United States Patent
`
`[19]
`
`[1 1]
`
`4,340,978
`
`[45] Jul. 27, 1982
`Buechel et al.
`
`
`
`[54] NEW JERSEY MENISCAL BEARING KNEE
`REPLACEMENT
`
`[75]
`
`Inventors:
`
`Frederick F. Buechel; Michael J.
`Pappas, both of Irvington, N.J._
`
`[73] Assignee: Biomedical Engineering Corp.,
`Newark, N.J.
`
`[21] Appl. No.: 162,070
`
`[22] Filed:
`
`Jun. 23, 1980
`
`Related U.S. Application Data
`
`[62]
`
`Division of Ser. No. 53,694, Jul. 2, 1979, Pat. No.
`4,309,778.
`
`Int. Cl.3 .............................................. .. A6lF 1/03
`[51]
`
`[52] U.S. Cl.
`......... ..
`3/1.911; 128/92 C
`[58] Field of Search ................................ .. 3/1.9—1.913;
`128/92 C, 92 CA
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`....................... 3/ 1.911
`3/1975 Waugh et al.
`3,869,731
`3/1.911
`3,964,106 6/1976 Hutter, Jr. et al.
`4,081,866 4/1978 Upshaw et al.
`........
`. ..... 3/1.911
`4,085,466 4/1978 Goodfellow et al
`.. 3/1.911 X
`4,094,017
`6/1978 Matthews et al.
`... ..
`...... 3/1.911
`4,224,696 9/1980 Murray et al.
`....................... 3/1.911
`
`Primary Examiner—Clifford D. Crowder
`Attorney, Agent, or Firm—Ca.re1la, Bain, Gilfillan &
`Rhodes
`
`[57]
`
`ABSTRACT
`
`A prosthesis for the surgical replacement of a dysfunc-
`tional knee joint is disclosed. The prosthesis includes a
`
`tibial platform, one or two tibial bearing inserts, and a
`femoral component.
`
`In a unicompartmental embodiment of the invention,
`the tibial platform includes a spike for securing the tibial
`platform to the tibia. The tibial platform, in the unicom-
`partmental embodiment, includes a track, which may be
`curved, and which is slidably engaged in dovetail fash-
`ion by a tibial bearing insert, typically of high molecular
`weight polyethylene. The superior surface of the tibial
`bearing insert is concave spherical, designed to slidably
`engage the inferior surface of the femoral component.
`The inferior surface of the femoral component is gener-
`ally convex spherical, with radius of curvature slightly
`smaller than the radius of curvature of the tibial bearing
`insert. In some embodiments the inferior ‘surface of the
`femoral component may have two or more differing
`radii of curvature at different points on such surface.
`Typically the tibial platform and the femoral compo-
`nent are constructed of cobalt-chromium alloy.
`
`In a bicompartmental or tricompartmental embodiment
`of the invention, the tibial platform includes two tracks,
`each of which may be curved, and each of which slid-
`ably engages in dovetail fashion a tibial bearing insert.
`The two tibial bearing inserts each engage, via their
`superior concave spherical surfaces, mating inferior
`convex surfaces of the femoral component. The two
`curved tracks are in general not concentric; rather, the
`center of each falls on a line normal to the plane of such
`curved track and passing through the center of curva-
`ture of the concave spherical surface of the tibial bear-
`ing insert of the other curved track.
`
`6 Claims, 76 Drawing Figures
`
`
`
`FORWARD
`POSITION
`OF
`IN S ERT
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1012 -1
`
`

`

`US. Patent J
`
`A Jul. 27, 1982
`
`Sheet 1 of 21
`
`4,340,978
`
`F'|G.|B
`
`FIG.lA
`
` SINGLE
`
`AXIS
`
`FIG. 3A
`POSITION or BEARING INSERTS
`AT
`90°FLEXlON WITH NO
`ROTATION
`,/02
`
`—
`
`‘
`(I02
`
`U)
`
` E
`
`FIG. 33
`P°5'T'°N °F BEAR”"G W" '
`sears AT 90 FLEXION
`WW... 50 AN 30° Ax.AL
`30°
`ROTATION
`_
`OVERHANG ’ "
`’
`\ /
`
`/\
`
`AXISAT15°
`
`. Zimmer Holdings, Inc. and Zimmer, Inc.
`’
`A
`.- Exhibit 1012 - 2
`
`

`

`U.S. Patent
`
`Ju1._27, 1982
`
`Sheet 2 of 21
`
`4,346,978
`
`FIG. 2A[
`a5°.FL__exIoN
`.
`%
`‘NORMAL
`
`~AXI$
`
`.
`Farm-lagsus
`
`% ’7°,’
`w
`,
`/
`
`V\’
`
`‘
`
`
`
`._~._»
`. “""
`=
`
`-__,_
`
`/JEXCESS.A
`POSTERIOR»
`
`,0,
`IDISPLACEMENT.
`.
`.
`-aesuurmc»
`,
`-
`may use or
`SINGLE amauus
`or CURVATURE V
`
`A
`
`A
`
`F|G.2B
`
`’n2o° FLEXION
`'
`V POSIBLE
`DISLOCATION
`
`—
`
`’
`
`.\ V
`>
`.
`
`.
`
`‘
`
`/ \
`
`—
`
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`
`+
`I
`I
`
`Zimmer Holdings, Inc. and Zimmer, Irjc.
`' Exhibit 1012 4 3
`
`~
`
`L
`
`

`

`"Patent fiJul.27, 1982
`
`Sheet3of21
`
`V
`
`4,340,978
`
` FIMG.4
`swnue PHASE
`OF WAL,KING '
`
`KNEE DISTRACTED
`INSERT FREE TO '
`DSLOCATE
`»
`
`//
`
`/_./"
`
`/
`
`FIG so
`
`
`
`HIGH compaessnon
`STRESS
`
`_ )\VvuUQ
`s‘.\V H‘.
`3 VIII,/IZTII4‘.
`
`
`
`D
`,
`
`
`
`
`
`I02
`
`0
`
`LIMIT
`Tg:VE'_p
`
`
`
`
`
`I09
`
`HIGH STRESS DUETO
`HIGHLY INCONGRUENT
`CONTACT
`
`'03
`
`Zimmer Holdings, Inc. and Zimmer, lnc_.
`Exhibit 1012 - 4 ‘
`
`

`

`U.S. Patent
`
`Jul. 27, 1982
`
`Sheet 4 of 21
`
`4,340,978 _
`
`Fl G. 5A
`ANATOMICAL RAMP
`
`_
`
`FIG. 5B
`‘
`
`‘
`
`HEIGHT
`
`V
`
`OXFORD paosmaszs
`RAMP HEIGHT
`
`‘ Zimmer Holdings, Inc. and Zimfiwerg Inc.
`'
`‘
`Exhibit 10.12 - 5
`
`

`

`US... Patent
`
`Jul. 27, 1932
`
`Sheet 5 of .21
`
`4,340,978
`
`Zimn'ier Holdings, Inc. and Zimmer, Inc. ._
`Exhibit 1012 - 6
`
`A
`
`

`

`U.S. Patent
`
`Jul. 27, 1982
`
`Sheet.6 of 21
`
`4,340,978
`
`Fl G.4 9
`
`H8
`
`ll/—\
`
`/21
`
`Zimmer Holdings, Inc._ and Zimmer, Inc.
`Exhibit 1012 - 7
`
`j
`
`

`

`V
`
`Patent J Jul. 27, 1§s2 ‘V
`
`4 Sheet7of 21
`
`4,340,978 %
`
`b
`* Zimmér Hdldings, Inc. and Zimmer, Inc.
`‘
`’
`' Exhibit1O12-8A -
`
`-
`
`

`

`U.S. Patent
`
`Jul. 27, 1982 _
`
`shéet 8 of 21
`
`4,340,978 I
`
`I
`
`F‘ 5- 23
`
`REPREstNrAnvE
`- GENERAL
`Axis./L ,_,/—-’
`_J
`
`
`
`Aurgmoa
`
`POSTERIOR
`
`
`
`Zimmer Hdldihgs, Inc. and Zimmer, Iric.‘ H
`Exhibit 1012 - 9
`
`

`

`US. Patent
`
`’Ju1._27,1982
`
`LL
`
`sheetéof 21
`
`4,340,978
`
`FIG. 25
`
`runs END -renos
`TO LIFT
`I33
`
`'3’
`
`\I
`
`33
`COMPRESSION
`LOAD IN FULL
`EXTENSION
`
`THIS EN D
`DEPRESSED
`
`IS
`
`Zimmer Holdings, Inc. and Zimmer, Inc-
`Exhibit 1012 - 10
`
`

`

`U.S. Patent
`
`Ju1.27, 1982
`
`Sheet 10 of 21
`
`4,340,978 %
`
`FlG.27
`
`PAT ELLA
`
`
`
`F|G.3I
`
`FEMORAL
`
`ANTERIOR
`
`ARTICULAR. CARTILI GE
`FOR PAT'ELLA- FEMORAL
`ART|CULATiON
`
`FEMUR
`
`INTERIOR VIEW OF
`DISTAL
`
`POSTERIOR
`FEMORAL
`ARTICULAR CARTILI GE
`FOR Tl BIO - FEMORAL
`ARTICULATION
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1012 - 11
`
`

`

`US. Patent
`
`1111. _27, 1932
`
`1
`
`Sheet11.of’21b
`
`14,340,978
`
`FIG. 28
`
`QUADRICEPS
`MUSCLE
`
`GROUP
`
`PATELLA
`
`
`
`PATELLA
`TENDON
`
`\
`‘
`
`TIBIO
`FEMORAL
`HEAVY
`COMPRESSION
`FORCE DURING \
`WALKING
`
`-
`I
`‘ TIBIA
`‘/I”
`»
`.
`i
`L“<>
`
`FAlG.28B
`
`
`
`F0,
`LOW
`COMPRESSION
`
`FORCE
`
`F !
`
`1
`
`,
`
`FIG. 298
`
`MODERATE
`
`COMPRESSION
`‘FORCE
`
`Fa
`
`
`
`‘
`
`
`PAT ELLA
`
`TIBIO
`FEMORAL
`\
`HEAVY
`compaessiou ,
`FORCE DURING \
`WALKING
`
`~
`
`‘r|a|A
`
`I
`'
`\.
`%
`
`‘
`
`\
`
`\.»"/’
`
`»
`
`Zimmer Holdings, ‘Inc. and Zimmer, Inc.
`A Exhibit 1012 - 12
`
`

`

`U.S.. Patent
`
`Jul. 27, 1982
`
`.Sheet 12 of 21
`
`4,340,978
`
`FIG. BOA
`
`F|G.3OB
`
` \
`
`‘
`
`LIGHT T0
`\~
`MODERATE
`\_
`TIBIO FEMORAL
`COMPRESSION FORCES \.
`DURING WALKING
`
`\
`g
`.,
`IV
`
`\/
`
`F|G.35B
`
`X
`
`35A
`F I
`..
`———->l:,
`
`'
`
`—
`
`DIFFERENCE IN Y
`DISPLACEMENT
`
`_
`
`MOTION OF POINT ON
`INTERMEDIATE TIBIAL BEARING
`COMPONENT CCURVATURE OF
`MOTION
`IN I:
`TRAC“)
`DIRECTION
`
`I
`
`or POINT on
`MOTION
`FEMUR
`
`
`
`.
`
`CENTER
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1012 - 13
`
`

`

`U.S. Patent A
`
`Jul. 2?, 1932‘
`
`Sheet 13 of 21
`
`4,340+978
`
`F|G.32A
`
`II7
`
`
`
`
`
`FORWARD
`POSITION
`- OF
`INSERT
`
`
`
`
`
`&C1§§§§
`§§§:§S§§A
`:"—__
`
`
`
`
`INWARD MOTION" OF SHIMS WHEN
`FEMUR MOVES
`POSTERIORLY
`
`Zim_mer Holdings, Inc. and Zimrner‘, Inc.
`Exmbfl1012-14
`
`

`

`U.S, Patent
`
`Jul. 27, 1982‘
`
`I
`
`Sheet 14 of 21
`
`4,340,978
`
`FIG. 33A
`|5°FLEXlON
`
`"‘_li
`I‘.
`//7
`/I6 \ CENTRAL
`
`
`POSITION
`OF
`INSERT
`
`15°
`
`
`
`
`
`
`
`FlG.33B
`KNEE IN FLEXION
`
`POSTERIOR
`POSITION OF
`INSERT
`
`H5.
`
`H7
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1012 - 15
`
`

`

`U.S.. Patent
`
`Jul. 27, 1982 .
`
`Siieet 15 Tar 21
`
`4,340,978
`
`F|G.37A
`
`
`
`ZSIJALLER HEIGHT
`
`F/P2 LARGER HEIGHT PROVIDES
`
`PROVIDES GREATER
`CENTER DISTANCE
`CHANGE FOR A GIVEN
`
`GREATER MEDIAL-LATERAL
`STABILITY
`
`V
`
`-
`
`AMOUNT OF INCONGRUITY
`
`F! G. 38A
`
`% OUTWARD
`
`SHIFT ALLOWABLE
`
`INWARD
`SHIFT
`
`:56
`
`:57
`
`-
`
`VECTOR
`
`OXFORD
`CENTERING
`
`‘Fl G. 383
`J CENTER! NG
`VECTOR
`
`
`
`:59
`
`'
`
`"I63
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1012 - 16
`
`

`

`U.S. Patent
`
`Jul. 27, 1982
`
`Sheet 16 of 21
`
`4,340,978
`
`F|G.39A
`
`FG.39B
`
`TENDS TO LIFT ANTERIOR
`
`PROSTHESIS TENDS T0 LIFT
`ON MED|AL BQRDER AND
`
`"R°V'DE5 ‘°°°“ TEN5'°"‘
`/54
`RE5'5TANCE
`
`PROVIDES LITTLE rensnon
`/65
`RESISTANCE
`
`
`
`HIGH
`COMPRES-
`S|0N
`STRESS
`
`)»TEN5lLE
`
`STRESS
`
`POTENTIAL
`FRACTURE
`
`
`
`STRESS CONCENTRATION. AT
`BOTTOM OF SLOT COUPLED
`WITH SPREADING EFFECT
`OF FIN BLADE
`
`F|G.4OA
`
`FiG.40B
`
`)
`
`1
`
`168
`
`_I5_7_
`
`/
`
`I58
`
`Zimmer Holdings, Inc. and Zimmer,» Inc. ‘O
`Exhibit 1012 - 17
`
`

`

`.,U.S. Patentj Ju1.27, 1982 A
`
`FlG.4IA
`
`
`
`I6 4
`
`.
`
`,
`
`Sheet 17 ofb21
`
`4,340,978
`
`I65
`
`FIG.4IB
`COMPRESSIVE
`RE ACTIVE PRESSURE
`RESISTING
`TILTING
`
`STRESS
`SUPPORT LOAD
`
`LOW
`COMPRESSIVE
`
`SHEAR STRESS
`HELPING TO
`
`
`
`F|G.42A
`LOAD
`
`
`
`FLEXIBLEPLASTICPLATFORM
`
`PLATFORM
`
`
`
`RIGIDMEDAL
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1012 - 18
`
`

`

`U.S. Patent
`
`Jul. 27, 1982
`
`‘Sheet 18 of 21
`
`V
`
`_ 14,340,978 .1
`
`Zimmer Holdings, Inc. and Zimmei, Ind.
`Exhibit 1012 - 19
`
`’
`
`

`

`U.S. Patent
`
`jul. 27, 1982
`
`Sheet 19 of 21
`
`4,340,978
`
`'
`
`Zimmer Holdings‘, Inc. and Zimmer,'|nc.
`Exhibit 1012 - 20
`
`x
`
`

`

`US. Patent
`
`Ju1.27, 1982
`
`Shéet 20 of 21 4
`
`14,340,978
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`‘
`Exhibit 1012 - 21
`
`

`

`US. Patent
`
`Jul. 27, 1982
`
`Sheet 21 of 21
`
`‘4,340,978
`
`
`
`Fl G. 53
`
`LI GAMENTS
`
` MALLELI
`
`F I G. 54
`
`ARTICULATING
`v SURFACES
`
`LIGAMENT
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1012 - 22
`
`

`

`1
`
`4,340,978
`
`2
`extension motion. Normal flexion-extension is, how-
`ever, characterized by a polycentric flexion-extension
`motion where rotation relative to the femur occurs
`about many axes. This polycentric motion, which re-
`sults from the action of the cruciate ligaments and con-
`dylar shape, allows for more efficient utilization of mus-
`cle forces by providing a posterior shift of the axis when
`effective quadriceps action is important and an anterior
`shift when hamstrings effectiveness is important. Fur-
`thermore, in the human knee it is this polycentric ac-
`tion, and the shape of the posterior condyles, which
`influence this motion so as to allow full flexion capabil-
`ity for the knee. Failure to provide appropriate knee
`geometry inhibits, when cruciate ligaments are present,
`this natural polycentric motion and thus tends to restrict
`muscle effectiveness and inhibit flexion. These restric-
`tions tend to increase both loading on the prosthesis
`(which increases wear or likelihood of deformation or
`breakage) and loading between prosthesis and bone
`(which increases the possibility of component loosen-
`ing).
`Other knee designs, such as the Townly type, avoid
`overconstraint by introducing incongruency of the ar-
`ticulating surfaces. The incongruency, while necessery
`to avoid overconstraint, unfortunately results in insta-
`bility and excessive contact stresses.
`It is further believed that loosening problems result
`from the direct attachment of plastic prosthetic compo-
`nents to bone through the use of relatively brittle ce-
`ment that is weak in tension. Specifically, it has been
`demonstrated that even relatively thick plastic compo-
`nents when loaded in a normal fashion produce undesir-
`able tensile stresses in the acrylic cement commonly
`used to secure such plastic components to bone. Such
`loading tends to produce bending of the plastic compo-
`nent which causes the ends of the plastic component to
`lift away from the bone, thereby subjecting the bone-
`cement attachment to tension. As is known, cement has
`very poor tensile fatigue properties. The bone to which
`the plastic prosthesis is cemented also appears to be
`adversely affected by tensile loads. Accordingly, it is
`believed that these combined effects contribute substan-
`tially to prosthetic loosening problems and, specifically,
`it has been noted where clinical failure due to loosening
`occurs in a knee prosthesis that it is almost always the
`plastic prosthesis component which loosens.
`Another prior art prosthesis problem exists with re-
`gard to knee endoprostheses for implantation in those
`cases wherein the cruciate ligaments are functionally
`absent but where the collateral ligaments are functional
`or at least reconstructable. In the absence of cruciate
`ligaments,
`the prosthetic replacement must provide
`anterior-posterior knee joint stability so as to replace
`that stability otherwise provided by the cruciates. Until
`recently most such cases were treated by a stable hinge-
`type knee prosthesis which, unfortunately, appears to
`suffer from the loosening problems described above and
`furthermore typically produces substantial bone loss as
`a result of the relatively great bone resection required
`for implantation. Necrosis of the bone, caused by al-
`tered mechanical bone stresses, is also a problem with
`the hinge-type knee prostheses. More recent attempts
`have been made to treat such cases with surface replace-
`ment prostheses such as the prostheses known as the
`Total Condylar and similar knee prostheses. However,
`these knee prostheses have theoretical point-contact
`bearing surfaces with their above—noted attendant prob-
`lems and,
`in addition, such prostheses tend to have
`
`NEW JERSEY MENISCAL BEARING KNEE
`REPLACEMENT
`
`This is a division, of application Ser. No. 53,694 filed
`July 2, 1979, now U.S. Pat. No. 4,309,778.
`TECHNICAL FIELD
`
`This invention relates to prosthetic joints generally,
`and more particularly to a prosthesis for replacement of
`a dysfunctional knee joint.
`BACKGROUND ART
`
`Referring now to prior art knee endoprostheses, and
`in particular to the prior art knee prostheses with patel-
`lo-femoral replacement, it has been observed that such
`prior art prostheses have poorly designed pate1lo-fem-
`oral interfaces in that they do not provide reasonable
`congruent patello-femoral contact or sliding engage-
`ment over any appreciable range of knee motion.
`More particularly, such prior art prostheses typically
`produce contact stresses which result in yielding and
`fatigue of the plastic bearing surface typically present in
`such prostheses. This result is caused by the fact that the
`bearing surface of the femoral component, over which
`the patella prosthesis must pass, generally has several
`regions or segments of differing shape. For example,
`there is typically a fairly long, singly curved segment
`blending into a first doubly curved segment blending
`again into a second, and different, doubly curved seg-
`ment. These varying segments or regions provide the
`femoral portion of the femoral-tibial articulation, and
`those segments or regions do not have a common gener-
`ating curve. Thus, when the patella prosthesis goes
`through its excursion over the femoral articular flange,
`the patella prosthesis undergoes a variety of contact
`conditions, namely, substantial portions of line contact,
`portions of point contact, and perhaps limited portions
`of area or congruent area contact. As is known, line
`contact and point contact conditions generally produce
`high contact stresses which produce yielding and sub-
`stantial wear of plastic prostheses. Hence, the extended
`wear life needed for successful prosthetic implantation
`is not realized.
`
`Referring next to typical prior art tibio-femoral knee
`prostheses, it has been observed that those prior art
`knee prostheses which allow axial rotation and anterior-
`posterior motion in addition to flexion-extension motion
`have incongruent contact (usually theoretical point-
`contact) between the femoral and tibial bearing sur-
`faces, producing excessive contact stresses leading to
`deformation and/or early wear and undesirably short
`prosthetic life. Also, wear products have been shown to
`produce undesirable tissue reactions which may con-
`tribute to loosening of the prosthetic components.
`Those prior art knee prostheses which do provide
`congruent or area bearing contact fail to provide the
`needed axial rotation, or when cruciates are present the
`needed anterior-posterior motion. This lack of axial
`rotation and anterior-posterior motion has been shown
`clinically and experimentally to result in deformation
`and loosening of the tibial components, and such pros-
`theses now appear to be falling into disuse.
`Current prostheses of the dislocatable cruciate retain-
`ing type, such as the Geomedic knee replacement
`shown in U.S. Pat. No. 3,728,742 issued Apr. 24, 1973 to
`Averill et al., that produce area contact provide only
`one axis of rotation relative to the femur for the flexion-
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1012 - 23
`
`

`

`4,340,978
`
`3
`instability and dislocation problems which result, at
`least in part, from these point-contact bearing surfaces.
`Where the cruciate ligaments are present, most sur-
`geons would prefer their retention, since they provide
`important internal stabilizers and,
`together with the
`condylar geometry of the femur and tibia, control the
`rotation axis of the knee. Furthermore, these ligaments
`provide anterior-posterior (A-P) stability. Thus,
`it is
`desirable to reserve the cruciate ligaments, even though
`reasonable stability can be provided by a properly de-
`signed full platform type prosthesis.
`In addition, the action of the cruciate ligaments pro-
`duces a shift in the rotation axis of the knee which may
`result in more efficient muscle utilization. Thus, preser-
`vation of these structures may provide better physiolog-
`ical function after knee replacement.
`Still, it is not clear that the physiological advantages
`gained in retaining the cruciates outweigh the disadvan-
`tages of the design compromises, such as increased
`bearing surface incongruency and reduced tibial pros-
`thesis bearing area, required to retain these ligaments.
`Thus, the desirability of retaining the cruciate ligaments
`in the cases of bicompartmental and tricompartmental
`replacement is not well established. The design de-
`scribed herein, however, eliminates or compensates for
`these design compromises, thus allowing the benefits of
`cruciate retention with minimal or no apparent loss in
`the abiliy of the prosthesis to withstand the. loads to
`which it is subjected.
`In unicompartmental replacement, the cruciates must
`be retained in any event since there is insufficient stabil-
`ity in their absence with a unicondylar replacement.
`Thus, for such cases a design which accommodates the
`cruciate ligaments is necessary.
`Unicompartmental replacement with a proper hear-
`ing design allows surgical restoration of a single dis-
`eased compartment, rather than the sacrifice of normal
`structures to replace all three compartments of the
`knee. Further, reducing the number of compartments
`replaced has the effect of reducing prosthesis wear
`products. Recent evidence strongly suggests that these
`wear products produce adverse physiological response
`to the prosthesis, including an increased tendency for
`the prosthesis to loosen from its boney attachment.
`A recent experimental knee concept,
`the Oxford
`knee, appears to provide a partial solution to the prob-
`lem of overconstraint while maintaining congruency by
`the use of meniscal floating elements. Unfortunately,
`this knee suffers from several design problems which
`appear to limit its usefulness. The present invention, the
`New Jersey Meniscal Bearing Knee Replacement
`(NJMBK) utilizes similar concepts in an improved fash-
`ion in order to avoid some of the anticipated difficulties
`of the Oxford design.
`The Oxford knee is shown in FIGS. 1A and 1B. The
`femoral components 101 consist of two metal spherical
`segments, each of constant radius. Bearing inserts 102
`are circular in shape with a shallow spherical superior
`surface and a flat inferior surface. The tibial onlays 103
`consist essentially of two flat plates with fixation by
`means of a fin 104 at the medial edge of each such flat
`plate.
`There are several serious problems with the design of
`the Oxford knee of FIGS. 1A and 1B. The most basic
`problem is the potential for dislocation of bearing in-
`serts 102 resulting from the limited flexion range of the
`device. As can be seen from FIGS. 2A and 2B the de-
`sign provides excellent congruent contact up to about
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`45
`
`_
`
`50
`
`55
`
`65
`
`‘
`
`4
`90° flexion. Beyond that point a surface of constant
`radius cannot provide proper contact within the geo-
`metric constraints imposed by having to fit the prosthe-
`sis to the human knee. Flexion substantially beyond 90“
`produces edge contact and resulting deformation and
`possible dislocation of bearing inserts 102. Although 90°
`of flexion is satisfactory from a functional standpoint, it
`is impractical to limit motion to this range, since activi-
`ties will be encountered (such as sitting onto a low
`chair, or returning to the standing position after sitting
`in a low chair) where flexion substantially exceeds 90°.
`The problem of insert dislocation is made more se-
`vere by axial rotation of the knee, as is shown in FIGS.
`3A and 3B. In FIG. 3A, there is shown the position of
`bearing inserts 102 at 90° flexion, but with no axial rota-
`tion of the knee. In FIG. 3B there is shown the position
`of bearing inserts 102 at 90° flexion, but with 15° (solid
`lines) and 30° (dashed lines) of axial rotation as well.
`There is a pronounced overhang of bearing inserts 102,
`with resultant risk of dislocation, under the combination
`of 90° flexion and 30° axial rotation of the knee.
`Normal distraction of one compartment of the knee
`during the swing phase of walking, as depicted in FIG.
`4, also leaves bearing insert 102 of the prior-art Oxford
`knee free to dislocate.
`A further disadvantage of the Oxford knee arises
`from the shallowness and placement of the arcs of the
`contact surfaces, as can be seen from FIGS. 5A and 5B.
`In FIG. 5A there is shown a normal knee joint, with the
`anatomical ramp height designated 105. Note, in FIG.
`5B, that the Oxford prosthesis ramp height 106 is sub-
`stantially less than the anatomical ramp height 105, and
`therefore the Oxford prosthesis provides less than nor-
`mal medial-lateral stability. Thus, when medial-lateral
`shear loads are encountered, additional stress is placed
`on the cruciate ligaments, which may be already com-
`promised by bone resection. Furthermore, such load-
`ing, in conjunction with flexion or extension, will pro-
`duce undesirable rubbing between the edges 107 of
`bearing inserts 102 and the cut edges 108 of the tibial
`bone.
`Other weaknesses of the Oxford design include lack
`of accommodation for patella replacement, and tibial
`plateau components with relatively poor load-bearing
`properties, as will be described later.
`An alternate embodiment of the Oxford knee which
`attempts to deal with the problem of dislocation is de-
`picted in FIGS. 6A—D. Unfortunately, this design has
`several deficiencies which make it unworkable, at least
`with materials now commonly used for such compo-
`nents. The anterior-posterior (A-P) travel
`limit
`is
`greatly restricted compared to that of the present inven-
`tion. There is substantial unsupported area 109 of plastic
`bearing insert 102, as can be seen from the cross-sec-
`tional view of FIG. 6C. Flexure of the plastic bearing
`insert 102 will occur, transferring load to the remaining
`areas and thus greatly increasing bearing compressive
`stresses. High stress will occur in the inner cavity at the
`head of retaining pin 110, particularly at the edge of
`retaining pin 110 and at the contact between the end of
`retaining pin 110 and the inner cavity, as can be seen
`from the cross-sectional view of FIG. 6D. Further-
`more, the use of retaining pin 110 makes installation of
`the bearing element difficult after implantation of femo-
`ral and tibial components, since it is necessary to sepa-
`rate the knee joint by stretching the ligaments an
`amount equal to the pin height in addition to the separa-
`tion normally required to install bearing inserts 102.
`
`Zimmer Holdings, Inc’. and Zimmer, Inc.
`Exhibit 1012 - 24
`
`

`

`5
`
`SUMMARY OF THE INVENTION
`
`4,340,978
`
`6
`FIGS. 5A and 5B compare the anatomical ramp
`height with the ramp height provided by the prior-art
`Oxford knee prosthesis.
`FIGS. 6A through 6D illustrate some of the disad-
`vantages which result from a design modification to
`partially constrain the bearing inserts of the prior-art
`Oxford knee.
`
`The present invention is directed to an improved
`prosthesis for the replacement of all or a portion of a
`dysfunctional human knee joint.
`An object of the present invention is to provide a
`knee prosthesis in which shift of the bearing insert with
`knee flexion is similar to the normal anatomical shift in
`the center of the area of contact between femoral and
`tibial condyles.
`A further object of the present invention is to provide
`a knee prosthesis which facilitates rotation about one or
`more axes, even in the presence of perfect congruency
`and rigidity of the bearing surfaces.
`A further object of the present invention is to provide
`a knee prosthesis with greater dislocation height, and
`hence improved dislocation characteristics, than are
`available with prior-art floating bearing insert type knee
`prostheses.
`A further object of the present invention is to provide
`a knee prosthesis with improved medial-lateral stability,
`substantially unaffected by axial rotation or anterior-
`posterior (A—P) shift of the bearing insert or inserts.
`A further object of the present invention is to provide
`a knee prosthesis which substantially reduces the possi-
`bility of tipping or dislocation of the bearing insert or
`inserts.
`A further object of the present invention is to provide
`a knee prosthesis which allows full flexion of the recon-
`structed knee.
`A further object of the present invention is to provide
`a knee prosthesis allowing retention of the cruciate
`ligaments and capable of both effective patello-femoral
`and tibio-femoral articulation.
`A further object of the present invention is to provide
`a knee prosthesis having reduced tendency toward loos-
`ening and collapse, as compared with prior-art floating
`bearing insert ‘type knee prostheses.
`A further object of the present invention is to provide
`a knee prosthesis allowing retention of the cruciate
`ligaments in which contact stresses between the tibial
`platform and the tibia are minimized.
`A further object of the present invention is to provide
`a knee prosthesis design which is adaptable to embodi-
`ments for unicompartmental, bicompartmental, and
`tricompartmental knee replacements.
`‘
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`A complete understanding of the invention may be
`obtained from the detailed description which follows,
`together with the accompanying drawings, wherein:
`FIGS. 1A and 1B are diagrammatic views of the
`prior-art Oxford knee.
`FIGS. 2A and 2B illustrate the prior-art Oxford knee
`at 85° and 120° (respectively) tlexion, showing the ex-
`cess posterior displacement of the bearing inserts at 85°
`flexion. Two possible dislocation modes of the bearing
`inserts are shown at 120° flexion.
`FIGS. 3A and 3B also depict the prior-art Oxford
`‘knee. FIG. 3A shows, in plan view, the position of the
`bearing inserts at 90° flexion with no rotation of the
`knee. FIG. 3B shows the positions of the bearing inserts
`at 90° tlexion in the presence of axial rotations of 15°
`and 30°.
`FIG. 4 illustrates the possibility of dislocation of the
`bearing inserts,
`in the prior-art Oxford knee,
`in the
`swing phase of walking.
`
`‘5
`
`20
`
`25
`
`30
`
`FIGS. 7 through 9 show the femoral component of
`the present invention, the New Jersey Meniscal Insert
`10 Knee.
`FIGS. 10 through 12 show the intermediate patella
`bearing component according to the present invention.
`FIGS. 13 and 14 show the patella fixturing compo-
`nent according to the present invention.
`FIGS. 15 through 17 show the tibial platform compo-
`nent according to the present invention.
`FIGS. 18 through 21 show the intermediate tibial
`bearing component according to the present invention.
`FIG. 22 illustrates the manner in which the surface of
`the femoral component according to the present inven-
`tion is generated by a series of segments of surfaces of
`revolution.
`FIG. 23 illustrates the manner in which the several
`bearing surfaces of the present invention are generated
`by rotating a common generating curve about a particu-
`lar generating axis at pairs of major generating radii.
`FIG. 24 shows the orientation of the patella prosthe-
`sis relative to the femoral component at full extension of
`the knee.
`FIG. 25 illustrates the role of the fixturing fins (of the
`patalla fixturing component) in resisting tipping loads.
`FIG. 26 shows" the button portion of the patella fix-
`turing component, which is used to retain the intermedi-
`35 ate patella bearing component.
`FIG. 27 shows the manner in which the present in-
`vention permits rotation of the patella with respect to
`the femoral bearing surface.
`FIGS. 28A and 28B illustrate the relatively low patel-
`40 lo-femoral compression force present at full extension
`of the knee.
`FIGS. 29A and 29B illustrate the somewhat greater
`patello-femoral compression force present in the load-
`bearing stance phase of the normal walking cycle.
`FIGS. 30A and 30B illustrate the much greater patel-
`lo-femoral compression force present in deep knee flex-
`ion.
`FIG. 31 is an inferior view of the distal femur, show-
`ing the femoral anterior articular cartilege involved in
`50 patello-femoral articulation, as well as the femoral pos-
`terior articular cartilege involved in tibio-femoral artic-
`ulation.
`FIGS. 32A and 32B show the manner in which the
`intermediate tibial bearing components are held in a
`55 forward position, in the tibial platform, by virtue of the
`shape of the bearing surface of the femoral component.
`FIGS. 33A and 33B show the manner in which the
`intermediate tibial bearing components move posteri-
`orly with flexion of the knee. FIG. 33A shows 15° flex-
`60 ion, while FIG. 33B shows 120° flexion.
`FIG. 34 is a cross-sectional view of the curved track
`of the tibial platform component according to the pres-
`ent invention.
`FIGS. 35A and 35B illustrate the manner in which
`65 the intermediate tibial bearing components move
`slightly closer together as they move forward and rear-
`ward from a central position in the curved track of the
`tibial platform component.
`
`45
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1012 - 25
`
`

`

`7
`FIG. 36 illustrates the manner in which the interme-
`diate tibial bearing components move slightly closer
`together as the femur moves posteriorly.
`FIGS. 37A and 37B show the manner in which the
`use of an eccentric bearing insert (i.e. the intermediate
`tibial bearing component) allows a relatively great in-
`ward shift of the bearing insert with little incongruency.
`FIGS. 33A through 38C illustrate several advantages
`of the intermediate tibial bearing component according
`to the present invention. The larger platform (relative
`to that of the circular bearing insert of the prior-art
`Oxford knee) is shown in FIG. 33A. FIG. 38B illus-
`trates the greater dislocation height of the present in-
`vention, and FIG. 38C illustrates the non~central spheri-
`cal radius of the present invention.
`FIGS. 39A and 39B illustrate the undesirable tensile
`stresses produced in the prosthesis-bone interface by the
`Maclntosh type tibial onlays of the prior-art Oxford
`knee.
`FIGS. 40A and 40B show the tibial platform of a
`unicompartmental version of the present invention.
`FIGS. 41A and 41B show the manner in which the
`spike of the tibial platform of the unicompartmental
`version of the present invention resists both tipping and
`compressive loads.
`FIGS. 42A and 42B compare the tibial platform com-
`ponent of the present invention with a prior-art prosthe-
`sis utilizing a flexible platform, which is ineffective in
`producing any load-sharing across the prosthesis-bone
`interface.
`FIGS. 43 and 44 show the femoral component of a
`unicompartmental version of the present invention.
`FIGS. 45 and 46 show an implanted bicompartmental
`version of the present invention, utilizing a pair of indi-
`vidual femoral components.
`FIGS. 47A and 47B show an implanted unicompart-
`mental version of the present invention.
`FIGS. 48, 49 and 50 illustrate an ankle prosthesis
`according to the present invention. FIG. 48 is a cross-
`sectional view of the prosthesis, as indicated in FIG. 50.
`FIGS. 51 and 52 show the implanted ankle prosthesis
`according to the present invention.
`FIGS. 53 and 54 show an anatomical ankle, for com-
`parison with the implanted ankle prosthesis of FIGS. 51
`and 52.
`FIG. 55 shows, in schematic cross-section, an alterna-
`tive track (consisting of just a shoulder, rather than a
`channel) suitable for applications where force loads
`applied to the prosthetic joint are such as to insure
`retention of the bearing insert against the shoulder.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`there is shown an
`Referring now to FIGS. 7-21,
`endoprosthesis embodying the present invention which
`has been referred to as a tricompartmental knee prosthe-
`sis and which includes the femoral component 111 best
`shown in FIGS. 7, 8, and 9; the patella prosthesis 112
`shown in FIG. 27 and comprising the intermediate pa-
`tella bearing component 113 best shown in FIGS. 10,
`11, and 12, and the patella fixturing component 114
`shown in FIGS. 13 and 14; and the tibial prosthesis 115
`shown in FIG. 27 and comprising the tibial platform
`component 116 best shown in FIGS. 15,