FR2847801A1 - Mobile shell fitting between anchoring cup and ball of hip prosthesis comprises outer convex and inner concave sections with fastening and ball retaining element - Google Patents

Abstract

The mobile shell (1) consists of an outer convex section (11) designed to pivot in the acetabular anchoring cup and made from a biocompatible plastic material, and a concave inner section (12) designed to pivot on the prosthesis ball (3). The mobile shell (1) consists of an outer convex section (11) designed to pivot in the acetabular anchoring cup and made from a biocompatible plastic material, and a concave inner section (12) designed to pivot on the prosthesis ball (3), made from a hard and rigid biocompatible material such as a cobalt/chrome alloy, ceramic or zircon. The inner section has a cylindrical or cylindrical/conical skirt extension that engages with a collar in the outer section, while displacement is limited by a ball retaining element (4) with high elastic properties and mechanical strength.

Description

Movable convexo-concave shell for joint prosthesis

  The present invention relates to a movable shell, intended to serve as a sliding surface between an anchor cap in the acetabular bone and a ball fixed to a stem of a femoral prosthesis, comprising a means of retaining said ball in order to '' avoid dislocation.

  A acetabular fixation acetabulum according to the prior art comprises a substantially hemispherical surface for articulation with the ball of the femoral prosthesis and an external shape offering asperities or grooves intended either for fixation by bone cement or for fixation by regrowth bone in said asperities.

  The use of "polyethylene on metal" or "polyethylene on ceramic" friction couples has drawbacks inherent in the most fragile material: wear by friction which creates particles which come between the articular surfaces, and creating this makes accelerated wear (leading to reoperation), sometimes associated with bone destruction due to activation of macrophages by the micro particles of polyethylene wear.

  The use of friction couples using rigid and very hard materials such as: metal on metal or ceramic on ceramic makes it possible to reduce this wear by a ratio of 10 to 1, and therefore to increase the longevity of the implant, but their use is only possible to date in the form of a fixed shell set in a bone anchor cap. (High Tech EP 0 453 694-Ai) The so-called mobile cups have recognized advantages in their current configurations, either for simple hip prostheses called cephalic (Pfizer EP 0 234 30 81 1Ai) or for total prostheses (Bouvet FR 2,662,930Ai), but are currently not possible with hard materials which are more resistant to wear.

  The present invention aims to remedy the aforementioned drawbacks in order to make possible the production of a movable shell 35, by proposing a reliable and simple assembly means, which can be produced during intervention by the surgeon or the operating personnel, therefore leaving by this "in situ" assembly - 2 a large choice of implant settings to allow adaptation to the patient's morphology, even in the event of friction friction in rigid materials, to ensure both optimal friction and retaining the ball of the hip prosthesis in the movable shell, while preserving the quality of the second articular slip between the acetabular anchoring cap and the external surface of the movable shell. This invention therefore relates to a system consisting of a movable shell whose external surface of non-rigid material is intended to serve as a sliding surface in an acetabular anchoring cap and whose internal surface of rigid material is articulated on a ball. also of rigid material, for hip femoral prosthesis - and of a means for retaining the femoral ball and for locking the rigid internal part in the external plastic part, in order to avoid dislocation.

  It is therefore both the functionality and the principle of the invention which are different from patents such as those of OrthoI.D. FR 00 00688, or Implantology EP 0 412 438 A2, 20 PRINCIPLE OF THE INVENTION: The said movable shell for its convex external part, intended to be articulated in the acetabular anchoring cap, is made of a biocompatible plastic material and having good tribological properties, preferably of high density polyethylene.

  Said movable shell for its concave internal part, intended to be articulated on the ball of the femoral prosthesis, is made of a rigid and hard biocompatible material having good tribological properties, preferably made of a metal alloy cobalt chromium, or alumina or zirconia ceramic. Its rounded inner rim, without a sharp angle aggressive for the femoral ball, constituting the opening plane of the rigid part, is located below, preferably between one and twelve millimeters, of the center of rotation of said femoral ball. This arrangement is fundamental for protecting the friction couple - ball on the rigid internal part of the movable shell, especially when they are made of rigid and very hard materials such as ceramic or 3 as cobalt chromium metal alloys, because these materials are extremely sensitive to scratching (for metal alloys) and tearing of grains (for ceramic), which occur in the event of punctual contact on the edge; The fact of shifting the lower opening plane by at least one millimeter, and preferably by four millimeters eliminates this risk of aggressive punctual contact because the ball is limited in its movement along the axis of revolution by the retention means The rigid internal part is preferably assembled under pressure and maintained in the external plastic part by at least one of the following means: penetration of the edges situated at the periphery and preferably parallel to the axis of revolution and in relief of the part rigid, in the corresponding cylindrical bore of the external plastic part whose diameter is between the dimension on the flat and the dimension at the top of said edges; - Retraction of at least one annular bead in relief relative to the cylindrical bore of the plastic external part, during the introduction of the rigid internal part which comprises at least one groove intended to receive said annular bead which can '' deploy there either by simple elastic relaxation, or by the mechanical action of the retention means.

  Said means for retaining the femoral ball in the rigid internal part is made of biocompatible plastic material (to avoid any abrasion with the neck and the ball of the hip femoral prosthesis), but having mechanical properties of elasticity and resistance to high fracture, preferably in Peek (polyaryletheretherketone) not reinforced with fibers due to their abrasive power. Said retention means is preferably in the form of a closed ring, perpendicular to the axis of revolution of the movable shell.

  - It has at its upper opening, oriented towards the pole of the movable shell, expansion means facilitating its expansion when it is locked on the rigid internal part, and can serve, in at least one configuration, as a means of retraction for the annular bead for locking the external plastic part.

  - It has at its lower internal opening a generally flared shape, preferably frustoconical, directed towards the femoral stem, the slope of which corresponds substantially to the slope 5 of the neck of the femoral prosthesis in order to ensure linear contact therewith to reduce abrasion wear.

  - It has at its lower periphery at least one means of attachment to the plastic outer part, preferably a shoulder, a bead or a groove locking with it10 ci or, in a different configuration, a rod of circular, square section, rectangular, or any combination of these sections, introduced "between leather and flesh" at the generally cylindrical or frustoconical junction of said retention means, and of the external plastic part.

  In this way the assembly produced can withstand the physiological extraction forces during hip movements: the extraction in the axis of revolution is controlled both by the annular bead, by the pressure assembly in the part external plastic (thanks to the penetration of the edges 20 located at the periphery and in relief of the rigid part, in the corresponding cylindrical bore of the external plastic part) and by the retention means adjacent to the lower opening of the cap.

  - the migration by sinking is controlled by the support pole 25 preferably in the form of a portion of a sphere perpendicular to the lower opening of the cap, in the pressure axis resulting from the load the rocker is blocked by the effect guidance and retention created by the difference in thickness between the cylindrical bore of the external plastic part and the raised edges intended for the tangential lateral tight adjustment of the rigid part. The passage in force of this tight adjustment zone occurs by an elastic deformation which after passage of the reliefs closes and contributes both to the holding in rocking and to the retention of said anchor cap, - the rotation between the internal and external parts is blocked thanks to the penetration into the external plastic part of the edges -5 situated at the periphery and preferably parallel to the axis of revolution and in relief of the rigid part.

  DESCRIPTION: Other advantages and aspects of the invention will emerge on reading the following description given by way of example and with reference to the appended drawings in which: FIG. 1 is an anterior exploded exploded view showing the overall appearance of the complete hip system with: - an anchor cap (2) in rigid metallic or ceramic material, in position 10 in the acetabular bone (20), - the convex-concave mobile shell (1) whose external surface ( 11) convex intended to be articulated in the concave sliding surface (21) of said anchor cap (2), and the concave internal surface (12) made of hard material intended to be articulated on the ball (3) d '' a femoral prosthesis (31), are in the assembled position with the retaining means (4) of the ball (3) - the femoral prosthesis (31) with its neck (32) and its ball (3) intended to slide on the concave surface of the internal part (12) made of hard material.

  FIG. 2 represents the convex-concave mobile shell 20 (1) assembled on the ball (3) and on the femoral prosthesis (31), and in particular the linear contact zone (43) between the lower internal opening of the means of retention (4) of the femoral ball (3), having a generally flared shape (42) preferably frustoconical, directed towards the femoral stem (31), the slope of which corresponds substantially to the slope of the neck (32) of the prosthesis femoral (31) to ensure linear contact (43) reducing abrasion wear.

  FIG. 3 represents all of the parts before assembly, and in particular an embodiment of the internal part 30 of rigid material (12) showing: - The edges (121) located at the periphery, preferably parallel to the axis of revolution (124) and in relief of the rigid part (12), so as to penetrate into the corresponding cylindrical bore (111) of the external plastic part (11) whose diameter is between the dimension on the flat and the dimension at the top of said edges (121) and their radial position around the pole (120), with the relief effect intended to make the -6 said edges (121) penetrate into the cylindrical bore (111) during the 'assembly, preferably by pressure, of said rigid part (12) in the external plastic part (11) in order to achieve their relative rotation blocking.

  - At least one means of attachment to the external part (11) of plastic, constituted in one embodiment, for example, by a groove (123) intended to receive the annular bead (113) of the external part ( 11) made of plastic, which can be deployed there, either by simple elastic relaxation, or by the mechanical action of the retention means (4).

  - The inside beginning of the rounded edge (125), without an aggressive sharp angle for the femoral ball (3), constituting the opening plane (126) of the rigid part (12), is located below, preferably between one and twelve millimeters, from the center of rotation 15 (30) of said femoral ball (3). This arrangement is fundamental for protecting the friction surfaces of the ball (3) and of the rigid internal part (12) of the movable shell (1), especially when they are made of rigid and very hard materials such as ceramic or than cobalt 20 chromium metal alloys, because these materials are extremely sensitive to scratching (for metal alloys) and grain tearing (for ceramics), which occur in the event of punctual contact on the edge.

  The fact of shifting the lower opening plane (126) by means of a cylindrical or conical skirt by at least one millimeter, and preferably by four millimeters, from the equator (127) of the hemispherical cavity (128) of the rigid part (12) eliminates this risk of aggressive punctual contact because the ball (3) is limited in its movement along the axis of revolution (124) by the retention means (4).

  Figures 4 and 5 show two embodiments of said means for retaining (4) the femoral ball (3) in the rigid internal part (12), which is preferably made of biocompatible plastic material to avoid any abrasion with the neck 35 (32) and the ball (3) of the hip femoral prosthesis (31), but having high elasticity and breaking strength mechanical properties, preferably made of Peek (polyaryletheretherketone) not reinforced with fibers due to their power abrasive. Said retention (4) and locking means is preferably in the form of a closed ring perpendicular to the axis of revolution (124) of the movable shell. 5 - It has at its upper opening (44), oriented towards the pole (120) of the movable shell (1), expansion means (45) constituted by notches, preferably with rounded bottom (450), facilitating its expansion when locked on the rigid internal part (12), and can serve, in at least one configuration, as a retraction means for the annular bead (113) of the external plastic part (11).

  - It has at its lower internal opening a generally flared shape (42) preferably frustoconical, directed towards the femoral stem (31), the slope of which corresponds substantially to the slope of the neck (32) of the femoral prosthesis (31) so ensuring a linear contact (43) reducing abrasion wear.

  - It comprises at its lower periphery at least one means for securing with the external plastic part (11), for example in the form of a bead (48) in relief locking with it, intended to force into the lower opening (114) of said external plastic part (11), or (fig. 5), in a different configuration preferably in the form of a rod (480) situated "between leather and flesh" at the junction generally cylindrical or frustoconical (49) of said retention means (4) and of locking means, and of the external plastic part (11).

  Figure 6 is a sectional view of the complete assembly, after assembly by the operator of the retention means (4) around the neck (32) of the femoral prosthesis (31) and then of the ball (3) on its cone (34), before locking of said retention means (4) both in the external plastic part (11) and on the rigid internal part (12) with, by way of example, an embodiment of the securing means between the retention means (4) and the convex external part (11) of plastic, in the form of a rod (480) of elastic material or also of shape memory alloy, of circular, square, rectangular, or any combination of these sections, introduced "between leather and flesh" at the junction (49) generally cylindrical or frustoconical of said - 8 retention means (4) and the external plastic part (11).

  Figure 7 is a sectional view of the completed assembly of the convexo-concave shell (1) with the ball (3) and the neck (32) hidden, and in particular of the fastening means in the form of a rod (480) which is preferably designed not to back up once introduced into the orifice (168) below the equator of the external plastic part (11).

  The invention is not limited to the embodiments shown in the accompanying drawings. 10

Claims (7)

  1 - Convex-concave mobile shell (1) intended to serve as a sliding surface between an anchoring cap (2) in the acetabular bone (20) and a ball (3) fixed on a stem of the femoral prosthesis (31) comprising: a convex external part (11) intended to be articulated in the acetabular anchoring cap (2), made of a biocompatible plastic material and having good tribological properties, preferably made of high density polyethylene.   - A concave internal part (12) intended to be articulated on the ball (3) of the femoral prosthesis (31), produced in a rigid and hard biocompatible material and having good tribological properties, preferably in a cobalt chromium metal alloy, or in alumina or zirconia ceramic. Said concave internal part 15 (12) is extended by a cylindrical or even cylindro-conical skirt 1, the internal edge of the rounded edge (125), without any sharp angle aggressive for the femoral ball (3), constituting the opening plane ( 126) of the rigid part, is situated below, preferably between one and twelve millimeters, from the center of rotation (30) of said femoral ball (3).   - At least one connection means between the external plastic part (11) and the rigid internal part (12), for example in the form of a bead (113) in relief intended to force through a groove (123) intended receiving said annular bead (113) from the external part (11) which can be deployed there, either by simple elastic relaxation, or by the mechanical action of the retention means (4).   - A retention means (4) making it possible to limit the displacement along the axis of revolution (124) of the ball (3) in order to avoid dislocation, preferably made of biocompatible plastic material to avoid any abrasion with the neck and ball (3) of the hip femoral prosthesis (31), and having high elasticity and breaking strength mechanical properties, preferably in Peek.   2 - Movable convexo-concave shell (1) according to claim 1 characterized in that the internal part (12) concave intended to be articulated on the ball (3) of the prosthesis - 10 femoral (31) has a plane of lower opening (126) offset by at least one millimeter, and preferably by four millimeters from the equator (127) of the hemispherical cavity (128) of the rigid part (12) in order to protect the ball (3) produced in 5 rigid and very hard material such as ceramic sensitive to grain tearing, or metallic cobalt chromium alloys sensitive to scratching, eliminating the risk of aggressive punctual contact.   3 - Convex-concave mobile shell (1) according to any one of claims 1 and 2 characterized in that the internal part (12) concave intended to be articulated on the ball (3) of the femoral prosthesis (31) has edges (121) located at the periphery and preferably parallel to the axis of revolution (124) and in relief of the rigid part (12), intended to penetrate into the corresponding cylindrical bore (111) of the part outer (11) of plastic whose diameter is between the dimension on the flat and the dimension at the top of said edges (121). This relief effect, intended to cause said edges (121) to penetrate into the cylindrical bore (111) during assembly, preferably by pressing, of said rigid part (12) in the plastic external part (11). allows their relative rotation lock.   4 - Convexo-concave mobile shell (1) according to any one of claims 1 to 3 characterized in that the retention means (4) of the femoral ball (3) has a linear contact area (43) of shape generally flared (42) preferably frustoconical, directed towards the femoral stem (31), the slope of which corresponds substantially to the slope of the neck (32) of the femoral prosthesis (31) in order to reduce wear by abrasion.   - Convex-concave mobile shell according to any one of Claims 1 to 4, characterized in that the retention means (4) of the femoral ball (3) in order to avoid dislocation, is preferably in the form of a '' a ring perpendicular to the axis of revolution (124) of the movable shell (1), introduced around the neck (32) of the femoral prosthesis (31), 35 before fixing on its cone (34), the ball ( 3) whose diameter is 0.5 to 3mm smaller than the inside diameter of said retention means (4). - 11   6 - Convex-concave mobile shell according to any one of claims 1 to 5 characterized in that the retention means (4) of the ball (3) femoral present at its upper opening (44), oriented towards the pole (120 ) of the 5 movable shell (1), expansion means (45) constituted by notches preferably with rounded bottom (450) facilitating its expansion when it is locked on the rigid internal part (12), and serving, in at least one configuration of retraction means for the annular bead (113) of the plastic external part (11).   7 - Convex-concave mobile shell according to any one of claims 1 to 6 characterized in that the retention means (4) of the femoral ball (3) has at least one means of attachment to the external plastic part (11 ) in the form of a raised bead (48) intended to force through the lower opening (114) of said plastic outer part (11).   8 - Convexo-concave mobile shell according to any one of Claims 1 to 7, characterized in that the retention means (4) of the femoral ball (3) has at least one means of attachment to the external plastic part preferably in the form of a rod (480) of elastic material or alternatively of shape memory alloy, of circular, square, rectangular section, or any combination of these sections, introduced "between leather and flesh" at the junction (49 ) generally cylindrical or frustoconical of said retaining means (4) and of locking, and of the plastic external part (11) and designed not to back down once introduced into the orifice (168) preferably located below the equator of the plastic outer part (11).