GB2294410A

GB2294410A - Apparatus and method for mixing orthopaedic cement

Info

Publication number: GB2294410A
Application number: GB9421738A
Authority: GB
Inventors: Ailsa Yvonne Farquhar Clark; Ergate Ayana
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-10-28
Filing date: 1994-10-28
Publication date: 1996-05-01
Also published as: GB9421738D0

Abstract

In preparing an acrylic resin orthopaedic bone cement from methyl methacrylate, unpleasant or noxious fumes are produced during the mixing of the components of the resin. The invention provides apparatus comprising an enclosed mixing chamber 12 having an externally operated stir paddle 36 and a vacuum chamber 14 in communication with the mixing chamber. In use, clamp 50 is closed, the vacuum chamber evacuated and the components of the cement placed in the mixing chamber. Any fumes produced in the mixing chamber during the mixing process are drawn into the vacuum chamber and contained therein by opening and closing the clamp. The mixing chamber also has a charcoal lining 28 to absorb the fumes. A second vacuum chamber may also be provided if two cement mixes are required during an operation. <IMAGE>

Description

MIXING APPARATUS This invention relates to mixing apparatus, and in particular to a apparatus for use in mixing materials which produce unpleasant or potentially harmful fumes or vapours.

Orthopaedic bone cement is used routinely in orthopaedic surgery to, for example, stabilise orthopaedic implants, such as replacement hip joints. One of the more popular cements in use is the acrylic resin prepared by polymerizing methyl methacrylate (2-methylpropenoic acid).

This cement sets quickly and thus must be prepared in theatre shortly before use. The cement is prepared by mixing a liquid and a powder, the mixing process typically being carried out manually in an open bowl. As the cement components are mixed, fumes are released. These fumes are unpleasant and have been implicated as being potentially harmful.

It is among the objects of the present invention to provide mixing apparatus which will obviate or mitigate these difficulties.

According to the present invention there is provided mixing apparatus comprising an enclosed mixing chamber having an externally operable mixing member and a vacuum chamber in fluid communication with the mixing chamber, whereby a proportion of fumes produced by material in the mixing chamber may be drawn into the vacuum chamber and contained therein prior to opening the mixing chamber.

In use, an operator may place material, such as the powder and liquid mixed to form orthopaedic cement as described above, in the mixing chamber, which is then closed. The operator then uses the mixing member to mix the material. During, or following, the mixing operation a communicating conduit between the mixing and vacuum chambers is opened such that gas flows from the mixing chamber into the vacuum chamber until the pressure in the chambers has equalised. Thus, a proportion of the fumes produced during the mixing operation are drawn into the vacuum chamber. The conduit is then closed and the mixing chamber opened to allow removal of the cement. Exposure to the fumes produced is thus minimised, and the sealed vacuum chamber may be exhausted to atmosphere at a convenient later time.

Preferably, the vacuum chamber is of relatively large volume, such that the majority of the fumes produced are drawn from the mixing chamber.

Preferably also, the mixing chamber incorporates a material for absorbing harmful or unpleasant fumes, for example the chamber has a charcoal lining.

Preferably also, the mixing chamber includes a removable mixing bowl.

Preferably also, the mixing and vacuum chambers are defined by separate vessels. The vessels may be mounted on a common base. The apparatus is thus in the form of a convenient, easily handled package. A plurality of vacuum chambers may be provided, such that more than one batch of cement may be mixed during an operation.

This and other aspects of the invention will now be described, by way example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of mixing apparatus in accordance with a preferred embodiment of the present invention; and Figure 2 is a sectional view on line 2 - 2 of Figure 1.

The drawings illustrate mixing apparatus 10 in accordance with a preferred embodiment of the present invention. The apparatus 10 is particularly suited for use in mixing orthopaedic cement in theatre and comprises a mixing chamber 12 and a vacuum chamber 14, both mounted on a base or tray 16. The chambers 12, 14 are linked by a flexible tube 18 and a further tube 20 extends from the vacuum chamber 14, ending in an adapter 22 suitable for connecting with a conventional theatre scavenging system.

The mixing chamber 12 includes a double walled outer bowl 24, the inner wall 26 of which is perforated to allow access to a charcoal lining 28 located between the inner and outer walls 26, 30. An inner mixing bowl 32 is provided inside the outer bowl 24 and accommodates a mixing member having a stir paddle 34 located within the bowl 32 linked to a stirring crank 36. A drive shaft 38 connects the paddle and crank 34, 36 and extends through the chamber lid 40. The shaft 38 extends through rubber packing 42 and a rubber seal 44 is also provided between the lid 40 and the outer bowl 24. The lid 40 is provided with a knurled outer edge 46 to facilitate rotation of the lid 40 to engage and disengage the corresponding screw threads 48 on the lid 40 and outer bowl 24.

The vacuum chamber 14 defines an enclosed volume which communicates with the interior of the outer bowl 24 via the tube 18. The first clamp 50 is provided on the tube 18, while a second clamp 52 is provided on the tube 20.

The apparatus 10 is prepared for use by first closing the clamp 50 and then pulling a vacuum in the chamber 14, through the tube 20. The second clamp 52 is then closed on the tube 20. The apparatus 10 may then be sterilised and delivered to the theatre. Shortly before a supply of cement is required, the lid 40 is removed and the cement powder and liquid placed in the inner bowl 32. The lid 40 is then replaced and tightened to ensure an air-tight seal.

The operator then rotates the stirring crank 34 to operate the paddle 34 and mix the cement powder and liquid. During the mixing operation the clamp 50 is released such that air and fumes are drawn from the mixing chamber 12 into the vacuum chamber 14. As the volume of the vacuum chamber 14 is relatively large compared to the mixing chamber 12, the majority of the fumes produced during the mixing operation are drawn into the vacuum chamber. Once the cement has been thoroughly mixed, the clamp 50 is closed before the lid 40 is removed to retrieve the mixed cement. The cement bowl 32 may be lifted free from the mixing chamber 12 to facilitate retrieval of cement, for example using a spatula.

The apparatus may then be set aside until the operation is completed. Following completion of the operation, the adapter 22 is connected to the scavenging system provided in the theatre. Once the adapter is thus connected, the clamp 52 is released, followed by the clamp 50, such that any fumes are drawn from the chamber 14 and expelled to atmosphere.

If two cement mixes are required during an operation, a second vacuum chamber may be provided. The second chamber is provided with the appropriate tubes 18, 20 and clamps 50, 52 in place and as such may simply replace the "used" vacuum chamber 14. The provision of a second vacuum chamber 14 may also be of assistance if, for some reason, the vacuum in the first chamber 14 is lost.

From the above description it will be clear to those of skill in the art that the mixing apparatus 10 provides a simple and convenient means of limiting exposure to unpleasant or harmful fumes. However, it will further be clear to those of skill in the art that the above-described embodiment of the invention, and the described use of the invention, are merely exemplary and that various modifications and improvements may be made to the apparatus and its mode of use without departing from the scope of the invention.

Claims

1. A mixing apparatus comprising an enclosed mixing chamber having an externally operable mixing member and a vacuum chamber in fluid communication with the mixing chamber, whereby a proportion of fumes produced by material in the mixing chamber may be drawn into the vacuum chamber and contained therein prior to opening the mixing chamber.

2. A mixing apparatus according to claim 1 wherein the vacuum chamber is of relatively large volume, such that the majority of fumes produced by material in the mixing chamber may be drawn from the mixing chamber.

3. A mixing apparatus according to claims 1 to 2 wherein the mixing chamber incorporates a material for absorbing harmful or unpleasant fumes.

4. A mixing apparatus according to claim 3 wherein the absorbing material is in the form of a charcoal lining for the mixing chamber.

5. A mixing apparatus according to any preceding claim wherein the mixing chamber includes a removable mixing bowl.

6. A mixing apparatus according to any preceding claim wherein the mixing ard vacuun chambers are defined by separate vessels which are mounted on a common base.

7. A mixing apparatus according to any preceding claim wherein a plurality of vacuum chambers are provided.

8. A mixing apparatus substantially as herein before described with reference to the accompanying drawings.

9. A method of mixing a material, which produces unpleasant or harmful fumes on mixing, comprising the steps of: placing the material in a mixing chamber comprising an externally operable mixing member and closing the mixing chamber, mixing the material using the externally operable mixing member, opening a communicating conduit between the mixing chamber and a vacuum chamber such that the fumes flow from the mixing chamber into the vacuum chamber until the pressure in the chambers has equalised, closing the conduit and opening the mixing chamber to allow removal of the mixed material.