Note: Descriptions are shown in the official language in which they were submitted.
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Bone Cement System
The invention relates to a bone cement system having a mixing facility for the
mixing and
dispensing of bone cement, a reservoir container for a monomer, and a
conveying means,
whereby the mixing facility comprises a mixing cylinder, the mixing cylinder
stores a bone
cement powder, the monomer can be conveyed from the reservoir container into
the mixing
cylinder by means of the conveying means, a sieve element is arranged between
the reservoir
container and the mixing facility to prevent the ingress of the bone cement
powder from the
mixing cylinder into the conveying means, the mixing facility comprises a
dispensing opening for
dispensing a bone cement that is obtained by mixing the bone cement powder and
the
monomer.
PMMA bone cements have been known for decades and are based on the
groundbreaking
work of Sir Charnley (Charnley, J.: Anchorage of the femoral head prosthesis
of the shaft of the
femur. J. Bone Joint Surg. 42 (1960) 28-30.). The basic structure of PMMA bone
cements has
remained the same ever since. PMMA bone cements consist of a liquid monomer
component
and a powder component. The monomer component generally contains the monomer,
methylmethacrylate, and an activator (N,N-dimethyl-p-toluidine) dissolved
therein. The powder
component consists of one or more polymers that are made by polymerization,
preferably
suspension polymerization, based on methylmethacrylate and co-monomers, such
as styrene,
methylacrylate or similar monomers, a radio-opaquer, and the initiator,
dibenzoylperoxide.
When mixing the powder component with the monomer component, swelling of the
polymers of
the powder component in the methylmethacrylate leads to the formation of a
dough that can be
shaped plastically. When mixing the powder component with the monomer
component, the
activator, N,N-dimethyl-p-toluidine, reacts with dibenzoylperoxide while
forming radicals. The
radicals thus formed trigger the radical polymerization of the
methylmethacrylate. Upon
advancing polymerization of the methylmethacrylate, the viscosity of the
cement dough
increases until the cement dough solidifies.
Polymethylmethacrylate bone cements can be mixed in suitable mixing beakers by
means of
spatulas by mixing the cement powder with the monomer liquid. This procedure
is
disadvantageous in that inclusions of air may be present in the cement dough
thus formed and
may later cause destabilization of the bone cement - also referred to as
cement. For this reason, it
is preferable to mix bone cement powder with the monomer liquid in vacuum
mixing systems,
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since mixing in a vacuum removes inclusions of air from the cement dough all
but completely
and thus attains optimal cement quality (Breusch SJ et al.: Der Stand der
Zementiertechnik in
Deutschland. Z Orthop. 1999, 137: 101-07). Bone cements mixed in a vacuum have
substantially lower porosity and thus show improved mechanical properties. A
large number of
vacuum cementing systems have been disclosed of which the following shall be
named for
exemplary purposes:: US6033105 A, US5624184 A, US4671263 A, US4973168 A,
U55100241
A, W099/67015 A1, EP1020167 A2, US5586821 A, EP1016452 A2, DE3640279 A1,
W094/26403 A1, EP0692229 A1, EP1005901 A2, US5344232 A.
A further development are cementing systems in which both the cement powder
and the
monomer liquid are already packed in separate compartments of the mixing
systems and are
mixed with each other in the cementing system only right before application of
the cement
(US5997544 A, EP0692229 A1, US6709149 B1). A drawback of all of these systems
is the
transfer of the monomer liquid into the cement powder and the complete mixing
of these two
components to obtain a homogeneous cement dough which must, in particular, not
contain any
regions of cement powder that has not been wetted by the monomer liquid. In a
mixing system
that is currently on the market in Europe, tubes that are arranged on the side
of the lower part of
the cartridge and penetrate through the cartridge wall are used to introduce
the monomer liquid
approximately into the middle of the cement powder through the application of
a vacuum. There
is no mixing facility provided at the tubes that might prevent the ingress of
cement powder into
the tubes during storage of the mixing system. Clogging of the tubes by cement
powder cannot
be excluded completely.
Another mixing system for the mixing and dispensing of bone cement is shown in
DE 698 12
726 T2. The mixing system comprises a mixing cylinder, whereby a sieve element
is arranged
between the reservoir container and the mixing facility to prevent ingress of
the bone cement
powder from the mixing cylinder into the conveying means. Said mixing systems
have proven to
be disadvantageous in that homogeneous and rapid mixing of the monomer and the
bone
cement powder cannot be ensured at all times.
Another variant was disclosed in EP 1 140 234 B1. In said mixing system, the
monomer liquid is
aspirated through the entire cement powder by means of a vacuum. The basic
approach, i.e. to
aspirate the monomer liquid through the entire cement powder in order to
achieve optimal
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mixing and prevent regions of non-wetted cement powder from forming is
feasible only if a
cement powder is used that swells very slowly after being wetted by the
monomer liquid. This
means that the high and medium viscosity PMMA bone cements, which currently
are most
commonly used in endoprosthetics, can be used not at all or with difficulties
since the cement
powder of these cements swells immediately after being wetted by the monomer
liquid and
forms a dough that renders further pervasion of the cement powder by the
monomer liquid
difficult or even impossible.
It is therefore the object of the invention to develop a bone cement system
that is not
associated with the aforementioned disadvantages, but is, in particular,
protected against
clogging by cement powder.
Accordingly, in a preferred embodiment, the invention is directed to a bone
cement system
(100) comprising a mixing facility (10) for mixing and dispensing of bone
cement, a reservoir
container (112) for a monomer, and a conveyor (122), wherein:
a) the mixing facility (10) comprises a mixing cylinder (20);
b) the mixing cylinder (20) stores a bone cement powder;
c) the conveyor (122) conveys the monomer from the reservoir container
(112)
into the mixing cylinder (20);
d) a sieve element (4) is arranged between the reservoir container (112)
and the
mixing facility (10) to prevent ingress of the bone cement powder from the
mixing cylinder (20) into the conveyor (122), the sieve element (4) having a
mesh size between 5 pm and 30 i.,trn;
e) the mixing facility (10) comprises a dispensing opening (23) for
dispensing the
bone cement mixed from the bone cement powder and the monomer;
f) the dispensing opening (23) comprises a shield (1) having at least one
through-opening (2); and
g) the ratio of the area of the through-opening (2) to the area of the
sieve element
(4) is at most 1 to 3, and the distance between the shield (1) and the sieve
element (4) is
between 1 mm and 10 mm..
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According to the invention, the dispensing opening comprises a shield with at
least one
through-opening and a ratio of an area of the through-opening to the area of
the sieve element
is no more than 1 to 3, and a distance between the shield and the sieve
element is at least 1
mm.
The invention allows the injection of monomer liquid from below into the bone
cement powder -
also referred to as cement powder - such that the injection system is
prevented from becoming
sticky, and mixing of the cement powder, as completely as possible, can be
achieved. The
bone cement system must not get sticky since this renders complete monomer
transfer from
the monomer reservoir container into the cement powder impossible. The result
of incomplete
monomer transfer would be that only a fraction of the intended monomer would
form a dough
with the cement powder. The resulting dough would therefore be more viscous
and the bone
cement - also referred to as cement - would have unpredictably changed
mechanical properties
after it hardens as compared to correctly mixed cement that is produced to
have a
predetermined ratio of monomer liquid to cement powder. The bone cement system
works such
that the application of a vacuum opposite from the through-opening generates a
negative
pressure in the feed opening and first the residual air present in the system
and then the
monomer liquid is aspirated into the intervening space. The air arriving first
moves through the
sieve element and carries along the cement powder that is present in the
intervening space
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through the through-opening in the direction of the mixing cylinder. As a
result, the intervening
space no longer contains cement powder and is empty. Subsequently, the monomer
liquid is
aspirated through the sieve element. Accordingly, the sieve element
facilitates the bone cement
powder not flowing into the conveying means and clogging same upon contact
with the
monomer liquid. Therefore, according to the invention, the sieve element
separates the
conveying means and the mixing cylinder such that no bone cement powder can
flow into the
conveying means.
An advantageous further development variant of the bone cement system
according to the
invention is characterized in that the mixing facility comprises a dispensing
opening for
dispensing a bone cement that is mixed from the bone cement powder and the
monomer. A
bone cement forms after mixing of the bone cement powder and the monomer.
Before it
hardens, said bone cement needs to be dispensed from the bone cement system
and,
preferably, implanted into the patient. It has proven to be advantageous for
this purpose to have
a dispensing opening being present through which the bone cement can be
pressed from the
mixing cylinder. Advantageously, the dispensing opening is designed to be
funnel-shaped.
Another advantageous further development is characterized in that the sieve
element is stored
in an intervening space that can be connected to the dispensing opening of the
mixing facility
and in which the conveying means ends. Both the dispensing opening of the
mixing facility and
the conveying means end in the intervening space. Accordingly, the monomer
flows from the
reservoir container through the intervening space into the mixing cylinder.
The sieve element
according to the invention is arranged in said intervening space. This
embodiment is
advantageous in that the sieve element is not arranged in said dispensing
opening through
which the mixed bone cement is dispensed later on. However, the sieve element
prevents the
bone cement powder from flowing from the mixing cylinder into the conveying
means.
Another advantageous further development is characterized in that the sieve
element has a
mesh size of less than 30 pm, in particular a mesh size between 5 pm and 25
pm. Said mesh
size ensures, on the one hand, that the bone cement powder cannot flow from
the mixing facility
into the conveying means. On the other hand, the flow of the monomer, in
particular liquid
monomer, from the reservoir container into the mixing cylinder is impeded only
to a minor
degree by the mesh of the sieve element. Accordingly, a sieve element with a
mesh size
CA 02708729 2015-11-17
between 30 pm and 5 pm represents a connection element between the reservoir
container
and the mixing facility that is open only on one side.
In another advantageous further development, the dispensing opening comprises
a shield with
at least one through-opening. Advantageously, the shield is arranged between
the mixing
facility, in particular the dispensing opening, and the sieve element. In this
context, the
dispensing opening determines the quantity of monomer that can flow into the
mixing cylinder
in a unit of time. Advantageously, the area of the through-opening is smaller
than the area of
the sieve element. Advantageously, the sieve element and the shield are part
of the intervening
space. Adjacent to said intervening space, there is, on the one hand, the
conveying means of
the reservoir container and, on the other hand, the dispensing opening of the
mixing facility.
The intervening space is designed such that it stores, approximately in the
middle thereof, the
sieve element, which is arranged essentially parallel to the shield. During
storage and transport
of the polymethylmethacrylate bone cement mixing system, the sieve element
prevents
penetration of the cement powder in the direction of the feed opening. The
bone cement
system works such that the application of a vacuum opposite from the through-
opening
generates a negative pressure in the feed opening and first the residual air
that is present in
the system and then the monomer liquid is aspirated into the intervening
space. The air arriving
first moves through the sieve element and carries along the cement powder that
is present in
the intervening space through the through-opening in the direction of the
mixing cylinder. The
intervening space then no longer contains cement powder and is empty.
Subsequently, the
monomer liquid is aspirated through the sieve element. Due to the low mesh
size of the sieve
element, this causes a marked reduction of the flow rate. To counteract this
loss in velocity, the
area of the sieve is made correspondingly large. This means that the volume
flow is not
impeded despite the slower flow rate of the liquid through the sieve element
due to the large
area thereof. The term, volume flow, is understood to mean the volume of
monomer liquid per
unit time that emanates from the feed opening. Subsequently, the monomer
liquid accumulates
in the intervening space and moves in the direction of the through-opening.
The bone cement system according to the invention is characterized in that a
ratio of an area of
the through-opening to the area of the sieve element is no more than 1 to 3,
preferably in that the
ratio of the area of the through-opening to the area of the sieve element is
between 1 to 4 and 1
to 20. The area of the through-opening being small compared to the area of the
sieve element
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accelerates the liquid in the dispensing opening in order for the volume flow
to be constant. This
means that a jet of monomer liquid is generated that is injected into the
cement powder that is
situated above the through-opening. The jet of monomer spreads in a funnel
shape with
increasing distance of travel. Due to the high velocity of the monomer jet,
the monomer can
pass through the cement powder in a sufficiently short time before the cement
powder swells to
any significant degree. Bone cement powder particles that have already swelled
are displaced
by the monomer jet.
Preventing an ingress of bone cement powder from the mixing cylinder into the
conveying
means is promoted by a distance between the shield and the sieve element being
at least
1 mm, preferably by the distance between the shield and the sieve element
being between
2 mm to 10 mm. The values specified above have been found surprisingly in
extensive
measurements to be particularly preferred in order to ensure that the monomer
entering the
mixing cylinder, on the one hand, carries along possible bone cement powder
residues from the
intervening space into the mixing cylinder, and, on the other hand, does not
provide the
intervening space too large such that the amount of bone cement powder
residues that is
deposited therein is as small as possible.
Depending on the bone cement powder that is used, it has proven to be
advantageous for the
through-opening to be provided to be circular, oval, star-shaped or slit-
shaped, in particular for
the shield to extend in a funnel shape. The shapes of the through-opening can
control the flow
behavior of the monomer into the bone cement powder. In particular star- or
slit-shaped
through-openings provide for a funnel-shaped spreading of the jet of monomer
liquid that enters
through the shield into the mixing cylinder. In addition, the shield can
extend to be funnel-
shaped. In this case, the shield works like a Venturi nozzle and effects
additional acceleration of
the monomer liquid that flows from the intervening space into the mixing
cylinder.
In order to mix the monomer with the bone cement powder as homogeneously as
possible, it
has proven to be advantageous for a mixing plunger to be arranged in the
mixing cylinder,
whereby the mixing plunger can be moved axially by means of an actuation rod
that is guided to
exit in a sealed manner at a first cylinder end. Advantageously, the first
cylinder end is situated
opposite from a second cylinder end, whereby the second cylinder end comprises
the
dispensing opening. Accordingly, the monomer flowing into the mixing cylinder
can be pulled
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even further into the mixing cylinder by means of the mixing plunger and/or
the actuation rod in
order to ensure homogeneous mixing of the cement powder and the monomer.
One particularity of the mixing facility according to the invention is that
plunger system can be
pushed axially into the mixing cylinder in order to dispense a bone cement
that is mixed from
the bone cement powder and the binding agent, in particular the monomer,
through the
dispensing opening. The dispensing opening is situated at a second cylinder
end of the mixing
plunger. The second cylinder end is situated opposite from the first cylinder
end. During
dispensation, the plunger system is pushed from the direction of the first
cylinder end in the
direction of the second cylinder end and, in turn, presses the ready-mixed
bone cement through
the dispensing opening. In an advantageous further development, the dispensing
opening
comprises a connection means, in particular a connection thread. Said
connection thread can
be used to screw the mixing cylinder into the bone cement system and/or to
connect the mixing
cylinder to a hose system via which the ready-made bone cement can be
introduced into the
bone. An applicator gun into which the mixing cylinder is to be clamped can be
used for this
activity. For ease of use of the applicator gun, the actuation rod can
comprise a predetermined
breakage point such that the actuation rod can be broken off at a defined
place. For dispensing
the ready-mixed bone cement, the actuation rod is pulled in the direction of
the plunger system
until the mixing plunger touches against the plunger system. The plunger
system, including the
mixing plunger that touches against it in front of it, can be pressed into the
mixing cylinder by
then breaking off the actuation rod.
In an advantageous further development, the dispensing opening comprises a
connection
means, in particular a connection thread. Said connection thread can be used
to screw the
mixing cylinder into the bone cement system to be described below and/or to
connect the mixing
cylinder to a hose system via which the ready-made bone cement can be
introduced into the
bone. An applicator gun into which the mixing cylinder is to be clamped can be
used for this
activity. For ease of use of the applicator gun, the actuation rod can
comprise a predetermined
breakage point such that the actuation rod can be broken off at a defined
place. For dispensing
the ready-mixed bone cement, the actuation rod is pulled in the direction of
the plunger system
until the mixing plunger touches against the plunger system. The plunger
system, including the
mixing cylinder that touches against it in front of it, can be pressed into
the mixing cylinder by
then breaking off the actuation rod.
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Moreover, it is advantageous for the reservoir element to store a reservoir
container for the
monomer. For production of the bone cement, the monomer must be introduced
into the bone
cement powder. The bone cement then hardens after a certain period of time. It
is therefore
obvious that the bone cement cannot be delivered such as to be in the device
and ready for
dispensation. It is therefore necessary for the bone cement powder and the
monomer to be
stored separately until shortly before dispensation of the bone cement. It is
therefore expedient
if the reservoir element comprises a reservoir container for the monomer.
Glass containers, in
particular, that are used as reservoir containers for the binding agent, in
particular the monomer,
have proven to be easy to disinfect. The reservoir element can comprise a
valve means to
control the inflow of the monomer. Said valve means controls and/or triggers
the inflow of the
monomer from the reservoir container into the device according to the
invention.
An advantageous further development of the bone cement system according to the
invention is
characterized in that the bone cement system comprises a base element, whereby
the base
element stores the mixing facility and the reservoir container. The base
element therefore
serves as platform both for the mixing facility according to the invention and
for the reservoir
element for the binding agent. The mixing facility according to the invention
and the reservoir
element can be arranged at and/or on the base element as some kind of
foundation of the bone
cement system. An advantageous development of the bone cement system according
to the
invention is characterized in that the base element comprises a coupling means
for a non-
positive and/or positive fit connection to the mixing facility, in particular
to a dispensing opening
of the mixing facility. Since the mixing facility according to the invention
is also to be used for
dispensing the bone cement, it is advantageous for the mixing facility to be
reversibly separable
from the base element. This can be attained by means of the coupling element
according to the
invention. The coupling element advantageously is a thread onto which the
dispensing opening
of the mixing facility can be screwed. This provides a secure connection
between the base
element and the mixing facility.
In another advantageous development, the base element can store the conveying
means. In
this case, the conveying means extends through the base element. The
intervening space can
also be arranged in the base element. By means of the connection means, it is
feasible to
connect the intervening space, and thus the conveying means, to the mixing
cylinder. In this
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context, according to the invention, the sieve element preventing ingress of
the bone cement
powder from the mixing cylinder into the conveying means is arranged in the
intervening space.
Further measures and advantages of the invention are evident from the claims,
the following
description, and the drawings. The invention is presented in the form of
multiple exemplary
embodiments in the drawings. In the figures:
Fig. 1 shows a schematic sectional drawing of a bone cement system
according to the
invention;
Fig. 2 shows a schematic sectional drawing of a mixing facility according
to the
invention; and
Fig. 3 shows a schematic sectional drawing of a dispensing opening of the
mixing
facility.
Figure 1 shows a bone cement system 100 according to the invention. The bone
cement system
100 comprises a mixing facility 10 for mixing and dispensing bone cement. Said
mixing facility
is stored on a base element 120 in the exemplary embodiment shown. Said base
element
120 also carries a reservoir element 110 for a monomer. The bone cement system
100 serves
for mixing the bone cement. For this purpose, bone cement powder is filled
into a mixing
cylinder 20 of the mixing facility 10. Said bone cement powder can
subsequently be mixed with
the monomer in order to form bone cement. As illustrated in Figure 1,
reservoir element 110 is
part of the bone cement system. Reservoir element 110 stores a reservoir
container 112 for the
monomer. An outflow of the monomer from the reservoir container 112 can be
controlled and/or
triggered via a valve means 115. Advantageously, the reservoir container 112
is a glass
container that is opened in its head region by the valve means 115. The
monomer then flows
through a conveying means 122 from the reservoir container 112 into the mixing
cylinder 20.
The transfer flow of the monomer is increased since a negative pressure is
present in the mixing
cylinder 20. The bone cement powder and the monomer can then be mixed easily
and simply by
means of the actuation rod and the mixing plunger 21. After mixing is
completed, the facility 10
can be unscrewed from the base element 120. For this purpose, the base element
120
comprises a coupling means 121 that acts in concert with a connection means 22
of the mixing
CA 02708729 2010-06-29
plunger. After separation of the mixing facility 10 from the base element 120
is effected, the
actuation rod 50 is shifted axially such that the mixing plunger 21 comes to
rest against the
plunger system 40. Subsequently, the actuation rod can be snapped off at the
predetermined
breakage point 51. The mixing facility 10 can now be integrated into a
cementing gun. Actuation
of the cementing gun moves a toothed rack with collar in the direction of the
plunger system 40.
The plunger system 40 is used for dispensing the bone cement. For this
purpose, the plunger
system 40 is designed to be axially movable and can be pressed axially into
the mixing cylinder
20. This allows the bone cement formed by mixing the bone cement powder and
the monomer
to be dispensed through a dispensing opening 23.
The prior art knows bone cement systems, in which the monomer liquid is stored
in containers
on the side of the mixing cylinder. Tubes are used to introduce the monomer
liquid
approximately in the middle of the cement powder that is arranged in the
mixing cylinder. It has
proven to be disadvantageous that the arrangement and design of the tubes do
not completely
exclude clogging of the tubes by cement powder. This can lead to the supplied
amount of
monomer being insufficient and a non-homogeneous bone cement region may result
therefrom.
In order to overcome this disadvantage, the bone cement system 100 according
to the invention
comprises a sieve element 4, like the one shown in Figure 2. Said Figure 2 is
a sectional
drawing analogous to the one in Figure 1 with the features in the area of the
dispensing opening
23 being shown in more detail. As is evident, the base element 120 stores the
mixing cylinder
of the mixing facility 10. The mixing cylinder 20 is connected to the base
element 120 by
means of a connection means, a thread in the present case. A shield 1 that
comprises at least
one through-opening 2 is situated below the dispensing opening 23 in the base
element. It is
evident that the through-opening has a width and therefore an area 5 that is
clearly smaller than
the area of the sieve element 4 that is arranged underneath. The width thereof
is indicated by
reference number 8. Advantageously, the area of the through-opening is 1/4 to
1/20 of the area
of the sieve element 4. The sieve element 4 prevents bone cement from the
mixing cylinder 20
from penetrating into and clogging the conveying means 122 during storage and
transport.
When the finished bone cement is to be mixed, the bone cement system is
connected to a
vacuum element. This generates a negative pressure in the mixing cylinder 20
and in an
intervening space 3 that stores the sieve element 4. Said negative pressure
aspirates residual
air from the intervening space 3 in the direction of the vacuum connection,
which is generally
arranged in the area of a first cylinder end 30. Said aspiration of the
residual air causes any
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cement powder that is still present in the intervening space 3 to be aspirated
through the
through-opening 2 of the shield 1 in the direction of the mixing cylinder 20.
Subsequently, the
monomer liquid can be aspirated through the sieve element 4. In the process,
the sieve element
4 advantageously has a mesh size of less than 30 pm. Due to this small mesh
size of the sieve
element 4, the flow rate of the monomer is reduced. In order to still achieve
homogeneous
passage of the liquid of the monomer into the mixing cylinder 20, the size of
the sieving area 4
must be adapted accordingly. The ratio of the area 5 of the through-opening 2
to the area 8 of
the sieve element 4 thus also determines the volume of a monomer liquid that
is aspirated into
the mixing cylinder 20 in a unit of time. Accordingly, the use, according to
the invention, of the
sieve element 4 allows to ensure homogeneous ingress of monomer into the
mixing cylinder 20
and simultaneously prevents clogging of the conveying means 122 by bone cement
powder.
Figure 3 shows another detail magnification of the intervening space 3 with
the integrated sieve
element 4 that serves to prevent ingress of the bone cement powder from the
mixing cylinder 20
through the through-opening 3 into the conveying means 122. The intervening
space 3 has a
V-shaped base 6 that has the effect of a nozzle on the monomer flowing from
the conveying
means 122. The sieve element 4 is arranged above said dispensing opening of
the conveying
means 122. Said sieve element can be a punched, woven or knitted structure
that is composed
of metals, plastic materials and/or combinations thereof.
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Reference numbers
1 Shield
2 Through-opening
3 Intervening space
4 Sieve element
Width of the through-opening
6 Base of the intervening space
8 Width of the sieve element
Mixing facility
Mixing cylinder
21 Mixing plunger
22 Connection means
23 Dispensing opening
First cylinder end
Second cylinder end
Plunger system
Actuation rod
51 Predetermined breakage point
52 Handle
100 Bone cement system
110 Reservoir element
112 Reservoir container
115 Valve means
120 Base element
121 Coupling means
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122 Conveying means
