FR2825263A1 - Shoulder joint prosthesis has cap on humerus to engage socket with movement limiting stop surfaces - Google Patents

Abstract

The shoulder joint prosthesis has a base (20) anchored (22) to the shoulder and with an engagement surface (26) to receive the head of the humerus. The humerus carries a cap plate (24) and socket have engaging surfaces (28) to control the joint movement. The contact surfaces can be spherical (32,34).

Description

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fixée à la cavité glénoïdienne de l'omoplate et de recevoir la tête de l'humérus ou d'un implant huméral. SHOULDER GLENE PROSTHESIS WITH MOBILE TRAY
The present invention relates to a shoulder prosthesis, and more particularly to a glenoid prosthesis with a movable plate capable of being

attached to the glenoid cavity of the scapula and receiving the head of the humerus or humeral implant.

 The human shoulder is a set of joints that unite the upper limb with the thoracic skeleton. The essential part of this set, the scapulo-humeral joint, connects the head of the humerus and the glenoid cavity of the scapula.

 The present invention relates more particularly to the glenoid prosthesis of this joint.

 Generally, a glenoid prosthesis comprises a monobloc polyethylene glenoid element, anchored using a cement in a space previously prepared by bone resection in the scapula at the level of the defective natural glenoid cavity.

 Also known from documents EP-776,636, FR-2,683. 142, FR-2.695. 313 and EP-963,742 two-part glenoid prostheses, comprising a base fixed to the scapula and a contact piece fixed relative to the base, having a sliding surface capable of receiving the head of the humerus.

 In the case of document EP-963,742, the contact piece can translate during assembly relative to the base. However, once in place, this part is immobilized relative to the base thanks to a

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 protrusion blocked in a housing which provides a complete and fixed connection between the base and the sliding part.

 Furthermore, the fact of designing a glenoid in one piece or in two immobile parts one in relation to the other makes it possible to respect the anatomy and physiognomy of this joint as well as possible.

 The bone / prosthesis junction being a zone subjected to strong stresses, the main drawback of these devices lies in the relative fragility of their anchoring, which is accentuated in particular when the prosthesis is not correctly implanted. However, it is essential that this junction is as solid as possible in order to allow movement of the joint and to avoid loosening.

 Also, many documents focus on the anchoring means and offer many solutions to ensure the sustainability of the connection between the prosthesis and the bone. However, despite their relative complexity, these solutions are not fully satisfactory due to a relatively large percentage of implantation failures, especially when the implant is not perfectly placed.

 In fact, the shear forces generated by the glenohumeral connection, that is to say the action of the humeral head on the glenoid implant, are significant and tend to destabilize the glenoid implant over time.

 Also, to reduce shear forces, current implants have a bearing surface with a radius of curvature significantly greater than the radius of curvature of the anatomical glenoid cavity corresponding substantially to the radius of curvature of the head of the humerus.

 However, this increase in the radius of curvature generates a quasi-punctual contact of the humeral head on the polyethylene glenoid prosthesis, resulting in an increase in pressure stresses and therefore increased wear of said polyethylene.

 Another disadvantage of existing glenoid prostheses lies in the fact that an implantation error of the prosthesis is difficult to recover later, if not impossible, which contributes to increasing the failure rate.

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 Also, the present invention aims to overcome the drawbacks of existing shoulder glenoid prostheses by proposing a new prosthesis guaranteeing a solid and reliable implantation over time and a correct and painless shoulder joint operation, even in installation error.

 To this end, the subject of the invention is a shoulder glenoid prosthesis comprising a base linked to the bone by anchoring means and a plate having a support and housing surface for a humerus head. , characterized in that it comprises connecting means between said base and said plate capable of authorizing a relative movement between these two elements once in place, in particular during a movement of the joint.

 Preferably, the connecting means comprise, at the surfaces in contact with the base and the movable plate, conjugated shapes which make it possible to keep said surfaces pressed against one another, while allowing sliding between them.

 Advantageously, the surfaces in contact with the base and the movable plate are substantially spherical.

 According to one embodiment, the surface of the base on which the movable plate is capable of bearing comprises at its periphery a rim projecting from said surface, defining a housing capable of receiving a part of the movable plate, a clearance being provided between said flange and the periphery of the part of the movable plate so as to allow relative movement between the plate and the base.

 Depending on the arrangement and the importance of the clearances and the shape of the rim, it is possible to control the degree of freedom of the relative movement and to define one or more directions of movement, as well as the amplitude of said movements.

 According to another characteristic of the invention, the means for keeping the contact surfaces of the base and the movable plate in contact comprise, at the side of the part of the movable plate, a groove in which is capable of accommodating a return, integral with the free end of the rim, extending over the entire periphery of said rim, means for

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 deformation at the part of the movable plate being provided to allow its introduction into the housing.

- la figure 3A est une vue en coupe se) on ! a direction)) !-))) de la figure 2 d'une première variante, - la figure 3B est une vue en coupe selon la direction II-III de la figure 2 d'une deuxième variante, - les figures 4A à 4E sont des vues schématiques de l'articulation d'épaule illustrant différentes combinaisons des surfaces de contact entre d'une part l'embase et le plateau mobile, et d'autre part, le plateau mobile et la tête de l'humérus, et - la figure 5 est une vue en coupe dans un plan horizontal d'une prothèse d'épaule illustrant une variante des moyens d'ancrage de la glène. Other characteristics and advantages will emerge from the description which follows of the invention, description given by way of example only and with reference to the appended drawings in which: - Figure 1 is a sectional view in a vertical plane of a shoulder prosthesis according to the invention, FIG. 2 is a perspective view of a glenoid prosthesis with a movable plate,

- Figure 3A is a sectional view se) on! a direction))! -))) of Figure 2 of a first variant, - Figure 3B is a sectional view along the direction II-III of Figure 2 of a second variant, - Figures 4A to 4E are schematic views of the shoulder joint illustrating different combinations of the contact surfaces between on the one hand the base and the mobile plate, and on the other hand, the mobile plate and the head of the humerus, and - Figure 5 is a sectional view in a horizontal plane of a shoulder prosthesis illustrating a variant of the means for anchoring the glenoid.

 In Figure 1, there is shown schematically a shoulder joint, in particular the scapulohumeral joint 10, connecting the head of a humerus 12 and the glenoid cavity of the corresponding scapula 14.

 By way of example, the head of the humerus 12 comprises a prosthesis 16 as defined in patent application WO 99/34756. This prosthesis is not more detailed since it is not the main object of the invention.

 In addition, the scapula 14 includes a glenoid prosthesis 18 placed in a space previously prepared by bone resection in said scapula, at the level of the defective natural glenoid cavity.

The preparation stage prior to implantation is also not described in detail, because within the reach of the practitioner, the prosthesis of the invention does not require any particular preparation.

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 According to the invention, the glenoid prosthesis 18, shown in detail in FIG. 2, comprises a base 20 linked to the bone by anchoring means 22 and a movable plate 24 having a support and support surface 26 of the head of the humerus 12, as well as means 28 of connection between said base 20 and said movable plate 24 capable of allowing a relative movement between these two elements once in place, in particular during a movement of the joint.

 This relative movement between the base 20 and the movable plate 24 makes it possible to substantially reduce, at the level of the anchoring means 22, the effects of the shearing forces generated by the movement of the head of the humerus 12 on the surface 26 d support and housing.

 Thus, when the arm rises as illustrated in FIG. 1, the head of the humerus 12 generates at the level of the support and housing surface 26 a shearing force which tends to move the movable plate relative to the base upwards, as indicated by arrow 27, which contributes to greatly reducing the effect of these forces at the anchoring means.

 Thus, by making less use of these anchoring means 22, their resistance is implicitly improved over time, which contributes to improving the quality of the anchoring and reducing the failure rate of the implants.

 The existing mobility between the base 20 and the movable plate 24 makes it possible to reduce the radius of curvature of the support and housing surface 26, and therefore to increase the contact surface between the head of the humerus and the plate in order to reduce the compression stresses at the level of the contact zone.

 On the other hand, this relative movement also makes it possible to compensate for any errors in positioning the prosthesis, by virtue of self-positioning of the movable plate 24, more particularly of the surface 26 of support and housing relative to the head of the humerus, this surface being able to move relative to the anchor.

 This self-positioning of the movable plate prevents, in the event of an implantation error, the appearance of a moment, produced by the effort of the head.

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 the humerus 12 on the glenoid prosthesis 14 when the latter are not perfectly aligned, which is liable to rapidly deteriorate the anchoring.

 According to one embodiment, the base 20 comprises a first bearing surface 30 in contact with the anatomic glenoid, a second bearing surface 32 on which the movable plate 24 is capable of bearing and a periphery preferably piriform. Advantageously, this base is metallic and the first bearing surface 30, preferably of convex shape, is covered with a porous biocompatible material intended to be osseointegrated.

 The movable plate 24, preferably made of polyethylene, comprises the surface 26 of support and housing on which the head of the humerus 12 is capable of bearing, a second surface 34 capable of bearing on the surface 32 of the base and a periphery substantially identical in shape to that of the base.

 In FIGS. 4A to 4E, various combinations of contact surfaces have been shown schematically between on the one hand the base 20 and the movable plate 24, and on the other hand, the movable plate 24 and the head of the humerus 12.

 In FIG. 4A, the base 20 and the movable plate 24 have planar contact surfaces, the movable plate 24 has a contact surface with the head of the concave humerus.

 In FIG. 4B, the base 20 has a substantially spherical concave contact surface with the movable plate 24, and the latter also has a contact surface with the head of the substantially spherical concave humerus 12.

 In FIG. 4C, the base 20 has a substantially spherical concave contact surface with the movable plate 24, and the latter has a contact surface with the head of the substantially spherical convex humerus 12.

 In FIG. 4D, the base 20 has a substantially spherical convex contact surface with the movable plate 24, and the latter has a

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 contact surface with the head of the humerus 12 also convex substantially spherical.

 In FIG. 4E, the base 20 has a contact surface with the substantially spherical convex movable plate 24, and the latter has a contact surface has a contact surface with the head of the substantially spherical concave humerus 12.

 The solutions illustrated in FIGS. 4B to 4E are particularly advantageous because they make it possible to significantly reduce the stresses on the anchoring means 22. According to these embodiments, the result of the efforts of the movable plate 24 on the base 20 always passes through the center of the spherical contact surface so that this result does not produce any moment with respect to said center. Thus, the stresses on the anchoring means 22 can be reduced significantly by appropriately positioning the center of the spherical surface relative to said means 22.

 The connecting means 28 comprise at the second bearing surfaces 32, 34 of the base and the movable plate of conjugated shapes which make it possible to keep these two surfaces pressed against one another, while allowing sliding between these last.

According to one embodiment, the bearing surface 32 of the base comprises at its periphery a flange 36 projecting from said surface
32 defining a housing 38 capable of receiving a part 40 of the movable plate 24, the second bearing surface 34 of the movable plate bearing against the surface 32.

 A clearance is provided between the rim 36 and the periphery of the part 40 of the movable plate so as to allow relative movement between the plate and the base.

 Depending on the arrangement and the importance of the games and the shape of the rim 36, it is possible to control the degree of freedom of the relative movement and to define one or more directions of movement, as well as the amplitude of said movements.

 Thus, in FIG. 3A, the rim 36 comprises two parallel portions in the direction B-B, perfectly adjusted to the part 40 of the plate according to the

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 direction A-A and has a clearance in direction B-B authorizing a translational movement in direction B-B.

 In FIG. 3B, there is, whatever the direction, a clearance between the rim 36 and the part 40 so that a movement between the plate and the base is permitted whatever the direction.

 Means for keeping the second bearing surfaces 32, 34 in contact are provided and comprise, at the part 40 of the movable plate, more particularly at its flank, a groove 42 in which one or more are likely to be housed lugs, or a return 44, integral with the end of the rim 36.

 As illustrated by the different figures, the holding means comprise a return 44 which extends over the entire periphery of the rim 36, deformation means at the level of the part 40 of the plate being provided to allow its introduction into the housing 38. According to one embodiment, these means comprise one or more grooves 46 at the level of the second bearing surface 34 of the plate, arranged near the periphery delimiting one or more deformable zones 48.

 As illustrated by the various figures, and by way of example only, the anchoring means 22 comprise two divergent screws 50, arranged substantially in alignment with the pillar of the scapula and the coracoid pillar, engaged in two bores 52, formed at the base 20, diametrically opposite, ensuring the divergent angular orientation of said screws.

 In addition, the base can include a positioning pad 54, projecting from the surface of the base oriented towards the scapula, preferably of frustoconical shape, and capable of being engaged in a housing formed in the glenoid. anatomical.

 In FIG. 5, another variant of the anchoring means is shown comprising at least one element inclined towards the rear of the patient in order to save space when the prosthesis is put in place.

 According to a preferred embodiment, the means 22 comprise pins 56 oblique to the surface 30, oriented towards the back of the patient,

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 preferably covered with a porous metallic material to allow fixation to the bone, as well as a tab 58 pressed against the bone, preferably prepared by resection, and held in place by a screw 60. according to a preferred arrangement, two pins 56 are provided, the screw being arranged in a vertical direction between the two pins 56.

 Of course, the invention is obviously not limited to the mode described above, but on the contrary covers all the variants thereof, in particular as regards the anchoring means, the shapes of the base and the movable plate, the degree of freedom and the direction of movement of the movable plate relative to the base.

Claims (10)

1. Shoulder glenoid prosthesis comprising a base (20) linked to the bone by anchoring means (22) and a movable plate (24) having a surface (26) for supporting and housing a humerus head (12), characterized in that it comprises means (28) for connection between said base (20) and said plate (24) capable of allowing relative movement between these two elements once in place, especially during a movement of the joint.  2. shoulder glenoid prosthesis according to claim 1, characterized in that the connecting means (28) comprise, at the contact surfaces (32,34) of the base and the movable plate, conjugated forms which keep said surfaces pressed against one another, while allowing sliding between them.  3. Shoulder glenoid prosthesis according to claim 2, characterized in that the contacting surfaces (32,34) of the base and the movable plate are substantially spherical.  4. Shoulder glenoid prosthesis according to claim 3, characterized in that the base (20) has a contact surface with the movable plate (24) concave.  5. Shoulder glenoid prosthesis according to claim 3, characterized in that the base (20) has a contact surface with the movable plate (24) convex.  6. Shoulder glenoid prosthesis according to any one of claims 2 to 5, characterized in that the bearing surface (32) of the base on which the movable plate (24) is capable of bearing comprises: its periphery a flange (36) projecting from said surface (32) defining a housing (38) capable of receiving a part (40) of the movable plate (24), a clearance being provided between said flange (36) and the periphery of the part (40) of the movable plate so as to allow relative movement between the plate and the base. <Desc / Clms Page number 11>  7. Shoulder glenoid prosthesis according to claim 6, characterized in that it comprises means for defining the degree of freedom of the relative movement and adjusting the amplitudes of movement according to the arrangement and the importance of the games and the shape of the rim (36).  8. Shoulder glenoid prosthesis according to claim 6 or 7, characterized in that means for keeping in contact the bearing surfaces (32, 34) of the base and the movable plate are provided, and comprise at the level from the side of the part (40) of the movable plate, a groove (42) in which one or more lugs are capable of being housed, or a return (44), integral with the end of the rim (36).  9. shoulder glenoid prosthesis according to claim 8, characterized in that the holding means comprise a return (44) which extends over the entire periphery of the rim (36), deformation means at the part (40) of the movable plate being provided to allow its introduction into the housing (38).  10. Shoulder glenoid prosthesis according to claim 9, characterized in that the deformation means comprise one or more grooves (46) at the level of the bearing surface (34) of the movable plate in contact with the base, arranged near the periphery defining one or more deformable zones (48).