Force limiting mechanisms for surgical instruments

Abstract

A force limiting device for a surgical instrument for preventing excessive force from being applied to the jaws (14) of the instrument. The instrument has a body having a drive shaft coupled to a pair of jaws; a support tube (56) secured to the drive shaft; and a pair of tracks (70) carrying a pivot pin (50) biased into one end of the tracks. A rod (18) is coupled to the pivot pin (50) and abuts the support tube (56) to cause the support tube to move and close the jaws when squeezed by a user. If the rod is overactuated, the pivot pin (50) will slide along the track (70) against the bias of a spring assembly (80), wherein the rod pivots about the support tube rather than the pivot pin. Thus, additional movement of the rod does not cause any additional force to be transmitted through the support tube to the drive shaft.

Description

[0001] Cross-references to related patent applications

[0002] This application claims priority to U.S. Provisional No. 62 / 881,078, filed on July 31, 2019. Technical Field

[0003] The present invention relates to surgical instruments and, more particularly, to a force limiting mechanism for limiting the amount of force applied to the jaws of an electrosurgical instrument. Background Art

[0004] Electrosurgical vessel sealers are used to occlude blood vessels and stop bleeding during surgical procedures. The electrodes of the vessel sealer are carried by a pair of opposing jaws and interconnected with an electrosurgical generator, which can selectively supply radio frequency (RF) energy to the electrodes. The user can close the jaws around the blood vessel to be sealed by squeezing a rod associated with a handle assembly. The blood vessel can then be sealed by supplying RF energy to the clamped blood vessel. A movable blade can be additionally incorporated into the jaws to cut the sealed blood vessel along the middle portion of the seal formed by the powered electrodes in response to the user activating a second trigger.

[0005] One problem that occurs when using an electrosurgical vessel sealer is that the user applies too much force to the jaw closure lever, which may result in damage to the device. Therefore, there is a need in the art for a method that can limit the amount of force that a user can apply to the jaws through the handle lever. Summary of the invention

[0006] The present invention prevents a user from applying excessive force to the jaws by changing the pivoting of a handle bar so that any additional applied force is not transmitted to the jaws. More specifically, the present invention includes a surgical instrument having: a body having a drive shaft extending along a longitudinal axis and connected to a pair of jaws movable between an open position and a closed position; a support tube fixed around the drive shaft to move with the drive shaft and having a stop extending from the drive shaft; a pair of tracks defined in the body and extending obliquely to the longitudinal axis; a rod having an upper end pivotally connected to the body by a pivot pin positioned in the pair of tracks, a lower end extending from the body and a middle portion engaged with the stop of the support tube; and a spring assembly positioned in the body and having a bearing surface biased to push the pivot pin into the first end of the track. The rod may include a fork having a pair of opposing teeth, the pair of opposing teeth respectively having a pair of holes formed therethrough, the pair of holes receiving the pivot pin. The middle portion of the rod may include a pair of inner bearing surfaces engaged with the stop of the support tube. The inner bearing surface may be curved. The rod may be pivoted about the pivot pin from a first position to a second position, in which the support tube positions the drive shaft so that the jaws are in an open position, and in which the support tube positions the drive shaft so that the jaws are in a closed position. The rod may be pivoted about the intermediate portion to a third position, in which 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 include a spring retainer fixed within the body. The spring retainer may include a collar and a flange extending from the collar. The spring assembly may include a spring having a first end positioned at least partially around the collar. The spring assembly may include a plunger extending from the second end of the spring and having a pin engaging surface abutting the pivot pin. The spring may be preloaded to prevent movement of the pivot pin until the rod is in the second position.

[0007] The present invention also includes a method of limiting the force applied to a surgical instrument. The first step includes providing the following: a body having a drive shaft extending along a longitudinal axis and connected to a pair of jaws movable between an open position and a closed position; a support tube fixed around the drive shaft to move with the drive shaft and having a stop extending from the drive shaft; a pair of tracks defined in the body and extending obliquely to the longitudinal axis; a rod having an upper end pivotally connected to the body by a pivot pin positioned in the pair of tracks, a lower end extending from the body and a middle portion engaged with the stop of the support tube; and a spring assembly positioned in the body and having a bearing surface, the bearing surface being biased to push the pivot pin into the first end of the track. Another step includes actuating the rod to move the rod from a first position to a second position so that the jaws move to a closed position. Another step includes continuing to actuate the rod so that the rod pivots about the middle portion and the pivot pin moves along the track. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention will be more fully understood and appreciated by reading the following detailed description in conjunction with the accompanying drawings, in which:

[0009] Figure 1 is a schematic diagram of an electrosurgical system having a pair of jaws carrying electrodes for electrosurgically treating tissue;

[0010] Figure 2 is an isometric view of components of a handle assembly for an electrosurgical vessel sealer according to the present invention;

[0011] Figure 3 is a front view of components of a partially disassembled handle assembly for an electrosurgical vessel sealer according to the present invention;

[0012] Figure 4 is a front elevational view of a partially disassembled handle assembly according to the present invention including an enlarged portion of the rod support tube;

[0013] Figure 5 is a front view showing a handle body of a lever pin track according to the present invention;

[0014] Fig. 6A is a partial front view of a disassembled handle assembly according to the present invention, including an enlarged portion of a spring assembly;

[0015] Figure 6B is an exploded view of a spring assembly according to the present invention;

[0016] Fig. 7A is an isometric view of a rod of a handle assembly according to the present invention;

[0017] Figure 7Bis a side view of a rod of a handle assembly according to the present invention;

[0018] Figure 8 is a front view of the handle assembly when the jaws of the electrosurgical vessel sealer are in an open position;

[0019] Fig. 9 is a front view of the handle assembly when the jaws of the electrosurgical vessel sealer are in a closed position; and

[0020] Fig.10 is a front view of the handle assembly when the jaws of the electrosurgical vessel sealer are in a fixed position. DETAILED DESCRIPTION

[0021] Referring to the accompanying drawings, wherein like numerals refer to like parts throughout, Figure 1 1, a vessel sealing system 10 is shown, which includes a vessel sealer 12 having a pair of opposing conductive jaws 14 interconnected with an electrosurgical generator 16 that can supply RF energy to electrodes of the jaws 14 to dry a blood vessel caught between the jaws 14. The size of the jaws 14 and the type of RF energy supplied will dry the blood vessel in an area having a specific width determined by the thermal spread of the energy supplied to the blood vessel. As is known in the art, the jaws 14 are pivotally mounted to the vessel sealer 12 to move between an open position and a closed position in response to user operation of a rod 18 extending from a body 20 of the sealer 12.

[0022] refer to Figure 2 and 3 , the vessel sealer 12 includes a handle assembly 24, which is composed of a housing body 26 surrounding a drive shaft 28. The drive shaft 28 is coupled to the jaws 14, so that longitudinal movement of the drive shaft 28 causes the jaws 14 to mechanically move between an open position and a closed position. The housing body 26 also encloses a cable 30 for delivering energy to the jaws 14 and a latch mechanism 32 for selectively retaining the rod 18 when it moves from a first position in which the jaws 14 are in an open state to a second position in which the jaws 14 are in a closed state. The housing body 26 partially encloses a knob 34, which is coupled to an outer shaft 36 surrounding the drive shaft 28 and supports the jaws 14, so that rotation of the knob 34 causes the jaws 14 to rotate 360 ​​degrees. The handle assembly 24 further includes a knife trigger 40 for extending a blade (not shown) between the jaws 14 to cut the treated blood vessel. The knife trigger 40 may include an interlock 42 that engages a tab 44 mounted to the lever 18 to prevent operation of the knife trigger 40 until the lever 18 has been moved to the second position to release the interlock 42 when the jaws 14 are closed.

[0023] The drive shaft 28 is coupled to the rod 18 so that movement of the rod 18 between its open and closed positions correspondingly moves the jaws 14 between its open and closed positions. More specifically, the rod 18 is pivotally mounted to the housing body 26 at the upper end 46 by a rod pivot pin 50. The rod 18 extends from the upper end 46 to a lower end 52 that protrudes from the housing body 26 for grasping by a user. An intermediate portion 54 of the rod 18 is captured within a rod support tube 56 that is fixed to the drive shaft 28.

[0024] refer to Figure 4 , the rod support tube 56 has a cylindrical body 58 extending between a proximal stop 60 and a distal stop 62. The rod support tube 56 is fixed to the drive shaft 28, for example, by a pin 64 extending therethrough, so that the rod support tube 56 causes longitudinal translation of the drive shaft 28 by movement of the rod 18, and thus opens and closes the jaws 14. A return spring 66 is positioned about the drive shaft 28 and biases the rod support tube 56 to a distal position set by the distal stop 62. The distal position of the rod support tube 56 positions the drive shaft 28 so that the jaws 14 are in the open position, and the proximal position of the rod support tube 56 positions the drive shaft 28 so that the jaws 14 are in the closed position. The return spring 66 biases the rod support tube 56 so that the jaws 14 are in the open position without any force applied by the rod 18. Movement of the rod 18 from the open position to the closed position will move the rod support tube 56 so that the jaws 14 are driven from the open position to the closed position.

[0025] refer to Figure 5 , the lever pivot pin 50 is positioned in a track 70 formed by the housing body 26. The housing body 56 is shown as being formed of two opposing body halves such that the track 70 is formed on two opposing housing bodies 26 and thus includes a pair of opposing tracks 70 on either side of a plane defined by the longitudinal axis XX for capturing opposing ends of the pivot pin 50. The tracks 70 extend obliquely to the longitudinal axis XX of the housing body 26 and are positioned proximate to a spring assembly retainer 72 formed by the housing body 26. The tracks 70 are configured to allow the lever pivot pin 50 to slide therein when a user moves the lever 18 beyond the fully closed position of the jaws 14, thereby limiting the amount of force applied by the lever 18 to the jaws 14. As described below, movement of the lever 18 beyond its closed position causes the lever 18 to pivot about its intermediate portion 54. Thus, the tracks 70 are oriented to allow the lever pivot pin 50 to rotate with the lever 18.

[0026] refer to Fig. 6A and 6B, the spring assembly 80 is positioned in the spring assembly retainer 72 of the housing body 26 proximate the track 70. The spring assembly 80 includes a spring retainer 82 having a collar 84 and a flange 86. The spring retainer 82 receives a first end 88 of a spring 90 to secure the spring 90 and the spring assembly 80 in the spring assembly retainer 72 of the housing body 26. The second end 92 of the spring 90 engages a plunger 94 having a flange 96 abutting the second end 92 of the spring 90 and a pin bearing surface 98 for engaging the lever pivot pin 50. When installed in the spring assembly retainer 72 of the housing body 26, the spring 90 is partially loaded and positioned so that the pin bearing surface 98 will engage the lever pivot pin 50 and apply a biasing force to urge the lever pivot pin 50 toward the proximal end of the track 70. Thus, the lever pivot pin 50 will remain at the proximal end of the track 70 of the housing body 26 until the force applied by the lever 18 to the pivot pin 50 overcomes the bias of the spring 90. Thus, the spring 90 is configured to be further compressed in response to a predetermined amount of force being applied to the pivot pin 50. As described below, after the lever 18 and the jaws 14 have reached the closed position, rotation of the lever 18 about its intermediate portion 54 will provide this force and cause the pivot pin 50 to move within the track 70 against the bias of the spring 90.

[0027] refer to Fig. 7A and 7B , the rod 18 is configured as a fork 100 that extends between two teeth 102 and 104 that define the middle portion 54 and the upper end 46 of the rod 18. The fork 100 extends around the rod support tube 56 and includes curved inner bearing surfaces 106 and 108. The curved inner bearing surfaces 106 and 108 engage the proximal stop 60 of the rod support tube 56 to apply a force that moves the rod support tube 56 longitudinally and forms a new pivot point for the rod 18 when the rod 18 is actuated beyond the closed position. The teeth 102 and 104 terminate at opposite upper ends 110 and 112, which include holes 114 and 116 formed therethrough, respectively. The holes 114 and 116 receive the rod pivot pin 50 and pivotally couple the rod 18 to the housing body 26 via the rod pivot pin 50 sliding within the track 70.

[0028] refer to Figure 8 , when the rod 18 is in the open position, the jaws 14 of the vessel sealer are open. In this position, the rod support tube 56 is in its most distal position, so that the drive shaft 28 has been longitudinally translated so that the drive shaft 28 has a fully open jaw 14. Due to the preload force applied by the spring assembly 80, the rod pivot pin 50 is maintained at the proximal end of the track 70.

[0029] refer to Fig. 9, such as by a user moving the rod 18 into the second position pulls the rod support tube 56 proximally along the longitudinal axis XX, thereby moving the drive shaft 28 longitudinally and closing the closed jaws 14. The rod pivot pin 50 remains at the proximal end of the track 70 because the force supplied by the preload of the spring assembly is configured to provide sufficient force to hold the rod pivot pin 50 in place when the rod 18 is pivoted to the closed position. When the jaws 14 are fully closed, the rod support tube 56 and the proximal stop 60 cannot make further proximal longitudinal movement, and the rod 18 and the jaws 14 are in the fully closed position.

[0030] refer to Fig.10 , additional movement of the rod 18 beyond the second, closed position in which the jaws 14 are fully closed causes the rod 18 to move into a bent state in which no additional force is applied to the rod support tube 56 or the jaws 14. When the rod support tube 56 has reached its proximal-most position, further application of force to the rod 18 causes the rod 18 to pivot about its middle portion 54, wherein the curved bearing surfaces 106 and 108 engage the proximal stop 60 of the rod support tube 56. The pivoting of the rod 18 about its middle portion 54 applies a force to the rod pivot pin 50 through the upper ends 110 and 112, which drives the rod pivot pin 50 distally in the track 70 against the pin bearing surface 98 of the spring assembly 80. If the rod 18 continues to be squeezed beyond the fully closed position, the preload of the spring 90 will be overcome and the rod pivot pin 50 will slide distally within the track 70 because the rod 18 is rotating about the new pivot point formed by the bearing surfaces 106 and 108 and the proximal stop 60. Since the rod 18 is pivoted about the new pivot point formed by the bearing surfaces 106 and 108 and the proximal stop 60, the rod 18 will not apply any longitudinal force to the rod support tube 56, which may over-compress the jaws 14 or damage the vessel sealer 12. Instead, the rod 18 will continue to rotate about the new pivot point, causing the rod pivot pin 50 to move along the track 70 against the bias of the spring 90. Thus, the rod 18 is effectively decoupled from the jaws 14, so that movement of the rod 18 beyond the closed position will not apply any additional closing force to the jaws 14, and the rod 18 will rotate to the flexed position without applying any more force to the drive shaft 28 through the rod bearing 58.

[0031] Thus, the present invention provides a method of limiting the amount of force that a user can apply to the jaws of the vessel sealer 12. Thus, the present invention helps control the quality of the seal by limiting the pressure applied to the clamped tissue and, therefore, the thickness of the clamped tissue. Controlling the clamped thickness can reduce over-drying, low burst pressure seals, charring, and reduce the likelihood of severing the compressed tissue. The present invention also reduces the likelihood of tissue tearing by limiting tissue gripping forces, i.e., if the user applies excessive organ manipulation forces, the tissue tends to slip rather than tear.

Claims

1. A surgical instrument comprising: a body having a drive shaft extending along a longitudinal axis and coupled to a pair of jaws movable between an open position and a closed position; a support tube secured about the drive shaft to move with the drive shaft and having a stopper extending from the drive shaft; a pair of rails positioned on opposite sides 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 extending from the body, and an intermediate portion engaging a stop of the support tube, wherein the intermediate portion has a pair of curved inner bearing surfaces engaging the stop of the support tube, wherein the lever includes a fork having a pair of opposing teeth, the pair of opposing teeth respectively having a pair of holes formed therethrough, the pair of holes receiving the pivot pin, and wherein the lever pivots about the pivot pin from a first position in which the support tube positions the drive shaft so that the pair of jaws are in the open position to a second position in which the support tube positions the drive shaft so that the pair of jaws are in the closed position; and a spring assembly including a spring retainer secured within the body, the spring retainer including a collar and a flange extending from the collar and having a bearing surface biased to urge the pivot pin into the first end of the pair of tracks, wherein the lever pivots about the intermediate portion to a third position in which the pivot pin has moved from a first end of the pair of tracks toward a second end of the pair of tracks against the bias of the spring assembly.

2. The surgical instrument of claim 1, wherein the spring assembly comprises a spring having one end positioned at least partially around the collar.

3. The surgical instrument of claim 1, wherein the spring is preloaded to prevent movement of the pivot pin until the lever is in the second position.

4. A method of limiting the amount of force applied to a surgical instrument, comprising the steps of: The following are provided: a body having a drive shaft extending along a longitudinal axis and coupled to a pair of jaws movable between an open position and a closed position; a support tube secured about the drive shaft to move with the drive shaft and having a stopper extending from the drive shaft; a pair of tracks defined in the body and extending obliquely to the longitudinal axis; a rod having an upper end pivotally coupled to the body by a pivot pin positioned in the pair of tracks, a lower end extending from the body, and a middle portion engaging the stop of the support tube, wherein the middle portion of the rod includes a pair of curved inner bearing surfaces engaging the stop of the support tube; and a spring assembly positioned in the body and having a bearing surface biased to urge the pivot pin into the first end of the pair of tracks, wherein the rod includes a fork having a pair of opposing teeth, the pair of opposing teeth each having a pair of holes formed therethrough, the pair of holes receiving the pivot pin, wherein an intermediate portion of the rod has a pair of curved inner bearing surfaces that engage a stop of the support tube, and wherein the spring assembly includes a spring retainer secured within the body and supporting a spring that biases a plunger having a surface into the pivot pin; actuating the lever to move the lever from a first position to a second position such that the jaws move from the open position to the closed position; and Continued actuation of the lever to a third position causes the lever to pivot about the intermediate portion and the pivot pin to move along the pair of tracks.

Images