CA2078228C - Improved floating bearing prosthetic knee - Google Patents
Improved floating bearing prosthetic knee Download PDFInfo
- Publication number
- CA2078228C CA2078228C CA002078228A CA2078228A CA2078228C CA 2078228 C CA2078228 C CA 2078228C CA 002078228 A CA002078228 A CA 002078228A CA 2078228 A CA2078228 A CA 2078228A CA 2078228 C CA2078228 C CA 2078228C
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- CA
- Canada
- Prior art keywords
- bearing
- bearing surface
- arcuate
- prosthetic device
- fixation means
- Prior art date
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Classifications
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2/38—Joints for elbows or knees
- A61F2/3868—Joints for elbows or knees with sliding tibial bearing
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
- A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
- A61F2/02—Prostheses implantable into the body
- A61F2/30—Joints
- A61F2/38—Joints for elbows or knees
- A61F2/3886—Joints for elbows or knees for stabilising knees against anterior or lateral dislocations
Abstract
A semiconstrained prosthetic knee for surgical replacement of a dysfunctional knee includes a tibial platform (22), a movable bearing element (16), and a femoral component (12). The femoral component (12) includes a polycentric convex bearing which slidably engages a movable bearing (16). The superior surface of the bearing element (16) is designed to congruently slidably engage the inferior surface of the bearing portion of the femoral component (12). The inferior surface of the femoral component (12) is generally convex with two or more offset portions of varying radii of curvature matching complementary superior surfaces of the bearing element (16). The inferior surface of the femoral component (12) may have more than one radius of curvature at different points along the convex surface. The superior surface of the tibial platform (22) is generally flat and includes at least one protrusion for controlling the movement of the bearing element (16).
Description
Wn ~2/08d2~ PCf/UB9'!/08520 __ , 20'~~22~
IMPROVED FLOATING BEARING PROST~iETIC KNEE
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1. FIELD OF THE IIJ~7EI~°PION
This invention relates to prosthetic aoints generally, and more particularly to an improved, unconstrained pzosthetic knee replacement for a dysfunctional knee.
z. PRIOR ART
Referring naw to prior art knee endoprostheses, there are basically two types of prosthetic replacement knees known generally as constrained and unconstrained knees. An ezample of an unconstrained or floating maniacal bearing knee is disclosed in Buechel et al Patent No. 4,390,9'78. An embodiment of the Buechle invention is manufactured and sold by Depuy, znc. of. Wausau, Indiana. Preferably, the bearing elements of these types of knees are manufactured with high density polyethylene such as that disclosed in ~acharia3es Patent i~o.
4,587,163 developed by Polteco znc. of Alameda, 0alifornia because of its superior wear resistant characteristics. Both classes of prior art prosthetic knees have had problems often . resulting in failures requiring additional surgery and repair or reconstruction.
Referring neat to tygic~al prior art tibial-femoral knee grostheses, prastheses which allow azial rotation and A-P
motion in addition to flezion-extension motion have incongruent contact (usually theoretical point-contact) between the femoral and tibi.al bearing surfaces;, have been found to produce excessive contact stresses..leading..to .deformation_and/or early .
.. _ .- .._.- ,_~cci-..~tl~- :Ii?~~~iic~lYS~'tBFt~~~tJlrCtcir~'ts:~'?r'.~iY-G
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Ct tClC'TiTt~3'1'~ Cf-lT:'r'"1 WO 92/0&424 PCT/US9~/0~520 pxoducts have been shown to produce undesirable tissue reactions which may contribute to loosening of the prosthetic components.
,. , Those prior,a'rt knee prostheses which do provide congruent or area bearing contact fail to grovide the needed a=ial rotation, or when cruciates are present the needed anterior-posterior motion. This lack of aaial rotation and anterior-posterior motion has been found clinically and experimentally to result in deformation and loosening of the tibial components. and such prostheses now appear to be falling into disuse.
Pre-existing constrained knees have often resulted in early failure as a result of hinge constrainment. The degree of rotation was limited to either only one plane or a very small arc causing a loosening and failure of the connection paints between the prosthesis and the tibia or femur. Also, as shown in U.S. Patent Ido. 4,219,893, very little flexibility was possible in the shape of the patello-femoral interfaces because of the requirement to maintain congruent patello-femoral contact over the range of motion of the knee. As a result, patello-femoral tracking problems became commonplace.
It was necessary to use a large circumference when used to resurface allografts resulting in problems with soft tissue necrosis andlor patello-femoral tracking problems as described above. Furthermore, most implants were known as custom devices since they had to be specially made to fit a particular patient's size and thus required excess manufacturing time and unnecessary delays.
' An additional, significant problem with prior art constrained knees results from the fact that the range of motion prevents the normal A-P movement of the inferior end of the femur relative to the posterior end of the tibia. This "sliding" movement is necessary in order to maintain the full range of motion desired in a prosthetic device.
Current prostheses of the dislocatable cruciate retaining type, such as the Geomedic knee replacement shown in U.S. Patent No. 3,728,742 to Averill et al, that produce area contact provide only one axis of rotation relative to the femur for the flexion-extension motion. Normal flexion-extension is, however, characterized by a polycentric flexion-extension motion where rotation relative to the femur occurs about many aaes.
This polycentric motion, which results from the action of the cruciate ligaments and condylar shape, allows for more efficient utilization of muscle forces by providing a posterior shift of the axis when effective quadriceps action is important and an anterior shift when hamstrings effectiveness is important. Furthermore, in the human knee it is this action and the A-P shift, and the shape of the posterior condyles, which influence this motion so as to allow full flexion WO 9210424 PC'f/tJS91/08520 ~1~~~~ ~
capability for the knee. Failure to provide appropriate knee geometry inhibits, when cruciate ligaments are present, this natural motion and thus tends to restrict muscle effectiveness and inhibit flezion. These,,'restrictions tend, to increase both loading on the prosthesis (which increases wear or likelihood of deformation or breakage) and loading between prasthesis and bone (which increases the possibility of component loosening).
Tt has been found that loosening problems result from the direct attachment of plastic prosthetic components to bone through the use of relatively brittle cement that is weak in tension. Specifically, it has been demonstrated that even relatively thick plastic components when loaded in a normal fashion produce undesirable tensale stresses in the acrylic cement commonly used to secure such plastic components to bone. Such loading tends to produce bending of the plastic component 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, these combined effects contribute substantially to prosthetic loosening problems and, specifically, it has been noted where clinical failure due to loosening occurs in a knee prosthesis that is almost always the plastic prosthesis component which loosens.
C\~'_.r 'vo 9ziosaza Pc-rius9mosszo 2~~82~8 Another prior art prosthesis problem exists with regard 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 constrained type knee prosthesis which may suffer from the loosening problems described above caused by the stresses described above. Necrosis of the bone, caused by altered mechanical bone stresses,' is also a problem with the prior art constrained knee prostheses.
Where the cruciate ligaments are present, most . surgeons 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 and A-P motion of the knee. Furthermore, these ligaments provide anterior-posterior stability. Thus, it is desirable to reserve the cruciate ligaments. even though seasonable stability can be provided by a properly designed full platform type prosthesis.
In addition, the action of the cruciate ligaments produces a shift in the rotation axis of the knee which results in more efficient muscle utilization. Thus, preservation of these structures provides better physiological function after knee replacement.
CVO 92/OFui2~ PGTlUS91f0~520 ~~'~a'~$ s It is not. however, clear that the physiological advantages gained in retaining the cruciates outweigh the disadvantages of the design compromises, such as increased bearing surface incongr.uer~cy and reduced tibi~al prosthesis bearing area, reguired to retain these ligaments. Thus,, the desirability of retaining the cruciate ligaments in the cases of unconstrained knee replacement is not well established.
A recent unconstrained knee concept, the New Jersey knee, appears to provide a partial solution to the problem of overconstraint while attempting to maintain congruency by the use of mensical floating elements. Unfortunately, this knee suffers from several design problems which appear to limit its usefulness.
The present invention, the PottengerlDraganich Knee utilizes new concepts combined in az improved design in order to avoid same of the anticipated difficulties of the prior art design.
SAY OF THE INVENTION
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 an improved semiconstrained knee prosthesis with a novel polycentric femoral component having different radii of curvature in different sagittal sections.
H'O 92/08424 PC"flUS91/0852a An object of the present invention is to provide a ' knee prosthesis which facilitates rotation about one or more axes in the presence of congruency of the bearing surfaces.
A further object of the present invention is to provide a knee prosthesis which substantially reduces the possibility of tipping and/or dislocation of the bearing insert or inserts in the absence of the anterior and posterior cruciate ligaments.
A further object of the present invention is to provide a knee prosthesis which allows full flexion of the reconstructed knee without applying shear forces.
A further object of the present invention is to provide a knee prosthesis where the tibiofemoral area contact controls the movement of the femoral component and thus ' increases quadriceps effectiveness.
An object of the present invention is to provide a knee prosthesis in which A-P sliding of. the bearing element with knee flexion allows 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 with improved medial-lateral stability, substantially unaffected by azial rotation or anterior-posterior (A-P) shift of the bearing element.
A further object of the present invention is to provide a knee prosthesis which includes constraints at the WO 921024 PCT/U59I/a~520 c limits of normal motion to compensate for missing cruciate ligaments and prevent dislocation.
A further object of the present invention in to provide a semiconstrained knee prosthesis where the femoral component may articulate in extremely close proximity with the ' tibia to eliminate patella baha problems.
In accordance with the foregoing and other objects, the unconstrained prosthetic knee of the present invention includes a femoral prosthesis having a condylar portion with at least two saggitally spaced arcuate segments of different radii, a tibial prosthesis having a bearing surface for supporting weight, and an intermediate load-bearing member having a thrust-bearing surface for matingly engaging the bearing surface of the tibial prosthesis and adapted to distribute weight and to transmit forces in a plane substantially perpendicular to the axis of the tibia and a mutually congruent superior surface for engaging the eondyles of the femoral prosthesis to provide area contact throughout the full range of flezion/eztension of the knee.
BRIEF BESCRIPTION OF THE pRAWINGS
A complete understanding of the invention may be obtained from the detailed description which follows, together with the accompanying drawings, wherein:
wo ~anosaza Pcrius9moaszo g Fig. 1 is.a perspective view of the unconstrained prosthetic knee of the present invention;
' Fig: 2 is an exploded perspective view of the tibial component and bearing element of the prosthetic knee of the present invention;
Fig. 3 is a vertical section taken generally along the line 3-3 of Fig. 1;
Fig. 4 is a vertical section taken generally along .".
the line 9-9 of Fig. 1;
Fig. 5 is a vertical section taken generally along the line 5-5 of Fig. 1;
Fig. 6 is a top plan view of the bearing element made in accordance with the present invention;
Fig. 7 is a front elevational view of the bearing element of Fig. 6;
Fig. 8 is a bottom view of the bearing element of Fig. 6;
Fig. 9 is a rear elevational view of the bearing element of Fig. 6;.
Fig. 10 is a side elevational view of the bearing element of Fig. 6;
Fig. 11 is a vertical section taken generally along the line 11-11 of Fig. 6;
Fig. 12 is a vertical section taken generally along the line 12-12 of Fig. 6;
WO 9?/08424 PCI"/US91/08520 Fig. Z3 is another vertical section taken generally along the line 13-13 of Fig. 6;
Fig. 14 is a diagrammatic representation o~ the assembled bearing, element and tibia portion showing the bearing element in its ~o,rwardmost position;
Fig. 15 is a diagrammatic representation similar to Fig. 19 showing the bearing element in its rearwardmost position;
Fig. 16 is a top plan viewr of the femoral component on a reduced scale;
Fig. 17 is a vertical section taken generally along the line 17-17 of Fig. 16;
Fig. 18 is a front elevational view of the prosthesis assembly implanted within a patient;
Fig. 19 is a real elevational view of the prosthesis assembly implanted within a patient;
Fig. 20 is a side elevational view of the prosthesis assembly in a generally. straight eztended position; and Fig. 21 is a diagrammatic representation of the prosthesis assembly with the knee shown in flezian.
BRIEF DESCRIPTION OF TFiE PREFERRED EfiBODIMENT
The floating bearing prosthetic knee. generally designated 10 in Fig. l, provides area contact as opposed to lane contact or point contact throughout the entire '. , ;:'.' ... . .' ~; .. ., ..
WO 92/~Sd24 PCfI'tJS91/0852n 2~'~~2~~3 flexion/extension range of the prosthesis. Through this design, some degree of rollback authomatically occurs as the knee flexes and additional rollback is allowed to will occur through the movement of the sliding bearing. ' Area contact throughout the full range of motion is obtained through the use of multiple arcuate sections along the path of,conduct of the condyles with the bearing insert. However, unlike prior art prosthetic knees of the prior axt, the different radii and arcuate portions of the condyles lie in different saggital or medial-lateral planes. Thus tibial-femoral area contact will occur in different longitudinal planes throughout the flexion/extension range of the knee. Area contact will occur simultaneously in two planes only at the point of transition between the respective arcuate portions.
The desirable prosthetic knee 19 satisfies at least five characteristics. One. the knee should have the normal polycentric motion of the normal knee joint. Two, unconstrained anterior-posterior motion and rotation would be vermitted within the normal range of motion of the knee.
Three, constrained A-P motion and rotation would occur at the limits of normal motion. Four, normal rollback of the femur with reenact to the tibia should occur during flexion of the knee. Five, tibial-femoral contact pressure should be minimized in order to reduce wear on the polyethylene bearing insert 16. The present invention to satisfies these five characteristics as described hereinafter.
WO 92/08d2d PC.'T/ US91/0~520 t2 l~,~oR corlPO~tl:~s Referring now in particular to Fig. l, the unconstrained knee, generally designated 10, is shown in perspective view to include~layfemoral component 12, a tibial component 14, and a bearing element 16. The femoral component 12 includes at least one upwardly extending stem 18 or other means for connection to the femur and a pair of condyles 20 on its inferior surface for engagement with the bearing portion 16. Preferably, the bearing element 16 is constructed of a tough, wear-resistant, resilient material such as high density polyethylene. The remaining elements of the prosthetic knee are metallic and preferably manufactured of a cobalt-chromium alloy material approved for use in prosthetic devices.
The tibial component includes a generally flat rigid platform 22 and a depending stem portion 24 for securing the tibial portion to the tibia. The superior surface of the femoral component and the implantable stern portion 2~1 and inferior surface of the platform 22 of the tibial component include a surface adapted for extramedullary porous ingrowth to secure the prosthetic device within the tibia and femur, respectively, of the host or allograph bone of the patient. By contrast, the condyles 20 of the femoral component are highly polished to reduce friction.
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Referring to the lower portion of Fig. 2, the tibial portion includes the platform 22 and the depending stem 24.
The platform is provided with a pair of laterally spaced, ., generally triangular-shaped, upward protrusions.26 and a centrally located aperture 28 for limiting the A-P movement of the bearing 16 described below.
More particularly, referring to Figs. 2, 5 and 6, the bearing 16 includes a centrally located generally rectangular opening 32 which is used to slidably connect the bearing to the top of the tibial component 22. The bearing 16 has a generally flat inferior surface 39 as shown in Fig. ~ which slidably engages the superior surface or platfarm 22. The aperture 32 includes, at its lower end, a ridge or lip 36, of similar configuration. Both the aperture 32 and the vertical wall of the bearing have smooth or rounded corners to reduce stress.
The bearing 16 is captured by a retaining means, generally designated 40, which includes a shoulder bolt 42, a retainer 44 and a spacer 46. The spacer 46 and retainer X14 are preferably manufactured of high density polypropylene, similar to that used for the bearing insert 16 and the shoulder bolt 42 would be made of stainless steel or cobalt-chromium alloy approved for use in this application.
The shoulder bolt 42 includes a lower threaded portion 4B which engages a plurality of threads 50 at the lowermost end of the aperture 28 within the stem 24 of the WO 92/08424 ~~Cb PCT/lJ591/08520 tibial component. .The shoulder sets the depth to prevent from the head.52 of the shoulder bolt from impeding the movement of the bearing insert 16~.v-, The retainer 46 includes an enlarged diameter ring 54 at its lowermost end which engages the .
platform 22 of the tibial portion 14 around the aperture 28 and extends upwardly coaaially with the shoulder bolt 42. , The retainer or retaining element 44 is generally square in shape and includes a lower square portion 56 which forms a clearance fit within the ridge 36 at the lower end of the aperture 32 in the bearing. as can be seen in Fig. 5. The upper end of the retainer includes an enlarged flange 58 which engages the top of the step or lip 36. The retainer 44 is dimensioned so that the distance between the underside of the head 52 of .the shoulder bolt and the top of the lip 36 provides a low tolerance clearance fit with the flange 5B of the retainer to allow the bearing 16 to slidably move on the platform 22 without becoming disengaged from the platform 22.
In this manner. the bearing is free to slide in an anterior posterior or A-P path. The retainer 44 will stop the movement in the A-P direction as the front and rear surfaces engage the front or inner surfaces of the lip 36.
The retaining means 40, in addition to permitting A-P
movement of the bearing 16 also permits pivotal movement generally about the center line of the shoulder bolt 42. Thus, depending upon the anterior or posterior displacement of the _ 15 bearing insert 16 relative to the retainer 44, the bearing insert and the retainer may pivot about the center line of the shoulder bolt 42 to provide freedom of movement. However, in order to prevent too much pivotal movement of~the bearing 16, particularly when in its anteriormost position, the triangular protrusions 26 provide a stop means.
The stop means includes the upward protrusions 26 and a pair of symmetrical cutouts 60 on the lower surface of the bearing insert lfi. In particular, each cutout includes a generally flat rear wall 62 and a generally curved inner wall 64 for engagement with the upward protrusions 26. As shown in Fig. 9, the height of the rear wall 62 permits the cutouts 60 to clear the top of the stops 26. Referring to Fig. 14, in its anterior-most position, the arcuate walls 64 of the bearing 16 engage the inner, generally right angle corner of the triangular protrusions 26 to virtually greclude most of the pivotal movement or rotational movement of the bearing insert 16. As the bearing 16 is moved towards its posterior-most position, as shown in Fig. 15, the bearing is free to rotate in either direction as shown by arrows A and B and are limited by the longer upstanding walls of the protrusions 26 which engage the flat walls 62 within the cutout 60.
Therefore, it can be seen that the bearing insert 16 is constrained but is permitted to move in the A-P direction from the eatremes as shown in Fig. 14 to that as shown in Fig.
W~O 92i08d2d t'C.'T/US9t108520 16 while, at the same time, it is free to pivot about an axis defined by the shoulder bolt 29 within the limits created by the stop means where the walls 62 and 64 of the cutouts 60 engage the triangular protrus~i.ons 26. These constraints, while permitting movement of the~bearing 16, control the movement of the femoral component as described hereinafter and thus create some rollback and allow for the further posteriax movement of the bearing insert.
These constraints at the limits of normal motion will compensate for missing cruciate ligaments and prevent dislocation of the components, i.e., the bearing insert, which has been seen to occur in popular prior art floating bearing prosthetic knees. In most circumstances, normal soft tissue will provide the primary restraining forces limiting motion of the components and, if necessary. the limits incorporated into the prosthesis 10 would function as secondary restraints.
Some rollback (approzimately 5 millimeters in the present embodiment) automatically occurs (i.e., is obligated to occur) when tibiofemoral contact moves from one arcuate segment to the other one. The rest of the normal amount of rollback is allowed to occur (but not obligated to occur) with the movement of the bearing insert. The amount of additional rollback that is allowed to occur is governed by the interaction of the posterior cruciate ligament and the condylar surfaces. The rollback of the femur with respect to the tibia during flezion WO 92/08424 PCT/US91108520 ...
-~~1~~~:~'~
of the knee is an important characteristic of the present prosthesis because it causes the patellar tendon to move anteriorly with respect to the femur which greatly increases.
the effectiveness of the quadriceps muscle. especially when rising from a chair. It~has bean found that many patients who have had total knee replacements cannot get up from a sitting position without assistance from their arms. Also, prior arm unconstrained knees are frequently found to "roll forward"
rather than backward during flexion. In the design of the present invention, the shoulder bolt retaining means 90 prevents roll forward and the bearing insert 16 recreates the normal situation and further helps to increase the quadriceps efficiency. Known prior art total knee replacements have attempted to utilize the femoral component to control the motion of the bearing insert, just the opposite of the knee of the present invention.
~'HE FEM012AL CUMPONE1QT
The femoral component 12 of the present invention includes generally a pair of condyles 20, securing posts 18 and a web portion which defines a patella track 'T0. The securing posts 18 provide means to secure the femoral component to the femur of a patient. As shown in Fig. 20, a pair of matched apertures are drilled into the femur and the end of the femur ' is formed with five generally flat surfaces as shown to fit ;;- : ; :',.. .. ,:, T. ... .,: ,.
WO 92/U842~3 P(_'T/US91/UB52U
within the flat surfaces 72a through 72e as shown. The , opposite Surfaces 72a and 72e are generally parallel to one another and perpendicular to the surface 72c. The angled surfaces 72b and 72d are approximately at 45 degrees with respect thereto. The entire surface of the flat surfaces 72a-a and the surfaces of the posts 1B are designed for extramedullary bone growth to secure the femoral component to the end of the femur.
Certain prior art prostheses propose the use of a femoral component in which the multicentric surfaces of the condyles were created by a common planar curve which created a design whereby every sagittal section along the condyle was polycentric. This design results in a situation where the condyles can only make area contact during approximately the initial 2~° of knee flexion thereby resulting in line contact and very high contact pressure which increases the wear of the bearing insert. In addition, prior art design of this type accomodates rollback of the femur with respect to the tibia and, particularly at maximum flexion, there is a tendency for the bearing insert to "pop out" or become dislocated.
The femoral component and sliding bearing of the present invention have congruent surfaces which allows for rotation and A-P motion within the range of normal A-P motion to prevent excessive anteriar and posterior drawer and rotation and dislocation of the bearing. The upper surface of the WO 92/08~2d POf/U591l08520 _t 9 bearing I6 is designed so that the inferior surfaces of the femoral component always have area contact at all flexion angles. Constant area contact is achieved by distributing the femoral contact areas on the bearing Z6 across the frontal plane such that different areas of the bearing 16 are contacted through different angles of knee flexion. Each contact area on the bearing has the same radius of curvature as the portion of .
the inferior surface of the femoral component 12 in contact with the bearing.
Referring to Figs. 6-I3, the bearing insert I6 is generally oval in shape with a pair of flat ends 80R and 80L.
The anterior or front side is a generally flat arcuate wall 82 which includes a pair of cutouts 60 at the lower right and left ends, respectively. The posterior side includes a relatively large, almost semicircular recess 8~ which grovides substantial clearance for the posterior crueiate ligaments. The top portion of the rear wall on either side of the recess 84 includes a short generally vertical arcuate wall portion 86 which merges into a generally arcuate. inwardly tapered lower wall portion 88. The tapered portions 88 merge with a pair of lower champhers at the bottom of the end walls 80R and 80L
which terminate at their front ends with the cutouts 60.
1~'~ 92/0&124 Pt'1"/US91/08520 ~o ~~~ a The superior surface of the bearing insert is described by a plurality of arcuate channels or grooves which are described in detail hereinafter in connection with the arcuate surfaces defined on the inferior contact surface of the femoral component. In order to add rigidity to the front wall portion 82, an upstanding flange 96 is included immediately anteriorly of the aperture 32. The outer edges of the top of the front wall 82 are softened by curves 98 as the transition to the top of the bearing insert 16.
The contact surfaces between the bearing insert 16 and the femoral component 12 are best understood if considered together. The ugper surface of the bearing 16 includes a plurality of arcuate surfaces for engagement with congruent arcuate surfaces on the inferior side of the femoral component 12. Referring to Fig, 6. four of the arcuate surfaces have been labelled L and two of the surfaces have been labelled S.
The four arcuate surfaces L are all generated using the same radius of curvature and similarly the twa arcuate surfaces labelled S are generated using the same but smaller radius, The arcuate surface S shown in section view in Fig. 12 is defined posteriorly of the arcuate surfaces L, one of which is shown in sectional view in Fig. 11. As Can be seen in Fig. 5.
the comglementary surface of the femoral component includes tvo ~2~os~2a Ycrms~ao~szo 2t ~~~o~~
four arcuate surfaces L and two arcuate surfaces S. One significant feature of the present invention is that the arcuate surfaces L and R lie in different saggital planes as shown and make contact during different degrees of flexion of the knee.
In particular, the arcuate surfaces L on the inferior surface of the femoral component are in contact with the arcuate surfaces L on the bearing 16 between approximately 0°
through 8° of flexion of the knee and the arcuate surfaces S of the femoral component are in contact with the arcuate surfaces S of the bearing 16 during approximately 8° through 140° of flexion of the knee. At the transition point, at approximately 8° of flexion, area contact occurs between all of the arcuate surfaces L and S on the femoral component 12 with all of the arcuate surfaces L and S on the bearing component 16.
Although the size of the patient will partially determine the size of the prosthesis, the following sizes have been found to be effective in trials. More particularly, referring to Fig. 3, the arcuate surfaces L are generated by radius R1 about a center point C. Center point C is slightly rearwardly defined relative to the past 18 and the radius Rl is approximately 1.60". The arcuate surfaces S are generated by a radius RZ about a center of rotation D. The radius R2 is approximately 0.75". The center of rotation D of radius R2 Iies on a line passing through the center of rotation C of R1 WO 92/08424 ~ 2 ~ PCT/U541/08520 so that the surfaces L and R have a tangent point T in order to have a smooth transition of tibia--femoral contact at approximately 8° of flexion,. ~Thus, area contact of the arcuate surfaces L occurs during the first 8° of flexion of the knee and area contact is transferred to the arcuate sections S at 'approximately 8° and continues through maximum flexion of about 140°.
The position of the femoral component 12 with regard to the bearing 16 is controlled by the center of rotation of curvature for the arcuate surfaces S or L which are in contact. The arcuate curves S are placed farther back on the bearing and will draw the femoral component posteriorly thus allowing obligatory rollback. Further rollback is permitted because the elongated aperture 32 in the bearing allows the bearing to move posteriorly on the tibial platform. As described previously, the constraints 26 and the retaining means 40 prevent anteriar movement of the bearing 15 beyond the anterior edge of the tibial component. Therefore, when rollback is occurring during flexion of the knee, no compensatory roll forward will occur between the bearing 16 and the tibial component 14. As the femoral component passes through approximately the 8° range, area contact is transferred between the arcuate surfaces L to the arcuate surfaces S, the transition continues smoothly because of the common tangent point of the respective arcuate surfaces. The constraints as dvo 9z~o~sza 2 ~ ~ p ,~ $ ~ ~ $ Pc-r~us~'iosszo previously described With respect to the bearing 16 prevent dislocation of the bearing element when implanted.
In an alternative embodiment, it is possible to obtain the same functionality and operation if, for example, the innermost or outermost complementary arcuate surfaces L
were eliminated. However, additional area contact can be obtained to decrease the pressure between the femoral,component and the bearing by providing the additional arcuate surfaces L
adjacent the center aperture 32.
In addition, the arcuate surfaces L and S are designed to obtain the mazimum amount of area contact possible within the permissible space. To this end, the arcuate surfaces 5 on the bearing l~b are approzimately 3/8" wide and approzimately 1-1!8" Long. As described previously, the radius R2, the radius for generating the arcuate surface S is approzimately 0.75" and lies in a sagittal plane. The transverse radius which defines the arcuate surface in the medial lateral plane as shown in Fig. 5 is approzimately .375"
Similarly, the arcuate surfaces L are approzimately 1.25" in length generated by the radius R1 in the sagittal plane and the radius in~the transverse plane R4 (Fig. 5) which defines a .
radius of curvature of the arcuate surfaces L in the transverse plane is approzimately 0.125" The center of rotation D is apgrozimately 0.375" posteriorly of the center of rotation C
and about 0.9" below the center of rotation C, The center PC'f/US91/08530 WO 9Z10~1~4 ~~7~~ z~
lines of the arcuate surfaces L are approximately 0.3" on either side of the center line of the areuate section S and the ' respective center lines of the arcuate sections S are y ..;., approximately 2.00" apart.
The knee prosthesis 10 of the present invention is the only design which gives area contact between the bearing 16 and the femoral component 12 in all degrees of flexion. The highest pressures on the knee joint are experienced during stair climbing where the knee is flexed to approzimate2y 90 degrees of flexion in which the prior art knees have only line contact ar point contact. Since polyethylene (the material used to form the bearing) wear appears to be related to excessive pressures, area contact is virtually as important in stair climbing as in walking. even though stair climbing is performed much less often. The prosthetic knee 10 also permits the use of the same component in the presence or absence of posterior cruciate ligaments. Generally speaking, semiconstsained knee prosthesis require the presence of posterior cruciate ligaments to prevent posterior subluzation of the tibia, On the other hand. constrained prosthesis, which do not allow rollback, require removal of the posterior cruciate ligaments because proper tension on the posterior cruciate ligaments would attempt to create posterior rollback which is prevented by the constraints. This could lead to dislocation of the components of the contrained prosthesis or rupture of the posterior cruciate ligaments.
WO 92/0&~2~b PC.'f/US91/08520 __ ~5 2~'~~225 In prior art designs in Which the arcuate surfaces of the condyles are created by using a common plane generating curve, all of the the sagittal sections of the c~ndyles are polycentric. On the contrary, the present invention has only one radius of contact in each sagittal plane and, therefore, is not created by a common plane generating curve. since all potential points of contact in the sagittal plane have the same radius of curvature, area contact can be obtained throughout the entire flexion arc of the knee in a manner which cannot be obtained by the prior art knees where the radii along the condyles changes while contacting the same area of the bearing insert.
Referring to Figs. 18-21, which show the prosthetie knee 10 of the present invention implanted in a patient, it can be seen in Fig. 20 that in the eztended position of the prosthesis, the bearing insert 16 moves to its anterior-most position with respect to the tibial component 14. In this position, the arcuate surfaces 1a an the respective tibial component and bearing insert 16 ors in engagement. As the knee flexes, rollback of the femur with respect to the tibia begins to occur to approximately the maximum gosition as shown in Fig.
21 where the bearing insert 16 has waved to its posterior-most position emulating, as close as possible, the normal knee.
Thus, it can be seen that the present invention defines and describes a prosthetic knee which morn closely wo ~2iosa2a Q~ ~~ ~ 6 P(.T/US91/OSS20 ~~~ a v simulates the normal knee movement than any prior art devices.
The prosthesis 10 provides normal polycentric motion for the knee joint and permits normal rollback of the femur with respect to the tibia during~:.f~lexion. The rotational and anterior-posterior, movement of the bearing insert is unconstrained for the normal range of motion but .is constrained at its limits. The design of the polycentric contact surfaces between the femoral component 12 and the bearing insert 16 assure for sufficient area contact throughout the flexion/extension range of the knee to minimize pressure and resultant wear on the bearing insert. While the foregoing detailed description has been given for clearness and understanding, no unnecessary limitations should be understood therefrom as some modifications will be obvious to those skilled in the art.
IMPROVED FLOATING BEARING PROST~iETIC KNEE
sAC~c~oo~D o~ Tx~ zrrvE~azo~
1. FIELD OF THE IIJ~7EI~°PION
This invention relates to prosthetic aoints generally, and more particularly to an improved, unconstrained pzosthetic knee replacement for a dysfunctional knee.
z. PRIOR ART
Referring naw to prior art knee endoprostheses, there are basically two types of prosthetic replacement knees known generally as constrained and unconstrained knees. An ezample of an unconstrained or floating maniacal bearing knee is disclosed in Buechel et al Patent No. 4,390,9'78. An embodiment of the Buechle invention is manufactured and sold by Depuy, znc. of. Wausau, Indiana. Preferably, the bearing elements of these types of knees are manufactured with high density polyethylene such as that disclosed in ~acharia3es Patent i~o.
4,587,163 developed by Polteco znc. of Alameda, 0alifornia because of its superior wear resistant characteristics. Both classes of prior art prosthetic knees have had problems often . resulting in failures requiring additional surgery and repair or reconstruction.
Referring neat to tygic~al prior art tibial-femoral knee grostheses, prastheses which allow azial rotation and A-P
motion in addition to flezion-extension motion have incongruent contact (usually theoretical point-contact) between the femoral and tibi.al bearing surfaces;, have been found to produce excessive contact stresses..leading..to .deformation_and/or early .
.. _ .- .._.- ,_~cci-..~tl~- :Ii?~~~iic~lYS~'tBFt~~~tJlrCtcir~'ts:~'?r'.~iY-G
i'.~i-C-!'r.~-tdiiar - .. _.
Ct tClC'TiTt~3'1'~ Cf-lT:'r'"1 WO 92/0&424 PCT/US9~/0~520 pxoducts have been shown to produce undesirable tissue reactions which may contribute to loosening of the prosthetic components.
,. , Those prior,a'rt knee prostheses which do provide congruent or area bearing contact fail to grovide the needed a=ial rotation, or when cruciates are present the needed anterior-posterior motion. This lack of aaial rotation and anterior-posterior motion has been found clinically and experimentally to result in deformation and loosening of the tibial components. and such prostheses now appear to be falling into disuse.
Pre-existing constrained knees have often resulted in early failure as a result of hinge constrainment. The degree of rotation was limited to either only one plane or a very small arc causing a loosening and failure of the connection paints between the prosthesis and the tibia or femur. Also, as shown in U.S. Patent Ido. 4,219,893, very little flexibility was possible in the shape of the patello-femoral interfaces because of the requirement to maintain congruent patello-femoral contact over the range of motion of the knee. As a result, patello-femoral tracking problems became commonplace.
It was necessary to use a large circumference when used to resurface allografts resulting in problems with soft tissue necrosis andlor patello-femoral tracking problems as described above. Furthermore, most implants were known as custom devices since they had to be specially made to fit a particular patient's size and thus required excess manufacturing time and unnecessary delays.
' An additional, significant problem with prior art constrained knees results from the fact that the range of motion prevents the normal A-P movement of the inferior end of the femur relative to the posterior end of the tibia. This "sliding" movement is necessary in order to maintain the full range of motion desired in a prosthetic device.
Current prostheses of the dislocatable cruciate retaining type, such as the Geomedic knee replacement shown in U.S. Patent No. 3,728,742 to Averill et al, that produce area contact provide only one axis of rotation relative to the femur for the flexion-extension motion. Normal flexion-extension is, however, characterized by a polycentric flexion-extension motion where rotation relative to the femur occurs about many aaes.
This polycentric motion, which results from the action of the cruciate ligaments and condylar shape, allows for more efficient utilization of muscle forces by providing a posterior shift of the axis when effective quadriceps action is important and an anterior shift when hamstrings effectiveness is important. Furthermore, in the human knee it is this action and the A-P shift, and the shape of the posterior condyles, which influence this motion so as to allow full flexion WO 9210424 PC'f/tJS91/08520 ~1~~~~ ~
capability for the knee. Failure to provide appropriate knee geometry inhibits, when cruciate ligaments are present, this natural motion and thus tends to restrict muscle effectiveness and inhibit flezion. These,,'restrictions tend, to increase both loading on the prosthesis (which increases wear or likelihood of deformation or breakage) and loading between prasthesis and bone (which increases the possibility of component loosening).
Tt has been found that loosening problems result from the direct attachment of plastic prosthetic components to bone through the use of relatively brittle cement that is weak in tension. Specifically, it has been demonstrated that even relatively thick plastic components when loaded in a normal fashion produce undesirable tensale stresses in the acrylic cement commonly used to secure such plastic components to bone. Such loading tends to produce bending of the plastic component 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, these combined effects contribute substantially to prosthetic loosening problems and, specifically, it has been noted where clinical failure due to loosening occurs in a knee prosthesis that is almost always the plastic prosthesis component which loosens.
C\~'_.r 'vo 9ziosaza Pc-rius9mosszo 2~~82~8 Another prior art prosthesis problem exists with regard 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 constrained type knee prosthesis which may suffer from the loosening problems described above caused by the stresses described above. Necrosis of the bone, caused by altered mechanical bone stresses,' is also a problem with the prior art constrained knee prostheses.
Where the cruciate ligaments are present, most . surgeons 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 and A-P motion of the knee. Furthermore, these ligaments provide anterior-posterior stability. Thus, it is desirable to reserve the cruciate ligaments. even though seasonable stability can be provided by a properly designed full platform type prosthesis.
In addition, the action of the cruciate ligaments produces a shift in the rotation axis of the knee which results in more efficient muscle utilization. Thus, preservation of these structures provides better physiological function after knee replacement.
CVO 92/OFui2~ PGTlUS91f0~520 ~~'~a'~$ s It is not. however, clear that the physiological advantages gained in retaining the cruciates outweigh the disadvantages of the design compromises, such as increased bearing surface incongr.uer~cy and reduced tibi~al prosthesis bearing area, reguired to retain these ligaments. Thus,, the desirability of retaining the cruciate ligaments in the cases of unconstrained knee replacement is not well established.
A recent unconstrained knee concept, the New Jersey knee, appears to provide a partial solution to the problem of overconstraint while attempting to maintain congruency by the use of mensical floating elements. Unfortunately, this knee suffers from several design problems which appear to limit its usefulness.
The present invention, the PottengerlDraganich Knee utilizes new concepts combined in az improved design in order to avoid same of the anticipated difficulties of the prior art design.
SAY OF THE INVENTION
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 an improved semiconstrained knee prosthesis with a novel polycentric femoral component having different radii of curvature in different sagittal sections.
H'O 92/08424 PC"flUS91/0852a An object of the present invention is to provide a ' knee prosthesis which facilitates rotation about one or more axes in the presence of congruency of the bearing surfaces.
A further object of the present invention is to provide a knee prosthesis which substantially reduces the possibility of tipping and/or dislocation of the bearing insert or inserts in the absence of the anterior and posterior cruciate ligaments.
A further object of the present invention is to provide a knee prosthesis which allows full flexion of the reconstructed knee without applying shear forces.
A further object of the present invention is to provide a knee prosthesis where the tibiofemoral area contact controls the movement of the femoral component and thus ' increases quadriceps effectiveness.
An object of the present invention is to provide a knee prosthesis in which A-P sliding of. the bearing element with knee flexion allows 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 with improved medial-lateral stability, substantially unaffected by azial rotation or anterior-posterior (A-P) shift of the bearing element.
A further object of the present invention is to provide a knee prosthesis which includes constraints at the WO 921024 PCT/U59I/a~520 c limits of normal motion to compensate for missing cruciate ligaments and prevent dislocation.
A further object of the present invention in to provide a semiconstrained knee prosthesis where the femoral component may articulate in extremely close proximity with the ' tibia to eliminate patella baha problems.
In accordance with the foregoing and other objects, the unconstrained prosthetic knee of the present invention includes a femoral prosthesis having a condylar portion with at least two saggitally spaced arcuate segments of different radii, a tibial prosthesis having a bearing surface for supporting weight, and an intermediate load-bearing member having a thrust-bearing surface for matingly engaging the bearing surface of the tibial prosthesis and adapted to distribute weight and to transmit forces in a plane substantially perpendicular to the axis of the tibia and a mutually congruent superior surface for engaging the eondyles of the femoral prosthesis to provide area contact throughout the full range of flezion/eztension of the knee.
BRIEF BESCRIPTION OF THE pRAWINGS
A complete understanding of the invention may be obtained from the detailed description which follows, together with the accompanying drawings, wherein:
wo ~anosaza Pcrius9moaszo g Fig. 1 is.a perspective view of the unconstrained prosthetic knee of the present invention;
' Fig: 2 is an exploded perspective view of the tibial component and bearing element of the prosthetic knee of the present invention;
Fig. 3 is a vertical section taken generally along the line 3-3 of Fig. 1;
Fig. 4 is a vertical section taken generally along .".
the line 9-9 of Fig. 1;
Fig. 5 is a vertical section taken generally along the line 5-5 of Fig. 1;
Fig. 6 is a top plan view of the bearing element made in accordance with the present invention;
Fig. 7 is a front elevational view of the bearing element of Fig. 6;
Fig. 8 is a bottom view of the bearing element of Fig. 6;
Fig. 9 is a rear elevational view of the bearing element of Fig. 6;.
Fig. 10 is a side elevational view of the bearing element of Fig. 6;
Fig. 11 is a vertical section taken generally along the line 11-11 of Fig. 6;
Fig. 12 is a vertical section taken generally along the line 12-12 of Fig. 6;
WO 9?/08424 PCI"/US91/08520 Fig. Z3 is another vertical section taken generally along the line 13-13 of Fig. 6;
Fig. 14 is a diagrammatic representation o~ the assembled bearing, element and tibia portion showing the bearing element in its ~o,rwardmost position;
Fig. 15 is a diagrammatic representation similar to Fig. 19 showing the bearing element in its rearwardmost position;
Fig. 16 is a top plan viewr of the femoral component on a reduced scale;
Fig. 17 is a vertical section taken generally along the line 17-17 of Fig. 16;
Fig. 18 is a front elevational view of the prosthesis assembly implanted within a patient;
Fig. 19 is a real elevational view of the prosthesis assembly implanted within a patient;
Fig. 20 is a side elevational view of the prosthesis assembly in a generally. straight eztended position; and Fig. 21 is a diagrammatic representation of the prosthesis assembly with the knee shown in flezian.
BRIEF DESCRIPTION OF TFiE PREFERRED EfiBODIMENT
The floating bearing prosthetic knee. generally designated 10 in Fig. l, provides area contact as opposed to lane contact or point contact throughout the entire '. , ;:'.' ... . .' ~; .. ., ..
WO 92/~Sd24 PCfI'tJS91/0852n 2~'~~2~~3 flexion/extension range of the prosthesis. Through this design, some degree of rollback authomatically occurs as the knee flexes and additional rollback is allowed to will occur through the movement of the sliding bearing. ' Area contact throughout the full range of motion is obtained through the use of multiple arcuate sections along the path of,conduct of the condyles with the bearing insert. However, unlike prior art prosthetic knees of the prior axt, the different radii and arcuate portions of the condyles lie in different saggital or medial-lateral planes. Thus tibial-femoral area contact will occur in different longitudinal planes throughout the flexion/extension range of the knee. Area contact will occur simultaneously in two planes only at the point of transition between the respective arcuate portions.
The desirable prosthetic knee 19 satisfies at least five characteristics. One. the knee should have the normal polycentric motion of the normal knee joint. Two, unconstrained anterior-posterior motion and rotation would be vermitted within the normal range of motion of the knee.
Three, constrained A-P motion and rotation would occur at the limits of normal motion. Four, normal rollback of the femur with reenact to the tibia should occur during flexion of the knee. Five, tibial-femoral contact pressure should be minimized in order to reduce wear on the polyethylene bearing insert 16. The present invention to satisfies these five characteristics as described hereinafter.
WO 92/08d2d PC.'T/ US91/0~520 t2 l~,~oR corlPO~tl:~s Referring now in particular to Fig. l, the unconstrained knee, generally designated 10, is shown in perspective view to include~layfemoral component 12, a tibial component 14, and a bearing element 16. The femoral component 12 includes at least one upwardly extending stem 18 or other means for connection to the femur and a pair of condyles 20 on its inferior surface for engagement with the bearing portion 16. Preferably, the bearing element 16 is constructed of a tough, wear-resistant, resilient material such as high density polyethylene. The remaining elements of the prosthetic knee are metallic and preferably manufactured of a cobalt-chromium alloy material approved for use in prosthetic devices.
The tibial component includes a generally flat rigid platform 22 and a depending stem portion 24 for securing the tibial portion to the tibia. The superior surface of the femoral component and the implantable stern portion 2~1 and inferior surface of the platform 22 of the tibial component include a surface adapted for extramedullary porous ingrowth to secure the prosthetic device within the tibia and femur, respectively, of the host or allograph bone of the patient. By contrast, the condyles 20 of the femoral component are highly polished to reduce friction.
~e~o ~aio~4aa ~~crivs9~io~sao ~0'~~2,~~
Referring to the lower portion of Fig. 2, the tibial portion includes the platform 22 and the depending stem 24.
The platform is provided with a pair of laterally spaced, ., generally triangular-shaped, upward protrusions.26 and a centrally located aperture 28 for limiting the A-P movement of the bearing 16 described below.
More particularly, referring to Figs. 2, 5 and 6, the bearing 16 includes a centrally located generally rectangular opening 32 which is used to slidably connect the bearing to the top of the tibial component 22. The bearing 16 has a generally flat inferior surface 39 as shown in Fig. ~ which slidably engages the superior surface or platfarm 22. The aperture 32 includes, at its lower end, a ridge or lip 36, of similar configuration. Both the aperture 32 and the vertical wall of the bearing have smooth or rounded corners to reduce stress.
The bearing 16 is captured by a retaining means, generally designated 40, which includes a shoulder bolt 42, a retainer 44 and a spacer 46. The spacer 46 and retainer X14 are preferably manufactured of high density polypropylene, similar to that used for the bearing insert 16 and the shoulder bolt 42 would be made of stainless steel or cobalt-chromium alloy approved for use in this application.
The shoulder bolt 42 includes a lower threaded portion 4B which engages a plurality of threads 50 at the lowermost end of the aperture 28 within the stem 24 of the WO 92/08424 ~~Cb PCT/lJ591/08520 tibial component. .The shoulder sets the depth to prevent from the head.52 of the shoulder bolt from impeding the movement of the bearing insert 16~.v-, The retainer 46 includes an enlarged diameter ring 54 at its lowermost end which engages the .
platform 22 of the tibial portion 14 around the aperture 28 and extends upwardly coaaially with the shoulder bolt 42. , The retainer or retaining element 44 is generally square in shape and includes a lower square portion 56 which forms a clearance fit within the ridge 36 at the lower end of the aperture 32 in the bearing. as can be seen in Fig. 5. The upper end of the retainer includes an enlarged flange 58 which engages the top of the step or lip 36. The retainer 44 is dimensioned so that the distance between the underside of the head 52 of .the shoulder bolt and the top of the lip 36 provides a low tolerance clearance fit with the flange 5B of the retainer to allow the bearing 16 to slidably move on the platform 22 without becoming disengaged from the platform 22.
In this manner. the bearing is free to slide in an anterior posterior or A-P path. The retainer 44 will stop the movement in the A-P direction as the front and rear surfaces engage the front or inner surfaces of the lip 36.
The retaining means 40, in addition to permitting A-P
movement of the bearing 16 also permits pivotal movement generally about the center line of the shoulder bolt 42. Thus, depending upon the anterior or posterior displacement of the _ 15 bearing insert 16 relative to the retainer 44, the bearing insert and the retainer may pivot about the center line of the shoulder bolt 42 to provide freedom of movement. However, in order to prevent too much pivotal movement of~the bearing 16, particularly when in its anteriormost position, the triangular protrusions 26 provide a stop means.
The stop means includes the upward protrusions 26 and a pair of symmetrical cutouts 60 on the lower surface of the bearing insert lfi. In particular, each cutout includes a generally flat rear wall 62 and a generally curved inner wall 64 for engagement with the upward protrusions 26. As shown in Fig. 9, the height of the rear wall 62 permits the cutouts 60 to clear the top of the stops 26. Referring to Fig. 14, in its anterior-most position, the arcuate walls 64 of the bearing 16 engage the inner, generally right angle corner of the triangular protrusions 26 to virtually greclude most of the pivotal movement or rotational movement of the bearing insert 16. As the bearing 16 is moved towards its posterior-most position, as shown in Fig. 15, the bearing is free to rotate in either direction as shown by arrows A and B and are limited by the longer upstanding walls of the protrusions 26 which engage the flat walls 62 within the cutout 60.
Therefore, it can be seen that the bearing insert 16 is constrained but is permitted to move in the A-P direction from the eatremes as shown in Fig. 14 to that as shown in Fig.
W~O 92i08d2d t'C.'T/US9t108520 16 while, at the same time, it is free to pivot about an axis defined by the shoulder bolt 29 within the limits created by the stop means where the walls 62 and 64 of the cutouts 60 engage the triangular protrus~i.ons 26. These constraints, while permitting movement of the~bearing 16, control the movement of the femoral component as described hereinafter and thus create some rollback and allow for the further posteriax movement of the bearing insert.
These constraints at the limits of normal motion will compensate for missing cruciate ligaments and prevent dislocation of the components, i.e., the bearing insert, which has been seen to occur in popular prior art floating bearing prosthetic knees. In most circumstances, normal soft tissue will provide the primary restraining forces limiting motion of the components and, if necessary. the limits incorporated into the prosthesis 10 would function as secondary restraints.
Some rollback (approzimately 5 millimeters in the present embodiment) automatically occurs (i.e., is obligated to occur) when tibiofemoral contact moves from one arcuate segment to the other one. The rest of the normal amount of rollback is allowed to occur (but not obligated to occur) with the movement of the bearing insert. The amount of additional rollback that is allowed to occur is governed by the interaction of the posterior cruciate ligament and the condylar surfaces. The rollback of the femur with respect to the tibia during flezion WO 92/08424 PCT/US91108520 ...
-~~1~~~:~'~
of the knee is an important characteristic of the present prosthesis because it causes the patellar tendon to move anteriorly with respect to the femur which greatly increases.
the effectiveness of the quadriceps muscle. especially when rising from a chair. It~has bean found that many patients who have had total knee replacements cannot get up from a sitting position without assistance from their arms. Also, prior arm unconstrained knees are frequently found to "roll forward"
rather than backward during flexion. In the design of the present invention, the shoulder bolt retaining means 90 prevents roll forward and the bearing insert 16 recreates the normal situation and further helps to increase the quadriceps efficiency. Known prior art total knee replacements have attempted to utilize the femoral component to control the motion of the bearing insert, just the opposite of the knee of the present invention.
~'HE FEM012AL CUMPONE1QT
The femoral component 12 of the present invention includes generally a pair of condyles 20, securing posts 18 and a web portion which defines a patella track 'T0. The securing posts 18 provide means to secure the femoral component to the femur of a patient. As shown in Fig. 20, a pair of matched apertures are drilled into the femur and the end of the femur ' is formed with five generally flat surfaces as shown to fit ;;- : ; :',.. .. ,:, T. ... .,: ,.
WO 92/U842~3 P(_'T/US91/UB52U
within the flat surfaces 72a through 72e as shown. The , opposite Surfaces 72a and 72e are generally parallel to one another and perpendicular to the surface 72c. The angled surfaces 72b and 72d are approximately at 45 degrees with respect thereto. The entire surface of the flat surfaces 72a-a and the surfaces of the posts 1B are designed for extramedullary bone growth to secure the femoral component to the end of the femur.
Certain prior art prostheses propose the use of a femoral component in which the multicentric surfaces of the condyles were created by a common planar curve which created a design whereby every sagittal section along the condyle was polycentric. This design results in a situation where the condyles can only make area contact during approximately the initial 2~° of knee flexion thereby resulting in line contact and very high contact pressure which increases the wear of the bearing insert. In addition, prior art design of this type accomodates rollback of the femur with respect to the tibia and, particularly at maximum flexion, there is a tendency for the bearing insert to "pop out" or become dislocated.
The femoral component and sliding bearing of the present invention have congruent surfaces which allows for rotation and A-P motion within the range of normal A-P motion to prevent excessive anteriar and posterior drawer and rotation and dislocation of the bearing. The upper surface of the WO 92/08~2d POf/U591l08520 _t 9 bearing I6 is designed so that the inferior surfaces of the femoral component always have area contact at all flexion angles. Constant area contact is achieved by distributing the femoral contact areas on the bearing Z6 across the frontal plane such that different areas of the bearing 16 are contacted through different angles of knee flexion. Each contact area on the bearing has the same radius of curvature as the portion of .
the inferior surface of the femoral component 12 in contact with the bearing.
Referring to Figs. 6-I3, the bearing insert I6 is generally oval in shape with a pair of flat ends 80R and 80L.
The anterior or front side is a generally flat arcuate wall 82 which includes a pair of cutouts 60 at the lower right and left ends, respectively. The posterior side includes a relatively large, almost semicircular recess 8~ which grovides substantial clearance for the posterior crueiate ligaments. The top portion of the rear wall on either side of the recess 84 includes a short generally vertical arcuate wall portion 86 which merges into a generally arcuate. inwardly tapered lower wall portion 88. The tapered portions 88 merge with a pair of lower champhers at the bottom of the end walls 80R and 80L
which terminate at their front ends with the cutouts 60.
1~'~ 92/0&124 Pt'1"/US91/08520 ~o ~~~ a The superior surface of the bearing insert is described by a plurality of arcuate channels or grooves which are described in detail hereinafter in connection with the arcuate surfaces defined on the inferior contact surface of the femoral component. In order to add rigidity to the front wall portion 82, an upstanding flange 96 is included immediately anteriorly of the aperture 32. The outer edges of the top of the front wall 82 are softened by curves 98 as the transition to the top of the bearing insert 16.
The contact surfaces between the bearing insert 16 and the femoral component 12 are best understood if considered together. The ugper surface of the bearing 16 includes a plurality of arcuate surfaces for engagement with congruent arcuate surfaces on the inferior side of the femoral component 12. Referring to Fig, 6. four of the arcuate surfaces have been labelled L and two of the surfaces have been labelled S.
The four arcuate surfaces L are all generated using the same radius of curvature and similarly the twa arcuate surfaces labelled S are generated using the same but smaller radius, The arcuate surface S shown in section view in Fig. 12 is defined posteriorly of the arcuate surfaces L, one of which is shown in sectional view in Fig. 11. As Can be seen in Fig. 5.
the comglementary surface of the femoral component includes tvo ~2~os~2a Ycrms~ao~szo 2t ~~~o~~
four arcuate surfaces L and two arcuate surfaces S. One significant feature of the present invention is that the arcuate surfaces L and R lie in different saggital planes as shown and make contact during different degrees of flexion of the knee.
In particular, the arcuate surfaces L on the inferior surface of the femoral component are in contact with the arcuate surfaces L on the bearing 16 between approximately 0°
through 8° of flexion of the knee and the arcuate surfaces S of the femoral component are in contact with the arcuate surfaces S of the bearing 16 during approximately 8° through 140° of flexion of the knee. At the transition point, at approximately 8° of flexion, area contact occurs between all of the arcuate surfaces L and S on the femoral component 12 with all of the arcuate surfaces L and S on the bearing component 16.
Although the size of the patient will partially determine the size of the prosthesis, the following sizes have been found to be effective in trials. More particularly, referring to Fig. 3, the arcuate surfaces L are generated by radius R1 about a center point C. Center point C is slightly rearwardly defined relative to the past 18 and the radius Rl is approximately 1.60". The arcuate surfaces S are generated by a radius RZ about a center of rotation D. The radius R2 is approximately 0.75". The center of rotation D of radius R2 Iies on a line passing through the center of rotation C of R1 WO 92/08424 ~ 2 ~ PCT/U541/08520 so that the surfaces L and R have a tangent point T in order to have a smooth transition of tibia--femoral contact at approximately 8° of flexion,. ~Thus, area contact of the arcuate surfaces L occurs during the first 8° of flexion of the knee and area contact is transferred to the arcuate sections S at 'approximately 8° and continues through maximum flexion of about 140°.
The position of the femoral component 12 with regard to the bearing 16 is controlled by the center of rotation of curvature for the arcuate surfaces S or L which are in contact. The arcuate curves S are placed farther back on the bearing and will draw the femoral component posteriorly thus allowing obligatory rollback. Further rollback is permitted because the elongated aperture 32 in the bearing allows the bearing to move posteriorly on the tibial platform. As described previously, the constraints 26 and the retaining means 40 prevent anteriar movement of the bearing 15 beyond the anterior edge of the tibial component. Therefore, when rollback is occurring during flexion of the knee, no compensatory roll forward will occur between the bearing 16 and the tibial component 14. As the femoral component passes through approximately the 8° range, area contact is transferred between the arcuate surfaces L to the arcuate surfaces S, the transition continues smoothly because of the common tangent point of the respective arcuate surfaces. The constraints as dvo 9z~o~sza 2 ~ ~ p ,~ $ ~ ~ $ Pc-r~us~'iosszo previously described With respect to the bearing 16 prevent dislocation of the bearing element when implanted.
In an alternative embodiment, it is possible to obtain the same functionality and operation if, for example, the innermost or outermost complementary arcuate surfaces L
were eliminated. However, additional area contact can be obtained to decrease the pressure between the femoral,component and the bearing by providing the additional arcuate surfaces L
adjacent the center aperture 32.
In addition, the arcuate surfaces L and S are designed to obtain the mazimum amount of area contact possible within the permissible space. To this end, the arcuate surfaces 5 on the bearing l~b are approzimately 3/8" wide and approzimately 1-1!8" Long. As described previously, the radius R2, the radius for generating the arcuate surface S is approzimately 0.75" and lies in a sagittal plane. The transverse radius which defines the arcuate surface in the medial lateral plane as shown in Fig. 5 is approzimately .375"
Similarly, the arcuate surfaces L are approzimately 1.25" in length generated by the radius R1 in the sagittal plane and the radius in~the transverse plane R4 (Fig. 5) which defines a .
radius of curvature of the arcuate surfaces L in the transverse plane is approzimately 0.125" The center of rotation D is apgrozimately 0.375" posteriorly of the center of rotation C
and about 0.9" below the center of rotation C, The center PC'f/US91/08530 WO 9Z10~1~4 ~~7~~ z~
lines of the arcuate surfaces L are approximately 0.3" on either side of the center line of the areuate section S and the ' respective center lines of the arcuate sections S are y ..;., approximately 2.00" apart.
The knee prosthesis 10 of the present invention is the only design which gives area contact between the bearing 16 and the femoral component 12 in all degrees of flexion. The highest pressures on the knee joint are experienced during stair climbing where the knee is flexed to approzimate2y 90 degrees of flexion in which the prior art knees have only line contact ar point contact. Since polyethylene (the material used to form the bearing) wear appears to be related to excessive pressures, area contact is virtually as important in stair climbing as in walking. even though stair climbing is performed much less often. The prosthetic knee 10 also permits the use of the same component in the presence or absence of posterior cruciate ligaments. Generally speaking, semiconstsained knee prosthesis require the presence of posterior cruciate ligaments to prevent posterior subluzation of the tibia, On the other hand. constrained prosthesis, which do not allow rollback, require removal of the posterior cruciate ligaments because proper tension on the posterior cruciate ligaments would attempt to create posterior rollback which is prevented by the constraints. This could lead to dislocation of the components of the contrained prosthesis or rupture of the posterior cruciate ligaments.
WO 92/0&~2~b PC.'f/US91/08520 __ ~5 2~'~~225 In prior art designs in Which the arcuate surfaces of the condyles are created by using a common plane generating curve, all of the the sagittal sections of the c~ndyles are polycentric. On the contrary, the present invention has only one radius of contact in each sagittal plane and, therefore, is not created by a common plane generating curve. since all potential points of contact in the sagittal plane have the same radius of curvature, area contact can be obtained throughout the entire flexion arc of the knee in a manner which cannot be obtained by the prior art knees where the radii along the condyles changes while contacting the same area of the bearing insert.
Referring to Figs. 18-21, which show the prosthetie knee 10 of the present invention implanted in a patient, it can be seen in Fig. 20 that in the eztended position of the prosthesis, the bearing insert 16 moves to its anterior-most position with respect to the tibial component 14. In this position, the arcuate surfaces 1a an the respective tibial component and bearing insert 16 ors in engagement. As the knee flexes, rollback of the femur with respect to the tibia begins to occur to approximately the maximum gosition as shown in Fig.
21 where the bearing insert 16 has waved to its posterior-most position emulating, as close as possible, the normal knee.
Thus, it can be seen that the present invention defines and describes a prosthetic knee which morn closely wo ~2iosa2a Q~ ~~ ~ 6 P(.T/US91/OSS20 ~~~ a v simulates the normal knee movement than any prior art devices.
The prosthesis 10 provides normal polycentric motion for the knee joint and permits normal rollback of the femur with respect to the tibia during~:.f~lexion. The rotational and anterior-posterior, movement of the bearing insert is unconstrained for the normal range of motion but .is constrained at its limits. The design of the polycentric contact surfaces between the femoral component 12 and the bearing insert 16 assure for sufficient area contact throughout the flexion/extension range of the knee to minimize pressure and resultant wear on the bearing insert. While the foregoing detailed description has been given for clearness and understanding, no unnecessary limitations should be understood therefrom as some modifications will be obvious to those skilled in the art.
Claims (17)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An improved prosthetic device performing a joint between a pair of human or animal bones, comprising:
first fixation means adapted for fixation to one of the bones;
a first bearing surface on said first fixation means, said first bearing surface including at least two, convex, laterally adjacent, arcuate bearing portions of differing radii;
second fixation means adapted for attachment to the other bone;
a generally planar, second bearing surface on said second fixation means, said second bearing surface having an axis which projects generally perpendicular thereto; and a bearing element between said first bearing surface and said second bearing surface and having a complementary concave surface on one side for rotatably engaging the arcuate bearing portions of the first bearing surface and an opposite surface mating in rotatable congruent bearing relationship with said second bearing surface, wherein said opposite surface also engages said second bearing surface over a medially-laterally constrained, predefined path of anterior-posterior sliding engagement, which path is independent from said rotatable engagement with said second bearing surface.
first fixation means adapted for fixation to one of the bones;
a first bearing surface on said first fixation means, said first bearing surface including at least two, convex, laterally adjacent, arcuate bearing portions of differing radii;
second fixation means adapted for attachment to the other bone;
a generally planar, second bearing surface on said second fixation means, said second bearing surface having an axis which projects generally perpendicular thereto; and a bearing element between said first bearing surface and said second bearing surface and having a complementary concave surface on one side for rotatably engaging the arcuate bearing portions of the first bearing surface and an opposite surface mating in rotatable congruent bearing relationship with said second bearing surface, wherein said opposite surface also engages said second bearing surface over a medially-laterally constrained, predefined path of anterior-posterior sliding engagement, which path is independent from said rotatable engagement with said second bearing surface.
2. A prosthetic device as claimed in claim 1 wherein said bearing element is freely rotatable through a prescribed arc in a plane generally perpendicular to said axis.
3. A prosthetic device as claimed in claim 1 wherein said second bearing surface is a substantially flat surface substantially perpendicular to said axis.
4. A prosthetic device as claimed in claim 1 wherein said second bearing surface is a nearly flat surface of revolution which is approximately perpendicular to said axis.
5. A prosthetic device as claimed in claim 1 wherein said bearing element is freely movable for both said anterior-posterior sliding engagement and said independent rotatable engagement in said plane generally perpendicular to said axis.
6. A prosthetic device as claimed in claim 1, wherein said first bearing surface comprises a pair of laterally spaced, arcuate bearing surfaces.
7. A prosthetic device as claimed in claim 1 wherein the first bearing surface has a pair of condylar portions, each condylar portion including two laterally spaced apart condyloid elements, each condyloid element having at least two bearing surfaces defined by laterally spaced, arcuate segments of different radii.
8. A prosthetic device for forming a joint between a pair of human or animal bones comprising:
first fixation means adapted for attachment to one of the bones including a pair of condylar portions;
a second fixation means adapted for attachment to the other bone including a generally flat bearing surface;
an intermediate bearing member having a complementary concave surface on one side for rotatably engaging the condylar portions, said intermediate bearing member having an opposite surface for mating in bearing relationship with the generally flat bearing surface of said second fixation means such that said intermediate member and said second fixation means bear on one another at a mutually congruent thrust bearing surface of revolution for permitting rotational motion between said intermediate member and said second fixation means while force is transmitted therebetween, and permitting independent sliding motion of said intermediate member relative to said second fixation means over a medially-laterally constrained, predefined path of anterior-posterior sliding movement.
first fixation means adapted for attachment to one of the bones including a pair of condylar portions;
a second fixation means adapted for attachment to the other bone including a generally flat bearing surface;
an intermediate bearing member having a complementary concave surface on one side for rotatably engaging the condylar portions, said intermediate bearing member having an opposite surface for mating in bearing relationship with the generally flat bearing surface of said second fixation means such that said intermediate member and said second fixation means bear on one another at a mutually congruent thrust bearing surface of revolution for permitting rotational motion between said intermediate member and said second fixation means while force is transmitted therebetween, and permitting independent sliding motion of said intermediate member relative to said second fixation means over a medially-laterally constrained, predefined path of anterior-posterior sliding movement.
9. A prosthetic device as claimed in claim 8 wherein said intermediate member in said congruent thrust bearing relationship with said second fixation means is freely movable in a plane approximately parallel to said generally flat bearing surface of said second fixation means while transmitting force to said second fixation means.
10. A prosthetic device as claimed in claim 9 wherein said mutually congruent thrust bearing surface is a nearly flat surface of revolution which is approximately parallel to said generally flat bearing surface of said second fixation means.
11. A prosthetic device as claimed in claim 10, further including stop means for limiting the movement of said congruent thrust bearing.
12. A prosthetic device for joining a pair of human or animal bones comprising:
a first prosthesis having a condylar portion and a fixation portion adapted to be fixed to one of said bones, said condylar portion including two laterally spaced apart bearing elements each having at least two arcuate segments of different radii;
a second prosthesis having a bearing surface means and a fixation portion being adapted to be fixed to the other one of said bones;
an intermediate load bearing member having a thrust bearing surface means for matingly engaging said bearing surface means in a plane substantially perpendicular to a longitudinal axis of said other one of said bones and a complementary surface having concave segments for rotatably engaging said arcuate segments;
wherein said arcuate segments and said concave segments are adapted to distribute weight and to transmit forces and to rotate freely relative to each other during said rotatable engagement;
wherein said bearing surface means and said thrust bearing surface means are adapted for supporting weight and being subjected to force during said mating engagement; and wherein said engagement between said thrust bearing surface means and said bearing surface means is operable to provide independent anterior-posterior and rotational freedom of movement for said intermediate load bearing member relative to said second prosthesis;
said arcuate segments being laterally spaced so as to allow said arcuate segments to independently rotatably engage said concave segments.
a first prosthesis having a condylar portion and a fixation portion adapted to be fixed to one of said bones, said condylar portion including two laterally spaced apart bearing elements each having at least two arcuate segments of different radii;
a second prosthesis having a bearing surface means and a fixation portion being adapted to be fixed to the other one of said bones;
an intermediate load bearing member having a thrust bearing surface means for matingly engaging said bearing surface means in a plane substantially perpendicular to a longitudinal axis of said other one of said bones and a complementary surface having concave segments for rotatably engaging said arcuate segments;
wherein said arcuate segments and said concave segments are adapted to distribute weight and to transmit forces and to rotate freely relative to each other during said rotatable engagement;
wherein said bearing surface means and said thrust bearing surface means are adapted for supporting weight and being subjected to force during said mating engagement; and wherein said engagement between said thrust bearing surface means and said bearing surface means is operable to provide independent anterior-posterior and rotational freedom of movement for said intermediate load bearing member relative to said second prosthesis;
said arcuate segments being laterally spaced so as to allow said arcuate segments to independently rotatably engage said concave segments.
13. A prosthetic device as claimed in claim 1 wherein said bearing element includes at least two complementary arcuate surfaces on one side for respectively engaging each arcuate portion of the first bearing surface.
14. A prosthetic device as claimed in claim 1 wherein said arcuate bearing portions of differing radii have a common tangent point.
15. A prosthetic device as claimed in claim 1 wherein said first bearing surface includes a pair of condylar portions, each condylar portion including three arcuate bearing portions of at least two differing radii.
16. A prosthetic device as claimed in claim 1 wherein said arcuate bearing portions are laterally spaced so as to allow said arcuate bearing portions to independently rotatably engage said concave surfaces.
17. A prosthetic device for forming a joint between a pair of human or animal bones comprising:
first fixation means adapted for attachment to one of the bones including a pair of condylar portions;
a second fixation means adapted for attachment to the other bone, including a generally flat bearing surface;
an intermediate bearing member having a complementary concave surface on one side for rotatably engaging the condylar portions, said intermediate bearing member having an opposite surface for mating in bearing relationship with the generally flat bearing surface of said second fixation means such that said intermediate member and said second fixation means bear on one another at a mutually congruent thrust bearing surface of revolution for permitting rotational motion between said intermediate member and said second fixation means while force is transmitted therebetween, and permitting sliding motion of said intermediate member relative to said second fixation means.
first fixation means adapted for attachment to one of the bones including a pair of condylar portions;
a second fixation means adapted for attachment to the other bone, including a generally flat bearing surface;
an intermediate bearing member having a complementary concave surface on one side for rotatably engaging the condylar portions, said intermediate bearing member having an opposite surface for mating in bearing relationship with the generally flat bearing surface of said second fixation means such that said intermediate member and said second fixation means bear on one another at a mutually congruent thrust bearing surface of revolution for permitting rotational motion between said intermediate member and said second fixation means while force is transmitted therebetween, and permitting sliding motion of said intermediate member relative to said second fixation means.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US61333190A | 1990-11-14 | 1990-11-14 | |
| US613,331 | 1990-11-14 | ||
| PCT/US1991/008520 WO1992008424A1 (en) | 1990-11-14 | 1991-11-14 | Improved floating bearing prosthetic knee |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2078228A1 CA2078228A1 (en) | 1992-05-15 |
| CA2078228C true CA2078228C (en) | 2000-04-11 |
Family
ID=24456884
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002078228A Expired - Fee Related CA2078228C (en) | 1990-11-14 | 1991-11-14 | Improved floating bearing prosthetic knee |
Country Status (8)
| Country | Link |
|---|---|
| US (1) | US5387240A (en) |
| EP (1) | EP0510178B1 (en) |
| AT (1) | ATE163354T1 (en) |
| AU (1) | AU9089891A (en) |
| CA (1) | CA2078228C (en) |
| DE (1) | DE69128961T2 (en) |
| ES (1) | ES2112897T3 (en) |
| WO (1) | WO1992008424A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE450460B (en) * | 1984-11-28 | 1987-06-29 | Albrektsson Bjoern | DEVICE IN ARTIFICIAL MENISH FOR A KNEE JOINT PROTECTION |
| GB8432267D0 (en) * | 1984-12-20 | 1985-01-30 | Thackray C F Ltd | Knee prosthesis |
| US4888021A (en) * | 1988-02-02 | 1989-12-19 | Joint Medical Products Corporation | Knee and patellar prosthesis |
| US4892547A (en) * | 1988-02-03 | 1990-01-09 | Biomet, Inc. | Partially stabilized knee prosthesis |
| FR2631814A1 (en) * | 1988-05-31 | 1989-12-01 | Scernp | SLIDING KNEE PROSTHESIS |
-
1991
- 1991-11-14 DE DE69128961T patent/DE69128961T2/en not_active Expired - Fee Related
- 1991-11-14 ES ES92901122T patent/ES2112897T3/en not_active Expired - Lifetime
- 1991-11-14 WO PCT/US1991/008520 patent/WO1992008424A1/en active IP Right Grant
- 1991-11-14 EP EP92901122A patent/EP0510178B1/en not_active Expired - Lifetime
- 1991-11-14 AU AU90898/91A patent/AU9089891A/en not_active Abandoned
- 1991-11-14 CA CA002078228A patent/CA2078228C/en not_active Expired - Fee Related
- 1991-11-14 AT AT92901122T patent/ATE163354T1/en not_active IP Right Cessation
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1992
- 1992-11-16 US US07/976,803 patent/US5387240A/en not_active Expired - Lifetime
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|---|---|
| AU9089891A (en) | 1992-06-11 |
| DE69128961T2 (en) | 1998-10-08 |
| ATE163354T1 (en) | 1998-03-15 |
| DE69128961D1 (en) | 1998-04-02 |
| ES2112897T3 (en) | 1998-04-16 |
| EP0510178B1 (en) | 1998-02-25 |
| WO1992008424A1 (en) | 1992-05-29 |
| EP0510178A1 (en) | 1992-10-28 |
| CA2078228A1 (en) | 1992-05-15 |
| US5387240A (en) | 1995-02-07 |
| EP0510178A4 (en) | 1993-02-24 |
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