U.S. patent application number 12/825724 was filed with the patent office on 2010-12-30 for wireless sensing module for sensing a parameter of the muscular-skeletal system.
This patent application is currently assigned to OrthoSensor. Invention is credited to Marc Stein.
Application Number | 20100331736 12/825724 |
Document ID | / |
Family ID | 43379281 |
Filed Date | 2010-12-30 |
United States Patent
Application |
20100331736 |
Kind Code |
A1 |
Stein; Marc |
December 30, 2010 |
WIRELESS SENSING MODULE FOR SENSING A PARAMETER OF THE
MUSCULAR-SKELETAL SYSTEM
Abstract
A sensing insert device (100) is disclosed for measuring a
parameter of the muscular-skeletal system. The sensing insert
device (100) can be temporary or permanent. Used intra-operatively,
the sensing insert device (100) comprises an insert dock (202) and
a sensing module (200). The sensing module (200) is a
self-contained encapsulated measurement device having a contacting
surface that couples to the muscular-skeletal system. The sensing
module (200) comprises one or more sensors (303), electronic
circuitry (307), and communication circuitry (320). The electronic
circuitry (307) operatively couples to the one or more sensors
(303) to measure the parameter. The communication circuitry (320)
couples to the electronic circuitry (307) to wirelessly transmit
measurement data. The communication circuitry (320) comprises a
data packetizer (422), a cyclic redundancy check circuit (413), a
transmitter (416), a matching network (414), and an antenna (412).
The sensing insert device (100) when inserted allows movement of
the muscular-skeletal system.
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.: |
12/825724 |
Filed: |
June 29, 2010 |
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Application
Number |
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Patent Number |
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61221761 |
Jun 30, 2009 |
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61221767 |
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61221874 |
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61221929 |
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Current U.S.
Class: |
600/587 |
Current CPC
Class: |
A61B 5/4509 20130101;
A61B 8/15 20130101; A61B 5/7239 20130101; A61B 5/4528 20130101;
A61B 5/6878 20130101; A61B 5/6846 20130101 |
Class at
Publication: |
600/587 |
International
Class: |
A61B 5/103 20060101
A61B005/103 |
Claims
1. A sensing system for measurement of a parameter of the
muscular-skeletal system comprising: a sensing module comprising:
one or more sensors; electronic circuitry operatively coupled to
the sensors; and communication circuitry coupled to the electronic
circuitry to transmit data from the one or more sensors comprising:
a data packetizer coupled to the electronic circuitry; a cyclic
redundancy check circuit coupled to the data packetizer; a
transmitter coupled to the cyclic redundancy check circuit.
2. The sensing system of claim 1 further including a receiving
circuit external to the sensing module to receive data from the one
or more sensors comprising: an antenna; a matching network coupled
to the antenna; a receiver coupled to the matching network; a
cyclic redundancy check circuit coupled to the receiver; and a data
packetizer coupled to the cyclic redundancy check circuit
3. The sensing system of claim 1 where the sensing module further
includes an encapsulated enclosure having a power source
therein.
4. The sensing system of claim 3 where the communication circuitry
further comprises: a matching network coupled to the transmitter;
and an antenna coupled to the matching network where the antenna is
within the encapsulated enclosure.
5. The sensing system of claim 3 where the enclosure includes a
surface for receiving the applied parameter, where the one or more
sensors underlie the surface, and where the electronic circuitry
underlies the one or more sensors.
6. The sensing system of claim 5 where the sensing module is in a
trial insert.
7. The sensing system of claim 5 where the sensing module is in a
final insert having at least one bearing surface to promote
movement of the muscular-skeletal system.
8. The sensing system of claim 1 where the electronic circuitry and
the communication circuitry are on a single application integrated
circuit to reduce the form factor and power consumption the sensor
module.
9. The sensing system of claim 1 where the transmission range of
the transmitter is 5 meters or less.
10. The sensing system of claim 1 where the sensing module is
transmit only to prevent device tampering.
11. The sensing system of claim 1 where a cyclic redundancy check
is performed on a transmission.
12. A prosthetic component for measuring a parameter of the
muscular-skeletal system comprising: a trial insert comprising: a
contacting surface; one or more sensors coupled to the contacting
surface; electronic circuitry operatively coupled to the sensors;
and communication circuitry coupled to the contacting surface to
transmit data from the one or more sensors comprising: a data
packetizer coupled to the electronic circuitry; a cyclic redundancy
check circuit coupled to the data packetizer; a transmitter coupled
to the cyclic redundancy check circuit.
13. The prosthetic component of claim 12 where the trial insert
further comprises: a dock having a cavity; and a sensing module
having the contacting surface where the one or more sensors,
electronic circuitry, and communication circuitry reside in the
sensing module and where the sensing module is placed in the
cavity.
14. The prosthetic component of claim 13 where the sensing module
further comprises: a matching network coupled to the transmitter;
and an antenna coupled to the matching network.
15. The prosthetic component of claim 12 where the trial insert has
substantially equal dimensions to the final insert.
16. The prosthetic component of claim 12 where the one or more
sensors are coupled between the contacting surface and a rigid
substrate and where the communication circuitry underlies the rigid
substrate.
17. A prosthetic component to measure a parameter of the
muscular-skeletal system comprising: a final insert having a
bearing surface; a sensing module within the final surface
comprising: a contacting surface coupled to the bearing surface;
one or more sensors coupled to the contacting surface; electronic
circuitry operatively coupled to the sensors; and communication
circuitry coupled to the electronic circuitry to transmit data from
the one or more sensors comprising: a data packetizer coupled to
the electronic circuitry; a cyclic redundancy check circuit coupled
to the data packetizer; a transmitter coupled to the cyclic
redundancy check circuit.
18. The prosthetic component of claim 17 where the sensing module
further includes: a matching network coupled to the transmitter;
and an antenna coupled to the matching network.
19. The prosthetic component of claim 17, where the sensing module
is hermetically sealed.
20. The prosthetic component of claim 17, where the one or more
sensors are coupled between the contacting surface and a rigid
substrate and where the communication circuitry underlies the rigid
substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the priority benefit of U.S.
provisional patent application Nos. 61/221,761, 61/221,767,
61/221,779, 61/221,788, 61/221,793, 61/221,801, 61/221,808,
61/221,817, 61/221,867, 61/221,874, 61/221,879, 61/221,881,
61/221,886, 61/221,889, 61/221,894, 61/221,901, 61/221,909,
61/221,916, 61/221,923, and 61/221,929 all filed 30 Jun. 2009; the
disclosures of which are hereby incorporated herein by reference in
their entirety.
FIELD
[0002] The present invention pertains generally to measurement of
physical parameters, and particularly to, but not exclusively to,
communication of sensor data and measurements in real-time.
BACKGROUND
[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 using
information from simulations, mechanical prototypes, and patient
data that is collected and used to initiate improved designs.
Similarly, the tools being used for orthopedic surgery have been
refined over the years but have not changed substantially. Thus,
the basic procedure for replacement of an orthopedic joint has been
standardized to meet the general needs of a wide distribution of
the population. Although the tools, procedure, and artificial joint
meet a general need, each replacement procedure is subject to
significant variation from patient to patient. The correction of
these individual variations relies on the skill of the surgeon to
adapt and fit the replacement joint using the available tools to
the specific circumstance.
BRIEF DESCRIPTION OF THE DRAWINGS
[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 illustration of an application of sensing
insert device in accordance with an exemplary embodiment;
[0007] FIG. 2 is an illustration of a sensing insert device placed
in a joint of the muscular-skeletal system for measuring a
parameter in accordance with an exemplary embodiment;
[0008] FIG. 3 is a perspective view of a medical sensing platform
comprising an encapsulating enclosure in accordance with one
embodiment;
[0009] FIG. 4 is a perspective view of a medical sensing device
suitable for use as a bi-compartmental implant and comprising an
encapsulating enclosure in accordance with one embodiment;
[0010] FIG. 5 is an exemplary block diagram of the components of
the sensing module in accordance with an exemplary embodiment;
[0011] FIG. 6 is a diagram of an exemplary communications system
for short-range telemetry according to one embodiment;
[0012] FIG. 7 is an illustration of a block model diagram of the
sensing module in accordance with an exemplary embodiment;
[0013] FIG. 8 is an exemplary assemblage that illustrates
propagation of ultrasound waves within the waveguide in the
bi-directional mode of operation of this assemblage in accordance
with one embodiment;
[0014] FIG. 9 is an exemplary cross-sectional view of an ultrasound
waveguide to illustrate changes in the propagation of ultrasound
waves with changes in the length of the waveguide in accordance
with one embodiment;
[0015] FIG. 10 is an exemplary block diagram of a propagation tuned
oscillator (PTO) to maintain positive closed-loop feedback in
accordance with an exemplary embodiment; and
[0016] FIG. 11 is a cross-sectional view of a layout architecture
of the sensing module in accordance with an exemplary
embodiment.
DETAILED DESCRIPTION
[0017] Embodiments of the invention are broadly directed to
measurement of physical parameters. Many physical parameters of
interest within physical systems or bodies can be measured by
evaluating changes in the characteristics of energy waves or
pulses. As one example, changes in the transit time or shape of an
energy wave or pulse propagating through a changing medium can be
measured to determine the forces acting on the medium and causing
the changes. The propagation velocity of the energy waves or pulses
in the medium is affected by physical changes in of the medium. The
physical parameter or parameters of interest can include, but are
not limited to, measurement of load, force, pressure, displacement,
density, viscosity, localized temperature. These parameters can be
evaluated by measuring changes in the propagation time of energy
pulses or waves relative to orientation, alignment, direction, or
position as well as movement, rotation, or acceleration along an
axis or combination of axes by wireless sensing modules or devices
positioned on or within a body, instrument, appliance, vehicle,
equipment, or other physical system.
[0018] In all of the examples illustrated and discussed herein, any
specific materials, temperatures, times, energies, etc. for process
steps or specific structure implementations should be interpreted
to illustrative only and non-limiting. Processes, techniques,
apparatus, and materials as known by one of ordinary skill in the
art may not be discussed in detail but are intended to be part of
an enabling description where appropriate.
[0019] Note that similar reference numerals and letters refer to
similar items in the following figures. In some cases, numbers from
prior illustrations will not be placed on subsequent figures for
purposes of clarity. In general, it should be assumed that
structures not identified in a figure are the same as previous
prior figures.
[0020] In the present invention these parameters are measured with
an integrated wireless sensing module or device comprising an i)
encapsulating structure that supports sensors and contacting
surfaces and ii) an electronic assemblage that integrates a power
supply, sensing elements, ultrasound resonator or resonators or
transducer or transducers and ultrasound waveguide or waveguides,
biasing spring or springs or other form of elastic members, an
accelerometer, antennas and electronic circuitry that processes
measurement data as well as controls all operations of energy
conversion, propagation, and detection and wireless communications.
The wireless sensing module or device can be positioned on or
within, or engaged with, or attached or affixed to or within, a
wide range of physical systems including, but not limited to
instruments, appliances, vehicles, equipments, or other physical
systems as well as animal and human bodies, for sensing and
communicating parameters of interest in real time.
[0021] FIG. 1 is an illustration of an application of sensing
insert device 100 in accordance with an exemplary embodiment. The
illustration shows the device 100 measuring a force, pressure, or
load applied by the muscular-skeletal system. In the illustration,
device 100 can collect load data for real-time viewing of the load
forces over various applied loads and angles of flexion. The
sensing insert device 100 can measure the level and distribution of
load at various points on the prosthetic component and transmits
the measured load data by way data communication to a receiver
station 110 for permitting visualization. This can aid the surgeon
in making any adjustments needed to achieve optimal joint
balancing.
[0022] In general, device 100 has at least one contacting surface
that couples to the muscular-skeletal system. As shown, a first and
a second contacting surface respectively couple to a femoral
prosthetic component 104 and a tibial prosthetic component 106.
Device 100 is designed to be used in the normal flow of an
orthopedic surgical procedure without special procedures,
equipment, or components. Typically, one or more natural components
of the muscular-skeletal system are replaced when joint
functionality substantially reduces a patient quality of life. A
joint replacement is a common procedure in later life because it is
prone to wear over time, can be damaged during physical activity,
or by accident.
[0023] A joint of the muscular-skeletal system provides movement of
bones in relation to one another that can comprise angular and
rotational motion. The joint can be subjected to loading and torque
throughout the range of motion. The joint typically comprises two
bones that move in relation to one another with a low friction
flexible connective tissue such as cartilage between the bones. The
joint also generates a natural lubricant that works in conjunction
with the cartilage to aid in ease of movement. Sensing insert
device 100 mimics the natural structure between the bones of the
joint. Insert device 100 has a contacting surface on which a bone
or a prosthetic component can moveably couple. A knee joint is
disclosed for illustrative purposes but sensing insert device 100
is applicable to other joints of the muscular-skeletal system. For
example, the hip, spine, and shoulder have similar structures
comprising two or more bones that move in relation to one another.
In general, insert device 100 can be used between two or more bones
allowing movement of the bones during measurement or maintaining
the bones in a fixed position.
[0024] The load sensor insert device 100 and the receiver station
110 forms a communication system for conveying data via secure
wireless transmission within a broadcasting range over short
distances on the order of a few meters to protect against any form
of unauthorized or accidental query. In one embodiment, the
transmission range is five meters or less which is approximately a
dimension of an operating room. In practice, it can be a shorter
distance 1-2 meters to transmit to a display outside the sterile
field. The transmit distance will be even shorter when device 100
is used in a prosthetic implanted component. Transmission occurs
through the skin of the patient and is likely limited to less than
0.5 meters. A combination of cyclic redundancy checks and a high
repetition rate of transmission during data capture permits
discarding of corrupted data without materially affecting display
of data
[0025] In the illustration, a surgical procedure is performed to
place a femoral prosthetic component 104 onto a prepared distal end
of the femur 102. Similarly, a tibial prosthetic component 106 is
placed to a prepared proximal end of the tibia 108. The tibial
prosthetic component 106 can be a tray or plate affixed to a
planarized proximal end of the tibia 108. The sensing insert device
100 is a third prosthetic component that is placed between the
plate of the tibial prosthetic component 106 and the femoral
prosthetic component 104. The three prosthetic components enable
the prostheses to emulate the functioning of a natural knee joint.
In one embodiment, sensing insert device 100 is used during surgery
and replaced with a final insert after quantitative measurements
are taken to ensure optimal fit, balance, and loading of the
prosthesis.
[0026] In one embodiment, sensing insert device 100 is a mechanical
replica of a final insert. In other words, sensing insert device
100 has substantially equal dimensions to the final insert. The
substantially equal dimensions ensure that the final insert when
placed in the reconstructed joint will have similar loading and
balance as that measured by sensing insert device 100 during the
trial phase of the surgery. Moreover, passive trial inserts are
commonly used during surgery to determine the appropriate final
insert. Thus, the procedure remains the same. It can measure loads
at various points (or locations) on the femoral prosthetic
component 104 and transmit the measured data to a receiving station
110 by way of an integrated loop antenna. The receiving station 110
can include data processing, storage, or display, or combination
thereof and provide real time graphical representation of the level
and distribution of the load.
[0027] As one example, the sensing insert device 100 can measure
forces (Fx, Fy, and Fz) with corresponding locations and torques
(e.g. Tx, Ty, and Tz) on the femoral prosthetic component 104 and
the tibial prosthetic component 106. It can then transmit this data
to the receiving station 110 to provide real-time visualization for
assisting the surgeon in identifying any adjustments needed to
achieve optimal joint balancing.
[0028] FIG. 2 is an illustration of a sensing insert device 100
placed in a joint of the muscular-skeletal system for measuring a
parameter in accordance with an exemplary embodiment. In
particular, sensing insert device 100 is placed in contact between
a femur 102 and a tibia 108 for measuring a parameter. In the
example, a force, pressure, or load is being measured. The device
100 in this example can intra-operatively assess a load on
prosthetic components during the surgical procedure. As mentioned
previously, sensing insert device 100 collects data for real-time
viewing of the load forces over various applied loads and angles of
flexion. It can measure the level and distribution of load at
various points on the prosthetic component and transmit the
measured load data by way data communication to a receiver station
110 for permitting visualization. This can aid the surgeon in
making any adjustments needed to achieve optimal joint
balancing.
[0029] A proximal end of tibia 108 is prepared to receive tibial
prosthetic component 106. Tibial prosthetic component 106 is a
support structure that is fastened to the proximal end of the tibia
and is usually made of a metal or metal alloy. The tibial
prosthetic component 106 also retains the insert in a fixed
position with respect to tibia 108. Similarly, a distal end of
femur 102 is prepared to receive femoral prosthetic component 104.
The femoral prosthetic component 104 is generally shaped to have an
outer condylar articulating surface. The preparation of femur 102
and tibia 108 is aligned to the mechanical axis of the leg. The
sensing insert device 100 provides a concave or flat surface
against which the outer condylar articulating surface of the
femoral prosthetic component 104 rides relative to the tibia
prosthetic component 106. In particular, the top surface of the
sensing module 200 faces the condylar articulating surface of the
femoral prosthetic component 104, and the bottom surface of the
insert dock 202 faces the top surface of the tibial prosthetic
component 106.
[0030] A final insert is subsequently fitted between femoral
prosthetic component 104 and tibial prosthetic component 106 that
has a bearing surface that couples to femoral component 104
allowing the leg a natural range of motion. The final insert is has
a wear surface that is typically made of a low friction polymer
material. Ideally, the prosthesis has an appropriate loading,
alignment, and balance that mimics the natural leg and maximizes
the life of the artificial components. It should be noted that
sensing module 200 can be placed a final insert and operated
similarly as disclosed herein. The sensing module 200 can be used
to periodically monitor status of the permanent joint.
[0031] The sensing insert device 100 is used to measure, adjust,
and test the reconstructed joint prior to installing the final
insert. As mentioned previously, the sensing insert device 100 is
placed between the femur 102 and tibia 108. The condyle surface of
femoral component 104 contacts a major surface of device 100. The
major surface of device 100 approximates a surface of a final
insert. Tibial prosthetic component 106 can include a cavity or
tray on the major surface that receives and retains an insert dock
202 and a sensing module 200 during a measurement process. It
should be noted that sensing insert device 100 is coupled to and
provides measurement data in conjunction with other implanted
prosthetic components. In other words, the prosthetic components
are the permanent installed components of the patient.
[0032] Insert dock 202 is provided in different sizes and shapes.
Insert dock 202 can comprise many different sizes and shapes to
interface appropriately with different manufacturer prosthetic
components. Prosthetic components are made in different sizes to
accommodate anatomical differences over a wide population range.
Insert dock 202 is designed for different prosthetic sizes within
the same manufacturer. In at least one embodiment, multiple docks
of different dimensions are provided for a surgery. For example,
the thickness of the final insert is determined by the surgical
cuts to the muscular-skeletal system and measurements provided by
sensing module 200. The surgeon may try two insert docks 202 of
different thicknesses before making a final decision. In one
embodiment, sensing insert device 100 selected by the surgeon has
substantially equal dimensions to the final insert used. In
general, insert dock 202 allows standardization on a single sensing
module 200 for different prosthetic platforms. Thus, the sensing
module 200 is common to the different insert docks 202 allowing
improved quality, reliability, and performance.
[0033] In one embodiment, one or more insert docks 202 are used to
determine an appropriate thickness that yields an optimal loading.
In general, the absolute loading over the range of motion is kept
within a predetermined range. Soft tissue tensioning can be used to
adjust the absolute loading. The knee balance can also be adjusted
within a predetermined range if a total knee reconstruction is
being performed and a sensing module 202 is used in each
compartment. Tibial prosthetic component 106 and device 100 have a
combined thickness that represents a combined thickness of tibial
prosthetic component 106 and a final (or chronic) insert of the
knee joint. Thus, the final insert thickness or depth is chosen
based on the trial performed using device 100. Typically, the final
insert thickness is identical to the device 100 to maintain the
measured loading and balance. In one embodiment, sensing module 200
and insert docks 202 are disposed of after surgery. Alternatively,
the sensing module 200 and insert docks 202 can be cleaned,
sterilized, and packaged for reuse.
[0034] The prosthesis incorporating device 100 emulates the
function of a natural knee joint. Device 100 can measure loads or
other parameters at various points throughout the range of motion.
Data from device 100 is transmitted to a receiving station 110 via
wired or wireless communications. In a first embodiment, device 100
is a disposable system. Device 100 can be disposed of after using
the sensing insert device 100 to optimally fit the joint implant.
Device 100 is a low cost disposable system that reduces capital
costs, operating costs, facilitates rapid adoption of quantitative
measurement, and initiates evidentiary based orthopedic medicine.
In a second embodiment, a methodology can be put in place to clean
and sterilize device 100 for reuse. In a third embodiment, device
100 can be incorporated in a tool instead of being a component of
the replacement joint. The tool can be disposable or be cleaned and
sterilized for reuse. In a fourth embodiment, device 100 can be a
permanent component of the replacement joint. Device 100 can be
used to provide both short term and long term post-operative data
on the implanted joint. In a fifth embodiment, device 100 can be
coupled to the muscular-skeletal system. In all of the embodiments,
receiving station 110 can include data processing, storage, or
display, or combination thereof and provide real time graphical
representation of the level and distribution of the load. Receiving
station 110 can record and provide accounting information of device
100 to an appropriate authority.
[0035] The sensing insert device 100, in one embodiment, comprises
a load sensing platform 121, an accelerometer 122, and sensing
assemblies 123. This permits the sensing device 100 to assess a
total load on the prosthetic components when it is being moved. The
system accounts for forces due to gravity and motion. In one
embodiment, load sensing platform 121 includes two or more load
bearing surfaces, at least one energy transducer, at least one
compressible energy propagating structure, and at least one member
for elastic support. The accelerometer 122 can measure
acceleration. Acceleration can occur when the load sensing device
100 is moved or put in motion. Accelerometer 122 can sense
orientation, vibration, and impact. In another embodiment, the
femoral component 104 can similarly include an accelerometer 127,
which by way of a communication interface to the sensing insert
device 100, can provide reference position and acceleration data to
determine an exact angular relationship between the femur and
tibia. The sensing assemblies 123 can reveal changes in length or
compression of the energy propagating structure or structures by
way of the energy transducer or transducers. Together the load
sensing platform 121, accelerometer 122 (and in certain cases
accelerometer 127), and sensing assemblies 123 measure force or
pressure external to the load sensing platform or displacement
produced by contact with the prosthetic components.
[0036] In at least one exemplary embodiment, an energy pulse is
directed within one or more waveguides in device 100 by way of
pulse mode operations and pulse shaping. The waveguide is a conduit
that directs the energy pulse in a predetermined direction. The
energy pulse is typically confined within the waveguide. In one
embodiment, the waveguide comprises a polymer material. For
example, urethane or polyethylene are polymers suitable for forming
a waveguide. The polymer waveguide can be compressed and has little
or no hysteresis in the system. Alternatively, the energy pulse can
be directed through the muscular-skeletal system. In one
embodiment, the energy pulse is directed through bone of the
muscular-skeletal system to measure bone density. A transit time of
an energy pulse is related to the material properties of a medium
through which it traverses. This relationship is used to generate
accurate measurements of parameters such as distance, weight,
strain, pressure, wear, vibration, viscosity, and density to name
but a few.
[0037] Incorporating data from the accelerometer 122 with data from
the other sensing components 121 and 123 assures accurate
measurement of the applied load, force, pressure, or displacement
by enabling computation of adjustments to offset this external
motion. This capability can be required in situations wherein the
body, instrument, appliance, vehicle, equipment, or other physical
system, is itself operating or moving during sensing of load,
pressure, or displacement. This capability can also be required in
situations wherein the body, instrument, appliance, vehicle,
equipment, or other physical system, is causing the portion of the
body, instrument, appliance, vehicle, equipment, or other physical
system being measured to be in motion during sensing of load,
pressure, or displacement.
[0038] The accelerometer 122 can operate singly, as an integrated
unit with the load sensing platform 121, and/or as an integrated
unit with the sensing assemblies 123. Integrating one or more
accelerometers 122 within the sensing assemblages 123 to determine
position, attitude, movement, or acceleration of sensing
assemblages 123 enables augmentation of presentation of data to
accurately identify, but not limited to, orientation or spatial
distribution of load, force, pressure, displacement, density, or
viscosity, or localized temperature by controlling the load and
position sensing assemblages to measure the parameter or parameters
of interest relative to specific orientation, alignment, direction,
or position as well as movement, rotation, or acceleration along
any axis or combination of axes. Measurement of the parameter or
parameters of interest may also be made relative to the earth's
surface and thus enable computation and presentation of spatial
distributions of the measured parameter or parameters relative to
this frame of reference.
[0039] In one embodiment, the accelerometer 122 includes direct
current (DC) sensitivity to measure static gravitational pull with
load and position sensing assemblages to enable capture of, but not
limited to, distributions of load, force, pressure, displacement,
movement, rotation, or acceleration by controlling the sensing
assemblages to measure the parameter or parameters of interest
relative to orientations with respect to the earths surface or
center and thus enable computation and presentation of spatial
distributions of the measured parameter or parameters relative to
this frame of reference.
[0040] Embodiments of device 100 are broadly directed to
measurement of physical parameters, and more particularly, to
evaluating changes in the transit time of a pulsed energy wave
propagating through a medium. In-situ measurements during
orthopedic joint implant surgery would be of substantial benefit to
verify an implant is in balance and under appropriate loading or
tension. In one embodiment, the instrument is similar to and
operates familiarly with other instruments currently used by
surgeons. This will increase acceptance and reduce the adoption
cycle for a new technology. The measurements will allow the surgeon
to ensure that the implanted components are installed within
predetermined ranges that maximize the working life of the joint
prosthesis and reduce costly revisions. Providing quantitative
measurement and assessment of the procedure using real-time data
will produce results that are more consistent. A further issue is
that there is little or no implant data generated from the implant
surgery, post-operatively, and long term. Device 100 can provide
implant status data to the orthopedic manufacturers and surgeons.
Moreover, data generated by direct measurement of the implanted
joint itself would greatly improve the knowledge of implanted joint
operation and joint wear thereby leading to improved design and
materials.
[0041] As mentioned previously, device 100 can be used for other
joint surgeries; it is not limited to knee replacement implant or
implants. Moreover, device 100 is not limited to trial
measurements. Device 100 can be incorporated into the final joint
system to provide data post-operatively to determine if the
implanted joint is functioning correctly. Early determination of a
problem using device 100 can reduce catastrophic failure of the
joint by bringing awareness to a problem that the patient cannot
detect. The problem can often be rectified with a minimal invasive
procedure at lower cost and stress to the patient. Similarly,
longer term monitoring of the joint can determine wear or
misalignment that if detected early can be adjusted for optimal
life or replacement of a wear surface with minimal surgery thereby
extending the life of the implant. In general, device 100 can be
shaped such that it can be placed or engaged or affixed to or
within load bearing surfaces used in many orthopedic applications
(or used in any orthopedic application) related to the
musculoskeletal system, joints, and tools associated therewith.
Device 100 can provide information on a combination of one or more
performance parameters of interest such as wear, stress,
kinematics, kinetics, fixation strength, ligament balance,
anatomical fit and balance.
[0042] FIG. 3 is a perspective view of a medical sensing platform
comprising an encapsulating enclosure in accordance with one
embodiment. In general, parameters of the muscular-skeletal system
can be measured with a sensing module 200 that in one embodiment is
an integral part of a complete sensing insert device 100. The
sensing module 200 is a self-contained sensor within an
encapsulating enclosure that integrates sensing assemblages, an
electronic assemblage that couples to the sensing assemblages, a
power source, signal processing, and wireless communication. All
components required for the measurement are contained in the
sensing module 200. The sensing module 200 has at least one
contacting surface for coupling to the muscular-skeletal system. A
parameter of the muscular-skeletal system is applied to the contact
surfaces to be measured by the one or more sensing assemblages
therein. As will be disclosed in further detail herein, the sensing
module 200 is part of a system that allows intra-operative and
post-operative sensing of a joint of the muscular-skeletal system.
More specifically, sensing module 200 is placed within a temporary
or permanent prosthetic component that has a similar form factor as
the passive prosthetic component currently being used. This has a
benefit of rapid adoption because the sensing platform is inserted
identically to the commonly used passive component but can provide
much needed quantitative measurements with little or no procedural
changes.
[0043] As shown, the sensing insert device 100 comprises an insert
dock 202 and the sensing module 200. Sensing insert device 100 is a
non-permanent or temporary measurement device that is used
intra-operatively to provide quantitative data related to the
installation of prosthetic components such as in joint replacement
surgery. The combination of the insert dock 202 and sensing module
202 has a form factor substantially equal to a final insert device.
The final insert device can be a passive component or sensored
incorporating sensing module 200. The substantially equal form
factor of sensing insert device 100 results in no extraneous
structures in the surgical field that can interfere with the
procedure. For example, a final insert device is designed to mimic
the function of the natural component it is replacing. The final
insert device allows natural movement of the muscular-skeletal
system and does not interfere with ligaments, tendons, tissue,
muscles, and other components of the muscular-skeletal system.
Similarly, sensing insert device 100 allows exposure of the
surgical field around the joint by having the similar form factor
as the final insert thereby allowing the surgeon to make
adjustments during the installation in a natural setting with
quantitative measurements to support the modifications.
[0044] In one embodiment, insert dock 202 is an adaptor. Insert
dock 202 is made in different sizes. In general, prosthetic
components are manufactured in different sizes to accommodate
variation in the muscular-skeletal system from person to person. In
the example, the size of insert dock 202 is chosen to mate with the
selected prosthetic implant components. In particular, a feature
204 aligns with and retains insert dock 202 in a fixed position to
a prosthetic or natural component of the muscular-skeletal system.
The insert dock 202 is a passive component having an opening for
receiving sensing module 200. The opening is positioned to place
the contacting surfaces in a proper orientation to measure the
parameter when used in conjunction with other prosthetic
components. The insert dock 202 as an adaptor can be manufactured
at low cost. Moreover, insert dock 202 can be formed for adapting
to different prosthetic manufacturers thereby increasing system
flexibility. This allows a standard sensing module 200 to be
provided but customized for appropriate size and dimensions through
dock 202 for the specific application and manufacturer
component.
[0045] The one or more sensing assemblages within sensing module
200 couple to the contacting surfaces of sensing module 200 for
receiving the applied parameter of the muscular-skeletal system. In
one embodiment, a sensing assemblage comprises one or more energy
transducers coupled to an elastic structure. The elastic structure
allows the propagation of energy waves. The forms of energy
propagated through the elastic energy propagating structures may
include, but is not limited to, sound, ultrasound, or
electromagnetic radiation including radio frequency, infrared, or
light. A change in the parameter applied to the contacting surfaces
results in a change a dimension of the elastic structure. The
dimension of the elastic structure can be measured precisely using
continuous wave, pulsed, or pulsed echo measurement. The dimension
and material properties of the elastic structure have a known
relationship to the parameter being measured. Thus, the dimension
is precisely measured and converted to the parameter. Other factors
such as movement or acceleration can be taken into account in the
calculation. As an example, a force, pressure, or load applied to
the one or more contacting surfaces of sensing module 200 is used
to illustrate a parameter measurement hereinbelow. It should be
noted that this is for illustration purposes and that the sensing
module 200 can be used to measure other parameters.
[0046] As will be shown ahead, the encapsulating enclosure can
serve in a first embodiment as a trial implant for orthopedic
surgical procedures, namely, for determining load forces on
prosthetic components and the musculoskeletal system. In a second
embodiment, the encapsulating enclosure can be placed within a
permanent prosthetic component for long term monitoring. The
encapsulating enclosure supports and protects internal mechanical
and electronic components from external physical, mechanical,
chemical, and electrical, and electromagnetic intrusion that might
compromise sensing or communication operations of the module or
device. The integration of the internal components is designed to
minimize adverse physical, mechanical, electrical, and ultrasonic
interactions that might compromise sensing or communication
operations of the module or device.
[0047] FIG. 4 is a perspective view of a medical sensing device
suitable for use as a bi-compartmental implant and comprising an
encapsulating enclosure in accordance with one embodiment. As
shown, the load sensing insert device 100 comprises two sensing
modules 200. Each sensing module 200 is a self-contained
encapsulated enclosure that can make individual or coordinated
parameter measurements. For example, the sensing insert device 100
can be used to assess load forces on a bi-compartmental knee joint
implant. In particular, both sensing modules 200 can individually,
or in combination, report applied loading forces. Bi-compartmental
sensing provides the benefit of providing quantitative measurement
to balance each compartment in relation to one another.
[0048] Similar to that described above, insert dock 202 is an
adaptor having two openings instead of one. Insert dock 202 can be
made in different sizes to accommodated different sized prosthetic
components and different manufacturers. The insert dock 202 with
two openings is a passive component for receiving two separate
sensing modules 200. The opening is positioned to place the
contacting surfaces in a proper orientation to measure the
parameter when used in conjunction with other prosthetic
components. In general, encapsulated enclosures can be positioned
on or within, or engaged with, or attached or affixed to or within,
a wide range of physical systems including, but not limited to
instruments, appliances, vehicles, equipments, or other physical
systems as well as animal and human bodies, for sensing and
communicating the parameter or parameters of interest in real time.
Similar to that described above, insert dock 202 as an adaptor can
be manufactured at low cost providing design flexibility and
allowing rapid adoption of quantitative measurement.
[0049] FIG. 5 is an exemplary block diagram of the components of
the sensing module 200 in accordance with an exemplary embodiment.
It should be noted that the sensing module could comprise more or
less than the number of components shown. As illustrated, the
sensing module includes one or more sensing assemblages 303, a
transceiver 320, an energy storage 330, electronic circuitry 307,
one or more mechanical supports 315 (e.g., springs), and an
accelerometer 302. In the non-limiting example, an applied
compressive force can be measured by the sensing module.
[0050] The sensing assemblage 303 can be positioned, engaged,
attached, or affixed to the contact surfaces 306. Mechanical
supports 315 serve to provide proper balancing of contact surfaces
306. In at least one exemplary embodiment, contact surfaces 306 are
load-bearing surfaces. In general, the propagation structure 305 is
subject to the parameter being measured. Surfaces 306 can move and
tilt with changes in applied load; actions which can be transferred
to the sensing assemblages 303 and measured by the electronic
circuitry 307. The electronic circuitry 307 measures physical
changes in the sensing assemblage 303 to determine parameters of
interest, for example a level, distribution and direction of forces
acting on the contact surfaces 306. In general, the sensing module
is powered by the energy storage 330.
[0051] As one example, the sensing assemblage 303 can comprise an
elastic or compressible propagation structure 305 between a
transducer 304 and a transducer 314. In the current example,
transducer 304 can be an ultrasound (or ultrasonic) resonator, and
the elastic or compressible propagation structure 305 can be an
ultrasound (or ultrasonic) waveguide (or waveguides). The
electronic circuitry 307 is electrically coupled to the sensing
assemblages 303 and translates changes in the length (or
compression or extension) of the sensing assemblages 303 to
parameters of interest, such as force. It measures a change in the
length of the propagation structure 305 (e.g., waveguide)
responsive to an applied force and converts this change into
electrical signals which can be transmitted via the transceiver 320
to convey a level and a direction of the applied force. In other
arrangements herein contemplated, the sensing assemblage 303 may
require only a single transducer. In yet other arrangements, the
sensing assemblage 303 can include piezoelectric, capacitive,
optical or temperature sensors or transducers to measure the
compression or displacement. It is not limited to ultrasonic
transducers and waveguides.
[0052] The accelerometer 302 can measure acceleration and static
gravitational pull. Accelerometer 302 can be single-axis and
multi-axis accelerometer structures that detect magnitude and
direction of the acceleration as a vector quantity. Accelerometer
302 can also be used to sense orientation, vibration, impact and
shock. The electronic circuitry 307 in conjunction with the
accelerometer 302 and sensing assemblies 303 can measure parameters
of interest (e.g., distributions of load, force, pressure,
displacement, movement, rotation, torque and acceleration) relative
to orientations of the sensing module with respect to a reference
point. In such an arrangement, spatial distributions of the
measured parameters relative to a chosen frame of reference can be
computed and presented for real-time display.
[0053] The transceiver 320 comprises a transmitter 309 and an
antenna 310 to permit wireless operation and telemetry functions.
In various embodiments, the antenna 310 can be configured by design
as an integrated loop antenna. As will be explained ahead, the
integrated loop antenna is configured at various layers and
locations on the electronic substrate with electrical components
and by way of electronic control circuitry to conduct efficiently
at low power levels. Once initiated the transceiver 320 can
broadcast the parameters of interest in real-time. The telemetry
data can be received and decoded with various receivers, or with a
custom receiver. The wireless operation can eliminate distortion
of, or limitations on, measurements caused by the potential for
physical interference by, or limitations imposed by, wiring and
cables connecting the sensing module with a power source or with
associated data collection, storage, display equipment, and data
processing equipment.
[0054] The transceiver 320 receives power from the energy storage
330 and can operate at low power over various radio frequencies by
way of efficient power management schemes, for example,
incorporated within the electronic circuitry 307. As one example,
the transceiver 320 can transmit data at selected frequencies in a
chosen mode of emission by way of the antenna 310. The selected
frequencies can include, but are not limited to, ISM bands
recognized in International Telecommunication Union regions 1, 2
and 3. A chosen mode of emission can be, but is not limited to,
Gaussian Frequency Shift Keying, (GFSK), Amplitude Shift Keying
(ASK), Phase Shift Keying (PSK), Minimum Shift Keying (MSK),
Frequency Modulation (FM), Amplitude Modulation (AM), or other
versions of frequency or amplitude modulation (e.g., binary,
coherent, quadrature, etc.).
[0055] The antenna 310 can be integrated with components of the
sensing module to provide the radio frequency transmission. The
substrate for the antenna 310 and electrical connections with the
electronic circuitry 307 can further include a matching network.
This level of integration of the antenna and electronics enables
reductions in the size and cost of wireless equipment. Potential
applications may include, but are not limited to any type of
short-range handheld, wearable, or other portable communication
equipment where compact antennas are commonly used. This includes
disposable modules or devices as well as reusable modules or
devices and modules or devices for long-term use.
[0056] The energy storage 330 provides power to electronic
components of the sensing module. It can be charged by wired energy
transfer, short-distance wireless energy transfer or a combination
thereof. External power sources can include, but are not limited
to, a battery or batteries, an alternating current power supply, a
radio frequency receiver, an electromagnetic induction coil, a
photoelectric cell or cells, a thermocouple or thermocouples, or an
ultrasound transducer or transducers. By way of the energy storage
330, the sensing module can be operated with a single charge until
the internal energy is drained. It can be recharged periodically to
enable continuous operation. The energy storage 330 can utilize
common power management technologies such as replaceable batteries,
supply regulation technologies, and charging system technologies
for supplying energy to the components of the sensing module to
facilitate wireless applications.
[0057] The energy storage 330 minimizes additional sources of
energy radiation required to power the sensing module during
measurement operations. In one embodiment, as illustrated, the
energy storage 330 can include a capacitive energy storage device
308 and an induction coil 311. External source of charging power
can be coupled wirelessly to the capacitive energy storage device
308 through the electromagnetic induction coil or coils 311 by way
of inductive charging. The charging operation can be controlled by
power management systems designed into, or with, the electronic
circuitry 307. As one example, during operation of electronic
circuitry 307, power can be transferred from capacitive energy
storage device 308 by way of efficient step-up and step-down
voltage conversion circuitry. This conserves operating power of
circuit blocks at a minimum voltage level to support the required
level of performance.
[0058] In one configuration, the energy storage 330 can further
serve to communicate downlink data to the transceiver 320 during a
recharging operation. For instance, downlink control data can be
modulated onto the energy source signal and thereafter demodulated
from the induction coil 311 by way of electronic control circuitry
307. This can serve as a more efficient way for receiving downlink
data instead of configuring the transceiver 320 for both uplink and
downlink operation. As one example, downlink data can include
updated control parameters that the sensing module uses when making
a measurement, such as external positional information, or for
recalibration purposes, such as spring biasing. It can also be used
to download a serial number or other identification data.
[0059] The electronic circuitry 307 manages and controls various
operations of the components of the sensing module, such as
sensing, power management, telemetry, and acceleration sensing. It
can include analog circuits, digital circuits, integrated circuits,
discrete components, or any combination thereof. In one
arrangement, it can be partitioned among integrated circuits and
discrete components to minimize power consumption without
compromising performance. Partitioning functions between digital
and analog circuit enhances design flexibility and facilitates
minimizing power consumption without sacrificing functionality or
performance. Accordingly, the electronic circuitry 307 can comprise
one or more Application Specific Integrated Circuit (ASIC) chips,
for example, specific to a core signal processing algorithm.
[0060] In another arrangement, the electronic circuitry can
comprise a controller such as a programmable processor, a Digital
Signal Processor (DSP), a microcontroller, or a microprocessor,
with associated storage memory and logic. The controller can
utilize computing technologies with associated storage memory such
a Flash, ROM, RAM, SRAM, DRAM or other like technologies for
controlling operations of the aforementioned components of the
sensing module. In one arrangement, the storage memory may store
one or more sets of instructions (e.g., software) embodying any one
or more of the methodologies or functions described herein. The
instructions may also reside, completely or at least partially,
within other memory, and/or a processor during execution thereof by
another processor or computer system.
[0061] The electronics assemblage also supports testability and
calibration features that assure the quality, accuracy, and
reliability of the completed wireless sensing module or device. A
temporary bi-directional interconnect assures a high level of
electrical observability and controllability of the electronics.
The test interconnect also provides a high level of electrical
observability of the sensing subsystem, including the transducers,
waveguides, and mechanical spring or elastic assembly. Carriers or
fixtures emulate the final enclosure of the completed wireless
sensing module or device during manufacturing processing thus
enabling capture of accurate calibration data for the calibrated
parameters of the finished wireless sensing module or device. These
calibration parameters are stored within the on-board memory
integrated into the electronics assemblage.
[0062] FIG. 6 is a diagram of an exemplary communications system
400 for short-range telemetry according to one embodiment. As
illustrated, the exemplary communications system 400 comprises
medical device communications components 410 of the sensing insert
device 100 (see FIG. 1) and receiving system communications
components 450 of the receiving system 110 (see FIG. 1). The
medical device communications components 410 are inter-operatively
coupled to include, but not limited to, the antenna 412, a matching
network 414, the telemetry transceiver 416, a CRC circuit 418, a
data packetizer 422, a data input 424, a power source 426, and an
application specific integrated circuit (ASIC) 420. The medical
device communications components 410 may include more or less than
the number of components shown and are not limited to those shown
or the order of the components.
[0063] The receiving station communications components 450 comprise
an antenna 452, the matching network 454, the telemetry receiver
456, the CRC circuit 458, the data packetizer 460, and optionally a
USB interface 462. Notably, other interface systems can be directly
coupled to the data packetizer 460 for processing and rendering
sensor data.
[0064] With respect to FIG. 1, in view of the communication
components of FIG. 6, the load sensing insert device 100 acquires
sensor data by way of the data input to the ASIC 420. Referring
briefly to FIG. 5, the ASIC 420 is operatively coupled to sensing
assemblies 303. In one embodiment, a change in the parameter being
measured by device 100 produces a change in a length of a
compressible propagation structure 305. ASIC 420 controls the
emission of energy waves into propagation structure 305 and the
detection of propagated energy waves. ASIC 420 generates data
related to transit time, frequency, or phase of propagated energy
waves. The data corresponds to the length of propagation structure
305, which can be translated to the parameter of interest by way of
a known function or relationship. Similarly, the data can comprise
voltage or current measurements from a MEMS structure,
piezo-resistive sensor, strain gauge, or other sensor type that is
used to measure the parameter. The data packetizer 422 assembles
the sensor data into packets; this includes sensor information
received or processed by ASIC 420. The ASIC 420 can comprise
specific modules for efficiently performing core signal processing
functions of the medical device communications components 410. The
ASIC 420 provides the further benefit of reducing the form factor
of sensing insert device 100 to meet dimensional requirements for
integration into temporary or permanent prosthetic components.
[0065] The CRC circuit 418 applies error code detection on the
packet data. The cyclic redundancy check is based on an algorithm
that computes a checksum for a data stream or packet of any length.
These checksums can be used to detect interference or accidental
alteration of data during transmission. Cyclic redundancy checks
are especially good at detecting errors caused by electrical noise
and therefore enable robust protection against improper processing
of corrupted data in environments having high levels of
electromagnetic activity. The telemetry transmitter 416 then
transmits the CRC encoded data packet through the matching network
414 by way of the antenna 412. The matching networks 414 and 454
provide an impedance match for achieving optimal communication
power efficiency.
[0066] The receiving system communications components 450 receive
transmission sent by medical device communications components 410.
In one embodiment, telemetry transmitter 416 is operated in
conjunction with a dedicated telemetry receiver 456 that is
constrained to receive a data stream broadcast on the specified
frequencies in the specified mode of emission. The telemetry
receiver 456 by way of the receiving station antenna 452 detects
incoming transmissions at the specified frequencies. The antenna
452 can be a directional antenna that is directed to a directional
antenna of components 410. Using at least one directional antenna
can reduce data corruption while increasing data security by
further limiting where the data is radiated. A matching network 454
couples to antenna 452 to provide an impedance match that
efficiently transfers the signal from antenna 452 to telemetry
receiver 456. Telemetry receiver 456 can reduce a carrier frequency
in one or more steps and strip off the information or data sent by
components 410. Telemetry receiver 456 couples to CRC circuit 458.
CRC circuit 458 verifies the cyclic redundancy checksum for
individual packets of data. CRC circuit 458 is coupled to data
packetizer 460. Data packetizer 460 processes the individual
packets of data. In general, the data that is verified by the CRC
circuit 458 is decoded (e.g., unpacked) and forwarded to an
external data processing device, such as an external computer, for
subsequent processing, display, or storage or some combination of
these.
[0067] The telemetry receiver 456 is designed and constructed to
operate on very low power such as, but not limited to, the power
available from the powered USB port 462, or a battery. In another
embodiment, the telemetry receiver 456 is designed for use with a
minimum of controllable functions to limit opportunities for
inadvertent corruption or malicious tampering with received data.
The telemetry receiver 456 can be designed and constructed to be
compact, inexpensive, and easily manufactured with standard
manufacturing processes while assuring consistently high levels of
quality and reliability.
[0068] In one configuration, the communication system 400 operates
in a transmit-only operation with a broadcasting range on the order
of a few meters to provide high security and protection against any
form of unauthorized or accidental query. The transmission range
can be controlled by the transmitted signal strength, antenna
selection, or a combination of both. A high repetition rate of
transmission can be used in conjunction with the Cyclic Redundancy
Check (CRC) bits embedded in the transmitted packets of data during
data capture operations thereby enabling the receiving system 110
to discard corrupted data without materially affecting display of
data or integrity of visual representation of data, including but
not limited to measurements of load, force, pressure, displacement,
flexion, attitude, and position within operating or static physical
systems.
[0069] By limiting the operating range to distances on the order of
a few meters the telemetry transmitter 416 can be operated at very
low power in the appropriate emission mode or modes for the chosen
operating frequencies without compromising the repetition rate of
the transmission of data. This mode of operation also supports
operation with compact antennas, such as an integrated loop
antenna. The combination of low power and compact antennas enables
the construction of, but is not limited to, highly compact
telemetry transmitters that can be used for a wide range of
non-medical and medical applications. Examples of potential medical
applications may include, but are not limited to, implantable
devices, modules within implantable devices, intra-operative
implants or modules within intra-operative implants or trial
inserts, modules within inserted or ingested devices, modules
within wearable devices, modules within handheld devices, modules
within instruments, appliances, equipment, or accessories of all of
these, or disposables within implants, trial inserts, inserted or
ingested devices, wearable devices, handheld devices, instruments,
appliances, equipment, or accessories to these devices,
instruments, appliances, or equipment.
[0070] The transmitter security as well as integrity of the
transmitted data is assured by operating the telemetry system
within predetermined conditions. The security of the transmitter
cannot be compromised because it is operated in a transmit-only
mode and there is no pathway to hack into medical device
communications components 410. The integrity of the data is assured
with the use of the CRC algorithm and the repetition rate of the
measurements. The risk of unauthorized reception of the data is
minimized by the limited broadcast range of the device. Even if
unauthorized reception of the data packets should occur there are
counter measures in place that further mitigate data access. A
first measure is that the transmitted data packets contain only
binary bits from a counter along with the CRC bits. A second
measure is that no data is available or required to interpret the
significance of the binary value broadcast at any time. A third
measure that can be implemented is that no patient or device
identification data is broadcast at any time.
[0071] The telemetry transmitter 416 can also operate in accordance
with some FCC regulations. According to section 18.301 of the FCC
regulations the ISM bands within the USA include 6.78, 13.56,
27.12, 30.68, 915, 2450, and 5800 MHz as well as 24.125, 61.25,
122.50, and 245 GHz. Globally other ISM bands, including 433 MHz,
are defined by the International Telecommunications Union in some
geographic locations. The list of prohibited frequency bands
defined in 18.303 are "the following safety, search and rescue
frequency bands is prohibited: 490-510 kHz, 2170-2194 kHz,
8354-8374 kHz, 121.4-121.6 MHz, 156.7-156.9 MHz, and 242.8-243.2
MHz." Section 18.305 stipulates the field strength and emission
levels ISM equipment must not exceed when operated outside defined
ISM bands. In summary, it may be concluded that ISM equipment may
be operated worldwide within ISM bands as well as within most other
frequency bands above 9 KHz given that the limits on field
strengths and emission levels specified in section 18.305 are
maintained by design or by active control. As an alternative,
commercially available ISM transceivers, including commercially
available integrated circuit ISM transceivers, may be designed to
fulfill these field strengths and emission level requirements when
used properly.
[0072] In one configuration, the telemetry transmitter 416 can also
operate in unlicensed ISM bands or in unlicensed operation of low
power equipment, wherein the ISM equipment (e.g., telemetry
transmitter 416) may be operated on ANY frequency above 9 kHz
except as indicated in Section 18.303 of the FCC code.
[0073] Wireless operation eliminates distortion of, or limitations
on, measurements caused by the potential for physical interference
by, or limitations imposed by, wiring and cables connecting the
wireless sensing module or device with a power source or with data
collection, storage, or display equipment. Power for the sensing
components and electronic circuits is maintained within the
wireless sensing module or device on an internal energy storage
device. This energy storage device is charged with external power
sources including, but not limited to, a battery or batteries,
super capacitors, capacitors, an alternating current power supply,
a radio frequency receiver, an electromagnetic induction coil, a
photoelectric cell or cells, a thermocouple or thermocouples, or an
ultrasound transducer or transducers. The wireless sensing module
may be operated with a single charge until the internal energy
source is drained or the energy source may be recharged
periodically to enable continuous operation. The embedded power
supply minimizes additional sources of energy radiation required to
power the wireless sensing module or device during measurement
operations. Telemetry functions are also integrated within the
wireless sensing module or device. Once initiated the telemetry
transmitter continuously broadcasts measurement data in real time.
Telemetry data may be received and decoded with commercial
receivers or with a simple, low cost custom receiver.
[0074] FIG. 7 is an illustration of a block model diagram 500 of
the sensing module 200 in accordance with an exemplary embodiment.
In particular, the diagram 500 shows where certain components are
replaced or supplemented with one or more Application Specific
Integrated Circuits (ASICs). Referring briefly to FIG. 5,
electronic circuitry 307 is coupled to the one or more sensing
assemblages and includes circuitry that can control sensor
operations. Electronic circuitry 307 includes multiple channels
that can operate more than one device. Sensing module 200 is
optimized to operate under severe power constraints. Electronic
circuitry 307 includes power management circuitry that controls
power up, power down, and minimizes power usage through the control
of individual blocks. The architecture is designed to enable only
blocks required for the current operation.
[0075] Referring back to FIG. 7, the ASIC provides significant
benefit in reducing power requirements allowing the module 200 to
be powered by a temporary power source such as a super capacitor or
capacitor. The ASIC and super capacitor have a small form factor
allowing module 200 to be integrated within a temporary or
permanent prosthetic component. Module 200 incorporates one or more
sensors comprising at least one transducer and a compressible
media, the operation of which is disclosed in detail herein. As
shown, a sensing assemblage comprises a transducer 502,
compressible propagation structure 504, and a transducer 506. It
should be noted that other sensors such as MEMS devices, strain
gauges, and piezo-resistive sensors can be used with the ASIC. In
particular, the ASIC incorporates A/D and D/A circuitry (not shown)
to digitize current and voltage output from these types of sensing
components. Transducers 502 and 506 operatively couple to
compressible propagation structure 504. In a non-limiting example,
transducer 506 to emits energy waves into compressible structure
504 while transducer 502 detects propagated energy waves.
Compressible propagation structure 504 is coupled to a load bearing
or contacting surface 508 and an encapsulating enclosure 510 of
sensing module 200. A parameter to be measured is applied to either
contacting surface 508, encapsulating enclosure 510, or both. In
one embodiment, springs 560 couple to contacting surface 508 and
encapsulating enclosure 510 to support compressible propagation
structure 504. In particular, springs 560 prevent cantilevering of
contacting surface 508, reduce hysteresis caused by material
properties of compressible propagation structure 504, and improve
sensor response time to changes in the applied parameter.
[0076] In one embodiment, a first ASIC includes a charging circuit
514 and power management circuitry 518. The power management
circuitry 518 couples to the charging circuit, other blocks of the
ASIC and external components/circuitry to minimize power
consumption of the integrated circuit. The charging circuit 514
operatively couples to an induction coil 512 and energy storage
516. In a non-limiting example, induction coil 512 couples to an
external coil that provides energy to charge energy storage 516.
Induction coil 512 and the external coil are placed in proximity to
each other thereby electro-magnetically coupling to one another.
Induction coil 512 is coupled to energy storage 516. Charging
circuit 514 controls the charging of energy storage 516. Charging
circuit 514 can determine when charging is complete, monitor power
available, and regulate a voltage provided to the operational
circuitry. Charging circuit 514 can charge a battery in sensing
module 200. Alternatively, a capacitor or super capacitor can be
used to power the first ASIC for a time sufficient to acquire the
desired measurements. A capacitor has the benefit of a long or
indefinite shelf life and fast charge time. In either charging
scenario, energy from the external coil is coupled to the induction
coil 512. The energy from induction coil 512 is then stored in a
medium such as a battery or capacitor.
[0077] The first ASIC further includes circuitry to operate and
capture data from the sensing assemblages. A parameter to be
measured is applied to compressible propagation structure 504. As
an example of parameter measurement, a force, pressure, or load is
applied across contacting surface 508 and encapsulating enclosure
510. The force, pressure, or load affects the length of the
compressible propagation structure 504. The circuitry on the first
ASIC forms a positive closed loop feedback circuit that maintains
the emission, propagation, and detection of energy waves in the
compressible propagation structure 504. The first ASIC operatively
couples to transducers 502 and 506 to control the positive closed
loop feedback circuit that is herein called a propagation tuned
oscillator (PTO). The first ASIC measures a transit time,
frequency, or phase of propagated energy waves. The measurement is
used to determine the length of compressible propagation structure
504. The energy waves emitted into compressible propagation
structure 504 can be continuous or pulsed. The energy waves can
propagate by a direct path or be reflected.
[0078] The first ASIC comprises an oscillator 520, a switch 522,
driver 524, matching network 526, MUX 528, and control circuit 536.
The oscillator 520 is used as a reference clock for the ASIC and
enables the PTO to begin emission of energy waves into the
compressible propagation structure 504. Oscillator 520 in the first
ASIC can be coupled to an external component such as a crystal
oscillator to define and provide a stable frequency of operation.
Switch 522 couples the oscillator 520 to MUX 528. Control circuit
536 operatively enables MUX 528 and switch 522 to couple oscillator
520 to driver 524 during a startup sequence. Driver 524 and
matching network 526 couple to transducer 506. Driver 524 drives
transducer 506 to emit an energy wave. Matching network 526
impedance matches driver 524 to the transducer 506 to reduce power
consumption during energy wave emission.
[0079] In one embodiment, transducer 506 emits one or more energy
waves into the compressible propagation structure 504 at a first
location. Transducer 506 is located at a second location of
compressible propagation structure 504. Transducer 506 detects
propagated energy waves at the second location and generates a
signal corresponding to the propagated energy waves. The first ASIC
further comprises a MUX 530, pre-amplifier 532 (e.g. preamp 532)
and a zero-crossing receiver or edge detect receiver. Zero-crossing
receiver or edge-detect receiver comprise detect circuit 534.
Control circuit 536 enables MUX 530 to couple transducer 502 to
preamp 532. Preamp 532 amplifies a signal output by transducer 502
corresponding to a propagated energy wave. In a non-limiting
example, the first ASIC comprises both a zero-crossing receiver and
an edge detect receiver. More multiplexing circuitry in conjunction
with control circuit 536 can be incorporated on the first ASIC to
select between the circuits. Similarly, multiplexing circuitry can
be used to couple and operate more than one sensor. The amplified
signal from preamp 532 is coupled to detection circuit 534.
Zero-crossing receiver is a detection circuit that identifies a
propagated energy wave by sensing a transition of the signal. A
requirement of detection can be that the signal has certain
transition and magnitude characteristics. The edge-detect receiver
detects a propagated energy wave by identifying a wave front of the
propagated energy wave. The zero-crossing receiver or edge-detect
receiver outputs a pulse in response to the detection of a
propagated energy wave.
[0080] Positive closed loop feedback is applied upon detection of
an energy wave after the startup sequence. Control circuit 536
decouples oscillator 520 from driver 524 through switch 522 and MUX
528. Control circuit 536 operatively enables switch 558 and MUX 528
to couple detection circuit 534 to driver 524. A pulse generated by
detection circuit 534 initiates the emission of a new energy wave
into compressible propagation structure 504. The pulse from
detection circuit 534 is provided to driver 524. The positive
closed loop feedback of the circuitry maintains the emission,
propagation, and detection of energy waves in propagation structure
504.
[0081] The first ASIC further comprises a loop counter 538, time
counter 540, register 542, and ADC 556. Loop counter 538, time
counter 540, and register 542 are operatively coupled to control
circuit 536 to generate a precise measurement of the transit time,
frequency, or phase of propagated energy waves during a measurement
sequence. In one embodiment, a measurement comprises a
predetermined number of energy waves propagating through the
compressible propagation structure 504. The predetermined number is
set in the loop counter 538. The loop counter 538 is decremented by
each pulse output by detection circuit 534 that corresponds to a
detected propagated energy wave. The positive closed loop feedback
is broken when counter 538 decrements to zero thereby stopping the
measurement. Time counter 540 measures a total propagation time of
the predetermined number of propagated energy waves set in loop
counter 538. The measured total propagation time divided by the
predetermined number of propagated energy waves is a measured
transit time of an energy wave. The measured transit time can be
precisely converted to a length of compressible propagation
structure 504 under a stable condition of the applied parameter on
the sensing assemblage. The applied parameter value can be
calculated by known relationship between the length of compressible
propagation structure 504 and the parameter. A result of the
measurement is stored in register 542 when loop counter 538
decrements to zero. More than one measurement can be performed and
stored. In one embodiment, the precision can be increased by
raising the number of propagated energy waves being measured in
loop counter 538.
[0082] In the example, energy waves are propagated from transducer
506 to transducer 5. Alternatively, control circuit 536 can direct
the propagation of energy waves from transducer 502 to transducer
506 whereby transducer 502 emits energy waves and transducer 506
detects propagated energy waves. An analog to digital converter
(ADC) 556 is shown coupled to an accelerometer 554. ADC 556 is a
circuit on the first ASIC. It can be used to digitize an output
from a circuit such as accelerometer 554. Accelerometer 554 can be
used to detect and measure when sensing module 200 is in motion.
Data from accelerometer 554 can be used to correct the measured
result to account for module 200 acceleration. ADC 556 can also be
used to provide measurement data from other sensor types by
providing a digitized output corresponding to voltage or current
magnitude.
[0083] A second ASIC can comprise CRC circuit 546, telemetry
transmitter 548, and matching network 508. The CRC circuit 546
applies error code detection on the packet data such as data stored
in register 542. The cyclic redundancy check computes a checksum
for a data stream or packet of any length. The checksums are used
to detect interference or accidental alteration of data during
transmission. Transmitter 548 is coupled to CRC 546 and sends the
data wirelessly. Matching network 550 couples telemetry transmitter
512 to antenna 552 to provide an impedance match to efficiently
transfer the signal to the antenna 552. As disclosed above, the
integration of the telemetry transmitter and sensor modules enables
construction of a wide range of sizes of the sensing module 200.
This facilitates capturing data, measuring parameters of interest
and digitizing that data, and subsequently communicating that data
to external equipment with minimal disturbance to the operation of
the body, instrument, appliance, vehicle, equipment, or physical
system for a wide range of applications. Moreover, the level of
accuracy and resolution achieved by the total integration of
communication components, transducers, waveguides, and oscillators
to control the operating frequency of the ultrasound transducers
enables the compact, self-contained measurement module
construction. In a further embodiment, the circuitry on the first
and second ASICs can be combined on a single ASIC to further reduce
form factor, power, and cost.
[0084] FIG. 8 is an exemplary assemblage 800 that illustrates
propagation of ultrasound waves 810 within the waveguide 806 in the
bi-directional mode of operation of this assemblage. In this mode,
the selection of the roles of the two individual ultrasound
resonators (802, 804) or transducers affixed to interfacing
material 820 and 822, if required, are periodically reversed. In
the bi-directional mode the transit time of ultrasound waves
propagating in either direction within the waveguide 806 can be
measured. This can enable adjustment for Doppler effects in
applications where the sensing module 808 is operating while in
motion 816. 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 816. An advantage is provided in situations
wherein the body, instrument, appliance, vehicle, equipment, or
other physical system 814, 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 812 of the body, instrument,
appliance, vehicle, equipment, or other physical system being
measured to be in motion 816 during sensing of load, force,
pressure, or displacement. Other adjustments to the measurement for
physical changes to system 814 are contemplated and can be
compensated for in a similar fashion. For example, temperature of
system 814 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.
[0085] The use of waveguide 806 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.
[0086] Referring back to FIG. 2, although not explicitly
illustrated, it should be noted that the load insert sensing device
100 and associated internal components move in accordance with
motion of the femur 108 as shown. The bi-directional operating mode
of the waveguide mitigates the Doppler effects resulting from the
motion. As previously indicated, incorporating data from the
accelerometer 121 with data from the other components of the
sensing module 200 helps assure accurate measurement of the applied
load, force, pressure, displacement, density, localized
temperature, or viscosity by enabling computation of adjustments to
offset this external motion.
[0087] 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.
[0088] 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.
[0089] FIG. 9 is an exemplary cross-sectional view of a sensor
element 900 to illustrate changes in the propagation of ultrasound
waves 914 with changes in the length of a waveguide 906. 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 908 compresses waveguide 906 thereby
changing the length of waveguide 906. Sensing circuitry (not shown)
measures propagation characteristics of ultrasonic signals in the
waveguide 906 to determine the change in the length of the
waveguide 906. 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.
[0090] As previously discussed, external forces applied to the
sensing module 200 compress the waveguide(s) thereby changing the
length of the waveguide(s). The sensing module 200 measures
propagation characteristics of ultrasonic signals in the
waveguide(s) to determine the change in the length of the
waveguide(s). These changes in length change in direct proportion
to the parameters of interest thus enabling the conversion of
changes in the parameter or parameters of interest into load (or
force) information.
[0091] As illustrated, external force 908 compresses waveguide 906
and pushes the transducers 902 and 904 closer to one another by a
distance 910. This changes the length of waveguide 906 by distance
912 of the waveguide propagation path between transducers 902 and
904. Depending on the operating mode, the sensing circuitry
measures the change in length of the waveguide 906 by analyzing
characteristics of the propagation of ultrasound waves within the
waveguide.
[0092] One interpretation of FIG. 9 illustrates waves emitting from
transducer 902 at one end of waveguide 906 and propagating to
transducer 904 at the other end of the waveguide 906. The
interpretation includes the effect of movement of waveguide 906 and
thus the velocity of waves propagating within waveguide 906
(without changing shape or width of individual waves) and therefore
the transit time between transducers 902 and 904 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.
[0093] 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.
[0094] 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 906. As will be
described below, positive feedback closed-loop circuit operation in
continuous wave (CW) mode adjusts the frequency of ultrasonic waves
914 in the waveguide 906 to maintain a same number or integer
number of periods of ultrasonic waves in the waveguide 906. 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.
[0095] In a pulse mode of operation, the phase detector measures a
time of flight (TOF) between when an ultrasonic pulse is
transmitted by transducer 902 and received at transducer 904. The
time of flight determines the length of the waveguide propagating
path, and accordingly reveals the change in length of the waveguide
906. In another arrangement, differential time of flight
measurements (or phase differences) can be used to determine the
change in length of the waveguide 906. A pulse consists of a pulse
of one or more waves. The waves may have equal amplitude and
frequency (square wave pulse) or they may have different
amplitudes, for example, decaying amplitude (trapezoidal pulse) or
some other complex waveform. The PTO is holding the phase of the
leading edge of the pulses propagating through the waveguide
constant. In pulse mode operation the PTO detects the leading edge
of with an edge-detect receiver rather than a zero-crossing or
transition as detected by a zero-crossing receiver used in CW
mode.
[0096] 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.
[0097] FIG. 10 is an exemplary block diagram 1000 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.
[0098] Recall that the load sensing insert device 100 when in
motion measures forces on the sensing assemblies by evaluating
propagation times of energy waves within the waveguides in
conjunction with the accelerometer data. The propagation tuned
oscillator (PTO) 4 measures a transit time of ultrasound waves 2
within the waveguide 3 in a closed-loop configuration. The digital
counter 20 determines the physical change in the length of the
waveguide. Referring to FIG. 5, the one or more accelerometers 302
determines the changes along x, y and z dimensions. The electronic
circuitry 307 in view of the accelerometer data from accelerometer
302 and the physical changes in length of the sensing assemblage 1
determines the applied loading (or forces).
[0099] 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.
[0100] 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.
[0101] 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.
[0102] 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.
[0103] The block diagram 1000 further includes counting and timing
circuitry. More specifically, the timing, counting, and clock
circuitry comprises a digital counter 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.
[0104] 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.
[0105] 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.
[0106] 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.
[0107] 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.
[0108] 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).
[0109] 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.
[0110] 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.
[0111] 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.
[0112] 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.
[0113] In general, measurement of the changes in the physical
length of individual waveguides can be made in several modes. Each
assemblage of one or two ultrasound resonators or transducers
combined with a waveguide can be controlled to operate in six
different modes. This includes two wave shape modes: continuous
wave or pulsed waves, and three propagation modes: reflectance,
unidirectional, and bi-directional propagation of the ultrasound
wave. In all modes of operation the changes in transit time within
the ultrasound waveguides change the operating frequency of the
propagation tuned oscillator 4 or oscillators. These changes in the
frequency of oscillation of the propagation tuned oscillator or
oscillators can be measured rapidly and with high resolution. This
achieves the required measurement accuracy and precision thus
enabling the capture of changes in the physical parameters of
interest and enabling analysis of the dynamic and static behavior
of the physical system or body.
[0114] 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.
[0115] FIG. 11 is a cross-sectional view of a layout architecture
of the sensing module 200 in accordance with an exemplary
embodiment. The blocks are operatively coupled together within the
encapsulated enclosure of the sensing module 200 and together form
an encapsulated force sensor 1100. It comprises a top steel plate
1104 coupled to a lower printed circuit board (PCB) 1118 by way of
spring retainer 1106, disc spring 1108, and spring post 1114. The
force sensor 1100 is biased with springs or other means of elastic
support to accurately maintain a required distance between the load
bearing or contact surfaces such as top cover 1102 and to minimize
hysteresis due to material properties of waveguide 1110.
[0116] The encapsulating force sensor 1100 supports and protects
the specialized mechanical and electronic components from external
physical, mechanical, chemical, and electrical, and electromagnetic
intrusion that might compromise sensing or communication operations
of the module or device. The encapsulating force sensor 1100 also
supports internal mechanical and electronic components and
minimizes adverse physical, mechanical, electrical, and ultrasonic
interactions that might compromise sensing or communication
operations of the module or device. Top cover 1102 and unitary main
body 1157 form the encapsulating enclosure. Unitary main body 1157
is a metal, plastic, or polymer body having sufficient strength and
rigidity to withstand forces, pressures, and loads of the
muscular-skeletal system. In particular, the sidewalls or bottom
surface do not deform under normal operating conditions. For
example, the unitary main body 1157 can be formed of polycarbonate
or other bio-compatible material. Moreover, unitary main body 1157
can be molded in a manufacturing process that allows detailed
features to be repeatably and reliably manufactured.
[0117] The physical layout architecture of sensor 1100 has the one
or more sensing assemblages overlying the electronic circuitry. A
force, pressure, or load is applied to a surface of sensor 1100.
The surface of sensor 1100 corresponds to top steel plate 1104.
Steel plate 1104 moves in response to a force, pressure, or load.
The steel plate 1104 can support the movement while maintaining a
seal with unitary main body 1157 that isolates an interior of the
enclosure. In general, a sensing assemblage is coupled between
steel plate 1104 and a substrate 1130. Substrate 1130 is a rigid
non-moveable substrate that is supported by the sidewalls of
unitary main body 1157. A periphery of substrate 1130 is in contact
with and supported by a support feature 1128 formed in the
sidewalls of unitary main body 1157. Substrate 1130 does not flex
under loading. The sensing assemblage translates a displacement due
to the force, pressure, or load applied to steel plate 1104 to a
signal. The signal is processed by electronic circuitry in the
enclosure to generate data corresponding to the force, pressure, or
load value. As shown, the sensing assemblage comprises upper piezo
1112, waveguide 1110, and lower piezo 1124. Upper piezo 1112 and
lower piezo 1124 are ultrasonic piezo-electric transducers.
[0118] Electronic circuitry to power, control, interface, operate,
measure, and send sensor data is interconnected together on a
printed circuit board (PCB) 1118. One or more cups 1120 are formed
in unitary main body 1157. In one embodiment, the components
mounted on PCB 1118 reside within cups 1120. One or more structures
1126 support and fix the position of the PCB 1118. The components
on PCB 1118 are suspended in the cups 1120 and do not have contact
with unitary main body 1157 thereby preventing interconnect stress
that could result in long-term reliability issues. The PCB 1118 is
mechanically isolated from substrate 1130. Thus, any force,
pressure, or loading on substrate 1130 is not applied to PCB 1118.
Flexible interconnect is used to connect from the electronic
circuitry on PCB 1118 to upper piezo 1112 and lower piezo 1124.
[0119] In one embodiment, more than one sensing assemblage couples
to predetermined locations of the steel plate 1104. Each sensing
assemblage can measure a parameter applied to steel plate 1104. In
combination, the sensing assemblages can determine a location or
region where the parameter is applied to the surface. For example,
the magnitude and position of the loading on the contacting surface
of sensing module 200 applied by femur 102 and tibia 108 to sensing
module 200 can be measured and displayed as shown in FIG. 2. In a
non-limiting example, three sensing assemblages can be spaced on a
periphery of steel plate 1104. In the example, each sensing
assemblage will measure a force applied to steel plate 1104. The
location of the applied force is closest to the sensing assemblage
detecting the highest force magnitude. Conversely, the sensing
assemblage detecting the weakest force magnitude is farthest from
the applied force. The measured force magnitudes in combination
with the predetermined locations where the sensing assemblages
couple to steel plate 1104 can be used to determine a location
where the parameter is applied.
[0120] The housing electrically insulates the internal electronic,
sensing, and communication components. The encapsulating force
sensor 1100 eliminates parasitic paths that might conduct
ultrasonic energy and compromise excitation and detection of
ultrasound waves within the sensing assemblages during sensing
operations. A temporary bi-directional electrical interconnect
assures a high level of electrical observation and controllability
of the electronic assembly within the encapsulating force sensor
1100. The temporary interconnect also provides a high level of
electrical observation of the sensing subsystem, including the
transducers, waveguides, and mechanical spring or elastic
assembly.
[0121] Ultrasound waveguide 1110 is coupled to the top cover 1102.
A force applied to the top cover 1102 compresses waveguide 1110.
Lower piezo 1124 and upper piezo 1112 are piezo-electric
transducers respectively coupled to waveguide 1110 at a first and
second location. Waveguide 1110 is a compressible propagation
medium for ultrasonic energy waves. The transducers emit energy
waves and detect propagated energy waves in waveguide 1110.
Electronic circuitry is coupled to lower piezo 1124 and upper piezo
1112 to measure transit time, frequency, or phase of the propagated
energy waves. The transit time, frequency, or phase of energy waves
propagating between the first and second locations of waveguide
1110 can be precisely measured and therefore the length of the
ultrasound waveguide 1110. The length of waveguide 1110 is
calculated by a known function relating material properties of the
waveguide 1110 to the parameter being measured. In the example, a
force, pressure, or load is calculated from the measured length of
waveguide 1110.
[0122] The encapsulated force sensor 1100 can accurately and
repeatedly measure one pound changes in load with changes in length
of a waveguide comprising 2.5 microns. The maximum change in the
present implementation is specified at less than 5.0 microns. This
assures that the size of the sensing module 200 throughout all
measurements remains within the required dimension (e.g., distance)
of the insert between the load bearing surfaces of the prosthetic
components.
[0123] An exemplary level of control of the compression or
displacement of the waveguides 1110 with changes in load, force,
pressure, or displacement is achieved by positioning the spring or
springs 1108 or other means of elastic support, including the
waveguides 1110 themselves, between the load bearing contact
surfaces to minimize any tendency of the load bearing contact
surfaces to cantilever. Cantilevering can compromise the accuracy
of the inclination of the load bearing contact surface whenever
load, force, pressure, or displacement is applied to any point near
a periphery of the load bearing contact surfaces. In one
embodiment, springs 1108 are disc springs. The spring 1108 is held
in a predetermined location by spring post 1114 and spring retainer
1104.
[0124] The walls of the unitary main body 1157 include a small gap
to enable the steel plate 1104 to move. The hermetic seal is also
flexible to allow the steel plate 1104 of the force sensor 1104 to
slide up and down, like a piston, for distances on the order of a
hundred microns without compromising integrity of the seal. The
hermetic seal completes manufacturing, sterilization, and packaging
processes without compromising ability to meet regulatory
requirements for hermeticity. The level of hermeticity is
sufficient to assure functionality and biocompatibility over the
lifetime of the device. Implant devices with total implant time
less than 24 hours may have less stringent regulatory requirements
for hermeticity. Unbiased electrical circuitry is less susceptible
to damage from moisture. The electronics in one embodiment are only
powered during actual usage. In another embodiment, the
encapsulated force sensor 1100 employs low duty cycles to serve as
a measurement-on-demand device to efficiently perform at low total
operating time when the electronics are powered on.
[0125] The encapsulating force sensor 1100 has a compact size
permitting it to fit for example within a trial insert, final
insert, prosthetic component, tool, equipment, or implant structure
to measure the level and incidence of the load on subsequent
implanted prosthetic devices. It can be constructed using standard
components and manufacturing processes. Manufacturing carriers or
fixtures can be designed to emulate the final encapsulating
enclosure of the sensing module 200. Calibration data can be
obtained during the manufacturing processing thus enabling capture
of accurate calibration data. These calibration parameters can be
stored within the memory circuits integrated into the electronics
assemblage of the sensing module 200. Testability and calibration
further assures the quality and reliability of the encapsulated
enclosure.
[0126] Examples of a wide range of potential medical applications
can include, but are not limited to, implantable devices, modules
within implantable devices, intra-operative implants or modules
within intra-operative implants or trial inserts, modules within
inserted or ingested devices, modules within wearable devices,
modules within handheld devices, modules within instruments,
appliances, equipment, or accessories of all of these, or
disposables within implants, trial inserts, inserted or ingested
devices, wearable devices, handheld devices, instruments,
appliances, equipment, or accessories to these devices,
instruments, appliances, or equipment.
[0127] 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.
* * * * *