Surgical saw with sensing technology for determining cut through of bone and depth of the saw blade during surgery

Sensing technology methods related thereto for determining cut through of bone and a depth of penetration of a working portion of a surgical instrument (e.g., an oscillating saw blade in a cut). A first sensor outputs a first signal representative of a displacement of the cutting edge of the saw blade in the cut. A second sensor outputs a second signal representative of a force applied to the cutting edge of the saw blade. As such, monitoring the first and/or second sensor may allow for the saw to be stopped upon completion of a cut (e.g., when the saw passes completely through a medium to be cut or upon reaching a predetermined depth for the cut).

BACKGROUND

Orthopedic sawing procedures may result in incorrect saw lengths or damage to a patient (i.e., if the sawing action continues after cut completion or if an incorrect cut depth is made), which can lead to surgical complications. Furthermore, in cases where the length of a cut made using a surgical saw is to be determined, determining the length for a cut can be a time consuming procedure which is undesirable when tissue is exposed and potentially subjected to infection.

As shown inFIG. 1, a cross section of a bone10having with a hard cortex12is shown. The bone10may be surrounded by a medium14that is less dense than the hard cortex12(e.g., soft tissue or air in the case of a bone exposed during a surgical procedure). In orthopedic procedures, it may be necessary to saw a bone10(e.g., saw a portion of a bone or completely through a bone). When cutting through all or a portion of a bone10, failure to arrest oscillation of the saw blade as soon as a cut is complete may result in unnecessary damage to the area around the cut. Furthermore, precise control over the depth of a cut may be needed in certain surgical operations.

Previously proposed techniques for sawing include the surgeon making a cut through the bone until the surgeon “feels” the saw blade pass completely through the bony structure or have the surgeon estimate a depth of the cut during the cutting operation. That is, the surgeon must rely on his or her senses and judgment alone to determine when the saw blade has passed completely through the bony structure or to a predetermined depth. Once the surgeon believes that he or she has passed completely through the structure or to the predetermined depth, the saw blade oscillation is arrested by the surgeon. Thereafter the surgeon may measure the length of the cut. A possible resulting complication of this procedure is that the surgeon may mistakenly “feel” the saw blade pass through a layer of differing density, thus falsely believing the cut to be complete. Additionally, the surgeon may not precisely “feel” the saw blade pass through the bone, thereby possibly damaging tissue on the opposite side of the bone.

Additionally, it may be necessary of a surgeon to measure the cut length once the cut is complete or stop cutting at a prescribed length that was predetermined by imaging software or a measurement jig. However, access to the anatomy that is cut may be limited, thus also limiting the ability to use such measurement jigs or other fixtures to control the depth of a cut. As such, traditional measurement techniques for verification of the cut length may be subject to error. As such, the process of sawing to a measured depth often includes inaccurate guess work. Conservative sawing may result in incomplete sawing (i.e., failure to saw completely through the bone or failure to saw to a predetermined depth), thus requiring multiple attempts. As such, sawing to a predefined depth is quite difficult. Additionally, it may be difficult to quickly arrest the saw blade motion upon cut completion. As such, the process may consume a substantial amount of surgical time resulting in a large cost per patient. By combining the sawing and depth measurement process into one accurate procedure, cost is reduced along with a decrease in patient morbidity.

SUMMARY

The present disclosure relates generally to systems, methods, and apparatuses for use in connection with determining when an instrument working portion (e.g., a cutting edge of a surgical saw) has completed a desired cut (i.e., has completed a cut of a certain length that may correspond to completely through a bone or partially through a bone). More specifically, the present disclosure presents embodiments related to a system and method for determining the length of a cut made through a bone of a patient without removing the saw blade from the cut formed in the bone. As such, in at least some embodiments herein, a saw is disclosed that automatically cease a cutting operation upon passing completely through a bone. Also, embodiments of a saw that automatically arrests a sawing action upon achieving a predetermined depth of cut are described. The present disclosure may thus include embodiments that allow for a saw blade to cut through a bone to a predetermined depth (e.g. measured from a portion of the bone or a cutting guide). Accordingly, the present disclosure may find application in the field of surgical sawing where the depth of the cut made in a bone is to be determined.

The present disclosure also includes embodiments of saw blade assemblies that may be specifically adapted for use for saw blade penetration measurement. Accordingly, the saw blade assemblies and saws disclosed herein may provide increased efficiency, reliability, and accuracy in relation to a saw blade penetration measurement system. For instance, in certain embodiments, a saw blade assembly may be used in conjunction with a saw as described herein to provide an improved platform to facilitate measurement of a cut created by the saw using a saw blade penetration measurement system without having to remove the saw blade from the cut during operation.

Systems for drill bit penetration measurement systems have been proposed such as described in U.S. Pat. No. 6,665,948, the entirety of which is incorporated herein by reference. In this regard, the description presented herein may provide adaptations, refinements, and/or additional features for use in connection with a saw blade penetration measurement system. As such, the present disclosure may facilitate improvements in the efficiency, accuracy, and or ergonomics of prior approaches to surgical saws.

Accordingly, a first aspect includes a saw blade assembly for use with a saw having a displacement sensor for outputting a signal representative of a displacement of the saw blade with respect to a reference point. The assembly includes a saw blade, a bushing, and an engagement member disposed on the bushing. The saw blade may include a cutting edge disposed at a distal end of the saw blade. Alternatively, the saw blade may include a cutting edge that extends along a length of the saw blade (e.g., along a majority or substantially all of the saw blade). The saw blade may include a shank that is adapted for engagement with a drive assembly that provides an oscillating motion of the saw blade during operation. The bushing may engage at least a portion of the saw blade or shank (e.g., through an aperture in the bushing or the saw blade). As such, the bushing may be constrainedly moveable relative to the blade or shank in a direction along a cutting direction of the saw blade. The engagement member is adapted for engagement with a displacement sensing arm of the displacement sensor. In this regard, the engagement member is engageable with the displacement sensing arm for corresponding movement between the bushing and the displacement sensing arm.

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, in an embodiment, an aperture may be provided at the bushing that may define an opening extending from a distal end of the bushing to a proximal end of the bushing. In this case, the distal end of the opening may comprise a reference surface. The reference surface may extend at least partially along a portion of the saw blade when disposed in the aperture. In other embodiments, the bushing may be conformably shaped relative to the body of the saw blade to facilitate the constrained movement relative to the oscillation of the blade. In such embodiments, the bushing may or may not extend about entirety of the shank. For example, the bushing may include a dished or concave surface that is alignable with the body or shank of the saw blade for constrained movement in a direction along the sawing axis. In any regard, the saw blade may be moved relative to the reference surface when making a cut in a medium so that the displacement between the saw blade and the bushing may be measured.

In any regard, the bushing may be disposable adjacent to the cutting edge of the saw blade (i.e., adjacent to the distal end of the saw blade). Accordingly, the reference surface may be alignable with the cutting edge of the saw blade to define a reference point from which displacement of the saw blade may be measured when making a cut using the saw blade. In this regard, the displacement sensing arm to which the bushing is engageable may be operatively engaged with a displacement sensor of a saw as will be described in greater detail below. In this regard, the saw blade may be advanceable relative to a medium to be cut to create a cut such that the cutting edge of the saw blade is displaced relative to the reference surface upon the advancement of the saw blade into the cut. Accordingly, when the engagement member operatively engages a displacement sensing arm of a displacement sensor, the displacement sensor may measure the displacement of the cutting edge from the reference surface.

In an embodiment, the reference surface may contact a peripheral portion extending about the cut (e.g., on at least a first side of the cut) upon advancement of the saw blade to create the cut. The bushing may be engageable against the peripheral portion extending about the cut so as to maintain the reference point stationary against the peripheral portion of the cut in a cutting direction. For instance, the bushing may be biased toward the distal end of the saw blade (e.g., under the influence of the displacement sensing arm or by another biasing member disposed relative to the saw blade and the bushing). In this regard, as the reference surface of the bushing may be maintained adjacent to the surface to be sawed, the accuracy of the displacement measure upon advancement of the saw blade may be improved given the proximity of contact of the bushing defining the reference surface relative to the location of the cut.

In various embodiments, the engagement member may include any appropriate mechanism for attachably connecting the bushing to a displacement sensing arm. In one particular embodiment, the engagement member may include a post extending from the bushing that is selectively engageable with the displacement sensing arm of the displacement sensor. In this regard, the post may facilitate relative pivotal movement between the post of the bushing and the displacement sensing arm (e.g., prior to engagement of the shank with the saw). Further still, the bushing may include a snap interface that engages the displacement sensing arm. As such, the snap interface may include fingers that snappingly engage the displacement sensing arm (e.g., at a configured distal portion thereof that is shaped to correspond to the fingers of the bushing). That is, the bushing may be snapped to a portion of the displacement sensing arm. In any regard, movement that engages the bushing with the displacement sensing arm may allow for improved ergonomics when engaging the saw blade assembly with a saw by allowing the shank to be aligned with the saw after engagement of the bushing with the displacement sensing arm.

In another embodiment, the saw may not include a bushing, but the blade or saw is received, guided or supported by a cutting guide or jig. The cutting guide or jig guides the saw blade or the saw along a sawing axis. A displacement sensor using the cutting guide or jig as a reference surface for measuring cutting depth may be provided where the displacement sensor may be in contact with a stationary portion of the cutting guide as the saw blade is advanced through the bone to determine the depth of a cut made.

In an embodiment, the saw blade assembly may be provided as a one-time use, disposable component for use in a surgery or other operation. In this regard, the saw blade assembly may include features that help reduce the likelihood that the saw blade is reused in contradiction of instructions regarding one time use. Such features may at least reduce the functionality of the saw blade assembly (e.g., potentially to the point where the saw blade assembly is incapable of reuse with the measurement system). For example, in an embodiment, the shank may include a destructible portion that is at least partially destructible during a cleaning process. Additionally or alternatively, the bushing (e.g., the engagement portion of the bushing) may comprise a destructible portion that, when destroyed, limits or prevents reuse with the measurement system. In this regard, the bushing or a portion thereof (e.g., an engagement portion) may be destroyed during a cleaning process to avoid reuse of the blade after cleaning. In one particular embodiment, the destructible portion may be meltable. As such, a melting temperature of the destructible portion may be greater than an operating temperature of the saw blade and less than an autoclave temperature. As such, the destructible portion may remain intact during operation of the saw blade assembly. However, upon undergoing a cleaning or sterilization process (e.g., autoclaving), the destructible portion may be at least partially degraded. In one embodiment, the melting temperature of the destructible portion is not less than about 60° C. and not greater than about 110° C. The destructible portion may also be destroyed upon exposure to a cleaning or sanitizing chemical or the like used in the cleaning process (e.g., as an alternative to or in addition to being meltable).

In view of the foregoing, the destruction of the destructible portion may alter the shape of the shank of the saw blade or the bushing such that engagement with a saw or a measurement system thereof may be at least partially prevented or degraded. For instance, the destructible portion may be used to at least partially establish registration between the shank and a chuck of the saw. Accordingly, upon destruction of the destructible portion, registration between the saw blade assembly and the chuck of the saw may be reduced (e.g., potentially to the point of inoperability of the saw blade). For example, the destructible portion may include a proximal end portion of the shank. In this regard, the destructible portion may include at least a portion of an engagement feature for engagement of the shank by the chuck. In an embodiment, the destructible portion may include at least a portion of at least one sidewall of the shank. Additionally or alternatively, the engagement feature may include a detent engageable by an engagement member in the chuck. As such, the destructible portion, after having been exposed to a cleaning process, may not be registerable with respect to assembly chuck of the saw. That is, the surface area of the engagement feature of the shank that is in contact with the chuck when the saw blade is engaged with the chuck may be at least reduced upon exposure of the destructible portion to a cleaning process. Further still, as the destructible portion may comprise at least a portion of the bushing, the bushing may be degraded in a cleaning process such that destruction of the destructible portion results in the bushing not being engageable with the displacement sensing arm.

A second aspect includes a method for use of a saw blade assembly with a saw having a displacement sensor for outputting a signal representative of a displacement of a cutting edge of the saw blade assembly with respect to a reference point. The method may include engaging a displacement sensing arm of the displacement sensor with an engagement member of a bushing. The bushing may be constrainedly moveable relative to a saw blade along a cutting direction of the saw blade during sawing. The engaging may result in corresponding movement of the bushing and the displacement sensing arm. The method may include aligning a shank of the saw blade with a chuck of the saw and securing the shank with the chuck of the saw to restrict movement between the saw blade and the motor assembly.

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 example, in an embodiment, the saw blade assembly may be provided in accord with any of the features and/or feature refinements described above in connection with the first aspect.

For example, in an embodiment, the method may include positioning a distal portion of the bushing adjacent to a cutting edge of the saw blade (e.g., at a distal portion thereof). In this regard, the method may also include contacting the cutting edge of the saw blade to a surface of a medium to be sawed. Accordingly, the distal portion of the bushing may contact the surface of the medium to be sawed. As such, the method may also include establishing the reference point when the cutting edge of the saw blade and the distal portion of the bushing are in contact with the surface of the medium to be sawed. The method may also include advancing the saw blade into the medium to be sawed, such that the cutting edge advances in relation to the distal portion of the bushing in contact with the surface of the medium to be sawed. Thus, the method may include producing relative movement of the displacement sensing arm relative to the displacement sensor upon advancing the saw blade into the medium. As the displacement sensing arm may be operatively engaged with the displacement sensor, the method may further include outputting a signal from the displacement sensor indicative of the amount of displacement of the cutting edge of the saw blade relative to the distal portion of the bushing. In other embodiments, the saw may include a displacement sensing arm in direct contact with a medium to be cut or a cutting guide disposed stationary relative to a medium to be cut. In this regard, relative motion between the saw blade and the medium to be cut may be measured by the displacement sensing arm.

A third aspect includes a saw blade assembly for use in a medical saw for single use applications. The saw blade assembly includes a saw blade with a cutting edge and a shank. The assembly also includes a bushing. The saw blade assembly includes a destructible portion. The cutting edge is disposed at a distal end of the saw blade. The shank is disposed adjacent to a proximal end of the saw blade, and a blade body member extends along a length of the saw blade between the distal end and the proximal end. The shank and/or bushing may include the destructible portion that is at least partially destructible during a cleaning process. The bushing may be at least partially captured by the shank such that the bushing is non-removably engaged with the shank when the destructible portion is intact. Upon destruction of the destructible portion, the bushing may no longer be engaged with the shank and/or an engagement portion may be destroyed, thus preventing engagement with the displacement sensing arm upon destruction of the destructible portion.

A number of feature refinements and additional features are applicable to the third 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 third aspect or any of the other aspects disclosed herein.

For example, in an embodiment, the destructible portion may be meltable. In this regard, a melting temperature of the destructible portion may be greater than an operating temperature of the saw blade and less than an autoclave temperature. For instance, the melting temperature of the destructible portion may be not less than about 60° C. and not greater than about 110° C. Additionally, as referenced above in connection with the first aspect, the destructible portion may be destroyed upon exposure to a cleaning or sanitizing chemical or the like used during a cleaning and/or sanitizing process.

As described above with respect to the first aspect, the destructible portion may comprise a proximal end portion of the shank. Thus, upon destruction of the destructible portion, at least a portion of the shank may undergo a change in shape. Accordingly, the destructible portion may include at least a portion of an engagement feature for engagement of the shank by a chuck of a saw. For instance, the destructible portion may include at least a portion of at least one sidewall of the shank. Additionally or alternatively, the engagement feature may include a detent engageable by the chuck (e.g., the detent features may correspond with a quick-change style chuck device where the detents are used to selectively retain the shank in the chuck device). Further still, the destructible portion, after destruction thereof, may prevent engagement of the bushing with the displacement sensing arm and/or may destroy engagement between the saw blade and the bushing.

Accordingly, in an embodiment, the destructible portion, after having been exposed to a cleaning process, may not be registerable with respect to the chuck device. In this regard, the surface area of the sidewall of the shank may be at least reduced upon exposure of the destructible portion to a cleaning process (e.g., an autoclave process or a chemical sanitation process).

A fourth aspect includes a method for a saw blade assembly for use in a medical saw for single use applications. The method includes exposing the saw blade assembly to a cleaning process and degrading at least a portion of a destructible portion. For example, the destructible portion may comprise a portion of the shank and/or a portion of a bushing provided with the saw blade assembly. In either case, the destructible portion may be degraded in response to the exposing such that the saw blade assembly is not functional after the degrading. Additionally, a number of feature refinements and additional features are applicable to the fourth 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 any of the aspects discussed herein.

For instance, in an embodiment the exposing may include autoclaving the saw blade. As such, the degrading may include melting at least a portion of the destructible portion in response to the autoclaving. The melting may occur at a temperature of not less than about 60° C. and not greater than about 110° C. In this regard, the destructible portion may withstand temperatures associated with normal operation of the saw blade, but may be degraded (i.e., melted) upon exposure to the autoclaving process. In another embodiment, the exposing may include applying a cleaning chemical to the saw blade such that the degrading includes removal of at least a portion of the destructible portion in response to applying the cleaning chemical.

As described above, in an embodiment the degrading may result in changing a shape of a shank of the saw blade. Thus, the degrading may include removing at least a portion of the destructible portion at a shank of the saw blade. The portion of the destructible portion removed may at least be a portion of an engagement feature for engagement of the shank by a chuck device of a saw. For instance, the destructible portion may include at least a portion of at least one sidewall of the shank or may include a detent engageable by the chuck device. In any regard, the degrading may result in reducing the registration of the shank with respect to a chuck device of a saw. Additionally or alternatively, a portion (e.g., an engagement portion) of a bushing of the saw blade assembly may comprise the destructible portion that is degraded to prevent the bushing from engaging with a displacement sensing arm.

A fifth aspect includes a saw including a saw blade penetration measuring system for determining, with respect to a reference point, a depth of penetration of a cutting edge of a saw blade in a cut. The saw includes a chuck for engagement with a shank of a saw blade. The chuck is operable to constrain a saw blade engaged by the chuck during sawing. The saw also includes a displacement sensing arm extending from the saw that may be engageable with a bushing member that is constrainedly moveable with respect to a saw blade engaged by the chuck. The saw also includes a displacement sensor disposed in a fixed relative position with respect to a saw blade engaged by the chuck. The displacement sensor is adapted for relative movement with respect to the displacement sensing arm. Accordingly, the displacement sensor is operative to output a first signal representative of the displacement of the sensing arm relative to the displacement sensor. The movement of the displacement sensing arm relative to the saw corresponds to displacement of the bushing relative to a saw blade engaged by the chuck. In this regard, movement of the displacement sensing arm relative to the saw and the corresponding movement of the saw blade relative to the bushing may be measured as an output of the displacement senor of the saw.

A number of feature refinements and additional features are applicable to the fifth 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 fifth aspect. Furthermore, any of the features discussed in relation to any other aspect discussed herein may be used with the fifth aspect.

For example, in an embodiment, the displacement sensor may be disposed internally to a saw housing and the displacement sensing arm may extend from the saw housing. Accordingly, the displacement sensing arm may extend from the saw housing. As such, at least a portion of the displacement sensing arm (e.g., a proximal portion thereof) may extend towards a saw blade engaged by the chuck. In an embodiment, the displacement sensing arm may include a hole engageable with a post of the bushing to effectuate corresponding movement of the displacement sensing arm and the bushing. In another embodiment, the bushing may have a snap interface such that a portion of the bushing snaps about a portion of the displacement sensing arm to engage therewith.

In an embodiment, the displacement sensor may include a linear variable differential displacement transducer (LVDT). Accordingly, a coil of the LVDT may be disposed in the housing and the displacement sensing arm may include a moveable core displaceable with respect to the coil of the LVDT. The displacement sensor may have a total measureable travel of at least about 2.5 inches (6.4 cm). However, any other appropriate type of displacement sensor (e.g., a relative or absolute position sensor) may be used such as, for example, an optical sensor or the like. Furthermore, other appropriate types of sensors or sensor systems may be employed including digital encoders, laser sensors, 3D triangulation based on imaging and fiducial markings, etc.

In an embodiment, the displacement sensing arm may be biased to a distal position relative to a saw blade engaged by the chuck. Additionally or alternatively, the displacement sensing arm may be selectively removable from the saw housing. Further still, the displacement sensing arm may be selectively retainable in a proximal position. The displacement sensing arm may be selectively removable from a passage extending through the saw housing, such that the passageway is selectively opened from a proximal end thereof to a distal end thereof (e.g., by removal of the displacement sensing arm and/or removal of an end cap or the like).

In an embodiment, the chuck of the saw may include a removable assembly engaged to a drive motor by way of a coupling receiver. The removable assembly may be attached to the saw by way of a release mechanism. As such, the chuck may be selectively removable from the saw.

In an embodiment, the saw may include a light emitter operable to emit light in a direction toward the saw blade retained by the chuck.

A sixth aspect includes a method for use of a saw including a saw blade penetration measuring system for determining, with respect to a reference point, a depth of penetration of cutting edge of a saw blade in a cut. The method includes engaging a shank of a saw blade with a chuck of the saw. The method also includes constraining the saw blade engaged by the chuck to limit relative axial movement between the saw and saw blade during sawing. The method further includes connecting a displacement sensing arm extending from the saw to a bushing member that is constrainedly moveable with respect to the saw blade engaged with the chuck.

A number of feature refinements and additional features are applicable to the sixth 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 sixth aspect. Furthermore, any of the features discussed in relation to any other aspect discussed herein may be used with the sixth aspect.

For example, the method may also include aligning a distal edge of the bushing with a cutting edge of the saw blade and moving the displacement sensing arm relative to a displacement sensor of the saw. However, in other embodiments, the displacement sensing arm may contact a cutting guide to establish a reference point. In any regard, the method may include establishing the reference point relative to the cutting edge of the saw blade. Furthermore, the method may include oscillating the saw blade to create a cut to advance the saw blade in the cut and detecting a relative movement of the saw blade relative to the reference point by way of corresponding movement of the displacement sensing arm relative to the displacement sensor. As such, a displacement may be measured. The saw may be stopped automatically in response to completion of a cut (i.e., sawing through a bone or the like) which may be determined upon monitoring a displacement sensor and/or a force sensor. Furthermore, a predetermined displacement may be set such that the saw may be stopped upon displacement of the saw blade to the predetermined displacement length. The method may include biasing the displacement sensing arm to a distal position, wherein the biasing maintains the distal edge of the bushing in contact with a medium into which the saw blade is advanced to create the cut.

A seventh aspect includes a saw including a saw blade penetration measurement system for determining, with respect to a reference point, a depth of a penetration of a cutting edge of a saw blade in a cut along a cutting axis when the cutting edge of the saw blade passes from a first medium to a second medium, the first medium contiguous with the second medium, the first medium having a first density, the second medium having a second density. The saw includes a first sensor outputting a first signal representative of a displacement, with respect to the reference point, of the cutting edge of the saw blade in the cut and a second sensor outputting a second signal representative of a force applied to the cutting edge of the saw blade. The saw also includes a chuck engageable with the saw blade. Accordingly, movement is constrained between the chuck and the saw blade. The saw also includes a motor that is operatively engaged with the chuck to oscillate the saw blade. The saw also includes a processor in electrical communication with the first and second sensors. The processor is configured in a first mode to output a third signal representative of the depth of penetration of the cutting edge of the saw blade when the cutting edge of the saw blade passes from the first medium to the second medium. The third signal may be based on the first and second signals.

A number of feature refinements and additional features are applicable to the seventh 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 seventh aspect. For example, any of the forgoing features described with respect to any other aspect disclosed herein may be utilized with the seventh aspect.

For example, in an embodiment the first sensor may include a linear variable differential displacement transducer (LVDT), a digital encoder, an optical displacement sensor, or any other appropriate displacement sensor. In an embodiment, the second sensor includes a load cell. The third signal may be output when a second time derivative of the first signal is greater than zero and a first time derivative of the second signal is less than zero.

In an embodiment, the first sensor may be a linear variable differential displacement transducer (LVDT), the second sensor may be a load cell, and the third signal may be output when the second time derivative of the first signal is greater than zero and a first time derivative of the second signal is less than zero. That is, upon passing fully through the bone, the saw may undergo a decrease in force applied to the cutting edge and accelerate when the cut is complete. That is, monitoring the first and second sensor for this occurrence may allow the saw to be stopped upon completion of a cut. In an embodiment, the bone surrounded by a second medium with a density less than the bone such that upon completion of the cut the saw experiences the decrease in force against the cutting edge and acceleration of the blade.

In an embodiment, the system may include a mode selector and the processor may be configured to operate in a mode selected from the group of modes consisting of the first mode wherein the third signal corresponds to completely cutting through a structure and a second mode, wherein the processor is configured such that the third signal corresponds to when the saw blade has reached a predetermined depth for the cut. The first sensor may be a linear variable differential displacement transducer, the second sensor may be a load sensor, and the processor, in the first mode, outputs the third signal when a second time derivative of the first signal is greater than zero and a first time derivative of the second signal is less than zero, thus indicating the saw has passed through the bone. Also, the processor, in the second mode may output the third signal in response to the measured displacement equaling a predetermined depth.

In an embodiment, the third signal may include an alert perceivable by a user of the saw. The alert may be an auditory alert. Additionally or alternatively, the alert may include a change in speed of the motor of the saw. For example, the alert may include stopping the oscillation of the motor of the saw.

A eighth aspect includes a surgical instrument that includes an instrument working portion adapted to engage a portion of a patient to perform a surgical operation. The surgical instrument also includes a light emitter adapted to emit light in a direction toward the patient when the instrument working portion is engaged with the portion of the patient to perform the surgical operation.

A number of feature refinements and additional features are applicable to the eighth 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 eighth aspect. For example, any of the forgoing features described with respect to any or all of the foregoing aspects may be utilized with the eighth aspect.

For example, in an embodiment, the surgical instrument may correspond to any of the foregoing saw embodiments for determining a depth of penetration of a saw blade in a cut. However, in other embodiments, the surgical instrument may comprise other types of surgical saws, a surgical grinder, a surgical chisel, or some other surgical instrument without limitation.

In an embodiment, the light emitter may include a light emitting diode (LED) light source. For instance, in an embodiment, the light source may be disposed within a housing of the surgical instrument. Alternatively, the light source may be disposed remotely from the surgical instrument and transmitted to the light emitter (e.g., by way of fiber optics or the like).

In an embodiment, the surgical instrument may include a measurement system for determining, with respect to a reference point, a depth of the instrument working portion when the instrument working portion passes from a first medium to a second medium. As such, any of the foregoing discussion with respect to embodiments of measurement systems may be provided in various embodiments without limitation. For instance, the surgical instrument may include a first sensor outputting a first signal representative of a displacement, with respect to the reference point, of the instrument working portion, a second sensor outputting a second signal representative of a force applied to the instrument working portion, and a processor in electrical communication with the first and second sensors. The processor may be configured in a first mode to output a third signal representative of the depth of penetration of the instrument working portion of the surgical instrument when the instrument working portion passes from the first medium to the second medium, the third signal based on the first and second signals.

In an embodiment, the light emitter may be selectively operable between two emitting states (i.e., always on and trigger depression) and a non-emitting state. For instance, the emitting state may occur upon operation of the instrument working portion, and the non-emitting state may occur upon cessation of operation of the instrument working portion. Additionally or alternatively, the light emitter may be selectively changed between the emitting state and non-emitting state by way of a state switch or the like.

A ninth aspect includes a saw including a saw blade penetration measurement system for determining, with respect to two reference points, completion of a cutting operation when the cutting edge of the saw blade passes from a first medium to a second medium, the first medium contiguous with the second medium, the first medium having a first density, the second medium having a second density. The saw may include first and second sensors for outputting, independently, the displacement of the saw blade relative to reference points established by each of the first and second sensors. A third sensor outputting a third signal representative of a force applied to the cutting edge of the saw blade may also be provided. The saw also includes a chuck engageable with the saw blade. Accordingly, movement is constrained between the chuck and the saw blade. The saw also includes a motor that is operatively engaged with the chuck to oscillate the saw blade. The saw also includes a processor in electrical communication with the first, second and third sensors. The processor is configured in a first mode to output a fourth signal representative of when the cutting edge of the saw blade passes from the first medium to the second medium based on at least one of the first, second or third signals (i.e., when the saw passes completely through a medium to be cut).

A number of feature refinements and additional features are applicable to the ninth 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 ninth aspect. For example, any of the forgoing features described with respect to any other aspect disclosed herein may be utilized with the ninth aspect.

Additionally, in an embodiment the first and sensors include a linear variable differential displacement transducer (LVDT). In an embodiment, the third sensor includes a load cell. The fourth signal may be output when a second time derivative of the first or second signal is greater than zero and a first time derivative of the third signal is less than zero.

In an embodiment, the first and sensors may be a linear variable differential displacement transducer (LVDT), the third sensor may be a load cell, and the fourth signal may be output based on the first, second, and/or third sensor outputs (e.g., when the second time derivative of one of the first and second signals is greater than zero and a first time derivative of the third signal is less than zero). In some embodiments, absolute values of force and displacement may also be used. In an embodiment, the first medium may be a bone surrounded by the second medium (e.g., air or surrounding soft tissue).

The system may include a mode selector and the processor may be configured to operate in a mode selected from the group of modes consisting of the first mode wherein the fourth signal corresponds to a condition when the saw has passed completely through the bone. In a second mode, the processor is configured such that the fourth signal corresponds to a when the saw blade has reached a predetermined depth of the cut. In this regard, the first and second sensors may be linear variable differential displacement transducers, the third sensor may be a load sensor, and the processor, in the first mode, outputs the fourth signal when a second time derivative of one of the first and second signals is greater than zero and a first time derivative of the third signal is less than zero. Also, the processor, in the second mode, may output the fourth signal in response to one or both of the first and second sensors outputting a signal corresponding to the predetermined depth.

In an embodiment, an output device presents an alert perceivable by a user of the saw based on the fourth signal. The alert may be an auditory alert. Additionally or alternatively, the speed of the motor of the saw is changed based on the fourth signal. For example, the oscillation of the motor of the saw is stopped based on the fourth signal.

A tenth aspect includes a sawing assembly having a displacement sensor for performing an automatic disabling of cutting when a predetermined cutting depth has been determined. The assembly includes a cutting guide or cutting jig, a saw having a blade and a displacement sensor for outputting a signal representative of a displacement of the saw blade with respect to a reference point. The saw blade has a cutting edge disposed at a distal end of the saw blade. The saw blade includes a shank that is adapted for engagement with a drive assembly that provides an oscillating motion of the saw blade. The cutting guide or cutting jig includes one or more apertures sized to receive at least a portion of the saw blade or shank through the aperture. As such, the cutting guide or cutting jig guides the saw blade in a direction along a cutting direction of the saw blade.

A number of feature refinements and additional features are applicable to the tenth aspect. These feature refinements and additional features may be used individually or in any combination. As such, each of the foregoing features described above may be, but are not required to be, used with any other feature or combination of features of the tenth aspect.

DETAILED DESCRIPTION

Certain terminology is used in the following description for convenience only and is not limiting. The words “right,” “left”, “lower” and “upper” designate directions in the drawings to which reference is made. The words “inwardly” and “outwardly” refer to directions toward and away from, respectively, the geometric center of the saw blade penetration measurement system and designated parts thereof. The terminology includes the words above specifically mentioned, derivatives thereof and words of similar import.

Additionally, as used in the claims and in the corresponding portion of the specification, the word “a” means “at least one”. Further, unless otherwise defined the word “about” when used in conjunction with a numerical value means a range of values corresponding to the numerical value plus or minus ten percent of the numerical value. Still further, the word “or” has the meaning of a Boolean inclusive “Or”. For example, the phrase “A or B” means “A” alone or “B” alone or both “A” and “B”.

Referring to the drawings in detail, where like numerals indicate like elements throughout there is shown a first embodiment of the saw blade penetration measurement system generally designated100, and hereinafter referred to as the “measurement system”100, in accordance with the present invention. The measurement system100is for determining, with respect to a reference point (not shown), a depth of penetration of the cutting edge16aof a saw blade16in a cut. The saw blade16may be oscillated by a drive24in a saw housing26of any typical well known surgical saw. In this regard and as may be appreciated below, a measurement system100may be provided with an existing surgical saw (e.g., as a retrofit). In further embodiments described in greater detail below, a measurement system400may be provided that is at least partially integrated into a saw50(e.g., as shown inFIGS. 8A-8C) and/or saw700shown inFIGS. 18-21C.

Referring toFIGS. 2, 5A, 5B and 5C, the measurement system100may include a saw blade displacement measurement assembly102, a saw blade load measurement assembly104, and a controller assembly106. The displacement measurement assembly102is connected to the saw housing26. The connection can be made by a variety of well known mounting methods such as a mount that clamps to the displacement measurement assembly102and is attached to the saw housing26by one or more threaded fasteners. Alternative methods such as welding or adhesive bonding could also be used. The displacement measurement assembly102may include a first sensor108that outputs a first signal108srepresentative of a displacement, with respect to the reference point, of the cutting edge16aof the saw blade16in the cut being sawed. The displacement measurement assembly102preferably has an extension110that is displaceable along a direction of sawing. The extension110has a distal end110athat can be placed in registry with the reference point when the cutting edge16aof the saw blade16is positioned at the outer surface of the medium to be cut and maintained in registry with the reference point throughout the sawing process. The reference point may be any anatomical structure proximal to the desired location of the cut to be sawed. Additionally or alternatively, the reference point may be established using a bushing disposed relative to the saw blade or with respect to a cutting guide as will be described in greater detail below. The extension110has a proximal end110bthat is attached to the first sensor102. In one embodiment, the sensor102may be a linear variable differential displacement transducer (“LVDT”), although other appropriate displacement sensors may also be used as described in greater detail below.

A second sensor118may be located within the housing26outputs a second signal representative of a force applied to the cutting edge16aof the saw blade16. In one embodiment, the second sensor118may be a hydraulic pressure transducer and a portion within the housing26and/or the drive24may form a hydraulic chamber connecting the second sensor118. In another embodiment, the second sensor118may include a load cell, such as a piezo-electric device, located within the housing26and/or the drive24. An electrical conductor electrically connects the piezo-electric device to the controller assembly106. In this regard, it may be appreciated that depending upon the drill configuration, the second sensor118may be arranged in various manners relative to the saw blade16. For instance, in a sagittal saw or an ultrasonic saw, an axial force (i.e., extending between the cutting edge and the attachment of the saw blade to the saw) may be applied relative to the distal cutting edge of the saw blade such that the second sensor118may measure the axial force to determine the force acting on the cutting edge. In a reciprocating saw, the load may be transverse (i.e., orthogonal to the attachment of the saw blade to the saw). Thus, the second sensor118may be configured to measure the load acting on the cutting edge, which may be orthogonal to an axis defined along the attachment of the saw blade to the saw.

The controller assembly106is in electrical communication with the first sensor108and/or the second sensor118. In an embodiment, the controller assembly106has a controller housing146integral with the saw housing26. However, with further reference toFIG. 13A, the controller housing146may also be provided as a remote unit. The controller assembly106includes a processor148in electrical communication with the first and second sensors108,118and with a mode selector150having a mode selector switch154and a display152having a reset button153. The display152, the reset button154and the mode selector switch154may be mounted in a panel156of the controller housing146. Alternatively, the display152or the reset button153or the mode selector154or any combination thereof could be separately housed in the remote control unit that communicates with the first and second sensors108,118by a wired or wireless link. Furthermore, the reset button153may be provided as a separate hardware portion such as a foot pedal or the like. In this regard, the hardware portion comprising the reset button153be in wired or wireless communication with the controller assembly106. In this regard, the foot pedal may be used to set or reset the reference point of the controller and/or to indicate a new sawing operation. The display152is for indicating the measured displacement of the cutting edge16aof the saw blade16to the user. The display152is controlled by the processor148. The display152may continuously indicate the changing displacement of the cutting edge16aof the saw blade16during the sawing of a cut and may also indicate the depth of the cut at the when the saw blade16passes from one medium to another (i.e., when the saw has passed completely through a bone).

For instance, with continued reference toFIGS. 13A and 13B, the display152may be a touch sensitive display (e.g., a resistive or capacitive type touch screen display). The display152may include an indication of a cut length160, the saw speed162, etc. The display152may also include patient information168. The controller unit106may include a port170for engagement of a wired plug connection172with the saw50. In this regard, the saw50may be connected to the controller assembly106to supply power to the saw50and communicate data between the saw50and the controller assembly106

Referring toFIGS. 1, 3, 4, 5, the processor148may be configured to operate in a first mode for cut length measurement for a cut that extends through the entirety of the medium to be cut. Thus, with reference toFIG. 5, the processor148may be configured to output a third signal148srepresentative of the depth of penetration of the cutting edge16aof the saw blade16when the cutting edge16aof the saw blade16passes from a first medium having a first density (i.e., bone12) to the second medium having a second density (i.e., a surrounding medium14such as air or soft tissue). The third signal148smay be based on the first and second signals108s,118s. Preferably, the third signal148sis output at a second time derivative of the first signal108sbeing greater than zero and a first time derivative of the second signal118sbeing less than zero. In other words a positive acceleration of the saw blade16and a concurrent reduction in the force applies to the cutting edge16aof the saw blade16trigger the third signal148s. However, the third signal148smay also be based on other mathematical transforms of the first or second signals108s,118sor raw values of the first signal108sor118s. For instance, the third signal148smay be based on the first and/or second derivative of the first signal108s(e.g., the displacement signal). For instance, the third signal148smay be generated upon a concurrent positive state of the first signal108s, a first derivative of the first signal108swith respect to time (e.g., a velocity signal), and a second derivative of the first signal108swith respect to time (e.g., an acceleration signal). In this regard, any one or more of the displacement signal, the velocity signal, and acceleration signal may be actually measured to derive the displacement signal, a velocity signal, and acceleration signal. Thus, the third signal148smay be dirt derived using a single sensor, such that the force sensor described above in an embodiment of the saw may not be employed in all embodiments.

The processor148is also configured to operate in a second mode for saw blade penetration measurement (e.g., using the mode selector150and mode selector switch154). The second mode of operation is directed to the case where a predetermined depth is established. As such, the processor148may monitor the first signal108sto determine when the predetermined depth is reached. Once reached, the third signal148smay be output. In this regard, the value of the first signal108salone may be used in the second mode of operation to cease the sawing when the predetermined depth is reached. As may be appreciated, rather than the second time derivative of the first signal108sthat indicates an acceleration of the blade, the value of the signal108salone may be utilized. That is, a “saw-to-depth” mode may be established where the saw operate until a predetermined depth to reach is determined by the first signal108s, and thereupon the operation of the saw is terminated once the predetermined depth is reached.

Additionally or alternatively, the third signal148smay be at least partially based on additional parameters other than the first signal108sand second signal118s. For instance, in at least some embodiments, the third signal148smay be at least partially based on a parameter associated with the oscillation of the saw blade16. For instance, the speed of the drive24oscillating the saw blade16, the resistance against the saw blade (e.g., is measured by the load on a motor driving oscillation of the saw blade), or another appropriate parameter regarding the oscillation of the blade16may be utilized in outputting the third signal148s. Further still, parameters such as the length of the cutting edge of the saw blade16, the bone to be sawed, or other appropriate parameters may be utilized in determining the third signal148s.

Furthermore, the generation of the third signal148smay at least partially be customized based on the patient. In this regard, information regarding the patient may be provided to the controller assembly106and utilized by the processor148in determining the third signal148s. For instance, a patient's age, sex, and/or other demographic information may be provided. As may be appreciated, the demographic data of the patient may provide a correlation to expected bone density or other parameter regarding an expected property of the patient's anatomy based on the demographic data of the patient. In this regard, the demographic data may be used to correlate an expected parameter associated with the patient's anatomy (e.g., bone density) that may be used as a factor in generation of the third signal148s. In addition, direct measurement of an anatomical parameter (e.g., bone density) for a given patient may be provided directly to the controller assembly106, thereby potentially eliminating the need to estimate the parameter based on demographic data.

Referring toFIG. 6, there is shown a block diagram of a first method for determining, with respect to a reference point, the depth of penetration of the cutting edge16aof a oscillating saw blade16in a cut when the cutting edge16aof the saw blade16transitions from a first medium having a first density, such as the hard outer cortex12of a cortical bone10, to a second adjacent medium14having a second density, such air or tissue surrounding the outer surface of the cortical bone10. (FIG. 1B).

An initial position of the cutting edge16aof the saw blade16relative to the reference point is established (Step205). The initial position may be established by placing the cutting edge16aof the saw blade16against the outer surface of the cortical bone to be sawed and by extending the distal end10aof the extension110of the displacement measurement assembly102to the reference point, such as an anatomical structure proximal to the desired location of the cut to be created. As will be appreciated in the discussion of the embodiments below, the reference point may also be established by a bushing member of a saw blade assembly that is engaged with a displacement sensing arm of a displacement sensor. For instance, the bushing member may have a reference surface contactable with the bone to be sawed. Further still, the reference point may be established relative to a cutting guide or the like.

In any regard, with the cutting edge16aof the saw blade16and the measurement system reference point in the above positions (i.e., aligned at a surface of the medium to be sawed), the measured displacement of the saw blade16is set to zero by pressing the reset button153. Upon commencement of sawing, a first signal representing the depth of penetration of the cutting edge16aof the saw blade16in the cut is output (Step210). A second signal representing a force applied to the cutting edge of the saw blade is output (Step215). A third signal based on the first and second signals and representative of when the cutting edge of the saw blade passes from the first medium to the second medium is output (Step225). Preferably, the third signal is output when the second time derivative of the first signal is greater than zero and a first time derivative of the second signal is less than zero. Additionally or alternatively and as described above, the third signal may be based only on the first signals and/or mathematical transforms thereof.

The third signal may cause an output device to generate an alert that may be perceivable by a user of the saw. As such, upon determination that the saw has passed through the bone (e.g., as described above), the alert may provide feedback to the user that the bone has been sawed through. As such, the alert may be an auditory alert such as a tone or the like. In another embodiment, the third signal may cause a change in the speed of the motor of the saw. For instance, the saw may be slowed such that the user may be alerted to the fact that the saw has passed through the bone. Further still, the saw may be automatically stopped at the occurrence of the third signal. It may be appreciated that any other user perceivable alert may be provided including, for example, a visual, tactic, or other type of user perceivable feedback.

Referring toFIG. 7, there is shown a block diagram of a second method for determining, with respect to a reference point, the length of a cut. The predetermined depth to be reached by the saw blade is provided (Step305). An initial position of the cutting edge16aof the saw blade16relative to the reference point is established (Step310), preferably in a manner similar to Step205discussed above. The displacement of the cutting edge16aof the saw blade16is continuously determined (Step315). The processor148may determine if the displacement of the cutting edge16aof the saw blade is equal to the predetermined depth provided in Step305. If the depth does not equal the predetermined depth (i.e., is less than the predetermined depth), the cutting procedure may continue. Once the displacement equals the predetermined depth, the saw may be stopped (Step325).

The components used to construct the present invention may include a variety of materials that are customarily used in the manufacture of surgical saws. One having ordinary skill in the art will readily appreciates the materials that most desirably may be used to construct the present invention. In one embodiment, however, the sawing mechanism, saw blade displacement measurement assembly, the saw blade load measurement assembly and the structural elements of the controller assembly may be constructed of a combination of polymeric materials (e.g., high strength plastic), polymers and stainless steel.

One embodiment of a saw with an improved displacement sensor including a displacement sensing arm that extends from the saw may be provided. For example, such a displacement sensing arm may be provided that may coordinate with a bushing member of a saw blade assembly that may be used with the saw. However, other embodiments are described below where the displacement sensing arm may coordinate (e.g., contact or be engaged with) a cutting guide to establish a reference point. However, in the case of a bushing, the bushing may move along the saw blade in a direction corresponding to the direction of cutting. 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 sawed when the cutting edge of the saw blade is in contact with the medium. As such, a reference point may be established when the bushing and cutting edge of the saw blade are both in contact with the medium to be sawed. As the bushing is located adjacent to (e.g., partially or fully surrounding the saw blade or operatively engaged with the saw blade), the bushing may facilitate contact with the medium at or very near the location to be sawed prior to creating a cut as described above. 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 cut created in the medium sawed. That is, the bushing may remain in intimate contact with the medium to be sawed adjacent to the cut created. This may prevent false displacement readings attributable to the foregoing problems associated with an offset extension110. Furthermore, the amount of contact of the saw may be localized at the location to be sawed, thus allowing for potentially less intrusion when performing sawing operations.

For example, with additional reference toFIGS. 8A-8C and 9, an embodiment of a saw50with a measurement system400is shown. The saw50may integrally include at least some components of the measurement system400to facilitate operation of the measurement system400in connection with the saw50(e.g., which may be according to the description above regarding measurement system100). For example, at least a portion of a displacement sensor410may be integrated into a housing26of the saw50. In this regard, the displacement sensor410may include a depth sensing arm412that is specifically adapted for engagement with a bushing452of a saw blade assembly60that may be engaged by the chuck420of the saw50.

In this regard, the depth sensing arm412may be used to establish a reference point from which displacement of the saw blade16may be measured as described above. In this regard, as follows herein, a general description of the features and operation of the saw50used in conjunction with the saw blade assembly60is provided.

As may be appreciated inFIGS. 8A-8C, the displacement sensor410may include a depth sensing arm412that may extend from the saw housing26. For example, the depth sensing arm412may extend distally (e.g., from a distal face30of the saw housing26) in a direction corresponding with the direction in which the saw blade16extends from a chuck420of the saw50. At least a portion of the displacement sensing arm412may extend from the saw housing26parallel to a cutting direction120of the saw50. The depth sensing arm412may also include a distal portion414that is adapted to engage a bushing452provided with the saw blade assembly60. As used herein, distal may correspond to a direction from the saw50toward the cutting edge16aof the saw blade16and proximal may correspond to a direction from the cutting edge16aof the saw blade16toward the saw50. In this regard, at least a portion of the depth sensing arm412(e.g., the distal portion414) may be adapted to engage the bushing452of the saw blade assembly60as will be described in more detail below. In any regard, at least a portion of the depth sensing arm412may extend into the housing26. With further reference toFIG. 9, the housing26may contain a coil416. As such, a proximal end418of the displacement sensing arm412may interface with the coil416of the displacement sensor410that may be disposed within the saw housing26.

Specifically, inFIG. 9, the depth sensing arm412is shown in a retracted position relative to the saw blade16. As such, this retracted position shown inFIG. 9may occur when the saw blade16is advanced relative to the bushing452during sawing (e.g., such that the portion of the saw blade extending beyond the distal edge of the bushing452would be disposed in the medium to be sawed). In this regard, the proximal end418of the displacement sensing arm412is disposed within the coil416of the displacement sensor410. Accordingly, the displacement sensor410may comprise an LVDT sensor as described above that is adapted to sense the position of a core422relative to a coil416. The displacement sensing arm412may incorporate a core422at the proximal end418thereof. Accordingly, as the proximal end418of the displacement sensing arm412is moved relative to the coil416, the location of the core422may be determined to provide an output corresponding to the position of the core422, and in turn the displacement sensing arm412relative to the saw housing26. That is, the depth sensing arm412may be displaceable relative to the coil416such that the displacement sensor410may be operable to sense a change in position of the depth sensing arm412relative to the saw housing26and output a measure of the displacement that may be used as described above in determining a depth of a cut. In an embodiment, the total measurable travel of the core422relative to the coil416may be at least about 2.5 in (6.4 cm). Furthermore, the resolution of the output of the displacement sensor410may be about 0.1% (e.g., about 0.002 inches (0.06 mm) for a sensor having a total measureable travel of 2.5 inches).

While a LVDT displacement sensor is shown and described in relation to the saw50shown 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 end418of the displacement sensing arm412to 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 coil416may define a passage424extending at least partially through the housing26. Specifically, the passage424may extend from a proximal face32of the housing26to the distal face30of the housing26. That is, the passage424may extend entirely though the housing26. An end cap34may be provided that is operable to close the proximal end of the passage424at the proximal face32of the saw housing26. Furthermore, a biasing member426(e.g., a coil spring) may be provided in the passageway424at a proximal end thereof. The biasing member426may be provided between the end cap34and the proximal end418of the displacement sensing arm412. In this regard, the biasing member426may act on the proximal end418of the displacement sensing arm412to bias the displacement sensing arm412distally relative to the passage424and saw housing26.

As such, the displacement sensing arm412may include features that selectively prevent ejection of the displacement sensing arm412from the distal end of the passage424. For example, the displacement sensing arm412may include at least one flat428that extends along a portion of the arm412. At the proximal and distal extents of the flat428, the displacement sensing arm412may include shoulders436that project from the flats428(best seen at the distal portion414inFIG. 8Band at the proximal portion418inFIG. 9). As such, at the proximal opening of the passage424, a selectively displaceable stop438may be disposed relative to the flat428such that the flat428may move relative to the stop438, but interfere with the shoulder436defined in the displacement sensing arm412to prevent passage of the shoulder436beyond the stop438. In this regard, the length of the displacement sensing arm412along which the flat428extends may be moveable relative to the stop438, and the stop438may limit proximal and distal movement of the displacement sensing arm412beyond the stop438.

However, the stop438may be displaceable upon depressing, for example, a button440provided on an exterior of the housing26. Thus, upon depressing the button440, the stop438may be displaced away from the displacement sensing arm412to allow the shoulder436to pass distally from the distal end of the passage424such that the displacement sensing arm412may be removed entirely from the passage424. The distal end of the flats438may include a detent442that may be engageable with the stop438so as to maintain the displacement sensing arm412in a proximally disposed, retracted position relative to the housing (e.g., as shown inFIG. 9). Once the button440is depressed and released, the detent442at the proximal end of the flat428of the displacement sensing arm412may be released by the stop438and the displacement sensing arm412may move proximally (e.g., under influence of the biasing member426). The displacement sensing arm412may move proximally until the shoulder436at the distal end of the flat428are engaged to prevent further distal movement of the displacement sensing arm412. Accordingly, the displacement sensing arm412may be retained in a retracted position (e.g., for improved visibility of the distal end of the saw blade16), released to be moveable relative to and biased proximally with respect to the housing26, and removable altogether from the housing26.

In the latter regard, removal of the displacement sensing arm412and biasing member426from the passage424may allow for separate cleaning (e.g., in an autoclave) of those members. Additionally, removal of the end cap34may allow for a cleaning apparatus (e.g., a brush or the like) to be passed through the full length of the passage424to facilitate cleaning thereof.

As referenced above, the distal portion414of the displacement sensing arm412may be adapted to engage a saw blade assembly60(e.g., a bushing452thereof) that is correspondingly adapted for use with the saw50. For instance, as shown inFIGS. 8A-8BandFIG. 9, the displacement sensing arm412may generally be linear along the proximal portion418of the displacement sensing arm412. In this regard, the proximal portion418may be adapted to be collinear with the passage424and moveable within the passage424.

Furthermore, the distal portion414of the displacement sensing arm412(e.g., the portion distal to the linear portion of the displacement sensing arm412) may extend from the linear portion of the displacement sensing arm412toward the saw blade assembly60that may be engaged by the chuck420of the saw50. In this regard, the linear portion of the displacement sensing arm412may be substantially parallel to and offset from the cutting direction120. The distal portion414may extend from the linear portion in a direction corresponding with the offset such that the distal portion414extends toward the saw blade assembly60. This may facilitate engagement between the displacement sensing arm412and the bushing454of the saw blade assembly60. As shown, inFIGS. 8A-8B and 9, the distal portion414may be an at least partially arcuate member extending along a radius of curvature toward the saw blade assembly60. However, the distal portion414may be shaped differently (e.g., the distal portion414may be a linear portion extending at an angle or perpendicularly from the proximal418toward the saw blade assembly60).

The saw blade assembly60may include a shank that is disposed adjacent to a proximal end of the assembly60. Furthermore, the assembly60may include a cutting edge at the distal end thereof. The cutting edge may include a cutting edge that, when oscillated serves to cut the medium into which the blade16is advanced as per a standard saw blade. The direction in which the saw blade is advanced during a cutting operation may be referred to as a cutting direction120that is generally orthogonal to the cutting edge. A blade member may extend between the shank and the cutting edge. The cutting edge, body, and shank may collectively define the saw blade16.

In addition to the saw blade16, the saw blade assembly60may also include a bushing452as referenced above. The bushing452may engage the blade member to facilitate relative movement of the bushing452relative to the blade member along a direction corresponding to the cutting direction120. For example, the bushing452may include an aperture through which at least a portion of the blade member may be disposed. The aperture may form an opening that extends at least in a direction corresponding to the cutting direction120of the saw blade16. The opening may be sized to receive the blade member therein such relative movement between the opening and the blade member is provided. As such, the saw blade16may be free to oscillate within the aperture, and the bushing452may slideably engage the member for relative movement therebetween that is constrained along the direction corresponding to the cutting direction120.

The bushing452may include an engagement member that is disposed on the bushing452and adapted for engagement with a displacement sensing arm412of a saw50to which the saw blade assembly60is engaged. For instance, the engagement member may include a post456extending from the bushing452(FIG. 10). The post may extend away from the cutting direction120of the saw blade assembly60. In an embodiment, the post may extend perpendicularly to the cutting direction120. Accordingly, the post may engage a hole provided on the distal portion of the displacement sensing arm412. In this regard, the post may extend into the hole. Movement of the bushing452relative to the saw blade16in a direction corresponding to the cutting direction120may result in the post acting on the hole such that the displacement sensing arm412undergoes corresponding movement upon movement of the bushing452relative to the saw blade16. In turn, as described above, the core at the proximal portion the displacement sensing arm412may also undergo corresponding movement relative to the coil416, which may be detected by the displacement sensor410and output as a displacement measure.

It may be appreciated that other arrangements for engaging the bushing452with the displacement sensing arm412may be provided so that the bushing452and displacement sending arm412undergo corresponding movement. For example, other structures such as clasps, fasteners, or other mechanisms may be utilized to engage the bushing452to the displacement sensing arm412. Furthermore, the bushing452may, in some embodiments, be integrally defined on the distal portion414of the displacement sensing arm412. In this regard, a standard saw blade16may be engaged with a chuck420of the saw50and the bushing452may be disposed relative to the blade16. In any regard, the bushing452may be pivotal relative to the displacement sensing arm412(e.g., in a direction perpendicular to the cutting direction120) to facilitate ease of engagement of the bushing452with the displacement sensing arm412or the bushing452with the saw blade16when engaging the saw blade16with the chuck420of the saw50.

For instance, with further reference toFIG. 14, a schematic section view of a saw blade16that has been advanced into a medium550is shown. The bushing452may be disposed about the saw blade16. As such, the bushing452may be disposed about the periphery of the cut556created upon advancement of the saw blade16into the medium550. That is, the bushing452may remain in contact with the surface552of the medium550upon advancement of the saw blade16into the medium550. In this regard, the bushing454may include a reference surface554at a distal portion thereof. The reference surface554may contact the surface552of the medium550to be sawed. As such, prior to initiation of the sawing when the cutting edge16aof the saw blade16is also in contact with the surface552, the displacement sensor410may be set to establish the reference point. Accordingly, as the saw blade16is advanced, the reference surface554may remain in contact with the surface552of the medium550. The reference surface554may contact the surface552about a periphery of the cut556. In an embodiment, the reference surface554may extend about a majority or substantially all of the saw blade16such that the reference surface554may also extend about a majority of or substantially all of the periphery of the cut556. The distally biased displacement sensing arm412may act on the bushing452(e.g., by way of post462received in hole464) to maintain the bushing452in contact with the surface552. In any regard, the displacement (d) of the cutting edge16aof the saw blade16relative to the reference surface554of the bushing454may be measured upon corresponding movement of the core422at the proximal end418of the displacement sensing arm412relative to the coil416.

In this regard, measurement of the displacement of the cutting edge16aof the saw blade16relative to the reference surface554of the bushing454that is maintained against the surface552of the medium550to be sawed may provide improved accuracy regarding the displacement of the cutting edge16ainto the cut556. As described above, as the reference surface554is maintained in contact with the medium550adjacent to the periphery of the cut556, there is less possibility for relative movement between the bushing452and the medium550that may introduce error into the measured displacement d. Furthermore, as the bushing452is in contact with the medium550adjacent to the cut556, the contact with the patient required to obtain the measurement is lessened as the extension110may not need to contact the patient in a location away from the cut556. Thus, the sawing operation is less invasive, thus improving patient outcomes.

A number of additional features may also be provided for the saw50and/or saw blade assembly60that are described in conjunction with the embodiment of the saw50. It may be appreciated that these features may be provided with other types of saws and/or saw blade assemblies60and are not required to be used in conjunction with a saw50and saw blade assembly60incorporating features for coordinated operation between the displacement sensor410and saw blade assembly60as described above.

For instance, as may be further appreciated with reference toFIGS. 11 and 12, a saw blade16may incorporate features that prevent reuse of the saw blade16. In this regard, surgical saw blades are often employed as single use items such that the blades are specifically designed to be used for a single procedure or portion thereof and disposed after use rather than being reused. There are several rationales for doing so, including the safety of the patient to ensure that the saw blade16to be used in a procedure has not been worn or damaged by use in previous procedures. In this regard, the features described below may help prevent the saw blade16from being reused. As may be appreciated, the saw blade16disclosed in this respect may be used in a saw blade assembly60as described above.

Specifically, the saw blade16may include a destructible portion466of the shank. The destructible portion466may be degraded or destroyed when exposed to common cleaning procedures to which surgical instruments are routinely exposed. Upon destruction of the destructible portion466, the shape of the shank may be altered. The altered shape of the shank may result in a reduced ability to engage the saw blade16with a chuck420. Such cleaning procedures may include exposure to steam cleaning at elevated heat and/or pressure in an autoclave process or may include exposure to cleaning chemicals or the like. In this regard, when, for example, the destructible portion466is exposed to temperatures associated with cleaning in an autoclave, the destructible portion466may be degraded or destroyed (e.g., by melting or other degradation due to heat) to prevent reuse of the saw blade assembly60. Accordingly, in an embodiment, the melting temperature of the destructible portion may be greater than an operating temperature (e.g., substantially similar to room temperature or 22.3° C.+/−20° C.). Accordingly, in an embodiment, the melting temperature may be not less than about 50° C. and not greater than about 130° C. In an embodiment, the melting temperature of the destructible portion may be not less than about 60° C. and not greater than about 110° C.

While autoclave cleaning is a common method of sterilization and cleaning of instruments between procedures, it may be appreciated that other methods of cleaning may be employed. As such, the destructible portion466may be adapted to be degraded or destroyed during such cleaning procedures. For example, the destructible portion466could alternatively or additional be adapted to be degraded or destroyed upon exposure to a cleaning element such as a cleaning chemical or the like. In any regard, upon an attempt to sterilize or otherwise clean the saw blade assembly60for reuse, the destructible portion466may be destroyed or degraded to the point of eliminating the effectiveness of the saw blade assembly60to prevent reuse of the saw blade assembly60.

With further reference toFIG. 11, one particular embodiment of a saw blade assembly60including a destructible portion466is shown where the destructible portion may include a portion of the shank of the saw blade assembly60. As shown, the destructible portion466includes a proximal end of the shank. As such, at least a portion of a sidewall and/or an endwall of the shank may be defined by the destructible portion466. As may be appreciated, the shank sidewall and endwall may be adapted for engagement with the chuck such that the chuck contacts the sidewalls and endwall (or tabs) upon engagement with the shank.

For instance, the chuck may include a correspondingly-shaped opening that is sized to have corresponding sidewalls that may contact the tabs when the shank is received in the chuck. As such, upon receipt of the shank in the chuck, the chuck may define a bearing surface interface that allows the chuck to impart an oscillating motion to the saw blade16.

Accordingly, when, as shown inFIG. 12, the destructible portion466is destroyed or degraded and may be removed. The result may be at least a lack of registration of the shank relative to the chuck. This may prohibit the ability of the saw blade assembly60to be used because the lack of registration may prevent the saw blade16from properly turning so as to at least inhibit the use of the saw blade assembly60in a procedure. Additionally or alternatively, the destructible portion466may be degraded to the point where the shank is no longer receivable by the chuck (or other attachment device).

As may also be appreciated inFIGS. 11 and 12, the shank may include chuck engagement features that may be engaged by the chuck to retain the saw blade assembly60relative to the chuck. For instance, the chuck may include retention pins that are biased to extend into the chuck opening in an engaged position to engage detents of the shank.

Furthermore, the saw50may include a removable chuck420that provides for quick interchange and/or removal of the chuck. As may further be appreciated fromFIG. 9, the saw50may include a drive having a motor432and gearbox434. The drive430may engage a chuck420. Specifically, the chuck420may be provided in removable engagement with the drive430such that the chuck420may be releasably engaged with the drive420. The chuck454may include a chuck drive coupling at a proximal end thereof. In this regard, the saw50may include a corresponding saw drive coupling that engages with the chuck drive coupling to impart oscillating motion from the drive430to the chuck420. In this regard, the chuck420may be detachable from the saw50.

As may be appreciated, when sawing using the saw50, a second sensor for measurement of force acting on the cutting edge16aof the saw blade16may also be provided. In this regard, a second sensor118′ (e.g., a force sensor such as piezoelectric crystal) may be disposed proximally to the saw drive430. In turn, force acting on the cutting edge16aof the saw blade16as it is advanced in the sawing process may be transferred to the second sensor118′ via the saw drive430. That is, the force acting on the cutting edge16aof the saw blade16may be transferred through the shank of the blade16to the chuck420, and the saw drive420. In turn, the drive430may act upon the second sensor118′ to produce an output corresponding to the force acting on the cutting edge16a. In this regard, it may be appreciated that the rigid assembly of the saw drive430, chuck420, and saw blade16may transmit the force acting on the cutting edge16aof the saw blade16to the second sensor118. It may further be appreciated that the saw drive430may be fixed relative to the saw housing26so as to impart oscillation to the chuck420. At least a majority of the force acting on the cutting edge16aof the saw blade16may be transferred to the second sensor118. In an embodiment, the second sensor118may have a range of measureable force from about 0 lbf (0 N) to about 100 lbf (445 N). In an embodiment, the second sensor118may have a range of measurable force from about 0 lbf (0 N) to about 25 lbf (111 N). The second sensor118may have a precision of at least about 1% of the maximum measureable force. Accordingly, in an embodiment, the second sensor may have a precision of at least about 0.25 lbf (1.1 N). In an embodiment, the second sensor118may have a precision of 0.5% (e.g., about 0.125 lbf (0.56 N) in an embodiment).

In this regard, the saw drive430, as shown best inFIG. 9, may be mounted to the saw housing26by way of a suspension member494. The suspension member494may be operatively engaged to the saw housing26and the saw drive430so as to maintain the saw drive430stationary to transfer force acting on the cutting edge16aof the saw blade16to the second sensor118. As such, the suspension member494may be supportively engaged to the saw drive430at a first end of the suspension member494. The suspension member494may also be affixed to the saw housing26. The suspension member494may allow for linear movement along the cutting direction120. In this regard, the suspension member494may comprise a spring member that allows for motion relative to the direction along the cutting direction120. The spring member may have a spring coefficient slight enough relative to the direction corresponding to the cutting direction120such that the force resulting from displacement of the suspension member494may be insignificant (e.g., less than about 1%, less than about 0.5% or even less than about 0.1%) of the force applied to the cutting edge16aof the saw blade16during the sawing operation.

As shown inFIGS. 15A-C, an embodiment of a saw50A with two measurement systems is shown. Displacement sensors similar to the displacement sensor410ofFIG. 9may be integrated into a housing of the saw50A. In this regard, the displacement sensors may each include a depth sensing arm412A, B that is specifically adapted for engagement with a bushing452A, B. In this regard, the depth sensing arms412A, B may be used to establish reference points from which displacement of the saw blade16may be measured as described above.

The displacement sensors may include a depth sensing arm412A, B that may extend from the saw housing. For example, the depth sensing arm412A, B may extend distally (e.g., from a distal face30of the saw housing) in a direction corresponding with the direction in which the saw blade16extends from a chuck of the saw50A. At least a portion of the displacement sensing arms412A, B may extend from the saw housing along the length of the saw blade16of the saw50A. The depth sensing arms412A, B may also include a distal portion414that is adapted to engage a bushing452A, B. As used herein, distal may correspond to a direction from the saw50A toward the cutting edge of the saw blade16and proximal may correspond to a direction from the cutting edge of the saw blade16toward the saw50A. In this regard, at least a portion of the depth sensing arms412A, B (e.g., the distal portion414) may be adapted to engage the bushings452A, B of the saw blade assembly. In any regard, at least a portion of the depth sensing arms412A, B may extend into the housing. The housing of the saw50A may contain components for both of the sensing arms412A, B that are shown within the housing26ofFIG. 9. As such, a proximal end of the displacement sensing arm412B also interfaces with a coil of a displacement sensor that may be disposed within the saw housing.

FIG. 15Cshows when the cut has been completed and one side of the medium550has been dislodged. This causes one of the bushings452B to release due to a lack of counter force from the medium550. When this occurs the processor will receive a signal from the position sensor associated with the second bushing452B that is quite different from a signal from the position sensor associated with the first bushing452A. In one embodiment, the processor will generate a signal indicating that the cut is complete when the signals from the two position sensors differ by greater than a previously defined threshold amount. This generated signal causes an automatic slowing of motion or stopping altogether of the saw motor. An output device may generate an alert (visual, tactile or audible) for a saw user based on the generated cut completion signal.

FIG. 16shows the saw50used with an exemplary cutting guide/jig480. In one embodiment, the cutting guide/jig480is U-shaped for receiving a portion of a patient's anatomy. The cutting guide/jig480includes two opposing walls. The walls include slot guides482that receive the saw blade16. The slot guides482can be thin enough to act as bearing members to the received saw blade16without cause undue friction during oscillation of the saw blade. As the saw blade16is received within the slot guides482a displacement sensing arm412uses the side of the cutting guide/jig480as a reference surface. Thus, the cutting block480may receive the saw blade in the slot guides482to direct the saw blade relative to the patient's anatomy. The displacement sensing arm412and related components (processor) generate a cutting depth value that takes into consideration the thickness of the wall of the cutting guide/jig480—provided the item being cut maintains contact with the interior wall of the cutting guide/jig480. Furthermore, the displacement sensing arm412may contact a portion of the cutting block480that is stationary relative to the anatomy to be cut rather than the anatomy itself.

In one embodiment, the cutting guide/jig480is adjustable for allowing different sized patient parts to be received. Also, the height, depth and width of the slot guides482is also adjustable for accepting different size and time type of cutting blades (e.g., reciprocating, ultrasonic, etc.) Also, guide(s) separate from or attachable to the cutting guide/jig480provide barriers for guiding motion of the housing of the saw in a desired cutting direction.

As shown inFIGS. 17A-C, the saw may also include a light emitter500disposed on a distal face30of the saw housing26. In this regard, the light emitter500may be operable to emit light in a direction toward the saw blade16when engaged with the chuck420. As such, the light emitter500may illuminate at least a portion of the saw blade16during the sawing operation to improve visibility of the medium being sawed. The light emitter500may include a light source such as, for example, an incandescent bulb, a light emitting diode (LED), a laser source, or other light source known in the art. Alternatively, a light source may be disposed remotely from the light emitter500and the light may be transmitted from the remote light source to the light emitter500using optical elements such as fiber optics or the like. It may further be appreciated that a light emitter500like the one shown in the accompanying figures may be provided with other types of surgical instruments without limitations. For example, a light emitter500of the type described herein may be provided with other types of saws, saws, or other surgical tools. Accordingly, the light emitter500may be appropriately disposed relative to the surgical field so as to direct light from the light emitter500toward the interface of the surgical tool with the portion of the surgical field contacted by the surgical tool.

The light emitter500may be selectively operated or may be operated when the saw50is operated. In this regard, the light emitter500may be selectively toggled on and off or may include different levels of intensity. The selector for the light emitter500may be at the controller housing146(e.g., a selectable option on the display152). The light emitter500may also be activated upon activation of the saw50. Additionally, the operation of the light emitter500may be selectable between operation with the saw500and selective toggling of the light emitter500.

In a further embodiment, the light emitter500may be adapted for use with any appropriate surgical instrument. In this regard, further examples of surgical instruments are shown inFIGS. 17A-C, respectively. For example, inFIG. 17A, a burr grinder600A is shown, inFIG. 17B, a second sagittal saw600B is shown with a first grip embodiment, and inFIG. 17C, a third sagittal saw600C is shown with a second grip embodiment. InFIG. 17A, the burr grinder600A may include an instrument working portion comprising a rotatable burr grinding bit610. In this regard, the burr grinding bit610may be contactable with the patient to perform a grinding operation. The burr grinder600A may also include one or more light emitters500. As may be appreciated, the light emitters500may be disposed on a distal face620of the burr grinder600A such that the light emitters500may be operable to emit light in a direction toward the patient when the burr grinding bit610is in contact with the patient. That is, the light emitter500may act to illuminate a surgical field in which the burr grinder600A is employed. In the case of a plurality of light emitters500, the light emitters may be spaced equally about a portion of the distal face620surrounding the working portion of the burr grinder600A. The light emitters500may be disposed within a housing of the burr grinder600A such that the light emitters500may be protected from environmental elements (e.g., fluid or the like) that may be present when the burr grinder600A is in use. As such, the light emitters500may include or be disposed behind a transparent or translucent shield630that may protect the light emitters500and/or light source associated with the light emitters500from such environmental elements. The light emitters500shown inFIG. 17Amay be operated according to any of the foregoing discussion regarding the light emitters500described above.

Furthermore, with further reference toFIGS. 17B and 17C, it may be appreciated that the light emitters500may be provided in connection with other surgical instruments. For instance, inFIG. 17B, a sagittal saw600B with a first grip embodiment (i.e., a pistol grip style grip) is shown. In this regard, it may be appreciated that a sagittal saw blade612may be provided as the working portion of the sagittal saw600B. As such, the sagittal saw blade612may be reciprocated such that contact of the distal portion of the sagittal saw blade612may act to cut anatomy of the patient. As such, the light emitters500may be disposed on a distal face of the sagittal saw600B such that the light emitters500may emit light toward the patient when the sagittal saw blade612contacts the patient in a cutting operation. Further still,FIG. 17Cshows another embodiment of a sagittal saw600C with a second grip embodiment. As may be appreciated, the light emitters500of the sagittal saw600C may be disposed about the sagittal saw blade612in a manner as described above with respect to the burr grinder600A.

With further reference toFIGS. 18-21C, an embodiment of a saw700that may also include a measurement system400for the measurement of the displacement of the leading edge16aof the saw blade16when advanced into a medium. In this regard, the saw700may include a displacement sensing arm412that extends from a saw housing26in a manner similar to that described above. With further reference toFIGS. 19 and 20, both of which depict internal components disposed within the saw housing26, the saw700may include a displacement sensor410. Specifically, the displacement sensor410may be a digital encoder720that is operative to output a signal representative of the displacement of the displacement sensing arm412with respect to the leading edge16aof the saw blade16.

In this regard, the proximal end418of the displacement sensing arm412may extend into the housing26of the drill700. Specifically, the proximal end418of the displacement sensing arm412may contact a shuttle710that is slideably engaged with a plurality of rails712extending in a direction parallel to the cutting direction120of the saw blade16. The shuttle710may further be engaged with a belt714. The belt714may be disposed about a plurality of gear hubs716aand716b. In this regard, the shuttle710may engage a point on the belt714such that as the shuttle710moves in sliding engagement along the rails712, the belt714imparts rotational motion to the gear hubs716aand716b.

The gear hub716bmay be fixed on a shaft718that extends into the digital encoder720. In this regard, rotation of the shaft718may be sensed by the digital encoder720and transformed into a corresponding displacement signal associated with the movement of the shuttle710when moved by the displacement sensing arm412. The shuttle710may be biased to a distal position.

Furthermore, the distal portion414of the displacement sensing arm412may engage a bushing452as described above. In this regard, the bushing452may be engaged with the saw blade16. Specifically, the bushing452may include a post732extending through an aperture730in the saw blade16. Specifically, the post732may extend between a first portion734of the bushing452on a first side of the saw blade16and the second portion736of the bushing452on a second side of the saw blade16opposite the first side of the saw blade16. In this regard, the bushing452may be captive relative to the saw blade16such that the bushing452may move with respect to the confines of the aperture730as the post732may constrain the bushing452within the aperture730. The bushing452may include an engagement portion738that engages the distal portion414of the displacement sensing arm412. Specifically, the engagement portion738may comprise a snap interface such that the engagement portion738snaps onto and is engageable with the distal portion414corresponding movement therewith. Thus, as may be appreciated, the bushing452may include a reference surface for 60 that is alignable with the distal edge16ato define a reference point relative to the distal edge16ais described above.

Furthermore, it may be appreciated that the aperture730in the saw blade16may generally be tapered or fan shaped such that the aperture extends across the greater lateral extent of the saw blade16towards the distal end thereof and converges to a lesser lateral extent of the saw blade16as the aperture extends proximally. This may be provided to account for the greater reciprocal distance traveled by the saw blade at the distal end thereof such that as the bushing452moved relative to the saw blade16in a proximal direction, the corresponding relative movement between the bushing452and saw blade16may be reduced given the relatively shorter stroke of the oscillations of the saw blade16at a proximal location.

In any regard, the bushing452, once engaged with the displacement sensing arm412may undergo corresponding relative movement therewith. As such, when the saw blade16is advanced into a medium, the reference edge460of the bushing452may move relative to the leading edge16aof the saw blade as the saw blade16is advanced during a sawing operation as described above. In turn, the relative movement between the bushing452and the leading edge of the saw blade16amay be detected by the digital encoder720as the displacement sensing arm412displaces the shuttle710along the rails712, thus turning the belt714on the gear hubs716aand716bthat is detectable by the digital encoder720.

FIG. 21Adepicts the chuck420of the saw700without a saw blade16disposed relative thereto. As may be appreciated, a lever740may be provided relative the chuck420. The lever470may be in operative communication with a clamping element742disposed within a receiving window744of the chuck420. In this regard, with further reference toFIG. 21B, as a saw blade assembly60including a bushing452and the saw blade16is advanced relative to the chuck420, the lever740may be displaced, thereby displacing the clamping element742and allowing the shank744of the saw blade16to be received in the receiving window7/44the chuck420. Upon return of the lever742to a home position, the clamping element742may clampingly engage the shank744of the saw blade16. Furthermore, the engagement portion738of the bushing452may be advanced relative to the proximal end414of the displacement sensing arm412for engagement there with when the shank744is engaged by the chuck420.

Furthermore, as described above, the saw blade assembly60for use in the embodiment of the saw700depicted inFIGS. 18-21Cmay include a destructible portion that prevents or use of the saw blade assembly60upon cleaning thereof. In this regard, for purposes of patient safety or the like, the saw blade assembly60may be a one-time use item such that attempted reuse after a cleaning operation may prevent engagement of the saw blade assembly60with the saw700. Specifically, the bushing452may comprise a destructible portion that is destroyed upon undergoing cleaning operation and the manner described above. Specifically, the post732may be destroyed upon undergoing a cleaning operation such that the first portion734and second portion736may be disassociated such that there are no longer maintained within the aperture730of the saw blade16.

Those skilled in the art will appreciate that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.