Abstract:
The invention relates to a relatively simple, low cost and effective apparatus for mixing and discharging bone cement into a discharging device such as a syringe, while also providing an improved mixing action and producing minimal fumes. The syringe may be connected to an exit port located between the first and second end of the apparatus. The apparatus is able to both prevent and enable communication between a mixing region of the apparatus and the exit port due to presence of a valve and may further comprise a base which may be integral with the valve so that movement of the base creates movement of the valve within the apparatus.

Description:
FIELD OF THE INVENTION 
     The invention relates to an apparatus for mixing bone cement and discharging the mixed bone cement from a mixing container into a discharging device such as a syringe or syringes. 
     BACKGROUND OF THE INVENTION 
     Orthopedic bone cement is used in many surgical procedures throughout the world to secure hip, knee and other metallic prostheses in an appropriate anatomical position. Orthopedic bone cement is also used in procedures such as vertebroplasty, which is used to treat osteoporosis, a condition which causes progressive bone loss, creating structural weakness and skeletal fragility in hundreds of thousands of people throughout the world every year. The vertebroplasty procedure involves the injection of bone cement via a needle or syringe into a vertebral body of a patient, thereby stabilising, strengthening and reinforcing the bone and alleviating chronic back pain and preventing further vertebral damage. 
     Conventionally, a number of different types of bone cement may be used in a powder/liquid form; the three main types used for vertebroplasty, for example, being calcium sulphate, calcium phosphate and variations of polymethylmethacrylate (PMMA). Special formulations of PMMA have also been developed that may include, for example, the addition of barium, (e.g. for use in X-ray) and the addition of hydroxyapetite (e.g. to promote bone growth). 
     Since different types of bone cement are used in different procedures, and since these different types of bone cement may have different physical properties, (e.g. viscosity), the apparatus and method by which the bone cement is prepared also varies. 
     UK Patent No. GB 2 276 560 describes a bone cement mixing device comprising a mixing bowl with a lid having a handle extending outwardly therefrom. A mixing paddle comprising a shaft and vanes extending outwardly therefrom extends into the bowl from the lid. A step up gear mechanism is provided between the paddle and the lid such that, as the handle rotates, the paddle also rotates. The drive wheel of the gear mechanism is also caused to rotate and drives the driven wheel which causes the shaft of the paddle to rotate about its own axis as the paddle moves around the bowl. 
     WO 95/22402 describes a device for mixing and delivering bone cement comprising a mixing chamber, a mixing element and drive means for causing rotation of the mixing element. The drive means may be a handle axially movable relative to the mixing chamber so that a gear mechanism between the handle and the mixing element translates axial movement of the handle into rotation of the mixing element. The device may be used in conjunction with a syringe so that the cylinder of the syringe forms the body of the mixing chamber and a plunger is slidably mounted at one end of the cylinder for causing ejection of the mixed cement. 
     U.S. Pat. No. 5,876,116 describes an integrated bone cement mixing and discharging apparatus for use in surgical procedures for affixing prostheses to a bone or joint structure for improving the strength, rigidity and movement of the bone/joint structure. The apparatus is used for mixing the bone cement components and delivering the mixed bone cement to a desired location. The apparatus comprises a mixing chamber that is integrally combined with a delivery chamber or tube that has one end incorporating a cement delivering outlet port. The two chambers are movable between two alternate positions, a first position wherein each chamber is sealed from the other and a second position wherein the two chambers are in direct communication with each other. The mixing chamber is therefore operated independently of the delivery chamber for preparing the bone cement and once prepared, transferred from the mixing chamber through the delivery chamber or tube for immediate use. 
     Conventionally, for vertebroplasty, the bone cement is prepared immediately prior to each procedure by manually mixing a powder and a liquid in a bowl using a spatula or the like, and then transferring the mixed bone cement into a syringe or delivery gun for application. 
     One conventional method for performing vertebroplasty using a low viscosity bone cement such as PMMA involves mixing a powder and liquid in an open bowl with a spatula, then pouring, scraping or aspirating the mixture into a syringe for injection by hand into a collapsing vertebral body. In this way, the bone cement can stabilise and strengthen the bone, thereby alleviating chronic back pain and preventing further vertebral damage by reinforcing the fractured bone. 
     An alternative method of performing vertebroplasty comprises mixing the components in a shaker and then aspirating, via a connector, into either a 10 ml syringe or a 220 ml syringe, which is then used to fill syringes of various sizes. Following the filling of the syringes, a biopsy needle or a biopsy needle with a catheter may be connected to the syringe and the bone cement mixture injected into the vertebra of the patient. 
     A further method for performing vertebroplasty involves mixing the liquid and powder in a shaker or in an open bowl with a spatula (as before), aspirating or pouring the mixture into a 10 ml syringe that is used with a delivery gun, then connecting a biopsy needle or a biopsy needle with a catheter to the syringe and injecting the bone cement mixture into the vertebra of the patient. 
     Thus, although conventionally the mixing of bone cement may be achieved using a number of different apparatus and methods, there is no apparatus available that allows for the quick, simple and effective mixing and discharging of bone cement directly into a variety or plurality of syringes. 
     In general, the manual transfer of mixed bone cement from the mixing bowl or shaker to the syringes is a messy and time-consuming process. These methods also have further disadvantages in that fumes produced during the mixing of the bone cement may be a problem for operators both within the orthopedic and radiology fields. 
     A first aspect of the present invention provides an apparatus for mixing and discharging bone cement compounds comprising a first end and a second end, with a longitudinal axis extending between the first end and the second end, a mixing region, at least one exit port, and valve means for preventing or enabling communication between the mixing region and at least one exit port, wherein the at least one exit port is located between said first end and said second end and wherein said valve is moveable along said longitudinal axis between a first position in which the valve prevents communication between the mixing region and the at least one exit port and a second position wherein the valve enables communication between the mixing region and the at least one exit port. 
     Although syringes to be filled could be attached directly to the exit port(s), in a preferred embodiment, connection means are provided on the exit port(s) for the connection of syringes. These connection means may comprise valves for preventing or enabling flow through the connection means from the exit port(s) to the syringe(s). Alternatively, the exit ports may be blocked via the use of stoppers which fit into the exit ports. The connection means may be provided in different sizes or in the form of an adaptor for different sized syringes. 
     Since the apparatus of the present invention may be used in conjunction with a plurality of different sized adaptors, it is possible to fill a wide range of different sized syringes using the same apparatus. Additionally, since the apparatus of the present invention may comprise more than one exit port, a plurality of syringes (either the same size or different sizes) may be filled at the same time, from the same batch of mixed bone cement. 
     Whilst the user may be able to judge when the valve is in the open or closed position, in a preferred embodiment, the apparatus of the present invention comprises means for locating the valve in the first position and/or means for locating the valve in the second position. 
     In a preferred embodiment, the apparatus of the present invention also comprises means for preventing the valve from being accidentally removed from the second end of the apparatus. In one embodiment, this means comprises at least one end-stop that is provided on the exterior surface of the valve and which abuts an opposing surface, such as a ledge, that is provided on the interior surface of the apparatus. 
     The apparatus of the present invention may further comprise a base, which allows the apparatus to be freestanding and so increasing ease of use. Due to the fact that the exit port(s) are provided between the first and second ends, the base may be provided at the second end of the apparatus. The base may therefore act as a support on which the apparatus stands and may be integral with or attachable to the apparatus and/or the valve. The base may also be associated with the valve, so that movement of the base causes movement of the valve. In a preferred embodiment, rotation of the base causes longitudinal or axial movement of the valve. This thereby aids manipulation of the valve within the apparatus and provides a simple means for moving the valve along the longitudinal axis of the apparatus. 
     It is possible to provide more than one exit port between the first end and the second end, thereby allowing for the connection of a plurality of syringes so that the operator may fill more than one syringe at a time. In this way, the present invention achieves easier transfer of mixed cement to more discharging syringes or the like, with the minimum of time, mess and effort. 
     Thus, the present invention provides a relatively simple, low cost and effective apparatus for mixing and discharging bone cement into a syringe(s), whilst also providing an improved mixing action and producing minimal fumes. 
    
    
     
       Preferred embodiments will now be described by way of example only, with reference to the accompanying drawings. 
         FIG. 1  is a side view of the mixing and discharging apparatus in accordance with a first embodiment of the invention, with the valve in the first position. 
         FIG. 2  is a side view of the mixing and discharging apparatus in accordance with a first embodiment of the invention, with the valve in the second position. 
         FIG. 3  is a side view of the valve positioned within the apparatus in a preferred embodiment. 
         FIG. 4  is a side view of the mixing and discharging apparatus in accordance with a second embodiment of the invention. 
         FIG. 5  is a perspective view of a preferred valve and mixing container, showing a one way clip feature. 
         FIG. 6  is a perspective view of a preferred base. 
         FIG. 7  is a side view of the mixing and dispensing apparatus in accordance with a second embodiment of the invention, depicting a plunger. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is useful with many different types of bone cement and syringe types and sizes. 
       FIGS. 1 and 2  show one embodiment of the mixing and discharging apparatus  10 . The mixing and discharging apparatus  10  comprises a first end  14 , which is generally uppermost when the apparatus is in use, and a second end  16 , which is lowermost when the apparatus is in use, with a longitudinal axis (L) extending between the first end  14  and second end  16 . The apparatus defines a mixing and discharging container  12 . In one embodiment, this comprises a bowl-shaped mixing region  13  at the first end  14 , which is in communication with a cylindrical discharging region  17 , at the second end  16 . 
     During use, the operator may hold the apparatus in one hand, while mixing with the other. Alternatively, use may be simplified by standing the apparatus upright upon the flat base  40 , which is provided at the second, or lowermost end  16  of apparatus. This provides added stability during mixing and discharging. 
     The mixing and discharging container  12  comprises at least one exit port  20  located on the side of the container between the first end  14  and the second end  16 . 
     The mixing and discharging apparatus  10  further comprises means for selectively preventing or enabling communication between the mixing region  13  and the exit port  20 . In this embodiment, the means comprises a cylindrical valve  30 , which is fitted into the discharging region  17  and is axially moveable between a first position ( FIG. 1 ), at which the mixing region  13  and exit port  20  are prevented from being in communication with each other because the valve  30  actually blocks the exit port  20 , and a second position ( FIG. 2 ) at which the mixing region  13  and the exit port  20  are enabled to be in communication with each other, since the valve  30  no longer blocks the exit port  20 . Other shapes of valve may be used, so long as the valve can be moved between an “open” ( FIG. 2 ) and “closed” ( FIG. 1 ) position. The exterior surface of the valve  30  may also comprise one or more moulded bi-directional friction seals  39 , as shown in  FIG. 3 , which create a seal between the valve  30  and the interior surface of the discharging region  17  of the container  12 . One end (i.e. the first, or uppermost end  32 ) of the valve is tapered to a point in this embodiment, to match the shape of a paddle and/or scraper, thereby minimising wastage and improving the mixing effects. 
     Prior to mixing, the valve of the apparatus is placed in the first position by the operator, by moving the valve along the longitudinal axis in the direction of the first end of the apparatus. Once the valve has reached the first position, an end-stop  38 , provided at the second, lower end of the valve  30 , abuts the second, lower end of the container, thereby locating the valve in the first position and preventing the valve from moving any further into the container. The upper end of the valve then acts as a closure for the mixing region  13 , closing this region off from the discharging region  17  and the exit port(s) in the wall of the discharging region  17 . 
     The bone cement components to be mixed are then placed in the mixing region  13  of the apparatus via an entry port (not shown), which is provided at the first end  14  of the container. 
     The components may then either be mixed by hand, using a spatula, or the like, or alternatively, as shown in  FIGS. 1 and 2 , the apparatus may further comprise a lid  60 , which is adapted to fit and seal to the first end  14  of the mixing container  12 . The lid may be fitted to the first end of the mixing container and locked into place in a number of ways, such as with clip means, or screw thread means. 
     The lid  60  may be used in conjunction with a handle  70  which is rotatably mounted in, and extending outwardly from the lid  70  and an “off-centred” paddle such as disclosed in GB 2 276 560, wherein rotation of the handle causes the paddle to rotate both around the bowl and also about its own axis. As also disclosed in GB 2 276 560, in this embodiment, the under side of the lid is preferably provided with a fixed, circular, toothed rack  64  which is coaxially arranged with the rotational axis of the handle  70 . The mixing paddle  72 , may comprise radially extending mixing blades  76  and be mounted on an axle  74  that is arranged coaxially with the rotational axis of the handle  70  and extends from the underside thereof. A cog wheel  75  may be fixedly attached to the upper part of the axle  74  for intermeshing engagement with the toothed rack  64 . The lid  60  is preferably provided with a seal (not shown), for sealing between the lid  60  and the mixing container  12 . 
     The present invention may further comprise a scraper paddle  78 , which helps to reduce wastage, whilst also improving the mixing effect. The scraper paddle  78 , shown in  FIGS. 1 and 2 , has a relatively thin profile to cut through cement but is shaped in the form of a paddle so as to assist in mixing, and, further, to extend out to the inner wall of the mixing region  13 , to scrape cement from the interior surface of the bowl. The scraper paddle is attached to the gear mechanism such that as the handle is rotated during mixing, the scraper paddle rotates around the mixing bowl in counter-rotation with the mixing paddle shaft  74 . The scraper paddle is preferably shaped so as to have a radially outer curve which essentially follows the shape of the inside surface of the mixing region  13  and a radially inner profile which is curved so as to pass by the paddle  72  during rotation. 
     The profile of the mixing paddle  72  in the mixing region  13  is preferably such that it will push the cement down towards the bottom of the mixing region  13 , as the components are mixed. As the two components mix, the volume of cement reduces and when completely mixed, the cement will be capable of being accommodated within the cylindrical dispensing region  17 . 
     At any time up to this point, a syringe or syringes  19  may be attached to the exit port  20 , directly or, if desired, via connection means (not shown). The connection means may comprise a valve for blocking or enabling the flow of cement into the syringe. 
     Alternatively, simple stopper means may be connected to the exit port(s) of the apparatus for blocking exit ports to which syringes are not connected. 
     The connection means may also be provided in different sizes or in the form of an adaptor for different sized syringes. Due to this feature, a plurality of different sized syringes can be filled from the apparatus of the present invention, with multiple syringes being filled at the same time and from the same batch of mixed cement. 
     Following mixing of the bone cement and connection of the syringes or stoppers to the apparatus, the operator then moves the valve  30  into the second position ( FIG. 2 ), by moving the valve  30  along the longitudinal axis away from the mixing region  13  of the container. End-stops  37 , provided on the exterior surface of the valve eventually contact an abutment surface, e.g. a ledge  33 , provided on the interior surface of the discharging region  17  of the apparatus (as shown in  FIG. 3 ), thereby providing means for locating the valve in the second position. At this point, the valve cannot be moved any further in that direction, thereby also preventing the valve  30  from being accidentally removed from the apparatus. The valve, in this position, acts as a closure to the discharging region such that cement cannot exit the apparatus from this end. 
     Once the valve is in the second position and no longer blocks the exit port(s), communication is enabled between the mixing region  13  and the exit port  20  and the mixed bone cement can flow out of the mixing region  13  of the container, to the exit port  20  under the force of gravity. The operator then draws back the plunger on the attached syringe(s)  19  to remove the mixed bone cement into the syringe(s)  19 , ready for use. If the cement is more viscous, the operator may also remove the lid from the apparatus and force cement down into the discharging region of the apparatus using a plunger (such as that described. hereinafter) or even a spatula. Following the filling of the syringe(s), the operator may move the valve back into the first position ( FIG. 1 ), thereby closing the exit port(s)  20  and preventing spillage of bone cement when the syringe(s) are detached from the apparatus. This also enables a second set of syringes to be filled once the first set is detached from the apparatus. 
     Next, a second, preferred embodiment of the invention will be described, with reference to  FIGS. 4 to 7 . Corresponding features are described with like reference numerals. 
       FIG. 4  shows a second embodiment of the apparatus  10 , having a first end  14  and a second end  16 . The apparatus comprises a hollow, cylindrical container  12  (also shown in  FIG. 5 ) with a mixing region  13  and an exit port or ports  20  disposed on the side of the container between the first end  14  and the second end  16 . 
     The valve  30  is again cylindrical in shape and moveable along the longitudinal axis (L) of the apparatus between a first position ( FIG. 4 ) wherein communication between the mixing region  13  and the exit port  20  is prevented, and a second position ( FIG. 7 ) wherein communication is enabled. 
     The exterior surface of the valve may also comprise sealing means, such as an O-ring(s)  72 , as shown in  FIGS. 4 and 7 . The O-ring  72  provides a better seal, so that none of the components can leak from the mixing region  13  into the discharging region  17  and/or exit port(s) while it is being mixed, and also prevents air from entering the mixing region. In this way, the O-ring helps to provide a better quality cement. Alternative sealing means may also be provided on the exterior surface of the valve, and/or the interior surface of the discharging region  17  for preventing the entry of air into the mixing region  13  and for preventing unmixed or mixed bone cement or components from leaking from the mixing region  13 . 
     As described in relation to the first embodiment, prior to mixing of the bone cement components, the valve  30  of the apparatus is placed in the first position by the operator. This may again be achieved by pushing the valve along the longitudinal axis of the container, however, in the embodiment shown in  FIGS. 4 to 7 , the controlled movement of the valve along the longitudinal axis is achieved via rotation of a base  440 , (with which the valve is associated), relative to the container  12 . 
     As shown in  FIG. 4 , the base  440  is positioned at the second end  16  of the mixing apparatus, surrounding the second end  16  of the container  12 , and a screw thread  34 , formed on the exterior surface of the valve  30  or the end-stop  38  of the valve  30  ( FIG. 5 ) is complimentary to and mates with a screw thread  42  formed on the interior surface of the base  440  ( FIG. 6 ). Thus, rotation of the base creates movement of the valve along the longitudinal axis of the apparatus. 
     Means for preventing rotation of the valve  30  in relation to the mixing container  12  and means for locating the valve  30  in the first position ( FIG. 4 ) or second position ( FIG. 7 ), is provided in this embodiment by the way of a ‘one way clip feature’. This clip feature is formed by clipping a projection  36 , formed on the exterior surface of the valve  30 , into an opening  24 , in the side of the mixing container  12 , as shown in  FIG. 5 . This feature limits the movement of the valve  30  along the longitudinal axis of the apparatus  10  or container  12 , whilst also preventing the valve from being accidentally removed from the second end  16  of the apparatus. 
     After the operator has placed the valve in the first position ( FIG. 4 ) and the mixing region is closed off from the discharging region  17  and the exit port(s)  20 , the bone cement components to be mixed are then placed by the operator into the mixing container  12 , via the entry port  18 , which is at the first, uppermost end  14  of the apparatus. 
     The cement components are then mixed, either by hand, or using a lid with a handle and a paddle, as described in GB 2 276 560 and in relation to the first embodiment. 
     Any time up to this point, syringe(s)  19  or stopper(s) (not shown) may be attached to the exit port(s)  20 , as described earlier. As also described earlier, the connection means may also be provided in different sizes or in the form of an adaptor for different sized syringes. 
     Once the components are fully mixed, the operator then rotates the base  440  in the opposite direction to before. The valve therefore moves along the longitudinal axis until the projection  36  of the clip abuts the end of the opening  24 , preventing any further movement in that direction and thereby locating the valve in the second position ( FIG. 7 ). At this point, communication is enabled between the mixing region  13  and the exit port(s)  20 . 
     In some situations, such as may be the case with particularly viscous bone cement mixtures, gravity alone may not be sufficient to force the mixed bone cement from the mixing region to the vicinity of the exit port. Therefore, the apparatus may further comprise plunger means  80 , as shown in  FIG. 7 . 
     Following the movement of the valve into the second position, the operator removes the lid  60  and inserts the plunger  80  into the container  12  at the first end  14 , thereby forcing the mixed bone cement towards the vicinity of the exit port  20 . 
     In order to aid insertion into the container, the plunger may comprise a screw thread  82 , formed on its exterior surface, which is complimentary to, and mates with, a screw thread  22  (as shown in  FIG. 5 ) formed on the internal surface of the mixing container  12 . This is preferably the same screw thread that is used to fasten the lid in place. Therefore, by rotating the plunger  80 , the plunger  80  advances into the container along the longitudinal axis. 
     As shown in  FIG. 7 , the first end  84  of the plunger which first enters the container  12  is substantially flat, with its outer perimeter  86  being cut away so that it tapers away from the end surface. Thus, when the plunger is fully inserted into the mixing and discharging apparatus, the substantially flat first end surface  84  of the plunger  80  contacts the substantially flat end surface  332  of the valve  30 , and forces any remaining mixed bone cement into a small area  88  available between the tapered edge  86  of the plunger  80  and the end surface  332  of the valve  30 . Due to the minimal free space available, this design thereby minimises wastage when the plunger is fully inserted into the mixing container  12 . 
     The plunger may also comprise grooves (not shown) that extend longitudinally along its exterior surface between its first end  84  and its second end  89 , so that air displaced from the mixing region due to entry of the plunger into the mixing region can escape out of the first end  14  of the apparatus. Alternatively, such grooves may be present on the interior walls of the apparatus itself. In a further arrangement, the plunger may have holes in its first  84  and second  89  end so that air between the plunger and the mixed bone cement can be vented. Due to these arrangements, air is not trapped in the apparatus with the bone cement and so is not transferred to the syringes when the cement is discharged. 
     Once the bone cement reaches the vicinity of the exit port, the syringe(s) can then be filled, ready for use. As described above, the valve may be moved back into the first position following the filling of the syringes, thereby ensuring that there is no spillage once the syringes are detached. This also enables a possible second filling of syringes.