Abstract:
A middle ear ossicle prosthesis in which the component for ossicular attachment comprises a surface bearing a plurality of discrete projections facing the ossicle to which it is attached which minimize total contact between the prosthesis and the ossicle. The prosthesis may comprise a loop forming a partial circle for encircling an ossicle, a piston for transmitting vibrations from the loop to the inner ear, and a rod solidly connecting the loop to the piston. The loop may have an upwardly turned end to facilitate placement of the loop over the ossicle. The projections may be provided in one row, two rows, or may be otherwise arrayed, and may be dissimilar from one another in configuration and dimensions.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority benefit of Application No. 61/529,590, filed Aug. 31, 2011. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    Numerous prior designs of ossicular prostheses have sought to establish functional continuity of the ossicular chain after damage to some or all of the ossicles secondary to disease or congenital anomaly. Frequently, when the stapes is damaged or diseased, re-establishment of a connection to the inner ear via stapedectomy or stapedotomy is also required. Prostheses most often are designed to attach to remaining healthy ossicles and replace the function of the ossicle(s) which are missing or diseased. 
         [0003]    In the case of the stapes, dysfunction often occurs as a result of a disease process called otosclerosis in which the footplate of the stapes becomes fused to the surrounding bone and no longer effectively transmits ossicular motion to the fluids of the inner ear. Most stapes prostheses over the last several decades have been constructed of either a circumferential or nearly circumferential wire loop or a broader ribbon-type (flat wire) loop which directly attaches to the long process of the incus. More recently, clip-type prostheses have been developed which are comprised of a complex-shape broad ribbon in which a more limited surface area of the incus is placed in contact with the flattened clip. In either case, the component for incus attachment is joined to a piston which fits into a hole (fenestra) in the stapes footplate created by the surgeon so that the piston can translate ossicular movement to the fluids of the inner ear. 
         [0004]    Ossicular prostheses which have been designed to replace the function of the stapes and attach to the incus have frequently caused necrosis/erosion (loss of bone tissue) in the area of the incus to which they are attached, as well as the bone more distal to the prosthesis attachment. This bone loss in the area of the prosthesis attachment can cause loosening of the prosthesis and resultant hearing loss because of piston migration out of the hole in the stapes footplate and/or de-coupling of the motion from the incus to the prosthesis. Ideally, the ossicular prosthesis which is designed to replace the function of the stapes will attach firmly and permanently to the long process of the incus without ever loosening or migrating away from its position of placement at the time of surgery. This is also true of prostheses which attach to the malleus and replace the function of the other ossicles. 
         [0005]    Bone/tissue loss in the area of the attachment of the stapes prosthesis to the incus is thought to be due to impaired blood supply to the long process of the incus after surgery. Prior to surgery, blood is supplied to the area of the long process from both the body of the incus distally to the long process, as well as from the opposite direction across the joint where the incus is joined to the stapes. Since the attachment between the stapes and incus is cut during surgery, the only blood supply to the long process of the incus after surgery flows distally to the long process from the body of the incus. Accordingly, blood flow to supply the area of the incus both at and distal to the prosthesis attachment ideally should not be restricted by the prosthesis itself. It is widely believed that a prosthesis which exerts sufficient mechanical pressure on blood vessels/mucosa near the surface of the incus can cause a restriction of blood flow sufficient to cause incus necrosis and subsequent failure of the prosthesis. 
         [0006]    Since the blood supply in the area of the prosthesis attachment is tenuous after surgery and most prostheses have areas of very broad or circumferential contact points with the long process, relatively large areas where blood vessels or delicate mucosa are located can be compressed by the prosthesis and cause death of the underlying or distal tissues. Efforts to reduce both the amount and the surface area of mechanical pressure exerted on the incus have resulted in new prostheses with broader and/or softer ribbons to contact the incus; new methods of crimping to achieve optimal pressure on the incus (tight enough to ensure good coupling of incus translation to that of the piston in the inner ear, but loose enough to reduce the chance of pressure necrosis); or a change in the shape of the ribbon or wire so that only opposing sides of the incus are grasped firmly. Nevertheless, all efforts to date share the common characteristic that at least some of the wire or ribbon is broadly in contact with the incus and consequently have the potential to cause pressure necrosis to the underlying mucosa and loss of bone in these areas of broad contact. 
         [0007]    In the case of prostheses which attach to the malleus to replace the function of the incus, stapes, or both, the prosthesis most often is placed in contact with the medial portion of the malleus. Contact is not usually made with the lateral aspect of the malleus because its lateral surface is integrated with the ear drum. The prosthesis component which contacts the malleus usually comprises a flat disc with a shallow depression in which the medial malleus lies. Commonly, the prosthesis “falls over” after surgery with a loss of contact with the malleus, with resultant hearing loss. Continuing malleus-prosthesis contact after surgery is initially dependent solely on the medial pressure the malleus exerts on the prosthesis. 
       SUMMARY  
       [0008]    The present invention relates to the concept that if a relatively large patch or area of contact between an ossicular prosthesis and an ossicle can be avoided, then disturbance to the underlying mucosa and blood vessels can be minimized with a reduction in the chance for necrosis. More particularly, broad contact may be minimized by a design in which discrete projections from the prosthesis&#39; ossicle interface surface space that surface away from the bone. Moreover, a very secure attachment between the ossicle and the prosthesis can be anticipated, due to the resistance to motion engendered by the partial embedment of these projections in the ossicle. A more secure attachment can be anticipated to reduce the chance of prosthesis translocation following surgery, which can cause surgical failure even in the absence of ossicular necrosis. 
         [0009]    It is an object of the invention to provide novel means of attachment for an ossicular prosthesis to an ossicle using a plurality of projections extending from a wire, loop, ribbon, clip, disc, or other prosthesis surface form or configuration which would serve as contact points between the ossicle to which they are attached and the prosthesis from which they arise. 
         [0010]    The projections can be of variable number, shape, length and arrangement according to the intended use in a particular patient&#39;s anatomy and disease process. 
         [0011]    The projections are inherently designed to minimize the surface area of prosthesis to ossicle contact, thereby minimizing the potentially damaging effect that broader contact may have, as described in “Background of the Invention.” They also have the advantage of attaching firmly to the ossicle via embedment of said projections which is anticipated to reduce the risk of surgical failure further by reducing the risk the prosthesis will move away from its position at the time of surgical implantation. 
         [0012]    In one embodiment, the projections are envisioned as having sharp ends which could enhance firm embedment in the ossicular bone to which they are in contact, creating a secure attachment without a significant amount of total contact between the prosthesis and the ossicle. 
         [0013]    In accordance with one embodiment of the invention, the prosthesis could be comprised of metal such as titanium with projections as described consisting of a different substance, such as hydroxyapatite which could fully integrate with underlying bone. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The drawings, when considered in connection with the following description, are presented for the purpose of facilitating an understanding of the subject matter sought to be protected. 
           [0015]      FIG. 1  is a side view, not drawn to scale, of a prosthesis according to at least one aspect of the invention. 
           [0016]      FIG. 2  is a perspective view of a prosthesis according to at least one other aspect of the invention. 
           [0017]      FIG. 3  is a cross sectional detail side view of a prosthesis according to a further aspect of the invention, and is drawn to enlarged scale. 
           [0018]      FIG. 4  is a cross sectional side view of a detail of a prosthesis according to still another aspect of the invention, and is drawn to enlarged scale. 
           [0019]      FIG. 5  is a side view, not drawn to scale, of a second embodiment of a prosthesis according to the present disclosure. 
           [0020]      FIG. 6  is a side view, not drawn to scale, of a third embodiment of a prosthesis according to the present disclosure. 
           [0021]      FIG. 7  is a side view, not drawn to scale, of a fourth embodiment of a prosthesis according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]      FIG. 1  shows a middle ear prosthesis such as a stapes prosthesis  5  comprising a loop  3  which is formed as a partial circle of at least one hundred eighty degrees, or as shown, three hundred to three hundred thirty degrees, for encircling an ossicle such as an incus  1  (seen in cross section in  FIG. 1 ). It would of course be possible to arrange the loop  3  as a full circle, by adding an element which closes the gap which exists when the loop  3  forms a partial circle as depicted and a suitable fastener for retaining the added element to the loop  3  (this option is not shown). The loop  3  bears a linear array of projections or spikes  2 , which may for example be arrayed as a row of spikes  2 , which project inwardly from the inner surface  6  of the loop  3 , and which make contact with the underlying incus  1 . The terms projection and spike, both in the singular and in the plural, will be used interchangeably herein. Inwardly signifies towards the center of the circle which would exist if the loop described a full circle. The surface  6  may be flat, curved, or complex. The loop  3  is attached by a rod  8  to a piston  4  which sits in a fenestra (not shown) and communicates with the inner ear so as to pass vibrations in a manner approximating that which would occur should all of the ossicles be functioning normally. It will be seen that only the points  7  of the spikes  2  make contact with the incus  1 . This limits the patch of contact between the prosthesis  5  and the incus  1  which would otherwise broadly occur with the inner surface  6 . The piston  4  is coupled to and terminates the rod  8 . 
         [0023]    The loop  3  may take various forms, such as a wire, ribbon, loop, or clip, disc, or other configurations. 
         [0024]    The loop  3  may comprise an upturned end  9  located at that end of the loop  3  which is opposite the rod  8 . The upturned end  9  may form an angle of greater than  90  degrees (not shown), which would enable the jaws of a clamp to both distract and compress the loop during placement or removal of the loop on an ossicle. The loop  3 , the piston  4 , and the rod  8  may be formed from a biocompatible material such as titanium or an alloy thereof. The spikes  2  may be formed from a material which simulates bone tissue, such as hydroxyapatite. Hydroxyapatite is desirable as it can fuse readily to natural bone tissue. 
         [0025]      FIG. 2  is a perspective view of a stapes prosthesis  15  according to at least one other aspect of the invention. The ossicle to which the stapes prosthesis  15  is engaged is omitted in  FIG. 2  for clarity of the view. In the stapes prosthesis  15 , a loop  13  which generally corresponds in function and structure to the loop  3  of  FIG. 1  is sufficiently broad so as to bear two rows of spikes  12 . The spikes  12  may be similar in function and structure to the spikes  2  of  FIG. 1 . Provision of two rows of spikes  12  increases the area of the ossicle such as the incus  1  of  FIG. 1  which serves as a support surface for the stapes prosthesis  15 , thereby increasing stability of contact over the single row of spikes  2  seen in  FIG. 1 . Other than the spikes  12 , the stapes prosthesis  15  may be similar in structure and function to the stapes prosthesis  5  of  FIG. 1 , such as by including a piston  14  and a rod  18 , which may be the structural and functional equivalents of the piston  4  and the rod  8  of  FIG. 1 . 
         [0026]    As depicted in  FIG. 2 , the rows of spikes  12  are staggered in that when viewed from the end as illustrated in  FIG. 1 , all of the spikes  12  would be seen because those spikes  12  farther from the observer may be located between adjacent spikes  12  of the row relatively closer to the observer. However, the spikes  12  may be disposed abreast of one another, or alternatively stated, not staggered if desired. 
         [0027]      FIG. 3  shows further features of the invention. These features will be described in terms of the stapes prosthesis  5  of  FIG. 1 , but will be understood to apply to any prosthesis according to the present invention. In one feature, a discrete projection  2 A from the loop  3  may differ in length (called out by the reference numeral L 1 ) and shape from the length (called out by the reference numeral L 2 ) and shape of another spike  2 B. The shape of the spike  2 A may be somewhat bullet shaped, whereas the shape of the spike  2 B may be substantially triangular. Of course, other shapes and dimensions may be substituted for those explicitly shown and described herein. 
         [0028]      FIG. 4  shows still another feature of the invention, and again, will be described in terms of the stapes prosthesis  5  of  FIG. 1 , but will be understood to apply to any prosthesis according to the present invention. A transition substance  10  may be disposed between the loop  3  and the spikes, such as a spike  2 C. This transition substance  10  may be a substance other than the constituent substance of the loop and the constituent substance of the spikes. For example, the transition substance  10  may be a polymeric material including a shape memory polymeric material or a metal including shape memory metal. Shape memory materials are those which assume their original configuration after forces which deform the object made from shape memory materials are removed. Heat or other influences may be necessary to return a shape memory material object to its original configuration. Nitinol is an example of a shape memory metal which may be employed. Should assembly of the stapes prosthesis  5  deform the spikes  2 , upon disassembly and with heat or other necessary influences supplied, the spikes  2  will reassume their original configuration. For example, should assembly cause the spikes  2  to bend from an original perpendicular orientation relative to the loop  3 , if fabricated from shape memory materials they will reassume the original perpendicular orientation when disassembled and heated if necessary to invoke the shape memory feature. 
         [0029]    While the discrete projections such as the spikes  2  have been described and shown as being tapered, there is no requirement that they be tapered in order to accomplish their mission of causing the loop of the prosthesis such as the loop  3  to be spaced apart from the bone such as the incus  1 . The projections may be cylindrical or flattened for example, with or without points such as the points  7 . 
         [0030]    A prosthesis utilizing the attachment element shown in the stapes prosthesis  5  may be used to secure a foreign body such as a magnet to an ossicle. The foreign body may perform a role of assisting in hearing, as is known in the art. The foreign body may comprise a magnet which is subjected to electrical or magnetic pulses so as to vibrate. 
         [0031]      FIG. 5  shows an ossicular prosthesis  20  having an enlarged head  22  which may be attached by a rod  24  to a piston  26 . The piston  26  may sit in a fenestra (not shown) and communicate with the inner ear so as to pass vibrations in a manner approximating that which would occur should all of the ossicles be undamaged. Alternatively, the rod may connect to another attachment element for fixation to another ossicle. The enlarged head  22  may generally assume the configuration of a disc having a first principal face  28  bearing projections  30  which may be the structural and functional equivalents of the projections or spikes  2  and  12  of  FIGS. 1 and 2 , respectively. An opposed principal face  32  is that from which the rod  24  projects. The rod serves as a vibration transmission element. The enlarged head  22  may have formed therein a recess  34  which is dimensioned and configured to seat an ossicle of the middle ear and which comprises a surface  36  from which the projections  30  project. The surface  36  may be curved and concave as shown. 
         [0032]    Several variations of the enlarged head are possible. One variation is shown in  FIG. 6 , which shows an ossicular prosthesis  40  having an enlarged head  42  which may be attached by a rod  44  to a piston  46 . The enlarged head  42  may bear a recess  48  which may be centered on the enlarged head  42  in at least one view as seen, and which, apart from its location relative to the enlarged head  42  may be the structural and functional equivalent of the recess  34  of the prosthesis  20 . The recess  48  may bear projections  50  which may be the structural and functional equivalents of the projections  30  of the ossicular prosthesis  20 . 
         [0033]    A further variation is shown in  FIG. 7 , which depicts an ossicular prosthesis  60  having an enlarged head  62  which may be attached by a rod  64  to a piston  66  or an attachment element for another ossicle (not shown). Unlike the prostheses  20  and  40 , the prosthesis  60  does not have a recess. Rather, projections  68  are fixed directly to a first principal face  70 , with the rod  64  being fixed to an opposed second face  72 . The projections  68  may be arrayed as a patch or linear array located off center on the enlarged head  62  as shown, or if desired, may be centered on the enlarged head or may cover the entire enlarged head (these options are not shown). 
         [0034]    It will be recognized that as employed herein, the term disc is intended only as a semantic convenience and should not be literally construed. The significance of a disc is that a disc presents two opposed principal or large faces among other surfaces, one which may support projections such as the projections  2 ,  12 ,  30 ,  50 , and  68  and optionally, a recess such as the recesses  34  and  48 , and the other of which supports or is coupled to the rod such as the rods  24 ,  44 , and  64 . 
         [0035]    Regardless of the precise nature of a middle ear prosthesis according to the present invention, it will be understood to comprise an ossicular attachment element which is dimensioned and configured to engage an ossicle of the inner ear, such as the loop  3  or  13  or any of the enlarged heads  22 ,  42 , and  62 , a plurality of projections which project from the ossicular attachment element in a direction facing the ossicle being engaged, such as the projections  2 ,  12 ,  30 ,  50 , and  68 , and a vibration transmission element which is connected to the ossicular attachment element and dimensioned and configured to pass vibrations conducted from the projections to another ossicle or directly to the inner ear, such as any of the rods  8 ,  18 ,  24 ,  44 , and  64 . The projections such as the projections  2 ,  12 ,  30 ,  50 , and  68  collectively define a discontinuous surface of dimensions and configuration to contact and engage the ossicle of the middle ear in a manner capable of supporting the middle ear prosthesis in operable position to transmit vibrations and maintain firm contact with the ossicle, while reducing the patch of contact between the prosthesis and the ossicle from that which would be present in the absence of the projections such as the projections  2 ,  12 ,  30 ,  50 , and  68 . 
         [0036]    The vibration transmission element, which is in the above description provided by the rods  8 ,  18 ,  24 ,  44 , and  64 , may be devoid of a piston such as the pistons  4 ,  14 ,  26 ,  46 , and  66 , should the end of the rods be sufficient in dimensions and configuration to fulfill the function provided by the pistons. For example, rods may be tapered along their length and terminate in an end of dimensions greater than that at the enlarged head such as the loops  3  and  13 , or the enlarged heads  22 ,  42 , and  62 . 
         [0037]    It will be recognized by those of skill in the art that although the figures illustrate a loop stapes prosthesis and a principal/opposed principal face design which is most often used to attach to the malleus, other prostheses which attach to any of the ossicles may utilize the novel principles. 
         [0038]    The invention may be thought of as the entire prosthesis, such as the stapes prostheses  5  and  15  or the prostheses  20 ,  40 , and  60 , or alternatively, as a substantial element of such a prosthesis. For example, the invention may be regarded as that portion of the stapes prosthesis  5  including the loop  3  and spikes  2 , but may possibly not include the piston  4  or even the rod  8 . If realized as a partial prosthesis, the invention may include a connector (not shown) enabling ready attachment of the rod  8 , piston  4 , or other members furthering the function of the inventive prosthesis. 
         [0039]    While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto. It is intended that the invention will be as broad in scope as the art will allow and that the application will be read likewise. Other embodiments for prostheses utilizing the attachment design described can be utilized in situations other than those involving attachment of a stapes prosthesis to the incus, or of the malleus to the stapes or stapes footplate. It can therefore be appreciated by those skilled in the art that other situations requiring secure attachment of a prosthesis to an ossicle can utilize the invention as claimed.