Abstract:
A porous implant system includes a gradient source adapted for transferring a gradient to an interface connected to an implant at a patient situs. The gradient source is controlled by a programmable controller. The implant is bonded to the patient by tissue ingrowth, which is facilitated by the gradient formed across the porous portion of the implant. A treatment method and includes the steps of providing a porous implant, connecting same to a gradient source through an interface, forming a gradient across the implant and controlling the operation of the gradient source according to a predetermined and preprogrammed treatment protocol.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to implants, and in particular to a porous implant system and treatment methodology for both orthopedic and soft tissue applications, which promotes tissue interdigitation and healing. 
   2. Description of the Prior Art 
   In the medical, dental and veterinary fields, implants are in widespread use for treating a variety of patient conditions. For example, in the field of orthopedics, joints are commonly replaced with implants after the original joints fail through degeneration, trauma and other causes. Such implants are typically designed to promote bone induction, bone replacement and soft tissue anchoring. Porous materials have been extensively used in the manufacture of joint prostheses for this purpose. Their open-lattice configurations tend to promote interdigitation, tissue ingrowth and tissue outgrowth whereby integration with the patients&#39; living tissues can occur. 
   Trabecular metal comprises a type of porous material, which is commonly used in orthopedic procedures. An example of such an implant is described in U.S. Pat. No. 5,456,723 entitled “Metallic Implant Anchorable to Bone Tissue for Replacing a Broken or Diseased Bone”. Porous thermoplastic materials have also been used for orthopedic implants. Examples are described in U.S. Pat. No. 4,164,794 and No. 4,756,862, both of which are entitled “Prosthetic Devices Having Coatings of Selected Porous Bioengineering Thermoplastics”. U.S. Pat. No. 5,443,512 for “Orthopedic Implant Device” and No. 6,087,553 for “Implantable Metallic Open-Celled Lattice/Polyethylene Composite Material and Devices” both describe orthopedic implants with metal and plastic composite constructions. All of these patents are incorporated herein by reference. 
   Trabecular metal and other porous implant materials, including thermoplastics, can promote tissue ingrowth under certain conditions. However, the depth of penetration of bone and soft tissue ingrowth may be limited by various biological factors. Moreover, depth and quality of tissue penetration, and the physical properties of the host/prosthesis interface, may be limited by both pathological and physiological host factors. 
   Another persistent problem with such implants relates to the potential for infection. Porous materials tend to encourage tissue ingrowth, but they can also accommodate microbes and metabolic agents. Digitization and integration can be hindered by the presence of toxins, wound drainage fluid and other substances, particularly when they are trapped in the porous material and closed within a surgery site after a medical procedure. 
   Artificial joints, implants and other prostheses are further susceptible to persistent problems with secure bonding to patients&#39; living tissue. Macro and micro motion in such connections can compromise replacement joints and cause their premature failure. In order to strengthen such connections, adhesives and cements have been developed for bone-to-implant bonds. Such adhesives and cements can be combined with antibiotic and antimicrobial agents. For example, ALAC identifies an acrylic cement loaded with antibiotic or antimicrobial agents (ABX). Polymethylenemethacralate (PMMA) cement is also used for this purpose. However, problems can be encountered with inducing such cements into the voids and latticework formed in the porous implant materials. 
   In the related fields of chronic wound care and post-operative incision healing, gradients of various kinds have been utilized. For example, thermodynamic (temperature) gradients can stimulate cell growth. Electrical, gravitational and magnetic fields have also been utilized for this purpose. Considerable research is currently being directed toward the use of biologics in various medical applications. Gradients can be established with biological agents for enhancing healing and countering infection. Pressure differentials and gradients have been applied to close separated tissue portions and promote their healing. Negative pressure gradients have been used to apply suction forces for draining bodily fluids and exudates. Positive pressure gradients have been used to irrigate wound sites and infuse them with pharmacological agents, such as antibiotics, growth factors, etc. 
   The present invention combines concepts from the porous implant field with gradient formation equipment and treatment protocols to promote tissue ingrowth for anchoring implants. Forming a gradient at a situs also facilitates drainage and the application of biologics, such as antibiotics, growth factors and other fluids for controlling infection and promoting healing. 
   The design criteria for implants include secure connections with living tissue, facilitating tissue ingrowth, infection resistance and permanency. Another design objective is applicability to a wide range of procedures, including prosthetic fixation, cosmetic and structural bone substitution, treatment of failed bone unions, bone defects, composite tissue defects and other conditions. Heretofore there has not been available a porous implant system and treatment method with the advantages and features of the present invention. 
   SUMMARY OF THE INVENTION 
   In the practice of the present invention, a porous implant system and treatment method are provided for various conditions, including orthopedic procedures such as total joint replacement (TJR). The system and method involves the application of a gradient to a porous implant material. The gradient can be formed with a wide variety of different forces and influences. A negative pressure differential creates a suction force across the implant whereby tissue ingrowth is encouraged. The negative pressure differential/suction mode of operation also functions to drain the implant situs and remove toxins, microbes and metabolic agents. In a positive pressure/infusion mode, various biologic and pharmacological agents can be infused throughout the implant and the patient situs for countering infection, promoting tissue growth, etc. An interface, such as a tube, a sponge or a membrane, is provided for connecting the porous material of the implant to a pressure differential source. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of the porous implant system embodying the present invention. 
       FIG. 2   a  is a perspective view of a total hip replacement (THR) procedure. 
       FIG. 2   b  is a cross-sectional view of a porous acetabular cup for the THR procedure. 
       FIG. 3  is a flowchart of a porous implant treatment procedure according to the method of the present invention. 
       FIG. 4  is an outline of a subprocedure of the treatment method, which subprocedure involves patient situs parameters. 
       FIG. 5  is an outline of a subprocedure of the treatment method, which subprocedure involves selecting a porous material type. 
       FIG. 6  is an outline of a subprocedure of the treatment method, which subprocedure involves selecting a gradient source. 
       FIG. 7  is an outline of a subprocedure of the treatment method, which subprocedure involves selecting a patient interface. 
       FIG. 8  is an outline of a subprocedure of the treatment method, which subprocedure involves selecting inputs/pharmacological agents/biologics. 
       FIG. 9  is a flowchart showing a treatment subprocedure. 
       FIG. 10   a  is a front, right side perspective view of a knee joint. 
       FIG. 10   b  is a cross-sectional view of the knee joint, showing the porous implant system applied to the patella. 
       FIG. 11  is a cross-sectional view of the porous implant system applied to a tibia. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   I. Introduction and Environment. 
   As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
   Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the embodiment being described and designated parts thereof. Said terminology will include the words specifically mentioned, derivatives thereof and words of a similar import. 
   Referring to the drawings in more detail, the reference numeral  2  generally designates a porous implant pressure differential system embodying the present invention. The system  2  interacts with a patient situs  4  through a porous implant  9 , which is connected to an interface  6 . The interface  6  is connected to a gradient source  5  through a gradient transfer  8 . The gradient source  5  is controlled by a controller  10 , which provides output to a monitor/display  12  and is powered by a power source  13 . Inputs  14  communicate with the patient situs  4  through the interface  6 , and exudate  16  is drawn therefrom to a collection receptacle  18 . Reperfusion of the patient&#39;s bodily fluids can occur along dashed line  20 . 
   Without limitation on the generality of useful applications of the system  2 , it can be applied to both human and animal patients and subjects in connection with a wide variety of medical, dental and veterinary conditions and treatments. For example, total joint replacements (TJRs) typically involve several procedures, which can benefit from the system  2 . It will be appreciated that the system and treatment method of the present invention are applicable to a wide range of medical, dental and veterinary procedures and conditions. 
   A total hip replacement (THR)  22  is shown in  FIGS. 2   a ,  2   b  and includes an acetabular cup assembly  24  and a femoral prosthesis  26 . As shown in  FIG. 2   b , the acetabular cup assembly  24  includes a porous component  28  and a bearing or wear component  30 , which can comprise a material such as polyethylene. Composite metal and plastic acetabular cups of this type are available from the Implex Corporation of Allendale, N.J. 
   The porous component  28  functions to distribute the pressure differential from the gradient source  5  through input and output lines (e.g., tubes, wires, etc.)  14   a ,  16   a  connected to an interface  6 . The lines  14   a ,  16   a  function as gradient transfers ( 8  in FIG.  1 ). In a negative pressure/suction mode, the porous implant system  2  facilitates tissue interdigitation for enhancing and expediting bonding with the patient. Preferably, both tissue ingrowth into the porous component  28  and outgrowth onto same are enhanced. Moreover, in a negative pressure mode, various pharmacological agents and biologics, such as antibiotics, growth factors, etc., can be drawn into the porous component  28  for expediting healing, reducing infection, etc. In a negative pressure gradient (suction) mode, fluid, toxins, microbes and metabolic products can be drained from the situs  4 . The risks of infection can thus be reduced and healing promoted by applying a pressure differential or other gradient to the porous component  28 . Interdigitized tissue and pharmacological agents drawn and/or injected into the situs  4  by a negative and/or positive pressure differential across same will tend to displace bodily fluids and toxins occupying the interstitial spaces in the porous implant, thus reducing or eliminating an environment in which microbes and metabolic products can develop and infect the situs  4 . 
   In a positive pressure/input mode the porous material  28  acts as a manifold to distribute the fluid input throughout the situs  4 . It will be appreciated that the controller  10  can be programmed to alternate between these functions. Moreover, they can occur simultaneously as the system  2  provides a fluid input at one side of the porous component  28  and exudate is drained from the other side thereof. 
   The gradient source  5  and the interface  6  can comprise, for example, components of a vacuum assisted closure (VAC) system and interface from Kinetic Concepts, Inc. of San Antonio, Tex. For example, the interface  6  can comprise various suitable sponge materials, or can comprise a length of tubing attached to the porous component  28 . 
     FIG. 3  is a flowchart showing an overview of a treatment method  50  of the present invention, utilizing the system  2  embodying the present invention. The process starts at  52  and proceeds to a patient situs parameters subprocedure  54 . A porous material type is selected at  56 , a gradient is selected at  58 , a patient interface is selected at  60  and inputs/pharmacological agents/biologics are selected at  62 . A treatment subprocedure occurs at  64  whereafter the methodology ends at  66 . These subprocedures will be discussed below. 
     FIG. 4  is an outline of the patient situs parameter considerations  54 . For soft tissue applications  68 , the system  2  is adapted for connecting tendons and joining separated tissue at the subcutaneous (SQ) layer of the patient at  70 ,  72  respectively. For example, a pair of porous material components  28  can be placed against soft tissue portions and bonded to same with tissue interdigitation. The porous material components  28  can then be mechanically drawn together for closure of the separated tissue portions. In an orthopedic interface  74 , such as the hip replacement discussed above, different considerations are taken into account if the situs is load bearing or not ( 76 ), and depending upon whether it includes wear surfaces ( 78 ), for example, in connection with a joint prosthesis. The situs  4  can comprise a diseased or damaged tissue location whereat a revision or reconstruction is performed at  80 . In orthopedic medicine, previous implants and prostheses are commonly replaced due to their failure, infection, ineffectiveness, etc. The system and method of the present invention can be used to advantage in such implant extraction and replacement procedures. 
   The interface  6  can comprise either permanent ( 82 ) or temporary components ( 84 ), or both. For example, biocompatible and absorbable components are designed to dissolve within the patient at  86 . By encouraging living tissue interdigitation, the system  2  can enhance the absorption of the interface  6  components. Their components are designed for removal. For example, the interface  6  can include tubing adapted for placement upon installation of the system  2 . After the system  2  has accomplished its purpose, such as draining a wound, applying and distributing biologics, etc., removable components can be extracted at  88 . 
     FIG. 5  shows the subprocedure  56  for selecting a porous material. Trabecular metal is shown at  90 . Porous thermoplastic materials ( 92 ) are also suitable for receiving tissue ingrowth and would benefit from a pressure differential. Moreover, biodegradable and absorbable porous materials ( 94 ) can be utilized for eventual absorption into the patient through replacement by the patient&#39;s living tissue. A composite material composition can be selected at  96 . 
     FIG. 6  shows the subprocedure  58  for selecting the gradient. As shown, biologic  98 , temperature  100 , electrical  102 , magnetic  104  and chemical  106  gradients can be utilized. A negative/suction pressure differential  108  can be utilized to drain the situs  4  and a positive/infusion pressure differential  110  functions to input various fluids and agents to the situs  4 . Drainage and infusion can be combined at  112 . These functions and operational modes can be sequenced for constant/intermittent operation ( 114 ) and can operate simultaneously. They can also be preprogrammed ( 116 ) with the controller  10 . For example, the gradient source  8  can pause in its operation and provide a substantially static pressure or other condition across the interface  6 . 
     FIG. 7  shows a subprocedure  60  for selecting the patient interface  6 . A hydrophilic or hydrophobic sponge  118  can be placed on the implant porous material portion  28 . Alternatively, it can directly receive a tube connected to the gradient source  5  ( 120 ). Membranes of porous, semi-permeable and impervious material can be utilized ( 122 ). As discussed above, the interface  6  can comprise multiple materials in a composite construction ( 124 ). Some or all the components of the interface  6  can be biodegradable and absorbable ( 126 ). The ALAC acronym identifies antibiotic or antimicrobial (ABX) loaded acrylic cement, which can also be utilized for installing the patient interface  6  ( 128 ). Polymethylmethacralate (PMMA) is another adhesive adapted for orthopedic applications, and can be used for adhering one or more of the components of the system  2  to a patient ( 130 ). 
     FIG. 8  shows the subprocedure  62  for selecting inputs/pharmacological agents/biologics, which are chosen to enhance healing, counter infection, etc. They can include antibacterial/antimicrobial agents (ABX)  132 , growth factors  134 , irrigation  136  (i.e., in conjunction with drainage of the situs  4 ) and reperfusion  138  of the patient&#39;s fluids and biologics. 
     FIG. 9  shows a treatment subprocedure  64  starting at  140  and including a diagnosis and prescription of a treatment protocol ( 142 ). Following suitable preparations at  144 , the implant is installed at  146  and the patient interface is installed at  148 . A gradient source(s) is connected at  150  and a gradient is applied at  152 . In a negative pressure differential/extraction mode, exudate is extracted at  154 . The negative pressure differential/extraction mode also encourages tissue interdigitation ( 158 ) for biointegration of the interface  6  into the patient&#39;s tissue. In a positive pressure differential input/supply mode, input substances are infused at  156  into the patient interface  6  for distribution by the porous component  28 . Various treatments and pharmacologicals are available for countering patient rejection of tissue transplants, and can be used in conjunction with the system  2  at  160 . The treatment results can be monitored at  162  through various sensors  11  associated with the monitor/display  12 , and through conventional medical inspections and observations. Components of the system  2  can be changed if additional treatment is indicated at  164 , and treatment parameters can be adjusted as indicated for optimum healing at  170  and components can be changed at  168 . Finally, non-permanent components can be extracted at  166  and the treatment ends at  172 . 
     FIG. 10   a  shows a knee joint  102 , a femur  104  and a tibia  106 . A patella  108  (kneecap) is connected to a quadriceps tendon  110  and and a patella tendon  112 .  FIG. 10   b  shows an implant  114 , which includes a porous, outer layer  116 . The implant  114  can comprise trabecular metal, porous thermoplastic and other porous materials, as described above. The implant  114  also includes an ultra high molecular weight plastic (UHMWP) inner layer  118  adapted for sliding with respect to the components of the knee joint  102  and providing a relatively low coefficient of friction. The implant  114  is temporarily secured to the tendons  110 ,  112  by sutures  120 , which can be absorbable. The porous outer layer  116  of the implant  114  receives tissue ingrowth, as described above, for permanent bonding. A gradient source  122  is connected to the implant  114  via first and second interfaces  124 ,  126 . The resulting system  128  provides drainage, irrigation, biologic application and other functions, as discussed above. 
     FIG. 11  shows a system  132  for reconstructing a tibia  134 . Damaged tibia tend to have high risks of infection, whereby drainage and the application of various antibiotics, antimicrobials and other biologics comprise important aspects of effective treatment. The system  132  includes a porous implant  136  connected to a gradient source  138  by first and second interfaces  140 ,  142 . 
   It will be appreciated that various other medical, dental and veterinary applications of the porous implant system and treatment methodology fall within the scope of the present invention. While certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.