Patent Description:
The present invention generally relates to instrumentation for forming an opening in bone for receiving an implant, and more particularly for forming an opening in a pedicle of a vertebra. Examples of instrumentation for forming an opening in bone are provided in <CIT>, which describes a combination drill, and <CIT>, which describes a diamond shaver including a drill.

<CIT> discloses a surgical tool having a distal end defining a burr surface configured to prevent skiving at an implant insertion site on a bone, the surgical tool being cannulated so as to receive a k-wire.

A technique commonly referred to as spinal fixation is employed for fusing together and/or mechanically immobilizing vertebrae of the spine. Spinal fixation may also be used to alter the alignment of adjacent vertebrae relative to one another so as to change the overall alignment of the spine. Such techniques have been used effectively to treat many degenerative conditions and, in most cases, to relive pain suffered by the patient.

In some applications, a surgeon will install implants, such as pedicle screws, into the pedicles of adj acent vertebrae (along one or multiple levels of the spine) and thereafter connect the screws with a spinal rod in order to immobilize and stabilize the vertebral column. Whether conducted in conjunction with interbody fusion or across single or multiple levels of the spine, the use of pedicle screws connected by fixation rods is an important treatment method employed by surgeons.

Prior to implantation of the implant, the target area, e.g. the pedicle, is incised to create an opening for receiving the implant. One problem a surgeon or other medical professional may face while creating such an incision within bone is skiving due to the shape and anatomy of the bone that is often angled with respect to the axis along which the instrumentation and implant are used. When the incision tool slips along a surface of the bone, the trajectory of the tool and the resulting opening becomes inaccurate for the placement of the implant.

There remains room for improvement in the design and use of instrumentation that prevents skiving which provides for surgical efficiency and maintains safety and accuracy for implanting an implant along a desired trajectory.

According to the invention, there is provided a system to prevent skiving at an implant insertion site on a bone as defined in claim <NUM> and in the corresponding dependent claims.

A first aspect of the present disclosure includes a surgical tool for use with a drill bit to prevent skiving at an implant insertion site on a bone, the tool includes a cannulated sleeve having a distal end defining a burr surface.

In other embodiments, the burr surface may be annular. The burr surface may be bulbous. The distal end and the cannulated sleeve may be of a single monolithic construction. The distal end may be detachable from the cannulated sleeve. The tool may be part of a kit that includes more than one distal end, each of the distal ends may define a burr surface having a different cutting surface from the others. The tool may be part of a system to prevent skiving at an implant insertion site on a bone that also includes a drill bit configured to be disposed within the cannulated sleeve. In a first configuration the cannulated sleeve and the drill bit may be rotationally coupled to each other and in a second configuration the cannulated sleeve and the drill bit may rotate independent of one another. The cannulated sleeve may have a lock at the proximal end of the cannulated sleeve to axially and rotationally couple the cannulated sleeve and the drill bit. The system be configured to be actuated by a robotic end effector. The distal end of the cannulated sleeve may define an opening.

A second aspect of the present disclosure includes a surgical system for use with a drill bit to prevent skiving at an implant insertion site on a bone, the system including a cannulated guide tube, an obturator configured to be disposed within the guide tube, and a burr tool configured to be disposed within the obturator, the burr tool having a distal end defining a burr surface.

In other embodiments, the guide tube, obturator, and burr tool may be coaxial when the obturator is positioned in the guide tube and the burr tool is positioned in the obturator. The burr tool may be configured to be spring-loaded into the obturator. The system may include a drill bit configured to be disposed within the guide tube.

Another aspect of the present disclosure includes a method of preparing an implant insertion site on a bone, the method including advancing a surgical system along an insertion axis, the system including a cannulated sleeve having a burr surface at a distal end and a drill bit disposed within the cannulated sleeve; and rotating the cannulated sleeve about the insertion axis to cause the burr surface to contact a surface of the bone that is not perpendicular to the insertion axis to form a pocket in the bone.

In other embodiments, the method may include drilling a hole into the bone at the pocket by rotating the drill bit. The method may include the step of rotationally coupling the cannulated burr sleeve and the drill bit with a lock. The method may include the step of retracting the cannulated sleeve. The method may include the step of disengaging the lock and retracting the cannulated sleeve relative to the drill bit. The pocket formed may have a substantially rounded surface.

Yet another aspect of the present disclosure includes a method of preparing an implant insertion site on a bone, the method including advancing a surgical system along an insertion axis, the system including a burr tool positioned within an obturator, the obturator positioned within a guide tube, and rotating the burr tool about the insertion axis to cause a distal burr surface of the burr tool to contact a surface of the bone that is not perpendicular to the insertion axis to form a pocket in the bone.

In other embodiments, the method may include the step of retracting the obturator and the burr tool from the guide tube. The method include the step of inserting a drill within the guide tube. The method may include the step of drilling a hole into the bone at the pocket by rotating the drill bit.

The present invention generally relates to cutting tools used for forming an opening for an implant during surgery. The cutting tools are designed to advantageously minimize or prevent skiving or slipping along a surface of the bone. This provides of the advantage of efficiently forming an accurately placed cannulation along a desired trajectory. Those of skill in the art will recognize that the following description is merely illustrative of the principles of the invention, which may be applied in various ways to provide many different alternative embodiments.

In describing certain aspects of the present inventions, specific terminology will be used for the sake of clarity. However, the inventions are not intended to be limited to any specific terms used herein, and it is to be understood that each specific term includes all technical equivalents, which operate in a similar manner to accomplish a similar purpose. In the drawings and in the description which follows, the term "proximal" refers to the end of the fixation members and instrumentation, or portion thereof, which is closest to the operator in use, while the term "distal" refers to the end of the fixation members and instrumentation, or portion thereof, which is farthest from the operator in use.

System <NUM> is designed to facilitate co-axial burring and drilling of a target location of bone. The system forms a landing zone on the surface of the bone, e.g. a pedicle of a vertebra, to prevent the subsequent drill from skiving during hole preparation during surgery, e.g. spinal surgery. Although described herein with reference to a burr surface, the disclosure contemplates any cutting feature capable of producing side cutting action, and the cutting geometry of the surface is not limited to a burr so long as this function is achieved.

System <NUM> includes an inner drill bit <NUM> and an outer cannulated sleeve <NUM> securable to drill bit <NUM> such that at least a portion of drill bit is positionable through sleeve <NUM>, as discussed in further detail below. At a proximal end of system <NUM>, a drive body <NUM> is connected to a drill bit <NUM>. Drive body <NUM> is rotatably coupled to drill bit <NUM> so that drive body <NUM> and drill bit <NUM> rotate in the same direction. A proximal end <NUM> of drive body <NUM> attaches to a robotic end effector <NUM> of a robotic device <NUM>, as shown in <FIG>. Robotic end effector <NUM> transmits torque via cross pin <NUM> to rotate drive body <NUM> and thus drill bit <NUM>.

Drill bit <NUM> extends along a longitudinal axis from a proximal end <NUM> to a distal end <NUM> thereof. Drill bit <NUM> includes a tapered region <NUM> which transitions to a cutting portion <NUM> at distal end <NUM> of drill bit <NUM>. Cutting portion <NUM> has a smaller width than the proximal portion of the drill bit <NUM>, measured in a direction perpendicular to the longitudinal axis of the drill bit. In other examples, the drill bit <NUM> may be another known cutting tool such as a reamer.

As shown in <FIG>, drill bit <NUM> includes a proximal portion <NUM> which is keyed along a portion of its length to rotationally lock the drill bit relative to sleeve <NUM>. Proximal portion <NUM> includes reduced diameter segments 127a, 127b, and 127c spaced apart along the axis of drill bit <NUM> for connecting drill bit <NUM> with sleeve <NUM>, described in further detail below.

Cannulated sleeve <NUM> is designed to be releasably locked to drill bit <NUM>. Sleeve <NUM> extends along a longitudinal axis from a proximal end <NUM> to a distal end <NUM>. Cannulated sleeve <NUM> has a body with a substanitially cylindrical shape. As shown in <FIG>, cannulated burr extension <NUM> attaches to distal end <NUM> of sleeve <NUM> and defines a passageway co-axial with a passageway <NUM> of sleeve <NUM> such that burr extension <NUM> and sleeve <NUM> form a continuous passageway. Alternatively, burr extension <NUM> and sleeve <NUM> may be constructed as a single, monolithic piece.

Burr extension <NUM> defines an annular distal outer burr surface <NUM> in the form of a burr. Outer burr surface <NUM> has a bulbous, rounded shape for finely cutting into bone. Burr surface <NUM> is a cutting surface for forming a pocket in the bone. The rounded portion and/or the distal edge include cutting features to cut into bone. The spherical shape of the outer burr surface <NUM> allows the burr to cut into an angled surface to cut a pocket in the pedicle by allowing for side cutting and partial front cutting. In instances in which the bone surface is at an angle of about <NUM>-<NUM> degrees, particularly, about <NUM>-<NUM> degrees, the burr surface is particularly advantageous to clear the material on the side. Although the illustrated embodiment shows outer burr surface <NUM> as spherical, the outer burr surface <NUM>' may instead be cylindrical, as shown in <FIG>. Further, the outer diameter of burr surface <NUM> is greater than a maximum diameter of the cutting portion <NUM> of drill bit <NUM>. Therefore, even if the burr sleeve were to experience slight skiving, because the diameter of the burr sleeve is larger than the drill bit, the pocket would still be large enough to create a surface for the drill bit to cut into without the drill bit skiving. Additionally, the outer diameter of burr surface <NUM> may be equal to or greater than a maximum diameter of the tulip head of the pedicle screw implant, as described in greater detail below.

Sleeve <NUM> defines passageway <NUM> extending through its entire length so that sleeve <NUM> is sized and shaped to receive drill bit <NUM>. As shown in <FIG>, proximal end <NUM> of sleeve <NUM> includes a spline member <NUM> extending around the circumference of sleeve <NUM> and having splines that extend in a direction parallel to the longitudinal axis of sleeve <NUM> to engage a corresponding internal spline member <NUM> a on lock assembly <NUM>.

As shown in <FIG>, lock assembly <NUM> includes an outer tubular member <NUM> which has a substantially cylindrical shape and includes an interior surface <NUM> defining a passageway <NUM> for receiving sleeve <NUM> and drill bit <NUM>. Interior surface <NUM> includes spline member <NUM> for mating with and engaging spline member <NUM> of sleeve <NUM> to rotationally couple sleeve <NUM> and outer tubular member <NUM>. A slot <NUM> extends through an outer surface and interior surface <NUM> of outer tubular member <NUM>. A button <NUM> is received within slot <NUM> and has a generally rectangular shape having two opposing rounded upper and lower surfaces. Button <NUM> includes a hole <NUM> for receiving a pin <NUM> therethrough to secure button <NUM> to tubular member <NUM>, as tubular member <NUM> includes an opening for receiving pin <NUM>, as shown in <FIG>.

Button <NUM> further defines through-opening <NUM> for receiving drill bit <NUM>. In a rest condition, button <NUM> is biased by a spring <NUM> so that spring <NUM> maintains secure engagement with drill bit <NUM>. As shown in <FIG>, button <NUM> engages a reduced diameter segment 127b of drill bit <NUM> to lock drill bit <NUM> relative to lock assembly <NUM> and to sleeve <NUM>. Thus, in a first configuration, with lock assembly <NUM> engaged, cannulated sleeve <NUM> is rotationally and axially locked with drill bit <NUM> due to lock assembly <NUM> and the keyed portions along drill bit <NUM>. In an actuated condition, when button <NUM> is depressed by a user, spring <NUM> is compressed and tubular member <NUM> and sleeve <NUM> are uncoupled from drill bit <NUM> such that the sleeve <NUM> can axially travel and rotate relative to drill bit <NUM>. In this manner, sleeve <NUM> can be moved together along drill bit <NUM> to a different location. For example, tubular member <NUM> can be moved proximally and engage reduced diameter segment 127a and axially locked at that location to control the depth of burr surface <NUM> relative to cutting portion <NUM> of drill bit <NUM>. This allows drill bit <NUM> to extend distally of burr surface <NUM> during drilling. Burr sleeve <NUM> can rotate relative to drill bit <NUM> in this retracted position to allow the burr sleeve to act like a tissue sleeve to prevent tissue wrap during the drilling of the hole.

For assembly, burr extension <NUM> is positioned within cannulated sleeve <NUM>, or alternatively, sleeve <NUM> may be pre-assembled with burr extension <NUM>. However, in some instances, it may be desirable to change the diameter of the burr surface, so burr extension <NUM> and cannulated sleeve <NUM> may be manufactured and sold as two pieces such that the appropriate size of burr extension <NUM> may be chosen based on the needs of the surgical procedure. Thus, an aspect of the present disclosure is a kit including cannulated sleeve <NUM> and at least one burr extension <NUM>. The kit may include a plurality of burr extensions <NUM> having different diameters and differentiated cutting surfaces to accommodate the needs of the surgical procedure. The kit may include lock assembly <NUM> and/or drill <NUM>.

With burr extension <NUM> and cannulated sleeve <NUM> attached so as to operate as a single integral construct, cannulated sleeve <NUM> is engaged with lock assembly <NUM>. Drill bit <NUM> is positioned within lock assembly <NUM> and sleeve <NUM> and engaged with drive body <NUM>. In an initial configuration, cutting portion <NUM> of drill bit <NUM> remains within passageway <NUM> defined by sleeve <NUM> and burr extension <NUM> so that it does not protrude distally of the distal end of burr extension <NUM>. Drive body <NUM> is loaded into robotic end effector <NUM>, shown in <FIG>. Actuation of robotic end effector <NUM> causes rotation of drive body <NUM> and thus drill bit <NUM>.

<FIG> illustrate the difficulties with drilling into the pedicle. As shown, the anatomy of the pedicle includes curved surfaces at the bone interface. As the axial force of the drill is transmitted, the drill may slide down the side of the pedicle, indicated by the arrow in <FIG>, resulting in skiving and a loss of the desired trajectory for hole preparation. Skiving results in sacrificed efficiency as well as accuracy.

In use, system <NUM> is positioned with outer surface <NUM> of burr extension above a pedicle, shown in <FIG>. The robotic end effector <NUM> is placed on haptic line trajectory and actuated causing burr extension <NUM> to cut into the surface of the pedicle that is angled or otherwise not perpendicular to the insertion axis, shown in <FIG>. The placement of sleeve <NUM> and outer burr surface <NUM> surrounding drill bit <NUM> forms a landing zone or shallow pocket within the bone, labeled as "L" in <FIG>. The landing zone or pocket mimics the shape of the outer burr surface <NUM>. Due to the angle of the trajectory, the burr sleeve produces a side cut on the bone surface. The formed pocket has a maximum width that is larger than a diameter of cutting portion <NUM> of drill bit <NUM>. Further, the formed pocket may have a maximum width that is equal to or larger than a diameter of the tulip head of the pedicle screw to facilitate proper seating of the tulip head to the desired depth in the bone.

After the pocket "L" is formed, button <NUM> can be depressed to disengage lock assembly <NUM> and to uncouple drill bit <NUM> relative to sleeve <NUM>. Lock assembly <NUM> and sleeve <NUM> are translated proximally in a retraction direction, shown between <FIG>. Sleeve <NUM> and lock assembly <NUM> can be egaged with reduced segment 127a so that cannulated sleeve and thus burr surface <NUM> is proximal to cutting portion <NUM> of drill bit <NUM> to act as a depth stop for burr surface <NUM>. Robotic end effector <NUM> drives drill bit <NUM> along the same trajectory and drill bit <NUM> drives into bone to cannulate the pedicle for implantation of an implant, e.g. pedicle screw. This pocket or landing zone "L" eliminates the skive angle which is normally present for pedicle screw placement and hole preparation, as is shown by the arrow in <FIG> making it easier to avoid skiving. As drill bit <NUM> drills into bone through pocket "L", the spherical shape of outer burr surface <NUM> creates a rounded, shallow pocket in bone, which facilitates cutting portion <NUM> to tend to get pulled toward the center of the pocket to prevent skiving. Additionally, during drilling, sleeve <NUM> may act as a soft tissue sleeve and may continue to surround drill bit <NUM> to protect the soft tissue as drill bit <NUM> drills into bone. Further, as discussed above, the pocket created by burr <NUM> may help to properly seat the tulip head of the pedicle screw, which may be particularly beneficial where a bone anatomy, e.g. a hypertrophied facet, prevents the full diameter of the tulip head from seating to the desired depth.

System <NUM> may be used with robotic systems during spinal surgery. Robotic systems such as robotic device <NUM> may be used throughout the pre-operative and intraoperative stages of the surgery. Preoperative planning for surgeries may include determining the bone quality in order to optimize bone preparation. Bone quality information, such as bone density or elastic modulus, can be ascertained from preoperative scans, e.g. CT scans. The bone quality data can be used to determine optimal properties for effective implant engagement. Examples of such methods are found in <CIT>, entitled "Patient Specific Bone Preparation for Consistent Effective Fixation Feature Engagement," <CIT>, entitled "Implant Design Using Heterogeneous Bone Properties and Probabilistic Tools to Determine Optimal Geometries for Fixation Features," and <CIT>, entitled "Implant Placement Planning. " In addition to preoperative imaging, robotic surgery techniques may employ imaging, such as fluoroscopy, during surgery. In such cases, systems integrating the surgical system with the imaging technologies facilitate flexible and efficient intraoperative imaging. Exemplary systems are described in <CIT>, entitled "System for Image-Based Robotic Surgery.

Robotic systems and methods may be used in the performance of spine surgeries. In some such instances, robotic systems and methods may be used in the performance of spine surgeries to facilitate the insertion of implants in the patient's spine as in, for example, <CIT>, entitled "Robotic Spine Surgery System and Methods. The robotic system generally includes a manipulator and a navigation system to track a surgical tool relative to a patient's spine. The surgical tool may be manually and/or autonomously controlled. Examples of robotic systems and methods that employ both a manual and a semi-autonomous are described in <CIT>, and entitled "Robotic System and Method for Transitioning Between Operating Modes," and <CIT>, entitled "Surgical Manipulator Capable of Controlling a Surgical Instrument in Multiple Modes.

A robotic controller may be configured to control the robotic arm to provide haptic feedback to the user via the robotic arm. This haptic feedback helps to constrain or inhibit the surgeon from manually moving the incision tool beyond predefined virtual boundaries associated with the surgical procedure. Such a haptic feedback system and associated haptic objects that define the virtual boundaries are described in, for example, <CIT>, entitled "Haptic Guidance System and Method," and <CIT>, entitled "Systems and Methods for Haptic Control of a Surgical Tool," and <CIT>, entitled "System and Method for Manipulating an Anatomy.

In some cases of autonomous positioning, a tool center point (TCP) of a surgical tool, such as sleeve <NUM> and/or drill bit <NUM> is brought to within a predefined distance of a starting point of a line haptic object that provides the desired trajectory. Once the tool center point is within the predefined distance of the starting point, actuation of an input causes the robotic arm to autonomously align and position the surgical tool on the desired trajectory. Once the surgical tool is in the desired position, the robotic system may effectively hold the rotational axis of the surgical tool on the desired trajectory by tracking movement of the patient and autonomously adjusting the robotic arm as needed to keep the rotational axis on the desired trajectory. Such teachings can be found in <CIT>, entitled "Systems and Methods for Haptic Control of a Surgical Tool.

During operation of a robotic surgical system, the operation of the surgical tool can be modified based on comparing actual and commanded states of the tool relative to the surgical site is described in <CIT>, entitled Techniques for Modifying Tool Operation in a Surgical Robotic System Based on Comparing Actual and Commanded States of the Tool Relative to a Surgical Site. " Further, robotic systems may be designed to respond to external forces applied to it during surgery, as described in <CIT>, entitled "Robotic System and Method for Backdriving the Same.

Further, because of the non-homogeneity of bone, applying a constant feed rate, a uniform tool path, and a constant rotational speed may not be efficient for all portions of bone. Systems and methods for controlling tools for such non-homogenous bone can be advantageous as described in <CIT>, entitled "Robotic Systems and Methods for Controlling a Tool Removing Material From a Workpiece.

<FIG> show a system <NUM> that includes a cannulated sleeve <NUM> and a drill bit <NUM>. System <NUM> includes many similar features as system <NUM>, except that system <NUM> utilizes a different lock assembly on cannulated sleeve <NUM>. As discussed above, with reference to system <NUM>, sleeve <NUM> includes burr extension <NUM> which may be manufactured as a single, monolithic piece or as two attachable pieces. The disclosure contemplates a kit including sleeve <NUM> and at least one burr extension <NUM>. The kit may include a plurality of burr extensions <NUM> having different diameters to accommodate the anatomy and needs of a surgical procedure.

Proximal end <NUM> of cannulated sleeve <NUM> includes lock assembly <NUM> for rotationally and axially coupling drill bit <NUM> and sleeve <NUM>. Lock assembly <NUM> includes spring-loaded button <NUM> positioned within tubular member <NUM>, and is substantially identical to button <NUM> of system <NUM>. As shown in <FIG>, ring <NUM> is attached, e.g. welded, to tubular member <NUM> and includes inner surface <NUM> that is keyed along a portion of the inner surface to mate with the keyed portion of drill bit <NUM> to rotatably couple the drill bit and sleeve <NUM> when lock assembly <NUM> is locked. In a rest condition, button <NUM> is biased by spring <NUM> so that the spring maintains secure engagement with drill bit <NUM>. As shown in <FIG>, button <NUM> engages reduced diameter segment 227b of drill bit <NUM> to lock the drill bit <NUM> relative to lock assembly <NUM> and to sleeve <NUM>. Thus, in a locked configuration, with lock assembly <NUM> engaged, cannulated sleeve <NUM> is rotationally and axially locked with drill bit <NUM>. In an actuated condition of button <NUM>, when button <NUM> is depressed by a user, spring <NUM> is compressed and sleeve <NUM> is disengaged from drill bit <NUM> and can be moved along drill bit <NUM>, as shown in <FIG>. In this configuration, sleeve <NUM> is retracted such that keyed ring <NUM> is not rotationally locked with drill bit <NUM>, but rather drill bit <NUM> can rotate for drilling and sleeve <NUM> can freely spin relative to the drill bit.

In use, system <NUM> is used in a similar manner to that described above with reference to system <NUM>, as described with reference to <FIG>.

<FIG> show system <NUM> according to another embodiment of the present disclosure. System <NUM> is similar in many respects to system <NUM> and is designed to facilitate co-axial burring and drilling of a target location of bone. The system forms a landing zone or pocket on the surface of the bone, e.g. a pedicle of a vertebra, to prevent the subsequent drill from skiving during hole preparation during surgery, e.g. spinal surgery. Generally, system <NUM> includes a burr tool disposed within a guide tube and rotated about an insertion axis to form a pocket on the surface of the bone. The burr tool is removed and the drilling tool is inserted within the guide tube and rotated about the insertion axis at the pocket to form the hole into which the implant will be inserted. Due to the pocket formed prior to drilling, the drill is prevented from skiving.

System <NUM> is designed for robotic use, as shown with a robotic arm in <FIG> and cylindrical sleeve <NUM> through which system <NUM> is designed to fit. System <NUM> includes guide tube <NUM>, obturator <NUM>, burr <NUM> and drill <NUM>. As shown in <FIG>, guide tube <NUM> extends from proximal end <NUM> to distal end <NUM> and includes a cannulation through the length of the guide tube. Proximal end <NUM> includes collar <NUM> extending around the circumference of the guide tube <NUM>. Distal end <NUM> includes teeth <NUM> extending around the circumference of the distal end. In the illustrated embodiment, teeth <NUM> are in the form of serrations each having a generally triangular shape and terminate at a point. The teeth may be formed to allow for engagement with the bone to dock the guide tube. Although in other examples, the distal end may have a knife-edge or other known sharp edge which may facilitate engagement with the bone. Guide tube <NUM> is cylindrical along a substantial portion of the length and tapers inwardly at distal end <NUM>.

As discussed above, guide tube <NUM> has an outer diameter sized to fit within sleeve <NUM> of the robotic system <NUM>. The inner diameter of guide tube <NUM> is sized to receive obturator <NUM> and the burr <NUM> within both the obturator and the guide tube. Additionally, with the obturator <NUM> and burr <NUM> removed from the guide tube <NUM>, the drill is receivable within the cannulation of the guide tube. An inner surface of guide tube <NUM> includes threaded portion <NUM> at proximal end <NUM> for threaded engagement with an outer surface of obturator <NUM>, as shown in <FIG>.

<FIG> shows obturator <NUM> which has a smooth outer surface to reduce trauma to the soft tissue during surgery. Obturator <NUM> is sized to fit within and coaxial with guide tube <NUM>. Obturator <NUM> has a generally cylindrical shape and is cannulated to receive burr <NUM> coaxial with the obturator. Obturator <NUM> extends between proximal end <NUM> and distal end <NUM>. At proximal end <NUM>, the outer surface includes threaded portion <NUM> corresponding to internal threaded portion <NUM> of guide tube <NUM>. Additionally, proximal end <NUM> includes cap <NUM> that has a diameter than the body of the obturator. As shown in <FIG>, collar <NUM> of guide tube <NUM> and cap <NUM> of obturator <NUM> may have substantially equal diameters and cap <NUM> is configured to proximally abut the collar of the guide tube. Distal end <NUM> is generally rounded to avoid trauma to soft tissue as the obturator moves through the soft tissue.

Burr <NUM> is spring-loaded into the system and receivable within obturator <NUM>. Burr <NUM> extends between proximal end <NUM> and distal end <NUM>. Proximal end <NUM> includes handle <NUM> for controlling rotation of the burr tool. Distal end <NUM> includes burr tip <NUM> for cutting the bone to create a pocket within the bone to prevent skiving of the drill during the drilling of a hole. Burr tip <NUM> includes cutting elements <NUM> positioned around the circumference of the burr tip with a sharp pointed tip <NUM>, best shown in <FIG>. The cutting elements <NUM> are convexly shaped separated from one another by concave surfaces around the circumference. From a bottom profile, the burr tip <NUM> has a substantially X shape.

Burr <NUM> includes a larger diameter portion <NUM> adjacent the handle <NUM> and a reduced diameter portion <NUM> separated from one another by engagement portion <NUM>, as shown in <FIG>. Spring <NUM> is positioned around engagement portion <NUM> and the burr may be pinned to obturator <NUM> at a position along second reduced diameter portion <NUM>, as shown in <FIG>.

Burr <NUM> is first spring-loaded into the obturator <NUM>, as shown in <FIG>, and then the obturator (with the burr therein) is loaded into guide tube <NUM>. Obturator <NUM> is threaded into guide tube <NUM>. When loaded into guide tube <NUM>, the guide tube, obturator <NUM> and burr <NUM> are all coaxial with one another. As obturator <NUM> is positioned within guide tube <NUM>, due to spring <NUM> burr <NUM> can move slightly axially to allow the burr to move from a first, proximal position in which burr tip <NUM> is within the guide tube <NUM> and/or obturator <NUM>, as shown in <FIG> and <FIG>, to a second, distal position in which burr tip <NUM> is exposed and distal to the obturator and guide tube, as shown in <FIG> and <FIG>. Further, burr <NUM> is rotatable in order to cut the bone to form the pocket.

As shown in <FIG>, the system <NUM> including the burr <NUM>, obturator <NUM> and guide tube <NUM>, is loaded into sleeve <NUM> and the robotic arm along an insertion axis and positioned against the pedicle bone. Burr <NUM> is rotated about the insertion axis to form the pocket in the pedicle bone, in which the drill or drill bit will subsequently be positioned and drilled. The pocket is formed within a bone surface that is not perpendicular to the insertion axis, as discussed above with reference to system <NUM>. The pocket is a shallow pocket with a substantially rounded surface which prevents skiving of the drill when the drill is positioned at the pocket.

After the pocket is formed, the obturator <NUM> and burr <NUM> are removed distally from the guide tube <NUM> and the drill <NUM> is placed within the guide tube, shown in <FIG>. Drill <NUM> is rotatably keyed to the guide tube <NUM> to rotationally lock them together such that the drill and thus guide tube are rotated at the pocket. The rotation of the drill causes formation of the hole within the pocket, as shown in <FIG>. An implant, such as a pedicle screw, may be implanted within the hole.

In an alternative embodiment, shown in <FIG> and <FIG>, the guide tube <NUM> and obturator <NUM> are used in conjunction with a spring-loaded awl <NUM> rather than burr <NUM>. Awl <NUM> includes a pointed tip <NUM> for engaging the bone.

Claim 1:
A system (<NUM>) comprising:
a surgical tool for use with a drill bit (<NUM>) to prevent skiving at an implant insertion site on a bone, the surgical tool including a cannulated sleeve (<NUM>) having a distal end defining a burr surface (<NUM>); and
the drill bit (<NUM>) configured to be disposed within the cannulated sleeve (<NUM>), wherein:
in a first configuration the cannulated sleeve (<NUM>) and the drill bit (<NUM>) are rotationally coupled to each other and in a second configuration the cannulated sleeve (<NUM>) and the drill bit (<NUM>) rotate independent of one another.