Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IMPROVED SPHERICAL KINEMATIC JOINT
1 BACKGROUND OF THE INVENTION
2 This invention relates generally to an improved globular
3 or spherical kinematic joint which, as known to those skilled
4 in the art, provides, kinematically, three degrees of freedom
5 of rotation; spherical kinematic joints are commonly used in
6 machinery applications such as heavy machinery and business
machinery and are also commonly used in various automotive
8 applications such as tie rod connections. Such joints
9 typically include a member providing a ball or spherical head,
10 an intermediate bearing insert providing a cavity or seat for
11 receiving the spherical head and a third member providing another
12 cavity or seat for receiving the bearing insert with the ball or
13 spherical head residing therein. Many applications require that
14 such joint he capable o~ resisting dislocation when it
is at its extreme limits of rotational movement and that it resist
16 separation under a load tending to pull the connected joint
17 members apart. The structure of such joints is well known to
18 those skilled in the art and it is also well known that such joint
19 may be comprised of many different structural elements.
As is further known, it ls often desired that such joints
21 eliminate or minimize axial play or slop between the connected
22 joint members. Joints illustrating this may be seen in UOS.
23 Patent Nos. 1,891,804 and 1,894,309 to W.A. Flumerfelt issued
December 20, 1932 and January 17, 1933, respectively; U.S.
Patent No. 1,985,728 to G.B. Ingersoll issued December 25, 1934;
26 U.S. Patent No. 3,220,755 to Gottschald et al. issued
27 November 30, 1965; and U.S. Patent No. 3,401,965, to W.C. Wehner
28 issued September 17, 1968. All of the joints disclosed in
29 these patents have provision for minimizing or eliminating axial
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1 play. These patent~ further illustrate two different types
2 of spherical kinematic ~oint structure or cons~ruction. In the
3 Flumerfelt and Ingersoll patents, the bearing inserts comprise
4 separate bearing insert segments which are assembled over the
ball or spherical head and are then inserted into a housing
6 where they are retained by various means. The Wehner patent
7 shows a different type of joint structure or construction
B which includes a load carrying bearing insert and a retaining
9 collar for preventing dislocation and tensile separation of
the connected joint members. The Gottschald et alO patent illustrates
11 a unitary construction wherein the bearing insert contains
12 multiple splits of the front face near the opening providing
13 a multiplicity of fingers or arcuate sections which expand
14 outwardly upon being forced into engagement with the ball or
lS spherical head; after such assembly, the bearing insert and
16 ball are then inserted into the cavity or sea~ of the third
17 member whereby the third member prevents outward expansion of
1~ the fingers thereby trapping the bearing insert on the ball.
19 Additional or secondary means are then provided to hold the
bearing insert in the cavity of the third member thereby providing
21 a joint that resists tensile separation and dislocation.
22 Recently, spherical kinematic joints have found applicatio
~3 in human joint prostheses. In Prosthetic applications, ease
24 of assembly and disassembly o the joint elements or members
are of great importance. The use o~ an intermediate bearing
26 insert comprised o a plurality of bearing segments uneonnected
27 when not assembied in the joint is undesirable in prosthetic
28 applications since handling and holding o~ the bearing segments
29 against the head while assembling the head and bearing segments
with the third member can be awkward,particularly to an
7~
l operating surgeon working inside of a surgical cavity. Although
2 a bearing insert having flexible fingers or arcuate sections
3 reduces the amount of assembly force that would be required
4 were the fingers not present, such flexible fingers can still be
5 quite awkward to the operating surgeon since to provide the
6 required or desired dislocation and separation resistance and
7 s-trength the fingers must be quite stiff which, in turn,
8 requires that considerable assembly force still be applied by the
9 operating surgeon.
As is well known to those skilled in the art, in prosthetic
11 joint applications, low assembly force and ease of assembly are
12 of great importance because of the need to minimize assembly
13 time and because of the difficulties under which the surgeon
1~ must operate. Often, the field of view is obscured and joint
elements or members are slippery because of coating with
1~ blood and fat which can result in dropping of the joint elements
17 thereby causing a further problem since such joints must be
18 s-terile and upon dropping they must be resterilized, or replaced,
19 while the surgical cavity remains open. Fur-ther, on occasion,
because of surgical emergency or other intra-operative difficul-
21 ties, it is desirable to be able to disassemble the joint
22 members, preferably in a manner which avoids the same difficulties
23 of assembly noted above, i.e., excessive disassembly forces
24 and multiple unconnected bearing insert members which are
difficult to handle. Thus, joints which are satisfactory
26 for machinery applications where fixtures and other tooling
27 may be conveniently used to assemble joint members need improve-
28 ment for their effective utilization in prosthetic joints.
29 Patents disclosing prosthetic joints include U.S. Patent
No. 3,813,699 to Richard P. Giliberty, issued June 4, 197~;
7~
1 ~U~S. Patent No. 3,863,273 to Robert G. Averill, issued
2 February 4, 1975; U.S. Patent No. 4,044,403 to D'Erricho issued
3 August, 1977i and U.S~ Patent No. 4,241,453 to Alex Khovaylo
4 issued December 30, 1~80. The prosthetic joint disclosed in -the
5 Giliberty patent provides a prosthetic joint which is resistant
6 to dislocation and separation and partially avoids the assembly
7 problems noted ahove by providing a unitary structure including bol :h
8 the bearincJ insert and the acetabular cup thereby minimizing
9 the handling of various joint members during the assembly and
10 disassembly process. However, the unitary structure of the bearin~
11 insert and the acetabular cup does not allow for ease of
12 assembly and di.sassembly with high separation resistance,
13 since the opening into the spherical cavity of the bearing insert
1~ which receives the ball-shaped femoral head is incapable of
lS substantial outward expansion or flexing upon being forced into
16 e~gagemerlt with the ball-shaped head and therefore the
17 Giliberty prosthetic joint requires either extremely high assembly
1~ or disassembly forces and/or relatively low .resistance to
19 dislocation and separation forces. The prosthetic joint dis-
20 closed in the Averill patent partially overcomes the problem of
21 excessively high assembly or disassembly forces by utilizing, as
in the Gottschald et al. patent, an intermediate bearing insert
23 provided with a plurality of arcuate sections at the entry into th
2 spherical seat for receiving the ball which arcuate sections upo:n
25 being forced into engagement with the femoral head still require a
26 generally undesirably high manual force to e~pand outwardly to ~`
27 permit entry of the ball-shaped head into the spherical seat of th
intermediate bearing insertO The Averill prosthetic joint also
29 utilizes a tab provided on the bearing insert to prevent separatlo:
of the bearing insert from the acetabular cup; however, such
7~
1 structure introduces undesirable axial play into the prosthetic
21 joint. Similarly, the prosthetic joint disclosed in the D'Erricho
3~ patent is also a partial solution to the above-noted assembly
4 problem in that the assembly forces required to assemble the
5 joint members are reduced below those required to assemble the
6 joint members of the Giliberty prosthesis given a predetermined
7 dislocation and separation resistance; this is accomplished
8 by the use of fle~ible lips provided on the bearing insert
9 aGting against the spherical head or ball of the first member
10 and/or the cavity in the third member or acetabular cup. Such
11 joint construction, however, is not readily disassemblable without
12 some damage to ~he bearing insert and does not provide the desirab e
13 combination of low force of manual assembly a~d hig~ separation
14 resistance needed by an operating surgeon intra-operatively.
15 The Khovaylo prosthetic joint provides structure which allows
16 for low assembly force of the bearing insert onto the head
17 but employs a solution similar to that disclosed in the D'Erricho
18 paten-t for asse~ly of the third member or acetabular cup onto the
19 bearing insert~ Further, the internal retaining ring of the
Khovaylo prosthetic joint operates in a manner which produces
21 end play between the spherical ball and the bearing insert.
22 Further, the Khovaylo prosthetic joint does not provide for
23 convenient assembly or disassembly of the bearing insert from
24 the third member or acetabular cup intra-operatively. As is
further known to those skilled in the prosthetic joint art,
26 physically separate acetabular cups and bearing inserts are
27 desirable in prosthetic joint applications in order to minimize th ,
28 cost of stocking various sized prostheses and in order to minimize
29 sterilization costs associated with such joir.ts.
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~5~
As is still further known to those skilled in the
art, the bearing inserts of the above-noted patents, provide
an overlap which, upon the bal]-shaped head being received
within the heari.ng insert and the bearing insert with the ball-
shaped head seated therein being received within the insert
housing, prevents dislocation of the ball-shaped head from the
bearing insert during rotational movement between the ball-
shaped head and the insert housing cup.
SUMMARY OF THE INVENTION
The present invention provides in an improved
spherical kinematic joint for providing three degrees of
rotational movement between two members and of the type includ-
ing: (i) a first component for engaging one of said two
members and providing a first seat having a first opening;
ti..i.) a second component for engaging the other of said two
members and including a neck and a head; (iii) a bearing insert
compri.sed of a plurality of physica]ly distinct bearing segments
arld providiny a second seat having a second opening; upon
ass~mbly of said joint, said head is received within said
~a ~econd sea-t with said neck extending through said second open-
lng, said bearing insert with said head received therein
received within said first seat and said first component con-
straining said bearing insert against outward expansion thereby
confining said head within said second seat whereby said
rotational movement between said two members is permitted, said
bearing insert providing an overlap angle for preventing dislo-
cation of said head from said bearing insert during said
rotati.onal movement; wherein the improvement comprises: means
for maintaining said plurality of physically distinct bearing
segments together in a sub-assembly to prevent separation there-
between prior to and during assembly with said first and second
components thereby facili-tating assembly of said spherical
5A.
S7~
kinernatic joint, at least portions of said sub-assembly expand-
ing outwardly to permit said head to be received wi-thin said
first seat, and said means engageable with said first component
upon assembly and said engagement of said means with said first
component causing said means to compress radially inward to
permit said bearing insert with said head received therein to
be received within said first seat of said first component.
The improved spherical kinemati.c joint of the present
invention overcomes the above-noted pri.or art problems by pro-
viding various bearing insert embodiments which allow ease andconvenience of assembly and disassembly, particularly assembly,
by providing a plurality of substantially physically distinct
bearing inserts in a sub-assembly such that the bearing inserts
are effectively a unitary structure for the purpose of assembly
and disassembly but which bearing segments expand easily with
~ow manual force during assembly and disassembly of the various
bear.ing lnsert embodiments from the head and/or cavity or
spherical seat in the third member, such as for example in the
prosthetic joint embodiments, an acetabular cup. Further,
~uch ease of assembly and disassembly can be accomplished while
ret~ining great dislocation and separation resistance and in
some embodiments is accomplished in a manner which does not
introduce significant axial play.
. ~ 6.
7~Z
" ,
DESCRIPTION OF THE DRAWINGS
2 FIG. 1 is a diagrammatic illustration, in cross-section,
3 showing the improved spherical kinematic joint of the present
4 invention, embodied as a prosthetic hip joint, implanted in a
pelvis and femur;
6 FIG. 2 is a cross-sectional view of a first embodiment of
7 a split bearing insert of the present invention;
8 FIG. 2 (a~ is a partial front view of a portion of the split
~ bearing insert shown in FIG. 2;
10 FIG. 3 is a cross-sectional view of an acetabular cup .
11 of the present invention, particularly useful when the improved
1~l spherical kinematic joint of the present invention is embodied
13 as a prosthetic hip joint;
1~ FIGS. ~(a) and (b) are, respectively, cross-sectional views
of alternate embodiments of retaining rings;
16 FIGS. 5(a)-(c) are, respectively, side, top and an
17¦ enlarged view of a release ring useful for disassembling the
18¦ elements of the improved spherical kinematic joint of the present
19¦ invention;
~ol FIGS. 6(a) and (b) are, respectively, sequential views,
21¦ in cross-section, illustrating assembly of one embodiment of the
22~ present invention;
231 FIGS. 7(a)-(c) are views illustrating the utility of scallopc
24 ¦ which may be provided on the various split bearing inserts of
251 the present invention to reduce the amount of radial expansion
26¦ required for assembly of the bearing inserts to the femoral head
27 ¦ of a femoral stem upon the improved spherical kinematic ,oint
28¦ of the present invention being embodied as a prosthetic joint;
2~ FIGS. 8(a) and (b) are cross-sectional, diagrammatic
illustrations sho~ing the advantage of providing greater engage-
J~;~
1,l ment between a retaining ring and the external grooves provided
2~ on a bearlng insert than between the retaining ring and the
3l internal circumferential groove provided on an acetabular cup,
4 upon the present invention being embodied as a prosthetic hip
S joint and utilizing a retaining ring; and
6 FIGS. 9(a)-(c), FIG. 10, FIG. 11, FIGS. 12(a)-(d), and
7 FIGS. 13-20 are, respectively, alternate embodiments of various
8 split bearing inserts of the improved spherical joint of the
9 present invention, particularly when embodied as a prosthetic
10~ hip joint.
16
L7
! ~6
27
28
6~.
~s~
1 DESCRIPTION OF THE PREFERRED EMBODIMENTS
i
21 Referring now to F~G~ 1, there is shown a first embodiment
3 of the improved spherical kinematic joint of the present invention
4 embodied as a prosthetic hip joint 10 which is shown implanted.
5 The prosthetic hip joint 10 includes the following components:
6 a femoral component 12, sometimes referred to in the art as an
7 intermedullary stem or femoral insert; a split bearing insert 20;
8 an acetabular cup 30; and a retaining ring 40.
9 The femoral component 12 includes a stem 14 which fixtures
10 the component into the medullary cavity of the proximal femur,
11 preferably but not exclusively with the aid of a grouting agent 15
12 a ball-shaped or spherical femoral head 16; and a neck region 18
13 which transfers load from the spherical femoral head 16 to the
1~ stem 14.
The split bearing insert 20, as may be better seen in
16 FIGS. 2 and 2(a), includes a plurality, a pair being shown,
17 of opposed identical split bearing segments or clam shell-shaped
1~ members 21-21; in this embodiment, each split bearing segment 21
19 is physically distinct from the other. Each segment 21 is pro-
vided with an outer spherical surface 22, an outer cylindrical
21 surface 23 and an outer annular tapered surface 24; additionally,
22 each segment 21 is provided with an inner spherical surface 25 and
23 a chamfer or inner annular tapered surface 26. Further, in the
embodiment shown, each segment 21 is provided with a generally
U-shaped longitudinally extending surface 29 which will be of the
27 same shape as the cross-hatched area of FIG. 2 but wi~hout the
gap. Each outer spherical surface 22 merges with the inner
28 end of an outer cylindrical surface 23 and the outer end of
29 each cylindrical surface 23 terminates with the inner end of
an outer annular tapered surface 24; similarly, each inner
1 annular tapered surface 26; and the outer ends of the annular
2 ¦tapered surfaces 24-26 intersect or merge as shown, preferably
3 Iwith a slight radius r. When placed in opposed relationship
4 as shown in FIG. 2, the inner spherical surfaces 25-25 of the
clam shell-shaped members 21-21 cooperatively provide a spherical
6 cavity or seat 27 for receiving the spherical femoral head 1~
7~ (FIG. 1) of the femoral component 12 (FIG. 1) and thus it will
8l be understood that the spherical cavity or seat 27 preferably
9 closely matches the shape of the spherical femoral head 16 with
the diameter of the femoral head 16 being larger than the opening
11 to the seat 27 provided by the chamfer 26. A pair of scallops
12 or beve:Led surfaces 28-28 may be provided on each member 21
13 contiguous with and merging into the longitudinally extending
1~ surfaces 29, beveled surfaces 28-28 facilitate the insertion
1~ of the spherical femoral head 16 of the femoral component 12
16 into the spherical cavity 27 by reducing the amount of expansion
17 of the split bearing insert 20 required for insertion. Lastly,
la an external circumferential groove 19 is provided in each
lg outer cylindrical surface 23 for receiving or at least partially
receiving, the flexible retaining ring 40 shown in FIG. 4(a). The
21 depth and width of the groove 19 are sufficient to permit
22 the retaining ring 40 to be received completely within the groove
23 upon the ring being compressed radially inwardly. It will
24~ be understood that, prior to the assembly of the spherical
prosthetic hip joint components for implantation, the first
2~ ~unction of the retaining ring 40, upon being received, or at
27 least partially received, within the external circumferential
28 grooves 19, is that of maintaining the clam shell-shaped members
~91 21-21 together in a sub-assembly and in generally opposed relatio~
3~ ship as illustrated in FIG. 2 with the generally U-shaped longituc .
31 inally extending surfaces 29 engaged in a plane of contact or
32 separation extending through the center line C/L.
~1~57~
i
The acetabular cup 30, as may be ~est seen in ~IG. 3, is
2 provided with a smooth outer spherical surface 31 which terminates
3 at the inner end of an outer annular tapered surface 32, the cup
4 is further provided with an inner spherical surface 33 which
5 merges at its outer end with the inner end of a cylindrical inner
6 surface 34 which at its outer end merges with the inner end of a
7 chamfer or inner annular tapered surface 35; the tapered
8 surfaces 32~35 intersect or merge at their outer ends as shown.
9 An internal circ~lmferential groove 37 is provided near the outer el ~d
10 of inner cylindrical surface 34 for receiving the retaining ring
11 shown in FIG. 4(a). The outer spherical surface 31 preferably
12 closely matches the acetabular cartilage or natural acetabulum
13 (FIG. 1), the acetabular articular cartilage not always being
14 presen-t depending upon the degeneracy of the joint, and the inner
15 ¦spherical surface 33 and inner cylindrical surface 34 cooperativel~
16 provide a cavity or seat 38 for receiving the split bearing insert
17 ¦20. PreEerably, the inner cylindrical surface 33 and inner
18 ¦cylindrical surface 34 of the acetabular ¢up 30 closely match
19 the outer spherical surfaces 22-22 and the outer cylindrical
2n ¦ surfaces 23-23 respectively, of the split bearing insert 20.
21 As is further shown in FIGS. 3 and 3(a), the acetabular cup 30
22 is provided with a plurality of radially disposed slots or
23 grooves 39 extending axially into the inner annular tapered
24 surface 35 and the outer portion of the inner cylindrical
surface 34; upon the retaining ring 40 being received within
26 the circumferential grooves 19 and 37 and upon the spherical
27 femoxal head 16, split bearing insert 20 and acetabular cup 30
being assembled as illustrated in FIG. 1, the radially disposed
29 grooves 39 are for providing external access to the retaining
ring 40 by the radially disposed prongs 44 of the release tool
31 46 shown in FIGS. 5(a) and 5~c) for disassembly of the split
32 bearing insert 20 and the spherical head 16 of the femoral
35~
1.
I
l llcomponent from the acetabular cup 30, as will be explained in
2 detail below.
3 The spherical prosthetic hip joint 10, embodying the present
4 improved spherical joint invention, is implanted as follows- the
5~ femoral component 12 is implanted in the femur as described above
6 and as illustrated in FIG. 1, the forward portion or chamfer 26
7 of the split bearing insert 20, with the retaining ring 40
8 residing, or at least partially residing, within the external
9 circumferential grooves 19 and maintaining the split bearing
10 segments 21-21 together in a sub-assembly as described above, is
11 forced (manual force supplied by the operating surgeon being more
12 than sufficient) into engagement with the spherical femoral head
13 16 which is larger in diameter than the opening to the seat 27
1~ whereupon the split bearing segments 21-21 expand radially by
~enerally pivoting outwardly (i.e. pivoting generally radially
16 ou-twardly) about their rearward portions (such expansion being
17 facilltated by the scallops 28 if provided) to allow the femoral
18 head to be received within the split bearing insert 20 and to
19 be seated within the spherical cavity or seat 27, then the acetab-
ular cup 30 is then pushed over the split bearing insert 20 to
21 cause the chamfer or inner annular tapered surface 35, as illustra .
22 ted in FIG. 6(a), to engage the retaining ring 40 and compress it
23 radially inwardly completely within the external circumferential
24 grooves 19 provided on segments 21~21 thereby allowing the
25 acetabular cup to pass over the retaining ring 40 until as .
26 illustrated in FIG. 6(b), the inner spherical surface 33 of the
27 acetabular cup meets or engages the outer spherical surfaces 22-22
28 ¦of the low-friction split bearing insert 20. At this point, the
29 external circumferential grooves 19-19 provided in the segments
21-21 are aligned axially with the internal circumferen-tial
31 groove 37 provided in the acetabular cup 30 whereupon the
~ S~2
1 retaining ring 40 expands radially outwardly to be partially
2¦~received within the internal circumferential ~roove 37 and
3 Ipartially within the external circumferential grooves 19-19.
4 The retaining ring 40 now performs its second func~
5 retains the acetabular cup on and over the split bearing insert
61 20 with the spherical femoral head 16 received therein thereby
7 preventing se~aration ~e~g. axial dislocation) between the
8 bearing insert (with the femoral head seated therein) and the
9 acetabular cup during joint rotation. All three components
10 of the spherical prosthetic hip joint 10 are now assembled and
11 the acetabular cup 30 is inserted within the acetabulam as
12 illustrated in FIG. 6(b)o
13 The manner in which such scallops or beveled surfaces 28-28
14 facilitate the insertion of the spherical femoral head 16 into
15 the spherical cavity 27 by reducing the amount of radially outward
16 expansi.on re~uired by the split bearing insert or segments
17 21-21 is il].ustrated diagrammatically in greater detail in
18 FIG.S. 7(a)-(c~. As illustrated in FIG. 7(b), upon the split
19 ~earing segment 21' not being provided with the scallops or
20 beveled surfaces 28-28, the segment must be expanded radially
21 outwardly a distance Ll to permit insertion of the spherical
22 head 16 into the spherical cavity or seat 27, whereas, upon the
23 split bearing segment 21 being provided with the scallops or
24 beveled surfaces 28-28 as illustrated in FIG. 7(c), the segment
21 must be expanded radially outwardly a lesser distance L2 to
26 permit such spherical femoral head insertion wherein, it will
27 be understood as illustrated, the distance L2 is less than
2~ the distance Ll by substantially the height S of the scallops
29 28-28.
In the embodiment of the present invention illustrated in
5752
1,
1 FIG. 6(b), the overlap angle ~ is approximately 30 ~nd the
21 rotational or pi~otal motion provided is approximately 60.
3 For disassembly, the release tool 46, FIG~o 5(a) and (b)
4 may then be inserted over the neck region 18 of the femoral
5 component 12, FIG~ 6(b), entry being permitted by the gap or
6 opening 48 provided in the release tool, FIG. 5(b), and the
7 radially disposed prongs 44 are inserted into the radial grooves
8 39 (~IG. 3) provided in the acetabular cup 30 to cause the
9 chamfered edges 47 of the release tool, FIG~ 5(c), to pass
10 over the retaining ring 40 and depress the ring completely
11 within the external circumferential grooves 19 19 provided on
12 the split bearing segments 21-21 allowing the withdrawal o
13 the acetabular cup 30 from over the split bearing insert 20
14 thereby disassembling the acetabular cup from the split bearing
insert 20 and the spherical femoral head 16 received within the
16 spherical cavity 27 or the insert 20. For further disassembly of
the split bearing insert 20 from the spherical femoral head 16,
18 force, readily supplied manually by the operating surgeon, is
19 applied to the split bearing insert 20 to pull i~ away from the
spherical femoral head 16 whereupon the split bearing insert
22 segments 21-21 move radially outwardly and the split bearing
insert 20 is readily withdrawn, facilitated by the scallops 28
231 if provided, rom over the spherical femoral head 16 leaving the
24 femoral component 12 implanted in the femur if desired. It will
be noted that by providing the release tool 46 (FIG~. 5(a) and
26 5(b)) with the gap or opening 48, a one piece release tool is
27 provided which may be utilized to disassemble the acetabular cup
28 from the split bearing insert 20 and spherical femoral head 16
2~ received within the cavity or seat 27, without requiring removal
of the femoral component 12 from -the femur (FIG. 1~.
7~%
1~ I It will be further understood by those skilled in the
2 art that the wearing properties of the split bearing insert 20
3 may be improved by dimensioning the split bearing segments 21-21
4 on the dimension of the spherical femoral head 16 such that upon
5 assembly of the bearing insert 20 to the spherical femoral head 16¦
6 ~a yap or space is provided between the generally U-shaped
7 longitudinally extending surfaces 29 (FIG. 2) to permit a
8 ¦lubricant, which in the case o-E a spherical prosthetic hip join-t
9 ¦is synovial fluld, to reach to the bearing surfaces of the
10 ¦spherical joint and aid in removal of wear debris from the bearing
ll ¦surfaces by providing convenient passages to the surrounding
12 ¦regions.
13 ¦ It wil] be further understood, that while in the preferred
1~ embodiments of the present invention the retaining ring 40 is
15 oE circular transverse cross-section, particularly because of
16 greater availability and lower cost of such circular cross-section~ ,
17 as illustrated in FIG. 4(b), other retaining ring cross-sections
18 m~y be utilized, such as square, rectangular, etc. may be L
19 u~ilized and, of course, the shapes of the e~ternal circumferentia L
grooves 19-19 on the segments 21-21 and the internal circumferenti Ll
21 groove 37 provided on the acetabular cup 30 will be of suitable
22 cross-sectional shape. It will be noted that the retaining ring
~3 and grooves need not be of complementary shape; it has been found
24 that a ring of circular cross-section will function properly
in a groove of yenerally rectangular cross-sectional shape with
26 ¦side walls generally perpendicular,and a bottom generally parallel
27 ¦to the outside cylindrical surface. Further, it will be understoo~
28 ¦and as illustrated in FIG. 4, the retaining ring 40' (FIG~ 4(b)),
29 is provided in transverse cross-section with a width "w" and a
height "h" whereas, since the transverse cross-sectional shape i
31 of the retaining ring 40, FIG. 4(a), is circular, both the width
75%
l and height of the retainin~ ring 40, in transverse cross-section,
2 are equal to the diameter "d."
3 It has been found to be desirable to provide gr~ater
4 engagement "e" as shown in FIG. 8ta), between the retaining
ring 40 and the external circumferential grooves 19-19 provided
6 in the bearing insert 20 than between the retaining ring 40 and
7 the internal circum~erentiai groove 37 provided in the acetabular
81 cup 30 in order to produce less possible protrusion of ~he
9 retaining ring 40, out of groove 19 during assembly. This
101 protrusion may be understood by reference to FIGS. '8(a) and
111 8(b). The smaller protrusion out of external ¢ircumferential
121 groove 19 of the bearing insert 20 allows the use o~ a smaller
13 chamfer or inner tapered annular surface 35 at the entrance into
14 the spherical cavity or seat 38 of the acetabular cup. This
smaller chamfer or inner annular tapered surface 35 produces
16 less interruption in the face or en~rance portion of the
17 acetabular cup 30 thus producing a better appearance and allows
18 the use of a thinner cup wall "t," FIG. 3, thereby allowing an
19 increased range of acetabular cup sizes that will fit over a
given bearing insert, e.g. bearing insert 20 of FI~. 2.
21 Referring again to FIG. 8, it may be seen that the
22 maximum protrusion PmaX occurs when one side of the ring is
23 pushed or falls fully into external groove 19 causing the other
24 side of the ring to protrude to the maximum extent. It will
25 be understood that the smallest maximum protrusion "P ," for
max
26 a given engagement "e" between the rin~ and groove is obtained
27 when the depth of the internal groove 37 is equal to the cross~
28 sectional diameter "d" of retaining ring 40. For this case, the
29 maximum protrusion ls: .
30 Pmax P ~ C (1)
~S7~;2
1 where P is the protrusion of the retaining ring 40 when its axis
2 coincides with the axis of the bearing insert and C is the clear-
3jlance between the ring and the bottom of the external groove 19
with the retaining ring is so aligned.
5 Now d = P + e
6 or P = d - e (2)
7 and
8 C = d - e (3)
9 Now, if the ring is placed so that one side is fully within groove
19 as shown in FIG. 8(b), then the protrusion P~aX is
11 PmaX - 2(d-e) (4
12 Thus, it may be seen that increasing "e" reduces Pma~.
13 With circular cross-sections in order to provide greater
14 engagement between the external bearing insert groove 19 and
lS the retaining ring 40 than between acetabular internal groove 37
16 and the retaining ring 40, it is necessary to taper the posterior
17 ~ace 37 of insert groove 19 to prevent retraction of the ring.
18 To prevent such retraction, the angle as shown in FIG. 2 may
be compuked from:
~ < cos 1(2e/d - 1) (5)
21
22 where "e" is engagement between the xetaining ring 40 and the
23 insert groove 11 and "d" is a cross sectional diameter of the
24 retaining ring 40. The outer diameter Dl of the retaining ring
40 is made essentially equal to the diameter D2 of the acetabular
26 cup internal groove 37 as shown in FIGS . 4 and 3, respectively.
27 Alternate embodiments of the improved spherical kinematic
28 joint of the present invention, also embodied as improved spher-
29 ical prosthetic hip joints, are provided and are illustrated in
FIGS. 9(a)-(c), 10, 11 and 12(a)-(d). These embodiments
S7~ 1
, I
1 linclude various alternate bearing inserts having various hinge
2 or pivot type connections between the spli~ bearing segments
3 11 at their rearward portions which reduce or eliminate the possibili :y
4 of the segments disengaging from each other and from the retaining
51 ring during assembly and disassembly of the components of the
61 improved spherical joint. It will be further understood that
7 these alternate embodiments include the femoral component 12,
8 acetabular cup 30, and in some embodiments, the retaining ring 40
9 of FIG. l; the alternate bearing inserts are given numerical-alpha
10l designations, e.y. 20A, 20B, etc. to distinguish them from the
11 bearing insert 20 of the first embodiment and where the structure
12 and surfaces ~f these alternate bearing insert embodiments are
13 identical to those of the first embodiment, they are given the
14 corresponding numerical designations but where different, they
are glven a numerical-alpha designation corresponding to the alpha
16 designation of the bearing insert alternate embodiment.
17 The first alternate embodiment, E'IG. 9(a), (b) and (c),
lB includes the split bearing insert 20A which includes a plurality,
19 a pair be;n~ shown, of opposed identical spl - be3rlng segments
20 ¦21A-21A each of which is provided at its rearward portion with an
21 outwardly extending tab 81 and an inwardly extending recess 83.
22 Upon assembly, as illustrated generally in FIGS~ 9(b) and (c),
23 the tabs 81 are recei~ed in the recesses 83 to cooperatively
24 provide a pivot or hinge-type connection, about which the
se~nents 21A-21A pivo-t outwardly to permit insertion of the
26¦ spherical femoral head 16 into the spherical cavity or seat 27A
l provided by the inner spherical surfaces 25A-25A of the segments
28¦ 21A-21A.
29 A second alternate embodiment is illustrated in FIG. 10
and includes the alternate split bearing insert 20B comprised
:
575~
1 of the plurality of opposed identical split bearing segments
2 21B-21B each of which members, as illustrated~ is provided at its
3 rearward portion with an inwardly extending hole 61 for receiving
4 one end of a flexible pin 63; otherwise, this further alternate
S embodiment further includes the spherical joint components describe ~d
6 hereinabove. Upon insertion of the flexible pin 63 into the
7 opposed and axially aligned holes 61-61, the spli.t bearing
8 segments 21B-21B pivot outwardly about the hinge type connection
9 provided cooperatively by the holes 61-61 and the flexible pin 63
to expand to the split bearing insert 20B radially outwardly to
11 permit the spherical femoral head 16 to be received within the
12 internal seat or cavity 27B provided internally of the split
13 bearing insert 20B by the inner spherical surfaces 25B-25B.
14 Referring to a third alterna-te embodiment illustrated in
FIG. 11, it will be understood that the split bearing insert 20C
16 is substantially identical to the split bearing insert 20
17 illustrated in FIG. 2 but wherein the split bearing segments 21--21
18 of FIG. 2 are physically distinct from each other, the split
19 segments 21C-21C of the embodiment of FIG. 11 are connected or
21 hinged together at their rearward portions by a relatively thin
integral member C. The alternate embodiment including the low-
22 friction split bearing insert 20C of FIG. 11 is assembled and
23 disassembled in substantially the identical manner as the
embodiment including the split bearing insert 20 of FIG. 2
except that upon radially outward expansion of the split bearing
26 insert 20C of FIG~ 11 to permit insertion of the spherical
27 femoral head 16 into the spherical cavity or seat 27, the split
28 beari.ng segments 21C-21C hinge or pivot radially outwardly about
29 the thin, flexible integral member C.
/
75~
l I
1 An alternate embodiment of the low-friction split bearlng
2 insert 20C illustrated in FIG. 11 is illustrated in FIGS. 12(a)-
3 (d); this alternate split bearing insert is identified with
4 numerical designation 20D. In this embodiment, the hinge or
S flexible member D is made sufficiently thick such that plastic
6 deformation occurs when the split bearing segments 21D~21D are
7 pivoted radially outwardly, as shown in FIG. 12(a) to permit
8 insertion of the spherical femoral head 16 of the femoral
9 component 12 into the split bearing insert 20D~ Further, the
10 inner spherical cavity or seat 27D provided in the interior of
11 the split bearing insert 20D is made sufficiently large such
12 that it is slightly larger than the spherical head 16 of the
13 spherical component 12 thereby providing some clearance
14 (indicated by numerical designation 46) between the spherical
cavity 27B and the spherical femoral head 16 when the acetabular
16 cup 30 is partia]ly assembled onto the plastic bearing insert
17 20D as illustrated in FIG. 12(b). A partial outer circumferential
18 ridge 43 is formed integrally on the outer cylindrical surface
19 23D of each split bearing segment 21D-21D which matches
internal circumferential groove 37 provided on the acetabular
21 cup when the cup and the split bearing insert 20D are fully
22 assembled. Assembly of this embodiment is as follows.
23 The femoral component 12 is implanted in the femur (FIG. 13 and
24 the split bearing insert 20D and ~he spherical femoral head 16
are assembled as illustrated in FIG~ 12(a) producing some
26 deformation of the hinge or spherical flexible member D thereby
27 producing some separation o~ the split bearing segments 21D-21D
28 at their forward portions or inferior aspect as illustrated
~9 in FIG. 12(a). The acetabular cup 30 is then partially assembled
onto the split bearing insert 20D as illustrated in FIG. 12(b)
31 forcing the segments 21D-21D together against the resistance of
57~~ 1
l ~the flexible member D. As assembly further progresses, the
2 chamfer or inner tapered annular surfaces 35 engages the partial
3 circumferential ridges ~3 and presses forward portions or inferior
4 aspect of the segments 21D-21D together as illustrated in FIG. 12(~ ).
5 This action is all.owed by the clearance 46 between the spherical
6 femoral head 16 and the inner spherical surface 25D of the
7 split bearing insert 20D and by the gap or spacing between the
8 generally U-shaped longitudinally extending surfaces 29. Upon
9 completion of assembly, the external, circumferential ridges
10 43 provided on the exterior of the split bearing insert 20D
11 will be axially aligned with the internal groove 37 provided on
12 the ~orward portion of the interior of acetabular cup 30 allowing
13 the ridges ~3 to engage the groove 37 by the spreading action of
14 h.inge segment or spherical bridge D. Disassembly or separation
15 oE the acetabular cup 30 from the split bearing insert 20D is
16 prevented by the wedging action of the spherical Eemoral head 16
18 against the forward portion of the inner spherical surfaces 25D
of the split bearing insert 20B and such separation will be
19 prevented where the contact tangent ~1, as illustrated in
20 FIG. 12(d) is greater than contact tangent ~2.
21 Disassembly is provided in the same manner described
above by using the release tool 46 of FIG. 5.
23 A still further alternate embodiment of the improved
24 spherical kinematic joint of the present invention, also
embodied as an improved spherical prosthetic hip joint, is
26 provided and is illustrated in FI~S. 13-20. This fur-ther
27 alternate embodiment includes an alternate split bearing insert
28 20E which includes a plurality of physically distinct split
29 bearing segments, namely the generally spherically-shaped primary
bearing segment 51 of FIG. 13 and either the generally annularly
31 shaped, radially or circumferentially split bearing segment or
57~
1 collar 61 of FIG. 14 provided with the external circumferential
21 groove 19 or the generally annularly shaped, radially or circum-
3j ferentially split bearing segment or collar 71 of FIG. 16 provided
4 with the partial or complete external circumferential ridge 43.
As shown in FIG. 13, the primary bearing segment 51 is
6 provided with an outer spherical surface 52, an outer cylindrical
7 surface 53 and an inner spherical surface 55; additionally, the
8 primary bearing segment 51 is provided at its forward portion
9 with an annular, radially outwardly extending projection 58
10 and an annular, radially inwardly extending groove 59.
11 The collar 61, of FIG. 14, is provided with an outer
12 cylindrical surface 63, in which is formed the external circum-
13 ferential groove 19, for receiving the retainin~ ring 40, an
1~ outer annular tapered surface 24, a chamfer or inner annular
tapered surface 26 and an inner cylindrical surface 65; addi-
16 tionally, the collar 61 is provided at its rearward portion with
17 an annular, radially inwardly extending projection 68 and an
annular, radially outwardly extending groove 69. Similarly, the
1~ collar 71 of FIG. 16 is provided with an outer cylindrical
21 surface 73~ an outer annular tapered surface 24 and a chamfer or
inner annular tapered surface 26 and an inner spherical surface 75
22 additionally, the collar 71 is provided at its rearward portion
23 with an annular, radially inwardly extending projection 78 and
24 an annular, radia].ly outwardly extending groove 79. It will be
noted and understood that the collars 61 and 71 are made of a
26 suitably flexible material and are split radially, or circum-
28 ferentially, as indicated respectively at 64 and 74 to p~rmit the
29 collars to be expanded radially outwardly or circumferentially
for assembly with the primary segment 51.
~57~
Prior to assembly with the ball--shaped or spherical
femoral head 16 of the femoral component 12 (FIGURE 1), the
primary bearing segment 51 and either of the collar 61 of
FIGURE 14, or the collar 71 of FIGURE 16, are assembled
together in a sub-assembly to facilitate handling by the surgeon
for the reasons noted above. More particularly, and as illus-
trated in FIGURE 17 with regard to collar 61 (it will be under-
stood that the collar 71 is assembled in the same manner), -the
collar 61 is expanded radially outwardly or circum~erentially
(preferably prior to the operation and prior to sterilization
or packaging) to permit the projection 68 to pass over the pro-
jection 58, and upon the collar 61 contrac-ting, the projection
68 is received within the groove 59 and the projection 58 is
received within the groove 69 whereupon the primary bearing
segmen-t 5] and collar 61 are assembled into a sub-assembly as
illustrated in FIGURE 18.
It will be further noted and understood that upon the
split bearing insert 20E includiny the collar 61, the flexible
retainincJ ring 40 is also utilized and is received within the
2~ cJroove 19 as illustrated in FIGURES 17 and 18; in this embodi-
men-t, the retaining ring 40 assists in maintaining the primary
bearing segment 51 and the collar 61 in a sub-assembly. How-
ever, it will be understood by those skilled in the art that it
is within the present invention to provide a collar which is
made of a more rigid material wherein the collar is comprised
of a plurality of annular segments provided in their outer
surface with a groove (e.g. groove 19) for receiving the
flexible retaining ring 40 which maintains the annular segments
together and on the primary bearing segment 51 to provide the
bearing insert sub-assembly.
~575
1 1 Thus, as illus-trated in FIG. 18, it will be understood that
2~upon Pither the collar 61 or the collar 71 being assembled
3¦~to the primary bearing segment 51, the same outside configuration
4~1of the bearing insert embodiments described above is provided.
51 Similarly, it will be understood that the inner spherical
6l surface 55 of the primary bearing segment 51 and either the
7 inner spherical surface 65 of the collar 61 or the inner
8 spherical surface 75 of the collar 71 cooperatively provide a
91 spherical cavity or seat preferably closely matching and
10 for receiving the spherical femoral head 16 (FIG. 1) of the
11 femoral component 12 (FIG. 1), such spherical seat being
12 identified in FIG. 18 as seat 57E. It will be further understood
13 that as with regard to the above-described embodiments of the
14 split bearing insert of the present invention, that the opening
15 to the spherical seat 57E provided by the chamfer 26 of the
16 collars 61 and 71 is smaller than the diameter of the spherical
head 16 o~ FIG. 1.
1~ Assembly of the split bearing insert 20E with the spherical
19 femoral head 16 of the femoral component 12 (FIG. 1), will now
20 be described with reference to FIGS. l9(a) through l9(d), with
21 the split bearing insert 20E illustrated therein comprised of
22 the collar 61 of FIG. 14; however, it will be.understood that
23 upon the split bearing insert 20E including the collar 71 of
24 FIG. 16 such assembly is made in a similar manner.
As illustrated in FIG. l9(a)~ upon the chamfer 26 of the
26 collar 61 (FIG. 14) being forced into engagement with the
27 spherical femoral head 16 (manual force supplied by the operating)
2~ surgeon being more than sufficient and such force being indicated
29 by the arrows 81 and 83) the collar 61 expands radially outwardly
or circumferentially at the split 64 and against the action
~$~75~
11l of the retaining ring 40, as illustrated in FIG. l9(b), to
2 permit the collar 61 to pass over the spherical femoral head 16
31 and permit the spherical femoral head 16 to ~e seated within the
4~ spherical cavity or seat 57E ~FIG. 18) of the split bearing;
5 the acetab~lar cup 30~ as with regard to the split bearing
6 insert 20 described above and illustrated in E~IGS. 6(a) and 6tb),
7 is then pushed over the spli~ bearing insert 20E to cause the
8 chamfer or inner annular tapered surface 35 of the acetabular
9 cup 30, FIG. 6(a) 7 to engage the retaining ring 40 and compress
10 it radially inwardly completely within the external circumferentia L
11 groove 19 provided on the collar 61 thereby allowing the acetabula
12 cup 30 to pass over the retaining ring 40 whereupon the split
13 bearing insert 20E with the spherical femoral head 16 seated
1~ therein are both completely seated within the spherical cavity
15 or seat 38 (FIG. 3) and the elements comprising this embodiment
16 of the present invention occupy the position shown in cross sectio]
17 in FIG. 20 with the retaining ring 40 residing partially within
18 the external groove 19 of the collar 61 and res.iding partially
29 wi.thin the internal groove of the acetabular cup 30 whereby the
retaining ring 40 maintains the bearing insert 20E within the
21 acetabular cup 30 during rotation of the joint.
22 Upon the collar 71 of FIG. 16 being assembled to the
23 ¦primary bearing segment 51 to provide the above-noted sub-assembly
24 ¦and upon this sub-assembly being assembled to the spherical
25 ¦femoral head 16 in the manner illustrated in FIGS. l9(a) through
26 l9(d) with regard to collar 61, the ridge 43 engages the
7 internal groove 37 of the acetabular cup 30 whereby the acetabular
2~ cup is retained on and over the split bearing insert and
29 separation between the bearing insert (with the femoral head
seated therein) and the acetabular cup is prevented during joint
~575~
rotation. It will be understood that as in the split bearing
insert 20D; FIGURE 12(d), a clearance, e.g. clearance 46 of
FIGURE 12(d) must be provided between -the inner spherical sur-
face 75 and the spherical femoral head 16 to allow contraction
of the collar 71 as the ridge 43 enters the cylindrical surface
33 of the acetabular cup 30 (FIGURE 3).
~ isassembly of the bearing insert 20E, whether in sub-
assembly with the collar 61 or the collar 71, may be provided
with the release ring 46 described above with regard to the
bearing insert 20 utilizing the retaining ring 40 or with
regard to the bearing insert 20D utilizing the circumferential
ridge 43.
In the embodiment of the present invention illustrated
in FIGURE 20, the overlap angle y is approximately 30 and the
ro-tational or pivotal motion provided is approximately 60.
Referring again generally to the present invention, it
will be unc~erstood that the alternate embodiments of the split
bearincJ insert shown in FIGURES 2, 9, 10, 11 and 12 are split
a].ong a plane (e.g. plane coincident with the center line C/L,
2~ oE Li'IGURE 2) oriented perpendicular with respect to the plane
8~-8~, E'IG~RE 2, defined by the opening to the spherical cavity
or seat 27 provided by the chamfer 26, and that the low-
friction split bearing insert alternate embodimen-t 20E of
F'IGURES 13 and 14 is split along a plane illustrated by line
87-87, FIGURE 13, which is oriented parallel to the plane indi-
cated by the line 85-85 defined by the opening to the spherical
cavity or seat 57E provided by the chamfer 26 of the collar 61,
FIGURE 14; in each embodiment, the split bearing insert is
comprised of a plurality of bearing segments and a plurality of
split bearing segments.
~ 24.
75%
1 ¦ Referring generally to all of the varlous embodiments of
2 ¦the improved beari.ng inserts of the present invention, it will
3 be noted by those skilled in the art that in the embodiments of
4 FIGS. 2, 9, 10 and 18 the respective bearing inserts are com-
5 prised of a plurality of bearing segmen-ts that are in fact
6 physically d.istinct and that the bearing inserts of FIGS. 11 and
7 12(a)-(d) are comprised of a plurality of bearing segments that
8 are physically distinct except for integral flexible members
9 C and D, respectively, pro~ided at their rearwarA portions; hence
the expxession "comprised of a plurality of 'substantially'
11 physically distinct bearing segments" is used in the appended
12 claims to describe both the bearing insert embodiments where
13 the bearing segments are in fact physically distinct and the
14 bearing insert embodiments when the bearing segments are
physically distinct except for the integral flexible members C
16 and D.
17 Referring now generally to the above specifically described
18 alternate embodiments of the improved spherical joint of the
19 present invention, it will be noted that such joint provides a
large, or substantial, overlap angle ~, as illustrated in
21 FIGS. 6(b) and ~l resulting in great dislocation resistance with
22 very low assembly and disassembly forces required. For outward
radial expansion of the various alternate embodiments of the
24 split bearing insert to permit insertion of the ball-shaped
head, e.g. spherical femoral head into the spherical seat or
26 cavity provided by the various alternate embodiments of the
split bearing insert, only a thin retaining ring needs -to be
28 flexed or expanded radially outwardly, or a relatively thin
29 integrally formed spherical plastic bridge, or opposed tabs,
or a flexible pin, needs to be flexed, or a radially split
S75i~ 1
i I
lllannular collar needs to be expanded radially outwardly. Similarly
2 ¦¦ acetabular cup 30 can be easily assembled and disassembled
3~¦to or from the various alternate embodiments of the split bearing
4 insert with the ball-shaped head, e.g. spherical femoral head,
5 seated therein by a small radially inward or radially outward
6 deflection of a thin retaining ring while great separation
7 resistance is provided. Furlnermore, in the en~odiments USilly
8 the retaining rlng 40, since there is no deformation of the
9 various split bearing inserts needed for either assembly operation
10 no axial play is introduced resulting in a well fitting split
11 bearing insert.
12 The femoral component 12 and the acetabular cup 30 may be
13 made of rigid implantable metal such as stainless steel, titanium,
14 or cobalt chromium alloy as well as certain suitable ceramics.
15 The various embodiments of split bearing insert may be made of any
16 m~terial suitable for articulation with the spherical head 16
17 with a sufficient strength to provide adequate dislocation and
18 separation resistance, and in the case of the split bearing insert
19 ZOE (FIGS. 13-20) any suitable material sufficiently flexible
to provide the desired function of the collars 61 and 71. A
2~ typical material found to be suitable for these split bearing
22 inserts is ultra-high molecular weight polyethylene (U~MWPE) and
23 suitable certain ceramics may also be satisfactorily used for
2~ those split bearing embodiments not utilizing a flexible hinge
or bridge or a flexible annular collar.
26 Referring again to the split beariny insert 20E of FIGS. 13-
27 20, it will be understood by those skilled in the art that the
28 sub-assembly including the primary bearing insert 51 and either
29 collar 61 or 71 may be disassembled from the acetabular cup 30
other than by use of the release ring 46, FIGS. 5(a)-5(c), and
752
Il I
llthe radially disposed slots or grooves 39 of the acetabular cup
2 30, FIG. 3, e.g. the forward portions of the collars 61 and 71
3l adjacent the respective splits 64 and 74 may be provided with
4 inwardly extending holes or slots into which the ends of
5 conventional clamps typically found in the operating room may
6 be inserted to squeeze the collar together thereby reducing the
71 circumference of the collars at the radial split whereby either
8i the retaining ring 40 of collar 61 or the ridge 43 of collar 71
9 is disengaged from the groove 37 of the acetabular cup 30 and
lO the bearing insert 20E with the femoral head 16 seated therein may
11 be separated from the acetabular cup 30, by manual force provided
12 by an operating surgeon being more than sufficient.
13 It will be still further understood by those skilled in the
14 art that various modifications and variations of the present inven
tion may be ~ade without departing from the spirit and the scope
17 th eof.
21
24
26
28
29
