FR2977791A1 - Implant i.e. scapula implant, for articulation prosthesis of shoulder, has articular part provided with groove that is arranged in wall delimiting periphery of conical cavity, where groove emerges from cavity - Google Patents

Abstract

The implant (1) has a base plate (2) for osseous anchoring, and an articular part (3) forming an articular joint surface (4), where the articular part includes a conical cavity (16), and the base plate includes a male conical part or a head (5). The male conical part is inserted into the conical cavity until complete wedging takes place. The articular part is provided with a groove (17) that is arranged in a wall delimiting a periphery of the conical cavity, where the groove emerges from the cavity.

Description

The present invention relates to an implant forming part of a joint prosthesis, in particular a scapula implant forming part of a shoulder joint prosthesis. A shoulder joint prosthesis comprises, in a well known manner, a humeral implant, including a medullary stem intended to be inserted into the medullary canal of the humerus, and a scapula implant intended to be fixed at the level of the glenoid cavity of the scapula, the medullary stem and scapula implant being able to cooperate with each other by respective complementary joint surfaces they form.

The scapula implant is in some cases monobloc but is frequently formed by the assembly of a bone anchor base and an articular part forming the articular surface. This articular surface may be concave, for the constitution of a so-called "anatomical" prosthesis, or may be convex, for the constitution of a so-called "inverted" prosthesis. In this second case, the joint piece is frequently called "glenosphere" with reference to its hemispherical shape, and the bone anchoring base is frequently referred to as "metaglene". The assembly of the articular part to the bone anchoring base is frequently achieved by the arrangement in one of these two elements of a conical cavity with a low slope and, in the other element, a male conical part. corresponding slope, this male conical portion being intended to be inserted into the conical cavity until jamming. With this type of existing implant, it appears that the strength of the assembly of the two elements to one another may not be sufficient to withstand the repeated forces exerted on the scapula implant by certain movements of the paired person. The present invention aims to overcome this essential disadvantage. Another disadvantage of this type of existing implant is the risk of a defective angular positioning of the articular part relative to the bone anchoring base, which is troublesome when the assembly part that comprises this joint piece is offset with respect to an axis passing through the center of the articular portion that forms this articular part. The separation of two elements whose assembly is defective can be particularly difficult and time consuming.

The present invention also aims to overcome this significant disadvantage. The implant concerned. According to the invention, the element comprising said conical cavity has at least one groove formed in its wall delimiting the periphery of this conical cavity, this groove opening into this cavity. The inventor has in fact discovered that such a groove makes it possible to increase by approximately 20% the tensile strength of the assembly of the articular part to the bone anchoring base, and to increase by approximately 30%. % the torsional strength of the same assembly, thereby obtaining a fully sufficient assembly strength to withstand the repeated forces exerted on the scapula implant by certain movements of the person fitted. The respective slopes of said conical cavity and said male conical portion could be identical; preferably, however, they are different from each other, from 3 to 10 minutes of angle, which, in combination with said groove, provides a perfectly resistant assembly of the articular part to the base bone anchor. This difference in slope is preferably 5 minutes of angle, and, according to one embodiment of the invention in this case, the slope of said conical cavity is 5 ° 45 'and that of said male conical portion is 5 ° 40 '. The elements may be of any suitable implantable material. In particular, the joint piece can be made of chromium and cobalt alloy and the bone anchoring base can be made of titanium, vanadium and aluminum alloy known under the reference TA6V.

Advantageously, the element not comprising the conical cavity has a lug adapted to be fitly engaged in said groove and to slide therein during the assembly of the two elements to one another. This groove and this lug thus form means for angular positioning of one element relative to the other, making it possible to ensure a determined angular orientation of the articular part relative to the bone anchoring base. Preferably, said groove and said lug are arranged radially on the respective elements. According to a possible embodiment of the invention, said groove is arranged on the articular part and said lug is arranged on the bone anchoring base.

The lug thus forms a means of locating the angular position of implantation of the bone anchoring base on the shoulder blade, and thus locating the angular position that the joint piece will have after being placed on this base. bone anchor.

One element could have a plurality of grooves and the other element could have a plurality of corresponding lugs. According to a preferred embodiment of the invention, however, one of said elements comprises a single groove as mentioned above and the other element comprises a single lug as mentioned above. The invention will be better understood, and other features and advantages thereof will become apparent, with reference to the attached schematic drawing, showing, by way of non-limiting example, a preferred embodiment of a scapula implant that 'it relates to. FIG. 1 is a perspective view showing, on the right of the figure, an anchoring base on the scapula at a first angle of view, and on the left of the figure, a joint piece intended to be mounted. on this anchoring base, this articular part being seen at a second angle substantially perpendicular to said first viewing angle; Figure 2 is a perspective view of the joint piece, similar to Figure 1 but after a pivoting of this articular part along its axis, at a 90 ° angle; Figure 3 is a view of the anchor base by its proximal face, along the axis of this base; Figure 4 is a view of the anchoring base and the articular part in section passing through their axes, before the assembly of the articular part to the base 25 anchoring; and Figure 5 is a view of the anchor base and the joint part similar to Figure 4, after the assembly of the joint part to the anchor base. FIG. 1 shows a scapula 1 implant forming part of a shoulder joint prosthesis, comprising a base 2 for anchoring to the scapula and an articular part 3 forming an articular surface 4. This articular surface 4 is intended to cooperate with a complementary articular surface that forms a medullary stem (not shown) intended to be inserted into the medullary canal of the humerus. The base 2 has a head 5 and an anchor tail 6.

The head 5 forms on its periphery a conical surface 7 having a slope of 5 ° 40 ', and thus constitutes a male conical portion of assembly to the joint piece 3. At its proximal face, it has a cavity 8 at the bottom curve, in the center of which opens a hole 9 arranged in the anchoring tail 6. This hole 9 is intended to receive a centering rod 15 that comprises the articular part 3; with reference to Figures 3 and 4, it appears that it has a proximal cylindrical portion and a distal hexagonal portion of smaller section opening into the bottom of this cylindrical portion. This distal hexagonal portion is adapted to fitly receive a corresponding hexagonal portion of an instrument for installing the base 2, to perform an angular orientation of this base 2 on the shoulder blade. The base 2 also comprises four holes 10a, 10b arranged around this central hole 8, intended to receive additional anchoring screws (not shown), and a lug 11 projecting radially from the proximal edge of the head 5.

As shown in Figure 3, a first pair of holes 10a is arranged in the same diametral plane as that in which the lug 11 extends, and a second pair of holes 10b is arranged in a diametral plane perpendicular to this plane. The axes of the two holes 10a, 10b of the same pair diverge with respect to the axis of the shank 6, taking into account the curvature formed by the bottom of the cavity 8.

As can be seen in FIG. 3, each hole 10a, 10b has, on a sector of its circumference, grooves formed in the base 2, and does not have any on the diametrically opposed sector; the sectors of the holes 10a comprising these grooves are turned towards the hole 9 while the sectors of the holes 10b comprising these grooves are turned on the opposite side to the hole 9. The screws intended to be engaged in these holes 10a, 10b have threaded conical heads ; the grooves of a hole allow an interruption of the threading of this hole, which allows a commitment of a screw in this hole with inclination towards the side of the hole on which is the sector devoid of grooves. The base 2 thus allows the screws engaged respectively in the upper hole 10a in the lower hole 10a can be optimally oriented for an anchoring respectively in the pillar of the coracoid and in the abutment of the scapula, thereby prohibiting an orientation of these screws may conflict with the anchor tail 6 or with the bone area in which the tail 6 is implanted; this base 2 also allows the screws engaged in the holes 10b are located in the thick part of said pillars by prohibiting an orientation of these screws may cause them to open out of these pillars. This system formed by holes comprising notched sectors and opposite sectors devoid of notches, and screws with conical threaded heads, was the subject of the French patent application No. 11 54791, in the name of the applicant , to which it will be possible to refer for further details. The anchoring tail 6 has for its part external circular projections of support in the bone of the scapula and a distal threaded cavity 13 for the possible establishment of an extension piece, for the case where a deeper bone anchorage of the base 2 would be required. The articular part 3 has, in addition to the articular surface 4 and the rod 15, a conically shaped cavity 16, a radial groove 17, a bottom cavity 18 and two housings 19. The cavity 16 opens into the face of the articular part 3 intended to be turned to the bone. It has a slope of 5 ° 45 'and is intended to receive the head 5 with jamming to achieve the assembly of the articular part 3 to the base 2. As can be seen in Figures 1 and 2, this cavity 16 is off-center with respect to the axis of the assembly of the articular part 3, thus making it possible to off-center the articular surface 4 with respect to the axis of the base 2. This decentering makes it possible to prevent the known problem for prostheses shoulder says "notch phenomenon". The groove 17 is arranged in the wall of the articular part 3 defining the periphery of the cavity 16 and opens into this cavity. It is adapted to receive the lug 11 in a controlled manner but with the possibility of sliding of this lug 11 in it during this assembly. The bottom cavity 18 reduces the amount of material constituting the joint part 3. The housing 19 are arranged diametrically opposite; they allow the gripping of the articular part 3 by an instrument allowing the manipulation of this articular piece and its impaction on the head 5. In the example shown, they are arranged in a plane perpendicular to that in which the groove 17 extends. In practice, the base 2 is placed on the shoulder blade with the possibility of locating the angular position of this base relative to the scapula, thanks to the lug 11. One or more screws are then placed in place. one or more of the holes 10a, 10b to secure the anchoring to the bone of this base 2. The articular part 3 is then assembled to the base 2 by engagement of its wall delimiting the periphery of its cavity 16 on the wall 7 of the head 5. During this engagement, the groove 17 and the lug 11 together form means for angular positioning of the articular part 3 relative to the base 2, to ensure adequate angular orientation of this articular part relative to this base. Once assembled, it appears that the resistance of this assembly to traction is of the order of 20% greater than the tensile strength of the assembly of a joint piece devoid of groove 17 to a base 2; the torsional strength of this assembly is moreover of the order of 30% greater than the torsional strength of the assembly of an articular part devoid of a groove 17 to a base 2, such as the illustrate the results detailed below. In confidential tests, the following disassembly loads were measured on five implants 1 according to the invention, during static tensile tests (2kN positioning force, tensile speed: 0.48 mm / min ): 1432 Newtons, 1450 Newtons, 1328 Newtons, 1320 Newtons, and 1261 Newtons, an average of 1358 Newtons; the following disassembly loads were measured on five implants whose articular parts are devoid of grooves as above, under the same test conditions: 1141 Newtons, 1115 Newtons, 1096 Newtons, 1180 Newtons and 1081 Newtons, an average of 1123 Newtons.

With regard to the torsion resistance, the following maximum torques were measured on five implants 1 according to the invention (delivery force of 2kN, torsion speed: 20 ° / min): 40.4 Nm, 32.5 Nm, 46.0 Nm, 33.5 Nm 34.6 Nm, an average of 37.4 Nm; the following maximum torques were measured on five implants whose articular parts are devoid of grooves as mentioned above, under the same test conditions: 28.5 Nm, 31.5 Nm, 29.4 Nm, 27.8 Nm 27 , 4 Nm is an average of 28.9 Nm The invention therefore provides a scapula 1 implant, or any other type of implant with a bone anchoring base and articular piece forming a joint surface, having the following key advantages: - to obtain an assembly resistance fully sufficient to withstand the repeated forces exerted on the implant 1 by certain movements of the fitted person; - Including means 11, 17 of angular positioning of an element 2, 3 relative to the other, able to ensure a specific angular orientation of the articular part 3 relative to the base 2, the lug 11 further forming means for locating the angular position of implantation of the base 2 on the scapula. The invention has been described above with reference to an embodiment provided by way of example. It goes without saying that it is not limited to this embodiment but that it extends to all other embodiments covered by the appended claims.

Claims (9)

CLAIMS1 - Implant (1) forming part of a joint prosthesis, in particular implant (1) of scapula forming part of a shoulder joint prosthesis, comprising a base (2) for bone anchoring and a articular piece (3) forming an articular surface (4), one of these two elements (3) comprising a conical cavity (16) with a slight slope while the other element (2) comprises a male conical part (5) corresponding, this male conical portion (5) being adapted to be inserted into said conical cavity (16) until complete wedging therein; characterized in that the element (3) comprising said conical cavity (16) has at least one groove (17) formed in its wall defining the periphery of the conical cavity (16), the groove (17) opening into this cavity. 2 - Implant (1) according to claim 1, characterized in that the respective slopes of said conical cavity (16) and said male conical portion (5) are different from each other, from 3 to 10 minutes d 'angle 3 - Implant (1) according to claim 2, characterized in that said difference in slope is 5 minutes of angle. 4 - Implant (1) according to claim 3, characterized in that the slope of said conical cavity (16) is 5 ° 45 'and in that the slope of said male conical portion (5) is 5 ° 40' . 5 - Implant (1) according to one of claims 1 to 4, characterized in that the joint piece (3) is chromium alloy and cobalt and in that the base (2) of bone anchoring is in titanium, vanadium and aluminum alloy known as TA6V. 6 - Implant (1) according to one of claims 1 to 5, characterized in that the element (2) not comprising the conical cavity (16) has a lug (11) adapted to be engaged in a manner adjusted in said groove (17) and to slide therein during the assembly of the two elements (2, 3) to one another. 7 - Implant (1) according to claim 6, characterized in that q said groove (17) and said lug (11) are arranged radially on the elements (2, 3) respectively. 8 - Implant (1) according to claim 5 or claim 6, characterized in that said groove (17) is arranged on the articular part (3) and said lug (11) is arranged on the base (2) of bone anchorage. 9 - Implant (1) according to one of claims 6 to 8, characterized in that one of said elements (3) comprises a single groove (17) as mentioned above and in that the other element (2) comprises a single lug (11) as mentioned above.