# Patent

## Title
Integrated position and parameter sensing for the muscular-skeletal system

## Abstract

A measurement system for capturing a transit time, phase, or frequency of energy waves propagating through a propagation medium is disclosed. The measurement system comprises a sensing module (200) and an insert dock (202). The sensing module (200) includes a load sensing platform (121), an accelerometer (122), and sensing assemblies (123). In one embodiment, a force or load applied by the muscular-skeletal system is measured. The force or load is applied to the sensing assembly (123). The accelerometer (122) generates motion data. The motion data includes acceleration data. The force or load measured by sensing assembly (123) in combination with the motion data captured by the accelerometer (122) is used to calculate a total force or load. A second accelerometer can be used to provide reference position information. The sensing assemblies (123) comprise a transducer (304), an elastic or compressible propagation structure (305), and a second transducer (314).

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the priority benefit of U.S. provisional patent applications Nos. 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 relates generally to accelerometers and force sensing, and more particularly, to real-time measurement or physical parameters relative to orientation, alignment, direction, and position by way devices incorporating accelerometers and load sensing components.
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 a load sensing insert device placed in contact between a femur and a tibia for measuring a parameter in accordance with an exemplary embodiment;
FIG. 2 is a perspective view of the medical device in accordance with one embodiment;
FIG. 3 is a block model diagram of a sensing module in accordance with one embodiment;
FIG. 4 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. 5 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. 6 is an exemplary block diagram of a propagation tuned oscillator (PTO) to maintain positive closed-loop feedback in accordance with an exemplary embodiment;
FIG. 7 illustrates one embodiment of accelerometer integration with the load sensing platform in accordance with an exemplary embodiment;
FIG. 8 is an exemplary block diagram of method steps for acquiring and utilizing accelerometer data to determine load forces in motion in accordance with one embodiment; and
FIG. 9 is a simplified cross-sectional view of an ultrasound waveguide for measuring changes in physical length due to external applied forces by measurement of a transmit time of ultrasonic waves in the ultrasound waveguide.



DETAILED DESCRIPTION
Embodiments of the invention are broadly directed to measurement of physical parameters, and more particularly, to real-time measurement of the parameter or parameters of interest relative to orientation, alignment, direction, or position as well as movement, rotation, or acceleration along any axis or combination of axes by load and position 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.
FIG. 1 is an illustration of a load sensing insert device 100 placed in contact between a femur 102 and a tibia 108 for measuring a parameter in accordance with an exemplary embodiment. In general, load sensing insert device 100 is placed in contact with or in proximity to the muscular-skeletal system to measure a parameter. In a non-limiting example, device 100 is used to measure a parameter of a muscular-skeletal system during a procedure such as an installation of an artificial joint. As illustrated, the device 100 in this example can intra-operatively assess a load on prosthetic components during the surgical procedure. It can collect load 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 a receiver station 110 for permitting visualization. This can aid the surgeon in making any adjustments needed to achieve optimal joint balancing.
The load sensing insert device 100, in one embodiment, comprises a load sensing platform 121, an accelerometer 122, and sensing assemblies 123. This permits the sensing device 100 to assess a total load on the prosthetic components when it is moving; it accounts for forces due to gravity and motion. In one embodiment, load sensing platform 121 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. The accelerometer 122 can measure acceleration. Acceleration can occur when the load sensing device 100 is moved or put in motion. Accelerometer 122 can sense orientation, vibration, and impact. In another embodiment, the femoral component 104 can similarly include an accelerometer 127, which by way of a communication interface to the load sensing insert device 100, can provide reference position and acceleration data to determine an exact angular relationship between the femur and tibia. The sensing assemblies 123 can reveal changes in length or compression of the energy propagating structure or structures by way of the energy transducer or transducers. Together the load sensing platform 121, accelerometer 122 (and in certain cases accelerometer 127), and sensing assemblies 123 measure force or pressure external to the load sensing platform or displacement produced by contact with the prosthetic components.
Incorporating data from the accelerometer 122 with data from the other sensing components 121 and 123 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.
The accelerometer 122 can operate singly, as an integrated unit with the load sensing platform 121, and/or as an integrated unit with the sensing assemblies 123. Integrating one or more accelerometers 122 within the sensing assemblages 123 to determine position, attitude, movement, or acceleration of sensing assemblages 123 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, the accelerometer 122 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 of device 100 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. Device 100 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.
In at least one exemplary embodiment, an energy pulse is directed within one or more waveguides in device 100 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.
A surgeon can affix a femoral prosthetic component 104 to the femur 102 and a tibial prosthetic component 106 to the patient's tibia 108. The tibial prosthetic component 106 can be a tray or plate affixed to a planarized proximal end of the tibia 108. The load sensing insert device 100 is fitted between the plate of the tibial prosthetic component 106 and the femoral prosthetic component 104. These three prosthetic components (104, 100 and 106) enable the prostheses to emulate the functioning of a natural knee joint. It can measure loads at various points (or locations) on the femoral prosthetic component 104 in view of the position and acceleration data and transmit the measured data to a receiving station 110. The receiving station 110 can include data processing, storage, or display, or combination thereof and provide real time graphical representation of the level and distribution of the load when the load sensing device 100 is stationary and in motion.
A proximal end of tibia 108 is prepared to receive tibial prosthetic component 106. Tibial prosthetic component 106 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 tibial prosthetic component 106 also retains the insert in a fixed position with respect to tibia 108. The insert is fitted between femoral prosthetic component 104 and tibial prosthetic component 106. The insert has at least one bearing surface that is in contact with at least condyle surface of femoral prosthetic component 104. The condyle surface can move in relation to the bearing surface of the insert such that the lower leg can rotate under load. The insert is typically made of a high wear plastic material that minimizes friction.
The condyle surface of femoral component 104 contacts a major surface of device 100. The major surface of device 100 approximates a surface of the insert. Tibial prosthetic component 106 can include a cavity or tray on the major surface that receives and retains an insert dock 202 and a sensing module 200 during a measurement process. Tibial prosthetic component 106 and device 100 have a combined thickness that represents a combined thickness of tibial prosthetic component 106 and a final (or chronic) insert of the knee joint.
In one embodiment, two devices 100 are fitted into two separate cavities, the cavities are within a trial insert (that may also be referred to as the tibial insert, rather than the tibial component itself) that is held in position by tibial component 106. One or two devices 100 may be inserted between femoral prosthetic component 104 and tibial prosthetic component 106. Each sensor is independent and each measures a respective condyle of femur 102. Separate sensors also accommodate a situation where a single condyle is repaired and only a single sensor is used. Alternatively, the electronics can be shared between two sensors to lower cost and complexity of the system. The shared electronics can multiplex between each sensor module to take measurements when appropriate. Measurements taken by device 100 aid the surgeon in modifying the absolute loading on each condyle and the balance between condyles. Although shown for a knee implant, device 100 can be used to measure other orthopedic joints such as the spine, hip, shoulder, elbow, ankle, wrist, interphalangeal joint, metatarsophalangeal joint, metacarpophalangeal joints, and others. Alternatively, device 100 can also be adapted to orthopedic tools to provide measurements.
The prosthesis incorporating device 100 emulates the function of a natural knee joint. Device 100 can measure loads or other parameters at various points throughout the range of motion. Data from device 100 is transmitted to a receiving station 110 via wired or wireless communications. In a first embodiment, device 100 is a disposable system. Device 100 can be disposed of after using the load sensing insert device 100 to optimally fit the joint implant. Device 100 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 sterilize device 100 for reuse. In a third embodiment, device 100 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, device 100 can be a permanent component of the replacement joint. Device 100 can be used to provide both short term and long term post-operative data on the implanted joint. In a fifth embodiment, device 100 can be coupled to the muscular-skeletal system. In all of the embodiments, receiving station 110 can include data processing, storage, or display, or combination thereof and provide real time graphical representation of the level and distribution of the load. Receiving station 110 can record and provide accounting information of device 100 to an appropriate authority.
In an intra-operative example, device 100 can measure forces (Fx, Fy, Fz) with corresponding locations and torques (e.g. Tx, Ty, and Tz) on the femoral prosthetic component 104 and the tibial prosthetic component 106. The measured force and torque data is transmitted to receiving station 110 to provide real-time visualization for assisting the surgeon in identifying any adjustments needed to achieve optimal joint pressure and balancing. The data has substantial value in determining ranges of load and alignment tolerances required to minimize rework and maximize patient function and longevity of the joint.
As mentioned previously, device 100 can be used for other joint surgeries; it is not limited to knee replacement implant or implants. Moreover, device 100 is not limited to trial measurements. Device 100 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 a problem using device 100 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, device 100 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. Device 100 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. 2 is a perspective view of the medical device in accordance with one embodiment. As illustrated, the load sensing insert device 100 can include a sensing module 200 and an insert 202. The sensing Module 200 can securely fit within the insert dock 202. The insert dock 202 can securely attach or slide onto the tibial prosthetic component 106 (see FIG. 1). The prosthetic components of FIG. 2 can be manually coupled prior to surgical placement or during the surgery. The sensing module 200 in other embodiments (without the insert dock 202) can affix directly to load bearing surfaces exposed to forces, for example, forces applied upon a load bearing component during flexion of the joint. Although illustrated as separate, in yet another embodiment, the sensing module 200 and insert dock 202 can be combined together as an integrated sensing module.
The sensing module 200 is an encapsulating enclosure with a unitary main body and load bearing contact surfaces that can be, but are not limited to, dissimilar materials, combined to form a hermetic module or device. The components of the encapsulating enclosure may also consist of, but are not limited to, bio-compatible materials. For medical applications, the encapsulating enclosure may be required to be hermetic. The encapsulating enclosure can comprise biocompatible materials, for example, but not limited to, polycarbonate, steel, silicon, neoprene, and similar materials.
As will be discussed ahead, electronic assemblage within the sensing module 200 integrates a power supply, sensing elements, ultrasound resonator or resonators or transducer or transducers and ultrasound waveguide 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 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. 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. 3 is an exemplary block diagram of the components of a sensing module. 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 or more sensing assemblages 303, a transceiver 320, an energy storage 330, electronic circuitry 307, one or more mechanical supports 315 (e.g., springs), and an accelerometer 302. In the non-limiting example, an applied compressive force can be measured by the sensing module.
The sensing assemblage 303 can be positioned, engaged, attached, or affixed to the contact surfaces 306. Mechanical supports 315 serve to provide proper balancing of contact surfaces 306. In at least one exemplary embodiment, contact surfaces 306 are load-bearing surfaces. In general, the propagation structure 305 is subject to the parameter being measured. Surfaces 306 can move and tilt with changes in applied load; actions which can be transferred to the sensing assemblages 303 and measured by the electronic circuitry 307. The electronic circuitry 307 measures physical changes in the sensing assemblage 303 to determine parameters of interest, for example a level, distribution and direction of forces acting on the contact surfaces 306. In general, the sensing module is powered by the energy storage 330.
As one example, the sensing assemblage 303 can comprise an elastic or compressible propagation structure 305 between a transducer 304 and a transducer 314. In the current example, transducer 304 can be an ultrasound (or ultrasonic) resonator, and the elastic or compressible propagation structure 305 can be an ultrasound (or ultrasonic) waveguide (or waveguides). The electronic circuitry 307 is electrically coupled to the sensing assemblages 303 and translates changes in the length (or compression or extension) of the sensing assemblages 303 to parameters of interest, such as force. It measures a change in the length of the propagation structure 305 (e.g., waveguide) responsive to an applied force and converts this change into electrical signals which can be transmitted via the transceiver 320 to convey a level and a direction of the applied force. In other arrangements herein contemplated, the sensing assemblage 303 may require only a single transducer. In yet other arrangements, the sensing assemblage 303 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.
The accelerometer 302 can measure acceleration and static gravitational pull. Accelerometer 302 can be single-axis and multi-axis accelerometer structures that detect magnitude and direction of the acceleration as a vector quantity. Accelerometer 302 can also be used to sense orientation, vibration, impact and shock. The electronic circuitry 307 in conjunction with the accelerometer 302 and sensing assemblies 303 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.
The transceiver 320 comprises a transmitter 309 and an antenna 310 to permit wireless operation and telemetry functions. In various embodiments, the antenna 310 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 the transceiver 320 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.
The transceiver 320 receives power from the energy storage 330 and can operate at low power over various radio frequencies by way of efficient power management schemes, for example, incorporated within the electronic circuitry 307. As one example, the transceiver 320 can transmit data at selected frequencies in a chosen mode of emission by way of the antenna 310. The selected frequencies can include, but are not limited to, ISM bands recognized in International Telecommunication Union regions 1, 2 and 3. 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.).
The antenna 310 can be integrated with components of the sensing module to provide the radio frequency transmission. The substrate for the antenna 310 and electrical connections with the electronic circuitry 307 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.
The energy storage 330 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 the energy storage 330, 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. The energy storage 330 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.
The energy storage 330 minimizes additional sources of energy radiation required to power the sensing module during measurement operations. In one embodiment, as illustrated, the energy storage 330 can include a capacitive energy storage device 308 and an induction coil 311. External source of charging power can be coupled wirelessly to the capacitive energy storage device 308 through the electromagnetic induction coil or coils 311 by way of inductive charging. The charging operation can be controlled by power management systems designed into, or with, the electronic circuitry 307. As one example, during operation of electronic circuitry 307, power can be transferred from capacitive energy storage device 308 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, the energy storage 330 can further serve to communicate downlink data to the transceiver 320 during a recharging operation. For instance, downlink control data can be modulated onto the energy source signal and thereafter demodulated from the induction coil 311 by way of electronic control circuitry 307. This can serve as a more efficient way for receiving downlink data instead of configuring the transceiver 320 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.
The electronic circuitry 307 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, the electronic circuitry 307 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.
FIG. 4 is an exemplary assemblage 300 that illustrates propagation of ultrasound waves 310 within the waveguide 306 in the bi-directional mode of operation of this assemblage. In this mode, the selection of the roles of the two individual ultrasound resonators (302, 304) or transducers affixed to interfacing material 320 and 322, if required, are periodically reversed. In the bi-directional mode the transit time of ultrasound waves propagating in either direction within the waveguide 306 can be measured. This can enable adjustment for Doppler effects in applications where the sensing module 308 is operating while in motion 316. 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 this external motion 316. An advantage is provided in situations wherein the body, instrument, appliance, vehicle, equipment, or other physical system 314, 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 the portion 312 of the body, instrument, appliance, vehicle, equipment, or other physical system being measured to be in motion 316 during sensing of load, force, pressure, or displacement. Other adjustments to the measurement for physical changes to system 314 are contemplated and can be compensated for in a similar fashion. For example, temperature of system 314 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 of waveguide 306 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 to FIG. 1, although not explicitly illustrated, it should be noted that the load insert sensing device 100 and associated internal components move in accordance with motion of the femur 108 as shown. The bi-directional operating mode of the waveguide mitigates the Doppler effects resulting from the motion. As previously indicated, incorporating data from the accelerometer 121 with data from the other components of the sensing module 200 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. 5 is an exemplary cross-sectional view of a sensor element 400 to illustrate changes in the propagation of ultrasound waves 414 with changes in the length of a waveguide 406. 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, an external force 408 compresses waveguide 406 thereby changing the length of waveguide 406. Sensing circuitry (not shown) measures propagation characteristics of ultrasonic signals in the waveguide 406 to determine the change in the length of the waveguide 406. 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 the sensing module 200 compress the waveguide(s) thereby changing the length of the waveguide(s). The sensing module 200 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 force 408 compresses waveguide 406 and pushes the transducers 402 and 404 closer to one another by a distance 410. This changes the length of waveguide 406 by distance 412 of the waveguide propagation path between transducers 402 and 404. Depending on the operating mode, the sensing circuitry measures the change in length of the waveguide 406 by analyzing characteristics of the propagation of ultrasound waves within the waveguide.
One interpretation of FIG. 5 illustrates waves emitting from transducer 402 at one end of waveguide 406 and propagating to transducer 404 at the other end of the waveguide 406. The interpretation includes the effect of movement of waveguide 406 and thus the velocity of waves propagating within waveguide 406 (without changing shape or width of individual waves) and therefore the transit time between transducers 402 and 404 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 the waveguide 406. As will be described below, positive feedback closed-loop circuit operation in continuous wave (CW) mode adjusts the frequency of ultrasonic waves 414 in the waveguide 406 to maintain a same number or integer number of periods of ultrasonic waves in the waveguide 406. 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 by transducer 402 and received at transducer 404. The time of flight determines the length of the waveguide propagating path, and accordingly reveals the change in length of the waveguide 406. In another arrangement, differential time of flight measurements (or phase differences) can be used to determine the change in length of the waveguide 406. 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 the first wave of each pulse with an edge-detect receiver rather than a zero-crossing receiver circuitry as used in CW mode.
One interpretation of FIG. 4 illustrates waves emitting from a transducer at one end of waveguide and propagating to a transducer at the other end of the waveguide. The interpretation further includes the effect of movement of the waveguide. The movement interprets the velocity of waves propagating within the waveguide (without changing shape or width of individual waves) and therefore the transit time between the transducers at each end of the waveguide. Movement can have the opposite effect on waves propagating in the opposite direction. The movement is evaluated to estimate the velocity of the waveguide and remove this contribution by averaging the transit time of waves propagating in both directions in turns, but not simultaneously.
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. 6 is an exemplary block diagram 600 of a propagation tuned oscillator (PTO) 4 to maintain positive closed-loop feedback in accordance with an exemplary embodiment. The measurement system includes a sensing assemblage 1 and propagation tuned oscillator (PTO) 4 that detects energy waves 2 in one or more waveguides 3 of the sensing assemblage 1. In one embodiment, energy waves 2 are ultrasound waves. A pulse 11 is generated in response to the detection of energy waves 2 to initiate a propagation of a new energy wave in waveguide 3. 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 load sensing insert device 100 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 of ultrasound waves 2 within the waveguide 3 in a closed-loop configuration. The digital counter 20 determines the physical change in the length of the waveguide. Referring to FIG. 3, The one or more accelerometers 302 determines the changes along x, y and z dimensions. The electronic circuitry 307 in view of the accelerometer data from accelerometer 302 and the physical changes in length of the sensing assemblage 1 determines the applied loading (or forces).
The sensing assemblage 1 comprises transducer 5, transducer 6, and a waveguide 3 (or energy propagating structure). In a non-limiting example, sensing assemblage 1 is affixed to load bearing or contacting surfaces 8. External forces applied to the contacting surfaces 8 compress the waveguide 3 and change the length of the waveguide 3. Under compression, transducers 5 and 6 will also be moved closer together. The change in distance affects the transit time 7 of energy waves 2 transmitted and received between transducers 5 and 6. The propagation tuned oscillator 4 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 of PTO 4 in conjunction with the pulse generator 10, the mode control 12, and the phase detector 14.
Notably, changes in the waveguide 3 (energy propagating structure or structures) alter the propagation properties of the medium of propagation (e.g. transit time 7). 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 by transducer 5 to a first surface of waveguide 3. Transducer 5 generates energy waves 2 that are coupled into waveguide 3. In a non-limiting example, transducer 5 is a piezo-electric device capable of transmitting and receiving acoustic signals in the ultrasonic frequency range.
Transducer 6 is coupled to a second surface of waveguide 3 to receive the propagated pulsed signal and generates a corresponding electrical signal. The electrical signal output by transducer 6 is coupled to phase detector 14. In general, phase detector 14 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 detector 14 can be a zero-crossing receiver. In a second embodiment, phase detector 14 can be an edge-detect receiver. In the example where sensing assemblage 1 is compressed, the detection of the propagated energy waves 2 occurs earlier (due to the length/distance reduction of waveguide 3) than a signal prior to external forces being applied to contacting surfaces. Pulse generator 10 generates a new pulse in response to detection of the propagated energy waves 2 by phase detector 14. The new pulse is provided to transducer 5 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 maintains energy waves 2 propagating in waveguide 3.
The transit time 7 of a propagated energy wave is the time it takes an energy wave to propagate from the first surface of waveguide 3 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 through waveguide 3. 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. The digital counter 20 in conjunction with electronic components counts the number of propagated energy waves to determine a corresponding change in the length of the waveguide 3. 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 diagram 600 further includes counting and timing circuitry. More specifically, the timing, counting, and clock circuitry comprises a digital timer 20, a digital timer 22, a digital clock 24, and a data register 26. The digital clock 24 provides a clock signal to digital counter 20 and digital timer 22 during a measurement sequence. The digital counter 20 is coupled to the propagation tuned oscillator 4. Digital timer 22 is coupled to data register 26. Digital timer 20, digital timer, 22, digital clock 24 and data register 26 capture transit time 7 of energy waves 2 emitted by ultrasound resonator or transducer 5, propagated through waveguide 3, and detected by or ultrasound resonator or transducer 5 or 6 depending on the mode of the measurement of the physical parameters of interest applied to surfaces 8. 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 tuned oscillator 4 in conjunction with one or more sensing assemblages 1 are used to take measurements on a muscular-skeletal system. In a non-limiting example, sensing assemblage 1 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 assemblage 1 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, assemblage 1 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, two assemblages 1 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 through waveguide 3 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 affect sensing assemblage 1 stay consistent or constant. Holding the number of energy waves propagating through waveguide 3 to an integer number is a constraint that forces a change in the time between pulses when the length of waveguide 3 changes. The resulting change in time period of each energy wave corresponds to a change in aggregate energy wave time period that is captured using digital counter 20 as a measurement of changes in external forces or conditions applied to contacting surfaces 8.
A further method of operation according to one embodiment is described hereinbelow for energy waves 2 propagating from transducer 5 and received by transducer 6. In at least one exemplary embodiment, energy waves 2 is an ultrasonic energy wave. Transducers 5 and 6 are piezo-electric resonator transducers. Although not described, wave propagation can occur in the opposite direction being initiated by transducer 6 and received by transducer 5. Furthermore, detecting ultrasound resonator transducer 6 can be a separate ultrasound resonator as shown or transducer 5 can be used solely depending on the selected mode of propagation (e.g. reflective sensing). Changes in external forces or conditions applied to contacting surfaces 8 affect the propagation characteristics of waveguide 3 and alter transit time 7. As mentioned previously, propagation tuned oscillator 4 holds constant an integer number of energy waves 2 propagating through waveguide 3 (e.g. an integer number of pulsed energy wave time periods) thereby controlling the repetition rate. As noted above, once PTO 4 stabilizes, the digital counter 20 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 of pulsed energy waves 2 emitted by transducer 5 can be controlled by pulse generator 10. The operation remains similar where the parameter to be measured corresponds to the measurement of the transit time 7 of pulsed energy waves 2 within waveguide 3. 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 of pulse generator 10, interface material or materials, where required, and ultrasound resonator or transducer 5. The frequency of the energy waves within individual pulses is determined by the response of the emitting ultrasound resonator 4 to excitation by an electrical pulse 11. The mode of the propagation of the pulsed energy waves 2 through waveguide 3 is controlled by mode control circuitry 12 (e.g., reflectance or uni-directional). The detecting ultrasound resonator or transducer may either be a separate ultrasound resonator or transducer 6 or the emitting resonator or transducer 5 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 tuned oscillator 4 and sensing assemblage 1 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 tuned oscillator 4 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. 7 illustrates one embodiment of accelerometer integration with the load sensing platform in accordance with an exemplary embodiment. The load sensing platform 700 is miniaturized to be placed on or within a body, instrument, appliance, vehicle, equipment, or other physical system 2 without disturbing the operation of the body, instrument, appliance, vehicle, equipment, or physical system. The load sensing platform 700 in various embodiments is mechanically and electrically coupled to the accelerometer 302 and the electronic circuitry 307 (see FIG. 3). This facilitates contacting the sources of load, force, pressure, displacement, density, viscosity, or localized temperature to be measured.
Two or more springs or other means of elastic support, support the load bearing or contacting surfaces 8. One or more assemblages 1 are used for measuring load each comprised of one or more ultrasound resonators or transducers. In the example, the assemblage 1 comprises transducers 5 and 6. Transducers 5 and 6 are respectively coupled to ultrasound waveguide 3 at a first location and a second location. Assemblage 1 is coupled, attached, or affixed to the load bearing or contacting surfaces 8. This arrangement facilitates translating changes in the parameter or parameters of interest into changes in the length or compression of the waveguide or waveguides 3 and converting these changes in the length or compression of the waveguide 3 or waveguides into electrical signals thus enabling load sensing platform 700 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 702. To achieve the required level of miniaturization, the length of the ultrasound waveguides 4 is on the order of a millimeter and resolution of compression or displacement is on the order of sub-microns.
FIG. 8 is an exemplary method 800 to evaluate prosthetic integrity by incorporating acceleration data with load sensing measurements in real-time. The method 800 can be practiced with more or less than the number of steps shown, and is not limited to the order shown. Reference will be made to the components of FIG. 1 and FIG. 3, although it should be noted that other components may perform the function. Briefly, the method 800 can be used to evaluate the kinematics of motion associated with a prosthetic implant.
At step 801, the load sensing platform 121 determines load data on the load sensing insert device 100. In particular, referring back to FIG. 3, the load bearing contact surfaces 306 transfer the loading to the sensing assemblages 303, which in the current example, compress in response to the loading. The load bearing surfaces 306 also move and tilt, which changes directional forces on the sensing assemblies 303. The force applied to load bearing surfaces 306 are conveyed in the compression characteristics of the elastic or compressible propagation structure 305.
At step 802, the sensing assemblies 123 determine changes in length of the compressible propagation structures. In the current example, the propagation structure 305 is an ultrasonic waveguide that changes in length in proportion to the compression. Electronic circuitry 307 determines this change in length by evaluating propagation time characteristics of ultrasonic signals within the waveguide to measure the applied load.
Briefly referring to FIG. 9, a simplified cross-sectional view 900 of the ultrasound waveguide illustrates how changes in physical length of the waveguide responsive to applied force affect changes in the propagation of ultrasound waves within the waveguide. As shown, the transit time 902 of the ultrasonic waves 2 in the waveguide 3 decreases to a transit time 904 when an external force pushes transducer 6 closer to transducer 5. In the example, the number of integer periods of the ultrasonic waves 1 remains constant. The integer number of periods is maintained due to closed-loop feedback conditions established by way of a propagation tuned oscillator (PTO) or phased lock loop (PLL). In turn, the measurement of changes 906 in physical length of the ultrasound waveguide 3 are determined by these changes in the transit time (904 to 902) of ultrasound waves 2 within the waveguide 3.
Referring back to FIG. 8, at step 803, the accelerometer 122 acquires motion data in a vector quantity indicating a magnitude and direction of the acceleration. The second accelerometer 127 can also be queried to provide its own acceleration data for establishing a reference point.
This enables sensing module to collect data on the physical parameter or parameters of interest relative to 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.
In one arrangement, as previously noted, the second accelerometer 127 can be queried for reference position information. A subset of the load sensing platform, inclusive of the ASIC (or some subset of it), and the telemetry circuitry, but not the load sensing components can be used. The second accelerometer 127 can be installed in a femoral trial insert to broadcast femoral position at the same time the tibial trial insert is broadcasting tibial position, so as to determine the exact angular relationship between the femur and tibia. The first broadcast (e.g. tibial data) can be on a different channel than the second broadcast (e.g., femur data).
At step 804, the electronic circuitry 307 can estimate the forces based on the load data, length changes, and the motion data to sense orientation, vibration, and impact. Logical vector additions and negations by way of integrated circuits are performed to determine vector sums of the corresponding quantities to convey direction and magnitude. The vector sums are then transmitted to the receiving station 110 for processing and presentation. In other arrangements, the individual measurements are wirelessly transmitted to the receiving station 110 and then processed to determine the load calculations.
This facilitates capturing data, measuring the parameter or 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
At step 805, the receiving station 110 assesses balance and stability of the prosthetic component in view of the load forces (e.g., vector sums). As one example, the receiving station visually displays the forces with the motion, for example, as an animation. The surgeon can then in view of the animation evaluate the kinematics of motion and a corresponding proper fit of the prosthetic components, or inserts. In conjunction with the first accelerometer 122, the electronic circuitry can assess the stress and strain on the bone due to the prosthetic component for various motions.
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

1. A sensing module configured to obtain force measurement comprising:
a load bearing structure configured to be coupled to a muscular-skeletal system;
a sensing assembly coupled to the load bearing structure where the sensing assembly is configured to apply a spring force to the load bearing structure, where the sensing module is configured to be inserted into an implantable orthopedic prosthetic, where the sensing assembly measures force data, where the force data is directly related to the force applied to the sensing assembly by the load bearing structure and where a processor can use the force data to determine the location of the force on the load bearing structure; and
at least one accelerometer, where the at least one accelerometer measures motion data, where a force measurement includes the force data and the motion data.

2. The sensing module of claim 1 where the spring force is provided by way of spring retainer, disc spring, and spring post.

3. The sensing module of claim 2 where the sensing assembly comprises a printed circuit board coupled to a plurality of sensing assemblages.

4. The sensing module of claim 3 where the load bearing structure comprises a steel plate.

5. The sensing module of claim 1 where the accelerometer acquires motion data in a vector quantity.

6. The sensing module of claim 1 where the accelerometer measures a direction and magnitude of acceleration.

7. The sensing module of claim 1 further including a second accelerometer coupled to the muscular-skeletal system to measure acceleration and establish a reference point.

8. The sensing module of claim 1 where the sensing assembly measures a transit time, frequency, or phase of an acoustic signal through a medium and where a change in force applied by the muscular-skeletal results in a change in length of the medium.

9. The sensing module according to claim 1 where prior to a load on the load bearing structure the sensing module is at an original position, where the spring force is used to return the sensing module to the original position when a load is applied to the load bearing structure.

10. A sensing module, comprising:
a load sensing platform configured to receive loading from a portion of an orthopedic system, where the load sensing platform comprises a load bearing structure coupled to a lower printed circuit board (PCB) by way of spring retainer, disc spring, and spring post, where the load sensing platform applies a spring force between a sensing assembly and the portion of the orthopedic system, where the sensing assembly is configured to measure a force and the location of the force on the load bearing structure; and
an accelerometer to produce motion data comprising acceleration data, where the sensing module is configured to be in an implantable orthopedic prosthetic.

11. The sensing module according to claim 10 where prior to a load on the load bearing structure the sensing module is at an original position, where the spring force is used to return the sensing module to the original position when a load is applied to the load bearing structure.

12. The module of claim 10 where the sensing assembly comprises a compressible propagation structure, where the length of the propagation structure corresponds to an applied force thereto, and where the length of the propagation structure is measured.

13. The module of claim 10, further including a second accelerometer, where the first accelerometer is on a first bone to provide first acceleration data, and the second accelerometer is on a second bone to provide second acceleration data, together used as a vector sum to determine effective motion.

14. The module of claim 10, where the sensing assembly comprises an elastic or compressible propagation structure between a first transducer and a second transducer.

15. The module of claim 10, where the load bearing structure comprises a steel plate.

16. The module of claim 10, where the accelerometer includes single-axis and multi-axis structures to detect magnitude and direction of the acceleration.

17. The module of claim 10, where the sensing assembly is positioned, engaged, attached, or affixed to load bearing contact surfaces having mechanical supports to provide proper balancing of load bearing contact surfaces.

18. The module of claim 10, further comprising a transceiver to transmit a level and a direction of the applied force to a receiving station.

19. The module of claim 10, where the processor is a state machine, pre-programmed logic, electronic circuitry, or a micro-controller.