Patent Publication Number: US-10321903-B2

Title: Surgical instrument for dispensing a fluid

Description:
BACKGROUND OF THE INVENTION 
     Technical Field of the Invention 
     The present invention relates to a surgical instrument for dispensing a fluid. In particular the invention may relate to a surgical instrument for dispensing a fluid to an operative site in the human or animal body. 
     Description of the Prior Art 
     WO2009/132331 discloses a minimally invasive (e.g. laparoscopic) applicator device which dispenses fluid and which may include a ratcheted trigger system to overcome backflow. WO02/064192 discloses a laparoscopic gel applicator. However, it has been recognised by the applicant that the devices disclosed in these documents do not provide any means to reduce the likelihood of accidental operation of the device before the device is intended to be used. 
     The present invention seeks to reduce the likelihood of accidental dispensing of fluid from a surgical instrument for dispensing a fluid. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention provides a surgical instrument for dispensing a fluid which includes a dispensing shaft, a dispensing assembly and a priming assembly operable to prime the dispensing shaft with the fluid before the dispensing assembly is operated. 
     Thus viewed from one aspect the present invention provides a surgical instrument for dispensing a fluid comprising:
         a housing;   a dispensing shaft which is elongate and which has a proximal end and a distal end, wherein the proximal end of the dispensing shaft is received in the housing and the distal end defines a dispensing opening for dispensing the fluid and the dispensing shaft includes a through bore which extends along the dispensing shaft from the proximal end to the dispensing opening at the distal end;   a dispensing assembly connected to the housing which includes a dispensing chamber which holds the fluid before it is dispensed, wherein the dispensing chamber is in fluid communication with the through bore of the dispensing shaft and the dispensing assembly is operable to move the fluid from the dispensing chamber along the through bore and dispense the fluid from the dispensing opening; and   a priming assembly connected to the housing which is operable to move an amount of the fluid into the through bore of the dispensing shaft to prime the through bore with the fluid before the dispensing assembly is operated.       

     By providing a priming assembly, the likelihood of accidental dispensing of fluid by a user of the surgical instrument may be reduced because the fluid will not be present in the through bore until the priming assembly is operated to prime the through bore with the fluid. In this way operation of the dispensing assembly will not dispense fluid from the dispensing opening until the priming assembly has been operated. Reducing the likelihood of accidental dispensing of fluid is advantageous because fluid may be dispensed in an undesirable location. For example, if the fluid is an adhesive, accidentally dispensed adhesive may contact unintended tissue in the human or animal body which may be undesirable. 
     Operation of the priming assembly may prepare the surgical instrument for use. 
     The housing may comprise a handle. The handle may allow the surgical instrument to be gripped in one hand to allow one-handed operation of the surgical instrument. The housing may comprise a body. The dispensing shaft may extend from the body. The housing may have a ‘pistol’ configuration in which the handle extends from the body in a similar configuration to a pistol handle extending from a pistol barrel. 
     The dispensing shaft is elongate and has a proximal end and a distal end. The proximal end of the dispensing shaft is received within the housing and the distal end defines a dispensing opening for dispensing the fluid. The dispensing shaft may have a longitudinal axis. The longitudinal axis of the dispensing shaft may define a proximo-distal axis for the surgical instrument. The proximo-distal axis may be oriented so that the distal direction is generally towards the distal end of the dispensing shaft and the proximal direction is generally away from the distal end. 
     The dispensing shaft may comprise an inner tube and an outer tube. The outer tube may be made of metal. The inner tube may be made of a polymer. The polymer may be polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP) or silicone. The polymer may be a non-stick or low friction polymer. This may assist the movement of the fluid along the through bore by reducing shear stress. For example, when the fluid is an adhesive or has a significant viscosity, a non-stick or low friction polymer may assist the flow of the fluid along the through bore. 
     The through bore may extend within the inner tube. 
     The dispensing assembly comprises a dispensing chamber. The fluid may be held in the dispensing chamber before it is moved into the dispensing shaft to be dispensed. An elongate plunger may be positioned to advance or retract within the dispensing chamber. When the plunger is advanced within the dispensing chamber, the fluid may be urged out of the dispensing chamber and into the dispensing shaft. The plunger may advance within the dispensing chamber in a distal direction. Fluid urged out of the dispensing chamber may enter the through bore of the dispensing shaft at the proximal end of the dispensing shaft. 
     The plunger may engage the internal surface of the dispensing chamber to form a seal. Alternatively the plunger may abut against a sealing disc which engages the internal surface of the dispensing chamber to form a seal. Advancement of the plunger may advance the sealing disc within the chamber. The plunger may include a proximal end and a distal end. The distal end of the plunger may abut the sealing disc. 
     Preferably the plunger abuts against a sealing disc which is slidably mounted within the dispensing chamber, wherein operation of the dispensing assembly causes the plunger to advance the sealing disc within the dispensing chamber to urge the fluid out of the dispensing chamber and along the through bore in the dispensing shaft. 
     The plunger may be connected to a plunger drive assembly. The plunger drive assembly may be a rack and pinion. The pinion gear wheel may be mounted within the housing. Turning the pinion gear wheel may engage the rack to advance or retract the plunger along the dispensing chamber. 
     The dispensing assembly may comprise a dispensing actuator. The dispensing actuator may be operable to drive the dispensing assembly. The dispensing actuator may be reciprocable between a first dispensing position and a second dispensing position. Movement of the dispensing actuator from the first dispensing position to the second dispensing position may advance the plunger and urge fluid out of the dispensing chamber and along the dispensing shaft. The dispensing actuator may be biased to return to the first dispensing position when it is released at the second dispensing position. 
     The dispensing actuator may be connected to the plunger drive assembly. For example, the dispensing actuator may be connected by an intermediate gear wheel to the pinion gear of the plunger drive assembly. 
     The dispensing actuator may be a trigger. The trigger may be reciprocable. The trigger may be mounted to the housing. The trigger may be mounted on the handle or the body of the housing. The trigger may be operable by a user&#39;s finger from a first trigger position to a second trigger position. The trigger may be biased by a spring to return to the first trigger position when the user&#39;s finger is released at the second trigger position. The spring may be attached to the housing at a first end and attached to the trigger at a second end. 
     Preferably the dispensing assembly includes a trigger mounted to the housing which is operable to dispense a predetermined amount of fluid each time the trigger is operated. 
     A pawl and ratchet may be connected to the trigger and a trigger gear wheel. The pawl may be connected to one of the trigger or the trigger gear wheel and the ratchet may be connected to the other of the trigger or the trigger gear wheel. The pawl may be moulded into the trigger. When the trigger is moved from the first trigger position to the second trigger position the pawl may engage the ratchet to turn the trigger gear wheel. When the trigger is moved from the second trigger position to the first trigger position the pawl and ratchet may disengage so that the trigger gear wheel does not turn. 
     Turning the trigger gear wheel may turn the pinion gear wheel to advance the plunger. An intermediate gear wheel may be connected between the trigger gear wheel and the pinion gear wheel. The relative sizes of the trigger gear wheel and pinion gear wheel may be chosen to provide a suitable gear reduction. This may provide a mechanical advantage to the operation of the trigger from the first trigger position to the second trigger position. The intermediate gear may contribute to the gear reduction. The overall gear ratio between the trigger gear wheel and the pinion gear wheel may be 4 to 1. Therefore a 10° rotation of the trigger may result in a 2.5° rotation of the pinion gear wheel. The size of the pinion gear wheel may be chosen to advance the rack by a predetermined amount when the trigger is operated from the first trigger position to the second trigger position. This will cause the plunger to advance by a predetermined amount to dispense a predetermined volume of the fluid. 
     An indexing wheel may be attached to the trigger gear wheel. The indexing wheel may enable the movement of the trigger between the first trigger position and the second trigger position to be indexed. The indexing wheel may include indentations on its circumference which engage an indexing formation on the housing to provide the indexing. The engagement of the indentations with the indexing formation may also provide an additional frictional force on the ratchet to assist the trigger to move from the second trigger position to the first trigger position without moving the ratchet. 
     The priming assembly may comprise a priming actuator. The priming actuator may be operable to drive the priming assembly. The priming actuator may be mounted to a proximal end of the housing. The priming actuator may be rotatably mounted to the housing. The priming actuator may be operable from a first priming position to a second priming position. The priming actuator may be rotatable from the first priming position to the second priming position. 
     The priming assembly may include a safety element which is moveable from an engaged position to a disengaged position. The safety element may prevent the priming assembly from being operated when it is in the engaged position. The safety element may be in the form of a pull tab connected to the priming actuator. In its engaged position, the pull tab may engage a recess on the housing to prevent the priming actuator from being operated from the first priming position to the second priming position. The pull tab may be separable from the priming actuator so that in its disengaged position, the pull tab is separated from the priming actuator and disengaged from the recess so that the priming actuator can be operated. 
     Preferably the priming assembly includes a safety element which is moveable from an engaged position to a disengaged position, wherein when safety element is in the engaged position it prevents the priming assembly from being operated and when the safety element is in the disengaged position the priming assembly is operable. 
     Operation of the priming actuator may cause the plunger to advance into the dispensing chamber. The plunger may advance in a distal direction. 
     If the priming actuator is rotatably mounted to the housing, rotation of the priming actuator may rotate a priming cap with an internal screw thread. The priming cap may be linearly moveable with respect to the priming actuator by the engagement of a spline feature on one of the priming cap or the priming actuator with a groove on the other of the priming cap or priming actuator. The internal screw thread on the priming cap may engage a complementary screw thread mounted on the plunger drive assembly. The priming cap may be connected to the proximal end of the plunger. In this way, rotation of the priming actuator may cause the internal screw thread on the priming cap to advance along the complementary screw thread on the plunger drive assembly. Since the plunger is connected to the priming cap, the plunger will advance distally with respect to the plunger drive assembly. The advancement of the plunger may prime the through bore of the dispensing shaft with fluid by advancing the sealing disc in the dispensing chamber and urging the fluid out of the dispensing chamber. 
     Preferably, the priming assembly and the dispensing assembly form an interlock so that the dispensing assembly cannot be operated until the priming assembly has been operated. The interlock may be moveable from a locked configuration in which it prevents the dispensing assembly from being operated to a released configuration in which the dispensing assembly is operable. The interlock may only be moveable to the released configuration once the priming actuator is in the second priming position. An advantage of the interlock may be that accidental operation of the dispensing assembly is not possible until the priming assembly has been operated and the priming actuator is in the second priming position. 
     The interlock may include a locking member. The locking member may be elongate and may be moveably mounted in the housing to contact a locking formation on the dispensing assembly and to contact the priming actuator. When the priming actuator is in the first priming position and the interlock is in the locked configuration, the locking member may be unable to move and may lock the trigger in the second trigger position by contact with the locking formation. 
     The priming actuator may include an interlock recess positioned so that when the priming actuator is in the second priming position, the interlock recess is aligned with the locking member to allow the locking member to move into the interlock recess. The spring bias on the trigger may then cause the locking formation to move the locking member into the interlock recess and this released configuration allows the trigger to move from the second trigger position to the first trigger position. Once the trigger is in the first trigger position, it is operable by the user. 
     Preferably the priming assembly includes a priming actuator which is operable from a first priming position to a second priming position and which includes an interlock recess; and the interlock includes a locking member which is able to enter the interlock recess when the priming actuator in the second priming position to release the interlock and allow the dispensing assembly to be operated. 
     The fluid may be a medical fluid. The fluid may be a liquid or a gel. The fluid may aid in the recovery or the comfort of the patient. The fluid may have a viscosity similar to water at room temperature. The fluid may have a higher viscosity than water at room temperature. The fluid may be a pharmaceutical agent, hemostatic solution, wound-healing agent, analgesic, anti-adhesive, adhesive, irrigation fluid or cooling fluid. The fluid may include an anesthetic, an antibiotic in fluid form, a growth factor, suspended stem cells, chondrocytes, other biologically active substances such as extra-cellular matrix, including proteoglycans, glycosaminoglycan (GAG), chondroitin sulfate, or an antihemorragic. 
     The fluid may be a bone cement. 
     The fluid may be an adhesive. The adhesive may be a collagen-based adhesive, a hydrogel, an albumin-based compound, a cyanoacrylate or a fibrin. 
     The fluid may be a cyanoacrylate adhesive. The cyanoacrylate adhesive may have a viscosity similar to water at room temperature. 
     In another embodiment, the fluid may be a fibrin adhesive. The fibrin adhesive may be a binary mixture in which two inactive precursor fluids are mixed to form the active fibrin adhesive. The dispensing assembly may comprise a first dispensing chamber for the first precursor fluid and a second dispensing chamber for the second precursor fluid. The dispensing assembly may include a first plunger for the first dispensing chamber and a second plunger for the second dispensing chamber. The first and second plungers may be advanced by a common plunger drive assembly. A mixing chamber may be located between the first and second dispensing chambers and the dispensing shaft. The first and second precursor fluids may mix in the mixing chamber to form the active fibrin adhesive before moving into the dispensing shaft. 
     To ensure sterility and prolong shelf-life, a medical fluid may be stored in a sealed glass container. The container may be a glass ampoule. If the fluid to be used in the surgical instrument of the present invention is stored in a sealed glass container, the surgical instrument may include a transfer assembly as described herein. The transfer assembly may enable the transfer of the fluid from the sealed glass container to the dispensing chamber. The fluid may be a cyanoacrylate adhesive which is stored in a sealed glass container. The cyanoacrylate adhesive may be stored in a sealed glass container to prevent contact with moisture which may cause the cyanoacrylate adhesive to polymerise. 
     In another embodiment, the fluid may be stored initially in the dispensing chamber. In this embodiment, a transfer assembly may not be required. 
     The surgical instrument may include a container in which the fluid is stored before the surgical instrument is used. The container may be a glass ampoule. The fluid may be transferred to the dispensing chamber by a transfer assembly. The transfer assembly may include a container holder which holds the container. The container holder may include a filter. The apertures of the filter may be sized to allow the fluid to pass but to retain any fragments of the container which are produced when the container is opened. 
     To release the fluid, the container may be opened. If the container is a sealed glass container this may result in glass fragments being produced. The transfer assembly may comprise a filter to retain any glass fragments produced in opening the sealed glass container. An advantage of this configuration is that it ensures that fluid which is transferred to the dispensing chamber is free of glass fragments. 
     The dispensing chamber may be attached to the transfer assembly. 
     The transfer assembly may be operable to open the container and transfer the fluid from the opened container to the dispensing chamber before the priming assembly is operated. 
     The transfer assembly may be moveably mounted to the housing. The transfer assembly may pivot with respect to the housing. The transfer assembly may be moveable between a first transfer position, a second transfer position and a third transfer position. 
     Movement of the transfer assembly from the first transfer position to the second transfer position may cause the container to be opened to release the fluid. The container may be opened by a projection on the transfer assembly being pushed into the container. When the container is a glass ampoule, this will break open the ampoule. Any container fragments created by the opening of the container will be retained by the filter. 
     The container may be made of a frangible material. An example of a frangible material is glass. The container may be a frangible container. 
     The container may be made of a material which during deformation tends to break up into fragments, rather than deforming plastically and remaining in one piece. 
     A polymer sleeve may at least partially surround the container. The polymer sleeve may be a PTFE sleeve. When the container is opened, the polymer sleeve may prevent the fluid from spilling out of the container holder. 
     The projection may be pushed into the container by relative movement of the container holder with respect to the projection. The transfer assembly may include a breaker section which is moveable with regard to a holder section. The projection may be located on the breaker section and the container holder may attached to the holder section. When the transfer assembly is moved from the first transfer position to the second transfer position, the holder section may move relative to the breaker section. For example, the breaker section may be moveably retained on the housing so that it cannot move as far as the holder section. In this way, moving the holder section to its maximum extent will move the holder section relative to the breaker section. 
     Once the fluid is released from the container, it may be directed to the dispensing chamber. A valve may be positioned between the container and the dispensing chamber. The valve may comprise an outer valve body and an inner valve member. The valve may be a plug valve. The valve member may be a cylinder with a cylindrical surface and axial ends. The valve body may be annular and encircle the valve member. The valve member may be attached to the housing at its axial ends and the valve body may be attached to the transfer assembly. In this way the valve member may act as a pivot around which the valve body and transfer assembly rotates when the transfer assembly moves between the first transfer position, second transfer position and third transfer position. This use of the valve member as a pivot for the transfer assembly may advantageously reduce the number of components required in the surgical instrument. 
     A transfer channel may be defined by the valve member. When the valve member is a cylinder, the transfer channel may be a channel on its cylindrical surface. The valve body may define a container holder opening which is in fluid communication with the container holder. The valve body may define a dispensing chamber opening which is in fluid communication with the dispensing chamber. 
     The valve member may further define a dispensing channel. The dispensing channel may be a diametrical channel through the valve member. 
     When the transfer assembly is in the first transfer position, the transfer channel may not be aligned with the container holder opening and the dispensing chamber opening. When the transfer assembly is in the second transfer position, the transfer channel may be aligned with the container holder opening and the dispensing chamber opening to provide a fluid path between the container holder opening and the dispensing chamber opening. In this way, fluid released from the container may flow from the container holder to the dispensing chamber when the transfer assembly is in the second transfer position. 
     Before the surgical instrument is used, the sealing disc may be located at a distal end of the dispensing chamber. To draw the released fluid through the transfer channel from the container holder when the transfer assembly is in the second transfer position, the sealing disc may be retracted proximally in the dispensing chamber. A pull member may be attached to the sealing disc to allow the user to retract the sealing disc. When the transfer assembly is in the first transfer position, the pull member may be restrained from movement by the housing. When the transfer assembly is moved from the first transfer position to the second transfer position, the pull member may move above the housing so that it is no longer restrained. 
     Once all the fluid has been drawn into the dispensing chamber and the sealing disc is fully retracted, the pull member may disengage from the sealing disc. The pull member may comprise two fingers which engage a recess on the sealing disc so that the sealing disc may be retracted. The recess may be in the form of a through-hole. The fingers may be retained in the recess by the inner surface of the dispensing chamber. At its proximal end, the dispensing chamber may define two slots which allow the fingers to disengage from the recess when the sealing disc is fully retracted. In this way, the pull member is disengaged and separated from the dispensing chamber and may be discarded. 
     After the pull member is discarded, the sealing disc may be fully retracted and the dispensing chamber contains the fluid to be dispensed. The transfer assembly may then be moved to the third transfer position. To reach the third transfer position, the transfer assembly may be pivoted about the valve member until the dispensing chamber opening is aligned with the dispensing channel. When the transfer assembly is in the third transfer position, the sealing disc may be aligned with the plunger. The priming actuator may then be operated. When the priming actuator is operated from the first priming position to the second priming position, the plunger may advance the sealing disc distally within the dispensing chamber and push the fluid through the dispensing chamber opening and the dispensing channel. The proximal end of the dispensing shaft may be received within the valve member and the through bore may be connected to the dispensing channel. Therefore fluid pushed through the dispensing channel may travel distally along the through bore and be dispensed from the dispensing opening at the distal end of the dispensing shaft. 
     If the fluid to be dispensed is not initially contained in a glass ampoule, a transfer assembly may not be required. In an alternative embodiment, the surgical instrument may be supplied initially with the fluid already present in the dispensing chamber and the plunger aligned with the sealing disc in a configuration similar to the third transfer position. The valve will not be required and the dispensing chamber opening will be in fluid communication with the proximal end of the dispensing shaft. 
     The fluid may be dispensed in discrete doses. Each dose may be a predetermined amount of fluid. A single dose may be known as a delivery. Each delivery may be of a predetermined volume. The dimensions of the dispensing chamber and plunger may be configured so that advancement of the plunger by a set distance dispenses the predetermined volume. 
     The predetermined volume of a delivery may be up to 50 mm 3 . The predetermined delivery volume may be from 10 mm 3  to 40 mm 3 . Preferably the predetermined delivery volume is from 20 mm 3  to 30 mm 3 , more preferably the predetermined delivery volume is approximately 25 mm 3 . 
     If the predetermined delivery volume is approximately 25 mm 3  and the internal diameter of the dispensing chamber is 7 mm, the plunger will advance approximately 0.65 mm for each separate delivery of fluid. 
     The surgical instrument may be capable of dispensing a predetermined number of deliveries. The predetermined number of deliveries may be up to 50 deliveries. Preferably the predetermined number of deliveries is from 20 to 50 deliveries, more preferably from 30 to 40 deliveries. The predetermined number of deliveries may be 35 deliveries. 
     After the dispensing actuator has been operated for a number of times equal to the predetermined number of deliveries, a hard stop on the dispensing assembly may prevent the dispensing actuator from being operated again. Preferably the hard stop feature prevents further operation of the trigger after the trigger has been operated a predetermined number of times. 
     Preferably the hard stop is provided by a stop projection on the plunger drive assembly engaging the housing. The stop projection may be located in a slot on the housing. The slot may be in an exterior surface of the housing so that the stop projection is visible to the user of the surgical instrument. The stop projection may advance in the slot as the plunger advances the sealing disc in the dispensing chamber. The hard stop may be provided by the stop projection reaching an end of the slot. The slot may be located so that the stop projection reaches the end of the slot when the predetermined number of deliveries is reached. 
     By being visible to the user, the relative position of the stop projection in the slot may advantageously indicate the number of deliveries the surgical instrument has made. An indicator or scale may be marked on the housing to allow the user to judge the number of deliveries more accurately. For example, if the stop projection is located at a first end of the slot initially and reaches the second end of the slot when the predetermined number of deliveries is reached, then if the stop projection is in the middle of the slot, approximately half of the predetermined number of deliveries have been made. 
     The surgical instrument may be suitable for use in a minimally invasive surgical procedure. The surgical instrument may be suitable for hernia mesh fixation. The surgical instrument may be a hernia mesh fixation device. 
     When the surgical instrument is a hernia mesh fixation device, the fluid may be a cyanoacrylate adhesive for securing a hernia mesh in place at the operative site in the human or animal body. The hernia mesh may be secured in place by a number of deliveries of adhesive from the surgical instrument. Each delivery of adhesive may have a similar function to a suture or tack. The hernia mesh may be secured in place by between 20 and 30 deliveries of adhesive. The hernia mesh may be secured in place by approximately 25 deliveries of adhesive. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       An embodiment of the invention will now be described by way of example only with reference to the accompanying drawings, in which like reference numerals indicate like parts and in which: 
         FIG. 1  is a view of the surgical instrument from the right hand side; 
         FIG. 2  is an exploded view of the surgical instrument from above the right hand side; 
         FIG. 3  is a view inside the housing of the surgical instrument from the left hand side; 
         FIG. 4  is an exploded view of the transfer assembly of the surgical instrument; 
         FIG. 5  is a view of the transfer assembly of the surgical instrument from the right hand side; 
         FIG. 6  is a cross-section of  FIG. 5  showing the valve of the transfer assembly in the second transfer position; 
         FIG. 7  is a magnified view of a part of  FIG. 6 ; 
         FIG. 8  is a view of the surgical instrument from the left hand side with the pull member disengaged from the dispensing chamber; 
         FIG. 9  is a view of the surgical instrument from the left hand side with the transfer assembly in the third transfer position; 
         FIG. 10  is a similar view to  FIG. 9  with the left hand side of the housing removed; 
         FIG. 11  is a cross-section from the right hand side showing the valve of the transfer assembly in the third transfer position; 
         FIG. 12  is a view of the priming assembly from the left hand side; 
         FIG. 13  is an exploded view of  FIG. 12 ; 
         FIG. 14  is a cross-section of the surgical instrument from the right hand side showing the priming assembly in the first priming position; 
         FIG. 15  is a cross-section of the surgical instrument from the right hand side showing the priming assembly in the second priming position; 
         FIG. 16  is an exploded view of the dispensing assembly from the right hand side; 
         FIG. 17A  is a view of the trigger gear wheel from the right hand side; 
         FIG. 17B  is a view of the trigger gear wheel from the left hand side; 
         FIG. 18A  is a view of the trigger from above the right hand side; 
         FIG. 18B  is a view of the trigger from the left hand side; 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWING FIGURES AND PREFERRED EMBODIMENTS 
     As shown in  FIG. 1 , the surgical instrument  10  comprises a housing  20  and a dispensing shaft  30 . The housing  20  comprises a handle  22  which allows the surgical instrument  10  to be gripped in one hand to allow one-handed operation of the surgical instrument  10 . The housing  20  also comprises a body  24 . The dispensing shaft  30  extends from the body  24 . The housing  20  has a ‘pistol’ configuration in which the handle  22  extends from the body  24  in a similar configuration to a pistol handle extending from a pistol barrel. 
     As shown in  FIGS. 1 and 2 , the dispensing shaft  30  is elongate and has a proximal end  31  and a distal end  32 . The proximal end  31  of the dispensing shaft  30  is received within the housing  20  and the distal end  32  defines a dispensing opening  33  for dispensing the fluid  12 . The fluid  12  is shown in  FIGS. 7 and 14 . The dispensing shaft has a longitudinal axis  34  which defines a proximo-distal axis for the surgical instrument  10 . The proximo-distal axis is oriented so that the distal direction is generally towards the distal end  32  of the dispensing shaft  30  and the proximal direction is generally away from the distal end  32 . 
     As shown in  FIG. 7 , the dispensing shaft  30  comprises an inner tube  35  and an outer tube  36 . The inner tube  35  defines a through bore  37  which allows the fluid  12  to pass along the dispensing shaft  30 . The outer tube  36  is made of metal and the inner tube  35  is made of PTFE for low friction to assist the movement of the fluid  12  along the through bore  37  by reducing shear stress. 
     The fluid  12  is a cyanoacrylate adhesive with a viscosity similar to water at room temperature. To ensure its sterility, the fluid  12  is stored in a sealed glass container  42  before the surgical instrument  10  is used. 
     As shown in  FIGS. 4 to 11 , the surgical instrument  10  include a transfer assembly  40  which enables transfer of the fluid  12  from the container  42  to a dispensing chamber  82 . The dispensing chamber  82  is attached to the transfer assembly  40 . 
     The transfer assembly  40  is moveably mounted to the housing  20 . The transfer assembly is moveable between a first transfer position (shown in  FIGS. 3, 6 and 7 ), a second transfer position (not shown in the Figures) and a third transfer position (shown in  FIGS. 9, 10 and 11 ). 
     The transfer assembly includes a container holder  44  which holds the container  42 . The container holder includes a filter  46 . The apertures of the filter  46  are sized to allow the fluid  12  to pass through the filter but to retain any fragments of the container  42  which are produced when the container  42  is opened. A PTFE sleeve  43  partially surrounds the container  42 . When the container  42  is opened, the PTFE sleeve  43  prevents the fluid  12  from spilling out of the container holder  44 . 
     Movement of the transfer assembly  40  from the first transfer position to the second transfer position causes the container  42  to be opened by a projection  48  on the transfer assembly  40  being pushed into the container  42  to break the wall of the container  42 . Any glass fragments created by the opening of the container  42  will be retained by the filter  46 . 
     The projection  48  is pushed into the container  42  by relative movement of the container holder  44  with respect to the projection  48 . The transfer assembly  40  includes a breaker section  50  which is moveable with regard to a holder section  52 . The projection  48  is located on the breaker section  50  and the container holder  44  is attached to the holder section  52 . 
     In the first transfer position (as shown in  FIGS. 3 and 6 ) the transfer assembly  40  is at an angle of approximately 25° to the longitudinal axis  34  of the dispensing shaft  30 . When the transfer assembly  40  is moved from the first transfer position to the second transfer position, the holder section  52  is moved to an angle of approximately 35° to the longitudinal axis  34 . The breaker section  50  is retained by the engagement of a hook member  49  with a catch  21  on the housing  20  (shown in  FIG. 16 ) so that it cannot move further than 25° to the longitudinal axis  34 . In this way, moving the holder section  52  to its maximum extent of approximately 35° will move the holder section  52  relative to the breaker section  50  and will cause the projection  18  to break open the container  42  and release the fluid  12 . 
     Once the fluid  12  is released from the container  42 , it is directed to the dispensing chamber  82 . As shown in  FIGS. 6, 7 and 11 , a valve  120  is positioned between the container  42  and the dispensing chamber  82 . 
     The valve  120  comprises an outer valve body  122  and an inner valve member  124 . The valve member  124  is a cylinder with a cylindrical surface and axial ends. The valve body  122  is annular and encircles the valve member  124 . The valve member  124  is attached to the housing  20  at its axial ends and the valve body  122  is attached to the transfer assembly  40 . In this way the valve member  124  acts as a pivot around which the valve body  122  and transfer assembly  40  rotates when the transfer assembly  40  moves between the first transfer position (see  FIG. 6 ), second transfer position and third transfer position (see  FIG. 11 ). 
     A transfer channel  126  is defined by the valve member  124  as a channel on its cylindrical surface. The valve member  124  further defines a dispensing channel  128  a diametrical channel through the valve member  124 . 
     The valve body  122  defines a container holder opening  130  which is in fluid communication with the container holder  44 . The valve body  122  also defines a dispensing chamber opening  132  which is in fluid communication with the dispensing chamber  82 . 
     When the transfer assembly  40  is in the second transfer position, the transfer channel  126  is aligned with the container holder opening  130  and the dispensing chamber opening  132  to provide a fluid path between the container holder opening  130  and the dispensing chamber opening  132 . In this way, fluid  12  released from the container  42  may flow from the container holder  44  to the dispensing chamber  82  when the transfer assembly  40  is in the second transfer position. 
     Before the surgical instrument  10  is used, a sealing disc  108  is located at a distal end of the dispensing chamber  82 . To draw the released fluid  12  through the transfer channel  126  from the container holder  44  when the transfer assembly  40  is in the second transfer position, the sealing disc  108  is retracted proximally in the dispensing chamber  82 . A pull member  54  is releasably attached to the sealing disc  108  to allow the user to retract the sealing disc  108 . As shown in  FIG. 3 , when the transfer assembly  40  is in the first transfer position, the pull member  54  is restrained from movement by the housing  20 . When the transfer assembly  40  is moved from the first transfer position to the second transfer position and the holder section  52  is moved to an angle of approximately 35° to the longitudinal axis  34 , the pull member  54  moves above the housing  20  so that it is no longer restrained. 
     Once all the fluid  12  has been drawn into the dispensing chamber  82  and the sealing disc  108  is fully retracted, the pull member  54  disengages from the sealing disc  108 . The pull member comprises two fingers  56  which engage a recess  110  on the sealing disc  108  so that the sealing disc  108  may be retracted. The recess  110  is in the form of a through-hole. The fingers  56  may be retained in the recess  110  by the inner surface  83  of the dispensing chamber  82 . At its proximal end, the dispensing chamber defines two slots  81  (shown in  FIG. 8 ) which allow the fingers  56  to disengage from the recess  110  when the sealing disc  108  is fully retracted. In this way, the pull member  54  is disengaged and separated from the dispensing chamber  82  (as shown in  FIG. 8 ) and is then discarded. 
     After the pull member  54  is discarded, the sealing disc  108  is fully retracted and the dispensing chamber  82  contains the fluid  12  to be dispensed. The transfer assembly  40  may then be moved to the third transfer position as shown in  FIGS. 9 to 11 . To reach the third transfer position, the transfer assembly  40  is pivoted about the valve member  124  until the dispensing chamber opening  132  is aligned with the dispensing channel  128  as shown in  FIG. 11 . 
     When the transfer assembly  40  is in the third transfer position, the sealing disc  108  is aligned with a plunger  84  as shown in  FIG. 14 . 
     As shown in  FIGS. 12 to 16 , the surgical instrument  10  further comprises a priming assembly  60 . The priming assembly  60  includes a priming actuator  62  which is operable to drive the priming assembly  60 . The priming actuator  62  is rotatably mounted to a proximal end of the housing  20 . The priming actuator  62  is rotatable from a first priming position shown in  FIG. 14  to a second priming position shown in  FIG. 15 . 
     The priming assembly  60  includes a safety element which is moveable from an engaged position to a disengaged position and which prevent the priming assembly  60  from being operated when it is in the engaged position. The safety element is in the form of a pull tab  64  attached to the priming actuator  62 . In its engaged position (as shown in  FIG. 14 ) the pull tab  64  engages a recess  28  on the housing  20  to prevent the priming actuator  62  from being operated. The pull tab  64  is separable from the priming actuator  62  so that in its disengaged position, the pull tab  64  is separated from the priming actuator  62  to allow the priming actuator  62  to be operated. 
     When the priming actuator  62  is rotated from the first priming position to the second priming position, a plunger  84  advances and pushes the sealing disc  108  distally within the dispensing chamber  82  to push the fluid  12  through the dispensing chamber opening  132  and the dispensing channel  128 . The proximal end  31  of the dispensing shaft  30  is received within the valve member  124  and the through bore  37  is connected to the dispensing channel  128 . Therefore fluid  12  pushed through the dispensing channel  128  may travel distally along the through bore  37  and be dispensed from the dispensing opening  33  at the distal end  32  of the dispensing shaft  30 . 
     Rotation of the priming actuator  62  from the first priming position to the second priming position rotates a priming cap  66  with an internal screw thread  65 . The priming cap  66  is linearly moveable with respect to the priming actuator  62  by the engagement of a spline feature  67  on the priming cap  66  with a groove  63  on the priming actuator  62 . The internal screw thread  65  on the priming cap  66  engages a complementary screw thread  87  mounted on a plunger drive assembly  86 . The priming cap  66  is connected to a proximal end  78  of the plunger  84 . In this way, rotation of the priming actuator  62  causes the internal screw thread  65  on the priming cap  66  to advance along the complementary screw thread  87  on the plunger drive assembly  86 . Since the plunger  84  is connected to the priming cap  66 , the plunger  84  will advance distally with respect to the plunger drive assembly  86  as shown in  FIGS. 14 and 15 . The advancement of the plunger  84  primes the through bore  37  of the dispensing shaft  30  with fluid  12  by advancing the sealing disc  108  in the dispensing chamber  82  and urging the fluid  12  out of the dispensing chamber  82 . 
     The priming assembly  60  includes an interlock  70  as shown in  FIGS. 12, 14 and 15 . The interlock  70  is moveable from a locked configuration in which it prevents the dispensing assembly  80  from being operated to a released configuration in which the dispensing assembly  80  is operable. The interlock  70  is only moveable to the released configuration once the priming actuator  62  is in the second priming position. An advantage of the interlock  70  is that accidental operation of the dispensing assembly  80  is not possible until the priming assembly  60  has been operated and the priming actuator  62  is in the second priming position. 
     As shown in  FIGS. 12 and 13 , the interlock  70  includes a locking member  72 . The locking member is elongate and is slidably mounted in the housing  20  to contact a locking formation  106  on the dispensing assembly  80  (see  FIGS. 14 and 15 ) and to contact the priming actuator  62 . When the priming actuator  62  is in the first priming position and the interlock  70  is in the locked configuration, the locking member  72  is unable to move and locks the trigger  94  in the second trigger position by contact with the locking formation  106 . 
     The priming actuator  62  includes an interlock recess  74  positioned so that when the priming actuator  62  is in the second priming position, the interlock recess  74  is aligned with the locking member  72  to allow the locking member  72  to move into the interlock recess  74 . The spring  96  exerts a force on the trigger  94  which causes the locking formation  106  to move the locking member  72  into the interlock recess  74  and this released configuration allows the trigger  94  to move from the second trigger position to the first trigger position. Once the trigger  94  is in the first trigger position, it is operable by the user. 
     As shown in  FIGS. 11, 14 and 15 , the dispensing assembly  80  comprises a dispensing chamber  82 . The fluid  12  is held in the dispensing chamber  82  before it is moved into the dispensing shaft  30 . The elongate plunger  84  is positioned to advance or retract within the dispensing chamber  82 . When the plunger  84  is advanced within the dispensing chamber  82 , the fluid  12  is urged out of the dispensing chamber  82  and into the through bore  37  of the dispensing shaft  30 . The plunger advances within the dispensing chamber  82  in a distal direction. Fluid  12  urged out of the dispensing chamber  82  enters the through bore  37  of at the proximal end  31  of the dispensing shaft  30 . 
     The plunger  84  has a distal end  79  which abuts against a sealing disc  108  which engages the internal surface  83  of the dispensing chamber  82  to form a seal. Advancement of the plunger  84  advances the sealing disc  108  within the dispensing chamber  82 . 
     As shown in  FIGS. 13, 14 and 15 , the plunger  84  is connected to a plunger drive assembly  86  which includes a rack  88  and pinion gear wheel  90 . The pinion gear wheel  90  is mounted within the housing  20 . Turning the pinion gear wheel  90  engages the rack  88  to advance or retract the plunger  84 . When the plunger  84  advances the sealing disc  108  is pushed along the dispensing chamber  82 . Retraction of the plunger  84  will not cause the sealing disc  108  to move because the plunger  84  abuts the sealing disc  108  instead of being physically connected to the sealing disc  108 . 
     The dispensing assembly  80  comprises a dispensing actuator  92  which is operable to drive the dispensing assembly  80 . The dispensing actuator  92  is connected by an intermediate gear wheel  104  to the pinion gear wheel  90  of the plunger drive assembly  86 . 
     As shown in  FIGS. 14, 15 and 16  the dispensing actuator  92  includes a reciprocable trigger  94  mounted to the housing  20  between the handle  22  and the body  24  of the housing  20 . The trigger  94  is operable by a user&#39;s finger from a first trigger position to a second trigger position. The trigger  94  is biased by a spring  96  to return to the first trigger position when the user&#39;s finger is released at the second trigger position. The spring  96  is attached to the housing  20  at a first end  95  and attached to the dispensing actuator  92  at a second end  97 . 
     As shown in  FIGS. 18A and 18B , a pawl  98  is moulded into the trigger  94  and a ratchet  100  is connected to a trigger gear wheel  102 . When the trigger  94  is moved from the first trigger position to the second trigger position the pawl  98  engages the ratchet  100  to turn the trigger gear wheel  102 . When the trigger  94  is moved from the second trigger position to the first trigger position the pawl  98  and ratchet  100  disengage so that the trigger gear wheel  102  does not turn. 
     As shown in  FIGS. 14 and 15 , turning the trigger gear wheel  102  will turn the intermediate gear wheel  104  to turn the pinion gear wheel  90  to advance the plunger  84 . The relative sizes of the trigger gear wheel  102 , intermediate gear wheel  104  and pinion gear wheel  90  are chosen to provide an overall gear ratio between the trigger gear wheel  102  and the pinion gear wheel  90  of 4 to 1. Therefore a 10° rotation of the trigger  94  results in a 2.5° rotation of the pinion gear wheel  90 . The size of the pinion gear wheel  90  is chosen to advance the rack  88  by a predetermined amount when the trigger  94  is operated from the first trigger position to the second trigger position. This will cause the plunger  84  to advance by a predetermined amount to dispense a predetermined volume of the fluid  12  from the dispensing opening  33  of the surgical instrument  10 . 
     As shown in  FIGS. 17A and 17B  an indexing wheel  101  is attached to the trigger gear wheel  102 . The indexing wheel  101  enables the movement of the trigger  94  between the first trigger position and the second trigger position to be indexed. The indexing wheel  101  includes indentations  99  on its circumference which engage an indexing formation  103  on the housing  20  (see  FIG. 16 ) to provide the indexing. The engagement of the indentations  99  with the indexing formation  103  also provides an additional frictional force on the ratchet  100  to assist the trigger  94  to move from the second trigger position to the first trigger position without moving the ratchet  100 . 
     The surgical instrument  10  dispenses the fluid  12  in discrete doses. A single dose is known as a delivery and each delivery is a predetermined volume of fluid  12 . The internal diameter of the inner surface  83  of the dispensing chamber  82  is chosen to be 7 mm so that advancement of the plunger  84  by a set distance of 0.65 mm will dispense a predetermined volume of approximately 25 mm 3 . 
     The surgical instrument  10  is capable of dispensing a predetermined number of deliveries which is 35 deliveries. After the dispensing actuator  92  has been operated 35 times, a hard stop on the dispensing assembly  80  prevents the dispensing actuator  92  from being operated again. The hard stop is provided by a stop projection  112  on the plunger drive assembly  86  (as shown in  FIG. 13 ) engaging the housing  20 . 
     As shown in  FIGS. 9 and 16 , the stop projection  112  is moveable within a slot  26  on the housing  20 . The slot  26  is in an exterior surface of the housing  20  so that the stop projection  112  is visible to the user of the surgical instrument  10 . The stop projection  112  advances in the slot  26  as the plunger  84  advances the sealing disc  108  in the dispensing chamber  82 . The hard stop is provided by the stop projection  112  reaching a distal end of the slot  26 . The slot  26  is located so that the stop projection  112  reaches the distal end of the slot  26  when the predetermined number of 35 deliveries is reached. By being visible to the user, the relative position of the stop projection  112  in the slot may provide a visual indication of the number of deliveries the surgical instrument  10  has made. 
     Use of the surgical instrument  10  in a hernia mesh fixation procedure will now be described. 
     The fluid  12  is a cyanoacrylate adhesive suitable for securing a hernia mesh in place at the operative site in the human or animal body. The hernia mesh is secured in place by a number of deliveries of adhesive from the surgical instrument  10 . Each delivery of adhesive has a similar function to a suture or tack. The hernia mesh is secured in place by approximately 25 deliveries of adhesive. Since the predetermined maximum number of deliveries of the device is 35 deliveries, there are approximately 10 extra deliveries of adhesive available for the surgeon to use as necessary. The surgeon may use some of these extra deliveries for closure of the peritoneum if appropriate. 
     The detailed sequence of the steps for using the surgical instrument  10  is as follows. In this description, it is assumed that a scrub nurse and a surgeon will be present during the procedure but the surgical instrument  10  may also be prepared and used by a single person. 
     The surgical instrument  10  is provided in sterile packaging with the transfer assembly  40  in the first transfer position at an angle of 25° to the longitudinal axis  34  of the dispensing shaft  30 . The scrub nurse removes the surgical instrument  10  from the packaging and moves the transfer assembly  40  to the second transfer position at an angle of 35° to break the container  42  within the container holder  44 . The move to the second transfer position aligns the dispensing chamber  82  and the container holder  44  with the transfer channel  126  on the valve  120 . Next the scrub nurse retracts the sealing disc  108  in the dispensing chamber  82  by pulling the pull member  54  to draw the adhesive fluid  12  into the dispensing chamber  82 . The pull member  54  self-detaches at the end of its travel and is discarded. 
     The scrub nurse then moves the transfer assembly  40  to the third transfer position (as shown in  FIGS. 9, 10 and 11 ) which moves the dispensing chamber  82  from alignment with the transfer channel  126  of the valve  120  to alignment with the dispensing channel  128 . 
     At this stage, the transfer sequence has been completed and the priming sequence can be started. To start the priming sequence the scrub nurse removes the safety element  64  which releases the priming actuator  62 . Next the scrub nurse rotates the priming actuator  62  which advances the plunger  84  to push the sealing disc  108  forward distally in the dispensing chamber  82  which in turn pushes adhesive fluid  12  through the dispensing channel  128  of the valve  120  and along the through bore  37  of the dispensing shaft  30  to near the dispensing opening  33  of the surgical instrument  10 . Once the priming actuator  62  has been rotated 320° from the first priming position to the second priming position, the locking member  72  of the interlock  70  is pushed backwards into the interlock recess  74  on the priming actuator  62  by the force of the spring  96  on the dispensing actuator  92 . This causes the trigger  94  to be released to the first trigger position which completes the priming sequence and the surgical instrument  10  is now ready for use. 
     The scrub nurse hands the surgical instrument  10  to the surgeon to use. When the surgeon uses a finger to pull the trigger  94  from the first trigger position to the second trigger position, the plunger drive assembly  86  advances the plunger  84  to make a delivery of fluid adhesive  12  from the dispensing opening  33 . When the surgeon releases the trigger  94  the dispensing actuator  92  is rotated by the spring  96  from the second trigger position back to the first trigger position without the ratchet  100  rotating, ensuring that the plunger  84  remains stationary. The Surgeon uses up to 25 deliveries of adhesive fluid  12  to attach the hernia mesh in the desired position.