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`5,282,868
`[11] Patent Number:
`[19]
`United States Patent
`
`
`Bahler Feb. 1, 1994 [45] Date of Patent:
`
`[54] PROSTHEI‘IC ARRANGEMENT FOR A
`COMPLEX JOINT, ESPECIALLY KNEE
`JOINT
`
`[76]
`
`Inventor: André Bahler, Kapfsteig 44,
`CPI-8032 Zurich, Switzerland
`
`[21] App1.No.: 898,141
`
`[22] Filed:
`
`Jun. 15, 1992
`
`Foreign Appliation Priority Data
`[30]
`Jun. 17, 1991 [CH]
`Switzerland ....................... 01797/91
`Jun. 17, 1991 [CH]
`Switzerland ....................... 01793/91
`
`Int. Cl.5 ................................................ A61F 2/38
`[51]
`[52] US. Cl.
`.......
`[58] Field of Search .............................. 623/ 16, 18, 20
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,085,466 4/1978 Goodfellow et al.
`................ 623/20
`4,207,627 6/1980 Cloutier ...............
`..... 623/20
`
`4,309,778
`1/1982 Buechel et a1.
`.
`623/20
`
`4,340,978 7/ 1982 Bucchel et a1.
`......
`623/20
`
`4,353,136 10/1982 Polyzoides et a1.
`.
`..... 623/20
`4,470,158
`9/1984 Pappas et a1.
`. 623/20
`
`4,728,332
`3/1988 Albrektsson
`.623/20
`.
`4,950,297
`8/1990 Elloy et a1.
`. 623/20
`
`5,007,933
`4/1991 Sidebothaxne
`..... 623/20
`.
`
`5,011,496 4/ 1991 Forte et al.
`........................... 623/20
`
`FOREIGN PATENT DOCUMENTS
`
`1567007 5/1980 United Kingdom .
`
`OTHER PUBLICATIONS
`
`“New Jersey Tricompartmental Total Knee System”.
`“A Manual of the Oxford Knee", published by OEC
`Orthopaedic Ltd. Bridgend, South Glamorgan, United
`Kingdom.
`
`Primary Examiner—David Isabella
`Attorney, Agent, or Firm—Frishauf, Holtz, Goodman 8L
`Woodward
`
`[57]
`
`ABSTRACT
`
`To permit movement of coupling elements (13, 130,
`13b) which carry joint surfaces (21) congruent with
`condylar portions (19) of the prosthesis, the coupling
`elements are slidable in guide tracks (35), which are
`curved, and are widened at their terminal portions. The
`coupling elements have elongated engagement
`ribs
`which fit into the guide track groove, with minimum
`clearance and play at the narrowest, central portion of
`the guide groove, while permitting limited twisting as
`well as sliding movement due to the widened regions of
`the guide track at its end region. The position of guide
`track-rib can be reversed, if desired. The elements slide
`on a slide surface 'and can be retained, for example by an
`interlocking connection, such as a dovetail.
`
`23 Claims, 16 Drawing Sheets
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 -1
`
`

`

`U.S. Patent
`
`Feb. 1, 1994
`
`Sheet 1 of. 16
`
`5,282,868
`
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`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 2
`
`

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`US. Patent
`
`Feb. 1, 1994
`
`Sheet 2 of 16
`
`5,282,868
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 3
`
`

`

`US. Patent
`
`Feb. 1, 1994
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`_Feb. 1, 1994
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`Feb. 1, 1994
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`US. Patent
`
`Feb. 1, 1994
`
`Sheet 6 of 16
`
`5,282,868
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`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 7
`
`

`

`US. Patent
`
`Feb. 1, 1994
`
`Sheet 7 of is
`
`5,282,868
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`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 8
`
`

`

`US. Patent
`
`Feb.1, 1994
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`Sheet 8 of 16
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`Feb. 1, 1994
`
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`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 11
`
`

`

`US. Patent
`
`Feb. 1, 1994
`
`Sheét 11 of 16
`
`5,282,868
`
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`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 12
`
`

`

`US. Patent
`
`Feb. 1, 1994
`
`Sheet 12 of 16
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`5,282,868
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`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 13
`
`

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`
`Feb. 1, 1994
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`US. Patent
`
`Feb. 1, 1994
`
`Sheet 14 of 15
`
`5,282,868
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 15
`
`

`

`US. Patent
`
`Feb. 1, 1994
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`

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`US. Patent
`
`Feb. 1, 1994
`
`Sheet 16 of 16
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`5,282,868
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`
`

`

`1
`
`5,282,868
`
`PROSTHETIC ARRANGEMENT FOR A COMPLEX
`JOINT, ESPECIALLY KNEE JOINT
`
`FIELD OF THE INVENTION
`
`The present invention relates to a prosthetic device
`for a joint, and more particularly for a complex joint,
`and especially for the knee joint, having a that pros-
`thetic part which contains an anchoring or attachment
`portion and at lent one rotary joint portion, adapted to
`be secured to one of the bones which form the joint, for
`example the femur, and a second part which also con-
`tains attachment elements or stems, adapted to be at-
`tached to the shin bone or tibia, and formed with a
`sliding surface. An intermediate part or element is pro-
`vided slidable between anterior and posterior directions
`and which, in association with a suitable section of the
`first portion, permits articulation of the joint.
`BACKGROUND
`
`Many solutions have been proposed for the problem
`of endoprosthetics, which permit unchangeable mainte-
`nance of a stable bone implantate joint, which will last
`for a very long time, ideally from implantation to the
`death of the patient or wearer of the prosthesis. There
`are, primarily, two factors which interfere with such
`lifetime implantation. For one, the interface between
`the bone-implantate is subject to changeable forces,
`which change both with respect to value as well as
`direction. Particularly shearing forces are involved. For
`another, biological reactions of tissues and degrading
`bones are a factor, especially reactions to foreign—body
`materials, and reactions to abraded particles from the
`prosthesis itself.
`The long lifetime, and particularly implanted lifetime,
`of a joint can be increased by reducing changeable
`forces engaging at the interface between the various
`prosthetic parts, and on the sliding surfaces thereof. The
`wear on the sliding surfaces should be minimized. Vari-
`ous solutions have been proposed, but not all of them
`can be applied at the same time. It is not sufficient to
`consider all the technical aspects of the joint; anatomi-
`cal as well as physiological changeable conditions must
`be considered. The complex kinematic which occurs in
`joints, and particularly in complex joints such as the
`knee joint, can make it difficult to compromise between
`conflicting solutions applicable to specific parts,
`to
`achieve the overall goal of lifetime reliability.
`It is well known that the wear and tear on slide bear-
`ings can be reduced by decreasing the per-square or
`area pressure of the respectively rubbing sliding parts.
`The surface or area pressure, and the resulting wear and
`tar on the bearing, is small when the contact surface of
`the two sliding elements is large. This contact bearing
`surface can be increased by making the sliding surfaces
`as large as possible and effectively congruent. Typical
`examples for such bearings are shown in FIG. 1, in
`which a straight slide bearing is schematically illus-
`trated, and in FIG. 2, which, schematically, illustrates a
`hinge or ball joint. The slide bearing of FIG. 1, in prin-
`ciple, can be considered as a hinge or ball joint in which
`the engaging surfaces have infinite radii. Yet, in spite of
`the common characteristic of minimal wear and tear,
`there are basic differences: The slide joint, FIG. 1, is
`free for translatory movement, but does not have an axis
`of rotation. The hinge or ball joint, on the other hand,
`has an axis of rotation, but is restrained from translatory
`
`10
`
`15
`
`20
`
`25
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`movement. This results in different relationships with
`respect to externally acting forces.
`Reference is again made to FIG. 1:
`A force, such as force F1 coming from above at an
`inclination, results in lateral shifting of the sliding head
`due to horizontal component of the force. This horizon-
`tal component of the force does not have any effect on
`the lower part of the sliding joint.
`A force similar to force F1, when applied to a hinge
`or ball joint, see FIG. 2, passes through the joint with-
`out causing any rotation thereof. The horizontal com-
`ponent of this force, however, results in an undesired
`shear force, which continuously changes its direction if
`the upper portion of the joint oscillates back and forth
`like a pendulum. Most simply, the hinge joint has the
`advantage of rotary movement, which, however,
`is
`obtained by accepting the disadvantage of translatory
`immobility, and shearing forces at the interface.
`Human body joints rarely are pure hinge joints or
`pure slide joints. Usually, and especially the knee joint
`provides a combination of both. A rotary movement
`and translatory movement can be superimposed upon
`each other.
`
`In order permit a combination of such movements, it
`is necessary to open the hinge joint, that is, it is neces-
`sary to reduce the congruence of theslide surfaces with
`respect to each other. Referring to FIG. 3, the contact
`surfaces are decreased which, however, substantially
`increases the area or surface pressure, and hence wear
`and tear on the joint. This wear and tear is further in-
`creased by repetitive translatory movement of the head
`of the joint on the slide surface. Due to the almost point
`or at best somewhat line contact, and hence a similar
`high surface pressure, a kneading process on the respec-
`tive joint parts results which, in turn, causes material
`fatigue of the lower joint portion or component. The
`non-congruent position of the elements does not neces-
`sarily prevent the occurrence of shear forces at the
`interface. Raised slide surfaces at the interface result in
`forces which are similar to those which arise in a pure
`hinge or ball joint. The result is increased wear and tear
`as well as shear forces at the interface, which has unde-
`sirable effects in all prostheses of this type.
`It has been proposed to use a combination of slide and
`ball joints, in which the sliding and ball joint compo.
`nents are located on two different planes, by using an
`intermediate element, see FIG. 4. The rotary movement
`of the ball joint and a translatory movement of the slide
`joint are vertically staggered, so that the translatory
`movement is available as a lower motion of the ball
`joint. The congruence ofjoint surfaces is fully retained;
`wear and tear is minimized The forces supplied by the
`ball joint are not transferred to the interface but, rather,
`translated into translatory movement by the intermedi-
`ate element. Prostheses are of this type are known, and
`have been referred to as meniscal knees.
`U.S. Pat. No. 4,309,778, Buechel and Pappas, de-
`scribes two difl'erent knee joint prostheses, which have
`also been referred to as the “Oxford Knee" and the
`“New Jersey Knee”. The “Oxford Knee” has two fem-
`oral portions, two intermediate portions and two tibial
`portions. The femoral portions each have a spherical
`segment which has a retention section, for retention on
`the femur. The tibial parts also have retention on the
`tibia. The tibial parts not only have retention sections
`for attachment to the tibia, but also a flat plateau on
`which the intermediate part can slide.
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 18
`
`

`

`5,282,868
`
`3
`Upon flexion of 90' and more, the intermediate part
`can slide over the flat or table-like surface and, possibly,
`can be entirely dislocated. A similar danger may occur
`if the tension of the remaining ligaments decreases after
`the operation and the femoral part lifts off the interme-
`diate part. A new operation of the knee joint will then
`become necessary.
`The “New Jersey Knee”, described for example in
`FIG. 15 of the referenced US Pat. No. 4,309,778, has a
`special arrangement to prevent loss of contact over the
`table or
`slide surface. Two dovetail-like, bowed
`grooves are provided on the tibia part; an engagement
`element is provided for the intermediate part element,
`fitting in the grooves through which the intermediate
`part element are constrained to be guided. The curves
`are directed towards the center, so that the intermediate
`part, upon bending of the knee, cannot slide backwardly
`in uncontrolled manner, and pushed over the surface or
`table, but, rather, engages the still remaining central
`projection from the bone. The dovetaile shape prevents
`dislocation or luxation of the joint,
`if the ligaments
`should lose tension or will have decreased tension or
`strength.
`The intermediate portions are constrained to be
`guided on a predetermined path which permits congru-
`ence of the joint surfaces between the femoral portion
`and the intermediate portion only in a single position of
`the joint.,For all other positions of the joint than the
`single one, an incongruence of joint surfaces results,
`which increases wear and tear of the engaging surfaces.
`Non-congruent conditions arise because the femoral
`parts, which are securely anchored in the femur, are
`always at the same distance from each other and have a
`common axis of rotation. The intermediate parts, how-
`ever, approach each other laterally upon sliding for-
`wardly and backwardly on the curved path or, respec-
`tively, separate from each other. Further, their axes of
`the hinge or ball joints continuously change their posi-
`tion with respect to each other. Similar situations ob-
`tain, in reverse sense, however, upon rotary movement
`about an axis which is perpendicular to the slide surface.
`The continuously changing degree of non-congruence
`of the surfaces of this prosthesis, and particularly of the
`hinge or ball joint surfaces, causes increased wear and
`tear and decreases the effect of a meniscal layer in a
`knee joint.
`US. Pat. No. 4,353,136, Polyzoides et al, describes an
`endoprosthetic knee joint having a femoral, a tibial part
`and an intermediate part. The femoral part has an at-
`tachment portion for attachment to the femur and two
`condyles. The tibial part has an attachment portion and
`projecting attachment ribs for attachment to the tibia.
`The side opposite the attachment surface has a flat bear—
`ing surface, with a groove to receive a rib of an interme-
`diate part. The rib of the intermediate part fits into the
`curved groove of the tibial part; two concave slide
`bearings provide counter surfaces for the condyles of
`the femoral part. This prosthesis has the advantage of
`congruence of the slide surfaces of a hinge or ball joint,
`and thus of low wear and tear.
`The curved groove and rib coupling does not, how-
`ever, permit translatory movement of the femoral part
`relative to the tibial part. It only permits rotation about
`the axis of the curve of the groove. This, then, is a
`classic hinge joint with additional freedom of rotation
`about an axis perpendicular to the hinge axis. Thus,
`forces which come at an inclination from above, see
`FIGS. 2-4, which occur, for example, due to muscle
`
`5
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`4O
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`pull or loading upon placing the foot of the wearer on
`the ground, will pass through the joint to the interface
`and there result in the undesired shearing forces. The
`principle of a meniscal knee is compromised in that the
`congruence of the joint surfaces, which reduces wear
`and tear, is obtained only by loss of the translatory
`capability, which protects the connection between the
`prosthesis and the joint. The natural knee kinematics,
`thus, are not entirely obtained with this joint. Besides
`that, the use of elements which prevent dissociation or
`luxation of the joint, for example at dovetail intercon-
`nection, is nearly impossible, especially to permit inser-
`tion of the intermediate portion at a later time, after the
`tibial portion or part has already been implanted. This
`has the disadvantages which have been discussed above
`in connection with the “Oxford Knee”.
`British Patent 1,567,007, Minns et al, describes a knee
`joint having a femoral part, a tibial part and an interme-
`diate part. The femoral part, as is customary, has an
`attachment element and a condyle. The tibial part also
`has an attachment element for connection to the tibia
`and a straight, dovetaile-shaped groove to receive a
`matching rib of the intermediate part. The intermediate
`part has a straight rib, fitting into the groove. The inter-
`mediate part, further, has a shallow glide bearing for
`articulation with the condyle of the femoral part. This
`structure also has the advantage of wear reducing con-
`gruence of the slide surfaces. The dovetail connection
`between rib and groove prevents luxation or dissocation
`of the intermediate part, and hence undesired separation
`from the tibial part.
`This structure permits translatory movement in the
`longitudinal direction of the groove. It does not permit
`rotational movement about an axis perpendicular to the
`plane of the tibial part, that is, essentially perpendicu-
`larly to the axis of the tibia. Such rotary movements,
`however, are superimposed practically with all move-
`ments of the knee joint, which results in continuous
`non-congruent engagement of the slide surfaces of the
`condyle from the femur and the intermediate part. The
`natural kinematics or relative movements of the parts of
`the knee joint are thus not adequately reproduced.
`THE INVENTION
`
`It is an object to provide a prosthesis for replacement
`of injured or diseased joints, and particularly complex
`joints, and especially knee joints, which is so con-
`structed that the components of the prosthesis are pro-
`tected; that, when in use, they have low wear and tear,
`and which permit not only congruence ofjoint surfaces,
`translatory and rotary movement of a knee having an
`intermediate or meniscal portion, but also effectively
`ensures reliable retention of the intermediate portion
`with respect to dissociation or luxation. The joint
`should permit approximately normal physiological
`movement of the natural joint, which it replaces.
`Briefly, the joint has an intermediate part which is
`guided with respect to another part, typically the tibial
`part, by a guide arrangement which includes a guide
`groove or guide track and a coupling portion operable
`in the guide track, and in which the guide track has a
`region in which it is widened beyond a fitting engage-
`ment with the coupling portion in order to permit the
`coupling portion freedom of movement with respect to
`the guide track—yet preventing removal of the cou-
`pling portion from the guide track.
`The prosthetic joint in accordance with the present
`invention permits movement or articulation which
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 19
`
`

`

`5,282,868
`
`5
`largely corresponds to the normal physiological move-
`ment of a natural joint, typically a natural knee joint.
`Upon flexion, the condyles shift from ventral to dorsal;
`at the same time, however, a limited rotary movement
`can occur. In flexion as well as in extension. similar
`conditions obtain as in a natural knee. In any position of
`the joint, congruence of the joint surfaces between the
`femoral part and the intermediate part is assured, since
`the intermediate parts are not tightly guided but, rather,
`can move in the respective tracks, typically grooves,
`with lateral play. Thus, the joint surfaces on the inter-
`mediate parts can remain aligned with respect to each
`other. Forces transferred from above are not further
`transferred to the interface but, rather, are converted in
`the intermediate part in translatory movement. The
`danger of dislocation of the intermediate part, upon
`flexion, is effectively eliminated, since the motion or
`articulation of the joint corresponds largely to that of a
`normal physical motion of a natural knee.
`The intermediate part can be a relatively small, ex-
`changeable element. Thus, it is possible to fit, during the
`knee replacement operation, intermediate parts of suit-
`able heights; sets with different heights can be provided.
`Such differently sized parts are suitable in order to
`compensate for flabbiness in ligaments or to correct
`axial misalignments. The intermediate part, as well as
`the femoral and tibial parts, can be made of different
`materials. For example, the intermediate part may be
`made of plastic and the parts of the prosthesis which are
`actually connected to the bones made of metal.
`The coupling portion can be guided within the track
`portion, typically a groove, by suitable shaping of the
`side walls of the grooves. This results in a particularly
`simple construction. In order to be able to widen the
`groove,
`in anterior and posterior position,
`in accor—
`dance with the present invention, the directions and
`shapes of the groove can also be changed. Preferably,
`the side walls of the groove,
`in a region extending
`towards the edge of the tibial plate, for example, are
`curved. The groove can extend in a curve about a cen-
`tral axis. The coupling portion itself may also have a
`suitable curvature along its longitudinal extent. This
`permits rotation upon flexion as well as extension which
`is similar to movement in a natural joint. Preferably, the
`spacing between the side walls of the groove is smallest
`approximately in the center of the groove. The width of
`the coupling portion corresponds approximately to this
`minimum spacing.
`In accordance with a particularly advantageous em-
`bodiment of the invention, the inner side wall of the
`groove is curved, whereas the outer side wall of the
`groove, particularly in the central region, has an essen-
`tially straight portion. The coupling portion, however,
`has the reverse situation in that the outer side wall of the
`coupling portion is curved and the inner side wall of the
`coupling portion, at least in the central region, has a
`straight portion. This permits maintenance of the lateral
`play between the guide portion of the intermediate
`element and the guide track to be small, so that the
`transverse stability of the knee will be high. This is
`particularly important for prostheses replacing a knee
`joint. The shape described provides both translatory
`movement in anterior/posterior direction and limited
`twisting movement of the intermediate part relative to
`the second or tibial part.
`The radius of curvature of the outer side wall of the
`coupling portion or coupling element can be the same
`or smaller than the radius of a concentric circle about
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`the inner side wall of the guide track, and which just is
`tangent to the straight section of the outer side wall of
`the guide track. The radius of this concentric circle can
`be about 1.3 to 2.6 times the radius of the curvature of
`the inner side wall of the guide track or guide groove.
`This dimensioning results in anterior and posterior wid-
`ening of the guide track or guide groove, which pro.
`vides the desired freedom of movement for the interme-
`diate part, in its movement in anterior or posterior di-
`rection, respectively.
`The curves need not be true circular curves; use of
`curves which are circular, however, has advantages
`from a manufacturing point of view. Other curves than
`circles can be used, for example elliptic curves.
`Preferably, the movability of the intermediate part is
`constrained by a slide plane or guide plane, to inhibit
`wobble. To provide for positive guidance in a vertical
`direction, thus, the guide track or guide groove and the
`matching surfaces of the coupling portion, can be of
`dovetail interengaging connection, T-shaped,
`tongue
`and groove shaped, polygonal or circqu cross section.
`Such shapes prevent loss of the coupling portion from
`the guide track if, due to some reasons, the retention of
`the ligaments of the joint decreases after the operation
`of joint reconstruction.
`The rotary bearing surfaces can be constructed in
`different manner in order to ensure rotary movement.
`In accordance with a preferred feature of the invention,
`two condyles are provided, and each condyle is fitted
`on a suitable, matching bearing surface on the interme-
`diate part. Preferably, the guide tracks or guide grooves
`are so arranged that they converge in anterior and pos-
`terior direction. The result will be a prosthesis in which
`the natural joint, for example in a knee joint, is closely
`approximated.
`In accordance with a feature of the invention, two
`separate intermediate parts are used, one each being
`formed with the coupling portion and fitting in its own
`guide groove. In accordance with another feature of the
`invention, a bridge-like connecting part can be pro-
`vided, coupling the individual intermediate parts to-
`gether. Such connection prevents relative shifting of
`the intermediate parts with respect to each other, and a
`possible non-congruence of the rotary joint surfaces, in
`engagement with the condyles. The reliability with
`respect to dissociation or luxation, further, is improved,
`since the two coupled intermediate parts are imprisoned
`in the curved grooves, and cannot exit therefrom in
`anterior or posterior ends of the grooves. Further, the
`coupling provides a degree of damping, or braking of
`translatory movement when the end points or limits for
`movement are reached. This braking is particularly soft
`or gradual if, by suitable selection of the radii of curva-
`ture of the tracks and/or of the coupling portions, the
`concave inner surfaces of the coupling portions can first
`engage with the convex side walls of the groove.
`Forming the coupling element as a cross-connecting
`bridge has the advantage that, if the intermediate parts
`are made of plastic, cold-flowing of the plastic material,
`and hence another factor which leads to material fa—
`tigue, and hence wear, is excluded.
`The construction of the joint can be formed in a
`mono-compartmental manner, that is, the joint portion
`of the first prosthesis element can be formed by a single
`condyle, and the matching receiving surface on a single
`intermediate part of sufficient size to be able to accept
`the single condyle.
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1015 - 20
`
`

`

`5,282,868
`
`7
`Preferably, and as an analog to a natural joint, the
`condyle is formed on the first prosthesis part and con-
`vex; the matching bearing surface of the intermediate
`part is then concave. It is also possible, however, to
`reverse this arrangement, where it is suggested by the
`anatomic structure, and to form the condyle on the
`intermediate part with the concave reception surface on
`the first prosthesis.
`The prosthesis is particularly suitable for knee joint
`replacement. In such a case, the second or tibial part can
`be formed with a suitable recess for the anterior and/or
`posterior cruciate ligament. The prosthesis can readily
`be shaped to provide such a recess or room for these
`ligaments, which has the advantage that the important
`function of the cruciate ligaments for proper knee
`movement is retained.
`
`The free path length of movement upon translation
`depends essentially on half of the difference in width
`between the guide track portion or guide groove por-
`tion and the coupling portion, as well as the radii of the
`concave side walls of the groove portion and the cou-'
`pling portion, respectively. There is a positive correla-
`tion, that means, the free path length increases at in-
`creasing difference in width and/or absolute size of the
`radii.
`
`As an example, the translatory extent of the guide
`track is assumed to be 15 mm. The radius of the outer
`side wall of a guide track portion in form of a groove is
`selected at 50 mm. This is suitable for a knee joint. The
`width difference then can be 1.13 mm. In a free transla-
`tory movement path of 25 mm, and a radius of 70
`mm—which is rather high—the width difference may
`be 2.25 mm. In both cases, thus, the lateral play or free-
`dom is within the limits of tolerances, which are normal
`for a stable knee joint. The lateral play or gap of the
`coupling portion in the guide groove, at the narrowest
`point, preferably is in the range of between 0.5 to 3 mm.
`In accordance with a suitable embodiment of the
`invention, the radius of curvature of the outer side wall
`of the groove is approximately 3 times the radius of
`curvature of the inner side wall. This dimensioning
`results, directly, in anterior and posterior expansion or
`widening of the guide track, which then will result in
`the desired freedom of movement for the coupling por-
`tion and hence the intermediate part in its movement
`between anterior and posterior direction. The radius of
`curvature of the outer side wall of the coupling portion
`is, preferably, about half the radius of curvature of the
`outer side wall of the groove. The curves may be ellipti-
`cal or have other shapes; a circular curve is preferred,
`however, since it is the easiest to fabricate.
`
`DRAWINGS
`
`FIG. I is a highly schematic diagram illustrating
`force relationships in a sliding joint, and causing transla-
`tory movement;
`-
`FIG. 2 is a highly schematic diagram showing shear
`forces which arise in a ball joint;
`FIG. 3 is a highly schematic diagram illustrating
`forces which arise in an “open” ball joint;
`FIG. 4 illustrates the force relationships in a compos-
`ite slide-ball joint;
`FIG. 5 is a top view, partly in section, taken along
`line V—V of FIG. 6 of a knee joint prosthesis, in which,
`for ease of illustration, the outlines of the intermediate
`parts are shown in chain-dotted configuration;
`FIG. 6 is a section along line Vl—VI of FIG. 5;
`FIG. 5A is a top view of another embodiment;
`
`8
`FIG. 6A is a section line through the embodiment of
`FIG. 5A;
`FIG. 5B is a top view of another embodiment show-
`ing a bridge connection of two intermediate part ele-
`ments;
`FIG. 6B is a section along line VIB—VIB of FIG.
`SB;
`FIG. GC illustrates a joint similar to the joint of FIG.
`6A in exploded view;
`FIG. 7 is a schematic top view of the second prosthe-
`sis part of either FIGS. 6, 6A or 6B, omitting the inter-
`mediate parts;
`FIG. 8 is a bottom view of an intermediate part;
`FIG. 9 is a top view of another embodiment of a knee
`joint prosthesis;
`FIG. 10A is a section along line X—X of FIG. 9;
`FIG.
`lOB illustrates the joint of FIG. 10A in ex-
`ploded View;
`FIG. 11 illustrates another shape of a guide track
`arrangement, different from that of FIG. 1;
`FIG. 12 is a knee joint prosthesis similar to that of
`FIG. 5, in which, however, the coupling portion is
`formed on the tibial or second prosthesis part;
`FIG. 13A is a cross section along line XIII—XIII of
`FIG. 12;
`FIG. 13B illustrates the joint of FIG. 13A in ex-
`ploded view;
`FIG. 13C is an upside-down detail view of an inter-
`mediate part;
`FIG. 14 is a view similar to FIG. 5 and illustrating a
`different arrangement of radii of curvature for the re-
`spective components of the knee;
`FIG. 15 is a cross-sectional view taken along line
`XV—XV of FIG. 14;
`FIG. 16 is a top view of another embodiment with the
`femoral part removed;
`FIG. 17 is a cross section along line XVII—XVII of
`FIG. 16;
`FIG. 18 is a top view illustrating yet another embodi-
`ment, with the femoral part removed;
`FIG. 19 is a cross section along line XIX—XIX of
`FIG. 18;
`FIG. 20 is a bottom view of an intermediate part for
`a single-condyle femoral part;
`FIG. 21 is a top view of the second prosthesis part,
`with the intermediate parts removed;
`FIG. 22 illustrates another embodiment of a knee
`joint prosthesis;
`FIG. 23 is a section line along XXIII—XXIII of FIG.
`22;
`FIG. 24 illustrates an alternative embodiment of a
`guide track to that shown in FIG. 23;
`FIG. 25 illustrates a prosthesis similar to that shown
`in FIG. 18, in which the coupling portion is formed on
`the second prosthesis part; and
`FIG. 26 is a cross section along line XXVI—XXVI of
`FIG. 25.
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`DETAILED DESCRIPTION
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`the force
`FIGS. 1—4 show, highly schematically,
`relationships and force transfer conditions when a force
`F1 is applied by, for example, the femur or a femoral
`part 11 to a tibial part 17, secured for example to the
`tibia 1. FIG. 3 in addition shows the intermediate or
`meniscal element 17. In the actual joint, the element 11
`is secured to the femur, not shown.
`Referring next to FIGS. 5 through 8:
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`E