Patent Publication Number: US-2011071469-A1

Title: Single Use Retractable Infusion or Transfusion Needle

Description:
FIELD OF INVENTION 
     This invention relates to retractable needles and more particularly to single use retractable infusion or transfusion needles. However, the invention is not limited to infusion or transfusion needles 
     BACKGROUND 
     Needle stick injuries are a serious health risk for health professionals. Single use retractable infusion or transfusion needles are known. These tend to require manual extraction of the needle from the patient. 
     U.S. Pat. No. 5,573,512 to van den Haak discloses a retractable infusion or transfusion needle assembly having a needle sub assembly sliceable within housing. The needle sub assembly is manually withdrawn from a patient into the housing or sheath. The user must grasp the housing and manually withdraw the cannula from the patient and into the housing whilst holding the housing against the patient&#39;s skin and preventing its movement. Whilst the needle sub assembly is locked in position once withdrawn and cannot be re-extended, if the user slips the entire assembly may be withdrawn, with the cannula point exposed and subsequent risk of needle stick injury. Further, it is possible for the user to easily twist or otherwise disturb the orientation of the cannula in the patient&#39;s vein during this extraction process, with subsequent risk of injury to the patient. 
     Auto-retracting needles have been proposed. However they suffer from constructions that allow auto-retraction to easily occur accidentally, particularly as a needle is being prepared for insertion or during insertion. If auto retraction accidentally occurs the needle and any other equipment attached to the needle, such as a whole blood collection bag, must be thrown away and a new assembly used. 
     SUMMARY OF THE INVENTION 
     To overcome at least some of the disadvantages of the prior art the present invention provides a single use retractable infusion or transfusion needle that enables a user to simultaneously withdraw a needle from a patient and into a housing without needing to manually withdraw the cannula for the patient but in which accidental auto-retraction is prevented or substantially reduced. 
     In one broad form the invention provides a needle assembly including:
         an elongate housing having a first aperture in a front end portion thereof and a second aperture in a rear end portion thereof;   an elongate hollow needle sub assembly slideably mounted within the elongate housing and having a needle point at a first end portion thereof and a second end portion adapted to be connected to a supply tube;   the needle sub assembly movable relative to the housing between an extended position, wherein the first end portion extends out of the housing through the first aperture and the needle point is located outside of the housing and a retracted position wherein the first end portion and the needle point is located and shielded within the housing;   biasing means biasing the needle sub assembly to the retracted position;   holding means having an operative position that, when the needle sub assembly is in the extended position, holds the needle sub assembly in the extended position against the action of the biasing means and prevents movement the needle sub assembly toward the retracted position;   release means movable to a release position for releasing the holding means from the operative position to allow movement from the extended to the retracted position;   locking means for locking the needle sub assembly when in the retracted position and preventing movement of the needle sub assembly toward the extended position to expose the needle point, and   means for preventing accidental activation of one or both of the release means or the holding means.       

     In one form the means for preventing accidental activation of the release means comprises blocking means that prevents movement of the release means toward the release position. 
     In another form the means for preventing accidental activation of the release means may comprise the release means itself and the release means may comprise a plurality of release members that must all be moved to a release position to release the holding means; when less than all of the plurality of release members are in the release position the holding means is not released. 
     In another form the means for preventing accidental activation of the release means may include both the blocking means and multiple release members. 
     In another broad form the invention provides a needle assembly including:
         an elongate housing having a first aperture in a front end portion thereof and a second aperture in a rear end portion thereof;   an elongate hollow needle sub assembly slideably mounted within the elongate housing and having a needle point at a first end portion thereof and a second end portion adapted to be connected to a supply tube;   the needle sub assembly movable relative to the housing between an extended position, wherein the first end portion extends out of the housing through the first aperture and the needle point is located outside of the housing and a retracted position wherein the first end portion and the needle point is located and shielded within the housing;   biasing means biasing the needle sub assembly to the retracted position;   holding means having an operative position that, when the needle sub assembly is in the extended position, holds the needle sub assembly in the extended position against the action of the biasing means and prevents movement the needle sub assembly toward the retracted position;   release means movable to a release position for releasing the holding means from the operative position to allow movement from the extended to the retracted position;   locking means for locking the needle sub assembly when in the retracted position and preventing movement of the needle sub assembly toward the extended position to expose the needle point, and   at least one movable blocking member that, in a blocking position, prevents movement of the release means to the release position.       

     In yet another broad form the invention provides a needle assembly including:
         an elongate housing having a first aperture in a front end portion thereof and a second aperture in a rear end portion thereof;   an elongate hollow needle sub assembly slideably mounted within the elongate housing and having a needle point at a first end portion thereof and a second end portion adapted to be connected to a supply tube;   the needle sub assembly movable relative to the housing between an extended position, wherein the first end portion extends out of the housing through the first aperture and the needle point is located outside of the housing and a retracted position wherein the first end portion and the needle point is located and shielded within the housing;   biasing means biasing the needle sub assembly to the retracted position;   holding means having an operative position that, when the needle sub assembly is in the extended position, holds the needle sub assembly in the extended position against the action of the biasing means and prevents movement the needle sub assembly toward the retracted position;   locking means for locking the needle sub assembly when in the retracted position and preventing movement of the needle sub assembly toward the extended position to expose the needle point, and   at least two release members movable to a release position for releasing the holding means from the operative position to allow movement from the extended to the retracted position,   said the holding means not released from the operative position unless all of the at least two release members are at the release position.       

     The locking means preferably includes at least one first leg that extends from one of the needle sub assembly and the housing and engages engagement means on the other of the needle sub assembly and the housing. Preferably the free end of the at least one first leg engages the engagement means. 
     Preferably the at least one first leg is resilient and is bent, flexed or otherwise distorted to allow movement to the retracted position. However, the at least one first leg may be relatively rigid and movable from the operative position. This may be by a pivoting or sliding action, for example. The at least one first leg may be biased to the locked or unlocked position, either by an external biasing member or by being resilient and bent away from the relaxed state. 
     The at least one first leg and engagement means are preferably configured so that the needle sub assembly can move from the extended position to the retracted position but not the other way. Preferably at least one first leg is angled to the longitudinal direction. 
     Preferably the at least one first leg is located on the housing and extends rearwards and radially inwards toward the needle sub assembly to engage engagement means on the needle sub assembly. Alternatively, the at least one first leg may be located on the needle sub assembly and extends forwards and radially outwards from the needle sub assembly to engage engagement means on the housing. 
     Preferably the at least one first leg comprises at least two opposed first legs that extend toward the needle sub assembly. Where two first legs are provided they need not be opposed and may, for example, be located at 90 degrees to each other. Multiple first legs may be provided. 
     The engagement means is preferably at least one flange or protrusion. However the engagement means may be at least one recess. 
     Preferably the engagement means is part of the needle sub assembly. More preferably the engagement means comprises a flange. 
     The shaft is preferably tubular and preferably the flange is a radially extending annular flange. However, the shaft and/or the flange may have a non circular end cross section. 
     The holding means preferably includes at least one second leg that extends from one of the needle sub assembly and the housing and engages second engagement means on the other of the needle sub assembly and the housing. Preferably the free end of the at least one second leg engages the second engagement means. 
     Preferably the at least one second leg is resilient may be bent, flexed or otherwise distorted to allow movement to the retracted position. However, the at least one second leg may be relatively rigid and movable from the operative position. This may be by a pivoting or sliding action, for example. The at least one second leg may be biased to the locked or unlocked position, either by an external biasing member or by being resilient and bent away from the relaxed state. 
     Preferably at least one second leg is angled to the longitudinal direction. 
     Preferably the at least one second leg is located on the needle sub assembly and extends rearwards and radially outwards toward the housing to engage engagement means on the housing. Alternatively, the at least one second leg is located on the housing and extends forwards and radially inwards toward the needle sub assembly to engage engagement means on the needle sub assembly. 
     Preferably the at least one second leg comprises two opposed legs that extend from the needle sub assembly. Where two second legs are provided they need not be opposed and may, for example, be located at 90 degrees to each other. Multiple first legs may be provided. 
     The second engagement means is preferably at least one flange or protrusion. However the engagement means may be at least one recess. 
     Preferably the engagement means is part of the housing. More preferably the engagement means comprises the rear end of the housing and most preferably the portion of the housing surrounding the second aperture. 
     Preferably the second aperture is sized to allow the second legs to pass through when deflected to the release position. 
     Preferably the second aperture is sized so the flange cannot pass therethrough. Preferably the second aperture is rectangular. 
     The release means preferably include at least one portion for moving the holding means to the release portion. Preferably the at least one portion is resilient and is flexed to move the holding means. However, the at least one portion may be relatively rigid and movable from the operative position. This may be by a pivoting or sliding action, for example. The at least one portion may be biased to the release or non release position, either by an external biasing member or by being resilient and bent away from the relaxed state. 
     The at least one portion is preferably part of the housing. 
     Preferably the assembly includes blocking means for blocking movement of the release means to the release position. 
     Preferably the assembly includes at least one volume into which the release means moves to release the holding means. 
     Preferably the blocking means blocks movement of the release means into the at least one volume. Preferably the blocking means extends into at least part of the volume. 
     In the preferred form, the housing comprises a hollow tubular body and the needle sub assembly comprises a hollow shaft having a needle mounted at one end thereof. The holding means comprises two diametrically opposed legs that extend radially outwards and backwards from the shaft that engage the rear end of the housing surrounding an aperture through which the rear of the shaft extends. The housing has two diametrically opposed arms that overlie the legs when the needle sub assembly is extended and which may be squeezed together to compress the legs inwards and allow the legs to pass through the aperture. A spring located between the front portion of the housing and a flange on the shaft urges the shaft backwards when the holding legs are released. The housing has two opposed locking legs that extend rearwards and inwards to lock the needle sub assembly in the retracted position. The legs engage the front surface of the flange on the shaft against which the spring bears. Preferably the legs on the housing are located adjacent the arms but positioned at 90 degrees circumferentially to the arms. 
     The invention shall be better understood from the following description of non-limiting examples. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view from above of a first example of the invention in an extended position. 
         FIG. 2  is an exploded perspective view from above of the first example. 
         FIG. 3  is a side view of the first example in an extended position. 
         FIG. 4  is a cross sectional side view from the side of the first example in an extended position. 
         FIG. 5  is a detail cross sectional side view from the side of part of the first example in an extended position. 
         FIG. 6  is a top view of the first example in an extended position. 
         FIG. 7  is a cross sectional view from above of the first example in an extended position. 
         FIG. 8  is a detail cross sectional view from above of part of the first example in an extended position. 
         FIG. 9  is an end view of the first example. 
         FIG. 10  is an axial cross sectional view of the first example taken along line AA in  FIG. 6 , with a safety locking clip shown, which is not shown in  FIG. 6 . 
         FIG. 11  is a perspective view from above of a first example of the invention in a retracted position. 
         FIG. 12  is a cross sectional side view from the side of the first example in a retracted position. 
         FIG. 13  is a detail cross sectional side view from the side of part of the first example in a retracted position. 
         FIG. 14  is a cross sectional view from above of the first example in a retracted position. 
         FIG. 15  is an exploded perspective view from above of a whole blood needle according to a second example of the invention. 
         FIG. 16  is a perspective view from above of a variation of a needle sub assembly that may be used in the housing of the first example. 
         FIG. 17  is a detail cross sectional side view from the side of part of a needle assembly including the needle sub assembly of  FIG. 16 . 
         FIG. 18  is a perspective view from above of a needle assembly according to a further example of the invention. 
         FIG. 19  is a perspective view from above of the needle assembly of  FIG. 18  activated to allow retraction. 
         FIG. 20  is an axial cross sectional view from above of the example of  FIG. 18  in a retracted position. 
         FIG. 21  is an exploded perspective view from above of a dialysis needle according to a further example of the invention. 
         FIG. 22  is a perspective cross sectional view of the example of  FIG. 21  in an extended position. 
         FIG. 23  is a perspective cross sectional view of the example of  FIG. 21  in an extended position but activated to allow retraction. 
         FIG. 24  is a perspective cross sectional view of the example of  FIG. 21  in a retracted position 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION 
     Referring to  FIGS. 1 to 14  there is shown a first example of a retractable infusion or transfusion needle assembly  10  according to a first example of the invention. The retractable needle assembly  10  has an elongate housing  12  in which a needle sub assembly  14  is movable between an extended position, shown in  FIG. 1  and a retracted position, shown in  FIG. 11 . 
     The needle sub assembly (see  FIG. 2 ) comprises a hollow shaft  16  having a cannula  18  mounted at a front end  20 . A plastics tube  22  may be mounted at the other end  24 . Fluid may thus be supplied via the plastics tube  22  and bore  17  of hollow shaft  16  to the cannula  18  or vice versa. In the extended position the point  26  of the cannula  18  extends out of housing  12  and may be inserted into a patient&#39;s vein. In the retracted position the cannula, and in particular its point  26 , is located within the housing  12  and is not exposed to the user. In the example substantially the entire cannula  18  extends out of the housing  12  in the extended position, but this is not essential. 
     Preferably the cannula  18  is mounted within the end  20  of the shaft  16 , as seen in  FIG. 4 . In this example the cannula is glued in the end of the shaft. This may also be achieved by injection moulding the shaft  16  around the cannula  18  during manufacture. The exact nature of the connection of the cannula  18  to the shaft  16  is not critical. 
     The shaft  16  has an annular flange  28  located between its ends. The length of the shaft  16  and the location of the flange  28  depend on the length of the housing  12 . 
     Located toward the upper end  24  of the shaft  16  are two resilient legs  30 . These legs  30  extend backwards and away from the axis of the shaft  16  and (as seen in  FIG. 8 ) at their free ends  32  have a surface  34  extending generally perpendicular to the axis of the shaft  16 . A small protrusion  36  extends backwards beyond the surface  34 . The legs  30  are flexible and may be bent toward the shaft  16  on application of an inwards directed force, springing back when the force is released. 
     The housing  12  comprises a main body  40  and an end body  42 . The main body  12  is elongate and has a generally cylindrical bore  44  within which the cannula  18  and front portion of shaft  16  are located. The bore  44  is preferably sized to be a snug fit with the flange  28  on the shaft  16  but to still allow free movement of the shaft within the bore  44 . The front end  46  of the main body  40  has a circular aperture  48 . The aperture  48  is sized to allow the cannula  18  and the end  20  of the shaft to extend through the aperture, as seen in  FIG. 4 . If desired the aperture  48  may be sized so that only the cannula  18  may extend out of the aperture  48 . 
     A spring  52  is located around the shaft  16  and extends between the flange  28  on the shaft  16  and a flange  50  adjacent the aperture  48 . The spring  52  has an outer diameter smaller than that of the flange  28  and so leaves an outer portion of the flange extending radially more than the spring  52 . The flange  50  need not be adjacent the aperture  48  and, if desired, may be located away from the aperture  48 . The spring  52  is more compressed in the extended position than in the retracted position and biases the shaft  16  and cannula  18  away from the front end  46 . 
     The bore  44  may be tapered toward the aperture  48  so that movement of the needle subassembly out of the housing  12  is limited by the flange  28  engaging the surface of the bore  44 . Movement of the needle sub assembly may also be limited by maximum compression of the spring or by other means. 
     The rear end  54  of the main body has two parallel arms  56  located on either side of the axis, best seen in  FIG. 2 . Each arm  56  has a longitudinally extending slot  58 . Each slot  58  is closed by cross piece  60  of arm  56 . The two arms  58  also define two vertical slots  62  between themselves. These slots  62  are sized so that the legs  30  on the shaft  16  may slide into and out of these slots. 
     The end body  42  is sized to slide over and lock to the rear end of the main body. The end body is preferably formed of a plastic and has apertures  62  that are a snap fit on protrusions  64  on the main body  40 . In this position the end body  42  surrounds the arms  56  and the slots  62 . Other forms of securing the end body  42  to the main body  40  may be used. If desired the end body  42  may be permanently affixed to the main body  40  after assembly be various means, such as gluing, welding or the like. 
     The end body  42  has a first pair of diametrically opposed resilient legs  66  that extend rearwards and inwards toward the longitudinal axis. When assembled the legs  66  extend into the slots  58 . The free ends  68  of these legs  66  extend inwards further than the outer diameter of the central annular flange  28  on shaft  16  and preferably engage with and are biased against the surface of the shaft  16 . In the extended position the flange  28  is located between the legs  66  and the front end  46 . 
     Located at 90 degrees to the first pair of legs  66  are a second pair of diametrically opposed resilient legs  70  that extend rearwards. The legs extend generally parallel to the shaft. Each leg  70  defines a slot  72  between itself and the body of the end body  42 . The slots  72  allow the legs  70  to be deflected inwards with a squeezing action. When assembled the legs  70  are located adjacent the slots  62  of the main body. When the needle sub assembly is in the extended position the legs  30  on the shaft  16  lie in the slots  62  and, preferably, the free end  31  of each leg  30  engages a corresponding leg  70 . This is not essential and in this position there may be free space between the respective legs  30  and  70 . The positioning of the legs  30  within slots  62  when in the extended position prevents the needle sub assembly turning relative to the housing  14 . Thus if the tube  22  places a twisting force on the shaft  16 , this will transferred to the patient via legs  30  and housing  14  rather than via the cannula  18 . Thus twisting of the cannula  18  in the patient is resisted and/or prevented. 
     If desired, the bore  44  in the main body may have a non circular cross section and the flange  28  may have a corresponding non circular cross section, thereby preventing relative rotation about the longitudinal axis. 
     The end of the end body  42  has a rectangular opening  74 . The width of this opening  74  is sized so that the legs  30  on the shaft cannot pass through the opening in their undeflected state. The legs  30  can only pass through the opening if deflected toward the shaft  16 . The height of opening  74  is less than the outside diameter of the flange  28  and the so flange cannot pass through the opening  74 . 
     The example has a wing assembly  100  mounted on the front end  46  of the main body  40 . The wing assembly  100  includes a central section  102  having a bore  104  and two wing members  106  that extend in generally diametrically opposite directions from the central section  102 . The central section  102  is a snap fit on the front end  46 , being retained by resilient legs  108 . Resilient legs  110  on the central section  102  engage in recesses  112  on the main body  40  and prevent rotation of the wing assembly  100  about the longitudinal axis relative to the main body, such as when the wings  106  are held together by the user in a generally vertical position as the cannula is inserted into the patient. 
     The assembly  10  is supplied in the extended state, shown in  FIG. 1 . In this state the cannula  18  extends out of the opening  48 . A needle sheath or cap  76  is press fitted over the free end  46  of the housing  12  and shields the cannula  18  until ready for use. The method and location of attachment of the cap  76  over the cannula is not critical. The invention may be used with various caps and therefore need not be a push fit and pull release. If desired the cap  76  may be mounted to the shaft  16 , rather than the housing  12 . The cap may be bonded to the housing  12  or shaft  16  rather than being a simple press fit. 
     In the extended state the spring  52  is compressed and so biases the needle sub assembly  14  toward the rear end. However, this is prevented by the legs  30 , and in particular surfaces  34 , engaging the surfaces  35  on the end of the end body  42 , as seen in  FIG. 8 . The protrusions  36  extend into the aperture  74  and prevent the legs  30  extending outwards. Protrusions  75  and  77  on the shaft  16  locate the shaft generally centrally in the aperture  74  and limit off axis movement. Without these protrusions, and in particular protrusions  75 , movement off axis could result in unintended release of the legs and retraction of the needle sub assembly. 
     As supplied the assembly  10  includes a protective shield  80 . This shield  80  has a cover portion  82  and two pairs of legs  84  and  86  that extend from the sides of the cover portion  82 . The first pair of legs  84  extends into the slots  72  between the legs  70  and the body of the end body  42 . The legs  84  extend past the legs and overlie portion  90  of the end body. The legs  84  prevent the legs  70  being squeezed inwards and squeezing legs  30  on the shaft  16  whilst the shield  80  is in place. Thus accidental release of the needle sub assembly  14  from the extended position is prevented whilst the shield  80  is in place. 
     The second pair of legs  86  extends downwards behind the end of the end body  42 . Each leg  86  has an inward extending protrusion  88  that clips around the tubing  22 . The legs  86  and protrusions  88  thus hold the shield  80  in place against accidental removal. Removal thus needs to be an intentional action. When the shield  80  is lifted off the end body  42  it is still clipped to the tubing  22  and so will slide back on the tubing but will not fall to the floor. The shield  80  may be removed from the tubing by pulling it off the tubing or can be disposed of with the needle assembly once the needle assembly has been finished with. 
     With the shield  80  in place the cannula may be inserted into the skin of a patient and taped in place. This can be done with or without shield  80 , due to the need to press both of the legs  70  inwards to release the sub assembly  14 . However, leaving the shield in place provides an additional level of safety. 
     The cannula  18  may be inserted into a patient by holding the housing  12  or using the flexible wings  100 . As the cannula is inserted, force is transmitted between the cannula  18  and the housing  12  via shaft  16  and legs  30 . The legs  30  are sized that they will not buckle or otherwise deflect to allow movement of the cannula  18  toward the retracted position. 
     When the cannula  18  needs to be removed the user removes the shield  80  from the end body  42  (if it has not already been removed). This allows the legs  70  to be squeezed inwards by the user, using a pinching or squeezing action. The legs  70  are squeezed inwards and contact the legs  30  on the shaft. Continued movement inwards deflects these legs  30  inwards until the surfaces  34  on the end of the legs no longer overlie the opposed surfaces  35  on the end of the end body  42 . At that instance the legs  30  are free to move through the opening in the end body  42  and the spring  52  moves the shaft  16  backwards, retracting the cannula  18  from the patient and into the housing  14 . The assembly may then be lifted from the patient&#39;s skin and disposed of. 
     It is necessary that both of the legs  70  be squeezed inwards together so as to deflect both of the legs  30  inwards. If only one leg  30  is squeezed inwards the surface  34  on the end of the other leg  30  will still overlie the opposed surface  35  on the end of the end body  42  and so prevent the spring  52  retracting the shaft  16 . 
     Because the needle sub assembly is held in the extended position by the legs  30  during insertion into the patient, the strength of the spring  52  has no relevance during the insertion phase. Thus the spring may be made sufficiently strong to withdraw the cannula  18  from the patient without help from the user. 
     Thus the user does not need to actively pull the needle sub assembly  14  from the patient&#39;s skin, with the cannula point  26  exposed, with the resultant risk of needle stick injury. Further the cannula point  26  is never exposed to the user and there is no cap, sheath or the like to be applied to cover the cannula. Accordingly, other forms of needle stick injury are not possible. 
     The retraction of the cannula  18  is a linear motion and does not require the user to actively pull on part of the assembly  10  or to hold the housing whilst pulling the needle sub assembly. Thus the risk of the cannula  18  being twisted or withdrawn at a different angle compared to than the angle it was inserted as it is removed is greatly reduced, if not eliminated totally. 
     The spring  52  pushes the shaft  16  rearwards until the flange  28  contacts the ends  68  of the legs  66  of the end body  42 . As the shaft moves backwards the flange  28  pushes the legs  66  outwards, continues its backwards motion and passes the legs  66 , which then snap back towards their unreflected state against the shaft  16 . Movement continues until the flange  28  contacts the end of the end body  42 . In this position the cannula point  26  is located wholly within the housing  14 , as seen in  FIGS. 12 &amp; 14  and the flange is located between the end of the end body  42  and the ends of the legs  66 . 
     The legs  66  may engage the spring, but because the flange  28  extends radially more than the spring there will be an outer portion of the flange  28  that extends radially beyond the position of the legs  66 . Attempting to extend the cannula  18  will result in the flange  28  contacting the ends  68  of the legs  66 . The legs  66  are sized so that normal “accidental” force will resist and prevent any significant movement. If a user deliberately attempts to extend the cannula by application of excessive force the angle of the legs will cause the legs to deflect inwards rather than deflect outwards. 
     Thus once the cannula has been retracted it cannot be accidentally or easily extended again and either reused or merely exposed. 
     In the preferred embodiments there is a small gap between the end of the legs and the inner end of the end body and this space is sized to accommodate the flange  28 . Thus once the cannula has been fully retracted the shaft is locked in position with relatively little free play. 
     In the preferred embodiments, in the undeflected state, the free ends of the legs extend to be radially inwards more than the cross bars  60  that define the end of the slots  58 . If a user attempts to remove the end body from the main body, as the end body is moved backwards, the free ends of the legs  68  are drawn backwards and contact the cross bars. This prevents separation of the end body  42  from the main body  40 . If excessive force is applied the angle of the legs will tend to cause the cross bars  60  to ride over the legs  66  trapping them in the closed slot  58  and preventing separation. 
     A second example of the invention, comprising a whole blood needle  210 , is shown in  FIG. 15 . The whole blood needle  210  is substantially the same as the first example 10 expect that the main body  240  is substantially longer that the first example and, accordingly, the shaft  216  and cannula  218  are longer. 
     The whole blood needle  210  does not have a wing sub assembly toward the free end and accordingly lacks the retention legs  118  and recesses  112  of the first example. Instead finger grips  219  are provided toward the free end  46 . The other components and features of the whole blood needle  210  are substantially the same as the first example and so the same numbers are used for the same features. The operation of the second example is the same as the first example and the description of the first example is applicable to the second example. 
     Whilst a single flange  28  is used both as an abutment for the spring  52  and to engage the legs  68  on the end body  42 , it will be appreciated that two separate flanges or other structures may be provided. 
       FIGS. 16 and 17  show a shaft  114  that is a variation of the shaft  16  of the first example. Similar parts are numbered the same. The shaft  114  includes a first flange  116  and a second flange  118 , located between the first flange  116  and the front end  20 . The first flange  116  is substantially the same diameter and provides the same locking function as the flange  28  of the first example, as discussed later. The second flange  118  is of a smaller diameter and acts as a retainer for the spring  52 . As seen in  FIG. 17 , the spring  52  bears against the flange  118  and not against the first flange  116 . 
       FIG. 17  shows the rear portion of the needle assembly when in the retracted state. As seen, the first flange  116  ties between the rear end of the housing and the legs  66 . Movement to extend the cannula out of the housing is prevented as previously described. 
     The second flange  118  is spaced along the shaft  14  a sufficient distance that in this fully retracted the legs  66  lie between the two flanges  116  &amp;  118 . Thus the flange  118  and spring  52  are distant from the engagement of the ends of the legs  66  with the flange  116  and so cannot affect the engagement of these components together. 
     The rear of the flange  118  is provided with a frusto conical circumferential surface  120  that allows the flange  118  to lie closer to the legs  66  in the retracted position than otherwise. Whilst preferred, this is not essential. If desired the circumferential surface  120  may extend parallel to the axis of the shaft  114 . This would require the flange  118  to be spaced further from the flange  116  to clear the legs  66 . 
     It will be appreciated that the legs  30  and  66  may be reversed and extend from the housing and shaft respectively. In each case the legs would need to extend in a forwards direction rather than a rearwards direction, as in the example. 
     Whilst the preferred forms of the examples utilize resilient legs  30 ,  66  and release arms  70 , it will be appreciated that the invention includes other holding, locking and release mechanisms. For example, the legs  30 ,  66  and arms  70  may be moved in total between their relevant states rather than just being bent. This movement may be by a sliding or pivoting action, for example. For example, the release arms  70  may be separate components slideably mounted on the housing and slide to push or pivot the legs  30  to the release position. Similarly, the legs  30  may be pivotably mounted on the shaft and pivoted by the release mechanism. Alternatively they may slide into a recess to reduce their effective size. 
     Whilst a pair of opposed legs  30 , and associated legs  70  are provided, the invention includes the use of more than two legs  30 . Further the legs need not be opposed. As an example, the legs  30  could be located at 90 degrees to each other. Release would thus require two substantially simultaneous pinching actions, such as by use of both hands, further reducing the likelihood of accidental auto-retraction. It will be appreciated that the legs  66  would need to be located in the two unoccupied quadrants around the shaft  16 . 
     Whilst the preferred examples of the invention utilize the shield and legs  30 ,  70 , it will be appreciated that it is not essential that both sets of features be used together. By using the shield to protect the release mechanism, it is possible, although not necessarily desirable, to utilize a single leg  30  to hold the needle sub assembly in the extended state. The presence of the shield prevents accidental auto-retraction. 
     Similarly, the use of two sets of legs  30 ,  70  substantially prevents accidental auto-retraction even when the shield is not present, and if desired, embodiments may be supplied without the shield. 
     The needle sub assembly may be released by increasing the effective size of the aperture through which the shaft extends.  FIGS. 18 to 20  show a further example in which the shaft  216  has a fixed annular flange  218 . The end  220  of the housing is defined in part by two opposed movable members  222  that define an aperture  224  between their ends  220  through which the end of the shaft  216  passes. The flange  218  bears against the ends  220 . The members  222  are pivotably mounted to the rest of the housing or end cap at hinges  226  so that inner and outer portions  228 ,  229  extend generally axially on either side of the hinges. The members  226  may be integral with the rest of the housing or end cap with the hinges being living hinges. 
     To retract the needle sub assembly the user simultaneously presses the inner portions  228  inwards. As shown in  FIG. 19 , the two members  222  pivot about the hinges  226  and the aperture  224  is enlarged, releasing the flange  218  and allowing the needle sub assembly to be retracted as previously described. 
     As shown in  FIGS. 18 to 20 , there may be provided a second aperture  232  located forwards of the end of the housing that retains the shaft. Once the needle sub assembly retracts, rearwards motion is limited by a central flange  234  bearing against the surrounding of this second aperture  232 . Forward motion will be prevented by legs  66  as previously described. 
     Alternatively, by making the aperture  224  with a width smaller than the width of a central flange on the shaft, that central flange will be retained in the housing. Alternatively by ensuring the maximum size of the aperture  224  is less than the size of the central flange, the central flange will be retained. 
       FIGS. 21 to 24  show a retractable needle  250  according to further example in which the housing includes an end cap  252  rotatably mounted to a main body  254 . The needle subassembly  256  is slideably mounted within the housing and locking in the retracted position is substantially as previously described. 
     The needle sub assembly  256  has a non circular retainer  258  at its rear end. In this example the retainer comprises two arms  260  that extend in diametrically opposite direction from the hollow shaft  262 . 
     The end wall  264  of the end cap  252  has an aperture  266  that corresponds to the shape of the retainer  260 . 
     The end cap is a snap fit on the main body and is retained by complimentary circumferential ridge  268  on the main body and circumferential groove  270  on the end cap. 
     In the extended state the end cap is positioned so the aperture  264  does not align with the retaining  260  and the arms  260  of retainer  258  bear against the end wall  264  of end cap  252 . 
     To retract the cannula, the user rotates the end cap  252  to align the aperture  266  with the retainer  260 . At this point the retainer  260  is free to move through the aperture  266  under the action of the spring  272 , as described with reference to other examples. 
     As with the other examples the hollow shaft has a flange  274  that cannot pass through the aperture  264 . The spring  272  drives the shaft backwards until the flange  274  contacts the end wall  264 . 
     The end cap  252  has rearwards projecting locking legs  276  that operate in a similar manner to the locking legs of other examples to engage the front surface of flange  274  to prevent forward movement of the needle sub assembly. 
     To prevent accidental rotation of the end cap detent members may be formed on the end cap and main body to resists rotation. These detent members may be sized so that they need to be broken, with a reasonable force, so that rotation and retraction needs to be conscious action by the user. It will also be appreciated that the needle sub assembly will have a shape such that rotation within the housing is prevented. 
     Unless the context clearly requires otherwise, throughout the description the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”. 
     It will be apparent to those skilled in the art that many obvious modifications and variations may be made to the embodiments described herein without departing from the spirit or scope of the invention.