Abstract:
The invention provides a surgical instrument comprising a handle ( 1 ) shaped to enable it to be freely rotated by the user&#39;s fingers about its longitudinally axis in the hand of the user, and held by the user at any angle of rotation about its longitudinal axis; the handle ( 1 ) having an elongate shaft ( 2 ) extending therefrom and a surgical tool ( 3 ) mounted on the shaft ( 2 ) at a location remote from the handle ( 1 ); the handle ( 1 ) being provided with actuato means ( 20, 15, 29 ) operatively linked through the shaft ( 2 ) to the surgical tool ( 3 ); the actuator means having an actuator surface ( 17, 31 ) or surfaces extending around substantially the entire circumference of the handle ( 1 ), whereby the actuator means is operable by applying pressure at substantially any circumferential location on the actuator surface ( 17, 31 ) or surfaces, to actuate the surgical tool ( 3 ). The surgical instrument is designed particularly to be held in a pen-like grip, rather than in the palm of the hand or in a scissors grip as is conventional, and is desined to be actuated from any rotated position.

Description:
FIELD OF THE INVENTION 
     This invention relates to surgical instruments, for use in laparoscopic or endoscopic surgery and/or open surgery. 
     BACKGROUND OF THE INVENTION 
     Laparoscopic and endoscopic surgical methods have become increasingly popular in recent years. Such methods typically involve making small incisions in the abdominal wall of a patient through which specially designed laparoscopic or endoscopic tools are inserted for carrying out the surgical procedure. Such tools typically have a miniaturised surgical implement such as forceps or scissors at the end of a long shaft to the other end of which is attached a handle and actuating mechanism. By the use of such tools, the surgeon can operate the instrument from outside the patient&#39;s body whilst monitoring the movement of the surgical tool within the body by means of an endoscope. 
     Such techniques of minimally invasive therapy (MIT), which have been commonly referred to as keyhole surgery, offer very substantial advantages over conventional open surgery in that only very small incisions in the patient&#39;s body wall are required thus substantially minimising patient trauma, dramatically reducing post-operative complications, and greatly reducing the opatient&#39;s recovery time. 
     As laparoscopic or endoscopic surgical techniques are generally more delicate than those of open surgery, the surgical instruments need to be particularly easy in manipulate and use. Hitherto, the surgical instruments used in MIT have been cumbersome to use. For example, many conventional laparoscopic instruments have off-centre scissor handles for actuating the surgical tool. The presence of such scissor-handle actuated mechanisms makes steady control and rotation of the instrument difficult. To overcome this problem, some tools are provided with a thumb wheel by which the actuator shaft is rotated independently from the scissor handles. However, such an arrangement is clumsy to use and often requires two hands to operate effectively. Thus, there remains a need for surgical instruments for use in surgery which are more easily manipulated, can be operated entirely by one hand, can be rotated freely, and operated just as effectively in any rotated position to enable the orientation of the surgical tool to be varied as required. It is an object of the present invention to provide such an instrument. 
     SUMMARY OF THE INVENTION 
     The present invention is based in part on the recognition that a surgical instrument can be manipulated with greater control and sensitivity when the instrument is held in a pen-like grip, i.e. with the non-functioning end of the instrument extending rearwardly from between the thumb and forefinger. Furthermore, the invention is based on the recognition that a surgical instrument can be made more responsive and easier to use if it can be rotated by the fingers to any position and can be actuated from a position anywhere around the circumference of the handle of the instrument. This is in contrast to existing surgical tools such as those disclosed in, for example EP-A-0535370 and EP-A-0598202, in which either a squeeze grip type actuation mechanism is provided, or an actuator lever is provided at a single location on the circumference of the instrument handle. 
     Accordingly, in a first aspect the invention provides a surgical instrument comprising a handle shaped to enable it to be freely rotated by the user&#39;s fingers a-cut its longitudinal axis in the hand of the user, and held by the user at any angle of rotation about its longitudinal axis; the handle having an elongate shaft extending therefrom and a surgical tool mounted on the shaft at a location remote from the handle; the handle being provided with actuator means operatively linked through the shaft to the surgical tool; the actuator means having an actuator surface or surfaces extending around substantially the entire circumference of the handle, whereby the actuator means is operable by applying pressure at substantially any circumferential location on the actuator surface or surfaces, to actuate the surgical tool. 
     The handle may be of generally circular cross-section, or it may be of a non-circular cross-section. For example it may be of polygonal cross-section, eg hexagonal or octagonal, but most preferably it is circular in cross-section. The term circumference as used herein is intended to refer to the perimeters of both circular and non-circular handles. 
     The actuator surface may be a continuous surface extending around the circumference of the handle or it may, alternatively, comprise an array of closely spaced discrete actuator elements. 
     The actuator means may be mechanical, electrical, pneumatic or hydraulic or any combination of these. 
     In one particular example of a mechanical arrangement, the actuator means is mechanically linked to an actuating rod disposed slidably within the elongate shaft, which rod is in turn linked to the surgical tool on the end of the shaft. 
     In one particular example of an electrical arrangement, the actuator means may comprise a switch or array of switches for controlling the flow of electrical current along the shaft to a diathermy tool (e.g. a diathermy hook) at the end thereof. 
     The surgical tool mounted at the end of the elongate shaft may be any one of the types of surgical tools conventionally used in laparoscopic or endoscopic surgery. Thus, for example, the surgical tool may be a miniaturised surgical instrument such as a pair of forceps, a clamp, a pair of scissors or a diathermy hook. Any of the aforesaid tools may optionally have a monopolar or bipolar diathermy capability. 
     The actuator means in one embodiment can be an array of radially displaceable actuator elements disposed around the circumference of the handle, means being provided for converting radial inward movement of an actuator element into longitudinal movement of the actuating roc within the elongate shaft. 
     For example, the actuator element may be provided with an edge or surface which functions as a cam follower or camming surface, for engaging and camming against a complimentary camming surface or cam follower associated with the actuating rod. 
     In one embodiment, each actuator element is provided with a wedging member having an inclined surface whereby radially inward movement of the actuator element urges the inclined surface of the wedging member into contact with a camming edge or surface associated with the actuator shaft, thereby to displace the camming edge or surface in a longitudinal direction. 
     A sufficiently large number of actuator elements are disposed around the circumference of the handle to ensure that the instrument can be actuated from substantially any location around its circumference. For this purpose, a minimum of three actuator elements is generally required, but preferably there are more than three actuator elements disposed around the circumference, more preferably there are at least six actuator elements, and in one particularly preferred embodiment there are eight actuator elements. In another particularly preferred embodiment, there are twelve actuator elements. 
     The handle is preferably of elongate form and is sufficiently small in cross section to enable it to be held in a pen-like grip, i.e. wherein the end of the handle remote from the actuator shaft extends away from the hand between the thumb and adjacent finger. 
     The handle may typically have a bulbous shape, being tapered towards the end remote from the surgical tool, increasing in diameter towards the central portion thereof and tapering again towards the actuator shaft. The actuator means typically is located within the bulbous or enlarged diameter central region of the handle. 
     The handle may be provided with means for effecting locking of the surgical tool in a given configuration. For example, where the surgical tool is in the form of a miniature pair of grasping forceps or a clamping tool, the locking means may be effective to lock the forceps or clamping tool in a clamping or gripping configuration. 
     In one embodiment, the handle is provided with first actuator means for effecting movement of a surgical tool at the end of the actuator shaft from a rest position to an actuated position; locking means for locking the surgical tool in the actuated position; and second actuator means operable to release the locking means to enable the surgical tool to return to the rest position. 
     Where the actuator means is mechanically linked to an actuating rod disposed slidably within the elongate shaft, which rod is in turn linked to the surgical tool on the end of the shaft, the locking means can take the form of a grasping member having a plurality of grasping portions which grasp the actuating rod to lock it in an actuated position, the second actuator means being operable to force the said grasping portions apart to release the grip on the actuating rod. 
     The actuating rod may be provided with a spiral track (e.g. a thread) or an array of annular ridges, which cooperate with the grasping portions to form a ratchet mechanism, the spiral track (e.g. thread) being preferred because many more grasping positions are possible within the same linear movement of the actuating rod. 
     The second actuator means is preferably arranged to be actuable from substantially any position around the circumference of the handle. 
     The advantages of the surgical instruments of the present invention reside in their ease of manipulation and lightness, and in particular in the ease with which the surgical tool can be rotated and actuated at any rotated position. The ability of the surgical instruments of the invention to be held in a pen-like grip, rather than in the palm of the hand, or in a scissors grip as is conventionally the case, and to be actuated from any rotated position, means that the tool can be operated with much greater sensitivity thereby enabling surgical procedures to be carried out more accurately, safely, efficiently and with reduced surgeon fatigue. 
     In another aspect, the invention provides an actuator device comprising an actuating rod movable in a reciprocating manner along an axis, the actuating rod having a grasping region defined by a length of the rod having a spiral track (eg a thread) at the surface thereof; biasing means for resiliently biasing the actuating rod in a first direction; actuator means for moving the actuating rod in a second direction opposite to the first direction against a restoring force of the biasing means; grasping means comprising a plurality of grasping portions for grasping the actuating rod at the grasping region to hold the rod in an actuated position against the said restoring force; and grasp releasing means for releasing the actuating rod from the grassing means, 
     The plurality of grasping portions typically takes the form of an annular array of radially inwardly directed grasping fingers formed from a resilient material (e.g. a metal disc spring); the clearance between the radially innermost edges of opposing grasping fingers being less than the diameter of the actuating rod; such that as the actuating rod is urged through the grasping means in one direction, the grasping fingers engage the spiral track at the surface of the actuating rod to prevent movement of the actuating rod in the reverse direction. 
     The grasp releasing means can take the form of a grasp releasing member having a conical or frustoconical surface which can be urged in an axial direction against the grasping fingers to lift them away from the spiral track to release the actuating rod. 
     The actuator device is particularly useful in the context of the surgical instruments of the present invention, but may well find uses in other technical fields. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be illustrated but not limited, any reference to the specific embodiments shown in the accompanying drawings, of which: 
     FIG. 1 is a side sectional elevation of a surgical instrument according to one embodiment of the invention; 
     FIG. 2 is a side elevation of the embodiment shown in FIG. 1; 
     FIG. 3 is a side sectional elevation of the handle portion of a surgical instrument according to a second embodiment of the invention; 
     FIG. 4 is a partial sectional elevation of a surgical instrument according to a third embodiment of the invention; 
     FIG. 5 is an isometric view of a component of the instrument shown in FIG. 4; 
     FIG. 6 is an isometric view of the grasping mechanism of the instrument shown in FIG. 4; 
     FIGS. 7 a  and  7   b  are enlarged elevations of actuating wedges and grasp releasing wedges respectively used in the instrument of FIG. 4; 
     FIG. 8 is a partial sectional elevation of an instrument according to a fourth embodiment of the invention; 
     FIG. 9 is a partial sectional elevation of an instrument according to a fifth embodiment of the invention; 
     FIG. 10 is an enlarged cross-section of a component of the instrument shown in FIG. 9; 
     FIG. 11 is a partial sectional elevation of a surgical instrument according to a sixth embodiment of the invention; and 
     FIG. 12 is an enlarged view of cart of the surgical instrument shown in FIG.  11 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2 it can be seen that the surgical instrument according to one embodiment of the invention comprises an elongate handle  1  having a shaft  2  extending from one end thereof, and a surgical tool  3  mounted at the distal end of the shaft  2 . The handle  1  in this embodiment is of elongate form and has a bulbous region  4  from which extends the shaft  2 , and a tapering handle extension  5 . In use, the tool is grasped between thumb, forefinger and the middle finger, as one would grip a pen, with the end  5  of the instrument extending rearwardly between the thumb and forefinger. The bulbous region  4  conceals an actuator assembly, the details of which can be seen in FIG.  1 . 
     Referring now to FIG. 1, it can be seen that the elongate shaft  2  comprises an outer effector tube  14  having slidably disposed within the hollow interior thereof an actuating rod  15 . A surgical tool housing  13  is mounted in the end of effector tube  14 , e.g. by silver soldering, a pair of forceps jaws  11  being pivotably mounted on the tool housing  13 . The forceps jaws  11  are linked via forceps linkage  12  to the distal end of the actuating rod  15 . 
     The other end of the effector tube  14  extends into and through the bulbous region  4  of the handle  1 . The effector tube  14  is provided with a radial flange  18  with an external thread  24  which mates with the internal thread of the generally conical junction member  16 . The proximal end  25  of the effector tube is also provided with an external thread upon which is mounted the pen-handle tail-piece  27 . The portion of the effector tube  14  passing through the bulbous region  4  of the handle  1  is provided with a slot  26  which allows a cam wheel actuator  20  to be fixedly mounted on the actuating rod  15 , the slot  26  having a sufficiently large axial dimension to enable the cam wheel actuator  20  to slide forward and backwards in a reciprocal manner in the slot. Attached to the outer surface of the effector tube  14 , to the rear of the slot  26 , is an annular collar  22  which has a radial flange  28  extending from the rear part thereof. A return spring  21  is mounted on the annular collar  22  and abuts against the flange  28  and the cam wheel actuator  20  so as to bias the cam wheel actuator  20  towards the front of the slot  26 . 
     Cam wheel actuator  20  has a plurality of inclined surfaces  29  around its outer circumference, each inclined surface  29  being separated from an adjacent inclined surface by means of a pair of axially aligned dividing walls  30 . 
     Disposed radially outwardly of the cam wheel actuator  20  is an array of actuating fingers  19  each of which has an inclined camming surface  19   a  complementary to the inclined surfaces  29  of the cam wheel actuator. The actuating fingers  19  are mounted on generally flexible actuating arms  31  which have a generally arcuate profile in cross-section and which are joined together at the distal end of the bulbous region  4  and secured to the effector tube  14  by cramping between the conical junction member  16  and the flange  18 . Thus, each actuating arm  31  is radially connected to a common hub  31   a  which is of thicker cross-section than the arcuate portion, the thicker hub  31   a  resting in front of flange  18 . Disposed around the outside of the array of actuator arms  31  is a flexible skin or boot  17  which encases the inner workings of the actuation mechanism. The boot  17 , which may be formed from an appropriately flexible plastics material, has an in-turned end portion which, together with hub  31   a , is clamped against flange  18  by screwing the threaded junction member  16  tightly onto the external thread  24  of the radial flange  18 . 
     The other end  31   b  of each actuator arm  31  is unsecured, but the end  17   a  of the boot  17  is clamped between the outer inclined surface  28   a  of flange  28  and the inner surface of the handle extension piece  5  as the handle extension piece  5  is screwed onto the threaded end  25  of the effector tube  14 . 
     In use, in order to cause the jaws of the forceps to close, the user of the instrument depresses any one or more of the actuator arms  31  thereby to urge the actuating finger  19  towards the cam wheel actuator. As the actuating finger  19  comes into contact with the cam wheel actuator, the inclined camming surface  19   a  of the actuating finger cams along the inclined surface  29  of the cam wheel actuator thereby forcing the actuator wheel to move rearwardly along the slot  26 . Since the cam wheel actuator is fixed to the actuating rod  15 , this has the effect of moving the rod  15  in a rearwards direction thereby causing the jaws of the forceps to close. 
     Once the pressure is released on the actuating arms  31 , the force of the return spring  21  urges the cam wheel actuator forwardly back along the slot to its rest position, thereby causing the actuating rod  15  to move forwardly with it, and thus opening the jaws of the forceps. 
     The embodiment of the invention illustrated in FIGS. 1 and 2 can be formed from a combination of materials. Thus, normally the forceps jaws  11 , forceps linkage  12 , linkage housing  13 , effector tube  14  and actuating rod  15  would be formed of surgical quality stainless steel but they need not be; instead other metals or an appropriately tough form of sterilisable plastics material may be used. The remaining components can be made either from a suitable metal or from a suitable sterilisable plastics material. 
     By making the instrument or parts thereof from a plastics material, the tool may be made lighter in weight and possibly cheaper to produce. Thus, a surgical instrument may be made fully disposable thereby avoiding the problems of the build up of contaminants within the instrument that can occur with tools intended for long term reuse. 
     Whether the instruments of the invention may be designed to be disposable or reusable, they should be formed from materials which are capable of withstanding the autoclaving or other sterilisation procedures typically used for surgical instruments. For autoclaving, such materials should preferably have the ability to withstand temperatures in excess of 134° without deforming or otherwise losing their integrity during the sterilising process. 
     One potential problem with surgical instruments used in laparoscopic techniques, and employing a coaxial actuator shaft arrangement, is that contaminants such as blood and other bodily fluids can migrate along the space between the inner and outer shafts and removal of such contaminants can be very difficult without dismantling the equipment after each use. In order to avoid this potential problem, in the instruments of the present invention, a sealing means may be provided between the actuator rod and effector tube to prevent or reduce substantially the likelihood of contaminants finding their way into the very small annular gap between the two. The sealing means could, for example, take the form of an O-ring or other seal formed from a low friction material which does not hinder movement of the actuator rod along the bore of the effector tube. 
     In order to eliminate completely the possibility of contaminants moving along the gap between the inner and outer coaxial shafts, the actuating rod may be provided with a flexible skirt which in turn is connected to the inner wall of the effector tube. The skirt acts as a barrier to contaminants. 
     Alternatively, the instrument may be constructed so as to be dismantled for cleaning and sterilising purposes. 
     The actuator mechanism illustrated in FIGS. 1 and 2 is a simple “open and close” mechanism. However, in many instances, it may be desirable that the actuator mechanism should provide some form of locking means for locking the jaws of the tool in the gripping or closed position. 
     A second embodiment of the invention, which has such a lacking facility, is shown in FIG.  3 . 
     The instrument, of which the handle is shown in FIG. 3, is similar in external appearance but has a modified actuator arrangement within the handle. Thus, as with the instrument shown in FIGS. 1 and 2, the instrument has an elongate handle  101 , and an actuator shaft with a surgical tool (not shown) mounted at its end. The handle  101  is shaped to enable it to be held in a pen-like grip between thumb, forefinger and index finger and has a bulbous region  104  at approximately its mid-point, and a pen handle tail piece  127 . The bulbous portion conceals the actuator mechanism. 
     As with the embodiment of FIGS. 1 and 2, the shaft comprises an outer effector tube  112  and an actuating rod  111  slidably disposed within the effector tube  112 . The effector tube  112  has a threaded end which screws into a threaded socket at the distal end of junction member  113 . The actuating rod  111  on the other hand extends through a central bore in the junction member  113  and into the interior of the bulbous portion  104  where the actuating mechanism is located. 
     The actuation mechanism comprises a generally cylindrical housing  117 , hereinafter referred to as the actuator retaining capsule. The actuator retaining capsule  117  has a threaded boss or spigot  117   a  extending axially from one end thereof, onto which is screwed the junction member  113 . At the other end, i.e. the end furthest from the shaft  12 , the actuator retaining capsule  117  is provided with an end piece  126  which fits tightly within the rearwardly facing open end of the capsule  117  and is secured therein by means of three small radially positioned screws (not shown). Alternatively, end piece  126  and capsule  117  can be secured together by means of a threaded union, adhesive, welding or by any other common fixing method. 
     End piece  126  has extending axially rearwardly therefrom a threaded spigot or boss portion  126   a  onto which is screwed the internally threaded pen handle tail piece  127  which is of elongate tapering form and, in this embodiment, is hollow for lightness. 
     Fixedly mounted (in this case by means of three small screws) within the actuator retaining capsule  117  is actuator cam release member  119 . Actuator cam release member  119  has a rearwardly oriented spigot portion  119   a  which has a radially inwardly inclined end surface  119   b , the purpose of the inclined end surface  119   b  being to assist in the dismantling of the instrument as will be described below. Spigot portion  119   a  serves as a support upon which is slidably mounted cam wheel actuator  121 . Cam wheel actuator  121  has a plurality of inclined surfaces  121   a  separated by means of axially aligned dividing walls  121   b . Each pair of adjacent dividing walls  121   b  and the inclined surface  121   a  therebetween define a camming slot  121   c  on the cam wheel. To the rear (i.e. furthest from the shaft) of the cam wheel actuator  121  is a grasping element or actuating cam wheel  122 . The grasping element or actuating cam wheel  122  has a radially outer annular portion  122   a  which abuts against the inner surface of the actuator retaining capsule  117 . Extending radially inwardly from the annular portion  122   a  are a plurality of grasping cams, each of which has a grasping portion  122   c . The radially inner surfaces of each grasping portion  122   c  are provided with grooves  122   b  of a radius smaller than the radius of actuating rod  111  so as to enable the grasping cams to more positively grasp the actuating rod  111 . In order to further enhance the grip of the grasping portions on the actuating rod  111 . the surface of the actuating rod  111  may be roughened. 
     Disposed rearwardly of the actuating cam wheel  122  is an annular member  124  which is arranged for sliding movement within the actuator retaining capsule  1 , 7 . Annular member  124  has a central recess for accommodating the end of actuating rod  111 . A first return spring  123  is arranged between a front face  124   a  of the annular member and a rear face  122   d  of the annular portion  122   a  of the actuating cam wheel  122  so as to bias the actuating cam wheel against the cam wheel actuator  121 . 
     Extending between the rear surface  124   b  of the annular member  124  and an end wall of the end piece  126  is a second return spring  125  which is of greater stiffness than the first return spring  123 . 
     The actuator retaining capsule  117  is provided with an array of slots  130  around its circumference at approximately its mid-point. Located outside the actuator retaining capsule  117  are a plurality of axially aligned actuating arms  131  arranged in an array around the circumference of the handle. In this embodiment, eight actuating arms  131  are provided although a smaller or greater number may be provided as desired. Each actuating arm is radially joined to a common hub  131   a  of wedge-shaped cross-section (e.g. by virtue of being integrally formed with the hub), the hub  131   a  being clamped between the junction member  113  and the end wall  117   b  of the capsule  117 . The rearward end of each actuating arm  131  is not clamped but is held in place by means of the outer skin or boot  114  which is formed of a flexible material and encloses and seals the entire bulbous portion. The boot is held in place by virtue of its in-turned end  114   a  being clamped between junction member  113  and the end wall  117   b  of the capsule  117 , and its rearward end being clamped between the inclined surface  126   b  of the capsule end portion  126  and the inner surface  127   a  of the tail piece. 
     Extending radially inwardly from about the mid-point of each actuating arm  131  is an actuating finger  120  the actuating finger being arranged to protrude through the slot  130  in the actuator retaining wall and into contact with the cam wheel actuator  121 . Each actuator finger  120  has an inclined camming surface  120   a  which in this embodiment has a sloping angle complimentary to that of the inclined surface  121   a  of the camming slot of the cam wheel actuator  121 . 
     Located forwardly of the cam wheel actuator  121  is a grasping cam wheel  118  which is identical in form to actuating cam wheel  122 . Grassing cam wheel  118  is held in place by virtue of its annular rim portion  118   a  being held between an in-turned end wall  117   c  of the actuator retaining capsule  117  and an end face of the actuator cam release member  119 . In front of the grasping cam wheel  118  and slidably mounted on the actuating rod  111  is grasp releasing ring  116  which has a pair of generally conical surfaces  116   a  and  116   b . The radially inner edge of the rearwardly facing surface  116   b  is radiussed, for reasons which will become apparent below. 
     Encircling the forwardly facing conical surface  116   a  of the grasp releasing ring  116  is grasp releasing actuator wheel  115  which comprises an array of spoke-like radial actuator elements  115   a  linked together at their radial outer ends by a thin flexible annulus  115   b . The annulus  115   b  lies outside the actuator retaining capsule  117  and the actuator elements  115   a  extend into the interior of the capsule  117  through slots  117   d . The actuator elements  115   a  protrude between adjacent pairs of actuator arms  131  and the flexible annulus  115   b  encircles the array of actuator arms  131 , forming an annular bulge in the boot  114  which allows easy visual location of the grasp releasing mechanism. 
     In use, the handle of the instrument is held in a pen grip as with the instrument of FIGS. 1 and 2. In order to close the jaws of a surgical tool at the end of the shaft, the user depresses any one or more of the actuator arms  131  arranged around the circumference of the handle. Depressing the actuator arm  131  causes the inclined camming surface of the associated actuating finger  120  to be urged into a camming slot  121   c  of the cam wheel actuator  121  and into contact with the inclined surface of the camming slot  121   c . As the inclined camming surface  120   a  of the actuating finger cams along the inclined surface  121   a  of the cam wheel actuator, it causes the cam wheel actuator  121  to be urged rearwardly along the spigot portion  119   a  of the actuator cam release member  119 . This in turn has the effect of urging the actuating cam wheel  122  rearwardly against the biasing force of the first return spring  123  and, since the cams of actuating cam wheel  122  are in tight gripping contact with the actuating rod  111 , also causes the actuating rod  111  to move rearwardly thereby causing the jaws of the tool to close. In the absence of the grasping cam wheel  118 , the force of the second return spring  125  would cause the annular member  124  to push the actuator rod  111  back along the effector tube  112  thereby opening the jaws of the tool at the end of the shaft. However, because the cams of the grasping cam wheel  118  are in gripping contact with the actuating rod  111 , the rod  111  is prevented from moving back along the effector tube  112  and thus the tool remains locked in the grasping position. In order to release the actuator shaft, the user depresses the grasp releasing actuator wheel  115  at any point or points on its circumference, thereby urging the spoke-like radial actuator elements  115   a  inwardly and into contact with the forward conical surface  116   a  of the grasp releasing ring  116 . As the inclined surface of the actuator element  115   a  cams along the conical surface  116   a , it forces the grasp releasing ring  116  in a rearwards direction against the grasping cam wheel  118 . The flexibility of the thin web portion  118   b  of the grasping cam wheel  118  enables the grasp releasing ring  116  to force the radially innermost grasping portions (cams) of the cam wheel  118  slightly apart thereby releasing their grip on the actuating rod  111  which is then restored to its rest position by the force of the second return spring  125 , and the jaws of the tool at the end of the shaft are caused to open. 
     The surgical instrument shown in FIG. 3 is designed such that the effector tube and actuating rod can be removed and disposed of at the end of each surgical operation, or alternatively sterilised and re-used. Removal of the effector tube  112  is achieved simply by unscrewing it from the junction member  113 . The actuating rod  111  is then removed by pulling it out from the handle  101 . Although the grassing cam wheel  118  and the actuating cam wheel  122  initially act to prevent retraction of the actuating rod from the handle, the gripping effect of the grasping cam wheel  118  is released by depressing the surface of the grasp releasing actuator wheel  115  in the manner described above whilst the gripping effect of the actuating cam wheel  122  is automatically released as the grasping portions  122   c  are pulled against the inclined surface of the actuator cam release member  119  which leads to the grasping portions  122   c  being forced a art sufficiently to release the actuating rod  111 . 
     Once the actuating rod and effector tube have been removed, the handle and actuator mechanism in the handle may be sterilised for reuse. At the start of the next surgical procedure, a new actuating rod  111  and effector tube  112  arrangement may simply be fitted by pushing the actuating rod into the handle until it engages and is gripped by the grasping cam wheel  118  and actuating cam wheel  122  and then screwing the effector tube  112  into place as described above. By making the actuator rod and effector tube disposable, the potential problem of blood, other bodily fluids and tissue contaminating the instrument is avoided. 
     FIGS. 4 to  7   b  illustrate grasping forceps in accordance with a third embodiment of the invention. As with the embodiment shown in the previous Figures, the grasping forceps has a handle, a shaft and a surgical tool (not shown) mounted at its end. The handle is shaped so as to enable it to be held in a pen-like grip between thumb forefinger and index finger and, as with the previous embodiments, has a bulbous region at approximately its mid-point, and a pen-handle tail piece. From the exterior, the grasping forceps appear very similar to the instruments of FIGS. 1 to  3 . However, the bulbous region conceals a modified actuation mechanism. 
     The actuation mechanism comprises a generally cylindrical housing (hereinafter referred to as the actuator retaining capsule) formed from a front capsule portion  206  and a rear capsule portion  210  each of generally closed ended cylindrical form. The two capsule portions  206  and  210  are connected together by means of a capsule junction block  224 . The rear end of the capsule junction block  224  is received within the end of rear capsule portion  210  and is held in place by means of a pair of screws  207 , only one of which is shown in the drawings. The leading portion of the capsule junction block  224  has an external thread  223  which engages an internal thread on the front capsule portion  206 . Rear capsule portion  210  has extending rearwardly therefrom a threaded spigot  215  which engages an internal thread on the tapering pen-handle tail piece  216 . The front capsule portion  206  also has a threaded spigot  218 , onto which is screwed internally threaded junction member  201 . The inner surface of the distal end of the junction member has a thread  217  into which the effector tube (not shown) can be screwed. 
     A cam wheel actuator  228  is slidably disposed within the rear end of the actuator retaining capsule. Cam wheel actuator  228  has a central bore which is threaded to engage and retain a correspondingly threaded end of the actuating rod  230 . Cam wheel actuator  228  is biased forwardly by means of return spring  229 . 
     As with the instruments illustrated in FIGS. 1 to  3 , the cam wheel actuator has a plurality (in this case  12 ) of inclined surfaces  227   a  around its outer circumference, each inclined surface  227   a  being separated from an adjacent inclined surface by means of axially aligned dividing walls  227   b . The inclined surfaces  227   a  and dividing walls  227   b , together with the radial slots  231  of rear surface  224   a  of the capsule junction block  224  define pockets into which actuating wedges  208  are located. Actuating wedges  208 , which are shown in enlarged form in FIGS. 7 a  and  7   b , extend outwardly through slots  209  in the wail of rear capsule portion  210 . The radially innermost ends of the actuating wedges  208  are tapered to allow them to be depressed closer to the central axis. An array of generally arcuate actuating arms  211  are arranged about the capsule such that their mid-sections bear against and hold in place the actuating wedges  208 . The actuating arms  211  are linked at one end by means of a common hub  211   a , the arrangement of the arms  211  with respect to the hub  211   a  being shown in FIG.  5 . The hub  211   a  sits about the spigot  218  of the forward capsule portion and is surrounded by an annular collar  202 . The ends  211   b  of the actuating arms remote from the common hub  211   a  taper and are retained within scalloped recesses  212  in an annular flange extending radially outwardly from the rear capsule portion. The ends  211   b  of the arms are held in place in the scalloped recesses by means of an annular collar  214  which encircles the end of the rear capsule portion  210 . 
     The actuator retaining capsule, actuating wedges  208  and actuating arms  211  are surrounded and concealed by a flexible boot  213  formed of an appropriately flexible thin plastics material. The flexible boot  213  has in-turned end portions  213   a  and  213   b  which are clamped between the junction portion  201  and the front capsule portion  206 , and the pen-handle tail piece  216  and rear capsule portion  210  respectively. 
     In use, actuation of the tool is achieved by depressing the flexible boot  213  and underlying actuating arms  211  and actuating wedges  208  to force the actuating wedges  208  radially inwardly in the slots  231 . As the actuating wedges  208  move radially inwardly, so the inclined surfaces  208   a  cam along the inclined surfaces  227   a  of the cam wheel actuator  228  thereby urging the cam wheel actuator  228  against the force of return spring  229  in a rearwards direction. Since the actuating rod  230  is screwed into the cam wheel actuator  228 , the actuating rod is also moved rearwardly thereby actuating the surgical tool at the end of the actuator shaft in a manner similar to that described in relation to FIGS. 1 to  3 . 
     When pressure on the flexible boot  213 , actuating arm  211  and actuating wedge  218  is released, the cam wheel actuator and actuating rod  230  remain locked in the retracted position, thanks to a grasping mechanism mounted in the capsule portion, as will now be described. 
     As can be seen from FIG.  4  and FIG. 6, the actuating rod  230  has a threaded end  230   a  which screws into the cam wheel actuator  228  and a second threaded region  222  which has a much finer thread (smaller pitch) than threaded end  220   a . A pair of disc springs  221   a  and  221   b  surround the finely threaded region  222  on the actuating rod  230  and are clamped in place between opposing surfaces  206   b  and  224   b  of the front capsule portion  206  and capsule junction block  224  respectively. 
     The disc springs  221   a  and  221   b , which are formed from a suitably resilient metal material, each have a plurality (in this case twelve) of radially inwardly directed grasping fingers  221   c ,  221   d . The rear disc spring  221   b  has an inner diameter slightly less than the outer diameter of the finely threaded region  222  on the actuating rod  230 . The forward disc spring  221   a  has an inner diameter larger than the outer diameter of the finely threaded region  222 . Disposed about the finely threaded region  222  and forwardly of the disc springs is a grasp releasing cam wheel  219  which has a plurality of inclined camming surfaces  220   a  separated by axially aligned dividing walls  220   b  which together define angled slots  220 . The rear surface of the grasp releasing cam wheel  219  is provided with a second inclined camming surface  219   a.    
     In this embodiment, the grasp releasing cam wheel  219  has an array of twelve angled slots  220  and these are staggered relative to the slots  231  defined by the capsule junction block  224  and cam wheel actuator  228 . Each slot  220  has disposed therein a grasp releasing wedge  204 , the radially outer end of which protrudes through slots  205  in the front capsule portion  206 , between the actuating arms  211 , and through slots  203  in the annular collar  202 . The radially outer ends of the grasp releasing wedges  204  are accommodated within an annular bulge  213   a  in the flexible boot  213 . 
     In use, as the actuator mechanism is actuated to move the actuating rod  230  in a rearwards direction towards the user, the fine thread  222  and the grasping fingers  221   d  of the rear disc spring  221   b  cooperate to form a ratchet mechanism which holds the actuating rod  230  in the retracted position against the forward biasing force of the return spring  229 . In this way, a grasping forceps tool at the forward end of the instrument can be locked in a clamping or grasping position. The effect is to give a large number of grasping positions within a short travelling distance of the actuating rod  230  (number of positions=[travel÷pitch]×number of fingers, typically [1.5÷0.25]×12=72). 
     When it is desired to release the actuating rod  230 , one or more of the grasp releasing wedges  204  are depressed such that the inclined camming surfaces  204   a  on the grasp releasing wedges  204  cam along the inclined surfaces  220   a  of the angled slots  220  to urge the grasp releasing cam wheel  219  in a rearwards direction. As the grasp releasing cam wheel  219  moves in a rearwards direction, it lifts the fingers  221   d  of the rear disc spring  221   b  away from the finely threaded portion  222  thus releasing their grasp on the actuating rod  230 . The actuating rod  230  is then free to move in an axial direction and is urged forwardly again by the return spring  229 . At the same time, the forward disc spring  221   a  acts as a return spring for the grasp releasing cam wheel  219  and urges it forwardly against the grasp releasing wedges  204  thereby displacing the grasp releasing wedges  204  outwardly to their rest position. 
     FIG. 8 illustrates a simple forceps arrangement which makes use of the same actuator retaining capsule and actuating arrangement as shown in FIG. 4 but omits the grasping/locking mechanism and the grasp releasing mechanism at the forward end of the capsule. Thus in this embodiment, depression of the actuating arms  211  and actuating wedges  208  displaces the cam wheel actuator  228  rearwardly against the force of the return spring  229 , but once the pressure on the actuating arms  211  and actuating wedges  208  is released, the return spring  229  restores the cam wheel actuator and hence the actuating rod  230  to its original position. Thus, as with the surgical instrument of FIG. 1, the instrument of FIG. 8 provides only a simple “open and close” mechanism. 
     FIG. 9 illustrates a further modification to the grasping forceps shown in FIG.  4 . In this embodiment, one of the grasp releasing wedges  204  is replaced by a grasp disabling wedge  331  the shape of which is illustrated more clearly in FIG.  10 . The grasp disabling wedge is similar in shape to the grasp releasing wedge  204  in the embodiment of FIG. 4 except that it is slightly longer and the radially inner end of the wedge has a hooked shape or toe  332  defined by inclined surfaces  332   a  and  332   b . The corresponding guide slot  333  has a cut away region or overhang  336  defined by inclined surface  336   a  and ridge  336   b . The grasp disabling wedge  331  is biased radially outwardly by means of a biasing leaf spring  334  which is mounted at one end in a slot  335  on the grasp releasing wedge  331  and at the other end is secured to the outer surface of the capsule by means of a retaining screw (not shown). The grasp disabling wedge  331  stands proud of the grasp releasing wedges  211  and the radially outer end  331   a  of the grasp disabling wedge is located in a small radial extension of the annular bulge on the flexible boot  213 . 
     In use, in order to disable the grasping mechanism, the grasp disabling wedge  331  is depressed, along with some of the grasp releasing wedges  204 , such that hook or toe  332  snaps over the ridge  336   b  and, in so doing, the grasp releasing cone is urged in a rearwards direction to lift the grasping fingers  221   d  of the disc spring  221   b  away from the fine threaded region  222 . On releasing, the grasp disabling wedge  331  prevents the fingers  221   d  from re-engaging thus disabling the grasping mechanism. When the instrument is subsequently actuated by depressing the actuating arms  211  and actuating wedges  208 , since the ratchet mechanism defined by the fine thread region  222  and the disc spring  221   b  has been disabled, the return spring  229  restores the actuating rod  230  to its original position when the pressure on actuator fingers  211  and actuator wedges  208  is released. In order to re-enable the grasping mechanism, one or more of the eleven grasp releasing wedges  204  are depressed thus urging the grasp releasing cone  219  in a rearwards direction, thereby releasing the grasp disabling wedge  331  which is restored to its rest position by the return spring  334 . 
     FIGS. 11 and 12 illustrate a further embodiment of the invention in the form of a diathermy instrument. In this embodiment, the actuating mechanism is similar to that shown in the preceding embodiments, except that the mechanical components of the actuator retaining capsule have been largely replaced by electrical components. 
     As shown in FIGS. 11 and 12, the actuating mechanism comprises an actuator retaining capsule, actuating wedges and an array of actuating fingers surrounded by a flexible boot of the same type as shown in FIG. 4, the simple forceps arrangement. The two halves of the actuator capsule are held together by means of junction block  412  which is threaded to engage corresponding threads on the front capsule portion, and is secured to rear capsule portion by means of screws (not shown). In this embodiment however, the junction block is modified in shape to accommodate electrical contact block  408  and wiring location ring  409 . 
     The rear portion of the actuator retaining capsule contains a cam wheel actuator  415  having an axially short contacting surface  416   a  and an axially longer contacting surface  416   b . Mounted behind the cam wheel actuator  415  within recess  421  are a pair of micro switches  418  and micro switch contact springs  417   a  and  417   b . Contact springs  417   a  and  417   b  are connected by means of an annular ring which is held in place by clamping between switch block  419  and the inner end wall of the rear capsule portion. A power supply cable  403  enters the Den-handle tail piece of the tool and extends into the capsule where it is connected to micro switches  418  and capacitors  420 . Wires  414  extend between micro switches  418  and actuator contact rings  406  and  407  in the forward part of the actuator capsule. Electrical contacts  404  and  405  protruding from the effector end  410  engage the actuator contact rings  406  and  407  respectively and electrical wires  401  extend along the interior of the effector tube to a diathermy hook (not shown) at the end thereof. 
     The effector tube end  410 , which has an axial split  411 , abuts against a conical portion  413  of the junction block  412 . As the effector tube is screwed into the conical junction member by means of thread  402 , the two halves of the split end of the effector tube  410  are forced apart by the conical portion  413  thereby ensuring positive contact between the electrical contacts  404  and  405  and the actuator contact rings  407  and  406  respectively. 
     In use, the diathermy instrument is actuated in a similar manner to the instruments shown in FIGS. 1 to  10 ; i.e. the actuator arms and actuator wedges arrangement surrounding the retaining actuator capsule are depressed so as to urge the cam wheel actuator  415  in a rearwards direction. An inclined surface  416   b  on the cam wheel actuator  415  cams along the in-turned end of micro switch contact spring  417   b  to depress the micro switch thereby switching on a source of current to the effector contact  404 . The current provided by switch  417   a  is sufficient to provide enough heat at the diathermy hook for coagulation, but is insufficient to generate a temperature which can efficiently cut through tissue. When it is desired to use the diathermy hook to cut through tissue, the actuator arm  411  and actuator wedge  408  are further depressed so as to displace the cam wheel actuator  415  rearwardly such that the shorter actuator contacting surface  416   a  engages the in-turned end of micro switch contact spring  417   a  to actuate micro switch  418   a . This permits a current suitable for tissue cutting to flow through the wires along the effector rod to the diathermy hook. On releasing, the actuator cam wheel  415  is returned to its rest position by a return spring (not shown) contained in cavity  421 , and acting on the rear of the actuator cam wheel  415  and the end of a cavity in the switch block  419 . 
     It will readily be apparent that numerous modifications and alterations may be made to the surgical instruments shown in the drawings and specifically described above, without departing from the principles underlying this invention. All such modifications and alterations are intended to be embraced by this application.