United States Patent
`
`[19]
`
`5,370,699
`9
`
`Hood et a1.
`[45] Date of Patent:
`Dec. 6 1994
`
`[11] Patent Number:
`
`||||||||l||||l|||lllllllllllilll||l|||||||llllllllllllllllllllllllIllllllll
`US005370699A
`
`[54] MODULAR KNEE JOINT PROSTHESIS
`
`[75]
`
`Inventorsz Roger W. Hood, Olathe, Kansz;
`Serafin Y. Samson, aneapolis;
`Robert D. Carter, Apple Valley, both
`of Minn.
`
`E
`
`i
`
`Ed
`
`[731 Assignee: Orthomet, Inc, Minneapolis, Minn-
`[2]] App]. No.: 7,161
`-
`. 21, 1993
`:
`F11
`22
`Int. Cl.5 ................................................ A61F 2/38
`51
`[52] US. Cl.
`...................................................... 623/20
`[58] Field of Search .............................. 623/16, 18, 20
`[56]
`Referencos Cited
`US. PATENT DOCUMENTS
`
`Jan
`
`3,748,662 7/1973 Helfet .
`3,774,244 11/1973 Walker 4
`3,816,855
`6/1974 Saleh .
`3,837,009 9/1974 Walker .
`3,869,729 3/1975 Attenborough .
`4,209,861
`7/1980 Walker et a1.
`.
`4,213,209 7/1980 Insall et a1.
`.
`4,257,129 3/1981 Volz .
`.
`4,298,992 11/1981 Burstein et a].
`.
`4,714,474 12/1987 Brooks, Jr. et a1.
`4,743,261 5/1938 Epinette ................................ 623/20
`4,822,362 4/1989 Walker et a1.
`........................ 623/20
`4,822,366 4/1989 Bolesky .
`4,865,607 9/ 1989 Witzel et al. .......................... 623/20
`4,936,847 6/ 1990 Manginelli .
`4,936,853
`6/1990 Fabian et al.
`4,938,769 7/1990 Shaw .
`4,944,760 7/1990 Kenna .
`4,950,298
`8/1990 Gustilo et al.
`
`.
`
`.
`
`.
`
`-
`5,002,547 3/1991 Poggie Ct 31-
`5,007,933 4/1991 Sidebotham et a1.
`5,037,423
`8/1991 Kenna .
`.
`5,047,058 9/1991 Roberts et a1.
`5,062,852 11/1991 Porr et a1. ............................. 623/20
`...... 623/20
`5,080,624
`1/1992 Jacobs et a1.
`
`...... 623/20
`5,080,675
`1/1992 L
`t
`1.
`5,108,442 4/1992 5:111:13............... 623/20
`
`5,152,297 10/1992 Luckman et a1. ..................... 623/20
`Primaty Examiner—David Isabella
`.
`.
`
`Attorney, Agent, or Erm—Frednkson & Byron
`
`ABSTRACT
`[57]
`An implantable knee joint prosthesis which comprises a
`tibial tray, an articulating tibial insert attached to the
`tibial tray, and a femoral condylar component adapted
`to cooperatively bear upon the tibial insert. The femoral
`component has an intercondylar recess having parallel
`lateral side walls and posterior and anterior bearing
`members defining the boundaries of the recess. The
`tibial insert includes an eminence extending superiorly
`into the intercondylar recess and dimensioned and
`shaped to provide defined stabilization limits for pre-
`venting posterior-anterior dislocation while allowing
`limited translation and essentially free rotation and an-
`gulation throughout most of the total range of articula-
`tion. Metal reinforcements serve to secure the insert to
`the tray. Bearing surfaces of the eminence and the inter-
`condylar recess are so shaped as to increase the area of
`contact between them as the degree of flexion of the leg
`increases to thereby limit the contact stress transmitted
`to the eminence and to reduce wear of the eminence.
`
`12 Claims, 7 Drawing Sheets
`
`
` 47
`
`46
`
`62
`
`64
`
`“W
`
`58 54 55
`
`42
`60
`
`57
`
`K
`
`52
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 -1
`
`

`

`US. Patent
`
`Dec. 6, 1994
`
`Sheet 1 of 7
`
`5,370,699
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 2
`
`

`

`US. Patent
`
`Dec. 6, 1994
`
`Sheet 2 of 7
`
`5,370,699
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 3
`
`

`

`US. Patent
`
`Dec. 6, 1994
`
`Sheet 3 of 7
`
`5,370,699
`
`Q\§kNN:\ Z
`
`immer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 4
`
`

`

`US. Patent
`
`Dec. 6, 1994
`
`Sheet 4 of 7
`
`5,370,699
`
`‘39- 7
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 5
`
`

`

`US. Patent
`
`Dec. 6, 1994
`
`Sheet 5 of 7
`
`5,370,699
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 6
`
`

`

`US. Patent
`
`Dec. 6, 1994
`
`Sheet 6 of 7
`
`5,370,699
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 7
`
`

`

`US. Patent
`
`Dec. 6, 1994
`
`Sheet 7 of 7
`
`5,370,699
`
`Vilflfl/w/IFIW!E
`
`
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 8
`
`
`
`
`

`

`1
`
`5,370,699
`
`MODULAR KNEE JOINT PROSTHESIS
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`
`The present invention relates to implantable knee
`joint prostheses for replacement of the engaging sur-
`faces of the femur and tibia of a dysfunctional human
`knee joint, and particularly to a modular system for
`allowing the physician to select and connect together
`appropriately sized components which provide poste-
`rior stabilization of the knee while allowing essentially
`free translation, rotation and angulation through the
`range of articulation of the knee, while still avoiding
`dislocation.
`
`10
`
`15
`
`20
`
`2. Brief Description of the Prior Art
`Implantable knee prostheses for diseased and/or dam:
`aged human knees have typically employed three com-
`ponents, namely, the femoral, tibial and patellar replace-
`ment components. These components are surgically
`implanted in patients whose knee joints have deterio-
`rated resulting from injury, arthritic disease processes
`or failed previous prostheses. Surgical procedures in-
`volve the trimming of the femur and tibial joint surfaces
`to accommodate the appropriately sized components of 25
`the prosthesis. Typically, the surgeon is required to
`have available a number of differently sized and config-
`ured knee joint prostheses on hand in order to make a
`judgment as to which prosthesis to employ in the surgi-
`cal procedure with the particular patient. In the past,
`the components of the knee prosthesis have been fac-
`tory assembled or, as described in US. Pat. Nos.
`4,936,853 and 4,822,366, separate modular component
`parts of the complete knee prosthesis are maintained at
`hand for assembly in the operating room at the time of 35
`surgical implantation.
`The selection of a particular prosthesis for a knee
`joint is based largely on the condition of the patient’s
`knee and depends upon whether there is little disease or
`injury of the bones,
`ligaments and other tissues or
`whether there are severely damaged joints which re-
`quire implantation of components that have greater
`inherent stability and augments for enhancing compo-
`nent fixation.
`
`30
`
`The knee joint prosthesis described and shown in
`US. Pat. No. 3,837,009 is exemplary of a posterior stabi-
`lized prosthesis. It includes a post that extends up-
`wardly from the tibial component into a slot between
`the femoral condyles in the femoral component. An axle
`affixed to the femoral component and passes through an
`elongated hole of carefully designed shape and size in
`the post. Forces that are transmitted between the axle
`and hole can be very large, and they act at a relatively
`great distance from the tibial plateau; as a result, there is
`a fairly high degree of risk of the tibial component be-
`coming dislodged from the tibia. A number of other
`known knee joint prostheses of the type that are de-
`signed to impart stability to the knee joint by mechani-
`cal action are similarly subject to failure. In some cases,
`the implantation of the prosthesis requires removal of a
`considerable amount of bone, and failure may include
`fracture of the remaining, weakened bone.
`Between the two extremes requiring simple, small
`components (see, for example, US. Pat. No. 3,774,244)
`on the one hand and prostheses constructed to have
`inherent mechanical stability on the other is a relatively
`wide range of damaged knee joints in which most of the
`articulating surface at the joint must be replaced but
`
`45
`
`50
`
`55
`
`65
`
`2
`most ligaments and other tissues that provide stability in
`the anatomical knee joint are undamaged or can be
`repaired so that essentially normal restraint and control
`of joint function are provided by remaining soft ana-
`tomical elements. Prostheses constructed for replace-
`ment of substantially all articulating surfaces of the
`bones at the joint are often referred to as “total” condy-
`lar joint prostheses, and a number of total knee joint
`prostheses of the condylar type have been proposed
`(see, for example, US. Pat. Nos. 3,748,662, 3,816,855
`and 3,869,729).
`Generally, a total knee joint prosthesis of the condy-
`lar replacement type includes a tibial component having
`a platform portion which replaces all of the superior
`surface of the tibial plateau and substitutes for the ana-
`tomical tibial condylar surfaces. The femoral compo-
`nent has laterally spaced-apart condylar portions joined
`by an intercondylar bridge and a patellar surface and
`thus affords replacement of substantially all of the sur-
`faces of the femur that engage the tibia and patella.
`Whether or not the cruciate ligaments are retained in a
`condylar replacement prosthesis depends on the design.
`The tibial component typically includes a tibial tray
`and stem (which may be integral or modular) for surgi-
`cal attachment to the tibia and a modular articulating
`surface member (also referred to as a tibial insert) that is
`attached by a variety of mechanisms to the superior
`surface of the metal tibial tray. The tibial insert is con-
`structed of a ultra high molecular weight polyethylene,
`a known polymer used for prosthesis bearing surfaces,
`and is shaped from a pair of laterally spaced concavities
`to receive the pair of laterally spaced-apart femoral
`condylar portions. The condylar portions of the femoral
`component are smoothly curved in the anterior-post-
`erior direction generally to match in lateral profile the
`shapes of the condylar surfaces of the femur and
`smoothly convexly curved in all cross sections along
`their anterior-posterior extents.
`Modular knee prostheses of this general description
`include both non-stabilized and posterior stabilized
`types. A non-stabilized modular knee prosthesis does
`not provide any substantial restraint against rotational
`and translational freedom of movement nor any mecha-
`nism to inhibit anterior-posterior dislocation on hyper-
`extension or flexion and are exemplified by the above
`referenced ’244 patent as well as the more recent US.
`Pat. No. 4,938,769. These total knee prostheses require
`only minor resection of bone for implantation, do not
`require severance of the posterior cruciate ligaments,
`and are suitable for relatively mild deterioration of the
`knee joint.
`Posterior stabilized knee prostheses are used in poste-
`rior cruciate ligament deficient knee joints. They are
`characterized by an eminence extending superiorly be-
`tween the parallel concavities of the tibial insert and
`into a recess or box-like intercondylar portion of the
`femoral component. The cruciate ligaments are nor-
`mally severed, although the collateral ligaments and
`tendons remain intact.
`
`The intercondylar recess is formed usually with par-
`allel lateral side walls spaced-apart by anterior and pos—
`terior bridge members which may act as camming mem-
`bers for bearing against anterior and posterior camming
`surfaces of the eminence through virtually the entire
`range or a portion of the range of flexion to inhibit
`dislocation of the joint at hyper extension and flexion.
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 9
`
`

`

`5,370,699
`
`3
`A number of posterior stabilized knee prostheses
`have been proposed and introduced for clinical use,
`including those. disclosed in US. Pat. Nos. 4,209,861,
`4,298,992, 4,213,209 and 5,007,933. The eminences and
`intercondylar portions disclosed in these patents have a
`variety of slows and dimensions to which greater or
`lesser degrees of restraint and freedom of relative move-
`ment are attributed. In the ’861 patent, virtue is ascribed
`to virtually total contact of the posterior camming sur-
`face and camming member through the entire range of 10
`flexion, and the lateral side walls of the eminence and
`the recess are quite closely spaced to allow minimal
`translation or varus-valgus movement and virtually no
`rotational movement.
`The ’992 patent discloses an eminence and recess
`shaped to provide positive camming surface and mem-
`ber contact only after substantial flexure. The lateral
`side walls of the eminence and recess disclosed in the
`’992 patent appear to be parallel and closely spaced,
`permitting little if any lateral translation or rotation.
`The eminence and recess lateral side walls disclosed in
`the ’209 patent are not parallel. The lateral walls of the
`eminence converge superiorly and away from the lat-
`eral side walls of the recess and also converge anteri-
`orly.
`The ’209 patent shows the spaced concavities of a
`tibial articulating surface member being smoothly radi-
`used with the rising side walls of the eminence to accept
`femoral condylar portions shaped to contact at least a
`portion of the side walls during articulation, rotation
`and translation. The degree of divergence between the
`side walls of the eminence and the walls of the recess
`superiorly limits the degree of lateral angulation and
`prevents extreme translation.
`The ’933 patent discloses an eminence and recess
`shaped to provide posterior camming surface and mem-
`ber contact from about 30° through full flexion. The
`lateral side walls of both the eminence and recess are
`relatively closely spaced and the parallel portions of
`both tend to converge superiorly. As in the ’209 patent,
`at least a portion of the lateral side walls of the emi—
`nence are angled to converge anteriorly. The angula-
`tion of the ’933 patent is relatively small to provide
`relatively limited rotation of the femoral and tibial com-
`ponents within a relatively limited range of flexion in
`comparison with the configuration disclosed in the ’209
`patent.
`The physiology of the normal knee is such that as the
`leg is flexed, the net force component tending to trans-
`late the femoral eondyles anteriorly of the tibial insert
`(referred to sometimes as a shear force) increases. As
`mentioned above, forward displacement of the femur is
`resisted, in the case of posterior stabilized knee prosthe-
`ses, by contact betWeen the respective posterior bearing
`surfaces of the tibial eminence and the intercondylar
`recess. The posterior bearing surface of the femoral
`component shown in the ’933 patent is sharply rounded
`and makes essentially point or line contact with the
`confronting bearing surface of the tibial eminence
`throughout the range of flexure of the leg. In somewhat
`similar fashion, the area of contact between the poste-
`rior bearing surfaces of the components shown in the
`’992, ’861 and ’209 patents appears to be essentially
`constant throughout the range of flexure in which these
`surfaces are in contact.
`
`4
`of the tibial insert to the tibial tray. Various attachment
`mechanisms of tibial insert to tibial trays have been used
`in the past; e.g., the matching dovetail and slot “snap-
`loc ” system of the AXIOM TM Total Knee System or
`the dovetails and locking pin of the CPD (Central Post
`Design) tibial components, both sold by the assignee of
`the present invention. In the context of a posterior stabi-
`lized knee prosthesis, such locking mechanisms have
`been disclosed in the ’209 patent and in US. Pat. Nos.
`4,714,474 and 5,007,933.
`Thus a number of posterior stabilized knee prosthesis
`have been proposed that provide varying degrees of
`restrained to unrestrained relative anteroposterior, rota-
`tional and translational movement of the femoral and
`tibial components. A need remains for a knee joint
`prothesis that provides appropriate roll back and a high
`degree of rotation and angulation to mimic the freedom
`of movement of the normal knee while advantageously
`limiting anteroposterior dislocation (subluxation).
`SUMMARY OF THE INVENTION
`
`There is provided, in accordance with the present
`invention, a total knee joint prosthesis of the condylar
`type which is constructed to provide essentially free
`translation, rotation and angulation throughout most of
`the total range of articulation and to provide restraint
`and control at and near full extension and at the high
`end of the range of flexion, and having securely at-
`tached components.
`More particularly, a knee joint prosthesis, according
`to the present invention, comprises a femoral compo-
`nent which includes a pair of laterally spaced-apart
`condylar portions having external surfaces that are
`smoothly curved in the anteroposterior direction gener-
`ally to match in lateral profile the shapes of the condy-
`lar surfaces of the femur and smoothly convexly curved
`in all cross sections along their anteroposterior extents.
`The condylar portions are interconnected by a box-like
`intercondylar portion which defines a recess that opens
`toward the tibial plateau and has spaced-apart lateral
`side walls, an anterior bearing surface and a posterior
`cam bearing surface.
`The tibial component of the prosthesis includes a
`tibial platform portion which may be made of ultra high
`molecular weight polyethylene and having on its rela-
`tively flat superior surface a pair of laterally spaced~
`apart concavities, each of which is shaped and dimen-
`sioned to receive and support in nested relation a re-
`spective condylar portion of the femoral component in
`all normal angulations of the knee. A central eminence
`extends upwardly from the relatively flat superior sur-
`face of the tibial component between the concavities
`and into the intercondylar recess of the femoral compo-
`nent.
`The lateral side walls of the tibial eminence have
`anteriorly extending and posteriorly extending surfaces
`and also angled surfaces in planes that converge anteri-
`orly from the parallel surfaces, the posteriorly extend-
`ing surfaces being essentially parallel to the respective
`lateral side walls of the recess and the anteriorly extend-
`ing surfaces being angled with respect to antero-post—
`erior planes. The width of the eminence is selected with
`respect to the distance between the parallel side walls of
`the recess such that no contact occurs in normal articu—
`lation and a relatively high degree of varus/valgus an-
`gulation, translation and/or rotation of the tibial and
`femoral components must take place before any contact
`occurs. The freedom of movement thus provided is
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 10
`
`5
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`65
`
`In conjunction with pOsterior stabilized knee prosthe-
`ses having a pronounced eminence, the forces brought
`to bear against the eminence requires secure attachment
`
`

`

`5,370,699
`
`6
`loads that otherwise would lead to wear or loosening of
`the femoral and/or tibial components.
`The knee joint prosthesis of the present invention is
`further characterized by a secure attachment of the
`tibial insert to the tibial tray that bears the loads placed
`on the eminence when it is contacted by the side walls
`and/or the anterior stop surface or posterior camming
`member.
`
`5
`such that the condylar portions must be displaced later-
`ally and out of the concavities before contact between
`the confrontingside walls of the tibial eminence and the
`recess is made.
`For the purpose of controlling the stress (force per
`unit area) that is transmitted anteriorly against the pos-
`terior bearing surface of the tibial eminence by the op-
`posing bearing surface of the recess,
`the respective
`bearing surfaces are so shaped as to increase their area
`of contact as the degree of flexion of the knee increases.
`These and other features of the invention are realized
`in a knee joint prosthesis comprising: a femoral compo-
`nent adapted to be implanted on the condylar portion of
`the femur and having a pair of laterally spaced-apart
`condylar portions, each of which has an external sur-
`face that is smoothly convexly curved in the antero-
`posterior direction and generally matches the shapes in
`lateral profile of the condylar surfaces of the femur and
`that is smoothly convexly curved in all cross sections
`along its antero—posterior extent. A box-like intercondy-
`lar portion interconnects the condylar portions and
`defines an intercondylar recess having lateral side walls
`spaced-apart a certain distance, an anterior stop surface
`and a posterior beating surface serving as a camming
`member. A tibial component is adapted to be implanted
`on the tibial plateau and includes a plate-like platform
`portion having on its superior surface a pair of laterally
`spaced-apart concavities to receive in nested relation
`the condylar portions of the femoral component. A
`central eminence extends superiorly from the platform
`portion and is adapted to be received in the intercondy-
`lar recess of the femoral component. The eminence has
`lateral surfaces, an anterior surface and a posterior sur-
`face. The relative positions and shapes of the anterior
`and posterior surfaces of the eminence and recess of the
`prosthesis, as implanted in the knee joint, permit sub-
`stantially free relative antero-posterior translation of the
`components while restraining excessive anterior and
`posterior movements. The lateral surfaces of the emi-
`nence includes posterior portions essentially parallel to
`the lateral side walls of the recess to define a width of
`the eminence substantially narrower than the distance
`between the spaced-apart lateral side walls, and anterior
`portions angled with respect
`to anterior-posterior
`planes for enabling medial/lateral translation and sub-
`stantial varus/valgus angulation and relative rotation
`between the tibial component and the femoral compo-
`nent within a substantial portion of the range of flexion.
`The respective posterior bearing surfaces of the tibial
`eminence and of the intercondylar recess are so shaped
`as to increase their area of contact as the degree of
`flexion of the leg increases.
`Thus in accordance with the present invention a high
`degree of freedom in rotation, angulation and transla-
`tion is involved in the fashion of a non-stabilized knee
`prosthesis while the posterior and anterior camming
`surfaces and members of the eminence and recess, re-
`spectively, provide anteroposterior stability with re—
`duced stress against the tibial eminence.
`The advantages of the joint of the present invention
`are kinematic in nature. The narrow eminence and lim-
`ited range of contact provide posterior rollback and
`prevent posterior tibial dislocation, thus mimicking the
`normal action of the posterior cruciate ligament. The
`collateral ligaments and remaining soft tissue structures
`provide the constraint in rotation and angulation within
`the wide range allowed by the prosthesis and absorb
`
`10
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`15
`
`20
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`25
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`3O
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`35
`
`40
`
`l
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`45
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`50
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`55
`
`65
`
`The tibial insert, fabricated of low friction, ultra high
`molecular weight polyethylene, has metal inserts fitted
`in it to reinforce its attachment upon the superior sur-
`face of the tibial tray. The attachment is accomplished
`by a pair of dovetail-shaped grooves in the inferior
`surface of the tibial insert shaped to receive a like pair of
`dovetail-shaped bosses on the superior surface of the
`tibial tray. A recess in the superior surface of the tray
`extends perpendicularly to the bosses and receives a
`metal pin reinforced bars extending inferiorly from the
`tibial insert to lock it in place. The dovetail-shaped
`grooves of the insert are reinforced with a metal insert
`to enhance the strength of attachment to the tray.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The features of the present invention can be best
`understood, together with further objects and advan-
`tages thereof, by reference to the following description
`taken together with the appended drawings in which
`like reference numbers refer to like parts, and which
`describe some embodiments of the present invention:
`FIG. 1 is an exploded perspective view of the assem-
`bly of one embodiment of the knee joint prosthesis of
`the present invention;
`FIG. 2 is an anterior elevation view of the femoral
`component of the knee joint prosthesis of FIG. 1;
`FIG. 3 is a side elevation view of the femoral compo-
`nent;
`FIG. 4 is a posterior elevation view of a femoral
`component in partial cross sections:
`FIG. 5 is a top view of the femoral component;
`FIG. 6 is a side cross section View along section lines
`6—6 of FIG. 4;
`FIG. 7 is an anterior elevation view of the tibial tray
`component of the knee joint prosthesis of FIG. 1;
`FIG. 8 is a top view of the tibial tray component;
`FIG. 9 is a side elevation view of the tibial tray com-
`ponent;
`FIG. 10 is an anterior elevation view of the first em—
`
`bodiment of a tibial insert of the knee joint prosthesis of
`FIG. 1;
`FIG. 11 is a side elevation view of the tibial insert of
`FIG. 10;
`FIG. 12 is a top view of the tibial insert of FIG. 10;
`FIG. 13 is a cross-section view of the tibial insert of
`FIG. 12 taken along lines 13—13 of FIG. 12;
`FIG. 14 is a bottom view of the tibial insert of FIG.
`10;
`FIG. 15 is partially broken away anterior view of the
`tibial insert of FIG. 10;
`FIGS. 16A to 16F are schematic, cross sectional
`views showing particularly the contact between ele-
`ments of the prosthesis as the leg is flexed through vari-
`ous angles; and
`FIG. 17 is a schematic view of the prosthesis of
`FIGS. 16A—16F showing restraint of anterior move-
`ment of the femur.
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 11
`
`

`

`7
`DETAILED DESCRIPTION OF THE
`
`5,370,699
`
`PREFERRED EMBODIMENTS
`Referring how to the drawings, and especially to
`FIG. 1 thereof, a knee joint prosthesis constructed in
`accordance with one embodiment of the invention is
`illustrated in exploded view. The prosthesis includes the
`femoral component 30 and tibial component 40 com-
`prising a tibial tray 42 and tibial insert 44. If desired, the
`tibial component 40 may be provided as an integral
`component fabricated, for example, from ultra high
`molecular weight polyethylene. In the depicted em-
`bodiment, the tibial insert 44 is fitted onto the proximal
`surface 46 of the tray 42 in a manner to be described.
`The femoral component 30 includes the two condyles
`32 and 34, a patellar groove 36 and an intercondylar
`recess 38 described in greater detail hereafter in con-
`junction with FIGS. 2-6.
`The tibial insert 44 has a pair of concavities 48, 49
`carved into the generally flat surface 47 for receiving
`the bearing surfaces of the condyles 32 and 34. Arising
`centrally from the insert is a superiorly projecting emi-
`nence 50 adapted to fit within the recess 38 of the femo-
`ral component 30 in a manner to be described hereafter.
`The tibial tray 42 includes an inferiorly extending
`tibial stem 52 to be received in the cavity created surgi-
`cally in the tibia for stabilizing its attachment thereto. A
`pair of longitudinally extending raised dovetails 54 and
`56 extend above the surface 46 of the tray 42 and match
`cutout grooves in the distal or inferior surface of the
`insert 44 in a manner to be described hereafter. Four
`holes 58, 60, 62, 64 are provided through the surface 46
`of the tibial tray 42 to receive tibial elements positioned
`against 4, the inferior surface 66 where necessary to
`achieve proper contact with the remaining tibial bone.
`FIGS. 2-6 depict in greater detail the design and
`features of the femoral component 30. The femoral
`component 30 is constructed in one piece, preferably of
`a biocompatible high-strength alloy, such as a cobalt-
`chrome alloy, that includes the two condylar compo-
`nents 32 and 34 each having an inferior, convexly
`shaped articular surface 33 and 35, respectively, which
`bear against the concavities 48, 49, respectively, of the
`tibial insert 44. The condylar portions 32, 34 are joined
`together by the patella region 36 depicted in FIG. 2 and
`the box-like bridging portion 70 depicted in the other
`figures. The box-like portion 70 defines the intercondy—
`lar recess 38 and includes parallel side walls 74 and 76
`spaced-apart a distance D. The intercondylar recess
`may simply be open at its top, as shown at 72 in FIG. 6,
`or may be supplied with a superior wall or roof. A
`sloping surface 78 extending generally inferiorly and
`anteriorly defines the anterior stop surface at one end
`wall of the recess 38. The posterior end wall of the
`recess 38 is defined by the camming bearing member 80,
`the bearing surface of which continuously varies from a
`gently rounded posterior section 81 to a somewhat
`more severely rounded anterior section 83. As shown
`best in FIG. 6, surface section 81 is formed on a radius
`that is much greater (at least twice as great) as that of
`the more severely rounded surface section 83.
`FIGS. 7—9 illustrate the tibial tray 42 in top and eleva-
`tion views. A pair of elongated, dovetail-shaped bosses
`54, 56 extend superiorly from the surface 46 of the tray
`42 and parallel to one another. An elongated recess 57 is
`cut into the surface 46 perpendicular to the direction of
`the bosses 54, 56. The tibial tray 42 corresponds to the
`prior art AXIOM TM tibial tray sold by the assignee of
`
`10
`
`15
`
`20
`
`25
`
`3O
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`the present invention, wherein the bosses 54, 56 and
`recess 57 act to retain a tibial insert 44 which has match-
`ing dovetail shaped grooves cut in its inferior surface
`and a boss 51 projecting from that surface that engages
`in the slot 57 when the dovetail bosses 54 and 56 are
`fully inserted into the matching grooves 53, 55. The
`through-holes 58, 60, 62, 64 each receive a cancellous
`screw in holes drilled into the tibia to aid in fixation of
`the tibial component.
`The grooves and bosses are shown more clearly in
`FIGS. 10 to 12 which illustrate a first embodiment of
`the tibial insert 44 of the present invention. In FIG. 10,
`an elevation view of the tibial insert 44 depicts an ante-
`rior view of the stop member 51 which snaps into the
`groove 57 and the elongated dovetail-shaped cutout
`grooves 53 and 55 that engage with the dovetail-shaped
`bosses 54 and 56, respectively. To attach the tibial insert
`44 to the tibial tray 42, the grooves 53 and 55 are lined
`up with the dovetail-shaped bosses 54 and 56 and ad-
`vanced in the direction of the arrow 61 depicted in FIG.
`11 until the projection 51 snaps into the groove 57.
`Turning now to the shape and construction of the
`eminence 50 and the concavities 48, 49, it should first be
`noted that the concavities 48, 49 are cut into the upper
`surface 47 of the tibial insert 44. The upper surface 47
`has an upper level 47’ connected with the lower level
`47” alongside the eminence 50.
`In FIG. 10, the eminence 50 is shown having parallel
`side walls of a width equal to ex, that is, narrower by
`a distance X than the distance D between the lateral side
`walls 74 and 76 of the recess 38 depicted in FIGS. 2-6.
`FIG. 10 also shows the stop surface 82 sloping anteri-
`orly and adapted to engage the sloping surface 78 of the
`bridging portion 70 depicted in FIGS. 3 and 6 upon
`hyper-extension of the knee joint prosthesis. The sur-
`face 82 is bounded by the anteriorly convergent planar
`side wall surfaces 84 and 86 which are oriented at an
`angle of about 15° to the posterior parallel side walls 88
`and 90. The posteriorly descending cam or bearing
`surface 92 has a slight convex curvature in a lateral
`direction and has a gentle concave curvature in the
`antero-posterior direction to act as a cam follower for
`the cam lobe bearing member 80 of the bridging portion
`70 depicted in FIGS. 3 and 6,’ the latter curvature being
`such as to match the antero-posterior curvature of the
`gently rounded surface 80.1 of the posterior bearing
`surface of the femoral component. A flattened peak 94
`caps the eminence 50 so that it fits generally within the
`opening 72 of the box 70.
`In operation, the articulating surfaces 33 and 35 bear
`against the dished-out concavities 48 and 49 and allow
`the knee joint to articulate between a hyper-extended
`and a fully flexed position. Normally there is no contact
`in the range of normal articulation or leg angulation
`from full extension to about 65°—70‘ (preferably 69") of
`flexion. However, if subluxation of the femoral compo-
`nent with respect to the tibial component occurs, as
`shown in FIG. 17, contact between the beating surfaces
`83 and 92 of the respective femoral and tibial compo-
`nents restrains dislocation of the knee.
`
`As normal flexion continues beyond e.g., 69‘, the
`posterior cam beating surface 83 contacts and bears
`against the posterior camming surface 92 and gradually
`rides up that surface as the degree of flexion increases
`through the remaining range to the fully flexed position.
`The relative positions of the respective posterior bear-
`ing surfaces is illustrated in FIGS. 16A-16F. As flexiOn
`continues beyond about 69°, the amount of contact
`
`Zimmer Holdings, Inc. and Zimmer, Inc.
`Exhibit 1014 - 12
`
`

`

`9
`between the respective bearing surfaces increases. In
`FIG. 16 D, for example, the area of contact between the
`posterior bearing surfaces is rather small as contact first
`occurs at 69°: whereas in FIG. 16 F, the contact area
`has substantially increased. Whereas the posterior bear-
`ing surface 83 of the femoral component is of metal, the
`opposing posterior bearing surface 92 of the tibial emi-
`nence is of polyethylene and is much softer and subject
`to damage. By increasing the area of contact between
`these surfaces, the anteriorly directed shear force is
`spread over a larger area as thi