Patent Description:
Despite the assistance that powered tools may provide, control of such instruments may be more difficult than hand-powered tools. In turn, unintended contact of the instrument with surrounding tissue (e.g., soft tissue surrounding the bone on which the operation is to occur) may cause damage to such surrounding tissue. In turn, reducing the risk of such unintended contact of the instrument with tissue may assist in improving surgical outcomes. Existing prior art includes <CIT>, which relates to a drill assembly and method for reducing plunge of a drill bit upon breaking through a workpiece. <CIT> discloses a measurement system and method for determining a depth of penetration of a working portion of a surgical instrument (e.g., a rotating drill bit in a bore). A first sensor outputs a first signal representative of a displacement of the leading edge of the drill bit in the bore. A second sensor outputs a second signal representative of a force applied to the leading edge of the drill bit. A processor outputs a third signal representative of the depth of penetration of the leading edge of the drill bit when the leading edge of the drill bit passes from a first medium having a first density to a second medium having a second density. The third signal is based on the first and second signals.

The presently claimed invention relates to an instrument for use in a surgical operation according to claim <NUM>. Further developments of the herein claimed invention are described in the dependent claims.

In view the foregoing, a measurement system may be used with an instrument for use in connection with operation of an instrument. A detection module may be provided in operative communication with the measurement system to measure one or more parameters measured by the measurement system. The detection module may arrest the instrument to help reduce the possibility of damaging tissue surrounding a bone on which the instrument operates. For example, <CIT>, <CIT>, <CIT>, and <CIT>, disclose various systems and approaches to monitoring a powered surgical instrument. However, such disclosures have conventionally been directed to the measurement of the position of a working portion of a tool relative to a bone of a patient. In turn, these contexts involve measurement of the depth of a bore created by a drill bit or arresting a working tool portion upon engagement of the working tool with a specific portion of the bone.

In the present disclosure, the instrument may comprise a powered burr tool for use in grinding a bone. The burr tool may be used to bore into a bone in a manner similar to a drill as described in the disclosures above. Additionally or alternatively, a burr tool may be used on a surface of a bone to grind a portion thereof. That is, the burr tool may be advanced radially relative to an axis of rotation of the burr tool. However, when using a burr tool, it may be more likely that the bone substrate fails, resulting in release of the instrument from the bone. Furthermore, given that a burr tool may be used to operate on an exterior surface of a bone, the potential that the instrument may slips from the external surface may be increased.

As such, the disclosure presented herein includes use of an instrument (e.g., a burr tool or other instrument) to operate on a bone. Furthermore, a measurement system may be utilized to measure one or more parameters related to the movement of the burr tool. In turn, a detection module may be provided to monitor the one or more parameters and control the instrument in response thereto. As such, the detection module may help reduce the potential of surrounding tissue damage when using a burr tool to perform an operation (e.g., a grinding operation) on an exterior portion of a bone. For instance, given that the measurement system may be operative to measure an applied force and/or displacement of the tool relative to a reference point, the measurement system may be operative to detect an instance in which the instrument slips from (i.e., suddenly loses contact with) the bone. Upon detection of such slippage or loss of contact, the instrument may be arrested to prevent and/or limit damage to surrounding tissue. Furthermore, the burr tool may be arrested upon completion of an operation relative to the bone (e.g., whether performed unicortically or bicortically).

As such, the measurement system may include a displacement sensor, acceleration sensor, and/or a force sensor that may be utilized to monitor the instrument. A detection module may in monitor for an acceleration that exceeds a threshold or a force acting on the burr tool is reduced relative to a threshold (e.g., that may be indicative that the instrument has slipped). The instrument may be arrested upon completion of such an operation. In another context, the measurement system may be able to detect rapid accelerations of the instrument (e.g., using the displacement sensor). These rapid accelerations may result from the instrument slipping from the bone. As such, detection of such rapid acceleration may also cause the instrument to arrest to prevent damage surrounding tissue.

Furthermore, the burr instrument may have a predetermined ramp-up speed in which the angular velocity of the burr instrument upon start up slowly accelerates along a ramp-up profile. This may assist in providing safety with the burr instrument to prevent unintentional contact of the burr instrument at high speed with soft tissue.

Accordingly, a first aspect relates to an instrument for use in a surgical operation. The instrument may include a drive system for rotationally driving a working tool engaged with the instrument about a working axis and a burr tool engaged with the instrument for rotation of the burr tool by the drive system about the working axis. The burr tool is contactably engageable with a medium. The instrument may also have a measurement system for monitoring the contactable engagement of the burr tool with the medium and a detection module in operative communication with the measurement system to detect a loss of the contactable engagement of the burr tool with the medium.

A number of feature refinements and additional features are applicable to the first aspect. These feature refinements and additional features may be used individually or in any combination. As such, each of the following features that will be discussed may be, but are not required to be, used with any other feature or combination of features of the first aspect.

For example, the measurement system may include an accelerometer for detecting an acceleration of the burr tool relative to the medium. The accelerometer may include a displacement sensor for outputting a displacement measure of the burr tool relative to the medium and an acceleration value may be determined based on a second derivative of the displacement measure. Additionally or alternatively, the accelerometer may measure an acceleration of the instrument directly. In either regard, the detection module may detect the loss of the contactable engagement of the burr tool with the medium in response to the acceleration of the burr tool relative to the medium exceeding an acceleration threshold value.

In an embodiment, the acceleration threshold value may be a value that is selectable by a user of the instrument. The acceleration threshold value may include a maximum acceleration magnitude value. Alternatively, the acceleration threshold value may include a maximum rate of change of the acceleration of the burr tool.

In an embodiment, the measurement system may include at least one force sensor. The at least one force sensor may be arranged relative to the burr tool to measure a force acing axially along the working axis. Also, the at least one force sensor may be arranged relative to the burr tool to measure a force acing radially relative to the working axis.

In an embodiment, the detection module may detect the loss of the contactable engagement of the burr tool with the medium in response to a reduction in force acting on the burr tool exceeding a force threshold value. The force threshold value may include a maximum rate of change of force and a loss of the contactable engagement of the burr tool is detected upon the rate of change in the force acting on the burr tool exceeding the maximum rate of change.

In an embodiment, the drive system may be operative to initiate rotation of the working tool such that a rotational speed of the working tool increases along a defined acceleration profile. The defined acceleration profile may be linear. Moreover, upon detection of the loss of the contactable engagement of the burr tool with the medium by the detection module, the drive system may be deactivated. Also, the instrument may include a brake in operative communication with the drive system. In turn, upon detection of the loss of the contactable engagement of the burr tool with the medium, the brake is activated to cease rotation of the working tool.

A second aspect is directed to a method for use of an instrument. The method includes operating an instrument to perform an operation relative to a bone of the patient by contacting a working portion of the instrument with the bone of the patient and monitoring the working portion of the instrument. The method also includes detecting a loss of contact between the working portion and the bone and arresting the instrument upon detection of the loss of contact between the working portion and the bone.

A number of feature refinements and additional features are applicable to the second aspect. These feature refinements and additional features may be used individually or in any combination. As such, each of the following features that will be discussed may be, but are not required to be, used with any other feature or combination of features of the second aspect.

For instance, the monitoring may include measuring one or more parameter using a measurement system of the instrument. Specifically, the measurement system may include an acceleration sensor and the one or more parameters may be an acceleration of the working tool relative to the bone. The detecting may include measuring the acceleration of the working tool relative to a bone that exceeds an acceleration threshold value.

Additionally or alternatively, the measurement system may include a force sensor and the one or more parameters may be a change in force acting on the working tool. In turn, the detecting may include measuring the change in force acting on the working tool that exceeds a force threshold value comprising a maximum rate of change in force.

The arresting may include ceasing operation of a drive system of the instrument. Additionally or alternatively, the arresting may include applying a brake to a drive system of the instrument.

A third aspect is directed to a method of use of a powered surgical burr tool. This method includes initiating rotation of the burr tool with the instrument. Specifically, the rotation of the burr tool accelerates according to an acceleration profile such that full speed of the burr tool is delayed by a known time after the initiating.

The following description is not intended to limit the invention to the forms disclosed herein. Consequently, variations and modifications commensurate with the following teachings, skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular applications(s) or use(s) of the present invention.

As described above, the present disclosure generally relates to an instrument <NUM> such as that shown in the figures. The instrument <NUM> may be a powered surgical instrument such as a drill, saw, reciprocating tool, or the like. In one embodiment, the instrument <NUM> may be engaged with a burr tool <NUM> like the one shown in <FIG>. The burr tool <NUM> may include a working portion <NUM> that may have fluted or ridged portions. The working portion <NUM> may allow for abrading or grinding a bone or other calcified or hardened substrate. As such, it may be appreciated the burr tool <NUM> may be used in a context similar to a drill bit, where the burr tool <NUM> is advanced axially along a working axis <NUM> about which the burr tool <NUM> is rotated. Additionally or alternatively, the burr tool <NUM> may be used to grind by advancing the burr tool <NUM> in a direction perpendicular to the working axis <NUM>. Moreover, a combination of radial and axial movement may also be used and monitored as described in greater detail below.

In this regard, as has been described in <CIT>, <CIT>, <CIT>, and <CIT>, various methodology and approaches to monitoring a tool as it is advanced bicortically or unicortically through a bone of a patient. In this regard, in the event the burr tool <NUM> is utilized in a manner similar to a drill bit where the burr tool <NUM> is advanced to create a bore in the bone, any of the methodology or structure utilized in the references described therein may be used in conjunction with the burr tool <NUM>. That is, the burr tool <NUM> may stand in the place of any tool, instrument, or drill bit described in any of the described disclosure. As such, as shown in <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, the burr tool <NUM> may be used with any type of measurement system described in the described references. As such, the burr tool <NUM> may be used to create a bore. Upon the burr tool <NUM> passing through a bone or a portion of a bone, the instrument driving the burr tool <NUM> may be arrested. This may prevent unintended damage to tissue surrounding the bone when using the burr tool <NUM>.

Referring to <FIG> and <FIG>, an instrument <NUM> may include a measurement system <NUM> that comprises a displacement sensor <NUM>, a force sensor <NUM>, and a controller assembly <NUM>. The displacement sensor <NUM> may be connected to the instrument housing <NUM>. The connection can be made by a variety of well known mounting methods such as a mount that clamps to the displacement sensor <NUM> and is attached to the instrument housing <NUM> by one or more threaded fasteners. Alternative methods such as welding or adhesive bonding could also be used.

The displacement sensor <NUM> may include a transducer <NUM> that outputs a displacement signal that is representative of a displacement, with respect to the reference point, of the leading edge 16a of the burr tool <NUM>. The displacement sensor <NUM> may have an extension <NUM> that is displaceable along a longitudinal axis. The extension <NUM> has a distal end 110a that can be placed in registry with the reference point when the leading edge 16a of the burr tool <NUM> is positioned relative to a bone (e.g., placed in contact therewith). The distal end 110a may be maintained in registry with the reference point throughout the process conducted using the burr tool <NUM>. The reference point can be any anatomical structure proximal to the location at which the burr tool <NUM> is used. The extension <NUM> has a proximal end 110b that is attached to the first sensor <NUM>. Preferably the transducer <NUM> is a linear variable differential displacement transducer ("LVDT").

Furthermore, it may be appreciated that the spacing of the extension <NUM> of the displacement sensor <NUM> from the burr tool <NUM> may introduce the potential for errors or other disadvantages in determining the displacement of the burr tool <NUM> relative to the reference point. For instance, as the extension <NUM> may contact a structure that is offset from the contact point between the leading edge 16a of the burr tool <NUM> and the medium to be subjected to an operation using the burr tool <NUM>. Accordingly, any movement between the structure contacted by the extension <NUM> and the medium on which the burr tool <NUM> is used may be falsely registered as relative movement of the burr tool <NUM> with respect to the reference point. Furthermore, there may not be a rigid structure to contact adjacent to the medium to be contacted, leading to displacement of the structure contacted by the extension <NUM> (e.g., such as in the case where the extension <NUM> may contact soft tissue adjacent to the medium to be contacted given the offset from the location to be contacted). Furthermore, the offset nature of the extension <NUM> relative to the contact between the burr tool <NUM> and the medium to be contacted may lead to other complications such as having to expose a greater surface of the medium to be contacted, which may adversely affect patient outcomes.

In this regard, and with further reference to <FIG>, an embodiment of an instrument <NUM> may be provided that includes an acceleration sensor <NUM>. An acceleration sensor <NUM> may be provided as an alternative to or in addition to the displacement sensor <NUM> described above. The acceleration sensor <NUM> may be a MEMS accelerometer, an optical accelerometer, a piezoelectric accelerometer, or any other appropriate accelerometer. In turn, the acceleration sensor <NUM> may be operative to determine an acceleration of the instrument <NUM>, which may be rigidly interconnected with the burr tool <NUM>. As such, an acceleration of the burr tool <NUM> may be sensed by the acceleration sensor <NUM>.

Further still, in either of the embodiments of an instrument <NUM> depicted in <FIG> or <FIG> may include a force sensor <NUM>. Specifically, the working portion load measurement assembly may include one or more force sensors. The one or more force sensors may be arranged to measure a force applied to the burr tool <NUM> when in use. A force sensor element may be arranged to measure an axial load acting on the burr tool <NUM> that results in advancement of the burr tool <NUM> as the burr tool <NUM> is advanced axially relative to the working axis <NUM>. In addition, one or more force sensor elements may be provided that are arranged to measure a force acting in a radial direction relative to the working axis <NUM>. In this regard, in a grinding operation where the burr tool <NUM> is advanced in a direction radial to the working axis <NUM>, a force acting on the burr tool <NUM> may be monitored. In turn, monitoring of the force acting on the burr tool <NUM> (e.g., either axially or radially) may assist in determining unintended slippage of the burr tool <NUM> as will be discussed in greater detail below.

Another embodiment of an instrument with a displacement sensor including a displacement sensing arm that extends from the instrument may be provided. For example, such a displacement sensing arm may be provided that may coordinate with a bushing member of a burr tool assembly that may be used with the instrument. In this regard, the bushing may move along the burr tool in a direction corresponding to the axis of rotation of the burr tool. Upon engagement of the bushing and the displacement sensing arm, the bushing and displacement sensing arm may undergo corresponding movement. As such, the bushing may be disposed in contact with the medium to be contacted when the leading edge of the burr tool is in contact with the medium. As such, a reference point may be established when the bushing and leading edge of the burr tool are both in contact with the medium to be contacted by the burr tool. As the bushing is located adjacent to (e.g., partially or fully surrounding the burr tool), the bushing may facilitate contact with the medium at or very near the location to be contacted prior to initiation of an operation using the burr tool. In this regard, the reference point may be more accurately maintained as the bushing may contact at least a portion of a periphery of the bone adjacent to where the burr tool is used to remove tissue. That is, the bushing may remain in intimate contact with the medium to be contacted adjacent to the burr tool. This may prevent false displacement readings attributable to the foregoing problems associated with an offset extension <NUM>. Furthermore, the amount of contact of the bushing may be localized at the location to be contacted by the burr tool, thus allowing for potentially less intrusion when performing operations using the burr tool.

For example, with additional reference to <FIG>, and <FIG>, an embodiment of an instrument <NUM> comprising an embodiment of a measurement system <NUM> is shown. The instrument <NUM> may be adapted for use with a burr tool assembly <NUM> (shown in <FIG>) that may include a bushing <NUM>. The instrument <NUM> may integrally comprise at least some components of the measurement system <NUM> to facilitate operation of the measurement system <NUM> in connection with the instrument <NUM> (e.g., which may be according to the description above regarding measurement system <NUM>). For example, at least a portion of a displacement sensor <NUM> may be integrated into a housing <NUM> of the instrument <NUM>. In this regard, the displacement sensor <NUM> may include a depth sensing arm <NUM> that is specifically adapted for engagement with a bushing <NUM> of a burr tool assembly <NUM> that may be engaged by the chuck <NUM> of the instrument <NUM>.

In this regard, the depth sensing arm <NUM> may be used to establish a reference point from which displacement of the burr tool <NUM> may be measured as described above. In this regard, as follows herein, a general description of the features and operation of the instrument <NUM> used in conjunction with the burr tool assembly <NUM> is provided.

The displacement sensor <NUM> may include a depth sensing arm <NUM> that may extend from the instrument housing <NUM>. For example, the depth sensing arm <NUM> may extend distally (e.g., from a distal face <NUM> of the instrument <NUM>) in a direction corresponding with the direction in which the burr tool <NUM> extends from a chuck <NUM> of the instrument <NUM>. As such, the chuck <NUM> may engage the burr tool <NUM>. At least a portion of the displacement sensing arm <NUM> may extend from the instrument housing <NUM> parallel to an axis of rotation <NUM> of the instrument <NUM>. The depth sensing arm <NUM> may also include a distal portion <NUM> that is adapted to engage a bushing <NUM> provided with the burr tool assembly <NUM> shown in <FIG>. As used herein, distal may correspond to a direction from the instrument <NUM> toward the leading edge 16a of the burr tool <NUM> and proximal may correspond to a direction from the leading edge 16a of the burr tool <NUM> toward the rear portion of the instrument <NUM>. In this regard, at least a portion of the depth sensing arm <NUM> (e.g., the distal portion <NUM>) may be adapted to engage the bushing <NUM> of the burr tool assembly <NUM> as will be described in more detail below. In any regard, at least a portion of the depth sensing arm <NUM> may extend into the housing <NUM>. The housing <NUM> may contain a coil <NUM>. As such, a proximal end <NUM> of the displacement sensing arm <NUM> may interface with the coil <NUM> of the displacement sensor <NUM> that may be disposed within the instrument housing <NUM>.

Specifically, in <FIG>, the depth sensing arm <NUM> is shown in a retracted position relative to the burr tool <NUM>. As such, this retracted position shown in Fig. <NUM> may occur when the burr tool <NUM> is advanced relative to the bushing <NUM> during an operation. In this regard, the proximal end <NUM> of the displacement sensing arm <NUM> is disposed within the coil <NUM> of the displacement sensor <NUM>. Accordingly, the displacement sensor <NUM> may comprise an LVDT sensor as described above that is adapted to sense the position of a core <NUM> relative to a coil <NUM>. The displacement sensing arm <NUM> may incorporate a core <NUM> at the proximal end <NUM> thereof. Accordingly, as the proximal end <NUM> of the displacement sensing arm <NUM> is moved relative to the coil <NUM>, the location of the core <NUM> may be determined to provide an output corresponding to the position of the core <NUM>, and in turn the displacement sensing arm <NUM> relative to the instrument housing <NUM>. That is, the depth sensing arm <NUM> may be displaceable relative to the coil <NUM> such that the displacement sensor <NUM> may be operable to sense a change in position of the depth sensing arm <NUM> relative to the instrument housing <NUM> and output a measure of the displacement of the burr tool relative to a reference point. In an embodiment, the total measurable travel of the core <NUM> relative to the coil <NUM> may be at least about <NUM> in (<NUM>). Furthermore, the resolution of the output of the displacement sensor <NUM> may be about <NUM>% (e.g., about <NUM> inches (<NUM>) for a sensor having a total measureable travel of <NUM> inches).

While a LVDT displacement sensor is shown and described in relation to the instrument <NUM> shown in the accompanying figures, it may be appreciated that other types of displacement sensors may be provided. For instance, the sensor may provide for the absolute or relative measurement of the position of the distal end <NUM> of the displacement sensing arm <NUM> to provide a displacement measure. For instance, in another embodiment, an optical displacement sensor may be provided. Other types of displacement sensors are also contemplated such as, for example, a capacitive displacement sensor, ultrasonic sensors, Hall effect sensors, or any other sensors known in the art capable of outputting an absolute or relative position measure.

In an embodiment, the coil <NUM> may define a passage <NUM> extending at least partially through the housing <NUM>. Specifically, the passage <NUM> may extend from a proximal face <NUM> of the housing <NUM> to the distal face <NUM> of the housing <NUM>. That is, the passage <NUM> may extend entirely though the housing <NUM>. An end cap <NUM> may be provided that is operable to close the proximal end of the passage <NUM> at the proximal face <NUM> of the instrument housing <NUM>. Furthermore, a biasing member <NUM> (e.g., a coil spring) may be provided in the passageway <NUM> at a proximal end thereof. The biasing member <NUM> may be provided between the end cap <NUM> and the proximal end <NUM> of the displacement sensing arm <NUM>. In this regard, the biasing member <NUM> may act on the proximal end <NUM> of the displacement sensing arm <NUM> to bias the displacement sensing arm <NUM> distally relative to the passage <NUM> and instrument housing <NUM>.

As such, the displacement sensing arm <NUM> may include features that selectively prevent ejection of the displacement sensing arm <NUM> from the distal end of the passage <NUM>. For example, the displacement sensing arm <NUM> may include at least one flat <NUM> that extends along a portion of the arm <NUM>. At the proximal and distal extents of the flat <NUM>, the displacement sensing arm <NUM> may include shoulders <NUM> that project from the flats <NUM>. As such, at the proximal opening of the passage <NUM>, a selectively displaceable stop <NUM> (best seen in Fig. <NUM>) may be disposed relative to the flat <NUM> such that the flat <NUM> may move relative to the stop <NUM>, but interfere with the shoulder <NUM> defined in the displacement sensing arm <NUM> to prevent passage of the shoulder <NUM> beyond the stop <NUM>. In this regard, the length of the displacement sensing arm <NUM> along which the flat <NUM> extends may be moveable relative to the stop <NUM>, and the stop <NUM> may limit proximal and distal movement of the displacement sensing arm <NUM> beyond the stop <NUM>.

However, the stop <NUM> may be displaceable upon depressing a button <NUM> provided on an exterior of the housing <NUM>. Other types of actuators may be used to control the stop <NUM> and a button <NUM> is provided as merely one example. Thus, upon depressing the button <NUM>, the stop <NUM> may be displaced away from the displacement sensing arm <NUM> to allow the shoulder <NUM> to pass distally from the distal end of the passage <NUM> such that the displacement sensing arm <NUM> may be removed entirely from the passage <NUM>. The distal end of the flats <NUM> may include a detent <NUM> that may be engageable with the stop <NUM> so as to maintain the displacement sensing arm <NUM> in a proximally disposed, retracted position relative to the housing (e.g., as shown in <FIG>). Once the button <NUM> is depressed and released, the detent <NUM> at the proximal end of the flat <NUM> of the displacement sensing arm <NUM> may be released by the stop <NUM> and the displacement sensing arm <NUM> may move proximally (e.g., under influence of the biasing member <NUM>). The displacement sensing arm <NUM> may move proximally until the shoulder <NUM> at the distal end of the flat <NUM> are engaged to prevent further distal movement of the displacement sensing arm <NUM>. Accordingly, the displacement sensing arm <NUM> may be retained in a retracted position (e.g., for improved visibility of the distal end of the burr tool <NUM>), released to be moveable relative to and biased proximally with respect to the housing <NUM>, and removable altogether from the housing <NUM>.

In the latter regard, removal of the displacement sensing arm <NUM> and biasing member <NUM> from the passage <NUM> may allow for separate cleaning (e.g., in an autoclave) of those members. Additionally, removal of the end cap <NUM> may allow for a cleaning apparatus (e.g., a brush or the like) to be passed through the full length of the passage <NUM> to facilitate cleaning thereof.

As referenced above, the distal portion <NUM> of the displacement sensing arm <NUM> may be adapted to engage a burr tool assembly <NUM> (e.g., a bushing <NUM> thereof) that is correspondingly adapted for use with the instrument <NUM>. For instance, the displacement sensing arm <NUM> may generally be linear along the proximal portion <NUM> of the displacement sensing arm <NUM>. In this regard, the proximal portion <NUM> may be adapted to be collinear with the passage <NUM> and moveable within the passage <NUM>. Furthermore, the distal portion <NUM> of the displacement sensing arm <NUM> (e.g., the portion distal to the linear portion of the displacement sensing arm <NUM>) may extend from the linear portion of the displacement sensing arm <NUM> toward the burr tool assembly <NUM> that may be engaged by the chuck <NUM> of the instrument <NUM>. In this regard, the linear portion of the displacement sensing arm <NUM> may be substantially parallel to and offset from the axis of rotation <NUM>. The distal portion <NUM> may extend from the linear portion in a direction corresponding with the offset such that the distal portion <NUM> extends toward the burr tool assembly <NUM>. This may facilitate engagement between the displacement sensing arm <NUM> and the bushing <NUM> of the burr tool assembly <NUM>. As shown, in <FIG>, the distal portion <NUM> may be an at least partially arcuate member extending along a radius of curvature toward the burr tool assembly <NUM>. However, the distal portion <NUM> may be shaped differently (e.g., the distal portion <NUM> may be a linear portion extending at an angle or perpendicularly from the proximal <NUM> toward the burr tool assembly <NUM>).

With further reference to <FIG>, an embodiment of a burr tool assembly <NUM> that may be used in conjunction with the instrument <NUM> is depicted. The burr tool assembly <NUM> may include a shank <NUM> that is disposed adjacent to a proximal end of the assembly <NUM>. There may be sharped fluted ridges disposed in a working portion <NUM> adjacent to the leading edge 16a of the burr tool assembly. These ridges may include cutting edges that, when rotated serves to abrade or grind the medium into which the burr tool <NUM> is advanced. In certain applications, the working portion <NUM> may be generally spherical. In other applications, the working portion <NUM> may be conical, ovoid, or any other appropriate shape. Moreover, the working portion <NUM> may be of any appropriate size for application in various different contexts in which the burr tool may be utilized. A cylindrical member <NUM> may extend between the shank <NUM> and the working portion <NUM>. The working portion <NUM>, cylindrical body <NUM>, and shank <NUM> may collectively define the burr tool <NUM>.

In addition to the burr tool <NUM>, the burr tool assembly <NUM> may also comprise a bushing <NUM> as referenced above. The bushing <NUM> may engage the cylindrical member <NUM> to facilitate relative movement of the bushing <NUM> relative to the cylindrical member <NUM> along a direction corresponding to the axis of rotation <NUM>. For example, the bushing <NUM> may include an aperture <NUM> through which at least a portion of the cylindrical member <NUM> may be disposed. The aperture <NUM> may form a cylindrical opening that extends at least in a direction corresponding to the axis of rotation <NUM> of the burr tool <NUM>. The cylindrical opening may be sized to receive the cylindrical member <NUM> therein such relative movement between the cylindrical opening and the cylindrical member <NUM> is provided. Moreover, the bushing <NUM> may be sized so as to be operable to pass over the working portion <NUM>. In this regard, the bushing <NUM> may surround the working portion <NUM> when the bushing is in a distal position such that the leading edge 16a of the working portion <NUM> is aligned axially with the distal edge of the bushing <NUM>. As such, the burr tool <NUM> may be free to rotate within the aperture <NUM> (e.g., even when the bushing <NUM> is disposed about the working portion <NUM>), and the bushing <NUM> may slideably engage the cylindrical member <NUM> for relative movement therebetween that is constrained along the direction corresponding to the axis of rotation <NUM>. Further still, as the bushing member <NUM> may surround the working portion <NUM> when in a biased, distal position, the working portion <NUM> may be at least partially shielded to prevent unintended contact with surrounding tissue. Moreover, as the working portion <NUM> is advanced relative to the bone to be the target to an operation, the bushing <NUM> may be moved proximally relative to the working portion <NUM> so as to allow measurement of the displacement of the working portion <NUM>. This may be particularly helpful in relation to monitoring the working portion <NUM> to detected unintended slippage that may otherwise lead to damage to the surrounding tissue.

The bushing <NUM> may include an engagement member <NUM> that is disposed on the bushing <NUM> and adapted for engagement with a displacement sensing arm <NUM> of an instrument <NUM> to which the burr tool assembly <NUM> is engaged. For instance, as depicted in <FIG>, the engagement member <NUM> may comprise a post <NUM> extending from the bushing <NUM>. The post <NUM> may extend away from the axis of rotation <NUM> of the burr tool assembly <NUM>. In an embodiment, the post <NUM> may extend perpendicularly to the axis of rotation <NUM>. Accordingly, the post <NUM> may engage a hole <NUM> provided on the distal portion <NUM> of the displacement sensing arm <NUM>. In this regard, the post <NUM> may extend into the hole <NUM>. Movement of the bushing <NUM> relative to the burr tool <NUM> in a direction corresponding to the axis of rotation <NUM> may result in the post <NUM> acting on the hole <NUM> such that the displacement sensing arm <NUM> undergoes corresponding movement upon movement of the bushing <NUM> relative to the burr tool <NUM>. In turn, as described above, the core <NUM> at the proximal portion <NUM> the displacement sensing arm <NUM> may also undergo corresponding movement relative to the coil <NUM>, which may be detected by the displacement sensor <NUM> and output as a displacement measure.

It may be appreciated that other arrangements for engaging the bushing <NUM> with the displacement sensing arm <NUM> may be provided so that the bushing <NUM> and displacement sending arm <NUM> undergo corresponding movement. For example, other structures such as clasps, fasteners, or other mechanisms may be utilized to engage the bushing <NUM> to the displacement sensing arm <NUM>. Furthermore, the bushing <NUM> may, in some embodiments, be integrally defined on the distal portion <NUM> of the displacement sensing arm <NUM>. In this regard, a standard burr tool <NUM> may be engaged with a chuck <NUM> of the instrument <NUM> and the bushing <NUM> may be disposed relative to the burr tool <NUM>. In any regard, the bushing <NUM> may be pivotal relative to the displacement sensing arm <NUM> (e.g., in a direction perpendicular to the axis of rotation <NUM>) to facilitate ease of engagement of the bushing <NUM> with the displacement sensing arm <NUM> or the bushing <NUM> with the burr tool <NUM> when engaging the burr tool <NUM> with the chuck <NUM> of the instrument <NUM>.

In any regard, the shank <NUM> of the burr tool assembly <NUM> may be engaged with the chuck <NUM> of the instrument <NUM>. In this regard, the burr tool <NUM> may be fixed relative to the instrument <NUM> in the direction along the axis of rotation <NUM>. In turn, the bushing <NUM> may be displaceable relative to the burr tool <NUM> along the axis of rotation <NUM>. In this regard, when the burr tool <NUM> is advanced relative to a medium during an operation, the bushing <NUM> may remain stationary at a reference point established prior to the operation and the displacement sensor <NUM> may be operable to detect the relative motion between the burr tool <NUM> and the bushing <NUM> retained in a stationary position relative to the reference point, thus providing a measure of the relative movement of the burr tool <NUM> relative to the reference point.

As may be appreciated, when using the instrument <NUM>, a force sensor for measurement of force acting on the leading edge 16a of the burr tool <NUM> may also be provided. In this regard, a force sensor 118a (e.g., a force sensor such as piezoelectric crystal) may be disposed proximally to the instrument drive assembly <NUM> (which may include the chuck <NUM>, gear drive <NUM>, and motor <NUM>). In turn, force acting on the leading edge 16a of the burr tool <NUM> as it is advanced axially may be transferred to the force sensor 118a via the drive system <NUM>. That is, the axial force acting on the leading edge 16a of the burr tool <NUM> may be transferred through the shank <NUM> of the burr tool <NUM> to the chuck <NUM>, and the drive system <NUM>. In turn, the drive <NUM> may act upon the force sensor 118a to produce an output corresponding to the force acting on the leading edge 16a. In this regard, it may be appreciated that the rigid assembly of the drive <NUM>, chuck <NUM>, and burr tool <NUM> may transmit the force acting on the leading edge 16a of the burr tool <NUM> to the force sensor 118a. It may further be appreciated that the drive assembly <NUM> may be fixed rotationally relative to the instrument housing <NUM> so as to impart rotation to the chuck <NUM>. However, the drive <NUM> may be preferably free to move in a direction along the axis of rotation <NUM> such that the at least a majority of the force acting on the leading edge 16a of the burr tool <NUM> may be transferred to the force sensor <NUM>.

In addition to the force sensor 118a that is capable of measuring an axial force acting on the burr tool <NUM>, a number of additional force sensors 118b may also be provided. These force sensors 118b may be arranged radially about the working axis <NUM>. In turn, a force acting on the burr tool <NUM> in a direction radial relative to the working axis <NUM> may be measured by the force sensors 118b. As such, if the burr tool <NUM> is advanced in a radial direction (e.g., to perform a grinding operation or the like), the radial force acting on the burr tool <NUM> may also be measured.

In an embodiment, the force sensors 118a and 118b may have a range of measureable force from about <NUM> N (<NUM> lbf) to about <NUM> N (<NUM> lbf). In an embodiment, the force sensors 118a and 118b may have a range of measurable force from about <NUM> N (<NUM> lbf) to about <NUM> N (<NUM> lbf). The force sensors 118a and 118b may have a precision of at least about <NUM>% of the maximum measureable force. Accordingly, in an embodiment, the force sensors 118a and 118b may have a precision of at least about <NUM> N (<NUM> lbf). In an embodiment, the force sensors 118a and 118b may have a precision of <NUM>% (e.g., about <NUM> N (<NUM> lbf)).

As such, a displacement sensor (e.g., <NUM> or <NUM>), an acceleration sensor <NUM>, and/or one or more force sensors (e.g., <NUM> or 118a or 118b) may be provided with a measurement system used with a burr tool <NUM>. As such, the various sensors may comprise a measurement system that may be used to monitor the burr tool <NUM> during operation. While the displacement and/or acceleration measured by the measurement system <NUM> may be used by the instrument <NUM> in conjunction with use of a burr tool <NUM> for creation of bore (e.g., to arrest the instrument upon passing through all or a portion of the bone), the measurement system <NUM> may also monitor the burr tool <NUM> during a grinding or boring operation. For instance, burr tools <NUM> may be used to shave a bone in the spine of a patient which may be conducted near blood vessels or nerves that may be damaged upon unintentional contact with the burr tool <NUM>.

In this regard, the burr tool <NUM> may be used in a manner such that a working portion of the burr tool <NUM> is contacted with a medium (e.g., a bone of a patient). The contacting engagement may comprise advancing the burr tool <NUM> axially along the working axis <NUM>, radially relative to the working axis <NUM>, and/or a combination thereof. In turn, use of the burr tool may include risk that the burr tool <NUM> may slip from the bone or other hard structure being ground using the burr tool <NUM>. Such loss of contact, which may be sudden) with the medium with which the burr tool <NUM> is in contact (which is also referred to herein as a slip) may increase the risk that surrounding tissue is inadvertently contacted by the working portion of the burr tool <NUM>. This contact may cause damage to surrounding tissue, and is therefor preferably minimized.

In turn, a detection module may be in operative communication with the measurement system. The detection module may monitor for any such loss of contact or slippage and may arrest the instrument <NUM> upon detecting any such slippage. The instrument <NUM> may cease operation of a drive of the instrument and/or apply a brake to cease rotation of the instrument.

One or more of a number of parameters may be monitored by the detection module. In turn, slippage or sudden loss of contact of the burr tool <NUM> with a medium with which the burr tool <NUM> is in contact may be detected based on one or more of the parameters monitored by the detection module. Specifically, when the burr tool <NUM> slips, the burr tool <NUM> may experience an unexpected and relatively large acceleration. As the burr tool <NUM> may be monitored for displacement relative to a reference point and/or the acceleration of the instrument may be monitored by an acceleration sensor <NUM>, the measurement system <NUM> may be operative to detect an acceleration of the burr tool <NUM>. For instance, an acceleration may be detected by a dedicated acceleration sensor or may be derived from a measured displacement of the burr tool <NUM> relative to a reference point. In the latter case, a signal representative of displacement may be output by a displacement sensor. A derivative may be determined reflecting a rate of change of the displacement (e.g., a velocity). A second derivative of the displacement sensor may also be calculated that is indicative of an acceleration of the burr tool <NUM>. In this regard, a displacement sensor along with a measurement system capable of processing the signal to arrive at an acceleration value may also be used as an acceleration sensor to determine an acceleration of a burr tool <NUM> for use in monitoring the burr tool <NUM> in a manner described herein.

Some minor accelerations may be associated with normal operations. As such, an acceleration threshold value may be established such that if the observed acceleration exceeds the acceleration threshold value, the instrument may be arrested. The acceleration threshold value may comprise a predetermined acceleration value. In other embodiments, the acceleration threshold value may be selectable by a user. Such an acceleration threshold value may comprise a magnitude of acceleration of the burr tool <NUM> and/or a value related to a maximum rate of change of the acceleration of the burr tool <NUM>. As such, a measured acceleration magnitude that exceeds the acceleration threshold value (e.g., due to slippage of the instrument <NUM>) may result in the instrument being arrested. This may prevent and/or limit damage to surrounding issue in the case of slippage. This monitoring may also occur during use of the burr tool <NUM> in an operation to create a bore. For instance, in the event of a bone failure or other fracture that result in slippage or other sudden acceleration, even in the case of creation of a bore, the instrument may be operative to arrest upon detection of such an acceleration to prevent and/or limit damage to surrounding tissue.

Furthermore, a slip of the instrument may also be accompanied by a decrease (e.g. a rapid decrease) in the force acting either axially or radially on the burr tool <NUM>. In turn, a rapid deceleration (e.g., indicated by a rate of decrease in force above a given magnitude in force reduction or a rate of change in force) may indicate the burr tool <NUM> has slipped from the bone. That is, a force threshold value may be established. The force threshold value may comprise a detection of a decrease in force greater than a predetermined magnitude or a predetermined rate in change of force. In response, the instrument <NUM> may be stopped (e.g., by deactivating the drive and/or applying a brake) upon the measured force exceeding the force threshold value. However, a decrease in force that occurs below the force threshold value may not interrupt operation. Such a condition may be present when a user is still contacting a desired medium, but with a lesser force than previously applied. The force threshold value may be controllable by a user to assist in preventing false detection of a loss of contact or slip.

As such, a detection module may be provided in connection with a controller of the instrument <NUM>. The detection module may monitor one or more signal provided from corresponding ones of one or more sensors (e.g., a displacement, acceleration, and/or force sensor). In response to one or more of the conditions described above, the detection module may be in operative communication with a drive control of the instrument to cease operation of the instrument and/or engage a brake to cease rotation of the instrument. The detection module may allow the predetermined thresholds for acceleration, rate of change in force, or other variables associated with monitoring of the instrument <NUM> to be adjusted.

The detection module may comprise any appropriate hardware, software, or combinations thereof. For instance, the module may be executed by a processor in operative communication with a memory that stores instructions for configuration of the processor to perform the monitoring and detection functions described above. In this regard, the processor may be in operative communication with a measurement system of an instrument. As such, the processor that executes the detection module may receive signals associated with displacement, acceleration, and/or force as described above. The processor may then apply rules in relation to a determination of whether the parameters monitored by the processor exceed a condition associated with a loss of contact of the burr tool <NUM>. For instance, the rules may relate to one or more of the acceleration threshold value and/or force threshold value described above. For instance, the processor of the detection module may apply a rule wherein if a monitored parameter exceeds the threshold value established for that parameter, a loss of contact is detected and the detection module may cease operation of the instrument and/or apply a brake. In some embodiments, a rule may be established that requires simultaneous occurrence of exceeding the threshold value for acceleration and force for detection of a loss of contact of the burr tool <NUM>. In other embodiments, structures other than a processor and memory may be provided to execute the detection module such as application specific integrated circuits (ASICs), field programmable gate arrays, or other appropriate hardware and/or software. Further still, the detection module may be integrated into an instrument controller or provided as an independent module for execution in connection with the instrument.

As a further safety feature of the instrument (e.g., that may be especially helpful for operations involving a burr tool <NUM>), upon initiation of rotation of the instrument <NUM>, the acceleration of the rotational speed of the instrument may be ramped such that top rotational speed of the instrument is reached relatively gradually. This value may be preset or adjustable by the user. In this regard, upon initiation of rotation, the instrument may begin to rotate relatively slowly with gradual (e.g., a set or variable increase over time) ramping up of the speed of the instrument. This may be a linear increase, an exponential increase, or stepped increase in speed without limitation.

Claim 1:
An instrument (<NUM>) for use in a surgical operation, comprising:
a drive system (<NUM>) for rotationally driving a working tool (<NUM>) engaged with the instrument (<NUM>) about a working axis (<NUM>);
a burr tool (<NUM>) engaged with the instrument (<NUM>) for rotation of the burr tool (<NUM>) by the drive system (<NUM>) about the working axis (<NUM>), wherein the burr tool (<NUM>) is contactably engageable with a medium;
a measurement system (<NUM>) including an accelerometer (<NUM>) and a displacement sensor (<NUM>), said measurement system (<NUM>) for monitoring the contactable engagement and disengagement of the burr tool (<NUM>) with the medium based on acceleration of the burr tool (<NUM>), and said displacement sensor (<NUM>) attached on an extension (<NUM>) outputting a displacement measure of the burr tool (<NUM>) from the medium; and
a detection module in operative communication with the measurement system (<NUM>) to detect a loss of the contactable engagement of the burr tool (<NUM>) with the medium.