Abstract:
The invention relates to a middle ear prosthesis comprising an artificial ear drum ( 20 ) and a tubular housing which is tightly joined to said ear drum. The housing consists of a coupling element ( 28 ) and a transmitting element ( 22 ). The coupling element ( 28 ) comprises firstly an open end area ( 30 ), configured for resting against the tympanic wall ( 32 ) of an ear, and secondly, inside its inner space, a retaining device ( 34 ) for a first ossicle part ( 26 ) which extends through a small, artificially created opening ( 36 ) in the stapes base-plate ( 38 ). The transmitting element ( 22 ) is connected to the ear drum ( 20 ), on the inner surface of which is attached a second ossicle part ( 24 ), which comes into contact with and is connected to the first ossicle part ( 26 ) when the coupling element ( 28 ) and transmitting element ( 22 ) are put together.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a middle ear prosthesis with a tubular housing. The prosthesis replaces eardrum (tympanic membrane) and ossicles of the middle ear which have been destroyed by otitis or similar. 
     2. Description of the Prior Art 
     It is presently known to repair the sound receiving and conducting mechanismus of the middle ear by surgical implantation of various types of prosthesis. Such repair involves total reconstruction of all three ossicles and the ear drum. 
     Such a middle ear prosthesis is known out of DE 4 407 847 A1. The tubular housing of this prosthesis is not only closed at its outwards showing end by an outer membrane replacing the eardrum. It is also provided at its inner end with an inner membrane. Said inner membrane is joined to the outer membrane by a transmission link that is located inside and that prestresses inwards outer and inner membrane. The surface of the outer membrane is bigger than the surface of the inner membrane. Sound transmission from the inner membrane to the stapes base plate occurs by a small quantity of the patient&#39;s own fat. This fat required for sound transmission is located outside the prosthesis between the inner membrane and the stapes base plate. 
     A disadvantage of this known middle ear prosthesis is that the achievable sound pressure at the stapes base plate is not high enough for normal hearing, since the transformation ratio of the two membranes is reduced. Furtheron the transmission path of the sound between the inner membrane and stapes base plate is subject to unsteadiness since the smallest inclusion of air in the fat or its dwindling and the thus occurring smallest air gap are already strongly influencing the transmission of sound. 
     EP 460 354 B1 discloses a middle ear prosthesis that does without its own housing. The artificial eardrum is tentered in an outer retaining ring inserted in a recess made especially for said ring in the petrous bone. The eardrum has a hole in its centre into which a thickened front area of an ossicle-substitute may be fitted. Thus, the ossicle-substitute may in a first place be arranged in the space behind the artificial eardrum. Then, the artificial eardrum is inserted, whereas the front end of the ossicle-substitute snaps into the hole of the eardrum. 
     Further middle ear prostheses are known out of EP 281 047 B1, DE 2 905 183 C3, DE 2 937 842 C3 and EP 203 785 B1. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the mentioned problems with the middle ear prosthesis by providing that the sound pressure prevailing in the inner ear is sufficient and that the sound transmission to the inner ear is guaranteed to be always secure and durable. 
     The middle ear prosthesis according to the invention replaces the function of the sound transmitting apparatus of a natural middle ear as completely as possible. It is hereby not depending on the function of the natural eustachian tube and/or the mucosa of the middle ear cavities. 
     The middle ear prosthesis according to the invention is used in the attendance of patients with chronic otitis media that durably weakens or hinders a normal sound transmission. Other afflictions with said same consequence are for example mucosal suppuration in the middle ear, suppuration of the bone in the middle ear (=suppuration of a cholesteatoma), chronic perturbation in the aeration of the auditory tube, malformations of the middle ear, permanent destructions of the sound conducting apparatus by trauma and tumours, etc. The middle ear prosthesis is depending neither on a mucosa lining nor on an aeration of the auditory tube. It consists of a housing divided for example in two parts that may at least be closed so as to be germ-tight. The inner space of the housing is thus safe against germs trying to penetrate from the outside. 
     The housing is provided with a holding device that temporarily fastens the ossicle part called hereinafter first ossicle part. Said holding device is removed, cut apart or otherwise discharged later, before the operation comes to an end. It may also be kept if it is flexible enough. 
     The first ossicle part is inserted through an artificial opening in the stapes base plate and directly stimulates the inner ear or it is placed onto this base plate. The direct sound transmission to the inner ear is thus assured. The loss of coupling fat or the like can no more be detrimental to said sound transmission. 
     The first ossicle part is moved by the artificial ear drum and/or by an electric actuation, particularly an electrodynamic or piezoelectric actuation. Such an electric actuation gets its tension from an amplifier, for example from the amplifier of a hearing aid. 
     During the operation, the inner space of the housing may be reached through the window. It allows the necessary manipulations inside the housing. Particularly the holding device may be reached through the window. Said window is closed by the cover part so as to be germ-tight. 
     The window may have different versions. The window may for example be provided between two parts of a housing consisting of a transmission part and a coupling part, whereas recesses or indentations on the edge side are provided in the overlapping area of the two parts. Said recesses are forming the window when positioned in a certain rotary position relative to one another, whereas, in another rotary position, they are closing completely. Housings consisting of three and more parts are also possible, the third and possibly further parts being allocated for constituting or locking a window area, for example by an axial slidable cylinder. Annular, cylindrical parts that are rotatable relative to the coupling part and/or transmission part and that have a window just as said part are also provided. The window may be either released or completely locked by rotation. 
     During the operative insertion of the middle ear prosthesis, the coupling part is inserted first and is attached in the best possible way to the wall of the eardrum around the oval window. It has proved to be particularly preferential to imitate as accurately as possible the course of the individual relief of the medial eardrum wall of the patient wearing the middle ear prosthesis when designing the free end area of the coupling part. A good adaptation to the eardrum wall is thus achieved which makes it possible to obtain, using appropriate connecting material, a proper closing and a secure fastening of the coupling part on the eardrum wall. 
     When the coupling part is inserted, in case of an opening in the stapes base plate, said opening is either already provided or it is arranged only then. It is preferably made by means of a laser. It is just big enough for the first ossicle part to fit through it. The first ossicle part is preferably a thin wire made of titanium or gold. The first ossicle part is fixed on the holding device or has already been fixed to it. The fixation is made in such a way that the first ossicle part is projecting into the inner ear to a desired extent. The fixation guarantees that the projection will neither fall short of nor exceed said extent. 
     It has proven to be particularly advantageous for the housing of the middle ear prosthesis according to the invention to seal the surrounding tissue in a germ-tight, preferably hermetic way. Thus, the inner space of the housing is securely protected against the penetration of germs. 
     The location and size of the housing of the middle ear prosthesis have well enough been determined by considerable measurements done on petrous bone preparations. Typically, an average maximal diameter of approximately 11 mm and a maximum length of approximately 20 mm have been found. 
     The housing preferably consists of the coupling part and of a transmission part, both being provided with connecting means for their junction to one another and to the housing. The transmission part is preferably provided with a second ossicle part. During the operational insertion, the connection between the two ossicle parts may be observed and preferably executed through the window. 
     For the implantation of the middle ear prosthesis, it has proven to be of advantage to provide the housing with connecting means for the mechanical fixation of the housing on the petrous bone of the wearer. Although it is possible and even desired to fill out the space of the middle ear around the prosthesis in order for the prosthesis to have a good seat, the mechanical anchorage in the bone guarantees a durable secure fixation during the operation and also later, in case of impacts. 
     When the middle ear prosthesis is provided with an eardrum, it has proven to be preferable to arrange the eardrum in an angle to the axis of the housing. The bigger said angle has been chosen, the bigger the surface of the eardrum. Angles of between 40° and 80° to the axis of the transmission part, and particularly an angle of approximately 53° have proven to be advantageous. The preferred artificial eardrum has thus got an out-of-round shape, particularly an elliptic one. Resonances are thus avoided. The big surface for sound pick-up is particularly advantageous. Surfaces of approximately 100 square millimeters are typically obtained. 
     For the second ossicle part, commercial parts may be used, for example the ossicle surrogate offered for sale by the enterprise Richards GmbH under the trade name TILT-TORP-PORP. It has a drilled shank into which the first ossicle part may be inserted. On its other end it has a ball-and-socket joint that allows compensating movements. Thus, a largely cylindrical, essentially one-dimensional movement may be transmitted to the inner ear liquid. A new prosthesis part may also be developed as second ossicle part that meets the requirements of this mechanical principle. 
     Since the middle ear prosthesis according to the invention has, when inserted, an essentially hermetically sealed inner space, the middle ear spaces are not aerated as they are in nature by the eustachian tube. When the actuation is purely electrical, pressure compensation is not necessary. If the prosthesis is provided with an eardrum, an artificial pressure compensation device is indispensable. It consists of an outer part that is accessible from the outside and that is hidden for example behind the ear in a way similar to the bone-anchored hearing aids working on body sound, and of an inner part that is located for example in the mastoid. This inner part has, in a first embodiment, a fine strainer, particularly a strainer blocking any kind of microbes and viruses. The material used for said strainer particularly consists in hollow fibres. Alternatively, the inner part may also have a pressure compensating membrane. Hereby, a flexible membrane is tentered in an own housing in a completely tight way, whereas it constitutes an absolute barrier between an outer chamber connected to the outer world and an inner chamber connected to the inner space of the prosthesis. Outer part, inner part and middle ear prosthesis are linked together by means of thin tubes, particularly silicone tubes, in a tight and durable way. 
     In order to take hold of the individual relief of the eardrum wall of a wearer and consequently to be able to provide the free end area of the coupling part with the desired shape or profile, several possibilities are available. Said shape may be obtained by a high-resolution spiral scanner and be directly transmitted via an intermediate stage of a processing machine for the free end area. On the other hand, the relief may also be scanned by means of direct measurements with rays, whereas the processing machine may be accordingly actuated directly or indirectly. The shape may also be scanned mechanically, a proper scanning apparatus having been developed to that purpose. The data obtained with this scanning apparatus may be used for the actuation of a processing machine. 
     Further advantages and characteristics of the invention will become clear in the remaining claims and in the following description of embodiments that are only examples and are not limiting the scope of the invention. Said embodiments are explained in more detail with the aid of the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG.  1 : shows a sectional drawing of a middle ear prosthesis with an added pressure compensating device, 
     FIG.  2 : shows an exploded view of a transmission part with a view on and through an operational window, 
     FIG.  3 : shows a representation of a coupling part according to the representation according to FIG. 2, 
     FIG.  4 : shows a top view on a cover plate, 
     FIG.  5 : is a sectional drawing of a housing in a view similar to the one in FIG. 1, but now with an additional electrodynamic actuation and with an external amplifier connected via a transmission link and 
     FIG.  6 : shows a representation similar to FIG. 5, but without an amplifier and now also without an eardrum, the actuation being exclusively piezoelectric. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The middle ear prosthesis of a first embodiment shown in FIGS. 1 to  4  has an artificial eardrum  20  that has an essentially oval blank. Its surface is bigger than the surface of a normal human eardrum (tympanic membrane), for example 1.5 times bigger. It is cut in a material that is biologically appropriate for the use as a prosthesis, more particularly in the material Millicell HA of the enterprise Millipore GmbH, in GORE-TEX 0.1 mm of the enterprise W. L. Gore &amp; Assoc. GmbH or in flexible silicone. Millicell, Millipore, GORE-TEX and Gore are protected trade marks. In practical use, the eardrum  20  is epithelized. 
     The eardrum  20  is tightly connected with a housing that is, in the embodiments shown in the FIGS. 1 to  4  and  5 , divided into two parts. The eardrum  20  is connected to a transmission part  22 . The latter has an essentially cylindrical area shown in the lower part of FIG.  2  and an area that is widening, starting from said cylindrical area and essentially running on an envelope of cone. The diameter of the cylindrical area is of approximately 8 mm. The widening area has corresponding measurements of approximately 11 mm. As FIG. 1 particularly shows, the eardrum  20  is located on one level, it runs in an angle of 35° to a longitudinal axis  23  of the transmission part  22 . Thanks to the inclination of the eardrum  20 , said eardrum  20  has a bigger surface than the natural eardrum. 
     On the inner side of the eardrum  20 , preferably on the centre of the surface, a second ossicle part  24  is durably fastened. In the embodiment of FIGS. 1 to  4  a commercial ossicle surrogate of the enterprise Richards GmbH is used. In the vicinity of the eardrum  20  it has a ball-and-socket joint. Underneath said ball-and-socket joint a hollow shank receives a first ossicle part  26  that still has to be discussed. The second ossicle part  24  runs underneath the ball-and-socket joint centrically to the centre line of the transmission part  22 . 
     The housing also has a coupling part  28 . It is as a whole a bit smaller than the transmission part  22  and is designed together with said transmission part  22  in such a way that both parts may be connected to one another in an easy, tight and durable way. This may particularly be achieved by insertion in longitudinal direction and by glueing. The coupling part  28  is essentially cylindrical. Its diameter is of approximately 6 mm, too. It has a free end area  30  that has a shape imitating as exactly as possible the individual relief of the eardrum wall of a wearer of the middle ear prosthesis. The thus resulting, individual shape may particularly be seen in FIG.  3 . As already explained above, several methods may be used to acquire or scan the shape of the individual relief of the eardrum wall. Reference is made to the patent application “Device for the mechanical scanning and acquisition of the eardrum shape of a middle ear” of the same applicant and of the same application date. The content disclosed in this application is made part of the content disclosed in the present application. 
     The free end area  30  is accordingly designed in such a way that it sits close to the eardrum  32 , as may be seen in FIG. 1. A tight-sealed closure may thus be achieved, liquid fixing and sealing agents may be used to connect the free end area  30  and the eardrum  32 . 
     In the coupling part  28 , a holding device  34  is provided for the first ossicle part  26 . Said ossicle part  26  is designed as a thin golden wire that closely fits through a very small, artificially provided opening  36  in a stapes base plate  38 , thus projecting with its lower, free end area into the inner ear  40 . In the embodiment shown, the holding device  34  is an essentially diagonally running wire on which the first ossicle part  26  is fastened or may be fastened. During the implantation of the middle ear prosthesis, the holding device  34  is cut through so that the first ossicle part  26 , which is connected to the second ossicle part  24 , may move freely back and forth through said holding device. 
     In all the three embodiments shown of the middle ear prosthesis, an access to the inner space is necessary for the connection of the two ossicle parts  24 ,  26  as well as for the cutting through of the holding device  34 . Other constructions with no such access are possible. For said access, a window  42  is provided in the transmission part  22 . This window  42  may be closed by a cover plate  44  as shown in FIG.  4 . Appropriate mechanical holding means are provided in order to ensure an accurate and tight fastening of the cover plate  44  on the transmission part  22  and on the coupling part  28 . In the embodiment shown, mandrels  46  are provided to fasten the cover plate  44 , the coupling part  28  is provided with a groove  48  formed by a projecting part and meant to receive the cover plate  44 . As shown in FIG. 3, the coupling part  28  too preferably has a recess  50  in its upper area, said recess being also designated as the lower window bay. 
     As shown in FIG. 4, the cover plate  44  has a connection  52 . Said connection is assigned to a tube  54 , both may be seen in FIG.  1 . The tube  54  is leading to an inner part  56  of a pressure equalizing device. Said inner part  56  is designed as a boxlike housing. It has two chambers, namely an outer chamber  58  and an inner chamber  60 . Both are hermetically separated from one another by a very flexible membrane  62 . In another embodiment, they are separated from one another by a fine filter sealed against bacteria and microbes but permeable to air. The fine filters that may be used here are particularly hollow fibre filters. 
     The outer chamber  58  is connected to an outer part  66  via another tube  64 . It is anchored in a bone  76  and is in parts accessible from the outside, see skin  78 . The construction used here is quite similar to the one used with so-called bone conducting hearing aids. The outer part  66  has a recess  68  into which a strainer  70  is inserted. Said strainer is preferably exchangeable. The strainer  70  hinders water, coarse dirt and the like to penetrate the tube  64 . The barrier against germs and the like is assured by either the membrane  62  or by the fine filter that replaces said membrane. Reference is made to the application of the same applicant with same application date “Pressure-equalizing device as a prosthetic replacement for a eustachian tube”. The content disclosed in this application is also part of the content disclosed in the present invention, 
     For the parts  22 ,  26 ,  28  and  44  as well as for  56 ,  66 , titanium is the material that is best suitable. According to FIG. 3, a strap-joint  72  fastened on the coupling part allows the fastening on the petrous bone. A screw  74  is provided to that purpose. 
     In the second embodiment represented in FIG. 5, a housing with an artificial eardrum  20  is used, said housing corresponding to the housing of the first embodiment. The modification compared to the first embodiment is that a ferromagnetic core  82 , more particularly a core made of a ferrite material, is provided in the tube-like guidance of the second ossicle part  24 . Around the area of the second ossicle part  24  outside the core  82 , a coil  84  that is connected to the housing is mounted. The second ossicle part  24  is made of a synthetic material or of another, non-conductive material. Coil  84  and core  82  are constituting together an electrodynamic actuation. The coil  84  is connected with a secondary coil  90  of a transformer via a supply tube  86  and possibly with the help of the connection in series of an implanted amplifier  88 . The secondary coil  90  is located underneath the skin  78 , whereas the corresponding primary coil  92  is located outside the skin  78 . The primary coil  92  is connected to the output of a hearing aid  94 . 
     In practical operation, a microphone inserted in or assigned to the hearing aid  94  receives sound information. This information is amplified in the hearing aid  94  and, if necessary, processed. The amplified signals are brought to the primary coil  92 . From there, they are transmitted to the secondary coil  90  and thus to the coil  84 . 
     In order to improve the power transfer of the transformer  90 ,  92 , converting the sound information in the hearing aid  94  into a high frequency band of for example the frequency of one megahertz is advisable. This occurs in a way similar to the carrier frequency technology used in telephone systems or accordingly. 
     As in the first embodiment, the movement of the eardrum  20  is still transmitted onto the two ossicle parts  24 ,  26 . That means that two movement actuations are active. On one hand, the ossicle parts  24 ,  26  are moved by the eardrum  20  and thus by the sound arriving directly to the eardrum  20 , on the other hand, they are moved by the electrodynamic actuation described above. The electrodynamic actuation may only assist the movement in certain frequency ranges, for example only in the high frequency range of the audible range. The electrodynamic actuation may thus preferably compensate a defective hearing that only concerns certain frequency ranges. The electrodynamic actuation may, however, also be active in the whole frequency range of the audible range. 
     In the third embodiment according to FIG. 6, several decisive amendments have been made. The housing is now in one piece, it consists of the coupling part  28  in which the window  42  is provided, said window  42  being covered by the cover plate  44 . Instead of an eardrum  20 , the housing is tightly closed at its end area opposite the free end area  30 . The housing thus has essentially a cupular shape. The closure in the end area may serve as window instead of the represented window  42 . 
     There is only one first ossicle part  26  provided, a second ossicle part has been omitted. The first ossicle part is connected to the inner wall of the coupling part  28  via a piezoelectric element  96  that is running across. A holding device  98  is provided. The piezoelectric element  96  has got the shape of a longish plate designed here as a double plate. When electrically stimulated, it executes movements in the longitudinal direction of the first ossicle part  26 . It is connected to the secondary coil  90  of a transformer via the supply tube  86 . The transmission and connection to a hearing aid  94  occur in the same way as in the example of an embodiment illustrated in FIG.  5 . 
     As opposed to the example of an embodiment illustrated in FIG. 5, the electric actuation now assumes the complete sound stimulation of the inner ear, since there is no eardrum provided. Selective hearing problems of the wearer of the ear prosthesis may be compensated by making the appropriate arrangements in the hearing aid  94 .