Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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WO 95/26689 ~ PCTIIB95100042
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MEASUREMENT OF NUCLEUS MATERIALS REMOVED
DURING DISCECTOMY
This invention relates to intervertebral discs. More particularly, ft relates
to a
method and apparatus for determining the amount of nuclear material removed
from
said disc during, and the shapes of the cavity created after lumbar surgery.
The normal intervertebral disc has an outer ligamentous ring called the
annulus
which binds the adjacent vertebrae together and is constituted of collagen
fibers that
are attached to the vertebrae and cross each other so that half of the
individual fibers
will tighten as the vertebrae are rotated in either direction, thus resisting
twisting or
torsional motion. Torsional movement between vertebral segments is further
restricted
by the facet joints.
Deep inside the annulus lies a nucleus pulposus of loose tissue which is
slippery
and slimy (having about 70-7596 water content) and moves about during bending
from
front to back or from side to side. Thus, as the opposing surfaces of the
vertebrae alter
their parallel relationship to each other with bending, the nuclear tissue
moves about
to fill up the change in distance (wedging) that occurs in the opposing ends
of the disc
space. With bending, the annulus will bulge on the downward wedged side and be
stretched tightly on the upward wedged side.
A classical disc hemiation occurs when the annular fibers are weakened or torn
and the inner tissue of the nucleus becomes permanently bulged, distended, or
extruded out of its normal annular confines. Leg pain in such case results
from this
nuclear tissue (or an intact weakened, bulging annulus) compressing a nerve
which
passes outward from the spinal canal to the leg.
A major cause of persistent, disabling back pain takes place when the annulus
becomes chronically inflamed by a degenerative process. Small nerves that come
from
branches encircling the outside of the annulus penetrate for a short distance
(perhaps
6 to 8 mm) into the annular fibers. Constant abnormal motion between the fiber
layers
of the annulus, due to loss of bonding between them, may stretch and grind the
tiny
'' pain fiber nerve endings. Thus the patient becomes sensitive to the
slightest
movement. These cases require some form of mechanical limitation to
intervertebral
disc motion at the painful segment. For the most persistent cases, bony
fusions are
often performed to stop the painful motion by permanently locking the
vertebrae
together. In many cases it may be preferred to allow some minor movement (less
than
67044-38
CA 02185919 2000-12-19
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that which causes the pain). Preserving some movement helps to prevent
mechanical
breakdown at nearby segments. At present, to attempt to make and maintain
these
flexible fusions is not reliably feasible.
One of the major treatments for low back pain (or leg pain), caused by a
hemiated disc, is discectomy surgery in which part or all of the nucleus
material is
removed. The major purpose of removing the nucleus material is decompression -
i.e.,
relief of the compression of the nerve caused, directly or indirectly, by the
nucleus.
There are many surgical techniques used to remove nucleus material, such as
open
surgery, Microdiscectomy (e.g., Arthroscopic MicroDiscectomy), serdiscectomy
and
Automated Percutaneous Lumbar Discectomy. Since the amount of removed nucleus
can directly affect the intradiscal pressure of the disc and the overall
results of the
discectomy surgery, it is desirable to know how much nucleus has been removed
from
the disc during the discectomy.
Although discectomy has a high rate of success in alleviating primary
symptoms, e.g., low back or leg pain, it often causes disc narrowing and
increase of
disc mobility which may again cause back pain at a later stage. U.S. Patent
5,047,055
(assigned to the same assignee as this application describes a prosthetic
disc nucleus implant which overcomes this limitation.
Since the disc nucleus implant will be used to occupy all the cavity space
created in
the discectomy surgery it is important to know and control the cavity size and
shape.
Therefiore, it is necessary to have a method and apparatus to measure the
discal cavity
size and shape during the surgery.
Capanna et al. S ine, 6, 810-614 [1981 ]) described a method for measuring the
'percentage of disc removal' during lumbar discectomy using discograms and
lumbosacral radiographs. However, this method does not provide a simple way to
give
the volume and is unable to define the shape of the cavity. Furthermore, it is
subject
to relatively large errors.
Other methods for estimating the amount of nucleus removed during or after
discectomy surgery have been discussed in the literature. One method often
used,
especially for cadaveric discs, is to collect all of the removed nucleus
materials and
weigh them directly on a balance. However, it is d'rfficult to be sure that
all the nucleus
materials have been collected and to weigh them during the operation.
Furthermore,
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67044-38
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since the nucleus materials have been either mixed with saline
solution or evaporated and then sucked out from the disc, in
Automated Percutaneous Lumbar Discectomy and Laser Discectomy
techniques, the weight of the removed nucleus material can not
be obtained directly. Another way of measuring the nucleus of
the material weight, especially in Automated Percutaneous
Lumbar Discectomy, is t=o install a filter in the suction tube,
separate the nucleus material from the flushing solution and
then weigh the nucleus material. However, the nucleus material
tends to absorb fluids resulting in a weight change after it
has been removed from t;he disc. This method does not give an
accurate measurement.
SUMMARY OF THE INVENTION
An aspect of this invention provides a method for
directly determining the volume of a nuclear material removed
during a discectomy, which comprises inserting a deflated
flexible expandable first container into the cavity left in the
disc after the removal, adding a liquid to the container to
cause it to expand until it fills the cavity and determining
the amount of liquid required to so expand the container.
Another aspect of the invention provides an apparatus
for use in determining the amount of a nuclear material removed
from a disc during a discectomy.
In a first major embodiment, the apparatus comprises:
(a) a flexible, expandable first container capable of being
expanded from an unexpanded state to an expanded state by a
fluid injected thereto, to fill the cavity, wherein the first
container is made of a physiologically compatible elastic
composition; (b) a source of the liquid in fluid connection
with the flexible, expandable first container; and (c) a holder
for carrying the expandable first container.
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67044-38
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In a second major embodiment, the apparatus
comprises: (a) a flexible, expandable first container capable
of being expanded from an unexpanded state to an expanded state
by a fluid injected thereto, to fill the cavity, wherein the
first container is made of a physiologically compatible elastic
composition; (b) a source of the liquid in fluid connection
with the flexible, expandable first container; and (c) valve
means interposed between the flexible, expandable first
container and a calibrated second container.
In a preferred embodiment of the apparatus, the
calibrated second container comprises syringe means comprising
a hollow tube, comprising an opening at each end thereof, to
contain the liquid and means to cause the liquid contained in
the tube to be injected into the second container means.
In another preferred embodiment, the apparatus may
comprise a flexible, collapsible bulb which is caused to
collapse by the applic<~tion of pressure applied to outer walls
thereof wherein the liquid, contained in the tube is injected
into the first container to which it is fluidly connected, and
causes the first container to expand.
In another preferred embodiment, the apparatus may
comprise a syringe having a calibrated barrel and an axially
and reciprocally movable plunger inserted therein or a
combination of a pipette with means to cause the liquid
contained therein to be expelled therefrom.
The means to cause the liquid to be expelled from the
pipette may comprise a flexible, collapsible bulb.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure lA is an elevational section view of the
apparatus of a first embodiment of the invention.
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67044-38
4a
Figures 1B-1D are sectional views showing various
positions of the bore of the valve means of the apparatus of
Figure lA.
Figure 2 is a top plan view of an intervertebral disc
with its nuclear material removed and a hole through one wall
of its annulus.
Figure 3 is an elevational sectional view of the disc
of Figure 2.
Figure 4 is an elevational sectional view of the
apparatus of Figure lA set up for calibration.
Figure 5 is an elevational sectional view of the
apparatus of Figure lA set up for measurement of the volume of
the nuclear cavity of an intervertebral disc.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring to Figure lA the apparatus of the
invention, designated by the numeral 1, comprises a calibrated
second container 10 comprising an opening 12 at one end and an
outlet stem 11 at the other end. Container 10 further
comprises injection means to cause the liquid to flow from the
container when pressure is applied to said injection means.
Outlet stem 11 comprises a distal portion lla adjacent the
barrel of the container and a proximal portion llb separated
from the distal portiOTl by valve means 20. The valve means may
be 2- or 3- way valves. The outlet stem portion and valve may
be unitary (as shown) or comprise two or more parts joined by
connecting means.
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W O 95/26689 pCT/IB95100042
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The upper, open portion of a flexible, expandable first container 31 (a
balloon
y ~ in the illustration) is stretched and draped over the flange 35 of an
outer tube 34. An
inner tube 33 is inserted into the mouth of the balloon 31 until its proximal
end passes
the distal opening in outer tube 34. The outer diameter of the inner tube 33
and inner
diameter of the outer tube 34 are so selected that the wall of balloon 31 is
held tightly
between them. Flange 35 may be an integral part of tube 34 or may comprise a
separate ring axially movable along the outer wall of tube 34.
Inner tube 33 is fluidly connected to valve means 20 through connecting tube
13 which is attached to the distal end of inner tube 33 and the outlet stem
portion 11 b.
A disc, the volume of whose nuclear cavity is to be determined by the method
of the invenflon, is illustrated in Figures 2 and 3 and designated by the
numeral 40.
The disc comprises a fibrous annulus 41 and a cavity 42 from which the nucleus
material has been removed in the surgeon's usual manner, e.g., curettage and
microdiscectomy with pituitary forceps. The disc further comprises a
longitudinal hole
43, extending from the outer wall 37 to the cavity, through which the nuclear
material
has been removed.
In the operation of the invention the volume of the apparatus between valve
means 20 and the proximal end of outer tube 34 is determined as follows. The
initial
volume of liquid L in container 10 is obtained from the marking a thereon. The
bore
22 of valve means 20 is turned to the position shown in Figure 1 B and vacuum
applied
through stem 21 whereby balloon 31 is evacuated and collapses. The bore 22 of
the
valve means is then turned to the position shown in Figure 1 D and liquid L is
allowed
to flow from container 10 through bore 22 and connecting tubes 13 and 33 into
first
container 31. Container 31 expands, filling the cavity in outer tube 34 until
the proximal
end 39 of the expanded balloon is flush with the proximal opening 44 of outer
tube 34.
A reading, b, is taken of the volume of liquid L in container 1. The
difference between
a end b is the volume of the measuring apparatus between valve means 20 and
the
proximal end 39 of expanded balloon 31.
The outer tube 34 of the apparatus 1 is then inserted into hole 43 of the disc
40
until the inner surface 36 of flange 35 of the outer tube abuts the outer wall
37 of the
disc. The length of outer tube 34 is so chosen that it does not extend into
the cavity
42 formed upon removal of the nuclear material from the disc. Liquid L is
allowed to
continue to flow until the expanded balloon fills the cavity 42 of the disc. A
reading is
i
W095126689 ~ PCTIlB95100042
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then taken of the volume c in container 1. The difference between b and c is
the
volume of the cavity 42 in the disc. ~ ~ t
The filling means comprises
a) rigid second container means, to contain the liquid, which
b comprise a barrel comprising open proximal and distal ends;
b) pressure means, at the proximal end of the barrel, to apply
pressure to the liquid and force it to flow out of the barrel at the distal
end thereof.
Flling means for use in the practice of this invention include syringes
wherein
a) the second container means comprises a pipette (e.g., catalog number
13-678, Fisher Scientific, Pittsburgh, PA 15219) and the pressure means
comprises a
bulbs or dispensers (e.g., catalog numbers 13-681-15, 13-68150, 13-681-61 and
14-
070, ibid). If a dispenser such as 13-681-15, which is electrically powered,
is used it will
be necessary to use a pressure controller therewith; or
b) the second container means comprises a cylindrical barrel, disposed
about a longitudinal axis and the pressure means comprises plunger means,
which is
inserted through the proximal opening of the barrel, and is axially and
reciprocally
movable therein (such a combination is, e.g., a syringe such as catalog number
14-823-
10, ibid).
Preferred filling means are syringes (such as catalog number 13-578, above) of
about
5 to about 10 ml capacity.
The materials of construction for use in the invention are biocompatible
materials
such as plastics and metals. The materials of construction must also be
compatible
with the measuring liquids.
The first container may be made from any physiologically compatible elastic
material such as natural, synthetic, silicone or polyurethane rubbers.
Liquids, L, for use in the practice of the invention include water and aqueous
solutions of pharmaceutically acceptable salts (e.g., saline).
It is sometimes desirable to ascertain the shape, as well as the volume, of
cavities formed in intervertebral discs during discectomy. This can easily be
accomplished using another embodiment of this invention wherein the liquid L
comprises a contrasting composition which causes the cavity to become visible
in an
imaging device. Such indicating compositions include both oil-based and water-
based
media such as iophendylate, meglumine iothalamate, diatriazoate meglumine and
WO 95126689 PCTIIB95100042
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Renogatrin (trademark) mixed with methylene blue. Water-based compositions are
preferred. Such imaging devices include computed tomography (CT) scanners and
magnetic resonance imaging (MRI). A preferred imaging device is a CT scanner
and
a most preferred liquid is 3096 aqueous Renogatrin containing methylene blue.
b
Alternatively, the apparatus can be calibrated as follows:
Outer tube 34, of the apparatus is inserted into a receiving container,
designated
2 and shown in Fig. 4, until a marking thereon indicating a known volume V.
The initial
volume a in container 1 is recorded. Valve 20 is turned so that the bore
thereof is in
the position shown in Figure 1 B. Vacuum is applied to the apparatus, from a
vacuum
source (not shown), through stem 21 of the valve, whereby the balloon 31 is
evacuated
and deflated.
The bore 22 of valve 20 is then turned until it assumes the position shown in
Figure 1 D at which time the liquid L flows from container 1 into the balloon
through the
valve and connecting tubes 13 and 33. As the balloon fills with the liquid it
expands
until it fills the whole empty space of the receiver 2. The volume b in the
container 1
is read and the total volume, VT, of the apparatus, proximally from valve
means 20, and
receiver is calculated as follows:
VT = a - b.
The volume of the apparatus, VA without the receiver, is then:
V"=VT-V.
In use the length of outer tube 34 will be so chosen that its proximal end
does
not extend beyond the inner wall of the annulus. The volume of the apparatus
must
then be recalculated to take into consideration any differences in volume
caused by a
change in the tube's length. The new volume V'" of the apparatus is given by
V',, = VA + YarrD'I
wherein D is the inner diameter of outer tube 34 and I, which may be positive
or
negative is the change in length of the outer tube.
The receiver 2 is then removed from the outer tube 34 and the balloon drained
and deflated through valve stem 21 of valve 20. Outer tube 34 with its
associated
balloon 31 and inner tube 33 are then inserted into the disc 40 through hole
43, as
described above. Container 10 is filled with liquid L until the level a and
the volume
WO 95/26689 ~ ~ ~ ~ ~ ~ ~ PCT/IB95100042
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corresponding to that level is recorded Valve 20 is opened to the position
shown in Fig.
1 D and the liquid flows into the balloon causing it to expand and fill cavity
42 of disc
40. The volume of liquid in container 10 drops to the level c and the volume
corresponding thereto is recorded. The volume V'T of the apparatus and cavity
from
volume 21 is given by b - c. The volume of the disc is then given by V'T - V'A
wherein
V'" is determined as above.
xam le
A). Apparatus and Assembly.
The measuring device consists of a 10 ml syringe (Reorder number 9604,
Becton-Dickinson, Rutherford, NJ 07070) comprising a male Luer fitting at its
distal end,
a bidirectional stopcock (Catalog number G-06464-72, Cole-Palmer, Niles, IL
60714),
a polypropylene extension tube and a small balloon. The bidirectional stopcock
has a
female Luer fitting at one end and a male Luer fitting at the other end. The
female Luer
fitting of the stopcock was connected to the syringe through its male Luer
end. The
extension tube was about 20 mm long, had an inner diameter of about 5 mm, an
outer
diameter of about 6 mm and a female Luer fitting at one end. The small balloon
was
inserted into the extension tube with the closed end of the balloon going into
the Luer
fitting side leaving some of the balloon outside of the tube. The open end of
the
balloon was then stretched and draped over the outside of the tube. Then the
male
Luer end of the stopcock was carefully inserted into the female Luer end of
the
extension tube with the balloon sitting inside of the tube until the tube is
securely
locked into the stopcock. The stopcock was turned to its open position and the
plunger of the syringe was slowly drawn back to create a vacuum in the system.
While
the system was still under vacuum the stopcock was turned to the off position.
The
syringe was then disconnected from the stopcock which maintained the vacuum
inside
of the balloon. The syringe was charged with a known amount of saline without
air in
it and reconnected to the stopcock. The device was ready to use.
B). Device Calibration.
A cavity, of nucleus shape, was created in a plastic block through a -
cylindrical window of about 7 mm diameter and about 10 mm length. The exact
volume
of the cavity was measured by first weighing the empty plastic block and then
weighing
the block with the nucleus shaped cavity filed with water (not to the
cylindrical window).
The difference between these two weights was 4.2 gm. Since the density of
water is
WO 95126689 PCT1IB95/00042
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1, the volume of the cavity is 4.2 cc. The extension tube of the device of
Part A was
inserted into the cylindrical window and the tip of the tube was aligned with
the end of
the window. The initial volume of saline in the syringe, before opening the
stopcock,
was 9.2 cc. After opening the stopcock, the saline was injected into the
balloon. The
balloon expanded until the whole volume of the cavity was filled with the
inflated
balloon. At this point, it was almost impossible to inject more saline into
the balloon.
The volume of saline in the syringe was again determined and found to be 4.8
cc. The
difference between the initial and final readings is the volume injected (4.4
cc). Since
the volume of the cavity is 4.2 cc. Therefore, the device had a dead volume of
about
0.2 cc which should be subtracted from the volume of liquid dispensed by the
syringe
in determining nucleus cavity volumes.
C). Determination of Disc Cavity Volume.
A discectomy was performed on a cadaveric lumbar disc using a pituitary
rongeur. The nucleus materials which were removed during discectomy were
carefuly
collected and weighed. The weight of the removed nucleus material was found to
be
2.4 g., which, assuming the density of the nucleus materials to be about 1,
would
correspond to a volume of about 2.4 ml. The volume of the cavity was then
measured
using the apparatus of section A. The volume of liquid, dispensed by the
syringe, was
2.5 ml. The dead volume of the system, 0.2 ml as determined in section B,
above, to
yield a value of 2.3 ml as the volume of the cavity. This value corresponds,
favorably,
to the volume determined by weighing the removed nucleus materials.
The volumes of the excavated cavities of other cadaveric discs were determined
by the above method. It was found that the directly measured volumes did not
differ
from the weights of the excavated nucleus materials by significant amounts.
Generally
the difference was less than about 0.2 cc. This accuracy is much better than
any other
methods and is good enough for most purposes.
The present invention is not limited to the described example. It is obvious
that
many changes and modifications may be made thereunto, without departing from
the
spirit and scope of the invention.
