FR3027213A1 - JOINT PROSTHESIS STRUCTURE FOR SMALL BONES - Google Patents

Abstract

This prosthesis structure comprises a prosthetic element (1) which comprises a spherical articulating head (5), a cup and a sliding core (2) intended to be received in this cup, this sliding core (2) forming a articulation cavity for receiving the articulation head (5). According to the invention, - the sliding core (2) comprises a retaining collar arranged at the entrance of said articulation cavity, defining an opening whose minimum diameter is in the range of 90 to 95% of the diameter of the hinge cavity; and - the sliding core (2) is assembled to said prosthetic element (1) before implantation of the prosthesis, by force insertion of the hinge head (5) into said hinge cavity.

Description

The present invention relates to a joint prosthesis structure for small bones, in particular for the restoration of a joint of a toe or hand, and in particular for the restoration of a trapezoid joint. metacarpal.

The invention also relates to a method of constituting this prosthesis structure. It is well known to design a trapezo-metacarpal joint prosthesis in four separate elements, namely a medullary stem intended to be inserted into the medullary canal of the first metacarpal, a cup intended to be placed in the trapezium, a cervix integral with a spherical articulation head, intended to be mounted on the medullary stem, and a sliding core intended to be mounted in the cup and to receive the articulation head in a spherical articulation cavity formed by this core . The publication of patent application No. FR 2,883,723 in particular illustrates a prosthesis of this type. Existing prostheses have a significant risk of dislocation given the low retention of the hinge head in the hinge cavity, or even the lack of such retention, and the present invention aims to remedy this. essential problem.

The prosthesis structure concerned comprises, in a manner known per se, a prosthetic element which comprises a spherical articulation head, a cup and a sliding core intended to be received in this cup, the sliding core forming a hinge cavity. intended to receive the hinge head. According to the invention, the sliding core comprises a retaining collar arranged at the inlet of said articulation cavity, delimiting an opening whose minimum diameter is in the range of 90 to 95% of the diameter of the articulation cavity; and - the sliding core is assembled to said prosthetic element before implantation of the prosthesis, by force insertion of the hinge head into said hinge cavity. The inventor has indeed found that the significant risk of dislocation above resulted from the practice of delivering a prosthesis with all its components separated from each other, and to manually perform the assembly of the hinge head to the core slip, during the procedure. This need to perform this assembly manually and during the procedure involves providing a low retentive neck, or an absence of collar, which results in low retention, or the lack of retention, above, and therefore the risk of resulting dislocation, which the practice has accommodated.

The inventor was then able to conceive the idea of achieving a high degree of retention of the hinge head by the sliding core, by providing a highly retentive collar, to assemble the head to the core before implantation. , especially in the factory at the time of manufacture of the components of the prosthesis, and deliver the prosthesis with the sliding core and the hinge head preassembled to each other. The assembly of the prosthesis is therefore carried out by placing the sliding core in the cup and not by the establishment of the hinge head in the hinge cavity that forms the sliding core. The method according to the invention comprises the steps of: - manufacturing said sliding core with a retaining collar located at the entrance of said articulation cavity, this collar delimiting an opening whose minimum diameter is in the range ranging from 90 to 95% of the diameter of the hinge cavity; - assembling said prosthetic element and said sliding core to one another by forcibly inserting the hinge head into said hinge cavity; - Packing and conditioning the components of the prosthesis with the assembly prosthetic element / slip core and preassembled. Preferably, the aforesaid minimum diameter is 92.5% of the diameter of the hinge cavity. This value could be determined as optimal. Said prosthetic element could comprise a bone anchoring part allowing it to be directly implanted in one of the bones whose articulation must be restored, and could in particular be a medullary rod integral with said hinge head. Preferably, however, said prosthetic element is a prosthetic neck and the prosthesis structure comprises a bone anchoring element, such as a medullary stem, intended to be implanted in one of the bones whose articulation must be restored. this bone anchoring element being separated from said neck and being intended to receive this neck by assembly.

The means for assembling the neck with this bone anchoring element are preferably such that they allow the neck to be oriented relative to the bone anchoring element before a fixed assembly of this neck to the latter. These means may in particular be of the type with nesting walrus cones.

Said core could be a core intended to be fixedly mounted in said cup; preferably, however, the prosthesis is of the so-called "dual mobility" type, that is to say that the cup has internally a substantially smooth and continuous hemispherical surface, and that the core externally has a smooth and continuous substantially hemispherical surface. , the core 10 being intended to be received in the cup with capacity for joint movement. The method preferably comprises the step of manufacturing said prosthetic element in the form of a neck integral with the hinge head, and manufacturing a bone anchoring element intended to be implanted in one of the bones of which the The joint must be restored, which is separated from said neck and to which this neck is intended to be assembled. The method preferably comprises the steps of making said cup with a smooth and continuous substantially hemispherical inner surface, and fabricating said slip core with a smooth and continuous spherical outer surface, so that the core can be received in the cup with capacity 20 of joint movement of this core vis-à-vis this cup. The invention will be well understood, and other features and advantages thereof will become apparent with reference to the accompanying schematic drawing; this drawing shows, by way of non-limiting example, a preferred embodiment of the prosthesis structure concerned. FIG. 1 is a perspective view of a neck and a sliding core that comprises this prosthesis structure, before assembly of this neck and this core; Figure 2 is a view of the neck and the core similar to Figure 1, after assembly of the neck to the core; Figure 3 is a perspective view of a cup which also includes the prosthesis structure; and FIG. 4 is a view of the core and the cup after assembly, in section passing through their axis of revolution. FIG. 1 shows a prosthetic neck 1 and a sliding core 2 making it possible to constitute, with the cup 3 visible in FIG. 3 and with a medullary stem (not shown), a trapezo-metacarpal joint prosthesis of the type called "double mobility". This marrow stem can in particular be identical to that described in the patent application publication No. FR 2,883,723; it is intended to be inserted into the medullary canal of the first metacarpal and has a mounting cavity of the neck 1, Morse taper, that is to say, low slope. This neck 1 forms, at one end, a hinge head 5 intended to be received, with capacity for joint movement, in a hinge cavity 6 formed by the core 2, visible in FIG. 4. At its opposite end, the neck 1 has a conical tip 7 of the same slope as the cavity that comprises the medullary stem, this tip 7 being intended to be wedged in this cavity so as to ensure the mounting of the neck 1 on the medullary stem. This neck 1 is made, as well as the cup 3 and the medullary stem, a biocompatible metal.

The core 2 is made of a material promoting sliding, especially high density polyethylene. It delimits the cavity 6 and, as particularly visible in Figure 4, comprises a retaining collar 8 arranged at the entrance of this cavity 6. This collar 8 defines an opening of the cavity 9 whose diameter is 92.5% the diameter of the cavity 6.

The collar 8 is intended to be forced through by the head 5 during assembly of the neck 1 to the core 2, and the head 5 is intended to be fitly received in the cavity 6, so as to form the entire visible in FIG. 2. During this crossing, the collar 8 deforms elastically and then returns to its original shape once this crossing has been completed; by its aforementioned dimension, it ensures a high degree of retention of the head 5 by the core 2. The assembly of the neck 1 to the core 2 is made in the factory at the time of manufacture of the constituent elements of the prosthesis, and the prosthesis is delivered with the pre-assembled collar 1-core 2 assembly visible in FIG. 2, the medullary stem and the cup 3.

The core 2 externally has a surface 2a of substantially hemispherical shape, smooth and continuous, and is intended to be received in the cavity 10 formed by the cup 3, with capacity for joint movement. This cup 3 thus presents internally a substantially hemispherical, smooth and continuous surface, as visible in FIG.

For the rest, the cup 3 is of known type, its outer shape being in particular as described in the patent application publication No. FR 2,883,723. In practice, after placement of the medullary stem in the first metacarpal and of the cup 3 in the trapezium, the assembly of the prosthesis is carried out by the placement of the core 2 in the cup 3. As can be seen from the foregoing, the invention provides a prosthetic joint structure for small bone, especially for the restoration of a joint of a finger of the foot or the hand, and in particular for the restoration of a trapezio-metacarpal joint, which has the decisive advantage of having a reduced risk of dislocation. The invention has been described above with reference to an exemplary embodiment. It goes without saying that it is not limited to this embodiment but that it is to all embodiments covered by the appended claims.

Claims (9)

REVENDICATIONS1. Bone prosthesis structure for small bones, in particular for articulation of a toe or hand, and in particular for a trapezio-metacarpal joint, comprising a prosthetic element (1) which comprises a hinge head ( 5) spherical, a cup (3) and a sliding core (2) to be received in this cup (3), the sliding core (2) forming a hinge cavity (6) for receiving the head articulation (5); characterized in that: - the sliding core (2) comprises a retaining collar (8) arranged at the inlet of said articulation cavity (6), delimiting an opening (9) whose minimum diameter is included in the range of 90 to 95% of the diameter of the hinge cavity (6); and - the sliding core (2) is assembled to said prosthetic element (1) before implantation of the prosthesis, by force insertion of the articulation head (5) into said articulation cavity (6). 2. prosthesis structure according to claim 1, characterized in that the aforementioned minimum diameter is equal to 92.5% of the diameter of the hinge cavity (6). 3. prosthesis structure according to claim 1 or claim 2, characterized in that said prosthetic element is a neck (1) of prosthesis and in that the prosthesis structure comprises a bone anchoring element intended to be implanted in the prosthesis. one of the bones whose joint must be restored, which is separated from said neck and to which this neck (1) is intended to be assembled. 4. prosthesis structure according to claim 3, characterized in that said bone anchoring element is in the form of a medullary stem. 5. prosthesis structure according to claim 3 or claim 4, characterized in that the means (7) for assembling the neck (1) to the bone anchoring element are such that they allow a neck orientation by relative to the bone anchoring element before a fixed assembly of this neck to the latter. 6. prosthesis structure according to one of claims 1 to 5, characterized in that the prosthesis is of the type called "dual mobility", that is to say that the cup (3) internally presents a substantially hemispherical surface and continues, and that the core (2) externally has a surface (2a) substantially hemispherical smooth and continuous, the core (2) being intended to be received in the cup (3) with capacity for joint movement. 7. Method of forming the prosthesis structure according to one of claims 1 to 6, characterized in that it comprises the steps of: - manufacturing said sliding core (2) with a retaining collar (8) located at the inlet of said articulation cavity (6), this collar delimiting an opening (9) whose minimum diameter is in the range of 90 to 95% of the diameter of the articulation cavity (6); - assembling said prosthetic element (1) and said sliding core (2) to each other by force insertion of the hinge head (5) into said hinge cavity (6); - Packing and conditioning the components of the prosthesis with the prosthetic element assembly (1) / slip core (2) and preassembled. 8. Method according to claim 7, characterized in that it comprises the step of manufacturing said prosthetic element in the form of a neck (1) integral with the hinge head (5), and to manufacture an element bone anchor for implantation in one of the bones whose joint is to be restored, which is separated from said neck and to which this neck is intended to be assembled. 9. A method according to claim 7 or claim 8, characterized in that it comprises the steps of manufacturing said cup (3) with a smooth and continuous substantially hemispherical inner surface, and manufacturing said slip core (2) with a spherical outer surface (2a) smooth and continuous, so that the core (2) can be received in the cup (3) with the ability of joint movement of the core vis-à-vis this cup.