U.S. patent number RE38,409 [Application Number 07/191,225] was granted by the patent office on 2004-01-27 for ball and socket bearing for artificial joint.
This patent grant is currently assigned to Joint Medical Products Corporation. Invention is credited to Douglas G. Noiles.
United States Patent |
RE38,409 |
Noiles |
January 27, 2004 |
Ball and socket bearing for artificial joint
Abstract
A ball and socket joint for implanting in the body is provided
wherein the socket portion of the joint can have various
orientations with respect to the patient's anatomy, and the
orientation used for a particular patient can be selected and/or
changed in situ, that is, during or after implantation of the
joint. In addition, the configuration of the joint, e.g.,
constrained versus semi-constrained, as well as the materials
making up the socket portion of the joint, e.g., plastic versus
metal, can be selected and/or changed in situ. The questions raised
in reexamination request Nos. 90/004,732, filed Aug. 26, 1997 and
90/005,596, filed Jun. 22, 1999, have been considered and the
results are reflected in this reissue.
Inventors: |
Noiles; Douglas G. (New Canaan,
CT) |
Assignee: |
Joint Medical Products
Corporation (Warsaw, IN)
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Family
ID: |
27044134 |
Appl.
No.: |
07/191,225 |
Filed: |
May 6, 1988 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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473431 |
Mar 8, 1983 |
4642123 |
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Reissue of: |
553520 |
Nov 21, 1983 |
04678472 |
Jul 7, 1987 |
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Current U.S.
Class: |
623/22.25;
623/23.39 |
Current CPC
Class: |
A61F
2/32 (20130101); A61F 2002/349 (20130101); A61F
2220/0041 (20130101); A61F 2/3609 (20130101); A61F
2002/3443 (20130101); A61F 2002/30662 (20130101); A61F
2002/3054 (20130101); A61F 2002/30975 (20130101); A61F
2220/0025 (20130101); A61F 2002/3241 (20130101); A61F
2002/3493 (20130101); A61F 2002/30426 (20130101); A61F
2002/3233 (20130101); A61F 2002/30433 (20130101); A61F
2002/3631 (20130101); A61F 2002/3208 (20130101) |
Current International
Class: |
A61F
2/32 (20060101); A61F 2/34 (20060101); A61F
2/36 (20060101); A61F 2/00 (20060101); A61F
2/30 (20060101); A61F 002/30 () |
Field of
Search: |
;623/16,18,19,20,21,22,23 |
References Cited
[Referenced By]
U.S. Patent Documents
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7104212 |
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May 1971 |
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DE |
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2244645 |
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Mar 1974 |
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DE |
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2323456 |
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Nov 1974 |
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DE |
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2513511 |
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Oct 1975 |
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DE |
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2845231 |
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May 1979 |
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DE |
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2903366 |
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Aug 1979 |
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DE |
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2950536 |
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Jul 1981 |
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DE |
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81/060262 |
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Jul 1981 |
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DE |
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123514 |
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Aug 1981 |
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65482 |
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EP |
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91315 |
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EP |
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FR |
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2154246 |
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FR |
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2343919 |
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FR |
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2416004 |
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Aug 1979 |
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FR |
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2445909 |
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Aug 1980 |
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FR |
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1126961 |
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Sep 1968 |
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GB |
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2007980 |
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GB |
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2029230 |
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GB |
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2052620 |
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Jan 1981 |
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GB |
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2013503 |
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Sep 1982 |
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GB |
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2117646 |
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Oct 1983 |
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GB |
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.
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|
Primary Examiner: Isabella; David J.
Attorney, Agent or Firm: Klee; Maurice M. Inz; Richard
A.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATION
This is a continuation-in-part of copending application Ser. No.
473,431, filed Mar. 8, 1983 no U.S. Pat. No. 4,642,123.
Claims
What is claimed is:
1. A ball and socket joint for implantation in a patient's body
comprising a ball portion and a socket portion, the ball portion
including: a ball; and first fixation means for attachment to a
first bony structure, said fixation means being connected to said
ball .Iadd.by a neck element.Iaddend.; and the socket portion
including: a bearing .[.for receiving.]. .Iadd.having an inner
bearing surface configured to receive and surround a portion of
.Iaddend.the ball .Iadd.wherein the ball in combination with the
neck element are free to move within the bearing in a plurality of
directions.Iaddend.; second fixation means for attachment to a
second bony structure, said second fixation means having a cavity
for receiving the bearing, said cavity having an opening defining a
.Iadd.first .Iaddend.plane through which the bearing enters the
cavity; and means for securing the bearing to the second fixation
means in any one of a plurality of selectable orientations after
the second fixation means has been attached to the second bony
structure, said plurality of selectable orientations being
angularly .[.displace.]. .Iadd.displaced .Iaddend.from one another
about an axis which is perpendicular to the .Iadd.first
.Iaddend.plane .[.defined by the opening of the cavity of the
second fixation means.]. ; the bearing .[.being.]. .Iadd.having a
configuration which is .Iaddend.non-symmetric with regard to
rotation about said axis .[.and.]. .Iadd.such that the angular
range of motion of the ball with the neck element within the
bearing relative to the axis is smaller in at least one first
direction than in at least one other direction, .Iaddend.said lack
of symmetry making at least one of the selectable angular
orientations of the bearing more preferred for physiological
reasons than others of said angular orientations, said means for
securing allowing said bearing to be secured to said second
fixation means in such a preferred orientation after said second
fixation means has been attached to the second bony structure.
2. The ball and socket joint of claim 1 wherein the means for
securing comprises bayonet spaces and lugs.
3. The ball and socket joint of claim 1 wherein the means for
securing includes two coaxial pin members and the bearing includes
two coaxial cylindrical surfaces which receive the pin members, the
pin members and the cylindrical surfaces allowing the bearing to
rotate within the cavity of the second fixation means about a
single axis, said single axis being orthogonal to the axis which
defines the plurality of selectable angular orientations, the
orientation of the single axis with respect to the anatomy of the
patient's body making at least one of the selectable angular
orientations of the bearing more preferred for physiological
reasons than others of said angular orientations.Iadd., said at
least one first direction being orthogonal to the single
axis.Iaddend..
4. The ball and socket joint of claim 1 wherein the bearing
includes a lip to restrain dislocations of the ball from the
bearing, the orientation of said lip with respect to the anatomy of
the patient's body making at least one of the selectable angular
orientations of the bearing more preferred for physiological
reasons than others of said angular orientations.Iadd., said at
least one first direction being in the direction of said
lip.Iaddend..
5. A prosthesis for implantation in a patient's body comprising: a
bearing .[.for receiving.]. .Iadd.having an inner bearing surface
configured to receive and surround a portion of .Iaddend.the ball
.[.portion.]. of a ball and socket joint.Iadd., said ball being
connected to a neck element and the ball in combination with the
neck element being free to move within the bearing in a plurality
of directions in the assembled joint.Iaddend.; fixation means for
attachment to a bony structure, said fixation means having a cavity
for receiving the bearing, said cavity having an opening defining a
.Iadd.first .Iaddend.plane through which the bearing enters the
cavity; and means for securing the bearing to the fixation means in
any one of a plurality of selectable orientations after the
fixation means has been attached to the bony structure, said
plurality of selectable orientations being angularly displaced from
one another about an axis which is perpendicular to the .Iadd.first
.Iaddend.plane .[.defined by the opening of the cavity of the
fixation means.]. ; the bearing .[.being.]. .Iadd.having a
configuration which is .Iaddend.non-symmetric with regard to
rotation about said axis .[.and.]. .Iadd.such that, in the
assembled joint, the angular range of motion of the ball with the
neck element within the bearing relative to the axis is smaller in
at least one first direction than in at least one other direction,
.Iaddend.said lack of symmetry making at least one of the
selectable angular orientations of the bearing more preferred for
physiological reasons than others of said angular orientations,
said means for securing allowing said bearing to be secured to said
fixation means in such a preferred orientation after said fixation
means has been attached to the bony structure.
6. The prosthesis of claim 5 wherein the means for securing
comprises bayonet spaces and lugs.
7. The prosthesis of claim 5 wherein the means for securing
includes two coaxial pin members and the bearing includes two
coaxial cylindrical surfaces which receive the pin members, the pin
members and the cylindrical surfaces allowing the bearing to rotate
within the cavity of the fixation means about a single axis, said
single axis being orthogonal to the axis which defines the
plurality of selectable angular orientations, the orientation of
the single axis with respect to the anatomy of the patient's body
making at least one of the selectable angular orientations of the
bearing more preferred for physiological reasons than others of
said angular orientations.Iadd., said at least one first direction
being orthogonal to the single axis.Iaddend..
8. The prosthesis of claim 5 wherein the bearing includes a lip to
restrain dislocations of the ball from the bearing, the orientation
of said lip with respect to the anatomy of the patient's body
making at least one of the selectable angular orientations of the
bearing more preferred for physiological reasons than others of
said angular orientations.Iadd., said at least one first direction
being in the direction of said lip.Iaddend...Iadd.
9. A ball and socket joint for implantation in a patient's body
comprising a ball portion and a socket portion, the ball portion
including: a ball; and first fixation means for attachment to a
first bony structure, said fixation means being connected to said
ball; and the socket portion including: a bearing for receiving the
ball; second fixation means for attachment to a second bony
structure, said second fixation means having a cavity for receiving
the bearing, said cavity having an opening defining a plane through
which the bearing enters the cavity; and means for securing the
bearing to the second fixation means in any one of a plurality of
selectable orientations after the second fixation means has been
attached to the second bony structure, said plurality of selectable
orientations being angularly displaced from one another about an
axis which is perpendicular to the plane defined by the opening of
the cavity of the second fixation means, said means for securing
comprising bayonet spaces and lugs;
the bearing being non-symmetric with regard to rotation about said
axis and said lack of symmetry making at least one of the
selectable angular orientations of the bearing more preferred for
physiological reasons than others of said angular orientations,
said means for securing allowing said bearing to be secured to said
second fixation means in such a preferred orientation after said
second fixation means has been attached to the second bony
structure. .Iaddend..Iadd.
10. A ball and socket joint for implantation in a patient's body
comprising a ball portion and a socket portion, the ball portion
including: a ball; and first fixation means for attachment to a
first bony structure, said fixation means being connected to said
ball; and the socket portion including: a bearing for receiving the
ball; second fixation means for attachment to a second bony
structure, said second fixation means having a cavity for receiving
the bearing, said cavity having an opening defining a plane through
which the bearing enters the cavity; and means for securing the
bearing to the second fixation means in any one of a plurality of
selectable orientations after the second fixation means has been
attached to the second bony structure, said plurality of selectable
orientations being angularly displaced from one another about an
axis which is perpendicular to the plane defined by the opening of
the cavity of the second fixation means;
the bearing being non-symmetric with regard to rotation about said
axis and said lack of symmetry making at least one of the
selectable angular orientations of the bearing more preferred for
physiological reasons than others of said angular orientations,
said means for securing allowing said bearing to be secured to said
second fixation means in such a preferred orientation after said
second fixation means has been attached to the second bony
structure, the means for securing including two coaxial pin members
and the bearing including two coaxial cylindrical surfaces which
receive the pin members, the pin members and the cylindrical
surfaces allowing the bearing to rotate within the cavity of the
second fixation means about a single axis, said single axis being
orthogonal to the axis which defines the plurality of selectable
angular orientations, the orientation of the single axis with
respect to the anatomy of the patient's body making at least one of
the selectable angular orientations of the bearing more preferred
for physiological reasons than others of said angular orientations.
.Iaddend..Iadd.
11. A ball and socket joint for implantation in a patient's body
comprising a ball portion and a socket portion, the ball portion
including: a ball; and first fixation means for attachment to a
first bony structure, said fixation means being connected to said
ball; and the socket portion including: a bearing for receiving the
ball; second fixation means for attachment to a second bony
structure, said second fixation means having a cavity for receiving
the bearing, said cavity having an opening defining a plane through
which the bearing enters the cavity; and means for securing the
bearing to the second fixation means in any one of a plurality of
selectable orientations after the second fixation means has been
attached to the second bony structure, said plurality of selectable
orientations being angularly displaced from one another about an
axis which is perpendicular to the plane defined by the opening of
the cavity of the second fixation means;
the bearing being non-symmetric with regard to rotation about said
axis and said lack of symmetry making at least one of the
selectable angular orientations of the bearing more preferred for
physiological reasons than others of said angular orientations,
said means for securing allowing said bearing to be secured to said
second fixation means in such a preferred orientation after said
second fixation means has been attached to the second bony
structure, the bearing including a lip to restrain dislocations of
the ball from the bearing, the orientation of said lip with respect
to the anatomy of the patient's body making at least one of the
selectable angular orientations of the bearing more preferred for
physiological reasons than others of said angular orientations.
.Iaddend..Iadd.
12. A prosthesis for implantation in a patient's body comprising: a
bearing for receiving the ball portion of a ball and socket joint;
fixation means for attachment to a bony structure, said fixation
means having a cavity for receiving the bearing, said cavity having
an opening defining a plane through which the bearing enters the
cavity; and means for securing the bearing to the fixation means in
any one of a plurality of selectable orientations after the
fixation means has been attached to the bony structure, said
plurality of selectable orientations being angularly displaced from
one another about an axis which is perpendicular to the plane
defined by the opening of the cavity of the fixation means, said
means for securing comprising bayonet spaces and lugs; the bearing
being non-symmetric with regard to rotation about said axis and
said lack of symmetry making at least one of the selectable angular
orientations of the bearing more preferred for physiological
reasons than others of said angular orientations, said means for
securing allowing said bearing to be secured to said fixation means
in such a preferred orientation after said fixation means has been
attached to the bony structure. .Iaddend..Iadd.
13. A prosthesis for implantation in a patient's body comprising: a
bearing for receiving the ball portion of a ball and socket joint;
fixation means for attachment to a bony structure, said fixation
means having a cavity for receiving the bearing, said cavity having
an opening defining a plane through which the bearing enters the
cavity; and means for securing the bearing to the fixation means in
any one of a plurality of selectable orientations after the
fixation means has been attached to the bony structure, said
plurality of selectable orientations being angularly displaced from
one another about an axis which is perpendicular to the plane
defined by the opening of the cavity of the fixation means; the
bearing being non-symmetric with regard to rotation about said axis
and said lack of symmetry making at least one of the selectable
angular orientations of the bearing more preferred for
physiological reasons than others of said angular orientations,
said means for securing allowing said bearing to be secured to said
fixation means in such a preferred orientation after said fixation
means has been attached to the bony structure, the means for
securing including two coaxial pin members and the bearing
including two coaxial cylindrical surfaces which receive the pin
members, the pin members and the cylindrical surfaces allowing the
bearing to rotate within the cavity of the fixation means about a
single axis, said single axis being orthogonal to the axis which
defines the plurality of selectable angular orientations, the
orientation of the single axis with respect to the anatomy of the
patient's body making at least one of the selectable angular
orientations of the bearing more preferred for physiological
reasons than others of said angular orientations.
.Iaddend..Iadd.
14. A prosthesis for implantation in a patient's body comprising: a
bearing for receiving the ball portion of a ball and socket joint;
fixation means for attachment to a bony structure, said fixation
means having a cavity for receiving the bearing, said cavity having
an opening defining a plane through which the bearing enters the
cavity; and means for securing the bearing to the fixation means in
any one of a plurality of selectable orientations after the
fixation means has been attached to the bony structure, said
plurality of selectable orientations being angularly displaced from
one another about an axis which is perpendicular to the plane
defined by the opening of the cavity of the fixation means; the
bearing being non-symmetric with regard to rotation about said axis
and said lack of symmetry making at least one of the selectable
angular orientations of the bearing more preferred for
physiological reasons than others of said angular orientations,
said means for securing allowing said bearing to be secured to said
fixation means in such a preferred orientation after said fixation
means has been attached to the bony structure, the bearing
including a lip to restrain dislocations of the ball from the
bearing, the orientation of said lip with respect to the anatomy of
the patient's body making at least one of the selectable angular
orientations of the bearing more preferred for physiological
reasons than others of said angular orientations. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field Of The Invention
This invention relates to artificial joints and in particular to
artificial joints of the ball and socket type.
2. Description Of The Prior Art
As is well known in the art, artificial hip and shoulder joints
conventionally employ ball and socket articulations. The socket is
embedded in one bony structure, for example, the pelvis for a hip
reconstruction. The ball is attached to an arm composed of a neck
and a stem or shaft, the stem or shaft being embedded in another
bony structure, for example, the femur for a hip
reconstruction.
A number of methods are known for retaining the ball in the socket.
In the most common method, referred to herein as the
"semi-constrained" construction, the patient's own anatomy, i.e.,
his muscles, tendons and ligaments, are used to retain the ball
within the socket. For this construction, a hemispherical socket
typically is used which allows the ball and its attached arm the
maximum amount of movement without contact of the arm with the edge
of the socket. The surgeon, when installing such a semi-constrained
joint, aligns the ball and socket as closely as possible with the
patient's natural anatomy so that the patient's movements do not
tend to dislocate the ball from the joint. As a general
proposition, such precise alignment is easiest the first time an
artificial joint is placed in a patient. Subsequent reconstructions
are much more difficult to align because of deterioration of
anatomical landmarks as a result of the first operation, the
healing process after the operation and changes in the anatomy
caused by the presence of the artificial joint.
In order to increase the inherent stability against dislocation of
such semi-constrained constructions, it has become conventional to
add a cylindrical portion to the hemispherical socket to make it
deeper. Although the ball is not physically constrained by the
socket by this adjustment, the ball does not have further to travel
than if just a hemisphere had been used and thus some reduction in
the propensity towards dislocation is achieved. Ball and socket
joints of this type generally provide an arc or range of motion of
approximately 115.degree. when a 28 mm diameter sphere is used and
the socket is made a few millimeters deeper than a hemisphere.
Larger ranges of motion can be obtained by keeping the size of the
arm attached to the ball constant and increasing the diameter of
the ball. In this way, the angular extent of the arm relative to
the ball becomes smaller. In the limit, if the ball could be made
progressively larger and larger, a range of motion of 180.degree.
could be achieved. In practice, however, the largest sphere in
common use in artificial joints, and in particular artificial hip
joints, has a diameter of 32 mm and provides a range of motion of
approximately 120.degree.. It should be noted however, that such
larger sphere sizes are not universally favored because frictional
torque increases with diameter.
A recent study by the Mayo clinic, which appeared in December, 1982
edition of The Journal of Bone and Joint Surgery, reported a
dislocation frequency of 3.2% for 10,500 hip joint implant
procedures using the semi-constrained construction. Such
dislocations essentially make the patient immobile and can
necessitate a second operation. As discussed above, the critical
alignment required for the semi-constrained construction is even
more difficult to achieve when a second implantation is performed.
Accordingly, even higher dislocation frequencies are encountered
for second and subsequent implantations.
An alternative to the semi-constrained construction is the
construction wherein the ball is physically constrained within the
socket. In this construction, a spherically-shaped bearing
surrounds the ball and serves as the socket. The bearing is
attached to a fixation element which is embedded in, for example,
the patient's pelvic bone. The bearing encompasses more than
one-half of the ball and thus constrains the ball and its attached
arm from dislocation.
The bearing is typically made from plastic, such as ultra-high
molecular weight polyethylene (UHMWPE), or metal. For plastic
bearings, the ball and bearing are usually assembled by forcing the
bearing over the ball. The more of the ball which is encompassed by
the bearing, the greater the required assembly force, and the
greater the constraining force to prevent postoperative dislocation
of the joint. In addition, the more that the bearing encompasses
the ball, the smaller the range of motion for the ball prior to
contact of the bearing with the arm attached to the ball.
An example of a constrained artificial joint employing a plastic
bearing is shown in Noiles, U.S. Pat. No. 3,996,625. As can be seen
in FIG. 1 of this patent, a plastic bearing 17 fitted with a metal
reinforcing band (un-numbered) extends beyond the diameter of ball
24 so as to physically constrain the ball within the bearing. The
bearing itself is attached to fixation element 12. The metal
reinforcing band is assembled over the lip of the opening of
bearing 17 after that bearing has been forced over sphere 24. The
reinforcing band increases the force required to dislocate the
joint. In practice, the design shown in FIG. 1 of U.S. Pat. No.
.[.3,966,625.]. .Iadd.3,996,625 .Iaddend.has been found to provide
a range of motion of approximately 85.degree. when a sphere
diameter of 28 mm is used and to resist direct dislocating forces
of several hundred pounds.
For constrained constructions such as that shown in U.S. Pat. No.
3,996,625, it has been found in use that a dislocating force is
created when the neck of the arm attached to the ball impinges on
the rim of the bearing. Because of the leverage associated with the
arm and the long bone of the patient to which it is attached, e.g.,
the patient's femur, the dislocating force produced when the neck
contacts the rim of the bearing can be considerable. For example, a
force on the order of 25 pounds applied to a patient's leg can
produce a dislocating force of over several hundred pounds because
of the leverages involved. This type of dislocation force can be
avoided by geometrically aligning the artificial joint with the
patient's anatomy so that the neck does not come in contact with
the rim of the bearing during normal motion of the patient's limb.
That is, the leverage based dislocation forces can be avoided in
the same way as dislocations are avoided in the
.[.seim-constrained.]. .Iadd.semi-constrained
.Iaddend.construction, i.e., through precise alignment of the
artificial joint with the natural anatomy of the patient.
Unfortunately, as is apparent from the geometry of the situation,
the more the socket bearing encompasses the ball, the greater the
restraining force on the ball, but at the same time the less the
range of motion prior to the neck impinging upon the edge of the
bearing to create undesired leverage. In practice, artificial hips
having the construction shown in U.S. Pat. No. 3,996,625 have been
found to suffer dislocation due to the leverage effect in fewer
than 0.5% of the implantations performed. This is significantly
better than the 3.5% dislocation frequency reported in the Mayo
clinic study discussed above, but an even lower dislocation
frequency is obviously desirable.
A constrained construction using a metal socket bearing is shown in
Noiles, U.S. Pat. Re. 28,895 (reissue of U.S. Pat. No. 3,848,272).
This construction provides approximately a 90.degree. range of
motion where the sphere diameter is 28 mm. In a practical sense,
the metal bearing can be said to be non-dislocatable. The force
required to extract the metal sphere from the enclosing metal
socket bearing is more than several thousand pounds. Accordingly,
is use, rather than the metal ball dislocating from the metal
socket bearing, any overly severe dislocating leverage will cause
the fixation element to be disrupted from the bone in which it has
been embedded.
As a general proposition, metal balls in metal socket bearings are
used in only a minority of joint reconstructions because the
medical profession is not in agreement that a metal sphere in a
metal bearing is as biologically acceptable as a metal sphere in a
UHMWPE plastic bearing, even though clinical use over 15 years has
failed to show the metal to metal joint to be inferior to a metal
to plastic joint.
A third type of artificial ball and socket joint, referred to as an
endoprosthesis, eliminates the fixation element associated with the
socket and simply uses a ball surrounded by a plastic socket
bearing in a spherical metal head, which head is placed in the
patient's natural socket but not secured to bone. For this
construction, the ball can rotate within the bearing up to the rim
of the bearing (the bearing is greater than a hemisphere so as to
be retained on the ball), and then the bearing and its attached
head rotates in the patient's socket. As with the semi-constrained
construction, anatomical alignment is used to avoid dislocations,
in this case between the metal head and the natural socket.
In view of the foregoing, it is apparent that in semi-constrained
and endoprosthesis hip joints, reconstructive geometry of the
prosthesic components is critical in ensuring the stability of the
prosthesis against dislocation. Moreover, in ball and socket
constructions which constrain the elements against dislocation, the
range of motion inherent in the prosthesis is reduced and thus
because of the possibility of leverage type dislocations, similar
demands are placed on the surgeon to establish the geometry of the
reconstruction within rather narrow limits.
Accordingly, an object of this invention is to provide a ball and
socket joint which provides the surgeon with increased latitude in
geometric positioning of the prosthetic components over those ball
and socket joints presently available.
A further object of the invention is to provide a ball and socket
joint the materials and configuration of at least a portion of
which can be selected and/or changed in situ, that is, during or
after implantation of the joint in the patient.
An additional object of the invention is to provide a ball and
socket joint including a bearing member which can be readily
replaced in situ with either a bearing member of the same or of a
different type depending on the patient's post-operative
history.
Another object of the invention is to provide a ball and socket
joint wherein (1) the socket portion of the joint has more than one
orientation with respect to the ball portion of the joint, the
preferred orientation being a function of the patient's anatomy,
and (2) the orientation of the socket portion with respect to the
ball portion can be selected and/or changed in situ, that is,
during or after implantation of the joint in the patient.
A further object of the invention is to provide a prosthetic ball
and socket joint of increased inherent range of motion which is
readily assembled and disassembled at the surgical site.
An additional object of the invention is to provide a ball and
socket bearing for an artificial joint which constrains the joint
from dislocating and at the same time provides a range of motion
which is greater than that available in the construction of the
constrained type described above.
SUMMARY OF THE INVENTION
To achieve these and other objects, the invention, in accordance
with one of its aspects, provides a ball and socket joint for
implantation in a patient's body comprising a ball portion and a
socket portion,
the ball portion including: a ball; and first fixation means for
implantation in a first bony structure, said fixation means being
connected to said ball; and
the socket portion including: a bearing for receiving the ball;
said bearing defining an orientation between itself and the
patient's body; second fixation means for implantation in a second
bony structure; and connecting means associated with the bearing
and the second fixation means for connecting the bearing to the
second fixation means in more than one orientation.
In accordance with a further one of its aspects, the invention
provides a ball and socket joint for implantation in a patient's
body comprising a ball portion and a socket portion,
the ball portion including: a ball; and first fixation means for
implantation in a first bony structure, said fixation means being
connected to said ball; and
the socket portion including: a bearing for receiving the ball,
said bearing being one member of a family of interchangeable
bearings, the family including at least one member which is made
from a different material or which has a different configuration or
which is both made from a different material and has a different
configuration from at least one other member of the family; second
fixation means for implantation in a second bony structure; and
connecting means associated with the bearing and the second
fixation means for interchangeably connecting any bearing in the
family to the second fixation means.
In accordance with an additional one of its aspects, the invention
provides a ball and socket joint for implanting in the body which
comprises: a ball; a cup with a spherical cavity, said cup to be
affixed to bone; and a bearing member surrounding a portion of the
ball and rotatable within said spherical cavity about only one
axis, said bearing member having an asymmetric opening therein, the
opening having an angular extent of less than 180.degree. in at
least one plane.
In accordance with another one of its aspects, the invention
provides an artificial joint of the ball and socket type for
implantation in the body which comprises: a ball; a bearing for
forming a socket to receive the ball, the bearing having an
asymmetric opening therein, the opening having an angular extent of
less than 180.degree. in a first plane; means for pivoting the
bearing about an axis lying in a plant other than the first plane;
and means for affixing the means for pivoting to bone.
In accordance with another of its aspects, the invention provides a
socket for a ball and socket joint for implantation in the body
which comprises (1) a cup with a cavity, and (2) a bearing for
receiving the ball of the ball and socket joint, said bearing being
constrained to rotate within said cavity about a single axis.
In accordance with certain preferred embodiments of the invention,
the asymmetric opening into the sockets is less in one direction
than it is at 90.degree. to this one direction. The socket bearing
is movably retained within the cup about an axis which is (1)
parallel to the face of the cup and (2) in the direction of the
greater opening in the socket bearing. The socket bearing is
retained within the cup by two stub half round pins integral with
the cup and extending part way through the wall thickness of the
socket. The axes of the half round pins coincide with an axis of
the spherical cup like cavity and they are also coaxial in the
direction of the greater opening in the socket bearing.
When the ball and the neck of the arm of the prosthesis move in the
direction of the lesser opening in the socket bearing, the total
range of motion is the sum of the arc of motion which the neck can
make within the bearing plus the arc of motion which the bearing
can make within the cup. The cup can be a hemisphere or even less.
Rotation of the ball is limited by impingement of the neck against
the rim of the cup, or alternatively, and most preferably, by
limiting the rotation of the socket bearing so that the neck comes
just up to, but not actually into contact with, the rim of the cup.
In this regard, reference is made to copending U.S. patent
application Ser. No. 553,518 to Alfred Frederick DeCarlo, Jr.,
filed simultaneously herewith and assigned to the assignee of the
present application. This application, the pertinent portions of
which are incorporated herein by reference, discloses a preferred
system for limiting the rotation of the socket bearing to keep the
neck of the arm of the prosthesis out of contact with the rim of
the cup.
When the diameter of the ball is approximately the 28 mm in common
use, and the socket bearing wall thickness is approximately 7 mm,
the inner diameter of the cup, and thus the outer diameter of the
bearing, is approximately 42 mm (28 mm+7 mm+7 mm). This outer
diameter for the bearing is larger than the largest diameter sphere
commonly used in semi-constrained artificial hip replacements, and
thus the present constrained construction achieves a greater range
of motion than the semi-constrained construction, and at the same
time, restrains the ball within the socket.
When the ball and the neck move in the direction of the greater
opening in the socket bearing, the neck contacts the flat side of a
stub half round pin, rather than the rim of the cup, or
alternatively, and most preferably, a web portion of the socket
bearing in the region of the stub half round pins (see, for
example, element 106 in FIGS. 13, 15 and 21 below). To allow the
neck and ball to move through the same arc in this direction, the
flat sides of the pins can be contoured. With this feature, the
total range of motion in all quadrants, using the above dimensions,
is approximately 135.degree..
To summarize, in accordance with the above preferred embodiments of
the invention, when motion is in the plane of the stub pins, the
total motion is by movement of the ball within the bearing. When
motion is at 90.degree. to the plane of the pins (the "90.degree.
plane"), the total motion is the sum of the motion of the ball
within the bearing and the motion of the bearing within the cup. In
other planes, the motion of the ball within the bearing is greater
than it is in the 90.degree. plane and the motion of the bearing
within the cup is less than it is in the 90.degree. plane. In this
way, the invention provides a constrained ball and socket
prosthesic joint with a total range of motion significantly greater
than hitherto generally available.
In connection with artificial hip joints, it is advantageous to
orient the cup in situ so that the axis of the stub pins is
inclined according to the anatomical requirements of the patient as
determined by the surgeon. For example, the axis can be inclined
somewhat upward in the forward direction. In this manner almost all
highly repetitive load bearing motions of the hip joint fall within
the motion capability of the sphere within the socket bearing.
Additional motion is furnished by movement of the bearing within
the cup in such activities as crossing the legs when seated, or in
significant abduction. To conveniently permit such orientation of
the stub pins, in certain embodiments of the invention, the cup
includes first and second portions, the first portion to be affixed
to bone, the second portion having associated therewith the pin
members are being moveable with respect to the first portion to
provide a plurality of possible orientations for the axis of
rotation of the bearing member within the spherical cavity.
In connection with both artificial hip joints and other types of
ball and socket joints, it is advantageous for the surgeon to have
as wide a range of joint configurations and materials to choose
from as possible. It is particularly advantageous for the surgeon
to be able to refine his selection of materials and configurations
during the operative procedure, after he has seen the diseased
joint and has a full appreciation of the patient's medical
condition and anatomy. Along these same lines, it is also
advantageous to be able to re-operate and change materials and/or
joint configurations as a function of the patient's post-operative
history without substantially disturbing the established fixation
of the joint to bony structures. For example, a patient originally
fitted with a semi-constrained joint may be found to be especially
prone to dislocations so that a constrained construction, perhaps
including a metal socket, would be more appropriate.
To achieve these types of flexibility, in accordance with certain
preferred embodiments of the invention, a family of interchangeable
socket bearings of different configurations and/or materials is
provided to the surgeon. Each of the bearings includes means for
interchangeably connecting the bearing to a fixation element for
the socket portion of the joint in such a way that the bond between
the fixation element and the patient's bone is not substantially
disturbed by the connecting process. In view of this easy
interchangeability, during the initial operation, the surgeon need
not choose the specific socket bearing to be used until after
completing the implantation of the fixation element, and during
subsequent operations, if any, he can substitute a different
bearing or replace a worn bearing without breaking the bond between
the fixation element and the patient's bone.
In the description of the preferred embodiments which appears
below, constructions are shown using both plastic and metal socket
bearings, as well as bearings employing a combination of metal and
plastic components. Also, various assembly and disassembly
constructions are illustrated. It is to be understood, of course,
that both the foregoing general description and the following
detailed description are explanatory only and are not restrictive
of the invention.
The accompanying drawings, which are incorporated in and constitute
part of the specification, illustrate the preferred embodiments of
the invention, and together with the description, serve to explain
the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an artificial joint embodying the
present invention.
FIG. 2 is an exploded view showing the components of the joint of
FIG. 1.
FIG. 3 is a cross-sectional view along lines 3--3 in FIG. 1 showing
the ball and the socket bearing partially inserted into the
cup.
FIG. 4 is a cross-sectional view along lines 3--3 of FIG. 1 showing
the range of motion of the ball within the socket bearing with the
socket bearing stationary.
FIG. 5 is a cross-sectional view along lines 3--3 of FIG. 1 showing
the range of motion of the ball within the socket bearing when the
socket bearing moves within the cup.
FIG. 6 is an exploded view of an alternate embodiment of the
invention wherein the cup includes two portions which are moveable
relative to each other.
FIG. 7 is a cross-sectional view along lines 7--7 in FIG. 6 after
the joint has been assembled.
FIG. 8 is a cross-sectional view along lines 8--8 in FIG. 6 after
the joint has been assembled.
FIG. 9 is an alternate embodiment of the embodiment shown in FIGS.
6-8 wherein a two piece metal socket bearing is used.
FIG. 10 is a cross-sectional view along lines 10--10 in FIG. 9
after the joint has been assembled.
FIG. 11 is an exploded view showing an alternative method for
rotatably retaining the socket bearing within the cup.
FIG. 12 is a cross-sectional view along lines 12--12 in FIG. 11
after the joint has been assembled.
FIGS. 13 and 14 show alternative socket bearings for use with the
present invention.
FIG. 15 is an exploded view of an artificial joint similar to that
shown in FIGS. 6-8 but employing a system of the type disclosed in
the DeCarlo patent application referred to above to limit the range
of motion of the socket bearing within the joint.
FIG. 16 is a cross-sectional view along lines 16--16 in FIG.
15.
FIG. 17 is a cross-sectional view along lines 17--17 of FIG.
15.
FIG. 18 is a perspective view of the outer surface of the bearing
member of FIG. 15.
FIGS. 19 and 20 are schematic diagrams illustrating the
relationships between the angular extents of the various components
of the artificial joint shown in FIGS. 15-17.
FIG. 21 is an exploded view of an artificial joint of the
semi-constrained type embodying the present invention and employing
a system of the type disclosed in the DeCarlo patent application
referred to above to limit the range of motion of the socket
bearing within the joint.
FIG. 22 is a cross-sectional view along lines 22--22 in FIG.
21.
FIG. 23 is a cross-sectional view along lines 23--23 in FIG.
21.
FIG. 24 is an exploded view of an artificial joint of the
constrained type constructed in accordance with the present
invention and including a metal reinforcing band to increase the
amount of force required to dislocate the joint. This embodiment
also employs a system of the type disclosed in the DeCarlo patent
application referred to above to limit the range of motion of the
socket bearing within the joint.
FIG. 25 is a cross-sectional view along lines 25--25 in FIG.
24.
FIG. 26 is a perspective view of a plastic socket bearing
constructed in accordance with the present invention and designed
to produce a completed joint of the non-rotating, constrained
type.
FIG. 27 is a front view of the bearing of FIG. 26.
FIG. 28 is a cross-sectional view along lines 28--28 in FIG.
27.
FIG. 29 is a cross-sectional view along lines 29--29 in FIG.
27.
FIG. 30 is a side view of the bearing of FIG. 26.
FIG. 31 is a side view of a plastic socket bearing constructed in
accordance with the present invention and designed to produce a
completed joint of the non-rotating, semi-constrained type.
FIG. 32 is a side view of a plastic socket bearing similar to the
bearing of FIG. 31 but including a lip to help restrain
dislocations of the completed joint.
FIG. 33 is an exploded view of an artificial joint of the
non-rotating, constrained type constructed in accordance with the
present invention and employing a metal socket bearing.
FIG. 34 is a cross-sectional view along lines 34--34 in FIG.
33.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference now to the drawings, wherein like reference
characters designate like or corresponding parts throughout the
several views, there is shown in FIG. 1 an assembly 20 of ball or
sphere 10, socket bearing 12 and cup 14 for a prosthetic joint. The
neck 16 of arm 30 is intermediate ball 10 and stem or shaft 18,
which stem or shaft is fixed to, for example, the femur bone at the
time of implant surgery.
FIG. 2 shows in more detail socket bearing 12 of assembly 20. The
preferred material for bearing 12 is ultra-high molecular weight
polyethylene (UHMWPE). Inner spherical bearing surface 21 of
bearing 12 is concentric with outer spherical bearing surface 22.
Cylindrical surfaces 24 are coaxial with each other and with the
center of spherical surfaces 21 and 22 and are tangent to surfaces
26. Small barb-shaped protuberances 28 serve a detent function
described below.
In the plane passing through the lines P--P in FIG. 2, socket
bearing 12 encompasses less than one half of ball 10. In the plane
passing through the lines S--S, the socket bearing encompasses more
than half of ball 10.
Owing to the resilience and elasticity of the plastic material of
socket bearing 12, socket bearing 12 can be snapped over ball 10.
The amount of interference between the equator of the ball and
socket bearing 12 depends on the angular extent of the bearing's
opening in the plane passing through the lines S--S in FIG. 2.
.[.the.]. .Iadd.The .Iaddend.amount of interference should be such
as will cause an elastic deformation of socket bearing 12 while the
bearing is being assembled over the ball 10. To aid in assembly,
socket bearing 12 can be heated to a non-destructive temperature
(for example 70.degree.-80.degree. C. for UHMWPE). Plastic in
general, and UHMWPE in particular, has a large coefficient of
thermal expansion and such thermal expansion due to heating
significantly aids in assembly.
As shown in FIG. 2, cup 14 has a hemispherical inner surface 32 and
two coaxial stub half pin members 34 which are structurally
integral with cup 14. The pins 34 are shown bevelled at 36.
Recesses 38 are provided at the inner rim of the cup at locations
90.degree. displaced from the pins 34. The exterior surface 40 of
cup 14 is of any conventional contour for fixation in bone whether
by use of cement, or without cement by means of impaction, screwing
in, or by bone ingrowth into porous metal or the like. Cup 14 is
normally made of metal, and it is to be understood that the metal
used is to be structurally and biologically suitable for surgical
implantation.
A step midway in the process of assembly is schematically shown in
FIG. 3 where bearing 12 has been positioned against neck 16 at 42
and the bearing 12 and arm 30 have been inserted into cup 14 with
neck 16 contacting the rim of cup 14 at 44. Cylindrical surface 24
of bearing 12 engages stub pin 34 as the entering rim 46 of bearing
12 contacts inner surface 32 of cup 14. At this time the bearing 12
is pressed firmly enough into cup 14 to compress protuberance 28,
allowing bearing 12 to be rotated clockwise about ball 10 and pin
34 while it is in contact with inner spherical surface 32.
When bearing 12 has been rotated sufficiently for protuberance 28
adjacent rim 46 to reach recess 38, protuberance 28 expands to
resist rotation in the reverse direction and thereby resist
disassembly of the ball and socket joint 20 unless a tool is
inserted into recess 38 to again compress protuberance 28 as
rotation in the disassembly direction is started.
The assembled joint is shown in FIG. 1, where the neck 16 of arm 30
can move through the arc from the position shown to that which is
symmetrically opposite. That is, the neck of the prosthesis can
move in the plane through lines P--P of FIG. 2 from a position of
contact with lower stub pin 34 to contact with upper stub pin 34.
When ball 10 has a diameter of 28 mm and the outer diameter of
bearing 12 is 42 mm, the arc or range of motion of neck 16 is
somewhat greater than 135.degree., depending on the design of the
neck 16.
To achieve this same range of motion in the plane through lines
S--S in FIG. 2 requires two motions. First, as shown in FIG. 4, the
neck 16 and ball 10 move through the angle A by the ball 10 turning
inside the socket bearing 12, at the completion of which neck 16
contacts the rim of bearing 12. Thereafter, as shown in FIG. 5, to
achieve the full range of motion A', ball 10 and bearing 12 rotate
in unison, at the completion of which neck 16 contacts cup 14.
Normally, until neck 16 reaches the rim of socket bearing 12,
socket bearing 12 will remain stationary relative to cup 14. This
is so because frictional torque is the product of friction force
times the distance from the center of rotation. Given similar
materials, finish and geometric accuracy, so that the coefficient
of friction for ball 10 and cup 14 against bearing 12 are equal,
the frictional force on inner surface 21 will be the same as that
on outer surface 22 when ball 10 rotates within cup 14, because the
load transmitted across the two bearing surfaces is the same. Since
the radius to the outer surface 22 is the greater, the frictional
torque at the outer surface will be greater and thus motion will
occur along surface 21 rather than surface 22.
For major oscillation of ball 10 and neck 16 in the plane through
lines P--P in FIG. 2, the entire excursion is due to rotation of
ball 10 within bearing 12. The total possible oscillation in all
planes is the same, however, the contribution made by rotation of
bearing 12 increases as the plane of oscillation moves from that
including the lines P--P to that including the lines S--S in FIG.
2.
As described above, bearing 12 constrains ball 10 from dislocation.
Further, socket bearing 12 is constrained within cup 14 by
cylindrical surfaces 24 being journaled by the stub half pins 34 in
all positions of bearing 12 as bearing 12 moves to allow arm 30 to
move through angle A'. In the complete assembly 20, the constraint
against dislocation of ball 10 by deformation of plastic bearing 12
is greater in magnitude than the force required to assemble bearing
12 over ball 10 because, in addition to the fact that the assembly
operates at the body temperature of 37.degree. C., the bearing 12
is now itself constrained against the deflection of dislocation by
being captured within metal cup 14.
FIGS. 6, 7 and 8 show an alternate construction intended to (1)
facilitate final assembly at the operative site, and (2) for hip
joint replacements, allow the axis of stub pins 34 to be inclined
accordingly to the anatomical requirements of the patient as
determined by the surgeon. Cup 14 now includes two
portions--portion 64 which is affixed in the patient's bone, and
retaining ring portion 74 which carries stub pins 34 and is
engageable with portion 64 at a number of locations to provide a
plurality of orientations for the axis through pins 34 about which
socket bearing 12 rotates. Portion 64 is shaped to accept and hold
retaining ring 74 by means of bayonet spaces 68 and lugs 70. Inner
spherical surface 72 is continuous with spherical surface 76 of
ring 74. Ring 74 carries stub half pin members 34, has recesses 38
and bayonet lugs 78. A particularly preferred construction for
portion 64, and, in particular, for the exterior surface of this
portion, is disclosed in copending U.S. patent application Ser. No.
553,519 to Douglas G. Noiles, filed simultaneously herewith and
assigned to the assignee of the present application. The pertinent
portions of this application are incorporated herein by
reference.
With the embodiment shown in FIGS. 6-8, the portion 64 of cup 14 is
implanted in the patient's bone by conventional techniques, or,
most preferably, by the techniques described in the
above-referenced copending application to Douglas G. Noiles. Ball
10 and bearing 12 are assembled into retaining ring 74 after stem
18 of arm 30 has been implanted in, for example, the patient's
femur, the assembly procedure being the same as that described
above with reference to FIG. 3 except that protuberance 28 is
compressed only once it contacts the back surface of ring 74. The
sub-assembly of ball 10, bearing 12 and retaining ring 74 is then
inserted into portion 64 in any of the several angular positions
the bayonet lug fittings will permit. A fraction of a turn in
either direction will engage the lugs 78 of ring 74 under lugs 70
of portion 64. Alternatively, lugs 78 can be beveled at either
their right or left hand leading edges so that insertion by
rotation in only one direction is facilitated, e.g., clockwise
rotation. The engagement of bayonet lugs 78 and 70 is locked by
conventional means, such as by one or more pins 80. Holes 79 and 81
for such locking pins can be precisely made in the cooperating
parts at the time of manufacture. Although only one hole 81 is
shown in FIGS. 6 and 7, a hole would normally be drilled at each
bayonet space 68 so that ring 74 can be locked in place for any of
its possible orientations.
An embodiment of the present invention similar to that shown in
FIGS. 6-8 but employing the system disclosed in the DeCarlo patent
application referred to above is shown in FIGS. 15-20. In this
embodiment, spherical surface 72 has associated therewith pin or
projection 50. This projection is located at the geometric pole of
the spherical cavity formed by spherical surfaces 72 and 76. As
shown in the figures, pin 50 has sloping sides 60.
Projection 50, in combination with aperture 13 formed in outer
surface 22 of bearing member 12, serves to constrain the rotation
of bearing 12 so as to prevent the bearing from being rotated out
of the spherical cavity once the joint is assembled and to limit
the rotation of the bearing so as to keep neck 16 just out of
contact with the rim of ring 74, e.g., on the order of a half a
millimeter above the rim. In particular, bearing 12 can rotate only
to the point where polar pin 50 and one of the end walls 52 or 54
of aperture 13 are in engagement. As discussed below, this
constrained condition for bearing 12 occurs automatically as the
joint is assembled without any additional assembly steps. Also, the
constraining of socket bearing 12 within the joint is accomplished
irrespective of the angular orientation chosen for retaining ring
74 with respect to body portion 64 of cup 14.
Aperture 13 has a long axis parallel to side walls 56 and 58 and a
short axis at 90.degree. to side walls 56 and 58. The angular
extent of aperture 13 along its short axis is sufficient to
accommodate polar pin 50. The angular extent of aperture 13 along
its long axis determines the range of motion of socket bearing 12.
As discussed above, a particularly preferred range motion for
bearing 12 is one in which neck 16 is kept just out of contact with
ring 74. In this case, as shown in FIGS. 19-20, the angular extent
(.alpha.) of aperture 13 along its long axis is determined by: (1)
the maximum angular extent (.beta.) of socket bearing 12: (2) the
minimum angular extent (.gamma.) of cup 14; (3) the angular extent
(.delta.) of polar pin 50; and the angular offset (.epsilon.) of
neck 16 from cup 14. In particular, the angular extent of aperture
13 is given by:
Similar relationships can be derived for other desired ranges of
motion for socket bearing 12.
The placement of pin 50 at the pole of the spherical cavity formed
by surfaces 72 and 76 allows retaining ring 74 to be inserted into
body portion 64 of cup 14 in any of the possible orientations
provided by the mating of bayonet lugs 78 with bayonet lugs 70.
That is, once socket bearing 12 is rotated about stub pins 34 until
at least some portion of aperture 13 is located over the central
axis of ring 74, ring 74 can be mated with body portion 64 in any
of their possible relative orientations, because, for each of those
orientations, aperture 13 will slip over projection 50. Since
placing aperture 13 about pin 50 results in the restraining of
bearing 12 in cup 14 without any further action by the surgeon, it
can be seen that assembly of the joint automatically produced the
desired restraining function.
A typical sequence of steps for implanting the prosthesis of the
embodiment shown in FIGS. 15-20 in a patient are as follows. Stem
18 of arm 30 is implanted by conventional techniques in, for
example, the patient's femur bone. Body portion 64 of cup 14 can
also be implanted by conventional techniques, or, most preferably,
by the techniques described in the above-referenced copending
application to Douglas G. Noiles. Bearing 12 is assembled into ring
74 and then ball 10 is forced into bearing 12. Alternatively,
bearing 12 can first be placed on ball 10 and that combination
assembled into ring 74. In either case, the sub-assembly of ball
10, bearing 12 and retaining ring 74 is then inserted into body
portion 64 in any of the several angular positions the bayonet lug
fittings will permit with polar pin 50 sliding into aperture 13. A
fraction of a turn in either direction will engage the lugs 78 of
ring 74 under lugs 70 of portion 64. Alternatively, as discussed
above, lugs 78 can be beveled at either their right or left hand
leading edges so that insertion by rotation in only one direction
is facilitated, e.g., clockwise rotation. To aid in the rotation of
ring 74, the ring can include apertures 122 for engagement with a
spanner wrench or the like. Note that because of the polar location
of pin 50, ring 74 and its attached bearing 12 can be rotated to
engage lugs 78 and 70 irrespective of where pin 50 is located along
the length of aperture 13. The engagement of bayonet lugs 78 and 70
is locked by one or more screws 83 which pass through openings 100
and 98 in lugs 70 and 78, respectively, and then through holes 102
to engage the bone into which cup 64 has been implanted.
For hip joints, the possibility of a number of orientations for the
axis of rotation of bearing 12 is used to place that axis in an
orientation in which the greater required range of motion is
aligned approximately with axis P--P. For example, the axis of
rotation can be oriented upward in the forward direction to achieve
this result. In this way, almost all of the highly repetitive
.[.lead.]. .Iadd.load .Iaddend.bearing motions of the joint will
occur along or close to this axis. As discussed above, motions
along or near to the axis of rotation of bearing 12 consist
primarily of ball 10 moving in bearing 12, rather than bearing 12
moving in cup 14. As also discussed above, the frictional torques
involved further favor movement of ball 10 in bearing 12.
Accordingly, by placing the axis of rotation of bearing 12 in a
favorable orientation, most repetitive motion will occur by
movement of ball 10. This is an important advantage because it
means that the joint will have low friction in that friction
increases with the diameter of the moving member and ball 10 has a
smaller diameter than bearing 12. Put another way, by orienting the
axis of rotation of the bearing 12 in the manner described above,
the joint of the present invention for the great majority of
motions of the patient's limb exhibits the frictional behavior of a
small ball, e.g., a 28 mm ball, while providing a range of motion
corresponding to a large ball, e.g., a 42 mm ball.
FIGS. 9 and 10 show another embodiment employing retaining ring 74
in which the socket bearing comprises two metal half bearings 82. A
groove 86 is formed along the junction of the bearings and ends
short of the edge of the bearing to form shoulders 88. Metal half
bearings 82 are brought together to encompass ball 10, and the
ball, half bearings, retaining ring 74 and portion 64 of cup 14 are
assembled in the same manner as described above in connection with
FIGS. 6-8.
Screws 94 having screw heads 96 are conveniently used both to lock
lugs 70 and 78 in place and to prevent socket bearing 12 from
rotating back out of retaining ring 74. Screw heads 96 ride in
groove 86 and engage shoulders 88 when socket bearing 12 has been
moved through its full range of motion about stub pins 34. Lugs 70
and 78 have appropriate openings 100 and 98, respectively, to
receive screws 94 and allow the screws to be engaged with, in this
case, threaded screw holes 102. Although only two openings 100 and
two threaded screw holes 102 are shown in FIGS. 9 and 10, such
openings and threaded holes would normally be provided at each lug
70 so that ring 74 can be locked in place for any of its possible
orientations.
As shown in FIGS. 9 and 10, and most clearly in FIG. 10, screw
heads 96 for the present embodiment lie above the plane of the
front face of retaining ring 74. So as to provide the same range of
motion of socket bearing 12 for this embodiment as for the
embodiment of FIGS. 6-8, stub pins 34 also lie above this plane, so
that the axis of rotation of socket bearing 12 is in the plane of
screw heads 96. For this arrangement, the motion of bearing 12, and
thus arm 30, is limited by screw head 96 contacting shoulder 88,
rather than by neck 16 contacting retaining ring 74.
A further embodiment of the present invention is shown in FIGS. 11
and 12. This embodiment employs means other than half stub pins 34
to define the axis of rotation of socket bearing 12 within cup 14.
In particular, a dovetail arrangement is used wherein male portion
90 of the dovetail is attached to socket bearing 12 and female
portion 92 of the dovetail is cut into surface 32 of cup 14. Socket
bearing 12 and cup 14 are assembled in a manner similar to that
shown in FIG. 3. That is, after socket bearing 12 has been placed
over ball 10, the ball and socket bearing are moved into cup 14
until the center of ball 10 lies at the center of the cup's
spherical cavity. Thereafter, socket bearing 12 is rotated so that
male portion 90 and female portion 92 of the dovetail engage with
each other. To retain socket bearing 12 within cup 14, screws 94
can be inserted into threaded holes 104 in cup 14 so as to block
the outward passage of male portion 90 of the dovetail from cup
14.
FIGS. 13 and 14 show alternate socket bearings for use with the
present invention.
In FIG. 13, cylindrical surfaces 24 do not extend completely
through the wall of bearing 12, but rather stop approximately half
way through to leave webs 106. So as to provide as large a range of
motion of arm 30 in the plane through lines P--P as possible (see
FIG. 2), the webs extend to just above height of stub pins 34 at
the end of bevels 36. In this way, as discussed above, the motion
of ball 10 in the plane through lines P-P is limited by arm 16
contacting webs 106. The webs, although small, help restrain ball
10 within bearing 12.
FIGS. 14 and 21-23 show embodiments of bearing 12 which do not
physically .[.contrain.]. .Iadd.constrain .Iaddend.ball 10. For
these embodiments, inner surface 21 of bearing 12 has a cylindrical
shape 108 beyond its equator. This provides a semiconstrained type
of construction having a greater depth than presently available.
Such a bearing can be used with the other components of the present
invention to provide the advantages, discussed above, of (1)
producing a wider range of motion, e.g., on the order of
135.degree., and (2) providing a level of friction characteristic
of a small ball for the majority of the motions of the patient's
limb.
FIGS. 24-25 show another embodiment of the present invention
wherein a plastic bearing 12 is fitted at its rim 118 with a metal
reinforcing band 120 to produce a constrained joint able to
withstand higher dislocation forces than, for example, the joints
including plastic bearings shown in FIGS. 1-8 and 15-20. For this
joint, the order of assembly is first to combine bearing 12 with
ring 74, then to force the bearing 12 over ball 10 and finally to
assemble band 120 to the rim of bearing 12. If the ball portion of
the joint has already been implanted in the patient, this assembly
order means that band 120 has to be placed over ball 10 before the
bearing is mounted onto the ball.
The constructions of FIGS. 6-8, 9-10, 15-20, 21-23 and 24-25
illustrate various .Iadd.joint .Iaddend.configurations which can be
interchangeably connected to body 64 by means of bayonet lugs 70
and 78 on body 64 and ring 74, respectively. These configurations
share the common characteristic that bearing 12 is free to rotate
about stub pins 34 in the final assembled joint. They differ from
one another in the degree of constraint imposed on the ball by the
bearing and/or the types of materials used to construct the
bearing. Because the bearings are free to rotate, these joints,
when applied to hip reconstructions, also share the characteristic
that there is a preferred orientation of the joint with respect to
the patient's anatomy, namely, an orientation wherein most of the
highly repetitive load bearing motions of the joint occur along or
close to the axis of rotation of the bearing.
FIGS. 26-34 show further examples of joint components which can be
interchangeably connected to body 64 by means of bayonet lugs 70
and 78 on body 64 and, in this case, on bearing 12, respectively.
These joint configurations have the common characteristic that
bearing 12 is stationary with respect to body 64. As with the
joints of the prior examples, these joints differ among themselves
in the degree of constraint imposed on the ball by the bearing
and/or the types of materials used to construct the bearing.
More particularly, FIGS. 26-30 show a construction of the
constrained type employing a plastic socket bearing to which has
been added a metal reinforcing band 120 at rim 118 of the bearing
so as to increase the bearing's ability to withstand dislocation
forces. As shown in the figures, the bearing includes a recess 126
at its pole which allows the bearing to be used with a body 64
which includes a polar pin 50. Of course, if body 64 does not have
a polar pin, the bearing need not have recess 126.
Assembly of a completed joint using this bearing is accomplished as
follows. First, bearing 12 is forced over ball 10 and band 120 is
forced over the bearing's rim 118. If the ball portion of the joint
has already been implanted in the patient, band 120 must be placed
over ball 10 before bearing is mounted onto the ball. The
sub-assembly of ball 10, bearing 12 and reinforcing band 120 is
then inserted into body 64 in any of the several angular positions
the bayonet lug fittings will permit. Polar pin 50 is received in
recess 126 during this process. Since the bearing of FIGS. 26-30 is
symmetric and thus does not define a particular orientation with
respect to the patient's anatomy, the specific .[.oritentation.].
.Iadd.orientation .Iaddend.of the bearing with respect to body 64
is immaterial. Once placed into body 64, a fraction of a turn in
either direction will engage the lugs 78 on the bearing under the
lugs 70 of body 64. If desired, as described above, lugs 78 can be
beveled at either their right or left hand leading edges so that
insertion by rotation in only one direction is facilitated, e.g.,
clockwise rotation. To aid in the rotation of bearing 12, the
bearing can include slots 128 for engagement with a spanner wrench
or the like. The engagement of bayonet lugs 78 and 70 is locked by
one or more screws 83 which pass through openings 100 and 98 in
lugs 70 and 78, respectively, and then through holes 102 in body 64
to engage the bone in which cup 64 has been implanted (see FIGS. 33
and 34).
FIG. 31 shows another plastic socket bearing of essentially the
same design as the bearing of FIGS. 26-30 except that rather
creating a constrained joint, this bearing produces a
semi-constrained joint. That is, the bearing of FIG. 31 does not
encompass more than one half of ball 10 and thus does not constrain
the ball within the joint. Assembly of a joint using this bearing
simply involves inserting and locking the bearing in body 64 using
bayonet lugs 78 and one or more bone screws, and then placing ball
10 into bearing 12 using the standard techniques employed in
semi-constrained surgical reconstructions.
FIG. 32 shows another plastic socket for use in a semi-constrained
reconstruction, in this case with an added lip 130 to help restrain
dislocations of ball 10 from the bearing. The lip can be
conveniently formed by gradually sloping the front surface of the
bearing as shown in FIG. 32. A suitable slope is on the order of
9.degree.. Unlike the symmetric bearings of FIGS. 26-31, the
bearing of FIG. 32 does define an orientation between itself and
the patient's anatomy. Accordingly, when installing this bearing,
the surgeon will choose an orientation of the bearing with respect
to body 64 which will place lip 130 in the most advantageous
position to inhibit dislocation. Other than this orientation step,
the installation procedure for a joint using this bearing is
identical to the installation procedure described above for the
bearing of FIG. 31.
FIGS. 33-34 show a non-rotating, constrained joint employing a
metal bearing. The bearing is composed of two half-bearings 132
which carry bayonet lugs 78. During assembly of the joint,
half-bearings 132 are placed about ball 10 and then held in place
by plastic retaining ring 134. The sub-assembly of ball 10 and
bearing 12 is then inserted into body 64 in basically the same
manner as the bearing of FIGS. 26-30. Typically, body 64 is made of
a titanium alloy, e.g., an alloy containing 6% aluminum and 4%
vanadium (see ASTM Spec. No. F136-79), while bearing halves 132, as
well as ball 10, are made of a cobalt-chromium alloy. As is known
in the art, titanium alloys are not wear resistant when in moving
contact with cobalt-chromium alloys and thus continual relative
movement between a titanium part and a cobalt-chromium part will
eventually result in significant wearing of the titanium part.
To prevent such wearing due to relative movement, the joint of
FIGS. 33-34 includes wedge 136 which serves to force half-bearings
132 into tight engagement with body 64. Wedge 136 passes through
slot 140 in bearing 12 and into recess 144 in retaining ring 134.
The head portion 148 of the wedge is struck with a hammer or the
like after bearing 12 has been positioned in body 64. The hammer
blow forces the bearing halves apart and locks them into position
with respect to body 64.
To prevent wedge 136 from working loose over time, bone screw 83
can be used to engage the head of the wedge as shown in FIG. 34. So
that the wedge can easily be removed, e.g., during replacement of
the bearing by a different type of bearing, the underside of head
148 can be cambered so that the wedge can readily be pried away
from the bearing. Because the wedging process causes the bearing
halves 132 to move away from each other by pivoting about their
point of contact opposite the location of the wedge, the interior
surfaces of the bearing halves can be contoured so that a spherical
surface is formed only after the outward movement of the bearing
halves. Alternatively, the interior surfaces can be made spherical
since the slight amount of play between ball 10 and bearing 12
caused by the wedging process can normally be tolerated in the
completed joint.
As can be seen most clearly in FIG. 33, edge 146 of bearing 12 is
not symmetric. More particularly, this edge allows ball 10 to move
through one angular range in the plane of FIG. 34 and a relatively
larger angular range in the plane orthogonal to the plane of FIG.
34. Accordingly, when installing this bearing, the surgeon will
choose an orientation of bearing 12 in body 64 which causes the
plane corresponding to the relatively larger range of angular
motion to coincide as closely as possible with the plane in which
the patient's limb normally moves through its largest range of
angular motion.
The nine joint configurations shown in FIGS. 6-8, 9-10, 15-20,
21-23, 24-25, 26-30, 31, 32, and 33-34 are each interchangeable
with each other. This interchangeability gives the surgeon the
flexibility of being able to choose, in situ, any of these
configurations or any other configuration constructed to mate with
body 64. In this way, a more perfect match between the requirements
of the patient and the characteristics of the artificial joint is
achieved.
From the foregoing, it is evident that the present invention
provides a constrained ball and socket joint which has a range of
motion greater than that generally available in artificial joints
whether of the constrained or semi-constrained type. Moreover, the
present invention provides an artificial joint which can be
oriented in the patient to provide low friction movement of a ball
of relatively small diameter for most of the patient's repetitive
activities. The limiting factor in providing the increased range of
motion is the outside diameter of the bearing. Accordingly, within
anatomical limits, it is advantageous for the bearing outside
diameter to be as large as possible.
The increased range of motion provided by the present invention
allows the patient to move his limb further than heretofore
possible in constrained joints without the arm of the prosthesis
impinging on the edge of the bearing. Accordingly, there is less
likelihood of dislocation when plastic bearings are used or
disruption of the bond between the fixation element and the bone to
which it is attached when metal bearings are used. Moreover, when
the range of motion of the present joint is greater than the
patient can take advantage of, the surgeon is afforded greater
latitude for variation in the orientation of the prosthetic
components with respect to the patient's anatomy without the hazard
of impingement.
In addition to these orientability and range of motion aspects, the
present invention, by providing interchangeable sockets, also gives
the surgeon the ability to select the most appropriate prosthesis
for the patient's specific requirements both during the initial
operation and, if necessary, during re-operations. As demonstrated
by the examples described above, the surgeon, in accordance with
the present invention, has a diverse family of ball and socket
joints to choose from extending from semi-constrained, fixed
bearings made of plastic through constrained, rotating bearings
made of metal, as well as a variety of configurations in between.
This choice plainly permits a better match between the requirements
of the patient and the capabilities of the prosthesis.
Numerous modifications and variations of the present invention are
possible in light of the above teachings. For example, ball 10,
socket bearing 12 and retaining ring 74 can be provided to the
surgeon as a unit, rather than being assembled at the surgical
site. Also, metal socket bearings can be used with one piece cups,
such as cup 14 shown in FIG. 1, rather than with a retaining ring
as shown in FIGS. 9 and 10. Furthermore, various connecting means
other than bayonet spaces and lugs can be used to attach ring 74 or
bearing 12 to body 64, such as, snap rings. In addition, a variety
of socket bearings other than those specifically illustrated herein
can be used to make up the family of interchangeable bearings
supplied to the surgeon. It is therefore understood that within the
scope of the appended claims, the invention may be practiced
otherwise than as specifically described.
* * * * *