Patent Description:
Contemporary knee replacements were developed in the early <NUM> and since then refinements in the surgical technique and improvements in the design and materials of the prosthesis have contributed to the knee currently being the most replaced joint in the body. As the outcomes and longevity of implanted knee prosthesis improved, orthopaedic surgeons recognized the importance of assessing and documenting performance of the implant.

Insall and his colleagues at the North American Knee Society developed a knee scoring system to assess the performance of the knee following knee replacement surgery. They published a Knee Society Score (KSS) in <NUM> based on set criteria and made the score available for use by orthopaedic surgeons worldwide. However, reliability, responsiveness and validity of the scoring system was found to be lacking over time primarily because of deficiencies in Patient Reported Outcome Measures (PROMs). The KSS was subsequently updated in <NUM> to include a more extensive section on PROMs and it is still widely used to reflect performance of knee replacements. Other PROMs in common use include Western Ontario MacMaster University Osteoarthritis Index (WOMAC) and the Oxford Knee Score.

Over the years, innovations in prosthetic design, implant materials and implantation techniques have resulted in better functioning of knee prosthesis and patient satisfaction rates have improved as a consequence. There is now greater emphasis on improvement of function following knee replacement surgery and the aim of the surgery has evolved to restoring quality of life.

Over the last decade, there has been greater demand by healthcare executives and funders for the Orthopaedic community to demonstrate the effectiveness of total knee replacement. Traditional outcome measures that were in common use before like the Knee Society Score are too subjective and insensitive hence, the development of specific outcome measures that are focused on the patient experience. The perspective of the recipient of the total knee replacement and fulfillment of his or her expectations post-operatively is now recognized as an important outcome measure. It is generally accepted that Patient Reported Outcome Measures (PROMs) are the most objective instruments available to us to date to assess outcomes following joint replacement surgery. PROMs are administered in the form of self-reported questionnaires. Commonly used PROMs include The New Knee Society Score, WOMAC and Oxford Knee Score. However, there are many limitations to PROMs and currently there is no single validated, reliable and responsive PROM to assess all aspects of total knee replacement surgery.

A return to previous activity levels is the ultimate goal of knee replacement surgery and an important component of outcome of the intervention. Low activity levels and specifically long periods of sedentary behavior are hazardous to general health. On the other hand, extremely high activity levels have been associated with early failure of the knee replacement. Hence, the aim should be for a more balanced activity profile following knee replacement surgery. Assessment of quantity of activity is currently done using crude instruments in the form of patient questionnaires, examples being the Lower Extremity Activity Score (LEAS) and the UCLA Activity score. There is a need for a more sensitive and accurate measure of the quantity of activity. Commercially available activity trackers have the potential for short-term activity assessment following knee replacement surgery. However, they are limited in conveying critical information on medium to long-term activity profiles.

PROMs are largely based on level of function, pain, quality of life and satisfaction. The scoring of PROMs is susceptible to a patient's subjectivity and is dependent upon a number of parameters including the patient's mental status, hospital experience, cultural background, socioeconomic status and body mass index. Patient bias and ability to recall events also affects PROMs. Other limitations include a floor/ceiling effect and lack of responsiveness.

Accelerometers are electromechanical devices or motion sensors that are used to measure proper acceleration. Proper acceleration is the acceleration of a body relative to a free-fall, or inertial, observer who is momentarily at rest relative to the body being measured. Accelerometry, which, is the science of quantifying movement through the use of accelerometers offers one the ability to give objective accurate information on the quantity of limb movement over a defined period. Accelerometers are commonly used in the healthcare space in the form of electronic devices that can be worn on the body. These are commonly referred to as wearables with one of the most popular applications being activity tracking. The devices are able to relay information regarding vital body functions including the pulse and parameters such as the number of steps taken, and distance travelled. Sophisticated activity trackers are also able to quantify activity. They can accurately distinguish sedentary behavior from light physical activity and vigorous activity.

There is evidence to show that excessive periods of sedentary behaviour is detrimental to one's health. Advanced degenerative disease of the knee reduces the quantity of activity and can potentially result in an increase in sedentary activity. Wearables are useful for the purposes of quantifying activity in patients following knee replacement surgery and alerting the healthcare worker of unhealthy patterns of physical behavior. The accuracy of quantifying movement improves the closer the measuring device or activity monitor is to the limb under assessment and long-term movement patterns in the order of weeks to months offer more useful information on activity than short-term quantification. Wearables worn on the thigh tend to be uncomfortable and can be a source of irritation making compliance a challenge and long-term wear impractical. The present invention aims, at least to some extent, to alleviate the drawbacks discussed above.

In <CIT> an orthopedic implant having a three-axis accelerometer is disclosed. The three-axis accelerometer is used to detect micro-motion in the implant. The micro-motion can be due to loosening of the implant. The implant is configured to couple to the muscular-skeletal system. In one embodiment, the implant is configured to couple to bone. An impact force is imparted to the bone or implant. The impact force can be provided via a transducer coupled to the implant In <CIT> a knee replacement prosthesis is shown, comprising a plurality of sensors and at least one of a femoral component, a patellar prosthesis, and a tibial component.

<CIT> discloses a joint monitoring system for measuring performance parameters associated with an orthopedic articular joint and comprises a force sensing module and an inertial measurement unit. The sensing module comprises a housing that engages with the joint articular surface having a medial portion and a lateral portion. The sensing module also includes a first and second set of sensors disposed within the housing.

<CIT> discloses an orthopaedic bearing comprising at least one capacitive sensing element arranged within the bearing material, and operable to measure a change in capacitance resultant from any compression or tension of the bearing during use. There is also provided a method of assessing an orthopaedic implant including an instrumented orthopaedic bearing.

<CIT> shows a telemetry system for monitoring an arthro-prosthetic device implanted on a patient and comprising a first and a second component, wherein the telemetry system comprises a first detection module configured to be implanted near the first component of the arthro-prosthetic device and a second detection module configured to be implanted near the second component of the arthro-prosthetic device.

In accordance with the disclosure there is provided an implantable electronic device which includes:.

The implantable electronic device is configured to be mounted in a blind cavity formed in the lateral aspect of the femoral or tibial condyle of the knee prosthesis. The blind cavity may have dimensions of <NUM> in length, <NUM> depth, and <NUM> breadth. Preferably, the blind cavity may have dimensions of <NUM> in length, <NUM> depth and <NUM> breadth.

The electromechanical motion sensor may be an accelerometer. The accelerometer may be a multi-axis accelerometer. The accelerometer may be a three-axis piezoelectric accelerometer.

The power source may include a battery which is configured to power the electromechanical motion sensor and the wireless communication module. The battery may have a lifespan of up to <NUM> years. The battery may be rechargeable battery. The battery may be configured to be received in the blind cavity.

The power source may include an inductive charger which includes a receiving circuit coupled to the battery. The receiving circuit may be coupled to the electromechanical motion sensor and the wireless communication module. The inductive charger may further include an inductive charging circuit which is operatively not mounted to the implantable electronic device, nor to the knee prosthesis but is configured inductively to power the receiving circuit.

The implantable electronic device may include a processor which is coupled to the electromechanical motion sensor, memory and the wireless communication module. The implantable electronic device may include first and second electromechanical motion sensors. The first electromechanical motion sensor is configured to be accommodated in a blind cavity formed in the lateral aspect of the femoral condyle of the knee prosthesis. The second electromechanical motion sensor is configured to be received in a second blind cavity formed in a lateral aspect of the tibial condyle of the knee prosthesis.

In accordance with another aspect of the invention, there is provided an endoprosthesis which is configured to be fitted to a subject as a replacement body part, the endoprosthesis having a first part articulating with a second part and an implantable electronic device as described above installed in a blind cavity defined in either one of the first part or second part. At least two implantable electronic devices as described above may be installed in two separate blind cavities, one defined in the first part and the other in the second part.

The endoprosthesis may be a knee prosthesis. The first part may be a femoral component and the second part may be a tibial component of the knee prosthesis. The blind cavity may be formed in a lateral aspect of a femoral condyle of the femoral component of the knee prosthesis. The blind cavity may have dimensions of <NUM> in length, <NUM> depth, and <NUM> breadth. The blind cavity may be configured to receive the implantable electronic device therein.

Another or second blind cavity may be formed in a lateral aspect of a tibial condyle of the tibial component of the knee prosthesis. This second blind cavity may have dimensions of <NUM> in length, <NUM> depth, and <NUM> breadth. A second implantable electronic device as described above may be received in the second blind cavity.

There is further disclosed an endoprosthesis activity monitoring system which includes:.

The endoprosthesis activity monitoring system may be configured to determine relative acceleration, rotation, or tilt of first and second implantable electronic devices received in separate blind cavities in the first and second parts of the endoprosthesis, respectively.

The disclosure will now be further described, by way of example, with reference to the accompanying drawings.

The following description is for illustrative purposes, the invention being defined by the appended claims. Those skilled in the relevant art will recognise that many changes can be made to the embodiments described, while still attaining the beneficial results.

In <FIG> reference numeral <NUM> refers generally to an endoprosthesis activity monitoring system in accordance with the invention. The system <NUM> includes an endoprosthesis <NUM>, which in this example embodiment is in the form of a knee prosthesis configured to be fitted as a replacement body part to a subject or patient (not shown). The knee prosthesis illustrated in this example happens to be a complete knee prosthesis. It is envisaged that the invention may also find application in partial knee prosthesis. In this example embodiment, the endoprosthesis activity monitoring system <NUM> includes at least two implantable electronic devices <NUM> (although only one implantable electronic device <NUM> has been illustrated in <FIG>) which are operatively mounted to or received within separate cavities provided in the endoprosthesis <NUM>, as will be explained in more detail below. The system <NUM> also includes an external remote device <NUM> which is configured wirelessly to interrogate the implantable electronic devices <NUM> in order to glean recordings or measurements from them. To this end, each implantable electronic device <NUM> includes a processor or CPU <NUM> and a wireless communication module <NUM> which is communicatively linked to the processor <NUM> and is configured to communicate with the remote device <NUM> using any suitable wireless communication protocol. Each implantable electronic device <NUM> also includes at least one accelerometer <NUM> which is configured to measure acceleration and rotation of at least part of the endoprosthesis <NUM>. The accelerometer <NUM> may be a three-axis piezoelectric MEMS accelerometer. The implantable electronic device <NUM> also includes memory <NUM> for storing recorded measurements, data or readings of the accelerometer <NUM> and a power source in the form of a battery <NUM>. The battery <NUM> may be a rechargeable battery. The battery <NUM> may be recharged, wirelessly through use of an inductive charger. Accordingly, a receiving circuit (not shown) may be connected to the rechargeable battery for coupling with an external inductive charger which is operatively brought into close proximity to the receiving circuit. Alternatively, power sources such as kinetic energy harvesters (not shown) may also be incorporated into the implantable electronic device <NUM> in order to recharge the battery <NUM>. The accelerometer <NUM> is configured to record and/or measure vibration, shock, tilt and rotation amongst others.

With reference to <FIG>, a conventional, prior art knee prosthesis <NUM> includes a femoral component <NUM> which is attached to a degraded distal end of the patient's femur <NUM> and a tibial component <NUM> which is connected to a tibia <NUM> of the patient. The femoral component <NUM> articulates with the tibial component <NUM> in order to form an artificial or replacement knee joint. In the event of a total knee replacement, a patellar prosthesis <NUM> may also be provided. With reference to <FIG>, the endoprosthesis <NUM> includes a first part in the form of a femoral component <NUM> and a second part in the form of a tibial component <NUM>. The femoral component <NUM> and the tibial component <NUM> articulate to form a knee joint. As illustrated in <FIG>, the endoprosthesis <NUM> may also include a patellar prosthesis fitted to a patella, although this has not been illustrated in <FIG>. The femoral component <NUM> includes a convexly curved, C-shaped head <NUM>. The head <NUM> has an anterior, pointed protrusion <NUM> which defines a prominent groove <NUM> for accommodating and facilitating tracking of the patella. The anterior, pointed protrusion <NUM> is joined to a pair of posteriorly bifurcating, convexly curved femoral condyles <NUM>. As can be seen in <FIG>, a laterally inwardly extending blind hole or cavity <NUM> having an oblong cross-section is provided in a lateral aspect of one femoral condyle <NUM> of the femoral component <NUM> of the endoprosthesis <NUM>. One of the two implantable electronic devices <NUM> is operatively received or accommodated in the blind cavity <NUM>. The blind cavity <NUM> has a length of <NUM>, a breadth of <NUM> and a depth of <NUM>. The tibial component <NUM> includes a tibial lining <NUM> which interfaces with the head <NUM> of the femoral component <NUM> and a tibial plate <NUM> which is secured to the tibia <NUM>. A second, laterally inwardly extending blind hole or cavity <NUM> is provided in a lateral aspect of the tibial plate <NUM> of the tibial component <NUM>. This second blind hole <NUM> is configured to accommodate the other implantable electronic device <NUM>. The second blind hole <NUM> has a length of <NUM>, a breadth of <NUM> and a depth of <NUM>, i.e. similar dimensions to the first cavity <NUM>. The endoprosthesis activity monitoring system <NUM> is therefore configured to measure, record and transmit relative acceleration data of the two implantable electronic devices <NUM> and, hence, of the femoral component <NUM> and the tibial component <NUM>.

Although it has not been illustrated in the Figures, it will be appreciated that additional accelerometers or implantable electronic devices <NUM> may be provided in or on the patellar prosthesis. Also, multiple accelerometers may be provided on either of, or both of the femoral and tibial components in dedicated cavities or openings. Each implantable electronic device <NUM> may include multiple accelerometers <NUM>.

The blind cavities <NUM>, <NUM> are provided in lateral aspects of the femoral component <NUM> and tibial component <NUM>, respectively, due to the fact that it is an area of the knee that has the least soft tissue cover and is easily accessible. In this manner, the accelerometers <NUM> installed in the endoprosthesis <NUM> are connected via a wireless digital communication interface to the remote device <NUM> and are configured to send or transmit accurate information about the type and intensity of activity of the knee to the remote device <NUM> via a thinnest aspect of the knee across the soft tissue using wireless transmission technology.

The endoprosthesis <NUM> will be made of strong materials that fit the purpose of the implant. The blind cavity <NUM> is provided on the most distal part of the lateral aspect of the lateral femoral condyle <NUM> (see <FIG>) which means it is as close as possible to the knee joint. Although this has not been illustrated, each of the pair of femoral condyles <NUM> of the endoprosthesis <NUM> may be provided with a blind cavity <NUM> and an associated implantable electronic device <NUM> received therein.

Post-operatively, acceleration and joint rotation data recorded by the accelerometers <NUM> is collected and stored in memory <NUM>. During a visit to a medical practitioner, the recorded and stored data can be downloaded to the remote device <NUM>, which may be in the form of a smartphone, PDA, watch, wearable device, tablet, laptop, or other computing device, via the wireless communication module <NUM>. The remote device <NUM> is configured to process the recorded data using suitable algorithms and/or artificial intelligence or machine learning techniques and to display the processed information to the medical practitioner. This may include information of relative acceleration, relative rotation, relative tilt, vibration or force measured across the respective implantable electronic devices <NUM>. The endoprosthesis activity monitoring system <NUM> in accordance with the invention provides for more accurate monitoring of the endoprosthesis <NUM> and permits medical reporting of accurate, in situ, data that will contribute to the health of the patient.

The endoprosthesis activity monitoring system <NUM> gives a healthcare practitioner an unprecedented level of objective information on physical activity of the limb or replacement body part and gives practitioners the ability to gain easy access to accurate information specific to activity levels of the replacement body part or prosthesis. Furthermore, the activity information analysed and stored can possibly allow for earlier diagnosis of implant specific problems such as loosening of the prosthesis and activity patterns which may lead to a decline in general health of the patient. Other indirect benefits would include motivation of patients with accelerometer-enhanced implants to be more active.

Claim 1:
An implantable electronic device which includes:
an electromechanical motion sensor which is configured to measure acceleration and rotation of the implantable electronic device;
memory (<NUM>) coupled to the electromechanical motion sensor; the memory (<NUM>) being configured to store data measured by the electromechanical motion sensor;
a wireless communication module (<NUM>) which is communicatively linked to the electromechanical motion sensor and/or memory (<NUM>) and is configured to communicate with a remote device (<NUM>); and
a power source configured to power the wireless communication module (<NUM>);
characterized in that the implantable electronic device (<NUM>) is configured to be mounted in a blind cavity formed in a lateral aspect of a femoral or tibial condyle of a knee prosthesis (<NUM>).