FR2651675A1 - Acetabular prosthesis cup and prosthesis provided with this cup - Google Patents

Abstract

The invention relates to a cup for an acetabular prosthesis. It is characterised in that: - on the one hand, the anchoring means (7) comprises a plurality of flat anchoring elements which project essentially perpendicular to the outer surface of the cup and do so over a certain predetermined height, measured perpendicular to the said outer surface, which elements extend in meridian planes (M1) and each comprise, designed to be operational in the direction of implantation of the cup, at least one so-called attacking ridge which pushes the osseous material aside as it passes, and at least one so-called retention stop which opposes the withdrawal and/or ejection of the cup thus implanted, and - on the other hand, these elements are divided into at least two groups, in each of which they are globally aligned, these groups being situated in meridian planes (M1) arranged essentially symmetrically at a predetermined angle (A1, A2) on each side of a likewise meridian but also median plane (M2) at the longitudinal opening (6) of the cup.

Description

 The invention relates to a cup for acetabular prosthesis as well as to the prosthesis provided with this cup.

 By acetabular prosthesis, a device intended to be implanted in the acetabular cavity will be understood for the purpose of replacing the physiological acetabulum (EP-145.339).

 It is generally intended to be used in conjunction with a femoral prosthesis.

 The present invention relates more particularly but not exclusively to the so-called cup element of an acetabular prosthesis of the type therefore comprising on the one hand a cup in particular of metallic material, of generally hemispherical envelope intended to be implanted in the acetabular cavity and, d 'other hand, a core also of substantially hemispherical envelope intended to be fitted into the aforementioned cup and comprising a bearing in particular hemispherical concave to receive the head of complementary shape of the cephalic prosthesis.

 Generally, the core is made of elastic material and as justification for the presence of the metal cup, we should remember that it is accepted in the orthopedic environment that direct bone-plastic contact is not desirable.

 The mere engagement of the prosthesis in the cavity is not sufficient to eliminate the risk of displacement of this prosthesis.

 We currently know how to obtain an effective anchoring between the prosthesis and the bone by forming a bone interface between the bone and the surface of the previously prepared cup, but this so-called biological anchoring is effective only after a period of time which is counted in weeks which prolongs the discomfort for the patient.

 To overcome this drawback, in addition to the special preparation of the surface of the cup, there is provided in the bone an anchoring means of the prosthesis which is mechanical which is effective as soon as the cup is placed.

 For example, this so-called primary anchoring means comprises (FR-A-2,598,908) screws and / or cylindrical or cylindro-conical points distributed over the entire surface of the cup.

 With the problem of anchoring the prosthesis, it is necessary to reconcile that of the elasticity which the said prosthesis must keep.

 Indeed, it has been observed that, when the elastic deformations of the hip are not followed by the cup, this promotes its loosening.

 The current trend is therefore oriented towards the design of acetabular prostheses (FR-A-2.589.059), the metal cup of which is, on the one hand, arranged to have a certain elasticity and, on the other hand, provided with biological and mechanical anchoring means, the situation of which on the surface of the cup is determined so as not to hinder the elastic deformations of the cup where it is desired to maintain them.

 Thus, on the one hand, the extent of the biological and / or mechanical anchoring zone is it substantially limited to a spherical cap whose polar axis is oriented generally along the natural axis of transmission of the forces from the femur to the iliac bone and, on the other hand, is the elasticity of the cup obtained by means of a plurality of slits which extend along the meridians of the cup from its equatorial edge to the edge of the aforementioned anchoring zone.

 Specifically in the case considered, the mechanical anchoring is ensured by means of two screws which are arranged parallel to the natural axis of transmission of the forces from the femur to the iliac bone and in the vicinity of this axis.

 This mechanical anchoring means thus limited makes it possible to increase the possibilities of deformation of the iliac bone but the screws are criticized for preventing the movements of physiological impaction of the prosthesis during walking.

 A result which the invention aims to obtain is a cup for acetabular prosthesis which overcomes the aforementioned drawbacks.

To this end, the invention relates to a cup for acetabular prosthesis, in particular characterized in that
- On the one hand, the anchoring means comprises a plurality of flat anchoring elements which project substantially normally to the external surface of the cup and this over a certain predetermined height, normally measured at said external surface, which elements extend in meridian planes and each comprise, arranged to be active in the direction of implantation of the cup, at least one so-called attack edge which spreads the bone material in its path and at least one so-called retention stop who opposes the withdrawal and / or ejection of the cup thus implanted, and
- on the other hand, these elements are distributed in at least two groups in each of which they are generally aligned, these groups being located in meridian planes arranged substantially symmetrically at a predetermined angle on either side of a plane also meridian but median at the elongated opening of the cup.

 The invention also relates to the prosthesis provided with this cup.

The invention will be better understood with the aid of the description below given by way of nonlimiting example with regard to the attached drawing which schematically represents
FIG. 1: top view, the cup of the acetabular prosthesis according to the invention,
FIG. 2: a section along II-II of FIG. 1,
- Figure 3: view on a larger scale and in partial section along a median plane,
- Figure 4: a section on IV-IV of Figure 3.

 Referring to the drawing, we see an acetabular prosthesis 1 comprising a shell 2 substantially hemispherical hollow called cup and, housed in this cup, a core 3 generally hemispherical associated with the cup by a means 4 of assembly in particular elastic such as a means d 'assembly by clipping.

 As shown in the drawing, in the wall 5 of the cup 2 is conventionally cut a slender opening 6 or slot which also extends substantially along a meridian of said cup so as to give it a certain elasticity.

 As also appears in the drawing, the cup 2 conventionally carries an anchoring means 7 in the bone wall 8 of the acetabulum 9 in which the prosthesis must be implanted in particular in a preferred direction I and for example along the polar axis 10 of the acetabulum 9 as refitted for the occasion, for example by milling.

 In known manner, the cup 2 is implanted by a succession of impacts, that is to say that its anchoring means is engaged in the wall of the bone by means of a succession of shocks developed by means of a tool. suitable classic (not shown).

According to the invention,
- On the one hand, the anchoring means 7 comprises a plurality of 11 flat anchoring elements which project substantially normally to the external surface 12 of the cup and this over a certain predetermined height H, normally measured at said external surface 12, which elements 11 extend in meridian planes Ml and each comprise, arranged to be active in the direction I of implantation of the cup, at least one edge 13 called attack, which spreads in its path the bone material 14, and at least one so-called retention stop 15 which opposes the withdrawal and / or the ejection of the cup 2 thus implanted, and
- On the other hand, these elements 11 are distributed in at least two groups 16 in each of which they are generally aligned, these groups 16 being located in meridian planes M1 arranged substantially symmetrically at an angle Al, A2 predetermined on the one hand and another of an equally meridian but median plane M2 at the elongated opening 6 of the cup 2.

 According to the invention, the anchoring elements 11 are located in that 17 of the hemispheres 17, 18 which, delimited in the cup 2 by a plane orthogonal T to the median plane M2 of its elongated opening 6, does not include this slender opening 6.

 According to the invention, each group 16 of anchoring elements 11 extends to the surface 12 of the cup 2 in a meridian angular sector S1 whose apex substantially coincides with the fictitious center 01 of the hemispherical cup and which is located approximately 150 from the equatorial plane E and its angular value is between 300 and 450.

 Each group 16 of anchoring elements 11 comprises three elements 11 which each extend over an angular sector S2 meridian of a value between 100 and 150.

According to the invention, each element ll has a generally triangular profile, one 19 of the sides 13, 15, 19 of the triangle known as the first side being substantially tangent to the cup and when we consider the cup 2 as extending above of a substantially horizontal plane P1 coinciding with its equatorial plane E, the anchoring element has on the one hand a second side 13 which forms an angle A3 between 300 and 400 below a plane P2 substantially parallel to the plane equatorial E and therefore constitutes the so-called attack edge and, on the other hand, a third rib 15 which forms an angle A4 between 0 and 180 above a plane P3 generally parallel to the equatorial plane
E and thus constitutes the abutment 15 called retention.

 According to the invention, the anchoring means 7 comprises four groups 16 of anchoring elements 11 arranged symmetrically on either side of the median plane M2 of the elongated opening 6 and, precisely, on the one hand, two groups each located in a meridian plane M1 forming with the median plane M2 an angle A1 of between 200 and 400 and in particular 300 and, on the other hand, two groups each located in a meridian plane M1 forming with the median plane M2 of l '' longilinear opening an angle A2 between 600 and 800 and in particular 700.

 This arrangement of the groups 16 of anchoring elements 11 combined with 1 has the configuration of each of the said groups 16 optimizes the anchoring of the cup 2 in the bone wall while allowing certain elastic deformations of said cup.

Indeed, a cup thus designed finds anchoring substantially in two distinct zones (not shown) symmetrically arranged in the upper part of the acetabulum in which upper part normally there is no deformation of the bone wall tangentially to the cup but in which the cup receives essentially actions which are appreciably normal to its external surface, which tend moreover
- to apply the cup as well as possible in its upper part so as to release the lower part which, in turn, deforms, and
- to pinch said lower part of the cup towards the median plane of the elongated opening where it is implanted so as to deform approximately like the physiological acetabulum.

 This is why the whole lower part of the cup must remain without anchoring and the slot must be unique.

 According to the invention, the elongated opening 6 extends along a predetermined width 1 and this from the equatorial edge 20 of the hemisphere to the pole 21 of the cup at the level of which it is connected to a circular cut 22 of small diameter d relative to the equatorial diameter D of the cup but in any case at least equal to the width 1 of the opening.

 This configuration of the elongated opening 6 gives the cup a deformability comparable to the physiological acetabulum from which it takes the same anterior and posterior horns.

 In accordance with the invention, the normal cross sections of each anchoring element 11, that is to say those situated in planes each perpendicular both to the surface of the cup and to the meridian plane which the element in question contains, d on the one hand, each have substantially the shape of an isosceles trapezium, the largest base of which is associated with the cup 2 and on the other hand, have decreasing areas from the section 1a closest to the equatorial plane to that most distant .

 This configuration of each element allows it, in a way, during the implantation, at first to elastically spread the bone material then, at a second time to find it taken in particular by its face 15 facing the equatorial plane and which constitutes the so-called retention stop behind which the bone material is closed.

Preferably, the cup 2 has at its base before insertion into the acetabular cavity 9 as rearranged
- on its external face 12, a diameter slightly greater than that of the inlet of said cavity 9 as refitted and
- on its internal face, a diameter equal to that of the core 3.

 Therefore, when placed in the cavity, the cup taken in isolation will elastically shrink, but when reintroduced into the cup of the core 3, it will return to its original diameter at its base, which will force it into the cavity 9 thus ensuring its fixing by separation of the two anterior and posterior horns.

 In order to present on its external surface 12 a diameter slightly greater than that of the cavity 9 as rearranged, while fully engaging in the cavity, and maintaining a constant radius R, it is preferably the entire external surface 12 which is produced according to a hemispherical shape of slightly larger diameter but whose center 02 of this hemispherical shape is offset towards the outside of the cup with a value B equal to half the difference in diameter.

 The internal face may have the same offset without harming the retention of the core, given its clip-on means 4.

 The cup can of course be made of any suitable material and for example titanium and its surface can undergo any surface treatment to promote bone regrowth.

Claims (10)

 1. Cup for acetabular prosthesis (1) of the type comprising a cap (2) substantially hemispherical hollow called cup and, housed in this cup, a core (3) generally hemispherical associated with the cup by means (4) of assembly in particular elastic like a snap-on assembly core,  said cup further comprising at least, on the one hand, a substantially elongated opening which, cut in its wall extends approximately along one of its meridians and therefore gives it a certain elasticity and, on the other hand, less an anchoring means in a bone wall such as that of the acetabular cavity (9) in which the cup must be implanted in particular in a preferred direction (I) of implantation for example along the polar axis (10) of a cavity condylar (9) such as the one refitted for the occasion,  this cup being CAI TERIZED in that  - On the one hand, the anchoring means (7) comprises a plurality of flat anchoring elements (11) which project substantially normally from the external surface (12) of the cup and this over a certain height (H ) predetermined, measured 1ement ;;, ent a said external surface (12), which elements (11) extend in meridian planes (M1) and each comprise, arranged to be active in the direction (I) of implantation of the cup, at least one edge (13) called attack which spreads, on its passage, the bone material (14) and at least one abutment (15) called retention which opposes withdrawal and / or ejection of the cup (2) thus implanted, and  - on the other hand, these elements (11) are distributed in at least two groups (16) in each of which they are globally aligned, these groups (16) being located in meridian planes (M1) arranged substantially symmetrically at an angle ( A1, A2) predetermined on either side of a plane also meridian median (M2) of the elongated opening (6) of the cup (2).  2. Cup according to claim 1 characterized in that the anchoring elements (11) are located in that (17) of the half-i-hemispheres (17, 18) which, delimited in the cup (2) by an orthogonal plane (T) in the median plane (M2) at its elongated opening (6,) does not include this elongated opening (6).  3. Cup according to claim 1 or 2 characterized in that each group (16) of anchoring elements (11) extends to the surface (12) of the cup (2) in a meridian angular sector (S1) the apex of which substantially coincides with the fictitious center (0î) of the hemispherical cup and which is located substantially 150 from the equatorial plane (E) and its angular value is between 300 and 450.  4. Cup according to any one of claims 1 to 3 characterized in that each group (16) of anchoring elements (11) comprises three elements (11) which each extend over an angular sector (S2) meridian with a value between 100 and 150.  5. Cup according to any one of claims 1 to 4 characterized in that each element (11) has a generally triangular profile, one (19) of the sides (13, 15, 19) of the triangle said first side being tangent when the cup is considered and when the cup (2) is considered to extend above a substantially horizontal plane (psi) merged with its equatorial plane (E), the anchoring element has on the one hand a second side (13) which forms an angle (A3) between 300 and 400 below a plane (P2) substantially parallel to the equatorial plane (E) and therefore constitutes the so-called attack edge and, on the other hand, a third rib (15) which forms an angle (A4) between 0 and 180 above a plane (P3) generally parallel to the equatorial plane (E) and thus constitutes the abutment (15) called retention.  6. Cup according to any one of claims 1 to 5 characterized in that the anchoring means (7) comprises four groups (16) four anchoring elements (11) arranged symmetrically on either side of the median plane (M2) of the elongated opening (6) and precisely, on the one hand, two groups each located in a meridian plane (M1) forming with the median plane (M2) an angle between 200 and 400 and in particular of 300 and, on the other hand, two groups each located in a meridian plane (M1) forming with the median plane (M2) of the elongated opening an angle (A2) between 600 and 800 and in particular 700.  7. Cup according to any one of claims 1 to 6 characterized in that the elongated opening (6) extends along a predetermined width (1) and this from the equatorial edge (20) of the hemisphere to pole (21) of the cup at which it is connected to a circular cutout (22) of small diameter (d) relative to the equatorial diameter (D) of the cup but in any case at least equal to the width (1) of the opening.  8. Cup according to any one of claims 1 to 7 characterized in that the normal cross sections of each anchoring element (11) that is to say those located in planes each perpendicular to both the surface of the cup and the meridian plane that the element in question contains, on the one hand, each have substantially the shape of an isosceles trapezium whose largest base is associated with the cup (2) and on the other hand, have decreasing areas from the section closest to the equatorial plane to the most distant.  9. Cup according to any one of claims 1 to 8 characterized in that it has at its base before insertion into the acetabulum (9) as refitted  - on its external face (12), a diameter slightly greater than that of the inlet of said cavity (9) as refitted and  - on its internal face a diameter equal to that of the core (3).  10. Prosthesis characterized in that it is provided with a cup according to any one of claims 1 to 9.