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FIELD OF THE INVENTION
This invention relates to a cranial lead system and, more particularly, a
system and method for affixing a brain lead or catheter which is
positioned through a cranial burr hole, so that the lead is secured in
position relative to the patient's brain without moving the distal end of
the lead.
BACKGROUND OF THE INVENTION
Systems for providing either electrical stimulation of the brain or
coupling as fluid to or from the brain are coming into increased use for
various purposes. Electrical stimulation of the brain is utilized for
relief of chronic pain and treatment of movement disorders. A typical
electrical brain stimulation system comprises a pulse generator
operatively connected to the brain by a lead. The lead has one or more
electrodes at its distal end, designed to be implanted within the
patient's brain at a precise location, so that the electrode or electrodes
are optimally and safely positioned for the desired stimulation. The lead
is connected to the pulse generator at its proximal end, and also needs to
be anchored with respect to a burr hole drilled in the patient's skull or
cranium, in order to reliably secure the electrodes at the target
location. Likewise, in the case of a catheter for providing fluid to the
brain or for providing drainage, it is necessary to be able to secure the
distal portion of the catheter that passes through the skull and transfers
the fluid at a predetermined exact location within the brain. Still
further, for a combined catheter and lead member, such secure and reliable
anchoring of the member so that the distal end is precisely located within
the skull, is very important. As used herein, the term lead, or lead-type
member, refers to any such cranial catheter or lead.
Reference is made to U.S. Pat. No. 5,464,446, "Brain Lead Anchoring
System," assigned to Medtronic, Inc., which is incorporated herein by
reference. The referenced patent illustrates an effective lead anchoring
system, and it discusses the method of providing access through the skull
by drilling a burr hole with a cranial drill, inserting a stimulation lead
through the burr hole and positioning it so that the electrode or
electrodes are at the desired stimulation site. The lead is positioned
using a stereotactic instrument, which permits a very precise movement
within the brain. Once the lead is positioned and tested to determine that
the results of stimulation are satisfactory, it is critical that the lead
is not moved, since even a small displacement can result in less than
optimal results, and even injury to the brain. Accuracy should be
maintained with .+-.0.5 mm.
The anchoring system of the '446 patent shows a basic anchor for fixing the
lead in place with the distal portion extended through the cranial burr
hole, and then securing it by bending it into a slit such that it is held
by a friction fit. However, the lead must first be removed from the
stereotactic instrument, such that this system does not provide a reliable
way for accurately securing the lead, or catheter, before it is bent into
the fixation position. Thus, such a system does not reliably preclude a
small movement of the distal end of the lead at the time of fixating, or
securing the lead in place. Rather, it is required that the lead be
removed from the stereotactic device before the lead can be fixed to the
skull.
In U.S. application Ser. No. 08/705,566, filed Aug. 29, 1996, assigned to
the same assignee as this invention, there is shown an apparatus and
method wherein a compression screw cap is screwed down onto a compressible
seal, the seal being flexible and compressed laterally against the outer
wall of the lead. This system provides a substantial improvement over the
prior art, and in particular enables securing the lead with respect to the
skull before it is stereotactically released. However, it is operative
only when the lead is to be positioned in the center of the burr hole. If,
however, the target localization procedure indicates that the lead must be
inserted off-center, this assembly and the procedure of using it is not
adequate; the lead must be bent in order to fix it through the iso-centric
burr hole cap, and this bending results in a lead displacement from the
stereotactically determined target. There thus remains a need in the art
for a reliable system which enables off-center, or eccentric placement of
the lead through the burr hole, without requiring stereotactic release of
the lead.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a brain treatment system,
having a fixation subassembly and procedure for fixing a brain lead
off-center, or eccentric from the center axis of the burr hole in the
patient's skull. This objective is to be met without stereotactic release
of the lead, so that the lead is secured to the patient's brain without
displacement of the lead distal end from the stereotactically determined
target.
There is provided a system and method for electrical and/or fluid treatment
of a patient's brain, having a subsystem for anchoring a lead or a fluid
catheter within a cranial burr hole within a patient's skull, wherein the
anchoring subsystem has a feed-through burr hole piece, and an adjustable
compressive element through which the lead is positioned. The compressible
element is movable laterally so that it can be positioned to the required
off-center position that has been identified by the target localization
procedure. The burr hole feed-through piece contains a radial slit through
which the lead passes, the slit further having an upper grooved portion
for receiving a compressible O-ring. A compression plate is placed over
the O-ring, and pressed down thereupon by a clamping screw, causing
compression of the O-ring and radially inward compressive force on the
lead outer surface, thereby securing the lead in place with respect to the
skull while it is still being stereotactically held. Following fixation by
the compressive O-ring, the lead is released from the stereotactic
instrument and secured through a burr hole cap, the proximal end of the
lead then being connected to an implantable stimulator device or pump.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of the anchoring subassembly of this
system, showing a lead being stereotactically held in position, the lead
being passed through the anchoring subassembly.
FIG. 2 is a top diagrammatic view of the plate that provides downward
pressure on the compressive O-ring, in accordance with the invention.
FIG. 3A is a top diagrammatic view of the burr hole feed-through piece of
this invention, illustrating the slit which is configured to retain the
adjustable O-ring and provide for eccentric anchoring of the lead; FIG. 3B
is a cross-sectional view taken across lines B--B of FIG. 3A, also showing
placement of the compression plate; FIG. 3C is a cross-sectional view of
the burr hole feed-through piece taken along lines C--C of FIG. 3A, also
showing the compression plate in position; FIG. 3D is a cross-sectional
view of the burr hole feed-through piece taken along lines D--D of FIG.
3A, also showing the compression plate; and FIG. 3E is a cross-sectional
view similar to FIG. 3C, of an alternate embodiment whereby the lead can
be placed at an angle to the burr hole piece axis.
FIG. 4A is a diagrammatic view showing the O-ring in position within the
retaining groove of the slit in the burr hole piece, with the lead
positioned through the center opening of the O-ring, and without any
downward force on the O-ring; FIG. 4B is a diagrammatic view the same as
FIG. 4A, but with the plate providing downward compression on the O-ring,
illustrating the inward compressive force by the O-ring which fixes lead
32.
FIG. 5 is a diagram illustrating the fixation subassembly of this invention
in position in a patient's skull, and illustrating the lead connected to a
stimulator or a pump device.
FIG. 6 is a flow diagram illustrating the primary steps taken in carrying
out the procedure of this invention, either for a test lead or for the
final DBS lead.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1, there is shown a cross-sectional view illustrating
the main components of the burr hole assembly portion of this invention.
This drawing is intended to be illustrative, and is not necessarily to
scale. A burr hole piece, or element 30 is positioned within a burr hole
which has been drilled in the patient's skull in a known manner. The piece
30 is affixed to the skull in a conventional manner, e.g., by suturing. A
lead, or catheter 32 is shown positioned through the burr hole piece, and
held stereotactically by a stereotactic member 35, shown schematically.
For an embodiment which utilizes a cranial lead for providing stimulation,
the lead carries electrodes positioned at the distal end portion, as
indicated at 33. For an embodiment where fluid is pumped to or withdrawn
from the brain, the catheter 32 has an axial lumen for carrying the fluid.
As used in this specification, the term "lead" embraces a lead for
transmitting stimuli to the brain, and also includes a catheter or
combination lead and catheter, and is not limited to any one specific type
element.
As seen in FIG. 1, the lead 32 is displaced off-center from the central
axis of the burr hole, i.e., it is eccentric with respect to the burr
hole. As discussed above, the target localization procedure may determine
that the proper target does not lie on the center axis of the burr hole
which has been drilled, and as a consequence the lead must be positioned
off-center. Burr hole piece 30 has a slit portion shown at 36, wherein is
placed an O-ring 37, which squeezes radially inward to grip lead 32, in a
manner described in more detail below. An annular opening at 38 receives a
compression plate 44, which in turn is clamped by clamping screw 41, which
is screwed into piece 30 on threads 40. The downward force of plate 44
compresses the O-ring, which is largely contained within slit 36, such
that the O-ring material, e.g., silicone rubber, compresses radially
inward and grips lead 32. When this has been achieved, the lead can be
removed from the stereotactic member 35, and connected to a stimulator or
flow delivery device 55, as illustrated in FIG. 5.
Referring to FIG. 2, there is shown a top diagrammatic view of plate 44,
which is laid down on top of O-ring 37. Plate 44 has a slit 45, which runs
from about the center axis of the plate radially toward the circumference,
having a width which is just larger than the outer circumference of lead
32. When placing the lead through to the brain, both piece 30 and plate 44
are rotated, so that the slits line up at the correct angle to permit
placement of the lead 32 through to the proper position in the brain.
Referring now to FIGS. 3A-3D, the important features of a first embodiment
of the burr hole piece 30 and the plate 44, for enabling an eccentric
placement of lead 32, are shown. It is noted that these figures are
illustrative of the concepts and elements of the invention, but are not
exactly drawn to scale. By way of reference, the burr hole piece 30 may
have, e.g. a diameter of 14 mm; and lead 32 has a typical diameter of
about 1.3 mm. Referring to FIG. 3A, there is seen a top view, looking in
the direction down through the top of the patients skull, at the burr hole
element which is positioned within the burr hole. The element is
preferably a solid piece of machined metal. A top edge 31, seen also in
FIGS. 3B-3D, is substantially flush with the top of the skull when piece
30 is placed and secured within the burr hole. Within top edge 31 there is
a surface 47, within which is drilled slit 36 which extends to the bottom
of the burr hole piece. Slit 36 has top width somewhat less than the
diameter of O-ring 37; and has an inner recessed groove shown at 48 in
FIGS. 3C and 3D, which containingly receives the O-ring 37. The inner edge
of groove 48 is also shown by the dashed line 36I in FIG. 3A.
FIG. 3B shows a cross-section of burr-hole piece 30 which is taken through
the center and along the slit, as indicated at B--B in FIG. 3A. This view
also includes plate 44, having its slit 45 lined up to coincide with slit
36. As seen, slit 36 extends to the bottom of element 30, and is eccentric
with respect to the center axis of element 30. Plate 44 is shown in
position, lying on surface 47, having plate slit 45 aligned with burr hole
piece slit 36. The center axis of lead 32 is shown positioned through the
center of O-ring 37. Referring to FIG. 3C, the view is taken along
cross-section C--C indicated in FIG. 3A, meaning that the view is in the
direction of slits 36 and 45. In this case, slit 36 is seen as a narrow
width, being just large enough to accommodate the lead 32. Note that in
this view also the slit 45 of plate 44 has a width that is just sufficient
to accommodate lead 32. Note also the containing groove or contour 48 of
slit 36, which receives the O-ring 37. This groove is configured to match
the outer geometry of the O-ring, so that the O-ring is held in place when
plate 44 is pressed downward. This groove also holds the small O-ring in
place while, e.g., in the package during transportation or during handling
by the doctor, whereby there are no loose components that can be lost.
FIG. 3D provides yet another view of the same embodiment, showing an
off-center view indicating slit 36 with the upper portion thereof defined
by containing surface 48.
Referring now to FIG. 3E, there is shown a view similar to that of FIG. 3C,
but illustrating an alternate embodiment which enables placement of the
lead 32 at an angle with respect to the axis of the burr hole piece. As
seen, slit 36 has tapered walls 36', which enables placement of the lead
32 at an angle with respect to burr hole and the axis (A--A) of the burr
hole piece 30. Thus, as illustrated, the lead 32 is positioned by the
instrument 35 to be at an angle to the axis which is perpendicular to the
top of the skull, thereby providing increased flexibility in directing the
lead to the desired brain location. Stated in another way, the direction
of the lead can be offset from the perpendicular to the burr hole ring
piece.
FIGS. 4A and 4B provide a diagrammatic representation of the compressive
force of O-ring 47. Without the plate 44 in position, as shown in FIG. 4A,
O-ring 37 fits somewhat loosely in the groove defined by surface 48, and
is not engaging lead 32 which has been positioned through the center of
the O-ring. In FIG. 4B, with the compressive plate 44 in position and
exerting a downward force, O-ring 37 is squeezed tightly into the cavity
provided by groove surface 48, with a resulting radially inward
compressive force which securely grips lead 32, and holds it in position.
The O-ring is preferably made of silicone rubber, but can be made of other
materials, and can have a doughnut or other ring-shaped geometry.
As seen in FIG. 5, after the lead has been secured within burr hole element
30 by the O-ring, it is released from the stereotactic instrument and
passed through a surface cap 52, and connected to an implantable
stimulator or pump device 55, for chronic operation. Cap 52 may be any
conventionally used cap, and may provide an upper surface which is
substantially flush with the patient's skull. Cap 52 conventionally has a
pathway for passing the lead 32 laterally to the side of the burr hole,
from which position it is then connected to device 55. Cap 52 and piece 30
are suitably used as shown in U.S. Pat. No. 5,464,446, for passing the
lead laterally. As used herein, device 55 communicates with the patient's
brain, either by delivering stimulus pulses or pumping fluid through lead
32.
Referring to FIG. 6, there are shown the primary steps of the method and
technique of securing the lead 32 in accordance with this invention.
Initially, as indicated at 55, the burr hole is drilled in the patient's
skull, using known techniques. It is determined whether the procedure is
to use a test lead, or the final procedure of implanting the DBS lead, as
indicated at 56, 58. For the initial test lead, at 60 physiological target
localization is performed. At 61, the target is identified, and the test
lead is removed. Then, at 62, the burr hole piece is placed and rotated to
the proper angle, so that the slit 36 provides entry of the lead 32 to the
proper location. Following this, as seen at 63, for either a test lead or
DBS type lead, target localization is performed, to position the lead
properly with respect to the brain portion which is to be stimulated, or
to which fluid is to be delivered. See, for example, U.S. Pat. No.
5,843,150, filed Oct. 8, 1997. At 64, 65, the loose plate 44 and clamping
element 41 are positioned loosely over the lead. The lead then is passed
down through the burr hole assembly and stereotactically positioned at the
correct position, as indicated at 68. When the correct position has been
confirmed, the loose plate is placed in position on surface 47, and the
clamping element is screwed into place, as indicated at 70. When this is
done, as explained above, the O-ring secures the lead in the proper
position, without movement of the distal tip. Following this, at 72 the
lead is released from the stereotactic instrument, and at 74 the lead is
passed through the upper cap 52, which cap is then secured to the
patient's skull. Finally, at 75, the lead is connected to the stimulator
or pump device 75, to complete installation of the system.
The burr hole fixation assembly of this invention allows reproducible,
non-destructive release of lead 32 from its fixed condition, by unscrewing
clamping screw 41. This feature is very important if, for whatever reason,
it is necessary to reposition lead 32. Thus, stereotactic repositioning
can be carried out simply by proceeding backward at any point in the
procedure illustrated by FIG. 6, fixing the lead position, and then
proceeding forward again.
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