Patent Description:
The present invention relates to surgical instruments and, more specifically, to a force limiting mechanism for limiting the amount of force applied to the jaws of an electrosurgical instrument.

Electrosurgical vessel sealers are used for the occlusion of blood vessels and halting of bleeding during surgical procedures. The electrodes of the vessel sealer are carried by a pair of opposing jaws and interconnected to an electrosurgical generator that can selective supply radiofrequency (RF) energy to the electrodes. A user may close the jaws around a vessel to be sealed by squeezing a lever associated with a handle assembly. The vessel may then be sealed by supplying the RF energy to the clamped vessel. A moveable blade may be additionally incorporated into the jaws for cutting of the sealed blood vessel along an intermediate portion of the seal created by the energized electrodes in response to user activation of a second trigger.

One problem that arises in the use of electrosurgical vessel sealers is the user applying too much force to the jaw closing lever, which can result in breakage of the device. Accordingly, there is a need in the art for an approach that can limit the amount of force that a user can apply to the jaws via the handle lever.

<CIT> and <CIT> disclose electrosurgical tools having a lever pivotally connected to the housing with a pivot point which, upon excess actuation force, shifts into a sliding pivot location.

The present invention prevents a user from applying too much force to the jaws by changing the pivoting of the handle lever so that any extra application of force is not transmitted to the jaws. The present invention is defined in Claim <NUM>. More specifically, the present invention comprises surgical instrument with a body having a drive shaft extending along a longitudinal axis and coupled to a pair of jaws that are moveable between an open and a closed position, a bearing tube having a cylindrical body secured around the drive shaft for movement therewith and having a stop extending therefrom; a pair of tracks positioned on opposing side of a plane defined by the longitudinal axis and extending obliquely to the longitudinal axis;a lever having an upper end pivotally coupled to the body by a pivot pin positioned in the pair of tracks, a lower end that extends out of the body, and an intermediate portion that is engaged with the stop of the bearing tube, the intermediate portion including a pair of tines with a pair of bearing surfaces on the inside of the pair of tines that are engaged with the stop of the bearing tube and that are curved; and a spring assembly comprising a spring holder, a spring that is partially loaded, and a plunger having a bearing surface positioned in the body and abutting the pivot pin to bias the pivot pin toward a proximal end of the pair of tracks. The lever may comprise a fork having a pair of opposing tines with a pair of holes formed therethrough, respectively, that accept the pivot pin. The intermediate portion of the lever includes a pair of inner bearing surfaces that are engaged with the stop of the bearing tube. The inner bearing surfaces are curved. The lever may be pivotal about the pivot pin from a first position, where the bearing tube positions the drive shaft so that the jaws are in the open position, to a second position, where the bearing tube positions the drive shaft so that the jaws are in the closed position. The lever may be pivotal about the intermediate portion into a third position where the pivot pin has moved from the first end of the track toward the second end of the track against the bias of the spring assembly. The spring assembly may comprise a spring holder secured within the body. The spring holder may comprise a ferrule and a flange extending from the ferrule. The spring assembly may comprise a spring having a first end at least partially positioned about the ferrule. The spring assembly comprises a plunger extending from a second end of the spring and having a pin engaging surface abutting the pivot pin. The spring may be pre-loaded to prevent movement of the pivot pin until the lever is in the second position.

The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:.

Referring to the figures, wherein like numeral refer to like parts throughout, there is seen in <FIG> a vessel sealing system <NUM> comprising a vessel sealer <NUM> having a pair of conductive opposing jaws <NUM> that are interconnected to an electrosurgical generator <NUM> that can supply RF energy to electrodes of jaws <NUM> for the desiccation of a blood vessel trapped between jaw <NUM>. The dimensions of jaws <NUM> and the type of RF energy supplied will produce desiccation of the blood vessel in a region of a particular width as determined by the thermal spread of the energy being supplied to the blood vessel. As is known in the art, jaws <NUM> are pivotally mounted to vessel sealer <NUM> for movement between an open position and a closed position in response to a user operating a lever <NUM> extending from the main body <NUM> of sealer <NUM>.

Referring to <FIG> and <FIG>, vessel sealer <NUM> includes a handle assembly <NUM> comprised of a housing body <NUM> that encloses a drive shaft <NUM>. Drive shaft <NUM> is coupled to jaws <NUM> so that longitudinal movement of drive shaft <NUM> will mechanically move jaws <NUM> between the open and closed positioned. Housing body <NUM> also encloses cabling <NUM> for delivering energy to jaws <NUM> as well as a latching mechanism <NUM> for selectively retaining lever <NUM> when it is moved from a first position, where jaws <NUM> are open, to a second position, where jaws <NUM> are closed. Housing body <NUM> partially encloses a knob <NUM> that is coupled to an outer shaft <NUM> that surrounds drive shaft <NUM> and supports jaws <NUM> such that rotation of knob <NUM> will rotate jaws <NUM> through <NUM> degrees. Handle assembly <NUM> further comprises a knife trigger <NUM> for extending a blade (not shown) between jaws <NUM> to sever a treated vessel. Knife trigger <NUM> may include an interlock <NUM> engaged with a tab <NUM> mounted to lever <NUM> to prevent operation of knife trigger <NUM> until lever <NUM> has been moved into the second position to free interlock <NUM> when jaws <NUM> are closed
Drive shaft <NUM> is coupled to lever <NUM> so that movement of lever <NUM> between its open and closed positions correspondingly moves jaws <NUM> between their open and closed positions. More specifically, lever <NUM> is pivotally mounted to housing body <NUM> at an upper end <NUM> by a lever pivot pin <NUM>. Lever <NUM> extends from upper end <NUM> to a lower end <NUM> that projects out of housing body <NUM> for grasping by a user. An intermediate portion <NUM> of lever <NUM> is captured within a lever bearing tube <NUM> that is secured to drive shaft <NUM>.

Referring to <FIG>, lever bearing tube <NUM> has a cylindrical body <NUM> that extends between a proximal stop <NUM> and a distal stop <NUM>. Lever bearing tube <NUM> is secured to drive shaft <NUM>, such as by a pin <NUM> extending therebetween, so that movement of lever bearing tube <NUM> by lever <NUM> causes longitudinal translation of drive shaft <NUM> and thus opening and closing of jaws <NUM>. A return spring <NUM> is positioned about drive shaft <NUM> and biases lever bearing tube <NUM> into a distal position set by distal stop <NUM>. The distal position of lever bearing tube <NUM> positions drive shaft <NUM> so that the jaws <NUM> are in the open position, and the proximal position of lever bearing tube <NUM> positions drive shaft <NUM> so that the jaws <NUM> are in the closed position. Return spring <NUM> biases lever bearing tube <NUM> so that jaws <NUM> are in the open position in absence of any force being applied by lever <NUM>. Movement of lever <NUM> from the open to the closed position will move lever bearing tube <NUM> so that jaws <NUM> are driven from the open to the closed position.

Referring to <FIG>, lever pivot pin <NUM> is positioned in a track <NUM> formed by housing body <NUM>. Housing body <NUM> is shown as formed from two opposing body halves such that track <NUM> is formed on both opposing housing body <NUM>, and thus comprises a pair of opposing tracks <NUM> on either side of a plane defined by longitudinal axis X-X for capturing the opposing ends of pivot pin <NUM>. Tracks <NUM> extends obliquely to the longitudinal axis X-X of housing body <NUM> and is positioned proximately to a spring assembly holder <NUM> formed by housing body <NUM>. Tracks <NUM> are configured to allow lever pivot pin <NUM> to slide therein when lever <NUM> is moved by a user past the fully closed position of jaws <NUM>, thereby limiting the amount of force applied by lever <NUM> to jaws <NUM>. As explained below, movement of lever <NUM> beyond its closed position will result in lever <NUM> pivoting around its intermediate portion <NUM>. As a result, tracks <NUM> are oriented to allow lever pivot pin <NUM> to rotate with lever <NUM>.

Referring to <FIG>, a spring assembly <NUM> is positioned in spring assembly holder <NUM> of housing body <NUM> proximately to tracks <NUM>. Spring assembly <NUM> comprises a spring holder <NUM> having a ferrule <NUM> and a flange <NUM>. Spring holder <NUM> accepts a first end <NUM> of a spring <NUM> for securing spring <NUM> and spring assembly <NUM> in spring assembly holder <NUM> of housing body <NUM>. A second end <NUM> of spring <NUM> is in engagement with a plunger <NUM> having a flange <NUM> abutting second end <NUM> of spring <NUM> and a pin bearing surface <NUM> for engaging lever pivot pin <NUM>. When mounted in spring assembly holder <NUM> of housing body <NUM>, spring <NUM> is partially loaded and positioned so that pin bearing surface <NUM> will engage lever pivot pin <NUM> and apply a biasing force pushing lever pivot pin <NUM> toward the proximal end of track <NUM>. As a result, lever pivot pin <NUM> will be held in the proximate end of tracks <NUM> of housing body <NUM> until a force is applied by lever <NUM> to pivot pin <NUM> overcomes the bias of spring <NUM>. Spring <NUM> is therefore configured to become further compressed is response to a predetermined amount of force being applied to pivot pin <NUM>. As explained below, rotation of lever <NUM> about its intermediate portion <NUM> after lever <NUM> and jaws <NUM> have reached the closed position will provide in this force and result in pivot pin <NUM> moving distilling within tracks <NUM> against the bias of spring <NUM>.

Referring to <FIG>, lever <NUM> is configured as a fork <NUM> that extends in two tines <NUM> and <NUM> that define the intermediate portion <NUM> and upper end <NUM> of lever <NUM>. Fork <NUM> extends around lever bearing tube <NUM> and includes curved inner bearing surfaces <NUM> and <NUM>. Curved inner bearing surfaces <NUM> and <NUM> engage proximal stop <NUM> of lever bearing tube <NUM> to apply a force that moves lever bearing tube <NUM> longitudinally and to create a new pivot point for lever <NUM> when lever <NUM> is actuated beyond the closed position. Tines <NUM> and <NUM> terminate in opposing upper ends <NUM> and <NUM> that include holes <NUM> and <NUM> formed therethrough, respectively. Holes <NUM> and <NUM> accept lever pivot pin <NUM> and pivotally couple lever <NUM> to housing body <NUM> via lever pivot pin <NUM> riding within tracks <NUM>.

Referring to <FIG>, jaws <NUM> of vessel sealer are open when lever <NUM> is in the open position. In this position, lever bearing tube <NUM> is in its distal most location so that drive shaft <NUM> has translated longitudinally so that drive shaft <NUM> has fully opened jaws <NUM>. Lever pivot pin <NUM> is held in the proximal end of tracks <NUM> due to the pre-load force applied by spring assembly <NUM>.

Referring to <FIG>, movement of lever <NUM> into the second position, such as by a user, pulls lever bearing tube <NUM> proximally along the longitudinal axis X-X, thereby moving drive shaft <NUM> longitudinally and closing close jaws <NUM>. Lever pivot pin <NUM> remains in the proximate end of tracks <NUM> as the force supplied by the pre-load of spring assembly is configured to provide enough force to keep lever pivot pin <NUM> in place while lever <NUM> is pivoted into the closed position. As jaws <NUM> full close, lever bearing tube <NUM> and proximal stop <NUM> are not capable of further proximal longitudinal movement and lever <NUM> and jaws <NUM> are in the fully closed position.

Referring to <FIG>, additional movement of lever <NUM> beyond the second, closed position where jaws <NUM> are fully closed results in lever <NUM> moving into a flexed state where no further force is imparted to lever bearing tube <NUM> or jaws <NUM>. As lever bearing tube <NUM> has reached its most proximal position, the further application of force to lever <NUM> will cause lever <NUM> to pivot about its intermediate portion <NUM> where curved bearing surfaces <NUM> and <NUM> engage proximal stop <NUM> of lever bearing tube <NUM>. Pivoting of lever <NUM> about its intermediate portion <NUM> imparts a force to lever pivot pin <NUM> via upper ends <NUM> and <NUM> that drives lever pivot pin <NUM> distally in tracks <NUM> against pin bearing surface <NUM> of spring assembly <NUM>. If lever <NUM> is continues to be squeezed past the fully closed position, the pre-load of spring <NUM> will be overcome and lever pivot pin <NUM> will slide distally within tracks <NUM> as lever <NUM> beings to rotate about the new pivot point created by bearing surfaces <NUM> and <NUM> and proximal stop <NUM>. As a result of lever <NUM> pivoting about the new pivot point created by bearing surfaces <NUM> and <NUM> and proximal stop <NUM>, lever <NUM> will not apply any longitudinal forces to lever bearing tube <NUM> that could over-compress of jaws <NUM> or damage vessel sealer <NUM>. Lever <NUM> will instead continue to rotate about the new pivot point such that lever pivot pin <NUM> is moved along tracks <NUM> against the bias of spring <NUM>. Lever <NUM> is thus effectively decoupled from jaws <NUM> so that movement of lever <NUM> beyond the closed position will not apply any additional closing force to jaws <NUM> and lever <NUM> will rotate into the flexed position without applying any more force to drive shaft <NUM> via lever bearing <NUM>.

Claim 1:
A surgical instrument, comprising:
a body (<NUM>) having a drive shaft (<NUM>) extending along a longitudinal axis and coupled to a pair of jaws (<NUM>) that are moveable between an open and a closed position;
a bearing tube (<NUM>) having a cylindrical body secured around the drive shaft for movement therewith and having a stop (<NUM>) extending therefrom;
a pair of tracks (<NUM>) positioned on opposing side of a plane defined by the longitudinal axis and extending obliquely to the longitudinal axis;
a lever (<NUM>) having an upper end (<NUM>) pivotally coupled to the body by a pivot pin (<NUM>) positioned in the pair of tracks, a lower end that extends out of the body, and an intermediate portion (<NUM>) that is engaged with the stop of the bearing tube, the intermediate portion including a pair of tines (<NUM>, <NUM>) with a pair of bearing surfaces (<NUM>, <NUM>) on the inside of the pair of tines that are engaged with the stop of the bearing tube and that are curved; and
a spring assembly (<NUM>) comprising a spring holder (<NUM>), a spring (<NUM>) that is partially loaded, and a plunger (<NUM>) having a bearing surface (<NUM>) positioned in the body and abutting the pivot pin (<NUM>) to bias the pivot pin toward a proximal end of the pair of tracks.