Abstract:
An implant device for cartilage regeneration in loading-bearing regions uses the osteochondral defect model. The implant is formed of resorbable polymeric materials. The implant is designed such that load is transmitted from the articulating surface of the bone platform through the implant to the entire area of subchondral bone of the bone platform. Application of load in this manner results in reduced subchondral bone resorption, leading to joint stabilization and maintenance of normal joint biomechanics. The implant allows for the incorporation therein of a resorbable scaffold or matrix material. The present implant solves the current inability to regenerate cartilage in load-bearing articulating surfaces using engineered scaffold devices.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to regeneration of cartilaginous tissue in load bearing regions and/or the tendency toward the resorption of subchondral bone and, more particularly, to an implant device for reducing the resorption of subchondral bone and thereby enhancing the regeneration of cartilaginous tissue in load bearing regions.  
       BACKGROUND OF THE INVENTION  
       [0002]     Current techniques for repair and/or regeneration of articular lesions (autogenous chondrocyte transplantation and mosaicplasty) are generally considered to be unsatisfactory due to the fact that they require the harvesting of healthy tissue. As such, research has focused on the development of engineered devices that have the ability to stimulate conduction of hyaline-like tissue into the treated regions without using autogenous tissue sources. Such devices would be considered optimized scaffolds.  
         [0003]     In vivo studies of articular cartilage regeneration typically utilize one of two animal models: the osteochondral defect and the full-thickness chondral defect. The osteochondral defect model is ideal for the generation of cartilage neotissue because access to the traumatized bone bed allows for recruitment of precursor cells, thereby enhancing the intrinsic wound healing response. In fact, osteochondral defects in the non-load-bearing areas heal spontaneously, albeit with fibrous tissue. The load-bearing region, however, is known to not heal spontaneously, and is characteristically accompanied by resorption of osseous walls and the formation of cavitary lesions.  
         [0004]     In cases where load-bearing surfaces have been investigated with good outcomes, care has been taken not to compromise the subchondral plate (e.g. full-thickness chondral defect model). However, because the chondral defect model does not generate a hematopoietic wound healing response, spontaneous regeneration does not occur and thus cellular therapies are usually used in such circumstances. One notable exception is mosaicplasty. Mosaicplasty in femoral condyle (osteochondral) defects has been shown to maintain subchondral bone structure, further indicating that application of physiologic force plays a role in maintaining subchondral bone integrity.  
         [0005]     Particularly, mosaicplasty utilizes cartilaginous plugs, but due to the need to harvest tissue from other sites, this technique is sometimes viewed as being suboptimal. Therefore, research has focused on the use of implant devices. In published U.S. patent application 2001/0039455A1, prosthetic bio-compatible polyurethane plugs that mimic the materials properties of the adjacent bone or cartilage tissue layer are described. These implants are intended to fill a cartilaginous defect with a non-resorbable cartilage-like material. However, application of load to subchondral bone is not described.  
         [0006]     The use of load during cartilage regeneration has been described in several publications. In U.S. Pat. No. 6,530,956 a resorbable cage-like scaffold is described that consists of high porosity material seeded with transplanted chondrocytes. Loading is discussed with respect to the cage-like scaffold for withstanding and resisting compressive forces so that cell growing compartments of the cage-like scaffold are protected during tissue regeneration.  
         [0007]     U.S. Pat. No. 6,511,511 describes a fiber-reinforced, porous, biodegradable implant in which the fibers act like struts to provide strength and stiffness to the scaffold and provide support for physiological loads. One particular embodiment is for osteochondral defects. Loading, however, is discussed only with respect to the device resisting high compressive stresses in the defect region thereby protecting the implant during tissue regeneration. In a similar manner, U.S. published U.S. patent application 2002/0119177 describes a method for reinforcing the mechanical and handling properties of a resorbable foam matrix using a mesh-like fabric. The primary purpose of the reinforcing mesh is to maintain the integrity of the foam component for surgical handling.  
         [0008]     In published U.S. patent application 2003/0108587, an implantable device is described that can induce compression, tension, shear and other biomechanical forces to cells in order to induce cell proliferation and thus wound healing. The device is essentially a bioreactor that exerts micromechanical stimulation to cells through materials properties or application of external forces. This is taught, however, with respect to the regeneration of cartilage and not with respect to the healing of the subchondral bone as in the present invention.  
         [0009]     Thus the need exists for a device for regeneration of articular cartilage that simultaneously applies load to subchondral bone.  
         [0010]     It is thus an object of the present invention to provide an implant for cartilage regeneration in load-bearing regions.  
         [0011]     It is thus another object of the present invention to provide an implant that applies a load from an articulating surface of a bone platform to an area of subchondral bone.  
         [0012]     It is yet another object of the present invention to provide a load bearing implant for that reduces subchondral bone resorption.  
       SUMMARY OF THE INVENTION  
       [0013]     In one form, the present invention is an implant device for applying a load to osteochondral defects. In another form, the present invention provides cartilage regeneration of osteochondral defects in load bearing regions. The implant may be fashioned as one integral device or may be fashioned as two or more portions that are attached to one another.  
         [0014]     The implant includes an upper platform structure and a lower platform structure with a load transfer structure situated there between. A fixation structure may be included that aids in anchoring the implant to the defect area. The implant is comprised of a resorbable polymeric material or materials such as polyesters (polylactide, polyglycolide, polycaprolactone, polydioxanone, or combination thereof), co-polymers of resorbable polymers, or blends thereof.  
         [0015]     The lower platform structure is preferably rigid (and alternatively the upper platform structure as well) and may be porous, or include pores or holes that allow for access to biologic elements (e.g. blood and bone marrow) from the subchondral bone. The implant also allows the receipt and retention of a resorbable scaffold or matrix material for cartilage regeneration in the defect area.  
         [0016]     Particularly, in one form there is provided an implant device for an osteochondral defect. The implant device includes a first plate made of a resorbable biocompatible material, a second plate made of the resorbable biocompatible material, and a load transfer structure made of the resorbable biocompatible material and situated between the first plate and the second plate.  
         [0017]     In another form, there is provided an implant device for an osteochondral defect. The implant device includes an upper plate made of a resorbable biocompatible polymer, a lower plate made of the resorbable biocompatible polymer and having a plurality of exposure bores, and a load transfer structure situated between the upper plate and the lower plate.  
         [0018]     In yet another form, there is provided an implant for load bearing bone articulation surfaces. The implant includes an upper plate made of a bio-resorbable polymer and having an upper center bore, a lower plate made of the bio-resorbable polymer and having a lower center bore surrounded by a plurality of exposure bores, and a plurality of load transfer supports situated between a lower surface of the upper plate and an upper surface of the lower plate, the load transfer supports surrounding the upper and lower center bores. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a diagrammatic view showing a tibial platform, representing an exemplary bone platform, being below the condyles of the femur; representing exemplary condyles; may also want to show patella.  
         [0020]      FIG. 2  is a block diagram illustrating an exemplary general form of a load bearing cartilage regeneration device in accordance with the principles of the subject invention;  
         [0021]      FIG. 3  is an enlarged perspective view of an exemplary embodiment of a load bearing cartilage regeneration device in accordance with the principles of the subject invention;  
         [0022]      FIG. 4  is a side view of the load bearing cartilage regeneration device of  FIG. 3 ;  
         [0023]      FIG. 5  is a sectional view of the load bearing cartilage regeneration device of  FIG. 4  taken along line  5 - 5  thereof, particularly showing the lower platform thereof;  
         [0024]      FIG. 6  is a sectional view of the load bearing cartilage regeneration device of  FIG. 4  taken along line  6 - 6  thereof, particularly showing the upper platform thereof; including the load transferring structure.  
         [0025]      FIG. 7  is an enlarged perspective view of another exemplary embodiment of a load bearing cartilage regeneration device in accordance with the principles of the subject invention;  
         [0026]      FIG. 8  is a side view of the load bearing cartilage regeneration device of  FIG. 7 ;  
         [0027]      FIG. 9  is a sectional view of the load bearing cartilage regeneration device of  FIG. 8  taken along line  9 - 9  thereof, particularly showing the lower platform thereof; including the load transferring structure.  
         [0028]      FIG. 10  is a side view of another exemplary embodiment of a load bearing cartilage regeneration device in accordance with the principles of the subject invention;  
         [0029]      FIG. 11  is a sectional view of the load bearing cartilage regeneration device of  FIG. 10  taken along line  11 - 11  thereof, particularly showing the lower platform thereof; including the load transferring structure.  
         [0030]      FIG. 12  is an enlarged bottom perspective view of an alternative upper platform utilizable with the various exemplary embodiments;  
         [0031]      FIG. 13  is a side view of the upper platform of  FIG. 12 ;  
         [0032]      FIG. 14  is an enlarged top perspective view of an alternative embodiment of a platform having integral load transfer structures for a two-piece load bearing cartilage regeneration device, the load transfer structures designed to engage mating structures on a mating platform of the two-piece load bearing cartilage regeneration device such as that depicted in  FIG. 16 ;  
         [0033]      FIG. 15  is a top view of the platform of  FIG. 14 ;  
         [0034]      FIG. 16  is an enlarged top perspective view of an exemplary mating platform for the platform structure of  FIG. 14 ;  
         [0035]      FIG. 17  is a side view of the exemplary mating platform of  FIG. 16 ;  
         [0036]      FIG. 18  is a sectional view of the exemplary mating platform of  FIG. 17  taken along line  18 - 18  thereof;  
         [0037]      FIG. 19  is a top plan view of the exemplary mating platform of  FIG. 16 ;  
         [0038]      FIG. 20  is a sectional view of the exemplary mating platform of  FIG. 19  taken along line  20 - 20  thereof;  
         [0039]      FIG. 21  is an enlarged top perspective view of another exemplary mating platform for the platform structure of  FIG. 14 ;  
         [0040]      FIG. 22  is a top plan view of the exemplary mating platform of  FIG. 21 ;  
         [0041]      FIG. 23  is a side view of the exemplary mating platform of  FIG. 21 ;  
         [0042]      FIG. 24  is a sectional view of the exemplary mating platform of  FIG. 23  taken along line  24 - 24  thereof;  
         [0043]      FIG. 25  is an enlarged top perspective view of another alternative embodiment of a platform having integral load transfer structures for a two-piece load bearing cartilage regeneration device, the load transfer structures designed to engage mating structures on a mating platform of the two-piece load bearing cartilage regeneration device;  
         [0044]      FIG. 26  is an enlarged top perspective view of yet another alternative embodiment of a platform having integral load transfer structures for a two-piece load bearing cartilage regeneration device, the load transfer structures designed to engage mating structures on a mating platform of the two-piece load bearing cartilage regeneration device;  
         [0045]      FIG. 27  is an enlarged top perspective view of an exemplary mating platform for the platform structures of FIGS.  25  and/or  26 ;  
         [0046]      FIG. 28  is a side view of the exemplary mating platform of  FIG. 27 ;  
         [0047]      FIG. 29  is a sectional view of the exemplary mating platform of  FIG. 28  taken along line  29 - 29  thereof;  
         [0048]      FIG. 30  is a top plan view of the exemplary mating platform of  FIG. 27 ;  
         [0049]      FIG. 31  is a sectional view of the exemplary mating platform of  FIG. 30  taken along line  31 - 31  thereof; and  
         [0050]      FIG. 32  is an enlarged side sectional view of a bone and cartilage platform depicting an exemplary load bearing cartilage regeneration device in accordance with the principles of the present invention implanted therein. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0051]     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.  
         [0052]     Referring now to  FIG. 1 , there is depicted a bone platform generally designated  40  being situated below condyles  42 . The bone platform  40  of  FIG. 1  is depicted as a tibial platform  40  of a tibia  41  while the condyles  42  are of a femur/knee. It should be appreciated that the tibial platform  40  and condyles  42  are representative of any similar bone platform. The tibial platform  40  supports a meniscus  44  that is over subchondral bone  45 . The tibial platform  40  is assumed to have an osteochondral defect. The subject invention provides an implantable device for the osteochondral defect. The condyles  42  typically exert a load represented by arrows L onto the tibial platform  40 . Particularly, the condyles  42  of the femur  43  exert physiological loading on the tibial platform  40  during normal joint use. The implant is actually intended for a medial femoral condylar (MFC) defect, and our initial data is in the MFC. Perhaps we should describe  FIG. 1  relating to a MFC defect, and mention the other load-bearing surfaces such as the tibia and patella? 
         [0053]     Referring now to  FIG. 2 , there is depicted a block diagram of a load bearing subchondral bone resorption reduction and/or cartilage regeneration implant device generally designated  50  (and, hereinafter, “load bearing implant device”, “implant” or the like) in accordance with the principles of the subject invention. The load bearing implant device  50  is representative of a general structure of the various embodiments of the present load bearing implant device shown and/or described herein.  
         [0054]     The load bearing implant device  50  includes a first or upper platform, plate or the like  52  and a second or lower platform, plate or the like  54 . It should be appreciated that the designations “first”, “second”, “upper” and “lower” are arbitrary. A load transfer structure  56  is interposed between the upper and lower platforms  52 ,  54 . The load transfer structure  56  may take various forms but supports and transfers loading (e.g. physiological loading) exerted on the upper platform  52  to the lower platform  54 . The lower platform  54  transfers the loading exerted thereon by the load transfer structure  56  to the substance of the area in which it is implanted (e.g. subchondral bone).  
         [0055]     The load bearing implant device  50  is also shown with a fixation device  58 . The fixation device  58  is depicted in dashed lines to indicate the optional nature thereof. Thus, the fixation device  58  is not a necessary portion of the implant  50 . It is preferable, however, that the implant has some sort of fixation device. The fixation device  58  extends generally axially from the lower platform  54  and is utilized to aid in mounting the load bearing implant device  50  into the bone platform. The fixation device  58  may take various forms which are suitable for mounting the implant into bone (e.g., tibia  41  or condyle  43 ).  
         [0056]     The upper and lower platforms  52 ,  54  are axially spaced from one another by the load transfer structure  56 . An area  60  between the upper platform  52  and the lower platform  54  may be utilized to retain a scaffold, matrix or the like of a resorbable material that supports cartilage regeneration (e.g. a bio or artificial material). As such, the area  60  may be termed a scaffold or matrix retention area. The load bearing implant device  50  is designed such that the scaffold or matrix may be inserted before or after the device  50  has been implanted into the bone platform. Whether or not the scaffold or matrix is inserted before or after implantation may depend on the particular form of the load bearing implant device  50 . Particularly, a one-piece implant design may have the scaffold before implantation thereof, while a two-piece implant may receive the scaffold after implantation thereof.  
         [0057]     The load bearing implant device  50  is comprised of a bio-resorbable (resorbable) material. The resorbable material is preferably a poly(ester)s such as poly(lactide), poly(glycolide), poly(caprolactone), poly(dioxanone) or any combination, co-polymer or blend thereof. Other types of resorbable material(s) may also be used.  
         [0058]     The lower platform  54  is preferably, but not necessarily, rigid yet porous. Such porosity may be effected by a porous material or the incorporation of bores, holes, pores or the like. As such the lower platform  54  allows the body access to biologic elements (bone and marrow) from the subchondral bone of the bone platform when the implant device  50  is implanted. The upper plate  52  is preferably likewise rigid, but may or may not be porous.  
         [0059]     The load transfer structure  56  may be rigidly attached to both the upper plate  52  and the bottom plate  54  such that the load bearing implant device  50  is generally of a unitary or single piece structure. Particularly, the load transfer structure  56  adjoins the lower surface  53  of the upper plate  52  and the upper surface  55  of the lower plate  54 . Alternatively, the load transfer structure  56  may be rigidly attached to the upper plate  52  and include a mechanism, structure or configuration that attaches or connects to the lower plate  54  via a mating mechanism, structure or configuration.  
         [0060]     It should be appreciated that the attributes of the general load bearing implant device  50  as described above is applicable to the various particular embodiments of the load bearing implant device described hereinafter. Therefore, unless noted otherwise, the load bearing implant devices described hereinbelow, have and/or exhibit the same attributes as those described for the implant device  50 .  
         [0061]     Referring now to  FIGS. 3-6 , there is depicted an exemplary embodiment of a load bearing implant generally designated  62  in accordance with the present principles. Initially, it should be appreciated that the load bearing implant  62  is shown inverted 180° with respect to the load bearing implant device  50  of  FIG. 3 . This is for ease of depicting the optional fixation device portion  70  thereof.  
         [0062]     The load bearing implant device  62  includes a first plate, platform or the like  64  having a plurality of exposure pores, holes, bores or the like  65 . The plurality of exposure holes  65  (here six of which are shown) are arranged in an annular manner about the plate  64 . The number and/or arrangement of the exposure holes  65  is generally arbitrary, but may be arranged to control the exposure of the defect area and scaffold to the normal joint environment. The greater the hole area (hole size and hole number), the greater the exposure. The plate  64  also includes a center hole or bore  76  that aids in insertion of the device  62  into the bone platform.  76  is the load-transferring mechanism, which in this case is a ring-shaped structure.  
         [0063]     The load bearing implant device  62  also includes a second plate, platform or the like  66  having a plurality of exposure pores, holes, bores or the like  67 . Again, the plurality of exposure holes  67  (here six of which are shown) are arranged in an annular manner about the plate  66 . The number and/or arrangement of the holes  67  is generally arbitrary, but may be arranged to control the exposure of the defect area and scaffold to the normal joint environment. The greater the hole area (hole size and hole number), the greater the exposure. The plate  66  also includes a center hole or bore  75  that aids in insertion of the device  62  into the bone platform. The center hole  75  is intended to be just another bore.  
         [0064]     The fixation device  70  comprises a tubular body  71  that axially projects from the second plate  66 . The tubular body  71  has an axial bore  72  that is aligned coaxially with the center holes  75  and  77  of plates  66  and  64  respectively. A plurality of fins (anchors)  73  radially project from the tubular body  71 . The fins  73  are fashioned as triangles. The fins may be embodied as ribs, barbs or the like and aid in the retention of the tubular body  71  in a bore in a defect area in the bone platform (see  FIG. 32  and accompanying description). Of course, the fixation device  70 , may takes other forms.  
         [0065]     The load bearing implant device  62  of  FIGS. 3-6  includes a load transfer structure  68 . The load transfer structure  68  is embodied as a plurality (e.g. four as shown) of arc shaped or arcuate walls, portions, sections or the like  76 . The arcuate walls  76  are situated about the center holes  75  and  77  of the plates  66  and  64 . In this embodiment, the load transfer structure  68  is rigidly attached to both the first and second plates  64  and  66  to comprise a one-piece load bearing implant device.  
         [0066]     The load bearing implant device  62  also defines a cartilage scaffold/matrix retention area  74  between the platforms  64  and  66 . The retention area  74  receives and retains a cartilage scaffold/matrix such as is known in the art.  
         [0067]     Referring now to  FIGS. 7-9 , there is depicted an alternative embodiment of the present load bearing implant device generally designated  80 . The load bearing implant device  80  is preferably made of the same material(s) as previously discussed. The load bearing implant device  80  has an upper or first plate or platform  82  and a lower or second plate or platform  84 . The upper plate  82  includes a plurality of bores or holes  83  for defect area exposure in like manner to the load bearing implant device  62 . The plurality of exposure bores  83  are arcuately spaced about a center bore  86 . The lower plate includes a plurality of bores or holes  85  for defect area exposure in like manner as the upper plate  82 . The plurality of bores  85  are arcuately spaced about the center bore  87 . The number, size and/or arrangement of the bores  83  and  85  of the respective plates  82  and  84  may be modified as appropriate.  
         [0068]     The load bearing implant device  80  also defines a cartilage scaffold/matrix retention area  90  between the platforms  82  and  84 . The retention area  90  receives and retains the cartilage scaffold/matrix.  
         [0069]     The load bearing implant device  80  of  FIGS. 7-9  also includes a load transfer structure  88 . The load transfer structure  88  is embodied as a plurality (e.g. six as shown) of columns, cylinders or the like  92 . The columns walls  92  are situated about the center holes  86  and  87  of the plates  82  and  84 . In this embodiment, the load transfer structure  88  is rigidly attached to both the first and second plates  82  and  84  to comprise a one-piece load bearing implant device. Placement of the load transfer columns  92  may vary as appropriate.  
         [0070]     Referring now to  FIGS. 10 and 11 , another alternative embodiment of a load bearing implant device is shown, generally designated  96 . The load bearing implant device  80  is preferably made of the same material(s) as previously discussed. The load bearing implant device  96  includes an upper plate  98  and a lower plate  100 . The upper plate  98  may or may not have exposure holes.. The lower plate  100  includes a plurality of exposure bores  101  that are arcuately arranged in the plate about a center bore  108 . The number, size and/or arrangement of the bores  101  of the plate  100  may be modified as appropriate.  
         [0071]     The load bearing implant device  96  also defines a cartilage scaffold/matrix retention area  104  between the platforms  98  and  100 . The retention area  104  receives and retains the cartilage scaffold/matrix.  
         [0072]     The load bearing implant device  80  of  FIGS. 10 and 11  includes a load transfer structure  102 . The load transfer structure  102  is embodied as a plurality (e.g. three as shown) of rectangular walls, blocks or the like  106 . The rectangular walls  92  extend radially from the center hole  108  of the plate  100 . In this embodiment, the load transfer structure  102  is rigidly attached to both the first and second plates  98  and  100  to comprise a one-piece or unitary load bearing implant device.  
         [0073]     Referring now to  FIGS. 12 and 13 , an alternative embodiment or modification of an upper plate or platform is shown, generally designated  110 . The upper plate  110  is preferably, but not necessarily, made of a polymeric material such as that described above. The upper plate  110  may be used in any of the implant embodiments shown herein. Particularly, the upper plate  110  may be used in place of the upper plate of any of the load bearing implant devices shown and/or described herein, or may be attached to the upper plate of any of the load bearing implant devices shown and/or described herein.  
         [0074]     The plate  110  is defined by a body  112  having a domed portion  114  surrounded by a rim  118 . The dome portion  114  defines a convex articulating surface  115  and thus a concave underside surface  117 . The configuration of the modified top  110  provides a condylar-shaped articulating surface. Preferably, but not necessarily, the plate  110  does not include exposure holes. In lieu of such exposure holes, the plate  110  may be porous or solid.  
         [0075]     As indicated above, one form of the present load bearing implant device is a two-piece design rather than a single piece design. It should be appreciated, however, that the load bearing implant device may be fashioned from more than two pieces if appropriate.  
         [0076]     Referring now to  FIGS. 14 and 15 , an alternative embodiment of an upper platform structure is shown, generally designated  120 , for a two-piece load bearing implant device. The upper platform structure  120  is again preferably made of a polymeric material as described above.  
         [0077]     The upper platform structure  120  includes a plate  122  having a plurality of exposure holes or bores  124  arcuately arranged about a center bore  123 . A load transfer structure  125  is integral with the plate  122  (i.e. a unitary structure). The load transfer structure  125  consists of a plurality (e.g., three as depicted) of rectangular blocks or walls  126  each having a mating structure  128 . Of course, the load transfer structure  125  may consist of columns, rings, wedges or the like. The rectangular blocks extend radially outward from the center hole  123  toward the periphery of the plate  122 . Each mating or attachment structure  128  includes first and second prongs  130  and  131 . Each prong extends axially upward then radially outward to define a hook shape. The hook shape provides mating of the prongs with a configured lower plate as shown in  FIGS. 16-20 .  
         [0078]     Referring now to  FIGS. 16-20 , there is depicted an exemplary lower platform structure generally designated  132  that may be used with the upper plate structure  120  of  FIGS. 14-15 . The upper and lower platform structures  120  and  132  provide a two-piece snap or press fit implant design. The lower plate structure  132  is defined by a platform or plate  134  having a plurality of exposure bores  136 . The plurality of exposure bores  136  are arcuately provided about a center bore  137 . Again, the size, number and/or arrangement of the exposure bores  136  are appropriate for the degree of exposure desired.  
         [0079]     The plate  134  further defines a rim  141  having a tapered, beveled, or radiused edge  138 . Extending radially outwardly from the center bore  137  is a plurality of rectangular bores  139  each of which has a ledge, shelf, protrusion, tab or the like  140  that extends therein as part of a connection, attachment or mating structure. Each bore and ledge combination is configured to receive a prong  130 / 131  of each load transfer structure  126 . This provides a snap or press fit attachment or connection of the upper platform structure  120  with the lower platform structure  132 .  
         [0080]     It should be appreciated that the upper platform structure  120  is shown with two prongs  130 / 131  on each load transfer structure  126 , while the receiving bores  139  of the lower plate structure  132  shows only one snap receiving structure  140  for clarity. In order to actually receive the upper platform structure onto the lower platform structure, there would either be only one prong on the load transfer structure of the upper platform structure, or there would be two receiving structures in the receiving bore.  
         [0081]     The two-piece structure of the load bearing implant device defined by the upper platform structure  120  and the lower platform structure  132  allows for easier manufacture of the implant device. Moreover, once the lower platform structure  132  is implanted into the patient, the resorbable cartilage scaffold/matrix is situated thereon. The upper platform structure  120  is then situated onto the lower platform structure  120 . This gives the user the ability to select the type of resorbable scaffold/matrix material to be used with the load bearing implant device.  
         [0082]     With the two-piece axial snap or press fit design of  FIGS. 14-20 , almost all of the force that will be exerted onto the implant device will be axial loading. As such, there the upper platform structure  120  will resist separation from the lower platform structure.  
         [0083]     Referring now to  FIGS. 21-24 , there is depicted an alternative embodiment of a lower platform structure, generally designated  150 , that may be used with the upper platform structure of  FIGS. 14-15 . The lower platform structure  150  provides a twist and lock configuration for receiving, attaching and retaining an upper platform structure. The lower platform structure  150  is preferably made of a resorbable polymeric material such as that described above. Moreover, the lower platform structure  150  is preferably a unitary piece.  
         [0084]     The lower platform structure  150  is defined by a disk-shaped body, plate or the like  152  defining a first surface  153  and an opposite second surface  155 . The plate  152  further defines an annular rim or periphery  157  having an annular taper, bevel or angled portion  158  transitioning between the rim  157  and the angled portion  158 .  
         [0085]     The plate  152  includes a plurality of exposure bores or holes  154  that are arranged about a center bore or hole  156 . As with previous plates, the size, number and arrangement of the exposure holes  154  and/or the center hole  156 , as well as whether to incorporate exposure holes or not, are subject to discretion depending on exposure factors. Additionally, the plate  152  has a plurality (e.g. three as shown) of configured bores  160  arranged about the center hole  156  and adjacent the exposure holes  154 . Each configured bore  160  is adapted to receive and retain a mating structure (e.g., mating structure  128  of  FIG. 14 ) of the load transfer structure (e.g., load transfer structure  125  of  FIG. 14 ) of the upper platform (e.g., upper platform structure  120  of  FIG. 14 ).  
         [0086]     Each configured bore  160  has a projection, ledge, shelf or the like  162  projecting into the interior of the bore. The ledge  162  defines a retention mechanism for a prong of the upper platform structure. Each prong would require a separate ledge. Thus, to receive the two-pronged load transfer structure of the upper platform structure of  FIGS. 14-15 , each configured bore  160  would require two ledge structures. Once a prong is inserted into the configured bore, a twist thereof sets the ledge into under each prong. This motion, twist locks the upper plate platform into the lower plate platform.  
         [0087]     In  FIG. 25 , there is depicted another exemplary embodiment of an upper platform structure generally designated  170 . The upper platform structure  170  provides another example of one portion of a two-piece load bearing implant structure. Particularly, the upper platform structure  170  provides a structure that is retained onto a lower plate (see, e.g., plate  210  of  FIGS. 27-31 ) in a press or snap fit manner.  
         [0088]     The upper platform structure  170  is made of a polymeric material such as that described above and includes a plate  172  and a plurality of load transfer structures  176  that each axially extend from an upper surface  175  of the plate  172 . The plate  172  also includes a center bore  174 .  
         [0089]     Each load transfer structure  176  is fashioned as a wedge having a mating structure  178  thereon. Each mating structure  178  is configured to be press fit received into a complementary lower platform structure or plate. Particularly, each mating structure  178  is here embodied as a truncated cone (cone section)  180  having two, diametrically opposed flanges  181 . While only two flanges  181  are shown, the cone section  180  may support more or less flanges  181  as deemed appropriate.  
         [0090]     Referring now to  FIG. 26 , there is shown another exemplary embodiment of an upper platform structure generally designated  190 . The upper platform structure  190  provides another example of one portion of a two-piece load bearing implant structure. Particularly, the upper platform structure  190  provides a structure that is retained onto a lower plate (see, e.g., plate  210  of  FIGS. 27-31 ) in a press or snap fit manner.  
         [0091]     The upper platform structure  190  is made of a polymeric material such as that described above and includes a plate  192  having a plurality of exposure bores  194  arranged about a center hole  196 . The plate  192  supports a plurality of load transfer structures  198  that each axially extend from an upper surface  195  of the plate  192 . Each load transfer structure  198  is configured as a column, tube or the like having a first conical section or annular taper  200  and a second conical section, cone or tapered head  202 . The cone  202  defines a skirt  203  that provides a manner of preventing the pulling out or reversal of the load transfer structure  198  when inserted into the corresponding lower platform structure. Cone  202  is intended to provide a mechanism for fixation into the subchondral bone.  
         [0092]     Referring now to  FIGS. 27-31 , there is depicted an exemplary lower platform structure, generally designated  210 , that can accommodate either one of the two exemplary upper platform structures  170  of  FIG. 25  and  190  of  FIG. 26 . The lower platform structure  210  is defined by a body  212  in the shape of a plate, platform or the like that is fashioned from a suitable resorbable polymeric material such as that described above. The plate  212  defines an annular rim or periphery  218  between a first surface  213  and a second surface  215 . Additionally, the plate  212  has an annular taper, bevel or angled surface  219  providing a transition between the rim  219  and the second surface  215 .  
         [0093]     The plate  212  further includes a plurality of exposure holes  216  that are arranged about a center bore  214 . The size, number and/or arrangement of the exposure bores  216  are modifiable as necessary. Situated between each exposure bore  216  is a receiving, reception or mating bore  220  for a plurality of receiving bores  220 . As best seen in  FIG. 31 , each receiving bore  220  is conical in shape and includes notches  221 . The notches  221  allow for the reception of the flanges  181  of the load transfer structures  180  of the upper platform structure  170  of  FIG. 25 , and the reception of the skirt  203  of the upper platform structure  190  of  FIG. 26 .  
         [0094]     Referring lastly to  FIG. 32 , there is depicted an exemplary illustration depicting a load bearing implant device  240  fashioned in accordance with the principles of the subject invention implanted into a defect area  230  of a bone platform  228 . A bore  236  has been formed in the subchondral bone  232  below the defect area in order to accommodate the fixation device  248  of the load bearing implant device  240 .  
         [0095]     The first or lower plate  244  of the load bearing implant device  240  is situated proximate and/or adjacent the subchondral bone  232  where the cartilage  234  meets the subchondral bone  232 . The second or upper plate  242  of the load bearing implant device  240  is situated at the surface of the cartilage  234 . A scaffold or matrix  252  is situated in between the two plates  242 ,  244  within the scaffold/matrix reception area of the load bearing implant device.  
         [0096]     In each embodiment, load or pressure exerted onto the load bearing implant device structure (e.g., upper plate) at the articulating surface transfers the physiologic load to the load transfer structure. The load transfer structure then transfers the load to the device structure (e.g., lower plate) adjacent the defect area of the subchondral bone. This exerted pressure on the subchondral bone reduces the resorption of subchondral bone and/or the stimulation of subchondral bone synthesis. The load bearing implant device itself is resorbable, being preferably made of a resorbable polymeric material or materials. The subject invention also aids in the regeneration of cartilage tissue in load bearing regions with the ability to receive and retain a resorbable, cartilage regeneration scaffold or matrix (mesh, foam or the like).