Surgical instrument

A surgical instrument (25), in particular a surgical cutting or drilling instrument, the surgical instrument (25) comprising: a drive unit; a cutting tool or drill bit (5) engageable with the drive unit; a measuring device (1) which is configured to measure the distance [x(t)] covered by the cutting tool or drill bit (5) along a cutting or drilling path with respect to time and relative to a reference position; a processing un and a digital data storage, wherein in the digital data storage reference data are stored which include at least N one data set specifying a reference graph GRef within a time window (11) in the range of a transition and defining a reference point of a transition (21′), wherein the time window (11) includes a first time period before the reference point of a transition (21′) and a second time period after the reference point of a transition (21′) and wherein the processing unit (14) suitably programmed to compare the recorded graph G with the at least one reference graph GRef and to find 1 lion of a transition (21) in the recorded graph G.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application filed Under 35 U.S.C. § 371 of International Application No. PCT/CH2019/000022 filed Jul. 22, 2019, which claims priority to CH00945/18 filed Jul. 31, 2018, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a surgical instrument and a method for bone screw length estimation from drilling characteristics.

From clinical observations one problem in orthopedic and trauma surgery is the determination of the required screw lengths for e.g. bi-cortical screw placement before inserting a screw into a bone fragment. Current mechanical depths gauges are rather inaccurate, unreliable and difficult to handle resulting in:prolonged surgery time;insertion of too long screws resulting in soft tissue irritation, pain and re-operation;insertion of too short screws resulting in osteosynthesis failure, re-operation;need for exchange of screws resulting in screw scrap, increased hardware costs.

2. Description of the Related Art

A surgical power drill including an integrated measurement system for determining when the leading edge of a surgical tool passes from a first medium to a second medium is known from US 2016/036756 MCGINGLEY ET AL. This known power drill comprises a displacement sensor that outputs a displacement signal representative of a displacement of the leading edge of the tool relative to a reference point, a calculation module in operative communication with the displacement sensor for generating a velocity signal and an acceleration signal based on the displacement signal and a processing module in operative communication with the calculation module that is configured to determine an occurrence of the leading edge of the tool passing from the first medium to the second medium based only on the displacement signal, the velocity signal and the acceleration signal. A drawback of this known surgical power drill is that the reference data used to determine the transition of the leading edge of the tool from a first medium to a second medium include only punctual threshold values for the displacement, velocity and acceleration of the tool solely at the instant of the transition of the tool from the first medium to the second medium.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide a surgical cutting or drilling device with means to determine a transition of the cutting tool or drill bit from a first medium having a first density to a second medium having a different second density during a cutting or drilling process which includes a numerical procedure of a significantly higher robustness using displacement characteristics only.

The invention solves the posed problem with a surgical instrument comprising the features of claim1and with a method for bone screw length estimation from drilling characteristics comprising the features of claim55.

The advantages of the surgical instrument can essentially be seen therein that:the determination of a transition of the cutting tool or drill bit is based on a plurality of reference graphs of the distance covered by the cutting tool or drill bit wherein each reference graph extends within a time window including a first time period before the reference point of the transition and a second time period after the reference point of the transition so that in the case of a surgical drilling device the significance of the detection of the point where the drill bit exits the cortex of a bone can be improved;the processing unit can report two values for the position of the transition of the drill bit from a first medium to a second medium which occur at the positions where the cutting tip of the drill bit exits the near cortex, respectively the far cortex of a bone. The surgeon can then decide whether unicortical or bicortical bone screws are to be applied; anddue to the use of a sole position sensor the measuring unit has a simple configuration and can hence be configured as a separate unit which can be temporarily attached to a standard surgical cutting or drilling device.

Further advantageous embodiments of the invention can be commented as follows:

In a special embodiment the digital data storage further stores a predefined threshold value for the similarity measure and wherein the processing unit is programmed to trigger a transition event and report the position x of transition if the threshold value for similarity is reached.

In a further embodiment the digital data storage is configured as a buffer to hold an actual time window of the current graph G of the distance [x(t)] at least as large as the window of the reference graph GRef.

In a further embodiment multiple reference graphs GRefare stored in the digital data storage, representing various drilling or cutting characteristics and the processing unit is suitably programmed to repeat the step of quantifying the agreement between the recorded graph G or the at least one portion of the recorded graph G to the reference graphs GRefby means of a similarity measure for all stored reference graphs GRefand finding the overall best fit between graph G and all reference graphs GRefto identify the position x of transition in the recorded graph G.

In another embodiment each reference graph GRefis specified by at least 10 values, preferably at least 20 values for the distance [x(t)] covered by a cutting tool or drill bit which are subsequent with respect to time within the second time period after the reference point of a transition.

In again another embodiment each reference graph GRefis specified by at least 30 values, preferably at least 40 values for the distance [x(t)] covered by a cutting tool or drill bit which are subsequent with respect to time within the first time period before the reference point of a transition.

By means of using a plurality of values for the distance [x(t)] covered by a cutting tool or drill bit before and after the reference point of a transition permits the advantage of an improved robustness of the algorithm because the detection of a transition of the cutting tool or drill bit is not restricted to features at the point of transition only but is performed by characterizing the motion of the cutting tool or drill bit before and after the point of transition. By this means wrongly positive events can be filtered and dismissed.

In a further embodiment the second time period after the reference point of a transition amounts to at least 0.1 seconds, preferably to at least 0.3 seconds within each reference graph GRef.

In a further embodiment the first time period before the reference point of a transition amounts to at least 0.3 seconds, preferably to at least 0.4 seconds within each reference graph GRef.

In a further embodiment the reference data specify a reference graph GRefwith a monotonously increasing distance [x(t)] covered by the cutting tool or drill bit in the first time period before reaching the reference point of a transition. Once the drill bit has exited the bone and comes to rest clearly after the exit the user performs an unintended further motion and further advances the drill bit. Using one of the devices known from prior art all criteria for a transition are fulfilled so that a wrong value for the point of the transition is detected and a significantly too long bone screw is selected and positioned in the bone. Due to the requirement of a constant advance velocity v>0 of the cutting tool or drill bit such an event can be filtered and dismissed.

In again a further embodiment the surgical instrument further comprises a surgical cutting or drilling device.

In another embodiment the surgical drilling device is a surgical power drill, wherein the drive unit comprises a motor and a spindle which is drivable by the motor and has a longitudinal axis so that the reference point is definable by a surface of an implant or a bone. The program performed by the processing unit permits bone screw length estimation based on drilling characteristics only.

In another embodiment the processing unit is one of a computer with a monitor, a tablet computer, a smartphone, a smartwatch or a smartglass.

In another embodiment the processing unit comprises a wireless communication device, preferably a Bluetooth module. The derived information, i.e. the measured position x of the cutting tip of the drill bit with respect to time as well as the computed point of transition may be transmitted wirelessly to an external device such as a computer with a monitor, a tablet computer, a smartphone, a smartwatch or a smartglass.

In yet another embodiment the surgical instrument further comprises a housing.

In a further embodiment the measuring device comprises attachment means, preferably an adaptor which is releasably affixable to the housing of the surgical power drill. This configuration permits the advantage that the measuring device can be configured as a separate unit which can be temporarily attached to a standard surgical power drill.

In a further embodiment the measuring device comprises clamps to releasably affix the measuring device to the housing.

In a further embodiment the adaptor is configured as a framework attachable to the housing, preferably an annular framework to be secured to the housing by means of a press fit or via a clamp collar.

In again a further embodiment the measuring device is integral with the housing.

In another embodiment the similarity measure applied to select the portion of the graph G which best fits the reference graph GRefto find the position x of transition in the recorded graph G is a pattern recognition approach, preferably a shape context descriptor.

In another embodiment the reference data specifies a statistical representation of a plurality of prospectively recorded graphs G in the range of a transition of a cutting tool or drill bit from a first medium having a first density to a second medium having a different second density during a cutting or drilling process.

In a further embodiment the reference data are continuously amended during the use of the cutting or drilling device.

In a further embodiment the amendment of the reference data is performed by machine learning algorithms, preferably by involving use of a neural network.

In another embodiment the measuring device comprises a contactless displacement sensor.

Preferably, the contactless displacement sensor is a triangulation distance sensor and comprises a light transmitter and a corresponding receiver.

In another embodiment the contactless displacement sensor comprises a LED light transmitter.

In a further embodiment the measuring device includes a laser device which comprises a laser module and one or more electronic light sensors, preferably charge-coupled devices (CCD) to perform laser triangulation for displacement assessment. The configuration of the measuring device with a use of a laser device for displacement assessment by means of triangulation permits a simple configuration of the measuring device without a mechanical arm between the displaceable member and the sensor. Thereby the work field of the surgeon is not occupied nor is the field of view obstructed. Contactless distance measurement reduces the contamination risk of the patient and does not influence the drilling process as opposed to mechanical contact measurement. Furthermore, a significantly larger measuring range is achieved, e.g. 15 cm-30 cm compared to 6.4 cm of the known devices so that a large variety of drill bits and drill sleeves with different lengths can be used.

In again a further embodiment the contactless displacement sensor is based on radar, preferably a millimeter-wave radar sensor.

In another embodiment the contactless displacement sensor is an ultrasonic distance sensor.

In a further embodiment the contactless displacement sensor comprises a reflector slideable along a drill bit and configured to abut an implant, a bone or an instrument.

In a further embodiment the processing unit additionally comprises a display or a loud speaker. The derived information may be provided on a display or speaker locally mounted to the drilling machine, wherein the main output parameters are: the current position x of the cutting tip of the drill bit which coincides with the measured distance x covered by the housing in the direction of the longitudinal axis and relative to the surface of the implant, the instrument or the bone; the current velocity of the forward moving drill bit; and the position of the cutting tip of the drill bit at the transition of the drill bit from a first medium to second medium, wherefrom the suitable implant length can be derived.

In another embodiment the measuring device comprises a casing to enclose the processing unit.

Preferably, the casing enclosing the processing unit is sterilizable.

In another embodiment the measuring device comprises: a first member, which is in a fixed position relative to the housing; and a longitudinal second member, which is displaceable essentially in the direction of the longitudinal axis of the spindle relative to the first member and which comprises a front end suitable to abut a surface of a bone or an implant.

In yet another embodiment the displaceable second member comprises a drill sleeve extending in the direction of the longitudinal axis to the front end of the second member.

In a further embodiment the first member of the measuring device and preferably the processing unit are insertable into a hollow space arranged in the housing of the surgical power drill.

In again a further embodiment the first member and preferably the processing unit are part of an electronic module which additionally comprises a power supply and/or a motor for driving the surgical power drill and wherein the power supply is configured to supply the first member and preferably the processing unit and the motor with electric energy.

In another embodiment the hollow space is arranged in a handle of the housing and configured to receive the electronic module.

In another embodiment the housing comprises a top part including a sterilizable window for covering the display.

Preferably, the top part is integral with the housing and forms a casing for the display.

In a further embodiment the housing comprises at least one sterile window to provide a window for the signal emitted by the contactless displacement sensor and a reflected signal receivable by the contactless displacement sensor.

In a further embodiment the sterile window is configured as a recessed window. Critical transparent surfaces are protected against mechanical impacts and scratching during sterilization and handling to avoid compromising the light beam inlet and outlet.

In again a further embodiment the casing is attachable to the housing by means of an adaptor and comprises a cavity configured to receive the electronic module.

In another embodiment the casing comprises a lid arranged at the rear end of the casing and Including a sterilizable rear window for covering the display.

In another embodiment the casing comprises at least one sterile front window to provide a window for the signal emitted by the contactless displacement sensor and a reflected signal receivable by the contactless displacement sensor.

In another embodiment the displaceable second member comprises a clamping portion for attachment to cylindrical structures with variable diameters.

In another embodiment the clamping portion of the displaceable second member is configured to provide a frictional fit to a drill bit. By this means the advantage can be achieved that the reflector can slide along a drill bit but will not move due to gravity or small impacts. This way the reflector is pushed against a surface of an instrument or implant without the need to accurately fit the geometry of the instrument or implant.

In a further embodiment the measuring device is positioned with respect to the housing that a beam emitted by the contactless displacement sensor is oriented at an offset angle to the longitudinal axis of the spindle. This configuration permits the advantage that the diameter of the displaceable second member can be reduced.

In a further embodiment the first member of the measuring device is positioned off-center to the longitudinal axis of the spindle. Therewith the advantage can be achieved that the laser beams (emitted and reflected) are not obstructed by the drill-bit. The view of the operator is less obstructed.

In a further embodiment the measuring device comprises at least one accelerometer. By this means the device can be operated by gestures rather than buttons. Example: taring is only possible when oriented vertical (within limits) pointing downwards. Switching back to taring mode by orienting the drill vertical pointing upwards. Sleep mode and wake-up by device movement to safe energy.

In another embodiment the measuring device additionally comprises gyroscopes and/or magnetometers. This configuration permits the advantage that the absolute orientation of the drill can be tracked to control the drilling direction.

In another embodiment the surgical instrument additionally comprises a calibration device.

In a further embodiment the processing unit is programmed to compute in real-time.

In a further embodiment the processing unit comprises a data memory to store data related to bone screw lengths, preferably including a safety margin, screw head length, tip section length and screw length increments.

In a further embodiment the processing unit is suitably programmed to control the rotational speed of the spindle of the surgical power drill or to stop the spindle when the point of a transition is detected.

In a further aspect of the invention a method for bone screw length estimation from drilling characteristics using the surgical power drill according to the invention, the method comprising the following steps: A) advancing the surgical power drill coaxially to the longitudinal axis of the spindle to drill a hole in a bone and by recording the position (x) of the cutting tip of the drill bit relative to a surface of a bone or of an implant in the drilling direction with respect to time; B) determining the distance [x(t)] covered by the drill bit relative to a surface of a bone or of an implant when the cutting tip of the drill bit exits a cortex of a bone by using the stored reference data to find the position of a transition of the drill bit from a first medium to a second medium in the recorded graph G; and C) selecting a bone screw having a length corresponding to the distance [x(t)] covered by the drill bit determined under step B) under consideration of a predefined safety margin.

In a further embodiment of the method the following steps are performed before step A):positioning the surgical power drill relative to a bone so that the front end of the displaceable second member and the cutting tip of the drill bit abut a surface of a bone or of an object; andif required, adding an offset value stored in the data storage to the relative position; andstoring the relative position as start point (x=0) for the measurement of the position (x) of the cutting tip of the drill bit relative to a surface of a bone in the drilling direction with respect to time.

In this case the second member comprises a drill sleeve extending in the direction of the longitudinal axis to the front end of the second member.

In a further embodiment of the method the following steps are performed before step A):positioning the surgical power drill relative to a bone so that the front end of the displaceable second member abuts a drill sleeve inserted in the soft tissue covering a bone to be treated; andadjusting the cutting tip of the drill bit secured in the engagement means of the surgical power drill relative to the displaceable second member so that the cutting tip of the drill bit abuts a surface of a bone; andif required, adding an offset value stored in the data storage to the relative position; andstoring the relative position as start point (x=0) for the measurement of the position (x) of the cutting tip of the drill bit relative to a surface of a bone or of an implant in the drilling direction with respect to time.

In this case a separate drill sleeve can be used.

In another embodiment of the method the following steps are performed before step A):positioning the drill bit secured in the engagement means relative to the displaceable second member by using a calibration device so that front end of the second member contacts a surface of the calibration device and the cutting tip of the drill bit abuts a stop protruding from the surface of the calibration device;storing the relative position as start point (x=0) for the measurement of the position (x) of the cutting tip of the drill bit relative to a surface of a bone or of an implant in the drilling direction with respect to time; andpositioning the surgical power drill relative to an implant, so that the front end of the displaceable second member abuts a surface of the implant.

Preferably, the first medium penetrated by the cutting tool or drill bit of the surgical instrument is cortical or trabecular bone.

Preferably, the surgical power drill according to the invention is used for the estimation of bone screw length.

DETAILED DESCRIPTION OF THE INVENTION

The following description of the different embodiments of the surgical instrument25is—exemplarily but not limiting—directed to a surgical drilling device configured as a surgical power drill2, wherein:the drive unit comprises a motor and a spindle13which is drivable by the motor and has a longitudinal axis7in the direction of which the drilling path extends;the engagement means are configured as a chuck6permitting to clamp a drill bit5; and whereinthe reference position is defined by a surface of an implant26or a bone.

The measuring device1can comprise a signal conditioner to convert analog signals generated by a sensor into digitized signals. Furthermore, the processing unit14can be provided with a timer or a clock to record the relative position x with respect to time.

Definitions

The following definition of terms and wordings currently used describe the exact meaning thereof as they are used throughout the present specification:

Position x of the cutting tip of the drill bit relative to a surface of a bone or of an implant:

During a drilling process the distance x covered by the housing12in the direction of the longitudinal axis7of the spindle13and relative to a surface of a bone or of an implant26is related with the position x of the cutting tip9of the drill bit5relative to a surface of a bone or of an implant26in the drilling direction because the drill bit5is firmly fixed in the chuck6of the surgical power drill2and positioned at the beginning of the drilling process as described in detail below.

Depending on the object into which a hole is drilled, e.g. a bone, there may be more than one point of transition21of the cutting tool or drill bit5from a first medium to a second medium, e.g. a first transition from cortical bone to cancellous bone (spongy bone) and a second transition from cortical bone to surrounding tissue. With respect to the one or more reference graphs GRefthe reference point of a transition is denoted with the reference numeral21′.

FIG.1illustrates an embodiment of the surgical power drill2according to the invention wherein the surgical power drill2essentially includes a housing12in which a motor and a spindle13driven by the motor are accommodated, a measuring device1releasably attached or fixed to the housing12and an adaptor15to secure the measuring device1to the housing12. The spindle13has a longitudinal axis7and comprises a chuck3at a front end for clamping a drill bit5. The measuring device1comprises a first member3, which is in a fixed position relative to the housing12and a longitudinal second member4, which is exemplarily but not limiting displaceable parallel or coaxial to the longitudinal axis7of the spindle13relative to the first member3. Alternatively, the measuring device1can be arranged at the housing12so that the second member4is displaceable at an angle relative to the longitudinal axis7of the spindle13. The systematic error which occurs due to this angulation (cosine error) can be easily compensated. This configuration has the advantage that the reflector can be smaller so that the measuring tip can be arranged closer to the drill bit5.

The displaceable second member4has a front end10, wherein in use the front end10of the displaceable second member4abuts the bone surface or a surface of an implant26, e.g. a bone plate or a drill sleeve. The drill bit5can be clamped in the chuck6and is provided with a cutting tip9. Furthermore, the displaceable second member4can comprise a drill sleeve23extending in the direction of the longitudinal axis7to the front end10of the second member4.

The measuring device1comprises a laser device for linear displacement assessment. This laser device comprises a laser module18with a laser light emitting means, a reflector20attached to a drill sleeve23forming the second member4which is slideable along the drill bit5and at least one electronic light sensor19, which is, exemplarily but not limiting, configured as a charge-coupled device (CCD) to perform laser triangulation for linear displacement assessment.

In another alternative embodiment the linear displacement assessment can be performed by using ultra sound position sensors.

To incorporate screw length determination in the drilling procedure so as to eliminate the step of depth measurement after drilling the hole in the bone the configuration of the measuring device1is based on the fact that during drilling an acceleration peak of the drill bit5occurs when the cutting tip9of the drill bit5exits a bone cortex as this is an unavoidable attribute of handheld drilling. Consequently, the housing12of the surgical power drill2together with the first member3of the measuring device1is subjected to the same acceleration.

The surgical instrument25further comprises a processing unit14and a digital data storage. The processing unit14is electronically directly or wirelessly connected to the measuring device1and suitably programmed to record a graph G of the distance [x(t)] covered by the cutting tool or drill bit5relative to the reference position and with respect to time during a cutting or drilling process. In the digital data storage reference data are stored which include one or more data sets each specifying a reference graph GRefof the distance [x(t)] covered by a cutting tool or drill bit5with respect to time and within a time window11in the range of a transition of the cutting tool or drill bit5from a first medium having a first density to a second medium having a different second density during a cutting or drilling process.

As illustrated inFIG.2multiple reference graphs GRefcan be stored in the digital data storage, representing various drilling or cutting characteristics. The processing unit14is suitably programmed to repeat the step of quantifying the agreement between the recorded graph G or the at least one portion of the recorded graph G to the reference graphs GRefby means of a similarity measure for all stored reference graphs GRefand finding the overall best fit between graph G and all reference graphs GRefto identify the position x of transition21in the recorded graph G.

Each of the one or more reference graphs GRefdefines a reference point of a transition21′ of the cutting tool or drill bit5from a first medium to a second medium, wherein the time window11includes a first time period before the reference point of a transition21′ and a second time period after the reference point of a transition21′. The processing unit14is suitably programmed to compare the recorded graph G or at least one portion of the recorded graph G with the at least one reference graph GRefby means of a similarity measure to quantify the agreement between the recorded graph G or at least one portion of the recorded graph G and the at least one reference graph GRefto find the position of a transition21in the recorded graph G. In the case that at least one portion of the recorded graph G is used for the comparison the at least one portion of the recorded graph G extends at least in a period of time as specified by the time window11. The processing unit14is programmed to compute in real-time. The digital data storage further stores a predefined threshold value for the similarity measure and the processing unit14is programmed to trigger a transition event and report the position x of transition21if the threshold value for similarity is reached.

A schematic representation of the process performed by the processing unit14in the case of drilling a hole through a bone is illustrated inFIG.3. The processing unit14can report two values for the position of a transition21of the drill bit5from a first medium to a second medium which occur at the positions where the cutting tip9of the drill bit9exits the near cortex [x(ta)], respectively the far cortex [x(tb)] of a bone so that the surgeon can then decide whether unicortical or bicortical bone screws are to be applied.

The digital data storage is particularly configured as a buffer to hold an actual time window of the current graph G of the distance [x(t)] at least as large as the window11of the reference graph GRef. Exemplarily but not limiting, each reference graph GRefis specified by about 30 values for the distance [x(t)] covered by a cutting tool or drill bit5which are subsequent with respect to time within the first time period before the reference point of a transition21′ and by about 10 values for the distance [x(t)] covered by a cutting tool or drill bit5which are subsequent with respect to time within the second time period after the reference point of a transition21′. Exemplarily, the first time period before the reference point of a transition21′ amounts to about 0.3 seconds and the second time period after the reference point of a transition21′ amounts to about 0.3 seconds. Additionally, the reference data inherently require a positive advance velocity v>0 of the cutting tool or drill bit5in the first time period before reaching the reference point of a transition21′. The similarity measure applied to select the portion of the graph G which best fits the reference graph GRefto find the position x of transition21in the recorded graph G can be a pattern recognition approach, exemplarily but not limiting a shape context descriptor. The reference data specifies a statistical representation of a plurality of prospectively recorded graphs G in the range of a transition of a cutting tool or drill bit5from a first medium having a first density to a second medium having a different second density during a cutting or drilling process. Furthermore, the reference data are continuously amended according to the use of the cutting or drilling device, wherein the amendment of the reference data can be performed by machine learning algorithms, preferably by involving use of a neural network.

The measuring device1particularly measures and records the relative motion between the displaceable second member4and the first member3which is fixed with respect to the housing12. Since the drill bit5is firmly clamped in the chuck6the relative motion between the displaceable second member4and the first member3coincides with the relative motion of the cutting tip9of the drill bit5with respect to the front end10of the displaceable second member4. Therefore, the measuring device1measures and records the relative motion of the drill bit5in the drilling direction in real time with respect to the bone surface or to the surface of an implant on which the front end10of the displaceable second member4of the measuring device1abuts. The motion of the drill bit5relative to the displaceable second member4of the measuring device1is a one-dimensional translational motion and the position x of the cutting tip9of the drill bit5relative to the front end10of the displaceable second member4at any moment is given by the x coordinate of the cutting tip9along the x-axis8which in this case forms the reference frame. The position x or x coordinate of the cutting tip9is set to 0 at the beginning of the drilling procedure, e.g. when the cutting tip9of the drill bit5is flush with the front end10of the displaceable second member4.

For this purpose the position x or x coordinate of the cutting tip9of the drill bit5with respect to time is recorded by the processing unit14which is integrated in the first member3of the measuring device1.

Exemplarily, but not limiting, the processing unit14is configured as a digital processing unit and comprises a microprocessor having a processor register to record the position of the second member4relative to the first member3. As described above the position of the second member4relative to the first member3coincides with the position x or x coordinate of the cutting tip9of the drill bit5relative to the front end10of the displaceable second member4.

The drill distance to the exit from the second cortex, i.e. the position x or x coordinate of the cutting tip9of the drill bit5when the cutting tip9exits the far cortex is automatically computed based on the process performed by the processing unit14. Based on this position x or x coordinate the required screw length, preferably including a safety margin can be estimated. For this purpose the processing unit14can comprise a data memory to store data related to bone screw lengths, preferably including safety margin, screw head length, tip section length and screw length increments.

The measuring device1and particularly the displacement sensors can be either integrated in the housing12or can be temporarily attachable thereto. In a temporarily attachable configuration the measuring device1comprises attachment means in the form of an adaptor15which is releasably affixable to the housing12of the surgical power drill2. This adaptor15is exemplarily but not limiting configured as an annular framework attachable to the housing12by means of a press fit or via a clamp collar. Alternatively, the measuring device1can comprise clamps to releasably affix the measuring device1to the housing12.

The measuring device1can comprise a wireless communication device, exemplarily configured as a Bluetooth module with signal conditioner. Via the wireless communication device the data may be transmitted wirelessly to an external computer with monitor, a tablet computer, a smartphone, a smartwatch or a smart glass to compute or indicate the derived information, i.e. the measured position of the cutting tip of the drill bit with respect to time, the computed velocity with respect to time and the computed point of transition may be transmitted wirelessly to an external device such as a computer with monitor, a tablet computer, a smartphone, a smartwatch or a smartglass. Alternatively, the derived data may be provided on a display or speaker locally mounted to the surgical power drill2.

Additionally, the measuring device1comprises a sterilizable casing16to enclose the processing unit14, the wireless communication device and the power supply22for the measuring device1, wherein the power supply22includes one or more rechargeable or non-rechargeable batteries arrangeable in the casing16.

Furthermore, the device25can additionally comprise a calibration device27as illustrated inFIGS.7and8and described in more detail below.

Another embodiment of the device25according to the invention is illustrated inFIG.4, wherein the device25ofFIG.2differs from the embodiment ofFIG.1only therein that the processing unit14is an external unit, e.g. a computer with monitor, a tablet computer, a smartphone, a smartwatch or a smartglass, and that the measuring device1comprises a wireless data transmission device17and the processing unit14includes a wireless data receiving device so that the measured distance x covered by the housing12in the direction of the longitudinal axis7and relative to a surface of an implant26or a bone can be transmitted from the measuring device1to the external processing unit14and recorded with respect to time. The external processing unit14can comprise a microprocessor similar to the embodiment ofFIG.1or can comprise a central processing unit.

A further embodiment of the device25according to the invention is illustrated inFIGS.5and6, wherein the measuring device1of the embodiment ofFIGS.5and6differs from the embodiment ofFIG.1therein that the first member3including the laser module18for emitting a laser beam and the receiver for triangulation, e.g. an electronic light sensor19in the form of a photodiode or a charge-coupled device (CCD) is configured as a part of an electronic module31. This electronic module31is insertable into a hollow space32formed in the handle33of the housing12, wherein the hollow space32extends from an opening34at the bottom of the handle33to the top part35of the housing12. The opening34can be closed by means of a cover36which is attachable to the bottom of the handle33.

Apart from the first member3the electronic module31comprises a display30which is arranged in an upper part37of the electronic module31, wherein this upper part37is shaped and dimensioned to fit into a respective cavity38configured in the top part35of the housing12. Furthermore, the electronic module31has a lower part40including the laser module18, the electronic light sensor19, the processing unit14and a power supply22for driving the surgical power drill2and for supplying the laser module18, the light sensor19and the processing unit14. Exemplarily, the power supply22can be a battery or an accumulator. The lower part40of the electronic module31is shaped and dimensioned to fit into the hollow space32in the handle33of the housing12. A laser window41is arranged at the front of the lower part40and just below the upper part37of the electronic module31so as to match the laser beam and the electronic light sensor19with respective windows42,43(FIG.6) in the housing12.

A first and a second sterile window42,43are arranged in the housing12of the surgical power drill2to provide windows for the laser beam emitted by the laser module18and the reflected beam received by the electronic light sensor19. The first and second sterile windows42,43are arranged in the front of the housing12and—when viewed in a front view—below the longitudinal axis7of the spindle13and located on opposite sides of a middle plane44of the surgical power drill2which contains the longitudinal axis7and at a distance from the middle plane44which permits the laser beam and the reflected beam to pass beside the spindle13and the chuck6of the surgical power drill2.

The top part35of the housing12forms a casing16for the display30, wherein the casing16is, exemplarily but not limiting, integral with the housing12of the surgical power drill2and encompasses the cavity38. This casing16comprises a third sterile window45for covering the display30. Further the casing16is arranged at the housing12opposite the handle33of the surgical power drill2. The third sterile window45is angled relative to a plane orthogonal to the longitudinal axis7of the spindle13and directed towards the rear end of the housing12.

Exemplarily but not limiting the measuring device1is suitably configured to control the rotational speed of the spindle13of the surgical power drill2so that the power supplied to the electric motor of the power drill2can be shut down when a peak is detected by means of the measuring device1to thereby prevent plunging of the drill bit5.

Again another embodiment of the device25according to the invention is illustrated inFIGS.12-15, wherein the measuring device1of the embodiment ofFIGS.12-15differs from the embodiment ofFIG.1therein that the first member3includes an electronic module31which comprises apart from the laser module18for emitting a laser beam and the receiver for triangulation, e.g. an electronic light sensor19in the form of a photodiode or a charge-coupled device (CCD) a display30. Further the electronic module31comprises the processing unit14and the power supply22for the measuring device1. The display30is arranged at the rear side46of the electronic module31. Similarly to the embodiment ofFIG.1the sterilizable casing16is attachable to the surgical power drill2and comprises a cavity38to receive the electronic module31. A sterile front window47is arranged in the front of the casing16to let through the laser beam emitted by the laser module18and the reflected beam reflected by means of the reflector20arranged at the second member4of the measuring device1.

The laser module18and the electronic light sensor19which receives the reflected beam to perform the triangulation are arranged laterally spaced from each other in the electronic module31so that—when viewed in a front view of the assembled first member3—the laser beam and the reflected beam pass above the longitudinal axis7of the spindle13.

The casing16comprises an adaptor15to secure the first member3of the measuring device1to the housing12, wherein the adaptor15is releasably affixable to the housing12of the surgical power drill2. This adaptor15is, exemplarily but not limiting, configured as an annular framework attachable to the housing12by means of a clamp collar48that is fixable, e.g. to the stationary part of the spindle13by means of a clamping screw49.

The clamp collar48is positioned at the casing16laterally offset with respect to a longitudinal central plane of the casing16to permit the laser beam and the reflected beam to pass beside the drill bit5. Furthermore, by means of the adaptor15the casing16is attached to the surgical power drill2at an angle with respect to the longitudinal axis7so that the laser beam is emitted at an angle to the longitudinal axis7permitting a reduced size of the reflector20of the second member4of the measuring device1.

The casing16is sterilizable and configured as a separate piece arranged on top of the housing10. The cavity38has an opening at the rear side of the casing16and can be closed by means of a lid51which is rotatable about an axis located at the lower side of the casing16and extending orthogonally to the longitudinal axis. The lid51comprises a sterile rear window52for covering the display30, wherein—when the lid51is closed —the rear window52is angled relative to a plane orthogonal to the longitudinal axis7of the spindle13and directed towards the rear end of the housing12.

Exemplarily but not limiting, an actuator53for a power switch of the electronic module31can be arranged at the inside of the lid51so that when the lid51is closed energy is supplied from the power supply22to the electronic components of the measuring device1. To operate the processing unit14, the laser module18and the electronic light sensor19one or more buttons54can be positioned at the rear side of the electronic module31. The sterile rear window52can be provided with recesses so as to provide weakened areas in the rear window52which permit to actuate the one or more buttons54when the lid51is in its closed position.

The processing unit14of the embodiments ofFIGS.1,4-6and12-15comprises a microprocessor or a central processing unit which includes a processor register to record the distance x covered by the housing12in the direction of the longitudinal axis7and relative to a surface of an implant26or a bone with respect to time during a drilling process.

It has to be noted that real-time feedback of current drill depth alone can be of high value for the surgeon. Further valuable information is delivered by the current drilling speed. This helps the surgeon to control his feed rate to avoid mechanical or heat damage of the bone or it can be used to estimate the bone quality.

FIG.16illustrates another embodiment of the reflector20which is not integral with or attached to a drill sleeve23. The reflector20is clampable onto the drill bit5in such a way that it can slide on the drill bit5so that the reflector20is independent from the configuration of the drill sleeve23. The reflector20has a disc shaped portion55and on each side adjoining thereto a clamping portion56comprising longitudinal slots so as to form tongues suitable to exert radial pressure onto the drill bit5.

The method for bone screw length estimation from drilling characteristics essentially comprises the steps: A) advancing the surgical power drill2coaxially to the longitudinal axis of the spindle13to drill a hole in a bone and by recording the position (x) of the cutting tip9of the drill bit5relative to a surface of a bone or of an implant26in the drilling direction with respect to time; B) determining the instant when the cutting tip9of the drill bit5exits a cortex of a bone by using the selected reference graph GRefand the reference position of the transition21′ of the drill bit5from a first medium to a second medium defined by the selected reference graph GRef; C) determining the distance [x(t)] covered by the drill bit5at the instant determined under step B); and D) selecting a bone screw having a length corresponding to the distance [x(t)] covered by the drill bit5determined under step C) under consideration of a predefined safety margin.

As described above the position x of the cutting tip9of the drill bit5relative to a surface of a bone or of an implant26in the drilling direction is set to zero at the beginning of the drilling process. However, this zero position of the cutting tip9of the drill bit5depends on the fact whether:1) the displaceable second member4comprises a drill sleeve23extending in the direction of the longitudinal axis7to the front end10of the second member4as illustrated inFIGS.3,4and11a-11e; or whether2) the drill sleeve is a separate member previously inserted in the soft tissue covering the bone to be treated; or whether3) the zero position of the cutting tip9is to be set with respect to an implant26, e.g. a bone plate. In case the drill bit5is guided in a drill sleeve23which during drilling contacts or attaches to a bone plate and hence doesn't allow the cutting tip9of the drill bit5to abut the upper surface of the bone plate (FIG.9) a calibration device27providing a physical stop28inside the drill sleeve23at a height corresponding with the upper surface of the bone plate can be used to determine the start point of the measurement (FIG.8). Alternatively, if the lengths of drill bit5and drill sleeve23are known, the start point can be computed from this data.

In the case of the above variant1) the method comprises before step A) the following steps:positioning the surgical power drill2relative to a bone so that the front end10of the displaceable second member4and the cutting tip9of the drill bit5abut a surface of a bone; andstoring the relative position as start point (x=0) for the measurement of the position x of the cutting tip9of the drill bit5relative to a surface of a bone in the drilling direction with respect to time.

In the case of the above variant2) the method comprises before step A) the following steps:positioning the surgical power drill2relative to a bone so that the front end10of the displaceable second member4abuts a drill sleeve23inserted in the soft tissue covering a bone to be treated; andadjusting the cutting tip9of the drill bit5secured in the chuck6of the surgical power drill2relative to the displaceable second member4so that the cutting tip9of the drill bit5abuts a surface of a bone; andstoring the relative position as start point (x=0) for the measurement of the position x of the cutting tip9of the drill bit5relative to a surface of a bone in the drilling direction with respect to time.

In the case of the above variant3) the method comprises before step A) the following steps (FIGS.9and10):positioning the drill bit5secured in the chuck6relative to the displaceable second member4by using a calibration device27(FIGS.7and8) so that front end10of the second member4contacts a surface29of the calibration device27and the cutting tip9of the drill bit5abuts a stop28protruding from the surface29of the calibration device27;storing the relative position as start point (x=0) for the measurement of the position x of the cutting tip9of the drill bit5relative to a surface of a bone or of an implant26in the drilling direction with respect to time; andpositioning the surgical power drill2relative to an implant26, e.g. a bone plate, so that the front end10of the displaceable second member4abuts a surface of the implant26(FIG.9).

FIG.17illustrates a further embodiment of the calibration device27. The reflector20as well as the calibration device27, e.g. illustrated inFIGS.7and8can be made for single use. In other embodiments the drill sleeve23according to one of the embodiments illustrated inFIGS.11a-11e,16and17can be configured as a disposable member as well and can for this purpose be connected to the calibration device27via a predetermined breaking point.