FR2868687A1 - Acetabular copula for hip prosthesis, has annular pad that retains femoral rod in insert and that is placed apart from spherical portion that extends from equator of insert - Google Patents

Abstract

The copula has a femoral rod (6) with a head (5) which cooperates with an insert (4), in the case of reduction of a luxation. An annular pad (7) retains the femoral rod in the insert and is placed apart from a spherical portion (8) that extends from the equator of the insert. The pad offers resistance to lever effect produced by a cervix of the femoral rod, during the reduction of the luxation.

Description

COTYLOID MOBILE CUP, FOR PROSTHESIS OF THE

HIP

  The present invention relates to an acetabulum cup for a hip prosthesis.

  Such a cup is intended to receive a spherical head of a femoral stem constituting a prosthesis cooperating with the cup being housed in a damaged joint cavity, in this case the acetabulum.

  Prior to the establishment of the spherical head of the femoral stem, is placed in the cup a biocompatible plastic insert such as polyethylene.

  Various cups of this type are known, some of which are intended to be fixed in the acetabulum by screws or, according to another type by compression locking generally called a Press-Fit acetabulum. The latter type of cupule is therefore retained in the acetabulum by impaction and compression, taking place essentially in the equatorial zone of the cup.

  It is also known, in a case which interests us more particularly, in case of dislocation and when the acetabulum is not or only slightly damaged, to use an acetabulum cup, of the type intended to be mounted mobile, unlike the previous ones, in the acetabulum of a patient and which comprises a substantially hemispherical polished outer metal part in rubbing contact with said acetabulum and an insert 2868687 2 also substantially hemispherical plastic disposed integrally inside the cup and having means of retentivity a head of a femoral stem, intended to cooperate freely with the insert after impaction engagement, in the case of a reduction of a dislocation.

  In this type of cup the femoral head is first impacted in the insert by means of a press and then fixed on the Morse taper extending the neck of the femoral stem, also by impaction with a slight hammer blow.

  Thus the movements of the mobile cup in the acetabulum are limited and can preserve the latter.

  In order to achieve this connection the polyethylene insert is systematically retentive of the femoral head which must be free relative to the cup. In order to ensure the retentivity of the femoral head, generally made of plastic, in the insert, it is known to dispose in the polyethylene insert of the movable cup, a ring also made of polyethylene inserted by force into said insert and becoming prisoner of the insert, while remaining mobile with respect thereto.

  A well-known disadvantage of this type of retentive means lies in the wear of the ring over time and also by the fact of a certain difficulty for the surgeon to position said ring.

  2868687 3 Nevertheless, in case of dislocation, the ring system is effective because it offers more resistance than a standard system.

  Indeed, during the attempt to reduce dislocation, the surgeon can block the flat portion of the movable cup on the cotylo5dien eyebrow and cause by leverage, the décoaptation of the femoral head out of the movable cup.

  The interest of the ring system is therefore to offer greater resistance to this constraint during the reduction of dislocation. By against the ring can be deformed and cause seizure of the femoral head in the movable cup. This lack of movement of the head in the cup can cause acetabular pain and premature wear of the acetabulum.

  There is a second type of movable cup whose polyethylene insert comprises retentive means which is not a ring. In fact, the retentivity means is constituted by a portion of sphere extending the equator of the insert, constituting in short a tightening.

  For the introduction of the femoral head in this type of insert is used a press which allows a snap force, by elastic deformation of the polyethylene constituting the insert.

  Nevertheless, in the case of dislocation, during the reduction, it has been noticed that a decoaptation 2868687 4 could intervene between the femoral head and the insert, which necessarily entails a new intervention.

  Thus, the present invention overcomes all of the aforementioned drawbacks of the different types of cups and in particular of mobile cups and for this purpose concerns an acetabulum cup, of the type intended to be mounted in the acetabulum of a patient and which is mobile. comprises a substantially hemispherical polished outer metal part, in rubbing contact with said acetabulum, and a plastic insert, also substantially hemispherical, arranged integrally inside the cup and comprising retentive means of a head of a femoral stem intended to cooperate freely with the insert by interlocking by impaction, in the case of a reduction of a dislocation, characterized in that the retentive means of the femoral head in the insert, integral with the movable cup, are constituted by an annular bead formed beyond a spherical portion extending the equator of the plast material insert which bead is intended to provide resistance to leverage produced by the neck of the femoral stem, during the reduction of dislocation, likely to produce a coaptation of the femoral head with respect to the insert of the cup.

  The advantage of such a bead made in extension of the spherical portion of the insert extending itself beyond the equator, ensures as much retention as a ring when the reduction is 2868687 5 dislocation, without the inconvenience.

  Indeed the resistance is much greater than the deformation, because the bead 7 is made in the mass of the insert 4 and it is possible to impact the intraoperative femoral head in the cup.

  Thus, it is avoided, during a reduction work that the neck of the femoral stem conflicts with the edge of the movable cup, itself blocked by the acetabular eyebrow, the neck of the stem being able to have a positive effect. lever likely to overcome the retentivity of the insert of the movable cup relative to the femoral head.

  The cylindrical bead according to the invention, by its predetermined height, will therefore fight against this leverage effectively.

  The present invention also relates to the features which will emerge during the following description, which should be considered in isolation or in all their possible technical combinations.

  This description, given by way of non-limiting example, will better understand how the invention can be made, with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of a hip prosthesis 2868687 6 complete with a movable cup according to the invention.

  FIG. 2 is a view, on a larger scale, of an insert constituting the movable cup according to FIG. 1.

  The acetabulum cup 1 generally designated in FIG. 1 is intended to be mounted in a patient's acetabulum 2.

  It comprises a polished outer metal part 3, substantially hemispherical, in frictional contact with said acetabulum 2.

  It also comprises a plastic insert 4, also substantially hemispherical, arranged integrally inside the cup and comprising retentive means of a head 5 of a femoral stem 6.

  The head 5 is intended to cooperate freely with the insert 4 after interlocking by impaction, in the case of a reduction of a dislocation.

  According to the invention, the retentive means of the femoral head in the insert, integral with the movable cup, are constituted by an annular bead formed beyond a spherical portion extending the equator of the plastic insert. . This bead is intended to provide resistance to leverage produced by the neck of the femoral stem, during the reduction of dislocation, likely to produce a coaptation of the femoral head relative to the insert of the cup.

  2868687 7 As can also be seen in Figure 1, a flared frustoconical zone is made in extension of the bead 7 to facilitate the engagement of the femoral head 5.

  The retentive bead 7 is made in the same mass of the plastic insert 4.

  Preferably the bead 7 of the insert 4 determines a straight circular outer edge of cylindrical section.

  According to another characteristic of the invention, the internal diameter D and the height H of the retentive bead 7 are of predetermined dimensions as a function of the diameter of the femoral head.

  Thus, for a femoral head with a diameter D1 of 22 mm, the height H1 of the retentive bead 7 is between 3 and 4 mm, and that for a femoral head 5 of diameter D2 of 28 mm, the height H2 the retentive bead 7 is between 2 and 3 mm.

  Thus also for a femoral head 5 of 22 mm the internal diameter D of the retentive bead 7 is between 20 and 21 mm, and that for a femoral head 5 of 28 mm the internal diameter D of the retentive bead 7 is included between 26 and 27 mm.

  As a practical example, the insert 4 shown in FIG. 2 is designed to receive a 28 mm femoral head 5 and is defined according to the following dimensions: The outside diameter of the insert 4 is 46 mm .

  The inner diameter of the insert 4, intended to receive the femoral head 5, is 28 mm.

  The radius R1 of the hemispherical zone located below the equator 9 is a radius of 14 mm corresponding to the diameter of the inner portion of diameter D4 of the insert 4.

  The diameter D of the bead 7 is 26.4 mm.

  The height H2 of the bead 7 is 2.75 mm. The angle alpha formed by the flaring insertion portion 11 is 78.

  The height H3 of this flared part is 3.6 mm.

  The total height H4 of the insert 4 is 35 mm.

  The height H5 of the equator 9 at the top of the insert 4 is 23 mm.

  The height H6 of the hollow inner portion of the insert 4 from its top to the base of said insert is 26 mm.

Claims (2)

9 CLAIMS   An acetabulum cup, of the type intended to be mounted movably in the acetabulum (2) of a patient and which comprises a substantially hemispherical polished outer metal part (3) in frictional contact with said acetabulum (2) and an insert ( 4) of plastic material, also substantially hemispherical, arranged integrally inside the cup and comprising retentive means of a head (5) of a femoral stem (6) intended to cooperate freely with the insert (4). ) by interlocking by impaction, in the case of a reduction of a dislocation, characterized in that the retentive means of the femoral head (5) in the insert (4), integral with the movable cup (1), are constituted by an annular bead (7) made beyond a spherical portion (8) extending the equator (9) of the plastic insert (4), which bead (7) is intended to provide resistance at a lever effect produced by the neck (10) of the femoral stem rale (6), during the reduction of dislocation, capable of producing a coaptation of the femoral head (5) relative to the insert (4) of the cup (1).   2. Cup according to claim 1 characterized in that the retentive bead (7) is formed in the mass of the insert (4) of plastic material.   3. Cup according to one of claims 1 or 2 characterized in that the bead (7) of the insert (4) determines a straight circular outer edge of cylindrical section.   4. Cup according to claim 3 characterized in that the internal diameter (D) and the height (H) of the retentive bead (7) are of predetermined dimensions as a function of the diameter of the femoral head (5).   5. Cup according to claim 4 characterized in that for a femoral head (5) of a diameter (Dl) of 22 mm, the height (Hl) of the rettenent bead (7) is between 3 and 4 mm.   6. Cup according to claim 4 characterized in that for a femoral head (5) of diameter (D2) of 28 mm, the height (H2) of the retentive bead (7) is between 2 and 3 mm.   7. Cup according to claims 4 and 5 characterized in that for a femoral head (5) of 22 mm the inner diameter (D) of the retentive bead (7) is between 20 and 21 mm.   8. Cup according to claims 4 and 6 characterized in that for a femoral head (5) of 28 mm the inner diameter (D) of the retentive bead (7) is between 26 and 27 mm.