Bone fixation monitoring system

Abstract

A system for monitoring ossification of an internally fixed fracture in a subject's bone includes an implantable fixation device and an external wireless reader operative to transmit relative load data experienced by a bone plate spanning the fracture to a data server, so that trends in changes in the additional bone support provided by the bone plate can be visualized. The implantable fixation device includes a primary load sensor and a reference load sensor, and the load value from the reference load sensor can be used to normalize the load value from the primary load sensor. The external wireless reader is in wireless communication with the implantable fixation device and is operative to receive a signal indicative of the load from each load sensor and to energize each load sensor via inductive charging.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 054,557, filed July 21, 2020, which is incorporated herein by reference in its entirety.

[0002] FIELD OF THE INVENTION FIELD OF THE DISCLOSURE The present disclosure relates generally to systems and methods for monitoring the healing / ossification of fractured bones. [Background technology]

[0003] Conventional bone fixation systems include bone plates with threaded holes for receiving fixation members, such as screws, configured to attach to underlying bone, including at least a pair of bone segments separated by a bone gap. The bone gap may be a defect caused by a traumatic event, an osteotomy, or the result of debridement of the joint of two separate bones to be joined in an arthrodesis procedure. Accordingly, the bone plate may be secured to the bone on either side of the bone gap via bone screws to promote union of the bone segments (e.g., fracture healing or joint ossification). The bone fixation system may further include temporary Kirschner wires (K-wires) that are temporarily inserted into the apertures of the bone fixation plate and the underlying bone segments to determine the appropriate length, rotation, and alignment of the bone segments prior to permanent plate fixation. Once the bone fixation plate is properly positioned, permanent bone screws may be inserted into one or more bone screw holes on either side of the bone gap and secured to the underlying bone. Summary of the Invention [Means for solving the problem]

[0004] A system for monitoring ossification of an internally fixed fracture in a subject's bone includes an implantable fixation device and an external wireless reader operative to transmit relative load data experienced by a bone plate spanning the fracture to a data server where trends in changes in the additional bone support provided by the bone plate can be visualized.

[0005] The implantable fixation device includes a primary load sensor and a reference load sensor, both in direct physical contact with the bone plate. The primary load sensor is provided on the bone plate at a first location operative to be positioned directly adjacent to the fracture. The primary load sensor may generally include a first strain sensor operative to monitor an amount of strain in the bone plate at the first location (primary strain) and a communication circuit operative to transmit a first wireless signal indicative of the amount of primary strain. The reference load sensor is provided on the bone plate at a second location spaced apart from the first location. The reference load sensor may include a second strain sensor operative to monitor an amount of strain in the bone plate at the second location (reference strain) and a communication circuit operative to transmit a second wireless signal indicative of the amount of reference strain.

[0006] The external wireless reader may receive the first and second wireless signals via the antenna, use the received indication of the primary strain and the received indication of the reference strain to determine an amount of relative support provided by the bone plate as a result of the fracture, and transmit the determined amount of relative support to a data server over a wireless communications network using a wireless communications radio. In one configuration, the amount of relative support provided by the bone plate as a result of the fracture may be calculated by dividing the primary strain value by the reference strain value.

[0007] A method for using these devices to obtain ossification data from an implantable smart fixation device provided within a subject's body may begin by energizing an external antenna provided with an external wireless reader to generate an alternating magnetic field and inductively energize each of the primary and reference load sensors. The external wireless reader can then receive wireless data signals from each load sensor, the wireless data signals indicating the amount of strain experienced by the bone plate at its respective location.

[0008] Additionally, a method for monitoring bone fracture ossification from multiple subjects via a data server may begin by receiving multiple bone ossification data points from multiple subjects via a wireless communication network. Each data point represents a measurement obtained from a smart fixation device secured to the subject's bone across the fracture. The measurement represents the amount of load borne by the fixation device across the fracture relative to the amount of load borne by the fixation device on the intact bone. The method further includes storing each of the multiple data points in non-volatile memory along with the date and time the measurement was taken and a patient identifier representing the source of the measurement. The data server may then provide a physician interface for graphically illustrating the change in measurements over time from each of the multiple different subjects.

[0009] In one configuration, the data server may maintain a machine learning prediction model that generates a predicted, patient-specific healing trajectory for each subject. The patient-specific healing trajectory includes a predicted trajectory and a confidence interval that represents the likely progression of healing progression beginning at bone fixation. The method further includes overlaying a plurality of data sets or an empirical trend line for the subject on a graphical representation of the predicted, patient-specific healing trajectory within the physician interface. The machine learning prediction model may be refined using at least a subset of the received plurality of data points and a plurality of secondary factors, including at least two of the nature and location of the fracture, the subject's height, weight, age, sex, metabolic profile, blood pressure, pre-existing conditions, complex risk factors, or comorbidities.

[0010] The data server may further calculate, for each subject, a forward healing trajectory extending forward in time from the subject's most recently acquired data point. This forward healing trajectory may also be overlaid on a graphical representation of the predicted patient-specific healing trajectory. The data server may provide a warning via the physician interface if one of the data points or the forward healing trajectory is outside the confidence interval.

[0011] As used herein, the terms "a," "an," "the," "at least one," and "one or more" are used interchangeably to indicate the presence of at least one of an item. Such items may also be present in plural unless clearly stated otherwise. All numerical values of parameters (e.g., quantities or conditions) in this specification, including the appended claims, should be understood to be modified in all instances by the term "about," regardless of whether "about" actually precedes the numerical value. "About" indicates that the stated numerical value tolerates some slight imprecision (being reasonably close to the exact value, being roughly or reasonably approximating a value, or being in the vicinity). Unless the imprecision provided by "about" is otherwise understood in the art, "about" as used herein at least accounts for the variation that can result from ordinary methods of measuring and using such parameters. Furthermore, the disclosure of a range includes the disclosure of all values and sub-ranges within that entire range. Each value within a range and the endpoints of that range are thereby disclosed as separate embodiments. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of a system for monitoring fracture healing. [Figure 2] FIG. 1 is a schematic diagram of an implantable smart fixation device for surgically repairing fractured bones. [Figure 3] FIG. 1 is a schematic side perspective view of an external wireless reader for wirelessly interfacing with an implantable smart fixation device. [Figure 4] FIG. 1 is a schematic diagram of a portable computing device in wireless communication with an implantable smart fixation device via an external antenna. [Figure 5] 5 is a schematic illustration of a progression of user interface display screens that may be displayed to a patient via a portable computing device such as that shown in FIGS. 3-4 during a measurement. [Figure 6] FIG. 1 is a schematic diagram of a method for acquiring and aggregating patient healing data from implantable smart fixation devices. [Figure 7] FIG. 1 is a schematic diagram of a patient-specific trendline drawn through multiple load ratio data points taken over time. [Figure 8] FIG. 10 is a schematic diagram of a physician interface that may display patient-specific healing trendlines constructed for one or more patients. [Figure 9] FIG. 1 is a schematic side perspective view of an external wireless reader anchored to a patient's upper thigh. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present technology generally relates to systems and devices that enable physicians to better understand the recovery and healing process of internally fixed fractures than is possible with more traditional forms of treatment. More specifically, the present design provides for periodic (even daily) testing of fracture healing progress while offering the convenience of conducting the testing outside the confines of a clinic or laboratory. Through the use of connected hardware and a centralized data management system, orthopedic surgeons may gain remote access to acquired diagnostic data drawn directly from the internal fixation system. Using this quantitative data, physicians may be better equipped to consult with patients, for example, in a virtual telemedicine-based manner. In this way, the present technology allows the level of care required to monitor the healing progress of internally fixed fractures to be monitored remotely.

[0014] Referring to the drawings, wherein like reference numerals are used to identify similar or identical components in the various views, FIG. 1 schematically illustrates a system 10 for remotely monitoring the healing / ossification of a fracture or other bone joint that has been internally fixed using a bone plate 12 and a plurality of permanent fixation members, such as bone screws 14 (better shown in FIG. 2 ). Generally, the system 10 includes a data server 20 and / or cloud computing system 22 that operates to receive patient data 24 from one or more patient monitoring systems 26 via a wireless communications network 28. The data server 20 / cloud computing system 22 can store the received patient data 24 in an associated non-volatile memory / database 30 and can visually present this data to a medical professional 32 via a hosted physician interface 34. The patient monitoring system 26 may be configured to periodically monitor the amount of load borne by the bone plate 12 spanning the fracture throughout the duration of the healing process. This load measurement may be normalized to the load carried by the bone plate 12 away from the fracture and may be periodically transmitted from the patient monitoring system 26 to the data server 20 where it may be aggregated with other patient data 24 to highlight fracture healing trends.

[0015] Continuing with reference to FIG. 1 , data server 20 may be implemented as one or more high-speed server computers or mainframe computing devices capable of handling bulk data processing and data visualization tasks. Meanwhile, cloud computing system 22 may operate as middleware for Internet of Things (IoT), Web of Things (WoT), and / or machine-to-machine (M2M) services, connecting a heterogeneous combination of electronic devices over a data network with a service-oriented architecture (SOA). As an example, cloud computing system 22 may be implemented as a middleware node to dynamically onboard heterogeneous devices, multiplex data from each of these devices, and provide different capabilities for routing the data through reconfigurable processing logic for processing and transmission to one or more destination applications. Wireless communication network 28 may be any available type of network, including a combination of a public distributed computing network (e.g., the Internet) and a secure private network (e.g., a local area network, a wide area network, a virtual private network). It may also include wireless and wired transmission systems (e.g., satellites, cellular networks, terrestrial networks, etc.). Most, if not all, data transaction functions may be performed over, for example, a wireless network, such as a wireless local area network (WLAN) or cellular data network operating according to 4G, 5G, LTE, LPWAN, LTE-M, CAT-M1, or NB-IoT protocols.

[0016] 1 , the patient monitoring system 26 generally includes an implantable smart fixation device 40 and an external (external) wireless reader 42 for interfacing with the smart fixation device 40. The external wireless reader 42 is configured to wirelessly receive data from the smart fixation device 40 through the patient's skin, for example, via a radio frequency (RF) data communication means such as RFID or NFC. In at least some embodiments, the external wireless reader 42 may be further configured to wirelessly provide power to the smart fixation device 40, such that the fixation device 40 may not require an internal battery to operate.

[0017] 2 , an implantable smart fixation device 40 may include a rigid bone plate 12 configured to span and be secured to opposing sides of a fracture 50 using a plurality of permanent fixation members, such as bone screws 14. The bone plate 12 may be formed from any suitable implantable material, such as, but not limited to, a metal (e.g., a titanium alloy) or a polymer, such as polyether ether ketone (PEEK). While this disclosure generally discusses the use of remote monitoring technology in connection with bone plate-type fixation devices, the technology may also be utilized with other rigid fixation members, such as implantable rods, pedicle screws, intervertebral implants, etc.

[0018] The smart fixation device 40 may generally include at least one primary load sensor 52 operative to sense the load borne by the plate 12 at the fracture 50. As the fracture heals / ossifies, the amount of load borne by the plate 12 at the fracture 50 should decrease (i.e., the load-bearing capacity of the healing bone increases accordingly). In many embodiments, the smart fixation device may further include at least one reference load sensor 54 operative to sense the load borne by the plate 12 at a location spaced from the fracture. The reference load sensor 54 may generally serve as a baseline for the amount of load borne by the plate 12 adjacent healthy or unfractured bone.

[0019] In one configuration, each load sensor 52, 54 may include one or more strain gauges 60 having electrical properties that change in a defined manner depending on the amount of strain experienced by the gauge / plate at that location. Examples of suitable strain gauges include resistive strain gauges, capacitive strain gauges, piezoelectric materials, electroactive polymer materials, etc. Each strain gauge 60 may be held in secure, rigid contact with the plate 12 so that the gauge experiences any bending or deflection of the plate. As is well established, strain and load are directly proportional, and therefore, measuring strain is one way of monitoring the load carried by the plate.

[0020] 2 , the smart fixturing device 40 further includes communication circuitry 62 electrically coupled to each strain gauge 60 and an antenna 64 in communication with the communication circuitry 62. The communication circuitry 62 is configured to receive measurements from the strain gauges 60 and provide the measurements to the antenna 64 in a form suitable for wireless transmission. The communication circuitry 62 may include a wireless transmitter or transponder that receives measurements from the strain gauges 60 and prepares the measurements for wireless transmission. For example, the communication circuitry 62 may include processing components such as (but not limited to) one or more of: (i) a memory configured to store the measurements; (ii) a digital-to-analog converter configured to convert the measurements to an analog format; (iii) a radio frequency (RF) modulator configured to modulate the measurements; (iv) an error correction encoder configured to encode the measurements; and other processing consistent with the wireless technology employed by the system.

[0021] In one example, the communication circuitry 62 may be configured as a passive radio-frequency identification (RFID) transponder. Alternatively, the communication circuitry 62 may be configured using any other wireless communication technology suitable for communicating through the skin, such as (but not limited to) battery-assisted passive RFID, active RFID, Bluetooth, and Wi-Fi. The communication circuitry 62 may further include a unique identifier (ID) that can be used to distinguish each load sensor from other sensors. In one embodiment, the unique ID may be the ID of an RFID tag. The antenna 64 is configured to convert electrical signals corresponding to the measurements from the communication circuitry 62 into radio waves and wirelessly transmit the measurements through the patient's skin to an external wireless reader 42 located outside the patient's body.

[0022] 2, the smart fixturing device 40 may include a power supply device 66 configured to provide power to the strain gauges 60 and the communication circuitry 62. In at least some embodiments, the power supply device 66 may include an energy harvesting device configured to harvest energy from a suitable energy source separate from the smart fixturing device 40. For example, the energy source may be radio waves transmitted from an external wireless reader 42. Alternatively, the power supply device 66 may harvest energy from the patient's body itself or from another external source, such as a source external to the patient's body. More broadly, the energy source may include (but is not limited to) sensed kinetic energy, electric fields, magnetic fields, etc. However, in preferred embodiments, the power supply device 40 does not include a typical electrochemical battery.

[0023] In one configuration, each load sensor 52, 54 may have its own dedicated communications circuitry 62, antenna 64, and / or power device 66 local to the respective load sensor (i.e., as an integrated package). In this configuration, the primary load sensor 52 may transmit a first wireless signal indicative of the amount of strain monitored by the primary load sensor 52 (i.e., a primary strain value), while the reference load sensor 54 may simultaneously transmit a second wireless signal indicative of the amount of strain monitored by the reference load sensor 54 (i.e., a reference strain value). In other embodiments, the smart stationary device 40 may have a common communications circuitry 62, antenna 64, and / or power device 66 that may be shared throughout the device 40 (i.e., each load sensor 52, 54 is in electrical communication with the shared communications circuitry 62, antenna 64, and / or power device 66). Further embodiments and disclosure of the smart stationary device 40 are provided in U.S. Patent Application Publication No. 2019 / 0038214, which is incorporated by reference in its entirety for all purposes.

[0024] As described above, the external wireless reader 42 is configured to wirelessly receive data from the smart fixation device 40 through the patient's skin. To facilitate these communications, the external wireless reader 42 typically includes one or more antennas 70, such as a radio frequency identification (RFID) antenna, that communicate with a portable computing device 72, as shown schematically in FIG. 3 . The antenna 70 may be configured to be attached directly to an external surface of the patient's body or clothing. This attachment may be facilitated by the use of one or more straps 73, harnesses, braces, adhesive patches, elastic sleeves, cuffs, or the like. In one particular embodiment, the antenna 70 may be provided within a flexible fabric carrier 74, which may be particularly suited to contouring to the user's body. The antenna 70 may generally comprise a looped coil having a length adapted to extend parallel to the bone plate 12 and a width adapted to extend across and / or circumferentially around the bone plate 12. The length may control the amount of plate with which the antenna can communicate, while the width may affect the depth of tissue at which the antenna receives a reliable signal. In one configuration, the length of antenna 70 is longer than the distance between primary load sensor 52 and reference load sensor 54. In another configuration, the length of antenna 70 is at least 10% longer than the distance between primary load sensor 52 and reference load sensor 54. In one embodiment, antenna 70 may have a length of about 20 cm to about 50 cm, or about 25 cm to about 40 cm. Similarly, antenna 70 may have a width of about 12 cm to about 20 cm, or about 14 cm to about 17 cm.

[0025] As shown in FIG. 4 , the portable computing device 72 may include short-range communication circuitry 76 and / or power transmission circuitry 78 in communication with the antenna 70. The short-range communication circuitry 76 may operate to receive digital information from the smart stationary device 40 via the antenna 70. In some embodiments, the short-range communication circuitry 76 may comprise a digital receiver or transceiver, such as an RFID transceiver or a Near Field Communications (NFC) transceiver. In one configuration, the antenna 70 may operatively communicate with each load sensor 52, 54 simultaneously, for example, by using different data transmission frequencies or by using different digital identifiers provided with the strain data. The power transmission circuitry 78 may include inductive charging circuitry that operates to provide an electromagnetic force (i.e., an alternating magnetic field) via the antenna 70 to inductively power the smart stationary device 40.

[0026] 4 , portable computing device 72 may further include a processor 80, a wireless communication radio 82, and a user interface 84. Wireless communication radio 82 may be operable to communicate with and via wireless communication network 28 and may comprise a BLUETOOTH or BLUETOOTH LOW ENERGY chipset, a Wi-Fi radio operative to communicate digitally using an IEEE 802.11 communication protocol, or a cellular radio operative to communicate in accordance with 4G, 5G, LTE, LPWAN, LTE-M, CAT-M1, NB-IoT protocols, etc. In some embodiments, portable computing device 72 may further include a subscriber identity module (SIM) card to facilitate communication over the cellular network.

[0027] Processor 80 may be embodied as one or more digital computers, data processing devices, and / or digital signal processors (DSPs), which may have one or more microcontrollers or central processing units (CPUs), read only memory (ROM), random access memory (RAM), electrically-erasable programmable read only memory (EEPROM), high-speed clocks, analog-to-digital (A / D) circuitry, digital-to-analog (D / A) circuitry, input / output (I / O) circuitry, and / or signal conditioning and buffering electronics. Processor 80 is configured to perform or implement one or more electronic functions through the execution of software or firmware code stored in non-volatile memory accessible by processor 80. For example, the processor 80 may be capable of executing code to read one or more strain values from the smart stationary device 40, code to select an average or filtered representative strain value, code to communicate with a user via a user interface 84, and / or code to communicate over the wireless communications network 28 via a wireless communications radio 82.

[0028] The portable computing device 72 may communicate with the antenna 70 using either a wired or wireless communication link. In one configuration, as generally shown in FIG. 3 , the portable computing device 72 may be electrically coupled to the antenna 70 through the use of a wired tether 86. Such a design may have the advantage of providing a self-contained diagnostic apparatus that relies only on a single power source. More specifically, in the absence of the wired tether 86, the antenna 70 would require a first power source to enable / power communication with both the sensor and the computing device 72, and the portable computing device 72 would require a second power source. Coupling the two elements reduces the need for consumers to maintain sufficient battery levels on two separate devices and also reduces device complexity. The wired tether 86 also allows the portable computing device 72 to be held in a convenient, accessible position during data acquisition without requiring a strained posture to view a screen that may otherwise be out of the patient's field of view. In one configuration, the antenna portion of the device may further include a holster or other anchoring mechanism for attaching and anchoring the portable computing device 72 when not in use.

[0029] In another embodiment, portable computing device 72 may communicate wirelessly with antenna 70 using a suitable wireless protocol. For example, in one configuration, portable computing device 72 may be a smartphone or tablet device that communicates wirelessly with antenna 70 (and / or communications circuitry thereon) using, for example, the Bluetooth protocol.

[0030] As further shown in Figure 4, the user interface 84 may include a visual display 88, such as an LCD or OLED display, and one or more input devices 90, such as buttons or a touchscreen digitizer. As shown generally in Figure 5, the display 88 may operate to provide one or more visual cues to the patient, such as indicating the start of a reading (92), verifying sensor alignment (94), directing the positioning and occurrence of a reference measurement (96), directing the positioning and occurrence of a load-bearing measurement (98), and / or uploading measurement data to a data server / cloud via wireless communication network 28 (100).

[0031] FIG. 6 schematically illustrates a method 110 for acquiring and aggregating patient healing data using the present system 10. The method 110 begins at 112, with the antenna 70 positioned facing outward in contact with or adjacent to a skin surface of the body. In some configurations, such as when using an RFID communication protocol, the antenna 70 may be positioned so that it is generally centered above / radially outward of the at least one implantable primary load sensor 52 and at least one implantable reference load sensor 54, with each load sensor 52, 54 in direct physical communication with the bone plate 12 or other bone fixation device. One or more straps 73 or sleeves may be used to hold the antenna 70 in place during testing, such as by wrapping it around a portion of the wearer's body. Once the antenna 70 is in place and secured to the wearer's body at 112, the portable computing device 72 can receive an indication at 114 that the patient / user wishes to begin testing and acquiring strain data. This instruction 114 may be received via input device 90 and may include, for example, pressing a physical or virtual button.

[0032] Upon receiving a start instruction at 114, the processor 80 may energize (at 116) the antenna 70 via the power transmission circuitry 78, thereby energizing and / or activating the sensors 52, 54. Following this, the processor 80 may check the presence and / or strength of data signals returned from each sensor 52, 54 to determine whether the device is operational and properly positioned (118). If the signal-to-noise ratio is too low (as shown generally at 94 in FIG. 5 ) or if the sensors are returning unexpected readings, the processor 80 may instruct the user to reposition the antenna or seek further assistance. If the sensors are operating well and returning appropriate signals, the processor 80 may instruct the user via the display 88 on how to position their body (120). For example, as shown at 96 in FIG. 5 , the display 88 may depict a picture of a sitting person to indicate that the patient should be in a sitting position. This position may be confirmed automatically, for example, through the expiration of a countdown timer, the actuation of a button by the user to confirm the attitude, or through orientation data obtained from an accelerometer or inertial measurement unit mounted on the antenna 70.

[0033] Once the user's location has been verified (directly or indirectly), the processor 80 may receive (at 122) measurement data from the load sensors 52, 54 via the antenna 70 and communications circuitry 76. Following receipt, this data may optionally be filtered or smoothed (at 124) by the portable computing device 72 to remove communication or measurement noise, erroneous harmonics, etc. Exemplary filtering techniques may employ the use of low-pass or band-pass filtering techniques and / or data averaging techniques to remove noise in the signal. Further techniques may include various clipping or sampling schemes that operate to isolate a subset of the total received signal that has a minimum average or total variance (e.g., root mean squared (RMS) variance).

[0034] Once any on-board data processing is complete (if any such processing is desired), the processor 80 may package (at 126) the strain data from the load sensors 52, 54 (in raw and / or filtered / clipped form) with a unique identifier corresponding to at least one of the subject's identity or the identity of the implantable smart immobilization device 40 or the strain sensors mounted thereon. Packaging such data may include generating a digital file in memory containing the sensor data in delimited format along with header or metadata information including date / time of reading, device data, environmental data, and / or subject / device identification data. The packaged data / data file is then transmitted (128) via the wireless communication network 28 to the data server 20, where it may be aggregated and / or recorded (132) in association with the unique patient identifier.

[0035] The system may be operatively configured (at 130) to use the difference readings between the primary load sensor 52 and the reference load sensor 54 to interpret the acquired strain data and determine the relative amount of support provided by the bone plate due to the fracture. In practice, such analysis may be performed using the processor 80 or alternatively by the data server 20. If the analysis is performed by the device processor 80, the results of the analysis are packaged with the filtered or raw data and a unique identifier prior to transmission of the information.

[0036] In one configuration, the relative amount of support provided by the bone plate can be expressed as the ratio of the strain sensed by the primary load sensor 52 to the strain sensed by the reference load sensor. As the bone heals, this value is expected to decrease toward 1.0 (representing variable biomechanical dynamics where strain may be non-uniform across the length of the bone). A ratio greater than 1.0 suggests that the bone plate is carrying a greater amount of load across the fracture compared to points away from the fracture.

[0037] In some embodiments, processor 80 may further normalize measurements or ratios obtained during a load-bearing position (e.g., a load-bearing ratio) with measurements or ratios obtained during no-load (e.g., a no-load ratio). For example, when monitoring a fracture in the femur, a load-bearing position may involve the patient standing upright, while a no-load position may involve the patient sitting. To accomplish this, method 110 may repeat the instruction / measurement steps (generally at 120-124) while instructing the patient via display 88 to position themselves in different body positions (shown diagrammatically at 120b in FIG. 6 and at 98 in FIG. 5). In one configuration, the first proposed body positioning is a reference position where there is substantially no load on the fracture. The second position may then be a position where a load is applied to the fracture.

[0038] In one configuration, the normalization referenced above may simply involve calculating the ratio of the primary strain to the reference strain as the ratio of changes in strain. Stated another way, the system may calculate the delta increase in strain at the fracture from the unloaded to the loaded position and then divide that value by a similarly calculated delta increase in strain at the reference position (i.e., from the unloaded to the loaded position). This normalization may remove ratio anomalies that may be caused by different baseline readings between sensors. In one configuration, as generally shown at 98 in FIG. 5, when commanding a loaded position, processor 80 may compare the strain from reference sensor 54 in the loaded position to the strain from that sensor in the unloaded position.

[0039] To ensure that sufficient load is applied to the bone to achieve meaningful data points, processor 80 can monitor the absolute and / or delta strain at the fracture to ensure it exceeds a predetermined threshold while in the prescribed load-bearing position. If the strain is below the threshold, processor 80 may instruct the wearer to apply a greater load to the fractured bone (as generally shown at 98 in FIG. 5). If the ratio or difference exceeds the threshold, a reading can be recorded with confidence that the bone in the load-bearing position is supporting a sufficient amount of load to make the results meaningful.

[0040] In other embodiments, instead of taking measurements during static loading conditions, the portable computing device 72 may instead instruct the patient to perform some dynamic movement (120). For example, the portable computing device 72 may instruct the patient to walk, perform certain stretches, or perform other functional activities such as standing from a sitting position or climbing stairs. In this configuration, instead of simply filtering and / or averaging the received strain readings to arrive at a single static strain value, the processor 80 may examine the strain readings over time to identify peak loads throughout the functional activity. These peak load values / ratios may then be normalized to the identified minimum load value / ratio, instead of requiring separate load-bearing and unloading positions.

[0041] Once the support ratio is obtained, this value may be similarly recorded in association with the subject's identifier. In one configuration, each patient may have multiple data points associated with their unique patient identifier. Each data point may represent test results obtained at a different time. FIG. 7 schematically illustrates multiple patient data points 140, each representing a stress ratio 142 obtained over time 144. As shown in FIG. 7, a trendline 146 may be constructed from these multiple data points 140 to represent the patient's healing progression over time.

[0042] Upon receiving a request from a user or medical professional 32 (at 134 in FIG. 6 ), the data server 20 may visually represent the aggregated patient data through a hosted user interface / physician interface 34, as shown in FIG. 8 . In one configuration, the physician interface 34 may be a web-based display that graphically illustrates the healing progress of one or more patients 148, for example, through the display of data points 140 and / or trend lines 146 acquired over time 142. In one configuration, the physician interface 34 may include an overview screen, as shown in FIG. 8 , that allows a physician to quickly review the progress and compliance of multiple patients, each of whom is using the system and periodically submitting their respective patient data 24 to the data server 20. Upon selecting any one patient, the physician interface 34 may transition from the overview screen to a more detailed graphical display of the selected patient's trends, as shown in FIG. 7 .

[0043] In one configuration, as also shown in FIG. 7 , the data server 20 can calculate and display patient-specific trajectory ranges 150 within which the patient's actual trend line 146 is expected to fall over time. In one configuration, the patient-specific trajectory ranges 150 may be statistical estimates based on one or more qualitative and / or quantitative attributes / metrics extracted from the patient's medical records or otherwise input into the data server 20. These characteristics may include factors such as the nature and location of the fracture, the patient's height, weight, age, sex, metabolic profile, blood pressure, pre-existing conditions, complex risk factors / comorbidities 152 (shown in FIG. 8 ), or other such factors that may affect healing. In some embodiments, the trajectory ranges 150 may be further influenced by empirical data obtained from previous patients. For example, the data server 20 may maintain machine learning models (e.g., supervised or unsupervised learning models) that function by using empirical evidence drawn from previous patients to improve the model's predictive accuracy for future patients. The patient-specific trajectory range 150 may include a predicted trajectory 154 with one or more confidence intervals 156 that diverge over time. In one configuration, the patient-specific trajectory range 150 may be a static trajectory range 150 that is calculated as of the day the bone is set (i.e., day 0) and is not updated. By not continually refining the model, medical professionals can understand whether the patient is healing as expected or if there are any unforeseen complications that need to be addressed.

[0044] In some embodiments, data server 20 may further attempt to extrapolate the trajectory at each step (i.e., where the most recent data point is always day 0 and the previous trend line is an additional input to the model). This forward trajectory 158 can provide advance notice to medical professionals if the direction of the curve's progression may be a cause for concern at a later date. For example, forward trajectory 158 in FIG. 7 predicts a delay in healing progress over the next one to two weeks, which may be outside of what is expected. This prediction can alert a physician that something may be complicating the healing process and may warrant further investigation. Furthermore, in one configuration, data server 20 may provide a warning via physician interface 34 if one of the data points or the forward healing trajectory falls outside the confidence interval. In this way, the more frequent monitoring provided by the system, along with enhanced data visualization and predictive analysis, may result in a more complete understanding of how a patient is healing relative to reasonable expectations. This improved understanding may allow physicians to intervene earlier if complications begin to arise. Similarly, this data may also serve to provide guidance regarding recommended physical therapy treatments and recommended overall patient activity levels.

[0045] In one configuration, in addition to being displayed to the physician via the hosted interface 34, the recorded patient data points 140, the patient-specific trajectory range 150, the forward trajectory 158, and / or one or more qualitative summaries may also be displayed to the patient via the display 88. In doing so, the healing process may be gamified, for example, by celebrating or offering virtual rewards when certain milestones are achieved. Similarly, the portable computing device may communicate advice or behavioral recommendations, either automatically or under remote guidance / input from the physician, to assist the patient in maintaining compliance with the prescribed course of treatment.

[0046] FIG. 9 schematically illustrates one method of securing the external wireless reader 42 and / or antenna 70 to a user's body, more specifically, to the upper thigh, as required for femoral fractures. In such use, securing to the body has presented challenges because the muscles of the upper thigh change thickness based on the patient's posture. For example, as a patient transitions from a sitting to a standing position, the circumference of the patient's thigh decreases significantly. If not accounted for, this decrease in leg circumference can cause the external wireless reader 42 to slip downward from its intended position. To prevent this slippage, in one embodiment, the external wireless reader 42 can include one or more elastic straps 160 configured to be secured around the patient's body. These elastic straps 160 preferably achieve a tension fit so that they are elastically stretched around the patient's limb while applying a compressive force against the patient's skin. In some embodiments, the external wireless reader 42 can further include one or more braces 162 configured to be secured around the joint of the fractured bone. For example, in a femur fracture, the external wireless reader 42 may include a knee brace 164 configured to extend around the patient's knee. The antenna 70 may then be rigidly positioned relative to this brace 162. Such a design may be advantageous because the circumference of the joint does not change significantly with posture, and similarly, the position of the fracture relative to the joint also remains constant. This design does not rely solely on contracting elastic straps to maintain positioning, which may prove uncomfortable for some patients. In an alternative embodiment, a waist brace or belt may be used in place of the knee brace 162.

[0047] This technology represents an advancement in physicians' ability to more actively monitor the healing progress of internally fixed fractures. Using this expanded quantitative monitoring, particularly suited to remote monitoring / telemedicine, physicians may gain a more complete picture of how bones are ossifying than has been available with existing practices. With this information, physicians can more aggressively adjust physical therapy regimens, advise patients on acceptable activity levels or diets, or even take proactive intervention steps if necessary. Because bones generally heal slowly, the device may not need to be worn constantly. Instead, the external wireless reader 42 may be more similar to a blood pressure cuff, needing to be worn only during examinations (which may only be needed a few times each week).

[0048] Further aspects and advantages of the present technology are provided in the following clauses. Item 1. A patient monitoring system for monitoring ossification of an internally fixed fracture in a bone of a subject, comprising: an implantable fixation device operative to be secured to the bone, the bone plate configured to be anchored to the bone on either side of the fracture; a primary load sensor operative to be positioned directly adjacent to the fracture, the primary load sensor provided on the bone plate at a first location, the first strain sensor operative to monitor an amount of strain (primary strain) in the bone plate at the first location, and communication circuitry operative to transmit a first wireless signal indicative of the amount of primary strain; and a reference load sensor provided on the bone plate at a second location spaced from the first location, the reference load sensor operative to monitor an amount of strain (primary strain) in the bone plate at the second location. and a reference load sensor including a second strain sensor operative to monitor an amount of primary strain (first order distortion) and a communication circuit operative to transmit a second wireless signal indicative of the amount of baseline strain; and an external wireless reader including an antenna, a processor, and a wireless communication radio, wherein the processor is configured to receive the first wireless signal and the second wireless signal via the antenna and transmit, using the wireless communication radio, a signal to a data server over a wireless communication network, the signal indicative of the amount of primary distortion, the amount of baseline strain, and further including a unique identifier corresponding to at least one of the subject or the implantable fixation device. Item 2. The patient monitoring system of clause 1, further comprising a data server in digital communication with the external wireless reader, wherein at least one of the processor or the data server is configured to use the received indication of primary strain and the received indication of reference strain to determine an amount of relative support provided by the bone plate as a result of the fracture, and store the determined amount of relative support in non-transitory memory in communication with at least one of the processor or the data server. Item 3. The patient monitoring system of clause 2, wherein the processor or data server is configured to determine the amount of relative support provided by the bone plate by calculating a ratio between the primary strain and the reference strain. Item 4. The patient monitoring system of clause 3, wherein the processor is further configured to prompt the subject to position the bone in a first unloaded position and separately position the bone in a second loaded position, determine an amount of primary strain in each of the first unloaded position and the second loaded position, and determine an amount of reference strain in each of the first unloaded position and the second loaded position, and at least one of the processor or the data server is configured to determine the amount of relative support provided by the bone plate by calculating a ratio of the difference in primary strain between the unloaded position and the loaded position to the difference in reference strain between the unloaded position and the loaded position. Item 5. The patient monitoring system of clause 4, wherein the external wireless reader further includes a display, and wherein the processor is configured to prompt the subject via the display to position the bone in a first unloaded position and separately in a second load-bearing position. Item 6. The patient monitoring system of clause 5, wherein the processor is configured to prompt the subject via the display to apply additional load to the bone when the primary strain in the load-bearing posture is less than a predetermined minimum threshold amount of strain. Item 7. The patient monitoring system of any one of clauses 4 to 6, wherein at least one of the processor or the data server is configured to determine the amount of relative support provided by the bone plate only if the primary strain in the load-bearing position exceeds a predetermined minimum threshold amount of strain. Item 8. A patient monitoring system as described in any one of clauses 1 to 7, wherein the external wireless reader further includes an inductive charging circuit operative to supply power to each of the primary load sensor and the reference load sensor via a magnetic field transmitted from the antenna. Item 9. The patient monitoring system of clause 8, wherein the external wireless reader comprises a wearable component in wired communication with the display device via a tether, the wearable component comprising an antenna disposed within a carrier having at least one strap configured to extend around a portion of the subject. Item 10. The patient monitoring system of clause 9, wherein the wearable component further includes a processor. Item 11. The patient monitoring system of clause 9 or 10, wherein the fabric carrier is further secured to a brace that operates to extend around the subject's joint. Item 12. A patient monitoring system according to any one of clauses 1 to 11, wherein the antenna has a length, and the length of the antenna is greater than the distance between the first position and the second position. Item 13. A method for monitoring ossification of fractures from a plurality of subjects, the method comprising: receiving, via a wireless communications network, a plurality of data sets from the plurality of subjects, each data set representing a plurality of strain measurements obtained from smart fixation devices affixed to the subject's bones across a fracture, the plurality of strain measurements including at least a first strain measurement (primary strain) indicative of an amount of load borne by the fixation device across the fracture and at least a second strain measurement (reference strain) indicative of an amount of load borne by the fixation device on the integral bone; calculating, for each of the plurality of data sets, a ratio of the amount of primary strain to the amount of reference strain; storing each data set and each calculated ratio in non-volatile memory along with a date and time of the strain measurement and along with a patient identifier representative of the source of the measurement; and providing a physician interface for graphically showing change in the ratio over time from each of a plurality of different subjects. Item 14. The method of clause 13, further comprising: maintaining a machine learning predictive model that generates a predicted patient-specific healing trajectory for each subject, the patient-specific healing trajectory including a predicted trajectory and a confidence interval representing a likely progression of healing progression beginning at bone fixation; the method further comprising overlaying a plurality of datasets for the subject on a graphical representation of the predicted patient-specific healing trajectory in a physician interface; the machine learning predictive model being refined using at least a subset of the received datasets and a plurality of secondary factors including at least two of the nature and location of the fracture, the subject's height, weight, age, sex, metabolic profile, blood pressure, pre-existing conditions, complex risk factors, or comorbidities. Item 15. The method of clause 14, further comprising: calculating, for each subject, a forward healing trajectory extending forward in time from the subject's most recently acquired data set; and overlaying the forward healing trajectory on a graphical representation of the predicted patient-specific healing trajectory. Item 16. The method of clause 15, further comprising providing a warning via a physician interface if one of the data sets or the positive healing trajectory is outside the confidence interval. Item 17. A method for obtaining bone ossification data from an implantable smart fixation device provided within a subject's body, the method comprising: energizing an external antenna to generate an alternating magnetic field and inductively energize a plurality of load sensors provided in contact with a bone plate secured to the bone spanning a fracture; receiving, via the external antenna, a wireless data signal from each of the plurality of load sensors, the wireless data signal indicative of an amount of strain experienced by the bone plate; identifying a representative strain value from each wireless data signal; and determining a relative amount of load borne by the bone plate spanning the fracture by dividing a first strain value indicative of an amount of strain experienced by the bone plate at the fracture by a second strain value indicative of an amount of strain experienced by the bone plate distal to the fracture. Item 18. The method of clause 17, further comprising prompting the subject via the electronic display to position the bone or the subject's body in a first unloaded position, and prompting the subject via the electronic display to position the bone or the subject's body in a second load-bearing position, wherein the bone plate experiences at least a predetermined minimum amount of strain in the load-bearing position, and wherein each of the first strain value and the second strain value comprises a difference between an amount of strain measured in the load-bearing position and an amount of strain measured in the unloaded position. Clause 19. The method of clause 18, further comprising providing a warning to the subject if the amount of strain in the load-bearing position is less than a predetermined minimum amount of strain.

[0049] Benefits, other advantages, and solutions to problems have been described with respect to particular embodiments. The benefits, advantages, solutions to problems, and any element(s) that may give rise to or enhance any benefit, advantage, or solution should not be construed as a critical, necessary, or essential feature or element of any or all claims unless such benefit, advantage, solution, or element is expressly recited in such claim.

[0050] Furthermore, embodiments and limitations disclosed herein are not available to the public under the doctrine of public domain if those embodiments and / or limitations (1) are not explicitly claimed in the claims, and (2) are equivalents or potentially equivalents of explicit elements and / or limitations in the claims under the doctrine of equivalents.

[0051] Additional embodiments of external wireless readers are provided in the appendix filed herewith.

[0052] [Embodiment] (1) A patient monitoring system for monitoring ossification of an internally fixed fracture in a bone of a subject, comprising: an implantable fixation device operative to be anchored to the bone, a bone plate configured to be secured to the bone on either side of the fracture; a primary load sensor disposed on the bone plate at a first location operative to be positioned immediately adjacent the fracture, the primary load sensor operative to monitor an amount of strain (primary strain) in the bone plate at the first location and a communication circuit operative to transmit a first wireless signal indicative of the amount of primary strain; an implantable fixation device including a reference load sensor disposed on the bone plate at a second location spaced from the first location, the reference load sensor including a second strain sensor operative to monitor an amount of strain (reference strain) in the bone plate at the second location and a communication circuit operative to transmit a second wireless signal indicative of the amount of reference strain; 1. An external wireless reader including an antenna, a processor, and a wireless communication radio, the processor comprising: receiving the first radio signal and the second radio signal via the antenna; and an external wireless reader configured to use the wireless communication radio to transmit a signal to a data server over a wireless communication network, the signal indicating the amount of the first-order distortion, the amount of the reference distortion, and further including a unique identifier corresponding to at least one of the subject or the implantable fixation device. (2) The data server further comprises: the data server digitally communicating with the external wireless reader; At least one of the processor or the data server determining a relative amount of support provided by the bone plate as a result of a fracture using the received indication of the primary strain and the received indication of the reference strain; and storing the determined amount of relative support in non-transitory memory in communication with at least one of the processor or the data server. (3) A patient monitoring system as described in embodiment 2, wherein the processor or the data server is configured to determine the amount of relative support provided by the bone plate by calculating the ratio between the primary strain and the reference strain. (4) The processor: prompting the subject to position the bone in a first unloaded position and separately to position the bone in a second load-bearing position; determining an amount of primary strain in each of the first unloaded position and the second loaded position; determining an amount of baseline strain in each of the first unloaded position and the second loaded position; A patient monitoring system as described in embodiment 3, wherein at least one of the processor or the data server is configured to determine the amount of relative support provided by the bone plate by calculating the ratio of the difference in primary strain between the unloaded position and the loaded position to the difference in reference strain between the unloaded position and the loaded position. (5) A patient monitoring system as described in embodiment 4, wherein the external wireless reader further includes a display, and the processor is configured to prompt the subject via the display to position the bone in the first unloaded position and separately in the second load-bearing position.

[0053] (6) A patient monitoring system as described in embodiment 5, wherein the processor is configured to prompt the subject via the display to apply additional load to the bone if the primary strain in the load-bearing posture is less than a predetermined minimum threshold amount of strain. (7) The patient monitoring system of embodiment 4, wherein at least one of the processor or the data server is configured to determine the amount of relative support provided by the bone plate only if the primary strain in the load-bearing position exceeds a predetermined minimum threshold amount of strain. (8) A patient monitoring system as described in embodiment 1, wherein the external wireless reader further includes an inductive charging circuit that operates to supply power to each of the primary load sensor and the reference load sensor via a magnetic field transmitted from the antenna. (9) The external wireless reader includes a wearable component that is in wired communication with the display device via a tether; A patient monitoring system as described in embodiment 8, wherein the wearable component comprises the antenna mounted within a carrier having at least one strap configured to extend around a portion of the subject. (10) A patient monitoring system as described in embodiment 9, wherein the wearable component further includes the processor.

[0054] (11) A patient monitoring system as described in embodiment 9, wherein the fabric carrier is further secured to a brace that operates to extend around the subject's joint. (12) A patient monitoring system as described in embodiment 1, wherein the antenna has a length, and the length of the antenna is greater than the distance between the first position and the second position. (13) A method for monitoring ossification of fractures in multiple subjects, comprising: receiving, via a wireless communications network, a plurality of data sets from a plurality of subjects, each data set representing a plurality of strain measurements obtained from smart fixation devices affixed to a bone of the subject across a fracture, the plurality of strain measurements including at least a first strain measurement (primary strain) indicative of an amount of load borne by the fixation device across the fracture and at least a second strain measurement (reference strain) indicative of an amount of load borne by the fixation device in a unitary bone; calculating, for each of the plurality of data sets, a ratio between an amount of primary distortion and an amount of reference distortion; storing each data set and each calculated ratio in non-volatile memory along with the date and time of said strain measurements and along with a patient identifier representative of the source of said measurements; providing a physician interface for graphically showing change in said ratio over time from each of a plurality of different subjects. (14) Maintaining a machine learning prediction model that generates a predicted patient-specific healing trajectory for each subject, the patient-specific healing trajectory including a predicted trajectory and a confidence interval representing a likely progression of healing progression beginning at bone fixation, the method further comprising overlaying the plurality of datasets for a subject on a graphical representation of the predicted patient-specific healing trajectory in the physician interface; 14. The method of claim 13, wherein the machine learning predictive model is refined using at least a subset of the received dataset and a plurality of secondary factors including at least two of the nature and location of the fracture, the subject's height, weight, age, sex, metabolic profile, blood pressure, pre-existing conditions, complex risk factors, or comorbidities. (15) calculating, for each subject, a forward healing trajectory extending forward in time from the most recently acquired data set for that subject; 15. The method of claim 14, further comprising overlaying the positive healing trajectory on the graphical representation of the predicted patient-specific healing trajectory.

[0055] (16) The method of embodiment 15, further comprising providing a warning via the physician interface if one of the data sets or the positive healing trajectory is outside the confidence interval. (17) A method for obtaining bone ossification data from an implantable smart fixation device provided in a subject's body, comprising: energizing an external antenna to generate an alternating magnetic field and inductively energize a plurality of load sensors disposed in contact with a bone plate secured to the bone across the fracture; receiving, via the external antenna, a wireless data signal from each of the plurality of load sensors, the wireless data signal indicative of an amount of strain experienced by the bone plate; identifying a representative distortion value from each wireless data signal; determining a relative amount of load carried by the bone plate across the fracture by dividing a first strain value indicative of an amount of strain experienced by the bone plate at the fracture by a second strain value indicative of an amount of strain experienced by the bone plate away from the fracture. (18) prompting the subject via an electronic display to position the bone or the subject's body in a first unloaded position; prompting the subject via the electronic display to position the bone or the subject's body in a second load-bearing position, wherein the bone plate experiences at least a predetermined minimum amount of strain in the load-bearing position; 18. The method of claim 17, wherein each of the first strain value and the second strain value comprises a difference between an amount of strain measured in the load-bearing position and an amount of strain measured in the unloaded position. (19) The method of embodiment 18, further comprising providing a warning to the subject if the amount of strain in the load-bearing posture is less than the predetermined minimum amount of strain.

Claims

1. 1. A patient monitoring system for monitoring ossification of an internally fixed fracture in a bone of a subject, comprising: an implantable fixation device operative to be anchored to the bone, a bone plate configured to be secured to the bone on either side of the fracture; a primary load sensor provided on the bone plate at a first location operative to be positioned immediately adjacent the fracture, the primary load sensor operative to monitor an amount of strain (primary strain) in the bone plate at the first location and a communication circuit operative to transmit a first wireless signal indicative of the amount of primary strain; an implantable fixation device including: a reference load sensor disposed on the bone plate at a second location spaced from the first location, the reference load sensor including a second strain sensor operative to monitor an amount of strain (reference strain) in the bone plate at the second location; and a communication circuit operative to transmit a second wireless signal indicative of the amount of reference strain; 1. An external wireless reader including an antenna, a processor, and a wireless communication radio, the processor comprising: receiving the first radio signal and the second radio signal via the antenna; an external wireless reader configured to use the wireless communication radio to transmit a signal to a data server over a wireless communication network, the signal indicating the amount of the first-order distortion, the amount of the reference distortion, and further including a unique identifier corresponding to at least one of the subject or the implantable fixation device; At least one of the processor or the data server: determining the magnitude of the primary strain in each of an unloaded position and a loaded position; determining the amount of the reference strain in each of the unloaded position and the loaded position; determining the amount of relative support provided by the bone plate by calculating a ratio of the difference in primary strain between the unloaded and loaded positions to the difference in reference strain between the unloaded and loaded positions. Patient monitoring systems.

2. the data server further comprising: the data server in digital communication with the external wireless reader; At least one of the processor or the data server determining the amount of relative support provided by the bone plate as a result of a fracture using the received indication of the primary strain and the received indication of the reference strain; and storing the determined amount of relative support in a non-transitory memory in communication with at least one of the processor or the data server.

3. 3. The patient monitoring system of claim 2, wherein the processor or the data server is configured to determine the amount of relative support provided by the bone plate by calculating a ratio between the primary strain and the reference strain.

4. The processor: configured to prompt the subject to position the bone in the unloaded position and alternatively to position the bone in the load-bearing position.

4. The patient monitoring system of claim 3.

5. 5. The patient monitoring system of claim 4, wherein the external wireless reader further includes a display, and the processor is configured to prompt the subject via the display to position the bone in the unloaded position and alternatively in the load-bearing position.

6. 6. The patient monitoring system of claim 5, wherein the processor is configured to prompt the subject via the display to apply additional load to the bone if the primary strain in the load-bearing posture is less than a predetermined minimum threshold amount of strain.

7. 5. The patient monitoring system of claim 4, wherein the at least one of the processor or the data server is configured to determine the amount of relative support provided by the bone plate only if the primary strain in the load-bearing position exceeds a predetermined minimum threshold amount of strain.

8. 10. The patient monitoring system of claim 1, wherein the external wireless reader further comprises an inductive charging circuit operative to provide power to each of the primary load sensor and the reference load sensor via a magnetic field transmitted from the antenna.

9. the external wireless reader comprises a wearable component in wired communication with the display device via a tether; 10. The patient monitoring system of claim 8, wherein the wearable component comprises the antenna disposed in a carrier having at least one strap configured to extend around a portion of the subject.

10. The patient monitoring system of claim 9 , wherein the wearable component further comprises the processor.

11. 10. The patient monitoring system of claim 9, wherein the fabric carrier is further secured to a brace that operatively extends around the subject's joint.

12. The patient monitoring system of claim 1 , wherein the antenna has a length, the length of the antenna being greater than a distance between the first location and the second location.

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