referring to fig1 , the instrument 10 has an inner member 11 and an outer member 12 . the members 11 and 12 are connected through an open lockbox 13 which has a gap between flanges 33 . the terms “ inner ” and “ outer ” are used to distinguish the members 11 and 12 , and their component parts , according to the members &# 39 ; respective positions at the open lockbox 13 . the inner member 11 is fitted generally within the inner surfaces of the open lockbox 13 and is captured by the flanges 33 . the outer member generally forms the outside surfaces of the open lockbox 13 . the inner member 11 has an inner shank 14 , an inner jaw 16 , and an inner ring handle 20 . similarly , the outer member 12 has an outer shank 15 , an outer jaw 17 , and an outer ring handle 21 . the ring handles , 20 and 21 , are designed for a surgeon to hold and manipulate the instrument 10 . the jaws , 16 and 17 , are designed to grasp tissue between the opposing seal surfaces 18 and 19 . each shank , 14 and 15 , has a respective ratchet stub 24 or 25 . ratchet teeth , 26 and 27 , are designed to interlock in a manner that hold the members , 11 and 12 , in position . the shanks 14 and 15 are deflected in the manner of a cantilever spring when the jaws are forced together by the surgeon . the deflection of the shanks 14 and 15 produces a spring restoring force that can be opposed by interlocking the ratchet teeth , 26 and 27 . the instrument 10 does not cause a short circuit when the ratchet teeth , 26 and 27 , are interlocked . this is accomplished by a suitable selection and placement of electrically insulating materials . in the preferred embodiment , the ratchet teeth 26 and 27 are composed of a polymeric material which is press - fit into the ratchet stubs 24 and 25 . a ratchet screw 28 is used in the preferred embodiment to secure the ratchet teeth 26 and 27 into the ratchet stubs 24 and 25 . during manufacture , the ratchet teeth 26 and 27 may be formed from a blank after the blank has been press fit into the ratchet stubs 24 and 25 . in a second embodiment , one of the members , 11 or 12 , includes the ratchet stub and ratchet teeth as in integral part of the member , while the other member , 12 or 11 , has an insulative layer that prevents a short circuit between the members 11 and 12 when the ratchets are engaged . the open lockbox 13 has the function of providing a pivoting joint for the members 11 and 12 . in addition , the flanges 33 provide lateral support to help maintain alignment of the jaws 16 and 17 . closed lockbox designs are typically used in standard hemostat designs , wherein an inner member is completely captured through a slot in an outer member . the open lockbox 13 in present invention has a gap between the flanges 33 that is different from a closed lockbox design . the gap in the open lockbox 13 provides convenient access to install an electrically insulated pivot . the electrically insulated pivot in the present invention comprises a shoulder washer 29 supporting a lockbox screw 30 . the shoulder washer 29 is composed of an electrically insulative material that prevents a short circuit between the members 11 and 12 . a large screw cap 31 fits over the head of the lockbox screw 30 . a small screw cap 32 fits over the threaded end of the lockbox screw 30 . each member 11 and 12 is connected to a pole of a bipolar electrosurgical generator . electrical connectors 22 and 23 are located on the ring handles 20 and 21 to provide a convenient point of connection . the members 11 and 12 are formed of an electrically conductive material , such as stainless steel . the exposed surfaces of the members , except for the connectors 22 and 23 and the seal surfaces 18 and 19 , are preferably spray coated with an insulating material . the characteristics of the bipolar electrosurgical current are determined by the design of the electrosurgical generator . in the preferred embodiment , the generator will have an output wherein the peak - to - peak voltage will not exceed 130 volts . this is because higher voltages can cause sparking which results in localized burning of tissue which may result in a failure of the tissue weld . the preferred embodiment has the generator capable of producing high frequency output current of at least 2 amps rms . high electrical current is important because it heats the tissue sufficiently to melt the collagen . lower electrical currents will often produce weak tissue welds with low bursting strength . during operation , the instrument 10 is used to grasp tissue between the seal surfaces 18 and 19 . the surgeon squeezes the ring handles 20 and 21 together , causing pressure to be applied to the tissue . the ratchet teeth 26 and 27 are interlocked at the appropriate ratchet setting , depending on the tissue type and tissue thickness . bipolar electrosurgical current is applied through the instrument and the tissue to cause the tissue to fuse . the jaws 16 and 17 have a structure and cross - section that resist bending under load . thus , for purposes of engineering analysis , the shank portions 14 and 15 act as a cantilever supported beam once the seal surfaces 18 and 19 have been mated . the length of this idealized cantilever beam extends from the lockbox screw 30 to the location of the respective ratchet subs 24 or 25 . it is possible to model each shank as a cantilever spring having a spring constant . each ratchet position is designed to transmit a particular closure force to the jaws 16 and 17 against the action of the restoring force of the cantilever spring . the spring constant is generally a function of young &# 39 ; s modulus of the shank material , the moment of inertia of the shank , and the length of the shank portion 14 and 15 . when the jaws 16 and 17 of the instrument 10 are closed together , each shank 14 and 15 approximates a cantilever - supported beam . it is properly assumed that the deflection of each shank 14 and 15 remains within the linear range of its stress - strain curve . the behavior of such a beam is well known to materials engineers . a large spring constant will result in large closure forces between the seal surfaces 18 and 19 . similarly , a small spring constant will result in a small closure forces between the seal surfaces 18 and 19 . the choice of a proper spring constant will depend on the length of the shank 14 or 15 and the distance between ratchet stops 26 and 27 . experimental results in animal studies suggest that the magnitude of pressure exerted on the tissue by the seal surfaces 18 and 19 is important in assuring a proper surgical outcome . tissue pressures within a working range of about 3 kg / cm 2 to about 16 kg / cm 2 and , preferably , within a working range of 7 kg / cm 2 to 13 kg / cm 2 have been shown to be effective for sealing arteries and vascular bundles . tissue pressures within the range of about 4 kg / cm 2 to about 6 . 5 kg / cm 2 have proven to be particularly effective in sealing arteries and tissue bundles . it is desirable to tune the spring constant of the shank portions 14 and 15 , in conjunction with the placement of the ratchet teeth 26 and 27 , such that successive ratchet positions will yield pressures within the working range . in one embodiment , the successive ratchet positions are two millimeters apart . pressure on the tissue can be described in several ways . engineers will recognize that the amount of pressure exerted on the tissue depends on the surface area of the tissue that is in contact with the seal surfaces . in the one embodiment , the width of each seal surface 18 and is in the range of 2 to 5 millimeters , and preferably 4 millimeters width , while the length of each seal surface 18 and 19 is preferably in the range of 10 to 30 millimeters . it has been found through experimentation that at least one interlocking ratchet position preferably holds the closure force between approximately 400 and 650 grams per millimeter of seal surface width . for example , if the width of the seal surface 18 and 19 is 4 millimeters , the closure force is preferably in the range of 1600 grams to 2600 grams . in one embodiment , the closure force is 525 grams per millimeter of width , yielding a closure force of 2100 grams for a 4 millimeter width seal surface 18 and 19 . it has been found experimentally that local current concentrations can result in an uneven tissue effect , and to reduce the possibility of this outcome , each seal surface 18 and 19 has a radiused edge in the preferred embodiment . in addition , a tapered seal surface 18 and 19 has been shown to be advantageous in certain embodiments because the taper allows for a relatively constant pressure on the tissue along the length of the seal surfaces 18 and 19 . the width of the seal surfaces 18 and 19 is adjusted , in certain embodiments , wherein the closure force divided by the width is approximately constant along the length . in one embodiment , a stop 37 , made from insulative material , is located in the instrument to maintain a minimum separation of at least about 0 . 03 millimeters between the seal surfaces 18 and 19 , as shown in fig1 . the stop 37 reduces the possibility of short circuits between the seal surfaces 18 and 19 . in another embodiment , the forceps instrument 10 includes a second or alternative stop 47 which is designed to maintain a minimum separation of at least about 0 . 03 millimeters between the seal surfaces 18 and 19 , as shown in fig1 . it is envisioned that the stop may be positioned proximate the lockbox 13 , proximate the lockbox screw 30 or adjacent the opposable seal surfaces 18 and 19 . preferably , the stop 37 and / or the stop 47 maintain a separation distance within the range of about 0 . 03 millimeters to about 0 . 16 millimeters . in certain embodiments , as shown in fig1 , the seal surfaces 18 and 19 comprise conductive regions 38 and insulative regions 39 arranged such that each conductive region 38 opposes an insulative region 39 when the opposable seal surfaces 18 and 19 are mated in opposition . the seal surfaces 18 and 19 , in certain embodiments , may be removable from its respective member 11 or 12 by standard mechanical interfaces , such as a pin and socket arrangement . fig2 shows an embodiment for a thirty - two millimeter curved seal surface . fig3 is a side view of fig2 . the members 11 and 12 in fig2 are formed from american iron and steel institute ( aisi ) 410 stainless steel . the length and cross sectional area of the shank portions 14 and 15 are shown in fig2 and 3 to provide a spring constant of twenty - five pounds per inch deflection . the embodiment shown in fig4 and 5 has a twenty millimeter curved seal surface . the embodiment shown in fig6 and 7 has a thirty - two millimeter straight seal surface . each embodiment in fig2 through 7 is designed to have the look and feel of a standard hemostat . fig8 , 9 and 10 show three views of a shoulder pin 34 that can be used , in certain embodiments , instead of the lockbox screw 30 to connect the members 11 and 12 . the shoulder pin 34 has at least one ramp surface 35 that engages one of the members 11 or 12 to cause increasing mechanical interference as the jaws 16 and 17 move toward each other . in one embodiment , the shoulder pin 34 forms part of the open lockbox 13 to aid alignment of the seal surfaces 18 and 19 . in another embodiment , the shoulder pin 34 is used without an open - lockbox 13 , and movably pins the members 11 and 12 together without a flange 33 . the interference fit may require the calibration of the instrument 10 to insure that the applied force will be sufficient to provide the appropriate working pressure between the seal surfaces 18 and 19 . a slightly higher spring constant in the shank portions 14 and 15 is preferably used , depending on the level of interference caused by the shoulder pin . a method of using the bipolar electrosurgical instrument comprises the following steps . a surgeon grasps the ring handles 20 and 21 on the instrument 10 to manipulate the jaws 16 and 17 . a vessel or vascular tissue is compressed between the opposable seal surfaces 18 and 19 . the opposable seal surfaces 18 and 19 preferably come together in aligned opposition due to the alignment action of the open - lockbox 13 , or in certain embodiments due to the alignment action of the shoulder pin 34 . the surgeon further deflects the shank portions 14 and 15 of the members 11 and 12 to engage the ratchet teeth 26 and 27 . the engagement of the ratchet teeth 26 and 27 hold the shank portions 14 and 15 in their deflected positions to provide a constant spring force that is transmitted as a closure force to the jaws 16 and 17 . an electrosurgical generator is connected to the instrument 10 through connectors 22 and 23 on the ring handles 20 and 21 . an electrical switch is used to close a circuit between the generator and the instrument 10 . the switch may be a footswitch such as valleylab &# 39 ; s catalog number e6009 , available from valleylab inc ., boulder colo . the electrosurgical current flows through an electrically conductive path on each of the inner and outer members 11 and 12 between its respective electrical connector , 22 or 23 , and its respective seal surface , 18 or 19 . an electrically insulative coating 36 substantially covers each member 11 and 12 to protect the surgeon against electrical arcs . an insulative sheath may also be used to cover the members or the component parts thereof , i . e ., handles 20 , 21 , shanks 14 and 15 and the outer surfaces ( non - opposing surfaces ) of the jaw members 16 , 17 . it is envisioned that the outer surface of the jaw members 16 and 17 may include a nickel - based material , coating , stamping , metal injection molding which is designed to reduce adhesion between the jaw members ( or components thereof ) with the surrounding tissue during activation and sealing . moreover , it is also contemplated that other components such as the shanks 14 , 15 and the ring handles 20 , 21 may also be coated with the same or a different “ non - stick ” material . preferably , the non - stick materials are of a class of materials that provide a smooth surface to prevent mechanical tooth adhesions . it is also contemplated that the tissue sealing surfaces 18 and 19 of the jaw members 16 and 17 , respectively , may be manufactured from one ( or a combination of one or more ) of the following “ non - stick ” materials : nickel - chrome , chromium nitride , medcoat 2000 manufactured by the electrolizing corporation of ohio , inconel 600 and tin - nickel . for example , high nickel chrome alloys and ni200 , ni201 (˜ 100 % ni ) may be made into electrodes or sealing surfaces by metal injection molding , stamping , machining or any like process . in addition these materials preferably include an optimal surface energy for eliminating sticking due in part to surface texture and susceptibility to surface breakdown due electrical effects and corrosion in the presence of biologic tissues . it is envisioned that these materials exhibit superior non - stick qualities over stainless steel and should be utilized on the instrument in areas where the exposure to pressure and rf energy can create localized “ hot spots ” more susceptible to tissue adhesion . as can be appreciated , reducing the amount that the tissue “ sticks ” during sealing improves the overall efficacy of the instrument . the tissue sealing surfaces 18 and 19 may also be “ coated ” with one or more of the above materials to achieve the same result , i . e ., a “ non - stick surface ”. for example , nitride coatings ( or one or more of the other above - identified materials ) may be deposited as a coating on another base material ( metal or nonmetal ) using a vapor deposition manufacturing technique . one particular class of materials disclosed herein has demonstrated superior non - stick properties and , in some instances , superior seal quality . for example , nitride coatings which include , but not are not limited to : tin , zrn , tiain , and crn are preferred materials used for non - stick purposes . crn has been found to be particularly useful for non - stick purposes due to its overall surface properties and performance . other classes of materials have also been found to reducing overall sticking . for example , high nickel / chrome alloys with a ni / cr ratio of approximately 5 : 1 have been found to significantly reduce sticking in bipolar instrumentation . one particularly useful non - stick material in this class is inconel 600 . bipolar instrumentation having electrodes made from or coated with ni200 , ni201 (˜ 100 % ni ) also showed improved non - stick performance over typical bipolar stainless steel electrodes . it is to be understood that the above described embodiments are only illustrative of the application of the principles of the present invention . numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention . the appended claims are intended to cover such modifications and arrangements .
a bipolar electrosurgical instrument has opposable seal surfaces on its jaws for grasping and sealing vessels and vascular tissue . inner and outer instrument members allow arcuate motion of the seal surfaces . an open lockbox provides a pivot with lateral support to maintain alignment of the lateral surfaces . ratchets on the instrument members hold a constant closure force on the tissue during the seal process . a shank portion on each member is tuned to provide an appropriate spring force to hold the seal surfaces together . during surgery , the instrument can be used to grasp and clamp vascular tissue and apply bipolar electrosurgical current through the clamped tissue . in one embodiment , the seal surfaces are partially insulated to prevent a short circuit when the instrument jaws are closed together . in another embodiment , the seal surfaces are removably mounted on the jaws .