Note: Descriptions are shown in the official language in which they were submitted.
~~~'~ ~i~0
The present invention relates to the mixing of
materials in the substantial absence of air. More particularly,
the present invention relates to the preparation of a bone cement
from a solid component and a liquid component by admixing the two
components under vacuum pressure, an apparatus to effect such
mixing and a kit to provide a surgeon with all the necessary
materials to prepare a two-component bone cement substantially
free of entrained air.
Additionally, the present invention relates to a method
1C of preparing a bone cement from a solid component and a liquid
component by admixing the two components under vacuum pressure,
wherein such admixture takes place under a predetermined degree
of chilling so as to control the rate of hardening of the cement,
and subsequently pressurizing the admixture to inhibit
entrainment of gaseous materials.
In many orthopedic surgical procedures, it is
necessary to employ a bonding material to set implants such as
pins and artificial joints in bone. The cement which is employed
for this purpose is generally a polymeric material which is
20 prepared by copolymerization of its components as needed.
Because of the necessity for a fairly quick setting material the
cement is almost universally prepared by a surgical assistant
during the course of the operation in the sterile field of the
operating room. The preparation of the cement involves admixture
of the cement components in a suitable reaction vessel to form a
uniform polymeric reaction product. The cement is usually a
(meth)acrylic material comprising a reaction product of a monomer
1
and a polymer, e.g. methylmethacrylate monomer and
polymethylmethacrylate or methylmethacrylate-styrene copolymer.
In order to provide a cement which has the desired properties and
which has the desired fixation of the implants, it is necessary
that the compounds be uniformly and thoroughly mixed so that a
homogeneous reaction product is produced. During the mixing and
subsequent reaction, there are produced various vapors which may
comprise a gaseous form of a volatile component or a gaseous
reaction product. Because of the noxious (and toxic) nature of
such vapors it is highly undesirable to be exposed to them,
particularly for extended periods of time in the course of
multiple preparations. Since it is necessary that the mixing be
parried out for extended periods of time in order to ensure a
uniform reaction product and a minimum concentration of volatile
reactants, the period of exposure to harmful vapors can be
substantial.
Nonetheless, despite the knowledge of the aforesaid
difficulties, all known techniques for the mixing of bone cements
have serious drawbacks, the most frequent beings
- poor mixing, depending on the individual mixing
technique;
- high exotherm, due to considerable amounts of
monomeric component necessary to produce a workable cement mass
by conventional mixing techniques; and
- creation of porosities, by inclusion and entrapment
of air bubbles as well as by evaporation of excess monomer
resulting in the degradation of the mechanical properties of the
cured cement.
In order to avoid these problems, various attempts to
provide vacuum mixing devices have been made.
2
~~~13~0
U.S. Patent 4,185,072, to Puderbaugh et al., discloses
an orthopedic cement mixer which comprises a mixing vessel within
an evacuable housing and mixing vanes operable from outside of
the housing. The housing is provided with vacuum conduits which
can be connected to a vacuum source for withdrawing vapors andlor
gaseous reaction products from within the housing.
U.S. Patent 4,277,184, to Solomon, discloses a
disposable orthopedic implement for mixing and dispensing bone
cement comprising a chamber having a barrel portion and a neck
portion; a member which is reciprocable within the barrel portion
of the chamber; a mixing member operatively and axially
receivable within the reciprocable member; and means for rotating
the mixing member within the barrel portion of the chamber.
U.S. Patent 4,463,875, to Tepic, discloses an apparatus
for preparing and applying a two-component cement, wherein the
components are vacuum packaged in elongated flexible fluid-tight
compartments and those compartments are confined fn abutting
relation with a seal existing around the abutting portions of the
compartments. In operation, one of the compartments is gradually
collapsed to force its contents to break through the abutting
wall portions into the other compartment while the extension of
the other compartment is controlled as it receives the contents
of the one compartment. Then the other compartment is gradually
collapsed to force its contents into the one compartment while
controlling the extension of the one compartment. The two
compartments are alternately collapsed and controlledly extended
until the components therein form a homogeneous cementitious
mixture. A nozzle is then attached to one of the compartments in
lieu of the other compartment and the one compartment is
collapsed to expel the mixture through the nozzle.
3
~04~300
Published Tnternational Patent Application WO 84/03830,
to Himeno, discloses an apparatus for mixing a bone cement
wherein the solid component of a bone cement is sealed in a
flexible bag along with a sterilizing gas. The gas is then
withdrawn through a hypodermic needle to evacuate the gases
within the bag. The liquid component of the bone cement is then
injected into the bag, and the bag kneaded to mix the cement.
After kneading the bag may be opened to remove the ready-to-use
cement.
U.S. Patent 4,551,135, to Gorman et al., discloses a
syringe for extrusion of a semi-plastic mass. The syringe is
designed so as to permit the mixing of two components of a
plasticizable mixture within the syringe barrel, i.e. a liquid
component may be injected into the syringe barrel containing
particulate solids while venting air therefrom or a liquid
component may be drawn into the syringe barrel which is only
partially filled with particulate solids.
European Published Patent Application 0 178 658 (and
U.S. Patent 4,721,390), to Lidgren, disclose a method for
producing bone cement for fixing prostheses. In order to prevent
large amounts of air from being stirred into the mixture, mixing
of the bone cement components occurs under vacuum. Preferably
the bone cement components are mixed in a feed device from which
the mixture may be pressed out, and to effect this aspect of the
invention there are provided an agitator which is connectable to
the feed device and a vacuum source which is also connectable to
the feed device.
Published Tnternational Patent Application WO 86/06618,
to Tepic, discloses a method of preparing a two component cement
wherein the evacuated interepaces between powder component
4
~~41300
particles are flooded with liquid component, followed by
mechanical homogenization of the resulting mass. The method is
preferably performed in a syringe-type container whereby the
liquid component in an ampoule is injected through the piston
member of the syringe, and the syringe is fitted with an axially
collapsible mixing element, so as to not interfere with movement
of the piston for extrusion of the cement from the syringe.
U.S. Patent 4,671,263, to Draenert, discloses a device
for applying bone cement wherein the bone cement, prior to its
application, is prepressurized at an adjustable pressure and then
applied at a controllable pressure. The prepressurization
suppresses bubble formation in the bone cement and the
controllable pressure aids desired stratification of the bone
cement around the prosthesis during application.
The brochures "MIT VAC~ Vacuum Mixing System" and
"ZIMMER~ Vacuum Mixing System" (Copyright 1996) both disclose a
bone cement mixing system providing a vacuum pump and either an
evacuable mixing bowl; or an evacuable housing (with mixer), for
mixing in a cartridge for a bone cement gun.
The brochure "DePuy Vacu-Mix~ Orthopedic Cement Mixing
System" (April 1977) discloses an open housing, for a mixing
bowl, which may be connected to a vacuum pump so as to draw off
vapors from above the mixing bowl.
The brochure "Stryker~ Mix Evac~" (copyright August
1978) discloses a disposable enclosed housing which comprises a
mixing vessel within a housing, a cover for the housing and a
mixing element operable through the cover. The housing may be
connected to a vacuum supply to draw air through the cover and
out through the housing thus preventing monomer vapors from being
released to the operating room atmosphere.
5
~~4i3~0
The advertisement "The Simplex Enhancement Vacuum
Mixer", JBJS, No. 2, 69-A, February 1987, discloses an evacuable
housing, having a cover equipped with an externally operable
mixing element, which will held a bone cement gun cartridge for
mixing of bone cement in the cartridge. The housing may be
connected to a vacuum source to allow mixing under vacuum
pressure.
The brochure "ZIMMER ~ Cement Centrifugation System'°
(Copyright 1984) discloses a syatem wherein after mixing of the
bone cement, the bone cement is placed in a cartridge for a bone
cement gun and centrifuged to help decrease cement porosity.
Numerous other devices have been conceived for the
conduct of mixing operations under a controlled atmosphere or
under vacuum. Illustrative of such devices are U.S. Patent
2,453,914, to Hollenback, which discloses a device for mixing
plaster compounds comprising a bowl, a cover for said bowl which
carries an externally operated mixer for the agitation of the
bowl contents and an orifice for attachment to a vacuum source to
de-aerate the bowl contents.
U.S. Patent 2,696,022, to Steinbock et al., discloses
an investment mixer comprising a mixer bowl, a cover therefor, an
agitator extending through the cover, and a fitting on the cover
for connection to a vacuum source.
U.S. Patent 2,973,187, to Wehmer, discloses a vacuum
spatulator comprising a mixer bowl, a cover therefor, an agitator
extending through the cover, and a fitting whereby the covered
bowl may be placed under vacuum.
U.S. Patent 3,131,912, to Steinbock, Jr., disclosea an
investment mixer comprising a mixing bowl, a cover for the mixing
bowl, an externally operated agitator extending through the
6
_%
mixing bowl, and a fitting on the cover allowing evacuation of
the atmosphere in the mixing bowl by connection to a vacuum
source.
U.S. Patent 3,343,817, to Carangelo et al., discloses
an apparatus for mixing materials in the absence of air
comprising a mixing bowl having an externally operated agitator
in the bottom thereof and a piston receivable within the mixing
bowl. The piston has an aperture therein so that, when it is
lowered into plane on materials to be mixed in the bowl, air
caught below the piston is expelled. When the piston contacts
the surface of materials to be mixed, the aperture is closed and
agitation initiated.
U.S. Patent 3,358,971, to Steinbock, Jr., discloses an
investment mixer comprising a mixer bowl, a cover therefor, an
agitator extending through said cover into said mixing bowl and
an aperture for removing gases within the mixing bowl by
connection to a vacuum pressure supply.
U.S. Patent 3,559,961, to Bergendal, discloses an
apparatus for the preparation of dental amalgams comprising a
container of two halves, one of which is fitted with an outlet
connectable to a vacuum pressure supply. Components to be formed
into an amalgam are placed within the container, the container
atmosphere is evacuated, and the evacuated container is then
agitated to mix the contents thereof.
U.S. Patent 3,610,586, to Price et al., discloses a
dental mixing system in which prepackaged ingredients to be mixed
for dental applications are stored within a container which
maintains the ingredients isolated from each other prior to
usage. The ingredients axe intermixed by placing the container
in a mixing device which rotates the base of the container while
7
~04i300
maintaining the cover stationary. A knife portion integral with
the container bottom severs an isolating membrane stretched over
a portion of the cover, during operation of the mixer, and
permits the ingredients to mix. 'Phrough rotation of the
container bottom, a homogeneous mixture is realized with a mixing
paddle integral with the stationary container top or cover.
U.S. Patent 3,640,510, to Lea, discloses a vacuum
mixing system for dental materials comprising a closed container,
an externally operated rotary stirring device therein and means
for applying vacuum pressure to the contents of the closed
container.
U.S. Patent 4,199,866, to Drury, discloses a dental
amalgamator which prevents mercury vapor, given off during
amalgamation, from polluting the air in the neighborhood of the
amalgamator. The amalgamator comprises a casing carrying a
capsule holder and a drive means for the holder, a lid movable to
a closed position in which it cooperates with the casing to form
an enclosure for a capsule held by the holder, the enclosure
having air inlets allowing air to flow from the atmosphere into
the enclosure. A vacuum pump is arranged to communicate with the
enclosure via a mercury filter medium, so that during
amalgamation air is drawn into the enclosure, over the capsule,
and then through the mercury filter where mercury vapors are
removed.
Nonetheless, a need continues to exist for a simple
two-component bone cement mixing system, which will allow mixing
under vacuum but which will require little in the way of
equipment. Moreover, a need also exists for a vacuum mixing
system which can be readily manipulated without fear of premature
loss of vacuum.
a
..
i~~~~.a~~~
In a first embodiment, the present invention provides
a two-component bone cement mixing system comprising:
' (A) a cartridge mixer means, having an interior volume
bontaining a first predetermined quantity of a free-flowing,
owdery, solid bone cement component under vacuum pressure, for
fixing said first predetermined quantity of a solid bane cement
omponent with a second predetermined quantity of a liquid bone
Cement component in the substantial absence of air to form a
third predetermined quantity of a fluid two-component bone
cement wherein the interior volume of said cartrid a mixer
~ g
means, measured in cubic centimeters, is represented by Vcm, said
first predetermined quantity of a free-flowing, powdery solid
bone cement component has a volume, measured in cubic
centimeters, represented by Vbc and Vcm/Vbc is about 1.5 to 3.5;
(B) container means, containing said second
predetermined quantity of a liquid bone cement component, for
holding a liquid bone cement component;
(C) fluid transfer means, operably connectable to said
cartridge mixer means and said container means, for fluidically
connecting said container means and said cartridge mixer means to
transfer said second predetermined quantity of a liquid bone
cement component from said container means to said cartridge
mixer means;
(D) plug means, receivable within said container
means, for automatically hermetically sealing said fluid transfer
means against passage of a material therethrough upon completion
of the transfer of said second predetermined quantity of a liquid
bone cement component from said container means to said cartridge
mixer means therethrough.
9
In a second embodiment, the present invention provides
a cartridge mixer, having an interior volume, useful fox the
mixing of a first predetermined quantity of a free-flowing,
powdery, solid bone cement component with a second predetermined
quantity of a liquid bone cement component to form a third
predetermined quantity of a fluid two-component bone cement,
wherein the interior volume of said cartridge mixer, measured in
cubic centimeters, is represented by Vcm, said first
predetermined quantity of a free-flowing, powdery solid bone '
cement component has a volume, measured in cubic centimeters,
represented by Vbc and Vcm/Vbe is about 1.5 to 3.5, said
cartridge mixer comprising
cartridge means, receivable within a bone cement gun,
for containing said third predetermined quantity of a fluid two-
component bone cement, said cartridge means including piston
means, operatively engageable by said bone cement gun and
moveable within said cartridge means, for dispensing of said
fluid two-component bone cement from said cartridge means;
mixer means, detachably connected to said cartridge
means, for agitating the contents of said cartridge means, said
mixer means including inlet port means for passage of a second
predetermined quantity of a liquid bone cement component into
said cartridge mixer;
hermetic sealing means for sealing said connected
cartridge means and mixer means against the ingress of air.
In a third embodiment, the present invention provides a
two-component bone cement kit comprisingt
(A) a vacuum packed cartridge mixer, defining an
interior volume, containing a first predetermined quantity of a
free-flowing, powdery, solid bone cement component, wherein the
~41300
interior volume of said cartridge mixer, measured in cubic
centimeters, is represented by Vcm, said first predetermined
quantity of a free-flowing, powdery solid bone cement component
has a volume, measured in cubic centimeters, represented by Vbc
and Vcm/Vbc is about 1.5 to 3.5, said cartridge mixer comprising:
a cartridge member, receivable within a bone
cement gun, comprising a hollow, air-impermeable cartridge body
member having a longitudinal axis, and a first open end and a
second open end spaced apart on said longitudinal axis,
an air-impermeable piston member, axially slidable
within said hollow cartridge body, disposed within said cartridge
body, proximate said first end of said cartridge body, to close
said first end of said cartridge body,
releasable hermetic sealing means for releasably
hermetically sealing said piston member to said cartridge body
proximate said first end of said cartridge body,
a mixer member comprising a hollow,. air-
impermeable mixer body having a longitudinal axis, and a first
open end and a second open end spaced apart on said longitudinal
axis,
releasable connection means for releasably
coaxially hermetically sealingly connecting said second end of
said cartridge body member to said second end of said mixer body
for fluidic communication between said cartridge body member and
said mixer body, and
cap means for hermetically sealing said first end
of said mixer body, said cap means including
self-sealing aperture means, pierceable by a
hollow needle, for fluidic communication with said interior
volume of said cartridge mixer through said hollow needle when
11
'..
~041,~00
pierced by said hollow needle and hermetically sealed closure of
said interior volume when said hollow needle is withdrawn, and
mixing means for agitating a material
contained within said interior volume of said cartridge mixer;
(B) an ampoule, defining an interior volume,
containing a second predetermined quantity of a liquid bone
cement component, said ampoule comprising a liquid bone cement
component impermeable body member having a longitudinal axis,
spout means, having a predetermined diameter, for fluidic
communication with said interior volume of said ampoule and
removable closure means for hermetically sealing said spout
means;
(C) an injector comprising
a hollow injector body member having a
longitudinal axis and a first open end and a second open end
spaced apart on said longitudinal axis, said hollow injector body
member slidingly, coaxially receivable of said ampoule,
a cap member, disposed on said second open end of
said hollow injector body for closure thereof, said cap member
including a fluid conduit, coaxial with said hollow injector
body, for passage of a fluid through said cap member,
hollow needle means, pierceable of said self-
sealing aperture means, hermetically connectable to said fluid
conduit, for passage of fluid into said interior volume of said
cartridge mixer,
resilient support means, hermetically sealingly
connecting said second end of said hollow injector body and said
cap member, for engagingly contacting said ampoule, said
resilient support means including a fluid passage tapering toward
and fluidically connected to said fluid conduit, said fluid
12
~0~3.~00
passage coaxial with said hollow injector body and receivable of
said ampoule spout means; and
(D) float means, having a specific gravity less than
said liquid bone cement component, for hermetically sealingly
closing said fluid passage in said resilient support means.
Figure 1 is a schematic, partially sectioned,
illustration of a double vacuum-packed cartridge mixer according
to the present invention.
Figure 2 is an isometric view of a bone cement
cartridge according to the present invention.
Figure 3 is a schematic, partially sectioned,
illustration of a first embodiment of a releasable hermetic
closure for a piston of a bone cement cartridge.
Figure 4 is a schematic, partially sectioned,
illustration of a second embodiment of a releasable hermetic
closure of a piston of a bone cement cartridge.
Figures 5A and 5B are schematic, partially sectioned,
illustrations of a third embodiment of a releasable hermetic
closure of a piston of a bone cement cartridge.
Figure 6 is an illustration of a container for liquid
bone cement component.
Figure 7 is a schematic, partially sectioned,
illustration of a liquid bone cement injector according to the
presently claimed invention.
Figure 8 is a sectional view of a bone cement gun
containing a bone cement cartridge.
Figures 9A and 3B are schematic, partially sectioned
illustrations of a pressure gauge for prepressurization of a bone
cement cartridge.
13
~0~1300
Figure 10 is a sectional view of the application of
bone cement to a bone cavity in a bone.
Figure 11 is a view partially in section illustrating
the deposition of bone cement into the femoral canal.
Figure 12 is a sectional view illustrating
pressurization of bone cement in the federal canal.
Figure 13 is a detailed view of the capped end of the
mixer body.
Figure 14 is a plan view of the underside of the cap
fixed on the first open end of the mixer body.
Figure 15 is a plan view of a protective disc mounted
on the underside of the cap fixed to the first open end of the
mixer body.
Figure 16 is a plan view of the mixing element
according to the present invention.
Figure 17 is an illustration of a technique for testing
for operability of the bone cement prepared according to the
present invention.
It is common practice, in joint surgery today, to
2C anchor components of replacement joints by using a bone cement
comprising a two-component resin which polymerizes during the
operation at normal temperatures and which, on account of its
properties, leads to an interlocking of the prosthesis component
in the bony sheath. Because of its physical properties, the
bone cement shrinks onto the prosthesis resulting in a closed
metal-to-cement contact.
The bone cements commonly used are
polymethylmethacrylate consisting of tree-flowing, powdery bead
polymers which are superficially dissolved by liquid monomers and
14
Lr
~0 .41300
embedded during the polymerization process. During mixing, the
polymer is immersed in the monomers. The polymethylmethacrylate
beads are superficially dissolved and embedded in a composite
manner. Such a composite structure can be compared with
concrete, where air bubbles are likewise included during mixing.
Moreover, when the monomer immerses. the polymer beads, filling
defects remain. These defects are termed "lee phenomena".
Furthermore, in the case of bone cements, the monomer liquid
evaporates during the exothermic polymerization, whereby further
bubbles are formed. The bubbles formed as mentioned above
constitute the major portion of the gas enclosures in bone
cements.
The chemical reaction of the above-mentioned bone
cements is initiated by a starter reaction, wherein, typically,
dibenzoyl peroxide is activated by an activator such as p-
aminotoluidine and then the radical chain polymerization is
started. This polymerization proceeds exothermically: The
monomer itself is stabilized by hydroquinone. Some bone cements
are further stabilized by chlorophyll with simultaneous coloring.
The storability of the monomer liquid van also be stabilized by
vitamin C.
In the processing phase, following the mixing phase,
the bone cement is applied to the femoral medullary canal or to
the bony acetabulum which are both prepared to anchor the
cemented prosthesis components; the application of the bone
cement is normally performed by hand and sometimes using a
syringe.
Using a syringe, the cement anchorage in the bone can
be markedly improved. Therefore, so-called "bone cement guns"
have been proposed, the principal of which is to impact the
~0~1~00
cement in the plugged medullasy canal to provide transverse
anchorage. With bone cement guns, the filling of the bone
bedding is performed in different ways. On the one hand, filling
is done from above in the downward direction or, on the other
hand, it is also performed in the other direction, i.e, upwardly
from below, by means of a long nozzle.
With the aforementioned techniques in mind, the
present invention provides a two-component bone cement mixing
system which allows preparation of the twa-component bone cement
under vacuum pressure, whereby gaseous inclusions are minimized,
and further allows the preparation of the bone cement in a
cartridge which may then be directly loaded into a bone cement
gun for immediate operative use. '
Turning now to Figure 1 of the drawing, there is
generally indicated at 1 a double vacuum-packed cartridge mixer
according to the present invention. The cartridge mixer
comprises a cartridge member 3 and a mixer member 5 which are
detachably connected to each other. The cartridge member 3, as
best seen in Figure 2, comprises a hollow, air-impermeable
cartridge body member 9 having a flange 11 at one end thereof
along with a collar 13 whereby the cartridge body member may be
mounted in a bone cement gun, as best seen in Figure 8. The wall
of the cartridge body member 9 may be reinforced with ribs 15 for
added strength.
An air-impermeable piston member 17 ie disposed within
the cartridge body 9 proximate a first end 19 thereof so as to
close the first end of the cartridge body member 9. The piston
member 17 is axially slidable within the hollow cartridge body 9.
The mixer member 5 comprises a hollow, air-impermeable
mixer body 21 having a first open end 23 and a second open end
16
embedded during the polymer
20 .4300
25. The second open end 25 of the mixer body member 21 is
provided with an internal screwthread (not.shown) which is
threadingly engageable of a screwthread 27 formed on the exterior
of the second open end 7 of cartridge body member 9. By
providing an O-ring 29 abutting the reinforcing rib 15' a
releasable coaxial hermetic seal of the cartridge body member to
the mixer body member may be obtained when the cartridge body
member and the mixer body member are threadingly engaged with one
another. Of course, any other form of detachable connection
capable of forming a hermetic seal may also be utilized, e.g., a
snap-tit with O-ring sealing element. In a similar manner, the
cap 31 in combination with an O-ring 33 hermetically seals the
first end 23 of the mixer body member 21. The cap 31 includes an
aperture 35 which is closed by a self-sealing element 37 such as
a rubber septum. The cap 31 is also provided with an additional
aperture 39 through which the shaft 41 of a mixing element 43
passes. The shaft 41 is axially moveable in the aperture 39 and
may also be rotated within the aperture 39. As may best be seen
in Fig. 13, the aperture 39 is surrounded by an upstanding,
circumferential wall 32 which forms a chamber 34 receivable of a
plurality of alternating O-rings and washers (two O-rings 36 and
38 and one washer 40 being illustrated). The chamber 34 is
closed by a cap member 42 which is threadingly engageable with
the outer circumference of wall 32, the cap member 42 having an
aperture 44 therein to allow passage of shaft 41 therethrough.
The use of multiple O-rings alternating with washers (to form a
packing box) is necessary in order to allow for reciprocal
movement of shaft 41 while maintaining vacuum pressure within the
mixer. The underside of the cap 31 (as best seen in Fig. 14) has
a number of interconnected grooves 48 formed therein, with at
17
204100
least one of the grooves communicating with aperture 35. A
porous membrane 47, e.g., a filter paper, is disposed over the
underside of cap 31 so as to cover the grooves 48. The porous
membrane 47 has an aperture 50 formed therein so as to permit
passage of shaft 41 therethrough. The porous membrane 47 is in
turn covered by a protective disc 52 (as best seen in Fig. 15).
The protective disc 52 has a central aperture 54 to permit
passage of shaft 41 therethrough. The protective disc 52 is
additionally provided with a plurality of apertures 56 (which may
vary in size, shape and pattern). The protective disc 52
protects the porous membrane 47 from being torn by mixing element
43. The function of the grooves 48, the porous membrane 47 and
the protective disc 52 will be explained hereinbelow. As best
seen in Fig. 16, the mixing element 43 comprises a plate 60
disposed substantially perpendicular to the shaft 41 and
conforming substantially to the internal arose section of the
cartridge body member and the mixer body member. The mixing
element 43 has a number of holes 62, 64 formed therein so as to
allow the mixer element to be reciprocated back and forth
through a body of polymeric material 46 contained within the
cartridge body member 9. The shaft 41 is provided with a
manually graspable handle 45 so as to facilitate manipulation of
the mixing element 43. In a preferred embodiment, the holes 62,
64 are circular in shape and disposed symmetrically about the
plate 60 relative to the shaft 41 (which is concentric with the
plate 60). The plate 60 is also circular in shape, and pairs of
holes (one larger 64 and one smaller 62) are disposed on
diameters of the plate and opposite one another relative to the
center of the plate. Most preferably, three pairs of holes are
used disposed on diameters of the plate which are offset 60° of
18
2~4~~4~
arc from the adjacent diameters upon which holes are disposed;
and each large hole 64 is immediately adjacent to two small holes
62 on the immediately adjacent diameters upon which holes are
disposed. The centers of the smaller holes 62 all fall on the
circumference of a first circle concentric with the plate 60; and
the centers of the large holes 64 all fall on the circumference
of a second circle concentric with the plate 60. Preferably, the
diameter of the first circle ie larger than the diameter of the
second circle.
In use, the cartridge member 3 is loaded with a
predetermined amount of a free-flowing, powdery polymeric
component 46 having a non-compacted volume, measured in cubic
centimeters, represented by Vbc, and the mixer member 5 is then
screwed onto the cartridge member so as to form a closed,
container having a volume, measured in cubic centimeters,
represented by Vcm. The ratio Vcm/Vbc is about 1.5 to 3.5,
preferably about 2.0, for reasons more fully explained
hereinafter. A hypodermic needle connected to a source of vacuum
pressure is then inserted through the rubber septum 37 in'
aperture 35 and a vacuum ie drawn within the cartridge mixer.
Care must be taken so that the tip of the needle may enter the
groove 48 but does pierce the porous membrane 47. This is
because the powdery polymeric material would otherwise be sucked
up through the needle and block further evacuation of air. The
grooves 48, accordingly, allow a uniform application.of vacuum
across the cross-section of the mixer, while the porous membrane
47 prevents powdery polymeric material from being withdrawn from
the mixer along with the air. The protective disc 52, in turn,
prevents the mixer element 43 from damaging the porous membrane
during handling prior to evacuation. Typically, a vacuum
19
2~4130
pressure of 30 millimeters of mercury or less is drawn in the
cartridge mixer. The vacuum packed cartridge mixer is then
vacuum packed within a container 49, such as an air-impermeable
plastic bag. This double vacuum packing helps to assure a long
and stable shelf life.
In order to provide a hermetic seal of the cartridge
mixer, it is necessary that the piston member 17 be hermetically
sealed also. However, the piston member 17 must also be axially
slidable within the cartridge body member 9 so as to be capable
ZO of forcing the fluid bone cement from the cartridge member when
the cartridge member ie mounted in a bona cement gun. In other
words, the piston member is not fitted within the cartridge
member in an air tight manner, but rather just sufficiently tight
to prevent leakage of the viscous cement mixture thereby.
Accordingly, a releasable hermetic seal is necessary for the
piston member. In this regard, Figure 3 illustrates one
embodiment of a releasable hermetic seal for the piston member 17
wherein a bead 51 of adhesive seals the piston in place. When
the piston is engaged by the plunger of a bone cement gun, the
20 bone cement gun plunger develops sufficient force to break the
bead and allow movement of the piston through the cartridge body
member 9. In a second embodiment, illustrated in Figure 4, a
thin layer of a resinous material 53 (e.g., polyethylene) is
disposed over the piston member 17. In a manner similar to that
of embodiment Figure 3, the thin layer resinous material 53 may
be broken by actuation of the plunger of a bone cement gun.
In a further embodiment, illustrated in Figures 5A and
5B, a thin diaphragm layer 55, e.g. of polyethylene, which is
air-impermeable, is disposed across the first end 19 of cartridge
30 body member 9 as shown in Figure 5A to form the hermetic seal.
~~41304
When a vacuum is drawn in the interior of the cartridge mixer,
the diaphragm layer 55 is bowed at 57 as shown in Figure 5B.
This embodiment not only provides a releasable hermetic seal,
which may once again be broken by the actuation of the plunger of
a bone cement gun, but also provides an indicator as to the
maintenance of vacuum pressure within the cartridge mixer. In
this regard, if the diaphragm layer 55 is bowed as shown in
Figure 5B, then this is a clear indication that vacuum pressure
has been maintained within the cartridge mixer. If, however,
after standing for long periods of time, a user finds tha
diaphragm layer 55 in the position illustrated in Figure 5A, then
this is a clear warning that vacuum pressure has been lost.
The liquid bone cement component 59 is preferably
contained within a glass ampoule 61 due to the noxious and toxic
nature of the liquid bone cement component, i.e. a (meth)acrylate
monomer. The glass ampoule 61 comprises a body member 63 having
a spout 65 and a removable closure 67 which may be broken off at
the weakened neck 69 of the ampoule when desired.
An injector 71, as illustrated in Figure 7, is utilized
to transfer monomer to the interior of the cartridge mixer. The
injector comprises a hollow injector body member 73 having a
first open end 75 and a second open end 77. The injector body
member 73 is coaxially receivable of the ampoule 61.
A cap 79 is disposed over the second open end 77 of the
injector body 73 for closure thereof. The cap member 79 includes
a fluid conduit 81, coaxial with the hollow injector body member
73, for passage of a fluid through the cap member. A hollow
needle 83 is hermetically connectable to the fluid conduit 81 so
as to allow a fluid medium to pass from the conduit 81 through
the hollow needle. A resilient support 85, e.g., of silicone
21
7
'~J
20~413~D0
rubber, hermetically, sealingly conneots the second end of the
hollow injector body and the cap member. Additionally, the
resilient support ie provided with a fluid passage tapering
toward and fluidically connected to the fluid conduit 81 in the
cap member 79. When the opened ampoule 61 is inserted into the
hollow injector body member 73, and the assembly then inverted to
the position of Figure 7 the resilient support 95 supports the
ampoule and the spout portion 65,of the ampoule is received
within the fluid passage 87.
It should be noted that temperature control is an
important part of the mixing process. For the "dough" type
cements in current use, such as Simplex ~ and Zimmer-Regularm, it
has now been found that chilling the mixing container and the
cement components aids in the prevention of excessively fast
curing. In particular, when mixing cements under a vacuum
pressure of 30 mm Hg or less, it has now been found desirable to
chill the mixer and the cement components (powder and liquid) to
a temperature below room temperature (20°C), preferably less than
15°C, most preferably to about 12°C (+2°C), prior to
bringing the
solid and liquid components together in the mixer. This chilling
is believed to be necessary due to the fact that, under vacuum
pressures of 30 mm Hg or less, oxygen, which normally interacts
with monomer free radicals to slow the polymerization of the
monomer, is in short supply and will not effectively inhibit the
polymerization reaction. In this regard, a thermometer or a
temperature indicating strip, e.g., of the liquid crystal type,
could be packaged with the mixer so as to allow the user to
ascertain whether the mixer and its contents have been
sufficiently chilled prior to use.
22
..
Prior to insertion of the opened ampoule 61 into the
injector body member 73, a polyethylene ball 89 is placed in the
ampoule, the polyethylene ball having a specific gravity less
than the monomeric material and thus floating on the surface of
the monomeric material. When the injector 71 is inverted so as
to insert the needle 83 through the rubber septum 37 of the
cartridge mixer, so as to inject monomeric material into the
vacuum packed polymeric material contained therein, the
polyethylene ball B9 will float on the surface of the monomer as
illustrated in Figure 7. As the monomer is drained from the
ampoule 61 through fluid passage 87, fluid conduit 81 and hollow
needle 83 into the cartridge mixer, by the vacuum pressure
maintained in the cartridge mixer, the polyethylene ball will
drop downward with the surface 91 of the liquid monomeric
material. When the monomeric material is drained from the
ampoule the polyethylene ball 89 will then hermetically seal the
fluid passage 87 formed in the resilient support 85. This will
prevent any air being drawn into the cartridge mixer around the
edge of the ampoule 61 and between the ampoule 61 and the hollow
body member 73. Thus, personnel transferring monomer to the
polymeric material in the cartridge mixer are not required to
closely monitor the progress of such transfer as they are with
conventional syringe techniques or conventional stop cocks. In
other words, when the contents of the ampoule are emptied, the
fluid passage 87 is automatically sealed by the polyethylene ball
89 acting as a floating plug. Once transfer of the monomer has
been completed, the needle 83 may be withdrawn from septum 37,
and mixing of the two-component bone cement may then be conducted
within the cartridge mixer. When the hollow needle is withdrawn
from the cartridge mixer, air rushing through the hollow needle
23
2~4~,~~0
B3 will violently disengage the polyethylene ball 89 from the
fluid passageway 87 in resilient support 85,. This violent
disengagement will cause the polyethylene ball 89 to bounce
around within the empty ampoule 61. The noise so-produced is a
further indication that a successful transfer of monomer into the
cartridge mixer has been parried out without leakage of air into
the cartridge mixer.
Tn regard to the above, vacuum evacuation of the
ampoule is ensured by the provision of a ratio of the interior
volume of the cartridge mixer (Vem), measured in cubic
centimeters, to the volume of the first predetermined quantity of
a free-flowing, powdery solid bone cement component (Vbe),
measured in cubic centimeters, in the range of Vcm/Vbe of about
1.5 to about 3.5, preferably about 2Ø This is because the
free-flowing, powdery solid bone cement component hae an
interstitial volume (free volume between solid particles) which
is about 40-50% of its total volume. If the cartridge mixer were
filled with the free-flowing powder, then liquid cement component
transfer to the cartridge mixer and evaporation of liquid monomer
under the low pressures therein would quickly equalize pressures
between the cartridge mixer and the ampoule which, in turn, would
eliminate the driving force for liquid transfer from the ampoule
to the cartridge mixer. This would prevent complete transfer of
the ampoule contents to the cartridge mixer, even though tha
"free volume" of 'the powder may have been sufficient to contain
the liquid volume of the ampoule contents. In order to provide
sufficient volume in the cartridge mixer to allow complete
transfer of the ampoule contents to the mixer, it has been found
desirable to provide a cartridge mixer having an interior volume
which is 1.5 to 3.5 times, preferably about 2.0 times, that of
24
~0~~300
the powdery component contained therein. This "excess free
volume" allows complete transfer of the required quantity of the
liquid component, previously placed in the ,ampoule, for the
quantity of the powdery component, previously placed in the
cartridge mixer.
Mixing is readily effected by merely causing
reciprocating motion of the mixing element 43 axially within the
cartridge mixer. Mixing may be further facilitated by some
rotation of the handle 45 during the reciprocating motion of the
mixing element 43.
After mixing is completed, rubber septum 37~may then be
pierced with a hollow needle so as to release the vacuum pressure
within the cartridge mixer. Alternatively, the mixer member 5
may be provided with a vent hole 12 (shown as formed in the mixer
body 21, but also could be provided in the cap 31) hermetically
sealed with a pressure-sensitive adhesive tape 14; and it would
only be necessary to peel away the tape to open vent hole 12 and
release the vacuum. The mixer member 5 may then be detached from
the cartridge member 3 and a suitable sap 93, as beet seen in
Figure 8, may be placed over the second open end 7 of the
cartridge body member 9. The cartridge body member 9 may then be
fitted in a conventional bone cement gun 95 as illustrated in
Figure e.
The bone cement may then be utilized in a normal
fashion, or, it may be subjected to a prepressurization
treatment, which has bean found to be effective in certain
instances. In this regard, it should be noted that in order to
minimize the amount of air entrapped in the viscous mixture as
air bubbles, the mixer is maximally evacuated of air. When the
liquid monomer component of the bone cement is introduced into
v.~
the mixing chamber, a small amount of the monomer will evaporate
and equilibrate at the partial vapor pressure of the liquid
monomer at that temperature. However, turbulence created by the
mixer element during mixing, i.e. cavitation, will cause the
monomer to boil. With higher vacuums, the mixture "cavitates"
more easily. The monomer which boils under these conditions, and
hence the bubbles of gaseous monomer formed in viscous mixture
will only partially collapse when the vacuum is released, and may
require a significant amount of time to collapse fully. Since
most bone cements harden within about 8 to 15 minutes of mixing,
the monomer bubbles may not have fully collapsed before
hardening. Moreover, the heat of polymerization generated during
the curing of the bone cement may actually cause the partially
collapsed gaseous monomer bubbles to re-expand. Therefore, it
has been found to be desirable to pressurize the bone cement
shortly after release of the vacuum, but prior to use, hence the
name "prepressurization" to accelerate the complete collapse of
bubbles of gaseous monomer.
In order to effect the prepressurization treatment,
the present invention provides a special pressure gauge cap 97
which may be fitted over the second open end 7 of the cartridge
body member 9.
As illustrated in Figure 9A, the cap 97 comprises a
flexible membrane 99 having two protrusions 101, 103 extending
substantially perpendicular therefrom; and a flange member 105
which may be screwed onto the end of the cartridge body member.
The flange member incorporates an arcuate gauge element lOT
having predetermined indicia 109 and 111 formed thereon. When
the cartridge body member is mounted in the bone cement gun and
subjected to pressure by movement of the plunger of the bone
26
~Wr
2041300
cement gun and aonoomitant movement of the piston member of the
cartridge member, the increase in pressure causes distension of
the membrane 99, as best seen in Figure 9B. The distension of
this membrane member causes the protrusions 101 and 103 to
effectively bend outwardly away from one another and the degree
of this bending is indicative of the internal pressure developed
in the cartridge body member. By applying pressure until such
time as the indicia 109 and 111 are substantially alic3ned with
the protrusions 101 and 103, respectively, a predetermined
pressure may be developed within the cartridge body member.
After maintaining the pressure, e.g. 75 psig, fox a predetermined
period of time, the pressure may be released and the cap 97
removed.
In operation, a closure cap 120 may then be connected
onto the open end 7 of the cartridge 9, as illustrated in Figure
10, and a tip 121 is selected for the particular type of
operation and is engaged with the front closure cap 120. (At
this point, it ie recommended that the first few cc°s of the
cement be wasted by squeezing the handle of the cement gun. This
would allow the surgeon a feel of the flow (viscosity) of the
cement from the nozzle of the cement gun prior to injecting it
into the patient. If the cement is too stiff, the surgeon should
abandon the use of the cement. Alternatively, the temperature of
the cement is indicative of the degree of cure and the
temperature may be used as the determinative factor in whether or
not the cement should be utilized. In this regard, as shown in
Fig. 17, a temperature sensitive tape, e.g., of the liquid
crystal type, 150 may form the wall of a small container into
which a few cc's of cement 152 is injected. Depending upon the
type of cement utilized, the tape will have a temperature range
27
2041:00
in which further utilization of the cement is permissible ("OK")
and above a certain temperature further utilization of the cement
is not permissible ("ABORT"). One indicia, "OK" or "ABORT", only
will be readily visible depending on the temperature of the
cement. The engagement between the front closure cap 120 and
the cartridge body member may be by means of a snap fit, an
internal threading or an external threading. When a prosthesis
is to be cemented to a plateau-type surface, holes 122 may be
drilled into the bone surface to create a cavity into which bone
cement 123 is to be injected, as shown in Figure 10. An
appropriate tip is selected which is configured to interfit with
the opening of the bone cavity. The end of the tip is tapered
inwardly to terminate in a portion having a diameter less than
Ithe diameter of the bone cavity. This allows the tapered portl.on
of the tip to be inserted into the bone cavity and form a seal
(about the diameter of the bone cavity. Thus, the cement is
.injected into a closed space so that pressure can build up to
force the cement to penetrate the trabeculae of the bone. Cement
is also deposited over the remaining bane surface to which the
prosthesis is to be attached. -
In the case of a long tubular bone canal, some type of
plug as shown in Figure 11 must be lodged in the canal to create
a closed space to prevent the extension of bone cement beyond the
point where it is useful and to facilitate more complete filling
and pressurization of the canal. Various means of plugging the
canal have been advocated, including plugs made of natural bone,
polyethylene or a bolus of doughy bone cement. Initially, a
long straight tip 121b, which has a diameter less than the
diameter of the canal to allow the tip to project into the bone
canal, is used to deposit bane cement into the long bone canal.
28
2~~130n
This tip 121b does not have a tapered end since the canal is
initially just being filled up. Then, a tip such as the femoral
canal pressurizer 140 and adapter 141, as shown in Figure 12, is
used to complete the filling of the canal and pressurize the
contents of the cavity. The tapered pressurizer seals off the
canal thereby enabling the pressure created upon injection of the
cement to force the cement to penetrate the bone.
Throughout the specification, r~ference has been made
to the air-impermeability of certain materials of construction
which are utilized in the present invention. It should be noted
that this terminology does not require perfect air-
impermeability, however, it does require a degree of air-
impermeability sufficient to prevent any significant loss of
vacuum pressure through the material over the expected storage
life of the vacuum packed materials, e.g. six months.
The mixing system disclosed in the present invention
may be provided in the form of a kit comprising a double vacuum
packed cartridge mixer filled with a first predetermined amount
of a solid, powdery bone cement component, an ampoule containing
a second predetermined amount of a liquid bone cement component,
an injector for transfer of the liquid bone cement component to
the cartridge mixer and a polyethylene ball for insertion in the
ampoule prior to insertion in the injector so as to provide a
positive sealing action to prevent air ingress into the cartridge
mixer upon passage of the predetermined quantity of monomer
thereto.
29
