NEEDLE RETRACTION MEDICAL DEVICE
TECHNICAL FIELD
This invention concerns a needle retraction device which may form part of or consist of
either a syringe for injection of fluid into a human or animal body or a body fluid
sampler, which is used for withdrawal of sample fluid from a human or animal body. In
either case the device is provided with a mechanism for automatic needle retraction in
order that the needle and a needle carrying hub are retracted, immediately following
use, into a hollow plunger which is inserted into a main hollow body of the device to
avoid the risk of needle-stick injury to users and other personnel. In the case of a
syringe the same plunger may also serves for expression of the injectable fluid just prior
to needle retraction.
BACKGROUND
Needle-stick accidents are particularly prevalent and carry a high risk of infection in the
field of phlebotomy (blood sampling). There is also a risk of needle-stick injuries during
the use of syringes for injection of fluids. Syringes and blood samplers with provision for
automatic needle retraction are disclosed in the applicant's earlier specification WO
92/018187. These devices, and other design variants subsequently developed,
comprise a tubular hollow body of suitable plastics material in one end of which plural
deflectable latches are integrally formed for the purpose of mounting a needle hub
against bias of a spring.
In use, a plunger having a hollow interior and a closed rear end is inserted into the
hollow body and pushed inwards until its front end forces apart the deflectable latches
to release the spring, which drives the hub and an attached needle assembly rearwards
into the interior of the plunger. This is now a well-known manner of automatically
retracting and encapsulating a needle. All that is required is the insertion and full
depression of the plunger. However, in some circumstances, the force required to be
applied to the plunger in order to deflect the latches outwards and bring about needle
retraction is considered unacceptably high. For example, single-handed operation of
the device is preferable and not all relevant medical staff have sufficiently strong hands
to manipulate with ease. It is, in any event, desirable to reduce the force required to
trigger needle retraction in such devices in order to achieve smoother operation.
The preferred material for the hollow body of such devices is polypropylene owing to its
good strength and suitability for moulding, particularly resistance to shrinkage during
moulding. For this reason, and other reasons related to detailed standards set for
production and operation criteria for such medical devices, it is not possible to change
the material. It is also important that the latches do not lose required strength/stiffness
for the initial retention of the needle hub against spring bias, including during application
of needle point load during use of the device.
The deflectable latches are formed integrally with the hollow body, that is to say they
are moulded in one piece. The latches extend longitudinally inside the hollow body from
body walling at or adjacent a first end of the body. In the production process for certain
known devices of the applicant a respective opening is formed radially inwards of each
of the latches.
BRIEF SUMMARY OF THE DISCLOSURE
With aforesaid object in view, of reducing the force required to trigger needle retraction,
the present invention provides a needle retraction medical device comprising a hollow
body having a first end and a second end, said first end being provided with a needle
mounting hub and with a plurality of releasable latches holding said needle mounting
hub against spring bias, the latches being formed integrally with the hollow body and
projecting longitudinally inside the hollow body from a proximal end at or adjacent the
first end of the hollow body to a free end, and a respective opening being provided in
the body radially inwards of each of the latches, and a plunger having a forward end
insertable into the body from the second end, a hollow interior and a closed rear end,
said plunger front end being operable, upon insertion of the plunger into the body, to
deflect the latches radially outwards and thereby release the needle mounting hub from
the latches so that the hub together with the needle mounted thereby retract under
spring action into the hollow interior of the plunger, characterised in that a respective
opening is also provided in the hollow body radially outwards of each of the latches so
that each latch connects to the material of the body only at each side of its proximal
end.
A further aspect of the invention is a hollow body prior to assembly with the needle hub
and spring and plunger, but in other respects still having the features just specified.
The invention is applicable to syringes, blood samplers, other body fluid samplers and
any other hollow body devices with needle retraction mechanisms.
The invention will be described further, by way of example, by reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partial perspective view of a cross-section through a hollow body of a prior
art blood sampler device;
Figure 2 is the same view of the same prior art device as in figure 1, but showing a
spring biased needle hub mounted into the hollow body as in the assembled blood
sampler device;
Figure 3 is the same view of the same prior art device as in figure 2 , but additionally
showing a front end of a plunger inserted into the body of the device just prior to
actuation of the needle hub retraction mechanism;
Figure 4 shows the same prior art device as pressure is exerted on the plunger to
deflect the latches;
Figure 5 shows the same prior art device after the spring has been released and the
needle hub has been retracted into the interior of the plunger;
Figures 6 to 10 are views corresponding to figures 1 to 5 , but showing the hollow body
and needle retraction mechanism in accordance with a first practical embodiment in
accordance with the present invention;
Figure 11 is a longitudinal cross-section through the same embodiment of the
assembled blood sampler device of the invention as shown in figures 6 to 10, along line
A-A of figures 15 and prior to actuation of the retraction mechanism;
Figures 12 to 14 are views comparable to figure 11 showing the sequence of operation
of the device as retraction of the needle hub takes place;
Figure 15 is an end view of the assembled blood sampler device shown in figure 11
(and in figures 7 to 10);
Figure 16 is a side view, to an enlarged scale compared to figures 11 to 15, of the
assembled blood sampler device in the needle hub retracted condition shown in figure
14;
Figures 17a to 17c are schematic side and perspective views of a latch in a prior art
needle retraction device;
Figures 18a to 18c are corresponding schematic side and perspective views of a latch
in a needle retraction device in accordance with the present invention;
Figures 19 and 20 are view corresponding to figures 6 and 10, namely partial
perspective views of a cross-section of a hollow body and needle retraction mechanism,
but in this case in accordance with a modified, second practical embodiment of the
invention where the connecting strap is of a cylindrical shape; and
Figure 2 1 is a view corresponding to figure 18c, namely an enlarged detail perspective
view of a latch in a needle retraction device in accordance with the second
embodiment.
DETAILED DESCRIPTION
First of all the conventional parts of a known automatic needle retraction blood sampling
needle holder will be described with reference to figures 1 to 16. The same reference
numerals are used throughout the drawings to designate corresponding parts.
The needle holder comprises a tubular hollow body 10 having a first end 11, in which a
needle mounting hub 13 is mounted against bias of a spring 14 by means of plural
deflectable latches 15, and a second open end 16. When the device is to be used a
known needle assembly (not shown), as used in phlebotomy, is secured into the hub 13
by screw threaded engagement in a threaded central bore 17 of the hub. Typically, a
first needle of this assembly extends outwards and is used to enter the vein of a patient
while a second needle, or an inner end of the same needle, extends axially into the
hollow body 10 and an evacuated blood collection vial is placed into the hollow body, a
septum of same being pierced by the inwardly extending needle tip so that blood will be
collected into the vial. When sampling is complete and the vial is removed, a plunger
20 having a hollow interior and a closed rear end 22 is inserted into the hollow body 10
and pushed inwards, as shown in the operation sequence of figures 11 to 14 and also
the sequence of figures 3 to 5 and figures 8 to 10, until its front end 24 forces apart the
deflectable latches 15 to release the spring 14. This drives the hub 13 and attached
needle assembly (not shown) rearwards into the interior of the plunger 20 to the
position shown in figures 5 , 10 and 14.
As shown four latches 15 are arranged at 90° spacing around the interior of the first end
of the hollow body 10. These latches 15 are moulded in one piece with the body 10
and extend longitudinally in the interior of the body from a proximal end attached to the
body 10, specifically to an end wall 19 of the body, to a free end which is formed with a
retaining enlargement 39. The enlargement 39 is of conventional wedge shaped form,
providing a shoulder 38 behind which a flange 33 of the needle hub 13 engages as well
as a sloping actuating surface 37 which is engaged by the front end 24 of the plunger
20 two bring about retraction of the needle hub in the operation outlined above.
As shown, a cylindrical wall 36 extends inwards from the inner periphery of the end wall
19 of the hollow body 10 as location means for the needle hub 13 and the spring 14.
In producing the hollow body 10 by moulding in one piece from suitable plastics material
with integral end wall 19, inner wall 36 and latches 15, openings 35 are formed radially
inwards of each latch 15, as shown in figures 1 to 5 . These openings 35, which are
narrow slots, extending in annular direction immediately to inner side of each latch 15,
are produced by a tool which fashions the latch in the moulding process. In this
particular embodiment these openings 35 are shown as extending annularly beyond the
sides of the proximal end or root of each latch 15. In other embodiments such openings
may not extend beyond the side edges of the respective latches.
Initially the latches 15 extend from the end wall 19 substantially parallel to the outer
walling and axis of the hollow body 10. An annular flange 33 of the needle hub 13
seats on the upper edge of the wall 36 with the helical spring 14 located around the
outside of the wall 36 and held under compression below the flange 33, as best shown
in figures 2 and 7 .
In use, the latches 15 are deflected outwards upon engagement of their actuating
surfaces 37 by the front end 24 of the plunger 20 and further application of force as the
plunger is pushed further inwards into the hollow body 10.
In the prior art device illustrated in figures 1 to 5 of the drawings, the deflection of the
latches 15, as shown in figures 4 and 5 , is by bending of same in an outwardly curving
manner from their initial upstanding position.
In accordance with the invention, in the embodiment illustrated in figures 6 to 10 and
also in figures 11 to 15, an additional opening 30 in the end wall 19 of the hollow body
10 is provided radially outwardly of each latch 15. These openings 30 are also in the
form of narrow slots extending in an annular direction. Also, in the illustrated
embodiment, these openings 30 extend annularly beyond the sides of the proximal end
or root of each latch 15. In other embodiments such openings may not extend beyond
the side edges of the respective latches. Thus, in embodiments in accordance with the
invention, there are openings 35, 30, both inside and outside the proximal end of each
latch 15 so each latch is connected only at the respective sides (or side edges) of its
proximal end. In this illustrated embodiment, because both the openings 30, 35 extend
annually beyond the sides of the respective latches 15, the connection to the main part
of the end wall 19 is provided by a short rectangular cross-sectional strap 3 1 .
Thus, in the embodiment of the invention, as illustrated in figures 6 to 15, the deflection
of the latches 15 is by a twisting of these connecting straps 3 1. The material of the
upstanding latches 15 is not bent but remains substantially straight, merely inclined
outwards relative to the axis of the body 10, as best shown in figures 9 and 10. Such
deflection requires less forced to accomplish and it has been found that the force
required for such deflection may be up to 75% less than force required for deflection by
bending of the latch as in the prior art structure.
Figures 17 and 18 illustrate in enlarged detail the contrast between the manner of
deflection in a prior art device (figures 17) and a device in accordance with the invention
as exemplified by the embodiment of figures 6 to 16 figure 18. In the prior art device
the proximal end of the latch is shown connected on all sides to the material of the
hollow body, namely projecting upwards from a continuous web of plastics material, and
the latch 15 when engaged by the actuating end 24 of the plunger 20 is deflected by
bending of the material forming the latch 15. In the device in accordance with the
invention, material is removed both in front and behind the latch (openings 35 and 30)
so that it is connected to the web of plastics material only at the side edges by way of
the connecting strap 3 1. This results in the latch deflecting as though it is pivoting along
a hinge line at its base, along the rear edge 32, namely the edge opposite the actuating
surface 37 where the force of the plunger 20 is applied, as indicated in figure 18b. The
material of the upstanding latch 15 is not deformed, as by bending in the prior art, as
the deformation only takes effect at the connections at the respective sides of the base
of the latch. As shown, these connections may advantageously be provided as short
rectangular connector portions or straps 3 1 by extending the respective openings 30,
35 beyond the side edges of the base of the latch 15, as already noted in the above
description of the illustrated embodiment of blood sampler device. These connecting
straps 3 1 twist to bring about the deflection of the latch 15.
In a modified embodiment, illustrated in figures 19 to 2 1, each connecting strap 4 1 has
a cylindrical shape, i.e. a rounded cross-section, as opposed to the square or rectangle
I cross section featured in the embodiment of Figures 6-10. The strap 4 1 is connecting
the latch 15 to the main part of the end wall 19 in the same manner as strap 3 1 with
openings 35, 30 both inside and outside the proximal end of each latch 15. The
deflection of the latches 15 is by a twisting of these connecting straps 4 1. The material
of the upstanding latches 15 is not bent, but remains substantially straight, merely
inclined outwards relative to the axis of the body, as best shown in figure 20. The
modified cylindrical shape of the strap 4 1 further reduces the force required to release
the latches 15, typically to less than 2/3 of force required with the rectangular shape of
connective strap 3 1.
In other embodiments, the details may vary. Moreover, as noted, the invention is
applicable to any other hollow body needle retraction mechanism.

CLAIMS
1. A needle retraction medical device comprising a hollow body having a first end
and a second end, said first end being provided with a needle mounting hub and with a
plurality of releasable latches holding said needle mounting hub against spring bias, the
latches being formed integrally with the hollow body and projecting longitudinally inside
the hollow body from a proximal end at or adjacent the first end of the hollow body to a
free end, and a respective opening being provided in the body radially inwards of each
of the latches, and a plunger having a forward end insertable into the body from the
second end, a hollow interior and a closed rear end, said plunger front end being
operable, upon insertion of the plunger into the body, to deflect the latches radially
outwards and thereby release the needle mounting hub from the latches so that the hub
together with the needle mounted thereby retract under spring action into the hollow
interior of the plunger, wherein a respective opening is also provided in the hollow body
radially outwards of at least some of the latches so that each such latch connects to
the material of the body only at each side of its proximal end.
2 . A needle retraction medical device comprising a hollow body having a first end
and a second end, said first end being provided with a plurality of releasable latches for
holding a needle mounting hub against spring bias, the latches being formed integrally
with the hollow body and projecting longitudinally inside the hollow body from a proximal
end at or adjacent the first end of the hollow body to a free end, and a respective
opening being provided in the first end of the body radially inwards of each of the
latches, wherein a respective opening is also provided in the hollow body radially
outwards of at least some of the latches so that each such latch connects to the
material of the body only at each side of its proximal end.
3 . A device according to claim 1 or 2 wherein the latches each have radially inwardly
directed retaining formations at their free end.
4 . A device according to claim 3 wherein the retaining formations of the latches
provide latching shoulders for engagement of the needle hub.
5 . A device according to any preceding claim wherein the latches each have sloping
actuating surfaces at their free end.
6 . A device according to any preceding claim wherein at least the openings which lie
radially outwards of the latches extend beyond the proximal ends of the latches in each
annular direction.
7 . A device according to any preceding claim wherein the openings which lie radially
outwards of the latches and the openings which lie radially inwards of those latches
extend beyond the proximal ends of the latches in each annular direction, thereby
providing connecting straps which mount each such latch to the hollow body and which
are capable of twisting to effect deflection of the latch.
8 . A device according to claim 7 wherein the connecting straps are of substantially
rectangular cross-section.
9 . A device according to claim 7 wherein the connecting straps are of substantially
circular cross-section.
10. A device according to any preceding claim wherein the latches are provided at
equally-angular spacing around the interior of the hollow body.
11. A device according to any preceding claim wherein four latches are provided in the
hollow body.