Medical injection devices

Details Medical injection devices Medical injection devices

1997-09-24

1999-07-27

Stright, Ronald

Surgery

Means for introducing or removing material from body for...

Treating material introduced into or removed from body...

604232, 604192, A61M 500

Patent

active

059282053

DESCRIPTION:

BRIEF SUMMARY
This invention relates to medical injection devices.
Some medical injection devices have a dose to be administered in a cartridge (usually known as a Schott syringe) whose leading end is closed by a membrane. The needle has a rear tip as well as a forward one, and before injection, this rear tip and the cartridge are brought together for the tip to pierce the membrane and thus open the needle passage to the fluid inside the cartridge. This application is concerned with a device in which the needle assembly is moved rearwardly to achieve the piercing, rather than one where the cartridge is shifted for that operation.
Before use, the leading tip, which is to be inserted in the patient, obviously has to be well protected. At the same time, there has to be an arrangement for pushing the needle assembly rearwardly to cause the rear tip to penetrate the membrane. While that could be done with the protection removed, that is awkward and dangerous.
It is the aim of this invention to provide an arrangement whereby the penetration of the membrane can safely be done with the needle protection still in place, that being removed afterwards just prior to injection.
According to the present invention there is provided an injection device including a barrel with a forward end cap for containing a cartridge of fluid to be injected, the cartridge being closed at its forward end by a membrane, and having a needle assembly that fits to said forward end in two modes, the first being a standby mode with the membrane intact and the second being a use mode with the membrane pierced by the rear end of the needle, the needle assembly having been shifted rearwardly with respect to the cartridge, wherein the forward end of the needle is initially protected by a sheath, and wherein the cap has a progressive application to the barrel, a first movement causing it to engage the sheath and a second movement pushing on the needle assembly to cause that to move from the first to the second mode position, subsequent removal of the cap taking the sheath off the needle to leave the device ready to use.
In other words, the cap is pushed on and then pulled off, this action automatically bringing the cartridge and the rear tip of the needle together, and then removing the protection of the forward end of the needle.
In the preferred form, the needle assembly has a snap engagement with the forward end of the cartridge in said first mode, this being released by the second movement of the cap.
The needle assembly may also have a snap fit engagement with the forward end of the cartridge in said second mode, this being achieved at the end of the second movement of the cap.
These snap engagements can each be provided by an annular rib and groove. Conveniently, the needle assembly will have two internal axially spaced annular ribs and the cartridge will have an annular groove around its leading end into which either of the ribs can engage.
Preferably, the sheath has an outward projection and the cap has an inward projection which snaps past the outward projection as the cap completes its first movement, the sheath being pulled off the needle by these projections hooking together on removal of the cap. These projections are conveniently annular ribs. Alternatively, the cap may be formed to grip the sheath by friction during its first movement and to remove the sheath by that grip.
The cap may be a push fit or a screw fit to the barrel.
For a better understanding of the invention, one embodiment will now be described, by way of example, with reference to the accompanying drawing, in which:
FIG. 1 is an axial section of the leading end of a medical injection device prior to use,
FIG. 2 is an axial section of that leading end with the device being prepared for use, and
FIG. 3 is an axial section of that leading end with a cap removed and the device ready for use.
The device is for administering a dose through a needle 1 from a cartridge 2. This will have a plunger (not shown) and it can itself be thrust forwards bodily to project the needle 1, the mechanism

REFERENCES:
patent: 1971687 (1934-08-01), Kratz
patent: 2880723 (1959-04-01), Adams
patent: 3820652 (1974-06-01), Thackston

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