Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Patent
1987-01-12
1989-02-28
Apley, Richard J.
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
604 87, 604 88, 623 16, 4332011, 222 82, 222 94, 215DIG8, A61M 3100
Patent
active
048081841
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method and apparatus for preparing a cement composed of a powder and a liquid component which polymerize when brought into contact with each other. The invention is especially useful in connection with a cement which is used for medical purpose, particularly as bone cement or denture base material.
BACKGROUND OF THE INVENTION
Many modern day bone cements of the two component powder/liquid type are known which, when thoroughly mixed together, undergo polymerization thereby forming a hard and more or less durable cement mass.
While the present invention can be used to prepare a variety of such cements, it is especially useful in the preparation of so-called bone cement used to anchor and support artificial joint components and other prostheses in natural bone. Accordingly, it will be described here specifically in that context.
The currently preferred bone cement is polymethylmethacrylate or so-called PMMA. PMMA is comprised of a powdered polymer and a liquid monomer. Upon mixing, these components polymerize within minutes so as to form a firm rigid bond between the prosthesis and the surrounding bone structure in which the prosthesis is placed.
The present procedure for preparing PMMA bone cement is to thoroughly mix the powder and liquid component in order to start polymerization whereby the cement mass turns to a putty or dough consistency. The partially cured cement is then applied to the bone structure to be treated, e.g. into the medullary canal of the femur which is receiving a femoral shaft of a hip joint prosthesis.
All known methods for mixing bone cement have serious drawbacks, the most essential being: to produce an applicable cement mass by conventional mixing techniques; as by evaporation of excess monomer resulting in significant degradation of the mechanical properties of the cured cement.
SUMMARY OF THE INVENTION
Accordingly, the present invention aims to provide an improved method and apparatus for preparing a two component cement which is independent from the individual mixing technique.
Another object of the invention is to provide such a method which by its reduced amount of liquid component necessary to produce an applicable cement mass lowers considerably the maximum temperature reached during polymerization.
Still another object of the invention is to provide such a method which eliminates porosities in the cured cement by exclusion of air and by prevention of monomer evaporation.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing:
FIG. 1 is a perspective view of the powder component particles in a tightly packed state as used for the invention;
FIG. 2 is a sectional view of the syringe type container for the powder component used in the apparatus according to the invention;
FIG. 3 shows the liquid component injection through the piston of the syringe type container in a sectional view;
FIG. 4 shows the liquid component injection through the plug of the syringe type container in a sectional view;
FIG. 5 is a sectional view of the syringe type container showing the internal mixing process step;
FIG. 6 is a sectional view of the syringe type container with an additional nozzle showing the extrusion process step;
FIG. 7 is a sectional view of the ampule used for the invention;
FIG. 8 is a diagram showing the dynamics of the flooding process of the invention.
DETAILED DESCRIPTION OF THE INVENTION
As illustrated in FIG. 1 the powdered component of the cement 1 is packed as tightly as possible in the container 4 (FIG. 2) and the container is evacuated. Thus void space 2 contains no, or very little air. When allowed to enter the container 4, the liquid component will flood (arrow 3) void space 2 between the powder particles. This is the initial phase of the mixing process producing a powder-liquid mixture without any, or with very little air inclusion.
FIG. 2 shows a pre-packaged powder component 1 in the container 4. Container 4 is of a syringe type with piston 5. The extrusion end 18 of the container is closed with a plug 6. An internal mixing device 7
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patent: 4463875 (1984-08-01), Tepic
patent: 4467588 (1984-08-01), Carveth
patent: 4516967 (1985-05-01), Kopfer
patent: 4551135 (1985-11-01), Gorman et al.
Apley Richard J.
Laboratorium fur experimentelle Chirurgie Forschungsinstitut
Prebilic Paul
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