FR2605878A1 - Prosthesis for small joints, in particular metacarpophalangial and interphalangial joints - Google Patents

Abstract

A prosthesis comprises a first element 1 having a convex extreme surface 33a, 33b and a first rod 4, and a second element 2 having a concave extreme surface 53a, 53b, congruent with the convex surface, and a second rod 6. The concave surface is contained within a spherical sector less than 180 DEG , so that, after cementless implantation, the joint surfaces 33a, 33b and 53a, 53b slide over each other, and can be moved with respect to each other in a direction which is longitudinal to the rods 4, 6, in order to provide the movements of the joint. In order to stabilise the prosthesis transversely, and to oppose relapses of orbital deviation, a ridge 54 between two symmetrical concave surfaces 53a, 53b of the second element engages in a groove 34 between two symmetrical convex surfaces 33a, 33b of the first element. The prosthesis is stabilised in rotation by lateral indentations 35a, 35b in the first element, receiving chamfers of a resected bone.

Description

Prosthesis for small joints in particular
metacarpophalangeal and interphalangeal
The present invention relates to a prosthesis for small joints, such as metacarpophalangeal and interphalangeal joints of the hand or foot which will be referred to below.

 the metacarpophalangeal and interphalangeal joints represent one of the election targets for rheumatoid disease.

This condition is manifested in these joints mainly by pain associated with a destruction of the articular structures seriously compromising the function of the hand.

 sick joints are frequently deformed, dislocated and subluxed, in the direction of a cubital bypass for the metacarpophalangeal joint. Likewise, joint fractures at this level lead to destruction and painful stiffness.

 In order to relieve the suffering of these individuals and restore their gripping function, the solution of resection followed by prosthetic devices was proposed.

 the prostheses proposed so far for these small joints can be classified into first and second groups: the prostheses of. first group are in fact "spacers" made of flexible elastomeric material within which the movement takes place; the prostheses of the second group are produced in two parts stabilized with respect to each other by connecting devices ensuring their relative movement.

 the prostheses of the first group are produced in a single piece of flexible material, comprising three parts: two conical rods and a central connecting part promoting movement in one direction.

 the disadvantages reported with this type of prosthesis consist of a deterioration of the material, an unsatisfactory functional result and a frequent recurrence of axial deviations. The deterioration of the material, such as silicone elastomer, results in its fragmentation, which induces local reactions to foreign bodies sufficiently large to require removal of the prosthetic material. The functional result is often limited in the absence of a stable bond between the members of the joint which results in a weak grip force. The flexible material constituting the prosthesis cannot combat the lateral restoring effect of the flexor and extensor tendons and there is frequently a recurrence of the ulnar deviations corrected at the time of implantation.

 The prostheses of the second group respond to criticisms of the prostheses of the first group, and have two parts made of more rigid materials, connected together by a link. This connection between the two parts of the prosthesis is rigid and also ensures joint mobility in a space plane by a hinge or ball joint type (GB-A-2 049 435). The diaphyseal anchoring of these prostheses is most frequently ensured by intramedullary sealing, using orthopedic cement.

 This rigid mechanical connection between the proximal and distal parts of these prostheses causes, during the usual movements of the prosthetic end, very high shear stresses at the anchorages of the prosthesis, as well as significant forces around the axis ensuring the link. These phenomena frequently involved prosthetic loosening, as well as risks of wear and fracture of the prosthetic joint. This type of prosthesis is in fact very sensitive to torsional forces, most often amplified by the distal lever arm and passed directly to the level of the connecting axis and anchors.

Finally, the use of orthopedic cement for fixing these prostheses is highly criticized, because it leads to a deterioration of the local bone capital and makes the sometimes necessary prosthesis changes very delicate,
The present invention aims to provide a prosthesis for small joints, such as metacarpophalangeal and interphalangeal joints, produced in two elements not interconnected by any connecting element, implanted without the use of cement, and stabilized at least partially in rotation.

 To this end, a prosthesis for small joints comprising a first element having a first butt with convex end surface and a first rod, and a second element having a second butt with concave end surface congruent to the convex surface and a second rod, is characterized in that the concave surface is a surface substantially of revolution included in a spherical sector less than 1800 so that the convex and concave surfaces slide one on the other and are movable relative to each other longitudinally to the rods .

 After implantation, the sliding of one of the concave and convex surfaces on the other ensures the stability of the movements of the joint. Efforts, in particular in shearing, are not practically reflected on the prosthesis, since the two elements are not directly linked, but are in contact with each other, and that the convex surface is not embedded in the concave surface and is freely movable relative to the convex surface and longitudinally along the rod axis.

 According to another characteristic of the invention aimed at stabilizing the prosthesis in a plane transverse to the axes of the rods in order to oppose recurrences of ulnar deviation, the convex surface is composed of two convex surfaces, preferably symmetrical with respect to a plane longitudinal of the first element containing the axis of the first rod, and forming between them a groove, and the concave surface is composed of two concave surfaces congruent with the two convex surfaces, preferably symmetrical with respect to a longitudinal plane of the second element containing l 'axis of the second rod, and forming between them a crest engaging in said groove.

 In addition, the invention provides that the first abutment comprises means for stabilizing in rotation about a longitudinal axis of the first element, in order to perfectly stabilize the prosthesis in a plane transverse to the bones of the joint. According to a preferred embodiment, the rotational stabilization means consist of two lateral notches made in the first butt at the junction between the latter and the first rod, said notches being intended to receive bevels of a resected bone d 'joint. Two sides of the notches are in a common plane oblique to the axis of the first rod, and preferably symmetrical with respect to this axis.

Other advantages and characteristics of the invention will appear more clearly on reading the following description of several preferred embodiments of the invention with reference to the corresponding appended drawings in which
- Figs.1 and 2 are longitudinal side and top views of a first element of a prosthesis according to the invention, respectively;
- Figs. 3 and 4 are sectional views taken along lines III-III and IV-IV of FIG. 1, respectively
- Fig. 5 is an end view, rod side, of the first element;
- Figs.6 and 7 are longitudinal side and top views of a second element of the prosthesis, respectively; and
- Fig.8 is a front view of a concave surface of the second element capable of sliding against a convex surface of the first element.

 A prosthesis according to the invention comprises a first monobloc element 1, called the proximal element, and a second monobloc element 2, called the distal element.

 As shown in Figs.1 and 2, the proximal element 1 is symmetrical with respect to a longitudinal plane having trace X1-X in Fig.2, and comprises a butt 3 and a frustoconical rod 4.

As illustrated in detail in particular in Figs. 3 to 5, the proximal end 3 has a transverse section substantially contained in a rectangle and offers two short parallel and symmetrical flat sides 31a and 31b. These two short sides as well as a large upper rib 32 delimit a convex surface 33a-33b partially frontal at the end 3, as shown in Figs. 2 and 4, and partly underlying the end 3, as shown in Figs. 3 and 5.The convex surface consists, according to the illustrated embodiment, by two surfaces 33a and 33b of portions of two substantially spherical caps, symmetrical and joined in the plane X1-X1. the caps have centers Ca and Cb aligned perpendicular to the plane of symmetry X1-X1 and therefore at the short sides 31a and 31b, and coplanarly s the axis of the rod 4. Side views, as shown in the
Fig. 1, the surfaces 33a and 33b have hemicycle-like contours. Typically, the caps have a radius substantially greater than half the width of the end piece 3 taken between the sides 31a and 31b, and the distance between the centers Ca and Cb is substantially greater than one third of this width and half of the large base 41 of the rod 4.

 According to other variants, the convex surfaces 33a and 33b bridge portions of caps of revolution, for example ellipsoidal.

 The convex front surface of the end piece 3 thus has a cusp line contained in the plane of symmetry X1-X1 and forming a central groove 34.

 On the side of the rod 4 at the large base of which the end piece 3 is attached, two symmetrical notches 35a and 35b are formed at the rear of the caps and are open in the direction of the rod. the notches are substantially similar to dihedrons delimited by a common plane 351, diametrical to the caps, inclined substantially at 450 with respect to the axis of the rod 11 and perpendicular to the plane of symmetry XI'XI, and respectively by two respective surfaces 352a and 352b converging symmetrically towards a diameter of the large base 41 of the rod perpendicular to the line of the centers Ca and Cb.

the notches thus form between them, a central spindle 36 along the plane X1-X1.

 The proximal rod 4 is terminated at its small base, by a hemispherical leave 42. It offers between the large base 41 and the leave 42 an irregular frustoconical surface which, according to the illustrated embodiment, is composed of flanges 43 forming between them annular grooves 44 regularly distributed along the rod. the irregularities of the frustoconical surface can be made of any implantable material and have a shape such that they provide the prosthesis with direct bone anchoring without interposition of cement.

 Referring now to Figs. 6 to 8, the distal element 2 also offers a clean butt 5 2 cooperating with the proximal end 3, and a frustoconical rod 6 similar to the proximal rod 4.

element 2 is also symmetrical with respect to a longitudinal plane X2-X2 coming substantially in extension from plane X 1-X1 during implantation of the prosthesis.

The distal end 5 has a generally parallelepiped shape having two small planar sides 51a and 51b and two large planar sides 52 respectively parallel and perpendicular to the plane of symmetry
X2-X2. A rear face of the end piece 2 defines a large base 61 of the rod 6.

 As shown in particular in FIG. 8, a front face of the end piece 5 offers a concave surface composed of two substantially spherical surfaces 53a and 53b, symmetrical and contiguous along the plane of symmetry X2-X-2 and perpendicular to the the axis of the rod 6. the concave surfaces 53a and 53b are congruent with the convex surfaces 33a and 33b of the proximal end 3, and have centers ca and cb arranged outside the end, in front of it, and aligned perpendicular to the plane Xl-Xl and coplanar to the axis of the rod 6. the concave surfaces 33a and 33b thus form between them a central crest 54 complementary to the proximal groove 34 and contained in the plane X2-X2.

As can be seen by comparing Figs. 1 and 2 and the
Figs. 6 and 7, the concave surfaces 53a and 53b of the distal end are portions of spherical surfaces included in sphere sectors having an apex angle significantly less than 1800, typically of the order of 30, so that the convex surfaces 33a and 33b of the proximal end are not embedded and retained in the concave surfaces, unlike a ball joint, and have freedom of movement in three-dimensional space relative to the concave surfaces.

 The distal rod 6 comprises, like the proximal rod 4, a hemispherical end 62, and a surface carrying irregularities made of any implantable material and of a shape such that they provide the prosthesis with direct bone anchoring, without interposition of cement ~ this surface can be, as in the illustrated embodiment, in the form of flanges 63 and annular grooves 44 regularly distributed along the rod 6.

 elements 1 and 2 are produced in one or more parts rigidly assembled together. These elements or parts of elements are obtained by machining or molding and are made of rigid materials, such that the proximal element 1 is made at least partially of metal at the articular surface 33a, 33b and that the distal element 2 is made at least partially of thermoplastic material at the articular surface 53a, 53b. The realization in several parts of each prosthetic element is justified by the association in the same element of different materials for which particular properties are sought.

 After implantation of the prosthesis, the proximal element 1 and the distal element 2 are not mechanically linked together. The stability of the movements is ensured by the sliding of the convex surfaces 33a and 33b respectively on the congruent concave surfaces 53a and 53b without there being any embedding of a convex surface in a concave surface as in a ball joint. Maintaining contact between these articular surfaces, necessary for joint stability and movement, is ensured by adjusting the tension of the peri-articular structures adjusted at the time of the intervention, by the ratio between the size of the implanted elements and that of bone resections. The torsional forces are therefore absorbed by flexible structures, without transmission of these to the anchorages of the prosthesis.

 The prosthesis according to the invention thus constitutes a sliding articular prosthesis for small joints of the hand or of the proximal metacarpophalangeal and interphalangeal foot.

 The stability of the prosthesis in the frontal plane necessary to oppose recurrences of ulnar deviation of the fingers is ensured by the splitting of the articular surfaces. the convex articular surfaces 33a and 33b are approximately spherical and contiguous, and in the sagittal groove 34 between these convex surfaces engages the distal crest 54 formed between the corresponding concave articular surfaces 53a and 53b. This arrangement is close to the anatomy where two proximal condyles articulate with the concave base of the distal phalanx. This type of joint can therefore be called "bycondylian", stabilized in the frontal plane by the size of two articular surfaces and by their interlocking, in particular at the crest 54 in the groove 34.

 The prosthetic elements 1 and 2 are anchored by the rods 4 and 6 which engage in exposed diaphyseal barrels after resection of the articular surfaces. the irregularly structured surfaces 43-44 and 63-64 of the proximal 4 and distal 6 stems are in contact with the bones and are gradually invaded by the regeneration of bone tissue. This regeneration thus ensures the cementless anchoring of the prosthesis according to the invention.

 In order to promote bone regrowth in the crevices of the prosthesis, such as the grooves 44 and 64, it is necessary to stabilize the prosthesis, in particular in rotation for the proximal element 1. If the peri-articular structures largely limit the torsional forces transmitted to the prosthetic elements, the embedding of the latter in the bone structures protects their anchoring against these stresses. In particular, the proximal end piece 3 with convex surfaces rests on the resected bone along the oblique plane 351 and not along a plane transverse to the axis of the rod 4. In other words, the resected bone in bevels engages in the notches 35a and 35b formed laterally at the junction of the end piece 3 and the rod 4 of the proximal element. These oblique cuts on the profile of the butt 3, not perpendicular to the major axis of the bone, therefore have a stabilizing anti-rotating effect.

Claims (12)

 1 - Prosthesis for small joints comprising a first element (1) having a first butt (3) with convex end surface (33a, 33b) and a first rod (4), and a second element (2) having a second butt (5 ) with a concave end surface (53a, 53b) congruent with the convex surface and a second rod (6), characterized in that the concave surface is a surface substantially of revolution included in a spherical sector less than 1800 so that the convex surfaces ( 33a, 33b) and concave (53a, 53b) slide one on the other and are movable relative to each other longitudinally to the rods (4, 6).  2 - Prosthesis according to claim 1, characterized in that the convex surface is composed of two convex surfaces (33a, 33b), preferably symmetrical with respect to a longitudinal plane (X1-Xl) of the first element (]) containing l axis of the first rod (4), and forming between them a groove (34), and in that the concave surface is composed of two concave surfaces (53a, 53b congruent with the two convex surfaces (33a, 33b), of # preferably symmetrical with respect to a longitudinal plane (X2-X2) of the second element (2) containing the axis of the second rod (6), and forming between them a crest (54) which can be engaged in said groove (34).  3 - Prosthesis according to claim 1 or 2, characterized in that the congruent surfaces (33a, 33b; 53a, 53b) are kept in contact by tension of peri-articular structures.  4 - Prosthesis according to any one of claims 1 to 3, characterized in that the first and second rods (4; 6) are intended to be anchored in diaphyseal barrels of bone segments.  5 - Prosthesis according to any one of claims 1 to 4, characterized in that the rods (4; 6) have surface crevices (44; 64) intended to be rehabited by bone tissue and to ensure only anchoring of the prosthesis.  6 - Prosthesis according to claim 5, characterized in that the rods (4, 6) are frustoconical, and the crevices are annular grooves (44; 64), preferably evenly distributed along the rods.  7 - Prosthesis according to any one of claims 1 to 6, characterized in that the first butt (3) comprises stabilization means in rotation (35a, 35b) around a longitudinal axis of the first element (1).  8 - Prosthesis according to claim 7, characterized in that the rotational stabilization means comprise two lateral notches (35a, 35b) formed in the first butt (3) at the junction between the latter and the first rod ( 4), said cuts being intended to receive bevels of a resected articulation bone.  9 - Prosthesis according to claim 8, characterized in that two sides of the notches (35a, 35b) are in a common plane (351) oblique to the axis of the first rod (4), and preferably symmetrical with respect to this axis.  10 - Prosthesis according to any one of claims 1 to 9, characterized in that the convex surface (33a, 33b) forms both a front surface and a surface underlying the first butt (3) and is between two flat sides (31a, 31b) of the first butt (3) parallel to the axis of the first rod (4).  11 - Prosthesis according to any one of claims 1 to 10, characterized in that the concave surface (53a, 53b) is between two perpendicular pairs of planar sides (51a, 51b; 52) of the second parallel butt (5) to the axis of the second rod (6).  12 - Prosthesis according to any one of claims 1 to 11, characterized in that the first and second abutments (3,5) at least at the convex (33a, 33b) and concave (53a, 53b) extremal surfaces are made of metal and thermoplastic material, respectively.