Abstract:
A cochlear implant system includes a subcutaneous housing which includes a main body and a bottom cover secured to the main body. A central cavity in a center of the subcutaneous housing is formed by a portion of an outer surface of the main body. A magnet is removably inserted into the central cavity and includes a cylindrical body with a central axis aligned with a removal axis of the central cavity, a groove extending circumferentially around the cylindrical body, and a top surface, which includes an outer edge, a plurality of ribs extending radially farther than the outer edge, and a plurality of abutments extending radially farther than the ribs. A compressive ring is seated in the groove of the cylindrical body and engages under a ledge in the central cavity when the magnet is inserted into the central cavity and biases the magnet against removal from the central cavity.

Description:
TECHNICAL FIELD 
       [0001]    The technical field relates to insertion, positioning, and securing of a magnet in an implanted part of a cochlear implant and an associated tool for its removal. 
       BACKGROUND 
       [0002]    Cochlear implants typically include an external device that is coupled to an implanted device. The coupling may be achieved through electromagnetic coupling, where coils transmit and/or receive information and/or energy. Consequently, external and internal devices each utilize a coil to transmit and to receive information and/or energy. The external device includes at least one coil and the internal device includes at least one coil. 
         [0003]    In order to align the coils of the external device and the internal device with respect to each other, one or more magnets are associated each coil. Thus, the two coils are aligned and the external device is pulled toward the implanted device by the magnets. The external device is thus held in the proper working position on top of the implanted device by magnetic force. 
         [0004]    The magnet of the implanted device may be encapsulated in a biocompatible housing to ensure compatibility with the body of the user in case the magnet is made of magnetic material that is itself not biocompatible. As shown is  FIG. 1A , generally the magnet  13  is mounted into a small hermetical part that is made of silicone, because silicone is biocompatible. To position this magnet under the skin in the correct position, the magnet  13  is inserted into a hole included in the silicone part  14 , in the center of the coil  12 . 
         [0005]    As shown on  FIG. 1B , in a different design, fixed magnet  104  is permanently installed into the hermetic housing  101  made of ceramic  105  and titanium  106 , in the center of coil  103 . Fixed magnet  104  is considered to be non-removable due to the way it is installed in the hermetic housing  101 . 
         [0006]    Most of the time, cochlear implants are compatible with low power magnetic resonance imaging (MRI) up to magnetic field strength of 1.5 tesla (T). At levels up to 1.5 T an implant is generally secure, minimal heat is generated, the magnetic characteristics of the implanted magnet remain stable, any artifact effects in the MRI are acceptable, and the implanted device is not displaced. 
         [0007]    However, when higher power MRI has to be performed on patients wearing a cochlear implant, some problems can occur, including demagnetization of the implanted magnet, strong force applied to tissues due to the magnetic field of the MRI interacting with the internal magnet, heat generation, and undesirable artifacts in the MRI results. 
         [0008]    To address these concerns, some cochlear implants are designed to enable removal magnets while the cochlear implant remains implanted in the user. The removal of the implanted magnet enables the use of high power MRI. As shown in  FIG. 1C , a magnet  503  is placed in the center of silicone molding  504 , where silicone lips  507  partially cover the top of the magnet  503 . A central hole and slots  508  between silicone lips  507  enable the removal of the magnet by deforming the silicone lips  507  when force is applied to the magnet  503 . 
         [0009]    While the design in  FIG. 1C  enables removal of the magnet  503 , the design does not provide sufficiently high stability for the magnet  503  when it is installed in the cochlear implant due to the elasticity of silicone. Further, when the magnet  503  is removed and replaced, it may be misaligned and have a secondary displacement due to torque. Furthermore, the design provides no specific solution to make the handling and removal of the magnet  503  easy for the healthcare provider. 
         [0010]    From EP2119474A2 it is known to provide the magnet in a releasable manner placed in a hole centered in a circular ceramic housing. The ceramic housing thus encircles the magnet. The document does not provide information on measures to facilitate the fast removal and replacement of the magnet. 
       SUMMARY 
       [0011]    The solution proposed in the disclosure resolves shortcomings noted above by providing a stable mounting solution for a magnet and a tool for its removal. Further, the solution is minimally invasive using a compact structure. The proposed solution takes into account specific tooling needed by a surgeon in order to grasp and remove a magnet from the surrounding housing. 
         [0012]    In an embodiment, a cochlear implant system includes a subcutaneous housing containing electronics for at least stimulation or collection of data and at least one antenna for communicating with an external device. The subcutaneous housing includes a main body having a U-shaped radial cross-section, a bottom cover secured to the main body, forming a hollow cavity bounded by an inner surface of the main body and the bottom cover, and a central cavity in a center of the subcutaneous housing formed by a portion of an outer surface of the main body. A magnet is removably inserted into the central cavity, the magnet including a cylindrical body with a central axis, the central axis aligned with a removal axis of the central cavity, a groove extending circumferentially around the cylindrical body, and a top surface. The top surface includes an outer edge, a plurality of ribs extending radially farther than the outer edge, and a plurality of abutments extending radially farther than the ribs. Further, a compressive ring is seated in the groove of the cylindrical body, wherein the compressive ring engages under a ledge in the central cavity when the magnet is inserted into the central cavity and biases the magnet against removal from the central cavity. 
         [0013]    In an embodiment, the cochlear implant system further includes a silicone rim surrounding the body and tapering radially outward. 
         [0014]    In an embodiment, the silicone rim includes two flaps extending outward, each flap including a support ring configured to accept a bone anchoring screw. 
         [0015]    In an embodiment, the cochlear implant system further includes a junction area formed as a part of the silicone rim between the two flaps, the junction area accommodating electrodes passing to the cochlear implant. 
         [0016]    In an embodiment, the bottom cover is a stamped titanium cover. 
         [0017]    In an embodiment, the stamped titanium cover includes a plurality of feedthroughs. 
         [0018]    In an embodiment, the main body is made of a biocompatible ceramic material. 
         [0019]    In an embodiment, the biocompatible material is one of zirconia toughened alumina, high purity alumina, and pure zirconia. 
         [0020]    In an embodiment, the top surface of the magnet includes three ribs and three abutments equally spaced around the outer circumference of the outer edge of the top surface, the abutments are in contact with a rim of the central cavity when the magnet is fully inserted into the central cavity, and the ribs are not in contact with the rim of the central cavity. 
         [0021]    In an embodiment, each rib has a smoothly tapered edge connected to the outer edge of the top surface, and a void is bounded by the outer edge of the top surface and the rim of the central cavity. 
         [0022]    In an embodiment, the cochlear implant system further includes a tool for removing the magnet from the central cavity, the tool including a handle portion, a second magnet installed on a first end of the handle portion, three blades extending from the first end parallel to a central axis of the handle portion, each blade terminating with a hook, wherein each blade is insertable in the void, each hook engages under a respective rib when the handle portion is rotated after insertion of the blades, and the second magnet attracts the magnet in the central cavity when the hooks engage under the ribs. 
         [0023]    In an embodiment, the magnet includes an outer casing made of a biocompatible material, and a magnetic core. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]      FIG. 1A  illustrates a top and a side view of a cochlear implant housing according to background art. 
           [0025]      FIG. 1B  illustrates a partial cross section view of a cochlear implant composed of a hermetic housing with a non-removable magnet according to background art. 
           [0026]      FIG. 1C  illustrates a top view of a cochlear implant housing according to background art. 
           [0027]      FIGS. 2A and 2B  illustrate a front view and a cross section view of an example of a cochlear implant with a removable magnet according to an embodiment of the disclosure. 
           [0028]      FIG. 2C  illustrates a top view and a cross sectional view of an example of a removable magnet assembly according to an embodiment of the disclosure. 
           [0029]      FIG. 2D  illustrates a further top view and cross sectional view of a further example of the dislosure. 
           [0030]      FIG. 3A  illustrates a perspective view of an example of cochlear implant with its magnet removed with a tool according to an embodiment of the disclosure. 
           [0031]      FIG. 3B  illustrates a detailed perspective view of an example of cochlear implant with its magnet removed from its place according to an embodiment of the disclosure. 
           [0032]      FIG. 3C  illustrates various stages of interaction between removal tool and magnet. 
           [0033]      FIG. 4  shows an exploded view of a magnet and magnet holder according to the disclosure. 
           [0034]      FIG. 5A  is a plane view of a further embodiment of the disclosure. 
           [0035]      FIG. 5B  is a plane view of yet another embodiment of the disclosure. 
           [0036]      FIG. 6A  discloses a further embodiment of the disclosure in two plane views. 
           [0037]      FIG. 6B  is a cross sectional view of the embodiment of  FIG. 6A . 
           [0038]      FIG. 6C  is a cross sectional view of the housing belonging to the embodiment of  FIG. 6A and 6B . 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    Embodiments of the present disclosure retain a cochlear implant magnet securely positioned in the center of the cochlear implant housing while maintaining a very compact structure. At the same time, the electronics and the coil of the cochlear implant are hermetically isolated. An interface between the magnet assembly and the cochlear housing has been designed to provide excellent alignment of the magnet within the cochlear implant housing. The interface also enables easy and safe removal of the magnet when needed. 
         [0040]      FIGS. 2A-B  illustrate an example of a cochlear implant with a subcutaneous housing  201  which has a compact structure and houses electronics  202  and one or more coils  203  for receiving and transmitting information and energy. Also feedthroughs (not shown) for connecting electrodes to the subcutaneous housing are part of the construction. Such electrodes can stimulate or measure electrophysiological signals in the patient&#39;s body. In other situations, the electrical connections to/from the inside of the housing may also or alternatively connect an electromechanical actuator such as vibrator for bone conduction or for stimulating the middle ear. 
         [0041]    A magnet  205  is installed removably in a central cavity  230  of housing  201 . The central cavity  230  is in the center of the annulus formed by the housing  201 . The magnet  205  creates a magnetic field that holds and centers an external device that includes one or more coils. The external device can thus communicate with the implanted cochlear implant or supply energy to the cochlear implant. 
         [0042]    The subcutaneous housing  201  may include a silicone rim  206  to provide a soft and ergonomic shape that helps preserve surrounding patient tissues when the cochlear implant is surgically implanted. The continuation of the silicone rim  206  forms two flaps  207 . Flaps  207  each include a reinforcing ring  208 . The rings  208  can be made of biocompatible material such as titanium, PEEK or PEKK, in order to allow the implant to be fixed onto the temporal bone of a patient. The implant can be fastened to the skull bone with screws that pass through rings  208 . 
         [0043]    An area between reinforcing rings  208  forms a junction  220 . The junction  220  can house or accommodate electrodes passing to feedthroughs from an external device. 
         [0044]    The main housing  201  is composed of a main body having a U-shaped cross sectional profile, referred to as U-shaped main body  210 . The U-shaped main body  210  forms a cavity which hermetically accommodates electronics  202  and coil  203 . The U-shaped main body  210  can be made of biocompatible ceramic such as zirconia toughened alumina, high purity alumina, or pure zirconia. A stamped titanium cover  211  is attached to the rim of the U-shaped main body  210  by laser welding to form a hermetically sealed cavity. 
         [0045]    Magnet  205  is guided directly by U-shaped main body  210  through a precisely sized diameter of central cavity  230 . The precise sizing of the diameter reduces free movement of the magnet  205  to only a rotation about removal axis  212  or a translation in the direction of the removal axis  212 . No pitching or tilting of magnet  205  relative to housing  201  is possible when the magnet is fully installed in the central cavity  230 . Removal axis  212  passes through the center of the central cavity  230  and is perpendicular to the plane of the top surface of main body  210 . 
         [0046]    The magnet  205  is preferably biocompatible. Thus, the magnet  205  may be constructed as a magnetic core  240  surrounded by a biocompatible housing  245 . The biocompatible housing  245  thus forms the outer surface of the magnet  205  and may be made of titanium. 
         [0047]    As illustrated in  FIG. 2C , the body of magnet  205  is radially symmetrical except for a portion at the top surface  223  of the magnet  205 . The top of the magnet  205  has an outer edge  218  which is radially surpassed by raised ribs  214  and abutments  215 .  FIG. 2C  illustrates an example with three ribs  214  and three abutments  215 . 
         [0048]    Abutments  215  extend radially farther out beyond the edge of the ribs  214 . The abutments  215  prevent the magnet  205  from passing completely through the central cavity  230  of the housing  201 , and in case of shock or impact directly on the removable magnet  205 , energy will be dissipated to the housing  201  and will not impact the patient&#39;s temporal bone by the small surface  216  of the removable magnet  205 , but by the entire surface  217  of the implant housing  212 . 
         [0049]    While abutments  215  are in contact with the rim of the central cavity  230 , the ribs  214  are sized smaller than the abutments  215 , so there is a gap  306  between the edge of ribs  214  and the rim of the central cavity. This gap  306  allows the insertion of a tool  303  to remove the magnet  205  as described below. The ribs  214  have a smooth transition  219  from the edge  218 , facilitating the rotation of tool  303  after it is inserted. 
         [0050]    Magnet  205  includes a silicone ring  213  that is calibrated to withstand a force induced by RMI of up to 3T. The silicone ring  213  is placed in a radial groove  235  in the body of magnet  205 . When the magnet  205  is inserted into central cavity  230 , the silicone ring  213  exerts force on both the magnet  205  and the inner walls of central cavity  230  to hold the magnet  205  securely in place. As shown in  FIG. 2B , the side profile of central cavity  230  has a ledge  236  under which silicone ring  213  is engaged, thus biasing the magnet  205  against removal from the central cavity  230 . 
         [0051]    As shown in  FIG. 3A , magnet  205  can be removed from the housing  302  with removal tool  303 . It may sometimes be necessary to remove the magnet  205 , such as when a very high level of MRI (e.g., above 3T) is needed. 
         [0052]    When the magnet is to be removed, a surgeon can make an incision above the magnet and lift the skin away from the magnet area. A tool  303  can then be inserted through the incision and used to remove the magnet  205 . As shown in detail in  FIG. 3B , the tool  303  has its own magnet  304  placed at the proximal edge of the tool in order to automatically align the tool  303  on the magnet  205 . As seen in  FIG. 3C  the surgeon has to insert the number of blades  305  at the proximal edge of the tool  303  into the gaps  306  defined between the outer edge of the magnet  218  and the rim of the central cavity  230 . This position is seen in the middle part of  FIG. 3C . Then, the tool  303  is turned counter-clockwise enough to lock the blades  305  under the ribs  214  via hooks  310 . This final position is shown in the left hand view of  FIG. 3C . In this position a secure engagement between tool and magnet has been established, and the tool and magnet may be lifted out of cavity  230  without further ado. As the surgeon exerts force on the magnet, the supporting force from the silicone ring  213 , which holds the magnet  205  in the cavity  230 , is overcome and the magnet is removed. The embedded magnet  304  holds the magnet  205  at the proximal edge of the tool  303  even after the magnet  205  is removed. The magnet  205  can be easily removed from the tool by hand if need be, and be dealt with in the usual flow of contaminated elements of the hospital. 
         [0053]    A new sterile magnet  205  may be put in place by hand, without using a tool. It is preferable to rinse and dry the central cavity  230  before installing the new magnet  205 . As the surgeon presses the new magnet  205  into cavity  230 , compression strength of the silicone ring  213  on the new magnet  205  is overcome, and the magnet  205  slides securely into its correct position. 
         [0054]      FIG. 4  discloses an exploded view of the magnet and its enclosure. The enclosure comprises a biocompatible housing  245  shaped as a bucket with an outwardly directed upper rim comprising the outer edge  218 , raised ribs  214  and abutments  215 . A lid  246  is provided and secured to the biocompatible housing  245  in a top recess  442 , and in  FIG. 2D  a weld line  243  is indicated for the fusing of lid  246  and biocompatible housing  245 . Other ways of fusing the lid to the housing could be used such as gluing or brazing. The various raised ribs  214  and abutments  215  are in the disclosed embodiment made as part of the housing  245 , but the skilled person would know, that there are many other options, such as providing these structural details as part of the lid. 
         [0055]      FIGS. 5A and 5B  discloses embodiments with two or four abutments  215  respectively dispersed evenly around the circumference of the magnet  205  and a commensurate number of ribs  214 . 
         [0056]    In  FIG. 6A , B and C a further embodiment is shown wherein the silicone ring  213  is provided as part of the implant, and the magnet  205  simply comprises the groove  235 . When the magnet is lifted out of the implant the silicone ring  213  stays with the implant. This is advantageus from a hygienic point of view, as the intersection between silicone ring and magnet groove will not lend itself as a hiding place for infecting agents during or after autoclaving. 
         [0057]    While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 
       List of Elements 
       [0058]    Number Element
     12  coil     13  magnet     14  silicone part     101  hermetic housing     103  coil     104  fixed magnet     105  ceramic     106  titanium     201  subcutaneous housing     202  electronics     203  coil(s)     204  feedthroughs     205  magnet     206  silicone rim     207  flaps     208  ring     209  axis     210  U-shaped main body     211  stamped titanium cover     212  removal axis     213  silicone ring     214  rib     215  abutment     216  bottom surface of magnet     217  surface of housing     218  outer edge of magnet top     219  transistion     220  junction     223  top surface of magnet     230  central cavity     235  groove     236  ledge     240  magnetic core     242  top recess     243  weldline     245  biocompatible housing     246  lid     303  removal tool     304  magnet in tool     305  blade     306  gap(s)     310  hook     503  magnet     504  silicone molding     507  silicone lips     508  slots