WIRELESS SENSING MODULE FOR SENSING A PARAMETER OF THE MUSCULAR-SKELETAL SYSTEM
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.
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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.
FIELDThe 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.
BACKGROUNDThe skeletal system of a mammal is subject to variations among species. Further changes can occur due to environmental factors, degradation through use, and aging. An orthopedic joint of the skeletal system typically comprises two or more bones that move in relation to one another. Movement is enabled by muscle tissue and tendons attached to the skeletal system of the joint. Ligaments hold and stabilize the one or more joint bones positionally. Cartilage is a wear surface that prevents bone-to-bone contact, distributes load, and lowers friction.
There has been substantial growth in the repair of the human skeletal system. In general, orthopedic joints have evolved using information from simulations, mechanical prototypes, and patient data that is collected and used to initiate improved designs. Similarly, the tools being used for orthopedic surgery have been refined over the years but have not changed substantially. Thus, the basic procedure for replacement of an orthopedic joint has been standardized to meet the general needs of a wide distribution of the population. Although the tools, procedure, and artificial joint meet a general need, each replacement procedure is subject to significant variation from patient to patient. The correction of these individual variations relies on the skill of the surgeon to adapt and fit the replacement joint using the available tools to the specific circumstance.
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:
Embodiments of the invention are broadly directed to measurement of physical parameters. Many physical parameters of interest within physical systems or bodies can be measured by evaluating changes in the characteristics of energy waves or pulses. As one example, changes in the transit time or shape of an energy wave or pulse propagating through a changing medium can be measured to determine the forces acting on the medium and causing the changes. The propagation velocity of the energy waves or pulses in the medium is affected by physical changes in of the medium. The physical parameter or parameters of interest can include, but are not limited to, measurement of load, force, pressure, displacement, density, viscosity, localized temperature. These parameters can be evaluated by measuring changes in the propagation time of energy pulses or waves relative to orientation, alignment, direction, or position as well as movement, rotation, or acceleration along an axis or combination of axes by wireless sensing modules or devices positioned on or within a body, instrument, appliance, vehicle, equipment, or other physical system.
In all of the examples illustrated and discussed herein, any specific materials, temperatures, times, energies, etc. for process steps or specific structure implementations should be interpreted to illustrative only and non-limiting. Processes, techniques, apparatus, and materials as known by one of ordinary skill in the art may not be discussed in detail but are intended to be part of an enabling description where appropriate.
Note that similar reference numerals and letters refer to similar items in the following figures. In some cases, numbers from prior illustrations will not be placed on subsequent figures for purposes of clarity. In general, it should be assumed that structures not identified in a figure are the same as previous prior figures.
In the present invention these parameters are measured with an integrated wireless sensing module or device comprising an i) encapsulating structure that supports sensors and contacting surfaces and ii) an electronic assemblage that integrates a power supply, sensing elements, ultrasound resonator or resonators or transducer or transducers and ultrasound waveguide or waveguides, biasing spring or springs or other form of elastic members, an accelerometer, antennas and electronic circuitry that processes measurement data as well as controls all operations of energy conversion, propagation, and detection and wireless communications. The wireless sensing module or device can be positioned on or within, or engaged with, or attached or affixed to or within, a wide range of physical systems including, but not limited to instruments, appliances, vehicles, equipments, or other physical systems as well as animal and human bodies, for sensing and communicating parameters of interest in real time.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Incorporating data from the accelerometer 122 with data from the other sensing components 121 and 123 assures accurate measurement of the applied load, force, pressure, or displacement by enabling computation of adjustments to offset this external motion. This capability can be required in situations wherein the body, instrument, appliance, vehicle, equipment, or other physical system, is itself operating or moving during sensing of load, pressure, or displacement. This capability can also be required in situations wherein the body, instrument, appliance, vehicle, equipment, or other physical system, is causing the portion of the body, instrument, appliance, vehicle, equipment, or other physical system being measured to be in motion during sensing of load, pressure, or displacement.
The accelerometer 122 can operate singly, as an integrated unit with the load sensing platform 121, and/or as an integrated unit with the sensing assemblies 123. Integrating one or more accelerometers 122 within the sensing assemblages 123 to determine position, attitude, movement, or acceleration of sensing assemblages 123 enables augmentation of presentation of data to accurately identify, but not limited to, orientation or spatial distribution of load, force, pressure, displacement, density, or viscosity, or localized temperature by controlling the load and position sensing assemblages to measure the parameter or parameters of interest relative to specific orientation, alignment, direction, or position as well as movement, rotation, or acceleration along any axis or combination of axes. Measurement of the parameter or parameters of interest may also be made relative to the earth's surface and thus enable computation and presentation of spatial distributions of the measured parameter or parameters relative to this frame of reference.
In one embodiment, the accelerometer 122 includes direct current (DC) sensitivity to measure static gravitational pull with load and position sensing assemblages to enable capture of, but not limited to, distributions of load, force, pressure, displacement, movement, rotation, or acceleration by controlling the sensing assemblages to measure the parameter or parameters of interest relative to orientations with respect to the earths surface or center and thus enable computation and presentation of spatial distributions of the measured parameter or parameters relative to this frame of reference.
Embodiments of device 100 are broadly directed to measurement of physical parameters, and more particularly, to evaluating changes in the transit time of a pulsed energy wave propagating through a medium. In-situ measurements during orthopedic joint implant surgery would be of substantial benefit to verify an implant is in balance and under appropriate loading or tension. In one embodiment, the instrument is similar to and operates familiarly with other instruments currently used by surgeons. This will increase acceptance and reduce the adoption cycle for a new technology. The measurements will allow the surgeon to ensure that the implanted components are installed within predetermined ranges that maximize the working life of the joint prosthesis and reduce costly revisions. Providing quantitative measurement and assessment of the procedure using real-time data will produce results that are more consistent. A further issue is that there is little or no implant data generated from the implant surgery, post-operatively, and long term. Device 100 can provide implant status data to the orthopedic manufacturers and surgeons. Moreover, data generated by direct measurement of the implanted joint itself would greatly improve the knowledge of implanted joint operation and joint wear thereby leading to improved design and materials.
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.
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.
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.
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.
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.
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.
The sensing assemblage 303 can be positioned, engaged, attached, or affixed to the contact surfaces 306. Mechanical supports 315 serve to provide proper balancing of contact surfaces 306. In at least one exemplary embodiment, contact surfaces 306 are load-bearing surfaces. In general, the propagation structure 305 is subject to the parameter being measured. Surfaces 306 can move and tilt with changes in applied load; actions which can be transferred to the sensing assemblages 303 and measured by the electronic circuitry 307. The electronic circuitry 307 measures physical changes in the sensing assemblage 303 to determine parameters of interest, for example a level, distribution and direction of forces acting on the contact surfaces 306. In general, the sensing module is powered by the energy storage 330.
As one example, the sensing assemblage 303 can comprise an elastic or compressible propagation structure 305 between a transducer 304 and a transducer 314. In the current example, transducer 304 can be an ultrasound (or ultrasonic) resonator, and the elastic or compressible propagation structure 305 can be an ultrasound (or ultrasonic) waveguide (or waveguides). The electronic circuitry 307 is electrically coupled to the sensing assemblages 303 and translates changes in the length (or compression or extension) of the sensing assemblages 303 to parameters of interest, such as force. It measures a change in the length of the propagation structure 305 (e.g., waveguide) responsive to an applied force and converts this change into electrical signals which can be transmitted via the transceiver 320 to convey a level and a direction of the applied force. In other arrangements herein contemplated, the sensing assemblage 303 may require only a single transducer. In yet other arrangements, the sensing assemblage 303 can include piezoelectric, capacitive, optical or temperature sensors or transducers to measure the compression or displacement. It is not limited to ultrasonic transducers and waveguides.
The accelerometer 302 can measure acceleration and static gravitational pull. Accelerometer 302 can be single-axis and multi-axis accelerometer structures that detect magnitude and direction of the acceleration as a vector quantity. Accelerometer 302 can also be used to sense orientation, vibration, impact and shock. The electronic circuitry 307 in conjunction with the accelerometer 302 and sensing assemblies 303 can measure parameters of interest (e.g., distributions of load, force, pressure, displacement, movement, rotation, torque and acceleration) relative to orientations of the sensing module with respect to a reference point. In such an arrangement, spatial distributions of the measured parameters relative to a chosen frame of reference can be computed and presented for real-time display.
The transceiver 320 comprises a transmitter 309 and an antenna 310 to permit wireless operation and telemetry functions. In various embodiments, the antenna 310 can be configured by design as an integrated loop antenna. As will be explained ahead, the integrated loop antenna is configured at various layers and locations on the electronic substrate with electrical components and by way of electronic control circuitry to conduct efficiently at low power levels. Once initiated the transceiver 320 can broadcast the parameters of interest in real-time. The telemetry data can be received and decoded with various receivers, or with a custom receiver. The wireless operation can eliminate distortion of, or limitations on, measurements caused by the potential for physical interference by, or limitations imposed by, wiring and cables connecting the sensing module with a power source or with associated data collection, storage, display equipment, and data processing equipment.
The transceiver 320 receives power from the energy storage 330 and can operate at low power over various radio frequencies by way of efficient power management schemes, for example, incorporated within the electronic circuitry 307. As one example, the transceiver 320 can transmit data at selected frequencies in a chosen mode of emission by way of the antenna 310. The selected frequencies can include, but are not limited to, ISM bands recognized in International Telecommunication Union regions 1, 2 and 3. A chosen mode of emission can be, but is not limited to, Gaussian Frequency Shift Keying, (GFSK), Amplitude Shift Keying (ASK), Phase Shift Keying (PSK), Minimum Shift Keying (MSK), Frequency Modulation (FM), Amplitude Modulation (AM), or other versions of frequency or amplitude modulation (e.g., binary, coherent, quadrature, etc.).
The antenna 310 can be integrated with components of the sensing module to provide the radio frequency transmission. The substrate for the antenna 310 and electrical connections with the electronic circuitry 307 can further include a matching network. This level of integration of the antenna and electronics enables reductions in the size and cost of wireless equipment. Potential applications may include, but are not limited to any type of short-range handheld, wearable, or other portable communication equipment where compact antennas are commonly used. This includes disposable modules or devices as well as reusable modules or devices and modules or devices for long-term use.
The energy storage 330 provides power to electronic components of the sensing module. It can be charged by wired energy transfer, short-distance wireless energy transfer or a combination thereof. External power sources can include, but are not limited to, a battery or batteries, an alternating current power supply, a radio frequency receiver, an electromagnetic induction coil, a photoelectric cell or cells, a thermocouple or thermocouples, or an ultrasound transducer or transducers. By way of the energy storage 330, the sensing module can be operated with a single charge until the internal energy is drained. It can be recharged periodically to enable continuous operation. The energy storage 330 can utilize common power management technologies such as replaceable batteries, supply regulation technologies, and charging system technologies for supplying energy to the components of the sensing module to facilitate wireless applications.
The energy storage 330 minimizes additional sources of energy radiation required to power the sensing module during measurement operations. In one embodiment, as illustrated, the energy storage 330 can include a capacitive energy storage device 308 and an induction coil 311. External source of charging power can be coupled wirelessly to the capacitive energy storage device 308 through the electromagnetic induction coil or coils 311 by way of inductive charging. The charging operation can be controlled by power management systems designed into, or with, the electronic circuitry 307. As one example, during operation of electronic circuitry 307, power can be transferred from capacitive energy storage device 308 by way of efficient step-up and step-down voltage conversion circuitry. This conserves operating power of circuit blocks at a minimum voltage level to support the required level of performance.
In one configuration, the energy storage 330 can further serve to communicate downlink data to the transceiver 320 during a recharging operation. For instance, downlink control data can be modulated onto the energy source signal and thereafter demodulated from the induction coil 311 by way of electronic control circuitry 307. This can serve as a more efficient way for receiving downlink data instead of configuring the transceiver 320 for both uplink and downlink operation. As one example, downlink data can include updated control parameters that the sensing module uses when making a measurement, such as external positional information, or for recalibration purposes, such as spring biasing. It can also be used to download a serial number or other identification data.
The electronic circuitry 307 manages and controls various operations of the components of the sensing module, such as sensing, power management, telemetry, and acceleration sensing. It can include analog circuits, digital circuits, integrated circuits, discrete components, or any combination thereof. In one arrangement, it can be partitioned among integrated circuits and discrete components to minimize power consumption without compromising performance. Partitioning functions between digital and analog circuit enhances design flexibility and facilitates minimizing power consumption without sacrificing functionality or performance. Accordingly, the electronic circuitry 307 can comprise one or more Application Specific Integrated Circuit (ASIC) chips, for example, specific to a core signal processing algorithm.
In another arrangement, the electronic circuitry can comprise a controller such as a programmable processor, a Digital Signal Processor (DSP), a microcontroller, or a microprocessor, with associated storage memory and logic. The controller can utilize computing technologies with associated storage memory such a Flash, ROM, RAM, SRAM, DRAM or other like technologies for controlling operations of the aforementioned components of the sensing module. In one arrangement, the storage memory may store one or more sets of instructions (e.g., software) embodying any one or more of the methodologies or functions described herein. The instructions may also reside, completely or at least partially, within other memory, and/or a processor during execution thereof by another processor or computer system.
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.
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.
With respect to
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.
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.
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.
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.
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.
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.
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.
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.
Wireless operation eliminates distortion of, or limitations on, measurements caused by the potential for physical interference by, or limitations imposed by, wiring and cables connecting the wireless sensing module or device with a power source or with data collection, storage, or display equipment. Power for the sensing components and electronic circuits is maintained within the wireless sensing module or device on an internal energy storage device. This energy storage device is charged with external power sources including, but not limited to, a battery or batteries, super capacitors, capacitors, an alternating current power supply, a radio frequency receiver, an electromagnetic induction coil, a photoelectric cell or cells, a thermocouple or thermocouples, or an ultrasound transducer or transducers. The wireless sensing module may be operated with a single charge until the internal energy source is drained or the energy source may be recharged periodically to enable continuous operation. The embedded power supply minimizes additional sources of energy radiation required to power the wireless sensing module or device during measurement operations. Telemetry functions are also integrated within the wireless sensing module or device. Once initiated the telemetry transmitter continuously broadcasts measurement data in real time. Telemetry data may be received and decoded with commercial receivers or with a simple, low cost custom receiver.
Referring back to
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.
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.
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.
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.
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.
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.
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.
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.
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.
Referring back to
For example, sensing modules or devices may be placed on or within, or attached or affixed to or within, a wide range of physical systems including, but not limited to instruments, appliances, vehicles, equipments, or other physical systems as well as animal and human bodies, for sensing the parameter or parameters of interest in real time without disturbing the operation of the body, instrument, appliance, vehicle, equipment, or physical system.
In addition to non-medical applications, examples of a wide range of potential medical applications may include, but are not limited to, implantable devices, modules within implantable devices, modules or devices within intra-operative implants or trial inserts, modules within inserted or ingested devices, modules within wearable devices, modules within handheld devices, modules within instruments, appliances, equipment, or accessories of all of these, or disposables within implants, trial inserts, inserted or ingested devices, wearable devices, handheld devices, instruments, appliances, equipment, or accessories to these devices, instruments, appliances, or equipment. Many physiological parameters within animal or human bodies may be measured including, but not limited to, loading within individual joints, bone density, movement, various parameters of interstitial fluids including, but not limited to, viscosity, pressure, and localized temperature with applications throughout the vascular, lymph, respiratory, and digestive systems, as well as within or affecting muscles, bones, joints, and soft tissue areas. For example, orthopedic applications may include, but are not limited to, load bearing prosthetic components, or provisional or trial prosthetic components for, but not limited to, surgical procedures for knees, hips, shoulders, elbows, wrists, ankles, and spines; any other orthopedic or musculoskeletal implant, or any combination of these.
As previously discussed, external forces applied to the sensing module 200 compress the waveguide(s) thereby changing the length of the waveguide(s). The sensing module 200 measures propagation characteristics of ultrasonic signals in the waveguide(s) to determine the change in the length of the waveguide(s). These changes in length change in direct proportion to the parameters of interest thus enabling the conversion of changes in the parameter or parameters of interest into load (or force) information.
As illustrated, external force 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.
One interpretation of
Changes in the parameter or parameters of interest are measured by measuring changes in the transit time of energy pulses or waves within the propagating medium. Closed loop measurement of changes in the parameter or parameters of interest is achieved by modulating the repetition rate of energy pulses or the frequency of energy waves as a function of the propagation characteristics of the elastic energy propagating structure.
In a continuous wave mode of operation, a phase detector (not shown) evaluates the frequency and changes in the frequency of resonant ultrasonic waves in the waveguide 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 143μ, although the wavelength within a waveguide may be longer than in unrestricted air.
In a pulse mode of operation, the phase detector measures a time of flight (TOF) between when an ultrasonic pulse is transmitted by transducer 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.
It should be noted that ultrasound energy pulses or waves, the emission of ultrasound pulses or waves by ultrasound resonators or transducers, transmitted through ultrasound waveguides, and detected by ultrasound resonators or transducers are used merely as examples of energy pulses, waves, and propagation structures and media. Other embodiments herein contemplated can utilize other wave forms, such as, light.
Recall that the load sensing insert device 100 when in motion measures forces on the sensing assemblies by evaluating propagation times of energy waves within the waveguides in conjunction with the accelerometer data. The propagation tuned oscillator (PTO) 4 measures a transit time of ultrasound waves 2 within the waveguide 3 in a closed-loop configuration. The digital counter 20 determines the physical change in the length of the waveguide. Referring to
The sensing assemblage 1 comprises transducer 5, transducer 6, and a waveguide 3 (or energy propagating structure). In a non-limiting example, sensing assemblage 1 is affixed to load bearing or contacting surfaces 8. External forces applied to the contacting surfaces 8 compress the waveguide 3 and change the length of the waveguide 3. Under compression, transducers 5 and 6 will also be moved closer together. The change in distance affects the transit time 7 of energy waves 2 transmitted and received between transducers 5 and 6. The propagation tuned oscillator 4 in response to these physical changes will detect each energy wave sooner (e.g. shorter transit time) and initiate the propagation of new energy waves associated with the shorter transit time. As will be explained below, this is accomplished by way of PTO 4 in conjunction with the pulse generator 10, the mode control 12, and the phase detector 14.
Notably, changes in the waveguide 3 (energy propagating structure or structures) alter the propagation properties of the medium of propagation (e.g. transit time 7). The energy wave can be a continuous wave or a pulsed energy wave. A pulsed energy wave approach reduces power dissipation allowing for a temporary power source such as a battery or capacitor to power the system during the course of operation. In at least one exemplary embodiment, a continuous wave energy wave or a pulsed energy wave is provided by transducer 5 to a first surface of waveguide 3. Transducer 5 generates energy waves 2 that are coupled into waveguide 3. In a non-limiting example, transducer 5 is a piezo-electric device capable of transmitting and receiving acoustic signals in the ultrasonic frequency range.
Transducer 6 is coupled to a second surface of waveguide 3 to receive the propagated pulsed signal and generates a corresponding electrical signal. The electrical signal output by transducer 6 is coupled to phase detector 14. In general, phase detector 14 compares the timing of a selected point on the waveform of the detected energy wave with respect to the timing of the same point on the waveform of other propagated energy waves. In a first embodiment, phase detector 14 can be a zero-crossing receiver. In a second embodiment, phase detector 14 can be an edge-detect receiver. In the example where sensing assemblage 1 is compressed, the detection of the propagated energy waves 2 occurs earlier (due to the length/distance reduction of waveguide 3) than a signal prior to external forces being applied to contacting surfaces. Pulse generator 10 generates a new pulse in response to detection of the propagated energy waves 2 by phase detector 14. The new pulse is provided to transducer 5 to initiate a new energy wave sequence. Thus, each energy wave sequence is an individual event of energy wave propagation, energy wave detection, and energy wave emission that maintains energy waves 2 propagating in waveguide 3.
The transit time 7 of a propagated energy wave is the time it takes an energy wave to propagate from the first surface of waveguide 3 to the second surface. There is delay associated with each circuit described above. Typically, the total delay of the circuitry is significantly less than the propagation time of an energy wave through waveguide 3. In addition, under equilibrium conditions variations in circuit delay are minimal. Multiple pulse to pulse timings can be used to generate an average time period when change in external forces occur relatively slowly in relation to the pulsed signal propagation time such as in a physiologic or mechanical system. The digital counter 20 in conjunction with electronic components counts the number of propagated energy waves to determine a corresponding change in the length of the waveguide 3. These changes in length change in direct proportion to the external force thus enabling the conversion of changes in parameter or parameters of interest into electrical signals.
The block diagram 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.
The measurement data can be analyzed to achieve accurate, repeatable, high precision and high resolution measurements. This method enables the setting of the level of precision or resolution of captured data to optimize trade-offs between measurement resolution versus frequency, including the bandwidth of the sensing and data processing operations, thus enabling a sensing module or device to operate at its optimal operating point without compromising resolution of the measurements. This is achieved by the accumulation of multiple cycles of excitation and transit time instead of averaging transit time of multiple individual excitation and transit cycles. The result is accurate, repeatable, high precision and high resolution measurements of parameters of interest in physical systems.
In at least one exemplary embodiment, propagation tuned oscillator 4 in conjunction with one or more sensing assemblages 1 are used to take measurements on a muscular-skeletal system. In a non-limiting example, sensing assemblage 1 is placed between a femoral prosthetic component and tibial prosthetic component to provide measured load information that aids in the installation of an artificial knee joint. Sensing assemblage 1 can also be a permanent component or a muscular-skeletal joint or artificial muscular-skeletal joint to monitor joint function. The measurements can be made in extension and in flexion. In the example, assemblage 1 is used to measure the condyle loading to determine if it falls within a predetermined range and location. Based on the measurement, the surgeon can select the thickness of the insert such that the measured loading and incidence with the final insert in place will fall within the predetermined range. Soft tissue tensioning can be used by a surgeon to further optimize the force or pressure. Similarly, two assemblages 1 can be used to measure both condyles simultaneously or multiplexed. The difference in loading (e.g. balance) between condyles can be measured. Soft tissue tensioning can be used to reduce the force on the condyle having the higher measured loading to reduce the measured pressure difference between condyles.
One method of operation holds the number of energy waves propagating through waveguide 3 as a constant integer number. A time period of an energy wave corresponds to energy wave periodicity. A stable time period is one in which the time period changes very little over a number of energy waves. This occurs when conditions that affect sensing assemblage 1 stay consistent or constant. Holding the number of energy waves propagating through waveguide 3 to an integer number is a constraint that forces a change in the time between pulses when the length of waveguide 3 changes. The resulting change in time period of each energy wave corresponds to a change in aggregate energy wave time period that is captured using digital counter 20 as a measurement of changes in external forces or conditions applied to contacting surfaces 8.
A further method of operation according to one embodiment is described hereinbelow for energy waves 2 propagating from transducer 5 and received by transducer 6. In at least one exemplary embodiment, energy waves 2 is an ultrasonic energy wave. Transducers 5 and 6 are piezo-electric resonator transducers. Although not described, wave propagation can occur in the opposite direction being initiated by transducer 6 and received by transducer 5. Furthermore, detecting ultrasound resonator transducer 6 can be a separate ultrasound resonator as shown or transducer 5 can be used solely depending on the selected mode of propagation (e.g. reflective sensing). Changes in external forces or conditions applied to contacting surfaces 8 affect the propagation characteristics of waveguide 3 and alter transit time 7. As mentioned previously, propagation tuned oscillator 4 holds constant an integer number of energy waves 2 propagating through waveguide 3 (e.g. an integer number of pulsed energy wave time periods) thereby controlling the repetition rate. As noted above, once PTO 4 stabilizes, the digital counter 20 digitizes the repetition rate of pulsed energy waves, for example, by way of edge-detection, as will be explained hereinbelow in more detail.
In an alternate embodiment, the repetition rate of pulsed energy waves 2 emitted by transducer 5 can be controlled by pulse generator 10. The operation remains similar where the parameter to be measured corresponds to the measurement of the transit time 7 of pulsed energy waves 2 within waveguide 3. It should be noted that an individual ultrasonic pulse can comprise one or more energy waves with a damping wave shape. The energy wave shape is determined by the electrical and mechanical parameters of pulse generator 10, interface material or materials, where required, and ultrasound resonator or transducer 5. The frequency of the energy waves within individual pulses is determined by the response of the emitting ultrasound resonator 4 to excitation by an electrical pulse 11. The mode of the propagation of the pulsed energy waves 2 through waveguide 3 is controlled by mode control circuitry 12 (e.g., reflectance or uni-directional). The detecting ultrasound resonator or transducer may either be a separate ultrasound resonator or transducer 6 or the emitting resonator or transducer 5 depending on the selected mode of propagation (reflectance or unidirectional).
In general, accurate measurement of physical parameters is achieved at an equilibrium point having the property that an integer number of pulses are propagating through the energy propagating structure at any point in time. Measurement of changes in the “time-of-flight” or transit time of ultrasound energy waves within a waveguide of known length can be achieved by modulating the repetition rate of the ultrasound energy waves as a function of changes in distance or velocity through the medium of propagation, or a combination of changes in distance and velocity, caused by changes in the parameter or parameters of interest.
It should be noted that ultrasound energy pulses or waves, the emission of ultrasound pulses or waves by ultrasound resonators or transducers, transmitted through ultrasound waveguides, and detected by ultrasound resonators or transducers are used merely as examples of energy pulses, waves, and propagation structures and media. Other embodiments herein contemplated can utilize other wave forms, such as, light. Furthermore, the velocity of ultrasound waves within a medium may be higher than in air. With the present dimensions of the initial embodiment of a propagation tuned oscillator the waveguide is approximately three wavelengths long at the frequency of operation.
Measurement by propagation tuned oscillator 4 and sensing assemblage 1 enables high sensitivity and high signal-to-noise ratio. The time-based measurements are largely insensitive to most sources of error that may influence voltage or current driven sensing methods and devices. The resulting changes in the transit time of operation correspond to frequency, which can be measured rapidly, and with high resolution. This achieves the required measurement accuracy and precision thus capturing changes in the physical parameters of interest and enabling analysis of their dynamic and static behavior.
These measurements may be implemented with an integrated wireless sensing module or device having an encapsulating structure that supports sensors and load bearing or contacting surfaces and an electronic assemblage that integrates a power supply, sensing elements, energy transducer or transducers and elastic energy propagating structure or structures, biasing spring or springs or other form of elastic members, an accelerometer, antennas and electronic circuitry that processes measurement data as well as controls all operations of ultrasound generation, propagation, and detection and wireless communications. The electronics assemblage also supports testability and calibration features that assure the quality, accuracy, and reliability of the completed wireless sensing module or device.
In general, measurement of the changes in the physical length of individual waveguides can be made in several modes. Each assemblage of one or two ultrasound resonators or transducers combined with a waveguide can be controlled to operate in six different modes. This includes two wave shape modes: continuous wave or pulsed waves, and three propagation modes: reflectance, unidirectional, and bi-directional propagation of the ultrasound wave. In all modes of operation the changes in transit time within the ultrasound waveguides change the operating frequency of the propagation tuned oscillator 4 or oscillators. These changes in the frequency of oscillation of the propagation tuned oscillator or oscillators can be measured rapidly and with high resolution. This achieves the required measurement accuracy and precision thus enabling the capture of changes in the physical parameters of interest and enabling analysis of the dynamic and static behavior of the physical system or body.
The level of accuracy and resolution achieved by the integration of energy transducers and an energy propagating structure or structures coupled with the electronic components of the propagation tuned oscillator enables the construction of, but is not limited to, compact ultra low power modules or devices for monitoring or measuring the parameters of interest. The flexibility to construct sensing modules or devices over a wide range of sizes enables sensing modules to be tailored to fit a wide range of applications such that the sensing module or device may be engaged with, or placed, attached, or affixed to, on, or within a body, instrument, appliance, vehicle, equipment, or other physical system and monitor or collect data on physical parameters of interest without disturbing the operation of the body, instrument, appliance, vehicle, equipment, or physical system.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
While the present invention has been described with reference to particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the invention.
Claims
1. A sensing 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.
Type: Application
Filed: Jun 29, 2010
Publication Date: Dec 30, 2010
Applicant: OrthoSensor (Sunrise, FL)
Inventor: Marc Stein (Chandler, AZ)
Application Number: 12/825,724
International Classification: A61B 5/103 (20060101);
