omitted if the selected stimulation current would be a repeat of a previous stimulation. By way of example only, if a stimulation current of 1 mA was applied to determine Ithresh for one channel, and a stimulation at 1 mA is later required to determine Ithresh for another channel, the algorithm may omit the stimulation and report the previous results. If the specific stimulation current required has not previously been used, a stimulation signal may still be omitted if the results are already clear from the previous data. By way of example only, if a stimulation current of 2 mA was applied to determine Ithresh for a previous channel and the present channel did not recruit, when a stimulation at 1 mA is later required to determine Ithresh for the present channel, the algorithm may infer from the previous stimulation that the present channel will not recruit at 1 mA because it did not recruit at 2 mA. The algorithm may therefore omit the stimulation and report the previous result.
In the interest of clarity,
Once Ithresh is found for channel 1, the algorithm turns to channel 2, as illustrated in
Although the multi-channel threshold hunting algorithm is described above as processing channels in numerical order, it will be understood that the actual order in which channels are processed is immaterial. The channel processing order may be biased to yield the highest or lowest threshold first (discussed below) or an arbitrary processing order may be used. Furthermore, it will be understood that it is not necessary to complete the algorithm for one channel before beginning to process the next channel, provided that the intermediate state of the algorithm is retained for each channel. Channels are still processed one at a time. However, the algorithm may cycle between one or more channels, processing as few as one stimulation current for that channel before moving on to the next channel. By way of example only, the algorithm may stimulate at 10 mA while processing a first channel for Ithresh. Before stimulating at 20 mA (the next stimulation current in the bracketing phase), the algorithm may cycle to any other channel and process it for the 10 mA stimulation current (omitting the stimulation if applicable). Any or all of the channels may be processed this way before returning to the first channel to apply the next stimulation. Likewise, the algorithm need not return to the first channel to stimulate at 20 mA, but instead may select a different channel to process first at the 20 mA level. In this manner, the algorithm may advance all channels essentially together and bias the order to find the lower threshold channels first or the higher threshold channels first. By way of example only, the algorithm may stimulate at one current level and process each channel in turn at that level before advancing to the next stimulation current level. The algorithm may continue in this pattern until the channel with the lowest Ithresh is bracketed. The algorithm may then process that channel exclusively until Ithresh is determined, and then return to processing the other channels one stimulation current level at a time until the channel with the next lowest Ithresh is bracketed. This process may be repeated until Ithresh is determined for each channel in order of lowest to highest Ithresh. If Ithresh for more than one channel falls within the same bracket, the bracket may be bisected, processing each channel within that bracket in turn until it becomes clear which one has the lowest Ithresh. If it becomes more advantageous to determine the highest Ithresh first, the algorithm may continue in the bracketing state until the bracket is found for every channel and then bisect each channel in descending order.
Although the hunting algorithm is discussed herein in terms of finding Ithresh (the lowest stimulation current that evokes a predetermined EMG response), it is contemplated that alternative stimulation thresholds may be useful in assessing the health of the spinal cord or nerve monitoring functions and may be determined by the hunting algorithm. By way of example only, the hunting algorithm may be employed by the system 10 to determine a stimulation voltage threshold, Vstimthresh. This is the lowest stimulation voltage (as opposed to the lowest stimulation current) necessary to evoke a significant EMG response, Vthresh. Bracketing, bisection and monitoring states are conducted as described above for each active channel, with brackets based on voltage being substituted for the current based brackets previously described. Moreover, although described above within the context of MEP monitoring, it will be appreciated that the algorithms described herein may also be used for determining the stimulation threshold (current or voltage) for any other EMG related functions, including but not limited to pedicle integrity (screw test), nerve detection, and nerve root retraction.
While this invention has been described in terms of a best mode for achieving this invention's objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the present invention. For example, the present invention may be implemented using any combination of computer programming software, firmware or hardware. As a preparatory step to practicing the invention or constructing an apparatus according to the invention, the computer programming code (whether software or firmware) according to the invention will typically be stored in one or more machine readable storage mediums such as fixed (hard) drives, diskettes, optical disks, magnetic tape, semiconductor memories such as ROMs, PROMs, etc., thereby making an article of manufacture in accordance with the invention. The article of manufacture containing the computer programming code is used by either executing the code directly from the storage device, by copying the code from the storage device into another storage device such as a hard disk, RAM, etc. or by transmitting the code on a network for remote execution. As can be envisioned by one of skill in the art, many different combinations of the above may be used and accordingly the present invention is not limited by the specified scope.
This application is an international patent application claiming the benefit of priority from commonly owned and co-pending U.S. Provisional Patent Application Ser. No. 61/196,264, entitled “Neurophysiologic Monitoring System,” and filed on Oct. 14, 2008, the entire contents of which is hereby expressly incorporated by reference into this disclosure as if set forth in its entirety herein.
| Number | Date | Country | |
|---|---|---|---|
| 61196264 | Oct 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13124608 | Dec 2011 | US |
| Child | 16935947 | US |
