DEVICE FOR MEASURING, PROCESSING AND TRANSMITTING IMPLANT PARAMETERS

Abstract

A device (1) for measuring, processing and transmitting implant parameters in osteosynthesis, the device (1) comprising: a biocompatible sterilizable housing (2); a strain sensor (3); an electronic unit (4) to process electrical signals provided by the strain sensor (3), wherein the housing (2) comprises (i) a measurement portion (5) of the height H5 comprising a cavity (51); and (ii) a compartment portion (6) of the height H6 with a cavity (61), and wherein the measurement portion (5) comprises at least two affixing means (7) for affixing the device (1) to an implant and wherein the electronic unit (4) is positioned in the cavity of the compartment portion (6).

Claims

1-70. (canceled)

71: A device for measuring, processing and transmitting implant parameters in osteosynthesis, the device comprising: a biocompatible sterilizable housing; a strain sensor; and an electronic unit electrically connected to the strain sensor and configured to process electrical signals provided by the strain sensor; wherein the housing comprises a measurement portion having a height H5, an upper surface, a lower contact surface and a measurement portion cavity, and a compartment portion having a height H6 with a compartment portion cavity, wherein the measurement portion comprises at least two affixing means for affixing the device to an implant, wherein the at least two affixing means are spaced apart from each other by a distance D, wherein the cavity of the measurement portion is arranged between the at least two affixing means, wherein the strain sensor is positioned in the measurement portion cavity, and wherein the electronic unit is positioned in the compartment portion cavity.

72: The device according to claim 71, wherein the at least two affixing means are configured for releasably affixing the device to the implant.

73: The device according to claim 71, wherein the height H5 of the measurement portion is smaller than the height H6 of the compartment portion.

74: The device according to claim 71, wherein the height H5 of the measurement portion does not exceed 4 mm.

75: The device according to claim 71, wherein the measurement portion is provided with a slot adjacent to the compartment portion, wherein the measurement portion has a length L5 measured along a line connecting centers of the at least two affixing means, and wherein the slot extends along 30% to 90% of the length L5 of the measurement portion.

76: The device according to claim 71, wherein the compartment portion has a top surface, wherein the upper surface of the measurement portion and the top surface of the compartment portion form a planar, upper free surface of the device.

77: The device according to claim 71, wherein the implant to which the device is affixable is a bone plate, wherein device has an L-shaped cross-sectional area orthogonal to a line connecting centers of the at least two affixing means, wherein the upper surface of the measurement portion and a top surface of the compartment portion form an upper free surface of the device wherein the measurement portion lies within a first leg of the L-shaped cross-sectional area of the device and the compartment portion lies within a second leg of the L-shaped cross-sectional area of the device, wherein the height H5 extends from the upper free surface of the device measured parallel to the second leg and the height H6 extends from the upper free surface of the device through the second leg and protrudes beyond the lower surface of the measurement portion such that the lower surface of the measurement portion is positionable on a top surface of the bone plate while the compartment portion extends beside the bone plate.

78: The device according to claim 71, wherein the measurement portion comprises a strain concentration area located in between the at least two affixing means, and wherein the strain sensor is configured to measure strain at the strain concentration area.

79: The device according to claim 71, wherein the compartment portion is mechanically connected to the measurement portion by means of a connection portion.

80: The device according to claim 71, wherein the strain sensor is sealed within the measurement portion cavity by a cover.

81: The device according to claim 71, wherein the at least two affixing means are through holes in the measurement portion for receiving fasteners.

82: The device according to claim 71, wherein the at least two affixing means are a subset of a plurality of through holes in the measurement portion for accommodating hole patterns of a plurality of different implants.

83: The device according to claim 71, wherein an undersurface of the at least two affixing means is configured to abut with a circular flat surface.

84: The device according to claim 71, wherein the at least two affixing means includes at least one fastener or at least one clamp.

85: The device according to claim 71, wherein the at least two affixing means includes at least one clamp, and wherein the at least one clamp is integral with the measurement portion.

86: The device according to claim 71, wherein the electronic unit comprises an electronic data processing device electrically connectable or connected to the strain sensor, a data memory electrically connected to the data processing device for storing data received from the data processing device, a data transmission device electrically connected to the data memory, and a power supply.

87: The device according to claim 71, wherein the device further comprises an antenna for wireless data transmission, which is recessed in a pocket in the housing.

88: The device according to claim 71, wherein at least one strain sensor is attached to an inner wall of the measurement portion cavity, which is closest to the lower contact surface.

89: The device according to claim 71, wherein the housing is made of a biocompatible non-biodegradable metallic or polymeric material.

90: A method for monitoring a medical implant using a device according to claim 86 affixed to the medical implant, the method comprising the following steps: A) obtaining measurement data by means of the strain sensor; B) performing real-time processing on the measurement data obtained in step A) by means of the data processing device; C) calculating statistical data based on the measurement data as processed in step B); D) storing the statistical data calculated in step C) in the data memory; E) inquiring and downloading selected statistical data stored in the data memory in step D) by means of an external data receiver; and F) transmitting the downloaded selected statistical data from the external data receiver to a computer for further data management and processing.

Description

A BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Several embodiments of the invention will be described in the following by way of example and with reference to the accompanying drawings in which:

[0089] FIG. 1 illustrates a perspective view of an embodiment of the device according to the invention;

[0090] FIG. 2 illustrates a sectional view of the housing of FIG. 1 orthogonal to the force transmission path;

[0091] FIG. 3 illustrates a perspective view of another embodiment of the device according to the invention with the cavity of the measurement portion hermetically sealed;

[0092] FIG. 4 illustrates a sectional view of the housing of a further embodiment of the device according to the invention along the force transmission path;

[0093] FIG. 5 illustrates a magnified view of detail A in FIG. 4;

[0094] FIG. 6 illustrates a perspective view of a further embodiment of the device according to the invention;

[0095] FIG. 7 illustrates a lateral view of the embodiment of FIG. 6; and

[0096] FIG. 8 illustrates a top view of the embodiment of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

[0097] FIGS. 1 and 2 illustrate an embodiment of the device 1 for measuring, processing and transmitting implant parameters in osteosynthesis according to the invention, wherein the device 1 essentially comprises a biocompatible sterilizable housing 2 which is partitioned into a measurement portion 5 of the height H5 and comprising a cavity 51 and a compartment portion 6 of the height H6 with a cavity 61, a strain sensor 3 arranged in the cavity 51 of the measurement portion 5, an electronic unit 4 to process electrical signals provided by the strain sensor 3, wherein the electronic unit 4 is positioned in the cavity 61 of the compartment portion 6. The measurement portion 5 comprises a plurality of affixing means 7 for affixing the device 1 to an implant. The cavity 51 of the measurement portion 5 is electrically connected to the cavity 61 of the compartment portion 6 to transmit electrical signals provided by the strain sensor 3 to the electronic unit 4 for further processing. The measurement portion 5 comprises a lower contact surface 9 configured to contact a top surface of a bone plate (not shown) and spaced apart therefrom by the height H5 an upper surface 10. Exemplarily, but not limiting, the relation H5:H6 is about 0.25 and the maximum height of the device 1 above the contact surface 9 is about 2 mm.

[0098] In alternative embodiments the relation H5:H6 may be greater than 0.25 but smaller than 0.5, preferably smaller than 0.35 so that the maximum height of the device 1 above the contact surface 9 does not exceed 4 mm, preferably 2 mm.

[0099] The strain sensor 3 is positioned in the cavity 51 of the measurement portion 5 in the proximity of the contact surface 9. The electronic unit 4 comprises an electronic data processing device electrically connectable or connected to the strain sensor 3, a data memory electrically connected to the data processing device and suitable to store data received from the data processing device, a data transmission device electrically connected to the data memory and a power supply. In alternative embodiments the device 1 may additionally comprise one or more additional sensors, an electronic signal conditioner and an analog-digital converter. Further, the device 1 comprises an antenna 21 for wireless data transmission, which is recessed in a pocket 22 in the housing 2.

[0100] The device 1 has an L-shape in a cross-section orthogonal to a line 13 connecting the centers 14 of the affixing means 7 so that the measurement portion 5 is positionable on a top surface of a bone plate while the compartment portion extends beside the bone plate. The upper surface 10 of the measurement portion 5 and a top surface 12 of the compartment portion 6 form an upper free surface of the device 1 which is planar and in the form of a straight surface. The measurement portion 5 comprises a strain concentration 8 area located in between the at least two affixing means 7, wherein the strain sensor 3 is configured to measure strain at the strain concentration area 8. The strain concentration area 8 is meant to be a region with reduced cross sectional area (transverse section) of the measurement portion 5 in order to maximize the local material strain under a given load running over the measurement portion 5. It can be realized by a cavity or a transverse groove from either side of the measurement portion 5. In the present embodiment the strain concentration area 8 includes the cavity 51 of the measurement portion 5 to accommodate the at least one strain sensor 3. The strain sensor 3 is attached to the inner wall of the cavity 51 of the measurement portion 5 which closest to the contact surface 9.

[0101] The compartment portion 6 is mechanically connected to the measurement portion 5 by means of the connection portion 15. This connection portion 15 is remote to the strain concentration area 8. Exemplarily, but not limiting, the compartment portion 6 and the measurement portion 5 are integral with the connecting portion 15. In alternative embodiments the connecting portion 15 is mountable to the compartment portion 6 and to the measurement portion 5.

[0102] The affixing means 7 are configured as through holes for receiving fasteners. Exemplarily, the affixing means 7 are configured as a plurality of through holes to accommodate various existing hole patters of available implants. Along the line 13 connecting the centers 14 of the affixing means 7 the housing 2 has an oblong shape with a first end 17, a second end 18 and a length L. The line 13 connecting the centers 14 of the affixing means 7 also defines the force transmission path, along which stresses induced by these forces occur. The compartment portion 6 is mechanically connected to the measurement portion 5 by means of the connection portion 15 over the full length L.

[0103] The compartment portion 6 comprises a cap 23 to close the cavity 61 of the compartment portion 6. The cavity 51 of the measurement portion 5 is sealed by a cover 16 so that the strain sensor 3 is located in a sealed cavity so that the sensor cavity and the compartment portion 6 form a hermetic or near-hermetic seal to the environment.

[0104] The housing 2 is made of a biocompatible but non-biodegradable metallic or polymeric material, preferably Titanium or Titanium alloys, Stainless Steel, Polyetheretherketone (PEEK) or Liquid Crystal Polymer (LCP). The power supply is a primary or rechargeable battery, a capacitor or a fuel cell, wherein the rechargeable battery or capacitor is chargeable by induction or by energy harvesting, by deriving thermal energy from a patient's body, kinetic energy from body movements, deformation energy from the implant under functional loading or by harvesting energy from surrounding electromagnetic fields.

[0105] In alternative embodiments the device 1 may additionally comprise further strain sensors 3 arranged in the measurement portion 5 and/or a second or more sensor(s) which are placed in the compartment portion 6.

[0106] A further embodiment of the device 1 according to the invention is illustrated in FIG. 3 which differs from the embodiment of FIGS. 1 and 2 only therein that the measurement portion 5 is provided with a vertical throughgoing slot 11 adjacent to the compartment portion 6. Exemplarily, but not limiting, the slot 11 extends over 50% of the length L5 of the measurement portion 5. In alternative embodiments the slot 11 may extend between 30 to 60% of the length L5 of the measurement portion 5. Due to the slot 11 stresses and strains are transmitted to the strain sensor 3 but not to the compartment portion 6.

[0107] In alternative embodiments the length L5 of the measurement portion 5 and the length L6 of the compartment portion 6 may be different and the slot 11 may extend over 30 to 60% of the shorter of the length L5 of the measurement portion 5 and the length L6 of the compartment portion. The connecting portion 15 may comprises more than slot 11 to reduce the cross-sectional area of the connection portion 15 between the measurement portion 5 and the compartment portion 6 maximum to 70%, preferably maximum to 60% of the shorter of the length L5 of the measurement portion 5 and the length L6 of the compartment portion 6. In other embodiments the one or more slots 11 may reduce the cross-sectional area of the connection portion 15 between the measurement portion 5 and the compartment portion 6 maximum to 50%, preferably maximum to 40% of the shorter of the length L5 of the measurement portion 5 and the length L6 of the compartment portion 6.

[0108] FIGS. 4 and 5 illustrates another embodiment which differs from the embodiment of FIGS. 1-3 only therein, that the strain concentration area 8 comprises a recess 19 in the contact surface 9 of the measurement portion 5 opposite the cavity 51 of the measurement portion 5 to reduce local transverse cross sectional area in relation to the transverse cross sectional area of the measurement portion 5.

[0109] A further embodiment of the device 1 according to the invention is illustrated in FIGS. 6-8 wherein the device 1 comprises:

A) a biocompatible sterilizable housing 2;
B) a strain sensor 3;
C) an electronic unit 4 electrically connected to the strain sensor 3 and configured to process electrical signals provided by the strain sensor 3, wherein
D) the housing 2 comprises
(i) a measurement portion 5 of the height H5 and comprising a cavity 51; and
(ii) a compartment portion 6 of the height H6 with a cavity 61, and wherein
E) the measurement portion 5 comprises:
at least two affixing means 7 for affixing the device 1 to an implant, wherein the at least two affixing means 7 are spaced apart from each other, wherein
the cavity 51 of the measurement portion 5 is arranged between the at least two affixing means 7; and wherein
the strain sensor 3 is positioned in the cavity 51 of the measurement portion 5; and wherein
F) the electronic unit 4 is positioned in the cavity 61 of the compartment portion 6.

[0110] The configuration of the embodiment of FIGS. 6-8 differs from the embodiments of FIGS. 1-5 only therein that the height H5 of the measurement portion 5 is exemplarily, but not limiting, essentially equal to the height H6 of the compartment portion 6. In alternative embodiments the height H5 of the measurement portion 5 may be different from the height H6 of the compartment portion 6. Furthermore, the affixing means 7 comprise two clamps 20a,20b to attach the device to a longitudinal rod, e.g. a spinal rod of a spinal fusion device. Exemplarily, the clamps 20a,20b are integral with the measurement portion 5. Each clamp 20a,20b includes a curved contact surface 9 forming a channel 24 with the shape of a portion of a circular cylinder with the diameter d so that a longitudinal rod is positionable in the channels 24 of both clamps 20a,20b. Thereby, the contact surface 9 is located at a lateral portion of the measurement portion 5 which is remote from the compartment portion 6.

[0111] Additionally, in alternative embodiments the device 1 according to the invention may comprise one or more of the following features: [0112] the electronic unit 4 additionally comprises an accelerometer-based event detector configured to control sleep- and wake-up stages of the electronic unit based on body movement; [0113] the electronic data processing device is electrically connectable to at least one sensor 3 through a signal conditioner and analog-digital converter allowing to process measured signals received from said at least one sensor; [0114] the data memory is electrically connected to said signal processing device allowing to store data received from said signal processing device; [0115] the data transmission device is electrically connected to said data memory for transmitting data received from said data memory to a remote data receiving device which is connectable to an external data processing device; [0116] the electronic data processing device comprises at least one peak-valley detector to extract extreme values corresponding to signal amplitudes from the measured signal, wherein the at least one peak-valley detector preferably extracts signal amplitudes in real-time; [0117] the at least one peak-valley detector is programmed to detect and supply signal amplitudes above a predefined amplitude threshold; and is programmed to count the detected amplitudes above said amplitude threshold; [0118] the at least one peak-valley detector is programmed to detect and supply the elapsed time between detected signal amplitudes above a predefined amplitude threshold defined as event-pause; [0119] the electronic data processing device is programmed to calculate statistically relevant data based on measurement data received from the one or more sensor(s) and to store the statistical data in the data memory; [0120] the electronic data processing device is programmed to calculate statistically relevant data for a defined and recurring time period; [0121] the data processing device is programmed for continuous data collection. the electronic data processing device is programmed to calculate statistically relevant data from signal amplitude values and counts obtained from the at least one peak-valley detector; [0122] statistically relevant values are selected from the following list, but not limited to, [0123] Arithmetic mean of amplitudes or event-pauses [0124] Standard deviation of amplitudes or event pauses [0125] Minimum and maximum amplitude or event pause [0126] Median and percentiles of amplitudes or event-pauses [0127] Histogram of amplitudes or event-pauses [0128] Total counts of amplitudes or event-pauses [0129] statistically relevant values are calculated for a defined number of largest detected amplitudes [0130] the data transmission device is configured as a wireless data transmitter based on a wireless technology standard, preferably Bluetooth, RFID, NFC or ZigBee; [0131] at least one of the one or more sensor(s) is suitable to obtain measurement data related to at least one of the following physical quantities: load applied to an implant, strain in an implant and relative displacement of implant parts; and [0132] the one or more sensor(s) is/are selected from the following group of measuring probes: inductivity meters, capacitance meters, incremental meters, strain gauges, particularly wire resistance or capacitive strain gauges, load cells, piezo based pressure sensors, accelerometers, gyroscopes, goniometers, magnetometers, humidity sensors, temperature sensors.

[0133] A preferred embodiment of the method for monitoring and/or controlling an implant essentially comprises the following steps: A) obtaining measurement data by means of the strain sensor 3; B) performing real-time processing on the measurement data obtained under step A) by e.g. employing one or several real-time min-max detectors with different sensitivity thresholds and respective peak counters; C) calculating statistical parameters, such as the sum of maxima and minima and the peak counts in real-time based on the processed data under step B); D) automatically storing the statistical parameters in the data memory at defined time points over the day cycle or on manual request; E) inquiring and downloading selected data stored in the data memory by means of an external data receiver; and F) transmitting the downloaded selected data from the external data receiver to an external computer for further data management and processing. The patient data can be exemplarily but not limiting recorded and analyzed in the central computer to efficiently produce statistical reference plots to improve the interpretation of the data. If a determination of the patient's activity is of interest, e.g. the number of steps per hour and the intensity distribution of the steps an activity histogram can be generated on the basis of the continuously recorded data. By this means a topical feedback related to the strain of the fracture can be obtained for the doctor and the patient so as to permit an active exerting of influence for the patient. For this reason, in step A) the measurement data is preferably continuously collected during a selectable period of time, preferably with a sampling frequency of 9-30 Hz, most preferably of 10-30 Hz.

[0134] Due to a selected evaluation interval between 4 hours and 24 hours for calculating the required statistical data by means of the data processing device the data to be transmitted via the data transmission device to an external data receiver can be significantly reduced. By this means, the energy demand for data transmission can be reduced which usually is the major part of the energy consumption of the data acquisition device so that an autonomous operation of the device 1 during at least four months can be achieved.

[0135] The patient can inquire and download data at any time or even withdraw from inquiring data for several weeks without losing data. The external data receiver may be a smartphone suitably programmed to inquire and download data from the device 1. The inquiry of data may be performed passively, e.g. via an automatic link acquisition of the smartphone once a week so as to permit the patient to be independent of the clinic. Therefore, in step E) the term for inquiring and downloading selected data is freely selectable by a user.

[0136] Exemplarily but not limiting an external data processing can be performed as follows: The data may be either downloaded and stored on the external computer or directly processed in the data receiving device, e.g. a smartphone. The sensor response is calibrated to physical units using a linear approach by utilizing a predefined or patient specific scale factor. A statistical relevant value will be selected for data processing, e.g. the arithmetic mean of amplitudes. if no calibration of the data was performed, the data accumulated over the elapsed recording time can be normalized to the maximum occurred value over time. Data will be plotted over time and provided to the user for therapeutic decision making. A decline in the curve indicates reduction in elastic deformation of the osteosynthesis through increased load sharing of the stiffening bone during healing, whereas no significant change of the curve indicates absence of healing or pathological bone healing. Based on the shape of the curve the user may decide for timely operational or non-invasive intervention or may steer physiotherapy for early regain of patient activity and weight bearing, or to accelerate the healing progression, or to avoid mechanical failure of the osteosynthesis.

[0137] The evaluation interval length determines scattering of the data from natural variances in functional loading of the patient. Longer evaluation intervals lead to reduced scattering. Hence, it can be beneficial to increase evaluation interval length during post processing by averaging several evaluation intervals or by applying filtering such as moving-average filtering.

Meaning of the Results and Presentation

[0138] The mentioned evaluations may be visualized by plotting the measured and processed values over time in absolute or relative terms (normalizing the sensor response to the initial postoperative response of the sensor). For instance, the healing process may be visualized with decreasing average amplitude from peak-valley detection over time. A threshold can be set for determining the optimal time point for implant removal. Mal-unions may be identified at an early stage and different dynamization protocols can be evaluated. The amplitude histogram or percentiles gives information about the patient's activity over time and therefore about the stimulation of the bone. For monitoring distraction implants or segment transport implants or segment transport implants, the current sensor value provides valuable information about the progression of the distraction process.

Application Examples of the Medical Device According to the Invention

[0139] 1) Monitoring of bone healing in osteosynthesis following the principle of secondary healing. The strain in a standard bone plate or intramedullary nail or external fixator rod measured by strain gauges could be acquired and processed with the device 1. Reduction of strain could be interpreted as enhanced load sharing of the bone and as progress in the bone consolidation. Knowledge about the healing progression is valuable information to detect non-unions at an early stage or to determine an optimal time-point for implant removal.

[0140] Mechanical stimulation of bone is known to promote bone formation. A tool to monitor dynamization of newly proposed dynamic implants and its progression over time is also an application field for the device 1. It offers the opportunity to acquire long term and continuous data rather than repeated short term measurements as done by known techniques.

[0141] 2) Monitoring of a distraction or segment transport implant. The method of distracting bone is used for generation of new bone tissue for critical size defects or bone lengthening. The distraction and bone consolidation process can be monitored by measuring the strain in e.g. the struts or Schanz pins of an external fixation construct used for bone segment transport, e.g. a Taylor Spatial Frame,

[0142] 3) Monitoring of implant failure. Catastrophic failure of orthopedic implants from physiological overloading is a common devastating problem leading to re-operation. Data delivered by the device according to the invention may be used for detection of early onset of implant failure. E.g. change in average valley strain over time might indicate onset of plastic implant deformation which might climax in catastrophic failure. Physiotherapy and weight bearing recommendations can be adjusted accordingly.

[0143] 4) Monitoring of spinal fusion. Fusing two or more vertebral body segments is a common orthopedic procedure in spinal surgery. Objective knowledge of the bony fusion status is important for therapeutic decision making. By measuring the spinal rod deformation, this process can be monitored. The drawback of known solutions in the field is their snap-shot nature, where measurements are only performed at distinct time points. Complex physiological loading at the spine makes interpretation of such isolated short-term measurements difficult. Data remains inconclusive. In contrast, the proposed invention utilizes continuous data collection with statistical evaluation, reducing the influencing of functional loading variances and thereby rendering the acquired data relevant.

[0144] In spine the device according to the invention may further be used for controlling deformity corrections such as scoliosis and early detection of implant failure.

[0145] Additional or alternative application examples may be: [0146] Measurement of blood sugar and counteraction by controlled release of Insulin. Blood sugar values are monitored and processed over a certain time period and used for controlling deliverance of medication. This can be realized as autonomous control loop inside the body. The values have to be transferred to an external receiver to control the process. [0147] Arterial blood gas monitoring (O.sub.2, CO.sub.2, blood pressure). [0148] Lactate concentrations.

[0149] Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the scope of the appended claims.

[0150] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.