referring initially to fig1 , a passively guarded , fillable injection syringe is shown and generally designated 10 . as shown in fig1 , the syringe 10 includes a substantially cylindrical syringe body 12 that is centered on a needle axis 14 and formed with a finger grip 16 at its proximal end . fig1 further shows that the syringe 10 includes an adapter 18 that is sized to fit within the syringe body 12 and includes a cylindrical portion that is also centered on the needle axis 14 . for the syringe 10 , a substantially cylindrical needle guard 20 is provided that is positioned co - axially with both the syringe body 12 and adapter 18 , and is sized to fit within the adapter 18 . for the embodiment shown , the guard 20 is formed with a slight taper characterized by a decreasing outside diameter in a distal direction . it can be further seen that the syringe 10 includes a plunger 22 that is formed with a grip flange 24 at its proximal end . as best seen in fig2 a , the passively guarded , fillable injection syringe 10 includes a straight , elongated hollow needle 26 that has a sharp , distal needle tip 28 . fig2 a also shows that the adapter 18 includes a substantially cylindrical portion that is centered on the needle axis 14 and has a proximal end 30 and an open distal end 32 . a standoff 34 is formed at the proximal end 30 of the adapter 18 to attach the proximal end of the needle 26 to the adapter 18 . as shown in fig2 a , from the standoff 34 , the needle 26 passes distally through the cylindrical adapter 18 and extends beyond the adapter &# 39 ; s open distal end 32 to the distal needle tip 28 . as best seen in fig2 a , the adapter 18 is sized to allow the cylindrical guard 20 to move axially along the needle 26 and within the cylindrical portion of the adapter 18 . cross - referencing fig2 a and 4 , it can be seen that the inverted plunger 22 has a substantially cylindrical portion 36 which extends from a closed proximal end 38 to an open distal end 40 . structurally , the cylindrical portion 36 surrounds a medicament chamber 42 and is slidingly mounted on the proximal end 30 of the adapter 18 . fig2 a and 4 further show that the plunger 22 is formed with a tang 44 that extends distally and inwardly ( i . e . toward the needle axis 14 ) from the cylindrical portion 36 of the plunger 22 . cross - referencing fig2 a and 5 , it can be seen that the syringe 10 includes an elastomeric seal 46 that is attached onto the proximal end 30 ( best seen in fig2 a ) of the adapter 18 . as shown , the seal 46 has a generally fusiform shape or spindle - like shape and is formed with a through - hole 48 . when the open distal end 40 of the plunger 22 is slid over the proximal end 30 of the adapter 18 , the seal 46 compresses between the adapter 18 and the cylindrical portion 36 of the plunger 22 to establish sealed fluid communication between the medicament chamber 42 and the lumen of the needle 26 . with this arrangement , the plunger 22 can be retracted to draw fluid through the needle 26 and into the chamber 42 and , in addition , the plunger 22 can be depressed to expel fluid from the chamber 42 and out of the needle &# 39 ; s distal tip 28 . the structure of the guard 20 can be best appreciated with initial reference to fig2 a and 6a . as shown there , the guard 20 extends from an open proximal end 50 to an open distal end 52 and is formed with an axially aligned slot 54 for interaction with the tang 44 . specifically , as shown in fig2 a and 3a , an axially aligned slit 56 formed in the adapter 18 allows the tang 44 to pass through the adapter 18 and interact with the slot 54 in the guard 20 . as best seen with cross - reference to fig2 a and 6a , the guard slot 54 has a proximal end that is formed as an abutment 58 and a distal end that is formed as a ramp 60 . with this arrangement , the tang 44 engages the abutment 58 during a proximal movement of the plunger 22 to engage the plunger 22 with the guard 20 . on the other hand , during a distal movement of the plunger 22 , the ramp 60 directs the tang 44 out of the slot 54 and disengages the guard 20 and plunger 22 . as seen in fig2 a and 6b , the guard 20 is also formed with a living hinge 62 that extends radially outward when in a relaxed , undeflected state . fig6 a further shows that the guard 20 is formed with two alignment guides 64 a , b which each extend radially outward from the cylindrical portion of the guard 20 . these alignment guides 64 a , b travel within a pair of corresponding slots 66 ( see fig3 a ) in the adapter 18 and maintain the guide 20 azimuthally aligned within the adapter 18 . by cross - referencing fig2 a with fig3 b , it can be seen that the syringe 10 includes a mechanism to lock the guard 20 in a distal position covering the needle tip 28 prior to an injection procedure . specifically , once locked by the mechanism , the guard 20 can only be unlocked by a movement of the plunger 22 . specifically , as shown , the cylindrical adapter 18 is formed with a cam lever 68 having a distal lever end 70 and a cam surface 72 . comparing fig2 a with fig2 b , it can be seen that the cam lever 68 is deflectable by the cylindrical portion 36 of the plunger 22 from a relaxed position ( fig2 b ) to a biased position ( fig2 a ). in the relaxed position ( fig2 b ), the cam surface 72 extends radially outward from the remaining cylindrical section of the adapter 18 . on the other hand , as shown in fig2 a , in the biased ( i . e . deflected ) position , the lever end 70 extends radially inward from the remaining cylindrical section of the adapter 18 . when the plunger 22 is in the distal position shown in fig2 a , the cylindrical portion 36 of the plunger 22 contacts the cam surface 72 and deflects the cam lever 68 into the biased position . functionally , as shown in fig2 a , when the cam lever 68 is in the biased position , the lever end 70 engages the hinge 62 of the guard 20 and prevents a proximal movement of the guard 20 relative to the needle 26 . when the plunger 22 is retracted as shown in fig2 b , the cam lever 68 relaxes into its undeflected , outward position ( as shown in fig3 b ) and allows the guard 20 to move distally relative to the needle 26 . fig2 a shows that the distal end of the cylindrical syringe body 12 is formed with a flange 74 that extends radially inward relative to the cylindrical portion of the syringe body 12 . in addition , as shown in fig2 a , the adapter 18 is formed with a raised distal tab 76 and a raised proximal tab 78 that is formed with a ramp . as shown , the proximal tab 78 is axially spaced from the distal tab 76 to create a gap between the tabs 76 , 78 . typically , as shown in fig3 a and 3b , four sets of tabs 76 , 78 are uniformly distributed about the circumference of the adapter 18 . functionally , the tabs 76 , 78 releasably hold the flange 74 of the syringe body 12 in the gap when the syringe body 12 is in an operational position and releases the flange 74 for proximal movement relative to the adapter 18 into a locking position . in the operational position , as shown in fig2 a , the syringe body 12 does not interfere with relative movement between the guard 20 and adapter 18 . in the locking position , as shown in fig2 e , the flange 74 deflects the cam lever 68 and holds the cam lever 68 in a position where the guard 20 is locked . after an injection , the syringe body 12 can be moved proximally relative to both the plunger 22 and the adapter 18 and into the locking position shown in fig2 e . this then locks the guard 20 into position covering the needle tip 28 and prevents inadvertent reuse of the syringe 10 . cross referencing fig2 e with fig7 , it can be seen that the finger grip 16 of the syringe body 12 is formed with a recess 80 at the body &# 39 ; s proximal end . specifically , as best seen in fig2 e , the recess 80 is sized and positioned to receive the grip flange 24 that is formed at the proximal end 38 of the plunger 22 . functionally , the plunger 22 can be advanced distally after an injection until the grip flange 24 is positioned in the recess 80 . with the grip flange 24 positioned in the recess 80 , subsequent movement of the plunger 22 relative to the syringe body 12 is effectively prevented . the syringe 10 is typically delivered to the end user configured as shown in fig2 a . specifically , as fig2 a shows , the plunger 22 is initially located in a distal position relative to the adapter 18 with the tang 44 extending into the slot 54 to prevent distal movement of the guard 20 . in this configuration , it can be seen that the cylindrical portion 36 of the plunger 22 holds the cam lever 68 deflected inward to lock the guard 20 and prevent proximal movement of the guard 20 . as illustrated by fig2 b , use of the syringe 10 begins by withdrawing the plunger 22 proximally . fig2 b shows this proximal movement of the plunger 22 has several effects . for one , initial proximal movement of the plunger 22 allows the cam lever 68 to relax outwardly from the needle 26 and unlock the guard 20 for proximal movement relative to the needle 26 . additional proximal movement of the plunger 22 engages the tang 44 with the proximal abutment 58 , causing the guard 20 to move proximally with the plunger 22 . also , proximal movement of the plunger 22 draws air through the needle 26 and into the medicament chamber 42 . once the guard 20 has been retracted as shown in fig2 b , the next step is to insert the exposed distal needle tip 28 into a medicament vial ( illustrated by surface 82 in fig2 c ). at this point , the plunger 22 can be depressed as shown in fig2 c to expel air into the vial and void the medicament chamber 42 . comparing fig2 b with fig2 c , it can be seen that during advancement of the plunger 22 , the ramp 60 formed at the distal end of the slot 54 directs the tang 44 out of the slot 54 and disengages the guard 20 from the plunger 22 . thus , as illustrated by fig2 c , after depressing the plunger 22 , distal movement of the guard 20 is only prevented by the contact between the guard 20 and the surface 82 . next , the plunger 22 can be withdrawn to fill the chamber 42 with medicament ( note fig2 b is representative of the configuration of the syringe 10 after the chamber 42 is filled with medicament ). from fig2 b , it can be seen that during withdrawal of the plunger 22 , the tang 44 reenters the slot 54 and engages the proximal abutment 58 . the result is that the plunger 22 engages the guard 20 and prevents distal advancement of the guard 20 relative to the needle 26 . as illustrated by fig2 b , when the needle 26 is removed from the vial , the distal tip 28 of the needle 26 remains unguarded and exposed . the syringe 10 is now ready for an injection . as illustrated by fig2 c , to inject a medicament into a patient , the distal tip 28 of the needle 26 is inserted into the patient ( represented by surface 82 ) and the plunger 22 depressed . as shown in fig2 c , the distal advancement of the plunger 22 releases the guard 20 . specifically , during advancement of the plunger 22 , the ramp 60 directs the tang 44 out of the slot 54 and disengages the guard 20 from the plunger 22 . once released , the guard 20 is free to move distally under the influence of a coil spring 84 that is interposed between the guard 20 and adapter 18 . thus , as the needle 26 is withdrawn from the patient , the needle 26 retracts proximally into the guard 20 which remains in contact with the patient &# 39 ; s skin ( represented by surface 82 ). fig2 d shows the syringe 10 after the needle 26 has been withdrawn from the patient and the needle 26 has passively retracted into the guard 20 . comparing fig2 c with fig2 d , it can be seen that the hinge 62 deflects to advance distally past the cam lever 68 . comparing fig2 d with fig2 e , it can be seen that once the syringe 10 has been removed from the patient ( fig2 d ), the plunger 22 and adapter 18 can be advanced distally relative to the syringe body 12 to lock the guard 20 in place ( fig2 e ). fig2 e also shows that this places the grip flange 24 of the plunger 22 in the recess 80 formed in the syringe body 12 . functionally , once the syringe 10 is in the configuration shown in fig2 e , the plunger 22 is disabled and the guard 20 completely covers the hollow needle 26 to protect the user from unwanted needle sticks and prevents inadvertent reuse of the syringe 10 . while the particular devices and methods as herein shown and disclosed in detail are fully capable of obtaining the objects and providing the advantages herein before stated , it is to be understood that they are merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims .
a passively guarded , fillable injection syringe includes an adapter for holding the proximal end of a hollow needle . an inverted plunger is slidingly mounted on the adapter to establish a medicament chamber that is in fluid communication with the needle . also , a substantially cylindrical needle guard is positioned on the needle for reciprocal axial movement under the influence of a spring which biases the guard and adapter in opposite axial directions . a mechanism is provided such that plunger movements that are required in a typical fill and inject procedure also function to control the position of the guard relative to the needle . initially , the guard is locked covering the needle tip . a plunger movement unlocks the guard and retracts the guard for syringe filling and injection . depressing the plunger to complete the injection releases the guard for distal movement under the spring force into a needle protecting position .