Syringe with integral safety cover

An apparatus and method of covering a needle on a syringe having a barrel and a hypodermic needle connected to the barrel includes the step of extending a telescoping cover engaged with the barrel until the telescoping cover covers the hypodermic needle.

BACKGROUND OF THE INVENTION 
This invention relates to syringes having hypodermic needles and methods 
and apparatus for covering such needles. 
Healthcare workers have become increasingly more aware of the risk of 
occupational exposure to contaminated blood and other potentially 
infectious bodily fluids. Needlestick injuries are one of the most common 
injuries in health care workers. Such injuries appear to be caused by 
unsafe devices rather than carelessness on the part of the worker. These 
injuries present the greatest risk of occupational exposure to Human 
Immunodeficency Virus (HIV) and Hepatitis B. 
The prior art includes devices intended to protect against needlestick 
injuries. Once such device includes a removable cover which is placed over 
a needle by inserting the needle into the cover while the user holds the 
cover between the forefinger and the thumb. This, however, presents a risk 
to the user because if the user misjudges the insertion of the needle into 
an opening in the cover, the needle may pass the cover and prick the thumb 
or forefinger. Or, if the user attempts to insert the needle into the 
cover rapidly, the needle may pierce through a wall of the cover again 
pricking the thumb or forefinger. These risks result from the necessity to 
move the needle and cover toward each other during installation of the 
cover. 
Another device known as the RMS retractable syringe, available from RMS 
Medical Systems Inc. of Vancouver, B.C. Canada, incorporates a metal 
retaining ring in a tip of a plunger of the syringe. The metal retaining 
ring locks onto a proximal end portion of a hypodermic needle connected to 
the syringe, when the plunger is fully depressed into a barrel of the 
syringe. If the plunger is then drawn outwardly of the barrel, the needle 
is pulled into the barrel and is automatically canted off-centre so that 
it cannot be easily forced out of the barrel. Much reliance is placed on 
the functioning of the metal retaining ring and the act of drawing the 
plunger from the barrel requires careful attention to how far the plunger 
is drawn out of the barrel, for if the plunger is drawn too far out, the 
needle becomes exposed. 
The above devices have inherent deficiencies in that with the simple cover 
device needle prick injuries are reduced only after the cover is in place 
and installation of the cover presents a great risk in itself. With the 
RMS device careful manufacturing techniques must be employed to 
manufacture and assemble the necessary metal and plastic components, with 
attendant costs. Furthermore, the requirement for careful attention while 
drawing out the plunger can be a burden to the health care worker using 
the device. 
BRIEF SUMMARY OF THE INVENTION 
In accordance with one aspect of the invention, there is provided an 
apparatus including a barrel having a first end portion for receiving a 
plunger and a second end portion operable to hold a hypodermic needle and 
a telescoping cover engaged with the barrel, operable to extend relative 
to the barrel to cover the hypodermic needle. 
Preferably, the apparatus includes a first releasable lock for releasably 
locking the telescoping cover to the barrel when the telescoping cover is 
in a non-extended position. 
The first releasable lock may include a receptacle in the telescoping cover 
and a tab on the barrel, the tab being operable to be received in the 
receptacle. 
The telescoping cover may have a wall portion defining the receptacle, and 
the tab may have a camming portion operable to bear against the wall 
portion when the telescoping cover is rotated relative to the barrel to 
disengage the tab with the receptacle thereby unlocking the telescoping 
cover relative to the barrel and permitting extension of the telescoping 
cover relative to the barrel. 
Preferably, the apparatus includes a second lock for locking the 
telescoping cover in an extended position fully covering the hypodermic 
needle. 
Preferably, the second lock is operable to permanently lock the telescoping 
cover in an extended position fully covering the hypodermic needle. 
The second lock may include an interfering surface on the barrel and a pawl 
on the telescoping cover, the pawl being operable to move past the 
inclined surface when the telescoping cover is extended relative to the 
barrel and the interfering surface being operable to interfere with 
movement of the pawl when the telescoping cover is forced in a direction 
tending to retract the telescoping cover relative to the barrel. 
The pawl may have a flexible portion operable to flex radially relative to 
the telescoping cover. 
Preferably, the cover includes a locking member extending axially relative 
thereto, the pawl being on the locking member. 
The apparatus may include an annular portion extending circumferentially 
around the barrel, the interfering surface being on the annular portion 
and the cover may include a plurality of pawls operable to move past the 
annular portion when the telescoping cover is sufficiently extended 
relative to the barrel to cover the needle, the interfering surface being 
operable to interfere with movement of the pawls when the telescoping 
cover is forced in a direction tending to retract the telescoping cover 
relative to the barrel after the telescoping cover has been sufficiently 
extended relative to the barrel to cover the needle. 
Preferably, the apparatus includes a support for supporting the telescoping 
cover in an extended position in which the needle is covered. 
Preferably, the pawls have respective inclined surfaces and preferably, the 
support includes an annular ring extending about the barrel, the annular 
ring having a support surface complementary to the inclined surfaces for 
mating with the inclined surfaces to support the telescoping cover. 
Preferably, the apparatus includes a first releasable lock for releasably 
locking the telescoping cover to the barrel when the telescoping cover is 
in a non-extended position and a second lock for locking the telescoping 
cover in an extended position when the telescoping cover is extended to 
fully cover the hypodermic needle. 
The first releasable lock may include a receptacle on the telescoping cover 
and a tab on the barrel, the tab being operable to be received in the 
receptacle when the telescoping cover is in the non-extended position. 
Preferably, the second lock includes an annular portion on the barrel and a 
pawl on the telescoping cover, the pawl being operable to ride over the 
annular portion when the telescoping cover is extended relative to the 
barrel and the annular portion being operable to interfere with movement 
of the pawl when the telescoping cover is forced in a direction tending to 
retract the telescoping cover relative to the barrel. 
Preferably, the pawl has a flexible portion operable to flex radially 
relative to the telescoping cover. 
Preferably, the cover includes a locking member extending axially relative 
thereto, the pawl being on the locking member. 
Preferably, the locking member has a hook spaced apart from the pawl to 
define the receptacle between the hook and the pawl. 
Preferably, the tab has a wedge shape and is dimensioned to be operable to 
be releasably jammed in the receptacle to secure the telescoping cover to 
the barrel such that upon rotation of the telescoping cover relative to 
the barrel, the tab is released from the receptacle, thereby unlocking the 
telescoping cover relative to the barrel and permitting extension of the 
telescoping cover relative to the barrel. 
Preferably, the telescoping cover has an opening having a shape 
complementary to the barrel such that the barrel is operable to generally 
guide the telescoping cover in longitudinal movement relative to the 
barrel. 
Preferably, the telescoping cover has a wall defining an opening through 
which the hypodermic needle extends, when the telescoping cover is in a 
non-extended position. 
Preferably, the cover is operable to be extended relative to the barrel 
until at least a portion of the wall is positioned beyond a distal end 
portion of the hypodermic needle. 
Preferably, the apparatus includes a first releasable lock for releasably 
locking the telescoping cover to the barrel when the telescoping cover is 
in a non-extended position. The first releasable lock may include a hook 
on the barrel, the hook defining a receptacle. In addition, the 
telescoping cover may have a hook which cooperates with the receptacle to 
lock the telescoping cover to the barrel when the telescoping cover is in 
a non-extended position. 
Preferably, the apparatus includes a second lock for locking the 
telescoping cover in an extended position fully covering the hypodermic 
needle, the second lock including a hook ring on the barrel, the hook ring 
including a radially planar surface and a concentric annular wall defining 
a receptacle. 
Preferably, the second lock further includes at least one resiliently 
deformable hook on the cover, the hook having a barb having an inclined 
surface and a radially planar surface, the barb being operable to 
resiliently deform as it is forced into the receptacle formed between the 
radially planar surface of the hook ring and the annular wall of the hook 
ring until the radially planar surfaces abut each other. In this position, 
the radially planar surface on the hook ring interferes with the radially 
planar surface on the hook and prevents counter movement of the 
telescoping cover in a direction tending to retract the telescoping cover 
relative to the barrel. 
Preferably, the apparatus includes a support for supporting the telescoping 
cover in an extended position in which the needle is covered. To 
facilitate this the telescoping cover may have an inside surface 
complementary to the shape of the concentric annular wall such that the 
concentric annular wall acts as a support surface for supporting the 
telescoping cover in an extended position in which the needle is covered. 
Preferably, the barrel has an outer surface and preferably, the telescoping 
cover has a plurality of hooks having respective axially extending walls 
positioned on the cover such that the axially extending walls ride on the 
outer surface of the barrel while the inside surface of the telescoping 
cover rides on the annular concentric wall of the hook ring as the 
telescoping cover is telescopically extended. 
In accordance with another aspect of the invention, there is provided a 
method of covering a needle on a syringe having a barrel and a hypodermic 
needle connected to the barrel. The method includes the step of extending 
a telescoping cover engaged with the barrel until the telescoping cover 
covers the hypodermic needle. 
Preferably, the method also includes the step of locking the telescoping 
cover in an extended position when the telescoping cover is extended to 
fully cover the hypodermic needle and preferably, the telescoping cover is 
permanently locked in an extended position when the telescoping cover is 
extended to fully cover the hypodermic needle. 
The telescoping cover may be releasably locked to the barrel when the 
telescoping cover is in a non-extended position and preferably, the 
telescoping cover is released from the barrel to permit extension of the 
telescoping cover relative to the barrel, by rotating the telescoping 
cover relative to the barrel. 
Preferably, the telescoping cover portion is supported while the 
telescoping cover covers the needle. 
In accordance with another aspect of the invention, there is provided a 
syringe including a barrel having a first and second opposite end 
portions, a plunger operable to be received in the first end portion, a 
hypodermic needle connected to the second end portion and a telescoping 
cover engaged with the barrel, operable to extend relative to the barrel 
to extend beyond the second end portion to cover the hypodermic needle. 
In accordance with another aspect of the invention, there is provided a 
method of covering a hypodermic needle on a syringe. The method includes 
the steps of supporting a cover in a first position, about a barrel of the 
syringe, moving the cover longitudinally relative to the barrel until the 
cover extends about the hypodermic needle.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, an apparatus according to a first embodiment of the 
invention is shown generally at 10. The apparatus includes a syringe shown 
generally at 12 and a telescoping cover 14 formed over the syringe as 
explained below. 
Barrel 
The syringe includes an elongated cylindrical barrel 16 formed of 
transparent or clear plastic having a plurality of graduations 18 and 
first length 20. The barrel 16 has first and second end portions 22 and 24 
and an outer cylindrical surface 26 extending between the end portions. 
The first end portion 22 has wall 27 defining a circularly shaped plunger 
hole extending through the barrel 16 and having an opening 28 for 
receiving an elongated plunger shown generally at 30. The plunger 30 has a 
shaft 21 operable to be received in the plunger opening 28 and has a 
thumb-actuated pressure pad 34 which enables a user to press the plunger 
30 into the plunger opening 28 to pressurize fluid within the plunger 
hole. 
The first end portion 22 also has first and second finger grip tabs 36 and 
38 extending radially outwardly of the plunger opening 28 to enable a user 
to grasp the first end portion 22. Thus, the user is able to grasp the 
finger grip tabs 36 and 38 with the forefinger and middle finger and 
actuate the plunger 30 with the thumb. 
The first end portion 22 further has a radially extending wedge-shaped tab 
40 disposed on the outer cylindrical surface 26, in spaced apart relation 
from the first finger grip tab 36. The wedge shaped tab 40 extends 
radially from the outer surface and has a camming portion 42 having first, 
second and third camming surfaces 44, 46 and 48. 
The second end portion 24 has first and second concentric annular portions 
50 and 52 which extend about the barrel 16. Referring to FIG. 2, the first 
concentric annular portion 50 has first and second radially planar 
surfaces 54 and 56 and an inclined surface 58 extending between the first 
and second radially planar surfaces 54 and 56. This inclined surface 58 
thus extends at an obtuse angle relative to the first inclined surface 58 
and extends at an acute angle relative to the second radially planar 
surface 56. In this embodiment, the obtuse angle is approximately 120 
degrees. 
The second concentric annular portion 52 has a second inclined surface 60 
and a third radially planar surface 62. The second inclined surface 60 
extends from the second radially planar surface 56 at an acute angle of 
approximately 45 degrees and the third radially planar surface 65 extends 
in a radial plane at a most distal position on the barrel 16. The second 
inclined surface 60 and the third radially planar surface 62 thus form a 
first apex 64 projecting radially outwardly of the barrel 16. 
The barrel 16 is terminated in a truncated conical end 66 having a slightly 
tapered conduit 68. A hypodermic needle assembly 70 includes a needle 
fastener 72 and a needle 74 having a needle point 76. The needle 74 is 
connected to the needle fastener 72 and the needle fastener 72 is secured 
to the slightly tapered conduit 68 by a friction-fit, in the convention 
manner. The needle assembly 70 has an overall length 78 less than the 
length 20 of the barrel. 
It will be appreciated therefore that it may be said that the apparatus 
includes a barrel 16 having a first end portion 22 for receiving a plunger 
30 and a second end portion 24 operable to hold a hypodermic needle 74. 
Telescoping cover 
Still referring to FIG. 2, the barrel 16 and telescoping cover 14 are 
formed together using a multiphase injection moulding process. The 
telescoping cover 14 is formed as a generally elongated tube 80 defined by 
a cylindrical wall 82 of transparent plastic so that the graduations 18 on 
the barrel 16 can be seen through the telescoping cover 14. The 
cylindrical wall 82 has inside and outside surfaces 84 and 86 and first 
and second end portions 88 and 90 and has a length 92 slightly greater 
than the length 20 of the barrel 16. The inside surface 84 defines a hole 
94 in the tube 80 in which the barrel 16 is received, the hole having a 
shape generally complementary to the shape of the outer surface 26 of the 
barrel 16, which, in this embodiment is circularly cylindrical. 
Referring to FIG. 1, a plurality of locking members 96 are formed 
diametrically opposite each other and extend axially relative to the 
cylindrical wall 82 at the first end portion 88 thereof. Each locking 
member 97 includes a flexible portion 98, a pawl 100 and a hook 102. The 
flexible portion 98 connects the pawl 100 to the cylindrical wall 82 and 
has sufficient resilience to allow the pawl 100 to have a little movement 
radially outwardly and to return the pawl 100 to its original position 
after such movement. The hook 102 is disposed most distal to the 
cylindrical wall 82 and the pawl 100 and hook 102 are spaced apart axially 
by a connecting wall 104. A receptacle 106 is defined between the pawl 100 
and the hook 102. The locking member 97 thus has a hook 102 spaced apart 
from the pawl 100 to define a receptacle 106 between the hook and the 
pawl. 
Referring to FIG. 2, the pawl 100 has an inclined surface 108 and a 
radially planar surface 110. The inclined surface 108 extends at an angle 
of approximately 45 degrees relative to the axis 112 of the cylindrical 
wall 82. The radially planar surface 110 is disposed more distal to the 
cylindrical wall 82 than the inclined surface 108 and extends from the 
inclined surface 108 in a radial plane relative to the axis 112. The 
radially planar surface 110 and inclined surface 108 thus form a second 
apex 114 disposed radially inwardly of the inside surface 84. 
The hook 102 has first and second radially planar surfaces 116 and 118 
which extend in respective spaced apart radial planes. An axially parallel 
surface 120 extends between the first and second radially planar surfaces 
116 and 118 at a distance such that the axially parallel surface 120 is 
coplanar with the second apex 114. 
The connection wall 104 has an inside surface 122 extending between the 
radially planar surface 110 of the pawl 100 and the first radially planar 
surface 116 of the hook 102. The receptacle 106 is thus defined by the 
radially planar surface 110 of the pawl 100, the inside surface 122 of the 
connecting wall 104 and the first radially planar surface 116 of the hook 
102. These surfaces are dimensioned and positioned on the locking member 
97 such that the tab 40 is operable to be snugly received in the 
receptacle 106. The pawl 100, connecting wall 104 and hook 102 are 
contiguous with the cylindrical wall 82 and thus the respective surfaces 
of these components act as a wall portion defining the receptacle 106. 
The second end portion 90 of the telescoping cover includes a generally 
disk-shaped end wall 124 extending in a radial plane relative to the 
cylindrical wall 82 and terminating the cylindrical wall. The end wall 124 
has a central opening 126 therein, shown in broken outline, for receiving 
the needle assembly 70 therethrough. Preferably, the central opening 126 
is dimensioned to have a diameter slightly greater than the diameter of 
the needle fastener so that the central opening 126 is of minimal size. 
Operation 
Referring to FIG. 2, the apparatus is shown in a position ready for use. In 
this position, the telescoping cover 14 is in a non-extended or retracted 
position relative to the barrel 16 and the tab 40 is received in the 
receptacle such that the first, second and third camming surfaces 44, 46 
and 48 are tightly received against the radially planar surface 110 of the 
pawl 100, the inside surface 122 of the connecting wall 104 and the first 
radially planar surface 116 of the hook 102. In this position, the 
telescoping cover 14 is releasably locked to the barrel 16. It will 
therefore be appreciated that the receptacle 106 on the telescoping cover 
14 and the tab 40 on the barrel 16 act as a first releasable lock for 
releasably locking the telescoping cover 14 to the barrel 16 when the 
telescoping cover 14 is in a non-extended position. 
It will be appreciated that syringes are provided separately from the 
needle assembly 70 and that the needle assembly 70 is removed from a 
separate package and fastened to the barrel 16 by placing the needle 
fastener 72 over the slightly tapered conduit 68, whereby the needle 
assembly is held thereon by a friction-fit. The slightly tapered conduit 
68 extends through the central opening 126 in the end wall 124 to 
facilitate fastening of the needle assembly 70. Thus, the telescoping 
cover 14 has a wall 124 defining an opening 126 through which the 
hypodermic needle extends 74, when the telescoping cover 14 is in a 
non-extended position. 
The syringe 12 is then used in the conventional manner to inject medication 
into a patient or to draw fluid from the patient. 
After use of the syringe 12, the outer surface 86 of the telescoping cover 
14 is gripped with one hand while the finger grip tabs 36 and 38 are 
grasped by the other hand and the telescoping cover 14 is rotated relative 
to the barrel 16 in the direction of arrow 128 shown in FIG. 1. Referring 
to FIG. 2, such rotation releases the tab 40 from the receptacle 106 
allowing the telescoping cover 14 to be positioned such that the tab 40 is 
between adjacent locking members (97), whereupon the telescoping cover 14 
may be telescopically extended relative to the barrel 16. The tab 40 is 
thus releasably jammed in the receptacle 106 to secure the telescoping 
cover 14 to the barrel 16 until the telescoping cover 14 is rotated 
relative to the barrel 16 to release the tab 40 from the receptacle 106, 
thereby unlocking the telescoping cover 14 relative to the barrel 16 and 
permitting extension of the telescoping cover 14 relative to the barrel 
16. 
The outer surface 26 of the barrel 16 and the hole 94 in the tubular 
telescoping cover 14 having a shape generally complementary to the shape 
of the cylindrical surface 26 of the barrel 16 acts to guide the 
telescoping cover 14 in axial movement relative to the barrel 16 as the 
telescoping cover 14 is extended relative to the barrel 16. Guiding of the 
telescoping cover 14 is enhanced by the apex 114 of the pawl and the 
axially parallel surface 120 of the hook 102 riding on the outer surface 
26 of the barrel 16 and by the inside surface 84 of the telescoping cover 
14 riding on the apex 64 of the second annular portion 52 as the 
telescoping cover 14 is extended relative to the barrel 16. 
When the telescoping cover 14 has been extended sufficiently, the pawl 100 
will come in contact with the first annular portion 50. Further axial 
movement of the telescoping cover 14 causes the inclined surface 108 on 
the pawl 100 to be pushed radially outwardly by the first inclined surface 
58 on the first annular portion 50 as the inclined surface 108 on the pawl 
100 rides over the inclined surface 58 on the first annular portion 50. 
When the apex 114 of the pawl 100 clears the second radially planar surface 
56 of the first annular portion 50, the resilience of the flexible portion 
98 returns the pawl 100 to its original position, whereupon the inclined 
surface 108 on the pawl 100 contacts the inclined surface 60 on the second 
annular portion 52 and the radially planar surface 110 on the pawl 100 
abuts the second radially planar surface 56 of the first annular portion 
50 as shown in FIG. 3. In this position, the second radially planar 
surface 56 of the first annular portion 50 interferes with the radially 
planar surface 110 on the pawl 100 and prevents counter movement of the 
telescoping cover 14 in a direction tending to retract the telescoping 
cover 14 relative to the barrel 16. In this position, because the locking 
members (97) are located at the first end portion 88 of the telescoping 
cover 14 and because the first and second annular portions 50 and 52 are 
located at the second end portion 24 of the barrel 16, the telescoping 
cover 14 is fully extended relative to the barrel 16. When the telescoping 
cover 14 portion is fully extended in this manner, because the length 92 
of the telescoping cover 14 is greater than the length 78 of the needle 
assembly 70, the end wall 124 is positioned beyond the needle point 76 of 
the hypodermic needle 74, whereupon the needle is fully covered and the 
user is guarded against needle prick injuries. Thus, it may be said that 
the apparatus includes a telescoping cover 14 engaged with the barrel 16, 
operable to extend relative to the barrel 16 to cover the hypodermic 
needle 74. 
The user cannot retract the telescoping cover 14 relative to the barrel 16 
due to the interference between the radially planar surface 110 on the 
pawl 100 and the radially planar surface 56 on the first annular portion 
50. The second radially planar surface 56 on the first annular portion 50 
thus acts as an interfering surface operable to interfere with movement of 
the pawl 100 when the telescoping cover 14 is forced in a direction 
tending to retract the telescoping cover 14 relative to the barrel 16 
after the telescoping cover has been sufficiently extended relative to the 
barrel 16 to cover the needle 74. The pawl 100 and the first annular 
portion 50 thus act as a second lock for permanently locking the 
telescoping cover 14 in an extended position when the telescoping cover 14 
is in an extended position fully covering the needle 74. 
The telescoping cover 14 is supported in the extended position by the 
mating of the inclined surfaces 60 and 108 on the pawl 100 and the second 
annular portion 52 and by the mating of the second annular surface 56 with 
the radially planar surface 110 on the pawl 100. Axial movement is 
prevented by the inclined surfaces 60 and 108 mating with each other and 
by the interference between the second radially planar surface 56 and the 
radially planar surface 110 on the pawl 100. Radial movement is prevented 
by the pawls 100 being disposed on diametrically opposite sides of the 
telescoping cover 14. Thus, the inclined surface 60 of the second annular 
portion 52 acts as a support surface complementary to the inclined 
surfaces 108 on the pawls 100 for mating with the inclined surfaces 108 on 
the pawls 100 to support the telescoping cover 14 in an extended position 
in which the needle 74 is covered. 
Second Embodiment 
Referring to FIG. 4, an apparatus according to a second embodiment of the 
invention is shown generally at 150. The apparatus includes a telescoping 
cover 14 and barrel 16 having components similar to that as shown in the 
first embodiment, which are designated by the same numerical references 
used in the description of the apparatus according to the first 
embodiment. 
The apparatus according to the second embodiment differs from the apparatus 
according to the first embodiment in that in place of the locking members, 
the apparatus according to the second embodiment includes a plurality of 
hooks 154 disposed on diametrically opposite locations around the first 
end portion 88 of the cylindrical wall 82, a mating hook ring 156 is 
formed on the second end portion 90 of the barrel 16 and a hook 157 is 
formed on the first end portion 22 of the barrel 16. 
The hooks 154 on the telescoping cover include a radially inwardly 
extending wall 158, an axially parallel wall 160 and a barb 162. The 
radially inwardly extending wall 158 extends radially inwardly from the 
cylindrical wall 82. The axially parallel wall 160 extends parallel to the 
axis 164 a short distance and the barb 162 terminates the axially parallel 
wall 160. The barb 162 has an inclined surface 166 and a radially planar 
surface 168. The inclined surface 166 extends outwardly toward the axially 
parallel wall 160 and the radially planar surface 168 extends radially 
inward from the inclined surface 166. 
The hook ring 156 extends about the second end portion 24 of the barrel 16 
and has a radially outwardly extending annular wall 170, a concentric 
annular wall 172 concentric with the barrel 16 and a lip 174 terminating 
the circular wall. The lip 174 has an inclined surface 176 converging 
toward the second end portion 24 of the barrel 16 and terminated in a 
radially planar surface 178 extending radially outwardly of the inclined 
surface 176. 
An annular receptacle 180 is thus formed between the radially planar 
surface 178 of the hook ring 156 and the annular wall 170 of the hook 
ring. The annular wall 170 of the hook ring 156 and the radially extending 
walls 158 of the hooks 154 are dimensioned such that the barbs 162 are 
operable to be snugly received between the concentric annular wall 172 and 
the outer surface 26 of the barrel 16 and between the radially outwardly 
extending annular wall 170 and the radially planar surface 178 on the hook 
ring 156. 
The hook 157 on the first end portion 22 has a shape similar to that of the 
hook ring 156 at the second end portion 24 with the exception that the 
hook 157 on the first end portion 22 is arcuate and extends through an 
angle 181 of approximately 10 degrees, seen best in FIG. 5. The hook 
includes a radially extending wall 182 and an axially parallel wall 184. 
The radially extending wall 182 serves to space the axially parallel wall 
184 from the outer surface 26 of the barrel 16 to form an arcuate 
wedge-shaped receptacle 186 operable to receive and grip one of the hooks 
154 formed in the telescoping covers. 
Operation 
Referring to FIG. 4, a retracted position of the cover 17, wherein the 
apparatus is ready for use is shown in fragmented, broken outline. In this 
position, the telescoping cover 14 is in a non-extended position relative 
to the barrel 16 and one of the hooks 154 is received in the receptacle 
186 such that the hook is tightly received against the axially extending 
wall 182 of the hook on the barrel 16. In this position, the telescoping 
cover is releasably locked to the barrel. It will therefore be appreciated 
that the receptacle 186 formed by the hook 157 on the barrel 16 and the 
hook 154 on the telescoping cover 14 act as a first releasable lock for 
releasably locking the telescoping cover 14 to the barrel 16 when the 
telescoping cover 14 is in a non-extended position. 
After use of the syringe, the outer surface 26 of the telescoping cover 14 
is gripped with one hand while the finger grip tabs are 36 and 38 grasped 
by the other hand and the telescoping cover 14 is rotated relative to the 
barrel 16 to release the hook 154 from the receptacle 186. The telescoping 
cover may then be positioned such that the barrel hook 157 is between 
adjacent hooks 154, whereupon the telescoping cover 14 may be 
telescopically extended relative to the barrel 16. The hook 154 is thus 
releasably jammed in the receptacle 186 to secure the telescoping cover 14 
to the barrel 16 until the telescoping cover 14 is rotated relative to the 
barrel 16 to release the hook 154 from the receptacle 186, thereby 
unlocking the telescoping cover 14 relative to the barrel 16 and 
permitting extension of the telescoping cover 14 relative to the barrel 
16. 
Guiding of the telescoping cover 14 is enhanced by the axially extending 
walls 160 of the hooks 154 riding on the outer surface 26 of the barrel 
16, while the inside surface 84 of the telescoping cover 14 rides on the 
annular concentric wall 172 of the hook ring 156. 
When the telescoping cover 14 has been extended sufficiently, the inclined 
surfaces 176 and 166 of the hook ring 156 and the hooks 154 engage and 
resiliently deform as the barbs 162 of the hooks 154 are forced into the 
receptacle 180 formed between the radially planar surface 178 of the hook 
ring and the annular wall 170 of the hook ring 156. 
In this position, the radially planar surfaces 178 and 168 abut each other 
whereupon the radially planar surface 178 on the hook ring 156 interferes 
with the radially planar surface 168 on the hooks 154 and prevents counter 
movement of the telescoping cover 14 in a direction tending to retract the 
telescoping cover 14 relative to the barrel 16. In this position, the 
telescoping cover 14 is fully extended relative to the barrel. When the 
telescoping cover is fully extended in this manner, because the length of 
the telescoping cover is greater than the length of the needle assembly, 
the needle is fully covered and the user is guarded against needle prick 
injuries. Furthermore, the user cannot retract the telescoping cover 14 
relative to the barrel 16. The hook ring 156 and the hooks 154 thus act as 
a second lock for permanently locking the telescoping cover 14 in an 
extended position when the telescoping cover 14 is in an extended position 
fully covering the needle 74. 
The telescoping cover 25 is supported in the extended position by the 
mating of the inside surface 84 of the telescoping cover 14 with the 
concentric annular wall 172 of the hook ring 156 and the tight grip on the 
hooks 154 provided by the hook ring 156. Thus, the concentric annular wall 
172 of the hook ring 156 acts as a support surface for supporting the 
telescoping cover 14 in an extended position in which the needle 74 is 
covered. 
It is a particular advantage of the invention that after the use of the 
syringe, the telescoping cover 14 may simply and quickly be rotated 
relative to the barrel 16 and drawn outwardly of the barrel 16, or 
telescopically extended relative to the barrel 16, in a direction away 
from the point 76 of the needle 74 until the needle is covered. Thus, the 
user's hands are kept away from the needle point 76 and there is no 
movement which would drive the needle 74 into the user's hand or body. 
Rather, all movement is away from the needle point 76. Thus, the operation 
of the apparatus presents little risk to the user and after operation of 
the device the risk of needle prick injuries is small as needle 74 is 
completely covered. 
While specific embodiments of the invention have been described and 
illustrated, such embodiments should be considered illustrative of the 
invention only and not as limiting the invention as construed in 
accordance with the accompanying claims.