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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a device used in the interventional
treatment of neurological disorders, and more particularly to a novel
electrode lead securing member which mounts to a burr hole in the
patient's skull and prevents undesirable translation of the implanted lead
as the external portion of the lead is manipulated during surgery.
2. Description of the Prior Art
The use of electrical stimulation of the brain for the purposes of
alleviating pain and the treatment of other neurological afflictions has
been utilized for a number of years, and in many instances has become the
standard of care. The technique comprises the implantation of a long
flexible electrical lead through a burr hole in the patient's skull, and
into electrical contact with the pathological section of the patient's
brain. The flexible lead comprises a plurality of long hetically wound
wires encased in a elastomeric sheath. The distal end of the wire leads
include electrical contacts and are placed in the brain. The proximal end
of the wire leads remain external to the skull, and is coupled to an
extension connector which joins the electrical wires to an electrical
generator.
As is clear from the delicacy of the surgical field, it is critical to
utilize robust instruments and implants which are not easily broken, and
which do not lend themselves easily to unwanted movements. In particular,
when an electrode lead is implanted, the position of the active tip is
critical. The effects of the field generated by the electrical contacts is
highly position dependent, and as a result, movement of the electrode
after proper positioning can reduce or eliminate all effectiveness of the
treatment. As it can be a very tedious process to find the appropriate
location within the brain for the active tip, it is also critical that
once the lead is situated, it should not be moved accidentally. Many of
the subsequent manipulations of the external portions of the electrode
leads, however, must be carried out after the active tip has been properly
positioned. It is, therefore, a considerable concern that there be a means
of securing the implanted portion of the electrode relative to the skull
and the brain, while permitting the external portion to be moved freely.
The additional feature which should be considered is that the surgeon
should be able to easily manipulate any such securing device with ease,
even when covered in slippery bodily fluids.
A device which is presently available in the art is illustrated in FIG. 1.
This device 10 is intended to hold a flexible wire lead 12 from moving,
but is not designed to seat in a hole in the patient's skull. Rather, it
is designed to be secured to soft tissue (for example in the vacinity of
the spinal column). The use of this device is, therefore, intended to
prevent gross movement of the electrode lead 12. It is comprised of a
first receiving member 14 which is cylindrical in shape. The lower portion
of the cylinder forms a tapered hole 16 having an opening which is
approximately the same diameter as the electrode lead 12. A second inner
seating member 18 fits within the receiving member, also having an axial
bore through which the electrode lead passes. The tip 20 of the seating
member 18 is thin-walled, such that the channel formed therethrough may
deflect inward if compressed. The second, seating member is permitted to
translate within the receiving member 14 from an an open position which
permits the lead 12 to freely slide through the assembly, to a closed
disposition in which the tip is forced into the narrowed end 16 of the
bore of the receiving member 14. In this position, the lead is friction
locked in place by the compressed walls of at the tip of the seating
member 18. The exterior surface of the receiving member further includes a
series of through holes 20 which permit the assembly to be secured to
adjacent tissue by sutures. Unfortunately, the device is very difficult to
manipulate in a surgical environment as it requires manual pushing and
pulling of small members which are seated within one another, and which
have no defined open and closed dispositions which demonstrably indicate
that the electrode lead is truly secure.
A more directly related device which is presently available in the art is
illustrated in FIG. 2, and is described in U.S. Pat. No. 5,464,446. It
comprises a first port member 22 which is cylindrical and seats in the
burr hole formed in the patient's skull 24. The exterior lateral surface
of the port includes a contoured circumferential flange portion 26 which
is intended to form a seal with the inner lateral surface 28 of the burr
hole. The upper portion of the port member includes an outwardly extending
rim 30 which seats against the exterior surface of the skull 30 around the
edge of the burr hole when the port is inserted fully in the burr hole.
This upper contour is also designed to mate with a cap section 32. The
central axis of the seating member 22 forms a channel through which the
electrode 34 seats and can slide prior to being locked in place. The cap
32 has a pair of channels formed therein; a first 36 which extends axially
along the same direction as the axial passage in the port member, and the
second 38 which extends out radially along the undersurface. The cap 32
engages the upper contour (and requires a suture 40 to hold the members
together) in such a way that the electrode lead is compressed and is
thereby locked in place. The use of a suture to secure the electrode, even
indirectly, is a considerable drawback as it is difficult to manipulate,
not easily reversible, and does not provide a readily obvious means for
ensuring that the lead is truly secured against movements when the
external portion is manipulated during the remainder of the surgery. Also,
the compression lock, as in the first example is not easily viewed as it
happens under the cap member.
The objects of the present invention are, therefore, clearly to provide an
electrode securing assembly which reliably, easily, reversibly, and
obviously locks an electrode lead to the skull, and most importantly,
prevents the unwanted movement of the implanted portion of a deep brain
stimulation lead during the manipulation of the external portion after the
active internal tip has been properly positioned.
More specifically, it is an object of the present invention to provide an
assembly which reliably mates with a burr hole in the skull and secures an
electrical lead such that it does not move within the skull, but which
permits free manipulation of the portion of the electrical lead which is
external to the skull.
Simultaneously, it is also an object of the present invention to provide a
mechanism which is easily manipulated by the surgeon under the conditions
of the surgical field.
SUMMARY OF THE INVENTION
The preceeding objects of the invention are provided by the present device
which comprises a first cylindrical port member which seats into a burr
hole in the skull, and a second electrode lead locking member which is
bayonet locked within the port member. More particularly, the port member
includes an outer surface contour which grips the inner surface of the
burr hole, and a laterally extending upper lip which seats against the
outer rim of the burr hole in the patient's skull. The inner surface of
the port member further includes a bayonet lock receiving structure, which
generally comprises a pair of diametrically opposed recesses.
Corresponding laterally extending elements on te external surface of the
lead locking portion are provided to fit in these recesses such that but
inserting and rotating the lead locking member, it is secured within the
port member. Further, the second electrode lead locking member includes a
central axial channel through which the electrode is passed, and which may
slide through the channel freely prior to being locked therein.
The upper portion of the lead locking member includes a sliding element
which may be manipulated easily between an offset position and an
occluding position. These alternate dispositions, and more particularly,
the movements between them, are transverse to the axis of the member and
the orientation of the electrode. Specifically, the sliding element is a
disc which is seated in the upper surface of the lead locking member. The
disc is initially offset relative to the hole which is the terminus of the
axial channel. The disc slides along a track in the upper surface of the
member into a closed position which partially blocks the hole. In this
occluding position, the sliding member partially narrows the channel, and
if there is an electrode lead extending therethrough, the lead is squeezed
by the sliding member and thereby prevented from continued relative
motion. The sliding member, or disc, may include at least one small recess
into which a tool may be inserted to facilitate the translation between
the open and closed positions. The track in which the sliding member
translates, may further include a tab, ratchet, catch, or other structural
feature by which the surgeon/user may readily recognize if the sliding
element has ben fully engaged at the open or closed position.
Unlike prior devices, two of which are described above, the manipulation of
the locking mechanism of the present invention is readily visible to the
user, as it involves the translation of a sliding member transverse to the
axial channel at the upper surface of the lead locking member. This
feature may prevent additional mistakes associated with incomplete
fixation of the lead in the locking mechanism.
The present device also resolves the difficulty of use which is a
limitation of the prior art devices. By providing recesses in which a
tool, for example a scissors, plyers, or other hand-held retractor, may
engage and manipulate the mechanism, the present invention eliminates a
substantial drawback to using similar prior art devices.
In addition, the reversibility of the locking mechanism is very easy to
achieve, i.e. simply reversing the bias of the sliding element away from
the hole or rotating and removing the lead locking member from the port
member, is a substantial advance over semi-permanent securing means which
require sutures to secure the assembly to the adjacent tissue, and sutures
to hold a lead locking cap member to the lead receiving member.
Additional advantages ofthe present invention shall be readily
understandable from the detailed description of certain preferred
embodiments described more completely in the following sections, and with
reference to the accompanying figures.
A BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a side cross section view of a prior art device for securing
an electrical lead;
FIG. 2 shows a side perspective view of another electrode securing device
of the prior art which couples to the skull;
FIG. 3 shows a cross-section view of a burr hole port which are an aspect
of the present invention;
FIGS. 4a and 4b show side cross-section and top views, respectively, of the
electrode lead locking portion of the present invention;
FIG. 5 shows a side cross section view of the assembly mounted in a burr
hole and locking an electrode disposed therethrough.
THE DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
While the present invention will be described more fully hereinafter with
reference to the accompanying drawings, in which particular embodiments
are shown, and with respect to methods of implantation, it is to be
understood at the outset that persons skilled in the art may modify the
invention herein described while achieving the functions and results of
this invention. Accordingly, the descriptions which follow are to be
understood as illustrative and exemplary of specific structures, aspects
and features within the broad scope of the present invention and not as
limiting of such broad scope. Like numbers refer to similar features of
like elements throughout.
Referring now to FIG. 3, the present invention comprises a cylindrical
skull port member 100 which is designed to securely fit within the burr
hole formed in a patient's skull,through which the surgeon implants the
active tip of the electrode lead. The cylindrical port member 100 includes
a central opening 102 and a round sidewall 104. The exterior surface 106
of the sidewall includes at least one circumferential rib 108, and
preferably multiple ribs 108. These ribs are preferably made of an
elastomeric material (for example silicone). These ribs are provided for
enhanced gripping and holding of the inner surface of the burr hole in the
skull. Other than these ribs, the exterior surface of the cylindrical port
is largely smooth, having only a laterally extending lip 110 at the upper
end. This lip 110 is provided so that as the port 100 is inserted into the
burr hole, the lip 110 seats against the upper surface of the skull and
prevents the port 100 from passing too deeply into the brain case.
The interior surface 112 of the port's central opening is also largely
smooth, being suited to receive therethrough the lead locking element
described hereinbelow with respect to FIGS. 4a, 4b, and, in combination
with the port member, FIG. 5. The central opening 102 does, however,
include engaging means for securing the leadlocking member therein. In the
present embodiment, this engaging means comprises a bayonet lock receiving
groove 114. In particular, the upper portion of the port includes a pair
of opposing lateral recesses 114 (one of which is shown in FIG. 3) which
extends downward from the upper surface for a short distance, and then
turns laterally, forming a partial circumferential groove.
Referring now to FIG. 4a, the lead locking element 120 is provided in a
side cross section view. The lead locking element 120 is generally
cylindrical in shape, having a pair of laterally extending posts 122a,122b
extending outwardly from the upper end of the element. These posts
122a,122b are provided to engage the grooves 114 in the upper inner
surface of the port member 100. The lead locking element 120 also includes
at least one (and preferably a plurality of circumferential elastomeric
ribs 124. The element 120 is designed to slide into the central opening
102 of the port member 100, with the elastomeric ribs 124 of the lead
locking element 120 gripping the inner surface 112 of the opening 102 in
the port 100. The laterally extending posts 122a,122b are then inserted
into the opposing grooves 114 in the central opening, and then rotated
such that the lead locking element 120 may not translate axially relative
to the port member.
The lead locking element 120 further includes an axial channel 126 through
which the brain stimulation lead may be passed. The lead may initially
loosely translate within the channel 126 so that the lead locking element
120 may freely slide along the lead and into the port member 100.
The upper surface 128 of the lead locking element 120 further includes a
lead locking mechanism, which is more evidently shown in FIG. 4b, which is
a top view of the element 120. More particularly, the upper surface 128 of
the lead locking element includes a partially covered track 130 in which
is seated a sliding element 132. The track 130 is adjacent to the upper
opening of the axial channel 126. Within the track 130 is a sliding
element 132 which may be selectively translated from one end of the track
to the other. A portion of the sliding element is maintained within the
covered portion of the track, while a portion remains free so that the
user may engage it. When in the open disposition, the sliding element does
not occlude the opening, however, when translated into the closed
position, the sliding element partially blocks the opening. More
importantly, this partial occlusion, when the stimulation lead is present
in the channel, compresses the lead sufficiently to prevent any further
axial movement of the lead. The track may also include ratcheting
conformations 134 which indicate to the user that the sliding element has
been fully translated into the closed position. This indication will
provide greater security to the surgeon by indicating that the device has
been fully locked.
In order to facilitate the selective manipulation of the sliding element
132, the sliding element 132 and the upper edge of the lead locking
element each include tool receiving recesses 134a,134b. A scissor-like
instrument (or other similar tool) may be utilized to translate the
sliding element from the open to closed position (or conversely, to open
the assembly by moving the sliding element from the closed to open
position).
Referring now to FIG. 5, in which a fully implanted and closed assembly is
provided in a side cross section, a description of the use of the present
invention is described. Preparation for the implantation of a deep brain
stimulation lead begins with the exposure of a portion of the skull
(usually above the crown of the head, above the motor cortex). A burr hole
140 is then formed in the skull. Fourteen millimeters is a standard burr
hole diameter. The port member 100 is then installed in the burr hole,
until the upper lip 110 seats against the skull surface. The exterior end
of the electrode is temporarily fastened to a fixed exterior structure,
for example the stereotactic surgical frame which is usually mounted by
screws to the patient's skull. Once this has been prepared, a cannula is
advanced into the patient's brain, often guided by computer imagery and
magnetic sensors. The cannula carries a microelectrode recordation device,
with which the surgeon tests to find the ideal location for the permanent
implant lead. Once found, the microelectrode recording lead is removed and
the active tip of the electrode 142 is advanced into the brain, to the
location which was identified. Once properly located, the cannula is
removed from the brain by being carefully slid up along the lead electrode
lead. This process must be carried out carefully so as not to disturb the
location of the active tip. Once the cannula is free of the brain, the
lead is manually held fixed at the port member 100, and the exterior end
of the lead is released as the cannula slides completely off the lead.
Once freed, the exterior end of the electrode is advanced through the lead
locking element 120, and the lead locking element is inserted into the
port member 100 and rotated into a secured disposition. The stylet, which
is a rigidity providing component of the electrode lead, is then removed.
The limp lead is then locked in place by the surgeon who translates the
sliding element 132 of the lead locking element 120 into the closed
disposition. The interior portion of the lead is thereby prevented from
any motion, while the exterior portion 144 of the lead is free to be
manipulated as necessary for connections to a signal generator, or other
electrical signal providing mechanism.
While there has been described and illustrated specific embodiments of new
and novel electrode lead securing assembly for reliably and securely
fixing an implanted electrode lead to the skull, it will be apparent to
those skilled in the art that variations and modifications are possible
without deviating from the broad spirit and principle of the present
invention which shall be limited solely by the scope of the claims
appended hereto.
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