Patent Publication Number: US-2021169560-A1

Title: Electrosurgical device

Description:
This application is a continuation of U.S. patent application Ser. No. 15/404,598 filed on Jan. 12, 2017, which claims priority to GB1600546.4 filed on Jan. 12, 2016, and GB1600558.9 filed on Jan. 12, 2016. Entire contents of each of the above-identified documents are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention described herein relate to an electrosurgical device, and in particular an electrosurgical forceps device wherein a mechanical blade provides a tissue cutting action in combination with electrosurgical electrodes providing a tissue coagulation or sealing effect. 
     BACKGROUND TO THE INVENTION AND PRIOR ART 
     Electrosurgical instruments provide advantages over traditional surgical instruments in that they can be used for coagulation and tissue sealing purposes. One such prior art arrangement is known from US2015/223870A1, which describes an endoscopic bipolar forceps including a housing and a shaft, the shaft having an electrosurgical end effector assembly at a distal end thereof, which includes two jaw members for grasping tissue therebetween. Each jaw member is adapted to connect to an electrosurgical energy source, enabling them to affect a tissue seal to tissue held therebetween. A drive assembly is included within the housing for moving the jaw members. A movable handle is also included, such that movement of the handle actuates the drive assembly to move the jaw members relative to each other. A knife channel is included within the end effector configured to allow reciprocation of a knife blade within the knife channel, to allow cutting of tissue. 
     Other prior art arrangements include U.S. Pat. Nos. 5,730,740, 5,104,397, 4,800,880, WO98/14124, US2012/0109186, U.S. Pat. No. 5,352,235, WO2014/074807, U.S. Pat. No. 7,846,161, WO2008/024911, U.S. Pat. Nos. 5,776,130, 6,039,733, 6,179,834, 7,131,971, 7,766,910, EP2628459, US2014/0221999, U.S. Pat. No. 7,083,618, US2009/0248020, US2015/0209103, U.S. Pat. Nos. 5,797,938 and 7,101,373. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention provide an improved surgical instrument having an end effector mounted on the end of an elongate shaft extending from a handle. The end-effector is capable of several different operations, including grasping, cutting, and sealing and/or coagulating tissue, and one of the operations is controlled by a trigger mechanism contained within the handle. In some embodiments, the end effector includes a pair of curved jaw members and a blade assembly having a cutting blade at its distal end. The trigger mechanism is arranged to drive the blade assembly longitudinally within the elongate shaft such that the cutting blade protrudes between the jaw members. In order to help the trigger mechanism push the blade assembly around the curved jaws, the distal end of the blade has a graduated flexibility such that it can more easily bend to the shape of the jaw members. The distal end of the blade may also be provided with a low friction coating so that it can more easily slide between the jaw members. 
     From a first aspect, there is provided a surgical instrument including:
         a handle,   a pair of curved first and second jaw members, one or both of the curved jaw members including a curved slot so as to form a curved track therebetween,   a blade assembly located for longitudinal movement into a deployed position within the curved track, the blade assembly including a cutting blade at its distal end,   a trigger mechanism located on the handle and movable between a first position and a second position, movement of the actuating mechanism from its first position to its second position causing the longitudinal movement of the blade assembly into its deployed position,       

     characterised in that the blade assembly being formed into at least two regions, a first region having a lateral flexibility greater than that of the second region, the first region being located distally of the second region and the arrangement being such that the second region is at least partially located within the curved track formed by the jaw members when the blade assembly is in its deployed position. 
     As such, the trigger mechanism is required to push the cutting blade around a curve, thus adding to the frictional forces working against the blade travel. This can therefore be reduced by making the blade gradually more flexible towards the distal end such that it is easier for the blade to follow the curved path between the jaws. 
     The blade assembly may be in the form of a bar, having a thickness substantially less than either its width or its length. 
     In some arrangements, the first region of the blade assembly is provided with one or more apertures so as to increase the lateral flexibility thereof, wherein the apertures may be in the form of one or more slots. Alternatively, the first region of the blade assembly may be provided with a single longitudinally extending slot. 
     In another arrangement, both the first and second regions of the blade assembly are provided with a single longitudinally extending slot, the width of the slot in the first region being greater than that of the slot in the second region. The slots in the first and second regions may also be contiguous. 
     In a further arrangement, the first region of the blade assembly is provided with a plurality of apertures. Further still, both the first and second regions of the blade assembly may be provided with a plurality of apertures, the number of apertures in the first region being greater than the number of apertures in the second region. 
     Where both the first and second regions of the blade assembly are provided with a plurality of apertures, the area of the apertures in the first region may be greater than the area of the apertures in the second region. 
     The apertures may be located within the body of the blade assembly. 
     Moreover, the apertures may be formed as cut-outs along an external surface of the blade assembly. 
     The thickness of the blade assembly may be less in the first region as compared with its thickness in the second region. 
     In some arrangements, at least a part of the blade assembly is coated with a low-friction coating. 
     The blade assembly may also be formed into at least three regions, a first distal region having a lateral flexibility greater than that of a second intermediate region, the second intermediate region having a lateral flexibility greater than that of a third proximal region. 
     In some arrangements, the handle may further comprise an actuating mechanism movable between a first position and a second position, movement of the actuating mechanism from its first position to its second position causing at least one of the curved jaw members to move relative to the other from a first open position in which the jaw members are disposed in a spaced relation relative to one another, to a second closed position in which the curved jaw members cooperate to grasp tissue therebetween. 
     Also described herein is a surgical instrument including:
         a handle,   a pair of curved first and second jaw members, one or both of the curved jaw members including a curved slot so as to form a curved track therebetween,   a blade assembly located for longitudinal movement within the curved track, the blade assembly including a cutting blade at its distal end,   a trigger mechanism located on the handle and movable between a first position and a second position, movement of the actuating mechanism from its first position to its second position causing the longitudinal movement of the blade assembly,   characterised in that at least a part of the blade assembly is coated with a low-friction coating.       

     As stated above, the trigger mechanism is required to push the cutting blade around a curve, thus adding to the frictional forces working against the blade travel. These frictional forces can therefore be reduced by coating the blade with a low friction material such that it is easier for the blade to follow the curved path between the jaws. 
     In some arrangements, the blade assembly may be coated using physical vapour deposition (PVD). Alternatively, the blade assembly may be coated using chemic vapour deposition. Suitable coatings may include low-friction polymer composites such as PTFE. 
     In some arrangements, the handle may further comprise an actuating mechanism movable between a first position and a second position, movement of the actuating mechanism from its first position to its second position causing at least one of the curved jaw members to move relative to the other from a first open position in which the jaw members are disposed in a spaced relation relative to one another, to a second closed position in which the curved jaw members cooperate to grasp tissue therebetween. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be further described by way of example only and with reference to the accompanying drawings, wherein like reference numerals refer to like parts, and wherein: 
         FIG. 1  is a side view of an electrosurgical instrument according to an embodiment of the present invention; 
         FIG. 2  is a side view of the handle of the electrosurgical instrument according to the embodiment of the present invention; 
         FIG. 3  is an exploded view of an electrosurgical instrument according to the embodiment the present invention; 
         FIG. 4  is a sectional view of the clamping mechanism of the electrosurgical instrument of  FIG. 3 , shown in an open configuration; 
         FIG. 5 a    is a sectional view of the clamping mechanism of the electrosurgical instrument of  FIG. 3 , shown in a closed configuration; 
         FIG. 5 b    is a sectional view of the clamping mechanism of the electrosurgical instrument of  FIG. 3 , shown in a closed configuration with tissue clamped therebetween; 
         FIG. 6  is a sectional view of part of the clamping mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 7  is a perspective view of the clamping mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 8 a - f    illustrate the assembly of a part of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 9 a - b    are sectional views of a part of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 10 a - c    show a blade guide part of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 11  shows a latch part of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 12  shows a blade angle adjustment part of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 13 a - b    are sectional views of the blade angle adjustment part of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 14 a - b    show a blade angle control wheel part of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 15 a - b    illustrate the rotational movement of the blade angle control wheel of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 16 a - d    illustrate the rotational movement of the end effector of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 17  is a sectional view of the electrosurgical instrument of  FIG. 3  illustrating a wiring path; 
         FIGS. 18 a - b    show further details of an electrical wiring path used in the electrosurgical instrument of  FIG. 3 ; 
         FIG. 19  shows further details of an electrical wiring path used in the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 20 a - b    are side views of part of the cutting mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 21  is a sectional view of part of the cutting mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 22  is a sectional view of another part of the cutting mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 23  is a partially transparent perspective view of part of the cutting mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 24 a - c    illustrate the assembly of one part of the cutting mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 25 a - c    are sectional views of the cutting mechanism and clamping mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 26 a - f    are sectional views illustrating the operation of the latching mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 27  is a graph illustrating the cutting mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 28 a - b    are line drawings illustrating the cutting mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 29 a - b    show a blade angle adjustment part of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 30  is a perspective view of part of the clamping mechanism of the electrosurgical instrument of  FIG. 3   
         FIG. 31  is a partially section view of the cutting mechanism and clamping mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 32  is a partially section view of the cutting mechanism and clamping mechanism of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 33  shows the blade angle control wheel part and the electrode control switch of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 34  shows the blade angle control wheel part of the electrosurgical instrument of  FIG. 3 ; 
         FIGS. 35 a - b    illustrate the handle of the electrosurgical instrument of Figure, held by users with different size hands; 
         FIGS. 36 a - c    illustrate the rotational movement of the end effector of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 37  illustrates the rotational movement of the blade angle control wheel of the electrosurgical instrument of  FIG. 3 ; 
         FIG. 38  is a schematic perspective view of an example end effector; 
         FIG. 39  is an enlarged perspective view of a part of the end effector of  FIG. 38 ; 
         FIG. 40  is a schematic sectional view of a part of the end effector of  FIG. 38 ; 
         FIG. 41  is a schematic perspective view of an alternative end effector; 
         FIG. 42  is an enlarged perspective view of a part of the end effector of  FIG. 41 , 
         FIG. 43  is a schematic sectional view of a part of the end effector of  FIG. 41 , 
         FIG. 44  is a schematic sectional view of a part of a further alternative end effector; 
         FIG. 45  is a representation of an electro-surgical system including a generator and an instrument in accordance with embodiments of the invention; 
         FIG. 46  further illustrates a latch part of the electrosurgical instrument of  FIG. 3 ; and 
         FIGS. 47 a - e    illustrate the distal end of the cutting blade used in the electrosurgical instrument of  FIG. 3 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of the invention will now be described. A brief overview of the whole embodiment will first be given, followed by detailed descriptions of particular aspects thereof. 
     1. OVERVIEW OF THE CONFIGURATION OF THE INSTRUMENT 
       FIG. 1  illustrates an electrosurgical instrument  1  according to an example of the present invention. The instrument  1  includes a proximal handle portion  10 , an outer shaft  12  extending in a distal direction away from the proximal handle portion, and a distal end effector assembly  14  mounted on a distal end of the outer shaft. The end effector assembly  14  may by way of example be a set of opposed jaws arranged to open and close, and comprising one or more electrodes arranged on or as the inner opposed surfaces of the jaws and which in use have connections to receive an electrosurgical radio frequency (RF) signal for the sealing or coagulation of tissue. The jaws are further provided with a slot or other opening within the inner opposed surfaces through which a mechanical cutting blade or the like may protrude, when activated by the user. In use, the handle  10  is activated by the user in a first manner to clamp tissue between the jaws  14 , and in a second manner to supply the RF current to the electrodes in order to coagulate the tissue. The jaws  14  may be curved so that the active elements of the instrument  1  are always in view. This is important in vessel sealing devices that are used to operate on regions of the body that obscure the user&#39;s vision of the device during use. The handle  10  may be activated by the user in a third manner to cause the blade to protrude between the jaws  14 , thereby cutting the tissue clamped between. Once the required cutting and sealing has been completed, the user can release the tissue from the jaws  14 . 
     The handle  10 , as shown by  FIG. 2 , comprises a casing  20  formed of two clamshell mouldings  300 ,  302  which houses all of the components required to operate and rotate the jaws  14 , coagulate and cut tissue. The clamshell mouldings in the assembled device are ultrasonically welded together, once the internal components have been assembled inside. The handle  10  includes a clamping handle  22  for clamping tissue between the jaws  14 , a trigger  24  for cutting the tissue, switch  26  for activating and deactivating the RF supply to the electrodes in the jaws  14  in order to coagulate tissue, and a rotation wheel  28  for rotating the jaws  14  in order to reach tissue from different angles. As such, the configuration of handle  10  is such that the instrument  1  and all its functions can be operated using a single hand, with all of the operational mechanisms being easily accessible. 
       FIG. 3  shows all of the features of instrument  1  required to perform its functions, including those housed within the two clamshell mouldings  300 ,  302  of the casing  20 . To clamp tissue between the jaws  14 , a clamping mechanism is actuated using the clamping handle  22 . The clamp handle  22  further comprises a collar  304 , the collar  304  comprising a hinge  306  that functions as a fulcrum around which the clamping handle  22  rotates. For example, the hinge  306  may be two outward facing pins that click in to corresponding mouldings  308  integral to the clamshell mouldings  300 ,  302  to thereby provide an anchor point around which the clamping handle  22  rotates. The clamping mechanism further comprises a collar moulding  310 , a spring  312 , and an inner moulding  314 , as further illustrated by  FIGS. 4 to 7 , all of which are threaded along a drive shaft  316 . 
     The collar  304  comprises a keyhole aperture  318  in which the collar moulding  310  sits. The aperture  318  has a larger diameter at the top than that at the bottom, wherein the collar moulding  310  is arranged to sit within the lower part of the aperture  318 , as illustrated by  FIG. 8 a   . In assembly, the collar moulding  310  easily fits through the larger part of the aperture  318  such that the collar  304  sits between two flanges  800 ,  802 , as shown by  FIGS. 8 b - c   . As shown by  FIG. 8 d   , the collar  304  is then pushed upwards to engage the smaller part of the keyhole aperture  318  with the collar moulding  310 . Once, the hinge  306  is connected to the hinge mouldings  308  within the casing  20 , the collar moulding  310  is retained within the lower part of the aperture  318  where it is free to move rotationally within the aperture  318 . 
     As shown in  FIG. 6 , the collar moulding  310 , spring  312  and inner moulding  314  are retained between protruding members  600 ,  602  such that they cannot travel axially beyond these protruding members  600 ,  602 . In this respect, the protruding members  602  at the proximal end of the drive shaft  316  are compressible so as to allow the drive shaft  316  to be passed through a channel  604  in the proximal end of the inner moulding  314 . The drive shaft  316  is pushed through the channel  604  until it reaches an opening  606 , wherein the protruding members  602  are no longer compressed such that they lie flush against the walls of the drive shaft  316 . Instead, the protruding members  602  fan out and push against the walls of the opening  606  such that the span of the protruding members  602  extends beyond the diameter of the channel  604 . Consequently, the drive shaft  316  cannot be pulled back through the channel  604  and is thus locked in place. 
     The distance between the protruding members  600 ,  602  is such that the spring  312  is at least partially compressed between the collar moulding  310  and the inner moulding  314 . This pre-compression is important for ensuring that the correct clamping load is applied when the clamping mechanism is activated, as will be described in more detail below. Both the collar moulding  310  and the inner moulding  314  comprise cavities  608 ,  610  into which the spring  312  extends. In particular, a substantial proportion of the length of the collar moulding  310  houses the spring  312 . This arrangement allows for a longer spring  312  which is important for ensuring that the spring  312  does not ever reach its solid length during use. 
     The main body of the drive shaft  316  lies within the outer shaft  12 , the distal end of the drive shaft  316  being coupled to both the distal end of the outer shaft  12  and the jaws  14 . The drive shaft  316  moves axially within the outer shaft  12  and it is this axial movement that moves the jaws  14  from an open to a closed position, as can be seen from  FIGS. 4 and 5   a . For example, the drive shaft  316  is coupled to the jaws  14  by means of a drive pin  400  in a cam slot  402 , whereby movement of the drive pin  400  within the cam slot  402  moves the jaws  14  between the open and closed position. The coupling between the drive shaft  316 , the outer shaft  12  and the jaws  14  is such that rotational movement of the drive shaft  316  is transferred to the outer shaft  12  and jaws  14 . 
     The outer shaft  12  and drive shaft  316  are coupled at a further point by means of a shaft moulding  320 . The shaft moulding  320  sits within a socket  322  of the casing  20 , and thus couples the outer shaft  12  to the casing  20 . The outer shaft  12  is attached to the shaft moulding  320  by any suitable means, for example, snap-fit tabs  900  that cooperate with corresponding notches  902  within the shaft moulding  320 , as shown in  FIG. 9 b   . The drive shaft  316  is threaded through the body of the shaft moulding  320  via an aperture (not shown) that matches the cross-sectional “T” shape of the drive shaft  316 , as illustrated by  FIG. 10 a   . The shaft moulding  320  is arranged such that it is free to rotate within the socket  322 . For example, the shaft moulding  320  may comprise cylindrical flange features  904 ,  906  that rotate within concentric mating faces  908 ,  910  provided within the clamshell mouldings  300 ,  302 . Therefore, the shaft moulding  320  rotates with the drive shaft  316 , which in turn translates this rotational movement to the outer shaft  12  and the jaws  4 . The shaft moulding  320  thus acts as a rotational and axial guide for the drive shaft  316 . 
     The clamping handle  22  comprises a latch  324  arranged to cooperate with a latch moulding  326  which sits within the proximal end  328  of the casing  20 . The latch moulding  326  may be held in place by any suitable means, for example, by means of a moulded pin  330  integral to one of the clamshell mouldings  300 ,  302 , as shown by  FIG. 3 , or by simply by the moulded walls  1100  integral to the clamshell moulding  300 , as shown by  FIG. 11 . When the clamping handle  22  is driven towards the casing  20  so as to close the jaws  14 , the latch  324  enters the casing  20  via an opening  1102  and engages with the latch moulding  326  so as to retain the clamping handle  22  in this position. As is shown in  FIGS. 26 a  to 26 f   , the latch moulding  326  comprises a two way spring  1104  and a cam path  1106  along which the latch  324  traverses. As shown in  FIG. 46 , the latch mechanism may also include an override component  4600  to allow the user to manually release the latch  324  if it gets stuck, and a lock-out component  4602  to disable the latch mechanism altogether. The override component  4600  and lock-out component  4602  may be provided on the latch moulding  326  or may be integral to the inside of the casing  20 . 
     As described above, the handle  10  further comprises a rotation wheel  28 , wherein the rotation wheel  28  is arranged to encase the inner moulding  314 . In this respect, the rotation wheel  28  and inner moulding  314  have interlocking members  1200 ,  1202 , as shown by  FIG. 12 . These interlocking members  1200 ,  1202  couple together such that the rotation wheel  28  and inner moulding  314  rotate together, whilst still allowing axial movement of the inner moulding  314  within the rotation wheel  28 , as can be seen from  FIGS. 13 a - b   . Therefore, rotation of the rotation wheel  28  causes rotation of the inner moulding  314 , which subsequently rotates the drive shaft  316  and the collar moulding  310 . For stability, the rotation wheel  28  comprises cylindrical faces  1204  that rotationally slide on internal mating faces (not shown) integral to the clamshell mouldings  300 ,  302 . 
     To enable the user to rotate the jaws  14 , the casing  20  has two openings  332 ,  334  through which scalloped portions  336  of the rotation wheel  28  protrude. The two openings  332 ,  334  are opposite one another on each side of the handle, and are trapezoidal in shape. In particular, the trapezoidal apertures have parallel sides orthogonal to the longitudinal axis of the handle, and one of the parallel sides may be longer than the other, the longer side being at the forward end of the aperture, and the shorter side being at the rearward end. The scalloped portions  336  are conveniently sloped so as to comfortably fit the thumb or fingers of the user. In this respect, the scalloped portions  336  are cut at an angle to the plane of rotation, as shown in  FIGS. 14 a - b   . In particular, the angle of the sloping part of the scalloped portions should be substantially equal to the angle of the external casing in the region of the rotation wheel  28 . 
     The rotation wheel  28  also comprises at least one stop member  1500  for limiting the degree of rotation, as illustrated in  FIGS. 5 a - b   . The stop member  1500  interacts with stop features  1502 ,  1504  integral to the casing  20 . As the rotation wheel  28  is rotated, the stop member  1500  is obstructed by the stop features  1502 ,  1504 , thereby preventing further rotation. For example, the stop features  1502 ,  1504  may limit the rotation wheel to 270° of rotation. Similarly, the shaft moulding  320  also comprises a stop member  1600  that interacts with stop features  1602 ,  1604  integral to the casing  20 , as shown by  FIGS. 16 a - d   . The stop member  1600  of the shaft moulding  320  and its respective stop feature  1602 ,  1604  are radially aligned with the stop member  1500  of the rotation wheel  28  and its respective stop features  1502 ,  1504  such that rotation is limited to the same extent. That is, as the rotation wheel  28  is turned, the radial point at which stop member  1500  on the rotation wheel  28  is obstructed will be the same as the radial point at which stop member  1600  on the shaft moulding  320  will be obstructed. For example, in  FIGS. 15 b  and 16 a   , the jaws  14  have been rotated 90° anticlockwise from a neutral orientation (shown in  FIG. 16 b   ). This rotational freedom means that the user can grasp at tissue from different angles without needing to rotate the whole instrument  1 . 
     As described above, the switch button  26  is provided for activating and de-activating the RF signal delivered to the electrodes in the jaws  14  via some appropriate circuitry, for example, two ingress-protected switches on a small printed circuit board (PCB)  338 . As shown in  FIG. 17 , the PCB  338  is connected to a connection cord  1700  for receiving the RF output from a generator (not shown) and electrical wiring  1702 ,  1704  for supplying the RF current to the electrodes in the jaws  14 , for example, one wire for the active electrode and one for the return electrode. As shown in  FIG. 17  and  FIGS. 18 a - b    the wires  1702 ,  1704  are wrapped underneath and around the shaft moulding  320  before entering a guide slot  1800  into the internal cavity  1802  of the shaft moulding  320  and down the outer shaft  12 . Wrapping the wires  1702 ,  1704  around the shaft moulding  320  in this way keeps the wires  1702 ,  1704  in a compact arrangement, so as to enable easy assembly, whilst allowing for the rotation of the drive shaft  316 . In this respect, the wires  1702 ,  1704  un-wind and re-wind with the rotation of the drive shaft  316 . Additionally, one of the clamshell mouldings  300  also comprises two moulded pockets  1900 ,  1902  located in series for housing the wire contacts  1904 ,  1906  that connect the active and return wires  1702 ,  1704  to the wiring  1908 ,  1910  of the ingress-protected switches  338 . The opposite clamshell moulding  302  comprises corresponding rib features (not shown) to retain the contacts  1904 ,  1906  within the pockets  1900 ,  1902 . As a result, the two wire contacts  1904 ,  1906  are longitudinally separated such that only one contact can pass through each pocket  1900 ,  1902 , thereby providing a physical barrier between each contact  1904 ,  1906  and any wiring. This prevents the risk of insulation damage to any of the wiring caused by the contacts  1904 ,  1906 , whilst also protecting the contacts  1904 ,  1906  themselves from any fluid that may make its way down the outer shaft  12  and into the casing  20 . 
     Turning to the cutting mechanism, a blade  340  for cutting tissue clamped between the jaws  14  is provided within a central track  342  along the length of the drive shaft  316 . The mechanism for actuating the blade  340  along the track  342  and between the jaws  14 , is operated via the trigger  24 . The trigger  24  actuates a drive assembly formed of a trigger moulding  344 , a blade drive moulding  346 , a blade collar moulding  348 , an extension spring  350  and a blade moulding  352 . The drive assembly is positioned between the shaft moulding  320  and the handle collar  304  of the clamping mechanism. As shown in  FIGS. 20 a - b   , the drive assembly functions as an offset slider-crank mechanism whereby the force exerted by the user on the trigger  24  is transferred into axial movement of the blade moulding  352  along the drive shaft  316 , which in turn drives the attached blade  340 . 
     As shown in  FIGS. 21, 22 and 23 , the blade moulding  352  is arranged to sit within the blade collar moulding  348 . As shown in  FIG. 22 , the blade collar moulding  348  comprises a lip  2200  the interlocks with a groove  2202  around the circumference of the blade moulding  352 . As shown on  FIG. 23 , the blade moulding  352  has a “T” shaped aperture  2300  for receiving the drive shaft  316  and blade  340 . The blade moulding  352  further comprises an internal cut-out  2100 , as shown by  FIG. 21 , for the proximal end of the blade  340 , wherein the end of the blade  2102  is shaped to match the internal cut-out  2100  of the blade moulding  352  so as to allow ease of assembly, as demonstrated by  FIGS. 24 a - c   . The blade moulding  352  is isolated rotationally from the blade collar moulding  348  such that the two mouldings can rotate concentrically. Consequently, the blade moulding  352  is able to rotate with the drive shaft  316 . 
     As described above, the jaws  14  may be curved. To enable the blade  340  to be pushed around the curve, whilst maintaining sufficient cutting ability, the frictional force of the cutting blade  340  through the curved track must be minimised. The frictional force is a product of the frictional coefficient of the blade  340  within the track  342 , and the force due to bending that the blade  340  exerts on the walls of the track  342 . This frictional force may be reduced, for example, by adding a low friction coating to the sides of the blade, and/or preferentially weakening the blade  340  to graduate the flexibility of the blade&#39;s distal end such that it is able to bend along the track  342  whilst remaining rigid in the direction of the cutting force. Preferential weakening may be provided, for example, by the provision of one or more apertures  354  in the distal end, as shown in  FIG. 3  and  FIGS. 47 a - c   , or by graduating the blade  340  thickness, as illustrated in  FIG. 47 d   . Alternatively, as illustrated by  FIG. 47 e   , patterned laser cuts  4712  or chemical etches in the distal end could be used to control the bending stiffness over a length of the blade, whereby the spacing between such cuts may be constant or gradually increase from the distal to proximal end. 
     In use, blood and tissue can build up within the distal end of the instrument  1 . In particular, blood and tissue can cause the blade  340  to stick within the drive shaft  316 . Therefore, the distal end of the drive shaft  316  may include cut-out portions  1000 ,  1002  in order to reduce the surface area of the drive shaft  316  to which blood and tissue build stick, as shown in  FIGS. 10 b - c   . For example, the cut-out portions may be such that the distal end comprises two side walls with no base support, or the distal end comprises a base support with bifurcated side walls. 
     2. OPERATION OF THE INSTRUMENT 
     Having described the overall configuration of the device, the overall operation of the electrosurgical instrument  1  in use will now be discussed. Following this, further detailed description of the configuration and operation of particular aspects of the device will be undertaken. 
     As discussed above, the handle  10  of the electrosurgical instrument is arranged to i) clamp tissue between a set of jaws  14 , ii) latch the jaws in place (if desired by the user), iii) deliver an RF signal to electrodes in the jaws  14  so as to coagulate the tissue clamped between, and iv) launch a blade  340  between the jaws  14  so as to cut the tissue clamped between. The handle  10  can also rotate the jaws  14  so as to allow the user to clamp tissue at different angles without needing to rotate the entire handle  10 . The result is that the tissue between the jaws can be sealed prior to or at the same time as being cut by the same electrosurgical instrument. Moreover, these effects can be achieved by the instrument via a one handed operation thereof by the surgeon. 
     2.1 Clamping Mechanism 
     To clamp tissue between the jaws  14 , the user squeezes the clamping handle  22  towards the proximal end  328  of the casing  20  until the latch  324  engages with the latch moulding  326  within the casing  20 . This movement pivots the drive handle  22  about its hinge  306 , as shown by  FIGS. 8 e - f   , and pushes the edge of the collar  304  against the flange  800  to drive the collar moulding  310 , the spring and the inner moulding  314  along the drive shaft  316  in the proximal direction, as illustrated by  FIGS. 4 and 5   a . As described above, the inner moulding  314  is attached to the drive shaft  316  via protruding members  602 . Therefore, as the inner moulding  314  is pushed back axially, the drive shaft  316  is also moved axially which drives the pin  400  in the cam slot  402  of the jaws  14 , thereby closing the jaws  14 . As such, the load from the drive handle  22  is transferred to the drive shaft  316  via the spring mechanism of the collar moulding  310 , spring  312  and inner moulding  314 . 
     Once tissue is clamped between the jaws  14 , as shown by  FIG. 5 b   , the spring  312  acts to limit the force loaded onto the tissue. Once the collar moulding  310 , spring  312  and inner moulding  314  have stopped moving axially, and as the collar  304  continues to drive against the flange  800 , the threshold compression force on the spring  312  is eventually reached such that the spring  312  begins to compress between the collar moulding  310  and inner moulding  314 . As the spring  312  compresses further, the drive handle  22  can be driven all the way into the latched position without exerting any more force on the clamped tissue. That is, the load of the drive handle  22  is no longer transferred to the drive shaft  316 , but is effectively absorbed by the spring  312 . As such, the spring  312  ensures that the correct amount of load is transferred onto the jaws  14 . Without the spring  312 , actuation of the drive handle  22  will continue to increase the load transferred to the drive shaft  316  and subsequently the jaws  14  and tissue. This could result in mechanical damage to the tissue as the user continues to squeeze the drive handle  22  in order to engage the latch  324 . 
     As discussed above, the cavities  608 ,  610  in the collar moulding  310  and inner moulding  314  act together to allow for a larger spring  312 . This allows for greater spring travel so that the spring  312  does not completely compress to its solid length during use. If the spring  312  was to reach its solid length, the spring would no longer absorb the load exerted by the drive handle  22  and the force would once again be transferred to the jaws  14 . 
     2.2 Latch Mechanism 
     Once tissue has been clamped between the jaws  14 , the jaws  14  can be locked into a closed position by engaging the latch  324  on the drive handle with the latch moulding  326  inside the casing  20  as shown by  FIGS. 26 a - f   . As the latch  324  enters the casing  20  via the opening  1102 , the latch  324  engages the latch moulding  326 , pushing the moulding  326  down within the casing  20  and thereby extending the spring  1104 . As shown in  FIGS. 26 b - c   , the latch  324  runs up the side of the cam path  1106  until it reaches its maximum position. At this point, the drive handle  22  cannot be compressed any further, and the spring  1104  pulls the latch moulding  326  back up inside the casing  20  such that the latch  324  slots into the “V” shaped pocket of the cam path  1106  to retain the drive handle  22  in the compressed position and the jaws  14  in the closed position, as shown in  FIG. 26   d.    
     In this latched position, the user&#39;s hand is free for operating the other functions of the instrument  1 , as will be discussed below. 
     To release the latch  324  from the casing  20  and open the jaws  14 , the user must squeeze drive handle  22  towards the casing  20  to release the latch  324  from the pocket of the cam path  1106 , as shown by  FIG. 26 e   . The force of the spring  1104  pulls the latch moulding  326  further up into the casing  20 , such that the latch  324  travels in the opposite direction down the side of the cam path  1106 , as shown by  FIGS. 26 e - f   , and back out of the opening  1102 . The latch moulding  326  will then return back to its original position within the casing  20 . 
     2.3 Cutting Mechanism 
     Whilst the jaws  14  are in a closed position, the user may need to cut the tissue clamped between. To cut the tissue, a blade  340  is driven between the jaws  14  by actuation of the drive assembly. 
     The drive assembly is a three pivot arrangement that acts as a slider-crank mechanism. As the user pulls the trigger  24  back towards the casing  20 , as shown by  FIGS. 25 b - c   , it levers the trigger moulding  344  around a pivot point A which is anchored to the casing  20 , for example, by means of outward facing pins  358  that connect with corresponding mouldings  356  integral to the clamshell mouldings  300 ,  302  shown in  FIG. 3 . This urges the pivot point B connecting the trigger moulding  344  and drive moulding  346  over its centre position, thereby driving the blade collar  348 , blade moulding  352  and blade  340  along the drive shaft  316  at a force sufficiently high that the blade  340  is able to cut the clamped tissue. In this respect, the load exerted on the trigger  24  is transferred to the blade collar  348  and blade moulding  352  via the trigger moulding  344  and drive moulding  346 . As the pivot point B moves over centre into its protracted position, the speed at which the blade collar  348  and blade moulding  352  are driven along the drive shaft  316  accelerates, thus increasing the force of the blade  340 . As such, the force at which the blade  340  cuts into the tissue increases without the user exerting any additional force on the trigger  24 . 
     The shaft moulding  320  acts as a stopping point for the blade collar  348  and blade moulding  352 . Consequently, the pivot point B always remains above the two other pivot points A, C with respect to the drive shaft  316 . 
     During actuation of the trigger  24 , the force exerted on the trigger  24  is big enough to overcome the compression force of the extension spring  350  such that it extends along the same plane as the drive shaft  316  to allow for the axial movement of the blade collar  348  and blade moulding  352 . On release of the trigger  24 , the extension spring  350  re-compresses to retract the drive assembly to its original position. In this respect, the tension of the extension spring  350  is strong enough to retract the blade  340  through thick tissue without the need for user intervention. 
     2.4 Shaft Rotation 
     During use, the user may need to reach tissue from different angles without needing to move the entire instrument  1 . Therefore, the jaws  14  are advantageously rotatable relative to the handle  10  by means of the rotation wheel  28 . This is particularly beneficial where the jaws  14  are on a curved track, such as those shown in  FIGS. 16 a - d   . As described above, the rotation wheel  28  is coupled to the inner moulding  314  via interlocking members  1200 ,  1202  such that the inner moulding  314  rotates with the rotation wheel  28 . As the end of the drive shaft  316  is connected to the inner moulding  314 , the drive shaft  316  also rotates which subsequently rotates the jaws  14  at its opposite end. 
     To facilitate this rotational movement without interfering with the operation of the clamping mechanism, the collar moulding  310  is rotationally isolated within the handle collar  304  such that the collar moulding  310  also rotates with the drive shaft  316 . Likewise, so as to allow drive shaft  316  rotation without interfering with the operation of the cutting mechanism, the blade moulding  352  is rotationally isolated within the blade collar  348 . 
     In order to transfer the rotational movement to the outer shaft  12 , the shaft moulding  320  is rotationally isolated within its socket  322 . As described above, the shaft moulding  320  acts as a rotational guide so as to control the rotational movement relative to the shaft  316  along the entire length of the instrument  1 . Additionally, the active and return wires  1702 ,  1704  are arranged within the casing  20  so as to prevent damage to these wires  1702 ,  1704  as a result of the rotating components. As described above, the wires  1702 ,  1704  are wrapped around the shaft moulding  320  so as to allow for the degree of rotation of the drive shaft  316 . Consequently, the wires  1702 ,  1704  un-wind and re-wind around the shaft moulding  320  as it rotates. 
     2.5 Electrode Activation 
     Whilst the jaws  14  are in a closed position, the user may wish to coagulate and seal the tissue clamped between. To do this, the user initiates electrode activation using the switch button  26  on the top of the casing  20 , positioned conveniently so that the user can easily access the button  26  whilst using the device single handed. In doing this, an appropriate RF signal is delivered to the electrodes in the jaws  14  so as to coagulate and seal the tissue. The RF signal may be a pure or blended waveform, depending on the desired effect. 
     Having given an overview of the configuration and operation of the device as a whole, further detailed description of the configuration and operation of particular aspects thereof will now be given. 
     3. CLAMPING MECHANISM ASSEMBLY AND OPERATION 
     As described above, the proximal handle portion  10  of the electrosurgical instrument  1  includes a first mechanism for actuating one aspect of a distal end effector assembly  14  such that the end effector assembly  14  moves between a first and second condition. For example, the end effector assembly  14  may be a set of opposed jaws  14  arranged to open and close. The mechanism used to trigger movement of these jaws  14  is the so called clamping mechanism comprising a drive handle  22  and two barrel shaped mouldings  310 ,  314  with a spring  312  compressed therebetween, all of which are threaded along an elongate bar  316  that extends between the jaws  14  and the handle  10 , as shown in  FIGS. 4 and 5   a - b.    
     As shown in  FIG. 8 a   , the drive handle  22  comprises a collar  304  in which the collar moulding  310  sits. The collar  304  comprises an aperture  318  shaped like a keyhole or a figure of eight. As such, the aperture  318  is formed of two contiguous apertures  804 ,  806 , wherein the top aperture  804  has a larger diameter across it than the bottom aperture  806 . 
     The collar moulding  310  is a cylindrical or barrel shaped component having two flange portions  800 ,  802  spaced apart longitudinally. The diameter of the proximal flange  800  is larger than both the upper and the lower apertures  804 ,  806 . The diameter of the distal flange  802  is smaller than the upper aperture  804  and larger than the lower aperture  806 . 
     During assembly, the collar moulding  310  is first inserted through the upper aperture  804 , as shown by  FIGS. 8 b - c   . As the distal flange  802  is smaller than the upper aperture  804 , it easily passes through, whereas the proximal flange  800  may be large enough to prevent the collar moulding  310  from advancing the entire way through the upper aperture  804 . As shown by  FIG. 8 d   , the collar  304  is then pushed upwards to engage the lower aperture  806  with the collar moulding  310 . 
     Once assembled, the collar moulding  310  remains within the lower aperture  806  of the collar  304  and is positioned such that its two flanges  800 ,  802  lie either side of the collar  304 , as shown in  FIG. 8 e   . As lower aperture  806  has a smaller diameter than both flanges  800 ,  802 , the collar moulding  310  cannot be removed by simply pushing the collar moulding  310  through the lower aperture  806 . In contrast, the body of the collar moulding  310  between the two flanges  800 ,  802  has a slightly smaller diameter than the lower aperture  806 . Therefore, the collar moulding  310  sits within the lower aperture  808  loosely enough to allow rotational movement. 
     As can be seen from  FIG. 8 e   , the longitudinal distance between the two flanges  800 ,  802  is only slightly larger than the thickness of the collar  304  such that the collar  304  sits snugly between the flanges  800 ,  802 . This ensures that movement of the drive handle  22  is transferred directly to the collar moulding  310  and subsequently to the other components of the clamping mechanism. This is particularly important for ensuring that the jaws  14  are responsive to the movement of the drive handle  22  and that there is not a delayed response between actuation of the drive handle  22  and movement of the jaws  14 . 
     Once the collar moulding  310  and drive handle  22  have been assembled, the remaining components can be assembled. 
     The drive shaft  316  is an elongated bar with one or more protruding members  602  located at its proximal end, as shown in  FIG. 6 . The protruding members  602  are flexible tabs that fan out from the surface of the drive shaft  316 . That is to say, the protruding members  602  are deformable such that they may be pressed flush against the surface of the drive shaft  316 , but will return to their original positions upon release of any resistive force. This allows the drive shaft  316  to be easily threaded through all of the components of the clamping mechanism during assembly, as will now be described. 
     The collar moulding  310  has an internal cavity divided into two parts. The first part is a narrow channel or slot  607  for receiving the drive shaft  316 , wherein the distal end of the collar moulding  310  comprises an opening  311 , as shown in  FIG. 3 , which matches the cross-sectional “T” shape of the drive shaft  316 . The diameter of the channel  607  is only slightly wider than that of the drive shaft  316  so as to provide a snug fit for stability. On insertion of the drive shaft  316 , the protruding members  602  are pressed flat to allow the drive shaft to be pushed all the way through. 
     The second part is a chamber  608  large enough to house one end of the spring  312 . The chamber  608  can extend over any suitable proportion of the length of the collar moulding  310 . For example, the length of the chamber  608  may be around 25% of the length of the collar moulding  310 , or as much as 75% of the length of the collar moulding  310 . 
     The chamber  608  is substantially larger than the collar moulding channel  607  such that as the drive shaft  316  is pushed through the collar moulding  310 , the protruding members  602  span back out to their original configuration when they reach the chamber  608 . 
     The collar moulding  310  and drive handle  22  assembly is threaded down along the drive shaft  316  until the collar moulding  310  reaches a second set of protruding members  600 . These protruding members  600  have a span wider than the opening  311  on the collar moulding  310  so as to provide an obstruction that prevents the collar moulding  310  from advancing further along the drive shaft  316 . As such, the protruding members  600  must be sufficiently rigid that the collar moulding  310  cannot be pushed passed the protruding members  600  by exerting some force or pressing the protruding members  600  inwards. 
     The drive shaft  316  is then threaded through the centre of the spring  312 . Preferably, the spring  312  has a diameter that is only slightly larger than that of the drive shaft  312  to provide a close fit between the spring  312  and the drive shaft  316 . The spring  312  is then pushed along the drive shaft  316  until the end of the spring  312  fills the collar moulding chamber  608 . 
     The inner moulding  314  is a cylindrical or barrel shaped component having an internal cavity divided into two sections. The first section is a chamber  610  in which one end of the spring  312  is housed such that the spring  312  is partially encased by the collar moulding  310  and inner moulding  314 . The second section is a narrow channel or slot  603  for receiving the proximal end of the drive shaft  316 . The channel  603  is divided into two parts  604 ,  606 . The first part of the channel  604  is shaped so as to allow the drive shaft  316  to be passed through, the flexible tabs  602  being pressed flat in doing so. As such, the diameter of the first channel part  604  is only slightly wider than that of the drive shaft  316  so as to provide a snug fit. The snug fit of the drive shaft  316  within both the collar moulding channel  607  and inner moulding channel  603  means that the drive shaft  316  is held firmly in place. This adds to the stability of the drive shaft  316  within the casing  20 , which is particularly important for ensuring maximum control of the end effector  14 . 
     The second part of the channel  606  provides a shoulder  605  into which the protruding members  602  can extend. Consequently, as the drive shaft  316  passes through the channel  604  and into the second channel part  606 , the flattened protruding members  602  fan back out to their original decompressed positions. Once the protruding members  602  have engaged with the shoulder  605  of the second channel part  606 , the drive shaft  316  cannot be pulled back through the first channel part  604  and is thus retained in the inner moulding  314 . As such, the diameter of the second channel part  606  must be sufficiently wide that the protruding members  602  are able to expand beyond the diameter of the first channel part  604 . To achieve this snap-fit connection, a protruding member  602  is only required on one side of the drive shaft  316 . 
     This snap-fit connection is such that any axial movement of the inner moulding  314  will be transferred to the drive shaft  316 . Similarly, any rotational movement of the inner moulding  314 , for example, by means of the rotation wheel  28  formed around the inner moulding  314 , is also transferred to the drive shaft  316 . 
     Therefore, to complete the assembly of the clamping mechanism, the drive shaft  316  is simply threaded through the collar moulding  310 , the spring  312  and finally the inner moulding  314 , until the protruding members  602  snap into the second channel part  606 . 
     Once assembled along the drive shaft  316 , the collar moulding  310 , the spring  312  and the inner moulding  314  are arranged such that the spring  312  is partially encased by the collar moulding  310  and inner moulding  314 . By providing the collar moulding chamber  608  and inner moulding chamber  610  in which a substantial portion of the spring  312  can be housed, a longer spring  312  can be used without using up any additional space within the handle  10 . As such, the larger the collar moulding chamber  608  and inner moulding chamber  610 , the longer the spring  312 . Furthermore, the distance between the protruding members  600 ,  602  means that the ends of the spring  312  are compressed by the end walls  612 ,  614  of the collar moulding chamber  608  and inner moulding chamber  610  respectively so that the spring  312  experiences an initial pre-compression upon installation. This is important for ensuring that when the handle  22  is actuated so as to activate the clamping mechanism, the correct load is applied to the jaws  14 . 
     Additionally, the inner moulding  314  may be contained within a further barrel shaped moulding such as the rotation wheel  28  shown in  FIGS. 13 a - b   . Here, the inner moulding  314  rotates with the rotation wheel  28 , but is free to move axially within the internal cavity  1300  of the rotation wheel  28 , moving between a first position as shown in  FIG. 13 a    and a second position as shown in  FIG. 13 b   . Consequently, rotation of the wheel  28  rotates the inner moulding  314 , which in turn rotates the drive shaft  316  and the jaws  14 . 
     Once all of the components have been assembled, the drive handle  22  can be installed inside the casing  20 . In this respect, the drive handle  22  is connected to the casing at its hinge  306 . For example, the hinge  306  may be two outwardly extending pins that mate with corresponding hinge mouldings  308  integral to the clamshell mouldings  300 ,  302 . This provides an anchor point around which the drive handle  22  can rotate. 
     Therefore, the above arrangement provides a mechanism for actuating the end effector assembly  14  which can be assembled easily and securely without the need for any additional components. 
     In use, the user squeezes the drive handle  22  towards the proximal end  328  of the casing  20 , thereby rotating the drive handle  22  about its hinge  306 . In doing this, the collar  304  pushes against the proximal flange  800 , thus moving the collar moulding  310  longitudinally. This longitudinal movement drives the spring  312 , inner moulding  314  and the drive shaft  316  back towards the proximal end of the handle portion  10 , as shown by  FIG. 5 a   . As the drive shaft  316  is coupled to the jaws  14 , for example, by means of a pin  400  and cam slot  402  arrangement, the jaws  14  are moved from the open to the closed position. As such, the load from the drive handle  22  is transferred to the drive shaft  316  via the spring mechanism of the collar moulding  310 , spring  312  and inner moulding  314 . This spring mechanism is particularly important as it acts to limit the force loaded onto any tissue that is clamped between the jaws  14 . 
     As the drive handle  22  is squeezed, the collar moulding  310 , spring  312  and inner moulding  314  continue to move axially until either the inner moulding  314  reaches its furthest proximal position such that the jaws  14  are fully closed, as shown in  FIG. 5 a   , or the jaws  14  are unable to close any further due to tissue  500  clamped between, as shown by  FIG. 5 b   , in which case the drive handle  22  has not been fully actuated such that it is held in place by the latch  324 . As the user continues to squeeze the drive handle  22  and the collar  304  continues to drive against the flange  800 , the threshold compression force on the spring  312  is eventually reached such that the spring  312  begins to compress between the collar moulding  310  and inner moulding  314 , as can be seen in  FIG. 5   b.    
     As the spring  312  compresses further, the drive handle  22  can be driven all the way into the latched position without exerting any more force on the clamped tissue  500 . That is, the load of the drive handle  22  is no longer transferred to the drive shaft  316 , but is effectively absorbed by the spring  312 . As such, the spring  312  ensures that the correct amount of load is transferred onto the jaws  14 . Without the spring  312 , actuation of the drive handle  22  will continue to increase the load transferred to the drive shaft  316  and subsequently the jaws  14  and tissue  500 . This could result in mechanical damage to the tissue  500  as the user continues to squeeze the drive handle  22  in order to engage the latch  324 . 
     Therefore, the pre-compression of the spring  312  is important for ensuring that the spring  312  bears the load of the handle  22  as soon as the inner moulding  314  reaches its axial limit. Similarly, having a longer spring  312  allows for greater spring travel so that the spring  312  does not completely compress to its solid length during use. If the spring  312  was to reach its solid length, the spring  312  would no longer absorb the load exerted by the drive handle  22  and the force would once again be transferred to the jaws  14 . 
     To retain the jaws  14  in the closed position, the latch  324  on the drive handle  22  must be engaged with the latch moulding  326  inside the proximal end  328  of the casing  20 , as shown in  FIGS. 26 a   - f.    
     As shown in  FIG. 11 , the latch moulding  326  is a single integrally moulded component comprising a body portion  1108 , a spring element  1104  and a cam path  1106 . The proximal end  328  of the casing  20  has parallel walls  1100  that define a channel  1110  in which the body portion  1108  sits. The width of the channel  1110  is such that the body portion  1108  is retained within the channel  1110  but is still able to slide up and down the channel  1110  during use, as will be described below. In this respect, the latch moulding  326  is preferably made of a low friction material, for example, polytetrafluoroethylene (PTFE), to allow the body portion  1108  to easily slide within the channel  1110  without sticking. For further stability within the channel  1112 , a moulded pin  330  may be provided in the casing  20  which engages with a cam slot  331  provided on the body portion  1108 , as shown in  FIG. 46 . 
     The spring  1104  is located at the end of the body portion  1108  and is arranged to bias the body portion  1108  up the channel  1110  towards the distal end of the casing  20 . The spring  1104  can be of any suitable configuration, for example, the spring  1104  may be an arcuate or loop shape such as that shown in  FIG. 11 . The cam path  1106  is a moulded projection formed on the body portion  1108 . The cam path  1106  comprises a first cam surface  1112 , a notch  1114  and a second cam surface  1116  to form a “V” shaped moulding. 
     The latch  324  is formed of an arm  1118  extending from the bottom of the drive handle  22 . The arm  1118  has a pin  1120  located at its end which is suitable for traversing the cam path  1106 . 
     In use, the latch  324  enters the casing  20  via an opening  1102 . The pin  1120  engages the latch moulding  326  such that the body portion  1108  is pulled down channel  1110  and the spring  1104  thereby being extended. As shown in  FIGS. 26 b - c   , the pin  1120  runs up the side of the first cam surface  1112  until it reaches the top of the “V”. At this point, the drive handle  22  cannot be compressed any further, and the spring  1104  pulls the body portion  1108  back up the channel  1110  such that the pin  1110  slots into the notch  1114 , thus retaining the drive handle  22  in the compressed position and the jaws  14  in the closed position, as shown in  FIG. 26   d.    
     Therefore, to latch the drive handle  22 , all the user has to do is to actuate the drive handle into the fully compressed position, wait for the pin  1110  to click into the notch  114  and then release the drive handle  22 . In this latched position, the user&#39;s hand is free for operating other functions of the instrument  1 , such as operating the cutting mechanism using the trigger  24 , rotating the jaws  14  using the rotation wheel  28  or operating the electrodes in the jaws  14  using the switch  26 . 
     To release the latch  324  from the casing  20  and open the jaws  14 , the user must squeeze drive handle  22  towards the casing  20  once more. This releases the pin  1120  from the notch  1114 , as shown by  FIG. 26 e   . As the pin  1120  exits the notch  1114 , the force of the extended spring  1104  pulls the body portion  1108  back up the channel  1110 , such that the pin  1120  runs down the side of the second cam surface  1116 , as shown by  FIGS. 26 e - f   . As the pin  1120  reaches the bottom of the second cam surface  1116 , it pushes the body portion  1108  further up the channel  1110  so that the pin  1120  can pass back out of the opening  1102 . The body portion  1108  will then return back to its original position within the channel  1110 . 
     Therefore, to release the drive handle  22 , all the user has to do is squeeze the drive handle  22  towards the proximal end of the casing  20  and then allow the drive handle  22  to return to its original open position. 
     Additionally, the latch moulding  324  may include an override button  4600  integrally formed on the body portion  1108  as shown in  FIG. 46 , wherein the override button  4600  is engaged so as to alter the position of the cam path  1106  such that the pin  1120  automatically disengages with the notch  1114  and releases the drive handle  22 . Consequently, if the latch mechanism was to fail for any reason, the user would be able to release the drive handle  22  to open the jaws  14 . 
     The body portion  1108  may also be provided with an integrated lock-out bar  4602  to allow the user to disengage the latch mechanism altogether, wherein the lock-out bar  4602  is moveable between a first and second position to manually slide the body portion  1108  within the channel  1110 . When the lock-out bar  4602  is in the first position, the body portion  1108  is in its normal position such that the latch mechanism operates as described above. The user may then move the lock-out bar  4602  to its second position, whereby the body portion  1108  is moved up the channel  1110  such that the pin  1120  can only traverse along the second cam surface  1116  and is thus prevented from engaging with the notch  1114 . 
     It will be appreciated that such a latch mechanism may also be suitable for many end effector assemblies. For example, such a latch may be provided on the trigger  24  for the cutting mechanism so as to retain the cutting blade  340  in the actuated position. 
     On release of the latch  324 , the drive handle  22  can be moved back to its original position. In doing this, the collar  304  releases the load exerted on the proximal flange  800  and pushes against the distal flange  802 , thus pulling the collar moulding  310  back to its original axial position. Consequently, the spring  312 , the inner moulding  314  and the drive shaft  316  are also pulled back axially, which in turn moves the jaws  14  back to the open configuration. 
     4. CUTTING MECHANISM ASSEMBLY AND OPERATION 
     Various further features and aspects relating to the structure and operation of the cutting mechanism will now be described. As described above, the proximal handle portion  10  of the electrosurgical instrument  1  includes a second mechanism for actuating a further aspect of a distal end effector assembly  14 . For example, the end effector assembly  14  may be a set of opposed jaws  14  and a blade  340 , wherein the distal end of the blade  340  is arranged to slide between the jaws  14  in order to cut tissue clamped between said jaws  14 . The mechanism used to trigger movement of the blade  340 , which is disposed within a central track  341  of the drive shaft  316 , is the so called cutting mechanism. The cutting mechanism comprises a drive arm  2000 , a blade drive moulding  346 , a blade collar moulding  348 , a blade moulding  352  and an extension spring  350 , all of which are coupled together to form a three pivot slider-crank mechanism, as shown in  FIGS. 20 a - b    and  FIGS. 31 and 32 . 
     The drive arm  2000  is formed of a trigger  24  and the trigger moulding  344 , wherein the trigger  24  is a finger gripping member for actuating the cutting mechanism and the trigger moulding  344  is a collar having a “C” shaped side profile and an aperture  364  through which the drive shaft  316  is threaded. The point which the trigger  24  and trigger moulding  344  meet provides a pivot point A about which the drive arm  2000  is rotated. This first pivot point A is anchored to the casing  20 , for example, by means of outward facing pins  358  that connect with corresponding mouldings  356  integral to the clamshell mouldings  300 ,  302 . 
     The distal end of the drive arm  2000 , that is, the end of the trigger moulding  344  is pivotally connected to the blade drive moulding  346  to form a second pivot point B. The blade drive moulding  346  is an “H” shaped frame having two parallel arms and a strut therebetween. As such, the parallel arms of the blade drive moulding  346  are pivotally connected at one end to the trigger moulding  344 , for example, by means of outward facing pins  366  and mating connectors  368 . At the opposite end, the parallel arms of the blade drive moulding  346  are also pivotally connected to the blade collar moulding  348  to form a third pivot point C, for example, by means of outward facing pins  372  and mating connectors  370 . 
     As shown in  FIGS. 21 to 23 , the blade collar moulding  348  is a cylindrical or barrel shaped component having a chamber  2104  in which the blade moulding  352  sits, wherein the blade moulding  352  is a cylindrical or barrel shaped component having a body  362  that fits inside the chamber  2104  of the blade collar moulding  348 . The blade moulding  352  further comprises a flange  360  having a diameter larger than that of the chamber  2104  such that the flange  360  abuts the distal lip  2200  of the blade collar moulding  348 , as shown in  FIG. 22 . Consequently, the flange  360  ensures that the correct end of the blade moulding  352  is interested to the blade collar moulding  348 . 
     The body  362  is provided with a small groove  2202  around its circumference so as to provide a shoulder with which the distal lip  2200  interlocks such that the blade moulding  352  and blade collar moulding  348  are coupled via a snap-fit connection. The distal lip  2200  mates with the groove  2202  so as to retain the blade moulding  352  within the blade collar moulding  348  whilst allowing the blade moulding  352  to freely rotate within the chamber  2104 . As such, the blade moulding  352  and blade collar moulding  348  are free to rotate concentrically. 
     Once the blade collar moulding  348  and blade moulding  352  have been assembled together, the blade  340  can be connected as illustrated by  FIGS. 24 a - c   . In this respect, the blade moulding  352  comprises a “T” shaped aperture  2300  which extends throughout its length, shaped as such so as to receive both the blade  340  and the drive shaft  316 , as shown by  FIG. 23 . 
     The proximal end of the blade  340  comprises a tab feature  2102  which extends beyond the general profile of rest of the blade  340 , that is, it does not lie in the same axial plane. As shown in  FIG. 24 c   , the body  362  further comprises a recess  2100  in which the tab  2100  is retained. To enable assembly, the proximal end of the blade  340  is cut away at a first point opposite the tab  2102  in order to provide a bevelled edge  2400 , and is cut away a second point adjacent to the tab  2102  to provide a recessed portion  2402 . As such, the proximal end of the blade  340  has an “L” shaped profile. 
     To assemble the blade  340  within the blade moulding  352  and blade collar moulding  348  assembly, the blade  340  is presented to the “T” shaped aperture  2300  at an angle to the longitudinal axis of the instrument  1  so that the tab  2102  and bevelled edge  2400  can be inserted to the internal cavity  2404  of the blade moulding  352 , as shown in  FIGS. 24 a - b   . The blade  340  is then pulled down in line with the longitudinal axis so as to push the tab  2102  into the recess  2100 , as shown by  FIG. 24 c   . As such, the tab  2102  is effectively hooked on to the shoulder  2406  of the blade moulding  352 , thereby retaining the proximal end of the blade  340  within the internal cavity  2404 . 
     The drive shaft  316  may then be threaded through the “T” shaped aperture  2300 , the blade  340  being received in the central track  342 , as illustrated by  FIGS. 22 and 23 . As such, longitudinal movement of the blade collar moulding  348  and blade moulding  352  assembly along the drive shaft  316  drives the blade  340  along the track  342 . 
     To complete the blade trigger assembly, an extension spring  350  extends between the blade collar moulding  348  and drive arm  2000 , for example, by means of hooks  2002 ,  2004 . 
     In use, the user pulls the trigger  24  back towards the casing  20 , as shown by  FIGS. 25 b - c   , so as to pivot the drive arm  2000  around the first pivot point A. In doing this, the second pivot point B is pushed forwards in the distal direction which cause the drive moulding  346  to push the blade collar moulding  348  and blade moulding  352  assembly along the drive shaft. The load exerted on the trigger  24  is therefore transferred to the blade collar moulding  348  and blade moulding  352  via the trigger moulding  344  and drive moulding  346 . As the proximal end of the blade  340  is retained inside the blade moulding  352  as described above, the blade  340  slides along the central track  342  with the blade collar moulding  348  and blade moulding  352  assembly. As the blade moulding  352  is rotationally isolated within blade collar moulding  348 , the draft shaft  316  can also be rotated without interfering with the operation of the cutting mechanism. 
     The functionality of the mechanism is optimised so as to provide good mechanical advantage at the beginning of the blade  340  travel, when the user&#39;s finger is extended and not as strong, and also at the end of the blade  340  travel, where there are more forces working against the blade  340  travel such as the force of the spring  350 , friction within the track  342  and the force required to penetrate thick tissue. As can be seen from  FIG. 27 , a constant force is applied to the trigger  24  by the user. The mechanism converts this trigger force into a high initial blade  340  force, which decreases as the blade  340  is driven along the track  342 , and increases again as the blade  340  reaches the jaws  14 . Therefore, as the pivot point B moves from its retracted position to its protracted position as shown by  FIGS. 28 a - b   , such that β&gt;90°, the speed at which the blade collar  348  and blade moulding  352  are driven along the drive shaft  316  accelerates, thus increasing the force of the blade  340 . As such, the mechanism is able to drive the blade  340  with enough force to effectively cut the tissue clamped between the jaws  14  without the user needing to exert any additional force on the trigger  24 . 
     Additionally, the cutting mechanism may be required to push the blade  340  around a curved set of jaws  14 , adding to the frictional forces working against the blade  340  travel. The frictional force is a product of the frictional coefficient of the blade  340  within the track  342 , and the force due to bending that the blade  340  exerts on the walls of the track  342 . 
     To reduce this frictional force, the lateral flexibility of the blade&#39;s distal end may be graduated. Such graduated flexibility may be achieved, for example, by preferentially weakening the blade  340  such that it is able to bend along the track  342  whilst remaining rigid in the direction of the cutting force. Preferential weakening may be provided, for example, by the provision of one or more apertures or slots  354  in the distal end, as shown in  FIG. 47 a   . Such apertures may be of constant or varying size of shape, depending on the degree of flexibility required. For example, in  FIG. 47 b   , two contiguous apertures  4702 ,  4704  having different sizes are provided, wherein the larger aperture  4702  provides a greater degree of flexibility than the smaller aperture  4704 . As another example, in  FIG. 47 c   , three apertures  4706 ,  4708 ,  4710  of varying size and shape are provided, the largest aperture  4706  being the most distal so as to provide more flexibility in this region. Preferential weakening may also be achieved by graduating the thickness of the blade  340  such that the distal end of the blade  340  is bevelled  4700 , as shown in  FIG. 47   d.    
     Alternatively, patterned laser cuts  4702  or chemical etches in the distal end may be used to control the bending stiffness over a length of the blade  340 , as shown in  FIG. 47 e   , whereby the spacing between such cuts may be constant or gradually increase from the distal to proximal end. 
     Preferably, the blade  340  is divided into at least three regions of varying flexibility. For example, a distal region, an intermediate region and a proximal region, wherein the distal region has a greater lateral flexibility than the intermediate region, and the intermediate region has greater flexibility than the proximal region. For example, the distal region may be formed of a bevelled end  4700  to give the greatest degree of flexibility, the intermediate region formed of an aperture  354  to provide a relatively lower amount of flexibility, and the proximal region formed of a solid bar to give even less flexibility, as illustrated by  FIG. 47 a   . In a further example shown by  FIG. 47 b   , the distal region includes a large aperture  4702  to give the greatest degree of flexibility, the intermediate region includes a smaller aperture  4704  to provide decreased flexibility and the proximal region is once again a solid bar having the lowest degree of flexibility. As such, the distal region, intermediate region and proximal region may be achieved using any suitable combination of the preferential weakening described above. 
     A further way of reducing the frictional force due to the curved track is to add a low friction coating to at least one side of the distal end of the blade  340 . For example, the blade may be coated, for example using physical vapour deposition (PVD) or chemical vapour deposition (CVD) processes, with a low friction or non-stick material, such as a PTFE composite or other low friction polymer composite. 
     5. DRAINAGE APERTURES 
     Various further features and aspects relating to the structure of the drive shaft  316  will now be described. As described above, the drive shaft  316  is an elongate bar having a “T” shaped cross-section, as illustrated by  FIG. 10 a   . The drive shaft  316  comprises a slot or track  342  along its length suitable for housing a further elongate member, such as the cutting blade  340  used in the cutting mechanism described above. In use, the cutting blade  340  is caused to slide along the length of the drive shaft  316  so as to drive the distal end of the cutting blade  340  between the jaws  14  in order to cut tissue clamped therebetween. 
     Over time, blood and tissue can start to build up within the distal end of the instrument  1 , particularly down the length of the outer shaft  12  and drive shaft  316 . This build-up of blood and tissue can cause the blade  340  to stick within the drive shaft  316 , thus reducing the functionality of the instrument  1 , in particular, that of the cutting mechanism. To combat this, portions of the distal end of the drive shaft  318  are cut out in order to reduce the area of contact between the drive shaft  316  and the blade  340  and thereby reduce the surface area to which blood and tissue can stick. 
     These cut out portions may be apertures such as the elongate windows  1000 ,  1002  shown in  FIGS. 10 b - c   , such that the distal end of the drive shaft  316  comprises a base support with bifurcated side walls. The cut out portions may also extend to the base of the drive shaft  316  such that the distal end comprises bifurcated side walls and an open bottom. In order to maximise the amount of drainage afforded by these apertures  1000 ,  1002 , the apertures are preferably more than 50% of the depth of the drive shaft  316 . 
     As such, these apertures  1000 ,  1002  provide drainage passages between the central track  342 , and the exterior of the drive shaft  316 . 
     6. ROTATION WHEEL AND SWITCH 
     Various further features and aspects relating to the operation of the thumbwheel (also referred to herein as a rotation wheel)  28  will now be described. The thumbwheel  28  is provided to allow the user to rotate the outer shaft  12  on which is mounted the end effector assembly  14 . However, in order to reduce space, and hence produce a more compact instrument, the inner volume  1300  of the thumbwheel  28  is also utilised to provide movement space for the inner moulding  314 , that forms part of the clamping mechanism described previously. With such an arrangement, a more compact mechanism can be obtained. 
     In more detail, the rotation wheel  28  (also referred to herein as a thumbwheel), comprises a plastic cog-like wheel, having a plurality of scallop portions  336  located around its external diameter. As such, the thumbwheel  28  takes the appearance of a cog, having the scalloped cut out portions arranged to receive a user&#39;s thumb, in an ergonomic fashion. In this respect, as shown in more detail in  FIGS. 13 a , 13 b   , and in particular in  FIG. 14 a   , the scallop portions are angled to the plane of rotation of the thumbwheel when in use, such that generally the thumbwheel or rotation wheel  28  is slightly frusto-conical in shape, being wider at a distal end from the user than it is at the proximal end towards the user. The scallop portions  336  each extend from the distal edge of the thumbwheel to the proximal edge, and are curved or saddle like in shape to receive a user&#39;s thumb, when in use. As shown in detail in  FIG. 14 a   , the angling of the scallop portions  336  to give the frusto-conical shape of the rotation wheel  28  generally matches the angle of the body of the instrument. In  FIG. 14 a    the dot-dash lines illustrate the angling of the scalloping  336  around the edge of the wheel  28 , which can be seen to be tangential to the angle of the outer walls of the instrument at the point around the wheel, and in particular of the portion of the outer walls of the instrument immediately in front of the wheel, in a distal direction. Such an arrangement where the angled scalloping of the outer rim of the rotation wheel matches the angling of the wall of the instrument around the wheel provides a comfortable and ergonomic design, which is easy to operate by the surgeon. 
     In terms of the number of scallop portions  336  around the outer diameter of the wheel  28 , as shown in one embodiment eight scallop portions are evenly distributed around the outer diameter of the wheel. In other embodiments, fewer, or larger number of scallop portions may be used, for example as few as six or seven, or as many as nine or ten. If a larger wheel  28  was to be employed, then a greater number of scallop portions  336  may be included, and conversely if a smaller wheel is employed then the number of portions may be fewer in number. In this respect, the actual size of each scallop portion  336  should typically remain the same, as the scallop portions have been ergonomically chosen so as to be able to receive a user&#39;s thumb comfortably. 
     Regarding the positioning of the thumbwheel  28  within the instrument, as shown in  FIG. 2 , the rotation or thumbwheel  28  is positioned vertically oriented beneath the switch  26 , and spaced from the thumbwheel in a direction orthogonal to a longitudinal axis defined for example by the longitudinal direction of drive shaft  316 . In particular, the hand-switch  26  lies directly on an axis orthogonal to such a longitudinal axis and which also passes through the thumbwheel  28 . Moreover, as shown in  FIGS. 14 a  and 14 b   , the switch  26  is relatively large in size, and extends from one side of the upper surface of the instrument to the other, above the thumbwheel. The switch  26  is curved in nature, generally to match the curved upper surface of the outer wall of the instrument, and has bumps, grooves, or other raised protrusions on the outer surface thereof, to aid with the user being able to grip the switch in order to be able to press it, with his or her thumb. The surface area of the switch  26  is relatively large, being in excess of 3 cm 2  or even 5 cm 2 . This provides a large surface area, to allow for ergonomic activation thereof by the user. The vertical orientation of the switch  26  directly above the thumbwheel  28  also allows for ergonomic activation. As explained elsewhere, the switch  26  in use operates to cause an RF coagulation signal to be fed to the end effector, for coagulation of any tissue located therein. 
     Concerning the ergonomics of the switch and thumbwheel,  FIGS. 35 a  and 35 b    are two respective photographs of different users with different size hands. As demonstrated, the switch  26 , being of a relatively large surface area is easy to operate by users with different hand sizes, at the same time as operating clamping handle  22  (and blade trigger  24 , if desired). 
     Returning to  FIG. 12 , as described previously the thumbwheel  28  has an internal cavity  1300  within which is received in use the inner moulding  314 . As described previously, the inner moulding  314  comprises an inner moulding chamber  610  and has a T-shaped cut through portion  1208  therein, into which the drive shaft  316  is received therethrough, and fastened therein, as described previously. The inner moulding  314  snap fits into the interior cavity of the wheel  28 , and flanges  1206 , as shown in  FIG. 12  and  FIGS. 29 a  and 29 b    are provided around the outer edge of the cylindrical interior cavity  1300  of the thumbwheel  28 , to hold the inner moulding  314  in place within the cavity, once it has been inserted therein. The interior cavity  1300  of the thumbwheel  28  is also provided with interlocking members  1200 , which interact with corresponding interlocking members  1202  provided around the outer circumference of the inner cylindrical moulding  314 . The respective interlocking members  1200  and  1202  comprise respective raised step portions that fit together side by side circumferentially around the inner surface of the cavity  1300  when the thumbwheel  28  and the inner cylindrical moulding  314  are in the correct rotational alignment with respect to each other. The respective interlocking members  1200  and  1202  are provided so that in use the inner cylindrical moulding  314  may slide from side to side within the interior cavity of the wheel  28 , but may not rotate within the wheel  28 . Instead, the interacting interlocking members  1202  and  1200  act so that the inner moulding  314  rotates with the rotation wheel  28 , as it is rotated. In this way, any rotational torque applied by the user  28  to the rotation wheel  28  is transferred to the inner moulding  314 , and then to the drive shaft  316 , in order to rotate the driveshaft, carrying the end effector.  FIGS. 29 a  and 29 b    show the inner moulding  314  inserted into the interior cavity of the thumbwheel  28 , and illustrate how the inner moulding  314  may slide axially within the inner cavity  1300  of the wheel  28 . 
       FIGS. 13 a  and 13 b    also show in more detail how the inner moulding  314  is able to move within the inner cavity  1300  of the wheel  28 . As described above, the drive shaft  316  passes through the T-shaped aperture  1208  in the inner moulding  314 , and is secured therein via snap fit protruding catch or latch members  602 , provided on the end of the drive shaft. That is, latch or catch members  602  are in the form of sprung metal tabs that are able to pass through the T-shaped aperture  1208  within the inner moulding  314 , and are then received in an inner moulding second channel part  606  forming a cavity which allows the spring tabs to spring apart, thus securing the drive shaft within the inner moulding. The inner moulding  314  is then pushed into the inner cavity of the thumbwheel  1208 , and is held in place by the snap fit tabs  1206 , as described above. The inner moulding may move axially within the inner cavity  1300  so as to abut against the inner surface of the distal wall of the wheel  28 , as shown in  FIG. 13 a   , or, at its opposite end of travel, to abut against the tabs  1206  at the distal edge of the wheel. Thus, the inner moulding  314  is provided with a degree of axial sliding movement within the cavity of the thumbwheel  28 , which is required as part of the mechanism to control the force applied by the user to material contained within the jaws, as described above. 
     The snap fit nature of the inner moulding  314  into the inner cavity of the thumbwheel  28  hugely improves the assembly of the device, and makes the device significantly easier, and hence cheaper to assemble. Likewise, in order to position the thumbwheel within the casing, as shown in  FIG. 33 , the outer distal wall  1310  of the thumbwheel  28  is concentric with and aligned to an internal supporting wall  1320 , provided as a projection from the casing of the device. This also allows for easy and accurate assembly and positioning of the wheel  28  within the casing. 
     7. ROTATIONAL CONTROL OF DRIVE SHAFT 
     As explained above, shaft  12  having end effector  14  thereon is rotatable to allow the end effector to be moved into desired rotational positions for the cutting and coagulation of tissue. However, in order that the wiring connections to the end effector are not placed under excess strain from the shaft being rotated in one direction too far such that the wiring becomes wound up, twisted, or placed under excessive strain, a mechanism to control the rotation of the shaft  12  is required, in particular to limit the amount of rotation, and thereby prevent excess strain on the wiring. In addition, providing positive control of the rotation of the shaft  12  improves the ergonomic experience of the instrument when in use, and enhances the user perception of quality. 
     In order to provide rotational control of the shaft in one embodiment an arrangement as shown in  FIGS. 15 a  and 15 b   , and  FIGS. 16 a  to 16 d    is employed. With reference to  FIG. 15 , here thumbwheel  28  having scallop portions  36  is provided on its proximal surface (i.e. rearward face, facing the user) with a ring  1506  that projects slightly from the proximal surface arranged concentric with the axis of the wheel  28 . The ring  1506  rests in use on guide stop features  1502  and  1504 , being projections from the inner surface of the outer casing, that project up to make contact with the outer circumference of the ring  1506 . Stop feature  1502  is smaller than stop feature  1504  due to their positioning on the casing with respect to the axis of the ring, but both stop features  1502  and  1504  have angled upper guide faces  1510  and  1512  (see  FIG. 15 a   ) respectively, that contact with the outer circumferential surface of ring  1506  forming part of the thumbwheel, and help to support and guide the thumbwheel in its rotation. 
     In addition, to providing a guiding function, stop features  1502  and  1504  also act as stop members to prevent the rotation of the thumbwheel past the angular position of the stop features. In this respect, the ring  1506  is provided with a rectangular stop projection  1500  radially extending therefrom. As the thumbwheel  28  is rotated the stop projection  1500  abuts against respective stop faces  1514  and  1516  of the stop features  1502  and  1504 . The stop faces are angled to be parallel to the rectangular stop projection  1500  when the stop position is angularly positioned so as to be abutted thereagainst. 
     The stop features  1502  and  1504  arranged as described above are positioned, and are of such a length so as to provide a known amount of rotation of the wheel  28  from stop feature  1500  to stop feature  1502 . In the presently described arrangement shown in  FIG. 15 a    and  FIG. 15 b    the stop features  1502  and  1504  are positioned on the casing with a spacing therebetween so as to allow the thumbwheel to rotate 270° from stop to stop. The amount of rotation can be varied slightly by increasing or decreasing the distance between the stop features, with the stop features being adapted in length and angle of the guide and stop faces accordingly so as to still meet the wheel and the stop features substantially normally, respectively. For example, the stop features may be positioned and shaped to provide angular rotation of the wheel of between 250° and 300°. 
     The above describes the rotational control that is applied to the thumbwheel (and then to the shaft via the thumbwheel).  FIGS. 16 a  to 16 d    show a further rotational control mechanism that is applied to the shaft at the opposite end of the shaft, using shaft moulding  320 . Here, shaft moulding  320  is provided with rectangular stop member  1600  projecting therefrom. The inner surface of the outer casing is further provided with respective moulded stop features  1602 , and  1604 , shown in the form of stepped feature providing respective stop surfaces that present to the rectangular stop member  1600  respective parallel stop surfaces at respective angular positions of the shaft moulding  320 . In the example shown, the moulded stop features are positioned on the casing and present respective stop surfaces to the stop member  1600  to permit a rotation of 270° of the shaft  12  carrying the end effector from stop to stop. In other embodiments, the moulded stop features  1602  and  1604  may be positioned to present stop surfaces to the stop member  1600  at other rotational angular positions of the moulding  320 , to provide a greater or lesser amount of rotation, for example from 180° to 360°, or more preferably from 250° to 300°, or most preferably 270°. 
     The respective rotation control mechanisms provided in the thumbwheel  28  and the shaft moulding  320  may be provided independently from each other i.e. they need not both be provided in any particular embodiment, but only one or the other may be provided to provide for rotational control of the shaft. However, it is advantageous in terms of operation and the perception of quality of the device for both the rotation control mechanisms to be provided in the same device, and to be aligned such that they provide for stopping of rotation at the same respective points, in either rotational direction. Such an arrangement means that the rotation of the shaft is stopped independently at both ends of the handle portion  10 , and it becomes very difficult for a user to force further undesirable rotation of the shaft past the allowed limits represented by the stops. 
     An alternative rotational control mechanism is shown in  FIGS. 36 and 37 .  FIG. 36  illustrates again the shaft moulding  320 , but here the moulding is provided with ring  3220  on which is mounted a primary rectangular stop member  3202  projecting radially therefrom, and secondary position marker members  3204 ,  3206 , and  3208 , positioned around the ring substantially equiangularly, preferably at orthogonal positions. The secondary position marker members  3204 ,  3206 , and  3208  constitute small raised projections that are not large enough to about against stop faces  3212  and  3214 . 
     Stop faces  3212  and  3214  are provided as integral mouldings with the outer casing, and are positioned here so as to permit the shaft moulding  320  to be rotated by 180°. In this respect, the stop member  320  abuts against the stop faces  3212  and  3214  at the ends of the rotation range, to prevent further rotation of the shaft moulding. Hence, as shown in  FIGS. 36   a ) to  c ), the shaft moulding  320  carrying the shaft  12  may rotate through 180°, to allow the end effector to be positioned rotationally as desired. 
     Also provided is a sprung projection  3216 , comprising a plastic projection of substantially triangular cross-section that projects upwardly from the moulding forming stop face  3214 , such that its tip contacts the outer circumferential surface of ring  3220 . The secondary position markers in the form of the small raised projections press against the tip of the sprung projection as the shaft moulding  320  rotates, causing the tip of the sprung projection to move out of its rest position to allow the respective projection to move past the tip. The effect of this operation is to provide some user feedback in that the user must apply more force to rotate the mechanism past the rotational positions where the raised projections contact the tip of the sprung projection, because sufficient force must be provided to cause the tip of the sprung projection to deflect, to allow the projection to move past the tip. The result of this is that the user feels an increase of force required to rotate the shaft past the rotational positions of the raised projections, and hence intuitively the user is provided with an indication of the rotational position of the shaft, and hence the end effector. Such a haptic feedback mechanism thus allows for user friendly and easy operation of the device. 
       FIG. 37  illustrates the corresponding thumbwheel  28  for the mechanism of  FIG. 36 . Here, the thumbwheel is also provided with respective small stops  3222 , arranged orthogonally at 90° intervals around the thumbwheel. A similar mechanism to the sprung projection  3216  may be provided, projecting from the casing, to provide similar haptic feedback as in the case of the shaft moulding  320 . In such an arrangement, haptic feedback as to the rotational position of the shaft is provided from both ends of the handle, and hence the user perception of the device is improved. 
     8. WIRING 
     Various further features and aspects relating to the wiring within the handle  2  will now be described. As described above, the switch button  26  is provided for activating and de-activating the RF signal for operating the electrodes in the end effector assembly  14  via some appropriate circuitry, for example, two ingress-protected switches on a small printed circuit board (PCB)  338 . As shown in  FIG. 17 , the PCB  338  is connected to a connection cord  1700  for receiving the RF output from a generator (not shown) and electrical wiring  1702 ,  1704  for supplying the RF current to the electrodes in the jaws  14 , for example, one wire for the active electrode and one for the return electrode. 
     In assembly, the wiring  1702 ,  1704  from the electrodes is fed down the outer shaft  12  alongside the drive shaft  316  and up to the shaft moulding  320 , as illustrated by  FIG. 17 . As shown in  FIG. 9 b   , the shaft moulding  320  is a cylindrical or barrel shaped component having an opening  912  at the distal end to receive the outer shaft  12 . The outer shaft  12  is attached to the shaft moulding  320 , for example, by snap-fit tabs  900  that cooperate with corresponding notches  902  within the shaft moulding  320 . Consequently, if the shaft moulding  320  rotates, the outer shaft  12  rotates with it. The shaft moulding  320  further comprises a further aperture  914  at the proximal end, the aperture  914  having a “T” shape so as to receive the drive shaft  316 , wherein the drive shaft  316  extends through the internal cavity  1802  of the shaft moulding  320  and down the length of the outer shaft  12 . As such, the drive shaft  316  is able to slide within the shaft moulding  320  and outer shaft  12 , but any rotational movement of the drive shaft  316  is transferred to the shaft moulding  320  and subsequently the outer shaft  12 . 
     As shown in  FIG. 18 a   , the electrode wires  1702 ,  1704  are fed out of the internal cavity  1802  through an opening  1800  in the wall of the shaft moulding  320  before being wrapped over and around the body  1804  of the shaft moulding  320 . Wrapping the wires  1702 ,  1704  around the shaft moulding  320  in this way keeps the wires  1702 ,  1704  in a compact arrangement so as prevent the wires  1702 ,  1704  from getting in the way when assembling the rest of the instrument  1 . Furthermore, wrapping the wires  1702 ,  1704  around the shaft moulding  320  means that as the shaft moulding  320  rotates with the drive shaft  316 , the wires  1702 ,  1704  un-wind and re-wind with said rotation without pulling on the wires  1702 ,  1704  and causing them to short. Specifically, wrapping the wires  1702 ,  1704  in this particular way allows for up to 270° of rotation, as described with reference to  FIGS. 15 a - b  and 16 a   - d.    
     The electrical wiring  1702 ,  1704  is then passed along the top of the casing  20 . In this respect, one of the clamshell mouldings  300  is provided with two pockets  1900 ,  1902  located in series for housing the wire contacts  1904 ,  1906  that connect the active and return wires  1702 ,  1704  to the wiring  1908 ,  1910  of the ingress-protected switches  338 . Consequently, all of the electrical wires  1702 ,  1704 ,  1908 ,  1910  are routed in and around the pockets  1900 ,  1902  so that only one contact  1904 ,  1906  is housed in each pocket  1900 ,  1902 . The routing of the wires may be aided by guide portions  1912 ,  1914 ,  1916  which direct one set of the wires  1702 ,  1910  around the outside of the pockets  1900 ,  1902 . Within each pocket the respective active wire  1702  is longitudinally aligned with wire  1908 , and return wire  1704  is longitudinally aligned with wire  1910 . 
     As a result, the two wire contacts  1904 ,  1906  are longitudinally separated such that only one contact can pass through each pocket  1900 ,  1902 , thereby providing a physical barrier between each contact  1904 ,  1906  and any wiring. This prevents the risk of insulation damage to any of the wiring caused by the contacts  1904 ,  1906  themselves. 
     The wires  1702 ,  1704 ,  1908 ,  1708  all enter their respective pockets  1900 ,  1902  through small openings  1918 ,  1920 ,  1922 ,  1924  in the walls of the pockets. Preferably, the dimensions of the apertures  1918 ,  1920 ,  1922 ,  1924  are such that only one electrical wire can fit through. The opposite clamshell moulding  302  also comprise corresponding rib features (not shown) to retain the contacts  1904 ,  1906  within the pockets  1900 ,  1902 , so as to form a substantially sealed housing. This is important for minimising the permeability of the pockets  1900 ,  19200  in order to protect the contacts  1904 ,  1906  from any fluid that may make its way down the outer shaft  12  and into the casing  20 , thus causing the contacts  1904 ,  1906  to short circuit. 
     9. END-EFFECTOR ASSEMBLIES 
     Example end-effector assemblies that may be used with the apparatus will now be described. The examples to be described are given for completeness only, and it should be understood that other designs of end-effector may also be used with the instrument, provided they are able to be driven by drive shaft  316 . That is, embodiments of the invention are not limited to the specific end-effectors described herein, and other designs of end-effector may also be used. 
       FIGS. 38 to 44  show example instruments where the electrically conductive stop members are disposed on one or both of the sealing electrodes. Referring to  FIG. 38 , an end effector shown generally at  3801  comprises an upper jaw  3802  pivotably connected to a lower jaw  3803  about a pivot  3804 . Flanges  3805  are present at the proximal end of upper jaw  3802 , while flanges  3806  are present at the proximal end of lower jaw  3803 . The flanges  3805  &amp;  3806  each have slots  3807  through which a drive pin  8  extends, such that proximal and distal movement of the drive pin  3808  (by means of a drive mechanism (not shown) causes the jaws  3802  &amp;  3803  to pivot between open and closed positions. 
     A metallic shim  3809  is present on the inward face of upper jaw  3802 , while a metallic shim  3810  is present on the inward face of lower jaw  3803 . When the jaws  3802  &amp;  3803  pivot into their closed position, the metallic shims  3809  &amp;  3810  come into close proximity one with the other, in order to grasp tissue (not shown) therebetween. 
     The upper shim  3809  has a generally planar surface, with the exception of a longitudinal groove (not visible in  FIG. 38 ) running the length thereof. The lower shim  3810  has a corresponding groove  3811 , the grooves in the shims  3809  &amp;  3810  accommodating the longitudinal movement of a cutting blade (not shown). The lower shim  3810  is also provided with a plurality of metallic stop members  3812 , disposed along the length of the shim and situated on either side of the groove  3811 . The stop members  3812  will now be described in more detail, with reference to  FIGS. 39 &amp; 40 . 
     Each metallic stop member  3812  is constituted by the upper dome of a stop element  3813 , which is enclosed in an insulating member  3814  such that it encapsulates the stop element isolating it from the remainder of the shim  3810 . Each insulating member  3814  and stop element  3813  is positioned in a corresponding aperture  3815  present within the shim  3810 , such that the upper portion of the insulating member forms an insulating ring  3816  around each stop member  3812 . 
     When the jaws  3802  &amp;  3803  are moved to their closed position (as shown in  FIG. 40 ), the stop members  3812  contact the upper shim  3809  maintaining a separation between the upper and lower shims of between 20 μm and about 350 μm (0.00079 inches to about 0.014 inches). In use, a coagulating electrosurgical voltage is supplied between the shims  3809  &amp;  3810 , and the separation of the shims ensures effective sealing of tissue grasped between the jaw members  3802  &amp;  3803 . In the meantime, electrical shorting between the shims is prevented, as the stop members  3812  are electrically isolated such they do not carry the same electric potential as the remainder of the shim  3810 . The metallic stop members  3812  are rigid, allowing for a consistent separation of the shim surfaces, while it is feasible that the electric potential of the stop elements  3813  can be monitored in order to detect when they contact the upper shim  3809  to give an indication of the closure of the jaws. 
       FIGS. 41 to 43  show an alternative arrangement in which the metallic stop members  3812  are mounted directly on the lower shim  3810 , without the provision of the insulating members surrounding the stop members. In this arrangement, insulating members  3817  are provided on the upper shim  3809 , in corresponding relationship to each of the stop members. In this way, when the jaws  3802  &amp;  3803  are closed, the insulating members  3817  ensure that there is no electrical shorting between the upper shim  3809  and the lower shim  3810 . The metallic stop members  3812  ensure that the appropriate separation of the jaw members is maintained during the application of electrosurgical energy in order to seal tissue grasped between the jaws. 
     Finally,  FIG. 44  shows a further alternative, in which the metallic stop members  3812  are once again mounted directly on the lower shim  3810 . In this arrangement, a metallic anvil  3818  is located opposite each of the stop members, each metallic anvil  3818  being surrounded by an insulating member  3819  in order to isolate it from the remainder of the upper shim  3809 . When the jaws are closed, metal-to-metal contact takes place between the stop members  3812  and the metallic anvils  3818 , with the isolation of the anvils ensuring that electrical shorting between the shims  3809  &amp;  3810  is once again avoided. Once again, the electric potential of each of the metallic anvils can be monitored in order to detect when they assume the potential of the lower shim, indicating closure of the jaws. 
     10. ELECTRO-SURGICAL SYSTEM 
     Referring now to  FIG. 45 , the instrument  1  in use is intended for connection to an electrosurgical generator  4500  having a controllable radiofrequency (RF) source therein (not shown) that in use produces an RF coagulation signal that coagulates or seals tissue when applied thereto via the electrodes of the end-effector of the instrument  1 . Electrosurgical generator  4500  includes control input switches  4504  and  4502 , to respectively allow the generator to be turned on and off, and to allow the power of the RF coagulation signal fed to the instrument  1  to be controlled. In these respects, the electrosurgical generator  4500  is conventional. 
     The instrument  1  is connected in use to generator  4500  by control and power line  4506 , which contains separate electrical lines to allow an RF signal to be fed to the end-effector of the instrument  1  via the internal wiring described previously, and also to allow a control signal to be received from the switch  26  of the instrument  1 , to command the electrosurgical generator to output an RF coagulation signal to the instrument  1 . In use the surgeon activates the generator via on-off switch  4504 , and selects the coagulation or sealing signal strength to be generated by the internal RF source using buttons  4502 . During a surgical procedure with the instrument when a sealing or coagulation RF signal is required at the end-effector, the surgeon controls the generator to produce such a signal by pressing the switch  26  on the instrument, the generated RF signal then being passed via the electrical lines  4506  to the end-effector. That is, pressing of the switch  26  in use causes an RF coagulation or sealing signal to be supplied to the appropriate electrodes contained within the end-effector. 
     11. SUMMARY 
     In view of all of the above, therefore, embodiments of the invention provide an advanced electrosurgical forceps instrument which allows for easy and ergonomic one-handed operation by the user, provides rotational flexibility of the end-effector, controls the force that is applied by the end-effector to the tissue being grasped so as to prevent excessive force being applied, and allows for a convenient mechanical cut of the grasped tissue whilst at the same time providing for electrosurgical coagulation or sealing of the tissue. Moreover, the instrument has been further designed so as to be simple and low-cost to construct, whilst providing a compact instrument through efficient use of the space available within the respective internal activation mechanisms. 
     Various further modifications to the above described embodiments, whether by way of addition, deletion or substitution, will be apparent to the skilled person to provide additional embodiments, any and all of which are intended to be encompassed by the appended claims.