Safety medical syringe with retractable needle

A syringe comprising:

• a hollow barrel including an opening at a proximal end of the barrel, an opening at a distal end of the barrel and a fluid chamber disposed within the barrel;
• a hollow plunger extending into the barrel via the proximal end opening and axially movable within the barrel toward and away from the distal end opening, wherein the plunger includes an end wall that is releasably secured to the plunger at an opening disposed at a distal end of the plunger and movable from the plunger distal end opening during use of the syringe to thereby facilitate access to a retraction cavity disposed within the plunger;
• and
• a needle assembly secured within and at a distal end of the barrel, the needle assembly including a needle holder, a resilient member that biases the needle holder toward the proximal end opening of the barrel, and securing means for releasably securing the needle holder at the barrel distal end against the bias of the resilient member;
• wherein:
• the plunger distal end and the securing means are configured such that, upon full depression of the plunger within the barrel, the securing means includes a first portion that is progressively torn from the needle holder and is forced toward the barrel distal end while at least one other portion of the securing means is prevented from moving toward the barrel distal end until the at least one other portion is torn from the needle holder after tearing of the first portion from the needle holder;
• and
• the plunger end wall, the needle holder and a needle secured to the needle holder are forced into the retraction cavity by the resilient member upon complete tearing from the needle holder of the first portion and the at least one other portion of the securing means.

A method of utilizing a syringe of the type including a hollow barrel with an opening at a proximal end of the barrel, an opening at a distal end of the barrel and a fluid chamber disposed within the barrel, a hollow plunger extending into the barrel via the proximal end opening and axially movable within the barrel toward and away from the distal end opening, the plunger including an end wall that is releasably secured to the plunger at an opening disposed at a distal end of the plunger, and a needle assembly secured within and at a distal end of the barrel, the needle assembly including a needle holder, a resilient member biasing the needle holder toward the proximal end opening of the barrel, a retaining member releasably secured to the needle holder via a reduced material section and a needle secured to the needle holder, the method comprising:

• facilitating aspiration of fluid through the needle and into a fluid cavity within the barrel by moving the distal end of the plunger toward the proximal end of the barrel;
• facilitating withdrawal of the aspirated fluid from the fluid cavity within the barrel by moving the distal end of the plunger toward the distal end of the barrel;
• and
• facilitating retraction of the needle holder within a retraction cavity defined within the plunger upon complete movement of the plunger into the barrel, wherein the plunger is configured to engage the needle holder upon complete movement of the plunger into the barrel such that the end wall of the plunger is forced within the plunger and the retaining member is forced to break away and separate from the needle holder along the reduced material section to facilitate retraction into the retraction cavity of the end wall, the needle holder and the needle secured to the needle holder into the retraction cavity.