Mixing apparatus

Abstract

An apparatus for opening a container of a component of a multi-part orthopaedic paste comprising a housing for receiving and enclosing the container. The housing has an outlet for delivery of the comp

Description

Field of Invention The present invention generally relates to devices for use in the preparation of multipart orthopaedic pastes. In particular embodiments relate to mixing apparatus forthe multi-part orthopaedic pastes and to devices for delivering or dispensing components of a multi-part orthopaedic paste. Background Orthopaedic pastes include bone cement, bone substitute and filler materials. It is common to provide orthopaedic pastes in a multi-part format which must be mixed to activate the paste prior to use. When mixed the components react resulting in the curing of the orthopaedic paste (for example by polymerisation). The curing of orthopaedic pastes in this manner can be considered to pass through a number of stages including a working phase, during which the cement has a suitable viscosity for application, and a setting phase, during which the orthopaedic paste will continue to solidify until fully hardened. To provide a consistent and homogenised results with minimum porosity, mixing may be performed using a device which mixes the multipart paste under vacuum (for example at around 550mmHg). Avariety of such devices are commercially available - for example, the Applicant's own HIVAC (RTM) range of products. The most common bone cement is polymethyl methacrylate ("PMMA") which is typically provided as a powder co-polymer (for example a polymethylmethacrylate powder) and a liquid monomer (for example methylmethacrylate monomer). It will be appreciated that one or both of the powder component and the liquid component may also include additional substances - these may, for example, include additives such as one or more of: stabilisers, initiators, accelerators, radio-opacifiers, and antibiotics. The components of multi-part orthopaedic pastes are generally provided as two sterile pre-packages which are of precisely measured quantities ready to be mixed. The liquid component (such as the monomer) may be packaged in a sealed container which must be opened prior to combining the components. This is particularly important as the liquid component of orthopaedic pastes is typically highly volatile (and for example methylmethacrylate fumes are unpleasant and potentially harmful). Due to the reactivity of the liquid component, the sealed container is typically a glass container and may be an ampoule with a thin neck to allow a head to be snapped off to open the container. Such ampoules may be manually snapped open, but this has been known to cause problems including glass shards being present in the paste mix, glove tears which comprise sterility or even direct injuries to users. Accordingly, devices have been proposed to aid the introduction of the liquid components during mixing. Such devices include both ampule opening devices which only open and dispense liquid from an ampule and integrated mixing systems including both an ampoule opening arrangement and a mixing chamber in which the liquid component is subsequently combined with a powder component. An integrated mixing system including an ampoule opener is, for example, shown in published International Patent application number WO2012 / 003916. An example of a device for breaking an ampoule of liquid monomer is also shown in the Applicant's own published International Patent Application WO2011 / 003625. Embodiments of the invention seek to provide alternative and / or improved devices for dispensing components of a multi-part orthopaedic paste from a container. Summary of Invention According to a first aspect of the invention, there is provided an apparatus for opening a container of a component of a multi-part orthopaedic paste. The apparatus comprises a housing for receiving and enclosing the container. The housing has an outlet for delivery of the component. The apparatus further comprises a striker, for opening the container during use; a latch, which holds the container and striker in an initial, spaced apart, configuration; and a trigger which releases the latch. The release of the latch enables the striker to impact and open the container. The container may be a frangible container. The component of a multi-part orthopaedic paste may be a liquid component. The liquid component may be combined with a powder after it is dispensed from the frangible container. The outlet may be a filtered outlet - for example the outlet may comprise one or more apertures of sufficiently small size to provide a filtering of the component being dispensed and / or may include a filtering element (such as a sintered plug). A filtered outlet may, in particular, be included when the frangible container is formed of glass to filter out any small glass shards. In contrast to known prior art devices, embodiments of the invention use an impact between a striker and the frangible container to cause the container to break and allow the component enclosed therein to be dispensed. It will be appreciated that an impact is a dynamic impingement or striking action between the components and uses kinetic energy to assist in fracturing the container (rather than purely relying on a static force provided by the user. The use of an impact rather than a snapping (by bending or shear) or crushing force may also be beneficial in providing a device which opens the container with predictable and consistent timing after triggering. The applicant has recognised that the use of an impact provides an improved reliability of fracturing the container whilst the provision of a trigger activated latch mechanism provides improved usability. For example, devices in accordance with embodiments may be relatively intuitive for the end user as a result of the provision of a trigger element. Embodiments of the invention may also reduce the risk of any of the component pooling within the remains of the container after opening (as may, for example, happen with a container having snappable neck) - such pooling can impact the precise ratio of the components being mixed which may in turn cause the cure time of the paste to vary which is undesirable for surgical timing. In embodiments the latch may hold the frangible container and striker apart prior to use. The latch may hold against an energy store which is configured to urge the frangible container and striker into dynamic contact. Advantageously, the use of a releasable energy store may enable devices of embodiments to apply substantially the same breaking force to the frangible container independent of end user variation and may ensure. In some embodiments the releasable energy store could be a pressure difference applied to one or both of the frangible container and striker. Forexample, the pressure difference may utilise vacuum pressure which is generally available for use when mixing an orthopaedic paste, for example the housing of the apparatus may be under vacuum prior to activation of the trigger. In other embodiments the releasable energy store may comprise a spring (for example a compression spring). The spring may for example bias the frangible container and striker toward one another. In embodiments the striker may be moveably mounted in the housing. The striker may be spring biased within the housing. The latch may retain the spring in an energised state, for example in a compressed state. The latch may hold the striker against the spring in a first position with energy stored in the spring. The trigger may cause the latch to release the striker such that it moves with the energy store of the spring providing the driving force to cause the striker to impact the frangible container. In some embodiments the latch may hold the frangible container in a first position, and release of the latch may enable the frangible container to travel to a second position. The frangible container may, therefore, be moveable with respect to the housing. In such embodiments the release and subsequent movement of the frangible container may cause the impact with the striker at the second position. The frangible container may be biased to the second position (and, as such, the latch may hold the frangible container against an energy store). Depending upon the configuration of the device the movement of the frangible container from the first position to the second position may be biased by one or more of gravity, spring force and / or vacuum force. In embodiments the latch may hold the frangible container by a head portion (for example engaging the narrowed neck portion of an ampoule). In embodiments in which the frangible container is moveable between first and second positions the striker may comprise a fixed head projecting inwardly from a wall of the housing. The frangible container may be an ampoule (for example a glass ampoule). The ampoule may comprise a body and a head connected to the body by a neck. Conventionally such ampoules are opened by snapping or shearing the head at the neck; the Applicant has, however, recognised that this is often unreliable. In particular, when an ampoule is opened by removal of the head it is possible for some of the contents to remain in the head portion - when combining components of a multi-part paste this may result in variation in the precise quantities of the components which are then mixed and impacting the quality of the final orthopaedic paste. Embodiment of the invention are configured such that the striker impacts the body of the ampoule. For example, the ampoule may have a base at the opposite end to the head and the striker may be aligned to impact the impact the base. It has been found that impacting at or close to the base of an ampoule causes the ampoule to shatter with no possibility of component remaining within the ampoule. As the ampoule is shattered within the housing of the apparatus this does not present any risk to the end user. In some embodiments the apparatus of the invention may be configured to open multiple frangible containers. Advantageously, embodiments may open multiple frangible containers simultaneously (i.e., as a result of a single user action). In some embodiments the housing may receive and enclose a plurality of frangible containers. The striker may comprise a plurality of strikers each striker being arranged to impact one of the frangible containers. Each frangible container and corresponding striker may be spaced apart in parallel. A common trigger may release the latch (or latches) to enable the strikers to each impact and fracture the corresponding frangible container. In embodiments the trigger may further comprise a safety mechanism to prevent unintended release of the latch. This may be particularly useful where the frangible container contains a liquid monomer (or other reactive and / or potentially harmful components). The safety mechanism may be moveable between an engaged position in which the safety mechanism impedes movement of the trigger and a disengaged position in which the safety mechanism does not impede movement of the trigger. The safety mechanism may be biased to the engaged position. In some embodiments the safety mechanism could be a simple manual feature which the end user must activate in a preparatory step prior to use of the trigger. In other embodiments the safety mechanism may be automatically moved to the disengaged piston when the housing is under vacuum. For example, at least a portion of the safety mechanism may be in fluid communication with the interior of the housing such that when the housing is under vacuum the resulting negative pressure can act on the portion of the safety mechanism. It may be particularly useful to provide the apparatus for opening a container as part of a mixing apparatus. As such, in another aspect of the invention there is provided an apparatus for mixing a multi-part orthopaedic paste. The apparatus comprises a mixing assembly having a body defining a mixing chamber, configured to receive or contain one component of the multi-part orthopaedic paste, and a mixing element moveably mounted in the body. The apparatus may further comprise an activator assembly in fluid communication with the mixing chamber and comprising an apparatus for opening a container in accordance with an embodiment. In another aspect an apparatus for mixing a multi-part orthopaedic paste may comprise a mixing assembly having a body defining a mixing chamber, configured to receive or contain one component of the multi-part orthopaedic paste, a mixing element moveably mounted in the body; and an activator assembly in fluid communication with the mixing chamber. The activator may comprise a housing for receiving and enclosing a container of another component of the multi-part orthopaedic paste, the housing having an outlet for delivery of the component into the mixing chamber. The activator may further comprise an actuation mechanism having a striker, for opening the container during use; a latch, which holds the frangible container and striker in an initial, spaced apart, configuration; and a trigger which releases the latch mechanism to enable the striker to impact and open the container. The mixing element may comprise a mixing head and a mixing shaft. The mixing shaft may include an actuation portion external to the mixing chamber. In some embodiments the mixing chamber is prefilled with a component of the multipart orthopaedic paste. For example, the mixing chamber may be prefilled with a powdered component of the multi-part orthopaedic paste. The apparatus may further comprise a base. The mixing assembly may be removably connected to the base. The activator assembly may be fixed relative to the base and in some embodiments the housing of the activator assembly may be integral with the base. The mixing assembly may comprise a cylindrical syringe dispenser. As such it will be appreciated that after mixing the assembly may be separated and used as a syringe dispenser to apply the orthopaedic paste as required. In embodiments the mixing assembly and the activator assembly may be relatively moveable between a first configuration in which the mixing assembly and activator assembly are in a first alignment and a flow path is open extending from the interior of a housing of the activator assembly to the mixing chamber and a second configuration in which the mixing assembly and activator assembly are in a second alignment and the flow path is closed. For example, in order to release the mixing assembly from the base it may be necessary to move the assembly into the second configuration. This may be novel in its own right and another aspect of the invention provides an apparatus for mixing a multi-part orthopaedic paste, the apparatus comprising: a mixing assembly having a body defining a mixing chamber and configured to receive or contain one component of the multi-part orthopaedic paste, a mixing element moveably mounted in the body and; an activator assembly, for containing and dispensing another component of a multi-part orthopaedic paste. Wherein the activator assembly is in fluid communication with the mixing assembly via a flow path extending from the interior of a housing of the activator assembly to the mixing chamber. The apparatus may have a first configuration in which the mixing assembly and activator assembly are in a first alignment and the flow path is open and a second configuration in which the mixing assembly and activator assembly are in a second alignment and the flow path is closed. The apparatus may be moveable between the first configuration and the second configuration by relative rotation of the body of the mixing assembly (for example rotation about its longitudinal axis). The apparatus may further comprise a base and wherein the activator assembly is fixed relative to the base and the mixing assembly is removably connected to the base. In embodiments the flow path may comprises an inlet extending through the body defining a mixing chamber, for example the inlet may extend through a side wall of the body. This may provide a relatively compact arrangement allowing the activator assembly to be mounted with or adjacent to the body. The flow path may further comprise a conduit formed in the piston of the mixing assembly. In the open alignment the flow path may extends sequentially from an outlet of the activator assembly to the inlet in the side wall. The flow path may then extend through the conduit in the piston and in to the mixing chamber. Advantageously, having the flow path extend through the piston may provide an additional closure of the flow path when the piston moves out of its initial position. Unless otherwise stated, each of the integers described may be used in combination with any other integer as would be understood by the person skilled in the art. Further, although all aspects of the invention preferably "comprise" the features described in relation to that aspect, it is specifically envisaged that they may "consist" or "consist essentially" of those features outlined in the claims. In addition, all terms, unless specifically defined herein, are intended to be given their commonly understood meaning in the art. Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following description or drawings. Description of the Drawings Embodiments of the invention may be performed in various ways, and embodiments thereof will now be described by way of example only, reference being made to the accompanying drawings, in which: Figure 1 shows a three-dimensional view of a bone cement mixing device in accordance with an embodiment; Figure 2 shows a longitudinal cross section through the device of figure 1; Figures 3A and 3B show perpendicular longitudinal cross-sectional views of an ampoule breaking arrangement of a device in accordance with an embodiment in a pre-use configuration; Figure 4A and 4B show the views of Figure 3A and 3B in a fired configuration; Figure 5 shows a cross sectional schematic of a bone cement mixing device in accordance with another embodiment; and Figure 6 shows a trigger and safety mechanism for use in embodiments. Detail Description of Embodiments It may be noted that upper and lower are used herein to conveniently refer to the device in its typical in use orientation (as shown in the figures). However, it will be appreciated that such references are not intended to be limiting and that the device may take any orientation in use. Likewise, any references to circumferential, radial or axial directions may be interpreted broadly as general geometric terms of orientation and, for example, do not exclude that a component may have a non-circular or irregular form. An apparatus 1 for mixing a multi-part orthopaedic in accordance with an embodiment, and as shown in figures 1 to 4, will now be described to assist in understanding of the invention. For clarity purposes this device will be described in the context of its typical use in mixing a PMMA bone cement and for convenience the apparatus will be referred to as a bone cement mixing device. It will, however, be appreciated that the device may be used (or adapted) for use with other types of orthopaedic pastes without departing from the scope of the present invention. The bone cement mixing device 1 of an embodiment includes a mixing assembly 10 having a body 11 defining a mixing chamber 12. The mixing chamber 12 is filled with a first component of the bone cement, in the form of polymethylmethacrylate powder, in use. It will be appreciated that in some embodiments the device 1 may be provided as a pre-filled device with a pre-measured quantity of powder in the mixing chamber 12. A mixing element 20 is moveably mounted in the mixing chamber 12 and comprises a mixing head 22 inside the chamber 12 and a mixing shaft 24 which extends from a proximal end 23 mounted to the mixing head to a distal end 25 outside of the chamber. The distal end 25 of the mixing shaft is an actuation portion used to move the mixing head during use. The distal end may include a handle 26 and / or may include a coupling (not shown) for attachment to a motive device (for example a surgical reamer). The mixing shaft 24 passes through a lid 30 which provides a sealed closure at the upper end of the body 11. The lower end of the mixing chamber 12 is closed by a piston 32 which is sealingly positioned within the body 11. The piston 32 is axially slidable within the body 11 and is used to force the bone cement from the mixing chamber in use via a nozzle (with such arrangements known in the art). The lower end of the body 11 is removably connected to a base 40 which supports the mixing device 1 on a surface during the initial stages of use. The device of embodiments also comprised as an activator 100 which is configured to introduce a second component of the bone cement, in the form of methylmethacrylate monomer liquid, into the mixing chamber 12 to activate the polymerisation reaction of the bone cement. The monomer liquid is contained in at least one sealed glass ampoule 110 which includes a body 112 having a base 114 and a head 116. As is conventional with ampoules, a narrowed neck 115 is provided between the body 112 and head 116 which may be used to snap or shear the head from the body to open the ampoule. The activator 100 includes a housing 120 which is configured to receive and enclose the ampoule 110 (or in some embodiments a plurality of ampoules). The housing is attached to the base 40 of the mixing device 1 and, in the embodiment of figures 1 and 2, it may be noted that the base 40 and housing are integrally formed (for example as a single moulding). An outlet 125 is provided in the housing 120 for the delivery of the liquid monomer into the mixing chamber 12 after opening of the ampoule 110 (as will have explained further below). In the illustrated embodiment it may be noted that the device 1 includes a pair of ampoules 110a and 110b which are mounted in a side-by-side, axially parallel, arrangement. It will be appreciated that the inclusion of a plurality of ampoules will be a design choice for a device dependent upon the quantity of bone cement being mixed and the required quantity of monomer liquid. In a device intended to use multiple ampoules the housing 120 will be sized and shaped to receive and hold each ampoule in either a common or separate chambers (with one or more outlets 125 associated with the or each chamber). In accordance with embodiments, a lower portion of the housing 120 of the activator includes a mechanism 200 for breaking the ampoule(s) 110. As best seen in the detailed sections of figures 3A and 3B, the mechanism 200 comprises a striker 210 in the form of a spike 214 (best disposed beneath each ampoule 110a, 110b is activated by means of a trigger 230 which projects outwardly from the housing 120. In this embodiment the trigger 230 comprises a pull tab which is pulled away from the housing 120 to activate the mechanism 200. The mechanism 200 further comprises a latch 220 which in this embodiment comprises a forked member having first and second latch members 222a and 222b. The latch 220 may extend through a slot in the housing 120 with the inward ends of the latch members 222 engaging into a recess or other retaining feature. In this initial position the latch 220 blocks movement of the striker 210 in the upward direction towards the ampoule(s) 110 so as to hold the striker and ampoule 110 in a spaced apart configuration. The mechanism 200 also includes an energy store in the form of a compression spring 250 the upper end of which engages the reverse side of a carrier portion 212 of the striker which connects both spikes 214a, 214b of the striker 210. The compression spring 250 is mounted on a shaft 252 and is retained by a spring retaining nut 254 which is threaded onto the shaft 252. The lower portion of the housing 120 includes a base wall 122 which extends transversely across the housing below the ampoule 110. It maybe noted that the base wall 122 is sloped downwardly towards the mixing chamber 122. The outlet 125 for delivery of the liquid monomer into the mixing chamber 12 is provided at, or proximal to, the intersection of an inner side wall portion 121 of the housing 120 and the base wall 122. The base wall 122 is provided with apertures 123a, 123b aligned with, and shaped and configured for, the spikes 214a, 214b. Whilst omitted from the diagram it will be appreciated that the apertures may be closed with a pierceable film or membrane to ensure there is no leak path through the base of the housing 120 in the event of an unplanned breakage of a vial for example during transit (and it will be appreciated that the membrane may, for example, be made of a self-healing material which can seal around the spikes during use). Operation of the embodiment will now be described. In the initial pre-use configuration shown in figure 3, the spring 250 is held in a compressed state between the rear of the striker 219 and the retaining nut 254. Due to the blocking position of the latch 220 the stored energy of the spring 250 cannot bias the striker 210 upward towards the ampoule 110. If the device is supplied pre-filled a measured quantity of polymer powder is already present in the mixing chamber 12 and the ampoules are already positioned within the housing 120 of the activator. Alternatively, the user may prepare the mixing device 1 by dispensing powder into the chamber 12 and positioning ampoules 110 in the housing 120. When the user is ready to mix the bone cement, they use the activator assembly 200 to introduce the liquid monomer into the mixing chamber 12. Prior to activation the user would normally connect a vacuum source to the mixing chamber 12. As the outlet 125 of the housing 120 is in fluid communication with the mixing chamber 12 this also provides vacuum to the interior of the housing 120. Figures 4A and 4B show the configuration of the activation mechanism 200 immediately following activation. The user pulls the trigger 230 outwardly with respect to the housing 120 to use the activator assembly 100. The trigger 230 displaces the latch 220 out of blocking alignment with the striker 210. This enables the energy stored in the spring 250 to be released and propels the striker 210 upward. The spikes 214a and 214b of the striker 210 pass through the corresponding apertures 123a and 122b in the base wall 122. As a result, the tips of the spikes dynamically impact the base of the 114 of each ampoule 110a 110b. The spring force of the spring 250 is selected to ensure that there is sufficient stored energy transferred to the striker 210 such that the impact with the ampoule base 114 will cause the ampoule to rupture (and typically to shatter). The spikes 214 of the striker are configured to sealingly engage around the apertures 123 (and the seal may be assisted by provision of a membrane or one or more sealing elements around the periphery of the apertures 123 and / or spikes 214). As the interior of the housing 120 is under vacuum the spikes will also be actively pulled into engagement with the apertures to assist sealing and prevent leakage. Following the breaking of the ampoules, the liquid monomer from the ampoules will be drawn by gravity and vacuum from the housing 120 through the outlet 125 and into the mixing chamber 12. To prevent the passage of glass fragments into the mixing chamber 12 the outlet may include a filter such as a sintered plug which the liquid monomer will pass through. Figure 5 shows an embodiment of the invention 1' schematically showing some alternative features. This embodiment illustrates both an alternate activation mechanism 200' and a modified fluid communication between the housing 120' and the mixing chamber 12'. It will be appreciated that these features are not interdependent and could be independently selected for any specific implementation of the invention. For example, the fluid communication arrangement of this embodiment could be applied to other embodiments such as those of figure 3 and 4 without modification to the activation mechanism. In the embodiment of figure 5 it will be noted that the striker 210' is a fixed member which projects inwardly from the base wall 122' of the housing 120'. The ampoule 110' is retained in a holder 118' which is slidably mounted within the housing 120'. The ampoule holder 118' initially retains the ampoule 110' in a spaced apart position with respect to the striker 210'. The general principle of this embodiment is that rather than releasing the striker for movement the ampoule is held and then released to cause an impact. It will be appreciated that due to the initial spaced apart arrangement, the ampoule 110' is already biased towards the striker 210' by a combination of gravity. Additionally, when the mixing chamber 12' is under vacuum this also creates a vacuum in the interior of the housing 120' (via the outlet 125') which further adds to the stored energy which is urging the ampoule towards the striker. Additionally, a spring bias may be included if additional force is required. Initially, the holder 118' and the ampoule 110' are retained such that the ampoule is spaced apart from the striker 210'. In some embodiments this retention may be provided using a mechanism of the type shown in figure 3 (but configured to retain and release the holder 118' rather than the striker 210) which would include a latch to initially hold the holder in position and a trigger to release the latch when the user was ready to use the device 1'. Alternatively, the trigger and latch arrangement could be of the type discussed below. The embodiment of figure 5 also shows an embodiment of the fluid communication between the housing 120' and the mixing chamber 12'. The housing 120' includes an outlet 125' (which as noted above may include a filter). The outlet 125' communicates with a corresponding inlet 13 which extends through the body 11 of the mixing chamber 12. The outlet 125' and inlet 13 jointly define a flow path extending from the interior of the housing to the interior of the mixing chamber. It may be noted that the flow path may also conveniently pass through a conduit 33 formed in the piston 32 of the mixing assembly (but that this is not essential and will depend upon the spatial arrangement between the components). When the device is in an initial configuration (as shown in figures 1, 2 and 5) the mixing assembly 10 and activator assembly 100 are in a first alignment which ensures that the inlet 13 and outlet 125' are contiguous and the flow path is open. This allows the liquid monomer to pass through the flow path into the mixing chamber 12. When the components of the bone cement have been successfully combined (and optionally prior to actual mixing), the mixing assembly 10 and activator assembly 100 can be moved to a second configuration in which the mixing assembly and activator assembly are in a second alignment. Movement to the second configuration is achieved by moving the mixing assembly 10 relative to the base 40 (whilst the activator assembly is fixed relative to the base). This movement may be part of a step of removing the mixing assembly 10 from the base 40 or a preliminary movement which is carried out before the mixing assembly is removed from the base (if the user prefers to mix the bone cement whilst the mixing assembly 10 is still on the base 40). The movement of the mixing assembly 10 may be an axial sliding movement or a rotation about the longitudinal axis. For example, the rotation could conveniently be the movement which also releases a coupling (for example a screw thread or bayonet interface) between the base 40 and the mixing assembly 10. When the mixing assembly is moved the inlet 13 and outlet 125 are misaligned and the flow path between the housing 120 and the mixing chamber 12 is closed. Where the flow path extends through a conduit 33 in the piston 32 this may further provide a convenient means for closing the inlet 13 in the mixing assembly 10. For example, the piston may be configured to move out of alignment with the inlet in response to a user action such as the above-mentioned movement of the mixing assembly relative to the base 40 or movement of the mixing element. This can prevent backflow of bone cement from the mixing chamber through the inlet 13. Additionally or alternatively the assembly may include a filter (such as a filter plug in the piston 32) which has a pore size selected such that the first component (such as a liquid monomer) of the bone cement can pass through, but which will prevent the passage of mixed bone cement. Figure 6 shows an alternative configuration of an activation mechanism 200" for use in embodiments. Whilst figure 6 shows the mechanism configured to hold and release an ampule holder 118" the skilled person would appreciate that the same configuration could be adapted to hold and release a moveable striker 210 of the type shown in other embodiments. The mechanism 200" comprises a latch 220" which is configured to provide a releasable engagement to the housing 120" and block movement of the ampoule holder 118" (or in other versions the striker 210) and maintain a spaced apart arrangement between the striker and the ampoule. The latch 220" comprises resiliently deformable detent arms 222" with enlarged heads 225 which engage a corresponding feature (for example an aperture) of the housing 120". A trigger 230" is configured as a button which mechanically contacts the head 225 of the latch 220" to disengage the latch from the housing 120". The mechanism of figure 6 also provides an example of a safety assembly 300 which is provided to prevent premature release of the latch 220". The safety assembly has a body portion 310 which abuts a portion of the latch 220" and prevents release movement of the latch when the safety is engaged. In this embodiment the body 310 is positioned internally between a pair of deformable detent arms 222" such that they are not able to move sufficiently toward one another to disengage the enlarged heads from the housing 120". The body 310 is biased towards this engaged position by a safety spring 320. Whilst some embodiments could have a manual deactivation for the safety 300 this would require additional user steps in use. To avoid this, it is useful for the safety to be automatically deactivated when the mixing device is ready for use. This can be carried out using the vacuum that is applied to the mixing chamber 12 and the interior of the activator housing 120". A conduit 330 may be provided which enables the internal pressure of the housing 120 to be applied to the safety 300 (whilst the external side of the safety is subject to atmospheric pressure). By exposing an interior side of the safety body 310 to the vacuum in the chamber and selecting a safety spring which is overcome by an appropriate pressure difference across the safety 300 the body 310 will move against the bias of the safety spring 320 when a pre-determined level of vacuum is reached within the housing 120". This causes the body 310 to move towards alignment with the base region of the arms 222" such that they can bend sufficiently to disengage the housing 120" when the trigger is pressed by the user. Although the invention has been described above with reference to preferred embodiments, it will be appreciated that various changes or modification may be made without departing from the scope of the invention as defined in the appended claims. For example, whilst the detailed embodiments are described with respect to the use of glass ampoules it will be appreciated that other frangible containers may be used (forexample depending upon the composition of the orthopaedic paste which is being mixed). It will be appreciated that glass generally fractures by shattering and may result in small fragments such that filtering may be required other forms of frangible container may break or yield in other ways (for example being locally fractured or pierced) such containers would still be considered within the scope of the present invention provided they are suitable for storage of a component of orthopaedic pastes and can be ruptured by an impact. References to a frangible container in the context of embodiments of the invention will, therefore, be understood to be intended to broadly relate to any container which can be readily opened in such a manner.

Claims

1. An apparatus for opening a container of a component of a multi-part orthopaedic paste, the apparatus comprising:a housing for receiving and enclosing the container, the housing having an outlet for delivery of the component; andan actuation mechanism comprising:a striker, for opening the container during use;a latch mechanism, which holds the container and striker in an initial, spaced apart, configuration; anda trigger which releases the latch mechanism to enable the striker to impact and open the container.

2. An apparatus as claimed in claim 1, wherein the latch mechanism holds the container and striker apart against an energy store configured to urge the container and striker into contact.

3. An apparatus as claimed in claim 2, wherein the energy store comprises a spring, the spring biasing the container and striker toward one another.

4. An apparatus as claimed in claim 3, wherein the striker is moveably mounted in the housing and spring biased.

5. An apparatus as claimed in claim 3 or 4, wherein the latch retains the spring in a compressed state.

6. An apparatus as claimed in any preceding claim, wherein the latch mechanism holds the container in a first position, and release of the latch enables the container to travel to a second position.

7. An apparatus as claimed in claim 6, wherein the striker comprises a fixed head projecting inwardly from a wall of the housing.

8. An apparatus as claimed in any preceding, wherein the container is an ampoule comprising a body and a head connected to the body by a neck and wherein the apparatus is configured such that the striker impacts the body of the ampoule.

9. An apparatus as claimed in claim 8, wherein the striker is aligned to impact a base of the ampoule, the base being at an opposite end to the head.

10. An apparatus as claimed in any preceding claim, wherein the housing receives and encloses a plurality of containers and wherein the striker comprises a plurality of strikers each striker being arranged to impact one of the containers.

11. An apparatus as claimed in claim 10, wherein each container and corresponding striker are spaced apart in parallel and a common trigger releases the latch or laches to enable the strikers to impact and fracture the corresponding container simultaneously.

12. An apparatus as claimed in any preceding claim, wherein the trigger further comprises a safety mechanism the safety mechanism being moveable between an engaged position in which the safety mechanism impedes movement of the trigger and a disengaged position in which the safety mechanism does not impede movement of the trigger.

13. An apparatus as claimed in claim 12, wherein the safety mechanism is biased to the engaged position.

14. An apparatus as claimed in claim 12 or 13, wherein the safety mechanism is moved to the disengaged piston automatically when the housing is under vacuum.

15. An apparatus for mixing a multi-part orthopaedic paste, the apparatus comprising: a mixing assembly havinga body defining a mixing chamber, configured to receive or contain one component of the multi-part orthopaedic paste,a mixing element moveably mounted in the body; andan activator assembly in fluid communication with the mixing chamber and comprising an apparatus for opening a container as claimed in any preceding claim.

16. An apparatus for mixing a multi-part orthopaedic paste, the apparatus comprising: a mixing assembly havinga body defining a mixing chamber, configured to receive or contain one component of the multi-part orthopaedic paste,a mixing element moveably mounted in the body; andan activator assembly in fluid communication with the mixing chamber, the activator assembly comprisinga housing for receiving and enclosing a container of another component of the multi-part orthopaedic paste, the housing having an outlet for delivery of the component into the mixing chamber; andan actuation mechanism comprising:a striker, for breaking the container during use;a latch mechanism, which holds the container and striker in an initial, spaced apart, configuration; anda trigger which releases the latch mechanism to enable the striker to impact and open the container.

17. An apparatus as claimed in claim 15 or 16, wherein the mixing chamber is prefilled with a component of the multi-part orthopaedic paste.

18. An apparatus as claimed in claim 15, 16 or 17, wherein the apparatus further comprises a base and wherein the mixing assembly is removably connected to the base.

19. An apparatus as claimed in any of claims 15 to 18, wherein the mixing assembly is a cylindrical syringe cement dispenser.

20. An apparatus as claimed in any of claims 15 to 19, wherein the mixing assembly and the activator assembly are relatively moveable betweena first configuration in which the mixing assembly and activator assembly are in a first alignment and a flow path is open extending from the interior of a housing of the activator assembly to the mixing chamber anda second configuration in which the mixing assembly and activator assembly are in a second alignment and the flow path is closed.

21. An apparatus for mixing a multi-part orthopaedic paste, the apparatus comprising: a mixing assembly having.a body defining a mixing chamber and configured to receive or contain one component of the multi-part orthopaedic paste, a mixing element moveably mounted in the body and.an activator assembly, for containing and dispensing another component of a multi-part orthopaedic paste, and in fluid communication with the mixing assembly via a flow path extending from the interior of a housing of the activator assembly to the mixing chamber; wherein.the apparatus has a first configuration in which the mixing assembly and activator assembly are in a first alignment and the flow path is open and a second configuration in which the mixing assembly and activator assembly are in a second alignment and the flow path is closed.

22. An apparatus as claimed in claim 20 or 21, wherein the apparatus is moveable between the first configuration and the second configuration by relative rotation of the body of the mixing assembly.

23. An apparatus as claimed in claim 22, wherein the apparatus further comprises a base and wherein the activator assembly is fixed relative to the base and the mixing assembly is removably connected to the base.5 24. An apparatuses claimed in any of claims 21 to 23, wherein the flow path comprisesan inlet extending through a side wall of the body defining a mixing chamber.

25. An apparatus as claimed in claim 24, wherein the flow path further comprises a conduit formed in the piston of the mixing assembly and wherein in the open 10 alignment the flow path extends sequentially from an outlet of the activator assembly to the inlet in the side wall through the conduit in the piston and to the mixing chamber.

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