Disposable safety syringe having a retractable needle cannula and cannula lock

A disposable safety syringe comprising a cylinder which is prefilled with fluid medication, a double ended hypodermic needle cannula, and a cannula lock by which the needle cannula is supported in an axially extended position so that an injection of the fluid medication may be administered. The cannula lock includes a clamp having a pair of oppositely disposed jaws between which the cannula is releasably retained. The fluid medication is carried within the syringe cylinder between piston and plug members, each of which members having respective suction heads which are arranged in spaced, face-to-face alignment with one another. The piston member is advanceable axially and distally through the syringe cylinder whereby to expulse the medication from the cylinder and move the suction head of the piston member into air-tight sealing engagement with the suction head of the plug member at the distal end of the cylinder. The needle cannula penetrates the sealed piston and plug members, such that a retraction of the piston member axially and proximally through the cylinder causes a corresponding withdrawal and relocation of the cannula from the jaws of the cannula lock to the interior of the cylinder, where said cannula is completely surrounded and shielded to prevent a reuse of the cannula and an accidental needle stick.

BACKGROUND OF THE INVENTION 
1. FIELD OF THE INVENTION 
This invention relates to a disposable safety syringe having a cannula lock 
for releasably retaining a needle cannula in an axially extended position 
at which an injection may be administered, and, more particularly, to 
engageable piston and plug members which are movable reciprocally through 
the syringe cylinder to expulse a fluid medication therefrom and to 
retract the cannula from the cannula lock for relocation to the interior 
of said cylinder. 
2. PRIOR ART 
In U.S. patent application Ser. No. 211,366 filed June 24, 1988, which 
application has been or will be assigned to the assignee of the present 
application, a combination retractable hypodermic needle cannula and 
cannula lock is disclosed for a reusable safety syringe. The 
aforementioned combination cannula and lock is interfaced with a prefilled 
medication carpule at the interior of the reusable syringe cylinder. By 
virtue of the foregoing, an efficient locking means was disclosed by which 
a double ended needle cannula could be either reliably retained in an 
axially extended position for administering an injection or released from 
the axially extended position to be retracted within and surrounded by an 
empty medication carpule. 
The invention disclosed in the present patent application is characterized 
by the same advantages as the invention disclosed in application Ser. No. 
211,366. However, this application relates to a disposable safety syringe 
having a needle cannula which is retractable from an axially extended 
position for administering an injection to the interior of the syringe 
cylinder, rather than the interior of a medication carpule, so that the 
syringe may be discarded with the cannula shielded by and irretrievably 
located within the cylinder thereof. What is more, the present invention 
includes the additional advantage of a piston-plug assembly which is 
movable reciprocally through the syringe cylinder for expulsing the fluid 
contents thereof via said cannula and for engaging and reliably retaining 
one end of the cannula so that said cannula may be easily and efficiently 
retracted into the cylinder. 
SUMMARY OF THE INVENTION 
In general terms, a disposable safety syringe is disclosed including a 
hollow cylinder which is prefilled with fluid medication, a retractable 
double ended hypodermic needle cannula, the proximal end of which 
communicates with the interior of the cylinder, and a cannula lock which 
is disposed at the distal end of the cylinder. The cannula lock is 
provided to releasably retain the cannula in an axially extended position 
relative to the cylinder so that an injection may be administered at a 
targeted tissue area of a patient. The cannula lock includes a clamp which 
has a pair of spaced jaws that are rotatable towards one another and into 
engagement with the cannula for locking the cannula therebetween. The 
locking jaws are surrounded by an outer sleeve which is integrally 
connected to the distal end of the cylinder and is sized to bias the jaws 
in locking engagement with the cannula. A piston is located at the 
proximal end of the cylinder and a plug is located adjacent the distal end 
of the cylinder in spaced, coaxial alignment with the cannula. The fluid 
medication is carried by the cylinder between the piston and the plug. 
Each of the piston and plug includes a concave suction head, such that the 
respective suction heads of the piston and plug are arranged in opposing, 
face-to-face alignment with one another. 
In operation, the piston is moved axially and distally through the syringe 
cylinder, whereby to cause a corresponding distal movement of the plug to 
the distal end of said cylinder where the proximal end of the cannula 
penetrates the plug. The continued distal advancement of the piston 
towards the plug causes a compression of the fluid medication located 
between said piston and plug, such that the fluid is expulsed from the 
cylinder via the cannula. The piston is relocated distally through the 
cylinder until the respective suction heads of the piston and plug are 
moved into engagement with one another at the distal end of the cylinder 
to form an air-tight seal therebetween, whereby the proximal end of the 
cannula now penetrates both the plug and the piston. The application of a 
suitable axial and distally directed force to the sealed piston and plug 
is transferred to the cannula retaining clamp at the distal end of the 
cylinder, so as to displace said clamp axially and distally relative to 
the outer sleeve by which the clamp is surrounded. Accordingly, the jaws 
of the clamp automatically rotate away from one another and out of 
engagement with the cannula so as to leave said cannula suspended only 
from the proximal end thereof at the sealed piston and plug. 
By applying an axial and proximal pulling force to the sealed piston and 
plug, the needle cannula is correspondingly withdrawn from the space 
between the jaws of the clamp to be retracted within the interior of the 
syringe cylinder. Accordingly, the cannula is completely surrounded and 
shielded by the cylinder. The syringe may now be discarded with the 
cannula irretrievably located in the cylinder thereof so as to prevent a 
reuse of said cannula and an accidental and potentially life threatening 
needle stick.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The disposable safety syringe having a retractable needle cannula and 
forming the present invention is best described by referring to the 
drawings, where FIG. 1 shows the safety syringe 1 in the packaged 
condition suitable for transport and storage prior to use. More 
particularly, syringe 1 includes a hollow cylinder 2 having an open 
proximal end and a substantially closed distal end. A flange 3 is formed 
around the proximal end of cylinder 2 to improve the handling of syringe 1 
during use. The cylinder 2 is preferably prefilled with a suitable supply 
of fluid mediation 4 which is to be expulsed therefrom to a patient by way 
of a hypodermic needle cannula 6. However, as an alternate embodiment of 
the invention, an optional needle cannula 8 may communicate with the 
interior of syringe cylinder 2 via a valve 10. In this manner, it would be 
possible to fill the cylinder 2 at the time of use with medication from an 
available external source of supply rather than prefill said cylinder 
prior to use. 
Located within the open proximal end of syringe cylinder 2 is a piston 12. 
Piston 12 is preferably formed from a relatively dense, resilient, and 
non-corrosive material, such as rubber, or the like. A screw threaded hole 
14 is formed at one end of piston 12. Screw threaded hole 14 is sized to 
receive and be mated to a detachable screw threaded piston stem 16, 
whereby to complete a piston assembly comprising piston 12 and stem 16 
which, as will soon be described, is adapted to slide axially and 
reciprocally through syringe cylinder 2 for expulsing the medication 4 
therefrom and for retracting the needle cannula thereinto. A 
concave-shaped suction head 18 extends from the opposite end of piston 12 
so as to be movable with said piston through cylinder 2. 
A plug member 20 is located within the syringe cylinder 2 and disposed 
distally therein relative to piston 12. Plug member 20 is preferably made 
from the same relatively dense material (i.e. rubber, or the like) as is 
piston 12. Secured at one end of plug 20 is a disk 22. Disk 22 is formed 
from a hard material, such as metal, that is resistant to penetration by 
the cannula 6. The disk 22 has a centrally disposed opening 24 formed 
therein which, in the packaged configuration of FIG. 1, is arranged in 
spaced, coaxial alignment with respect to the longitudinal axis of cannula 
6. Extending from the opposite end of plug 20 is a concave-shaped suction 
head 26. The suction heads 18 and 26 of piston 12 and plug 20 are 
initially arranged in spaced, face-to-face alignment with one another with 
the fluid medication of cylinder 2 carried therebetween. Piston 12 and 
plug 20 are sized to form fluid-tight seals against the walls of cylinder 
2 and thereby prevent the inadvertent escape or contamination of such 
fluid from the cylinder. As will soon be disclosed in greater detail 
hereinafter when referring to FIG. 3, the concave suction heads 18 and 26 
of piston 12 and plug 20 are adapted to engage one another and form an 
efficient seal therebetween. 
The cannula lock 30 of disposable syringe 1 will now be described. Since 
the cannula lock 30 is substantially similar to that previously disclosed 
in patent application Ser. No. 211,366 filed June 24, 1988, only a brief 
description of said cannula lock will be provided. The cannula lock 30 
includes a cylindrical outer sleeve 32 which is integrally connected to 
and extended outwardly from the distal end of syringe cylinder 2. The 
outer sleeve 32 has a relatively narrow, tapered bore 34 extending 
longitudinally through the distal end thereof. The tapered bore 34 is 
particularly sized to receive and releasably retain a clamp or chuck 36, 
which is adapted to either lock the needle cannula 6 in an axially 
extended position or release the needle cannula to be retracted within and 
completely surrounded by the syringe cylinder 2. 
More particularly, the aforementioned clamp or chuck 36 includes a hollow, 
generally cylindrical base 38 and a pair of parallel aligned jaws 40. The 
jaws 40 are normally spaced from one another and adapted to rotate 
relative to the base 38 so as to releasably receive and reliably retain 
the needle cannula 6 in the space therebetween. The exterior surfaces of 
jaws 40 have a tapered configuration to match the taper of the distal bore 
34 of sleeve 32 so that clamp 36 is adapted to slide axially through the 
distal bore 34. An annular lip 42 is formed around the bottom of base 38. 
In the packaged configuration of FIG. 1, lip 42 is spaced proximally from 
the distal end of cylinder 2 so as to extend slightly therewithin. 
Cannula 6 is a conventional double ended, hollow needle cannula of the type 
commonly associated with many hypodermic syringes. However, cannula 6 
includes a high friction, raised or textured medial surface 44 and another 
high friction, textured surface 45 located adjacent the proximal end 
thereof. A small aperture 46 is formed in the proximal end of cannula 6 
through which fluid from the syringe cylinder 2 is expulsed. A removable 
needle sheath 47 is also provided to surround cannula 6 during storage and 
handling to preserve the sterility of the cannula and prevent an 
accidental needle stick prior to use. 
In the assembled relationship of FIG. 1, the needle cannula 6 is positioned 
within the space between the opposing jaws 40 of the clamp 36. The 
combination needle cannula 6 and clamp 36 is then located within the 
distal bore 34 of sleeve 32 so as to secure cannula 6 in an axially 
extending position for administering an injection. That is, locating the 
tapered jaws 40 of clamp 36 within the similarly tapered bore 34 of sleeve 
32 causes the jaws to rotate towards one another and into frictional 
engagement with the cannula 6 at the medially disposed textured surface 44 
thereof so as to oppose any axial displacement of said cannula relative to 
clamp 36. 
FIG. 2 of the drawings shows the safety syringe 1 in the pre-injection 
state with needle sheath 47 removed to expose cannula 6 for administering 
an injection. That is to say, the health care worker grasps syringe 
cylinder 2 by locating his fingers below flange 3 and his thumb against 
piston stem 16. An axial and distally directed force is then applied (in 
the direction of reference arrow 58) to piston stem 16 to drive piston 12 
in a distal direction through cylinder 2. The axial and distally directed 
force is transferred from piston stem 16 to plug 20 via piston 12 and the 
continuous column of fluid within cylinder 2. Accordingly, a corresponding 
axial force is applied to drive plug 20 through cylinder 2 and towards the 
needle cannula 6, until the proximal end of cannula 6 penetrates the plug 
20 at the hole 24 in disk 22. The proximal relocation of plug 20 through 
syringe cylinder 2 continues until said plug 20 is moved onto contact with 
the annular lip 42 of clamp 36 below the distal end of cylinder 2. 
FIG. 3 of the drawings shows the safety syringe 1 in the injection state. 
More particularly, the distal end of the needle cannula 6 is suitably 
located at a targeted tissue area of the patient. The health care worker 
then resumes the application of the axial and distally directed force to 
piston stem 16 to continue to drive piston 12 through cylinder 2 and 
towards plug 20. Inasmuch as the distal relocation of plug 20 is blocked 
by lip 42, the fluid medication within cylinder 2 is compressed between 
the distally advancing piston 12 and the stationary plug 20. Accordingly, 
the fluid medication within cylinder 2 is expulsed form the cylinder and 
delivered to the patient via the aperture 46 and the hollow needle cannula 
6. What is more, the respective concave suction heads 18 and 26 of piston 
12 and plug 20 are flattened against one another so as to form a planar, 
air-tight seal and thereby attach the piston 12 and plug member 20 
together at the distal end of cylinder 2. At the same time, the proximal 
end of needle cannula 6 penetrates the piston 12. Therefore, the cannula 6 
is firmly anchored to both plug 20 and piston 12 at the distal end of 
cylinder 2. 
FIG. 4 shows the safety syringe 1 in the post-injection state after the 
fluid medication has been expulsed from the syringe cylinder 2 and the 
distal end of cannula 6 has been removed from the tissue of the patient. 
With the piston 12 and plug 20 sealed together and located at the distal 
end of cylinder 2 and in contact with the annular lip 42 of clamp 36, a 
suitable axial and distally directed force is applied to clamp 36 at the 
inwardly projecting lip 42 thereof by way of the piston stem 16 and the 
union of piston 12 and plug 20. The axial force applied from piston stem 
16 to clamp 36 overcomes the former engagement of clamp 36 by the tapered 
bore 34 of outer sleeve 32. Hence, the clamp 36 is displaced axially 
relative to the outer sleeve 32 and, more particularly, distally relative 
to the distal bore 34 of sleeve 32 whereby to permit the opposing jaws 40 
of clamp 36 to rotate away from one another and out of engagement with the 
needle cannula 6. Therefore, cannula 6 is now supported only at the 
proximal end thereof by the sealed combination of piston 12 and plug 20 so 
as to be free for withdrawal from the space between the jaws 40. 
FIG. 5 of the drawings shows the safety syringe 1 in the retracted state 
with needle cannula 6 located within and completely surrounded by the 
empty syringe cylinder 2. That is, the health care worker applies an axial 
and proximal pulling force (in the direction of reference arrow 50) to the 
piston stem 16 to relocate the needle cannula 6 from the axially extended 
position, at which the injection was administered, to a relatively 
proximal position within cylinder 2. The pulling force applied to piston 
stem 16 is transferred to the cannula 6 by way of the sealed piston 12 and 
plug 20. Accordingly, the cannula 6 is withdrawn from the space between 
the jaws 40 of clamp 36 to be retracted within the cylinder 2. By virtue 
of the foregoing, the cannula 6 is safely shielded by the cylinder, 
whereby to prevent a reuse of the cannula and avoid an accidental and 
possibly life threatening needle stick. 
Thereafter, the piston stem 16 may be detached from the piston 12 and 
discarded. The syringe 1 may also be discarded with the cannula 6 
irretrievably located and shielded at the interior of the cylinder 2. Also 
by virtue of the present invention, the attachment of cannula 6 to the 
relatively dense material of piston 12 and plug 20 will cause said cannula 
to be automatically canted when said cannula is retracted into the 
cylinder. In this manner, it would be possible to prevent the return of 
the canted cannula to the axially extended position (of FIG. 3) in the 
event that the piston stem and the cannula connected thereto were to be 
inadvertently moved axially and distally through the cylinder. 
As a further advantage of the present invention, it may be noted that in 
the packaged configuration of FIG. 1, the axially spaced piston 12 and 
plug 20 completely isolate the fluid medication 4 from the needle cannula 
6. Accordingly, the possibility of a corrosive reaction between the 
cannula and the fluid will be avoided. Moreover, by isolating the fluid 4 
in the manner disclosed, there will be less chance of contamination. Thus, 
the syringe 1 of the present invention provides many of the same 
advantages as would be provided by a syringe in which a medication filled 
carpule is received, but the added cost and storage inconveniences that 
are associated with such carpules are eliminated. 
It will be apparent that while a preferred embodiment of the invention has 
been shown and described, various modifications and changes may be made 
without departing from the true spirit and scope of the invention. For 
example, the disclosed safety syringe has particular application as a 
dental syringe. However, it is to be understood and this use is for 
purposes of example only, and the advantages of this invention and the 
teachings of this application are applicable to other types of syringes, 
as well.