DE8304914U1 - Spherical kinematic joint - Google Patents

Description

Spherical kinematic joint

Description

The invention relates generally to an improved globular kinematic joint which, as is known to those skilled in the art, kinematically provides three degrees of freedom of rotation; spherical kinematic joints are commonly used in machine applications such as heavy machinery and business machinery and are also commonly used in
various automotive applications, such as tie rod connections. Such joints typically comprise a member providing a ball or spherical head, a center bearing insert providing a cavity
or support for the spherical headpiece

and a third part which provides another cavity or support for receiving the bearing insert with the ball or spherical head therein. Many applications require that such a joint be able to resist displacement when at its extreme limits of rotational movement and that it resist separation under a load which tends to pull the connected joint parts apart. The structure of such joints is well known to those skilled in the art and it is also well known that such joints can be composed of many different structural elements.

As is also known, it is often desirable for such joints to eliminate or minimize axial play or slop between the connected joint members. Joints illustrating this can be seen in U.S. 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; U.S. Patent No. 3,220,755 to Gottschald et al, issued November 30, 1965; and U.S. Patent No. 3,401,965 to W.C. Wehner, issued September 17, 1968. All of the joints shown in these patents have provisions to minimize or eliminate axial play. These patents illustrate two different types of spherical kinematic joint structure or design. In the Flumerfelt and Ingersoll patents, the bearing inserts include separate bearing insert segments that are fitted over the ball or spherical head and then inserted into a housing where they are retained by various means. The Wehner patent shows a different type of joint structure or design that includes a load-bearing bearing insert and a restraining collar to prevent displacement and

4 · fr » * ·

Separation of the connected joint parts by tension. The patent by Gottschald et al describes a unified

tary construction, wherein the bearing insert has many cuts on the front side near the opening, which has a plurality of fingers or curved portions that expand outward after being inserted into

forced into engagement with the ball or spherical head; after this engagement, the ! bearing insert and the ball are inserted into the cavity or seat of the

j &iacgr;&ogr; third part, whereby the third part prevents outward expansion of the finger, thereby retaining the bearing insert on the ball. An additional or second device is then provided to retain the bearing insert in the cavity of the third part, thereby creating a joint which resists separation and displacement due to tension.

More recently, spherical kinematic joints have found application in human joint prostheses. In prosthetic applications, the ease of assembly and disassembly of the joint elements or parts is of great importance. The use of a central bearing insert made of a plurality of bearing segments which are unconnected when not assembled in the joint is undesirable in prosthetic applications because the handling and posture of the bearing segments relative to the headpiece during assembly of the headpiece and the bearing segments with the third part may be inconvenient, particularly for an operating surgeon working within the operative space. Although a

Bearing insert with flexible fingers or curved sections reduces the amount of installation force required where the \ fingers are not present, such

j flexible fingers but for the operating surgeon quite

35 can be disadvantageous because to create the required or desired displacement and separation resistance and

the force the fingers must be quite rigid, which

on the other hand, requires that a considerable amount of reconstruction force must be applied by the operating surgeon.

As is known to those skilled in the art, in prosthetic joint applications, low assembly force and ease of assembly are of great importance due to the need to minimize assembly time and the difficulties under which the surgeon must work. Often the field of vision is obscured and joint elements or parts are slippery due to a coating of blood and fat, which can lead to dropping of the joint elements, causing a further problem since such joints must be sterile and after dropping they must be re-sterilized or replaced while the surgical opening remains open. Furthermore, occasionally due to a surgical emergency or other difficulties during surgery, it is desirable to be able to disassemble the joint parts, preferably in a manner which avoids the same assembly difficulties previously mentioned, i.e. excessive disassembly forces and numerous unconnected bearing insert parts which are difficult to handle. Thus, joints that are satisfactory for machinery applications, where fixations and other devices are conveniently used to assemble joint parts, require improvement for their effective use in prosthetic joints.

Patents showing prosthetic joints include Richard P. Giliberty's US Patent 3,813,699 issued June 4, 1974, Robert G. Averill's US Patent 3,863,273 issued February 4, 1975, D'Erricho's US Patent 4,044,403 issued August 1977, and Alex Khovaylo's US Patent 4,241,463 issued December 30, 19G0. The prosthetic joint disclosed in the Giliberty patent provides a prosthetic joint that is resistant to displacement and separation.

and partially avoids the assembly problems previously indicated by grinding a unitary structure including the bearing insert and acetabular shell, thus minimizing handling of the various joint parts during the assembly and disassembly process. However, the unitary structure of the bearing insert and acetabular shell does not allow for easy assembly and disassembly under high separation resistance, since the opening into the spherical cavity of the bearing insert, which receives the spherical femoral head, is not capable of significant outward expansion or bending when constrained to engage the spherical head and therefore the Giliberty prosthetic joint requires either extremely high assembly and disassembly forces and/or relatively low resistance to displacement and separation forces. The prosthetic joint disclosed in the Averill patent partially overcomes the problem of excessively high set-up or break-down forces by using, as in the Gottschald et al patent, an intermediate bearing insert provided with a plurality of arcuate sections at the entrance to the spherical seat for receiving the ball, which arcuate sections, after being forced into engagement with the femoral head, still require a generally undesirably high manual force to expand outward to allow the spherical head to enter the spherical seat of the intermediate bearing insert. The Averill prosthetic joint also uses a projection provided on the bearing insert to prevent separation of the bearing insert from the acetabular shell; however, such a structure introduces undesirable axial play into the prosthetic joint. Similarly, the prosthetic joint disclosed in the D'Erricho patent is also a partial solution to the assembly problem noted above, in that the assembly forces required to assemble the joint parts

are lowered below those required to assemble the articular parts of the Giliberty prosthesis with a predetermined resistance to displacement and separation; this is achieved by the use of flexible lips provided on the bearing insert and acting against the spherical head or ball of the first part and/or the cavity of the third part or the acetabular cup. However, such a joint design is not readily disassemblable without damaging the bearing insert and does not provide the desired combination of low manual assembly force and high separation resistance required by an operating surgeon during surgery. The Khovaylo prosthetic joint provides a structure which allows for low assembly force of the bearing insert to the head, but uses a solution similar to that disclosed in the D'Erricho patent for assembling the third part or acetabular shell to the bearing insert. Furthermore, the inner retaining ring of the Khovaylo prosthetic joint operates in a manner which creates end play between the spherical BaI ¹ and the bearing insert. Furthermore, the Khovaylo prosthetic joint does not provide for convenient assembly or disassembly of the bearing insert from the third part or acetabular shell during surgery. As is known to those skilled in the art of prosthetic joints, physically separate acetabular shells and bearing inserts are not desirable when used in prosthetic joints. desirable to minimize the inventory of prostheses of different sizes and to minimize the sterilization costs associated with such joints.

As is also known to those skilled in the art, the bearing inserts in the aforementioned patents provide an overlap that, after receiving the spherical head within the bearing insert and receiving the bearing insert with the spherical head supported therein in the insert,

housing prevents displacement of the spherical head from the bearing insert during rotation between the spherical head and the insert housing shell.

The improved spherical kinematic joint of the present invention overcomes the above-mentioned problems of the known joints by providing various bearing ^insert embodiments which allow for easy and convenient assembly and disassembly, particularly assembly, by providing a plurality of substantially physically separate bearing inserts in a subassembly such that the bearing inserts are effectively in a unitary structure for assembly and disassembly purposes, but wherein the bearing segments expand easily under little manual force during assembly and disassembly of the various bearing insert embodiments from the headpiece and/or the cavity or spherical seat in the third part, such as in the prosthetic joint embodiments, an acetabular cup. Furthermore, such easy assembly and disassembly can be accomplished while maintaining a high resistance to displacement and separation and in some embodiments is accomplished in a manner which does not introduce significant axial play.

Figure 1 is a diagrammatic representation showing in cross-section the improved spherical kinematic joint of the invention in one embodiment as a prosthetic hip joint implanted in a pelvis and femur;

Figure 2 is a cross-sectional view of the first embodiment of a split bearing insert according to the invention;

Figure 2(a) is a partial front view of the split bearing insert shown in Figure 2;

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Figure 3 is a cross-sectional view of an acetabular shell according to the invention, which is particularly suitable when the spherical kinematic joint according to the invention is in the form of a prosthetic hip joint;

Figures 4 (a) and (b) are cross-sectional views of alternative embodiments of the retaining rings;

Figures 5 (a) to (c) are side views, top views and enlarged views of a release ring suitable for detaching the elements of the spherical kinematic joint according to the invention;

Figures 6 (a) and (b) are sequential cross-sectional views illustrating the structure of an embodiment of the invention;

Figures 7(a) through (c) are views illustrating the use of prongs that may be provided on various notched inserts according to the present invention to reduce the amount of radial expansion required for assembly of the bearing inserts on the femoral head of a femoral rod on the improved spherical kinematic joint of the present invention configured as a prosthetic joint;

Figures 8 (a) and (b) are diagrammatic representations in cross-section showing the advantage of creating a greater engagement between a retaining ring and the outer grooves provided on a bearing insert than between the retaining ring and the inner circular groove provided on the acetabular shell when the invention is used as a pro-

is designed as a thetic hip joint and uses a retaining ring; and

Figures 9(a) to (c), Figure 10, Figure 11, Figures 12(a) to (d) and Figures 13 to 20 are alternative embodiments of various split bearing inserts of the spherical joint according to the invention, particularly when implemented as a prosthetic hip joint.
10

In Figure 1, a spherical kinematic joint according to the invention is shown in one embodiment as a prosthetic hip joint 10 in an implanted form. The prosthetic hip joint 10 comprises the following components: a femoral component 12, sometimes referred to by those skilled in the art as an intermedullary bar or femoral insert, a split bearing insert 20, an acetabular cup 30, and a retaining ring 40.

2C The femoral component 12 includes a shaft 14 which fixes the component in the medullary cavity of the proximal femur, preferably but not exclusively by means of a casting agent 15, a ball-shaped or spherical femoral head 16, and an attachment region 18 which transfers the load from the spherical femoral head 16 to the shaft 14.

The split bearing insert 20, as better seen in Figures 2 and 2(a), comprises a plurality of opposing identical split bearing segments or clamshell-like shell-shaped members 21-21, a pair of which are shown, in this embodiment each split bearing segment 21 being physically separate from the other. Each segment 21 is provided with an outer spherical surface 22, an outer cylindrical surface 23 and an outer annular tapered

surface 24; in addition, each segment 21 is provided with an inner spherical surface 25 and a beveled edge or an inner annular tapered surface 26. Further, in the illustrated embodiment, each segment 21 is provided with a generally U-shaped longitudinally extending surface 29 which is of the same shape as the obliquely hatched area of Figure 2, but without the gap. Each outer spherical surface 22 merges with the inner end of an outer cylindrical surface 23 and the outer end of each cylindrical surface 23 terminates with the inner end of an outer annular tapered surface 24; similarly, each inner circular tapered surface

26 and the outer ends of the circular tapered surfaces 24-26 or merge as shown, preferably with a small radius r. When placed in an opposed arrangement as shown in Figure 2, the inner spherical surfaces 25-25 of the clam-like shell-shaped members 21-21 together create a spherical cavity or seat 27 for receiving the spherical femoral head 16 (Figure 1) of the femoral component 12 (Figure 1) and thus it is understood that the spherical cavity or seat 27 preferably closely conforms to the shape of the spherical femoral head 16, the diameter of the femoral head 16 being slightly larger than the opening to the seat.

27 created by the beveled edge 26. A pair of serrations or beveled surfaces 28-28 may be provided on each member 21 adjacent and merging with the longitudinally extending surfaces 29, the beveled surfaces 28-28 facilitating insertion of the spherical femoral head 16 of the femoral component 12 into the spherical cavity 27 by reducing the amount of stretching of the split bearing insert 20 required for insertion. Finally, an outer circular circumferential groove 19 is provided in each outer cylindrical

Surface 23 is provided for receiving or at least partially receiving the flexible retaining ring 40 shown in Figure 4(a). The depth and width of the groove 19 are sufficient to allow the retention ring 40 to be fully received in the groove after the ring is compressed radially inward. It will be understood that prior to assembly of the components of the spherical prosthetic hip joint for implantation, the first function of the retaining ring 40 after being received or at least partially received in the externally circular groove 19 is to hold the scalloped shell-like members 21-21 together in a subassembly and in a generally opposed relationship as shown in Figure 2, with the generally U-shaped longitudinally extending surfaces 29 engaging in a plane of contact or separation extending through the centerline C/L.

The acetabular shell 30, as best seen in Figure 3, is provided with a smooth outer spherical surface 31 terminating at the inner end of an outer circular tapered surface 32, the shell being further provided with an inner spherical surface 33 merging at its outer end with the inner end of a cylindrical inner surface 34 merging at its outer end with the inner end of a bevelled edge or inner circular tapered surface 35 , the tapered surfaces 32 to 35 intersecting or merging at their outer ends as shown. An inner circular circumferential groove 37 is provided near the outer end of the inner cylindrical surface for receiving the retaining ring as shown in Figure 4(a). The outer spherical surface 31 is preferably closely adapted to the acetabular cartilage or the natural acetabulum (Figure 1), whereby the acetabular articular cartilage is not always present depending on the degeneration.

tion of the joint, and the inner spherical surface 33 and the inner cylindrical surface 34 together provide a cavity or support 38 for receiving the split bearing insert 20. Preferably, the inner cylindrical surface 33 and the inner cylindrical surface 34 of the acetabular shell 30 closely conform to the outer spherical surfaces 22-22 and the outer cylindrical surfaces 23-23 of the split bearing insert 20. As further shown in Figures 3 and 3(a), the acetabular shell 30 is provided with a plurality of radially arranged slots or grooves 39 extending axially into the inner circular tapered flat 35 and into the outer portion of the inner cylindrical surface 34, wherein upon receipt of the retaining ring 40 into the circular circumferential grooves 19 and 37 and upon assembly of the spherical femoral head 16, the split bearing insert 20 and the acetabular shell 30 as shown in Figure 1, the radially arranged grooves 39 to provide external access to the retention ring 40 by means of the radially arranged prongs of the release tool 46, as shown in Figures 5(a) and 5(c), for disassembly of the split bearing insert 20 and the spherical head 16 of the femoral component from the acetabular shell 30, as will be explained in more detail below.

The spherical prosthetic hip joint 10, which is an embodiment of the present invention, is implanted as follows: The femoral component 12 is implanted in the femur as previously described and shown in Figure 1, with the front portion or beveled edge 26 of the split bearing insert 20 being brought into engagement with the spherical femoral head 16 with the retaining ring 40 bearing or at least partially bearing in the outer circular grooves 19 and holding the slotted bearing segments 21-21 together in a subassembly as previously described.

23 I

is forced (the manual force exerted by the operating surgeon is more than sufficient) larger in diameter than the opening to the support 27, whereupon the split bearing segments 21-21 expand radially by a general outward pivoting (ie a generally radially outward pivoting) about their rear portions (such expansion being assisted by the prongs 28, if provided) to permit the femoral head to be received in the split bearing insert 20 and to permit its seating within the spherical cavity or support 27, whereupon the acetabular cup 30 is then slid over the split bearing insert 20 to engage the beveled edge or inner circular tapered surface 35 as shown in Figure 6 (a) with the retaining ring 40 and press it radially inwardly entirely within the outer circular grooves 19 provided on the segments 21-21, thereby allowing the acetabular cup to pass over the retaining ring 40 until, as shown in Figure 6(b), the inner spherical surface 33 of the acetabular cup abuts or engages the outer spherical surfaces 22-22 of the low friction split bearing insert 20. At this point, the outer circular grooves 19-19 provided in the segments 21-21 are axially aligned with the inner circular groove 37 provided in the acetabular shell 30, whereupon the retaining ring 40 expands radially outwardly to be received partially within the inner circular groove 37 and partially within the outer circular grooves 19-19. The retaining ring 40 now performs its second function; it holds the acetabular shell on and over the split bearing insert 20 with the spherical femoral head 16 received therein, thereby preventing separation (e.g. axial displacement) between the bearing insert (with the femoral head 16 supported therein) and the acetabular shell 30.

cle head) and the acetabular shell during joint rotation. All three components of the spherical prosthetic hip joint 10 are now united and the acetabular shell 30 is inserted into the acetabulum as shown in Figure 6 (b).

The manner in which such serrations or beveled surfaces 28-28 facilitate the insertion of the spherical femoral head 16 into the spherical cavity 27 by reducing the amount of radially outward extension required of the split bearing insert or segments 21-21 is shown in greater detail in the diagram in Figures 7(a) to (c). As shown in Figure 7(b), if the slotted bearing segments 21' are not equipped with the prongs or beveled surfaces 28-28, the segment must be expanded radially outwardly by a distance L1 to allow the spherical head 16 to be introduced into the spherical cavity or seat 27, while if the slotted bearing segment 21 is equipped with the prongs or beveled surfaces 28-28, as shown in Figure 7(c), the segment 21 must be expanded radially outwardly by a lesser distance L2 to allow such introduction of the spherical femoral head, it being understood, according to the illustration, that the distance L2 is less than the distance L1 by substantially the height S of the prongs 28-28.

In the embodiment of the present invention shown in Figure 6(b), the overlap angle γ is approximately 30° and the intended rotational movement or pivoting movement is approximately 60°.

For removal, the release tool 46, Figures 5 (a) and (b), can then be inserted over the attachment area 18 of the femoral component 12, Figure 6 (b), with entry through the gap or opening 48 provided in the

release tool, Figure 5(b), and the radially arranged sparrows 44 are inserted into the radial grooves 39 (Figure 3) provided in the acetabular shell 30 to cause the bevelled edges 47 of the release tool, Figure 5(c), to project over the

retaining ring 40 and to press the ring fully into the outer circular grooves 19-19 provided on the slotted bearing segment ii-21, thereby permitting the removal of the acetabular cup 30 from above the split bearing insert 20, whereby the acetabular cup is removed from the split bearing insert 20 and is received by the spherical femoral head 16rder within the spherical cavity 27 or insert 20. To further disassemble the split bearing insert 20 from the spherical femoral head 16, a force, which can be easily applied manually by the operating surgeon, is applied to the split bearing insert 20 to pull it away from the spherical femoral head, whereupon the split bearing insert segments 21-21 migrate radially outward and the split bearing insert 20 is easily pulled off, facilitated by the prongs 28, if provided, from above the spherical femoral head 16, leaving the femoral component 12 implanted in the femur, if any. It is noted that by providing the release tool 46 (Figures 5(a) and 5(b)) with the gap or opening 48, a one-piece release tool is provided which can be used to pull the acetabular shell from the split bearing insert 20 and the spherical femoral head 16 received within the cavity or seat 27, without requiring removal of the femoral component 12 from the femur (Figure 1).

It will be further understood by those skilled in the art that the wear characteristics of the split bearing insert can be improved by sizing the split bearing segments 21-21 to the dimension of the spherical femoral head 16 such that after assembly of the bearing insert 20 to the spherical femoral head 16, a gap or space is provided between the generally U-shaped longitudinally extending surfaces 29 (Figure 2) to allow a lubricant, which in the case of a spherical prosthetic hip joint is synovial fluid, to reach the bearing surfaces of the spherical joint and assist in the removal of wear debris from the bearing surfaces by providing suitable passages to the surrounding areas.

It will be further understood that although in the preferred embodiments of the present invention the retaining ring 40 has a circular oblique cross-section, particularly because of the greater accessibility and lower cost of such a round cross-section as shown in Figure 4(b), other retaining ring cross-sections such as square, rectangular, etc. may be used and of course the shapes of the outer circular grooves 19-19 on the segments 21-21 and the inner circular groove 37 provided on the acetabular shell 30 are of suitable cross-sectional shape. It is noted that the retaining ring and grooves need not be of complementary shape; it has been found that a ring having a round cross-section works adequately in a groove having a substantially rectangular cross-sectional shape with side walls that are substantially vertical and a bottom that is substantially parallel to the cylindrical surface on the outside. It is further understood and illustrated in Figure 4 that the retaining ring 40' (Figure 4 (b)) is provided with an oblique transverse

section with a width "w" and a height "h", while due to the round shape of the oblique cross-section of the retaining ring 40, Figure 4 (a), both the width and the height of the retaining ring 40 in the oblique cross-section are equal to the diameter "d".

It has been found desirable to provide a greater engagement "e" than indicated in Figure 8(a) between the retaining ring 40 and the outer circular grooves 19-19 in the bearing insert 20 than between the retaining ring 40 and the inner circular groove 37 in the acetabular shell 30 to make protrusion of the retaining ring 40 from the groove 19 less likely during assembly. This protrusion can be understood by reference to Figures 8(a) and 8(b). The less protrusion from the outer circular groove 19 of the bearing insert 20 allows the use of a smaller beveled edge or inner circular tapered surface 35 at the entrance to the spherical cavity or seat 38 of the acetabular shell. This smaller beveled edge or inner circular tapered surface 35 creates less disruption in the front surface or entry portion of the acetabular shell 30, thereby producing a better appearance and allowing the use of a thinner shell wall "t", Figure 3, thereby allowing an increased range of acetabular shell sizes to fit over a given bearing insert, e.g., the bearing insert 20 of Figure 2.

Referring to Figure 8, it can be seen that the maximum protrusion P occurs when one side of the

Max

ring is pushed or falls completely into the outer groove 19, causing the other side of the ring to protrude to the maximum extent. It is understood that the minimum maximum protrusion "P" is obtained for a given engagement "e ⁿ between the ring and the groove.

when the depth of the inner groove 37 is equal to the cross-sectional diameter "d" of the retaining ring 40. In this case, the maximum protrusion is:

P _max = P ∗ C (1)

where P is the projection of the retaining ring 40 when its axis coincides with the axis of the bearing insert and C is the distance between the ring and the bottom of the outer groove 19 with which the retaining ring is thus aligned. Now

d = P + e

or P = d - e (2)

and C = d - e (3)

If the ring is now mounted so that one side lies entirely within the groove 19, as shown in Figure 8 (b), then the projection P "" is equal to

^? max ^{= 2(d} - ^{e) (4)}

Thus, it can be seen that a growing "e" increases the value

for P “ reduced,
Max

In circular cross sections, in order to provide a greater engagement between the outer bearing insert groove 19 and the retaining ring 40 than between the acetabular inner groove 37 and the retaining ring 40, it is necessary to make the posterior surface 37 of the insert groove 19 tapered to avoid retraction of the ring. To avoid such retraction, the angle shown in Figure can be calculated from

θ <cos" ¹ (2e/d - 1) (5)

where "e" is the engagement between the retaining ring 40 and the insert groove 11 and "d" is a cross-sectional diameter of the retaining ring 40. The outer diameter D1 of the retaining ring 40 is designed to be substantially equal to the diameter D2 of the inner groove 37 of the acetabular shell as shown in Figures 4 and 3, respectively.

Alternative embodiments of the improved spherical kinematic joint of the invention, also embodied as improved spherical prosthetic hip joints, are provided and shown in Figures 9(a)-(c), 10, 11 and 12(a)-(d). These embodiments include various alternative bearing inserts having various hinge or pin type connections between the split bearing segments at their rear portions which reduce or eliminate the possibility of the segments becoming disengaged from each other and from the retaining ring during assembly and disassembly of the components of the improved spherical joint. It is further understood that these alternative embodiments include the femoral component 12, the acetabular shell 30 and, in some embodiments, the retaining ring 40 of Figure 1; the alternative bearing inserts are indicated by alpha numerical designations, e.g.

2OA, 2OB, etc., to distinguish them from the bearing insert of the first embodiment, and where the structures and surfaces of these alternative bearing insert embodiments are identical to the first embodiment, they have been given the corresponding numerical designations, but where they are different, they have been given alpha numerical designations corresponding to the alpha designations of the bearing insert of the alternative embodiment.

The first alternative embodiment, Figure 9 (a), (b) and (c) includes the split bearing insert 20A having a plurality, a pair is shown, of opposed

identical split bearing segments 21α-Γ1α, each provided at its rear portion with an outwardly extending projection 81 and an inwardly extending recess 83. When assembled, as generally shown in Figures 9(b) and (c), the projections 81 are received in the recesses 83 to together provide a pin or hinge type connection about which the segments 21A-21A pivot outwardly to permit insertion of the spherical femoral head 16 into the spherical cavity or seat 27A provided by the inner spherical surfaces 25A-25A of the segments 21A-21A.

A second alternative embodiment is shown in Figure 10 and includes the alternative split bearing insert 20B which is comprised of a plurality of opposed identical split bearing segments 21B- 21B, each of which is provided at its rear end with an inwardly extending hole 61 as shown for receiving one end of a flexible pin 63; further, this further alternative embodiment includes the spherical joint components described above. Upon insertion of the flexible pin 63 into the opposed and axially aligned holes 61-61, the split bearing segments 21B-21B pivot outwardly about the hinge-type connection provided together by the holes 61-61 and the flexible pin 63 to expand radially outwardly toward the split bearing insert 2OB to permit receipt of the spherical femoral head 16 into the inner seat or cavity 27B provided inside the split bearing insert 2OB by the inner spherical surfaces 25B-25B.

With reference to a third alternative embodiment shown in Figure 11 it will be understood.

that the split bearing insert 2OC is substantially identical to the split bearing insert 20 shown in Figure 2, but wherein the split bearing segments 21-21 of Figure 2 are physically separated from one another, while the split segments 21C-21C of the embodiment of Figure 11 are connected or pivotally connected to one another at their rear portions by a relatively thin integral member C. The alternative embodiment including the low friction split bearing insert 2OC of Figure 11 is assembled and disassembled in a substantially identical manner to the embodiment including the split bearing insert 20 of Figure 2, except that after radially outwardly expanding the split bearing insert 2OC n"h Figure 11 to allow insertion of the spherical femoral head 16 into the spherical cavity or seat 27, the split Fold or swivel bearing segments 21C-21C radially outwards around the thin, flexible integral part C.

An alternative embodiment of the low friction bearing insert 20C as shown in Figure 11 is shown in Figures 12(a) through (d); this alternative split bearing insert is identified by the numerical designation 2OD. In this embodiment, the hinge or flexible member D is made sufficiently thick that plastic deformation occurs when the split bearing segments 21D-21D are pivoted radially outward as shown in Figure 12(a) to permit insertion of the spherical femoral head 16 of the femoral component 12 into the split bearing insert 2OD. Furthermore, the inner spherical cavity or seat 27D provided inside the split bearing insert 2OD is designed to be sufficiently large so that it is slightly larger than the spherical head 16 of the spherical component 12, thereby providing some clearance (indicated by the numerical designation 46)

given) between the spherical cavity 27B and the spherical femoral head 16 when the acetabular cup 30 is partially assembled on the plastic bearing insert 2OD as shown in Figure 12(b). A partially outer circular protrusion 43 is integrally formed on the outer cylindrical surface 23D of each split bearing segment 21D-21D which matches the inner circular groove 37 provided on the acetabular cup when the cup and the split bearing insert 2OD are fully assembled. The arrangement of this embodiment is as follows. The femoral component 12 is implanted in the femur (Figure 1) and the split bearing insert 20D and the spherical femoral head 16 are assembled as shown in Figure 12(a), creating some deformation of the hinge or spherical flexible member D, thereby creating some separation of the split bearing segments 21D-21D at their anterior portions or inferior aspects as shown in Figure 12(a). The acotabular shell 30 is then partially placed on the split bearing insert _20D1 as shown in Figure 12(b), thereby forcing the segments 21D-21D together against the resistance of the flexible member D. As assembly proceeds, the beveled edge or inner circular tapered surfaces 35 engage the partially circular encircling protuberances 43 and compress the front portions or lower aspect of the segments 21D-21D as shown in Figure 12. This action is permitted by the clearance 46 between the spherical femoral head 16 and the inner spherical surface 25D of the split bearing insert 2OD and by the gap or clearance between the generally U-shaped longitudinally extending surfaces 29. Upon completion of assembly, the outer circular encircling protuberances 43 formed on the outside of the

split bearing insert 20D are axially aligned with the inner groove 37 provided on the front part of the inner surface of the acetabular shell 30, thereby allowing the projections to engage the groove 37 through the extension of the hinge segment or spherical bridge D. Disassembly or separation of the acetabular shell 30 from the split bearing insert 2OD is prevented by wedging of the spherical femoral head 16 against the front part of the inner spherical surfaces 25D of the split bearing insert 2OB and such separation is prevented where the contact tangent φ1 is greater than the contact tangent φ2 as shown in Figure 12(d).

Dismantling is provided in the same manner as previously described, using the release tool 46 of Figure 5.

Another alternative embodiment of the improved spherical kinematic joint according to the present invention, which is designed as an improved spherical prosthetic hip joint, is provided and is shown in Figures 13 through 20. This further alternative embodiment includes an alternative split bearing insert 2OE that includes a plurality of physically separate split bearing segments, namely the generally spherically shaped primary bearing segments 51 of Figure 13 and either the generally circularly shaped radially or circularly circumferentially split bearing segment or bead 61 of Figure 14 provided with the outer circularly circumferential groove 19 or the substantially circularly shaped radially or circularly circumferentially split bearing segment or bead 71 of Figure 16 provided with the partial or complete outer circularly circumferential boss 43.

As shown in Figure 13, the primary bearing segment 51 is provided with an outer spherical surface 52, an outer cylindrical surface 53 and an inner spherical surface 55; in addition, the primary bearing segment 51 is provided at its front part with a circular, radially outwardly extending projection 58 and a circular, radially inwardly extending groove 59.

jQ The bead 61 of Figure 14 is provided with an outer cylindrical surface 63 in which the outer circular groove 19 is provided for receiving the retaining ring 40, an outer circular tapered surface 24, a bevelled edge or an inner

2g circular tapered surface 26 and an inner cylindrical surface 65; in addition, the bead 61 is provided at its rear part with a circular radially inwardly extending projection 68 and a circular radially outwardly extending groove 69. Similarly, the bead 71 of Figure 16 is provided with an outer cylindrical surface 73, an outer circular tapered surface 24 and a beveled edge or inner circular tapered surface 26 and an inner spherical surface 7? in addition, the bead 71 is provided at its rear part with a circular radially inwardly extending projection 78 and a circular radially outwardly extending groove 79. It will be noted and understood that the beads 61 and 71 are made of a suitably flexible material and are radially or circumferentially split as indicated at 64 and 74 to permit expansion of the beads radially outwardly or circumferentially for assembly with the primary segment 51.

Before assembly with the ball-like or spherical femoral head 16 of the femoral component 12

(Figure 1), the primary bearing segment 51 and either the bead 61 of Figure 14 or the bead 71 of Figure 16 are brought together in a subassembly to facilitate handling by the surgeon for the reasons stated above. In particular, and as shown in Figure 17 with reference to the bead 61 (it is understood that the bead 71 is assembled in the same manner), the bead 61 is expanded radially outwardly or circumferentially (preferably prior to surgery and prior to sterilization or packaging) to allow the projection 68 to pass over the projection 58 and upon contraction of the bead 61, the projection 68 is received in the groove 59 and the projection 58 is received in the groove 69, whereupon the primary bearing segment 51 and the bead. 61 are assembled in a sub-arrangement, as shown in Figure 18.

It is further noted and understood that after the split bearing insert 2OE including the bead 61

2ü the flexible retaining ring 40 is also used and is received in the groove 19 as shown in Figures 1 and 18; in this embodiment, the retaining ring 40 assists in maintaining the primary bearing segment 51 and the bead 61 in a subassembly. However, it will be understood by those skilled in the art that it is within the scope of the present invention to provide a bead made of a more rigid material wherein the bead is comprised of a plurality of circular segments provided on their outer surface _with a groove (e.g., the groove 19) for receiving the flexible retaining ring 40 which holds the circular segments together and on the primary bearing segment 51 to create the bearing insert subassembly.

Thus, as shown in Figure 18, it is understood that after the arrangement of either the bead 61 or the bead 71 on the primary bearing segment 51, the same

external configuration of the bearing insert embodiments described above. Similarly, it is understood that the inner spherical surface 55 of the primary bearing segment 51 and either the inner spherical surface 65 of the bead 61 or the inner spherical surface 75 of the bead 71 together provide a spherical cavity or abutment that conforms to and receives the femoral head 16 (Figure 1) of the femoral component 12 (Figure 1), the spherical abutment being identified in Figure 18 as abutment 57E. It is to be further understood that, considering the previously described embodiments of the split bearing insert according to the present invention, the opening to the spherical seat 57E provided by the beveled edge 26 of the beads 61 and 71 is less than the diameter of the spherical head 16 of Figure 1.

The arrangement of the split bearing insert 2OE with the spherical femoral head 16 of the femoral component 12 (Figure 1) will now be described with reference to Figures 19(a) to 19(d), the split bearing insert 2OE shown here including the bead 61 of Figure 14; however, it will be understood that such an arrangement is made in a similar manner on the split bearing insert 2OE including the bead 71 of Figure 16.

As shown in Figure 19(a), upon forcing the beveled edge 26 of the bead 61 (Figure 14) into engagement with the spherical femoral head 16 (the manual force exerted by the operating surgeon is more than sufficient and such force is indicated by arrows 81 and 83), the bead 61 expands radially outward or circularly around the gap 64 and against the action of the retaining ring 40 as shown in Figure 19(b) to

To allow the bead 61 to pass over the spherical femoral head 16 and to allow the spherical femoral head 16 to be supported in the spherical cavity or the support 57E (Figure 18) of the split bearing; the acetabular cup 30 is then pushed over the split bearing insert 2OE with respect to the split bearing insert 20 as previously described and shown in Figures 6(a) and 6(b) to cause the beveled edge or inner circular tapered surface 35 of the acetabular cup 30, Figure 6(a), to engage and compress the retaining ring 40 radially inwardly entirely within the outer circular groove 19 provided on the bead 61, thereby allowing the acetabular cup 30 to pass over the retaining ring 40, whereupon the split bearing insert 2OE with the spherical femoral head 16 supported therein are both supported entirely within the spherical cavity or seat 38 (Figure 3) and the elements which make up this embodiment of the present invention assume the position shown in cross-section in Figure 20 with the retaining ring 40 partially located within the external groove 1S of the bead 61 and partially located within the internal groove of the acetabular shell 30, whereby the retaining ring 40 holds the bearing insert 2OE within the acetabular shell 30 during rotation of the bone.

After attachment of the bead 71 of Figure 16 to the primary bearing segment 51 to create the aforementioned subassembly and after attachment of this subassembly to the spherical femoral head 16 in the manner shown in Figures 19(a) to 19(d) with respect to the bead 61, the boss 43 engages the inner groove 37 of the acetabular cup 30/ thereby retaining the acetabular cup on and above the split bearing insert and providing a separation between the bearing insert (with the femoral head supported therein) and the acetabular

shell is avoided during joint rotation. It will be understood that as in the split bearing insert 20D, Figure 12 (d), a clearance, i.e., the gap 46 of Figure 12, must be provided between the inner spherical surface 75 and the spherical femoral head 16 to allow contraction of the bead 71 as the boss 43 enters the cylindrical surface 33 of the acetabular shell 30 (Figure 3).

Disassembly of the bearing insert 2OE, either in the subassembly with the bead 61 or the bead 71, can be provided with the release ring 46 described above, with respect to the bearing insert 20 using the retaining ring 40 or with respect to the bearing insert 2OD using the circular protrusion 43.

In the embodiment according to the invention shown in Figure 20, the overlap angle f is approximately 30° and the intended rotation or pivoting movement is approximately 60°.

Referring again generally to the present invention, it is understood that the alternative embodiments of the split bearing insert of Figures 2, 9, 10, 11 and 12 are split in a plane (e.g., the plane coincident with the center line C/L of Figure 2) perpendicular to the plane 85-85, Figure 2, defined by the opening of the spherical cavity or seat 27 provided with the beveled edge 26, and that the alternative embodiment of the low friction bearing insert 2OE of Figures 13 and 14 is split along a plane represented by the line 87-87. Figure 13, which is aligned parallel to the plane indicated by the line 85-85 defined by the opening to the spherical cavity or seat 57E provided by the beveled edge 26 of the bead 61, Figure 14.

can be seen; in each embodiment, the bearing insert is composed of a plurality of bearing segments and a plurality of split bearing segments.

Referring generally to all of the various embodiments of the improved bearing inserts of the present invention, it will be understood by those skilled in the art that in those embodiments of Figures 2, 9, 10 and 18, the respective bearing inserts are composed of a plurality of bearing segments which are actually physically separate and that the bearing inserts of Figures 11 and 12(a) through (d) are composed of a plurality of bearing segments which are physically separate except for the integral flexible portions C and D, respectively, provided on their rear portions; thus, the term "composed of a plurality of ^{substantially} physically separate bearing segments" is used in the appended claims to describe both the bearing insert embodiments in which the bearing segments are actually physically separate and the bearing insert embodiments when the bearing segments are physically separate except for the integral flexible portions C and D.

Referring now generally to the above specifically described alternative embodiments of the improved spherical joint of the present invention, it is noted that such a joint provides a large or substantial overlap angle γ as shown in Figures 6(b) and 20, which results in a large resistance to displacement while requiring very low set-up and release forces. For the radial outward expansion of the various alternative embodiments of the split bearing insert to facilitate the insertion of the ball-shaped head, for example the ball-shaped femoral head, into the ball-shaped

position or cavity provided by various alternative embodiments of the split bearing insert, it is only necessary to bend or expand a thin retaining ring radially outward, or a relatively thin integrally formed spherical plastic bridge, or opposing projections, or a flexible pin, or expand a radially split circular bead radially outward. Similarly, the acetabular cup 30 can be easily assembled and disassembled to or from various alternative embodiments of the split bearing insert with the ball-shaped head, e.g., spherical femoral head, supported therein by a small radially inward or radially outward deflection of a thin retaining ring while providing a large separation resistance. Furthermore, in the embodiments using the retaining ring 40, since no deformation of the various split bearing inserts is required for an assembly operation, no axial play is introduced, thereby achieving a well-fitting bearing insert.

The femoral component 12 and the acetabular shell 30 may be made of rigid implantable metal such as stainless steel, titanium or cobalt-chromium alloy, as well as certain suitable ceramics. The various embodiments of the split bearing insert may be made of a material suitable for articulating with the spherical head 16, having sufficient strength to provide adequate resistance to displacement and separation, and in the case of the split bearing insert 20E (Figures 13 to 20) of any suitable material sufficiently flexible to provide the desired function of the beads 61 and 71. A typical material found suitable for these split bearing inserts is polyethylene of

ultra high molecular weight PE (DHMWPE) and suitable certain ceramics can also be used satisfactorily for these split bearing designs without the use of a flexible hinge or bridge or a flexible circular bead.

Referring again to the split bearing insert 2OE of Figures 13 and 20, it will be understood by those skilled in the art that the subassembly including the primary bearing insert 51 and the bead 61 or 71 can be separated from the acetabular shell 30 in a manner other than by use of the release ring 46, Figures 5(a) to 5(c) and the radially arranged slots or grooves 39 of the acetabular shell 30, Figure 3, e.g.

the front parts of the beads 61 and 71 adjacent the respective gaps 64 and 74 may be provided with inwardly extending holes or slots into which the ends of conventional clamps such as are typically found in the operating room may be inserted to compress the bead, thereby reducing the circumference of the beads at the radial incision, thereby releasing either the retaining ring 40 of the bead 61 or the boss 43 of the bead 71 from the groove 37 of the acetabular shell 30 and allowing the bearing insert 2OE with the femoral head 16 supported therein to be separated from the acetabular shell 30 by manual force exerted more than adequately by the operating surgeon.

Claims (31)

Pr. rar. r.si. &Ggr;. I=TS:; L ~ ~J ·. g C ^: rr.-Phys. ClAU- .-·&Ggr;&iacgr;,-;·. AL ■■ -i.-inq. Fi-AfJ? :. ^;-r~ --J-:· 5" Michael J. Pappas, 61 Gould Place, Caldwell, New Jersey 07006/USA
and Frederick F. Buechel, 112 Orange Avenue, Irvington, New Jersey o7111/USA
10 20 Spherical kinematic joint tn sayings 25 1 _t Spherical kinematic joint for creating three degrees of rotational movement between two parts, comprising (i) a first component for engaging one of the two parts and creating a first support, (ii) a second component for engaging the other of the two parts and including a lug and a head piece, 35 «&bull;&bull;Ill 1» ·■&euro;· (iii) a bearing insert made of a plurality of substantially physically separate bearing segments, which provides a second support with an opening, wherein after assembly of the joint the head piece in the second support, the projection extends through the opening and the bearing insert is received in the first support and the first component forces the bearing insert against an external extension, whereby the head piece in the second support, whereby the rotational movement is provided between the two parts, wherein the bearing insert has an overlap angle to prevent displacement of the head piece from the bearing insert during rotational movement, characterized by means for maintaining the plurality of substantially physically separate bearing segments together in a subassembly, thereby facilitating assembly of the spherical kinematic joint, the subassembly expanding outwardly to permit receipt of the head piece in the first rest. 2. Kinematic joint according to claim 1, characterized in that the opening generally defines a first plane and wherein the bearing insert is split along at least a second plane oriented in a predetermined manner with respect to the first plane to provide a plurality of substantially physically separate bearing segments. 3. Spherical kinematic joint according to claim 2, characterized in that the second plane is oriented substantially perpendicular to the first plane. 4. Spherical kinematic joint according to claim 2, characterized in that the second plane is oriented substantially parallel to the first plane. 5. A spherical kinematic joint according to claim 3, characterized in that the plurality of substantially physically separate segments comprise front and rear portions, the front portions defining the opening and once the front portions are forced into engagement with the headpiece, the bearing segments pivot outwardly about the rear portions to expand the subassembly to allow the headpiece to pass through the opening and the to enable insertion and inclusion in the second edition. 6. Spherical kinematic joint according to claim 5, _: 20 characterized in that each of the bearing segments is provided at its rear part with an outwardly extending projection and an inwardly extending recess, the projection of each bearing segment being intended to be received in the recess of another bearing segment, and the projections and recesses in cooperation provide means by which the bearing segments pivot outwardly and also prevent separation of the bearing segments by sliding by preventing relative movement therebetween in the second plane. 7. Spherical kinematic joint according to claim 5, characterized in that the spherical kinematic joint further comprises a flexible pin and each of the bearing segments is provided at its rear part with an inwardly extending hole, wherein upon axial alignment of said holes and receipt of said flexible pin in said holes, said pin and said holes cooperate to provide means by which the bearing segments pivot outwardly and also prevent separation by displacement of the bearing segments by preventing relative movement therebetween in the second plane. 8. Spherical kinematic joint according to claim 5, characterized in that the plurality of substantially physically separate bearing segments are provided with a hinge at the rear parts which connects the bearing segments and wherein the bearing segments pivot outwardly about the hinge to expand the bearing insert. 9. Spherical kinematic joint according to claim 8, characterized in that the hinge is a flexible part which is formed integrally with the rear parts of the bearing segments. 10. A spherical kinematic joint according to claim 4, characterized in that the plurality of substantially physically separate bearing segments comprises a primary bearing segment and at least one generally annular bearing segment, the primary bearing segment and the generally annular bearing segment together providing the second support and the generally annular bearing segment defining the opening, and when the generally annular bearing segment is forced into engagement with the head piece, the generally annular bearing segment expands outwardly to enable the headpiece passes through the opening and can be inserted into the second support and secured in place. 11. A spherical kinematic joint according to claim 10, characterized in that the means for retaining the bearing segments in a subassembly includes a groove formed in one of the primary bearing segments or the generally annular bearing segment and a lug provided on the other of the primary bearing segment or the generally annular bearing segment, the support lug being provided for receipt in the groove. 12. Spherical kinematic joint according to claim 10, characterized in that at least one generally annular bearing element comprises at least one flexible unitary annular bearing segment. 13. Spherical kinematic joint according to claim 1, characterized in that it comprises a means for preventing separation between the first component and the bearing insert. 14. A spherical kinematic joint according to claim 13, characterized in that the means for preventing separation between the first component and the bearing insert comprises at least one indentation on either the first component or the bearing insert and a lug is provided on the other of the first component or the bearing insert, the lug being arranged to engage the indentation. 15. A spherical kinematic joint according to claim 14, wherein the recess comprises a first groove provided on the first component and a second groove provided on the bearing insert, and wherein the boss comprises a retaining ring partially received in each of the grooves. 16. Spherical kinematic joint according to claim 14, characterized in that the approach is an integrally formed, generally annular elevation. 17. Spherical kinematic joint according to claim 14, characterized in that the first component or the bearing insert is equipped with a means for allowing external access to the lug to enable the lug to be released from engagement with the notch, whereby the bearing insert can be separated from the first component. 18. Spherical kinematic joint according to claim 15, characterized in that the first component or the bearing insert is provided with at least one slot for providing external access to the retaining ring to enable the retaining ring to be released from the first groove, thereby allowing the separation of the bearing insert from the first component. 19. Spherical kinematic joint according to claim 1, characterized in that the means for holding the bearing segments together in a subassembly also prevents separation between the first component and the bearing insert. 20. Spherical kinematic joint according to claim 1 or 5, characterized in that the head piece and the second support are spherical. 21. A joint according to claim 13, characterized in that the means for preventing separation comprises a retaining ring, wherein the bearing segments are physically separate and are provided with external grooves for at least partially receiving the retaining ring, and upon at least partially receiving the retaining ring in the external grooves prior to insertion of the head piece into the second support, the retaining ring maintains the bearing segments together in the subassembly. 22. Joint according to claim 21, characterized in that the first component is equipped with an internal groove for alignment with the external grooves and for at least partially receiving the retaining ring, wherein after partial reception of the retaining ring in the external and internal grooves, the retaining ring is also provided for maintaining the bearing insert with the head piece fixed therein in the first support during the rotary movement. 23. Ball joint according to claim 22, characterized in that the transverse cross-sectional shape of the retaining ring has a predetermined height and the depth of the inner groove is less than half the predetermined height. 24. Ball-shaped joint according to claim 23, characterized in that the transverse cross-sectional shape of the retaining ring is circular and the predetermined height is the diameter of the circular cross-sectional shape and the depth of the inner groove is less than half the diameter. 25. Ball-shaped joint according to claim 1, characterized in that the bearing segments with Prongs are provided to reduce the amount of outward expansion of the subassembly required to enable the headpiece to be received in the first rest.
10 26. A spherical joint according to claim 5, characterized in that the plurality of substantially physically separate bearing segments include a pair thereof and in that each bearing segment is provided with an outer spherical surface, an outer cylindrical surface, an outer circular tapered surface, an inner spherical surface, an inner circular tapered surface, and a generally U-shaped longitudinally extending surface, the outer spherical surface merging with the inner end of the outer cylindrical surface and the outer end of the cylindrical surface terminating in the inner end of the outer circular tapered surface, the inner spherical surface terminating at the inner end of the inner circular tapered surface, the outer ends of the inner and outer circular tapered surfaces being crossed, and wherein the generally U-shaped longitudinally extending surfaces of each bearing segment are in generally opposed relation to the generally U-shaped, longitudinally extending surface of the other bearing segment are arranged. 27. Ball-shaped joint according to claim 26, characterized in that each bearing segment is provided with a pair of teeth which is attached to the inner circular tapered surface and the generally U-shaped longitudinally extending
surface and merges with it, whereby the
Serrations facilitate the insertion of the headpiece into the second support by reducing the amount of outward expansion of the subassembly required to permit the headpiece to pass through the opening and be inserted into and received within the second support.
10 28. Ball-shaped joint according to claim 4, characterized in that the bearing segments comprise a generally spherical primary bearing segment with a front part and a generally my circular shaped radially split collar with a rear portion, the front and rear portions being provided with corresponding complementary shaped adapter parts and wherein upon radially outward expansion of the collar and contraction of the adapter part to engage each other, the primary bearing segment and the collar form a subassembly. 29. Joint according to claim 28, characterized in that g e k e &eegr;&eegr; - shows that the primary bearing segment with a spherical outer surface and a cylindrical outer surface and a spherical inner surface and wherein the collar is provided with a cylindrical outer surface, a circular tapered outer surface, a circular tapered inner surface and a spherical inner surface, the spherical surfaces together forming the second support and the complementarily shaped adaptation means forming a circular, radially outwardly extending projection and a circular, radially inwardly extending groove, which on the front part of the primary bearing segment 10 and includes an annular, radially inwardly extending projection and a circular, radially outwardly extending groove provided at the rear part of the collar. 30. Spherical kinematic joint according to claim 1, characterized in that the joint is a prosthetic hip joint and the Parts of the pelvis and the femur are. 10 31. Spherical kinematic joint according to claim 1, characterized in that the joint is a prosthetic shoulder joint and the parts are the humerus and the shoulder blade.