Abstract:
The application relates to a vacuum mixing device for bone cement, where the monomer is pressed into a mixing container due to the surrounding vacuum and a gas volume present in the monomer container.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 13/257,031 filed Sep. 16, 2011, which application is a national phase entry under 35 U.S.C. §371 of International Application No. PCT/EP2010/001665 filed Mar. 17, 2010, published as International Publication No. WO 2010/105807 A1, which claims priority from German Patent Application No. 10 2009 013 211.2 filed Mar. 17, 2009, the disclosures of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a vacuum mixing device for bone cement and to a method for producing bone cement. 
       BACKGROUND OF THE INVENTION 
       [0003]    Mixing devices for bone cement are known. 
         [0004]    Such a generic mixing device is shown, for example, in the applicant&#39;s German patent application DE 10 2007 041 666 A1. When preparing bone cement, a powder, in particular a PMMA powder, is typically mixed with a liquid monomer. Vacuum mixing systems are known so as to avoid the formation of bubbles and/or to prevent harmful gaseous substances that develop during preparation from escaping into the environment. These are systems in which the mixing container comprises a connection for a vacuum hose, via which the container is placed under a vacuum during the mixing process. 
         [0005]    Known conventional system often require relatively complicated operation, in which the user must perform several steps associated with sources of errors. In particular, it is important to precisely adhere to the predefined mixing ratio between the monomer and powder. 
         [0006]    For this purpose, for example, systems are known in which the monomer is suctioned into the mixing container based on a vacuum that is present in the mixing container. Such conventional systems generally have a valve through which air can flow into the monomer container, so that the existing liquid is completely discharged from the monomer container. Such a system is described, for example, in the European patent specification EP 0 725 647 B1. 
         [0007]    The disadvantage of such a system is that the bone cement can become contaminated with microbes from the ambient air, in particular if this system is not operated in a sterile environment. 
       SUMMARY OF THE INVENTION 
       [0008]    In contrast, it is the object of the invention to at least reduce the aforementioned disadvantages of the prior art. 
         [0009]    It is in particular an object of the invention to be able to provide a vacuum mixing system for bone cement which enables simple and safe handling. 
         [0010]    The object of the invention is already achieved by a vacuum mixing device and by a method for preparing bone cement according to any one of the independent claims. 
         [0011]    Preferred embodiments and refinements of the invention are disclosed in the respective dependent claims. 
         [0012]    The invention relates first to a vacuum mixing device for bone cement, comprising a mixing chamber in which a monomer can be mixed with the powder. So as to avoid the formation of bubbles and prevent harmful gases from escaping, the mixing chamber can be connected to a vacuum source, in particular to a vacuum pump. 
         [0013]    The vacuum mixing device moreover comprises a monomer container, which can be coupled to the mixing chamber. The monomer is preferably already contained in the monomer container upon delivery of the vacuum mixing device and thus does not need to be withdrawn from a separate container and added. The term “can be coupled” means that the vacuum mixing device comprises means for forming a passage in which the monomer flows from the monomer container into the mixing container connected to the monomer container. 
         [0014]    According to the invention, the closed monomer container is filled partially with a gas, the volume of which is calculated such that, when a vacuum is present, the monomer is displaced by the gas and thus flows into the mixing container. 
         [0015]    The monomer container is preferably not subject to over-pressure, but instead has, for example, substantially atmospheric pressure. This enables a simpler design of the container, and the monomer is prevented from escaping in an uncontrolled manner in the event of damage. 
         [0016]    If the monomer container is, for example, under atmospheric pressure and a vacuum source is applied that generates a vacuum of approximately 0.5 bar in the mixing container, the gas volume in the monomer container must consequently account for at least half the volume. 
         [0017]    The invention enables an entirely closed design of the vacuum mixing device, so that there is no risk during mixing for microbes from the air that is suctioned in to contaminate the bone cement. 
         [0018]    The gas that is used can be air in the simplest case, but other gases, in particular those that form a preserving protective atmosphere, are also conceivable. Nitrogen or a noble gas may also be used, for example. 
         [0019]    In a preferred embodiment of the invention, the gas volume is so large that the monomer flows into the mixing container up to a predefined fill level, or fully, when a vacuum is present. 
         [0020]    A predefined residual fill quantity can be determined, for example, by the height of the cannula protruding into the monomer container during mixing. Depending on the embodiment, complete emptying of the monomer container is also possible. 
         [0021]    In this embodiment of the invention, the amount of liquid to be dispensed can be exactly gauged, because the monomer container is emptied fully automatically and the user has no influence on the residual quantity remaining in the monomer container, as is the case, for example, with filling using a syringe. 
         [0022]    In a preferred embodiment of the invention, at least 20%, and more preferably 40%, of the volume of the monomer container is filled with the gas. 
         [0023]    In a refinement of the invention, the monomer container has a membrane and the vacuum mixing device comprises a piercing cannula, by means of which the membrane can be pierced and the monomer thus flows via the cannula into the mixing container. 
         [0024]    This embodiment of the invention enables, in particular, the use of commercially available monomer vials made of glass, which are provided with a membrane. The monomer is thus stored in a safe and sterile manner in the monomer vial. 
         [0025]    The invention further relates to a vacuum mixing device which comprises a mixing container, which can be connected to a vacuum source. The vacuum mixing device comprises a monomer container, which can be coupled to the mixing container. 
         [0026]    So as to enable a particularly simple design of the device, the monomer container is disposed on a handle, which can also be used to actuate a mixing blade in the mixing chamber, wherein the monomer can be mixed manually with the powder using this mixing blade by moving the mixing blade up and down. 
         [0027]    A rod is connected to the handle so as to move the mixing blade. 
         [0028]    According to the invention, the rod is guided in a plate, which can be used as a plunger for expelling the bone cement after the bone cement has been prepared. 
         [0029]    The rod preferably comprises a channel, which is used to join the mixing container to the monomer container, which is to say to allow the monomer to flow into the mixing container. 
         [0030]    The invention enables a design of a vacuum mixing device which is particularly easy to handle, wherein, as in a preferred embodiment of the invention, the handle together with the monomer container can be broken off after the mixing process is complete and the mixing container is employed as a kind of cartridge in a dosing gun. To this end, the plate, which initially serves to guide the rod, is used as a plunger for pushing the bone cement out of the mixing container. 
         [0031]    According to one embodiment of the invention, the monomer container comprises a monomer vial disposed in a receiving unit. This embodiment of the invention makes is possible, among others, to use commercially available monomer vials and, as in a preferred embodiment of the invention, the remaining monomer container does not have to be designed to be vacuum-sealed because, for example, a membrane that is present on the monomer vial can served as a sealing element. 
         [0032]    In a special embodiment of the invention, the receiving unit is designed to be telescoping. A monomer vial held in the receiving unit can thus be pushed onto a cannula, for example. 
         [0033]    The invention further relates to a vacuum mixing device comprising a mixing chamber and a monomer container, which can be coupled to the mixing chamber. 
         [0034]    According to the invention, the monomer container engages in the coupled state and is preferably locked in this engaged state. 
         [0035]    Thus, the user cannot break the connection between the monomer container and mixing container once it has been established. The monomer thus enters the mixing container completely, and there is no risk of the user separating the monomer container as a result of improper use before the container is emptied. 
         [0036]    In a refinement of the invention, the vacuum mixing device comprises a safety bolt which, upon removal, releases the monomer container for movement into the coupled state. Such a safety container prevents accidental actuation of the device. 
         [0037]    The vacuum mixing device preferably comprises means for blocking reinsertion of the removed safety bolt. Once the safety bolt has been pulled, it thus also serves as a tamper-proofing element, making it immediately apparent if the vacuum mixing device has been previously used and therefore consumed. 
         [0038]    The invention further relates to a method for preparing bone cement. To this end, a monomer is mixed with a powder in a mixing container and a vacuum is applied to the mixing container, at least while mixing. 
         [0039]    According to the invention, when the vacuum is present, the monomer is pressed out of the monomer container into the mixing container by a gas that expands as a result of the vacuum. 
         [0040]    The method makes a fully closed design of the mixing system possible. 
         [0041]    During preparation, the mixing cup and monomer container are thus preferably protected from the penetration of outside air. 
         [0042]    In one embodiment of the invention, the monomer container is pierced by means of a cannula and the monomer is conducted via the cannula into the mixing container. 
         [0043]    In this connected position, the monomer container engages such that the inflow of monomer can no longer be interrupted. 
         [0044]    In a refinement of the invention, the monomer container is separated from the mixing container after the bone cement has been prepared, and the mixing container is used as a cartridge for a dosing gun. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]    The invention will be described in more detail hereafter with reference to the drawings, these being  FIG. 1  to  FIG. 6 , which show schematic views of embodiments of the invention. 
           [0046]      FIG. 1  to  FIG. 4  show schematic views of an exemplary embodiment of a handle comprising a monomer container for a vacuum mixing device according to the invention. 
       
    
    
       [0047]    The entire vacuum mixing device will be described in more detail with reference to  FIGS. 5 and 6 . 
       DETAILED DESCRIPTION 
       [0048]      FIG. 1  is a schematic view of a monomer container  10  designed as a handle for a mixing blade (not shown). The monomer container  10  has a substantially cylindrical shape and comprises an actuating button  11  for releasing the monomer (not shown). 
         [0049]    In order to be able to press the actuating button  11 , a safety bolt  12  having a handle  13 , which forms a finger hole, is provided, which must be removed first. 
         [0050]    After the safety bolt  12  has been removed, the actuating button  11  can be pressed and the monomer flows, with a vacuum in the mixing container, into the mixing container (not shown) via a channel (not shown) that is embedded in the rod  6 . 
         [0051]      FIG. 2  shows a sectional view of the monomer container  10  shown in  FIG. 1  in a starting state, which is to say prior to use. 
         [0052]    The monomer container  10  comprises a lower housing part  15  and an upper housing part  16 , which is also designed as the actuating button  11 . 
         [0053]    The housing parts  15 ,  16  are used to accommodate a commercially available monomer vial  17  made of glass, which is sealed with a membrane  18 . 
         [0054]    The monomer fills the monomer vial  17  approximately half in this exemplary embodiment. The fill level is predefined by the line  25 . 
         [0055]    The monomer container  10  further comprises a cannula  19 , which is connected to a channel  20  that is embedded in the rod  6 . 
         [0056]    The cannula  19  and the membrane  18  of the monomer vial  17  are held apart from each other by the safety bolt  12  so that accidental actuation is not possible. 
         [0057]    The safety bolt  12  comprises a spring-loaded tongue so as to compensate for manufacturing tolerances of the monomer vial  17 . 
         [0058]    As soon as the safety bolt  12  has been pulled out, the monomer vial  17  slides into a position in which the safety bolt  12  cannot be re-inserted. 
         [0059]      FIG. 3  shows a sectional view of the monomer container  10  after actuation. 
         [0060]    When the actuating button is pressed, the upper housing part  16  and the lower housing part  15  are pushed inside each other, whereby the monomer vial  17  is pushed onto the cannula  19  which pierces the membrane  18  so that the monomer can enter the mixing container (not shown) via the channel  20 . 
         [0061]    Because of the air volume that is present above the fill level  25  and the vacuum that is present in the mixing container, the monomer is emptied to a low residual fill level, which is predefined by the position of the cannula  19 . 
         [0062]    In order to define an exact position of the cannula  19  relative to the monomer vial  17 , a ring  21  is provided in the lower housing part, with the monomer vial  17  being seated on this ring in the actuated state. 
         [0063]      FIG. 4  shows a detail view of the head of the monomer container shown in  FIG. 3 . The engagement of the monomer container will be described in more detail with reference to this figure. 
         [0064]    The upper housing part comprises catch hooks  22 , which in the actuated state engage beneath catch lugs  23  of the lower housing part. For this purpose, the catch hooks  22  are beveled. It is not possible to pull them apart after engagement. 
         [0065]    So as to further increase the protection from manipulation, ribs  24  are provided on the lower housing part, which substantially prevent the use of a tool to push the catch hooks inward from beneath and thus return the monomer vial to the original position. 
         [0066]      FIG. 5  is a schematic view of the entire vacuum mixing device. 
         [0067]    The monomer container  10  is designed as a handle, which is connected via a rod  6  to a mixing blade (not shown). 
         [0068]    The mixing container  2  is preferably already prefilled with the powder. 
         [0069]    In order to ensure that the powder does not enter the rod  6 , a filter, and more particularly a filter plate, is provided (not shown) at the lower end of the rod. 
         [0070]    When the vacuum mixing device  1  is used, a vacuum pump is connected to a vacuum connection  3  on the mixing container  2 . A nonwoven fabric (not shown) that is embedded in the vacuum connection prevents bone cement from escaping. 
         [0071]    A withdrawal opening, which initially is still screwed to a base  5 , is located at the bottom of the mixing container  2 . 
         [0072]    The user (not shown) first connects the mixing container  2  to the vacuum. 
         [0073]    Then, he pulls the safety bolt and pushes the actuating button  11  of the monomer container. 
         [0074]    Because of the vacuum, the monomer (not shown) is displaced by the gas trapped in the monomer container  10  and flows via the rod  6  into the mixing container  2 . To this end, the rod  6  comprises lateral openings above the mixing blades (not shown). 
         [0075]    The user then uses the monomer container  10  as a handle so as to move the mixing blades (not shown) in the mixing container  2  and thus prepare the bone cement. 
         [0076]    Thereafter, the user pulls the mixing blade all the way to the top and completely breaks off the rod  6  together with the monomer container  10  at a predetermined breaking point. 
         [0077]    Moreover, the user unscrews the base  5 , whereby the withdrawal opening is uncovered. 
         [0078]    The mixing container  2  can now be utilized as a cartridge for a dosing gun (not shown). To this end, the cover  7  of the mixing container  2 , in which the rod  6  is also guided, serves as a plunger. The cover  7  can, for this purpose, be connected to the remaining mixing container  2  so that it detaches at a particular force and can then be pushed forward. The cover can, for example, be pressed into a groove of the cylindrical housing of the mixing container  2 . 
         [0079]      FIG. 6  shows a further perspective view of a vacuum mixing device  1 . In this view, the base ( 5  in  FIG. 5 ) has already been unscrewed, so that the withdrawal opening  4  is visible. 
         [0080]    The invention enables particularly simple and safe handling of bone cement. 
         [0081]    The invention is, of course, not limited to a combination of the aforedescribed characteristics, but a person skilled in the art can combine all the features to the extent this is expedient. 
       LIST OF REFERENCE NUMERALS 
       [0082]      1  Vacuum mixing device 
         [0083]      2  Mixing container 
         [0084]      3  Vacuum connection 
         [0085]      4  Withdrawal opening 
         [0086]      5  Base 
         [0087]      6  Rod 
         [0088]      7  Cover 
         [0089]      10  Monomer container 
         [0090]      11  Actuating button 
         [0091]      12  Safety bolt 
         [0092]      13  Handle 
         [0093]      14  Tongue 
         [0094]      15  Lower housing part 
         [0095]      16  Upper housing part 
         [0096]      17  Monomer vial 
         [0097]      18  Membrane 
         [0098]      19  Cannula 
         [0099]      20  Channel 
         [0100]      21  Ring 
         [0101]      22  Catch hook 
         [0102]      23  Catch lug 
         [0103]      24  Rib 
         [0104]      25  Fill level