Patent Description:
Various robotic systems have been developed to assist in MIS procedures. Robotic systems can allow for more instinctive hand movements by maintaining natural eye-hand axis. Robotic systems can also allow for more degrees of freedom in movement by including an articulable "wrist" joint that creates a more natural hand-like articulation. In such systems, an end effector positioned at the distal end of the instrument can be articulated (moved) using a cable driven motion system having one or more drive cables that extend through the wrist joint. A user (e.g., a surgeon) is able to remotely operate the end effector by grasping and manipulating in space one or more controllers that communicate with a tool driver coupled to the surgical instrument. User inputs are processed by a computer system incorporated into the robotic surgical system, and the tool driver responds by actuating the cable driven motion system. Moving the drive cables articulates the end effector to desired angular positions and configurations.

Some end effectors also include a knife that is able to be advanced and retracted between opposing jaws to cut or sever tissue grasped between the opposing jaws. Improvements to the design and function of the knife are desirable to improve the efficiency of the end effector and any procedures undertaken with the end effector.

<CIT> describes an electrosurgical instrument that includes a housing having a shaft attached thereto which connects a pair of first and second jaw members such that the jaw members are movable relative to one another to grasp tissue therebetween. The instrument also includes a four-bar handle assembly attached to the housing for actuating a drive rod assembly. The handle assembly includes a handle and a cam-like piston which cooperate to impart a uniform closure pressure against tissue grasped between the jaw members. The instrument also includes a rotating assembly for rotating the jaw members, a knife assembly for separating tissue and a pair of electrical leads connect the jaw members to a source of electrical energy. The electrical leads include slack loops disposed in the rotating assembly which permit rotation of the jaw members about the axis.

<CIT> describes an electrosurgical instrument that includes first and second jaw members each including an outer jaw housing, a tissue-treating plate, and a longitudinally-extending knife channel defined therethrough. The electrosurgical instrument also includes a knife actuator and a knife assembly operably coupled to the knife actuator. The knife actuator is configured to advance at least a portion of the knife assembly through the knife channel to cut tissue disposed between the jaw members. The knife assembly includes an elongated shaft having a proximal portion coupled to the knife actuator and a distal portion defining at least one aperture therethrough. The knife assembly also includes a knife blade having a sharpened distal end configured to cut tissue and at least one raised portion extending through the aperture defined by the elongated shaft.

<CIT> describes a surgical stapler instrument for applying lateral lines of staples to tissue while cutting the tissue between those staple lines. The instrument includes a handle portion, an implement portion, a reciprocating section, a drive member and a movable actuator. The implement portion includes a staple cartridge and an anvil. The reciprocating section is adapted to move back and forth along an axis of the implement portion. The movable actuator is associated with the handle portion and is engaged with the drive member such that motion of the actuator causes the drive member to move back and forth between first and second drive positions separated by a first distance.

<CIT> describes an end effector that includes first and second jaws movable between open and closed positions, a guide track defined in the second jaw, and a cutting element extendable into the guide track and longitudinally movable within the guide track. A retention feature is positioned within the guide track and operatively couples the cutting element to a drive rod. The drive rod is actuatable to move the cutting element within the guide track, and the retention feature is larger than a width of an opening to the guide track such that the retention feature is retained within the guide track as the cutting element moves.

<CIT> describes an electrosurgical stapling apparatus that uses thermogenic energy as well as surgical fasteners or staples for strengthening tissue, providing hemostasis, tissue joining or welding. The thermogenic energy also strengthens tissue in proximity to a staple line and knife cut line and provides hemostasis along the staple and cut lines formed by the staples and a knife blade during surgical stapling. The use thermogenic energy provides short-term hemostasis and sealing, and reduces or prevents staple line and cut line bleeding, while the stapling features provide short and long-term tissue strength and hemostasis. The stapling apparatus further substantially reduces or prevents knife cut line bleeding by energizing a knife blade for cauterizing tissue while it is being cut. In one embodiment, energy is applied to the anvil to energize the staples as they make contact with the anvil.

The following figures are included to illustrate certain aspects of the present disclosure, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, without departing from the scope of this disclosure. The scope of the invention is defined by claim <NUM>.

The present disclosure is related to surgical tools and, more particularly, to end effectors having improved knife attachment and functionality.

Embodiments discussed herein describe an end effector for a surgical tool, where the end effector includes opposing first and second jaws, and a knife slot defined in one or both of the first and second jaws. A knife is extendable through the knife slot and may be operatively coupled to a knife rod at a retention feature secured to a distal end of the drive rod. More specifically, a central notch may be defined in the retention feature, and the knife may define a locking feature receivable within the central notch to axially constrain the knife to the retention feature and the knife rod. In at least one embodiment, the central notch extends into a material of the drive rod. Securing the knife to the drive rod at the locking feature and the central notch may prove advantageous in transmitting axial loads from the knife to the drive rod, and thus helping to prevent premature failure of the knife.

In some embodiments, a blade is provided at a leading end of the knife and includes a leading cutting edge extending perpendicular to a sealing plane provided between the opposing first and second jaws when the opposing first and second jaws are closed, and an angled cutting edge extending from the leading cutting edge at a transition point. The angled cutting edge extends from the leading cutting edge at an angle offset from perpendicular to the sealing plane. Having the leading cutting edge perpendicular to the sealing plane may provide a longer stroke length for the knife.

In some embodiments, the trailing end of the knife may provide a reduced trailing profile defined by a first arcuate surface extending from a top of the knife and transitioning to a second arcuate surface that transitions to a third arcuate surface. The reduced trailing profile may prove advantageous as the knife traverses the knife slot, which may be curved. While other knives without the reduced trailing profile may catch or contact portions of the curved knife slot, the reduced trailing profile eliminates this friction generating inefficiency.

<FIG> is a block diagram of an example robotic surgical system <NUM> that may incorporate some or all of the principles of the present disclosure. As illustrated, the system <NUM> can include at least one set of user input controllers 102a and at least one control computer <NUM>. The control computer <NUM> may be mechanically and/or electrically coupled to a robotic manipulator and, more particularly, to one or more robotic arms <NUM> (alternately referred to as "tool drivers"). In some embodiments, the robotic manipulator may be included in or otherwise mounted to an arm cart capable of making the system portable. Each robotic arm <NUM> may include and otherwise provide a location for mounting one or more surgical instruments or tools <NUM> for performing various surgical tasks on a patient <NUM>. Operation of the robotic arms <NUM> and associated tools <NUM> may be directed by a clinician 112a (e.g., a surgeon) from the user input controller 102a.

In some embodiments, a second set of user input controllers 102b (shown in dashed line) may be operated by a second clinician 112b to direct operation of the robotic arms <NUM> and tools <NUM> via the control computer <NUM> and in conjunction with the first clinician 112a. In such embodiments, for example, each clinician 112a,b may control different robotic arms <NUM> or, in some cases, complete control of the robotic arms <NUM> may be passed between the clinicians 112a,b as needed. In some embodiments, additional robotic manipulators having additional robotic arms may be utilized during surgery on the patient <NUM>, and these additional robotic arms may be controlled by one or more of the user input controllers 102a,b.

The control computer <NUM> and the user input controllers 102a,b may be in communication with one another via a communications link <NUM>, which may be any type of wired or wireless telecommunications means configured to carry a variety of communication signals (e.g., electrical, optical, infrared, etc.) according to any communications protocol. In some applications, for example, there is a tower with ancillary equipment and processing cores designed to drive the robotic arms <NUM>.

The user input controllers 102a,b generally include one or more physical controllers that can be grasped by the clinicians 112a,b and manipulated in space while the surgeon views the procedure via a stereo display. The physical controllers generally comprise manual input devices movable in multiple degrees of freedom, and which often include an actuatable handle for actuating the surgical tool(s) <NUM>, for example, for opening and closing opposing jaws, applying an electrical potential (current) to an electrode, or the like. The control computer <NUM> can also include an optional feedback meter viewable by the clinicians 112a,b via a display to provide a visual indication of various surgical instrument metrics, such as the amount of force being applied to the surgical instrument (i.e., a cutting instrument or dynamic clamping member).

<FIG> is an isometric side view of an example surgical tool <NUM> that may incorporate some or all of the principles of the present disclosure. The surgical tool <NUM> may be the same as or similar to the surgical tool(s) <NUM> of <FIG> and, therefore, may be used in conjunction with a robotic surgical system, such as the robotic surgical system <NUM> of <FIG>. Accordingly, the surgical tool <NUM> may be designed to be releasably coupled to a tool driver included in the robotic surgical system <NUM>. In other embodiments, however, aspects of the surgical tool <NUM> may be adapted for use in a manual or hand-operated manner, without departing from the scope of the disclosure.

As illustrated, the surgical tool <NUM> includes an elongated shaft <NUM>, an end effector <NUM>, a wrist <NUM> (alternately referred to as a "wrist joint" or an "articulable wrist joint") that couples the end effector <NUM> to the distal end of the shaft <NUM>, and a drive housing <NUM> coupled to the proximal end of the shaft <NUM>. In applications where the surgical tool is used in conjunction with a robotic surgical system (e.g., the robotic surgical system <NUM> of <FIG>), the drive housing <NUM> can include coupling features that releasably couple the surgical tool <NUM> to the robotic surgical system.

The terms "proximal" and "distal" are defined herein relative to a robotic surgical system having an interface configured to mechanically and electrically couple the surgical tool <NUM> (e.g., the housing <NUM>) to a robotic manipulator. The term "proximal" refers to the position of an element closer to the robotic manipulator and the term "distal" refers to the position of an element closer to the end effector <NUM> and thus further away from the robotic manipulator. Alternatively, in manual or hand-operated applications, the terms "proximal" and "distal" are defined herein relative to a user, such as a surgeon or clinician. The term "proximal" refers to the position of an element closer to the user and the term "distal" refers to the position of an element closer to the end effector <NUM> and thus further away from the user. Moreover, the use of directional terms such as above, below, upper, lower, upward, downward, left, right, and the like are used in relation to the illustrative embodiments as they are depicted in the figures, the upward or upper direction being toward the top of the corresponding figure and the downward or lower direction being toward the bottom of the corresponding figure.

During use of the surgical tool <NUM>, the end effector <NUM> is configured to move (pivot) relative to the shaft <NUM> at the wrist <NUM> to position the end effector <NUM> at desired orientations and locations relative to a surgical site. To accomplish this, the housing <NUM> includes (contains) various drive inputs and mechanisms (e.g., gears, actuators, etc.) designed to control operation of various features associated with the end effector <NUM> (e.g., clamping, firing, cutting, rotation, articulation, etc.). In at least some embodiments, the shaft <NUM>, and hence the end effector <NUM> coupled thereto, is configured to rotate about a longitudinal axis A<NUM> of the shaft <NUM>. In such embodiments, at least one of the drive inputs included in the housing <NUM> is configured to control rotational movement of the shaft <NUM> about the longitudinal axis A<NUM>.

The shaft <NUM> is an elongate member extending distally from the housing <NUM> and has at least one lumen extending therethrough along its axial length. In some embodiments, the shaft <NUM> may be fixed to the housing <NUM>, but could alternatively be rotatably mounted to the housing <NUM> to allow the shaft <NUM> to rotate about the longitudinal axis A<NUM>. In yet other embodiments, the shaft <NUM> may be releasably coupled to the housing <NUM>, which may allow a single housing <NUM> to be adaptable to various shafts having different end effectors.

The end effector <NUM> can exhibit a variety of sizes, shapes, and configurations. In the illustrated embodiment, the end effector <NUM> comprises a combination tissue grasper and vessel sealer that include opposing first (upper) and second (lower) jaws <NUM>, <NUM> configured to move (articulate) between open and closed positions. As will be appreciated, however, the opposing jaws <NUM>, <NUM> may alternatively form part of other types of end effectors such as, but not limited to, a surgical scissors, a clip applier, a needle driver, a babcock including a pair of opposed grasping jaws, bipolar jaws (e.g., bipolar Maryland grasper, forceps, a fenestrated grasper, etc.), etc. One or both of the jaws <NUM>, <NUM> may be configured to pivot to articulate the end effector <NUM> between the open and closed positions.

<FIG> illustrates the potential degrees of freedom in which the wrist <NUM> may be able to articulate (pivot) and thereby move the end effector <NUM>. The wrist <NUM> can have any of a variety of configurations. In general, the wrist <NUM> comprises a joint configured to allow pivoting movement of the end effector <NUM> relative to the shaft <NUM>. The degrees of freedom of the wrist <NUM> are represented by three translational variables (i.e., surge, heave, and sway), and by three rotational variables (i.e., Euler angles or roll, pitch, and yaw). The translational and rotational variables describe the position and orientation of the end effector <NUM> with respect to a given reference Cartesian frame. As depicted in <FIG>, "surge" refers to forward and backward translational movement, "heave" refers to translational movement up and down, and "sway" refers to translational movement left and right. With regard to the rotational terms, "roll" refers to tilting side to side, "pitch" refers to tilting forward and backward, and "yaw" refers to turning left and right.

The pivoting motion can include pitch movement about a first axis of the wrist <NUM> (e.g., X-axis), yaw movement about a second axis of the wrist <NUM> (e.g., Y-axis), and combinations thereof to allow for <NUM>° rotational movement of the end effector <NUM> about the wrist <NUM>. In other applications, the pivoting motion can be limited to movement in a single plane, e.g., only pitch movement about the first axis of the wrist <NUM> or only yaw movement about the second axis of the wrist <NUM>, such that the end effector <NUM> moves only in a single plane.

Referring again to <FIG>, the surgical tool <NUM> may also include a plurality of drive cables (obscured in <FIG>) that form part of a cable driven motion system configured to facilitate actuation and articulation of the end effector <NUM> relative to the shaft <NUM>. Moving (actuating) one or more of the drive cables moves the end effector <NUM> between an unarticulated position and an articulated position. The end effector <NUM> is depicted in <FIG> in the unarticulated position where a longitudinal axis A<NUM> of the end effector <NUM> is substantially aligned with the longitudinal axis A<NUM> of the shaft <NUM>, such that the end effector <NUM> is at a substantially zero angle relative to the shaft <NUM>. Due to factors such as manufacturing tolerance and precision of measurement devices, the end effector <NUM> may not be at a precise zero angle relative to the shaft <NUM> in the unarticulated position, but nevertheless be considered "substantially aligned" thereto. In the articulated position, the longitudinal axes A<NUM>, A<NUM> would be angularly offset from each other such that the end effector <NUM> is at a non-zero angle relative to the shaft <NUM>.

In some embodiments, the surgical tool <NUM> may be supplied with electrical power (current) via a power cable <NUM> coupled to the housing <NUM>. In other embodiments, the power cable <NUM> may be omitted and electrical power may be supplied to the surgical tool <NUM> via an internal power source, such as one or more batteries, capacitors, or fuel cells. In such embodiments, the surgical tool <NUM> may alternatively be characterized and otherwise referred to as an "electrosurgical instrument" capable of providing electrical energy to the end effector <NUM>.

The power cable <NUM> may place the surgical tool <NUM> in electrical communication with a generator <NUM> that supplies energy, such as electrical energy (e.g., radio frequency energy), ultrasonic energy, microwave energy, heat energy, or any combination thereof, to the surgical tool <NUM> and, more particularly, to the end effector <NUM>. Accordingly, the generator <NUM> may comprise a radio frequency (RF) source, an ultrasonic source, a direct current source, and/or any other suitable type of electrical energy source that may be activated independently or simultaneously.

In applications where the surgical tool <NUM> is configured for bipolar operation, the power cable <NUM> will include a supply conductor and a return conductor. Current can be supplied from the generator <NUM> to an active (or source) electrode located at the end effector <NUM> via the supply conductor, and current can flow back to the generator <NUM> via a return electrode located at the end effector <NUM> via the return conductor. In the case of a bipolar grasper with opposing jaws, for example, the jaws serve as the electrodes where the proximal end of the jaws are isolated from one another and the inner surface of the jaws (i.e., the area of the jaws that grasp tissue) apply the current in a controlled path through the tissue. In applications where the surgical tool <NUM> is configured for monopolar operation, the generator <NUM> transmits current through a supply conductor to an active electrode located at the end effector <NUM>, and current is returned (dissipated) through a return electrode (e.g., a grounding pad) separately coupled to a patient's body.

The surgical tool <NUM> may further include a manual release switch <NUM> that may be manually actuated by a user (e.g., a surgeon) to open the jaws <NUM>, <NUM>. The release switch <NUM> is movably positioned on the drive housing <NUM>, and a user is able to manually move (slide) the release switch <NUM> from a disengaged position, as shown, to an engaged position. In the disengaged position, the surgical tool <NUM> is able to operate as normal. As the release switch <NUM> moves to the engaged position, however, various internal component parts of the drive housing <NUM> are simultaneously moved, thereby resulting in the jaws <NUM>, <NUM> opening, which might prove beneficial for a variety of reasons. In some applications, for example, the release switch <NUM> may be moved in the event of an electrical disruption that renders the surgical tool <NUM> inoperable. In such applications, the user would be able to manually open the jaws <NUM>, <NUM> and thereby release any grasped tissue and remove the surgical tool <NUM>. In other applications, the release switch <NUM> may be actuated (enabled) to open the jaws <NUM>, <NUM> in preparation for cleaning and/or sterilization of the surgical tool <NUM>. In some applications, the surgical tool <NUM> is first decoupled from the robotic manipulator and the associated motors, following which the user can actuate the manual release switch <NUM> to move the associated inputs and drive the cables once the motors are disengaged.

<FIG> is an enlarged isometric view of the distal end of the surgical tool <NUM>. More specifically, <FIG> depicts an enlarged view of the end effector <NUM> and the wrist <NUM>, with the jaws <NUM>, <NUM> of the end effector <NUM> in the closed position. The wrist <NUM> operatively couples the end effector <NUM> to the shaft <NUM>. In some embodiments, however, a shaft adapter may be directly coupled to the wrist <NUM> and otherwise interpose the shaft <NUM> and the wrist <NUM>. Accordingly, the wrist <NUM> may be operatively coupled to the shaft <NUM> either through a direct coupling engagement where the wrist <NUM> is directly coupled to the distal end of the shaft <NUM>, or an indirect coupling engagement where a shaft adapter interposes the wrist <NUM> and the distal end of the shaft <NUM>. As used herein, the term "operatively couple" refers to a direct or indirect coupling engagement between two components.

To operatively couple the end effector <NUM> to the shaft <NUM>, the wrist <NUM> includes a first or "distal" clevis 402a and a second or "proximal" clevis 402b. The clevises 402a,b are alternatively referred to as "articulation joints" of the wrist <NUM> and extend from the shaft <NUM>, or alternatively a shaft adapter. The clevises 402a,b are operatively coupled to facilitate articulation of the wrist <NUM> relative to the shaft <NUM>. As illustrated, the wrist <NUM> also includes a linkage <NUM> arranged distal to the distal clevis 402a and operatively mounted to the jaws <NUM>, <NUM>.

As illustrated, the proximal end of the distal clevis 402a may be rotatably mounted or pivotably coupled to the proximal clevis 402b at a first pivot axis P<NUM> of the wrist <NUM>. In some embodiments, an axle may extend through the first pivot axis P<NUM> and the distal and proximal clevises 402a,b may be rotatably coupled via the axle. In other embodiments, however, such as is depicted in <FIG>, the distal and proximal clevises 402a,b may be engaged in rolling contact, such as via an intermeshed gear relationship that allows the clevises 402a,b to rotate relative to each other similar to a rolling joint.

First and second pulleys 406a and 406b may be rotatably mounted to the distal end of the distal clevis 402a at a second pivot axis P<NUM> of the wrist <NUM>. The linkage <NUM> may be arranged distal to the second pivot axis P<NUM> and operatively mounted to the jaws <NUM>, <NUM>. The first pivot axis P<NUM> is substantially perpendicular (orthogonal) to the longitudinal axis A<NUM> of the shaft <NUM>, and the second pivot axis P<NUM> is substantially perpendicular (orthogonal) to both the longitudinal axis A<NUM> and the first pivot axis P<NUM>. Movement of the end effector <NUM> about the first pivot axis P<NUM> provides "yaw" articulation of the wrist <NUM>, and movement about the second pivot axis P<NUM> provides "pitch" articulation of the wrist <NUM>.

A plurality of drive cables, shown as drive cables 408a, 408b, 408c, and 408d, extend longitudinally within a lumen <NUM> defined by the shaft <NUM> (or a shaft adaptor) and extend at least partially through the wrist <NUM>. The drive cables 408a-d may form part of the cable driven motion system housed within the drive housing <NUM> (<FIG>), and may comprise cables, bands, lines, cords, wires, woven wires, ropes, strings, twisted strings, elongate members, belts, shafts, flexible shafts, drive rods, or any combination thereof. The drive cables 408a-d can be made from a variety of materials including, but not limited to, a metal (e.g., tungsten, stainless steel, nitinol, etc.), a polymer (e.g., ultra-high molecular weight polyethylene), a synthetic fiber (e.g., KEVLAR®, VECTRAN®, etc.), an elastomer, or any combination thereof. While four drive cables 408a-d are depicted in <FIG>, more or less than four may be employed, without departing from the scope of the disclosure.

The drive cables 408a-d extend proximally from the end effector <NUM> and the wrist <NUM> toward the drive housing <NUM> (<FIG>) where they are operatively coupled to various actuation mechanisms or devices that facilitate longitudinal movement (translation) of the drive cables 408a-d within the lumen <NUM>. Selective actuation of the drive cables 408a-d applies tension (i.e., pull force) to the given drive cable 408a-d in the proximal direction, which urges the given drive cable 408a-d to translate longitudinally within the lumen <NUM>.

In the illustrated embodiment, the drive cables 408a-d each extend longitudinally through the proximal clevis 402b. The distal end of each drive cable 408a-d terminates at the first or second pulleys 406a,b, thus operatively coupling each drive cable 408a-d to the end effector <NUM>. In some embodiments, the distal ends of the first and second drive cables 408a,b may be coupled to each other and terminate at the first pulley 406a, and the distal ends of the third and fourth drive cables 408c,d may be coupled to each other and terminate at the second pulley 406b. In at least one embodiment, the distal ends of the first and second drive cables 408a,b and the distal ends of the third and fourth drive cables 408c,d may each be coupled together at corresponding ball crimps (not shown) mounted to the first and second pulleys 406a,b, respectively.

In at least one embodiment, the drive cables 408a-d may operate "antagonistically". More specifically, when the first drive cable 408a is actuated (moved), the second drive cable 408b naturally follows as coupled to the first drive cable 408a, and when the third drive cable 408c is actuated, the fourth drive cable 408d naturally follows as coupled to the third drive cable 408c, and vice versa. Antagonistic operation of the drive cables 408a-d can open or close the jaws <NUM>, <NUM> and can further cause the end effector <NUM> to articulate at the wrist <NUM>. More specifically, selective actuation of the drive cables 408a-d in known configurations or coordination can cause the end effector <NUM> to articulate about one or both of the pivot axes P<NUM>, P<NUM>, thus facilitating articulation of the end effector <NUM> in both pitch and yaw directions. Moreover, selective actuation of the drive cables 408a-d in other known configurations or coordination will cause the jaws <NUM>, <NUM> to open or close. Antagonistic operation of the drive cables 408a-d advantageously reduces the number of cables required to provide full wrist <NUM> motion, and also helps eliminate slack in the drive cables 408a-d, which results in more precise motion of the end effector <NUM>.

In the illustrated embodiment, the end effector <NUM> is able to articulate (move) in pitch about the second or "pitch" pivot axis P<NUM>, which is located near the distal end of the wrist <NUM>. Thus, the jaws <NUM>, <NUM> open and close in the direction of pitch. In other embodiments, however, the wrist <NUM> may alternatively be configured such that the second pivot axis P<NUM> facilitates yaw articulation of the jaws <NUM>, <NUM>, without departing from the scope of the disclosure.

In some embodiments, an electrical conductor <NUM> may also extend longitudinally within the lumen <NUM>, through the wrist <NUM>, and terminate at an electrode <NUM> to supply electrical energy to the end effector <NUM>. In some embodiments, the electrical conductor <NUM> may comprise a wire, but may alternatively comprise a rigid or semi-rigid shaft, rod, or strip (ribbon) made of a conductive material. The electrical conductor <NUM> may be entirely or partially covered with an insulative covering (overmold) made of a non-conductive material. Using the electrical conductor <NUM> and the electrode <NUM>, the end effector <NUM> may be configured for monopolar or bipolar RF operation.

In the illustrated embodiment, the end effector <NUM> comprises a combination tissue grasper and vessel sealer that includes a knife (not visible), alternately referred to as a "cutting element" or "blade. " The knife is aligned with and configured to traverse a guide track or "knife slot" (not visible) defined longitudinally in one or both of the upper and lower jaws <NUM>, <NUM>. The knife may be operatively coupled to the distal end of a drive rod <NUM> (alternately referred to as "knife rod," "actuation rod," or "push rod") that extends longitudinally within the lumen <NUM> and passes through the wrist <NUM>. Longitudinal movement (translation) of the drive rod <NUM> correspondingly moves the knife within the knife slot(s). Similar to the drive cables 408a-d, the drive rod <NUM> may form part of the actuation systems housed within the drive housing <NUM> (<FIG>). Selective actuation of a corresponding drive input will cause the drive rod <NUM> to move distally or proximally within the lumen <NUM>, and correspondingly move the knife in the same longitudinal direction.

The drive rod <NUM> may comprise a rigid or semi rigid elongate member, such as a rod or shaft (e.g., a hypotube, a hollow rod, a solid rod, etc.), a wire, a ribbon, a push cable, or any combination thereof. The drive rod <NUM> can be made from a variety of materials including, but not limited to, metal (e.g., tungsten, nitinol, stainless steel, etc.), a polymer, or a composite material. The drive rod <NUM> may have a circular cross-section, but may alternatively exhibit a polygonal cross-section without departing from the scope of the disclosure.

<FIG> is another enlarged isometric view of the end effector <NUM>, according to one or more embodiments of the present disclosure. The upper jaw <NUM> (<FIG> and <FIG>) is omitted from <FIG> to enable viewing of various internal features of the end effector <NUM>.

In the illustrated embodiment, a knife <NUM> (mostly occluded) is shown received within a portion of the electrode <NUM> of the lower jaw <NUM> and, more particularly, within a portion of an insulator <NUM> coupled to the electrode <NUM>. In its retracted position, as shown in <FIG>, the knife <NUM> may also be partially received within a knife housing <NUM> mounted to the end effector <NUM> between the upper and lower jaws <NUM>, <NUM>. The lower jaw <NUM> provides or otherwise defines a knife slot <NUM> through which the knife <NUM> may traverse upon distal actuation of the drive rod <NUM>. While the knife slot <NUM> is shown provided in the lower jaw <NUM>, in some embodiments, the knife slot <NUM> may be cooperatively defined by both the upper and lower jaws <NUM>, <NUM>.

As described in more detail below, the knife housing <NUM> defines a central passageway through which the drive rod <NUM> is able to extend to move the knife <NUM> along the knife slot <NUM>. Upon firing the end effector <NUM>, the drive rod <NUM> is moved (urged) distally, which correspondingly moves the knife <NUM> out of the knife housing <NUM> and into the knife slot <NUM>. After firing is complete, the drive rod <NUM> is retracted proximally, which pulls the knife <NUM> proximally and back into the knife housing <NUM> until it is desired to again fire the end effector <NUM>.

<FIG> are enlarged isometric views of the knife <NUM> and the knife housing <NUM>, according to one or more embodiments. In <FIG>, the knife <NUM> is shown in a first or "stowed" position, where the knife <NUM> is at least partially received within a cavity <NUM> defined by the knife housing <NUM> and sized to receive and "stow" the knife <NUM> when not in use. In <FIG>, the knife <NUM> is shown in a second or "extended" position, where the knife <NUM> is extended distally out of the cavity <NUM>.

As mentioned above, the knife <NUM> may be operatively coupled to the distal end of the drive rod <NUM> (shown in dashed lines in <FIG>). A central passageway <NUM> is defined through the knife housing <NUM> and provides a conduit through which the drive rod <NUM> is able to extend to move the knife <NUM> into and along the knife slot <NUM> (<FIG>). In at least one embodiment, the cavity <NUM> may form part of or communicate with the central passageway <NUM>. In some embodiments, the drive rod <NUM> may comprise a solid shaft, but may alternatively comprise a tube or tubular structure. Moreover, the drive rod <NUM> may be made of a variety of flexible materials including, but not limited to, a metal or metal alloy (e.g., a nickel-titanium alloy or "nitinol"), a plastic or thermoplastic material, a composite material, or any combination thereof. The drive rod <NUM> may also comprise a braided cable construction of a metal (e.g., stainless steel, tungsten, etc.), or any of the aforementioned materials, and such braided cable may be radially constrained to support axial loads.

In some embodiments, as illustrated, a flexible sheath <NUM> (e.g., a hypotube or the like) may cover at least a portion of the drive rod <NUM>. The sheath <NUM> may support and help prevent buckling of the drive rod <NUM> when assuming compressive loads during articulation of the wrist <NUM> (<FIG> and <FIG>) and opening and closure of the jaws <NUM>, <NUM> (<FIG> and <FIG>). Similar to the drive rod <NUM>, the flexible sheath <NUM> may be made of a variety of flexible materials including, but not limited to, a metal or metal alloy (e.g., a nickel-titanium alloy or "nitinol"), a metallic coil, a plastic or thermoplastic material, a composite material, a braided tubular, or any combination thereof.

The knife <NUM> may be attached to the distal end of the drive rod <NUM> at a connecting or "retention" feature <NUM>. The retention feature <NUM> may comprise any attachment or coupling means that removably or permanently fixes the knife <NUM> to the drive rod <NUM>. For example, the retention feature <NUM> may comprise, but is not limited to, a crimped engagement, a welded interface, an adhesive attachment, an interference or shrink fit, an overmold (e.g., a shaped block of material or a support block), one or more mechanical fasteners, or any combination thereof. In at least one embodiment, the retention feature <NUM> may comprise a metal tube crimped or press fit to the distal end of the drive rod <NUM>.

Upon firing the end effector <NUM> (<FIG> and <FIG>), the drive rod <NUM> is moved (urged) distally through the central passageway <NUM>, which correspondingly moves the knife <NUM> to the extended position and otherwise out of the cavity <NUM> and into the knife slot <NUM> (<FIG>). As the drive rod <NUM> translates distally, the sheath <NUM> supports the drive rod <NUM> against axial buckling resulting from compressive loading on the drive rod <NUM>. After firing is complete, the drive rod <NUM> is retracted proximally, which correspondingly pulls the knife <NUM> proximally and back to the stowed position and otherwise into the cavity <NUM> until it is desired to again fire the end effector <NUM>.

Some end effectors, such as the end effector <NUM> of <FIG> and <FIG>, can articulate in two planes simultaneously, which requires the knife <NUM> and the drive rod <NUM> to traverse the articulation joints while still applying adequate cut force. Moreover, moving knife <NUM> in the retract direction may result in contacting a hard stop, retract overdrive prevention, or positional locator to be fed into manufacturing settings or controls schemes. In some cases, this can cause the knife <NUM> to prematurely fail and otherwise separate from the retention feature <NUM> and/or the drive rod <NUM>. According to embodiments of the present disclosure, and as described in more detail below, the knife <NUM> may be operatively coupled to the retention feature <NUM> and the drive rod <NUM> with a mechanical locking feature, which helps assume any axial loading resulting, including retract, retraction overdrive prevention, and positional locating loadings.

<FIG> are side and exploded isometric views, respectively, of the knife <NUM> as coupled to the distal end of the drive rod <NUM>, according to one or more embodiments. As illustrated, the retention feature <NUM> may be secured to the distal end of the drive rod <NUM>. The retention feature <NUM> may be made of a material capable of allowing the knife <NUM> to be welded thereto. In at least one embodiment, for example, the retention feature <NUM> may be made of a metal, such as stainless steel. In embodiments where the knife <NUM> is made of Nitinol, the retention feature <NUM> may also be made of Nitinol.

As illustrated, the retention feature <NUM> may comprise a short tubular length or tube. More specifically, the retention feature <NUM> may comprise a tubular body <NUM> having a first or "distal" and 704a and a second or "proximal" end 704b opposite the distal end 704a. The tubular body <NUM> may provide an inner conduit or passageway sized to receive the distal end of the drive rod 416a. As mentioned above, the body <NUM> of the retention feature <NUM> may be secured to the drive rod <NUM> in a variety of ways including, but not limited to, crimping, press fitting, shrink fitting, an adhesive, or any combination thereof.

Once the retention feature <NUM> is secured to the distal end of the drive rod <NUM>, a central notch <NUM> may be cut into and otherwise defined in the body <NUM> at a location between the distal and proximal ends 704a,b. As illustrated, the central notch <NUM> may extend through the side wall of the body <NUM> and partially into the underlying material of the drive rod <NUM>. In some embodiments, the central notch <NUM> may be defined and otherwise formed via grinding or through a grinding process, but could alternatively be formed through other processes, such as laser cutting, wire electrical discharge machining (EDM), milling, chemical etching, water jetting, stamping, or the like. In some embodiments, the depth of the central notch <NUM> into the material of the drive rod <NUM> may stop short of the centerline of the drive rod <NUM>. In other embodiments, however the depth of the central notch <NUM> may extend past the centerline of the drive rod <NUM>, without departing from the scope of the disclosure.

In some embodiments, as illustrated, the knife <NUM> may provide and otherwise define a locking feature <NUM> sized or configured to be received within the central notch <NUM> when the knife <NUM> is properly mounted to the retention feature <NUM>. In one or more embodiments, the locking feature <NUM> may be laser cut into the body of the knife <NUM>, but could alternatively be defined via other manufacturing or forming processes, without departing from the scope of the disclosure.

In the illustrated embodiment, the locking feature <NUM> comprises a generally rectangular projection or tab that extends from the bottom of the main body of the knife <NUM>. In other embodiments, however, the locking feature <NUM> may exhibit other geometric shapes including, but not limited to, angled, arcuate, rounded, or any combination thereof. In some embodiments, when mounting the knife <NUM> to the retention feature <NUM>, the locking feature <NUM> may extend into the central notch <NUM> but not contact the bottom of the central notch <NUM>, such as the material of the drive rod <NUM>. In such embodiments, a gap <NUM> may be defined between the bottom of the central notch <NUM> and the outer extent of the locking feature <NUM>. In other embodiments, however, the locking feature <NUM> may be designed and otherwise configured to contact or rest on the bottom of the central notch <NUM>.

As best seen in <FIG>, once the locking feature <NUM> is received within the central notch <NUM>, the knife <NUM> may be welded to the outer surface of the retention feature <NUM> at one or more locations. More specifically, the knife <NUM> may be welded to the retention feature <NUM> at a first weld 710a located distal to the central notch <NUM>, and a second weld 710a located proximal to the central notch <NUM>. In other embodiments, however, one of the welds 710a,b may be omitted, without departing from the scope of the disclosure. In some applications, the gap <NUM> may prove advantageous in ensuring that there is intimate (direct) contact between the retention feature <NUM> and the blade <NUM>, which can promote more robust welds 710a,b.

In some embodiments, the length L<NUM> of the distal weld 710a may be smaller than the length L<NUM> of the proximal weld 710b. This may prove advantageous since the stress concentration region of the drive rod <NUM> (e.g., the proximal notch corner) is further away from where the drive rod <NUM> exits the retention feature <NUM> such that it takes less of the bending loading (from articulation and retraction) further away from the proximal edge. In addition, the retraction loads commonly result in the primary loading of the proximal-most region of the weld, so having a more robust (longer) proximal weld may help mitigate separation of the knife <NUM> from the retention feature <NUM>. In other embodiments, however, the length L<NUM> of the distal weld 710a may be larger than the length L<NUM> of the proximal weld 710b, or the lengths L<NUM>, L<NUM> may be the same, without departing from the scope of the disclosure.

In some embodiments, the length from the proximal end of the central notch <NUM> to the proximal end of the retention feature <NUM> may be longer than the length from the distal end of the central notch <NUM> to the distal end of the retention feature <NUM>. This may help accommodate the longer length L<NUM> versus the shorter length L<NUM>, but may also prove advantageous in helping with fatigue life as there is larger length between the bending flexible region of the knife rod <NUM> to the area of the central notch <NUM>.

In at least one embodiment, the locking feature <NUM> may be received within the central notch <NUM> such that a distal end 714a of the locking feature <NUM> contacts and otherwise engages an opposing distal end 714b of the central notch <NUM>, and thereby axially constrains the knife <NUM> to the retention features <NUM> and the drive rod <NUM>. More particularly, engaging the opposing distal ends 714a,b may prove advantageous in transmitting axial loads from the knife <NUM> to the drive rod <NUM> and thus helping to prevent premature failure of the knife <NUM>; e.g., separation of the knife <NUM> from the retention feature <NUM>. More particularly, when the knife <NUM> is positionally located or retracted, as briefly mentioned above, the knife <NUM> is moved proximally and stowed within the knife housing <NUM> (<FIG>). During a retraction after firing or a positional locating sequence, an axial load is applied on the drive rod <NUM> to return the knife <NUM> and/or force the knife <NUM> into axial engagement with the knife housing <NUM>. Having the opposing distal ends 714a,b in contact allows the knife <NUM> to transmit a resulting axial load caused by contact with the knife housing <NUM> directly to the drive rod <NUM>. If the opposing distal ends 714a,b were not in contact, the resulting axial load applied to the knife <NUM> would be assumed by the welds 710a,b, which could result in the knife <NUM> separating from the retention feature <NUM> at the welds 710a,b.

Accordingly, while the welds 710a,b may help vertically constrain the knife <NUM> to the drive rod <NUM> via the retention feature <NUM>, receiving the locking feature <NUM> within the central notch <NUM> may provide additional axial constraint and load transfer that helps prevent the knife <NUM> from prematurely separating from the drive rod <NUM>. Consequently, the locking feature <NUM> enables sustaining of higher and increased retraction, retract over drive prevention, and positional locating loads.

As best seen in <FIG>, in some embodiments, an end notch <NUM> may be cut into and otherwise defined in the distal end of the drive rod <NUM>. As illustrated, the end notch <NUM> may extend through the distal end 704a of the retention feature <NUM> and partially into the material of the drive rod <NUM>. The end notch <NUM> may be defined and otherwise formed through any of the processes mentioned above for forming the central notch <NUM>. In at least one embodiment, as illustrated, the end notch <NUM> may extend orthogonal to the central notch <NUM>.

In some embodiments, as best seen in <FIG>, the knife <NUM> may provide and otherwise define an end tab <NUM> sized to be received within the end notch <NUM>. Receiving the end tab <NUM> in the end notch <NUM> may help laterally stabilize the knife <NUM> when mounted to the retention feature <NUM>. Moreover, receiving the end tab <NUM> in the end notch <NUM> may further prove advantageous in transferring axial loads in the fire direction directly from the drive rod <NUM> to the end tab <NUM>. In at least one embodiment, the knife <NUM> may further be welded to the distal end of the drive rod <NUM> at the interface between the end tab and the end notch <NUM>.

<FIG> are side and exploded isometric views, respectively, of another example of the knife <NUM> as coupled to the distal end of the drive rod <NUM>, according to one or more additional embodiments. The knife <NUM> shown in <FIG> may be similar in some respects to the knife <NUM> shown in <FIG>, and therefore may be best understood with reference thereto, where like numerals will correspond to like components not described again in detail.

Similar to the knife <NUM> of <FIG>, for example, the knife <NUM> of <FIG> includes the retention feature <NUM> secured to the distal end of the drive rod <NUM>, and the central notch <NUM> is defined in the retention feature <NUM> and may extend partially into the underlying material of the drive rod <NUM>. Moreover, the knife <NUM> provides the locking feature <NUM> sized to be received within the central notch <NUM>, and the knife <NUM> can be secured to the outer surface of the retention feature <NUM> using one or both of the welds 710a,b (see <FIG>), as generally described above. Furthermore, the end tab <NUM> provided by the knife <NUM> may be received within the end notch <NUM> defined in the distal ends of the drive rod <NUM> and the retention feature <NUM>.

Unlike the knife <NUM> of <FIG>, however, the knife <NUM> of <FIG> may include a dual-edge blade <NUM> provided at a distal or "leading" end 804a of the knife <NUM>. The blade <NUM> is the sharp portion of the knife <NUM> opposite a proximal or "trailing" end 804b of the knife <NUM> and configured to sever or otherwise cut through tissue as the end effector <NUM> (<FIG> and <FIG>) fires and advances the knife <NUM> during operation. In the illustrated embodiment, the blade <NUM> may include a first or "leading" cutting edge 806a and a second or "angled" cutting edge 806b that extends from the leading cutting edge 806a at a transition point <NUM>.

The leading cutting edge 806a may extend substantially orthogonal or perpendicular to a centerline <NUM> of the drive rod <NUM>. Moreover, as explained in more detail below, the leading cutting edge 806b may also extend perpendicular to the sealing plane of the end effector <NUM> (<FIG> and <FIG>). As best seen in <FIG>, the angled cutting edge 806b extends from the leading cutting edge 806a at the transition point <NUM> and at an angle <NUM> offset from perpendicular to the centerline <NUM> (or the sealing plane of the end effector <NUM>). The angle <NUM> may range between about <NUM>° and about <NUM>°, and any subset therebetween.

In some embodiments, the transition point <NUM> may comprise a sharp corner or transition between the leading and angled cutting edges 806a,b. In other embodiments, however, transition point may comprise an arcuate or curved transition between the leading an angled cutting edges 806a,b, without departing from the scope of the disclosure.

Referring briefly to <FIG>, illustrated is an enlarged side view of the end effector <NUM> with the knife <NUM> during firing, according to one or more embodiments. More specifically, the end effector <NUM> is depicted in <FIG> in phantom, thus allowing a view of the knife <NUM> in the process of firing and otherwise being advanced distally (or proximally) within the knife slot <NUM> (<FIG>).

As illustrated the end effector <NUM> includes the upper jaw <NUM> and the lower jaw <NUM>, and a gap <NUM> is defined between the upper and lower jaws <NUM>, <NUM> when the jaws <NUM>, <NUM> are closed. The upper jaw <NUM> provides an upper surface 904a and the lower jaw <NUM> provides an opposing lower surface 904b. The lower surface 904b may be the same structure as the electrode <NUM> (<FIG> and <FIG>) attached to or forming part of the lower jaw <NUM>. In some embodiments, the upper surface 904a may also comprise an electrode, but may otherwise comprise a planar sealing surface made of a nonconductive material (e.g., an insulator).

When the jaws <NUM>, <NUM> are in the closed position, as shown in <FIG>, the upper and lower surfaces 904a,b oppose each other and cooperatively form a sealing plane <NUM> that extends through the gap <NUM>. The sealing plane <NUM> is alternately referred to as a "tissue capturing section" since the sealing plane <NUM> is the location where tissue can be grasped between the upper and lower jaws <NUM>, <NUM> in preparation for cutting with the knife <NUM>. As illustrated, as the knife <NUM> traverses the knife slot <NUM> (<FIG>), the leading cutting edge 806a extends substantially perpendicular to the sealing plane <NUM>.

In some embodiments, as illustrated, the entirety of the leading cutting edge 806a may be disposed below the sealing plane <NUM> and within the knife slot <NUM> (<FIG>) defined in the lower jaw <NUM>. In such embodiments, the transition point <NUM> may also be disposed below the sealing plane <NUM>. In other embodiments, however, it is contemplated herein that the leading cutting edge 806a may extend to or above the sealing plane <NUM>, thus also providing the transition point <NUM> at or above the sealing plane <NUM>, without departing from the scope of the disclosure. In either scenario, the leading cutting edge 806a may be arranged and otherwise configured to cut tissue that may be located below the sealing plane <NUM>, such as tissue that may migrate or "milk" into the knife slot <NUM> upon closing the jaws <NUM>, <NUM>. It is also contemplated herein to alter the arrangement of the leading cutting edge 806a and the angled cutting edge 806b such that the angled cutting edge 806b is positioned fully below the sealing plane <NUM>, and only the leading cutting edge 806a is present in the sealing plane <NUM>.

The leading cutting edge 806a being perpendicular to the sealing plane at <NUM> may also prove advantageous in providing a longer stroke length for the knife <NUM>. More specifically, other knife designs, such as the knife <NUM> depicted in <FIG>, exhibit a fully angled cutting edge (extending top to bottom) that extends distally further than the distal location of the leading cutting edge 806a. As will be appreciated, this can limit how far the knife <NUM> can be advanced within the knife slot <NUM> (<FIG>) since the angled bottom or "leading tip" of the fully angled cutting edge will engage the distal end of the knife slot <NUM>. This can also result in breakage of the leading tip of the fully angled cutting edge by repeatedly engaging the distal end of the knife slot <NUM>. Moreover, the leading tip can cause friction as the knife <NUM> traverses the curvature of the knife slot <NUM>. In contrast, the leading cutting edge 806a extends perpendicular to the sealing plane <NUM> and thereby demonstrates a decrease in the active length of the knife <NUM>, thus increasing potential overall cut length of the knife <NUM> along the knife slot <NUM>.

Referring again to <FIG>, unlike the knife <NUM> of <FIG>, the trailing end 804b of the knife <NUM> of <FIG> may include or otherwise define a reduced trailing profile <NUM>. The reduced trailing profile <NUM> may prove advantageous as the knife <NUM> traverses the knife slot <NUM> (<FIG>). As shown in <FIG>, the knife slot <NUM> is curved, and sometimes referred to as a Maryland-style knife track. Other knife designs, such as the knife <NUM> of <FIG>, provide or exhibit a full trailing profile that may catch or contact portions of the knife slot <NUM> provided in the upper jaw <NUM> (<FIG> and <FIG>) as the knife traverses the knife slot <NUM> when firing or retracting. Contacting the knife slot <NUM> during firing or retracting generates frictional loading and inefficiencies.

In contrast, the reduced trailing profile <NUM> of the knife <NUM> of <FIG> provides less surface area at the trailing end 804b and is therefore less prone to catch or contact portions of the knife slot <NUM> provided in the upper jaw <NUM> (<FIG> and <FIG>). More particularly, the reduced trailing profile <NUM> allows the knife <NUM> to navigate the curved knife slot <NUM> more easily and without significant frictional loading, including significant reduction in frictional drag when passing through tissue. Moreover, the reduced trailing profile <NUM> may lead to a significant reduction in sensitivity to cutting tissue in non-perpendicular orientations (e.g., cutting in the curvature of the knife slot <NUM>, blade tilt, misalignment, etc.). The reduced trailing profile <NUM> also enables larger manufacturing tolerances due to less sensitivity. Lastly, the reduced trailing profile <NUM> may potentially reduce the amount of tissue particulate pulled back into the jaws <NUM>, <NUM> (<FIG> and <FIG>), since there will be less tissue build-up.

In some embodiments, as illustrated, the reduced trailing profile <NUM> may include a first arcuate surface 816a extending from a top <NUM> of the knife <NUM>, and the first arcuate surface 816a transitions to a second arcuate surface 816b, which then transitions to a third arcuate surface 816c. Accordingly, in at least one embodiment, the reduced trailing profile <NUM> may include three contiguous arcuate surfaces 816a-c. As illustrated, the first and third arcuate surfaces 816a,c may each be convex surfaces, and the second arcuate surface <NUM> be may be a concave surface.

In one or more embodiments, a first straight surface 820a may interpose the first and second arcuate surfaces 816a,b, and a second straight surface 820b may interpose the second and third arcuate surfaces 816b,c. In at least one embodiment, the first and second straight surfaces 820a,b may extend perpendicular to each other. Moreover, in at least one embodiment, a third straight surface 820c may extend from the third arcuate surface 816c, and the third straight surface 820c may extend generally parallel to the first straight surface 820a and perpendicular to the second straight surface 820b.

In some embodiments, the third straight surface 820c may extend substantially perpendicular to the centerline <NUM> of the drive rod <NUM>. In other embodiments, however, the third straight surface 820c may extend at other angles relative to the centerline <NUM>, without departing from the scope of the disclosure. In at least one embodiment the third straight surface 820c may be used to help positionally locate the knife <NUM> within the knife housing <NUM> (<FIG> and <FIG>) or to act as a hard stop or over-drive prevention feature. More specifically, as the knife <NUM> is retracted to the stowed position, as described above, the third straight surface 820c may be configured to engage a portion of the knife housing <NUM> within the cavity <NUM> (<FIG>). In other embodiments, however, as the knife <NUM> is retracted to the stowed position, the first straight surface 820a may alternatively be used to the knife housing for retraction, hard stops, over-drive prevention, and positional locating loads.

Still referring to <FIG>, in some embodiments, a bottom <NUM> (shown in dashed lines) of the knife <NUM> at the leading end 804a (e.g., on the end tab <NUM>) may be curved and otherwise exhibit a radius. Having a curved bottom <NUM> may prove advantageous in helping to prevent the knife <NUM> from catching in the knife slot <NUM> (<FIG>) when the knife <NUM> is moved in the distal direction (i.e., the "fire" direction). The curved bottom <NUM> may also result in less surface contact on the bottom of the knife <NUM> that might engage the bottom of the knife slot <NUM>.

Claim 1:
An end effector (<NUM>) for a surgical tool (<NUM>), comprising:
opposing first and second jaws (<NUM>, <NUM>), and a knife slot (<NUM>) defined in one or both of the first and second jaws;
a knife (<NUM>) extendable through the knife slot and operatively coupled to a drive rod (<NUM>) at a retention feature (<NUM>) secured to a distal end of the drive rod;
an end notch (<NUM>) defined in the distal end of the drive rod and extending through a distal end (704a) of the retention feature; and
an end tab (<NUM>) defined by the knife and sized to be received within the end notch to laterally stabilize the knife as mounted to the retention feature,
wherein a central notch (<NUM>) is defined in the retention feature between a proximal end (704b) of the retention feature and the distal end of the retention feature, wherein the central notch extends into the drive rod, and wherein the knife defines a locking feature (<NUM>) receivable within the central notch to axially constrain the knife to the retention feature and the drive rod.