Patent Description:
Many pedicle screws utilize a coupling element or tulip, which engages the pedicle screw head and is pivotable and/or rotatable in relation to the axis of the screw shank (e.g., polyaxial to the shank axis). While this ability more easily facilitates alignment of the tulip with the longitudinally linked rods, it may cause the pedicle screw to be difficult to handle. The use of an insertion instrument typically provides more positive control over the placement of the pedicle screw.

Prior to the placement of the pedicle screw into the vertebral body, many insertion instruments utilize devices, such as, for example, a guidewire or K-wire to aid in the introduction of the pedicle screw into the vertebral body and to control its trajectory so that it may be more accurately secured to the vertebral body.

Screw insertion instruments exist that use a stylet in place of a guidewire for introducing the pedicle screw into the vertebral body. Such instruments hold the stylet and screw at fixed positions such that the stylet extends distally from the tip of the screw by a small distance. Because pedicle screws are available in various lengths, a screw insertion instrument capable of holding the stylet at a variable location may be advantageous in certain situations.

Document <CIT> discloses a stylet screw driver assembly having a screw driver/ratcheting handle assembly which houses a stylet, pre-assembled to a set length based on the screw length in use, fixed in place by a spring-loaded button mechanism located on the proximal end of the ratcheting handle. The spring-loaded button mates with the stylet assembly, providing various stylet protrusion lengths.

In an embodiment of the disclosure, a stylet holder may be releasably couplable with a cannulated screw driving instrument. The stylet holder may be able to retain a stylet head at one of multiple discrete locations, such that a user may vary a distance that a point of the stylet extends from a distal end of the instrument by choosing which of the discrete locations to insert the stylet head into before coupling the stylet holder to the instrument. The stylet holder may include a channel extending along an axis, and the multiple discrete locations may be defined by ribs opposed sides of the channel. The stylet holder may further include a series of apertures, each aperture opening into the channel at one of the multiple discrete locations. The stylet holder may be couplable to the instrument by inserting the stylet, followed by the stylet holder, into a cannulation of the instrument while the stylet head is retained within one of the multiple discrete locations within the stylet holder.

The instrument may include a ratcheting handle capable of rotation in one direction about a central axis of the instrument relative to other components of the instrument. A ratcheting function of the handle may be provided by a gear disposed within the handle, and a pawl fixed to the handle shaped to allow the gear to rotate relative to the handle in only one direction about the central axis. The handle may be lockable to reversibly disable the ratcheting function. The ratcheting function may be reversibly disabled by actuation of a post moveable radially relative to the central axis. The post may include post on a radially inner end, and the post teeth may engage the gear when the post is in a radially inner position. The handle may include a retainer biased to engage the post when the post is in the radially inner position to prevent the post from travelling out of the radially inner position. The retainer may be manipulable to release the post from the radially inner position, and the post may be biased to move to a radially outer position when released by the retainer. The gear may be engageable by a clip of the stylet holder to facilitate the releasable coupling between the stylet holder and the instrument. The gear may include an annular groove, and the clip may be moveable between a position wherein it may engage the annular groove and a position wherein it may not engage the annular groove.

According to the invention a screw driving instrument may include a handle, a passage extending through the handle and along a central axis of the instrument, and an insert receivable in a portion of the passage extending through the handle. The insert may include a clip engageable to the handle, a pillar including a channel extending axially to define an elongate slot on one side of the pillar, and axial column of recesses on at least one side of the channel.

In some arrangements according to any of the foregoing, the recesses may be defined by a column of radially extending ribs on the at one side of the channel.

In some arrangements according to any of the foregoing, the instrument may include a column of apertures opening into the channel and extending along an opposite side of the pillar from the elongate slot, each aperture being axially aligned with one of the recesses.

In some arrangements according to any of the foregoing, the instrument may include opposed pairs of recesses defined on two sides of the channel.

In some arrangements according to any of the foregoing, the instrument may include a column of apertures opening into the channel and extending along an opposite side of the pillar from the elongate slot, each aperture being axially aligned with one of the opposed pairs of recesses on the sides of the channel.

In some arrangements according to any of the foregoing, the handle may include a ratchet mechanism. The ratchet mechanism may include a gear disposed within a body of the handle and including an axial bore through which the insert is insertable. The ratchet mechanism may further include a pawl fixed to the handle allowing rotation of the body of the handle relative to the gear in only one direction about the central axis of the instrument.

In some arrangements according to any of the foregoing, the ratchet mechanism may comprise a post disposed within the body of the handle and having a radially inner end with post teeth. The post may be actuatable between a radially inner position wherein the post teeth engage the gear and prevent rotation of the body of the handle relative to the gear about the central axis of the instrument and a radially outer position wherein the post teeth do not engage the gear.

In another embodiment, a screw driving instrument may include a cannulated drive shaft including a distal end defining a drive head and extending along a central axis of the instrument. The instrument may further include a stylet including a proximal end defining a stylet head. The instrument may further include a stylet holder engageable to the instrument and including a pillar configured to retain the stylet head at one of a variety of discrete positions relative to the instrument while the stylet holder is coupled to the instrument.

In some arrangements according to any of the foregoing, the stylet holder may be couplable to the instrument such that the stylet head may not be removable from the pillar while the stylet holder is coupled to the instrument.

In some arrangements according to any of the foregoing, the instrument may include a ratcheting handle.

In some arrangements according to any of the foregoing, the ratcheting handle may be releasably engageable with the drive shaft.

In some arrangements according to any of the foregoing, the handle may include a gear and pawl assembly providing ratcheting function to the handle, the gear including a bore through which the pillar is received while the stylet holder is coupled to the instrument.

In some arrangements according to any of the foregoing, reversible coupling between the stylet holder and the instrument may be facilitated by a clip of the stylet holder being engageable with the gear.

In some arrangements according to any of the foregoing, the handle may be reversibly lockable such that ratcheting is prevented while the handle is locked.

A method (not claimed) of use of a screw driving instrument may include disposing a portion of a stylet within a stylet holder capable of retaining the portion of the stylet at multiple locations along an axis such that the portion of the stylet is retained at one of the multiple locations along the axis. The method may further include inserting the stylet and stylet holder into the instrument such that a distal end of the stylet extends out of a distal end of the instrument while the portion of the stylet is retained at the one of the multiple locations along the axis.

In some arrangements according to any of the foregoing, the method may include creating a pilot hole in a solid object with the stylet, and introducing a screw into the pilot hole with the instrument. The method may further include removing the stylet holder and stylet from the instrument after introducing the screw into the pilot hole.

In some arrangements according to any of the foregoing, the stylet holder may be removed from the instrument by use of opposed ends of a removal tool to simultaneously depress a button to decouple the stylet holder from the instrument with one of the opposed ends and wedge between the instrument and stylet holder with another of the opposed ends.

In some arrangements according to any of the foregoing, the multiple locations may be discrete and predefined.

In some arrangements according to any of the foregoing, the multiple locations along the axis may be predefined by recesses extending axially along at least one side of a channel extending along a portion of the stylet holder.

In some arrangements according to any of the foregoing, the instrument may include a ratcheting handle capable of being locked to reversibly disable ratcheting.

When referring to specific directions and planes in the following disclosure, it should be understood that, as used herein, the term "proximal" means closer to the operator/surgeon, and the term "distal" means further away from the operator/surgeon.

A screw driving instrument <NUM> for inserting a screw, such as a cannulated pedicle screw <NUM>, into an object, such as a vertebral pedicle, is illustrated in a fully assembled state in <FIG>, and in a state that is fully assembled except for the pedicle screw <NUM> and an extension assembly <NUM> in <FIG>. The instrument <NUM> and its components extend generally along a central axis X. As used herein, the terms "axial," "radial," and "tangential" refer to directions relative to the central axis X, except where specified otherwise. Further, where the central axis X is illustrated with regard to any component of the instrument <NUM> in FIGS. 2A - <NUM>, it indicates that component's orientation relative to the central axis X in the fully assembled state of the instrument <NUM> as shown in <FIG>.

The instrument <NUM> includes a ratcheting handle <NUM> at its proximal end, with a stylet holder <NUM> disposed through the handle <NUM>. A stylet <NUM> extends along the central axis X from a proximal end of the stylet holder <NUM> to a distal tip of the stylet <NUM> that extends distally beyond a distal tip of the attached pedicle screw <NUM>. A drive assembly <NUM> is connected at a distal end of the handle <NUM>. As shown in <FIG>, the drive assembly <NUM> includes a sheath assembly <NUM> and a cannulated driver <NUM> that extends proximally from the sheath assembly <NUM> into the handle <NUM> and distally from the sheath assembly <NUM> to drive the pedicle screw <NUM>. The sheath assembly <NUM> further includes a knob <NUM> near its proximal end and a tube <NUM> extending through and distally beyond the knob <NUM>. The tube <NUM> as shown in <FIG> includes a threaded section <NUM> at its distal end, but in alternative arrangements the tube <NUM> may include other coupling features, and in further arrangements the threaded section <NUM> or other coupling features may be located away from the distal end of the tube <NUM>.

Returning to <FIG>, an extension assembly <NUM> may be coupled to the drive assembly <NUM>, such as by internal threading engaged with the threaded section <NUM> of tube <NUM>, or by other coupling features the extension assembly <NUM> and tube <NUM> may have. The extension assembly <NUM> holds a head or tulip feature of the pedicle screw <NUM> at a distal position relative to the drive assembly <NUM> such that the driver <NUM> may drivingly engage the pedicle screw <NUM>.

For a more detailed description of a similar drive assembly, extension assembly, and pedicle screw, and of the interaction of those components, reference can be made to <CIT>. For a more detailed description of the interaction between drive and extension assemblies specifically, reference can be made to <CIT>, and for a more detailed description of a similar drive assembly alone, reference can be made to <CIT>. For a more detailed description of an exemplary bone screw that may be compatible with the instrument <NUM> of the present disclosure if modified at least with cannulation, reference can be made to <CIT>, though it should be understood that the instrument <NUM> is compatible with a broad variety of cannulated screws known and unknown in the art.

An exemplary arrangement of parts for the ratcheting handle <NUM> is illustrated in <FIG>, with a cross-section of the fully assembled handle <NUM> shown in <FIG>. In an exemplary method of assembling the handle <NUM>, a pawl <NUM> is inserted into a cavity <NUM> in a body <NUM> of the handle <NUM>. The body <NUM> includes a first arm 207a and a second arm 207b extending in mutually opposite radial directions. The cavity <NUM> extends from a first opening <NUM> shown <FIG> at a radial extremity of the first arm 207a to a second opening <NUM> at a radial extremity of the second arm 207b. A handle recess <NUM> at a proximal side of the body <NUM> opens distally into the cavity <NUM>.

The pawl <NUM> is positioned within the first arm 207a such that the pawl tapers to be narrower with increasing proximity to the central axis X. The pawl <NUM>, once positioned, is secured with a pawl pin <NUM> that may be inserted through a corresponding hole in the first arm 207a of the body <NUM>. The pawl pin <NUM> of the illustrated arrangement includes threading for engaging threads in the corresponding hole in the first arm 207a. The pawl pin <NUM> fixes the pawl <NUM> in place within the first arm 207a, but the pawl <NUM> is able to pivot about the pawl pin <NUM>.

A washer <NUM> is inserted into a disc shaped space within an externally threaded proximal annulus 202a of a proximal adapter <NUM>. The proximal annulus 202a is then threaded into a threaded distal opening of the body <NUM>. A gear <NUM> is inserted into the cavity <NUM> through the handle recess <NUM>. An externally threaded neck <NUM> of a distal adapter <NUM> is inserted through the proximal adapter <NUM> and washer <NUM> into the cavity <NUM> and threaded into an internal bore of the gear <NUM>. A flat radial shoulder <NUM> of the distal adapter <NUM> seats against the washer <NUM> to prevent the gear <NUM> from moving axially after the neck <NUM> is threaded into the washer <NUM> while allowing the gear <NUM> and distal adapter <NUM> to rotate smoothly about the central axis X.

A block <NUM> is inserted into the first opening <NUM>, followed by a block spring <NUM> and a lock screw <NUM>. The lock screw <NUM> is threaded into the first opening <NUM> to close the first opening <NUM> and hold the block spring <NUM> against the block <NUM>. The pawl <NUM>, block <NUM>, and gear <NUM> are thus positioned with respect to one another within the cavity <NUM> approximately as shown in <FIG>. The pawl <NUM> is asymmetrical to permit the gear <NUM> to rotate in only one direction about the central axis X. More specifically, the pawl <NUM> is shaped and located such that, if the gear <NUM> rotates in a counter-clockwise direction from the perspective of <FIG>, a gear tooth <NUM> will act to compress the pawl <NUM> against the pawl pin <NUM>, causing the gear <NUM> against the pawl <NUM>. However, if the gear <NUM> rotates in a clockwise direction from the perspective of <FIG>, the pawl <NUM> will pivot about the pawl pin <NUM> and permit the gear teeth <NUM> to pass by. When rotation of the gear <NUM> causes the pawl <NUM> to pivot, the pawl <NUM> pushes the block <NUM> back toward the lock screw <NUM>. The block spring <NUM> pushes back on the block <NUM> to cause the block <NUM> to push, in turn, on the pawl <NUM>, thereby causing the pawl <NUM> to return to position between each gear tooth <NUM> when the gear <NUM> rotates. The block <NUM> and block spring <NUM> thereby prevent the pawl <NUM> from skipping over gear teeth <NUM> and ensures rotation of the gear <NUM> in the binding direction will consistently be prohibited.

Because the pawl pin <NUM> is fixed within the first arm 207a of the body <NUM>, but the gear <NUM> is free to rotate relative to the body <NUM>, the foregoing description of <FIG> similarly to movement of the body <NUM> relative to the gear <NUM>. In other words, the pawl <NUM> permits the body <NUM> to be rotated relative to the gear <NUM> in a counter-clockwise direction from the perspective of <FIG>, but not in a clockwise direction. As such, if there is resistance on the gear <NUM> through the adapters <NUM>, <NUM>, torque applied to the body <NUM> in the counter-clockwise direction is not transferred to the adapters <NUM>, <NUM>, but torque applied to the body <NUM> in the clockwise direction is applied to the adapters <NUM>, <NUM> by action of the pawl <NUM> against the gear <NUM>.

In continued reference to <FIG> and <FIG>, a retainer spring <NUM> is inserted into the cavity <NUM> through a second arm aperture <NUM> on a surface of the second arm 207b, followed by a retainer <NUM>. Next, a lock post spring <NUM> is inserted into the cavity <NUM> through the second opening <NUM> and retainer <NUM>, and a lock post <NUM> is inserted through the second opening <NUM>, lock post spring <NUM>, and retainer <NUM>. The lock post <NUM> is secured within the cavity by inserting a lock post pin <NUM> through a corresponding hole in the second arm 207b of the body <NUM> and through a post track <NUM> defined through the lock post <NUM>. In the illustrated arrangement, the lock post pin <NUM> includes threads for engaging threads of the corresponding hole in the second arm 207b. Securing the lock post <NUM> within the cavity <NUM> also prevents the retainer <NUM> from being removed through the second arm aperture <NUM>.

The lock post <NUM> and retainer <NUM> cooperate to selectively lock and release the body <NUM> relative to the gear <NUM>. A radially inner end of the lock post <NUM> includes post teeth <NUM> for engaging the gear <NUM>. The post track <NUM> permits some radial movement of the lock post <NUM> relative to the lock post pin <NUM>, while a shape of the cavity <NUM> within the second arm 207b restricts the lock post <NUM> to only radial movement. At a radially innermost position available to the lock post <NUM>, the post teeth <NUM> engage the gear <NUM>, thereby preventing the body <NUM> and gear <NUM> from rotating relative to one another about the central axis X in both the clockwise and counterclockwise directions. When the lock post <NUM> is pushed in to the radially innermost position, such as by pressure on a lock post button <NUM> on a radially outer end of the lock post <NUM>, the retainer spring <NUM> biases the retainer <NUM> into engagement with a post notch <NUM> of the lock post <NUM>. When engaged in the post notch <NUM>, the retainer <NUM> prevents the lock post <NUM> from travelling out of the radially innermost position, so the post teeth <NUM> remain in engagement with the gear <NUM> after pressure is removed from the lock post button <NUM>. Pressure may be applied to the retainer <NUM> through the second arm aperture <NUM> to compress the retainer spring <NUM> and move the retainer <NUM> out of engagement with the post notch <NUM>, thereby releasing the lock post <NUM> from the radially innermost position. When the retainer <NUM> is pushed out of engagement with the post notch <NUM>, the lock post spring <NUM> biases the lock post <NUM> radially outward and away from the gear <NUM>, freeing the gear <NUM> and body <NUM> to rotate relative to one another about the central axis X in the direction permitted by the pawl <NUM>.

The distal adapter <NUM> includes a core <NUM> and a cover <NUM> surrounding a distal portion of the core <NUM> as shown in <FIG>. The core <NUM> in turn includes an axial passage <NUM> extending through an entire axial length of the distal adapter <NUM>. The axial passage <NUM> includes a polygonal portion <NUM> at its distal end. The polygonal portion <NUM> has a polygonal axial cross-section shaped to receive and drive a polygonal head <NUM> of the driver <NUM>, shown in <FIG>. As noted above, additional details regarding interaction between a similar handle and drive assembly can be found in the '<NUM> publication. Returning to <FIG>, a proximal end of the polygonal portion <NUM> of the axial passage <NUM> is defined by an annular shelf <NUM> extending radially into the axial passage <NUM>. The core <NUM> is structured to transfer distal axial force on the shoulder <NUM> to the shelf <NUM> so that the shelf <NUM> can, in turn transfer the distal axial force to the polygonal head <NUM> of the driver <NUM>.

The core <NUM> and cover <NUM> include an opposed outer ridge <NUM> and inner ridge <NUM>, respectively. The outer ridge <NUM> extends to contact an interior of the cover <NUM> and the inner ridge <NUM> extends to contact an exterior of the core <NUM>, so the outer ridge <NUM> and inner ridge <NUM> cooperate to define an annular pocket <NUM> between the core <NUM> and the cover <NUM>. An adapter spring <NUM> is disposed within the pocket <NUM> surrounding the core <NUM> and extending between the outer ridge <NUM> and inner ridge <NUM>. The adapter spring <NUM> thereby acts to bias the cover <NUM> distally toward a resting position relative to the core <NUM>. Thus, if the cover <NUM> is forced proximally along the core <NUM> from the resting position, the adapter spring <NUM> will bias the cover <NUM> to return to the resting position when the force is removed.

In arrangements wherein the polygonal head <NUM> of the driver <NUM> has an interference fit within the polygonal space <NUM>, a distal portion of the core <NUM> may expand radially outward around the polygonal space <NUM> when the polygonal head <NUM> is inserted. In such arrangements, the cover <NUM> restricts the expansion of the core <NUM>. The cover <NUM> may therefore be retracted proximally to facilitate insertion and removal of the polygonal head <NUM> of the driver <NUM> into the distal adapter <NUM>.

As shown in <FIG>, the gear <NUM> includes an internal bore <NUM> extending from its proximal face to its distal face, and a distal portion of the bore <NUM> includes internal threading <NUM> for engaging the threaded neck <NUM> of the distal adapter <NUM>. The gear <NUM> further includes a teethed portion <NUM>, having the gear teeth <NUM> for engaging the pawl <NUM> and post teeth <NUM>, and a raised portion <NUM>. The raised portion <NUM> has a narrower diameter relative to the central axis X than the teethed portion <NUM>. The raised portion <NUM> includes an annular groove <NUM> for engagement with a clip <NUM> of the stylet holder <NUM> shown in <FIG>.

The stylet holder <NUM> illustrated in <FIG> includes a tablet <NUM>, a pillar <NUM>, the clip <NUM>, and a clip spring <NUM>. The clip <NUM> in turn includes a gap <NUM>, a clip button <NUM>, and a shim <NUM> that extends into the gap <NUM>. The stylet holder <NUM> acts as an insert receivable in the handle <NUM>, and retains the stylet <NUM> in a fixed position when the instrument <NUM> is assembled as shown in <FIG> or <FIG>.

In a process for assembling the stylet holder <NUM> of the illustrated arrangement, the clip spring <NUM> is into a lateral slot <NUM> within the tablet <NUM>. Next, the clip <NUM> is inserted into the lateral slot <NUM> to push against the clip spring <NUM>. The pillar <NUM> is inserted from a proximal side of the tablet <NUM> though a tablet opening <NUM> and through the gap <NUM> in the clip <NUM>. The pillar <NUM> includes a flat head <NUM> that seats inside a counter bore of the tablet opening <NUM> such that a proximal face of the tablet <NUM> and a proximal face of the flat head <NUM> are coplanar or the flat head <NUM> is slightly recessed from the proximal face of the tablet <NUM>. The flat head <NUM> can be secured within the counter bore of the tablet opening <NUM>, such as by adhesive or a weld. The clip pin <NUM> is inserted through a corresponding hole in the tablet <NUM> and into the clip track <NUM>. The clip track <NUM> allows the clip <NUM> to translate within the lateral slot <NUM> in a direction perpendicular to the central axis X.

The stylet holder <NUM> may be installed within the instrument <NUM> by inserting the pillar <NUM> into the bore <NUM> of the gear <NUM> and the axial passage <NUM> of the core <NUM>. When the stylet holder <NUM> reaches an installed location, wherein the tablet <NUM> is within the proximal face of the tablet <NUM> is within the handle recess <NUM> and the proximal face of the tablet <NUM> is coplanar with or slightly distal of proximal faces of the arms 207a, 207b, the clip <NUM> may engage the annular groove <NUM> of the gear <NUM>. The clip spring <NUM> biases the clip <NUM> into a position wherein the shim <NUM> extends into the annular groove <NUM>, thereby coupling the stylet holder <NUM> to the instrument <NUM>. The clip <NUM> can be disengaged from the annular gear <NUM> by applying pressure to the clip button <NUM> to compress the clip spring <NUM> and move the shim <NUM> out of the annular groove <NUM>. The stylet holder <NUM> and stylet <NUM> may be removed from the instrument <NUM> after the clip <NUM> is disengaged from the annular groove <NUM>, such as by hooking a finger or removal tool under a tablet notch <NUM> opposite from the clip button <NUM>.

Turning to <FIG>, with continued reference to <FIG>, the stylet <NUM> includes a shank <NUM> ending distally in a point <NUM>, and ending proximally at a stylet head <NUM>. The stylet head <NUM> has a cylindrical shape with its circular faces defined on planes parallel to the central axis X. A height of the cylindrical shape of the stylet head <NUM>, defined as a distance between the two circular faces, is greater than a diameter of the shank <NUM>. The pillar <NUM> of the stylet holder <NUM> includes an axial channel <NUM> for accepting the stylet head <NUM>. As shown in <FIG>, the channel <NUM> extends to an external perimeter of the pillar <NUM> on one side, forming an elongate slot extending axially along the pillar <NUM> to a distal end of the pillar <NUM>. <FIG> and <FIG> show a column of pillar apertures <NUM> extending axially along a side of the pillar <NUM> opposite from the elongate slot defined by the channel <NUM>. The pillar apertures <NUM> open into the channel <NUM>. A column of parallel, generally radially extending ribs <NUM> extends axially down each of two opposed sides of the channel <NUM>, defining an axial column of recesses between the ribs <NUM> on the two opposed sides of the channel <NUM>. The ribs <NUM> therefore define opposed pairs of recesses <NUM> on opposite sides of the channel <NUM>, with each opposed pair of recesses being axially aligned with one of the pillar apertures <NUM>. The opposed pairs of recesses <NUM> are each shaped and dimensioned to receive the circular faces of the stylet head <NUM>, while a width of the channel <NUM> between opposed pairs of ribs <NUM> is less than the height of the cylindrical shape of the stylet head <NUM>, but greater than or equal to the diameter of the shank <NUM>. The opposed pairs of recesses <NUM> and pillar apertures <NUM> thus define discrete, predefined locations along the central axis X wherein the stylet holder <NUM> can retain the stylet head <NUM>.

To prepare the instrument <NUM> for use, the stylet head <NUM> is slotted into the channel <NUM> of the pillar <NUM> such that the two circular faces of the stylet head <NUM> are received in an opposed pair of recesses <NUM> and edge of the stylet head <NUM> extends into the pillar aperture <NUM> axially aligned with the opposed pair of recesses. A fit of the stylet head <NUM> within the opposed pair of recesses <NUM> and the pillar aperture <NUM> allows the stylet head <NUM> to rotate relative to the pillar <NUM>. The stylet <NUM> is then turned to axially align the shank <NUM> with the pillar <NUM> within the channel <NUM>. The stylet <NUM> is then be inserted through the bore <NUM> of the gear <NUM> and guided through the instrument <NUM> to protrude from a distal end of the driver <NUM>. The stylet holder <NUM> is inserted into the instrument <NUM> and coupled to the handle <NUM> via the annular groove <NUM> of the gear <NUM> as discussed above.

With the stylet holder <NUM> installed within the instrument <NUM> while the stylet head <NUM> is disposed within the channel <NUM>, the stylet <NUM> is largely constrained into alignment with the central axis X of the instrument <NUM>. The pillar <NUM> extends into the axial passage <NUM> of the distal adapter <NUM>, and the axial passage <NUM> of the distal adapter <NUM> is dimensioned to prevent the stylet head <NUM> from exiting the channel <NUM>. Other features that the shank <NUM> passes through between the axial passage <NUM> of the distal adapter <NUM> and the distal end of the driver <NUM> are narrower than the axial passage <NUM>, and therefore serve to further constrain the stylet <NUM> within the instrument <NUM>.

Selection and placement of the stylet <NUM> may be in view of details specific to a patient, operation, or fastener. For example, in some arrangements, the stylet <NUM> is selected or constructed to have a desired length determined in view of the instrument <NUM> and the screw <NUM>. In further arrangements, the opposed pair of recesses <NUM> and pillar aperture <NUM> into which the stylet head <NUM> is disposed before the stylet holder <NUM> is inserted into the handle <NUM> are selected in view of the length of the stylet <NUM>, instrument <NUM>, and screw <NUM>. In further arrangements, the length of the stylet <NUM>, the opposed pair of recesses <NUM> and aperture <NUM>, or both, are selected such that the point <NUM> of the stylet <NUM> will be a predetermined distance from a tip of the screw <NUM> when the instrument <NUM> is fully assembled. In yet further arrangements, the predetermined distance is <NUM>, <NUM>, or <NUM>.

The drive assembly <NUM> includes the sheath assembly <NUM> and the driver <NUM>, which is insertable through the sheath assembly <NUM> as shown in <FIG> such that the distal end of the driver <NUM>, defined by a drive head <NUM>, extends distally beyond the tube <NUM>. The drive head <NUM> is any known screw driving feature suitable for driving engagement with a head of the screw <NUM>. For a more detailed description of an exemplary drive head and engagement thereof with an exemplary bone screw, reference can be made to the '<NUM> patent. The knob <NUM> is axially actuatable relative to the tube <NUM> of the sheath assembly <NUM> between a locked position, wherein the sheath assembly <NUM> is rotationally coupled to the driver <NUM>, and an unlocked position, wherein the sheath assembly <NUM> is free to rotate relative to the driver <NUM>. In the illustrated example, the unlocked position, shown in <FIG>, is distal of the locked position, shown in <FIG>.

Assembly of the instrument <NUM> of the illustrated arrangement includes inserting the driver <NUM> into the sheath assembly <NUM>. The sheath assembly <NUM>, with the knob <NUM> in the unlocked position, is rotated about the driver <NUM> to thread the threaded portion <NUM> of the tube <NUM> into engagement with the extension assembly <NUM>. For a more detailed description of the interaction between an exemplary driver and extension assembly as may be modified for use with the instrument <NUM> of the present disclosure, reference can again be made to the '<NUM> patent. The knob <NUM> is then actuated to the locked position to rotationally couple the sheath assembly <NUM> to the driver <NUM>. In the illustrated example, the knob <NUM> includes an L-shaped track <NUM> in cooperation with a boss <NUM> extending radially outward from the tube <NUM> and through the L-shaped track <NUM>, permitting the knob <NUM> to rotate about the tube <NUM> a short distance when the knob <NUM> is in the locked position. The user may therefore turn the knob <NUM> after actuating the knob <NUM> to the locked position to locate the boss <NUM> away from a vertical leg of the L-shaped track, enabling the application of axial force on the knob <NUM> without moving the knob <NUM> to the unlocked position. Rotational force on the knob <NUM> is transferred to the tube <NUM> by edges of the L-shaped track <NUM> bearing on the boss <NUM>.

In some arrangements, the rotational coupling and uncoupling of the sheath assembly <NUM> and driver <NUM> is achieved by cooperation of internal contours and a moveable spline element (not illustrated) within the knob <NUM>. The spline element is axially and rotationally coupled to the tube <NUM>, but axially uncoupled from the knob <NUM>. Axial actuation of the knob <NUM> therefore causes the internal contours of the knob to move relative to the spline element while the spline element remains in a constant axial location relative to the tube <NUM>. Movement of the knob <NUM> axially into the locked position causes the internal contours of the knob <NUM> to guide the spline element radially into engagement with the splined portion <NUM> of the driver <NUM>, thereby rotationally coupling the tube <NUM> and sheath assembly <NUM> to the driver <NUM>. Similarly, movement of the knob <NUM> axially into the unlocked position causes the internal contours of the knob <NUM> to guide the spline element radially out of engagement with the spline portion of the driver <NUM>, thereby rotationally uncoupling the tube <NUM> and sheath assembly <NUM> from the driver.

For a more detailed description of locking and unlocking of a similar knob and drive assembly, reference can be made to the '<NUM> patent.

The instrument <NUM> and its components described above may be made of any material or combination of materials suitable for driving known screws into solid objects. In medical applications particularly, biocompatible or non-toxic materials are preferred, as are materials that are suitable for sterilization and repeated use. Stainless steel, titanium, and alloys thereof are specifically contemplated as suitable for any part of the driver. However, some components, including but not limited to the handle body <NUM>, adapters <NUM>, <NUM>, block <NUM>, post <NUM>, washer <NUM>, or any sub-components thereof, may be made of any of a wide variety of rigid polymers. Additionally, any component of the instrument other than necessarily flexible components such as springs or the core <NUM> of the distal adapter <NUM> may be made of ceramic.

<FIG> illustrates a removal tool <NUM> for removing the stylet holder <NUM> and stylet <NUM> from the instrument <NUM>. The removal tool <NUM> includes a first grip 534a and a second grip 534b joined at a hinge <NUM>. A first leaf spring 536a and second leaf spring 536b are attached to the first grip 534a and second grip 534b, respectively, and at rest curve toward the opposite grip 534a, 534b. The grips 534a, 535b of the illustrated arrangement are wider than the leaf springs 536a, 536b, so the leaf springs 536a, 536b may pass by each other to contact the opposite grip 534a, 534b.

The first grip 534a is integrally connected to a hook 540a on an opposite side of the hinge <NUM>, and the second grip 534b is integrally connected to a wedge 540b on the opposite side of the hinge <NUM>. The hook 540a is shaped to match a contour of the clip button <NUM>, and the wedge 540b is shaped to slide under the tablet notch <NUM>. The removal tool <NUM> therefore cooperates with shapes of the tablet <NUM> and clip <NUM> to facilitate removal of the stylet holder <NUM> and styled <NUM> from the instrument. The removal tool <NUM> may be positioned such that when the grips 534a, 534b are drawn close to one another, the hook 540a covers the clip button <NUM>, and the wedge 540b slides under the tablet notch <NUM>. The hook 540a pushes the clip button <NUM> to disengage the clip <NUM> from the annular groove <NUM> of the gear <NUM> while the wedge 540b pushes the tablet <NUM> proximally. The removal tool <NUM> can therefore be used to easily remove the stylet holder <NUM> and stylet <NUM> from the instrument <NUM>.

As noted above with regard to the instrument <NUM>, the removal tool <NUM> can be made from any of a variety of materials including metals, such as stainless steel, titanium, or alloys thereof, rigid polymers, or, with the exception of the leaf springs 536a, 536b, ceramic. Again, in medical applications, materials that are non-toxic, biocompatible, and conducive to sanitization and reuse are preferred.

In an exemplary process for use of the instrument <NUM>, the handle <NUM>, stylet holder <NUM>, and drive assembly <NUM> are separately assembled, as described above. The extension assembly <NUM> is coupled to the screw <NUM>. A stylet <NUM> is constructed at a desired length or selected from a plurality of stylets <NUM> having various predetermined lengths. The drive assembly <NUM> is inserted into the extension assembly <NUM>. The drive head <NUM> is positioned for driving engagement with the head of the screw <NUM>. With the knob <NUM> in the unlocked position, the drive assembly <NUM> is rotated about the driver <NUM> such that the threaded portion <NUM> of the tube <NUM> engages the extension assembly <NUM>, thereby retaining the drive head <NUM> in driving engagement with the head of the screw <NUM>. The knob <NUM> is then actuated to the locked position. The cover <NUM> of the distal adapter <NUM> of the handle <NUM> is retracted proximally relative to the core <NUM> while the polygonal head <NUM> of the driver <NUM> is inserted into the polygonal portion <NUM> of the axial passage <NUM> of the distal adapter <NUM>. After the polygonal head <NUM> is seated against the annular shelf <NUM> of the distal adapter <NUM>, the cover <NUM> is allowed to return distally over the core <NUM>, compressing the core <NUM> around the polygonal head <NUM>. The stylet <NUM> is disposed within one of multiple discrete, predefined locations within the stylet holder <NUM>, each of the predefined locations corresponding to the pillar apertures <NUM> and opposed pairs of recesses <NUM> in the pillar <NUM> such that the stylet <NUM> will extend a desired distance distally beyond the tip of the screw <NUM> when the instrument <NUM> is fully assembled. The stylet <NUM> and stylet holder <NUM> are inserted into the handle <NUM> such that the stylet <NUM> extends through the handle <NUM>, drive assembly <NUM>, and screw <NUM>, and the clip <NUM> engages the annular groove <NUM> on the raised portion <NUM> of the gear <NUM>. The foregoing steps may be performed in any order that results in an assembled instrument <NUM> generally as shown in <FIG> and <FIG>.

The point <NUM> of the stylet <NUM> is used to pierce an exterior surface of a solid object, such as, for example, a bone, or specifically a vertebral pedicle, thereby providing a pilot hole. However, the presently described process can be implemented on any solid object. Force is applied to the instrument <NUM> until the tip of the screw <NUM> enters the pilot hole. The handle <NUM> is used to drive the screw <NUM> into the object. Action of the pawl <NUM> on the gear <NUM> provides the handle <NUM> with a ratcheting function, such that torque applied to the handle <NUM> in a direction that drives the screw <NUM> into the object is transferred to the screw <NUM>, but torque applied to the handle <NUM> in an opposite direction causes the handle <NUM> to rotate relative to the instrument <NUM> without being transferred to the screw <NUM>. When the screw <NUM> reaches a desired depth in the object, the extension assembly is decoupled from the screw <NUM> and the instrument <NUM> is withdrawn. At any stage after the screw <NUM> engages the pilot hole, the stylet holder <NUM> and stylet <NUM> are removed from the instrument <NUM> by pulling proximally on the tablet <NUM> by hand or with the removal tool <NUM>. If necessary at any stage, torque is applied to the instrument <NUM> beyond the handle <NUM> in a direction opposite from that used to drive the screw <NUM> into the object by depressing the post button <NUM> to cause the post teeth <NUM> to lock the gear <NUM> relative to the body <NUM> of the handle <NUM> before turning the handle <NUM>. Ratcheting function is then restored by depressing the retainer <NUM> to allow the post <NUM> to return radially outward and disengage the gear <NUM>. Though use of the instrument <NUM> to drive the screw <NUM> into bone is disclosed as one example, the instrument <NUM> can be used to drive a screw into any other material.

Claim 1:
A screw driving instrument (<NUM>), comprising:
a handle (<NUM>);
a passage extending through the handle and along a central axis (X) of the instrument (<NUM>); and
an insert (<NUM>) receivable in a portion of the passage extending through the handle (<NUM>), the insert (<NUM>) including:
a clip (<NUM>) engageable to the handle (<NUM>);
a stylet (<NUM>) including a stylet head (<NUM>); and
a pillar (<NUM>) including a channel (<NUM>) defining an elongate slot and opposed pairs of recesses (<NUM>) defined on two opposed sides of the channel (<NUM>), wherein the recesses (<NUM>) define a plurality of discrete positions wherein the stylet head (<NUM>) may be received in the channel (<NUM>).