FR2628315A1 - Bone cavity implant e.g. for hip prosthesis - has metal ring with three bosses penetrated by screws, collar preventing spread of cement and plastics core - Google Patents

Abstract

The bone cavity in plant has a cup or metal ring receiving a plastic core. The ring periphery has bosses (1i) taking support from the restructured cavity of the iliac bone surrounding a circular space of constant thickness. This insures in a corresp. way a cement layer thickness previarsly disposed in the cavity. The bosses are external and are situated in the lower part of the ring, formed radially in the ring edge bottom. There are at least three bosses angularly off-set by 120 deg. creating a tripod support for the passage of a cortical screw (1j). The ring has a collar with a dia. slightly less than that of the cavity limiting the cement flow. USE - For inserting hip prosthesis in pelvis.

Description

 Cotyloidal implant.

 The invention relates to the technical sector of banister protes in particular.

 It is known in hip arthroplasty to use cotyloidal implants, able to replace the cotyloid cavity of the iliac bone in which the head of the femur engages. Such implants generally comprise a cup or metal ring capable of being fixed by means of cement or screws in the cotyloid cavity. In the bore of this ring is centered and positions a core of plastic material including polyethylene having a hemispherical internal cavity for receiving a femoral head belonging to a prosthetic element.

 The general external shape of the ring is most often hemispherical and can be fixed within the bony acetabulum by means of a suitable cement. This method of attachment is relatively easy to use but may have drawbacks in terms of the quality of the fixation over time. with risks of loosening under the effect of the aging of the cement whose qualities are altered.

 However, it turned out that to maintain the initial quality of a cement, or at least greatly reduce their degeneration. it is necessary that the cement layer is uniform. This condition is not respected with current implants in which the cup or ring, given its conformation, does not ensure such consistency thickness. On the contrary, the hemispherical forms concerned tend to create, at the time of implantation, differences in thickness resulting from the pressures generated necessary for such implantation.

 To overcome these disadvantages and solve the problem, the invention is fixed. for the purpose of producing an implant whose periphery of the ring is arranged with means able to bear with restructured acetabulum portions of the iliac bone while providing a circular space of constant thickness to ensure correspondingly , a uniform thickness to the cement layer previously disposed in said acetabulum.

 Advantageously, the problem is solved in that the support means are constituted by external bosses established in the lower part of the ring.

 These bosses are formed radially in the bottom of the periphery of the ring, and are at least three in angularly offset by 120 to provide a tripod support.

 Another problem may also arise at the time of the establishment of the ring which can cause the overflow of the cement of the acetabular cavity if one exerts sufficient pressure and if one wants to have a uniform distribution of the cement with regard to to the ring.

 To solve this problem, the upper outer peripheral edge of the ring has a flange whose diameter is very slightly less than the diameter of the restructured acetabulum to limit the creep of the cement and increase its compression, the outer bearing edge of said flange being located in an arc of circle of the same radius considered in the same vertical plane as that of the bearing bosses, and circular grooves are formed between the collar and the bosses.

 In addition, to improve the anchoring, it is expected to double the cement fixation by screws.

 This desire to fasten by screws a sealed acetabulum makes it possible to compensate for the aging of the cement, but above all to avoid the creation of a soft interface (> between the cement and the bone, an interface which, if it can remain stable in time, generally evolves towards an enlargement, generator loosening.It is this notion of immediate suppression of bone micro-movements / acetabular metal is the goal sought in the screwing.In fact, it is assumed that the implants are positioned in a living bone with different mechanical structures depending on the location and that the metal implant changes immediately.

 It is therefore possible for an acetabulum to be fixed by cement in hard zones that may become soft, no longer stressed, or in soft areas. which are likely to become harsh, receiving new constraints.

 Screw fixation of the acetabulum therefore seeks to eliminate this random and dangerous period where the bone acetabulum may present micro-movements, making the bed of an interface and possibly the bed of a subsequent loosening.

 For this purpose, the bosses are drilled from one side to allow the passage of cortical screws.

 It appears that the two upper screws are anchored in the anterior and posterior column of the acetabulum so that the stresses are in. the axis desdite = screws and therefore not sheared.

 As indicated the bore of the ring, generally hemispherical, and intended to receive a nucleus of complementary shape in polyethylene and in which is engaged the femoral head.

 It is sometimes necessary to remove this polyethylene core in case of wear problems, which proves difficult and delicate.

 Indeed, given the properties of polyethylene, the core is cold to be freely engaged in the acetabulum.

Under the effect of increasing the temperature, the core expands and is held by force in the acetabulum. Consequently, the problems posed to allow its extraction are conceived.

 To solve such a problem, the upper part in particular of the hemispherical bore of the ring is arranged, in combination with a corresponding part of the core, to, on the one hand, ensure the angular indexing of said core, and on the other hand on the other hand, to allow, if necessary, its extraction by means of a grasping organ.

 Advantageously, the upper part of the hemispherical bore of the ring has a hole capable of cooperating with a bearing flange that the core presents, said counterbore having two diametrically opposite flats cooperating with two flats formed on the flange. to ensure immobilization in rotation of said core, a notch being formed opposite each of the flats of the counterbore to give free access to the corresponding portion of the flange of the core for its extraction.

 These and other features will emerge. from the rest of the description.

To fix the object of the invention without limiting it in the accompanying drawings
- Figure 1 is a perspective view illustrating the metal ring and the core according to the invention.

 - Figure 2 is a sectional view showing the implant according to the invention set up in the bone acetabulum.

 - Figure 3 is a bottom view of the ring according to the invention.

 - Figure 4 is a plan view illustrating the removal of the core.

 - Figure 5 is. a sectional view of the core according to the invention.

 - Figure 6 is a plan view of the ring according to the invention.

 - Figure 7 is a sectional view along the broken line 7-7 of Figure 6.

 In order to make more concrete the object of the invention, it is now described in a nonlimiting form of réalisatjo #, illustrated in the figures of the drawings.

 The metal ring <i) consists in a known manner of an outer shape (la) preferably spherical without excluding other forms such as frustoconical, truncated spherical.

The ring internally has a housing (lc) in spherical cap followed by a clearance (ld) cylindrical or conical, for rotational support of the head (T1) of the femoral stem (T).

The hemispherical bore (tic) (ld) thus formed opens into a countersink (1e) which has in two diametrically opposite zones flats (1f) whose middle portion is notched in (ig>.

 Outwardly. the annea # presents from the upper outer peripheral edge. a collar (1h) whose diameter is very slightly less than the diameter of the restructured acetabulum to limit the creep of the cement and increase its compression setting as shown in Figure 2.

 In the bottom of the sphere. are formed radially and in a regular distribution, bosses (1i) as indicated which can be traversed by countersunk holes (1j) opening into the spherical cap. Preferably. but not limited to, there are three holes distributed at 120 '.

 Enf4n, between the flange (lh) and the bosses (li) are formed circular grooves or grooves (1k) parallel to each other.

 The core (2> of plastics of the polyethylene type has externally a spherical bearing (2a) corresponding to the spherical cap (1c) of the ring, then a cylindrical or conical bearing C2b> corresponding to the clearance (1d) of the ring and a flange (2c> of diameter corresponding to that of the countersink (1c) of the ring, with diametrically opposite flats (2d) corresponding to the flats (1f) of the ring.

Internally. the core has a cylindrical or conical bore (2e> followed by a hemispherical cavity (2f> for housing the head (T1) of the femoral stem,
It is now necessary to describe the mounting of the implant thus produced.

 In a known manner, the surgeon operates a restructuring of the bone acetabulum of the pelvic bone in order to be able to receive the ring via a suitable cement (C). Given the external configuration of the ring, with its flange (1h), streaks (lku and bosses (li), we obtain a good distribution of cement1 in particular a uniform thickness, and also a better distribution of pressure in particular in the upper half of the acetabulum.To reinforce the anchoring, increase the stability of the implant, and improve the transmission of forces in the anterior and posterior columns of the acetabulum, the ring can then be fixed by cortical screws ( 3) through the countersunk holes Cli> made on the bosses (li), and screwing into the acetabulum.It should be noted that the tripod support thus produced is oriented respectively in the positions posterosuperior, anterosuperior and inferior.

 The core <2) is then set up and indexed angularly in the ring by the flats (2d) cooperating with the flats (if) of the ring, as can be seen in Figure 4, it is possible to remove and to replace conveniently the core which is the wearing part, thanks to the notches (ig) of the flats which make it possible to engage between the flats <2d) and the bottom of the cuts (read) the active parts <Ol) of a tool d 'extraction.

 The advantages are clear from the description, the uniform distribution of the cement, the stable fixing of the ring by the tripod support, and the easy interchangeability of the core by the forms facilitating extraction are emphasized.

 In addition, it is expected to have a single core model for the different ring models.

Claims (9)

An acetabular implant comprising a cup or metal ring receiving a core (2) made of plastic, characterized in that the periphery of the ring is arranged with means <li> able to bear with the part of the restructured cotyle of the iliac bone while providing a circular space of constant thickness to ensure in a corresponding manner, a thickness to the cement layer (c> previously disposed in said acetabulum. -2- Implant according to claim 1, characterized in that the support means are constituted by bosses (li) external established in the lower part of the ring. -3- Implant according to claim 2, characterized in that the bosses (11) are formed radially in the bottom of the periphery of the ring. -4- Implant according to claim 3, characterized in that the bosses (li) are at least three in being angularly offset from 120 to provide a tripod support. -5- Implant according to any one of claims 1 and 4, characterized in that the upper outer peripheral edge of the ring has a flange <1h> whose diameter is very slightly less than the diameter of the restructured acetabulum to limit the creep of the cement and increase its compression, the outer bearing edge of said flange being located in a circular arc, of the same radius considered in the same vertical plane as that of the bearing bosses Cli>. -6- Implant according to claims 1, 4 and 5, characterized in that circular ridges tlk) are formed between the flange and the bosses. -7- Implant according to claim 4, characterized in that the bosses (li) are drilled from one side to allow the passage of cortical screws. Implant according to claim 1, characterized in that the upper part, in particular of the hemispherical bore (1c) of the ring, is arranged, in combination with a corresponding part of the core, in order firstly to provide the angular indexing said core and, on the other hand, allow, if necessary, its extraction by means of a gripping member.  -9- Implant according to claim 8, characterized in that the upper portion of the hemispherical bore (lc) of the ring has a recess (the> adapted to cooperate with a collar <2c> support that the core presents said counterbore having two flats (lof) diametrically opposed cooperating with two flats (2d) formed on the flange to ensure rotational indexing of said core, a notch (lg) being formed opposite each flats of the countersink to give a free access to the corresponding part of the collar of the core for its extraction.