Driver tool and method

In one aspect, a surgical driver is provided that includes a driver shaft, a handle rotatably connected to the driver shaft, and a resilient, elongate pin extending transverse to the driver shaft. The pin is operably engaged with the driver shaft and the handle so that torque applied to the handle causes turning of the driver shaft. The pin is configured to deflect to limit the torque applied to the driver shaft.

FIELD

The disclosure relates to surgical instruments and, more specifically, to surgical instruments for driving bone screws or other elements of medical devices.

BACKGROUND

Surgical drivers are known for driving bone screws into bone. Surgical drivers may also be used to adjust elements of medical devices, such as adjusting a set screw of a bone plate. Some surgical drivers have torque limiting features that limit the risk of overtightening, for example, a screw being driven into bone. These prior surgical drivers may have complicated mechanisms to limit torque that increase the cost of the surgical driver. Due to their cost, the surgical driver may be reused in different procedures. The surgical driver is cleaned before being reused, which involves additional resources to clean the surgical driver and keep track of the surgical driver within, for example, a hospital.

SUMMARY

In accordance with one aspect of the present disclosure, a surgical driver is provided including a driver shaft, a handle rotatably connected to the driver shaft, and a resilient elongate pin. The resilient elongate pin extends transverse to the driver shaft and is operably engaged with the driver shaft and handle such that torque applied to the handle for turning the handle causes turning of the driver shaft. The pin is configured to deflect to limit the torque applied to the driver shaft. The elongate pin deforms in a manner similar to a beam such that the deformation of the pin in response to torque applied to the handle is predictable and highly accurate.

In another aspect, a surgical driver is provided that includes a driver shaft, a handle rotatably connected to the driver shaft, and a resilient member operably engaged with the driver shaft and handle. The surgical driver includes a plurality of raised ridge members each having a ramp surface for deflecting the resilient member upwardly and an upper surface along which the deflected resilient member travels as the handle turns relative to the driver shaft. Each raised ridge member includes a vertical surface extending at a different inclination relative to the upper surface than the ramp surface and a corner connecting the top surface and the vertical surface. A lower surface extends between adjacent ones of the raised ridge members, with the resilient member striking the lower surface as the resilient member rebounds from the deflected configuration. The impact of the resilient member snapping downward from the upper surface of one of the raised ridge members and against the adjacent lower surface provides a tactile and audible indication of the resilient member having deformed in response to the torque applied to the handle exceeding a predetermined torque limit of the surgical driver.

In accordance with another aspect of the present disclosure, a surgical driver is provided that includes a driver shaft, a handle rotatably coupled to the driver shaft, and a resilient member. The resilient member is operably engaged with the driver shaft and the handle such that torque applied to the handle for turning the handle causes turning of the driver shaft. The surgical driver further includes a plurality of pockets each configured to receive the resilient member therein with the resilient member spaced from surfaces of the pockets prior to application of torque to the handle. In this manner, the pockets generally do not apply a load against the resilient member prior to a user applying torque to the handle. This limits creep in the resilient member during storage and transit of the surgical driver and preserves the accuracy of the device. The pockets include ramp surfaces adapted to deflect the resilient member out of the pockets to limit torque applied to the handle when the handle is turned. In one form, the ramp surface of a pocket deflects the resilient member out of the pocket in response to the torque applied to the handle exceeding a predetermined torque limit for the surgical driver.

DETAILED DESCRIPTION

With reference toFIGS. 1 and 2, a torque-limiting driver10is provided that includes a shaft12with a distal end portion14adapted to be connected to, for example, a bone screw16(seeFIG. 14), a set screw of a bone plate, a pedicle screw, or another torque to lock device. The driver10includes a handle18rotatably connected to a proximal end portion20of the shaft12. The driver10allows a user to turn the handle18in direction22and cause the shaft12to also turn in direction22about longitudinal axis79to drive, for example, a bone screw into bone. With reference toFIGS. 2 and 3, the driver10has a torque limiting mechanism27that includes a resilient detent member, such as a resilient elongate pin30, which is operable so that turning of the handle18likewise causes turning of the shaft12. The torque limiting mechanism27disengages the handle18from the shaft12once the torque applied to the handle18exceeds a predetermined torque limit for the driver10so that handle18rotates relative to the shaft12. This keeps the shaft12from applying torque to the bone screw that exceeds the torque limit of the driver10. In one form, the pin30deflects to disengage the handle18from the shaft12once the torque applied to the handle18exceeds the predetermined torque limit for the driver10. The pin30may be of a metallic material, such as nitinol, and may have super-elastic properties. With reference toFIGS. 8 and 9, an intermediate portion30A of the pin30extends through the shaft12and a nut33threadingly engaged with the shaft12. The pin intermediate portion30A is held against upward or downward movement by the nut33. The pin30has halves30B,30C extending outward from openings35of the nut33that are deflected by the handle18and each operate as a cantilever beam as torque is applied to the handle18. In another form, the resilient detent member has only one portion extending outward from the shaft12and contacting the handle18.

Turning toFIG. 4, the pin30has ends portions32,34sized to be received in pockets36of a contiguous pocket structure38of the handle18. The pocket structure38includes raised ridges40and the pin end portions32,34move over the raised ridges40when the torque applied to the handle18exceeds the predetermined torque limit for the driver10. More specifically, as the handle18is turned in direction22to drive the bone screw or other element engaged with the shaft12into bone, the pin end portions32,34engage ramp surfaces42of the ridges40and the pin30resists further turning of the handle18about the shaft12. The pin30may deflect and bend in response to the torque applied to the handle18. The ramp surfaces42deflect the end portions32,34in both a rotary direction (seeFIGS. 6 and 7) and an axial direction (seeFIGS. 8 and 9), as discussed in greater detail below. Although the pin30deflects, the pin30transfers the torque applied to the handle18to the shaft12which, in turn, transfers the torque to the bone screw16. The driver10may be used in non-surgical applications, such as in, for example, the automotive and bicycle fields of endeavor.

Once the torque the user is applying to the handle18reaches the predetermined torque limit for the driver10, the pin end portions32,34deflect up onto lands or upper surfaces44of the ridges40. The ridge upper surfaces44slide beneath the pin end portions32,34as the user continues to turn the handle18which allows the handle18to turn relative to the shaft12. Once the handle18has turned far enough to align the pin end portions32,34with the next pockets36, the pin end portions32,34are no longer held in an upwardly deflected position by the ridges40and rebound downward into the next pockets36. The pin end portions32,34rebound downward and strike lower surfaces, such as floor surfaces110, of the next pockets36. The impact of the pin end portions32,34provide an audible and tactile indication to the user that the user has reached the predetermined torque limit for the driver10. Further, because the pin end portions32,34are in the next pockets36, the user may move the driver10to another bone screw and again turn the handle18in direction22to drive the bone screw into bone until the predetermined torque limit has been reached. In this manner, the driver10may be used to quickly drive several bone screws or other elements one after the other using the same torque output.

With reference toFIGS. 2 and 3, the driver10includes a nut33having a threaded engagement33A with the proximal portion20of the shaft12. The nut33has one or more pairs of diametrically opposed through openings35that can be aligned with a through opening46of the shaft12by turning the nut33about the shaft12. The pin30extends through one of the nut openings35, through the shaft opening46, and through an opposed nut opening35. The nut openings35are sized to form a slip fit connection with the pin30. By turning the nut33about the shaft12during assembly (and before inserting the pin30), the axial position of the nut33can be set which in turn sets the axial position of the pin30once the pin30has been inserted through the nut openings35and the shaft opening46. Further, adjusting the axial position of the pin30within the pockets36allows the manufacturer to set the predetermined torque limit for the driver10. More specifically, positioning the pin free end portions32,34axially lower in pockets36requires the pin free end portions32,34to travel farther in the axial and rotary directions up the ramp surfaces42before reaching the upper surfaces44. The material of the pin30must deflect a greater distance to permit this farther deflection of the pin end portions32,34. The increased deflection of the pin30translates into a higher predetermined torque limit for the driver10. Conversely, positioning the pin free end portions32,34axially higher in the pockets36requires the pin free end portions32,34to travel a shorter distance in axial and rotary directions up the ramp surfaces42before reaching the upper surfaces44. The material of the pin30has to deflect a smaller distance which translates into a lower predetermined torque limit for the driver10.

The handle18includes a handle body49and a cap50that is connected to the handle body49. The handle body49is captured between the pin30and a seat51of the shaft12. In one form, the handle body49is made of Radel® plastic and the shaft12is made of a metal, such as stainless steel. The handle body49has a surface49A that contacts a surface51A of the shaft seat51. The materials of the handle body49and shaft12as well as the geometry of the interface between surfaces49A,51A may be selected to minimize frictional resistance to turning of the handle body49relative to the shaft12. Although users may press downwardly in direction92with varying amounts of pressure, the operation of the pin30and ridges40is unaffected by high pressure or low pressure applied to the handle body49. In other words, the torque required to deflect the pin free ends32,34over the ridges40is generally independent of the pressure the user is applying to handle18in direction92. In one form, a low friction bushing such as a Teflon® bushing can be used to further limit friction between the handle18and the shaft12.

The cap50keeps debris out of the torque limiting mechanism27. In one form, the cap50has an annular wall52and an inner surface60thereof that resists movement of the pin30in directions62. The cap50thereby keeps the pin30extending through the nut33and shaft12which, in turn, axially constrains the handle body49between the pin30and the shaft seat51. In some forms, there is a gap between each pin end portion32,34and the annular wall52during normal operation of the driver10so that there is no contact between the pin30and the cap50that can affect the torque limit of the driver10.

The cap50may have a lip54extending inwardly from the wall52that engages a groove56(seeFIG. 5) of the handle body49. The engagement between the lip54and the groove56forms a snap-fit that retains the cap50on the handle body49. In another form, the cap50and handle body49may be chemically welded together or secured together using fastener(s). The cap50and the handle body49may be made from the same or different materials, including plastics such as Radel® and polyether ether ketone (PEEK) and including metallic materials such as aluminum and stainless steel. One or more of the components of the driver10may be, for example, injection molded, machined, or3D printed.

With reference toFIG. 3, the handle body49includes an inner sleeve72with a through opening70sized to receive the upper portion20of the shaft12. The handle body49has vertical webs74and horizontal webs74extending outward from the inner sleeve72. The webs74,76form a grid-like outer shape of the handle body49with recesses78. The fingers of a user may extend around outer portions of the webs74,76and into the recesses78as the user grasps the handle18.

With reference toFIGS. 4 and 5, the pin30may extend radially outward from the shaft12and position the pin end portions32,34in the pockets36A,36B. The handle body49includes a torque limiting portion100having a the contiguous pocket structure38including the recessed pockets36and the raised ridges40. The contiguous pocket structure38has an annular shape with the pockets36and ridges40arranged in a continuous, uninterrupted pattern of one pocket36followed by one ridge40, followed by one pocket36, etc. around the contiguous pocket structure38. The contiguous pocket structure38allows a user to quickly and easily apply the maximum predetermined torque permitted by the driver10to one surgical device after another. For example, the surgical driver10may be used to sequentially drive a first bone screw into bone until the torque applied to the handle18reaches the predetermined torque limit, drive a second bone screw into bone until the torque applied to the handle18reaches the predetermined torque limit, and tighten a set screw on a bone plate to the predetermined torque limit. The user can perform these operations quickly in sequence without having to re-calibrate the driver10before each operation.

With reference toFIG. 5, the pocket36A and the ridge40A will be discussed in greater detail, although the remainder of the pockets36and ridges40may be identical to the pocket36A and ridge40A. The pocket36A includes an upper opening102through which the pin30shifts downward into the pocket36A in direction92and upwardly in direction90out of the pocket36A. Prior to a user applying torque to the handle18, the pin30has an initial, undeflected configuration wherein the pin30is straight and the pin end portion32is received in the pocket36A. The pin end portion32is spaced from the surfaces of the pocket36A including the floor surface110and the ramp surface42A. The pin end portion34is likewise received in the pocket36B (seeFIG. 6) spaced from the surfaces of the pocket36B such that the handle body49does not apply a load against either end portion32,34. Because the pin end portions32,34are spaced from the surfaces of the pockets36A,36B, the handle body49generally does not apply a load against the pin30when the driver10is not in use. The lack of loading against the pin30limits the creep in the material of the pin30such as during transport or storage. Creep in the material in the form of permanent set of the pin30could change the properties of the pin30and change the predetermined torque limit of the driver10.

The ridge40A includes a ramp surface42A oriented at an angle112relative to the floor110. The angle112may be in the range of approximately 25 degrees to approximately 75 degrees, such as 50 degrees. The ramp surfaces42may each be a planar, inclined surface. In another form, the ramp surfaces42each have a curvature such as being concave or convex. The ramp surfaces42may also have a complex helical shape. The ramp surfaces42may have surface portion(s) configured to affect the frictional resistance to movement of the pin30along the ramp surfaces42, such as projections, recesses, or other structures. The materials of the pin30and handle body49may be, for example, super elastic nitinol and Radel® plastic, and the coefficient of friction between the materials selected to contribute to the predetermined torque limit of the driver10.

The ridge40E is on an opposite side of the pocket36A from the ramp surface42A and includes a vertical surface114. The vertical surface114contacts the pin30if the handle18is turned in a loosening direction116. The vertical surface114extends at angle117relative to the floor surface110that is larger than the angle112. In one form, the angle117is in the range of approximately 68 degrees to approximately 128 degrees, such as 98 degrees. The angle117is larger than angle112so that the vertical surface114extends more vertically than the ramp surface42A. In this manner, the vertical surface114engages the pin30when the user turns the handle18in loosening direction116and permits the user to turn an element, such as a bone screw, in direction116. Due to the more vertical profile of vertical surface114, the vertical surface114generally does not cam the pin30upwardly in direction90such that the pin30remains operatively engaged with the handle body49. This allows the user to apply a higher amount of torque to the handle18in direction116than in direction22. In one form, the vertical surface114and angle117are configured to cam the pin end portion32up onto the ridge40E in response to the torque applied to the handle in direction116exceeding a second predetermined torque limit. The first and second predetermined torque limits that may be applied by turning the handle18in directions22,116may be the same or different, and may be tailored to a particular application.

With reference toFIGS. 6 and 7, turning the handle18in tightening direction22to drive an element imparts rotary deflection to the pin30by shifting the end portions32,34in direction22. More specifically, the pin30is straight and extends radially outward from the shaft12prior to a user applying a torque to the handle18as shown inFIG. 6. Once the user has connected the shaft12with an element, such as a bone screw engaged with bone, turning the handle18in direction22causes the ramp surfaces42A,42B to rotationally shift the pin end portions32,34as shown inFIG. 7. This deflects the end portions32,34distances120,122from the initial positions thereof in the rotary direction22.

Turning toFIGS. 8 and 9, the ridges40will be discussed in greater detail. In the initial, undeflected configuration, the pin30has a central longitudinal axis121extending perpendicular to the longitudinal axis79of the shaft12as shown inFIG. 8. As the user applies torque to the handle18, the ramp surfaces of the ridges40bend the pin end portions32,34axially upward in direction90as the pin end portions32,34reach the ridge upper surfaces44. InFIG. 9, the pin end portions32,34are shown having reached the ridge upper surfaces44after the torque limit of the driver10has been reached. The ridge upper surfaces44extend at an angle137from an axis perpendicular to the shaft longitudinal axis79. Thus, in order for the pin end portions32,34to reach the ridge upper surfaces44, the pin end portions32,34are deflected distances134,136in the axial direction. This required axial deflection of the pin30contributes to setting the torque limit for the driver10. For example, larger axial distances134,136require more torque to be applied to the handle18and smaller axial distances134,136require less torque to be applied to the handle18.

The predetermined torque limit provided by the driver10is a resultant of the force required to strain the pin30in two directions, i.e., in the axial and rotary directions, plus the frictional resistance between the pin end portions32,34and the ramp surfaces42of the handle body49. These parameters may be adjusted to provide a particular predetermined torque limit for the driver10.

With reference toFIGS. 6-9, a method of using the surgical driver10to drive an element, such as a bone screw, is provided to show the axial and rotational deformation that occurs in the pin30as the pin30limits the torque applied to the bone screw.

InFIG. 6, the cap50of the driver tool10is removed to show the shaft12, the handle body49, and the pin30in the initial configuration prior to a user turning the handle18in the tightening direction22. The pin end portions32,34are received in the pockets36A,36B and are spaced from the associated ramp surfaces42A,42B. With reference toFIG. 8, the shaft12, handle body49, and pin30are in the initial configuration before the user applies turns the handle18in direction22. With the driver10in the initial configuration, the user may connect the distal end portion14of the shaft12to a head portion151(seeFIG. 14) of the bone screw16and position a shank portion153of the bone screw against a bone.

The user then turns the handle18in direction22, which turns the handle body49about the shaft12as shown inFIG. 7. The movement of the handle body49around the shaft12brings the ramp surfaces42A,42B into engagement with the pin end portions32,34. The ramp surfaces42A,42B shift the pin end portions32,34in rotary direction22with the handle body49. The pin30resists the pin end portions32,34deflecting in the rotary direction22which provides resistance to turning of the handle body49relative to the shaft12. The pin end portions32,34deflect the rotary distances120,122before the ramp surfaces42,42B cam the end portions32,34upward onto the upper surfaces44A,44B of the ridges40A,40B. In this manner, each half of the pin30achieves a first maximum type of strain due to movement of the pin end portions32,34in the rotary direction22before the pin end portions32,34may shift upward onto the wall upper surfaces44A,44B.

The halves of the pin30also achieve a second maximum strain due to the ridge ramp surfaces42A,42B camming the pin end portions32,34axially upward in direction90. With reference toFIG. 9, the ramp surfaces42cam the pin end portions32,34axially upward distances134,136in direction90from the initial positions thereof (seeFIG. 8) to fully deflected positions thereof (seeFIG. 9). The pin end portions32,34must be deflected to the fully deflected positions before the ridge upper surfaces44may slide beneath the pin end portions. In this manner, each half of the pin30achieves the second maximum type of strain due to the movement of the pin end portions32,34in the axial direction90before the pin end portions32,34shift onto the ridge upper surfaces44A,44B.

In the fully deflected position of the pin end portions32,34, the ridges40orient the pin end portions32,34to extend at the angle137(seeFIG. 9) from the undeflected, horizontal orientation (seeFIG. 8). The torque limit for the driver10may be tailored by configuring the ridges40to bend the pin portions32,34so that the pin portions32,34extend at larger or smaller angles137. For example, by increasing the angle137of the fully deflected position of the pin end portions32,34, the pin30is subjected to more strain in the pin30to climb the ramp surfaces42and increases the torque limit of the driver10. Conversely, decreasing the angle137of the fully deflected position of the pin end portions32,34reduces the strain in the pin30and reduces the torque limit of the driver10.

Once the user applies torque to the handle18that exceeds the torque limit of the driver10, the pin end portions32,34shift off of the ramp surfaces42A,42B and onto the upper surfaces44A,44B of the ridges40A,40B. When the pin end portions32,34shift off of the ramp surfaces42A,42B, the pin end portions32,34offer much less resistance to movement of the ridges40A,40B past the end portions32,34in the rotary direction22. Despite this sudden decrease in resistance, the user continues to apply torque to the handle18which causes the handle18to turn farther around the shaft12in direction22and slides the ridge upper surfaces44A,44B below the pin end portions32,34.

With reference toFIG. 10, the ridge upper surface44A is shown sliding beneath the pin end portion32as the user continues to turn the handle18in direction22after the pin end portions32,34have shifted onto the upper surfaces44A,44B of the ridges40A,40B. The ridges40each include a corner139between the upper surface44and the vertical surface117. In one form, the corner139is a substantially right angle corner having an angle143that is in the range of approximately 68 degrees to approximately 128 degrees, such as 98 degrees. The angle143is smaller than the angle141between the ramp surface42and the upper surface44, with the angle141being in the range of approximately 100 degrees to approximately 160 degrees, such as 130 degrees. The angle143is smaller than the angle141to provide an abrupt drop-off for the pin30, which allows the pin ends32,34to quickly increase velocity as they shift off the ridges40and maximize the force of impact against the floor surfaces110.

The user continues to turn the handle18in direction22until the pin end portions32,34reach the next pockets36C,36D. Once the ridges40A,40B turn past the pin end portions32,34, the pin end portions32,34can rebound from the deflected configurations thereof and the pin30can return to the undeflected, straight configuration thereof. With reference toFIG. 11, the pin end portions32,34snap downward in direction92into the pockets36C,36D as the pin30rebounds. The pin end portions32,34travel in vertical direction92beyond their initial vertical positions and strike the floor surfaces110C,110D of the pockets36C,36D. The impact of the end portions32,34against the floor surfaces110C,110D provides audible and tactile feedback to the user that the driver10has reached the torque limit for the driver10. The end portions32,34bounce back upward in direction90away from the floor surfaces110C,110D to their initial, undeflected vertical positions wherein the end portions32,34are spaced from the surfaces of the pockets36C,36D. The user may then move the driver10to the next bone screw, lock nut, etc. and the process is repeated to torque the next bone screw, lock nut, etc. to the torque limit of the driver10.

The predetermined torque limit for the driver may be in the range of, for example, approximately 5 inch-pounds to approximately 35 inch-pounds, such as 20 inch-pounds. As discussed above, the driver10may be used repeatedly to torque different elements to the maximum torque permitted by the driver10. As one example, the driver10may be used to secure four bone plates to a sternum with each bone plate having four bone screws and at least one set screw. The driver10would in this example be used to drive at least 16 bone screws and four set screws. The driver10could be discarded after use.

The driver18may be configured to permit a user to apply different maximum torque to different devices. For example, the first three ridges40the pin end portions32,34encounter may be identical and be configured to require ten inch-pounds for the pin end portions32,34to deflect over the ridges40. The next ridge40that each pin end portions32,34encounter may be different than the first three end portions40, with the next ridge40requiring fifteen inch-pounds for the pin end portions32,34to deflect over the ridge40. Further, the ridges40can be shaped to present different torque profiles, such as offering less resistance initially to the pin end portions32,34and then sharply increasing resistance. Each ridge40or pocket36can have a different geometry to provide a different maximum torque and torque profile as desired for a particular application.

With reference toFIG. 12, another torque limiting driver300is provided that is similar in many respects to the driver10discussed above. The driver300includes a shaft302and a handle304that is rotatable relative to the shaft302. With reference toFIG. 13, the driver300includes a pin306extending through a through opening308of the shaft302. The handle304includes an internal contiguous structure310including pockets312and ridges314. The pin306includes opposite end portions307each received in a diametrically opposed pocket312. The ridges314have ramp surfaces316that deflect the pin end portions307in an axial direction318and a rotary direction320as the handle304is turned in direction320. In this manner, the pin end portions307shift out of respective pockets312in response to the torque applied to the handle304exceeding a predetermined value, which limits the torque the surgical driver300can apply to a member such as a bone screw or bone plate set screw. One difference between the driver300and the driver10is that the driver300does not include a cap for securing the pin306in the driver300. Instead, the driver handle304includes a sidewall322that retains the pin306within the through opening308of the shaft302.

With reference toFIG. 15, another torque limiting driver400is provided that is similar in many respects to the driver10discussed above. The driver400includes a handle402rotatably connected to a shaft404. The driver400has a resilient pin406extending through an opening408of the shaft404. The resilient pin406has end portions that engage ridges410of the handle410and deflect to limit torque the driver400may apply to an element such as a bone screw412.

One difference between the torque limiting drivers10,400is that the driver400has a handle body414captured between the pin406and a nut416. The nut416is connected to the shaft404at a threaded connection420. The predetermined torque limit of the driver400may be adjusted by turning the nut416, which shifts the handle body414in direction422or424. Shifting the handle body414in direction422increases the torque limit of the driver400because the end portions of the pin406will sit lower in pockets associated with the ridges410such that the pin end portions will have to travel axially and rotationally farther to deflect over the ridges410. Conversely, shifting the handle body414in direction424decreases the torque limit of the driver400because the pin end portions will sit higher in the pockets and will have to travel axially and rotationally shorter distances to deflect over the ridges410. Because the nut416is threadingly engaged with the shaft404, the torque limit of the driver400can be infinitely adjusted since the nut416is not limited to fixed positions along the shaft404.

Those skilled in the art will recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above-described embodiments without departing from the spirit and scope of the invention, and that such modifications, alterations, and combinations are to be viewed as being within the scope of the claims.