Needle assembly

Abstract

A needle assembly 100, such as a butterfly needle assembly, including a needle 104 coupled to a housing 102, the tip 106 of the needle extending from a forward end 107 of the housing in an in-use posi

Description

Technical field The invention relates to a needle assembly. Background Needle assemblies, such as butterfly needles, may be used to collect fluid from a patient (for example, blood collection) or to infuse fluid into a patient (for example, intravenous fluids or medications). Such needle assemblies typically comprise a housing and a needle, the needle extending from a forward end of the housing for insertion into a patient. A pair of flexible wings may also extend from the housing to allow a user or medical professional to grip the assembly during insertion of the needle into a patient, and optionally tape the needle assembly to the skin of the user during the fluid collection / infusion. The needle assembly may be connected to a fluid collection container or a fluid source by a length of flexible tubing, to allow fluid to be collected from the patient in the collection container or fluid to be infused into the patient from the fluid source. Needle assemblies may comprise needle retraction mechanisms, which are operable to retract the needle into the housing after use of the needle assembly (i.e. after the fluid has been collected or infused). Known needle retraction mechanisms may comprise a low force trigger button which may be pressed to initiate needle retraction, typically by releasing a spring that acts to urge the needle into the housing. Generally, needle retraction is initiated while the needle is still inserted in the patient, and so it is important for patient comfort that the needle retraction mechanism can be actuated by the user / medical professional easily and with minimal force. However, use of a low force trigger button may also increases the likelihood of accidental actuation / misfire of the needle retraction mechanism during use of the needle assembly to collect or infuse fluid. For example, the user may accidentally press the trigger button while gripping the needle assembly to undertake fluid collection or infusion. 06 05 25 This problem has been addressed in some needle assemblies by increasing the force that the user needs to apply to the trigger button in order to actuate needle retraction. While this reduces the chance of the trigger button being accidentally pressed, it also makes it more difficult for the user to purposely initiate needle retraction and may cause 5 discomfort to the patient, as the user is required to apply a high force to the needle assembly to actuate the needle retraction mechanism while the needle is still inserted within the patient. There exists a need for a needle assembly with an improved needle retraction 10 mechanism that addresses the above-mentioned problems. Summary According to the invention in a first aspect, there is provided a needle assembly 15 comprising: a housing; a needle coupled to the housing and having a needle tip at a forward end of the needle, the needle being in an in use position in which the needle tip extends from a forward end of the housing; a biasing member configured to urge the needle from the in use position to a retracted position in which the needle tip is within the housing; and a trigger mechanism configured to retain the needle in the in use position 20 against the urging of the biasing member, the trigger mechanism comprising a trigger rotatable with respect to the housing and configured to, upon application of a rearward force, cause release of the needle and thereby allow the biasing member to move the needle from the in use position to the retracted position. 25 Optionally, the trigger is rotatable with respect to the housing about an axis of rotation that is perpendicular to a longitudinal axis of the housing. Optionally, the needle assembly further comprises a needle carrier, the needle being fixed to the needle carrier, and the biasing member being configured to urge the needle 30 from the in use position to the retracted position via the needle carrier. Optionally, the biasing member is disposed between the needle carrier and an inner surface of the housing. Optionally, the trigger mechanism comprises a retention surface configured to engage the needle carrier to retain the needle in the in use position. Optionally, movement of the trigger in the substantially rearward direction causes the retention surface and the needle carrier to disengage to release the needle. Optionally, the substantially rearward movement of the trigger causes the trigger mechanism to rotate from a first rotational orientation in which the retention surface engages the needle carrier, to a second rotational orientation in which the retention surface and the needle carrier are disengaged. Optionally, the trigger mechanism comprises a trigger body comprising the retention surface, and wherein the trigger is rotationally coupled to the trigger body such that rotation of the trigger causes rotation of the trigger body from the first rotational orientation to the second rotational orientation. Optionally, the trigger mechanism is axially fixed relative to the housing. Optionally, the retention surface is curved and configured to engage a corresponding curved surface of the needle carrier. Optionally, the trigger mechanism comprises a release channel and wherein movement of the trigger in the substantially rearward direction causes the needle carrier and the release channel to align such that the needle carrier can move therethrough. Optionally, the trigger body defines the release channel. Optionally, the trigger body is substantially U-shaped. Optionally, the housing defines an aperture, and wherein at least a portion of the trigger extends through the aperture and is moveable therein. Optionally, opposed walls of the aperture are configured to limit forward and rearward movement of the trigger. 06 05 25 Optionally, the biasing member is configured to be held in a primed state between the needle carrier and the inner surface of the housing when the needle is in the in use position. 5 Optionally, the housing comprises a stop surface configured to engage the needle carrier when the needle is in the retracted position to prevent further movement of the needle carrier under the force of the biasing member. Optionally, the needle assembly is a butterfly needle assembly for fluid collection from a 10 patient and / or fluid infusion into a patient. According to the invention in a further aspect, there is provided a kit of parts for assembly into a needle assembly, the kit of parts comprising: a housing; a needle coupled to the housing and having a needle tip at a forward end of the needle, the needle being in an 15 in use position in which the needle tip extends from a forward end of the housing; a biasing member configured to urge the needle from the in use position to a retracted position in which the needle tip is within the housing; and a trigger mechanism configured to retain the needle in the in use position against the urging of the biasing member, the trigger mechanism comprising a trigger rotatable with respect to the housing and 20 configured to, upon application of a rearward force, cause release of the needle and thereby allow the biasing member to move the needle from the in use position to the retracted position. Optionally, the trigger is rotatable with respect to the housing about an axis of rotation 25 that is perpendicular to a longitudinal axis of the housing. Optionally, the needle assembly further comprises a needle carrier, the needle being fixed to the needle carrier, and the biasing member being configured to urge the needle from the in use position to the retracted position via the needle carrier. 30 Optionally, the trigger mechanism comprises a retention surface configured to engage the needle carrier to retain the needle in the in use position. Optionally, movement of the trigger in the substantially rearward direction causes the 35 retention surface and the needle carrier to disengage to release the needle. Optionally, the substantially rearward movement of the trigger causes the trigger mechanism to rotate from a first rotational orientation in which the retention surface engages the needle carrier, to a second rotational orientation in which the retention 5 surface and the needle carrier are disengaged. Optionally, the trigger mechanism comprises a trigger body comprising the retention surface, and wherein the trigger is rotationally coupled to the trigger body such that rotation of the trigger causes rotation of the trigger body from the first rotational 10 orientation to the second rotational orientation. Optionally, the trigger mechanism is axially fixed relative to the housing. Optionally, the retention surface is curved and configured to engage a corresponding 15 curved surface of the needle carrier. LO CXI LO Optionally, the trigger mechanism comprises a release channel and wherein movement of the trigger in the substantially rearward direction causes the needle carrier and the release channel to align such that the needle carrier can move therethrough. Optionally, the trigger body defines the release channel. Optionally, the trigger body is substantially U-shaped. Optionally, the housing defines an aperture, and wherein at least a portion of the trigger extends through the aperture and is moveable therein. Optionally, opposed walls of the aperture are configured to limit forward and rearward movement of the trigger. Optionally, the biasing member is disposed between the needle carrier and an inner surface of the housing. Optionally, the biasing member is configured to be held in a primed state between the needle carrier and the inner surface of the housing when the needle is in the in use position. Optionally, the housing comprises a stop surface configured to engage the needle carrier when the needle is in the retracted position to prevent further movement of the needle carrier under the force of the biasing member. Optionally, the needle assembly is a butterfly needle assembly for fluid collection from a patient and / or fluid infusion into a patient. According to the invention in a further aspect, there is provided a needle assembly comprising: a housing; a needle coupled to the housing and having a needle tip at a forward end of the needle, the needle being in an in use position in which the needle tip extends from a forward end of the housing; and a biasing member configured to urge the needle from the in use position to a retracted position in which the needle tip is within the housing. The needle assembly further comprises a trigger mechanism configured to retain the needle in the in use position against the urging of the biasing member, and operable to cause release of the needle and thereby allow the biasing member to move the needle from the in use position to the retracted position. Optionally, the trigger mechanism comprises a trigger configured, in a stowed position, to retain the needle in the in use position, and in an operable position to cause release of the needle. The trigger may be positioned further within the housing in the stowed position than in the operable position. Optionally, the trigger may extend from the housing by a first distance in the stowed position, and by a second distance which is greater than the first distance in the operable position. In some arrangements, the trigger may be completely separated from the housing in the operable position (i.e. removed completely from the housing). Optionally, the at least a portion of the trigger is moveable in a direction substantially perpendicular to a longitudinal axis of the housing from the stowed position to the operable position. Optionally, the needle assembly further comprises a needle carrier, the needle being fixed to the needle carrier, and the biasing member being configured to urge the needle from the in use position to the retracted position via the needle carrier. Optionally, the at least a portion of the trigger comprises a retention surface configured to engage a corresponding surface of the needle carrier to retain the needle in the in use position against the urging of the biasing member when the trigger is in the stowed position, and wherein movement of the trigger to the operable position disengages the retention surface from the corresponding surface of the needle carrier. Brief description of drawings Figure 1 shows a perspective view of an exemplary needle assembly with a needle in an in use position; Figure 2 shows a cross-section view of the exemplary needle assembly of Figure 1; Figure 3 shows a perspective view of an exemplary needle carrier and needle for use in a needle assembly; Figure 4 shows a perspective view of an exemplary trigger mechanism for use in a needle assembly; Figure 5 shows a perspective view of an exemplary rear part of a housing for use in a needle assembly; Figure 6 shows a perspective view of an exemplary forward part of a housing for use in a needle assembly; Figure 7 shows an exploded view of an exemplary needle assembly; Figure 8 shows a perspective view of an exemplary needle assembly with a needle in a retracted position; and Figure 9 shows a cross-section view of the exemplary needle assembly of Figure 8. Detailed description Generally disclosed herein is a needle assembly comprising a housing and a needle, wherein the needle is in an in use position in which a needle tip of the needle extends from a forward end of the housing. The needle assembly comprises a biasing member, such as a compression spring, configured to urge the needle into a retracted position in which the needle tip is located within the housing. The needle is retained in the in use position, against the urging of the biasing mechanism, by a trigger mechanism. In one embodiment, the trigger mechanism comprises a trigger which may be moved in a substantially rearward direction (i.e. in a direction away from the needle tip) to release the needle and allow the biasing member to move the needle to the retracted position. In an alternative embodiment, the trigger may be moveable from a stowed position, in which the needle is retained in the in use position, to an operable position, to release the needle, wherein the trigger is positioned further within the housing in the stowed position than in the operable position. The needle assembly may be a butterfly needle assembly for fluid collection from a patient and / or fluid infusion into a patient. The needle assembly may be suitable for use in a blood collection or blood transfusion procedure, or for use in an intravenous catheter / angiocatheter / angiocath, or any other process in which fluid is collected or infused into a patient. Movement of the trigger in a substantially rearward direction to initiate retraction of the needle, or else in a direction away from the housing (i.e. from the stowed position to the operable position), decreases the probability of a user accidentally initiating retraction of the needle. This is because movement of the needle assembly, and / or a component thereof, in a rearward direction, or a direction away from the housing, is not typically a movement that a user would undertake during insertion of the needle into a patient and the subsequent fluid collection / infusion. Typically, a user may move the needle assembly into position by gripping the housing (or butterfly wings in needle assemblies comprising butterfly wings) and then applying a forward force to the needle assembly to insert the needle into an injection site. While the user may therefore apply a squeezing force to the housing of the needle assembly (or components thereof) and / or a forward force to the housing of the needle assembly (or components thereof) during use, the user is unlikely to apply a rearward force (i.e. a force in a direction away from the needle tip) or a force in a direction away from the longitudinal axis of the housing during normal use of the needle assembly. The user is therefore required to intentionally move the trigger which they otherwise would not do in the normal course of use of the needle assembly, in order to trigger retraction of the needle. This mechanism of activation also enables, a low force trigger to be used, therefore increasing patient comfort. As used herein, the terms "forward" and "front" refer to the patient facing end of the needle assembly or component thereof. In other words, the front end of the needle assembly is the end proximal to the site into which the needle is inserted during use. Likewise, the term "rear" refers to the non-patient end of the needle assembly or component thereof. In other words, the term "rear" means distant / distal or remote from the site into which the needle is inserted during use. Further, the term longitudinal is used to encompass a direction along or parallel to a longitudinal axis of the needle assembly. Figure 1 shows an exemplary needle assembly 100. The needle assembly 100 comprises a housing 102 and a needle 104. The needle 104 comprises a needle tip 106 at a forward end thereof. In the arrangement shown in Figure 1, the needle is in an in use position, in which the needle tip 106 extends from an open forward end 107 of the housing 102 such that the needle tip 106 can be inserted into a patient. The needle 104 is movable with respect to the housing 102, as will be described in more detail below. The housing 102 shown is generally cylindrical; however, the skilled person would understand that the housing may have any shaped cross-section. The housing 102 comprises two parts, a rear part 108a and a forward part 108b. The rear part 108a and the forward part 108b are fixed to each other by virtue of a snap fit connection. In the exemplary arrangement of Figure 1, the forward part 108b comprises opposed lugs which snap fit into corresponding apertures of the rear part 108b. The skilled person will appreciate that alternative connections may be used, such as latches, adhesives, hinged arrangements, etc. in order to connect the forward and rear parts 108a, 108b to each other. Additionally, the skilled person would understand that the housing 102 may take any suitable configuration As can be seen in Figure 2, which is a cross-section view of the needle assembly 100 of Figure 1, a plurality of components of the needle assembly 100 are at least partially received within the housing 102. The needle assembly 100 comprises a needle carrier 110, a biasing member 112 and a trigger mechanism 114. At least a portion of each of the needle carrier 110, the biasing member 112 and the trigger mechanism 114 are received within the housing 102. Figure 3 shows the needle carrier 110 and needle 104 in isolation. The needle carrier 110 is coupled to the needle 104 such that movement of the needle carrier 110 causes corresponding movement of the needle 104. In the arrangement shown in Figures 1 to 3, the needle carrier 110 defines a bore that extends at least partially through the length of the needle carrier 110 and which receives at least a portion of the needle 104 therein to couple the needle 104 to the needle carrier 104 (e.g. by interference fit, adhesive etc.). The skilled person will however appreciate that the needle 104 may be coupled to the needle carrier 110 using alternative coupling means. The needle carrier 110 comprises a shoulder 118. As will be described in more detail below, an end of the biasing member 112 abuts the shoulder 118 of the needle carrier 110 to impart a biasing force onto the needle carrier 110 (and therefore the needle 104). In the arrangement of Figure 3, the needle carrier 110 comprises a first portion 120 and a second portion 122. The first portion 120 and the second portion 122 are generally cylindrical and the second portion 122 has a smaller diameter than the first portion 120 such that the shoulder 118 is defined at the junction between the first and second portions 120, 122. The skilled person will appreciate than in alternative needle carriers, alternative shoulders / abutment surfaces against which the biasing member 112 abuts may be defined. For example, the needle carrier 110 may be of constant diameter and comprise one or more radially extending projections against which the biasing member 112 may abut. As can be seen in Figure 2, in the exemplary needle assembly 100, the biasing member 112 is disposed between the needle carrier 110 and the housing 102. When the needle 104 is in the in use position, the biasing member 112 is retained in a primed state between the needle carrier 110 and the housing 102, as shown in Figure 2. A first end of the biasing member 112 abuts the shoulder 118 of the needle carrier 110, and a second end of the biasing member 112 abuts an inner surface 128 of the housing 102 (visible in Figure 2). In the configuration shown in Figures 1 and 2, in which the needle 104 is in the in use position, the biasing member 112 is retained in a primed state between the shoulder 118 of the needle carrier 110 and the inner surface 128 of the housing 102 by the trigger mechanism 114. In the arrangements disclosed herein, the exemplary biasing member 112 comprises a compression spring, which is located around the second portion 122 of the needle carrier 110. The skilled person will appreciate that alternative biasing members may be used in alternative arrangements however. Alternative embodiments include, but are not limited to, a polymer spring moulded into the needle base, an elastomer, a rubber band, foam or a gas strut. The trigger mechanism 114 is shown in isolation in Figure 4. The trigger mechanism 114 comprises a trigger 132 and a trigger body 134. The trigger 132 extends from the trigger body 134. The trigger mechanism 114 further comprises a retaining portion 136, and in the arrangement of Figure 4, the trigger body 134 comprises the retaining portion 136. The trigger mechanism 114 is rotatably coupled to the housing 102. The trigger mechanism 114 is rotatable with respect to the housing 102 about an axis 137. The axis 137 is perpendicular to a longitudinal axis 138 of the needle assembly 100 (and the housing 102), as can be seen in Figure 1. The trigger body 134 is substantially U-shaped. The exemplary trigger body 134 shown in Figure 4 comprises opposed lugs 140a, 140b. The opposed lugs 140a, 140b extend outwardly from the trigger body 134, and in the arrangement of Figure 4, extend outwardly from opposed walls 142a, 142b of the trigger body 134. The opposed lugs 140a, 140b of the trigger body 134 are received within corresponding apertures of the housing 102. In the exemplary arrangement shown in Figures 1-4, the opposed lugs 140a, 140b are cylindrical and are received within corresponding circular apertures of the housing 102. In exemplary arrangements, the corresponding apertures are defined by slots 143a, 143b of the rear part 108a and slots 145a, 145b of the forward part 108b of the housing. The slots 143a, 143b and 145a, 145b comprise an open end. The slots 143a, 143b and 145a, 145b comprise curved slots, and specifically semi-circular slots, such that when the open ends of each of the corresponding slots are aligned, and the rear and forward parts 108a, 108b are connected, circular apertures are formed. The slots 143a, 143b are defined by the rear part 108a of the housing 102. One of the slots 143a is visible in Figure 5, which shows the rear part 108a of the housing 102 in isolation, and the skilled person will appreciate that the other slot 143b is similar but opposed. As can be seen in Figure 5, the slots 143a, 143b are defined by an inner surface of the rear part 108a of the housing 102. The slots 145a, 145b are defined by the forward part 108b of the housing 102. Slot 145b is visible in Figure 6, which shows the forward part 108b of the housing 102 in isolation. The skilled person will appreciate that the slot 145a is similar but opposed. On connection of the rear part 108a and forward part 108b, the slot 143a of the rear part 108a aligns with the slot 145a of the forward part 108b, and the slot 143b of the rear part 108a aligns with the slot 145b of the forward part 108b to define the corresponding apertures. The corresponding apertures may be dimensioned to allow rotation of the lugs 140a, 140b therein, such that the trigger mechanism 114 may rotate with respect to the housing 102. The skilled person will appreciate that the lugs may be provided on the housing with corresponding apertures being defined by the trigger body. Further, alternative rotational coupling mechanisms may be used to rotatably couple the trigger mechanism 114 and the housing 102. The retaining portion 136 of the trigger mechanism 114 comprises a retention surface 144 (visible in Figure 4) configured to abut the needle carrier 110 to prevent axial movement of the needle carrier 110, and therefore the needle 104, in a rearward direction. That is, the retention surface 144 retains the needle 104 in the in use position, against the force of the biasing member 112, when the retention surface 144 and the needle carrier 110 are abutting one another. The retention surface 144 of the trigger mechanism 114 is configured to abut an end face, and specifically a rear end face, of the needle carrier 110. In the exemplary trigger mechanism 114 shown in Figure 4, the retention surface 144 is curved; however the skilled person would understand that other shaped surfaces may be used. The retention surface 144 is curved in a direction about the axis of rotation 137 of the trigger mechanism 114. The end face of the needle carrier 110 comprises a correspondingly curved portion; however the skilled person would understand that other shaped surfaces may be used. The curved shape of the retention portion 144 and the end face of the needle carrier 110 facilitates rotation of the trigger mechanism 114 relative to the needle carrier 110 to draw the retention surface 144 out of engagement with the needle carrier end face, as will be described in further detail below. The trigger body 134 defines a release channel 150 configured to allow the needle carrier 110 to move therein. That is, the release channel 150 is shaped and dimensioned such that the needle carrier 110 can move within the release channel 150. The release channel 150 is angularly spaced with respect to the retaining portion 136 about the axis of rotation 137 of the trigger mechanism 114. In the exemplary arrangement shown in Figure 4, the release channel 150 is defined by the free space created by the substantially U-shaped trigger body 134. Specifically, the free space between the opposed walls 142a, 142b of the trigger body 134. In alternative arrangements, in which the trigger body 134 is a different shape, the release channel 150 may comprise a bore than extends through the trigger body 134, or alternatively, the trigger body 134 may not define a release channel 150 but rather be movable to create a free volume with the housing 102 through which the needle carrier 110 may move (i.e. the needle carrier 110 may not move “through” a portion of the trigger body 134). The trigger 132 of the trigger mechanism 134 extends, at least partially, through an aperture 154 defined by the housing 102, as can be seen in Figures 1 and 2. The trigger 132 is moveable within the aperture 154. The needle assembly 100 comprises stops configured to limit the movement of the trigger 132. More specifically, the stops are configured to the limit the extent of rotation of the trigger mechanism 114 about the axis of rotation 137. In the exemplary arrangement of Figures 1 and 2, the stops comprise a forward wall 156a of the aperture, and an opposed rear wall 156b of the aperture 154. As can be seen in Figures 5 and 6, the aperture 154 is defined by slots 158 and 160 defined in the rear part 108a and the forward part 108b of the housing 102 respectively. The slots 158 and 160 are open at one end. The slots 158 and 160 are configured such that when the open ends of the slots 158 and 160 are aligned, and the rear part 108a and the forward part 108b are connected together, the aperture 154 is formed. The rear part 108a comprises opposed legs 162a, 162b which define fixing apertures 164a, 164b respectively. The opposed legs 162a, 162b are configured to be received within corresponding guide channels 166a, 166b of the forward part 108b of the housing 102. The guide channels 166a, 166b comprise lugs 168a, 168b configured to engage the corresponding fixing apertures 164a, 164b to fix the forward and rear parts 108b, 108a together. Only the guide channel 166b and lug 168b are visible in Figure 6, however the skilled person will appreciate the guide channel 166a and lug 168a are similar but located on an opposed side of the front part 108b of the housing 102. The skilled person will appreciate that alternative connection mechanisms may be used, such as screw threads, hinges, latches etc. The skilled person will also appreciate that alternative ways are available to define the aperture in the housing. The housing 102, and in the exemplary arrangement described herein, the rear part 108a of the housing 102, may further define a stop surface 169 (visible in Figure 2). The stop surface 169 comprises an inner surface of the housing 102 located at the rear of the needle assembly 100. The stop surface 169 may be located at a position along the length of the housing 102 to define the retracted position of the needle 104, as will be explained below. As can be seen in Figure 1, the needle assembly 100 further com prises wings, or butterfly wings, 170a, 170b. The wings 170a, 170b are coupled to the housing 102 by a mount 172, which in the arrangement shown in Figure 1, is a tubular mount that locates around the housing 102. That is, the tubular mount defines a passage within which the housing 102 is received. The wings 170a, 170b extend laterally with respect to the housing 102. The wings 170a, 170b are flexible. A first surface 174a, 174b of each of the wings 170a, 170b may be substantially smooth, while an opposed surface (not visible in Figure 1) of each of the wings 170a, 170b may be textured to facilitate gripping of the wings 170a, 170b. Each wing 170a, 170b may be deformed about the housing 102 to facilitate gripping of the needle assembly 100. For example, wings 170a, 170b may be deformed about the housing such that the respective first surfaces 174a, 174b contact each other. The skilled person will appreciate that alternative needle assemblies need not have the wings 170a, 170b. An exemplary method of assembling the needle will now be described with reference to Figures 1 to 7. The needle carrier 110 and the needle 104 may be fixed together, both axially and rotationally. For example, the needle 104 may be received within a bore of the needle carrier 110 and secured therein by virtue of an interference fit and / or an adhesive to prevent relative axial and rotational movement therebetween. The biasing member 112 is positioned such that a first end of the biasing member 112 abuts the shoulder 118 of the needle carrier 110. Positioning the biasing member 112, which as described above is a compression spring in this example, comprises locating the biasing member 112 around the second portion 122 of the needle carrier 110. The needle carrier 110, needle 104 and biasing member 112 subassembly may be inserted into the forward part 108b of the housing 102, as shown in Figure 7, by applying a forward force to the subassembly. The forward force may be applied to the subassembly until the at least a portion of the needle 104 passes through the open forward end 107 defined by the forward part 108b of the housing 102, and the second end of the biasing member 112 contacts the inner surface 128 of the forward part 108b of the housing 102. In this position, the biasing member 112 is in an extended, or noncompressed, state. The trigger mechanism 114 and the rear part 108a of the housing 102 may then be coupled to the forward part 108b of the housing 102 and the subassembly (formed of the needle carrier 110, needle 104 and biasing member 112). Coupling the trigger mechanism 114 and the rear part 108b of the housing to the forward part 108b and the subassembly causes the biasing member 112 to be compressed, or primed, and the needle 104 to be placed in the in use position. The retention surface 144 of the trigger mechanism 114 may be brought into abutment with the rear end of the needle carrier 110, and a forward force is then applied to the trigger mechanism 114 to compress the biasing member 112 between the shoulder 118 of the needle carrier 110 and the inner surface 128 of the forward part 108b of the housing 102. The forward force is applied to the trigger mechanism 114 until the opposed lugs 140a, 140b of the trigger mechanism 114 locate within and abut the walls of the slots 145a, 145b of the forward part 108b of the housing 102. In this position, the biasing member 112 is in the compressed, or primed, state and the needle 104 is in the in use position. The forward force may be applied to the trigger mechanism 114 via the rear part 108a of the housing 102. That is, the retention surface 144 may be brought into abutment with the rear end of the needle carrier 110, and the rear part 108a may then be located over the trigger mechanism 114 such that a forward force applied to the rear part 108a to connect the rear part 108a to the forward part 108b, causes a forward force to be applied to the trigger mechanism 114 to compress the biasing member 112. Alternatively, the trigger mechanism 114 may be located within the rear part 108a, for example, by locating the opposed lugs 140a, 140b of the trigger mechanism 114 within the corresponding slots 143a, 143b of the rear portion 108a, and then the trigger mechanism 114 and rear part 108a may together be moved into engagement with the needle carrier 110 and the forward part 108b of the housing. A forward force is applied to the rear part 108a until the rear part 108a connects to the forward part 108b. Connecting the rear part 108a to the forward part 108b may comprise aligning the legs 162a, 162b of the rear part 108a with the corresponding guiding channels 166a, 166b of the forward part 108b, and applying a forward force to the rear part 108a to move the legs 162a, 162b within the guiding channels 166a, 166b until the lugs 168a, 168b engage the fixing apertures 164a, 164b. Once the rear and forward parts 108a, 108b are connected, the biasing member 112 is held in the primed position. Furthermore, the trigger mechanism 114 is rotatably coupled to the housing 102 by virtue of the opposed lugs 140a, 140b locating within the apertures formed by the slots 143a, 143b and 145a, 145b. Connection of the rear part 108a and the forward part 108b further forms the aperture 154 by aligning the slots 158 and 160. The trigger 132 extends through the aperture 154, and abuts the forward wall 156a of the aperture 154. In this rotational position of the trigger mechanism 114, the retention surface 144 is in engagement with the needle carrier 110. Although the present device has been described in relation to a front body and rear body the skilled person will understand that other ways are available for forming the housing. For example, there may be an upper body and a lower body or a housing and a rear cap which closes an aperture in the rear of the housing. Additionally, any suitable mechanism may be used to connect parts of the housing. For example, but not limited to, adhesive, a screw thread, spring clips. Use of the needle assembly 100 will now be described. Figures 1 and 2 show the needle assembly 100 in a ready to use configuration. The needle 104 is in the in use position, in which the needle tip 106 extends from the open forward end 107 of the housing 102. Axial movement of the needle 104 is prevented in the in use position by the trigger mechanism 114. Specifically, axial movement of the needle carrier 110 is prevented when the needle 104 is in the in use position, by the engagement of the retention surface 144 of the trigger mechanism 114 and the rear end of the needle carrier 110. As such, the biasing member 112 is held in a primed position between the housing 102 and the needle carrier 110. Prior to use of the needle assembly 100, the trigger mechanism 114 is in a first rotational orientation. In the first rotational orientation, the trigger mechanism 114 prevents the needle 104 from moving relative to the housing 102 under the force of the biasing member 112. The first rotational orientation may encompass a rotational range about the axis of rotation 137, within which the trigger mechanism 114 can rotate and still retain the needle 104 in the in use position. In the first rotational orientation, which as described above may encompass a rotational range, the retention surface 144 of the trigger mechanism 114 engages the needle carrier 110 to prevent movement of the needle 104 with respect to the housing 102. In the first rotational orientation, the trigger 132 abuts the forward wall 156a of the aperture 154 of the housing 102, or else is within a threshold angular range from the forward wall 156a, about the axis of rotation 137. It is noted that while the trigger mechanism 114 is rotatable with respect to the housing 102, the axial position of the trigger mechanism 114 with respect to the housing 102 is fixed. In the exemplary arrangement shown, the axial position of the trigger mechanism 114 is fixed by virtue of the opposed lugs 140a, 140b of the trigger mechanism 114 locating within the corresponding apertures formed by the rear and forward parts 108a, 108b of the housing 102. Rotation of the trigger mechanism 114 with respect to the housing 102 is resisted by virtue of frictional forces between the retention surface 144 and the needle carrier 110. The biasing member 112 applies a force to the needle carrier 110 that pushes the needle carrier 110 into abutment with the retention surface 144 of the trigger mechanism 114. A threshold force needs to be applied to the trigger mechanism 114 to overcome the frictional forces and rotate the trigger mechanism 114 such that the retention surface 144 is disengaged from the needle carrier 110. The needle assembly 100 may be used to collect a fluid from, or infuse a fluid into, a patient. In use, the needle assembly 100 is moved into position towards an injection site of a patient. In arrangements in which the needle assembly 100 comprises the butterfly wings 170a, 170b, a user may use the butterfly wings 170a, 170b to grip and manoeuvre the needle assembly 100 during use. The user may deform the butterfly wings 170a, 170b towards one another such that the surfaces 174a, 174b of the respective butterfly wings 170a, 170b are brought into face-to-face engagement and gripped, for example, between a thumb and finger of the user. In arrangements without butterfly wings, the user may grip the housing 102 to guide the needle assembly 100 towards the injection site. The needle assembly may then be guided towards the injection site. The user may at this stage (or before) also connect the needle assembly to a fluid collection container, if a fluid is being collected from a patient, or a fluid source if a fluid is being infused into a patient. The user then inserts the needle 104 into the user and undertakes the relevant medical procedure, which in this example is either fluid collection or fluid infusion. Once the medical procedure has been completed the user may actuate the trigger mechanism to retract the needle 104 into the housing 102 to prevent needle stick injuries. The user actuates the trigger mechanism by moving the trigger mechanism 114 into a second rotational orientation, in which the retention surface 144 is disengaged from the needle carrier 110. Figure 8 shows a perspective view of the needle assembly 100 with the trigger mechanism 114 in the second rotational orientation and the needle 104 in a retracted position, and Figure 9 shows a cross-section view of the trigger mechanism 114 in the second rotational orientation and the needle 104 in a retracted position. To move the trigger mechanism 114 into the second rotational orientation to release the biasing member 112, the user applies a force F to the trigger 132 in a substantially rearward direction (shown schematically by arrow F in Figure 9). This causes the trigger mechanism 114 to rotate about the axis of rotation 137 (shown schematically by arrow R in Figure 9), towards the rear of the needle assembly 100. This causes the retention surface 144 to disengage the needle carrier 110. In the exemplary arrangement disclosed herein, the retention surface 144 rides over the rear surface of the needle carrier 110 until the retention surface 114 no longer abuts the rear surface of the needle carrier 110. The needle carrier 110 is then free to move in a rearward direction within the housing 102 under the force of the biasing member 112. The user may apply force F to the trigger 132 until the trigger 132 contacts the rear wall 156b of the aperture 154. The rear wall 156b of the aperture 154 is configured to limit the rearward movement of the trigger 132 to prevent the trigger mechanism 114 from being moved into a rotational orientation in which a portion thereof could act to again interfere with the rearward movement of the needle carrier 110 under the force of the biasing member 112. As mentioned above, in order to draw the retention surface 144 out of engagement with the needle carrier 110, the user is required to overcome the frictional forces therebetween. It will be appreciated that these frictional forces may be relatively low since the forces applied by the biasing member 112 can be relatively low. As such, some resistance is provided (e.g. to prevent accidental rotation of the trigger mechanism 114 into the second rotational orientation under the force of gravity), but the user is not required to apply significant force to the trigger 132 in order to move the trigger mechanism 114 into the second rotational orientation. Prevention of accidental initiation of needle retraction is instead provided by requiring the user to apply a force to the trigger mechanism 114 in a substantially rearward direction, which is not a direction in which the user would typically apply a force during insertion of the needle assembly into a patient. When the trigger mechanism 114 is in the second rotational orientation, the release channel 150 is aligned with the needle carrier 110. As such, the needle 104 is free to move in a rearward direction within the housing 102 under the force of the biasing member 112. The needle 104 moves within the housing 102 under the force of the biasing member 112 until the rear end of the needle carrier 110 contacts the stop surface 169 defined by the rear part 108a of the housing 102, as shown in Figure 9. In this position, the needle carrier 110, and therefore the needle 104, are prevented from moving any further within the housing 102 in the rearward direction. The needle 104 is in the retracted position. When the needle 104 is in the retracted position, the needle tip 106 is received within the housing 102 and is located at a predetermined distance from the open forward end 107 defined by the forward part 108b of the housing 102. Once the needle 104 is in the retracted position, the user is safe to remove the needle assembly 100 from the injection site without risk of a needle stick injury. As mentioned, in order to initiate needle retraction in the needle assembly 100 disclosed herein, the user is required to apply a force to the trigger in a substantially rearward direction, away from the needle end of the needle assembly 100. The user would not typically apply a force in a rearward direction during use of the needle assembly 100 to undertake the medical procedure, and therefore the chances of the user accidentally initiating needle retraction are reduced. The skilled person will appreciate a trigger mechanism operable by a user action in a substantially rearward direction, may be achieved using alternative needle assemblies / trigger mechanisms to those shown in Figures 1-9. For example, the trigger may comprise a slide button, such that the user may operate the trigger mechanism by apply a force in a rearward direction to slide the slide button towards the rear of the device. In such arrangements, the trigger may not be rotatable but instead moved axially in a rearward direction, for example parallel to the longitudinal axis of the needle assembly. Movement of the slide button in the rearward direction may act to disengage a retention surface of the trigger mechanism from the needle carrier, either by initiation rotation of the retention surface relative to the needle carrier, or otherwise (e.g. disengaging a lug of the trigger mechanism from a recess of the needle carrier, by relative rotational or axial movement between the trigger mechanism and the needle carrier). The skilled person will be familiar with methods by which relative mechanical movement may be initiated, e.g. by using corresponding angled surfaces to initiate rotation, or guide track / lug arrangements to initiate relative rotation and / or axial movement. The skilled person will be able to envisage further trigger arrangements which are operable by a user moving a trigger in a rearward direction. In addition, although the present embodiment describes a trigger mechanism operable by a user in a substantially rearward direction, the skilled person would understand that the trigger mechanism may be rotatable in any other suitable direction. For example, the trigger may be rotatable in a direction perpendicular to the longitudinal axis of the needle assembly. Even more specifically, the trigger may be rotatable in an upward direction away from the surface of the patient’s skin in order to align the retraction channel with the needle carrier to enable retraction of the needle. In such an embodiment the aperture shape would be configured in such a way to allow the parallel rotation of the trigger. In another embodiment, the needle assembly may comprise a “grenade pin” trigger mechanism comprising a trigger that can be pulled out of the housing (partially or completely) in order to initiate needle retraction. Similarly to the needle assembly 100 described above, such needle assemblies comprise a housing; a needle coupled to the housing and having a needle tip at a forward end of the needle, the needle being in an in use position in which the needle tip extends from a forward end of the housing; and a biasing member configured to urge the needle from the in use position to a retracted position in which the needle tip is within the housing. Such arrangements, may further comprise a trigger mechanism comprising a trigger configured, in a stowed position, to retain the needle in the in use position against the urging of the biasing member and, in an operable position, configured to cause release of the needle and thereby allow the biasing member to move the needle from the in use position to the retracted position. The trigger is positioned further within the housing in the stowed position than in the operable position. In other words, the user is required to pull the trigger away from / out of the housing in order to release the needle. The trigger may comprise a retention surface / retention pin that is at least partially received in the housing (e.g. through an aperture defined by the housing) in the stowed position, and that interacts with the needle to retain the needle in the in use position. In arrangements in which the needle is fixed to a needle carrier, the retention surface / retention pin engages a corresponding surface of the needle carrier to retain the needle in the in use position. At least a portion of the trigger may extend from the housing when the trigger is in the stowed position such that the user can grip the trigger and apply a force thereto in a direction away from the housing. The user may pull the trigger out of the housing (either partially or completely) so as to disengage the retention surface / retention pin from the needle carrier, and thereby cause release of the needle and allow the biasing member to move the needle to the retracted position. Alternatively, the retention surface / retention pin may have a surface which the needle carrier abuts and rearward motion of the retention surface / retention pin allows rearward motion of the needle carrier. In exemplary arrangements, the retention surface / retention pin may be moveable in a direction substantially perpendicular to the longitudinal axis of the housing to move the trigger from the stowed position to the operable position. Advantageously, by requiring movement of the trigger in a direction away from the housing, the probability of the user accidentally initiating retraction of the needle is reduced, since the user is unlikely to undertake this type of movement when using the needle assembly. The skilled person will be able to envisage further embodiments of the invention without departing from the scope of the appended claims.

Claims

30 05 251. A needle assembly comprising:a housing;5 a needle coupled to the housing and having a needle tip at a forward end of theneedle, the needle being in an in use position in which the needle tip extends from a forward end of the housing;a biasing member configured to urge the needle from the in use position to a retracted position in which the needle tip is within the housing; and10 a trigger mechanism configured to retain the needle in the in use position againstthe urging of the biasing member, the trigger mechanism comprising a trigger rotatable with respect to the housing and wherein rearward movement of the trigger upon application of a rearward force is configured to cause rotation of the trigger towards the rear of the needle assembly and release the needle and thereby allow the biasing15 member to move the needle from the in use position to the retracted position.

2. A needle assembly according to claim 1, wherein the trigger is rotatable with respect to the housing about an axis of rotation that is perpendicular to a longitudinal axis of the housing.

203. A needle assembly according to any preceding claim, further comprising a needle carrier, the needle being fixed to the needle carrier, and the biasing member being configured to urge the needle from the in use position to the retracted position via the needle carrier.

254. A needle assembly according to claim 3, wherein the trigger mechanism comprises a retention surface configured to engage the needle carrier to retain the needle in the in use position.30 5. A needle assembly according to claim 4, wherein movement of the trigger in thesubstantially rearward direction causes the retention surface and the needle carrier to disengage to release the needle.

6. A needle assembly according claim 4 or 5, when dependent directly or indirectly35 on claim 2, wherein the substantially rearward movement of the trigger causes the trigger30 05 25mechanism to rotate from a first rotational orientation in which the retention surface engages the needle carrier, to a second rotational orientation in which the retention surface and the needle carrier are disengaged.5 7. A needle assembly according to claim 6, wherein the trigger mechanismcomprises a trigger body comprising the retention surface, and wherein the trigger is rotationally coupled to the trigger body such that rotation of the trigger causes rotation of the trigger body from the first rotational orientation to the second rotational orientation.10 8. A needle assembly according to claim 6 or 7, wherein the trigger mechanism isaxially fixed relative to the housing.

9. A needle assembly according to any of claims 6 to 8, wherein the retention surface is curved and configured to engage a corresponding curved surface of the needle 15 carrier.

10. A needle assembly according to any of claims 3 to 9, wherein the trigger mechanism comprises a release channel and wherein movement of the trigger in the substantially rearward direction causes the needle carrier and the release channel to 20 align such that the needle carrier can move therethrough.

11. A needle assembly according to claim 10, when directly or indirectly dependent on claim 8, wherein the trigger body defines the release channel.25 12. A needle assembly according to claim 11, wherein the trigger body issubstantially U-shaped.

13. A needle assembly according to any preceding claim, wherein the housing defines an aperture, and wherein at least a portion of the trigger extends through the 30 aperture and is moveable therein.

14. A needle assembly according to claim 13, wherein opposed walls of the aperture are configured to limit forward and rearward movement of the trigger.30 05 2515. A needle assembly according to claim 3, or any of claims 4 to 14 when dependent directly or indirectly on claim 3, wherein the biasing member is disposed between the needle carrier and an inner surface of the housing.5 16. A needle assembly according to claim 15, wherein the biasing member isconfigured to be held in a primed state between the needle carrier and the inner surface of the housing when the needle is in the in use position.

17. A needle assembly according to any of claims 3 to 16, wherein the housing10 comprises a stop surface configured to engage the needle carrier when the needle is in the retracted position to prevent further movement of the needle carrier under the force of the biasing member.

18. A needle assembly according to any preceding claim, wherein the needle 15 assembly is a butterfly needle assembly for fluid collection from a patient and / or fluid infusion into a patient.

19. A kit of parts for assembly into a needle assembly, the kit of parts comprising:a housing;20 a needle coupled to the housing and having a needle tip at a forward end of theneedle, the needle being in an in use position in which the needle tip extends from a forward end of the housing;a biasing member configured to urge the needle from the in use position to a retracted position in which the needle tip is within the housing; and25 a trigger mechanism configured to retain the needle in the in use position againstthe urging of the biasing member, the trigger mechanism comprising a trigger rotatable with respect to the housing and wherein rearward movement of the trigger upon application of a rearward force is configured to cause rotation of the trigger towards the rear of the needle assembly and release the needle and thereby allow the biasing30 member to move the needle from the in use position to the retracted position.

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