Abstract:
An orthopaedic implant includes a body member having a first region with a first porosity and a second region with a second porosity. At least one physical characteristic of the first porosity is different than at least one physical characteristic of the second porosity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a non-provisional application based upon U.S. provisional patent application Ser. No. 61/088,452, entitled “ORTHOPAEDIC IMPLANT”, filed Aug. 13, 2008, which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to orthopaedic devices, and, more particularly, to orthopaedic implants. 
         [0004]    2. Description of the Related Art 
         [0005]    Most orthopaedic implants are formed from a metallic material suitable for a given implant, such as a hip implant, knee implant, glenoid implant, etc. In the case of articulating joints, the implant may include a non-metallic load bearing surface, such as an ultra high molecular weight polyethylene (UHMWPE). The UHMWPE is bonded to the metallic body of the implant, and provides the implant with good wear characteristics and low friction. 
         [0006]    It is also known to provide an implant with a porous bony ingrowth surface. For example, a hip implant may include a porous surface on the stem which is intended to allow bony ingrowth of the proximal end of the femur bone. Such a porous surface may be in the form of a metal porous surface which is bonded, such as by heat sintering, to the stem of the implant. Examples of porous surfaces of this type include a woven mesh, a fiber mesh and particles. 
         [0007]    Porous surfaces of the type described above which are used with implants are continuous over a specified region of the implant and have the same physical properties throughout. The porous surface is formed with the intent of allowing only one type of ingrowth, such as bone ingrowth or soft tissue ingrowth. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a porous ingrowth material with varying features along the length and width of an implant, such as an orthopaedic implant. 
         [0009]    The invention in one form is directed to an orthopaedic implant, including a body member having a first region with a first porosity and a second region with a second porosity. At least one physical characteristic of the first porosity is different than at least one physical characteristic of the second porosity. 
         [0010]    The invention in another form is directed to an orthopaedic implant, including a body member having a first porosity and a spatially discrete second porosity. At least one physical characteristic of the first porosity is different than at least one physical characteristic of the second porosity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]    The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
           [0012]      FIG. 1  is a stem with two different regions of ingrowth material; 
           [0013]      FIG. 2  is a cross-section of three layers of material, the uppermost being tapered; 
           [0014]      FIG. 3  is cross-section of multiple layers of ingrowth material with different thicknesses; 
           [0015]      FIG. 4  is a device for genoid replacement showing porous regions optimized for: a) polyethylene molding, b) bone ingrowth, and c) soft tissue attachment and ingrowth; and 
           [0016]      FIG. 5  is a device for tibial replacement showing porous regions optimized for: a) polyethylene molding, b) bone ingrowth, and c) soft tissue attachment and ingrowth. 
       
    
    
       [0017]    Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    Referring now to the drawings, the ingrowth material of the present invention allows the porous material to be optimized differently for each type of tissue ingrowth desired. Examples include the following:
   1. Soft tissue ingrowth in some regions and bone in another region. For example, the superior-lateral portion of a revision hip stem ( FIG. 1 , Ingrowth Region  10 ) could be optimized to encourage the ingrowth of the abductor muscle and tendon attachment, while other portions of the stem can be covered with an ingrowth material designed to encourage bone ingrowth ( FIG. 1 , Ingrowth Region  12 ). Soft tissues include, but are not limited to, tendons, ligaments, muscle, and cartilage.   2. Cortical bone ingrowth in some regions, and cancellous bone in other regions.   
 
         [0021]    This type of customization of the porous ingrowth material enables an implant design that encourages ingrowth of certain tissues in some regions and occludes certain tissue ingrowth in other regions. For example, in an implant that seeks to reattach a tendon, soft tissue ingrowth may be desired in some portion of the implant, but bone ingrowth is desired in another. If one tissue or the other were to grow throughout the ingrowth material, it could prevent ingrowth of the second tissue. The ingrowth material features can be customized in each region to promote the growth of one type of tissue and/or discourage the growth of other type(s) of tissue. 
         [0022]    The present invention further provides that therapeutic agents can be delivered to only certain regions of an implant. In implants that allow for the delivery of therapeutic agents (such as the drug delivery implants disclosed in U.S. patent application Ser. No. 12/540,676, entitled “DRUG DELIVERY IMPLANTS”, filed on even date herewith), the porous ingrowth material of the present invention can be tailored to deliver more or less of a therapeutic agent to particular tissues and regions of tissues. 
         [0023]    This ability to tailor the implant can also aid the manufacturing process. For example, the pore shape/interconnection size can be customized to optimize insert moldability in one region and bone ingrowth in another. 
         [0024]    A non-exhaustive list of examples of features or physical characteristics that can be varied according to the present invention include the following:
   Pore size   Pore shape   Pore density (% porosity)   Pore interconnection size/shape   Surface roughness   Surface treatment (for example: a chemically etched surface in some regions and EP surface in another)   Surface coating (for example: hydroxyapatite only in some regions, an antibacterial coating in another)   Material—implantable metals, polymers, and ceramics   Ability to deliver therapeutic agents and in what amount   Specifics of the porous material (for example, in a laminate material, the thickness of one or more layers can be varied medially to laterally)
       The layer can taper (see  FIG. 2 )   Layers with different, but constant, thicknesses can be stacked (See  FIG. 3 )   
       Type of Porous Material—a sintered, powdered metal ingrowth material in one region and a laminate metal in another   The scale of modifications includes macroscopic (for example pore size), microscopic (for example grain structure, microscale surface texture/treatments) and nanoscale (for example nanoscale surface texture/treatments).   
 
         [0039]    Any or all of the features described herein can be varied within the ingrowth material of a given implant. This can be applied to any implant with tissue ingrowth material (examples include, but are not limited to, primary and revision hip, knee, shoulder, and elbow prostheses; cartilage replacement plugs; soft tissue attachment screws; and spinal fusion devices). Two examples of such devices are shown in  FIGS. 4 and 5 . Referring to  FIG. 4 , a glenoid replacement is shown having a porous region  14  designed for polyethelene molding (with polyethylene  16  affixed thereto), a porous region  18  designed for bone ingrowth, and a porous region  20  designed for soft tissue ingrowth and attachment. Referring to  FIG. 5 , a tibial replacement is shown having a porous region  22  designed for polyethelene molding (with polyethylene  24  affixed thereto), a porous region  26  designed for bone ingrowth, and a porous region  28  designed for soft tissue ingrowth and attachment. 
         [0040]    While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.