Mixing Apparatus

Abstract

An apparatus suitable for mixing a multi-part orthopaedic paste 1, comprises of a body 10 of closed internal volume, a separator 50, an actuator / mixing element 20. The separator divides the closed vol

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 for combining two 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. However, more recently there have been some attempts to provide the liquid component in a pouch or container formed from a flexible film material. One such arrangement is disclosed for example in published European Patent EP1685812. Mixing devices which do not use a standard glass ampoule present different design challenges and opportunities (particularly for example if the sealed container is flexible and able to at least partially conform to a space provided in the device). An example of such a device is shown, for example in published European Patent EP3490700 in which a bladder is provided in a base of the device and can be pierced by a cannula in an initial step of use of the mixing apparatus. Embodiments of the invention seek to provide alternative and / or improved devices for dispensing components of a multi-part orthopaedic paste. In particular, embodiments seek to provide improved or alternative devices which are specifically adapted and optimised for use with a component which is initially provided in a sealed in a pouch or container formed from a flexible film material. Summary of Invention According to an aspect of the invention there is provided an apparatus for mixing a multi-part orthopaedic paste. The apparatus comprises a body defining an internal volume. A separator is slidably received within the body and may extend generally transversely within the internal volume. The separator divides the internal volume into a first chamber, configured to receive or contain a first component of the multipart orthopaedic paste, and a second chamber configured to receive or contain a second component of the multi-part orthopaedic paste. The separator is moveable between a first position, in which the second chamber has a first volume, and a second position, in which the second chamber has a second, reduced volume, and in which the volume of the first chamber and at least part of the first volume of the second chamber define, in combination, a mixing chamber. The apparatus further comprises an actuator which moves the separator from the first position to the second position. Movement of the separator causes the second component to be expelled into the mixing chamber. According to another aspect of the invention there is provided an apparatus for mixing a multi-part orthopaedic paste. The apparatus comprises a body defining an internal volume. A separator is slidably received within the body and may extend generally transversely within the internal volume. The separator divides the internal volume into a first chamber, configured to receive or contain a first component of the multipart orthopaedic paste, and a second chamber configured to receive or contain a second component of the multi-part orthopaedic paste. The separator is moveable between a first position, in which the second chamber has a first volume, and a second position in which the second chamber has a second, reduced volume, and the second component is expelled from the second chamber. The apparatus further comprising a mixing element. The mixing element is coupled to the separator to move the separator from the first position to the second position. The mixing element and separator decouple to mix the components in the mixing chamber. In another aspect of the invention there is provided a pre-filled mixing assembly for multi-part orthopaedic paste. The apparatus comprises a body defining a closed volume. A separator divides the closed volume into a first chamber containing a first component of the multi-part orthopaedic paste, and a second chamber containing a second component of the multi-part orthopaedic paste. An actuator displaces the separator to combine the first chamber and at least part of the second chamber to define a mixing chamber within the closed volume. A mixing element for mixing the first and second components in the mixing chamber. According to an aspect of the invention there is provided an apparatus for mixing a multi-part orthopaedic paste, the apparatus comprising: a body and a piston slidably located within the body. A separator in the form of a piston defines a transverse wall separating two chambers within the body. A first chamber of the two chambers is a mixing chamber and may be configured to receive or contain a first component of the multi-part orthopaedic paste. A second chamber of the two chambers comprises a storage chamber and may be configured to receive or contain a second component of the multi-part orthopaedic paste. A fluid passageway extends between the first and second chambers. The piston is moveable between a first position in which the second chamber has a first volume and a second position in which the second chamber has a second, reduced volume. Movement of the piston to the second position causes the second component of the multi-part orthopaedic paste to be expelled into the first chamber though the fluid passageway. The apparatus further comprises an actuator which moves the piston from the first position to the second position. The actuator decouples from the piston in the second position. In another aspect of the invention, there may be provided an apparatus for mixing a multi-part orthopaedic paste, the apparatus comprising: a body; a separator may comprise a piston slidably located within the body and defining a transverse wall separating two chambers within the body. A first chamber may comprise a mixing chamber, configured to receive or contain a first component of the multi-part orthopaedic paste. A second chamber may comprise a storage chamber, configured to receive or contain a second component of the multi-part orthopaedic paste. A fluid passageway may extend between the first and second chambers. The piston may comprise a piston head defining the transverse wall, and a mixing element. The piston head and mixing element may be coupled together to expel the second component from the second chamber and the piston head and mixing element may decouple to mix the components in the mixing chamber. The piston head and mixing element may be coupled when initially moved in a first axial direction. The piston head and mixing element may decouple when the mixing head is subsequently moved in a second, axially opposite, direction. In embodiments the actuator is coupled to the separator when moving the separator from the first position to the second position. When coupled together the separator and actuator move together. The coupling may comprise an inter-engagement between the separator and actuator. In other embodiments the coupling may simply be as a result of abutment between the separator and actuator. In embodiments the actuator decouples from the separator when the separator is in the second position. Typically, the body may be cylindrical (for example a tube shape, with closures at a first and second end). The separator may extend generally radially with respect to the cylinder. The actuator may extend axially along the body. The separator may move axially between the first position and the second position. The separator may generally extends transversely within the internal volume to provide a distinct division between the chambers. In some embodiments the separator could engage the inner side walls of the body but this is not essential in all embodiments (particularly for example in one or both of the components of the multipart paste are contained in a secondary container such as a pouch). In some embodiments the separator may extends across substantially the whole transverse cross section of the internal volume. For example the separator may be a piston which is slideable mounted in the body. The apparatus may further comprise a retaining mechanism. The retaining mechanism may engage the separator upon reaching the second position. The retaining mechanism may comprise at least one resiliently deformable engagement member. The retaining mechanism may for example comprise a sprung latch ora snap fit feature. The retaining mechanism may for example comprise complementary engagement features between the separator and the body. For example, one of the separator or the body may comprise a sprung latch member and the other of the body or separator may comprise a detent (for example a recess or aperture) for capturing a head of the latch member. In some embodiments the complementary engagement feature of the body may be formed in the base of the body. In some embodiments the body may comprise a closure piston (for example a closure piston which closes one end of the body, and which is used for dispensing orthopaedic paste after mixing) and the complementary engagement feature of the body may be provided on the closure piston. The retaining mechanism may irreversibly engage the separator. For example, once the separator reached the second position the retaining mechanism may prevent the separator from being returned to the first position by the actuator. In some embodiments engagement of the separator by the retaining mechanism may decouple the actuator from the separator. In some embodiments the engagement of the separator by the retaining means may cause the separator to disengage from the actuator. For example, a coupling between the actuator and the separator may be released. The actuator may be coupled to the separator when moving in a first direction and may be decoupled from the separator when moving in a second, opposing, direction. The first and second directions may be axially aligned. The movement in the first direction may be movement from the first position to the second position. The actuator and separator may be coupled via at least one releasable connector. The holding force between the at least one releasable connector may be less than the holding force of the retaining mechanism. As such, the releasable connector may automatically disengage if the actuator moves in a direction away from the retaining mechanism after the retaining mechanism engages the separator. The actuator may be a mixing element, which may be moveably mounted in the mixing chamber. The mixing element may comprise a mixing head (located within the body) and a mixing shaft (extending in an axial direction through the body to an external actuation element). The mixing head may engages / disengage the separator. Accordingly, the actuation element may be used for both release of the second component of the multi-part orthopaedic paste and for mixing of the orthopaedic paste components. The second component of the multi-part orthopaedic paste contained in the second chamber may comprise a pouch formed of a pierceable or burstable material. It will be appreciated that storing the component in a pouch may be advantageous since a pouch can be sealed prior to use both to maintain sterility and to reduce the risk of leakage or unintended mixing during storage or transit. Further the provision of a pouch may remove any requirement for the transverse wall separating two chambers to seal with the body. For example, the transverse wall may simply be a general physical division which may for example be generally aligned with the inner surfaces of the body but without a strict sealing tolerance. The separator may comprise at least one piercing element for opening the pouch in use. The piercing element may be moved to penetrate the pouch when the separator moves between the first position and the second position (and in some embodiments the piercing element may burst or rupture the pouch when the separator is in a third intermediate position between the first and second positions. In embodiments in which the retaining mechanism comprises at least one engagement member (for example, a resiliently deformable engagement member such as a spring arm) the piercing element may be integrally formed with the engagement member of the retaining mechanism. A fluid passageway may extend between the first and second chambers. For example, the passageway may be formed at a peripheral edge between an outer edge of the separator and an interior sidewall of the body. The fluid passageway may, for example, be formed in a portion of the interior sidewall (for example an axially extending portion). Movement of the separator into axial alignment with the portion of the sidewall may result in opening of the fluid passageway extending between the first and second chambers. For example, the potion of the interior sidewall may comprise at least one axially extending recesses or channel. Additionally or alternatively, the fluid passageway extending between the first and second chambers may be formed in the separator (for example extending axially through the separator). The fluid passageway extending between the first and second chambers may comprise a plurality of fluid passageways. The plurality of fluid passageways may for example provide a plurality of parallel flow paths. Embodiments of the invention may be particularly beneficial to pre-filled mixing devices. For example, embodiments may provide a pre-filled device which is relatively compact since the internal volume of the device uses generally the same volume for storage of components of the multi-part orthopaedic paste prior to use and for mixing the paste in use. Further, the use of the same space for storage and mixing of the paste can be advantageous in that any unintended leakage of the components prior to use can be safely contained within the enclosed (and typically sealed) volume of the device. For example a leakage of a component in an embodiment may merely result in the premature activation of the orthopaedic paste, whilst this might make the paste and / or device un-usable it would not present a hazard to users and may mean any leakage is advantageously self-limiting. 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 2A shows a longitudinal cross section through a portion of the device of figure 1 in an initial configuration; Figures 2B shows the cross section of Figure 2A in a second configuration; Figure 2C shows the cross-section of Figure 2A in a third configuration; Figure 3 shows an exploded view of the components of Figure 2; Figure 4 shows a longitudinal cross section through a bone cement mixing device in accordance with another embodiment; and Figure 5A shows a longitudinal cross section through a portion of the device of Figure 4 in an initial configuration; Figures 5B shows the cross section of Figure 5A in a second configuration; Figure 5C shows the cross-section of Figure 5A in a third configuration; and Figure 5D shows the cross-section of Figure 5A in a fourth configuration. 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 for mixing a multi-part orthopaedic 1 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 cylindrical tubular body 10 defining a mixing chamber 12. In use, 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 22 to a distal end 25 outside of the chamber. The proximal end 23 is connected by any convenient means (for example a complementary threaded portions as shown in Figure 3) to the mixing head 22. 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 an aperture in a lid 30 which provides a closure at the upper end of the body 10. As is known in the art, the lid may include an inlet for connection to a vacuum source to allow mixing in the device 1 to be carried out under vacuum. The lower end of the body 10 is closed by a displacement piston 32 (shown in figure 2) which is sealingly positioned within the body 10. The piston 32 is axially slidable within the body 10 and is used to force mixed bone cement from the mixing chamber in use via a nozzle (with such arrangements known in the art). The lower end of the body 10 is provided with a base 40 which supports the mixing device 1 on a surface during the initial stages of use. The mixing device 1 in accordance with embodiments includes a separator 50 which is slidably located within the body 10 and divides the interior of the body 10 between an upper mixing chamber 12 and a lower storage chamber 13. As will be explained further below, in the initial (pre-use) configuration shown in figure 1 the separator 50 is coupled to the mixing head 22 and the mixing shaft 24 acts as an actuator for the separator 50. The storage chamber 13 accommodates the second component of the multi-part orthopaedic paste contained within a pouch 60 formed of a pierceable or burstable material. The pouch 60 is sized and shaped to match the profile of the storage chamber 13 and sits above the displacement piston 32. It will be appreciated that the pouch 60 may be pre-disposed in the chamber 13 in some embodiments so as to provide a pre-filed device. In other embodiments the user may insert a pouch into the chamber 13 in an initial set up step before using the device 1. A detailed cross-sectional view of the lower portion of the device 1 is shown in Figure 2A and some of the key components of the device 1 are shown in exploded view in figure 3. The mixing head 22 and separator 50 extend radially across the body of the device 1. The separator 50 and mixing head 22 are sized and shaped to generally match the interior cross section of the body (for example they are circular in cross section when the body is cylindrical). The separator 50 and the mixing head 22 are provided with complementary engagement features, for example in the illustrated embodiment the separator includes a plurality of axially (and upwardly) projecting tabs 52 which are received in matching cut outs or recesses 28 (shown by the dotted lines in figure 3). The complementary engagement features 52 and 28 provide an initial coupling between the mixing head 22 and separator 50. The side of the separator 50 opposite to the mixing element 20 (i.e., the lower face of the separator) includes dual purpose spiked arms 54. The spiked arms 54 extend axially from a base at the separator 50 to tips 55 at their distal end. The spiked arms 54 are formed from a resilient material and include a latch shoulder 56 in an intermediate position between the tip 55 and the separator 50. The spiked arms 54 include at least a pair of arms which are spaced apart radially such that they can be resiliently deflected in use (as will be explained below). The dispensing piston 32 includes a sealing member around its periphery 33 to provide a leak resistant seal to the interior wall of the body 10. A recess 34 is provided in a central region of the dispensing piston 32 which is sized and shaped to receive the spiked arms 54 of the separator 50 so as to provide a retaining mechanism (as will be explained below). A mouth 35 of the recess 34 has a reduced width with a radial shoulder defined by the reduction in width. The pouch 60 is disposed axially between the separator 50 and the dispensing piston 32. The pouch is typically a flexible material so that it can conform to the chamber 13. It will be appreciated that the specific material will depend upon the orthopaedic paste being mixed. For example, in the case of PMMA cement it will be appreciated that the second component may typically be methylmethacrylate monomer liquid which is highly volatile and restricts the selection of materials which can be used to form the pouch 60. Use of the device 1 of figures 1 to 3 will now be described with particular reference to figures 2A to 2C which show the configuration of the device in sequence. The user starts by either selecting a device which is pre-filled or providing the required quantities of the bone cement components into the mixing chamber 12 and the storage chamber 13. A vacuum is then applied to the mixing chamber 12. When the user is ready to initiate mixing of the bone cement the separator 50 is axially advanced from its first position as shown in figure 2A in the direction of arrow A (i.e., downwardly) using the mixing element 20. It will be appreciated that this is achieved by grasping the handle 26 and using it to move the shaft 24 down which is, advantageously, a particularly intuitive way to initiate use. As the separator 50 moves axially downwardly the tips 55 of the spiked arms 54 first engage and then must pierce the pouch 60. This enables the methylmethacrylate monomer liquid to leave the pouch 60. The user continues to move the separator 50 downward reducing the volume of the storage chamber 13 and the pouch 60. At least one fluid passageway is provided around or through the separator 50 (for example apertures through the separator or a space between the separator and side wall of the body) such that as the separator 50 moves down the contents of the pouch must be expelled into the mixing chamber 12. It will be appreciated that the vacuum in the mixing chamber 12 will also assist the drawing of the liquid into the chamber. When the separator 50 reaches the second position shown in figure 2B the volume of the storage chamber 13 has been reduced to its minimum. This fully downward position of the separator 50 is specifically selected such that the pouch 60 must be fully compressed between the separator 50 and dispensing piston 32. This ensures that the component in the pouch is accurately and precisely dispensed into the mixing chamber. In this second position, the spiked arms 54 perform their second function of acting with the complementary recess 34 to provide a retention mechanism for the separator 50 have passed downwardly through the (compressed) pouch 60 and entered the recess 34 of the dispensing piston 32. The spiked arms 54 must deflect radially inwardly as they pass through the reduced mouth 35 of the recess 34. The deflection of the arms is assisted by the angled faces of the tips 55 and a taper formed on the subsequent surface which help to cam the arms 54 radially inwardly as they move axially forward across the reduced width mouth 35. When the separator 50 has reached the fully forward position of figure 2B the enlarged head of the arms 54 has moved axially past the mouth 35 and the arms can snap radially outwardly such that the shoulders of the mouth 35 and the rearward face of the head of the arms 54 engage. As such, the shoulder of the mouth 35 provides a detent which engages and retains the latch feature of the arms 54. It will be appreciated that this provides a snap fit engagement between the body 10 (via the displacement piston 32) and the separator 50 which is irreversible by the user. Advantageously, the snap fit engagement of the separator 50 may provide an audible indication to the user that the separator has reached the fully downward position. With the liquid monomer dispensed the user may proceed to mix the bone cement using the mixing element 20. As shown in figure 2C the mixing head 22 is moved upwardly in the direction of arrow B using the handle 26 and mixing shaft 24. As the retention between the separator 50 and the retention mechanism (formed by the arms 54 and recess 34) is significantly stronger than any engagement between the separator 50 and the mixing head 22 the mixing head 22 will detach from the separator 50. The separator remains at the bottom of the housing 10, engaged to the dispensing piston 32 and the mixing head may be freely moved through the mixing chamber to prepare the bone cement. Once the separator 50 has been detached the mixing action may be similar to existing devices which makes use of embodiments simple and intuitive for end users. A bone cement mixing device 401 in accordance with another embodiment is shown in figures 4 and 5. Features of this device which are generally equivalent to those of the first embodiment have been provided with corresponding reference numerals prefixed with a 4. The device 401 of the second embodiment includes a body 410 which is subdivided into a mixing chamber 412 and a storage chamber 413 by a separator 450. It may be noted that in this embodiment the separator 450 is essentially formed as a piston which extends fully across the chambers and sealingly engages the inner walls of the body 410. The device 401 also includes a mixing assembly 420 which is similar to the assembly of the first embodiment and has a mixing head 422 moveable via a shaft 424. The body 410 of this embodiment is sealed at one end by a lid 430 and at the other end by a delivery piston 432. In the embodiment of figure 4 there is no engagement features provided between the separator 450 and the mixing head 422. Instead, the mixing head 422 simply abuts and pushes against the separator 450 when moved in a first (downward) direction and disengages and moves separately to the separator 450 when moved in a second (upward) direction. It will be appreciated that the interaction arrangements of the separator and mixing head from each illustrated embodiment may be used interchangeably without departing from the scope of the invention. The embodiment of figures 4 and 5 includes an arrangement in which the fluid passageway extending between the mixing chamber 412 and storage chamber 413 is selectively opened based upon the axial position of the separator 450. This is enabled by the provision of fluid passageways which extend along a specific axial portion of the device 401. The fluid passageways are formed by a plurality of generally axially extending channels 460 formed along the inner wall of a portion of the body 410. It can be seen that the plurality of channels 460 comprises a series of axially parallel and circumferentially spaced apart channels. For manufacturing purposes, the portion of the body 410 which includes the channels (and which also forms the walls of the storage chamber 413) may be formed by a separate body portion 410b which is coupled to and sealed with the main body 410. It will, however, be appreciated that this is optional. As shown in figure 5A, initially the separator 450 is positioned such that it engages and seals against the inner walls of the body 410 above the portion of the walls in which the channels 460 are provided. It may be noted that in this initial position the separator 450 may overlap with the channels 460 provided at least a portion of the separator seals against the wall of the body 410 above the channels. To initiate combining the components of the bone cement the user pushes the mixing head 422 downward using the shaft 424 with the lower surface of the mixing head pushing against the upper surface of the separator 450. This urges the separator 450 into the position shown in figure 5B, and as shown in the detailed view, the upper portion of the separator 450 which previously sealed against the body 410 moves axially into align with the channels 460. This alignment enables a leak path to be opened around the separator 450 to allow fluid flow as represented by the arrow F. It will be appreciated that the fluid flow will be assisted by the mixing chamber 412 being under vacuum and that the flow F occurs in each channel around the circumference of the separator 450. As shown in figure 5C, the user can continue to move the separator 450 downwardly progressively reducing the volume of the storage chamber 413 (and increasing the volume of the mixing chamber 412) to cause all of the component in the chamber to be expelled through the channels 460. The final (lower) position of the separator 450 is shown in figure 5D. In this position the separator 450 abuts the discharge piston 432 and can no longer move downward. Optionally the separator 450 and the discharge piston 432 may inter-engage to lock the position of the separator 450 (for example in a snap fit manner similar to that described in the first embodiment). It can be noted that in the final position the separator 450 has moved axially beyond alignment with the channels 460. This is useful in ensuring that no unmixed bone cement component remains trapped between the separator 450 and the channels 460 so as to ensure accurate mixing. With the separator 450 in the position of figure 5D the user may now move the mixing head 422 upward and utilise it for mixing in the conventional manner. When moved axially upwards the head 422 will separate from the separator 450 to leave the separator in the expelled position as shown in figure 5D. 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, it may be appreciated that the second embodiment described above could include features such as a retaining mechanism or a pouch as described in the first embodiment. Whilst embodiments of the invention may be arranged to be filled with the components of the multi-part orthopaedic paste prior to use it may be appreciated that they may be well suited for use as pre-filed devices. Such pre-fill devices are supplied with pre-measured sterile quantities of components in each chamber. Embodiments may have additional advantages when used for pre-fill devices - for example in embodiments the mixing head is moved downward during the initial action of dispensingthe component (for example monomer liquid) from the storage chamber and this could help to disrupt the component already in the mixing chamber (for example the powder component) before mixing commences. This could, for example, help provide improved mixing in powders which might be prone to settling and / or caking in the mixing chamber during transit or storage.

Claims

1. An apparatus for mixing a multi-part orthopaedic paste, the apparatus comprising:a body defining an internal volume;a separator slidably received within the body and extending transversely within the internal volume to define:a first chamber, configured to receive or contain a first component of the multi-part orthopaedic paste, anda second chamber configured to receive or contain a second component of the multi-part orthopaedic paste;wherein the separator is moveable betweena first position in which the second chamber has a first volume anda second position in which the second chamber has a second, reduced volume, and in which the volume of the first chamber and at least part of the first volume of the second chamber define, in combination, a mixing chamber;the apparatus further comprising an actuator which moves the separator from the first position to the second position such that the separator causes the second component to be expelled into the mixing chamber.

2. An apparatus as claimed in claim 1, wherein the actuator decouples from the separator when the separator is in the second position.

3. An apparatus as claimed in claim 1 or 2, wherein the apparatus further comprises a retaining mechanism which engages the separator upon reaching the second position.

4. An apparatus as claimed in claim 3, wherein the retaining mechanism comprises at least one resiliently deformable engagement member.

5. An apparatus as claimed in claim 3 or 4, wherein the retaining mechanism irreversibly engages the separator.

6. An apparatus as claimed in any of claims 3 to 5, wherein engagement of the separator by the retaining mechanism decouples the actuator from the separator.

7. An apparatus as claimed in any preceding claim, wherein actuator is coupled to the separator when moving in a first direction and is decoupled from the separator when moving in a second, opposing, direction.

8. An apparatus as claimed in any preceding claim wherein the actuator and separator are coupled via at least one releasable connector.

9. An apparatus as claimed in any preceding claim, wherein the actuator is a mixing element.

10. An apparatus as claimed in claim 9, wherein the mixing element comprises a mixing head located within the body and a mixing shaft extending in an axial direction through the body to an external actuation element.

11. An apparatus as claimed in any preceding claim, wherein the retaining mechanism comprises at least one resiliently deformable engagement member.

12. An apparatus as claimed in any preceding claim, wherein second component of the multi-part orthopaedic paste contained in the second chamber comprises a pouch formed of a pierceable or burstable material.

13. An apparatus as claimed in claim 12, wherein the separator comprises at least one piercing element.

14. An apparatus as claimed in claim 13, wherein the piercing element is integrally formed with a retaining mechanism which engages the separator upon reaching the second position.

15. An apparatus as claimed in any preceding claim, wherein a fluid passageway extends between the first and second chambers and is formed at a peripheral edge between an outer edge of the separator and an interior sidewall of the body.

16. An apparatus as claimed in claim 15, wherein a fluid passageway is formed in a portion of the interior sidewall, and wherein movement of the separator into axial alignment with the portion of the sidewall opens the fluid passageway extending between the first and second chambers.

17. An apparatus as claimed in claim 16 wherein the portion of the interior sidewall comprises at least one axially extending recesses or channels formed in the interior side wall.

18. An apparatus as claimed in any of claims 1 to 15, wherein a fluid passageway extending between the first and second chambers is formed in the separator.

19. The apparatus as claimed in any preceding claim wherein a fluid passageway extending between the first and second chambers comprises a plurality of fluid passageways.

20. An apparatus for mixing a multi-part orthopaedic paste, the apparatus comprising:a body defining an internal volume the volume including a mixing chamber;a separator slidably received within the body and extending transversely within the internal volume to define:a first chamber, configured to receive or contain a first component of the multi-part orthopaedic paste, anda second chamber configured to receive or contain a second component of the multi-part orthopaedic paste;wherein the separator is moveable betweena first position in which the second chamber has a first volume anda second position in which the second chamber has a second, reduced volume, and the second component is expelled from the second chamber,the apparatus further comprising a mixing element and wherein the mixing element is coupled to the separator to move the separator from the first position to the second position and the mixing element and separator decouple to mix the components in the mixing chamber.

21. An apparatus as claimed in claim 20, wherein the separator and mixing element are coupled when initially moved in a first axial direction and decouple when the mixing element is subsequently moved in a second, axially opposite, direction.

22. A pre-filled mixing assembly for multi-part orthopaedic paste, the apparatus comprising:a body defining a closed volume;a separator dividing the closed volume into:a first chamber containing a first component of the multi-part orthopaedic paste, anda second chamber containing a second component of the multipart orthopaedic paste;an actuator which displaces the separator to combine the first chamber and at least part of the second chamber to define a mixing chamber within the closed volume; anda mixing element for mixing the first and second components in the mixing chamber.

23. The pre-filed mixing assembly of claim 21, wherein the mixing element comprises the actuator.

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