Abstract:
A safety needle-bearing medical advice ( 10 ) is provided. Specifically, a safety device for injecting medicinal fluid into a patient is provided. The device comprises a hollow housing ( 20 ), a needle assembly ( 40 ) and a plunger ( 30 ). The needle assembly ( 40 ) releasably retains a needle ( 45 ) in an extended position in which the sharpened tip of the needle is exposed for use. At the end of an injection stroke, the plunger ( 30 ) engages the needle assembly ( 40 ), such that the needle ( 45 ) is released and retracted into a cavity ( 38 ) within the plunger. The device ( 10 ) includes structure for reducing the dead-space volume, which represents the amount a fluid remaining in the device at the end of an injection stroke. In addition, preferably the device ( 10 ) includes structure for minimizing the volume of potential air bubbles trapped in the medicinal fluid prior to an injection.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to syringes for administering injections of medicinal fluids to a patient or withdrawal of fluid, such as blood from a patient. More specifically, the invention relates to such devices having a retractable needle feature for rendering the device non-reusable and safely disposable.  
         BACKGROUND OF THE INVENTION  
         [0002]    Various types of medical devices employ a needle for piercing the skin of a patient for diagnostic or therapeutic purposes. One such device is a hypodermic syringe. Handling of such needle-bearing medical devices after the needle is withdrawn from the patient can result in transmission of various pathogens, most notably human immune virus (HIV), to uninfected medical personnel, due to an inadvertent needle stick. Accordingly, it is desirable to provide a device for injecting medication or withdrawing fluid, wherein the needle is retracted into the housing of the device after use. 
       
    
    
       [0003]    The following detailed description of the preferred embodiments will be better understood when read in conjunction with the figures, in which:  
         [0004]    [0004]FIG. 1 is an exploded perspective view of a safety hypodermic syringe having a retractable needle, manifesting aspects of the present invention;  
         [0005]    [0005]FIG. 2 is an exploded perspective view of a needle subassembly of the syringe illustrated in FIG. 1;  
         [0006]    [0006]FIG. 3 is an exploded perspective view of a plunger subassembly of the syringe illustrated in FIG. 1;  
         [0007]    [0007]FIG. 4 is a cross-sectional view of the syringe illustrated in FIG. 1;  
         [0008]    [0008]FIG. 5 is a cross-sectional view of the syringe illustrated in FIG. 4, showing the needle in a retracted position;  
         [0009]    [0009]FIG. 6 is an enlarged fragmentary cross-sectional view of the forward end of the syringe illustrated in FIG. 1;  
         [0010]    [0010]FIG. 7 is an enlarged fragmentary cross-sectional view of the forward end of the syringe illustrated in FIG. 1, orthogonal to FIG. 6;  
         [0011]    [0011]FIG. 8 is an enlarged fragmentary cross-sectional view of the forward end of the barrel of the syringe illustrated in FIG. 1; and  
         [0012]    [0012]FIG. 9 is an enlarged fragmentary cross-sectional view of the forward end of the barrel of the syringe illustrated in FIG. 1, orthogonal to FIG. 8. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0013]    Referring now to the figures in general, and more specifically to FIG. 1, a retractable needle safety hypodermic syringe is designated generally  10 . The syringe  10  includes a barrel  20 , a plunger  30  reciprocally displaceable within the barrel, and a needle assembly  40  attachable to the forward end of the barrel. The needle assembly releasably retains a needle  45 , such that after use, the needle is retracted into the barrel  20 , so that the needle is shielded after use to prevent inadvertent contact with the contaminated needle after use.  
         [0014]    The barrel is a generally hollow cylinder having a tip  22  configured to cooperate with the needle assembly  40 . The rearward end of the barrel is generally open for receiving the plunger  30 . The plunger  30  is reciprocally displaceable within the barrel for drawing fluid into the barrel or expelling fluid from the barrel.  
         [0015]    The plunger  30  comprises a substantially rigid elongated plunger rod  32  and a piston  35  attach to the forward end of the plunger rod  32 . The piston  35  forms a fluid tight seal with the interior surface of the barrel  20 . As discussed further below, the piston  35  is axially compressible at the end of the injection stroke to reduce the dead space at the forward end of the barrel. Dead space refers to the volume in the barrel in which a fluid can reside at the end of an injection stroke. Effectively, the dead space volume of a syringe is the amount of medication that is wasted because the fluid in the dead space cannot be injected.  
         [0016]    The forward end or head  33  of the plunger rod  32  is configured to matingly engage the needle assembly  40 . In the present instance, the plunger head  33  is substantially frustoconical. The plunger rod  32  is hollow, having a cavity  38  for receiving the needle  45  after retraction. The plunger head  33  has an opening or orifice through which the needle passes into the cavity  38  during retraction. This orifice is sealed by a displaceable plug  36 . The plunger rod may be a substantially hollow cylinder. However in the present instance, the plunger rod is  80  generally u-shaped channel having an opened top edge as shown in FIGS. 4 and 5. The plunger rod further comprises a circumferential flange  37  adjacent the rearward end wall of the cavity  38 . The flange  37  is a locking element that mates with an annular rib  28  that protrudes inwardly from the inner surface of the barrel  20 . The locking flange  37  and the locking rib  28  lock the plunger  30  against rearward displacement at the end of an injection stroke. Specifically, as the plunger  30  is displaced forwardly, the locking flange  37  rides over the rearward face of the locking rib  28 , which is tapered. The forward face of the locking rib  28  forms a substantially square shoulder that cooperates with the flange  37  to impede rearward displacement of the plunger  30 .  
         [0017]    Referring now to FIG. 2, the details of the needle assembly  40  are most clearly seen. The needle assembly  40  includes the needle  45 , a spring  75  biasing the needle rearwardly, a needle retainer  50  releasably retaining the needle against the bias of the spring, a needle fitting  60  attached to the rearward end of the needle to provide an engagement surface for the needle retainer, and a cap  70  enclosing the forward end of the needle assembly.  
         [0018]    The needle retainer  50  comprises a pair of radially deformable axially elongated fingers  54  extending rearwardly from a substantially cylindrical body  52 . The rearward portion of the cylindrical body  52  is configured to form an interference fit with the interior of the tip  22  of the barrel  20 . In this way, a fluid tight seal is formed between the needle retainer  50  and the tip  22  so that fluid cannot leak out of the barrel between the tip  22  and the needle retainer  50 . The needle retainer  50  has a bore for receiving the needle fitting  60 . The fingers  54  have inwardly projecting latches engaging the rearward end of the needle fitting  60  to retain the needle against the rearward bias of the spring  75 .  
         [0019]    The needle fitting is a hollow substantially cylindrical element. The rearward end of the needle fitting  60  flares outwardly forming a generally frustoconical head. The frustoconical head mates with the inner surface of the fingers  54 . Adjacent the frustoconical head  62  is an annular sealing rib  67  that protrudes from the surface of the needle fitting. The sealing rib  67  forms an interference fit with the inner bore of the needle retainer  50  to form a fluid-tight seal between the needle fitting  60  and the inner bore of the needle retainer. However, the interference fit between the sealing rib  67  and the needle retainer  50  is not sufficient to retain the needle against the rearward bias of the spring  75 . The inner bore of the needle fitting forms a reservoir for receiving the rearward end of the needle and epoxy for bonding the needle to the needle fitting. The lowermost portion of the reservoir forms a plenum  63  in fluid communication with the needle  45 . The reservoir is constricted forward of the plenum  63  to a diameter closely corresponding to the outer diameter of the needle. In this way, the constriction operates to center the needle within the reservoir.  
         [0020]    A vent passage  64  in fluid communication with the plenum  63  extends through the width of the needle fitting head  62 . The vent passage  64  provides fluid communication between the interior of the barrel  20  and the plenum  63 . If the vent passage is aligned with the needle retainer fingers  54  so that the fingers overlap the vent passages, fluid flow through the vent passages will be either blocked or reduced. Accordingly, the fingers  54  should be located so that they do not overlap with the vent passages  64 . Alternatively, and preferably, a circumferential vent groove  65  may be formed on the exterior surface of the needle fitting rearward of the sealing rib  67 . The vent groove  65  intersects the vent passage  64  to form a fluid pathway around the fingers  54  to eliminate any problems associated with blockage of the vent passage  64  by the fingers. Configured in this manner, the fluid seal between the needle retainer and the barrel is immediately adjacent the fluid seal between the needle fitting and the needle retainer, and the fluid passage through the needle fitting and to the needle  45  is immediately rearward of the fluid seal between the needle fitting and the needle retainer. Since the fluid passage is immediately adjacent the rearward-most fluid seal, the space within the device in which air bubbles could potentially become trapped is minimized.  
         [0021]    The cap  70  is a hollow cylinder having a generally closed forward end with a reduced diameter opening. The forward end of the needle fitting  60  has a reduced diameter portion configured to project through the reduced diameter opening of the cap. A plurality of axially spaced circumferential ridges are formed on the interior surface of the cap. The cap ridges cooperate with a plurality of corresponding axially spaced circumferential locking ridges  56  on the exterior of the needle retainer  50 . In this way, the cap and the needle retainer enclose the needle assembly  40  so that the needle assembly is a separable assembly that can be attached to the barrel  20 . As shown in FIG. 6, the spring  75  is disposed within the needle retainer  50  circumscribing the needle fitting  60  bearing against the cap  70  and the head  62  of the needle fitting.  
         [0022]    Referring again to FIG. 1, the tip  22  of the barrel  20  comprises a pair of locking windows  27  that cooperate with a pair of locking tabs  55  on the needle assembly  40  to attach the needle assembly to the barrel. The tip  22  includes a pair of axial alignment grooves  26  extending between the locking windows  27  and the forward end of the tip. The alignment grooves  26  are configured to receive the locking tabs  55  to provide proper alignment between the needle assembly  40  and the barrel  20  so that the locking tabs  55  are aligned with the locking windows  27 .  
         [0023]    The tip further comprises a pair of opposing clearance grooves  25  aligned with the needle retainer fingers  54 . The clearance grooves  25  provide space for the outward radial displacement of the fingers  54 . The tip  22  further includes a plurality of protrusions  24  projecting inwardly from the inner surface of the tip to fill the space adjacent the area in which the needle retainer fingers  54  are received. The protrusions  24  reduce the area between the fingers  54  and the interior of the tip, other than the clearance grooves  25  for the fingers. In this way the protrusions  24  substantially reduce the dead space between the needle retainer and the interior of the tip.  
         [0024]    Configured in this manner, the device operates as follows. The needle assembly  40  is inserted into the tip  22  of the barrel so that the locking tabs  55  of the needle retainer  50  are aligned with the alignment grooves  26  of the tip. The needle assembly  40  is inserted into the tip until the locking tabs  55  engage the locking windows  27  to substantially permanently attach the needle assembly to the barrel  20 .  
         [0025]    The fluid is drawn into the barrel by inserting the sharpened tip of the needle  45  into a fluid container and drawing the plunger  30  rearwardly. The needle  45  is then inserted into a patient and the fluid is injected into the patient by displacing the plunger  30  forwardly. At the end of the injection stroke, the head  33  of the plunger rod  32  engages the fingers  54  of the needle retainer  50  and the piston  35  engages the forward end of the barrel  20 . Continued forward displacement of the plunger axially compresses the piston  35  and drives the frustoconical head of the plunger rod against the inwardly tapered surfaces of the fingers  54 , thereby wedging the fingers apart. In other words, the plunger radially displaces the fingers outwardly. At the same time, the plug  36  that seals the opening at the forward end of the plunger engages the head  62  of the needle fitting  60 , displacing the plug rearwardly into the cavity of the plunger so the plunger opening is not obstructed. Once the fingers  54  are displaced radially outwardly out of engagement with the needle fitting, the needle is released and the spring  75  propels the needle and attached needle fitting rearwardly into the cavity  38  in the plunger so that the sharpened tip of the needle is shielded against inadvertent contact.