Abstract:
A safety needle cannula module in interchangeable combination with a safety syringe and plunger module, wherein the safety needle cannula module is formed with one of a variety of needle cannula sizes and wherein said safety syringe may be one of a variety of syringe sizes. The safety needle cannula module with needle cannula of desired size is attached to a safety syringe module wherein said safety syringe is a desired size. After medication is injected into a body with the safety needle cannula and the safety syringe, the safety syringe module reacts with the safety needle cannula module and further causes said safety needle cannula to be automatically retracted and disposed within the hollow plunger said safety syringe module.

Description:
This application is a divisional of U.S. patent application Ser. No. 09/453,393 filed on Dec. 3, 1999 now U.S. Pat. No. 6,099,500. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a single-use syringe for injecting medicine into a patient More particularly, the invention relates to a safety syringe having a retractable needle cannula that renders the needle cannula harmless after it is used. 
     2. Background of the Related Art 
     Many communicable diseases can be spread through the penetration or scratching of the skin by a needle that was previously used by another having the disease. Spreading of the disease in this manner may occur by accident, such as with medical personnel making injections, or it may occur through misuse, such as by intravenous drug users using a previously used needle cannula. 
     Various syringes have been invented, designed and developed to retract the needle into the syringe or the plunger inside of the syringe. Some of these devices are U.S. Pat. No. 4,973,316 (Dysarz), U.S. Pat. No. 4,978,343 (Dysarz), U.S. Pat. No. 5,180,369 (Dysarz), U.S. Pat. No. 5,267,961 (Shaw), U.S. Pat. No. 5,019,044 (Tsao), U.S. Pat. No. 5,084,018 (Tsao), U.S. Pat. No. 5,385,551 (Shaw), U.S. Pat. No. 5,389,076 (Shaw), and U.S. Pat. No. 5,201,710 (Caselli). These designs have needles which retract at the end of the injection. Most of these designs have not reached the market due, at least in part, to problems associated with the expense of manufacturing, poor reliability or user acceptability. However, even though some of these designs operate poorly or are costly, they have still been commercialized due to the great need in hospitals or clinics for any type of safety syringe. 
     Most of the existing safety syringe designs allow for automatic retraction of the needle cannula into the plunger barrel of the syringe when the plunger is fully extended into the syringe. The automatic retraction is triggered when the plunger makes physical contact with the distal end of the syringe barrel. Typically, the end of the plunger is provided with a disengageable or sacrificial member at the distal end and the needle cannula is secured by a disengageable or sacrificial member. When the plunger reaches the fully extended position, the physical contact between the plunger and the needle cannula causes activation of the two respective disengageable or sacrificial members. In this manner, the end of the plunger barrel is opened and presented to receive the needle cannula. The needle cannula, no longer secured in position, is biased into the plunger barrel by a spring. 
     Conventional syringes are typically available in modular systems or kits in which approximately ten different sizes of syringes and approximately ten different sizes of needle cannulas can be used interchangeably. This allows an inventory of twenty items to be used in approximately 100 different combinations in accordance with the present need. However, the safety syringes presently available and described in the above patents are not modular and require stocking of an integral safety syringes for each combination of syringe size and needle cannula size desired, for example 100 different safety syringes. Particularly, in light of the greater cost of these syringes, the cost, distribution and storage of safety syringes is much greater than conventional syringes. 
     Despite the prevalence of modular conventional syringes, the emergence of a multitude of safety syringe designs and the increasing public outcry for safety syringes, the complexities of the safety syringe mechanisms have limited the number of attempts to design a safety syringe that is modular. Two such attempts include modular syringe tip designs that are combined with a conventional syringe as described in U.S. Pat. No. 5,891,093 (Dysarz) and U.S. Pat. No. 5,935,113 (Dysarz). Compared with the foregoing automatically retracting safety syringes, these two designs can be considered to have safety needle cannula assemblies that are self-contained and manually operated, while being connectable to a conventional syringe with a conventional locking arrangement While these devices serve the aforementioned need for modularity, the obvious drawbacks to the devices include the manual retraction mechanism and the additional length that the needle cannula assembly adds to the syringe. 
     Therefore, there remains a need for a modular safety syringe system or kit that provides a selection of syringe modules having various sizes and a selection of needle cannula modules having various sizes that can be combined on site to form an automatically retractable safety syringe of a desired configuration It would be desirable if the automatically retractable safety syringe had similar length and usability as a conventional syringe. It would be further desirable if the used automatically retractable safety syringe was compact and secure against accidental needle sticks. 
     SUMMARY OF THE INVENTION 
     The invention provides a kit of components for assembling modular safety syringes. The kit comprises two or more safety syringe modules having different diameters and two or more safety needle cannula modules. Each safety syringe module has a syringe barrel; a safety plunger extending through a proximal end of the syringe barrel, wherein the safety plunger having a plunger barrel, a sliding gasket formed along the perimeter of the plunger barrel near the distal end for sealing the plunger against the interior sidewalls of the syringe barrel, a sealing member covering an opening in the distal end of the plunger barrel, and a rigid member adjacent the sealing member, and a connector formed in the distal end of the syringe barrel. Each of the two or more safety needle cannula modules have a housing having a connector formed at a proximal end of the housing and a cannula passage formed through a distal end of the housing; a needle cannula extending through the cannula passage; a slidable piston flange coupled to the needle cannula; a retaining member securing the slidable piston flange in the proximal end of the housing, and a spring disposed within the housing to bias the slidable piston flange in the direction of the plunger opening from the distal end towards the proximal end. The connectors in the two or more safety syringe modules are sealably securable to the connectors in the two or more safety needle cannula modules. Accordingly, securing any one of the two or more safety needle cannula modules to any one of the two or more safety syringe modules provides alignment of the rigid member of the plunger with the retaining member of the safety needle cannula module and alignment of the slideable piston flange with the sealing member of the plunger. 
     Preferably, the rigid member of the plunger is an end ridge, possibly sloped. The retaining element is selected from a shear plate, break plate, a friction ring, a sacrificial membrane, or a snapon ring. Where the retaining element is a shear plate or a break plate, it may optionally include first and second concentric notches formed therein, preferably such that the rigid member is aligned to contact the retaining element between the first and second concentric notches. Similarly, the sealing member is selected from a break plate, a friction plug, a sacrificial membrane, a snapon plug. The connectors are selected from threads, luer-loks, or snap-on fittings. 
     Another aspect of the invention provides an improvement to a medical device having an elongate hollow body; a movable hollow member slidable axially in the body; a retraction mechanism including a needle extending from the body for injecting or collecting fluid, a needle holding member having an unretracted position, a spring for applying retraction force to the needle holding member in a retraction direction, and a retaining element capable of holding the needle holding member against the retraction force provided by the spring; and a cap releasably sealing a passage in the end of the movable hollow member that is positioned within the body; the retaining element being triggered to retaining the needle holding member for retraction of the needle in response to selective movement of the movable member, and the cap being retainingd from the passage of the movable hollow member in response to the selective movement of the movable member. The improvement comprises a sloping end ridge formed on the end of the movable hollow member to contact the retaining element upon selective movement of the movable member. For example, the retaining element may be selected from a break plate, a friction ring, a sacrificial membrane, or an interference fit and may be triggered by failing, sliding, or disengaging. Particularly, the retaining element or cap may be sloped along with the sloping end ridge. 
     Yet another aspect of the invention provides an improvement to a medical device having an elongate hollow body; a movable hollow member slidable axially in the body; a retraction mechanism including a needle extending from the body for injecting or collecting fluid, a needle holding member having an unretracted position, a spring for applying retraction force to the needle holding member in a retraction direction, and a retaining element capable of holding the needle holding member against the retraction force provided by the spring; and a cap releasably sealing a passage in the end of the movable hollow member that is positioned within the body; the retaining element being triggered to release the needle holding member for retraction of the needle in response to selective movement of the movable member, and the cap being released from the passage of the movable hollow member in response to the selective movement of the movable member. The improvement comprises a spring shield coupled to the needle holding member and extending around the spring, wherein the spring is disposed concentrically around the needle. Preferably, the spring shield is a tube disposed concentrically around the spring, where the spring shield has an outer diameter that is less that an internal diameter of the passage in the movable hollow member. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the above recited features and advantages of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
     FIG. 1 is an elevation view of the safety needle cannula module and the safety syringe and plunger module. 
     FIG. 2 is an elevation view of the safety needle cannula module fixed to the safety syringe and plunger module. 
     FIG. 3 is a section elevation of the safety needle cannula module shown fixed to the safety syringe module. 
     FIG. 3A is a section elevation of two safety syringes having different syringe barrel diameters. 
     FIG. 3B is an enlarged section elevation of the needle cannula module. 
     FIG. 3C is an enlarged section elevation of the first end of the plunger module. 
     FIG. 3D is an enlarged section elevation of the threaded connection between the safety needle cannula module and the syringe module. 
     FIG. 4 is a section view of the safety needle cannula module and the safety syringe module as taken through FIG.  3 . 
     FIG. 5 is a section view of the safety syringe module and a plan view of the safety plunger module within the safety syringe module. 
     FIG. 6 is a section elevation of the safety plunger module moving toward the safety needle cannula module. 
     FIG. 7 is a section elevation of the first end of the safety plunger module touching the safety needle cannula module. 
     FIG. 8 is a section elevation of the safety needle cannula module point loading the first end of the plunger module. 
     FIG. 9 is a section elevation of the slideable piston and needle cannula thrusting into the plunger module. 
     FIG. 10 is a section elevation of the safety needle cannula and the slideable piston inside of the safety plunger module. 
     FIG. 11 is a section elevation of the safety needle of the second preferred embodiment. 
     FIG. 12 is a section elevation of the first end of the plunger module with a slope. 
     FIG. 13 is a section elevation of the sloping first end of the plunger module point loading the slideable piston barrier. 
     FIG. 14 is a section elevation of the needle and base plate thrusting into the plunger module. 
     FIG. 15 is a section elevation of the needle, the spring shield and the base plate inside of the plunger. 
     FIG. 16 is a plan view of the notches on the shear plate and concentrated load plate. 
     FIG. 17 is a plan view of the notches on the shear plate and concentrated load plate. 
     FIG. 18 is a plan view of the notches on the shear plate and concentrated load plate. 
     FIG. 19 is a plan view of the notches on the shear plate and concentrated load plate. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a modular safety syringe system or kit that provides a selection of safety syringe modules having various sizes and a selection of needle cannula modules having various sizes that can be combined on site to form an automatically retractable safety syringe of a desired configuration. In addition to requiring a common interface between the safety syringe module and needle cannula module, as with conventional modular systems, the present invention also requires and facilitates a specific cooperative relationship between the syringe plunger module and the needle cannula module. 
     Each safety syringe module of the present invention includes a syringe barrel, a safety plunger extending through a proximal end of the syringe barrel, and a connector formed in the distal end of the syringe barrel. A syringe barrel may be of any length and diameter, as dictated by the volume of fluid to be delivered through the syringe, and will include a connector have a fixed diameter. In systems sets or kits having a pity of syringes with different diameters, each syringe should have a connector with a common diameter and a common connection type. For example, three syringe barrels may be provided with diameters of 2, 2.5 and 3 centimeters, respectively, but each of the three syringe barrels should have a connector of the same type, such as threads, and of the same diameter, such as 1.5 centimeters. It should be recognized that in sets having syringes with wide variations in syringe barrel diameter, the set may include a first subset of syringes having a first common connector with a first common diameter and a second subset of syringes having a second common connector with a second common diameter. The present invention contemplates any number of subsets, each subset having the same or different type of connector, and each subset having the same or different connector diameter. It should be recognized that the term “diameter” as used herein shall not be limited to the dimensions of a circular opening, but shall include the dimensions of any shape of opening, for example shapes like squares, triangles, ovals, and rectangles. 
     The safety plungers of the present invention have suitable lengths and diameters to work in a cooperative relationship inside the syringe barrels. It is anticipated that each syringe of a different diameter will have a corresponding safety plunger of suitable size. The safety plunger has a plunger barrel, a sliding gasket formed along the perimeter of the plunger barrel near the distal end for sealing the plunger against the interior sidewalls of the syringe barrel, and a removable member sealing a central opening in the distal end of the plunger barrel. The safety plunger will also include a lip or similar structure that engages a critical portion of the needle cannula module as described below. 
     The safety needle module has a connector that is designed to be coupled to the connector on the safety syringe module. These connectors may be of various types, including but not limited to male/female threads, snapon, and luer-lok tips. In systems, sets or kits having a plurality of safety needle modules with different cannula diameters, gauges, types or lengths, each safety needle module should have a connector with a common diameter and a common connection type. For example, three safety needle modules may be provided with, but not limited to, 16G, 20G and 30G cannulas, respectively, but each of the three modules should have a connector of the same type, such as male threads, and of the same diameter, such as 1.5 centimeters. Furthermore, it should be recognized that the safety needle modules will preferably all have the same type of connector, such as male threads or the male portion of a luer-lok, and the safety syringe modules will preferably all have the same type of connector that mates with the needle module connector, such as female threads of the female portion of a luer-lok. In the case where there are subsets of syringes having connectors with different diameters, then there will also be subsets of safety needle modules having connectors with the same mating diameters. 
     The safety needle module includes a housing having the connector at the proximal end and a cannula passage through the distal end A needle cannula coupled to a slidable piston flange extends through the cannula passage. The slidable piston flange is secured to the housing by a disengageable, sacrificial or retaining member. A spring is disposed within the housing to bias the slidable piston flange, and consequently the needle cannula, away from the distal end towards the proximal end. The spring surrounds the needle cannula and is maintained in a biased or spring loaded condition between the distal end of the housing and the slidable piston flange. It is important that the spring provide sufficient force to move the needle cannula into the plunger barrel upon release, but the spring should not be so strong as to fatigue or cause failure to the disengageable or sacrificial member that secures the slidable piston flange to the housing. 
     It should be recognized that the disengageable or sacrificial members in the safety plunger and in the safety needle module may take many forms, including plates that can fail, break or shatter as described in U.S. Pat. No. 5,180,369 (Dysarz) incorporated by reference herein, frictionally engaged retaining rings and plugs as described in U.S. Pat No. 5,285,551 incorporated by reference herein, sacrificial membranes, interference fits, and the like. 
     It is a critical aspect of the invention that a rigid component of the safety plunger is disposed at an appropriate position to engage and actuate the retaining member in the safety needle module and that a rigid component of the safety needle module is disposed at an appropriate position to engage and actuate the sealing member in the safety plunger. Since syringes typically have cylindrical barrels, although they could just as well have any shaped cross-section, the positions of the two rigid components, the sealing member and the retaining member can be described in terms of concentric members having a specific radial distance from the axial centerline of the needle cannula. While two of the concentric members are in the safety plunger and the other two concentric members are in the needle module, the members must achieve a standard, fixed or consistent cooperative relationship when assembled and, consequently, must have standard radii or other dimension and threads specified for each of the two rigid components, the sealing member and the retaining member. For any given set or subset of safety syringe modules and safety needle modules, these radii must be the same regardless of the syringe diameter or the cannula gauge. In other words, the size and alignment of the members accounting for the automatic retraction must be consistent in order for the retraction to occur. 
     Consistent alignment of the members, including alignment of a rigid plunger member with the needle retaining member and alignment of the rigid safety needle member with the plunger sealing member, can be achieved either by (a) using a constant plunger barrel diameter regardless of syringe diameter, or (b) using plunger barrels having a diameter just smaller than the syringe barrel, but having a diameter at the distal end that is reduced, or perhaps even increased, to form or achieve the fixed radii of the rigid plunger component The former option is less desirable, because the plunger barrel could wobble from side to side and the gasket member would not receive as much physical support. 
     Now referring to the Figures, FIG. 1 is an elevation view of the system or kit of the present invention. The system includes a separate safety syringe module and a safety needle cannula module. The safety syringe module includes a safety plunger  1  and a syringe module  2 . A syringe connector  6  is shown formed in the distal end of the syringe barrel  2 , preferably forming a set of female threads. Finger tabs  4  are shown at the proximal end of the syringe barrel  2 . The syringe barrel  2  is a hollow elongated barrel with an inside surface and an outside surface. The safety plunger  1  is also an elongated barrel with an inside surface and an outside surface. The safety plunger is shown disposed within the syringe barrel  2  with a thumb flat  5  shown at the proximal end of the safety plunger. 
     The safety needle cannula module  3  is shown with a needle cannula  8  extending from the distal end of a housing  46  having male threads that are attachable to the female threads formed on the syringe connector  6  of the syringe barrel  2 . A needle protector cap  7  is shown removeably fixed to the distal end of the safety needle cannula module  3  to prevent any contamination to the needle cannula  8  and to further protect the needle cannula point  10 . Gripping members or wings  11  are also shown formed on the exterior of the safety needle cannula module  3  to allow for ease of gripping the safety needle cannula module  3  while threading the safety needle cannula module  3  to the syringe connector  6  of the safety syringe module. 
     FIG. 2 is an elevation view of the safety needle cannula module  3  suitably attached to the safety syringe module  12  via a treaded connection. The needle protector  7  that was protecting the needle cannula  8  in FIG. 1 has been removed and the assembled device consisting of the two modules  3 ,  12  is ready to be used. 
     FIG. 3 is a section elevation of the device, as taken through FIG.  2 . The safety plunger  1  is shown formed into a frustoconical surface or other tapered surface  15  at the distal end and a sliding gasket  13  is shown having syringe sealing surfaces. The plunger sealing member  14  is shown in this embodiment as a push in barrier borne on the distal end of the cone  15 , where the cone  15  has a diameter matching up with a retaining member  23 , shown in this embodiment as a point load plate. The sealing member  14  has sufficient strength to stand typical hydraulic pressures that can be exerted on it while the plunger is thrusting medicament into a body, however, the sealing member will fail or disengage and be pushed into the plunger cavity  17  whenever the force applied on the thumb flat is provided as a concentrated load applied to the sealing member. In the embodiment where the sealing member is a push in barrier, it is preferable that a point load or an eccentric load is applied to the barrier. 
     The term “concentrated load”, as used herein, means a load or force that is directed at a specific member or portion of a member, as opposed to a load of similar magnitude that is spread out over a large surface area For example, when a syringe has been filled with medicine, the advancing plunger applies a load to the fluid in the syringe that pushes against all surfaces exposed to the fluid. By contrast, when all the medicine has been dispensed, the rigid member of the advancing plunger makes contact with a portion of the retaining member such that the entire amount of force applied to the thumb flat is directed against that portion of the retaining member. It is this latter load that is refered to as a “concentrated load.” 
     The housing  46  has a threaded connector  9  formed on the proximal end of the needle cannula module  3  and the connector  9  is shown suitably meshed and fixed to the female threads  18  formed on the syringe connector  6 , shown in this embodiment as an extended collar. The connection formed between the threads of the two modules should be a fluid (gas and liquid) tight connection. A needle passage  19  is shown formed in the distal end of the safety needle cannula module  3  that allows the needle cannula  8  to retract into the inside of the safety plunger  1  without oscillating transversably. 
     The needle cannula  8  is shown suitably fixed to a slideable piston  20  by adhesive or friction or some other means by design choice. The distal end of the slideable piston  20  is near the cannula flat  21 . A slideable piston flange  22  is formed near the proximal end of the slideable piston  20 . A retaining member  23 , shown in this embodiment as a point load plate, secures the proximal end of the slideable piston  20  to the housing  46 . A biased spring  24  is compressed between the cannula flat  21  and the slideable piston flange  22  in order to bias the slideable piston flange, and consequently the needle cannula, toward the plunger barrel. 
     The point load plate  23  is shown formed on the slideable piston flange  22  and extends near the inside surface of the housing  46  of the safety needle cannula module  3 . The point load plate  23  is suitably fixed to the inside surface of the safety needle cannula module by adhesive, plastic, welding, friction, snapon or some other suitable means by design choice. 
     FIG. 3A is a section elevation of two safety syringe modules  12 ,  12 ′ as might be provided as part of a kit of components for on site assembling of automatically retractable safety syringes. The two safety syringe modules  12 ,  12 ′ have syringe barrels  2 ,  2 ′ with different diameters for drawing and injecting different quantities of fluid. Despite the different syringe barrel diameters, each safety syringe module  12 ,  12 ′ is coupled through the same type (here, common pitch and style threads) and same size (here, diameter x and length) of connectors to a safety needle cannula module  3 . The diameters of the safety plungers  1 ,  1 ′ and the gaskets  13 ,  13 ′ are dictated by the different diameters of the syringe barrels  2 ,  2 ′. However, according to the present invention, even though the plunger diameter changes with the syringe diameter, the safety plunger  1  must maintain a rigid component or end ridge  30  at a fixed radial distance y from the axial centerline of the syringe to be in alignment with the retaining member  23  of the safety needle cannula module  3 . Similarly, the slideable piston flange of the needle cannula module  3  must be maintained in alignment with the sealing member of the plunger  1 . 
     FIG. 3B is an enlarged section elevation as taken from FIG. 3 showing more clearly the safety needle cannula module  3 . The safety needle cannula module  3  has a connector  39  suitably fixed or assembled to the syringe connector  6  formed on the distal end of the syringe barrel  2 , shown here as male threads  39  on the connector  9  mating with female threads  18  formed on the syringe barrel  2 . The biased spring  24  is shown compressed between the slideable piston flange  22  and the cannula flat  21 . The needle cannula  8  is shown suitably secured to the slideable piston  20 . The proximal end of the needle cannula  8  is shown with a cannula flange  25 . The slideable piston flange  22  is formed on the proximal end of the slideable piston  20 , allowing the biased spring  24  to thrust against the slideable piston flange  22 . 
     In one preferred embodiment, the slideable piston flange  22  is held, secured or fixed to a point load plate  23 . The point load plate  23  is preferably provided with a first break away notch  31  and a second breakaway notch  34  formed in the proximal side of the point load plate  23 . The breakaway notches could be formed on the distal side of the point load plate  23  or the proximal side of the point load plate  23  by design choice. The point load plate  23  is designed to fail when a point load is applied or when a concentrated load is applied to the necessary location. It should be recognized that the failure mode of the point load plate may include breaking, shattering, tearing or otherwise releasing the slideable piston flange. Most preferably, the point load plate  23  is suitably fixed to the inside surface of the safety needle cannula module  3  with a snap on fluid and gas tight connection, although it should be recognized that adhesives or other means could be utilized to secure applied by design choice. 
     FIG. 3C is an enlarged section elevation of the push in barrier  14  secured to the end ridge  30  at the first end of the rigid plunger member or cone  15 . While the barrier is shown attached at the distal-most surface of the end ridge, it should be recognized that the barrier may be attached to an inner surface of the end ridge  30 , the cone  15  or another surface of the plunger. Further, while it is preferred that the end ridge  30  or a portion of the barrier  14  extend distally from the end of the sliding gasket, it is anticipated that the gasket could be made compressible so that the “end ridge” is normally recessed but, upon compression of the gasket, presents itself to contact the retaining member. 
     The sliding gasket  13  is shown attached to the plunger, preferably along the outer surface of the cone  15 . The push in barrier  14  is shown with a break off notch  32  that is circunferential in this particular figure, however, break off notches could be included in any number, pattern or dimension Specifically, the break off notch  32  could bisect the push in barrier  14  in various directions by design choice. The push in barrier  14  should be strong enough to withstand any hydraulic pressure applied to its distal (medicament exposed) side, but should be unable to withstand any point loading, concentrated load or eccentric load directed on the barrier without breaking away from the end ridge  30 . Where any unequally applied load is generated on the push in barrier  14 , the push in barrier will break off at or near the break of notch  32 . Again, it should be recognized that the failure mode of the push in barrier may include breaking, shattering, tearing or otherwise rendering access to the plunger cavity  17 . 
     FIG. 3D is an enlarged section elevation of the snap on connection as taken through FIG.  3 B. The point load plate  23  is shown with a snap on channel  27  formed at the outer circumference of the plate. A snap on rib  28  is shown formed on the inside circumference essentially near the proximal end of the safety needle cannula module  3 . A backing ridge  29  is shown as another means of securing the point load plate  23  in position. Part of the syringe connector  6  and syringe barrel  2  are shown for reference. 
     FIG. 4 is a section plan view as taken through FIG.  3 . The syringe barrel wall  2  is shown at the outer periphery and the outside diameter of the syringe connector  6  is shown as a hidden (dashed) line. The inside diameter of the syringe extension  6  is shown as a solid line for reference purposes. The first break away notch  31  and the second break away notch  34  are part of the point load plate  23  and are shown around the cannula flange  25 . The cannula  33  is shown at near the cannula flange  25 . 
     FIG. 5 is another section elevation as taken through FIG.  3 . Here, the break off notch  32  is shown on the inside and the outer periphery of the push in barrier is shown around the break off notch  32 . The sliding gasket  13  is shown rubbing on the inside surface of the syringe barrel  2 . 
     FIG. 6 is another enlarged section elevation of the safety plunger  1  in the proximity of, and being moved toward, the safety needle cannula module  3 . As shown, the safety plunger  1  is moving in a closing direction  35  toward the distal end of the syringe barrel. The rigid component or end ridge  30  is moving toward the point load plate  23  between the connector  9  and the slideable piston flange  22 . The push in barrier  14  is also moving into the slideable piston flange  22  and the cannula flange  25 . The exposed side of the cannula flange  25  could be flush with the piston flange  22  by design choice. A centerline  38  is shown for reference purposes. 
     FIG. 7 is a section elevation of the distal side of the push in barrier  14  thrusting into the proximal side of the cannula flange  25  while continuing to move in a closing direction  35 . If the cannula flange  25  were flush with the slideable piston flange  22 , the distal side of the push in barrier  14  would first come into contact with the proximal side of the slideable piston flange. In either case, the result is substantially the same. 
     FIG. 8 is a section elevation view of the break away ring  36  being disengaged from the point load plate  23 . The breakaway ring  36  is defined by the first break away notch  31  and the second breakaway notch  34  formed in the point load plate  23 . As the end ridge  30  is thrust into the point load plate  23 , the plate is supported on the outside periphery by the snap on rib  28  and the backing ridge  29  thereby not allowing any deflection along the outside periphery of the point load plate  23 . The point load plate  23  is also supported near the center of the point load plate by the slideable piston flange  22 . The slideable piston flange  22  is supported by the slideable piston  20  which, in turn, bas a distal end supported by the cannula flat  21  to prevent any deflection between the slideable piston flange  22  and the point load plate  23 . Because of this support and the load applied by the end ridge, the point load plate fails at the first break away notch  31  and the second break away notch  34 , thereby forming the break away ring  36  which is thrust into the safety needle cannula module chamber  37 . As the break away ring  36  is thrust into the safety needle cannula module chamber  37 , the slideable piston flange  22  and the slideable piston  20  are thrusting into the push in barrier with a point load or a concentrated load thus causing break off notch  32  formed in the push in barrier  14  to fail and allowing the push in barrier to be thrust in an inward direction  68  into the inside of the safety plunger  1 . 
     FIG. 9 is a section elevation view of the slideable piston flange  23 , and the slideable piston  20  being thrust in an inward or proximal direction  68  into the inside of the safety plunger module  1  by the biased spring  24  having a distal end that is thrusting on the cannula flat  21  and a proximal end thrusting on the slideable piston flange  22 . 
     FIG. 10 is a section elevation view of the needle cannula  8  and slideable piston  20  having been retracted inside of the safety plunger  1 . The biased spring  24  is now an relaxed, elongated spring  24 . Optionally, the spring may be either loose or suitably fixed at the distal end to the cannula flat  21 . The push in barrier  14  is shown as being separated from the end of the plunger and being inside the safety plunger  1 , but it is anticipated that the barrier may remain partially attached to the end ridge. 
     FIG. 11 is a section elevation of the safety syringe  40  of a second preferred embodiment. There are two variations or differences between the safety syringe  40  of the second preferred embodiment and the safety syringe  12  of the first preferred embodiment These variations include a sloping end ridge  41 , a spring shield  42 , and the elimination of the slideable piston. 
     The spring shield  42  is seen protecting the coiled biased spring  47  from catching anything that might impede the spring&#39;s ability to thrust the needle cannula shaft  44  all the way into the elongated hollow plunger  45 . The spring shield  42  is contained in the safety cannula housing  46  with the distal end of the needle cannula shaft  44  extending out from the distal end of the safety cannula housing  46 . A coiled, biased spring  47  is coiled about the needle cannula shaft  44 . The proximal end of the coiled biased spyringe  47  pushes against the base plate  48  and the distal end of the coiled biased spring  47  pushes against the cannula flat  49 . The syringe barrel  50  is shown as an elongated hollow barrel with an outside surface and an inside surface. The outside surface of the elongated hollow plunger  45  has an outer surface that is only slightly smaller than the inside surface of the syringe  50 . 
     FIG. 12 is an enlarged section elevation of the safety cannula housing  46 . The needle cannula shaft  44  has a distal end terminating in a point, a proximal end and a cannula  52  formed on the inside of the needle cannula shaft  44 . The needle cannula shaft  44  is shown with the distal end extending past the distal end of the safety cannula container  46 , through the needle passage  53 , through the coiled biased spring  47  wherein the proximal end of the needle cannula shaft  44  is suitably fixed to the base plate  48 . The needle cannula shaft  44  may be fixed to the base plate  48  by adhesive, welding, friction or any other suitable means by design choice. The coiled biased spring  47  has a distal end biased against the needle flat  49  and a proximal end biased against the distal side of the base plate  48 . The coiled biased spring  47  is contained by the needle cannula shaft  44  on the inside circumference of the coiled biased spring  47  and by the inside surface of the spring shield  42 . The spring shield  42  is shown with the first end near or touching the needle flat  49 . The proximal end of the spring shield  42  is shown fixed to the distal side of the base plate  48 . The spring shield  42  is shown with the distal end near or touching the needle flat  49  to prevent any deflection or bending of the spring  47  or the needle cannula shaft  44 . The needle flange  54  is shown suitably fixed to the proximal side of the base plate  48 . The retaining member or shear plate  55  is shown with a first notch  56  and a second notch  57  wherein the shear plate  55  will withstand the maximum amount of hydraulic or pneumatic pressure that the syringe is designed to produce. However, when a point load or a concentrated load is applied to the shear plate  55  at a particular point, the shear plate  55  will fail at the first notch  56  and the second notch  57  or at another location on the shear plate  55 . 
     The shear plate  55  is suitably secured to the base plate  48  on the inside with adhesive or some other suitable means, preferably forming a fluid tight barrier therebetween. The outside perimeter of the shear plate  55  is shown suitably fixed to the inside of the safety cannula housing  46  by adhesive or other suitable means, preferably forming a fluid tight barrier. 
     The safety cannula housing  46  is shown suitably fixed to the syringe connector  58  that is formed at the distal end of the syringe  50 , preferably including threads  59  but optionally including any type connector. 
     The sloping end ridge  41  is shown near the shear plate  55 . As the elongated hollow plunger  45  is pushed toward the needle cannula shaft  44  in a shear plate direction  60 , the concentrated load plate  61  is shown with a slope  62  relative to the centerline  38 . This slope  62  allows the sloping end ridge  41  to impact the shear plate  55  at only one point thereby exerting a point load on a small area, thereby initiating failure of the shear plate  55  and starting a progressive tearing process on the shear plate  55 . The concentrated load plate  61  is thrust into a corner on the proximal side of the base plate  48  thereby exerting a concentrated load on the concentrated load plate  61 , which load is in excess of the load that any hydraulic fluid would have applied during the operation of the safety syringe. In this manner, the concentrated load plate  61  will shear in one area and progressively tear away the entire outer periphery of the concentrated load plate  61  as the plunger  45  is thrust further toward the shear plate  55 . 
     Where the concentrated load plate or other sealing member  61  is sloped, an optional spacer  70  may be used, preferably attached to the face of the member  61 , to reduce or eliminate space in the syringe that will trap fluid therein. The spacer  70  is preferably made from a soft and easily compressible material to allow the 
     FIG. 13 is an enlarged section elevation of the sloping end ridge  41  thrusting into the shear plate  55  in a shear plate direction  60 . The break off ring  63  is now broken away from the shear plate  55 . The corner of the base plate  48  is being pushed against by the concentrated load plate  61 , causing the concentrated load plate  61  to progressively fail, tear or shear off of the sloping end ridge  41 . The concentrated load plate  61  is shown moving in an inward direction  68 . Because the end ridge does not protrude from the end of the plunger past the plunger gasket, the plunger gasket is shown as being somewhat compressed. 
     FIG. 14 is an enlarged section elevation of the needle cannula shaft  44  surrounded by the coiled biased spring  47  (in the process of unbiasing) and the spring shield  42  rusting past the remainder of the shear plate  61  as the needle is thrusted into the elongated hollow plunger  45  in an inward direction  68 . 
     FIG. 15 is a section elevation of the safety syringe  40  with the needle cannula shaft  44  safely in the elongated hollow plunger  45 . The coiled spring  15  now unbiased is holding the needle cannula shaft  44  and the base plate  48  in the elongated hollow plunger  45 . The needle cannula shaft  44  is now unable to come back out of the needle tunnel  53  to injure others or to be reused. There are other means of holding the elongated hollow plunger  45  inside of the syringe  50 . 
     FIGS. 16,  17 ,  18  and  19  show various notch configurations suitable for use on either the shear plate  55  or the concentrated load plate  61 . FIG. 16 has the notches forming concentric circles  64 . FIG. 17 has radial notches  65 . FIG. 18 has spiral notch(es)  66 . FIG. 19 has star notches  67 . There could be an infinite number of notch configurations by design choice. 
     Although the syringes and syringe systems described in detail above have been found to be most satisfactory and preferred, many variations are possible. For example the point load plate may not have notches in the first or second side, the point load plate may be square or rectangular, the concentrated load plate may be of various thicknesses or the safety needle cannula module may be axially offset. 
     Although the invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art, that additions, modifications, subtractions, deletions and other changes not specifically described, may be made in the embodiment herein It should be understood that the details herein are to be interpreted as illustrations and are not in a limiting sense.