WO2010038004A1

WO2010038004A1 - Needle hub with ratchet mechanism for permanent connection to syringe nozzle

Info

Publication number: WO2010038004A1
Application number: PCT/GB2009/002255
Authority: WO
Inventors: Abdul Khaliq Malik
Original assignee: Abdul Khaliq Malik
Priority date: 2008-10-02
Filing date: 2009-09-21
Publication date: 2010-04-08
Also published as: GB2464112A9; GB2464112B; GB2464112A; GB0818059D0

Abstract

Disposable hypodermic syringes are used extensively in clinical ophthalmology and other medical/surgical practices, and an accidental needle/cannula fly-off as a projectile under normal operating conditions is a distinct risk in these syringes especially those utilizing the Luer type interlocking arrangement. An integral pawl-ratchet mechanism operating in an azimuthal mode/plane and incorporated within the design of the syringe barrel and the needle/cannula respectively, is described herein as a built-in safety protection against accidental fly off of the needle/cannula as a projectile in Luer-lock syringes. An integral pawl-ratchet mechanism operating in an axial mode/plane provides both mechanical interlocking facility and safety protection against needle/cannula fly off as a projectile in most disposable syringes used in medical clinical practices. A combination of bom axial and azimuthal modes of ratchet-pawl mechanisms may also be used for enhanced protection against accidental needle/cannula fly-off in all types of disposable syringes.

Description

NEEDLE HXJB WITH RATCHET MECHANISM FOR PERMANENT CONNECTION TO SYRINGE NOZZLE

Field of Invention

The present invention relates to the adaptation of the ratchet-pawl mechanism for the prevention of any accidental fly off of the needle/cannula as a projectile in disposable syringes under normal operating conditions.

Background

Disposable hypodermic syringes are used extensively in medical practice. An unassembled disposable syringe package comprises two component parts: the needle/cannula and a syringe barrel with a piston plunger (Fig.1). A syringe with a hypodermic needle is used in general medical/surgical clinical applications, whereas a syringe with a cannula is used mainly in ophthalmology and other related clinical applications.

For the device to work as an integral syringe unit for the delivery of fluid from the syringe barrel to the needle/cannula, first the needle/cannula must be interlocked into the syringe barrel to attain a fluid-tight seal between the respective components. This is achieved in most cases, using a popular 'Luer-lock' type locking mechanism, where a fluid-tight compressive seal between the plastic-hub C of the needle/cannula and the elongated plastic tip N of the syringe barrel (Fig.1), is formed when the needle/cannula locking lugs 'L' are screwed clockwise into the spiral grooves G, cut into the underside of the cylindrical collar OHo, which is an extension of the syringe barrel and surrounds the elongated tip N. Subsequently the needle/cannula is secured in place, due to the combined frictional restraining forces setup at the compressive seal, and that between the needle lugs L and the side-wall rib 'mn' of the spiral grooves (Fig.2).

However, an inadvertent failure of the Luer-lock has been reported [Refe.1-7], where a sudden ejection of the needle/cannula as a projectile occurred under normal piston operational conditions. This raises serious safety doubts concerning the overall integrity of the Luer-lock arrangement in medical clinical applications, hitherto considered as a 'safe' practice. Especially, in clinical ophthalmology, an accidental ejection of the needle/cannula as a projectile can result in a catastrophic damage to the eye/tissue being treated.

It has been observed (Ref.1) that the ejection of the needle/cannula as a projectile during the normal pressurization phase of the piston occurs, when the needle/cannula lugs L during the initial coupling phase, inadvertently fall short from their terminal lock-position (=120° clockwise). The critical lug positions giving rise to dangerous needle/cannula fly off is observed to lie (Fig.3) within a band ~ 70°-105° clockwise. These undesirable conditions can arise due to unavoidable human error and negligence. Thus the syringes with Luer-lock mechanism including other types that use 'screwing' of the needle/cannula into spiral grooves or threads provided within the syringe barrel for locking purposes, lack built-in mechanical safety protection against accidental needle/cannula fly off as a projectile.

It is also observed (Ref.1) that during the needle/cannula fly-off in a Luer-lock syringe, the needle/cannula first rotates anticlockwise with the lugs moving outwards along the rib 'nm' (Fig.2), and the needle/cannula flies off as a projectile in an axial direction, after the lugs have reached the exit-end of the rib/grooves. Thus an anticlockwise rotation of the needle/cannula is a precursor to its fly-off as a projectile in an outward axial direction, and its inhibition in Luer- lock disposable syringes is an inherent protection against accidental fly off of the needle/cannula as a projectile. Summary of the Invention

To overcome the problems of disruptive motion of the needle/ cannula in disposable syringes, the present invention proposes the adaptation of the ratchet/pawl mechanism within the design of the syringe. The invention and its embodiments prevent an accidental axial fly-off of the needle/cannula as a projectile in disposable syringes while ensuring a fluid-tight seal between the requisite syringe component parts for the transfer of fluid from the barrel to the needle/cannula

The ratchet and pawl features of the mechanism are incorporated within the design of the needle/cannula and the syringe barrel respectively. The ratchet is arranged as an integral cylindrical wheel in the deign of the needle/cannula and the pawl as a flexible cantilever with the fixed end embedded within the inner surface of the syringe-barrel collar that surrounds the elongated tip and the ratchet wheel, and its distal end is a shoe that rides and engages with the ratchet.

The surface profile of the engaging teeth of the ratchet wheel and that of the shoe of the pawl are made saw-tooth like, and the orientation of these saw-teeth select between permissible and inhibited mode of motion of the needle/cannula in any given plane.

In a preferred embodiment for the inhibition of an accidental fly off of the needle/cannula as a projectile in an axial direction, especially in Luer-lock disposable syringes, the said ratchet-pawl arrangement operating in an azimuthal mode is used, where the 'sloping portion' of the sawtooth teeth of the ratchet wheel point clockwise (fig.10). In this mode the ratchet/pawl mechanism inhibiting the anticlockwise rotation of the needle/cannula, also prevents its disruptive outward axial fly-ofifas a projectile.

The said ratchet-pawl arrangement in an azimuthal plane does not interfere with the normal functioning of the Luer-lock arrangement i.e. to attain a mechanical coupling between the needle/cannula and the syringe barrel resulting in a fluid-tight seal between the two components to ensure fluid transfer from the syringe barrel to the needle/cannula.

Another embodiment of the present invention includes the ratchet-pawl arrangement operating in an axial mode to attain both the mechanical coupling between the needle/cannula and the. syringe barrel with a resulting fluid-tight seal between the two components, and also as a built-in protection against any accidental fly off of the needle/cannula as a projectile, in all types of disposable syringes used in medical practice, Here the sloping portion 'a-b' of the saw-teeth on the ratchet wheel is aligned from left to right (Fig.7a).

These and other objects of the invention will be evident from the following description, taken together with the attached drawings and appended claims.

Drawings:

Fig l illustrates the cross-sectional view of the needle and the piston chamber of a typical conventional disposable hypodermic syringe with a Luer-lock coupling arrangement.

Fig.2 illustrates the details of the Luer type lock arrangement

Fig.3 illustrates the cone-lug position for a 'perfect' and 'imperfect' coupling' between the needle/cannula and the syringe barrel.

Fig.4 depicts the syringe barrel Q with an extended cylindrical collar OH and the spiral grooves

G.

Fig.5 illustrates the schematic form of the ratchet-pawl arrangement PA operating in an axial mode.

Fig.6 illustrates in an isometric view of a cantilever type pawl PA in an axial mode. Fig.7(a) Illustrates the engaging and matching saw-tooth like teeth-notches of the ratchet-pawl arrangement with the sloping-portion 'ab' of the ratchet teeth aligned left to right . Fig.7(b) Illustrates the engaging and matching saw-tooth like notches of the ratchet-pawl arrangement with the sloping portion 'ab' of the ratchet teeth aligned right to left . Fig.8 illustrates the mechanical equivalent representation of an axial ratchet-pawl arrangement. Fig.9 illustrates the rounded saw-tooth notches of the ratchet in axial mode. Fig.10 illustrates the mechanical equivalent representation of a ratchet-pawl arrangement in an azimuthal mode.

Fig.11 shows the relative radii and radius of curvatures for the various components of an axial ratchet-pawl arrangement.

Fig.12 illustrates an isometric view of a disposable syringe operating in an axial mode that restricts outward axial motion of the needle. Fig.13 is a cross-sectional view 'AA' on Fig.12. Fig.14 is a cross-sectional view 'BB' on Fig 13.

Fig.15 illustrates the syringe collar with integrated three pawls (PAl, PA2 & PA3) in axial mode.

Fig.16 illustrates the design of an axial ratchet wheel incorporated within the needle/cannula design.

Fig.17 illustrates a 3-D view of a typical needle/cannula with an integrated ratchet wheel for an axial mode.

Fig.18 illustrates an isometric view of a disposable syringe with an intergraded ratchet-pawl arrangement to inhibit anti-clockwise rotation of the needle/cannula Fig.19 represents a cross-sectional view AA on Fig.18.

Fig.20 represents a cross-sectional view BB on Fig 19. It illustrates, cantilever type pawls (PRl, PR2, PR3), the water-tight compression-seal between the needle conical hub C and the elongated tip N of the syringe barrel, and the needle lugs L screwed within the spiral groove G. Fig.21 shows a cross-sectional view of a disposable syringe in an azimuthal mode incorporating three pawls (PRi, PR₂ & PR3) positioned 120 degrees apart along the circumference of the syringe collar.

Fig.22 illustrates the details of needle/cannula with an integrated ratchet in an azimuthal mode. Fig.23 illustrates the 3-D view of an integrated 1 ratchet in azimuthal mode. Fig.24 illustrates the details of a needle locking lug L with increased surface area with the side wall 'ran' of the spiral-grooves G within the syringe collar.

Fig.25 illustrates a composite azimuthal and axial mode ratchet-pawl arrangement for simultaneous inhibition of outward axial and the anticlockwise rotational motion of the needle/cannula

Fig.26 illustrates the relative location of the three axial and three azimuthal pawls within the syringe collar.

Fig.27. illustrates a composite axial and azimuthal mode ratchet wheel as incorporated within the design of the needle/cannula Fig.28 illustrates a 3-D view of the needle/cannula with a composite ratchet wheel.

Detailed description of the invention:

Description of a typical Luer-lock mechanism in disposable syringes.

Drawings 1-3 relate to the description of a conventional Luer-lock arrangement used for the coupling of the needle and the syringe barrel in disposable syringes:

Fig.1 illustrates the essential component parts of a typical Luer-lock type disposable syringe used for fluid transfer.

O, C and L constitute the main parts of the needle/cannula, where O is a small bore metallic needle/cannula capillary, connected to a plastic hub with variable cross-section, where a cylindrical section B leads to a conical section C. L are two locking lugs positioned diametrically opposite on the rim of the conical hub C.

N, T, Q, G and OH₀ are the main constituent parts of the syringe barrel, where Q is the cylindrical barrel that accommodates the piston T, N is an elongated tip (in the shape of a nozzle) as an extension of the syringe barrel, OH₀ is an extension of the syringe barrel in the form of a collar that surrounds the tip N. G are clockwise running spiral grooves cut in the underside of the collar OH₀.

Inserting the locking lugs L of the needle/cannula into the spiral grooves G and turning the needle/cannula clockwise couples Ae needle/cannula to the syringe barrel thereby forming a compressive fluid-tight seal between the elongated tip N and the hub of the needle/cannula C. The present invention proposed herein utilises the said Luer-lock arrangement for the coupling between the needle/cannula and the syringe barrel to attain a fluid-tight seal between these two components, but the said syringe collar OH₀ is extended in length to OH, beyond the distal end of the syringe tip N as illustrated in Fig.4 in order to enclose the ratchet wheel of the needle/cannula

Sequence of events leading to an accidental needle/cannula fly-off as a projectile in Luer- lock disposable syringes under normal piston operation

Fig.3 illustrates that when the needle/cannula locking lugs L are turned clockwise within the spiral grooves G, a stable locking is attained with a fluid-tight seal formed between the needle/cannula hub C and the barrel elongated tip N, with a resulting through fluid passage between the syringe barrel Q to the metallic needle/cannula O.

However when the needle/cannula locking lugs fall short from the 120° terminal locking position and are positioned within a band approximately 105° -70°, the locking between the needle/cannula and the syringe barrel is 'unstable', in a sense that the through fluid passage is maintained but the sum of the restraining frictional forces at the compressive seal between N and C (Fig.1) and that between locking lugs L and the side surface of the spiral grooves 'mn' (Fig.2) are diminished. On the other hand, for the locking lugs positioned between the band 0°- 70°, the needle/cannula is not coupled to the syringe barrel and the fluid flow between the needle/cannula and the syringe barrel is not achieved..

During an 'unstable' coupling, the increase in pressure within the syringe barrel due to operation of the piston T, is felt at the lug L and due to the diminished frictional forces, the lug L slides down and along the surface 'mn' of the spiral groove Upon reaching the terminal position 'm ', the needle/cannula acquires an axial flight

The principle of operation of the present invention for the control of the needle/cannula motion in disposable syringes

The present invention invokes the concept of mechanical ratchet and pawl mechanism for the control of rotational and/or axial motion of the needle/cannula in disposable syringes. The ratchet pawl mechanism operating in an azimuthal plane/mode is used for the control of the rotational motion of the needle/cannula which in turn prevents the disruptive outward axial fly off of the needle/cannula, whereas that operating in an axial plane/mode is used for the direct inhibition of an outward axial motion of the needle/ cannula

For the syringe, with the ratchet-pawl arrangement to operate in an azimuthal mode/plane, the function of the pawl is simulated as a flexible cantilever within the design of the syringe barrel OH (Fig.4) and is an extension of the syringe barrel Q. The cantilever pawl extends radially in clockwise direction as illustrated in Figs.10 and 19. Figs 19 and 20 illustrate a plural arrangement of three pawls PRl, PR2 & PR3 in an azimuthal plane. The ratchet for operation in an azimuthal plane is simulated as a 'ratchet wheel' in the design of the said needle/cannula O, with the plane of the wheel orthogonal to the axis (Figs. 22 and 23).

For the syringe, with the ratchet-pawl arrangement to operate in an axial mode/plane, the function of the pawl is simulated as a flexible cantilever within the design of the syringe barrel OH (Fig.4), and the cantilever extends radially inwards and proximally from the syringe collar (Fig. 15). Figs 13 and 14 illustrate a plural arrangement of three pawls PAl, PA2 & P A3 in an axial plane/mode. The ratchet for the operation in an axial plane is incorporated as a 'ratchet wheel' in the design of the said needle/cannula O, with the plane of the wheel orthogonal to the axis (Figs.16 and 17).

A set of three plural pawls distributed 120 degrees apart (Figs.13 and 19) around the circumference of OH provide stability and symmetry for the ratchet (i.e. the needle/cannula).

The flexible cantilever pawls in detail comprise a short arm A and an engaging (grabbing) shoe

S as illustrated in Figs. 5 and 6. The fixed proximal end of A (Figs 5 & 10) is embedded within the body of the syringe collar OH, and is therefore stationary with respect to the mutual axial and rotational planes of motion of the needle/cannula.

The distal shoe S of the pawl is provided with a set of engaging saw-tooth like notches at its underside (Fig.6) to engage and match the surface saw-teeth of the ratchet R.

Multiple notches at the shoe ensure positive contact with the ratchet surface and easy manoeuvrability.

Fig 8 depicts the mechanical equivalent representation of a cantilever type pawl-ratchet arrangement of the invention. Here the arm A acts as a mechanical spring, and depending on the direction of the applied force it either acts as a simple flexible cantilever or a stiff spring in compression. For a forward motion of the ratchet R in the direction of the arrow as shown in Fig.8, the arm A behaves as a flexible cantilever, permitting the shoe S to move upwards thereby permitting R to move past the pawl unimpeded

For a motion of R against the direction of the arrow, the vertical edges of the saw-teeth of the ratchet and the pawl engage and the arm A is driven in compression and the motion of the ratchet R i.e. the needle/cannula is impeded

The overall resistance to motion of me ratchet (i.e. the syringe needle) past the pawl is determined by the width 'w' and the various radii of the saw-tooth notches of the shoe S (Figs.6 & 11). In Fig.11, n and r₂ represent the lower and the upper position radii of the ratchet saw-tooth notches, and Ru and R₉ represents the curvature of the engaging pawl notches. Reduced curvatures R_n and Rp of the pawl notches stiffen the through-put motion of the needle, whereas enlarged curvatures lead to an easy motioα Thus curvatures R₀ and Rp may be altered to achieve a desired degree of friction between the ratchet and the pawl.

The profile of the engaging and matching notches for bom the pawl S and the ratchet R are sawtooth-like as illustrated in Figs 5, 6, 7, and 10, and the permissible direction of needle/cannula in any selected plane/mode is determined by the orientation of the 'sloping' portion of the saw teeth on the ratchet wheel.

In Fig.7a, the saw-tooth notches on the ratchet for an axial mode, slope from left to right, thus for an impressed force on the ratchet, the permissible motion of the ratchet is from left to right direction, and its motion right to left is inhibited. Similarly in Fig.7b, where the 'slope' of the saw-tooth notches on the ratchet surface, is from right to left, thus the permissible direction of motion of the ratchet is from right to left and its motion from left to right in this particular case is inhibited.

Similarly, for a ratchet-pawl arrangement in an azimuthal mode, if the 'slope' of the saw-teeth of the ratchet point in clockwise direction (Fig.10), then the permissible ratchet motion is also in the clockwise direction; and its rotation in the anticlockwise direction is inhibited.

In a preferred embodiment of the invention, the integral ratchet-pawl mechanism of the syringe operates in an azimuthal mode/plane to inhibit anticlockwise rotation of the needle/cannula and thereby prevent the disruptive outward axial fly-off of the needle/cannula as a projectile in Luer-lock type of disposable syringes.

Drawings in Figs.18-24 relate to the description of an integral ratchet-pawl arrangement in an azimuthal mode and its role in inhibiting the anticlockwise rotational motion of the needle/cannula

For this configuration, three pawls PRi, PR₂ and PR₃ (Figs.19 & 20) in an azimuthal plane are spaced circurnfrentiallyl20 degrees apart at the distal edge and along the inner surface of the collar OH. Fig.18 illustrates an isometric view of the said arrangement The pawls engage with a common ratchet R arranged as a wheel on the cylindrical section B of the needle/cannula hub (Figs.22 & 23). The engaging surface notches of both the ratchet and the pawls are saw-tooth like, cut parallel to the axis of rotation and the 'sloping' portion of the saw tooth on the ratchet aligned clockwise as shown in Figs.10 &19). The surface profile of the engaging notches of both the ratchet R and the pawls (PRi, PR2 and PR3) can be a simple saw-tooth (Fig.8) or for an easy manoeuvrability, the sloping section of the saw-tooth part of the ratchet surface, is rounded as shown in Fig.9.

The said ratchet-pawl arrangement in an azimuthal mode inhibits an anticlockwise rotation of the needle/cannula and thereby prevent the outward axial fly off of the needle/cannula as a projectile at all times in Luer type disposable syringes and in other similar syringes that utilize a screw and thread arrangement for achieving mechanical locking between the needle/cannula and the syringe barrel.

According to the dynamics of operation of the Luer-lock arrangement, an anticlockwise force (torque) plus an axial outward force acts upon the lugs L (Fig.20) when the piston T is actuated inwards. The resulting forces thereby rotate the lugs (and hence the needle/cannula) anticlockwise along the ribs of the spiral grooves G. Sequence wise, thus an anticlockwise rotation of the needle/cannula within the spiral grooves always precedes an outward axial fly off of the needle/cannula The needle/cannula outward axial fly-off superimposed with a spin, occurs when the lugs reach the end of the spiral grooves G.

Here a simple analogy is that of a nut and (right handed thread) bolt, where an outward axial displacement of the nut occurs when the nut is acted upon with an anticlockwise force (torque). However, if the outer surface of the nut is provided with suitable notches that act as a pawl, and the notches engage with a fixed ratchet, then the outward displacement of the nut is inhibited.

The ratchet-pawl arrangement operating in azimuthal plane does not on its own; facilitate the formation of a water-tight seal between the needle/cannula and the syringe barrel. To achieve this, the needle locking lugs L must be screwed clockwise into the spiral grooves G within the collar OH of the syringe barrel (Fig.20); this anyhow is a normal practice in any Luer-lock arrangement. The said ratchet/pawl arrangement in an azimuthal mode does not interfere with or hinder these locking manoeuvres. In another embodiment of the invention the integral ratchet-pawl mechanism operates in an axial plane/mode to inhibit an outward axial motion of the needle/cannula and also to attain a fluid-tight seal between the needle/cannula and the syringe barrel in all types of disposable syringes.

Drawings in Figs.12-17 relate to the description of an integral ratchet-pawl arrangement in an axial mode and its role in inhibiting an outward axial motion of the needle/cannula

For this function, three axially aligned pawls PAi, PA2 and PA3 (Figs. l3&14) spaced circufrentiallyl20 degrees apart along the inner surface of the syringe collar OH, are used. The three pawls engage with a common ratchet R arranged as a wheel on the cylindrical section of the needle/cannula hub B (Fig. 16). Fig.12 illustrates an isometric view of the said arrangement. The engaging surface notches of both the ratchet and the pawls are saw-tooth like, cut circumferentially with the 'sloping-portion' of the saw tooth of the ratchet pointing axially inwards i.e. towards the conical section C as shown in Figs 14,16 &17. The surface profile of the engaging notches of both the ratchet and the pawls can be a simple saw-tooth (Fig.8) or for an easy manoeuvrability, the sloping section of the ratchet surface alone is rounded as shown in Fig.9.

Pushing the needle hub C against the elongated tip N in the presence of the said ratchet-pawl arrangement in axial mode, attains a fluid-tight compressive seal between the needle/cannula and the syringe barrel, and at the same time the outward axial motion of the needle/cannula is inhibited.

The said ratchet-pawl arrangement does not hinder the application of bom an axial force and clockwise twist on the needle hub C, and both manoeuvres facilitate the formation of a fluid- tight seal between the needle and the syringe barrel..

Once formed, the integrity of the seal is maintained, as the ratchet-pawl arrangement inhibits any backward movement of the needle at all times.

In another embodiment of the invention the axial and azimuthal modes of the ratchet/pawl mechanisms are combined to inhibit simultaneously both the anti-clockwise rotation and the outward axial motion of the needle/cannula in all types of disposable syringes.

The drawings in Figs. 25-28 relate to the description of the combined azimuthal and axial mode ratchet-pawl mechanism, and its role in simultaneously inhibiting an anticlockwise rotational and an outward axial motion of the needle/cannula:

For this configuration, both the radial pawls (PRl, PR2 and PR3) and the axial pawls (PAl, PA2 and PA3) are made an integral part of the collar OH as shown in Figs 25 and 26. 'R' acts as a common ratchet. The ratchet surface is provided with a saw-tooth like surface notches cut and aligned axially inwards (i.e. towards the elongated tip N), superimposed with another set of circumferential saw-tooth notches arranged and aligned clockwise as indicated in Figs. 27 and 28.

To inhibit the needle-motion in both outward axial and anticlockwise rotational directions concurrently, the said axial pawls point inwards (i.e. towards the tip N), and the said azimuthal pawls are aligned in clockwise direction

In the present configuration, a water-tight seal between the needle/cannula and the syringe barrel is formed by pushing the needle inwards through the said system of ratchet-pawl arrangement, onto the tip N. The system permits both inward axial motion and clockwise rotation of the needle/cannula, essential for attaining a fluid-tight seal. In another embodiment of the invention the contact surface area between the locking lugs and the spiral-grooves is enhanced to retard the anticlockwise rotational motion of the needle/ cannula within the groove.

To increase the friction between the locking lugs L and the side walls of the spiral groove ribs 'mn' (Fig.2) in order to impede the anticlockwise rotation of the needle/cannula, is illustrated in Fig.24. Here a substantial surface area of the lug L makes contact with the lower rib 'mn' of the groove G, resulting in an increased contact frictional resistance, thereby reducing the chances of anticlockwise rotation of the needle/cannula under adverse operational conditions. This design differs from the conventional Luer-lock type arrangement, where only the edge of the locking lug L makes a point contact with the rib 'mn' or 'qiq' and the frictional resistance to needle rotational motion is minimal (Fig 2).

References

1. Malik A, Zia R, Patel K. Accidental Ejection of a cannula from Luer-locked syringe during wound hydration process, causing IOL drop, Vitreous Loss and Haemorrhage. XXVI Congress of the European Society Cataract and Refractive Surgeons, Berlin Sept, 2008; Complex Cataract, Paper 410.00

2. Fletcher S J. Failure of a Luer-lock. Anaesthesia 2005; 60(2): 206.

3. Holmes K , Snow D , et al. More problems with Luer-lock connections. Anaesthesia 2006: 61(1): 72-73.

4. Osher R- Iris damage by inadvertent cannula injection. J. Cataract Refract. Surg. 2006; 33(2):339-341.

5. Gupta D, Burton B et al. Iatrogenic retinal detachment due to cannula slippage despite use of Luer-lock syringe system. J Cataract Refract. Surg. 2008:34(9): 1612.

6. 'Two-piece Luer-lock may not be locked'. Health Devices 2000; 29(5): 190-191.

7. 'Equipment failure: Luer-lock'. Anaesthesia Intensive Care 1987;15(2):249

Claims

ClaimsWhat is claimed:

1. A syringe with an integral ratchet-pawl mechanism comprising: i) a barrel having a fluid chamber, a proximal end, a distal end and a frusto-conical tip extending from the said distal end having a passageway there through in fluid communication with said chamber, a collar at the distal end of the barrel surrounding said conical tip and incorporating:

(a) at the distal end at least one flexible cantilevered pawl with its proximal end buried within the body of the syringe collar and the cantilevered arm extending radially clockwise with a shoe at its distal end incorporating several saw-tooth like teeth at its underside as a part of an arc in an azimuthal plane to engage with a mating ratchet wheel surface incorporated within the needle/cannula assembly as described here under, and

(b) at the proximal end, spiral grooves cut within the underside surface and running clockwise to receive the locking tabs located on the rim at the proximal end of the hub of the under mentioned needle/cannula assembly; and ii) a needle/cannula assembly comprising: a) a metallic needle/cannula capillary having a proximal end, a distal end and a lumen there through, a hub having an open proximal end with a cavity therein, and a distal end joined to said proximal end of said metallic capillary so that said lumen is in fluid communication with said cavity, b) a rim at the proximal end of the said conical hub with a pair of protruding locking tabs, c) a ratchet wheel at the distal cylindrical section of the said hub and orthogonal to the axis with the 'sloping' portion of the saw-teeth engaging surface teeth pointing in clockwise direction, to engage with its said pawl shoe counterpart incorporated within the said syringe collar, said needle/cannula assembly being connected to the said barrel by pushing the needle/cannula assembly axially inwards and turning clockwise so that the locking tabs of the said rim of the said hub engage and rotate within the said spiral grooves at the underside surface of the said collar so that: a) a fluid-tight seal is formed between the said conical tip of the barrel and the said conical hub of the needle/cannula assembly thereby providing a passageway there through in fluid communication from barrel chamber to needle/cannula tip, and b) the said ratchet wheel at the said hub of the said needle/cannula is engaged with its counterpart shoe of the said cantilever pawl of the said syringe collar of the said barrel thereby permitting axial motions and clockwise rotation of the needle/cannula but inhibiting an anticlockwise rotation of the needle/cannula in an azimuthal plane and thereby prevent any accidental outward axial fly-off of the needle/cannula as a projectile as according to the sequence of events leading to the needle/cannula fly-off an anticlockwise rotation of the needle/cannula is a precursor to its outward axial fly-off as a projectile under normal piston operational conditions; and iii) a plunger including an elongated plunger rod having a longitudinal axis for drawing fluid into and out of said chamber by movement of said plunger relative to said barrel.

2. The syringe of claim 1 wherein at least one cantilevered pawl comprises a plurality of pawls arranged circumferentially along the internal surface of the said collar of the barrel and all pawl shoes engage with a common ratchet of the said hub of the needle assembly.

3. The syringe of claim 1 whereby the means of providing a built-in mechanical safety against an accidental fly-off of the needle/cannula as a projectile under normal piston operation in Luer-lock disposable syringes includes the said integral ratchet-pawl mechanism operating in an azimuthal plane/mode.

4. The syringe of claim 2 whereby the means of providing a built-in mechanical safety against an accidental fly-off of the needle/cannula as a projectile under normal piston operation in Luer-lock disposable syringes includes the integral ratchet-pawl mechanism with plurality of said cantilevered pawls operating in an azimuthal plane/mode.

5. The syringe of claim 1, wherein reversing the direction of the 'sloping' portion of the sawteeth on the said ratchet wheel surface with matching alterations on the pawl shoe, permits anticlockwise rotational of needle/cannula motion in an azimuthal plane.

6. The syringe of claim 1, whereby adjusting the locking lugs on the needle hub to embrace an increased contact surface area with the side walls of the spiral groove within the syringe collar in the absence of the said ratchet-pawl mechanism, retards the anticlockwise rotation of the needle/cannula and thereby reduce the risk of needle/cannula fly off as a projectile.

7. The syringe of claim 1 wherein the pawl-ratchet mechanism is arranged to operate in an axial plane/mode wherein the cantilevered pawl extends radially inwards and proximally from the said syringe collar and the shoe at the distal end of the cantilever engages with the ratchet wheel orthogonal to the axis with the surface saw-tooth 'cuts' running circumferentially and the 'sloping' portion of the saw-teeth point inwards in order to inhibit an outward axial motion of the needle/cannula while permitting an inward axial and rotational motions.

8. The syringe of claim 7 wherein the requisite mechanical coupling between the needle/cannula and the syringe barrel is attained through the said ratchet-pawl mechanism operating in an axial plane/mode and there is no need for the said locking tabs and the spiral grooves within the underside of the said syringe collar for this purpose.

9. The syringe of claim 7 wherein at least one cantilever pawl comprises a plurality of cantilevered pawls dispersed circumferentially along the internal surface of the collar of the syringe barrel and all the pawl shoes engage with a common ratchet wheel of the said hub of the needle/cannula assembly.

10. The syringe of claim 7 whereby the means of providing a built-in mechanical safety against an accidental fly-off of the needle/cannula as a projectile under normal piston operation in disposable syringes includes the said integral ratchet-pawl mechanism operating in an axial plane/mode.

11. The syringe of claim 9 whereby the means of providing a built-in mechanical safety against an accidental fly-off of the needle/cannula as a projectile under normal piston operation in disposable syringes includes the said integral ratchet-pawl mechanism with plurality of said cantilevered pawls operating in an axial plane/mode. I l

12. The syringe of claim 7 whereby reversing the direction of the said 'sloping' portion of the saw-teeth on the said ratchet surface and matching alterations to the said pawl shoe, permits an outward axial motion including free rotational motions of the needle/cannula

13. The syringe of claim 7 wherein at least one cantilever pawl comprises a plurality of pawls dispersed circumferenually and the pawl shoes displaced relative to each other axially provides a vernier mode of operation, useful to accommodate the variability in component dimensions when locking different needle systems to the syringe barrel.

14. The syringe of claim 7 wherein at least one ratchet-pawl in an axial mode prevents uncoupling of the needle/cannula from the syringe barrel after initial use and thereby satisfy the healthcare directives for disposal of syringes under such conditions.

15. A syringe whereby the azimuthal and axial modes of operation of the syringes of claim 2 and claim 7 respectively are combined to provide an enhanced inhibition of outward axial motion of the needle/cannula in disposable syringes.

16. The syringe of claim 15 comprising plurality of axial and azimuthal pawls with a single composite ratchet wheel with surface saw-teeth in axial mode superimposed on saw-teeth in an azimuthal mode of operation provides an enhanced inhibition of outward axial motion of the needle/cannula in disposable syringes.

17. The syringe of claim 10 wherein the plurality of axially aligned -pawl-ratchet arrangement providing a fluid-tight seal between the conical tip of the barrel and the hub of the needle thereby eliminates the need for the spiral grooves within the collar of Ae barrel and locking lugs on the needle hub in disposable syringes.

18. The syringe of claim 10 whereby the said arrangement of ratchet-pawl operating in an axial mode/plan is an alternative to Luer-lock mechanism for attaining mechanical coupling and fluid-tight seal between the needle/cannula and the syringe barrel in disposable syringes.