WO2025264915A1 - Determining a state arising during a medical procedure involving a bone via monitoring acoustic emissions - Google Patents

Abstract

A system for determining one or more states arising during a medical procedure in which force is applied to a bone via a medical component includes a sensor responsive to acoustic emissions during the medical procedure. The sensor is configured to be placed in acoustic connection with at least one of the bone and the medical component during the medical procedure. The system further includes electronic circuitry in communicative connection with the sensor. The electronic circuitry is configured to analyze data from the sensor over time during the medical procedure to determine the one or more states on the basis of predetermined criteria.

Description

DETERMINING A STATE ARISING DURING A MEDICAL PROCEDURE

INVOLVING A BONE VIA MONITORING ACOUSTIC EMISSIONS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of U.S. Provisional Patent Application Serial

No. 63/662,125, filed June 20, 2024, the disclosure of which is incorporated herein by reference.

BACKGROUND ART

[0002] The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference.

[0003] In a number of medical procedures (including, for example, surgical procedures and non-surgical or minor procedures) involving application of forces to bones, there is a risk of injury resulting, for example, from bone fracture or instrument movement. In cranial surgery, for example, commercially available skull clamps include skull pins, which are typically singleuse devices including a point, shaft, and clamp insertion end (FIG. 1). A plurality of (for example, three) pins are inserted into three sockets within an Integra Life Sciences Mayfield

(or similar device with variable pin number and position) skull clamp (FIG. 2) and are pushed into the skin and onto the skull to ensure immobilization of the head for neurosurgical procedures.

[0004] In rare but occasionally catastrophic cases, the force applied to the skull by the clamp through a force application pin leads to skull fracture, destabilizing the head clamp and putting the patient at risk of additional complications. Of greatest concern is the risk of the fracture line or penetrating pin lacerating the underlying soft tissues of the brain, intracranial vessels, and lining of the brain known as the dura mater. Such injury can result in catastrophic bleeding that may be undetected for many hours during the surgery. In such cases, intervention may not occur until detection of the complication on post-operative examination or imaging.

[0005] Far more common than skull fracture, with an incidence rate on the order of at least hundreds of cases per year on average, patients sustain injuries associated with movement or slipping of the head within the clamp due to inadequate clamping pressure. In many of these cases, the injury is in the form of a scalp laceration of sizable length that requires surgical closure.

[0006] A number of systems have been developed for acoustic emission (AE) detection and interpretation in materials science. There are, for example, a number of studies wherein beams of rock which were subjected to three-point bending at various load levels were instrumented for detection of AE. Such studies demonstrated that an AE event rate followed a distinguishable pattern that was similar across cases and might be indicative of failure. See, for example, Winner, R. A., Lu, G., Prioul, R., Aidagulov, G., & Bunger, A. P., Acoustic emission and kinetic fracture theory for time-dependent breakage of granite. Engineering Fracture

Mechanics, 199, 101-113 (2018). Similar patterns of failure precursors in bone have not been identified.

SUMMARY OF THE INVENTION

[0007] A system for determining one or more states arising during a medical procedure (for example, a surgical procedure) in which force is applied to a bone (that is, to either a human bone or other animal bone) via a medical component includes a sensor responsive to acoustic emissions during the medical procedure. The sensor may be positioned during the medical procedure to receive acoustic emissions resulting from the medical procedure. In a number of embodiments, the sensor is configured to be placed in acoustic connection with at least one of the bone and the medical component during the medical procedure. Acoustic connection with the bone may, for example, be achieved via direct contact with the bone or via one or more intervening acoustically transmissive media. The system further includes electronic circuitry in communicative connection with the sensor. The electronic circuitry is configured to analyze data from the sensor over time during the medical procedure to determine the one or more states on the basis of predetermined criteria. The one or more states may include a state of the bone related to fracture thereof or a state of the medical component. In a number of embodiments, the electronic circuity is configured to output the one or more states during the medical procedure based upon monitoring of acoustic emission events over time. Changes in acoustic emission events or statistical characterization thereof over time are associated with the one or more states. In a number of embodiments, an acoustic emission event occurs when a sampled acoustic emission exceeds a determined threshold amplitude level. The electronic circuity may, for example, be configured to output at least one of a state of stability of the bone, a state of impending fracture of the bone, a state of fracture of the bone, a state of movement of the medical component relative to the bone, and a state of impending movement of the medical component relative to the bone. The electronic circuitry may be configured to output a plurality of states. In a number of embodiments, the medical component is a force application component of a clamp.

[0008] The predetermined criteria associated with the state of stability of the bone may include a decreasing acoustic emission event rate after force is either first applied or changed

(either, increased or decreased). The predetermined criteria associated with a fracture of the bone may include a period of acoustic emission following the first application of force or the increase in force which has a waveform exhibiting predetermined statistical properties. The predetermined criteria associated with a fracture of the bone which occurs during a period subsequent to force being either first applied or increased may include at least one of (i) a period of increased acoustic emission event frequency prior to fracture of the bone, increased acoustic emission event amplitude prior to the fracture of the bone, and a change in one or more quantifiable statistical properties of a time series of acoustic emission events, and (ii) and a period of acoustic emission which has a waveform exhibiting predetermined statistical properties following the fracture of the bone.

[0009] The electronic circuitry may include a processor system and a memory system in communicative connection with the processor system. The memory system may include one or more software algorithms stored therein and executable by the processor system to analyze data from the sensor. The electronic circuitry may further include a user interface system via which information regarding the one or more states may be provided to one or more individuals during the medical procedure.

[0010] The sensor (or sensors) may, for example, include at least one of a transducer, a microphone, an accelerometers, a vibrating wire, an inclinometer, a tiltmeter, and an optical interferometry system. In a number of embodiments, the sensor includes a transducer, optionally a transducer comprising a piezoelectric material. In a number of embodiments, the sensor includes a transducer.

[0011] The electronic circuitry may include an amplifier in connection with the sensor to receive an electrical signal output from the sensor. The electronic circuity may further include an analog-to digital converter in connection with an output of the amplifier, an output of the analog-to digital converter being in communicative connection with the processor system.

[0012] The medical component may be acoustically conducting, and the sensor may be in acoustical connection to the medical component or to an acoustically conducting second component which is acoustically connected to the medical component. Alternatively, the sensor is attached to a third component, which is different from the medical component, and the third component is an acoustic conducting component that contacts the bone or is in close proximity to the bone. The medical component may, for example, include a metal, the second component may, for example, include a metal, and/or the third component may, for example, include a metal. In a number of embodiments, the sensor is acoustically connected to the medical component. The sensor may, for example, be attached (that is, physically attached or connected) to the medical component.

[0013] The sensor may, for example, be acoustically connected to a force application pin of a clamp, a needle, a screw, or a fiducial. In a number of embodiments, the sensor is acoustically connected to the medical component, which is a force application pin of a clamp, or to the second component, which is a component of the skull clamp other than the force application pin of the clamp. The system may, for example, include a clamp such as a skull clamp. The skull clamp may include a plurality offorce application pins, and the system may include a plurality of sensors. One (or more) of the plurality of sensors may be acoustically connected to one of the plurality of force application pins, and another (or more) of the plurality of sensors may be acoustically connected to another of the plurality of force application pins.

[0014] A method for determining one or more states arising during a medical procedure in which force is applied to a bone via a medical component includes: placing a sensor responsive to acoustic emissions in acoustic connection with at least one of the bone and the medical component during the medical procedure, and analyzing the data from the sensor via electronic circuitry in communication with the sensor to determine the one or more states.

[0015] As described above, the predetermined criteria associated with the state of stability of the bone may include a decreasing acoustic emission event rate after force is either first applied or changed. The predetermined criteria associated with a fracture of the bone may include a period of acoustic emission following the first application offorce or the increase in force which has a waveform exhibiting predetermined statistical properties. The predetermined criteria associated with a fracture of the bone which occurs during a period subsequent to force being either first applied or increased may include at least one of (i) a period of increased acoustic emission event rate prior to fracture of the bone, increased acoustic emission event amplitude prior to the fracture of the bone, and a change in one or more quantifiable statistical propertied of a time series of acoustic emission events, and (ii) and a period of acoustic emission which has a waveform exhibiting predetermined statistical properties following the fracture of the bone. [0016] The electronic circuitry may include a processor system and a memory system in communicative connection with the processor system. The memory system may include one or more software algorithms stored therein and executable by the processor system to analyze data from the sensor. The electronic circuitry may further include a user interface system via which information regarding the one or more states may be provided to one or more individuals during the medical procedure.

[0017] As further described above, the sensor (or sensors) may, for example, include at least one of a transducer, a microphone, an accelerometers, a vibrating wire, an inclinometer, a tiltmeter, and an optical interferometry system. In a number of embodiments, the sensor includes a transducer, optionally a transducer comprising a piezoelectric material. In a number of embodiments, the sensor includes a transducer.

[0018] The electronic circuitry may include an amplifier in connection with the sensor to receive an electrical signal output from the sensor. The electronic circuity may further include an analog-to digital converter in connection with an output of the amplifier, an output of the analog-to digital converter being in communicative connection with the processor system.

[0019] The medical component may be acoustically conducting, and the sensor may be acoustically connected to the medical component or to an acoustically conducting second component which is acoustically connected to the medical component. Alternatively, the sensor may be acoustically connected to a third component, which is different from the medical component, and the third component is an acoustic conducting component that contacts the bone or is in close proximity to the bone. The medical component may, for example, include a metal, the second component may, for example, include a metal, and/or the third component may, for example, include a metal. In a number of embodiments, the sensor is acoustically connected to the medical component. The sensor may, for example, be physically attached or connected to the medical component.

[0020] The sensor may, for example, be acoustically connected to a force application pin of a clamp, a needle, a screw, or a fiducial. In a number of embodiments, the sensor is acoustically connected to the medical component, which is a force application pin of a clamp, or to the second component, which is a component of the skull clamp other than the force application pin of the clamp. The system may, for example, include a clamp such as a skull clamp. The skull clamp may include a plurality of force application pins, and the system may include a plurality of sensors. One (or more) of the plurality of sensors may be acoustically connected to one of the plurality offorce application pins, and another (or more) of the plurality of sensors may be acoustically connected to another of the plurality of force application pins.

[0021] A system for determining one or more states arising during a medical (for example, surgical) procedure in which force is applied to a skull includes a skull clamp including one or more force application components configured to apply force to the skull, and a sensor responsive to acoustic emissions during the medical procedure. The sensor is configured to be placed in acoustic connection with at least one of the skull and the skull clamp during the medical procedure. The system may further include electronic circuitry in communicative connection with the sensor. The electronic circuitry may be configured to analyze data from the sensor over time during the medical procedure to output the one or more states on the basis of predetermined criteria.

[0022] The one or more states may, for example, include a state of the skull related to fracture thereof or a state of the force application component. In a number of embodiments, the electronic circuity is configured to output at least one or a state of stability of the skull, a state of impending fracture of the skull, a state of fracture of the skull, a state of movement of the force application component relative to the bone, and a state of impending movement of the medical component relative to the bone. The predetermined criteria associated with the state of stability of the skull may, for example, include a decreasing acoustic emission event rate after force is either first applied or changed. The predetermined criteria associated with a fracture of the skull may, for example, include a period of acoustic emission following the first application of force or the increase in force which has a waveform exhibiting predetermined statistical properties. The predetermined criteria associated with a fracture of the skull which occurs during a period subsequent to force being either first applied or increased may include (i) at least one of a period of increased acoustic emission event rate prior to fracture of the skull, increased acoustic emission amplitude prior to the fracture of the skull, and a change in one or more quantifiable statistical propertied of a time series of acoustic emission events, and (ii) a period of acoustic emission which has a waveform exhibiting predetermined statistical properties following the fracture of the skull.

Observed changes in acoustic emission events over time may, for example, occur immediately upon application of force or in a delayed manner relative to the application of force.

[0023] A medical device includes a sensor in acoustic connection therewith. The sensor is responsive to acoustic emissions which may be created during a medical procedure (for example, during application offorce to a bone). The medical component or device may, for example, be a force-application component which is configured to apply force to a bone. The force-application component may, for example, be used to apply force in a clamp system. In a number of embodiments, the force application component is a force-application pin used in a skull clamp system.

[0024] The present devices, systems, and methods, along with the attributes and attendant advantages thereof, will best be appreciated and understood in view of the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0025] FIG. 1 illustrates schematically a commercially-available skull pin.

[0026] FIG. 2 illustrates schematically an embodiment of a commercially available skull clamp.

[0027] FIG. 3 illustrates schematically the skull clamp of FIG. 2 illustrating an acoustic sensor hereof attached at the pin on the single pin side of the skull clamp.

[0028] FIG. 4A illustrates a schematic illustration of a representative embodiment of an AE detecting pin hereof in which an AE transducer is placed in connection with a shaft of the pin.

[0029] FIG. 4B illustrates a photograph of a studied embodiment in which an AE transducer is attached to a shaft of a pin via a coupling or connector system.

[0030] FIG. 5 illustrates schematically a representative embodiment of electronic circuity hereof which includes a reading and recording system, including a pre-amplifier, an analog to digital conversion system, a data acquisition/analysis system, software for configuring the system and displaying data in real time, and a data storage system.

[0031] FIG. 6 illustrates relative locations of testing sites on a human skull, wherein testing notes for each site are included in Table 1 of FIG. 7 hereof.

[0032] FIG. 7 illustrates Table 1 setting forth testing notes for each test site illustrated in FIG.

6.

[0033] FIG. 8 illustrates graphically examples (a-c) of waveforms interpreted as AE generated from bone fracturing; wherein, in all cases the 200 microseconds prior to and 100 microseconds after the event is triggered are recorded (hence the timescale wherein the trigger time of the event is at 200 microseconds).

[0034] FIG. 9 illustrates graphically examples of event types not associated with skull fracture, wherein panels a-b) illustrate waveforms generated while tightening the clamp; panel c) illustrates a waveform observed during torsional external loading of the clamp; and panel d) illustrates a waveform generated during operation of pneumatic surgical drill while grinding the bone.

[0035] FIG. 10A illustrates graphically definitions of waveform metrics used herein.

[0036] FIG. 10B illustrates a crossplot of waveform metrics showing ranges in which events are filtered as likely to be caused by non-fracture sources ("non-AE") wherein rise time is set forth versus average waveform frequency, and wherein average waveform frequency is the average of the Fourier spectrum obtained by Fast Fourier Transform and rise time and event duration are defined in FIG. 10A.

[0037] FIG. 10C illustrates a crossplot of waveform metrics setting forth average waveform frequency versus event duration.

[0038] FIG. 10D illustrates a crossplot of waveform metrics setting forth rise time versus event duration.

[0039] FIG. 11 illustrates timelines of AE occurrence for stable conditions under incremental increases of load at location 3, wherein the loads up to 70 lbs. (311.4 N) are classified as stable, and wherein panel a) illustrates event amplitude, panel b) illustrates event frequency

( also known as "event rate", which is the inverse of period of time between successive events), and panel c) illustrates cumulative events.

[0040] FIG. 12 illustrates timelines of AE occurrence for stable conditions under incremental increases of load at location 4, wherein the loading to 40 lbs. (177.9 N) showed stability of the skull, and wherein panel a) illustrates event amplitude, panel b) illustrates event frequency (also known as "event rate", which is the inverse of period of time between successive events, and panel c) illustrates cumulative events.

[0041] FIG. 13 illustrates timelines of AE occurrence at location 4, focusing on a period immediately following increase of loading to 60 lbs. (266.9 N), wherein panel a) illustrates event amplitude, panel b) illustrates event frequency (also known as "event rate", which is the inverse of period of time between successive events), and panel c) illustrates cumulative events.

[0042] FIG. 14 illustrates a timeline of AE occurrence at location 4, showing event frequency, and indicating a lack of fracturing at higher loads, which may, for example, be a result of the bushing/shoulder of the pin coming to rest on intact skull after the breakage immediately following load increase to 60 lbs. (266.9 N).

[0043] FIG. 15 illustrates a distribution of events by event amplitude, wherein the amplitude in decibels is a logarithmic quantity so that linear behavior in the semi log plot indicates power law decay of the magnitude-frequency distribution, and wherein non-AE events have a much heavier, non-power law tail of large magnitude events compared to events that are associated (by filtering) as AE-related.

[0044] FIG. 16 illustrates aftershock frequency, wherein panel a) illustrates the first 10 seconds after loading to 60 lbs. (266.9 N), and panel b) illustrates time following a second burst fracturing occurrence, and wherein both graphs indicate log-linear behavior of the cumulative events and hence hyperbolic decay of the event rate, and further wherein the shift time t_o (per cite) is taken herein as 1 second.

[0045] FIG. 17 illustrates timelines of AE occurrence at location 3, indicating stable behavior with loading to 70 lbs. (311.4 N) and delayed failure following additional loading to 80 lbs.

(355.9 N) wherein panel a) illustrates event amplitude, panel b) illustrates event frequency

(also known as "event rate", which is the inverse of period of time between successive events), and panel c) illustrates cumulative events.

[0046] FIG. 18 illustrates in panel a) a distribution of number of events by amplitude, showing power-law distribution for AE events during entirety of test and AE events only during the time of listening wherein the equipment and specimen were untouched, wherein the unfiltered events contain a much higher proportion of large amplitude events, with a heavy tail not following the power-law relationship observable for the periods in which it is reasonable to attribute most events to fracturing, and in panel b) a semi-log linear plot of cumulative events after the main failure at 1363 seconds of test time, indicating hyperbolic decay of the aftershock event rate, wherein the time shift is t_o=1 second.

[0047] FIG. 19 illustrates timeline of AE occurrence at location 5, indicating initial instability upon first loading to 40 lbs. (177.9 N) with additional failure occurring in a delayed manner while holding at 40 lbs. (177.9 N), wherein load was sustained for additional increases, but with trailing events to each load increase pointing toward additional damage, wherein panel a) illustrates event amplitude, panel b) illustrates event frequency (also known as "event rate", which is the inverse of period of time between successive events), and panel c) illustrates cumulative events.

[0048] FIG. 20 illustrates Omori law decay of event frequency (also known as "event rate", which is the inverse of period of time between successive events)fol lowing multiple event bursts, with t_o=1 second and the plotted aftershock periods of (referenced to event timeline in FIG. 19), wherein panel a) illustrates 46-220 seconds, showing hyperbolic decay of event frequency following initial loading, panel b) illustrates 46-500 seconds, showing deviation from hyperbolic decay that can be interpreted as new failure of the skull corresponding to the burst of events between 220-224 seconds panel c) illustrates 224-530 seconds, showing hyperbolic decay of event frequency following the burst of events between 220-224 seconds, and panel d) illustrates 549-644 seconds, showing hyperbolic decay of event frequency following loading to 50 lbs. (222.4 N).

[0049] FIG. 21 illustrates: panel a) a waveform generated by cadaver skull fracture, panel b) a waveform generated by cadaver skull subjected to pin slippage, panel c) a power spectrum of the waveform from fracture, panel d) a power spectrum of the waveform from slippage

(wherein the slippage waveform is visibly similar but the frequency content more evenly distributed across a broader spectrum), panel e) cumulative events generated for a model skull with increasing hanging weight (showing almost no events from the single pin (Pin 1) and the vast majority of events from one of the pins on the two-pin side (Pin 2)), including events occurring in the periods between addition of weight (circles indicating occurrence of each event).

DESCRIPTION

[0050] It will be readily understood that the components of the embodiments, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations in addition to the described representative embodiments.

Thus, the following more detailed description of the representative embodiments, as illustrated in the figures, is not intended to limit the scope of the embodiments, as claimed, but is merely illustrative of representative embodiments.

[0051] Reference throughout this specification to "one embodiment" or "an embodiment"

(or the like) means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearance of the phrases "in one embodiment" or "in an embodiment" or the like in various places throughout this specification are not necessarily all referring to the same embodiment.

[0052] Furthermore, described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments. One skilled in the relevant art will recognize, however, that the various embodiments can be practiced without one or more of the specific details, or with other methods, components, materials, et cetera. In other instances, well known structures, materials, or operations are not shown or described in detail to avoid obfuscation.

[0053] As used herein and in the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, reference to "a sensor or transducer" includes a plurality of such sensors or transducers and equivalents thereof known to those skilled in the art, and so forth, and reference to "the sensor" or "the transducer" is a reference to one or more such sensors or transducers and equivalents thereof known to those skilled in the art, and so forth. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each separate value, as well as intermediate ranges, are incorporated into the specification as if individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contraindicated by the text.

[0054] The terms "electronic circuitry," "circuitry" or "circuit," as used herein include, but are not limited to, hardware, firmware, software, or combinations of each to perform a function(s) or an action(s). For example, based on a desired feature or need, a circuit may include a software controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), or other programmed logic device. A circuit may also be fully embodied as software. As used herein, "circuit" is considered synonymous with "logic." The term "logic," as used herein includes, but is not limited to, hardware, firmware, software, or combinations of each to perform a function(s) or an action(s), or to cause a function or action from another component. For example, based on a desired application or need, logic may include a software controlled microprocessor, discrete logic such as an application specific integrated circuit (ASIC), or other programmed logic device. Logic may also be fully embodied as software.

[0055] The term "processor," as used herein includes, but is not limited to, one or more of, or virtually any number of, processor systems or stand-alone processors, such as microprocessors, microcontrollers, central processing units (CPUs), and digital signal processors (DSPs), in any combination. The processor may be associated with various other circuits that support operation of the processor, such as random access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read only memory (EPROM), clocks, decoders, memory controllers, or interrupt controllers, etc. These support circuits may be internal or external to the processor or its associated electronic packaging. The support circuits are in operative communication with the processor. The support circuits are not necessarily shown separate from the processor in block diagrams or other drawings.

[0056] The terms "memory system," "memory," "storage," or the like, as used herein, refer to a collection of electronic components that store data and/or instructions. In computerized systems, a processor system can quickly access information stored in a memory system.

Memory allows storage and retrieval of information and may, for example, include primary memory and secondary memory. Primary memory includes, for example, RAM, cache memory, etc. Secondary memory includes, for example, hard drives, hard disk drives etc.

[0057] The term "controller," as used herein includes, but is not limited to, any circuit or device that coordinates and controls the operation of one or more input and/or output devices. A controller may, for example, include a device having one or more processors, microprocessors, or central processing units capable of being programmed to perform functions.

[0058] The term "software," as used herein includes, but is not limited to, one or more computer readable or executable instructions that cause a computer or other electronic device to perform functions, actions, or behave in a desired manner. The instructions may be embodied in various forms such as routines, algorithms, modules, or programs including separate applications or code from dynamically linked libraries. Software may also be implemented in various forms such as a stand-alone program, a function call, a servlet, an applet, instructions stored in a memory, part of an operating system or other type of executable instructions. It will be appreciated by one of ordinary skill in the art that the form of software is dependent on, for example, requirements of a desired application, the environment it runs on, or the desires of a designer/programmer or the like.

[0059] As described above, surgical procedures involving application offorces to bones involve a risk of injury resulting, for example, from fracture or use of insufficient clamping force. Earlier intervention in case of skull fracture could, in some cases, save a patient's life.

In other cases, it could enable a modification that would enable the surgery to be carried out successfully by correcting the stress prior to completion of the fracture or by pausing the surgery to reposition the pin and, if needed, obtain imaging to document lack of catastrophic complications. In cases of insufficient clamping pressure, the presence of a system that is able to detect and therefore safeguard patients from skull fracture could be an essential enabling step to more secure (that is, higher-force) clamping protocols. Such protocols could significantly reduce or eliminate clamp slippage (that is, undesirable movement relative to the bone during a procedure) and the resulting patient injuries.

[0060] A number of representative embodiments, of device, systems, and methods hereof are described in connection with the application of force to the skull via a skull clamp.

However, one skilled in the art will appreciate that the device, systems, and methods hereof may be used in any medical procedure involving application of appreciable force to bone. Example of such procedures include instrumented fixation of a fracture or unstable bone or joint. Orthopedic instruments that grab or apply force to bones during surgery and fixation include, for example, lobster claw clamps, point-to-point clamps, external and internal fixation instrumentation including nails, plates, and screws, and intermedullary nails.

[0061] In the devices, systems, and methods hereof acoustic emissions (AE) resulting from application of force to a bone undergoing a medical procedure are measured via one or more sensors or transducers responsive to such acoustic emissions. The one or more sensors are positioned during the medical procedure to receive acoustic emissions resulting from the medical procedure. The one or more sensors may, for example, be placed in acoustic connection with at least one of the bone undergoing application of force and with a medical component or device used in the medical procedure during the medical procedure. To be placed in acoustic connection with at least one of the bone and the medical component, the one or more sensors need not be in direct contact (that is, direct physical contact or attachment) therewith. In that regard, the one or more sensors may, for example, be placed in acoustic connection with the source of acoustic emission via intervening acoustic transmissive media. The sensor or transducer may, for example, be placed in connection with the skin or other tissue (particular when the tissue is in close vicinity or proximity to the bone or to the interfacial region of the bone and the medical component or device used to apply force to the bone). Close proximity ensures that acoustic emission signals are transmitted to the sensor or transducer in a manner to enable determination of one or more states as described herein. It is desirable in certain embodiments that the sensor or transducer be placed in acoustic connection with the bone or with the medical component in a manner that minimizes attenuation of AE signals resulting from the medical procedure to the sensor or transducer. Direct physical contact of such a sensor or transducer with the bone during a surgical procedure is difficult. In a number of embodiments, the sensor or transducer may be placed in acoustic connection with a component (or a plurality of components) in acoustic connection with or in physical contact with the bone. The component is desirably formed of a material through which acoustic emissions are readily transmitted. Such a component may, for example, be a metal component. In the case of cranial surgeries in which a skull clamp is used, such a component may include one or more of the pins used to apply clamping force to the skull. In certain cranial surgeries, pins are not used in clamping or otherwise. Various other components may be used to place a sensor or transducer in acoustic connection with the skull or other bones such as needles, fiducial components used in providing fixed references in imaging localization, nails, plates, screws, etc.

[0062] In cases in which a sensor or transducer hereof is applied directly to the skin, an acoustic couplant may be used to couple the sensor or transducer to the skin. Such couplants, which are typically moderately viscous, nontoxic liquids, pastes, or gels, facilitate the transmission of sound energy between a transducer and the test piece. An adhesive on a bottom surface of a transducer patch may, for example, function as an acoustic couplant. In cases in which a transducer is used in connection with a compressive clamping element applied to skin, a transducer hereof may be attached to an outer or upper surface of the compressive element, however, the transducer is desirably placed between the skin and the inner or bottom surface of the clamping element, and a couplant is desirably present between the transducer and the skin.

[0063] Observation of the acoustic emission or AE in bone, as represented by the skull in the present studies, showed distinctive indicators of a number of types of behavior relative to bone fracture. In that regard, stability of the bone is indicated by a decreasing event rate immediately after the clamping force is applied or changed (that is, increased or decreased).

The acoustic emission or AE event rate is the number of AE events generated in a unit of time

(that is, acoustic emission events/second). Immediate/rapid failure of the bone is indicated by a protracted period of AE following the force increase that includes adherence to statistical properties that are associated with fracture of quasi-brittle, porous materials other than bone. Time-delayed breakage of bone is indicated by a period of increased event rate/frequency and amplitude (and/or a change in one or more quantifiable statistical properties of a time series of acoustic events) in the lead up to failure and hyperbolically- decaying event frequencies following failure. Statistical measures or properties that may be determined in characterizing a times series of acoustic events include, for example, the coefficient of variation of the period between events. Acceleration of the event rate may also change in a manner that relates to the event rate. Such observations and/or characterizations demonstrate that a bone such as the skull can fail in either an immediate or quick manner or in a delayed manner and that the waveforms, amplitudes, and temporal patterns are able to discern if the bone is stable, has just failed, or is progressing towards failure. The observations hereof open a path for acoustically-detecting equipment to be installed in acoustic connection with bone to be used, for example, as an alerting system that will enable detection of bone failure or progression toward bone failure to, for example, trigger remedial action. The presence of such a system could also open a path towards more secure clamping protocols in skull clamping cases wherein the primary risk is related to insufficient or non-robust immobilization of the skull by the clamping apparatus.

[0064] An example of acoustic emission is the cracking sound produced by a material during fracture. Sometimes AE is audible. However, most often such AE is inaudible to the human ear, but is able to be detected by specialized equipment. Prior to the present studies, there have been observations of AE patterns of failure precursors in materials such as rock and concrete, but such observations have not been identified in bone. It was hypothesized by the present inventors, that bone, as a type of porous, quasi-brittle material (which possess traits of both brittle and ductile materials) may exhibit discernible AE patterns before, during, and after failure.

[0065] In the case of quasi-brittle materials such as rock, concrete, and (as demonstrated in the present studies) bone, failure occurs progressively. Progressive failure has been described as "microcrack coalescence." When the material is sufficiently stressed, microscopic cracks may form as material bonds break. Such crack may be associated with generation of AE, with a magnitude (amplitude) of the event being related to the size of the microcrack. A decline in event rate may, for example, be related to a depletion of microscopic flaws that are the sites most prone to micro-cracking. An acceleration of the event rate may, in turn, taken as evidence of microcrack coalescence. During such a stage of failure, microcracks may begin interacting with one another via the concentration of stress that results from the internal load within the material shifting in response to microscopic, localized failure. The result may be an increased likelihood of microcrack generation in the vicinity of another microcrack. That feedback loop eventuates interconnection among microcracks to form a macroscopic crack accompanied by structural failure. The feedback loop may, for example, be halted by performing at least one of repositioning and relaxing the applied force.

[0066] In view of evidence that bone failure may be an AE-generating, quasi-brittle fracturing process, it was hypothesized that periods of decreasing or vanishing event rate may indicate bone stability while a transition to increasing event rate and magnitude can be indicative of progression to failure. In leveraging existing equipment for AE detection (which was modified for specific application to AE detection in bone as described herein), an important challenge to overcome is how to acoustically couple an AE transducer to the bone.

In the representative case of use of a skull clamp in cranial surgery, a sensor or transducer was placed in acoustic connection with a clamping pin in such a manner that the pin's primary affixing function was not compromised. Another challenge was to demonstrate detection of AE events associated with bone fracture under application of force thereto (for example, of the human or an animal skull under clamping conditions) would provide recognizable patterns indicating various states such as, for example,: a) stability, b) failure that rapidly occurs during initial clamping, and c) failure that occurs in a delayed manner after clamping.

[0067] In a number of representative embodiments studied herein, systems hereof included an acoustic emission detection sensor or transducer coupled to a skull pin that inserts into a skull clamp (for example, a Mayfield or similar skull clamp). FIG. 1 illustrates schematically a commercially available skull pin 5. Skull pin 5 includes a contact point 10 for contacting the skull positioned at the end of a shaft 14. A shoulder 16 connects shaft 14 to an insertion shaft or insertion end 18 via which pin 5 is connected to clamp 30 (see, for example, FIG. 2).

In that regard, insertion shaft 18 may be inserted into a socket of a pin mount 32 of skull clamp 30. FIG. 2 illustrates schematically an embodiment of commercially available skull clamp 30 (for example, a Mayfield skull or similar clamp) for use herein. Skull clamp 30 includes pin mount 32 for a single pin 5 (as described above) and a double pin mount 34 for mounting two pins 5a(l) and 5a(2). A first screw drive 38 is used to adjust force on pin 5, and a second screw drive36a is used to adjust force on pins 5a(l) and 5a(2) (via double pin mount 34). A ratchet mechanism 40 is used to adjust the width between clamp arms 42 and

42a to appropriately position pins 5, 5a(l), and 5a(2) in operative connection or contact with a patient's skull.

[0068] The acoustic emission sensor was placed in communicative connection with electronic circuitry such that signals from the acoustic emission sensor are transmitted to the electronic circuity to measure, analyze, and/or store information or data contained in such signals overtime. In that regard, the electronic circuitry may include a device or system, which is in communicative connection with the acoustic emission sensor, for reading and recording acoustic emission signals that are generated in association with damage that is incurred by the skull or that are otherwise generated during surgical procedures. In a number of embodiments, that system includes a pre-amplifier, a data acquisition system, and a computer/computer software for controlling and/or configuring the system, displaying data in real time, and recording data. Furthermore, the electronic circuitry may include an analysis system incorporating an interpretation methodology which, for example, infers or determines progression of bone damage under sustained load (for example, by analyzing frequency and/or amplitude of detected acoustic events). Such components are described in further detail below. [0069] An acoustic emission (AE) sensor system (see FIGS. 3 through 5) may, for example, include one or more acoustic emission (AE) detection transducer(s) 50 coupled to one or more skull pins 5, 5a(l), and 5a(2) that insert into skull clamp 30. There may be internal or external connection of a transducer to a skull pin. Alternatively, a pin with intrinsic transducer properties may be used. In a number of studied embodiments, AE transducer 50 was connected only to single pin 5 which is operatively attached to screw-drive 36 of clamp 30. It may be desirable, in a number of embodiments, to attach transducers to more than one skull pin or to all skull pins. In other embodiments, a transducer may be connected to the head clamp system itself. In a number of studies of slippage hereof, AE sensors 50 were attached to each of pin 5, pin 5a(1), and pin 5a(2) as illustrated in FIG. 3.

[0070] In a number of studied embodiments, an attachment mechanism for AE sensor(s) 50 included a tightly-fitted bushing 60 that slipped over pin shaft 14 (see, for example, FIGS. 4A and 4B). Bushing 60 was positioned against shoulder 18 and included a surface that was matched to AE transducer 50 to enable acoustic coupling. In a number of studied embodiments as, for example, illustrated in FIG. 4A, acoustically-coupled bushing 60 was connected to a transducer mounting plate 62, to which AE transducer 50, a connector 52, and a cable 54 were connected. AE transducers 50 and connecting components therefor are unique to studied embodiments of skull clamp AE sensor systems hereof and may be acoustically coupled to pins and/or other elements in any suitable manner.

[0071] The pin and a coupling mechanism for and AE sensor may, for example, be manufactured together, either as one piece or as multiple pieces that are pre-assembled and cannot be disassembled (for example, because of adhesive or a very tight fit among the pieces). Alternatively, the AE coupling bushing and/or other connector may be supplied separately from the pins. In such embodiments, the user may be required to assemble the system by, for example, pushing the bushing over the pin prior to attaching the clamp to the patient. The latter embodiment may, for example, include a version in which such additional pieces are attached to or intrinsic to the head clamp.

[0072] When using a bushing on the pin shift, it may be desirable to use a pin with a longer shaft compared to standard, commercially available pins. Otherwise, the bushing may press against the skin as the clamping force is applied.

[0073] In the studied embodiments, the AE transducer 50 was a commercially-available piezoelectric transducer that is optimized to detect the waveforms generated by microcracking of rocks. In such studies, a MISTRAS MINI30S, 300 kHz integral cable gluable acoustic emission sensor (available from MISTRAS Group, Inc. of Princeton Jet., New Jersey US) was used. In other embodiments, the transducer may be customized through, for example, selection of the geometry and materials (of, for example, a piezoelectric material) and a housing to optimally detect AE generated by bone generally or by specifical bones

(such as the human skull etc.). Also, the transducer shape may, for example, be optimized for ease of use with skull pins, including adjustments to the transducer size and surface curvature. In a number of embodiments, a piezoelectric transducer may be developed with curvature and size to match directly to the pin shaft, thereby eliminating the need for a bushing and flat mounting surface. Additionally, one may develop an embodiment wherein the transducer attaches to the back of the pin, eliminating the need for the bushing. One may also acoustically couple the transducer to the skull clamp body, whereby AE transmitted to the skull clamp body via the one or more force application pins thereof are transmitted to the transducer.

[0074] In a number of studied embodiments, the AE transducer was coupled to a mounting platform on the bushing as described above with glucose couplant and held in place with heat-shrink that is used for cladding of electrical cables. The coupling may readily be made more robust so it will not become decoupled even if impacted. Representative modifications may, for example, include making a rim around the mounting stage to avoid decoupling by sliding. Additionally, a magnetic or mechanical clamping may be used to hold the transducer securely to the stage.

[0075] The transducer used in the studies hereof included a piezoelectric material (as described above) to convert stress waves into an electrical signal (for example, voltage) that can be amplified and then transmitted to the data acquisition system. In other embodiments, the transducer may, for example, be constructed by coupling the pin to optical fiber with, for example, a Fiber Bragg Grating (FBG) or similar detector that converts an acoustic signal to an optical signal that is read by an FBG or similar interrogator. The fiber may, for example, be coupled to the pin by affixing it to the outside of the pin or manufacturing the pin with the fiber inside. Furthermore, other acoustic sensors, transducers or detectors may be used such as, for example, high-sensitivity microphones, accelerometers, vibrating wires, inclinometers, tiltmeters, and optical interferometry systems. More than one type of acoustic emission sensor may be used. Redundant sensor may be used one or more positions in the system.

[0076] Referring, for example, to the representative embodiment of FIG. 5, electronic circuitry 100 may include a system for reading and recording of acoustic emissions (AE) that are generated in association with the force applied to and, potentially damage that is incurred by the skull or otherwise generated during surgical procedures. In representative embodiments of the system hereof, electronic circuitry 100 includes a sequential combination a pre-amplifier 110, a data acquisition (analog to digital conversion) system 120, and a computer system 130. In studied embodiments, the pre-amplifier was a MISTRAS

2/4/6 Preamplifier, a 20/40/60 dB single-ended/differential AST preamplifier with series filter (having a filter range or 100-1200), and powered by 28V DC. The data acquisition system included a MISTRAS Express-8 PCI-express bus AE system on a card with 8 AE channels, 16 bit, 10 MSample/sec A/D, and 1.2 MHz bandwidth with waveform capture. As known in the computer arts, computer system 130 may include a processor system and a memory system in communicative connection with the processor system. One or more algorithms may be stored in the memory system which are executable by the processor system. Computer system 130 may, for example, provide control of the overall system (for example, configuring the detection and recording settings) and also provide for displaying data in real time. In that regard, computer system 130 may further include a user interface system (including, for example, a visual display, an audio system on or more input system such as keyboards, touchscreens mouses, voice recognition, etc. as known in the computer arts). The memory system may include, or computer system 130 may be, in communication with a memory or storage system 140 for recording data.

[0077] In a number of studied embodiments (as, for example, described above) commercially available, off-the-shelf laboratory equipment, was configured for determination of various states or conditions related to a medical procedure in which force is applied to a bone form acoustic emissions from the bone and/or a device-bone interface.

The determined state may, for example, be a state of an instrument used in connection with the bone (including, for example, stability, movement or slippage relative to the bone, etc.) or a state of the bone (including, for example, the bone states of stability breakage/fracture, or impending breakage/fracture). In the studied embodiments, such state determinations were made through readily selected or determined settings that include pre-amplification, low- and high-pass frequency filters, a detection mode (triggered versus continuous), a trigger level, a sampling frequency, and a signal recording length. In the case of other embodiments, off-the-shelf equipment may be unnecessarily complicated because such equipment is designed to be flexible for use with a wide range of AE applications. An embodiment of the technology hereof for commercial embodiment may, for example, include the components described above, but may be designed and built to be robust and user-friendly in an operating theater. For example, a pre-amplifier may be integrated into the same chassis as a data acquisition system and need not have adjustments for amplification level, because the requirement for amplification will be generally consistent from one patient to another. The data acquisition system may, for example, be incorporated into a compact chassis with, for example, a USB or PCI connection to a computer. The software may be run on a computer, which could be an off-the-shelf laptop or PC. Alternatively, the system could be a self-contained instrument or system with built-in computing, display, and storage. The storage system may be incorporated within a laptop/PC, a self-contained unit as described above, network-based storage, etc. The laptop/PC or self-contained unit may, for example, be connect to a high capacity storage system for archiving data after a surgical procedure is completed.

[0078] Various connections for data etc. can be achieved via wired or wireless connectivity.

Various communication methodologies hereof may use local networks, cellular networks and/or the internet. The AE sensor or detector was, for example, connected to the preamplifier via a commercially-available wire with suitable connectors on each end. In other embodiments, the signal could be received, amplified, and converted to a digital signal via a small hardware system that could mount directly to the Mayfield or other skull clamp. The digital signal could then be transmitted to the recording system either via a wired or wireless connection such as BLUETOOTH* (which is a short-range wireless technology standard used for exchanging data and is overseen by Bluetooth Special Interest Group, headquartered in

Kirkland, Washington) or Wi-Fi connection. The signal could be incorporated into multi-tool displays or be displayed independently.

[0079] The analysis or interpretation methodology hereof may, for example, determine or infer progression of bone damage under sustained load by, for example, analyzing the AE data using predetermined criteria (for example, include criteria for increasing frequency and/or amplitude of detected acoustic events). In a number of embodiments, the methodology includes discerning or distinguishing AE generated by bone fracture as distinct from signals generated by operations such as tightening the clamp, cutting/grinding the skull, or impacting the clamp or skull as a part of surgical procedures. Such discernment was achieved in studies hereof based on differences among the waveforms generated by those various sources. In a number of studies, visual discernment was used. In other embodiments, such discernment or distinction may be automated achieved using signal processing methods. Such automation can also use artificial intelligence such as Machine Learning methods. Machine Learning algorithms (including algorithms for classification, regression, etc.) and models may, for example, use reinforcement learning with training upon data from known sources. [0080] Data acquisition and analysis may, for example, include monitoring the time period between AE events. The inverse of that time period is the event frequency. Further, one may monitor and analyze metrics associated with the AE events that can indicate increasing acoustic energy. Such metric may, for example, include amplitude, number of threshold crossings made by the signal ("AE counts"), and signal duration. A decreasing or vanishing event rate may, for example, be interpreted as indicative of a lack of or absence of progression of damage to the skull (that is, structural stability). In the case of a time-delayed failure, as discussed further below, an increase in event frequency and/or acoustic energy may, for example, be interpreted as progression of failure so that intervention can take place.

In a case in which intervention has been taken by reducing force to divert progression to instability, a subsequent decrease or vanishing of event rate may, for example, be interpreted as indicative of successful intervention (associated with stability). In the case of immediate or quick skull failure during a clamping process, an anomalously large number of events and/or anomalously high AE energy may, for example, be interpreted as potentially indicative of failure so that inspection can take place and remediation can be performed if needed.

[0081] Various studies of the use and efficacy of the devices, systems, and methods hereof were conducted via laboratory experiments conducted on cadaver skulls. The procedures in a number of skull fracture studies included:

1) Mounting an AE detection pin in the single pin side of a Mayfield clamp and standard pins in the dual pin side.

2) Removing the skin from the area of attachment for the single pin. However, equivalent data was observed without removing the skin from the area.

3) Starting the Reading and Recording system.

4) Attaching the clamp to the skull in a typical manner, involving manually squeezing the clamp until the indicator on the screw drive shows 20-40 lbs. of force (89-177.9 N) is applied and held constant by the calibrated spring inside the screw drive and reacted by the ratcheting length adjustment of the clamp.

5) Monitoring the progression of AE. If AE event frequency and energy decline or vanish, interpret that the skull is stable under the present load.

6) Turn the screw drive on the clamp to increase loading. Increments varied from 5-20 lbs. (22.2-89 N) from one test to another and from one loading stage within a test to another.

7) Repeat the cycle of monitoring, interpreting, and increasing load until: a) there is evidence of failure of the skull, or b) the loading range of the clamp is maximized (around 100 lbs. (444.8 N)).

8) In cases when the skull is observed to be stable under maximum clamping pressure, the clamp is removed, and the skull is manually weakened through thinning the bone around or at the pinning point with a high powered surgical drill to simulate a patient with a skull that is abnormally weak due to development stage, degenerative disease, or injury of the target area or adjacent bony tissues.

[0082] Outcomes including stability, instantaneous failure, and time-delayed failure were all observed to generate distinctive, interpretable AE signals in such studies. After a brief description of the observed waveform types, those three outcomes are discussed further below. The bone stability/fracture experiments were run on a roughly 80 mm x 50 mm section of skull on the frontal bone of a male cadaver. There were six locations tested, with each eventually involving thinning of the skull over a circular region roughly 15 mm in diameter. Because some of these locations were used for calibration and others for establishing repeatability, not all tests are discussed herein. Instead, three illustrative cases are discussed. Such cases are referenced to the locations illustrated in FIG. 6 to maintain ability to reference the results to the original data sets. Table 1 of FIG. 7 sets forth further test procedure notes for such locations.

[0083] In a number of studies, the electronic circuitry/recording system was set in a triggered mode. In that mode, the system continuously monitors the signal coming from the

AE transducer, holding a user-defined length of signal in memory temporarily, and discarding it continuously if the signal amplitude fails to cross a defined threshold. The threshold was set to be as low as possible without incurring frequent spurious triggering of the system by ambient noise (that is, acoustic environmental noise and/or electrical noise within the recording system). Such threshold(s) are readily determined for the circumstances of a particular use of the devices, systems, and methods hereof.

[0084] During periods of the experiments when the specimen and apparatus were attached, under load, but not being impacted by operations such as clamp tightening/removal, skull grinding, etc., the waveforms associated with detected events have waveforms similar to the examples shown in FIG. 8. In addition to there being a lack of other plausible sources for events during these "quiet observation" periods of the experiments, the waveforms bear some similarity to those observed from fracture of rock, concrete, and bone. Thus, such waveforms may be reasonably interpreted to be caused by fracturing of the bone.

[0085] Other event types were observed, with examples illustrated in FIG. 9. Such events included waveforms generated while tightening the clamp (panels 9a and 9b), a waveform observed during torsional external loading of the clamp (panel 9c), and a waveform generated during operation of pneumatic surgical drill while grinding the bone (panel 9d). [0086] The results of FIG. 8, panel c demonstrate, for example, that different waveforms associated with different events may be discerned or discriminated to differentiate wave forms associated with bone state. Moreover, events, states or conditions other than bone state may be determined via waveform analysis. For example, the systems and methods hereof may also be used to determine or detect the movement or slipping of an instrument (for example, a force application pin) relative to/along the bone as discussed further below.

[0087] Regarding fracturing of the bone, based on the observation that events reasonably associated with fracturing are discernable by waveform from other events, it is desirable to examine each waveform and discard events that do not match a typical AE waveform. In that regard, there are potentially thousands of events. However, methods may be applied to automate, in a high-fidelity manner, discerning of such waveforms. In the present studies, a simple filter was constructed based on the rise time, waveform frequency, and event duration. These and other metrics associated with waveforms are illustrated in FIG. 10A. The waveform frequency was obtained from the Fourier transform of the waveform and is not the same as the event frequency. The event frequency is the inverse of the time period between events. Also, the amplitude can be measured either directly from the mV output from the transducer-preamplifier system or converted to a logarithmic decibel scale.

In the above equation, V_max is the peak voltage of the waveform in microvolts and A_gain is the preamplifier gain in decibels (dB).

[0088] A simple filter was developed for the present studies by firstly proposing that events in the "listening periods" where load is held constant and there is no touching of the specimen will be mostly AE associated with fracture. By distinguishing/coding those events and generating crossplots of waveform metrics as illustrated in FIG. 10B through 10D, it was clear that most events of very long duration, high rise time, and low waveform (average) frequency occur during periods where non-fracture processes are likely sources. Crossplots of waveform metrics may, for example, be used to demonstrate ranges in which events are filtered as likely to be caused by non-fracture sources ("non-AE"), for a) rise time versus average waveform frequency, b) average waveform frequency versus event duration, and c) rise time versus event duration, wherein average waveform frequency is the average of the

Fourier spectrum obtained by Fast Fourier Transform and rise time and event duration as defined in FIG. 10. Thresholds were set for those based on the data from location 3 (see

FIG. 6) and used for the rest of the locations/tests.

[0089] In case 1 of the studies hereof, stable conditions characterized by generation of a few low energy events that quickly diminish were observed at multiple locations, with the illustrative tests selected from locations 3 and 4 (see FIG. 6). Those locations are useful because, at both locations, stability is observed upto a certain load. The period of stability is presented in such a case. Upon further application of load, the skull fractured. For location 3, the fracture occurred in a time-delayed manner, which will be further discuss in connection with Case 3 below. At location 4, the fracture occurred immediately upon increasing the load, which is elaborated in in connection Case 2 below. By choosing such tests, it was possible to observe both stable and unstable behavior manifested at the same locations, with the transition caused by increasing the clamping force.

[0090] At location 3, the skull was weakened by grinding with a mechanical surgical drill to a uniform thickness of 2 mm over a circular region with diameter of 10 mm. An initial loading was applied, ratcheting to 20 lbs. (89 N). Load was then applied in 10 lb. (44.5 N) increments.

The skull was stable up to 70 lbs. (311.4 N) of loading. Stability was determined by the paucity of events at each of those load levels. A number of events classified as AE were generated during the ~6 seconds screw drive 36 was being turned by hand - approximately

3000 events with the first application of the clamp and typically a couple hundred additional

AE with each load increase. However, there were few events in the periods following initial clamping and subsequent load increases (FIG. 11). The events that did occur were of small energy (compared to those that were subsequently shown for cases of failure). The event frequency also diminished rapidly after load application. In the following minutes, events were very infrequent and did not increase in frequency. Throughout the test, and other tests carried out in this series, the pattern of low energy events with infrequent occurrence and diminishing event frequency was consistently observed when the structural integrity of the skull was stable under the applied clamping force.

[0091] Behavior indicating stability of the skull under loading was also observed at location

4, where again the skull was weakened by grinding with a mechanical surgical drill to a uniform thickness. In location 4, the thickness was 2 mm over a circular region with diameter of 10 mm. An initial loading was applied, ratcheting up 40 lbs. (177.9 N) over a period of 38 seconds. After this initial loading, only one, low-amplitude event was generated (FIG. 12).

That observation lead to the determination that the skull was stable under the 40 lbs. (177.9

N) loading. [0092] Case 2 provides an illustrative example of rapid failure of the skull upon increasing clamping load is obtained from location 4 (FIG. 6). Once again, at this location on the frontal bone, the skull was weakened by grinding with a pneumatic surgical drill to a uniform thickness of 2 mm over a circular region with diameter of 10 mm.

[0093] Location 4 presented in Case 1 as a stable example up to 40 lbs. (177.9 N) of load.

FIG. 13 shows the loading up to 40 lbs. (177.9 N), as previously presented in FIG. 12.

However, FIG. 13 further shows the preponderance of events that ensue when load was increased by tightening screw drive 36 to 60 lbs. (266.9 N). The contrast of behavior after the screw drive was no longer being turned is apparent. Here the events are shown to continue at a significant rate, which is in contrast to the stable cases (FIG. 11 and 12) wherein there are few if any trailing events after clamping loading is applied.

[0094] During the testing, there were no outward signs that skull fracture had taken place following tightening of the clamp to 60 lbs. (266.9 N). After completing loading to higher levels, the clamp was removed and at that point it was observed that fracture had occurred at some time during the loading. It appears that after fracturing, the bushing around the shoulder of the pin came to rest on intact skull and the load was transferred to the intact skull via the pin shoulder. That load transfer allowed additional loading to be applied without perception that the skull had already fractured after loading to 60 lbs. (266.9 N) (FIG. 14).

[0095] While the fracturing was not perceptible to sight, sound, or touch during the experiment, the AE that were generated were observed in real time, and provided indication that fracture had already occurred at 60 lbs. (266.9 N). If this were a surgical situation, the AE data would have provided the information necessary for real-time warning to the team and inspection and remedial action would have been set in motion immediately after the fracture took place.

[0096] In addition to the observation after testing of the existence of a punch-like fracture forming a ring around the pin, post-processing of the data corroborated with further evidence that the events during and immediately after the increasing of the load to 60 lbs.

(266.9 N) were associated with fracture. For example, there is a power law relationship between the magnitude of the AE and the number of events generated at each magnitude, as shown in FIG. 15. The power law relationship is similar to the classical Gutenberg-Richter law that accompanies fracture of rock, including the amplitude of AE events. Gutenberg, B., and Richter, C. F., "Seismicity of the Earth and associated phenomena." MAUSAM1, no. 2,

174-176 (1950). [0097] Following increase of the load to 60 lbs. (266.9 N), it was observed from FIG. 13 that the event frequency decreased for about 10 seconds. Then there was another burst of events, most likely indicating addition fracturing. That observed result was followed by another decrease in event frequency. Plotting the cumulative events for the first 10 seconds, and then again the cumulative events following the second burst of events shows that both distribute as log-linear with time (FIG. 16). Thus, the event frequency (the derivative of the cumulative events) is decaying hyperbolically (that is, like l/(t+t_o), wherein t is the time since the fracture was created and t_o is a time shift that is a fitting parameter determined for the data). Hyperbolic decay of event frequency after rock fracture has previously been associated with earthquakes, but also has been shown to occur after rock fracture at laboratory scale. In the present studies, the evidence shows that fracture of the skull is also associated with aftershocks, and the aftershocks follow a hyperbolic decay in frequency. Hence, the

Gutenberg-Richter law distribution of AE amplitudes and Omori law decay of event frequency after fracturing are promising as indicators that can be used to ascertain whether a suspicious burst of events is indicative of skull fracture or if it is generated by operational noise (such as grinding or clamping), which do not generate such distributions.

[0098] Taken together, a persistent period of event generation, a power law distribution of event amplitudes, and hyperbolic decay of event frequency are all observed to be associated with rapid failure of the skull and therefore provide a promising way forward for detection of failure that takes place concurrently with application of the skull clamping force.

[0099] In Case 3, two tests provided illustrative examples of time-delayed skull failure after clamping. The first was the test at location 3, which was stable up to 70 lbs. (311.4 N) of loading, recalling from the discussion of FIG. 11. However, upon increasing the load to 80 lbs.

(355.9 N), the behavior substantially changed. FIG. 17 illustrates the timeline of loading and event amplitude, frequency, and cumulative events. This timeline began with the aforementioned stable loading to 70 lbs. (311.4 N). After the load was increased to 80 lbs., there were initially no trailing events, and the situation appeared again to be stable. That apparent stability was maintained for around 150 seconds. However, about 150 seconds after loading to 80 lbs. (355.9 n; at test time of 1100 seconds), events began to occur with regularity. The event rate and event amplitude both steadily increased over a period of 260 seconds.

[0100] Eventually, at test time of 1363 seconds, the skull failed suddenly, accompanied by an audible crack. The pin rapidly extended into the skull and the load was reduced suddenly to only a few pounds offorce. That moment is shown in FIG. 17 by the sudden drop in load corresponding to the peak of both event amplitude and event frequency at test time of 1363 seconds. Similar to the case of rapid failure, there is a power law distribution of event amplitudes (FIG. 18, panel a) and a hyperbolic decay of event frequency following the observed failure (FIG. 18, panel b).

[0101] Upon removal of the clamp and pin, a punch-type failure was observed, with the rupture surface generated by fracturing comprising a tight ring around the pin tip. This cylindrical plug of bone was displaced 5 mm relative to its original position at the beginning of the experiment. As a result of this displacement, the spring within the clamp extended, thus reducing most of the load (to ~10 lbs. (~44.5 N)).

[0102] That result indicates that skull breakage need not occur coincident with application of clamping force. It can also fail in a time-delayed manner at load levels insufficient to generate instantaneous breakage. In this example at location 3, the failure was striking and readily perceived when it happened. However, even had there not been accompanied by an audible crack, the AE signature is distinctive and would have readily enabled alerting a surgical team of the failure.

[0103] Location 5 provides an example of detection of a time-delayed failure of the skull that was not perceived via human observation at the time of breakage. The evolution of AE amplitude, frequency, and cumulative events is shown in FIG. 19. In this test, the load was rapidly increased to 40 lbs. (117.9 N) and then incrementally increased to 80 lbs. (355,9 N) over a period of about 20 minutes. At no point during the test was there perceptible damage to the skull. However, after releasing the clamp at the end of the test, a clearly visible, punch-type skull fracture was observed.

[0104] Without AE detection, there would have been no indication the fracture was occurring. With AE detection, it was strongly suspected from the AE data that fracturing was occurring based on the data presented in FIG. 19. The evidence in the form of the large number of events continuing through the period of time while holding a load of 40 lbs.

(117.9 N; 41 seconds to 530 seconds). In the details, there is initial evidence that breakage took place immediately during clamping, owing to the hyperbolic decay in event frequency from the time the loading was completed (around 41 seconds) to the large burst of events from 220-224 seconds (FIG. 20, panel a). At 120 seconds there was a small burst of events, showing large amplitude and frequency (FIG. 19), but those events fell within the hyperbolic decay law and so could still be interpreted as aftershocks stemming from a single failure event occurring during initial loading. However, at 220 seconds, the event rate and event amplitudes substantially increased (FIG. 19), and the hyperbolic decay law is strikingly broken (FIG. 20, panel b). This burst of events was therefore reasonably interpreted as a new failure of the skull, followed again by a period of hyperbolic decay of the event frequency (FIG. 20, panel b). Following this burst, the event frequency again decayed hyperbolically (FIG. 20, panel c).

[0105] The above pattern of AE would have been clearly recognized as evidence of skull fracture that would otherwise have been imperceptible, but at a high-risk of inducing laceration as a result of the intrusion of the pin into the intracranial space as opposed to displacement of a larger, blunter fragment inward with separation between the pin and intracranial contents. For the location 5 example, the skull remained able to sustain the pin load in spite of the extensive damage that was sustained. But, with each increase of load, there was a hyperbolic decay of trailing events (one representative example is shown in

FIG. 20, panel d), indicating damage was progressing with each subsequent loading.

[0106] Summarizing, the above results stability/fracture studied conducted at locations 3 and 5 indicate a distinctive pattern of AE in the lead up to time delayed failure. The event frequency and event energy both increase in a manner different from the stable conditions and, following event bursts, the event frequency decays hyperbolically in a manner that is not observed when the skull is stable. Hence, detection of this signature during surgical procedures may be used to trigger remedial action, such as reducing clamping pressure (to induce stability), thus preventing complete failure of the skull.

[0107] In the above studies, application of clamping force via a skull pin affixed in a Mayfield skull clamp resulted in failure of the frontal bone of a cadaver skull when the bone was ground to a reduced thickness. This grinding to reduced thickness was intended to roughly mimic the effects of bone degenerative disease, congenital thinness, and/or congenital fragility - all of which are known to be risk factors that can lead to skull fracture under clamping force.

[0108] Observation of the acoustic emission (AE) generated near the site of the single-pin side attachment of the skull clamp showed distinctive indicators of three types of behavior.

The first observed behavior is stability of the skull, indicated by a decreasing event rate immediately after the clamping force is applied or increased. Because the stability is able to be ascertained by this paucity of events, there is a path by which a treatment team could choose higher clamping force when necessary to prevent movement-related injury to the patient. In that regard, insufficient clamping force may sometimes be used in current practice to avoid fracture. However, insufficient clamping force may result in slippage and associated injury (for example, via laceration). A fracture event may also result in reduced compression of the clamp system, which could then consequently result in a laceration from slipping of the force application pin.

[0109] The second observed behavior is immediate failure of the skull under increased clamping force, indicated by a protracted period of AE following the force increase. AE during this period is indicative of fracture both due to its preponderance, waveform shape(s), and adherence to statistical properties that are known to associate with fracture of quasi-brittle, porous materials. Specifically, the number of events for a given AE amplitude decreases as a power law of increasing amplitude. Additionally, the trailing events occur with a frequency

(reciprocal of the time period between events) that suggests hyperbolic decay.

[0110] In the example of rapid failure, the fracture of the skull was verified after unclamping, but was perceptible immediately following clamping only by the real-time monitoring of AE. Hence, real-time AE is shown in such cases to provide a promising diagnostic whereby practitioners can ascertain the occurrence of skull fracture to (for example, quickly) take remedial action.

[0111] The third type of observed behavior is time-delayed breakage of the skull. Examples are shown where the time delay is around 200 and 1400 seconds following clamping force increase. Those observed result show a clear potential that the skull can fail in a delayed manner, even if it appears stable upon first application of the clamping force.

[0112] In cases of delayed failure in the studies hereof, there was a characteristic period of increase event frequency and amplitude in the lead up to failure. This observation provides a promising path whereby such event intensification could be used to alert a treatment team that the skull is progressing towards failure so that remedial action can be taken to prevent it by performing at least one of repositioning the pin and reducing pin pressure.

[0113] Together, the observations of the studies hereof show that the bone of the skull can fail in either an immediate or delayed manner and that the waveforms, amplitudes, and temporal patterns are distinctive in such a way that stability, immediate failure, and delayed failure can be determined. This opens the path for acoustically-detecting equipment to be installed on, for example, skull pins to provide an alerting system that will, for example, enable detection of skull failure to trigger remedial action. The presence of such a system may also open a path towards more secure clamping protocols in cases where the salient risk is related to insufficient or non-robust immobilization of the skull by the clamping apparatus.

[0114] AE detection of slippage has also been demonstrated with experimental studies on both a cadaver skull and a plastic model skull. For both the cadaver and plastic model skulls, slippage was deliberately induced by attaching weights to the skull clamp while supporting the skull on a secondary frame. The tests included either increasing the attached weight or decreasing the pinning force under a fixed attached weight until slippage occurred.

[0115] Observations resulting from such studies include that waveforms generated for the cadaver skull from slippage (FIG. 21, panels a-b) exhibit differences in subtle ways from fracture (that is, in the details of the frequency content; see FIG. 21, panels c-d). That observation opens a path for classification of events based on waveform and/or frequency content. A further observation was obtained for studies on a model skull with an AE sensors 50 on each of three pins 5, 5a(1), and 5a(2) (see FIG. 3). In a representative study, the skull was clamped with a small, 5-pound clamping force. Subsequently, hanging weights were added, one at a time, progressively increasing the load, attempting to pull the clamp off from the skull (that is, to induce slippage). It was observed that, as the hanging weight is increased, one of the pins on the two-pin side (pin 5a(l)) generated far more AE events compared to the other two pins (pins 5 and 5a(2), see FIG.21, panel e). There were no events generated at pin 5 during the studies and the event data thus lies on the Time axis. Slippage eventually commenced at that pin location. Hence, with the development of the data set and with waveform classification, there is a clear pathway to recognize when one or more pins is/are progressing towards slippage so that remedial steps can be taken. In general, one observes more events at the pin of the two-pin side (that is, one of pin 5a(l) and 5a(2) that eventually slips. The pins on the two-pin side should not be generating events in excess of the single-pin if the source is fracturing because the single pin has double the force compared to the force on each of the pins on the two-pin side. If a pin on the two-pin side is generating events, the observance of such events provide an opportunity to provide notice that remedial action is advisable because of probable impending slippage. The fracture and slippage studies hereof demonstrate that devices, systems, and methods hereof provide indications of sites of interest, both spatially and temporally, during procedures involving application of force to bones.

[0116] The foregoing description and accompanying drawings set forth a number of representative embodiments at the present time. Various modifications, additions and alternative designs will, of course, become apparent to those skilled in the art in light of the foregoing teachings without departing from the scope hereof, which is indicated by the following claims rather than by the foregoing description. All changes and variations that fall within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

WHAT IS CLAIMED IS:

1. A system for determining one or more states arising during a medical procedure in which force is applied to a bone via a medical component, comprising: a sensor responsive to acoustic emissions during the medical procedure, the sensor being configured to be placed in acoustic connection with at least one of the bone and the medical component during the medical procedure, and electronic circuitry in communicative connection with the sensor, the electronic circuitry being configured to analyze data from the sensor over time during the medical procedure to determine the one or more states on the basis of predetermined criteria.

2. The system of claim 1 wherein the one or more states comprise a state of the bone related to fracture thereof or a state of the medical component.

3. The system of claim 2 wherein the electronic circuity is configured to output the one or more states during the medical procedure based upon a monitoring of acoustic emission events over time.

4. The system of claim 3 wherein the electronic circuity is configured to output at least one of a state of stability of the bone, a state of impending fracture of the bone, a state of fracture of the bone, a state of movement of the medical component relative to the bone, and a state of impending movement of the medical component relative to the bone.

5. The system of claim 4 wherein the predetermined criteria associated with the state of stability of the bone comprise a decreasing acoustic emission event rate after force is either first applied or changed.

6. The system of claim 4 wherein the predetermined criteria associated with a fracture of the bone include a period of acoustic emission following the first application of force or the increase in force which has a waveform exhibiting predetermined statistical properties.

7. The system of claim 4 wherein the predetermined criteria associated with a fracture of the bone which occurs during a period subsequent to force being either first applied or increased include (i) a period of at least one of increased acoustic emission event rate prior to fracture of the bone, increased acoustic emission event amplitude prior to the fracture of the bone, and a change in one or more quantifiable statistical properties of a time series of acoustic emission events, and (ii) a period of acoustic emission which has a waveform exhibiting predetermined statistical properties following the fracture of the bone.

8. The system of claim 4 wherein the medical component is a force application component of a clamp.

9. The system of any one of claims 1 through 8 wherein the electronic circuitry comprises a processor system and a memory system in communicative connection with the processor system, the memory system comprising one or more software algorithms stored therein and executable by the processor system to analyze data from the sensor.

10. The system of claim 9 wherein the electronic circuitry further comprises a user interface system via which information regarding the one or more states may be provided to one or more individuals during the surgical procedure.

11. The system of any one of claims 1 through 8 wherein the sensor comprises at least one of a transducer, a microphone, an accelerometer, a vibrating wire, an inclinometer, a tiltmeter, and an optical interferometry system.

12. The system of claim 11 wherein the sensor comprises a transducer, optionally a transducer comprising a piezoelectric material.

13. The system of claim 11 wherein the electronic circuitry comprises an amplifier in connection with the sensor to receive an electrical signal output from the sensor.

14. The system of claim 13 wherein the electronic circuity further comprises an analog-to digital converter in connection with an output of the amplifier, an output of the analog-to digital converter being in communicative connection with the processor system.

15. The system of any of claims 1 through 8 wherein the medical component is acoustically conducting and the sensor is in acoustical connection to the medical component or to an acoustically conducting second component which is acoustically connected to the medical component, or the sensor is acoustically connected to a third component, which is different from the medical component, and the third component is an acoustic conducting component that contacts the bone or is in close proximity to the bone.

16. The system of claim 15 wherein the medical component comprises a metal, the second component comprises a metal, and/or the third component comprises a metal.

17. The system of claim 15 wherein the sensor is attached to the medical component.

18. The system of claim 15 wherein the sensor is acoustically connected to a force application pin of a clamp, a needle, a screw, or a fiducial.

19. The system of claim 15 wherein the sensor is acoustically connected to the medical component, which is a force application pin of a clamp, or to the second component, which is a component of the skull clamp other than the force application pin of the clamp.

20. The system of claim 19 wherein the system comprises a clamp which is a skull clamp.

21. The system of claim 20 wherein the skull clamp comprises a plurality offorce application pins and the system comprises a plurality of sensors, one of the plurality of sensors being acoustically connected to one of the plurality of force application pins and another of the plurality of sensors being acoustically connected to another of the plurality of force application pins.

22. A method for determining one or more states arising during a medical procedure in which force is applied to a bone via a medical component, comprising: placing a sensor responsive to acoustic emissions in acoustic connection with at least one of the bone and the medical component during the medical procedure, and analyzing data from the sensor via electronic circuitry in communication with the sensor to determine the one or more states on the basis of predetermined criteria.

23. The method of claim 22 wherein the one or more states comprise a state of the bone related to fracture thereof or a state of the medical component.

24. The method of claim 23 further comprising outputting the one or more states during the medical procedure via the electronic circuitry based upon a monitoring of acoustic emission events over time.

25. The method of claim 24 wherein the electronic circuity is configured to output at least one of a state of stability of the bone, a state of impending fracture of the bone, state of fracture of the bone, a state of movement of the medical component relative to the bone, and a state of impending movement of the medical component relative to the bone.

26. The method of claim 25 wherein the predetermined criteria associated with the state of stability of the bone comprise a decreasing acoustic emission event rate after force is either first applied or changed.

27. The method of claim 25 wherein the predetermined criteria associated with a fracture of the bone include a period of acoustic emission following the first application of force or the increase in force which has a waveform exhibiting predetermined statistical properties.

28. The method of claim 25 wherein the predetermined criteria associated with a fracture of the bone which occurs during a period subsequent to force being either first applied or increased include (i) at least one of a period of increased acoustic emission event rate prior to fracture of the bone, increased acoustic emission event amplitude prior to the fracture of the bone, and changes in one or more quantifiable statistical properties of a times series of acoustic emission events, and (ii) a period of acoustic emission which has a waveform exhibiting predetermined statistical properties following the fracture of the bone.

29. The method of claim 25 wherein the medical component is a force application component used in a clamp.

30. The method of any one of claims 22 through 29 wherein the electronic circuitry comprises a processor system and a memory system in communicative connection with the processor system, the memory system comprising one or more software algorithms stored therein and executable by the processor system to analyze data from the sensor.

31. The method of claim 30 wherein the electronic circuitry further comprises a user interface system via which information regarding the one or more states may be provided to one or more individuals during the surgical procedure.

32. The method of any one of claims 22 through 29 wherein the sensor comprises at least one of transducers, a microphone, an accelerometers, a vibrating wire, an inclinometer, a tiltmeter, and an optical interferometry system.

33. The method of claim 32 wherein the sensor comprises a transducer, optionally a transducer comprising a piezoelectric material.

34. The method of claim 32 wherein the electronic circuitry comprises an amplifier in connection with the sensor to receive an electrical signal output from the sensor.

35. The method of claim 34 wherein the electronic circuity further comprises analog-to digital converter in connection with an output of the amplifier, an output of the analog-to digital converter being in communicative connection with the processor system.

36. The method of any of claims 22 through 29 wherein the medical component is acoustically conducting and the sensor is acoustically connected to the medical component or to an acoustically conducting second component which is acoustically connected to the medical component, or the sensor is acoustically connected to a third component, which is different from the medical component, and the third component is an acoustic conducting component that contacts the bone or is in close proximity to the bone.

37. The method of claim 36 wherein the medical component comprises a metal, the second component comprises a metal, and/or the third component comprises a metal.

38. The method of claim 35 wherein the sensor is attached to the medical component.

39. The method of claim 36 wherein the sensor is acoustically connected to a force application pin of a clamp, a needle, a screw, or a fiducial.

40. The method of claim 36 wherein the sensor is acoustically connected to the medical component, which is a force application pin of a clamp, or to the second component, which is a component of the skull clamp other than the force application pin of the clamp.

41. The method of claim 40 wherein the system comprises a clamp which is a skull clamp.

42. The method of claim 41 wherein the skull clamp comprises a plurality of force application pins and the system comprises a plurality of sensors, one of the plurality of sensors being acoustically connected to one of the plurality of force application pins and another of the plurality of sensor being acoustically connected to another of the plurality of force application pins.

43. A system for determining one or more states arising during a medical procedure in which force is applied to a skull, comprising: a skull clamp comprising one or more force application components configured to apply force to the skull, and a sensor responsive to acoustic emissions during the medical procedure, the sensor being configured to be placed in acoustic connection with at least one of the skull and the skull clamp during the medical procedure.

44. The system of claim 43 further comprising electronic circuitry in communicative connection with the sensor, the electronic circuitry being configured to analyze data from the sensor over time during the medical procedure to output the one or more states on the basis of predetermined criteria.

45. The system of claim 44 wherein the electronic circuity is configured to output the one or more states during the medical procedure based upon a monitoring of acoustic emission events over time.

46. The system of claim 45 wherein the one or more states comprises a state of the skull related to fracture thereof or a state of the one or more force application components.

47. The system of claim 46 wherein the electronic circuity is configured to output at least one or a state of stability of the skull, a state of impending fracture of the skull, a state of fracture of the skull, a state of movement of the one or more force application components relative to the bone, and a state of impending movement of the medical component relative to the bone.

48. The system of any one of claims 44 through 46 wherein the predetermined criteria associated with the state of stability of the skull comprise a decreasing acoustic emission event rate after force is either first applied or changed.

49. The system of any one of claims 44 through 46 wherein the predetermined criteria associated with a fracture of the skull include a period of acoustic emission following the first application of force or the increase in force which has a waveform exhibiting predetermined statistical properties.

50. The system of any one of claims 44 through 46 wherein the predetermined criteria associated with a fracture of the skull which occurs during a period subsequent to force being either first applied or increased include (ii) at least one of a period of increased acoustic emission event rate prior to fracture of the skull, increased acoustic emission amplitude prior to the fracture of the skull, and a change in one or more quantifiable statistical properties of a time series of acoustic emission events, and (ii) a period of acoustic emission which has a waveform exhibiting predetermined statistical properties following the fracture of the skull.

51. A device for use during a medical procedure, device comprising a sensor in acoustic connection therewith, the sensor being responsive to acoustic emissions created during the medical procedure.

52. The device of claim 51 wherein the device includes a force-application component configured to apply force to a bone and the sensor is acoustically connected to the force-application component.

53. The device of claim 51 wherein the device is a force-application pin used in a skull clamp system and the sensor is acoustically connected to the pin.