Covidien 2002
`Ethicon Endo-Surgery, Inc. v. Covidien AG
`IPR2015-01275
`
`

`
`EP 0 986 990 A1
`
`Description
`
`BACKGROUND OF THE INVENTION
`
`Surgical procedures necessarily involve the
`[0001]
`transection of vessels as surgeons seek to explore,
`remove, or repair tissue defined systems. Transection is
`carried out with a variety of cutting instruments ranging
`from a cold scalpel to electrosurgical devices. As such
`vessels are cut, it generally is necessary to accommo-
`date bleeding by microsurgical or similar approaches, or
`where smaller vessels are encountered, by a sealing
`and congealing procedure. This latter procedure typi-
`cally is carried out by heating the involved tissue and flu-
`ids through the application of electrical current at RF
`frequencies developed by an electrosurgical generator.
`Effective sealing of smaller vessels is important to sur-
`gical procedures, inasmuch as even a small blood flow
`not only can obscure the surgeon's field of view, but also
`may accumulate with the risk of hematoma or significant
`blood loss.
`
`[0002] While a variety of electrosurgical instruments
`have been developed to achieve hemostasis, many are
`of marginal effectiveness for certain surgical tasks, par-
`ticularly those involving small vessels and small, highly
`localized tissue regions of interest. To carry out such
`somewhat delicate surgical procedures requisite to
`such regions, practitioners typically employ forceps,
`instruments of common utility which, in effect, represent
`a thin extension of the thumb and forefinger function of
`the surgeon. Forceps generally serve to provide a tissue
`or vessel grasping function, having working ends or tip
`portions which may be of diminutive dimension enabling
`the surgeon to locate and grasp small vessels which
`have a tendency to retract into tissue following their
`being cut. By applying bipolar, RF current from a noted
`electrosurgical generator across the outer working end
`tips of the forceps, a sealing or congealing of tissue or
`vessels can be achieved without substantial riskto adja-
`cent tissue. In effect, the well defined tips of the bipolar
`forceps provide a more precise attainment of hemosta-
`sis.
`
`[0003] Another surgical application for bipolar forceps
`has been referred to as "coagulative paintihg" where
`typically, the side surfaces of the electrically active tip
`regions of the forceps‘ fines are drawn over the surface
`of membranous tissue such as the mesentery. Done
`properly, this action congeals the small, microvessels
`within such thin tissues.
`
`Electrosurgically driven forceps heretofore
`[0004]
`made available to surgeons, however, have exhibited
`operational drawbacks, which,
`in turn, have compro-
`mised their surgical effectiveness. To effectively carry
`out hemostasis, the electrically operative tips of the for-
`ceps should efficiently conduct a proper current flow
`through the tissue grasped. When that current is insuffi-
`cient, coagulation of the tissue or vessel is compro-
`mised. When the current is excessive, correspondingly
`
`excessive heating occurs with a potential for the gener-
`ation of damaging electrical arcing. Excessive heating
`also results in the phenomenon of tissue and blood
`coagulum sticking to the surface of the instrument. This
`results in the development of a layer of increased elec-
`trical impedance between the electrodes of the instru-
`ment and that
`tissue which may subsequently be
`grasped for the purpose of treatment. Additionally, such
`sticking tissue evokes a disruption of the coagulated
`surface which,
`in itself, may compromise the intended
`hemostatic
`effect. Consequently,
`bipolar
`forceps
`designs have been seen to incorporate highly polished
`electrode surfaces for the purpose of
`reducing the
`extent of tissue sticking as well as to facilitate their
`cleaning when sticking does occur. Unfortunately, when
`such modification of the forceps is carried out, the origi-
`nal grasping function of the forceps is substantially com-
`promised.
`
`[0005] Another problem encountered with the use of
`bipolar forceps of conventional design has been associ-
`ated with their use in conjunction with thin tissue. As
`such tissue is grasped between the opposed bipolar
`electrodes of the instruments, only a low tissue related
`impedance is witnessed by the electrosurgical genera-
`tor associated with the instrument, which conventionally
`reacts to decrease its output toward zero as tissue
`impedance approaches a zero value.
`[0006] Use of the bipolar forceps also becomes prob-
`lematic in conjunction with the noted "coagulative paint-
`ing" procedure where the side surfaces
`of
`the
`instrument are drawn across the surface of membra-
`
`nous tissue. The electrical model involved in this proce-
`dure is one wherein current is caused to flow from the
`
`side surface of one fine, thence across a thin layer of tis-
`sue to the oppositely disposed spaced apart electrically
`operant tine. This calls for maintenance of the spacing
`between the two fines to avoid short circuiting the sys-
`tem and for a control over what is,
`in effect, a moving
`line source of heat applied to the affected tissue. Very
`often, a misjudgment may lead to the tearing of tissue in
`the procedure. Of course,
`it also is necessary for the
`surgeon to maintain a spacing between tine electrodes
`of the instrument to achieve requisite performance.
`[0007] Approaches to minimizing the phenomenon of
`tissue sticking to the operative tips of bipolar forceps
`have been advanced by the medical instrument indus-
`try. For example, designs have propounded the use of
`forceps’ legs having cross-sectional areas and which
`exhibit conductivity sufficiently high to maintain electri-
`cally operative portions for
`the instruments below
`threshold temperatures considered to evoke tissue
`sticking. Similarly, the temperature of the grasping tips
`of the forceps has been reduced by enlarging the cross-
`sectional radii of the forceps sufficiently to maintain cur-
`rent density and resultant tissue heating below the
`threshold temperature evoking sticking. See in this
`regard, U.S. Pats. Nos. 3,685,518; 4,492,231; and
`5,196,009. However, the election of a large cross-sec-
`
`

`
`EP 0 986 990 A1
`
`tional area at the grasping tips of the forceps for pur-
`poses of heat conduction compromises the basically
`sought precision of the forceps type instrument with
`respect to grasping and localized coagulation of smaller
`blood vessels, e.g. vessels smaller than about 1 mm in
`diameter.
`
`[0008] An approach to limiting the heating of the tissue
`or vessel being coagulated with bipolar forceps has
`been to utilize a layer of a ceramic material having a
`thermal conductivity much lower than that of the metal
`used in the structure of the forceps. U.S. Pat. No.
`5,151,102 describes such an arrangement wherein a
`plurality of silver filled epoxy electrodes are embedded
`within the ceramic coatings. However, Joulean heating
`with bipolar systems occurs within the tissue which, for
`such arrangements, has no effective pathway through
`which to dissipate, resulting in an enhancement of the
`sticking problem which now occurs at the ceramic layer.
`[0009]
`To regain the originally desired grasping fea-
`ture of forceps, the utilization of a roughened or tooth-
`like surface in conjunction with the electrically operative
`ends of the forceps has been proposed as represented
`in U.S. Pats. Nos. 5,330,471 and 5,391,166. By dispos-
`ing a layer of insulation on the teeth of one or both of the
`grasping surfaces, electrical current only passes along
`the sides of the electrode surfaces which are outwardly
`disposed from the grasping surfaces. Thus, the utility of
`the forceps is compromised to the extent that only
`thicker tissues can be grasped and coagulated effi-
`ciently. In general, serrated or multi—pyramidally config-
`ured grasping surfaces prove difficult to clean during
`surgery due to the recesses and grooves which tend to
`trap tissue debris and coagulum.
`[0010] U.S. Pat. No. 5,403,312 describes a combina-
`tion of an electrosurgical forceps form of instrument
`which additionally carries out a stapling function.
`Intended for the grasping of thicker tissue components,
`the device described employs operative forceps tips
`with mutually offset or staggered electrode regions suit-
`able for more extended thickness‘ of tissue as opposed
`to thin tissue. By mounting the electrode regions within
`a plastic support member, an otherwise desired feature
`for heat removal is compromised permitting the elec-
`trodes to reach temperatures during tissue coagulation
`that can exceed sticking threshold temperatures with
`the noted undesirable cleaning requirements.
`[0011]
`Some investigators have proposed the utiliza-
`tion of temperature sensors such as thermocouples
`which are incorporated within the bipolar forceps instru-
`ments. Propounded in U.S. Pats. Nos. 5,443,463;
`4,938,761; and 5,540,684, the approach requires that a
`special control system be provided which precludes the
`utilization of the ubiquitous conventional electrosurgical
`generator currently available in operating theaters
`throughout the world. Further, the othenlvise simple con-
`struction of the forceps must be abandoned to a less
`desirable, highly complex instrumentation with such an
`approach.
`
`BRIEF SUMMARY OF THE INVENTION
`
`invention is addressed to
`The present
`[0012]
`improved surgical forceps and the methods by which
`they may be used with the bipolar outputs of electosur-
`gical generators of conventional design and which
`achieve a highly efficient hemostasis of grasped tissue
`or vessels. This result is realized through the develop-
`ment of current paths exhibiting desirable current densi-
`ties and more ideal current path configurations. These
`forceps employ electrically insulative spacer regions or
`assemblies in conjunction with the mutually inwardly
`facing electrically conductive tissue grasping surfaces
`of the two movable tines of the instruments. The spacer
`arrangement serves to space the tissue grasping sur-
`faces apart an optimum distance, T, when substantially
`in a closed orientation. Configurations for this spacer
`assembly achieve the ideal current path lengths devel-
`oping hemostasis without the presence of recurrent
`sticking phenomenon. This avoidance of sticking is
`achieved while the grasping feature of the forceps is not
`compromised and an ability to clean them effectively
`and efficiently is achieved.
`[0013]
`These spacer regions or assemblies of the
`present
`invention then provide for an importantly
`improved grasping of tissue even though the exposed
`metal portions of the grasping surfaces are made to
`have smooth surfaces in order to minimize sticking to
`tissue or coagulum and to facilitate their cleaning when
`tissue debris or coagulum does accumulate.
`[0014]
`In a preferred embodiment for the forceps, the
`two tines thereof are formed having inwardly disposed
`and highly polished electrically conductive tissue grasp-
`ing surfaces. Located upon one of these surfaces, for
`example,
`is an array of very thin electrically insulative
`regularly spaced discrete strips of electrically insulative
`material such as alumina. These strips are quite dimin-
`utive and barely tactilely discernible, and achieve the
`noted spacing distance, T, having a minimum value of
`about 0.005 inch. A variety of configurations for the
`spacer regions or assemblies are disclosed providing
`for the achievement of the noted operational improve-
`ments.
`
`Preferably, the forceps of the invention are fab-
`[0015]
`ricated such that each tine incorporates a thermally
`conductive material such as copper in an amount suffi-
`cient to maintain the temperature at the tip region during
`typical use below about 60°C to 85°C. This temperature
`regime for the forceps is predicated upon a conventional
`duty cycle of use and is achieved with practicality
`through the use of laminar composites of thermally con-
`ductive copper and mechanically stronger, particularly,
`higher modulus stainless steel. The electrically insula-
`tive spacers are fashioned, for example, of aluminum,
`which readily is deposited upon one or both of the
`inwardlyfacing stainless steel surfaces. Biocompatibility
`of the entire forceps assemblage is maintained through
`an electro-deposited biocompatible metal coating such
`
`

`
`EP 0 986 990 A1
`
`as chromium which coats both the stainless steel and
`
`copper laminate while not affecting the alumina spacer.
`[0016]
`Another aspect of the invention looks to an
`improvement
`of
`that
`feature
`of
`surgical
`forceps
`employed to achieve the noted coagulative painting. In
`this regard, the tines are formed having a generally rec-
`tangular cross section at their tip regions. This cross
`section enhances the available current path deriving
`area of the side surfaces for purposes of coagulative
`painting. Additionally, the forceps may be made with rel-
`atively blunt nose components to permit a more local-
`ized but still effective coagulative painting.
`[0017] Other objects of the invention will, in part, be
`obvious and will, in part, appear hereinafter.
`[0018]
`The invention, accordingly, comprises the
`apparatus and method possessing the construction,
`combination of elements, arrangement of parts, and
`steps which are exemplified in the following detailed
`description.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0019]
`
`Fig. 1 is a perspective view of a bipolar forceps cou-
`pled by a bipolar cable to the bipolar terminals of an
`electrosurgical generator;
`Fig. 2 is a partial sectional view of a prior art for-
`ceps;
`Fig. 3 is a sectional view taken through the plane 3-
`3 in Fig. 2;
`Fig. 4 is a partial sectional view of another forceps
`of the prior art;
`Fig. 5 is a graph relating load impedance to normal-
`ized power for two typically encountered electrosur-
`gical generators;
`Fig. 6 is a partial sectional view of forceps of the
`prior art;
`Fig. 7 is a sectional view taken through the plane 7-
`7 seen in Fig. 6;
`Fig. 8 is a partial sectional view of one embodiment
`of forceps and method of their use according to the
`invention with portions exaggerated to reveal struc-
`ture;
`Fig. 9 is a sectional view taken through the plane 9-
`9 in Fig. 8;
`Fig. 10 is a plan view of a tip region of a tine of the
`forceps described in Fig. 8;
`Fig. 11 is a partial sectional view of the forceps
`shown in Fig. 8 with a full closure orientation;
`Fig. 12 is a partial sectional view of a preferred
`embodiment of the invention with portions exagger-
`ated to reveal structure;
`Fig. 12A is a partial sectional view according to Fig.
`12 showing a laminar composite structure of line
`components;
`Fig. 13 is a sectional view taken through the plane
`13-13 in Fig. 12;
`
`Fig. 14 is a plan view of the forceps of Fig. 12 with-
`out exaggerated dimension;
`Fig. 15 is a plan view of a tip region of a tine of the
`forceps of another embodiment of the invention;
`Fig. 16 is a sectional view of forceps incorporating
`the tip region shown in Fig. 15;
`Fig. 17 is a plan view of the tip region of a tine of
`another embodiment of forceps according to the
`invention;
`Fig. 18 is a plan view of the tip region of a line of
`another embodiment of forceps according to the
`invention;
`Fig. 19 is a sectional view taken through the plane
`19-19 in Fig. 18;
`Fig. 20 is a partial sectional view of another embod-
`iment of forceps according to the invention;
`Fig. 21 is a partial sectional view of a tooth-like
`structure seen in Fig. 20;
`Fig. 22 is a partial sectional view of another embod-
`iment of the invention with portions exaggerated to
`reveal structure;
`Fig. 23 is a partial sectional view of one tip region of
`the embodiment of Fig. 22;
`Fig. 24 is a partial sectional view of the embodiment
`of Fig. 22 showing tissue grasping surface spacing;
`Fig. 25 is a partial sectional view of another embod-
`iment of the invention with portions exaggerated to
`reveal structure;
`Fig. 26 is a partial sectional view of the embodiment
`of Fig. 25 showing relative grasping surface spac-
`ing;
`Fig. 26A is a partial sectional view of the embodi-
`ment of Fig. 25 showing an alternate arrangement
`or an electrically insulative spacer assembly;
`Fig. 27 is a pictorial representation of the side sur-
`face mode and method of utilization of forceps
`according to the invention;
`Fig. 28 is a sectional view of forceps according to
`the invention employed in the manner shown in Fig.
`27;
`Fig. 29 is a sectional view of forceps according to
`the prior art being utilized in the mode shown in Fig.
`27;
`Fig. 30 is a partial sectional view of forceps accord-
`ing to the invention being used in another version of
`the mode described in connection with Fig. 27;
`Fig. 31 is a sectional view of the tip region of for-
`ceps according to the invention for supporting a
`geometric analysis thereof; and
`Fig. 32 is a sectional view of the tip region of for-
`ceps according to the prior art for supporting a com-
`parative analysis with respect to Fig. 31.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`The bipolar electrosurgical forceps of the
`[0020]
`invention perform in conjunction with conventional elec-
`trosurgical generators having bipolar outputs. These
`
`

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`EP 0 986 990 A1
`
`generators are common in essentially all operating
`theaters and generate radio frequency voltage or power
`typically in response to the depression of a foot pedal on
`the part of the surgeon. Referring to Fig. 1, such a gen-
`erator is represented generally at 10. Device 10 pro-
`vides a bipolar, as opposed to monopolar, output at
`receptacles 12 and 14. The applied voltage level or
`power level at receptacles or outputs 12 and 14 may be
`selected by the user by adjustment of a control knob as
`at 16. Activation of the power outputs at receptacles 12
`and 14 is provided by a foot pedal switch 18 which is
`connected to generator 10 via a cable 20. Outputs 12
`and 14 are coupled to the respective plugs 22 and 24 of
`a bipolar cable 26, the opposite end of which terminates
`in two receptacles 28 and 30. Receptacles 28 and 30
`are electrically connected with corresponding connector
`posts (not shown) which are recessed within a connec-
`tor housing 32 of a bipolar forceps represented gener-
`ally at 34. Forceps 34 are formed of two, somewhat
`resilient thermally and electrically conductive tines or
`support members 36 and 38 which are mounted within
`the connector housing 32 and extend longitudinally out-
`wardly therefrom in a mutually angularly oriented fash-
`ion to respective tip regions 40 and 42.
`lnwardly
`disposed in mutual facing relationship at the tip regions
`40 and 42 are electrically conductive flat tissue grasping
`surfaces represented, respectively, at 44 and 46. These
`surfaces 44 and 46 are coated with an electrically insu-
`lative material such as alumina, which,
`in turn, for the
`present embodiment
`is gang ground to produce a
`sequence of stripes or parallel bands of alternating
`electrically conductive metal and electrically insulative
`material. The stripes for surfaces 44 and 46 are mutu-
`ally aligned such that when the tines 38 and 36 are
`squeezed to a closed or tissue grasping orientation, the
`electrically conductive stripes or bands at surfaces 44
`and 46 move toward a mutual contact while the electri-
`
`cally conductive surfaces adjacent to them are mutually
`aligned such that a directly confronting current path
`through tissue may be developed between them. To pro-
`vide for bipolar performance, the surfaces of fines 36
`and 38 located reanrvardly of the tip regions 40 and 42
`are coated with an electrically insulative material such
`as a nylon. In general, forceps as at 34 are constructed
`to be sterilizable by autoclaving or the like. Tines 36 and
`38 may be mounted within the connector housing 32
`using an epoxy potting agent within the interior of a
`plastic shell. Other mounting techniques will occur to
`those who are art-skilled.
`
`Looking to Figs. 2 and 3, an approach to the
`[0021]
`design of bipolar surgical forceps in the past is revealed
`with the purpose of analysis.
`In the figure, forceps 52
`are fashioned having two electrically conductive tines
`54 and 56, the rearwardly disposed portions of which
`are coated with an electrically insulative polymeric
`material as shown, respectively, at 58 and 60. The elec-
`trically operant tip regions of fines 54 and 56 are shown,
`respectively at 62 and 64. Tip regions 62 and 64 are
`
`configured having flat bare metal and polished, tissue
`grasping surfaces shown, respectively, at 66 and 68,
`and the cross-sections of the tip regions are somewhat
`semi-circular in configuration. Surfaces 66 and 68 are
`shown grasping tissue 70. Because of the smooth, all
`metal contact surfaces 66 and 68, upon actuation of the
`electrosurgical system by, for example, closing a switch
`such as at foot pedal 18 (Fig. 1), a radio frequency volt-
`age difference is applied across the tip regions 62 and
`64, and electrical current is caused to flow, for the most
`part, through the portion of tissue 70 in contact with the
`surfaces 66 and 68. This heats such tissue or blood ves-
`
`sel 70 sufficiently to carry out its thermocoagulation.
`While the provision of smooth grasping surfaces 66 and
`68 functions advantageously to minimize the sticking of
`tissue or blood coagulum to such surfaces,
`their
`smoothness defeats the basic function of forceps which
`is to grasp tissue and hold it. Often, the tissue or blood
`vessel grasped at 70 slips out of the engagement before
`coagulation can be carried out. While the current pass-
`ing through tissue 70 directly confronts it and passes
`therethrough to carry out Joulean heating as repre-
`sented by dashed current flux lines 72, the larger con-
`tact area has been observed to promote higher current
`levels which, in turn, lead to higher heating rates which
`promotes the sticking of tissue or coagulum to the
`grasping surfaces 66 and 68. Often, when the tip
`regions 62 and 64 are opened to release the thus-coag-
`ulated tissue or vessels, sticking causes an avulsion of
`the sealing layer of a coagulum to somewhat defeat the
`procedure.
`In addition, even a very thin layer of desic-
`cated tissue residue or blood coagulum will introduce a
`large electrical resistance at the interface between the
`tip regions 62 and 64 and any subsequent tissue or
`blood vessel which is grasped. This detracts from the
`operational capability of the instrument and calls for
`cleaning or changing instruments during the surgical
`procedure. Where a very thin layer of tissue is grasped
`or a very small vessel
`is grasped between the tip
`regions 62 and 64, a reduced load impedance is wit-
`nessed by the associated electrosurgical generator as
`at 10.
`It is the characteristic of such generators that as
`such load impedance reduces and approaches zero,
`the output voltage of the generator will decrease and
`approach zero volts to the extent that no voltage differ-
`ence will be applied across the tip regions 62 and 64. It
`follows that no current for carrying out Joulean heating
`will flow through the grasped tissue or blood vessel and
`no coagulation can be achieved.
`
`Particularly where miniature forceps are uti-
`[0022]
`lized, the bare tissue grasping surfaces 66 and 68 may
`be driven into mutual contact to cause a short circuit.
`
`This is illustrated in connection with Fig. 4 where a
`smaller or more diminutive tissue component 74 is seen
`being grasped between the grasping surfaces 66 and
`68, however, those surfaces are in contact with each
`other in the vicinity of location 76 to cause a short
`circuiting. Of course, arcing is a possibility as the sur-
`
`

`
`EP 0 986 990 A1
`
`10
`
`faces closely approach each other. Note that the electri-
`cally insulative coatings 58 and 60 are in contact under
`this geometry but often will not prevent
`the short
`circuiting.
`
`To achieve a performance of bipolar forceps
`[0023]
`which approaches optimal, it is necessary to appreciate
`the operational characteristics of the ubiquitous electro-
`surgical generators which are present in essentially all
`operating theaters. While numerous brands of these
`generators are extant throughout the world, they, for the
`most part, have a somewhat similar output characteris-
`tic. Referring to Fig. 5, normalized curves relating load
`impedance to power representative of two convention-
`ally
`encountered
`electrosurgical
`generators
`are
`revealed at 80 and 82. Curves 80 and 82 have similar
`
`shapes at relatively lower load impedances and, as in
`the case of most electrosurgical generators on the mar-
`ket, a maximum power output is achieved in the neigh-
`borhood of 100 ohms. As load impedance increases
`beyond peak value, then as evidenced by the curves,
`the normalized power reduces and will fall off with a
`characteristic somewhat associated with each individ-
`
`if the load impedance increases
`ual generator. Thus,
`excessively, power falls off and inefficient coagulation is
`the result. Similarly, as the load impedance approaches
`zero, to the point of shorting out, no power is available
`also. Efficient coagulation is found to occur with load
`impedances somewhere in the range of 10 to 150
`ohms, and the goal of the instant design is to achieve
`efficient coagulation for essentially most circumstances
`encountered in surgery with bipolar forceps while avoid-
`ing a sticking phenomena.
`[0024] With the above characteristic curves in mind, it
`also should be observed that the electrically operant,
`tissue engaging grasping regions of the forceps will per-
`form in conjunction with a load resistance which,
`in its
`simplest form, may be expressed as follows:
`
`R=%'
`
`(1)
`
`where A is the total area through which current can flow,
`i.e.
`it is the area which the current delivering surface
`confronts including that region which may flare out from
`the edge of an electrode defining portion of the forceps
`tissue contacting surface. L is the length of the pathway
`taken by the current, and p is the characteristic resistiv-
`ity of the tissue engaged.
`[0025] The undesirable phenomena of sticking is not
`necessarily a result of the total power delivered from the
`forceps to the tissue but is a function of the power den-
`sity or power per unit area delivered from the electrode
`surfaces. Thus, if the power density is controlled at the
`operational surfaces of the instruments, sticking may be
`minimized by an arrangement where current is being
`distributed over larger surface areas. A further aspect is
`concerned with the efficiency of delivering this current
`into the tissue to achieve a Joulean heating of it. This
`delivery should be the most efficient for carrying out
`
`coagulation and sealing. Coagulation should occur with
`the least amount of dwell time and be so localized as
`
`not to adversely affect tissue which is adjacent that
`being coagulated or sealed. These aspects are in the
`interest of both the patient and the surgeon.
`
`Investigators have endeavored to overcome
`[0026]
`the poor grasping aspect and tendency to evoke sticking
`occasioned with bare surface bipolar forceps by turning
`to the expedient of coating the tissue grasping surfaces
`of the tip regions of the forceps. Looking to Figs. 6 and
`7, such an arrangement is depicted in sectional fashion.
`In Fig. 6, the forceps is represented in general at 84
`having tines 86 and 88 with respective tip regions 90
`and 92. Tip regions 90 and 92 have respective grasping
`surfaces 94 and 96 which, at least in part, are covered
`with a continuous coating of electrically insulative mate-
`rial shown,
`respectively, at 98 and 100. Continuous
`coatings 98 and 100 may be provided, for example, as a
`ceramic and thus incorporate a frictional aspect improv-
`ing the tissue grasping ability of the device 84.
`In this
`regard, a component of tissue is shown in the drawings
`at 102. Fig. 7 reveals, however, that by so coating the
`grasping surfaces with a ceramic insulator, current flow
`is restricted essentially to the outer edges of the tip
`regions 90 and 92. Such a current flux path arrange-
`ment is in Fig. 7 at dashed lines 104 and 106. While the
`arrangement achieves improved grasping and reduced
`heating with a corresponding reduced likelihood of the
`sticking of tissue or coagulum to the grasping surfaces,
`if the tissue or blood vessel 102 has a small thickness,
`then little or no electrical contact may be achieved at the
`tip region edges with the result of little or no current flow.
`Such low current flow lowers the efficiency of requisite
`Joulean heating of the tissue to achieve coagulation.
`However, if the tissue 102 is relatively thick, then suffi-
`cient heating and coagulation may be achieved
`because of the added contact of electrode surface with
`tissue.
`
`[0027] Referring to Figs. 8-10, a depiction of an initial
`embodiment of forceps according to the invention is por-
`trayed with some exaggeration of scale to facilitate the
`description thereof. The forceps are represented gener-
`ally at 110 and include two tines 112 and 114 which are
`electrically conductive and extend, respectively, to tip
`regions 116 and 118. Rearwardly of the tip regions 116
`and 118, the tines 112 and 114 are coated, respectively,
`with an electrically insulative coating shown, respec-
`tively, at 117 and 119. Coatings 120 and 122 preferably
`are formed of nylon, while the tines 112 and 114 are
`formed of a metal, for example, a 300 or 400 series
`stainless steel, nickel, tungsten, copper, or alloys of
`such metals. in a preferred arrangement, the tines 112
`and 114 are formed of a laminar composite which com-
`bines a thermally conductive metal such as copper with
`a biocompatible and higher modulus metal such as
`stainless steel. The higher modulus of the stainless
`steel
`layer affords mechanical characteristics which
`more closely match conventional stainless steel forceps
`
`

`
`11
`
`EP 0 986 990 A1
`
`12
`
`(e.g., forceps closure force and forceps tine deflection
`during grasping).
`In general,
`the stainless steel
`is
`inwardly facing to establish the base for tissue grasping
`surfaces. Inasmuch as certain of the thermally conduc-
`tive materials such as copper are not biocompatible, the
`composites preferably are covered with an electro-
`deposited layer of a compatible material such as chro-
`mium.
`In addition, the inwardly facing stainless steel
`member (on embodiments with ceramic strips on only
`one side) assures that any wear of the biocompatible
`coating by the repeated contact with the ceramic strips
`will only expose an underlying layer of biocompatible
`metal (viz, stainless steel). Tip regions 116 and 118 are
`configured having inwardly disposed substantially flat
`tissue grasping surfaces shown, respectively, at 120
`and 122. Surfaces 120 and 122 preferably are made as
`smooth as practical in order to avoid a sticking phenom-
`ena as much as possible. In this regard, the surfaces at
`120 and 122 should meet a surface finish specification
`of less than 32 microinch finish or better, and preferably
`about 16 microinch or smoother. These highly polished
`surfaces become available at the grasping location of
`the forceps 110 because of the utilization of electrically
`insulative spaced apart spacer
`regions which are
`mounted, for the present embodiment, upon both of the
`grasping surfaces 120 and 122. The spacer regions are
`implemented as thin strips of alumina. In this regard, an
`array of such strips as at 124a-124f are provided at
`grasping surface 120 while a corresponding array as at
`126a-126f are provided at grasping surface 120. The
`strips 124a-124f are shown having a thickness T1 uni-
`formly along the array and they are evenly spaced apart
`longitudinally along a grasping length LG. Note that this
`is a portion of the grasping surface 120, the entire longi-
`tudinal extent of which is represented at LE. For the
`present embodiment, spacer regions also are mounted
`or formed upon grasping surface 122. In this regard, the
`regions are implemented as strips 126a-126f which are
`dimensioned and located in correspondence with the
`array of strips 124a-124f. The array of strips 126a-126f
`are shown to have a thickness T2. Note that the initial
`
`strips 124a and 126a at the respective ends or distal
`ends of tip regions 116 and 118 are located at the outer
`peripheral extents thereof. This provides an initial
`"snagging" geometry at the very tip of the forceps, a
`location most beneficial to achieving the requisite grasp-
`ing function required by the surgeon.
`In this regard,
`should only one strip or region be employed with the for-
`ceps,
`it preferably is located at the position of strips
`124a or 126a.
`
`Figs. 8 and 9 depict the forceps 110 as grasp-
`[0028]
`ing a component of tissue or vessel as at 132. This is to
`depict one aspect of the selection of the thickness‘ T1
`and T2 as well as the relative positioning of the strip
`arrays 124a-124f and 126a-126f. Note that the individ-
`ual strips of these arrays both extend across the periph-
`ery of
`the grasping surfaces and virtually to the
`longitudinal extent of their respective tines; they are in
`
`substantially parallel relationship, and are aligned for
`movement into mutual contact when in a closed orienta