Abstract:
A mounting for fixing a transmitter or receiver to a surface comprises a mounting pad and a transmitter or receiver housing, the mounting pad having a face for applying to the surface and an opposite face and being provided with a first mating component of a rotatable connection and the transmitter or receiver housing having a second cooperating mating component of the rotatable connection, whereby the two components are mateable to mount the transmitter or receiver housing rotatably on the opposite face of the mounting pad.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mounting for a transmitter or a receiver, in particular to a mounting for a magnetic or aerial coil. Mountings in accordance with preferred embodiments of the invention may be useful in devices used to stimulate muscles in the human body, for example devices used in the treatment of foot-drop. 
     2. Description of the Related Art 
     Many patients who have suffered a stroke or other conditions, for example dorsiflexor injuries, peripheral nerve injuries, neuropathies, drug toxicities or diabetes, suffer from foot-drop. Foot-drop (or dropfoot) is an inability to lift the front of the foot (dorsiflexion), making it difficult to swing the leg forward in walking. Foot-drop caused by damage to the central nervous system (rather than to the peripheral nerve which controls the lower leg dorsiflexor muscles) can be alleviated by electrically stimulating the peroneal nerve, causing the lower leg dorsiflexor muscles to contract. Stimulation may be caused through the skin (transcutaneous stimulation) or via an implanted stimulator (subcutaneous stimulation). To cause contraction of the dorsiflexor muscles during the swing phase of gait only, a sensor is used to detect this phase. The sensor is typically a switch located under the heel inside the shoe. The switch is connected to an electrical stimulator on or under the surface of the leg. 
     A conventional unit for the treatment of foot-drop comprises a heel sensor, a controller and an electrical stimulator. The heel sensor, the controller and the electrical stimulator are connected by wires. 
     The present inventors have described in an earlier published patent application (WO01/60445) a unit for the treatment of foot-drop wherein the heel sensor and electrical stimulator communicate via a radio transmitter and receiver. In a preferred embodiment, an implanted multi-channel stimulator activates foot lift by stimulating the common peroneal nerve above the knee. The stimulation activates the dorsiflexors which lift the foot. The stimulating electrode is located under the skin just above the knee while the stimulator is located under the skin on the thigh. The stimulating electrode and stimulator are implanted by surgery under local anaesthesia. The implanted stimulator is controlled by an external control unit. The control unit transmits energy and control signals into the stimulator using a wired connection to a lightweight transmitting coil located on the skin over the implanted stimulator. The stimulation is activated by a wireless heel switch located in the shoe. The multiple channels of stimulation make it possible for the clinician to adjust the movement of the foot to ensure a balanced foot lift even when the device has been implanted for a period of time. 
     In devices such as this, the transmitting coil must be mounted on the skin. This can be achieved using an adhesive Velcro® pad which is attached to the skin, to which the transmitting coil is mounted using a cooperating Velcro® pad. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the present invention relates to a mounting for fixing a transmitter or receiver to a surface, the mounting comprising a mounting pad and a transmitter or receiver housing, the mounting pad having a face for applying to the surface and an opposite face and being provided with a first mating component of a rotatable connection and the transmitter or receiver housing having a second cooperating mating component of the rotatable connection, whereby the two components are mateable to mount the transmitter or receiver housing rotatably on the opposite face of the mounting pad. 
     Preferably, the transmitter or receiver housing is a transmitting or receiving antenna housing. More preferably, the transmitting or receiving antenna housing is a transmitting or receiving coil housing. Highly preferably, the transmitting or receiving coil housing is a magnetic coil housing or an aerial coil housing. 
     In a preferred embodiment, the face of the mounting pad for applying to the surface is an adhesive face. Alternatively, the mounting pad may be provided with adhesive tape extending beyond the edge of the mounting pad for fixing the mounting pad to the surface. An adhesive surface of the adhesive tape may be applied to the opposite face of the mounting pad from the face for applying to the surface, such that the adhesive fixes the adhesive tape to the mounting pad in addition to fixing the adhesive tape to the surface. Alternatively, a non-adhesive surface of the adhesive tape may be applied to the face of the mounting pad for applying to the surface. In this case, the adhesive fixes the adhesive tape to the surface only. The adhesive tape must be fixed to the mounting pad by welding or by additional adhesive. 
     Preferably, the transmitter or receiver housing is in the form of a dish and the mounting pad is in the form of a plate, such that when the two components are mated the mounting pad sits at least substantially within the transmitter or receiver housing. 
     Preferably, one of the first and second mating components is a flanged boss and the other of the first and second mating components is a cooperating hole. More preferably, the cooperating hole has a first portion through which the flanged boss can pass and a second portion within which the flanged boss can sit but through which the flanged boss cannot pass. Highly preferably, the first portion and the second portion of the cooperating hole are divided by a flexible waist through which the flanged boss can be urged. 
     Preferably, the mounting is suitable for mounting to the human or animal body, in particular the mounting preferably has suitable size and weight for mounting to the human or animal body. Preferably, the mounting has a diameter of 10 cm or less, for example 5 cm or less, and a thickness of 2 cm or less. Preferably, the mounting has a weight of 50 g or less, more preferably 25 g or less. 
     Preferably, if the mounting is provided with adhesive as described above, the adhesive used is non-toxic. 
     In a second aspect, the present invention relates to a transmitter or receiver housing, constituting one component of a mounting as described above. 
     In a third aspect, the present invention relates to a mounting pad, constituting one component of a mounting as described above. 
     In a fourth aspect, the present invention relates to an electrical stimulation unit comprising a sensor, a transmitter, a transmitter mounting as described above and a stimulator, wherein the sensor controls the transmitter to transmit a signal to the stimulator. 
     Preferably, the sensor controls the transmitter by means of a controller. 
     The electrical stimulation unit may be intended for the treatment of foot-drop, in which case the sensor may be a pressure sensor for placing on the heel and the stimulator may be a stimulator for the peroneal nerve. 
     In a fifth aspect, the present invention relates to the use of a mounting as described above in mounting a transmitter or receiver on the human or animal body. 
     In a sixth aspect, the present invention relates to a method of producing nerve stimulation using an electrical stimulation unit as described above, comprising the steps of: 
     the sensor detecting a stimulus; 
     the sensor transmitting a signal to the controller; 
     the controller controlling the transmitter to transmit a signal to the stimulator; and 
     the stimulator producing nerve stimulation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to a preferred embodiment as illustrated in the accompanying drawings, in which: 
         FIG. 1  shows schematically a foot-drop treatment unit of the invention; 
         FIG. 2  shows a perspective view of the separated mounting pad and transmitting coil housing of the invention; 
         FIG. 3  shows a perspective view of the mating mounting pad and transmitting coil housing of the invention; and 
         FIG. 4  shows a perspective view of the mating mounting pad of the invention and means for mounting the mated mounting pad to a patient. 
     
    
    
     DETAILED DESCRIPTION 
     In the foot-drop treatment unit shown in  FIG. 1 , a heel sensor  10  is placed under the heel  12  of the patient. A control unit  14 , which communicates with the heel sensor  10  via a radio link (not shown), is attached to the belt  16  of the patient. A magnetic transmitting coil  18  is mounted on the skin of the leg  20  of the patient on the thigh using a mounting  21  ( FIG. 2 ) comprising a transmitting coil housing  22  and mating mounting pad  24  as described below. The magnetic transmitting coil  18  is positioned over a stimulator  26  positioned under the skin of the leg  20  of the patient and communicates with the stimulator  26  by a magnetic signal (not shown). The magnetic transmitting coil is connected to the control unit  14  by a wire  28 . The stimulator  26  is connected by an implanted wire (not shown) to a stimulation electrode  30 , positioned under the skin of the leg  20  of the patient above the knee. 
     The mounting  21  ( FIG. 2 ) comprises a plastics transmitting coil housing  22  and a plastics mating mounting pad  24 . The transmitting coil housing  22  has the form of a circular dish  32  provided with a lateral rim  34 . The centre  36  of the concave surface  38  of the dish  32  is provided with a cylindrical boss  40  having a flange  42  around its distal end  44 . At one side  46  of the dish  32  a plate  48  having the form of a circle segment is mounted parallel to the lateral rim  34 . Within the dish  32  under the plate  48  the transmitting coil  18  is mounted. The wire  28  passes through a hole (not shown) in the dish  32 . The wire  28  runs across the concave surface  38  of the dish through a conduit  51  and is attached to the transmitting coil  18  under the plate  48 . 
     The mating mounting pad  24  has the form of a circular plate  50  with a depressed circular central region  52  surrounded by a rim  53 . The diameter of the circular plate  50  is smaller than the diameter of the transmitting coil housing dish  32 . A hole  54  in the depressed region  52  has the form of a circle  56  joined to the longer side of an ellipse  58  via a waist  59 . The circle  56  is centred on the centre  60  of the depressed region  52 . Slots  61  are located in the depressed region  52  separated from each side of the waist  59  by strips  63  and following the shape of the waist  59 . The depressed region  52  is provided with a further hole  62 . To the lower surface  65  of the rim  53  of the circular plate  50  is applied the adhesive surface  66  of an annular single sided adhesive tape  64  ( FIG. 4 ) which extends beyond the rim  53 . Part of the adhesive surface  66  serves to attach the adhesive tape  64  to the surface  65 . The part of the adhesive surface  66  extending beyond the rim  53  is covered with a release tape (not shown). Alternatively, the rim  53  may be attached to the back of the adhesive tape  64 , such that the entire adhesive surface  66  of the adhesive tape  64  can be used to mount the mating mounting pad  24  to the patient. 
     In use, the release tape (not shown) is removed from the adhesive tape  64  of the mating mounting pad  24 . The adhesive surface  66  of the adhesive tape  64  is applied to the leg  20  of the patient at the thigh directly above the stimulator  26 , to attach the mated mounting pad  24  to the leg  20 . In an alternative embodiment, the upper surface of the rim  53  of the mated mounting plate  24  is provided with adhesive, for example double sided adhesive tape, and the annular adhesive tape  64  is not used. The mating mounting pad  24  will remain on the leg  20  of the patient for several days until the adhesive (not shown) is dissolved by bathing or showering. 
     When the patient wishes to use the foot-drop treatment unit, the transmitting coil housing  22  is mounted to the mating mounting pad  24 . This is done by applying the concave surface  38  of the dish  32  to the mating mounting pad  24  such that the boss  40  passes through the hole  54  of the mating mounting pad  24  at the ellipse  58 . Lateral sliding of the transmitting coil  22  relative to the mating mounting pad  24  forces the boss  40  against the strips  63 . The strips  63  deform by movement into the slots  61 , widening the waist  59 . This allows the boss  40  to click through the waist  59  such that the centre  36  of the dish  32  is aligned with the centre  60  of the depressed region  52  and the boss  40  sits within the hole  54  at the circle  56  of smaller diameter, with the mating mounting pad  24  within the dish  32  ( FIG. 3 ). The diameter of the flange  42  of the boss  40  is such that the boss  40  cannot pass back through the hole  54  at the circle  56 , and the width of the waist  59  is such that the boss  40  cannot slide into the ellipse  58  portion of the hole  54 . The boss  40  does not contact the leg  20  of the patient. 
     The transmitting coil  18  is now positioned close to the leg  20  of the patient, and is separated from the leg  20  of the patient by the plate  48 . 
     The hole  62  in the mating mounting pad  24  allows water to drain from the mounting  10  so that the adhesive (not shown) is not dissolved too quickly on bathing or showering. 
     Rotational movement of the transmitting coil housing  22  relative to the mating mounting pad  24  is possible, since the cylindrical boss  40  is free to rotate within the hole  54 . 
     Once the transmitting coil  18  has been mounted to the leg  20  in this way and the heel sensor  10  has been placed under the heel  12  (for example in a shoe (not shown)), the foot-drop treatment unit may be used. Pressure and lack of pressure of the heel  12  on the floor (not shown) are detected using the heel sensor  10 . This information is communicated to the control unit  14  via the radio link. The control unit  14  performs analysis on the information from the heel sensor  10  to detect when the patient wishes to step forward. At these times, a signal is sent from the control unit  14  to the magnetic transmitting coil  18  via the wire  28 . The magnetic transmitting coil  18  produces a magnetic signal in response. This magnetic signal passes through the skin of the leg  20  and causes the stimulator  26  to produce a stimulating signal (not shown) at the stimulation electrode  30 . This stimulating signal causes the dorsiflexor muscles in the leg  20  to contract, dorsiflexing the foot of the patient to enable a step forward to be taken. 
     The preferred embodiment of the present invention has several advantages over conventional foot-drop treatment unit mountings. First, the magnetic coil housing  22  can be mounted to the mounting pad  24  with one hand. This may be particularly important for patients who also suffer from upper body paralysis. Secondly, the magnetic coil housing  22  can be manipulated through clothing during mounting to the mounting pad  24 . Thirdly, the magnetic coil housing  22  is rotatable on the mounting pad  24 , in contrast to the conventional Velcro® pad. This has the advantage that the coil housing  22  may be adjusted after fastening. The coil housing  22  will also rotate under torsional force from the wire  28  which connects the coil to the control unit  14 , to prevent a twisted wire  28  or inadvertent disconnection of the magnetic coil housing  22 . Fourthly, whereas a Velcro® attachment will form even if the two pads are substantially misaligned (provided there is some overlap), the proposed mounting accurately locates the coil at the desired place. This facilitates precise mounting of the coil even when the mounting  10  is not in sight, for example when it is hidden under clothing. 
     Whilst the invention has been described with reference to the illustrated preferred embodiment, it will be recognised that various modifications are possible within the scope of the invention. 
     For example, the transmitting coil mounting  21  of the invention has been described in the context of a foot-drop treatment unit. However, the transmitting or receiving coil mounting  21  might be used in a variety of devices, for example to stimulate other types of muscle contraction (e.g. heart contraction in a pacemaker), to interrogate a subcutaneous sensor, or to stimulate drug release from an implant.