System and Methods for Nerve Monitoring
A system and related methods for performing nerve detection during surgical access using ultrasound testing during surgery.
This application is a continuation of U.S. patent application Ser. No. 11/528,981, filed on Sep. 27, 2005 (now issued as U.S. Pat. No. 8,568,317), which claims priority to U.S. Provisional Patent Application Ser. No. 60/721,425, filed on Sep. 27, 2005, the entire contents of which are hereby expressly incorporated by reference into this disclosure as if set forth in its entirety herein.
BACKGROUND OF THE INVENTION1. Field
The present invention relates generally to a system and related methods for performing at least one of bone integrity testing and nerve detection during surgical access using both neurophysiologic testing and ultrasound testing during surgery.
2. Discussion
It has been estimated that somewhere between 50 and 70 million people suffer from chronic back pain in the United States. In most cases, conservative therapies, including, for example, bed rest and physical therapy will succeed in alleviating, or at least significantly reducing the back pain. Still, a significant number of patients are unaided by conservative therapies alone and undergo spinal surgery before finding relief. The rate at which caregivers and patients opt for surgery also continues to grow as medical technology advances and surgical options increase. In all, approximately 750,000 spine surgeries are performed per year in the United States alone.
When necessary, spine surgery may provide great benefit to the patient, often allowing patients to resume activities long since abandoned because of the debilitating pain. Spine surgery, however, is not without risk. Operating on or near the spine generally means operating in close proximity to delicate neural tissue, such as the spinal cord and nerve roots. Damage to the neural tissue, which may be caused (for example) by inadvertent contact with a surgical instrument and/or implant while accessing the spinal target site or inadvertent contact of an implant or surgical instrument and/or implant before or during pedicle screw placement. One way to mitigate this risk is to conduct neurophysiologic monitoring during the procedure and/or recovery period. Neurophysiologic monitoring generally consists of stimulating neural tissue and analyzing responses (generally electrical waveforms) generated by the stimulus. While such neurophysiologic monitoring has proved an exceedingly valuable tool in efforts to prevent neurological damage during spine surgery there is still room for further improvements. The present invention is directed at such an improvement.
SUMMARY OF THE INVENTIONAccording to a broad aspect, the present invention includes a surgical system, comprising a surgical instrument having at least one stimulation electrode for transmitting a stimulation signal for performing neurophysiologic testing during surgery and/or at least one transducer for transmitting and/or receiving signals for performing ultrasound-based testing during surgery. The testing may include, but is not necessarily limited to, pedicle integrity testing associated with the use of pedicle screws (e.g. hole formation, preparation, and screw placement) and surgical access.
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.
The present invention is directed towards enabling safe and reproducible spinal surgery by aiding in, among other things, access to a target site in the spine (including but not necessarily limited to a pedicle) and pedicle screw implantation (including but not necessarily limited to formation and preparation of pilot holes and screw placement). To do so the present invention integrates a host of imaging and neurophysiologic assessment capabilities together in a single, user-friendly and surgeon directed system.
The neuromonitoring system 10 includes a control unit 12, a patient module 14, an EMG harness 16, including eight pairs of EMG electrodes 18 and a return electrode 22 coupled to the patient module 14, and one or more of a host of surgical accessories 24 capable of being coupled to the patient module 14 (preferably via a stimulation handpiece 28 and accessory cables 26), and a pair of peripheral nerve stimulation (PNS) electrodes (one positive and one negative) 29 also coupled to the patient module 14. The surgical accessories 24 may include, but are not necessarily limited to, devices for performing pedicle screw tests (such as a screw test probe 30, tap member 32, bone awl 34), surgical access components (such as a K-wire 36, one or more dilating cannula 38, 40, a tissue retractor assembly 42), and neural pathology monitoring devices (such as a nerve root retractors 44, 45), any of which may also be fitted with one or more ultrasound transducers 55 for imaging of surrounding tissue during use. The neuromonitoring system 10 accomplishes neuromonitoring by having the control unit 12 and patient module 14 cooperate to send stimulation signals to one or more stimulation electrodes or electrode regions on the various surgical accessories, while sensors detect muscle activity caused by the stimulation signal.
A block diagram of the neuromonitoring system 10 is shown in
The patient module 14 is connected via a data cable 50 (or optionally via wireless communication) to the control unit 12, and contains the electrical connections to all electrodes, EMG signal conditioning circuitry, stimulator drive and steering circuitry, ultrasound signal conditioning and receiving circuitry and a digital communications interface to the control unit 12. In use, the control unit 12 is situated outside but close to the surgical field (such as on a cart adjacent the operating table) such that the display 46 is directed towards the surgeon for easy visualization. The patient module 14 should be located between the patient's legs, or may be affixed to the end of the operating table at mid-leg level using a bedrail clamp. The position selected should be such that the EMG leads surgical accessories 24 can reach their farthest desired location without tension during the surgical procedure.
The information displayed to the user on the display 46 may include, but is not necessarily limited to, alpha-numeric and/or graphical information regarding any of the requested modes (e.g., Twitch Test, Free-Run EMG, Screw Test (Basic, Difference, Dynamic), Detection, and Nerve Retractor), myotome/EMG levels, stimulation levels, past stimulation events, stimulation site images, ultrasound images, etc. . . . In one embodiment, set forth by way of example only, this information may include at least some of the following components (depending on the active mode) as set forth in Table 1:
The neuromonitoring functionality of the neuromonitoring system 10 is based on assessing the evoked response of the various muscle myotomes monitored by the system 10 in relation to a stimulation signal transmitted by the system 10 (via patient module 14). This is best shown in
In one embodiment, EMG response monitoring is accomplished via 8 pairs EMG electrodes 18 (placed on the skin over the muscle groups to be monitored), a common electrode 20 providing a ground reference to pre-amplifiers in the patient module 14, and an anode electrode 22 providing a return path for the stimulation current. It should be appreciated that any of a variety of known electrodes can be employed, including but not limited to surface pad electrodes and needle electrodes. It should also be appreciated that EMG electrode placement depends on a multitude of factors, including for example, the spinal level and particular nerves at risk and user preference, among others. In one embodiment (set forth by way of example only), an exemplary EMG configuration is described for Lumbar surgery in Table 2, Thoracolumbar surgery in Table 3, and Cervical surgery in Table 4 below:
A basic premise underlying the methods employed by the system 10 for much of the neurophysiologic monitoring conducted is that neurons and nerves have characteristic threshold current levels (IThresh) at which they will depolarize, resulting in detectable muscle activity. Below this threshold current, stimulation signals will not evoke a significant EMG response. Each EMG response can be characterized by a peak-to-peak voltage of Vpp=Vmax−Vmin, shown in
The neuromonitoring system 10 capitalizes on and enhances the information derived from Ithresh by (a) employing methods designed to find Ithresh quickly, accurately, and efficiently; (b) analyzing Ithresh according to predetermined safety indicator levels; and (c) displaying Ithresh and related safety indication data in a simple and meaningful way. Armed with the useful information conveyed by the system 10, the surgeon may detect early on any problem or potential problem and then act to avoid and/or mitigate the situation. By way of general example only, an excessively high Ithresh or an increase over a previous Ithresh measurement during Nerve Retractor mode may indicate a deterioration of nerve root function caused by excessive and/or prolonged retraction. During Screw Test and Detection modes, a low Ithresh value may indicate a breach in the pedicle, or the close proximity of a nerve, respectively.
To quickly determine Ithresh, the system 10 may employ a variety of suitable algorithms and techniques which are described in detail in the “NeuroVision Applications,” all of which are incorporated by reference below, as if they were set forth herein in their entireties. One exemplary threshold hunting algorithm, illustrated by way of example only in
After the bracket containing the threshold current Ithresh has been determined, the initial bracket is successively reduced via the bisection method 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. In one embodiment, the midpoint of this final bracket may be defined as Ithresh; however, any value falling within the final bracket may be selected as Ithresh without departing from the scope of the present invention.
During some functions (e.g. Screw Tests and Detection) stimulations may stop after Ithresh is determined for the channel possessing the lowest Ithresh. For other functions (e.g. Nerve Retractor), however, it may useful to determine Ithresh for every channel. To accomplish this quickly, the hunting algorithm may employ additional methods allowing it to omit certain stimulations, thereby reducing the number of stimulations and time required to obtain an Ithresh value on each channel. As demonstrated in
By way of example only, the various functional modes of the neuromonitoring system 10 may include the Basic Screw Test, Difference Screw Test, Dynamic Screw Test, MaXcess® Detection, and Free-run EMG, all of which will be described briefly below. The Basic Screw Test, Difference Screw Test, and Dynamic Screw Test modes 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 commonly owned U.S. Pat. No. 7,664,544 entitled “System and Methods for Performing Percutaneous Pedicle Integrity Assessments” and commonly owned U.S. Pat. No. 7,657,308, entitled “System and Methods for Performing Dynamic Pedicle Integrity Assessments,” the entire contents of which are both hereby incorporated by reference as if set forth fully herein. The MaXcess® Detection 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 k-wire 62, dilator 64, cannula 66, 68, retractor assembly 70. This mode is described in greater detail within commonly owned U.S. Pat. No. 8,068,912 entitled “System and Methods for Determining Nerve Proximity, Direction, and Pathology During Surgery,” the entire contents of which is hereby incorporated by reference as if set forth fully herein. Although not described herein, various other functional modes may be performed by the system 10, such as for example only, MEP and SSEP functions which are described in detail within commonly owned and co-pending Int'l 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 are hereby incorporated by reference as if set forth fully herein; The Twitch Test mode which is described in detail in commonly owned U.S. Pat. No. 8,538,539 entitled “System and Methods for Assessing the Neuromuscular Pathway Prior to Nerve Testing,” the entire contents of which is hereby incorporated by reference as if set forth fully herein; and Nerve Retractor mode which is described in greater detail within commonly owned U.S. Pat. No. 7,522,953 entitled “System and Methods for Performing Surgical Procedures and Assessments,” the entire contents of which are hereby incorporated by reference as if set forth fully herein.
In one embodiment one or more of the surgical accessories 24 including, but not necessarily limited to screw test probe 30, tap member 32, bone awl 34, k-wire 36, dilating cannulae 38, 40, retractor assembly 42, by way of fixed or releasable linkage to a stimulation handpiece 28. Turning to
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 Screw test, Difference Screw Test, and/or Dynamic Screw Test modes. For the Basic Screw Test a screw test probe 30, such as that illustrated in
In Difference Screw Test mode, a baseline threshold value is determined by directly stimulating a nerve. Screw test probe 30 may preferably be used, and the probe is advanced through the surgical corridor to the surgical target site (i.e. the nerve to be directly stimulated). Button 52 on the stimulation handpiece 28 is pressed to initiate stimulation and a baseline threshold is established. Screw test probe 30 may then be maneuvered to the next stimulation target site (e.g. pilot hole or screw head) and stimulation is initiated to determine the actual threshold value Ithresh. The actual threshold is compared to the baseline threshold. The difference between the actual and baseline thresholds is calculated to provide an indication of the safety level. Details and results, including the baseline, actual, and difference thresholds among other things may be displayed for the user on GUI display 46.
Dynamic Screw Test mode continuously monitors threshold values while one or more surgical accessories are in use, for example forming a pilot hole. For dynamic screw tests an electric coupling device, such as, by way of example only, stimulation clip 58 is coupled to stimulation handpiece 28, as illustrated in
With reference to
Again with reference to
Stimulation results and other relevant data for the screw test modes are conveyed to the user on display 46, as illustrated in
The neuromonitoring system 10 may perform nerve proximity testing, via the MaXcess® Detection mode, to ensure safe and reproducible access to surgical target sites. Using the surgical access components 36-40, 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 36-40 are designed to bluntly dissect the tissue between the patient's skin and the surgical target site. Access components 36-40 preferably utilize stimulation handpiece 28 and stimulation clip 58 (in the same manner as described above and shown in
Additional and/or alternative surgical access components such as, by way of example only, a tissue retraction assembly 42 (
An exemplary screen display of the Detection mode for display on display 46 is illustrated by way of example only 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. Stimulated and/or Free-run results for any function may be replaced with, or more preferably, augmented with a display of the actual waveform for each channel, as well as audible sounds distinctive to each level of safety (safe, unsafe, in between).
To augment the neurophysiologic assessments, such as for example only those described above, performed by the neuromonitoring system 10, the system 10 may be further equipped to conduct and display ultrasound imaging of proximate body tissues (e.g. bone during pilot hole formation and preparation and/or screw implantation and nerves and/or vasculature during surgical access). To do so, the system 10 may employ intraoperative ultrasound tailored to allow use within bone, such as, by way of example only, the ultrasound system described in U.S. Pat. No. 6,579,244, entitled “Intraosteal Ultrasound During Surgical Implantation.” Specifically, at least one ultrasound transducer 55 may be deployed to the surgical target site during surgery. Under the direction of control unit 12, acoustic signals of a predetermined frequency, ranging between 50 kHz and 16 MHz, are emitted from the transducer(s) 55 through the surrounding body tissue. The signals reflect off tissue boundaries and are thereafter received back at the transducer, converted into electric signals, and processed by the control unit 12 into viewable images. The images may be viewed on the screen display 26.
Preferably, at least one transducer is mounted on or within one or more of the surgical accessories 24 (such as screw test probe 30, dilating cannula 38, 40, or retraction assembly 42, shown in
For the purposes of example only,
A basic principle underlying the effective use of ultrasound during and/or after pilot hole formation and preparation is the distinctive acoustical characteristics of bone relative to other soft tissues in the body, and more importantly, the varying acoustical characteristics exhibited by bone itself, depending upon its different properties, such as (by way of example only) the type of bone (i.e. cortical or cancellous), bone density, and bone composition. Different acoustical characteristics can include, among others, the velocity, amplitude, and attenuation of sound waves as they pass through tissue. Methods abound in the prior art for quantifying different properties of bone by using ultrasound to determine one or more of its acoustical characteristics and additional methods are known in the prior art for processing ultrasound signals to generate a viewable image of tissue. The present invention makes advantageous use of this information, as well as the general makeup of the boney tissue within the pedicle, to assist surgeons in guidance of surgical instrumentation (including but not limited to tap member 34 and pedicle access probe/awl 36) through the cancellous bone of the interior pedicle and into the vertebral body without breaching the cortical wall.
With reference to
In addition to the image guidance aspect of ultrasound, ultrasound may be used to determine various properties and/or conditions of bone (via any of a number of suitable methods known to the prior art which may be implemented by the system 10) which may also provide useful information. By way of example only, cracks in the pedicle bone, along with their relative position, may be detected using ultrasound. The system 10 may thus detect a breach in the outer wall of the pedicle by ultrasound detection as well as by the nerve monitoring described above. Additional warning indicia such as graphics and/or audible tones may be employed to warn of any danger detected by the system 10 using ultrasound. By way of further example, the system 10 may utilize ultrasound to determine the density of the bone instrument 24 is in contact with. In the event the instrument encounters cortical bone an auditory or visual alert may be initiated thereby providing additional warning of impending breach if the current trajectory is maintained.
Ultrasound during surgical access may also be used to enhance the nerve detection function described above and proceeds along the same premise as that described for imaging bone. Acoustic signals, generally in the range of 2 MHz-16 MHZ for nerve imaging, are emitted from the transducer 55 located on or within the surgical access components (such as, cannulae 38, 40, and/or retraction assembly 42). The signals reflect of tissue boundaries, such as the interface between fat and muscle or muscle and nerves, and are thereafter received and processed to form a viewable image of the tissue relative to the transducer, which is displayed on screen display 46. Nerves are distinguished from other tissue based on their shape and/or color on the image, as illustrated in
Ultrasound may be utilized on system 10 in conjunction with one the neurophysiologic assessment functions, or, it may be used as a stand alone feature. In one embodiment ultrasound is preferably activated from the GUI display 46 by selecting the appropriate command. When ultrasound imaging is utilized in conjunction with nerve monitoring according to the present invention, the ultrasound image is preferably displayed together with the nerve monitoring data thereby allowing the user to receive all the useful information provided by the system 10 at one time without the need to switch between screen views. FIG. 26-28—illustrate, by way of example only, an exemplary screen display for the Basic, Difference, and Dynamic screw test modes, respectively, with the combined ultrasound imaging image 84. In one embodiment, the ultrasound display includes colorized tissue boundaries. The soft cancellous bone 400 may be shown in green representing the preferred instrument positioning. The middle region 410 may be represented in yellow and the cortical bone in red. The distal end of the surgical instrument is represented, by way of example only, as a target finder 430.
It may also be advantageous for neurophysiologic assessment data and/or ultrasound images captured by the system 10 to be viewable by persons not present in the operating room. It is contemplated that the data and images may be transmitted to one or more remote locations and viewable by authorized persons. This may be accomplished by any number of data transmission methods. In one example, the images may be transmitted to a remote user via remote monitoring software such as that described in detail in the commonly owned and co-pending U.S. patent application Ser. No. 11/418,589, entitled “System and Methods for Performing and Monitoring Neurophysiologic Assessments,” filed on May 5, 2006, the entire contents of which are incorporated by reference herein as if set forth in its entirety.
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. By way of 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.
Claims
1. A method for safely avoiding nerve tissue during access to a surgical target site during surgery, comprising conducting both neurophysiologic testing and ultrasound testing to detect the presence of nerve tissue near an instrument equipped with at least one electrode for emitting a stimulation signal and at least one ultrasound transducer for emitting ultrasound signals while advancing the instrument to the surgical target site.
2. The method of claim Error! Reference source not found., wherein the ultrasound testing uses a signal having a frequency in the range of 50 kHz to 16 MHz.
3. The method of claim Error! Reference source not found., wherein the neurophysiologic testing and ultrasound testing are performed substantially simultaneously.
4. The method of claim Error! Reference source not found., wherein said transducer is located at a distal end of said instrument and is configured to transmit ultrasound signals through body tissue to nerve tissue near the surgical instrument during surgical access.
5. The method of claim 4, wherein the transducer is further configured to receive ultrasound signals after they reflect off at least the nerve tissue adjacent to the surgical instrument.
6. The method of claim 5, wherein the transducer is an array transducer.
7. The method of claim 6, wherein the transducer includes multiple elements arranged in a circular pattern about the distal end of the surgical instrument.
8. The method of claim 1, comprising the further step of displaying an image of the ultrasound testing on a display screen.
9. The method of claim 8, wherein the image depicts the position of the distal end of the surgical instrument in relation to the nerve tissue.
10. The method of claim 9, wherein the image is displayed together with data associated with the neurophysiologic testing.
Type: Application
Filed: Oct 25, 2013
Publication Date: Feb 20, 2014
Inventors: James Gharib (San Diego, CA), Albert Pothier (San Diego, CA)
Application Number: 14/063,184
International Classification: A61B 19/00 (20060101); A61B 8/08 (20060101); A61B 5/00 (20060101); A61B 8/00 (20060101); A61B 5/04 (20060101);
