Abstract:
The present invention provides integration between an implant system and therapeutic agent delivery system. The implant may include a prosthesis that restores biomechanical function while decreasing long-term disability and pain by replacing damaged or degenerate tissues, or a reconstructive implant such as a bone plate. The therapeutic agent delivery system may include one or more channels either permanently or reversibly attached to the implant. The channels may receive medication from an external pump via a percutaneous catheter. The channels deliver the medication to one or more medicating surfaces of the implant to treating proximate tissues.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of the following: 
         [0002]    U.S. Provisional Application No. 60/763,069 filed Jan. 27, 2006, which is entitled THERAPEUTIC AGENT ELUDING IMPLANT WITH PERCUTANEOUS SUPPLY (Applicants&#39; Docket No. MLI-53 PROV). 
         [0003]    The foregoing is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0004]    1. The Field of the Invention 
         [0005]    The present invention relates generally to systems and methods for supplying therapeutic agents to the area surrounding medical implants through the integration of percutaneous delivery mechanisms with implant structures. 
         [0006]    2. The Relevant Technology 
         [0007]    Functional restoration of tissue structures is the primary objective of prosthesis applications. Primarily, prostheses successfully retain or replace function, although their application disrupts nearby tissues leading to pain, discomfort, and potentially infections. The current general (e.g., oral route) and local (e.g., regional pain pump) applications of therapeutic agents, such as analgesics and anesthetics, to treat the localized symptoms are known to have unwanted side effects or to ineffectively distribute the therapeutic agent locally around the prosthesis. 
         [0008]    Regional pain pumps are currently being used to treat post-surgical discomfort through the manual placement of a percutaneous catheter within the surgical site with or without the use of suture to secure the placement of the catheter tip. Placement of the catheter tip is crucial to the outcome of the treatment. Unfortunately, placement of the catheter tip is highly variable and very cumbersome for the surgeon. Accordingly, the pain medication may be ineffectively delivered, and the process of placing the catheter may add to the patient&#39;s discomfort and the length and complexity of the steps carried out by the surgeon. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. 
           [0010]      FIG. 1  is a perspective view of a therapeutic agent source, a percutaneous therapeutic agent delivery structure, a cutaneous interface, a therapeutic agent interface, and a channel delivery structure. 
           [0011]      FIG. 2A  is a cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , with one channel. 
           [0012]      FIG. 2B  is a cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , with two channels. 
           [0013]      FIG. 2C  is cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , together with a cannula positioned at an entry port. 
           [0014]      FIG. 2D  is cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , together with a cannula introduced into a enclosure. 
           [0015]      FIG. 3A  is cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , together with a balloon-tipped connector positioned at an entry port. 
           [0016]      FIG. 3B  is a cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , together with a balloon-tipped connector introduced into an enclosure, and the balloon partially inflated. 
           [0017]      FIG. 3C  is a cross-sectional view of an embodiment of the therapeutic agent inter face in  FIG. 1 , together with a balloon-tipped connector introduced into an enclosure, and the balloon fully inflated. 
           [0018]      FIG. 4A  is a cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , together with a screw-tipped connector. 
           [0019]      FIG. 4B  is a cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , together with a screw-tipped connector introduced into an enclosure. 
           [0020]      FIG. 5A  is a cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , together with a needle-tipped connector positioned at an entry port. 
           [0021]      FIG. 5B  is a cross-sectional view of an embodiment of the therapeutic agent interface in  FIG. 1 , together with a needle-tipped connector introduced into an enclosure. 
           [0022]      FIG. 6A  is a cross-sectional view of a segment of the prosthesis surface, with a circular channel affixed within a groove on the surface, wherein the centroid of the channel is positioned at the surface of the prosthesis. 
           [0023]      FIG. 6B  is a cross-sectional view of a segment of the prosthesis surface, with a circular channel affixed within a groove on the surface, wherein the centroid of the channel is positioned below the surface of the prosthesis. 
           [0024]      FIG. 6C  is a cross-sectional view of a segment of the surface of a prosthesis, with a circular channel affixed within a conduit below the surface. 
           [0025]      FIG. 6D  is a cross-sectional view of a segment of the surface of a prosthesis, with a rectangular channel cut into the surface. 
           [0026]      FIG. 6E  is a cross-sectional view of a segment of the surface of a prosthesis composed of two parts, with a circular channel below the surface. 
           [0027]      FIG. 6F  is a cross-sectional view from above of a segment of a prosthesis, with a channel between the upper and lower surfaces of the implant. 
           [0028]      FIG. 6G  is a cross-sectional view of a segment of the surface of a prosthesis with a semi-circular channel affixed to the surface. 
           [0029]      FIG. 6H  is a cross-sectional view of a segment of the surface of a prosthesis, with a circular channel below the surface. 
           [0030]      FIG. 6I  is a cross-sectional view of a segment of the surface of a prosthesis, with a rectangular channel cut into the surface and a layer of material over the conduit. 
           [0031]      FIG. 6J  is a perspective view of a femoral prosthesis of a knee implant, with subsurface channels according to  FIG. 6F . 
           [0032]      FIG. 7A  is a perspective view of a femoral prosthesis of a knee implant, with which a therapeutic agent delivery structure with channels is affixed via links. 
           [0033]      FIG. 7B  is a front elevation view of the femoral prosthesis shown in  FIG. 7A  in position on a patient&#39;s knee. A therapeutic agent delivery structure is affixed to the femoral prosthesis, and a therapeutic agent source, a percutaneous therapeutic agent delivery structure, a cutaneous interface, and therapeutic agent interface are connected to the therapeutic agent delivery structure. 
           [0034]      FIG. 8A  is a cross-sectional view of an embodiment of the link in  FIG. 7A , in which a barb-tipped link is positioned outside a chamber on the prosthesis surface to connect a channel to the chamber. 
           [0035]      FIG. 8B  is a cross-sectional view of an embodiment of the link in  FIG. 7A , in which a protrusion-tipped link is positioned outside the boundary between a bone and a prosthesis. 
           [0036]      FIG. 8D  is a cross-sectional view of an embodiment of the link in the  FIG. 7A , in which a protrusion-tipped link is positioned outside an irregularly-edged boundary between a bone and a prosthesis. 
           [0037]      FIG. 8E  is a cross-sectional view of an embodiment of the link in  FIG. 7A , in protrusion-tipped link is positioned outside a chamber on the prosthesis surface. 
           [0038]      FIG. 9  is a side elevation view of a knee prosthesis including a therapeutic agent delivery structure. 
           [0039]      FIG. 10  is a perspective view of a posterior fusion system including a therapeutic agent delivery structure. 
           [0040]      FIG. 11  is a perspective view of an elbow prosthesis including a therapeutic agent delivery structure. 
           [0041]      FIG. 12A  is a superior perspective view of a breast prosthesis including a therapeutic agent delivery structure. 
           [0042]      FIG. 12B  is a posterior perspective view of the breast prosthesis of  FIG. 12A . 
           [0043]      FIG. 13  is a perspective view of a hip prosthesis including a therapeutic agent delivery structure. 
           [0044]      FIG. 14A  is a perspective view of a bone plate including a therapeutic agent delivery structure. 
           [0045]      FIG. 14B  is a perspective view of an alternative embodiment of a bone plate including a therapeutic agent delivery structure. 
           [0046]      FIG. 15  is a perspective view of a shoulder prosthesis including a therapeutic agent delivery structure. 
           [0047]      FIG. 16  is a perspective view of an intervertebral disk implant including a therapeutic agent delivery structure. 
           [0048]      FIG. 17  is a perspective view of a calf implant including a therapeutic agent delivery structure. 
           [0049]      FIG. 18  is a perspective view of a wrist prosthesis including a therapeutic agent delivery structure. 
           [0050]      FIG. 19  is a side elevation view of a cochlear implant including a therapeutic agent delivery structure. 
           [0051]      FIG. 20  is a perspective view of an external fixation device fastened in a bone of a patient and including a therapeutic agent delivery structure. 
           [0052]      FIG. 21  is a perspective view of an intervertebral body fusion prosthesis including a therapeutic agent delivery structure. 
           [0053]      FIG. 22  is a side elevation view of a temporo-mandibular joint prosthesis including therapeutic agent delivery structure. 
           [0054]      FIG. 23  is a perspective view of a chin prosthesis including a therapeutic agent delivery structure. 
           [0055]      FIG. 24  is a perspective view of an ankle prosthesis including a therapeutic agent delivery structure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0056]    The present invention provides various configurations of a system in which a therapeutic agent source is connected to a therapeutic agent interface, which in turn is permanently or reversibly connected to one or more channels positioned on or embedded in implant surfaces. Therapeutic agents may be carried from the therapeutic agent source, through the interface, and through the channels to one or more locations on medicating surfaces of the implant. The channels may communicate with a plurality of openings of various diameters through which the therapeutic agents flow and come in contact with the bodily tissues surrounding the implant. With the system installed, a controlled measured flow of a therapeutic agent can pass directly from the channels of the implant to the surrounding bodily tissues, thereby accurately treating only the regional area of concern. 
         [0057]      FIG. 1  shows a perspective view of one embodiment of the invention. A therapeutic agent source  20  is connected to a conduit  22 , such as a catheter. The conduit  22  percutaneously passes into a patient&#39;s body through a cutaneous interface  24 , and connects to a therapeutic agent interface  40 . A local therapeutic agent delivery structure  60 , or structure  60 , also connects to the therapeutic agent interface  40 , and is adhered to, integrally formed with, or embedded in the body of an implant which has been implanted in a patient&#39;s body. In this embodiment, the implant takes the form of a prosthesis  50  configured to replace a bony structure, such as the femoral portion of a knee joint. 
         [0058]    The therapeutic agent delivery structure  60  has a channel  62  that originates at a first vend  64  connected to the therapeutic agent interface  40 . The channel  62  terminates at a second end  66  along a medicating surface  68  of the prosthesis  50 . The medicating surface  68  has, at various intervals, a plurality of openings  70 . With the prosthesis  50  in the implanted state, a therapeutic agent can pass from the therapeutic agent source  40 , percutaneously through the conduit  22 , through the cutaneous interface  24  to the therapeutic agent interface  40 . The therapeutic agent is conveyed into the structure  60 , along the channel  62 , and passes out the openings  70 . 
         [0059]    In this manner, a therapeutic agent selected by a medical practitioner, such as a chemical agent for alleviating pain, can be dispensed directly to the location of a prosthesis. Such treatment increases the effectiveness of the medication, decreases the potential for unwanted side effects, minimizes the likelihood of infection, and provides a simple medication pathway for any infections that do develop. Additionally, a system according to the present invention can be employed for dispensing other beneficial substances or effects to a prosthesis site. Such substances and effects may include anesthetic agents, analgesic agents, anti-inflammatory agents, anti-rejection agents, growth factors, antibiotics, anti-adhesion factors, saline, glycosaminoglycan varieties, collagen varieties, bio-nutrients, gene-delivery vehicles, stem cells, light, sound, electromagnetic energy, and/or any other therapeutic substance or effect that is desirable to be dispensed to the prosthesis site. 
         [0060]    Referring again to  FIG. 1 , the therapeutic agent source  20  is a mechanism, such as a “pain pump,” that creates a controlled pressure gradient between a therapeutic agent reservoir and a connecting body such as the conduit  22 . The conduit  22  may be branching or non-branching, and may be integrally formed with the channels  62 , or may be separate from and permanently or reversibly connectable to the channels  62 . The medicating surface  68  may be positioned to release the medication into an intra-articular space  26  between the articulating surfaces of the prosthesis  50  and those of an adjacent bone or prosthesis, or to soft tissues  28  proximate the implantation site. In other embodiments, other tissues proximate the implantation site, such as bone tissues, may receive the medication. 
         [0061]    Optionally, the conduit  22  and/or the channel  62  may include flow control valves and filters in series along their length. The tubing surface may be treated to increase biocompatibility (e.g., with fluorine or functional groups), block the clotting cascade (e.g., with heparin), provide antimicrobial properties (e.g., with silver), and/or minimize inflammation (e.g., with nitric oxide). 
         [0062]    The cutaneous interface  24  shown in  FIG. 1  may also be of multiple configurations. In one variation, there is direct contact between the patient dermis and the conduit  22 , and the dermis is sutured around the conduit  22  to form the cutaneous interface  24 . In other variations, the cutaneous interface  24  is formed by a polymer structure (not shown) that is congruent with patient dermis on its exterior and with one or more conduits  22  passing through the interior surfaces. In one alternative, a specified length of the conduit  22  is encapsulated by the polymer structure to create a congruent interface between the polymer structure and the conduit  22 . The dermis is sutured around the exterior surface of the polymer structure. 
         [0063]    In another alternative, two parallel conduits  22  of equal length are employed; both lengths may pass through the polymer structure to reach different implant channels, or different portions of a single implant channel. In yet another alternative, the cutaneous interface  24  is formed by a polymer structure that is congruent with the patient dermis on its exterior and with the conduit  22 , and with secondary tubing such as aspiration tubing or a power supply cord on the interior surface. Equal lengths of the conduit  22  and the secondary tubing are encapsulated by the polymer structure to create a congruent interface. The dermis is sutured around the exterior surface of the polymer structure. 
         [0064]    The therapeutic agent interface  40  may be constructed in a variety of designs and from varying materials.  FIGS. 2 through 5  illustrate some exemplary embodiments for the therapeutic agent interface  40 . Each of the embodiments of  FIGS. 2 through 5  may have an enclosure  402 , an entry port  404 , and one or more openings  406 . Any of the embodiments described may have one opening  406 , or multiple openings  406 , depending on the requirements of the specific application. These illustrations provide only examples and should not be considered to be restrictive of the scope of the invention. 
         [0065]      FIGS. 2A through 2E  depict various embodiments of the therapeutic agent interface  40 , in which the entry port  404  is covered with a reversibly attaching interface  430  and is needleless. An associated cannula  410 , which is on the terminus of the conduit  22 , can be inserted in the entry port  404  to permit unrestricted therapeutic agent flow between the conduit  22  and the therapeutic agent delivery structure  60 .  FIG. 2A  depicts a therapeutic agent interface  40  with an entry port  404  and one opening  406 . Any of the four cannulas  410  shown in  FIG. 2E  can be inserted in the entry port  404  to permit therapeutic agent flow into the enclosure  402 . The therapeutic agent then exits the therapeutic agent interface  40  through the opening  406 .  FIG. 2B  depicts a design identical to  FIG. 2A  except that two openings  406  are present, allowing for therapeutic agent to flow out of the enclosure  402  in two directions to enter the structure  60 , or more precisely, to enter two different channels  62 , or two different portions of a single channel  62 . 
         [0066]      FIG. 2C  illustrates a cannula  410  as, it is being inserted into the entry port  404 . The heart-shaped tip  414  penetrates the reversibly attaching interface  430 , which covers the entry port  404 .  FIG. 2D  illustrates the cannula  410  in place, post-insertion. Therapeutic agent can now flow freely from the therapeutic agent source  20 , through the conduit  22 , into the therapeutic agent interface  40  via the entry port  404 , and out of the therapeutic agent interface  40  through openings  406  into the structure  60 . The openings  406  may have different diameters to provide for a greater flow rate of medication to one channel  62 , or to one portion of a channel  62 . 
         [0067]      FIG. 2E  illustrates various designs for the tip of the cannula  410 . Designs include a triangular tip  412 , the heart-shaped tip  414 , a speherical tip  416 , and a semi-spherical tip  418 . These tip designs enhance repeated cannula insertion and removal from the reversibly attaching interface  430  of the entry port  404 , while minimizing accidental distraction of the conduit  22  from the therapeutic agent interface  40 . The designs pictured in  FIG. 2E  represent only some of the possible configurations of the cannula  410 ; other embodiments of the invention may include the alternative tip configurations. 
         [0068]    Referring to  FIGS. 3A ,  3 B, and  3 C, a balloon-tipped connector  420  is depicted in association with the therapeutic agent interface  40 . The enclosure  402  is depicted with a rounded internal cavity  422 , one entry port  404  and two openings  406 . In  FIG. 3A , the balloon-tipped connector  420  is shown prior to insertion into the entry port  404 .  FIG. 3B  depicts the balloon-tipped connector  420  inserted into the entry port  404 , with the balloon partially inflated. The balloon-tipped connector  420  may be filled with air or with a liquid, such as saline. 
         [0069]    The balloon is fully inflated in the  FIG. 3C . The round shape of the internal cavity  422  is congruent to the inflated balloon-tipped connector  420 , creating a sealed boundary to the entry port  404 . In this state therapeutic agent can flow freely from the conduit  22  (shown in  FIG. 1 ), through the balloon-tipped connector  420  into the enclosure  402 , and out of the openings  406 . The embodiment of the therapeutic agent interface  430  that permits selective withdrawal of the connector  420  from the internal cavity  422 . If a biocompatible liquid is used to fill the balloon of the connector  420 , the liquid may simply be released into the internal cavity  422  by rupturing the balloon. 
         [0070]    A screw-tipped connector  426  and therapeutic agent interfaces  40  are depicted in  FIGS. 4A and 4B .  FIG. 4A  depicts the empty enclosure  402  with an irregular cavity  424  and a reversibly attaching interface  430  on the entry port  404 . The geometry of the screw-tipped connector  426  is configured to mate with the irregular cavity  424  when the tip is inserted and rotated, as shown in  FIG. 4B . Once inserted, a sealed boundary to the entry port  404  is created, allowing therapeutic agent to flow freely from the conduit  22  (shown in  FIG. 1 ), through the screw-tipped connector  426  into the enclosure  402 , and out of the openings  406 . The screw-tipped connector  426  may be removed by rotating it in the opposite direction to permit withdrawal from the irregular cavity  424 . 
         [0071]      FIGS. 5A and 5B  depict a tubular shaped needle cannula  428  and a therapeutic agent interface  40 . In  FIG. 5A , the bevel-tipped needle cannula  428  is shown before insertion into the entry port  404 .  FIG. 5B  depicts the needle cannula  428  inserted into the reversibly attaching interface  430  on the entry port  404 . Thus connected, therapeutic agent can flow freely from the conduit (shown in  FIG. 1 ), through the needle cannula  428  into the enclosure  402 , and out of the openings  406 . Use of the needle cannula  428  facilitates repeated cannula insertion into and removal from the reversibly attaching interface  430 . 
         [0072]    The therapeutic agent delivery structure  60  depicted in  FIG. 1  can be constructed and configured in a variety of ways. The channels  62  and the openings  70  that comprise the therapeutic agent delivery structure  60  may be composed of the materials which make up the surface of the prosthesis, or may be composed partially or entirely of unlike materials. Furthermore, the structure  60  may be fully or partially embedded within the body of the prosthesis  50  and/or adhered to the surface of the prosthesis  50  via permanent or reversible attachment. 
         [0073]    The shape and number of the channel(s)  62  and the shape, number and location of the openings  70  may vary.  FIGS. 6A through 6I  are cross-sectional views of prosthesis surfaces illustrating possible configurations of the channel  62  and the openings  70  shown in  FIG. 1 . The variations illustrated in  FIGS. 6A through 6I  are considered to be illustrative and not restrictive of the scope of the invention. 
         [0074]      FIG. 6A  illustrates a circular channel  62  which is composed of a material  74  that may be the same as, similar to, or dissimilar to that of the prosthesis  50 . The channel  62  of  FIG. 6A  is partially embedded in the prosthesis  50 . The material  74  can either be permanently or reversibly attached using mechanical elements such as snaps, clips, threaded fasteners, and the like, or chemical elements such as biodegradable adhesives. A channel bore  72  is the open area in the channel  62  through which the therapeutic agent is conveyed. In the embodiment pictured in  FIG. 6A , the centroid  96  (indicated by dashed lines) of the channel bore  72  is substantially in-plane with a surface  52  of the prosthesis  50 . An opening  70  is shown passing through the material  74  from the channel bore  72  to the space outside the channel bore  72 . 
         [0075]    In the embodiment depicted in  FIG. 6B , a circular channel  62  is composed of a material  74  that may be the same as, similar to, or dissimilar to that of the prosthesis  50 . The channel  62  of  FIG. 6B  is partially embedded in a groove  58  on the surface  52  of prosthesis  50 . As in the embodiment of  FIG. 6A , the material  74  can either be permanently or reversibly attached using mechanical or chemical elements. In this embodiment, the centroid  96  of the channel bore  72  ties below the surface  52  of the prosthesis  50 . Because the centroid  96  of the channel bore  72  lies below the surface  52 , and the width of the channel  62  is wider than the a edges of the groove  58 , the material  74  can be pressed or snapped into the groove  58 , and the edges of the groove  58  will aid in retaining the channel  62 . An opening  70  is shown passing through the unlike material  74  from the channel bore  72  to the space outside the channel bore  72 . 
         [0076]    In the embodiment depicted in  FIG. 6C , a circular channel  62  is composed of a material  74  that may be the same as, similar to or dissimilar to that of the prosthesis  50 . The channel  63  of  FIG. 6C  is entirely embedded within the prosthesis  50 . The sides of the opening  70  are composed partially of the material  74  and partially of the material of which the prosthesis  50  is formed. The centroid  96  of the channel bore  72  lies within the prosthesis  50 . 
         [0077]      FIG. 6D  depicts a channel  62  of a generally rectangular shape, in which three sides of the channel  62  are entirely embedded in the prosthesis  50 . A material  74  forms the top side of the channel  62  of  FIG. 6D  and is flush with the surface  52  of the prosthesis  50 . An opening  70  opens out through the material  74 . As in previous embodiments, the material  74  may be the same as, similar to, or unlike that of the prosthesis  50 , and may be secured through the use of mechanical or chemical elements. 
         [0078]    A prosthesis  50  composed of two parts is illustrated in  FIG. 6F . A first part  54  has a first partial channel  76  created on a first joining surface  80 . A second part  56  has a second partial channel  78  on a second joining surface  82 , with an opening  70  passing through the prosthesis surface  52 . When the two parts  54 ,  56  are joined the complete channel  62  is formed between the joining surfaces  80 ,  82 . The channel  62  depicted in this embodiment is circular; however it could be square, rectangular or of any closed shape that can be formed by the joining of the two partial channels  76 ,  78 . 
         [0079]    An alternative channel and opening configuration is illustrated in  FIGS. 6F and 6J .  FIG. 6J  displays a perspective view of a femoral prosthesis  14  of a knee replacement system, with an outer edge  92  and an inner edge  94 . A channel such as that described in  FIG. 6A  is affixed to the outer edge  92 . The femoral prosthesis  14  has several parallel channels  84  which traverse the prosthesis, below the prosthesis surface by penetration of a drill bit through the prosthesis. Each channel  84  has a first end  86 , which is at an outer edge  92  of the femoral prosthesis  14 , and a second end  88  which opens at an inner edge  94  of the femoral prosthesis  14 . 
         [0080]      FIG. 6F  displays a cross section of a portion of the channel  84  at the second end  88 , as seen from above. The drill bit incompletely penetrates the outer edge  92 , so the second end  88  is smaller in diameter than the channel  84 . Returning to  FIG. 6J , the channel  62  has openings  70 , and exit connections  90  at the outer edge  92  where the channel  62  meets the first ends  86  of the channels  84 . When therapeutic agent flows into the channels  62 , it can flow out the openings  70 , and through the exit connections  90 , into the channels  84  and out the second ends  88 . This configuration of channels  62  and channels  84  allows therapeutic agents to reach the body tissues surrounding the inner edge  94  of the prosthesis as well as the outer edge  92 . The relatively small diameter of the second ends  88  may help to control the flow rate of the therapeutic agent from the second ends  88  relative to the flow rate through the openings  70 . 
         [0081]      FIG. 6G  depicts a semi-circular channel  62  lying on the prosthesis surface  52 . The channel  62  is composed of a material  74 , which may be the same as, similar to, or unlike that of the prosthesis  50 . The material  74  may be adhered to the prosthesis surface  52  through the use of mechanical or chemical elements. The openings  70  provide egress for the therapeutic agent through the unlike material  74 . 
         [0082]      FIG. 6H  depicts a circular channel  62  entirely embedded within the prosthesis  50 . The channel  62  and opening  70  are formed completely by the surrounding prosthesis  50 . Accordingly, no separate structure need be added to form the channel  62 . 
         [0083]      FIG. 6I  depicts a rectangular channel  62  created on the surface  52  of the prosthesis A layer of material  74  seals the top aspect of the channel  62 . The material  74  may be the same as, similar to, or unlike that of the prosthesis  50 . An opening  70  passes through the unlike material  74  to provide an exit path for the therapeutic agent. 
         [0084]      FIG. 7A  illustrates channels  62  which lie on or protrude from the surface of a femoral prosthesis  14 , such as the channel  62  illustrated in  FIG. 6A . A plurality of links  500  holds the channels  62  in place. Each link  500  may permanently or reversibly attach channels  62  and/or conduits  22  to the prosthesis  14 . Each link  500  may optionally be biodegradable, and may be formed of a polymer, metal, ceramic, composite, or any combination thereof. 
         [0085]      FIG. 7B  shows a similar femoral prosthesis  14  in place on a patient&#39;s femur, with a therapeutic agent flow structure  60  affixed to the femoral prosthesis. The structure  60  in this example is composed of two channels  62 , which extend from the therapeutic agent interface  40  and are held in place by links  500 .  FIGS. 8A through 8E  illustrate a variety of embodiments of the links  500 , which may provide permanent or removable attachment of the channels  62  to the prosthesis  14 , or to any other medical implant. 
         [0086]    In  FIG. 8A , a link  500  with a first end  502  and a second end  504  is depicted. The first end  502  terminates in two protruding curved fingers  506 , which form a gap  512  with a diameter sized to hold a channel  62 . The second end  504  terminates in a barbed tip  508  with two opposing barbs  510 . A prosthesis  50  with a chamber  550  is adjacent to the link  500 . The chamber  550  opens to the surface of the prosthesis  50  at an opening  552 , and two lips  554  extend partially across the opening  550 . When the link  500  is inserted through the opening  552  into the chamber  550 , the barbs  510  compress to fit through the lips  554 . Once inside the chamber  550 , the barbs  510  expand back to their original position and prevent the link  500  from coming out of the chamber  550 . Either prior to or after attachment of the links  500  to the prosthesis  50 , the channel  62  can be pressed into the gap  512  within the curved fingers  506 . 
         [0087]    A plurality of chambers  550  may be present in the prosthesis  50  to receive a plurality of links  500 , alternatively, the chamber  550  may be elongated, so as to form a groove in the prosthesis  50  to receive multiple links  500 . 
         [0088]    Advantageously, this embodiment permits the surgeon to decide, interoperatively, whether or not to implant the channel  62  with the prosthesis  50 . A plurality of channels  62  may be provided to the surgeon, and the surgeon may be able to select from them to optimize characteristics such as the volume of medication delivered, the exact distribution pattern of the medication, and the location at which medication will be delivered. As mentioned previously, the links  500  may be formed of a biodegradable material. Alternatively, the links  500  may be designed to remain in place permanently, or may be made frangible, for example, through the use of a necked-down cross section between the first and second ends  502 ,  504  to permit the first end  502  to be broken away when removal of the channel  62  is desired. Such variations may also be used with other link embodiments, such as those of  FIGS. 8B through 8E . 
         [0089]      FIG. 8B  illustrates a link  500  with a hooked tip  520  on the second end  504 . The hooked tip  520  terminates in a single hook  522 . The adjacent prosthesis  50  has a chamber  550  sized to hold the hooked tip  520 , and has a single lip  554 , which extends partially across an opening  552 . Prior to insertion into the opening  552 , the link  500  is oriented so the hook  522  is lined up with the lip  554 . As the link  500  is inserted through the opening  552 , the hook  522  compresses to slide past the lip  554 , and then expands back to its original position. Once the link  500  has been inserted, the hook  522  prevents the link  500  from coming out of the chamber  550 . Either prior to or after attachment of the links  500  to the prosthesis  50 , the channel  62  can be pressed into the gap  512  between the curved fingers  506 . 
         [0090]    The link  500  illustrated in  FIG. 8C  is particularly suitable for use when a prosthesis is cemented to a bone. For example, the link  500  of  FIG. 8C  may be advantageously used with an interbone prosthesis such as a knee, elbow or hip prosthesis. In this application, an “interbone” prosthesis is a prosthesis that operates at the junction of two bones to help facilitate, limit, or otherwise control relative motion between the bones. Thus, interbone prostheses include articulating joints, and also include joints connected by flexible soft tissues without articulating surfaces. An interbone prosthesis may include a prosthesis for each of the adjoining bone structures, or may include only a single prosthesis for one bone of the joint. 
         [0091]    Returning to  FIG. 8C , the link  500  is shown adjacent to a prosthesis  50 , which is being attached to a prepared bone  560 . A layer of cement  562  fills a separation  564  between the bone  560  and the prosthesis  50 . The link  500  has a second end  504  with a tip  530 . A plurality of protrusions  532  encircles the tip  530 . These protrusions may be helical protrusions such as common threads or concentric protrusions such as ribs. The protrusions create additional surface area on the outside of the tip  530 . When the link  500  is pushed into the separation  564 , the cement  562  surrounds the ribbed tip  530  and fills in the spaces between the protrusions  532 . When the cement  562  is cured, the link  500  is permanently affixed between the prosthesis  50  and the bone  560 . Either prior to or after attachment of the links  500  to the prosthesis  50 , the channel  62  can be pressed into the gap  512  between the curved fingers  506 . 
         [0092]    The link  500  illustrated in  FIG. 8D  is similar to the link  500  in  8 C. However, in this embodiment, the separation  564  between the prosthesis  50  and the prepared bone  560  has helical or concentric edges  566  which are designed to mate with the protrusions  532  on the tip  530 . The helical or concentric edges  566  may be tapped so as to mate with helical protrusions, or ribbed to mate with concentric protrusions. When the prosthesis  50  is cemented to the prepared bone  560  with the link  500  in place, the helical or concentric edges  566  will mate with the protrusions  532 , making the attachment of the link  500  stronger. 
         [0093]      FIG. 8E  also displays a link  500  with protrusions  532  on the tip  530 . A prosthesis  50  with a chamber  550  is shown next to the link  500 . The chamber  500  has helical or concentric sides  568  which are designed to mate with the protrusions  532  on the tip  530 . File helical or concentric edges  568  may be tapped so as to mate with helical protrusions, or ribbed to mate with concentric protrusions. When the link  500  is inserted in the chamber  550 , the helical or concentric sides  568  will mate with the protrusions  532 , preventing the link  500  from coming back out of the chamber  550 . Alternatively, the helical or concentric sides  568  may simply resist withdrawal of the protrusions  532  from the chamber  550 , thereby requiring the application of a deliberate threshold pullout force before the link  500  will detach from the prosthesis  50 . 
         [0094]    As another alternative, the channels  62  used may be biodegradable, in addition to or in the alternative to the use of biodegradable links. The channels  62  may simply be formed of a bioabsorbable material, and may be designed to absorb within a time frame longer than that during which the therapeutic agent will be needed. Biodegradable channels  62  may be used with or without biodegradable links. 
         [0095]    The embodiment depicted in  FIG. 1  illustrates the invention as applied to a knee prosthesis. However, it is appreciated that the invention can be applied to many other implants, including other body part prostheses. For example, the invention may be applied to interbone constrained, semi-constrained or unconstrained joint prostheses such as hip, facet or wrist prostheses. The present invention may alternatively be applied to intrabone implants such as bone plates or rods. It may be applied to percutaneous restorative implants such as an external fixation devices. In addition, it may be applied to other prostheses such as cosmetic implants and artificial organs. 
         [0096]      FIGS. 9 through 24  illustrate a variety of alternative applications of the invention. In each illustration, both the therapeutic agent interface  40  and the therapeutic agent delivery structure  60  are depicted as being composed of unlike materials adhered to the outer surface the corresponding prosthesis. However, as discussed above in the descriptions of  FIGS. 2  through the therapeutic agent interface  40  may be constructed in a variety of configurations from a variety of biocompatible materials. In addition, as discussed above in the descriptions of  FIGS. 6A through 6I , the channels  62  depicted in  FIGS. 9 through 24  may be constructed from a variety of materials and may be partially embedded, entirely embedded, or not embedded at all in the surface of the prosthesis. It is appreciated that various features of the above-described examples of therapeutic agent interfaces  40  and channels  62  can be mixed and matched to form a variety of other alternatives, particularly when combined with any of the applications illustrated in  FIGS. 9 through 24 . 
         [0097]      FIG. 9  displays an example of an application of the invention to an interbone prosthesis. A femoral prosthesis  14 , a patellar prosthesis  16 , and a tibial prosthesis  18  are shown as they would be positioned on a patient&#39;s knee. A therapeutic agent interface  40  is positioned adjacent to the femoral prosthesis  14 , and a therapeutic agent delivery structure  60  with two channels  62  is positioned on the outer surface of the femoral prosthesis  14 . Similarly, a second therapeutic agent interface  40  is positioned adjacent to the patellar prosthesis  16 , and a therapeutic agent delivery structure  60  with two channels  62  is positioned around the prosthesis  16 . A third therapeutic agent interface  40  is positioned adjacent to the tibial prosthesis  18 , and a therapeutic agent delivery structure  60  with two channels  62  is positioned on the tibial prosthesis  18 . When a conduit  22  such as depicted in  FIG. 1  is connected to each therapeutic agent interface  40 , a measured flow of therapeutic agent can be delivered to each therapeutic agent interface  40 , into the therapeutic agent delivery structures  60 , through the channels  62 , and to proximate tissues through the openings  70 . 
         [0098]    If desired, a single branching conduit (not shown) may be coupled to all three of the therapeutic agent interfaces  40  to deliver therapeutic agents to all three structures  60 . Variations in conduit sizing, valves, or the like may be used to control the relative flow rates of therapeutic agents to the structures  60 . Alternatively, separate conduits  60  and/or separate therapeutic agent sources  20  may be connected to the three therapeutic agent interfaces  40 . Such variations may be used in conjunction with any embodiment of the invention. 
         [0099]      FIG. 10  depicts a perspective view of another interbone prosthesis: a pedicle screw  100  and its associated link body  102  mounted on a rod  104 , as in a posterior spinal fixation system. A therapeutic agent delivery structure  60  encircles the outer surface of the link body  102 . A therapeutic agent interface  46  lies on the side of the link body  102  and two channels  62  extend from the therapeutic agent interface  40  in opposite directions, terminating on opposite sides of the link body  102 . The layout of the therapeutic agent delivery structure  60  depicted is only one possible arrangement; for example the therapeutic agent interface  40  could lie on the top of the link body  102 , with multiple channels  62  encircling the top, bottom and sides. Alternatively or additionally, multiple channels  62  may extend between pedicle screws  100  and associated link bodies  102 . Structures  60  with channels  62  may additionally or alternatively be coupled to the pedicle screw  100  and/or the rod  104 . 
         [0100]    An interbone elbow prosthesis is illustrated in  FIG. 11 . The prosthesis comprises an ulnar prosthesis  110  and a humeral prosthesis  114 . A hinge joint  118  joins the two prosthesis  110 ,  114 . A therapeutic agent delivery structure  60  is affixed to the ulnar prosthesis  110 , connecting to a therapeutic agent interface  40  which lies adjacent to the hinge joint  118 . Two channels  62  extend in opposite directions from the therapeutic agent interface  40 , and encircle the ulnar prosthesis  110 . Alternatively or additionally, a therapeutic agent delivery structure  60  could be affixed to the humeral prosthesis  114 . 
         [0101]      FIGS. 12A and 12B  illustrate application of the invention to a restorative or cosmetic prosthesis.  FIG. 12A  depicts a superior perspective view of a breast prosthesis  120 , and  FIG. 12B  depicts a posterior perspective view of the same prosthesis  120 . A therapeutic agent delivery structure  60  is affixed to the prosthesis  120 , with a therapeutic agent interface  40  in a posterior location. Multiple channels  62  extend from the therapeutic agent interface  40 , encircle the prosthesis  120  and terminate with their second ends  66  also on the posterior side of the prosthesis  120 . In this embodiment of the invention, channel configurations which lie below the surface of the prosthesis, such as those pictured in  FIGS. 6C ,  6 D,  6 H or  6 I, may be preferred, as they would be invisible and not create ridges on the surface of the prosthesis. 
         [0102]    A perspective view of an interbone hip prosthesis  130  is illustrated in  FIG. 13 . The prosthesis  130  has an acetabular prosthesis  131  with a bearing support  132  and bearing surfaces  134 . A femoral prosthesis  135  has a femoral stem  136  and a femoral ball  138  which are joined by a neck  139 . One therapeutic agent interface  40  (not visible in  FIG. 13 ) is affixed to the bearing support  132 , and a therapeutic agent delivery structure  60  encircles the bearing support prosthesis  132 . A second therapeutic agent interface  40  is located on the neck  139 , and a second structure  60  encircles the neck  139 . 
         [0103]      FIG. 14A  depicts a perspective view of a bone implant  140  such as a “bone plate,” which is configured to attach to the outside surface of the bone to stabilize a fracture. A therapeutic agent interface  40  lies on an upper surface  142  of the bone prosthesis  140 . A therapeutic agent flow structure  60  extends from the therapeutic agent interlace  40  to a first edge  144  and then splits to form two channels  62 . The channels  62  run from the first edge  144  around corners on a second edge  146  and a third edge  148 . The channels  62  terminate at the ends of the second and third edges  146 ,  148 . Openings  70  release the therapeutic agent to surrounding tissues, such as the fractured bone, surrounding soft tissues, and other tissues that were disturbed during implantation of the bone implant  140 . 
         [0104]    An alternative arrangement for the therapeutic agent delivery structure  60  is depicted in  FIG. 14B . In this arrangement, the therapeutic agent interface  40  lies on the upper surface of the bone prosthesis  140 , and two channels  62  extend from the therapeutic agent interface  40  and also lie on the upper surface  142 . The two channels  62  extend the length of the bone prosthesis  140  and terminate at their second ends  66 . Again, openings  70  release the therapeutic agent to surrounding tissues. 
         [0105]      FIG. 15  depicts an interbone shoulder replacement system, which includes a humeral prosthesis  150  with a bearing surface  156  and a separate glenoid prosthesis  154 , which is shaped to fit over the bearing surface  156 . A therapeutic agent interface  40  and a therapeutic agent delivery structure  60  are positioned on the glenoid prosthesis  154  such that a pair of channels  62  encircles the prosthesis  154 . Another therapeutic agent interface  40  and a therapeutic agent delivery structure  60  are positioned on the humeral prosthesis  150 , in a trough  158 , which lies distal to the bearing surface  156 . The therapeutic agent interface  40  lies within the trough  158 , as do the channels  62  which extend from the therapeutic agent interface  40  and encircle the humeral prosthesis  150 . 
         [0106]    A perspective view of an interbone intervertebral disc replacement system is depicted in  FIG. 16 . The intervertebral disc replacement system includes a superior prosthesis  160  and an inferior prosthesis  170 . The superior prosthesis  160  has a superior endplate  162 . On the upper or superior side of the superior endplate  162  is an endplate fixation structure  164 , which is designed to be secured to a first vertebral body (not pictured). On the lower or inferior side of the superior endplate  162  is a bearing surface  166 . The inferior prosthesis  170  has an inferior endplate  172 , with an endplate fixation structure  174 , which is designed to be secured to a second vertebral body (not pictured). On its upper or superior side, the inferior endplate  172  has a bearing surface  176 , which is designed to lay adjacent to the bearing surface  166  when both the superior  160  and inferior  170  prostheses are implanted. 
         [0107]    A therapeutic agent delivery structure  60  is affixed to an outer edge  168  of the superior endplate  162 , and a second therapeutic agent delivery structure  60  is affixed to an outer edge  178  of the inferior endplate  172 . On each endplate edge  168 ,  178 , a therapeutic agent interface  40  is affixed, and a channel  62  extends out from each lateral side of the therapeutic agent interface  40  to encircle the edge  168 ,  178 . 
         [0108]    A cosmetic calf implant  180  is depicted in  FIG. 17 . The implant  180  is generally elliptical in shape with a concave posterior or ventral surface  182 , and convex anterior or dorsal surface  184 . A therapeutic agent interface  40  is affixed immediately adjacent to the rim  186  on the anterior surface  184 , and a channel  62  extends laterally in each direction to encircle the prosthesis on the rim  186 . 
         [0109]      FIG. 18  depicts an interbone wrist prosthesis  190  with two therapeutic agent delivery structures  60  in place. The prosthesis  190  has a distal radius prosthesis  192  and a carpal prosthesis  194 , which meet at an artificial articular surface  196 . A therapeutic agent interface  40  is affixed to the radius prosthesis  192 , and a channel  62  extends laterally in each direction to encircle the radius prosthesis  192 , just proximal to the artificial articular surface  196 . Similar to the arrangement on the radius prosthesis  192 , a therapeutic agent interlace  40  is fixed to the carpal prosthesis  194 , and a channel  62  extends laterally in each direction to encircle the carpal prosthesis  194  just distal to the artificial articular surface  196 . 
         [0110]    A restorative cochlear implant  200  is illustrated in  FIG. 19 . The implant  200  has a main body  202 , from which extends a long wire-like cochlear electrode  204 . A therapeutic agent interface  40  is affixed near one end of the main body  200 , and one channel  62  extends along a segment of the length of the cochlear electrode  204 . 
         [0111]      FIG. 20  depicts an intrabone percutaneous external fixation device  210 . The device  210  consists of a plurality of circular link bodies  212 , which are lined up in a row and joined by a central rod  219 . Each link body  212  has an adjustable fastener assembly  214 . A bone fixation rod  216  extends laterally from one side of each link body  212 , perpendicular to the central rod  219 . At the tip of each bone fixation rod  216  is a point  218 , which is fixed in a bone segment. In the example in  FIG. 20 , three link bodies  212  with associated bone fixation rods  216  are depicted. The device  210  may be used to encourage the healing of fractured bone, lengthen a fractured or otherwise damaged bone structure, or perform a variety of other functions. 
         [0112]    Attached to the central link body  212  is a therapeutic agent interface  40 , from which extends three channels  62 . One channel  62  extends directly down the bone fixation rod  216 , which is attached to the central link body  212 , and the other two channels  62  extend laterally in opposite directions along the central rod  219 . When each lateral channel  62  reaches a link body  212 , it turns perpendicularly and extends down the associated bone fixation rod  216 . Each channel  62  terminates at the base of the point  218 . In this embodiment of the invention, the openings  70  are located subcutaneously near the second ends  66  of the channels  62 , instead of being evenly distributed along the channels  62 . At this location the openings  70  are subcutaneous yet not in the bone. 
         [0113]      FIG. 21  illustrates an interbone intervertebral body fusion implant  220 . It has an anterior end  222  and a posterior end  224 , and a first lateral side  230  and a second lateral side  232 . Along a superior side  226  are two rows of toothlike endplate fixation surfaces  228 . Located on the lateral sides  230 ,  232  are a plurality of bone ingrowth spaces  234 . A therapeutic agent interface  40  is affixed on the lateral side  230 . A channel  62  reaches from each side of the therapeutic agent interface  40  and extends around to both of the lateral sides  230 ,  232 . The channels  62  undulate around the bone ingrowth spaces  234  and terminate with their second ends  66  near the anterior end  222 . In this depiction of the invention the therapeutic agent interface  40  is shown the first lateral side  230 ; however it could be located on the second lateral side  232 , the anterior end  222 , or the posterior end  224 , or even on the interior of the implant  220 . 
         [0114]    An interbone temporo-mandibular joint prosthesis  240  is depicted in  FIG. 22 . The temporo-mandibular joint prosthesis  240  comprises an articular fossa prosthesis  242  and a mandibular plate  244  with an artificial articular surface  246 . The two prostheses  242 ,  244  join and articulate at the artificial articular surface  246 . Each prosthesis  242 ,  244  has a plurality of bone screw holes  248 . The articular fossa prosthesis  242  has an exterior surface  250 , on which a therapeutic agent interface  40  is affixed. A single channel  62  extends across the exterior surface  250  and terminates at a second end  66 . The mandibular plate  244  has an exterior surface  252 . A therapeutic agent interface  40  is affixed on the distal end of the plate  244 , from which a single channel  52  extends in a proximal direction, terminating at a second end  66 , near the artificial articular surface  246 . 
         [0115]      FIG. 23  illustrates a cosmetic or restorative chin implant  260 . The implant  260  is generally crescent-shaped, with a central anterior curve  262 , which terminates at either end in a prong  264 . A therapeutic agent interface  40  is affixed on the implant  260  on one side between the anterior curve  262  and one prong  264 . A channel  62  extends from each side of the therapeutic agent interface  40  in each direction. One channel  62  runs from the interlace  40  and terminates near the tip of the closest prong  264 , while the other channel runs in the opposite direction from the interface  40 , follows the line of the anterior curve  262 , and terminates near the tip of the opposing prong  264 . 
         [0116]      FIG. 24  illustrates an interbone ankle prosthesis  270 . The prosthesis  270  comprises a tibial prosthesis  272  and a talar prosthesis  274 . The tibial prosthesis  272  is generally U-shaped, with an artificial articular surface  276  on the inside of the U. The talar prosthesis  274  has an elongated wedge shape, designed to fit inside the U formed by the tibial prosthesis  272 . An artificial articular surface  278  is located on the outer surface of the talar prosthesis  274 , where it contacts the artificial articular surface  276  on the inside of the tibial prosthesis  272 . A therapeutic agent interface  40  is affixed to the tibial prosthesis  272 , adjacent to, but not on, the artificial articular surface  276 . Two channels  62  extend from the therapeutic agent interface  40 , and follow the shape of the U such that they outline and lie just outside the artificial articular surface  276 . 
         [0117]    As indicated previously,  FIGS. 9 through 24  provide only a limited set of examples. The principles and structures of the present invention may be used with a wide variety of medical implants, including but not limited to interbone prostheses, non-joint prostheses, reparatory implants, and cosmetic implants, and artificial organs. 
         [0118]    The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. It is appreciated that various features of the above-described examples can be mixed and matched to form a variety of other alternatives. As such, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the claims, are to be embraced within their scope.