Line of cotyloid implants of different sizes

A line of cotyloid implants of different sizes including a cup intended to be fastened in a cotyloid cavity and including a substantially hemispherical polar portion and an equatorial portion extending the polar portion, the polar portion and the equatorial portion delimiting a substantially hemispherical inner cavity, an insert pivotally mounted in the inner cavity delimited by the polar and equatorial portions of the cup, the insert delimiting an inner cavity having an inner spherical surface portion and intended to pivotally and retentively mount a prosthetic femoral head, where the height of the equatorial portions of the cups of the various cotyloid implants belonging to the line varies in a decreasing manner as a function of the increase in the size of the cotyloid implants.

TECHNICAL FIELD

The present invention relates to a line of cotyloid implants, and more particularly a line of so-called “dual mobility” cotyloid implants.

BACKGROUND

A dual mobility cotyloid implant includes, in a known manner, on one hand a cup intended to be fastened in a cotyloid cavity and including a substantially hemispherical polar portion and an equatorial portion extending the polar portion, said polar portion and the equatorial portion delimiting a substantially hemispherical inner cavity, and on the other hand an insert pivotally mounted in the inner cavity delimited by the polar and equatorial portions of the cup, the insert being outwardly delimited by an outer spherical surface portion and itself delimiting an inner cavity having an inner spherical surface portion and intended to pivotally and retentively assemble a prosthetic femoral head.

The present of such an equatorial portion makes it possible to limit the risks of an insert leaving the corresponding cup, and therefore the risks of luxation of the implant. Such a cotyloid implant therefore limits repeated surgeries.

It must, however, be noted that the risks of luxation remain significant when the “jumping distance,” i.e. the distance separating the bottom of the cup and the edge delimiting the opening thereof, is small, which is normally the case for the small implant sizes.

In order to limit the risks of luxation for small implant sizes, it is known to provide a substantial and constant equatorial portion height for all of the implants belonging to a line so as to ensure a satisfactory jumping distance for all of the implants.

However, the equatorial portion of the cup of such a cotyloid implant may, for large implants, come into conflict with the muscles or tendons situated close to the acetabular bone, and in particular with the patient's psoas, and therefore cause pain for the patient.

In order to reduce the risks of luxation, it is also known to offset the centers of the outer and inner spherical surface portions of the insert so that the center of the inner spherical surface portion is situated on the bottom side of the inner cavity delimited by the insert. These arrangements make it possible to ensure optimal repositioning of the insert relative to the cup in the upright position of the patient, due to the torque created by the forces exerted on the prosthetic femoral head, which causes the insert to rotate until it is in the balanced position.

It must, however, be noted that the offset between these two centers may not be sufficient to ensure optimal repositioning of the insert for large implants. Indeed, the larger the implant, the more the friction between the outer surface of the insert and the inner surface of the cup are significant and thereby oppose the torque created by the forces exerted on the prosthetic femoral head and aiming to replace the insert, which can cause a risk of luxation of the femoral prosthetic head and thus damage the reliability of the implant.

BRIEF SUMMARY

The present invention aims to resolve these drawbacks.

The invention provides a line of cotyloid implants that have a simple structure and are economical and reliable, while also making it possible to avoid the risks of luxation and conflict with the patient's body.

To that end, the invention relates to a line of cotyloid implants of different sizes of the type comprising:a cup intended to be fastened in a cotyloid cavity and including a substantially hemispherical polar portion and an equatorial portion extending the polar portion, the polar portion and the equatorial portion delimiting a substantially hemispherical inner cavity.an insert pivotally mounted in the inner cavity delimited by the polar and equatorial portions of the cup, the insert delimiting an inner cavity having an inner spherical surface portion and intended to pivotally and retentively mount a prosthetic femoral head,

characterized in that the height of the equatorial portions of the cups of the various cotyloid implants belonging to the line varies in a decreasing manner as a function of the increase in the size of the cotyloid implants.

Thus, the height of the equatorial part of the cup of the smallest implant can be defined as significant in order to promote the stability of the small implants, without this being detrimental for the large implants. Indeed, due to the decrease in the height of the equatorial portions as a function of the increase in the size of the cotyloid implants, the height of the equatorial portions of the cups of the large implants is small such that the cups thereof are not likely to create conflicts with the patient's body, and in particular the patient's psoas. As a result, the line according to the invention makes it possible to avoid the risks of luxation, while also avoiding the risks of conflicts with the patient's body.

Preferably, the height of the equatorial portions of the cups of the various cotyloid implants belonging to the line decreases homothetically or by levels between two successive sizes of cotyloid implants.

According to one embodiment, the equatorial portion of each cup extends over the entire periphery thereof.

Advantageously, each insert is outwardly delimited by an outer spherical surface portion, and the center of the inner spherical surface portion of the insert of at least one of the cotyloid implants is offset relative to the center of the outer spherical surface portion of said insert, towards the bottom of the inner cavity delimited by said insert. Preferably, the centers of the outer and inner spherical surface portions of the insert of at least one of the cotyloid implants are offset along the axis of symmetry of the insert.

Advantageously, the distance between the center of the outer spherical surface portion of the insert of a cotyloid implant and the center of the inner spherical portion of said insert varies in a manner increasing as a function of the increase in the size of the cotyloid implants. These arrangements make it possible to ensure optimal repositioning of the insert relative to the cup for all of the implants belonging to the line, and more particularly for large implants.

The distance between the center of the outer spherical surface portion of the insert of a cotyloid implant and the center of the inner spherical surface portion of said insert increases, for example homothetically or by levels between two successive sizes of cotyloid implants.

According to one embodiment, each cup has a smooth and polished inner surface.

Advantageously, the inner cavity of each insert has a spherical surface portion extending over more than a half-sphere and extended towards the opening of the insert by a forked tapered portion.

Preferably, each cup comprises, on its outer surface, bone anchoring means. The bone anchoring means advantageously include a thread extending over at least a portion of the outer surface of the polar portion, and preferably also over at least one portion of the outer surface of the equatorial portion.

It should be noted that the cotyloid implants belonging to the line can use cemented fastening or biological fastening.

Preferably, each insert is made from polyethylene, and each cup is metal, preferably stainless steel or a chrome-cobalt alloy.

Advantageously, the outer surface of each cup is rough and preferably at least one portion of the outer surface of the cup is covered with a titanium coating.

Preferably, the equatorial portion of each cup is inwardly delimited by a forked tapered surface towards the opening of said cup. These arrangements make it possible to facilitate the reinsertion of the insert into the cup in case of luxation of the latter, and therefore prevent a repeat surgical operation. Moreover, these arrangements make it possible to increase the amplitude of movement of the prosthetic femoral neck, while also reducing the risks of conflict between the latter and the cup.

DETAILED DESCRIPTION

The line of cotyloid implants according to the invention can for example include six cotyloid implants of different sizes, i.e. different diameters. The cotyloid implants belonging to the line can use cemented fastening or biological fastening.

As shown inFIG. 1, each cotyloid implant2comprises a metal cup3intended to be fastened in a cotyloid cavity of a patient and including a hemispherical polar portion4and an equatorial portion5extending the polar portion4. The polar portion4and the equatorial portion5delimit a substantially hemispherical inner cavity6. The equatorial portion5extends over the entire periphery of the cup and delimits the opening thereof. The equatorial portion5is advantageously inwardly delimited by a forked tapered surface extending from the polar portion to the opening of the cup. The equatorial portion5is advantageously outwardly delimited by a cylindrical surface.

Preferably, each cup3comprises, on its outer surface, bone anchoring means (not shown in the figures). The bone anchoring means can for example include a thread arranged on the outer surface of the equatorial portion5.

Each cup3is preferably made from stainless steel or a chrome-cobalt alloy. Each cup3advantageously has a smooth and polished inner surface and a rough outer surface. Preferably, at least one portion of the outer surface of each cup3is covered with a titanium coating.

Each cotyloid implant2also comprises an insert7made from polyethylene pivotally mounted in the inner cavity6delimited by the polar and equatorial portions4,5of the cup. Each insert7is outwardly delimited by an outer spherical surface portion8and itself delimits an inner cavity9intended to pivotally and retentively mount a prosthetic femoral head10. The inner cavity9of each insert has an inner spherical surface portion11extending over more than a half-sphere and extended towards the opening of the insert by a forked tapered portion12.

As shown inFIG. 1, the center C1of the outer spherical surface portion8of the insert of the smallest cotyloid implant2is combined with the center C2of the inner spherical surface portion11of said insert.

As shown inFIG. 2, the center C2of the inner spherical surface portion11of the insert of the largest cotyloid implant2is offset by a distance D relative to the center C1of the outer spherical surface portion8of said insert, along the axis of symmetry of the insert and towards the bottom of the inner cavity9delimited by said insert.

The height h of the equatorial portions5of the cups3of the various cotyloid implants2belonging to the line varies in a decreasing manner as a function of the increase in the size of the cotyloid implants. Preferably, the height of the equatorial portions5of the cups3of the various cotyloid implants belonging to the line decreases homothetically or by levels between two successive sizes of cotyloid implants. It should be noted that the height h is maximal for the smallest cotyloid implant and minimal for the largest cotyloid implant.

Advantageously, the distance D between the center C1of the outer spherical surface portion8of the insert of a cotyloid implant and the center C2of the inner spherical surface portion11of said insert varies in an increasing manner as a function of the increase in the size of the cotyloid implants. The distance D between the center C1of the outer spherical surface portion8of the insert of a cotyloid implant and the center C2of the inner spherical surface portion11of said insert increases for example homothetically or by levels between two successive sizes of cotyloid implants. It should be noted that the distance D is null for the smallest cotyloid implant and maximal for the largest cotyloid implant.

FIG. 3shows a cotyloid implant2that differs from that shown inFIG. 1essentially in that the equatorial portion5is cylindrical. The amplitude of movement A1of a prosthetic femoral neck11inside the cotyloid implant2is shown inFIG. 3by illustrating the two extreme positions of the prosthetic femoral neck11.

FIG. 4illustrates the amplitudes of movement A1and A2of a prosthetic femoral neck11respectively inside the cotyloid implant ofFIG. 3and inside the cotyloid implant ofFIG. 1. As shown inFIG. 4, inwardly delimiting the equatorial portion5of each cup by a forked tapered surface towards the opening of said cup makes it possible to increase the amplitude of movement of the prosthetic femoral neck11inside the cotyloid implant.

As goes without saying, the invention is not limited solely to the embodiment of this line of cotyloid implants described above as an example, but on the contrary encompasses all alternative embodiments.