Retractable needle medical device for injecting fluid from a pre-filled cartridge

A medical device, comprising:

• a hollow barrel having an open rearward end;
• a cartridge containing a quantity of fluid;
• an inner housing slidably displaceable within the barrel, and having an opening for receiving the cartridge;
• a needle having a sharpened tip in fluid communication with the cartridge;
• an axially displaceable plunger operable to expel fluid from the cartridge;
• a first lock releasably retaining the needle in a projecting position in which the sharpened tip of the needle is exposed for use;
• a second lock releasably retaining the needle in a retracted position in which the sharpened tip of the needle is shielded against inadvertent contact;
• and
• a biasing element biasing the needle rearwardly.

A method for injecting medication from a medical device having a needle with a sharpened tip, comprising the steps of:

• piercing a patient with the needle;
• injecting fluid from a first cartridge into the patient;
• retracting the needle into a retracted position after injecting fluid so that the sharpened tip is shielded against inadvertent contact;
• releasably locking the needle in the retracted position;
• re-extending the needle so that the sharpened tip is exposed;
• injecting fluid from the cartridge into the patient after re-extending the needle;
• and
• retracting the needle a second time so that the sharpened tip is shielded against inadvertent contact.

A medical device, comprising:

• a hollow barrel having an open rearward end;
• a cartridge containing a quantity of fluid;
• an inner housing slidably displaceable within the barrel, and having an opening for receiving the cartridge;
• a needle having a sharpened tip in fluid communication with the cartridge;
• an axially displaceable plunger operable to expel fluid from the cartridge;
• a first lock releasably retaining the needle in a projecting position in which the sharpened tip of the needle is exposed for use;
• a second lock releasably retaining the needle in a retracted position in which the sharpened tip of the needle is shielded against inadvertent contact;
• a guide for impeding rotation of the housing relative to the barrel during retraction;
• and
• a biasing element biasing the needle rearwardly.