WO1992018183A1

WO1992018183A1 - Combined syringe and needle shield

Info

Publication number: WO1992018183A1
Application number: PCT/US1991/002579
Authority: WO
Inventors: Daniel Andreas Talonn; Alan Bernard Ranford
Original assignee: Sherwood Medical Company
Priority date: 1991-04-15
Filing date: 1991-04-15
Publication date: 1992-10-29
Also published as: CA2085371C; CA2085371A1

Abstract

The invention provides a medication containing syringe (150) which includes first (166) and second (210) tubular members; a plunger rod assembly (154); a distal needle assembly (176) and a collar member (186). The first tubular member (166) includes distal and proximal ends and a slidable member (171) received therein which is adapted to retain a prefilled quantity of medication distally thereof. The plunger rod assembly includes a reciprocally mounted plunger rod (154) adapted to operatively contact the slidable member (171) through the proximal end of the first tubular member (166). The needle assembly (176) includes distal and proximal ends and a needle hub (174) thereon, wherein the needle hub (174) is mounted adjacent the distal end of said first tubular member (166) and the needle assembly (176) also includes a distal needle point (179) on the distal end thereof and the proximal end of the needle assembly is adapted to be in fluid communication with the medication retained distally of the slidable member (171). The collar means (186) is operatively connected to the distal end of the first tubular member (166) and the second tubular member (210) is positioned about the first tubular member (166) and the collar means (186). The second tubular member (210) includes distal and proximal ends and is designed to slidably contact the collar means (186) longitudinally movable over the first tubular member (166) and the collar means (186) between a retracted position wherein the distal needle point (179) is exposed and an extended position wherein the distal needle point (179) is protected. The second tubular member (210) further includes a tapered section (216) on the distal end thereof and the outer diameter of the distal end of the tapered section (216) is substantially smaller than the outer diameter of the proximal end of the second tubular member (210) and when the second tubular member (210) is in the retracted position, the distal end of the second tubular member (210) is adjacent to the needle hub (174) and the distal end of the first tubular member (166).

Description

COMBINED SYRINGE AND NEEDLE SHIELD

TECHNICAL FIELD

This application is directed to an invention which is a development of our European Patent Application No. 350 186.

This invention relates to syringes and, for example to a conventional syringe of the type adapted to receive a medication-containing cartridge therein but having a novel extendable needle shield primarily for the purpose of preventing or minimizing accidental needle sticks.

BACKGROUND ART

Most syringes used today for medical, laboratory or dental purposes are sold as disposable items intended to be used only once. Disposal of such syringes has posed a safety hazard for the individuals who use the syringes as well as for those who dispose of them. With the onset of AIDS, the concern for infection due to accidental needle sticks from used syringes has increased and a number of different devices have been proposed to minimize the possibility of spreading infectious disease due to accidents of this type.

One approach to this problem is to provide an extendable needle shield which, after the syringe has been used, can be pushed to an extended position where it covers the needle, making it difficult for an individual to accidentally contact the needle. A common feature of such constructions is that when the needle shield is pushed to its extended position, it is locked so that it cannot be retracted (thus exposing the needle) except by application of extraordinary force.

A number of such constructions have been proposed to satisfy the general requirement that the needle be permanently covered after the syringe has been used. Some of these constructions involve complex locking mechanisms and, in others, locking occurs automatically when the shield is fully extended. These known devices satisfy many of the functional requirements of a needle shield but require, in most cases, modification of the standard syringe construction. This is highly undesirable for many manufacturers because of the sizable investment they may have already made in their existing molding equipment for producing the syringes. Constructions have also been proposed which include an opening or slot in the side of the shield. This is undesirable because the needle can extend through the opening if the needle or the needle shield is deflected when the needle shield is in the extended position. Other proposed devices include open ended needle shields which may not block access to the needle point by small fingers.

Those devices which lock in response to axial movement of the needle shield to the extended position, (i.e., without any rotation) have certain inherent drawbacks that result primarily from the requirement that substantial forces be exerted to lock the shield in its extended position. In the first place, the likelihood of unintentional and irreversible locking is greater with such devices than with those devices which require rotation to lock. Also, in certain constructions, it may be difficult to verify that the needle shield is locked upon extension without attempting to retract the shield, which increases the possibility of unintended exposure of the needle. In addition to the design requirements described above, the design of this type of dental syringe must allow for the insertion of a medication cartridge through the proximal end of the dental syringe. Additionally, the outer diameter of the distal end of the needle shield should be minimized so that the dentist is able to better observe the needle of the dental syringe during the use thereof and so that the distal end of the needle shield does not interfere with the placement or use of other instruments which may simultaneously be present in the patient's mouth. Accordingly, it is an object of this invention to provide a protective needle shield of the type described above which can be added at minimal expense to conventional hypodermic or dental syringes.

Another object of the present invention is to provide a relatively inexpensive protective shield which satisfies the functional requirements of a needle shield and which includes none of the drawbacks mentioned above.

Another object of the present invention is to provide an extendable needle shield for a dental syringe which performs all of the necessary functions of such a shield and which is particularly well suited to an automated process of manufacture.

A further object of the present invention is to provide an extendable needle shield for a standard hypodermic or dental syringe which is improved both from the points of view of functional utility and cost of manufacture.

A still further object of the present invention is to provide an inexpensive method of assembling a protective needle shield and dental syringe.

DISCLOSURE OF THE INVENTION

In accordance with the invention, a needle shield is mounted coaxially on a syringe barrel. The needle shield includes one or more elongated keys on its inner surface. A collar is provided on the distal end of the barrel adjacent to the needle or needle hub. The collar may be a separate part or it may be integrally formed with the barrel and includes on its outer surface at least one locking slot. The key slides in a path outside of the locking slot and can be rotated into the locking slot when the needle shield is extended. Both the collar and shield can be molded from plastic materials so that the cost of the shield is relatively low.

In the preferred embodiment, the needle shield includes a plurality of elongated locking keys and the collar includes a plurality of locking slots. Each locking slot is defined by opposing walls, at least one of which includes a ramp over which the keys can ride when the shield is in its extended position and subsequently rotated to an extended and locked position. As the keys are rotated into the locking slots, rearward movement of the needle shield to its retracted position is prevented by a surface on the collar at the back of each locking slot. In accordance with one feature of the present invention, protrusions on the collar and the forward portions of the keys are shaped such that during assembly, the keys are directed into keyways formed between the locking slots as the collar is moved relative to the needle shield. Thus, the construction is well suited to an automated process in which the collar and needle shield are secured to the standard hypodermic or dental syringe by machine. A further feature of the present invention is the provision of a needle shield having a reduced diameter distal end to allow for the attachment of a needle protecting needle sheath thereon.

Other features of the present invention are set forth hereinafter in the detailed description of the preferred embodiments. BRIEF DESCRIPTION. OF THE DRAWINGS

Figure 1 is a perspective view of an embodiment of the present invention shown mounted on a conventional dental syringe with the needle shield in the extended position; Figure 2 is a side elevation view, partially in cross- section taken along lines 11—11 as shown in Figure 1 and shown with the medication cartridge in the dental syringe and with the needle shield in the retracted position;

Figure 3 is a fragmentary side cross-sectional view also taken along lines 11—11 as shown in Figure 1 and shown with the needle shield in the extended position;

Figure 4 is an enlarged scale, fragmentary side sectional view taken along lines 13—13 as shown in Figure 2 and showing details of the collar and needle shield thereof;

Figure 5 is a fragmentary sectional view taken along lines 14—14 in Figure 2 and showing a portion of the needle shield in the extended position prior to rotation of the needle shield; Figure 6 is a fragmentary sectional view taken along lines 14—14 in Figure 2 and showing a portion of the needle shield in the extended and locked position after rotation; and

Figure 7 is an enlarged scale, perspective view of the collar shown in Figure 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the preferred embodiment, the invention is intended to be used in conjunction with a standard hypodermic syringe; however, a protective needle shield in accordance with the invention may be modified for use with any medical, laboratory or dental device having a needle, such

SUBSTITUTE SHEET as a blood collection tube holder or dental syringe with a double ended needle (as described hereinafter) without departing from the contemplated scope of the present invention. Accordingly, as used herein, the term "syringe" is intended to include any medical or scientific device including a needle wherein it is desired to protect a user from accidental needle sticks.

In describing the invention, the "distal end" of a part refers to the end of the part closest to the needle point. The "proximal end" of a part refers to the end furthest from the needle point.

An embodiment of the present invention is illustrated in Figures 1 through 7 with the collar and needle shield adapted for use on a conventional dental syringe of the type adapted to receive a medication cartridge removably mounted therein. The dental syringe of the present embodiment is generally designated as dental syringe 150.

As illustrated in Figures 1 and 2, the dental syringe 150 of the present embodiment includes an elongate and tubular cartridge holder assembly 166 adapted to receive a conventional medication cartridge 167 therein. A conventional injector assembly 152 is mounted on the proximal end of the cartridge holder assembly 166. The distal end of the cartridge holder assembly 166 includes a double ended needle assembly 176 mounted therein and a tubular collar assembly 186 mounted thereon. The collar assembly 186 slidably contacts an elongate and tubular needle shield assembly 210 which is longitudinally movable over the cartridge holder assembly 166 and the collar assembly 186. A conventional needle sheath assembly 220 is removably mounted on the distal end of the needle shield assembly 210.

As illustrated in Figure 2, the cartridge holder assembly 166 of the present embodiment includes an elongate and tubular proximal barrel section 168. a tapered barrel

SUBSTITUTESHEET section 170 fixedly mounted on the distal end thereof and an integral distal barrel section 172 on the distal end of the tapered barrel section 170. The proximal end of the proximal barrel section 168 includes a pair of radially extending retention flanges 169. the function of which are described hereinafter. The interior surface of the proximal barrel section 168 has a generally uniform internal diameter which is adapted to receive a conventional medication cartridge 167 therein. As illustrated in Figure 2, the medication cartridge 167 referred to herein is a commercially available medication cartridge having an injectable medication therein, one example of which is a 1.8 ml cartridge which contains a 2% lidocaine HCl injection with epinephrine in a concentration of 1:100,000 manufactured by Astra

Corporation of Worchester, Massachusetts, U.S.A. The medication cartridge 167 includes an elongate glass cylinder 165 with a rubber piston or plunger member 171 movably mounted in the proximal end of the cylinder 165. The distal end of the medication cartridge 167 includes a metal cap 173 fixedly mounted on a reduced portion of the cylinder 165. The metal cap 173 includes a central orifice (not shown) positioned over a needle pierceable diaphragm 175. As further illustrated in Figure 2, the tapered barrel section 170 at the distal end of the cartridge holder assembly 166, decreases in external diameter from the distal end of the proximal barrel section 168 to a smaller diameter and integrally connected, cylindrically-shaped distal barrel section 172. The external surface of the distal barrel section 172 preferably includes four equally spaced ribs 184 thereon (Figure 3) . The distal end of the ribs 184 extend from the distal end of the distal barrel section 172 so that the outer diameter of the

SUBSTITUTESHEET distal barrel section 172 is generally uniform about and along the longitudinal axis thereof.

The barrel section 172 surrounds the needle hub 174 of the integral double ended needle assembly 176 as illustrated in Figure 2. The needle assembly 176 further includes an elongate and hollow distal needle section 178 which extends beyond the distal end of the cartridge holder assembly 166 to a sharpened distal needle point 179 and an integral and elongate hollow proximal needle section 180 which extends into and within the distal end of the cartridge holder assembly 166 to a sharpened proximal needle point 181 located proximally of the tapered barrel section 170. A cylindrical cartridge positioning hub 182 is located on the proximal side of the needle hub 174 and extends proximally from the needle hub 174 to a location generally adjacent to the midpoint of the tapered barrel section 170. The positioning hub 182 encircles and supports the majority of the proximal needle section 180 and is adapted to contact the distal end of the medication cartridge 167 when the medication cartridge 167 is inserted into the cartridge holder assembly 166 as described hereinafter.

As illustrated in Figures 3 and 7, the tubular collar assembly 186 of the present embodiment preferably includes six equally spaced and integrally formed triangularly- shaped protrusions 188 which extend radially from the circumferential surface of the collar assembly 186. The apex of each of the triangularly-shaped protrusions 188 is positioned along the proximal side of the collar assembly 186 to assist in the assembly of the present embodiment as described hereinafter. Each of the protrusions 188 also include angled surfaces 188A and 188B, side surfaces 192. and a distal surface 196 which extend perpendicularly from the surface of the collar assembly 186. A recessed slot 194 extends distally from the apex of

SUBST.TUTESHEET each of the triangularly shaped protrusions 188 to a sloped distal surface 194A, the function of which is described hereinafter. The distal surface 196 of each protrusion 188 forms a generally circumferential surface along the distal side of the protrusion 188 approximately midway along the external surface of the collar assembly 186. The side surfaces 192 of each adjacent pair of protrusions 188 form keyways 190 therebetween, the function of which is described hereinafter. A radially extending and spherical detent 208 is positioned in the keyways 190 between each pair of protrusions 188 such that the distal edge of each spherical detent 208 is located slightly distal to the distal surface 196 of each protrusion 188 and the proximal edge of each spherical detent 208 is located slightly proximal to the side surfaces 192 of each protrusion 188. As illustrated in Figures 5 and 6 , a pair of parallel walls, 202 and 204. are positioned radially along the lengthwise dimension of the collar assembly 186 adjacent to the distal surface 196 of each protrusion 188. The walls, 202 and 204, form a rectangularly shaped locking slot 206 therebetween, the function of which is described hereinafter. The walls, 202 and 204, preferably include a ramp shaped wall surface on the external side thereof and a perpendicular wall surface on the internal side thereof. The surface of the locking slot 206 is slightly elevated relative to the level of the keyways 190, i.e., the collar diameter at the locking slots 206 is slightly greater than the collar diameter at the keyways 190. This slight increase in collar diameter at the locking slots 206 removes some of the slack or wobble which may occur between the needle shield assembly 210 (described hereinafter) and the collar assembly 186 to decrease the likelihood that the needle shield assembly 210 will wobble or move relative to the cartridge holder assembly 166 when the needle shield

SUBSTITUTE SHEET assembly 210 is moved to a locked and extended position (Figure 3) described hereinafter.

As illustrated in Figure 4, the internal surface of the collar assembly 186 includes a wedge-shaped internal tooth member 212 adjacent to the proximal end of the collar assembly 186 which is adapted to engage the outer surface of the distal barrel section 172 and retain the collar assembly 186 on the distal barrel section 172 of the cartridge holder assembly 166 during assembly of the present embodiment as described hereinafter. The collar assembly 186 of the present embodiment is molded of a rigid plastic material such as a polycarbonate resin so that the collar assembly 186 causes a slight deformation of the ribs 184 and distal barrel section 172 as the collar assembly 186 placed on the distal barrel section 172 of the cartridge holder assembly 166. Alternately, raised yieldable ribs (not shown) may be formed on the distal barrel section 172 or gaps may be formed in the tooth member 212 on the collar to function in the same manner as described above with respect to the preferred embodiment. Additionally, other means of interlocking the collar 186 to the distal barrel section 172 such as ultrasonic welding or adhesives are contemplated and may be used without departing from the scope of the present invention. With reference to Figures 1 and 2 of the drawings and as heretofore described, the cartridge holder assembly 166 of the present embodiment includes a conventional injector assembly 152 mounted on the proximal end thereof. The injector assembly includes a bore 153 therethrough for slidably receiving an elongate plunger rod 154 therein. The plunger rod 154 is provided with a conventional enlarged and circular finger ring 156 at the proximal end thereof and a triangularly-shaped and sharpened barb member 158 extending from the distal end thereof. The injector assembly 152 further includes a generally cylindrical body

SUBSTITUTE SHE! section 151 having a proximally positioned enlarged oval- shaped finger flange 160 which is adapted to be grasped by the fingers of the user. A cylindrical locking ring 162 is slidably positioned on the body section 151 of the injector assembly 152 distal to the finger flange 160. The body section 151 also includes a generally cylindrically-shaped and resilient, body member 164 which extends distally from the finger flange 160. The body member 164 includes an integral and frustoconically-shaped distal portion 161 having a retaining lip or rim 164A thereon. A pair of longitudinally extending slots or channels 165 are provided on opposite lateral sides of the body member 164. Each channel 165 includes a triangularly-shaped recess 163 adjacent to the distal end thereof which is adapted to receive one of the retention flanges 169 from the cartridge holder assembly 166 therein, as will be discussed more fully hereinafter.

As illustrated in Figures 3 and 4, the needle shield assembly 210 of the present embodiment preferably includes an elongate and tubular proximal shield section 214 having three equally spaced and rectangularly-shaped elongate keys 198 integrally formed along the interior surface thereof and a tapered shield section 216 which decreases in external diameter from the distal end of the proximal shield section 214 to an integral distal shield section

218. The keys 198 preferably extend lengthwise between the distal and proximal ends of the proximal shield section 214 and include triangularly-shaped distal ends and flat- proximal ends, the function of which are described hereinafter. An end rim 222 is formed along the inner surface of the proximal end of the proximal shield section 214 and is adapted to extend radially inwardly therefrom. Three equally spaced and inwardly extending oblong-shaped detents 200 are formed along the internal surface of the distal end of the needle shield assembly 210. These

SUBSTITUTESHEET detents 200 are preferably spaced approximately thirty degrees from an adjacent key 198 and include sloped distal surfaces, the function of which are described hereinafter. The distal shield section 218 of the needle shield assembly 210 is a cylindrically shaped tubular member having a centrally located needle aperture 211 therein, as illustrated in Figures 2 and 3. The needle aperture 211 of the distal shield section 218 is sized to allow the distal needle section 178 and the needle hub 174 of the needle assembly 176 to pass therethrough. The tapered shield section 216 and the reduced diameter distal shield section 218 allow the dentist to observe the entire distal needle section 178 of the needle assembly 176 during a dental procedure and does not interfere with any other instruments which may be simultaneously present in the patient's mouth. Additionally, the use of the tapered shield section 216 and the smaller sized needle aperture 211 reduces the likelihood that a child or person with small fingers may accidentally contact the distal needle point 179 when the needle shield assembly 210 is in the extended position as described hereinafter.

As briefly described above, the needle sheath assembly 220 is adapted to be removably attached to the distal shield section 218 of the needle shield assembly 210. As illustrated in Figures 1 and 2, the needle sheath assembly 220 includes an elongate and tubular body section 221 which is adapted to protect the distal needle section 178 and distal needle point 179 of the needle assembly 176 prior to ' use of the present embodiment. The proximal end of the needle sheath assembly 220 includes an enlarged rim member 223. The proximal end of the needle sheath assembly is adapted to be attached to the distal section 218 of the needle shield assembly 210 by frictional contact, adhesives or heat staking therebetween.

SUBSTETUTE SHEET Assembly of the dental syringe 150 is relatively simple and may be automated. Initially, the collar assembly 186 is positioned within the proximal shield section 214 of the needle shield assembly 210 by inserting the collar assembly 186 through the distal end of the proximal shield section 214 so that the triangularly-shaped distal ends of the keys 198 are position between the triangularly-shaped protrusions 188 and in the appropriate keyways 190 on the collar assembly 186. The tapered shield section 216 and integral distal shield section 218 are then placed on the distal end of the proximal shield section 214 so that the tapered shield section 216 is retained on the distal end of the proximal shield section 214. This may be accomplished by ultrasonic welding, adhesives or interlocking mechanical engagement of a grooved sidewall 226 with a complementary distally extending projection 228 located at the distal end of the proximal shield section 214 as illustrated in Figure 2. The needle shield assembly 210 and collar assembly 186 are then telescoped over the distal end of the cartridge holder assembly 166 so that the tooth member 212 of the collar assembly 186 is forced over the distal barrel section 172 by the needle shield assembly 210 until the proximal end of the collar assembly 186 is engaged on the distal barrel section 172 in a predetermined location.

In the present embodiment, the rim member 223 of the needle sheath assembly 220 is then attached to the distal shield section 218 of the needle shield assembly 210. Alternately, if the needle assembly 176 is separate from the distal barrel section 172, the needle hub 174 of the needle assembly 176 is attached to the distal barrel section 172, as described above, and then the needle sheath assembly 220 is attached to the distal shield section 218. It is also contemplated that the other assembly methods described above with respect to the preferred embodiment

SUB_STITUTE SHEET are readily adaptable for the assembly of the dental syringe 150 of the present embodiment.

The dental syringe 150 of the present embodiment may be used in a conventional manner to perform various dental procedures. Initially, the user may insert a medication cartridge 167 into the proximal end of the cartridge holder assembly 166. The plunger rod 154 of the injector assembly 152 is then moved proximally to a retracted position and the injector assembly 152 is attached to the cartridge holder assembly 166 by inserting the retention flanges 169 of the cartridge holder assembly 166 into the recesses 163 located in channels 165 of the injector assembly 152. The user may then lock the injector assembly 152 on the proximal end of the cartridge holder assembly 166 by moving the locking ring 162 distally along the body member 164 to compress the frustoconically-shaped distal portion 161 of the body member 164 to retain the retention flanges 169 of the cartridge holder assembly 166 within the recesses 163 in the channels 165 of the body member 164. The user may then grasp the finger ring 156 on the injector assembly 152 and move the plunger rod 154 distally until the barb member 158 pierces and is seated in the plunger member 171 on proximal end of the medication cartridge 167 and the proximal needle point 181 pierces the diaphragm 175 through the orifice in the metal cap 173 on the distal end of the medication cartridge 167.

As illustrated in Figure 2, the medication cartridge 167 is loaded in the cartridge holder assembly 166 and the needle shield assembly 210 is in the retracted position. In the retracted position, the needle shield assembly 210 is positioned about the cartridge holder assembly 166 so that the proximal end of the proximal shield section 214 is adjacent to the lip 164A of the body member 164 on the injector assembly 152; the needle aperture 211 on of the distal shield section 218 is adjacent to the needle hub 174

SUBSTITUTESHEET of the needle assembly 176 and the needle sheath assembly 220 encloses the distal needle section 178 and distal needle point 179 of the needle assembly 176. In the retracted position, the triangularly-shaped distal ends of the keys 198 are positioned in the keyways 190 between the side surfaces 192 of the protrusions 188 and in contact with the proximal edge of the spherical detents 208 on the collar assembly 186. Additionally, the detents 200 on the needle shield 210 are aligned within the slots 194 on the protrusions 188 so that the proximal surface of the detents % 200 will contact the sloped distal surface 194A of the slots 194 to releasably retain the needle shield assembly 210 in the retracted position.

In order to administer an injection, the needle sheath assembly 220 is initially removed from the distal shield section 218 to expose the distal needle point 179 of the needle assembly 176. The user may then administer the injection in a conventional manner by inserting the distal needle point 179 into the injection site while grasping the finger flange 160 and moving the finger ring 156 on the plunger rod 154 distally with respect to the finger flange 160. The distal movement of the plunger rod 154 causes the barb member 158 to move the plunger member 171 distally in the cylinder 165 of the medication cartridge 167 and dispense the medication through the distal needle point 179 on the needle assembly 176 and into the injection site.

Once the contents of the dental syringe 150 have been injected into the patient, the needle shield assembly 210 ^• is pushed distally to the extended position as shown in Figures 1 and 3. As the needle shield assembly 210 is moved to the extended position, the keys 198 will slide longitudinally in the keyways 190 over the spherical detents 208 on the collar assembly 186 and the angled distal surfaces on the detents 200 on the needle shield assembly 210 will slide over the angled detenting surfaces

Sf -T.TUTESHEET 194A on slots 194 to release the needle shield assembly 210 from the retracted position. As the needle shield assembly 210 reaches the extended position, the spherical detents 208 on the collar 186 will signal the user that the needle shield assembly 210 has reached the fully extended position by releasing from the flat proximal ends of the keys 198, once the keys 198 pass beyond the spherical detents 208. Additionally, as illustrated in Figure 3, when the needle shield assembly 210 reaches the extended position, the end rim 222 on the proximal end of the needle shield assembly 210 will contact the proximal end of the collar assembly 186 to prevent further distal movement of the needle shield assembly 210 along the cartridge holder assembly 166 and the collar assembly 186. As generally illustrated in Figures 3 and 5, when the needle shield assembly 210 is in the extended position, the tapered shield section 216 and the distal shield section 218 of the needle shield assembly 210 extend beyond the distal needle point 179 of the needle assembly 176 and the end rim 222 on the proximal end of the proximal shield section 214 contacts the proximal end of the collar assembly 186. In this extended position, the proximal end of the keys 198 are positioned adjacent to the proximal side of the keyways 190 and the flat-proximal ends of the keys 198 are located along the distal edge of the spherical detents 208 and adjacent to the walls, 202 and 204 and locking slots 206.

If the user desires to lock the needle shield assembly 210 in a locked and extended position (Figure 3) rather than the releasable extended position described above, the user may rotate the needle shield assembly 210 clockwise or counterclockwise about the cartridge holder assembly 166 and the collar assembly 186. Rotation of the needle shield assembly 210 will cause the keys 198 on the needle shield assembly 210 to move over the ramp shaped surface of the

SUBSTITUTE SHEET adjacent walls, 202 or 204, on the collar assembly 186 until the keys 198 fall into the locking slots 206 formed therebetween. When the keys 198 are positioned in the locking slots 206, the flat-proximal end of each key 198 abuts against the distal surface 196 of one of the protrusions 188 so that the shield cannot be moved proximally and returned to the retracted position. Because of the interlocking relationship between the sides of the keys 198 and the perpendicular side surfaces of the walls, 202 and 204, the needle shield assembly 210 can no longer be rotated and, accordingly, the needle shield assembly 210 is in a locked and extended position (Figure 6) .

In certain situations, it may be desirable to move the needle shield assembly 210 to the extended position (Figure 5) without having the needle shield assembly 210 in a locked and extended position (Figure 6) . For example, if a dental syringe 150 is preloaded with the medication cartridge 167 at a location remote from the patient; stored on a dental tray prior to use or if the user desires to verify that the medication cartridge 167 is properly seated in the cartridge holder assembly 166, it may be preferable to extend the needle shield assembly 210 beyond the distal needle point 179 so that the needle shield assembly 210 functions as a temporary protective element prior to the actual use of the dental syringe 150. Use of the dental syringe 150 in this manner is facilitated by the spherical detents 208 on the collar assembly 186. As described above, these spherical detents 208 are located in each of the keyways 190 between the protrusions 188 so that when the needle shield assembly 210 is pushed to the extended position, the flat-proximal end of each of the keys 198 will release from the spherical detents 208 and the end rim 222 of the needle shield assembly 210 will contact the proximal end of the collar 186. The spherical detents 208 prevent the needle shield assembly 210 from being

ITUTE SHEET accidentally or inadvertently retracted unless sufficient proximal force is applied to the needle shield assembly 210 to move the keys 198 proximally over the spherical detents 208. Once the injection has been administered, the needle shield assembly 210 may be moved distally to the extended position and then rotated so that the keys 198 fall into the locking slots 206 to lock the needle shield assembly 210 in the locked and extended position as described above. In this light, it should be appreciated that the present invention provides a safety dental syringe which allows a medication cartridge to be inserted into the dental syringe through the proximal end thereof. Additionally, the reduced diameter distal end of the present invention allows the user to observe the distal end of the needle during a dental procedure and does not interfere with any other instruments which may be present in the patient's mouth. The relatively small size of the needle aperture in the distal end of the needle shield also prevents accidental contact with the distal needle point when the needle shield is in the extended position.

Finally, the cylindrical shape of the distal end of the needle shield allows the user to move the needle shield to the extended position to verify that the medication cartridge is properly seated in the cartridge holder without removing the needle sheath.

It should be further understood that the above described embodiments may be modified in certain aspects for use on nearly any medical, or laboratory syringe. Additionally, it is anticipated that the present invention may be used with a prefilled syringe wherein the use of a separate medication between a proximal plunger member and the distal barrel section. Therefore, the foregoing is intended to be descriptive of the preferred form of the embodiments described above while the scope of the present invention is intended to be defined by the following claims.

Claims

1. A medication containing syringe comprising:

a first tubular member having distal and proximal ends and a slidable member adapted to retain a prefilled quantity of medication distally thereof;

a plunger rod assembly including a reciprocally mounted plunger rod adapted to operatively contact said slidable member through said proximal end of said first tubular member;

a double ended hollow needle assembly including distal and proximal ends and a needle hub thereon, wherein said needle hub is mounted adjacent said distal end of said first tubular member, said needle assembly includes a distal needle point on said distal end thereof and said proximal end of said needle assembly is adapted to be in fluid communication with the medication retained distally of said slidable member and said needle point of said needle assembly extends distally beyond said distal end of said first tubular member;

collar means operatively connected to said first tubular member; and a second tubular member positioned about said first tubular member and said collar means, said second tubular member having distal and proximal ends and slidably contacts said collar means, said second tubular member being longitudinally movable over said first tubular member and said collar means between a retracted position wherein said distal needle point is exposed and an extended position wherein said distal needle point is protected and said second tubular member further includes a tapered section on the distal end thereof and the outer diameter of said distal end of said tapered section is substantially smaller than the outer diameter of said proximal end of said second tubular member and when said second tubular member is in said retracted position, said distal end of said second tubular member is adjacent to said needle hub and said distal end of said first tubular member.

2. The medication containing syringe of claim 1, wherein locking means are provided between said second tubular member and said collar means and said second tubular member is rotatably movable from said extended position to a locked and extended position wherein said second tubular member is prevented from being returned to said retracted position.

3. The medication containing syringe of claim 2, wherein said second tubular member and said collar means each include a key or a cooperating keyway thereon to facilitate the longitudinal sliding movement of said second tubular member along said collar means and said first tubular member.

4. The medication containing syringe of claim 3, wherein said key is provided on an interior surface of said second tubular member and said locking means includes a plurality of walled recesses about the periphery of said collar means to lock a portion of said key between said walls when said second tubular member is moved from said extended position to said locked and extended position.

5. The medication containing syringe of any one of claims 1 - 4, wherein said tapered section of the distal end of said second tubular member includes a funnel- shaped portion having an attachment means on the distal end thereof, and wherein a hollow needle sheath is removably mounted on said attachment means to protect said distal needle point when said second tubular member is in said retracted position.

6. A prefilled syringe comprising:

an elongate first tubular member having distal and proximal ends;

a slidable member slidably operatively mounted in said first tubular member and adapted to retain a prefilled medication distally thereof;

an injector assembly operatively associated with said first tubular member and including a reciprocally mounted plunger rod adapted to extend into said proximal end of said first tubular member and operatively engage said slidable member to enable reciprocal movement thereof;

a double ended hollow assembly having distal and proximal ends, wherein said needle assembly is operatively associated with said distal end of said first tubular member and said distal end of said needle assembly includes a distal needle point thereon and said proximal end of said needle assembly is adapted to be in fluid communication with the prefilled medication contained in said first tubular member; collar means operatively associated with said first tubular member; and an elongate second tubular member positioned about said first tubular member and said collar means, said second tubular member having distal and proximal ends and being longitudinally movable over said first tubular member and collar means between a retracted position wherein said distal needle point is exposed and an extended position wherein said distal needle point is protected and said second tubular member further includes a tapered section on the distal end thereof and the outer diameter of said distal end of said tapered section is substantially smaller than the outer diameter of said proximal end of said tubular member and when said second tubular member is in said retracted position, said distal end of said second tubular member is adjacent to said needle hub and said distal end of said first tubular member.

7. The prefilled syringe of claim 6 wherein said second tubular member slidably contacts said collar means and locking means are provided between said second tubular member and said collar means.

8. The prefilled syringe of claim 6 wherein said second tubular member is slidable in a keyway on said collar means and is rotatable about said first tubular member in said extended position between a releasable extended position and a locked and extended position.

9. The medication containing syringe of any one of Claims 1 - 5, which has a hollow needle sheath means mounted on the distal end of said second tubular member.