FR2954691A1 - Prosthesis for replacing articulation between metacarpal bone and carpal trapezius bone of patient's hand, has oblong body whose central cores are made of flexible material with rigidity higher than that another material of body - Google Patents

Abstract

The prosthesis has a block (10) placed at a part of a flexible material i.e. silicone elastomer. The block has oblong bodies and anchoring tab (24), each has multiple longitudinal axes (12, 16, 22, 26), where the tab is integrated to each body so that two axes are perpendicular between the axes. A connection unit (30) connects each body and arranged, so that another two axes are appreciably orthogonal and remaining axes are collinear. One of the oblong bodies has central cores (42, 43) made of another material with rigidity more than the former material. The latter material is a mixture of the former material and a material of reinforcement e.g. glass fiber carbon fibers, doping agent e.g. talc and aluminum oxide.

Description

PROSTHESIS FOR THE REPLACEMENT OF A HAND JOINT.

The present invention relates to prostheses for the replacement of a hand joint between a carpal bone and a metacarpal bone, which find a particularly advantageous application as replacement prostheses of the joint between the trapezoid bone and the first metacarpal. Such prostheses are known, in particular trapezo-metacarpal prostheses which are in one piece flexible, for example made of silicone elastomer, such as those described in US-A-3,875,594, 4,158,893, 4,198,713. , 4,313,232, 4,367,562, and 4,871,367. There is even one developed by one of the inventors cited in the present patent application, which is a so-called "flexible universal joint" prosthesis. a material such as a silicone elastomer, which has the essential and original characteristic of taking into account the physiology of a joint such as that which exists between a carpal bone, the trapezium, and the first metacarpal, that is to say a articulation with two axes. This prosthesis objectively gives satisfactory results for a certain number of cases over a long period of time, with the disappearance of pain in 96% of cases and a significant improvement in function, in particular the opposition and the force of the thumb-index pliers. Its probability of survival at 15 years is 98.17%. The present invention however aims to achieve an improvement of this prosthesis called "cardan", and thus a prosthesis "cardan" having in itself an even more reliable structure conferring a greatly increased survival time, while facilitating the work of the Practitioner who realizes this implantation. More specifically, the subject of the present invention is a prosthesis for the replacement of a hand joint between a bone of the first metacarpal and the trapezium, said prosthesis consisting of a one-piece block made of a first flexible material having a given rigidity, said block comprising: a first oblong body defining a first longitudinal axis; a first anchoring tab defining a second longitudinal axis, said first tab being arranged to be able to be plugged into the medullary canal of the metacarpal bone, said so-called first tab being secured to the first oblong body substantially in its middle and so that the first and second axes are substantially perpendicular to each other, • a second oblong body defining a third longitudinal axis, • a second anchoring tab defining a fourth longitudinal axis, said second tab being arranged to be adapted to be plugged into a n orifice made in the carpal bone, said second tab being secured to the second oblong body substantially in its middle and so that the third and fourth axes are substantially perpendicular to each other, and • elastic connection means interconnecting the first and second oblong bodies, said connecting means being arranged so that the first and third axes are substantially orthogonal and the second and fourth axes are substantially collinear, characterized in that at least one of the two following elements, the first and second oblong body, comprises a central core made of a second material having a rigidity greater than that of the first material. Other features and advantages of the present invention will become apparent from the following description given with reference to the accompanying drawings for illustrative but not limiting purposes, in which: FIG. 1 is a perspective view of an embodiment of the prosthesis according to the invention to replace a joint between the trapezius bone belonging to the carp and the first metacarpal, the two carpal and metacarpal bones being evoked in broken lines, FIG. 2 is a block diagram which makes it possible to explain the 30 The structure of the prosthesis according to the invention, and Figure 3 is a longitudinal sectional view of the embodiment according to Figure 1, to highlight the essential characteristics of the prosthesis according to the invention.

It is first of all specified that, in the figures, the same references designate the same elements, whatever the figure on which they appear and whatever the form of representation of these elements. Similarly, if elements are not specifically referenced in one of the figures, their references can be easily found by referring to another figure. It is also stated that the figures represent a preferred embodiment of the object according to the invention, but that there may be other embodiments that meet the definition of this invention.

It is further specified that, when, according to the definition of the invention, the object of the invention comprises "at least one" element having a given function, the embodiment described may comprise several of these elements. Conversely, if the embodiment of the object according to the invention as illustrated has several elements of identical function and if, in the description, it is not specified that the object according to this invention must obligatorily comprise a number particular of these elements, the object of the invention may be defined as comprising "at least one" of these elements. Lastly, it should be noted that when, in the present description, an expression defines, by itself, without a specific particular mention concerning it, a set of structural characteristics, these characteristics may be taken, for the definition of the object of the protection requested, when technically possible, either separately, or in full and / or partial combination.

The present invention relates, with reference to the three appended figures, a prosthesis for the replacement of a hand joint between the first metacarpal 1 and the trapezoidal bone 2. The prosthesis consists of a block 10 in one piece. a first flexible material having a given rigidity.

This block comprises a first elongated body 11 defining a first longitudinal axis 12, a first anchoring tab 14 defining a second longitudinal axis 16, the first tab being arranged to be able to become stuck in the medullary canal of the first metacarpal 1, this first tab being integral with the first oblong body 11 substantially in the middle and so that the first and second pins 12, 16 are substantially perpendicular to each other, a second oblong body 21 defining a third longitudinal axis 22, a second anchoring tab 24 defining a fourth longitudinal axis 26, this second tab being arranged to be able to be plugged into an orifice made in the trapezoidal bone 2, this second tab being further secured to the second oblong body substantially in the middle and so that the third and fourth axes 22, 26 are substantially perpendicular to each other.

The block 10 further comprises elastic connection means 30 interconnecting the first and second oblong bodies 11, 21, this elastic connection means having a function of maintaining the first and third axes 12, 22 in a substantially orthogonal position and the second and fourth axes 16, 26 in substantially collinear position.

According to an important feature of the present invention, at least one of the following two elements which have been defined above, namely the first and second oblong bodies 11, 21 comprises a central core 42, 41, 43, 44 made of a second material having greater rigidity than the first material.

According to a preferred embodiment, the first material has a hardness of the order of 21/22 Shores A. Advantageously, if the first material is a silicone elastomer, the second material is a mixture of this first material and reinforcement material.

According to possible embodiments and which give good results, the reinforcing material consists of at least one of the following bodies: carbon fibers, glass fibers, dopant constituted by at least one of the following materials: aluminum, talc. In a very advantageous and even preferential manner, the two elements 11, 21, defined above each comprise, as illustrated in FIG. 3 in section, at least one central core 42, 43. In a very preferred embodiment, the elastic connection means 30 interconnecting the first and second oblong bodies 11, 21 are constituted, as illustrated in the three figures, but more clearly in Figures 1 and 2, a wall having substantially the shape of a substantially regular tetrahedron 50 FIG. 2, two opposite edges 51, 52 of which are integral with the lateral wall respectively of the first and second oblong bodies 11, 21, substantially parallel respectively to the first and third axes 12, 22. One of the advantages presented by the prosthesis according to FIGS. the invention is constituted by the fact that the block 10 which is in one piece can be easily obtained by molding, by mixing or introducing the reinforcing material in the first material, at the time of molding. Such a prosthesis finds a particularly advantageous application as an articular prosthesis between the trapezium and the first metacarpal. In addition, the tab 24 intended to be implanted in an orifice made in the trapezoidal bone 2 or the like may comprise, throughout its length, visual references to promote its cutting to a length adapted to the depth of this orifice. In general, the prosthesis according to the invention can be defined as follows: A central part, of tetrahedral shape, the two opposite edges 51, 52, orthogonal to each other, form the two hinges of this so-called prosthesis "Cardan" because it has precisely two axes perpendicular to each other. On the two edges thus described, are connected, with the aid of a flexible narrowed portion which acts as a hinge, two reinforcements parallel to the hinge, that is to say the two oblong bodies 11, 21 defined ci above, on which are respectively implanted in their middle, the two tabs 14, 24 advantageously of quadrangular shape, also called "tails".

The prosthesis thus comprises two tails respectively integral reinforcements which act as hinges on the two opposite edges of the central tetrahedron.

These tails serve to fix the prosthesis in the two bones to be articulated, namely the first metacarpal on the distal side and the trapezium on the proximal side; The distal tail of the prosthesis will fully engage, after preparation for the grater, in the medullary canal of the first metacarpal. As for the proximal tail, it will fix, after adequate preparation, in a housing or orifice formed in the trapezium. - The insertion of this proximal tail in the trapezium requires its cutting on demand, so as not to exceed in the articulation between the trapezium and the scaphoid. It should be noted that this prosthesis is perfectly in place as soon as it is implanted without any sealing, simply by fitting it into the two bones, because of the muscle tone that normally applies the first metacarpal to the trapezium. Its flexibility allows it to adapt to all the movements to which it is subjected. A prosthesis according to the invention implants in the same way as similar prostheses of the prior art as those recalled in the preamble of the present description. Also, for the sake of simplifying this description, its implementation will not be described here.

Claims (8)

REVENDICATIONS1. Prosthesis for the replacement of a hand joint between a metacarpal bone, the first metacarpal (1) and a carpal bone trapezium (2), said prosthesis consisting of a block (10) in one piece in a first flexible material having a given rigidity, said block comprising: a first oblong body (11) defining a first longitudinal axis (12), a first anchoring tab (14) defining a second longitudinal axis (16), said first leg being arranged to be able to be plugged into the medullary canal of the metacarpal bone (1), said first tab being secured to the first oblong body (11) substantially in the middle and so that the first and second axes (12) , 16) are substantially perpendicular to each other, • a second oblong body (21) defining a third longitudinal axis (22), • a second anchoring tab (24) defining a fourth longitudinal axis (26), said second leg being arranged e to be able to be plugged into an orifice made in the carpal bone (2), said second tab being secured to the second oblong body substantially in the middle and so that the third and fourth axes (22, 26) are substantially perpendicular to each other, connecting means (30) interconnecting the first and second oblong bodies (11, 21), said connecting means being arranged so that the first and third axes (12, 22) are substantially orthogonal and the second and fourth axes (16, 26) are substantially collinear, characterized in that at least one of the following two elements, the first and second oblong body (11, 21), comprises a central core (42). , 43) made of a second material having a stiffness greater than that of the first material. 2. Prosthesis according to claim 1, characterized in that the first material has a hardness of a value of the order of 21/22 Shores A. 3. Prosthesis according to one of claims 1 and 2, characterized in that the first material is a silicone elastomer and the second material is a mixture of the first material and a reinforcing material. 4. Prosthesis according to claim 3, characterized in that the reinforcing material consists of at least one of the following bodies: carbon fibers, glass fibers, dopant consisting of at least one of the following materials: aluminum oxide, talc. 5. Prosthesis according to one of the preceding claims, characterized in that said two elements (11, 21) each comprise at least one central core (42, 43). 6. Prosthesis according to one of the preceding claims, characterized in that the elastic connecting means (30) interconnecting the first and second oblong bodies (11, 21) consist of a wall having substantially the shape of a substantially regular tetrahedron (50) whose two opposite edges (51, 52) are integral with the side wall respectively of the first and second oblong bodies (11, 21), substantially parallel respectively to the first and third axes (12, 22) respectively. 25 7. Prosthesis according to one of the preceding claims, characterized in that said block in one piece is obtained by molding. 8. Prosthesis according to claim 8 when dependent on claim 3, characterized in that said reinforcing material is mixed with the first material at the time of molding.