Patent Description:
Additionally, during a revision surgery in which the spine rod is removed, it can be to the surgeon's advantage to cut the rod in order to facilitate easier removal. Also, the surgeon may not have the correct drivers to unscrew the locking caps that mount the spine rod to the pedicle screws. In this scenario, it is also advantageous to have a device that will cut the rod on either side of the pedicle screw. Then the sections of the rod between screws can be easily lifted out. The remaining small sections of rod still attached to the pedicle screws can then be "helicoptered" out. <CIT> discloses a surgical cutting system and method. <CIT> discloses a rod cutting debris collector and guide.

Preferable and/or optional features are provided in claims <NUM> to <NUM>.

The following detailed description of an exemplary embodiment of the subject disclosure will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, there is shown in the drawings an exemplary embodiment. It should be understood, however, that the subject application is not limited to the precise arrangements and instrumentalities shown.

Reference will now be made in detail to an exemplary embodiment of the subject disclosure illustrated in the accompanying drawings. Wherever possible, the same or like reference numbers will be used throughout the drawings to refer to the same or like features. It should be noted that the drawings are in simplified form and are not drawn to precise scale. In reference to the disclosure herein, for purposes of convenience and clarity only, directional terms such as upper, lower, top, bottom, above, below and diagonal, are used with respect to the accompanying drawings. Such directional terms used in conjunction with the following description of the drawings should not be construed to limit the scope of the subject disclosure in any manner not explicitly set forth.

Referring now to the Figures, there is shown a cutter <NUM> in accordance with an exemplary embodiment of the subject disclosure. The cutter <NUM> may be used to cut/mill spine rods, including, for example, a spine rod <NUM> affixed to a spine <NUM> of a patient using spine rod screws <NUM> having proximally attached tulips <NUM> (see <FIG> and <FIG>). The cutter <NUM> may be employed, for example, to cut implanted spine rods of varying lengths and diameters (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, etc.), as well as those affixed to a spine using structures other than screws <NUM> and those constructed from various materials, such as, for example, stainless steel, titanium, or cobalt chrome. Although the cutter <NUM> is described herein and shown in the Figures as operable to cut spine rods (such as spine rod <NUM>), it should be appreciated that the cutter <NUM> and other embodiments contemplated by the subject disclosure may be used to cut/mill other types of implants, and that various embodiments of the subject disclosure are not intended to be limited for use with any particular size, type or category of implant(s).

As best shown in <FIG> and <FIG>, the cutter <NUM> includes a gearbox <NUM>, primary and secondary milling bits <NUM>, <NUM>', and a shaft e.g., a threaded lead screw <NUM> operatively coupled to and extending through the gearbox <NUM>, an input coupling <NUM> (which e.g., may include a Hudson connector or similar connector for coupling to a driving source) coupled rigidly to the proximal end of the primary milling bit <NUM>, a knob <NUM> coupled to the proximal end of the lead screw <NUM>, chip collectors <NUM>, <NUM>' coupled to the distal end of the gearbox <NUM> and respectively circumscribing the primary and secondary milling bits <NUM>, <NUM>', and an implant coupler <NUM> coupled to the distal end of the lead screw <NUM> and guided for longitudinal translation by the chip collectors <NUM>, <NUM>', e.g., via guide rails <NUM>, <NUM>'. In the illustrated exemplary embodiment, the primary milling bit, the secondary milling bit and the lead screw are spaced apart along a substantially linear path, and a longitudinal axis of the primary milling bit and a longitudinal axis of the secondary milling bit are substantially parallel to a longitudinal axis of the lead screw.

As best shown in <FIG>, the primary and secondary milling bits <NUM>, <NUM>' respectively include distal cutting ends <NUM>, <NUM>' for cutting implants e.g., the spine rod <NUM>, and proximal drive ends <NUM>, <NUM>' with respective drive grooves <NUM>, <NUM>' for operatively coupling to the gearbox <NUM>. The cutting ends <NUM>, <NUM>' include notched or rounded edges <NUM>, <NUM>' to reduce chipping and spiral flutes <NUM>, <NUM>' for transporting chips and other fragments cut/milled from the spine rod <NUM> proximally toward center regions <NUM>, <NUM>' of the bits <NUM>, <NUM>'. In one exemplary embodiment, at least the cutting ends <NUM>, <NUM>' of the primary and secondary milling bits <NUM>, <NUM>' are made from tungsten carbide, though it should be appreciated that other portions of the milling bits <NUM>, <NUM>' may also be made of tungsten carbide, or that any or all portions thereof may be constructed using alternative materials. It should also be appreciated that the cutting ends <NUM>, <NUM>' may be center or edge cutting and/or or have rounded edges <NUM>, <NUM>', and that various exemplary embodiments of the subject disclosure are not intended to be limited to any particular type of cutting end or manner of cutting the spine rod <NUM> or other implant.

With reference to <FIG> and <FIG>, the gearbox <NUM> includes a housing <NUM> with a distal plate <NUM> enclosing translation and milling drive assemblies <NUM>, <NUM> operable respectively to translate the gearbox <NUM> distally with respect to the lead screw <NUM> or along a longitudinal extent of the lead screw and to drive the secondary milling bit <NUM>' in response to a rotational driving force applied to the input coupling <NUM>, as well as various washers <NUM> and bushings 275a, 275b, 275c, 275d, 275e and 275f to protect the various components of the drive assemblies <NUM>, <NUM> from wear and to properly position, align and space the components within the housing <NUM>. In the exemplary embodiment depicted in the Figures, the driving force is supplied e.g., by a drill <NUM> with a flexible drive shaft <NUM>, though it should be appreciated that the rotational driving force may be applied to the input coupling <NUM> in other ways, such as, for example, via a rigid drive shaft, and that various exemplary embodiments of the subject disclosure are not intended to be limited to any particular manner of applying a driving force to the input coupling <NUM>.

As best shown in <FIG>, the translation drive assembly <NUM> includes a first worm screw <NUM> having a longitudinal bore <NUM> receiving the proximal drive end <NUM> of the primary milling bit <NUM> and a longitudinally extending drive rib <NUM> engaging the drive groove <NUM> of the primary milling bit <NUM>, a first worm gear <NUM> operatively coupled to the first worm screw <NUM>, a shaft <NUM> extending longitudinally through the first worm gear <NUM> and bounded at one end by an end cap <NUM> and circlip (not shown) inside the housing <NUM> and on the other end by an alignment receptacle <NUM> (<FIG>) on the inside of the housing <NUM>, a second worm screw <NUM> disposed rotatably on and circumscribing the shaft <NUM> and coupled rigidly to the first worm gear <NUM>, a second worm gear <NUM> operatively coupled to the second worm screw <NUM> and having a hexagonal socket <NUM> and a longitudinal through bore <NUM> circumscribing the lead screw <NUM>, and a hexagonal lead nut <NUM> positioned within the hexagonal socket <NUM> and threadedly engaged with the lead screw <NUM>.

As best shown in <FIG> and <FIG>, the milling drive assembly <NUM> includes a first spur gear <NUM> circumscribing the primary milling bit <NUM> distally of the first worm screw <NUM> and having a longitudinally extending drive rib <NUM> engaging the drive groove <NUM> of the primary milling bit <NUM>, a free-spinning second spur gear <NUM> operatively engaging the first spur gear <NUM> and rotatably circumscribing the lead screw <NUM> distally of the second worm gear <NUM>, and a third spur gear <NUM> operatively engaging the second spur gear <NUM>, circumscribing the secondary milling bit <NUM>' and having a longitudinally extending drive rib <NUM> engaging the drive groove <NUM>' of the secondary milling bit <NUM>'.

Although the components of the translation and milling drive assemblies <NUM>, <NUM> described herein and illustrated in the Figures operate together to translate the gearbox <NUM> distally with respect to the lead screw <NUM> and to drive the secondary milling bit <NUM>', it should be appreciated that the translation and milling drive assemblies <NUM>, <NUM> may include other arrangements of the same or different components to effectuate these functions, and that various embodiments of the subject disclosure are not intended to be limited to any specific components or arrangement of components for translating the gearbox <NUM> or driving the secondary milling bit <NUM>'. It should also be appreciated that the translation and milling drive assemblies <NUM>, <NUM> may include non-gear components, such as hydraulic and/or electrical components, and that various embodiments of the subject disclosure are not intended to be limited to any type or class of components.

As best shown in <FIG>, <FIG>, and <FIG>, the chip collectors <NUM>, <NUM>' circumscribe the primary and secondary milling bits <NUM>, <NUM>' and respectively include proximal funnel-shaped ends <NUM>, <NUM>' coupled to the distal plate <NUM> of the housing <NUM>, generally cylindrical body portions <NUM> having internal chip collection cavities <NUM> in communication with the milling bits <NUM>, <NUM>' and outer surfaces provided with longitudinally extending guide rails <NUM>, <NUM>', longitudinal bores <NUM> extending from the distal bottoms of chip collection cavities <NUM> to the distal ends of the body portions <NUM>, <NUM>', and cutouts <NUM> shaped to receive the spine rod <NUM> and facing transversely to and intersecting the longitudinal bores <NUM> at the distal ends of the body portions <NUM>, <NUM>'. The internal diameters of bores <NUM> at the distal ends of the chip collectors are equal to or slightly larger than the external diameters of the primary and secondary milling bits <NUM>, <NUM>' to effectively retain or seal the chip collection cavities <NUM> and prevent chips and other fragments removed from the spine rod <NUM> from escaping the cavities <NUM>. In the exemplary embodiment depicted in the Figures, the cutouts <NUM> are U-shaped to receive the spine rod <NUM>, though it should be appreciated that the cutouts <NUM> may be shaped differently to receive other types of implants.

As best shown in <FIG> and <FIG>, the implant coupler <NUM> includes a proximal threaded receptacle <NUM> coupled to the distal end of the lead screw <NUM> and a generally cylindrical coupling body <NUM> having an outer surface provided with longitudinally extending grooves <NUM>, <NUM>' respectively and slidably engaging with the guide rails <NUM>, <NUM>' of the chip collectors <NUM>, <NUM>' and a distal end <NUM> provided with a socket <NUM> e.g., a helicopter socket and a hollow receptacle <NUM> shaped e.g., to receive a tulip <NUM> of a spine rod screw <NUM> for properly orientating and aligning the cutter <NUM> during a cutting/milling operation. In alternative exemplary embodiments, the implant coupler may or may not include a hollow receptacle e.g., the implant coupler may be of smaller diameter or a cylinder having a socket for engaging a rod similar to socket <NUM>. In this alternative embodiment, the coupler does not receive the tulip <NUM> and engages only with the spine rod <NUM>.

The socket <NUM> is shaped to releasably receive the spine rod <NUM> and includes helicopter cutouts having respective and radially aligned or diametrically opposed receipt channels <NUM>, <NUM>' and locking channels <NUM>, <NUM>'. The locking channels <NUM>, <NUM>' are also configured to align planarly with the cutouts <NUM> of the chip collectors <NUM>, <NUM>' so that the primary and secondary milling bits <NUM>, <NUM>' can properly align with the spine rod <NUM> during operation of the cutter <NUM>. It should be appreciated that the receipt channels <NUM>, <NUM>' and locking channels <NUM>, <NUM>' may be shaped differently to receive differently shaped rods and other implants. It should also be appreciated that the implant coupler <NUM> may include structures in addition to or in lieu of the socket <NUM> for releasably receiving the spine rod <NUM> or other implant.

To operate the cutter <NUM> to cut/mill the spine rod <NUM>, a user first aligns the cutter <NUM> (see <FIG>) and engages the hollow receptacle <NUM> of the implant coupler with a tulip <NUM> of a spine rod screw <NUM>, while at the same time aligning the receipt channels <NUM>, <NUM>' of the implant coupler <NUM> with the spine rod <NUM> (see <FIG>). Once the spine rod <NUM> is received completely within the receipt channels <NUM>, <NUM>' of the implant coupler <NUM>, the user rotates the cutter <NUM> counterclockwise (when viewed distally from the proximal side of the cutter <NUM>) to position the spine rod <NUM> fully within the locking channels (see <FIG>), thereby locking the spine rod <NUM> rigidly in position with respect to the cutter <NUM> and aligning the primary and secondary milling bits <NUM>, <NUM>' with the spine rod <NUM>. The user then applies a clockwise driving force to the input coupling <NUM>. Clockwise rotation of the input coupling <NUM> drives the primary milling bit <NUM>, which in turn causes the drive groove <NUM> of the primary milling bit <NUM> to engage the drive rib <NUM> of the first spur gear <NUM> and rotate the gear <NUM> clockwise with the primary milling bit <NUM>. Rotation of the first spur gear <NUM> causes the free-spinning second spur gear <NUM> to rotate counterclockwise about the lead screw <NUM> which, in turn, causes the third spur gear <NUM> to rotate clockwise. As the third spur gear <NUM> rotates, the drive rib <NUM> of the third spur gear <NUM> engages the drive groove <NUM>' of the secondary milling bit <NUM>' causing the bit <NUM>' to also rotate clockwise with the third spur gear <NUM>. Since the first, second and third spur gears <NUM>, <NUM>, <NUM> are similarly sized and include the same number of teeth, the third spur gear <NUM> rotates at the same speed and in the same clockwise direction as first spur gear <NUM> to ensure that the primary and secondary milling bits <NUM>, <NUM>' rotate clockwise at the same speed. It should be appreciated, however, that the spur gears <NUM>, <NUM>, <NUM> may be sized differently and/or include different numbers of teeth, and that the secondary milling bit <NUM>' may rotate at a different speed or in a different rotational direction compared to the primary milling bit <NUM>.

Rotation of the primary milling bit <NUM> also causes the drive groove <NUM> of the primary milling bit <NUM> to engage the drive rib <NUM> of the first worm screw <NUM> causing it to rotate clockwise with the primary milling bit <NUM>. Rotation of the first worm screw <NUM> causes rotation of the first worm gear <NUM> and second worm screw <NUM> about the shaft <NUM> which, in turn, causes clockwise rotation of the second worm gear <NUM> and hexagonal lead nut <NUM> about the lead screw <NUM>. Since the lead nut <NUM> threadedly engages with the lead screw <NUM> and because engagement of the implant coupler <NUM> with the spine rod <NUM> prevents longitudinal displacement of the lead screw <NUM>, the clockwise rotation of the hexagonal lead nut <NUM> causes the lead screw <NUM> to produce a distal force on the lead nut <NUM>, thereby causing the gearbox <NUM> (with coupled milling bits <NUM>, <NUM>' and chip collectors <NUM>, <NUM>') to translate distally along the lead screw <NUM> guided by engagement of the guide rails <NUM>, <NUM>' of the chip collectors <NUM>, <NUM>' with the grooves <NUM>, <NUM>' of the implant coupler <NUM>. In another embodiment, the device may use a compound gear set instead of worm drive gears.

The gearbox <NUM> translates distally until the distal cutting ends <NUM>, <NUM>' of the primary and secondary milling bits <NUM>, <NUM>' contact the spine rod <NUM>, at which point cutting/milling of the spine rod <NUM> begins. The cutouts <NUM> of the chip collectors <NUM>, <NUM>' engage with the spine rod <NUM> and help guide the milling bits <NUM>, <NUM>' as they advance therethrough. Chips and other fragments removed from the spine rod <NUM> are transported proximally by the spiral flutes <NUM>, <NUM>' of the primary and secondary milling bits <NUM>, <NUM>' into the chip collection cavities <NUM> of the chip collectors <NUM>, <NUM>', where they are deposited and maintained during the cutting/milling operation. The primary and secondary milling bits <NUM>, <NUM>' continue to translate distally until they cut through the spine rod <NUM>, at which point the cutting/milling operation ends (<FIG>) and the cutter <NUM> is removed from the patient.

Overcutting is prevented by the proximal top surfaces of cutouts <NUM> which engage with the spine rod <NUM> to prevent the distal center-cutting ends <NUM>, <NUM>' of the primary and secondary milling bits <NUM>, <NUM>' from translating too far distally into the patient. In other words, owing to their abutment with the spine rod, the proximal top surfaces of cutouts of the chip collectors prevent further distal penetration of the cutting ends of the primary and secondary milling bits once the spine rod is cut thereby. For example, the largest diameter of spine rods is currently <NUM>. Therefore, there will be a hard stop on the travel of the cutters at a distance slightly greater than <NUM>. The cylindrical guides concentric to the cutters have a cutout that accepts the spine rod. The furthest travel of the cutters is limited to not extend past these guides.

After completion of the cutting/milling operation, the chip collectors <NUM>, <NUM>' are removed from the cutter <NUM> so that the chips and other fragments cut/milled from the spine rod <NUM>, as well as any chips and fragments remaining in the spiral flutes <NUM>, <NUM>' of the primary and secondary milling bits <NUM>, <NUM>', may be accessed and discarded. In at least some exemplary embodiments, removal of the chip collectors <NUM>, <NUM>' may be facilitated by first detaching the implant coupler <NUM> from the cutter <NUM>. This may be effectuated by first rotating the knob <NUM> counterclockwise to retract the distal end of the lead screw <NUM> from the threaded receptacle <NUM> of the implant coupler <NUM> and then sliding the coupler <NUM> distally to disengage the guide rails <NUM>, <NUM>' of the chip collectors <NUM>, <NUM>' from the grooves <NUM>, <NUM>' of the implant coupler <NUM>. The cutter <NUM> may then be reset to perform a new cutting/milling operation by first reattaching the chip collectors <NUM>, <NUM>' and the implant coupler <NUM> and then translating the gearbox <NUM> proximally into its initial position by applying a counterclockwise rotational force to the input coupling <NUM> manually or by using the drill <NUM> or other mechanism.

<FIG>, <FIG>, <FIG> and <FIG> disclose further exemplary embodiments of the subject disclosure, which include a clamping mechanism for applying clamping force to an implant during cutting of the implant. The various clamping mechanisms of these embodiments hold the implant firmly and steady in place to prevent chattering of the implant, i.e., resist vibrations of the implant, caused by milling. For brevity, only those elements of the implant cutters shown in <FIG>, <FIG>, <FIG> and <FIG> that materially depart in structure and/or function from their counterparts shown in <FIG>, or are otherwise necessary for a proper understanding of the subject disclosure, will be described in detail.

Referring to <FIG>, there is shown an exemplary embodiment of a clamping mechanism <NUM> operatively connected to the implant coupler <NUM>' for applying a clamping force to an implant <NUM> during cutting of the implant. The clamping mechanism <NUM> comprises an axially extending elongated shaft <NUM> have threads threadedly engaging the implant coupler e.g., about its proximal end 902a. The threaded shaft includes a handle <NUM> at a proximal end thereof and an implant engageable tip <NUM> at a distal end thereof operable to clampingly engage the implant, e.g., spine rod <NUM>. While the elongated threaded shaft <NUM> threadedly engages at least the implant coupler <NUM>', it is understood that one or both of knob <NUM>' and threaded lead screw <NUM>' may be correspondingly internally threaded to engage with the external threading of the shaft <NUM>. That is the lead screw <NUM>' and/or knob <NUM>' can include a longitudinal through hole having internal threads. However, to minimize resistance to turning of the threaded shaft by the handle <NUM>, the knob <NUM>' and the threaded lead screw <NUM>' are provided with smooth-walled internal bores of slightly larger diameter than the diameter of the threaded shaft.

Referring to <FIG>, there is shown an exemplary embodiment of a clamping mechanism <NUM> operatively connected to the implant coupler <NUM>" for applying clamping force to an implant <NUM> during cutting of the implant. The clamping mechanism <NUM> comprises a set screw receiver <NUM> radially or laterally projecting from the implant coupler <NUM>" and a laterally extending set screw <NUM> threadedly engaging the implant coupler at the set screw receiver and operable to clampingly engage the implant. The set screw has a socket <NUM> or other tool engageable structure that permits the set screw to be advanced into the implant coupler until it firmly engages the implant. Milling of the implant can then be performed with minimal or no vibration of the implant occurring during milling.

Claim 1:
A cutter (<NUM>) for cutting an implant (<NUM>), characterized by:
a gearbox (<NUM>);
a primary milling bit (<NUM>), a secondary milling bit (<NUM>') and a lead screw (<NUM>) spaced apart along a substantially linear path and operatively coupled to the gearbox;
an input coupling (<NUM>) coupled to the primary milling bit; and
an implant coupler (<NUM>) coupled to the lead screw,
wherein the gearbox is operable to translate with respect to the lead screw and to drive the secondary milling bit in response to a rotational driving force applied to the input coupling, wherein the gearbox comprises:
a translation drive assembly (<NUM>) operable to translate the gearbox with respect to the lead screw in response to the rotational driving force applied to the input coupling, and
a milling drive assembly (<NUM>) operable to drive the secondary milling bit in response to the rotational driving force applied to the input coupling.