CERAMIC JOINT IMPLANT PROVIDED WITH LOCKING DEVICES FOR ITS SCREWING

Abstract

The invention relates to a joint prosthesis implant (1) comprising: - a main body (2) mainly of ceramic and comprising an external articular surface (8) of ceramic of concave or convex shape, - at least one clamping screw (5) configured to allow clamping of the main body (2) on the patient's bone or on an intermediate element (3) fixed to said bone, - at least one added ring (4) in the main body (2; 200) configured to distribute the mechanical stresses from the tightening of the clamping screw (5) homogeneously within the main body (2), said added ring (4) comprising a first organ (41) and a second organ (42) distinct from each other.

Description

[0001] The invention relates to a joint prosthesis implant. More specifically, the invention relates to a joint prosthesis implant whose external articular surface is made of ceramic.

[0002] Several types of joint prostheses are already known in the state of the art, for example shoulder prostheses, hip prostheses or even knee prostheses.

[0003] All of these joint prostheses comprise two implants, each having an external articular surface intended to come into contact with each other, thus reproducing the joint. In order to reproduce the best possible quality of articulation, it is known to use favorable pairs of materials for these external articular surfaces in contact, these pairs being able to be two so-called "hard" materials or a "hard" material and a so-called "soft" material. The known "hard" materials used in joint prosthesis implants are Cobalt Chrome alloy, titanium alloy stainless steel or even ceramic. The so-called "soft" materials can be plastic, for example very high molecular weight polyethylene (UHMWPE) or polyetheretherketone (PEEK) or PEKK (poly ether ketone ketone) and their derivatives.

[0004] Cobalt Chrome is an alloy particularly appreciated by manufacturers of joint prosthesis implants because it has exceptional tribological and mechanical properties which allow the implant in question to be screwed and tightened (using one or more screws located in the implant) either directly into the patient's bone, or into an element itself fixed to the patient's bone (for example a metaglene for a reverse total shoulder prosthesis), without risk of damaging the implant.

[0005] However, the latest standards in force (and in particular the updated standard of Delegated Regulation (EU) 2020 / 217 of 4 October 2019 REACH) tend to prohibit the use of cobalt chromium as a material for joint prosthesis implants on the grounds that cobalt is considered a potentially carcinogenic, mutagenic or toxic substance for the patient. Therefore, alternative hard materials should be considered.

[0006] A known hard material is ceramic. This material has the advantage of being biocompatible and particularly suitable for friction given its hardness properties. However, ceramic is a very poorly ductile material and the very strong and localized mechanical stresses resulting from the aforementioned tightening using one or more screws risk causing cracks within the ceramic, or even breaking it. Such a risk is unacceptable either for the surgeon during the operation or for the patient who may have to replace their prosthesis too quickly. In addition, it is currently not authorized to replace a ceramic implant after a break in the ceramic of a first implant. It is therefore mandatory to move towards another pair of materials.

[0007] To overcome these drawbacks, joint prosthesis implants are already known in the state of the art, comprising an element added by clipping between a glenosphere, the external articular surface of which is made of ceramic, and a tightening screw intended to be introduced by tightening into the patient's bone (or into an intermediate metaglene when the patient's bone is a glenoid). This added element makes it possible to distribute the mechanical stresses resulting from the tightening of the tightening screw, in a homogeneous manner within the ceramic glenosphere so that the latter does not crack or break. However, such solutions are not satisfactory since they do not guarantee the good holding of said added element, whether during tightening of the tightening screw or over time, after the operation.Indeed, it has been observed that this added element, under the action of local stresses applied by the screw head when tightening the latter, deforms significantly, which causes it to unclip from the glenosphere. Therefore, these solutions do not guarantee a homogeneous distribution of the mechanical stresses resulting from tightening within the ceramic glenosphere, which risks cracking or breaking during the operation or very quickly after it. In addition, after the operation and during the life of the prosthesis, this added element also undergoes local stresses which can cause similar inconvenience, leading to identical consequences for the integrity of the ceramic glenosphere.

[0008] The invention aims in particular to enable the use of such a ceramic implant provided with an added element which overcomes all of the aforementioned drawbacks.

[0009] To this end, the invention relates to an implant comprising: a main body mainly made of ceramic and comprising a ceramic articular external surface of concave or convex shape, at least one tightening screw configured to allow the tightening of the main body on the patient's bone or on an intermediate element fixed to said bone, at least one ring inserted in the main body and forming with the latter a chamber trapping the head of the tightening screw and comprising a bearing surface forming a stop for said head of the tightening screw, the inserted ring being configured to be in contact with the tightening screw during said tightening, the inserted ring (4) comprising a central orifice crossed by the tightening screw, the inserted ring being configured to distribute the mechanical stresses resulting from the tightening of the tightening screw in a homogeneous manner within the main body,the added ring comprising a first member forming the external surface of the added ring and comprising means for clipping to the main body and a second member forming a spacer between the first member and the clamping screw, said second member being assembled within the first member, forming said bearing surface and defining the central orifice, the first member and the second member being two members distinct from each other and comprising locking means configured to prevent any separation between them after assembly.

[0010] Thus, it is possible to produce a ceramic (or mainly ceramic) joint prosthesis implant that is both functional and robust and that does not risk cracking or breaking when tightening the clamping screw (or after the operation). Indeed, the joint prosthesis implant according to the invention makes it possible to reduce the mechanical stresses transmitted to the main body, resulting from the tightening of the clamping screw, compared to the solutions of the prior art, thanks in particular to the assembly between the first member and the second member of the added ring. As the stresses transmitted in fineto the main body of the glenosphere, by the first member of the added ring, are distributed homogeneously within the main body, thus drastically reducing the risks of cracking or breaking of the main ceramic body, whether during the tightening operation of the tightening screw or after the operation. By "homogeneous distribution of mechanical stresses resulting from the tightening of the screw", we mean that the stresses are distributed over the entire surface of the main body in contact with the added ring (more precisely with its first member), which thus makes it possible to avoid the application to the main ceramic body of a stress which would be greater than the elastic limit and which would cause a breakage of the ceramic.Thanks to a large radial contact surface of the first member of the ring attached to the main body, it is possible to have a distribution of forces over a larger surface of the main body so that the localized stresses are as low as possible.

[0011] The second member also prevents any deformation of the first member when screwing the clamping screw into the patient's bone or into the intermediate element fixed to said bone. Thus, any unclipping between the clipping means of the first member of the attached ring and the main body of the glenosphere is prevented, which further secures the use of the implant.

[0012] Furthermore, the locking means of the assembly between the first member and the second member prevent any separation between them after assembly, both when screwing the clamping screw into the patient's bone or into the intermediate element fixed to said bone and before the operation (for example due to vibrations transmitted to the attached ring during transport of the implant) or after the operation (for example due to vibrations resulting from the patient's activities). This thus optimizes the robustness and good performance over time of the implant.

[0013] The added ring (and therefore the first member and / or the second member) can be made of any material allowing good distribution of mechanical stresses within the main body. The first member and / or the second member can in particular be made entirely or partly of metal, plastic or ceramic. It can also be made of several different materials including a composition of the aforementioned materials.

[0014] According to other optional characteristics of the joint prosthesis implant according to the invention taken alone or in combination: the first member comprises a tapped portion and the second member comprises a corresponding threaded portion, the threaded portion and the tapped portion being configured to allow the second member to be screwed with the first member, preferably, the direction of screwing of the second member with the first member being reversed to that carried out when tightening the clamping screw, the tapped portion and the threaded portion have a left-hand pitch or a right-hand pitch, preferably between 0.5 mm and 2 mm, the threaded portion preferably being a metric thread, an artillery thread or a square thread, the locking means comprise a circular groove and a collar configured to engage in said groove, the groove being formed on the first member or on the second member and the collar being respectively formed on the second member or the first member,the locking means comprise at least one clip and at least one orifice configured to be passed through by the clip, the clip being formed on the first member or on the second member and the orifice being respectively formed on the second member or the first member, the first member comprises elastically deformable peripheral means, the main body is a glenosphere, the clamping screw being configured to allow clamping between the glenosphere and a metaglene fixed on the patient's glenoid, the glenosphere has a diameter of between 30 and 46 mm, and / or the main body is a ceramic tibial plateau, a knee condyle, an anatomical glenoid, a hip acetabulum or a ceramic cup.

[0015] The invention also relates to a joint prosthesis comprising an implant according to any one of the preceding variants. Brief description of the figures

[0016] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which: [ Fig. 1 ] there figure 1 is a sectional view of a joint prosthesis implant according to the invention, [ Fig. 2 ] there figure 2 is a sectional view of the implant of the figure 1 assembled to a metaglene, [ Fig. 3 ] there figure 3 is a perspective view ( Figure 3A ), from above ( Figure 3B ) and in couple (3C) of a reported ring as present in the implant of the figures 1 And 2 , [ Fig. 4 ] there figure 4 is a perspective view ( Figure 4A ), from above ( Figure 4B ) and in couple (4C) of a first member of the ring reported from the figure 4 , [ Fig. 5 ] there Figure 5 is a perspective view ( Figure 5A ), from above ( Figure 5B ) and in couple (5C) of a second organ of the ring reported from the figure 4 . Detailed description

[0017] It has been represented on the figures 1 And 2 a joint prosthesis implant according to a first embodiment of the invention, designated by the general reference 1. On the Figures 3A to 5C , a fitted ring is shown, designated by the general reference 4 or one of its two constituent parts. It should be noted that similar elements between the figures are designated by identical references.

[0018] The joint prosthesis implant 1 thus described comprises: a main body 2 mainly made of ceramic and comprising an external articular surface 8 made of ceramic of concave or convex shape, at least one clamping screw 5 configured to allow the clamping of the main body 2 on the patient's bone or on an intermediate element 3 fixed to said bone, at least one added ring 4 in the main body 2 and forming with the latter a chamber 12 trapping the head 6 of the clamping screw 5 and comprising a bearing surface 7 forming a stop for said head 6 of the clamping screw 5, the added ring 4 being configured to be in contact with the clamping screw 5 during said clamping, the added ring 4 comprising a central orifice 13 crossed by the clamping screw 5, the added ring 4 being configured to distribute the mechanical stresses resulting from the tightening of the clamping screw 5 in a homogeneous manner within the main body 2.The added ring 4 comprises a first member 41 forming the external surface of the added ring 4 and comprising clipping means 14 to the main body 2 and a second member 42 forming a spacer between the first member 41 and the clamping screw 5, said second member 42 being assembled within the first member 41, forming said bearing surface 7 and defining the central orifice 13, the first member 41 and the second member 42 being two members distinct from each other and comprising locking means 51, 52 configured to prevent any separation between them after assembly.

[0019] In the embodiment described in support of the figures, the main body 2 corresponds to a glenosphere 2 whose tightening screw 5 allows tightening with an intermediate element 3 fixed to the bone, in this case the metaglene 3.

[0020] The ceramic glenosphere 2 can have a diameter ranging from 30 to 46 mm, can be centered or eccentric and can be lateralized if necessary.

[0021] Glenosphere 2 and metaglene 3 are assembled to each other by means of clamping screw 5. In order to ensure an even better assembly, a Morse taper (not shown) is provided between glenosphere 2 and metaglene 3.

[0022] The glenosphere 2 comprises a housing 9 sized to receive the attached ring 4 and formed with the latter the chamber 12 trapping the head 6 of the clamping screw 5.

[0023] The joint prosthesis implant described therefore corresponds to a glenoid implant for a reverse shoulder prosthesis. Nevertheless, the characteristics described in the context of this embodiment can be applied to any prosthesis comprising an articular implant having a ceramic articular surface and being screwed and tightened by means of at least one tightening screw, on the patient's bone or on an intermediate element fixed to said bone. By way of example, the invention also relates to hip or knee prosthesis implants.

[0024] The type of ceramic used for the main body may be any type of ceramic known to those skilled in the art. For example, it may be alumina, zirconia or a composite material. Since ceramic is a hard material, it may be used in the context of a “hard / hard” or “hard-soft” material pair. In this second example, the so-called “soft” material may be ultra-high molecular weight polyethylene (UHMWPE), polyetheretherketone (PEEK), PEKK (poly ether ketone ketone) or their derivatives.

[0025] As previously specified, the added ring 4 is clipped within the housing 9 of the glenosphere 2, via clipping means, partially present on its first member 41, and thus forms, with the housing 9, the chamber 12 trapping the head 6 of the clamping screw 5. More precisely, the clipping means are materialized by teeth present at the ends of elastically deformable peripheral means (taking the form of fins 21), together forming a rib 14, and by a circular groove 16 formed within the housing 9 of the glenosphere 2 and the shape of which makes it possible to receive and block the rib 14 formed by the teeth, so as to allow the clipping of the first member 41 of the added ring 4. More precisely, the elasticity conferred on the first member 41 by its elastically deformable fins 21 makes it possible to deform it sufficiently to introduce the rib 14 within the groove 16.When the fins 21 return to their initial shape, the rib 14 becomes wedged in the groove 16, thus causing the first member 41 to be clipped into the housing 9 of the glenosphere 2. Thus, there is a large contact surface between the first member 41 and the glenosphere 2, namely the entire radial contact zone between the rib 14 and the groove 16. It is thus possible to distribute homogeneously over the entirety of this large contact surface between the housing 9 of the glenosphere 2 and the added ring 4 and therefore, . in fine , to minimize the force of the stresses undergone locally by the ceramic glenosphere 2, which reduces the risk of cracks or breakage of the latter.

[0026] As already mentioned, the attached ring 4 comprises a first member 41 (visible in Figures 4A to 4C). This first member mainly ensures the function of assembly to the glenosphere 2. In the embodiment described, this assembly is carried out by clipping the first member 41 into the housing 9 of the glenosphere 2. To do this, the first member is provided with teeth present at the ends of elastically deformable peripheral means (in the form of fins 21), together forming the rib 14. These fins 21 are split (as is particularly visible in Figures 3A , 4A and 4C ) in order to give the first member 41 sufficient elastic properties for its clipping into the groove 16.

[0027] The ring further comprises a second member 42 whose positioning and shape make it possible to constrain the first member 41 in its clipped position, in particular when tightening the clamping screw 5. This second member 42 corresponds to a spacer between the first member and the clamping screw 5 and therefore acts as a lock for the first member 41. This second member 42 ( Figures 5A to 5C), cylindrical in shape, has a diameter smaller than that of the first member 41, which allows it to be assembled within the first member 41. In the embodiment described, this assembly is carried out by screwing. To do this, the second member 42 comprises a radial and external threaded portion 11 of a shape complementary to the internal radial tapped portion 10 of the first member 41. Advantageously, the screwing of the second member 42 with the first member 41 is reversed to that carried out when tightening the clamping screw 5. In other words, the direction of screwing between the second member 42 and the first member 41 is reversed relative to the direction in which the glenosphere will be screwed either into the patient's bone or into the metaglene 3. Thus, the risks of unscrewing between the first member 41 and the second member 42 during the step of tightening the clamping screw 5 are reduced.Advantageously, the tapped portion 10 and the threaded portion 11 have a left-hand pitch or a right-hand pitch. Furthermore, the threaded portion 11 preferably represents a metric thread, an artillery thread or a square thread. Finally, the pitch of the tapped portion 10 and the threaded portion 11 can be standardized and / or a fine pitch. In this sense, the pitch is advantageously between 0.5mm and 2mm, which makes it possible to have a very fine pitch.

[0028] The second member 42 comprises a collar 52 at its distal end which, when the second member 42 is in the final position within the first member 41 (i.e. once it is completely screwed in), engages in the circular groove 51 provided in the first member 41. Thus this final position between the first member 41 and the second member 42 is locked in such a way that any separation between them is made impossible. In a variant not shown, these locking means (i.e. the collar and the groove) could be provided respectively on the first member and on the second member.According to another variant of the invention, not shown, the locking means may, alternatively or cumulatively, comprise at least one clip and at least one orifice configured to be passed through by the clip, also making it possible to lock the assembly in the final position between the first member and the second member of the added ring. This clip and this orifice may be respectively provided on the first member and on the second member and vice versa. In order to lock with greater locking force, the locking means may comprise several clips and several dedicated through orifices and / or several collars and several dedicated grooves.

[0029] Furthermore, this second member 42 comprises an internal counterbore which forms said bearing surface 7 ( Figures 3A to 3C) for the screw head 6 and has a through hole which defines the central hole 13 crossed by the tightening screw 5. The second member 42 therefore comprises a bearing surface 7 forming a stop for the head 6 of the screw 5 when tightening the latter.

[0030] The added ring 4 comprises a large area of ​​contact between the first member 41 and the second member 42, namely the entire contact surface between the thread 11 of the second member and the tap 10 of the first member 41. Thus, when tightening the clamping screw 5, stresses are applied to the second member 42 which, due to its more rigid configuration than the first member 41, assumes a large part of it and transmits only a smaller part of it. This smaller portion is distributed homogeneously to the first member 41 via the contact area between the tap 10 and the thread 11, then the resulting part is itself transmitted to the internal face of the housing 9 of the ceramic glenosphere 2, mainly via the radial contact between the rib 14 and the groove 16, but also via the direct contact between the deformable fins 21 and the internal face of the housing 9 of the glenosphere 2.This results in less transmission and a more homogeneous distribution of the stresses resulting from the tightening of glenosphere 2 on metaglene 3, which contributes to. in fine to a reduction in the strength of the stresses locally experienced by the ceramic glenosphere 2, reducing the risk of cracks or breakage of the latter.

[0031] As already mentioned, the invention is not limited to the embodiments presented. Indeed and as mentioned previously, the invention can be applied to any type of joint implant having a ceramic articular surface and being screwed and tightened by means of at least one tightening screw, on the patient's bone or on an intermediate element fixed to said bone. By way of example, the invention also relates to hip or knee prosthesis implants. List of references

[0032] 1: implant 2: main body / glenosphere 3: metaglene 4: insert ring 5: clamping screw 6: head of the clamping screw 7: bearing surface 8: external articular surface 9: housing of the main body 10: tapped portion / tap 11: threaded portion / thread 12: chamber 13: central orifice of the ring 14: rib 16: groove 21: elastically deformable fins 41: first member of the insert ring 42: second member of the insert ring 51: groove 52: collar

Claims

1. Joint prosthesis implant (1) comprising: - a main body (2) mainly made of ceramic and comprising an external articular surface (8) made of ceramic of concave or convex shape, - at least one tightening screw (5) configured to allow the tightening of the main body (2) on the patient's bone or on an intermediate element (3) fixed to said bone, - at least one added ring (4) in the main body (2) and forming with the latter a chamber (12) trapping the head (6) of the tightening screw (5) and comprising a bearing surface (7) forming a stop for said head (6) of the tightening screw (5), the added ring (4) being configured to be in contact with the tightening screw (5) during said tightening, the added ring (4) comprising a central orifice (13) crossed by the tightening screw (5), the added ring (4) being configured to distribute the mechanical stresses resulting from the tightening of the tightening screw (5) in a homogeneous manner within the main body (2),the added ring (4) comprising a first member (41) forming the external surface of the added ring (4) and comprising clipping means (14) to the main body (2) and a second member (42) forming a spacer between the first member (41) and the clamping screw, said second member (42) being assembled within the first member (41), forming said bearing surface (7) and defining the central orifice (13), the first member (41) and the second member (42) being two members distinct from each other and comprising locking means (51, 52) configured to prevent any separation between them after assembly., 2. Implant (1) according to the preceding claim, in which the first member (41) comprises a threaded portion (10) and the second member (42) comprises a corresponding threaded portion (11), the threaded portion (11) and the threaded portion (10) being configured to allow the second member (42) to be screwed with the first member (41), preferably, the direction of screwing of the second member (42) with the first member (41) being reversed to that carried out when tightening the clamping screw (5).

3. Implant (1) according to the preceding claim, in which the tapped portion (10) and the threaded portion (11) have a left-hand pitch or a right-hand pitch, preferably between 0.5mm and 2mm, the threaded portion (11) preferably being a metric thread, an artillery thread or a square thread.

4. Implant (1) according to one of the preceding claims, wherein the locking means comprise a circular groove (51) and a collar (52) configured to engage in said groove (51), the groove (51) being formed on the first member (41) or on the second member (42) and the collar (52) being respectively formed on the second member (42) or the first member (41).

5. Implant (1) according to one of the preceding claims, in which the locking means comprise at least one clip and at least one orifice configured to be passed through by the clip, the clip being formed on the first member (41) or on the second member (42) and the orifice being respectively formed on the second member (42) or the first member (41).

6. Implant (1) according to one of the preceding claims, in which the first member (41) comprises elastically deformable peripheral means (21).

7. Implant (1) according to one of the preceding claims, in which the main body (2) is a glenosphere (2), the clamping screw (5) being configured to allow clamping between the glenosphere (2) and a metaglene (3) fixed on the patient's glenoid.

8. Implant (1) according to the preceding claim, in which the glenosphere (2) has a diameter of between 30 and 46 mm.

9. Implant (1) according to one of claims 1 to 6, in which the main body (2) is a ceramic tibial plateau, a knee condyle, an anatomical glenoid, a hip acetabulum or a ceramic cup.

10. Joint prosthesis comprising an implant (1) according to any one of the preceding claims.