Abstract:
An implantable device including a housing having a stud projecting percutaneously through an incision in the patient&#39;s skin. The stud defines a peripheral surface extending longitudinally inwardly from the stud outer end. The longitudinal peripheral surface is used as a substrate to carry a peripheral fibrous layer which extends longitudinally along the stud from its outer end adjacent to the skin incision to below the patient&#39;s epidermal and dermal skin layers for promoting laterally directed soft tissue ingrowth. The housing also defines a lateral shoulder surface oriented substantially perpendicular to the longitudinal peripheral surface. The shoulder surface also carries a porous layer conducive to promoting tissue ingrowth. The porous layers on the device allows tissue ingrowth into the interstices of both porous layers to form an enhanced infection resistant barrier while also providing improved device anchoring.

Description:
RELATED APPLICATIONS 
   This application claims the benefit of U.S. provisional application 60/462,265 filed Apr. 12, 2003. 

   FIELD OF THE INVENTION 
   This invention relates generally to medical devices intended to be surgically implanted in a patient&#39;s body. More particularly, the invention is directed to an implantable percutaneous device, and method of implantation, especially configured to promote soft tissue ingrowth for creating an infection resistant barrier and for anchoring the implanted device in place. 
   BACKGROUND OF THE INVENTION 
   It is generally known that a porous outer surface can be used on an implantable medical device to promote bone ingrowth to facilitate device anchoring. It has also been suggested that the application of a porous surface to a percutaneous implantable device can be helpful for promoting tissue ingrowth. For example, see European Patent Publication 0367354B1 published Sep. 5, 1990 entitled “A percutaneous implant”. It is also noted that so called “dacron cuffs” have been used to accommodate tissue ingrowth for anchoring percutaneous catheters. 
   SUMMARY OF THE INVENTION 
   The present invention is directed generally to medical devices and more particularly to a structural configuration and method of implantation for promoting tissue ingrowth around a percutaneously projecting portion, or stud, of the medical device so as to create an infection resistant barrier, provide effective anchoring and inhibit marsupialization (which reduces vascularization of the local tissue). 
   An implantable device in accordance with the invention includes a housing having a projecting stud defining an outer end and a peripheral surface extending longitudinally inwardly from said outer end. A longitudinally extending porous peripheral layer is formed on the peripheral surface characterized by a porosity conducive to promoting tissue ingrowth. When the device is implanted, the stud projects through a skin incision and places the porous peripheral layer adjacent to the skin surrounding the incision. The device is intended to be implanted so that the porous layer is oriented substantially perpendicular to the patent&#39;s skin plane adjacent to the incision site and extends longitudinally below the skin surface. 
   A porous layer in accordance with the invention is preferably formed by mounting a layer of fibrous material on the projecting stud of the implantable device housing. The fibrous layer is preferably fabricated from bio compatible metallic materials, such as titanium, nitinol, silver, or stainless steel, or from polymeric materials, such as polyolefins, Teflon, nylon, Dacron, or silicone. Fibers can be wound directly onto the housing stud or alternatively a separate structure (e.g., mesh or sintered polymeric or metallic material) can be fabricated and then attached to the stud using mechanical or adhesive techniques. To adequately promote soft tissue ingrowth, the resulting fibrous layer should preferably contain pore sizes on the order of 50 to 200 microns with a porosity of 60 to 95%. 
   A preferred implantable device in accordance with the invention includes a housing having a stud projecting percutaneously through an incision in the patient&#39;s skin. The stud defines a peripheral surface extending longitudinally inwardly from the stud outer end. The longitudinal peripheral surface is used as a substrate to carry the aforementioned fibrous layer. The peripheral fibrous layer is located so that when implanted, it extends to below the patient&#39;s epidermal and dermal skin layers for promoting laterally directed soft tissue ingrowth. 
   In accordance with the invention, the housing also defines a lateral shoulder surface oriented substantially perpendicular to the longitudinal peripheral surface. The shoulder surface, when implanted, is located just inwardly from the patient&#39;s outer skin surface. The shoulder surface also carries a porous layer conducive to promoting tissue ingrowth. The provision of both lateral and longitudinal porous layers on the device allows tissue ingrowth, i.e., tissue growth into the interstices of both porous layers, to promote vascularization and form an enhanced infection resistant barrier while also providing improved device anchoring. 
   Moreover, it may sometimes be desirable to selectively incorporate appropriate substances into, or adjacent to, the porous layers for various medical reasons such as promoting tissue healing and infection resistance and inflammation. Such substances are known in the literature and include, e.g., antibiotics, silver compounds, and steroid based agents. 
   Embodiments of the invention can be advantageously used with a wide variety of medical devices adapted for percutaneous implantation. By way of example, such devices include implantable hearing aids which can percutaneously project into the ear canal and catheters, cables, and/or sensors which can project percutaneously to provide access to various internal sites, e.g., access to the abdominal cavity, to the inner eye, to the circulatory system, etc. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
       FIG. 1  schematically depicts an exemplary medical device (i.e., a hearing aid, percutaneously implanted in a patient&#39;s ear canal) which can advantageously utilize the teachings of the present invention; 
       FIG. 2  is an enlarged schematic representation showing a conventional medical device penetrating the epidermis and dermis skin layers shortly after implantation; 
       FIG. 3  is a schematic representation similar to  FIG. 2  showing skin downgrowth around the conventional medical device typically occurring after implantation; 
       FIG. 4  schematically shows part of a device housing having a portion, or stud, adapted to project percutaneously in accordance with the invention having longitudinally and laterally extending surfaces for respectively supporting porous layers; 
       FIG. 5  is a side sectional view of the device housing of  FIG. 4  also showing an optional end cap; 
       FIG. 6  is an enlarged schematic representation of a fibrous mesh which can form a porous layer in accordance with the invention; 
       FIG. 7  is similar to  FIG. 5  but additionally represents the inclusion of an optional supplemental agent for cooperating with the porous layer to promote tissue healing and/or resist infection and inflammation; 
       FIG. 8  is a schematic representation similar to  FIG. 3  but representing tissue ingrowth into the interstices of longitudinal and lateral porous layers in accordance with the present invention; 
       FIGS. 9A-9D  illustrate various configurations showing the use of a transitional surface installed on a housing stud to beneficially modify healing; 
       FIG. 10  schematically depicts the use of an invention embodiment in a vascular application where a catheter, cable, or sensor extends percutaneously through the patient&#39;s skin layers; 
       FIG. 11  schematically depicts the use of an invention embodiment in an ocular application for providing access to the inner eye via a percutaneous catheter, cable, or sensor; 
       FIG. 12  is an isometric view of one preferred embodiment of the invention intended for implanting adjacent to a patient&#39;s ear canal to promote hearing (as generally depicted in  FIG. 1 ); and 
       FIGS. 13A ,  13 B, and  13 C respectively show top, side, and end views of the device of  FIG. 12 . 
   

   DETAILED DESCRIPTION 
   Attention is initially directed to  FIG. 1  which schematically depicts an exemplary application of the teachings of the invention.  FIG. 1  represents a fragmentary front view of a patient&#39;s head  20  (i.e., as seen when looking at the patient&#39;s face) showing the patient&#39;s ear  22 , pinna  24  (sometimes referred to as “auricle”), and an ear canal  26 . The soft tissue space behind the pinna  24  is often referred to as the retro-auricular space or cavity  28 . 
     FIG. 1  also depicts a generic hearing aid  30  implanted within a recess  32  behind the patient&#39;s ear canal  26 . The recess  32  can be readily formed by a relatively simple surgical procedure involving for example, tunneling through the space  28 . The recess nominally extends from a proximal end  36  to a distal end  38  located at an incision site  40  opening into the ear canal  26 . The hearing aid  30  depicted in  FIG. 1  is comprised of a generally elongate, e.g., cylindrical, tubular housing  42  having a proximal end  44  and a distal end  46 . The housing  42  is preferably formed of a biocompatible material, e.g., titanium. 
   The tubular housing  42  typically contains electronic circuitry for driving a sound generator, i.e., an electroacoustic transducer (not shown) located within the housing proximate to the distal end  46 . The housing distal end, as shown in  FIG. 1 , preferably projects percutaneously through the incision site  40  into the ear canal  26  to locate the transducer in or immediately adjacent to the ear canal. 
     FIG. 2  schematically depicts the housing distal end  46  in greater detail generally showing the formation of the patient&#39;s skin layers  50  (i.e., dermis  54  and epidermis  56 ) adjacent to the incision site  40 , shortly after implantation of the housing  42 .  FIG. 3  schematically illustrates how, in a typical prior art implantation, the epidermis  56  and other tissue layers, over a period of time, can grow downwardly along the longitudinal surface  58  of the housing  42 . This tissue downgrowth, as depicted in  FIG. 3 , tends to produce sinus tracts  59 , susceptible for infection. Continued downgrowth can lead to marsupialization and ultimately can result in expulsion of the implant, e.g. hearing aid  30 , from the patient&#39;s body. 
   The present invention is directed primarily to means for creating an infection resistant barrier around the housing distal end  46  at the percutaneous penetration, i.e., incision, site  40  in order to effectively anchor the implanted device and avoid the aforementioned problems associated with tissue downgrowth. Briefly, the infection resistant barrier is formed by promoting tissue ingrowth into a porous layer(s) formed on orthogonal (longitudinal and lateral) surfaces of the housing  42 . 
   Attention is now directed to  FIGS. 4 and 5  which illustrate a preferred manner of configuring the housing distal end  46  in accordance with the present invention. As shown, the housing  42  includes a lateral shoulder  60  which forms a reduced diameter stud  62  extending longitudinally therefrom and terminating at outer end surface  64 . The stud  62  defines a longitudinally extending peripheral surface  66 . The peripheral surface  66  typically has a circular cross section but other cross sectional shapes, e.g., oval, hexagonal, etc. can be used. Moreover, although, the outer end surface  64  is shown as being flat, in certain applications, it is preferable that the end surface have a different profile, e.g., conical or spherical. 
   In accordance with the invention, a first porous layer, or surface,  70  is formed along a longitudinally extending portion of the peripheral surface  66 . The porous layer  70  is preferably formed by a mesh  72  of intersecting fibers  74  as depicted in  FIG. 6 . The fibers can be of any suitable biocompatible material such as a metal, e.g., titanium, nitinol, silver, or stainless steel or a polymeric material, e.g., polyolefins, Teflon, nylon, Dacron, or silicone. The mesh  72  is preferably formed by cross winding the fibers  74  in multiple layers to define a porosity conducive to promoting tissue ingrowth, e.g., with pore sizes within a range of 50 to 200 microns and having a porosity of 60 to 95%. The resulting porosity of the mesh  72  is a function of several factors including the diameter of the fibers  74  and the spacing between adjacent fibers. 
   The mesh  72  can be formed by directly winding the fibers  74  on the peripheral surface  66  acting as a substrate. Alternatively, the mesh  72  can be formed as an integral structure and then attached to the peripheral surface  66  by suitable mechanical or adhesive means. As an alternative to winding the fiber mesh  72 , a porous surface  70  can be formed by a sintered mass of metal or polymeric material having the aforementioned porosity characteristics. 
   In accordance with the invention, as seen in  FIG. 5 , a second porous layer, or surface,  80  is provided oriented substantially perpendicular to the longitudinally extending porous surface  70 . The porous layer  80  is formed on the laterally oriented surface  82  formed by shoulder  60 . The porous layer  80  is preferably formed by a disk  84  formed of porous material having a central aperture for passing stud  62 . The disk  84  can be adhered or mechanically attached to the lateral shoulder surface  82 . The disk  84  can be formed of a fiber mesh ( FIG. 6 ) or a sintered mass, as previously described, to provide porosity characteristics consistent with the previously mentioned porosity characteristics. 
     FIG. 8  illustrates the stud  62  percutaneously penetrating the patient&#39;s skin layers  50  and shows how the soft tissue grows into the orthogonal porous layers  70  and  80  to create a closed infection resistant barrier around the stud. The ingrowth into the porous layers  70  and  80  additionally promotes vascularization as the dermis grows into and entwines with the mesh. It is also pointed out that  FIG. 8  demonstrates the use of an optional cap  86  adapted to be mounted on the stud outer end for protection of the tissue around the incision during the healing process. 
   It is pointed out that it is sometimes desirable to include one or more substances on the stud  62  to promote tissue healing and/or resist infection and inflammation. Suitable substances are known in the literature and include, for example, antibiotics, silver compounds, and steroid based agents. Such substances can be deposited on the stud  62  as shown in  FIG. 7 , for example, as a sublayer  90  applied to the peripheral surface  66  beneath the porous layer  70 . Alternatively, the substances can be incorporated within the mesh or sintered material of the porous layers  70  and  80 . 
     FIG. 9A  depicts the device of  FIGS. 4 and 5  but further shows the utilization of a transitional layer, or surface,  92  mounted on the stud peripheral surface  66  between the peripheral porous surface  70  and the stud outer end  64 . The transitional surface  92  can have the same or a different porosity and/or composition as the porous surface  70  and can be variously configured as shown, for example, in  FIGS. 9B ,  9 C,  9 D. The transitional surface  92  is intended to beneficially modify the healing response of the adjacent tissue cells after implantation. 
   For convenience in explanation, the description thus far has mostly merely referred to a “stud” percutaneously projecting through the patient&#39;s skin layers. It should be understood that the term “stud” as used herein, is not intended to connote any particular structural configuration but rather to generically refer to any member percutaneously projecting from an orthogonal shoulder surface. In different applications, the stud can variously comprise a catheter, a cable, a sensor or other member which projects percutaneously from a lateral shoulder surface.  FIG. 10  depicts an exemplary application of the invention showing a catheter, cable, or sensor  94  which projects percutaneously for providing vascular access.  FIG. 11  depicts a further exemplary application where a catheter, cable, or sensor  96  projects percutaneously for providing access to the inner eye. 
   Attention is now directed to  FIGS. 12 and 13A ,  13 B,  13 C which depict a preferred embodiment  100  of the invention configured for use as a hearing aid in the manner schematically represented in  FIG. 1 . The embodiment  100  comprises a housing  102  having a body portion  103  and a stud portion  104 . The body  103  has a substantially rectangular (with rounded corners) cross-section ( FIG. 13A ) defined by short sides  105  and long sides  106 . The body extends longitudinally in a forward direction from a rear face  108  to a laterally oriented shoulder surface  110 . The stud  104  extends forwardly from the shoulder surface  110  and terminates at a stud outer face  114 . The body  103  houses electronic circuitry (not shown) for driving a sound generator, e.g., electroacoustic transducer (not shown), mounted in the stud proximate to the outer face  114 . It is intended that when implanted, the stud  104  will project percutaneously to place the stud face  114  in the patient&#39;s ear canal. 
   As previously described, in order to promote healthy tissue ingrowth for anchoring the housing  102  and forming a bacteria resistant barrier, a porous layer comprising a first portion of porous material  116  is formed on the longitudinally extending peripheral surface  118  of stud  104  and a second portion of porous material  120  is formed on the laterally extending shoulder surface  110 . 
   From the foregoing, it should now be appreciated that the application describes a method and apparatus for creating an enhanced infection resistant barrier around a percutaneously projecting member. Embodiments of the invention are useful in a wide variety of medical applications for creating an infection resistant barrier, for effective anchoring, and for avoiding the development of adverse conditions such as marsupialization. Although only a limited number of embodiments have been specifically described herein, it should be recognized that modifications, variations and other equivalent arrangements will occur to those skilled in the art coming within the spirit of the invention and the intended scope of the appended claims.