Medical Device with Retractable Needle

Abstract

A tamperproof retractable non-reusable syringe has a one piece hollow outer body with a barrel for a slidable plunger, a transition zone and a smaller diameter nose portion. An elongated needle holder and spring combination is installable from the rear of the outer body, guided into the nose portion and held by cooperating inwardly and outwardly facing surfaces oriented in the direction of retraction at the most constricted part of the transition zone where the nose begins. The plunger has an opening with a dislodgable stopper for receiving parts of the retraction mechanism. The stopper and the head of the needle holder are of significantly reduced diameter from the injection fluid chamber to resist blowing out prematurely. In one embodiment the head of the needle holder is surrounded by a separable retainer member which is slidingly removed by contact with the tip of the plunger after the stopper is mostly or fully removed to avoid cumulation of force required for retraction after the injection. In a second embodiment the head of the needle holder is clamped and held by constricting forces imposed by stress on the outer body induced by interference fit. Release occurs by slight expansion on the barrel by contact of the plunger tip with a small internal ramp in the outer barrel. Both embodiments have a plunger cap configured to enter an opening in the outer body to provide an additional tamperproof feature. The retraction cavity is provided with venting structures to assure that all uninjected fluid is retained within the syringe body.

1 - 28 . (canceled) 
   
   
       29 . A medical device comprising a needle retraction mechanism disposed inside a body, the needle retraction mechanism comprising a needle holder grounded against forward movement inside the body and supporting a forwardly extending needle in fixed relation to the needle holder, the needle holder comprising a head further comprising an inner head supporting the needle in fixed relation to the inner head, and a retainer member surrounding the inner head and disposed in substantially fixed relation to the inner head prior to retraction, the inner head being biased toward a retraction position by a retraction spring and held in place prior to retraction by attachment to the retainer member and by contact between the retainer member and an inner wall of the body, the retainer member cooperating with the inner head to provide a fluid seal between the needle and the body and being detachable from the inner head by the application of a retraction force to the needle holder outwardly of the inner head and in a direction coaxial to the needle, the retraction force being applied as the result of forward motion of a plunger relative to the body to initiate retraction, the plunger further comprising a plunger head having a sealing element slidably engaging the body, the plunger sealing element being the only structure maintaining the plunger head inside the body following retraction.