FR2852819A1 - Knee prosthesis, has condyles and glenoid cavities with interior parts having radius of curvature more than radius of curvature of their posterior parts to ensure posterior stabilization - Google Patents

Abstract

The prosthesis has a femoral implant (2) forming two lateral condyles defining a concave femoral throchlea (11). A tibial implant (3) has a tibial base (14) and an articular plate (21) with a convex median spine. The condyles and the glenoid cavities of the plate have interior parts whose radius of curvature is more than the radius of curvature of posterior parts (101, 241) to ensure posterior stabilization.

Description

i

  The present invention relates to total knee prostheses of the postero-stabilized type.

  In the technical field that is the object of the invention, it is known from many previous proposals. In general, a total knee prosthesis has a femoral implant adaptable to the lower epiphyseal end of the femur. According to a known proposal, this femoral implant has two lateral condyles having in the sagittal plane, a posterior portion in a circular arc centered on the point of rotation of the prosthesis. These two lateral condyles delimit between them a median cavity defining a posterior stabilization abutment surface.

  Such a total prosthesis further comprises, to cooperate with the femoral implant, a tibial implant comprising a tibial base adaptable on the upper epiphyseal end of the tibia. This tibial base is arranged to present a well opening on its upper face so as to receive a pin protruding from the underside of an articular plate. The upper face of the articular plate is arranged to present two glenoid cavities cooperating with the condyles of the femoral implant. The glenoid cavities have a posterior part in a circular arc centered on the point of rotation of the prosthesis. The glenoid cavities are separated by a median rib forming a postero-stabilizing spur at its anterior portion, adapted to cooperate with the abutment surface of the medial cavity of the femoral implant. Such a total prosthesis thus offers a posterior stabilization function during the relative displacement between the tibia and the femur.

  Such a total knee prosthesis is characterized by the imposed binding of the tibia to the femur in the sagittal plane with a simple possibility of relative pivoting on a fictitious axis which can be considered to be generally perpendicular to the sagittal plane. Such a limitation of movement relative to a single degree of freedom does not make it possible to reproduce the natural anatomical movements known as "lift off" in the frontal plane, that is to say the possibility of slight pivoting of the tibia with respect to the femur . This results in significant constraints imposed either on the elements in contact and sliding of the total prosthesis, or on the means for anchoring the elements of the prosthesis on the epiphyses opposite the femur and the tibia. The constraints are responsible for pain or loosening of the implants.

  In an attempt to overcome these disadvantages, it has been proposed a total knee prosthesis whose femoral implant is adapted to present a forced exhaust relative to the rib of the tibial implant. This exhaust not only tends to wear the upper edges of the rib, but leads to exert on it torsional stresses 5 promoting the appearance of cracks in the material constituting the articular plate.

  The object of the present invention is to overcome the drawbacks stated above by proposing a new postero-stabilized total knee prosthesis offering a post-stabilization function, with a possibility of relative rotation of the tibia with respect to the knee while limiting the stresses exerted on the bone anchors of the femoral and tibial implants as well as on the elements of the prosthesis in contact.

  To achieve such an objective, the prosthesis according to the invention comprises: a femoral implant forming two lateral condyles delimiting between them a concave femoral trochlea in the frontal plane, the lateral condyles possessing in the sagittal plane a posterior portion in an arc of a circle centered on a point of rotation, - and a tibial implant comprising: * a tibial base in which is arranged a well opening 20 in the upper face of the base, * and an articular plate having: * on its underside, a pion adapted to be pivotally received in the well of the tibial base, * on its upper face, two glenoid cavities cooperating with the condyles and having in the sagittal plane, a posterior portion in a circular arc centered on the point of rotation of way that the prosthesis has a single center of rotation in its normal kinematic domain, the two glenoid cavities being separated from each other by a median convex pin in the frontal plane to cooperate with the femoral trochlea.

  According to the invention: the femoral trochlea and the median spine of the articular plate are respectively concave and convex in a continuous manner, from their posterior part to their anterior part, so as to allow a relative limited displacement in the sagittal plane between the plateau articular and femoral implant, when the prosthesis is outside its normal kinematic domain, - the condyles of the femoral implant and the glenoid cavities of the articular plate have anterior parts with a radius of curvature greater than the radius of curvature of the parts posteriorly in an arc of a circle so as to cooperate with each other to ensure the postero-stabilization of the prosthesis after a relative limited displacement in the sagittal plane between the articular plate and the femoral implant.

  According to an advantageous feature of embodiment, the anterior portions of the glenoid cavities and the anterior part of the median spine are raised with respect to the posterior portions of the glenoid cavities and to the posterior portion of the median spine, respectively, so as to constitute a surface of the medial spine. continuous anterior support providing post-stabilization of the prosthesis.

  According to another advantageous embodiment, the glenoid cavities are connected to the median spine by intermediate zones of inflection, their posterior part to their anterior part and the condyles are connected to the trochlea by intermediate zones of inflection, from their posterior part to their anterior part.

  According to another aspect of the invention, each glenoid cavity has in the frontal plane a rounded shape to define a tipping point for the associated condyle so as to allow a tilting of the other condyle for the reproduction of natural movements said of "lift off".

  The prosthesis according to the invention is also designed to have a maximum bearing surface. Thus, the femoral implant and the articular plate are shaped to be in surface contact on substantially the entire surface of the glenoid cavities and the median spine, and for a bending angle of the prosthesis to a value of 1. order of 00.

  Likewise, the femoral implant and the articular plate are shaped to be in surface contact on at least the posterior portions of the glenoid cavities and the median spine, during flexion of the prosthesis over an angular range varying from order from 0 to 130.

  Finally, the femoral implant and the articular plate are shaped to be in contact on the entire surface of the glenoid cavities and the median spine, for a bending angle of the prosthesis equal to a value of the order of - 5 '.

  Various other features appear from the description given below with reference to the accompanying drawings which show, by way of non-limiting examples, embodiments of the subject of the invention.

  Figs. 1 and 2 are views respectively posterior and an exploded perspective view of a total knee prosthesis according to the invention.

  Fig. 3 is a cross-sectional view taken substantially along the line III-III of FIG. 1.

  Fig. 4 is an elevational sectional view taken substantially along the line IV-IV of FIG. 3.

  Figs. 5 and 6 are elevational views showing the prosthesis according to the invention in two characteristic positions for the same bending value of the prosthesis. Figs. 7A, 7B are views of the prosthesis according to two characteristic positions of. flexion namely O 'and 900.

  The rigs. 8A and 8B show the surface area of contact between the tibial implant and the femoral implant for the two characteristic bending positions illustrated respectively in FIGS. 7A, 7B.

  As is apparent from the figures, the subject of the invention relates to a total knee prosthesis i conventionally comprising a femoral implant 2 and a tibial implant 3 intended to be adapted respectively after resection, on the lower femoral epiphysis and the epiphysis high tibial. As is apparent from the following description, this total knee prosthesis is of the postero-stabilized type and is particularly implanted in the case of ablation of the posterior cruciate ligament.

  The femoral implant 2 considered according to a lateral view parallel to the sagittal plane of the prosthesis, has a substantially U-shaped shape comprising a so-called anterior limb 5 and a posterior branch 6 of shorter length (FIG 4). delimits by its inner surface, a housing 8 of adaptation on the femoral epiphysis. The femoral implant 2 is shaped to have, by its external surface, two lateral condyles 10 extending substantially parallel by delimiting between them, an intercondylar fossa or a femoral trochlea il.

  Each condyle 10 has in the sagittal plane (FIG 4), a posterior portion 10, in a circular arc centered on the point of rotation of the prosthesis, schematized by the point P, and extended by an anterior portion 102 having a radius of curvature greater than the radius of the posterior portion 101. Each condyle 10 has in the frontal plane, that is to say transversely to the sagittal plane (FIG 3), a convex and rounded profile, defined by a first radius of curvature of value given for the posterior part 10, and by a second radius of curvature of greater value than the first radius of curvature for the anterior part 102, as is apparent from FIGS. 1 and 2.

  As it appears more precisely in FIG. 3, the femoral trochlea 11 has, transversely to the sagittal plane, a concave and rounded profile, defined by a first radius of curvature of given value for the posterior portion 11, and by a second radius of curvature of greater value than the first radius of curvature. curvature for the anterior portion 112. According to one feature of the invention, the femoral trochlea 11 is concave continuously or continuously, from its posterior portion 11 to its anterior portion 112. The posterior portion 11, of the femoral trochlea 11 has in the sagittal plane, an arcuate profile centered on the point of rotation P. This posterior portion 11, is extended by the front portion 112 which has a radius of curvature greater than the radius of the posterior portion 111. conventional, the posterior portion 112 of the femoral trochlea 11 is able to cooperate with the natural protuberance or with an artificial button present é or carried by the not shown patella. The trochlea 11 is connected continuously on both sides, the lateral condyles 10 by intermediate zones of inflection.

  The tibial implant 3 comprises a tibial base 14 having a medullary anchoring stem 15 extending from an upper plate 16 intended to rest against a resected surface of the tibial plateau. The anchor rod 15 delimits a central well 17 opening into the upper face of the plate 16.

  The tibial implant 3 also comprises an articular plate 21 having on its underside, a pin 22 adapted to be pivotally received in the well 17 of the tibial base 14 to allow pivoting of the articular plate 21 relative to the tibial base 14. The articular plate 21 has on its upper face, two Glenoidal cavities 24 intended to cooperate with the condyles 10 and separated from each other by a median spine 25.

  The median spine 25 thus has in the frontal plane, that is to say transverse to the sagittal plane, a convex and rounded profile which is uninterrupted or continuous, from its posterior part 25, to its anterior part 252. This profile the convex profile of the median spine 25 is defined by an evolving radius of curvature increasing from its posterior part 25 to its anterior part 252. Advantageously, this convex profile is defined by a first radius of curvature of given value for the posterior portion 25, and by a second radius of curvature of greater value than the first radius of curvature for the anterior portion 252. The median spine 25 has in the sagittal plane a posterior portion 25, extending in an arc of a circle centered on the rotation point P of the prosthesis and extended by the anterior portion 252 having a radius of curvature greater than the radius of curvature of the anterior portion 251. The median spine 25 is connected to the continuously, from its posterior part to its anterior part and from both sides, to the glenoid cavities 24, by intermediate zones of inflection.

  Each glenoid cavity 24 has in the sagittal plane (FIG 4), a posterior portion 24, in a circular arc centered on the point of rotation P of the prosthesis, and extended by an anterior portion 242 having an upper radius of curvature 20 at the radius of curvature of the posterior portion 241. Each glenoid cavity 24 has, transversely to the sagittal plane (3), a concave and rounded profile defined by a first radius of curvature of given value for the posterior portion 24, and by a second radius of curvature of greater value than the first radius of curvature for the anterior portion 242. Advantageously, the anterior portions 242 of the glenoid cavities 24 and the anterior portion 252 of the median spine are raised with respect to the portions respectively. posterior 24, glenoid cavities 24 and at the posterior portion 25, the median spine 25 so as to constitute an anterior support surface e continues ensuring the postero-stabilization of the prosthesis.

  The median spine 25 and the glenoid cavities 24 constitute, by their respective posterior portions 251, 24, in a circular arc, bearing zones for the posterior portions 111, 0l of the femoral trochlea 11 and the condyles 10, which are congruent between them. The prosthesis 1 according to the invention thus has a unique center of rotation P in its normal kinematic domain. Advantageously, the femoral implant 2 and the articular plate 21 are shaped so that the condyles 10 and the femoral trochlea 11 are in contact on substantially the entire surface of the glenoid cavities 24 and the median spine 5 25 and this, for a bending angle of the prosthesis to a value of the order of 00. Thus, as is clear from Figs. 7A, 8A, the contact or bearing surface illustrated by the dark area S substantially represents the entire upper surface of the articular plate 21, excluding a thin edge extending at the end of the portion earlier. It should be noted that for the position of hyper extension of the prosthesis (of the order of -5 flexion), the femoral implant 2 and the articular plate 21 are shaped so that the condyles 10 and the femoral trochlea 11 are in contact over the entire surface of the glenoid cavities 24 and the median spine 25.

  When bending the prosthesis 1 over an angular range in particular from 0 to 1300, the bearing surface decreases. However, the femoral implant 2 and the articular plate 21 are shaped so that the condyles 10 and the femoral trochlea 11 are in surface contact on at least the posterior portions 241, 25, glenoid cavities 24 and the median spine. 25 over the bending range of O 'to 130, so that the bearing surface S remains large as is clear from Figs. 7B and 8B. The prosthesis according to the invention thus has a maximum congruence for bending angles between -5 and 130, which allows a distribution of stresses over a large area. This results in a very significant reduction in the wear of the articular plate 21, a reduction in the risk of occurrence of cracks as well as a reduction in the production of particles of the material constituting the articular plate 21.

  According to another characteristic of the invention, the femoral trochlea 11 and the median spine 25 of the articular plate 21 are respectively concave and convex, without discontinuity or in a continuous manner, from their posterior part to their anterior part to allow relative limited displacement. in the sagittal plane between the articular plate 21 and the femoral implant 2, when the prosthesis leaves its normal kinematic domain.

  In a complementary manner, when the prosthesis 1 comes out of its normal kinematic domain during, for example, a stumble that may result in anteroposterior subluxation, the condyles 10 and the glenoid cavities 24 are intended to cooperate by their anterior parts. , 242 so as to ensure the postero-stabilization of the prosthesis. Preferably, the anterior portion 252 of the median spine 25 also cooperates with the anterior portion 112 of the femoral trochlea when the prosthesis is outside its normal kinematic range. The anterior portions 242, 252 of the glenoid cavities 24 and of the median spine 25 are raised with respect to the posterior portions 241, 25, thus making it possible to permanently urge the tibial implant towards its posterior part. When the prosthesis 1 comes out of its normal kinematic domain (FIG 6), it appears in the sagittal plane, a relative displacement or rolling between the articular plate 21 and the femoral implant 2. The anterior parts identified 242, 252 of the The glenoid cavities 24 and the median spine thus constitute a continuous anterior abutment surface over the entire width of the prosthesis and over a large depth making it possible to ensure the postero-stabilization of the prosthesis in a progressive manner and without any stitches. 15 abutment by the diffusion of forces, thus causing no constraints to the elements in contact and means of anchoring the prosthesis.

  Furthermore, it should be noted that the prosthesis 1 according to the invention allows in the bending movement ranging from -5 to 1300, a tilting of the femoral implant in valgus and varus from 30 to 50 (lift off) without loss of congruence of the condyle 10 opposite the tilting which remains in contact with the surface of the articular plate, and without appearance of interference. Indeed, each Glenoid cavity 24 has by its rounded shape in the frontal plane, a tilting point for the associated condyle 10, thus allowing the other condyle 10 to tilt.

  The invention is not limited to the examples described and shown since various modifications can be made without departing from its scope.

Claims (6)

  1 - Total postero-stabilized knee prosthesis, comprising: - a femoral implant (2) forming two lateral condyles (10) defining between them a femoral trochlea (11) concave in the frontal plane, the lateral condyles (10) having in the sagittal plane, a posterior portion (101) in an arc centered on a point of rotation (P), - and a tibial implant (3) comprising: * a tibial base (14) in which a well (17) is arranged opening into the upper face of the base, 10 * and an articular plate (21) having: * on its underside, a pin (22) adapted to be pivotally received in the well (17) of the tibial base, * on its upper face, two Glenoid cavities (24) cooperating with the condyles (10) and having in the sagittal plane, a posterior portion (241) in an arc of a circle centered on the point of rotation (P) so that the prosthesis has a unique center of rotation (P) in its normal kinematic domain , the two glenoid cavities (24) being separated from each other by a median spine (25) convex in the frontal plane to cooperate with the femoral trochlea (11), characterized in that: - the femoral trochlea (11) and the spine median (25) of the articular plate (21) are respectively concave and convex in a continuous manner, from their posterior part to their anterior part, so as to allow a relative limited displacement in the sagittal plane between the articular plate (21) and the femoral implant (2), when the prosthesis is outside its normal kinematic range, - the condyles (10) of the femoral implant (2) and the glenoid cavities (24) of the articular plate (21) have anterior parts (102, 242) with a radius of curvature greater than the radius of curvature of the posterior portions (10, 241) in an arc of a circle so as to cooperate with each other to ensure the postero-stabilization of the prosthesis after a displacement. t limited relative in the sagittal plane between the articular plate (21) and the femoral implant (2).   2 - postero-stabilized total knee prosthesis according to claim 1, characterized in that the anterior portions (242) of the glenoid cavities (24) and the anterior part (252) of the median spine (25) are raised in relation respectively to at the posterior portions (241) of the glenoid cavities (24) and at the posterior portion (251) of the median spine (25) so as to constitute a continuous anterior abutment surface ensuring the postero-stabilization of the prosthesis.   3 - total postero-stabilized knee prosthesis according to claim 1 or 2, characterized in that the glenoid cavities (24) are connected to the median spine (25) by intermediate zones of inflection, their posterior portion to their anterior part and in that the condyles (10) are connected to the trochlée (11) by intermediate zones of inflection, their posterior part to their anterior part.   4 - postero-stabilized total knee prosthesis according to one of claims 1 to 3, characterized in that each Glenoid cavity (24) has in the frontal plane a rounded shape to define a tilting point for the associated condyle (10) in order to allow a tilting of the other condyle for the reproduction of natural movements called "lift off".   - Total postero-stabilized knee prosthesis according to one of claims 1 to 4, characterized in that the femoral implant (2) and the articular plate (21) are shaped to be in surface contact on substantially all of the surface 20 of the glenoid cavities (24) and the median spine (25), and for a bending angle of the prosthesis to a value of the order of 00.   6 - total prosthesis according to claim 5, characterized in that the femoral implant (2) and the articular plate (21) are shaped to be in surface contact on at least the posterior portions (241, 251) of the glenoid cavities ( 24) and 25 of the median spine (25), during the bending of the prosthesis over an angular range varying from 0 to 130.   7 - total prosthesis according to claim 5, characterized in that the femoral implant (2) and the articular plate (21) are shaped to be in contact on the entire surface of the glenoid cavities (24) and the spine median (25), for a bending angle of the prosthesis equal to a value of the order of -5.