FR2630322A1 - Artificial cotyle for hip prostheses - Google Patents

Abstract

The present invention relates to an artificial cotyle for a hip prosthesis, intended to be fixed with or without cement into the acetabulum of the iliac bone and comprises an outer face, preferably made of metal, which can be inscribed in a sphere, and at least two anchoring elements arranged parallel on the outer face 2. According to the invention, these anchoring elements are arranged along a direction with an orientation forming with the opening plane P of the cotyle 1 an angle of approximately 56 to 76 DEG , so as substantially to coincide with the orientation of the resultant of the forces of the abductor muscles and of the weight of the body when the cotyle is fixed, and forming an angle beta of approximately 5 to 20 DEG , preferably 15 DEG , with the plane P' which is perpendicular to the opening plane of the cotyle 1 and parallel to the frontal plane of the body, when the cotyle is in the fastening position in the acetabulum. Application: orthopaedic surgery.

Description

The present invention generally relates to hip prostheses, and essentially relates to an artificial acetabulum intended to be fixed with or without cement in the acetabular cavity of the iliac bone. -
The invention finds particular application in the field of orthopedic surgery.

 It will be recalled that a total hip prosthesis comprises an acetabular or acetabular part generally of hollow hemispherical shape forming an endoprosthesis of the acetabular cavity and a femoral part with a spherical head mounted on a rod and coming to be housed in said acetabular part, thus reconstituting a artificial coxo-femoral joint.

The long-term evolution of total hip prostheses revealed an increasing number of loosening of the artificial acetabulum:
The causes of loosening are mainly due to the following four problems - excessively high friction torque; - intolerance of materials - intolerance of wear debris - fixation - of the poorly designed and poorly made acetabulum.

 The first three problems have been largely resolved by the development and use of new materials such as ceramics for the heads of femoral parts and special metal alloys, in particular based on titanium, for the external covering of the acetabulum. .

 The problem of fixing the artificial acetabulum in the acetabular cavity is much more difficult to solve and many solutions have already been proposed, but have not proved to be completely satisfactory.

 For a long time, this fixing was carried out by means of a cement, in particular of acrylic nature. This state of the art is for example described in French patents n02,060,179 and n02.O88,764.

 However, in order to ensure a more intimate contact between the prosthetic part and the bone, we moved towards cementless fixation, which led to the development of new forms of artificial acetabulum.

 Among these new forms, there are essentially screwed acetabular cups, which have a peripheral screw thread on their external face and the impacted hemispherical acetabular cups, respecting the anatomy of the pelvis.

 The screwed cups are for example described in French patent n02.099.259.

 However, recent observations have led to question the quality of bone regrowth in the external turns of this type of acetabulum.

 In addition, the impacted acetabulum is generally fixed to the pelvis either using simple pins distributed on the external face of the acetabulum, or using screws fixed through holes provided in the acetabulum, or again using at least two anchoring elements such as studs or studs, arranged in parallel on the external face of the acetabulum.

 However, these known means of fixing do not turn out to be entirely satisfactory and undesirable loosening of the acetabulum is still observed.

 The present invention ~ therefore aims to solve the technical problem consisting in the provision of an artificial acetabulum of a new design which can be fixed with or preferably without cement securely in the acetabular cavity of the iliac bone, in the best bone regrowth conditions.

 The solution, in accordance with the present invention to solve the technical problem posed, consists of an artificial acetabulum for hip prosthesis, intended to be fixed with or without cement in the acetabular cavity of the iliac bone, of the type comprising an external face of preferably metallic, inscribable in a sphere and at least two anchoring elements arranged on said external face, characterized in that said anchoring elements are arranged in a direction of orientation forming with the opening plane of the acetabulum an angle d '' approximately 56 to 760, so as to substantially coincide with the direction of orientation of the resultant of the forces of the abductor muscles and of the body weight when the acetabulum is fixed, and forming an angle of approximately 5 to 200, preferably 150 with the plane perpendicular to the opening plane of said acetabulum and, parallel to the frontal plane of the body, when said acetabulum is in the fixing position in the acetabulum cavity.

 This mechanical fixation is sufficient at first to ensure a biological fixation by bone regrowth in the peripheral structures of the acetabulum while limiting micromovements, and in the long term to guarantee a secure and durable fixation of the acetabulum without risk of loosening.

 According to a particular characteristic of the invention, the above-mentioned anchoring elements are adapted to the texture of the bone support in which they are to be fixed and are produced for example in the form of interchangeable pins, full, hollow and / or split.

 Advantageously, these tenons are of constant circular cross section. It has in fact been found that the use of anchoring elements with a triangular or quadrangular cross section causes a greater fibrous reaction than for circular studs.

 This gives great flexibility and the surgeon responsible for fixing the artificial acetabulum can select the type of anchor to be used according to the bone texture of each patient, which will also contribute to the quality and safety of the fixation.

 In the case of hollow anchoring elements, it will be possible to accelerate bone regrowth and further improve the fixation, by providing a "padding" of said anchoring elements, in particular using a bone graft. , taken for example from the femoral head or, where appropriate, from artificial grafts such as, for example, hydroxyapatite blocks. The effects obtained by using hollow anchoring elements are independent of the direction of orientation of these elements.

The invention will be better understood and other aims, characteristics and advantages thereof will appear more clearly on reading the explanatory description which follows, made with reference to the appended schematic drawings given solely by way of non-limiting examples illustrating several currently preferred embodiments of the invention and in which - FIG. 1 represents a side view of a cup conforming to
the invention, comprising two anchoring elements - Figure 2 is a top view - Figure 3 is a top view, similar to Figure 2, of a
cup according to a particular embodiment of the invention,
comprising three anchoring elements of unequal lengths - Figure 4 is a cross-sectional view of a cup according to
the invention illustrating the use of a solid anchor pin - Figure 5 is a view similar to Figure 4 illustrating
the use of a hollow and split anchor pin; and - Figure 6 is a sectional view along line VI-VI of the
figure 5.

 With reference to the appended figures, a cup 1 in accordance with the invention is produced in the form of a hollow body whose external surface 2 can be inscribed in a sphere. Generally, this cup will be of substantially hemispherical shape and the external surface 2 will be made of any suitable material, with the exception of plastics, and preferably of a metallic material.

 In the case of cementless fixing, the external surface 2 will be porous, in order to facilitate bone regrowth.

 The acetabulum 1 comprises at least two anchoring elements 3 arranged in parallel on the external face 2 and intended to be introduced into housings produced for this purpose in the acetabular cavity of the iliac bone, for example by means of a phantom template .

 The number of anchoring elements can be any, preferably two or three, and these elements will be distributed so as to come into the position of use in the zone of greatest compression substantially defined, seen from above, by an angle d '' about 30 to about 900.

 According to the invention, the anchoring elements 3 are arranged in a direction of orientation forming with the opening plane P of the acetabulum 1 an angle of about 56 to 760, so that this direction substantially coincides with the direction of orientation of the resultant of the forces of the abductor muscles and of the weight of the body, when the acetabulum is fixed, and forming an angle of approximately 5 to approximately 200, preferably 150 with the plane P '(see FIG. 2) perpendicular to the opening plane P of the acetabulum, and parallel to the frontal plane of the body, when said acetabulum is in the fixing position in the acetabulum cavity.

 The term frontal plane of the standing body is understood to mean the vertical plane passing substantially through the axis of the shoulders.

 The cup will be positioned so that the anchoring studs 3 are always inclined towards the front of the body, which includes the concept of "right cup", "left cup" and requires the creation of a specific cup for each side of the hip.

 This inclination will limit the increase in anterior stresses with the tendency to anterior subluxation in the horizontal plane, partly responsible for the loosening.

 The originality of the present invention also lies in the very great adaptability of the fixation resulting from the provision of anchoring elements specifically shaped and chosen according to the texture of the bone support receiving the acetabulum.

 By way of example, we can use tenons with a solid circular cross-section (Figure 4), about 8 mm in diameter, and 10 mm long; des.plots hollow, preferably split, (Figures 5 and 6) inside desauels we will make a bone padding, or pads. split that could spread like an ankle, by the impaction of a wedge element.

 These studs can be removable and interchangeable, for example by being screwed into tapped holes provided on the external surface of the acetabulum.

 These studs can also be made directly at the same time as the cup and form a single piece with the latter.

 For an even better adaptability of the fastening, the anchoring elements 3 can be made of unequal length (Figure 3). The short studs are thus preferably located towards the front, where there is a thin bone wall and the longest studs towards the rear, where there is a thicker bone wall.

 The advantages of the acetabulum which have just been described are therefore numerous - Safe and durable fixation - compliance with the anatomophysiological requirements of the joint; - very high adaptability depending on the quality of the bone support - easier bone regrowth.

Claims (4)

1. Artificial acetabulum for hip prosthesis, intended to be fixed with or without cement in the acetabular cavity of the iliac bone, of the type comprising an external face, preferably metallic, inscribable in a sphere and at least two anchoring elements arranged in parallel on said external face, characterized in that said anchoring elements (3) are arranged in an orientation direction forming with the opening plane P of the acetabulum an angle of about 56 to 760, so as to coincide substantially with the direction of orientation of the resultant of the forces of the abductor muscles and of the weight of the body when the acetabulum is fixed, and forming an angle of approximately 5 to 200 preferably 154 with the plane P 'perpendicular to the plane of opening of said acetabulum and parallel to the frontal plane of the body, when said acetabulum (1) is in the fixing position in the acetabulum cavity. 2. An artificial cup according to claim 1, characterized in that the above-mentioned anchoring elements (3) are adapted to the texture of the bone support in which they are to be fixed. 3. artificial cup according to claim 1 or 2, characterized in that the above-mentioned anchoring elements (3) are produced in the form of pins which are preferably removable and interchangeable, full, hollow and / or split, preferably of circular cross section. . 4. artificial cup according to one of claims 1 to 3, characterized in that the above-mentioned anchoring elements (3) are of unequal lengths.