Pre-filled retractable needle injection ampoules

A method for providing an injection from a medical device, comprising the steps of:

• providing a medical device comprising a barrel, a needle having a sharpened tip projecting forwardly from the barrel, a biasing element biasing the needle rearwardly, and a mounting stem disposed within the barrel;
• releasably retaining the mounting stem in a fixed axial position relative to the barrel by an arm attached to the mounting stem and engaging a recess in the barrel;
• providing a cartridge comprising a fluid container containing a quantity of medicinal fluid and a slidable seal forming a fluid-tight seal with the container;
• attaching the seal to the stem to connect the cartridge to the medical device;
• retaining the seal in a fixed axial position while displacing the fluid container forwardly over the seal to expel the fluid from the container and through the needle;
• and
• displacing the fluid container further forwardly after the fluid container engages the arm, thereby disengaging the arm from the recess and causing the needle to be released for retraction.

A medical device for providing an injection of fluid, comprising:

• a hollow housing having a central axis;
• an ampoule of fluid comprising a container having a length, an open end forming a rim and a plug sealing the open end, wherein the container comprises a fluid chamber having a length that extends from a rearward end of the plug to the rearward end of the container;
• a needle having a sharpened tip operable between a projecting position in which the sharpened tip projects forwardly from the housing and a retracted position in which the sharpened tip is shielded against inadvertent contact;
• a biasing element biasing the needle toward the retracted position;
• a stem disposed within the housing configured to matingly engage the ampoule plug to attach the plug to the stem wherein the stem is operable in connection with the ampoule to provide an injection of fluid through the needle from the ampoule by displacing the ampoule forwardly relative to the stem;
• and
• a latch releasably retaining the stem at a fixed axial position during the injection wherein when the ampoule is mounted on the stem, the latch is spaced from the rim of the container a distance substantially similar to the length of the fluid chamber so that at the end of the injection the ampoule engages the latch;
• wherein after the ampoule engages the latch, continued forward displacement of the ampoule operates to effectuate release of the needle.