FR2996443A1 - Resurfacing cup for head such as humeral head, of long bone in shoulder, has concave interior surface that is delimited for receiving head such as humeral head, of long bone, and height of cup on external radius lies between specific values - Google Patents

Abstract

The cup (2) has a concave interior surface (6), where the cup has approximately the shape of hollow segment of a sphere. The concave interior surface is delimited for receiving a head such as humeral head, of a long bone. A height of the cup on the external radius lies between 0.70 and 0.82. A bone anchoring such as axially shifted anchoring grooves, is placed on the concave interior surface of the cup, where the bone anchoring is arranged in preference to proximity of an equatorial side (5) of the cup.

Description

The present invention relates to a resurfacing cup for a head of a long bone, such as a humeral head. The deterioration of the humeral head of a humerus, either by accidental or other necrosis of the humeral head, or by damage to the articular cartilage of this humeral head, causes a poor articulation of the humeral head within the glenoid cavity, which limits the mobility of the joint and causes pain to the patient. A first solution to compensate for deterioration of the humeral head is to perform the implantation of a total shoulder prosthesis comprising a humeral stem intended to be engaged in the medullary canal of the humerus, a humeral neck portion and a head of substantially hemispherical shape. This first solution strongly undermines the bone capital since it requires the resection of the humeral neck and the diaphyseal part of the humerus.

A second solution to compensate for deterioration of the humeral head is to perform only the implantation of a so-called resurfacing cup which has a hollow spherical cap shape, and which fits on the humeral head after preparation of the latter. A first advantage of this second solution lies in the possibility of maintaining a maximum of bone capital, since the humeral neck and the entire diaphyseal part are preserved. A second advantage of this second solution lies in the possibility of taking the resurfacing cup used or having lost its function, by a total shoulder prosthesis, while the recovery of a total shoulder prosthesis often requires the installation of a so-called revision prosthesis which further decreases the bone capital. However, a resurfacing cup generally has a height substantially equal to the external radius of the latter, and therefore an external height / radius ratio equal to about 1. This results in the necessity of producing, particularly for cupules of large diameter, a resection significant humeral head to ensure the implantation of the cup, which kicks the bone capital and complicates the possible recovery of the resurfacing cup by a total shoulder prosthesis due in particular the need to put shims. The present invention aims to remedy these disadvantages.

The technical problem underlying the invention therefore consists in providing a resurfacing cup which is of simple and economical structure, while preserving as much as possible the bone capital of the patient. To this end, the present invention relates to a resurfacing cup for a head of a long bone, such as a humeral head, the resurfacing cup having substantially a hollow spherical cap shape and delimiting a concave inner surface intended to receive the head of a long bone, characterized in that the ratio of the height of the cup to the outer radius of the cup is between 0.70 and 0.82.

Such a value of the ratio of the height of the cup to the outer radius of the cup allows, whatever the diameter of the cup, to reduce the height of the cup, and thus to limit the height of bone cutting necessary for the cup. implantation of the cup. This results in a bone gain to facilitate the surgical procedure and the possible recovery of the resurfacing cup. According to one embodiment of the invention, the ratio of the height of the cup to the outer radius of the cup is about 0.76. According to one embodiment of the invention, the outer radius of the cup is between 20 and 27 mm.

Preferably, the cup comprises bone anchoring means provided on its inner surface, and preferably near the equatorial edge of the cup. The bone anchoring means advantageously comprise at least one series of anchoring grooves, each series of anchoring grooves comprising a plurality of anchoring grooves extending substantially perpendicularly to the axis of the cup and axially offset. others. The presence of the anchoring grooves makes it possible to improve the primary fixation of the cup on the bone by creating reliefs intended to penetrate into the bone. Advantageously, each anchoring groove advantageously extends substantially parallel to the equatorial edge of the cup. According to one embodiment of the invention, each anchoring groove has a triangular section. The orientation of each anchor groove is preferably adapted to facilitate the mounting of the cup on the head of the long bone and to make it difficult to remove the cup. According to one characteristic of the invention, the top of each anchoring groove is located in continuity with the inner surface of the cup. Each anchor groove has for example a maximum depth of about 0.5 mm. According to one embodiment of the invention, the bone anchoring means comprise a single series of anchoring grooves, each anchoring groove 5 being annular. According to another embodiment of the invention, the bone anchoring means comprise several series of anchoring grooves, the series of anchoring grooves being angularly offset from each other with respect to the axis of the cup, and preferably evenly distributed around the axis of the cup. These arrangements allow to adapt the primary holding force of the cup on the bone, which is a function of the impaction force and the attachment surface in the bone, so that this force is substantially constant whatever the diameter of the spherical surface of the cup. Advantageously, the sets of anchor grooves comprise the same number of anchor grooves, each anchor groove of a series being located in the same plane as an anchoring groove of each of the other series. The anchoring grooves belonging to each series extend angularly for example over an angle of approximately 50 to 80 °. Preferably, the cup comprises a plurality of fixing studs formed on its inner surface and offset with respect to the axis of the cup, each fixing stud extending substantially parallel to the axis of the cup. According to one embodiment, the attachment studs extend perpendicularly to the equatorial edge of the cup. The cup preferably comprises between two and six attachment studs, and for example three studs. Advantageously, the number of sets of anchor grooves is identical to the number of fixing studs. Each fixing stud preferably has a free end delimited by a substantially semi-spherical surface in order to facilitate the introduction of said fixing stud into a complementary bore previously prepared in the head of the long bone. The fixing studs may for example be equidistant. Preferably, the distance separating the axis of each attachment stud and the axis of the cup is equal to approximately half the outer radius of the spherical cap. According to one embodiment of the invention, the length of each attachment stud is adapted such that the free end of each fixing stud does not exceed the equatorial edge of the cup, and advantageously is located in withdrawal of the equatorial edge of the cup. These provisions simplify the surgical procedure in case of surgical recovery by allowing the sawing of the bone under the equatorial plane of the cup.

According to one characteristic of the invention, each fixing stud has anchoring asperities, such as annular anchoring ribs. According to one embodiment of the invention, each attachment stud is frustoconical, and has for example a taper of about 3%.

According to another embodiment, each fastening stud has a triangular or Y-shaped section. According to yet another embodiment, each fastening stud is substantially cylindrical. Advantageously, the outer surface of the cup comprises a plurality of marks each representing the angular position of a fixing stud. Each marker is preferably formed in the equatorial portion of the cup. These arrangements facilitate the pre-positioning of the cup before its impaction on the bone. According to a feature of the invention, the inner surface of the cup is coated with an osteoconductive coating promoting bone growth, such as a coating of titanium or hydroxyapatite. Preferably, each attachment pad is also coated with an osteoconductive coating promoting bone growth, such as a coating of titanium or hydroxyapatite.

The cup may be made of metal, for example a chromium-cobalt alloy, or ceramic, for example alumina or zirconia. The cup preferably has a polar portion and an equatorial portion extending the polar portion. The cup is delimited externally by a portion of spherical surface having a substantially constant radius. The inner surface of the cup is for example delimited by a spherical surface portion extending from the equatorial edge of the cup, and a substantially flat portion extending from the spherical surface portion and substantially perpendicular to the cup axis The cup may have a thickness of between 1 and 3 mm, and preferably less than 2 mm. The thickness of the cup can be substantially constant. The present invention further relates to a range of resurfacing cups having a plurality of resurfacing cups of the invention of different sizes, wherein each resurfacing cup has a substantially identical outer aperture height ratio. In any case, the invention will be better understood with the aid of the description which follows with reference to the appended diagrammatic drawing showing, by way of nonlimiting examples, several embodiments of this resurfacing cup. Figure 1 is a perspective view of a resurfacing cup according to a first embodiment of the invention. Figure 2 is a cross-sectional view of the resurfacing cup of Figure 1. Figure 3 is a top view of the resurfacing cup of Figure 1. Figure 4 is a partial view, on an enlarged scale, of Figure 5 is a perspective view of a resurfacing cup according to a second embodiment of the invention. Figure 6 is a cross-sectional view of the resurfacing cup of Figure 5. Figure 7 is a schematic top view of a resurfacing cup according to a third embodiment of the invention. Figure 8 is a perspective view of a resurfacing cup according to a fourth embodiment of the invention. Figure 9 is a perspective view of a resurfacing cup according to a fifth embodiment of the invention. Figures 1 to 4 show a resurfacing cup 2 for a humeral head. The resurfacing cup 2 may be made of metal, for example a chromium-cobalt alloy, or ceramic, for example alumina or zirconia. The cup 2 has a thickness of between 1 and 3 mm, and preferably less than 2 mm. The resurfacing cup 2 has a pole portion 3 and an equatorial portion 4 extending the pole portion 3 towards the equatorial edge 5 of the cup. The resurfacing cup 2 substantially has a hollow spherical cap shape and delimits a concave inner surface 6 for receiving the humeral head of a humerus. The resurfacing cup 2 comprises bone anchoring means provided on its inner surface, near the equatorial edge 5 of the cup. As shown in Figures 2 and 4, the bone anchoring means comprise three annular anchoring grooves 7 axially offset from each other. Each anchor groove 7 extends parallel to the equatorial edge 5 of the cup and perpendicular to the axis A of the cup.

Each anchor groove 7 has a triangular section and is oriented to facilitate the mounting of the cup on the humeral head and make it difficult to remove the cup of the latter. Each anchor groove 7 preferably has a maximum depth of about 0.5 mm. As shown more particularly in Figure 4, the top of each anchor groove 7 is located in the continuity of the inner surface 6 of the cup. The resurfacing cup 2 also comprises three fixing studs 8 formed on its inner surface. The fixing studs 8 extend parallel to the axis A of the cup and perpendicularly to the equatorial edge 5 of the cup. The fixing studs 8 are offset relative to the axis of the cup and are equidistant. Each fixing stud 8 is substantially cylindrical and has a free end delimited by a substantially semi-spherical surface. The length of each fastening stud 8 is advantageously adapted so that the free end of each fastening stud 8 is slightly set back from the equatorial edge 5 of the cup. In addition, the distance separating the axis of each attachment stud 8 and the axis A of the cup is equal to about half the outer radius of the spherical cap. The ratio of the height H of the cup to the outer radius R of the spherical cap is between 0.70 and 0.82, and is preferably about 0.76. The inner surface of the cup and the outer surface of each attachment pad 8 is coated with an osteoconductive coating promoting bone ingrowth, such as a coating of titanium or hydroxyapatite.

The outer surface of the cup comprises a plurality of markers (not shown in the figures) each representing the angular position of a fastening pad. Each marker is preferably formed in the equatorial portion of the cup.

FIGS. 5 and 6 show a cup according to a second embodiment which differs from that shown in FIGS. 1 to 4 essentially in that the fixing studs 8 has a Y-shaped cross section. FIG. 7 represents a cup according to FIG. a third embodiment which differs from that shown in Figures 1 to 4 essentially in that the bone anchoring means comprise four sets of S anchor grooves. The sets S of anchoring grooves are angularly offset from each other with respect to the axis A of the cup, and are preferably regularly distributed around the axis A of the cup. Each series S of anchor grooves has three anchor grooves 7. Each anchor groove 7 of a series S is located in the same plane as an anchoring groove 7 of each of the other series. The anchoring grooves 7 belonging to each series S extend angularly for example over an angle α of between 50 and 80 °. The angle a is preferably identical for each series, and is for example equal to 60 ° for a cup having an outer radius of 25 mm, equal to 75 ° for a cup having an outer radius of 20 mm, and equal to 55 ° for a cup with an outer radius of 27 mm. FIG. 8 shows a cup according to a fourth embodiment which differs from that shown in FIGS. 1 to 4 essentially in that the cup does not comprise an anchoring groove and comprises four fixing studs 8 having a cross-section in FIG. 9 shows a cup according to a fifth embodiment which differs from that shown in FIGS. 1 to 4 essentially in that the cup does not have an anchoring groove, and in that it comprises four fastening studs 8 frustoconical. The fixing studs 8 have for example a taper of about 3%. According to this embodiment, each attachment stud 8 has anchoring asperities promoting the anchoring of the cup on the humeral head.

As goes without saying, the invention is not limited to the embodiments of this resurfacing cup, described above as examples, it encompasses all variants.

Claims (11)

REVENDICATIONS1. Resurfacing cup (2) for a head of a long bone, such as a humeral head, the resurfacing cup (2) having substantially a hollow spherical cap shape and delimiting a concave inner surface (6) for receiving the head of a long bone, characterized in that the ratio of the height (H) of the cup to the outer radius (R) of the cup is between 0.70 and 0.82. 2. resurfacing cup according to claim 1, wherein the cup comprises bone anchoring means (7) provided on its inner surface, and preferably near the equatorial edge (5) of the cup. 3. resurfacing cup according to claim 2, wherein the bone anchoring means comprise at least one series (S) of anchoring grooves, each series (S) comprising a plurality of anchor grooves (7) s' extending substantially perpendicular to the axis (A) of the cup and axially offset from each other. 4. resurfacing cup according to claim 3, wherein the bone anchoring means comprise a single series of anchor grooves, each anchoring groove (7) being annular. 5. Resurfacing cup according to claim 3, wherein the bone anchoring means comprise several series (S) of anchoring grooves, the series (S) being angularly offset from each other with respect to the axis ( A) of the cup. The resurfacing cup according to claim 5, wherein the series of anchor grooves have the same number of anchor grooves (7), each anchor groove (7) of a series being located in the same plane than an anchor groove (7) of each of the other series. 7. resurfacing cup according to one of claims 1 to 6, 35 wherein the cup has a plurality of fixing studs (8) provided on its inner surface and offset from the axis (A) of the cup, each fixing stud (8) extending substantially parallel to the axis of the cup. The resurfacing cup according to claim 7, wherein the number of series (S) of anchor grooves is the same as the number of fastening studs (8). The resurfacing cup according to claim 7 or 8, wherein the length of each attachment pad (8) is adapted such that the free end of each attachment pad does not protrude beyond the equatorial edge (5) of the cup. 10. resurfacing cup according to one of claims 7 to 9, wherein the outer surface of the cup comprises a plurality of pins each representing the angular position of a fixing stud. The resurfacing cup according to one of claims 1 to 10, wherein the inner surface of the cup is coated with an osteoconductive coating promoting bone ingrowth, such as a coating of titanium or hydroxyapatite.