GB2550583A

GB2550583A - Bone cement mixer

Info

Publication number: GB2550583A
Application number: GB1609038.3A
Authority: GB
Inventors: Charles Cattermole David
Original assignee: Cattalytic Solutions Ltd
Current assignee: CATTALYTIC SOLUTIONS LIMITED,
Priority date: 2016-05-23
Filing date: 2016-05-23
Publication date: 2017-11-29
Also published as: WO2017203233A1; GB201609038D0

Abstract

There is disclosed a bone cement mixer 10 comprising a mixing chamber 12 having a chamber outlet 14; at least one mixing paddle 18, 20 disposed within the mixing chamber 12 and a piston member 24 slidable within a dispensing tube 26 which can be coupled to the chamber outlet 14. An axially moveable shaft 118 is provided to drive the piston member 24 away from the chamber outlet 14. In use, the piston member 24 can be slid within the dispensing tube 26 and away from the chamber outlet 14, thereby drawing bone cement through the chamber outlet 14 and into the dispensing tube 26. The shaft may form part of a drive mechanism comprising a rotatable input.

Description

BONE CEMENT MIXER

The invention relates to a bone cement mixer for mixing bone cement.

Orthopaedic bone cement is widely used to secure hip, knee and other prostheses in the appropriate anatomical position. The bone cement is typically made by mixing together two components, such as polymethylmethacrylate powder and methylmethacrylate monomer liquid. Originally the bone cement was mixed by hand using a bowl and a spatula. The bone cement was then typically transferred into a syringe and dispensed by the surgeon in the appropriate location. However, potentially harmful fumes are emitted when the two components are mixed, and therefore it is desirable to mix the bone cement under a vacuum. WO 2004/069396 describes a bone cement mixer which has a bowl and a dispensing tube attached to an outlet of the bowl. A lid covers the open top of the bowl and is provided with a vacuum port to which a vacuum source is attached to extract any harmful fumes. The mixer also comprises a handle which can be rotated by hand to cause a mixing paddle to rotate about an offset axis, and a scraper to rotate about a central axis. To transfer the bone cement to the dispensing tube a valve must be opened and a vacuum from the vacuum source is applied to the dispensing tube.

Whilst such an arrangement may be satisfactory, in some cases the mixing paddle may not properly mix the bone cement. Further, the arrangement for transferring the bone cement to the dispensing tube is relatively complex and requires a number of valves and a vacuum source.

It is therefore desirable to provide an improved bone cement mixer which may provide better mixing and/or which may have an improved arrangement for transferring bone cement to a dispensing tube.

According to a first aspect there is provided a bone cement mixer, comprising: a mixing chamber having a chamber outlet; at least one mixing paddle disposed within the mixing chamber; a piston member slidable within a dispensing tube which can be coupled to the chamber outlet; and a shaft axially moveable to drive the piston member away from the chamber outlet such that, in use, the piston member is slidable within the dispensing tube so as to draw bone cement through the chamber outlet and into the dispensing tube. In use, the mixing paddle may be rotated to mix bone cement and then the shaft may be axially moved or extended to drive the piston member within a dispensing tube so as to draw the mixed bone cement out of the mixing chamber. The piston member may be arranged to seal against the dispensing tube such that driving the piston member away from the chamber outlet forms a vacuum within the dispensing tube, thereby causing bone cement to be drawn into the dispensing tube. The chamber outlet may be located towards the bottom of the chamber.

The shaft may be arranged such that it can be axially extended through the chamber outlet so as to drive the piston member away from the chamber outlet. The shaft may be located within the mixing chamber.

The shaft may form part of a drive mechanism comprising a rotatable input. The drive mechanism may be configured such that rotation of the rotatable input in at least one direction causes the shaft to axially move so as to drive the piston member away from the chamber outlet. The bone cement mixer may further comprise a handle operable to rotate the rotatable input.

The drive mechanism may comprise an inner elongate threaded member disposed within and threadedly engaged with an outer elongate threaded member. The inner threaded member may have an outer thread and the outer elongate threaded member may have an inner thread. The inner and outer threaded members may be capable of relative rotation. Relative rotation between the inner and outer threaded members may cause relative axial movement. One of the threaded members may be arranged to be rotatably driven (e.g. directly driven) by the rotatable input. The other threaded member may form at least a part of the shaft. For example, the inner threaded member or the outer threaded member could form the shaft. It may be possible to inhibit (or restrict) rotation of the shaft such that rotation of the rotatable input in at least one direction causes the shaft to axially move (or extend with respect to the other threaded member) so as to drive the piston member away from the chamber outlet.

The shaft may extend through the chamber outlet.

The inner elongate threaded member may form the shaft. The outer elongate member may form a sleeve. The sleeve may surround the shaft and may be arranged to be directly driven by the rotatable input. At least one mixing paddle may be coupled to the outer elongate threaded member such that rotation of the rotatable input causes the mixing paddle to rotate. There may be first and second mixing paddles.

The shaft may be rotationally engageable with the piston member such that the piston and shaft are rotationally coupled together. If the piston member is prevented or inhibited from rotating, rotationally engaging the shaft with the piston member would inhibit rotation of the shaft. The piston member may be inhibited from rotating, and this may be achieved in a number of ways. The piston member may be sealed within an outlet of the mixing chamber or within a dispensing tube and the friction may sufficiently inhibit rotation of the piston member. Alternatively, the piston member could be keyed with the mixing chamber outlet or the dispensing tube, or the piston member could be non-circular. Rotation of the rotatable input in a first direction may cause the shaft to rotate with respect to the piston member. Rotation of the rotatable input in a second opposing direction may cause the shaft to rotationally engage with the piston member. With the shaft engaged with the piston member, the piston member may prevent or inhibit rotation of the shaft. This may mean that rotation of the rotatable input causes the shaft to extend, thereby driving the piston member. The drive mechanism may be configured such that rotation of the rotatable input in the first direction and/or the second direction causes the at least one mixing paddle to rotate.

The shaft may comprise at least one first engagement feature and the piston member may comprise at least one corresponding second engagement feature. Rotation of the rotatable input in a second direction may cause the at least one first engagement feature to engage with the at least one second engagement feature, thereby rotationally engaging the shaft with the piston member. There may be a plurality of circumferentially arranged first engagement features and/or a plurality of circumferentially arranged second engagement features. The or each first engagement feature and/or the or each second engagement feature may comprise a ramp.

Rotation of the rotatable input in a first direction may cause the shaft to rotate relative to the piston member. The shaft and piston member may form a ratchet allowing relative rotation when the shaft is rotated in a first direction and causing rotational engagement when the shaft is rotated in a second direction.

The bone cement mixer may further comprise a dispensing tube having a first open end arranged to be coupled to the chamber outlet. The bone cement mixer may further comprise a dispensing nozzle arranged to be coupled to the first open end of the dispensing tube. The dispensing tube may be arranged to cooperate with a dispensing gun for dispensing bone cement from the dispensing tube.

The piston member may seal or may be arranged to seal the chamber outlet. The dispensing tube may be coupled to the chamber outlet.

The at least one mixing paddle may form an auger. The or each mixing paddle may be configured such that rotation of the at least one mixing paddle in the second direction forces bone cement downwards.

The bone cement mixer may further comprise a lid from which the at least one mixing paddle depends.

According to a second aspect there is provided a bone cement mixer, comprising: first and second coaxially arranged mixing paddles; and a drive mechanism coupled to the first and second mixing paddles and having a rotatable input, wherein the drive mechanism is configured such that rotation of the rotatable input causes contra-rotation of the first and second mixing paddles with respect to one another. The contra-rotation of the first and second mixing paddles may provide a shearing action which may improve mixing. The first mixing paddle may be a lower mixing paddle and the second mixing paddle may be an upper mixing paddle. The rotatable input may be arranged to directly drive the first mixing paddle.

The first mixing paddle may be configured such that when the rotatable input is rotated in at least a first direction the first mixing paddle rotates to draw bone cement upwards. The second mixing paddle may be configured such that when the rotatable input is rotated in at least a first direction the second mixing paddle rotates to push bone cement downwards. The drive mechanism may be configured such that rotation of the rotatable input in a first direction causes the first mixing paddle to rotate in a first direction and the second mixing paddle to rotate in an opposite second direction.

The drive mechanism may have at least a first configuration in which rotation of the rotatable input causes contra-rotation of the first and second mixing paddles, and a second configuration in which rotation of the rotatable input causes the first and second mixing paddles to rotate in the same direction. Thus, the bone cement mixer may be operated in the first configuration in which the paddles contra-rotate so as to mix bone cement, and in a second configuration in which the paddles are locked together and rotate together to dispense bone cement from a mixing chamber.

The drive mechanism may comprise a gear mechanism comprising a first gear having a first axis, wherein the rotatable input is arranged to drive (e.g. directly drive) the first mixing paddle and the first gear about the first axis; a second gear having a second axis parallel to and offset from the first axis and arranged to be driven by the first gear; and a third gear having a third axis which is coaxial with the first axis, wherein the third gear is arranged to be driven by the second gear and is arranged to drive (e.g. directly drive the second mixing paddle. The first and second gears may have gear teeth on an outer circumference, and the third gear may be annular and have gear teeth on an inner circumference. The third gear may be annular and the first and second gears may be located within the third gear. The gear mechanism may be configured such that when the rotatable input is rotated in a first direction the first paddle, which may be the lower paddle, and the first gear rotate in the first direction; the first gear may drive the second gear such that it rotates in a second opposite direction; and the second gear may drive the third gear to rotate in the second direction. This may cause the third gear to drive the second paddle, which may be the upper paddle, in the second direction. Similarly, rotation of the rotatable input in the second direction may cause the first paddle to rotate in the second direction and the second paddle to rotate in the first direction.

In the first configuration the first gear may be engaged with the second gear. In the second configuration the first gear may be disengaged from the second gear and the rotatable input may be arranged to drive both the first and second mixing paddles such that they rotate in the same direction. In the second configuration the rotatable input may be arranged to directly drive the first and second mixing paddles. Thus, rotation of the rotatable input in the first direction may cause the first and second paddles to rotate in the first direction, and rotation of the rotatable input in the second direction may cause the first and second paddles to rotate in the second direction. The first gear may be axially moveable. In the first configuration the first gear may be in a first position (in which it is engaged with the second gear). In the second configuration the first gear may be in a second position axially offset from the first position (in which it is disengaged from the second gear). A button may be provided which is operable to axially move the first gear from the first position to the second position, for example by pulling or depressing it.

The first gear may be part of a first gear member. In the first configuration the first gear member may be disengaged from the second mixing paddle, and in the second configuration the first gear member may be engaged or engageable with the second mixing paddle. For example, the first gear member may be provided with a first engagement feature which in the first configuration is disengaged (for example by being spaced) from second engagement feature of the second mixing paddle. In the second configuration, the first engagement feature may be engaged or engageable with the second engagement feature such that rotation of the rotatable input directly drives the first mixing paddle and the first gear member which also directly drives the second mixing paddle. In one arrangement the first engagement feature is a pin or projection (such as an axially extending pin or projection) and the second engagement feature may be a pin or projection.

The drive mechanism may be configured such that in the second configuration, rotation of the rotatable input causes the first and second mixing paddles to angularly align and rotate together. The angular alignment may be achieved by way of the first and second engagement features. It may be necessary to rotate the rotatable input in a particular direction to achieve the desired angular alignment. For example, in the first configuration, the rotatable input may be rotated in a first direction to cause the mixing paddles to contra-rotate and mix bone cement, the drive mechanism may then be moved to the second configuration (e.g. by moving the first gear member to the second position), and then the rotatable input may be rotated in a second opposite direction causing the mixing paddles to angularly align and rotate together in the same direction.

The first mixing paddle may comprise a first flight. The second mixing paddle may comprise a second flight. The first and second flights may have the same direction of twist. With the first and second paddles angularly aligned, the first and second flights may cooperate to form an auger.

The bone cement mixer may further comprise a handle operable to rotate the rotatable input.

The bone cement mixer may further comprise a mixing chamber, such as a mixing bowl, within which the first and second mixing paddles are disposed. The mixing chamber may have a chamber outlet to which a dispensing tube can be coupled. The chamber outlet may be located towards the bottom of the chamber. The bone cement mixer may further comprise a lid from which the first and second mixing paddles depend. At least a part of the drive mechanism may be housed within the lid. At least a part of the gear mechanism may be housed within the lid. The gear mechanism may be housed within the lid.

The invention also relates to a bone cement mixer in accordance with the first aspect and the second aspect. Any features of the second aspect may be applied to the first aspect, and any features of the first aspect may be applied to the second aspect.

According to a further aspect there is provided a bone cement mixer, comprising: a mixing chamber having a chamber outlet; first and second coaxially arranged mixing paddles disposed within the mixing chamber; a drive mechanism coupled to the first and second mixing paddles and having a rotatable input, wherein the drive mechanism is configured such that rotation of the rotatable input causes contra-rotation of the first and second mixing paddles with respect to one another; a piston member slidable within a dispensing tube which can be coupled to the chamber outlet; and a shaft axially moveable to drive the piston member away from the chamber outlet such that, in use, the piston member is slidable within the dispensing tube so as to draw bone cement through the chamber outlet and into the dispensing tube.

The invention may comprise any combination of the features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 schematically shows a perspective view of a bone cement mixer;

Figure 2 schematically shows an exploded view of the bone cement mixer of Figure 1;

Figure 3 schematically shows a cross-sectional view of the bone cement mixer of Figure 1 with the drive mechanism in a mixing configuration;

Figure 4 schematically shows a perspective view of the first gear member of the gear mechanism of the drive mechanism of Figure 3;

Figure 5 schematically shows a perspective view of the third gear member of the gear mechanism of the drive mechanism of Figure 3, together with the upper mixing paddle;

Figure 6 schematically shows a plan view of the gear mechanism;

Figure 7 schematically shows an enlarged end view of the threaded shaft member of the drive mechanism;

Figure 8 schematically shows the piston member with a section cut away;

Figure 9 schematically shows a cross-sectional view of the bone cement mixer of Figure 1 with the drive mechanism in a transfer configuration; and

Figure 10 schematically shows a cross-sectional view of the bone cement mixer of Figure 1 including the dispensing tube with the piston member spaced away from the mixing bowl outlet.

Figure 1 shows a bone cement mixer 10, otherwise referred to as an orthopaedic cement mixing apparatus, for mixing bone cement that may be used to secure an orthopaedic implant, such as a hip prosthesis, in place. The bone cement mixer 10 generally comprises a mixing chamber, in the form of a bowl 12, having a bowl outlet 14 with a lid 16 covering the open top of the bowl 12. Lower and upper coaxially arranged mixing paddles 18, 20 are located within the bowl 12 and depend (i.e. hang from) the lid 16. A handle 22 is also provided which is operable to cause the mixing paddles 18, 20 to rotate about a central axis A. A piston member 24 is provided which seals the bowl outlet 14 and a dispensing tube 26 is attached to the bowl outlet 14 with the piston member 24 located within the tube 26. The lid 16 is also provided with a vacuum port 126 (shown in Figure 2) to which a vacuum source (not shown) can be connected.

In use, the piston member 24 seals the bowl outlet 14 and a dispensing tube 26 is attached to the bowl outlet 14 such that the piston member 24 is located within it. The lid 16 is removed bone cement mixture, such as polymethylmethacrylate powder and methylmethacrylate monomer liquid, is placed within the mixing bowl 12. The lid 16 is then replaced such that it seals the open top of the mixing bowl 12 with the mixing paddles 18, 20 disposed within the mixing bowl 12 and the bone cement mixture. A vacuum source is attached to the vacuum port 126 so as to extract harmful chemicals from the mixing bowl 12. The handle 22 is then operated by rotating it in a first direction (e.g. clockwise) about the axis A. This cause the mixing paddles 18, 20 to contra-rotate and mix the bone cement mixture. A button 28 is then depressed and the handle 22 is rotated in a second opposing direction (e.g. anti-clockwise). This causes the mixing paddles 18, 22 to angularly align and rotate together to form an auger which forces the bone cement mixture downwards. At the same time, the piston member 24 is driven away from the bowl outlet 14 and within the dispensing tube 26. This causes the bone cement to be drawn into the dispensing tube 26. The dispensing tube 26 can then be removed from the bowl outlet 14 and a dispensing nozzle (not shown) can be attached to the open end. The dispensing tube 26 can then be attached to a dispensing gun (not shown) which can be operated by a surgeon or the like to push the piston member 24 towards the dispensing nozzle to dispense bone cement.

Referring now to Figures 2 and 3, the bone cement mixer 10 comprises a drive mechanism which is coupled between the handle 22 and the lower and upper mixing paddles 18, 20. The drive mechanism comprises a gear mechanism comprising a first gear member 32, a second gear member 34 and a third gear member 36.

As shown in Figure 4, the first gear member 32 is substantially cylindrical and comprises an upper portion 38 having a smaller diameter than a lower portion 40. A shoulder 42 is formed between the upper and lower portions 38, 40. First gear teeth 44 are provided towards the lower end of the lower portion 40. The upper end of the first gear member 32 is closed and forms the button 28 (Figure 2) whilst the lower end is open to a hollow interior having a larger diameter lower section 46 and a smaller diameter upper section 47. The inner surface of the lower section 46 is provided with an axially extending projection 48 (or pin) which has a chamfered corner 50. The shoulder 42 is also provided with a series of ramped projections 52 (in this case six) that are circumferentially spaced. The ramp faces 54 of the ramped projections 52 are all inclined in the same direction. The upper portion 38 is provided with three axially extending and circumferentially spaced ribs 55 with a circumferential groove 56 provided in each rib 55. Each groove 56 is defined by a lower ramped edge 58 and an upper edge 60. Referring back to Figures 2 and 3, the first gear member 32 is rotatably located within a central opening 62 of the lid 16; the axis of the opening 62 being coaxial with the central axis A of the mixer 10. The lower portion 40 of the first gear member 32 is located within the central opening 62 with the upper portion 38 projecting from the opening 62. The inner surface of the central opening 62 is provided with a series of formations 64 that cooperate with the ramped projections 52 such that with the first gear member 32 in an initial first position (Figure 3) the first gear member 32 can only be rotated in a first direction (e.g. a clockwise direction) about a first axis that is coaxial with the central axis A.

The second gear member 34 has a second gear teeth 66 and a shaft portion 68 that is rotatably received within a circular recess or opening 70 (Figure 3) on the interior of the lid. The circular opening within which the shaft portion 68 is received has an axis parallel to but offset from the axis of the opening 62 and as such the second gear member 34 is rotatable about a second axis offset from the first axis. As shown in Figure 5, the third gear member 36 comprises an annular member 72 having third gear teeth 74 on an inner surface of the annular member 72, and a cover member 76. The third gear member 36 also comprises an axially extending sleeve 78 that is coaxial with the annular member 72 (and the series of gear teeth 74). The sleeve 78 extends downwardly from the cover member 76 and is open at both ends. The upper end 80 is located within the annular member 72 and defines an annular recess 82 in the cover member 76. The upper end 80 of the sleeve 78 is also provided with an axially extending ramped projection 84 that, as will be described in detail below, is arranged to cooperate with the axially extending projection 48 of the first gear member 32. The third gear member 36 is rotatably coupled to the lid 16 such that it can rotate about a third axis that is coaxial with the central axis A.

Referring now to Figure 6, the gear mechanism is assembled within the lid 16 such that the first and third gear members 32, 36 are rotatable about the central axis A, and such that the second gear member 34 is rotatable about an axis parallel to and offset from the central axis. The second gear member 34 is located within the annular member 72 of the third gear member 36 such that the second and third gear teeth 66, 74 mesh together. The first gear member 32 is also partially disposed within the annular member 72. With the first gear member 32 in the initial first position, the first gear teeth 44 are also meshed with the second gear teeth 66. Thus, rotation of the first gear member 32 in a first direction drives the second gear member 34 causing it to rotate in a second opposing direction. In turn, the second gear member 34 drives the third gear member 36 in the second direction. This means that the first and third gear members 32, 36 rotate about a common central axis but in opposing directions (i.e. they contra rotate).

Referring back to Figure 2, the handle 22 comprises a radially extending arm 86 and a grip member 88 rotatably coupled to the distal end of the arm 86 about an axis parallel to and offset from the central axis A. The proximal end of the arm comprises a handle opening 90 coaxial with the central axis A and a rotatable annular base 92 which is also coaxial with the central axis A. The rotatable base 92 is snap fitted into an annular recess 94 provided in the top of the lid 16 and which surrounds the central opening 62. The upper portion 38 of the first gear member 32 which projects from the central opening 62 is received within the handle opening 90. The inner surface of the handle opening 90 comprises three axially extending and circumferentially spaced slots 96, and each slot 96 receives one of the ribs 55 to rotatably couple the handle 22 and first gear member 32 together. The slots 96 and ribs 55 transfer a rotational force from the handle 22 to the first gear member 32 such that rotation of the handle 22 about the central axis A causes the first gear member 32 to rotate about the central axis A. Further, the slots 96 and ribs 55 also allow the first gear member 32 to axially move within the handle opening 90, whilst still allowing a transfer of rotational force between the handle 22 and first gear member 32.

As shown in Figure 5, the upper mixing paddle 20 comprises first and second paddle sections 98, 100 that are attached to the sleeve 78 of the third gear member 36 and are diametrically opposite. Thus, rotation of the third gear member 36 causes the upper paddle 20 to rotate about the central axis A. The upper paddle sections 98, 100 have a twist and therefore may be referred to as flights. In this embodiment the upper paddle sections 98, 100 and therefore the upper paddle 20 has a right-hand twist.

Thus, in use, rotation of the upper paddle 20 in the anti-clockwise direction drives bone cement downwards. Each paddle section 98, 100 also has a central opening 102, 104 which allows the paddle sections 98, 100 to mix bone cement rather than simply pushing it around the mixing bowl 12.

Referring to Figures 2 and 3, the bone cement mixer 10 also comprises an elongate axially extending sleeve 106 which is coaxial with the central axis A. A lower portion of the sleeve 106 is provided with a collar 108 of a larger diameter, and the lower mixing paddle 18 is attached to this collar 108. The sleeve 106 has a lower sleeve portion 107 which projects below the collar. The lower mixing paddle 18 comprises first and second paddle sections 110, 112 that are attached to the collar 108 and are diametrically opposite. The lower paddle sections 110, 112 are in the form of blades and have a twist, and therefore may be referred to as flights. In this embodiment the lower paddle sections 110, 112 and therefore the lower paddle has a right-hand twist. Thus, in use, rotation of the lower paddle 18 in the clockwise direction drives bone cement upwards. Conversely, rotation of the lower paddle 18 in the anti-clockwise direction drives bone cement downwards.

As best seen in Figure 3, the sleeve 106 is received within the sleeve 78 of the third gear member 36 and is free to rotate within it. The collar 108 has the same outer diameter as that of the sleeve 78 and the upper face of the collar 108 abuts the lower surface of the sleeve 78. The upper end of the sleeve 106 projects from the upper end 80 of the sleeve 78 and, as shown in Figure 2, is provided with an axially extending slot 114. The upper end of the sleeve 106 is received within the hollow interior of the first gear member 32 such that it is located within the smaller diameter upper section 47.

An axially extending rib (not shown) is provided on the inner surface of the hollow upper section 47 and is located within the slot 114 to rotatably couple the first gear member 32 to the sleeve 106. Thus, rotation of the first gear member 32 about the central axis A causes the sleeve 106 to rotate and thus causes the lower mixing paddle 18 to rotate about the central axis A. As shown in Figure 3, with the first gear member 32 in the initial axial position the upper end of the sleeve 106 is spaced from the end of the hollow upper section 47. The slot 114 and rib (not shown) allow relative axial movement between the first gear member 32 and the sleeve 106 whilst still transferring a rotational force between the two. A lower portion of the sleeve 106 has a threaded section 116 on its inner surface. A shaft 118 is also provided which has a threaded section 120 on its outer surface. The threaded shaft 118 is located within the sleeve 106 and the two are threadedly engaged. In the initial configuration (shown in Figure 2) the end of the shaft 118 terminates towards the end of the lower section 107 of the sleeve 106. As shown in Figure 7, the lower end face of the shaft 118 comprises four axially extending engagement projections 122 that are circumferentially spaced. Each engagement projection 122 has a ramped face 123 and all of the ramped faces 123 are inclined in the same direction. As will be described in detail below, these engagement projections 122 are arranged to cooperate with corresponding engagement projections provided on the piston member 24.

The lid 16 houses the gear mechanism with the first and second paddles 18, 20 being coaxially arranged and supported by the lid 16. The handle 22 is attached to the rotatable input (the first gear member 32) of the gear mechanism and is attached to the lid 16 to form a lid assembly which can be attached to the mixing bowl 12 (complete with the mixing paddles 18, 20). The inner rim of the lid 16 is also provided with an annular seal 124 such that the lid 16 can be sealed to the upper rim of the mixing bowl 12. Further, as mentioned above, the lid 16 comprises a vacuum port 126 to which a vacuum source can be connected.

As shown in Figure 2, the mixing bowl 12 is rotationally symmetric and has an open top 128. The bowl outlet 14 is a circular opening located at the bottom of the mixing bowl 12 and coaxial with the central axis A. The bottom of the bowl 12 also comprises an opening 130 having a threaded inner surface, with the bowl outlet 14 opening into the opening 130. Located within the bowl outlet 14 is the piston member 24 which is a cylindrical component having an annular seal 132 on its outer surface. The piston member 24 is dimensioned such that it can be press-fitted within the bowl outlet 14 in the form of a bung to seal the bowl outlet 14. Referring to Figure 8, the piston member 24 has a central blind opening 134 in the upper surface which is coaxial with the central axis A. The diameter of the opening 134 is slightly larger than the outer diameter of the lower section 107 of the sleeve 106 such that it can be rotatably received therein. The bottom of the opening 134 is provided with four axially extending engagement projections 136 that are circumferentially spaced. Each engagement projection 136 has a ramped face 138 and all of the ramped faces 138 are inclined in the same direction. These engagement projections 136 are arranged to cooperate with the corresponding engagement projections 122 provided on the end of the shaft 118. As shown in Figure 3, with the piston member 24 located within the bowl outlet 14 and with the lid assembly (complete with mixing paddles 18, 20) attached to the bowl 12, the lower section 107 of the sleeve 106 is located within the opening 134 and is rotatable within it. The end of the shaft 118 abuts the bottom of the opening 134 and the engagement projections 122 on the end of the shaft 118 cooperate with the engagement projections 136 at the bottom of the opening 134 to form a ratchet. Specifically, when the shaft 118 is rotated with the sleeve 106 in a first direction (which in this embodiment is clockwise), the engagement projections 122 ride over the engagement projections 136 due to the ramp faces 123, 138 and the shaft 118 rotates with respect to the piston member 24. However, when rotated in a second opposite direction (in this embodiment anti-clockwise) the engagement projections 122, 136 engage with one another so as to rotationally engage the shaft 118 with the piston member 24 such that the shaft 118 cannot rotate relative to the piston member 24 in the second direction.

The bone cement mixer 10 may be supplied as a kit of parts comprising a mixing bowl 12, a piston member 24, a dispensing tube 26 and the lid assembly (including the lid 16, mixing paddles 18, 20 and the drive assembly).

In use, the piston member 24 is inserted into the bowl outlet 14 from the bottom (i.e. from outside of the mixing bowl 12) and it is axially pushed upwards until it reaches a stop provided by an annular ridge. Bone cement mixture is then placed into the interior of the mixing bowl 12 and the lid 16 is secured over the open top 128 of the bowl 12 such that the mixing paddles 18, 20 are located within the mixing bowl 12 and such that the lower end section 107 of the sleeve 106 is located within the blind opening 134 of the piston member 24. A vacuum source (not shown) is then attached to the vacuum port 126 of the lid 16 to extract any harmful gases generated by the bone cement.

Initially, and as best shown in Figure 3, the drive mechanism is in a first mixing configuration in which the first gear member 32 is located in a first axial position in which it is in a raised position such that it is engaged with second gear member 34. In the first position the upper surface of the first gear member 32, which forms the button 28, is substantially flush with the upper surface of the arm 86 and the ramped projections 52 are engaged with the formations 64. Since the ramped projections 52 are engaged with the formations 64, the handle 22 can only be rotated about the central axis A in a first direction, which in this embodiment is the clockwise direction. If it is attempted to rotate the handle 22 in the second (anti-clockwise) direction then the vertical faces of the ramped projections 52 abut the formations 64 and prevent any rotation. This prevents the bone cement mixer from being operated incorrectly. As the handle 22 is rotated about the central axis A in the first direction (which in this embodiment is clockwise), the ramped faces 54 of the projections come into contact with the formations 64 and the rotational force causes the first gear member 32 to move axially downwards slightly to permit rotation of the handle 22. As the handle 22 is rotated in the first direction, the first gear member 32 is directly driven and rotated about the central axis A by the cooperation of the slots 96 of the handle 22 with the ribs 55 of the first gear member 32. The first gear member 32 drives the second gear member 34 about a second axis which is parallel to and offset from the first central axis A such that it rotates in an opposite second direction (anti-clockwise in this embodiment). In turn, the second gear member 34 drives the third gear member 36 such that the third gear member 36 rotates in the second direction (anti-clockwise) about a third axis which is coaxial with the central axis A. The rotation of the third gear 36 in the second direction (anti-clockwise) causes the sleeve 78 to rotate about the central axis A and as such the upper mixing paddle 20 also rotates in the second direction (anti-clockwise) so as to mix the bone cement within the mixing bowl 12. The twist of the upper mixing paddle 20 causes the bone cement to be pushed downwards as the upper mixing paddle 20 is rotated in the second direction. As the handle 22 is rotated in the first direction, the first gear member 32 also directly drives the sleeve 106 by the cooperation of the rib (not shown) on the inner surface of the upper hollow section 47 and the slot 114 in the outer surface of the sleeve 106. The rotation of the sleeve 106 causes the lower mixing paddle 18 to rotate about the central axis in the first direction (clockwise) to mix the bone cement within the mixing bowl 12. The twist of the lower mixing paddle 18 causes the bone cement to be drawn upwards as the mixing paddle 18 rotates in the first direction. The contra-rotation of the lower and upper mixing paddles 18, 20 provides improved mixing of the bone cement mixture. Further, the upper paddle 20 pushes the bone cement mixture down and the lower paddle 18 draws the bone cement mixture upwards. This also contributes to improved mixing of the bone cement mixture.

As the sleeve 106 rotates in the first direction the threaded shaft 118 disposed within the sleeve 106 is also rotated in the first direction by virtue of the threaded engagement between the two. As the shaft 118 rotates in the first direction, the engagement projections 122 ride over the corresponding engagement projections 138 of the piston member as the ramped surfaces 123, 138 contact one another. This means that the threaded shaft 118 continues to rotate with the sleeve 106 in the first direction as the handle 22 is rotated in the first direction about the central axis A.

Referring to Figure 9, after mixing has been completed a dispensing tube 26 having a threaded outer first end is screwed into the base of the mixing bowl outlet 14 such that it is located within the opening 130 adjacent to the piston member 24. The drive mechanism is then moved into a second transfer configuration in which the bone cement mixture is transferred or “dumped” into the dispensing tube 26. In order to move the drive mechanism into the second dispensing mechanism the button 28 formed by the upper surface of the first gear member 32 is axially depressed such that it is recessed within the handle arm 86. As the button 28 is depressed the entire first gear member 32 moves axially downwards into a second position in which it is disengaged from the second gear member 34. The first gear member 32 is moved to a position in which the gear teeth 44 are located within the annular recess 82 of the third gear member 36, and such that the lower open section 46 of the first gear member 32 surrounds the upper end 80 of the sleeve 78 of the third gear member 36. As the first gear member 32 is moved to the second position the ramped edges 58 of the ribs 55 ride over an edge of the opening 62 such that the edge sits within the grooves 56. This keeps the first gear member 32 in the correct position. With the first gear member 32 in the second axial position it is still rotatably coupled (i.e. engaged) with the arm 86 of the handle 22 by means of the ribs 55 and slots 96, and with the shaft 106 by means of the rib (not shown) and the slot 114.

To start the transfer of the bone cement mixture into the dispensing tube 26, the handle 22 is rotated in the second direction (which in this embodiment anti-clockwise) about the central axis A. As the handle 22 is rotated in the second direction it directly rotationally drives the first gear member 32 about the central axis A in the second direction. The first gear member 32 (and therefore the handle 22) also directly rotationally drives the sleeve 106 about the central axis A in the second direction. This causes the lower mixing paddle 18 to rotate about the central axis A in the second direction. Further, as the handle 22 is rotated in the second direction, depending on the angular position, the first gear member 32 rotates with respect to the third gear member 36 such that the gear teeth 44 move within the annular recess 82. After a certain amount of relative rotation between the first and third gear members 32, 36 the vertical end face of the axial projection 48 of the first gear member 32 comes into contact with the vertical end face of the axial projection 84 of the third gear member 36. The axial projections 48, 84 are positioned such that when they are in contact with one another the upper mixing paddle 20 is angularly aligned with the lower mixing paddle 18 such that the paddle sections 98, 100,110, 112 cooperate to form an auger having a twist (which in this embodiment is a right hand twist). Once the axial projections 48, 84 are engaged with one another and the mixing paddles 18, 20 are angularly aligned, further rotation of the handle 22 in the second direction (anti-clockwise) causes the first gear member 32 (and therefore the handle 22) to directly drive the third gear member 36 in the second direction by virtue of the engagement of the projections 48, 84. This causes the lower and upper mixing paddles 18, 20 to rotate together in the same direction, the second direction, with them angularly aligned. The projections 48, 84 have chamfered corners such that if they are above one another when the first gear member 32 is axially depressed relative movement between the first and third gear members 32, 36 occurs such that the first gear member 32 can be fully depressed.

As the handle 22 is rotated in the second direction the auger formed by the lower and upper paddles 18, 20 rotates in the second direction so as to force bone cement downwards towards the bowl outlet 14. Further, rotation of the handle 22 in the second direction causes the sleeve 106, which is threadedly engaged with the shaft 118, to rotate in the second direction. Rotation of the shaft 118 in the second direction causes the engagement projections 122 on the end of the shaft 118 to engage with the engagement projections 136 of the piston member 24. With the engagement projections 122, 136 engaged, the shaft 118 and piston member 24 are rotationally engaged. Since the piston member 24 is tightly sealed within the bowl outlet 14 by the seal 132, the piston member 24 resists any rotation. Wth the end of the shaft 118 rotationally engaged with the piston member 24, the piston member 24 inhibits (or prevents) and rotation of the shaft 118. This means that the threaded sleeve 106 starts to rotate in the second direction with respect to the shaft 118. Of course, preventing rotation of the piston member 24 could be provided in any other suitable way such as by using a non-circular piston member 24 or by keying it with the outlet. Referring to Figure 10, due to the threaded engagement of the sleeve 106 and the shaft 118, rotation of the sleeve 106 with respect to the shaft 118 causes the shaft 118 to start to axially extend from the end of the sleeve 106. As the shaft 118 extends (or moves axially) it drives the piston member 24 out of the bowl outlet 14. Continued rotation of the handle 22 in the second direction causes further axial movement of the shaft 118 which drives the piston member 24 away from the bowl outlet 14 and downwards within the dispensing tube 26. Since the piston member 24 is sealed within the dispensing tube 26 movement of the piston member 24 away from the bowl outlet 14 causes a negative pressure which starts to draw bone cement through the bowl outlet 14 and into the dispensing tube 26. The auger effect of the rotating mixing paddles 18, 20 together with the suction caused by moving the piston member 24 downwards and away from the bowl outlet 14 within the dispensing tube 26 results in an efficient transfer of bone cement mixture into the dispensing tube.

Once sufficient bone cement mixture has been transferred to the dispensing tube 26 by rotating the handle 22, the dispensing tube 26 is unscrewed from the bowl outlet 14, and the shaft 118 is withdrawn from the bone cement mixture. A dispensing nozzle (not shown) can then be screwed onto the threaded end of the dispensing tube 26, and the dispensing tube 26 can be loaded into a dispensing gun such that bone cement can be dispensed by a surgeon, or the like.

The bone cement mixer described above comprises a single drive mechanism having a single handle which can be rotated in a first direction to mix bone cement, and then rotated in a second opposing direction to transfer bone cement into a dispensing tube. This alleviates the need to provide a separate arrangement for transferring bone cement into a dispensing tube. The bone cement mixer is particularly compact, simple to use, and relatively inexpensive. The components may all be manufactured from a plastics material such as polymethylpentene (PMP) and it may be possible to manufacture them using additive manufacturing techniques (e.g. 3D printing). The bone cement mixer may be single-use item, and therefore may be disposed of after use.

Although it has been described that the bone cement mixer has contra-rotating coaxial paddles and an axially moveable shaft that can move a piston member to cause the transfer of bone cement into a dispensing tube, in other embodiments there may be a single paddle that rotates in one direction, or there may be multiple paddles non-coaxially arranged. Further, there could be multiple paddles that are arranged to always rotate together.

Furthermore, in other embodiments there may be contra-rotating coaxial paddles, but there may be no axially moveable shaft for driving a piston member. In such an arrangement bone cement would have to be transferred into the dispensing tube using another method (for example using a vacuum or by manually transferring it using a spatula or the like).

In the above embodiment it has been described that the transfer mechanism comprises a threaded shaft threadedly engaged within a threaded sleeve and that the sleeve is rotated relative to the shaft to cause it to axially drive the piston member. However, in other embodiments a threaded shaft could be rotated relative to a threaded sleeve so as to cause the threaded sleeve to drive the piston member. Further, other mechanisms or arrangements could be provided for axially driving the piston member away from the mixing bowl outlet and within the dispensing tube. For example, an axially extending rod could be provided which could be manually moved along the central axis to manually drive the piston member downwards. Of course, there may be other arrangements for driving the piston member using a rod or shaft from within the mixing bowl.

It has been described that the handle 22 is first rotated in a first direction that is clockwise, and then it an opposite second direction that is anti-clockwise. However, it should be appreciated that the first direction could be anti-clockwise and the second direction could be clockwise. In such an arrangement it may be necessary to change the twist of the mixing paddles (if they have a twist) from a right hand twist to a left hand twist.

Further, it has been described that a handle is provided that is rotatable about the central axis to drive the drive mechanism. However, the handle could be rotated about a different axis (such as a parallel axis), or about an axis perpendicular to the central axis. In yet another arrangement, the drive mechanism could have a rotatable input arranged to be driven by an electric motor. For example, a socket could be provided for engagement with a bit attached to a drill. In another arrangement the bone cement mixer could be loaded into a mixing machine which automatically drives the rotatable input.

Although it has been described that the invention relates to a bone cement mixer, the mixer could be for mixing any suitable type of mixture such as adhesive, sealant, food, or chemicals, for example.

Claims

CLAIMS:

1. A bone cement mixer, comprising: a mixing chamber having a chamber outlet; at least one mixing paddle disposed within the mixing chamber; a piston member slidable within a dispensing tube which can be coupled to the chamber outlet; and a shaft axially moveable to drive the piston member away from the chamber outlet such that, in use, the piston member is slidable within the dispensing tube so as to draw bone cement through the chamber outlet and into the dispensing tube.

2. A bone cement mixer according to claim 1, wherein the shaft is arranged such that it can be axially extended through the chamber outlet so as to drive the piston member away from the chamber outlet.

3. A bone cement mixer according to any preceding claim, wherein the shaft forms part of a drive mechanism comprising a rotatable input, and wherein the drive mechanism is configured such that rotation of the rotatable input in at least one direction causes the shaft to axially move so as to drive the piston member away from the chamber outlet.

4. A bone cement mixer according to claim 3, further comprising a handle operable to rotate the rotatable input.

5. A bone cement mixer according to claim 3 or 4, wherein the drive mechanism comprises an inner elongate threaded member disposed within and threadedly engaged with an outer elongate threaded member, wherein one of the threaded members is arranged to be rotatably driven by the rotatable input, and wherein the other threaded member forms at least a part of the shaft, and wherein rotation of the shaft can be inhibited in use such that rotation of the rotatable input in at least one direction causes the shaft to axially move so as to drive the piston member away from the chamber outlet.

6. A bone cement mixer according to claim 5, wherein the inner elongate threaded member forms the shaft, and wherein the outer elongate member forms a sleeve.

7. A bone cement mixer according to claim 5 or 6, wherein at least one mixing paddle is coupled to the outer elongate threaded member such that rotation of the rotatable input causes the mixing paddle to rotate.

8. A bone cement mixer according to any of claims 5-7, wherein the shaft is rotationally engageable with the piston member.

9. A bone cement mixer according to claim 8, wherein rotation of the rotatable input in a first direction causes the shaft to rotate with respect to the piston member, and wherein rotation of the rotatable input in a second opposing direction causes the shaft to rotationally engage with the piston member.

10. A bone cement mixer according to claim 9, wherein the shaft comprises at least one first engagement feature and wherein the piston member comprises at least one corresponding second engagement feature, and wherein rotation of the rotatable input in a second direction causes the at least one first engagement feature to engage with the at least one second engagement feature, thereby rotationally engaging the shaft with the piston member.

11. A bone cement mixer according to any preceding claim, further comprising a dispensing tube having a first open end arranged to be coupled to the chamber outlet.

12. A bone cement mixer according to claim 11, further comprising a dispensing nozzle arranged to be coupled to the first open end of the dispensing tube.

13. A bone cement mixer according to claim 11 or 12, wherein the dispensing tube is arranged to cooperate with a dispensing gun for dispensing bone cement from the dispensing tube.

14. A bone cement mixer according to any preceding claim, wherein the piston member is arranged to seal the chamber outlet.

15. A bone cement mixer according to claim 14 when appended to claim 11, wherein the dispensing tube is coupled to the chamber outlet and wherein the piston member seals the chamber outlet.

16. A bone cement mixer according to any preceding claim, wherein the at least one mixing paddle forms an auger.

17. A bone cement mixer according to any preceding claim, further comprising a lid from which the at least one mixing paddle depends.

18. A bone cement mixer substantially as described herein with reference to the accompanying drawings.