System and Method
Field of Invention
The present invention relates to systems and methods and more particularly systems and methods for stimulating bone tissue growth in the proximity of bone implants.
Background
Bone-anchored implants are widely used in orthopaedic and orthodontic reconstructions for procedures including joint replacement (arthroplasty) , joint fusion (arthrodesis) , bone realignment (osteotomy) , and dental implants. Such implants require strong fixation to withstand the biomechanical loads of activities of daily life, with current fixation methods delineated as cemented versus cementless.
In cementless fixation, implants are initially stabilised using design features, such as keels and pegs, or adjunct devices, such as screws or compressive anchors. Long-term fixation is then dependent on harnessing the innate regenerative properties of bone to establish direct structural and functional connections to the host tissue - osseointegration. It takes more than three months for biological fixation to reach peak strength, during which time patients are advised to moderate their activities of daily living. Successful osseointegration is ultimately dependent on the mechanical loading environment in the periprosthetic bone via mechanotransduction pathways. Excessive micromotion, mechanical displacements of the implant surface leading to motion between the implant and bone, causes the formation of a fibrous capsule and deprivation from mechanical load results in resorption of periprosthetic bone. Both complications pose a loosening risk for patients: the most common complication associated with cementless arthroplasty . Cementless fixation is preferable due to shorter operation times, which improves procedural efficiency for clinicians and reduces perioperative infection risk for patients, and ongoing biological maintenance of the implant-bone interface, which avoids the progressive and irreparable degradation of a cement layer. However, cementless fixation is not recommended for all patients, and is often contraindicated in patients with low bone density or low metabolism, such as osteoporotic or elderly patients. Survivorship of cementless implants is also lower in joints with less suitable bone stock for anchoring and restraint, such as glenoid components in anatomical total shoulder arthroplasty and tibial components in total knee arthroplasty.
Research and development in this technical field has so far focused on passive measures, such as stiffness-matched implants, hydroxyapatite coatings, or piezoelectric implants. Others have sought to influence cellular pathways using orthobiologics, such as recombinant human bone morphogenetic protein 2 (rhBMP-2) , though use has been limited by problems with heterotopic ossification. External stimulation using ultrasound and electromagnetic fields have also been investigated as standalone treatments.
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US2004038180 describes a dental implant, that comprises surface regions of a first type which have osseointegrative, inflammation- inhibiting, infection-combating and/or growth-promoting properties , and surface regions of a second type which consi st of a material which is liquefiable by mechanical oscillations .
US2006052782 describes an orthopaedic implant , such as a bone plate , for the fixation of bone where the implant also has at least one microchip and at least one sensor connected to the microchip .
US2019159725 describes a device for inductive heating of a foreign metallic implant are di sclosed .
The present di sclosure describes systems and methods for providing enhanced os seointegration in patients with bone implants .
Summary
Aspects and examples of the invention are set out in the claims and aim to addres s at least a part of the above described technical problem, and other problems .
Embodiments of the di sclosure may be useful in prosthetics which restore the function of a j oint , such as in prostheses for arthroplasty, for example artificial j oints and other prosthetics which may be used in hip arthroplasty, knee arthroplasty and so forth . Embodiments may be employed to improve cementles s fixation by enhanced os seointegration . Thi s may return patients to activity faster and more safely than current technologies , with as sociated societal and economic benefits . Enhancing os seointegration could also widen suitability for cementles s fixation to older patients , who are currently contraindicated for cementless procedures due to reduced activity level s and metaboli sm . Embodiments may stimulate and sustain os seointegration . Embodiments may provide enhanced osseointegration and could improve early fixation in implants with higher loosening rates . Accordingly, embodiments of the di sclosure provide cementless implants and implant components . Such implants may be provided in tibial components for knee prostheses , such as total knee prostheses . Embodiments may provide interventional stimulation and could al so be used as a non-invasive first-line treatment for example a non-invasive first-line treatment to address problems which may be caused by loosening of the implant in the bone. Embodiments may provide an alternative to revision surgery, which is associated with poor patient outcomes and additional periods of inactivity during recovery.
An aspect of the invention provides a bone implant system for stimulating growth in bone tissue cells of a human or animal patient. The system comprises: a bone implant; and an apparatus configured to be carried by the bone implant. The apparatus comprises: an energy provider, configured to obtain energy from an energy source disposed outside a body of the patient; and a stimulator configured to provide, based on energy from the energy provider, an alternating electrical stimulus to a bone into which the bone implant is implanted.
In another aspect there is provided a bone implant system for stimulating growth in bone tissue cells of a human or animal patient. The system comprises: a bone implant; and an apparatus. The apparatus configured to be carried by the bone implant, the apparatus comprises: an energy provider, comprising an electromagnetic coupler configured to obtain electromagnetic energy via an electromagnetic field from an energy source disposed outside a body of the patient, wherein the electromagnetic coupler is carried by an external surface of the bone implant system. The apparatus further comprises a stimulator configured to provide, based on energy from the energy provider, at least one of electrical or mechanical stimulus to a bone into which the bone implant is implanted .
In a further aspect of the invention there is provided a bone implant system for stimulating growth in bone tissue cells of a human or animal patient. The system comprises a bone implant; and an apparatus configured to be carried by the bone implant. The apparatus comprises: an energy provider, configured to obtain energy from an energy source disposed outside a body of the patient; and a stimulator. The stimulator is configured to provide, based on energy from the energy provider , stimulus to a bone into which the bone implant i s implanted . The stimulator i s al so configured to provide a return signal via the energy provider , wherein the return signal indicates the fixation of the bone implant to said bone .
In another aspect an energy source for use with a bone implant system for stimulating growth in bone tis sue cell s of a human or animal patient i s provided . The energy source comprises an electromagnetic coupler for coupling with an energy provider of the bone implant system, said bone implant system compri sing said energy provider and a stimulator . The energy source further comprises a controller, configured to : control the electromagnetic coupler to interrogate said bone implant system using an interrogation signal thereby al so to cause the stimulator to provide a stimulus to a bone into which the bone implant is implanted, and to determine , based on a response to the interrogation signal , an indication of the fixation of the bone implant .
In another aspect a method of determining fixation of a bone implant using an apparatus carried by said bone implant i s provided . The method compri ses : interrogating a stimulator of an apparatus carried on a bone implant using an interrogation signal , wherein the stimulator i s configured to provide a stimulus to a bone into which the bone implant i s implanted, and the interrogation signal i s at least partially reflected by the stimulator to provide a return signal that is indicative of the fixation of the bone implant . The return signal i s transmitted by an energy provider of the apparatus . The method further compri ses receiving the return signal from the apparatus , and determining the fixation of the bone implant based on the return signal .
In the above method the step of determining the fixation of the bone implant may compri se analysing a di fference between the interrogation signal and the return signal to determine the fixation of the bone implant . Al so , the return signal may be based on at least one of an : a ) electrical impedance of the stimulator that i s indicative of fixation of the bone implant ; and b ) electrical coupling of the stimulator that i s indicative of fixation of the bone implant . The method may be implemented using any one of the bone implant systems described herein .
The bone implant system may compri se an exterior conductive surface for providing the stimulus to the bone for example wherein, the exterior conductive surface is a surface of the implant or wherein the exterior conductive surface i s a surface of the apparatus . Such apparatus may be provided by an insert . The apparatus may otherwise be integrated into or otherwi se carried by the implant system . The apparatus may be at least partially covered ( e . g . encapsulated) by the exterior conductive surface .
The stimulator may compri se at least two conductive elements for providing an alternating electric field . For example , a first one of these at least two conductive elements may be provided by at least a portion of the exterior conductive surface . A second one of the at least two conductive elements may be encapsulated in the body of the implant electrically insulated from the bone . In such an arrangement , the second one of the at least two elements may comprise a capacitive element - for example it may have sufficient capacitance to allow an alternating electric field to be applied between this otherwise electrically insulated ( e . g . , i solated) second conductive element and the first conductive element . It may be configured to allow the stimulator to provide a time varying voltage between the at least two conductive elements .
The stimulator may be configured so that the alternating electrical stimulus comprises a time varying charge . For example , the system may be configured so substantially no current flows from the conductive elements into the bone . The bone implant system may comprise an electromagnetic coupler .
The electromagnetic coupler may be at least partially encapsulated in a polymer casing .
The polymer casing may provide a spacing between the electromagnetic coupler and all conductive parts of the bone implant system . The electromagnetic coupler may extend from the body of the implant - for example it may protrude from the system suf ficiently to allow RF coupling ( e . g . inductive coupling ) with an RF energy source outside the body of the human or animal subj ect .
Typically, the polymer casing is at least partially transparent to radio frequency signals in the range 3 Hz to 9 GHz .
The electromagnetic coupler may comprise at least one of an inductive coupler and a capacitive coupler, such as an antenna .
The stimulator may compri se an electromechanical element configured to provide a mechanical stimulus . The electromechanical element may compri se a piezoelectric transducer . An electrode of the electromechanical element may comprise at least a portion of the exterior conductive surface . The electromechanical element may be provided on the exterior surface of the bone implant or may be provided in the body of the bone implant and i s mechanically coupled to the body of the bone implant . The electromechanical element may be at least partially encapsulated in the body of the bone implant .
The electromechanical element may compri se a plurality of piezoelectric transducers arranged such that each of the plurality of piezoelectric transducers may be configured to provide a mechanical stimulus to the bone ti s sue at a location corresponding to the location of each piezoelectric transducer .
The stimulator may be configured to provide a return signal via the energy provider , wherein the return signal i s indicative of fixation of the bone implant to said bone .
The energy provider may be configured to transmit the return signal provided by the stimulator . The stimulator may compri se an electromechanical element and an electrical response of the electromechanical element to an electrical signal may be indicative of fixation of the bone implant . The electrical response may comprise an apparent impedance . The electromechanical element may comprise a piezoelectric transducer .
The electromechanical element may compri se a plurality of piezoelectric transducers arranged such that each of the plurality of piezoelectric transducers provide a return signal indicative of fixation of the bone implant at a location corresponding to the location of said each piezoelectric transducer . The stimulator may be configured to provide an alternating electrical stimulus to the bone , wherein an electrical coupling of the stimulator to said bone i s indicative of fixation of the bone implant . The stimulator may comprise an exterior conductive surface for providing the alternating electrical stimulus to said bone and an electrical coupling between the exterior conductive surface and said bone may be indicative of fixation of the bone implant .
The stimulator may compri se at least two conductive elements for providing an alternating electric field .
The apparatus may comprise a logic element configured to control the stimulator to provide stimulus to a bone into which the bone implant i s implanted based on at least one of : energy from the energy provider ; and the return signal .
The stimulator of the bone implant system may be configured to provide oscillating stimulus of said bone ti s sue cell s .
The apparatus may be at least partially positioned on the exterior surface of the bone implant optionally wherein the apparatus is at least partially encapsulated in the body of the bone implant .
The apparatus may protect the energy provider and stimulator from damage . The apparatus may compri se a casing into which the energy provider and stimulator are at least partially embedded . The energy provider and stimulator may be provided in the apparatus ( for example the casing) out of a wear path of the bone implant .
The bone implant system may compri se an energy source , configured to be di sposed outside the body for supplying energy to the energy provider of the apparatus .
The controller may be configured to analyse a di fference between the interrogation signal and the response to the interrogation signal to determine the fixation of the bone implant . The response may compri se one of a return signal and a modulation of the interrogation signal caused by the bone implant . The response may be based on at least one of an : a ) electrical impedance of the stimulator that i s indicative of fixation of the bone implant ; and b ) electrical coupling of the stimulator that i s indicative of fixation of the bone implant .
The controller may be configured to adj ust a stimulus provided by the stimulator based on the determined fixation .
The interrogation signal i s mediated by a time varying H-field, such as a radio frequency field, for example having a frequency of 3 Hz to 9 GHz .
Brief Description of Drawings
Some practical implementations will now be described, by way of example only, with reference to the accompanying drawings in which :
Figure 1 shows a bone implant system for stimulating growth in bone tis sue cell s of a human or animal patient ;
Figure 2 shows an active bone implant system for use in a total knee replacement ;
Figure 3 shows a pas sive bone implant system for use in a total knee replacement ; Figure 4 shows an active bone implant system for use in stem cap ; and
Figure 5 shows an active bone implant system for use in an orthopaedic screw .
Specific Description
Figure 1 shows a bone implant system for stimulating growth in bone tis sue .
The bone implant system 500 of Figure 1 compri ses a bone implant 530 ; and an apparatus 532 configured to be carried by the bone implant 530 . The apparatus 532 compri ses an energy provider 512 . The energy provider 512 compri ses an electromagnetic coupler 512a configured to obtain electromagnetic energy via an electromagnetic field from an energy source 540 di sposed outside a body of the patient . The electromagnetic coupler 512a i s carried by an external surface of the bone implant system 530 . The apparatus 532 further comprises a stimulator 517 which i s configured to provide , based on energy from the energy provider , an electrical stimulus to a bone into which the bone implant is implanted .
The stimulator 517 compri ses an electrical element 518 including a first conductive element 518a and a second conductive element 518b for providing an alternating electric field between the conductive elements 518a and 518b . The stimulator 517 is also connected to the energy provider 512 . The stimulator 517 may thus be configured to provide oscillating stimulus of said bone ti ssue cells and may be configured to produce an electrical stimulus compri sing an oscillating electrical field . For example , the conductive elements 518a , 518b may be connected to the electromagnetic coupler 512a which can provide an alternating voltage between the conductive elements 518a , 518b .
The apparatus 532 is carried on the bone implant 530 . The energy provider 512a of the element i s connected to the first and second conductive elements 518a , 518b . The second conductive element 518b may be encapsulated in a body of the implant 530 which is electrically insulated from the bone.
In addition, or as an alternative, to the electrical stimulus, the stimulator 517 may comprise an electromechanical element 520 configured to provide a mechanical stimulus. The stimulator 517 may comprise any number of: electromechanical elements and/or electrical elements.
A controller 540 may also be provided and configured to: provide an alternating H-field for inductive coupling with electromagnetic coupler 512a to interrogate said bone implant system 500. The H- field may provide an interrogation signal (for example an electromagnetic field from an energy source disposed outside a body of the patient) . This may also cause the stimulator 517 to provide a stimulus to a bone into which the bone implant 530 is implanted. The controller 540 may be configured to determine, based on a response to the interrogation signal, an indication of the fixation of the bone implant 530.
The stimulator 517 may also provide a return signal via the energy provider 512 (for example via the electromagnetic coupler 512a) , wherein the return signal indicates the fixation of the bone implant 530 to said bone.
The apparatus 532 may also comprise a logic element configured to control the stimulator 517 to provide stimulus to a bone into which the bone implant is implanted based on at least one of: energy from the energy provider; and the return signal.
In operation, an electromagnetic field is received by the energy provider 512 (for example the electromagnetic coupler 512a) from an energy source disposed outside the body of a patient (for example the controller 540) . The received electromagnetic field generates an alternating electric field across the first and second conductive elements. The alternating electric field provides an electrical stimulus to the bone surrounding the bone implant. If the stimulator alternatively comprises or further comprises an electromechanical element the received electromagnetic field causes the stimulator ( in particular the electromechanical element ) to produce a mechanical stimulus that oscillates di splacement of the bone ti s sue cell s thereby providing a stimulus .
In response to the received electromagnetic field, the stimulator 517 provides a return signal via the energy provider, wherein the return signal indicates the fixation of the bone implant 530 to said bone .
The energy provider 512 may transmit the return signal provided by the stimulator 517 to a controller 540 that determines based on a response to the interrogation signal , an indication of the fixation of the bone implant . The controller 540 may adj ust the stimulus provided by the stimulator 517 based on the determined fixation .
Described below are four examples of a bone implant system such as that described with reference to Figure 1 . The four examples relate to :
• an active bearing in a total knee replacement with electromechanical stimulation ;
• a pas sive bearing in a total knee replacement with mechanical stimulation ;
• an active stem cap with electromechanical stimulation ; and
• a pas sive screw cap with electrical stimulation .
It will be appreciated however that these systems may be employed with dif ferent types of implants e . g replacement of other j oints , and other types of prothesi s and/or fixation implants .
Active bearing with electromechanical stimulation
Figure 2 shows a bone implant system 100 for stimulating growth in bone ti s sue cell s of a human or animal patient .
Components 110 are embedded into a casing 132 which i s the polyethylene bearing of a total knee replacement implant 130 . The embedded components 110 comprise : an antenna 112 ; a rechargeable battery 114 ; a printed circuit board 116 that compri ses a microproces sor ( a logic element ) 116a , non-volatile memory 116b and a near-field communication chip 116c ; an electrical contact pin 118 ; and two thicknes s mode piezoelectric transducers 120a , 120b . The polyethylene bearing 132 and embedded components 110 are an example of the apparatus 532 described above . The embedded antenna 112 is an example of the energy provider 512 and the electrical contact pin 118 is an example of an electrical element 518 and the piezoelectric transducers 120 are an example of an electromechanical element .
As well as the polyethylene bearing 132 the total knee replacement implant 130 has a metallic femoral component 134 and a metallic tibial component 136 . The polyethylene bearing 132 i s positioned between the femoral and tibial components 134 , 136 . The embedded components 110 are provided within the polyethylene bearing 132 . The polyethylene bearing 132 is interlocked with tibial component 136 via a mechanical interlock 138 on a tibial side of the bearing 132 . The femoral component 134 engages with sockets in the femoral side of the bearing 132 to form the total knee replacement 130 .
A radio frequency transmitter 140 such as a near field RF reader , separate and external to the total knee replacement implant 130 i s also provided . The radio frequency transmitter 140 is outside the body of the patient and i s operated by a user to control the stimulus provided by the bone implant system 100 . The radio frequency transmitter 140 i s in communication with a computing system 142 . The radio frequency transmitter 140 and computing system 142 are an example of the controller 540 described above .
The arrangement and connections of the bone implant system 100 will now be described in detail .
The antenna 112 i s embedded within the bearing 132 and extends around the circumference of the bearing 132 to form a loop . The antenna 112 i s electrically connected to the rechargeable battery 114 and the printed circuit board 116 . Both the rechargeable battery 114 and printed circuit board 116 are embedded within the bearing 132 .
The rechargeable battery 114 electrically connects both to the antenna 112 and the printed circuit board 116 .
The printed circuit board 116 has electrical connections to the antenna 112 , the rechargeable battery 114 , the two thicknes s mode transducers 120a and 120b and the electrical contact pin 118 . The microproces sor 116a , non-volatile memory 116b , and near- field communication chip 116c are provided on the printed circuit board 116 .
The thicknes s mode transducers 120a , 120b are embedded in the polyethylene bearing 132 in proximity to the tibial facing surface of the bearing 132 that engages with the tibial component 136 . The transducers 120a , 120b are spaced from one another with a lateral transducer 120a positioned towards a lateral side of the bearing 132 and a medial transducer 120b positioned toward a medial side of the bearing 132 . The thickness mode transducers 120 are electrically connected to the printed circuit board 116 .
The electrodes of the transducers 120 are optionally electrically i solated from the tibial component by non-conductive layers 111 , for example formed from an epoxy adhesive , that acoustically match the transducers 120 to the bearing 132 and tibial component 136 .
The electrical contact pin 118 is partially embedded in the polyethylene bearing 132 and extends through the tibial facing surface to electrically contact with the tibial component 136 . The electrical contact pin 118 i s electrically connected with the printed circuit board 116 .
The embedded components 110 are positioned out of the wear paths of the bearing 132 . Thi s protects the components from stres s and/or strain as a result of wear of the bone implant thereby protecting the components 100 from failure due to the wear that the knee replacement may experience . Furthermore , the positioning of the components 100 out of the wear paths of the bearing 132 prevents exposure of the components 100 to the bone ti s sue that might occur because of wear to the bearing 132 .
The function of the system 100 will now be described in detail .
The embedded components 110 are configured to provide at least one of electrical or mechanical stimulation to the bone tis sue surrounding the knee replacement implant 130 ( for example the periprosthetic tis sue ) in particular around the bearing 132 and tibial component 136 but may al so provide stimulation around the femoral component 134 . The electrical stimulation and the mechanical stimulation stimulate growth in the cell s of the bone tis sue for example the stimulus induces at least one of osteogenesi s (bone growth ) and angiogenesis (blood vessel growth) .
The casing 132 as well as functioning as the bearing for the total knee replacement 130 protects the embedded components 110 from damage/ failure and provides a hermetic seal to the exterior of the casing 132 .
The radio frequency transmitter 140 is configured to transmit radio frequency signals to the antenna 112 of the implant 130 . The transmitted radio frequency signal s may contain instructions for providing stimulus to the bone tis sue . The radio frequency transmitter 140 i s also configured to receive and analyse signal s transmitted from the antenna 112 .
The radio frequency transmitter 140 i s configured to transmit and receive radio frequency signals to and from the antenna 112 . The antenna 112 receives radio- frequency signal s from the radio frequency transmitter 140 and converts the radio frequency signal into an electrical signal which is sent to the printed circuit board 116 . The electrical signal is based on the radio frequency signal received by the antenna 112 . The electrical signal provides energy to the microproces sor 116a of the printed circuit board 116 . The antenna 112 i s al so configured to transmit return signals produced by the electrical contact pin and transducers . The computing system 142 is configured to program radio frequency signals transmitted by the radio frequency transmitter and analyse return signal s received by the transmitter or other receiver from the antenna 112 .
The rechargeable battery 114 of the system i s configured to provide an electrical signal to the printed circuit board 116 and particularly the microprocessor 116a . The electrical signal from the battery al so provides energy to the printed circuit board 116 and the mounted components (microproces sor 116a , non-volatile memory 116b and near field communication chip 116c ) . The battery 114 can be recharged via energy received from the antenna .
The microprocessor 116a is configured to control mechanical displacement of the two piezoelectric transducers 120a , 120b based on an electrical signal received from the antenna 112 . The microproces sor 116a i s al so configured to control and provide an alternating electrical charge on the surface of the electrical contact pin 118 based on the electrical signal received from the antenna 112 . The alternating electrical charge is applied via the electrical contact pin 118 to the surface of the tibial component 136 of the total knee replacement 130 .
The microproces sor 116a i s configured to control the transducers 120a , 120b and provide an alternating electrical charge on the electrical contact pin 118 based on an electrical signal from the battery 114 .
The rechargeable battery 114 and microproces sor 116a may be configured to provide an initial stimulus treatment and/or an ongoing stimulus that does not require energy or signal from the antenna 112 .
The microproces sor 116a i s further configured to receive return signals indicative of fixation of the total knee replacement 130 to the surrounding bone tis sue . The return signal s are generated by the partial reflection of the electrical signal s sent by the microproces sor 116a to control the transducers 120a , 120b and the alternating electrical current on the surface of the electrical contact pin 118 .
In addition, the microprocessor 116a i s configured to store data on the non-volatile memory 116b . The stored data may compri se information on the stimulus that has been provided by the system 100 . For example , the stored data may compri se the time , duration, amplitude and frequency of the stimulus . The near field communication chip 116c i s addressable to read data stored on the non-volatile memory 116b using a reader external to the total knee replacement .
The medial transducer 120b i s configured to receive control signal s from the microprocessor 116a and, based on the received control signals , i s configured to produce mechanical waves that predominantly emit from the bearing in the locality of the medial transducer 120b i . e . the mechanical waves generated by the medial transducer emit predominantly from the medial side of the bearing 132 .
The lateral transducer 120a i s configured to receive control signals from the microprocessor 116b and based on the received control signal s i s configured to produce mechanical waves that predominantly emit from the bearing 132 in the locality of the lateral transducer 120a i . e . the mechanical waves generate by the lateral transducer 120a emit predominantly from the lateral side of the bearing 132 .
Optionally, the electrodes of the transducers 120 are electrically i solated from the tibial component 136 by non-conductive layers 111 that acoustically match the transducers 120 to the bearing 132 and tibial component 136 .
The electrical contact pin 118 i s also configured to receive control signal s generated by the microproces sor 116a to produce a stimulus . Based on received control signal an alternating electrical charge ( for example a time-varying charge ) i s generated on the surface of the electrical contact pin 118 . The electrical contact pin 118 and tibial component 136 are arranged such that an alternating electrical charge on the surface of the electrical contact pin 118 i s applied to the surface of the tibial component 136 .
On receipt of a control signal each of the transducers 120 and electrical contact pin 118 are configured to provide a return signal in response to the control signal . For example , the control signal may be partially reflected by the transducers and electrical contact pin to provide a control signal . The return signal s provided by the transducers and electrical contact pin are indicative of the fixation of the total knee replacement 130 to the surrounding bone ti s sue .
The operation of the bone implant system 100 to stimulate bone growth will now be described .
To stimulate bone ti s sue growth using the bone implement system 100 an interrogation signal for example a radio frequency signal in the range of 3Hz to 9GHz i s transmitted from the radio frequency transmitter 140 to the antenna 112 . The interrogation signal i s configured to provide stimulus instructions to the microproces sor 116a . The interrogation signal i s received by the microprocessor 116a via the antenna 112 . Based on the received interrogation signal the microprocessor 116a controls displacement of at least one of the thicknes s mode transducers 120 , and/or the electrical charge on the electrical contact pin 118 .
The microproces sor 116a then generates control signal s based on the received interrogation signal . The control signal s are used to control the transducers 120 and electrical contact pin 118 and the control signal s are sent by the microprocessor 116a to the transducers 120 and electrical contact pin 118 .
The microprocessor 116a stores on the non-volatile memory 116b information on the stimulus that has been provided . The stored data may compri se the time , duration, amplitude and frequency of the control signal s that were provided to each of the transducers 120 and electrical contact pin 118 , information on the return signal s may al so be stored in the non-volatile memory 116b . The near field communication chip 116c can be addres sed to read data stored on the non-volatile memory 116b using a reader 144 external to the total knee replacement 130 . Thi s allow for a treatment record to be obtained .
The thicknes s mode transducers 120 receive control signal s from the microproces sor 116a . On receipt of a control signal the transducers 120 oscillate , in accordance with instructions in the control signal , to generate mechanical waves within the bearing 132 . The mechanical waves generated by the oscillations are transmitted through the bearing 132 into the bone ti s sue surrounding the implant . The mechanical waves may al so be transmitted directly into the tibial and/or femoral component 134 of the bone implant 130 without travelling through the bearing 132 .
The medial transducer 120b produces mechanical waves that predominantly emit from the bearing 132 in the locality of the medial transducer 120b i . e . the mechanical waves generated by the medial transducer 120b emit predominantly from the medial side of the bearing 132 .
The lateral transducer 120a produces mechanical waves that predominantly emit from the bearing 132 in the locality of the lateral transducer 120a i . e . the mechanical waves generated by the lateral transducer 120a emit predominantly from the lateral side of the bearing 132 .
The emitted mechanical waves stimulate bone tis sue growth for example the stimulus induces at least one of osteogenesi s (bone growth) and angiogenesi s (blood vessel growth ) . The arrangement of transducers 120 , such as the medial and lateral transducer 120a , 120b , carried at dif ferent positions in the bearing 132 allows for mechanical stimulus to be applied separately and speci fically to di fferent areas of the bone ti ssue surrounding the total knee replacement 130 . The charge on the surface of the electrical contact pin 118 i s controlled by control signals generated by the microproces sor 116a to produce an electrical stimulus . The microproces sor 116a control s , via a control signal , an alternating electrical charge on the surface of the electrical contact pin 118 based on the interrogation signal received from the antenna 112 . The alternating electrical charge i s conducted to the surface of the tibial component 136 that i s in electrical contact with the electrical contact pin 118 .
The alternating electrical charge on the surface of the tibial component 136 and via the electrical contact pin 118 generates an alternating electric field acros s the total knee replacement 130 and in particular in the bone tis sue surrounding the total knee replacement 130 . The alternating electric field in the surrounding bone tis sue stimulates growth in the cell s of the bone ti s sue for example the electrical stimulus induces at least one of osteogenesi s (bone growth ) and angiogenesis (blood vessel growth) .
The bone implant system 100 al so provides an indication of the fixation of the bone implant 130 to the surrounding bone ti s sue . Information on the fixation of the bone implant 130 to the surrounding bone can be used to inform treatment for example the stimulus provided by the bone implant system 100 can be adj usted based on thi s information .
On receipt of a control signal each of the transducers 120 and electrical contact pin 118 as well as providing a stimulus al so provides a return signal in response to the control signal . The return signal s provided by the transducers 120 and electrical contact pin 118 are indicative of the fixation of the total knee replacement to the surrounding bone tis sue .
For example , the control signal may be partially reflected by the stimulator to provide a return signal .
In this example , the return signal from each of the transducers 120a , 120b i s based on an electrical impedance of the transducer which varies depending on the fixation of the total knee replacement to the surrounding bone tis sue .
The return signal from each of the transducers 120 provides in particular an indication of the fixation in the locality of the transducer . For example , a return signal from the medial transducer 120b provides an indication of the fixation on the medial side of the total knee replacement 130 and a return signal from the lateral transducer 120a provides an indication of the fixation on the lateral side of the total knee replacement 130 .
The return signal from the electrical contact pin 118 i s based on a resonance of the electrical contact pin 118 and tibial component 136 . For example , the interaction of the alternating electric field ( generated by the alternating electric charge ) and the bone ti s sue may af fect an electrical resonance of the embedded components 110 and in particular the electrical contact pin 118 . The change in resonance ( a change in a degree of interaction between the bone tis sue and the alternating electric field) i s indicative of the fixation of the total knee replacement .
The return signal s from the transducers 120 and electrical contact pin 118 (which are an example of a stimulator ) are then stored in the non-volatile memory 116b and/or sent to and transmitted by the antenna 118 and received by the radio frequency transmitter 140 external to the total knee replacement . The received return signals are analysed by a computing system 142 of the radio frequency transmitter 140 to determine the fixation of the total knee replacement to the bone ti s sue .
Adj ustments can be made to the stimulus treatment based on the determined fixation to promote further growth in poorly fixed regions . The determined fixation can provide an early warning of loosing of the total knee replacement 130 and an indication that intervention or further stimulus is required .
The return signal may be provided to the microproces sor 116a which may be programmed to determine the fixation of the total knee replacement 130 based on the return signal s and dynamically update a pre-programmed treatment regime based on the determined fixation . The pre-programmed treatment regime may compri se a series of control signal s that are sent to the stimulator . The frequency, duration, and instructions carried by the control signals may vary and may be dynamically updated based on a determined fixation of the total knee replacement 130 .
Passive bearing in a total knee replacement with mechanical stimulation
Another bone implant system 200 for stimulating growth in bone tis sue cells of a human or animal patient will now be described and is shown in Figure 3 . The bone implant system i s similar to the bone implant system of Figure 2 . The bone implant system of Figure 3 however operates pas sively without a battery, microproces sor, or near field communication chip . Furthermore , the stimulator compri ses four piezoelectric transducers 220a , 220b , 220c and 220d, which are an example of electromechanical elements rather than the two piezoelectric transducers 120 and electrical contact pin 118 described in the example of Figure 3 .
Components 210 are embedded into a polyethylene casing that forms the bearing 232 of a total knee replacement implant 230 . The embedded components 210 compri se : an antenna 212 and four piezoelectric transducers 220 . The polyethylene bearing 232 and embedded components 210 are an example of the apparatus 532 described above . The embedded antenna 212 i s an example of the energy provider 512 and the piezoelectric transducers 220 are an example of an electromechanical element .
As well as the polyethylene bearing 232 , the total knee replacement implant 230 has a metallic femoral component 234 and a metallic tibial component 236 . The polyethylene bearing 232 i s positioned between the femoral and tibial components 234 , 236 . The polyethylene bearing 232 i s interlocked with the tibial component 236 via a mechanical interlock 238 on a tibial side of the bearing 232 . The femoral component 234 engages with sockets in the femoral side of the bearing 232 .
A radio frequency transmitter 240 separate to the total knee replacement implant i s al so provided . The radio frequency transmitter 240 is outside the body of the patient and i s operated by a user to control the stimulus provided by the bone implant system 200 . The radio frequency transmitter 240 i s in communication with a computing system 242 . The radio frequency transmitter 240 and computing system 242 are an example of the controller 540 described above .
The arrangement and connections of the system 200 will now be described in detail .
The antenna 212 i s embedded within the bearing 232 and extends around the circumference of the bearing 232 to form a loop . The antenna 212 i s electrically connected to each of the four piezoelectric transducers 220a, 220b , 220c, and 220d .
The thicknes s mode transducers 220 are embedded in the polyethylene bearing 232 at di fferent positions within the bearing 232 .
A first piezoelectric transducer 220a is positioned anterolaterally in the bearing 232 ; a second piezoelectric transducer 220b i s positioned in a posterolateral location ; a third piezoelectric transducer 220c i s positioned anteromedially and a fourth piezoelectric transducer 220d i s positioned in a posteromedial location within the bearing 232 .
The embedded components 210 in particular the transducers 220 are positioned out of the wear paths of the bearing 232 . Thi s protects the components from stress and/or strain as a result of wear of the implant thereby protecting the embedded components 220 from failure due to the wear that the knee replacement may experience . Furthermore , the positioning of the embedded components 210 out of the wear paths of the bearing 232 prevents exposure of the embedded components 210 to the bone ti ssue that might occur because of wear to the bearing 232 during use .
The function of the system 200 will now be described in detail .
The bone implant system 200 i s configured to provide mechanical stimulation to the bone ti s sue surrounding the knee replacement implant 230 ( for example the periprosthetic ti s sue ) in particular to bone ti s sue around the bearing 232 and tibial component 236 . The mechanical stimulation stimulates growth in the cell s of the bone ti ssue for example the stimulus induces at least one of osteogenesi s (bone growth ) and angiogenesis (blood vessel growth) .
The radio frequency transmitter 240 i s configured to transmit and receive radio frequency signals to and from the antenna 212 . The transmitted radio frequency signals contain instructions for controlling a stimulus provided by the bone implant system to the bone ti s sue . The radio frequency transmitter 240 i s al so configured to receive and analyse signal s transmitted from the antenna 212 .
The computing system 242 is configured to program radio frequency signals transmitted by the radio frequency transmitter 240 and analyse return signal s received by the transmitter 240 or other receiver from the antenna 212 .
The casing 232 as well as functioning as the bearing 232 for the total knee replacement 230 protects the embedded components 210 from damage and provides a hermetically sealed environment for the embedded components 210 .
The antenna 212 i s configured to communicate with the radio frequency transmitter 240 . The antenna 212 receives radio-frequency signals from the radio frequency transmitter 240 and converts the radio frequency signal s into control signals which are sent to the piezoelectric transducers 220 via an electrical connection between the antenna 212 and the piezoelectric transducers 220 . The control signals are based on the radio frequency signal received by the antenna 212 . The antenna 212 i s also configured to receive and transmit return signals received from the transducers 220 . The return signal s being indicative of fixation of the total knee replacement to the surrounding bone ti s sue . The return signal s are generated by the partial reflection of the control signal s sent by the antenna 212 to the transducers 220 .
The anteromedial transducer 220a is configured to receive control signals from the antenna 212 and, based on the received control signals , the transducer 220a produces mechanical waves that predominantly emit from the bearing in the locality of the anteromedial transducer 220a i . e . the mechanical waves generated by the anteromedial transducer 220a emit predominantly from an anteromedial section of the bearing .
The anterolateral transducer 220b i s configured to receive control signals from the antenna 212 and, based on the received control signals , the transducer 220 produces mechanical waves that predominantly emit from the bearing 232 in the locality of the anterolateral transducer 220b i . e . the mechanical waves generated by the anterolateral transducer 220b emit predominantly from an anterolateral section of the bearing .
The posteromedial transducer 220c i s configured to receive control signals from the antenna 212 and, based on the received control signal s , produces mechanical waves that predominantly emit from the bearing in the locality of the posteromedial transducer 220c i . e . the mechanical waves generated by the posteromedial transducer 220c emit predominantly from a posteromedial section of the bearing 232 .
The posterolateral transducer 220d i s configured to receive control signals from the antenna 212 and, based on the received control signals , the transducer produces mechanical waves that predominantly emit from the bearing 232 in the locality of the posterolateral transducer 232 i . e . the mechanical waves generated by the posterolateral transducer 220d emit predominantly from an posterolateral section of the bearing 232 . Optionally, the electrodes of the transducers 220 are electrically i solated from the tibial component 236 by non-conductive layers that acoustically match the transducers 220 to the bearing 232 and tibial component 236 .
On receipt of a control signal each of the piezoelectric transducers 220 are configured to provide a return signal in response to the control signal . For example , the control signal may be partially reflected by the piezoelectric transducers 220 to provide a control signal . The return signal s provided by the piezoelectric transducers 220 are indicative of the fixation of the total knee replacement 230 to the surrounding bone ti ssue .
The operation of the bone implant system 200 to stimulate bone growth will now be described .
To stimulate bone growth using the bone implant system 200 an interrogation signal for example a radio frequency signal in the range of 3Hz to 9GHz i s transmitted from the radio frequency transmitter 240 to the antenna 212 . The interrogation signal i s configured to provide stimulus instructions to the transducers 220 . The interrogation signal i s received by the antenna 212 and based on the received interrogation signal a control signal i s sent by the antenna 212 to the transducers 220 . The control signal controls displacement of at least one of the thickness mode piezoelectric transducers 220 .
The transducers 220 receive control signal s from the antenna 212 and on receipt of a control signal the transducers 220 oscillate , in accordance with instructions in the control signal , to generate mechanical waves within the bearing 232 . The mechanical waves generated by the oscillations are transmitted through the bearing 232 into the bone ti s sue surrounding the bone implant 230 .
The transducers 220 produce mechanical waves that predominantly emit from the bearing 232 in the locality of the transducer 220 for example the mechanical waves generated by one of the medial transducers 220c , 220d emit predominantly from the medial side of the bearing 232 .
Application of mechanical waves to the bone ti s sue stimulates bone tis sue growth for example the stimulus induces at least one of osteogenesi s (bone growth ) and angiogenesis (blood vessel growth) . The arrangement of transducers 220 , such as the medial and lateral transducers , carried at di f ferent positions either on or in a bone implant 230 allows for stimulus to be applied separately and speci fically to di fferent areas of the bone ti s sue surrounding the bone implant .
The bone implant system 200 al so provides an indication of the fixation of the bone implant 230 to the surrounding bone ti s sue . Information on the fixation of the bone implant to the surrounding bone can be used to inform treatment provided by the bone implant system 200 .
On receipt of a control signal from the antenna 212 each of the transducers 220 as well as providing a stimulus to the bone ti s sue also provides a return signal in response to the control signal . The return signal s provided by the transducers 220 are indicative of the fixation of the total knee replacement to the surrounding bone ti s sue .
The control signal may be partially reflected by the stimulator to provide a return signal .
In this example , the return signal from each of the transducers 220 i s based on an electrical impedance of the transducer which varies depending on the fixation of the total knee replacement 230 to the bone .
The return signal from each of the transducers 220 provides an indication of the fixation of the bone implant 230 to the bone tis sue in the locality of the transducer . For example , a return signal from one or more of the medial transducers 220c , 220d provides an indication of the fixation on the medial side of the total knee replacement and a return signal from one or more of the lateral transducers 220a , 220b provides an indication of the fixation on the lateral side of the total knee replacement .
The return signal s from the transducers 220 are sent to and transmitted by the antenna 212 and received by the radio frequency transmitter 240 external to the total knee replacement .
The received return signal s are analysed by a computing system 242 of the radio frequency transmitter 240 to determine the fixation of the total knee replacement 230 to the bone ti s sue .
Adj ustments can be made to stimulus treatment , in particular the instructions encoded into the interrogation signal , based on the determined fixation to promote further growth in poorly fixed regions . The determined fixation can provide an early warning of loosing of the total knee replacement 230 and an indication that intervention or further stimulus from the bone implant system 200 i s needed to improve the fixation of the bone implant 230 .
Shear mode transducers have been found to provide ef fective mechanical stimulation in the bone implant systems 100 and 200 and may be used in place of or in combination with the thicknes s mode transducers 120a, 120b , 220a , 220b , 220c, and 220d . Furthermore , other types of electromechanical transducers and transducer modes may be used in place of or in combination with the thicknes s mode transducers 120a , 120b , 220a, 220b , 220c , and 220d .
An active stem cap with electromechanical stimulation
Another bone implant system 300 for stimulating growth in bone tis sue cells of a human or animal patient will now be described and i s shown in Figure 4 . The bone implant system 300 is similar to that of Figure 2 however the bone implant 330 of the bone implant system 300 i s a stem cap 330 with a di f ferent geometry to the total knee replacement 130 of Figure 2 . The bone implant system 300 of Figure 4 has several alterations to the casing 132 and the embedded components 110 to optimi se the system for use in a stem cap 330 . In more detail , the bone implant system 300 comprises a bone implant 330 compri sing a polyethylene stem cap 332 having a head section 332a and a threaded body section 332b extending from the head section 232a ; and a metal stem 334 into which the body section 332b of the stem cap 332 i s threaded . The bone implant system 300 has several components 310 that are embedded into the polyethylene stem cap 332 . The polyethylene stem cap 332 acts as a casing for these embedded components 310 . The embedded components 310 are an antenna 312 ; a rechargeable battery 314 ; a printed circuit board 316 that has a microproces sor ( a logic element ) 316a , non-volatile memory 316b and a near- field communication chip 316c ; an electrical contact pin 318 ; and a tube piezoelectric transducer 320 . The stem cap 332 and embedded components 310 are an example of the apparatus 532 described above . The embedded antenna 312 is an example of the energy provider 512 and the electrical contact pin 318 i s an example of an electrical element 518 and the piezoelectric transducers 320 are an example of an electromechanical element .
A radio frequency transmitter 340 i s also provided . The radio frequency transmitter 340 i s provided outside the body of the patient and i s operated by a user to control the stimulus provided by the bone implant system 300 . The radio frequency transmitter 340 is in communication with a computing system 342 . The radio frequency transmitter 340 and computing system 342 are an example of the controller 540 described above .
The arrangement and connection of the system 300 will now be described in detail .
The body 332b of the stem cap 332 i s threaded into the metal stem 334 of the bone implant 330 . The head of the stem cap 332a extends from the metal stem 334 .
The antenna 312 is positioned within the head of the stem cap 332a and also extends from the metal stem 334 . The antenna 312 is embedded in the head of the steam cap 332a and extends around the circumference of the head to form a loop . The antenna 312 is electrically connected ( either directly or via intermediate components ) to the rechargeable battery 314 and the printed circuit board 316 which are both embedded within the body of the stem cap 332b .
The rechargeable battery 314 i s electrically connected to both the antenna 312 and the printed circuit board 316 .
The printed circuit board 316 has electrical connections to the antenna 312 , the rechargeable battery 314 , the tube transducer 320 and the electrical contact pin 318 . The microproces sor 316a , nonvolatile memory 316b , and near- field communication chip 316c are provided on the printed circuit board 316 .
The tube piezoelectric transducer 320 is partially embedded in the body of the polyethylene stem cap 332b and an outer electrode of the tube piezoelectric transducer 320 i s pre- stressed in contact with the metal stem 334 of the bone implant 330 .
The electrical contact pin 318 i s al so partially embedded in the body of polyethylene stem cap 332b and extends through the surface of the stem cap body to electrically contact with the metal stem 324 of the bone implant 330 into which the body of the stem cap 332b i s threaded . The electrical contact pin 318 i s electrically connected with the printed circuit board 316 .
The components embedded within the stem cap are positioned out of the wear paths of the stem cap 332 . This protects the components 310 from stres s and/or strain as a result of wear of the bone implant 330 thereby protecting the components 310 from failure due to the wear that the stem cap 332 may experience . Furthermore , the positioning of the components 310 out of the wear paths of the stem cap 332 prevents exposure of the components 310 to the bone ti ssue that might occur because of wear . The embedded components 310 are protected from damage/ f ailure by the stem cap 332 . In particular , the embedded components 310 are protected during implantation of the implant , which may involve hammering the implant into place . The stem cap 332 protects the embedded components from failure due to any stres ses that the cap may experience as a result of implantation
The rechargeable battery 314 and microproces sor 316a may be configured to provide an initial stimulus treatment and/or an ongoing stimulus that does not require energy or signal from the antenna 312 . The rechargeable battery 314 i s configured such that it can be recharged using the antenna 312 .
The function of the components of the system 300 will now be described in detail .
The bone implant system 300 i s configured to provide at least one of electrical or mechanical stimulation to the bone tis sue surrounding the bone implant 330 ( for example the periprosthetic tis sue ) in particular around metal stem 324 of the bone implant 330 . The electrical stimulation and the mechanical stimulation stimulate growth in the cell s of the bone tis sue for example the stimulus induces at least one of osteogenesi s (bone growth ) and angiogenesi s (blood vessel growth ) and in particular around the proximal portion of the metal stem 324 .
The radio frequency transmitter 340 i s configured to communicate with the antenna 312 embedded within the head of the stem cap 332a . The radio frequency transmitter 340 transmits radio frequency signals to the antenna 312 . The transmitted radio frequency signal s contain instructions for providing stimulus to the bone ti s sue surrounding the bone implant 330 . The radio frequency transmitter 340 i s al so configured to receive and analyse signal s transmitted from the antenna 312 .
The computing system 342 is configured to program radio frequency signals transmitted by the radio frequency transmitter and analyse return signal s received by the transmitter or other receiver from the antenna 312 .
The casing 332 as well as functioning as the part of the bone implant protects the embedded components 310 from damage and provides a hermetically sealed environment for the embedded component s 310 .
The antenna 312 i s configured to communicate with the radio frequency transmitter 340 and can receive radio frequency signal s from the radio frequency transmitter 340 . The antenna 312 converts the radio frequency signal into an electrical signal which i s sent to the printed circuit board 316 . The electrical signal is based on the radio frequency signal received by the antenna and contains instructions for providing a stimulus . The electrical signal provides energy to the microprocessor 316a of the printed circuit board 316 .
The antenna 312 is al so configured to transmit return signal s from the stimulator which compri ses the tube piezoelectric 320 and the electrical contact pin 318 to the radio frequency transmitter 340 or other receiving device external to the body of the patient .
The microprocessor 316a is configured to control mechanical displacement of the tube piezoelectric transducer 320 based on an electrical signal received from the antenna 312 . The microproces sor 316a i s al so configured to control and provide an alternating electrical charge on the surface of the electrical contact pin 318 based on the electrical signal received from the antenna 312 . The alternating electrical charge i s applied via the electrical contact pin 312 to metal stem 334 .
The rechargeable battery 314 of the system 300 can energi se the microproces sor 316a . The microproces sor 316a may be preprogramed to control the tube piezoelectric transducer 320 and provide an alternating electrical charge on the electrical contact pin 318 without an electrical signal from the antenna 312 . The battery 314 can be recharged via energy received from the antenna 312 .
The microproces sor 316a i s al so configured to receive return signals indicative of fixation of the bone implant 330 to the surrounding bone ti s sue . The return signal s are generated by the partial reflection of the electrical signal s sent by the microproces sor 316a to control the transducer 320 and the alternating electrical current on the surface of the electrical contact pin 318 .
In addition, the microprocessor 316a i s configured to store data on the non-volatile memory 316b . The stored data may compri se information on the stimulus that has been provided by the bone implant system 300 . For example , the stored data may comprise the time , duration, amplitude and frequency of the stimulus that was provided .
The near field communication chip 316c i s configured to be addressable to read data stored on the non-volatile memory 316b using a reader external to the bone implant 300 .
The tube piezoelectric transducer 320 is configured to receive control signal s from the microprocessor 316a and based on the received control signal s produces mechanical waves that emit from the stem cap 332 in the locality of the tube piezoelectric transducer 320 . The tube piezoelectric 320 i s configured to operate in a radial mode such that mechanical waves are radially emitted from the stem cap 332 .
An outer electrode of the tube piezoelectric transducer i s configured to electrically and physically contact an inner surface of the metal stem 334 .
The electrical contact pin 318 i s also configured to receive control signal s generated by the microproces sor 316b to produce a stimulus . Based on a received control signal an alternating electrical charge i s generated on the surface of the electrical contact pin 318 . The electrical contact pin 318 i s arranged such that an electrical charge on the surface of the electrical contact pin 318 i s applied to the inner surface of the metal stem 334 of the bone implant 330 .
On receipt of a control signal each of the transducer 320 and electrical contact pin 318 are configured to provide a return signal in response to the control signal . For example , the control signal may be partially reflected by the stimulator to provide a control signal . The return signal s provided by the stimulator is indicative of the fixation of the bone implant to the surrounding bone ti s sue .
The operation of the bone implant system 300 to stimulate bone growth will now be described .
To stimulate bone growth using the bone implement system 300 an interrogation signal for example a radio frequency signal in the range of 3Hz- 9GHz i s transmitted from the radio frequency transmitter 340 to the antenna 312 . The interrogation signal i s configured to provide stimulus instructions to the microproces sor 316a . The interrogation signal i s received by the microprocessor 316a via the antenna 312 . Based on the received interrogation signal the microprocessor 316a controls displacement of at least one of the tube piezoelectric transducer 320 , and/or the electrical charge on the electrical contact pin 318 .
Upon receipt of the interrogation signal , the microprocessor 316a generates control signal s based on the received interrogation signal and sends these controls signal s to the tube piezoelectric transducer 320 and the electrical contact pin 318 . The control signals are used to control the stimulator .
The microproces sor 316a also stores the details of the stimulus that has been provided on the non-volatile memory 316b . For example , the stored data may compri se the time , duration, amplitude and frequency of the control signals that were provided to each of the tube piezoelectric transducer 320 and the electrical contact pin 318 . The stored data may also compri se information on the return signals and fixation of the bone implant 330 . The near field communication chip 316c can be addres sed to read data stored on the non-volatile memory 316b using a reader external to the bone implant 330 which allows for a treatment record to be obtained . The tube piezoelectric transducer 320 receives a control signal from the microprocessor 316a. On receipt of a control signal the transducer 320 oscillates, in accordance with instructions in the control signal, to generate mechanical waves within the body of the stem cap 332 and in the metal stem 334. The mechanical waves generated by the oscillations are transmitted through the body of the stem cap 332b and metal stem 334 into the bone tissue surrounding the bone implant 330.
The tube piezoelectric transducer 320 produces mechanical waves that predominantly emit from the body of the stem cap in the locality of the transducer. In this example, the mechanical waves emit radially from the metal stem to provide a stimulus to the surrounding bone tissue.
Application of mechanical waves to the surrounding bone tissue stimulates bone tissue growth for example the stimulus induces at least one of osteogenesis (bone growth) and angiogenesis (blood vessel growth) . Additional transducers, may be carried at different positions in the body or head of the stem cap which would allow for mechanical stimulus to be applied separately and specifically to different areas of the bone tissue surrounding the bone implant 330.
The charge on the electrical contact pin 318 is also controlled by control signals generated by the microprocessor 316a to produce a stimulus. The microprocessor 316a controls, via a control signal, an alternating electrical charge on the surface of the electrical contact pin 318 which is based on the interrogation signal received from the antenna 312. The alternating electrical charge is conducted to the metal stem 334 that is in electrical contact with the electrical contact pin 318.
The alternating electrical charge on the surface of metal stem 334 and electrical contact pin 318 generates an alternating electric field in proximity to the bone implant 330 and in particular in the surrounding bone tissue. The alternating electric field in the surrounding bone tissue stimulates growth in the cells of the bone tis sue for example the stimulus induces at least one of osteogenesi s (bone growth ) and angiogenesis (blood vessel growth) .
The bone implant system 300 al so provides an indication of the fixation of the bone implant to the surrounding bone ti s sue . Information on the fixation of the bone implant 330 to the surrounding bone can be used to inform treatment for example the stimulus provided by the bone implant system 300 can be adj usted based on thi s information .
On receipt of a control signal each of the tube piezoelectric transducer 320 and electrical contact pin 318 as well as providing a stimulus al so provides a return signal in response to the received control signals . The return signal s provided by the stimulator are indicative of the fixation of the bone implant 330 to the surrounding bone ti s sue .
For example , the control signal may be partially reflected by the stimulator to provide a return signal .
In thi s example , the return signal from tube piezoelectric transducer 320 i s based on an electrical impedance of the transducer which varies depending on the fixation of the bone implant 330 to the surrounding bone tis sue .
The return signal from each of the tube piezoelectric transducer 320 provides in particular an indication of the fixation in the locality of the transducer .
The return signal from the electrical contact pin 318 i s based on an electronic resonance of the electrical contact pin 318 and metal stem 334 .
For example , the interaction of the alternating electric field ( generated by the alternating electric charge ) and the bone ti s sue may affect an electrical resonance of the components of the bone implant system 330 ( for example the electrical contact pin 318 and metal stem 334 ) . The change in resonance ( a change in a degree of interaction between the bone ti s sue and the alternating electric field) i s indicative of the fixation of the bone implant 330 .
The return signal s from the tube piezoelectric transducer 320 and the electrical contact pin 318are then sent to and transmitted by the antenna 312 and received by the radio frequency transmitter 340 external to the bone implant 330 . The received return signal s are analysed by a computing system 342 of the radio frequency transmitter 340 to determine the fixation of the bone implant 330 to the bone tis sue .
Adj ustments can be made to stimulus treatment , in particular the instructions encoded into the interrogation signal , based on the determined fixation . For example , adj ustments may be made to promote further growth in poorly fixed regions of the bone implant . The determined fixation can provide an early warning of loosing of the bone implant 330 and an indication that intervention or further stimulus is required .
A passive screw cap with electrical stimulation
Another bone implant system 400 for stimulating growth in bone tis sue cells of a human or animal patient will now be described and is shown in Figure 5 . The bone implant system i s similar to that of Figure 4 however the stem cap 332 i s configured for insertion into an orthopaedic screw 430 and al so operates pas sively without the need for a battery, microproces sor , near field communication chip or tube piezoelectric transducer .
In more detail , the bone implant system 400 comprises a bone implant 330 comprising a polyethylene stem cap 432 having a head section 432a and a threaded body section 434b extending from the head section 432a ; and a metal orthopaedic screw 434 into which the body section 432b of the stem cap 432 i s threaded or otherwi se secured ( for example by adhesive ) . The bone implant system 400 further comprises an antenna 412 and an electrical contact pin 418 that are embedded in the polyethylene stem cap 432 which acts as casing for these embedded components 410 . The polyethylene stem cap 432 and embedded components 410 are an example of the apparatus 532 described above . The embedded antenna 412 i s an example of the energy provider 512 and the electrical contact pin 418 i s an example of an electrical element 518 .
A radio frequency transmitter 440 i s also provided . The radio frequency transmitter 440 is provided outside the body of the patient and i s operated by a user to control the stimulus provided by the bone implant system 400 . The radio frequency transmitter 440 is in communication with a computing system 442 . The radio frequency transmitter 440 and computing system 442 are an example of the controller 540 described above .
The arrangement and connection of the system 400 will now be described in detail .
The radio frequency transmitter 440 i s provided outside the body of the patient and i s operable by a user to control the stimulus provided by the bone implant system .
The body of the stem cap 432b is threaded into the orthopaedic screw 434 , the head of the stem cap 432a extends from the orthopaedic screw 434 .
The antenna 412 is positioned within the head of the stem cap 432a and also extends from the orthopaedic screw 434 . The antenna 412 i s embedded in the head of the stem cap 432a and extends around the circumference of the head to form a loop .
The electrical contact pin 418 is partially embedded in the polyethylene stem cap 432 and extends through the surface of the body 432b to electrically contact with the metal orthopaedic screw 434 into which the body of the stem cap 432b i s threaded . The antenna 412 i s electrically connected to the electrical contact pin 418 .
The components 410 embedded within the stem cap 432 are positioned so as to protect these components 410 from damage and/or failure .
The components 410 are positioned so that mechanical stres ses arising in the screw as a result of implantation are not passed to the components 410 thereby protecting the components from failure. The components may also be positioned out of the wear paths of the stem cap 432. This protects the components 410 from stress and/or strain as a result of wear of the bone implant 430 thereby protecting the components from failure due to the wear that the bone implant 430 may experience. Furthermore, the positioning of the components 410 out of the wear paths of the stem cap 432 prevents exposure of the components 410 to the surrounding bone tissue that might occur because of wear.
The function of the parts of the system 400 will now be described in detail.
The bone implant system 400 is configured to provide electrical stimulation to the bone tissue surrounding the bone implant 430 (for example the periprosthetic tissue) in particular around the orthopaedic screw 434. The electrical stimulation stimulates growth in the cells of the bone tissue for example the stimulus induces at least one of osteogenesis (bone growth) and angiogenesis (blood vessel growth) .
The radio frequency transmitter 440 is configured to communicate with the antenna 412. The radio frequency transmitter transmits radio frequency signals to the antenna 412. The transmitted radio frequency signals contain instructions for providing stimulus to the bone tissue. The radio frequency transmitter 440 is also configured to receive and analyse signals transmitted from the antenna 412. The radio frequency transmitter 440 is provided outside the body of the patient and is operated by a user to control the stimulus provided by the bone implant system 400.
The computing system 442 is configured to program radio frequency signals transmitted by the radio frequency transmitter 440 and analyse return signals received by the transmitter 440 or other receiver from the antenna 412. The casing 432 protects the embedded components 410 from damage and/or failure and provides a hermetically sealed environment for the embedded components 410 .
The antenna 412 i s configured to communicate with the radio frequency transmitter 440 . The antenna 412 can receive radiofrequency signal s from the radio frequency transmitter 440 and convert the radio frequency signal into an electrical signal which i s sent as a control signal to the electrical contact pin 418 . The control signal is based on the radio frequency signal received by the antenna 418 . The antenna 412 i s al so configured to transmit return signal s from the stimulator ( the tube piezoelectric 420 and the electrical contact pin 418 ) to the radio frequency transmitter 440 or another receiver external to the bone implant 430 and patient .
The control signal i s configured to control and provide an alternating electrical charge on the surface of the electrical contact pin 418 based on the radio frequency signal received from the antenna 412 . The alternating electrical charge is applied via the electrical contact pin 418 to the orthopaedic screw 434 .
The antenna 412 i s also configured to receive and transmit return signals indicative of fixation of the bone implant 430 to the surrounding bone .
The electrical contact pin 412 i s also configured to receive control signal s to produce a stimulus . Based on a received control signal an alternating electrical charge is generated on the surface of the electrical contact pin 418 . The electrical contact pin 418 i s arranged such that an electrical charge on the surface of the electrical contact pin 418 i s applied to the metal orthopaedic screw 434 .
On receipt of a control signal the electrical contact pin 418 i s configured to provide a return signal in response to the control signal . For example , the control signal may be partially reflected by the stimulator to provide a return signal . The return signal s provided by the stimulator are indicative of the fixation of the bone implant 430 to the surrounding bone ti s sue .
The operation of the bone implant system 400 to stimulate bone growth will now be described .
To stimulate bone growth using the bone implement system 400 an interrogation signal for example a radio frequency signal in the range of 3Hz- 9GHz i s transmitted from the radio frequency transmitter 440 to the antenna 412 . The interrogation signal i s configured to provide stimulus instructions . The interrogation signal i s received by the antenna 412 and based on the received interrogation signal the antenna generates a control signal that control s the electrical charge on the electrical contact pin 418 . The control signal i s sent from the antenna 412 to the electrical contact pin 418 .
The charge on the electrical contact pin 418 is controlled by the control signal to produce a stimulus . The control signal generates an alternating electrical charge on the surface of the electrical contact pin 418 . The alternating electrical charge i s conducted to the orthopaedic screw 434 that i s in electrical contact with the electrical contact pin 418 .
The alternating electrical charge on the surface of orthopaedic screw 434 and electrical contact pin 418 generates an alternating electric field in proximity to the bone implant 430 and in particular in the surrounding bone ti s sue . The alternating electric field in the surrounding bone ti s sue stimulates growth in the cell s of the bone tis sue for example the stimulus induces at least one of osteogenesi s (bone growth ) and angiogenesi s (blood ves sel growth) .
The bone implant system 400 al so provides an indication of the fixation of the bone implant 430 to the surrounding bone ti s sue . Information on the fixation of the bone implant 430 to the surrounding bone can be used to inform treatment for example the stimulus provided by the bone implant system 400 can be adjusted based on this information.
On receipt of a control signal the electrical contact pin 418, as well as providing a stimulus, also provides a return signal in response to the control signal. The return signal provided by the electrical contact pin 418 is indicative of the fixation of the bone implant 430 to the surrounding bone tissue.
For example, the control signal may be partially reflected by the electrical contact pin 418 to provide a return signal.
In this example, the return signal from the electrical contact pin 418 is based on an electronic resonance of the electrical contact pin 418 and orthopaedic screw 434.
For example, the interaction of the alternating electric field (generated by the alternating electric charge) and the bone tissue may affect an electrical resonance of the components of the bone implant system 400 (for example the electrical contact pin 418 and orthopaedic screw 434) . The change in resonance (a change in a degree of interaction between the bone tissue and the alternating electric field) is indicative of the fixation of the bone implant 430.
The return signal from the electrical contact pin 418 is then sent to and transmitted by the antenna 412 and received by the radio frequency transmitter 440 or other receiver external to the bone implant 430.
The received return signals are analysed by a computing system 442 to determine the fixation of the bone implant 430 to the bone tissue .
Adjustments can be made to stimulus treatment, in particular the instructions encoded into the interrogation signal, based on the determined fixation for example to promote further growth in poorly fixed regions of the bone implant. The determined fixation can provide an early warning of loosing of the bone implant and an indication that intervention or further stimulus is required.
Further features and generalisations of the example bone implant systems will now be described.
The example bone implant systems 100,200,300, and 400 comprise components encased in a casing (for example the polyethylene bearing 132,232 and the screw cap 332,432) that is suitable for implantation into bone tissue. The casing protects the embedded components whilst allowing communication of an energy provider (for example antenna 112,212,312,412) with an external transmitter/ receiver . The casing is configured to either function as part of a bone implant (for example the bearing 132) or to be inserted or carried on a bone implant (for example the orthopaedic screw 432) . The bone implant systems 100,200,300, and 400 describe examples of bone implants that the casing (and in general the bone implant system) may be used with but the casing may be used with other bone implants to provide similar bone implant systems.
The bone implant systems described above and in particular the apparatus 532 such as the casing (132,232,332,432) and embedded components (110,210,310,410) , can be applied as a permanent or temporary augment for bone contacting implants, including but not limited to joint replacement components, orthopaedic screws (including all application-specific variants: pedicle, locking, bone, dental, osteotomy, fracture, etc) , intervertebral bodies, osteotomy plates, fracture fixation devices (including all application-specific variants: plates, intramedullary nails, neck of femur implants, etc) , dental implants, jaw implants, bone- anchored prosthetic limb adapters, and limb-salvage megaprostheses . The shape of the casing and the configuration of components within the casing can be adapted to any particular bone implant .
Applicable orthopaedic surgeries include but are not limited to total and partial knee replacement, high tibial osteotomy, spinal fusion, intervertebral disc replacement, facet joint replacement and fusion, vertebral body tethering, total hip replacement , hip hemiarthroplasty, periacetabular osteotomy, anatomical and reverse total shoulder replacement , shoulder hemiarthroplasty, ankle replacement and fusion, subtalar j oint replacement and fusion, elbow replacement , wri st replacement , fracture fixation, tooth replacement , j aw reconstruction, and trans femoral and transhumeral prosthetic limb adapter implantation .
The casing in the examples described above i s polyethylene but other material s that provide a suitable enclosure for example an hermetic enclosure for the embedded components and which are preferably at least partially transparent to radio frequency signals may al so be suitable . For example , polymers such as : Poly (methyl methacrylate ) , polyurethane , Polyoxymethylene , Polyether ether ketone , Polyamide ; or ceramics such as alumina, zirconia , alumnia-zirconia may be used to form the casing .
In bone implant systems where an electrical stimulus i s applied the apparatus 532 may compri se a dielectric material .
The apparatus 532 may be secured to the bone implant in any number of ways for example using an adhesive , mechanical lock or thread .
In the bone implant systems 100 , 200 , 300 and 400 a coil antenna has been used as an energy provider . Other types of energy provider may be used for example other types of antenna may be implemented as an alternative or in addition to the antennas described above . The energy provider may have a capacitive element that may be recharged using an radio frequency signal . The capacitive element may be implanted into the bone pre-charged . Energy providers that utili se ultrasound or magnetic fields may be an alternative to the radio frequency antenna .
The energy provider i s positioned in the bone implant such that a radio frequency signal can be received and/or transmitted from the antenna . For example , the energy provider i s positioned in part of the casing that extends from any metallic or otherwi se radio frequency opaque parts of the bone implant . The energy provider may be provided as part of the printed circuit board, in such cases the printed circuit board is positioned in the implant such that a radio frequency signal can be received and/or transmitted from the energy provider . For example , the printed circuit board is positioned in part of the casing that extends from any metallic or otherwi se radio frequency opaque parts of the bone implant .
A logic element ( for example the microprocessors of the bone implant systems 100 and 300 ) may be pre-programmed with a treatment regime and may provide control signal s to the stimulator based on thi s pre-programmed regime using energy provided by the rechargeable battery . Thi s allows for the bone implant system to operate without the radio frequency transmitter or any other external energy source . For example , the rechargeable battery and microproces sor may be configured to provide an initial stimulus treatment and/or ongoing stimulus that does not require energy from the energy provider . The return signal s from the stimulator may be provided to the microproces sor which may be programmed to determine the fixation of the bone implant and dynamically update a preprogrammed treatment regime based on the determined fixation .
The microproces sor may al so be replaced by another logic element for example that i s configured to provide control signal s , based on an electrical signal from the energy provider , to the stimulator . Logic elements may al so be included in addition to the microproces sor to increase the functionality of the bone implant system for example to add further signal proces sing .
The bone implant system may compri se active components ( for example battery, microproces sor , near field communication chip and nonvolatile memory) or may be passive compri sing only pas sive components ( for example an antenna , piezoelectric transducers and electrical contact pin ) . In the example bone implant systems that have active components , 100 and 300 , the bone implant system may be configured to bypass these active components to operate in a pas sive mode as described for the pas sive bone implant systems , 200 and 400. In addition, active components may be added to the passive bone implant systems, 200 400, and 500 to increase the functionality of these example systems.
The example bone implant systems 100,200,300, 400 and 500 each comprise differently configured stimulators having one or more electrical and/or electromechanical elements. However, the number, positioning and type of the elements of the stimulator may be altered in the examples given to achieve different bone tissue stimulus and in addition may be changed to adapt the bone implant systems of these examples to different bone implant geometries. For example, it may be advantageous to include additional electrical and/or electromechanical elements for example additional piezoelectric transducers and electrical contact pins, and/or to change or add different types of electrical and/or electromechanical elements to the above examples or when considering other bone implant systems that utilise a different type of bone implant to use different configurations. For example, different types of piezoelectric transducers that could be implemented as electromechanical elements, in combination or otherwise, include but are not limited to: disc transducers operated in thickness or radial mode; plate transducers operated in thickness or shear mode; ring transducers operated in thickness mode; tube transducers operated in axial, radial or wall-thickness mode; and sphere/hemisphere transducers operated in radial or wallthickness mode. The electrical and/or electromechanical elements may be carried on the bone implant (for example positioned in the casing) to achieve stimulation of bone tissue growth in different areas around the bone implant. Furthermore, mechanical stimulation may be provided by electromechanical elements other than piezo electric transducers and electrical stimulation may be provided by electrical elements that produce an alternating electrical field by other means. Such alternative stimulators may replace or be included in addition to the stimulators described in the example bone implant systems 100,200,300,400, 500. The electromechanical elements (for example the transducers) may be positioned in regions of the implant to provide targeted stimulus to a particular area surrounding the bone implant for example in the bone implant systems 100 and 200 described above the transducers ( or additional transducers ) may be positioned anteriorly, posteriorly, and/or distally to provide targeted stimulus . Electromechanical elements ( for example the transducers in casings 132 , 232 , 323 , 432 and 532 ) may be configured to emit mechanical waves in any direction into the bone tis sue surrounding the bone implant . The mechanical waves may be for example pres sure waves or shear waves . For example , in the bone implant system 100 the transducers may be configured to emit mechanical waves towards the femoral component and/or the tibial component . The electrical contacts described herein can be of any shape and/or size . The alternating electrical current may be applied to one or more parts of the bone implant system for example the bone implant system 100 can be configured to provide an alternating current to the femoral component 134 to enable or provide additional stimulation of the bone adj acent to the femoral component 134 .
Dif ferent stimulus treatments may be applied using bone implant systems such as those described above . The time interval , frequency, modulation and amplitude of the stimulation may all be varied to provide di f ferent treatments that stimulate bone growth . For the example , the electromechanical element ( for example piezoelectric transducers ) may be configured and controlled to provide a mechanical stimulus that oscillates di splacement of the bone ti s sue cell s with an amplitude in a range of 1 pm to 800 um and the electrical element may be configured to produce an oscillating electrical field with an amplitude in a range of in the range 1 pC/m2 to 1 C/m2 . For example , and alternating electrical charge applied to the electrical contact pin may be configured and controlled to produce an electrical stimulus compri sing an oscillating electrical field with an amplitude in a range of in the range 1 pC/m2 to 1 C/m2 . The mechanical and electrical stimulus may be produced with a frequency range of 0 . 1 Hz to 500 MHz . A duty cycle in the range of 0 . 01% to 100% may be used and a modulation frequency in the range 1 Hz to 1 MHz can be implemented. The duration of the stimulus may be in the range 1 minute to 12 hours and the stimulus may be applied in time intervals for example in the range 1 hour to 168 hours. The stimulus may be adjusted based on a determined bone fixation from the return signals provided by the bone implant system.
The stimulus provided by the stimulator of the bone implant system may be limited to prevent damage to the patient and in particular to the surrounding bone tissue. For example, the electrical stimulus which in the examples above is an alternating electric field generated in the bone tissue may be limited to 1 C/m2. The mechanical stimulus which in the examples above are mechanical pressure waves that displace bone tissue cells may be limited to displacing the bone tissue cells by lum and/or limited to applying a pressure of less than 2MPa to the surrounding bone tissue. For example, a bone facing surface of the bone implant system may be oscillated by the stimulator with an amplitude in a range of 1 pm to 1 urn leading to a corresponding displacement of the bone tissue cells .
In the examples described above, radio frequency signals have been used to control and receive information from the stimulator. However, electromagnetic signals in other frequency ranges may also be suitable.
The above examples are to be understood as illustrative examples. Further examples are envisaged. It is to be understood that any feature described in relation to any one example may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the examples, or any combination of any other of the examples. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.