Surgical drill equipped with a measuring device to measure the length of a through-hole within a bone and measuring unit that can be coupled to a surgical drill

Abstract

A surgical drill (1) having: a support body (2) provided with a handle (3); a chuck (4) mounted rotatably on the support body (2) about an axis (5) of rotation and configured to tighten a drill bit (6) adapted to drill a hole (7) passing through a bone (8); and a measuring unit (11) that is configured to measure a length (L) of the through-hole (7) while drilling the through-hole (7) and is provided with a measuring device (12) configured to measure without contact a distance (D) that varies as the drill bit (6) penetrates the bone (8).

Description

[0001] SURGICAL DRILL EQUIPPED WITH A MEASURING DEVICE TO MEASURE THE LENGTH OF A THROUGH-HOLE WITHIN A BONE AND MEASURING UNIT THAT CAN BE COUPLED TO A SURGICAL DRILL

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This Patent Application claims priority from Italian Patent Application No. 102023000026718 filed on December 14, 2023, the entire disclosure of which is incorporated herein by reference.

[0004] TECHNICAL FIELD

[0005] The present invention relates to a surgical drill equipped with a measuring device to measure the length of a through-hole within a bone.

[0006] In addition, the present invention relates to a measuring unit that can be coupled to a surgical drill.

[0007] Lastly, the present invention relates to a method of measuring a length of a hole through a bone.

[0008] PRIOR ART

[0009] From clinical observations, a problem in orthopedic and trauma surgery is determining the required screw lengths, for example for bicortical screw placement, before inserting a screw into a bone fragment. Today's mechanical depth gauges are quite inaccurate, unreliable and difficult to handle, and this leads both to long surgery times (due to the time taken to measure the length of each individual hole) and sometimes to the insertion of screws that are too long, resulting in soft tissue irritation and pain, or screws that are too short, resulting in (partial or total) failure of osteosynthesis.

[0010] A surgical drill equipped with a depth measuring device is described in patent application W02015006296A1. This well-known surgical drill includes a telescopic rod with a sleeve that slides along the drill bit during operation and whose distal end engages the proximal surface of a bone, a brake mechanism suitable for stopping the movement of the telescopic rod relative to the drill bit, and an actuator that engages the brake mechanism in response to a control signal indicating when the drill bit penetrates the bone. A sensor measures the electrical current drawn by the drilling device's motor. When the drill bit perforates the distal side of the bone, the friction force generated by the drill bit rubbing against the bone suddenly decreases, resulting in a rapid decrease in the electrical current drawn by the motor. The sudden decrease in the current drawn by the motor is measured by a sensor, and a processor compares the change in the electrical current data received from the sensor with a predetermined threshold change in current or current drop level. The length of the drill bit extending beyond the distal end of the sleeve is measured using a depth scale or gauge attached to the telescopic rod. Alternatively, the length of the drill bit extending beyond the distal end of the sleeve is measured with a digital gauge. A drawback of this well-known surgical drill is that it includes two different measuring devices, the first one to detect when the drill bit comes out of a bone by measuring the electrical current drawn by the motor and the second to determine the drill depth, which involves a complex electrical and mechanical measuring system.

[0011] Another surgical drill provided with a depth measuring device is described in patent application US2015066030A1 . This well-known surgical drill includes a measuring device configured as a linear variable differential displacement transducer (LVDT) connected to the housing, wherein the measuring device is configured to measure the distance covered by the housing in the direction of the longitudinal axis and relative to a bone surface during a drilling process. The measuring device comprises a processing unit including one or more differentiators to determine the first and second time derivatives of the distance travelled with respect to time. Furthermore, the measuring device includes an additional sensor to measure the force applied to the drill bit and the use of a third signal indicating the instant in time when the drill bit comes out of the bone cortex, where the third signal is emitted when the second time derivative (acceleration) of the first signal (displacement) is greater than zero and the first time derivative of the second signal (force applied to the drill bit) is less than zero. A disadvantage of this well-known surgical drill is that, due to the rod connecting the movable drill bit to the sensor of the measuring device, the measuring device has an unhandy configuration that results in cumbersome handling for the surgeon. In addition, the rod obstructs the surgeon's view of the surgical site. Patent application US20231 13352A1 and patent application US2021307764A1 describe a surgical drill equipped with a measuring device to measure the length of a through-hole within a bone, wherein the measuring device is oriented towards the end of the drill bit and is configured to measure without contact a parallel distance between the measuring device and a reference surface arranged around the drill bit. Patent application US20231 13352A1 provides a peak detector that identifies an acceleration peak and / or a jerk peak when the drill bit comes out of the cortex of a bone; the position of the drill bit when it comes out of the cortex is calculated based on the acceleration and / or jerk peaks.

[0012] DESCRIPTION OF THE INVENTION

[0013] One object of the present invention is to provide a surgical drill equipped with a measuring device for measuring the length of a through-hole within a bone, and a measuring unit that can be coupled to a surgical drill, which allow the length of the hole to be measured quickly and accurately and, at the same time, are easy and inexpensive to manufacture.

[0014] A further object of the present invention is to provide a method of measuring a length of a hole through a bone.

[0015] The present invention provides a surgical drill equipped with a measuring device for measuring the length of a through-hole within a bone, a measuring unit that can be coupled to a surgical drill, and a method of measuring a length of a hole through a bone, as claimed in the attached claims.

[0016] The claims describe preferred embodiments of the present invention forming an integral part of the present specification.

[0017] BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting embodiments thereof, in which:

[0019] • Figure 1 is a schematic view of a surgical drill provided in accordance with the present invention and equipped with a measuring device to measure the length of a through-hole within a bone;

[0020] • Figures 2-6 are five schematic views showing the drilling of a through- hole within a bone;

[0021] • Figure 7 is a schematic view of a bone with a through-hole;

[0022] • Figures 8, 9 and 10 are three diagrams showing the evolution over time of the distance, speed and acceleration between the surgical drill and a reference surface while drilling the through-hole; and

[0023] • Figures 1 1 and 12 are schematic views of two alternative embodiments of the surgical drill in Figure 1 .

[0024] PREFERRED EMBODIMENTS OF THE INVENTION

[0025] In Figure 1 , number 1 indicates, as a whole, a surgical drill comprising a support body 2 provided with a handle 3.

[0026] The surgical drill also includes a chuck 4, which is mounted rotatably on the support body 2 about an axis 5 of rotation, is driven into rotation by a motor arranged in the support body 2 and is configured to tighten a drill bit 6 adapted to drill a hole 7 (shown in Figure 7) passing through a human bone 8 (shown schematically in Figures 2-7). As is known, the human bone 8 comprises an external cortical part 9 (i.e., a cortex), which is harder and more resistant, and an internal cancellous part 10, which is less hard and resistant (and greater in size).

[0027] The surgical drill further comprises a measuring unit 1 1 which is configured to measure a length L (shown in Figure 7) of the through-hole 7 while drilling the through-hole 7. That is, as soon as the surgeon has finished drilling the through- hole 7, the measuring unit 1 1 is capable of communicating to the surgeon the length L of the through-hole 7.

[0028] The measuring unit 1 1 comprises a measuring device 12 which is integral with the support body 2, oriented toward the end of the drill bit 6, and configured to measure without contact a distance D parallel to the axis 5 of rotation and existing between the measuring device 12 and a reference surface 13 which is in front of the measuring device 12. By way of example, the measuring device 12 consists of a time-of-flight (i.e. “ToF”) LIDAR laser distance sensor. The reference surface 13 may be any surface that is stationary (i.e., that does not move when drilling the through-hole 7) and is located in front of the measuring device 12; the reference surface 13 may for example be part of the bone 8 next to the point where the through-hole 7 is drilled, or the reference surface 13 that is “seen” by the measuring device 12 and with respect to which the distance D is measured may be the external surface of the bone 8 located next to the through-hole 7.

[0029] The measuring unit 11 comprises a processing device 14 which is connected to the measuring device 12 in order to cyclically receive the distance D measured by the measuring device 12. The processing device 14 is also configured, among other things, to calculate an advancement speed V of the drill bit 6 by deriving in time the distance D measured by the measuring device 12.

[0030] According to a preferred embodiment shown in Figure 1 , the measuring device 12 is arranged next to the chuck 4.

[0031] According to a preferred embodiment shown in Figure 1 , the measuring unit 11 comprises an annular-shaped fastener 15 that is fitted around the support body 2 next to the chuck 4 and supports at least the measuring device 12. In other words, the fastener 15 can be threaded around the support body 2 by passing through the chuck 4 and can therefore potentially be mounted on the support body 2 and removed from the support body 2; thus, the measuring unit 1 1 can be an accessory that is coupled to the surgical drill 1 when needed. Alternatively, the fastener 15 could be integrated into the support body 2 and therefore may not be removable from the support body 2.

[0032] In the embodiment shown in the attached figures, the fastener 15 also supports the processing device 14 which is thus connected to the measuring device 12 by physical wiring. According to an alternative embodiment, the processing device 14 could be physically separated from the fastener 15 and could therefore communicate with the measuring device 12 via radio frequency (e.g., using the Bluetooth® communication standard); in this embodiment, the processing device 14 could consist of software (“App”) installed in a mobile phone or in a tablet computer (which allow the measurement of the length L of the through-hole 7 to be displayed in real time).

[0033] The measuring unit 1 1 comprises a container 16, which is removable, houses on the inside all the other components of the measuring unit 1 1 , is made of sterilisable material (preferably plastic material) and can be attached to any type of surgical drill 1 (possibly via a universal adapter). In this way, the container 16 can be sterilized separately (i.e., when it is empty) and can thus be fitted around the measuring unit 11 to isolate the measuring unit 11 , i.e., to make the surgical drill 1 coupled to the measuring unit 1 1 sterile. In this respect, it is important to note that the measuring unit 1 1 is electrically powered by its own battery and communicates wirelessly and therefore does not require wires protruding from the container 16. The only peculiarity of the container 16 is that it has a transparent window at least in the area of the measuring device 12.

[0034] Lastly, the measuring unit 1 1 also includes a 3-axis accelerometer 17 which is configured to measure accelerations along three directions (axes) to which the support body 2 of the surgical drill 1 is subjected. The processing device 14 is also configured, among other things, to determine an angle of inclination of the axis 5 of rotation with respect to the vertical based on the acceleration measurements provided by the 3-axis accelerometer 17.

[0035] In Figures 2-6, the drilling of the hole 7 through the bone 8 is shown sequentially.

[0036] Initially (Figure 2), the drill bit 6 is rested against the external surface of the bone 8 and is therefore stationary waiting to start drilling the bone (8); when the drill bit 6 is in this position (i.e., it is stationary and in contact with the external surface of the bone 8), the operator of the surgical drill 1 (i.e., a surgeon) sends a calibration signal to the processing device 14 of the measuring unit 1 1 , resulting in the processing device 14 performing two operations: a distance Di is measured when the drill bit 6 is in contact with the external surface of the bone 8, and an initial angle of inclination of the axis 5 of rotation (i.e., of the support body 2) is determined with respect to the vertical before drilling the bone 8.

[0037] Once the calibration stage is completed, the operator activates the surgical drill 1 by rotating the drill bit 6 and therefore starting the drilling of the bone 8 (as shown in Figure 3). The processing device 14 is configured to determine an instant Ti of start of drilling of the bone 8. In particular, the processing device 14 is configured to determine the instant Ti of start of drilling of the bone 8 when the accelerations measured by the 3-axis accelerometer 17 in a predetermined frequency band exceed a threshold value; that is, when the drill bit 6 begins to rotate around the axis 5 of rotation and begins to penetrate the bone 8, a series of vibrations are generated at a certain frequency in the support body 2 which can be easily detected by the 3-axis accelerometer 17 to determine the instant Ti of start of drilling of the bone 8. When the drill bit 6 starts to perforate the external part 9 of the bone 8, which is harder and more resistant, the drill bit 6 advances at a (relatively) low speed Vi; as shown in Figures 8-10, this stage starts at instant Ti and ends at instant T2 when the drill bit 6 finishes crossing the external part 9 of the bone 8 and comes into contact with the internal part 10 of the bone 8 (Figure 4).

[0038] The processing device 14 is configured to determine the instant T20f first drilling of the external cortical part 9 when the advancement speed V of the drill bit 6 exceeds a threshold value THS after the instant Ti of start of drilling of the bone 8; that is, when the drill bit 6 passes from the external part 9 of the bone 8 to the internal part 10 of the bone 8, the advancement speed V of the drill bit 6 increases and therefore the processing device 14 determines the instant T2 of first drilling of the external cortical part 9, by detecting this increase in speed (i.e. , when the advancement speed V of the drill bit 6 exceeds the threshold value THS). According to a preferred embodiment, the processing device 14 is configured to calculate the instant T2 of first drilling of the external cortical part 9 anticipating by a predetermined time advance AT the instant at which the advancement speed V of the drill bit 6 exceeds the threshold value (THS) after the instant Ti of start of drilling of the bone 8; this takes into account the fact that the advancement speed V of the drill bit 6 exceeds the threshold value THS when the drill bit 6 is already in the internal part 10 of the bone 8 and therefore with a small delay (equal to the time advance AT) with respect to the actual instant T2 of first drilling of the external cortical part 9.

[0039] Next (Figure 4), the drill bit 6 starts to perforate the internal part 10 of the bone 8 that is less hard and resistant and therefore the drill bit 6 advances at a speed V2 which is medium (i.e., it is intermediate between an advancement speed V3 in air and the advancement speed Vi through the external part 9 of the bone 8); as shown in Figures 8-10, this stage begins at instant T2 and ends at an intermediate instant T3 when the drill bit 6 finishes crossing the internal part 10 of the bone 8 and comes into contact with the external part 9 of the bone 8 (Figure 5) on the opposite side of the point of entry into the bone 8. The processing unit 14 is configured to determine the intermediate instant T3 when the advancement speed V of the drill bit 6 drops below the threshold value THS after the instant T2 of first drilling of the external cortical part 9.

[0040] Next (Figure 5), the drill bit 6 starts to perforate the external part 9 of the bone 8 (on the opposite side of the point of entry into the bone 8), which is harder and more resistant, and therefore the drill bit 6 advances at speed Vi which is low (lower than speeds V2 and V3); as shown in Figures 8-10, this stage starts at instant T3 and ends at an instant T4 when the drill bit 6 finishes crossing the external part 9 of the bone 8 and exits the bone 8 (Figure 6).

[0041] Lastly (Figure 6), the drill bit 6 exits the bone 8 (on the opposite side of the point of entry into the bone 8) thus completing the drilling of the through-hole 7 and then switches to speed V3 which is high (higher than speeds Vi and V2) as it is an advancement in air.

[0042] The processing unit 14 is configured to determine an instant T4 of second drilling of the external cortical part 9 (i.e., an instant T4 of end of drilling of the bone 8) when the advancement speed V of the drill bit 6 exceeds the threshold value THS after the intermediate instant T3; that is, when the drill bit 6 passes from the external part 9 of the bone 8 to the air, the advancement speed V of the drill bit 6 increases and therefore the processing device 14 determines the instant T4 of second drilling of the external cortical part 9 (i.e., the instant T4 of end of drilling of the bone 8), by detecting this increase in speed (i.e., when the advancement speed V of the drill bit 6 exceeds the threshold value THS). According to a preferred embodiment, the processing device 14 is configured to calculate the instant T4 of second drilling of the external cortical part 9 (i.e., the instant T4 of end of drilling of the bone 8), anticipating by the predetermined time advance AT the instant at which the advancement speed V of the drill bit 6 exceeds the threshold value THS after the intermediate instant T3; this takes into account the fact that the advancement speed V of the drill bit 6 exceeds the threshold value THS when the drill bit 6 is already out of the external part 9 of the bone 8 and therefore with a small delay (equal to the time advance AT) with respect to the actual instant T4 of second drilling of the external cortical part 9 (i.e., the instant T4 of end of drilling of the bone 8).

[0043] The following describes how the measuring unit 1 1 (and in particular the processing device 14 of the measuring unit 1 1 ) determines the length L of the hole 7 passing through the bone 8 when drilling the through-hole 7.

[0044] As previously mentioned, the processing device 14 calculates the advancement speed V of the drill bit 6 by deriving in time the distance D measured by the measuring device 12. In fact, the drill bit 6 is axially (i.e., along the axis 5 of rotation) fully integral with the support body 2 and therefore the distance D travelled by the support body 2 is identical to the distance D travelled by the drill bit 6 (and vice versa).

[0045] At the beginning of the drilling of the through-hole 7, the processing device 14 determines, through the signal of the operator (surgeon), when the drill bit 6 is stationary and in contact with the external surface of the bone 8 which is used as the reference surface 13 for measuring the distance D. The processing device 14 determines the instant T1 of start of drilling of the bone 8 by detecting an increase in the vibrations measured by the 3-axis accelerometer 17; alternatively, the processing device 14 could determine the instant T1 of start of drilling of the bone 8 when the advancement speed V of the drill bit 6 increases (i.e., it goes from zero to a value higher than zero) after the operator (surgeon) has signalled that the drill bit 6 is stationary and in contact with the external surface of the bone 8.

[0046] The processing device 14 determines an intermediate stage of drilling of the bone 8 when the advancement speed V of the drill bit 6 increases (exceeds the threshold value THS) after the start instant T1 (i.e., it switches from the speed Vi of drilling of the harder and more resistant external part 9 of the bone 8 to the speed V2 of drilling of the internal part 10 of the bone 8). In other words, the processing device 14 determines the instant T2 of start of the intermediate stage of drilling of the bone 8 (i.e., the instant T2 of first drilling of the external cortical part 9) when the advancement speed V of the drill bit 6 increases after the start instant T1 (i.e., it switches from the speed Vi of drilling of the harder and more resistant external part 9 of the bone 8 to the speed V2 of drilling of the internal part 10 of the bone 8). Similarly, the processing device 14 determines the intermediate instant T3 when the advancement speed V of the drill bit 6 decreases after the instant T2 of first drilling of the external cortical part 9 (i.e., it switches from the speed V2 of drilling of the internal part 10 of the bone 8 to the speed Vi of drilling of the harder and more resistant external part 9 of the bone 8).

[0047] In other words, the processing device 14 determines, when the advancement speed V of the drill bit 6 increases after the start instant T1, the instant T2 of first drilling of the external cortical part 9 that is consecutive to the start instant T 1 and at which the intermediate stage of drilling of the bone 8 starts; furthermore, the processing device 14 determines, when the advancement speed

[0048] V of the drill bit 6 decreases after the instant T2 of first drilling of the external cortical part 9, the intermediate instant T3 that is consecutive to the instant T2 of first drilling of the external cortical part 9 and at which the intermediate stage of drilling of the bone 8 ends.

[0049] Lastly, the processing device 14 determines the instant T4 of second drilling of the external cortical part 9 (which is the end of the drilling of the bone 8 and is consecutive to the intermediate instant T3) when the advancement speed

[0050] V of the drill bit 6 increases again after the intermediate stage, i.e. after the intermediate instant T3 (i.e., it switches from the speed V2 of drilling of the harder and more resistant external part 9 of the bone 8 to the speed V3 of advancement in air); the instant T4 of second drilling of the external cortical part 9 can be determined simply by observing the change in the speed V of the drill bit 6.

[0051] Lastly, the processing device 14 calculates the length L of the through- hole 7 as the difference between a distance Di measured before the instant T1 of start of drilling of the bone 8 or at the instant T1 of start of drilling of the bone 8 (preferably, the measured distance Di is measured a little earlier than the start instant T1 when the drill bit 6 is still stationary and resting against the external surface of the bone 8) and a distance D4 measured at the instant T4 of second drilling of the external cortical part 9.

[0052] In summary, the processing device 14 is configured to: determine the instant T1 of start of drilling of the bone 8, determine the intermediate stage of drilling of the bone 8 when the advancement speed V of the drill bit 6 increases after the start instant T1, determine the instant T4 of end of drilling of the bone 8 when the advancement speed V of the drill bit 6 increases again after the intermediate stage; and calculate the length L of the through-hole 7 as the difference between the distance Di measured before the start instant Ti or at the start instant Ti and the distance D4 measured at the end instant T4.

[0053] As mentioned above, the processing device 14 is configured to assume that the drill bit 6 is resting on the bone 8 before the instant Ti of start of drilling of the bone 8; in particular, the processing device 14 is configured to receive a signal from the operator (the surgeon) indicating when the drill bit 6 is resting on the bone 8 and therefore the operator (the surgeon) is ready to start drilling the bone 8.

[0054] According to a preferred embodiment, the processing device 14 is configured to determine, by processing the measurements provided by the 3-axis accelerometer 17, the acceleration A along the axis 5 of rotation at the instant T2 of first drilling of the external cortical part 9 and at the instant T4 of second drilling of the external cortical part 9; the processing device 14 confirms the determination of the instant T2 of first drilling of the external cortical part 9 and of the instant T4 of second drilling of the external cortical part 9 only if the acceleration A along the axis 5 of rotation at the instant T2 of first drilling of the external cortical part 9 and at the instant T4 of second drilling of the external cortical part 9 exceeds a threshold value. In other words, the acceleration A along the axis 5 of rotation is used not to determine the instants T2 and T4 but to confirm the determination of the instants T2 and T4 so as to avoid “false positives" and thus detect any inconsistencies.

[0055] As mentioned above, the processing device 14 is configured to determine an initial angle of inclination of the axis 5 of rotation with respect to the vertical prior to the drilling of the bone 8; preferably, the processing device 14 is also configured to determine the angle of inclination of the axis 5 of rotation with respect to the vertical during the drilling of the bone 8, and thus signal to the operator (the surgeon) if a difference between the initial angle of inclination of the axis 5 of rotation with respect to the vertical prior to the drilling of the bone 8 and the angle of inclination of the axis 5 of rotation with respect to the vertical during the drilling of the bone 8 exceeds a threshold value. In this way, the operator (the surgeon) is helped and guided in keeping the surgical drill 1 always in the same position to drill a perfectly cylindrical hole 7.

[0056] According to a preferred embodiment, the measuring unit 1 1 comprises a screen 18 (schematically shown in Figure 1 ) displaying (if necessary) an arrow showing the operator (the surgeon) in which direction to move the handle 3 of the support body 2 to bring the angle of inclination of the axis 5 of rotation with respect to the vertical during the drilling of the bone 8 back to the initial angle of inclination of the axis 5 of rotation with respect to the vertical.

[0057] In summary, the start instant Ti corresponds to the moment in which the drill bit 6 starts perforating on one side the external part (cortex) 9 of the bone 8, entering the bone 8, and the instant T4 of second drilling of the external cortical part 9 corresponds to the moment in which the drill bit 6 finishes perforating on the opposite side the external part (cortex) 9 of the bone 8, exiting the bone 8, and therefore it coincides with the instant T4 of end of drilling of the bone 8.

[0058] According to a possible embodiment, the threshold value THS is between 2 and 4 mm / s and is preferably 3 mm / s, while the time advance AT is between 30 and 70 ms and is preferably 50 ms.

[0059] To summarize the above, the drilling of the through-hole 7 involves three main steps: calibration, drilling, and display of the results. Calibration is the first step and requires the operator (the surgeon) to position the drill bit 6 on the external surface of the bone 8, orienting it at the desired angle for drilling; by pressing a calibration button, the processing device 14 performs two initial operations: it detects (by using the 3-axis accelerometer 17) and memorizes the angle of inclination of the axis 5 of rotation with respect to the vertical and records the distance Di from the work surface via the measuring device 12. After a short calibration countdown, the system is ready to begin the procedure of drilling of the bone 8.

[0060] The start of the measurement (i.e., the determination of the instant T1 of start of drilling of the bone 8) is determined when the 3-axis accelerometer 17 detects the vibrations of the motor of the surgical drill 1 in operation. From now on, the processing device 14 performs, for example, 20 measurements per second (one every 50 milliseconds), constantly monitoring both the instantaneous distance D via the measuring device 12 and the advancement speed V (calculated as the first derivative of the distance D in time). The crucial point is the detection of the crossing of the external cortical part 9 and this is done by monitoring the advancement speed V: when a change in the advancement speed V that exceeds the threshold value THS is detected, it is assumed that an external cortical part 9 has been perforated, and the distance D2 or D4 is recorded, as measured with an advance equal to the time advance AT before the threshold value THS is exceeded. This approach allows the points of entry into and exit from the external cortical part 9 to be identified accurately.

[0061] Throughout the drilling of the bone 8, the processing device 14 also maintains constant control of the angle of inclination of the axis 5 of rotation with respect to the vertical (which must remain as constant as possible and therefore equal to the initial angle of inclination of the axis 5 of rotation with respect to the vertical detected prior to the drilling of the bone 8); if the surgical drill 1 changes its inclination significantly during the drilling of the bone 8, the screen 18 shows directional arrows that guide the operator (the surgeon) towards the correct alignment.

[0062] In the embodiment described above, the whole measurement process is based on the analysis of the advancement speed V of the drill bit 6, and the accelerations measured by the 3-axis accelerometer 17 are mainly used to detect the start of the drilling (i.e., to determine the instant T1 of start of drilling of the bone 8) through characteristic vibrations, whereas the passage through the external cortical part 9 is identified when the advancement speed V exceeds the threshold value THS. The 3-axis accelerometer 17 still maintains an important role as a secondary verification system: its data are used as a double check to confirm the actual crossing of the external cortical part 9, and this combined approach allows the reliability of the system to be increased and the false positives to be significantly reduced when detecting the actual crossing of the external cortical part 9.

[0063] According to an alternative embodiment, the processing device 14 does not use the advancement speed V of the drill bit 6 but uses instead the acceleration A of the support body 2 along the axis 5 of rotation measured by the 3-axis accelerometer 17; in this embodiment and with reference to what is shown in Figure 10, the processing device 14 is configured to: determine the instant T2 of first drilling of the external cortical part 9 when the acceleration A along the axis 5 of rotation as measured by the accelerometer 17 is positive and exceeds, in absolute value, a threshold value THA1 after the instant T 1 of start of drilling of the bone 8; determine the intermediate instant T3 when the acceleration along the axis 5 of rotation as measured by the accelerometer 17 is negative and exceeds, in absolute value, a threshold value THA2 after the instant T2 of first drilling of the external cortical part 9; and determine the instant T4 of second drilling of the external cortical part 9 when the acceleration along the axis 5 of rotation as measured by the accelerometer 17 is positive and exceeds, in absolute value, a third threshold value THA3. In absolute value, the three threshold values THA1 , THA2 and THA3 can be equal or different (as shown in Figure 10).

[0064] The processing device 14 provides the operator with continuous feedback via the screen 18, where the current distance D, the number of perforated external cortical parts 9, the total distance from an external cortical part 9 to an external cortical part 9, and any errors or signalling (such as an incorrect inclination of the surgical drill 1 ) can be read.

[0065] In the embodiment shown in Figures 1 and 1 1 , the measuring device 12 is integral with the support body 2 and points towards a reference surface 13 that is, in use, integral with the bone 8 (i.e., it does not move relative to the bone 8). In the embodiment shown in Figure 1 , the reference surface 13 is part of the bone 8 and arranged next to the through-hole 7. The embodiment shown in Figure 1 1 comprises a tubular guide element 19 (therefore centrally drilled), which is arranged around the drill bit 6 (i.e., it contains the drill bit 6 on the inside), allowing the drill bit 6 to slide freely in relation to the tubular guide element 19; the function of the tubular guide element 19 is mainly to guide the advance movement of the drill bit 6. In use (i.e., during the drilling of the bone 8), the tubular guide element 19 is rested against the external surface of the bone 8 and is maintained in contact with the external surface of the bone 8. In the embodiment shown in Figure 11 , the tubular guide element 19 supports a reflector 20 which is integral with the tubular guide element 19 and represents the reference surface 13 for the measuring device 12 (i.e., the measuring device 12 points at the reflector carried by the tubular guide element 19).

[0066] In the embodiment shown in Figure 12, the measuring device 12 is, in use, integral with the bone 8 and points towards a reference surface 13 which is integral with the support body 2. In particular, the measuring device 12 is attached to the tubular guide element 19, whereas the reflector 20 which is the reference surface 13 for the measuring device 12 (i.e., it is pointed at by the measuring device 12) is integral with the support body 2.

[0067] The embodiments described herein may be combined with each other without departing from the scope of protection of the present invention.

[0068] The surgical drill 1 described above has many advantages.

[0069] Firstly, the surgical drill 1 described above allows the length L of the hole to be measured in real time while drilling the hole 7 and therefore without any delay and without any additional operation. In other words, the surgeon simply has to drill the hole in the bone 8 in a fully conventional manner and, once the hole 7 has been drilled, the measuring unit 11 communicates the length L of the hole 7 to the surgeon.

[0070] In addition, the surgical drill 1 described above allows the length L of the hole 7 to be measured with extreme precision (with a measurement error of less than a millimetre).

[0071] Finally, the surgical drill 1 described above is relatively simple and inexpensive to make, as all the physical components of the measuring unit 1 1 are commercially available or easily manufactured.

[0072] It should be noted that the measuring unit 11 is substantially ‘universal1as it can be easily adapted to (mounted on) virtually all surgical drills on the market, even as an after-sales accessory.

[0073] LIST OF REFERENCE NUMBERS IN THE FIGURES

[0074] 1 surgical drill

[0075] 2 support body

[0076] 3 handle

[0077] 4 chuck 5 axis of rotation

[0078] 6 drill bit

[0079] 7 through-hole

[0080] 8 bone

[0081] 9 external part

[0082] 10 internal part

[0083] 11 measuring unit

[0084] 12 measuring device

[0085] 13 reference surface

[0086] 14 processing device

[0087] 15 fastener

[0088] 16 container

[0089] 17 accelerometer

[0090] 18 screen

[0091] 19 tubular guide element

[0092] 20 reflector

[0093] T instant of time

[0094] D distance

[0095] V speed

[0096] A acceleration

[0097] THS threshold speed value

[0098] THA1 threshold acceleration value

[0099] THA2 threshold acceleration value

[0100] THA3 threshold acceleration value

Claims

CLAIMS1) A surgical drill (1 ) comprising: a support body (2) provided with a handle (3); a chuck (4) mounted rotatably on the support body (2) about an axis (5) of rotation and configured to tighten a drill bit (6) adapted to drill a hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10); and a measuring unit (11 ) that is configured to measure a length (L) of the through-hole (7) while drilling the through-hole (7) and comprises a measuring device (12) configured to measure without contact a distance (D) that varies as the drill bit (6) penetrates the bone (8) and a processing device (14) configured to calculate an advancement speed (V) of the drill bit (6) by deriving in time the distance (D) measured by the measuring device (12); the surgical drill (1 ) is characterized in that the processing device (14) is configured to: determine an instant (Ti) of start of drilling of the bone (8); determine an intermediate stage of drilling of the bone (8) when the advancement speed (V) of the drill bit (6) increases after the start instant (Ti); determine an instant (T4) of end of drilling of the bone (8) when the advancement speed (V) of the drill bit (6) increases again after the intermediate stage; and calculate the length (L) of the through-hole (7) as the difference between a distance (Di) measured before the start instant (Ti) or at the start instant (Ti) and a distance (D4) measured at the end instant (T4).2) The surgical drill (1 ) according to claim 1 , wherein the processing device (14) is configured to: determine an instant (T2) of first drilling of the external cortical part (9) when the advancement speed (V) of the drill bit (6) exceeds a first threshold value (THS) after the instant (Ti) of start of drilling of the bone (8); determine an intermediate instant (T3) when the advancement speed (V) of the drill bit (6) drops below the first threshold value (THS) after the instant (T2) of first drilling of the external cortical part (9); and determine an instant (T4) of second drilling of the external cortical part (9) coinciding with the end instant (T4) when the advancement speed (V) of the drill bit (6) exceeds the first threshold value (THS) after the intermediate instant (T3).3) The surgical drill (1 ) according to claim 2, wherein the processing device (14) is configured to: calculate the instant (T2) of first drilling of the external cortical part (9) anticipating by a predetermined time advance (AT) the instant at which the advancement speed (V) of the drill bit (6) exceeds the first threshold value (THS) after the instant (T1) of start of drilling of the bone (8); and calculate the instant (T4) of second drilling of the external cortical part (9) anticipating by the predetermined time advance (AT) the instant at which the advancement speed (V) of the drill bit (6) exceeds the first threshold value (THS) after the intermediate instant (T3).4) The surgical drill (1 ) according to claim 2 or 3, wherein: the measuring unit (11 ) comprises an accelerometer (17) configured to measure the acceleration (A) of the support body (2) at least along the axis (5) of rotation; and the processing device (14) is configured to: determine, by processing the measurements provided by the accelerometer (17), the acceleration (A) along the axis (5) of rotation at the instant (T2) of first drilling of the external cortical part (9) and at the instant (T4) of second drilling of the external cortical part (9); and confirm the determination of the instant (T2) of first drilling of the external cortical part (9) and of the instant (T4) of second drilling of the external cortical part (9) only if the acceleration (A) along the axis (5) of rotation at the instant (T2) of first drilling of the external cortical part (9) or at the instant (T4) of second drilling of the external cortical part (9) exceeds a second threshold value.5) The surgical drill (1 ) according to claim 1 , wherein: the processing device (14) is configured to: determine, when the advancement speed (V) of the drill bit (6) increases after the start instant (T1), a first intermediate instant (T2) that is consecutive to the start instant (T1) and at which the intermediate stage of drilling of the bone starts (8); and determine, when the advancement speed (V) of the drill bit (6) decreases after the first intermediate instant (T2), a second intermediate instant (T3) that is consecutive to the first intermediate instant (T2) and at which the intermediate stage of drilling of the bone (8) ends; and the end instant (T4) is consecutive to the second intermediate instant (T3).6) The surgical drill (1 ) according to one of claims 1 to 5, wherein the processing device (14) is configured to assume that the drill bit (6) is resting on the bone (8) before the instant (Ti) of start of drilling of the bone (8).7) The surgical drill (1 ) according to claim 6, wherein the processing device (14) is configured to receive a signal from an operator indicating when the drill bit (6) is resting on the bone (8) and therefore the operator is ready to start drilling the bone (8).8) The surgical drill (1 ) according to one of claims 1 to 7, wherein the measuring unit (1 1 ) comprises an accelerometer (17) configured to measure the acceleration (A) of the support body (2) at least along the axis (5) of rotation.9) The surgical drill (1 ) according to claim 8, wherein the processing device (14) is configured to determine the instant (Ti) of start of drilling of the bone (8) as a function of the acceleration (A) measured by the accelerometer (17) and in particular when the acceleration (A) measured by the accelerometer (17) in a predetermined frequency band exceeds a first threshold value.10) The surgical drill (1 ) according to one of claims 1 to 9, wherein the processing device (14) is configured to determine an angle of inclination of the axis (5) of rotation with respect to the vertical.11) The surgical drill (1 ) according to claim 10, wherein the processing device (14) is configured to: determine an initial angle of inclination of the axis (5) of rotation with respect to the vertical prior to the drilling of the bone (8), determine the angle of inclination of the axis (5) of rotation with respect to the vertical during the drilling of the bone (8), and signal to a user if a difference between the initial angle of inclination of the axis (5) of rotation with respect to the vertical prior to the drilling of the bone (8) and the angle of inclination of the axis (5) of rotation with respect to the vertical during the drilling of the bone (8) exceeds a fourth threshold value.12) The surgical drill (1 ) according to claim 1 1 , wherein the processing device (14) is configured to receive a signal from an operator indicating when the drill bit (6) is resting on the bone (8), and therefore the operator is ready to start drilling the bone (8), and to determine the initial angle of inclination of the axis (5) of rotation with respect to the vertical when it receives the signal from theoperator.13) The surgical drill (1 ) according to claim 1 1 or 12, wherein the measuring unit (1 1 ) comprises a screen (18) displaying an arrow showing the operator in which direction to move the handle (3) of the support body (2) to bring the angle of inclination of the axis (5) of rotation with respect to the vertical during the drilling of the bone (8) back to the initial angle of inclination of the axis (5) of rotation with respect to the vertical.14) The surgical drill (1 ) according to one of claims 1 to 13, wherein the measuring device (12) is integral with the support body (2) and points towards a reference surface (13) which, in use, is integral with the bone (8).15) The surgical drill (1 ) according to claim 14, wherein the reference surface (13) is part of the bone (8) and arranged next to the through-hole (7).16) The surgical drill (1 ) according to one of claims 1 to 13, wherein the measuring device (12) is, in use, integral with the bone (8) and points towards a reference surface (13) which is integral with the support body (2).17) The surgical drill (1 ) according to claim 16, comprising a tubular guide element (19) which is arranged around the drill bit (6) and, in use, is rested against an external surface of the bone (8) and supports the measuring device (12).18) A measuring unit (1 1 ) configured to be mounted on a support body (2) of a surgical drill (1 ) provided with a chuck (4) mounted rotatable and supporting a drill bit (6) adapted to drill a through-hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10) so as to measure a length (L) of the through-hole (7) while drilling the through-hole (7); the measuring unit (1 1 ) comprises a measuring device (12) configured to measure without contact a distance (D) that varies as the drill bit (6) penetrates the bone (8) and a processing device (14) configured to calculate an advancement speed (V) of the drill bit (6) by deriving in time the distance (D) measured by the measuring device (12); the measuring unit (11 ) is characterized in that the processing device (14) is configured to: determine an instant (T2) of start of drilling of the bone (8) when the advancement speed (V) of the drill bit (6) decreases the first time; determine an intermediate stage of drilling of the bone (8) when the advancementspeed (V) of the drill bit (6) increases after the start instant (T2); determine an instant (T5) of end of drilling of the bone (8) when the advancement speed (V) of the drill bit (6) increases again after the intermediate stage; and calculate the length (L) of the through-hole (7) as the difference between a distance (Di) measured at the start instant (T2) and a distance (D4) measured at the end instant (T5).19) A method of measuring a length (L) of a through-hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10) while drilling the through-hole (7) by means of a surgical drill (1 ) provided with a support body (2) on which a chuck (4) supporting a drill bit (6) is mounted rotatable about an axis (5) of rotation; the method comprising the steps of: measuring without contact, cyclically and by means of a measuring device (12), a distance (D) that varies as the drill bit (6) penetrates the bone (8); and calculating an advancement speed (V) of the drill bit (6) by deriving in time the distance (D) measured by the measuring device (12); the method is characterized in that it comprises the steps of: determining an instant (T2) of start of drilling of the bone (8) when the advancement speed (V) of the drill bit (6) decreases the first time; determining an intermediate stage of drilling of the bone (8) when the advancement speed (V) of the drill bit (6) increases after the start instant (T2); determining an instant (T5) of end of drilling of the bone (8) when the advancement speed (V) of the drill bit (6) increases again after the intermediate stage; and calculating the length (L) of the through-hole (7) as the difference between a distance (Di) measured at the start instant (T2) and a distance (D4) measured at the end instant (T5).20) A surgical drill (1 ) comprising: a support body (2) provided with a handle (3); a chuck (4) mounted rotatably on the support body (2) about an axis (5) of rotation and configured to tighten a drill bit (6) adapted to drill a hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10); anda measuring unit (11 ) that is configured to measure a length (L) of the through-hole (7) while drilling the through-hole (7) and comprises a measuring device (12) configured to measure without contact a distance (D) that varies as the drill bit (6) penetrates the bone (8) and a processing device (14) configured to calculate an advancement speed (V) of the drill bit (6) by deriving in time the distance (D) measured by the measuring device (12); the surgical drill (1 ) is characterized in that the processing device (14) is configured to: determine an instant (Ti) of start of drilling of the bone (8); determine an instant (T2) of first drilling of the external cortical part (9) when the advancement speed (V) of the drill bit (6) exceeds a first threshold value (THS) after the instant (T1) of start of drilling of the bone (8); determine an intermediate instant (T3) when the advancement speed (V) of the drill bit (6) drops below the first threshold value (THS) after the instant (T2) of first drilling of the external cortical part (9); determine an instant (T4) of second drilling of the external cortical part (9) when the advancement speed (V) of the drill bit (6) exceeds the first threshold value (THS) after the intermediate instant (T3); and calculate the length (L) of the through-hole (7) as the difference between a distance (Di) measured before or at the instant (T1) of start of drilling of the bone (8) and a distance (D4) measured at the instant (T4) of second drilling of the external cortical part (9).21) The surgical drill (1 ) according to claim 20, wherein the processing device (14) is configured to assume that the drill bit (6) is resting on the bone (8) before the instant (T1) of start of drilling of the bone (8).22) The surgical drill (1 ) according to claim 21 , wherein the processing device (14) is configured to receive a signal from an operator indicating when the drill bit (6) is resting on the bone (8) and therefore the operator is ready to start drilling the bone (8).23) The surgical drill (1 ) according to claim 20, 21 or 22, wherein the measuring unit (1 1 ) comprises an accelerometer (17) configured to measure the acceleration (A) of the support body (2) at least along the axis (5) of rotation.24) The surgical drill (1 ) according to claim 23, wherein the processing device (14) is configured to determine the instant (T1) of start of drilling of the bone (8) as a function of the acceleration (A) measured by the accelerometer25) The surgical drill (1 ) according to claim 23 or 24, wherein the processing device (14) is configured to determine the instant (Ti) of start of drilling of the bone (8) when the acceleration (A) measured by the accelerometer (17) in a predetermined frequency band exceeds a second threshold value.26) The surgical drill (1 ) according to claim 23, 24 or 25, wherein the processing device (14) is configured to: determine, by processing the measurements provided by the accelerometer (17), the acceleration (A) along the axis (5) of rotation at the instant (T2) of first drilling of the external cortical part (9) and at the instant (T4) of second drilling of the external cortical part (9); and confirm the determination of the instant (T2) of first drilling of the external cortical part (9) and of the instant (T4) of second drilling of the external cortical part (9) only if the acceleration (A) along the axis (5) of rotation at the instant (T2) of first drilling of the external cortical part (9) or at the instant (T4) of second drilling of the external cortical part (9) exceeds a third threshold value.27) The surgical drill (1 ) according to one of claims 23 to 26, wherein the processing device (14) is configured to determine an angle of inclination of the axis (5) of rotation with respect to the vertical.28) The surgical drill (1 ) according to claim 27, wherein the processing device (14) is configured to: determine an initial angle of inclination of the axis (5) of rotation with respect to the vertical prior to the drilling of the bone (8), determine the angle of inclination of the axis (5) of rotation with respect to the vertical during the drilling of the bone (8), and signal to a user if a difference between the initial angle of inclination of the axis (5) of rotation with respect to the vertical prior to the drilling of the bone (8) and the angle of inclination of the axis (5) of rotation with respect to the vertical during the drilling of the bone (8) exceeds a fourth threshold value.29) The surgical drill (1 ) according to claim 28, wherein the processing device (14) is configured to receive a signal from an operator indicating when the drill bit (6) is resting on the bone (8), and therefore the operator is ready to start drilling the bone (8), and to determine the initial angle of inclination of the axis (5) of rotation with respect to the vertical when it receives the signal from theoperator.30) The surgical drill (1 ) according to claim 29, wherein the measuring unit (1 1 ) comprises a screen (18) displaying an arrow showing the operator in which direction to move the handle (3) of the support body (2) to bring the angle of inclination of the axis (5) of rotation with respect to the vertical during the drilling of the bone (8) back to the initial angle of inclination of the axis (5) of rotation with respect to the vertical.31) The surgical drill (1 ) according to one of claims 20 to 30, wherein the processing device (14) is configured to calculate the instant (T2) of first drilling of the external cortical part (9) anticipating by a predetermined time advance (AT) the instant at which the advancement speed (V) of the drill bit (6) exceeds the first threshold value (THS) after the instant (T1) of start of drilling of the bone (8); and calculate the instant (T4) of second drilling of the external cortical part (9) anticipating by the predetermined time advance (AT) the instant at which the advancement speed (V) of the drill bit (6) exceeds the first threshold value (THS) after the intermediate instant (T3).32) The surgical drill (1 ) according to one of claims 20 to 31 , wherein the measuring device (12) is integral with the support body (2) and points towards a reference surface (13) which, in use, is integral with the bone (8).33) The surgical drill (1 ) according to claim 32, wherein the reference surface (13) is part of the bone (8) and arranged next to the through-hole (7).34) The surgical drill (1 ) according to one of claims 20 to 31 , wherein the measuring device (12) is, in use, integral with the bone (8) and points towards a reference surface (13) which is integral with the support body (2).35) The surgical drill (1 ) according to claim 34, comprising a tubular guide element (19) which is arranged around the drill bit (6) and, in use, is rested against an external surface of the bone (8) and supports the measuring device (12).36) A measuring unit (1 1 ) configured to be mounted on a support body (2) of a surgical drill (1 ) provided with a chuck (4) mounted rotatable and supporting a drill bit (6) adapted to drill a through-hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10) so as to measure a length (L) of the through-hole (7) while drilling the through-hole (7);the measuring unit (1 1 ) comprises a measuring device (12) configured to measure without contact a distance (D) that varies as the drill bit (6) penetrates the bone (8) and a processing device (14) configured to calculate an advancement speed (V) of the drill bit (6) by deriving in time the distance (D) measured by the measuring device (12); the measuring unit (11 ) is characterized in that the processing device (14) is configured to: determine an instant (Ti) of start of drilling of the bone (8); determine an instant (T2) of first drilling of the external cortical part (9) when the advancement speed (V) of the drill bit (6) exceeds a first threshold value (THS) after the instant (T1) of start of drilling of the bone (8); determine an intermediate instant (T3) when the advancement speed (V) of the drill bit (6) drops below the first threshold value (THS) after the instant (T2) of first drilling of the external cortical part (9); determine an instant (T4) of second drilling of the external cortical part (9) when the advancement speed (V) of the drill bit (6) exceeds the first threshold value (THS) after the intermediate instant (T3); and calculate the length (L) of the through-hole (7) as the difference between a distance (Di) measured before or at the instant (T1) of start of drilling of the bone (8) and a distance (D4) measured at the instant (T4) of second drilling of the external cortical part (9).37) A method of measuring a length (L) of a through-hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10) while drilling the through-hole (7) by means of a surgical drill (1 ) provided with a support body (2) on which a chuck (4) supporting a drill bit (6) is mounted rotatable about an axis (5) of rotation; the method comprises the steps of: measuring without contact, cyclically and by means of a measuring device (12), a distance (D) that varies as the drill bit (6) penetrates the bone (8); and calculating an advancement speed (V) of the drill bit (6) by deriving in time the distance (D) measured by the measuring device (12); the method is characterized in that it comprises the steps of: determining an instant (T1) of start of drilling of the bone (8); determining an instant (T2) of first drilling of the external cortical part (9) when the advancement speed (V) of the drill bit (6) exceeds a first threshold value(THS) after the instant (Ti) of start of drilling of the bone (8); determining an intermediate instant (T3) when the advancement speed (V) of the drill bit (6) drops below the first threshold value (THS) after the instant (T2) of first drilling of the external cortical part (9); determining an instant (T4) of second drilling of the external cortical part (9) when the advancement speed (V) of the drill bit (6) exceeds the first threshold value (THS) after the intermediate instant (T3); and calculating the length (L) of the through-hole (7) as the difference between a distance (Di) measured before or at the instant (T1) of start of drilling of the bone (8) and a distance (D4) measured at the instant (T4) of second drilling of the external cortical part (9).38) A surgical drill (1 ) comprising: a support body (2) provided with a handle (3); a chuck (4) mounted rotatably on the support body (2) about an axis (5) of rotation and configured to tighten a drill bit (6) adapted to drill a hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10); and a measuring unit (11 ) that is configured to measure a length (L) of the through-hole (7) while drilling the through-hole (7) and comprises a measuring device (12) configured to measure without contact a distance (D) that varies as the drill bit (6) penetrates the bone (8) and a processing device (14); the surgical drill (1 ) is characterized in that the measuring device (12) comprises: an accelerometer (17) configured to measure the acceleration (A) of the support body (2) at least along the axis (5) of rotation; and a processing device (14) configured to: determine an instant (T1) of start of drilling of the bone (8) as a function of the acceleration (A) measured by the accelerometer (17); determine an instant (T2) of first drilling of the external cortical part (9) when the acceleration (A) along the axis (5) of rotation as measured by the accelerometer (17) is positive and exceeds, in absolute value, a first threshold value (THA1 ) after the instant (T1) of start of drilling of the bone (8); determine an intermediate instant (T3) when the acceleration (A) along the axis (5) of rotationas measured by the accelerometer (17) is negative and exceeds, in absolute value, a second threshold value (THA2) after the instant (T2) of first drilling of the external cortical part (9); determine an instant (T4) of second drilling of the external cortical part (9) when the acceleration (A) along the axis (5) of rotation as measured by the accelerometer (17) is positive and exceeds, in absolute value, a third threshold value (THA3); and calculate the length (L) of the through- hole (7) as the difference between a distance (Di) measured before or at the instant (T1) of start of drilling of the bone (8) and a distance (D4) measured at the instant (T4) of second drilling of the external cortical part (9).39) The surgical drill (1 ) according to claim 38, wherein the processing device (14) is configured to assume that the drill bit (6) is resting on the bone (8) before the instant (T1) of start of drilling of the bone (8).40) The surgical drill (1 ) according to claim 39, wherein the processing device (14) is configured to receive a signal from an operator indicating when the drill bit (6) is resting on the bone (8) and therefore the operator is ready to start drilling the bone (8).41) The surgical drill (1 ) according to claim 38, 39 or 40, wherein the processing device (14) is configured to determine the instant (T1) of start of drilling of the bone (8) when the acceleration (A) measured by the accelerometer (17) in a predetermined frequency band exceeds a fourth threshold value.42) The surgical drill (1 ) according to one of claims 38 to 41 , wherein the processing device (14) is configured to determine an angle of inclination of the axis (5) of rotation with respect to the vertical as a function of the acceleration (A) measured by the accelerometer (17).43) The surgical drill (1 ) according to claim 42, wherein the processing device (14) is configured to: determine an initial angle of inclination of the axis (5) of rotation with respect to the vertical prior to the drilling of the bone (8), determine the angle of inclination of the axis (5) of rotation with respect to the vertical during the drilling of the bone (8), and signal to a user if a difference between the initial angle of inclination of the axis (5) of rotation with respect to the vertical prior to the drilling of the bone (8) and the angle of inclination of the axis (5) of rotation with respect to the vertical during the drilling of the bone (8) exceeds a fourththreshold value.44) The surgical drill (1 ) according to claim 43, wherein the processing device (14) is configured to receive a signal from an operator indicating when the drill bit (6) is resting on the bone (8), and therefore the operator is ready to start drilling the bone (8), and to determine the initial angle of inclination of the axis (5) of rotation with respect to the vertical when it receives the signal from the operator.45) The surgical drill (1 ) according to claim 44, wherein the measuring unit (1 1 ) comprises a screen (18) displaying an arrow showing the operator in which direction to move the handle (3) of the support body (2) to bring the angle of inclination of the axis (5) of rotation with respect to the vertical during the drilling of the bone (8) back to the initial angle of inclination of the axis (5) of rotation with respect to the vertical.46) The surgical drill (1 ) according to one of claims 38 to 45, wherein the measuring device (12) is integral with the support body (2) and points towards a reference surface (13) which, in use, is integral with the bone (8).47) The surgical drill (1 ) according to claim 46, wherein the reference surface (13) is part of the bone (8) and arranged next to the through-hole (7).48) The surgical drill (1 ) according to one of claims 38 to 45, wherein the measuring device (12) is, in use, integral with the bone (8) and points towards a reference surface (13) which is integral with the support body (2).49) The surgical drill (1 ) according to claim 48, comprising a tubular guide element (19) which is arranged around the drill bit (6) and, in use, is rested against an external surface of the bone (8) and supports the measuring device (12).50) A measuring unit (1 1 ) configured to be mounted on a support body (2) of a surgical drill (1 ) provided with a chuck (4) mounted rotatable and supporting a drill bit (6) adapted to drill a through-hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10) so as to measure a length (L) of the through-hole (7) while drilling the through-hole (7); the measuring unit (1 1 ) comprises a measuring device (12) configured to measure without contact a distance (D) that varies as the drill bit (6) penetrates the bone (8);the measuring unit (1 1 ) is characterized in that it comprises: an accelerometer (17) configured to measure the acceleration (A) of the support body (2) at least along the axis (5) of rotation; and a processing device (14) configured to: determine an instant (Ti) of start of drilling of the bone (8) as a function of the acceleration (A) measured by the accelerometer (17); determine an instant (T2) of first drilling of the external cortical part (9) when the acceleration (A) along the axis (5) of rotation as measured by the accelerometer (17) is positive and exceeds, in absolute value, a first threshold value (THA1 ) after the instant (T1) of start of drilling of the bone (8); determine an intermediate instant (T3) when the acceleration (A) along the axis (5) of rotation as measured by the accelerometer (17) is negative and exceeds, in absolute value, a second threshold value (THA2) after the instant (T2) of first drilling of the external cortical part (9); determine an instant (T4) of second drilling of the external cortical part (9) when the acceleration (A) along the axis (5) of rotation as measured by the accelerometer (17) is positive and exceeds, in absolute value, a third threshold value (THA3); and calculate the length (L) of the through- hole (7) as the difference between a distance (Di) measured before or at the instant (T1) of start of drilling of the bone (8) and a distance (D4) measured at the instant (T4) of second drilling of the external cortical part (9).51) A method of measuring a length (L) of a through-hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10) while drilling the through-hole (7) by means of a surgical drill (1 ) provided with a support body (2) on which a chuck (4) supporting a drill bit (6) is mounted rotatable about an axis (5) of rotation; the method comprises the step of measuring without contact, cyclically and by means of a measuring device (12), a distance (D) that varies as the drill bit (6) penetrates the bone (8); the method is characterized in that it comprises the steps of: measuring, by means of an accelerometer (17), the acceleration (A) of the support body (2) at least along the axis (5) of rotation; determining an instant (T1) of start of drilling of the bone (8) as a function of the acceleration (A) measured by the accelerometer (17);determining an instant (T2) of first drilling of the external cortical part (9) when the acceleration (A) along the axis (5) of rotation as measured by the accelerometer (17) is positive and exceeds, in absolute value, a first threshold value (THA1 ) after the instant (T1) of start of drilling of the bone (8); determining an intermediate instant (T3) when the acceleration (A) along the axis (5) of rotation as measured by the accelerometer (17) is negative and exceeds, in absolute value, a second threshold value (THA2) after the instant (T2) of first drilling of the external cortical part (9); determining an instant (T4) of second drilling of the external cortical part (9) when the acceleration (A) along the axis (5) of rotation as measured by the accelerometer (17) is positive and exceeds, in absolute value, a third threshold value (THA3); and calculating the length (L) of the through-hole (7) as the difference between a distance (Di) measured before or at the instant (T1) of start of drilling of the bone (8) and a distance (D4) measured at the instant (T4) of second drilling of the external cortical part (9).52) A surgical drill (1 ) comprising: a support body (2) provided with a handle (3); a chuck (4) mounted rotatably on the support body (2) about an axis (5) of rotation and configured to tighten a drill bit (6) adapted to drill a hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10); and a measuring unit (1 1 ) that is configured to measure a length (L) of the through-hole (7) while drilling the through-hole (7) and comprises a measuring device (12) configured to measure without contact a distance (D) that varies as the drill bit (6) penetrates the bone (8) and a processing device (14); the surgical drill (1 ) is characterized in that the measuring device (12) is, in use, integral with the bone (8) and points towards a reference surface (13) which is integral with the support body (2).53) The surgical drill (1 ) according to claim 52, comprising a tubular guide element (19) which is arranged around the drill bit (6) and, in use, is rested against an external surface of the bone (8) and supports the measuring device (12).54) A measuring unit (1 1 ) configured to be mounted on a support body (2) of a surgical drill (1 ) provided with a chuck (4) mounted rotatable and supporting a drill bit (6) adapted to drill a through-hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10) so as to measure a length (L) of the through-hole (7) while drilling the through-hole (7); the measuring unit (1 1 ) comprises a measuring device (12) configured to measure without contact a distance (D) that varies as the drill bit (6) penetrates the bone (8); the measuring unit (11 ) is characterized in that the measuring device (12) is, in use, integral with the bone (8) and points towards a reference surface (13) which is integral with the support body (2).55) The measuring unit (1 1 ) according to claim 54 and comprising a tubular guide element (19) which is arranged around the drill bit (6) and, in use, is rested against an external surface of the bone (8) and supports the measuring device (12).56) A method of measuring a length (L) of a through-hole (7) passing through a bone (8) having an external cortical part (9) and an internal cancellous part (10) while drilling the through-hole (7) by means of a surgical drill (1 ) provided with a support body (2) on which a chuck (4) supporting a drill bit (6) is mounted rotatable about an axis (5) of rotation; the method comprises the step of measuring without contact, cyclically and by means of a measuring device (12), a distance (D) that varies as the drill bit (6) penetrates the bone (8); the method is characterized in that the measuring device (12) is, in use, integral with the bone (8) and points towards a reference surface (13) which is integral with the support body (2).57) The measuring method according to claim 56, comprising a tubular guide element (19) which is arranged around the drill bit (6) and, in use, is rested against an external surface of the bone (8) and supports the measuring device (12).

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