U.S. patent application number 14/294304 was filed with the patent office on 2014-09-25 for systems and methods for performing neurophysiologic assessments with pressure monitoring.
The applicant listed for this patent is NuVasive, Inc.. Invention is credited to Allen Farquhar, James E. Gharib, David Ivanko, Scot Martinelli, Benjamin VerHage.
Application Number | 20140288389 14/294304 |
Document ID | / |
Family ID | 37680020 |
Filed Date | 2014-09-25 |
United States Patent
Application |
20140288389 |
Kind Code |
A1 |
Gharib; James E. ; et
al. |
September 25, 2014 |
Systems and Methods for Performing Neurophysiologic Assessments
with Pressure Monitoring
Abstract
Systems and methods for performing neurophysiologic assessments
of neural tissue including nerve pathology monitoring which may be
augmented by adding the ability to assess or monitor the pressure
being exerted upon a nerve or nerve root before, during and/or
after retraction.
Inventors: |
Gharib; James E.; (San
Diego, CA) ; Farquhar; Allen; (Portland, OR) ;
Martinelli; Scot; (Mountain Top, PA) ; Ivanko;
David; (San Diego, CA) ; VerHage; Benjamin;
(New York, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NuVasive, Inc. |
San Diego |
CA |
US |
|
|
Family ID: |
37680020 |
Appl. No.: |
14/294304 |
Filed: |
June 3, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11490717 |
Jul 20, 2006 |
8740783 |
|
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14294304 |
|
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|
60701305 |
Jul 20, 2005 |
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Current U.S.
Class: |
600/301 |
Current CPC
Class: |
A61B 5/04001 20130101;
A61B 5/4029 20130101; A61B 5/0488 20130101; A61B 5/4893 20130101;
A61B 5/05 20130101 |
Class at
Publication: |
600/301 |
International
Class: |
A61B 5/04 20060101
A61B005/04; A61B 5/00 20060101 A61B005/00 |
Claims
1. A method for assessing the pathology of a nerve, comprising the
steps of: retracting a nerve within a patient using a nerve
retractor having a plurality of pressure sensors and at least one
stimulation electrode situated on a nerve contacting head of the
retractor, wherein said at least one stimulation electrode is
configured to deliver an electrical stimulation signal to a nerve
within a patient; delivering an electrical stimulation signal to
said nerve with said stimulation electrode; detecting an
neuromuscular response evoked by said stimulation signal using at
least one electrical sensor in electrical communication with said
at least one stimulation electrode to detect neuromuscular
responses evoked by said stimulation signal; using a control unit
communicatively linked to said stimulation electrode and said
electrical sensor to identify a relationship between said
stimulation signal and said neuromuscular response; calculating the
pressure exerted on at least two locations along said nerve by said
nerve retractor using a processing unit communicatively linked to
said pressure sensors; and displaying pressure mapping data on a
display linked to said processing unit in at least two dimensions
based on said calculated pressure exerted on said at least two
locations along said nerve.
2. The method of claim 1, wherein said display further provides at
least one of additional alpha-numeric and graphic indicia relating
to said calculated pressure.
3. The method of claim 2, wherein said alpha-numeric and graphic
indicia includes at least one of a maximum pressure value, time
value, color, chart, and a graph.
4. The method of claim 1, wherein said control unit includes a
display and said display provides at last one of alpha-numeric and
graphic indicia relating to said identified relationship.
5. The method of claim 1, wherein said identified relationship is
the lowest stimulation current necessary to evoke a neuromuscular
response.
6. The method of claim 5, wherein said control unit is configured
to perform a threshold hunting algorithm to identify the lowest
stimulation current necessary to evoke a neuromuscular
response.
7. The method of claim 1, wherein said control unit and said
processing unit are a single unit.
8. The method of claim 1, wherein said control unit and said
processing unit are distinct units.
9. The method of claim 1, wherein said pressure mapping data is
3-dimensional pressure mapping data.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 11/490,717 filed Jul. 20, 2006, now U.S. Pat. No. 8,740,783,
which claims the benefit of priority from commonly owned and
co-pending U.S. Provisional Application No. 60/701,305 entitled
"System and Methods for Determining Nerve Proximity, Nerve
Direction, and Nerve Pathology During Surgery" filed Jul. 20, 2005,
the entire contents of which are expressly incorporated by
reference into this disclosure as if set forth herein in its
entirety.
BACKGROUND OF THE INVENTION
[0002] I. Field of the Invention
[0003] 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 neurophysiologic assessments with additional pressure
monitoring.
[0004] II. Description of Related Art
[0005] 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.
[0006] 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. Often, in order to
reach the surgical target site the delicate nerve tissue must be
retracted out of the surgical corridor. A typical nerve retractor
serves to pull or otherwise maintain the nerve outside the area of
surgery, thereby protecting the nerve from inadvertent damage or
contact by the "active" instrumentation used to perform the actual
surgery. While generally advantageous in protecting the nerve, it
has been observed that such retraction can cause nerve function to
become impaired or otherwise pathologic over time due to the
retraction. In certain surgical applications, such as spinal
surgery, it is not possible to determine if such retraction is
hurting or damaging the retracted nerve until after the surgery
(generally referred to as a change in "nerve health" or "nerve
status").
[0007] The present invention is directed at eliminating, or at
least reducing the effects of, the above-described problems.
SUMMARY OF THE INVENTION
[0008] The present invention includes a system and methods capable
of performing a variety of neurophysiologic assessments, and
particularly nerve pathology monitoring (via Nerve Retractor mode),
by combining neurophysiology monitoring with any of a variety of
instruments used in or in preparation for surgery (referred to
herein as "surgical accessories"). Other assessments performed by
the system 10 may include one or more of, but not necessarily
limited to, neuromuscular pathway status (Twitch Test), pedicle
integrity testing (Screw Test), nerve proximity testing during
surgical access (Detection), nerve pathology monitoring (Nerve
Retractor), and detection of spontaneous muscle activity (Free Run
EMG-which may be conducted alone or in conjunction with any other
assessment). The nerve pathology monitoring of the present
invention may be augmented by equipping a nerve root retractor with
one or more pressure sensing technologies and/or providing an
additional system or device for assessing or monitoring the
pressure being exerted upon a nerve or nerve root before, during
and/or after nerve retraction.
[0009] The fundamental method steps for performing the nerve
pathology assessments (as well as many of the other assessments
which may be performed) according to the present invention include:
(a) stimulating one or more nerves with the surgical accessory
(e.g. nerve retractor among others); (b) measuring the response of
nerves innervated by the stimulation of step (a); (c) determining a
relationship between the surgical accessory and the nerve based
upon the response measured in step (b); and (d) communicating this
relationship to the surgeon in an easy-to-interpret fashion.
[0010] The step of stimulating one or more nerves may be
accomplished by applying any of a variety of suitable stimulation
signals to an electrode(s) on the surgical accessory, including
voltage and/or current pulses of varying magnitude and/or
frequency. The stimulating step may be performed at different times
depending upon the particular surgical accessory in question. For
example, with regard to neural pathology monitoring, stimulation
may be performed before, during and/or after retraction of the
nerve root, regardless of whether additional pressure sensing
features for monitoring the pressure being exerted upon a retracted
nerve or nerve root are employed.
[0011] The step of measuring the response of nerves innervated by
the stimulation step may be performed in any number of suitable
fashions, including but not limited to the use of evoked muscle
action potential (EMAP) monitoring techniques (that is, measuring
the EMG responses of muscle groups associated with a particular
nerve). According to one aspect of the present invention, the
measuring step is preferably accomplished via monitoring or
measuring the EMG responses of the muscles innervated by the
stimulated nerve(s).
[0012] The step of determining a relationship between the surgical
accessory and the nerve based upon the measurement step may be
performed in any number of suitable fashions depending upon the
manner of measuring the response, and may define the relationship
in any of a variety of fashions (based on any number of suitable
parameters and/or characteristics). By way of example, for neural
pathology assessments according to the present invention, the
relationship may be, by way of example only, whether the
neurophysiologic response of the nerve has changed over time. Such
changes may be quickly determined using a hunting algorithm to
determine a stimulation threshold current level at various times
during the procedure. According to one embodiment, these parameters
may be augmented with information regarding the pressure being
exerted upon a retracted nerve or nerve root.
[0013] The step of communicating this relationship to the surgeon
in an easy-to-interpret fashion may be accomplished in any number
of suitable fashions, including but not limited to the use of
visual indicia (such as alpha-numeric characters, light-emitting
elements, and/or graphics) and audio communications (such as a
speaker element). By way of example, for nerve pathology
monitoring, the determined threshold value may be visually
displayed as a simple numerical value on the display. In addition,
color coded graphics may be displayed to indicate the relative
safety level indicated by the threshold value. When pressure
sensing capabilities are added to the nerve root retractor
according to one aspect of the present invention, the step of
communicating the relationship to the user may also include
information about the pressure being exerted upon a retracted nerve
or nerve root, such as the retraction duration, the extent of
retraction, and/or the resulting pressure.
[0014] The nerve pathology monitoring function of the present
invention may be augmented with additional pressure sensing
capabilities. This may be accomplished by positioning one or more
pressure sensors on the nerve retractor and communicatively linking
the pressure sensor to pressure mapping software on the control
unit or other processor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] 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:
[0016] FIG. 1 is a flow chart illustrating the fundamental steps of
the neurophysiology-based surgical system according to the present
invention;
[0017] FIG. 2 is a perspective view of an exemplary system 10
capable of performing neurophysiologic assessments such as for
example, detecting pedicle breaches, nerve proximity (detection),
nerve pathology, neuromuscular pathway status, and spinal cord
health.
[0018] FIG. 3 is a block diagram of the system 10 shown in FIG.
2;
[0019] FIG. 4 is a graph illustrating an exemplary single pulse
stimulation signal according to one embodiment of the present
invention;
[0020] FIG. 5 is a is a graph illustrating an exemplary multipulse
stimulation signal according to one embodiment of the present
invention;
[0021] FIG. 6 is a graph illustrating an exemplary EMG response to
the stimulus of FIG. 3 or 4;
[0022] FIG. 7 is a graph illustrating a plot of peak-to-peak
voltage (Vpp) for each given stimulation current level (I.sub.Stim)
forming a stimulation current pulse train according to the present
invention (otherwise known as a "recruitment curve");
[0023] FIGS. 8-9 are perspective and side views, respectively, of
an exemplary nerve root retractor assembly according to one
embodiment of the present invention;
[0024] FIG. 10 is a perspective view of an exemplary nerve root
retractor forming part of the assembly of FIGS. 8 and 9, according
to one embodiment of the present invention;
[0025] FIG. 11 is an exemplary screen display illustrating one
embodiment of the Nerve Retractor mode for performing neural
pathology monitoring according to one embodiment of the present
invention;
[0026] FIG. 12 is a perspective view of an exemplary nerve root
retractor including a pressure sensor according to one embodiment
of the present invention;
[0027] FIG. 13 is a perspective view of the system of FIG. 2
adapted to perform additional pressure sensing functions according
to one embodiment of the present invention;
[0028] FIG. 14 is an exemplary multi-function screen display of the
pressure sensing features of the system 10 according to one
embodiment of the present invention;
[0029] FIG. 15 is an exemplary full screen display of the
2-dimensional pressure mapping feature according to one embodiment
of the present invention;
[0030] FIG. 16 is an exemplary full screen display of the
3-dimensional pressure mapping feature according to one embodiment
of the present invention;
[0031] FIG. 17 is an exemplary full screen display of the pressure
distribution chart feature according to one embodiment of the
present invention;
[0032] FIG. 18 is an exemplary full screen display of the pressure
vs. time chart feature according to one embodiment of the present
invention;
[0033] FIG. 19 is a perspective view of the system of FIG. 2
adapted to perform additional pressure sensing functions according
to a different embodiment of the present invention; and
[0034] FIG. 20 is an exemplary screen display illustrating one
embodiment of the Nerve Retractor mode for performing neural
pathology monitoring augmented by pressure monitoring according to
one embodiment of the present invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
[0035] 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.
[0036] The present invention is capable of performing a variety of
neurophysiologic assessments, and particularly nerve pathology
monitoring (via Nerve Retractor mode), by combining neurophysiology
monitoring with any of a variety of instruments used in or in
preparation for surgery (referred to herein as "surgical
accessories"). Other assessments performed by the system 10 may
include one or more of, but not necessarily limited to,
neuromuscular pathway status (Twitch Test), pedicle integrity
testing (Screw Test), nerve proximity testing during surgical
access (Detection), and detection of spontaneous muscle activity
(Free Run EMG--which may be conducted alone or in conjunction with
any other mode). As will be described in greater detail below, the
nerve pathology monitoring of the present invention may be
augmented by equipping a nerve root retractor 29 with one or more
pressure sensing technologies and/or providing an additional system
or device for assessing or monitoring the pressure being exerted
upon a nerve or nerve root before, during and/or after nerve
retraction. It is expressly noted that, although described herein
largely in terms of use in spinal surgery, the neuromonitoring
system 10 and related methods of the present invention are suitable
for use in any number of additional surgical procedures where
neurological impairment due to nerve retraction is a concern.
[0037] FIG. 1 illustrates the fundamental method steps for
performing the nerve pathology assessments (as well as many of the
other assessments which may be performed) according to the present
invention, namely: (a) stimulating one or more nerves with the
surgical accessory (e.g. nerve retactor); (b) measuring the
response of nerves innervated by the stimulation of step (a); (c)
determining a relationship between the surgical accessory and the
nerve based upon the response measured in step (b); and (d)
communicating this relationship to the surgeon in an
easy-to-interpret fashion.
[0038] FIGS. 2-3 illustrate, by way of example only, a surgical
system 10 provided in accordance with a broad aspect of the present
invention. The surgical system 10 includes a control unit 12, a
patient module 14, an EMG harness 16 including 8 pairs of EMG
electrodes 18 and a return electrode 22 coupled to the patient
module 14, and a host of surgical accessories 24 capable of being
coupled to the patient module 14 via one or more accessory cables
26. In the embodiment shown, the surgical accessories 24 include
(by way of example only) a screw test assembly 27 and a nerve root
retractor assembly 28. Other surgical accessories not shown here
may include, but are not necessarily limited to, a K-wire, a
sequential dilation access system (e.g. dilating and working
cannulae), taps, pedicle access probes, tissue retractor
assemblies, and surface electrodes etc. . . . Additional
components, such as for example an MEP stimulator (not shown) may
also be connected to the system 10.
[0039] The control unit 12 includes a touch screen display 30 and a
base 32, which collectively contain the essential processing
capabilities for controlling the surgical system 10. The patient
module 14 is connected to the control unit 12 via a data cable 34
(or optionally via wireless communication), which establishes the
electrical connections and communications (digital and/or analog)
between the control unit 12 and patient module 14. The main
functions of the control unit 12 include receiving user commands
via the touch screen display 30, activating stimulation in the
selected mode (e.g. Nerve Retractor), processing signal data
according to defined algorithms (described below), displaying
received parameters and processed data, and monitoring system
status and reporting fault conditions. The touch screen display 30
is preferably equipped with a graphical user interface (GUI)
capable of communicating information to the user and receiving
instructions from the user. The display 30 and/or base 32 may
contain patient module interface circuitry that commands the
stimulation sources, receives digitized signals and other
information from the patient module 14, processes the EMG responses
to extract characteristic information for each muscle group, and
displays the processed data to the operator via the display 30.
[0040] The step (a) of stimulating one or more target tissues with
the surgical accessory 24 is accomplished be coupling one or more
surgical accessories 24 equipped with an electrode region(s) to a
stimulation source (e.g. the patient module) communicatively linked
to the control unit 12. Preferably, multiple coupling options are
included with the system 10 to accommodate the variety of surgical
accessories and functions performed by the system 10. By way of
example only, a stimulation handpiece 36 (FIG. 1) may connect to
the patient module 14 via an accessory cable 26 at one end, and
couple a surgical accessory 24 (e.g. nerve retractor 29--thereby
forming nerve retractor assembly 28; or a pedicle probe
member--thereby forming screw test assembly 27) at the other end.
The stimulation handpiece 36 may include one or more buttons 38 for
selectively initiating stimulation according to the selected
function. In a preferred embodiment the stimulation handpiece 36 is
reusable and sterilizable. By way of further example only, an
electric coupling device such as, by way of example only,
stimulation clip 40 and/or stimulation clip 42 (FIG. 1) may be
provided to couple surgical accessories 24 (such as for example, a
tap member, access probe, tissue retractor assembly, and/or various
cannulae) to the system 10 such that stimulation signals may be
transmitted through the tool during use. The electric coupling
device may be used alone or using in conjunction with stimulation
handpiece 36, as is shown. Various other connectors may also be
employed to couple the surgical accessory to the stimulation
source, such as for example, a male/female type socket connection
and other commonly know electrical connectors.
[0041] The step (b) of measuring the response of nerves innervated
by the stimulation of step (a) may be performed in any number of
suitable fashions, including but not limited to the use of evoked
muscle action potential (EMAP) monitoring techniques (that is,
measuring the EMG responses of muscle groups associated with a
particular nerve). In a preferred 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. A preferred EMG electrode for use
with the system 10 is a dual surface electrode which is shown and
described in detail in the commonly owned and co-pending U.S.
patent application Ser. No. 11,048,404, entitled "Improved
Electrode System and Related Methods," filed on Jan. 31, 2005,
which is expressly incorporated by reference into this disclosure
as if set forth in its entirety herein. It should be appreciated
however, 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 cord level and particular nerves at risk and user
preference, among others. In one embodiment (set forth by way of
example only), the preferred EMG configuration is described for
Lumbar surgery in Table 1, Thoracolumbar surgery in Table 2, and
Cervical surgery in Table 3 below:
TABLE-US-00001 TABLE 1 Lumbar Spinal Color Channel Myotome Nerve
Level Red Right 1 Right Vastus Medialis Femoral L2, L3, L4 Orange
Right 2 Right Tibialis Anterior Common L4, L5 Peroneal Yellow Right
3 Right Biceps Femoris Sciatic L5, S1, S2 Green Right 4 Right
Medial Gastroc. Post Tibial S1, S2 Blue Left 1 Left Vastus Medialis
Femoral L2, L3, L4 Violet Left 2 Left Tibialis Anterior Common L4,
L5 Peroneal Gray Left 3 Left Biceps Femoris Sciatic L5, S1, S2
White Left 4 Left Medial Gastroc. Post Tibial S1, S2
TABLE-US-00002 TABLE 2 Thoracolumbar Spinal Color Channel Myotome
Nerve Level Red Right 1 Right Abductor Median C6, C7, C8, T1
Pollicis Brevis Orange Right 2 Right Vastus Medialis Femoral L2,
L3, L4 Yellow Right 3 Right Tibialis Anterior Common L4, L5
Peroneal Green Right 4 Right Abductor Hallucis Tibial L4, L5, S1
Blue Left 1 Left Abductor Median C6, C7, C8, T1 Pollicis Brevis
Violet Left 2 Left Vastus Medialis Femoral L2, L3, L4 Gray Left 3
Left Tibialis Anterior Common L4, L5 Peroneal White Left 4 Left
Abductor Hallucis Tibial L4, L5, S1
TABLE-US-00003 TABLE 3 Cervical Spinal Color Channel Myotome Nerve
Level Red Right 1 Right Deltoid Axilliary C5, C6 Orange Right 2
Right Flexor Median C6, C7, C8 Carpi Radialis Yellow Right 3 Right
Abductor Median C6, C7, C8, T1 Pollicis Brevis Green Right 4 Right
Abductor Hallucis Tibial L4, L5, S1 Blue Left 1 Left Deltoid
Axillary C5, C6 Violet Left 2 Left Flexor Median C6, C7, C8 Carpi
Radialis Gray Left 3 Left Abductor Median C6, C7, C8, T1 Pollicis
Brevis White Left 4 Left Abductor Hallucis Tibial L4, L5, S1
[0042] The step (c) of determining a relationship between the
surgical accessory and the nerve based upon the response measured
in step (b) may be performed in any number of suitable fashions
depending upon the manner of measuring the response, and may define
the relationship in any of a variety of fashions based on any
number of suitable parameters and/or characteristics). By way of
example only, the step of determining a relationship, within the
context of a nerve pathology assessment, may involve identifying
what stimulation current level is required to evoke a significant
muscle response (i.e. the relationship between the surgical
accessory (and more specifically the stimulation signal emitted
from the surgical accessory) and the nerve may be defined as the
stimulation threshold current level, described below).
[0043] 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 (I.sub.Thresh) at which they will depolarize, resulting in
detectable muscle activity. Below this threshold current,
stimulation signals, such as the single pulse signal shown by way
of example only in FIG. 4 and the multi-pulse signal shown by way
of example only in FIG. 5, will not evoke a significant EMG
response. Each EMG response can be characterized by a peak-to-peak
voltage of V.sub.pp=V.sub.max-V.sub.min, shown in FIG. 6. Once the
stimulation threshold (I.sub.Thresh) is reached, the evoked
response is reproducible and increases with increasing stimulation
until saturation is reached as shown in FIG. 7. This is known as a
"recruitment curve." In one embodiment, a significant EMG response
is defined as having a V.sub.pp of approximately 100 uV. The lowest
stimulation signal current, I.sub.stim that evokes this threshold
voltage (V.sub.Thresh) is called I.sub.Thresh. Finding I.sub.thresh
is useful in making neurophysiologic assessments because it
provides a relative indication as to the degree of communication
between a stimulation signal and nerve tissue. For example, as the
degree of electrical communication between a stimulation signal and
a nerve decreases, I.sub.thresh will increase. Conversely, as the
degree of communication between the stimulation signal and a nerve
increases, I.sub.thresh will decrease.
[0044] The system 10 capitalizes on and enhances the information
derived from I.sub.thresh by quickly, accurately, and efficiently
finding I.sub.thresh and comparing the determined value against
predetermined safety indicator levels. 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 I.sub.thresh or an increase over a previous
I.sub.thresh measurement during Nerve Retractor mode may indicate a
deterioration of nerve root function caused by excessive and/or
prolonged retraction. On the opposite hand, a decrease in Ithresh
over previous measurements may indicate During Screw Test and
Detection modes, a low I.sub.thresh value may indicate a breach in
the pedicle, or the close proximity of a nerve, respectively.
[0045] To quickly determine I.sub.thresh, 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 is
described hereafter in only brief detail. The threshold hunting
algorithm utilizes a bracketing method and a bisection method to
find I.sub.thresh. The bracketing method finds a range (bracket) of
stimulation currents that must contain I.sub.thresh. To accomplish
this, the algorithm directs stimulation to begin at a predetermined
current level (based on the selected function). For each subsequent
stimulation, the current level is doubled from the previous current
level. This doubling continues until a until a stimulation current
recruits, that is, results in an EMG response with a V.sub.pp
greater or equal to V.sub.thresh (e.g. 100 uV). This first
stimulation current to recruit, together with the last stimulation
current to have not recruited, forms the initial bracket. If the
stimulation current threshold, I.sub.thresh, of a channel exceeds a
maximum stimulation current, that threshold is considered out of
range.
[0046] After the bracket containing the threshold current
I.sub.thresh 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 I.sub.thresh is bracketed by stimulation currents separated
by the predetermined width. In one embodiment, the midpoint of this
final bracket may be defined as I.sub.thresh; however, any value
falling within the final bracket may be selected as I.sub.thresh
without departing from the scope of the present invention.
[0047] During some functions (e.g. Screw Tests and Detection)
stimulations may stop after I.sub.thresh is determined for the
channel possessing the lowest I.sub.thresh. For other functions
(e.g. Nerve Retractor), however, it may useful to determine
I.sub.thresh 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 I.sub.thresh value on each channel.
I.sub.thresh is still found using the bracketing and bisection
methods described above, however the algorithm will omit
stimulations for which the result is predictable from data
previously acquired. When a stimulation signal is omitted, the
algorithm proceeds as if the stimulation had taken place. This
permits the algorithm to proceed to the next required stimulation
immediately, without a time delay inherently associated with each
stimulation signal. To further reduce the number of stimulations
required over the time frame of an entire surgical procedure, the
algorithm may confirm previously obtained I.sub.thresh values (e.g.
by stimulation at current levels just below and at/or just above
I.sub.thresh and determining whether the resulting responses are
consistent with the previously acquired I.sub.thresh value), rather
than initiating stimulations from the beginning each time a
function is performed.
[0048] The final step (d) of communicating this relationship to the
surgeon in an easy-to-interpret fashion may be accomplished in any
number of suitable fashions, including but not limited to the use
of visual indicia (such as alpha-numeric characters, light-emitting
elements, and/or graphics) and audio communications (such as a
speaker element). By way of example only, the determined
I.sub.thresh value may be visually displayed as a simple numerical
value on display 30. In addition, color coded graphics may be
displayed to indicate the relative safety level indicated by the
I.sub.thresh (e.g. "green" for a range of stimulation thresholds
below (or above, depending on the selected mode) a predetermined
safe value, "red" for a range of stimulation thresholds above (or
below, depending on the mode) a predetermined unsafe value, and
"yellow" for the range of stimulation thresholds in between the
predetermined safe and unsafe values--designating caution). When
pressure sensing capabilities are added to the nerve root retractor
according to one aspect of the present invention, the step of
communicating the relationship to the user may also include
information about the pressure being exerted upon a retracted nerve
or nerve root, such as the retraction duration, the extent of
retraction, and/or the resulting pressure. In one embodiment, set
forth by way of example only, the information shown on the display
30 may include at least some of the following components (depending
on the active mode) as set forth in Table 1:
TABLE-US-00004 TABLE 1 Screen Component Description Spine An image
of the human body/skeleton showing the electrode placement Image on
the body, with labeled channel number tabs on each side (1-4 on the
left and right). Left and right labels will show the patient
orientation. The channel number tabs may be highlighted or colored
depending on the specific function being performed. Myotome & A
label to indicate the Myotome name and corresponding Spinal Level
Level(s) associated with the channel of interest. Names Menu A drop
down navigation component for toggling between functions. Display
Shows procedure-specific information including stimulation results.
Area Color Enhances stimulation results with a color display of
green, yellow, or Indication red corresponding to the relative
safety level determined by the system. Mode Graphics and/or name to
indicate the currently active mode (Twitch Indicator Test, Free-Run
EMG, Basic Screw Test, Dynamic Screw Test, Difference Screw Test,
Detection, Nerve Retractor). In an alternate embodiment, Graphics
and/or name may also be displayed to indicate the instrument in
use, such as the dilator, K-wire, retractor blades, screw test
instruments, and associated size information, if applicable, of the
cannula, with the numeric size. If no instrument is in use, then no
indicator is displayed. Stimulation A graphical stimulation
indicator depicting the present stimulation Bar status (i.e. on or
off and stimulation current level) Sequence Shows the last seven
stimulation results and provides for annotation of Bar results. EMG
EMG waveforms may be optionally displayed on screen along with the
waveforms stimulation results. Pressure Data regarding pressure
being exerted upon a retracted nerve or nerve Indicia root, such as
the duration of retraction, the extent of retraction, and/or the
resulting pressure.
[0049] By way of example only, the various functional modes capable
of being performed by system 10 may include, but is not necessarily
limited to, the Twitch Test, Free-run EMG, Basic Screw Test,
Difference Screw Test, Dynamic Screw Test, MaXcess.RTM. Detection,
Nerve Retractor, MEP Auto, MEP manual, and SSEP modes, all of which
are described only briefly hereafter. The Twitch Test mode is
designed to assess the neuromuscular pathway via the so-called
"train-of-four test" 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 Int'l 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 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 Int'l Patent App. No. PCT/US02/35047
entitled "System and Methods for Performing Percutaneous Pedicle
Integrity Assessments," filed on Oct. 30, 2002, and
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 MaXcess.RTM. 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, retractor
assembly 70. This mode is described in greater detail within Int'l
Patent App. No PCT/US02/22247, 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
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 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 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 Int'l
Patent App. No. PCT/US02/30617, entitled "System and Methods for
Performing Surgical Procedures and Assessments," filed on Sep. 25,
2002, the entire contents of which is hereby incorporated by
reference as if set forth fully herein.
[0050] Nerve pathology monitoring as it may be performed by the
system 10 during Nerve Retractor mode is described hereafter in
more detail. The system 10 preferably accomplishes neural pathology
monitoring via the Nerve Retractor mode, specifically by
determining a baseline stimulation threshold (again, stimulation
threshold is the value I.sub.thresh) with direct contact between
the nerve retractor 29 and the nerve, prior to retraction.
Subsequent stimulation thresholds are determined during retraction
and they are compared to the baseline threshold. Significant
changes in the stimulation threshold may indicate potential trauma
to the nerve caused by the retraction and are displayed to the user
on the display 30. An increase in I.sub.thresh over time is an
indication that the nerve function is deteriorating. By monitoring
this the surgeon may intra-operatively assess if the retracted
nerve is being damaged or otherwise compromised (such as due to a
prolonged surgery), such that it can be temporarily released to
allow it to recover before returning to retraction to continue with
the surgery. It's believed that releasing the nerve root in this
fashion will prevent or reduce the adverse effects (nerve function
compromise) that may otherwise result from prolonged retraction.
Changes in I.sub.thresh in the opposite direction (i.e. decreases
in I.sub.thresh over time) may indicate that the surgical procedure
is improving or aiding a previously unhealthy nerve, such as during
spinal decompression surgery. For accurate and timely information,
I.sub.thresh may preferably be determined for each channel
according to the multi-channel hunting algorithm described
above.
[0051] The nerve root retractor assembly 28, shown in a preferred
embodiment in FIGS. 8-10, comprises the stimulation handpiece 36
employed with a selectively removable nerve root retractor 29. The
nerve root retractor 29 has a generally angled orientation relative
to the longitudinal axis of the stimulation handpiece 36. The
distal end 44 is generally curved and includes an arcuate nerve
engagement surface 46 equipped with, by way of example only, at
least one stimulation electrode 48. As best shown in FIG. 10, the
nerve root retractor 29 is preferably removable from the
stimulation handpiece 36. To accomplish this, the stimulation
handpiece 36 includes a detachable cap member 50. Threads 52 are
provided on the proximal end of the nerve root retractor 29 to
allow a threaded coupling engagement between the stimulation
handpiece 36 and the nerve root retractor 29. During such
engagement, electrical contacts 54 on the nerve root retractor 29
become electrically coupled to the stimulation handpiece 36 such
that, upon activation of one or more of the buttons 38 a
stimulation current signal will be transmitted from the control
unit 12 and/or patient module 14 and delivered to the stimulation
electrode(s) 48 on the nerve root retractor 29 for the purpose of
performing neural pathology monitoring according to the present
invention. The nerve root retractor 29 is preferably disposable
and, as described above, the stimulation handpiece 36 is preferably
reusable and sterilizable. It should be understood that while the
nerve retractor 29 is shown primarily in use with the stimulation
handpiece 36 to form nerve retractor assembly 28, nerve retractor
29 may be used with any suitable handle and/or may include a fixed
handle. When nerve retractor 29 is used without stimulation
handpiece 36 it may be coupled to the system 10 via one of the
electric coupling devices 40, 42, a male/female type electrical
coupler, or any other form of electric coupling.
[0052] In use, the nerve root retractor 29 is introduced into or
near a surgical target site in order to hook and retract a given
nerve out of the way. According to the present invention, the nerve
root may be stimulated (monopolar or bipolar) before, during,
and/or after retraction in order to assess the degree to which such
retraction impairs or otherwise degrades nerve function over time.
To do so, the user may operate one or more buttons 38 of the
stimulation handpiece 36 to selectively transmit a stimulation
current signal, according to the algorithm described above, from
the patient module 14 to the electrode(s) 48 on the engagement
surface 46 of the nerve root retractor 29. By monitoring the
myotome(s) associated with the nerve root being retracted (via the
EMG harness 16) and assessing the resulting EMG responses to
preferably determine I.sub.thresh (via the control unit 12), the
system 10 can assess whether (and the degree to which) such
retraction impairs or adversely affects nerve function over time.
With this information, a user may wish to periodically release the
nerve root from retraction to allow nerve function to recover,
thereby preventing or minimizing the risk of long-term or
irreversible nerve impairment. Similarly, an unhealthy nerve may be
monitored in the same manner to determine if nerve function
improves due to a particular procedure, such as spinal nerve
decompression surgery.
[0053] The nerve retraction monitoring feature of the present
invention is best viewed with regard to FIG. 11. The screen display
for the Nerve Retractor mode may include any of a variety of
indicia capable of communicating parameters associated with the
nerve retraction monitoring feature of the present invention to a
surgeon, including but not limited to, channel windows containing
one or more of the channel number, myotome name, spinal level,
baseline I.sub.thresh, previous I.sub.thresh, current I.sub.thresh,
and the associated waveform, and various selection tabs for one or
more of starting baseline stimulation, starting retraction
stimulation, stopping stimulation, activating free-run EMG
monitoring and adjusting the sensitivity of the free-run EMG,
noting the retraction site, mode selection, annotating results, and
remote messaging.
[0054] As described above, the nerve pathology assessments (Nerve
Retractor mode) conducted by the system 10 may be further augmented
via the use of any number of pressure sensing technologies working
in addition to the stimulation based nerve monitoring described
above and throughout this disclosure. The pressure sensing features
contemplated herein offer added safety and qualitative assessment
features by providing the ability to monitor how much pressure is
being applied to a particular nerve during nerve root retraction.
This pressure may be a function of, among other factors, the degree
of retraction (that is, distance the nerve is moved during
retraction) and the duration of retraction. In any case, the
pressure resulting on a nerve during retraction--if too high in
magnitude and/or too long in duration--may result in neurologic
deficit of varying degrees. By monitoring the pressure according to
the present invention, a user may selectively reduce the degree of
retraction (such as by moving the retractor assembly 28 and nerve
closer to the "natural" position of the nerve) and/or periodically
releasing the nerve to avoid and/or minimize any resulting
neurologic deficit due to retraction.
[0055] The pressure sensing technologies may include any number of
commercially available and/or publicly known pressure sensing
technologies, and/or those later developed. The commercially
available and/or publicly known pressure sensing technologies
include, but are not necessarily limited to, the
piezoelectric-based pressure sensing technique shown and described
in U.S. Pat. No. 5,769,781 to James Chappuis, the capacitive-based
pressure mapping system shown and described in U.S. Pat. No.
5,010,772 to Bourland et. al., the strain gauge-based pressure
sensing technology shown and described in U.S. Pat. No. 4,784,150
to Voorhies et. al., the pressure sensitive ink-based technique
shown and described in U.S. Pat. No. 5,989,700 to Krivopal, and
that shown and described in U.S. Pat. No. 6,272,936 to Oreper et.
al.
[0056] Augmenting the nerve pathology monitoring with pressure
sensing capabilities may be accomplished in any number of suitable
manners, including but not limited to equipping the nerve retractor
assembly 28 (and more specifically, one or more of the nerve root
retractor 29, the stimulation handpiece 36, the distal end 44, and
the nerve engagement surface 46) with one or more pressure sensing
technologies. By way of example only, with reference to FIG. 9,
this may be done by equipping the nerve engagement surface 46 with
a pressure sensor 56. By way of example only, the pressure sensor
56 illustrated in FIG. 12 is a capacitive foam grid (comprising any
number of suitable grid units) adhered to nerve engagement surface
46 of nerve retractor 29. While pressure sensor 56 is shown herein
having a small number of relatively large grid units, this is done
for illustrative purposes. It will be readily understood by those
skilled in the art that that any number of grid units and unit
sizes may be utilized, and sensor 56 preferably comprises a large
number of relatively small grid units to increase precision. To
communicatively link the pressure sensor 56 to a processor unit, a
data cable (not shown) may be run along the nerve retractor 29, and
is preferably integrated within the interior of nerve retractor 29,
and from there may be connected to the processing unit via cable
58. Alternatively, wireless communication may be used to link the
pressure sensor and processing unit. As will be discussed below,
the processor may be control unit 12 or an additional dedicated
processor may be employed for pressure sensing features. In use,
pressure applied to the capacitive foam grid induces voltage
responses corresponding to the affected grid units. The voltage
responses are relayed to the processor which translates the
response into one or more of numerical and/or graphical (e.g.
color) indicia relating to pressure, which may be displayed to the
surgeon.
[0057] According to a further embodiment of the present invention,
a separate system or device may be employed for assessing or
monitoring the pressure being exerted upon a nerve or nerve root
before, during and/or after nerve retraction. Such a separate
system may supplant (that is, take the place of) and/or augment
(that is, serve in along with) the nerve root retractor 29 equipped
with pressure sensing capabilities described above.
[0058] With reference to FIG. 13, according to one embodiment, set
forth by way of example only, the pressure sensing features of the
system 10 are controlled via a separate processing unit 60 while
the EMG based nerve monitoring features are controlled via control
unit 12 (as described throughout the description). Processing unit
60 is preferably a personal workstation or laptop computer (by way
of example only) running pressure sensing software designed to
interface with the pressure sensor 56 and display pressure data to
the user on the processor screen 62. One such software program, by
way of example only, is the X3 Series software distributed by
XSENSOR.TM. Technology Corporation, Calgary Canada. In use,
processing unit 60 is preferably arranged near the control unit 12
such that the surgeon may view nerve pathology data from the
display 30 and pressure data from screen 62 at the same time.
[0059] As previously mentioned, pressure applied to the retracted
nerve may be a function of, among other factors, the degree of
retraction (that is, distance the nerve is moved during retraction)
and the duration of retraction, either of which may result in
neurologic deficit of varying degrees. With reference to FIG. 14,
various pressure mapping features of the present embodiment that
allow the surgeon to asses both the extent and duration of pressure
applied to the retracted nerve are illustrated. FIG. 14 illustrates
by way of example, a multi-function screen view of the pressure
sensing software. The multi-function screen may include (by way of
example only) a 2-dimensional (2-D) grid map 64, a 3-dimensional
(3-D) grid map 66, and a pressure distribution chart 68, and a
pressure vs. time (PvT) chart 70, a legend 72, and a tool bar 74.
The tool bar 74 and legend 72 may be found on all screen views of
the pressure mapping software. The tool bar 74 allows the user to
select between different view screens, among other functions (such
as for example, selecting the desired sensor range and precision).
The legend 74 indicates the numerical pressure value associated
with a specific color (e.g. in one example red indicates the
highest pressure of the selected range, 15.0 PSI in FIG. 14).
[0060] FIGS. 15-18 illustrate exemplary embodiments of the full
screen displays. FIG. 15 is a full screen display of the 2-D grid
map 64, wherein various colors are used (according to the legend
72) to indicate the amount of pressure measured for each grid unit
on the sensor 56. A reference marker 76 is included which
corresponds to a specific corner of the pressure sensor 56, to help
orient the viewer. FIG. 16 illustrates the full screen display of
the 3-D grid map, wherein various colors (according to the legend
72) are again used to indicate the amount of pressure measured on
the grid units of sensor 56. FIG. 17 illustrates the full screen
display of the pressure distribution graph 68, wherein the vertical
axis indicates the percentage of grid units at the given moment
which are under a measured pressure falling within the pressure
intervals on the horizontal axis. FIG. 18 shows the full screen
display of a PvT graph, wherein the maximum pressure measured on
sensor 56 is charted against the retraction time.
[0061] Utilizing the various functions of the pressure mapping
software, the surgeon may keep be kept aware to the extent which
pressure is applied to a nerve throughout retraction, and also the
length of time which a nerve is retracted. In addition, the 2-D and
3-D maps 64, 66 also allow the surgeon to quickly assess not only
the extent and duration of the pressure, but also the position,
orientation, and center mass of the nerve retractor 29 on the
nerve. By way of example only, should either of the grid maps
indicate that pressure is highest around one edge it may indicate
that the nerve is not resting in the ideal position (e.g. centered
and flat against the nerve engagement surface 46) and the surgeon
may act to reposition the nerve relative to the nerve retractor.
Pressure data collected by the processor 60 may preferably be
viewed in real time, however, the processor 60 may also save the
data for the entire procedure and the surgeon may go back and view
any data from the same procedure at any time.
[0062] In another embodiment, set forth herein by way of example
only and depicted in FIG. 19, the pressure sensing features of the
system 10 are controlled via the control unit 12 and the pressure
features may be fully integrated with the Nerve Retractor mode
described above. In this embodiment, both the pressure sensor 56
and the stimulation electrode 48 are communicatively linked to the
patient module 14 and pressure data is preferably viewed from
within the Nerve Retractor screen display (discussed above with
reference to FIG. 11). An embodiment of the Nerve Retractor screen
display when system 10 is augmented with pressure sensing
capabilities according to this embodiment is illustrated by way of
example only in FIG. 20. In the example shown, the screen display
includes, among its other features, a pressure selection tab 78 for
initiating pressure monitoring (preferably at the same time nerve
retraction) begins, a maximum pressure readout 80, and a timer
readout 82. Selecting the pressure selection tab 78 using the GUI
activates the pressure sensor 56 and starts the timer. The running
time is displayed to the user in the timer readout 82. The maximum
pressure measured on the sensor 56 is displayed with constant real
time updating. Although not shown herein, it will be appreciated
that any of a number of various features such as the 2-D and 3-D
grid maps, pressure distribution, and pressure vs. time graph may
also be generated and displayed in this embodiment. This may be
accomplished, for example only, by providing one or more pop-up
windows displaying the data and/or rearranging the screen view.
Pressure data measured by the system 10 is recorded and saved such
that it may be accessed again if necessary. Pressure data may also
be included in procedure reports generated by the system 10 such
that an accurate record is easily obtained.
[0063] While the pressure sensing features herein have been
described above in terms of monitoring retraction pressure on
nerves it will be understood that monitoring retraction pressure
may be useful for any number of different body tissues which must
be retracted out of the way during surgery. By way of example only,
it may be extremely beneficial to monitor retraction pressure on
the larynx and/or esophagus which must be retracted during anterior
cervical procedure.
[0064] It may also be advantageous to communicate pressure related
data captured by the system 10 to persons not present in the
operating room. It is contemplated that the data may be transmitted
(along with the nerve pathology and other neurophysiologic
assessment data) 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 data 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.
[0065] 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
scope of the appended claims.
* * * * *