U.S. patent application number 12/825898 was filed with the patent office on 2010-12-30 for high precision processing of measurement data for the muscular-skeletal system.
This patent application is currently assigned to OrthoSensor. Invention is credited to Marc Stein.
Application Number | 20100331680 12/825898 |
Document ID | / |
Family ID | 43379281 |
Filed Date | 2010-12-30 |
United States Patent
Application |
20100331680 |
Kind Code |
A1 |
Stein; Marc |
December 30, 2010 |
HIGH PRECISION PROCESSING OF MEASUREMENT DATA FOR THE
MUSCULAR-SKELETAL SYSTEM
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.
Inventors: |
Stein; Marc; (Chandler,
AZ) |
Correspondence
Address: |
Orthosensor, Inc.
1560 Sawgrass Corporate Pkwy, 4th Floor
Sunrise
FL
33323
US
|
Assignee: |
OrthoSensor
Sunrise
FL
|
Family ID: |
43379281 |
Appl. No.: |
12/825898 |
Filed: |
June 29, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61221889 |
Jun 30, 2009 |
|
|
|
61221761 |
Jun 30, 2009 |
|
|
|
61221767 |
Jun 30, 2009 |
|
|
|
61221779 |
Jun 30, 2009 |
|
|
|
61221788 |
Jun 30, 2009 |
|
|
|
61221793 |
Jun 30, 2009 |
|
|
|
61221801 |
Jun 30, 2009 |
|
|
|
61221808 |
Jun 30, 2009 |
|
|
|
61221817 |
Jun 30, 2009 |
|
|
|
61221867 |
Jun 30, 2009 |
|
|
|
61221874 |
Jun 30, 2009 |
|
|
|
61221879 |
Jun 30, 2009 |
|
|
|
61221881 |
Jun 30, 2009 |
|
|
|
61221886 |
Jun 30, 2009 |
|
|
|
61221894 |
Jun 30, 2009 |
|
|
|
61221901 |
Jun 30, 2009 |
|
|
|
61221909 |
Jun 30, 2009 |
|
|
|
61221916 |
Jun 30, 2009 |
|
|
|
61221923 |
Jun 30, 2009 |
|
|
|
61221929 |
Jun 30, 2009 |
|
|
|
61221889 |
Jun 30, 2009 |
|
|
|
Current U.S.
Class: |
600/437 |
Current CPC
Class: |
A61B 5/4509 20130101;
A61B 8/15 20130101; A61B 5/7239 20130101; A61B 5/6878 20130101;
A61B 5/4528 20130101; A61B 5/6846 20130101 |
Class at
Publication: |
600/437 |
International
Class: |
A61B 8/00 20060101
A61B008/00 |
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.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] 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
[0002] 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
[0003] 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.
[0004] 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
[0005] 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:
[0006] 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;
[0007] FIG. 2 is a simplified cross-sectional view of a sensing
module in accordance with an exemplary embodiment;
[0008] FIG. 3 is an exemplary assemblage for illustrating
reflectance and unidirectional modes of operation in accordance
with an exemplary embodiment;
[0009] 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;
[0010] 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;
[0011] FIG. 6 is a simplified flow chart of method steps for high
precision processing and measurement data in accordance with an
exemplary embodiment; and
[0012] 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
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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).
[0017] 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.
[0018] 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.
[0030] 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.
[0031] 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).
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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.
[0036] 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.
[0037] 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.
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.
[0042] 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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
143.mu., although the wavelength within a waveguide may be longer
than in unrestricted air.
[0055] 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.
[0056] 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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.
[0066] 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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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.
[0071] 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.
[0072] 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.
* * * * *