Abstract:
An injection syringe ( 10 ) has an elongated syringe body ( 12 ) including a tube ( 18 ), a perforated front wall ( 26 ) for receiving an injection needle ( 70 ), and a rear actuating plunger ( 14 ) movably mounted inside the tube ( 18 ). A mobile needle shield ( 16 ) is externally movable along the syringe body ( 12 ) between a retracted position and an active position. An axial coupling mechanism ( 54 ) is provided between the shield ( 16 ) and the actuating plunger ( 14 ) for their simultaneous displacement towards the front on a common section. A release mechanism ( 58 ) is provided for releasing the coupling mechanism ( 54 ) to disengage the actuating plunger ( 14 ) and the needle shield ( 16 ) when the needle shield ( 16 ) is finally set in place.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an injection syringe of the type comprising, on the one hand, an elongate syringe body comprising a tube and a perforated front wall capable of receiving an injection needle and, on the other hand, a rear actuating plunger mounted so that it can move inside the tube, which syringe further comprises a mobile needle shield that can move externally along the syringe body between a retracted position drawn back from the injection end of the needle and an active protecting position in which the front end of the shield is forward of the injection end of said needle, there also being means of axial coupling between the shield and the actuating plunger to cause them to move simultaneously forward along a common portion. 
     A syringe of the aforementioned type is described, for example, in international patent application WO-97/02855 filed in the name of the applicant company. 
     In the syringe described in that document, the needle protector or shield consists of a tube that can be moved externally along the syringe body. The tube is fixed permanently to the rear end of the actuating plunger. This end is equipped with a disk on which a finger can press when the syringe is actuated. 
     Thus, the actuating plunger and the needle shield can be moved simultaneously and cover travels of the same length. 
     The minimum travel of the needle shield has a length equal to the sum of the lengths corresponding, on the one hand, to the length of the syringe body filled with liquid for injection and, on the other hand, to the length of the needle projecting from the body, to which is added a travel that prevents a finger from touching the end of the needle. 
     In order to allow the needle shield to move beyond the end of the needle, it is appropriate that after injection, the piston should be free to slide in the syringe body over a length roughly equal to the length of the portion of the needle that projects from the syringe body. 
     Thus, the syringe body has to be very long, even though only the rear part of the body is actually intended to contain the liquid for injection. 
     In addition, in order to withdraw liquid, it is necessary for the needle to project into the syringe body. Thus, the needle cannot be interchangeable. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide an injection syringe that makes it possible to reduce the length of the syringe body, thus making the use of standard and interchangeable needles possible. 
     To this end, a subject of the invention is an injection syringe of the aforementioned type, characterized in that it comprises means of releasing the coupling means to disconnect the actuating plunger and the needle shield during the final phase of the fitting of the needle shield. 
     According to some particular embodiments, the injection syringe has one or more of the following features: 
     said release means can be actuated under the control of the needle shield sliding along the syringe body; 
     it comprises a strong pointer identifying an intermediate position of the shield as it slides along the syringe body, in which position the needle shield is immediately upstream of the release means; 
     the means of axial coupling comprise means of elastically engaging the needle shield with the actuating plunger ( 14 ) and the release means are designed to disengage said means of elastic engagement; 
     the release means comprise a cam/follower arrangement carried by the needle shield and the syringe body, which arrangement is designed to cause the elastic deformation of the needle shield with a view to disengaging the means of elastic engagement as the needle shield moves; 
     the needle shield has an operating zone designed to cause the simultaneous movement of the shield and of the actuating plunger along said common portion, which common portion corresponds to the travel of the actuating plunger at the time of injection; and 
     the coupling means are designed to axially secure the needle shield and the actuating plunger together in both directions over said common portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood with the aid of the description which will follow, which is given solely by way of example and made with reference to the drawings in which: 
     FIG. 1 is a view in longitudinal section of a syringe according to the invention, prior to use; 
     FIG. 2 is a view in longitudinal section of the syringe of FIG. 1, depicted fitted with a needle; 
     FIG. 3 is a view in longitudinal section of the same syringe ready to inject; 
     FIG. 4 is a view in longitudinal section of the same syringe depicted after injection and after the needle has been removed from the body of the patient; and 
     FIG. 5 is a view in longitudinal section of the syringe after the needle shield has been fitted. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The injection syringe  10  depicted in FIG. 1 has an overall shape with symmetry of revolution about an axis X—X. This syringe is a use-once syringe. It is supplied ready to use, already containing a medical fluid for injection. 
     The syringe essentially comprises an elongate syringe body  12 , a rear actuating plunger  14  mounted so that it can move inside the body  12  and a needle shield  16  mounted so that it can move by sliding on the outside of the syringe body. 
     The syringe body  12  comprises a cylindrical glass tube  18 , open at both ends. The liquid for injection, denoted  20 , is held inside the glass tube  18  between a front piston  22  and a rear position  24 . These pistons are made of elastomer. 
     At the front, the glass tube  18  is extended by a needle support  26  forming the front wall of the syringe body. The front end of the tube  18  is push-fitted into the needle support  26 . 
     Forward of the glass tube  18 , the needle support  26  delimits a chamber  28  for housing the front piston  22 . This chamber extends the duct delimited by the glass tube  18 . It has a length slightly greater than that of the front piston  22 . In addition, it has a diameter slightly smaller than that of the front piston  22 , to ensure that the latter is wedged firmly in place. 
     Formed on the wall of the chamber  28  is a longitudinal canal  30  opening at a first end inside the glass tube  18  and at its other end into an injection passage  32 . The latter is formed axially in an external lump  34  intended to receive the injection needle. 
     The external surface of the lump  34  is approximately frustoconical and defines a Luer hub of suitable dimensions to receive standard injection needles. The lump  34  is surrounded by an integrally-formed skirt  36 . On the inside, this skirt has a screw thread intended to collaborate with tabs provided on the mounting fitting of standard needles. 
     A cap  38  is pushed onto the skirt  36  to protect the attachment end of the needle. 
     At its rear end, the glass tube  18  carries a pushed-on and bonded finger support ring  40 . This finger support ring forms an annular protrusion around the tube  18 . It also comprises two radially projecting lugs. These form supports for two fingers of the hand during injection. 
     The actuating plunger  14  comprises, on the one hand, the rear piston  24  and, on the other hand, a rigid push rod  42 , the front end of which is engaged inside the syringe body  12 . This front end is equipped with a threaded lump  44  received in a corresponding recess of the rear piston  24 , so as to secure these axially together in both directions. 
     The plunger push rod  42  has a tubular overall shape. At its rear end it has a flared portion  46 . This portion is bordered at its free end by radial fingers  48  distributed at the periphery of the piston rod. The flared portion defines, with the main part of the rod  42 , a shoulder  49 . 
     The needle shield  16  is generally in the form of a tube or sleeve  50 . It is made of an elastically deformable semi-rigid material. Along a part of its length it has two diametrically opposed longitudinal slots  51  designed for the passage of the lugs of the finger support ring  40 . 
     Moreover, at its rear end, the needle shield  16  has a disk or roundel  52  for the thumb to rest against during injection. This roundel is connected by snap-fastening to the rear end of the tube  50 . 
     Along its length, the shield  16  has means  54  for coupling the plunger  14  and the shield  16  in terms of translation. These means  54  secure these parts together in both directions. They comprise a ring of radial apertures  56  passing through the wall of the tube  50 . Engaged in these apertures are the radial fingers  48  provided at the rear end of the plunger push rod  42 . 
     Thus, coupling is provided by elastic engagement of the fingers  48  in the apertures  56 . 
     The front and rear edges delimiting the apertures  56  collaborate with the fingers  48  to secure the piston and the shield together respectively at the rear and at the front. 
     Forward of the apertures  56 , when considering the direction in which the plunger  14  is pushed into the body  12 , there are means  58  for releasing the coupling between the plunger  14  and the shield  16 . 
     In the embodiment depicted, the release means  58  comprise internal projections  60  delimiting ramps  62  designed to collaborate with the finger support ring  40 , so as to locally deform the tube  50  in the region of the radial apertures  56 . The projections  60  have a thickness that increases progressively toward the rear of the syringe and which ends in straight-cut faces  64  bordering the apertures  56 . The ramps  62  thus converge toward the axis of the syringe in the direction of the rear of the syringe. They constitute cam surfaces designed to collaborate with the periphery of the finger support ring  40  which constitutes a cam-follower; the ramps  62  and the support ring  40  together form a cam-and-follower arrangement. 
     Advantageously, the distance separating the coupling means  54  from the disk  52  is very slightly greater than the total length of the longest standard needle that can be mounted on the syringe. In practice, this length is very slightly greater than 1″ (2.54 cm) and for example is 2.6 cm. 
     Between the coupling means  54  and the disk  52  there are snap-fastening means  66  designed to lock the needle shield in its active protecting position in which the front end of the shield is forward of the injection end of the needle. 
     The snap-fastening means  66  comprise elastically deformable tabs projecting toward the inside of the tube  50 . These tabs delimit ramps  68 , the normal to which is oriented toward the front of the syringe. 
     The ramps  68  are designed to collaborate with the periphery of the finger support  40 , forming a cam surface which causes them to deform elastically as they pass the finger support ring  40  during the movement of the shield  16 . 
     To the rear of the snap-fastening means  66 , the internal surface of the shield  16  is frustoconical and flares out toward the disk  52 . Immediately before the disk  52 , the inside diameter of the shield is equal to the outside diameter of the plunger push rod  42  at its end carrying the fingers  48 . 
     The syringe depicted in FIG. 1 is assembled as follows. 
     First of all, the glass tube  18  is filled with the liquid  20  for injection, which is contained therein between the two pistons  22  and  24 . The front end of the glass tube  18  is then fitted with the needle carrier  26  and the protective cap  38 . Once the finger support ring has been fitted at the rear end of the glass tube  18 , the plunger push rod  42  is screwed into the rear piston  24 . The protective tube  50  equipped with the disk  52  is finally fitted around the syringe body. It is mounted around the finger support ring  40  by elastic deformation. 
     Likewise, during assembly, the fingers  48  penetrate the apertures  56  by elastic deformation of the tube  50  as the fingers  48  pass the projections  60 . 
     In order to use the syringe depicted in FIG. 1, the practitioner first of all removes the protective cap  38  and equips the needle holder  26  with an injection needle  70  equipped with a Luer hub fitting  72 , as depicted in FIG.  2 . 
     The plunger  14  is then gradually pushed into the syringe body, by pressing on the disk  52 . The pushing in of the actuating plunger  14  causes the simultaneous movement in the syringe body of the pistons  22  and  24  and of the liquid  20  for injection. 
     The front piston  22  then enters the chamber  28  as depicted in FIG.  3 . As the length of the chamber  28  is slightly greater than that of the piston  22 , the liquid  20  is free to flow through the longitudinal canals  30 . 
     When the actuating plunger  14  is later pushed into the syringe body, since the front piston  22  is immobilized, the liquid for injection flows through the canals  30  to reach the injection needle  70 . 
     If the liquid  20  contained in the syringe body is designed to be injected by itself, the practitioner then carries out injection in the conventional way. When the rear piston  24  comes into contact with the front piston  22 , all the liquid  20  contained between them has been discharged through the injection needle  70 . 
     If, on the other hand, the liquid  20  initially contained in the syringe has to be combined, during extemporaneous mixing, with an active substance contained in an intermediate container, the liquid  20  is injected into the container by depressing the plunger  14 . 
     When the rear piston  24  comes into contact with the front piston  22 , opposition to the subsequent movement of the needle shield  16  is encountered by the practitioner. This opposition constitutes a pointer indicating that, for subsequent depression of the shield, the piston will become detached. 
     The opposition is formed by the projections  60  coming into contact with the finger support ring  40  simultaneously with contact between the two pistons  22  and  24 . The force needed to overcome this opposition corresponds to the force needed to deform the shield under the action of the ramps  62  collaborating with the finger support ring  40 . 
     Under these conditions, it is possible for the practitioner to completely empty the syringe without fitting the needle shield and thus to re-use the syringe to inject the preparation. 
     In order to draw up the injectable preparation obtained by the mixing of the active substance and of the liquid  20 , the practitioner extracts the plunger  14  from the syringe body by pulling on the rear end of the tube  50 . Under the action of the depression formed between the front pistons  22  and  24 , the preparation is drawn back up inside the syringe body  12 . 
     As the diameter of the chamber  28  is slightly smaller than the diameter of the piston  22 , the latter remains jammed in the chamber  28  when the injectable preparation is being drawn up. 
     Injection is then carried out as described earlier. 
     At the end of injection, whether or not this has been preceded by a phase of extemporaneous mixing of substances for injection, the syringe is in the position depicted in FIG.  4 . 
     By continuing to apply force to the disk  52 , the practitioner causes local deformation of the tube  50  in the region of the means  54  for coupling the plunger  14  and the needle shield. 
     What happens is that the ramps  62  engage around the finger support ring  40 . As the shield  16  moves in the direction of the arrow F 4  of the tube  50 , the plunger push rod  14  is immobilized with respect to the syringe body, on the one hand, by the fact that the rear piston  24  is resting against the front piston  22  and, on the other hand, by the shoulder  49  resting against the finger support ring  40 . 
     Under the action of the deformation of the tube  50 , the radial apertures  56  move away from the fingers  48 , which therefore find themselves disengaged from the apertures. 
     Thus, the coupling between the actuating plunger  14  and the needle shield  16  is released and the external sliding of the needle shield  16  continues along the syringe body  12  while the plunger  14  is immobile within the syringe body. 
     The needle shield continues to move until the front end thereof is forward of the injection end of the needle, as depicted in FIG.  5 . 
     In this position, the snap-fastening tabs  66  bend down in front of the finger support ring  40 , thus locking the needle shield  16  in its active protecting position, therefore preventing it from returning as a result of tension exerted on the tube  50 . 
     In the position depicted in FIG. 5, the fingers  48  provided at the rear end of the plunger push rod  42  are immediately forward of the disk  52 , where the inside diameter of the shield is designed to receive the latter. 
     The detachment of the plunger from the shield at the end of injection, during the final phase of fitting the needle shield, makes it possible to reduce the length of the syringe body. Thus, the syringe body can be equipped with a standard needle that can be attached using a Luer hub, because there is no need for the needle to extend up inside the syringe body.