Patent Application
20060235542
The invention relates to implants for skeletal joints. In particular, the invention relates to implants having a bearing surface for restoring articular function to joints.
Movable skeletal joints include abutting joint components lined with articular cartilage. Degenerative and traumatic damage to the articular cartilage can result in pain and restricted motion. Surgical joint repair is frequently utilized to alleviate the pain and restore joint function. During this surgery, a prosthetic bearing implant is interposed between the opposed bones of the joint to ease joint articulation. In some cases, the bearing implant is attached to one joint component and articulates with another joint component. In other cases, the bearing implant is in the form of a spacer that articulates with both abutting joint components. In cases of limited damage, it has been proposed to repair discrete defects on an articular surface. In cases of more extensive damage, entire joint compartments are replaced. In many cases, all of the articulating joint surfaces are replaced.
The present invention provides a bearing implant for replacing a portion of an articular joint defined by abutting joint components.
In one aspect of the invention, the bearing implant includes a first portion and a second portion opposite the first portion joined to the first portion. At least one of the first and second portions includes a surface defined by a plurality of segments. The segments are movable relative to one another to conform to an abutting joint component. At least one of the first and second portions defines a bearing surface engageable in joint articulating relationship with an abutting joint component.
In another aspect of the invention, the bearing implant comprises a relatively flexible layer; a plurality of discrete, relatively inflexible segments separate from the flexible layer; and a way to intraoperatively attach the segments to the flexible layer to form a flexible segmented implant engageable by the abutting joint components.
In another aspect of the invention, a method comprises: inserting a first, relatively flexible first component into the joint; and joining a plurality of relatively inflexible segments to the first component in the joint to define a surface engageable with a joint component.
Various examples of the present invention will be discussed with reference to the appended drawings. These drawings depict only illustrative examples of the invention and are not to be considered limiting of its scope.
Embodiments of a flexible segmented bearing implant include a body having opposed top and bottom portions. At least one of the top and bottom portions is configured to articulate with an abutting joint component. The bearing implant may function as a replacement for damaged or diseased cartilage of a skeletal joint to sustain continued joint function. The bearing implant may be used to replace a portion of any skeletal joint including, but not limited to, joints of the hip, knee, shoulder, spine, elbow, wrist, ankle, jaw, and digits of the hand and foot. The implant may be configured to replace a relatively small defect within the joint, an entire compartment of the joint, and/or the total joint. The abutting joint component with which the implant articulates may be another implant and/or the natural joint surface. The bearing implant may have a top bearing surface and a bottom fixation surface, a top fixation surface and a bottom bearing surface, or top and bottom bearing surfaces.
The bearing surface may be made of any material suitable for articulation with natural or prosthetic opposing bearing surfaces. For example, the bearing surface may be made of metal, ceramic, polymer, hydrogel, and/or other materials The bearing surface may be flexible to facilitate intraoperative flexing, cutting, and/or otherwise shaping of the bearing surface to fit a surgical site. Flexibility may be imparted by the material used for the articular surface. For example, the bearing surface may include polymers, thin metals, and/or other suitable flexible materials. For example, polymers may include polyolefins, polyesters, polyimides, polyamides, polyacrylates, polyketones, and/or other suitable materials. For example the bearing surface may include ultrahigh molecular weight polyethylene.
Flexibility may also be imparted by segmenting the bearing surface. The segments may be in the form of polygons, circles, ellipses, freeform curves, and/or other suitable shapes. The segments may be in the form of elongated strips, short segments, and/or other suitable shapes. The segments may be arranged in linear patterns, curved patterns, and/or other suitable patterns. The segments may be formed from a continuous piece of bearing material by cutting, scoring, punching, molding, and/or otherwise forming the bearing surface. The segments may be completely separated or they may include some interconnecting and/or overlapping bearing material. The segments may be joined to a separate opposing portion. For example, the top surface of the implant may be defined by segments joined to the opposing bottom portion of the implant to support the segments. The segments may be formed before or after the opposing portions are joined. For example a piece of bearing material may be joined to the opposing portion and subsequently the bearing surface may be formed into discrete segments. In another example, the segments may be provided as discrete segments to which the opposing portion is subsequently joined. The segments may abut one another, overlap one another, or be spaced apart. The bearing material may be relatively more rigid than the opposing surface material. For example, the segments may have rigid, hard bearing surfaces and the opposing portion may be relatively flexible such that the implant conforms to the underlying anatomic surface. The opposing portion may permit relative motion of the bearing surface segments during articulation. The bearing surface segments may be able to pivot to orient the segments relative to an abutting articular component. For example the segments may be able to rock relative to one another to orient each segment bearing surface normal to the abutting articulating component. The segments may be able to move sufficiently relative to the opposing portion to conform the segmented bearing surface to the shape of the abutting bearing component. The segments may be shaped and arranged such that the implant flexes into a predetermined shape corresponding to a desired anatomic shape. For example, the segments may be configured so that the implant flexes into a dished, channeled, ridged, and/or other suitable shape.
The bearing surface may include a lubricant to ease articulation. For example, the bearing surface may include hyaluronic acid and/or a hydrodynamically lubricated hydrogel layer. For example, the bearing surface may include hyaluronic acid impregnated into the surface. The bearing surface may include a hydrogel having a three dimensional network of polymer chains with water filling the void space between the macromolecules. The hydrogel may include a water soluble polymer that is crosslinked to prevent its dissolution in water. The water content of the hydrogel may range from 20-80%. The high water content of the hydrogel results in a low coefficient of friction for the bearing due to hydrodynamic lubrication. Advantageously, as loads increase on the bearing component, the friction coefficient decreases as water forced from the hydrogel forms a lubricating film. The hydrogel may include natural or synthetic polymers. Examples of natural polymers include polyhyaluronic acid, alginate, polypeptide, collagen, elastin, polylactic acid, polyglycolic acid, chitin, and/or other suitable natural polymers and combinations thereof. Examples of synthetic polymers include polyethylene oxide, polyethylene glycol, polyvinyl alcohol, polyacrylic acid, polyacrylamide, poly(N-vinyl-2-pyrrolidone), polyurethane, polyacrylonitrile, and/or other suitable synthetic polymers and combinations thereof.
The bearing surface may attach to the opposite portion by bonding, mechanical fasteners, porous interdigitation, and/or other suitable attachment methods. For example, the opposite portion may include an open porous structure in which a portion of the bearing surface is integrated to attach the bearing surface to the opposite portion.
A fixation surface may fix the implant to an underlying anatomic surface to support the bearing surface in generally fixed relationship relative to the surgical site. The fixation surface may be solid or porous. The fixation surface may be configured to be cemented in place, to be press-fit in place, to receive tissue ingrowth, and/or to be anchored to tissue in any other suitable tissue anchoring configuration. For example, the fixation surface may include an open porous structure for placement adjacent to body tissue to receive tissue ingrowth to anchor the implant adjacent the tissue. A porous structure may be configured to promote hard and/or soft tissue ingrowth. The porous structures may be in form of an open cell foam, a woven structure, a grid, agglomerated particles, and/or other suitable structures and combinations thereof.
The fixation surface may include any suitable material including, but not limited to, metals, polymers, ceramics, hydrogels and/or other suitable materials and combinations thereof. For example, a polymer fixation surface may include resorbable and/or non-resorbable polymers. Examples of resorbable polymers include polylactic acid polymers, polyglycolic acid polymers, and/or other suitable resorbable polymers. Examples of non-resorbable polymers include polyolefins, polyesters, polyimides, polyamides, polyacrylates, polyketones, and/or other suitable non-resorbable polymers. A metal fixation surface may include titanium, tantalum, stainless steel, and/or other suitable metals and alloys thereof. The fixation surface may provide a suitable surface for hard tissue ingrowth. For example, the fixation surface may include a porous tantalum material having a structure similar to that of natural trabecular bone. Such a material is described in U.S. Pat. No. 5,282,861 entitled “Open Cell Tantalum Structures For Cancellous Bone Implants And Cell And Tissue Receptors”. The material is fabricated by vapor depositing tantalum into a porous matrix. The fixation surface may include protruding pegs or other bone engaging features to further enhance the connection of the fixation surface to tissue.
Tissue growth promoting substances may be included in the implant and/or added at the time of surgery. Examples of tissue promoting substances include hydroxyapitite, particulate bone, bone growth proteins, autologous tissue derived growth factors, bone marrow aspirate, stem cells, and/or other tissue growth promoting substances.
The fixation surface may be flexible to facilitate intraoperative flexing, cutting, and/or otherwise shaping of the fixation surface to fit a surgical site. Flexibility may be imparted by the material used for the fixation surface. For example, the fixation surface may include polymers, thin metals, hydrogels, and/or other suitable flexible materials.
Flexibility may also be imparted by segmenting the fixation surface. The segments may be in the form of polygons, circles, ellipses, freeform curves, and/or other suitable shapes. The segments may be in the form of elongated strips, short segments, and/or other suitable shapes. The segments may be arranged in linear patterns, curved patterns, and/or other suitable patterns. The segments may be formed from a continuous piece of fixation surface material by cutting, scoring, punching, molding, and/or otherwise forming the fixation surface. The segments may be completely separated or they may include some interconnecting and/or overlapping fixation material. The segments may be formed before or after the bearing surface and fixation surface are joined. For example a piece of bearing material may be joined to a piece of fixation surface material and subsequently the fixation surface may be cut to form discrete segments. In another example, the segments may be provided as discrete segments to which a bearing material is subsequently joined. The segments may overlap one another, abut one another, or they may be spaced apart. The fixation surface material may be relatively more rigid than the bearing material. For example, the segments may be relatively rigid and the bearing surface may be relatively flexible such that the fixation surface segments flex relative to one another due to bending of the bearing surface. The segments may be shaped and arranged such that the implant flexes into a predetermined shape corresponding to a desired anatomic shape. For example, the segments may be configured so that the implant flexes into a dished, channeled, ridged, and/or other suitable shape.
The top and bottom portions may be joined with an intermediate layer of flexible material. An intermediate layer may be molded between the top and bottom portions. The top and bottom surfaces may both be segmented. For example, the top portion may define a bearing surface including segments having a hard, smooth bearing surface and the bottom portion may define a fixation surface including segments having a porous bone ingrowth configuration. In another example, the top and bottom portions may both define bearing surfaces. The flexible layer may be sufficiently thick and resilient that the top and bottom surface segments may flex relative to one another. For example, the bottom segmented surface may flex to conform to the shape of an underlying joint component, such as a bone surface, and the top segmented surface may flex independently of the bottom surface to conform to an abutting articulating joint component.
The implant may be formed of discrete segments in which each segment includes a top and bottom joint contacting surface and the discrete segments may be joined together with a flexible material to allow flexing of the implant. For example each segment may have a smooth, relatively non-porous top bearing surface and a rough, relatively porous bone ingrowth bottom surface and the segments may be joined with a flexible material between their sides to permit relative motion of the segments.
The top and bottom surfaces may be joined during manufacture and provided as a flexible implant shaped for a specific anatomic application. The implant may be able to be shaped intraoperatively to fit a surgical site such as by flexing, cutting, and/or tearing the implant. The implant may also be provided as separate top and bottom portions that are joined intraoperatively. For example, one of the components may be supplied as discrete segments and the other supplied as a continuous layer for joining intraoperatively. For example, the bottom surface may be provided as discrete fixation segments that are positionable in a desired pattern on an underlying anatomic surface and the top surface may be provided as a continuous flexible bearing layer that is joined to the segments intraoperatively to form the implant. In another example, the bottom surface may be provided as a continuous flexible layer that is positionable on the underlying anatomic surface and the top surface may be provided as discrete bearing surface segments that are placed on the bottom surface intraoperatively in a desired pattern. In another example, both the top and bottom surface may be provided as discrete segments joined together intraoperatively by a flexible intermediate layer.
The top and bottom surfaces may be joined intraoperatively with mechanical fasteners, adhesives, and/or other suitable joining methods. Mechanical fasteners may include posts, screws, teeth, hook and loop arrangements, and/or other suitable mechanical fasteners. Adhesives may include biologic adhesives, synthetic adhesives, one-part adhesives, multi-part adhesives, heat activated adhesives, light activated adhesives, and/or other suitable adhesives. For example, adhesives may include fibrin adhesive, cyanoacrylate adhesive, bone cement, epoxy, and/or other suitable adhesive. For example, the top and bottom surfaces may be joined by coating one with a first part of a two-part adhesive and the other with a second part, or an activator, of the two-part adhesive and then contacting them intraoperatively to cause the adhesive to cure and join them. In another example, one of the top and bottom surfaces may include a hook arrangement and the other may include a loop arrangement that fasten together on contact. Where the implant includes segments in which each segment includes both a top and a bottom operative surface, the segments may be intraoperatively joined by employing the joining method between the sides of adjacent segments.
A fixation surface may be joined to the underlying anatomic surface with mechanical fasteners, adhesives, bone ingrowth, and/or other suitable joining method. Mechanical fasteners may include posts, screws, teeth, hook and loop arrangements, and/or other suitable mechanical fasteners. Adhesives may include fibrin adhesive, cyanoacrylate, bone cement, epoxy, and/or other suitable adhesive.
Bearing and fixation surfaces may be formed by casting, molding, extruding, machining, and/or other suitable forming processes and combinations thereof.
In the illustrative example, the bottom portion 22 is formed into a grid of discrete, generally planar segments 30 separated by parting lines 32. The parting lines 32 facilitate intraoperative flexing, tearing, cutting, and/or otherwise shaping the implant 10. For example, the parting lines 32 result in a thinner region 34 along which the implant 10 is more flexible. The parting lines 32 may be relatively narrow (not shown) so that the segments 30 abut one another in an unflexed state and appear as one continuous bottom surface. In this configuration, the implant 10 will be more flexible in a direction that tends to open the parting lines 32 and be more rigid in a direction that tends to press the segments 30 together. Alternately, the parting lines 32 may be relatively wide (as shown) to provide a gap between segments 30 to facilitate flexing of the implant 10 both in directions that tend to open the parting lines 32 (
The parting lines 32 also facilitate cutting, tearing and/or otherwise shaping the bottom portion 22. The parting lines 32 present thinner regions 34 of the implant that may be more easily cut with a knife, scissors, shears, or other cutting instrument. The parting lines 32 may extend all the way through a difficult to cut bottom portion 22, such as a metal bottom portion 22 (as shown), so that only the top portion 20 need be cut intraoperatively. With some materials, the parting lines 32 may make it possible to tear away unneeded segments. The number and shape of the segments 30 and parting lines 32 may be tailored to define predetermined implant shapes corresponding to different surgical sites, differing patient anatomy, and/or different defect shapes and/or sizes. The user can selectively shape the implant along a desired parting line to match the implant shape to the particular use.
In use, the implant 10 is compared to a cartilage region that is to be repaired. The shape of the desired replacement is noted and then the implant is flexed, torn, cut and/or otherwise reshaped along the parting lines 32 to approximate the desired replacement. The implant 10 is then anchored to the underlying tissue by cementing, press fitting, and/or juxtaposing it for hard and/or soft tissue ingrowth. In the illustrative example, holes are drilled into underlying bony tissues and the pegs 28 are pressed into the holes with the segments 30 abutting the underlying bony tissues to facilitate bony ingrowth into the pegs 28 and segments 30 to anchor the implant 10.
The intermediate layer 56 may define a gradient from a harder and/or stiffer material at the surface 52 to a softer and/or less stiff material toward the bottom. The gradient may be defined by placing a softer material in the center of the intermediate material 56. Examples of suitable materials include silicones, urethanes, low density polyethylene, elastomers, and/or other suitable materials.
The intermediate layer 56 may also include a fluid. As the implant is loaded, pressure is redistributed in fluid from loaded to unloaded areas of the implant and increases conformity and contact area of the flexible implant with the abutting joint surface.
The intermediate layer 56 may define a gradient geometrically. For example, voids 57, 58, 59 may be formed in the intermediate layer to change the stiffness of the intermediate layer 56. The voids may extend under multiple segments as shown at 57 or they may be tailored for discrete segments as at 58 and 59. Any combination of voids may be utilized to achieve the desired stiffness. The voids 57, 58, 59 may be empty or filled. For example, they may be filled with a gas, liquid, a gel, and/or some other substance.
Although examples of a bearing implant and its use have been described and illustrated in detail, it is to be understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. The invention has been illustrated in the context of a tibial articular implant. However, the bearing implant may be configured in other shapes and for use at other locations within a patient's body. Accordingly, variations in and modifications to the bearing implant and its use will be apparent to those of ordinary skill in the art, and the following claims are intended to cover all such modifications and equivalents.
This application is a continuation-in-part of U.S. application Ser. No. 11/107,765, filed Apr. 15, 2005.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11107765 | Apr 2005 | US |
| Child | 11402334 | Apr 2006 | US |
