CA1185752A - Spherical kinematic joint - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An improved spherical kinematic joint which allows ease and convenience 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 low manual force during assembly and disassembly of the various bearing insert embodiments from the head and/or cavity or spherical seat in another joint element or member, such as for example in the prosthetic joint embodiments, an acetabular cup.
Further, such ease of assembly and disassembly can be accomplished while retaining great dislocation and separation resistance and can be accomplished in a manner which does not introduce significant axial play.

Description

~ 5~2 IMPROVED SPHERICAL KINEMATIC JOINT

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~;

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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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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.

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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.

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" , 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.

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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.

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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~

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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 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~.

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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) 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 :
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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.

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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 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.

Claims (61)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In an improved spherical kinematic joint for providing three degrees of rotational movement between two members and of the type including:

(i) a first component for engaging one of said two members and providing a first seat having a first opening;
(ii) a second component for engaging the other of said two members and including a neck and a head;
(iii) a bearing insert comprised of a plurality of physically distinct bearing segments and providing a second seat having a second opening;
upon assembly of said joint, said head is received within said second seat with said neck extending through said second opening, said bearing insert with said head received therein received within said first seat and said first component constraining 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 dislocation of said head from said bearing insert during said rotational movement;
wherein the improvement comprises:
means for maintaining said plurality of physically distinct bearing segments together in a sub-assembly to prevent separation therebetween prior to and during assembly with said first and second components thereby facilitating assembly of said spherical kinematic joint, at least portions of said sub-assembly expanding outwardly to permit said head to be received within 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.

2. An improved kinematic joint according to Claim 1 wherein said opening generally defines a first plane and wherein said bearing insert is split along at least one second plane oriented in a predetermined manner with respect to said first plane to provide said plurality of physically distinct bearing segments.

3. An improved spherical kinematic joint according to Claim 2 wherein said second plane is oriented substantially perpendicular to said first plane.

4. An improved spherical kinematic joint according to Claim 2 wherein said second plane is oriented substantially parallel to said first plane.

5. An improved spherical kinematic joint according to Claim 3 wherein said plurality of physically distinct bearing segments have forward and rearward portions, said forward portions defining said opening and upon said forward portions being forced into engagement with said head, said bearing segments pivot outwardly about said rearward portions to expand said sub-assembly to permit said head to pass through said opening and be inserted into and received within said second seat.

6. An improved spherical kinematic joint according to Claim 5 wherein each of said bearing segments is provided at its rearward portion with an outwardly extending tab and an inwardly extending recess, said tab of each bearing segment for being received within the recess of another bearing segment, said tabs and recesses cooperatively providing means by which said bearing segments pivot outwardly and also preventing shear-ing separation of said bearing segments by preventing relative motion therebetween in said second plane.

7. An improved spherical kinematic joint according to Claim 5 wherein said improved spherical kinematic joint further includes a flexible pin and wherein each of said bearing segments is provided at its rearward portion with an inwardly extending hole, upon said holes being axially aligned and said flexible pin being received within said holes, said pin and holes cooper-atively providing means by which said bearing segments pivot outwardly and also preventing shearing separation of said bear-ing segments by preventing relative motion therebetween in said second plane.

8. An improved spherical kinematic joint according to Claim 5 wherein said plurality of physically distinct bearing segments are provided with a hinge at said rearward portions connecting said bearing segments and wherein said bearing seg-ments pivot outwardly about said hinge to expand said bearing insert.

9. An improved spherical kinematic joint according to Claim 8 wherein said hinge is a flexible member formed integral-ly with said rearward portions of said bearing segments.

10. An improved spherical kinematic joint according to Claim 4 wherein said plurality of physically distinct bearing segments comprise a primary bearing segment and at least one generally annular bearing segment, said primary bearing segment and said generally annular bearing segment cooperatively pro-viding said second seat and said generally annular bearing seg-ment defining said opening, and upon said generally annular bearing segment being forced into engagement with said head, said generally annular bearing segment expanding outwardly to permit said head to pass through said opening and be inserted into and seated within said second seat.

11. An improved spherical kinematic joint according to Claim 10 wherein said means for maintaining said bearing seg-ments in a sub-assembly comprise interlocking projection and groove formed respectively on said bearing segments.

12. An improved spherical kinematic joint according to Claim 10 wherein said at least one generally annular bearing segment comprises at least one flexible unitary annular bearing segment.

13. An improved spherical kinematic joint according to Claim 1 further including means for preventing separation between said first component and said bearing insert upon assembly.

14. An improved spherical kinematic joint according to Claim 13 wherein said means for preventing separation between said first component and said bearing insert comprise engageable groove and projection formed respectively on said first compon-ent and bearing insert.

15. An improved spherical kinematic joint according to Claim 14 wherein said groove comprises a first groove provided on said first component and said projection comprises a retain-ing ring partially received in a second groove provided on said bearing insert.

16. An improved spherical kinematic joint according to Claim 14 wherein said projection is an integrally formed generally annular ridge.

17. An improved spherical kinematic joint according to Claim 14 wherein said first component is provided with means for permitting external access to said projection to permit said projection to be disengaged from said groove thereby per-mitting said bearing insert to be separated from said first component.

18. An improved spherical kinematic joint according to Claim 15 wherein said first component is provided with at least one slot for providing external access to said retaining ring to permit said retaining ring to be disengaged from said first groove thereby permitting said bearing insert to be separated from said first component.

19. An improved spherical kinematic joint according to claim 1 wherein said means for maintaining said bearing seg-ments together in a sub-assembly also prevents separation between said first component and said bearing insert.

20. An improved spherical kinematic joint according to Claim l or 5 wherein said head and said second seat are spherical.

21. An improved joint according to Claim 19 wherein said means for preventing separation comprises a retaining ring and wherein at least one of said physically distinct bearing seg-ments is provided with an external groove for at least partially receiving said retaining ring and wherein said first component is provided with an internal groove for being aligned with said external groove and for at least partially receiving said retaining ring.

22. An improved spherical joint according to Claim 21 wherein the transverse cross-sectional shape of said retaining ring has a predetermined height and wherein the depth of said internal groove is less than one-half of said predetermined height.

23. An improved spherical joint according to Claim 22 wherein said transverse cross-sectional shape of said retaining ring is circular and wherein said predetermined height is the diameter of said circular cross-sectional shape and wherein the depth of said internal groove is less than one-half of said diameter.

24. An improved spherical joint according to Claim 1 wherein said bearing segments are provided with scallops for reducing the amount of outward expansion of said sub-assembly required to permit said head to be received within said first seat.

25. An improved spherical joint according to Claim 5 wherein said plurality of physically distinct bearing segments comprise a pair thereof and wherein each of said bearing seg-ments is provided with an outer spherical surface, an outer cylindrical surface, an outer annular tapered surface, an inner spherical surface, an inner annular tapered surface, and a generally U-shaped longitudinally extending surface, said outer spherical surface merging with the inner end of the outer cylindrical surface and the outer end of the cylindrical surface terminating with the inner end of said outer annular tapered surface, said inner spherical surface terminating with the inner end of said inner annular tapered surface, the outer ends of the inner and outer annular tapered surfaces intersecting, and wherein the generally U-shaped longitudinally extending surfaces of each bearing segment are for being placed in generally opposed relationship with the generally U-shaped longitudinally extending surface of the other bearing segment.

26. An improved spherical joint according to Claim 25 wherein each of said bearing segments is provided with a pair of scallops contiguous with and merging into said inner annular tapered surface and said generally U-shaped longitudinally extending surface, said scallops facilitating said insertion of said head into said second seat by reducing the amount of out-ward expansion of said sub-assembly required to permit said head to pass through said opening and be inserted into and received within said second seat.

27. An improved spherical joint according to Claim 4 wherein said bearing segments comprise a generally spherically shaped primary bearing segment having a forward portion and a generally annularly shaped, radially split collar having a rear-ward portion, said forward and rearward portions provided respectively with complimentarily shaped mating means, and upon said collar being expanded radially outwardly and contracting said mating means for engaging each other to form said primary bearing segment and said collar into a sub-assembly.

28. An improved joint according to Claim 27 wherein said primary bearing segment is provided with a spherical outer sur-face and a cylindrical outer surface and a spherical inner sur-face, and wherein said collar is provided with a cylindrical outer surface, an annular tapered outer surface, an annular tapered inner surface and a spherical inner surface, said spherical surfaces cooperatively providing said second seat, and said complimentarily shaped mating means comprising an annular, radially outwardly extending projection and an annular, radially inwardly extending groove provided on said forward portion of said primary bearing segment and an annular, radially inwardly extending projection and an annular, radially outwardly extending groove provided on said rearward portion of said collar.

29. An improved spherical kinematic joint according to Claim 1 wherein said joint is a prosthetic hip joint and where-in said members are the pelvis and femur.

30. An improved spherical kinematic joint according to Claim 1 wherein said joint is a prosthetic shoulder joint and wherein said members are the humerus and scapula.

31. An improved spherical prosthetic joint for providing three degrees of rotational movement between two bones, compris-ing:
a first component for engaging one of said two bones and providing internally a first seat;
a second component for engaging the other of said two bones and including a neck and a spherical head;
a bearing insert comprising a generally semi-hemispherically shaped primary bearing segment having a forward portion and a generally annularly shaped, radially split collar having a rearward portion, said primary bearing segment and said collar cooperatively providing internally a second seat having an opening, said second seat for receiving said head and said forward and rearward portions provided respectively with complementarily shaped mating means, upon engagement of said complementarily shaped mating means said collar for being expanded radially outwardly to permit said head to be inserted through said opening and received within said second seat and upon said head being received within said second seat said collar contracting radially inwardly, and upon said collar being expanded radially outwardly and contracting radially inwardly said mating means forming said primary bearing segment and said collar into a sub-assembly to prevent separation therebetween during said radial expansion and contraction and prior to and during assembly with said first and second components;
said bearing insert and said first component provided with cooperative retaining means for retaining said bearing insert within said first seat upon insertion of said bearing insert into said first component; and upon said head being received within said second seat with said neck extending through said opening, said bearing insert for being received and retained within said first seat with said first component confining said head within said second seat whereby said rotational movement between said two bones is permitted, said bearing insert providing an overlap angle for preventing dislocation of said head from said bearing insert during said rotational movement.

32. An improved spherical prosthetic joint according to Claim 31 wherein said cooperative retaining means comprise a first groove provided internally on said first component and a second groove provided externally on said collar and a retaining ring for being partially received within said grooves, said retaining ring also for assisting said complementarily shaped mating means in forming said primary bearing segment and said collar into said sub-assembly, and wherein said first component is provided with at least one slot providing external access to said retaining ring whereby said retaining ring can be com-pressed into said second groove to permit said bearing insert to be removed from said first component and said joint disassem-bled.

33. An improved spherical prosthetic joint according to Claim 31 wherein said cooperative retaining means comprise a groove provided internally on said first component and a ridge provided externally on said collar, said ridge for being received within said groove, and wherein said first component is provided with at least one slot providing external access to said ridge to permit said collar to be contracted radially to permit said bearing insert to be removed from said first compon-ent and said joint disassembled.

34. An improved spherical prosthetic joint according to Claim 31 wherein said primary bearing segment is provided with outer and inner spherical surfaces and an outer cylindrical surface having an inner end, said outer spherical surface termin-ating at the outer end of said outer cylindrical surface, where-in said collar has a forward portion provided with outer and inner annular tapered surfaces each having outer and inner ends and wherein said collar is provided with an outer cylindrical surface having an outer end and an inner spherical surface hav-ing an outer end terminating with the inner end of said inner annular tapered surface, said outer end of said outer cylindrical surface terminating at the inner end of said outer annular tapered surface and said outer and inner annular tapered sur-faces merging at their outer ends, said inner spherical surfaces cooperatively providing said second seat, and wherein said complementarily shaped mating means comprise an annular radially outwardly extending projection and an annular radially inwardly extending groove provided on the forward portion of said primary bearing segment and an annular radially inwardly extending projection and an annular radially outwardly extending groove provided on said rearward portion of said collar.

35. An improved joint according to Claim 31 or 34 wherein said first component is generally semi-hemispherically shaped and is provided with outer and inner spherical surfaces, outer and inner annular tapered surfaces each having outer and inner ends, and an inner cylindrical surface having outer and inner ends, said outer spherical surface terminating at the inner end of said outer annular tapered surface, said outer and inner annular tapered surfaces merging at their outer ends, said inner end of said cylindrical surface merging with the outer end of said inner spherical surface and the outer end of said cylindrical surface merging with the inner end of said inner annular tapered surface, said inner spherical and cylindrical surfaces providing said first seat.

36. An improved spherical prosthetic joint for providing three degrees of rotational movement between two bones, compris-ing:

(a) a first component for engaging one of said two bones and providing internally a first seat;
(b) a second component for engaging the other of said two bones and including a neck and a spherical head;
(c) a bearing insert comprising:
(i) a pair of opposed clam shell-shaped bearing members separated by a plane of separation and providing inter-nally a second seat having an opening, said second seat for receiving said head, (ii) resilient means for maintaining said bearing members together in a sub-assembly to prevent separation there-between prior to and during assembly with said first and second components and for permitting said sub-assembly to expand out-wardly to permit said head to be inserted through said opening and received within said second seat, upon said head being received within said second seat said resilient means for con-tracting said sub-assembly with said neck extending through said opening, and (iii) aligning means for preventing shearing separation between said bearing members in said plane of separation prior to and during assembly with said first and second components;
and (d) upon said head being received within said second seat with said neck extending through said opening, said bearing insert for being received and retained within said first seat with said first component confining said head within said second seat whereby said rotational movement between said two bones is provided, said bearing insert providing an overlap angle for preventing dislocation of said head from said bearing insert during said rotational movement.

37. An improved spherical prosthetic joint according to Claim 36 wherein an external groove is formed in each of said clam shell-shaped bearing members, and wherein said resilient means comprise a retaining ring for being at least partially received in said grooves.

38. An improved spherical prosthetic joint according to Claim 36 wherein said aligning means comprises an outwardly extending tab and an inwardly extending recess provided at the rearward portion of each of said clam shell-shaped bearing members, each tab of each bearing member for being received within the recess formed in the other of said bearing members.

39. An improved spherical prosthetic joint according to Claim 36 wherein said aligning means comprises a flexible pin and wherein each of said bearing members is provided at its rearward portion with an inwardly extending hole, said pin for being received within said holes.

40. An improved spherical prosthetic joint according to Claim 36 wherein said aligning means comprises a flexible member formed integrally with said rearward portions of said bearing members.

41. An improved spherical prosthetic joint for providing three degrees of rotational movement between two bones, compris-ing:
(a) a first component for engaging one of two said bones and providing internally a first seat;
(b) a second component for engaging the other of said two bones and including a neck and a spherical head;
(c) a bearing insert comprising:
(i) a pair of opposed clam shell-shaped bearing members separated by a plane of separation and providing inter-nally a second seat having an opening, said second seat for receiving said head and said clam shell-shaped bearing members having rearward portions, (ii) a hinge provided at said rearward portions about which hinge said clam shell-shaped bearing members pivot outwardly and expand to permit said head to be received into said second seat;
(d) said bearing insert and said first component provided with cooperative retaining means for retaining said bearing insert within said first seat upon insertion of said bearing insert into said first component; and (e) upon said head being received within said second seat with said neck extending through said opening, said bearing insert for being received and retained within said first seat with said first component constraining said bearing members against pivoting outwardly thereby confining said head within said second seat whereby said rotational movement between said two bones is permitted, said bearing insert providing an over-lap angle for preventing dislocation of said head from said bearing insert during said rotational movement.

42. An improved spherical prosthetic joint according to Claim 41 wherein said hinge comprises an outwardly extending tab and an inwardly extending recess provided at the rearward portion of each of said clam shell-shaped bearing members, each tab of each bearing member for being received within the recess formed in the other of said bearing members.

43. An improved spherical prosthetic joint according to Claim 41 wherein said hinge comprises a flexible pin and where-in each of said bearing members is provided at its rearward portion with an inwardly extending hole, said pin for being received within said holes.

44. An improved spherical prosthetic joint according to Claim 41 wherein said hinge comprises a flexible member formed integrally with said rearward portions of said bearing members.

45. An improved spherical prosthetic joint according to Claim 41, 42 or 43 wherein said hinge also prevents shearing separation of said bearing members along said plane of separa-tion.

46. An improved spherical prosthetic joint according to Claim 41 wherein said cooperative retaining means comprise an internal groove formed in said first component and an at least partial circumferential integral ridge formed externally on each of said clam shell-shaped bearing members, said ridges for being received within said groove upon said bearing insert being received within said first seat.

47. An improved spherical prosthetic joint according to Claim 41 wherein said cooperative retaining means comprise an internal groove formed in said first component, an external groove formed in each of said clam shell-shaped bearing members, and a retaining ring for being partially received in said grooves upon said bearing insert being received within said first seat.

48. An improved spherical prosthetic joint according to Claim 42 further including resilient means for maintaining said clam shell-shaped bearing members together in a sub-assembly to prevent separation therebetween prior to and during assembly with said first and second components and for permitting said sub-assembly to pivot about said hinge and expand outwardly to permit said head to be inserted into said second seat.

49. An improved spherical prosthetic joint according to Claim 48 wherein an external groove is formed in each of said clam shell-shaped bearing members, and wherein said resilient means comprises a retaining ring for being at least partially received in said grooves.

50. An improved spherical prosthetic joint according to Claim 36 or 41 wherein each of said pair of clam shell-shaped bearing members is provided with an outer spherical surface, an outer cylindrical surface, an outer annular tapered surface, an inner spherical surface, an inner annular tapered surface, and a generally U-shaped longitudinally extending surface, said outer spherical surface merging with the inner end of the outer cylindrical surface and the outer end of the cylindrical surface terminating with the inner end of said outer annular tapered surface, said inner spherical surface terminating with the inner end of said inner annular tapered surface, the outer ends of the inner and outer annular tapered surfaces intersecting, and wherein said generally U-shaped longitudinally extending sur-faces are for being placed in generally opposed relationship defining said plane of separation.

51. An improved spherical prosthetic joint according to Claim 50 wherein each of said clam shell-shaped bearing members is provided with a pair of scallops contiguous with and merging into said inner annular tapered surface and said generally U-shaped longitudinally extending surface, said scallops facili-tating said insertion of said head into said second seat by reducing the amount of outward expansion of said sub-assembly required to permit said head to pass through said opening and be inserted into and received within said second seat.

52. An improved joint according to Claim 36 or 41 wherein said first component is generally semi-hemispherically shaped and is provided with outer and inner spherical surfaces, outer and inner annular tapered surfaces each having outer and inner ends, and an inner cylindrical surface having outer and inner ends, said outer spherical surface terminating at the inner end of said outer annular tapered surface, said outer and inner annular tapered surfaces merging at their outer ends, said inner end of said cylindrical surface merging with the outer end of said inner spherical surface and the outer end of said cylin-drical surface merging with the inner end of said inner annular tapered surface, said inner spherical and cylindrical surfaces providing said first seat.

53. An improved prosthetic joint according to Claim 37, 47 or 49 wherein said first component is provided with at least one slot providing external access to said retaining ring whereby said retaining ring can be compressed into said external grooves to permit said bearing insert to be removed from said first component and said joint disassembled.

54. An improved spherical prosthetic joint according to Claim 31, 36 or 41 wherein said joint is a prosthetic hip joint and wherein said bones are the pelvis and femur.

55. An improved spherical prosthetic joint according to Claim 31, 36 or 41 wherein said joint is a prosthetic shoulder joint and wherein said bones are the humerus and scapula.

56. An improved spherical kinematic joint according to Claim 13 further including means for separating said first com-ponent and said bearing insert after assembly.

57. An improved spherical kinematic joint according to Claim 13 wherein said means for preventing separation between said first component and said bearing insert comprise engageable projection and groove formed respectively on said first compon-ent and said bearing insert.

58. An improved prosthetic joint according to Claim 21 wherein at least one of said grooves is provided with a tapered face for facilitating prevention of retraction of said ring thereby inhibiting unwanted separation between said first com-ponent and said bearing insert.

59. An improved joint according to Claim 58 wherein said at least one of said grooves is said external groove and wherein said tapered face is the posterior face of said external groove.

60. An improved spherical joint according to Claim 25 wherein said pair of bearing segments are provided at said rearward portions with an integrally formed flexible member about which said bearing members pivot outwardly.

61. An improved spherical kinematic joint according to Claim 1 wherein said means comprise a retaining ring, wherein said first component is provided with an inner annular taper at said first opening, wherein said bearing segments are pro-vided with external grooves adjacent said second opening and said grooves for receiving said retaining ring, upon said assembly said bearing insert with said head received therein being inserted through said first opening and into said first seat and said inner annular taper engaging said retaining ring and compressing said ring radially inwardly completely within said external grooves permitting said bearing insert with said head received therein to pass through said first opening and be seated within said first seat.