Patent Document

REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 14/223,121, filed on Mar. 24, 2014, which is a continuation of U.S. patent application Ser. No. 13/311,695, abandoned, filed on Dec. 6, 2011, which is a divisional of U.S. patent application Ser. No. 11/548,407, abandoned, filed on Oct. 11, 2006, which claims the priority benefit of U.S. provisional patent application Ser. No. 60/726,625, filed on Oct. 14, 2005. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to ultrasonic surgical systems and, more particularly, to an ultrasonic device that is optimized to allow surgeons to perform cutting, coagulation, and fine dissection required in fine and delicate surgical procedures such as a thyroidectomy. 
       BACKGROUND OF THE INVENTION 
       [0003]    Ultrasonic surgical instruments are finding increasingly widespread applications in surgical procedures by virtue of the unique performance characteristics of such instruments. Depending upon specific instrument configurations and operational parameters, ultrasonic surgical instruments can provide substantially simultaneous cutting of tissue and homeostasis by coagulation, desirably minimizing patient trauma. The cutting action is typically effected by an end-effector at the distal end of the instrument, which transmits ultrasonic energy to tissue brought into contact with the end-effector. Ultrasonic instruments of this nature can be configured for open surgical use, laparoscopic or endoscopic surgical procedures including robotic-assisted procedures. 
         [0004]    Ultrasonic surgical instruments have been developed that include a clamp mechanism to press tissue against the blade of the end-effector in order to couple ultrasonic energy to the tissue of a patient. Such an arrangement (sometimes referred to as a clamp coagulator shears or an ultrasonic transector) is disclosed in U.S. Pat. Nos. 5,322,055; 5,873,873 and 6,325,811. The surgeon activates the clamp arm to press the clamp pad against the blade by squeezing on the handgrip or handle. 
         [0005]    Some current designs of clamp coagulator shears utilize a foot pedal to energize the surgical instrument. The surgeon operates the foot pedal while simultaneously applying pressure to the handle to press tissue between the jaw and blade to activate a generator that provides energy that is transmitted to the cutting blade for cutting and coagulating tissue. Key drawbacks with this type of instrument activation include the loss of focus on the surgical field while the surgeon searches for the foot pedal, the foot pedal getting in the way of the surgeon&#39;s movement during a procedure and surgeon leg fatigue during long cases. 
         [0006]    Various methods have been disclosed for curved end effector balancing, which include repositioning the mass along the end effector. The drawbacks of such methods are i) high stresses in the curved region, which makes the end effector more prone to fracture if it comes in contact with metal during surgery; ii) a shorter active length, which limits the vessel size that can be operated on, (the active length is defined as the length from the distal end of the blade to where the displacement is one half of the displacement at its distal end); and/or iii) the inability to separately balance orthogonal displacements. 
         [0007]    Some current designs of clamp coagulator shears utilize handles that are either of a pistol or scissors grips design. The scissor grip designs may have one thumb or finger grip that is immovable and fixed to the housing and one movable thumb or finger grip. This type of grip may not be entirely familiar to surgeons who use other open-type surgical instruments, such as hemostats, where both thumb and finger grips move in opposition to one another. Current designs have scissor arms that rotate around a fixed pivot or rotation point that is perpendicular to the longitudinal axis of the working element. This approach is limited since the relative motion between the two arms is completely rotational. This feature limits the ability to control the pressure profile between the two working ends when fully closed. 
         [0008]    Some current designs of clamp coagulator shears are not specifically designed for delicate procedures where precise dissection, cutting and coagulation are required. 
         [0009]    An exemplary procedure is a thyroidectomy where precise dissection, cutting and coagulation is required to avoid critical blood vessels and nerve bundles. 
         [0010]    It would be desirable to provide an ultrasonic surgical instrument that overcomes some of the deficiencies of current instruments. The ultrasonic surgical instrument described herein overcomes those deficiencies. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0011]    The novel features of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to organization and methods of operation, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings in which: 
           [0012]      FIG. 1  is a perspective view illustrating an embodiment of an ultrasonic surgical instrument in accordance with the present invention; 
           [0013]      FIG. 2  is a perspective assembly view of  FIG. 1 ; 
           [0014]      FIG. 3A  is a perspective view of one embodiment of a waveguide and blade in accordance with the present invention; 
           [0015]      FIG. 3B  is an elevation view of the waveguide and blade of  FIG. 3A ; 
           [0016]      FIG. 3C  is an elevation view of an alternate embodiment of a waveguide and blade in accordance with the present invention; 
           [0017]      FIG. 3D  is an elevation view of an alternate embodiment of a waveguide and blade in accordance with the present invention; 
           [0018]      FIG. 3E  is an elevation view of an alternate embodiment of a waveguide and blade in accordance with the present invention; 
           [0019]      FIG. 3F  is an alternate view of the embodiment of the waveguide and blade of  FIG. 3E ; 
           [0020]      FIG. 3G  is an elevation view of an alternate embodiment of a waveguide and blade in accordance with the present invention; 
           [0021]      FIG. 4  is a graph illustrating the displacement profile of the present invention and the prior art; 
           [0022]      FIG. 5  is a graph illustrating an alternate displacement profile of the present invention and the prior art; 
           [0023]      FIG. 6A  is an elevation view of the waveguide and blade of  FIGS. 3E-F  illustrating one embodiment of the radius of curvature of the blade; 
           [0024]      FIG. 6B  is an exploded view of one embodiment of the blade of  FIG. 6A  and a radius cut; 
           [0025]      FIG. 6C  is an alternate view of the embodiment of  FIG. 6A ; 
           [0026]      FIG. 6D  is a section view of the embodiment of  FIG. 6B ; 
           [0027]      FIG. 7A  is an elevation view of an end effector in accordance with the present invention; 
           [0028]      FIG. 7B  is a plan view of the end effector of  FIG. 7A ; 
           [0029]      FIG. 8  is a perspective view from proximal to distal end of a clamp member in accordance with the present invention; 
           [0030]      FIG. 9A  is a plan view of a tissue pad in accordance with the present invention; 
           [0031]      FIG. 9B  is a plan view of the opposite face of the tissue pad of  FIG. 9A ; 
           [0032]      FIG. 9C  is an elevation view the tissue pad of  FIGS. 9A-B ; 
           [0033]      FIG. 10A  is a perspective view of an alternate expression of the clamp member; 
           [0034]      FIG. 10B  is a perspective view of the clamp member of  FIG. 10A  and a first tissue pad; 
           [0035]      FIG. 10C  is a perspective view of the clamp member of  FIG. 10A  and a first and second tissue pad; 
           [0036]      FIG. 11A-B  are an alternate expressions for a first and second tissue pad; 
           [0037]      FIG. 11C  is a perspective view of an alternate expression of a clamp arm for use with the tissue pads of  FIGS. 11A-B ; 
           [0038]      FIG. 11D  is an alternate view of the clamp are of  FIG. 11C ; 
           [0039]      FIG. 11E  is a cut-away view of an assembled clamp arm and tissue pad assembly of  FIGS. 11A-D   
           [0040]      FIG. 12A  is a perspective view of an alternate embodiment of a clamp arm having a distal connection point; 
           [0041]      FIG. 12B  is a perspective view of an alternate embodiment of a tissue pad having a distal connection member; 
           [0042]      FIG. 12C  is a perspective view of an assembled clamp arm and tissue pad of  FIGS. 12A-B ; 
           [0043]      FIG. 13  is a partial view of the distal end of the ultrasonic instrument in accordance with the present invention; 
           [0044]      FIG. 14  is an exploded elevation view of one part of the clamp arm and clamp member and cam members; 
           [0045]      FIG. 15  is an exploded view of the outer shroud and cam slots; 
           [0046]      FIG. 16A  is an elevation view of an ultrasonic instrument and pushbutton assembly in accordance with the present invention; 
           [0047]      FIG. 16B  is an elevation view of the two piece assembly of a push button in accordance with the present invention; 
           [0048]      FIG. 16C  is a cut-away elevation view showing the interface among the switch housing, transducer, waveguide and housing; 
           [0049]      FIG. 16D  is a perspective elevation view of a switch housing in accordance with the present invention; 
           [0050]      FIG. 16E  is an alternate view of the switch housing of  FIG. 16D ; 
           [0051]      FIG. 16F  is a view of a flex circuit in accordance with the present invention; 
           [0052]      FIG. 16G  is an electrical schematic of the hand switch circuit; 
           [0053]      FIG. 17A  is an elevation view of an ultrasonic instrument in accordance with the present invention as may be grasped by a user; 
           [0054]      FIG. 17B  is an exploded view of the finger and thumb interface of a ultrasonic instrument in accordance with the present invention; 
           [0055]      FIG. 18  is an elevation view of an ultrasonic instrument in accordance with the present invention as may be grasped by a user and defining a center of gravity; 
           [0056]      FIG. 19A  is a perspective view of a two-piece torque wrench in accordance with the present invention; 
           [0057]      FIG. 19B  is a perspective view of a hand wrench in accordance with the present invention; 
           [0058]      FIG. 19C  is an elevation view of the hand wrench of  FIG. 19B ; 
           [0059]      FIG. 19D  is a cross sectional end view of the distal end of a hand wrench depicting cantilever arm and teeth geometry; 
           [0060]      FIG. 19E  is a cross sectional view of an adaptor depicting spline gear geometry; 
           [0061]      FIG. 19F  is a perspective view of an adaptor for use with a hand wrench in accordance with the present invention; and 
           [0062]      FIG. 19G  is a partial perspective view of a hand wrench interfacing with an ultrasonic instrument in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0063]    Before explaining the present invention in detail, it should be noted that the invention is not limited in its application or use to the details of construction and arrangement of parts illustrated in the accompanying drawings and description. The illustrative embodiments of the invention may be implemented or incorporated in other embodiments, variations and modifications, and may be practiced or carried out in various ways. Further, unless otherwise indicated, the terms and expressions employed herein have been chosen for the purpose of describing the illustrative embodiments of the present invention for the convenience of the reader and are not for the purpose of limiting the invention. 
         [0064]    Further, it is understood that any one or more of the following-described embodiments, expressions of embodiments, examples, etc. can be combined with any one or more of the other following-described embodiments, expressions of embodiments, examples, etc. 
         [0065]    The present invention is particularly directed to an improved ultrasonic surgical clamp coagulator apparatus which is configured for effecting tissue cutting, coagulation, and/or clamping during surgical procedures, including delicate surgical procedures, such as a thyroidectomy. The present apparatus is configured for use in open surgical procedures. Versatile use is facilitated by selective use of ultrasonic energy. When ultrasonic components of the apparatus are inactive, tissue can be readily gripped and manipulated, as desired, without tissue cutting or damage. When the ultrasonic components are activated, the apparatus permits tissue to be gripped for coupling with the ultrasonic energy to effect tissue coagulation, with application of increased pressure efficiently effecting tissue cutting and coagulation. If desired, ultrasonic energy can be applied to tissue without use of the clamping mechanism of the apparatus by appropriate manipulation of the ultrasonic blade. 
         [0066]    As will become apparent from the following description, the present clamp coagulator apparatus is particularly configured for disposable use by virtue of its straightforward construction. As such, it is contemplated that the apparatus be used in association with an ultrasonic generator unit of a surgical system, whereby ultrasonic energy from the generator unit provides the desired ultrasonic actuation for the present clamp coagulator apparatus. It will be appreciated that a clamp coagulator apparatus embodying the principles of the present invention can be configured for non-disposable or multiple use, and non-detachably integrated with an associated ultrasonic generator unit. However, detachable connection of the present clamp coagulator apparatus with an associated ultrasonic generator unit is presently preferred for single-patient use of the apparatus. 
         [0067]    With specific reference now to  FIGS. 1 and 2 , an embodiment of a surgical system  19 , including an ultrasonic surgical instrument  100  in accordance with the present invention is illustrated. The surgical system  19  includes an ultrasonic generator  30  connected to an ultrasonic transducer  50  via cable  22 , and an ultrasonic surgical instrument  100 . It will be noted that, in some applications, the ultrasonic transducer  50  is referred to as a “hand piece assembly” because the surgical instrument of the surgical system  19  is configured such that a surgeon may grasp and manipulate the ultrasonic transducer  50  during various procedures and operations. A suitable generator is the GEN04 (also referred to as Generator 300) sold by Ethicon Endo-Surgery, Inc. of Cincinnati, Ohio. A suitable transducer is disclosed in co-pending U.S. patent application filed on Oct. 10, 2006, Ser. No. ______ (Attorney Docket # END5747USNP1), entitled MEDICAL ULTRASOUND SYSTEM AND HANDPIECE AND METHODS FOR MAKING AND TUNING, the contents which are incorporated by reference herein. 
         [0068]    Ultrasonic transducer  50 , and an ultrasonic waveguide  80  together provide an acoustic assembly of the present surgical system  19 , with the acoustic assembly providing ultrasonic energy for surgical procedures when powered by generator  30 . The acoustic assembly of surgical instrument  100  generally includes a first acoustic portion and a second acoustic portion. In the present embodiment, the first acoustic portion comprises the ultrasonically active portions of ultrasonic transducer  50 , and the second acoustic portion comprises the ultrasonically active portions of transmission assembly  71 . Further, in the present embodiment, the distal end of the first acoustic portion is operatively coupled to the proximal end of the second acoustic portion by, for example, a threaded connection. 
         [0069]    The ultrasonic surgical instrument  100  includes a multi-piece handle assembly  68  adapted to isolate the operator from the vibrations of the acoustic assembly contained within transducer  50 . The handle assembly  68  can be shaped to be held by a user in a conventional manner, but it is contemplated that the present ultrasonic surgical instrument  100  principally be grasped and manipulated in a scissor-like arrangement provided by a handle assembly of the instrument, as will be described. While multi-piece handle assembly  68  is illustrated, the handle assembly  68  may comprise a single or unitary component. The proximal end of the ultrasonic surgical instrument  100  receives and is fitted to the distal end of the ultrasonic transducer  50  by insertion of the transducer into the handle assembly  68 . The ultrasonic surgical instrument  100  may be attached to and removed from the ultrasonic transducer  50  as a unit. The ultrasonic surgical instrument  100  may include a handle assembly  68 , comprising mating housing portions  69  and  70  and an ultrasonic transmission assembly  71 . The elongated transmission assembly  71  of the ultrasonic surgical instrument  100  extends orthogonally from the instrument handle assembly  68 . 
         [0070]    The handle assembly  68  may be constructed from a durable plastic, such as polycarbonate or a liquid crystal polymer. It is also contemplated that the handle assembly  68  may alternatively be made from a variety of materials including other plastics, ceramics or metals. Traditional unfilled thermoplastics, however, have a thermal conductivity of only about 0.20 W/m° K (Watt/meter-° Kelvin). In order to improve heat dissipation from the instrument, the handle assembly may be constructed from heat conducting thermoplastics, such as high heat resistant resins liquid crystal polymer (LCP), Polyphenylene Sulfide (PPS), Polyetheretherketone (PEEK) and Polysulfone having thermal conductivity in the range of 20-100 W/m° K. PEEK resin is a thermoplastics filled with aluminum nitride or boron nitride, which are not electrically conductive. The thermally conductive resin helps to manage the heat within smaller instruments. 
         [0071]    The transmission assembly  71  includes a waveguide  80  and a blade  79 . It will be noted that, in some applications, the transmission assembly is sometimes referred to as a “blade assembly”. The waveguide  80 , which is adapted to transmit ultrasonic energy from transducer  50  to the tip of blade  79  may be flexible, semi-flexible or rigid. The waveguide  80  may also be configured to amplify the mechanical vibrations transmitted through the waveguide  80  to the blade  79  as is well known in the art. The waveguide  80  may further have features to control the gain of the longitudinal vibration along the waveguide  80  and features to tune the waveguide  80  to the resonant frequency of the system. In particular, waveguide  80  may have any suitable cross-sectional dimension. For example, the waveguide  80  may have a substantially uniform cross-section or the waveguide  80  may be tapered at various sections or may be tapered along its entire length. 
         [0072]    Ultrasonic waveguide  80  may, for example, have a length substantially equal to an integral number of one-half system wavelengths (nλ/2). The ultrasonic waveguide  80  and blade  79  may be preferably fabricated from a solid core shaft constructed out of material, which propagates ultrasonic energy efficiently, such as titanium alloy (i.e., Ti-6Al-4V), aluminum alloys, sapphire, stainless steel or any other acoustically compatible material. 
         [0073]    Ultrasonic waveguide  80  may further include at least one radial hole or aperture  66  extending therethrough, substantially perpendicular to the longitudinal axis of the waveguide  80 . The aperture  66 , which may be positioned at a node, is configured to receive a connector pin  27 , discussed below, which connects the waveguide  80 , to the handle assembly  70 . 
         [0074]    Blade  79  may be integral with the waveguide  80  and formed as a single unit. In an alternate expression of the current embodiment, blade  79  may be connected by a threaded connection, a welded joint, or other coupling mechanisms. The distal end of the blade  79  is disposed near an anti-node  85  in order to tune the acoustic assembly to a preferred resonant frequency f o  when the acoustic assembly is not loaded by tissue. When ultrasonic transducer  50  is energized, the distal end of blade  79  or blade tip  79   a  is configured to move substantially longitudinally (along the x axis) in the range of, for example, approximately 10 to 500 microns peak-to-peak, and preferably in the range of about 20 to about 200 microns at a predetermined vibrational frequency f o  of, for example, 55,500 Hz. Blade tip  79   a  also preferably vibrates in the y axis at about 1 to about 10 percent of the motion in the x axis. 
         [0075]    The blade tip  79   a  provides a functional asymmetry or curved portion for improved visibility at the blade tip so that a surgeon can verify that the blade  79  extends across the structure being cut or coagulated. This is especially important in verifying margins for large blood vessels. The geometry also provides for improved tissue access by more closely replicating the curvature of biological structures. Blade  79  provides a multitude of edges and surfaces, designed to provide a multitude of tissue effects: clamped coagulation, clamped cutting, grasping, back-cutting, dissection, spot coagulation, tip penetration and tip scoring. 
         [0076]    Blade tip  79   a  is commonly referred to as a functional asymmetry. That is, the blade (functionally, the blade provides a multitude of tissue effects) lies outside the longitudinal axis of waveguide  80  (that is, asymmetrical with the longitudinal axis), and accordingly creates an imbalance in the ultrasonic waveguide. If the imbalance is not corrected, then undesirable heat, noise, and compromised tissue effect occur. 
         [0077]    It is possible to minimize unwanted tip excursion in the y and z axes, and therefore maximize efficiency with improved tissue effect, by providing one or more balance asymmetries or balancing features proximal to the blade functional asymmetry. 
         [0078]    Referring now to  FIGS. 3A-G , transmission assembly  71  includes one or more balancing features placed at blade  79 , at a position proximal and/or distal to the distal most node  84 . In addition, the balancing features at the waveguide  80  are shaped to balance the two orthogonal modes in the y and z axes, separately. The size and shape and location of the balance features allow flexibility to reduce stress at the blade  79 , make the active length longer and separately balance the two orthogonal modes. 
         [0079]      FIGS. 3A-B  show a single balance cut  82  at the waveguide  80  distal to node  84 . In this embodiment balance cut  82  has side walls perpendicular to the longitudinal axis of waveguide  80  and the bottom cut is parallel to the longitudinal axis of waveguide  80 . In this embodiment the high stresses experienced during operation are localized at the balancing cut  82 , which is away from the more sensitive curved region at the blade  79 . 
         [0080]      FIG. 3C  shows two balancing features  82  and  82   a , one distal and one proximal to the node  84 . Adding second balance cut  82   a , proximal to node  84  further eliminates the orthogonal bending modes thereby providing a more pure longitudinal motion (x direction) and removing the overlapping bending modes (y and z direction). Accordingly, the blade  79  is better balanced and has a longer active length. 
         [0081]      FIG. 3D  shows two balancing features  82   c  and  82   a , distal and proximal to the node  84 . An angled bottom cut at balance feature  82   c  allows individual balancing of the bending mode in the z direction. 
         [0082]      FIGS. 3E-F  show two balancing features  82  and  82   d , distal and proximal to the node  84 . The side walls of balance feature  82   d  are angled with respect to each other in the x-z plane and provide for individual balancing of the bending mode in the y direction. The angled side walls define an included angle θ of between 1° and about 90°, preferably between about 15° and about 25°, and more preferably between about 19° and about 21°. The weight removed at each balance feature is a function of multiple parameters including the radius of curvature at blade tip  79   a  and the desired level of removal of the overlapping bending modes in the y and z direction. In an illustrative example, the balance cut  82  represents a weight reduction of about 0.003 to about 0.004 oz., and most preferably about 0.0034 oz. The balance cut  82   d  represents a weight reduction of about 0.004 to about 0.005 oz., and most preferably about 0.0043 oz. 
         [0083]      FIG. 3G  shows one balance cut  82   e  in the curved blade region in addition to balance feature  82 , distal to node  84 . Balance cut  82   e  allows for balancing as well as improved acoustic performance as a result of wide frequency separation of transverse modes from the fundamental frequency, which is the longitudinal mode frequency. 
         [0084]    As would be apparent to one skilled in the art, any combination of balance cuts  82  through  82   e  are possible to provide balancing of a waveguide and curved blade. 
         [0085]      FIG. 4  shows that the profile produced by the balancing cut features of  FIG. 3E  produces a 1.3 mm longer active length along the longitudinal displacement direction than is available from an LCS-05 ultrasonic clamp coagulator, sold by Ethicon Endo-Surgery, Inc. (where they axis is representative of the ratio between the displacement anywhere along blade tip  79   a  and the displacement at the most distal end of blade tip  79   a ). A longer active length is desirable for cutting and coagulating large vessels, for example, 5-7 mm vessels. 
         [0086]      FIG. 5  shows that the profile produced by the balancing features of  FIG. 3E  produces a 2.5 mm longer active length (along the vector sum of displacements in the x, y and z directions) than is available from an LCS-05 ultrasonic clamp coagulator, which is desirable for cutting and coagulating large vessels, for example, 5-7 mm vessels. 
         [0087]    Referring back to  FIGS. 1 and 2  an outer tubular member or outer shroud  72  attaches to the most proximal end of handle assembly  70 . Attached to the distal end of the outer shroud  72  is a distal shroud  76 . Both the outer shroud  72  and distal shroud  76  may attach via a snap fit, press fit, glue or other mechanical means. Extending distally from the distal shroud  76  is the end-effector  81 , which comprises the blade  79  and clamp member  56 , also commonly referred to as a jaw, in combination with one or more tissue pads  58 . A seal  83  may be provided at the distal-most node  84 , nearest the end-effector  81 , to abate passage of tissue, blood, and other material in the region between the waveguide  80  and the distal shroud  76 . Seal  83  may be of any known construction, such as an o-ring or silicon overmolded at node  84 . 
         [0088]    Referring now to  FIGS. 6A-D  and  7 A-B, blade  79  is curved along with the associated clamp member  56 . This is illustrative only, and blade  79  and a corresponding clamp member  56  may be of any shape as is known to the skilled artisan. One benefit of the invention, however, is the ability to perform finer, more delicate surgical procedures. It is also multifunctional and able to dissect tissue as well as coagulate and transect. 
         [0089]    The ability to finely dissect is enabled primarily by the tapering of the end effector  81 . The end effector is tapered in two planes, which mimics typical hemostats. This allows the user to create windows in the tissue and then spread the tissue apart more easily. The blade  79  and clamp member  56  are tapered in both the x and z directions from the proximal end to the distal end. The pad  58  is only tapered in the Z direction. That is, the clamp pad  58  has a constant thickness, but the width of the clamp pad  58  at the distal end is less than the width at the proximal end. Accordingly, the surface area of section A is greater than the surface area of section B. 
         [0090]    In addition to the taper, the radius at the distal end of the blade  79  and clamp member  56  also promotes fine dissection. The radius at the tip of the clamp member  56  is approximately 0.040 inches, and the blade radius is approximately 0.045 inches. 
         [0091]    With specific reference to  FIG. 6A , blade  79  is defined by an inside radius R 1  and an outside radius R 2  measured at a distance D 1  from the longitudinal axis. The dimensions R 1 , R 2  and D 1  are selected in combination with the balance cuts previously discussed. In one embodiment R 1  is from about 0.80 inches to about 1.00 inches and most preferably about 0.95 inches; R 2  is from about 0.90 inches to about 1.10 inches and most preferably about 1.04 inches; and D 1  is from about 0.90 inches to about 1.10 inches and most preferably about 0.99 inches. 
         [0092]      FIGS. 6B and 6D  further illustrate a second expression of the blade  79 . Illustrated is a radius cut  90  in blade  79  to provide two back cutting edges  92  and  92   a . As will be appreciated by the skilled artesian, radius cut  90  also provides a balance asymmetry within the functional symmetry to help balance the orthogonal modes. The back cutting edges  92  and  92   a  are positioned opposite the clamp pad  58  ( FIG. 7B ) to allow the surgeon to perform tissue cutting procedures without the assistance of the clamp pad  58 . Preferably, the radius cut is distal to the most distal tip of blade  79  to allow for a blunt radius tip for tissue dissection as discussed above. In one example of the second expression of blade  79 , a radius cut R 3  is swept across an angle Φ measured at a distance D 2  from the longitudinal axis and starting a distance D 3  from the distal tip of blade  79 . In one embodiment R 3  is from about 0.030 inches to about 0.060 inches and most preferably about 0.050 inches; angle Φ is from about 20° to about 35° and most preferably about 30°; D 2  is about 0.90 inches to about 1.10 inches and most preferably about 0.99 inches; and D 3  is from about 0.085 inches to about 0.11 inches and most preferably about 0.09 inches. 
         [0093]    In a third expression of blade  79 ,  FIG. 6C  illustrates a taper defined by angle Ω relative to an axis parallel to the longitudinal axis of waveguide  80  from the proximal end of blade  79  to the distal end of blade  79 . In one embodiment the taper may be on the blade surface that contacts tissue pad  58  ( FIG. 7A ). Alternatively, the taper may be the defined by the opposite surface comprising radius cut  90 . Referring to  FIG. 6C , angle Ω ranges from about 0.5° to about 5°, and preferably from about 1.5° to about 2°. 
         [0094]    Referring back to  FIG. 2 , waveguide  80  is positioned within cavity  59  of handle assembly  68 . In order to properly locate the waveguide  80  both axially and radially, pin  27  extends through opening  66  of waveguide  80  (located at a node) and engages channel  28  (formed by the mating of housing portions  69  and  70 ). Preferably pin  27  is made of any compatible metal, such as stainless steel or titanium or a durable plastic, such as polycarbonate or a liquid crystal polymer. In a first expression of one embodiment, pin  27  is partially coated with an elasto-meric material  30 , such as silicon for that portion  29  of pin  27  that extends through waveguide  80  and uncoated for that portion of pin  27  that engages members  69  and  70 . The silicone provides insulation from the vibrating blade throughout the length of hole  66 . This enables high efficiency operation whereby minimal overheating is generated and maximum ultrasonic output power is available at the blade tip for cutting and coagulation. The lack of insulation allows pin  27  to be held firmly within handle assembly  68  due to the lack of insulation, which would provide deformation and movement if pin  27  were completely coated with an insulating material. 
         [0095]    Referring now to  FIGS. 8 and 9A -C a first expression of clamp member  56  has a shaped slot  57  for accepting one or more tissue pads. This configuration prevents mis-loading of the tissue pads and assures that the appropriate pad is loaded at the correct location within clamp member  56 . For example clamp member  56  may comprise a T-shaped slot  57  to accept a T-shaped flange  55  of clamp pad  58 . Two mechanical stops  59  and  59   a , when depressed, engage the proximal end of clamp pad  58  to secure the clamp pad within clamp member  56 . As would be appreciated by those skilled in the art, flanges and corresponding slots may have alternate shapes and sizes to secure the clamp pads to the clamp arm. The illustrated flange configurations shown are exemplary only and accommodate the particular clamp pad material of one embodiment, but the particular size and shape of the flange may vary, including, but not limited to, flanges of the same size and shape. For unitary tissue pads, the flange may be of one configuration. Further, other tab stops are possible and may include any of the multiple methods of mechanically attaching the clamp pads to the clamp arm, such as rivets, glue, press fit or any other fastening means well know to the artisan. 
         [0096]    Referring to  FIGS. 10A-C , in a first expression of an alternate embodiment, clamp pad  58  consists of a first tissue pad  58   b  and a second pad portion  58   a , which may be an insert within pad  58   b . Tissue pad  58   b  may comprise a tissue engaging surface having saw tooth-like teeth and proximal portion  58   a  may have a smoother surface relative to pad  58   b . The advantage of two separate components  58   a  and  58   b  is that each pad may be constructed from different materials. For example, having a two-piece tissue pad allows the use of a very lubricious material at the distal end that is not particularly resistant to high temperatures compared to a very high temperature material at the proximal end that is not particularly lubricious because the proximal end is an area of lower amplitude. Such a configuration matches the tissue pad materials to the amplitude of the blade  79 . 
         [0097]    In a second expression of an alternate embodiment of the present invention, clamp pad  58   b  is formed from TEFLON® or any other suitable low-friction material. Clamp pad  58   a  is formed from a base material and at least one filler material, which is a different material from the base material. The surface of proximal clamp pad  58   a  may be smoother than distal clamp pad  58   b , or proximal clamp pad  58   a  may also have a similar type saw-tooth configuration. 
         [0098]    Several benefits and advantages are obtained from one or more of the expressions of the invention. Having a tissue pad with a base material and at-least-one filler material allows the base material and the at-least-one filler material to be chosen with a different hardness, stiffness, lubricity, dynamic coefficient of friction, heat transfer coefficient, abradability, heat deflection temperature, glass transition temperature and/or melt temperature to improve the wearability of the tissue pad, which is important when high clamping forces are employed because tissue pads wear faster at higher clamping forces than at lower clamping forces. In experiments, a 15% graphite-filled polytetrafluoroethylene tissue pad showed substantially the same wear with a 7 pound clamping force as a 100% polytetrafluoroethylene tissue pad showed with a 1.5 pound clamping force. Having a flexible clamping arm and/or a flexible tissue pad should also improve the wearability of the tissue pad due to the ability of the flexible member to more evenly distribute the load across the entire surface of the tissue pad. Further benefits and expressions of this embodiment are disclosed in U.S. provisional patent application, Ser. No. 60/548,301, filed on Feb. 27, 2004 and commonly assigned to the assignee of the present application. 
         [0099]    In a third expression of an alternate embodiment, a tissue pad with a base material and at least two filler materials allows the base material and the at-least-two filler materials to be chosen with a different hardness, stiffness, lubricity, dynamic coefficient of friction, heat transfer coefficient, abradability, heat deflection temperature, and/or melt temperature to improve the wearability of the tissue pad, which is important when high clamping forces are employed because tissue pads wear faster at higher clamping forces than at lower clamping forces. In experiments, a 15% graphite-filled, 30% PTFE-filled polyimide tissue pad showed substantially the same or better wear with a 4.5 pound clamping force as a 100% polytetrafluoroethylene tissue pad showed with a 1.5 pound clamping force. The advantage of a 15% graphite-filled, 30% PTFE-filled polyimide tissue pad is increased heat resistance, which improves the overall wear resistance of the tissue pad. This polyimide-composite clamp pad has a useful heat resistance up about 800° F. to about 1200° F., as compared to a useful heat resistance up to about 660° F. of a PTFE clamp pad. Alternatively, other materials are also useful for a portion of the tissue pad, such as ceramics, metals, glasses and graphite. 
         [0100]      FIGS. 10A-C  disclose a first expression of an embodiment of attaching a two part clamp pad  58   a - b  to a clamp member  56 . In  FIG. 10A , at least two slots  57   a  and  57   b  are shaped to accept two correspondingly shaped flanges  55   a  and  55 ′. In this example, T-slot  57   a  accepts a corresponding T-flange  55   a  of clamp pad  58   a , and wedge-shaped slot  57 ′ accepts a corresponding wedge-shaped flange  55 ′ of clamp pad  58   b.    
         [0101]      FIGS. 11A-E  illustrate a second expression of attaching a clamp pad  58   c  to a clamp arm  56   c . Clamp pad  58   c  comprises one or more protrusions  62  for insertion into one or more corresponding apertures  63  in clamp arm  56   c . If a second or more clamp pad(s)  58   d  is also used in accordance with the previous discussion, then clamp pad  58   c  further comprises corresponding aperture  61  for accepting one or more clamp pad(s)  58   d . Clamp arm  56   c  has corresponding aperture(s)  63  for accepting protrusions  62 , as well as a corresponding cavity  64  for accepting the one or more clamp pad  58   d .  FIG. 11E  illustrates the components assembled together prior to staking. Clamp pad  58   d  fits inside the aperture  61  and cavity  64 , and pad  58   c  is aligned with clamp arm  56   c  so that protrusions  62  align with chamfered aperture  63 . Protrusions  62  have additional height beyond the top surface of clamp arm  56   c  to provide additional material to fill the chamfered volume during staking. Heat is applied to protrusions  62  above the clamp arm  56   c ; the protrusions deform and take the shape of the chamfered volume. 
         [0102]      FIGS. 12A-C  illustrate a third expression of attaching a clamp pad  58   d  to a clamp arm  56   d . In addition to a T-shaped flange  55 , clamp pad  58   d  further comprises a hook-like protrusion or clip  65  for attaching to a corresponding opening  66  at the distal tip of clamp arm  56   d . In this expression, the distal tip of clamp arm  56   d  is open and the clamp pad  58   d  is inserted from the distal to proximal direction until the hook clip engages opening  66 . Hook clip  65  may be biased closed so when clip  65  engages opening  66 , clip  65  applies compressive forces against opening  66 . 
         [0103]    A first expression for a method for inserting a clamp pad on a clamp arm includes a) inserting a first clamp pad having a first width dimension greater than a second width dimension and having a first-shaped flange into a clamp arm having a slot that accepts the first-shaped flange; and b) engaging a pad stop to secure the clamp pad within the clamp arm. In a second expression of the method, the clamp pad consists of a second clamp pad fabricated from a base material and at least one filler material, which is a different material from the base material. The second clamp pad may have a second-shaped flange for engaging a second-shaped slot on the clamp arm. The tissue surfaces of the clamp pads may be smooth or have tissue gripping features, such as a saw-tooth configuration. 
         [0104]    A first expression for a method for replacing clamp pads would include the steps of: a) disengaging a pad stop; b) removing a first clamp pad from the clamp arm; c) removing a second clamp pad from the clamp arm, wherein at least one of the first or second clamp pads has a first width dimension greater than a second width dimension; d) inserting third and fourth clamp pads into the clamp arm wherein at least one of the third or fourth clamp pads has a first width dimension greater than a second width dimension; and e) engaging a pad stop to secure the third and fourth clamp pads within the clamp arm. In a second expression of this method one of the third and fourth clamp pads may be fabricated from a polymeric material such as TEFLON, and the other clamp pad may be fabricated from a base material and at least one filler material, which is a different material from the base material. The tissue surfaces of the clamp pads may be smooth or have tissue gripping features, such as a saw-tooth configuration. 
         [0105]    Referring to  FIGS. 13-15 , a clamp arm  60  is configured for use with the present ultrasonic surgical instrument  100  and for cooperative action with blade  79  and clamp member  56 . The clamp arm  60  is rotatably mounted to the distal end of outer shroud  72 , detailed below, and connectably attaches at the distal end of thumb ring or actuation member  34 . Clamp pad  58  mounts on the clamp member  56  for cooperation with blade  79 , with rotational movement of the clamp arm  60  positioning the clamp pad in substantially parallel relationship to, and in contact with, blade  79 , thereby defining a tissue treatment region. By this construction, tissue is grasped between clamp pad  58  and blade  79 . Pivotal movement of the clamp member  56  with respect to blade  79  is affected by the provision of a pair of camming members on the clamp arm  60  that interface with the outer shroud  72 . The outer shroud  72  is grounded to handle  68 . 
         [0106]    A first expression of clamp arm  60  comprises jaw-carrying member  60   a  and mating member  60   b . Jaw-carrying member  60   a  includes two camming members  94   a  and  94   b  for mating with two corresponding camming slots  95   a  and  95   b  located outer shroud  72 . Mating member  60   b  includes two camming members  96   a  and  96   b  for mating with two corresponding camming slots  97   a  and  97   b  located outer shroud  72 . Corresponding camming members  94   a / 94   b  and  96   a / 96   b  (and corresponding camming slots  95   a / 95   b  and  97   a / 97   b ) may align along common axes perpendicular to the longitudinal axis of waveguide  80  or camming members may be offset to facilitate the assembly process. Members  60   a  and  60   b  fixedly attach to each other as shown in  FIG. 13  to form clamp arm  60  via press fit or snap fit. Other attaching methods are available as is known to those skilled in the art, such as welding, glue, screwing, etc. Once assembled, clamp arm  60  defines an opening  93  for receiving outer shroud  72  and the interlocking of the respective cam members and cam slots. Alternatively, members  60   a  and  60   b  may be assembly around outer shroud  72  and all three elements mated together in one operation. One benefit of the cam open and closure mechanism is that it can provide both a rotational motion and linear motion of the clamp arm  60  and clamp member  56  thereby providing better control of the pressure profile between clamp pad  58  and blade  79 . 
         [0107]    In a second expression of clamp arm  60 , the camming members may be replaced with spherical elements that interface with cam slots. Alternatively camming members may be replaced with spherical depressions for receiving ball bearings that interface with the cam slots. Other camming mechanism would be useful as is well known to the skilled artisian. 
         [0108]    With solid camming members and corresponding slots, the force delivered between the clamp pad  58  and blade  79  is directly related to the force that the user applies at the thumb ring  35  and finger ring  36 . In a third expression of clamp arm  60 , a force limiting element  98 , such as an elastomer or coil or leaf spring, may be inserted within one or more cam slots and provide a force limit to the coaptation force seen at the end effector  81 . Preferably, the spring constant of an elastomer or spring ranges from 10-500 lb./in. 
         [0109]    Outer shroud  72 , distal shroud  76  and clamp arm  60  may be constructed from any number of biocompatible materials, such as titanium, stainless steel or plastics. Preferably, however, these elements are constructed of either 7075 or 6061 T6 aluminum. The aluminum provides a large benefit in terms of heat dissipation. Devices of the prior art have sheaths and clamp arms made of stainless steel. Typical values for thermal conductivity for aluminum are around 250 W/m K. The values for stainless steel are around 16 W/m K. Thus, aluminum has approximately 15 times greater capability to transmit heat through the same amount of volume. 
         [0110]    The inventors have found through testing of similar inputs (clamp force and blade displacement), the present invention operates approximately 150° F. lower in temperature than instruments of the prior art. The aluminum components more effectively draw the heat away from the pad and the blade, thus keeping the end effector cooler than other prior art instruments. 
         [0111]    Referring now to  FIGS. 1, 2 and 16A -G housing  68  includes a proximal end, a distal end, and a cavity  59  extending longitudinally therein. Cavity  59  is configured to accept a switch assembly  300  and the transducer assembly  50 . 
         [0112]    In one expression of the current embodiment, the distal end of transducer  50  threadedly attaches to the proximal end of transmission rod  80 . The distal end of transducer  50  also interfaces with switch assembly  300  to provide the surgeon with finger-activated controls on surgical instrument  19 . 
         [0113]    Transducer  50  includes a first conductive ring  400  and a second conductive ring  410  which are securely disposed within the transducer body  50  as is described in co-pending application Ser. No. ______ (Attorney docket no. END5747USNP2). 
         [0114]    Switch assembly  300  comprises a pushbutton assembly  310 , a flex circuit assembly  330 , a switch housing  350 , a first pin conductor  360  and a second pin conductor  370 . Switch housing  350  is saddle-shaped and is supported within handle assembly  68  by way of corresponding supporting mounts on switch housing  350  and housing portions  69  and  70 . Housing  350  defines a first receiving area  353  for a dome switch, and a second receiving area  351  for a dome switch. 
         [0115]    With particular reference now to  FIGS. 16D  and E, pins  360  and  370  are electrically connected to dome switch  332  and  334  via conductors  337  and  335 , respectively, at one end and to the distal end of transducer  50  at a second end. Pins  360  and  370  each have a spring-loaded tip  361  and  371  that interface with transducer  50  as shown in  FIG. 16C . Each end  361  and  371  have a 0.050 inch working travel to allow for manufacturing tolerances associated with the stackup of the assembled parts. Slidably attached to housing  68  are two triggers  320  and  322 , each comprising first and second halves  320   a ,  320   a  and  322   a ,  322   b , respectively. Shown in  FIG. 16B  is trigger  320 , which comprises ridges  321   a  and  b  and contact surface  323  (made up of mating surfaces  323   a  and  323   b ). When assembled, triggers  320  and  322  slidably attach to housing  68  and contact surfaces  323  and  325  mechanically engage dome switches  332  and  334 , respectively. Ridges  321  and  326  provide interface between the user and triggers  320  and  322 . Ridges  321  and  326  are designed to provide as much surface area for the user to depress in order to activate the instrument. 
         [0116]    In a second expression of switch assembly  300  elastomeric connectors having copper traces etched onto the elastomer press fit into switch housing  350  to provide the electrical interconnect between transducer  50  and flex circuit  330 . One end of the elastomer connectors electrically engage dome switches  332  and  334  via conductors  337  and  335 . The other end of the elastomer connectors slidably interface with conductors  400  and  410  of transducer  50 . Compression of the elastomer connectors allow a working travel of up to 20% of the total height of the elastomer connectors to allow for manufacturing tolerances associated with the stackup of the assembled parts. 
         [0117]    A flex circuit  330  provides for the electro-mechanical interface between pushbuttons  321  and  322  and the generator  30  via transducer  50 . Flex circuit comprises two dome switches  332  and  334  that are mechanically actuated by depressing pushbuttons  321  or  322  axially in the x direction. Dome switches  332  and  334  are electrical contact switches, that when depressed provide an electrical signal to generator  30  as shown by the electrical wiring schematic of  FIG. 16G . Flex circuit  330  also comprises two diodes within a diode package  336  and conductors,  335  and  337  as is known to those in the art, that connect to pins  360  and  370 , respectively, which in turn provide electrical contact to ring conductors  400  and  410 , which in turn are connected to conductors in cable  22  that connect to generator  30 . 
         [0118]    Flex circuit  330  generally sits within a channel  352  of switch assembly  350  so that dome switches  332  and  334  interface with the corresponding backing surfaces  351  and  353 . Backing surfaces provide a firm support for the dome switches during operation, discussed below. Dome switches  332  and  334  may be fixedly attached to backing surfaces  351  and  353  by any convenient method, such as, an adhesive. 
         [0119]    As is readily apparent, by depressing pushbuttons  321  and  322  the corresponding contact surfaces  323  and  324  depress against corresponding dome switches  332  and  334  to activate the circuit illustrated in  FIG. 16G . When the surgeon depresses  321  pushbutton, the generator will respond with a certain energy level, such as a maximum (“max”) power setting; when the surgeon depresses pushbutton  322 , the generator will respond with a certain energy level, such as a minimum (“min”) power setting, which conforms to accepted industry practice for pushbutton location and the corresponding power setting. 
         [0120]    Referring now to  FIGS. 17A-B , the pushbutton axial actuation reduces stress on the surgeon&#39;s fingers and allows the fingers to actuate force in a more ergonomic position preventing stresses at the hands and wrists. The switch movement also allows comfortable button activation in less than optimal hand positions, which surgeons often encounter throughout a typical procedure. 
         [0121]    At the proximal end of each access ring  35  and  36  are protrusions  37  and  38 , respectively, that allow the surgeon to rest his or her pinky finger for added control and comfort. This also allows the surgeon to use the pinky when clamping on tissue, thereby reducing the force on the other fingers. Each access ring  35  and  36  includes a soft-touch surface on the interior and exterior surfaces whether by inserting fingers into the access rings or palming the access rings. This feature allows a greater number of hand sizes to comfortably use the device. 
         [0122]    Referring to  FIG. 18 , access rings  35  and  36  define a length L. Preferably, the center of gravity of the surgical instrument  100  in combination with the transducer  50  is positioned within length L, more preferably within length L 1 , and most preferably within length L 2 . This position of the center of gravity allows the instrument to balance within the surgeon&#39;s hand to provide more precise control of the instrument and eliminate hand fatigue during procedures. 
         [0123]    Referring now to  FIGS. 18 and 19A -E, a two-piece torque wrench  450  is shown. The torque wrench includes a hand wrench  500  and an adaptor  550 . In one embodiment, hand wrench  500  is provided with cantilever arms  501  disposed in an annular fashion about the centerline of hand wrench  500 . Cantilever arms  501  include teeth  501   a  disposed, in one embodiment, in an inward perpendicular fashion in relation to cantilever arms  501 . Teeth  501   a , in one embodiment of the current invention, are disposed with a cam ramp  501   b  at a 25° angle with respect to the perpendicular angle between arm  501  and teeth  501   a . Lumen  502  extends the entire length of hand wrench  500  for accepting adaptor  550 . 
         [0124]    Adaptor  550  has a longitudinal shaft  552  with cantilevered tabs  554  at its distal end. At the proximal end of shaft  552  are spline gears  556  projecting in a perpendicular fashion along the outer circumference of shaft  552 . Spline gears  556  include cam ramps  556   a  disposed at an angle from about 23° to about 28° with respect to the perpendicular angle between the outer circumference of shaft  552  and spline gears  556 . Shaft  552  further defines a lateral opening (not shown) proximal to spline gears  556  for accepting curved blade  79 , discussed below. Adaptor further includes an interface  560  rigidly connected to shaft  552  and defining an opening for rigidly engaging the distal end of instrument  19 . Optionally, a skirt  558  surrounds spline gears  556  to prevent glove snags due to moving parts and forms a cavity  559 . 
         [0125]    In assembly, torque wrench opening  502  is aligned with shaft  552  and guided along substantially the entire length of shaft  552  until the tabs  554  flex inward and capture shoulder  505  (not shown) at the distal end of hand wrench  500 . Hand wrench lip  503  engages the distal end of optional skirt  558  allowing cantilever teeth  501   a  to slidably engage spline gears  556 . Cam ramp  501   b  slidably engages retainer cam ramps  29   b . The torque wrench assembly  450  slidably engages the distal end of instrument  19  and is held rigidly in place. Flat surfaces  560   b  and  560   a  of interface  560  mate with flat surfaces  565   b  ( FIG. 18 ) and  565   a  (not shown) at the distal end of activation member  34  (clamp arm  60 ) and rail  562  slidably engaging slot  564  on clamp arm  60  and distra shroud  76  and outer shroud  72  all provide structural support to maintain adapter  550  firmly engaged with instrument  19 . 
         [0126]    Clockwise annular motion or torque is imparted to hand wrench  500  through paddles  504 . The torque is transmitted through arms  501  and teeth  501   a  to gears  556 , which in turn transmit the torque to the waveguide  80  via clamp arm assembly  60  via outer shroud  72  via insulated pin  27 . When a user imparts 5-12 lbs. of torque, the ramps  501   b  and  556  cause the arms  501  to move or flex away from the centerline of wrench  500  ensuring that the user does not over-tighten the waveguide  80  onto transducer  50 . When a counter-clockwise torque is applied to wrench  500  via paddles  504 , the perpendicular flat sides of teeth  501   a  and  556  abut allowing a user to impart a torque to the interface between the waveguide  80  and transducer  50  in proportion to the force applied to the paddles facilitating removal of the instrument  100  from the transducer  50 . The torque wrench  450  may be constructed from a durable plastic, such as polycarbonate or a liquid crystal polymer. It is also contemplated that the wrench  450  may alternatively be made from a variety of materials including other plastics, ceramics or metals. 
         [0127]    In another embodiment (not shown), the paddles and cantilever arm assembly may be separate components attached by mechanical means or chemical means such as adhesives or glue. 
         [0128]    Preferably, the ultrasonic clamp coagulator apparatus  19  described above will be processed before surgery. First, a new or used ultrasonic clamp coagulator apparatus is obtained and if necessary cleaned. The ultrasonic clamp coagulator apparatus can then be sterilized. In one sterilization technique the ultrasonic clamp coagulator apparatus is placed in a closed and sealed container, such as a plastic or TYVEK bag. Optionally, the ultrasonic clamp coagulator apparatus can be bundled in the container as a kit with other components, including a torque wrench  450 . The container and ultrasonic clamp coagulator apparatus, as well as any other components, are then placed in a field of radiation that can penetrate the container, such as gamma radiation, x-rays, or high-energy electrons. The radiation kills bacteria on the ultrasonic clamp coagulator apparatus and in the container. The sterilized ultrasonic clamp coagulator apparatus can then be stored in the sterile container. The sealed container keeps the ultrasonic clamp coagulator apparatus sterile until it is opened in the medical facility. 
         [0129]    While the present invention has been illustrated by description of several embodiments, it is not the intention of the applicant to restrict or limit the spirit and scope of the appended claims to such detail. Numerous variations, changes, and substitutions will occur to those skilled in the art without departing from the scope of the invention. Moreover, the structure of each element associated with the present invention can be alternatively described as a means for providing the function performed by the element. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.

Technology Category: a