U.S. patent number 3,879,767 [Application Number 05/441,350] was granted by the patent office on 1975-04-29 for prosthesis for articulating body structures.
This patent grant is currently assigned to Cutter Laboratories, Inc.. Invention is credited to James A. Stubstad.
United States Patent |
3,879,767 |
Stubstad |
April 29, 1975 |
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.
Inventors: |
Stubstad; James A. (Lafayette,
CA) |
Assignee: |
Cutter Laboratories, Inc.
(Berkeley, CA)
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Family
ID: |
26915267 |
Appl.
No.: |
05/441,350 |
Filed: |
February 11, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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220877 |
Jan 26, 1972 |
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Current U.S.
Class: |
623/21.19;
128/DIG.21 |
Current CPC
Class: |
A61F
2/30907 (20130101); A61F 2/4003 (20130101); A61F
2/4014 (20130101); A61F 2/4261 (20130101); Y10S
128/21 (20130101); A61F 2002/30878 (20130101) |
Current International
Class: |
A61F
2/30 (20060101); A61F 2/42 (20060101); A61F
2/40 (20060101); A61f 001/24 () |
Field of
Search: |
;3/1
;128/92C,92CA,92R,334R,DIG.21 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1,047,640 |
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Jul 1953 |
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FR |
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976,768 |
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Apr 1964 |
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DT |
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Other References
"Teflon Hip Prostheses in Dogs" by J. D. Leidholt et al. .
The Journal of Bone & Joint Surgery, Vol. 47-A, No. 7, pp.
1414-1420, October 1965 .
"Silicone Rubber Implants for Replacement of Arthritic or Destroyed
Joints in the Hand" by Alfred B. Swanson. .
Surgical Clinics of North America, Vol. 48, No. 5, Oct. 1968, pp.
1113-1127..
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Primary Examiner: Frinks; Ronald L.
Attorney, Agent or Firm: Owen, Wickersham & Erickson
Parent Case Text
This is a continuation, of application Ser. No. 220,877 filed Jan.
26, 1972 now abandoned.
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.
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.
* * * * *