GB1603102A

GB1603102A - Bone cement preparation in piston extrusion apparatus

Info

Publication number: GB1603102A
Application number: GB14117/77A
Authority: GB
Original assignee: National Research Development Corp UK; National Research Development Corp of India
Current assignee: National Research Development Corp UK; National Research Development Corp of India
Priority date: 1977-04-04
Filing date: 1977-04-04
Publication date: 1981-11-18
Also published as: CH618872A5; DE2814353A1; IE780654L; IE46704B1

Description

(54) BONE CEMENT PREPARATION IN PISTON EXTRUSION APPARATUS (71) We, NATIONAL RESEARCH DEVELOPMENT CORPORATION, a British Corporation established by Statute, of Kingsgate House, 66-74 Victoria Street, London, S.W.1, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention concerns the preparation of bone cement, as used in the securement of endoprosthetic joint replacement, in piston extrusion apparatus.

Currently, bone cement is of acrylic form prepared, immediately prior to use, by mixing a powder and liquid with the resultant active cement being conveyed and applied to the relevant bone site by the surgeon in a direct manual procedure. This procedure is unsatisfactory in various respects. Firstly, the procedure is messy since the cement cures fairly rapidly, usually within about ten minutes, and it is appropriate to convey the cement immediately after mixing when it is still of a relatively liquid consistency. Secondly, since the mixing necessarily entraps air in the cement, some air remains in the cement when applied to the bone site and this can give rise to a laminated cement structure with inherent weaknesses. A corresponding disadvantage arises from the fact that the cement is not applied to the site in a continuous manner, and that the cement is likely to change in consistency during the period of application.

Thirdly, the fact that the cement is applied non-continuously and, in the case of a deep elongated site such as a medullary canal, is pushed from the outer to inner regions of the site relative to the bone, results in entrapment of blood and bone debris to produce yet further sources of mechanical weakness.

An object of the present invention is to make available a more satisfactory procedure for the preparation and application of bone cement.

According to the present invention there is provided a method of preparing bone cement which comprises mixing the cement in a vessel defined by, or located within, a piston extrusion apparatus, said apparatus having a detachably securable nozzle which is detached to provide access to said vessel for mixing said cement and is thereafter secured for dispensing of the mixed cement.

In addition it is proposed that the cement can be consolidated after mixing and prior to dispensing, by alternative detachable connection of a closure member in place of said nozzle and by operation of said apparatus with said vessel closed.

The benefits of the invention are firstly that the cement is mixed in, and can then be conveyed in and applied directly to the site from the one vessel, with a consequent reduction in mess, waste, and time involved.

Secondly, consolidation of the cement by compression can provide greater strength by reducing the volume of entrapped air.

Moreover application by extrusion can be substantially continuous with entrapped air passing to atmosphere on ejection from the nozzle. Thirdly, application through a nozzle can be more readily controlled and allows cement deposition to be effected outwardly from the inner region of the site.

The last possibility is particularly beneficial in that blood and bone debris is effectively floated from the site on the exposed surface of the cement, whence it can be cleared, rather than entrapped in the cement. The overall benefits which can be attained by use of the invention are convenience, speed, and increased cement strength.

While the invention can be carried out with an apparatus which is wholly disposable, it is preferred that use be made of an extrusion gun of a form comprising a re usuable assembly including a barrel, a handle projecting laterally from one end portion of said barrel, a rod mounted for longitudinal reciprocation in said barrel and manually operable by use of said handle to move from said one end portion to the other end portion of said barrel, and an apertured cap releasably connected with said other end portion of said barrel, and further comprising a disposable cartridge including a body of open-ended hollow cylindrical form longitudinally slidably receivable in said barrel, an end plug slidably receivable in said body to serve as a piston movable therein by said rod, and defining with said body, when located towards said one end thereof, said vessel, and a nozzle locatable to be held between said body and said apertured cap to cap the other end of said body and to project through said apertured cap.

In addition as noted above, this extrusion gun can include a closure cap alternatively locatable in place of the nozzle.

In use of this extrusion gun in carrying out the invention, the cartridge is located in the barrel with its end plug adjacent the one end of the body nearer to the rod, but without either of the caps or the nozzle in position.

The cartridge then forms a vessel in which the cement can be mixed. Conveniently for this purpose, the barrel is in two interconnectable longitudinal parts of which one carries the handle and rod, while the other is of hollow cylindrical form open at one end to receive the cartridge body and opened at the other end to receive the rod but restrain the cartridge body. The last-mentioned barrel part can then be separated to facilitate its support when cement is mixed therein.

After mixing, the closure cap is located and held by the apertured cap, and the cement then is consolidated by manually operating the instrument so that the rod pushes the end plug of the cartridge along its body. When the cement is consolidated, the nozzle is substituted for the closure and the cement then applied to the site by further operation to eject cement through the nozzle. Substitution of the nozzle for the closure cap is suitably preceded by slight withdrawal of the rod to avoid overflow of cement due to pressurisation during consolidation. Also, a layer of flexible material, such as that used for surgical gloves, can be located between the closure cap and cartridge body to facilitate the substitution of the end caps.

In order that the invention may be more fully understood the preferred extrusion gun will now be described, by way of example with reference to the accompanying drawings in which: Figure 1 schematically illustrates one embodiment of the gun in partially sectioned side view with its closure cap located; and Figure 2 duplicates part of Figure 1 but with its nozzle located.

The illustrated instrument is of the preferred form having a re-usuable assembly 10 of metal and a disposable cartridge 30 of plastics material. The assembly 10 is of pistol-grip form with a barrel 11 in two longitudinal separable parts 12 and 13. The rear barrel part 12 houses the gun action and has a handle 14 extending laterally therefrom. The action includes a toothed rod serving as a ratchet 15 which extends coaxially through the barrel and co-operates with a pawl 16. This pawl is pivotally mounted at 17 within the barrel part 12, and urged by a spring 18 to engage a stop 19.

The action is operated by a trigger 20 pivoted at an intermediate point 21 therealong in the handle, extending at its upper end into the adjacent barrel to co-operate with the ratchet, extending at its lower end forwardly from the handle, and is urged by a spring 22 in an anticlockwise manner towards a datum position as shown.

The action operates in a relatively straightforward manner in that pulling of the trigger towards the handle pushes the ratchet forward, the ratchet movement rotates the pawl against its spring bias, and, as each tooth of the ratchet passes over the pawl, the pawl springs back against its stop to prevent rearward movement of the ratchet. Release of the trigger allows the same to return to its datum position under spring action.

The ratchet is rotatably mounted in the barrel part 12 to allow disengagement from the trigger and pawl whereby the ratchet can be withdrawn after a desired forward movement. The barrel parts 12 and 13 are releasably connected by a bayonet fitting 23, and the barrel part 13 has an apertured cap 24 similarly connected thereto by a further bayonet fitting 25. The barrel part 13 is of substantially open-ended hollow cylindrical form, but has a restricted end opening at its rear end by virtue of an inwardly projecting flange 26. It is to be noted that the forward end of the ratchet can pass into the barrel part 13.

The disposable cartridge 30 comprises an open-ended cylindrical body 31 dimensioned for sliding receipt into the free end of the barrel part 13 with the cap 24 removed.

The body 31 is of such a length as to project by a small proportion from the barrel when the body engages the flange 26. An end plug 32 dimensioned for slidable receipt in the rear end of the body serves as a piston movable by the ratchet. A closure cap 33 (Figure 1) of flanged solid disc form is located over the free end of the body 31 and secured by the cap 24 which seats over the cap 33 to connect with the barrel. The cap 33 can be replaced, as described above, by a nozzle 34 (Figure 2) which projects through the aperture of cap 24.

While the invention has been described with more particular reference to a preferred form of extrusion gun and the illustrated embodiment thereof, it has been indicated in the foregoing introductory passages that this is not intended to be limiting. The invention can clearly be put into effect by use a suitably modified form of wholly disposable syringe. However, the preferred use of an extrusion gun apparatus can equally clearly leads to economy. Moreover, the preferred form of gun may itself take various more specific forms, particularly in terms of its re-usuable assembly and the action thereof. Indeed in a simplified form an assembly more like a conventional syringe is possible, but an assembly giving mechanical advantage in operation is preferable bearing in mind the rapidly increasing viscosity of bone cement when mixed to an activated condition.

WHAT WE CLAIM IS: 1. A method of preparing bone cement which comprises mixing the cement in a vessel defined by, or located in, a piston extrusion apparatus, said apparatus having a detachably securable nozzle which is detached to provide access to said vessel for mixing said cement and is thereafter secured for dispensing of the mixed cement 2. A method according to Claim 1 wherein said apparatus is an extrusion gun comprising a re-usuable assembly including a barrel, a handle projecting laterally from one end portion of said barrel, a rod mounted for longitudinal reciprocation in said barrel and manual operable by use of said handle to move from said one end portion to the other end portion of said barrel, and an apertured cap releasably connected with said other end portion of said barrel, and further comprising a disposable cartridge including a body of openended hollow cylindrical form longitudinally slidably receivable in said barrel, an end plug slidably receivable in said body to serve as a piston movable therein by said rod and defining with said body, when located towards said one end thereof, said vessel, and a nozzle locatable to be held between said body and said apertured cap to cap the other end of said body and to project through said apertured cap.

3. A method according to Claim 1 or 2 which comprises consolidating said cement after mixing and prior to dispensing the same, by alternative detachable connection of a closure member in place of said nozzle and by operation of said apparatus with said vessel closed.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

33 can be replaced, as described above, by a nozzle 34 (Figure 2) which projects through the aperture of cap 24.

While the invention has been described with more particular reference to a preferred form of extrusion gun and the illustrated embodiment thereof, it has been indicated in the foregoing introductory passages that this is not intended to be limiting. The invention can clearly be put into effect by use a suitably modified form of wholly disposable syringe. However, the preferred use of an extrusion gun apparatus can equally clearly leads to economy. Moreover, the preferred form of gun may itself take various more specific forms, particularly in terms of its re-usuable assembly and the action thereof. Indeed in a simplified form an assembly more like a conventional syringe is possible, but an assembly giving mechanical advantage in operation is preferable bearing in mind the rapidly increasing viscosity of bone cement when mixed to an activated condition.

WHAT WE CLAIM IS: 1. A method of preparing bone cement which comprises mixing the cement in a vessel defined by, or located in, a piston extrusion apparatus, said apparatus having a detachably securable nozzle which is detached to provide access to said vessel for mixing said cement and is thereafter secured for dispensing of the mixed cement
2. A method according to Claim 1 wherein said apparatus is an extrusion gun comprising a re-usuable assembly including a barrel, a handle projecting laterally from one end portion of said barrel, a rod mounted for longitudinal reciprocation in said barrel and manual operable by use of said handle to move from said one end portion to the other end portion of said barrel, and an apertured cap releasably connected with said other end portion of said barrel, and further comprising a disposable cartridge including a body of openended hollow cylindrical form longitudinally slidably receivable in said barrel, an end plug slidably receivable in said body to serve as a piston movable therein by said rod and defining with said body, when located towards said one end thereof, said vessel, and a nozzle locatable to be held between said body and said apertured cap to cap the other end of said body and to project through said apertured cap.
3. A method according to Claim 1 or 2 which comprises consolidating said cement after mixing and prior to dispensing the same, by alternative detachable connection of a closure member in place of said nozzle and by operation of said apparatus with said vessel closed.