FIELD OF THE INVENTION

[0001] This invention relates to control of prosthetic devices and, in particular, control of transcutaneous prostheses.

BACKGROUND

[0002] Following amputation of limbs or digits it is common to fit an external (exo-) prosthetic device that is attached to the body via a skin interface. These devices typically use a custom made socket secured with straps or clamps to the stump that remains following amputation. There are, however, a number of disadvantages of such exo-prosthetic devices, including discomfort due to inflammation and pressure sores, the requirement for a new socket if the stump changes shape, and inefficient or unnatural movement where a joint is involved where the prosthesis is moved by muscle groups situated at a distance from the attached prosthesis.

[0003] More recently, transcutaneous or 'endo-exo' prostheses have been proposed in which there is direct skeletal fixation of the prosthesis to the amputation stump. Typically this involves insertion of a metal implant into the residual skeleton to act as a bone anchor for the prosthesis, with a transcutaneous component to which the external portion of the prosthesis is then fixed. In this way, the prosthesis is effectively attached to the patient's skeleton, avoiding many of the disadvantages of traditional exo-prostheses.

[0004] To ensure secure skeletal fixation of a transcutaneous prosthesis, the bone anchor portion will normally be engineered, for example with an appropriate surface treatment, to encourage osseous integration. It has also been proposed, for example in WO 01/97718 (the entire contents of which are incorporated herein by reference), to surface treat the transcutaneous portion of the prosthesis to stimulate fibrous tissue ingrowth. The goal is to attach the skin to the implant to prevent movement of the skin and shear forces separating epithelial cells at the interface and underlying dermis, which otherwise might lead to infection. Clinical experience has shown such bone-anchored devices to be very promising (see: Kang et al, Osseocutaneous l Integration of an Instraosseous Transcutaneous Amputation Prosthesis Implant Used for Reconstruction of a Transhumeral Amputee: Case Report; Hand Surg

2010;35A:1130-1134).

[0005] However, despite the clinical success of transcutaneous prostheses, in practice the function and control of prosthetic limbs and digits remains poor.

[0006] Traditionally, prosthetic limbs have been body-powered; muscle contraction has provided the activation force, via linkages, to effect movements of the prosthesis or to actuate switches that control the motions of an electrically powered prosthesis.

[0007] More recently, myoelectric prostheses have been offered, in which electromyographic (EMG) signals from voluntarily contracted muscles in a patient's residual limb are detected and used to control movements of a prosthesis, such as wrist supination/pronation or hand opening / closing for example. In this case, the movements of the prosthesis are driven by electric motors and the electromyographic signals are used to control the motors.

[0008] Existing myoelectric prostheses typically use skin-surface electrodes to detect muscle action potentials. For a prosthetic hand, typically two skin electrodes are used, overlying antagonistic muscles (forearm flexors and extensors) to open and close the hand. Further movements (e.g. wrist rotation) are achieved by the same muscles using a mode switch. This results in cumbersome and unintuitive control.

[0009] EP1043003 describes an example of myoelectric prosthesis using skin- surface electrodes. US 2010/0030341 describes another example of a myoelectric prosthesis using skin-surface electrodes in which signals from the surface electrodes are transmitted wirelessly to a receiver for further processing within the prosthesis.

[0010] It has also been proposed to use implanted electrodes to detect

electromyographic signals for use in control of a prosthetic device. Farnsworth et al (Wireless in vivo EMG Sensor for Intelligent Prosthetic Control; IEEE Solid-State Sensors, Actuators and Microsystems Conference, 2009: 358-361 ) describe an example of using electromyographic signals to control a prosthesis. In this example, a wireless inductively coupled system is used to transmit signals from an implanted sensor system to a prosthetic limb. As they explain, by employing wireless transmission of the signals, it avoids the need to have any wires passing through the skin, which would be prone to infection. WO 201 1/028087 describes another example in which a pair of implanted electrodes in a single muscle of a residual limb are used to control a prosthesis. Weir et al (Implantable Myoelectric Sensors (IMESs) for Intramuscular Electromyogram Recording; IEEE Transactions on Biomedical Engineering, Vol. 56, No. 1 , January 2009) have similarly proposed a system of implanted myoelectric sensors, from which signals are sent to an external telemetry controller over a transcutaneous, wireless magnetic link, for control of a prosthetic limb.

SUMMARY OF THE INVENTION

[0011] Embodiments of the invention are aimed generally at providing improved approaches to control of prosthetic devices, especially transcutaneous prosthetic devices.

[0012] A general proposition of the present invention is to use the transcutaneous portion of a transcutaneous prosthesis to carry signals from an internal part of a prosthesis control system to an external part of a prosthesis control system or vice versa. The transcutaneous portion of the prosthesis may, for example, carry signals from implanted electrodes to an external controller, carry power signals from an external power source to implanted components and/or carry other control signals from an external controller to implanted components.

[0013] In a first aspect, the invention provides a transcutaneous prosthesis for attachment to a patient comprising: an internal portion for implantation in a bone of the patient; an external portion including a prosthetic part operable to perform one or more mechanical movements; a transcutaneous portion linking the internal and external portions and intended to extend through the patient's skin surface; and a control system to control the one or more mechanical movements of the prosthetic part, the control system comprising external components within said prosthetic part and internal components intended for implantation in the patient; wherein said transcutaneous portion has a bore extending within it that houses an electrical connector for transmission of electrical signals between the external and internal components of the control system.

[0014] The internal components of the control system preferably comprise a plurality of implantable electrodes for sensing signals, such as electromyographic and/or nerve signals, from the patient's body.

[0015] This approach, whilst avoiding the need for wireless communication and power transfer, enables electrodes to be placed directly on the muscle rather than on the skin, which leads to more accurate capture of signals with greatly reduced crosstalk. The number of control channels can be greatly increased, for example using 10 or more, 20 or more, or 30 or more electrodes, on corresponding muscles, to reflect the number of muscles used to control a particular movement of the body part that the prosthesis has replaced. For example, hand movement is controlled by 32 muscles. This approach is not possible with skin surface electrodes, which would not be able to accurately distinguish signals from individual muscles in the forearm without contamination of signals from adjacent muscles.

[0016] The signals from the electrodes may either be amplified in-situ by an amplifier integrated into the body of the electrode, or at an electronic site within the body.

Amplified signals may be processed by implanted components of the control system, by external components of the control system or by a combination of the two. For example, the external components of the control system may include a processor, with signals from the electrodes being transmitted to the processor via the electrical connector within the bore of the transcutaneous portion of the prosthesis, with the body of the prosthesis acting as the electrical return for example.

[0017] Preferably, the internal components of the control system include a multiplexer adapted to receive signals from the plurality of implantable electrodes, multiplex the signals, and output the multiplexed signal to be transmitted to the processor via the electrical connector. This has the advantage that the electrical connector need only be a single cable passing through the transcutaneous portion of the prosthesis.

[0018] Each electrode can be connected to the multiplexer by a connecting wire to provide a hard-wired connection for transmission of signals from the electrode to the multiplexer. In some embodiments each electrode-connecting wire is connected to the multiplexer with a plug and socket connector to enable individual electrodes to be disconnected and therefore more easily replaced in the event of failure. In other embodiments, all of the connecting wires can be connected to the multiplexer by a single connector.

[0019] In some embodiments, signal-processing circuitry is associated with each electrode for processing the signal from the electrode prior to it being transmitted to the external components of the control circuitry (via the multiplexer where used). The electrode and its associated signal-processing circuitry (provided as an integrated circuit for example) may conveniently be provided in a single package for implantation at the intended site for the electrode. The signal-processing circuitry may, for example, amplify and/or filter the electrode signal prior to onward transmission to the multiplexer / other control system components.

[0020] Preferably the bore of the transcutaneous component is hermetically sealed to resist moisture ingress. The seal may be a feed-through composed of, for example, metal in glass. This will permit transfer of power to the implanted components and simultaneous telemetry of signals from the electrodes.

[0021] Typically, the external components of the control system will include a power supply (for example battery source) that can be connected to the electrical connector within the bore of the transcutaneous portion of the prosthesis to supply power to the internal components of the control system. Signals will be demultiplexed externally and converted to analogue voltages if required.

[0022] In some cases it may also be desirable to sense one or more operational parameters of the prosthesis and feed them back to the patient. For example, a pressure sensor can be used to sense grip force in a prosthetic hand to provide tactile-like feed back to the patient.

[0023] In some embodiments, therefore, the external components of the control system include a sensor (e.g. a pressure sensor) for sensing an operational parameter of the prosthetic part and the internal components of the control system include a nerve electrode for implantation adjacent a sensory nerve to stimulate the nerve in response to a signal from the sensor. The sensor signals can be sent to a nerve electrode via the electrical connector in the bore of the transcutaneous portion of the prosthesis. In some embodiments this will require multiplexing of feedback signals externally and demultiplexing internally.

[0024] In some embodiments the prosthetic part may be detachable from the transcutaneous part of the prosthesis, and the prosthesis further comprises a plug and socket connector for electrically connecting external components of the control system to the electrical connector in the bore of the transcutaneous portion of the prosthesis.

[0025] The prosthetic part may be, for example, a prosthetic limb, prosthetic hand, prosthetic foot or prosthetic digit.

[0026] In a second aspect, the invention provides a control system for a

transcutaneous prosthesis, the prosthesis including a transcutaneous portion having a bore within it, the control system comprising: external components for locating within an external portion of the prosthesis; internal components intended for implantation in a patient; and an electrical connector that can be housed within the bore of the transcutaneous portion of the prosthesis, one end of the electrical connector being for connection to an external component of the control system and the other end of the electrical connector being for connection to an internal component of the control system, whereby the electrical connector can transmit electrical signals between the external and internal components of the control system through the transcutaneous portion of the prosthesis.

[0027] In a third aspect, the invention provides a transcutaneous portion for a prosthetic device, the prosthetic device being a device according to the first aspect above, the transcutaneous portion intended to extend through a patient's skin surface and be connected at one end to an implantable portion of the prosthetic device and connected at the other end to an external portion of the prosthetic device, the transcutaneous portion comprising an internal bore extending from at or near said one end to at or near said other end, the bore being suitable to accommodate one or more electrical conductors for transcutaneous transmission of electrical signals.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] An embodiment of the invention is now described by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a schematic cross-section of a transcutaneous prosthesis in accordance with an embodiment of the present invention, shown in situ;

FIG. 2 is a schematic of the implanted portion of the control system of the prosthesis shown in figure 1 ; and

FIG. 3 is a photograph of a prototype transcutaneous prosthesis in accordance with an embodiment of the invention, used to conduct experiments that are discussed below.

DETAILED DESCRIPTION

[0029] Fig. 1 shows a transcutaneous prosthesis, in this example for a prosthetic limb, such as a forearm and a hand.

[0030] The prosthesis includes a first portion 10 which is secured in the

intramedullary canal of a bone in the residual limb. This component can be coated with a material to encourage osseous integration. It may also be shaped, for example fluted, to resist rotation. A second portion 14 of the prosthesis extends through the skin and may be given a non-stick surface on its exterior portion to discourage adhesion of bacteria and thus help prevent infection.

[0031] In accordance with the present invention, the transcutaneous portion of the prosthesis 14, that is the portion that passes from one side of the skin to the other, has an internal bore 16 that carries an electrically conductive cable 18. In some embodiments the bore 16 may be adapted to carry multiple cables.

[0032] The cable 18 is used to transmit signals from implanted sensors that control movements of the prosthesis in the manner described further below. The cable 18 is also used to transmit power from an external power source, for example a

rechargeable battery housed in the prosthetic limb, to the sensors and other implanted components of the control system for the prosthesis. The cable 18 can also be used to transmit signals from sensors in the external part of the prosthesis, for example pressure sensors in fingers of a prosthetic hand, to internal components of the control system that drive stimulator electrodes to stimulate sensory nerves (e.g. medial/lateral cutaneous nerve of forearm) to provide feedback from the prosthesis to the patient.

[0033] As shown in figure 2, the control system may include a series of electrodes for sensing electromyographic signals and/or nerve signals. In this schematic drawing, six sensors 20 are shown. In practice, it may be desirable to use many more. For example, for a prosthetic hand, it may be desirable to use a separate sensor for each of the muscles that control hand movement, to enable the prosthesis to better and more intuitively mimic natural hand movements.

[0034] The implanted electrodes sense muscle or nerve signals and these signals are transmitted to a processor in the prosthetic limb / hand, which interprets the signals to control motors that drive movements of the prosthetic limb / hand.

[0035] In this example, the signals from the sensors 20 are transmitted to an implanted multiplexer 22, where the signals are multiplexed for transmission through the cable 18 in the transcutaneous portion 14 of the prosthesis. The multiplexer may receive analogue or digital signals from the electrodes. The multiplexer may be sealed within a hermetic package or encapsulated within a sealant. The signals are received in the external portion of the prosthesis, where they are de-multiplexed and subsequently processed to drive the movement of the prosthetic limb / hand.

[0036] The electrodes 20 may be joined to the multiplexer 22 as a single sealed unit. Alternatively, the electrodes 20 can be attached to the multiplexer 22 intra-operatively using a plug and socket arrangement allowing replacement of electrode units 20 should a fault arise. These junctions are sealed with implant-grade silicone.

[0037] In one exemplary embodiment, using muscle electrodes to sense electromyographic signals, the muscle electrodes can have one or more of the following characteristics:

a. 3x ~5mm diameter circular Au/Pd or Pt/lr electrodes plated onto a flexible polyimide substrate with electronic components mounted directly on the reverse side.

b. The electrodes may be a dipole or a tripole design.

c. The electrodes can be arranged linearly with an interelectrode distance of ~5mm in tripole design with the central electrode as the reference. d. The outer 2 electrodes will be the recording electrodes in both designs. e. Electrically conductive paths will be made from the electrodes through the polyimide (thus providing minimal path for moisture tracking).

f. Components for an operational amplifier + full-wave rectifier, or an instrumentation amplifier, or an analogue to digital converter with associated serial data processing may be situated on the non-electrode side of the substrate.

g. Amplifier circuitry will be <5mm from the EMG electrodes h. Amplifier circuitry will be encapsulated in medical grade silicone, the electrodes will not be encapsulated.

i. A region of the electrode will be used for attaching to the muscle. For example an incorporated Dacron "backing" will provide a surgical anchor for suturing.

j. The electrode will be attached to the muscle surface for example by suturing onto the surface of the muscle using the Dacron backing with non-absorbable sutures.

[0038] A preferred integral electrode/amplifier unit incorporated with the electrodes can provide both immediate amplification of the differential signal from the electrode and electrical buffering of the signal to greatly minimise the effects of leakage currents. Signals from each electrode/amplifier unit can be led to a central electronic package containing either an AD converter and a microcontroller or a digital multiplexer.

Experimental Results

[0039] The following is a description of an experiment conducted using the bone- anchored prosthesis illustrated in fig. 3 to demonstrate the efficacy of an embodiment of the invention. The prosthesis includes a simple, single bi-polar electrode 20.

[0040] Under General Anaesthesia, an animal (in this case a sheep) was placed in a right lateral position. Left leg was shaved and prepped with betadine and

chlorhexidine, and draped.

[0041] An incision was made over the tibia, 10cm inferior to knee joint. Dissection was made down to bone, the bone was drilled and reamed. The bone-anchored device was inserted into the tibia.

[0042] A separate incision was made over the lateral aspect of the superior leg.

Dissection was made down to the peroneus tertius muscle. The electrode was tunnelled under the intervening skin bridge and sutured onto the muscle.

[0043] The skin was closed around the bone-anchored device with absorbable sutures. The incision overlying muscle was closed in layers. Non-adhesive dressings were applied. The animal was then allowed to convalesce for 24 hours. [0044] Following convalescence, on a weekly basis, the animal was placed on treadmill and signals captured using EMG measuring equipment. The animal was walked on the treadmill every week for 12 weeks.

[0045] At each treadmill session, EMG signals were recorded (at 1000 samples per second (sps), 100-500Hz band-pass; and 10,000sps 0.1 -5000Hz band-pass) by attaching the lead from a recording device to the external part of the bone-anchored device using a plug and socket interface.

[0046] Signals from overlying surface electrodes were used for comparison. The absolute values were taken prior to signal analysis. Power and Frequency analysis were used to identify muscle activations. Signal to noise ratio (SNR) was calculated as the ratio between the average activation EMG signals and the average non- activation EMGs.

[0047] Analysis of the resultant data showed the SNR was greater in muscle (5.07) vs surface electrodes (1.62). The quality of signal did not deteriorate over the experimental period. The device functioned correctly throughout and there were no post-operative complications. 50Hz noise and movement artefact were observed with a band-pass of 0.1 -5000Hz, this noise was removed by a 100-500Hz band-pass filter.

[0048] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.