Prosthesis For Articulating Body Structures

Abstract

An article for the relief of pain and restricted movement of joints resulting from arthritic disease or trauma comprising a relatively thick contoured or cup-like member with a curved smooth surface provided by a layer of biocompatible elastomer and the opposite surface covered by a biocompatible tissue-ingrowth receptive material. The prosthesis is so shaped to enable it to cover and become firmly attached to the articulating surface of a bone in a joint.

Parent Case Text

This is a continuation, of application Ser. No. 220,877 filed Jan. 26, 1972 now abandoned.

Description

BACKGROUND OF THE INVENTION

This invention relates to an article which enables free articulating motion between bones of a joint in an animal body. In particular, the invention relates to an article for assuring free movement between the articulating surfaces of the bones in a joint which are scarred or show signs of deterioration as a result of injury, disease, or aging and which have resulted in restriction of motion and painful sequelae.

Many individuals are afflicted with painful joints from arthritic disease or trauma, where two or more bones articulate in ginglymus or sliding contact as in the upper or lower extremities. Direct surgical approaches have been taken in an attempt to alleviate the sources of painful irritation, swelling, and immobility of these joints such as surgically resecting the arthritic joint and implanting artificial joints such as the metacarpal-interphalangeal, or excising and replacing totally affected bones such as the carpal lunate of the wrist. These approaches are so drastic that even though they may be generally successful, they are usually reserved for those advanced cases where the joint or bone is so degenerated as to require such drastic measures of replacement of the joint or bone.

In those cases where the bone in the area of arthritic involvement has not progressed to the stage of serious degeneration and the surgeon hesitates to perform total joint replacement surgery, the attempt is usually made to alleviate the patient's discomfort by more conservative means, such as injection of corticosteroids or other medication into the afflicted joint or by oral administration of a variety of anti-inflammatory agents. This form of treatment rarely provides permanent relief from this painful and incapacitating disease.

Prior to the availability of prosthetic devices for arthritic joints (especially in the upper extremity) it had been common practice to reposition a layer of natural tissue between the resected ends of adjacent bones to reduce painful contact and to improve alignment of the joint in procedures known as resection orthoplasty or pseudoarthrosis. This approach has not proven to be as predictable, stable, or long lasting as desired.

Relief from pain and increased motion has been reported to result from a somewhat less traumatic procedure involving minimal bone resection by surgically placing thin membranes of cellophane or silicone over or between the articulating surface of an afflicted joint (Breck, L. W., Clinical Orthopedics and Related Research, No. 54, 133 (1967), Kessler, I, Plastic and Reconstructive Surgery, 47, 252 (1971). However, these membranes are subject to migration or rolling from the site unless secured to the bone as by sutures or by tissue ingrowth into one side of a membrane which has ingrowth material attached to that side. Such corrective measures, using membranes, must necessarily be restricted to those upper extremity joints subjected only to light load-bearing forces, such as the wrist in normal activities, since heavier load-bearing forces imposed on the membrane would tend to erode the surface of the membrane to the point where it would no longer adequately separate the two bones.

Another surgical approach, short of total joint excision has been the insertion of a pad-like sheet of synthetic sponge material (Ivalon, foamed polyvinylalcohol) between adjacent articulating bones (Cobey, M. C. Clinical Orthopedics and Related Research No. 54, 139, (1967). This approach is limited to those joints where synovial fluid is still present and a portion of the original articular surface is intact. Sponge-like material, while providing good cushioning and separation initially, remains subject to bio-mechanical and chemical degradation with time, due to its inherent thin and porous structure.

Kessler, I. (ibid.) using silicone interpositional plates, demonstrated by clinical experience the need for stabilization of the plates. To achieve stability and fixation of his implant, he molded a lens-shaped prosthesis to which he fixed a Dacron covered stem for intramedullary insertion. Kessler's results appear clinically acceptable for the relief of pain and restoration of function. Kessler's approach requires surgery involving resection of a considerable portion of bone to accommodate the relatively thick head of the prosthesis, dislocation of the joint with attendant resection of joint tissues, and the broaching of an intramedullary cavity in the bone to receive the stem of the prosthesis.

The present invention provides an article adapted to relieve the pain and to increase the motion of a joint afflicted with arthritic disease or trauma, and the article of this invention is adapted to prevent further erosion of the articulating surfaces of the joint. It provides for greater ease of surgical emplacement, thus minimizing the trauma to tissues of the joint which results from the surgical procedure. In its simplest form, the surgery involved in the emplacement of the article of this invention requires essentially no resectioning of the bone or drilling into the bone for emplacement of an intramedullary stem.

The article of this invention is biocompatible, i.e., is not attacked by and does not deleteriously affect body environment, tissue or body fluids; hence it can be left in place permanently. A feature of the article of this invention is that it is contoured or shaped to cover an articulating surface of bone and can be trimmed to fit as desired at the time of surgery.

The article of this invention is adapted to attach quickly and securely to the bone over a large area, thus preventing migration or slipping of the article away from the surface of the bone it is designed to cover. Furthermore, the article is adapted to provide long term use.

In the event the prosthesis of this invention must be removed post-surgically, such as if there should be a development of infection from some cause or other, this removal can be accomplished easily, and post infection healing can take place without attendant contracture of tissues at the joint, as would be the case in other procedures involving resection of significant amounts of bone.

The above and other advantages will become apparent from the description which follows.

SUMMARY OF THE INVENTION

The article of this invention is a shaped, somewhat flexible, cup-like prosthetic member having essentially an inner or concave surface and an outer or convex surface. One of the surfaces is made of open-pore, tissue-ingrowth-receptive material capable of attaching to bone, and the other surface is smooth and is provided by a relatively thick layer of somewhat stiff but still flexible material capable of acting as a sliding joint surface.

Both materials are biocompatible, i.e., they are essentially nonreactive or are not reacted upon unfavorably by body tissues or fluids. For example, the tissue-ingrowth-receptive material may be fabric, such as mesh or velour, made from a synthetic polymer. The smooth-surfaced layer may be made of an elastomeric material or of a natural tissue material such as tanned collagen or reconstituted fibrinogen. The two surfaces of the article may be made of the same material, such as polyurethane, in which one surface is smooth and non-porous and the other surface has open pores and is receptive to tissue ingrowth.

Depending upon which articulating surface of which bone is to be covered by the article, the fabric surface may be on either the convex surface or the concave surface of the article. For example, to cover the head of the humerus bone of the shoulder, the article will have the fabric on the concave surface. To use the article in the wrist, for example to provide a smooth articulating surface between the radius bone of the lower arm and adjacent carpal bone or bones of the hand, the fabric will be on the convex surface of the article for attachment to the hollow or concave surface at the end of the radius bone.

Although not essential to the design or function of the shaped prosthesis, an intramedullary stem may be provided on the fabric-covered side of the prosthesis. When present, this stem is formed at the time of the molding operation and is made of elastomer which may be reinforced and additionally secured to the cup-shaped member by stitching. The outer surface of the intramedullary stem is covered with tissue-ingrowth fabric or other tissue-ingrowth material, which may also be secured to the elastomer body of the stem by stitching and vulcanization. The stem may be any of a number of shapes, usually round or oval, and is meant to be placed into the intramedullary portion of a bone for additional stabilization of the prosthesis. This provision of a stem satisfies a well-established convention among some orthopedic surgeons of utilizing the hollow bone canal for positive, prompt, and mechanical fixation.

In utilizing the present prosthesis, the surgeon exposes the articulating surface of the afflicted bones of the joint, contours the surface of the bone, if necessary, and scarifies or roughens the surface to obtain a raw bleeding surface to invite tissue ingrowth, and places the fabric side of the appropriate sized prosthesis against the scarified surface of the bone. If the prosthesis has a stem, the intramedullary canal is first reamed before emplacement of the prosthesis. The prosthesis is then temporarily secured or affixed, by virtue of its own congruent geometry and by the small intramedullary stem (if present), or by suturing peripheral edges of the prosthesis to the bone. Following a few weeks (from 1 to 3 weeks) of immobilization of the joint, the prosthesis will have become further and more permanently united to the bone as a result of bony or fibrous tissue ingrowth in the fabric surface.

A BRIEF DESCRIPTION OF THE DRAWINGS

The invention and some modes of carrying it out will be illustrated by the specific description herein and by the annexed drawings, wherein:

FIG. 1 is a perspective view of a contoured joint liner prosthesis for the shoulder embodying the principles of this invention.

FIG. 2 is a cross-sectional view in elevation of a portion of the prosthesis of FIG. 1.

FIG. 3 is a perspective view of another form of the prosthesis for the wrist, also embodying the principles of this invention.

FIG. 4 is a somewhat diagrammatic skeletal view of a wrist showing the prosthesis of FIG. 3 in phantom, as emplaced in the radius bone.

FIG. 5 is a view in elevation of a modified form of the prosthesis for the wrist having an attached stem; a portion is in section to show the construction of the prosthesis.

FIG. 6 is a view in elevation with a portion in cross section of a prosthesis generally like that of FIG. 1 but with a stem attached.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show a cup-like prosthesis 10 comprising a contoured hollowed-out cap for covering the head of the humerus. This cap is approximately hemispherical and has a smooth outer or convex surface 12 provided for by a relatively thick layer 14 of elastomer, preferably silicone rubber. Its inner or concave surface 16 consists of tissue-ingrowth-receptive fabric preferably Dacron velour, and between the velour covering 16 and the rubber layer 14 there is a thin layer 18 of elastomer such as silicone rubber reinforced with fabric such as Dacron mesh. Dacron stitching 20 may be used to secure the velour covering 16 to the reinforced rubber layer 18.

The elastomer 14 may be the silicone rubber available in commerce under the trademark Silastic (made by Dow Corning Corp.), but other elastomers may be used instead, such as a fluorosilicone rubber, or polyurethane, or in some instances a higher density polyethylene or polypropylene polymer. Silicone rubber is a preferred elastomer due to its ease of fabrication, wide clinical acceptance, minimal tissue response and known compatibility in joint applications.

The elastomeric layer may be internally reinforced with a biocompatible fibrous material, especially with Dacron or Teflon mesh. This elastomeric layer, with or without reinforcing material is advantageously from 0.060 to 0.250 inch in thickness and the ingrowth-receptive surface is usually from 0.005 to 0.025 inch in thickness.

The tissue-ingrowth material may be a mesh or velour of a suitable polymer such as polyethylene terephthalate available in commerce under the trademark Dacron, or polymerized tetrafluoroethylene (Teflon), or polyurethane. Dacron velour is a preferred tissue-ingrowth material because of the ease with which it can be backed with elastomer and because partial penetration by the elastomer of only one side of the velour structure occurs, leaving the opposite, open pore, velour surface unimpregnated by the elastomer. Thus the encouragement of and receptivity to ingrowth of bone tissue is not substantially reduced.

In the use of prosthesis 10, the surgeon exposes the head of the humerus, having separated or incised the connecting soft tissues, and scarifies the humeral head to provide a bloody surface. The prosthesis 10 is pressed against the head of the humerus; a few stitches through the tapered edge 22 and periosteal tissue temporarily secures the prosthesis. After 1 to 3 weeks of immobilization of the joint, bony or fibrotic tissue ingrowth into the fabric surface 16 securely and permanently anchors the prosthesis. At the time of surgery, any spurs or rough surfaces, resulting from the desease or trauma are removed from the articulating surface of the scapula against which slides the head of the humerus covered with the prosthesis 10. Thus prepared, the joint will remain mobile whether or not cartilage or synovial fluid is present in the joint in normal or reduced amount.

A prosthesis 30 for the wrist, as shown in FIG. 3, has a shape similar to that of a clam shell, i.e., it is a shallow oblong cup-like article. It has a smooth concave surface 32 on one side, as may be provided by a fairly thick layer of silicone rubber, and a covering 34 preferably of Dacron velour, on the opposite or convex side. Between the velour covering 34 and the silicone rubber layer 32 is a thin Dacron mesh reinforced layer of silicone rubber (not visible) which is stitched to the velour with Dacron thread.

FIG. 4 shows how the prosthesis 30 may be placed into the distal end of a radius bone 36 to fit the natural depression in this bone, so that adjacent lunate 38 and scaphoid 40 bones of the wrist may slide freely against the smooth surface 32 of the prosthesis 30. The surface of the shallow depression in the radius bone 36 is roughened or scarified by the surgeon prior to emplacement of the prosthesis 30 to produce a bleeding surface and remove any irregularities or arthritic spurs. As in the shoulder joint prosthesis, following immobilization of the joint for 1 to 3 weeks, fibrous or bony tissue will have grown into the velour covering 34 and provide permanent fixation. It is again not essential for synovial fluid to be present in the space between the prosthesis 30 and the adjacent carpal bones in order for the joint to move freely, although minimal amounts of fluid adequate for lubrication are to be expected in virtually all cases.

A modified form of prosthesis 50 for use in the wrist is shown in FIG. 5. This modified prosthesis 50 has essentially the same oval cup-shaped configuration as the prosthesis 30 except for an intramedullary stem 52 which extends longitudinally from about the center portion of the convex side. The stem 52 may provide additional stability to the prosthesis when emplaced. An articulating cup-shaped portion 54 has essentially the same construction as the prosthesis 30, i.e., an elastomeric (e.g., silicone rubber) layer 56 providing a smooth concave surface 57, a tissue-ingrowth covering 58 (e.g., Dacron velour) on the convex side, and a mesh reinforced elastomeric layer 60 (e.g., Dacron and silicone rubber) in between. The stem 52 may be made of silicone rubber and may contain one or more layers 62 of reinforcing fabric such as Dacron mesh within the body of the stem 52 to provide a degree of stiffness and mechanical stability to the prosthesis. The layer or layers 62 of mesh may be flat or twisted at the time the prosthesis 50 is molded and cured. Dacron stitching 64 in a through-and-through pattern at the base of the articulating portion 54 further secures this portion to the stem 52.

The stem 52 has an outer covering 66, e.g., of Dacron velour, contiguous with the velour covering 58. This covering 66 is attached to the elastomeric body of the stem 52 by an intermediate layer (not visible here) of reinforced elastomer such as silicone rubber to which the velour 58 is later vulcanized and to which it may additionally be stitched. This intermediate layer is also sealed to the silicone body of the stem 52 by vulcanization, thereby accomplishing a bond between the stem 52 and the velour covering 58. Peripheral stitches 68 run around the edge of the prosthesis 50 and serve to join cut edges of the tissue-ingrowth-receptive covering 66 where it has been trimmed to fit. Then stitches 68 also extend into the body of the prosthesis 50 an amount sufficient to pick up reinforcing fibers therein and may, in some cases, extend through the entire stem of the prosthesis.

The stem 52 may be circular or oval in cross section and is preferably of uniform size throughout its length, or it may be tapered towards its outer end. In the illustrated configuration it is circular and of uniform diameter. The diameter of the stem 52 is no larger than the diameter of the intramedullary canal into which it is to be inserted and preferably is somewhat smaller.

A prosthesis 70, shown in FIG. 6, is a modification of the prosthesis 10 for the shoulder, having an intramedullary stem 71 attached to the concave side. The structure of the prosthesis 70 is essentially the same as that for the wrist prosthesis 50. It has a relatively thick convex layer 72 of elastomer such as silicone rubber, an intermediate layer 73 of reinforced elastomer, such as Dacron-mesh-reinforced silicone rubber, an internal core 74 in the stem 72, which may be made of silicone rubber impregnated and reinforced with Dacron mesh or fibers, and an outer covering 75, such as Dacron velour secured, as described previously, to the concave side of the cup-shaped portion 76 and to the stem 71. The stem 71 in this configuration is circular and essentially of uniform diameter throughout its length.

In order to implant those contoured prostheses of this invention which have a stem, the surgery is essentially the same as described above except that the intramedullary canal of the particular bone involved must first be reamed to a depth to accommodate the stem of the prosthesis.

In one of the methods of making the article of this invention, a layer of fabric, preferably Dacron velour, is pressed against a layer of unvulcanized silicone rubber preferably reinforced with Dacron mesh for about one to five minutes. The composite layer is vulcanized at about 300.degree. to 350.degree.F. for several minutes and is then stitched through and through in a suitable pattern with Dacron thread to further secure the velour fabric to the reinforced silicone rubber. The reinforced silicone rubber layer is usually from 0.015 to 0.030 inch thick. The composite layer may be notched with several pie-shaped wedges in essentially a circular pattern so that when the edges of the wedges are stitched together a more or less cup-shaped form is achieved. This is draped over a suitably shaped mold so that the silicone rubber layer is facing outwardly. Alternatively, the composite layer may be stretch draped over the mold. A relatively thick layer of unvulcanized silicone rubber is applied to the composite layer on the mold and a suitably shaped female mold is placed over this layer. While held under mild spring-clamped pressure of about 5 to 20 p.s.i., the complete composite is heated at about 300.degree. to 350.degree.F. for about 10 to 15 minutes to vulcanize the layers together and is then cured out of the mold for from 1 to 3 hours. The article is trimmed as necessary, e.g., to the appropriate cup-shape, washed in pyrogen-free distilled water, sterilized, dried, and suitably packaged ready for use.

The velour surface on the thus shaped article is on the inside or concave surface. For a prosthesis requiring the fabric or tissue-ingrowth surface on the convex surface or side, the shaped article may be flipped inside out or the fabric and elastomer layers may be assembled in the mold in reverse fashion from what was described above.

The thickness, reinforcement, choice of polymer, cushioning, and method of construction of the prosthesis may vary, depending on the amount of load-bearing forces one might anticipate at the particular joint involved. For example, in the ankle, the elastomeric layer of the prosthesis might be thicker so as to withstand for long periods of time the heavier loads that would be imposed on it. The elastomeric layer of a prosthesis in the wrist may be thinner since the loads are generally less. In any event, the thickness, durability, and wear potential of the materials of choice can be selected so as to provide a smooth articulating surface which will function for a reasonable number of years acceptable to the patient and the surgeon. The elastomeric layer may vary from 0.060 to 0.250 inch in thickness. The fabric coating is preferably about 0.005 to 0.025 inch thick so that the thickness of the complete prosthesis will be between 0.065 and 0.275 inch.

The prostheses of this invention are not limited to those specific embodiments described in detail but include countoured or shaped articles of similar construction designed to conform substantially to a rounded or a depressed articulating surface of a bone in a joint, as for example in the hand, ankle, knee, hip, elbow, or mandible. These prostheses will provide long-lasting utility in the relief of pain and freedom of motion, particularly in those joints of the upper extremities where lighter load-bearing forces are experienced.

Clinical trials of the prostheses of this invention have uniformly been successful, partly because of the simplicity of the structure and partly because of the well documented biocompatibility of the preferred materials from which these prostheses have been made. Surgeons have particularly acclaimed the ease of implantation, the simplicity of use, and the minimal risk associated with the prostheses. For example, six human arthritic wrists have been restored to pain-free functional use, one with a stemmed prosthesis like the prosthesis 50 of FIG. 5 and five with simpler contouredcup prostheses like the prosthesis 30 of FIG. 3. Ongoing animal tests in small primates of silicone-surfaced humeral heads articulating against normal glenoid shoulder sockets have all shown encouraging results, demonstrating that cuffed shoulder prostheses like that of FIG. 1 will also make a satisfactory joint-repair prosthesis when released to human clinical trials.

To those skilled in the art to which this invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

Claims

I claim:

1. A countoured prosthesis adapted to cover an articulating surface of a skeletal member comprising a flexible shell shaped to cover said articulating surface and having one side a smooth relatively firm surface provided by biocompatible elastomeric material and having the other side of a reticular three-dimensional, open-pore, tissue-ingrowth-receptive structure means for enabling tissue ingrowth thereinto below the surface with subsurface intertwining and intermeshing of tissue with said structure means, said structure means being secured to said elastomeric material by partial penetration of said elastomeric material into substantially the whole back of said structure means.

2. In a prosthesis for covering an articulating portion of a skeletal member, the improvement comprising a relatively thick, flexible, cup-like member having a first side with biocompatible reticular, three-dimensionally tissue-ingrowth receptive means for enabling subsurface growth of tissue to enter, grow through, intertwine, and intertangle therewith for firm, deep, inner attachment with body tissues, and a second side of smooth biocompatible elastomer providing a slidable surface preventing tissue ingrowth and attachment, said tissue-ingrowth receptive means being secured to said elastomer by partial penetration of said elastomer into substantially the whole back of said tissue-ingrowth receptive means.

3. A prosthesis as in claim 2 wherein said first side is convex and said second side is concave.

4. A prosthesis as in claim 3 wherein said first side has a stem consisting of elastomer which is contiguous with and extends outwardly from said first side.

5. A prosthesis as in claim 4 wherein a biocompatible, tissue-ingrowth-receptive material covers and is secured to said stem by partial penetration of said elastomer into substantially the whole back of said tissue-ingrowth-receptive material.

6. A prosthesis as in claim 4 wherein at least a portion of said elastomer and said stem contains reinforcing fabric.

7. A prosthesis as in claim 2 wherein said first side is concave and said second side is convex.

8. A prosthesis as in claim 7 wherein said first side has a stem of elastomeric material contiguous with and extending outwardly from said first side.

9. A prosthesis as in claim 8 wherein said biocompatible tissue-ingrowth receptive means extends over said stem and is secured to said stem by partial penetration of said elastomer into substantially the whole back of said tissue-ingrowth receptive means.

10. A prosthesis as in claim 8 wherein at least a portion of said elastomer and a portion of said stem contain reinforcing fabric.

11. A prosthesis as in claim 2 wherein at least a portion of said elastomer contains reinforcing fabric.

12. In a prosthesis for covering the articulating surface of the head of a humerus bone, the improvement comprising, a flexible cap-like member having a smooth convex surface provided by a relatively thick layer of biocompatible elastomer and a concave surface covered by a separate discrete covering of tissue-ingrowth-receptive material having a tri-dimensional reticular open-pore structure means for enabling tissue to grow thereinto and become interlocked and intertwined therewith below the surface thereof when said prosthesis is emplaced on the head of a said humerous bone, said tissue-ingrowth-receptive material being secured by partial penetration of said elastomer into substantially the whole back of said tissue-ingrowth-receptive material.

13. A prosthesis as in claim 12 wherein fabric reinforcement lies within said elastomer.

14. A prosthesis as in claim 13 wherein said tissue-ingrowth-receptive material is secured to said reinforcement by stitching.

15. A prosthesis as in claim 14 wherein a stem consisting of elastomer and covered by tissue-ingrowth-receptive material extends outwardly from about the central portion of said concave surface, said tissue-ingrowth-receptive material being secured by partial penetration of said elastomer into substantially the whole back of said tissue-ingrowth-receptive material on said stem.

16. A prosthesis for covering the articulating surface of the distal end of a radius bone, comprising, a contoured cup-like member having a smooth concave surface provided by a relatively thick layer of biocompatible elastomer and a convex surface of said elastomer covered by a tissue-ingrowth-receptive material secured to said elastomer by partial penetration of said elastomer into substantially the whole back of said tissue-ingrowth-receptive material, said tissue-ingrowth-receptive material having a tridimensional reticular open-pore structure means for enabling tissue to grow thereinto and to become intertwined and interlocked therewith below the surface means when said prosthesis is emplaced on a said radius bone.

17. A prosthesis as in claim 16 wherein fabric reinforcement lies between said elastomer and said tissue-ingrowth-receptive material.

18. A prosthesis as in claim 17 wherein said tissue-ingrowth-receptive material is secured to said reinforcement by stitching.

19. A prosthesis as in claim 18 wherein a stem consisting of elastomer and covered by tissue-ingrowth-receptive material extends outwardly from about the central portion of said convex side, said tissue-ingrowth receptive material being secured by partial penetration of said elastomer into substantially the whole back of said tissue-ingrowth-receptive material on said stem.