Patent Publication Number: US-2015087891-A1

Title: Osteoconductive Implantable Component for a Bone Conduction Device

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates generally to an implantable component for use with a bone conduction device, and more particularly, to an osteoconductive implantable component for a bone conduction device. 
     2. 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 auditory prostheses, commonly referred to as bone conduction devices, convert a received sound into vibrations. The vibrations are transferred through teeth and/or bone to the cochlea, causing generation of nerve impulses, which result in the perception of the received sound. Bone conduction devices are suitable to treat a variety of types of hearing loss and may be suitable for individuals who cannot derive sufficient benefit from acoustic hearing aids, cochlear implants, etc., or for individuals who suffer from stuttering problems. 
     SUMMARY 
     In one aspect of the invention, an implantable component configured to couple an external bone conduction device to a recipient is provided. The implantable component comprises an osteoconductive body comprising a first surface configured to be positioned substantially parallel to and abutting a surface of the recipient&#39;s skull, a second surface opposing the first surface, and a lateral surface connecting the first and second surfaces, wherein the body is a porous-solid scaffold configured to promote growth of the recipient&#39;s skull bone in a manner that interlocks the osteoconductive body with the recipient&#39;s skull. 
     In another aspect of the present invention, an implantable component configured to couple an external element to a recipient is provided. The implantable component comprises a body comprising a first surface configured to be positioned substantially parallel to and abutting a surface of the recipient&#39;s skull, a second surface opposing the first surface, and a lateral surface connecting the first and second surfaces, and a plurality of features configured to promote bone growth from the surface of the recipient&#39;s skull in a manner such that the bone growth interlocks with the plurality features so as to prevent movement of the implantable component with respect to the recipient&#39;s skull. 
    
    
     
       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 cross-sectional schematic diagram of an osteoconductive implantable component in accordance with embodiments presented herein configured for use with a percutaneous bone conduction device; 
         FIG. 2  is a cross-sectional schematic of an osteoconductive implantable component in accordance with embodiments presented herein configured for use with a transcutaneous bone conduction device; 
         FIG. 3A  is a lower-perspective view of an osteoconductive implantable component in accordance with embodiments presented herein; 
         FIG. 3B  is a upper-perspective view of the osteoconductive implantable component of  FIG. 3A ; 
         FIG. 3C  is a cross-sectional view of the osteoconductive implantable component of  FIG. 3A ; 
         FIG. 4  is a side view of an osteoconductive implantable component in accordance with embodiments presented herein secured to a recipient with a bonding agent; 
         FIG. 5A  is a upper-perspective view of an osteoconductive implantable component in accordance with embodiments presented herein; 
         FIG. 5B  is a cross-sectional view of the osteoconductive implantable component of  FIG. 5A ; 
         FIG. 6A  is an upper-perspective view of an osteoconductive implantable component in accordance with embodiments presented herein; 
         FIG. 6B  is a cross-sectional view of the osteoconductive implantable component of  FIG. 6A ; 
         FIG. 7  is a cross-sectional view of an osteoconductive implantable component in accordance with embodiments presented herein; 
         FIG. 8  is an enlarged view of a portion of an osteoconductive implantable component in accordance with embodiments presented herein; 
         FIG. 9A  is a side view of an osteoconductive implantable component in accordance with embodiments presented herein secured to a recipient with a bonding agent; 
         FIG. 9B  is a lower-perspective view of the osteoconductive implantable component of  FIG. 9A ; 
         FIG. 10A  is a lower-perspective view of an osteoconductive implantable component in accordance with embodiments presented herein; 
         FIG. 10B  is a bottom view of an osteoconductive implantable component in accordance with embodiments presented herein; 
         FIG. 11A  is a bottom view of an osteoconductive implantable component in accordance with embodiments presented herein; 
         FIG. 11B  is a bottom view of an osteoconductive implantable component in accordance with embodiments presented herein; and 
         FIG. 12  is a side view of an osteoconductive implantable component in accordance with embodiments presented herein. 
     
    
    
     DETAILED DESCRIPTION 
     In certain circumstances, a bone conduction device may be coupled to a recipient using a percutaneous solution wherein a percutaneous abutment extends from an implantable component attached to the recipient&#39;s skull bone via one or more bone screws. The percutaneous bone conduction device mechanically attaches to a portion of the abutment that is disposed outside of the recipient&#39;s skin. In other circumstances, a bone conduction device may be coupled to a recipient using a variety of transcutaneous solutions. For example, a transcutaneous bone conduction (or a portion thereof) may include a magnetic plate that magnetically couples to a magnetic implantable component attached to a recipient&#39;s skull via one or more bone screws. Transcutaneous bone conduction devices may include active or passive implant components. 
     A wide range of individuals may be candidates for bone conduction devices. In certain circumstances, individuals may have skull bones that are thinner than the skull bone of an average bone conduction recipient. The thinness of the skull may be due to, for example, age (i.e., young children naturally have thinner skull bones that adults) or as a result of trauma or a medical condition (e.g., cancer, etc.). In certain individuals, the skull bone may be also or alternatively compromised as a result of trauma or medical condition. Thin or compromised skull bones may affect the ability to attach an implantable component to a recipient&#39;s skull, thereby limiting the candidates who may receive certain bone conduction devices. 
     Embodiments of the present invention are generally directed to an osteoconductive implantable component for use in coupling a bone conduction device to a recipient. The implantable component is configured to be implanted adjacent to a recipient&#39;s bone and is configured to promote bone ingrowth and/or ongrowth to interlock the implantable component with the recipient&#39;s bone so as to prevent movement of the implantable component with respect to the recipient&#39;s skull. In certain circumstances, the osteoconductive implantable component eliminates the need for bone screws and/or enables use shorter bone screws (relative to traditional arrangements) so as to be suitable for use in individuals with thin or compromised skull bones. 
       FIG. 1  is a cross-sectional view of an osteoconductive implantable component  100  in accordance with embodiments presented herein. The osteoconductive implantable component  100  is configured to couple a percutaneous bone conduction device  102  to a recipient. 
     The percutaneous bone conduction device  102  comprises a housing  104  and a sound input element  106 . The sound input element  106  may be, for example, a microphone, telecoil or similar device configured to receive (detect) sounds. In the present example, sound input element  106  is located on housing  104 , but may alternatively be positioned on a cable extending from bone conduction, positioned in a recipient&#39;s ear, subcutaneously implanted in the recipient, etc. Sound input element  106  may also be a component that receives an electronic signal indicative of sound, such as, for example, from an external audio device. For example, sound input element  106  may receive a sound signal in the form of an electrical signal from a device electronically connected to sound input element  106 . Additionally, multiple sound input elements  106  may be provided. 
     Bone conduction device  102  comprises a sound processor  108 , a transducer (actuator)  110 , and/or various other operational components (not shown in  FIG. 1 ) all disposed in housing  104 . A portion of the housing  104  has been omitted from  FIG. 1  to illustrate portions of the sound processor  108  and the transducer  110 . 
     In operation, sound input element  106  converts received sound signals into electrical signals. These electrical signals are processed by the sound processor  108  to generate control signals that cause vibration of transducer  110 . In other words, the transducer  110  converts the electrical signals received from the sound processor  108  into mechanical vibrations. The transducer  110  may be, for example, an electromagnetic transducer, piezoelectric transducer, etc. 
     As shown, the osteoconductive implantable component  100  comprises a body  112  that primarily has an osteoconductive structure. As used herein, an osteoconductive structure is a structure that promotes the growth of a recipient&#39;s bony tissue into the structure, referred to as bone ingrowth, so as to interlock the structure with the bony tissue. In addition to bone ingrowth, an osteoconductive structure may also be configured to promote bone ongrowth. In the specific embodiment of  FIG. 1 , the osteoconductive body  112  is a porous mesh or scaffold that allows for vascular and cellular migration, attachment, and distribution through the exterior pores. 
       FIG. 1  illustrates an example in which the osteoconductive body  112  has a plurality of pores  130  and a generally trabecular (bone-like) structure. That is, body  112  is a porous-solid scaffold comprising an irregular three-dimensional array of struts. The term “strut” refers to the structural members (e.g., rods, beams, plates, shells columns, etc.) within a porous-solid material. In other words, the term strut is a general term to refer to the actual material elements (i.e., non-air portions) that form the porous-solid body. The array of struts is considered to be “irregular” because the struts and pores  130  are not arranged in any systematic manner. 
     The body  112  has a first surface  114  that is configured to be positioned abutting the recipient&#39;s skull bone and a second surface  116  substantially parallel to the first surface  114 . The first surface  114  is separated from the second surface by a lateral surface  118 . A threaded aperture  117  extends from the first surface  114  into the body  112 . The threaded aperture  117  is configured to receive a threaded abutment  120 . The body  112  is positioned below the recipient&#39;s skin  132  (e.g., adjacent to fat  128  and/or muscle  134 ). However, the abutment  120  extends from the body  112  through the skin  132 . That is, the abutment  120  is a percutaneous element. 
     Bone conduction device  102  further includes coupling apparatus (coupler)  140  that is configured to attach 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  140 , abutment  120 , and the osteoconductive implantable component  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 sensation. As such, the osteoconductive implantable component  100  interlocks so as to be substantially rigidly attached to the recipient&#39;s skull bone  136  and to prevent movement of the implantable component  100  with respect to the recipient&#39;s skull  136 . This rigid attachment enables the implantable component  100  to support bone conduction device  100  (when attached to the abutment  120 ) and enables the transfer of the vibrations from the abutment  120  to the skull bone  136 . 
       FIG. 2  is a cross-sectional view of another osteoconductive implantable component  200  configured to couple a transcutaneous bone conduction device  202  to a recipient. Similar to the embodiment of  FIG. 1 , the transcutaneous bone conduction device  202  comprises a housing  204  and a sound input element  206 . In the present example, sound input element  206  is located on housing  204 . 
     Bone conduction device  202  comprises a sound processor  208 , a transducer (actuator)  210 , an external plate  246 , and/or various other operational components (not shown in  FIG. 2 ) all disposed in housing  204 . A portion of the housing  204  has been omitted from  FIG. 2  to illustrate portions of the sound processor  208 , the transducer, and the plate  246 . 
     As shown, the osteoconductive implantable component  202  comprises a body  212  that primarily has an osteoconductive structure. Similar to the embodiments of  FIG. 1 , the body  212  is porous-solid scaffold comprising an irregular three-dimensional array of struts that allows for vascular and cellular migration, attachment, and distribution through the exterior pores  230 . The body  212  has a first surface  214  that is configured to be positioned abutting the recipient&#39;s skull bone and a second surface  216  substantially parallel to the first surface  214 . The second surface  216  is separated from the first surface by a lateral surface  218 . The body  212  is positioned below the recipient&#39;s skin  132  (e.g., adjacent to fat  128  and/or muscle  134 ). Disposed in the body  212  between the first surface  214  and the second surface  216  is an implantable plate  222 . Implantable plate  222  may be a permanent magnet or include magnetic material that generates and/or is reactive to a magnetic field. 
     External plate  246  disposed in bone conduction device  202  may be in the form of a permanent magnet and/or in another form that generates and/or is reactive to a magnetic field. More specifically, the external plate  246  is configured to generate or otherwise establish a magnetic attraction with the implantable plate  222  that is sufficient to hold the bone conduction device  202  against the skin  132  of the recipient. 
     In accordance with certain embodiments presented herein, the implantable plate  222  may disposed at the top surface  216  of the body  212 . Additionally or alternatively, the osteoconductive features (e.g., pores  230 ) may be disposed at the top surface  216  of the body  212 . 
     In operation, sound input element  206  converts received sound signals into electrical signals. These electrical signals are processed by the sound processor  208  to generate control signals that cause vibration of transducer  210 . In other words, the transducer  210  converts the electrical signals received from the sound processor  208  into mechanical vibrations. The transducer  210  is mechanical coupled to the external plate  246 , while the external plate  246  is magnetically coupled to the implantable plate  222 . As such, the vibrations generated by transducer  210  are transferred from the transducer  210  to the external plate  246  and then are transcutaneously transferred across the skin  132  to the implantable plate  222 . The transcutaneous transfer may be accomplished as a result of mechanical conduction of the vibrations through the skin  132 , resulting from the bone conduction device  202  being in direct contact with the skin, and/or from the magnetic field between the external plate  246  and the implantable plate  222 . As such, these vibrations are transferred without penetrating the skin with a solid object such as an abutment as detailed above with respect to a percutaneous bone conduction device. 
     In the embodiment of  FIG. 2 , the osteoconductive implantable component  200  interlocks with the recipient&#39;s bone (via ingrowth and/or ongrowth) so as to be substantially rigidly attached to the recipient&#39;s skull bone  136  and to prevent movement of the implantable component  200  with respect to the recipient&#39;s skull  136 . This rigid attachment enables the implantable component  200  to support bone conduction device  100  (when magnetically attached) and enables the transfer of the vibrations to the skull bone  136 . 
     As described above with reference to  FIGS. 1 and 2 , embodiments presented herein are directed to osteoconductive implantable components for use with percutaneous or transcutaneous bone conduction devices. In general, osteoconductive implantable components for use with percutaneous bone conduction devices include a threaded aperture or other mechanism for attachment to a percutaneous abutment. Osteoconductive implantable components for use with transcutaneous bone conduction devices generally include a magnetic implantable plate for magnetic coupling to an external magnetic plate. Merely for ease of illustration, embodiments of the present invention will be primarily described with reference to osteoconductive implantable components having a threaded aperture for use with a percutaneous abutment. It is to be appreciated that the various embodiments presented herein may be modified for use in different percutaneous arrangements (i.e., different abutment attachment mechanisms) or in transcutaneous arrangements (i.e., to include an implantable magnetic plate for coupling to an external magnetic plate). 
       FIGS. 3A and 3B  are lower-perspective and upper-perspective views, respectively, of an osteoconductive implantable component  300  in accordance with embodiments presented herein.  FIG. 3C  is a cross-sectional view of the osteoconductive implantable component  300 . 
     As shown, the osteoconductive implantable component  300  comprises a body  312  formed by a first (bottom) surface  314 , a second (top) surface  316 , and a lateral (side) surface  318  connecting the bottom surface  314  to the top surface  316 . As used herein, a “bottom” surface refers to a surface of an implantable component that is configured to be implanted facing a recipient&#39;s skull bone, while a “top” surface refers to a surface configured to be implanted facing a recipient&#39;s skin. 
     The body  312  of  FIGS. 3A and 3B  has a generally rectangular shape where the lateral surface  318  generally has four sides connected by rounded corners. The generally rectangular shape of body  312  is merely illustrative and other shapes are possible. For example, in alternative embodiments the body  312  may have a flat-circular (disc) shape. 
     Returning to the embodiments of  FIGS. 3A-3C , each of the lateral surface  318  and the bottom surface  314  has a plurality of apertures or pores  330  disposed therein. The pores  330  are the inlets for channels/tunnels  332 A,  332 B, and  332 C ( FIG. 3C ) that extend (partially or fully) through the main portion of body. As such, the body  312  is a porous-solid scaffold comprising a regular three-dimensional array of struts. The array of struts is considered to “regular” because the struts, pores  330 , and channels  332 A,  332 B, and  332 C, are arranged in a systematic manner (i.e., an organized structure). 
     Reference numbers  332 A in  FIG. 3C  refer to channels that extend through the body  312  between surfaces of the lateral surface  318  in a first direction and are referred to as transverse channels. Reference numbers  332 B refer to channels that extend through the body  312  between surfaces of the lateral surface  318  in a second direction that is substantially orthogonal to the first direction. For ease of illustration, the channels  332 B are shown using dashed lines and are referred to as longitudinal channels  332 B. Additionally, reference numbers  332 C refer to channels that extend from the bottom surface  314  through a portion of the body  312  in a directional that is orthogonal to both the transverse channels  332 A and the longitudinal channels  332 B. This third set of channels  332 C are sometimes referred to herein as vertical channels  332 C. 
     In the mesh structure of  FIGS. 3A-3C , certain transverse channels  332 A intersect with certain longitudinal channels  332 B and vertical channels  332 C. In alternative embodiments, the transverse channels  332 A, longitudinal channels  332 B, and vertical channels  332 C may be configured such that channels do not intersect one another. It is to be appreciated that these arrangements of channels  332 A,  332 B, and  332 C are merely illustrative and that other arrangements are possible. For example, in certain embodiments, the osteoconductive features (e.g., pores  330 ) may be disposed at the top surface  316  of the body  212 . 
     The body  312  includes a substantially solid central region  334  (i.e., a region that does not include any channels  332 A,  332 B, or  332 C). Extending from top surface  316  into this central region  334  is a threaded aperture  317  that is configured to receive and mate with a threaded abutment. Integrated with surface  316  above the central region  334  is a generally frustoconical member  336  having an opening  338  therein in which a portion of a threaded abutment may be disposed. 
     The body  312  may be made from, for example, titanium or a titanium alloy. In certain embodiments, the pores  330  may have diameters in the arrange of approximately 0.2 millimeters (mm) to approximately 0.8 mm and the supporting titanium structure (i.e., struts) may have a thickness between approximately 0.1 mm to approximately 0.9 mm. The pores  330  and channels  332 A,  332 B, or  332 C may be formed by, for example, milling, drilling, turning, Electro Beam Melting, laser processing, or a similar production process. 
     In certain embodiments, one or more surfaces  314 ,  316 , and/or  318  of body  312  may have a surface roughness configured to further promote bone ongrowth. For example, the surfaces of body  314 ,  316 , and/or  318  may have a medium arithmetic roughness (Ra) between approximately 0.9 μm to approximately 2 μm. The surfaces  314 ,  316 , and/or  318  can also have a course Ra from approximately 1.6 μm to approximately 25 μm. The surfaces  314 ,  316 , and/or  318  may be roughened via grit blasting, plasma-spraying, acid etching, laser modified, combinations thereof, or similar processes. 
     In the embodiments of  FIGS. 3A-3C , the osteoconductive implantable component  300  is attached to the bone through the bone ingrowth and/or bone ongrowth promoted by the structure of body  312 . In general, the porous-solid structure of body  312  allows for vascular and cellular migration, attachment, and distribution through the exterior pores  330  into the body  312 , thereby interlocking the osteoconductive implantable component  300  with the recipient&#39;s skull bone. This interlocking provides for long-term, substantially rigid attachment to the recipient&#39;s skull bone that is sufficient to support a bone conduction device and to transfer vibration received from the bone conduction device to the recipient&#39;s skull bone. 
     Sufficient osteoconduction to interlock the osteoconductive implantable component  300  with the recipient&#39;s skull bone to support a bone conduction device and to transfer vibration may take some time after the initial surgery (e.g., several weeks or months). In certain embodiments, the recipient&#39;s tissue (e.g., skin, fat, and/or muscle) retains the osteoconductive implantable component  300  in position relative to the skull bone to enable the osteoconduction. However, in accordance with certain embodiments presented herein, a secondary attachment mechanism may be provided to retain the osteoconductive implantable component  300  in position relative to the skull bone to facilitate the osteoconduction. 
     For example,  FIG. 4  is a side view of an embodiment in which a bonding agent  450  is used to initially secure osteoconductive implantable component  300  to a recipient&#39;s skull bone  136 . In the embodiment of  FIG. 4 , the bonding agent  450  is disposed on the bottom surface  314  between the pores  330 . That is, the bonding agent  450  is disposed on the surface such that it does not interfere with the osteoconduction. In certain embodiments, the bonding agent  450  is bone cement. The bone cement may be, for example, ionomeric bone cement or poly methyl methacrylate (PMMA) bone cement. In other embodiments, the bonding agent  450  may be any biocompatible adhesive now known or later developed. In certain embodiments, the bonding agent  450  may be configured to be resorbed by the recipient&#39;s bone after fibrotic encapsulation that may occur during osteoconduction. 
       FIGS. 5A and 5B  are perspective and cross-sectional views, respectively, of an osteoconductive implantable component  500  that is similar to the osteoconductive implantable component  300  of  FIGS. 3A-3C . In particular, the osteoconductive implantable component  500  comprises a body  312  formed by a bottom surface  314 , a top surface  316 , and a lateral surface  318  connecting the bottom surface  314  to the top surface  316 . The lateral surface  318  and the bottom surface  314  have a plurality of pores  330  disposed therein that form inlets of channels/tunnels  33 A,  332 B, and  332 C that extend (partially or fully) through the main portion of body  312 . In other words, the body  312  is a porous-solid scaffold. 
     In the embodiment of  FIGS. 5A and 5B , the osteoconductive implantable component  500  also comprises an attachment member  552  extending from a surface of lateral surface  318 . As shown, the attachment member  552  includes an aperture (through-hole)  554  that extends there through. The aperture  554  is configured such that a bone screw  556  may be inserted therein to secure the osteoconductive implantable component  500  to the recipient&#39;s skull bone during osteoconduction. For ease of illustration, the bone screw  556  has been omitted from  FIG. 5B . 
     As noted above, the porous-solid structure of body  312  allows for vascular and cellular migration, attachment, and distribution through the exterior pores  330  into the body  312 , thereby interlocking the osteoconductive implantable component  300  with the recipient&#39;s skull bone. This interlocking provides for long-term, substantially rigid attachment to the recipient&#39;s skull bone that is sufficient to support a bone conduction device and to transfer vibration received from the bone conduction device to the recipient&#39;s skull bone. The bone screw  556  is only used to retain the osteoconductive implantable component  500  in position during osteoconduction, but is not required to secure the osteoconductive implantable component  500  when supporting a bone conduction device. As such, the bone screw  556  may be shorter than bone screws used in conventional arrangements and, accordingly, may be used in recipient&#39;s having thin or compromised skull bones. In certain examples, the bone screw  556  may extend in a recipient&#39;s skull less than 2 mm 
       FIGS. 6A and 6B  are perspective and cross-sectional views, respectively, of an osteoconductive implantable component  600  that is similar to the osteoconductive implantable component  300  of  FIGS. 3A-3C . In particular, the osteoconductive implantable component  600  comprises a body  312  formed by a bottom surface  314 , a top surface  316 , and a lateral surface  318  connecting the bottom surface  314  to the top surface  316 . The lateral surface  318  and the bottom surface  314  have a plurality of pores  330  disposed therein that form inlets of channels/tunnels  332 A,  332 B, and  332 C that extend (partially or fully) through the main portion of body  312 . In other words, the body  312  is a porous-solid scaffold. 
     In the embodiment of  FIGS. 6A and 6B , the osteoconductive implantable component  600  also comprises two apertures (through-holes)  654 A and  654 B extending from the top surface  316  to bottom surface  314  (i.e., extending through the body  312 ). The apertures  654 A and  654 B are configured such that bone screws  656 A and  656 B may be inserted in to the apertures  654 A and  654 B, respectively, to secure the osteoconductive implantable component  600  to the recipient&#39;s skull bone during osteoconduction. For ease of illustration, the bone screws  656 A and  656 B have been omitted from  FIG. 6B . 
     As noted above, the porous-solid structure of body  312  allows for vascular and cellular migration, attachment, and distribution through the exterior pores  330  into the body  312 , thereby interlocking the osteoconductive implantable component  600  with the recipient&#39;s skull bone. This interlocking provides for long-term, substantially rigid attachment to the recipient&#39;s skull bone that is sufficient to support a bone conduction device and to transfer vibration received from the bone conduction device to the recipient&#39;s skull bone. The bone screws  656 A and  656 B may only be used to retain the osteoconductive implantable component  600  in position during osteoconduction and/or to secure the osteoconductive implantable component  600  when supporting a bone conduction device. Due to the osseoconductive nature of the implantable component  600 , the bone screws  656 A and  656 B may be shorter than bone screws used in conventional arrangements and, accordingly, may be used in recipient&#39;s having thin or compromised skull bones. In certain examples, the bone screws  656 A and  656 B may each extend in a recipient&#39;s skull less than 2 mm 
       FIG. 7  is a cross-sectional view of osteoconductive implantable component  300  in an embodiment in which a coating or surface treatment  760  is applied to the osteoconductive implantable component  300 . The surface treatment  760  is configured to provide the osteoconductive implantable component  300  with a modified surface that promotes faster and stronger bone formation, better stability during the healing process and improved performance in circumstances with poor bone quality and quantity. In one specific such example, the surface treatment  760  to is a Hydroxyapatite (HA) or similar coating  760  with a thickness in range of approximately 5 nanometers (nm) to approximately 20 μm. In certain embodiments the HA coating may be resorbable. 
     In further embodiments, the surface treatment  760  is an osteoinductive biomaterial that is configured to actively stimulate new bone growth. In one such embodiment, the osteoinductive surface treatment  760  comprises bone morphogenetic proteins (BMPs). An implantable component that is osteoconductive (provided by body  312 ) and osteoinductive (provided by surface treatment  760 ) may serve as a scaffold for currently existing osteoblasts, but may also trigger the formation of new osteoblasts, promoting faster integration of the implantable component  300  with the recipient&#39;s skull bone. 
       FIGS. 3A-7  illustrate embodiments in which the bodies of osteoconductive implantable component have a regular three-dimensional array of struts. That is, the pores and channels in  FIGS. 3A-7  are arranged in a systematic manner.  FIG. 8  illustrates an alternative embodiment in which an implantable component has a trabecular (bone-like) structure. More specifically,  FIG. 8  illustrates an enlarged view of a portion  825  of a body of an implantable component configured to be implanted adjacent to a recipient&#39;s bone and is configured to promote bone ingrowth and/or ongrowth to interlock the implantable component with the recipient&#39;s bone. In the embodiments of  FIG. 8 , the portion  825 , as well as the remainder of the osteoconductive implantable component, is a porous-solid scaffold that comprises an irregular three-dimensional array of struts. Similar to the above embodiments, the irregular scaffold of  FIG. 8  allows for vascular and cellular migration, attachment, and distribution through the exterior pores into the scaffold. The porous solid scaffold  FIG. 8  may be formed, for example, from a solid titanium structure by chemical etching, photochemical blanking, electroforming, stamping, plasma etching, ultrasonic machining, water jet cutting, electrical discharge machining, electron beam machining, or similar process. 
       FIGS. 3A-8  primarily illustrates embodiments in which the body of an osteoconductive implantable component has a porous structure to facilitate bone ingrowth and/or ongrowth so as to interlock the implantable component with the recipient&#39;s skull bone. In the above embodiments, the bottom (i.e., bone-facing) surface has the same structure as the rest of the implantable component (i.e., generally porous). In alternative embodiments, the body and bottom surface of an osteoconductive implantable component may have different structures/arrangements.  FIGS. 9A-10D  illustrate embodiments in which a bottom surface may include one or more surface features. 
     For example,  FIGS. 9A and 9B  illustrate an embodiment in which the bottom surface of an osteoconductive implantable component  900  includes a plurality of surface features configured to promote osteoconduction, while the body of the implantable component is generally solid.  FIG. 9A  is a side view of the osteoconductive implantable component  900 , while  FIG. 9B  is a lower-perspective view of a portion of the bottom surface of the osteoconductive implantable component  900 . 
     As shown, the osteoconductive implantable component  900  comprises a body  912  formed by a bottom surface  914 , a top surface  916 , and a lateral surface  918  connecting the bottom surface  914  to the top surface  916 . The body  912  has a generally rectangular shape where the lateral surface  918  generally has four sides connected by rounded corners. The rectangular shape of body  912  is merely illustrative and other shapes are possible. 
     Extending from top surface  916  into the body  912  is a threaded aperture (not shown) that is configured to receive and mate with a threaded abutment. Integrated with surface  916  is a generally frustoconical member  936  having an opening (not shown) therein in which a portion of a threaded abutment may be disposed. 
     Extending from bottom surface  916  are a plurality of protrusions  966 . The protrusions  966  are each separated from one another and have tapered ends  967  configured to be positioned abutting a recipient&#39;s skull bone. The protrusions  966  also each include one or more transverse grooves  968  that extend substantially parallel to the bottom surface  914  of the body  912 . When implanted abutting a recipient&#39;s skull bone, the protrusions  966  are configured to promote bone growth in a direction that is substantially perpendicular to a surface the recipient&#39;s skull (i.e., between the protrusions  966 ) and in a direction substantially parallel (i.e., non-perpendicular) to the surface of the recipient&#39;s skull (i.e., into the grooves  968 ). As such, after a bone growth period, portions of one or more of the plurality of the protrusions  966  are disposed between the non-perpendicular bone growth and the surface of the recipient&#39;s skull. In general, the protrusions  966  encourage bone growth that interlocks the osteoconductive implantable component  900  with the recipient&#39;s bone so as to prevent movement of the implantable component with respect to the recipient&#39;s skull. 
     As shown in  FIG. 9B , the protrusions  966  are arranged into a plurality of rows. It is to be appreciated that the row arrangement of  FIG. 9B  is illustrative and that other arrangements for protrusions are possible. It also to be appreciated that the shapes of protrusions  966  of  FIGS. 9A-9B  are also illustrative and other shapes that promote interlocking of the bone with an implantable component are possible. 
     As noted, the body  912  of  FIGS. 9A and 9B  is generally solid. In further embodiments, osteoconductive surface features, such as protrusions  966 , may be used in combination with a porous-solid scaffold as described above with reference to  FIGS. 3A-8 . 
       FIGS. 10A ,  10 B,  11 A, and  11 B illustrate further surface features that may be formed at a bottom surface of an implantable component. In general, the surface features shown in  FIGS. 10A-10D  are configured to promote osseointegration of an implantable component with a recipient&#39;s skull bone. As used herein, osseointegration generally refers to the anchorage of an implantable component to a recipient&#39;s bone by the formation of bony tissue around portions of a component. Although osteoconduction and osseointegration are related, osseointegration does not necessarily include the growth of tissue into portions of an implantable component. 
       FIG. 10A  illustrates a lower-perspective view of a bottom surface  1014  of an osteoconductive implantable component  1000 . As shown, the osteoconductive implantable component  1000  comprises a body  1012  formed by a bottom surface  1014 , a top surface  1016 , and a lateral surface  1018  connecting the bottom surface  1014  to the top surface  1016 . The body  1012  has a generally flat-circular (disc) shape within a plurality of pores  1030 . 
     In the example of  FIG. 10A , a plurality of protrusions  1066  extend from the bottom surface  1014 . The protrusions of  FIG. 10  have a generally pyramidal shape. When implanted abutting a recipient&#39;s skull bone, the protrusions  1066  are configured to promote bone growth in a direction that is substantially perpendicular to a surface of the recipient&#39;s skull (i.e., between the protrusions  1066 ). As such, the recipient&#39;s skull bone grows around the protrusions  1066 . 
     As noted, the protrusions  1066  of  FIG. 10A  have a generally pyramidal shape. It is to be appreciated that the pyramidal shape of  FIG. 10A  is merely illustrative and that other shapes are possible. For example,  FIG. 10B  illustrates an arrangement in which a plurality of rounded or dome-shaped protrusions  1076  extend from a bottom surface  1015  of an implantable component. 
     It is to be appreciated that the protrusions shown in  FIGS. 10A and 10B  may be used in combination with a porous scaffold as described above with reference to  FIGS. 3A-8 . In certain such embodiments, a bottom surface may include both osteoconductive pores (as described above) and protrusions as describe above with reference to  FIGS. 10A-10B . 
       FIGS. 11A and 11B  illustrate further embodiments in which the surface features comprise a pattern of grooves disposed in a bottom surface of an implantable component. For ease of illustration,  FIGS. 11A and 11B  illustrate portions of bottom surfaces  1114 A and  1114 B, respectively of an implantable component. 
       FIG. 11A  illustrates a pattern  1170 A of intersecting linear grooves  1172 A (i.e., grooves formed as straight lines).  FIG. 11B  illustrates a pattern  1170 B of intersection curved grooves  1172 B (i.e., grooves formed as curved lines). The grooves  1172 A or  1172 B may have a depth in the range of approximately 50 μm to approximately 200 μm and a width in the range of approximately 70 μm to approximately 350 μm. The shape of the grooves  1172 A or  1172 B can be wedge shaped (with or without a bottom radius), u-shaped with a bottom radius and straight sides, etc. 
     In the embodiments of  FIGS. 11A and 11B , the grooves  1172 A and  1172 B, respectively, are configured to promote bone growth in a direction that is substantially perpendicular to a surface of the recipient&#39;s skull. As such, the recipient&#39;s skull bone grows around sections of the bottom surfaces  1114 A and  1114 B between grooves  1172 A and  1172 B, respectively. 
     In certain embodiments of  FIGS. 11A and 11B , one or more of the grooves  1172 A and/or  1172 B include portions that, when the implantable component is implanted, are substantially parallel to a surface of the recipient&#39;s skull to promote bone growth in a direction that is substantially parallel to the surface of the recipient&#39;s skull. In other embodiments, or more of the grooves  1172 A and/or  1172 B include portions that, when the implantable component is implanted, are positioned at an angle relative to a surface of the recipient&#39;s skull to promote bone growth at an angle relative to the surface of the recipient&#39;s skull. 
     It is to be appreciated that the grooves shown in  FIGS. 11A and 11B  may be used in combination with a porous scaffold as described above with reference to  FIGS. 3A-8 . In certain such embodiments, the bottom surfaces  1114 A and  1114 B may include both osteoconductive pores (as described above) and grooves as describe above with reference to  FIGS. 11A-11B . 
       FIG. 12  illustrates a further embodiment of an osteoconductive implantable component  1200  that includes grooves. As shown, the osteoconductive implantable component  1200  comprises a body  1212  formed by a bottom surface  1214 , a top surface  1216 , and a lateral surface  1218  connecting the bottom surface  1214  to the top surface  1216 . The body  1212  has a generally flat-circular (disc) shape. 
     In the embodiment of  FIG. 12 , a bone screw  1256  is integrated with body  1212  and extends from bottom surface  1214  and a plurality of grooves  1274  are formed into the bottom surface  1214  around the bone screw  1256 . Additionally, a plurality of grooves  1272  are disposed in the lateral surface  1218 . The grooves  1272  and  1274  may have a depth in the range of approximately 50 μm to approximately 200 μm and a width in the range of approximately 70 μm to approximately 350 μm. The shape of the grooves  1272  or  1272  can be wedge shaped (with or without a bottom radius), u-shaped with a bottom radius and straight sides, etc. The grooves  1272  and  1274  may have the same or different arrangements. 
     As shown in  FIG. 12 , a plurality of pores  1230  is disposed in the grooves  1272  into the body  1212 . Similar pores  1230  may be disposed in the grooves  1274 . The pores  1230  are inlets for channels (not shown) that extend (partially or fully) through the main portion of body  1212 . As such, body  1212  is a porous-solid scaffold comprising a regular three-dimensional array of struts that is configured to promote osteoconduction with a recipient&#39;s skull bone. In alternative embodiments, the pores  1230  may be disposed in the lateral surface  1218  and bottom surface  1214  at locations between grooves  1230 . 
     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.