U.S. patent application number 10/842192 was filed with the patent office on 2004-11-11 for neurophysiological apparatus and procedures.
Invention is credited to Ferree, Bret A..
Application Number | 20040225228 10/842192 |
Document ID | / |
Family ID | 33425208 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040225228 |
Kind Code |
A1 |
Ferree, Bret A. |
November 11, 2004 |
Neurophysiological apparatus and procedures
Abstract
Neurophysiological instruments and techniques are improved
through various enhancements. Stimulation of an instrument is
possible while it is advancing into the spine or elsewhere,
alerting the surgeon to the first sign the instrument or device
(screw) may be too near a nerve. A directional probe helps surgeons
determine the location of the hole in the pedicle. Electrically
insulating sleeves prevent shunting into the soft tissues.
According to a different improvement, the same probe to be used to
stimulate different devices, such as screws and wires. Electrical
impulses may be recorded from non-muscle regions of the body,
including the spine and other portions of the central nervous
system as opposed to just the extremities.
Inventors: |
Ferree, Bret A.;
(Cincinnati, OH) |
Correspondence
Address: |
John G. Posa
Gifford, Krass, Groh, Sprinkle,
Anderson & Citkowski, P.C.
280 N. Old Woodward Ave., Suite 400
Birmingham
MI
48009-5394
US
|
Family ID: |
33425208 |
Appl. No.: |
10/842192 |
Filed: |
May 10, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60468981 |
May 8, 2003 |
|
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|
60530427 |
Dec 17, 2003 |
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Current U.S.
Class: |
600/554 |
Current CPC
Class: |
A61B 17/7092 20130101;
A61B 5/4566 20130101; A61B 5/4893 20130101; A61B 5/389 20210101;
A61B 2017/00039 20130101; A61B 17/1626 20130101; A61B 5/24
20210101; A61B 17/1671 20130101 |
Class at
Publication: |
600/554 |
International
Class: |
A61B 005/05 |
Claims
I claim:
1. Neurophysiological apparatus, comprising: a system including an
electrical stimulator and an electrical sensor that allows
real-time or continuous monitoring as to the placement of a device
relative to a nerve during a surgical procedure.
2. The apparatus of claim 1, wherein the device is a probe, tap,
wire, screw, or pin.
3. The apparatus of claim 1, further including a component that
allows the device to rotate during placement without interfering
with the monitoring.
4. The apparatus of claim 3, wherein the component is a clip or
sleeve that fits around the shaft of a rotating instrument.
5. The apparatus of claim 1, wherein the sensor is a spinal
sensor.
6. The apparatus of claim 1, wherein the sensor is adapted for
placement around at least a portion of a pedicle.
7. The apparatus of claim 1, including a direction sensor including
a tip that is with a partially circumferentially insulated.
8. The apparatus of claim 1, wherein the system further includes an
alert if a stimulus was generated but not sensed.
9. The apparatus of claim 1, wherein the system further includes an
alert if the device is or is being improperly placed.
10. The apparatus of claim 1, wherein the system further includes
an alert if the device should be placed within a pedicle.
11. The apparatus of claim 1, including multiple stimulators or
sensors associated with multiple vertebrae.
12. A neurophysiological method, comprising the steps of: placing a
device in a vertebral body; electrically stimulating one or more
nerves; and sensing at least one electrical impulse at the device
to determine how close the device is to a nerve.
13. The neurophysiological method of claim 12, including the step
of stimulating one or more spinal nerves.
14. The neurophysiological method of claim 12, including the step
of stimulating one or more peripheral nerves.
15. The neurophysiological method of claim 12, including the step
of stimulating a spinal cord.
16. The neurophysiological method of claim 12, including the step
of stimulating a portion of a brain.
17. The neurophysiological method of claim 12, including the step
of sensing an impulse at multiple devices based upon a single
stimulus.
18. The neurophysiological method of claim 12, including the step
of sensing one or more electrical impulses at an extremity to
determine the effectiveness of the stimulus.
19. The neurophysiological method of claim 12, wherein the device
is an instrument.
20. The neurophysiological method of claim 12, wherein the device
is a pedicle screw.
21. The neurophysiological method of claim 12, wherein the muscle
is a paraspinal muscle.
22. The neurophysiological method of claim 12, further including
the step of alerting a user if a stimulus was not sensed.
23. The neurophysiological method of claim 12, further including
the step of alerting a user if the device is improperly placed.
24. The neurophysiological method of claim 12, wherein the step of
sensing at least one electrical impulse includes sensing the
amplitude of the stimulus.
25. The neurophysiological method of claim 12, wherein the step of
sensing at least one electrical impulse includes sensing the time
between the application of the stimulus and the time of sensing the
stimulus.
26. The neurophysiological method of claim 12, wherein the step of
sensing at least one electrical impulse includes sensing the
velocity of the stimulus.
27. The neurophysiological method of claim 12, wherein the step of
comparing the amplitude, velocity, or time interval between
stimulation and sensing to values derived previously during the
surgical procedure.
28. The neurophysiological method of claim 12, wherein the step of
comparing the amplitude, velocity, or time interval between
stimulation and sensing to one or more predefined reference
values.
29. The neurophysiological method of claim 12, wherein the device
forms part of a retractor or other surgical instrument.
30. The neurophysiological method of claim 12, wherein the sensor
forms part of a retractor or other surgical instrument.
31. A neurophysiological method, comprising the steps of:
electrically stimulating a device associated with a surgical
procedure; placing a sensor in a non-muscle region of a patent
undergoing the procedure; and detecting impulses from the device at
the sensor to determine whether the device has been, or is being,
properly placed.
32. The method of claim 31, including the step of placing the
sensor in a spine or other region of a central nervous system.
33. The method of claim 31, including the step of placing the
sensor in a vertebral body.
Description
REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. Provisional
Patent Application Serial Nos. 60/468,981, filed May 8, 2003, and
Ser. No. 60/530,427, filed Dec. 17, 2003, the entire content of
both of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to neurophysiological techniques and,
in particular, to improved instruments and procedures to ensure
accurate, real-time, temporary or permanent placement of surgically
implanted devices.
BACKGROUND OF THE INVENTION
[0003] Pedicle instrumentation is often used to facilitate spinal
fusion. Pedicle screws extend through the pedicles of vertebrae and
into the body of the vertebrae. The screws are connected by rods or
plates to eliminate motion between the vertebrae that are fused
together.
[0004] Misplaced pedicle screws can injury the nerves and blood
vessels that surround the vertebrae. Numerous techniques are used
to help surgeons guide screws into the pedicles of the vertebrae.
For example, surgeons often use x-rays including fluoroscopy to
confirm the position of pedicle screws.
[0005] Nerve compression by pedicle screws can also be determined
through electrical stimulation of the pedicle screws. Prior-art
techniques involve recording electrical impulses in the legs or
arms after electrical stimulation of the pedicles. High
conductivity of the electrical impulses suggests the pedicle screws
are too close to spinal nerves. High conductivity is determined by
recording electrical impulses in the legs or arms of a patient
after applying electrical impulses of relatively low amplitude to
the pedicle screws.
[0006] Prior art "neurophysiology" techniques have several
deficiencies. First, existing systems rely on the conductivity
through a patient's body from the pedicle screw to electrodes in
extremities or electrodes on the skin of the extremities. False
negative values, low conductivity, can occur if the nerves or the
skin do not conduct electricity well. Damaged nerves can be
relatively poor conductors of electricity. Second, electrical
impulses of relatively high magnitudes must be used to overcome the
resistance of the skin, muscles, and nerves. Stimulation by
electrical impulses of large amplitude can damage nerves. Third,
the variable resistance of patient's bodies leads to a relatively
wide range of "normal" values recorded from the extremities. The
wide range of normal values decreases the sensitivity and the
specificity of the prior art technologies.
[0007] NuVasive, Inc. of San Diego, Calif. offers a product that
uses "screw test" technology to determine if a screw or similar
device is being positioned close to a nerve during a surgical
procedure. Surgeons typically use NuVasive's system to stimulate
screws, guidewires, and taps placed into the pedicles of vertebrae.
Recording surface electrodes are placed over the legs of the
patient. Nerves conduct electricity very efficiently, such that
electrical stimulation of the metal objects placed into the
vertebrae can be recorded in the legs.
[0008] Using the NuVasive system, an electrical charge is sent
through the screw, and a circle lights up on a computer screen
giving a simple number to indicate the amount of charge reaching
sensors placed on the patient's leg muscles. A high number, such as
a 20, suggests the screw is clear of the nerve. A lower reading,
like a 3, indicates the nerve is being stimulated and the surgeon
needs to consider moving the screw. Thus, the lower the amplitude
needed to record activity in the legs, the closer the metal objects
are to the spinal nerves.
[0009] Research has shown that if the surface electrodes record
electrical activity with stimulation of less than 8 milliamps, the
metal objects are too close to the spinal nerves. The system can
also be used in the cervical spine. The surface electrodes are
placed on the arms for recording stimulation of devices placed into
the cervical spine.
[0010] The NuVasive system has a several shortcomings. For one, the
system does not yield real-time data. Nor does the system allow for
efficient, repeated stimulation of instruments that are turned.
This is due to the fact that the NuVasive system uses a ball-tipped
stimulating probe, and the ball of the probe slips off the circular
shaft of the instruments. In addition, while the system helps
surgeons identify holes in the pedicle, it does not identify the
location of the hole in the pedicle. Also, the instruments and
screws that are placed into the spine cannot touch the skin,
muscles, and subcutaneous tissues surrounding the spine during
electrically stimulation. If the metal instruments touch the
surrounding tissues during stimulation, the electricity can be
shunted from the vertebrae. Shunting of electricity can lead to
false recordings in the legs or arms (during stimulation in the
cervical spine). Furthermore, the existing NuVasive system requires
two different probes; one to stimulate screws and a second probe to
stimulate wires.
SUMMARY OF THE INVENTION
[0011] This invention improves upon neurophysiological techniques
through provision of several enhancement features. According to one
aspect of this invention, stimulation of an instrument is possible
while it is advancing into the spine or elsewhere, alerting the
surgeon to the first sign the instrument or device (screw) may be
too near a nerve. Early identification of misdirected instruments
or screws may thus help prevent nerve damage.
[0012] A different aspect involves a directional probe that helps
surgeons determine the location of the hole in the pedicle. Yet a
further aspect provides an insulation sleeves to prevent shunting
into the soft tissues. According to a different improvement, the
same probe to be used to stimulate different devices, such as
screws and wires.
[0013] One embodiment of the invention involves a clip that allows
the use of continuous monitoring during curette, pedicle probe,
tap, pedicle screw, and/or lateral mass screw insertion. The clip
fits around the cylindrical shafts of these and instruments used to
insert devices, including screws. The clip allows the shafts of the
instruments to rotate without rotating the probe that sends
electrical impulses for the testing. The surgeon may rotate an
instrument to insert a tap, for instance, while an assistant
repeatedly fires the probe. Thus, the surgeon can detect a breach
of the pedicle wall as soon as it occurs rather than after the tap,
etc. is fully inserted. Theoretically, early detection of a breach
in the pedicle may prevent nerve injury and prevent enlarging a
mal-aligned hole.
[0014] Other apparatus and methods of this invention improve upon
existing neurophysiology technology in that electrical impulses are
recorded from the spine rather than the extremities. Recording the
impulses closer to the stimulated pedicle screws overcomes the
deficiencies of prior-art techniques as outlined above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a lateral view of the side of the current probe
and a novel clip of the present invention;
[0016] FIG. 2 is an exploded view of the invention of FIG. 1;
[0017] FIG. 3A is a lateral view of a curette to "sound" the
pedicle and the probe with a clip attachment;
[0018] FIG. 3B is a lateral view of the probe of FIG. 1 attached to
the curette of FIG. 3A;
[0019] FIG. 3C is a cross section of the shaft of an instrument
surrounded by the novel clip of the present invention;
[0020] FIG. 4 is a lateral view of an alternative embodiment
instrument shaft;
[0021] FIG. 5 is a lateral view of the embodiment of the instrument
drawn in FIG. 4;
[0022] FIG. 6 is the lateral view of an instrument to retract the
soft tissues during pedicle screw or instrument stimulation;
[0023] FIG. 7 shows the insulated soft tissue retractor drawn in
FIG. 6;
[0024] FIG. 8A is a lateral view of the probe and the novel
tip;
[0025] FIG. 8B is an axial cross section of a vertebra and probes
with the novel tips;
[0026] FIG. 9A is a lateral view of a screw driver, pedicle screw,
and a novel insulating sleeve;
[0027] FIG. 9B is a lateral view of apparatus drawn in FIG. 9A;
[0028] FIG. 9C is a cross section of the apparatus drawn in FIG.
9B;
[0029] FIG. 9D is a lateral view of the apparatus drawn in FIG.
9B;
[0030] FIG. 10A is a lateral view of an alternative embodiment of
the insulation sleeve, pedicle screw, and sleeve expander;
[0031] FIG. 10B is a lateral view of the apparatus drawn in FIG.
10A;
[0032] FIG. 10C is an axial cross section of the sleeve, screw, and
sleeve expander drawn in FIG. 10A;
[0033] FIG. 10D is an axial cross section of an alternative
embodiment of the sleeve expander drawn in FIG. 10C;
[0034] FIG. 11A is a lateral view of an alternative embodiment of
the insulating sleeve;
[0035] FIG. 11B is an exploded view of the embodiment of the
invention drawn in FIG. 11A;
[0036] FIG. 11C is a cross section of the apparatus drawn in FIG.
11A;
[0037] FIG. 12A is a lateral view of an alternative embodiment of
the novel sleeve, a screw, and a screwdriver;
[0038] FIG. 12B is a lateral view of the apparatus drawn in FIG.
12A;
[0039] FIG. 13A is a sagittal cross section through an alternative
embodiment of that drawn in FIG. 3;
[0040] FIG. 13B is a sagittal cross section through an alternative
embodiment of that drawn in FIG. 13A;
[0041] FIG. 14A is a sagittal cross section of an alternative
embodiment of invention drawn in FIG. 13B;
[0042] FIG. 14B is an exploded lateral view of the embodiment of
the invention drawn in FIG. 14A;
[0043] FIG. 14C is a sagittal cross section of an alternative
embodiment of the invention drawn in FIG. 14A;
[0044] FIG. 14D is an exploded lateral view of the embodiment of
the invention drawn in FIG. 14C;
[0045] FIG. 15A is a sagittal cross section of an alternative
embodiment of the invention drawn in FIG. 14C;
[0046] FIG. 15B is an exploded lateral view of the embodiment of
the invention drawn in FIG. 15A;
[0047] FIG. 16A is a lateral view of an alternative embodiment of
the invention drawn in FIG. 14A;
[0048] FIG. 16B is an oblique view of an alternative embodiment of
the invention drawn in FIG. 16A;
[0049] FIG. 17A is a lateral view of an alternative embodiment of
the invention drawn in FIG. 14A;
[0050] FIG. 17B is an exploded lateral view of the embodiment of
the invention drawn in FIG. 17A;
[0051] FIG. 18 is an oblique view of a portion of a vertebra and
the preferred apparatus;
[0052] FIG. 19A is a view of the dorsal aspect of a portion of a
vertebra and a recording electrode;
[0053] FIG. 19B is a view of the dorsal aspect of a portion of a
vertebra and a recording electrode;
[0054] FIG. 20A is a view of the dorsal aspect of a portion of a
vertebra and a recording electrode on the inferior lateral surface
of a pedicle;
[0055] FIG. 20B is a view of the dorsal aspect of a portion of a
vertebra and a recording electrode;
[0056] FIG. 21A is an oblique view of the apparatus drawn in FIG.
18;
[0057] FIG. 21B is an exploded view of the apparatus drawn in FIG.
21A;
[0058] FIG. 21C is a view of the top of the connecting component,
the recording and stimulating electrodes;
[0059] FIG. 22 is an oblique view of a portion of a vertebra, a
pedicle instrument or screw, and the recording electrode;
[0060] FIG. 23 is an oblique view of a portion of a vertebra, a
pedicle screw, recording and stimulating electrodes use in an
alternative embodiment of the apparatus;
[0061] FIG. 24 is a view of apparatus according to the invention
including a stimulating probe;
[0062] FIG. 25 is a view of the posterior aspect of the spine;
[0063] FIG. 26 is the view of the front of an alternative
embodiment of the device drawn in FIG. 24;
[0064] FIG. 27A is a posterior view of the spine similar to the
view described in FIG. 25;
[0065] FIG. 27B is a posterior view of the spine as described in
FIG. 27A;
[0066] FIG. 28 is a posterior view of the spine, similar to the
view drawn in FIG. 27B;
[0067] FIG. 29 is a posterior view of the spine similar to the view
drawn in FIG. 28;
[0068] FIG. 30 is a posterior view of the spine, similar to the
view drawn in FIG. 29, showing the alternative use of a reference
electrode;
[0069] FIG. 31 is an axial view of a pedicle;
[0070] FIG. 32A is a lateral view of a needle-tipped stimulating or
recording electrode;
[0071] FIG. 32B is a lateral view of an alternative embodiment of
the tip of the electrode drawn in FIG. 32A;
[0072] FIG. 32C is a lateral view of an alternative embodiment of
the tip of the electrode drawn in FIG. 32A;
[0073] FIG. 33 is an oblique view of an alternative embodiment of
the invention;
[0074] FIG. 34A is a lateral view of another embodiment of the
invention drawn in FIG. 33;
[0075] FIG. 34B is an anterior view of the embodiment of the device
drawn in FIG. 34A;
[0076] FIG. 34C is an oblique view of the embodiment of the device
drawn in FIG. 34A;
[0077] FIG. 35 is an anterior view of another embodiment of the
device drawn in FIG. 33;
[0078] FIG. 36 is a posterior view of a peripheral nerve and
another embodiment of the invention; and
[0079] FIG. 37 is a lateral view of a nerve root retractor that
stimulates the spinal nerves.
DETAILED DESCRIPTION OF THE INVENTION
[0080] FIG. 1 is a lateral view of the side of the current probe
102 and a novel clip 104 according to this invention. One end of
the clip snaps around instruments. The second end of the clip snaps
over the tip of the probe. Alternatively, a second probe tip could
be manufactured that incorporates the novel tip end. FIG. 2 is a
detached view of the probe and tip of FIG. 1.
[0081] FIG. 3A is a lateral view of a curette 302 used to "sound"
the pedicle and the probe 102 with a clip attachment 104. The shaft
of the instrument 302 may be machined with a groove 310 to
cooperate with the clip. FIG. 3B is a lateral view of the probe of
FIG. 1 attached to the curette of FIG. 3A. FIG. 3C is a cross
section.
[0082] FIG. 4 is a lateral view of an alternative embodiment,
wherein the shaft of the tap has a raised portion 402 to cooperate
with a clip 404. The raised portion 402 avoids the stress riser
created by a groove in the shaft. FIG. 5 is a lateral view of the
embodiment of the instrument drawn in FIG. 4. The clip of the probe
surrounds the shaft of the pedicle screw insertion tool. The clip
rides on the enlargement of the shaft.
[0083] FIG. 6 is the lateral view of an instrument 602 used to
retract the soft tissues during pedicle screw or instrument
stimulation. The retraction instrument is made of plastic or other
material that does not conduct electricity in the preferred
embodiment.
[0084] As an alternative to the insulated soft tissue retractor of
FIG. 6, an insulated sleeve drawn in FIG. 7 may be used. FIG. 7 is
an axial cross section through a vertebra and the surrounding
muscles, skin, and subcutaneous tissues. A plastic sleeve would be
particularly useful when stimulating percutaneous guide pins
inserted into the pedicles. The insulating sleeve 706 prevents the
transmission of electricity from the guide pin to the muscles or
surrounding soft tissue. A similar apparatus could be used for
testing modular taps. For example, the handle of a tap could be
removed, thus allowing the insulating sheath to be placed over the
tap.
[0085] Although the NuVasive monitoring system helps surgeons
identify breaches of the walls of the pedicles, the system does not
suggest where the pedicle wall has been breached. According to this
invention, however, since the probe tip may be insulated
circumferentially around the majority of the tip of the probe, the
non-insulated portion of the tip can be rotated within the pedicle
to determine the direction that requires the least amount of
stimulation to record activity in the lower extremity.
[0086] FIG. 8A is a lateral view of the probe and a tip according
to the invention. The dark area of the tip conducts electricity.
The remainder of the tip 806 is insulated to prevent the conduction
of electricity.
[0087] FIG. 8B is an axial cross section of a vertebra and probes
using these tips. The medial walls of the pedicles have been
breached. The probe on the left side of the drawing has the
non-insulted portion of the tip directed toward the hole in the
pedicle. The probe on the right side of the drawing has the
insulated portion of the tip facing the hole in the pedicle. Less
current will be required to stimulate the nerves on the left side
of the drawing. For example, the surface electrodes could record
activity in the lower extremity with stimulation of the probe at 4
milliamps with the exposed (conducting) area of the probe directed
toward the medial wall of the pedicle (probe on the left side of
the drawing) and the surface electrodes could record electrical
activity in the lower extremities with stimulation of the probe at
10 milliamps with the exposed (conducting) area of the probe
directed toward the lateral wall of the pedicle (probe on the right
side of the drawing). Thus, the surgeon knows the medial wall of
the pedicle has been breached. Consequently, the surgeon knows to
redirect the pedicle screw more laterally, away from the holes in
the pedicle
[0088] FIG. 9A is a lateral view of a screwdriver 902, pedicle
screw 904, and an insulating sleeve 906. The insulating sleeve is
preferably constructed of a flexible material that does not conduct
electricity. For example, the sleeve could be made of plastic or
natural or synthetic rubber. The sleeve can be seen folded back
over itself at 908 just above the pedicle screw.
[0089] FIG. 9B is a lateral view of apparatus drawn in FIG. 9A. The
insulating sleeve 906 has been unfolded and placed over the head of
the pedicle screw. The insulating sleeve prevents the transmission
of electricity into the tissues that surround the spine.
Electricity from stimulating the shaft of the screwdriver, of the
shaft of the screwdriver exits through the threads of the screw.
The sleeve enables the screwdriver to lie against the muscles of
the spine without stimulating the muscles of the spine.
[0090] FIG. 9C is a cross section of the apparatus drawn in FIG.
9B. The flexible insulation sleeve can be stretched to fit tightly
against the shaft of the screwdriver and the pedicle screw.
[0091] FIG. 9D is a lateral view of the apparatus drawn in FIG. 9B.
The insulation sleeve may be removed by pulling on a cord 980 which
tears the sleeve. Alternative mechanisms can be used to remove the
sleeve from the screw. For example, the sleeve could be pulled from
the screw while exerting counter pressure on the screw by the
screwdriver. The sleeve could also be folded on itself as the
sleeve is removed from the screw.
[0092] FIG. 10A is a lateral view of an alternative embodiment of
an insulating sleeve 1002, pedicle screw 1004, and screwdriver with
a sleeve expander 1006. The sleeve is drawn in its expanded shape.
The tip of the sleeve expander fits into the pedicle screw. In the
preferred embodiment, the sleeve expander is flush with the top of
the pedicle screw. The sleeve in this embodiment of the device is
made of material that plastically deforms at its tip. The sleeve
does not transmit electricity.
[0093] FIG. 10B is a lateral view of the apparatus drawn in FIG.
10A with the sleeve in its contracted shape. The tip of the sleeve
contracts to surround the head of the pedicle screw. Ideally the
sleeve is more rigid than sleeve drawn in FIG. 9A. The rigidity of
the sleeve enables it to be forced over the screw by pushing on the
top of the sleeve. This embodiment of the device would be easier to
use after the screw has been placed into the spine.
[0094] FIG. 10C is an axial cross section of the sleeve 1002, screw
1004, and sleeve expander 1006 in FIG. 10A. The sleeve expander
1006 fits into the opening in the pedicle screw. FIG. 10D is an
axial cross section of an alternative embodiment of the sleeve
expander 1016, a screw 1014, and the sleeve 1012. The tip of the
sleeve expander in this case is round to fit in the circular
opening in the pedicle screw.
[0095] FIG. 11A is a lateral view of an alternative embodiment of
the insulating sleeve. 1108 assembled over a pedicle screw 1110.
FIG. 11B is an exploded cross-sectional view of the embodiment of
the invention drawn in FIG. 11A. FIG. 11C is a cross section of the
apparatus drawn in FIG. 11A. FIG. 12A is a lateral view of an
alternative embodiment of the novel sleeve 1202, a screw 1204, and
a screwdriver 1206. The insulating sleeve is placed over the
pedicle screw and screwdriver prior to insertion of the pedicle
screw into the spine.
[0096] FIG. 12B is a lateral view of the apparatus drawn in FIG.
12A. The sleeve has been pulled off of the pedicle screw.
Longitudinal force on the sleeve may be used to split the sleeve
along a pre-stressed area in the sleeve.
[0097] FIG. 13A is a sagittal cross section through an alternative
embodiment of the invention, wherein a probe 1302 is placed into
the center of an instrument 1304. The illustration shows
application of the probe to a tap. Placing the instrument onto or
into the center of the instrument allows rotation of the instrument
during repeated stimulation of the instrument.
[0098] FIG. 13B is a sagittal cross section through an alternative
embodiment of that drawn in FIG. 13A. The probe connects to an
intermediate piece 1330 that connects to the center of the
instrument.
[0099] FIG. 14A is a sagittal cross section of an alternative
embodiment of invention drawn in FIG. 13B. The spherical end of an
electrode 1404 is captured in the instrument by a cannulated,
threaded cap 1406. The shaft of the instrument 1410 conducts
electricity. The joint between the tip of the electrode allows
movement between the electrode and the instrument, while
maintaining continuous contact between the two components. FIG. 14B
is an exploded lateral view of the embodiment of the invention
drawn in FIG. 14A.
[0100] FIG. 14C is a sagittal cross section of an alternative
embodiment of the invention utilizing a flat-tipped electrode 1440
captured by a threaded component 1444. The joint between the
electrode and the instrument allows rotation. FIG. 14D is an
exploded lateral view of the embodiment of the invention drawn in
FIG. 14C. Connections between electrodes of alternative shaped tips
and instruments of alternative shapes are contemplated so long as
the joints between the components permit rotation and keep the two
components in contact.
[0101] FIG. 15A is a sagittal cross section of an alternative
embodiment of the invention, wherein an electrode 1550 is threaded
over the shaft of the instrument 1552. The threaded connection
between the electrode and the instrument holds the two components
together. Rotation may occur across the flat surfaces of the two
components. FIG. 15B is an exploded lateral view of the embodiment
of the invention drawn in FIG. 15A.
[0102] FIG. 16A is a lateral view of an alternative embodiment of
the invention drawn in FIG. 14A. A wire 1660 for the electrode is
connected to a ratcheting component 1664 on the shaft of the
instrument. The ratcheting component permits advancement of screws
and taps with small rotations of the handle of the instrument
forward and backward. The electrode does not wrap around the
instrument because the handle of the instrument does not require
rotation through 360 degrees.
[0103] FIG. 16B is an oblique view of an alternative embodiment of
the invention drawn in FIG. 16A. The electrode is connected to a
conducting component within the handle of the instrument. The
conducting component transmits electrical impulses between the
electrode and the shaft of the instrument. The ratcheting mechanism
prevents wrapping the cord of the electrode around the instrument
as the instrument is rotated.
[0104] FIG. 17A is a lateral view of an alternative embodiment of
the invention including an electrode 1780 connected to a collar
that rotates around the shaft of the instrument. The collar is held
between projections from the shaft of the instrument. The collar
remains in contact with the shaft of the instrument. Rotation
between the shaft of the instrument and the collar prevents
wrapping the cord of the electrode around the instrument as a screw
or tap is advanced. FIG. 17B is an exploded lateral view of the
embodiment of the invention drawn in FIG. 17A. The rotating collar
is held on the shaft of the instrument by a removable threaded
component 1788.
[0105] FIG. 18 is an oblique view of a portion of a vertebra and
preferred apparatus including a recording electrode 1802 placed
around a portion of the pedicle of a vertebra 1800. The recording
electrode is connected to a monitor 1804. The area 1806 represents
a pedicle probe, tap, screw, or other instrument that will be
placed into the pedicle. The pedicle instrument or screw is
connected to a stimulating electrode. The recording and stimulating
electrodes can be connected by third component 1810. The connecting
component is represented by the area of the drawing with diagonal
lines. In the preferred embodiment, the connecting component 1810
is radiolucent and made of a material that conducts electricity
poorly.
[0106] FIG. 19A is a view of the dorsal aspect of a portion of a
vertebra and a recording electrode 1802. The lamina of the vertebra
has been removed to better illustrate the pedicles of the vertebra.
The arms of the recording electrode can be seen surrounding the
inferior, medial, and lateral surfaces of the pedicle. The
recording electrode was inserted from the inferior and/or lateral
side of the vertebra.
[0107] FIG. 19B is a view of the dorsal aspect of a portion of a
vertebra and a recording electrode 1802. The recording electrode
can be seen over the medial, superior, and inferior surfaces of a
pedicle. The recording electrode was inserted from the medial side
of the pedicle. A laminectomy could be performed to aid placement
of the electrode.
[0108] FIG. 20A is a view of the dorsal aspect of a portion of a
vertebra and a recording electrode 1802 on the inferior lateral
surface of a pedicle. FIG. 20B is a view of the dorsal aspect of a
portion of a vertebra and a recording electrode. The recording
electrode has been advanced over the pedicle. The arms of the
recording electrode can be spring loaded to ease insertion of the
electrode over the pedicle.
[0109] FIG. 21A is an oblique view of the apparatus drawn in FIG.
18. The connector 1810 aligns the instrument or screw to be
inserted into the pedicle with the arms of the recording electrode.
For example, pedicle screws can be directed into the center of the
arms of the recording electrode. Thus, if the arms of the recording
electrode surround a portion of the pedicle, the pedicle screw or
instrument can be directed into the center of the pedicle.
[0110] FIG. 21B is an exploded view of the apparatus drawn in FIG.
21A. A removable handle is also illustrated. The removable handle
can be placed over the recording electrode after placement of the
connecting component over the recording component.
[0111] FIG. 21C is a view of the top of the connecting component,
the recording and stimulating electrodes. The radiolucent
connecting component allows surgeons to view insertion of the
stimulating electrode between the arms of the recording electrodes
with fluoroscopy. The arms of the recording electrode surround a
portion of the pedicle.
[0112] FIG. 22 is an oblique view of a portion of a vertebra, a
pedicle instrument or screw, and the recording electrode. The
pedicle instrument can be seen penetrating the wall of the pedicle.
The recording electrode can be moved up and down or around the
pedicle to aid detection of the electrical impulse.
[0113] FIG. 23 is an oblique view of a portion of a vertebra, a
pedicle screw, recording and stimulating electrodes use in an
alternative embodiment of the apparatus. The recording electrode
detects impulses in the spinal canal, nerves, muscles, vertebrae,
and other spinal tissues or tissues that surround the spine. For
example, the recording electrode could be placed on a spinal nerve,
or the thecal sac. Penetration of the pedicle screw or instrument
would be predicted by recording electrical impulses from the spinal
nerve or thecal sac after stimulating the pedicle instrument with
electrical impulses with relatively low amplitudes. The recording
electrode could also be placed in other spinal tissues such as the
paraspinal muscles. Fluid or other material could be placed around
the pedicle to aid the conduction of electrical impulses. For
example, saline could be placed into the spinal canal during the
stimulation and recording of the electrical impulses.
[0114] The invention also anticipates reversing the stimulating and
the recording electrodes. That is, electrical impulses could be
recorded from pedicle screws or instruments after stimulating a
portion of the spine. For example, the outer wall of the pedicle
could be stimulated. Additionally, the sensitivity and specificity
of the apparatus, as well as prior art apparatus, could be improved
by measuring the time between stimulation and recording the
electrical impulses. Relatively high rates of electrical conduction
suggest the pedicle screw or instrument lies on or too near a
nerve.
[0115] FIG. 24 is a view of apparatus according to the invention
including a stimulating probe 2406 used to stimulate the spinal
nerves (or other nerves). The stimulating probe is inserted into a
port on the device marked "Stimulus". A recording cable 2408 is
inserted into a port on the device marked "Instrument". The
recording cable attaches to an instrument placed in the pedicle.
For example, the "Instrument" recording cable could be attached to
the ratcheting instrument described in FIG. 16A. The ratcheting
instrument is used to insert screws or taps into the vertebrae.
[0116] A second recording cable 2410 is inserted into a port on the
device marked "Muscle". The "Muscle" recording cable may include a
bundle of wires. The wires within the "Muscle" recording cable
attach to leads placed over muscles. For example, the "muscle"
leads could be placed over the myotomes of both lower extremities
or both upper extremities. Alternatively, the "Muscle" cable could
be attached to leads over the gluteal muscles, the paraspinal
muscles, or tissues of the body.
[0117] A green indicator light indicates safe placement of the
pedicle instrument. The green light illuminates if the "Muscle"
recording cable sends an electrical impulse into the device after
stimulation of a spinal nerve (alternatively other nerves could be
stimulated) and the "Instrument" recording cable does not send an
electrical impulse into the device after stimulation of the spinal
nerve. A 6 ma stimulus could be delivered to the stimulus probe.
Alternative stimuli between 0.01 ma to 40 ma could be
delivered.
[0118] A red indicator light indicates a potentially misplaced
pedicle instrument. The red light illuminates if the "Instrument"
recording cable sends an electrical impulse into the device after
stimulation of the spinal nerve or the "Muscle" recording cable
fails to send an electrical impulse into the device. Two additional
lights are used to determine why the red light illuminated. A
"Muscle" light illuminates if the "Muscle" recording cable fails to
send an electrical impulse into the device. Failure of the "muscle"
recording cable to send an electrical impulse into the device
suggests the nerve was not properly stimulated. An "Instrument"
light illuminates if the "Instrument" cable sends an electrical
impulse into the device. Illumination of the "Instrument" light
alerts the surgeon the pedicle instrument has received an
electrical impulse. The pedicle instrument receives an electrical
impulse, if the instrument has breached the walls of the pedicle
and the instrument is lying against the stimulated nerve. The
device may also have ports that receive ground and reference
electrodes.
[0119] Existing systems monitor all of the myotomes of both
extremities. An electrical stimulus is delivered to the instrument
within the pedicle. Detection of the electrical impulse after low
levels of stimulation, for example 8 ma, in any myotome is
indication of a potentially misplaced pedicle instrument. A
preferred embodiment of this invention records from the instrument
or screw within the pedicle rather than stimulating the instrument
or screw within the pedicle. Recording leads over the muscles are
used to confirm an electrical impulse has been applied to a spinal
nerve (or other nerve). As such, recording a stimulus from any
muscle in the extremities or potentially other muscles such as the
gluteal or paraspinal muscles indicates the stimulus has been
properly delivered. Recording from fewer, multiply innervated
muscles, simplifies the device. Recording from fewer muscles and
recording from the gluteal or paraspinal muscles also assists the
surgeon. The present invention decreases the amount of time
surgeons must spend applying the recording leads over multiple
myotomes of both extremities while using prior art systems. The
simplicity of the device enables surgeons to test and monitor their
patients. The device does not require a highly compensated
Neurophysiologist to interpret the data. Other embodiments of the
invention eliminate the need to monitor any of the muscles.
[0120] FIG. 25 is a view of the posterior aspect of the spine. The
lamina have been removed to better illustrate the pedicles 2502 and
the nerves 2504. The black circle in the center of one of the white
circles indicates the cross section of an instrument within the
pedicle (for example) a screw, tap, or curette.
[0121] In the embodiment of the invention depicted in FIG. 24, an
electrical stimulus is delivered to the lower spinal nerve at point
S. A recording electrode is attached at R to the instrument within
pedicle. One or more additional recording electrodes are placed
over muscles. A second stimulus is delivered to the spinal nerve at
S', or, alternatively at S". If the pedicle instrument breaches the
medial wall (spinal canal side) or the inferior wall of the
pedicle, and the instrument lies against the spinal nerve,
stimulation of the lower spinal nerve will stimulate the instrument
in the pedicle. If the pedicle instrument breaches the lateral or
superior wall of the pedicle, and the instrument lies against the
spinal nerve, stimulation of the upper spinal nerve will stimulate
the instrument within the pedicle. Instruments in adjacent pedicles
on the same side of the spine may be tested simultaneously by
stimulating a single spinal nerve. For example, stimulation of the
L4 nerve simultaneously tests the integrity of the medial and
inferior walls of the L4 pedicle and the superior and lateral walls
of the L5 pedicle. Simultaneous testing of instruments within the
pedicles requires a multi-channel device.
[0122] Prior art systems may detect a hole or a crack in a pedicle,
but they do not indicate the location of the crack or hole in the
pedicle. If surgeons know the location of the hole in the pedicle,
then they can reposition a screw and safely direct the screw away
from the hole in the pedicle. This invention helps surgeons
determine if the misplaced pedicle instrument was placed through
the inferior and/or the medial surface of the pedicle or through
the superior and/or lateral wall of the pedicle.
[0123] FIG. 26 is the view of the front of an alternative
embodiment of the device drawn in FIG. 24. The multi-channel device
can be used to simultaneously test instruments in more than one
pedicle. The cables extending from ports on right side of the
device marked "Instrument 1" and "Instrument 2" can be attached to
instruments in different pedicles. The stimulus probe can be used
to deliver electrical impulses to a spinal nerve. The cables
extending from the ports marked "Muscle 1 & Muscle 2" can be
attached to surface electrodes over muscles supplied by the
stimulated nerve. A single recording electrode may also be used
when testing the instruments in two pedicle screws. For example,
the cable attached to "Instrument 1" could be attached to a tap in
the left LA pedicle.
[0124] The cable attached to "Instrument 2" could be attached to a
screwdriver attached to a pedicle screw in the left L5 pedicle. The
cables extending from the "Muscle 1" and/or "Muscle 2" ports could
be attached to needle electrodes placed into the Gluteus Medius and
the Gluteus Maximus Muscles of the left buttock. The Gluteus Medius
is innervated by the superior gluteal nerve. The superior gluteal
nerve arises from the LA, L5, & S1 nerves. The Gluteus Maximus
is innervated by the inferior gluteal nerve. The inferior gluteal
nerve arises from the L5, S1, and S2 nerves. Surface electrodes
could be used rather than needle electrodes. A stimulus could be
applied to the left L4 nerve root. The LA nerve root courses along
the inferior and medial surfaces of the L4 pedicle, and the
superior and lateral portion of the L5 pedicle.
[0125] The indicator lights are similar to the indicator lights
drawn in FIG. 24. If both green lights illuminate, then device did
not detect electrical impulses from either instrument in the
pedicles, and the device detected an electrical impulse from the
recorded muscles. The device may use a reference recording lead to
compare to the muscle recording lead. The device may contain a
microprocessor. If the muscle recording lead receives a much
stronger impulse than the reference electrode receives, then the
nerve has likely been stimulated properly. Alternatively, the
microprocessor may compare the impulses received by the recording
electrodes to reference values. The reference values enable the
device to indicate if the nerve has been properly stimulated or the
soft tissues around the nerve were mistakenly stimulated. The
device may use a ground lead.
[0126] The red light by the large number one will illuminate if the
instrument attached to the cable from the "Instrument 1" port
receives an electrical impulse or the device fails to receive an
impulse from both or either "Muscle" recording electrodes.
Similarly, the red light by the large number two will illuminate if
the instrument attached to the cable from the "Instrument 2" port
receives an electrical impulse or the device fails to receive an
impulse from both or either "Muscle" recording electrodes. The
"Instrument 1 & 2" and the "Muscle 1 & 2" lights are used
as described in the text of FIG. 24, to indicate if the instruments
have been stimulated or the muscles were not stimulated.
[0127] FIG. 27A is a posterior view of the spine similar to the
view described in FIG. 25. The dark circles represent instruments
in the pedicles. R1 and R2 represent recording electrodes that are
attached to the instruments in the pedicles. S1, S2, & S3
represent a few of the possible stimulation sites. The figure
illustrates a nerve may be stimulated below the pedicle, at the
level of the pedicle, or above the pedicle. Stimulation of the
nerve below the pedicle relies on transmission of the impulse in a
caudal direction to test the superior and lateral aspects of the
pedicle below the stimulated nerve and transmission of the impulse
in a caudal direction to stimulate the muscle. Stimulation of the
nerve below the pedicle relies on transmission of the impulse in a
cephalic direction to test the inferior and medial surfaces of the
pedicle above the stimulated nerve. Spinal nerves carry electrical
impulses in both cephalic and caudal directions. Motor portions of
the nerves transmit impulses away from the spinal cord to the
muscles (caudal direction). Sensory portions of the nerves transmit
impulses from the sensation receptors to the spinal cord (cephalic
direction). The device drawn in FIG. 26 could be used to test the
instruments in the adjacent pedicles drawn in FIG. 27A. A single
stimulus delivered at S3 would test the instruments in both
pedicles. Additional stimulus sites could be used to complete the
testing. For example, stimulus sites S4 and S2 could be used to
complete the testing.
[0128] FIG. 27B is a posterior view of the spine as described in
FIG. 27A. The cross sections of pedicle instruments are seen in all
of the pedicles. The drawing illustrates other embodiments of the
invention. The embodiments drawn in FIG. 27B do not require
monitoring the muscles in the extremities. In one embodiment of the
invention the recording electrodes are placed in or over the
nerves. Techniques well know to those specialists who perform EMG
testing could be used to locate the nerves. Alternatively, the
electrodes could be placed on or in the nerves under direct
observation.
[0129] A stimulus is applied at S1. The recording electrodes are
attached to the instrument in the pedicle (R1) and another portion
of the stimulated nerve. If the R2 electrode detects the stimulated
impulse and the R1 electrode does not detect the impulse, then it
is unlikely the pedicle instrument is contacting the stimulated
nerve. A multi-channel device could be used to test the instruments
in more than one pedicle simultaneously. The R2 electrode could be
placed in a spinal nerve or a peripheral nerve that has components
that arise from the stimulated nerve. For example, for testing the
pedicles in the lumbar spine, the R2 electrode could be placed in
the sciatic nerve (L4, L5, S1, S2, & S3) or branches from the
sciatic nerve, the femoral nerve (L2, L3, & LA) or branches
from the femoral nerve, or other nerves. The spinal nerve
components that form the sciatic and femoral nerves are listed in
parentheses behind the words sciatic nerve and femoral nerve
respectively. Naturally other nerves would be stimulated and
recorded when testing instruments in the cervical and thoracic
spine.
[0130] The invention is more sensitive and more accurate than
prior-art devices. Prior-art devices may record a false positive if
electrical impulses are delivered through a crack in the pedicle,
but the instrument is contained within the pedicle. The present
invention allows testing with smaller electrical impulses. The
smaller impulses are less likely to stimulate a pedicle instrument
through cracks in the pedicle. Prior art devices may record a false
negative if the recording electrodes over the muscles in the
extremities fail to detect an impulse. As noted previously, nerves
that conduct impulses poorly, poor conduction through the surface
electrodes, etc., may falsely indicate the instrument is safely
contained in the pedicle.
[0131] Prior-art systems generally send multiple stimuli of
increasing amplitude into the instrument within the pedicle. Prior
art systems attempt to record the amount of stimuli necessary to
record the impulse over the lower extremities. Recording an impulse
over the lower extremities decreases the probability of a false
negative result. Stimulating pedicle instruments with multiple
stimuli with increasing amplitude is time consuming and requires
sophisticated software. The present invention improves upon prior
art devices by generally only requiring the application of a single
stimulus per pedicle instrument undergoing testing. Some
embodiments of the invention allow testing pedicle instruments in
multiple vertebrae with the application of a single stimulus.
[0132] Note that the invention may also be used to test nerves
while retracting nerves or performing other spinal procedures. The
distance between S1 and R2 could be predetermined. In fact, S1 and
R2 could extend from the same instrument. Electrical impulses could
be periodically delivered to the nerve at S1 during surgery. For
example, the electrical impulses could be delivered at a frequency
of one per minute. The microprocessor within the monitor could
signal an alarm, for example, illuminate a light bulb, if the
amplitude of the impulse detected at R2 decreased when compared to
a reference amplitude obtained by stimulating the nerve before
manipulating the nerve during the operation. The microprocessor
could also cause an alarm to signal if the time between the
stimulus delivered at S1 and recorded at R2 increased when compared
to a reference time obtained for the nerve before manipulating the
nerve during the operation.
[0133] Standard reference amplitudes and velocities may also be
preprogrammed into the microprocessor. Standard reference
velocities require fixed distances between S1 and R2. The S1
impulse could be delivered through a nerve root retractor or a
stimulus probe. A stimulus delivering retractor is drawn in FIG.
37. As noted above, R2 may lie anywhere along the course of the
spinal nerve, nerves supplied by the spinal nerve, or muscles
supplied by the spinal nerve. The device alerts surgeons of
potential nerve injury before the nerve injury occurs. For example,
excessive retraction of a nerve root may injure the nerve root. The
device detects diminished nerve function within seconds or minutes
of the excessive retraction. Embodiments of the invention for use
with peripheral nerves are described in FIG. 36.
[0134] In the drawings, R4 represents an alternative recording
position. One or more R4 electrodes could be placed over or in
muscles of the body including muscles in the extremities, the
muscles in the buttock, the muscles about the shoulder, or muscles
about the spine. In contrast to prior-art devices, the R4 electrode
may be used to confirm the nerve has been properly stimulated. Any
muscle innervated by the stimulated muscle may be monitored. A
single muscle that is supplied by multiple nerve roots may be
monitored while testing instruments in pedicles at different levels
of the spine. For example, the gluteus medius muscle could be
monitored to confirm the L4, L5, or S1 nerves have been
successfully stimulated. The gluteal muscles and the skin over the
muscles are easily reached during surgeries on the lumbar spine.
Prior-art systems require monitoring of many muscles of the body.
Failure to detect stimulation of one of the muscles may lead to a
false negative reading. A false negative reading fails to properly
detect an instrument, such as a pedicle screw, is compressing or
injuring a nerve. Prior-art systems typically require monitoring
over four separate locations over each extremity. Preparing the
skin over multiple sites and placing the electrodes over multiple
sites is time consuming.
[0135] The present invention alerts surgeons if the R4 electrode is
improperly placed or if the R4 electrode/electrodes has/have
shifted during the operation. The red light on the device and the
muscle light on the device illuminate if the R4 electrode does not
record an impulse. The novel invention enables surgeons to monitor
the paraspinal muscles. The paraspinal muscles area easily
accessible in the surgical field. Prior art devices do not use the
paraspinal muscles. Surgical exposure of the spine may injure the
paraspinal muscles or the nerves to the muscles. Injury to the
nerves to the paraspinal muscles or injury of the paraspinal
muscles may cause prior art devices and methods to yield a false
negative result, if the devices fail to record an impulse. Failure
of prior art methods and devices to detect stimulation of the
paraspinal muscles could indicate: (a) that the pedicle instrument
is contained within the pedicle, (b) the nerve to the paraspinal
muscle is not functioning properly, (c) the paraspinal muscles are
not functioning properly or, (d) the stimulated muscle has not been
recorded. Explanations (b), (c), and (d) lead to false negative
results. Thus, prior-art systems do not monitor the paraspinal
muscles. The present invention alerts the surgeon if injury to the
nerves to the paraspinal muscles or the paraspinal muscles
precludes monitoring the muscles. If the surgeon is unable to
detect recordings from the paraspinal muscles after delivering a
stimulus to the nerves, then the surgeon is alerted to monitor
other muscles, such as the gluteal muscles. The ventrally,
segmentally, innervated intertransversalis muscles are monitored in
one embodiment of the invention. Other paraspinal muscles may be
monitored.
[0136] FIG. 28 is a posterior view of the spine, similar to the
view drawn in FIG. 27B. An alternative embodiment of the invention
is illustrated in the drawing. S1 represents stimulation of a
peripheral nerve such as the sciatic nerve, femoral nerve, branches
the sciatic nerve, branches of the femoral nerve, or other
peripheral nerve. R3 & R4 represent recording sites on or in
the spinal nerves. Alternative R3 & R4 sites include nerves
within the thecal sac, the spinal cord, or the brain. The R3 &
R4 sites are monitored to confirm the nerve has been stimulated
correctly. The R1 & R2 are monitored to detect stimulation of
the instruments within the pedicles. A single electrical stimulus
from S1 could be used to test multiple pedicles simultaneously.
Stimulation of the sciatic nerve may allow simultaneous testing of
the pedicles near the L4, L5, S1, S2, & S3 nerves. Stimulation
of the femoral nerve may allow testing of the pedicles near the L2,
L3, and L4 nerves. A multi-channel device allows simultaneous
testing of multiple pedicles.
[0137] FIG. 29 is a posterior view of the spine similar to the view
drawn in FIG. 28. The alternative embodiment of the invention
stimulates multiple spinal nerves simultaneously. S1 represents a
stimulus delivered over the nerves in the thecal sac, the spinal
cord, or the brain. An electrical or magnetic stimulus may be used.
R1B, R2B, R3B, & R4B are recording sites to confirm the spinal
nerves near the pedicles undergoing testing are properly
stimulated. R1A, R2A, R3A, & R4A are recording sites from the
instruments that lie within the pedicles. If R1B, R2B, R3B, or R4B
fail to detect an impulse, the device will alert the surgeon that
the pedicle instruments at the R1A, R2A, R3A, or R4A sites
respectively, has not been adequately tested. Failure to detect an
impulse at a RnB site signals the stimulus was not applied to the
surface of the pedicle by the nerve monitored by the RnB electrode.
A S1 needle electrode may be placed through the dura. The S1 site
may be cephalad or caudal to the tested pedicles. If all RB sites
record impulses and none of the RA sites record impulses, then all
of the instruments are likely contained within the pedicles. A
multi-channel device, with at least four groups of alarm lights
like those illustrated in FIG. 24, could be used in this embodiment
of the invention.
[0138] FIG. 30 is a posterior view of the spine, similar to the
view drawn in FIG. 29, showing the alternative use of a reference
electrode. A microprocessor within the device compares the impulse
detected by the R2 electrode to the impulse detected by the
reference (R3) electrode. The microprocessor triggers an alarm,
such as illuminating a light bulb, if the stimulus received by R2
is below a preset value or the stimulus received by R2 is near or
below that received by R3. The alarm alerts the surgeon that the
electrodes at the R2 or S1 sites are not properly contacting the
spinal nerve.
[0139] FIG. 31 is an axial view of a pedicle. The drawing
illustrates an alternative embodiment of the invention. The black
circle represents the cross section of an instrument in the
pedicle. S1 represents a stimulation site. R1 represents a
recording site on the instrument in the pedicle. R2 represent a
recording site on the pedicle. If the R1 electrode detects a
smaller signal than the R2 electrode the instrument is likely
contained in the pedicle.
[0140] FIG. 32A is a lateral view of a needle-tipped stimulating or
recording electrode. The area of the drawing with diagonal lines
represents insulating material. The needle tipped electrode is
generally placed in nerves or muscles. FIG. 32B is a lateral view
of an alternative embodiment of the tip of the electrode drawn in
FIG. 32A. The balled tipped probe is generally placed on nerves or
muscles. FIG. 32C is a lateral view of an alternative embodiment of
the tip of the electrode drawn in FIG. 32A. The curved tip is
easier to insert through the neuroforamina. The tip may help the
surgeon direct the electrode to the S1 position drawn in FIG.
30.
[0141] FIG. 33 is an oblique view of an alternative embodiment of
the invention. This embodiment of the invention demonstrates the
use of stimulating (S1) and recording (R1) electrodes in an
instrument. For example the instrument may be a cannula as drawn in
FIG. 33. Other than the electrodes, the instrument is made of a
non-electrical conducting material in the preferred embodiment of
the device. A monitor with microprocessor measures the amplitude
and velocity of an impulse delivered from S1 to R1. Rapid transfer
of a high amplitude impulse suggests the cannula is against a
tissue that readily transfers impulses. Nerves transmit impulses
better than muscles transmit impulses. The novel cannula could be
used to alert surgeons when the instrument is against a nerve.
Surgeons could use the novel cannula to navigate between the nerves
in muscles. For example, surgeons could use the device for
trans-psoas approaches to the spine.
[0142] FIG. 34A is a lateral view of another embodiment of the
invention drawn in FIG. 33. Recording and stimulating electrodes
are used in the walls of a stylet or a blunt dissector. Other than
the electrodes, the stylet or dissector is made of a material that
conducts electricity poorly. The stylet can be used within a
cannula. The blunt tip helps surgeons separate the fibers of
muscles. The electrodes and the monitor alert surgeons when the
instrument lies against a nerve. FIG. 34B is an anterior view of
the embodiment of the device drawn in FIG. 34A. FIG. 34C is an
oblique view of the embodiment of the device drawn in FIG. 34A.
FIG. 35 is an anterior view of another embodiment of the device
drawn in FIG. 33. The electrodes are incorporated into the ends of
a retractor.
[0143] FIG. 36 is a posterior view of a peripheral nerve and
another embodiment of the invention. This embodiment of the
invention may be used to protect peripheral nerves during
non-spinal operations. The nerve is stimulated at one location S1.
Recording electrodes/electrode are placed in another location along
the nerve or a branch of the nerve (R1). Alternatively recording
electrodes/electrode may be placed in muscles that are supplied by
the stimulated nerve (R2). A device, with a microprocessor,
delivers electrical impulses at S1 periodically during the
operation. For example, the device may deliver one impulse per
minute. The device measures the amplitude of the impulses recorded
at R1 and/or R2 and the time between the delivery of the stimulus
and recording of the stimulus. The device triggers an alarm, for
example illuminates a light bulb, if the amplitude or velocity of
the transmitted stimulus deteriorates during the surgical
procedure.
[0144] The microprocessor may also be programmed to compare the
recorded values for the stimulus to standard values. The distance
between S1 and R1 or R2 could be fixed or measured to enable the
microprocessor to calculate velocity figures. For example, this
embodiment of the device could be used during hip replacement
surgery. A needle electrode (S1) could be placed into the sciatic
nerve at the level of the sciatic notch. The S1 electrode could be
sutured into place. Alternatively, the mechanisms use to hold
pacemaker electrodes in position could be used to hold the S1
electrode in the tissues near the sciatic nerve while the tip of
the S1 electrode lies in the nerve. The device would quickly alarm
the surgeon if sciatic nerve function deteriorated during surgery.
The device would alert the surgeon to diminish traction on the
sciatic nerve before the injury became permanent. This embodiment
may be used on other peripheral nerves in the body. It may also be
used to detect additional causes of nerve injury such as pressure
on the nerve or surgical dissection around the nerve.
[0145] FIG. 37 is a lateral view of a nerve root retractor that
stimulates the spinal nerves. The retractor can be used to deliver
the stimulus at the S1 site as described in FIG. 30.
[0146] According to this invention, electric impulses may be
recorded from an instrument placed into and possibly through the
pedicle of a vertebra. Peripheral nerves, spinal nerves, the
sciatic nerve, the femoral nerve, or a plexus of nerves may be
stimulated. Recording electrodes are also placed over spinal
nerves. A recording electrode may be placed through the dura. If
the recording electrode over, or within, a nerve detects an impulse
transmitted through the nerve and the recording electrode on an
instrument placed into a pedicle does not detect an impulse, then
it is likely the instrument within the pedicle does not breach the
walls of the pedicle. Alternatively, the spinal nerves could be
stimulated with recording electrodes placed over or in peripheral
nerves, the nerves in the thecal sac, and the
instrument/instruments in the pedicles.
[0147] Stimulation and/or recording electrodes can be used over the
dura or through the dura cephald and/or caudal to the level the
pedicle screw or screws are inserted. Multiple pedicle screws could
be tested simultaneously by a single stimulating impulse. For
example, a trans-dural stimulating electrode could be placed
cephald to the pedicle screws. A second trans-dural recording
electrode could be placed caudal to the pedicle screws.
Alternatively, multiple recording electrodes could be placed over
or in the spinal nerves near the pedicle screws. The recording
electrodes listed above could be changed to stimulating electrodes
and the stimulating electrodes listed above could be changed to
recording electrodes. If recording electrodes placed on instruments
within the pedicles do not detect an electrical impulse, but the
recording electrodes over or within the nerves detect an impulse,
then the screws, curettes, or taps are likely within the pedicles.
Testing of the invention will likely determine thresholds (for
stimulation and recording) at which penetration of the pedicle wall
by an instrument is unlikely. Techniques well known to those who
perform EMG testing could be used to help locate spinal and
peripheral nerves.
[0148] An electrode placed over or within a myotome may be used to
confirm stimulation of a nerve. For example, if an electrode over
the L5 myotome detects a impulse applied to the L5 nerve and a
recording electrode from an instrument in a pedicle near the L5
nerve does not record an impulse, it is unlikely the instrument
within the pedicle near the L5 nerve penetrates the wall of the
pedicle. The invention eliminates the need for repeated stimulation
at successively higher impulses as used in prior art systems. Prior
art systems use successively higher impulses to record a value in
the extremities in an effort to avoid a false negative. Failure to
record a stimulus over the myotome in prior art systems may confirm
the instrument does not penetrate the walls of the pedicle.
Alternatively, failure to record a stimulus over the myotome in
prior art systems may indicate a problem with the conductivity of
the nerve, the junction between skin and the electrode, or other
technical problem. Recording and/or stimulating electrodes can be
placed in or over the tissues about the spine including the disc,
the gluteal muscles, muscles about the hip or shoulder girdle, or
the extremities.
[0149] Velocity calculations and measurements (of transmittance of
the electrical impulse) may also be used. A single monitor or
instrument may have recording and stimulating electrodes. A fixed
distance between the recording and stimulating electrodes would
ease velocity calculations. For example, a non-conducting cannula
with one or more stimulating electrodes and one or more recording
electrodes may be used in trans-psoas approaches. An impulse that
travels with high velocity from the stimulating electrode to the
recording electrode suggests the cannula is near or against a
nerve. Stimulation may be in the range of 0.01 ma-50 ma.
* * * * *