Implant Assessment Using Acoustic Emission

Abstract

The present disclosure provides a method of identifying a loose joint implant by analyzing acoustic emissions from the implant. The present disclosure further provides an apparatus for measuring acoustic data and analyzing acoustic emissions from a joint implant.

Description

[0001] This application is a divisional application of patent application 201880065347.0, which has entered the Chinese national phase of PCT application with international application number PCT / US2018 / 063361 and international application date of November 30, 2018.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS

[0003] This application claims the benefit of U.S. Provisional Application No. 62 / 593,210, filed on November 30, 2017, which is incorporated herein by reference in its entirety. Technical Field

[0004] The present disclosure provides a method of identifying a loose joint implant by analyzing acoustic emissions from the implant. The present disclosure further provides an apparatus for measuring acoustic data and analyzing acoustic emissions from a joint implant. Background Art

[0005] Total knee replacement (TKA) has become a routine and successful surgical procedure. In the United States, over 95% of total knee replacements are performed for osteoarthritis. As of 2010, over 600,000 total knee replacements were performed annually in the United States. By 2030, the number of total knee replacements performed annually in the United States is expected to grow by 673% to 3.48 million procedures.

[0006] Failures of TKAs are considered to fall into two groups. Problems within the first two years are considered early failures, and typically patients will begin to experience problems shortly after surgery. Failures that occur after two years are considered late failures. The top three causes of failure are (1) infection, (2) instability, and (3) aseptic loosening. Infection can be detected by testing blood or fluid drawn from the joint area. Instability can be diagnosed by assessing gait and joint motion. The current best practice for diagnosing loosening is to identify a gap between the bone and the implant on an X-ray image, which is considered definite loosening only after 30% of the bone around the implant is lost. As the damage progresses, the cost and risk of revision surgery to correct a failed implant increases significantly. Summary of the invention

[0007] In one aspect, the present disclosure provides and includes a method for identifying a loose implant in a joint, the method comprising the steps of positioning a plurality of acoustic sensors at a corresponding plurality of locations around the joint, moving the joint, receiving signals from the acoustic sensors during the movement of the joint, identifying signals from two or more of the plurality of acoustic sensors corresponding to a common acoustic event, identifying the location of the acoustic event within the joint, and providing a health indication related to the joint.

[0008] In one aspect, the present disclosure provides and includes a method for identifying a location, the method comprising: calculating a first time delay between a first time when a first signal is received from a first acoustic sensor among the multiple acoustic sensors and a second time when a second signal is received from a second acoustic sensor among the multiple acoustic sensors, and calculating a first geometric surface of a possible location of the acoustic event based on the first time delay. In one aspect, a method for identifying a location further comprises: calculating a second time delay between the first reception time and a third time when a third signal is received from a third acoustic sensor among the multiple acoustic sensors, calculating a second geometric surface of a possible location of the acoustic event based on the second time delay, and determining an intersection line of the first geometric surface and the second geometric surface. In one aspect, a method for identifying a location further comprises determining a location where the first geometric surface intersects with the implant.

[0009] In one aspect, the present disclosure provides and includes a method of identifying a location, the method comprising: calculating a first amplitude difference between a first signal amplitude of a first signal from a first acoustic sensor of the plurality of acoustic sensors and a second signal amplitude of a second signal from a second acoustic sensor of the plurality of acoustic sensors, and calculating a first geometric surface of a possible location of the acoustic event based on the first amplitude difference. In one aspect, a method of identifying a location further comprises adjusting the first time delay based on a predetermined speed of signal propagation in each of the one or more types of tissue and within the signal path.

[0010] In one aspect, the present disclosure provides and includes a method for calculating a first time delay, the method comprising: identifying one or more types of tissue between the implant and the first acoustic sensor, identifying one or more signal paths from the implant to the first acoustic sensor, and adjusting the first time delay based on a predetermined speed of signal propagation in each of the one or more types of tissue and within the signal paths.

[0011] In one aspect, the present disclosure provides and includes a method for identifying a loose implant in a joint, the method comprising the steps of positioning an acoustic sensor proximate to the joint, moving the joint, receiving signals from the acoustic sensor during the movement of the joint, analyzing the signals to identify attributes associated with a health state of the joint, and providing a health indication related to the joint.

[0012] In one aspect, the present disclosure provides and includes a method of analyzing a signal, the method comprising: calculating a rise time and an amplitude from the signal, comparing the rise time to a first threshold and comparing the amplitude to a second threshold, and determining that when the rise time exceeds the first threshold and the amplitude exceeds the second threshold, the signal indicates a loose implant. In one aspect, the method of analyzing a signal in the present disclosure is performed only when the signal contains a dominant frequency within a predetermined band.

[0013] In one aspect, the present disclosure provides and includes a method for analyzing a signal, the method comprising: calculating a power spectral density (PSD) of the signal, calculating a first local power of the PSD within a predetermined first frequency band, comparing the first local power to a first threshold, and determining that when the first local power exceeds the first threshold, the signal indicates a loose implant.

[0014] In one aspect, the present disclosure provides and includes a method of analyzing a signal, the method comprising: calculating a power spectral density (PSD) of the signal, calculating a first local power of the PSD within a predetermined first frequency band, calculating a second local power of the PSD within a predetermined second frequency band, and comparing the first local power to the second local power. In one aspect, the comparison of the first local power to the second local power comprises: calculating a ratio of the first local power to the second local power, and determining that when the ratio exceeds a threshold, the signal indicates a loose implant. In one aspect, the comparison of the first local power to the second local power comprises: calculating a difference between the first local power and the second local power, and determining that when the difference exceeds a threshold, the signal indicates a loose implant.

[0015] In one aspect, the present disclosure provides and includes a method for analyzing a signal, the method comprising: calculating a power spectral density (PSD) of the signal, calculating a first maximum value of the PSD within a predetermined first frequency band, calculating a second maximum value of the PSD within a predetermined second frequency band, and comparing the first maximum value with the second maximum value.

[0016]

[0013] In one aspect, the present disclosure provides and encompasses a method of providing an indication of health associated with a joint, the method comprising evaluating a total number of acoustic events indicative of a loose implant to determine a diagnostic indication of a loose implant.

[0017] In one aspect, the present disclosure provides and includes a device for identifying a loose implant in a joint, the device comprising the following steps: a plurality of acoustic sensors configured to be placed in contact with the patient's skin at a corresponding plurality of locations around the joint, a processor configured to receive signals from the acoustic sensors during movement of the joint, wherein the processor is configured to: identify signals corresponding to a common acoustic event from two or more of the plurality of acoustic sensors, compare attributes of the signals, identify the location of the acoustic event within the joint, and provide a health indication related to the joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Aspects of the present disclosure are described herein with reference to the accompanying drawings by way of example only. With specific reference now to the drawings in detail, it is emphasized that the details shown are exemplary and are for the purpose of illustrative discussion of aspects of the present disclosure. In this regard, the description and drawings, considered individually and together, enable those skilled in the art to understand how to practice aspects of the present disclosure.

[0019] Figure 1A and Figure 1B are anterior and posterior views of a patient's legs while assessing right leg mobility in accordance with the present disclosure.

[0020] Figure 1C An example sensor assembly according to the present disclosure is depicted.

[0021] Figure 1D is a front partial view of a patient's leg during assessment of loosening in accordance with the present disclosure.

[0022] Figure 1E Another example sensor assembly according to the present disclosure is depicted.

[0023] Figure 2 An implant evaluation system according to the present disclosure is depicted.

[0024] Figure 3 is an illustration of a knee with an implant and an acoustic sensor in accordance with the present disclosure.

[0025] Figure 4A and Figure 4B is a graph of signals from two spatially separated acoustic sensors in accordance with the present disclosure.

[0026] Figure 5A Depicted are properties of representative acoustic signals according to the present disclosure.

[0027] Figure 5B Describes a method for analyzing Figure 5A The threshold of the acoustic signal.

[0028] Figure 6A method of detecting loosening of an implant by increasing the amplitude of a resonant frequency according to the present disclosure is depicted.

[0029] Figure 7 A method of detecting loosening of an implant by evaluating local power of a frequency window in accordance with the present disclosure is depicted.

[0030] Fig. 8A and Figure 8B is a graph of signals from acoustic sensors on two patients in accordance with the present disclosure.

[0031] Figure 8C and Fig.8D According to the present disclosure Fig. 8A and Figure 8B A plot of the power spectral density (PSD) of a signal. DETAILED DESCRIPTION

[0032] This description is not intended to be a detailed catalog of all the different ways in which the present disclosure can be implemented or all the features that can be added to the current disclosure. For example, the features shown in relation to one embodiment can be incorporated into other embodiments, and the features shown in relation to a specific embodiment can be deleted from the embodiment. Therefore, the present disclosure contemplates that in some embodiments of the present disclosure, any feature or feature combination set forth herein may be excluded or omitted. In addition, according to the current disclosure, it will be apparent to those skilled in the art that various changes and additions to the various embodiments proposed herein will be apparent without departing from the present disclosure. In other cases, known structures, interfaces, and processes are not shown in detail to avoid unnecessarily obscuring the present invention. It is intended that any part of this specification should not be interpreted as a negation of any part of the full scope of the present invention. Therefore, the following description is intended to illustrate some specific embodiments of the present disclosure, rather than to exhaustively indicate all its permutations, combinations, and variations.

[0033] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those of ordinary skill in the art to which the present disclosure belongs. The terms used in the description of the present disclosure are only for the purpose of describing specific aspects or embodiments and are not intended to limit the present disclosure.

[0034] All publications, patent applications, patents and other references cited herein are incorporated by reference in their entirety for teachings relevant to the sentence and / or paragraph in which the reference is presented. References to the techniques employed herein are intended to represent techniques commonly understood in the art, including changes to those techniques or substitutions of equivalent techniques that are obvious to those skilled in the art.

[0035] Unless the context indicates otherwise, it is specifically intended that the various features of the present disclosure described herein can be used in any combination. In addition, the present disclosure also contemplates that in some embodiments of the present disclosure, any feature or feature combination set forth herein can be excluded or omitted.

[0036] The method disclosed herein includes and comprises one or more steps or actions for realizing the described method. Without departing from the scope of the present disclosure, the method steps and / or actions can be interchanged with each other. In other words, unless the correct operation of the embodiment requires specific steps or action sequences, otherwise, without departing from the scope of the present disclosure, the order and / or use of specific steps and / or actions can be modified.

[0037] As used in the description of the present disclosure and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0038] As used herein, "and / or" refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of a combination when interpreted in the alternative ("or").

[0039] As used herein, the terms "about" and "approximately" when referring to measurable values ​​such as length, frequency, or acoustic measurements are meant to encompass variations of ±20%, ±10%, ±5%, ±1%, ±0.5%, or even ±0.1% of the specified amount.

[0040] As used herein, phrases such as "between X and Y" and "between about X and Y" should be interpreted to include X and Y. As used herein, phrases such as "between about X and Y" mean "between about X and about Y" and phrases such as "from about X to Y" mean "from about X to about Y."

[0041] As used herein, a "patient" can be a human or animal subject.

[0042] As used herein, "tissue" includes all biological material in the body, including bone, ligaments, tendons, cartilage, and muscle.

[0043] As used herein, "lossy" refers to a property of a material that causes high attenuation or dissipation of energy.

[0044] The method disclosed in the present invention is different from existing algorithms for analyzing acoustic signals, for example, the method involving envelope functions and vector functions provided in U.S. Publication No. 2016 / 0015319. Specifically, Publication '319 implements a data analysis method in which each waveform is analyzed in the time domain using a waveform envelope function (Hilbert transform). Envelope classification is separated into different types, which are separated using vector functions associated with health states. On the other hand, the method disclosed in the present invention uses signals captured on multiple sensors to analyze acoustic events. These signals are more robust, less likely to be caused by noise effects (i.e., triboelectric effects, sensor skin friction), and can be modified to localize. The method disclosed in the present invention also features power spectrum analysis to analyze signals extending beyond the time domain. Without being limited by theory, loose implants have enhanced vibration capabilities, wherein the possible degree of vibration and the damping of the natural vibration (frequency resonance) are related to the degree of looseness. The method disclosed in the present invention includes analysis of specific frequency amplitudes, local power (specific frequency band power), and signal fall times to derive an indication of the possibility of loose implants.

[0045] In one aspect, the acoustic measurements of the present disclosure may be collected by a device comprising: a plurality of acoustic sensors configured to be placed in contact with the patient's skin at a corresponding plurality of locations around a joint; a processor configured to receive signals from the acoustic sensors during joint movement, wherein the processor is configured to: identify signals from two or more of the plurality of acoustic sensors corresponding to a common acoustic event, compare properties of the signals, identify the location of the acoustic sensors within the joint, and provide a health indication related to the joint. In one aspect, the acoustic measurements of the present disclosure may be collected by an Orthosonos device. In one aspect, if two or more signals from two or more of the plurality of acoustic sensors are generated within a sufficiently short time frame (such as within about 0.01 seconds, within about 0.005 seconds, within about 0.004, within about 0.003 seconds, within about 0.0025 seconds, within about 0.002 seconds, within about 0.0015 seconds, or within about 0.001 seconds), they are identified as corresponding to a common acoustic event.

[0046] Figure 1A and Figure 1B 1 is a front view and a rear view of a patient's leg 100 during assessment of right leg 110 looseness according to the present disclosure. In one aspect, the right knee 112 has an implant (in Figure 1A and Figure 1B112) and are being evaluated. In one aspect, three sensors 120, 122, and 124 have been placed at approximately evenly distributed locations around the right thigh 102 above the knee 112, and two sensors 130 and 132 have been placed on the front and back sides of the calf 104 below the knee 112. In one aspect, the number of sensors placed on the thigh 102 or calf 104 is generally in the range of 1 to 8, but can be any number (such as from 1 to 4, from 1 to 6, from 2 to 8, and from 4 to 8) of sensors and arranged in any pattern with vertical and circumferential spatial separation. In one aspect, the sensors placed around the thigh 102 or calf 104 are evenly distributed. In one aspect, the sensors placed around the thigh 102 or calf 104 can have different separation distances. In one aspect, a pair of sensors (e.g., sensor 130 and sensor 132) are placed on opposite sides of the thigh 102 or calf 104. In one aspect, a pair of sensors (e.g., sensor 120 and sensor 122) are closer to one side of the leg 110. In one aspect, the location of the sensor can be selected to improve the connection with the bone. In one aspect, the sensor 130 is positioned directly on the tibia (at Figure 1A In one aspect, the sensor 130 can be repositioned to avoid causing pain to the patient. In one aspect, the sensor 130 can be repositioned to rest flush against the patient's skin. In one aspect, the sensor 130 can be repositioned to accommodate the unique shape of the patient's joint.

[0047] Although the accompanying drawings shown in this article are mainly associated with knee implants, the same method and apparatus can be successfully applied to assess implants in other joints (e.g., hips, spine, and shoulders). Anything in this application should not be interpreted as limiting the application of the disclosed method and apparatus to specific joints or implant types, or limiting application to the mankind.

[0048] Figure 1C Another example sensor assembly 150 according to the present disclosure is depicted. The design and construction of assembly 150 is illustrative, and alternative arrangements, including assemblies mounted only above or below a joint, assemblies adhered locally around the sensor location, sensors temporarily affixed or otherwise held in position proximate to a joint, and other harnesses and attachments known to those skilled in the art, are contemplated. Included in various aspects of assembly 150 are assemblies 150 that perform equivalent functions for positioning an acoustic sensor proximate to a joint other than the knee.

[0049] In one aspect, the acoustic sensors are placed at location 160 and location 162. In one aspect, the acoustic sensors at location 160, location 162 are held in contact with the skin by assembly 150. In one aspect, the acoustic sensors are acoustically coupled to the tissue at location 160, location 162. In one aspect, the acoustic sensors are placed Figure 1C In one aspect, the sensor assembly 150 is worn for a diagnostic protocol that defines motion (e.g., moving from a seated position to a standing position or climbing a set of stairs). In one aspect, the sensor assembly 150 is worn for a period of time that continues normal activity, wherein the sensor assembly 150 includes data collection and storage capabilities to acquire and retain signals from the acoustic sensor until the data record is uploaded to a computer or other data storage system.

[0050] Figure 1D is a front partial view of a patient's leg 110 during assessment of looseness in accordance with the present disclosure. In one aspect, acoustic sensors 172A and 172B are placed on the skin proximate the medial and lateral condyles of the anterior tibial spine 170 adjacent the lower leg 104.

[0051] Figure 1E Another sensor assembly 180 according to the present disclosure is depicted. Sensor 182A and sensor 182B are located on assembly 180 such that both sensors 182A, 182B maintain contact with the skin of the calf 104 on the medial and lateral sides of the anterior tibial spine 170 .

[0052] Figure 2 An implant assessment system 200 according to the present disclosure is depicted. In one aspect, there are four acoustic sensors 202 connected to a processor 204 via cables 206. In one aspect, the sensors 202 communicate wirelessly with the processor 204. In one aspect, the sensors 202 include a memory for storing signals and subsequently uploading the recorded signals to the processor 204. In one aspect, the processor 204 includes a data collection system ( Figure 2 ), the data collection system is configured to receive signals from the acoustic sensors and convert them into digital data. In one aspect, the processor 204 includes a memory ( Figure 2 204 ), the memory is configured to store a portion of the digital data generated from the signal received from the acoustic sensor 202. In one aspect, the processor 204 can be connected to other systems or programs instead of the server 220, such as a cloud-based storage system or an electronic medical record.

[0053] In one aspect, processor 204 is coupled to server 220 as shown by cable 210. In one aspect, cable 210 comprises a communication network ( Figure 2 ), the communication network may include network switches, hubs, wired or wireless communication paths (such as Bluetooth and Ethernet and wifi), wireless access points, and non-volatile storage devices that can be selectively connected to the processor 204 and the server 220. In one aspect, the server 220 includes a database in which digital data or attributes of digital data are stored.

[0054] Determining the health status of a joint that has been partially or completely replaced with an implant or a healthy joint by analyzing acoustic signals as described herein is different from other assessment methods commonly used to evaluate joints, such as computerized axial tomography (CAT or CT) scans and medical ultrasound.

[0055] CAT scans emit electromagnetic radiation at X-ray frequencies that travels through the patient to a receiver that measures the received X-rays. Measurements are taken from different angles to produce cross-sectional images of a particular area. In contrast, the devices and methods disclosed herein utilize passive acoustic transducers to capture pressure waves generated within the body, so they do not emit energy, do not form images, the transducers do not move relative to the patient during a single evaluation session, and the signals are primarily analyzed for direct indications of joint failure, rather than for tissue imaging purposes.

[0056] Medical ultrasound creates images also known as sonograms. Sonograms are generated by using a probe to send ultrasound pulses into tissue where the sound reverberates from various elements of the tissue, with different tissues reflecting the sound to varying degrees. The ultrasound transducer then captures the reflected signal and determines the timing and intensity of the signal. In A mode, the transducer scans a single line and plots the varying response along that line. In B mode, the linear array of transducers in the probe is arranged to produce an image of a two-dimensional (2D) plane through the tissue. In C mode, the reflected signal is gated to form a planar image at a defined depth. Ultrasound is effective for imaging the soft tissues of the body. In contrast, the devices and methods disclosed herein utilize passive acoustic transducers and do not emit energy, do not form images, the transducer does not move relative to the patient during a single assessment session, and the signal is primarily analyzed for direct indications of joint failure, rather than for tissue imaging purposes.

[0057] Figure 3 is an illustration of a knee 300 with an implant 320 and acoustic sensors 340, 342, and 344 according to the present disclosure. The implant 320 has a femoral component 310 adhered to a femur 302, a tibial component 322 having a stem 324 extending into a tibia 304, and a spacer 326. In one aspect, the natural patella 306 can be preserved.

[0058] In one aspect, three acoustic sensors 340, 342, 344 are located in a common horizontal plane and at various locations around the knee, separated from an acoustic event source 336 by distances 330, 332, and 334. In one aspect, distances 330, 332, and 334 are not equal. In another embodiment, the plane is not horizontal. In one aspect, the acoustic event source 336 is at the interface between the tibia 304 and the stem 324.

[0059] When an acoustic event occurs at source 336, a "shock wave" (also referred to as an acoustic signal) propagates outward from source 336 in all directions. The shock wave propagates at a speed associated with the material through which the shock wave passes. The attenuation of the shock wave is also material-dependent. In one aspect, the attenuation of the shock wave when passing through the metal of stem 324 is lower than when the shock wave passes through soft tissue, e.g., the signal retains its strength. Similarly, the velocity of the shock wave in a metal stem 324 will be higher than in soft tissue.

[0060] Each path 330, 332, 334 will have a different overall length and different materials in the path. In one aspect, path 330 passes through stem 324, tibia 304, and soft tissue, while paths 332, 334 pass only through bone and soft tissue. In one aspect, the shock wave initiated at source 336 will arrive at each of acoustic sensors 340, 342, and 344 at different times (referred to as the "time of flight" for that path) and with different signal amplitudes.

[0061] The location of source 336 can be calculated using one or both of the difference in arrival time and the difference in amplitude of the received signal at acoustic sensor 340, acoustic sensor 342, acoustic sensor 344. If the material between source 336 and sensor 340, sensor 342, sensor 344 is uniform, a sphere of possible locations around each of sensors 340, sensor 342, sensor 344 with different diameters can be modeled based on the difference in arrival time plus the common offset duration. The common offset duration is increased until the three spheres intersect at a single point, which is an estimate of the location of source 336. However, in the knee or other joints, the structure is not uniform. A computer model must be used to model the location of acoustic sensor 340, acoustic sensor 342, acoustic sensor 344 on the joint and the structure and composition of the underlying tissue. A surface can be modeled around each of sensors 340, sensor 342, sensor 344 with different shapes that reflect the material between the sensor and the surface, and the intersection point can be identified as before. In one aspect, the estimated location of source 336 is determined when the three surfaces pass within a defined distance of each other, since there may not be a single point where all three surfaces intersect within a common offset duration.

[0062] Similarly, the relative amplitudes of the signals received at the various sensors 340, 342, 344 may be used to determine the shape and size of a sphere modeled around each of sensors 340, 342, 344. In general, the amplitude attenuation of a signal will be greater when the signal passes through a greater thickness of tissue or a more lossy tissue, such as muscle, than bone.

[0063] In one aspect, an additional acoustic sensor ( Figure 3 302 and detects signals originating from source 336, in which case the acoustic path may pass through one or more of tibial component 322, spacer 326, femoral component 310, and femur 302. In one aspect, there are multiple paths between source 336 and an acoustic sensor, such as sensor 340, and the signal from source 336 may arrive at different times and have different amplitudes along these multiple paths. In one aspect, the analysis will determine the signal characteristics associated with only one of the multiple signals received by the sensor.

[0064] Figure 4A and Figure 4B 400 and 440 are graphs of signals 402 and 442 received by two spatially separated acoustic sensors according to the present disclosure. Signal 402 has a maximum amplitude at a peak 410 occurring at time t1. Signal 402 has a corresponding maximum amplitude at a peak 450 occurring at time t2. Figure 2 The signal processing electronics of the illustrated system 200 will compare one or more aspects of the signals 402, 442 to determine whether they are common signals. In the example, the signals 402, 442 originate from a common acoustic event. Since the maximum amplitude of the signal 442 at the peak 450 is less than the maximum amplitude of the signal 402 at the peak 410, the source of the common signal may be farther away from the sensor of the signal 442 than the sensor of the signal 402. This relative distance will also be apparent in the difference between time t1 and time t2.

[0065] Figure 5A Depicts the properties of a representative acoustic signal 502 according to the present disclosure. Figure 5A A threshold having an upper limit 520A and a lower limit 520B is established around a point 504 (time t0) where the signal 502 exceeds the threshold, at which point the signal 502 crosses the lower limit 520B. The signal 502 has a peak amplitude at point 506 and then decays over time until the last trip of the signal 502 outside the threshold is at point 508, at which point the signal 502 crosses the upper limit 520A. The "rise time" 530 ('the time from the first threshold crossing to the highest voltage point on the waveform') is defined as the time interval from point 504 (time t0) to point 506 (time t1). In one aspect, the signal processing electronics determines that the first deviation of the signal 502 from the previous noise is at point 510 (time t3), and uses the time interval 534 between points 510 and 506 to calculate the rise time of the signal 502.

[0066] "Fall time" 532 ('the time from the highest voltage point on the waveform to the last threshold crossing') is defined as the time interval from point 506 to point 508 (i.e., time t2). In one aspect, the fall time is determined using different features of the signal 502 (e.g., the last detectable sine wave at the dominant frequency of the signal 502).

[0067] In one aspect, one or both of the rise time and the fall time are related to one of the components of the implant (e.g., Figure 3 The natural frequency of an object can be determined by suspending the object using a lightweight, inextensible, flexible line (e.g., fishing line) and providing an impulse stimulus, such as a classic "pencil lead breaking" force.

[0068] A fully attached implant will be inhibited from vibrating at its natural frequency by the surrounding bone and cement. However, a loose implant will have a certain ability to vibrate, where the degree of possible vibration and the damping of natural vibrations are related to the degree of looseness. Therefore, the peak amplitude and fall time 532 of signal 502 are properties of signal 502 that are related to the looseness of the implant in the joint being evaluated.

[0069] On the one hand, signal 502 between time t0 and time t2 is considered to be associated with " acoustic event ", and this acoustic event is caused by the mechanical interaction between the element, nearby bone and adjacent tissue of implant.This type of mechanical interaction can comprise the friction between the surface of adjacent tissue, the friction between the element of implant or the motion and collision between the element and bone of implant.Healthy tissue has the acoustic event of the background level of the motion between ligament and bone surface for example.

[0070] In one aspect, the number of acoustic events indicates the health of the joint. A healthy joint will have fewer and lower amplitude acoustic signals than a malfunctioning joint. The total number of acoustic events captured while a person performs a set sequence of movements is included as part of the algorithm calculation to indicate joint looseness.

[0071] Figure 5B Describes a method for analyzing Figure 5A The threshold 540 of the acoustic signal 502 is determined. The threshold 540 has an upper limit 540A and a lower limit 540B. The limit 540A, the limit 540B and Figure 5A The difference between the limits 520A and 520B is that the signals exceeding the limits 520A and 520B are determined as acoustic events, rather than background noise, while the signals exceeding the limits 540A and 540B are determined as acoustic events associated with specific joint health conditions. On the one hand, the signal 502 exceeding the threshold 540 is associated with a loose implant.

[0072] In one aspect, threshold 540 is determined based on observational data recorded from patients with healthy or loose implants, following an optimization function such that the greatest number of faulty implants contain acoustic events crossing such threshold, while healthy implants have the least number of events crossing the threshold.

[0073] Figure 6 Depicted is a method of detecting loosening of an implant by increasing the amplitude of a resonant frequency according to the present disclosure. Figure 1A and Figure 1B The PSD 602 ​​(solid line) of an example signal acquired by the acoustic sensor from a "healthy" implant and the PSD 604 (dashed line) of an example signal acquired by the acoustic sensor from a "faulty" implant are shown. Using the received signal (e.g. Figure 5A and Figure 5B The PSD is generated by performing a Fast Fourier Transform (FFT) of the signal 502 of FIG. 5A. In one aspect, the two implants have similar designs and are known to have a natural frequency 610. A frequency band 612 (also referred to as a "window") has been selected that encompasses the natural frequency 610. In one aspect, the frequency band 612 extends from approximately 20 kHz to 40 kHz.

[0074] PSD 602 ​​has several modest peaks within frequency band 612. PSD 604 of a faulty implant shows much larger peaks within frequency band 612. In one aspect, the maximum amplitude of the peaks within frequency band 612 is compared to threshold 614, wherein an amplitude exceeding threshold 614 indicates that the associated implant is damaged. In one aspect, the ratio of the amplitude of PSD 604 to the amplitude of PSD 602 ​​is compared to the threshold. In one aspect, the area under PSD 604 within frequency band 612 (referred to as "local power") is compared to the local power of PSD 602 ​​within frequency band 612. In one aspect, the ratio of the local powers is compared to a threshold. In one aspect, the difference between the local powers is compared to a threshold.

[0075] On the other hand, PSD 602 ​​is associated with a baseline acoustic signal measured shortly after surgery, while PSD 604 is associated with an acoustic signal measured at the same joint over time. This approach has the advantage of avoiding inter-individual variability in implant surgery details and resulting joint structure.

[0076] Figure 7 Depicted is a method for detecting loosening of an implant by evaluating the local power of signals 702 and 704 within a frequency band according to the present disclosure. On the one hand, four frequency bands 710, 720, 730, and 740 have been defined. Each of the signals 702 (solid line) and 704 (dashed line) has a local power associated with each frequency band 710, 720, 730, and 740. On the one hand, the ratio or difference of the local power of the signals 702 and 704 within a common frequency band is compared. On the one hand, the ratio of the local power of the signal 702 in two frequency bands (e.g., frequency band 710 and frequency band 730) is compared with the same ratio of the local power of the signal 704 in the same frequency band. This has a normalizing effect because the frequency bands (e.g., 740) can be predetermined to capture a baseline signal that is not related to loosening. On the one hand, the frequency bands are not of the same width.

[0077] In one aspect, the frequency limits of frequency band 710 are from 17kHz to 42kHz. In one aspect, the frequency limits of frequency band 710 are from 5kHz to 55kHz, such as from 5kHz to 50kHz, from 5kHz to 45kHz, from 10kHz to 55kHz, from 10kHz to 50kHz, from 10kHz to 40kHz, from 15kHz to 55kHz, from 15kHz to 50kHz, from 15kHz to 45kHz, from 5kHz to 42kHz, from 10kHz to 42kHz, from 15kHz to 42kHz, from 17kHz to 45kHz, from 17kHz to 50kHz, or from 17kHz to 55kHz. In one aspect, the frequency limits of frequency band 720 are from 55kHz to 75kHz. In one aspect, the frequency limits of frequency band 720 are from 45kHz to 80kHz, such as from 45kHz to 75kHz, from 50kHz to 75kHz, from 55kHz to 80kHz, from 60kHz to 80kHz, from 65kHz to 80kHz, from 70kHz to 80kHz, from 75kHz to 80kHz, from 55kHz to 70kHz, from 55kHz to 65kHz, or from 55kHz to 60kHz. In one aspect, the frequency limits of frequency band 730 are from 80kHz to 105kHz. In one aspect, the frequency limits of frequency band 730 are from 75kHz to 200kHz, such as from 75kHz to 190kHz, from 75kHz to 180kHz, from 75kHz to 170kHz, from 75kHz to 160kHz, from 75kHz to 150kHz, from 75kHz to 140kHz, from 75kHz to 130kHz, from 75kHz to 120kHz, from 75kHz to 110kHz, from 75kHz to 105kHz, from 80kHz to 200kHz, such as from 80kHz to 190kHz, from 80kHz to 180kHz, from 80kHz to 170kHz, from 80kHz to 160kHz, from 80kHz to 150kHz, from 80kHz to 140kHz, from 80kHz to 130kHz, from 80kHz to 120kHz, or from 80kHz to 110kHz. In one aspect, the frequency limits of frequency band 740 are from 200kHz to 400kHz.In one aspect, the frequency limits of frequency band 740 are from 105kHz to 500kHz, such as from 105kHz to 400kHz, from 105kHz to 410kHz, from 105kHz to 420kHz, from 105kHz to 430kHz, from 105kHz to 440kHz, from 105kHz to 450kHz, from 105kHz to 460kHz, from 105kHz to 470kHz, from 105kHz to 480kHz, from 105kHz to 490kHz, from 200kHz to 500kHz, from 200kHz to 490kHz, from 200kHz to 480kHz, from 200kHz to 470kHz, from 200kHz to 460kHz, from 200kHz to 450kHz, from 200kHz to 440kHz, from 200kHz to 430kHz, from 200kHz to 420kHz, or 200kHz to 410kHz.

[0078] Fig. 8A and Figure 8B 800 and 820 of signal 802 and signal 822 from acoustic sensors on two patients in accordance with the present disclosure. Signal 802 is received from an acoustic sensor near a "well-functioning" implant, while signal 822 is received from an acoustic sensor near a "faulty" implant. Signal 802 has a clear waveform with a main frequency, a clear rise time and fall time, a low amplitude low frequency element that increases in amplitude after time 0.0006, and very little high frequency noise. Signal 822 has a lower maximum amplitude than signal 802, has no clear single frequency, and does not show a clear rise time and fall time. At first glance, one might decide that the implant associated with signal 802 is more compromised than the implant associated with signal 822.

[0079] Figure 8C and Fig.8D According to the present disclosure Fig. 8A and Figure 8B 840 and 860 of PSDs 842 and 862 of signals 802 and 822. PSD 842 has a first peak 846 and a second, larger peak 844. PSD 862 has a peak 866 at approximately the same frequency as peak 846 and a second, larger peak 864 at approximately the same frequency as peak 844. In one aspect, a ratio of the amplitude of peak 846 to the amplitude of peak 844 is calculated and compared to a ratio of the amplitude of peak 866 to the amplitude of peak 864. For example, the ratio of peak 846 to peak 844 is 0.27, while the ratio of peak 866 to peak 864 is 0.71, wherein an increase in the ratio is associated with degradation of the implant associated with signal 822.

[0080] In one aspect, the specific frequencies of the peaks compared by the ratio may vary slightly from person to person. In one aspect, the amplitude of the highest peak in a first frequency band, such as frequency band 870, can be compared to the amplitude of the highest peak in a second frequency band, such as frequency band 872. In one aspect, the ratio need not be that the lower frequency band is above the higher frequency band, for example, either frequency band can define the numerator or denominator of the ratio. In one aspect, the local powers within frequency bands 870, 872 can be compared by ratio or difference.

[0081] Based on the foregoing, it will be appreciated that the present disclosure may be embodied in various ways, including but not limited to the following:

[0082] Embodiment 1. A method for identifying a loose implant in a joint, the method comprising the steps of positioning a plurality of acoustic sensors at a corresponding plurality of locations around the joint, moving the joint, receiving signals from the acoustic sensors during the movement of the joint, identifying signals corresponding to a common acoustic event from two or more of the plurality of acoustic sensors, identifying the location of the acoustic event within the joint, and providing health indications related to the joint.

[0083] Embodiment 2. A method according to embodiment 1, wherein the step of identifying a location comprises: calculating a first time delay between a first time when a first signal is received from a first acoustic sensor among a plurality of acoustic sensors and a second time when a second signal is received from a second acoustic sensor among the plurality of acoustic sensors, and calculating a first geometric surface of a possible location of the acoustic event based on the first time delay.

[0084] Embodiment 3. A method according to Embodiment 2, wherein the step of identifying a location further comprises: calculating a second time delay between a first receiving time and a third time when a third signal is received from a third acoustic sensor among a plurality of acoustic sensors, calculating a second geometric surface of a possible location of the acoustic event based on the second time delay, and determining an intersection line of the first geometric surface and the second geometric surface.

[0085] Embodiment 4. The method according to embodiment 2, wherein the step of identifying the position further comprises determining the position where the first geometric surface intersects with the implant.

[0086] Example 5. A method according to Example 2, wherein the step of calculating the first time delay includes: identifying one or more types of tissue between the implant and the first acoustic sensor, identifying one or more signal paths from the implant to the first acoustic sensor, and adjusting the first time delay based on a predetermined speed of signal propagation in each of the one or more types of tissue and within the signal path.

[0087] Embodiment 6. A method according to embodiment 1, wherein the step of identifying a location comprises: calculating a first amplitude difference between a first signal amplitude of a first signal from a first acoustic sensor among a plurality of acoustic sensors and a second signal amplitude of a second signal from a second acoustic sensor among a plurality of acoustic sensors, and calculating a first geometric surface of a possible location of the acoustic event based on the first amplitude difference.

[0088] Embodiment 7. The method of embodiment 6 further comprises: adjusting the first time delay based on a predetermined speed of signal propagation within each of one or more types of tissue and within the signal path.

[0089] Example 8. A method for identifying a loose implant in a joint, the method comprising the steps of positioning an acoustic sensor proximate to the joint, moving the joint, receiving signals from the acoustic sensor during the joint movement, analyzing the signals to identify attributes associated with a health state of the joint, and providing health indications related to the joint.

[0090] Example 9. A method according to Example 8, wherein the step of analyzing the signal includes: calculating a rise time and an amplitude based on the signal, comparing the rise time with a first threshold and comparing the amplitude with a second threshold, and determining that when the rise time exceeds the first threshold and the amplitude exceeds the second threshold, the signal indicates a loose implant.

[0091] Embodiment 10. The method of embodiment 8, wherein the step of analyzing the signal is performed only when the signal contains a dominant frequency within a predetermined band.

[0092] Embodiment 11. The method of embodiment 10, wherein the predetermined band is associated with the implant.

[0093] Example 12. A method according to Example 8, wherein the step of analyzing the signal includes: calculating the power spectral density (PSD) of the signal, calculating a first local power of the PSD within a predetermined first frequency band, comparing the first local power with a first threshold, and determining that when the first local power exceeds the first threshold, the signal indicates a loose implant.

[0094] Embodiment 13. The method of Embodiment 12, wherein the predetermined frequency band includes a resonant frequency associated with the implant.

[0095] Embodiment 14. A method according to Embodiment 8, wherein the step of analyzing the signal comprises: calculating the power spectral density (PSD) of the signal, calculating the first local power of the PSD within a predetermined first frequency band, calculating the second local power of the PSD within a predetermined second frequency band, and comparing the first local power with the second local power.

[0096] Embodiment 15. The method of embodiment 14, wherein the comparing step comprises calculating a ratio of the first local power to the second local power, and determining that when the ratio exceeds a threshold value, the signal indicates a loose implant.

[0097] Embodiment 16. The method of embodiment 14, wherein the comparing step comprises calculating a difference between the first local power and the second local power, and determining that when the difference exceeds a threshold, the signal indicates a loose implant.

[0098] Embodiment 17. A method according to Embodiment 8, wherein the step of analyzing the signal comprises: calculating the power spectral density (PSD) of the signal, calculating a first maximum value of the PSD within a predetermined first frequency band, calculating a second maximum value of the PSD within a predetermined second frequency band, and comparing the first maximum value with the second maximum value.

[0099] Example 18. The method of Example 8, wherein the step of providing a health indication related to the joint comprises: evaluating a total number of acoustic events indicative of a loose implant to determine a diagnostic indication of a loose implant.

[0100] Embodiment 19. A device for identifying a loose implant in a joint, the device comprising the following steps: a plurality of acoustic sensors configured to be placed in contact with the patient's skin at a corresponding plurality of locations around the joint; a processor configured to receive signals from the acoustic sensors during joint movement, wherein the processor is configured to: identify signals corresponding to common acoustic events from two or more of the plurality of acoustic sensors, compare properties of the signals, identify the location of the acoustic event within the joint, and provide health indications related to the joint.

[0101] Although the present disclosure has been described with reference to specific aspects, it will be appreciated by those skilled in the art that various changes may be made and equivalents may be substituted for its elements without departing from the scope of the present disclosure. In addition, many modifications may be made to the specific circumstances or materials of the teachings of the present disclosure without departing from the scope of the present disclosure. Therefore, the present disclosure is not intended to be limited to the specific aspects disclosed, but the present disclosure will include all aspects falling within the scope and spirit of the appended claims.

Claims

1. A device for identifying a loose implant in a joint, the device comprising: an acoustic sensor configured to be placed in contact with the patient's skin at a location proximate to the joint, a processor configured to receive signals from the acoustic sensor during movement of the joint, and A non-transitory computer readable medium, electrically coupled to the processor and comprising instructions stored thereon, which when executed on the processor, perform the following steps: analyzing the signal to identify a property associated with a joint health state only if the signal includes a dominant frequency within a predetermined band, and providing health indications related to said joints, Wherein, analyzing the signal comprises: Calculate the power spectral density PSD of the signal, calculating a first local power of the PSD within a predetermined first frequency band, comparing the first local power to a first threshold, and When the first local power exceeds the first threshold, it is determined that the signal is indicative of a loose implant.

2. The device according to claim 1, wherein: The predetermined band includes a resonant frequency associated with the implant.

3. A device for identifying a loose implant in a joint, the device comprising: an acoustic sensor configured to be placed in contact with the patient's skin at a location proximate to the joint, a processor configured to receive signals from the acoustic sensor during movement of the joint, and A non-transitory computer readable medium, electrically coupled to the processor and comprising instructions stored thereon, which when executed on the processor, perform the following steps: analyzing the signal to identify a property associated with a joint health state only if the signal includes a dominant frequency within a predetermined band, and providing health indications related to said joints, Wherein, analyzing the signal comprises: Calculate the power spectral density PSD of the signal, calculating a first local power of the PSD within a predetermined first frequency band, calculating a second local power of the PSD within a predetermined second frequency band, and The first local power is compared to the second local power.

4. The device according to claim 3, wherein: The comparing the first local power with the second local power comprises: calculating a ratio of the first local power to the second local power, and When the ratio exceeds a threshold, it is determined that the signal is indicative of a loose implant.

5. The device according to claim 3, wherein: The comparing the first local power with the second local power comprises: calculating a difference between the first local power and the second local power, and When the difference exceeds a threshold, it is determined that the signal is indicative of a loose implant.

6. A device for identifying a loose implant in a joint, the device comprising: an acoustic sensor configured to be placed in contact with the patient's skin at a location proximate to the joint, a processor configured to receive signals from the acoustic sensor during movement of the joint, and A non-transitory computer readable medium, electrically coupled to the processor and comprising instructions stored thereon, which when executed on the processor, perform the following steps: analyzing the signal to identify attributes associated with joint health, and providing health indications related to said joints, Wherein, analyzing the signal comprises: Calculate the power spectral density PSD of the signal, calculating a first maximum value of the PSD within a predetermined first frequency band, calculating a second maximum value of the PSD within a predetermined second frequency band, and The first maximum value is compared to the second maximum value.

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