Needle assemblies

Abstract: A spinal-epidural needle assembly has a rearwardly-extending sleeve 16 on the epidural needle 1 that has a series of circumferentially-extending ribs 22 on its outer surface. The spinal needle has a collar 32 extending forwardly from its hub 31 and slidable along outside of the sleeve 16 of the epidural needle. The collar 32 has a small elastomeric pad 33 on its inner surface, which is slidable along a smooth region 20 to one side of the ribbed region 21. The spinal needle 2 is locked longitudinally relative to the epidural needle 1 by twisting its collar 32 so that the elastomeric pad 33 slides laterally over the ribbed region 21 with the ribs 22 gripping into the pad.

Description: This invention relates to needle assemblies of the kind comprising a first needle and a second needle insertable within the first needle, the first needle having a hub at its rear end with a rearwardly-extending member, the second needle having a hub at its rear end with a forwardly-extending member, one of the members being insertable within the other member, and the external surface of the one member and the internal surface of the other member having cooperating gripping formations. The invention is more particularly concerned with spinal-epidural needle assemblies. Spinal-epidural needle assemblies are used for the administration of spinal and epidural anaesthetic fluid. The epidural needle is inserted, in the usual way, into the epidural space. A spinal needle is then inserted through the epidural needle until its tip punctures the dura and enters the subarachnoid space. A syringe is attached to the machine end of the spinal needle and spinal anaesthetic is administered through the spinal needle to produce a rapid but short-lived anaesthetic block. The spinal needle is then removed, leaving the epidural needle in position. An epidural catheter is inserted through the epidural needle so that its patient end is located in the epidural space. The needle is then removed, leaving the catheter in position so that anaesthetic fluid can be administered, as necessary, into the epidural space to produce a longer-lasting anaesthetic effect. Once the tip of the spinal needle has been correctly inserted, its position must be maintained while the anaesthetic fluid is administered. This can be difficult to do because, although the epidural needle is retained relatively securely by the frictional contact with the tissue through which it is inserted, the spinal needle has a relatively low-friction engagement with the bore of the epidural needle. The anaesthetist must hold the spinal needle during connection of the spinal needle to the syringe and during the administration of the spinal anaesthetic. If the needle should slip, there is the risk of it puncturing the distal wall of the subarachnoid space or of it being pulled out into the epidural space. Various proposals have been suggested for arrangements by which the spinal needle can be fixed relative to the epidural needle once the spinal needle has been correctly inserted. In Anaesthesia 1990: 45: 593 -594 and Acta Anaesthesiologica Scand 1994: 38: 439-441, J Simsa describes a metal screw clamp attached to the epidural needle hub by which the spinal needle can be fixed in position. In EP 0564859A there is described an assembly where the spinal needle makes a bayonet-like connection with the epidural hub so that the two can be locked together, but this only enables the spinal and epidural needles to be fixed at one location. EP 0696437 which is the closest prior art, describes an assembly in which the spinal needle hub has a resilient locking tab that engages between a series of teeth formed on an extension of the epidural hub. This arrangement requires the user to hold the tab in the released position while inserting the spinal needle; also, the space between the teeth limits the precision with which the spinal needle can be locked in position. It is an object of the present invention to provide an improved needle assembly. According to the present invention there is provided a needle assembly of the above-specified kind, characterised in that one of the gripping formations includes an elastomeric member, and the other of the gripping formations comprises first and second elongate regions extending parallel to one another side-by-side along the respective member, that the first region is configured to receive the elastomeric member as a sliding fit along its length, and that the second region is provided with surface formations that enable the elastomeric member to be slid laterally over the surface formations when the two members are twisted relative to one another but prevent longitudinal movement of the elastomeric member along the second region so that the two members are locked longitudinally with one another. The surface formations are preferably provided by a series of parallel ribs extending laterally in the second region. The series of ribs may comprise alternate long and short ribs. The rearwardly-extending member is preferably insertable within the forwardly-extending member. The two needles are preferably rotatable relative to one another to a limited extent after being locked longitudinally with one another. The second hub may be rotatable to a limited extent relative to the forwardly-extending member. The elastomeric member is preferably shorter than the second region. The elastomeric member is preferably provided on the inner surface of the other member. A spinal-epidural needle assembly according to the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an exploded perspective view of the assembly; Figure 2 is a perspective view of the assembly in an unlocked state; Figure 3 is a lateral cross section of the assembly in an unlocked state; Figure 4 is a perspective view of the assembly in a locked state; Figure 5 is a sectional side elevation view of the hubs of the assembly in a locked state; Figure 6 shows a part of Figure 5 to a larger scale; Figure 7 is an exploded, perspective view of an alternative assembly; and Figure 8 is a sectional side-elevation view of the hubs of the alternative assembly in a locked state. With reference first to Figure 1, the assembly comprises an epidural needle assembly I and a spinal needle assembly 2, which can be locked with the epidural needle assembly at various different longitudinal positions. The epidural needle assembly 1 comprises a conventional epidural, Tuohy needle 10 with a plastics hub 11 bonded at its rear end. The rear end of the hub 11 comprises a rearwardly-extending cylindrical spigot 12 having a circumferential groove 13 about midway along its length. A short stop 14 projects rearwardly from the rear face of a square flange 15 at the forward end of the spigot 12. The epidural needle assembly 1 is completed by a cylindrical sleeve 16 of a rigid plastics material, which is a snap-fit on the spigot 12. The sleeve 16 has an internal rib 17 located to engage the groove 13 on the spigot 12 so as to lock the sleeve against longitudinal movement but to allow it to rotate about the spigot. At its forward end, a channel 18 is formed around the inside of the sleeve 16 to receive the stop 14 on the flange; the channel only extends around the sleeve by about 180°, so as to limit rotation of the sleeve about the spigot 12 to the same extent. On its external surface, the sleeve 16 has two elongate regions 20 and 21 extending longitudinally side-by-side along the sleeve. One region 20 is smooth and has a slightly smaller radius than the remainder of the sleeve, forming a shallow longitudinal channel. The other gripping region 21 is a continuation of the first region 20 but has a series of outwardly-projecting surface formations in the form of parallel, shallow gripping ribs 22 extending circumferentially across the region. The ribs 22 are triangular in profile with a sharp apex and are about 0.25mm high. The ribs 22 alternate between short and long ribs at a pitch of 0.5mm. The spinal needle assembly 2 comprises a conventional spinal needle 30 and hub 31 of the conventional kind but with a hollow cylindrical collar 32 fixedly bonded to the hub and extending forwardly from it. The length of the collar 32 is the same as that of the sleeve 16 and its internal diameter is the same as the external diameter of the sleeve so that it is a close sliding fit on the sleeve. The collar 32 carries a small gripping pad 33, in a shallow recess 34 (Figure 6) on the inside of the collar at its forward end. The pad is of an elastomeric material, such as natural rubber, polyurethane or any other material with which the ribs will grip. The pad 33 is held in position by means of an enlarged head 35 on the pad 33, which is a snap fit in an aperture 36 through the wall of the collar. Alternatively, the pad could be moulded directly onto the collar, such as by injection moulding from a lower melting temperature plastics material. The thickness of the pad 33 and the depth of the recess 34 are such that the inner surface of the pad projects in beyond the inner surface of the collar. The outside of the collar 32 is shaped with knurls 37 to improve grip. In use, the epidural needle 10 is inserted into the epidural space, in the usual way. The spinal needle 30 is then inserted through the epidural hub 11 and into the epidural needle 10. When the forward end of the collar 32 approaches the rear end of the sleeve 16, the user ensures that the sleeve is rotated fully clockwise, against the stop 14, and that the spinal needle 30 is oriented with the elastomeric gripping pad 33 aligned with the smooth channel 20 in the sleeve 16. In this orientation, the spinal needle assembly 2 can slide freely into the epidural needle assembly 1 to the desired extent, as shown in Figures 2 and 3. The ribs 22 on the sleeve 16 serve as convenient depth markers and numbers could be printed alongside the ribs in the channel 20. When the spinal needle assembly 2 has been inserted to the desired extent, it is locked in position relative to the epidural needle assembly 1 simply by twisting spinal needle assembly through about 45° relative to the epidural needle assembly, as shown in Figures 4, 5 and 6. This moves the elastomeric pad 33 laterally from the smooth channel 20 across the ribs 22, which bite into and grip the underside of the pad. The circumferential orientation of the ribs 22 enables the pad 33 to move laterally, along the length of the ribs, but prevents longitudinal displacement, transversely of the ribs, so that the spinal needle assembly 2 is locked longitudinally relative to the epidural needle assembly 1. Because the sleeve 16 is rotatable on the epidural hub 11, it is still possible to rotate the spinal needle assembly 2 anticlockwise through 180° without releasing the locking engagement of the pad 33. When it is necessary to remove the spinal needle assembly 2, it is twisted through 180° until the stop 14 prevents further rotation of the sleeve 16. The collar 32 is then twisted through a further 45° anticlockwise so that the pad 33 moves laterally relative to the ribbed region 21 and into the smooth channel 20, thereby enabling the spinal needle assembly 2 to be pulled rearwardly out of the epidural needle assembly 1. The grip between the elastomeric pad and the ribs has the advantage that locking can be achieved at any longitudinal position, enabling infinitely variable positioning of the spinal needle relative to the epidural needle. The elastomeric pad 33 is relatively short compared with the length of the collar 32 so that the entire length of the pad is gripped by the gripping ribs 22 at all longitudinal positions of the collar relative to the sleeve, except at extreme rear positions of the collar. This ensures that the same force is required to lock and unlock the two assemblies 1 and 2, at all longitudinal positions. In an alternative arrangement, the elastomeric pad could extend along the entire length of the collar. In such an arrangement, a constant locking force could be achieved by providing locking ribs along only a short part of the sleeve, at its rear end, so that the same number of ribs are gripped at all longitudinal positions of the collar. Various other modifications are possible, for example, the elastomeric member could be provided on the outer surface of the inner locking member instead of on the inner surface of the outer locking member. In such an arrangement, the ribs or other gripping surface formations would be provided on the inside of the outer locking member. In the above arrangement, the sleeve 16 having the gripping region 21 is rotatable to a certain extent about the epidural hub 11, to enable orientation of the spinal needle 30 as desired. Although this has certain advantages, it does mean that the sleeve 16 has to be rotated to its furthest extent in opposite directions, both when locking and unlocking the collar 32. If the sleeve 16 is already fully rotated in the locking direction when the collar 32 is slid into position, it means that the collar only has to be twisted through a relatively small angle to lock. However, to unlock, the user has to twist the collar 32 to rotate the sleeve 16 to its full extent in the opposite direction before the collar can be released from the sleeve. The need to rotate the collar through different angles to achieve locking and unlocking can be confusing. In the arrangement shown in Figures 7 and 8, the sleeve 16' is locked onto the spigot 12' in a way that prevents the sleeve rotating on the spigot. In particular, the spigot 12' has a radially-projecting rib 40, which lies in a corresponding recess 41 on the inside of the sleeve 16'. The outside of the spigot 12' and the inside of the sleeve 16' have cooperating tapers so that the sleeve is a tight fit on the spigot, and they have an engaging ring 42 and recess 43, which are a snap fit together to prevent axial displacement after assembly. The collar 32' has an inwardly-projecting flange 44 at its rear end, which is a snap fit in a channel 45 formed around the outside of the forward end of the spinal needle hub 31'. The engagement of the flange 44 in the channel 45 allows the spinal needle assembly 2' to be rotated relative to the collar 32'. The spinal needle hub 31' is of cylindrical shape and circular section, having a lug 46 projecting radially outwardly. The lug 46 indicates the orientation of the spinal needle 30', since this is fixed with the hub 31', and also locates with a slot 47 in the hub 48 of a stylet assembly (only the hub of which is shown) so that the stylet is correctly oriented at the tip of the spinal needle. The stylet hub 48 is a push fit over the rear end of the spinal needle hub 31'. In use, the user holds the spinal needle assembly 2' by the collar 32' and aligns this, in the way described earlier, with the sleeve 16' so that the spinal needle assembly can be slid forwardly to the desired position. When this position has been reached, the collar 32' is twisted through about 45° so that its pad engages the gripping region on the sleeve 16'. With the spinal needle assembly 2' locked in this way against axial displacement relative to the epidural needle assembly 1', the spinal needle can be rotated, if desired, by gripping the spinal needle hub 31' and twisting it relative to the collar 32'. To remove the spinal needle assembly 2', the collar 32' is simply twisted back through the same angle so that the grip is released and the spinal needle assembly can be pulled out of the epidural needle assembly. It can be seen that, in this arrangement, locking and unlocking are achieved by twisting through the same angle.

Claims: A needle assembly comprising a first needle (1) and a second needle (2) insertable within the first needle (1), the first needle (1) having a hub (11) at its rear end with a rearwardly-extending member (16), the second needle (2) having a hub (31) at its rear end with a forwardly-extending member (32), one of the members being insertable within the other member, and the external surface of the one member and the internal surface of the other member having cooperating gripping formations, characterised in that one of the gripping formations includes an elastomeric member (33), and the other of the gripping formations comprises first and second elongate regions (20 and 21) extending parallel to one another side-by-side along the respective member (16), that the first region (20) is configured to receive the elastomeric member (33) as a sliding fit along its length, and that the second region (21) is provided with surface formations (22) that enable the elastomeric member (33) to be slid laterally over the surface formations (22) when the two members (16 and 32) are twisted relative to one another but prevent longitudinal movement of the elastomeric member along the second region (21) so that the two members are locked longitudinally with one another. A needle assembly according to Claim 1, characterised in that the surface formations are provided by a series of parallel ribs (22) extending laterally in the second region (21). A needle assembly according to Claim 2, characterised in that the series of ribs (22) comprises alternate long and short ribs. A needle assembly according to any one of the preceding claims, characterised in that the rearwardly-extending member (16) is insertable within the forwardly-extending member (32). A needle assembly according to any one of the preceding claims, characterised in that the two needles (1 and 2) are rotatable relative to one another to a limited extent after being locked longitudinally with one another. A needle assembly according to any one of the preceding claims, characterised in that the second hub (31') is rotatable to a limited extent relative to the forwardly-extending member (32'). A needle assembly according to any one of the preceding claims, characterised in that the elastomeric member (33) is shorter than the second region (21). A needle assembly according to any one of the preceding claims, characterised in that the elastomeric member (33) is provided on the inner surface of the other member (32).

Inventors: COLLINS MICHAEL NORMAN, COLLINS, MICHAEL NORMAN
Applicants: SMITHS GROUP PLC
Application year: 1997
Main classification: A61B17
IPC codes: A61M25, A61B17