Patent Publication Number: US-2022233783-A1

Title: Pen needle

Description:
TECHNICAL FIELD 
     This invention relates to a pen needle device and to a method of using such a device. The pen needle devices may be useful as a single-use disposable needle device such as are typically configured for attachment to an injection device, cartridge or syringe. 
     BACKGROUND ART 
     Injection devices are commonly used by patients to self-administer injections of medicament such as insulin. Such devices are typically provided in a pen-like body which contains a syringe cartridge of medicament and a delivery mechanism which is arranged to dispense the medicament via a needle in response to a user pressing a button or trigger. 
     As such injection devices can be either reusable, either by replacing the cartridge of medicament or by delivering multiple separate injections until the medicament within the device has been fully consumed, it is common to arrange the device to receive a disposable, single-use, needle device. Such needle devices are generally referred to as “pen needles”. 
     Pen needles comprise a body or hub which is configured to be attached to the injection device in use (for example by means of a screw thread) and which supports the needle. Typically, the needle is a double ended needle having a forward (distal) end for use in penetrating the skin of a user, and a rearward (proximal) end which pierces a septum of the cartridge in the injection device when the pen needle is attached to the device. 
     It is known to provide pen needles with a shroud which is arranged to cover the needle after use to reduce the risk of accidental needle-stick injuries after use or during disposal of the needle device. An example of such a device is the BD AutoShield Duo Pen Needle available from Becton Dickinson (www.bd.com) 
     EP 1949928 A (BECTON DICKINSON CO) 30 Jul. 2008 discloses a pen needle in which the needle retracts inside the hub after use. EP 1949929 A (BECTON DICKINSON CO) 30 Jul. 2008 discloses a pen needle with both injection and non-injection end shields. 
     WO 2009/012612 A (ALCATEL SHANGHAI BELL CO LTD ET AL) 29 Jan. 2009 discloses a pen needle with a spring-loaded shield that can be deployed by operation of a button. 
     WO 2016/181127 A (OWEN MUMFORD LTD) 17 Nov. 2016 discloses a pen needle with a manually operable shield that allows both the forward and reward parts of the needle to be covered after use. 
     Some pen needle devices have spring-loaded shields that can be automatically activated when the needle is withdrawn from the injection site. However, problems can occur if the shield deploys before the injection is complete, leading to injection of less than the desired amount of medicament, or the deposit of medicament on the surface of the skin. 
     This invention aims to address at least some of the problems encountered with the deployment of shields or shrouds in previous pen needle devices. 
     SUMMARY OF INVENTION 
     The invention provides a pen needle comprising:
         a housing defining a central cavity with a distal end having a distal opening and a proximal end having a proximal opening;   a needle carrier located within the central cavity and supporting a needle that extends through the central cavity such that a distal end of the needle projects from the distal end of the cavity through the distal opening;   a distal shroud positioned around the needle and located within the central cavity at the distal end, the distal shroud including formations that, when engaged with the housing, limit axial movement of the distal shroud in a distal direction;   a distal compression spring positioned around the needle and located between the needle carrier and the distal shroud, wherein the compression spring acts to urge the distal shroud away from the needle carrier towards the distal opening; and   a proximal member located within the central cavity at the proximal end;   wherein the proximal member is movable in use between a first position, in which a distal end of the proximal member engages a proximal end of the distal shroud to hold the formations in engagement with the housing, and a second position in which the proximal member is closer to the proximal opening and the distal end of the proximal member is not engaged with the proximal end of the distal shroud such that the formations are movable out of engagement with the housing and the distal shroud is movable in a distal direction by the distal compression spring to project from the distal opening and to surround the distal end of the needle projecting from the distal opening.       

     The invention also provides a method of using the pen needle, comprising:
         with the proximal member in the first position, connecting a cartridge housing to the proximal end of the housing so as to engage the proximal end of the proximal member; and   disconnecting the cartridge housing from the proximal end of the housing, thereby releasing the proximal member so as to disengage the distal end of the proximal member from the proximal end of the distal shroud thereby releasing the formations to move out of engagement with the housing and moving the distal shroud in a distal direction by the distal compression spring to project from the distal opening and to surround the distal end of the needle projecting from the distal opening.       

     The proximal end of the housing can have formations for connecting a cartridge housing to the pen needle, wherein, when connected, the cartridge housing holds the proximal member in the first position, and when disconnected, allows the proximal member to move to the second position. 
     The proximal member can comprise a proximal shroud positioned around the needle and located within the central cavity at the proximal end. The pen needle can further comprise a proximal compression spring positioned around the needle and located between the needle and the proximal shroud, wherein the proximal compression spring acts to urge the proximal shroud away from the needle carrier towards the proximal opening; wherein the proximal shroud is movable by the proximal compression spring between the first position and the second position. A proximal compression spring can be positioned around the needle and located between the needle and the proximal shroud, wherein the proximal compression spring acts to urge the proximal shroud away from the needle carrier towards the proximal opening; 
     By arranging the proximal shroud to engage the distal shroud and hold it in engagement with the housing, deployment of the distal shroud can be controlled to take place after the proximal shroud has deployed to shroud the proximal end of the needle. In this way the likelihood of early activation of the distal shroud can be reduced. 
     The distal end of the proximal shroud can engage in the proximal end of the distal shroud in the first position to hold the formations in engagement with the housing. In the second position, the distal end of the proximal shroud is not engaged in the proximal end of the distal shroud such that the formations are movable out of engagement with the housing. 
     The formations on the distal shroud can comprise deformable formations having ramped external surfaces that are engageable with corresponding ramped internal surfaces on the housing; the action of the distal compression spring causing the deformable formations to deform and disengage from the formations in the housing when the distal end of the proximal shroud is disengaged from the proximal end of the distal shroud. 
     The distal shroud can comprise further formations that are engageable with distal end formations in the housing to prevent disengagement of the distal shroud from the housing when moved in a distal direction by the distal compression spring to project from the distal opening and to surround the distal end of the needle projecting from the distal opening. 
     The proximal end of the needle can be located within the proximal shroud when the proximal shroud is in the second position. In the first position of the proximal shroud, the proximal end of the needle can project beyond the proximal end of the proximal shroud by a length that is less than the length of the distal end of the proximal shroud engaged with the proximal end of the distal shroud. 
     The proximal shroud can include a latch for holding it in the second position. 
     The proximal shroud can comprise an actuator plate at its proximal end by which force can be applied to the proximal shroud to rotate it within the housing and to move it axially against the proximal compression spring. 
     The proximal shroud can engage the needle carrier by means of a pin and track arrangement, such that rotation of the proximal shroud relative to the needle carrier moves the pin from a first track portion in which the proximal shroud is held in the first position against the proximal compression spring, to a second track portion in which the proximal shroud is axially movable to the second position by the proximal compression spring. The pin and track arrangement can comprise a pin on an outer surface of the proximal shroud and a track formed in a wall of the needle carrier. The track in the wall of the carrier can comprise a pin seat defining the first track portion, and a transition channel extending axially and azimuthally along the wall of the carrier from the first track portion to the second track portion extending axially along the wall of the carrier. The track can further comprise an assembly channel extending axially along the carrier wall to connect to the transition channel on the opposite side of the pin seat to the second track portion. 
     The proximal opening of the housing can include an internal screw thread by means of which a cartridge housing can be attached, such that screwing the cartridge housing onto the housing applies axial and rotational force to the actuator plate. 
     The housing can include internal formations that engage the needle carrier to locate it axially and rotationally. 
     The method can comprise:
         with the proximal shroud in the first position, connecting a cartridge housing to the proximal end of the housing so as to engage the proximal end of the proximal shroud and to rotate the proximal shroud in the housing and move it axially against the proximal compression spring; and   disconnecting the cartridge housing from the proximal end of the housing, thereby releasing the proximal compression spring so as to move the proximal housing to the second position to initially surround the proximal end of the spring, and to subsequently disengage the distal end of the proximal shroud from the proximal end of the distal shroud, thereby releasing the formations to move out of engagement with the housing so as to move the distal shroud in a distal direction by the distal compression spring to project from the distal opening and to surround the distal end of the needle projecting from the distal opening.       

    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a pen needle in a pre-use state, viewed from the proximal end. 
         FIG. 2  is a perspective view of the pen needle of  FIG. 1 , viewed from the distal end. 
         FIG. 3  is a cross-sectional view of the pen needle of  FIG. 1  in a pre-use state. 
         FIG. 4  is a cross-sectional view of the pen needle of  FIG. 1  at ninety degrees to the view of  FIG. 3 . 
         FIG. 5  is a cross-section view of the housing of the pen needle of  FIG. 1 . 
         FIG. 6  is a cross-section view of the housing of the pen needle of  FIG. 1  at ninety degrees to the view of  FIG. 5 . 
         FIG. 7  is a perspective view of the needle carrier and needle. 
         FIG. 8  is a close-up view of the sub-assembly of the needle carrier and non-patient end needle shroud in a pre-use state. 
         FIG. 9  is a close-up view of the inside of the collar of the needle carrier. 
         FIG. 10  shows the positions of the patient end needle shroud and the non-patient end needle shroud on the needle carrier in a pre-use state of the device. 
         FIG. 11  shows the patient end needle shroud in perspective from the proximal end. 
         FIG. 12  shows the non-patient end needle shroud in perspective from the distal end. 
         FIG. 13  shows the non-patient end needle shroud in perspective from the proximal end. 
         FIG. 14  is a perspective view of the housing from the proximal end and showing the orientation of the patient end needle shroud and distal spring in the housing in a pre-use state. 
         FIG. 15  is a perspective view of the sub-assembly that comprises the needle carrier, needle, proximal spring and non-patient end needle shroud in a pre-use state viewed from the proximal end. 
         FIG. 16  is a cross-section view of the sub-assembly of  FIG. 15 . 
         FIG. 17  is a perspective view of the sub-assembly of  FIG. 15 . 
         FIG. 18  is a cross-sectional view of the pen needle attached to the cartridge of a pen type drug delivery device and ready for an injection to be made. 
         FIG. 19  is a view of the position of the non-patient end needle shroud relative to the needle carrier when the pen needle is attached to the cartridge housing of a pen type drug delivery device (with housing omitted for clarity). 
         FIG. 20  is a perspective view from a proximal end of the pen needle after use. 
         FIG. 21  is a cross-sectional view of the pen needle after use. 
         FIG. 22  is a cross-sectional view of the pen needle after use at 90 degrees to the view of  FIG. 21 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIGS. 1 to 6  illustrate a pen needle  1  in a pre-use state. The pen needle  1  comprises a needle  3 , a needle carrier  5 , a patient end (distal) needle shroud  7  and distal compression spring  9 , a non-patient end (proximal) needle shroud  11  defining a proximal member, and proximal compression spring  13 , a screw-threaded hub  15  and a housing  17 . 
     The proximal (non-patient) end of the pen needle  1  is the end nearest to the medicament delivery device, typically a pen type injector. The distal (patient) end is the opposite end, furthest from the medicament delivery device. 
     The housing  17  is tubular, defining a central cavity with a generally cylindrical cross-section and with a patient (distal) end opening  19  at a distal end of the housing  17  and a non-patient (proximal) end opening  21  at a proximal end of the housing  17 . A patient (distal) end  23  of the needle  3  extends outside of the housing  17  in a distal direction, through the patient end opening  19 . The length of the exposed portion of the needle  3  that extends outside of the housing  17  is pre-determined and is chosen according to the desired depth to which the needle is to be inserted into a patient, for example the exposed portion may be 4 mm long. The non-patient (proximal) end  25  of the needle  3  does not extend past the non-patient end opening  21 , it remains set back from the opening by a distance that is sufficient to reduce the risk of a needlestick injury. The housing  17  has a pair of needle shield guidance ribs  27 , as best seen in  FIGS. 5 and 6 , aligned longitudinally and arranged diametrically opposite each other on the internal surface of the housing  17 . The ribs  27  are each provided at a proximal end with a ramped deflector surface  29  and at a distal end with an abutment shoulder  31 . 
     The needle carrier  5  is illustrated in detail in  FIGS. 7 to 10 . It, also, is tubular with a generally cylindrical cross-section. It has an external stepped profile that creates three adjoining sections that decrease in diameter along its longitudinal axis from its proximal end to its distal end. The section nearest to the proximal end is a collar  33  which is used to attach the needle carrier  5  to the housing  17 . The middle section is a needle shroud guidance barrel  35  which constrains movement of the patient end needle shroud  7  and the non-patient end needle shroud  11 . The distal section is a needle sleeve  37  which is used to hold the needle  3  in place relative to the needle carrier  5  by means of an adhesive located in an annular void between the internal surface of the needle sleeve  37  and the external surface of the needle  3 . 
     The proximal section, collar  33 , is joined to the intermediate section, i.e. needle shroud guidance barrel  35 , at its distal end by an annular transverse plate  39 . The proximal end of the collar  33  has a flange  41  with an external diameter that is larger than the external diameter of the collar  33  and that is approximately the same diameter as the external diameter of the housing  17  at its proximal end. Located on the external surface of the collar  33  are a longitudinal alignment rib  43  and an annular stop bead  45 . The inside of the collar  33  is provided with a screw thread  47  that is complementary to a screw thread  49  provided on a cartridge housing  51  of a pen type drug delivery device (as shown in  FIG. 18 ), to facilitate connection of the pen needle  1  to the cartridge housing  51 . Also located inside the collar  33  and on the lip between the transverse plate  39  and the inside surface of the needle shroud guidance barrel  35  are two tongue deflection ramps  53  and two assembly slots  55 , as shown in  FIG. 9 . The two tongue deflection ramps  53  are diametrically oppositely located on the lip, as are the two assembly slots  55 , and they are all equally spaced around the lip. 
     The intermediate section, the needle shroud guidance barrel  35 , has at its distal end and located within its wall a pair of guidance slots  57  for guiding movement of the patient end needle shroud  7 . The guidance slots  57  extend longitudinally to approximately the mid-point of the needle shroud guidance barrel  35  and on diametrically opposite sides of it. Located within the wall of the needle shroud guidance barrel  35 , towards its proximal end and on diametrically opposite sides of it, there is also a pair of continuous channels which together provide a means for assembling the non-patient end needle shroud  11  into the needle carrier  5  and for controlling its motion during use of the pen needle  1 . Each continuous channel is formed from an axially extending assembly channel  59 , a transition channel  61  and an axially extending locking channel  63  which in combination resemble an inverted ‘U’ formation when looked at in a plan view, with the patient end  23  of the needle  3  uppermost (for example as illustrated in  FIG. 8 ). The assembly channel  59  forms the left hand side leg of the ‘U’, the transition channel  61  forms the bottom of the ‘U’ and the locking channel  63  forms the right hand leg of the ‘U’. The assembly channel  59  runs in a longitudinal direction from the interface between the collar  33  and the needle shroud guidance barrel  35  to a point approximately mid-way along the length of the needle shroud guidance barrel  35 , in line with the assembly slots  55 . The transition channel  61  is slanted in an upwards direction from left to right (i.e. extends axially and azimuthally) and the distally located side of it is a track pin cam surface  65 . A track pin recess  67  is located at the point at which the right hand end of the track pin cam surface  65  meets the locking channel  63 . A part of the locking channel  63  is a track pin capture slot  69  which has a mouth  71  at its distal end that is relatively wide compared to the width of its blind end  73  which is at the proximal extremity of the locking channel  63 . A first track portion with a track pin seat  75  is located adjacent to the transition channel  61 , approximately mid-way between the intersections with the assembly channel  59  and the locking channel  63 . The diameter of the transition channel  61  is narrowed on either side of the track pin seat  75 , such that its width is slightly less than the diameter of the track pins  77 . A first narrow  79  is located between the track pin cam surface  65  and the left hand edge of the track pin seat  75 . A second narrow  81  is located between the track pin cam surface  65  and the tip of a finger  83  that extends longitudinally from the right hand edge of the track pin seat  75 . 
     The patient end needle shroud  7  is illustrated in detail in  FIG. 11 . It is generally tubular, with a shroud portion  85 . The shroud portion  85  has a circular cross-section and a partially closed distal end  87 , with a circular needle aperture  89  located co-axially with the longitudinal axis Hof the patient end needle shroud  7 . Guidance bosses  91  are located adjacent to the proximal end of the shroud portion  85 , on each side of the patient end needle shroud  7 . The guidance bosses  91  extend radially outwardly from the external surface of the shroud portion  85 . The shroud portion  85  also has a pair of deformable locating formations in the form of flexible lock-out legs  93 , attached to the proximal end of the shroud portion  85  and diametrically opposed on each side of the patient end needle shroud  7 . The flexible lock-out legs  93  extend longitudinally outwardly from the proximal end of the shroud portion  85 , in line with the external surface of the shroud portion  85  and as an extension of it and are equally spaced with the guidance bosses  91  around the circumference of the shroud portion  85 . The flexible lock-out legs  93  have a stem  95  and a retention head  97 . Each retention head  97  has a ramped external surface  99  on its radially outwardly directed face. 
     The non-patient end needle shroud  11  is illustrated in detail in  FIGS. 12 and 13 . It is also generally tubular, with a shroud portion  101  that has a circular cross-section. An actuator plate  103  is formed at the proximal end of the shroud portion  101 . The actuator plate  103  is sized to fit within the collar  33 , so that it can be moved axially relative to the needle carrier  5 . The actuator plate  103  has at least a portion with a transversal width that is larger than the internal diameter of the screw threaded pen needle attachment portion of a cartridge housing  51 , to which the pen needle  1  is intended to be fitted. The actuator plate  103  has a circular needle aperture  105  located co-axially with the longitudinal axis Il-Il of the non-patient end needle shroud  7 . A spring guidance tube  107  extends in a distal direction from the distal side of the actuator plate  103  past the end of the shroud portion  101  and is co-axially aligned with the longitudinal axis Il-Il. The internal diameter of the spring guidance tube  107  is larger than the external diameter of the needle  3 . The external diameter of the spring guidance tube  107  is smaller than the internal diameter of the proximal spring  13 . The spring guidance tube  107  extends outside of the shroud portion  101 . The annular surface between the external circumference of the spring guidance tube  107  and the internal circumference of the shroud portion  101  provides a proximal spring seat  109  for the proximal spring  13 . Located at diametrically opposite positions on the shroud portion  101  are flexible lock-out tongues  111 . The lock-out tongues  111  are provided in the wall of the shroud portion  101 , between its proximal and distal ends. The radially external surface of each lock-out tongue  111  has a biasing surface  113  between its proximal and distal ends. Each lock-out tongue  111  is fixed at its proximal end to the shroud portion  101  and at its distal end it is free to move and has an abutment surface  115 . Each lock-out tongue  111  is biased outwardly such that in the absence of any externally radially applied force the biasing surface  113  extends outwardly at an oblique angle from the external surface of the shroud portion  101 , such that the abutment surfaces  115  extend at least partially outside of the shroud portion  101  in a radial direction. Track pins  77  are located adjacent to the distal end of the shroud portion  101  at diametrically opposite positions. The track pins extend radially outwardly and have a circular cross-section. The lock-out tongues  111  and the track pins  77  are equally spaced around the circumference of the shroud portion  101 . 
     The first step in assembly of the pen needle  1  is to locate the patient end needle shroud  7  into the housing  17 , as illustrated in  FIG. 14 . The housing  17  is provided on its internal surface with two pairs of longitudinally aligned, diametrically oppositely located, boss guiding ribs  117 , each pair of which ribs  117  defining between them a boss guiding channel  119 . Two diametrically oppositely located ramped retention head abutment surfaces  121  are also provided on the internal surface of the housing  17 . The boss guiding channels  119  and the retention head abutment surfaces  121  are equally spaced around the internal circumference of the housing  17 . A guiding boss  91  is located within the boss guiding channel  119  when the patient end needle shroud  7  is located within the housing  17 . The ramped surfaces  99  of the retention heads  97  of the lock-out legs  93  are brought into abutment with the retention head abutment surfaces  121 . Thus movement of the patient end needle shroud  7  relative to the housing  17  is prevented in a rotational direction by the boss guiding channels  119  and in an axial direction by the retention head abutment surfaces  121 . 
     The second step is to locate the distal spring  9  inside the housing  17  and in particular to seat it within the patient end needle shroud  7 . The internal proximally facing surface of the shroud portion  85  acts as a distal spring seat for the distal spring  9 . 
     The third step is to create a sub-assembly from the needle  3 , needle carrier  5 , proximal spring  13  and non-patient end needle shroud  11 . The sub-assembly is illustrated in  FIGS. 15, 16 and 17 . The needle  3  is fixed into the needle sleeve  37  using an adhesive. The proximal spring  13  is located around the spring guidance tube  107  of the non-patient end needle shroud  11  and seated on the proximal spring seat  109 . The free length of the proximal spring  13  is longer than the spring guidance tube  107 . The non-patient end needle shroud  11  is co-axially aligned with the needle carrier  5  and rotated to a position in which each of the two track pins  77  is aligned with an assembly slot  55  and an assembly channel  59  and each of the two flexible lock-out tongues  111  is aligned with a tongue deflection ramp  53 . The non-patient end needle shroud  11  is then inserted axially into the needle carrier  5 , each track pin  77  passes through an assembly slot  55  and enters an assembly channel  59  and the biasing surface  113  of each flexible lock-out tongue  111  engages with a tongue deflection ramp  53  such that each lock-put tongue  111  is deflected radially inwardly, to assume an orientation that allows it to enter the needle shroud guidance barrel  35 . The non-patient end needle shroud  11  is moved axially forwards and when each of the track pins  77  contacts a track pin cam surface  65  the inclined orientation of the track pin cam surface  65  causes the non-patient end needle shroud  11  to rotate in a clockwise direction, when viewed from the proximal end of the safety pen needle, so that the track pin  77  enters the transition channel  61 . Axial movement of the non-patient end needle shroud is ceased when each of the track pins  77  is longitudinally aligned with a track pin seat  75 . The force applied to the non-patient needle shroud  11  by the assembly equipment to cause its distally directed axial movement is then removed and the non-patient end needle shroud  11  is then moved in a proximal axial direction by a force provided by the proximal spring  13 , so that each of the track pins  77  is seated within a track pin seat  75  (first position). In order to align the track pins  77  within the track pin seats  75  the track pins  77  must be forced through the first narrow  79 . A moderate assembly force is sufficient to deflect the respective parts of the needle carrier  5  to open up the narrow  79  so that the track pins  77  can pass through. 
     The fourth step is to locate the needle carrier sub-assembly within the housing  17 . The needle carrier sub-assembly is rotated until the longitudinal alignment rib  43  is aligned with a rib alignment channel  123  provided in the housing  17 , the inter-engaging formations locating the carrier against rotation. The needle carrier  5  and the housing  17  are then brought together axially until the axial movement is arrested when the annular stop bead  45  snap-fits into annular stop channel  125 , the inter-engaging formations locating the carrier axially in the housing. 
     Finally, the pen needle  1  is placed in a primary container, typically a complementarily shaped plastics container (not shown) that is provided with a foil seal in order to maintain the sterility of the pen needle  1  before use. 
     A typical use of a pen needle  1  is for the delivery of a drug from a medicament cartridge of a pen type drug delivery device.  FIG. 18  shows the pen needle  1  fitted to a cartridge housing  51  by means of screw threads  47  and  49  respectively. The cartridge housing  51  has an annular end face  127  at its distal end which contacts the actuator plate  103  of the pen needle. The cartridge housing  51  is advanced into the pen needle  1  as it is screwed in, at a certain point its end face  127  contacts the actuator plate  103  and causes the non-patient end needle shroud  11  to move axially in a distal direction. The track pins  77  contact the track pin cam surfaces  65  and cause the non-patient end needle shroud  11  to rotate in a clockwise direction, when viewed from the proximal end of the pen needle  1 . The rotation continues until axial movement of the actuator plate  103  stops when the distal face of the actuator plate  103  contacts the proximal face of the annular transverse plate  39 . The track pins  77  are each located at that point within a track pin recess  67 , as shown in  FIG. 19 . In order to locate the track pins  77  within the track pin recesses  67  the track pins  77  must be forced through the second narrow  81 . The force applied to the pen needle  1  by the user when they are screwing it on to the cartridge housing  51  is sufficient to deflect the finger  83  to open up the narrow  81  so that the track pins  77  can pass through. When the pen needle  1  has been fully engaged with the cartridge housing  51  the needle  3  has pierced the septum of a cartridge (not shown) and an injection of the medicament can be delivered to the patient. When the injection has been completed the pen needle  1  is removed from the cartridge housing  51  to allow it to be placed in a bin for disposal. The action of unscrewing the pen needle  1  from the cartridge housing causes the patient end needle shroud  7  and the non-patient end needle shroud  11  to be deployed, such that the respective patient end of the needle  23  and non-patient end of the needle  25  are covered, in order to prevent needle-stick injuries. 
     The operation of the non-patient end needle shroud  11  will be described first. Unscrewing the pen needle  1  from the cartridge housing  51  allows the non-patient end needle shroud  11  to be driven in a proximal direction by the force from the proximal spring  13 . The track pins  77  move in a proximal direction in a second track portion and the motion control track  129  guides their movement, such that they do not move towards the transition channel  61 . The mouth  71  assists with the guidance of the track pins  77 . In any case, the second narrow  81  prevents the track pins  77  from passing back into the transition channel  61 , because the width of the neck is less than the diameter of the track pins  77  and the force provided by the proximal spring  13  is insufficient to deflect the finger  83 . The track pins  77  rest in the blind ends  73  once the pen needle  1  has been unscrewed from the cartridge housing  51 , thus limiting the proximal movement of the non-patient end needle shield  11 . 
     Simultaneous with the movement of the track pins  77 , the lock-out tongues  111  move axially in a proximal direction relative to the needle carrier  5 . When the abutment surfaces  115  move past the annular transverse plate  39 , the lock-out tongues  111  move radially outwards, so that the distance between the two most radially outwards points of the lock-out tongues  111  is greater than the internal diameter of the needle shroud guidance barrel  35 . The non-patient end needle shroud  11  cannot then be pushed back in an axial direction by a distance sufficient to uncover the non-patient end  25  of the needle  3  because the rotation of the non-patient end needle shroud  11  has caused the lock-out tongues  111  to move out of alignment with the tongue deflection ramps  53 . Instead the abutment surfaces  115  provided on the lock-out tongues  111  engage and latch with the proximal face of the annular transverse plate  39  of the needle carrier  5 , so that there can be no axial movement in a distal direction ( FIG. 21 ). 
     Operation of the patient end needle shroud  7  is driven by the distal spring  9 . The movement of the non-patient end needle shroud  11  in a proximal direction from its first position to a second position has withdrawn the spring guidance tube  107  from its previous position between the flexible lock-out legs  93  of the patient end needle shroud  7 , such that the flexible lock-out legs  93  are able to flex. The force applied to the patient end needle shroud  7  by the distal spring  9  causes the flexible lock-out legs  93  to flex radially inwardly as a result of interaction of the ramped surfaces  99  on the retention heads  97  with the ramped deflector surfaces  29  on the inside of the housing  17 . The radially inwards movement of the flexible lock-out legs  93  allows the needle shroud  7  to move axially forwards (distally) until guidance boss formations  91  reach the distal, blind, ends of the boss guiding channel formations  119  in the housing  17 , thereby limiting any further distal movement ( FIG. 22 ). The retention heads  97  pass the needle shield guidance ribs  27  and thus the flexible lock-out legs  93  expand radially outwardly. If a force is applied to the patient end needle shroud  7  in a proximal direction then the retention heads  97  will each come into abutment with an abutment shoulder  31  on the needle shroud guidance ribs  27 , thereby preventing exposure of the patient end  23  of the needle  3  and thereby guarding against a needlestick injury. 
     It is sometimes the case that a user may not fully screw the pen needle  1  on to the cartridge housing  51 . The pen needle  1  of the present invention has a geometry that can cope with a situation in which the pen needle  1  is only partially screwed on to the cartridge housing  51 . The length of the non-patient end needle shroud  11  is selected so that if even if the user only screws the pen needle  1  onto the cartridge housing body  41  for one revolution, the track pins  77  will move out of the transition channel  61  and into the locking channel  63 . In such a scenario the track pins  77  would not be located within the track pin recesses  67 , but upon unscrewing of the pen needle  1  from the cartridge housing  51  the track pins  77  would move towards the blind end  73  of the locking channel  63 , guided by the motion control track  129 , in the usual manner. 
     If the pen needle  1  is pushed onto a cartridge housing  51 , but the screw threads  47  and  49  are not engaged, then the non-patient end needle shroud  11  will only have been moved forwards axially in a distal direction by an extent such that the track pins  77  will remain within the transition channel  61 . If the user then removes the pen needle  1  from the cartridge housing  51 , for example because they have changed their minds about making an injection, then the non-patient end needle shroud  11  will return to its pre-use state, with the track pins  77  returning to the track pin seats  75 , ready for future use. 
     Accidental disassembly of the pen needle  1  or deployment of the patient and non-patient end needle shrouds  7  and  11  is prevented because the forces associated with such accidental acts are not sufficient to push the track pins  77  through either the first narrow  79  or the second narrow  81 . 
     The configuration of the non-patient end needle shroud/proximal shroud  11  (proximal member) means that actuation of the patient end shroud/distal shroud  7  can be effected by removal of the cartridge housing  51 , thus providing a way to avoid some of the problems associated with other designs. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  pen needle 
               3  needle 
               5  needle carrier 
               7  patient end needle shroud 
               9  distal spring 
               11  non-patient end needle shroud 
               13  proximal spring 
               15  hub 
               17  housing 
               19  patient end opening 
               21  non-patient end opening 
               23  patient end of needle 
               25  non-patient end of needle 
               27  needle shroud guidance rib 
               29  ramped deflector surface 
               31  abutment shoulder 
               33  collar 
               35  needle shroud guidance barrel 
               37  needle sleeve 
               39  annular transverse plate 
               41  collar flange 
               43  longitudinal alignment rib 
               45  annular stop bead 
               47  screw thread 
               49  screw thread 
               51  cartridge housing 
               53  tongue deflection ramp 
               55  assembly slot 
               57  guidance slot 
               59  assembly channel 
               61  transition channel 
               63  locking channel 
               65  track pin cam surface 
               67  track pin recess 
               69  track pin capture slot 
               71  mouth 
               73  blind end 
               75  track pin seat 
               77  track pin 
               79  first narrow 
               81  second narrow 
               83  finger 
               85  shroud portion 
               87  partially closed distal end 
               89  circular needle aperture 
               91  guidance boss 
               93  flexible lock-out leg 
               95  stem 
               97  retention head 
               99  ramped surface 
               101  shroud portion 
               103  actuator plate 
               105  circular needle aperture 
               107  spring guidance tube 
               109  proximal spring seat 
               111  lock-out tongue 
               113  biasing surface 
               115  abutment surface 
               117  boss guiding rib 
               119  boss guiding channel 
               121  retention head abutment surface 
               123  rib alignment channel 
               125  annular stop channel 
               127  annular end face 
               129  motion control track 
               130  shield