Patent Publication Number: US-11389180-B2

Title: Bone fixture for a medical prosthesis

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 14/837,091 entitled “Bone Fixture for a Medical Prosthesis,” filed Aug. 27, 2015, which claims priority to U.S. Provisional Application No. 62/042,963 entitled “Bone Fixture for a Medical Prosthesis,” filed Aug. 28, 2014. The content of these applications is hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     Field of the Invention 
     The present invention relates generally to bone fixtures. 
     Related Art 
     Hearing loss, which may be due to many different causes, is generally of two types, conductive and/or sensorineural. Conductive hearing loss occurs when the normal mechanical pathways of the outer and/or middle ear are impeded, for example, by damage to the ossicular chain or ear canal. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain. 
     Individuals suffering from conductive hearing loss typically receive an acoustic hearing aid. Hearing aids rely on principles of air conduction to transmit acoustic signals to the cochlea. Typically, a hearing aid is positioned in the ear canal or on the outer ear to amplify received sound. This amplified sound is delivered to the cochlea through the normal middle ear mechanisms resulting in the increased perception of sound by the recipient. 
     In contrast to acoustic hearing aids, certain types of implantable auditory prostheses, sometimes referred to as implantable acoustic auditory prostheses, convert a received sound into output mechanical force (vibration) for delivery to the recipient. The vibrations are transferred through the recipient&#39;s teeth, bone, and or other tissue to the cochlea. The vibrations cause movement of the cochlea fluid that generates nerve impulses resulting in perception of the received sound by the recipient. Acoustic auditory prostheses are suitable to treat a variety of types of hearing loss and may be prescribed for individuals who cannot derive sufficient benefit from acoustic hearing aids, cochlear implants, etc., or for individuals who suffer from stuttering problems. Implantable acoustic auditory prostheses include, for example, bone conduction devices, middle ear auditory prostheses (middle ear implants), direct acoustic stimulators (direct cochlear stimulators), or other partially or fully implantable auditory prosthesis that deliver vibrations to a recipient to directly or indirectly generate movement of the cochlea fluid. 
     SUMMARY 
     In one aspect of the present invention, a bone fixture for an auditory prosthesis is provided. The bone fixture comprises a self-drilling threaded body configured to be inserted into a recipient&#39;s bone and including a bone removal mechanism, and a coupling section attached to a proximal end of the threaded body that includes a connector interface located entirely proximal to the threaded body. 
     In another aspect of the present invention, an apparatus is provided. The apparatus comprises a body configured to be screwed into a recipient&#39;s bone, a coupling section attached to a proximal end of the body configured for attachment to a connector mechanism, a screw thread extending around the body, and a bone removal mechanism configured to form a hole in the recipient&#39;s bone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are described herein in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a side view of a bone fixture in accordance with embodiments presented herein implanted in a recipient and attached to a percutaneous bone conduction device; 
         FIG. 2A  is a side view of a bone fixture in accordance with embodiments presented herein; 
         FIG. 2B  is cross-sectional view of the bone fixture of  FIG. 2A ; 
         FIG. 2C  is perspective view of the bone fixture of  FIG. 2A ; 
         FIG. 2D  is a schematic diagram illustrative the removal of bone fragments during insertion of the bone fixture of  FIG. 2A ; 
         FIG. 3A  is a side view of a bone fixture that includes a drill tip in accordance with embodiments presented herein; 
         FIG. 3B  is enlarged view of the drill tip shown in  FIG. 3A ; 
         FIG. 3C  is a perspective view of the drill tip shown in  FIG. 3A ; 
         FIG. 4A  is a side view of a implantable magnet secured to a recipient with a bone fixture in accordance with embodiments presented herein; and 
         FIG. 4B  is a cross-sectional view of the implantable magnet and bone fixture of  FIG. 4A . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention are generally directed to a bone fixture for a medical prosthesis such as an implantable auditory prosthesis. The bone fixture includes a self-drilling threaded body that is configured to be inserted into a recipient&#39;s bone. The threaded body includes a bone removal mechanism configured to cut away parts of the bone that are in the path of the threaded body and to remove portions of the cut parts of the bone, sometimes referred to herein as bone fragments, from the hole. The bone fixture also comprises a coupling section that is attached to a proximal end of the threaded body. The coupling section is configured to be positioned external to the recipient&#39;s bone and includes a connector interface that is entirely/completely proximal to the threaded body. 
     There are different types of medical prostheses that may be partially or fully implanted into a recipient, including implantable auditory prostheses such as bone conduction devices (e.g., percutaneous, transcutaneous, transcutaneous active, etc.), middle ear auditory prostheses, direct acoustic stimulators, etc. It is to be appreciated that bone fixtures in accordance with embodiments presented herein may be used in connection with any of the above or other implantable auditory prostheses or other medical prostheses (e.g., facial prostheses). However, merely for ease of description, embodiments of the present invention are primarily described herein with reference to use of the bone fixture with bone conduction devices. 
       FIG. 1  is a cross-sectional view of a bone fixture  100  in accordance with embodiments presented herein. The bone fixture  100  is shown implanted in a recipient&#39;s bone  136  so as to couple a bone conduction device  102  to the recipient. As described further below, the bone fixture  100  comprises a self-drilling threaded body (shank)  104  that is configured to be inserted (e.g., screwed) into the recipient&#39;s bone  136 . The bone fixture  100  also comprises a coupling section  106  that is attached to the proximal end of the threaded body  104 . 
     The coupling section  106  is positioned entirely external to (i.e., outside of) the recipient&#39;s bone  136  and is configured for attachment to a connector mechanism. For example, the coupling section  106  includes a connector interface in the form of a threaded aperture (not shown in  FIG. 1 ) that is configured to receive and mate with a threaded component of abutment  120 . The bone fixture  100  is generally positioned below the recipient&#39;s skin  132  (e.g., adjacent to fat  128  and/or muscle  134 ). However, the abutment  120  extends through the recipient&#39;s skin  132 . That is, the abutment  120  is a percutaneous abutment. As such, the bone conduction device  102  is sometimes referred to herein as a percutaneous bone conduction device  102  because the bone conduction device is attached to the recipient via the percutaneous abutment  102 . 
     The percutaneous bone conduction device  102  comprises a housing  110  and a sound input element  112 . The sound input element  112  may be, for example, a microphone, telecoil, audio input, etc. that is configured to receive and/or detect sound signals. In the embodiment of  FIG. 1 , sound input element  112  is located on housing  110 . In alternative embodiments, the sound input element  112  may be positioned on a cable extending from housing  110 , positioned in a recipient&#39;s ear, subcutaneously implanted in the recipient, etc. Additionally, multiple sound input elements  112  may also be provided. 
     Percutaneous bone conduction device  102  also comprises a sound processor  114 , a transducer (actuator)  116 , and/or various other operational components (not shown in  FIG. 1 ) all disposed in housing  110 . A portion of the housing  110  has been omitted from  FIG. 1  to illustrate portions of the sound processor  114  and the transducer  116 . 
     In operation, sound input element  112  converts received sound signals into electrical signals. These electrical signals are processed by the sound processor  114  to generate control signals that cause vibration of transducer  116 . In other words, the transducer  116  converts the electrical signals received from the sound processor  114  into mechanical vibrations. The transducer  114  may be, for example, an electromagnetic transducer, piezoelectric transducer, etc. 
     Percutaneous bone conduction device  102  further includes a coupler  122  that is configured to be attached to the exposed portion of abutment  120  (i.e., the portion outside of the skin  132 ). The mechanical force generated by the transducer  110  is transferred through the coupler  122 , abutment  120 , and the bone fixture  100  to effect vibration of the recipient&#39;s skull bone  136  and eventual movement of fluid within the recipient&#39;s cochlea, thereby causing a hearing percept. 
     As noted above,  FIG. 1  illustrates a percutaneous bone conduction device  102  that is attached to a recipient using a percutaneous abutment  120  and a bone fixture  100 . It is to be appreciated that bone fixtures in accordance with embodiments presented herein, such as bone fixture  100 , can be used with other types of bone conduction device devices, including passive and active transcutaneous bone conduction devices. 
     A passive transcutaneous bone conduction device utilizes an external transducer within an external component that is attached to a recipient using external and implantable magnetic plates. An active transcutaneous bone conduction device utilizes an implantable transducer that is directly or indirectly coupled to the recipient&#39;s bone. Bone fixtures in accordance with embodiments presented herein may be used to secure an implantable magnetic plate or an implantable transducer to a recipient. 
     Conventional percutaneous and transcutaneous bone conduction devices, including passive and active arrangements, utilize bone fixtures that require predrilling of a hole in the recipient&#39;s bone. That is, conventional bone fixtures require a surgeon to use a power drill to predrill holes for the bone fixtures and then to insert the bone fixtures into the predrilled holes. This necessarily requires a process where the surgeon drills into the recipient&#39;s skull bone to create the hole that will receive the bone fixture. More particularly, a surgeon typically first drills a relatively small guide or pilot hole in the bone and then uses a larger drill bit to widen the hole so as to receive a bone fixture. The need to drill a hole within the skull bone is a mental impediment that may prevent some potential recipient&#39;s from undergoing the needed surgical procedure for use of a bone conduction device. 
     As such, presented herein are bone fixtures that eliminate the need to predrill holes in a recipient&#39;s bone. More specifically, bone fixtures in accordance with embodiments presented herein are “self-drilling” in that the bone fixtures are configured to create/form a hole in the bone into which the threaded body  204  is inserted without the need for predrilling. That is, the self-drilling bone fixtures in accordance with embodiments presented herein perforate the surface of the recipient&#39;s bone and, during insertion, remove bone fragments from the recipient to form the hole into which the bone fixture is implanted. The self-drilling bone fixtures presented herein not only simplify the surgical procedure by removing two surgical steps (i.e., pilot hole drilling and widening drilling), but also makes the surgery less dramatic from a recipient perspective (i.e., the recipient no longer has to accept that the surgeon will use a power drill to drill a hole into the recipient&#39;s skull bone). 
       FIG. 2A  is a side view of a self-drilling bone fixture  200  in accordance with embodiments of the present invention.  FIG. 2B  is cross-sectional view of the bone fixture  200  and also illustrates a cross-sectional view of an abutment  220  that is configured to be mechanically coupled to the bone fixture  200 .  FIG. 2C  is a perspective view of the bone fixture  200 , while  FIG. 2D  is a schematic diagram illustrating operation of the self-drilling bone fixture  200  during insertion into the recipient&#39;s bone. 
     As shown, the bone fixture  200  comprises a threaded body  204 , sometimes referred to herein as a threaded shank, that is configured to be inserted (i.e., screwed) into a recipient&#39;s bone. The threaded body  204  has a distal end  226  and a proximal end  224  that is attached to a coupling section  206 . The distal end  226  is configured to be first inserted into the bone, while proximal end  224  is configured to be positioned adjacent the surface of the recipient&#39;s bone. For ease of illustration, the bone fixture  200  is shown in  FIGS. 2A-2D  prior to insertion into the recipient&#39;s bone. 
     The threaded body  204  includes an external/outer screw thread  228  that is configured to mate with the recipient&#39;s bone. The external screw thread  228  extends from adjacent the proximal end  224  to adjacent the distal end  226 . Due to the presence of the external screw thread  228 , the threaded body forms a male bone screw for installation in the recipient&#39;s bone. 
     As shown in  FIG. 2B , in one specific embodiment the external screw thread  228  has a core/minor diameter  229  of approximately 1.5 millimeters (mm) and an outer/major diameter  231  of approximately 3.0 mm. The external screw thread  228  may also have a pitch  233  of approximately 0.6 mm. As used herein, the “pitch” refers to the linear distance between the same point of two adjacent turns. The external screw thread  228  further includes substantially sharp crests/tips  235  having, for example, a flat surface with a width of less than or equal to 0.05 mm. The substantially sharp crests increase the amount of bone that is positioned between the threads, thereby maximizing the strength of the bone that is used by the bone fixture  200  to drill into the skull. Additionally, the external screw thread  228  may have a thread angle  237  of approximately nineteen (19) degrees, with a leading flank angle  239  of approximately two (2) degrees and a following flank angle  241  of approximately seventeen (17) degrees. The larger flank angle  241  provides stability/support to the screw thread since the load forces are downwards on the thread as the bone fixture drills itself into the bone. In certain embodiments, the leading flank angle  239  and the following flank angle  241  may each have a tolerance of approximately +/−two (2) degrees without significantly affecting the self tapping/drilling performance of the bone fixture. 
     The threaded body  204  is a self-drilling and self-tapping screw/element that combines thrilling (threading and drilling, performed in the reverse order) action and actual insertion into a single driving step, instead of separate drilling, tapping, and installing steps. More specifically, the threaded body  204  is self-drilling because the threaded body includes a bone removal mechanism  230  configured to create/form a hole in the bone into which the threaded body  204  is inserted. To form the hole, the bone removal mechanism  230  is configured to perforate the bone and then to cut away parts of the bone that are in the path of the threaded body  204 , thereby generating bone fragments. The bone removal mechanism  230  is further configured to remove a number of the bone fragments from the hole. 
     In the embodiments of  FIGS. 2A-2D , the bone removal mechanism  230  comprises a distal cutting tip  232  that perforates the bone and that cuts the bone fragments as the threaded body  204  is advanced (turned) into the bone. The distal cutting tip  232  may have different arrangements but, in general, is significantly sharper than the tips of conventional bone fixtures that do not have the ability to perforate a recipient&#39;s bone. The distal cutting tip  232  also includes one or more cutting edges/surfaces  280  that are not included in conventional bone fixtures. As the threaded body  204  is turned into the bone, the cutting edge(s)  280  cut away the bone fragments to open up the hole. In the specific arrangement shown in  FIGS. 2A-2C , the distal cutting tip  232  has a general conical shape and includes a distally facing point. The distal cutting tip  232  may be a nail point, a cone point, a Type 17 point, a Type 23 point, etc. 
     The bone removal mechanism  230  also comprises a bone transport channel  234 . The bone transport channel  234  is an elongate groove that forms a discontinuity in the through the external screw thread  228 , though bone transport channel  234  may make less than a complete turn around the threaded body  204 . The bone transport channel  234  is sometimes referred to herein as being “transverse” to the external screw thread  228  because, as is evident from  FIG. 2D , the bone transport channel  234  has a pitch that is substantially larger than the pitch  233  of the external screw thread  228 . Therefore, the bone transport channel  234  extends angularly across the external screw thread  228 . In one illustrative embodiment, the pitch of the transport channel is approximately 8 mm/revolution, while the pitch  233  of the external screw thread  228  is approximately 0.6 mm/revolution. external screw thread  228 . The bone transport channel  234  follows a general helical path 
     In operation, the bone transport channel  234  is configured to transport/channel bone fragments from the region of distal cutting tip  232  to an outer surface of the recipient&#39;s bone (i.e., out from the hole created by the bone fixture  200 ). More specifically, as noted above, the turning of the threaded body  204  into the bone causes the cutting edge(s)  280  to cut away bone fragments and thereby open up the hole. The cutting edge(s)  280  are positioned relative to the distal end  274  of the bone transport channel  234  such that a number of the bone fragments are collected by the distal end  274  of the bone transport channel  234 . Again, as the threaded body  204  is turned, the bone fragments are forced through the bone transport channel  234  to the outer surface of the bone.  FIG. 2D  is a schematic diagram illustrating a path  243  for bone fragments through bone transport channel  234  to the outer surface of the bone. 
     The bone transport channel  234  may, in certain arrangements, extend from adjacent the distal cutting tip  232  to the base of the coupling section  206 . In accordance with certain embodiments presented herein, the bone transport channel  234  has core diameter/width  272  that is less than or equal to the size of the bone fixture thread. The bone fixture thread size is the distance between the outer diameter (i.e., the crests  235 ) of the thread down to the core diameter (i.e., valley of the thread), not including the transport channel when those are intersecting). As such, there need not be a 1:1 ratio between the number of bone fragments that are cut and the number of bone fragments that are removed via the bone transport channel  234  as compression of some bone fragments and bone may be useful. For example, in one embodiment the external screw thread  228  has a pitch of approximately 0.8 mm and the bone transport channel  234  has core diameter/width  272  of approximately 0.7 mm. 
     As noted, in addition to being a self-drilling screw (i.e., having features that enable the formation of a hole in the recipient&#39;s bone), the threaded body  204  is also a self-tapping screw. That is, as the threaded body  204  is advanced into the hole created by the bone removal mechanism  230 , the threaded body  204  is configured to “tap” the hole (i.e., the threaded body  204  is configured to further cut the bone at the outer surface of the hole to create an internal screw thread that mates with the external screw thread  228 ). In the embodiments of  FIGS. 2A-2C , the threaded body  204  includes a relatively large discontinuity/gap  236  in the distal end of the external screw thread  228 . The gap  236  forms a tap which creates the internal screw thread within the hole. More specifically, a portion  281  of the external screw thread  228  that is adjacent to the gap  236  forms the tap to create the internal screw thread within the bone hole. Portion  281  is the first part of the external screw thread  228  that contacts the bone as the bone fixture  200  is advanced into the bone. 
     In summary, it is to be appreciated that here there is a difference between the “drilling” and “tapping” features of bone fixture  200 . In general, the drilling features create the core cavity (hole) into which the bone fixture  200  is inserted. The drilling is performed by, for example, parts  274 ,  230 ,  237 ,  280 ,  232 , among others. In contrast, the tapping features are used to create the internal screw threads in the bone that mate with the external screw thread  228 . Generally, portion  281  of the external screw thread  228  that comes in contact with the bone first is the part that performs the tapping. As noted above, a third component is the design of the external screw thread  228 , namely the use of a following flank angle  241  that is substantially larger than the leading flank angle  239 , which assists in driving the bone fixture  200  downwards into the bone as it is advanced into the bone. 
     As noted above, attached to the proximal end  224  of the threaded body  204  is a coupling section  206 . The coupling section  206  includes a flange  244  that is configured to function as a stop mechanism when bone fixture  200  is installed into the bone. More specifically, the flange  244  has a substantially planar bottom surface  246  that is configured to be positioned adjacent to (e.g., abut/contact) the top surface of the recipient&#39;s bone when the bone fixture  200  is inserted into the recipient&#39;s bone. As such, the flange  244  may prevent the bone fixture  200  from potentially penetrating completely through the recipient&#39;s bone. 
     Flange  244  may have a diameter  248  that is greater than or equal to the maximum outer diameter  250  of the external screw thread  228 . Although flange  244  is illustrated in  FIGS. 2A-2C  as being circular, flange  244  can be configured in a variety of shapes. Also, the diameter and thickness  252  of flange  244  can vary depending on, for example, the particular intended application of the bone fixture  200 . 
     The coupling section  206  further includes an elongate central member  254  extending proximally from the flange  244 . An optional outer member  258  surrounds a portion of the elongate central member  254 . The elongate central member  254  may have, for example, a circular, oval, protruding or recessed hex, or another other multi-lobe cross-sectional shape that lies on a plane normal to a central longitudinal axis  219  of the bone fixture  200 . That is, elongate central member  254  may have an elongate tubular, hexagonal, or other shape. In general, the elongate central member  254  has a diameter  260  that is less than or equal to the diameter  248  of the flange  244 . 
     In certain embodiments, the elongate central member  254  and/or the outer member  258  include features that mate with a tool for installation of the bone fixture  200  in to the recipient&#39;s bone. For example, in an exemplary embodiment the elongate central member  254  has a hexagonal cross-sectional shape such that a female hex-head socket wrench can be used to apply torque to the bone fixture  200 . In other embodiments, the elongate central member  254  has a tubular shape (i.e., circular cross-section) and thus does not have a protruding hex for engagement with a hex-head socket. In such embodiments, the outer member  258  may include the features that are configured to engage with an installation tool. 
     Disposed in the elongate central member  254  is a connector interface  262  that is configured for mechanical attachment to a connector mechanism of, for example, an abutment, implantable magnet, implantable vibrator, etc. In the embodiment of  FIGS. 2A-2C , the connector interface  262  is a threaded aperture  264  with an internal screw thread  266  configured to mate with the external screw thread on a connector mechanism. 
       FIG. 2B  illustrates an example connector mechanism  268  that forms part of a screw  231  of a percutaneous (i.e., skin-penetrating) abutment  220 . The connector mechanism  268  is a threaded body  256  with an external screw thread  270 . In operation, the connector mechanism  268  is threaded into connector interface  262  so that external screw thread  270  mates with internal screw thread  266 , thereby rigidly attaching abutment  220  to the bone fixture  200 . The rigid attachment between the abutment  220  and the bone fixture  200  enables the transfer of vibrations from a percutaneous bone device to the recipient&#39;s bone so as to evoke a hearing percept. 
     As noted above, the connector interface  262  is a screw interface (i.e., includes an internal screw thread  266  for mating with an external screw thread of a connector mechanism). It is also to be appreciated that the use of a screw interface is illustrative and that other types of connector interfaces could be used in alternative embodiments. Furthermore, it is to be appreciated that the connection of connector interface  262  to a percutaneous abutment  220  is also merely illustrative. The connector interface  262  could alternatively be attached to a connector mechanism of, for example, an abutment, implantable magnet, implantable vibrator, etc. (i.e., the bone fixture  200  in accordance with embodiments of the present invention may be used in both percutaneous and transcutaneous arrangements). 
     In the embodiments of  FIGS. 2A-2D , the coupling section  206  in general, and the connector interface  262  in particular, is entirely proximal to the threaded body  204 . That is, although the coupling section  206  is attached to the threaded body  204 , no portion of the connector interface  262  or other part of the coupling section  206  extends into the threaded body  204  (i.e., the coupling section  206  terminates at the bottom surface  246  of the flange  244 ). In this way, when the bone fixture  200  is inserted into the recipient&#39;s bone, the entirety of the coupling section  206  is proximal to (i.e., external or outside) the recipient&#39;s bone. 
     As noted above, the threaded body  204  is self-drilling so as to remove bone from the recipient as the threaded body is advanced into the bone (i.e., no hole is drilled into the bone before the threaded body  204  is inserted). In order to reduce the amount of bone that is removed during insertion, the threaded body  204  may have a diameter that is significantly smaller than conventional bone fixtures that are not self-drilling. More specifically, since conventional bone fixtures are not self-drilling, the diameter of such conventional bone fixtures is selected to, for example, merely ensure that the bone fixture remains securely within the bone. In order to prevent the possibility of breakage, conventional bone fixtures are intentionally made with a large diameter that accommodates a significant part of the connector interface for attachment to a connector mechanism of an abutment, magnet, etc. 
     However, as noted, a self-drilling bone fixture removes the bone as it is advanced into the recipient&#39;s bone and the thinner the threaded body, the less bone that is removed. Accordingly, the diameter of the threaded body  204  of  FIGS. 2A-2D  is minimized through placement of the connector interface  262  entirely outside of the threaded body  204 . In certain embodiments, the diameter of threaded body  204  is approximately 3 mm, which is substantially smaller (e.g., approximately 33% smaller) than a 4.5 mm diameter of conventional bone fixtures that include all or part of the connector interface within the threaded body. If a substantially thin threaded body, such as that shown in  FIGS. 2A-2D , were used with a conventional arrangement in which part of all of the connector interface is within the threaded body, the threaded body would be susceptible to strain and potential breakage during insertion (e.g., breakage resulting from the existence of thin walls within a threaded body that includes all of part of a conventional connector interface). 
     The threaded body  204  and coupling section  206  may be formed as a unitary piece (e.g., the bone fixture  200  is formed from a single piece of material in a monolithic structure). Bone fixture  200  can also be formed from a material that has the ability to integrate into surrounding bone tissue (i.e., may be formed from a material that exhibits acceptable osseointegration characteristics). In one embodiment, the bone fixture  200  is formed from titanium. Additionally, the bone fixture  200  or portions thereof may include a coating, such as Hydroxyapatite, to facilitate osseointegration. 
     In general, the threaded body  204  has a length that is sufficient to securely anchor the bone fixture  200  to the recipient&#39;s bone without penetrating entirely through the bone. The length of the body can therefore depend, for example, on the thickness of the bone (e.g., skull) at the implantation site and/or the intended application. As such, the dimensions of the various features of the bone fixture  200  may also vary. 
     The bone fixture  200  shown in  FIGS. 2A-2D  is illustrative and bone fixtures in accordance with embodiments of the present invention may have different sizes and/or configurations. For example,  FIG. 3A  illustrates a bone fixture  300  that includes a different distal cutting tip than the tip shown in the arrangement of  FIGS. 2A-2D . 
     More specifically, the bone fixture  300  of  FIG. 3A  includes a threaded body  304  and a coupling section  306 . The coupling section  306  is substantially the same as coupling section  206  of  FIGS. 2A-2D  and, as such, is not described further herein. 
     The threaded body  304 , which is configured to be screwed into a recipient&#39;s bone, comprises an external/outer screw thread  328  configured to mate with the recipient&#39;s bone. Similar to the embodiment of  FIGS. 2A-2D , the threaded body  304  is a self-drilling and self-tapping screw. The threaded body  304  is self-drilling because the threaded body includes a bone removal mechanism  330  that is configured to form a hole in the bone into which the threaded body  304  is inserted. To form the hole, the bone removal mechanism  330  cuts away bone fragments and removes the bone fragments from the created hole. 
     In the embodiment of  FIG. 3A , the bone removal mechanism  330  comprises a distal cutting tip  332  that is configured to perforate the bone and to cut away the bone fragments as the threaded body  304  is advanced (turned) into the bone. The distal cutting tip  332  of  FIG. 3A  is a drill tip/point, namely a twist drill bit tip with multiple cutting edges  380 .  FIG. 3B  is an enlarged side view of the twist drill bit tip  332  of  FIG. 3A , while  FIG. 3C  is a bottom perspective view of the twist drill bit tip  332 . 
     The bone removal mechanism  330  also comprises a bone transport channel  334 . The bone transport channel  334  is an elongate groove that forms a discontinuity in the external screw thread  328 . The bone transport channel  334  follows a general helical path through the external screw thread  328  and is generally transverse to the external screw thread  328  (i.e., has a pitch  383  that is substantially larger than the pitch  333  of the external screw thread  328 ). Therefore, the bone transport channel  334  extends angularly across the external screw thread  328 . 
     The bone transport channel  234  may, in certain arrangements, extend from adjacent the distal cutting tip  332  to the base of the coupling section  306 . In accordance with certain embodiments presented herein, the bone transport channel  234  has core diameter/width  372  that is less than or equal to the thread pitch  333 . 
     In operation, the bone transport channel  334  is configured to transport/channel bone fragments from the region of twist drill bit tip  332  to an outer surface of the recipient&#39;s bone (i.e., out from the hole created by the bone fixture  300 ). More specifically, the turning of the threaded body  304  into the bone causes the cutting edge(s)  380  of the twist drill bit tip  332  to cut away bone fragments and thereby open up the hole. The cutting edge(s)  380  are positioned relative to the distal end  374  of the bone transport channel  334  such that a number of the bone fragments are collected by the distal end  374 . Again, as the threaded body  304  is turned, the bone fragments are forced through the bone transport channel  334  to the outer surface of the bone. 
     In addition to being a self-drilling screw (i.e., having features that enable the formation of a hole in the recipient&#39;s bone), the threaded body  304  is also a self-tapping screw. That is, as the threaded body  304  is advanced into the hole created by the bone removal mechanism  330 , the threaded body  304  is configured to tap the hole (i.e., further cut the bone at the outer surface of the hole to create an internal screw thread that mates with the external screw thread  328 ). In the embodiments of  FIGS. 3A and 3B , the threaded body  304  includes a discontinuity/gap  336  in the distal end of the external screw thread  328 . The gap  336  operates as a tap that creates the internal screw thread within the hole. More specifically, a portion  381  of the external screw thread  328  that is adjacent to the gap  336  forms the tap to create the internal screw thread within the bone hole. Portion  381  is the first part of the external screw thread  328  that contacts the bone as the bone fixture  300  is advanced into the bone. 
     In summary, it is to be appreciated that here is a difference between the “drilling” and “tapping” features of bone fixture  300 . In general, the drilling features create the core cavity (hole) into which the bone fixture  200  is inserted. In contrast, the tapping features are used to create the internal screw threads in the bone that mate with the external screw thread  328 . 
     Embodiments of the present invention have been primarily described herein with reference to bone fixtures for attachment to a percutaneous abutment. However, as noted above, it is to be appreciated that these embodiments are merely illustrative and bone fixtures in accordance with embodiments of the present invention may be used to, for example, secure an implantable transducer to the recipient&#39;s bone, secure an implantable magnetic plate to a recipient&#39;s bone, etc. For example,  FIGS. 4A and 4B  are side and cross-sectional views, respectively, of an implantable magnet case  490  that is configured to have one or more magnets (not shown in  FIGS. 4A and 4B ) positioned therein. The implantable magnet case  490  is attached to a bone fixture  400  that is configured to be inserted into a recipient&#39;s skull. 
     The bone fixture  400  includes a threaded body  404  and a coupling section  406 . The threaded body  404  may be, similar to the threaded bodies  204  or  304  described above, a self-cutting and self-tapping element for insertion into the recipient&#39;s bone without the need to first drill a hole. The coupling section  406  is configured for attachment to the implantable magnet case  490 . More specifically, the coupling section  406  includes a connector interface in the form of a threaded aperture  464  with an internal screw thread  466  configured to mate with an external screw thread  470  of a connector mechanism  468  of the implantable magnet case  490 . In operation, the connector mechanism  468  is threaded into aperture  464  so that external screw thread  470  mates with internal screw thread  466 , thereby rigidly attaching the implantable magnet case  490  to the bone fixture  400 . 
     It is to be appreciated that the above embodiments are not mutually exclusive and may be combined with one another in various arrangements. 
     The invention described and claimed herein is not to be limited in scope by the specific preferred embodiments herein disclosed, since these embodiments are intended as illustrations, and not limitations, of several aspects of the invention. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.