United States. Patent [191
`Waugh et al.
`'
`
`[54] ARTICULATED TWO-PART PROSTHESIS
`REPLACING THE KNEE JOINT
`[75] Inventors: Theodore R. Waugh; Richard C.
`Smith, both of Irvine; Sanford H.
`Anzel, Orange; Caesar F. Orofino,
`Orange, all of Calif.
`[73] Assignee: The Regents of the University of
`California
`Feb. 14,1973
`[221 Filed:
`[211 App1.No.:332,509
`
`[52] U.S. Cl. ..................................... .. 3/1, 128/92 C
`[51] Int. Cl. ............................................ .. A61f 1/24
`[58] Field of Search..... 3/1; 128/92 C, 92 CA, 92 R
`
`[56]
`
`3,715,763
`3,728,742
`3,774,244
`
`References Cited
`UNITED STATES PATENTS
`2/1973
`Lind .......................................... .. 3/1
`4/1973
`Link ......... ..
`3/1
`11/1973 Walker ..................................... .. 3/1
`OTHER PUBLICATIONS
`Vitallium Surgical Appliances (catalog), Austenal
`Medical Div., Howmet Corp., New York, N.Y., 1964,
`page 62 relied upon, M.G.H. Femoral Condule Re‘
`placements, No. 6662 and Elliot Knee Plates, No.
`69646.
`Muller-Charnley Type Total Hip Prosthesis (Adver
`tisement by Howmedica International, lnc.), The .lour»
`
`3,869,731
`. [111
`[45] Mar. 11, 1975
`
`nal of Bone & Joint Surgery British Vol. 53-B, No. 2,
`May 1971.
`Vitallium Surgical Appliances (catalog), Austenal
`Medical Div., Howmet Corp., New York, N.Y., 1964,
`page 30, McBride Acetabulum Cups, No. 6429.
`
`Primary Euzmincr-Ronald L. Frinks
`
`ABSTRACT
`[57]
`The invention provides a two-part knee prosthesis
`comprising components which, respectively, are im~
`planted in the distal end surface of the femur and the
`proximal end surface of the tibia and which co
`operate to provide a substituted articulated knee joint.
`The femoral component has an upwardly directed an
`terior ?n for upward driven implantation into the dis
`tal part of the femur shaft and two transversely spaced
`femoral condyle replacement support members each
`of which has a downwardly directed bearing surface
`which is curved in cross section and in side elevation,
`the curvature in side elevation being on successively
`decreasing radii from the anterior portion to the pos‘
`terior portion of the prosthesis, The tibial component
`is generally circular and ?at in configuration whereby
`it will lie on the prepared proximal surface of the tibia
`and its upper surface has a circular upwardly facing
`groove therein which receives the two transversely
`spaced femoral condyle replacement support member
`surfaces of the femoral prosthesis.
`3 Claims, 8 Drawing Figures
`
`Smith & Nephew Ex. 1054
`IPR Petition - USP 8,377,129
`
`

`
`P,r1TENTE[]HARl
`
`1 I975
`
`3,859,731
`
`~mm1q2
`
`

`
`PMENTEUHMH NW5
`
`3,868,731
`
`Mnegz
`
`
`
`/
`
`30
`
`38
`//
`
`\
`
`’
`
`2 6
`
`
`
`

`
`3,869,731
`
`5
`
`20
`
`25
`
`30
`
`35
`
`40
`
`1
`ARTICULATED TWO-PART PRYOSTHESIS
`REPLACING. TI'IE'KNEE JOINT
`BACKGROUND OF THE INVENTION
`The normal human knee is a joint which —is con
`structed to permit movement in flexion and rotation.
`Flexion is the normal bending of the knee and may be
`performed through an angular movement from approx
`imately —6° to 150°. Rotation is the relative movement
`of the tibia and femur about their vertical intramedul
`lary axes and is permitted by a range of motion in the
`knee joint from approximately —l5 to +15, an arc of ‘
`30°. The condylar curves of the distal femur are not
`simple curves but move relatively to the tibial plateau
`in flexion of the knee in such a waythat the areas of
`contact on the condyles constantly change in location
`because of rolling and sliding movements, and also
`each distal femoral condyle surface presents a curve of
`constantly decreasing radii as the amount or degree of
`flexion increases. Exact reproduction of the structure
`and operation of a normal, healthy knee would be ideal
`in knee arthroplasty but has never been achieved.
`Many forms of knee arthroplasty have been de
`scribed in the literature and used in practice, all of
`which are based on one of two principles. The ?rst re
`quires the interposition of materials between the bony
`surfaces after removal of synovial membranes and ar
`ticular cartilage, while in the second the knee joint is
`resected and replaced by a metal hinge (Walldius 1957,
`Shiers I960). Material interposed between the bony
`surfaces has included Chromicised pig’s bladder (Baer
`I918), facia lata (Putti I920), skin (Brown, McGraw
`and Shaw 1958), nylon (Kuhns and Potter 1950) and
`Vitallium (Campbell 1940). Such materials often had
`serious disadvantages. Chromicised pig’s bladder was
`not tolerated by the tissues, and fascia lata, skin and
`nylon wore away after a short time. Hinge arthroplasty
`can work well but the hinge prosthesis does not permit
`the complex movements of the knee in flexion and ro
`tation, and resection of the knee joint results in unde
`sirable shortening of the limb if for any reason the pros
`thesis must be removed for subsequent arthrodesis.
`
`SUMMARY OF THE INVENTION
`The present invention overcomes these disadvan
`tages of known knee arthroplasty and provides a two
`part knee prosthesis including a distal femoral compo
`nent having two transversely spaced bearing surfaces
`facing the tibia and corresponding closely in position
`and shape to the normal human femoral condyles and,
`in cooperation with this femoral component, a tibial
`component consisting of a generally circular ?at bear
`ing plate constructed and adapted to rest on, and be at
`tached to, the prepared proximal plateau surface of the
`tibia and in its upper surface having a circular upwardly
`facing concentric groove which receives the bearing
`surfaces of the support members of the femoral compo
`nent. The lower central axis or bottom of this groove
`is level, ‘by which it is meant that it lies in one plane.
`This two-part prosthesis permits reproduction of the
`?exional, rotational, rolling and sliding movements of
`the normal human knee.
`DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a perspective view showing the two-part
`prosthesis provided by the invention in place in associa
`tion with the ?exed human knee;
`'
`
`50
`
`60
`
`65
`
`2
`‘FIG. 2 is a lateral or side elevational view of the knee
`joint and the implanted prostheses shown in FIG. 1 with
`> the knee joint simulating 0° flexion.
`FIGS. 3 and 4 are, respectively, top and posterior ele
`vational views of the femoral prosthesis provided by the
`invention;
`FIGS. 5, 6 and 7 are, respectively, top, posterior and
`bottom views of the tibial prosthesis provided by the
`invention,
`and
`FIG. 8 is an anterior perspective view showing the
`preferred method of preparing the proximal tibial pla
`teau for implanting the tibial prosthesis.
`DESCRIPTION OF THE INVENTION
`The invention is a two-part prosthesis which may be
`substituted for the malfunctioning or diseased human
`knee, leaving the cruciate and collateral ligaments in
`place and functioning normally. The parts of the pros
`thesis are implanted, respectively in the distal femur
`and proximal tibia plateau after suitable preparation
`thereof, and when implanted permit flexion, rotation,
`rolling and sliding movements substantially reproduc~
`ing those movements of the normal human knee.
`The femoral component of the two-part prosthesis
`provided by the invention is preferably of integral con
`struction and may be made by die casting, molding or
`otherwise suitably forming stainless steel, cobalt
`chrome alloy, titanium or other suitable metallic im
`plant‘material. This component is disclosed in FIGS. 1
`to 4 of the drawings and comprises a lower part which
`is designated generally by the letter A and which pro
`vides two downwardly facing bearing surfaces which
`substitute for the condyles of the femur and which rest
`on and co-operate with the tibial component provided
`by the invention. The femoral component also com
`prises an upper part B which extends upwardly from
`the lower part A and is constructed and adapted to be
`driven upwardly into the femur shaft in order to im
`plant the component into the femur.
`The lower part A of the femoral prothesis compo;
`“nent”a)mprises‘two'sbbstantiam! parallel transversely
`spaced support members 2, 4, each of which has on its
`bottom a downwardly facing bearing surface which are
`45
`shown at 6, 8 and each of which is convex and curved
`in both cross section and in side elevational views.
`These bearing surfaces are spaced apart by a distance
`substantially equal to the spacing of the natural femoral
`condyles and they therefore substitute for these con
`dyles in cooperating with the tibial component of the
`prosthesis to provide knee action in the operation of
`the two-part prosthesis provided by the invention. The
`transverse or cross sectional curvature of each of these
`bearing surfaces is a regular .curve forming part of a .cir
`cle and is of relatively shallow depth. However, the lat
`eral or side elevational shape of the bearing surface of
`each support member is not a simple curve forming
`part of a circle, but is formed of a continuous series of
`curves of constantly diminshing radii from the anterior
`portion of the curve at C to the posterior portion at D.
`This curvature is‘ particularly shown in FIG. 2 of the
`drawings, in which the anterior portion is designated by
`the letter C and the posterior portion by the letter D,
`the anterior portion being at the front of the knee and
`the posterior portion being at the rear of the knee when
`the prosthesis is in place. It will be seen that the curva
`ture near the anterior portion has a relatively long ra>
`
`55
`~
`
`

`
`3,869,731v
`
`15
`
`25
`
`35
`
`40
`
`3
`dius and that the radius of curvature of each increment
`of length of the bearing surface decreases as the surface
`approaches the posterior end, being a minimum at D.
`The curvature of each of these bearing surface repro
`duces that of the natural femoral condyle in the same
`location in the human knee. Each of the contact or
`bearing surfaces 6, 8 is polished to a mirror ?nish, while
`the other parts of the component may have a dull fin-.
`ish.
`The upper part 'B of the femoral component provides
`meansfor connecting the support members and bear
`ing surfaces of the lower part A to the femoral shaft,
`and this part provides a V-shaped assembly of three
`elongated thin fins which are constructed and adapted
`to be implanted in the osteotomized areas of the femur
`and which serve the purpose of stabilizing and main
`taining-the placement of the component. These fins are
`provided by a central upwardly extending ?n 10 which
`has inverted V-shaped and two ?ns l2, 14 each of
`which extends forwardly and upwardly from the lower
`end of one of the arms of the inverted V-shaped central
`fin 10 and which are connected to the upper surfaces
`of the two support members 2, 4. Each of the three fins
`10, 12, 14 of this upper part B is inverted V-shaped in
`cross section to provide an upwardly facing edge 16,
`permitting the upper part B of the component to be
`driven into the distal surface of the femur and upwardly
`into the femur shaft after removal of the condyles in the
`operative procedure of implanting the prosthesis. Fins
`l2 and 14 form an angle slightly more than 90° with re
`spect to fin 10 to provide stability’ of the femoral unit
`in full flexionv with the tibial prosthesis.
`The tibial component of the prosthesis is disclosed in
`FIGS. 1, 2 and 5 to 8 and, as particularly shown in FIG.
`8, is adapted to be connected to and rest on the proxi
`mal plateau surface of the tibia after preparation
`thereof in the suggested manner described hereinafter.
`The tibial component is shaped as a disc being of gener
`ally flat circular configuration having an upper surface
`20, a lower surface 22 and an outer peripheral wall 24.
`The component is C-shaped in plan, having the two
`arms 26, 28 separated by space 29, and its upper sur
`face 20 is provided with a circular concave groove 30
`which is concentric withthe side wall 24 and which in
`cross section is part circular and has the same cross
`sectional shape and dimension as that of each of the
`downwardly facing surfaces 6, 8 of the support mem
`bers 2, 4 of the femoral component, by reason of which
`such surfaces are received in and exactly fit the spaced
`parts of the circular upwardly facing groove in the tibial
`component when the parts are in place.
`' The lower surface 22 of the tibial component is gen
`erally ?at but is formed with two groups of curved rings
`or ridges 32, 34. One group 32 is formed on the bottom
`‘ surface of one arm of the C-shaped component, while
`the other group is formed on the bottom surface of the
`other arm. The ridges of each group are part circular
`and concentric in plan and those of one group are
`curved oppositely to those of the other. Each ring or
`ridge is shaped as a triangle in cross section and has a
`sharp edge 36 so that it will bite firmly into the bone of
`the prepared tibial plateau.
`The tibial component of the prosthesis is fabricated
`from ultra high molecular weight polyethylene or other
`suitable implant material, and has a wire 40 positioned
`in a groove formed in its side wall 24. The wire serves
`as an X_ray locator and as a reference line to permit ob
`
`4
`servation of wear characteristics of the material of the
`prosthesis while in use. X-rays taken at one‘ year or
`some such interval will indicate’any variations in dis
`tance between the bottom edge of the femoral compo
`nent and the wire.
`.
`'
`The two prosthetic components are designed to work
`together in a unit in such a fashion as to emulate the
`normal motion characteristics of a healthy human
`' knee. Due to the configuration of the condyles there
`are both flexion and rotational motions involved in the
`flexion of the human knee, and the configuration of the
`prostheses permits both motions. The position of the
`bearing surfaces 6, 8 in the laterally spaced parts of
`groove 30 in the tibial prosthesis and the shape of the
`bearing surfaces themselves permit ?exion of the tibia
`with respect to the femur from approximately-6° to
`approximately +150° thus substantially reproducing
`the range of flexional movement of the human knee.
`The lateral or side elevation shape of each of the bear
`ing surfaces 6, 8 closely approximates the average con
`?guration of the surface of the correspondingly posi»
`tioned femoral condyle and thus permits a combined
`rolling and sliding motion of the bearing surfaces of the
`femoral component on the tibial component which cor
`responds to the motions of the normal human condyles.
`The circular shape of the groove 30 of the tibial com
`ponent permits relative rotational movement of the fe
`moral and tibial components corresponding to the
`same movement of parts of the human knee, the hear
`ing surfaces 6, 8 riding levelly in the groove 30 during
`rotational movement of the knee and without riding up
`on the sides of the groove. The two components of the
`prosthesis are designed so that in use the theoretical
`limits of motion are from -6° to +l50° of ?exion and
`i 15° of rotation.
`If the nature of the case requires or permits it, the fe~
`moral component of the complete prosthesis may con
`sist of only one of the support members 2, 4 and the tib-l
`ial component may consist of only one-half of the cir
`cular tibial component described above.
`
`45
`
`50
`
`55
`
`60
`
`65
`
`A SUGGESTED SURGICAL PROCEDURE
`UTILIZING THE PROSTHESIS PROVIDED BY THE
`INVENTION
`-
`The patient lies supine on the operating room table,
`with a padded pressure tourniquet in place on the
`thigh. The knee is draped free and the distal portion of
`the table may be dropped so that the knee hangs at 90°
`of flexion if desired. A long medial parapatellar incision
`is made and the patella is subsequently everted and dis
`placed laterally. This provides excellent exposure of
`the anterior aspect of the entire knee joint. Care should
`be taken not to detach a significant part of the patella
`tendon insertion on the tibia, for if this is inadvertently
`done the prolonged immobilization required for heal
`ing jeopardizes the attainment of flexion.
`With the knee in extension and using an air saw and
`special blades a transverse plane cut is made in the dis
`tal femur perpendicular to both the AP and lateral ana
`tomical axes of the tibia, removing the prominent por
`tion of each of the frontal condyles and leaving a plane
`surface or plateau. Care should be taken not to sever
`the cruciate ligaments, if present. This cut may be com
`pleted with the knee ?exed or extended. The thickness
`of this cut will preferably be approximately ‘A inch and
`additional bone may be easily removed later.
`
`

`
`3,869,731
`
`20
`
`25
`
`30
`
`40
`
`45
`
`5
`The knee must now be ?exed to 90° and the posterior
`condyles removed in the frontal plane. A template is
`available for determining the maximum amount of the
`posterior condyles that should be removed. The tem
`plate is placed on the cut surface with its top edge
`aligned with the anterior edge of the osteotomy and the
`posterior osteotomy is made along the bottom edges of
`the template. It is important that an adequate amount
`of posterior condyle bone be removed as failure to do
`so will prevent flexion beyond 90°. However, removing
`too much bone will bring the prosthesis forward and
`cause it to interfere with the excursion of the patella
`during extreme flexion. The femoral template is de
`signed so that it may be implaced against freshly cut
`bone of the femur in order to accurately show the
`proper position for osteotomy of the posterior con
`dyles. The posterior corners are now removed
`(“rounded of ") by a 45° cut which representsa minor
`trim of the sharp corners made by the ?rst two osteoto
`mies.
`A femoral saw guide is now placed in position on the
`condyles, the reference line on the topedge of the saw
`guide indicating the location of the anterior edge of the
`prosthesis, if emplaced without methyl methacrylate.
`The air saw is then used to cut slots for the reception
`of the fins 10, 12, 14 of the prosthesis. A femoral trial
`prosthesis is then inserted to verify the femoral osteoto
`mies, and is then removed with an extractor. If utiliza
`tion of methyl-methacrylate is desired, the fin slots are
`enlarged and undermined with the air saw ‘to accommo
`date fins and cement. The trial prosthesis is identical in
`size and configuration to the prosthesis which is actu
`ally used and which has been described, except that the
`contact or weight-bearing surfaces are not polished to
`a mirror finish. This device is utilized in surgery some
`what like an instrument used to determine the proper
`fit between prosthesis and bone without risking a regu
`lar prosthesis to the exposure of being scratched or
`damaged-by such handling.
`‘
`Attention is then directed to the tibial surface. The
`menisci, ifpresent, should be excised. Four sagittal cuts
`are made for the tibial prosthesis and two transverse
`cuts are made 1/8 inch beneath the articular surface of
`the tibia, and the sections of the tibial plateau are re
`moved. It is important that these cuts be ‘complete, as
`irregular fractures may occur posteriously otherwise. A
`similar midline transverse cut is made to an AP depth
`of ‘A inch only, and this is joined by a frontal cut at right
`angles in order to accommodate the anterior bridging
`portion of the tibial prosthesis. The ?nal prepared tibial
`plateau surface is shown in FIG. 8 with the tibial com
`ponent in place on the plateau. The prosthesis rests on
`freshly cut surfaces of the tibial plateau and surrounds
`the cruciate ligaments except in the direct posterior. If
`methyl methacrylate is not to be utilized with the tibial
`prosthesis, the extreme medial and lateral parts of tibial
`plateau should be retained for stabilization of the pros
`thesis. If cement is to be utilized, the extreme medial
`and lateral parts of the plateau may be removed with
`out seriously jeopardizing the stability. Minor adjust
`ments should be made with air saw so that a satisfactory
`fit of the trial tibial prosthesis is accomplished. Minor
`variations between medial and lateral cuts in the tibia
`may be made in order to compensate for varus or val
`gus deformity. Considerable care should be taken to
`retain the middle portion of the tibial plateau so that
`most of the insertion of the anterior cruciate ligament
`
`6
`is preserved. The trial tibial prosthesis is used to verify
`the tibial osteotomies. lf methyl methacrylate is to be
`utilized, two drill holesshould be placed in the tibial
`surface to anchor the cement. The trial tibial compo
`nent is very similar to the regular tibial prosthesis,
`which has been described, except that it is fabricated
`of steel, does not have an X-ray locator wire, and the
`bottom surface is smooth. it also is to be used as though
`it were an instrument in order to determine the proper
`fit of the regular prosthesis.
`When correct bone preparation has been determined
`by use of both trial prostheses, the femoral prosthesis
`may be implanted. If methyl methacrylate is not used,
`the femoral prosthesis is pushed into place using a pros
`thesis seater. When emplaced, the prosthesis may be
`seated or set by light mallet taps on the handle of the
`seater. If cement is used the cement should be mixed
`and handled in accordance with the manufacturer’s in
`structions. When in a dough-like state, small portions
`of cement should be inserted in the fin slots and a thin
`(approximately 1/8 inch) layer of cement placed on the
`freshly cut surfaces which will receive the prosthesis.
`The femoral prosthesis is then pushed slowly into place
`using the femoral prosthesis pusher. The prosthesis
`may be coined into the cement by taps with a mallet
`against the prosthesis pusher. Any excess cement
`should be removed with curettes.
`If cement is not used, the tibial prosthesis is placed
`in position while the knee is still in 90° flexion. After
`the prosthesis is inserted, the knee is slowly brought to
`full extension. lf cement is utilized, with the kene still
`in 90° flexion, a thin (l/l6 inch to 1/8 inch) layer of ce
`ment is spread on the prepared tibial surface. The tibial
`prosthesis is emplaced, taking care not to push or
`exude cement to the posterior. If cement is pushed be
`yond the prosthesis posterior, it may impinge during
`flexion, thereby limiting the amount of flexion to be ob
`tained. While it is not recommended that methyl meth
`acrylate be used to build up the prosthesis or correct
`major deformities, minor abnormalities may be offset
`by this technique in order to provide an axis of weight
`bearing that is perpendicular to the tibia and parallel
`with the floor. After implantation of the prosthesis, the
`knee is slowly returned to full extension. (0° flexion).
`During the elevation from flexion to extension, the sur<
`geon must feel the pressure required to compensate for
`varus or valgus, remembering that excessive pressure in
`either direction will result in migration of the uncured
`cement.
`The patella is then reduced and the absence of the
`impingement on the anterior portion of the prosthesis
`confirmed. The cut is closed in layers with interrupted
`sutures over suction drains in the usual fashion.
`The recommended postoperative routine includes
`immobilization in a splint or dressing with the knee is
`extension for 5 to 7 days, at which time the initial bulky
`dressing is replaced. Mobilization is continued as toler
`ated in balanced suspension with protective weight
`bearing started at seven days. Quadriceps exercises are
`encouraged, but flexion beyond 60° is discouraged for
`2 weeks until quadriceps healing is advanced and post
`operative reaction in the joint is diminished. At three
`weeks, inadequate flexion can be encouraged by a gen
`tle manipulation under anesthesia.
`it will be understood that the described surgical pro
`cedure included in this specification imposes no limita
`tion on the invention and that departures may be made
`
`55
`
`65
`
`

`
`3,869,731
`
`15
`
`8
`2. As a new article of manufacture, a femoral pros
`thesis forming part of a two part knee prosthesis, com
`prising a unitary, one-piece device constructed and
`adapted to be connected to the distal end of the femur
`and replace the condyle surfaces thereof, said prosthe
`sis‘having a lower part having two transversely spaced
`' substantially parallel condyle replacing members each
`of which has a downwardly facing bearing surface
`which is shaped in anterior to posterior direction as a
`continuously changing curve of constantly decreasing
`radii and is shaped in transverse cross section as'a curve
`forming part ofa circle and a shallow depth, and means
`for connecting’ the prosthesis to the femur by upward
`driving implantation, comprising two fins extending up
`wardly from the upper surfaces of the condyle replac
`ing members, respectively, and having upwardly facing
`upper edges, and a third fin of triangular shape extend
`ing upwardly from the upper surfaces of the condyle
`replacing members at the anterior parts thereof and
`having upwardly converging upper edges extending
`from the anterior parts of the upper edges ofthe first
`two fins.
`3. As a new article of manufacture, a tibial prosthesis
`forming part of a two-part knee prosthesis, comprising
`a circular disc shaped device having upper and lower
`surfaces and a side wall and having an opening extend
`ing from one part of the side wall to the center of the
`device whereby the device is C-shaped, a shallow
`groove in the upper surface of the device extending
`throughout substantially the entire length thereof and
`therefore also being C-shaped, the groove being of uni
`form cross sectional shape and depth and in each of its
`cross-sections its bottom being formed as a curve form
`ing part of a circle.
`
`7
`from this described procedure within the scope of the
`invention.
`We claim:
`1. A two-part prosthetic device for arthoplasty of the
`knee joint, comprising a component for replacing at
`least a part of the distal end of the femur and a compo
`nent for replacing at least a part of the proximal end of
`the tibia, the femoral component comprising a unitary
`integrally formed device constructed and adapted-to be
`connected to the distal end of the femur and serve in
`lieu of the condyle surfaces thereof, said femoral com
`ponent having an upper part having ‘an upwardly di
`rected bone fixation element for upward implantation
`in thefemur shaft and a lower part providing two sub
`stantially parallel transversely spaced support members
`which serve in lieu of the natural condyles, each of said
`support members having a downwardly facing bearing
`surface the anterior to posterior shape of which is a
`continuously changing curve of constantly decreasing
`radii and the transverse cross sectional shape of which
`is a curve forming part of a circle and of shallow depth,
`the tibial component being disc shaped and having
`upper and lower surfaces and a side wall and being con
`structed and adapted to lie with its lower surface on
`and connected to the prepared plateau surface of the
`proximal tibia, the tibial component having an opening
`extending from the posterior part of its side wall to its
`center whereby the component is C-shaped, the tibial
`component having a groove in its upper surface which
`is C-shaped in plan, following the C-shape of the com
`ponent, to receive the support members of the femoral
`component, the groove being of uniform cross sec
`tional shape and shallow depth throughout its length
`and its bottom shaped in each transverse cross section
`as a curve forming part of a circle.
`
`25
`
`30
`
`35
`
`’
`
`*
`
`*
`
`*
`
`*
`
`=|<
`
`45
`
`50
`
`55
`
`60
`
`65