WO2006045607A1 - Implant monitoring system - Google Patents

Implant monitoring system Download PDF

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Publication number
WO2006045607A1
WO2006045607A1 PCT/EP2005/011511 EP2005011511W WO2006045607A1 WO 2006045607 A1 WO2006045607 A1 WO 2006045607A1 EP 2005011511 W EP2005011511 W EP 2005011511W WO 2006045607 A1 WO2006045607 A1 WO 2006045607A1
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WO
WIPO (PCT)
Prior art keywords
implant
monitoring system
patient
dental
sensor
Prior art date
Application number
PCT/EP2005/011511
Other languages
French (fr)
Inventor
Robert Puers
Wim Claes
Ignace E. Naert
Siegfried V. N. Jaecques
Original Assignee
K.U. Leuven Research And Development
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to GBGB0424065.1A priority Critical patent/GB0424065D0/en
Priority to GB0424065.1 priority
Application filed by K.U. Leuven Research And Development filed Critical K.U. Leuven Research And Development
Publication of WO2006045607A1 publication Critical patent/WO2006045607A1/en

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Classifications

    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61CDENTISTRY; APPARATUS OR METHODS FOR ORAL OR DENTAL HYGIENE
    • A61C19/00Dental auxiliary appliances
    • A61C19/04Measuring instruments specially adapted for dentistry
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/0002Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network
    • A61B5/0031Implanted circuitry
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/45For evaluating or diagnosing the musculoskeletal system or teeth
    • A61B5/4538Evaluating a particular part of the muscoloskeletal system or a particular medical condition
    • A61B5/4542Evaluating the mouth, e.g. the jaw
    • A61B5/4557Evaluating bruxism
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B90/00Instruments, implements or accessories specially adapted for surgery or diagnosis and not covered by any of the groups A61B1/00 - A61B50/00, e.g. for luxation treatment or for protecting wound edges
    • A61B90/06Measuring instruments not otherwise provided for
    • A61B2090/064Measuring instruments not otherwise provided for for measuring force, pressure or mechanical tension
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B2562/00Details of sensors; Constructional details of sensor housings or probes; Accessories for sensors
    • A61B2562/02Details of sensors specially adapted for in-vivo measurements
    • A61B2562/0261Strain gauges
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/45For evaluating or diagnosing the musculoskeletal system or teeth
    • A61B5/4504Bones
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/45For evaluating or diagnosing the musculoskeletal system or teeth
    • A61B5/4528Joints
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00Detecting, measuring or recording for diagnostic purposes; Identification of persons
    • A61B5/45For evaluating or diagnosing the musculoskeletal system or teeth
    • A61B5/4538Evaluating a particular part of the muscoloskeletal system or a particular medical condition
    • A61B5/4542Evaluating the mouth, e.g. the jaw
    • A61B5/4547Evaluating teeth

Abstract

An implant monitoring system for in vivo monitoring of mechanical loading on an implant placed in a patient. At least one sensor unit which is arranged to be operatively connected to the implant. A measuring unit receives an output signal from said sensor unit. A transmitter means is transmitting information to the patient regarding the mechanical loading on the implant. Processing means forming built-in intelligence in the system is arranged to activate said transmitter means without the need of any external input to the system. Also disclosed is a dental implant monitoring system, comprising' at least one sensor arranged to be operatively connected to the implant; and a body actuator which is arranged to transmit, by means of a vibration and/or electrical stimulation signal, information to the patient regarding a mechanical loading detected by the sensor.

Description

IMPLANT MONITORING SYSTEM

Field of the invention

The inventive concept herein described generally relates to monitoring of mechanical loading on implants placed in a patient allowing continuous monitoring and the detection and warning of the patient at set load levels, e.g. in case of a dangerous load level or a potentially dangerous load level.

The inventive concept is especially, but not exclusively, useful for performing an in vivo monitoring of the mechanical loading on one or more dental implants. However, it may also be used for other implant applications, such as the monitoring of an orthopeadic prosthesis or an orthopeadic bone- healing implant (nails, plates, etc).

Background of the invention

Implants used for bone fracture healing and implants to be osseointegrated within the bone itself, such as dental implants, suffer from the lack of control on the bone fracture healing and the bone/implant material integration, respectively. After the implant has been put in place, little or nothing is known about the bone/implant interface, which leads to a mechanical system that is not sufficiently well understood.

The healing and integration judgment must be based on generally accepted values based on experience of the medical staff. This lack of control results in a therapy of the patient that is based on the use of safety: widely accepted margins for loading are used, leading to a grossly overestimated recuperation and immobilization time. Severe economical losses are the consequence.

More and more data becomes available on the benefits on the bone modeling and remodeling process, when implants are mechanically stimulated.

These findings has raised the interest in the development and use of sensor elements integrated with the implants, which can be used to warn the patient in case he overloads the implant.

Wired, as well as wireless sensors have been realized, with the main goal to understand the in vivo loading behavior. Most sensors make use of a piezoresistive strain gauge, that is attached to the implant structure. In the case of wired monitoring, the strain gauges are connected to a table top measuring unit. Wires hence need to trespass the human skin in orthopaedic applications, and need to come out of the mouth in the case of dental applications. Whereas this is suitable and acceptable in a learning phase (the novel measurements need to be fully understood as nobody has done them before at the implant level), for the actual use in therapy and healing this is not acceptable. Also, the wiring influences the normal chewing behavior and limits the use to a hospital environment.

First attempts have been carried out to produce wireless systems, i.e. by using similar sensor elements, but by introducing miniaturized microelectronic circuits that provide the signal amplification and coding to transmit the detected load information to the outside world, incorporated within the implant itself.

This technique has revealed to be very attractive in many senses. At first, the patient is now able to move freely, day and night, and it becomes possible to track the load variations under normal life circumstances. The diagnosis - in case of malfunction - is more reliable, since no wired connection to the registration equipment are needed. Moreover, the possibility of obtaining constant information on the actual load conditions allow the physicians to optimize the revalidation therapy up to maximal load, that results in an improved healing rate (due to the positive input of the mechanical loading) and faster re-integration of the patient in his daily life. Excessive loads on the other hand can also be detected, avoiding early failure of an implant/prosthesis and hence avoiding costly re-operations.

US 6 034 296 discloses an implantable sensing system for a bone fixation device. A telemetry unit is powered and, thereby activated, by a generated strain signal. The strain signal is transmitted to an external receiver in which the strain signal is analyzed. This document does not disclose or suggest any internal signal processing or internal signal evaluation. Nor does this document disclose an means for transmitting any information directly to the patient.

All these advantages lead to an increasing acceptance of these monitoring methods, that is still hampered by the fact that for the immediate interpretation of the signals a doctor is still needed.

SUMMARY OF THE INVENTION

According to a first aspect of the inventive concept there is provided an implant monitoring system for in vivo monitoring of mechanical loading on an implant placed in a patient. The monitoring system comprises at least one sensor unit which is arranged to be operatively connected to the implant; a measuring unit for receiving an output signal from said sensor unit; a transmitter means for transmitting information to the patient regarding the mechanical loading on the implant; and processing means forming built-in intelligence in the system and being arranged to activate said transmitter means without the need of any external input to the system.

Thus, according to this first aspect of the inventive concept there is provided a solution to the above mentioned problem. Clinical and medical expertise may be integrated within the confined space of the internal circuitry.

The patient can now be constantly monitored and warned if he overloads or is risking to overload his implant or prosthesis.

Another advantage obtained thereby is that the patient, by receiving such warnings from the monitoring system, will be able to learn the acceptable load levels, i.e. will be able to improve the healing or osseointegration rate by applying a non-dangerous but still not to weak mechanical loading.

The signal processing means may preferably be arranged to activate said transmitter means as a warning of a dangerous or a potentially dangerous load level, e.g. when the measured mechanical loading exceeds a set load level in the system. It is possible to use two or more warning levels, optionally with associated different warning signals to the patient.

In a preferred embodiment, the warning is activated during a predetermined period of time which may be chosen small enough for the patient to become aware of the overload or the potential dangerous load, but at the same time without giving any unpleasant feeling for the patient.

The set load level may be reconfigurable, e.g. by including bi-directional wireless communication means for remote reconfiguring.

The sensor unit may comprise at least one sensor for detecting at least one of strain, pressure, acceleration and force.

The system may further comprise means for storing information originating from at least one of the sensor unit, the measuring unit and the processor means.

In a presently preferred embodiment, the transmitter means comprises a body actuator for transmitting said information to the patient by means of a vibration signal and/or an electrical stimulation signal. For dental applications, such a body actuator may be configured and arranged to be placed in the oral cavity of the patient.

The system may comprise a patient portable unit for receiving said information regarding the mechanical loading on the implant.

For the dental application especially, the implant monitoring system may further comprise a prosthesis or supporting structure in which the monitoring system is wholly or partly integrated. The prosthesis may be a temporary prosthesis in the since that it may be removed from the monitored implant(s) after the completed use of the monitoring system. Thereafter, conventional dental components may be inserted, such as abutments and artificial crowns. As an alternative, the "smart" prosthesis may be in the form of a non-temporary prosthesis, i.e. in the form of a final prosthesis not to be replaced directly after completed use of the electronics. The functioning of the "smart" prosthesis might be considered as temporary, however. In practice, batteries may need to be changed to keep the monitoring system operational. After a "risky" initial healing period, e.g. 3-6 months, the patient might choose to have the batteries removed and to keep the prosthesis, with the non-functional electronics still in place. This would avoid the cost of making a second, definitive prosthesis.

The functionality of the implant monitoring system according to the first aspect of the inventive concept may be expanded by including also bi-directional wireless communication means for verification, calibration, returning and resetting of modi operandi.

The implant monitoring system according to the first aspect of the inventive concept may be used for monitoring dental implants, orthopaedic bone-healing implant, such as a nail, a plate or the like, or an orthopaedic prosthesis.

The system of the present invention can also be included in any metallic, ceramic or polymeric implant that is used to restore bone or that needs to establish bone-implant interfaces.

The integration of the system of the present invention in a bone healing implant/prosthesis allows to continually monitor and, in case of overload, to warn the patient. This provides the important advantage that the revalidation programme can be started and the normal daily activities resumed in an earlier phase of the healing process.

According to a second aspect of the inventive concept there is provided a dental implant monitoring system for in vivo monitoring mechanical loading on a dental implant placed in a patient, comprising at least one sensor arranged to be operatively connected to the implant; and a body actuator which is arranged to transmit, by means of a vibration stimulation signal and/or an electrical stimulation signal, information to the patient regarding a mechanical loading detected by said sensor. Said body actuator is configured and arranged to be placed in the oral cavity of the patient. The body actuator may comprise a vibration-type actuator for emitting a mechanical vibration stimulation signal to the patient or an audible stimulation signal.

In a preferred embodiment of the system according to the second aspect, the system also comprises processing means for evaluating, internally in the monitoring system, the output from the sensor and for activating said actuator in response to the evaluation.

According to a third aspect of the inventive concept there is provided a dental prosthesis for in vivo monitoring mechanical loading on a dental implant, comprising a supporting structure arranged to be engaged with said implant; at least one sensor which is supported by the supporting structure, and a body actuator which is supported by the supporting structure and arranged to transmit, by means of a vibration stimulation signal and/or an electrical stimulation signal, information to the patient regarding a mechanical loading detected by said sensor.

The dental prosthesis according to the third aspect may further comprise, as described for the other aspects, processing means for evaluating the output from the sensor and for activating said actuator in response to the evaluation.

Such processing means may advantageously also be supported by or integrated with the supporting structure.

The dental prosthesis according to the third aspect may be a temporary prosthesis, intended to be later replaced with a final prosthesis, wherein said supporting structure is thus arranged to be engaged only temporarily with the implant. It may also be in the form of a final prosthesis.

Brief description of the drawings

The invention will now further be described with reference to some embodiments illustrated in the enclosed drawings, in which

Figs 1 to 3 illustrate a dental prosthesis incorporating an embodiment of a monitoring system according to the present invention; Fig. 4 illustrates schematically a setup for monitoring mechanical loading on a dental implant;

Fig. 5 is a schematic circuit diagram of a complete datalogger unit connected to an actuator;

Fig. 6 is a perspective view and a top view illustrating the placement of strain gauges on a dental implant abutment;

Fig. 7 is a schematic cross sectional view illustrating the placement of strain gauges in a cavity of an orthopeadic implant/prosthesis;

Fig. 8 illustrates schematically a setup for monitoring mechanical loading on an orthopaedic bone-healing implant;

Fig. 9 is a schematic diagram of a nulling block circuit;

Fig. 10 is a schematic diagram of a multi-gauge nulling block circuit;

Fig. 11 is a schematic circuit diagram of a complete sensor chip incorporating the multi-gauge nulling block in Fig. 10;

Fig. 12 is a full circuit diagram of the internal electronics; and

Fig. 13 is a schematic diagram illustrating bone response as a function of stimulus intensity.

Some illustrative embodiments for implementing the inventive monitoring system will now be described with reference to the drawings.

Normally, the monitoring system is preferably geometrically adapted to the site where the monitoring is to take place. In some applications, the system may have a typical volume of less than 1 cm^.

Figs 1 to 4 illustrate an embodiment of a dental implant application of the present invention. A dental prosthesis 1 is to be temporarily attached to the jaw bone 2 of a patient (Fig. 3) via a number of abutments 3, each of which is supported by a dental implant. The dental implants are inserted into the jaw bone 2 of the patient and the mechanical loads applied on the implants and, thereby, on the implant/bone interfaces, are to be monitored by the system. When the monitoring is completed, the prosthesis 1 is removed from the patient.

The prosthesis 1 is provided with an internal cavity 4 adapted to receive an electronic unit (Fig. 5) referred to as the datalogger unit 5 and including i.a. central processing features. All electronic components may be assembled on a hybrid substrate in order to cope with the miniaturization demand. The prosthesis 1 also presents a cavity 6 which is placed in front of the datalogger 5 and is adapted to receive (as indicated by an arrow in Fig. 3) a body actuator 7 here in the form of a vibrating actuator. All wires 8 are connected to the datalogger 5. Batteries 9 are stocked symmetrically at either side of the prosthesis l.The batteries 9 may be inserted at the buccal side so that easy replacement can be carried out. A screwed cover on battery holders enables this.

In preferred embodiments, the sensor means for detecting the mechanical loading on the implant(s) comprises one or more strain gauges 10 attached to the implant(s) to be monitored. The sensor means is placed such that sufficient sensitivity can be obtained. Fig. 6 shows an example of a strain sensor on a dental abutment 3, equipped with three strain gauges 10. The strain gauges 10 are glued on the abutment 3, parallel with the abutment's axis, spaced 120° from each other. A dedicated mounting setup has been developed to enable repeatable and more accurate placement of the strain gauges 10.

After gluing the strain gauges 10 on the abutment 3 and connecting the different wires 8, a layer of silicone, a shrink sleeve and another layer of silicone are applied to the instrumented abutment 3 to insulate the strain gauges 10 and the connections from the wet oral environment in order to avoid short circuits. The measurements of the strain gauge or multiple gauges is performed in a unique way, using nulling procedure, that is described below.

Fig. 7 schematically illustrates how a strain sensor may be applied in an orthopaedic application of the present invention. An orthopaedic prosthesis 20 may be provided with a cavity 22, in which a strain sensor 24 is attached and which houses also the electronic circuits 26 receiving the output from sensor 24.

Fig. 8 schematically illustrates a set up for external monitoring mechanical loading on an orthopaedic bone-healing implant 30.

In the illustrated monitoring system, the strain gauges 10 are coupled to a dedicated interface circuit 30 (Fig. 5) to retrieve the mechanical load signal in response to a load on the implant(s). A current controlled semi Wheatstone bridge is used, so that not only low power consumption values can be achieved, but that also self-test and calibration become possible. This information is then sampled by a digital system incorporated in the monitoring system.

The digital system comprises a memory unit 32, which is used to store the load signal trace in time - or a selection thereof, and a decision unit 36, which continuously checks the signal for large values. In case a (set) level is trespassed, preferably based on individual patient data (maximal load allowable), a warning signal is created internally in the implant monitoring system itself, e.g. by the vibration actuator 7 which in the present dental embodiment is located close to the monitored implant. This alarm signal is used to inform the patient that excessive or potential dangerous loads are occurring and that he should adapt his behavior to avoid damage to the bone/implant system.

In a preferred embodiment, the vibration signal is activated during a predetermined period of time. The time period is preferable chosen such that the patient is aware of an overload on his prosthesis but at the same time doesn't experience any unpleasant feeling. The predetermined period of time may be set on an individual basis.

The monitoring system here described may operate in different modes.

In the normal mode, the system constantly measures the load and compares it to a preset value. However, the system may also be operated in a communication mode, which may be achieved e.g. by the application of an external magnetic field. In the communication mode, the system may perform different functions:

Firstly, the system may transmit all measured and stored information over a radio link, allowing medical supervision (indicated at reference numeral 50 in Fig. 12 and at reference numeral 52 in Fig. 8)

- Secondly, an external system 54 may then command the internal monitoring system to go into a listening mode: new settings can be (re)programmed in the device to monitor e.g. at other sampling rates, or to tune the device in the correct operation range, e.g. to cancel for undesired drift effects, which inevitably occur in these systems. This allows even to retune the monitoring system if it would have drifted into an erroneous operation, guaranteeing a prolonged life time of the implanted electronic monitoring system, hi a preferred embodiment, it allows the physicians to set the alarm level to the individual patient's need.

The herein illustrated embodiment of the monitoring system may be designed to collect data over a longer period, without the patient noticing it, improving the comfort of life as well as taking care of his health at the same time.

In a preferred embodiment the system is battery powered, using commercial batteries 9 with a capacity of 25mAh to 100OmAh, depending on the space available (according to the implant used and the requested monitoring period).

The module may be read out after a certain monitoring period by transmitting all the data that are stored in the memory 32. It is preferred that the data can be read (on request) over a distance of at least 15 cm. The captured data may be stored and processed by an external PC 54 as indicated in Fig. 4.

The entire implantable monitoring system comprises several individual building blocks, which are illustrated in Fig. 5. The sensor interface chip 30 comprises low power analogue circuit that converts the minute strain gauge signal 29 into a signal that can be handled by the digital processing unit 36. With all implants, one of the problems is that the forces that are used to fix the implant to or into the bone are quite large, and do even overshadow the biological forces themselves. If no precautions are taken, this will mean that the signal that is sensed can totally obscure the biological signal. Therefore, it is preferable that a nulling or calibration procedure is performed in-situ, prior to starting the actual biological measurements.

Fig. 9 illustrates the method that is used for this purpose: Once the implant is well fixed in place, the sensor strain gauge is measured against a fixed resistor Rref, with IDAC ~ 0 current, and IRJ?F and IgQ at their fixed values. The output of the bridge ΔV is then sampled. This output voltage is thus equal to the prestrain load imposed by the fixation of the implant, and is by no means a biological load signal. This voltage will then be used to feed the third current source, IQ ACJ that will receive a digital word to compensate the strain gauge for this offset. Once this Irj AC ^s se* to this value, the output of the amplifier becomes 0 Volt. This procedure is carried out for all strain gauges 10 used in the implant. The procedure allows a unique and versatile application to all implants.

In Fig. 10 the nulling or in-situ calibration procedure of the system is expanded for 18 strain gauges 10. It shows the introduction multiplexers (MUX) to switch between the 18 different strain-gauge channels. Compensation for every strain-gauge channel separately is carried out after placement of the prosthesis. The digital words needed for compensation are programmed into an on-chip nulling memory REG, composed of registers, using the PROG/SEL- block. In the measurement mode, when a particular strain-gauge channel is measured, the digital word belonging to that particular channel is fetched from REG and offered to the DAC so that offset-compensated measurements are performed. The output voltage V of the multi-gauge measurement setup is amplified by a switched-capacitor amplifier. This amplifier samples the output voltages V of the 18 different strain-gauge channels consecutively at 2 kHz so that the sampling frequency of each channel equals 111 Hz satisfying the minimum sample-frequency requirement of 100 Hz. The selection of a strain- gauge channel is done by applying its 5 -bit channel-number at the input of the PROG/SEL-block. To reduce the power consumption a special clock φ sample is employed to clock the current sources IREF, ISG and IDAC switching off these currents during most of the time of the switched-capacitor amplifier's reset phase.

hi the complete sensor interface chip 30 (Fig. 11), the multi-gauge nulling block is followed by an amplifier AMP, a sample-and-hold S/H circuit and an analog-to-digital converter ADC. Also a 128 kHz relaxation clock- oscillator CLOCK and two bi-phasic non-overlapping clock generators are implemented. The digital output is then fed to a decision unit (not shown in Fig. 11), that handles the data in accordance with the user specifications.

Fig. 12 schematically illustrates a block diagram of the entire integrated circuit. It is implemented as a Finite State Machine (FSM). The digital part contains a programmable data processing unit 36 including selectable algorithms with adjustable parameters. This unit 36 is implemented to reduce the required data-storage-capacity on board of the datalogger, which is restricted by the available space to incorporate the datalogger in the prosthesis. This unit ensures that only clinically relevant data are stored in the memory. The digital unit also includes a programming unit to program the compensation words into the on-chip nulling memory REG via the PROG/SEL-block. Moreover, the datalogger 5 is capable to compensate itself for the offsets introduced in the strain-gauge channels. This compensation may be carried out automatically by commanding the datalogger 5 wirelessly to compensate towards a user-definable output value for a selectable strain-gauge channel. This is performed by the nulling block in combination with the programming unit. Successive approximation is employed to determine the required compensation word to be stored into the nulling memory. The automatic nulling is carried out for each channel after placement of the prosthesis before the beginning of the measurements. The sampling unit controls the 5 -bit channel-select decoder included in the PROG/SEL-block of the sensor interface. It ensures that the different strain-gauge channels are measured in the correct sequence. The sampling unit also controls the storage of processed data in the SRAM, which is dependent on the number of selected strain-gauge channels for the measurement.

There is a delay between the selection of a strain-gauge channel and the availability of the measured data of that channel at the sensor interface output. The sampling unit takes this into account when the output data are stored in the SRAM. A transmission unit 37 supervises the transmission of stored data in selectable data packages of 256 bytes. To achieve a correct communication, the data bytes are Manchester-encoded and an extra 3 -bit header per byte is added as well as an extra parity byte per data page. A receiving unit 38of the datalogger 5 takes care of the reception and validation of these commands and appropriate actions are taken by the controller if a correct command is received. The controller 34 orchestrates and supervises the total system. After programming, the actual status of the datalogger 5 can be verified by calling the device status bytes. The controller 34 also ensures that normal operation is reassumed after a possible lock during communication by means of programmable Watch Dog Timers (WDT).

At startup of the system (after implantation or installment) the device is programmed in a self-calibration mode, to automatically cancel out the offset values of the sensor(s). After this, the radio receiver 38 is informed to program the device in it's normal mode, i.e. to continuously monitor the strain. If a preset value is trespassed, or any other combinations of signals occur that are considered dangerous for the implant or bone, an alarm signal is created. The device itself is equipped with an actuator (at 7 in the illustrated embodiment) that informs the patient. This actuator may be an audible signal, a vibration signal, an electrical stimulation signal or a combination thereof.

The present invention may be implemented as a autonomous strain monitoring unit, i.e. a device which uses an intelligent, low power electronic circuit that provides the signal conditioning, the memory and the telemetry functions, and that is expanded with a bidirectional communication link to not only retrieve information from the implant monitoring system, but also to provide new data to the implant monitoring system to keep it in the operational range (drift, calibration data, etc.). The bidirectional communication link may also be arranged such that the system can be tuned to the individual patient's needs, such as the alarm triggering level.

As indicated above, the signal processing means may preferably be arranged to activate the actuator as a warning of a dangerous or a potentially dangerous load level, e.g. when the measured mechanical loading exceeds a set load level in the system. As schematically illustrated in Fig. 13, it is possible to use two or more warning levels, optionally with associated different warning signals to the patient.

Fig. 13 schematically illustrates the bone response (formation or resorption) as a function of stimulus intensity. The stimulus may be the equivalent strain induced by loading of the implant. The relationship between bone response and mechanical stimuli was recognized as early as the 19th century ("Wolffs law") and a large body of knowledge has since been has been accumulated. Fig. 13 is a illustrative summary of the current consensus. Bone will resorb when insufficiently stimulated ("underload", "disuse atrophya", "stress shielding"). It will remain unchanged ("dead zone") while the stimulus is in a certain interval. A slightly more intense stimulus will cause minimal bone formation ("lazy zone"). "Mild overload" is the most potent osteogenic stimulus. Severe or pathological overload will again cause bone resorption, but the cellular mechanism behind this resorption is different from the mechanism behind underload-caused resorption. This figure further illustrates the relevance of having one or more different alerts. The arrows illustrate at which mechanical loads a first and a second alert could be respectively generated.

Claims

1. An implant monitoring system for in vivo monitoring of mechanical loading on an implant placed in a patient, said system comprising:
- at least one sensor unit which is arranged to be operatively connected to the implant;
- a measuring unit for receiving an output signal from said sensor unit;
- a transmitter means for transmitting information to the patient regarding the mechanical loading on the implant; and
- processing means forming built-in intelligence in the system and being arranged to activate said transmitter means without the need of any external input to the system.
2. An implant monitoring system as claimed in claim 1, wherein said signal processing means is arranged to activate said transmitter means as a warning of a dangerous or a potentially dangerous load level.
3. An implant monitoring system as claimed in claim 2, wherein said processing means is arranged to activate the warning to the patient when the measured mechanical loading exceeds a set load level in the system.
4. A dental implant monitoring system as claimed in claim 3, wherein said processing means is arranged to activate said actuator for a predetermined period of time.
5. An implant monitoring system as claimed in claim 3 or 4, wherein said set load level is reconfigurable.
6. An implant monitoring system as claimed in claim 5, further comprising bi-directional wireless communication means for remote reconfiguring of said set load level.
7. An implant monitoring system as claimed in any of the preceding claims, wherein said sensor unit comprises at least one sensor for detecting at least one of strain, pressure, acceleration and force.
8. An implant monitoring system as claimed in any of the preceding claims, further comprising means for storing information originating from at least one of the sensor unit, the measuring unit and the processor means.
9. An implant monitoring system as claimed in any of the preceding claims, wherein said transmitter means comprises a body actuator for transmitting said information to the patient by means of a vibration signal and/or an electrical stimulation signal.
10. An implant monitoring system as claimed in claim 9, wherein said body actuator is configured and arranged to be placed in the oral cavity of the patient.
11. An implant monitoring system as claimed in any of the preceding claims, further comprising a patient portable unit for receiving said information regarding the mechanical loading on the implant.
12. An implant monitoring system as claimed in any of the preceding claims, further comprising a temporary or final prosthesis or supporting structure with which the monitoring system is wholly or partly integrated.
13. An implant monitoring system as claimed in any of the preceding claims, further comprising bi-directional wireless communication means for verification, calibration, retiming and resetting of modi operandi.
14. An implant monitoring system as claimed in any of claims 1 to 13, wherein said implant comprises a dental implant.
15. An implant monitoring system as claimed in any of claims 1 to 13, wherein said implant comprises an orthopaedic bone-healing implant, such as an orthopaedic nail or an orthopaedic plate.
16. An implant monitoring system as claimed in any claims 1 to 13, wherein said implant comprises an orthopaedic prosthesis.
17. A dental implant monitoring system for in vivo monitoring mechanical loading on a dental implant placed in a patient, comprising at least one sensor arranged to be operatively connected to the implant; and a body actuator which is arranged to transmit, by means of a vibration stimulation signal and/or an electrical stimulation signal, information to the patient regarding a mechanical loading detected by said sensor.
18. A dental implant monitoring system as claimed in claim 17, wherein said body actuator is configured and arranged to be placed in the oral cavity of the patient.
19. A dental implant monitoring system as claimed in claim 17, wherein said body actuator comprises a vibration-type actuator for emitting a mechanical vibration stimulation signal to the patient.
20. A dental implant monitoring system as claimed in claim 17, wherein said body actuator comprises a vibration-type actuator for emitting an audible stimulation signal to the patient.
21. A dental implant monitoring system as claimed in claim 17, wherein said body actuator is arranged to emit an electrical stimulation signal to the patient.
22. A dental implant monitoring system as claimed any of claims 17-21, wherein, when the body actuator is activated, the system is arranged to activate said body actuator for a predetermined period of time.
23. A dental monitoring system as claimed in any of claims 17-22, wherein the sensor is integrated with the dental implant.
24. A dental monitoring system as claimed in any of claims 17-23, wherein the sensor is integrated with an abutment to be attached to said dental implant.
25. A dental monitoring system as claimed in any of claims 17-24, further comprising a prosthesis to be temporarily attached to said dental implant during the use of the monitoring system, wherein at least one of the sensor and the actuator is integrated with the prosthesis.
26. A dental implant monitoring system as claimed in any of claims 17-
25, further comprising processing means for evaluating the output from the sensor and for activating said actuator in response to the evaluation.
27. A dental implant monitoring system as claimed in any of claims 17-
26, wherein said sensor is arranged to detect at least one of strain, pressure, acceleration and force.
28. A dental implant monitoring system as claimed in claim 27, wherein said sensor comprises at least one strain gauge.
29. A dental prosthesis for in vivo monitoring mechanical loading on at least one dental implant, comprising a supporting structure arranged to be engaged with said implant; at least one sensor which is supported by the supporting structure, and a body actuator which is supported by the supporting structure and arranged to transmit, by means of a vibration stimulation signal and/or an electrical stimulation signal, information to the patient regarding a mechanical loading detected by said sensor.
30. A dental prosthesis as claimed in claim 29, wherein the dental prosthesis is a temporary prosthesis, intended to be later replaced with a final prosthesis, and wherein said supporting structure is thus arranged to be engaged only temporarily with the implant.
PCT/EP2005/011511 2004-10-29 2005-10-27 Implant monitoring system WO2006045607A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GBGB0424065.1A GB0424065D0 (en) 2004-10-29 2004-10-29 Implantable strain controlling unit
GB0424065.1 2004-10-29

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WO2006045607A1 true WO2006045607A1 (en) 2006-05-04

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WO (1) WO2006045607A1 (en)

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