US20100331633A1 - System and method for short range telemetry to measure a parameter of the muscular-skeletal system - Google Patents

Abstract

A sensing insert device (100) is disclosed for measuring a parameter of the muscular-skeletal system. The sensing insert device (100) can be temporary or permanent. Used intra-operatively, the sensing insert device (100) comprises an insert dock202 and a sensing module200. The sensing module (200) is a self-contained encapsulated measurement device having at least one contacting surface that couples to the muscular-skeletal system. The sensing module (200) comprises one or more sensors (303), electronic circuitry (307), and communication circuitry (320). The electronic circuitry (307) operatively couples to the one or more sensors (303) to measure the parameter. The communication circuitry (320) couples to the electronic circuitry (307) to wirelessly transmit measurement data. The sensing module (200) wirelessly sends one or more data packets where each data packet comprises sensor data and a priority level. The data packet can further include a cyclic redundancy check.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims the priority benefit of U.S. provisional patent applications No. 61/221,761, 61/221,767, 61/221,779, 61/221,788, 61/221,793, 61/221,801, 61/221,808, 61/221,817, 61/221,867, 61/221,874, 61/221,879, 61/221,881, 61/221,886, 61/221,889, 61/221,894, 61/221,901, 61/221,909, 61/221,916, 61/221,923, and 61/221,929 all filed 30 Jun. 2009; the disclosures of which are hereby incorporated herein by reference in their entirety.
FIELD
• The present invention pertains generally to measurement of physical parameters, and particularly to, but not exclusively to, communication of sensor data and measurements in real-time.
BACKGROUND
• The skeletal system of a mammal is subject to variations among species. Further changes can occur due to environmental factors, degradation through use, and aging. An orthopedic joint of the skeletal system typically comprises two or more bones that move in relation to one another. Movement is enabled by muscle tissue and tendons attached to the skeletal system of the joint. Ligaments hold and stabilize the one or more joint bones positionally. Cartilage is a wear surface that prevents bone-to-bone contact, distributes load, and lowers friction.
• There has been substantial growth in the repair of the human skeletal system. In general, orthopedic joints have evolved using information from simulations, mechanical prototypes, and patient data that is collected and used to initiate improved designs. Similarly, the tools being used for orthopedic surgery have been refined over the years but have not changed substantially. Thus, the basic procedure for replacement of an orthopedic joint has been standardized to meet the general needs of a wide distribution of the population. Although the tools, procedure, and artificial joint meet a general need, each replacement procedure is subject to significant variation from patient to patient. The correction of these individual variations relies on the skill of the surgeon to adapt and fit the replacement joint using the available tools to the specific circumstance.
BRIEF DESCRIPTION OF THE DRAWINGS
• Various features of the system are set forth with particularity in the appended claims. The embodiments herein, can be understood by reference to the following description, taken in conjunction with the accompanying drawings, in which:
• FIG. 1 is an illustration of an application of sensing insert device in accordance with an exemplary embodiment;
• FIG. 2 is an illustration of a sensing insert device placed in a joint of the muscular-skeletal system for measuring a parameter in accordance with an exemplary embodiment;
• FIG. 3 is a perspective view of a medical sensing platform comprising an encapsulating enclosure in accordance with one embodiment;
• FIG. 4 is a perspective view of a medical sensing device suitable for use as a bi-compartmental implant and comprising an encapsulating enclosure in accordance with one embodiment;
• FIG. 5 is an exemplary block diagram of the components of the sensing module in accordance with an exemplary embodiment;
• FIG. 6 is a diagram of an exemplary communications system for short-range telemetry according to one embodiment;
• FIG. 7 is an illustration of a block model diagram of the sensing module in accordance with an exemplary embodiment;
• FIG. 8 is an exemplary assemblage that illustrates propagation of ultrasound waves within the waveguide in the bi-directional mode of operation of this assemblage in accordance with one embodiment;
• FIG. 9 is an exemplary cross-sectional view of an ultrasound waveguide to illustrate changes in the propagation of ultrasound waves with changes in the length of the waveguide in accordance with one embodiment;
• FIG. 10 is an exemplary block diagram of a propagation tuned oscillator (PTO) to maintain positive closed-loop feedback in accordance with an exemplary embodiment;
• FIG. 11 is a cross-sectional view of a layout architecture of the sensing module in accordance with an exemplary embodiment;
• FIG. 12 is a simplified cross-sectional view of an embodiment of the load sensing platform in accordance with an exemplary embodiment;
• FIG. 13 is a flowchart of a method for sensor data communications in accordance with an exemplary embodiment; and
• FIG. 14 is an illustration of an exemplary data packet containing sensor data.
DETAILED DESCRIPTION
• Embodiments of the invention are broadly directed to measurement of physical parameters. Many physical parameters of interest within physical systems or bodies can be measured by evaluating changes in the characteristics of energy waves or pulses. As one example, changes in the transit time or shape of an energy wave or pulse propagating through a changing medium can be measured to determine the forces acting on the medium and causing the changes. The propagation velocity of the energy waves or pulses in the medium is affected by physical changes in of the medium. The physical parameter or parameters of interest can include, but are not limited to, measurement of load, force, pressure, displacement, density, viscosity, localized temperature. These parameters can be evaluated by measuring changes in the propagation time of energy pulses or waves relative to orientation, alignment, direction, or position as well as movement, rotation, or acceleration along an axis or combination of axes by wireless sensing modules or devices positioned on or within a body, instrument, appliance, vehicle, equipment, or other physical system.
• In all of the examples illustrated and discussed herein, any specific materials, temperatures, times, energies, etc. for process steps or specific structure implementations should be interpreted to illustrative only and non-limiting. Processes, techniques, apparatus, and materials as known by one of ordinary skill in the art may not be discussed in detail but are intended to be part of an enabling description where appropriate.
• Note that similar reference numerals and letters refer to similar items in the following figures. In some cases, numbers from prior illustrations will not be placed on subsequent figures for purposes of clarity. In general, it should be assumed that structures not identified in a figure are the same as previous prior figures.
• In the present invention these parameters are measured with an integrated wireless sensing module or device comprising an i) encapsulating structure that supports sensors and contacting surfaces and ii) an electronic assemblage that integrates a power supply, sensing elements, ultrasound resonator or resonators or transducer or transducers and ultrasound waveguide or waveguides, biasing spring or springs or other form of elastic members, an accelerometer, antennas and electronic circuitry that processes measurement data as well as controls all operations of energy conversion, propagation, and detection and wireless communications. The wireless sensing module or device can be positioned on or within, or engaged with, or attached or affixed to or within, a wide range of physical systems including, but not limited to instruments, appliances, vehicles, equipments, or other physical systems as well as animal and human bodies, for sensing and communicating parameters of interest in real time.
• FIG. 1 is an illustration of an application of sensinginsert device100 in accordance with an exemplary embodiment. The illustration shows thedevice100 measuring a force, pressure, or load applied by the muscular-skeletal system. In the illustration,device100 can collect load data for real-time viewing of the load forces over various applied loads and angles of flexion. The sensinginsert device100 can measure the level and distribution of load at various points on the prosthetic component and transmits the measured load data by way secure short-range communication109 to a receiver for permitting visualization. This can aid the surgeon in making any adjustments needed to achieve optimal joint balancing.
• The sensinginsert device100 can measure the level and distribution of load at various points on the prosthetic component and transmits the measured load data by way secure short-range communication109 to a receiver for permitting visualization.
• In general,device100 has at least one contacting surface that couples to the muscular-skeletal system. As shown, a first and a second contacting surface respectively couple to afemoral prosthetic component104 and atibial prosthetic component106.Device100 is designed to be used in the normal flow of an orthopedic surgical procedure without special procedures, equipment, or components. Typically, one or more natural components of the muscular-skeletal system are replaced when joint functionality substantially reduces a patient quality of life. A joint replacement is a common procedure in later life because it is prone to wear over time, can be damaged during physical activity, or by accident.
• A joint of the muscular-skeletal system provides movement of bones in relation to one another that can comprise angular and rotational motion. The joint can be subjected to loading and torque throughout the range of motion. The joint typically comprises two bones that move in relation to one another with a low friction flexible connective tissue such as cartilage between the bones. The joint also generates a natural lubricant that works in conjunction with the cartilage to aid in ease of movement. Sensinginsert device100 mimics the natural structure between the bones of the joint.Insert device100 has a contacting surface on which a bone or a prosthetic component can moveably couple. A knee joint is disclosed for illustrative purposes butsensing insert device100 is applicable to other joints of the muscular-skeletal system. For example, the hip, spine, and shoulder have similar structures comprising two or more bones that move in relation to one another. In general,insert device100 can be used between two or more bones allowing movement of the bones during measurement or maintaining the bones in a fixed position.
• The loadsensor insert device100 and thereceiver station110 forms a communication system for conveying data via secure wireless transmission within a broadcasting range over short distances on the order of a few meters to protect against any form of unauthorized or accidental query. In one embodiment, the transmission range is five meters or less which is approximately a dimension of an operating room. In practice, it can be a shorter distance 1-2 meters to transmit to a display outside the sterile field. The transmit distance will be even shorter whendevice100 is used in a prosthetic implanted component. Transmission occurs through the skin of the patient and is likely limited to less than 0.5 meters. A combination of cyclic redundancy checks and a high repetition rate of transmission during data capture permits discarding of corrupted data without materially affecting display of data.
• In the illustration, a surgical procedure is performed to place a femoralprosthetic component104 onto a prepared distal end of thefemur102. Similarly, a tibialprosthetic component106 is placed to a prepared proximal end of thetibia108. The tibialprosthetic component106 can be a tray or plate affixed to a planarized proximal end of thetibia108. Thesensing insert device100 is a third prosthetic component that is placed between the plate of the tibialprosthetic component106 and the femoralprosthetic component104. The three prosthetic components enable the prostheses to emulate the functioning of a natural knee joint. In one embodiment,sensing insert device100 is used during surgery and replaced with a final insert after quantitative measurements are taken to ensure optimal fit, balance, and loading of the prosthesis.
• In one embodiment,sensing insert device100 is a mechanical replica of a final insert. In other words, sensinginsert device100 has substantially equal dimensions to the final insert. The substantial equal dimensions ensure that the final insert when placed in the reconstructed joint will have similar loading and balance as that measured by sensinginsert device100 during the trial phase of the surgery. Moreover, passive trial inserts are commonly used during surgery to determine the appropriate final insert. Thus, the procedure remains the same. It can measure loads at various points (or locations) on the femoralprosthetic component104 and transmit the measured data to a receivingstation110 by way of an integrated loop antenna. The receivingstation110 can include data processing, storage, or display, or combination thereof and provide real time graphical representation of the level and distribution of the load.
• As one example, thesensing insert device100 can measure forces (Fx, Fy, and Fz) with corresponding locations and torques (e.g. Tx, Ty, and Tz) on the femoralprosthetic component104 and the tibialprosthetic component106. It can then transmit this data to the receivingstation110 to provide real-time visualization for assisting the surgeon in identifying any adjustments needed to achieve optimal joint balancing.
• FIG. 2 is an illustration of asensing insert device100 placed in a joint of the muscular-skeletal system for measuring a parameter in accordance with an exemplary embodiment. In particular, sensinginsert device100 is placed in contact between afemur102 and atibia108 for measuring a parameter. In the example, a force, pressure, or load is being measured. Thedevice100 in this example can intra-operatively assess a load on prosthetic components during the surgical procedure. As mentioned previously,sensing insert device100 collects data for real-time viewing of the load forces over various applied loads and angles of flexion. It can measure the level and distribution of load at various points on the prosthetic component and transmit the measured load data by way data communication to areceiver station110 for permitting visualization. This can aid the surgeon in making any adjustments needed to achieve optimal joint balancing.
• A proximal end oftibia108 is prepared to receive tibialprosthetic component106. Tibialprosthetic component106 is a support structure that is fastened to the proximal end of the tibia and is usually made of a metal or metal alloy. The tibialprosthetic component106 also retains the insert in a fixed position with respect totibia108. Similarly, a distal end offemur102 is prepared to receive femoralprosthetic component104. The femoralprosthetic component104 is generally shaped to have an outer condylar articulating surface. The preparation offemur102 andtibia108 is aligned to the mechanical axis of the leg. Thesensing insert device100 provides a concave or flat surface against which the outer condylar articulating surface of the femoralprosthetic component104 rides relative to thetibia prosthetic component106. In particular, the top surface of thesensing module200 faces the condylar articulating surface of the femoralprosthetic component104, and the bottom surface of theinsert dock202 faces the top surface of the tibialprosthetic component106.
• A final insert is subsequently fitted between femoralprosthetic component104 and tibialprosthetic component106 that has a bearing surface that couples tofemoral component104 allowing the leg a natural range of motion. The final insert is has a wear surface that is typically made of a low friction polymer material. Ideally, the prosthesis has an appropriate loading, alignment, and balance that mimics the natural leg and maximizes the life of the artificial components. It should be noted thatsensing module200 can be placed a final insert and operated similarly as disclosed herein. Thesensing module200 can be used to periodically monitor status of the permanent joint.
• Thesensing insert device100 is used to measure, adjust, and test the reconstructed joint prior to installing the final insert. As mentioned previously, thesensing insert device100 is placed between thefemur102 andtibia108. The condyle surface offemoral component104 contacts a major surface ofdevice100. The major surface ofdevice100 approximates a surface of a final insert. Tibialprosthetic component106 can include a cavity or tray on the major surface that receives and retains aninsert dock202 and asensing module200 during a measurement process. It should be noted thatsensing insert device100 is coupled to and provides measurement data in conjunction with other implanted prosthetic components. In other words, the prosthetic components are the permanent installed components of the patient.
• Insert dock202 is provided in different sizes and shapes.Insert dock202 can comprise many different sizes and shapes to interface appropriately with different manufacturer prosthetic components. Prosthetic components are made in different sizes to accommodate anatomical differences over a wide population range.Insert dock202 is designed for different prosthetic sizes within the same manufacturer. In at least one embodiment, multiple docks of different dimensions are provided for a surgery. For example, the thickness of the final insert is determined by the surgical cuts to the muscular-skeletal system and measurements provided bysensing module200. The surgeon may try two insertdocks202 of different thicknesses before making a final decision. In one embodiment,sensing insert device100 selected by the surgeon has substantial equal dimensions to the final insert used. In general,insert dock202 allows standardization on asingle sensing module200 for different prosthetic platforms. Thus, thesensing module200 is common to thedifferent insert docks202 allowing improved quality, reliability, and performance.
• In one embodiment, one ormore insert docks202 are used to determine an appropriate thickness that yields an optimal loading. In general, the absolute loading over the range of motion is kept within a predetermined range. Soft tissue tensioning can be used to adjust the absolute loading. The knee balance can also be adjusted within a predetermined range if a total knee reconstruction is being performed and asensing module202 is used in each compartment. Tibialprosthetic component106 anddevice100 have a combined thickness that represents a combined thickness of tibialprosthetic component106 and a final (or chronic) insert of the knee joint. Thus, the final insert thickness or depth is chosen based on the trial performed usingdevice100. Typically, the final insert thickness is identical to thedevice100 to maintain the measured loading and balance. In one embodiment,sensing module200 and insertdocks202 are disposed of after surgery. Alternatively, thesensing module200 and insertdocks202 can be cleaned, sterilized, and packaged for reuse.
• Theprosthesis incorporating device100 emulates the function of a natural knee joint.Device100 can measure loads or other parameters at various points throughout the range of motion. Data fromdevice100 is transmitted to a receivingstation110 via wired or wireless communications. In a first embodiment,device100 is a disposable system.Device100 can be disposed of after using thesensing insert device100 to optimally fit the joint implant.Device100 is a low cost disposable system that reduces capital costs, operating costs, facilitates rapid adoption of quantitative measurement, and initiates evidentiary based orthopedic medicine. In a second embodiment, a methodology can be put in place to clean and sterilizedevice100 for reuse. In a third embodiment,device100 can be incorporated in a tool instead of being a component of the replacement joint. The tool can be disposable or be cleaned and sterilized for reuse. In a fourth embodiment,device100 can be a permanent component of the replacement joint.Device100 can be used to provide both short term and long term post-operative data on the implanted joint. In a fifth embodiment,device100 can be coupled to the muscular-skeletal system. In all of the embodiments, receivingstation110 can include data processing, storage, or display, or combination thereof and provide real time graphical representation of the level and distribution of the load. Receivingstation110 can record and provide accounting information ofdevice100 to an appropriate authority.
• Thesensing insert device100, in one embodiment, comprises aload sensing platform121, anaccelerometer122, andsensing assemblies123. This permits thesensing device100 to assess a total load on the prosthetic components when it is being moved. The system accounts for forces due to gravity and motion. In one embodiment,load sensing platform121 includes two or more load bearing surfaces, at least one energy transducer, at least one compressible energy propagating structure, and at least one member for elastic support. Theaccelerometer122 can measure acceleration. Acceleration can occur when theload sensing device100 is moved or put in motion.Accelerometer122 can sense orientation, vibration, and impact. In another embodiment, thefemoral component104 can similarly include anaccelerometer127, which by way of a communication interface to thesensing insert device100, can provide reference position and acceleration data to determine an exact angular relationship between the femur and tibia. Thesensing assemblies123 can reveal changes in length or compression of the energy propagating structure or structures by way of the energy transducer or transducers. Together theload sensing platform121, accelerometer122 (and in certain cases accelerometer127), andsensing assemblies123 measure force or pressure external to the load sensing platform or displacement produced by contact with the prosthetic components.
• In at least one exemplary embodiment, an energy pulse is directed within one or more waveguides indevice100 by way of pulse mode operations and pulse shaping. The waveguide is a conduit that directs the energy pulse in a predetermined direction. The energy pulse is typically confined within the waveguide. In one embodiment, the waveguide comprises a polymer material. For example, urethane or polyethylene are polymers suitable for forming a waveguide. The polymer waveguide can be compressed and has little or no hysteresis in the system. Alternatively, the energy pulse can be directed through the muscular-skeletal system. In one embodiment, the energy pulse is directed through bone of the muscular-skeletal system to measure bone density. A transit time of an energy pulse is related to the material properties of a medium through which it traverses. This relationship is used to generate accurate measurements of parameters such as distance, weight, strain, pressure, wear, vibration, viscosity, and density to name but a few.
• Incorporating data from theaccelerometer122 with data from theother sensing components121 and123 assures accurate measurement of the applied load, force, pressure, or displacement by enabling computation of adjustments to offset this external motion. This capability can be required in situations wherein the body, instrument, appliance, vehicle, equipment, or other physical system, is itself operating or moving during sensing of load, pressure, or displacement. This capability can also be required in situations wherein the body, instrument, appliance, vehicle, equipment, or other physical system, is causing the portion of the body, instrument, appliance, vehicle, equipment, or other physical system being measured to be in motion during sensing of load, pressure, or displacement.
• Theaccelerometer122 can operate singly, as an integrated unit with theload sensing platform121, and/or as an integrated unit with thesensing assemblies123. Integrating one ormore accelerometers122 within thesensing assemblages123 to determine position, attitude, movement, or acceleration of sensingassemblages123 enables augmentation of presentation of data to accurately identify, but not limited to, orientation or spatial distribution of load, force, pressure, displacement, density, or viscosity, or localized temperature by controlling the load and position sensing assemblages to measure the parameter or parameters of interest relative to specific orientation, alignment, direction, or position as well as movement, rotation, or acceleration along any axis or combination of axes. Measurement of the parameter or parameters of interest may also be made relative to the earth's surface and thus enable computation and presentation of spatial distributions of the measured parameter or parameters relative to this frame of reference.
• In one embodiment, theaccelerometer122 includes direct current (DC) sensitivity to measure static gravitational pull with load and position sensing assemblages to enable capture of, but not limited to, distributions of load, force, pressure, displacement, movement, rotation, or acceleration by controlling the sensing assemblages to measure the parameter or parameters of interest relative to orientations with respect to the earths surface or center and thus enable computation and presentation of spatial distributions of the measured parameter or parameters relative to this frame of reference.
• Embodiments ofdevice100 are broadly directed to measurement of physical parameters, and more particularly, to evaluating changes in the transit time of a pulsed energy wave propagating through a medium. In-situ measurements during orthopedic joint implant surgery would be of substantial benefit to verify an implant is in balance and under appropriate loading or tension. In one embodiment, the instrument is similar to and operates familiarly with other instruments currently used by surgeons. This will increase acceptance and reduce the adoption cycle for a new technology. The measurements will allow the surgeon to ensure that the implanted components are installed within predetermined ranges that maximize the working life of the joint prosthesis and reduce costly revisions. Providing quantitative measurement and assessment of the procedure using real-time data will produce results that are more consistent. A further issue is that there is little or no implant data generated from the implant surgery, post-operatively, and long term.Device100 can provide implant status data to the orthopedic manufacturers and surgeons. Moreover, data generated by direct measurement of the implanted joint itself would greatly improve the knowledge of implanted joint operation and joint wear thereby leading to improved design and materials.
• As mentioned previously,device100 can be used for other joint surgeries; it is not limited to knee replacement implant or implants. Moreover,device100 is not limited to trial measurements.Device100 can be incorporated into the final joint system to provide data post-operatively to determine if the implanted joint is functioning correctly. Early determination of aproblem using device100 can reduce catastrophic failure of the joint by bringing awareness to a problem that the patient cannot detect. The problem can often be rectified with a minimal invasive procedure at lower cost and stress to the patient. Similarly, longer term monitoring of the joint can determine wear or misalignment that if detected early can be adjusted for optimal life or replacement of a wear surface with minimal surgery thereby extending the life of the implant. In general,device100 can be shaped such that it can be placed or engaged or affixed to or within load bearing surfaces used in many orthopedic applications (or used in any orthopedic application) related to the musculoskeletal system, joints, and tools associated therewith.Device100 can provide information on a combination of one or more performance parameters of interest such as wear, stress, kinematics, kinetics, fixation strength, ligament balance, anatomical fit and balance.
• FIG. 3 is a perspective view of a medical sensing platform comprising an encapsulating enclosure in accordance with one embodiment. In general, parameters of the muscular-skeletal system can be measured with asensing module200 that in one embodiment is an integral part of a completesensing insert device100. Thesensing module200 is a self-contained sensor within an encapsulating enclosure that integrates sensing assemblages, an electronic assemblage that couples to the sensing assemblages, a power source, signal processing, and wireless communication. All components required for the measurement are contained in thesensing module200. Thesensing module200 has at least one contacting surface for coupling to the muscular-skeletal system. A parameter of the muscular-skeletal system is applied to the contact surfaces to be measured by the one or more sensing assemblages therein. As will be disclosed in further detail herein, thesensing module200 is part of a system that allows intra-operative and post-operative sensing of a joint of the muscular-skeletal system. More specifically,sensing module200 is placed within a temporary or permanent prosthetic component that has a similar form factor as the passive prosthetic component currently being used. This has a benefit of rapid adoption because the sensing platform is inserted identically to the commonly used passive component but can provide much needed quantitative measurements with little or no procedural changes.
• As shown, thesensing insert device100 comprises aninsert dock202 and thesensing module200.Sensing insert device100 is a non-permanent or temporary measurement device that is used intra-operatively to provide quantitative data related to the installation of prosthetic components such as in joint replacement surgery. The combination of theinsert dock202 andsensing module202 has a form factor substantially equal to a final insert device. The final insert device can be a passive component or sensored incorporatingsensing module200. The substantially equal form factor ofsensing insert device100 results in no extraneous structures in the surgical field that can interfere with the procedure. For example, a final insert device is designed to mimic the function of the natural component it is replacing. The final insert device allows natural movement of the muscular-skeletal system and does not interfere with ligaments, tendons, tissue, muscles, and other components of the muscular-skeletal system. Similarly,sensing insert device100 allows exposure of the surgical field around the joint by having the similar form factor as the final insert thereby allowing the surgeon to make adjustments during the installation in a natural setting with quantitative measurements to support the modifications.
• In one embodiment,insert dock202 is an adaptor.Insert dock202 is made in different sizes. In general, prosthetic components are manufactured in different sizes to accommodate variation in the muscular-skeletal system from person to person. In the example, the size ofinsert dock202 is chosen to mate with the selected prosthetic implant components. In particular, afeature204 aligns with and retainsinsert dock202 in a fixed position to a prosthetic or natural component of the muscular-skeletal system. Theinsert dock202 is a passive component having an opening for receivingsensing module200. The opening is positioned to place the contacting surfaces in a proper orientation to measure the parameter when used in conjunction with other prosthetic components. Theinsert dock202 as an adaptor can be manufactured at low cost. Moreover, insertdock202 can be formed for adapting to different prosthetic manufacturers thereby increasing system flexibility. This allows astandard sensing module200 to be provided but customized for appropriate size and dimensions throughdock202 for the specific application and manufacturer component.
• The one or more sensing assemblages withinsensing module200 couple to the contacting surfaces ofsensing module200 for receiving the applied parameter of the muscular-skeletal system. In one embodiment, a sensing assemblage comprises one or more energy transducers coupled to an elastic structure. The elastic structure allows the propagation of energy waves. The forms of energy propagated through the elastic energy propagating structures may include, but is not limited to, sound, ultrasound, or electromagnetic radiation including radio frequency, infrared, or light. A change in the parameter applied to the contacting surfaces results in a change a dimension of the elastic structure. The dimension of the elastic structure can be measured precisely using continuous wave, pulsed, or pulsed echo measurement. The dimension and material properties of the elastic structure have a known relationship to the parameter being measured. Thus, the dimension is precisely measured and converted to the parameter. Other factors such as movement or acceleration can be taken into account in the calculation. As an example, a force, pressure, or load applied to the one or more contacting surfaces ofsensing module200 is used to illustrate a parameter measurement hereinbelow. It should be noted that this is for illustration purposes and that thesensing module200 can be used to measure other parameters.
• As will be shown ahead, the encapsulating enclosure can serve in a first embodiment as a trial implant for orthopedic surgical procedures, namely, for determining load forces on prosthetic components and the musculoskeletal system. In a second embodiment, the encapsulating enclosure can be placed within a permanent prosthetic component for long term monitoring. The encapsulating enclosure supports and protects internal mechanical and electronic components from external physical, mechanical, chemical, and electrical, and electromagnetic intrusion that might compromise sensing or communication operations of the module or device. The integration of the internal components is designed to minimize adverse physical, mechanical, electrical, and ultrasonic interactions that might compromise sensing or communication operations of the module or device.
• FIG. 4 is a perspective view of a medical sensing device suitable for use as a bi-compartmental implant and comprising an encapsulating enclosure in accordance with one embodiment. As shown, the loadsensing insert device100 comprises two sensingmodules200. Eachsensing module200 is a self-contained encapsulated enclosure that can make individual or coordinated parameter measurements. For example, thesensing insert device100 can be used to assess load forces on a bi-compartmental knee joint implant. In particular, both sensingmodules200 can individually, or in combination, report applied loading forces. Bi-compartmental sensing provides the benefit of providing quantitative measurement to balance each compartment in relation to one another.
• Similar to that described above,insert dock202 is an adaptor having two openings instead of one.Insert dock202 can be made in different sizes to accommodated different sized prosthetic components and different manufacturers. Theinsert dock202 with two openings is a passive component for receiving twoseparate sensing modules200. The opening is positioned to place the contacting surfaces in a proper orientation to measure the parameter when used in conjunction with other prosthetic components. In general, encapsulated enclosures can be positioned on or within, or engaged with, or attached or affixed to or within, a wide range of physical systems including, but not limited to instruments, appliances, vehicles, equipments, or other physical systems as well as animal and human bodies, for sensing and communicating the parameter or parameters of interest in real time. Similar to that described above,insert dock202 as an adaptor can be manufactured at low cost providing design flexibility and allowing rapid adoption of quantitative measurement.
• FIG. 5 is an exemplary block diagram of the components of thesensing module200 in accordance with an exemplary embodiment. It should be noted that the sensing module could comprise more or less than the number of components shown. As illustrated, the sensing module includes one ormore sensing assemblages303, atransceiver320, anenergy storage330,electronic circuitry307, one or more mechanical supports315 (e.g., springs), and anaccelerometer302. In the non-limiting example, an applied compressive force can be measured by the sensing module.
• Thesensing assemblage303 can be positioned, engaged, attached, or affixed to the contact surfaces306. Mechanical supports315 serve to provide proper balancing of contact surfaces306. In at least one exemplary embodiment, contact surfaces306 are load-bearing surfaces. In general, thepropagation structure305 is subject to the parameter being measured.Surfaces306 can move and tilt with changes in applied load; actions which can be transferred to thesensing assemblages303 and measured by theelectronic circuitry307. Theelectronic circuitry307 measures physical changes in thesensing assemblage303 to determine parameters of interest, for example a level, distribution and direction of forces acting on the contact surfaces306. In general, the sensing module is powered by theenergy storage330.
• As one example, thesensing assemblage303 can comprise an elastic orcompressible propagation structure305 between atransducer304 and atransducer314. In the current example,transducer304 can be an ultrasound (or ultrasonic) resonator, and the elastic orcompressible propagation structure305 can be an ultrasound (or ultrasonic) waveguide (or waveguides). Theelectronic circuitry307 is electrically coupled to thesensing assemblages303 and translates changes in the length (or compression or extension) of thesensing assemblages303 to parameters of interest, such as force. It measures a change in the length of the propagation structure305 (e.g., waveguide) responsive to an applied force and converts this change into electrical signals which can be transmitted via thetransceiver320 to convey a level and a direction of the applied force. In other arrangements herein contemplated, thesensing assemblage303 may require only a single transducer. In yet other arrangements, thesensing assemblage303 can include piezoelectric, capacitive, optical or temperature sensors or transducers to measure the compression or displacement. It is not limited to ultrasonic transducers and waveguides.
• Theaccelerometer302 can measure acceleration and static gravitational pull.Accelerometer302 can be single-axis and multi-axis accelerometer structures that detect magnitude and direction of the acceleration as a vector quantity.Accelerometer302 can also be used to sense orientation, vibration, impact and shock. Theelectronic circuitry307 in conjunction with theaccelerometer302 andsensing assemblies303 can measure parameters of interest (e.g., distributions of load, force, pressure, displacement, movement, rotation, torque and acceleration) relative to orientations of the sensing module with respect to a reference point. In such an arrangement, spatial distributions of the measured parameters relative to a chosen frame of reference can be computed and presented for real-time display.
• Thetransceiver320 comprises atransmitter309 and anantenna310 to permit wireless operation and telemetry functions. In various embodiments, theantenna310 can be configured by design as an integrated loop antenna. As will be explained ahead, the integrated loop antenna is configured at various layers and locations on the electronic substrate with electrical components and by way of electronic control circuitry to conduct efficiently at low power levels. Once initiated thetransceiver320 can broadcast the parameters of interest in real-time. The telemetry data can be received and decoded with various receivers, or with a custom receiver. The wireless operation can eliminate distortion of, or limitations on, measurements caused by the potential for physical interference by, or limitations imposed by, wiring and cables connecting the sensing module with a power source or with associated data collection, storage, display equipment, and data processing equipment.
• Thetransceiver320 receives power from theenergy storage330 and can operate at low power over various radio frequencies by way of efficient power management schemes, for example, incorporated within theelectronic circuitry307. As one example, thetransceiver320 can transmit data at selected frequencies in a chosen mode of emission by way of theantenna310. The selected frequencies can include, but are not limited to, ISM bands recognized in InternationalTelecommunication Union regions1,2 and3. A chosen mode of emission can be, but is not limited to, Gaussian Frequency Shift Keying, (GFSK), Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), Minimum Shift Keying (MSK), Frequency Modulation (FM), Amplitude Modulation (AM), or other versions of frequency or amplitude modulation (e.g., binary, coherent, quadrature, etc.).
• Theantenna310 can be integrated with components of the sensing module to provide the radio frequency transmission. The substrate for theantenna310 and electrical connections with theelectronic circuitry307 can further include a matching network. This level of integration of the antenna and electronics enables reductions in the size and cost of wireless equipment. Potential applications may include, but are not limited to any type of short-range handheld, wearable, or other portable communication equipment where compact antennas are commonly used. This includes disposable modules or devices as well as reusable modules or devices and modules or devices for long-term use.
• Theenergy storage330 provides power to electronic components of the sensing module. It can be charged by wired energy transfer, short-distance wireless energy transfer or a combination thereof. External power sources can include, but are not limited to, a battery or batteries, an alternating current power supply, a radio frequency receiver, an electromagnetic induction coil, a photoelectric cell or cells, a thermocouple or thermocouples, or an ultrasound transducer or transducers. By way of theenergy storage330, the sensing module can be operated with a single charge until the internal energy is drained. It can be recharged periodically to enable continuous operation. Theenergy storage330 can utilize common power management technologies such as replaceable batteries, supply regulation technologies, and charging system technologies for supplying energy to the components of the sensing module to facilitate wireless applications.
• Theenergy storage330 minimizes additional sources of energy radiation required to power the sensing module during measurement operations. In one embodiment, as illustrated, theenergy storage330 can include a capacitiveenergy storage device308 and aninduction coil311. External source of charging power can be coupled wirelessly to the capacitiveenergy storage device308 through the electromagnetic induction coil or coils311 by way of inductive charging. The charging operation can be controlled by power management systems designed into, or with, theelectronic circuitry307. As one example, during operation ofelectronic circuitry307, power can be transferred from capacitiveenergy storage device308 by way of efficient step-up and step-down voltage conversion circuitry. This conserves operating power of circuit blocks at a minimum voltage level to support the required level of performance.
• In one configuration, theenergy storage330 can further serve to communicate downlink data to thetransceiver320 during a recharging operation. For instance, downlink control data can be modulated onto the energy source signal and thereafter demodulated from theinduction coil311 by way ofelectronic control circuitry307. This can serve as a more efficient way for receiving downlink data instead of configuring thetransceiver320 for both uplink and downlink operation. As one example, downlink data can include updated control parameters that the sensing module uses when making a measurement, such as external positional information, or for recalibration purposes, such as spring biasing. It can also be used to download a serial number or other identification data.
• Theelectronic circuitry307 manages and controls various operations of the components of the sensing module, such as sensing, power management, telemetry, and acceleration sensing. It can include analog circuits, digital circuits, integrated circuits, discrete components, or any combination thereof. In one arrangement, it can be partitioned among integrated circuits and discrete components to minimize power consumption without compromising performance. Partitioning functions between digital and analog circuit enhances design flexibility and facilitates minimizing power consumption without sacrificing functionality or performance. Accordingly, theelectronic circuitry307 can comprise one or more Application Specific Integrated Circuit (ASIC) chips, for example, specific to a core signal processing algorithm.
• In another arrangement, the electronic circuitry can comprise a controller such as a programmable processor, a Digital Signal Processor (DSP), a microcontroller, or a microprocessor, with associated storage memory and logic. The controller can utilize computing technologies with associated storage memory such a Flash, ROM, RAM, SRAM, DRAM or other like technologies for controlling operations of the aforementioned components of the sensing module. In one arrangement, the storage memory may store one or more sets of instructions (e.g., software) embodying any one or more of the methodologies or functions described herein. The instructions may also reside, completely or at least partially, within other memory, and/or a processor during execution thereof by another processor or computer system.
• The electronics assemblage also supports testability and calibration features that assure the quality, accuracy, and reliability of the completed wireless sensing module or device. A temporary bi-directional interconnect assures a high level of electrical observability and controllability of the electronics. The test interconnect also provides a high level of electrical observability of the sensing subsystem, including the transducers, waveguides, and mechanical spring or elastic assembly. Carriers or fixtures emulate the final enclosure of the completed wireless sensing module or device during manufacturing processing thus enabling capture of accurate calibration data for the calibrated parameters of the finished wireless sensing module or device. These calibration parameters are stored within the on-board memory integrated into the electronics assemblage.
• FIG. 6 is a diagram of anexemplary communications system400 for short-range telemetry according to one embodiment. As illustrated, theexemplary communications system400 comprises medicaldevice communications components410 of the sensing insert device100 (seeFIG. 1) and receivingsystem communications components450 of the receiving system110 (seeFIG. 1). The medicaldevice communications components410 are inter-operatively coupled to include, but not limited to, theantenna412, amatching network414, thetelemetry transceiver416, aCRC circuit418, adata packetizer422, adata input424, apower source426, and an application specific integrated circuit (ASIC)420. The medicaldevice communications components410 may include more or less than the number of components shown and are not limited to those shown or the order of the components.
• The receivingstation communications components450 comprise anantenna452, thematching network454, thetelemetry receiver456, theCRC circuit458, thedata packetizer460, and optionally aUSB interface462. Notably, other interface systems can be directly coupled to the data packetizer460 for processing and rendering sensor data.
• With respect toFIG. 1, in view of the communication components ofFIG. 6, the loadsensing insert device100 acquires sensor data by way of the data input to theASIC420. Referring briefly toFIG. 5, theASIC420 is operatively coupled to sensingassemblies303. In one embodiment, a change in the parameter being measured bydevice100 produces a change in a length of acompressible propagation structure305.ASIC420 controls the emission of energy waves intopropagation structure305 and the detection of propagated energy waves.ASIC420 generates data related to transit time, frequency, or phase of propagated energy waves. The data corresponds to the length ofpropagation structure305, which can be translated to the parameter of interest by way of a known function or relationship. Similarly, the data can comprise voltage or current measurements from a MEMS structure, piezo-resistive sensor, strain gauge, or other sensor type that is used to measure the parameter. The data packetizer422 assembles the sensor data into packets; this includes sensor information received or processed byASIC420. TheASIC420 can comprise specific modules for efficiently performing core signal processing functions of the medicaldevice communications components410. TheASIC420 provides the further benefit of reducing the form factor ofsensing insert device100 to meet dimensional requirements for integration into temporary or permanent prosthetic components.
• TheCRC circuit418 applies error code detection on the packet data. The cyclic redundancy check is based on an algorithm that computes a checksum for a data stream or packet of any length. These checksums can be used to detect interference or accidental alteration of data during transmission. Cyclic redundancy checks are especially good at detecting errors caused by electrical noise and therefore enable robust protection against improper processing of corrupted data in environments having high levels of electromagnetic activity. Thetelemetry transmitter416 then transmits the CRC encoded data packet through thematching network414 by way of theantenna412. The matchingnetworks414 and454 provide an impedance match for achieving optimal communication power efficiency.
• The receivingsystem communications components450 receive transmission sent by medicaldevice communications components410. In one embodiment,telemetry transmitter416 is operated in conjunction with adedicated telemetry receiver456 that is constrained to receive a data stream broadcast on the specified frequencies in the specified mode of emission. Thetelemetry receiver456 by way of the receivingstation antenna452 detects incoming transmissions at the specified frequencies. Theantenna452 can be a directional antenna that is directed to a directional antenna ofcomponents410. Using at least one directional antenna can reduce data corruption while increasing data security by further limiting where the data is radiated. Amatching network454 couples toantenna452 to provide an impedance match that efficiently transfers the signal fromantenna452 totelemetry receiver456.Telemetry receiver456 can reduce a carrier frequency in one or more steps and strip off the information or data sent bycomponents410.Telemetry receiver456 couples toCRC circuit458.CRC circuit458 verifies the cyclic redundancy checksum for individual packets of data.CRC circuit458 is coupled todata packetizer460.Data packetizer460 processes the individual packets of data. In general, the data that is verified by theCRC circuit458 is decoded (e.g., unpacked) and forwarded to an external data processing device, such as an external computer, for subsequent processing, display, or storage or some combination of these.
• Thetelemetry receiver456 is designed and constructed to operate on very low power such as, but not limited to, the power available from thepowered USB port462, or a battery. In another embodiment, thetelemetry receiver456 is designed for use with a minimum of controllable functions to limit opportunities for inadvertent corruption or malicious tampering with received data. Thetelemetry receiver456 can be designed and constructed to be compact, inexpensive, and easily manufactured with standard manufacturing processes while assuring consistently high levels of quality and reliability.
• In one configuration, thecommunication system400 operates in a transmit-only operation with a broadcasting range on the order of a few meters to provide high security and protection against any form of unauthorized or accidental query. The transmission range can be controlled by the transmitted signal strength, antenna selection, or a combination of both. A high repetition rate of transmission can be used in conjunction with the Cyclic Redundancy Check (CRC) bits embedded in the transmitted packets of data during data capture operations thereby enabling the receivingsystem110 to discard corrupted data without materially affecting display of data or integrity of visual representation of data, including but not limited to measurements of load, force, pressure, displacement, flexion, attitude, and position within operating or static physical systems.
• By limiting the operating range to distances on the order of a few meters thetelemetry transmitter416 can be operated at very low power in the appropriate emission mode or modes for the chosen operating frequencies without compromising the repetition rate of the transmission of data. This mode of operation also supports operation with compact antennas, such as an integrated loop antenna. The combination of low power and compact antennas enables the construction of, but is not limited to, highly compact telemetry transmitters that can be used for a wide range of non-medical and medical applications. Examples of potential medical applications may include, but are not limited to, implantable devices, modules within implantable devices, intra-operative implants or modules within intra-operative implants or trial inserts, modules within inserted or ingested devices, modules within wearable devices, modules within handheld devices, modules within instruments, appliances, equipment, or accessories of all of these, or disposables within implants, trial inserts, inserted or ingested devices, wearable devices, handheld devices, instruments, appliances, equipment, or accessories to these devices, instruments, appliances, or equipment.
• The transmitter security as well as integrity of the transmitted data is assured by operating the telemetry system within predetermined conditions. The security of the transmitter cannot be compromised because it is operated in a transmit-only mode and there is no pathway to hack into medicaldevice communications components410. The integrity of the data is assured with the use of the CRC algorithm and the repetition rate of the measurements. The risk of unauthorized reception of the data is minimized by the limited broadcast range of the device. Even if unauthorized reception of the data packets should occur there are counter measures in place that further mitigate data access. A first measure is that the transmitted data packets contain only binary bits from a counter along with the CRC bits. A second measure is that no data is available or required to interpret the significance of the binary value broadcast at any time. A third measure that can be implemented is that no patient or device identification data is broadcast at any time.
• Thetelemetry transmitter416 can also operate in accordance with some FCC regulations. According to section 18.301 of the FCC regulations the ISM bands within the USA include 6.78, 13.56, 27.12, 30.68, 915, 2450, and 5800 MHz as well as 24.125, 61.25, 122.50, and 245 GHz. Globally other ISM bands, including 433 MHz, are defined by the International Telecommunications Union in some geographic locations. The list of prohibited frequency bands defined in 18.303 are “the following safety, search and rescue frequency bands is prohibited: 490-510 kHz, 2170-2194 kHz, 8354-8374 kHz, 121.4-121.6 MHz, 156.7-156.9 MHz, and 242.8-243.2 MHz.” Section 18.305 stipulates the field strength and emission levels ISM equipment must not exceed when operated outside defined ISM bands. In summary, it may be concluded that ISM equipment may be operated worldwide within ISM bands as well as within most other frequency bands above 9 KHz given that the limits on field strengths and emission levels specified in section 18.305 are maintained by design or by active control. As an alternative, commercially available ISM transceivers, including commercially available integrated circuit ISM transceivers, may be designed to fulfill these field strengths and emission level requirements when used properly.
• In one configuration, thetelemetry transmitter416 can also operate in unlicensed ISM bands or in unlicensed operation of low power equipment, wherein the ISM equipment (e.g., telemetry transmitter416) may be operated on ANY frequency above 9 kHz except as indicated in Section 18.303 of the FCC code.
• Wireless operation eliminates distortion of, or limitations on, measurements caused by the potential for physical interference by, or limitations imposed by, wiring and cables connecting the wireless sensing module or device with a power source or with data collection, storage, or display equipment. Power for the sensing components and electronic circuits is maintained within the wireless sensing module or device on an internal energy storage device. This energy storage device is charged with external power sources including, but not limited to, a battery or batteries, super capacitors, capacitors, an alternating current power supply, a radio frequency receiver, an electromagnetic induction coil, a photoelectric cell or cells, a thermocouple or thermocouples, or an ultrasound transducer or transducers. The wireless sensing module may be operated with a single charge until the internal energy source is drained or the energy source may be recharged periodically to enable continuous operation. The embedded power supply minimizes additional sources of energy radiation required to power the wireless sensing module or device during measurement operations. Telemetry functions are also integrated within the wireless sensing module or device. Once initiated the telemetry transmitter continuously broadcasts measurement data in real time. Telemetry data may be received and decoded with commercial receivers or with a simple, low cost custom receiver.
• Referring toFIG. 13, a flowchart is illustrated of amethod1300 for sensor data communications in accordance with an exemplary embodiment. Themethod1300 can be practiced with more or less than the number of steps shown and is not limited to the order shown. To describe themethod1300, reference will be made to the components ofFIG. 5, although it is understood that themethod1300 can be implemented in any other manner using other suitable components. Generally,method1300 is directed to non-secure applications for one-way transmission communications, for example, where an implanted medical device or sensor transmits data to a receiving station (e.g.,110 seeFIG. 1) but does not receive confirmation from the receiving station, although in various embodiments, the implanted medical device includes an integrated receiver for receiving confirmation and acknowledgement communications.
• Themethod1300 can start in a state wherein thesensing insert device100 has been inserted and powered on, for example, within a knee prosthesis implant. The medical device can be powered on via manual intervention, for example, by the surgeon or technician implanting the medical device during a surgical procedure, or the device can turn on automatically after a duration of time or at certain time intervals, for example, 1 hour after manual activation, or every 10 seconds after power up, depending on an operating mode.
• In astep1302, the medical device acquires sensor data such as load information (e.g., force, location, duration, etc.) from thesensing module200. Theelectronic circuitry307 generates the load data by way of thesensing assemblies303, for instance, by converting changes in length of ultrasonic propagation structures (waveguides) to force data. In astep1304, thesensing module200 evaluates data bounds on the load data. In astep1306,sensing module200 assigns priorities based on the data bounds. Sensor data outside a predetermined range or above a predefined threshold can be flagged with a priority or discarded. For example, sensor data that falls outside a safe range or exceeds a safe level (e.g., applied force level, angle of flexion, excessive rotation) is prioritized accordingly.
• In astep1308, thesensing module200 generates a packet of data including the sensor data, priority, and any corresponding information. In astep1310, thesensing module200 determines its communications mode based on operating mode and priority level. The operating mode indicates whether thesensing module200 is operating in a power saving mode (e.g., standby) or other power management mode and takes into account information such as remaining battery life and drain. In astep1312, a Cyclic Redundancy Check (CRC) can be appended to the data packed. In other embodiments, more sophisticated forward error correction schemes (e.g., block coding, convolutional coding) can be applied along with secure encryption or key-exchange cryptographic protocols.
• The cyclic redundancy check (CRC) is a non-secure form of message digest designed to detect accidental changes to raw computer data. The CRC step comprises calculating a short, fixed-length sequence, known as the CRC code, for each block of data and sends or stores them both together. When a block is read or received the receiving station110 (FIG. 1) repeats the calculation; if the new CRC does not match the one sent (or in some cases, cancel it out) then the block contains a data error and the receivingstation110 may take corrective action such as rereading or requesting the block be sent again. Briefly,FIG. 14, illustrates anexemplary data packet1400 containing sensor data (e.g., Fx, duration, location), a priority level (e.g., 1 to 10), and a CRC.
• Returning toFIG. 13, in astep1314, thetransceiver320 then transmits the data packet based on the priority level and operating mode. For instance, a low priority data packet can be appended with previous low-priority data packets and then transmitted over a single communication channel as a data stream, or at staggered time intervals to conserve power (e.g., scheduled to transmit every 10 seconds). The bundled packet data can then be decoded at the receivingstation110 and thereafter processed accordingly. Alternatively, a high priority packet can be transmitted immediately instead of a delayed time or the scheduled transmit intervals. Depending on the communication mode (e.g., priority level, operating mode), the transceiver may transmit the same high priority packet multiple times in a redundant manner to guarantee receipt. This ensures that the data is received and processed at the receivingstation110 in the event an immediate course of action or response is necessary, for example, to ensure the patient's safety or to report a warning.
• The sensor data can be transmitted at the selected frequencies in the chosen mode of emission by way of theantenna310. In certain configurations, theantenna310 is an integrated loop antenna designed into a substrate of thesensing module200 for maximizing power efficiency. As an example the chosen frequencies can include, but are not limited to, ISM bands recognized in InternationalTelecommunication Union regions1,2, and3 and the chosen mode of emission may be, but is not limited to, Gaussian Frequency Shift Keying, (GFSK) or others version of frequency or amplitude shift keying or modulation.
• The receiving station110 (seeFIG. 1)110 receives packets of data broadcast in the specified mode of emission on the specified frequencies and verifies the cyclic redundancy check checksum for individual packets of data or bundled packet data. Data that cannot be verified may be discarded. Data that are verified are forward to an external data processing device, such as an external computer, for subsequent processing, display, or storage or combination thereof.
• FIG. 7 is an illustration of a block model diagram500 of thesensing module200 in accordance with an exemplary embodiment. In particular, the diagram500 shows where certain components are replaced or supplemented with one or more Application Specific Integrated Circuits (ASICs). Referring briefly toFIG. 5,electronic circuitry307 is coupled to the one or more sensing assemblages and includes circuitry that can control sensor operations.Electronic circuitry307 includes multiple channels that can operate more than one device.Sensing module200 is optimized to operate under severe power constraints.Electronic circuitry307 includes power management circuitry that controls power up, power down, and minimizes power usage through the control of individual blocks. The architecture is designed to enable only blocks required for the current operation.
• Referring back toFIG. 7, the ASIC provides significant benefit in reducing power requirements allowing themodule200 to be powered by a temporary power source such as a super capacitor or capacitor. The ASIC and super capacitor have a small formfactor allowing module200 to be integrated within a temporary or permanent prosthetic component.Module200 incorporates one or more sensors comprising at least one transducer and a compressible media, the operation of which is disclosed in detail herein. As shown, a sensing assemblage comprises atransducer502,compressible propagation structure504, and atransducer506. It should be noted that other sensors such as MEMS devices, strain gauges, and piezo-resistive sensors can be used with the ASIC. In particular, the ASIC incorporates A/D and D/A circuitry (not shown) to digitize current and voltage output from these types of sensing components.Transducers502 and506 operatively couple tocompressible propagation structure504. In a non-limiting example,transducer506 to emits energy waves intocompressible structure504 whiletransducer502 detects propagated energy waves.Compressible propagation structure504 is coupled to a load bearing or contactingsurface508 and an encapsulatingenclosure510 ofsensing module200. A parameter to be measured is applied to either contactingsurface508, encapsulatingenclosure510, or both. In one embodiment, springs560 couple to contactingsurface508 and encapsulatingenclosure510 to supportcompressible propagation structure504. In particular, springs560 prevent cantilevering of contactingsurface508, reduce hysteresis caused by material properties ofcompressible propagation structure504, and improve sensor response time to changes in the applied parameter.
• In one embodiment, a first ASIC includes a chargingcircuit514 andpower management circuitry518. Thepower management circuitry518 couples to the charging circuit, other blocks of the ASIC and external components/circuitry to minimize power consumption of the integrated circuit. The chargingcircuit514 operatively couples to aninduction coil512 andenergy storage516. In a non-limiting example,induction coil512 couples to an external coil that provides energy to chargeenergy storage516.Induction coil512 and the external coil are placed in proximity to each other thereby electro-magnetically coupling to one another.Induction coil512 is coupled toenergy storage516.Charging circuit514 controls the charging ofenergy storage516.Charging circuit514 can determine when charging is complete, monitor power available, and regulate a voltage provided to the operational circuitry.Charging circuit514 can charge a battery insensing module200. Alternatively, a capacitor or super capacitor can be used to power the first ASIC for a time sufficient to acquire the desired measurements. A capacitor has the benefit of a long or indefinite shelf life and fast charge time. In either charging scenario, energy from the external coil is coupled to theinduction coil512. The energy frominduction coil512 is then stored in a medium such as a battery or capacitor.
• The first ASIC further includes circuitry to operate and capture data from the sensing assemblages. A parameter to be measured is applied tocompressible propagation structure504. As an example of parameter measurement, a force, pressure, or load is applied across contactingsurface508 and encapsulatingenclosure510. The force, pressure, or load affects the length of thecompressible propagation structure504. The circuitry on the first ASIC forms a positive closed loop feedback circuit that maintains the emission, propagation, and detection of energy waves in thecompressible propagation structure504. The first ASIC operatively couples totransducers502 and506 to control the positive closed loop feedback circuit that is herein called a propagation tuned oscillator (PTO). The first ASIC measures a transit time, frequency, or phase of propagated energy waves. The measurement is used to determine the length ofcompressible propagation structure504. The energy waves emitted intocompressible propagation structure504 can be continuous or pulsed. The energy waves can propagate by a direct path or be reflected.
• The first ASIC comprises anoscillator520, aswitch522,driver524,matching network526,MUX528, andcontrol circuit536. Theoscillator520 is used as a reference clock for the ASIC and enables the PTO to begin emission of energy waves into thecompressible propagation structure504.Oscillator520 in the first ASIC can be coupled to an external component such as a crystal oscillator to define and provide a stable frequency of operation. Switch522 couples theoscillator520 toMUX528.Control circuit536 operatively enablesMUX528 and switch522 tocouple oscillator520 todriver524 during a startup sequence.Driver524 andmatching network526 couple totransducer506.Driver524 drivestransducer506 to emit an energy wave.Matching network526impedance matches driver524 to thetransducer506 to reduce power consumption during energy wave emission.
• In one embodiment,transducer506 emits one or more energy waves into thecompressible propagation structure504 at a first location.Transducer506 is located at a second location ofcompressible propagation structure504.Transducer506 detects propagated energy waves at the second location and generates a signal corresponding to the propagated energy waves. The first ASIC further comprises aMUX530, pre-amplifier532 (e.g. preamp532) and a zero-crossing receiver or edge detect receiver. Zero-crossing receiver or edge-detect receiver comprise detectcircuit534.Control circuit536 enablesMUX530 tocouple transducer502 topreamp532.Preamp532 amplifies a signal output bytransducer502 corresponding to a propagated energy wave. In a non-limiting example, the first ASIC comprises both a zero-crossing receiver and an edge detect receiver. More multiplexing circuitry in conjunction withcontrol circuit536 can be incorporated on the first ASIC to select between the circuits. Similarly, multiplexing circuitry can be used to couple and operate more than one sensor. The amplified signal frompreamp532 is coupled todetection circuit534. Zero-crossing receiver is a detection circuit that identifies a propagated energy wave by sensing a transition of the signal. A requirement of detection can be that the signal has certain transition and magnitude characteristics. The edge-detect receiver detects a propagated energy wave by identifying a wave front of the propagated energy wave. The zero-crossing receiver or edge-detect receiver outputs a pulse in response to the detection of a propagated energy wave.
• Positive closed loop feedback is applied upon detection of an energy wave after the startup sequence.Control circuit536 decouplesoscillator520 fromdriver524 throughswitch522 andMUX528.Control circuit536 operatively enablesswitch558 andMUX528 tocouple detection circuit534 todriver524. A pulse generated bydetection circuit534 initiates the emission of a new energy wave intocompressible propagation structure504. The pulse fromdetection circuit534 is provided todriver524. The positive closed loop feedback of the circuitry maintains the emission, propagation, and detection of energy waves inpropagation structure504.
• The first ASIC further comprises aloop counter538,time counter540, register542, andADC556.Loop counter538,time counter540, and register542 are operatively coupled to controlcircuit536 to generate a precise measurement of the transit time, frequency, or phase of propagated energy waves during a measurement sequence. In one embodiment, a measurement comprises a predetermined number of energy waves propagating through thecompressible propagation structure504. The predetermined number is set in theloop counter538. Theloop counter538 is decremented by each pulse output bydetection circuit534 that corresponds to a detected propagated energy wave. The positive closed loop feedback is broken when counter538 decrements to zero thereby stopping the measurement.Time counter540 measures a total propagation time of the predetermined number of propagated energy waves set inloop counter538. The measured total propagation time divided by the predetermined number of propagated energy waves is a measured transit time of an energy wave. The measured transit time can be precisely converted to a length ofcompressible propagation structure504 under a stable condition of the applied parameter on the sensing assemblage. The applied parameter value can be calculated by known relationship between the length ofcompressible propagation structure504 and the parameter. A result of the measurement is stored inregister542 whenloop counter538 decrements to zero. More than one measurement can be performed and stored. In one embodiment, the precision can be increased by raising the number of propagated energy waves being measured inloop counter538.
• In the example, energy waves are propagated fromtransducer506 totransducer5. Alternatively,control circuit536 can direct the propagation of energy waves fromtransducer502 totransducer506 wherebytransducer502 emits energy waves andtransducer506 detects propagated energy waves. An analog to digital converter (ADC)556 is shown coupled to anaccelerometer554.ADC556 is a circuit on the first ASIC. It can be used to digitize an output from a circuit such asaccelerometer554.Accelerometer554 can be used to detect and measure when sensingmodule200 is in motion. Data fromaccelerometer554 can be used to correct the measured result to account formodule200 acceleration.ADC556 can also be used to provide measurement data from other sensor types by providing a digitized output corresponding to voltage or current magnitude.
• A second ASIC can comprise CRC circuit546,telemetry transmitter548, andmatching network508. The CRC circuit546 applies error code detection on the packet data such as data stored inregister542. The cyclic redundancy check computes a checksum for a data stream or packet of any length. The checksums are used to detect interference or accidental alteration of data during transmission.Transmitter548 is coupled to CRC546 and sends the data wirelessly.Matching network550 couples telemetrytransmitter512 toantenna552 to provide an impedance match to efficiently transfer the signal to theantenna552. As disclosed above, the integration of the telemetry transmitter and sensor modules enables construction of a wide range of sizes of thesensing module200. This facilitates capturing data, measuring parameters of interest and digitizing that data, and subsequently communicating that data to external equipment with minimal disturbance to the operation of the body, instrument, appliance, vehicle, equipment, or physical system for a wide range of applications. Moreover, the level of accuracy and resolution achieved by the total integration of communication components, transducers, waveguides, and oscillators to control the operating frequency of the ultrasound transducers enables the compact, self-contained measurement module construction. In a further embodiment, the circuitry on the first and second ASICs can be combined on a single ASIC to further reduce form factor, power, and cost.
• FIG. 8 is anexemplary assemblage800 that illustrates propagation of ultrasound waves810 within thewaveguide806 in the bi-directional mode of operation of this assemblage. In this mode, the selection of the roles of the two individual ultrasound resonators (802,804) or transducers affixed to interfacingmaterial820 and822, if required, are periodically reversed. In the bi-directional mode the transit time of ultrasound waves propagating in either direction within thewaveguide806 can be measured. This can enable adjustment for Doppler effects in applications where thesensing module808 is operating while inmotion816. Furthermore, this mode of operation helps assure accurate measurement of the applied load, force, pressure, or displacement by capturing data for computing adjustments to offset thisexternal motion816. An advantage is provided in situations wherein the body, instrument, appliance, vehicle, equipment, or otherphysical system814, is itself operating or moving during sensing of load, pressure, or displacement. Similarly, the capability can also correct in situation where the body, instrument, appliance, vehicle, equipment, or other physical system, is causing theportion812 of the body, instrument, appliance, vehicle, equipment, or other physical system being measured to be inmotion816 during sensing of load, force, pressure, or displacement. Other adjustments to the measurement for physical changes tosystem814 are contemplated and can be compensated for in a similar fashion. For example, temperature ofsystem814 can be measured and a lookup table or equation having a relationship of temperature versus transit time can be used to normalize measurements. Differential measurement techniques can also be used to cancel many types of common factors as is known in the art.
• The use ofwaveguide806 enables the construction of low cost sensing modules and devices over a wide range of sizes, including highly compact sensing modules, disposable modules for bio-medical applications, and devices, using standard components and manufacturing processes. The flexibility to construct sensing modules and devices with very high levels of measurement accuracy, repeatability, and resolution that can scale over a wide range of sizes enables sensing modules and devices to the tailored to fit and collect data on the physical parameter or parameters of interest for a wide range of medical and non-medical applications.
• Referring back toFIG. 2, although not explicitly illustrated, it should be noted that the loadinsert sensing device100 and associated internal components move in accordance with motion of thefemur108 as shown. The bi-directional operating mode of the waveguide mitigates the Doppler effects resulting from the motion. As previously indicated, incorporating data from theaccelerometer121 with data from the other components of thesensing module200 helps assure accurate measurement of the applied load, force, pressure, displacement, density, localized temperature, or viscosity by enabling computation of adjustments to offset this external motion.
• For example, sensing modules or devices may be placed on or within, or attached or affixed to or within, a wide range of physical systems including, but not limited to instruments, appliances, vehicles, equipments, or other physical systems as well as animal and human bodies, for sensing the parameter or parameters of interest in real time without disturbing the operation of the body, instrument, appliance, vehicle, equipment, or physical system.
• In addition to non-medical applications, examples of a wide range of potential medical applications may include, but are not limited to, implantable devices, modules within implantable devices, modules or devices within intra-operative implants or trial inserts, modules within inserted or ingested devices, modules within wearable devices, modules within handheld devices, modules within instruments, appliances, equipment, or accessories of all of these, or disposables within implants, trial inserts, inserted or ingested devices, wearable devices, handheld devices, instruments, appliances, equipment, or accessories to these devices, instruments, appliances, or equipment. Many physiological parameters within animal or human bodies may be measured including, but not limited to, loading within individual joints, bone density, movement, various parameters of interstitial fluids including, but not limited to, viscosity, pressure, and localized temperature with applications throughout the vascular, lymph, respiratory, and digestive systems, as well as within or affecting muscles, bones, joints, and soft tissue areas. For example, orthopedic applications may include, but are not limited to, load bearing prosthetic components, or provisional or trial prosthetic components for, but not limited to, surgical procedures for knees, hips, shoulders, elbows, wrists, ankles, and spines; any other orthopedic or musculoskeletal implant, or any combination of these.
• FIG. 9 is an exemplary cross-sectional view of asensor element900 to illustrate changes in the propagation of ultrasound waves914 with changes in the length of awaveguide906. In general, the measurement of a parameter is achieved by relating displacement to the parameter. In one embodiment, the displacement required over the entire measurement range is measured in microns. For example, anexternal force908 compresses waveguide906 thereby changing the length ofwaveguide906. Sensing circuitry (not shown) measures propagation characteristics of ultrasonic signals in thewaveguide906 to determine the change in the length of thewaveguide906. These changes in length change in direct proportion to the parameters of interest thus enabling the conversion of changes in the parameter or parameters of interest into electrical signals.
• As previously discussed, external forces applied to thesensing module200 compress the waveguide(s) thereby changing the length of the waveguide(s). Thesensing module200 measures propagation characteristics of ultrasonic signals in the waveguide(s) to determine the change in the length of the waveguide(s). These changes in length change in direct proportion to the parameters of interest thus enabling the conversion of changes in the parameter or parameters of interest into load (or force) information.
• As illustrated,external force908 compresses waveguide906 and pushes thetransducers902 and904 closer to one another by adistance910. This changes the length ofwaveguide906 bydistance912 of the waveguide propagation path betweentransducers902 and904. Depending on the operating mode, the sensing circuitry measures the change in length of thewaveguide906 by analyzing characteristics of the propagation of ultrasound waves within the waveguide.
• One interpretation ofFIG. 9 illustrates waves emitting fromtransducer902 at one end ofwaveguide906 and propagating totransducer904 at the other end of thewaveguide906. The interpretation includes the effect of movement ofwaveguide906 and thus the velocity of waves propagating within waveguide906 (without changing shape or width of individual waves) and therefore the transit time betweentransducers902 and904 at each end of the waveguide. The interpretation further includes the opposite effect on waves propagating in the opposite direction and is evaluated to estimate the velocity of the waveguide and remove it by averaging the transit time of waves propagating in both directions.
• Changes in the parameter or parameters of interest are measured by measuring changes in the transit time of energy pulses or waves within the propagating medium. Closed loop measurement of changes in the parameter or parameters of interest is achieved by modulating the repetition rate of energy pulses or the frequency of energy waves as a function of the propagation characteristics of the elastic energy propagating structure.
• In a continuous wave mode of operation, a phase detector (not shown) evaluates the frequency and changes in the frequency of resonant ultrasonic waves in thewaveguide906. As will be described below, positive feedback closed-loop circuit operation in continuous wave (CW) mode adjusts the frequency ofultrasonic waves914 in thewaveguide906 to maintain a same number or integer number of periods of ultrasonic waves in thewaveguide906. The CW operation persists as long as the rate of change of the length of the waveguide is not so rapid that changes of more than a quarter wavelength occur before the frequency of the propagation tuned oscillator (PTO) can respond. This restriction exemplifies one advantageous difference between the performance of a PTO and a Phase Locked Loop (PLL). Assuming the transducers are producing ultrasonic waves, for example, at 2.4 MHz, the wavelength in air, assuming a velocity of 343 microns per microsecond, is about 143μ, although the wavelength within a waveguide may be longer than in unrestricted air.
• In a pulse mode of operation, the phase detector measures a time of flight (TOF) between when an ultrasonic pulse is transmitted bytransducer902 and received attransducer904. The time of flight determines the length of the waveguide propagating path, and accordingly reveals the change in length of thewaveguide906. In another arrangement, differential time of flight measurements (or phase differences) can be used to determine the change in length of thewaveguide906. A pulse consists of a pulse of one or more waves. The waves may have equal amplitude and frequency (square wave pulse) or they may have different amplitudes, for example, decaying amplitude (trapezoidal pulse) or some other complex waveform. The PTO is holding the phase of the leading edge of the pulses propagating through the waveguide constant. In pulse mode operation the PTO detects the leading edge of with an edge-detect receiver rather than a zero-crossing or transition as detected by a zero-crossing receiver used in CW mode.
• It should be noted that ultrasound energy pulses or waves, the emission of ultrasound pulses or waves by ultrasound resonators or transducers, transmitted through ultrasound waveguides, and detected by ultrasound resonators or transducers are used merely as examples of energy pulses, waves, and propagation structures and media. Other embodiments herein contemplated can utilize other wave forms, such as, light.
• FIG. 10 is an exemplary block diagram1000 of a propagation tuned oscillator (PTO)4 to maintain positive closed-loop feedback in accordance with an exemplary embodiment. The measurement system includes asensing assemblage1 and propagation tuned oscillator (PTO)4 that detectsenergy waves2 in one ormore waveguides3 of thesensing assemblage1. In one embodiment,energy waves2 are ultrasound waves. A pulse11 is generated in response to the detection ofenergy waves2 to initiate a propagation of a new energy wave inwaveguide3. It should be noted that ultrasound energy pulses or waves, the emission of ultrasound pulses or waves by ultrasound resonators or transducers, transmitted through ultrasound waveguides, and detected by ultrasound resonators or transducers are used merely as examples of energy pulses, waves, and propagation structures and media. Other embodiments herein contemplated can utilize other wave forms, such as, light.
• Recall that the loadsensing insert device100 when in motion measures forces on the sensing assemblies by evaluating propagation times of energy waves within the waveguides in conjunction with the accelerometer data. The propagation tuned oscillator (PTO)4 measures a transit time ofultrasound waves2 within thewaveguide3 in a closed-loop configuration. Thedigital counter20 determines the physical change in the length of the waveguide. Referring toFIG. 5, the one ormore accelerometers302 determines the changes along x, y and z dimensions. Theelectronic circuitry307 in view of the accelerometer data fromaccelerometer302 and the physical changes in length of thesensing assemblage1 determines the applied loading (or forces).
• Thesensing assemblage1 comprisestransducer5,transducer6, and a waveguide3 (or energy propagating structure). In a non-limiting example, sensingassemblage1 is affixed to load bearing or contactingsurfaces8. External forces applied to the contactingsurfaces8 compress thewaveguide3 and change the length of thewaveguide3. Under compression,transducers5 and6 will also be moved closer together. The change in distance affects thetransit time7 ofenergy waves2 transmitted and received betweentransducers5 and6. The propagation tunedoscillator4 in response to these physical changes will detect each energy wave sooner (e.g. shorter transit time) and initiate the propagation of new energy waves associated with the shorter transit time. As will be explained below, this is accomplished by way ofPTO4 in conjunction with thepulse generator10, themode control12, and thephase detector14.
• Notably, changes in the waveguide3 (energy propagating structure or structures) alter the propagation properties of the medium of propagation (e.g. transit time7). The energy wave can be a continuous wave or a pulsed energy wave. A pulsed energy wave approach reduces power dissipation allowing for a temporary power source such as a battery or capacitor to power the system during the course of operation. In at least one exemplary embodiment, a continuous wave energy wave or a pulsed energy wave is provided bytransducer5 to a first surface ofwaveguide3.Transducer5 generatesenergy waves2 that are coupled intowaveguide3. In a non-limiting example,transducer5 is a piezo-electric device capable of transmitting and receiving acoustic signals in the ultrasonic frequency range.
• Transducer6 is coupled to a second surface ofwaveguide3 to receive the propagated pulsed signal and generates a corresponding electrical signal. The electrical signal output bytransducer6 is coupled tophase detector14. In general,phase detector14 compares the timing of a selected point on the waveform of the detected energy wave with respect to the timing of the same point on the waveform of other propagated energy waves. In a first embodiment,phase detector14 can be a zero-crossing receiver. In a second embodiment,phase detector14 can be an edge-detect receiver. In the example wheresensing assemblage1 is compressed, the detection of the propagatedenergy waves2 occurs earlier (due to the length/distance reduction of waveguide3) than a signal prior to external forces being applied to contacting surfaces.Pulse generator10 generates a new pulse in response to detection of the propagatedenergy waves2 byphase detector14. The new pulse is provided totransducer5 to initiate a new energy wave sequence. Thus, each energy wave sequence is an individual event of energy wave propagation, energy wave detection, and energy wave emission that maintainsenergy waves2 propagating inwaveguide3.
• Thetransit time7 of a propagated energy wave is the time it takes an energy wave to propagate from the first surface ofwaveguide3 to the second surface. There is delay associated with each circuit described above. Typically, the total delay of the circuitry is significantly less than the propagation time of an energy wave throughwaveguide3. In addition, under equilibrium conditions variations in circuit delay are minimal. Multiple pulse to pulse timings can be used to generate an average time period when change in external forces occur relatively slowly in relation to the pulsed signal propagation time such as in a physiologic or mechanical system. Thedigital counter20 in conjunction with electronic components counts the number of propagated energy waves to determine a corresponding change in the length of thewaveguide3. These changes in length change in direct proportion to the external force thus enabling the conversion of changes in parameter or parameters of interest into electrical signals.
• The block diagram1000 further includes counting and timing circuitry. More specifically, the timing, counting, and clock circuitry comprises adigital counter20, adigital timer22, adigital clock24, and adata register26. Thedigital clock24 provides a clock signal todigital counter20 anddigital timer22 during a measurement sequence. Thedigital counter20 is coupled to the propagation tunedoscillator4.Digital timer22 is coupled to data register26.Digital timer20, digital timer,22,digital clock24 and data register26capture transit time7 ofenergy waves2 emitted by ultrasound resonator ortransducer5, propagated throughwaveguide3, and detected by or ultrasound resonator ortransducer5 or6 depending on the mode of the measurement of the physical parameters of interest applied tosurfaces8. The operation of the timing and counting circuitry is disclosed in more detail hereinbelow.
• The measurement data can be analyzed to achieve accurate, repeatable, high precision and high resolution measurements. This method enables the setting of the level of precision or resolution of captured data to optimize trade-offs between measurement resolution versus frequency, including the bandwidth of the sensing and data processing operations, thus enabling a sensing module or device to operate at its optimal operating point without compromising resolution of the measurements. This is achieved by the accumulation of multiple cycles of excitation and transit time instead of averaging transit time of multiple individual excitation and transit cycles. The result is accurate, repeatable, high precision and high resolution measurements of parameters of interest in physical systems.
• In at least one exemplary embodiment, propagation tunedoscillator4 in conjunction with one ormore sensing assemblages1 are used to take measurements on a muscular-skeletal system. In a non-limiting example, sensingassemblage1 is placed between a femoral prosthetic component and tibial prosthetic component to provide measured load information that aids in the installation of an artificial knee joint.Sensing assemblage1 can also be a permanent component or a muscular-skeletal joint or artificial muscular-skeletal joint to monitor joint function. The measurements can be made in extension and in flexion. In the example,assemblage1 is used to measure the condyle loading to determine if it falls within a predetermined range and location. Based on the measurement, the surgeon can select the thickness of the insert such that the measured loading and incidence with the final insert in place will fall within the predetermined range. Soft tissue tensioning can be used by a surgeon to further optimize the force or pressure. Similarly, twoassemblages1 can be used to measure both condyles simultaneously or multiplexed. The difference in loading (e.g. balance) between condyles can be measured. Soft tissue tensioning can be used to reduce the force on the condyle having the higher measured loading to reduce the measured pressure difference between condyles.
• One method of operation holds the number of energy waves propagating throughwaveguide3 as a constant integer number. A time period of an energy wave corresponds to energy wave periodicity. A stable time period is one in which the time period changes very little over a number of energy waves. This occurs when conditions that affectsensing assemblage1 stay consistent or constant. Holding the number of energy waves propagating throughwaveguide3 to an integer number is a constraint that forces a change in the time between pulses when the length ofwaveguide3 changes. The resulting change in time period of each energy wave corresponds to a change in aggregate energy wave time period that is captured usingdigital counter20 as a measurement of changes in external forces or conditions applied to contactingsurfaces8.
• A further method of operation according to one embodiment is described hereinbelow forenergy waves2 propagating fromtransducer5 and received bytransducer6. In at least one exemplary embodiment,energy waves2 is an ultrasonic energy wave.Transducers5 and6 are piezo-electric resonator transducers. Although not described, wave propagation can occur in the opposite direction being initiated bytransducer6 and received bytransducer5. Furthermore, detectingultrasound resonator transducer6 can be a separate ultrasound resonator as shown ortransducer5 can be used solely depending on the selected mode of propagation (e.g. reflective sensing). Changes in external forces or conditions applied to contactingsurfaces8 affect the propagation characteristics ofwaveguide3 and altertransit time7. As mentioned previously, propagation tunedoscillator4 holds constant an integer number ofenergy waves2 propagating through waveguide3 (e.g. an integer number of pulsed energy wave time periods) thereby controlling the repetition rate. As noted above, oncePTO4 stabilizes, thedigital counter20 digitizes the repetition rate of pulsed energy waves, for example, by way of edge-detection, as will be explained hereinbelow in more detail.
• In an alternate embodiment, the repetition rate ofpulsed energy waves2 emitted bytransducer5 can be controlled bypulse generator10. The operation remains similar where the parameter to be measured corresponds to the measurement of thetransit time7 ofpulsed energy waves2 withinwaveguide3. It should be noted that an individual ultrasonic pulse can comprise one or more energy waves with a damping wave shape. The energy wave shape is determined by the electrical and mechanical parameters ofpulse generator10, interface material or materials, where required, and ultrasound resonator ortransducer5. The frequency of the energy waves within individual pulses is determined by the response of the emittingultrasound resonator4 to excitation by an electrical pulse11. The mode of the propagation of thepulsed energy waves2 throughwaveguide3 is controlled by mode control circuitry12 (e.g., reflectance or uni-directional). The detecting ultrasound resonator or transducer may either be a separate ultrasound resonator ortransducer6 or the emitting resonator ortransducer5 depending on the selected mode of propagation (reflectance or unidirectional).
• In general, accurate measurement of physical parameters is achieved at an equilibrium point having the property that an integer number of pulses are propagating through the energy propagating structure at any point in time. Measurement of changes in the “time-of-flight” or transit time of ultrasound energy waves within a waveguide of known length can be achieved by modulating the repetition rate of the ultrasound energy waves as a function of changes in distance or velocity through the medium of propagation, or a combination of changes in distance and velocity, caused by changes in the parameter or parameters of interest.
• It should be noted that ultrasound energy pulses or waves, the emission of ultrasound pulses or waves by ultrasound resonators or transducers, transmitted through ultrasound waveguides, and detected by ultrasound resonators or transducers are used merely as examples of energy pulses, waves, and propagation structures and media. Other embodiments herein contemplated can utilize other wave forms, such as, light. Furthermore, the velocity of ultrasound waves within a medium may be higher than in air. With the present dimensions of the initial embodiment of a propagation tuned oscillator the waveguide is approximately three wavelengths long at the frequency of operation.
• Measurement by propagation tunedoscillator4 andsensing assemblage1 enables high sensitivity and high signal-to-noise ratio. The time-based measurements are largely insensitive to most sources of error that may influence voltage or current driven sensing methods and devices. The resulting changes in the transit time of operation correspond to frequency, which can be measured rapidly, and with high resolution. This achieves the required measurement accuracy and precision thus capturing changes in the physical parameters of interest and enabling analysis of their dynamic and static behavior.
• These measurements may be implemented with an integrated wireless sensing module or device having an encapsulating structure that supports sensors and load bearing or contacting surfaces and an electronic assemblage that integrates a power supply, sensing elements, energy transducer or transducers and elastic energy propagating structure or structures, biasing spring or springs or other form of elastic members, an accelerometer, antennas and electronic circuitry that processes measurement data as well as controls all operations of ultrasound generation, propagation, and detection and wireless communications. The electronics assemblage also supports testability and calibration features that assure the quality, accuracy, and reliability of the completed wireless sensing module or device.
• In general, measurement of the changes in the physical length of individual waveguides can be made in several modes. Each assemblage of one or two ultrasound resonators or transducers combined with a waveguide can be controlled to operate in six different modes. This includes two wave shape modes: continuous wave or pulsed waves, and three propagation modes: reflectance, unidirectional, and bi-directional propagation of the ultrasound wave. In all modes of operation the changes in transit time within the ultrasound waveguides change the operating frequency of the propagation tunedoscillator4 or oscillators. These changes in the frequency of oscillation of the propagation tuned oscillator or oscillators can be measured rapidly and with high resolution. This achieves the required measurement accuracy and precision thus enabling the capture of changes in the physical parameters of interest and enabling analysis of the dynamic and static behavior of the physical system or body.
• The level of accuracy and resolution achieved by the integration of energy transducers and an energy propagating structure or structures coupled with the electronic components of the propagation tuned oscillator enables the construction of, but is not limited to, compact ultra low power modules or devices for monitoring or measuring the parameters of interest. The flexibility to construct sensing modules or devices over a wide range of sizes enables sensing modules to be tailored to fit a wide range of applications such that the sensing module or device may be engaged with, or placed, attached, or affixed to, on, or within a body, instrument, appliance, vehicle, equipment, or other physical system and monitor or collect data on physical parameters of interest without disturbing the operation of the body, instrument, appliance, vehicle, equipment, or physical system.
• FIG. 11 is a cross-sectional view of a layout architecture of thesensing module200 in accordance with an exemplary embodiment. The blocks are operatively coupled within the encapsulated enclosure of thesensing module200 and together form an encapsulatedforce sensor1100. It comprises atop steel plate1104 coupled to a lower printed circuit board (PCB)1118 by way ofspring retainer1106,disc spring1108, andspring post1114. Theforce sensor1100 is biased with springs or other means of elastic support to accurately maintain a required distance between the load bearing or contact surfaces such astop cover1102 and to minimize hysteresis due to material properties ofwaveguide1110.
• The encapsulatingforce sensor1100 supports and protects the specialized mechanical and electronic components from external physical, mechanical, chemical, and electrical, and electromagnetic intrusion that might compromise sensing or communication operations of the module or device. The encapsulatingforce sensor1100 also supports internal mechanical and electronic components and minimizes adverse physical, mechanical, electrical, and ultrasonic interactions that might compromise sensing or communication operations of the module or device.Top cover1102 and unitarymain body1157 form the encapsulating enclosure. Unitarymain body1157 is a metal, plastic, or polymer body having sufficient strength and rigidity to withstand forces, pressures, and loads of the muscular-skeletal system. In particular, the sidewalls or bottom surface do not deform under normal operating conditions. For example, the unitarymain body1157 can be formed of polycarbonate or other biocompatible material. Moreover, unitarymain body1157 can be molded in a manufacturing process that allows detailed features to be repeatably and reliably manufactured.
• The physical layout architecture ofsensor1100 has the one or more sensing assemblages overlying the electronic circuitry. A force, pressure, or load is applied to a surface ofsensor1100. The surface ofsensor1100 corresponds totop steel plate1104.Steel plate1104 moves in response to a force, pressure, or load. Thesteel plate1104 can support the movement while maintaining a seal with unitarymain body1157 that isolates an interior of the enclosure. In general, a sensing assemblage is coupled betweensteel plate1104 and asubstrate1130.Substrate1130 is a rigid non-moveable substrate that is supported by the sidewalls of unitarymain body1157. A periphery ofsubstrate1130 is in contact with and supported by asupport feature1128 formed in the sidewalls of unitarymain body1157.Substrate1130 does not flex under loading. The sensing assemblage translates a displacement due to the force, pressure, or load applied tosteel plate1104 to a signal. The signal is processed by electronic circuitry in the enclosure to generate data corresponding to the force, pressure, or load value. As shown, the sensing assemblage comprises upper piezo1112,waveguide1110, and lower piezo1124. Upper piezo1112 and lower piezo1124 are ultrasonic piezo-electric transducers.
• Electronic circuitry to power, control, interface, operate, measure, and send sensor data is interconnected together on a printed circuit board (PCB)1118. One ormore cups1120 are formed in unitarymain body1157. In one embodiment, the components mounted onPCB1118 reside withincups1120. One ormore structures1126 support and fix the position of thePCB1118. The components onPCB1118 are suspended in thecups1120 and do not have contact with unitarymain body1157 thereby preventing interconnect stress that could result in long-term reliability issues. ThePCB1118 is mechanically isolated fromsubstrate1130. Thus, any force, pressure, or loading onsubstrate1130 is not applied toPCB1118. Flexible interconnect is used to connect from the electronic circuitry onPCB1118 to upper piezo1112 and lower piezo1124.
• In one embodiment, more than one sensing assemblage couples to predetermined locations of thesteel plate1104. Each sensing assemblage can measure a parameter applied tosteel plate1104. In combination, the sensing assemblages can determine a location or region where the parameter is applied to the surface. For example, the magnitude and position of the loading on the contacting surface ofsensing module200 applied byfemur102 andtibia108 tosensing module200 can be measured and displayed as shown inFIG. 2. In a non-limiting example, three sensing assemblages can be spaced on a periphery ofsteel plate1104. In the example, each sensing assemblage will measure a force applied tosteel plate1104. The location of the applied force is closest to the sensing assemblage detecting the highest force magnitude. Conversely, the sensing assemblage detecting the weakest force magnitude is farthest from the applied force. The measured force magnitudes in combination with the predetermined locations where the sensing assemblages couple tosteel plate1104 can be used to determine a location where the parameter is applied.
• The housing electrically insulates the internal electronic, sensing, and communication components. The encapsulatingforce sensor1100 eliminates parasitic paths that might conduct ultrasonic energy and compromise excitation and detection of ultrasound waves within the sensing assemblages during sensing operations. A temporary bi-directional electrical interconnect assures a high level of electrical observation and controllability of the electronic assembly within the encapsulatingforce sensor1100. The temporary interconnect also provides a high level of electrical observation of the sensing subsystem, including the transducers, waveguides, and mechanical spring or elastic assembly.
• Ultrasound waveguide1110 is coupled to thetop cover1102. A force applied to thetop cover1102 compresseswaveguide1110. Lower piezo1124 and upper piezo1112 are piezo-electric transducers respectively coupled towaveguide1110 at a first and second location.Waveguide1110 is a compressible propagation medium for ultrasonic energy waves. The transducers emit energy waves and detect propagated energy waves inwaveguide1110. Electronic circuitry is coupled to lower piezo1124 and upper piezo1112 to measure transit time, frequency, or phase of the propagated energy waves. The transit time, frequency, or phase of energy waves propagating between the first and second locations ofwaveguide1110 can be precisely measured and therefore the length of theultrasound waveguide1110. The length ofwaveguide1110 is calculated by a known function relating material properties of thewaveguide1110 to the parameter being measured. In the example, a force, pressure, or load is calculated from the measured length ofwaveguide1110.
• The encapsulatedforce sensor1100 can accurately and repeatably measure one pound changes in load with changes in length of a waveguide comprising 2.5 microns. The maximum change in the present implementation is specified at less than 5.0 microns. This assures that the size of thesensing module200 throughout all measurements remains within the required dimension (e.g., distance) of the insert between the load bearing surfaces of the prosthetic components.
• An exemplary level of control of the compression or displacement of thewaveguides1110 with changes in load, force, pressure, or displacement is achieved by positioning the spring or springs1108 or other means of elastic support, including thewaveguides1110 themselves, between the load bearing contact surfaces to minimize any tendency of the load bearing contact surfaces to cantilever. Cantilevering can compromise the accuracy of the inclination of the load bearing contact surface whenever load, force, pressure, or displacement is applied to any point near a periphery of the load bearing contact surfaces. In one embodiment, springs1108 are disc springs. Thespring1108 is held in a predetermined location byspring post1114 andspring retainer1104.
• The walls of the unitarymain body1157 include a small gap to enable thesteel plate1104 to move. The hermetic seal is also flexible to allow thesteel plate1104 of theforce sensor1104 to slide up and down, like a piston, for distances on the order of a hundred microns without compromising integrity of the seal. The hermetic seal completes manufacturing, sterilization, and packaging processes without compromising ability to meet regulatory requirements for hermeticity. The level of hermeticity is sufficient to assure functionality and biocompatibility over the lifetime of the device. Implant devices with total implant time less than 24 hours may have less stringent regulatory requirements for hermeticity. Unbiased electrical circuitry is less susceptible to damage from moisture. The electronics in one embodiment are only powered during actual usage. In another embodiment, the encapsulatedforce sensor1100 employs low duty cycles to serve as a measurement-on-demand device to efficiently perform at low total operating time when the electronics are powered on.
• The encapsulatingforce sensor1100 has a compact size permitting it to fit for example within a trial insert, final insert, prosthetic component, tool, equipment, or implant structure to measure the level and incidence of the load on subsequent implanted prosthetic devices. It can be constructed using standard components and manufacturing processes. Manufacturing carriers or fixtures can be designed to emulate the final encapsulating enclosure of thesensing module200. Calibration data can be obtained during the manufacturing processing thus enabling capture of accurate calibration data. These calibration parameters can be stored within the memory circuits integrated into the electronics assemblage of thesensing module200. Testability and calibration further assures the quality and reliability of the encapsulated enclosure.
• Examples of a wide range of potential medical applications can include, but are not limited to, implantable devices, modules within implantable devices, intra-operative implants or modules within intra-operative implants or trial inserts, modules within inserted or ingested devices, modules within wearable devices, modules within handheld devices, modules within instruments, appliances, equipment, or accessories of all of these, or disposables within implants, trial inserts, inserted or ingested devices, wearable devices, handheld devices, instruments, appliances, equipment, or accessories to these devices, instruments, appliances, or equipment.
• FIG. 12 is a simplified cross-sectional view of an embodiment of theload sensing platform121 in accordance with an exemplary embodiment. Theload sensing platform121 is placed, engaged, attached, or affixed to or within a physical system with a portion of the system contacting the load bearing or contacting surfaces of the load sensing platform. As disclosed inFIG. 1 the load sensing platform can be used intra-operatively to measure parameters of the muscular-skeletal system during joint replacement surgery. In the example, theload bearing platform121 is placed in a joint of the muscular-skeletal system to measure force, pressure, or load and the location where the force, pressure, or load is applied. The lowerload bearing surface8 contacts thetibial component106 of the artificial knee. The upperload bearing surface8 contacts thefemoral component104 of the artificial knee. Not shown are the muscles, ligaments, and tendons of the muscular-skeletal system that apply a compressive force, pressure, or load on thesurfaces8 of theload sensing platform121. Theload sensing platform121 has a form factor that allows integration in tools, equipment, and implants. Theload sensing platform121 is bio-compatible and can be placed in an implant or attached to the muscular-skeletal system to provide long term monitoring capability of natural structures or artificial components.
• A compact sensing platform is miniaturized to be placed on or within a body, instrument, appliance, vehicle, equipment, or other physical system without disturbing the operation of the body, instrument, appliance, vehicle, equipment, or physical system. This facilitates contacting the sources of load, force, pressure, displacement, density, viscosity, or localized temperature to be measured. The non-limiting example ofload sensing platform121 can include circuitry disclosed inFIG. 5. Two or more springs or other means ofelastic support315 support the load bearing or contactingsurfaces8. One or more assemblages each comprised of one or two ultrasound resonators or transducers are coupled between load bearing surfaces8.
• As shown, asingle sensing assemblage1 is centrally located inload sensing platform121.Sensing assemblage1 is a stack comprising theupper transducer6, thelower transducer5, and thewaveguide3. In one embodiment, thewaveguide3 is cylindrical in shape having a first end and a second end.Transducers5 and6 respectively overlie the first and second ends ofwaveguide3. An interface material can be used to attach and enhance acoustical coupling between a transducer and waveguide. The stack is positioned in contact with, attached, or coupled to the load bearing or contactingsurfaces8. Electrical interconnect such as a flex interconnect couples to terminals oftransducers5 and6. The flex interconnect (not shown) electrically connectstransducers5 and6 toelectronic circuitry307 of thesensing module200.
• The upperload bearing surface8 is a surface of anupper substrate702. An interior surface of theupper substrate702 couples totransducer6. Similarly, the lowerload bearing surface8 is a surface of alower substrate704. An interior surface of the lower substrate couples to thetransducer5. A load, force, or pressure applied acrossload bearing surfaces8 can compress or lengthenwaveguide3. This arrangement facilitates translating changes in the parameter or parameters of interest into changes in the length or compression of the waveguide orwaveguides3 and converting these changes in the length or compression of thewaveguide3 or waveguides into electrical signals by way oftransducers5 or6 thus enablingsensing assemblage1 to sense changes in the physical parameters of interest with minimal disturbance to the operation of the external body, instrument, appliance, vehicle, equipment, or physical system. To achieve the required level of miniaturization, the length of theultrasound waveguides3 is on the order of 10 millimeters in length. The measurable resolution of compression or displacement of waveguide is on the order of sub-microns.
• One ormore springs315 or other means of elastic support, support the load bearing or contactingsurfaces8. The one or more springs control a compression ofload sensing platform121. For example,waveguide3 can comprise a polymer material suitable for energy wave propagation. In one embodiment, the polymer material changes dimension when a parameter to be measured is applied towaveguide3. A relationship is known between the polymer material and a measured dimension. Changes in dimension are measured and the parameter calculated by way of the known relationship. The polymer material can exhibit mechanical hysteresis whereby the material in-elastically responds to changes in the applied parameter. In the example, the length ofwaveguide3 responds to the force, pressure, or load applied across contactingsurfaces8. Moreover, the polymer material may not rebound in a timely fashion as the force, pressure or load changes.Springs315 aid in the transition aswaveguide3 responds to different levels of compression.Springs315 bring theload sensing platform121 to an accurate and repeatable quiescent state or condition. Springs further prevent the cantilevering ofload bearing surfaces8 that can reduce an accuracy of measurement. Cantilevering becomes more prevalent as forces, pressures, and loads are applied towards the periphery of a contact area of load bearing surfaces8.
• In one embodiment, thesprings315 that supportload bearing surfaces8 are disc springs or a wave springs. Disc springs are capable of maintainingwaveguide3 at a precise length. The compression of thewaveguide3 is very accurate over the measurement range. The compression of the disc springs can be monotonic over the range of applied levels of force, pressure, or load. In one embodiment, the surfaces of the disc springs are polished to assure smooth compression with changes in force applied to contact surfaces8. A further benefit of the disk springs is that they eliminate or minimize cantilevering of the load supporting substrate that can compromise the accuracy due to the inclination of load bearing surfaces8. In the illustration, twosprings315 are shown that are located on the periphery ofload sensing platform121. Although not shown,other springs315 may reside in theload sensing platform121 at other predetermined locations. Typically, the contact area where the parameter is applied to load bearingsurfaces8 is within an area bounded bysprings315.
• In one embodiment, asubstrate706 is resides betweenupper substrate702 andlower substrate704.Sensing assemblage1 couples through an opening insubstrate706 to couple to the interior surfaces ofsubstrates702 and704 to measure a force, pressure, or load applied across load bearing surfaces8. In the example,substrate702 moves as a force, pressure, or load is applied whilesubstrate704 remains in a fixed position. Thus, a force, pressure, or load applied to contactingsurface8 changes a distance betweensubstrates702 and704 and therefore the length ofwaveguide3.Substrates704 and706 are planar to one another separated by a predetermined spacing.Substrates704 and706 remain in the fixed relation to one another under loading.
• Springs315 are placed between an upper surface ofsubstrate706 and the interior surface ofsubstrate702. As disclosed in the example, springs315 are disc springs. The disc springs are concave in shape. The disc spring is formed having a centrally located circular opening. The surface ofsprings315 proximally located to the circular opening contacts the upper surface ofsubstrate706. The surface ofsprings315 proximally located to the outer edge ofsprings315 contacts the interior surface ofsubstrate702. A force applied across theload bearing surface8 ofload sensing platform121 will compresssprings315 andwaveguide3. The amount of compression ofwaveguide3 over a measurable range can be very small but will provide precision accuracy of the parameter. For example,waveguide3 may be compressed less than a millimeter for a force measurement ranging from 5 to 100 lbs. In the example, the length ofwaveguide3 is precisely measured using acoustic energy wave propagation. The measured length is then converted to the force, pressure, or load. Thesprings315 support movement of thewaveguide3 upon a change in force, pressure, or loading. For example, springs315 repeatably return theload sensing platform121 to a precise quiescent state upon releasing an applied force. The characteristics ofsprings315 are known over the measurement range ofload sensing platform121. The calculated measured value of the parameter can include compensation due tosprings315.
• Spring315 are in a fixed location inload sensing platform121. The disc springs are located on the periphery of theload sensing platform121. Spring posts708 andspring retainers710 are used to align and fixsprings315 in each predetermined location.Spring post708 alignssubstrate702 tosubstrate706.Spring post708 andspring retainer710 aligns to corresponding openings insubstrate706. In one embodiment, a cap ofpost708 fits into a corresponding cavity of the interior surface ofsubstrate702.Spring retainer710 is a sleeve that overliespost708.Post708 andspring retainer710 couples through a corresponding opening insubstrate706.Spring retainer710 has a lip that overlies and contacts the upper surface ofsubstrate706. Thespring post708 andspring retainer710 couple through the opening in the disc spring. The edge of the opening rests against the edge of the lip ofretainer710 thereby retaining and holdingspring315 in the predetermined location.Spring315 can move vertically allowingwaveguide3 to change length due to the parameter being applied to contact surfaces8.
• In one embodiment,load sensing platform121 can locate a position where the parameter is applied on a load bearing surface. Locating the position can be achieved by using more than onesensing assemblages1. In one embodiment, threesensing assemblages1 couple to load bearing or contactingsurface8 at three predetermined locations. The parameter is measured by eachsensing assemblages1. The magnitudes of each measurement and the differences between measurements of thesensing assemblages1 are compared. For example, the location of the applied parameter is closer to the sensing assemblage that generates the highest reading. Conversely, the location of the applied parameter will be furthest from the sensing assemblage that generates the lowest reading. The exact location can be determined by comparison of the measured values of each sensing assemblage in conjunction with knowledge of the predetermined locations where each assemblage contacts load bearing or contactingsurface8.
• While the present invention has been described with reference to particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the invention.

Claims (20)

1. A system to measure a parameter of the muscular-skeletal system comprising:

a sensing module comprising:

a substrate having a contacting surface for coupling to at least one bone of the muscular-skeletal system;

one or more sensors coupled to the substrate; and

electronic circuitry operatively coupled to the sensors; and

a transmitter coupled to the electronic circuitry where the sensor module wirelessly sends one or more data packets and where each data packet comprises measured parameter data and a priority level.

2. The system ofclaim 1 where the sensing module is operatively fitted within an orthopedic prosthesis such that the contacting surface couples to the at least one bone.

3. The system ofclaim 2 where the sensing module is fitted within a final insert having at least one bearing surface.

4. The system ofclaim 3 where the sensing module is placed in a trial insert and where the trial insert is substantial equal in dimensions to the final insert.

5. The system ofclaim 1 where the sensing module evaluates data bounds of the measured parameter and where a priority level is assigned corresponding to the data bounds.

6. The system ofclaim 5 where a communication mode is based on priority level and operating mode.

7. The system ofclaim 6 where an operating mode includes one or more power saving modes.

8. The system ofclaim 6 where the priority level corresponds to when the one or more data packets are transmitted.

9. The system ofclaim 1 where each data packet includes a cyclic redundancy check.

10. The system ofclaim 1 where the one or more sensors measures a transit time, frequency, or phase.

11. A method of transmitting measurement data from an orthopedic component comprising the steps of:

measuring a parameter of the muscular-skeletal system with a sensing module coupled to the muscular-skeletal system;

evaluating sensor data bounds; and

assigning priority level based on the data bounds and measured parameter data.

12. The method ofclaim 11 further including the steps of:

generating packet data where the packet data comprises measured parameter data and the priority level; and

sending one or more data packets to a receiver where the transmission can be immediate or delayed based on the priority level.

13. The method ofclaim 12 further including the steps of:

assessing an operating mode where the operating mode comprises one or more power saving modes; and

determining a communication mode based on the priority level and the operating mode.

14. The method ofclaim 13 further including the step of applying a cyclic redundancy check.

15. The method ofclaim 14 further including a step of measuring a force, pressure, or load applied by the muscular-skeletal system.

16. A prosthetic component to measure a parameter of the muscular-skeletal system comprising:

an insert having at least one bearing surface that allows articulation with at least one bone of the muscular-skeletal system where the insert includes:

a sensing module comprising:

one or more sensors; and

electronic circuitry operatively coupled to the sensors; and

a transmitter coupled to the electronic circuitry where the sensor module wirelessly sends one or more data packets and where each data packet comprises measured parameter data and a priority level.

17. The prosthetic component ofclaim 16 where the insert comprises a dock having an opening where the sensing module is inserted in the opening and where the insert is a trial insert for providing measurement data to optimally install one or more prosthetic components.

18. The prosthetic component ofclaim 16 where the sensing module evaluates data bounds and where a priority level is assigned corresponding to the data bounds and a parameter measurement.

19. The prosthetic component ofclaim 18 where a communication mode is based on priority level and operating mode, where an operating mode includes one or more power saving modes and where the communication mode corresponds to when the one or more data packets are transmitted.

20. The prosthetic component ofclaim 19 where each data packet includes a cyclic redundancy check.

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