WO2008022808A1

WO2008022808A1 - Joint prosthesis, and method for measuring wear in said joint prosthesis

Info

Publication number: WO2008022808A1
Application number: PCT/EP2007/007568
Authority: WO
Inventors: Marion Baum; Marcus Hientzsch; Joachim Boese-Landgraf; Thomas Otto; Thomas Gessner; Jörg Schaufuß
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.; Klinikum Chemnitz Gmbh
Priority date: 2006-08-25
Filing date: 2007-08-23
Publication date: 2008-02-28
Also published as: DE102006051173A1

Abstract

The invention relates to a joint prosthesis (1) to be used in humans, animals, or a corresponding simulator. Said joint prosthesis (1) comprises a first (2) and a second (3) joint part. Both joint parts are movable relative to one another. At least one of the joint parts is equipped with a sensor (4) or several sensors for determining the temperature and the thickness of an area located near or on the boundary surface (5) between both joint parts (2, 3). The invention further relates to a corresponding measuring method.

Description

Joint prosthesis and method for measuring wear in this joint prosthesis

The present invention relates to a joint prosthesis and to a method for measuring wear in this joint prosthesis.

The market for joint endoprostheses and orthopedics is one of the largest markets in the field of medical technology and life sciences with approximately 180,000 hip joint operations in Germany and approximately 1.5 million operations worldwide. Meanwhile, the cost of private and public health insurance has risen to an unacceptably high level. This results in the demands for a future longer life of the implant, the observation of the condition and the timely detection of the loosening of the implants and the lowering of the costs for operations and rehabilitation. At certain permanent loads high temperatures occur in the artificial joint, causing damage to the synovial fluid and associated reduced lubrication. Due to the thus further increased friction can cause not only higher friction moments and harmful temperatures for the tissue surrounding the joint. Hip replacement testing is performed in hip joint simulators according to testing standards such as ISO TR 9325 and 9326 or ISO 14242. Here, the artificial joints are clamped in a defined, anatomically correct position in the simulator and the physiological movement sequence simulated. The articulating joint components are preferably tested in bovine serum. The regular test duration is 5 million cycles at a frequency of 1 Hz, which corresponds to a test time of about 8 weeks. Subsequently, the prostheses are removed and the wear can be determined by geometry or weight determinations as well as particle analyzes of the abrasion products.

A significant disadvantage of the current state of the art is that the current state of the endoprosthesis can not be accurately recognized or observed. The resolution of the non-invasive analysis methods, such as X-ray or magnetic resonance examination, is too low to detect a loosening or positional change. X-ray image recordings and computer-aided image analysis today enable resolutions of up to 0.1 mm.

The permanent in vivo-state detection of endoprostheses is therefore not possible until today. As soon as pain occurs in the patient, which indicates a loosening of the prosthesis, the condition of the same usually so bad that the prosthesis must be completely replaced. In addition, for example, hip replacements are now used on ever younger patients and the number of possible revisions is limited to two. This is mainly due to the inoperable stability of the prosthesis in the femur and the natural aging of the bone.

Based on this prior art, it is the object of the present invention to provide a joint prosthesis, which early detects overloading or incorrect loading and impending failure of the prosthesis and thus allows the early initiation of medical measures to the total wear time of Prosthesis and to increase the quality of life of the patient.

The joint prosthesis according to the invention for use in humans or animals contains a first and a second joint part, wherein both joint parts are movable relative to one another and at least one of the joint parts has a sensor for determining the thickness of a region located near or at the interface between the two joint parts.

An independent claim relates to a corresponding measuring method, wherein measured values of the sensor are read out telemetrically and preferably periodically.

Of course, the wear is best detected in the interface between the two joint parts, but this was previously not possible by an integrated sensor system. There is practically no joint space between the two joint parts, but only lent an interface which is lubricated with synovial fluid. The determination according to the invention of the thickness of the representative region, preferably made of wear-resistant material, which adjoins the interface, preferably always takes place in the same position or the same load of the corresponding patient. This should be done, for example, in each case with a "standing" patient (upright posture). This ensures that, especially in the point of highest surface pressure even with a relatively severely worn joint prosthesis no extensive "joint gap" arises because due to the upright posture, for example, in a hip joint, the first and the second hinge part are pressed together. By measuring the thickness of the area adjacent to the interface, a meaningful measurement of the wear in the area of the interface is then possible.

The invention is therefore based on the idea that, when monitoring the thickness of a certain area adjacent to the interface and possibly additional monitoring of the temperature at the interface, which provides additional information about overloads, the overall condition (ie temperature and wear) in the joint can be continuously recorded or measured.

Thanks to integrated microsensors, the function, quality and wear of total endoprostheses can be monitored.

Standardized wear tests of endoprostheses are carried out with special simulators. A very promising alternative or supplement to This time-consuming methodology is a micro-sensor based online condition assessment of the joints. Today, the condition of the prostheses, once inserted, can only be determined randomly in the context of radiographic examination methods (X-ray). The integrated joint monitoring system should be able to be used in a further development also in vivo and recognize an increased risk of damage such as increased temperature or the wear-related failure or the occurrence of aseptic loosening. This monitoring would allow for early screening and, if necessary, surgery, significantly reduce the cost of revision surgery and address the current health-related burden of X-ray and non-permanent readings.

Increased stress on the joint by the patient may lead to an increased temperature on the patient

Interface between joint socket and condyle come. By constantly monitoring the wear of the joint components or the temperature at the interface, the patient could be warned by a signal at increased risk of damage and actively prolong the life of the prosthesis by his behavior. By additionally integrating vibration and distance sensors close to the interface, micro-loosening can be detected in good time and prosthesis components replaced in good time.

An online wear and condition recording of endoprostheses offers the possibility to facilitate time-consuming prosthesis tests and to monitor the current condition of the prosthesis at any time. The invention relates to the development and integration on of various measuring methods and measuring systems for the online wear and condition detection of total endoprostheses for human patients. On the one hand, the invention based on intelligent microsensor technology should result in the introduction of a new quality criterion and a novel experimental monitoring in the in-vitro testing of joint endoprostheses. Here, new insights into the temporal, local and load-dependent wear behavior can be gained as well as an increase in the speed and efficiency of the implant tests can be achieved.

On the other hand, in vivo use can prevent critical situations that can cause increased wear by permanently monitoring the prosthesis. The time of a much less complex partial operation could be determined in time by a constant wear control and thus a complete revision of the components can be avoided.

This invention describes a system for online wear and condition detection of joint endoprostheses. The integrated into the prosthesis system consists of one or more sensor modules that receive their signals in the prosthesis and transferred after first processing to a receiver, for example via a telemetry unit. For this purpose, the necessary units for microelectronic data processing, energy supply and data transmission must also be integrated in the joint or in the immediate vicinity.

For in vivo use, aspects of biocompatibility must be taken into account or not endangered. Miniaturized modules can be mounted directly in the prosthesis or encapsulated as an implantable electronic unit not encapsulated in the joint. The recipient of data outside the body may be devices that the patient carries with him and the comfort of life not restrict (eg, abdominal bags, watches, etc.).

The integration of autonomous sensor systems serves the purpose of permanently monitoring the function and quality as well as the wear of the endoprostheses.

This is intended, on the one hand, to improve prosthetic checks and, on the other hand, to control the condition, in particular the wear, during in vivo use. The purpose of this monitoring is to extend the duration of the prosthesis by avoiding critical stress conditions such as excessive temperatures or excessive wear, and, if necessary due to wear, allowing for early examination and surgery.

The intelligent joint serves to improve wear tests, medical decision-making, the cost and effort optimization of revision surgeries and the patient due to shorter surgical and rehabilitation times.

The sensors must be positioned as close as possible to the interface of the two partners in order to avoid signal losses and time delays. In order not to change or impair the surface properties and stability of the prostheses, particularly small sensors (microsensors) or sensors based on thin functional layers are integrated. These sensors measure physical quantities of capacity, temperature and heat radiation. Possible parameters are also pressure, Force, acceleration or vibration. By means of integrated electrodes which generate a field by applying an electric voltage, the distance between the sensor and the joint ball and thus the wear of the wear shall be determined by evaluating a capacitance change. For example, PtIOO sensors (or Pt10000 sensors) and thermopiles measure the friction-induced temperature increase in the joint. Fast conversion of the measured variables into digital signals takes place in the processing and evaluation unit. From there, the data is transmitted by telemetry to the outside to a receiver. The maximum transmission distance should not exceed 1 m for energy reasons. The patient carries the recipient on the body and receives it fully automatically

Signal at increased risk of wear and can adjust his load or seek medical advice if necessary.

Advantageous developments of the present invention are described in the dependent claims.

An advantageous development provides that the joint prosthesis is a hip joint prosthesis for use in the simulator or humans and the first joint part is an artificial hip joint socket and the second joint part is an artificial femoral head.

A further advantageous embodiment provides that the first joint part or at least one hinge socket part belonging to the joint part (which then frictionally engages with the other joint part) is made of a wearable material, preferably plastic, particularly preferably polyethylene, very preferably ultra-high molecular weight polyethylene (UHMWPE). is. Under "wearable material" Thus, a material is understood that generates a maximum measurable abrasion of up to 0.1 mm per year when used in a hip joint prosthesis of a human). Alternatively, "in contrast to this" wear-resistant materials "possible, for example, those of titanium or a titanium alloy or a cobalt-chromium-molybdenum alloy or chromium-nickel alloy or from high-purity alumina or zirconium zei show hardly measurable abrasion - gen.

Correspondingly, the second joint part can also be produced from titanium or a titanium alloy, a cobalt-chromium-molybdenum alloy or a chromium-nickel alloy or else, for example, from highly pure aluminum oxide or zirconium.

The sensor for determining the thickness of the area adjoining the interface can be embodied in various ways, particularly preferably capacitive sensors or temperature sensors are possible here, but which can then achieve an at least indirect measurement because of their immediate proximity to the interface.

In the case of a capacitive sensor, it preferably has two-surface electrodes and changes in capacitance in the region between these two electrodes are detected, wherein changes in the capacitance can be attributed to the change in thickness of the region to be measured.

The first electrode is preferably close to or directly at the interface in the first joint part and the second electrode near or directly at the

Interface arranged in the second hinge part. This is particularly in the case that the first joint part is a Hüftpfannenteil and the second joint part is a femoral head made of a metal, such as titanium, advantageous, since the corresponding surface of the second joint part itself _, can form the electrode. In the event that both electrodes are to be connected to a corresponding processing and evaluation unit for producing a closed measuring circuit, it is advantageous for better signal transmission to connect both joint parts.

In this arrangement, the joint part is equipped, for example, with a first electrode which is separated from the interface by a region of "wearable material" (defined above), in particular plastic, preferably polyethylene, more preferably ultra-high molecular weight polyethylene (UHMWPE). This can be produced, for example, by providing a blind hole in an acetabular cup made of the corresponding material or a hip joint socket inlay made of this material and repelling it from the boundary surface. As a result, there are no leakage problems from the interface to the sensor. The thickness of the wearable area perpendicular to

Interface is in this capacitive design in the installed state advantageously 0.3 mm to 5 mm, preferably between 0.5 mm and 3 mm, more preferably 1 mm to 2 mm.

Another embodiment provides that the first and second electrodes are both accommodated in the first joint part (for example an acetabular cup prosthesis) and the second joint part (for example a femoral head) can be arranged such that at least one specific wear of the first and / or the second joint part are influenced by the second joint part, the field lines between the first and second electrode. This means, for example, that with progressive wear, the second joint part (ie the femoral head) even deeper into the

Field lines between the first and second electrode engages and thus changes the 'measured capacitance. The advantage of this is that metrologically only from one side, ie always beyond the thigh bone in the case of a hip joint prosthesis, a metrological evaluation can be carried out to the downstream processing and evaluation unit.

Another type of sensor mentioned above is a temperature sensor. This can be accommodated in the first joint part (which is embodied, for example, as an acetabular cup), the temperature sensor being separated from the interface by a region of wearable material, in particular plastic, particularly preferably polyethylene, very particularly preferably ultra-high molecular weight polyethylene (UHMWPE). The thickness of this region (minimum thickness) towards the interface is in this case again 0.3 mm to 5 mm, preferably 0.5 mm to 3 mm, particularly preferably 1 mm to 2 mm, in the installed state.

When measuring the temperature itself, a resistance temperature sensor or a heat radiation sensor (thermopile) can then be used. Preferably, these sensors are housed in blind holes in the hip joint socket or hip socket prosthesis. With decreasing distance to the boundary surface (ie with wear of the wearable material present in the border area), it happens a long-term increase in the mean temperature at the location of the sensor under stress. This can then give an idea of the size of the wear. Of course, even short-term overloads are easily measurable, since, for example, in the case of a

Increase in temperature in the synovial fluid over 42 ⁰ C a failure or overloading of the hip joint prosthesis is detected.

As an alternative to this resistance measurement, it is also possible to measure the heat radiation in the corresponding area; here it is advantageous that, on the one hand, there is a closed space between the boundary surface and the thermopile. However, the separating area made of wear-resistant material should not be too thick, otherwise due to the specific heat capacity of polyethylene, for example, the measurement accuracy suffers or the temperature influence can only be detected to a limited extent in isolation. In this case, it is useful to provide an area filled with air or vacuum, for example, between an area of wearable material and the thermopile, so that the measuring accuracy is increased. This area may, for example, be arranged in the shape of a truncated cone, so as to also provide a transition from the measuring area to

To achieve the diameter of the thermopile, bundling optics etc. can be used to further increase the measuring accuracy.

Further advantageous developments are described in the remaining dependent claims.

The invention will now be explained with reference to several figures.

Fig. 1 is a diagram for clarification of Contexts in a sensor-equipped joint prosthesis according to the invention,

2 shows a cross section through a hemispherical socket insert made of UHMW-

PE,

FIGS. 3a, 3b show examples of capacitive sensor arrangements as well

FIGS. 4a, 4b show examples of temperature measurement based sensor systems.

FIG. 1 shows possibilities of sensor technology or evaluation for a joint prosthesis according to the invention. Sensors for measuring the acceleration, the pressure or the force and, preferably, the temperature and the position / distance sensors are possible here for the sensors. These are evaluated with the processing and evaluation unit associated with the sensors (on-chip / hybrid evaluation is possible, Mixed Signal Processing - ASIC and Datalogger). A transmission can take place via telemetry / transponder, whereby for the signal and energy transfer between 1 MHz and 2.4 Ghz can be used. In this case, the energy supply preferably takes place wirelessly, with a supply via batteries also being possible. In all implanted parts is to pay attention to the biocompatibility, this applies both to the materials of the joint prosthesis itself, but also in particular for the corresponding sensors or processing and evaluation, which preferably, together with corresponding transponder or batteries, within the pelvis can be accommodated.

FIG. 2 shows a joint socket according to the invention ultra high molecular weight polyethylene (UHMWPE) layer. On the outside of this joint socket insert, which forms a first joint part 2, a blind hole is shown with a sensor indicated cross-hatched therein. In the hemisphere, a second joint part (not shown) insertable, in this case, an artificial femoral head made of a cobalt-chromium-molybdenum alloy. The diameter of the artificial femoral head and the inner diameter of the first joint part 2 are coordinated so that there is virtually no joint gap in the installed state (in the area of this "interface" the lubrication takes place via synovial fluid).

FIGS. 3a and 3b show examples of capacitive sensor arrangements in a joint prosthesis according to the invention.

FIG. 3a shows a section through a joint prosthesis 1 according to the invention, comprising a first joint part 2 and a second joint part 3, wherein both joint parts are movable relative to one another. The first joint part 2 is a hip joint socket in UHMWPE. The corresponding second joint part 3 is an artificial femoral head made of a cobalt-chrome

Molybdenum alloy, which is associated with a femur, respectively. The joint parts have a sensor or a sensor arrangement for determining the wear in the region of a boundary surface. The interface is indicated by the reference numeral 5. At the top, a blind hole is shown, which serves to receive the sensor arrangement or a processing and evaluation unit (not shown), which is likewise preferably housed in the body and possibly by an associated telemetry unit from outside the body. Pers is readable. This readout can either take place permanently (storage of the measured values then takes place in the processing and evaluation unit and is read out, for example, at the monthly interval or at the annual interval). Alternatively, a signaling unit should be provided in the processing and evaluation unit, which emits an alarm at a certain overload (for example, carrying too high a load through the prosthesis wearer).

In the foreground, however, the measurement of the wear in the region of the interface is shown in FIG. 3 a, whereby this measurement is also preferably provided at the location with the highest surface pressure. Above this area, there is provided a planar electrode provided in the first joint part 2, which is denoted by 6a. A capacitance is measurable between this first electrode 6a and a second electrode 6b, which is formed by the hip head itself due to the metal surface of the femoral head, whereby the height of the capacitance depends on the thickness "d" of a range of wearable material.

The conditions shown in FIG. 3a relate to the "initial state", that is to say for a newly inserted joint prosthesis. In this case, between the two electrodes is the area of wearable material, which for example is made of polyethylene, particularly preferably of ultrahigh molecular weight polyethylene (UHMWPE) in the initial thickness, eg 1 mm. This makes the production on the one hand simple, since a corresponding blind hole from the interface-repellent side of the acetabulum ninlays is possible. Wear over time is now detectable, for example, so that wear of the wearable material takes place and Thus, a capacitance change between the first and second electrode can be measured.

In addition, a certain loosening (increased freedom of movement) within the joint can be detected, for example, by a change in the measured value that then fluctuates more rapidly over time, which indicates wear.

The thickness of the wearable material d, as shown in Figure 3a, is presently 1 mm in the installed state. Depending on the material pairing, when using a ceramic material (for example for a femoral head), the thickness d may be only 0.5 mm.

FIG. 3b shows a further embodiment of a joint prosthesis according to the invention which has a first part 2 and a second part 3. Here, a first electrode 7a and a second electrode 7b are arranged within the first joint part, a

Installation can be done here again by appropriate blind holes. The thickness or wear of a dimension denoted by d ¹ (this substantially corresponds to the size d shown in FIG. 3 a) can be determined from the fact that, as a result of wear in the region of the interface, the first joint part experiences wear and hence the measured one Capacitance between first electrode 7a and second electrode 7b changes or additionally changes again by the entry of the material made of another material

Hüftkopfes 3. Advantageous in this variant is that the entire processing and evaluation unit on a joint side (namely on the side of the first joint part) can be accommodated.

FIG. 4 a shows a further section in the limit surface 5. Here, however, a resistance thermometer (in this case a Modeil PT 100 or PT 1000) mounted in a blind hole, the sensor is with its measuring tip at a distance of a range of wearable material d ¹ '(in this case 1 mm) from the beginning of

Interface separated. Again, the sensor is in turn connected to a processing and evaluation unit according to the invention. Of course, this can also be given in addition to the capacitive sensors shown in FIGS. 3a and 3b in order to achieve an even more comprehensive measurement evaluation.

FIG. 4b shows a further application of a temperature sensor. Here, in the interface 5 between see first joint part 2 and second joint part 3, the temperature determined. For this purpose, a thermopile / heat radiation sensor 8 is provided. This is in turn housed in a blind hole, the tip of the blind hole tapers conically. At the forefront of the blind hole (towards the interface 5) there is once again an area of wearable material which is d ¹ "= 1 mm in the starting position. This is preferably somewhat lower than in the aforementioned methods, since the heat radiation sensor provides a clearer measurement result, the less material is present between the heat radiation sensor and the actual interface. Of course, instead of the blind hole arrangement shown here, a corresponding area of wearable material can be inserted as a separate part. As a result, the material properties with regard to the measurement can be optimized, but this results in a more complex production or under certain circumstances a higher risk in solving this extra part. The present invention exploits the possibilities of microsystem integration in medical implants, especially hip joint prostheses, during the life and quality inspection phase. An on-line monitoring is demonstrated, which is realized by new integration methods and different sensor principles. For this purpose, two detection principles were defined to determine the current state of the prosthesis. With this integrated temperature and wear rate measurement, dangerous situations can be identified in later use for the patient. For the experimental investigations, prosthesis heads and pans of type ABG II from Stryker with UHMWPE (ultra high molecular weight polyethylene) standard inlays were used. in the

On the one hand the temperature behavior under high load and fast movement was investigated. For this purpose, 5 referenced temperature sensors of type PT100 were placed and cast in the pan only one millimeter from the interface. After only a short time, a temperature could be measured which reached a level that was already dangerous for proteins. This means a lower coefficient of friction, since the lubrication through the synovia (joint fluid), which consists of 80% of proteins, decreases. This starts a kind of vicious cycle, because the worse friction increases the temperature further, the joint fluid fails more and more and the material properties of the PE deteriorate with increasing temperature. This condition can be avoided by monitoring. A temperature difference remaining due to the residual thickness was calculated both analytically and determined simulatively.

The monitoring of the current state of wear and The remaining layer thickness of the PE is another aspect which will be discussed in more detail. To implement this monitoring, a capacitive measuring method was developed and integrated. Smallest and depending on the wear occurring capacity changes can thus be detected by integrated electrodes and an AD7747 circuit of the company Analog Devices. If the residual thickness reaches a certain threshold value, the sensor can send a signal to the monitoring device.

Claims

21Patentansprüche

1. Joint prosthesis (1) for use in humans or animals, comprising a first (2) and a second (3) joint part, wherein both joint parts are movable relative to one another, characterized in that at least one of the joint parts has a sensor (4) for determining the thickness of a near or at the interface between two joint parts (2, - 3) located area.

2. Joint prosthesis according to claim 1, characterized in that the joint prosthesis is a hip joint prosthesis another prosthesis such as a spinal prosthesis, a knee prosthesis or the like for use in humans.

3. Joint prosthesis according to one of the preceding claims, characterized in that the first joint part (2) is an artificial or non-artificial acetabulum and the second joint part (3) is an artificial or non-artificial Hüftköpf.

4. joint prosthesis according to any one of the preceding claims, characterized in that the first joint part (2) wholly or at least belonging to the joint part Gelenkpfanneninlay of a wearable material, preferably plastic, particularly preferably polyethylene, most preferably ultra-high molecular weight polyethylene (UHMWPE) , 22

5. joint prosthesis according to one of the preceding claims, characterized in that the second hinge part (3) at least partially made of titanium or a titanium alloy or cobalt-chromium molybdenum alloy or chromium-nickel alloy or a ceramic material.

6. Joint prosthesis according to one of the preceding claims, characterized in that the sensor (4) is a capacitive sensor, wherein this preferably two spaced-apart E- electrodes (6a, 6b, 7a, 7b).

7. Joint prosthesis according to claim 6, characterized in that the first electrode (6a) near or at the interface (5) in the first joint part and the second electrode (6b) near or at the

Interface (5) in the second hinge part (3) is arranged.

8. joint prosthesis according to claim 7, characterized in that in the second joint part (3) the surface itself forms the electrode (6b).

9. Joint prosthesis according to one of claims 7 or 8, characterized in that in the first joint part (2) the first electrode (6a) by a range of wearable material, which in particular of plastic, preferably polyethylene, particularly preferably ultrahigh molecular weight impor- tant polyethylene (UHMWPE) is separated from the interface.

10. Joint prosthesis according to claim 9, characterized in that the thickness (d) of the wearable

Area perpendicular to the interface in the installed state 0.3 mm to 5 mm, preferably 0.5 mm 23

3 mm, particularly preferably 1 mm to 2 mm.

11. A joint prosthesis according to claim 7, characterized in that the first (7a) and the second (7b) electrode in the first hinge part (2) are housed and the second hinge part (3) is so north- andenbar that at least for a certain wear of the first (2) and / or the second (3) joint part, the field lines and / or the capacitance between the first (7a) and the second (7b)

Electrode be influenced.

12. joint prosthesis according to one of claims 1 to 6, characterized in that the sensor (4) is a temperature sensor.

13. Joint prosthesis according to claim 12, characterized in that the temperature sensor in the first joint part (2) is housed, wherein the temperature sensor by a range of wearable material, in particular synthetic material, particularly preferably polyethylene, most preferably ultra-high molecular weight polyethylene (UHMWPE ) is separated from the interface (5).

14. A joint prosthesis according ^'to claim 13, characterized thereby marked, that the thickness of the region is of wear resistant material in the installed condition 0.3 mm to 5 mm, preferably 0.5 mm to 3 mm, particularly preferably 1 mm to 2 mm.

15. Joint prosthesis according to claim 12, characterized in that the temperature sensor is a resistance temperature sensor or a heat radiation sensor (8). 24

16. Joint prosthesis according to one of the preceding claims, characterized in that the sensor is arranged substantially punctually and preferably in the region of the force introduction and / or the highest surface pressure of the interface (5).

17. Joint prosthesis according to one of the preceding claims, characterized in that the sensor (4) is connected to a processing and evaluation unit, which is preferably housed in the body and can be read by an associated telemetry unit from outside the body.

18. Joint prosthesis according to claim 17, characterized in that the processing and evaluation unit are preferably connected only to sensor parts in the region of the first (2) and / or alternatively of the second joint part (3).

19. A method for measuring the thickness of a near or at the interface between two joint parts

(2; 3) in a joint prosthesis according to one of the preceding claims, wherein measured values of the sensor (4) are read telemetrically, preferably periodically.