Source: https://patents.justia.com/patent/6893467
Timestamp: 2019-12-10 05:49:14
Document Index: 406845670

Matched Legal Cases: ['arts 9', 'art 9', 'art 12', 'arts 7', 'art 9', 'arts 8']

US Patent for Knee prosthesis Patent (Patent # 6,893,467 issued May 17, 2005) - Justia Patents Search
Justia Patents Knee Joint BoneUS Patent for Knee prosthesis Patent (Patent # 6,893,467)
a femoral component which more or less reproduces the form of the femoral articulation of the knee; it is fixed to the bone, either directly via a rehabilitation surface, or indirectly by means of an acrylic resin;
a tibial surface fixed to the upper end of the tibia, either directly, or by means of an acrylic resin; and
a patellar surface fixed to the posterior face of the patella, either directly or by means of an acrylic resin.
These metal components are generally made of chromium-cobalt, of titanium or of stainless steel, or of other metals and alloys, in particular ceramics.
The sliding and shock-absorbing components separating the metal components are generally made of polyethylene; they can either be made integral with the tibial component or fixed plateau or can be movable relative to the latter with a variable degree of mobility in rotation (horizontal plane), in antero-posterior displacement (sagittal plane), and in medio-lateral displacement (frontal plane); whether they are fixed or movable, the polyethylene sliding components called “inserts” articulate with the femoral component via two femoral condyles, an internal one and an external one, these condyles having a certain congruence with the two respective concave surfaces, called glenoid cavities, of the polyethylene insert. A prosthesis is said to have a movable “plateau” when the insert has a free axial rotation. The prosthesis according to the invention is preferably of this type.
either a third femoral condyle engaging in a third cavity on the upper face of the insert;
or a stud on the upper face of the insert engaging in a cavity (nest) situated between the two femoral condyles;
or different forms of cams situated between the femoral condyles and bearing on an elevation on the upper part of the insert.
In all cases, however, there are angulations in a frontal plane, rendering the contact between the components discontinuous.
The physiology requirements of the knee must be respected, in particular the displacements and respective positions of the femur relative to the tibia: rolling/sliding with retreat of the point of contact of the femur on the insert during flexion (90°), and advance of the femur during extension (0°), which conditions the moment of action of the patellar tendon, which controls the efficacy of the muscular propulsion and, by this means, the comfort of the patient and the quality of walking, of going up and down stairs, and of standing up from a low position. These relationships must be ensured, during the movements, by the form of the articular surfaces of the prosthetic components (determined by the design of the prosthesis) and in particular by a cam effect between the femur and the insert, in cooperation with balanced tensioning of the collateral ligaments of the knee joint, determined by the action of the surgeon and by ancillary instrumentation respecting this requirement.
In certain types of prostheses, the polyethylene insert is fixed relative to the tibia. In this case, the tangential rolling/sliding movements, the shearing movement and all the movements of rotation take place in the contact zone between the femoral condyles and the tibial glenoid cavities. When these contacts are over a small surface area, high pressure can be reached in the polyethylene. Their designers generally recommend a pressure of less than or equal to 10 Mpa in the polyethylene zones where bearing is constant, that is to say in the zones near the walking position. An ideal pressure of 4 Mpa is desirable. However, in the prostheses with a low congruence (linear of punctiform articular surfaces between femur and polyethylene insert), pressure of over 30 Mpa are currently measured, and can even reach 50 Mpa. This leads to rapid degradation of the polyethylene, possibly necessitating further surgery to change the prosthetic implants. A contact surface of greater than 400 mm2 is recommended. The state of the art, in the field of prosthetic joints, has led to the manufacture of prostheses in which the polyethylene inserts are congruent in relation to the femoral surface, a corollary of this congruence being that the insert must be movable in rotation relative to the tibial seat. These implants are referred to as prostheses having a movable plateau. In such cases, the articular congruence can be respected, making it possible to obtain a high degree of surface contact. With this type of prosthesis, pressures of the order of 4 to 8 Mpa are currently obtained in the polyethylene, which promotes the useful life of the latter.
Various congruent prostheses exist, but they all have two major disadvantages, which the present invention aims to correct:
the congruence of the contact between the condyles and the tibial glenoid cavities is present particularly near extension but diminishes during flexion;
the congruence is envisaged in only one plane: the sagittal plane; thus, considerable stresses can arise in the contact zones during movements of inclination or lift-off, or rotation, or in combination in these three directions, particularly when the surfaces include angulations.
To obviate this, the various surfaces must be tangential in relations to one another in the two spatial planes (sagittal and frontal) in order to permit sliding movements without sudden stops and without angular contacts in these three directions.
(3) Stability Requirements
retention of the two cruciate ligaments;
retention of only the posterior cruciate ligament, although it has been shown that in this case the antero-posterior displacement does not have satisfactory kinematics;
finally, stabilization of the prosthesis by a central mechanism intended to guide the femur in relation to the tibia.
This latter type of mechanism is in fact the most effective for keeping the stability in accordance with the kinematics of the knee, and it is a device of this type with which the present invention is concerned.
the most traditional is that of a rod which comes into contact with a vertical central stud of variable shape;
other mechanisms use a cam cooperating with a central abutment which has a profile complementing this cam; for example, the third and central femoral condyle; situated between the two lateral condyles;
in other prosthesis configurations, there can be a third, central condyle which itself is in the form of a transverse cylinder which is engaged in a transverse cylinder ending at its front part in the form of a cam.
A disadvantageous effect of this latter configuration is a total absence of freedom of antero-posterior movement between the femoral component and the tibial insert when the cylinder has the same transverse axis as the two lateral condyles. It is therefore a mechanism of the so-called hinge type, which can be responsible for considerable pressures in the articulation between the patella and the femur. The mechanism of rolling/sliding is not respected and one of the consequences can be the existence of considerable patellar pain. The recovery of a certain forward/rearward mobility in the zone of contact between polyethylene insert and tibial plateau is not sufficient to overcome this disadvantage; this mobility situated at a different level than normal generates a parasite movement referred to as “roll forward”, during which the tibia moves back in flexion relative to the femur, which can lead to disengagement of the prosthetic components.
Another source of problems lies in the fact that, between the bearing phase and the oscillating phase of walking, there is a separating of the femoral metal component relative to the polyethylene insert, which in English is referred to by the term lift-off. This lift-off is seen principally between 40 and 70° flexion of the knee, principally in the zone from 50 to 70°. This generally involves the separating of the lateral condyle relative to the lateral tibial plateau. This lift-off, which exists physiologically (about 1.8 mm) can attain amplitudes of several millimeters, sometimes 5 mm or more, in the case of certain prostheses.
In the concept proposed according to the invention, the resultant of the transmissions of the stresses is preferably directed to the central part of the tibial seat, about its central element of fixation which is called a stem and is fitted at the center of the upper end of the tibial bone. The aim of this type of transmission is to reduce as much as possible the medio-lateral torque effect which is responsible for the loosening or for predominant wear of one of the two compartments.
The concave-convex engagement in the frontal and sagittal planes between the central depression of the femur and the torus (the median projection of the insert) has the benefit of offering a congruent and progressive bearing during the lift-off movements, irrespective of the angle of flexion of the knee.
This form of contact between the femoral metal component and the polyethylene insert additionally makes it possible to vary the contacts in a continuous manner via the progressive engagement of the contact surface, avoiding the shocks and vibrations which, when they are transmitted to the anchoring points of the metal components in the tibial or femoral bone, are a source of vibrations which once again favor the loosening of the prosthetic components, which leads to the latter being changed.
the congruence intended to protect the longevity of the polyethylene used and to diminish its wear;
kinematics intended to give a functioning which is comfortable for the patient.
a congruence with a large contact surface between the femoral component and the insert, irrespective of the angle of flexion, makes it possible to reduce the pressures exerted on the polyethylene;
the congruence must diminish during flexion, the large contact surface being necessary in the bearing sector from 0 to 60°, but the sector of flexion beyond 90° does not require a large contact surface because:
the use of this sector is more rare;
congruence extended to all degrees of flexion, in particular beyond 90°, results in a prosthesis which is subject to considerable stress, hence a risk of excessive stressing of the anchoring points;
the high level of surface congruence is necessary, but without angular contact and without flat parts or bends of the tenon and mortise type involved in the movements of LIFT-OFF or lateral inclination, irrespective of the angle of flexion:
This is frontal congruence.
the kinematics must respect the true rolling/sliding of the knee. This is defined in the following way: the point of contact of the femoral component relative to the insert is a few millimeters in front of the center of this insert in extension at 0° and retreats several mm behind the center of the insert when the flexion exceeds 15 to 20°, without the femoral component and the femoral bone segment displacing rearward relative to the tibial component or the tibial bone segment. This is distinguished from false rolling/sliding in which the femoral component and the femoral bone retreat under a cam effect relative to the tibial component of the prosthesis or relative to the tibial bone, which phenomenon must be avoided since it generates:
a system with three zones of bearing between the femoral component and the insert;
a system having medio-lateral continuity of the contact between the bearing surfaces of the femoral component and of the insert;
a succession of concave or convex surface segments having the form of a spiral in profile;
the concave parts of the femoral surface corresponding to convex tori of the surface of the insert;
in the frontal plane, a succession of condyle/insert engagements, being concave-convex, then convex-concave, then concave-convex, going from the medial condyle to the lateral condyle;
in the sagittal plane, the three femoral surfaces-medial, central and lateral—have a downwardly directed convexity, while the three surfaces of the insert have an upwardly directed concavity, so as to have a central zone of saddle shape but a continuous medio-lateral contact.
It is also an object of the invention to make available a knee prosthesis in which the general shape of the three zones-lateral, central and medial—of the femoral component are determined by a spiral curve in the sagittal plane, the general shape of the three zones-lateral, central and medial—of the insert being also determined by a spiral curve in the sagittal plane, the generating spiral curve of the insert being derived from the generating spiral curve of the femoral component. These two spiral curves are calculated with the aim of reproducing the true rolling/sliding according to the definition given above.
in a frontal plane: movement called lift-off, that is to say sliding lift and angulation of a condyle and angulation, with a contact remaining congruent between the femoral component and the insert both in the lateral cavity of the insert and on all or part of the central dome, irrespective of the angle of flexion;
in a sagittal plane: a movement of flexion with preferably a natural roll/glide of the femoral component on the insert, that is to say a displacement of the point of contact of the femur on the insert from a few millimeters in front of the center of the insert, in position of extension 0, to a few millimeters behind the center of the insert, in the flexed position, but without displacement of the femoral component itself, or of the bone segment which carries it, relative to the tibial component (absence of translation);
in a horizontal plane: rotation relative to a vertical axis, of which the amplitude varies depending on whether the insert is movable in rotation or not relative to the tibial component; according to the invention, the insert is preferably free on axial rotation.
More precisely, seen in cross section through a frontal plane, the surface of the insert directed toward the corresponding surface of the femoral component and coming into continuous contact in the medio-lateral (transverse) direction with the latter comprises two lateral curve segments with the concavity directed upward and one central curve segment whose convexity is directed toward the femoral component, the convexity of the central part connecting tangentially on each side to the concave parts with a profile which corresponds substantially to the associated condylar part of the femoral component, the whole forming a curve direction discontinuity or sharp edge, like a sinusoid.
the frontal generating curve is a geometric element of the design but does not correspond totally to the zone of contact between the prosthetic components (femur and insert) because the femoral component of this prosthesis has only two conventional condyles separated by a discontinuous zone (notch) whereas, according to the present invention, there is total continuity from one margin of the femoral component to the other.
In said US patent, the generating curve portion called K3 is a design element, but not a zone of continuous material for bearing of the femoral component on the insert, like the central radius of the prosthesis according to the invention. The frontal generating curve of the US prosthesis passes through a polycentric sagittal curve which comprises four segments of different radii from front to back, whereas, according to the present invention, the frontal zone passes through a spiral generating curve.
Likewise, the precise form to adopt for the curve in the frontal plane is defined by the need for an angulation of approximately 5° between the femoral component and the insert during the lateral lifting referred to as lift-off (or varus-valgus).
This distinguishes the prosthesis according to the invention from that of WO 98/46171 A in which, although there is a continuity with three bearing surfaces—two condyles and an intercondylar cam—the conformity in the frontal plane concerns only the lateral cavities of the insert and the corresponding condyles, but not the central part.
The attached diagrammatic drawings illustrate an embodiment of the invention in greater detail. They do not of course imply any limitation. In said drawings:
The knee prosthesis illustrated in FIG. 1 comprises a femoral component 1 which is generally of metal and can be implanted in the femur of the patient, a tibial component 2 which is also of metal and can be implanted in the tibia of the patient, and an insert 3 which is generally of a plastic material such as polyethylene.
As has been explained above, the complementary nature of the surfaces of parts 9 and 10 which come into mutual contact during the relative displacement of the femoral component 1 and of the insert 2 is not absolute and must provide some play or “laxity” permitting a sliding take-off movement, or lift-off, of a condylar part, with an amplitude of approximately 2 to 5 mm in the frontal plane, an overall antero-posterior laxity or “drawer”, in a sagittal plane, also of between 2 and 5 mm, and a rotation about a vertical axis, in a horizontal plane, of the order of 8°, but which can be less when the insert 3 is itself movable relative to the tibial component 2.
As has been mentioned above, the precise shape of the projecting part 9 forming a cam in the sagittal plane is determined by X-rays of the knee joint, bent in a large number of different positions, and it is not defined by a precise mathematical equation. This cam is such that, at an angle of flexion of 0°, the center of the bearings of the femur on the insert is a few millimeters in front of the center of the insert and such that it is a few millimeters behind this center starting from a certain degree of flexion of between 15° and 20°.
It will be noted that the hollowed central part 12 of the femoral component 1 connects to the lateral parts 7 of this component 1 via a radius of curvature R2 which is constant from front to rear. Likewise, the convex central part 9 of the insert 3 directed toward the femoral component 1 connects to the hollowed lateral parts 8 of this insert via a radius of curvature R′2 which is constant from front to rear.
The prosthesis according to the invention has the advantage of respecting the physiological kinematics of the knee, that is to say the preferred rolling/sliding movement of the joint, with retreat of the point of contact of the femur on the insert from extension to flexion, which optimizes the moment of action of the extensor apparatus and, consequently, the force of propulsion of the knee, when walking upward, when walking downward, and when standing up.
maintaining a large contact surface during the flexion of the knee, which, as a corollary, generates a low pressure in the polyethylene and thus minimal wear of the prosthesis;
maintaining congruence during the movements of inclination in the frontal plane, thus an absence of shocks and mechanisms of tearing or loosening;
conferring on this device a good stability of the components relative to one another during the rearward displacements and lateral inclination;
maintaining a total medio-lateral contact surface from extension to complete flexion, the surface decreasing progressively by the contacting of spiral curves.
3. The prosthesis as claimed in claim 1, wherein the projecting central part (9) of the insert (3) and the hollowed central part (10) of an intercondylar space of the femoral component (1) have, in the sagittal plane, two curvatures which cooperate cam-like, said cam-like motion being such that, at an angle of flexion of 0°, the center of the bearings of the femoral component against the insert is a few millimeters in front of the center of the insert (3), such that said center retreats a few millimeters behind the center of the insert, as the prosthesis enters into flexion.
the concave surface segments of the femoral component corresponding to convex tori on the bearing surface of the insert;
5. A knee prosthesis, which is implantable in the knee joint of a patient, said prosthesis comprising a femoral component (1) which is implantable in the femur of the knee joint; a tibial component (2) which is implantable in the tibia of the knee joint; and an intermediate insert (3) which is interposed between the tibial component and the femoral component of said prosthesis, said insert being selectively rigidly integral with the tibial component or movable in rotation about a vertical axis relative to the tibial component, said femoral component comprising two lateral parts (7), each with a condylar surface which bears against and is movable in two lateral cavities (8) of a complementary profile provided in the insert, and includes a hollowed central part (10) arranged between said lateral parts and which bears on a projecting central part (9) of the insert, the projecting central part (9) of the insert (3), which is directed toward the femoral component (1) having a convex shape in a frontal plane, and a concave shape in a sagittal plane, the hollowed central part (10) of the femoral component (1) having a concave shape in a frontal plane, and a convex shape in a sagittal plane extending from the front to the rear of the femur of the knee joint, so as to facilitate the femoral component (1) straddling the projecting central part (9) of the insert during relative displacements thereof and to cooperate cam-like therewith, said knee prosthesis having the femoral component (2) and the insert (3) come into mutual surface contact during the relative movements between said femoral component and said insert in the absence of any discontinuities, flats and sharp edges and cooperate through the straddling of any concave parts and convex parts of said femoral component and of said insert during the entirety of these movements within, respectively, each of the sagittal and frontal planes, wherein transversely in a frontal plane, the insert (3), which is directed towards the mutual contact surface of the femoral component and coming into continuous medio-lateral contact with the femoral component (1) is a curve (S2) which includes a projecting central part (9) having an inwardly curved central portion possessing a convexity which is directed towards the femoral component and which connects tangentially on opposite sides thereof to lateral cavity (8) having a shape corresponding substantially with that of a therewith associated condylar part of the femoral component (1), forming an undulating curve across the entire extent thereof in the absence of discontinuities, flats and sharp edge, in a generally sinusoidal configuration, and wherein transversely in a frontal plane, the surface of the femoral component (1), which is directed towards the complementary surface of the insert coming into continuous medio-lateral contact with the insert (3) defines a curve (S1) which includes a hollowed central part (10) having an undulating shape with a concavity which is directed towards the insert and which connects tangentially on opposite sides thereof to the lateral parts (7) of the femoral component (1), forming an undulating curve in the absence of any discontinuities, flats and sharp edges of generally a sinusoidal configuration across the entirety thereof, which follows the surface of the femoral component from its most frontal part to the rearmost part thereof and of the insert, said mutual contact surface of the femoral component (1) being defined by a spiral curve, said spiral curve consisting of a plurality of continuously varying radii along the extent thereof extending in the sagittal plane following said sinusoidal configuration from medial to lateral, and said mutual contact surface of the insert being defined by a spiral curve, said spiral curve consisting of a plurality of continuously varying radii along the extent thereof extending in the sagittal plane in correlation with the configuration of at least a portion of the spiral curve in the sagittal plane of said femoral component.
6. A knee prosthesis, which is implantable in the knee joint of a patient, said prosthesis comprising a femoral component (1) which is implantable in the femur of the knee joint; a tibial component (2) which is implantable in the tibia of the knee joint; and an intermediate insert (3) which is interposed between the tibial component and the femoral component of said prosthesis, said insert being selectively rigidly integral with the tibial component or movable in rotation about a vertical axis relative to the tibial component, said femoral component comprising two lateral parts (7), each with a condylar surface which bears against and is movable in two lateral cavities (8) of a complementary profile provided in the insert, and includes a hollowed central part (10) arranged between said lateral parts and which bears on a projecting central part (9) of the insert, the projecting central part (9) of the insert (3), which is directed toward the femoral component (1) having a convex shape in a frontal plane, and a concave shape in a sagittal plane, the hollowed central part (10) of the femoral component (1) having a concave shape in a frontal plane, and a convex shape in a sagittal plane extending from the front to the rear of the femur of the knee joint, so as to facilitate the femoral component (1) straddling the projecting part (9) of the insert during relative displacements thereof and to cooperate cam-like therewith, said knee prosthesis having the surfaces of the femoral component (1) and of the insert (3) come into mutual surface contact during the relative movements between said femoral component in the absence of any discontinuities, flats and sharp edges and cooperate through the straddling of concave parts and convex parts thereof during the entirety of these movements within, respectively, each of the sagittal and frontal planes, wherein transversely in a frontal plane, the mutual contact surface of the insert (3), which is directed towards the complementary mutual contact surface of the femoral component (1) and coming into continuous medio-lateral contact with the femoral component (1) is a curve (S2) which includes a projecting central part (9) having an inwardly curved central portion possessing a convexity which is directed towards the femoral component (1) and which connects tangentially on opposite sides thereof to each said lateral cavity (8) having a shape corresponding substantially with that of a therewith associated lateral part of the femoral component (1), forming an undulating curve in a generally sinusoidal configuration, and wherein transversely in a frontal plane, the surface of the femoral component (1), which is directed towards the complementary surface of the insert coming into continuous medio-lateral contact with the insert (3) defines a curve (S1) which includes a hollowed central part (10) having an undulating shape with a concavity which is directed towards the insert and which connects tangentially on opposite sides thereof to the lateral parts (7) of the femoral component (1), forming an undulating curve in the absence of any discontinuities, flats and sharp edges of generally a sinusoidal configuration, which follows the mutual contact surface of the femoral component and of the insert from its most frontal part to the rearmost part thereof, the femoral contact surface of the femoral component being defined by the combination of a spiral curve in the sagittal plane following an undulating curve of sinusoidal type in a frontal plane, said spiral curve consisting of a plurality of continuously varying radii along the extent thereof the contact surface of the insert (3) being defined by the combination of a spiral curve in the sagittal plane in conformance with at least a portion of the spiral curve of the femoral component, said spiral curve consisting of a plurality of continuously varying radii along the extent thereof and of an undulating curve of sinusoidal configuration in the frontal plane, said two surfaces being in a concave-convex engagement in each of said two planes, whereby the two surfaces provide for a continuous transverse medio-lateral contact from complete extension to complete flexion of the prosthesis.
7. The prosthesis as claimed in claim 6, wherein the lateral parts and the hollowed central part (10) of the femoral component (1) extending transversely through at least one sagittal plane, have the shape of a spiral of any geometrical form, said spiral curve consisting of a plurality of continuously varying radii along the extent thereof, and wherein extending transversely through a sagittal plane, the complementary lateral parts (8) and projecting central part (9) of the insert (3) also have the shape of a spiral of any geometrical form, said spiral curve consisting of a plurality of continuously varying radii along the extent thereof.
6344059 February 5, 2002 Krakovits et al.
2621243 October 1987 FR
WO 0106961 February 2001 WO
Patent number: 6893467
Inventor: Michel Bercovy (75015 Paris)
Application Number: 10/048,112
Current U.S. Class: Knee Joint Bone (623/20.14); Having Member Secured To Femoral And Tibial Bones (623/20.21)