Abstract:
An adjustable length prosthesis is used for ossicular replacement or reconstruction. The prosthesis uses a pair of bioactive heads connected by a shaft. The shaft is bendable to accommodate angulation for better anatomical fit. The shaft is flexibly received in the head and trimmable with a scissors or scalpel to simplify length adjustment and prevent chipping and breakage of the bioactive portion. The prosthesis can be used as a total or a partial prosthesis and need not be disassembled and reassembled during the trimming process. The prosthesis can be stabilized on the footplate with a sharpened shaft extension or wire core.

Description:
FIELD OF THE INVENTION 
     This invention relates to an ossicular prosthesis used for replacement and reconstruction and, more particularly, to an adjustable length ossicular prosthesis. 
     BACKGROUND OF THE INVENTION 
     Due to disease, trauma, or congenital malformation, the ossicles of the middle ear are sometime damaged. If this damage results in a discontinuity of bone between the tympanic membrane and the oval window, no sound conducts and hearing loss results. Some or all of these ossicles can be replaced with a small prosthesis. The material of choice for many years has been and, for some surgeons, continues to be the patient&#39;s own bone. Usually, the incus body will be harvested and reshaped into a strut that bridges whatever gap exists between the tympanic membrane and the oval window. Although this is an effective method of reconstruction, the time required to harvest and sculpt the incus bone into a usable prosthesis has caused many to search for a suitable synthetic replacement. 
     Plastic prostheses used for reconstruction of the ossicular chain have been used for some time. A total prosthesis is generally shaped like a nail or tack and replaces all three bones of the middle ear. A partial prosthesis replaces the malleus and the incus ossicles. This prosthesis is similar in shape, but has a hollow cylinder for the reduced portion of the prosthesis. The hollow cylinder fits over the head of the stapes. All plastic prosthesis require that a disc of cartilage be placed between the head of the implant and the tympanic membrane. These discs are harvested during surgery. The disc prevents the implant, in most cases, from eroding the tympanic membrane and becoming dislodged over time “extruding”. 
     Improvements have used movable joints to allow angular adjustment or bendable wire cores. Later, bioactive prostheses were developed. A bioactive material is one which incorporates into the surrounding tissues in the same manner that natural bone would. The bioactive material is usually a calcium phosphate ceramic, such as hydroxylapatite. To trim this type of prosthesis a diamond bur mounted on a surgical drill is used. However, due to the brittle nature of the material, it will sometimes shatter or chip during the trimming process. Bioactive bendable prosthesis use a bioactive ceramic head joined to a bioactive ceramic shaft by a bendable intermediate portion. Such a prosthesis can be angulated for better fit. However, the ceramic shaft must still be trimmed to length. 
     The present invention is directed to solving one or more of the problems discussed above in a novel and simple manner. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention there is disclosed an ossicular prosthesis which is adjustable in length. 
     Broadly, there is disclosed herein an adjustable length ossicular prosthesis including a head formed of a bioactive or bioinert material for contacting a tympanic membrane when implanted in a human ear. The head includes a through opening. A flexible sleeve is mounted to the head at the through opening. The flexible sleeve includes a through opening coaxial with the head through opening. An elongate shaft has a near end extending through the sleeve through opening and the head through opening. The flexible sleeve through opening is adapted to grip the shaft under static conditions but permit the shaft to move axially to adjust shaft length. Means are associated with a distal end of the shaft for contacting a footplate or stapes when implanted in a human ear. 
     It is a feature of the invention that the flexible sleeve is formed of a biocompatible material. In one aspect the flexible sleeve is formed of an elastomer such as silicone. Alternatively, the flexible sleeve is formed of a plastic such as Teflon®. The sleeve is held to the head by an adhesive or by mechanical interlock. 
     It is another feature of the invention that the shaft is formed of a malleable material to produce a bendable shaft. According to one aspect of the invention the shaft is made of titanium. 
     It is a further feature of the invention that the shaft is defined by alternating enlarged portions and reduced portions and the sleeve expands as the enlarged portions pass through it and contract as the reduced portions pass through. This provides a slip lock mechanism. 
     It is an additional feature of the invention that the near end of the shaft on the opposite side of the head as the distal end is trimmed. 
     It is still another feature of the invention that the contacting means comprises a smaller bioactive head for contacting a footplate when implanted in a human ear. 
     In accordance with another aspect of the invention the contacting means further comprises a cylinder receivable on the smaller head. The cylinder has a counterbore for receiving the head of a stapes when implanted in a human ear. 
     It is yet another feature of the invention that the shaft extends slightly through the contacting means to form an extended tip to allow surgical fixation of the shaft to a footplate or stapes. 
     More particularly, an adjustable length prosthesis is used for ossicular replacement or reconstruction. The prosthesis uses a pair of bioactive heads connected by a shaft. The shaft is bendable to accommodate angulation for better anatomical fit. The shaft is flexibly received in the head and trimmable with a scissors or scalpel to simplify length adjustment and prevent chipping and breakage of the bioactive portion. The prosthesis can be used as a total or a partial prosthesis and need not be disassembled and reassembled during the trimming process. The prosthesis can be stabilized on the footplate with a sharpened shaft extension or wire core and can be used to protect the cochlea from pressure trauma. 
     Further features and advantages of the invention will be readily apparent from the specification and from the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of an adjustable length ossicular prosthesis according to the invention viewed looking in an outer direction; 
     FIG. 2 is a perspective view of the prosthesis of FIG. 1 viewed looking in an inner direction; 
     FIG. 3 is a partial sectional view taken along the line  3 — 3  of FIG. 1; 
     FIG. 4 is a detailed view of an encircled portion of a shaft of FIG. 3; 
     FIG. 5 is a perspective view of the prosthesis of FIG. 1 with its length adjusted for a partial reconstruction; 
     FIG. 6 is an elevation view illustrating the prosthesis of FIG. 1 in a human ear when used for total reconstruction; and 
     FIG. 7 is an elevation view illustrating the prosthesis of FIG. 1 in a human ear when used for partial reconstruction. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 1 and 2, an adjustable length ossicular prosthesis  10  according to the invention is illustrated. In accordance with the invention, the prosthesis  10  can be selectively used for total repair or replacement, as discussed below relative to FIG. 6, or partial repair or replacement, as discussed below relative to FIG.  7 . 
     The prosthesis  10  includes an enlarged head  12  for contacting a tympanic membrane when implanted in a human ear. A flexible sleeve  14  is mounted to the head  12 . An elongate shaft  16  has an outer end  18  and a distal or inner end  20 . As used herein, the relative terms inner and outer relate to relative position of the prosthesis  10  when placed in a human ear for its intended operation. The shaft  16  extends between the sleeve  14  and a second, smaller head  22 . The smaller head  22  is selectively mounted to a cylinder  24  for partial replacement or reconstruction. 
     The enlarged head  12  is generally circular and has rounded edges. As is apparent to those skilled in the art, the head  12  can be designed using many different shapes and sizes adapted to fit different circumstances. The head  12  comprises a ceramic head. Advantageously, the head  12  is formed of a bioactive material such as hydroxylapatite. Alternatively, it could be formed of a bioglass or even natural bone. The enlarged head  12  is of a shape adapted to contact the tympanic membrane or an ossicle in a human ear. The size of the head  12  is in the range of 2.5 mm to 5.0 mm diameter and 0.5 mm to 2.0 mm thickness. 
     Referring also to FIG. 3, the head  12  includes an outer surface  26  adapted to contact the tympanic membrane and an inner surface  28 . The head  12  includes a relatively small throughbore  30  and a larger coaxial counterbore  32 . The throughbore  30  has a diameter slightly larger than a maximum diameter of the shaft  16  to receive the same. The counterbore  32  is formed at the inner surface  28 . 
     The flexible sleeve  14  comprises an expanding cylinder of a size to be received in the head counterbore  32 . The sleeve  14  is permanently attached to the head  12 . It could be mechanically attached by being directly molded into the head  12 . Alternatively, the sleeve  14  could be held in the counterbore  32  using a suitable adhesive or even use a pivoting ball in a socket. The sleeve  14  is formed of a flexible biocompatible material, such as an elastomer or plastic. For example, the sleeve  14  could be formed of an elastomer such as silicone or a plastic such as Teflon®. It. The sleeve  14  is generally cylindrical in shape and includes a through opening  34  which is coaxial with the head through opening  30 . 
     The shaft  16  is formed of a malleable material such as titanium to be bendable. The shaft  16  is adapted to interlock with the sleeve  14 . Particularly, as shown in greater detail in FIG. 4, the shaft  16  is defined by a series of alternating enlarged and reduced cross sectional portions. Particularly, the shaft  16  includes reduced portions  36  alternating with enlarged portions  38 . The reduced portions  36  are from 0.1 mm to 0.3 mm in diameter and 0.1 mm to 0.3 mm in length. The enlarged portions  38  are from 0.2 mm to 0.5 mm in diameter and from 0.1 mm to 0.3 mm in length. A preferred arrangement is one in which the alternating segments occur in 0.5 mm increments. The enlarged portion  38  and reduced portion  36  are joined by frustoconical portions  40  to aid in length adjustment. 
     While the shaft  16  is described as being bendable, the prosthesis  10  could be provided with a non-bendable shaft as necessary or desired. 
     In accordance with the invention, the flexible sleeve  14  is adapted to grip the shaft  16 . Particularly, the through opening  34  is adapted to provide a cross-sectional shape generally similar to that of the shaft  16 . The through opening  34  includes alternating enlarged portions  42  and reduced portions  44 . The opening enlarged portions  42  are of similar size to the shaft enlarged portions  38  and the opening reduced portions  44  are of a similar size to the shaft reduced portions  36 . The axial spacing of the enlarged portions  42  and the reduced portions  44  corresponds to the similar spacing of the shaft enlarged portions  38  and reduced portions  36 . The flexible sleeve  14  may be molded directly onto the shaft  16  to form the through opening  34 . 
     The smaller head  22  is formed of a bioactive ceramic material, similar to the enlarged head  12 . It is rigidly secured to the shaft distal end  20  via a press fit or using an adhesive. The small head  22  is adapted to contact the oval window or footplate in the human ear when the prosthesis  10  is used for total reconstruction. The cross section of the smaller head may be circular, oval or square and is from 0.4 mm to 1.0 mm in diameter. Its length is from 0.5 mm to 2.0 mm. 
     The shaft distal end  20  extends through the smaller head  22  to form an extended sharpened tip  45 . This is done to allow surgical fixation of the shaft  16  to the footplate of the stapes by drilling a hole in the footplate and extending the tip  45  into the hole. As a result, the prosthesis  10  can be stabilized on the footplate with a sharpened shaft extension or wire core. 
     The cylinder  24  is a bioactive ceramic cylinder, similar to the heads  12  and  22 . For example, the cylinder  24  may be formed of hydroxylapatite. The cylinder  24  includes an inner end  46  and a smaller outer end  48 . The outer end has a counterbore  50  shown in phantom. The counterbore  50  is of a size and shape corresponding to the smaller head  22  for receiving the same. An enlarged counterbore  52  is positioned at the inner end  46 . The cylinder  24  enables the prosthesis  10  to be used for partial reconstruction. Particularly, with the outer counterbore  50  receiving the smaller head  22 , the inner end counterbore  52  can engage the head of the stapes. The cylinder outer counterbore  50  may contain a polymeric lining, such as silicone or Teflon® to enhance assembly and hold the cylinder  24  in place during implantation. The cylinder inner counterbore  52  is from 1.0 mm to 2.0 mm in diameter and from 0.5 mm to 2.0 mm in depth. 
     For ossicular replacement or reconstruction, the surgeon can adjust length in increments determined by the configuration of the shaft  16 . Particularly, in the example discussed above, the surgeon can adjust length in 0.5 mm increments defined by spacing between the reduced portions  36 . By compressing the enlarged head  12  and smaller head  22 , the implant is shortened by forcing the shaft  16  outwardly, as illustrated in FIG.  5 . The flexible sleeve  14  expands as the enlarged portions  38  pass through the smaller portions  44  of the through opening  34  and contracted as the smaller portions  36  pass therethrough. By adjusting the mechanical properties of the material of the sleeve  14  or changing the ratio of the enlarged portions  38  and reduced portions  36  of the shaft  16 , the tightness of the slip lock may be adjusted. The slip lock should be loose enough to allow easy length adjustment by the surgeon, but tight enough to prevent slippage after implantation. The near end  18  of the shaft that extends outwardly from the head  12 , see FIG. 5, can then be cut off by the surgeon prior to implantation. 
     Although the sleeve  14  and shaft  16  are illustrated having alternating reduced and enlarged cross-sections, such structure is not required in accordance with the teachings of the invention. In fact, one of the two elements could have such a cross-section with the other having a fixed cylindrical cross-section, provided suitable gripping is evident. Moreover, both could have fixed cylindrical cross-section with suitable gripping to prevent slippage. Likewise, the shaft  16  could be formed of a coiled spring or helical thread received in a helical through opening of the sleeve  14 . The shaft  16  would then be screwed in or out. This design could be used to protect the cochlea from pressure trauma. 
     In the illustrated embodiment of the invention, the enlarged head  12 , the smaller head  22  and the cylinder  24  are of a bioactive material. Alternatively, these elements could be formed of a bioinert material. 
     Referring to FIG. 6, the prosthesis  10  is illustrated fitted in a human ear for total reconstruction or replacement. Particularly, the enlarged head  12  contacts the tympanic membrane T. The smaller head  22  contacts the footplate F of the oval window W. The shaft tip  45  is shown, in phantom, in a hole H drilled by the surgeon in the footplate F. 
     Referring to FIG. 7, the prosthesis  10  is illustrated fitted in a human ear for partial reconstruction or replacement. Particularly, the enlarged head  12  contacts the tympanic membrane T. The smaller head  22  is mounted to the cylinder  24  which receives the head of the stapes S. 
     Thus, in accordance with the invention there is provided an ossicular prosthesis which provides simple length adjustment and angular orientation.