US20100331680A1

US20100331680A1 - High precision processing of measurement data for the muscular-skeletal system

Info

Publication number: US20100331680A1
Application number: US12/825,898
Authority: US
Inventors: Marc Stein
Original assignee: Orthosensor Inc
Current assignee: Orthosensor Inc
Priority date: 2009-06-30
Filing date: 2010-06-29
Publication date: 2010-12-30
Also published as: US8424384B2; US20100331894A1; US20100326194A1; US8690929B2; US20100331735A1; US20100326210A1; US20100331718A1; US8337428B2; US9492119B2; US20100331683A1; US20120283600A1; US8516907B2; US20100331663A1; US8689647B2; US20100331737A1; US20100328077A1; US20100331633A1; US20100331682A1; US8324975B2; US20140148676A1

Abstract

A measurement system measures a parameter of a muscular-skeletal system. The measurement system is placed in proximity to the muscular-skeletal system such that the parameter to be measured is applied to a sensing assemblage (3). The measurement system further comprises a digital counter (20), a digital timer (22), a digital clock 24, and a data register (26). The digital counter (20) is preset to a predetermined number of measurement cycles. The digital timer (22) measures an elapsed time of a measurement sequence comprising the predetermined number of measurement cycles. The digital counter (20) is decremented each measurement cycle until a zero count is reached thereby stopping the measurement sequence. The digital timer (22) measures an elapsed time of the measurement sequence. The parameter value can be related to the elapsed time. The precision of a parameter measurement can be modified by changing the predetermined number of measurement cycles.

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 electronic devices and signal processing techniques for high precision sensing at optimal operating points.

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 as information from simulations, mechanical prototypes, and long-term patient joint replacement data 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 exemplary block diagram of a propagation tuned oscillator (PTO) to maintain positive closed-loop feedback in accordance with an exemplary embodiment;

FIG. 2 is a simplified cross-sectional view of a sensing module in accordance with an exemplary embodiment;

FIG. 3 is an exemplary assemblage for illustrating reflectance and unidirectional modes of operation in accordance with an exemplary embodiment;

FIG. 4 is an exemplary assemblage that illustrates propagation of ultrasound waves within a waveguide in the bi-directional mode of operation of this assemblage;

FIG. 5 is an exemplary cross-sectional view of a sensor element to illustrate changes in the propagation of ultrasound waves with changes in the length of a waveguide;

FIG. 6 is a simplified flow chart of method steps for high precision processing and measurement data in accordance with an exemplary embodiment; and

FIG. 7 is an illustration of a sensor placed in contact between a femur and a tibia for measuring a parameter in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

Embodiments of the invention are broadly directed to measurement of physical parameters, and more particularly, to a method for analyzing measurement data that achieves accurate, repeatable, high precision and high-resolution measurements. The system disclosed herein relates to real-time measurement of load, force, pressure, displacement, density, viscosity, or localized temperature by a sensor. In one embodiment, the method includes evaluating changes in a transit time of energy pulses or propagating waves within elastic energy propagating structures as a function of an operating point and controlling the resolution of measurements of the changes in this transit time to achieve optimal operating point conditions.
In a first embodiment, a wireless sensing module comprises one or more sensing assemblies, one or more load surfaces, an accelerometer, electronic circuitry, a transceiver, and an energy supply. The wireless sensing module measures a parameter applied to the sensing module. In one embodiment, the wireless sensing module measures force, such as an applied load, and transmit the measurement data to a secondary system for further processing and display. For example, the wireless sensing module can be used for intra-operative sensing of a joint implant during surgery to the muscular-skeletal system or as a long term implanted sensor in an artificial joint or implanted in the natural muscular-skeletal system. In the example, the electronic circuitry in conjunction with the sensing assemblies accurately measures physical displacements of the load surfaces on the order of a few microns along various physical dimensions. It does this by evaluating propagation characteristics of ultrasonic energy waves in one or more waveguides of the sensing assemblies that physically change in response to the applied forces. In particular, it measures changes in propagation time due to changes in the length of the waveguides; physical length changes which occur in direct response to the applied force.
A method disclosed herein includes setting the precision level and resolution of captured data to optimize a trade-off between measurement resolution versus real-time operation. In one embodiment, the measurement resolution is adjusted corresponding to the ultrasonic frequency of the sensor. This can further include modifying the bandwidth of the transceiver providing data communications that deliver the data in real-time. For instance, by way of example, the wireless sensing module over-samples data measurements through a series of repeated measurements based on the ultrasonic frequency, accumulates the over-sampled data specific to achieving a numerical dynamic range, estimates a single data measurement from the over-sampled data, and determines if the precision of the single data measurement for a given bandwidth is achieved at an optimal operating point, and furthermore without compromising resolution of the measurements.
More specifically, in this embodiment, the electronic circuitry is designed, or programmed, to evaluate tradeoffs between i) measurement resolution versus length of the waveguide propagation medium, ii) frequency of the ultrasonic energy waves or repetition rate or energy pulses, and iii) bandwidth of the sensing and data capture operations. In view of the tradeoffs, the system controls the operation of the wireless sensing module to achieve a specific resolution of measurement data and controls processes which include adjusting the ultrasonic frequency, sampling frequency, data rate and bandwidth in real-time. For instance, by way of example, the wireless sensing module can increase the sampling rate, increase the ultrasonic frequency, and increase the data rate as an applied load further displaces a load surface along a graded displacement curve (e.g., predetermined threshold levels).
In one embodiment, the method can include accumulating multiple cycles of excitation and transit time of ultrasonic energy waves. This improves the level of resolution of measurement of changes in length or other aspect of the elastic energy propagating structure instead of averaging transit time of multiple individual excitation and transit cycles. In particular, the electronic circuitry controls a digital counter to run through multiple measurement cycles, each cycle having excitation and transit phases such that there is not lag between successive measurement cycles, and capture the total elapsed time. The digital counter can be set to achieve a specific numerical dynamic range, for instance, as a user adjustable parameter.
This method for analyzing measurement data can be applied generally to real-time measurement of the muscular-skeletal system. Disclosed hereinbelow, an analysis is performed on data generated by elastic energy propagating structures or media of a wide range of lengths as required by the application, including compact elastic energy propagating structures or media on the order of a millimeter to elastic energy propagating structures or media that are orders of magnitude longer. Submicron resolution is achieved over this broad range of lengths of elastic energy propagating structures or media, when operated in conjunction with data capture and processing circuitry implementing this method of capturing and analyzing measurement data.
In one embodiment, a propagation tuned oscillator (PTO) is provided to maintain positive closed-loop feedback of energy waves in one or more energy propagating structures of a sensing system. The energy waves propagate through a medium in an energy propagating structure. A positive feedback closed-loop circuit causes the oscillator to tune the resonant frequency of the energy waves in accordance with physical changes in the one or more energy propagating structures; hence the term, propagation tuned oscillator. Detection of a propagated energy wave through at least a portion of the medium is detected by the PTO. The detection of the propagated energy wave initiates an energy wave emission into the medium thereby sustaining a process by which energy waves continually propagate through the medium.
In general, the PTO is used to measure a parameter. The parameter is applied to the medium of the energy propagating structure. The parameter causes a physical change in the medium. In one embodiment, the physical change is a dimensional change such as a change in length resulting from externally applied forces or pressure. The physical changes in the energy propagating structures change in direct proportion to the external applied forces and can be precisely evaluated to measure the applied forces.
FIG. 1 is an exemplary block diagram 100 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.
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 100 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.
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. 2 is a simplified cross-sectional view of a sensing module 101 in accordance with an exemplary embodiment. The sensing module (or assemblage) is an electro-mechanical assembly comprising electrical components and mechanical components that when configured and operated in accordance with a sensing mode performs as a positive feedback closed-loop measurement system. The measurement system can precisely measure applied forces, such as loading, on the electro-mechanical assembly. The sensing mode can be a continuous mode, a pulse mode, or a pulse echo-mode.
In one embodiment, the electrical components can include ultrasound resonators or transducers, ultrasound waveguides, and signal processing electronics, but are not limited to these. The mechanical components can include biasing springs 32, spring retainers and posts, and load platforms 6, but are not limited to these. The electrical components and mechanical components can be inter-assembled (or integrated) onto a printed circuit board 36 to operate as a coherent ultrasonic measurement system within sensing module 101 and according to the sensing mode. As will be explained ahead in more detail, the signal processing electronics incorporate a propagation tuned oscillator (PTO) or a phase locked loop (PLL) to control the operating frequency of the ultrasound resonators or transducers for providing high precision sensing. Furthermore, the signal processing electronics incorporate detect circuitry that consistently detects an energy wave after it has propagated through a medium. The detection initiates the generation of a new energy wave by an ultrasound resonator or transducer that is coupled to the medium for propagation therethrough. A change in transit time of an energy wave through the medium is measured and correlates to a change in material property of the medium due to one or more parameters applied thereto.
Sensing module 101 comprises one or more assemblages 1 each comprised one or more ultrasound resonators. As illustrated, waveguide 3 is coupled between transducers 5 and 6 and affixed to load bearing or contacting surfaces 8. In one exemplary embodiment, an ultrasound signal is coupled for propagation through waveguide 3. The sensing module 101 is placed, attached to, or affixed to, or within a body, instrument, or other physical system 18 having a member or members 16 in contact with the load bearing or contacting surfaces 8 of the sensing module 101. This arrangement facilitates translating the parameters of interest into changes in the length or compression or extension of the waveguide or waveguides 3 within the sensing module 101 and converting these changes in length into electrical signals. This facilitates capturing data, measuring parameters of interest and digitizing that data, and then subsequently communicating that data through antenna 34 to external equipment with minimal disturbance to the operation of the body, instrument, appliance, vehicle, equipment, or physical system 18 for a wide range of applications.
The sensing module 101 supports three modes of operation of energy wave propagation and measurement: reflectance, unidirectional, and bi-directional. These modes can be used as appropriate for each individual application. In unidirectional and bi-directional modes, a chosen ultrasound resonator or transducer is controlled to emit pulses of ultrasound waves into the ultrasound waveguide and one or more other ultrasound resonators or transducers are controlled to detect the propagation of the pulses of ultrasound waves at a specified location or locations within the ultrasound waveguide. In reflectance or pulse-echo mode, a single ultrasound or transducer emits pulses of ultrasound waves into waveguide 3 and subsequently detects pulses of echo waves after reflection from a selected feature or termination of the waveguide. In pulse-echo mode, echoes of the pulses can be detected by controlling the actions of the emitting ultrasound resonator or transducer to alternate between emitting and detecting modes of operation. Pulse and pulse-echo modes of operation may require operation with more than one pulsed energy wave propagating within the waveguide at equilibrium.
Many parameters of interest within physical systems or bodies can be measured by evaluating changes in the transit time of energy pulses. The frequency, as defined by the reciprocal of the average period of a continuous or discontinuous signal, and type of the energy pulse is determined by factors such as distance of measurement, medium in which the signal travels, accuracy required by the measurement, precision required by the measurement, form factor of that will function with the system, power constraints, and cost. 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 the non-limiting example, pulses of ultrasound energy provide accurate markers for measuring transit time of the pulses within waveguide 3. In general, an ultrasonic signal is an acoustic signal having a frequency above the human hearing range (e.g. >20 KHz) including frequencies well into the megahertz range. In one embodiment, a change in transit time of an ultrasonic energy pulse corresponds to a difference in the physical dimension of the waveguide from a previous state. For example, a force or pressure applied across the knee joint compresses waveguide 3 to a new length and changes the transit time of the energy pulse When integrated as a sensing module and inserted or coupled to a physical system or body, these changes are directly correlated to the physical changes on the system or body and can be readily measured as a pressure or a force.
FIG. 3 is an exemplary assemblage 200 for illustrating reflectance and unidirectional modes of operation in accordance with an exemplary embodiment. It comprises one or more transducers 202, 204, and 206, one or more waveguides 214, and one or more optional reflecting surfaces 216. The assemblage 200 illustrates propagation of ultrasound waves 218 within the waveguide 214 in the reflectance and unidirectional modes of operation. Either ultrasound resonator or transducer 202 and 204 in combination with interfacing material or materials 208 and 210, if required, can be selected to emit ultrasound waves 218 into the waveguide 214.
In unidirectional mode, either of the ultrasound resonators or transducers for example 202 can be enabled to emit ultrasound waves 218 into the waveguide 214. The non-emitting ultrasound resonator or transducer 204 is enabled to detect the ultrasound waves 218 emitted by the ultrasound resonator or transducer 202.
In reflectance mode, the ultrasound waves 218 are detected by the emitting ultrasound resonator or transducer 202 after reflecting from a surface, interface, or body at the opposite end of the waveguide 214. In this mode, either of the ultrasound resonators or transducers 202 or 204 can be selected to emit and detect ultrasound waves. Additional reflection features 216 can be added within the waveguide structure to reflect ultrasound waves. This can support operation in a combination of unidirectional and reflectance modes. In this mode of operation, one of the ultrasound resonators, for example resonator 202 is controlled to emit ultrasound waves 218 into the waveguide 214. Another ultrasound resonator or transducer 206 is controlled to detect the ultrasound waves 218 emitted by the emitting ultrasound resonator 202 (or transducer) subsequent to their reflection by reflecting feature 216.
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.
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 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.
FIG. 6 is a simplified flow chart 600 of method steps for high precision processing and measurement data in accordance with an exemplary embodiment. The method 600 can be practiced with more or less than the steps shown and is not limited to the order of steps shown. The method steps can be practiced with the aforementioned components or any other components suitable for such processing, for example, electrical circuitry to control the emission of energy pulses or waves and to capture the repetition rate of the energy pulses or frequency of the energy waves propagating through the elastic energy propagating structure or medium.
In a step 602, the process initiates a measurement operation. In a step 604, a known state is established by resetting digital timer 22 and data register 26. In a step 606, digital counter 20 is preset to the number of measurement cycles over which measurements will be taken and collected. In a step 608, the measurement cycle is initiated and a clock output of digital clock 24 is enabled. A clock signal from digital clock 24 is provided to both digital counter 20 and digital timer 22. An elapsed time is counted by digital timer 20 based on the frequency of the clock signal output by digital clock 24. In a step 610, digital timer 22 begins tracking the elapsed time at the same time that digital counter 20 starts decrementing. In one embodiment, digital counter 20 is decremented as each energy wave propagates through waveguide 3 and detected by transducer 6. Digital timer 20 counts down until the preset number of measurement cycles has been completed. In a step 612, energy wave propagation is sustained by propagation tuned oscillator as digital counter 20 is decremented by the detection of a propagated energy wave. In a step 614, energy wave detection, emission, and propagation continue while the count in digital counter 20 is greater than zero. In a step 616, the clock input of digital timer 22 is disabled upon reaching a zero count on digital counter 20 thus preventing digital counter 20 and digital timer 22 from being clocked. In one embodiment, the preset number of measurement cycles provided to digital counter 20 is divided by the elapsed time measured by digital timer 22 to calculate a frequency of propagated energy waves. Conversely, the number can be calculated as a transit time by dividing the elapsed time from digital timer 22 by the preset number of measurement cycles. Finally, in a step 618, the resulting value is transferred to register 26. The number in data register 26 can be wirelessly transmitted to a display and database. The data from data register 26 can be correlated to a parameter being measured. The parameter such as a force or load is applied to the propagation medium (e.g. waveguide 3) such that parameter changes also change the frequency or transit time calculation of the measurement. A relationship between the material characteristics of the propagation medium and the parameter is used with the measurement value (e.g. frequency, transit time, phase) to calculate a parameter value.
The method 600 practiced by the example assemblage of FIG. 1, and by way of the digital counter 20, digital timer 22, digital clock 24 and associated electronic circuitry analyzes the digitized measurement data according to operating point conditions. In particular, these components accumulate multiple digitized data values to improve the level of resolution of measurement of changes in length or other aspect of an elastic energy propagating structure or medium that can alter the transit time of energy pulses or waves propagating within the elastic energy propagating structure or medium. The digitized data is summed by controlling the digital counter 20 to run through multiple measurement cycles, each cycle having excitation and transit phases such that there is not lag between successive measurement cycles, and capturing the total elapsed time. The counter is sized to count the total elapsed time of as many measurement cycles as required to achieve the required resolution without overflowing its accumulation capacity and without compromising the resolution of the least significant bit of the counter. The digitized measurement of the total elapsed transit time is subsequently divided by the number of measurement cycles to estimate the time of the individual measurement cycles and thus the transit time of individual cycles of excitation, propagation through the elastic energy propagating structure or medium, and detection of energy pulses or waves. Accurate estimates of changes in the transit time of the energy pulses or waves through the elastic energy propagating structure or medium are captured as elapsed times for excitation and detection of the energy pulses or waves are fixed.
Summing individual measurements before dividing to estimate the average measurement value data values produces superior results to averaging the same number of samples. The resolution of count data collected from a digital counter is limited by the resolution of the least-significant-bit in the counter. Capturing a series of counts and averaging them does not produce greater precision than this least-significant-bit, that is the precision of a single count. Averaging does reduce the randomness of the final estimate if there is random variation between individual measurements. Summing the counts of a large number of measurement cycles to obtain a cumulative count then calculating the average over the entire measurement period improves the precision of the measurement by interpolating the component of the measurement that is less than the least significant bit of the counter. The precision gained by this procedure is on the order of the resolution of the least-significant-bit of the counter divided by the number of measurement cycles summed.
The size of the digital counter and the number of measurement cycles accumulated may be greater than the required level of resolution. This not only assures performance that achieves the level of resolution required, but also averages random component within individual counts producing highly repeatable measurements that reliably meet the required level of resolution.
The number of measurement cycles is greater than the required level of resolution. This not only assures performance that achieves the level of resolution required, but also averages any random component within individual counts producing highly repeatable measurements that reliably meet the required level of resolution.
FIG. 7 is an illustration of a sensor 700 placed in contact between a femur 702 and a tibia 708 for measuring a parameter in accordance with an exemplary embodiment. In general, the sensor 700 is placed in contact with or in proximity to the muscular-skeletal system to measure a parameter. In a non-limiting example, sensor 700 can be operated in continuous wave mode, pulse mode, and pulse echo-mode to measure a parameter of a joint or an artificial joint. Embodiments of sensor 700 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. Sensor 700 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 sensor 700 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.
Sensor 700 can be size constrained by form factor requirements of fitting within a region the muscular-skeletal system or a component such as a tool, equipment, or artificial joint. In a non-limiting example, sensor 700 is used to measure load and balance of an installed artificial knee joint. A knee prosthesis comprises a femoral prosthetic component 704, an insert, and a tibial prosthetic component 706. A distal end of femur 702 is prepared and receives femoral prosthetic component 704. Femoral prosthetic component 704 typically has two condyle surfaces that mimic a natural femur. As shown, femoral prosthetic component 704 has single condyle surface being coupled to femur 702. Femoral prosthetic component 704 is typically made of a metal or metal alloy.
A proximal end of femur 708 is prepared to receive tibial prosthetic component 706. Tibial prosthetic component 706 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 706 also retains the insert in a fixed position with respect to femur 708. The insert is fitted between femoral prosthetic component 704 and tibial prosthetic component 706. The insert has at least one bearing surface that is in contact with at least condyle surface of femoral prosthetic component 704. 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.
In a knee joint replacement process, the surgeon affixes femoral prosthetic component 704 to the femur 702 and tibial prosthetic component 706 to femur 708. The tibial prosthetic component 706 can include a tray or plate affixed to the planarized proximal end of the femur 708. Sensor 700 is placed between a condyle surface of femoral prosthetic component 704 and a major surface of tibial prosthetic component 706. The condyle surface contacts a major surface of sensor 700. The major surface of sensor 700 approximates a surface of the insert. Tibial prosthetic component 706 can include a cavity or tray on the major surface that receives and retains sensor 700 during a measurement process. Tibial prosthetic component 706 and sensor 700 has a combined thickness that represents a combined thickness of tibial prosthetic component 706 and a final (or chronic) insert of the knee joint.
In one embodiment, two sensors 700 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 706. One or two sensors 700 may be inserted between femoral prosthetic component 704 and tibial prosthetic component 706. Each sensor is independent and each measures a respective condyle of femur 702. 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 sensor 700 aid the surgeon in modifying the absolute loading on each condyle and the balance between condyles. Although shown for a knee implant, sensor 700 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, sensor 700 can also be adapted to orthopedic tools to provide measurements.
The prosthesis incorporating sensor 700 emulates the function of a natural knee joint. Sensor 700 can measure loads or other parameters at various points throughout the range of motion. Data from sensor 700 is transmitted to a receiving station 710 via wired or wireless communications. In a first embodiment, sensor 700 is a disposable system. Sensor 700 can be disposed of after using sensor 700 to optimally fit the joint implant. Sensor 700 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 sensor 700 for reuse. In a third embodiment, sensor 700 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, sensor 700 can be a permanent component of the replacement joint. Sensor 700 can be used to provide both short term and long term post-operative data on the implanted joint. In a fifth embodiment, sensor 700 can be coupled to the muscular-skeletal system. In all of the embodiments, receiving station 710 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 710 can record and provide accounting information of sensor 700 to an appropriate authority.
In an intra-operative example, sensor 700 can measure forces (Fx, Fy, Fz) with corresponding locations and torques (e.g. Tx, Ty, and Tz) on the femoral prosthetic component 704 and the tibial prosthetic component 706. The measured force and torque data is transmitted to receiving station 710 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, sensor 700 can be used for other joint surgeries; it is not limited to knee replacement implant or implants. Moreover, sensor 700 is not limited to trial measurements. Sensor 700 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 sensor 700 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, sensor 700 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. Sensor 700 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.
The present invention is applicable to a wide range of medical and nonmedical applications including, but not limited to, frequency compensation; control of, or alarms for, physical systems; or monitoring or measuring physical parameters of interest. The level of accuracy and repeatability attainable in a highly compact sensing module or device may be applicable to many medical applications monitoring or measuring physiological parameters throughout the human body including, not limited to, bone density, movement, viscosity, and pressure of various fluids, localized temperature, etc. with applications in the vascular, lymph, respiratory, digestive system, muscles, bones, and joints, other soft tissue areas, and interstitial fluids.
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 high precision method to measure a parameter corresponding to the muscular-skeletal system comprising the steps of:

presetting a measurement sequence for a predetermined number of measurement cycles;

generating a sum corresponding to the measurement sequence; and

measuring an elapsed time of the measurement sequence.

2. The method of claim 1 further including a step of increasing the predetermined number of measurement cycles to raise measurement precision.

3. The method of claim 1 further including a step of dividing the sum corresponding to the measurement sequence by the elapsed time.

4. The method of claim 3 further including the steps of:

applying the parameter to a medium during the measurement sequence;

emitting an energy wave into the medium;

detecting a propagated energy wave;

counting each detected propagated energy wave; and

stopping the measurement sequence when a count of detected propagated energy waves equals the predetermined number of measurement cycles.

5. The method of claim 4 further including a step of emitting an energy wave into the medium upon detection of each propagated energy wave to sustain energy wave propagation during the measurement sequence.

6. The method of claim 5 further including a step of maintaining an integer number of energy waves in the medium during the measurement sequence.

7. The method of claim 5 further including a step of relating a transit time, frequency, or phase measured during the measurement sequence to generate a parameter measurement.

8. The method of claim 1 further including the steps of:

setting a counter to the predetermined number of measurement cycles;

decrementing the counter upon detection of each propagated energy wave; and

stopping the measurement sequence when the counter decrements to zero.

9. The method of claim 8 further including the steps of:

dividing the predetermined number of measurement cycles by the elapsed time; and

storing a result in a data register.

10. The method of claim 9 further including the steps of:

placing a sensing module in proximity to the muscular-skeletal system such that the parameter to be measured is applied directly or indirectly to the sensing module; and

controlling an operation of the sensing module wirelessly to achieve a specific resolution of measurement data; control processes that include adjusting an ultrasonic frequency, a sampling frequency, a waveguide length, a data rate, and bandwidth in real-time.

11. A method of measuring a parameter of the muscular-skeletal system comprising the steps of:

placing a sensing assemblage in proximity to the muscular-skeletal system;

setting a precision level and resolution of captured data to optimize a trade-off between measurement resolution versus ultrasonic frequency prior to a measurement sequence; and

adjusting a bandwidth of a transceiver providing data communications to deliver the captured data in real-time.

12. The method of claim 11, further including a step of optimizing the tradeoff by evaluating measurement resolution versus a length of a waveguide propagation medium;

13. The method of claim 11 further including a step of optimizing the tradeoff by adjusting the frequency of the ultrasonic energy waves or repetition rate or energy pulses;

14. The method of claim 11 further including a step of optimizing the tradeoff by adjusting a bandwidth of sensing and data capture operations.

15. The method of claim 11, comprising accumulating multiple cycles of excitation and transit time of ultrasonic energy waves.

16. The method of claim 11, comprising controlling a digital counter to run through multiple measurement cycles, each cycle having excitation and transit phases such that there is not lag between successive measurement cycles, and capturing a total elapsed time.

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

a sensor placed in proximity to the muscular-skeletal system;

a digital counter coupled to a sensor where a signal corresponding to a measurement cycle of the sensor clocks the digital counter;

a digital timer to measure an elapsed time of a measurement sequence where the measurement sequence comprises a predetermined number of measurement cycles;

a data register coupled to the digital timer to store a number calculated from the predetermined number of measurement cycles and the elapsed time of the measurement sequence.

18. The measurement system of claim 17 where the precision of a parameter measurement increases by increasing the predetermined number of measurement cycles.

19. The measurement system of claim 18 further including a clock operatively coupled to the digital counter and the digital timer where a parameter value relates to a time period of a measurement cycle and where the digital timer elapsed time is a sum of individual parameter measurements.

20. The measurement system of claim 19 where the measurement system comprises one or more sensing assemblies, one or more load surfaces, an accelerometer, electronic circuitry, a transceiver, and an energy supply, where the measurement system measures forces, such as an applied load, and transmits the measurement data to a secondary system for further processing and display.